Design Optimization of a Cartesian Parallel Manipulator

This paper introduces a new 3-DOF translational parallel manipulator named the Cartesian Parallel Manipulator (CPM). The manipulator consists of a moving platform that is connected to a fixed base by three limbs. Each limb is made up of one prismatic and three revolute joints and all joint axes are parallel to one another. In this way, each limb provides two rotational constraints to the moving platform and the combined effects of the three limbs lead to an over-constrained mechanism with three translational degrees of freedom. The manipulator behaves like a conventional X-Y-Z Cartesian machine due to the orthogonal arrangement of the three limbs. Two actuation methods are analyzed. However, the rotary actuation method is discarded because of the existence of singularities within the workspace. For the linear actuation method, there exists a one-to-one correspondence between the input and output displacements of the manipulator. However, each limb structure is exposed to a relatively large moment about an axis perpendicular to the prismatic joint axis. In order to compensate for this shortcoming, a method to maximize the stiffness is suggested. Finally, a numerical example of the optimal design is presented.