Research On A Novel Humanoid Mechanical Leg

Aiming at the problems of high moment inertia, low bearing capacity and can’t meet the requirements of motion characteristics of humanoid robot of serial mechanism used in the current humanoid mechanical legs, a novel parallel humanoid mechanical leg was proposed by a analyzing of different types of parallel mechanisms, which was based on the study of the structural characteristics of ankle joint and keen joint at the viewpoint of bionics.The layout feature of this parallel humanoid mechanical leg was described. The degree of freedom is three that was calculated by using screw theory. The inverse position equations of the mechanism were derived in closed forms. Then by a analyzing of the structural constraint of the parallel machine leg, the shapes of orientation and position workspaces were described and the effects of design parameters on the workspace volume were studied.The analytic expressions of the velocity and force Jacobian matrix were derived by using vector method. Maneuverability was defined as the performance index of linear velocity Jacobian matrix. Condition number was defined as the performance indexes of angular velocity, force and moment Jacobian matrix. Then the distribution of the evaluation indexes were drew out on the workspace respectively to analyze properties of the kinematic and mechanical transmission.Global performance indexes were defined and atlases of these indexes were drew by using the physical model technique. Based on the atlases of global performance indexes, the relationship of velocity and force Jacobian matrix of the parallel machine leg was studied.By using genetic algorithm, the optimal combination of the parameters of the mechanical leg was selected. The structure of ankle joint was optimized. Finally, the parts of the mechanical leg were designed.The study find that, for this kind of lower-mobility parallel mechanical leg, the angular velocity Jacobian matrix and force Jacobian matrix reflect the same properties of transmission as well as the force Jacobian matrix and linear velocity Jacobian matrix. Besides, the results of simulation indicate that the properties of the kinematic and mechanical transmission of the foot are almost not affected by the movement of keen joint.After optimization, the mechanical leg has a good balance in the properties of the kinematic and mechanical transmission and has a compact structure.