Accurate Joint Offset Calibration for Quadrupedal Robots.

Joint calibration is one of the fundamental works to ensure the locomotion performance of quadrupedal robots. Inaccurate joint offset calibration accuracy will incur foot-tip position errors and significant disturbances to locomotion performance, especially in highly dynamic scenarios. This paper proposes an accurate joint offset calibration method for quadrupedal robots. We derive the leg kinematic error model based on the product of the exponentials formula and use the iterative least squares algorithm to obtain the joint offset of the quadrupedal robot. Considering the influence of the body frame on the calibration of the abduction/adduction (Ab/Ad) joint, the offset of the Ab/Ad joint is modified by the angle between the z-axis of the body frame and that of the leg frame. We verify the effectiveness of the proposed method on an experimental quadrupedal robot, where the maximum foot-tip position error is decreased from 13.97mm to 2.25mm after calibration.