Emulation of a space robot using a hydraulic manipulator on ground

To verify the tasks of one of the Space Station manipulator, the Canadian Space Agency is developing a hardware-in-the-loop simulation system. A hydraulic robot manipulating mockup of the space payload reproduces the contact forces occurring during insertion and extraction. The control law allowing a good performance requires a very accurate torque tracking for the hydraulic robot. With good force sensing in the hydraulic cylinder the torque control can be achieved in constraint motion but not in free motion. A controller using a feedforward term to compensate the velocity related effect is presented and tested experimentally. It is shown that this controller achieves very good results both in free motion and in a constrained task