Permanent preloading by acceleration for statically balancing MEMS devices

Abstract

Static balancing is used to reduce the actuation stiffness in a translational stage compliant mechanism. The planar and monolithic compliant mechanism is preloaded using a buckling beam of which the top part is guided by a double folded flexure. Hooks, that lock the top part of the beam in place, ensure a permanent static balancing of the entire device. The preloading action is caused by an external shaking or shock to the device. A theoretical micro electromechanical system (MEMS) model with a radius of 18.6 mm is developed and a scale 6:1 prototype is fabricated and tested for static balancing, first eigenfrequency (EF) and eigenmode (EM). Finite element modelling is used to predict static balancing and EM behaviour. Experiments on two equally fabricated prototypes show a reduction of -123 % and -126% actuation stiffness where -104.5% was predicted. The expected reduction for the designed MEMS device is 98.4%. The experimental first EF of the prototype is 3.10±0.25 Hz against a theoretical value of 3.09 Hz. The theoretical first EF of the MEMS model is 21.8 HZ. The prototypes are successfully preloaded by applying shaking or shock by hand. The predicted minimal energy requirement for this is found to be 4.9e-3 J, while 6.4e-3 J and 5.9e-3 J were calculated based on experimental results. The expected minimal energy required for preloading the designed MEMS device is 1.0e-5 J.