Effect of Actuator Torque Degradation on Behavior of a 6-DOF Industrial Robot

Actuator faults of robot manipulators may occur during their lifetime after long time in operation. There are several kinds of actuator failures such as locked joints, free-swinging joints, and loss of actuator torque effectiveness. The main goals of this paper are (i) to classify the loss of torque effectiveness, called torque degradation, into three divergent cases: Boundary Degradation of Torque (BDT), Boundary Degradation of Torque Rate (BDTR), and Proportional Degradation of Torque (PDT); and (ii) to analyze their effect on behavior of a typical industrial robot. The possible failures might degrade the whole system performance or in some certain cases leading to unavoidable damages. In normal operation, we do not have a controller designed specifically for these faults. In order to have a better understanding on how the mentioned problems affect robot operations, with an assumption that the knowledge of robot parameters are known, a closed-loop control law is used to demonstrate the control ability in dealing with these cases. By taking advantage of MATLAB/Simscape Multibody, the quasi-physical model of robot is employed instead of expensive prototypes and experiments. Simulation results show that the joint responses according to different types of failures. In many cases, the robot cannot track the reference trajectories properly.