Oil film thickness measurement method based on real part of ultrasonic reflection coefficient

Abstract

A method for measuring oil film thickness based on the real part of ultrasonic reflection coefficient belongs to the field of ultrasonic monitoring of lubrication status. The present invention is aimed at the upper limit problem of oil film thickness measurement of the existing ultrasonic reflection coefficient amplitude method. First, the gap between the friction matrix a and the friction matrix b is made into an air layer, and the ultrasonic reflection signal of the interface between the friction matrix a and the air layer is collected as a reference signal; then, lubricating oil is added between the friction matrix a and the friction matrix b to form an oil film layer, and the ultrasonic reflection signal of the interface between the friction matrix a and the oil film layer is collected as an oil film reflection signal; the reference signal and the oil film reflection signal are Fourier transformed respectively, and the reflection coefficient of the oil film layer is calculated; the real part information of the reflection coefficient is extracted to obtain the real part of the reflection coefficient; the thickness of the oil film layer is calculated according to the real part of the reflection coefficient and the center frequency of the ultrasonic signal. The method of the present invention can increase the upper limit of oil film thickness measurement by tens of microns and achieve higher oil film thickness measurement accuracy.

Description

Technical Field

[0001] The invention relates to an oil film thickness measurement method based on the real part of ultrasonic reflection coefficient, and belongs to the field of ultrasonic monitoring of lubrication state. Background Art

[0002] In mechanical equipment, the lubricating oil film formed between the friction surfaces is a key factor in reducing friction and wear and ensuring stable operation of the equipment. When the oil film thickness is too small, the oil film will break at the point of greater impact, and the friction pair will be in a dry friction state, causing the contact surface temperature to rise and friction and wear to intensify. When the oil film thickness is too large, the load-bearing capacity of the equipment will be affected and unnecessary energy loss will be caused. Therefore, real-time monitoring of the changes in the oil film thickness is crucial to ensuring the stable operation of the equipment and improving the mechanical efficiency of the equipment.

[0003] The oil film thickness measurement methods mainly include electrical measurement method, optical measurement method and ultrasonic measurement method. The electrical measurement method requires an electrically insulating plane or a completely isolated contact unit to install the sensor, and its measurement accuracy is easily affected by environmental factors; the optical measurement method requires that the material to be measured has good light transmittance, or a visual optical window needs to be installed on the material to be measured. These restrictions determine that the electrical measurement method and the optical measurement method are difficult to apply to the actual measurement of oil film thickness. Unlike the electrical measurement method and the optical measurement method, the ultrasonic measurement method has the characteristics of strong penetration and high sensitivity. It does not require the material to be measured to be light-transmissive and will not damage the test environment. It is the oil film thickness measurement method with the most development potential and application prospects.

[0004] When using ultrasound to measure the thickness of the oil film, the thickness of the oil film needs to be characterized by the amplitude of the ultrasonic reflection coefficient. When the amplitude of the reflection coefficient of the oil film layer approaches 1, the change in the amplitude of the reflection coefficient is extremely small. At this time, a small reflection coefficient amplitude measurement error will also lead to a large oil film thickness measurement error. Therefore, in the actual measurement process, in order to achieve a higher oil film thickness measurement accuracy, the upper limit of the reflection coefficient amplitude is usually taken as 0.95. In other words, when the ultrasonic frequency changes within a certain range, there is an upper limit to the measurement of the oil film thickness, which to a certain extent limits the practical application of ultrasonic measurement technology for oil film thickness.

[0005] In summary, analyzing the measurement upper limit of the ultrasonic reflection coefficient amplitude method and improving the ultrasonic measurement accuracy of oil film thickness are of great research significance for optimizing ultrasonic measurement technology and promoting the practical application of ultrasonic measurement technology in the field of lubrication condition monitoring. Summary of the invention

[0006] In view of the upper limit problem of oil film thickness measurement of the existing ultrasonic reflection coefficient amplitude method, the present invention provides an oil film thickness measurement method based on the real part of the ultrasonic reflection coefficient.

[0007] The present invention provides an oil film thickness measurement method based on the real part of ultrasonic reflection coefficient, comprising:

[0008] The ultrasonic transducer is arranged on the upper surface of the friction substrate a; a pulse transceiver is used to send periodic pulses to excite the ultrasonic transducer, so that the ultrasonic transducer sends an ultrasonic signal with a preset width;

[0009] Firstly, the gap between the friction substrate a and the friction substrate b is made into an air layer, and the ultrasonic reflection signal of the interface between the friction substrate a and the air layer is collected as a reference signal;

[0010] Then, lubricating oil is added between the friction substrate a and the friction substrate b to form an oil film layer, and an ultrasonic reflection signal at the interface between the friction substrate a and the oil film layer is collected as an oil film reflection signal;

[0011] Perform Fourier transform on the reference signal and the oil film reflection signal respectively, and calculate the reflection coefficient of the oil film layer according to the transformation results; extract the real part information of the reflection coefficient to obtain the real part of the reflection coefficient;

[0012] The thickness of the oil film is calculated based on the real part of the reflection coefficient and the center frequency of the ultrasonic signal.

[0013] According to the oil film thickness measurement method based on the real part of ultrasonic reflection coefficient of the present invention, the calculation method of the oil film layer reflection coefficient includes:

[0014]

[0015] Where R is the reflection coefficient of the oil film in the frequency domain, B(t) is the reflection signal of the oil film in the time domain, and T(t) is the reference signal in the time domain; Represents Fourier transform, which converts a signal from the time domain to the frequency domain.

[0016] According to the oil film thickness measurement method based on the real part of ultrasonic reflection coefficient of the present invention, the thickness of the oil film layer is much smaller than the half wavelength of ultrasound.

[0017] According to the oil film thickness measurement method based on the real part of ultrasonic reflection coefficient of the present invention, the process of extracting the real part information of the reflection coefficient and obtaining the real part of the reflection coefficient includes:

[0018] When the ultrasonic signal propagates in the three-layer medium structure formed by the friction matrix a, the oil film layer and the friction matrix b, the ultrasonic signal will be reflected and transmitted at the interface of the three layers of medium. The reflection coefficient R of the oil film layer in the frequency domain is expressed as:

[0019]

[0020] Where z1 is the acoustic impedance of friction matrix a, z3 is the acoustic impedance of friction matrix b, f is the center frequency of ultrasonic signal, h is the thickness of oil film layer, ρ2 is the density of lubricating oil, and c2 is the sound velocity of lubricating oil;

[0021] Extract the real part information of the reflection coefficient R of the oil film layer in the frequency domain and obtain the real part of the reflection coefficient:

[0022]

[0023] Where R Re is the real part of the reflection coefficient, and z2 is the acoustic impedance of the lubricating oil.

[0024] According to the oil film thickness measurement method based on the real part of ultrasonic reflection coefficient of the present invention, the real part of the reflection coefficient R Re The expression of the oil film thickness h is transformed into:

[0025]

[0026] According to the real part of the reflection coefficient R Re The oil film thickness h is calculated using the center frequency f of the ultrasonic signal.

[0027] According to the oil film thickness measurement method based on the real part of the ultrasonic reflection coefficient of the present invention, after the ultrasonic transducer sends out an ultrasonic signal, it receives an ultrasonic reflection signal and transmits the ultrasonic reflection signal to the pulse transceiver.

[0028] According to the oil film thickness measurement method based on the real part of the ultrasonic reflection coefficient of the present invention, the ultrasonic reflection signal received by the pulse transceiver is collected by a data acquisition card.

[0029] According to the oil film thickness measurement method based on the real part of ultrasonic reflection coefficient of the present invention, the friction matrix b is arranged on a macro-micro composite displacement platform, and the macro-micro composite displacement platform is used to adjust the thickness of the oil film layer between the friction matrix a and the friction matrix b.

[0030] According to the oil film thickness measurement method based on the real part of ultrasonic reflection coefficient of the present invention, the thickness of the oil film layer is between 0 and 100 microns.

[0031] Beneficial effects of the present invention: The present invention solves the oil film thickness by establishing a theoretical relationship between the oil film thickness and the real part of the reflection coefficient. Compared with the original reflection coefficient amplitude measurement method, the method of the present invention can increase the upper limit of the oil film thickness measurement by tens of microns and can achieve higher oil film thickness measurement accuracy, which has important engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1It is a schematic flow chart of the oil film thickness measurement method based on the real part of ultrasonic reflection coefficient according to the present invention;

[0033] Figure 2 It is a schematic diagram of the change of the reflection coefficient amplitude and the real part of the reflection coefficient with the product of frequency and thickness;

[0034] Figure 3 It is a schematic diagram of an experimental platform configured for the method of the present invention;

[0035] Figure 4 It is a schematic diagram of the real part spectrum of the reflection coefficient of the oil film layer;

[0036] Figure 5 The diagram is a comparison of the measurement results of measuring the oil film thickness using the method of the present invention and the existing ultrasonic reflection coefficient amplitude method. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0039] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0040] Specific implementation method 1. Combination Figure 1 and Figure 3 As shown, the present invention provides an oil film thickness measurement method based on the real part of ultrasonic reflection coefficient, comprising:

[0041] The ultrasonic transducer is arranged on the upper surface of the friction substrate a; a pulse transceiver is used to send periodic pulses to excite the ultrasonic transducer, so that the ultrasonic transducer sends an ultrasonic signal with a preset width;

[0042] Firstly, the gap between the friction substrate a and the friction substrate b is made into an air layer, and the ultrasonic reflection signal at the interface between the friction substrate a and the air layer is collected as the reference signal required for calculating the reflection coefficient;

[0043] Then, lubricating oil is added between the friction substrate a and the friction substrate b to form an oil film layer, and an ultrasonic reflection signal at the interface between the friction substrate a and the oil film layer is collected as an oil film reflection signal;

[0044] Perform Fourier transform on the reference signal and the oil film reflection signal respectively, and calculate the reflection coefficient of the oil film layer according to the transformation results; extract the real part information of the reflection coefficient to obtain the real part of the reflection coefficient;

[0045] The thickness of the oil film is calculated based on the real part of the reflection coefficient and the center frequency of the ultrasonic signal.

[0046] Further, the calculation method of the oil film layer reflection coefficient includes:

[0047]

[0048] Where R is the reflection coefficient of the oil film in the frequency domain, B(t) is the reflection signal of the oil film in the time domain, and T(t) is the reference signal in the time domain; Represents Fourier transform, which converts a signal from the time domain to the frequency domain.

[0049] Furthermore, the thickness of the oil film layer is much smaller than half the wavelength of ultrasound.

[0050] Furthermore, the real part information of the reflection coefficient is extracted, and the process of obtaining the real part of the reflection coefficient includes:

[0051] The solution of oil film thickness is based on the oil film thickness h and the real part of the reflection coefficient R Re Theoretical relationship between:

[0052] When the ultrasonic signal propagates in the three-layer medium structure formed by the friction matrix a, the oil film layer and the friction matrix b, the ultrasonic signal will be reflected and transmitted at the interface of the three layers of medium. For the oil film whose thickness is much smaller than the half wavelength of the ultrasonic wave, the reflection coefficient R of the oil film layer in the frequency domain is expressed as:

[0053]

[0054] Where z1 is the acoustic impedance of friction matrix a, z3 is the acoustic impedance of friction matrix b, f is the center frequency of ultrasonic signal, h is the thickness of oil film layer, ρ2 is the density of lubricating oil, and c2 is the sound velocity of lubricating oil;

[0055] Extract the real part information of the reflection coefficient R of the oil film layer in the frequency domain and obtain the real part of the reflection coefficient:

[0056]

[0057] Where R Re is the real part of the reflection coefficient, and z2 is the acoustic impedance of the lubricating oil.

[0058] The real part of the reflection coefficient R Re The expression of the oil film thickness h is transformed into:

[0059]

[0060] According to the real part of the reflection coefficient R Re The oil film thickness h is calculated using the center frequency f of the ultrasonic signal.

[0061] Combination Figure 2 As shown in the figure, although the real part of the reflection coefficient and the amplitude of the reflection coefficient both increase with the increase of the frequency-thickness product, when the upper limits of the real part of the reflection coefficient and the amplitude of the reflection coefficient are both taken as 0.95, the frequency-thickness product corresponding to the real part of the reflection coefficient has a larger range of variation. At the same time, since the real part of the reflection coefficient is more sensitive to the change of the frequency-thickness product, when the range of the frequency-thickness product is constant, the real part of the reflection coefficient has a larger range of variation. Therefore, when the frequency of the ultrasonic wave is constant, the real part of the reflection coefficient method can achieve a larger oil film thickness measurement range and higher oil film thickness measurement accuracy than the reflection coefficient amplitude method.

[0062] Going a step further, combined Figure 3 As shown, after the ultrasonic transducer 1 sends out an ultrasonic signal, it receives an ultrasonic reflection signal and transmits the ultrasonic reflection signal to the pulse transceiver 2 .

[0063] The ultrasonic reflection signal received by the pulse transceiver 2 is collected by the data acquisition card 3. The data collected by the data acquisition card 3 is processed in real time by the computer 4, and the measurement result of the oil film thickness is output.

[0064] The friction matrix b is arranged on a macro-micro composite displacement platform 5, and the macro-micro composite displacement platform 5 is used to adjust the thickness of the oil film layer 7 between the friction matrix a6 and the friction matrix b8.

[0065] As an example, the material of friction substrate a is aluminum; the material of friction substrate b is steel.

[0066] As an example, the oil film layer thickness is between 0-100 microns. Specific embodiment:

[0068] Establish as Figure 3The oil film thickness calibration and ultrasonic measurement experimental platform shown in the figure is used to verify the effectiveness of the method of the present invention. A periodic pulse is emitted by the pulse transceiver 2, and the ultrasonic transducer 1 emits an ultrasonic signal after being excited. The ultrasonic signal passes through the substrate a and is emitted at the substrate a-air interface. The reflected signal returns along the original path and is recorded by the data acquisition card 3 as the reference signal required for calculating the oil film thickness. After the reference signal is measured, a certain amount of lubricating oil is added between the substrate a and the substrate b to form a lubricating oil film. The thickness of the lubricating oil film is changed by the macro-micro composite displacement stage 5, and the reflected signal of the oil film layer is recorded by the data acquisition card 3. The reference signal and the oil film reflection signal are respectively Fourier transformed by the computer 4 to calculate the reflection coefficient of the oil film layer, and then the real part of the reflection coefficient of the oil film layer is obtained, such as Figure 4 The oil film thickness is calculated using the real part of the reflection coefficient, and the calculation result at the center frequency of the ultrasonic transducer is selected as the measurement result of the oil film thickness. Figure 5 It can be seen from the comparison results that the method of the present invention can increase the oil film thickness measurement range of the existing reflection coefficient amplitude method by tens of microns, and even if the oil film thickness is located in the measurement area of ​​the reflection coefficient amplitude method, the measurement accuracy of the method of the present invention is better than that of the reflection coefficient amplitude method, which fully demonstrates the advantages of the method of the present invention.

[0069] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A method for measuring oil film thickness based on the real part of ultrasonic reflection coefficient, characterized in that include, The ultrasonic transducer is arranged on the upper surface of the friction substrate a; a pulse transceiver is used to send periodic pulses to excite the ultrasonic transducer, so that the ultrasonic transducer sends an ultrasonic signal with a preset width; Firstly, the gap between the friction substrate a and the friction substrate b is made into an air layer, and the ultrasonic reflection signal of the interface between the friction substrate a and the air layer is collected as a reference signal; Then, lubricating oil is added between the friction substrate a and the friction substrate b to form an oil film layer, and an ultrasonic reflection signal at the interface between the friction substrate a and the oil film layer is collected as an oil film reflection signal; Perform Fourier transform on the reference signal and the oil film reflection signal respectively, and calculate the reflection coefficient of the oil film layer according to the transformation results; extract the real part information of the reflection coefficient to obtain the real part of the reflection coefficient; The thickness of the oil film layer is calculated based on the real part of the reflection coefficient and the center frequency of the ultrasonic signal; The calculation method of the oil film layer reflection coefficient includes: Where R is the reflection coefficient of the oil film in the frequency domain, B(t) is the reflection signal of the oil film in the time domain, and T(t) is the reference signal in the time domain; It represents Fourier transform, which converts the signal from time domain to frequency domain; The process of extracting the real part information of the reflection coefficient and obtaining the real part of the reflection coefficient includes: When the ultrasonic signal propagates in the three-layer medium structure formed by the friction matrix a, the oil film layer and the friction matrix b, the ultrasonic signal will be reflected and transmitted at the interface of the three layers of medium. The reflection coefficient R of the oil film layer in the frequency domain is expressed as: Where z1 is the acoustic impedance of friction matrix a, z3 is the acoustic impedance of friction matrix b, f is the center frequency of ultrasonic signal, h is the thickness of oil film layer, ρ2 is the density of lubricating oil, and c2 is the sound velocity of lubricating oil; Extract the real part information of the reflection coefficient R of the oil film layer in the frequency domain and obtain the real part of the reflection coefficient: Where R Re is the real part of the reflection coefficient, z2 is the acoustic impedance of the lubricating oil; The real part of the reflection coefficient R Re The expression of the oil film thickness h is transformed into: According to the real part of the reflection coefficient R Re The oil film thickness h is calculated using the center frequency f of the ultrasonic signal.

2. The oil film thickness measurement method based on the real part of ultrasonic reflection coefficient according to claim 1 is characterized in that: The thickness of the oil film layer is much smaller than the half wavelength of ultrasound.

3. The oil film thickness measurement method based on the real part of ultrasonic reflection coefficient according to claim 2 is characterized in that: After the ultrasonic transducer sends out the ultrasonic signal, it receives the ultrasonic reflection signal and transmits the ultrasonic reflection signal to the pulse transceiver.

4. The oil film thickness measurement method based on the real part of ultrasonic reflection coefficient according to claim 3 is characterized in that: The ultrasonic reflection signal received by the pulse transceiver is collected by a data acquisition card.

5. The oil film thickness measurement method based on the real part of ultrasonic reflection coefficient according to claim 4 is characterized in that: The friction matrix b is arranged on a macro-micro composite displacement platform, and the macro-micro composite displacement platform is used to adjust the thickness of the oil film layer between the friction matrix a and the friction matrix b.

6. The oil film thickness measurement method based on the real part of ultrasonic reflection coefficient according to any one of claims 1 to 5, characterized in that: The thickness of the oil film is between 0-100 microns.

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