FORCE AND POSITION CONTROL OF ROBOT MANIPULATOR
Abstract
The research presented in this dissertation concerns two major problems involving mechanical manipulators which are operated under computer control: (1) manipulator compliance based on joint torque control, and (2) cartesian motion control of many degree-of-freedom manipulators by a force convergent method. The application of robot manipulators to batch manufacturing product assembly requires the control and monitoring of both robot force and position. A good force sensing technique is imperative to increase the robot's capabilities in this area. A fast reliable force servo system based on the proper sensing technique is also needed to increase the speed of robot operations. This dissertation analyzes currently existing force sensing techniques concluding that a joint torque sensing technique will result the best performance in a force servo system. A new simple, high gain, wide bandwith torque servo system using a joint torque sensor system has been developed and has been verified by using a single joint manipulator. An accurate method of selecting the force servo joints to provide compliance has also been developed. In addition, a complete and consistent algorithm for performing compliance is presented. Secondly, a simple practical Cartesian path control scheme for a many degree-of-freedom manipulator is described in which the position of the end-effector is controlled by directly exerting forces at the mass center of the end-effector by the joint actuators. A force convergent method employing a wrist force sensory is used to estimate actuator torques to apply such that the correct forces are applied at the mass center of the end-effector. The control method automatically compensates for gravity torques, internal friction and the changing configuration of the manipulator. The control scheme is also independent of the number of degrees of freedom of the manipulator. The path of the control point of the manipulator is based on the Cartesian path control method proposed by Paul (2) however any Cartesian path may be followed. The control scheme operates in Cartesian coordinate directly instead of present methods which control the joints of the manipulator. A simulator of a multiple degree of freedom manipulator to verify the method using the kinematic data of the JPL Stanford Arm is also described.
Degree
Ph.D.
Subject Area
Electrical engineering
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