The Development Of A Novel Humanoid Mechanical Coxa Joint

This paper aims to do research in structural features of the coxa joint and its applications. We try to design a novel humanoid mechanical coxa joint based on the model of the 2-DOF(degree of freedom) spherical parallel mechanism.(1)The structural features about this coxa joint is introduced and the the forward and inverse position equations are given.Combined with constraints of the coxa joint, the shapes of orientation and position workspaces are described and the effects of design parameters on the workspace volume are studied.(2)The Jacobin Matrix is derived by Analyzing the kinematics of coxa joint. Then the evaluation indexes of kinematic in the coxa joint are defined. And the distribution of the evaluation indexes are drew out on the workspace respectively.(3)The force Jacobin Matrix is derived by analyzing the statics of coxa joint and solving the transfer equations using principle of virtual work.Then the evaluation indexes of statics in the coxa joint are defined.And the distribution of the evaluation indexes are drew out on the workspace respectively.(4)The global performance evaluation indexes of kinematics and statics in this 2-DOF(degree of freedom) spherical parallel mechanism are defined.By using the physical model technique,the relationship between the global performance evaluation indexes and the structural parameters of the coxa joint are analyzed,which provided the base for the parameters optimized of the coxa joint.(5)The multi-objective optimized design method based on physical model technique is proposed,which aims to optimize parameters in coxa joint.The structural parameters are choosed and a prototype of coxa joint is designed with the consideration of its technology of process and assembling.Compared to the existed coxa joints which belong to serial mechanism, our new coxa joint possesses a large number of advantages, such as simple structure, motion decoupling, strong carrying capacity, small motion inertia, small motion error and easy installation. This is a relatively ideal coxa joint in humanoid robot.