Improved positional accuracy of robots with high nonlinear friction using a modified impulse controller
This paper presents a modified impulse controller to improve the steady state positioning of a SCARA robot having characteristics of high nonlinear friction. A hybrid control scheme consisting of a conventional PID part and an impulsive part is used as a basis to the modified controller. The impulsive part uses short width torque pulses to provide small impacts of force to overcome static fiction and move a robot manipulator towards its reference position. It has been shown that this controller can greatly improve a robot’s accuracy in position tracking. However, the system in attempting to reach steady state will inevitably enter into a small limit cycle whose amplitude of oscillation is related to the smallest usable impulse. It is shown in this paper that by modifying the impulse controller to adjust the width of successive pulses, the limit cycle can be shifted up or down in position so that the final steady state error can be even further reduced.