Input signal effects on the locomotion of a robotic colonoscope activated by a flexible shaft

Abstract

Most robotic colonoscopes do not allow sufficient space for high capacity motors since their power sources are equipped in their bodies. Therefore, a robotic colonoscope activated by an external motor through a flexible shaft has been presented. Unfortunately, robot rotations resulting from excessive input torque are observed under some input voltage signals. These rotations occur when the load torque on the flexible shaft exceeds a critical torque value, which is the maximum torque satisfying the rigid body condition. The excessive-torque effect must be eliminated since each rotation causes a velocity reduction as well as twisting of the colon. Therefore, to suppress the rotation by reducing the load torque, the input and load torques are investigated in connection to the input signal. Conclusively, the maximum load torque of the triangular function is the smallest among the input signals and does not exceed the critical torque, which causes the rotation of the robot body. To verify the usefulness of the theoretical and experimental load torque results, in-vitro tests are performed in an acrylic pipe and excised colon for all input functions. As expected with the load torque results according to the input signal, the robot with the triangular function achieves the best performance regardless of experimental environment.