Asymmetrical 3-dof spherical parallel mechanisms

The paper deals with the structural synthesis of asymmetrical non-overconstrained 3-dof spherical parallel mechanisms (SPM). Most of SPM described in the literature are composed of three identical limbs, and they can be called symmetrical SPM. New SPM composed of three structurally distinct limbs, which we name asymmetrical SPM, are disclosed. This paper addresses the type synthesis of asymmetrical non-overconstrained SPM. Firstly, a mobility analysis is presented in order to find the degree of freedom of the limbs. In a second step the geometrical conditions of the limb assembly that achieves the spherical motion are established. Finally, limb architectures of asymmetrical non-overconstrained SPM are enumerated. The resulting kind of scientific catalogue is comprehensive under the hypothesis of non-paradoxical mobility. Moreover SPM 4-dof limbs without idle pairs were never revealed before.