Robot Simulations Based on Bipedal Spring-Mass Model With Variable Slack Length and Stiffness

This paper proposed an extension of bipedal spring-mass model with variable slack length and stiffness. Since conventional bipedal spring-mass model has problems to accomplish stepping and low speed walking, we solve it by adjusting slack length of spring leg. Moreover, to produce heel-strike and toe-strike running, the stiffness of spring is changed to get running gaits with different frequencies. In order to imitate the human foot rolling behavior, we synchronize motion of center of pressure with that of center of mass. Based on the proposed methods, simulations of a human size robot achieve walking, heel-strike, and toe-strike running. Walking at a speed of 1 m/s can generate the double-humped ground reaction force. Heel-strike and toe-strike running gaits at a speed of 4.5 m/s are accomplished. The frequencies of two running gaits are consistent with those in human motion capture data. Joints angular positions of walking and heel-strike running are similar to those of human data. Therefore, the proposed model turns out to be effective in generating human-like walking and running behaviors.