The external shape of a humanoid robot is with a great importance whenever application of service robots is targeted and for which the acceptance criterion is looked for. Moreover, the use of full size humanoid robots as a test-bed to increase our understanding of the human behaviour when achieving locomotion and/or manipulation tasks requires also the design of slim and smart mechanisms for the several joints of the humanoid robot. When analysing human being’s musculo-skeleton structure, a quite impressive performances in terms not only of power to mass ratio but also of power to volume index, can be pointed out. Trying to reproduce these performances may also be helpful to enhance the devices dedicated to investigate the human/robot interaction such as rehabilitation devices based on parallel mechanisms.
On the other hand, and to be accepted by the general public, humanoid robots must have an anthropomorphic shape. This represents an additional constraint which was also considered in this work. The kinematic studies and solutions proposed in this research area are based mainly on observation of the movements of a human being. Indeed, an articulation of human being has several degrees of freedom (dof) constrained by ligaments and are operated by muscles related to the skeleton by tendons that can not only store energy but also change the joint stiffness. This model was used as a reference for proposing new kinematic structures adapted to a humanoid robot. In this issue, questions related to the number of dof, range of motion and joint efforts was lead to propose new hybrid mechanisms able to reproduce human behavior via these links. The kinematic structure proposed was ensure the production of all movements in terms of speed and effort. Particular attention has been paid to the efficiency of this structure to reduce its energy consumption and weight. Thus, it is important to try to give satisfactory answers to these questions while providing the best possible anthropomorphic morphology. Two new innovative hybrid mechanisms, dedicated to two classes of spherical linkages are proposed. The first class will cover the modules of the hip, shoulder and trunk, while the second will focus on the modules of the ankle, neck and wrist. Our humanoid robot called HYDROïD (HYDraulic andROïD) has been studied, designed and built.