Compliant movement primitives in a bimanual setting

Simultaneously achieving low trajectory errors and compliant control without explicit models of the task was effectively addressed with Compliant Movement Primitives (CMP). For a single-robot task, this means that it is accurately following its trajectory, but also exhibits compliant behavior in case of perturbations. In this paper we extend this kind of behavior without explicit models to cover bimanual tasks, where the relative motion of the robots is maintained. In the presence of an external perturbation on any of the robots, they will both move in synchrony in order to maintain their relative posture, and therefore not exert force on the object they are carrying. Thus, they will act compliantly in their absolute task, but remain stiff in their relative task. To achieve compliant absolute behavior and stiff relative behavior, we combine joint-space CMPs with the symmetric control approach used for bimanual robot configurations. To reduce the necessary feedback reaction of symmetric control, we further augment it by applying a virtual force vector at the end-effector, calculated through the measured external joint torques on the perturbed robot. Real-world results on two Kuka LWR-4 robots in a bimanual setting confirm the applicability of the approach.