1. Beira, R., Lopes, M. Praca, M., Santos-Victor, J., Bernardino, A., Metta, G., Becchi, F. and Saltaren, R.: Design of the robot-cub (iCub) head. Proceedings of the IEEE International Conference on Robotics and Automation. Orlando, USA, 94-100, 2006.;
2. Zecca, M., Roccella, S., Carrozza, M.C., Miwa, H., Itoh, K., Cappiello, G., Cabibihan, J.J., Matsumoto, M., Takanobu, H., Dario, P. and Takanishi, A.: On the development of the emotion expression humanoid robot WE-4RII with RCH1. Proceedings of the Fourth IEEE/RAS International Conference on Humanoid Robots. 1, 235-252, 2004.;
3. Hirth, J., Schmitz, N. and Berns, K.: Emotional Architecture for the Humanoid Robot Head ROMAN. Proceedings of the IEEE International Conference on Robotics and Automation, Roma, 2150-2155, 2007.;
4. Sabater, J.M., Garcia, N., Perez, C., Azorin, J. M., Saltaren, R.J. and Yime, E.: Design and analysis of a spherical humanoid neck using screw theory. Proceedings of the First IEEE/RAS-EMBS International Conference on Biomedical Robotics and Biomechatronics, Pisa, 1166-1171, 2006.;
5. Stewart, D.: A platform with six degrees of freedom. Proceedings of the Institution of Mechanical Engineers, 180(1), 371-378, 1965.;