Optimal design of a novel 4-degree-of-freedom parallel mechanism with flexible orientation capability

摘要

This article proposes a novel spatial parallel kinematic mechanism with three kinematic limbs and 4 degrees of freedom. Its mobile platform can realize two translations and two rotation movements. Of note is that this mechanism can realize flexible A-/B-axis rotation (rotations about the x- and y-axes) and the transformation between vertical machining mode and horizontal machining mode. Using Tilt and Torsion angle description method, the kinematics analysis of this parallel kinematic mechanism is carried out. On this basis, the geometrical parameters, including parameters of three limbs and mobile platform, are optimized. In view of the particularity of configuration, the limb in the postposition with two active inputs is analyzed first and then the remaining two identical limbs. In the optimal design, motion/force transmissibility is taken into consideration, and the local transmission index is used as the performance evaluation criterion to investigate the orientation capability of this parallel kinematic mechanism. Using performance atlases method, the optimal kinematic design of the 4-degree-of-freedom parallel kinematic mechanism is carried out and a set of preferable optimized parameters is obtained at last. By virtue of the kinematic advantages, the proposed parallel kinematic mechanism can be used as the modular machining unit in five-axis machine centers. Based on this work, a machine tool with high flexibility has been developed to process the five faces of a workpiece within one setup.