Force-based disturbance observer for dynamic force control and a position/force hybrid controller

In this paper, a force-based disturbance observer (DOB) and a force control system using the DOB are proposed to obtain dynamic force control under disturbances. A DOB can reduce the effect of disturbances and modeling errors on robots. In a conventional DOB, an acceleration response is fed back to a reference, enabling highly precise position control. In other words, the effect of disturbances is decreased by emphasizing the effect of inertial forces. When a force controller is implemented, however, inertial forces are regarded as disturbances respect to a force response. Because inertial forces increase according to the acceleration, conventional DOBs are not suitable for dynamic force control. In the proposed DOB, a force response is fed back instead of an acceleration response. The effect of inertial forces is thus eliminated, thereby improving the tracking performance of force controllers. The proposed method's validity is verified analytically and experimentally. A position/force hybrid controller and a DOB for the controller are proposed as an extension of the proposed DOB. A bilateral controller is given as an example of the proposed hybrid controller, and its tracking performance is demonstrated experimentally.