Design of a small biped mechanism with 7 DOFs legs and double spherical hip joint

Most of low-cost and small-size humanoid robots have been developed by using the conventional mechanism and simple control units. The conventional mechanism has a unique structure when the pose of feet and waist is fixed, and the small humanoid robot has to walk with bending knee joints without waist joints. On the other hand, these small humanoid robots perform low capability in the dynamic walking because of the open-loop hardware and low computation performance. In order to improve these problems, a small biped mechanism with 7 DOFs and a double spherical hip joint has been developed in this paper. There are two primary advantages compared with those small humanoid robots. First, the new biped mechanism can realize motions which are more similar to human beings. Secondly, a foot-force sensory system is designed to make the hardware close-loop, and a quick response stability control is proposed to realize the dynamic walking control. The effectiveness of our proposed small humanoid robot was confirmed by experiments on an actual 14 DOFs small biped mechanism.