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.

A simple, compact, yet powerful robotic winch, called ldquoWinch-Bot,rdquo is presented in this paper. The Winch-Bot is an underactuated robot having only one controllable axis. Although hanging a load with merely one cable, it is capable of moving it in a large workspace by swinging the load dynamically based on parametric self-excitation. The generated trajectories can be used for a variety of tasks, from moving material to cyclic inspection of surfaces. The basic principle and design concept of the Winch-Bot are first described, followed by dynamic modeling and analysis. Two trajectory generation problems are solved. One is point-to-point transfer of a load, and the other is the tracking of a continuous path. It will be shown that the system can track a given geometric trajectory, although the tracking velocity cannot be determined arbitrarily due to the underactuated nature of dynamics. A prototype Winch-Bot is designed and built, and point-to-point, continuous path, and parametric excitation control are implemented.