Design of the parallel mechanism for a hybrid mobile robot in wind turbine blades polishing

Efficient and precise processing of large-scale parts is an uprising problem in industry. In this paper, a method to polish large-scale wind turbine blades using hybrid mobile robots is proposed. The robot combines an automated guided vehicle (AGV), a 2-DoF 3-parallelogram hybrid module and a 1T2R parallel module. This paper focuses on the design of the 1T2R parallel mechanism. In order to realize flexible A/B axis rotational capacity and efficient transmission of driving units, two 1T2R parallel mechanisms actuated by ball screw drives are derived under the guidance of a type synthesis approach based on Grassmann line geometry and a line-graph method. Under the description of Tilt and Torsion (T&T) angles, kinematics (especially the parasitic motion) of the proposed mechanisms is investigated. To carry out the dimension synthesis, performance evaluation indices including good transmission and constraint workspace, maximum orientation capacity, global transmission and constraint index and global average parasitic motion are defined. The performance atlases are plotted in the parameter design space. By comparing the parasitic motion and the motion/force transmission and constraint performance of the two mechanisms, 3-RCU mechanism is identified to develop the parallel module and its kinematic optimization is carried out. The CAD model with a set of optimal parameters is presented. The work in this paper lays the foundation for the development of the hybrid mobile robot, and the configuration design and parameter optimization in this paper can be further applied to the design of other parallel mechanisms.