Prescribed contact establishment of a robot with a planar surface under position and stiffness uncertainties

Robot arms that operate in unstructured and dynamic environments often need to establish contact with a planar surface, while avoiding the appearance of excessive contact forces. This is a difficult task given that exact knowledge of the robot or the environment model parameters is not available. In this paper a novel, continuous in time, controller is designed, capable of establishing and maintaining contact of the robot with a planar surface of unknown stiffness and position. The proposed control scheme guarantees that the resulted contact force, normal to the surface, is a priori bounded by user-defined bounds, while imposing prescribed transient and steady-state performance attributes on the post-contact position and orientation error response. All remaining closed-loop signals are also kept bounded. The controller is validated via experimental studies performed on a KUKA LWR 4+ robot. Additionally, a comparison is conducted with a relative approach from the literature. The results verify the theoretical findings.