Frictional driving mechanism based on wave propagation (1st report, measurement and simulation of earthworm locomotion)

An earthworm moves on the ground by propagating an expansion/contraction wave of its own body. Friction force due to the propagating wave is produced at the contact surface. In this study we measure in detail the locomotion pattern of the earthworm when it moves straight on two plane plates having a different friction coefficient. The amplitude, period, duration, and phase of the propagating wave on the earthworm are measured. Then we calculate numerically the locomotion pattern of the earthworm using a simple model consisting of the body which can expand and contract and normal and tangential contact springs at the surface of the body. It is found that the waveform of the actual earthworm is adequate for producing locomotion with high efficiency and velocity.