Unified Impedance and Hybrid Force-Position Controller with Kinestatic Filtering

Abstract

Interaction control is a mature, but still, current area of research in robotics. Various approaches have been developed for passive and active force regulation and tracking, e.g. impedance control, direct force and hybrid force-position control. The latter method implements a force feedback outer loop on top of a position controller inner loop, where commands are issued with respect to a compliant frame. However, if the compliant frame undergoes a rigid transformation, e.g. in order to specify the same task relative to another reference frame, then commands can be rendered non-compliant with the task at hand. As a consequence, the robot can be damaged or hurt somebody, this is further aggravated by the rigidness of a position controller. In the present paper, we propose a unified impedance and hybrid force-position control scheme to address such issues. The unified controller benefits from the impedance control compliance while an explicit force value can be achieved. Furthermore, we augment the designed controller with a kinestatic filter, which ensures that the commanded pose and wrench are consistent with a given task model. We validate the designed system through experiments with a lightweight robot (LWR). The proposed approach finds applications in industrial settings where interactions with the environment are required in order to fulfill a task and the system must be robust w.r.t. input commands.