A three-legged four degrees-of-freedom parallel manipulator with foldable moving platform

This paper introduces a three-legged parallel manipulator with foldable platform able to perform four degrees of freedom. Two limbs are integrated on a planar mechanism while the remaining limb is capable to perform spatial motions. The result of this topological arrangement is a limited-dof parallel manipulator with the versatility to adopt three operation modes. The simplicity of the topology is such that the displacement analysis yields closed-form solutions. In that concern, the forward position analysis concludes that there are up to eight solutions given the input joint variables of the mechanism. The instantaneous kinematics is approached by resorting to the theory of screws. The input-output equations of velocity and acceleration are simple and compact owing to the properties of reciprocal screws. Numerical examples, which are validated with ADAMS,TM show the reliability of the method of kinematic analysis employed in the contribution.