Abstract: A novel 2-TPR/2-TPS spatial 4-DOF parallel mechanism is proposed. The proposed mechanism is composed of a moving platform connected to a fixed platform by means of four actuated limbs. The two of the four limbs are adjacent TPS serial manipulators and the other two are adjacent TPS serial manipulators. Each TPR limb consists of a Hoke joint T connecting to the fixed platform, a prismatic pair P, and a revolute pair R connecting to the moving platform. Each TPS limb consists of a Hoke joint T connecting to the fixed platform, a prismatic pair P, and a spherical pair S connecting to the moving platform. Moving character and singularity of this mechanism are analyzed by using the screw theory. The moving platform of this mechanism has 2 translational DOFs, and they are translational movings along the plane which passes through the two TPR limbs. The moving platform of this mechanism also has 2 rotational DOFs, and they are rotational movings that are rotated the lines in the plane which passes through the second rotational axes of each Hoke joint of the two TPR limbs. The prismatic pair of each limb can be actuated. Four possible types of singular configuration of this mechanism are achieved.

Key words: Singular configuration, 4 degrees of freedom, Moving character, Parallel mechanism, Screw theory