The pendulum of Q-Flex accelerometer is formed by special processing such as laser cutting and acid etching of quartz material. Its coefficient of thermal expansion is extremely small, about 1/10 to 1/20 of ordinary glass. However, quartz glass is a brittle material, and the thickness of the flexure beam is only 0.03mm, making it prone to fracture.
In practical applications, accelerometers may often be subjected to vibration, impact, rapid temperature changes, and other harsh environments, posing significant challenges to their accuracy and stability. Moreover, uneven thickness of the flexure beam edges can also reduce the reliability of the pendulum. Therefore, studying the shock resistance performance of quartz flexure accelerometers is essentially investigating the shock resistance capacity of the pendulum component.
This article primarily introduces two measures to improve the shock resistance performance of Q-Flex accelerometer
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1.Material improvement
The technical requirements for the materials used in the flexural beams are.
1.1 Material parameter requirements
The tensile strength should be high and the modulus of elasticity E and stiffness k should be small.
1.2 Small elastic aftereffect.
Elastic aftereffect refers to the phenomenon that when an object is subjected to a fixed load, its deformability increases slowly with time, and when the load disappears, it cannot return to its original state immediately. The size of the elastic aftereffect of the flexible beam directly affects the output hysteresis loop of the accelerometer, which is too large and leads to unstable output and reduced linearity.
1.3 High fatigue strength.
Q-Flex accelerometer is very sensitive to positive and negative accelerometer, often in irregular reciprocating motion when working, especially to the pulse output system, the vibration frequency of the flexible beam is very high.
1.4 Easy processing.
The thickness of quartz flexible beam is only 0.03mm, through laser cutting, acid etching and other special processing, processing is difficult and less efficient. Currently commonly used "strength to elasticity ratio" to measure the material is good or bad. It refers to the strength limit and the ratio of the modulus of elasticity, within the allowable range, increase the ratio can improve the stability of the accelerometer.
Ion implantation improves the performance of flexural beams. When high-energy ions are injected into the surface layer of a material with an ion implanter, it can greatly improve its mechanical and physical properties. For example, injecting Au+, N+, etc. into the joint parts of a flexural beam can improve its fatigue life and corrosion resistance. In addition, with the popularity of carbon fiber, there is a short carbon fiber quartz composite material, whose fracture resistance is 4 times that of pure quartz glass.
2.Structural improvement
The transient dynamics analysis shows that the Q-Flex accelerometer has the weakest shock-resistance in the direction of output axis, because in the direction of pendulum axis, the flexure beam is mainly subjected to tensile or compressive stress and the value is small, and in the direction of input axis there is a magnetic yoke limitation, and it can only oscillate up to 0.019 mm. therefore, it is necessary to focus on the improvement of the shock-resistant performance of the quartz pendulum in the direction of output axis.
2.1 In the structural design, the center of the torque converter, the center of gravity of the pendulum assembly, and the limiting support are made to coincide in the direction of the input axis as much as possible. However, due to the complexity of the pendulum assembly, complete coincidence of the three points is almost impossible, and the magnitude of the impact force on the flexure beam is proportional to the distance of non-coincidence.
2.2 Increasing the width of the flexural beam.
Thickness h1 is the most important factor affecting the stiffness, sensitivity and intrinsic frequency of the flexural beam, and the smaller h1 is within the permissible range, the better the performance, and it is not advisable to change its value. The increase of the width b1 of the flexure beam has less influence on the above performance, and it can largely reduce the shear stress of the flexure beam in the direction of the output axis.
2.3 Increase the transition fillet of the fixed end of the flexure beam.
Under the action of acceleration load, the stress at the intersection of the pendulum beam and the outer ring is the largest. The transition fillet of the pendulum used in this thesis is 0.4mm, increasing the transition fillet can reduce the stress concentration and improve the service life.
Summary
This article proposes methods to improve the shock resistance of quartz flexure accelerometers from material and structural perspectives. It's worth noting that Ericco's ER-QA-02B quartz flexure accelerometer boasts shock parameters of 1000g, 0.5ms, 1/2sin, suitable for applications with high environmental and precision requirements. In addition, the shock parameters of the ER-QA-03C series are 150g, 0.5ms, 1/2sin. The zero offset repeatability of ER-QA-03C1 is ≤15 μg, and the scale factor repeatability is ≤15ppm. Apart from aerospace applications, it can also be used for static and dynamic acceleration measurements.
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