Kinematic optimal design of a 2-degree-of-freedom 3-parallelogram planar parallel manipulator

• A kind of spray-painting robot with a 3-parallelogram PPM is proposed.
• Several more efficient performance indices for analysis and design are defined.
• The optimization method gives more options and higher prospective.
• An optimum 2-DOF 3-parallelogram PPM for a spray-painting robot is identified.

A 2-degree-of-freedom (2-DOF) 3-parallelogram planar parallel manipulator (PPM) can follow an arbitrary planar curve and keep the end-effector in a definite posture. Such features are valuable for spray-painting robots. Considering these advantages, authors proposed a new spray-painting robot containing a 2-DOF 3-parallelogram PPM. In order to obtain a spray-painting robot with the best performance, the 2-DOF 3-parallelogram PPM should possess the largest workspace and most stable transmissibility. This study addresses the performance evaluation and kinematic optimization of this manipulator. First, the kinematics of the manipulator is analyzed, and performance indices that consider desirable workspace and transmissibility are proposed. Then, the process to determine optimal geometry parameters by using performance atlases is presented. Finally, a 2-DOF 3-parallelogram PPM with desirable workspace and transmissibility is identified.