Many Japanese water supply pipes had reached the end of their life period. Based on the critical situation, a pipe inspection has been strongly required. It is also required to inspect the piping in hazardous environments such as a nuclear reactor and chemical plant. In addition, a pneumatic actuator has an advantage that is no risk of electric leakage or short circuits. They can be safely used in damp and hazardous area such as in water supply pipe and flammable fluid pipeline. Therefore, many inchworm type pipe inspection robots using pneumatic soft actuators such as pneumatic artificial muscles and flexible cylinders were developed. However, most inchworm type robots must hold the pipe by changing the diameter of the robot to get propulsional force , and extend longitudinaly to travel in the pipe. Therefore, the outer diameter of the robot should not be extremely different to the inner diameter of applied pipe in order to decrease the volume change for holding pipe. The limitation of radial size of the robot leads to be easily stuck in the pipe. It causes to be difficult to retrieve the robot in an emergency. In ideal, a slim pipe propulsion mechanism for inspection robot whose outer diameter is less than one third of pipe diameter is suitable. In addition, to decease the cleaning cost after inspection, a propulsion mechanism that is cheap enough to be disposable is desirable. In this study, we proposed a slim and low-cost pipe propulsion mechanism uisng pneumatic soft actuators with elastic/rigid fiber constraint. As a soft actuator, Extension type Flexible Pneumatic Actuator (we call it “EFPA” for short) was used. Elastic/rigid fiber constraints can realize both "proportional type constraint" by elastic fibers and "saturation type constraint" by rigid fibers in the axial direction in order to realize coiling and extensional motions. A prototype pipe propulsion mechanism uisng EFPA with elastic/rigid fiber constraints was also developed. The traveling test in pipe by changing the timing of switching between coiling and extending motions was also carried out. As a result, it could be confirmed that the tested mechanism could travel in 100 A pipe with inner diameter of 100 mm by giving simple supply or exhaust to EFPA, even if the outer diameter of the mechanism is 26 mm (that is one fourth of pipe). The wireless control system via Bluetooth that can operate the mechanism by selecting a pre-programmed sequence program according to a transmitted character code from a tablet or mobile phone. By using the tested control system, the pipe traveling test using a propulsion mechanism that two EFPAs with elastic/rigid fiber constraints were connected in serial was also carried out. As a result, it could be confirmed that the mechanism could travel smoothly in 80A pipe with the average speed of 13.7 mm/s.
