In this paper, we develop two mechanisms for improving humanoid robot motions. The double spherical joint is a six DOF mechanism whose axes intersect in one point. This mechanism is used for humanoid hip joints with a waist joint function without increasing the actuator. The backlash clutch realizes a high torque driving and a free joint using backlash mechanisms is used for knee joints. The free mode will play a role in humanoid behavior that is dynamically coupled with the environment. The humanoid robot with these two mechanisms is developed and results of preliminary experiments are shown.

Use of compliance in muscle is the inherent skill of a human. By using the potential energy charged in the compliant members, we can skillfully equalize the characteristics of muscles and body. Integrating the skill of compliance will provide robots with higher mobility, dexterity and safety and extends the fields of applications. The main research issues of the skill of compliance are tuning passive compliance, planning compliant motion and designing control law. To achieve the skill, we focus on the planning compliant motion considering the kinetic energy. In this paper, we propose to design a compliant motion through iterative model identification and motion design. A humanoid robot with passive compliance is used to integrate the skill of compliance and shows fast swing charging and discharging the kinetic energy.

Design of mechanical compliance would be one of the most important technical foci in making humanoid robots really interactive with the humans. For safety insurance mechanical compliance should be developed for humanoid robots. The introduction of the passive compliance to humanoid robots has large possibility for achieving human skill by using the dynamical energy stored in the compliant members. Programmable passive compliance plays an important role in coping with the changing environments and task execution. We evaluate the effectiveness of the passive compliance for the realization of human skill and design a programmable passive compliance mechanism 'PPC cybernetic shoulder' which is a four degree of freedom shoulder mechanism for humanoid robots using a closed kinematic chain. The programmability of the PPC cybernetic shoulder is evaluated by experiments.