In ultrasonic reflection measurements of lubricant film thickness, an incident wave is needed as a reference signal and is typically calibrated under controlled ex-situ conditions. However, existing calibration methods have two limitations: 1) significant measurement errors are introduced due to the discrepancy between the calibration environment and the varying operational conditions (for example, temperature), and 2) disassembly of tribo-pairs is necessary. To address these issues, a novel method that enables in-situ adaptive calibration of incident signals is proposed. Particularly, it is found that the variation of the reflected signal against lubricant film thickness can well fit a circle in the polar coordinate, where the desirable incident signals can be extracted using the size and the location of the established circle. Importantly, the circle is iteratively updated to adapt to the variation of the working environment. This novel approach of calibrating incident signals, named the “circle-fitting method”, does not require knowledge of the acoustic properties of tribo-pairs and is thus temperature independent. For experimental validation, two test setups of a micrometer-driven calibration rig and a tilting pad thrust bearing platform have been used separately to implement ultrasound measurements of lubricant film thickness, demonstrating accurate results as evidenced by error analysis. Specifically, in the experiment with the micrometer-driven calibration rig, the measurements yielded an amplitude estimation error of 0.2% and a phase estimation error of 0.66%.

中文翻译：

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超声波润滑膜厚度测量入射信号的原位自适应校准


在润滑油膜厚度的超声反射测量中，需要入射波作为参考信号，并且通常在受控的非原位条件下进行校准。然而，现有的校准方法有两个局限性：1） 由于校准环境和不同的操作条件（例如温度）之间的差异，会引入严重的测量误差，以及 2） 需要拆卸摩擦优化对。为了解决这些问题，提出了一种能够对入射信号进行原位自适应校准的新方法。特别是，发现反射信号随润滑油膜厚度的变化可以很好地拟合极坐标中的圆，其中可以使用已建立圆的大小和位置提取所需的入射信号。重要的是，该循环会迭代更新以适应工作环境的变化。这种校准入射信号的新方法称为“圆拟合法”，不需要了解摩擦对的声学特性，因此与温度无关。为了进行实验验证，分别使用了微米驱动的校准台和可倾瓦推力轴承平台的两个测试装置来实施润滑油膜厚度的超声测量，误差分析证明了准确的结果。具体来说，在使用千分尺驱动的校准装置进行实验时，测量结果产生了 0.2% 的振幅估计误差和 0.66% 的相位估计误差。