CONTACT FORCE AND POSITION CONTROL IN CONSTRAINED ROBOTS : THEORY AND EXPERIMENTS

Abstract

Control of robot manipulators during execution of tasks that require the end-effector to come into contact with objects in its work environment represents an important class of control problem. In this thesis, three different control schemes to simultaneously control the position and contact force for the constrained robot systems are studied. They are as follows: 1. Local regulation control scheme, 2. Trajectory tracking control scheme, 3. Adaptive force and position control scheme. First, a procedure for local regulation of position and contact force based on a local state realization is studied. Next, a feedback control algorithm is studied which ensures tracking of time varying position and force trajectories such that the position and force tracking error in the closed-loop system approaches zero exponentially. Finally an adaptive controller for constrained robot systems with uncertain dynamic model parameters is presented which ensures zero steady-state motion error and bounded force error. These control schemes were used to develop force/position control laws for a 2-dof parallelogram robot and simulations were done using this robot. Simulation results verified the satisfactory performance of the proposed control schemes. An experimental facility was also developed for performing experiments in robot contact task control. It consisted of a 2-dof parallelogram robot driven by direct-drive motors. A force/torque sensor was installed at the end of the last link to measure the contact force. The constraint surface was a rigid wall. The complete facility was controlled using a PC. This thesis explains the development of the hardware and software components of the above mentioned controller. The results of the real-time experiments conducted to verify the performance of the three proposed control schemes are presented which show the feasibility of the proposed control schemes. Transition control from noncontact motion to contact motion was also performed using this facility and the results of this experiment are also presented.