Bidirectional Spiral Pulley Negative Stiffness Mechanism for Passive Energy Balancing

J Zhang, AD Shaw, MR Amoozgar, MI Friswell (Swansea University) & BKS Woods (University of Bristol)

Journal of Mechanisms and Robotics, Vol. 11, No. 5, October 2019, article 054502


The energy balancing concept seeks to reduce actuation requirements for a morphing structure by strategically locating negative stiffness devices to tailor the required deployment forces and moments. One such device is the spiral pulley negative stiffness mechanism. This uses a cable connected with a pre-tension spring to convert decreasing spring force into increasing balanced torque. The kinematics of the spiral pulley are first developed for bidirectional actuation developed and its geometry is then optimized by employing an energy conversion efficiency function. The performance of the optimized bidirectional spiral pulley is then evaluated through the net torque, the total required energy and energy conversion efficiency. Then, an additional test rig tests the bidirectional negative stiffness property and compares the characteristics with the corresponding analytical result. Exploiting the negative stiffness mechanism is of significant interest not only the field of morphing aircraft, but also in many other energy and power reduction applications.

Paper Availability

This material has been published in the Journal of Mechanisms and Robotics, Vol. 11, No. 5, October 2019, article 054502, the only definitive repository of the content that has been certified and accepted after peer review. Copyright and all rights therein are retained by ASME.

Link to paper using doi: 10.1115/1.4043818

Journal of Mechanisms and Robotics