CN117629024A - Method and device for detecting thickness of air film of porous medium air bearing in real time - Google Patents
Method and device for detecting thickness of air film of porous medium air bearing in real time Download PDFInfo
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Abstract
The invention relates to the technical field of air bearing, in particular to a method for detecting the thickness of an air film of a porous medium air bearing in real time, wherein the porous medium air bearing is provided with an air film, an air inlet channel, a first detection through hole for communicating the air inlet channel and a second detection through hole for communicating the air film, and pressure sensors are arranged in the first detection through hole and the second detection through hole; the method comprises the following steps: constructing a component judgment model based on the porous medium air bearing; modeling and analyzing the porous medium air bearing by using a flow numerical simulation method to obtain radial position pressure models with different air film thicknesses; extracting the pressure value of the second detection through hole based on radial position pressure models under different air film thicknesses to obtain a judgment model; acquiring signals of a plurality of pressure sensors and performing signal preprocessing to obtain processed signals; and inputting the preprocessed signals into a judgment model to judge, so as to obtain the thickness of the air film.
Description
Technical Field
The invention relates to the technical field of air bearing, in particular to a method and a device for detecting the thickness of an air film of a porous medium air bearing in real time.
Background
With the development of chips, the process of high-end chips is continuously shrinking, which puts higher and higher precision demands on the processing and detecting equipment of the chips. Meanwhile, enterprises need to improve the productivity and the efficiency of chips, the processing and detecting equipment of the chips are also required to have higher speed and precision, the air bearing and an air bearing moving table formed by the air bearing have the advantages of high precision, good stability, long service life, small friction and the like, and can well meet various requirements of the semiconductor industry, such as a high-precision high-speed electronic component chip mounter, a high-precision high-speed wafer laser dicing machine, a negative pressure preloaded high-speed Gao Jingjing round table and the like, and the air bearing is essentially a moving table air bearing rail supporting mode, but has irreplaceable functions in the semiconductor industry due to the advantages of low gas viscosity, cleanliness, non-contact and the like.
An air bearing is a non-contact bearing, and a micron-sized air film is formed by high-pressure air, and has certain bearing capacity and rigidity. Because the thickness of the air film is very small, the situation that the thickness of the air film collapses frequently occurs in practical engineering application, namely the contact of the opposite air bearing surfaces of the bearing causes the gradual failure of the air bearing. In order to solve the problem, firstly, the change condition of the thickness of the air outlet film is detected in real time by a certain means, and in the real-time detection method, the current scheme generally detects the change of the thickness of the air film by arranging a displacement sensor outside the air film.
Externally disposed displacement sensors generally include non-contact laser sensors, non-contact capacitance/inductance sensors, contact displacement sensors, and the like. On the premise of realizing micron-scale precision, the three sensors need a large space to be mechanically fixed, and secondly, the laser sensor and the capacitance sensor have requirements on materials of a detection surface and the like, which definitely greatly reduces the universality of a detection scheme, the contact sensor needs contact measurement, and the air bearing generally moves, so that a probe of the contact displacement sensor is damaged. Therefore, the detection method by the displacement sensor is not beneficial to the general and compact online detection of the air bearing.
In summary, on the premise of micron-scale precision application, research on a small, flexible and universal detection device and method has important significance.
Disclosure of Invention
The invention aims to provide a method and a device for detecting the thickness of a gas film of a porous medium air bearing in real time, so as to solve the problem that the conventional method for detecting the thickness of the gas film in real time cannot realize universal detection under micron-scale precision.
In order to solve the technical problems, the first technical scheme adopted by the invention is to provide a method for detecting the thickness of an air film of a porous medium air bearing in real time, which comprises the following steps:
constructing a component judgment model based on the porous medium air bearing;
modeling and analyzing the porous medium air bearing by using a flow numerical simulation method to obtain radial position pressure models with different air film thicknesses; extracting the pressure value of the second detection through hole based on the radial position pressure models under different air film thicknesses to obtain the judgment model;
acquiring signals of a plurality of pressure sensors and performing signal preprocessing to obtain processed signals;
and inputting the preprocessed signals into the judgment model to judge, so as to obtain the thickness of the air film.
In some embodiments of the first technical solution, the judgment model formula is as follows: pressure=a·x 3 +b.x 2 +c.x+d, where pressure is the pressure value, x is the film thickness, a, b, c, d is the coefficient to be determined, where the coefficient to be determined can be determined by the least squares method.
In some embodiments of the first technical solution, the method for determining the coefficient to be determined includes the following steps: constructing a gas film thickness-pressure data set based on data points of the judgment model, and assuming that the gas film thickness-pressure data set obeys a polynomial; constructing a fitting curve based on polynomials, and obtaining the square error of the fitting curve and the air film thickness-pressure data set; taking the minimum value of the square error as the basis of the optimal approximation function coefficient, enabling the partial derivative of the square error to the approximation function coefficient to be zero, and obtaining an expression of the optimal approximation function coefficient; substituting the number of data points into the expression of the best approximation function coefficient to obtain the coefficient to be determined of a, b, c, d.
In some embodiments of the first technical solution, the data set is represented as follows: p (P) i (x i ，y i ) (i=1, 2,3,., m), where x i For film thickness at different data points, y i Refers to the corresponding pressure values at the different data points.
In some embodiments of the first aspect, the polynomial equation is expressed as follows: in the above, x i For film thickness, θ at different data points n To approximate the function coefficients.
In some embodiments of the first aspect, theThe square error is expressed as follows: in the above, x i For film thickness at different data points, y i Refers to the corresponding pressure values at the different data points.
In some embodiments of the first aspect, the step of acquiring signals of the plurality of pressure sensors and performing signal preprocessing to obtain processed signals specifically includes: extracting a pressure detection signal of a pressure sensor arranged in the first detection through hole and extracting a pressure detection signal of a pressure sensor arranged in the second detection through hole; comparing the value of the pressure detection signal of the pressure sensor of the first detection through hole with a preset value; when the value of the pressure detection signal of the first detection through hole is the same as a preset value, performing linear transformation on the pressure detection signal of the pressure sensor arranged in the second detection through hole to obtain a second air pressure value signal, and processing the second air pressure value signal to obtain a processed pressure value; and when the value of the pressure detection signal of the first detection through hole is not the same as the preset value, continuing to extract the pressure detection signal of the pressure sensor of the first detection through hole and extracting the pressure detection signal of the pressure sensor arranged in the second detection through hole.
The second technical scheme adopted by the invention is to provide a device for detecting the thickness of an air film of a porous medium air bearing in real time, which comprises a porous medium restrictor, an air bearing base and a pressure sensor; the air bearing base is arranged on the porous medium restrictor and sleeved outside the porous medium restrictor; the air bearing base is provided with a first detection through hole, an air inlet and an air inlet channel, the first detection through hole and the air inlet channel are communicated with the air inlet channel, the air inlet channel is covered by the surface of the porous medium restrictor, and the air film thickness real-time detection device of the porous medium air bearing forms an air film at the bottom of the porous medium restrictor; the porous medium restrictor is provided with a plurality of second detection through holes, and the second detection through holes extend from the porous medium restrictor to the air bearing base; the first detection through holes and the second detection through holes are internally provided with pressure sensors, the detection parts of the pressure sensors face the air film, and the pressure sensors are used for detecting the pressure values of the air film and the air inlet channel and transmitting the pressure values to the air film thickness real-time detection device so as to detect the thickness of the air film.
In some embodiments of the second aspect, the inlet channel comprises a plurality of annular channel bodies; the annular channel bodies are coaxially arranged, and the annular channel bodies are communicated with the air inlet.
In some embodiments of the second aspect, the plurality of second detection through holes are uniformly circumferentially arranged around the axis of the annular channel body.
The beneficial effects of the invention are as follows:
according to the air film thickness real-time detection method provided by the first scheme, as the air bearing is provided with the second detection through hole for detecting the air film pressure value and the first detection through hole for detecting the air inlet channel pressure value, and the pressure sensors are arranged in the first detection through hole and the second detection through hole, the pressure sensors can detect the pressure values of different positions of the air film, and according to the knowledge of hydrodynamics, a certain relation exists between the air flow pressure value at a certain position and the clearance value at the position to form a judgment model, so that when the pressure sensors measure the real-time pressure values at a plurality of positions, the real-time air film thickness can be obtained through the judgment model, and the air film thickness can be detected in real time.
In addition, the invention utilizes the inherent airflow information of the air bearing, does not need to adopt a large space for mechanical fixation, and can realize the detection of the airflow pressure by utilizing the pressure sensor, so that the detection of the thickness of the air film can be carried out no matter how the guide rail is made of materials, and the invention has the advantage of good universality.
The air film thickness real-time detection device that the second scheme provided, because pressure sensor is small in size, pressure sensor distributes and locates in first detection through-hole and the second detection through-hole, when gas lets in to the intake duct from the air inlet to after wearing out porous medium restrictor and forming the air film, pressure sensor can directly detect the pressure in the through-hole, in order to obtain air film thickness, this scheme can be with in the embedded air bearing mechanical structure body of pressure sensor through reasonable design promptly, in order to realize the real-time detection of air film thickness, have the advantage of stronger compact structure.
Drawings
In order to more clearly illustrate the technical solutions of the present invention, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic view of the overall structure provided by the preferred embodiment of the present invention;
FIG. 2 is a schematic view of a partial (excluding detection processing means) structure provided in the preferred embodiment of the present invention;
FIG. 3 is a top view of a partial (excluding detection processing means) structure provided in a preferred embodiment of the present invention;
FIG. 4 is a cross-sectional view taken along the direction A-A in FIG. 3 provided by a preferred embodiment of the present invention;
FIG. 5 is a cross-sectional view taken in direction B-B of FIG. 3, provided by a preferred embodiment of the present invention;
FIG. 6 is a schematic view of an air bearing base structure according to a preferred embodiment of the present invention;
FIG. 7 is a top view of an air bearing base structure provided in a preferred embodiment of the present invention;
FIG. 8 is a schematic view of a porous media restrictor provided in a preferred embodiment of the present invention;
FIG. 9 is a schematic diagram of a numerical simulation grid model of a porous media restrictor provided by a preferred embodiment of the present invention;
FIG. 10 is a pressure cloud of a flow field of a porous media restrictor provided in a preferred embodiment of the present invention at a gas film thickness of 12 microns;
FIG. 11 is a graph of radial position pressure models for a second sensing through hole provided in a preferred embodiment of the present invention at different gas film thicknesses;
fig. 12 is a graph of film thickness and second sensed via pressure (judgment model) provided by a preferred embodiment of the present invention.
The reference numerals are as follows:
1. an air-float guide rail;
2. a porous media restrictor; 20. a second detection through hole;
3. an air bearing base; 30. a first detection through hole; 31. an air inlet; 32. an air inlet channel; 320. an annular channel body; 33. an air outlet; 34. a placement groove;
4. a pressure sensor;
5. a detection processing section; 50. a PCB circuit board; 51. a microprocessor; 52. a memory chip; 53. an LED lamp processing circuit;
6. and (5) an air film.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.
An air bearing is a non-contact bearing, and a micron-sized air film is formed by high-pressure air, and has certain bearing capacity and rigidity. Because the thickness of the air film is very small, the situation that the thickness of the air film collapses frequently occurs in practical engineering application, namely the contact of the opposite air bearing surfaces of the bearing leads to the gradual failure of the air bearing, in order to solve the problem, the change situation of the thickness of the air film is detected in real time through a certain means, and the current scheme on the real-time detection method generally detects the change of the thickness of the air film by arranging a displacement sensor.
In the prior art, a noncontact laser sensor, a noncontact capacitance/inductance sensor, a contact displacement sensor and the like are generally adopted for detecting the change of the thickness of the air film by arranging the displacement sensor, and the problem of reduced generality is caused by adopting the sensor, namely, the displacement sensor can directly detect the change of the thickness of the air film by detecting the change of the displacement, but on the premise of realizing micron-scale precision, the three sensors all need a large space for mechanical fixation, and the aim of using the air film with good universality cannot be realized.
In addition, the special problems of the displacement sensors of different types exist, such as the laser sensor and the capacitance sensor have requirements on materials of a detection surface, such as a test bench (CN 202222753583.8) for measuring the thickness of a gas film of a radial air bearing, which definitely greatly reduces the universality of a detection scheme; for example, the contact sensor needs to perform contact measurement, and the air bearing generally moves, which damages the probe of the contact displacement sensor, and frequent corresponding replacement is also unfavorable for the general detection of the air films of different air bearings.
In order to solve the above problems, the present solution provides a device for detecting the thickness of an air film of a porous medium air bearing in real time, referring to fig. 1 to 8, which includes an air-floating guide rail 1, a porous medium restrictor 2, an air-floating bearing base 3, a pressure sensor 4 and a detection processing component 5; from the bottom to the top of air film 6 thickness real-time detection device, air supporting guide rail 1, porous medium restrictor 2, air supporting bearing base 3, pressure sensor 4 and detection processing part 5 are installed in proper order, and the core lies in, utilize the inherent air current characteristic of air supporting bearing to carry out air film 6 thickness detection, convert the atmospheric pressure characteristic of air current into displacement value, so just realized the commonality of on-line measuring, again because the device that detects the air current is extremely small and exquisite, can embed in the air supporting bearing machinery body in a flexible way, just so realized compactedness.
In the embodiment of the application, referring to fig. 1,2, 4 and 5, the porous medium restrictor 2 is installed on the air-float guide rail 1, and the air-float guide rail 1 is based on the dynamic-static pressure effect of gas, so as to realize smooth movement without friction and vibration, and has the characteristics of high motion precision, cleanliness, no pollution and the like, and can obtain higher guide precision with lower manufacturing precision due to the error homogenization effect, and the air-float guide rail 1 is generally used in measuring instruments and precision machines by forming a closed-loop system with servo drive.
In the embodiment of the present application, referring to fig. 3 to 5, regarding the porous medium restrictor 2, the porous medium restrictor 2 is mounted on the air-floating guide rail 1, the top of the porous medium restrictor 2 is further coaxially mounted with the air-floating bearing base 3, the porous medium restrictor 2 and the air-floating bearing base 3 are connected by interference fit and adhesion, the bottom of the porous medium restrictor 2 extends out of the air-floating bearing base 3 to form the air-flow outlet 33, after the arrangement, the porous medium restrictor 2 can be fixed with the air-floating bearing base 3, and after the air flows from the air-floating bearing base 3 to the porous medium restrictor 2, the air film 6 can be formed between the porous medium restrictor 2 and the air-floating guide rail 1.
It should be noted that the length of the bottom of the porous medium restrictor 2 extending beyond the air bearing base 3 is about 1 mm.
In the embodiment of the application, please refer to fig. 4 to 8, four second detection through holes 20 are provided on the porous medium restrictor 2, the four second detection through holes 20 extend from the porous medium restrictor 2 to the air bearing base 3, pressure sensors 4 are provided in the four second detection through holes 20, the pressure sensors 4 are arranged towards the air film 6, after the arrangement mode is adopted, the pressure sensors 4 can directly detect air flow pressure information from the air film 6 and transmit the air flow pressure information to the detection processing component 5 to judge the thickness of the air film 6.
In some embodiments of the present application, referring to fig. 8, four second detection through holes 20 are uniformly circumferentially arranged around the central axis of the porous medium restrictor 2, and after the arrangement manner is adopted, the four second detection through holes 20 can detect and determine the thickness of different positions of the air film 6 in real time.
In some possible embodiments of the present application, the porous medium restrictor 2 is provided with a plurality of second detection through holes 20, that is, the number of the second detection through holes 20 is more than four, and the plurality of second detection through holes 20 may be uniformly arranged around the circumference of the air film 6, so long as the second detection through holes are not affected by each other, and a person skilled in the art can design a reasonable number of the second detection through holes 20 according to the actual requirement of the person.
It should be noted that the porous medium restrictor 2 is mainly composed of a porous medium, and the porous medium may be selected from the group including, but not limited to, porous graphite, porous ceramic, porous silicon carbide and porous steel, which are suitable for the porous medium commonly used in the air bearing field, and may be selected by those skilled in the art.
Referring to fig. 4 to 8, referring to the air bearing base 3, the bottom of the air bearing base 3 is coaxially provided with the porous medium restrictor 2, the air bearing base 3 is sleeved outside the porous medium restrictor 2, the top of the air bearing base 3 is provided with the pressure sensor 4 and the detection processing component 5, the air bearing base 3 is provided with the first detection through hole 30, the air inlet 31 and the air inlet 32, the first detection through hole 30 and the air inlet 31 are both communicated with the air inlet 32, the air inlet 32 is covered by the surface of the porous medium restrictor 2, the pressure sensor 4 is arranged in the first detection through hole 30, the air film thickness real-time detection device of the porous medium air bearing forms the air film 6 at the bottom of the porous medium restrictor 2, after the arrangement mode is adopted, when air enters from the air inlet 31, the air flows to the air inlet 32, the air of the air inlet 32 passes through the porous medium restrictor 2, and the air film 6 is formed between the porous medium restrictor 2 and the air floating guide rail 1.
It should be noted that the first detection through hole 30 is used for detecting the air flow pressure of the air inlet channel 32, the second detection through hole 20 extending from the porous medium restrictor 2 to the air bearing base 3 is used for detecting the air flow pressure of the air film 6, and when the pressure sensor 4 detects the information of the two, the signal is output to the detection processing part 5 for detection.
In some embodiments of the present application, referring to fig. 6, a porous medium placing groove 34 is provided at the bottom of the air bearing base 3, a porous medium restrictor 2 is placed in the porous medium placing groove 34, and the porous medium restrictor 2 and the porous medium placing groove 34 are connected by interference fit gluing; and the top of the porous medium placing groove 34 is provided with an air inlet channel 32, the air inlet channel 32 is communicated with the air inlet 31, and after the arrangement mode is adopted, the porous medium restrictor 2 can be fixed in the air bearing base 3.
In some embodiments of the present application, referring to fig. 6 and 7, the air inlet 32 includes two annular channel bodies 320, the two annular channel bodies 320 are coaxially arranged with the air bearing base 3, the two annular channel bodies 320 are communicated with the air inlet 31 through a connecting pipe, and after the arrangement, the annular channel bodies 320 can transmit air for the porous medium restrictor 2 to form the air film 6.
With reference to fig. 1, referring to the above-mentioned pressure sensor 4, the first detecting through hole 30 and the plurality of second detecting through holes 20 are provided with the pressure sensor 4, the detecting parts of the plurality of pressure sensors 4 face the air film 6, the pressure sensor 4 is used for detecting the pressure values of the air film 6 and the air inlet channel 32 and transmitting the pressure values to the detecting processing part 5 to detect the thickness of the air film 6, after adopting this arrangement mode, the detection of the thickness of the air film 6 is performed by utilizing the air flow pressure characteristic of the air film itself, and no special detecting surface or fixing mechanism requiring a large space is needed as a displacement sensor is needed, so the scheme has universality no matter being applied under the micron precision or other precision.
It should be noted that the pressure sensor 4 is mounted on the air hole on the back of the base by screw threads for detecting the air pressure at a specific location.
In some embodiments of the present application, the pressure sensor 4 outputs an analog voltage of 0.2-2.7V, corresponding to a gas pressure of 0-500 Kpa.
Referring to fig. 1, referring to the above-mentioned detection processing unit 5, the detection processing unit 5 includes a PCB circuit board 50, a microprocessor 51, a memory chip 52, and an LED lamp processing circuit 53, where the PCB circuit board 50 is electrically connected to the microprocessor 51, the memory chip 52, the LED processing circuit, and the pressure sensor 4, after the arrangement is adopted, the output analog voltage of the pressure sensor 4 is read by the microprocessor 51 through an I2C communication protocol, the voltage information is converted into air pressure information through an algorithm inside the microprocessor 51, and the thickness of the air film 6 is predicted according to air pressure values at different positions determined according to a preset determination model inside the microprocessor 51.
In practical application, the air bearing is suspended at an initial height, the height is limited by a mechanical structure, and due to external and internal disturbance, the thickness of the air film 6 can slightly move, the PCB 50 detects the real pressure value of each pressure detection port in real time in the process, and transmits the value to a judgment model for judgment and comparison, namely the calibration curve of FIG. 12 is compared, so that the real-time value of the thickness of the air film 6 is obtained, and the real-time detection of the thickness of the air film 6 is realized.
From the foregoing, the present invention provides a device for detecting the thickness of an air film of a porous medium air bearing in real time, and hereinafter provides a method for detecting the thickness of an air film of a porous medium air bearing in real time, which comprises the following steps:
s1, constructing a component judgment model based on a porous medium air bearing;
it should be noted that the entire judgment model is embedded in the microprocessor 51.
S1.1, modeling and analyzing the porous medium air bearing by using a flow numerical simulation method to obtain radial position pressure models with different air film 6 thicknesses;
the pressure values of the four second detection through holes 20 under different thicknesses of the air film 6 are calculated through a flow numerical simulation method, a numerical simulation grid model is shown in fig. 9, the air pressure flowing out of the second detection through holes 20 is the pressure required to be detected by the pressure sensor 4 in the suspension process, the measured air flow pressure values of the air film 6 have a unique determined relation with the thickness of the air film 6, the simulation result of the finite volume method is shown in fig. 10, fig. 10 is a pressure cloud diagram of a flow field when the thickness of the air film 6 is 12 micrometers, it can be seen that the pressure of the second detection through holes 20 presents a certain characteristic, a pressure curve is drawn along the diameter direction, and the numerical simulation pressure values of the second detection through holes 20 under different thicknesses of the air film 6 are different from the figure.
It should be noted that the method of flow numerical simulation carries out modeling analysis on the porous medium air bearing to obtain radial position pressure models with different air film thicknesses, and the numerical modeling analysis is based on a certain loop pressure value P, so that the obtained pressure value and air film thickness calibration model is also suitable for the condition that the loop pressure value is P.
S1.2, extracting a pressure value of the second detection through hole 20 based on radial position pressure models under different air film 6 thicknesses to obtain a judgment model;
the pressure value of the second detection through hole 20 is extracted, a curve of the thickness of the air film 6 and the pressure of the second detection through hole 20 is drawn as shown in fig. 12, it can be seen from the figure that the thickness of the air film 6 and the pressure value of the second detection through hole 20 are in one-to-one correspondence, a certain functional relationship is formed, the relationship can be fitted by using a cubic polynomial, and the functional expression is as follows:
pressure＝a·x 3 +b·x 2 +c·x+d
in the above formula, pressure is a pressure value, x is the thickness of the air film 6, a, b, c, d is a coefficient to be determined, wherein the coefficient to be determined can be determined by a least square method, and the specific determining method is as follows:
s1.2.1, constructing a thickness-pressure data set of the air film 6 based on data points of a judgment model, and assuming that the thickness-pressure data set of the air film 6 obeys a polynomial;
wherein the numerical simulation determines that there are at least four data points in FIG. 12, which constitute data set P i (x i ，y i ) (i=1, 2,3,., m), where x i For the thickness of the air film 6 at different data points, y i Refers to the corresponding pressure values at the different data points.
Suppose that each data point within P is assumed to obey P i (x i ，y i ) (i=1, 2,3,) m polynomial f (x i ) M is the number of actual data points, polynomial f (x i ) The expression is as follows:
in the above, x i For the thickness of the air film 6 at different data points, theta n To approximate the function coefficients.
S1.2.2, constructing a fitting curve based on a polynomial, and obtaining the square error of the fitting curve and the thickness-pressure data set of the air film 6;
wherein, setting fitting values of the fitting curve at each point and a data set P i (x i ，y i ) Error azimuth S of (2):
in the above, x i For the thickness of the air film 6 at different data points, y i Refers to the corresponding pressure values at the different data points.
S1.2.3, taking the minimum value of the square of the error as the basis of the optimal approximation function coefficient, and enabling the partial derivative of the square of the error to the approximation function coefficient to be zero so as to obtain an expression of the optimal approximation function coefficient;
wherein, according to the least square method, the optimal approximation function coefficient theta j The sum of squares of the errors S should be minimized, in which case the S function is specific to the function coefficient θ j The partial derivatives of (2) should satisfy:
the above arrangement yields the following set of equations:
the above equation set is converted into a matrix form, resulting in the following expression:
then there are:
Xθ＝Y
thereby obtaining the following steps:
θ＝X -1 Y
s1.2.4, substituting the number of data points into the expression of the best approximation function coefficient to obtain a, b, c, d coefficient to be determined.
Wherein, let the n =3, then there is:
d＝θ 0 、c＝θ 1 、b＝θ 2 、a＝θ 3
thus, four coefficients to be determined of a, b, c, d are finally obtained.
S2, signals of a plurality of pressure sensors 4 are obtained and are subjected to signal preprocessing, so that processed signals are obtained;
when external high-pressure gas enters a series of annular channel bodies 320 through the gas inlet 31, then the high-pressure gas enters the porous medium restrictor 2, the pressure of the high-pressure gas gradually decreases under the effect of the obstruction of pores in the porous medium restrictor 2 to gas flow, then the high-pressure gas enters between the porous medium and the guide rail and then flows out from the periphery of the porous medium, the process enables the gas in the gas film 6 to have a certain pressure, the moving part can be suspended, friction-free suspension support is realized, and therefore, the gas flows out from the first detection through hole 30 and the second detection through hole 20, and the pressure sensor 4 can detect the gas pressure information of the gas flow.
S2.1, extracting a pressure detection signal of the pressure sensor 4 arranged in the first detection through hole 30 and extracting a pressure detection signal of the pressure sensor 4 arranged in the second detection through hole 20;
s2.2, comparing the value of a pressure detection signal of the pressure sensor of the first detection through hole with a preset value;
when the value of the pressure detection signal of the first detection through hole 30 is the same as the preset value, performing linear transformation on the pressure detection signal of the pressure sensor arranged on the second detection through hole 20 to obtain a second detection through hole 20 air pressure value signal, and processing the second air pressure value signal to obtain a processed pressure value;
when the value of the pressure detection signal is not the same as the preset value, the extraction of the pressure detection signal of the pressure sensor of the first detection through hole 30 and the extraction of the pressure detection signal of the pressure sensor provided to the second detection through hole are continued.
The Voltage value of the pressure sensor 4 of the first detection through hole 30 is recorded as a voltage_inlet, and then the Voltage value is read by the microprocessor 51, the microprocessor 51 converts the Voltage value into an air pressure value according to linear conversion, whether the loop pressure in the first detection through hole 30 is required to be detected to be a preset value P or not, if the Voltage value of the pressure sensor 4 of the first detection through hole 30 is equal to the preset value P, the pressure detection signal of the pressure sensor of the second detection through hole 20 is subjected to linear conversion, and the processed Voltage value is obtained; if the voltage value of the pressure sensor 4 of the first detection through hole 30 is not equal to the preset value P, the detection is continued.
When the air pressure value in the first detection through hole is the same as the preset value P, the Voltage value of the pressure sensor 4 of the second detection through hole 20 is recorded as voltage_gap_x, and then is read in by the microprocessor 51, and the microprocessor 51 converts the Voltage value into the air pressure value according to linear transformation: pressure=k×v, where Pressure is a Pressure value, k is a linear conversion coefficient of the Pressure sensor 4, and v is a voltage value output by the Pressure sensor 4.
And S3, inputting the preprocessed signals into a judging model in the microprocessor 51 for judgment, and obtaining the thickness of the air film 6.
In practical application, the air bearing is suspended at an initial height, the height is limited by a mechanical structure, and due to external and internal disturbance, micro-motion can occur in the thickness of the air film 6, when the sensor detects the air flow pressure, the air flow pressure is input into a judging model of the microprocessor 51 to judge, and the thickness of the air film 6 at different detection through hole positions is judged in real time.
While the foregoing is directed to the preferred embodiments of the present invention, it will be appreciated by those skilled in the art that changes and modifications may be made without departing from the principles of the invention, such changes and modifications are also intended to be within the scope of the invention.
Claims (10)
1. The method for detecting the thickness of the air film of the porous medium air bearing in real time comprises the steps of enabling the porous medium air bearing to be provided with an air film, an air inlet channel, a first detection through hole used for communicating with the air inlet channel and a second detection through hole used for communicating with the air film, wherein pressure sensors are arranged in the first detection through hole and the second detection through hole;
the method is characterized by comprising the following steps of:
constructing a component judgment model based on the porous medium air bearing;
modeling and analyzing the porous medium air bearing by using a flow numerical simulation method to obtain radial position pressure models with different air film thicknesses;
extracting the pressure value of the second detection through hole based on the radial position pressure models under different air film thicknesses to obtain the judgment model;
acquiring signals of a plurality of pressure sensors and performing signal preprocessing to obtain processed signals;
and inputting the preprocessed signals into the judgment model to judge, so as to obtain the thickness of the air film.
2. The method for detecting the thickness of the air film of the porous medium air bearing in real time according to claim 1, wherein the judgment model formula is expressed as follows:
pressure＝a·x 3 +b·x 2 +c·x+d
in the above formula, pressure is a pressure value, x is a film thickness, a, b, c, d is a coefficient to be determined, wherein the coefficient to be determined can be determined by a least square method.
3. The method for detecting the thickness of the air film of the porous medium air bearing in real time according to claim 2, wherein the method for determining the coefficient to be determined comprises the following steps:
constructing a gas film thickness-pressure data set based on data points of the judgment model, and assuming that the gas film thickness-pressure data set obeys a polynomial;
constructing a fitting curve based on polynomials, and obtaining the square error of the fitting curve and the air film thickness-pressure data set;
taking the minimum value of the square error as the basis of the optimal approximation function coefficient, enabling the partial derivative of the square error to the approximation function coefficient to be zero, and obtaining an expression of the optimal approximation function coefficient;
substituting the number of data points into the expression of the best approximation function coefficient to obtain the coefficient to be determined of a, b, c, d.
4. The method for detecting the thickness of the air film of the porous medium air bearing in real time according to claim 3, wherein,
the dataset is represented as follows:
P i (x i ,y i )(i＝1,2,3,…,m)
in the above, x i For film thickness at different data points, y i Refers to the corresponding pressure values at the different data points.
5. The method for detecting the thickness of the air film of the porous medium air bearing in real time according to claim 3, wherein,
the polynomial formula is expressed as follows:
in the above, x i For film thickness, θ at different data points n To approximate the function coefficients.
6. The method for detecting the thickness of the air film of the porous medium air bearing in real time according to claim 3, wherein,
the square error is expressed as follows:
in the above, x i For film thickness at different data points, y i Refers to the corresponding pressure values at the different data points.
7. The method for detecting the thickness of the air film of the porous medium air bearing according to claim 1, wherein the step of acquiring signals of a plurality of pressure sensors and performing signal preprocessing to obtain processed signals specifically comprises the following steps:
extracting a pressure detection signal of a pressure sensor arranged in the first detection through hole and extracting a pressure detection signal of a pressure sensor arranged in the second detection through hole;
comparing the value of the pressure detection signal of the pressure sensor of the first detection through hole with a preset value;
when the value of the pressure detection signal is the same as a preset value, performing linear transformation on the pressure detection signal of the pressure sensor arranged in the second detection through hole to obtain a second air pressure value signal, and processing the second air pressure value signal to obtain a processed pressure value;
and when the value of the pressure detection signal is not the same as the preset value, continuing to extract the pressure detection signal of the pressure sensor of the first detection through hole and extracting the pressure detection signal of the pressure sensor arranged in the second detection through hole.
8. A device for detecting the thickness of a gas film of a porous medium air bearing in real time, which is characterized in that the method for detecting the thickness of the gas film of the porous medium air bearing in real time is applied to any one of claims 1 to 7;
the device comprises a porous medium restrictor, an air bearing base and a pressure sensor;
the air bearing base is arranged on the porous medium restrictor and sleeved outside the porous medium restrictor;
the air bearing base is provided with a first detection through hole, an air inlet and an air inlet channel, the first detection through hole and the air inlet channel are communicated with the air inlet channel, the air inlet channel is covered by the surface of the porous medium restrictor, and the air film thickness real-time detection device of the porous medium air bearing forms an air film at the bottom of the porous medium restrictor;
the porous medium restrictor is provided with a plurality of second detection through holes, and the second detection through holes extend from the porous medium restrictor to the air bearing base;
the first detection through holes and the second detection through holes are internally provided with pressure sensors, the detection parts of the pressure sensors face the air film, and the pressure sensors are used for detecting the pressure values of the air film and the air inlet channel and transmitting the pressure values to the air film thickness real-time detection device so as to detect the thickness of the air film.
9. The apparatus for detecting the thickness of a gas film according to claim 8, wherein,
the air inlet channel comprises a plurality of annular channel bodies;
the annular channel bodies are coaxially arranged, and the annular channel bodies are communicated with the air inlet.
10. The apparatus for detecting the thickness of a gas film according to claim 8, wherein,
the plurality of second detection through holes are uniformly circumferentially arranged around the axis of the annular channel body.
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