Force-differential steering of a track-based robotic colonoscope: experimental evaluation in single and multi-bend pipes

This work presents a laboratory-scale track-based robotic colonoscope incorporating a force-differential steering mechanism. A syringe-driven hydraulic system selectively retracts individual tracks to generate asymmetric track-wall contact forces for steering. A theoretical model was developed to describe the relationships between hydraulic input, normal-force modulation, and steering torque and to provide a first-order framework for the mechanism. The prototype, was tested with force sensing and an IMU, was evaluated for straight propulsion and steering in single- and multi-bend flexible pipes. Hydraulic actuation tests showed a near-linear increase in track-wall normal force with increasing syringe input, although the measured force was substantially lower than the theoretical prediction. Steering experiments showed that motion without active steering produced approximately 35° of yaw before traction loss, whereas force-differential steering increased the yaw angle to approximately 45° and enabled negotiation of a 120° bend. Tests under different friction conditions further showed that reduced wall friction impaired steering performance. In a continuous S-shaped pipe, two of three independent trials successfully completed both bends, while one trial exhibited incomplete yaw recovery, indicating trial-to-trial variability and sensitivity to traction conditions. Overall, these results provide proof-of-concept evidence for force-differential steering in a tracked robotic colonoscope and demonstrate that straight propulsion and active planar steering can be achieved within a common tracked locomotion architecture. Further miniaturisation, improved hydraulic control, and evaluation in more physiologically representative environments are required before clinical applicability can be assessed.