Design and development of a Schonflies-motion parallel robot with articulated platforms and closed-loop passive limbs

The Delta-like parallel robot, which contains three open-ended Pa-(4S)1 passive limbs, plays an important role in high-speed pick-and-place operations. To meet the demand in high-speed and high-precision applications, this paper presents a novel articulated-platform parallel robot TH-HR4 with Scho & BULL;nflies motion under the guidance of a modified type synthesis method based on Grassmann Line Geometry and Line Graph. With the benefit of the adopted, the inherent error of the closed-loop passive limb in the presented parallel robot is avoided when compared with that of the open-ended passive limb caused by elastic deformation. Robot design and kinematics are then provided. To investigate the characteristics of motion/force transmissibility and constrainability of the presented articulated-platform parallel robot, the equivalent transmission and constraint wrenches analysis is presented by considering that the transmission and constraint wrenches in the articulated-platform parallel robots should be applied to the end-effector but not the sub-platforms. Then, the motion/force performance indices which include the input transmission index (ITI), the modified output transmission index (MOTI), the medial transmission index (MTI), and the constraint transmission index (CTI) are extended to evaluate the kinematic performance of the proposed articulated-platform parallel robot. Dimension synthesis of the TH-HR4 robot is carried out, by adopting the performance atlas method, to make the robot realize a good transmission and constraint workspace. Based on these foundations, a prototype of the TH-HR4 parallel robot with optimal geometrical parameters has been developed. Performance tests and applications indicate that the HR4 parallel robot can generate high-precision and high-speed operations.