A transferable force controller based on prescribed performance for contact establishment in robotic assembly tasks

In industrial robotics, controller parameters for force control must be adjusted to the specific robot that performs a task and they must be re-adjusted when the same task is to be performed by another robot. We address this challenge by proposing a transferable force controller for contact establishment between robot and surface. The controller is implemented based on task frame formalism. The proposed controller is based on prescribed performance control (PPC) and does not rely on a dynamic model of the environment. Due to the inherent robustness of PPC, it can be used to ensure similar performance for the same task across different robots and environments. The proposed controller is validated experimentally in a simple contact establishment task performed by three different robots (Universal Robots UR5, Franka Emika Panda, Denso Wave VS087) and three different board materials providing different stiffness (steel, aluminum, PVC). The PPC is found to yield an up to two orders of magnitude smaller variance of closed-loop settling time across all robots and materials than a conventional impedance controller.