可應用於微加速計之兩種對稱型懸吊結構研究

Abstract

本論文研究重點在於研究微加速計的懸吊結構，從各方面探討各種參數對其彈簧係數之影響，使微加速度計之靈敏度得以提高以及結構上之誤差能夠相應的減少，達到優化的效果。本文提出一種新的點對稱式懸吊配置，能夠使得平面雙軸之彈簧係數即使受到製程尺寸誤差的影響，仍然保持相同，進而使得雙軸之靈敏度也能相等，減少訊號誤差以及電性上修正的麻煩。本文中也提出一種新型的螺旋式懸吊結構，將與現今最常使用之蜿蜒式彈簧相互比較，並透過有限元素分析軟體ANSYS®執行特性模擬，分析點對稱懸吊配置之蜿蜒式以及螺旋式彈簧各方面之優缺。 利用ANSYS®軟體之共振模擬判斷其共振模態以及共振頻率，並推算出彈簧係數，得知在相同平面K值下，螺旋彈簧的Z軸K值較小，表示其Z軸靈敏度較高，適合用於三軸加速度計。同時在相同平面K值時，螺旋彈簧所佔之面積較小，代表有效質量塊面積更大，整體靈敏度相對更高。而後藉由調整彈簧位置對旋轉模態之共振頻率影響，瞭解螺旋彈簧位置距中心須較遠，才能使旋轉共振頻率大於直線共振頻率，使元件不易出現旋轉的情形。最後模擬Y軸3G之加速度，觀察X軸位移與Y軸位移之比值，推算出螺旋彈簧之耦合誤差較蜿蜒彈簧小。

In this study, our research focuses on the suspension structure of the micro accelerometer. In order to achieve optimal results we explore various parameters in all aspects to understand its influences on spring coefficient, expecting the higher micro-accelerometer's sensitivity as well as the deviation of the structure be reduced accordingly. This paper presents a new “point symmetrical” suspension configuration, it remains the same spring coefficient of two plane axes even if disturbed by the size deviations from process, and thus keeps equal sensitivity of two axes, reducing the error of the electrical signals. This paper also proposes a new “coil suspension structure”, it compares with the most commonly used serpentine spring through the finite element analysis software ANSYS® and then analyzes the pros and cons of two springs with point symmetrical configuration.

The spring coefficient K can be calculated from determination of the resonance with its resonant modes as well as resonant frequency by using the ANSYS ® simulation software. On the condition of the same K value at plane axes, the coefficient K of coil spring at Z-axis is smaller implicating its applicability of the three-axis accelerometer due to its higher sensitivity at Z-axis. Meanwhile in the same plane K value the smaller area is needed for coil spring. It means that overall sensitivity is relatively higher because of a larger effective mass of the block. By adjustment of the spring and its impact on the resonant frequency of rotation mode, we understand the need to position coil spring a little farther from the center in order to make spin resonant frequency greater than linear resonance frequency, so that element prevents from spinning. Finally it is concluded that the coupling error of coil spring is smaller than winding spring by observing the ratio of X-axis displacement over Y-axis displacement when simulating 3G on Y-axis acceleration.