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Evaluation methodology for mechatronic systems Wijewardene, Duminda C. 2004

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EVALUATION  METHODOLOGY FOR  MECHATRONIC SYSTEMS  By Duminda C. Wijewardene B.Tech (Eng)., The Open University of Sri Lanka, 1999  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE In THE FACULTY OF GRADUATE STUDIES Mechanical Engineering  THE UNIVERSITY OF BRITISH COLUMBIA December 2004 © Duminda C. Wijewardene, 2004  Abstract  With the ever increasing demand for engineering products and systems having added functionalities, compactness and energy efficiency, more and more mechanical products and systems are being integrated with electronics and sophisticated computer control giving rise to a whole new breed of products and systems termed 'mechatronic systems.' These systems are complex and "mixed" in nature due to the integration of components of different types and belonging to different engineering disciplines, thus requiring new approaches in design and evaluation of such systems. Furthermore, the evaluation of existing systems which have been modified using advanced computer control and integration of electronics, is necessary in order to assess their effectiveness. This thesis addresses the issue of evaluation of a mechatronic system, particularly one which has been modified by adding electronic/computer control systems. The existing components in the system should be able to cope with the new requirements imposed by the control system. A novel evaluation method is developed to determine the degree of integration of the components in a mixed system, based on energy flow, giving particular attention to the power domain of the system. To test the usefulness of the methodology, the developed methodology is applied to a practical mechatronic system, the electro-hydraulic manipulator system of an industrial fish cutting machine which has been developed in the Automation Industrial Laboratory of the University of British Columbia. Computer simulations are carried out  ii  as well on the system to investigate effectiveness of the method, since it is largely dependent on a valid model of the evaluated system.  iii  Table of Contents  Abstract  ii  List of Figures  vii  L i s t of Tables  x  G r a p h i c Symbols  xi  Acknowledgements  xiii  Chapter 1  1  Chapter 2  Introduction  1.1 Preliminary Remarks  1  1.2 Motivation  3  1.3 Research Objectives  4  1.4 Organization of the thesis  4  Theoretical B a c k g r o u n d  6  2.1 Introduction  6  2.2 What is Mechatronics?  6  2.3 Mechatronic Design Process  9  2.4 Modeling of Mechatronic Systems  11  2.5 Evaluation of Mechatronic Systems  13  2.6 Literature Review  14  2.6.1  Design Methodologies  14  2.6.2  Modeling Methodologies  15  2.6.3  Mechatronic Design Evaluation Methodologies  16  2.7 Summary Chapter 3  21  Experimental System  23  3.1 Introduction  23  3.2 Background  23  3.3 System Description  24  3.3.1  Mechanical System  25  3.3.2  Pneumatic System  26  iv  3.3.3  Chapter 5  27  3.4  System Operation  30  3.5  Process Control  31  3.5.1  33  3.6 Chapter 4  Hydraulic System  Process Control Requirements  Summary  35  M o d e l i n g of the Electro-Hydraulic M a n i p u l a t o r System  36  4.1  Introduction  36  4.2  Modeling of Electro-Hydraulic Servo System  37  4.2.1  Modeling of Hydraulic Cylinder  38  4.2.2  Modeling of the Flow Control Servo Valve  41  Operation of the Servo Valve  42  Dynamic Equation of the Servo Valve  43  4.2.3  Modeling of the Hydraulic Pump  48  4.2.4  Modeling of Hydraulic Lines  50  4.3  Modeling Approach  51  4.4  Summary  52  System Evaluation Methodology and its Application  53  5.1  Introduction  53  5.2  Evaluation Methodology  53  5.2.1  56  Analysis of the Evaluation Methodology  5.3  Hydraulic Servo Systems and their Energy Transfer  5.4  Requirement Specification for the Electro-Hydraulic Manipulator System 5.4.1  5.4.2  61  64  Determination of the Maximum Velocity and Acceleration of the Moving Assembly  64  Sizing of Linear Actuators  67  Pressure Requirements  67  Flow Requirements  69  5.4.3  Efficiency Considerations  70  5.4.4  Energy Losses in Pipelines  72  5.4.5  Flow Control Servo Valve  75  v  5.4.6  5.4.7  Pump  78  Sizing of Pump  79  5.5  Application of the Evaluation Methodology  79  5.6  Validation through Simulation  84  5.6.1  Selected System Data  85  5.6.2  Simulation Results  86  5.7 Chapter 6  Energy Losses in Pipelines between Servo Valve and  Summary  91  Conclusions a n d Recommendations  92  6.1  Introduction  92  6.2  Contributions  92  6.3  Significance of the Research  93  6.4  Suggestions for Future Work  94  Bibliography  96  A p p e n d i x : Specifications  99  A . 1 Hydraulic Pump Properties  99  A . 2 Hydraulic O i l Properties  101  A.3 F l o w Control Servo Valve  101  vi  List of Figures  Figure 2.1  Representation of Mechatronics  7  Figure 2.2  B l o c k diagram of a generalized mechatronic system  8  Figure 2.3  F l o w chart of mechatronic design procedure  10  Figure 2.4  Energy flow in an electro-mechanical system where each system is coupled by a pure energy transformer  Figure 2.5  Energy flow when electrical system designed in conventional manner  Figure 2.6  18  18  Energy flow when mechanical system designed in conventional manner  19  Figure 3.1  The Industrial Fish Processing machine "Iron Butcher"  24  Figure 3.2  Picture of the Mechanical fish conveying mechanism  24  Figure 3.3  Picture of the Pneumatic system  26  Figure 3.4  Schematic diagram of the electro-hydraulic manipulator system  28  Figure 3.5  Picture of the Servo-valve block and Power block  29  Figure 3.6  Picture of the Cutting, Inspection and standby zones of the machine.  31  Figure 3.7  Block diagram of the Architecture of the process control system  32  Figure 4.1  The generalized Block diagram of the electro hydraulic servo system  37  Figure 4.2  Schematic representation of the cylinder variables  38  Figure 4.3  B l o c k diagram of the cylinder dynamics  41  Figure 4.4  Schematic of the two spool flow control servo valve with pressure control  42  vii  Figure 4.5  Block diagram of the servo valve dynamics  48  Figure 5.1  Simple block diagram of the power flow between components of a system  54  Figure 5.2  Variation of power expression with constant available power  57  Figure 5.3  Variation of power expression with variable available power  57  Figure 5.4  Relationship plot of P  58  Figure 5.5  Variation of Efficiency vs Index  59  Figure 5.6  Variation of the Overall Mechatronic Index  60  Figure 5.7  Energy flow between components of the electro-hydraulic  n  (available)  and P  n  (required)  with / /  manipulator  63  Figure 5.8  Schematic diagram for the force balance for the fish cutting table .... 65  Figure 5.9  Assumed Velocity profile of the cutter table movement  66  Figure 5.10  Schematic diagram for force balance in piston and cutter table  68  Figure 5.11  Simplified schematic of the 4/3-way flow control directional servo valve  75  Figure 5.12  Block diagram for the power flow among the different components in the electro-hydraulic system  82  Figure 5.13  Behavior of piston displacement  87  Figure 5.14  Pressure variation at piston bore side  88  Figure 5.15  Variation of flow rate at piston bore side  89  Figure 5.16  Variation of pump pressure  90  viii  Figure 5.17  Variation of pump output power  90  Figure A . l  Pump shaft speed vs. flow characteristics of the original pump  100  Figure A.2  Pump shaft speed vs. Volumetric efficiency characteristics of the original pump  Figure A.3  Pump shaft speed vs. overall efficiency characteristics of the original pump  ix  List of Tables  Table 3.1  Features of the process control systems  34  Table 5.1  Piston assembly parameters  67  Table 5.2  Calculated cylinder pressures  69  Table 5.3  Modified cylinder pressures requirement according to efficiency.  71  Table 5.4  Line pressure drop between cylinders and servo valves  74  Table 5.5  Modified pressure values with frictional losses  74  Table 5.6  Supply pressures for servo valve  77  Table 5.7  Power and efficiency values of components in the system  83  Table A. 1  Hydraulic pump properties  99  Table A.2  Hydraulic oil properties  101  Table A.3  FCV specifications  101  x  Graphic Symbols ANSI Symbols of Hydraulic components Hydraulic line pj] j ot  m  e  Lines crossing  <»  I  Lines connecting  I  Hydraulic tank (Reservoir)  Electric motor  Variable displacement pump  Positive displacement pump  Linear actuator with single rod piston  Filter or Strainer  Accumulator, Gas charged  xi  Check Valve  TT ^ I_L  Three-position, four-way flow control valv  <  Pilot pressure operated  •  Spring centered pilot controlled valve  (Source : Esposito, 1988)  xii  Acknowledgement  I wish to take this opportunity to thank number of people for their valuable assistance rendered to me during my period of research at the University of British Columbia, Vancouver, Canada. First and foremost I wish to express my sincere gratitude to my supervisor, Professor Clarence W. de Silva for his continuous support, guidance and invaluable patience. His vast knowledge and wisdom in the field of engineering makes him one of a kind and I had been very fortunate to have him as my academic and research supervisor, and truly consider him as a role model. I thank Mr. P. D. Sarath Chandra, Head, Department of Mechanical Engineering at the Open University of Sri Lanka for letting me have this opportunity for pursuing my higher studies overseas and guiding me throughout and for his valuable advice and support given to me all throughout my academic career. Funding of my research was provided by The Asian Development Bank, Ministry of Science and Technology, Sri Lanka, The Open University of Sri Lanka and trough my supervisor through the Natural Sciences and Engineering Research Council (NSERC) of Canada, which is gratefully appreciated. I wish to thank three special people, Poi Loon Tang, Nazly Pirmoradi, and Harsh Perera, who gave me strength and courage, listened to all problems and showed what true friendship really means. Also my other lab mates who always stood by me, Yang Cao, Richard McCourt, Ying Wang, Jason Zhang, Kenneth Wong, Mohammed Alrasheed, Tao Fan and Saeed Behbahani deserves thanks.  xiii  My gratitude also goes to all the staff in the Department of Mechanical Engineering, UBC for their kind assistance. Last but definitely not least, I wish to thank my loving parents and my brother for the support and encouragement given to me all through my life.  xiv  Chapter 1 Introduction  Chapter 1  Introduction  1.1 Preliminary Remarks Electromechanical products and systems, which mainly consist of mechanical systems with electrical power sources, have been utilized in many fields such as the transportation filed and industry since the early part of the 20 century. However, these systems are designed th  using conventional design approaches, with each component designed in its respective domain and then integrated on a rather adhoc basis. The development of the microprocessor and advanced control system technologies in the 1960's made a significant contribution towards the advancement of electromechanical systems. Not only did these systems integrate electrical, electronics, control and information technologies, but also they approached the design, development and implementation in a somewhat integrated manner. As a result engineers were able to produce truly mechatronic products and systems offering significantly enhanced functionality, flexibility and performance. These systems were also more reliable, accurate and precise, cost effective and mechanically less complex as compared to nonmechatronic products or systems. With today's advanced technologies of analog and digital electronics, computer control, and micro-electromechanical systems (MEMS) with embedded sensor actuator technologies, the field of Mechatronics has seen rapid development and is applicable in almost in every field. Some of these are summarized below.  1  Chapter I Introduction  •  •  Manufacturing and Production Engineering •  Modern computer numerical controlled (CNC) machine tools  •  Industrial robots  •  Automated storage and retrieval systems (AS/RS)  •  Modern industrial machines  •  Rapid prototyping systems  Transportation •  Antilock breaking systems (ABS), active suspension systems, emission control systems, used in automotive systems.  •  Automatic flight navigation systems, flight control, landing gear mechanisms, used the in aviation industry.  •  Un-manned and automated ground transit (monorail, sunway, automated guided transit).  •  Consumer Products •  Household appliances such as automatic washing machines, vacuum cleaners, and dish washers.  •  Office equipment such as photocopy, fax, and scanning machines.  •  Computer components such as hard disk drives, CD/DVD drives, and thermal dissipation systems.  These are just a few of the applications and devices of mechatronic systems in use today. Apart from these three categories, mechatronic systems can be found in the areas of medical, space, and military.  2  Chapter I Introduction One reason for these systems to be widely used is their numerous functionalities, which they offer over their counterparts. Some important properties are listed below. •  Supervision with fault detection and diagnosis  •  Optimization of performance and efficiency  •  Less complicated kinematics due to decentralized drives  •  Intelligent behavior  •  Integrated process management.  1.2 Motivation Designing of a mechatronic system with optimized characteristics as outlined previously is more difficult than in the case of for example a purely mechanical system or a purely electrical system. Mechatronic systems consist of components from different domains such as mechanical, electrical, electronic and information technologies, thus rather than designing each component separately in its respective domain, the total system will have to be treated in a concurrent manner and the designing of components has to be carried out using an integrated approach. Eventhough the performance of an existing non-mechatronic system can often be improved by integrating more elaborate control systems, such an approach neither cost effective not optimal.  The key to an integrated mechatronic design methodology is modeling and simulation. Through analysis and simulation of the whole system as well as its sub-systems it w i l l be possible to arrive at an optimal design solution. User friendly modeling techniques that can be applied to multi-domain systems are needed here. Significant amount of research has been carried out in modeling and simulation for engineering systems, and this has resulted in  3  Chapter I Introduction several successful techniques. The Bond Graph technique (Paynter) and more recently, modeling by the use of Unified Modeling Language (UML) are some of the popular modeling techniques. One of the areas that has not received sufficient attention is evaluation of a mixed system and through that assessment of an existing system. Evaluation is a key aspect of refining a system model and it may lead to design optimization criteria. Furthermore, an evaluation criteria can be used as a measure how well the components of the system are matched or integrated.  1.3 Research Objectives The main objective of the research presented in this thesis is to develop a mechatronic evaluation methodology for assessment of and existing product or system. The developed evaluation criterion may also be used to select the most appropriate components for a system. A representative model of the system is a prerequisite for applying the developed methodology. For this reason, modeling of an industrial device will be carried out and the results will be critically analyzed. Subsequently, the developed technique for system evaluation will be applied to the industrial device and compared with a conventional design approach.  1.4 Organization of the Thesis This chapter has provided an introduction to mechatronic systems and products and the reason for their wide application. The motivation for the present work was given followed by formal objectives of this research. Chapter 2 begins by exploring the theoretical background necessary for the thesis. A literature review on some basic definitions of mechatronics, some important modeling  4  Chapter 1 Introduction techniques, which have been developed in the past as well as new concepts are be looked in to. Finally, relevant design techniques and evaluation methodologies are discussed.  Chapter 3 mainly describes the fish processing machine on which the simulation and the evaluation criteria developed in the thesis w i l l be applied. Detailed description of the workings of the machine and its sub-systems is presented. Chapter 4 deals with the modeling of the electro-hydraulic manipulator system, which is an integrated subsystem of the fish cutting machine considered in the present work. Dynamics of various components and their behavior are discussed followed by some simulations carried out using a hydraulic system model. The relevance of the developed index on the dynamic behavior of the system is indicated. Chapter 5 presents the evaluation methodology which is developed in the present work. This is tested on the industrial fish-processing machine. The components of the existing machine are selected in accordance with a mechatronic design approach and the mismatch between the newly selected components and the existing components is analyzed using the developed evaluation criterion. Chapter 6 concludes the thesis. It summarizes the overall integration; outlines the main contributions made, and presents recommendations for future work.  5  Chapter 2 Theoretical Background  Chapter 2 Theoretical Background 2.1 Introduction  The theoretical background relating to the field of mechatronics, which forms the basis of the thesis is discussed in this chapter. The basic idea of mechatronics, the design concepts and existing evaluation methodologies are presented. A literature review of the underling work is carried out. 2.2 What is Mechatronics  This has been a common question among researchers, academicians and engineers and several attempts have been made to answer it. Various definitions and explanations have been put forward and still new ideas are being published. Chapterl addressed this question to some degree. The present section will elaborate on it further. Yasakawa Electric in Japan was the first to introduce the term mechatronics and the company obtained a trademark in 1972. According to its definition " The word mechatronics, is composed of "mech" from mechanism and "tronics" from electronics. In other words, technologies and developed products will be incorporating electronics more and more into  mechanisms, intimately and organically, and making it impossible to tell where one ends and the other ends" ( Yasakawa, 1969)  Among the various definitions for mechatronics the one which is most widely used is " Mechatronics is the synergetic integration of mechanical engineering with electronics and  6  Chapter 2 Theoretical Background intelligent computer control in the design and manufacturing of industrial products and  processes'" (Harshima, el al, 1996)  Yet, another good definition was put forward by Burr as " Mechatronics is a technology which combines mechanics with electronics and information technology to form both functional interaction and spatial integration in components, modules, products and  systems" (Burr, 1990)  By considering some of these proposed definitions, Mechatronics can be considered as a muti-disciplinary field with mechanical, electrical, electronics and information technologies being integrated from the initial design steps to the final production and operation in a synergistic manner, in arriving at better products and systems. This can be represented as shown by figure 2.1  Fig- 2.1 Representation of Mechatronics.  7  Chapter 2 Theoretical Background A generalized view of a mechatronics system can be represented as in figure 2.2 Energy source  f5"  i  Information processing  t  D/A converter  p  Actuator  k w  Process (Mechanism)  c i/i c E _o D  ron ract  A, ^ .s  >  A/D converter 1  Sensor  W  . Mechatronics. system. Figure 2.2 - Generalized Mechatronic system. There will be energy and information flow between the different domains and in fact, these considerations can be used when designing the system in an integrated manner. According to this view some important components can be identified, which are common to a mechatronics system. Namely; •  Mechanical system:  This consists mainly of the system/plant, which is being manipulated, and can consist of either a purely mechanical system or a mixed system such as an electro-mechanical system.  •  Sensors:  State of the system is measured by using sensors, and this information is sent to the controllers for further processing and taking control actions.  •  Processor:  Necessary corrective or manipulative action to be taken will be decided upon in the processing section. This forms the  controller.  Usually  micro-controllers,  a  digital  computer, or analog and digital hardware will be used.  8  <D +-»  c _C  Chapter 2 Theoretical Background •  Actuators:  Actuators are responsible for making the corrective actions or manipulative actions to be applied to the system/plant.  2.3 Mechatronics Design Process A great deal of research has been carried out in the field of engineering design leading to many different design methodologies and practices. Almost in all of these methodologies, may it be conventional design or mechatronic design, the procedure starts off with some design specifications  and ends with a suitable design solution to meet the design  specifications.  The design procedure for a general mechatronic product or system can be represented as in figure 2.3. The complete design process should be able to generate the necessary details of the product/system in order for the production to be carried out. Furthermore, the design process would not be a simple step-by-step sequential procedure. Any one solution may require a number of iterations through various parts of the process and uses a concurrent design approach. The initial step begins with understanding the nature of the required product/system and finding out the specifications/requirements. Since mechatronic systems deal with components belonging to different domains, the functional requirements of each domain should also be realized. One of the ideas behind mechatronics is that functionality can be achieved either by the solutions in the physical domain (mainly mechanical, electrical) or by the information processing in the electronics or software domain or both.  9  Chapter 2 Theoretical Background  System requirements Conceptual design System modeling  Evaluation  Detail design Design optimization Prototype  Figure 2.3 The mechatronic design procedure  In the conceptual design phase, the generation of concepts to achieve the desired requirements and functionalities are put forward. However, in a design process there could be more than one solution concept for a particular design. Therefore, evaluation of these solution concepts should be carried out in order to find the best design solution. Evaluation will be carried out through modeling process.  10  Chapter 2 Theoretical Background  2.4 Modeling of Mechatronic Systems Modeling plays a major role in mechatronics design in evaluating the generated conceptual design concepts as well as means of introducing synergy into mechatronic systems (de Silva, 2004). Models of mechatronic systems should be closely related to the physical components of the system and since specialists from various disciplines are involved, it would be advantageous if each specialist could study the performance of the overall system in his or her own domain. That is, the performance of the system has to be evaluated from multiple point view. Typical viewpoint that are important in this respect are: •  Physical models  •  Graphical representation (Graphical models) •  Bond graphs  •  Linear graphs  •  Iconic diagrams  •  Time domain models  •  Animation  •  Control engineering models •  Block diagrams  •  State-space representations  •  Bode plots  •  Nyquist plots  11  Chapter 2 Theoretical  Background  The traditional modeling approach often used in engineering is mathematical modeling. That is, the real world physical systems and processes are represented by mathematical relationships and are solved using suitable analytical or numerical techniques. The development of a suitable system modeling approach for muti-domain systems, such as mechatronic systems requires unified and systematic modeling techniques. In the past, research has been carried out in finding a methodology that can address the issue of mutidomain systems. One such well-known and most widely used technique is the Bond graph modeling method. This method was elucidated by Henry Paynter at Massachusetts Institute of Technology in 1959 and was originally intended for thermodynamic (energy-based) systems. Roesnbrg, Karnopp, Thoma and others have further developed this method, and it has become a powerful modeling technique. The method uses power and information flow between elements of the system through their power and information ports, respectively. All physical processes are described using several elementary components, or elements. Namely;  •  Sources of effort and/Zow (denoted by S E and SF, respectively)  •  Accumulation of effort and flow (denoted by I and C, respectively)  •  Dissipation of power (denoted by R)  •  Transformers of power (denoted by T F and GY)  •  Branches of effort and flow ( denoted by e and f, respectively)  •  Junctions of common effort and common flow (denoted by 0 and 1, respectively)  The processes that these components represent are described by constitutive relations expressed in terms of ports and internal variables. For further information regarding bond  12  Chapter 2 Theoretical Background  graph methodology the reader is directed to the references (Karnopp, et a/.,2000; de Silva,2004). The development of computer and software engineering has led to the use of the Object Oriented approach (OO approach) in the modeling of multi-domain systems. When properly applied to a complex muti-domain system, it yields robust models consisting of reusable, easy to maintain components (Rumbaugh, et al, 1991). Evaluation and validation of the developed models is done through simulation and experimentation, and the results checked against suitable evaluation criteria. The refinement of models or conceptual designs can take place in accordance with the evaluation criteria. Detailed design generation and physical embodiments or prototyping of the concepts and designs have to be carried out next and the selection of components and the overall integration of the system have to be done. Techniques such as hardware-in-the-loop simulation may be used for evaluation purposes. Further multi-criteria design optimization may take place before the final product is manufactured for the end use. 2.5 Evaluation of Mechatronic Systems A mechatronic system can either be a completely new system or a conventional electromechanical system which had been modified with sophisticated computer-electronic sub systems. In either case a suitable evaluation methodology is required to assess the performance of the overall mechatronic system. When designing a mechatronic system as a new design, at the stage of conceptual design, several candidate solutions will be put forward for a particular design. Each of these solutions should inherit the properties of a mechatronic  13  Chapter 2 Theoretical  Background  system and satisfy the requirements to an optimum degree. A desirable way in which this can be accomplished is by having an evaluation index or criteria to perform the evaluation task.  On the other hand, when an existing electro-mechanical system has been modified using sophisticated electronic hardware and computer software, there will be an additional burden on the original system due to the increased performance demanded by the new subsystems. Some of the components of the original system may not operate at their optimal performance due to this reason. Therefore, evaluation methodologies are required to assess the performance of such a retrofitted system.  2.6 Literature Review Among the vast number of literature found on Mechatronics, one can broadly categorize the available work into: •  Design methodologies  •  Modeling methodologies  •  Evaluation methodologies.  A selected set of the relevant literature is reviewed now.  2.6.1 Design Methodologies Mechatronic design  is mainly aimed at effective,  integrated and concurrent design  approaches, and many in the field have published methodologies and approaches for this purpose. Design for control (DFC) (Li, et al, 2001) is a technique based on designing a system concurrently based on satisfying the control requirements. D F C emphasizes obtaining a simple dynamic model of the mechanical structure first, followed by the controller design  14  Chapter 2 Theoretical Background  and performance evaluation. In their approach, the total design process is considered as a mapping from the requirement space (RS) to the structural space (SS). The RS and SS are further subdivided into real-time behavior (RTB) and non-real-time behavior (Non-RTB), and real-time parameters (RTP) and non-real-time parameters (Non-RTP) respectively. The designing is then treated as an integrated framework which considers both RTB and Non RTB requirements simultaneously and configuring both RTP's and Non -RTP's concurrently. One main idea behind this approach is that the mechanical structure is designed in such a manner, which results in a simple dynamic model thus enabling controller design at a latter stage. Modularization approach (Ross, et al., 2000) addressed the particular application to automobile technology. The approach is to have separate modules based on their functionalities. By doing so, a complex system can be easily represented by a modularized model and integration, and modeling of such a system can be carried out in an efficient manner. Each module is designed in a concurrent manner and integration of modules is done again in a concurrent manner to arrive at the total design. The methodology was successfully implemented on a drive by wire stems for an automobile to illustrate its applicability in designing mechatronic systems. 2.6.2 Modeling Methodologies The area of modeling plays a major role in the development of mechatronic systems and products. This area is so far the one where most research has been carried out. The main issue that the modeling of a mechatronic system faces is the multi-domain nature. Modeling techniques capable of handling such systems effectively have to be devised. One effective  15  Chapter 2 Theoretical Background  method which is the bond graph modeling technique, which was discussed in section 2.4. Developments in this field are progressing steadily (Youcef-Toumi, 1996; Hussein, 2000) One recent approach in this field is the composable modeling (Paredis,2001). The concept is based on the integrated modeling by combining form (CAD models) and behavior (simulation models) of mechatronic systems as component objects. By combining these component objects to each other through their ports, design engineers can create both system level design description and virtual prototype of the system. The most recent modeling approach that is currently being investigated is the use of an Object Oriented Language (OOL). Designing and modeling with the help of a Unified Modeling Language (UML) has been successfully applied for modeling of mechatronic systems (Mrozek, 2002). 2.6.3 Mechatronic Design Evaluation Methodologies Mouliantis, et al, (2001) proposed a methodology for evaluation of a mechatronic system at the conceptual design stage by introducing a mechatronics index vector (MIV). The MIV is then used to constrain the design solution space according to two criteria that characterizes a mechatronic system, namely, Intelligence and Flexibility. Accordingly, the MTV is given by,  (2.1)  where IM: Intelligence Measure FM: Flexibility Measure 16  Chapter 2 Theoretical  Background  The evaluation process is carried out by choosing those alternatives that maximize the next evaluation score (ES) given by, lE v{i)MIV{i)  +  MI  E S  =  ~  v  ^w (j)C(j) c  1\ v  <  ^  W  j  where, w w  MIV  : weight factor vector for the elements of the MIV  c  : weight factor vector for the general design criteria  C  : general design criteria vector  i, j  : the number of elements of MIV or mechatronic weight factor vector and the number of elements of the rest  design criteria vector or the w  c  vector,  respectively.  In 2003, the MIV was further enhanced by including another element inherent in a mechatronics system, namely, the complexity. Accordingly the MIV was represented as IM MTV = FM  (2.3)  CM The additional element, CM, represents the complexity measure. It should be noted that the formulation of this MIV was based on fuzzy operators.  In 2003, de Silva (de Silva,2003) proposed an evaluation methodology considering loading effects when different systems belonging to separate domains are interconnected. The approach can be illustrated by considering the design of an electro-mechanical system.  17  Chapter 2 Theoretical Background  An electro-mechanical system can be considered as an integration or coupling of an electrical system and a mechanical system as depicted in figure 2.4  Electrical Dynamics v-  Ideal Energy Transformer  Energy Dissipation  Mechanical Dynamics co-  Energy Dissipation  Electrical System  Mechanical System  Figure 2.4 An electro-mechanical system. Assume that the energy flow is from the electrical system to the mechanical system during operating conditions. An electrical power of vi will flow into the port of the energy transformer while a mechanical power of TCO will flow out of the port of the energy transformer. Since the energy transformer is considered to be ideal the power input will be equal to the power output. If the system was to be designed in the conventional manner, the electrical system would be designed neglecting the effects of the mechanical system. That is, the mechanical system will be treated as a fixed load as shown in figure 2.5. Mechanical svstem (fixed load)  Electrical system  Figure 2.5 Electrical system design in conventional manner. A design index / is introduced, which reflects the degree to which a particular design satisfies the design requirements. Let I be the design index for the electrical system when designing ce  18  Chapter 2 Theoretical Background  in a conventional manner. Similarly, if the mechanical system is designed in a conventional manner, the electrical system will be treated as a fixed source as shown in figure 2.6. Electrical system (fixed source)  w  Mechanical System  Figure 2.6 Mechanical system designed in conventional manner Let I  cm  be the design index corresponding to the conventional design case. When the two  systems are interconnected, due to dynamic interactions between them, neither the mechanical design requirements nor the electrical design requirements will be satisfied at the levels indicated by I  cm  and I , respectively. They will be satisfied at a lower level given by ce  the design indices /,„ and I . The evaluation criteria proposed is to maximize a "mechatronic e  design quotient" MDQ given by the expression (de Silva, 2003).  a I +a I MDQ = — -^ !2-?2  !L  2  (2.4)  where, a and or are weighting factors indicating the influence of the electrical and c  m  mechanical subsystems on the overall system. The most recent methodology for evaluation was put forward by Hehenberger, and Zeman in 2004 (Hehenberger and Zeman,2004). The evaluation criterion for the best conceptual design solution is obtained by introducing a "Degree of mechatronic coupling" DoMC. A complex mechatronic system is first decomposed into several domains, which are called discipline pillars. Each pillar characterizes a domain specific component, which is  19  Chapter 2 Theoretical Background structured into several hierarchal levels corresponding to the degree of detailing.  The  "Mechatronic pillar design" model developed by the researchers distinguishes between two different views on the design model. Domain-specific components utilizing only one domain of Mechatronics are characterized by one pillar, whilst mechatronic modules utilizing several domains of Mechatronics such as, mechanical and electronic, are characterized by other pillars, and the respective domain-specific components are merged. Therefore, a mechatronic module designates the "smallest" indivisible mechatronic subsystem within the set of mechatronic subsystems. The DoMC may be categorized into a relative degree, which evaluates the intensity of coupling in a selected design structure, independently of the size of the structure while the absolute degree reflects the size of the structure.  Accordingly, the absolute degree of mechatronic coupling for the coupling parameter DPi is given by  DoMC  u/w  (D^=(7V„,-l)  N -%  AD;  m  (2.5)  where, N  : Number of pillars (domains), which are involved in the determination of  Hi  DP AH  : Domain-specific design range for DP resulting from pillar /  A Z>  : Resulting design range for parameter DP  ij  t  20  Chapter 2 Theoretical Background  The relative degree of coupling for the coupling parameter DP is given by t  DoMC  reI  (DP,)  (2.6)  where, Ns is the number of different pillars of the model. To analyze the module, all DoMC(DPj) are added for each parameter DPj :  DoMC,  DoMC,module,rel  (2.7) 1 2DoMC (DP ) rd  DP  where N  DP  t  (2.8)  i=l  is the number of design parameters in the coupling level.  The degree of mechatronic coupling reflects the complexity of the system's functionality and can be used as an assessment tool for selecting the best design. Therefore, the best design according to the methodology is the one with the lowest complexity. 2.7 Summary Chapter 2 dealt with the theoretical background necessary for the present thesis. A detailed description of mechatronic systems and how such systems are designed were presented. The background of the available methodologies of modeling, design and evaluation was elaborated. The following chapter will describe a specific industrial mechatronic system, the  21  Chapter 2 Theoretical Background automated industrial fish processing machine, using which the evaluation methodology developed in the present work will be tested.  22  Chapter 3 Experimental System  Chapter 3  Experimental System  3.1 Introduction This chapter presents an experimental system, which is used in assessing the methodology developed in this thesis specifically, an industrial fish-processing machine developed in our laboratory will be discussed. The workings of the machine as well as the description of various subsystems will be given. 3.2 Background Fish processing is a major resource-based industry in British Columbia, Canada. Various fish processing machines are used in these industries and one of the major concerns has been the wastage of fish during processing. One such machine is the "Iron Butcher" which was designed and built at the turn of the century and widely used in the industry. The typical wastage of fish during processing of this machine was estimated at being around 5%, which inflicts an annual revenue loss about 25 million dollars, in the province of British Columbia, alone. The main reason behind the wastage of fish is due to the lack of active sensing and feedback control in these original machines. The Industrial Automation Laboratory at the University of British Columbia (UBC), undertook the task of addressing these deficiencies and has successfully developed an innovative fish processing machine by employing advanced sensing and actuation technologies to detect and position the fish accurately at the cutter, and as a result minimizing the fish wastage by about 3%. This accounts to a saving of around 15 million dollars annually. The machine was developed by a team of researchers  23  Chapter 3 Experimental System  headed by Professor CW. de Silva and has been successfully tested in the fish processing industry. 3.3 System Description Figure 3.1 shows a view of the Intelligent Iron butcher developed at the Industrial Automation Laboratory of UBC (de Silva, 1992). The process of fish cutting is carried out by three main subsystems namely, •  Mechanical system  •  Pneumatic system  •  Hydraulic system  Figure 3.1 Industrial fish processing machine "The Intelligent Iron butcher."  24  Chapter 3 Experimental System Each of these systems will be responsible in providing different functionalities to the overall system in order for the fish cutting process to be carried out in an efficient manner. The separate functionalities provided by these respective sub systems can be categorized as, •  Fish motion  •  Fish stabilization and cutter vertical motion  •  Cutter horizontal motion  3.3.1 Mechanical System The mechanical system will be responsible for conveying the fish from the feeding zone to the cutting zone. The fish conveying system is powered by an A C induction motor, where the rotary motion is transformed into a linear push-pull stroke of a three copper sliding bars through a mechanical linkage as shown in figure 3.2.  Proximity sensor "  Figure 3.2 Mechanical fish conveying  25  mechanism.  Chapter 3 Experimental System  The top of the copper bars contains a matrix of retaining pins pointing upwards and these pins fold in one direction only. The purpose is to move the fish in the forward direction without allowing it to move backwards when the pins are retracted. 3.3.2 Pneumatic System The task of the pneumatic system is twofold. One is to stabilize or hold the fish stationary while the matrix of retaining pins move backwards, and the other being the operation of the vertical cutter blade movement. Figure 3.3 shows the pneumatically operated fish holding mechanism and the vertical cutter blade assembly.  Figure 3.3 Pneumatic system  26  Chapter 3 Experimental System  The fish holding mechanism comprises 3 pneumatically operated single acting cylinders, which are connected through a mechanical linkage to the holders. The cylinders are actuated by operating a four-way, five port double solenoid valve according to the signals received from the machine controller. The vertical cutter blade assembly is comprised of a blade connected to a piston and actuated by a solenoid valve. The power for the system is delivered through an air compressor. The main components of the system are the compressor, three single acting cylinders, double acting cutter cylinder, and four-way five port double solenoid valves. The specifications of each components used can be found in Appendix A.  3.3.3 Hydraulic System The hydraulic system is one of the most important assemblies of the machine. The main task of the system is to position the cutter blade assembly in accordance with the guild position of the fish head, as determined by the vision system, to minimize the wastage of fish meat. The task is carried out by the Cartesian electro-hydraulic manipulator system. The schematic diagram of the basic electro-hydraulic manipulator system is show in figure 3.4.  /  27  Chapter 3 Experimental System  X Piston Cutter Blade table  _Position  1  Transducer  Position Load Block  Transducer  AA/VU  1  Y W MA/  1  —i VvV  _Seryo V_a]ye Block^  Variable displacement pump Oil reservoir Power Block Figure 3.4 Schematic diagram of the electro-hydraulic manipulator system. The manipulator system can be broadly classified into three main sub sections, namely, the power block, servo-valve block and the load block. The power block is responsible for providing sufficient energy to the overall manipulator system, and consists of an electric-motor-driven variable displacement pump, heat exchangers, filters and other small accessories. The servo-valve block consists of two, two-stage flow control electro-hydraulic servo-valves, which are responsible for controlling the hydraulic fluid flow into the power  28  Chapter 3 Experimental  System  cylinders. It also acts as an interface between the electric domain and the hydraulic cylinders of the load block. The flow control servo-valve consists of a closed loop pressure control valve (double jet flapper valve) and a spring centered second stage, which features a dual spool arrangement. Finally, the load block consists of two double acting single rod power cylinders, each for positioning the X and Y axes of the table. In addition to the mentioned elements, the system consists of two magneto-restrictive displacement sensors and six pressure transducers for the purpose of measuring the system variables for control. The process control will be discussed in sections to follow. Figure 3.5 shows the main components of the servo-valve block and the load block  Figure 3.5 The servo-valve block and the load block.  29  Chapter 3 Experimental System  3.4 System Operation The fish are fed manually from the fish feeder platform intermittently on to the conveying mechanism. The fish entering are held between the matrix of retaining pins, which point upwards from the conveying platform. During the first half cycle of the conveying motion, the fish are pushed forward due to the forward movement of the pins and in the other half the pins move backward. However, since the pins are retractable in this direction the fish will not move back with the pins, because during this time period the pneumatic fish holding mechanism has its holders pointing down preventing the fish from being moved backwards. The cycle time for the fish conveying mechanism is estimated to be approximately 1.24 seconds, making the fish-processing rate to be 48 fish/minute. During the backward motion of the conveyer there will be one fish in the cutting zone and another fish in the standing-by zone. At this time an image of the fish in the standing-by zone is captured by using the primary CCD camera and the information is transferred through a frame grabber card to the vision computer for image processing. The vision algorithm determines the exact position the cutter has to be located in order to cut the fish with minimum fish wastage. The desired X-Y coordinates are sent as a reference input to the electro-hydraulic servo-valves, which then regulates the desired flow-rates for the power cylinders to locate themselves in accordance with the required position. When the fish in the standing-by zone is moved to the cutter zone due to the forward motion of the conveyer, the operations of the system is synchronized such that, the blade has already been positioned at the desired location. When the fish arrives at the cutting zone the pneumatic actuator of the cutter is activated thereby releasing the vertical cutter blade. It should be noted that cutting of the fish, which was previously in the standingby zone and the image capturing of the fish presently in the standing-by zone occur during  30  Chapter 3 Experimental System  the backward motion of the conveyer. A second CCD camera captures an image of the processed fish to assess the quality of the cut and make necessary modifications to the machine operation based on this information. The cutting, inspection and stand-by zone of the system is shown in figure 3.6  Figure 3.6 Cutting, Inspection and standby zones of the machine.  3.5 Process Control The general architecture of the process control system used in the fish-cutting machine is explained now. The 'process' response/performance is measured by 'process variables' and the control system is responsible in regulating the process variables to obtain the required action in the process, generating necessary 'control inputs.' For example, for the entire  31  Chapter 3 Experimental System  system the process goal is the cutting of fish head with minimum wastage of fish, and the process input and process output are the fish with and without head, respectively. The architecture of the generalized process control system can be represented as shown in figure 3.7. Process output  Process input  =>  Process A Control input  Process variable Sensor  End effector  Interface  Actuator  Measuremet  Control element  3L"  Interface y:  Controller Figure 3.7 Architecture of the process control system. The total process of fish cutting has been decomposed into four main processes namely; •  Fish motion  •  Fish stabilization  •  Cutter vertical motion  •  Cutter table motion in horizontal plane  32  Chapter 3 Experimental System  The four control systems will run in parallel having four control inputs to control these four processes. Note that each of the four processes may not contain all the elements shown in figure 3.7.  3.5.1 Process Control Requirement The activation of the total process occurs when the main switch of the machine is turned on. Basically this action is achieved by turning on the switch of the induction motor of the fish conveying mechanism. At the end of the push stroke several process actions have to be activated. These can be summarized as •  Push the holder down of the fish stabilization mechanism  •  Capture an image of the fish in the stand by zone  •  Release the cutter blade to cut the fish  As soon as the fish is cut the cutter is raised immediately. At the end of the pull stroke before beginning the push stroke again the following process actions have to be activated: •  Pull back the holder in the fish stabilization mechanism in order for the fish to be pushed.  •  Position the cutter table assembly based on the information previously captured by the CCD camera.  These actions are initiated by measuring the various process variables through appropriate sensors. Three limits switches, a proximity sensor and position transducers are used for this purpose. Two of the limit switches are located under the conveying platform, one to indicate the end of the push stroke and the other to indicate the end of the pull stroke. The cutter limit switch is located at the end of the downward stroke to indicate the end of  33  Chapter 3 Experimental System  cutting. A proximity sensor placed under the platform of the conveying mechanism at the end of the pull stroke activates the hydraulic cutter positioning system. The above features of the process control systems are tabulated in table 3.1.  T a b l e 3.1  C o n t r o l System  F i s h motion  Features of the process control systems. Fish  Cutter  Cutter horizontal  stabilization  vertical  motion  motion Process action  Process variable  Fish  Holder  movement  motion  None  Time  Cutter motion  Cutter table motion  Time  Time, Image, Position, Pressure  Sensor  None  Limit switch  Limit switch  Proximity sensor, CCD camera, Linear displacement transducer, Pressure transducer  Actuator  Induction  Pneumatic  motor  solenoid valve solenoid valve control proportional  Pneumatic  Electro-hydraulic flow valves  E n d effector  Sliding  Single acting Double acting Double acting single  copper bars  pneumatic  pneumatic  cylinders  cylinder  rod hydraulic cylinders  C o n t r o l input  Rotation  Air flow  Air flow  Hydraulic oil flow  C o n t r o l type  Open-loop  Open-loop  Open-loop  Close-loop digital  analog  analog  analog  34  Chapter 3 Experimental System  3.6 Summary The experimental setup of the industrial fish processing machine known as the Intelligent Iron Butcher which has been designed and developed in the Industrial Automation Laboratory of UBC was discussed. The operation and the control architecture employed on the machine have been explained. In the next chapter the modeling considerations of the electro-hydraulic manipulator system of this machine will be studied.  35  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  4.1 Introduction This chapter is devoted to the development of physical models for each component/sub system of the electro-hydraulic manipulator system of the industrial fish cutting machine. The model derivation will be based on physical fundamentals and first principles and many assumptions are made in order to keep the model complexity at a lower level. Once the model of the total system is formulated the dynamic behavior of the system as well as the various energy components will be studied using simulations, and the relevance of modeling to the mechatronic index developed in this work will be discussed. In order to understand the behavior of hydraulic servo mechanisms or hydraulic systems, modeling of the system has to be done, typically with an extensive theoretical modeling exercise of the entire system. Hydraulic systems are highly complex and nonlinear in most cases, opening an avenue for research to be carried out on these systems. The main problem encountered during research carried out in this field is the unavailability of the numerical values for the physical parameters, during the modeling phase. For example, some of the parameters of components such as servo valves are not reveled by the manufactures due to proprietary nature of the information. The outcome will be that these models cannot be used in precise quantitative analysis. They can be successfully used however, for qualitative analysis and behavior analysis. In the present chapter, the theoretical development of the necessary analytical models will be illustrated. For simulation studies, a simpler model will be used, which will suffice in the present study and for the analysis of the developed  36  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  evaluation methodology. Note that, simplification is done such that the physical structure of the model is retained. By doing so, we can account for nonlinearities related to some important physical phenomena such as dynamic friction. 4.2 Modeling of Electro-Hydraulic Servo Systems For the purpose of developing an analytical model, the total electro-hydraulic system is sub divided into five subsystems, as follows: •  Actuator: In the system studied in the thesis, this will be a linear actuator, which is a cylinder, and the load connected to it, which is the cutter table  •  Pipelines connecting the actuator and the flow control servo valve  •  Electro-hydraulic flow control servo valve  •  Pipe lines connecting the servo valve and the pump  • Pump. The system can be represented by the block diagram shown in figure 4.1. Reservoir Power supply  Motor  —.  Pump ,  •  Ref. Input  Servoamplifier  ^ Servo-valve actuator  Servow valve  J  1 •  b  4  Hydraulic actuator  —•>  Load  Signal modification circuit Figure 4.1 The generalized Block diagram of the electro-hydraulic servo system.  37  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  4.2.1 Modeling of the Hydraulic Cylinder The mathematical modeling of linear actuator or cylinders, has been extensively carried out in the past (Merritt, 1967; Viersma, 1980). A number of researchers have also addressed the issue of accounting nonlinearities such a Coulomb friction into these models. Usually, in modeling a hydraulic cylinder, most of the parameters required may be well known before hand. However, validation of the developed model through experimental analysis will greatly enhance the accuracy of the models. The theoretical models may be simplified by neglecting the insignificant dynamic effects, nonlinearities, and so on. The most important effects which lead to the development of an accurate model are: •  Oil compressibility  •  Frictional effects  •  Geometrical asymmetry due to piston-and-rod side areas  •  Actuator stiffness.  The dynamic equations for the differential cylinder are governed by the cylinder pressure dynamics in the cylinder chambers, and the piston motion. Figure 4.2 shows a schematic diagram of the piston-cylinder assembly. I X X X,  Cylinder  servo valve  Figure 4.2 Schematic representation of the hydraulic cylinder variables.  38  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  The cylinder pressure dynamics can be found by applying the generalized continuity equation to each of cylinder cambers, V,  Q -Qu=v +-r±h  h  Ph  For head side  pp  h  (4.1) Qr + Q  U  where, Q , Q , f Li  Le  ~ Qu =  V. r + - ^ - P r PPr  V  Wd  Sidt  are the internal and external leakage flows and the effective bulk  modulus of the hydraulic fluid, respectively. The respective volumes denoted by "V" include both the chamber and the line between chamber and the servo valve. These volumes can be expressed in the form given by f  v„=v,  h  +  L ^ —+ x A =  V  V +xA h0  J  2  (4.2)  (L  I  x  2  \  )  a A = V  r0  -  axA  where, Vu, , Vy , and Vbo ,Vro are the pipeline volumes of bore side, rod side, and initial r  volumes of bore side and rod sides, respectively. The length of the cylinder is given by L. Also note that, A =A h  (4.3)  Assuming the initial chamber volumes to be equal, that is assuming that the piston is at the center in the beginning, the cylinder pressure dynamic expressions can be derived by using equations (4.1) - (4.3), resulting in,  39  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  P =-^(Q -Ax h  h  +  Q -Q ) Li  uh  (4.4) Pr=jr(Qr+<*A*-Q -Q ) u  Uir  where, Cb and C are the hydraulic capacitance of bore side and rod side cylinder chambers, r  respectively. In using these equations we can usually neglect the external leakage flow, but the internal leakage flow can be easily estimated if the flow is considered to be laminar. In this case, Qu=Cu(Pr-P>)  (4,5)  where, Cu is the internal leakage flow coefficient. The cylinder motion dynamics can be found by applying Newton's second law to the forces acting on the cylinder; i.e., m x + F (i) = (p - ap ) A - F m  r  h  r  exl  (4.6)  Note that the total mass (m ) will include the piston mass, and the mass of the fluid tot  in the cylinder chambers and in the pipelines. In normal practice, however, the mass of fluid is neglected since it is insignificant compared to the mass of the piston. The frictional component of the equation (4.6), Ffx) can be found by using available models such as Stribeck friction model. The dynamic equations given here for the cylinder can be graphically represented as shown in figure 4.3 and can be used as a submodel when modeling the total hydraulic servo system.  40  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  Pressure dynamics for bore side chamber  Motion dynamics  Equation (4.4) Pb  Equation (4.6)  x  Pressure dynamics for rod side chamber Q  Equation (4.4)  Figure 4.3 Block diagram of the cylinder dynamics.  4.2.2 Modeling of the Flow Control Servo-Valve The servo valve which is used in the fish cutting machine differs from the conventional type which typically uses a double flapper nozzle pilot stage and a single spool boost stage with feedback wire. The main disadvantage of such a conventional servo valve is the cost. The valve employed in the fish cutting machine uses a two-spool boost stage and a flapper nozzle pressure control pilot stage. The main advantages and disadvantages of such a valve are summarized below: •  Since no feedback wire is needed between the nozzle flapper stage and the boost stage, the assembly and manufacturing becomes less complex, thereby making such valves less costly than their conventional counterparts.  •  They offer higher flexibility due to the ability to adjust each spool independently.  41  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  •  Higher safety since the flow can be cutoff completely by either of the spools in the event of a spool stick.  •  However, the performance of these types of valves under open loop conditions is not satisfactory. Operation of the Servo-Valve Figure 4.4gives a schematic diagram of the flow control servo valve employed in the fish cutting machine.  Pivot plate Flapper Nozzle Spool A Spool B  Figure 4.4 A schematic of the two spool flow control servo valve with pressure control. [Source: http://www.sauer-danfoss.com/]  42  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  As seen, this differs considerably from the conventional types that are commonly used. According to the operation, the valve may be sectioned into two important stages, namely, a torque motor actuated double nozzle pressure control flapper nozzle pilot stage and a two spool boost sage. The principle of operation behind this valve may be outline as follows. The pressure control pilot stage generates a differential pressure between the two chambers adjacent to the flapper, proportional to the current given to the torque motor. This differential pressure acts on both sides of the boost stage spools and the movement of the spools meters the flow in and out of the valve. Since the spools are centered using springs, the displacement of the boost stage spools is proportional to the differential pilot pressure and inversely proportional to the total stiffness (spring + flow forces). In figure 4.4, the directions of pressures acting on the boost stage valves and the flow paths are indicated, for the case where the flapper is displaced toward the right. Dynamic Equations of the Servo Valve When developing the dynamic equations for a servo valve, it is convenient to consider the system as an interconnection of three subsystems, and one is able to develop dynamic equations for these subsystems. The subsystems and their relevant states are as follows: •  The pilot stage :  this stage consists of the flapper, torque motor dynamics with flapper displacement and its velocity taken as their states, (x^ and Xf)  •  Pressure chambers :  the states of the system can be considered as the chamber pressures, PM and p . cn2  43  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  •  Boost stage :  the boost stage consists of the two spools A and B. Therefore, the sates can be considered as their displacements and the velocities, x _ x . x b , and x b m  sa  s  S  for spools A and B, respectively. Therefore, the dynamics of the pilot stage subsystem is given by the expression (Li, 2000):  Mx f  f  + Bx f  f  + Kx f  f  = A„(P - P ) + A7CC% [ ( X -x M  M  /0  f  f P -(x M  f0  -x  f  f P  ch2  + h(x ,i) f  (4.7) ' where, Mf, Bf and Kf are the combined inertia, damping, and the stiffness of the flapper, respectively. Parameters A and Q/ are the respective area and the coefficient of discharge of n  the nozzle, respectively. The flapper displacement Xf is taken as positive when the displacement is from left to right, and when Xf=0, the gap between the nozzle and the flapper is termed null nozzle-flapper gap, given by xp. The expression h(x ,i) represents the force f  on the flapper generated by the torque motor with a current input of / . Therefore, the dynamics for the pilot stage can be written as,  x =f (x x ,i,p p ) f  p  r  f  Mt  ch2  (4.8)  The states for the system are the flapper displacement and velocity, while the current and the chamber pressers are taken as the inputs to the system.  44  Chapter 4 Modeling of the Electro-Hydraulic  Manipulator System  The second stage is the dynamics for the pressure chambers, which are the pressures in upper and lower chambers connecting the pilot stage and the boost stage, and can be expressed as  P =PM  (4.9) Pchl = P  Ql(PM>Xf)-V2{t) v (t) 2  where,  Q (p ,x ) x  M  f  and  the flow rates into the upper and lower chambers,  Q (p ,x }aiQ 2  ch2  f  respectively. The parameters Vj(t),  and /? are the volumes in the chambers and the bulk  V (t) 2  modulus of the fluid, respectively. The flow-rates indicated here are a contribution of the flow from the pilot supply orifice; the leakage flows through nozzles and spools. By combining these results, the expressions for the respective flow-rates can be found by this.  O =C  a  c  A \-(v ^  p  { p ,  -p p«)  pilot supply orifice  pilot supply orifice  )-C  Kd (x  c^d  n  [  x  +x ) I  v  2  f  0  +  x  f  )  ^  P  M  leakage through nozzel  leakage through nozzel  &P<*\  nd  y  UM{Lio+x  ^ » r{Ps -P ) d  C  b  M  l 2 K L i o + X h )  leakage through spools  leakage through spools  (4.10) The leakage flow in these equations is obtained by assuming a laminar flow between of an annulus between a circular shaft and a concentric cylinder (Merrit,1967). Parameters Q/, Qo and C are the coefficient of discharge of orifice to supply, gap between flapper and nozzle, r  and the radial clearance between the bore. The supply pressures in the pilot stage and the  45  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  boost stage are given by p and p b, respectively. Investigation into equation (4.9) will reveal sp  S  that the chamber pressure dynamics will be governed by the chamber volumes and can be expressed, considering that the spools are at the center position, i  = K - A  v  x  a - A  x  b  (4.11)  where, Vj and V „ are the fluid volumes in all lines and chambers between the spool ends 0  2  and the flapper. Considering equations (4.9) - (4.11), the state equations for the chamber pressure dynamics can be expressed in the form of Pchl ~ fch\ (Pch\ ' f X  > a' b' a> b^) X  X  X  X  (4.12) Pchl ~ fchl (Pch2 ' f X  , ai b-> a-> b) X  X  X  X  The pressures in the respective chambers will be the states, and the displacements of the flapper, spools and velocities of spools will be the inputs to the chamber pressure subsystem. Finally, the dynamics for the boost stage subsystem can be expressed by applying force balance to the spool, and can be expressed in the form given in equation (4.13). As mentioned previously, the total force will comprise the force components by the spring, transient flows and steady state flows. Mx s  a  + B x + 2K x = (p s  a  s  a  ch2  - p ) A, - B (x , p )x - K (x , p )x M  f  a  a  a  f  a  a  a  (4.13) M  A  + sb B  x  + .< b 2K  x  = {PM - PM )A ~  46  B  ( b>Pb) bx  f  x  K  ( b,Pb) b x  f  x  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  The dynamics of the boost stage can be finally expressed in the form of a ~ fspooll { a ' a ' P ch\ ~ Pchl' Pa )  X  X  X  (4.14)  b ~ f spool1 { b > b ' Pchl ~ Pchl' Pb )  X  X  X  For the boost stage dynamics, the spool displacement velocities are considered as the states and the differential chamber pressure and work port pressures are considered as the inputs to the system. The output of the system (FCV) is the metered flow in and out of the work ports. It can be shown that these flows are given in the form, (Li, 2000)  Cvur r t n n\ d a —\Pa~Pr) L  wx  x  I »l {Pa~ PT) ~7Z TT \ nd  +  C  ti  1 0  (.P sb ~ Pa ) \~~  x >0  for  a  Qa =  (4.15) u a*  c  —\Psb ~ Pa)  wx  , —;—N  + 1 0  \P  ~  T  77  l2/*(Z, +x )  Up(L +x )  ( *» ~ > ) l2p(L x )  ( *> ~ " ) l2p(L x )  0  a  for  r~ l0  x (0 a  a  For Q , b  \ (n ip  n\ \  2  C  w  X  '  K P s b  P  h  )  P  m+  Pf  P  h  P  l0+  for  x >0 h  h  (4.16) r ,r rtn r7\ I ^C* {p ~ P ) d *—{Pb-PT) /, \ U  L  sh  wx  +  a  1 0  h  1td C] {p ~ P ) r i 77 rb  47  h  T  /or  x (0 h  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  Finally, the total system can be depicted as shown in the form of a block diagram as depicted in figure 4.5.  Pub  PL  Flow dynamics Eqs. (4.15)(4.16)  Pssp  Pilot Pal , stage dynamics ' Eq (4.8) PM  x  a  Boost Pch. stage dynamics PL —• Eq. (4.14) Pub  Chamber pressure dynamics  :  •  X  B  Eq. (4.12)  Pch2  Psb Psp  Figure 4.5 Block diagram of the servo valve dynamics. 4.2.3 Modeling of the Hydraulic Pump Models for hydraulic pumps are available in the literature with varying degrees of complexity. A simple model will be developed in the present study since it will be sufficient to demonstrate the intended task. The pump model can be developed by applying torque  48  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  balance and pressure dynamics to the pump. Applying Newton's second law to the pump, yields, J e + Td = p  where, J , 7}, Td , T,h , and T p  T - J -T  f  eo  aux  d  Vv  thco  (4.17)  ai  are the moment of inertia of pump, the frictional torque,  drive torque, theoretical torque and the torque required to drive the auxiliary components, respectively. The friction torque of the pump can be modeled using the expression (Mali, 1988) T (0) = T d + sign(e) c O + f  v  T  e T  s O  eX  P  c.  (4.18)  The ideal pump flow is given by v theo  e  2K  (4.19)  where V heo is the theoretical displacement of the pump and will depend on the pumping t  mechanism used. In the present study, the pump used is a positive displacement axial flow pump. In this case the displacement can be given by V =zd A ton<x lhm  c  c  (4-20)  where, z, d , A and a are the number of axial pistons, pitch circle diameter, effective piston c  c  area and the tilt angle of the swash plate. As the pump is integrated into a hydraulic circuit, a pressure load will act on the pistons which will be transformed into a force. The resulting theoretical torque is expressed as v LK  49  (4.21)  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  where, P is the load pressure. The pressure dynamics for the pump can be developed by L  writing continuity equations for the pump chambers, which yields,  (4.22) J  Where, Vo is the chamber volume, and Q is the leakage flow. The parameter C is the L  Li  leakage discharge coefficient. In arriving at this equation the external leakages have been taken to be negligible. Therefore, by using equations, (4.17) - (4.22), a simple model for the pump can be developed. 4.2.4 Modeling of Hydraulic Lines The dynamics of the pipelines in a hydraulic system play an important role in modeling, especially if the pipelines are considered to be long. According to Beater (1999), the effects can be neglected as long as the length (L ) is below a certain value, defined by pipe  (4.23) where, c and f^  are the sonic velocity in the selected oil and f  nuix  is the frequency of the  system. In most cases the frequency will be in the lower range, and the effects of pipeline dynamics can be neglected. Previous studies carried out on the fish processing machine shows that the frequency is considerably lower, thus pipeline dynamics has been neglected in the present modeling exercise.  50  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  4.3 Modeling Approach Modeling of the system is carried out by simplifying the dynamic models obtained in the previous sections. The reasons for doing so are the high complexity and nonlinearity of the system. For the servo valve, a reduced order liner model is used ( Li, 2001). According to the work carried out by him, the model is reduced by making several assumptions, and yet the behavior of the linear model is closely related to the nonlinear model. The assumptions made in linearizing are: •  Size of the model is reduced to a 5 order model  •  For the boost stage dynamics, the total spool displacement is considered instead of  th  those of individual spools •  For the chamber pressure dynamics only the differential pressure is considered  •  The transient component of the flow forces and leakage flows past the spools are neglected.  •  The pilot stage dynamics, boost stage dynamics and the chamber pressure dynamics found earlier are linearized at the equilibrium condition, which is given by: o flapper displacement (xf) is zero o chamber pressures, p  cnl  = p ia = p c  o spool displacements x = Xb = 0 a  o spool velocities x = Xb = 0 a  o chamber volumes Vi = V = V 2  o work pressures p ~Pba  Ps /2  51  Chapter 4 Modeling of the Electro-Hydraulic Manipulator System  4.4 Summary In this chapter the main focus was the development of a mathematical model for the electrohydraulic manipulator system used in the industrial fish cutting machine. Since most hydraulic systems possess a high degree of nonlinearity the model was simplified, yet retaining a high degree of closeness to the actual model of the system. A main focus of this section was the modeling of the two-stage two spool flow control servo valve using a pressure control pilot. In the next chapter, the development of the mechatronic evaluation methodology is discussed along with the validation of the method through simulation using the model developed in this section.  52  Chapter 5 System Evaluation Methodology and its Application  Chapter 5 System Evaluation Methodology and its Application 5.1 Introduction  The main objective of the present chapter is to develop a methodology for the evaluation of a mechatronic design, based on the energy flow between system components. The developed methodology will be applied to a practical system, which is the automated fish-cutting machine as described in Chapter 3 and modeled in Chapter 4, to ascertain its applicability.  5.2 E v a l u a t i o n Methodology  As mentioned in Chapter 2, mechatronics systems consist of various components belonging to different engineering disciplines or domains, and the assessment of the level of integration of these components plays a major role in design evaluation. In evaluating such multi-domain system, one needs to find a unified approach, which would integrate all components from different domains. Energy and information flow can be considered as the unifying thread since the flow of energy and information occurs between various components of a multidomain system. The methodology developed here is applicable for components in the power domain where the energy flow is significant, rather than in the information domain. Components in the power domain can include those from mechanical, hydraulic, pneumatic, and electrical domains. A mechatronics index (MI) is developed based on the matching of power and efficiency between components, in order to determine the degree of integration.  53  Chapter 5 System Evaluation Methodology and its Application Consider n number of components in the power domain of a mechatronic or mixed system as shown in figure 5.1.  r"  p  Hin)  r  -  P  2(m)  P  ~~5>  Component 1  /( (out)  (  Component 2  =>  '"j>i  Component n  Figure 5.1 B l o c k diagram of the power flow between components of a system. A component w i l l have a power input and a power output denoted by P, as shown in the figure, and the power output will usually depend on the efficiency of the particular component. For example, i f components 1 and 2 are to be connected, power output of component 1 w i l l be the power input for component 2, assuming that there is no power loss in between them. For the system to be integrated optimally based on energy flow, the available power for a component should be as close as possible to the required power. Based on the preceding argument, indices for each components can be defined described below. Index for component i,  {^i(in) in) available  / . = 1V, (max) "*"^7i  (P \  i(in) required  +P i(in) available  i(in) required )  where, - Efficiency of component i  54  }  (5.1)  Chapter 5 System Evaluation Methodology and its Application  ^li (max)  -  Maximum efficiency of component i. This efficiency will depend on the selected component and will have an upper bound. For example, if the component is working on a thermodynamic cycle its maximum efficiency will be considered as the Carnot cycle efficiency.  E[(available)  -  Actual power which is available for component i.  Pi(required)  -  Actual power that is required by component i according to the design requirements.  Similarly, for the n th component the index is given by,  In order for the component to be matched or integrated optimally, the corresponding indices should be minimized. The overall mechatronic index (MI) for the system based on this argument can be expressed as  MI =11(1-1,) i=i  (5.2)  where, n - number of components in the power domain Consequently, the objective is to maximize the overall mechatronics index (MI), for achieving optimum integration.  55  Chapter 5 System Evaluation Methodology and its Application  5.2.1 Analysis of Evaluation Methodology Consider the power expression in equation 5.1, which is given by  (P \  n(in) available  (P \  -P  )  2  n{in) required )  +P  n(in) available  n(in) required  It can be seen by observing the expression in equation (5.3) that when the available power is greater than the required power, an over-design condition exists and an under-design case will exist when the available power is less than the actual power required. Let us consider two cases where in one case the available power is a constant value and in the other a variable. Figures 5.2 and 5.3 represent the behavior of the power expression given by equation (5.3), for both constant available power and variable available power inputs for a particular component or device. For the purpose of analysis, the available power is kept constant at 50 HP and required power is varied between 10-90 HP in the first case, and for the second case the available power is varied between 10-90 HP while keeping the required power at 50 HP. In both cases it is seen that for the under-design as well as the over-design situation the power expression increases and it is at its minimum level when the available power and the required power match.  56  Chapter 5 System Evaluation Methodology and its Application  Figure 5.3 Variation of power expression with variable available power  57  Chapter 5 System Evaluation Methodology and its Application According to equation (5.1), i f we treat the efficiency expression to be unchanged the individual component index /, for a component i, will be minimized when the available power agrees with the required power, satisfying the argument that for a component to be optimally integrated or matched the individual indices should be minimized. The variation of the component index with the available power and the required power is shown in figure 5.4.  Figure  5.4 Relationship plot of I / with respect to P, (available) and P,  58  (required)-  Chapter 5 System Evaluation Methodology and its Application  Now keep the power expression (5.3) unchanged and consider the effects of variation of component efficiency in equation (5.1) on the component index and the overall index, as plotted in Figure 5.5.  Figure 5.5  Variation of the Index with respect to Efficiency.  From figure 5.5, it is evident that as the component efficiency (rf) increases the individual Index for the respective component decreases while the overall index (Ml) increases. The behavior of the overall mechatronic index (MT) with component indices 7, and I  i+J  is given in figure 5.6 in the form of a surface plot and a bar plot. It is clear from the graphs that as the individual component indices are minimized the overall mechatronic index will reach a maximum value. According to equation (5.2), the theoretical maximum for the MI, is unity, which is clearly seen from figure 5.6. Thus, a maximum value for the overall index MI indicates a somewhat optimal integration and matching of the components in the power domain of a mechatronic system.  59  Chapter 5 System Evaluation Methodology and its Application  60  Chapter 5 System Evaluation Methodology and its Application  5.3 Hydraulic Servo Systems and their Energy Transfer Before proceeding with the application of the evaluation methodology to the electrohydraulic manipulator system of the fish-cutting machine it will be worthwhile to briefly introduce the applications and principles of hydraulic servo systems. Hydraulic servo systems have been widely used in industry where large forces or torques are required, accurate control responses are necessary, fast stiff response of resisting loads is needed and manual control of motion involving substantial forces is essential. These systems have many advantages over other types of control such as electrical or pneumatic systems. The main advantages are (Merrit, 1967; de Silva, 1989; Will  etal., 1999):  •  Ability to produce high forces/Torques and have higher load stiffness.  •  Can be operated in continuous, reversing, intermittent, and stalled conditions.  •  Hydraulic fluid acts as a lubricant as well as a cooling medium.  •  Greater flexibility due to linear and rotary actuators.  •  Availability of compact systems with longer component life span.  •  Ease of overloading protection.  •  Actuators have higher speed of response.  As in many systems, hydraulic systems possess some disadvantages as well. Some of the disadvantages are: •  Undesirable in high temperature working environments.  •  Dynamic characteristics of the system are highly nonlinear and relatively difficult to control.  •  Contamination of fluid cannot be avoided. This may cause clogging of the various hydraulic components.  61  Chapter 5 System Evaluation Methodology and its Application  •  Somewhat costly compared to other systems.  The basic structure of a hydraulic servo system can be summarized as below. A standard, valve-controlled system is considered for the purpose of this explanation. •  The hydraulic power supply. This is usually a pump, which converts the available energy, typically mechanical energy from an electric motor or IC engine.  •  Control elements. These are usually valves, which are used to control the direction of the pump flow, the level of power produced and to control the amount of fluid and pressure to the actuating elements.  •  Actuating elements. The hydraulic power is finally converted back into usable mechanical power by using the actuating elements such as cylinders (linear actuators) and motors (rotary actuators).  •  Connecting elements, which consist mainly of pipelines or horses. These elements act as the connecting medium between the main elements mentioned above and are means of transmission of hydraulic fluid.  •  Fluid storage and conditioning elements such as reservoirs, accumulators, and heat exchangers, to ensure sufficient quantity and quality, and cooling of the fluid.  The main components along with their interconnections are depicted in figure 5.7, in the form of a block diagram. The unifying thread between these components is chosen to be the energy transfer among them. The energy transfer is taken as the power flow between them and always given by the product of the effort and flow variables (Karnopp, et al.,2000).  62  Chapter 5 System Evaluation Methodology and its Application  Electric motor CO  il  il  Variable displacement pump A~ s,p  QT,P  s,p  il  Pinelines between pump and servo valve  Ps,p'x  Pr,p',x7%  QT,P>.  - .1  >  o c  >  £ >5  o  00 ^  PT,SV x Qs,sv X,  c  o  T,svy  GT>  TV  Qs, svy  00 (D  to  13  cu  Ix  p *  Pi,  2  Gi*  G2  Qly  x  c o  c o  S « O  S~  O  •a § OH  P2,  O  ^3  DH  O  T3  Figure 5.7 Energy flow between components of the electro-hydraulic manipulator.  According to figure 5.7, the power conversions which take place are from electrical to mechanical, mechanical to hydraulic and hydraulic to mechanical, respectively. In each  63  Chapter 5 System Evaluation Methodology and its Application  component a certain amount of power will be lost and also during transmission of fluid power, energy will be dissipated in the transmission lines. In the next several sections these power outputs and power losses will be calculated using first principles, for each of the system components and the match between the available power to the required power will be estimated so as to apply the developed evaluation methodology.  5.4 Requirement Specification for the Electro-Hydraulic M a n i p u l a t o r System  The evaluation methodology is applied to the electro-hydraulic manipulator subsystem on the automated fish-cutting machine. A schematic diagram of the electrohydraulic manipulator system is given in figure 3.4 of Chapter 3.  5.4.1 Determination of the M a x i m u m Velocity and Acceleration of the M o v i n g Assembly  The first step here would be to find the required force and speed requirements of the actuation system. The force and the speed for the system would be the force required to move the fish cutting assembly table in both X and Y directions and the speed at which it has to be moved, respectively. Figure 5.8 shows a simplified representation of the cutter table in one direction of motion.  64  Chapter 5 System Evaluation Methodology and its Application  Velocity V A  ^  Mass M ^ ^ ^  A  ^  Force F  • Friction Force F  f  Figure 5.8 Force balance for the fish cutting table.  The time required to position the cutter table is found by Time to reach desired position = (Total cycle time) - (Time for image processing) (Cutting time) According to the research carried out previously (Rahhbari, 2001), these values are found to be as follows: Time to reach the desired position = (Total cycle time) - (Time for image processing) - (Cutting time) Specifically, Time to reach desired position = (1240ms) - (170ms) - (240ms) = 830ms -0.8 s  Maximum displacement of the moving mass is found to be 50.8 x 10" m. Therefore, 3  by considering the above requirements, the maximum velocity and the acceleration of moving table can be calculated as shown below, considering a triangular velocity profile.  65  Chapter 5 System Evaluation Methodology and its Applicatio  C/]  0.1  0.2  0.3  0.4  0.5  0.6  0.7  0.8  0.9  1.0  T i m e (s)  Figure 5.9 Velocity profile of the cutter table movement. The area under the curve is the distance traveled by the piston. Therefore, the maximum velocity of the piston V  max  is given by  50.8xl0" x2 03  V _ =—55  (5.4)  = 0.127 m/s The maximum acceleration of the piston can be found by applying V = U + at  where,  V- final velocity U - initial velocity a - acceleration t — time  66  (5.5)  Chapter 5 System Evaluation Methodology and its Application  According to this equation, the acceleration is computed as a = 0.3175 m/s  2  5.4.2 Sizing of Linear Actuators As mentioned previously, the linear actuators used in the experimental setup are two pistoncylinder units. The physical parameters of the selected pistons for the system are gien in Table 5.1 Table 5.1 Piston assembly parameters. Piston bore diameter (D bore)  3.81 x 10~ m  Piston rod diameter  2.54 x 10" m  U2  U2  (D i) ro<  Stroke (L)  50.8 x 10" m U2  Moving mass in X direction (M )  32.7 kg (measured)  Moving mass in Y direction (M )  55.7 kg (measured)  x  y  The main design parameters, which have to be found for the component selection are the pressures and flow rates into and out of the cylinders. Structural parameters of the components are neglected in this study, as our main focus is on power flow. Pressure Requirement Figure 5.10 gives a simplified schematic diagram of the piston and cutter table assembly, moving in the indicated direction. In the figure: • •  b and p are the cylinder pressures at the cap end and the rod end respectively.  P  r  Qb and Q are the flow rate into the cap end and the rod end sides of the cylinder, r  respectively. •  Ab and A are the bore end and the rod end cross section areas, respectively.  •  M is the mass of the cutting table  r  67  Chapter 5 System Evaluation Methodology and its Application  •  Ff is the net friction force acting on the moving mass (cutter table)  o i is a subscript denoting the specific direction coordinate; X and Y in the considered case.  A ,i  A ,i  h  r  I  Pb,,  Mi  Qb,i  Qr.i  Figure 5.10 Schematic diagram for force balance in the piston and the cutter table.  Applying Newton's second law to the system yields, in the X direction: Pr.xA.x  ~ Pb, A.x x  ~  r  F  f o r  =  x  M  x  retraction (5.6)  Pb,x b, A  x  - P ,xKx T  ~ f F  =  f o r  x *  M  extension  Similarly, for the Y direction: Pr,y r,y A  ~ P b,y b,y A  ~ f F  =  y'J  M  f  ° retraction r  (5.7) Pb,y b,y A  ~  Pr,y r,y A  ~ f F  =  M y  J  f01  " extension  Previous studies carried out on the system assembly table reveal that the net friction force, Ff is around 1200 N and is significantly higher than the frictional forces applied on the piston by the cylinder walls, seals, etc. (Tafazoli, 1996). It is also known that the cylinder used is of high precision type and the leakage losses of these types are virtually zero. The net frictional force is the combined effect of static,  68  Chapter 5 System Evaluation Methodology and its Application  Coulomb and viscous friction components. For initial calculations, the effect of the hydraulic fluid compressibility is neglected. By using equations (5.6) and (5.7), and the values in Table 5.1, cylinder pressures are calculated, and are tabulated in table 5.2. The cylinder return pressure is assumed to be maintained at 300 psi. Table 5.2 Calculated cylinder pressures.  Cylinder  Retraction  Cylinder for X  Pb.x  22.1 (320.5)  20.69 (300)  direction  Pr.x  20.69 (300)  56.38 (817.5)  Cylinder for Y  Pb,y  22.2 (322)  20.69 (300)  direction  Pr.y  20.69 (300)  56.52 (819.25)  Pressures (bar),(psi)  Extension Flow Requirement The flow requirement in and out of the cylinders to achieve the desired motion, can be formulated and found by using the flow continuity equation for an incompressible fluid given as Q = VA  where, Q = flow-rate V = velocity of the moving mass or piston A = cross sectional area  69  (5.8)  Chapter 5 System Evaluation Methodology and its Application  By applying equation (5.8), the following values for flow-rates into the cap side and the rod side of the cylinders were calculated: •  Flow rate in or out from cap-side of the cylinder, Q b, , Q b, = 1.4478 x 10 " m /sec, 04  x  3  y  (2.29 gal/min) •  Flow rate in or out from rod-side of the cylinder, Q , , Qr, = 8.0391 x 10 ~ m /sec, 05  r x  3  y  (1.27 gal/min) 5.4.3 Efficiency Considerations The overall efficiency of a hydraulic cylinder will be a contribution of volumetric efficiency and hydro-mechanical efficiency. The volumetric efficiency in this case is neglected since high precision cylinders are chosen with the present application. This means the leakages are negligible or considered nonexistent. The hydro-mechanical efficiency on the other hand cannot be neglected due to the frictional force of the seal on the piston head. The seal friction under a given set of working conditions cannot be easily calculated due to the multiplicity of variables involved. Therefore, either measurements have to be obtained by practical experimentation or simulations, but in most cases manufactures will provide graphs to find the required values. According to the empirical formulae and graphs given by the manufacturer (Refer Appendix A ) the calculation of friction force for low fiction type cylinder is given by F = \2D r  r  +30 F D p  r  +6 F D p  h  where, F  r  = running friction force (lbs-force)  D , Db = rod and bore diameters (inches) r  F  p  = friction factor for low seal friction type cylinder 70  (5.9)  Chapter 5 System Evaluation Methodology and its Application  Using equation (5.9) the friction forces on the respective cylinders in X and Y directions can be calculated. Then, the hydro-mechanical efficiency of the cylinder can be expressed as T  ^ '  cyl nder  _ Theoretical force developed - Friction force Theoretical force developed (5.10) F  ~  F  c f  Also,  POWer O U t p U t / cylinder  „  •  .  _  Power input  P  „  u  l  (cylinder)  r>  W -  1  J  J  P  in{cylinikr)  The power developed by the cylinder, out (cylinder)  P  = P\Qr ~ PhQb = P Q ~ P Q, h  h  (5A2)  r  By using equations (5.9) - (5.12), the required pressures for each cylinder are calculated and the results are tabulated in table 5.3.  Table 5.3 Modified cylinder pressures requirement according to efficiency  Cylinder  Retraction  Cylinder for X  Pb,x  24.6 (356.7)  20.69 (300)  direction  Pr,x  20.69 (300)  60.9 (883.05)  Cylinder for Y  Pb,y  24.7 (357.7)  20.69 (300)  direction  Pr,y  20.69 (300)  61.01 (884.65)  Pressures (bar),(psi)  Extension  71  Chapter 5 System Evaluation Methodology and its Application  5.4.4 Energy Losses in Pipelines Energy losses in pipelines occur due to three main causes, namely, • Friction •  Restrictions  •  Leakages Out of these three typs of losses, the most significant are the losses due to friction in  pipelines. The pressure drop due to friction can be calculated by using Darcy's equation: (5.13)  where, Ap = pressure drop /  = friction factor  L  = pipeline length  D u = internal pipe diameter ne  p  - fluid density  VUne  = fluid velocity in pine line  The friction factor/will depend on the Reynolds number and the type of flow, that is whether laminar Or turbulent. The Reynolds number is given by Re =  where,  line  v  v = kinematic viscosity of the fluid  72  (5.14)  Chapter 5 System Evaluation Methodology and its Application The friction factor/for laminar flow and turbulent flow, respectively, can be calculated by using  f =—  for laminar flow  Re  (5.15) / =0.1364. _  for turbulent flow  1  r  0 2 5  (ReJ  The flow regime is laminar if Re < 2000, and turbulent if Re > 4000. The information regarding the pipe diameters and the oil viscosities used for the system is given in Appendix A. For the pipelines connecting both cylinders, the flow can be calculated to be in the laminar range (Using equations 5.8 and5.14). The respective pressure drops in the pipelines connecting the X and Y cylinders with the flow control servo-valve can be calculated by using equations (5.13 - 5.15). The energy loss per unit time, or the power loss, due to the frictional losses in the pipelines can also be easily calculated once these pressure drops and flow rates in the pipes are known ,by using nn - , =  P  A  e  lr s  PuneQune  (5-16)  where, PUne-ioss =  Power loss in line (W)  The line pressure drops calculated according these equations are given in Table 5.4. . The pressure drop due to leakages and restrictions in the pipe lines is taken to be negligible.  73  Chapter 5 System Evaluation Methodology and its Application  Table 5.4 Line pressure drop between cylinders and servo valves Pressure drop (A p) Pipeline bar  psi  Cylinder X bore side and servo-valve  34.48 x 10"  Cylinder X rod side and servo-valve  18.71 x 10 "°  0.27  Cylinder Y bore side and servo-valve  58.62 x 10  0.85  Cylinder Y rod side and servo-valve  31.8 x 10 "°  U3  3  0 3  3  0.50  0.46  The pressures seen at the end of the pipeline, which are pressures seen by the servo valve, can be then calculated according to the values given in Table 5.3. The modified pressure values with the frictional losses incorporated are given in Table 5.5. Table 5.5 Modified pressure values with frictional losses. Extension Cylinder Cylinder Pressures (bar) (psi)  P'  b,x  Pb,x+  Ap  ,x  b  forX direction Cylinder for Y direction  P'r,x  Pr,x~  P' b . y  Pb,y+  P  Pb,y~  r,y  &P  r,x  A p b . y  A p  ,y  b  74  24.63 (357.2)  Retraction p ,xb  20.67 (299.73)  P r  24.73 (358.55)  P b , y  A /?  20.66 (299.54)  Pb,y+  L\p  i  X  +  Ap  A p  b  20.65 (299.5)  , X  ,  r  x  60.92 (883.32)  b,y  20.63 (299.15)  , y  61.04 (885.11)  h  Chapter 5 System Evaluation Methodology and its Application  5.4.5 Flow Control Servo Valve Figure 5.11 shows a simplified diagram of the 4/3 - way directional flow control servo valve, which is used to control the flow in and out of the actuators. The demanded flow to the actuators is supplied by the pump flow and regulated by the flow control servo valve by creating an appropriate pressure drop across the valve.  From pump Ps  Q  t  -To tank  Qi  II QaP  a  From actuator  To actuator  Figure 5.11 Simplified schematic diagram of the 4/3-way flow control directional servo valve.  The respective flows from the pump and the actuator into the valve, and flows to the tank and the actuator out of the valve are represented by the notation given in figure 5.11. The respective pressures are also indicated along side with the flows. Note that this case represents the actuator movement in one direction. For the case in which the direction of the actuator is reversed, the directions of flows Q and Qb will also be reversed. a  75  Chapter 5 System Evaluation Methodology and its Application  The general relationship between the valve opening, pressure drop, and the controlled flow through the valve can be given by the orifice equation Q = C A-JAP d  (5.17)  VP  where, Cd, A, p and AP , denote the coefficient of discharge, area of orifice, density of hydraulic fluid, and the pressure difference across the orifices, respectively. Applying equation (5.17) to the servo valve when the actuator is extending, one has 2  I  Q = C A^—yJP - P a  d  s  valve to actuator  a  (5.18) actuator to valve  Q = C A l—JP -P VP h  d  h  The load pressure P is defined as the pressure difference across the load, and is given by the L  expressions P =P — P L  a  for extension  h  (5.19) P =P —P L  h  a  for retraction  If the properties of both orifices are considered to be the same, by considering equations (5.17) through (5.19), one can express the flow to the actuator as Q=^r4 s- -p, p  p  L  (5.20)  VP  It can be assumed that the return line from the valve to the tank to be properly sized, and if so, the return pressure will be negligible compared to the supply pressure.  76  Chapter 5 System Evaluation Methodology and its Application  That is, (5.21)  P « P T  X  Then equation (5.20) can be expressed as (5.22)  4P  By using equation (5.22) the supply pressure needed to create the desired flow for actuation can be estimated and are listed in Table 5.6. The calculation is based on the value for density of the selected oil, and Cd = 0.85 and area A to be the fully open position (Walters,2000) Table 5.6 Supply pressures for servo valve. Cylinder  X  Stroke  Ext.  Y Retr.  Ext.  Retr.  Supply pressure to the servo valve (P ) psi 255.09 644.60 256.63 646.74 s  If we consider the flow rates required for these pressures, the maximum flow rates occur during the extension cycle of each cylinder. Taking into account the leakages in the servo valve, the required flow rates at the inlet of the valve will be higher than those of the outlet. The expressions for the flow rates are Q ,=Q -Q, t  s  (5.23)  where, Q , Q , Q ,Q and Q are the flow rates from cylinder bore end, cylinder rod end, a  b  s  t  t  pump to valve, valve to tank and leakage respectively.  77  Chapter 5 System Evaluation Methodology and its Application  Assuming a leakage flow of 0.85 gal/min (Appendix A) the required flow rates given below. •  Flow-rate required by the valve for cylinder (X) extension Q = 3.14 gal/min  •  Flow-rate required by the valve for cylinder (Y) extension Q = 3.14 gal/min  •  Flow-rate required by the valve for cylinder (X) retraction Q = 2.12 gal/min  •  Flow-rate required by the valve for cylinder (Y) retraction Q = 2.12 gal/min  sx  sy  sx  sy  Therefore, according to the fluid circuit shown in figure 3.4 in chapter 3, the total maximum flow rate required will be the total of these above values, when extending , specifically, Q  =  s(Tot)v  6.28 gal/min  (5.24)  5.4.6 Energy Losses in Pipelines between Servo Valve and Pump The main component of energy loss between the servo valve and the pump will be the losses in the pipelines due to friction. The other losses such as the losses at bends and restrictions are insignificant compared to the frictional loss, and hence they will be neglected in the present analysis. The length of the pipeline and the diameters are found to be 7.47 m and 19 mm each, respectively. By using equations (5.13) - (5.15) the pressure drop in the pipeline can be calculated as given below. •  From the calculated value for the flow in the pipeline, it is seen that the flow is in the laminar region. Re = 816<2000  •  The pressure drop is calculated to be 3.83 psi.  78  (5.25)  Chapter 5 System Evaluation Methodology and its Application  5.4.7 Sizing of Pump The pump is the main energy source of a hydraulic system and is responsible in providing the necessary system pressure and flow. Usually, the pump will be driven by an electric motor. The required pressure and the flow rate can be calculated as described next. The pressure required by the system will be the sum of the maximum values of pressures required by the cylinders, pressure drop between the cylinders and servo valves, pressure required by the servo valves, pressure drop between the servo valves and the pump, and any other unaccounted pressure losses, as expressed by Px eq(pump)  Pm a x , x , y ( c y l i n d e r s )  ~^-Ploss(pipe bet.cyl -servo)  P m a x,x,y(servo-valve)"^"/^loss(pipebet.  servo - pump)  (5.26)  "^"^ loss(other)  By substituting suitable values in equation (5.26) it can be calculated that the required system pressure is 1690 psi, allowing for a unaccounted pressure loss of 1% (Walters,2000) The flow rate required by the system will be the maximum flow rate which was calculated earlier as 6.28 gal/min.  5.5 Application of the Evaluation Methodology The developed evaluation methodology is applied to the electro-hydraulic system. The first step in doing so is to estimate the actual power inputs and outputs for each existing component of the system and compare with the recommended or required values.  79  Chapter 5 System Evaluation Methodology and its Application The existing pump operates at a speed of 1800 rpm giving a theoretical flow rate of 10 gal/min (Appendix A). The theoretical hydraulic fluid power (PHyd-r) is given by the relation  The units will be in Horse power (HP), when Q and p T  T  are taken in gal/min and psi,  respectively. The volumetric efficiency of the pump (n ) is found to be 97%, from the vol  manufacturer catalog, according to  P n _ lvol-—p  Hyd-actual V- *)  T  1  Hyd-theo.  Similarly, the mechanical efficiency of the pump is given by 7-)  ^mech-theo.  'Imech ~ p  sc /-JQ\ K~>  mech—actual.  The overall efficiency of the system is  Vomeral ^mech^vol  (- ) 5  30  The actual mechanical power is obtained from data sheets as, P ech-actual=^™> m  (5.31)  By using equations (5.27) - (5.31), the actual mechanical power input and the actual hydraulic power in and out of the pump can be calculated. Also the actual torque {T ) and act  the actual flow-rate (Q ) out of the pump can be calculated and are listed below. act  80  Chapter 5 System Evaluation Methodology and its Application p Hyd-actual  ^mech P  mech-actal  = 16.98 HP = 89% = 22 HP (from data-sheets)  ^mech—theo.  = 19.73 HP  Qout-act  = 9.7 gal/min  T  = 770.3 Ib.in.  input-act  The pressure drop in line from the pump to the servo valves can be calculated as previously done using equations (5.13) - (5.15), and for this case as well, the flow is found to be laminar. The pressure drop is calculated to be approximately 6 psi. Now the pressure and the flow available for the servo valves are, 2994 psi and 9.7 gal/min, respectively. The existing servo valves of the machine has a pressure rating of 3000 psi and flow capacity of alO gal/min. If the desired motion is to be performed by the actuator (cylinder), the same flow rates calculated previously, which are 3.14 gal/min and 2.12 gal/min each, should be provided to both servo valves individually for extension  and retraction,  respectively. Since the maximum of the supply pressure P in servo a valve occurs when the s  cylinder is in retraction, calculation relating to this pressure will be carried out. Note that this flow rate has accounted for a leakage of 0.85 gal/min present in the servo valves. By investigating the load-flow curves of the servo valve catalog the required flow rate of 2.12 gal/min can be obtained at 14 mA current setting of the spool and at a differential pressure of 1100 psi. Differential pressure is defined as &P = PS~PL  (5-33)  where, p and p are the supply pressure to the servo valve and theload pressure between the s  L  cylinder side of the servo valve, respectively. For a supply pressure of 2994 psi, one can calculate the load pressures for both servo valves. The cylinder retraction case is considered  81  Chapter 5 System Evaluation Methodology and its Application  here since it gives the highest load pressure. Other parameters such as the flow rate and the cylinder back pressure are kept the same as in the matched conditions. The efficiency of the servo valve is given by the expression 77  (5.34)  =PL  •servo Ps  It can be varified that the maximum power transfer occurs at (5.35)  3  Ps  Thus, the maximum efficiency of a servo valve is limited to 66.7% (Watton, 1989). The new values for the available power at each component can be calculated as in section 5.4. The power flow between the components in the case of the system sizing situation, which has been carried out in present Chapter, and the power flow between the same components for the actual case are depicted in figure 5.12.  P(>ut(cyl-X) req  X  p r  <D  out (cyl-X) availT3  u  I  1  •4 g  Pout(sv-X) req  !<C T J  in(cylinder-X) req I Pout(sv-X) avail  I  "1  Pin(sv-X) req ' Pin(sv-X) avail ] ^  OH  Pin( cylinder-X) avail I  ou/ (pump) req Pout (pump) avail Pout(cyl-Y) req P(>ut(cyl- Y) avail  P  1  "l  *in(cylinder-Y) req 1I  out(sv-Y) req P  r~"! Pin(sv-Y) req I  t  &2| Pout(sv-Y) avail (cylinder-Y) avail • tri  Pin(sv- Y) avail  OH  r in (pump) req  P in (pump) avail  Figure 5.12 Power flow among various components of the hydraulic system.  82  Chapter 5 System Evaluation Methodology and its Application  The values of the parameters in figure 5.12 along with their calculated required values are summarized in Table 5.7. Table 5.7 Power and efficiency values of the components in the system. Component  Cylinder  Servo-valve  Pump  X  Y  X  Y  HP  0.254  0.256  0.797  0.810  6.2  Pin (available) HP  1.221  1.228  3.700  3.700  22  rj (Efficiency) %  81  81  63  63  87  tf max  95  95  66.7  66.7  88  Pin (required)  Using equation (5.1) and the values in Table 5.7, the individual mechatronic indices can be calculated, and these values are given below. cylinder(X)  :  0.232  hylmder(Y)  — 0-23157  /  =021431  1  / 1  seivo-valve(X)  U  i  i  l  ^  J  (5.36)  1  =0 21117  serv()-valve(Y)  I  pump  " - ^  1  1  1  '  =0.15786  According to the values given in equation (5.36) the best component match is evident for the pump since its value is smallest compared to the others. This means that the pump and the electric motor are matched in an optimal manner. The overall Mechatronic index MI can be determined using equation (5.2), and as mentioned previously, the objective will be to maximize the overall index MI  83  Chapter 5 System Evaluation Methodology and its Application MI  —  (1  —  hylintler(X)  ) (1  _  ^cyliniler(Y)  )0  —  ^ servovalve(X )  Accordingly,  )0  _  ^ serwvalve(Y)  ) 0 ~ ^,,„m/) )  (5.37)  M / = 0.3080 Let us assume that the efficiency of the cylinder X is increased to 90%. Then according to the present argument the index for cylinder X should decrease and the overall index MI should increase. The index for cylinder X and the overall index MI is calculated and the results shown below. W ( x ) =0-2207 (5.38) MI  =0.3126  These numbers are consistent with the expected values.  5.6 Validation through Simulation The main purpose of conducting simulation is to validate the developed methodology. A simulation is carried out using the simplified model of the hydraulic system, as presented, using Matlab® Simulink and FAMIC® Automation Studio software. The procedure carried out in this section can be summarized by the steps: •  A system having similar requirements as the hydraulic system of the fish cutting machine is constructed and the individual component sizing is done in a manner similar to that discussed in this Chapter.  •  The individual component indices as well as the overall mechatronic index of the system are established.  84  Chapter 5 System Evaluation Methodology and its Application  •  A scenario is selected so as to degrade or mismatch one of the components, which in turn will increase the component's index and will decrease the overall mechatronics index, which indicates according to the evaluation methodology, that the system performance has degraded.  •  Important parameters of the system which influence the system performance as well as the power flow will be examined through the simulation results, and commented upon.  5.6.1 Selected System Data The main requirement of the system is to position a cutter table similar to that of the fish cutting machine, within a time span of 0.15 seconds. The distance to be moved is taken as 2 inches. The main components necessary to achieve this task are below •  3-phase induction electric motor.  •  Variable displacement hydraulic pump  •  3/4 way flow control servo valve  •  Double acting cylinder.  •  Auxiliary components such as filters and non-return valves. According to the requirements of the system, the pump requirement was found to be:  a 1200 RPM pump delivering fluid at 9.83 1/min. The load to be moved by the piston was taken as a 50 kg table and a 1200 N frictional force. According to the efficiencies and the power requirement, the indices and the overall mechatronic index for the system are as follows: •  7 , ^ = 0.1137  •  I  sem>  = 0.2060  85  Chapter 5 System Evaluation Methodology and its Application  0.2157  "  I  •  MI =0.5519  cylinder =  Now, the internal friction of the cylinder is increased by 40% of its initial value, thereby reducing its overall efficiency. Treating the other parameters of the system to be unchanged, the new value for the cylinder index and the overall index are calculated and are given by 0.2632  "  / cylinder =  •  MI = 0.5185  As expected, the individual component index has increased from 0.2157 to 0.2632 while the overall index MI has decreased from 55.2% to 51.85%, which means a system mismatch has occurred resulting in possible degradation of the system performance.  5.6.2 Simulation Results Figure 5.13 shows the behavior of the piston displacement for the two situations considered before. The time necessary for the piston to extend to the desired position of 2 inches when the internal frictional force is increased, has increased to approximately 0.2 seconds. This indicates that the system performance has degraded.  86  Chapter 5 System Evaluation Methodology and its Application  Figure 5.14 shows the head side pressure variation for both conditions. As it can be seen from the graph, the variation of the pressure will be nonuniform making the system to  87  Chapter 5 System Evaluation Methodology and its Application  vibrate. This is mainly due to the higher pressure needed by the cylinder to achieve the system performance.  Time (ms)  Figure 5.14 Variation of cylinder bore side pressure. The variation of the flow into the bore side during extension of the piston is illustrated is figure 5.15. It is evident from the results that the time duration over which the flow has to be supplied during extension has increased, which in turn is an indication of the delay in reaching the desired position.  88  Chapter 5 System Evaluation Methodology and its Application  0  500  1000  1500  2000  2500  3000  Figure 5.15 Variation of cylinder bore side flowSimilarly, the variation of the pressure and the power at the pump can be illustrated as in figures 5.16 and 5.17, respectively. It is seen that the pressure delivered by the pump is slightly higher than in the case where a lower frictional force is present. The reason for this is the additional flow required by the piston demands more pressure from the pump to create the necessary flow rate. The power variation also shows a similar pattern, and furthermore a power fluctuation is evident in the results.  89  Chapter 5 System Evaluation Methodology and its Application  500  600  700  800  900  1000  1100  1200  1300  Figure 5.16 Variation of pump pressure.  1400  1500  • Time (ms)  Time (ms)  Figure 5.17 Variation of pump delivery power.  90  Chapter 5 System Evaluation Methodology and its Application  5.7 Summary In this chapter the developed evaluation methodology was presented followed by an analysis and validation of the methodology. The effect of the individual component index valueson the overall mechatronic index was investigated. Application of the methodology was demonstrated on a real industrial application, the electro-hydraulic manipulator system of the industrial fish processing machine. The behavior of the index based on real component selection was studied. Several simulation tests were carried out using Matlab® Simulink and FAMIC® Automation Studio. The system behavior was investigated with reference to the developed methodology. As expected, the index showed an influence on the system performance, which is an indication that the developed methodology can be useful as an index for evaluation of a design, particularly component matching in the power domain. In the concluding Chapter, the research carried out in the present work will be summarized and further developments and improvements that should be done related to the evaluation methodology will be indicated.  91  Chapter 6 Conclusions and Recommendations  Chapter 6 Conclusions and Recommendations 6.1 Introduction  The work presented in this thesis focuses on the development of a methodology for evaluating a mechatronic system or design, particularly an existing system. The developed methodology is then used to evaluate the degree of component integration or component matching of the electro-hydraulic manipulator system of the automated fish cutting machine, which has been designed at the Industrial Automation Laboratory, University of British Columbia. Mathematical modeling of the main components in the electro-hydraulic system, specially the electro-hydraulic flow control servo valve, which differs significantly from the conventional type, is presented in this thesis. This final chapter summarizes the primary contributions of the research, outlines the significance of these contributions, and suggests possible future work on the research for further enhancement the developed methodology. 6.2  Contributions  The major contributions made in this thesis are as follows: 1) A novel evaluation methodology for the evaluation of an existing mechatronic system was developed. This evaluation methodology is based on the energy flow between various components belonging to different domains. Based on the degree of component integration, a Mechatronic index was formulated to measure the degree of component matching. The feasibility and the effectiveness of the technique were demonstrated by implementing it on the electro-hydraulic manipulator system of an industrial fish cutting machine.  92  Chapter 6 Conclusions and Recommendations  2) The developed index was analyzed mathematically to demonstrate the appropriateness of the methodology. 3) Indices of individual components of the electro-hydraulic manipulator were found and the overall mechatronic index for the system was established. The effect on the index of selecting a better choice of components was demonstrated. 4) Mathematical modeling of the individual components of the system was presented, especially the electro-hydraulic flow control servo valve employed in the machine. 5) The effect of the index on the overall system performance was verified through simulation studies.  6.3 Significance of the Research When dealing with multi-domain systems such as mechatronic systems, one needs to find the best match of various components in order to achieve the optimal behavior mechatronic systems. Furthermore, when assessing existing systems, it is desirable to have a measure for evaluating how well the components are integrated so as to achieve the expected characteristics. The developed evaluation methodology directly achieves these two goals, by not only providing a tool for mechatronic design but also as an assessment tool for a wide range of multi-domain systems.  93  Chapter 6 Conclusions and Recommendations  6.4 Suggestions for Future Work There are many issues and aspects that still needed to be investigated in the context of the research reported in this thesis. The following are some directions for possible future research: 1) The developed methodology is mainly based on energy flow between components in the system, which implies that only components in the power domain have been considered. A vital aspect of mechatronic systems is the components and operations in the information domain, such as sensors and signal conditioning devices. Integration of these components plays a major role in the overall system performance. Not only does one need to match/integrate the components in the information domain but integration of components in the information domain and power domain also has to be incorporated. A major challenge of incorporating the information domain is to determine a suitable design metric for components in this domain. It may not be as straightforward as in the case of components belonging to the power domain, where the design metric or the unifying thread has been selected as the energy flow. A recommended design metric or the unifying thread for the information domain may be entropy. If the mechatronic index can be modified to reflect the integration of components in the information domain as well, then certainly, a better reflection of the degree of integration or component matching can be achieved thought it. 2) The index can also be further enhanced to incorporate other attributes of a mechatronics system, such as intelligence, controllability, reliability, flexibility, and complexity.  94  Chapter 6 Conclusions and Recommendations  3) Currently, research is being carried out on the optimization of multi-domain systems. The applicability of the developed index in optimizing these systems should be explored. 4) The index has been tested only on the electro-hydraulic manipulator system, which is only one subsystem of the industrial fish cutting machine. Extension of the idea to other subsystems of the machine, for example, the pneumatic system and the mechanical systems, will give an overall evaluation index for the entire fish cutting machine. 5) Accurate modeling of hydraulic systems is a complex and a tedious task. Since the main objective of the modeling carried out in this study was to establish the relation of the index on the system performance, several assumptions were made in order to keep the model tractable. A more thorough investigation is necessary to realize a rather accurate model of the electro-hydraulic manipulator system of the fish cutting machine.  95  Bibliography  Bibliography  [I]  Automation Studio, User's Manual, FAMIC® Technologies Inc., QC, Canada.  [2]  Craig, K., De Vito, M., Mattice, M., La Vigna, C , and Teolis, C , "Mechatronic Integrated Modeling," Proc. IEEE/ASME Int. Conf. on Advanced Intelligent Mechatronics, Atlanta, GA, pp. 17-25, 1999.  [3]  Cundiff., J.S., FLUID POWER CIRCUITS AND CONTROLS - Fundamentals and Applications, CRC Press, Boca Raton, FL, 2002.  [4]  de Silva, C.W., Control Sensors and Actuators, Prentice-Hall Inc., Englewood Cliffs,  NJ, 1989.  [5]  de Silva, C.W., MECHATRONICS - An Integrated Approach, CRC Press, Boca Raton, FL, 2004.  [6]  de Silva, C.W., "Sensing and Information Acquisition for Intelligent Mechatronic Systems," Proceeding of the Symposium on Information Acquisition, Chinese Academy of Sciences, Hefei, China, pp. 9-18, Nov. 2003.  [7]  de Silva, C.W., "Research Laboratory for Fish Processing Automation," International Journal of Robotics and Computer-Integrated Manufacturing, Vol.9, No.l, pp. 49-60, 1992.  [8]  Esposito, A., Fluid Power with Applications, Prentice-Hall Inc., Englewood Cliffs, NJ, 1988.  [9]  Grante, C , and Anderson, J., "A Method for Evaluating Functional Content in Mechatronic Systems using Optimization," Res. Eng. Design, Vol. 14, pp. 224-235, 2003.  [10] Hehenberger, P. and Zeman, K., "Evaluation of Mechatronic Design Concepts with Special Consideration of Couplings Between The Domains," Proc. 9th Mechatronics Forum International Conference, Ankara, Turkey, pp. 09-14, September 2004. [II] Hussein, B.A., "On Modeling of Mechatronic Systems - A Geometrical Approach," Mechatronics, Vol. 10, pp. 307-337, 2000. [12] Isermann, R., "Modeling and Design Methodology for Mechatronics System," IEEE/ASME Trans. Mechatronics, Vol. 1, No. 1, pp 16-28, 1996. [13] Jelali, M. and Kroll, A., HYDRAULIC SERVO-SYSTEMS - Modeling, Identification and Control, Springer-Verlag, London, UK, 2003.  96  Bibliography  [14] Karnopp, D. C , Margolis, D. L., and Rosenberg, R. C , SYSTEM DYNAMICS Modeling and Simulation of Mechatronic Systems, John Wiley & Sons Inc., New York, NY, 2000. [15] Li, P.Y., "Dynamic Redesign of a Flow Control Servo-valve using a Pressure Control Pilot," Proc. ASME International Mechanical Engineering Congress and Exposition, New York, NY, pp. 07-16, 2001. [16] Li, Q., Zhang, W.J., and Chen, L., "Design for Control - A Concurrent Engineering Approach for Mechatronic Systems Design," IEEE/ASME Trans. Mechatronics, Vol. 6, No. 2, pp. 161-169, June 2001. [17] Merritt, HE., Hydraulic Control Systems, John Wiley & Sons Inc., New York, NY, 1967. [18] Mori, T., Mechatronics, Yasakawa Internal Trademark Application Memo, No. 21.131.01, 1969. [19] Moulianitis, V.C., Aspragathos, N.A., and Dentsoras, A.J., "An Index for the mechatronic design of systems and products," Proc. First Nat. Conf. on Recent Advances in Mech. Eng., Patras, Greece, pp. 06-12, September 2001. [20] Mrozek, Z., "Design of Mechatronics System with Help of UML Diagrams," Proc. 3rd Workshop on Robot Motion and Control, Bukowy-Dworek, Poland, 2002. [21] Paredis, C.J.J., Diaz-Calderon, A., Sinha, R., and Khosla, P.K., "Composible Models for Simulation Based Design," Engineering with Computers, Vol. 17, Springer-Verlag Ltd., London, UK, pp. 112-128, 2001. [22] Rahbari, R., A New Inference Method for Multivariable Fuzzy Systems with Application in Industrial Control, Ph.D. Thesis, Department of Mechanical Engineering, University of British Columbia, Vancouver, Canada, 2001. [23] Tafazoli, S.B., Identification of Frictional Effects and Structural Dynamics for Improved Control of Hydraulic Manipulators, Ph.D. Thesis, Department of Electrical  and Computer Engineering, University of British Columbia, Vancouver, Canada, 1996.  [24] Ullman, D.G., The Mechanical Design Process, McGraw-Hill Inc., New York, NY, 1992. [25] Viersma, T.J., Analysis, Synthesis and Design of Hydraulic Servo systems and Pipelines, Elsevier Science, Amsterdam, The Netherlands, 1980. [26] Walters, R.B., Hydraulic and Electro-hydraulic Control Systems, Kluwer Academic Publishers, Dordrecht, The Netherlands, 2000. [27] Watton, J., FLUID  POWER SYSTEMS - Modeling, Simulation, Microcomputer Control, Prentice-Hall., Englewood-Cliffs, NJ, 1989.  97  Analog and  Bibliography  [28] Will, D., Strohl, FL, and Gebhardt, N., HYDRAULIK - Grundlagen, Komponenten, Schaltungen, 2nd Edition, Springer, Berlin, 1999. [29] Youcef-Toumi, K., "Modeling, Design, and Control - A Necessary Step in Mechatronics," IEEE/ASME Trans. Mechatronics, Vol. 1, No. 1, pp. 29?-38, 1996.  98  Appendix Appendix  Specifications  A . l O p e n C i r c u i t V a r i a b l e Displacement P u m p  T a b l e A . l H y d r a u l i c p u m p properties S A U E R & S U N D S T R A N D Series L F r a m e Size  23  Delivary @ max. R P M •  GPM  19.5  •  1/min  73.8  Displacement •  In3/Rev  1.41  •  Cc/Rev  23  Input Speed •  Max R P M  3200  Pressure •  M a x (psi)  3000  •  M a x (Bar)  210  [Source: http://www. sauer-danfoss. com/]  99  Appendix  20 S 15. O 10 o  V  5  E  1000  Psi  3000 Psi  0  500  1000  1500  2000  3000  2500  Shaft Speed (RPM) Figure A . l Pump  100  Outlet Flow  •  1000 P s i  95 o  3000 Psi !  .1 90 u PQ 500  1000  1500  2000  2500  3000  Shaft Speed (RPM) Figure A . 2 Volumetric Efficiency  £  9  5  £ 90 CD  'M 85 SB 80  1000 Psi  3000 Psi  > O 500  1000  1500 2000 Shaft Speed (RPM)  2500  3000  !  Figure A . 3 Overall Efficiency  [Source: http://www.sauer-danfoss.com/ ]  100  Appendix A . 2 H y d r a u l i c O i l Properties Table A . 2 H y d r a u l i c oil properties E S S O ™ N U T O H G r a d e 32 Density k g / m  872  3  32.6  Viscosity c S t @ 40 ° C c S t @ 100 ° C  5.4  Viscosity Index  97  P o u r Point ° C  -36  F l a s h Point ° C  206 [Source: http://www, esso. com/ ]  A . 3 F l o w C o n t r o l Servo Valve  Table A . 3 F C V Specifications  SAUER & SUNDSTRAND MVC113 Rated supply pressure (Psi)  3000  Rated Flow ( G P M )  10 +15% to-10%  Leakage ( G P M )  0.85  [Source: BLN 95-8964-6 Technical manual ]  101  


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