Abstract
A determinant D as a criterion, in terms of structural and material properties, is theoretically derived to determine if the bistability can occur for micro mechanically bistable mechanisms. When D < 0, the mechanism will display bistable behavior if an appropriate force is applied to push the bistable mechanism; while D > 0, bistable behavior cannot occur. The proposed V-beam bistable mechanisms have been successfully fabricated with different beam length and tilted angle. Experiments were conducted to validate the theoretical study for bistability. Comparing the theoretical solutions to the experimental results, it shows that both agree well with each other. It also concludes that to design an enabled bistable V-beam mechanism, the tilted angle should be larger, for the same beam length; while the beam length has to be longer for the same titled angle. The ratio of beam thickness to width, t/w, has effect on bistable phenomena of V-beam mechanism. It is more easily found bisatble phenomena when V-beam mechanism with smaller t/w value. It is found that t/w value had better less than 1 as the structure dimension being sub millimeter. The developed determinant D is used to predict if a designed bistable mechanism can equip with bistable behavior or not, providing the structural sizes and material properties. As a result, researchers can save their trial works when design a bistable mechanism. The V-beam with larger tilted angle up to 5° have been successfully fabricated to act as a bistable mechanisms, in comparison to 3.5° tilted angle in the existing literatures. Microsprings are often used in MEMS actuators to transmit force and to restore its original position by its spring force after a movement. Due to larger stiffness and better capability of resisting lateral forces, box microspring has the advantages of resisting induced transverse forces and preventing lateral deformation, comparing to other microsprings. To have better operation, the nonlinear behavior of microspring should be avoided when it is utilized in MEMS devices. It is known that the sizes of microspring can significantly affect the performance of microspring. In this work, we report the effect of box microspring sizes on the nonlinear deformation of microspring. The width of vertical beam of rectangular frames WS, the thickness of microspring T, the width of horizontal beam of rectangular frames BS, and the spring number of box microspring N are used as the parameters to investigate the effect of the sizes on the nonlinear force. The finite element software COMSOL Multiphysics is employed as the simulation tool. From simulation results, nonlinear deformation of micro box spring is regressed as Duffing equations. Moreover, from simulation data, the linear spring constant k and cubic spring constants k3 of Duffing equation could be determined and expressed in terms of T, BS, WS, and N by utilizing the regression analytical method. It is found that nonlinear deformation is harder found for thicker, wider, and more turns springs. The simulated results of this work can be used to design the microspring in an actuator such that the nonlinear deformation may be avoided.