A force-mediated controller for cooperative object manipulation

We consider cooperative manipulation by multiple robots assisting a leader, when information about the manipulation task, environment, and team of helpers is unavailable, and without the use of explicit communication. The shared object being manipulated serves as a physical channel for coordination, with robots sensing forces associated with its movement. Robots minimize force conflicts, which are unavoidable under these restrictions, by inferring an intended context: decomposing the object's motion into a task space of allowed motion and a null space in which perturbations are rejected. The leader can signal a change in context by applying a sustained strong force in an intended new direction. We present a controller, prove its stability, and demonstrate its utility through experiments with (a) an in-lab force-sensitive robot assisting a human operator and (b) a multi-robot collective in simulation.