本研究導入車-橋互制模型於封閉式磁性編碼器，透過了解車-橋互制系統的歷史演進與其優劣，進一步選擇適合的數學理論模型進行振動響應之推導。透過數學描述掃描台車與封閉式結構間的動力模型，藉由理論模型掌握關鍵影響因子得到實驗參數。同時，透過有限元素模擬找出封閉式結構的振動模態，與衝擊錘實驗所得到的模態進行比對，驗證有限元素模型的可行性與可信度，並利用模擬得到的振動模態輔助後續實驗數據的分析。本研究以加速規作為感測器，獲取掃描台車與封閉式結構的加速度響應。於實驗的結果中，掃描台車及結構的加速度響應與速度成正相關，藉由兩者加速度響應誤差的比對，發現掃描台車於結構模態三產生較大的加速度誤差響應，研究發現，此現象是由於受到離心力影響，掃描台車在低預壓力下無法忠實呈現與結構相同的加速度響應。除此之外，本研究並發現該位移誤差響應的來源主要來自50赫茲以下環境低頻振動。經實驗驗證，增加預壓力能有效降低位移誤差的響應。最後，透過實驗分析，本研究能夠精準描述預壓力與量測氣隙變化量之間的關係。

In this research, the vehicle-bridge interaction model is applied on an enclosed magnetic encoder. Through studying evolution of vehicle-bridge interaction system including its advantages and disadvantages between different theoretical models, the most suitable mathematical model is selected to derive the vibration responses and dynamic behavior between scanning head and enclosed structure by math. Therefore, the experimental parameters can be identified by figuring out the main factors from the theoretical model. Furthermore, vibration modes of the enclosed structure can be obtained by FEM simulations. In order to verify the feasibility and credibility of the finite element model, the modes from simulation are compared with the modes obtained from impact hammer experiment. After the verification, it is validated that the FEM simulation can assist analyzing the experiment data subsequently. In the experiment, the accelerometers are placed on the structure to capture the acceleration responses of scanning head and enclosed structure. From experimental results, the acceleration responses of the scanning head and the structure are positively correlated to velocity. By comparing the acceleration error response of the two, it is found that the acceleration error response is the largest when third mode is excited. Due to lower preload and centrifugal force, the scanning head can’t faithfully present the structure’s acceleration response. From displacement error response, the source of error is found to be caused mainly from environmental vibrations at low frequency range which is under 50 Hz. Besides, it is proved that increasing the preload can effectively reduce the response of displacement error. In the summary, this study proposes a method to accurately predict the relationship between preload and the dynamic variation of measuring gap.

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