Compliant Movement Primitives in a Bimanual Setting

TL;DR

This paper extends Compliant Movement Primitives to bimanual robots, enabling them to maintain relative posture under external perturbations while acting compliantly in absolute tasks, demonstrated on real Kuka robots.

Contribution

It introduces a method combining CMPs with symmetric control and force copying for bimanual tasks without explicit models.

Findings

Robust bimanual compliance demonstrated on real robots.

Maintains relative posture under external disturbances.

Effective in real-world two-robot experiments.

Abstract

Simultaneously achieving low trajectory errors and compliant control \emph{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 bimanual tasks. 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 thus 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 well known symmetric control approach. To reduce the necessary feedback reaction of symmetric control, we further augment it with copying of a virtual force vector at the end-effector, calculated through the measured external joint torques. Real-world results on two Kuka LWR-4 robots in a bimanual setting confirm the applicability of the approach.