Accuracy-improved ultrasonic phase algorithm for measuring lubricant film thickness

The reflected ultrasonic waves are generally used for the determination of the lubricant film thickness, which consist of a directly reflected wave at the first solid-lubricant interface and the other reflected waves passing through the oil layer. The whole reflected waves are generally utilized in current available ultrasonic algorithms. However, the directly reflected wave is independent on the lubricant film, which can be ignored for improving the measurement accuracy. In the present work, an accuracy-improved ultrasonic phase algorithm is proposed based on the reflection coefficient phase of the other reflected waves passing through the oil layer, rather than that of the whole reflected waves. Both experimental and finite element analysis results show that the proposed new algorithm possesses a high sensitivity and a robust anti-noise interference ability, which effectively improves the measurement accuracy, especially for thin films. With comparison to the current available phase algorithm, the maximum measurement error of lubricant film thickness decreased from 45 % to 6 %.