Gait Patterns of Quadrupeds and Natural Vibrations of Their Musculoskeletal Systems (Excitation of Natural Vibration by Local Feedback Control)

Abstract

Quadruped animals switch gait patterns depending on speed to minimize energy consumption. This is similar to the phenomenon that excited natural vibration modes are switched depending on excitation frequency in a multi-degree-of-freedom system. Therefore, in this paper, it is assumed that quadruped animals move by using the natural vibration of their own musculoskeletal systems. To verify this idea, we made an experimental apparatus that has a simple structure modeled after the actual musculoskeletal system of a quadruped animal. The apparatus consists of a body, a shoulder, a waist, and four legs. Each leg is excited by a DC motor fixed to the shoulder or waist. First, it was clarified that the apparatus has natural vibration modes similar to the gait patterns (trot, pace, and gallop) of quadruped animals by free vibration tests. Next, the apparatus was driven by forced vibration in which four DC motors were excited with the phase angle of gait patterns. The energy consumption of the motors was minimized when the excitation frequency corresponded to the natural frequency. Finally, the apparatus was driven by self-excited vibration generated by decentralized control in which four DC motors controlled locally are used. The vibration modes were similar to trot, pace, and gallop patterns. The frequencies of self-excited vibration corresponded to the natural frequencies.