A Dynamical-System-Based Approach for Controlling Robotic Manipulators During Noncontact/Contact Transitions.

Many daily life tasks require precise control when making contact with surfaces. Ensuring a smooth transition from free motion to contact is crucial as incurring a large impact force may lead to unstable contact with the robot bouncing on the surface, i.e., chattering. Stabilizing the forces at contact is not possible as the impact lasts for less than a millisecond, leaving no time for the robot to react to the impact force. We present a strategy in which the robot adapts its dynamic before entering into contact. The speed is modulated so as to align with the surface. We leverage the properties of autonomous dynamical systems for immediate re-planning and handling unforeseen perturbations and exploit local modulations of the dynamics to control for the smooth transitions at contact. We show theoretically and empirically that by using the modulation framework, the robot can stably touch the contact surface, even when the surface's location is uncertain, at a desired location, and finally, leave the surface or stop on the surface at a desired point.