Design and implementation of a visual feedback control system driven by wires

This paper introduces a visual feedback control method for a multiple degree of freedom mechanical system driven by wires. This system is a small serial-link robot. It consists of a small-diameter tube and two pairs of wires, which are connected to the interior of the terminal link, which pass through the interior of every other link. The mechanical system is driven by electrical motors via tension in the wires. One pair of wires is for side-to-side motion while the other pair is for up-and-down motion. Such a mechanism is frequently used in medical and industrial devices, such as endoscopes. Furthermore, a compact CCD camera is mounted on the terminal link and functions as a vision sensor. The control system consists of a visual feedback control loop and a minor loop that directly controls the sum of all the joint angles. The control law of the minor loop is designed based on a Lyapunov's theory. On the other hand, the outer visual feedback control loop is designed to track a target point detected by the vision sensor. Each loop is connected by an image Jacobian number and its inverse, which are continually updated during operations. This control method is evaluated experimentally. It is anticipated that this system will be used in a variety of applications in the future.