The life period of many Japanese water supply pipes has been expired. Based on the critical situation, a pipe inspection has been strongly required. The pipe inspection in hazardous environments such as a nuclear reactor and chemical plant is also required. 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 were developed. However, most inchworm type robots must hold the pipe by changing the diameter of the robot to get propulsive force, and extend longitudinally 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 thin 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 the previous study, the slim and low-cost pipe propulsion mechanism using Extension type Flexible Pneumatic Actuator (we call it “EFPA” for short) with elastic/rigid fiber constraint was proposed and tested. 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, even if the outer diameter of the mechanism is 26 mm, that is one fourth of pipe. In the next step, in order to apply the pipe inspection robot into typical pipe of nuclear reactor with inner diameter of less than 20 mm, a thin type EFPA was proposed. The thin EFPA consists of a rubber tube coved by a bellows type nylon sleeve manufactured by handmade. In addition, a thin EFPA with built-in axial fiber restrain was proposed and tested to realize coiling motion for holding the pipe. The thin pipe inspection robot that consist of a typical thin EFPA is sandwiched between two EFPAs with built-in axial fiber restrain was also proposed and tested. In addition, to realize propulsion by simple on/off operation of valve, the delay generator using orifice was installed into pipeline before top end EFPA for holding 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. The pipe traveling tests using the tested robot in straight and bent pipe with diameter of less than 20 mm were also carried out. As a result, it could be confirmed that the robot could travel smoothly in thin bent pipe with radius of curvature of more than 100 mm and inner diameter of 16 mm.
