CN110657749B - Micro-distance measuring device, method and equipment based on imaging - Google Patents
Micro-distance measuring device, method and equipment based on imaging Download PDFInfo
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Abstract
The disclosure provides a micro-distance measuring device, method and equipment based on imaging, comprising an illuminating light source, an object to be measured, an imaging system and a CCD camera connected with a processor; the illumination light source sequentially comprises two optical fiber laser sources, a light beam displacement device, rotary ground glass and a collimating lens, light beams are emitted to an object to be detected through the rotary ground glass and then through the collimating lens, the imaging system is a 4f imaging system with a pupil placed at a frequency spectrum plane, the CCD camera is arranged at the position of an imaging plane of the imaging system and used for detecting the maximum light intensity value and the central light intensity value of the position of the imaging plane, and the processor obtains the size between two end points of the object to be detected according to the light beam wavelength when the ratio of the central light intensity value to the maximum light intensity value is minimum, the distance between the two light beams on the rotary ground glass and the focal length of the collimating lens; according to the method, the size of the object can be calculated only by carrying out imaging light intensity analysis on the object to be measured, the measurement range can reach the micron level, and the precision can reach four thousandths.
Description
Technical Field
The present disclosure relates to the field of macro measurement technologies, and in particular, to a macro measurement apparatus, method, and device based on imaging.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The microspur measurement is always one of the indispensable operations in laboratories, industrial manufacturing and even national defense construction. The existing macro measuring devices can be roughly classified into a conventional macro measuring device and a new macro measuring device. The traditional microspur measuring device such as a vernier caliper, a micrometer screw (micrometer), a micrometer and the like can reach the accuracy of one micrometer and millimeter at most so as to measure the dimension of one hundredth millimeter, and the device has the advantages of simple operation and low cost.
The inventor of the present disclosure finds that, when the measurement scale is further reduced and the precision requirement is further improved, the measurement requirement cannot be met by using the conventional device, and the measurement object is easily damaged due to artificial force application and other reasons during measurement, so that a large artificial error exists. The novel macro measuring device mostly utilizes an optical principle, such as an optical projector, a laser interferometer, an optical microscope and the like, and has higher measuring precision which can reach the micron and nanometer level, but the measuring devices need higher cost or more complex operation and algorithm.
Disclosure of Invention
In order to solve the defects of the prior art, the disclosure provides a micro-distance measuring device, a micro-distance measuring method and micro-distance measuring equipment based on imaging, the size of an object can be calculated by carrying out imaging light intensity analysis on the object to be measured, the measuring range can reach the micrometer level, and the error rate can reach four thousandths.
In order to achieve the purpose, the following technical scheme is adopted in the disclosure:
the present disclosure provides, in a first aspect, an imaging-based macro measurement apparatus.
A microspur measuring device based on imaging comprises an illumination light source, an object to be measured, an imaging system and a CCD camera connected with a processor;
the illumination light source sequentially comprises two optical fiber laser sources, a light beam displacement device, rotary ground glass and a collimating lens, wherein the light beam displacement device is used for adjusting the distance between light beams emitted by the two optical fiber laser sources on the rotary ground glass, and the light beams are emitted to an object to be measured through the collimating lens after passing through the rotary ground glass;
the imaging system is a 4f imaging system with a pupil placed on a frequency spectrum plane, the CCD camera is arranged at the position of an imaging plane of the imaging system and used for detecting the maximum light intensity value and the central light intensity value of the position of the imaging plane, and the processor obtains the size between two end points of the object to be detected according to the light beam wavelength when the ratio of the central light intensity value to the maximum light intensity value is minimum, the distance between two light beams on the rotating ground glass and the focal length of the collimating lens.
As some possible realization modes, the size between two end points of the object to be measured is at least 40 μm.
As some possible implementations, the distance between the rotating ground glass and the collimating lens is equal to the focal length of the collimating lens.
A second aspect of the present disclosure provides an imaging-based macro measurement method.
A microspur measuring method based on imaging utilizes the microspur measuring device of the present disclosure, and comprises the following steps:
obtaining a light intensity function at the imaging surface of the imaging system according to the cross spectral density function of the illumination light source, the transfer function of the object to be measured and the impulse response function of the imaging system, and obtaining a central light intensity function according to the light intensity function at the imaging surface of the imaging system;
the CCD camera stores the detected light intensity value in a gray value form, and the processor calculates the ratio of the central light intensity value to the maximum light intensity value according to the gray value;
the light beam displacement device is used for regulating and controlling the distance between the two light beams on the ground glass surface to enable the ratio of the central light intensity value to the maximum light intensity value to be minimum, and the size of the object to be measured is obtained according to the wavelength of the light beams, the distance between the two light beams on the rotating ground glass and the focal length of the collimating lens.
As some possible implementations, the cross-spectral density function of the illumination source is:
wherein, ω is0Is the beam waist of each beam, vxAbscissa, x, representing points on the frosted glass surface1And x2Abscissa representing point on illumination light source face, f1The focal length of the collimating lens, λ is the wavelength of the light beam, k is 2 π/λ is the wavenumber, C0Is a constant.
As some possible implementations, the transfer function of the object under test is represented as the addition of two dirac functions:
O(x)＝δ(x-d/2)+δ(x+d/2)
by way of further limitation, the impulse response function of the imaging system is:
wherein, J1As a first order Bessel function, pxIs the abscissa of the point at the imaging plane, f is the focal length of the thin lens in the 4f imaging system, and R is the radius of the pupil.
By way of further limitation, the light intensity function at the imaging plane of the imaging system is:
wherein the content of the first and second substances,
further, the central light intensity function is:
wherein the content of the first and second substances,
as some possible implementations, the calculation formula of the size of the object to be measured is:
d＝λf1/l
wherein d is the distance between two end points of the object to be measured, lambda is the wavelength of the light beam, and f1The distance l is the distance between the light beams emitted by the two fiber laser sources on the rotating ground glass, and is the focal length of the collimating lens.
A third aspect of the present disclosure provides a macro measurement apparatus comprising the imaging-based macro measurement device of the present disclosure.
Compared with the prior art, the beneficial effect of this disclosure is:
1. according to the content disclosed by the disclosure, the size of the object can be calculated by carrying out imaging light intensity analysis on the object to be measured, the measurement range can reach the micron level, and the precision can reach four thousandths.
2. The present disclosure reduces the resolution of the 4f imaging system by placing the pupil at the spectral plane of the imaging system so that the ratio of the detected normalized central intensity value to the maximum intensity value is less than 1 but close to 1, making the measurement more accurate.
3. According to the technical scheme, the light beam displacement device is arranged and used for adjusting the distance between light beams emitted by the two optical fiber laser sources on the rotating ground glass, and then the light beam displacement device is used for adjusting and controlling the distance between the two light beams on the ground glass surface to enable the ratio of the central light intensity value to the maximum light intensity value to be minimum, at the moment, the size of an object to be tested can be accurately obtained according to the light beam wavelength, the distance between the two light beams on the rotating ground glass and the focal length of the collimating lens, the light path structure is simple, and the testing accuracy is high.
4. According to the method, the shot light intensity value is recorded by the CCD camera through the gray value, and the gray value can be read and processed by the commercial software matlab, so that the light intensity identification capability is greatly improved, the ratio of the central light intensity value to the maximum light intensity value can be obtained only by detecting and comparing the gray value, and the rapid detection of the size of the object to be detected is realized.
Drawings
Fig. 1 is a schematic structural diagram of an imaging-based macro measurement apparatus according to embodiment 1 of the present disclosure.
Fig. 2 is a distribution diagram of light intensity values at an imaging plane of the imaging system according to embodiment 1 of the present disclosure.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
Example 1:
as shown in fig. 1, embodiment 1 of the present disclosure provides an imaging-based macro measurement apparatus, which mainly includes an illumination light source, an object to be measured, an imaging system, and a CCD camera connected to a computer.
Wherein: the illumination light source is built by two optical fiber laser sources, a light beam displacement device (the distance between the two optical fibers can be accurately regulated and controlled), rotating ground glass and a collimating lens;
an imaging system, a 4f imaging system consisting of two identical thin lenses, with a pupil placed at its spectral plane, also called telecentric;
furthermore, the CCD camera records the light intensity values captured in grey scale values, and the grey scale values can be read and processed by the commercial software matlab. For simplicity and clarity of analysis here we consider only the horizontal case.
(1) Illumination light source
The beamlets emitted from the two optical fiber laser sources are irradiated on the rotating ground glass surface and are horizontally arranged at an interval of l, and the beam waist of each beamlet is omega0The light beam displacement device can accurately regulate and control the size of l.
Assuming a Gaussian distribution for each beamlet, the light intensity distribution on the frosted glass face can be described as:
wherein v isxThe abscissa represents the point on the ground glass surface. After being scattered by the rotating ground glass, the light beams are collimated by the collimating lens, and the emergent light beams are the target illumination light source. In the space-frequency domain, the corresponding cross-spectral density function is:
in the formula x1、x2The abscissa indicates the point on the illumination light source plane. f. of1The focal length of the collimating lens is shown, lambda is the wavelength of the light beam, and k is 2 pi/lambda is the wave number; substituting the formula (1) into the formula (2), simplifying to obtain:
wherein C is0Is a constant.
(2) Object to be measured
Because we only need to measure the distance between any two end points of the object to be measured when performing microspur measurement, the object is replaced by two pinholes with a distance d, and considering that the size of the pinhole cannot affect the distance result, the transfer function of the object can be expressed as the addition of two dirac functions:
O(x)＝δ(x-d/2)+δ(x+d/2) (4)
the CCD camera used is a commercial camera, the common pixel size is about 4 μm, and the size of the object captured by the CCD camera occupies at least 10 pixels in order to detect the object information. Thus, the dimension d of the object to be measured is at least 40 μm.
(3) Imaging system
For the imaging system we use a telecentric imaging system, which is a 4f imaging system that places the pupil at the spectral plane. The Rayleigh diffraction limit distance of the imaging system is dR0.61 λ f/R, where f is the focal length of the thin lens in the 4f imaging system and R is the radius of the pupil. The pupil is placed at the spectral plane of the 4f imaging system in order to reduce the resolution of the imaging system such that the later detected normalized imaging intensity ratio I (0)/I (ρ) is satisfiedx)maxLess than 1 but close to 1. The measurement will thus be more accurate (explained later), where I (0) is the central intensity value, I (p)x)maxThe maximum light intensity value.
(4) Light intensity at the image plane
Based on fig. 1, the light intensity at the imaging plane can be obtained by the following formula:
I(ρx)＝∫∫W(x1,x2)O*(x1)O(x2)h*(x1,ρx)h(x2,ρx)dx1dx2 (5)
where rhoxAs the abscissa of the point at the imaging plane, h (x, ρ)x) Is an impulse response function of a telecentric imaging system expressed as:
wherein J1Is a first order bessel function.
Substituting equations (3), (4) and (6) into equation (5) can simplify:
wherein the content of the first and second substances,
the distribution of the imaging light intensity values according to the equations (7) and (8) is shown in fig. 2, wherein the corresponding parameter values are selected as follows: λ 532nm, f1150mm, f 250mm, R1.5 mm and ω050.8 μm. We have found that I (0)/I (p) can be aidedx)maxValues to analyze imaging effects: i (0)/I (rho)x)maxThe smaller value means that the central region of the imaging light intensity distribution is recessed downwards, i.e. the two pinholes are separated into more images, and the images are easier to distinguish (the imaging quality is high).
For the central intensity value I (0), it can be obtained according to equation (7):
wherein
As can be seen from this, it is,
the value plays an important role in the imaging quality. Because of the fact that
The smaller the value, the smaller the central intensity value I (0), mathematically proven I (0)/I (ρ)x)maxThe smaller the value, the higher the imaging quality.
For the
The only variable is/, which is regulated by the beam displacement means. When it is satisfied with
I.e. d ═ λ f1At/l, the magnitude of the term reaches the minimum. Corresponding I (0)/I (rho) at the same timex)maxIs at a minimum, i.e., imaging quality is best.
This means that: experimentally, the size of l is regulated and controlled by a light beam displacement device, and when the light intensity distribution detected by a CCD camera meets I (0)/I (rho)x)maxWhen the value is the minimum value, then the equation d ═ λ f1The/l holds. According to known lambda, f1The distance between two pinholes and the size omega of sub-light spot on the frosted glass surface can be calculated0Beam wavelength λ, focal length f of thin lens in telecentric imaging system1Is irrelevant.
(5) Error analysis
The error of this system mainly comes from the CCD camera. The CCD camera records the light intensity value through a gray scale value, wherein the gray scale value is 0-255, 0 represents black, 255 represents white, and the gray scale value must be an integer. If the maximum intensity value I (p) is assumedx)maxThe corresponding gray scale value is 255, then the gray scale value corresponding to the size of I (0) itself can beThere can be a decimal number, and the last recorded by the CCD camera is an integer number, and therefore an error occurs with an error rate:
when the imaging quality is best, I (0)/I (rho)x)maxThe value should be less than 1 but as close to 1 as possible to reduce random errors. The reason is that: when I (0)/I (rho)x)maxWhen the value is not less than 1, namely the value is constant to 1, the CCD camera cannot be used for acquiring the minimum value, namely the size of the object cannot be measured. Further, when I (0)/I (ρ)x)maxWhen the value approaches 1, the ratio corresponding to the random error is reduced because the corresponding gray scale value cardinality is large.
In addition, the error is also caused by instability of the laser light source, such as Quantel brand, model number: eylsa's single frequency continuous fiber laser with intensity noise < 0.1%. Therefore, the CCD camera is a major error source for the measuring device.
The following is presented as a specific example:
two very thin laser beams are emitted by two fiber lasers with wavelength lambda being 532nm and are irradiated on the frosted glass surface. Wherein the effect of the fiber laser can also be replaced by: the light beam emitted by the gas or solid laser is coupled by the single-mode fiber and directly strikes the ground glass after being emitted from the fiber. The diameter of the inner core of the common single-mode optical fiber on the market is about 1 micron. The light beam emitted from the optical fiber is divergent, the size of sub light spots on the frosted glass surface can be controlled by regulating the distance between the emitting end of the optical fiber and the frosted glass, and the beam waist size is about dozens of micrometers. In addition, the distance between the two sub light spots on the frosted glass surface is accurately regulated and controlled by a light beam displacement device.
The ground glass is controlled by a motor, and the rotating speed is usually 15-20 Hz. The light beam emitted from the rotating ground glass is collimated by the collimating lens (the distance between the ground glass and the collimating lens is usually the focal length of the collimating lens), and then the target illumination light beam can be obtained. Then, the object to be measured is placed closely at the rear surface of the collimating lens and at the input surface of the telecentric imaging system. The telecentric imaging system consists of a thin lens 1, a pupil and a thin lens 2, wherein the input surface of the telecentric imaging is the front focal surface of the thin lens 1, and the output surface is the back focal surface of the thin lens 2. The pupil is placed at the spectral plane of a 4f imaging system consisting of a thin lens 1 and a thin lens 2.
The CCD camera connected with the computer is arranged at the output surface, namely the image surface. The focal length of the collimating lens and the focal length of the thin lenses 1 and 2 have no specific requirements, and the commercial common specification is selected.
The light intensity values captured by the CCD camera are stored in the form of gray values. The parameter size is selected as follows: λ is 532 nm; f. of1＝150mm；f＝250mm；R＝1.5mm；ω0I (0)/I (ρ) can be calculated by reading the gray scale value with the commercial software matlab at 50.8 μmx)maxThe value is obtained. The light beam displacement device is used for regulating and controlling the size of the distance l between two light beams on the frosted glass surface to enable the I (0)/I (rho)x)maxThe value is minimal. This time it can be guaranteed:
i.e. d ═ λ f1L is calculated as follows. According to known lambda, f1And l value, we can finally realize the measurement of the macro.
Since the pixel size of the current commercial CCD camera is about 4 μm, and the size of the object to be measured by the CCD camera occupies at least 10 pixels, the system is suitable for measuring objects above 40 μm. The error rate, as analyzed above, was around 0.4%.
In summary, we propose a method and a device based on imaging microspur measurement, which is used in the micron level and has high precision. The method has important application prospect in the fields of laboratory measurement, industrial manufacturing, national defense construction and the like.
Example 2:
the embodiment 2 of the present disclosure provides a macro measurement device, which includes the macro measurement apparatus based on imaging according to the embodiment 1 of the present disclosure.
The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure, and various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.
Claims (9)
1. A microspur measuring device based on imaging is characterized by comprising an illumination light source, an object to be measured, an imaging system and a CCD camera connected with a processor;
the illumination light source sequentially comprises two optical fiber laser sources, a light beam displacement device, rotary ground glass and a collimating lens, wherein the light beam displacement device is used for adjusting the distance between light beams emitted by the two optical fiber laser sources on the rotary ground glass, and the light beams are emitted to an object to be measured through the collimating lens after passing through the rotary ground glass;
the imaging system is a 4f imaging system with a pupil placed on a frequency spectrum plane, the CCD camera is arranged at the position of an imaging plane of the imaging system and used for detecting the maximum light intensity value and the central light intensity value of the position of the imaging plane, and the processor obtains the size between two end points of the object to be detected according to the light beam wavelength when the ratio of the central light intensity value to the maximum light intensity value is minimum, the distance between two light beams on the rotating ground glass and the focal length of the collimating lens.
2. The imaging-based macro measurement device of claim 1, wherein the dimension between two end points of the object to be measured is at least 40 μm.
3. The imaging-based macro measurement device of claim 1, wherein a distance between the rotating ground glass and the collimating lens is equal to a focal length of the collimating lens.
4. An imaging-based macro measurement method, characterized in that the macro measurement apparatus according to any one of claims 1 to 3 is used, and the steps are as follows:
obtaining a light intensity function at the imaging surface of the imaging system according to the cross spectral density function of the illumination light source, the transfer function of the object to be measured and the impulse response function of the imaging system, and obtaining a central light intensity function according to the light intensity function at the imaging surface of the imaging system;
the CCD camera stores the detected light intensity value in a gray value form, and the processor calculates the ratio of the central light intensity value to the maximum light intensity value according to the gray value;
the light beam displacement device is used for regulating and controlling the distance between the two light beams on the ground glass surface to enable the ratio of the central light intensity value to the maximum light intensity value to be minimum, and the size of the object to be measured is obtained according to the wavelength of the light beams, the distance between the two light beams on the rotating ground glass and the focal length of the collimating lens.
5. The imaging-based macro measurement method of claim 4, wherein the cross spectral density function of the illumination source is:
wherein, ω is0Is the beam waist of each beam, vxAbscissa, x, representing points on the frosted glass surface1And x2Abscissa representing point on illumination light source face, f1The focal length of the collimating lens, λ is the wavelength of the light beam, k is 2 π/λ is the wavenumber, C0And is constant, i is the distance between the light beams emitted by the two fiber laser sources on the rotating ground glass.
6. The imaging-based macro measurement method according to claim 3, wherein the transfer function of the object under test is represented as the addition of two dirac functions:
O(x)＝δ(x-d/2)+δ(x+d/2)
wherein d is the distance between two end points of the object to be measured, x represents the abscissa of a point on the illumination light source surface, and δ represents the dirac function.
7. The imaging-based macro measurement method of claim 6, wherein the impulse response function of the imaging system is:
wherein, J1As a first order Bessel function, pxIs the abscissa of the point at the imaging plane, f is the focal length of the thin lens in a 4f imaging system, R is the pupil radius, λ is the beam wavelength, and x represents the abscissa of the point on the illumination source plane.
8. The imaging-based macro measurement method of claim 7, wherein the light intensity function at the imaging plane of the imaging system is:
wherein the content of the first and second substances,
further, the central light intensity function is:
wherein the content of the first and second substances,
wherein, ω is0For the beam waist of each beam, f1The focal length of the collimating lens is, d is the distance between two end points of the object to be measured, l is the distance between the light beams emitted by the two optical fiber laser sources on the rotating ground glass, k is 2 pi/lambda is the wave number, and lambda is the wavelength of the light beams.
9. The imaging-based macro measurement method according to claim 4, wherein the size of the object to be measured is calculated by the formula:
d＝λf1/l
wherein d is the distance between two end points of the object to be measured, lambda is the wavelength of the light beam, and f1The distance l is the distance between the light beams emitted by the two fiber laser sources on the rotating ground glass, and is the focal length of the collimating lens.
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