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A Novel Threshold Accelerometer for Airbag Restraint Systems

Most accidents occur due to the malfunction of airbag restraint systems under interferences such as electromagnetic and pulse noises. As a result, modern inertial measuring and controlling systems including vibration isolation systems, systems in aircrafts and airbag restraint systems require threshold accelerometers not only to have the characteristics of fast response, high sensitivity, low cost and good reliability but also to resist any outside disturbances. Among these accelerometers, since it needs to sense the threshold acceleration and switch the circuit between On and Off states depending on the acceleration amplitude, the threshold accelerometer with post-buckling beams is an integration of a threshold sensor and an inertial driven actuator. The inertial force used to actuate the accelerometer and supply a stable contact force when the circuit is switched on is different from the electrostatic force and electro-thermal force widely used in microactuators. When the outside acceleration is less than a certain value, the threshold accelerometer can switch off the circuit automatically. Therefore, with its perfect anti-jamming capability on electromagnetic and vibration interferences, the mechanical threshold accelerometer is an excellent device in airbag restraint systems in automobiles or other safe-arming systems.

 

Bistable post-buckling mechanisms which possess excellent performance in decreasing power consumption are very useful in the design of a wide variety of microdevices. The performance of the threshold accelerometer depends largely on the design of the threshold sensing element. Fortunately, the nonlinear post-buckling bent-beam structure can fulfill the requirements of the static design of the threshold accelerometer. As is konwn, the bistability and the nonlinear stiffness occur when a vertical force is applied to the middle of the bent-beam. Although some compressed bistable buckled beams are really excellent structures, the dimension consistency of the residual-compressive-stress beams in the MEMS bulk production cannot be easily achieved. Consequently, post-buckling bent beams are considered in designing threshold accelerometers. Due to the strong nonlinearity of the post-buckling beam, the dynamics of the bent-beam system is also nonlinear. Besides the nonlinear stiffness, the influences of the damping force and contact force on the dynamics of a threshold accelerometer should also be taken into full consideration to improve the accelerometer’s overall performance.

 

Taking advantage of the bistability of the bent-beam, several kinds of bistable microacturators have been fabricated and applied as the subsystems in various MEMS fileds. Based on the post-buckling theory of large deflection beams, a novel micro-machined threshold accelerometer is designed by utilizing the nonlinear stiffness of post-buckling beams. The accelerometer consists of eight oblique micro-beams with an inertial mass in the middle to ensure its single moving direction and an electrical contact part fabricated on the bottom of the inertial mass. When the acceleration reaches the threshold, the beams buckle and close the threshold accelerometer, and when it gets down to be a certain value, the accelerometer opens quickly under the effect of the elastic force developed by the post-buckling beams. Compared with the design models of other threshold accelerometers with linear beam structures, the nonlinear post-buckling beams are introduced as threshold sensing elements. A number of design factors such as the air film damping and the contact force are taken into full consideration, thus establishing the dynamic equation of the accelerometer under coupled forces. With the results of the dynamic simulation, supported by previous buckling experiments, the accelerometer can provide accurate threshold sensing without false actuations under interferences outside, especially electromagnetic and vibration interferences, and hence their wide applications in safe-arming systems.

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Comments

I think that some accidents occur due to airbag malfunction but most of the time when youre dealing with used auto Airbags the malfunction can be a dash light or air bag sensor. Im not an expert in this field but I understand airbags and airbag deployment on all automobiles.

As a acceleration sensing and inertial driving device, the threshold accelerometer is used to transfer the hazard level of the crash accidents to the airbag control system. And then, based on the dangerous signal from the threshold accelerometer, the aigbag can be triggered immediately to protect the human body. Sometimes, the false signals are sent out from the threshold accelerometer due to nterferences of pulse noises, which leads to a misoperation. So many new design factors are considered to improve the contact reliabilty and threshold acceleration sensing ability which can provide an accurate triggering signal to the control system.

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