Design of a Bending Section Auto-Driven Mechanism for Colonoscope

Abstract

Colon cancer is the second leading cause of cancer-related death in the United States. Colonoscopy is the best technology available to detect and treat abnormalities within the colon. It is a procedure that enables a gastroenterologist to evaluate the appearance of the inside of the colon by inserting a flexible tube with about 3/8 in diameter into the anus, and then advancing it slowly, under visual control, into the rectum and through the colon. This procedure is often onerous due to that the driving of the bending section (tip) of the scope and perforation may occur with the rate of 1 out of 1700 procedures. The tip driving system consists of two angulation knobs, two chain-sprocket mechanisms, a series of ring-pivot mechanism, and two pair of wires. Rotating each knob extends and retracts a pair of wires which changes the orientation of the bending section. The up/down angulation knob generates an elevation motion and the left/right angulation knob generates an azimuth motion. Based on the traditional colonoscopy, this work developed an intelligent technology to extend and enhance the diagnostic and surgical capability of the instrument. This intelligent colonoscope includes an image-based control of the tip to release a doctor from onerous work, advanced imaging systems for diagnostics, and advanced human-machine interfaces to facilitate the doctor's operation in an effective manner. In the realization of the bending section driving automation, the driving mechanism design is one of the key issues. In our design of the bending section motion control mechanism, the handle of the colonoscope and the motors are fixed on a holder. The holder can travel along a track. The track can be fixed on any flat surface such as a desk in order to enlarge the motion range of the colonoscope body. Belt mechanism is used to translate the motion from motors to the knobs. The belt pulley is fixed on the driving knob through four equally distributed screws. In order to keep the belt tied all the time, a rocker mechanism with a spring is used between the motor and the knob. Two motors are used to drive the two angulation knobs. Two limit switches are used to identify the homing position of the two motors. The driving torque is limited through the constraint of the current supplied to the motor by an amplifier to avoid the damage to the mechanical system. Together with the motion control system, the mechanism has been lab-tested using an artificial colon. It is observed that the mechanism performs well to accomplish the automation of the knob driving tasks. The system has also been tested using a pig in the animal lab of a hospital satisfactory results have been obtained.