Disclosure of Invention
The invention aims to solve the problem that the real-time continuous change of the thickness of a bearing lubricating film cannot be effectively monitored by using a single probe through the method, and provides an ultrasonic measurement method and system for the thickness of the bearing lubricating film.
The technical scheme adopted by the invention for solving the technical problems is as follows:
according to one aspect of the invention, the ultrasonic measurement method for the thickness of the lubricating film of the bearing comprises the following steps:
acquiring an initial reference signal by using an ultrasonic probe;
secondly, acquiring an ultrasonic reflection pulse signal of an oil film layer under the operation of a bearing;
thirdly, performing fast Fourier transform on the reference signal acquired in the first step and the reflected pulse signal acquired in the second step respectively to obtain a reflection coefficient of the lubricating film layer;
step four, calculating a phase angle of a later reflected wave lagging a former reflected wave by using the reflection coefficient of the lubricating film layer obtained in the step three;
step five, obtaining the thickness of the lubricating film based on the phase angle of the later reflected wave which is calculated in the step four and lags behind the former reflected wave;
the average value of the lubricating film thickness in the effective bandwidth in the lubricating film thickness spectrum or the film thickness value corresponding to the optimal frequency point in the effective bandwidth (generally, the value corresponding to the reference signal peak frequency point) is used as the final lubricating film thickness.
Based on another aspect of the invention, a system for ultrasonically measuring the thickness of a bearing lubricating film comprises an ultrasonic pulse generation console, an ultrasonic pulse generation receiver, an ultrasonic probe, a high-speed acquisition device and a data processing unit, wherein:
the ultrasonic pulse generation console is used for controlling the ultrasonic pulse generation receiver to send out ultrasonic excitation and transmitting the ultrasonic excitation to the ultrasonic probe;
the ultrasonic probe is used for sending out ultrasonic pulses and receiving the ultrasonic pulses reflected back through the lubricating film; and transmitting the received ultrasonic pulses to an ultrasonic pulse generating receiver;
the ultrasonic pulse generating receiver transmits the received ultrasonic pulse to the high-speed acquisition device, and the ultrasonic pulse is transmitted to the data processing unit through the high-speed acquisition device and finally displayed.
The invention has the beneficial effects that: the invention provides an ultrasonic measurement method and system for the thickness of a bearing lubricating film, the method and the system are used for solving and obtaining the thickness of the oil film by establishing a quantitative relation between a hysteresis phase angle and a reflection coefficient obtained by measurement and utilizing a linear relation between the hysteresis phase angle and the thickness of the oil film, the method is used for converting the reflection coefficient obtained by measurement into the hysteresis phase angle, the measurement range of the thickness of the oil film of a single probe is greatly improved relative to a spring model, the continuous and accurate measurement of the thickness of the oil film from 0 to tens of microns can still be realized under a high-frequency probe, and the method can be combined with a resonance model to realize the measurement of the thickness. In addition, the method for calculating the film thickness is a direct calculation method, complex numerical iteration solution is not needed, and real-time online measurement of the dynamic film thickness is facilitated.
Detailed Description
The first embodiment is as follows: the ultrasonic measurement method for the thickness of the lubricating film of the bearing is realized by the following steps:
acquiring an initial reference signal by using an ultrasonic probe;
step two, when the bearing runs, acquiring an ultrasonic reflection pulse signal of the lubricating oil film layer;
thirdly, performing fast Fourier transform on the reference signal acquired in the first step and the reflected pulse signal acquired in the second step respectively to obtain a reflection coefficient of the lubricating film layer;
step four, calculating a phase angle of a later reflected wave lagging a former reflected wave by using the reflection coefficient of the lubricating film layer obtained in the step three;
step five, obtaining the thickness of the lubricating film based on the phase angle of the later reflected wave which is calculated in the step four and lags behind the former reflected wave;
and taking the average value of the thickness of the lubricating film in the effective bandwidth (the reference signal amplitude is attenuated to a bandwidth range corresponding to-6 dB) in the lubricating film thickness frequency spectrum or the film thickness value corresponding to the optimal frequency point in the effective bandwidth (generally, the value corresponding to the peak frequency point of the reference signal) as the final lubricating film thickness.
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: the specific process of the step one is as follows:
and under the condition that the bearing has no lubricating film or the thickness of the lubricating film is more than 300 mu m, acquiring the reflected pulse wave of the reference interface by using the ultrasonic probe, and taking the acquired reflected pulse wave as an initial reference signal.
The third concrete implementation mode: the second embodiment is different from the first embodiment in that: the specific process of the third step is as follows:
carrying out fast Fourier transform on the oil film layer reflection pulse signal to obtain a Fourier transform value AmPerforming fast Fourier transform on the reference signal to obtain a Fourier transform value Aref(ii) a Then obtaining the reflection coefficient of the oil film layer based on the following formula;
wherein: r is the reflection coefficient of the lubricating film layer, RrefIs a reference reflection coefficient.
The fourth concrete implementation mode: the third difference between the present embodiment and the specific embodiment is that: the specific process of the step four is as follows:
wherein: in is a natural logarithmic function, im (R) is the imaginary part of R,
representing the phase angle at which the latter reflected wave lags behind the former reflected wave, and r representing the reflection coefficient of the ultrasonic pulse incident on the steel from the lubrication film through the lubrication film-steel interface.
The fifth concrete implementation mode: the fourth difference between this embodiment and the specific embodiment is that: in the fifth step, the thickness of the lubricating film is obtained based on the phase angle of the latter reflected wave lagging the former reflected wave calculated in the fourth step, and the specific process is as follows:
wherein h represents the thickness of the lubricating film, f represents the frequency of the ultrasonic wave, and c is the transmission speed of the ultrasonic wave in the lubricating film.
The thickness of the film corresponds to each ultrasonic frequency, so that the thickness spectrum of the lubricating film can be obtained. Ideally, when the film thickness is uniform, the film thickness corresponding to each ultrasonic frequency is equal, however, the film thickness corresponding to different frequencies has a slight error due to the influence of noise and the like during measurement, and in order to obtain a film thickness measurement value with higher accuracy, the average value of the film thickness of the lubricating film within an effective bandwidth (a bandwidth range corresponding to attenuation of a reference signal amplitude of-6 dB) in the lubricating film thickness spectrum or the film thickness value corresponding to an optimal frequency point within the effective bandwidth (generally, a value corresponding to a reference signal peak frequency point) is generally used as the final lubricating film thickness.
The sixth specific implementation mode: this embodiment will be described with reference to fig. 1. The ultrasonic measurement system for the thickness of the lubricating film of the bearing in the embodiment comprises an ultrasonic pulse generation console, an ultrasonic pulse generation receiver, an ultrasonic probe, a high-speed acquisition device and a data processing unit, wherein:
the ultrasonic pulse generation console is used for controlling the ultrasonic pulse generation receiver to send out ultrasonic excitation and transmitting the ultrasonic excitation to the ultrasonic probe;
the ultrasonic probe is used for sending out ultrasonic pulses and receiving the ultrasonic pulses reflected back through the lubricating film; and transmitting the received ultrasonic pulses to an ultrasonic pulse generating receiver;
the ultrasonic pulse generating receiver transmits the received ultrasonic pulse to the high-speed acquisition device, and the ultrasonic pulse is transmitted to the data processing unit through the high-speed acquisition device and finally displayed.
In the present embodiment, the ultrasonic probe is a piezoelectric element as a member for generating an ultrasonic pulse and receiving a reflected ultrasonic pulse.
The principle of the novel ultrasonic measurement method for the thickness of the thin-layer lubricating film is as follows:
as shown in fig. 2a), when an ultrasonic pulse is incident on the steel oil interface, multiple reflection and transmission occur in the oil film layer, and the latter reflected wave lags behind the former reflected wave by a phase angle Δ β, as shown in fig. 2b), the magnitude of the phase angle depends on the thickness h of the oil film layer and the sound velocity c thereof, and the quantitative relationship can be expressed as:
Δβ=2πf(2h/c) (1)
in the formula: f represents the frequency of the ultrasonic wave.
Assuming the incident wave is:
Pi=Aexp(iωt) (2)
according to the virtual source method, each reflected wave is:
in the formula r
a-b、t
a-bRepresenting the reflection coefficient and transmission coefficient of ultrasonic waves incident to the medium b from the medium a through the interface a-b, t
b-aRepresenting the transmission coefficient, r, of an ultrasonic wave incident on the medium a from the medium b through the a-b interface
b-cRepresenting the reflection coefficient of the ultrasonic wave incident to the medium c from the medium b through the interface b-c.
n represents the order of reflection, z
aAnd z
bAnd z
cRepresenting the acoustic impedances of the media a, b, c, respectively, which is the product of the acoustic speed c and the density p of the medium, i.e. z
E=ρ
Ec
EAnd E may be a, b or c.
When the oil film layer is very thin, the reflected waves are superposed to form an indistinguishable superposed reflected wave, and the superposed reflected wave obtained by superposing the reflected waves is as follows:
the reflection coefficient can be expressed as:
due to rb-crb-a< 1 and n → ∞, then R can be simplified to:
in general, Δ β < 2 π, and thus the lag phase angle, can be expressed as
When the media on both sides of the oil film layer are the same material, z is the samea=zcAnd then-ra-b=rb-c=rb-aR, the above formula is further simplified:
in the above formula, im (R) represents the imaginary part of the reflection coefficient R.
In general, incident waves cannot be directly measured, so in practice, a reference wave is often used to replace the incident wave, and the actual measurement is as follows:
comparing the formula (8) with the formula (1), it can be easily found that when Delta beta is more than or equal to 0 and less than 2 pi,
to oneIn general, the film thickness to be measured is in this interval. And further:
fig. 3 is a schematic diagram of a typical ultrasonic measurement.
1) An initial reference signal is acquired.
When no lubricating oil exists between the two steel plates, the reference signal is obtained by using the ultrasonic probe and is stored in the program variable. When lubricating oil exists between the two steel plates, an ultrasonic probe is utilized to obtain the ultrasonic pulse reflected wave of the oil film layer. Fig. 4 shows a typical reference signal and an oil film layer reflection signal obtained.
2) And then carrying out fast Fourier transform on the reference signal and the oil film layer reflected wave signal to obtain an amplitude spectrum and a phase spectrum thereof, as shown in fig. 5a) and 5 b).
3) Then, the oil film layer reflection coefficient spectrum is obtained according to equation (9), as shown in fig. 6a) and 6 b).
4) The phase and amplitude spectra of the reflection coefficients are combined to obtain a lag phase angle spectrum according to equation (8), as shown in fig. 7.
5) From the obtained hysteresis phase spectrum, a film thickness spectrum was obtained according to equation (10), as shown in fig. 8.
6) Then the calculated average value of the film thickness within the attenuation-6 dB bandwidth (within the current-6 dB bandwidth, 7-13.7 MHz) is obtained, and the finally obtained film thickness is about 0.89 mu m.
Detailed description of the invention
As shown in FIG. 9, the effectiveness of the measurement method of the present invention is demonstrated by a steel-oil-steel oil film thickness ultrasonic measurement test bench. In the figure, 1 is a micro-displacement mobile platform, 2 is an oil tank, 3 is oil, 4 is a steel sheet III, 5 is an iron cover with a water tank, 6 is a steel sheet II, 7 is a steel sheet I, 8 is an ultrasonic probe, and 9 is water. 3 steel sheets are bonded together to form a wedge-shaped gap so as to form an oil film thickness of less than 70 microns, wherein the oil film thickness of the wedge-shaped gap is calibrated. The ultrasonic probe is fixed in position, and the oil tank is moved through the micro-displacement moving platform, so that the thickness of an oil film at the position measured by the ultrasonic probe is changed.
The measured results are shown in fig. 10 and 11. For an ultrasonic probe with the center frequency of 10MHz, the data measured by a spring model and a lagging phase model of the invention are basically consistent with the set film thickness within 1-11 μm, the data measured by the spring model and the set film thickness begin to deviate, and the deviation degree is larger when the film thickness is larger. The lag phase model is well matched with the set film thickness; the measuring range can be extended to the resonance model, the measuring blind area between the spring model and the resonance model when a single probe is used for measuring is overcome, and the advantages of the method are shown.
The above-described calculation examples of the present invention are merely to explain the calculation model and the calculation flow of the present invention in detail, and are not intended to limit the embodiments of the present invention. It will be apparent to those skilled in the art that other variations and modifications of the present invention can be made based on the above description, and it is not intended to be exhaustive or to limit the invention to the precise form disclosed, and all such modifications and variations are possible and contemplated as falling within the scope of the invention.