OPTIMIZATION OF A FORWARD-SWEPT COMPLIANT MECHANISM

A coupled 3 degree-of-freedom contact-aided compliant mechanism called the Forward Swept Compliant Mechanism (FSCM) is designed optimized for coupling orthogonal translational motion. The purpose of this mechanism is to allow desirable wing morphing passively in an ornithopter wing structure to improve free flight pitch agility via sweeping the wing tip forward during downstroke. This new contact-aided compliant mechanism design, based on the coupled three degree of freedom Bend-Twist-and-Sweep Compliant Mechanism, was developed to couple motion in bending to forward sweep during downstroke to destabilize the downstroke, and thereby increasing pitch agility. This is made possible due to an axial rotation of the mechanism, positioning the angled compliant joint such that the axis of deformation is skewed from the lifting direction. A multi-objective optimization problem was formulated and solved using a multi-objective genetic algorithm. The objectives of this optimization were to maximize forward sweep while minimizing bending, twist, peak stress, and mass. During the optimization, 3084 designs were simulated throughout 37 generations. The complete data set from the optimization was used to understand the relationship between each design variable and each objective, as well as in a random forest of regression trees to determine each variable's importance to each objective. Two designs were chosen and compared for performance tradeoffs, where additional shape change is achieved at the expense of higher peak stress. The first design achieved the desired 2 degrees of forward sweep, and the second design achieved 5 degrees of forward sweep at the expense of larger bending and a higher peak stress.