Adaptive control of a six dof robot manipulator

Abstract

Robot manipulators are used in the industry for industrial applications such as pick and place, painting, packaging, assembly, welding and machining. Performance improvement of the robots is important for increasing efficiency and accuracy in the tasks where the robots are used. Control algorithm is a vital part of the robot that effects the performance of the robot. The performance of the control algorithms based on the dynamic model of the robot may degrade under uncertainties associated with the dynamic model of the robot if they are not accounted for. Generally, adaptive or robust control is used to cope with these uncertainties. Adaptive control includes an online parameter adaptation mechanism to take these uncertainties into account. Adaptive control has the advantage of the online performance improvement over robust control. Therefore, adaptive control is an appealing approach for the control of the robot manipulators in the presence of disturbances and uncertainties in the dynamic model of the robot. In this study an adaptive control algorithm proposed by an earlier study implemented on a six-DOF robot manipulator. Experiments are accomplished on a Stäubli RX160 robot manipulator. An integral term is also added to the original control law to reduce steady-state errors. Performance of the adaptive control algorithm is compared to performace of the two non-adaptive approaches for varying payloads, namely computed torque control and passivity-based control. This thesis consists of five chapters. In the first chapter purpose of the thesis, literature review and basic information about the industrial robot system used in the experiments are given. Second chapter mentions basics of kinematic and dynamic modeling of robot manipulators as well as models for friction and spring effects. Third chapter gives theoretical background for the control algorithms implemented in the experiments. Control laws and block diagrams for computed torque control, passivity-based control and adaptive control are given. Fourth chapter gives the experimental results of this study. Position errors, velocity errors, torque values and rms position errors for varying payloads are compared to each other for the three controllers implemented in the experiments. Finally concluding remarks are given in the fifth chapter.