1. School of Mechanical Engineering and Automation, Dalian Polytechnic University, Dalian 116034, P. R. China
2. School of Information Science and Engineering, Dalian Polytechnic University, Dalian 116034, P. R. China
3. Department of Mathematical Sciences, Giuseppe Luigi Lagrange, Politecnico di Torino, Corso Duca Degli Abruzzi 24, Torino, Italy