1. Department of Mechanics, Mathematics and Management (DMMM), Polytechnic University of Bari, Via Orabona 4, Bari 70125, Italy;
2. Centre for Power Transmission and Motion Control (PTMC), Department of Mechanical Engineering, University of Bath, Claverton Down, Bath BA2 7AY, UK e-mails: ;
3. Centre for Power Transmission and Motion Control (PTMC), Department of Mechanical Engineering, University of Bath, Claverton Down, Bath BA2 7AY, UK e-mail:
4. Department of Mechanics, Mathematics and Management (DMMM), Polytechnic University of Bari, Via Orabona 4, Bari 70125, Italy e-mail: