  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.
