Design optimisation of parallel joint mechanism for humanoid spine

This article presents the adaptation of an existing parallel mechanism to design vertebra joints that can be used to compose the vertebral column of a biped robot. The mechanism was imagined for the design of a flight simulator [1]. It is composed of a bottom platform and a top platform connected by two articulated arms and a vertical central rod. Both arms are used to pitch and roll the top platform about the center. The contribution of this paper consists of adapting the mechanism for the design of a pitch-roll vertebra joint, taking into account the specifications of forward, backward and left/right sideways bending amplitudes given for a humanoid robot. The objective of the study is to optimize the different length ratios of the mechanism in order to have a reduced torque required for the bending motions. The parallel system is compared with the serial mechanism equipped with a pitch and a roll revolute joints with concurrent concurring rotation axes.