An extended ultrasonic time-of-flight method for measuring lubricant film thickness

Abstract

An extended ultrasonic time-of-flight (TOF) method is proposed for measuring the thickness of lubricant film. Based on the spectrum analysis method of superimposed pulses, the extended TOF determines the travel time of ultrasonic wave and subsequently the film thickness in frequency domain. The method extends the measurable range of the original TOF method to the lubricant films of superimposed reflected pulses, which usually processed by the resonance model. The extended TOF gives another interpretation to the resonance phenomenon described by the resonance model. In theory and practice, the extended TOF integrates the resonance model and the original TOF method into one approach. This solved the problem that film thickness monitoring program needs to alter between time and frequency domains according to the changing of film thickness. A precision experimental apparatus was designed for verifying the correctness of the method. The lubricant films of different thickness were measured repeatedly and the measuring accuracy was analyzed.

A Comparison of Adaptive Ultrasound Reflectometry Calibration Methods for Use in Lubrication Films

“…It is seen that the sum in Equation (4) equals −R 1 R l (t) and further equals the sum in Equation (3). With this realisation, it is seen that T l (t) is given by Equation (6).…”

“…Ultrasound transducers are a promising sensor technology because they are considered to be noninvasive. They are considered noninvasive primarily due to the high penetrability of ultrasonic waves, which allows for convenient placement of the ultrasound transducers without disturbing the system structure, design, and lubrication properties [1][2][3]. The most common use of ultrasound transducers in lubrication film monitoring is ultrasound reflectometry.…”

Ultrasonic Interferometric Procedure for Quantifying the Bone–Implant Interface

“…for the overall complex reflection coefficient of the three-layer system [24]. From this equation, one can also derive simplified reflection models like Liquid Spring Model [22,23,25,31], Resonance Model [17] or the Time-of-Flight Method [27]. Each of them is only valid for a limited range of thicknesses and frequencies, respectively.…”

“…For example, the time-and frequency-related investigation of ultrasound reflected at a thin layer is a typical approach with regard to tribological systems. In this field, it is used to determine the thickness of lubricant films, some of which are less than 100 µm thick, such as those found in ball bearings [21][22][23][24][25][26][27]. However, this approach has not yet been applied to medical problems where rough, non-geometric surfaces as well as very inhomogeneous, highly damping materials with not exactly known probabilities and strong individual deviations are found [28][29][30].…”

Review of ultrasonic-based technology for oil film thickness measurement in lubrication

“…However, by analyzing the time interval between two echoes, it is found that the minimum point phenomenon is caused by the definite time interval between two echoes instead of the resonance phenomenon [29]. Focusing on these two different explanations about the formation mechanism of the minimum point, the superposition principle of waves has been used to analyze the minimum point phenomenon.…”