Gravity based autonomous calibration for robot manipulators

This paper presents an autonomous method to calibrate joint torque sensors for advanced robots; as a by-product, the position sensors can also be calibrated. When one joint of a manipulator is rotated the gravity torque exerted on the joint varies sinusoidally with rotation angle. By means of sinusoidally curve fitting, the bias of the torque sensor and the gain of the position sensor can be found directly. The gravity vector expressed in the defined base coordinates, can also be found. We then determine the torque sensor gain as well as the rotation angle offset, by attaching a known load to robot in different end positions. Experimental results are shown for the first two joints of the Sarcos dextrous arm