Scalable collective impedance control of an object via a decentralized force control method

Employing impedance control during manipulation of an object provides a mean to control its dynamic interactions with the environment. This paper presents a decentralized algorithm to achieve a desired multi-dimensional impedance behavior of the object during a collective manipulation without inter-agent communication. The proposed algorithm introduces the concept of “virtual coordination” arising from an agent-level assumption, which demands every agent to locally coordinate with one “virtual teammate”. Since the real population of the team is unknown to the agents, the resultant force applied to the manipulated object would be directly scaled with the team population. Although this scaling effect proves useful during position control of the object, it leads to a deviation from the desired dynamic response when employed in an impedance control scheme. To minimize such deviations, a gradient descent algorithm is implemented to determine a scaling parameter defined on the control action. The simulation results of a multi-robot system with different populations and formations verify the effectiveness of the proposed method in both generating the desired impedance response and estimating the population of the group. Eventually, as two case studies, the introduced algorithm is used in robotic collective manipulation and human-assistance scenarios.