Constraint forces applied on limbs of 3-RPS parallel manipulator in static equilibrium

To know constraint forces of joints in static equilibrium is one of the important bases for mechanical design. As a 3 degree-of-freedom (dof) in-parallel manipulator, 3-RPS is has found wide applications. Static characteristics of 3-RPS are presented in this paper taking gravity into account. With constructed static equilibrium equations of 3-RPS, constraint forces of passive joints applied on each link have been obtained. Static analysis shows that each link is subjected to push/pull, bending and twisting torque in general. In particular, when centre of mass (CM) of link is on line through centres of joints fixed on platform and base respectively, or when gravity is omitted, each link will not bear twisting moment. Finally an example is provided to demonstrate static characteristics of 3-RPS.