由轉子不平衡反應進行線上鑑別軸承係數

On-Line Identification of Bearing Coefficients from Unbalance Response

油膜軸承之軸承係數隨轉速而變，由Tiwari等人所推導之不平衡反應方程式中得知，未知數數目為方程式數目的二倍，無論量測數目的多寡，皆須以至少兩次試運轉的方式鑑別出軸承係數，亦即必須停機做第二次不平衡配重之調整配置，以獲得足夠之振動訊號。本文假設在某一轉速區間內的軸承係數曲線為二階多項式，再利用此轉速區間內若干個轉速的不平衡振動反應，計算出該多項式的係數。其憂點符合以軸承係數為轉速之函數的假設，以勵主一次試運轉的情形下鑑別出軸承係數，不必停機，可進行線上鑑別軸承係數之作業。同時可降低雜訊效應，又有利於內插法求取其他特定轉速下之軸承係數。

It is well known that the bearing coefficients of oil film journal bearings are speed dependent. From the derivation of Tiwari et al., the numbers of unknown coefficients are twice the number of the equations relating to unbalance responses. That means at least two unbalance test runs are necessary to solve the bearing coefficients, no matter how many measurements are made, and the rotating machines have to stop once to adjust the unbalance configurations for the second test run. In this study, second order polynomials are assumed to fit the bearing coefficients in a specific speed range, and unbalance measurements are made at several rotating speeds in that speed range to solve for the polynomial coefficients. The advantages of this approach are that it fulfills the conditions of speed-dependent coefficients, and the bearing coefficients can be obtained with only one test run. It is not necessary to stop the machines, and on-line identification of bearing coefficients can be achieved. Noise reduction and interpolation for the bearing coefficients at other speeds can also be easily attained.