Dual optimization of contact-aided compliant mechanisms for passive dynamic shape change

A dual optimization method for optimizing contact-aided compliant mechanism design parameters and their spatial distribution in a dynamic ornithopter wing structure for increased pitch agility is presented. This methodology separates the task into two separate optimization problems where, first, a computationally efficient rigid-body dynamics model is used to determine the optimal stiffness and spatial distribution of the compliant mechanisms and, second, a detailed compliant mechanism design is developed and optimized that achieves the desired nonlinear stiffness. A rigid-body mechanics model of the wing structure is used to find the location and stiffness of a contact-aided compliant mechanism that will induce the forward sweep passively by coupling lift loads to forward sweep. The forward-swept compliant mechanism is then developed and optimized to achieve the desirable coupling. The free-flight pitch agility of an ornithopter is shown to increase via sweeping the wings forward during downstroke. A free-flight experiment is performed, and the novel contact-aided compliant mechanism is shown to induce the desired forward sweep during downstroke.