Spiral pulley negative stiffness mechanism for passive energy balancing

This article discusses the development, analysis, and testing of a mechanism designed to passively balance the energy requirements of mechanical systems and smart structures in order to reduce the size and weight of their actuation systems and to minimize the associated energy consumption. This passive energy balance is achieved by coupling a negative stiffness mechanism to the positive stiffness of the mechanical system being driven, thereby creating a net zero stiffness system which can be actuated with minimal energy requirements. The negative stiffness mechanism proposed here uses a cable spooling around a spiral-shaped pulley to convert decreasing forces in a pre-stretched linear extension spring into increasing torque output, thereby creating a torsional spring with negative output stiffness. An analytical model of the system was developed, and the geometry of the spiral pulley was optimized for a representative design case. An experimental demonstrator was then built and tested, confirming the ability of the concept to drastically reduce torque and energy required to actuate a representative load.