Decentralized Collaborative Load Transport by Multiple Robots

With the rapid progress of the robotic technology, it is becoming increasingly common to have multiple robots working together for material transport, cooperative assembly, etc. To ensure the proper handling of the load, especially if it is fragile or needs to be moved rapidly, the constraint force needs to be carefully managed. Tight force coordination is possible if all robots share their force information and the grasp geometry is completely known. When this is not the case, a common approach is to use the leader/follower strategy, where the leader provides the position control for the load and other robots comply based on the individual contact force measurements. This paper considers an alternate decentralized motion and force control method, where all robots participate in the control of the load without sharing any position and force information. Under centralized squeeze force control, robot motion is not affected. However, when the force control is decentralized, a perturbation term is added to the motion control loop. We show that the nominal exponential stability of the motion loop preserves the closed loop stability in the presence of this perturbation. Simulation and experimental results are included to demonstrate the proposed approach.