FORCE CONTROL OF ROBOT MANIPULATORS

Abstract

Sensory feedback has been recognised as the key to the development of intelligent robot manipulators. In recent years, the concept of force feedback is generally accepted to be essential for tasks where the robot is in contact with the workpiece. A properly applied force can reduce the positioning accuracy necessary to perform a given task and in fact make possible assembly tasks which would otherwise be impossible. In an effort to promote the greater use of robots, a force control manipulator has been developed in this project. The design and implementation of a force control robot is presented in this thesis. The system consists of a microcomputer, a force sensing wrist and the PUMA 560 robotic manipulator. The original controller for the robot has been bypassed and the manipulator is directly controlled by the microcomputer. A positional control system has been designed and implemented replacing the original factory-supplied positional system. A force control loop which can follow any desired endpoint force requiremert has also been designed and implemented in this project. The combined system incoroperating force and position system was successfully tested on the PUMA 560 robot. The system was developed for operations where the endpoint forces are monitored and controlled like grinding or polishing. In these operations, the end effector, with the appropriate tool, moves slowly along the surface of the workpiece while maintaining a desired normal force against the surface. With such an operating environment in mind, the conventional independent joint approach was adopted for the design of the position control system. The force controller, supplementing the position system, is also designed with each joint as an independent system. This approach has the advantage of a shorter design and implementation phase as compared to the case when coupling among different axes are taken into account.