(1993-) Three types of pipe inspection robots, Thes-I, Thes-II, Thes-III, were developed for the gas pipes of 50mm and 150mm in diameters.

Thes-I is the robot for the gas pipe of 50mm in diameter. The rolling wheel of the robot has four spring wires radial attached around it, and free rollers are installed at the end of the spring with some inclination angle. As the free rollers are pressed on inside wall of the pipe and driven to the circumference direction, it generates screw motion and moves along the pipe. The Thes-I has a pair of rolling wheels rotating to the opposite direction to cancel reaction torque. The main feature of the mechanism is that, as the free rollers are supported by spring wires and the inclination angle of the free rollers changes according to the magnitude of the resistance force, it shows the function of load sensitive transmission and automatically reduces the velocity and increases the thrusting force when it encounters large resistance force for propulsion as shown in Fig.2. Thes-I of Photo.2 is 300mm in length and 310g in weight.

Thes-II is too for the gas pipe of 50mm in diameter. As shown in Fig.3, it drives a pair of wheels, which is supported by spring plates by means of micro-geared motors and directly produces thrusting motion along the pipe. We introduced a design concept called "Whole Stem Drive", and multiple Thes-IIs are arrayed along the stem as shown in Photo.2, to produce stable thrusting force. Thes-II could easily move with long distance along the pipe with some elbow joints.

Thes-III is the robot for gas pipe of 150mm in diameter. Several robots were already made for this end, but it was difficult to make smooth pass through the elbow joint where the pipe bends deep and some obtrusions exist around it. To solve this problem, Thes-III introduced the layout of the active wheels arraying radial in a "wheel plane", and drive the wheels while pressing them on inside the pipe with spring force. But if the wheels are driven like this, the wheel plane tends to be inclined and it can not maintain vertical posture in relation to the pipeline axis. Thes-III thus introduced the detect wheels for each active wheels to detect the inclination angle of the active wheel to the pipeline axis, and at the same time, feedback control was executed to maintain the vertical posture. Thanks to these, Thes-III can easily follow the bending of the pipeline and it smoothly makes tight turn on the elbow joints.

1. Shigeo Hirose, Hidetaka Ohno, Takeo Mitsui, and Kiichi Suyama : Design of In-Pipe Inspection Vehicles for 25, 50, 150 Pipes, Proc. ICRA, Detroit, pp.2309-2314 (1999)