High-speed sliding-inchworm motion mechanism with expansion-type pneumatic hollow-shaft actuators for in-pipe inspections

Conventional mechanisms for in-pipe locomotion involved difficulties with high-speed movement in narrow pipes. Previously, we introduced a new mechanism that used a single device to produce both impellent and holding forces via a sliding-inchworm motion. This involved cyclical impelling and holding movements, producing longer strokes and higher speeds than those of previous techniques. This study built on our previous work by presenting a detailed discussion, model, and advanced evaluation of this new technique. The robot locomotion was re-conceptualized to highlight why it was significantly fast. Two different sliding-inchworm motion patterns, called single- and dual-drive, were also theoretically analyzed, indicating that the single-drive pattern should be three times faster than the dual-drive pattern. Rolling resistance, key to improving the actuator performance, was evaluated with a friction model via experiments. The major factors affecting the rolling resistance were identified, and the main cause of the rolling resistance was concluded to be elastic hysteresis loss. The results of the rolling resistance investigation were integrated into a static model that considered force generation, and the range of the optimal roller radius was determined to be larger than 1.83 mm. Finally, the propulsion performance of a prototype mechanism for horizontal, vertical, and bent pipes with diameters of 53 mm was evaluated. The results exhibited that the proposed mechanism was able to achieve average speeds of 100 mm/s and 40 mm/s for horizontal and vertical pipes, respectively, and to facilitate passage through a 90-degree bent pipe. These experimental results agreed well with the motion models presented in this study.