Research On Novel MEMS Inertial Switch With Adjustable Threshold

MEMS inertial switch has wide application prospects in medical,industrial,automotive,fuze,aerospace and other fields because of the advantages of low energy consumption,small size,easy integration,etc.Novel adjustable threshold MEMS inertial switch is designed to research goals of improving closing performance,threshold accuracy,and realizing adjustable threshold.Switch structure parameters are determined and the performances are verified by the method of combining theoretical analysis and finite element simulation.Switches are fabricated based on UV-LIGA technology and the performances are tested by dropping hammer device.Inertial switch model is established to analysis the influencing factors of closing performance and threshold accuracy.In the closing performance,contact duration is proportional to the reciprocal of the square root of contact stiffness,and contact damping can be used to solve the bounce problem.The threshold error calculated of traditional switches is43%,so the nonlinear spring is used to reduce the threshold error to 15.5%.Finally,the spring stress is prefabricated by means of the V-type electric heating driver to achieve the purpose of adjusting the switching threshold.On the basis of the application requirements,switch structure is designed.Mass structure is determined according to the operating frequency,the range of which is[1000,10000rad/s].A friction electrode with friction and low contact stiffness is designed to enhanced contact.The bow-shaped nonlinear spring is used as the supporting spring of the switch to improve the accuracy of the switching threshold according to the threshold characteristics of the nonlinear spring.A novel adjustable inertial switch is designed with a adjusting spring and driving structure.The performances of the switch are analyzed through Abaqus software for finite element simulation.In the closing performance,a comparative simulation experiment was carried out to verify the effect of the friction electrode,which showing that the contact duration of the friction switch is 150%longer than that of the flexible switch,and that the rigid,flexible switches have bounce problem while friction switch has’t.In terms of threshold error,switch with nonlinear spring is analyzed,which showing whose threshold error is 5%while that of traditional switches is 43%.The thresholds adjusting form high-g to low-g is realized,that is200g,120g,60g with three-threshold switch and[30,110g]with continual-threshold switch.Switches are fabricated based on the technology of UV-LIGA photolithography and precision micro electroforming process.The overall size of the switch is 5×5×0.26mm~3.The switch performance is tested by dropping hammer device.Firstly,the closing performance of the switch is tested.The results show that the contact duration of the switch increases with the increasing of the acceleration amplitude(the minimum contact duration is 200μs),and there is no bounce problem during the closing of the switch.Secondly,the accuracy of the switch threshold is tested.Under the acceleration of 1,2,3,4,and 6 ms pulse width,the switch threshold is always distributed in the interval[190,230g],and the switch threshold error is17%,which improves the threshold accuracy of the traditional switch by 135%.Finally,the switch thresholds are adjusted by applying voltage.The test results are as follows:the thresholds of the three-threshold switch are 210,110,60g;the threshold of the continual-threshold switch range in[30,110g].In short,novel adjustable threshold MEMS inertial switch improves the closing characteristics and threshold characteristics,and reaches the goal of adjusting the threshold from low-g to high-g.