A COMPARISON STUDY OF ACTUATORS AND PATH PLANNERS FOR INCREASING ROBOT SAFETY

Abstract

Since robotic arms operating close to people are increasingly common, there is a need to better understand how they can be made safe, while still providing the required performance. The objective of this thesis is to study and compare various actuators and methods for improving robot safety. It begins with a study of the safety and performance of a one degree of freedom (DOF) robotic arm whose parameters are mostly derived from the first joint of a 6-DOF industrial robot. The use of electric actuator (EA), series elastic actuator (SEA), pneumatic actuator (PA) and hybrid pneumatic electric actuator (HPEA) with model-based controllers to drive the robotic arm, and the collision between the arm and a human head, are simulated. The simulation employs dynamic models of the robot, actuators, and collision. The addition of a compliant covering to the arm, and the use of collision detection and reaction strategies are also studied. The performance and safety of the robot are quantified using root mean square error (RMSE) between the desired and actual joint angles in the trajectory, and maximum impact force (MIF), respectively. When compliant covering and the collision reaction strategy “withdrawing the arm (WTA)” are both applied, and the detection delay is 25 ms, the MIF reduced by 65% or more. Furthermore, when the desired closed-loop bandwidth is chosen individually, EA has the best performance, and SEA and PA are the safest. The HPEA is the best choice when considering both safety and performance. Next, the relationship between the joint angles and the reflected mass of a 3-DOF planar robot is studied. A novel optimal path planner for reducing the reflected mass is then proposed. Simulation results show the planner can reduce the MIF by 75%, while still being able to bring the robot’s end-effector to the target position precisely.