Kinematics and Performance Analysis of Two Types of 3-RPS Parallel Mechanisms

Two types of 3-RPS parallel mechanisms are proposed, the limb kinematic chain consists of arc prismatic pair P, a revolute pair R, and a spherical joint S. Mobility, kinematics and transmission efficiency coefficients of these two types of parallel mechanisms are analyzed via screw theory. The rotational center of moving platform of first parallel mechanism is the center of arc of arc rods, and moving platform rotates around the Z-axis with respect to the other two directions is decoupled. In the second parallel mechanism, the rotational center of moving platform is an intersection point of three straight lines, which passing through each center of arc rod and the center of spherical joint, and this intersection point changes with the posture of the moving platform. In addition, the transmission efficiency coefficient of these two types of parallel mechanisms relates to the direction of movement of arc prismatic pair of limb kinematic chains.