G.  Tonietti, Schiavi, R., and Bicchi, A., ?Design and Control of a Variable Stiffness Actuator for Safe and Fast Physical Human/Robot Interaction?, in Proc. IEEE Int. Conf. on Robotics and Automation, 2005, pp. 528-533. 

A.  Bicchi and Tonietti, G., ?Design, Realization and Control of Soft Robot Arms for Intrinsically Safe Interaction with Humans?, in Proc. IARP/RAS Workshop on Technical Challenges for Dependable Robots in Human Environments, 2002, pp. 79-87.