(1972-1975). Photo. 1, shows Active Cord Mechanism model ACM III. On the evening of December 26, 1972, for the first time in the world we succeeded in producing artificial serpentine movement at a speed of approximately 40 cm/sec using the principles of a serpentine movement which is the same as actual snakes. The entire length of the device is 2 m, and it has 20 joints. Each joint consists of servo-mechanisms that can bend to the left and right. To make contact with the ground, casters were installed along the direction of the body, and characteristics were added that make it easy to slide in the direction of the torso and difficult to slide in the normal direction. The propulsion motion was conducted by inputting command values which impart sinusoidal bending motions to the head joint servo-mechanism, and that bending signal was shifted at a fixed speed to the following joint servo-mechanisms. When this is done, the body as a whole begins to move by sending a wave to the rear, but in order for the torso to slide over the floor surface with the casters, all of the torso joints produced a serpentine movement like the flow of water which trace the same loci. This principal of propulsion corresponds to the swimming motion of eel. We were also successful with experiments in slalom motion between poles set up in an open space.

Photo. 2, and Photo. 3, show the experimental conditions of installing tactile sensors, based on limit switches, onto the sides of all the joints of the ACM III. It is indispensable to know the tactile conditions between the torso and the environment in an Active Cord Mechanism, but as indicated in Fig. 1(b) ,it is no good to simply bend the joint that is touched by an object, but as indicated in Fig. 1(c) ,it is best that both neighboring joints also bend at a speed one-half in the opposite direction at the same time. This control closely corresponds with the kind of "lateral inhibition" type neural net indicated in Fig. 2 which is seen in the nervous system. Using lateral inhibition type controls, the ACM III is capable of smooth movement which autonomously coiled around optionally shaped objects as in Photo. 2, , and of propulsion while following along a labyrinth in the shape of the labyrinth, as in Photo. 3, , by combining this lateral inhibition control with angular information shift control.