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Kinematic, force and dexterity analyses of planar robotic grasping Saliba, Michael A.


The grasping of an object or workpiece is an important step of robotic manipulation and is the main function of a robot hand. This has been a subject of considerable research. Robotic hands that can conform to the shape of a workpiece can provide efficient and stable handling, and furthermore, through suitable sensors, can serve as means for extracting information regarding the workpiece. But, for reasons of cost, size and weight, conformability of a robotic hand should be realized with the least possible number of actuators. In this study, a planar robotic gripper, suitable for the grasping and handling of a variety of objects, is designed, analysed, constructed and tested. The design has two fingers, four links, and two actuators, but can be directly extended to more links while keeping the number of actuators unchanged. This robotic end effector exhibits two distinctive features. First, it utilizes fewer number of actuators than it has degrees of freedom, thus providing quantifiable savings in weight, size, complexity and cost. Second, it is capable of conforming to different shapes and sizes of object through autonomous, sequential switching of the actuator drives between links. An analysis of the mechanics of the grasping process using a hand of this type is carried out, and simulated results are compared to the experimental results. Close agreement is exhibited in these comparisons. The analysis is extended to a six degree-of-freedom gripper, and to grippers having simultaneous, rather than sequential, link motion. In the final part of the study, a new method for the measurement of dexterity in grasping is proposed, based on the results obtained from the analyses and simulations. Accordingly, a robotic hand of the types analysed can be assigned a Grasping Dexterity value, defined as a measure of the ability of the hand to achieve successful grasps under a variety of situations in the shortest possible time.

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