System-Level Optimization of Passive Energy Balancing

A common issue with morphing structures is that the actuators must work against significant structural and aerodynamic stiffness. The concept of passive energy balancing (PEB) aims to ameliorate this, and thereby reduces system mass, by connecting negative stiffness elements to the actuated degrees of freedom. However, these devices can be complex to design and will also add their own mass to the system. It is therefore difficult to determine the potential for system-level mass saving without significant detailed design effort. This work treats a PEB device as essentially a local energy storage mechanism. This framework leads to an approach to optimization that will deliver a lightweight PEB mechanism in addition to reducing actuator requirements. It also allows a high-level method to obtain an approximate evaluation of system-level benefits with only basic information about the application being considered, by comparing general properties of the actuators used to the energy storage properties of the underlying materials used in the PEB device. The work concludes with a case study that shows how the PEB can potentially reduce system mass both through reduced energy consumption requirements and actuator mass savings, and can work particularly well for actuators with nonideal stroke/force profiles.