A robust manipulation strategy based on impedance control parameters changes and smooth trajectories

This paper proposes a new manipulation strategy that combines smooth trajectories with an impedance controller which parameters are adapted in time of execution. The proposal uses a single control law during all manipulation phases, i.e. when the robot is in contact with the object, and during regrasping when the robot moves freely in space. The manipulator impedance changes during the different manipulation phases and this is achieved modifying mass, stiffness and damping parameters of the controller. Controller stability is further enhanced by the adoption of smooth trajectories that are generated using a compact and computationally light Squeezed Screws Planner. Additionally, the approach shows good response to the occurrence of unplanned contact or collisions. Experimental results with an industrial manipulator unscrewing a jar cap, provides interesting data about performance and show the benefits of the adopted manipulation strategy.