1. Institute of Robotics, Bulgarian Academy of Sciences , 1113 Sofia , Bulgaria
2. Industrial Automation University of Chemical Technologies and Metallurgy , 1756 Sofia , Bulgaria
3. Istituto di Scienze e Tecnologie della Cognizione, Consiglio Nazionale delle Ricerche , Padova , Italy
4. Institute of Information and Communication Technologies, Bulgarian Academy of Sciences , 1113 Sofia , Bulgaria