Design of an Impact/Force Switching Controller

Intelligent interaction control is required in many fields of application. Being able to switch between optimized controllers based on specific operating conditions is of extreme importance to maximize the task performance. Considering the robot in interaction with its environment, two main task phases can be identified: 1) free-space approaching motion, and 2) con- tact. Optimizing the controllers to deal with such task phases and (continuously) switching among them when appropriated is the main focus of this paper. Such goals become even more ambitious considering a sensorless (i.e., without any force/torque sensor) position-controlled manipulator (a common situation for the most of the robots on the market). To deal with the proposed context, a sensorless optimal switching impact/force (OSIF) controller is proposed, in which the high-level controller (composed of an optimized impact controller, an optimized force controller, and a continuous switching mechanism to select the proper controller to be activated) is implemented together with the low-level controller (composed by a position control fed by an impedance control-based reference signal). In addition, the output of the switching mechanism is used to adapt the Cartesian impedance control parameters (i.e., stiffness and damping parameters) to ensure a continuous and smooth transition between the two high- level controllers. Experimental tests have been performed on a Franka EMIKA panda robot to validate the proposed controller, showing impact control and force-tracking (with zero/limited force overshoots) capabilities.