Kinematic analysis and motion planning of a biped robot with 7-DOF and double spherical hip joint

Most of conventional biped robots without waist joint walk with bending knee joints and canpsilat move lower limb when the position of feet and waist are fixed. This paper proposes a novel biped mechanism with 7 DOFs and double spherical hip joint, which has two advantages compared to the conventional biped mechanism. First, the double spherical joint can realize the basic function of the waist motion without waist joint, which makes it possible for the humanoid robot to walk erectly. Second, when the position of feet and waist are fixed, the robot can rotate the legs in a manner similar to that of human. In this paper, we mainly discuss the analysis of motion characteristics, kinematic solution and motion planning of the complex mechanism. And the proposed method has been validated by experiments.