This paper describes an in-pipe microrobot to which the motion of an earthworm is applied. A new locomotive unit for the robot is proposed, and the unit was made of two plates connected with an Flexible Micro Actuator (FMA) and four linkages as the legs. The static and dynamic characteristics of FMA were experimentally investigated, and the nonlinear stiffness and the viscous damping were identified. From the driving experiments with a prototype of the robot, which was composed of the three locomotive units, the maximum speed of 2.2mm/s and the maximum traction load of 0.22N were obtained in a pipe 21mm in diameter. The speed of the robot was also theoretically analyzed by taking account of the delay of shrinking of FMA, which was estimated with the identified characteristics, the theoretical speed agreed well with the measured speed.
