Flexible Rotary Shaft Power Transmission for Robotic Pull Colonoscopy: Design and Experimental Characterization

Abstract

Robotic colonoscopy systems aim to support navigation through tortuous anatomy and address known ergonomic limitations of conventional colonoscopy; however, many existing platforms rely on complex onboard actuation, limiting distal tip miniaturization and increasing device complexity. This work presents the FlexPower Colonoscope (FPC), a robotic pull colonoscopy platform that delivers motor torque from an off-board actuator to a distal locomotion module through a flexible rotary shaft. By separating actuation from the intraluminal device, the architecture enables a compact distal tip while supporting greater torque delivery than onboard distal actuation approaches and future development of low-cost, replaceable patient-contact components. A benchtop experimental study was conducted to characterize flexible-shaft power transmission under varying input voltage, input current, and shaft radius of curvature conditions representative of colonic anatomy. Rotational speed was measured using a digital tachometer across multiple curvature configurations and analyzed using multivariate ordinary least squares regression. The resulting predictive model relates shaft rotational speed to electrical inputs and curvature, enabling estimation of distal locomotion performance. A functional prototype incorporating a worm-gear drivetrain, microtextured traction treads, and a joystick-controlled physician handle was fabricated using rapid manufacturing methods. Under conservative motor inputs (4.5 V, 1.2 A), the system achieved distal locomotion speeds of approximately 2 mm/s and an estimated effective rimpull of 5.2 N. Ex vivo demonstrations in porcine colon tissue supported the preliminary feasibility of distal tread locomotion driven by off-board motor torque through the flexible shaft.