Ludo C. Visser, Raffaella Carloni, Ramazan Unal, Stefano Stramigioli. Modeling and design of energy efficient variable stiffness actuators. In IEEE International Conference on Robotics and Automation, ICRA 2010, Anchorage, Alaska, USA, 3-7 May 2010. pages 3273-3278, IEEE, 2010. [doi]