An identification procedure for rate-dependent friction laws of robotic manipulator with limited motion range

This paper proposes an identification procedure for rate-dependent friction of robotic manipulators of which the motion is limited due to the configuration or the environment. The procedure is characterized by following three features: (i) the function for the curve fitting is defined by linear interpolation and extrapolation of sampled velocity-force pair points, (ii) each joint is controlled by high gain PID position controller of some cycles of sinusoidal desired trajectory with different frequencies, and (iii) the velocity-force pairs are obtained from each cycle with subtracting the effect of the gravity and the inertia. The procedure was validated with an industrial robotic manipulator YASKAWA MOTOMAN-HP3J, which has six harmonic-drive joints of the reduction ratios of 81.5 to 224. The experimental results show that the procedure has achieved a sufficient accuracy with the 20 degrees of motion of each joint.