Compliance Control of a 6-Link Electro-Hydraulic Manipulator

An electro-hydraulic manipulator using hydraulic actuators has many nonlinear elements, and its parameter fluctuations are greater than those of an electrically driven manipulator. So it is quite difficult to obtain stable control performance. In this report, we have applied a disturbance estimation and compensation type robust control to all the axes in a 6-link electro-hydraulic manipulator. From the results, it was confirmed that the performance of trajectory tracking and attitude regulating was greatly improved by the disturbance observer, the model of which is the same for each axis. On the other hand, for autonomous assembly tasks, it is said that compliance control is one of the most available methods in contact task. Therefore we have proposed a compliance control based on the position control by a disturbance observer for our manipulator system. To realize more stable contact work, the states in the compliance loop are fedback, where not only displacement but also the velocity and acceleration are considered. We have also applied this compliance control to the Peg-in-Hole insertion task and proposed new methods of (1) rotating of the end-effector periodically in order to reduce the friction force, (2) random searching for the center of a hole and (3) trajectory modification to reduce the impact force. As a result of these new methods, it could be experimentally confirmed that the Peg-in-Hole insertion task with a clearance of 0.007 mm could be achieved.