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UBC Theses and Dissertations

Intelligent hierarchical control of a deployable manipulator Goulet, Jean-Francois

Abstract

This thesis focuses on the development and implementation of an intelligent hierarchical controller for a deployable manipulator that may be used in space- and ground-based applications. The emphasis is on the use of knowledge-based tuning of the low-level controllers so as to realize accurate operation under complex and incompletelyknown conditions, with a degree of autonomy. The robot that is investigated consists of two links: one free to slew (revolute joint) while the other allowed to deploy (prismatic joint). A three-level hierarchical system is developed, to control the manipulator. In the bottom layer of the hierarchy, a conventional proportional-integral-derivative (PID) controller is used, for regulating the manipulator joints. The middle layer monitors the performance of the joints of the manipulator, preprocesses the response signals, and extracts the performance parameters, based on a step-input response. The top layer makes inferences for appropriate tuning actions on the PID servos. A decision table is developed using linguistic rules of expert knowledge in tuning PID servos, in order to facilitate fast decision making in the top layer. The knowledge that is contained in this rulebase is acquired from available sources, and represented and processed using the fuzzy logic theory. The governing equations of motion for the ground-based manipulator are developed using the Lagrangian procedure. A Turbo C program is written for the groundbased simulations of the system, which incorporates the manipulator model and the hierarchical control system. Extensive ground-based simulations are carried out for trajectory following tasks. The space-based simulations are also carried out, making use of an existing Fortran program for a robot model tracking a trajectory. These simulations incorporate proportional-derivative control, along with the feedback linearization technique (FLT). An extensive study is carried out to determine the sensitivity of the performance of the control system to changes in the knowledge base. The developed control system is implemented on an existing prototype manipulator, in laboratory. The control software is written in Watcom C, and the manipulator is controlled using the QNX operating system, for real-time operation. A number of trajectory-following experiments were carried out. The study shows a good level of agreement between the ground-based simulations and experiments, with excellent performance of the manipulator when operated under the hierarchical control system. Since the space-based simulations also show good performance through the hierarchical control system, it can be concluded that the developed control system is an appropriate option for controlling space-based manipulators as well. The study further shows that, even in the absence of autotuning, knowledge-based tuning of the servo controllers of the manipulator at strategic task configurations can lead to a significant improvement in performance of practical manipulators.

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