Continuous path tracing by a cable-suspended, under-actuated robot: The winch-bot

Abstract

A simple, under-actuated robotic winch, called the “Winch-Bot,” is developed for surface inspection of a large object. The Winch-Bot, placed over an object surface, has only one actuator for tracing a free geometric path in a vertical plane. The cable length is controlled in relation to the direction of the cable so that the inspection end-effecter hanging at the tip of the cable can follow the path dynamically despite the lack of full degrees of freedom. We analyze the tracing dynamics, address under what conditions a given geometric path can be traced (traceability conditions), and prove under what conditions the tracing motion is repetitive. A controller utilizing partial feedback linearization is proposed, and simulations are used to validate the explored traceability criteria and to confirm the controller's performance improvement.