Optimization-Based Application Point Determination of External Wrench for Gravity Compensation of Space Manipulator

This paper presents how to optimize the application point of the external wrench, which is utilized for gravity compensation of the space manipulator on the ground. Specifically, we need to determine an appropriate application point on a link of a robot manipulator which ultimately minimizes the joint torque and external wrench applied. To this end, we reconstruct the body Jacobian matrix as a function of the translation and orientation components of the transformation matrix from the ith joint frame to the application point frame, using the product-of-exponentials-based kinematics and applying it to the optimization problem. While performing the optimization, it is evident that the orientation component does not affect the optimization result if the diagonal element of the weighting matrix for the external wrench in the objective function has the same value. The benefits of the proposed method are shown through a comparative simulation study with an existing gravity compensation strategy.