Compliant movement primitives in a bimanual setting

Abstract

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 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 jointspace 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.

Convergence of Dynamical Movement Primitives with Temporal Coupling

“…Such behavior is desired in general, since it helps to retain the coordination between the degrees of freedom of the robot. It resulted from the fact that e had a significant magnitude, which in turn caused τ a to be significantly larger than τ , see (7). The robot was released at t ≈ 10 s, and the controller described by (8) Fig.…”

“…The block denoted 'Robot' includes the internal controller of the robot. The 'DMP' block corresponds to the computations in (1) - (7), and the PD controller together with the feedforward termÿ c is specified in (8).…”

“…Online motion modulation using DMPs has been widely considered in the literature. For instance, adaptation based on force/torque measurements was developed in [5], obstacle avoidance was explored in [4], [6], and DMPs with compliant behavior were developed in [7], [8]. Functionality for modification of DMPs by means of lead-through programming was presented in [9], [10].…”

A Control Scheme With a Novel DMP-Robot Coupling Achieving Compliance and Tracking Accuracy Under Unknown Task Dynamics and Model Uncertainties

“…Its main result is a new control structure that is easily implementable. In contrast to previously published works [8], [9], [10], [11] it does not require the learning of a feedforward or coupling term (offline or iteratively) to compensate uncertain task dynamics. It is successfully employed by adapting to different uncertain dynamics (e.g with the arm holding objects of different weight) without compromising compliance.…”

“…Compliant movement primitives (CMP) have been proposed to improve the tracking accuracy while maintaining compliant robot behavior without requiring explicit models of task dynamics [8], [9]. They require robots which allow active torque control and joint torque sensing.…”