1. Robotics Research Center, Yanshan University, Qinhuangdao, Hebei 066004, China
2. Department of Aerospace Engineering, Ryerson University, Toronto, ON, Canada, M5B 2K3
3. School of Mechanical Engineering, Tianjin University, Tianjin 300072, China
4. King's College London, University of London, London WC2R 2LS, UK
5. Dipartimento di Ingegneria Industriale e Meccanica, Università di Catania, 95125 Catania, Italy