Abstract-Cooperative manipulation in robotic teams likely results in an increased manipulation performance due to complementary sensing and actuation capabilities or increased redundancy. However, a precise coordination of the involved manipulators is required in order to avoid undesired stress on the manipulated object. Extending the workspace of the robots by means of mobile platforms greatly enlarges the potential task spectrum but simultaneously poses new challenges for example in terms of increased kinematic errors. In this paper we show how kinematic errors in the closed kinematic chain originating from uncertainties in the geometry of object and manipulators limit the cooperative task performance. We extend an impedance-based coordination control scheme towards mobile multi-robot manipulation to limit undesired internal forces in the presence of kinematic uncertainties. Furthermore, we employ a task-space decoupling approach to reduce the impact of disturbances at the mobile platforms on the end effectors. The presented control scheme for cooperative, mobile dualarm manipulation is applicable in real-time and suitable for a team of heterogeneous manipulators. We evaluate the presented architecture by means of a large-scale experiment with four 7DoF manipulators on two mobile platforms.

Abstract-The interaction of a single human with a team of cooperative robots, which collaboratively manipulate an object, poses a great challenge by means of the numerous possibilities of issuing commands to the team or providing appropriate feedback to the human. In this paper we propose a formationbased approach in order to avoid deformations of the object and to virtually couple the human to the formation. Here the human can be interpreted as a leader in a leader-follower formation with the robotic manipulators being the followers. The results of a controllability analysis in such a leader-follower formation suggest that it is beneficial to measure the state of the human (leader) by all physically cooperating manipulators (followers). The proposed approach is evaluated in a full-scale multi-robot cooperative manipulation experiment with humans.

Cooperative manipulation, where several robots jointly manipulate an object from an initial configuration to a final configuration while preserving the robot formation, poses a great challenge in robotics. Here, we treat the problem of designing motion primitives for cooperative manipulation such that the robots move in formation and are robust with respect to external disturbances. Individual robot trajectories are generated by Dynamic Movement Primitives (DMPs) and coupled by a formation control approach enabling the DMPtrajectories to preserve a given formation while performing the manipulation. The proposed control scheme achieves an increased adaptability under external disturbances. The approach is evaluated in a full-scale experiment with two prototypical cooperative manipulation and synchronized motion tasks.

Abstract-Cooperative manipulation, where several robots collaboratively transport an object, poses a great challenge in robotics. In order to avoid object deformations in cooperative manipulation, formation rigidity of the robots is desired. This work proposes a novel linear state feedback controller that combines both optimal goal regulation and a relaxed form of the formation rigidity constraint, exploiting an underlying distributed impedance control scheme. Since the presented control design problem is in a biquadratic LQR-like form, we present an iterative design algorithm to compute the controller. As an intermediate result, an approximated state-space model of an interconnected robot system is derived. The controller design approach is evaluated in a full-scale multi-robot experiment.

The interaction of a human with a team of cooperative robots, which collaboratively manipulate an object, poses significant challenges for the control design. In this work we propose a formation-based approach to map the human input to the motion of the object cooperatively manipulated by multiple manipulators which feature local compliance control at the end-effector level. The formation-based approach guarantees that the reference trajectories maintain a desired geometry with respect to each other. Without being in touch with the object the human operator is part of the formation and guides the robots explicitly. Here the human can be interpreted as a leader in a leader-follower formation with the robotic manipulators being the followers. We analyze the system consisting of human operator and multi-robot manipulation task in both the transient phase and the steady-state for which we derive the equilibrium of the object pose from the human input and show its stability. A controllability analysis suggests that it is beneficial to make the state of the human accessible to all manipulators in order to reduce internal stress on the object. The proposed approach is evaluated in a full-scale multi-robot cooperative manipulation experiment with a human.