Multiple robot force control with delayed force measurements

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 geometry is completely known. When this assumption does not hold, a common decentralized scheme is the leader/follower strategy, where the leader provides the position control for the load and the other robots comply based on the individual contact force measurement. We consider an intermediate scenario where the force information is shared among the robots, but the information is delayed. We showed that under integral force feedback, the closed loop stability is robust with respect to the force measurement delay. Furthermore, if the delays can be measured, the feedback gains may be scaled to ensure stability for arbitrary delays. Simulation and experimental results are included to demonstrate these results.