New Experimental Results on the Compensation of Static Friction in Passive Joints of Robotic Manipulators

The progress made in friction compensation in robotics was concentrated on friction losses in the actuated joints. The newly emerging parallel manipulators however, possess considerable number of passive joints. This paper discusses the influence of passive joint friction (PJF) in robot's dynamics and its impact on control performance. It gives a basic framework on the modeling, the detection of such phenomena and provides experimental examples achieved on a spatial parallel robot. All proposed methods do not require additional sensors and use only the actuators for detection and compensation. Due to its dependency on the robot's configuration, even small magnitudes of PJF can affect the system's behavior, especially at unfavorable configurations.