1. MOE Key Laboratory for Mechanism Theory and Equipment Design, International Centre for Advanced Mechanisms and Robotics, Tianjin University, Tianjin 300350, China e-mail:
2. Advanced Kinematics and Reconfigurable Robotics Lab, School of Natural and Mathematical Sciences, King's College London, Strand, London WC2R 2 LS, UK e-mail:
3. Chair of Mechanisms and Robotics, MOE Key Laboratory for Mechanism Theory and Equipment Design, International Centre for Advanced Mechanisms and Robotics, Tianjin University, Tianjin 300350, China; Advanced Kinematics and Reconfigurable Robotics Lab, School of Natural and Mathematical Sciences, King's College London, Strand, London WC2R 2 LS, UK e-mail: