1. “E. Piaggio” Research Center, University of Pisa, Pisa, Italy
2. Advanced Robotics Department of the Italian Institute of Technology, Genova, Italy
3. DLR Institute of Robotics and Mechatronics, Wessling, Germany
4. Department of Bioengineering, Faculty of Engineering, Imperial College London, London, UK
5. Robotics and Mechatronics Group of the Control Laboratory, EL/CE Faculty of Electrical Engineering, Mathematics and Computer Science, University of Twente, Enschede, Netherlands
6. Department of Mechanical Engineering, Faculty of Applied Sciences, Vrije Universiteit Brussel, Brussels, Belgium