Sensorless Null-Space Admittance Control for Redundant Manipulators

Abstract:
Compared to traditional 6DOF manipulators, redundant manipulators offer increased dexterity. The additional degree( s) of freedom allow to attain the same TCP pose with an infinite number of joint configurations. In this paper, we present a control scheme that allows to modify the joint configuration within the manipulator null-space, i.e. without affecting the TCP pose, on the fly by physical human-robot interaction. To do so, a null-space admittance control law is proposed that augments the existing motion control structure. The scheme relies on the estimation of joint load torques solely based on motor speed and motor current measurements. Hence, the proposed method does not require additional sensing and can be realized by means of software changes only. Experimental validation is provided by means of measurement data gathered from an ABB YuMi1 manipulator.