Limitations of PID Control of Assembly Robots

Abstract

Assembly automation is increasingly taking advantage of robot technology to achieve greater efficiency and productivity. To keep pace with industrial requirements robot manipulators are often required to have the ability to handle payloads of a range of weights and to follow trajectories with high speed and accuracy. Any control scheme used in this task must achieve fast but stable motion of the manipulator. The conventional and most widely used control scheme is the PID controller. However, as payloads become heavier and delivery speed faster, there is a limit to the usefulness of the fixed gain PID controller. In particular, this controller cannot compensate for the inertia changes and variations in coupling torques associated with relative motion of the manipulator links and different payloads. For this reason its application is limited to conditions of load and speed close to those for which it is tuned.