CN114076579A - Three-dimensional roughness detection device and method based on polarization imaging - Google Patents
Three-dimensional roughness detection device and method based on polarization imaging Download PDFInfo
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Abstract
The invention discloses a three-dimensional roughness detection device and a method based on polarization imaging, wherein the device comprises an imaging system and a detection system; the imaging system comprises a light beam collimation assembly and a polarization modulation assembly, wherein the light beam collimation assembly is used for emitting parallel light with a set wavelength, and the parallel light emitted by the light beam collimation assembly is modulated by the polarization modulation assembly to form two beams of circularly polarized light with opposite rotation directions to irradiate a target area on the surface to be measured; the detection system comprises a focus-dividing plane type polarization detector for acquiring a polarization image of a target area of the surface to be detected. The three-dimensional reconstruction of the surface is carried out through the collected polarization image, then the correction of the three-dimensional model is carried out by utilizing a four-step phase shift method, finally, a reference plane is calculated by utilizing a least square method, and the plane roughness is calculated on the basis of the reference plane. The device and the method can eliminate the problem of metal surface flare and can complete the three-dimensional roughness detection of the metal surface without contact.
Description
Technical Field
The invention belongs to the technical field of image processing, and particularly relates to a three-dimensional roughness detection device and method based on polarization imaging.
Background
With the rapid development of manufacturing technology, the technological level is continuously improved, and higher requirements are put forward for the evaluation of the surface quality of parts. The surface structure evaluation method is also gradually developed from the separation evaluation of single two-dimensional shape error, waviness and surface roughness to the comprehensive evaluation of three-dimensional surface functions. In the field of science and engineering, two-dimensional evaluation methods based on contour lines have been widely used for nearly half a century; three-dimensional measurement methods and techniques have been gradually gaining attention in the industry since the advent of about 1970. At the beginning of the development of the technology, the research progress is very slow, because the calculation of a large number of three-dimensional parameters is mainly completed manually. With the advent and continuous development of computer science, especially the application of microchip technology, new possibilities are brought to the research of the analysis roughness of the three-dimensional topography of the metal surface.
The current roughness detection methods mainly include three methods: line profile (perception Z (x)), area topography (perception Z (x, Y) or Z (x) as a function of Y), area ensemble. However, for a kind of metal surface with a reflective surface, whether a probe type or an optical type is used, there is a certain limitation.
In a patent "method and device for detecting appearance defects" 201880071426.2 in the prior art, an appearance defect detecting device is provided in particular to solve the problem that the detection of the appearance defects in the prior art on the surface of a material to be detected made of metal or semitransparent materials is easily affected by reflected light spots, so that the accuracy is low. The method comprises the steps of acquiring images with different polarization degrees by utilizing multi-angle cameras at different positions, fusing the acquired images to solve the problem of metal surface flare, and meanwhile enhancing defect detail textures. However, the invention has the disadvantages that the arrangement of a plurality of groups of cameras is high in equipment cost, and the replacement of the polaroids with different angles by adopting the mechanical rotating wheel is easy to cause the error expansion, so that the requirements on the imaging precision are not met.
In the prior art, a patent of monocular polarization three-dimensional reconstruction method 201810664105.5 discloses that polarization images with different polarization angles at the same position are obtained by rotating a polarizer, and then normal vectors of the surface of an object are obtained by utilizing stocks vector calculation. Due to the ambiguity of the azimuth angle, the reconstructed three-dimensional model is inaccurate, and the shape from shading (sfs, light and shade shape recovery method) is used for eliminating ambiguity to finally obtain the three-dimensional shape of the surface of the object to be measured. However, the invention has the defects that the detection process is complicated, a certain error is caused by mechanically rotating the polaroid, the azimuth ambiguity can be eliminated by a shading recovery shape method, and the calculation amount is increased. Three-dimensional imaging is carried out through a light and shade recovery method, multi-angle distribution polishing needs to be carried out, the imaging system is complex, and the light source cannot guarantee that the arrangement angle position is completely accurate.
Disclosure of Invention
The purpose of the invention is as follows: the invention provides a three-dimensional roughness detection device based on polarization imaging, and provides a three-dimensional roughness detection method based on polarization imaging.
The technical scheme is as follows: the invention relates to a three-dimensional roughness detection device based on polarization imaging, which comprises an imaging system and a detection system, wherein the imaging system is used for imaging a three-dimensional surface of a workpiece; the imaging system comprises a light beam collimation assembly and a polarization modulation assembly, wherein the light beam collimation assembly is used for emitting parallel light with a set wavelength, and the parallel light emitted by the light beam collimation assembly is modulated by the polarization modulation assembly to form two beams of circularly polarized light with opposite rotation directions to irradiate a target area on the surface to be measured;
the detection system comprises a focus-dividing plane type polarization detector for acquiring a polarization image of a target area of the surface to be detected.
Preferably, the beam collimation assembly comprises a 450nm blue LED light source and a first lens for forming parallel light.
Preferably, the polarization modulation assembly comprises a linear polarizer, a polarization grating and a second lens for forming parallel light, which are arranged along the optical path; the polarization grating is used for modulating the incident beam into two light waves with opposite rotation directions and a set included angle.
Preferably, a third lens for converging the parallel light is arranged between the sub-focus planar polarization detector and the surface to be measured.
Furthermore, the polarization position of the linear polarizer is randomly placed, and after passing through the polarization grating, the light beam is modulated into two beams with a certain included angle, wherein one beam is left-handed circularly polarized light, and the other beam is right-handed circularly polarized light. The diffraction angle of the polarization grating can separate an incident beam into two beams of light with a certain included angle, and the two beams of light have mutually overlapped parts. Two light waves with opposite rotation directions are adjusted by the second lens and then parallelly enter the surface to be measured, a certain optical path difference exists in the overlapping part of the two light waves, and the light waves irradiate the overlapping area of the target surface to interfere with each other to generate interference fringes.
Furthermore, two beams of circularly polarized light with different rotation directions generated by the polarization grating form interference fringes on the surface to be measured, and the structured light imaging is similar to structured light imaging and is lower for projection equipment. The height of the three-dimensional model of the surface to be measured can be further calculated through subsequent calculation by using the texture picture of the surface to be measured with the stripes, which is obtained by the polarization imaging system. Interference fringes generated by circularly polarized light with different rotation directions can be used for correcting the problem of inaccurate model caused by azimuth ambiguity when three-dimensional reconstruction is carried out according to polarization information, so that strong reflection flare on the surface of a component can be eliminated, the imaging effect is better, and the effect of real-time three-dimensional reconstruction can be realized.
Furthermore, the sub-focus plane type polarization detector can acquire four polarization images under the condition of single exposure. According to the polarization detector, the miniature polaroids are added in front of each pixel of the detector, all the miniature polaroids are integrated on a focal plane in an integrated mode, and the four pixels are in a group and are respectively sensitive to polarization vectors in different directions. The focusing plane type polarization detector directly or indirectly obtains polarization components or polarization states of the current pixel in different directions by utilizing the response of the current pixel and the surrounding pixels of the current pixel, and calculates the polarization information of the target through combination, reconstruction and other modes. The polarization imaging of the focus-dividing plane type polarization detector is carried out, meanwhile, no light splitting element exists, the structure is compact, the size is small, the quality is small, the stability is high, four images with different polarization degrees can be imaged simultaneously, the polarization angle is fixed, manual adjustment is not needed, and errors of a reconstruction model caused by errors can be reduced.
Furthermore, the first lens, the second lens and the second lens all play a role in changing a light path, namely parallel light is changed into convergent light or convergent light is changed into parallel light, and the convex lens with set curvature is selected to complete the building of the platform.
The invention relates to a three-dimensional roughness detection method based on polarization imaging, which comprises the following steps:
(1) acquiring polarized images with different polarization degrees of a target area of the surface to be detected by using a polarization imaging system;
(2) carrying out three-dimensional shape reconstruction on the target area of the surface to be detected by utilizing the polarization image data information of the target area of the surface to be detected;
(3) correcting the reconstructed three-dimensional shape by adopting a four-step phase shift method;
(4) and extracting the surface roughness profile, and calculating to obtain a three-dimensional roughness parameter value.
Preferably, in the step (1), two beams of circularly polarized light with opposite rotation directions are adopted to generate interference on the surface to be measured, and the interference fringe image is detected by the focus-splitting plane type polarization detector to obtain a plurality of images with different polarization directions.
Preferably, in the step (2), according to the polarization image information obtained by the focus-splitting planar polarization detector, the polarization information of the optical wave, including the linear polarization degree P of the optical wave, is calculated by using the Stokes vectorlAnd the polarization angle ψ is as follows:
in the formula, I represents the total intensity of light waves, Q represents the light intensity difference of linearly polarized light of 0 degrees and 90 degrees, and U represents the light intensity difference of linearly polarized light of 45 degrees and 135 degrees;
estimating an incidence angle theta by using the micro-surface element emergent light polarization degree P of the surface to be measured and the target surface reflectivity information n; according to the change of the light intensity received by the detector along with the change of the angle of the polarizer, the azimuth angle is obtained by fitting the change curve
Normal vector
The mapping relation with the polarization characteristic parameter is expressed as follows:
assuming that the surface three-dimensional surface equation is z ═ f (x, y), p (x, y), and q (x, y) are the partial derivatives of the surface equation to the x and y axes, respectively, the normal vector formula is obtained as follows:
the normal vectors of different shapes and different curvature positions of the surface of the object are integrated, so that the relative depth of the object can be obtained, and the three-dimensional shape of the surface of the object is finally obtained.
Preferably, the three-dimensional parameters of the surface roughness are calculated in the step (4), the reference plane is calculated by adopting a least square plane method, the surface roughness profile is extracted by taking the height of the reference plane as a standard, and the calculated number average value of the distances from each point on the profile to the reference plane is used as the three-dimensional roughness parameter value.
Further, the Stokes formula uses four parameters with light intensity characteristics to represent different polarization states of the light wave, and the four parameters are Stokes vectors, and the expression is as follows:
i, Q, U and V are four parameters of Stokes, wherein I represents the total intensity of the light wave, Q represents the light intensity difference of 0-degree linearly polarized light and 90-degree linearly polarized light, U represents the light intensity difference of 45-degree linearly polarized light and 135-degree linearly polarized light, and V represents the light intensity difference of right-handed circularly polarized light and left-handed circularly polarized light; in the formula I0°I90°I+45°I-45°Respectively representing the light intensity of the light wave passing through a horizontal linear polarizer, a vertical linear polarizer, a + 45-degree linear polarizer and a-45-degree linear polarizer; i isrAnd IlRespectively representing the light intensity of the light wave passing through an ideal right-hand circular polarizer and a left-hand circular polarizer. The polarization information of the light wave, including the linear polarization degree P of the light wave, can be calculated according to the Stokes vectorlAnd the polarization angle ψ is as follows:
the Stokes vector may describe fully polarized light, partially polarized light, and fully unpolarized light. The four elements forming the Stokes vector are all time average values of light intensity, and can be obtained by a focusing plane type polarization detector at one time.
By utilizing the polarization degree P of the emergent light of the micro-planar elements on the target surface and the reflectivity information n of the target surface, the estimation of the incident angle theta can be realized, and the formula is as follows:
the light intensity received by the detector changes along with the angle change of the polarizer, the change rule is expressed as follows, then a change curve is fitted, and the phase angle corresponding to the maximum light intensity is the azimuth angle
The formula is as follows:
I＝Ip·cos2θ
further, the relative depth information of the object is obtained by integrating normal vectors of different shapes and different curvature positions of the surface of the object, and the three-dimensional shape of the surface of the object is finally obtained by resolving the depth information, wherein the expression is as follows:
z＝f(x,y)＝∫∫p(x,y)dx+q(x,y)dy。
furthermore, interference is generated on the surface of the metal part to be measured according to two beams of circularly polarized light with opposite rotation directions, and interference fringe images are detected by the focusing plane type polarization detector through the imaging system to obtain four images with different polarization directions of 0 degree, 45 degrees, 90 degrees and 135 degrees, namely the images under the four phase shift conditions of 0 degree, 90 degrees, 180 degrees and 270 degrees. And then, the height information of the surface of the part is calculated by adopting a four-step phase shift method, and the three-dimensional shape of the surface of the object is further corrected. The correction of the three-dimensional shape is carried out by adopting a four-step phase shift method, so that the phase angle ambiguity problem generated when the surface three-dimensional reconstruction is carried out by using the polarization information in the prior art can be avoided, and the three-dimensional reconstruction model is more accurate. The phase angle ambiguity is caused by the fact that the fitted light intensity variation curve is a chord function and has two most significant positions. Further, the four-step phase shift method adopted in the present application is prior art.
Furthermore, the microscopic concave-convex characteristics of the measured surface can be represented fully and reasonably by using three-dimensional parameters. And calculating three-dimensional parameters of the surface roughness, calculating a reference plane by adopting a least square plane method, taking the height of the plane as the standard for calculating each roughness parameter, extracting the surface roughness profile, and calculating to obtain three-dimensional roughness parameter values. The method comprises the following specific steps:
let the equation for the reference plane be: and z is ax + by + c, and n data points and data coordinates p (x) can be obtained according to the reconstructed three-dimensional reconstruction model of the surface to be measured, wherein z is f (x, y)i,yi,zi) N, (i ═ 1.. n). By means of the least squares method, the parameters of the plane can be solved: a, b and c, and further solving a roughness parameter Ra.
Error terms defining a single data point: deltai＝axi+byi-zi+ c; for n sets of data, a least squares problem is defined for all data:
the arguments a, b, c of the reference plane equation to be calculated are uncorrelated, and F (a, b, c) is differentiated from a, b, c respectively and made to be 0, and the specific formula is as follows:
writing a, b, c to one side of the equation to obtain
Writing the above equation in matrix form:
and determining a reference plane equation by solving the calculated a, b and c.
The main parameter of surface roughness is the profile arithmetic mean deviation Ra, which is used to calculate the distance z from each point on the profile to the reference in the specified sampling rangeiIs calculated as the average of the counts. The arithmetic mean height of the surface is represented by Sa in the three-dimensional surface roughness, and the arithmetic mean of the distances between the measured profile surface and the reference surface over the sampling region D is represented by the mathematical expression: is composed of
In the formula IxThe length of the sampling region D in the X-axis direction; lyThe length of the sampling region D in the Y-axis direction; n is the number of sample points of the sampling area D in the Y-axis direction; m is the number of sample points of the sampling region D in the X-axis direction.
Has the advantages that: the method applies the polarization imaging technology to the measurement of the roughness of the metal surface, solves the problem of poor imaging effect caused by light reflection of the metal surface, simultaneously reconstructs the three-dimensional appearance of the metal surface by utilizing the acquired polarization information, and finally evaluates the three-dimensional roughness of the target surface according to the appearance information, thereby providing a new possibility for the development of non-contact three-dimensional roughness detection of the metal surface. In addition, because the images with different polarization angles are obtained by adopting the focus-dividing plane type polarization detector, the problem of angle errors caused by the replacement of the polaroid by the traditional mechanical rotating wheel is solved.
Drawings
FIG. 1 is a flow chart of a three-dimensional roughness detection method based on polarization imaging according to the present invention;
FIG. 2 is a schematic structural diagram of a three-dimensional roughness measurement device based on polarization imaging according to the present invention;
FIG. 3 is a schematic diagram of the working principle of the polarization grating of the present invention;
FIG. 4 is a schematic diagram of a sub-focus planar polarization detector according to the present invention acquiring four polarization images in a single exposure;
FIG. 5 is a flow chart of the three-dimensional topography reconstruction of the target area of the surface to be measured according to the present invention;
FIG. 6 is a schematic diagram showing the relationship between the incident angle, the azimuth angle and the surface normal of the target area of the surface to be measured according to the present invention;
FIG. 7 is a graph showing the variation of the degree of polarization and the angle of incidence under different reflectivities according to the present invention;
FIG. 8 is a diagram showing the variation curves of the light intensity and the polarizer angle according to the present invention.
Detailed Description
The technical solution of the present invention is further described in detail with reference to the accompanying drawings and examples.
A three-dimensional roughness detection device based on polarization imaging is shown in figure 1 and comprises an imaging system and a detection system; the imaging system comprises a 450nm blue light LED light source 1 for detecting metal materials, and light beams formed by the LED light source 1 are irradiated to a target area of a surface to be detected 6 through a first lens 2, a linear polarizer 3, a polarization grating 4 and a second lens 5 in sequence; the detection system comprises a focus-splitting plane type polarization detector 8, and a third lens 7 for converging parallel light is arranged between the focus-splitting plane type polarization detector 8 and the surface to be detected 6.
In this embodiment, the polarization position of the linearly polarizing plate can be arbitrarily placed, and after passing through the polarization grating, the light beam is modulated into two light beams having a certain included angle, where one light beam is left-handed circularly polarized light and the other light beam is right-handed circularly polarized light, as shown in fig. 3. The diffraction angle of the polarization grating can separate an incident beam into two beams of light with a certain included angle, and the two beams of light have mutually overlapped parts. Two light waves with opposite rotation directions are adjusted by the second lens and then parallelly enter the surface to be measured, a certain optical path difference exists in the overlapping part of the two light waves, and the light waves irradiate the overlapping area of the target surface to interfere with each other to generate interference fringes.
In this embodiment, the sub-focus plane type polarization detector is mainly to add a micro-polarizer in front of each pixel of the detector, all the micro-polarizers are integrated on the focus plane in an integrated manner, and four pixels are a group and are respectively sensitive to polarization vectors in different directions. Therefore, four polarization images are obtained under the condition of single exposure, as shown in fig. 4, two beams of circularly polarized light with opposite rotation directions generate interference on the surface of the metal component to be measured, the interference fringe image is detected by the focusing planar polarization detector through the imaging system, and four images with different polarization directions of 0 °, 45 °, 90 ° and 135 ° are obtained, namely, the images under the four phase shifting conditions of 0 °, 90 °, 180 ° and 270 °.
In this embodiment, the first lens is configured to convert a light beam emitted by the light source into parallel light, the second lens is configured to convert the emitted light beam into parallel light, and the third lens is configured to converge reflected light of the target region of the surface to be measured to an image acquisition window of the focus-splitting planar polarization detector. When the platform is built, the first lens, the second lens and the third lens are all convex lenses with set curvatures.
A three-dimensional roughness detection method based on polarization imaging is disclosed, as shown in FIG. 2, the method comprises the following steps:
(1) acquiring polarized images with different polarization degrees of a target area of the surface to be detected by using a polarization imaging system;
(2) carrying out three-dimensional shape reconstruction on the target area of the surface to be detected by utilizing the polarization image data information of the target area of the surface to be detected;
(3) correcting the reconstructed three-dimensional shape by adopting a four-step phase shift method;
(4) and extracting the surface roughness profile, and calculating to obtain a three-dimensional roughness parameter value.
In the embodiment, in the step (1), a time-sharing polarization imaging rotation polarizer or a simultaneous polarization imaging focus splitting plane is used for image acquisition to obtain a polarization image; furthermore, the design requirements of the invention can be met by a polarization imaging system which can obtain the same-position polarization images with different polarization degrees.
In this embodiment, in the step (2), the three-dimensional topography reconstruction is performed on the target region of the surface to be measured, as shown in fig. 5, first, according to the Stokes formula, four parameters with light intensity characteristics are used to represent different polarization states of the light wave, and the four parameters are Stokes vectors, and the expression is as follows:
i, Q, U and V are four parameters of Stokes, wherein I represents the total intensity of the light wave, Q represents the light intensity difference of 0-degree linearly polarized light and 90-degree linearly polarized light, U represents the light intensity difference of 45-degree linearly polarized light and 135-degree linearly polarized light, and V represents the light intensity difference of right-handed circularly polarized light and left-handed circularly polarized light; in the formula
Respectively representing the light intensity of the light wave passing through a horizontal linear polarizer, a vertical linear polarizer, a + 45-degree linear polarizer and a-45-degree linear polarizer; i isrAnd IlRespectively representing the light intensity of the light wave passing through an ideal right-hand circular polarizer and a left-hand circular polarizer. The polarization information of the light wave, including the linear polarization degree P of the light wave, can be calculated according to the Stokes vectorlAnd a polarization angle psi.
The Stokes vector may describe fully polarized light, partially polarized light, and fully unpolarized light. The four elements forming the Stokes vector are all time average values of light intensity, and can be obtained by a focusing plane type polarization detector at one time.
In this embodiment, the incident lightThe spatial relationship among the angle, the azimuth angle and the surface normal is shown in fig. 6, and θ in fig. 6 is an incident angle, that is, an included angle between the observation direction and the normal direction;
is the azimuth angle, i.e., the incident azimuth angle of the light;
is the surface normal. The estimation of the incidence angle theta can be realized by utilizing the polarization degree P of the emergent light of the micro-planar elements of the target surface and the reflectivity information n of the target surface, and the relation among the polarization degree P, the reflectivity information n of the target surface and the incidence angle theta satisfies the following formula:
the variation curves of the polarization degree and the incidence angle under different reflectivities are shown in fig. 7, and the estimation of the incidence angle theta is completed according to the polarization degree P and the target surface reflectivity information n.
In this embodiment, the light intensity received by the detector changes with the angle of the polarizer, and the change rule satisfies that I is Ip·cos2Theta, the fitted variation curve is shown in fig. 8, and the phase angle corresponding to the maximum intensity of light is the azimuth angle.
In this embodiment, the mapping relationship between the normal vector and the polarization characteristic parameter can be expressed as:
the normal vector distribution of the target surface reflects gradient information of the shape change of the object surface, and the surface three-dimensional surface equation is assumed to be z ═ f (x, y), p (x, y), and q (x, y) are respectively the partial derivatives of the surface equation to the x and y axes, namely the gradient information of the object surface. The normal vector formula can be further derived:
the method comprises the following steps of integrating normal vectors of different shapes and different curvature positions on the surface of an object to obtain relative depth information of the object, and finally obtaining the three-dimensional shape of the surface of the object by resolving the depth information, wherein the expression is as follows:
z＝f(x,y)＝∫∫p(x,y)dx+q(x,y)dy。
in this embodiment, the height information of the surface of the component is calculated from the image obtained by detection by the focal plane type polarization detector by using a four-step phase shift method, and the three-dimensional shape of the surface of the object is further corrected. The correction of the three-dimensional shape is carried out by adopting a four-step phase shift method, so that the phase angle ambiguity problem generated when the surface three-dimensional reconstruction is carried out by using the polarization information in the prior art can be avoided, and the three-dimensional reconstruction model is more accurate. The phase angle ambiguity is caused by the fact that the fitted light intensity variation curve is a chord function and has two most significant positions.
Furthermore, the microscopic concave-convex characteristics of the measured surface can be represented fully and reasonably by using three-dimensional parameters. And calculating three-dimensional parameters of the surface roughness, calculating a reference plane by adopting a least square plane method, taking the height of the plane as the standard for calculating each roughness parameter, extracting the surface roughness profile, and calculating to obtain three-dimensional roughness parameter values. The method comprises the following specific steps:
let the equation for the reference plane be: and z is ax + by + c, and n data points and data coordinates p (x) can be obtained according to the reconstructed three-dimensional reconstruction model of the surface to be measured, wherein z is f (x, y)i,yi,zi) N, (i ═ 1.. n). By means of the least squares method, the parameters of the plane can be solved: a, b and c, and further solving a roughness parameter Ra.
Error terms defining a single data point: deltai＝axi+byi-zi+ c; for n sets of data, a least squares problem is defined for all data:
the arguments a, b, c of the reference plane equation to be calculated are uncorrelated, and F (a, b, c) is differentiated from a, b, c respectively and made to be 0, and the specific formula is as follows:
writing a, b, c to one side of the equation to obtain
Writing the above equation in matrix form:
and determining a reference plane equation by solving the calculated a, b and c.
The main parameter of surface roughness is the profile arithmetic mean deviation Ra, which is used to calculate the distance z from each point on the profile to the reference in the specified sampling rangeiIs calculated as the average of the counts. The arithmetic mean height of the surface is represented by Sa in the three-dimensional surface roughness, and the arithmetic mean of the distances between the measured profile surface and the reference surface over the sampling region D is represented by the mathematical expression: is composed of
In the formula IxThe length of the sampling region D in the X-axis direction; lyThe length of the sampling region D in the Y-axis direction; n is the number of sample points of the sampling area D in the Y-axis direction; m is the number of sample points of the sampling region D in the X-axis direction.
According to the experimental results, the comparison results obtained by calculating the metal surfaces with different roughness formed by turning, boring and end milling are shown in the following table 1:
TABLE 1
| Turning Ra 0.8 μm | Vehicle Ra 1.6 μm | Vehicle Ra 3.2 μm | Vehicle Ra 6.3 μm | |
| Calculated value (mm) | 1.209μm | 2.186μm | 3.724μm | 6.902μm |
| Boring Ra 0.8 μm | Boring Ra 1.6 μm | Boring Ra 3.2 μm | Boring Ra 6.3 μm | |
| Calculated value (mm) | 1.025μm | 2.048μm | 3.780μm | 6.826μm |
| End mill Ra 0.8 μm | End Ra 1.6 μm | End Ra 3.2 μm | End Ra 6.3 μm | |
| Calculated value (mm) | 1.369μm | 2.056μm | 4.023μm | 6.854μm |
As can be seen from the above table, the deviation between the roughness parameter value calculated by the method and the actual roughness parameter value is in a reasonable range.
In conclusion, according to polarization imaging of different metal surfaces to be detected, a polarization diagram is obtained for three-dimensional reconstruction, a four-step phase shift method is used for correcting the reconstructed surface, and finally, the reconstructed data is used for evaluating and calculating three-dimensional roughness parameters, so that non-contact three-dimensional roughness detection of the metal surface is realized, and the detection speed is greatly improved on the premise of meeting the requirement on accuracy.
Claims (8)
1. The utility model provides a three-dimensional roughness detection device based on polarization imaging which characterized in that: comprises an imaging system and a detection system; the imaging system comprises a light beam collimation assembly and a polarization modulation assembly, wherein the light beam collimation assembly is used for emitting parallel light with a set wavelength, and the parallel light emitted by the light beam collimation assembly is modulated by the polarization modulation assembly to form two beams of circularly polarized light with opposite rotation directions to irradiate a target area of the surface to be measured (6);
the detection system comprises a focus-splitting planar polarization detector (8) for acquiring a polarization image of a target area of the surface to be measured (6).
2. The three-dimensional roughness detection device based on polarization imaging as claimed in claim 1, wherein: the light beam collimation assembly comprises a 450nm blue light LED light source (1) and a first lens (2) used for forming parallel light.
3. The three-dimensional roughness detection device based on polarization imaging as claimed in claim 1, wherein: the polarization modulation component comprises a linear polarizer (3) arranged along a light path, a polarization grating (4) and a second lens (5) for forming parallel light; the polarization grating (4) is used for modulating the incident light beams into two beams of circularly polarized light with opposite rotating directions and a set included angle.
4. The three-dimensional roughness detection device based on polarization imaging as claimed in claim 1, wherein: and a third lens (7) for converging parallel light is arranged between the focus-dividing plane type polarization detector (8) and the surface to be measured (6).
5. A three-dimensional roughness detection method based on polarization imaging is characterized in that: the method comprises the following steps:
(1) acquiring polarized images with different polarization degrees of a target area of the surface to be detected by using a polarization imaging system;
(2) carrying out three-dimensional shape reconstruction on the target area of the surface to be detected by utilizing the polarization image data information of the target area of the surface to be detected;
(3) correcting the reconstructed three-dimensional shape by adopting a four-step phase shift method;
(4) and extracting the surface roughness profile, and calculating to obtain a three-dimensional roughness parameter value.
6. The three-dimensional roughness detection method based on polarization imaging as claimed in claim 1, wherein: in the step (1), two beams of circularly polarized light with opposite rotation directions are adopted to generate interference on the surface to be detected, and the interference fringe image is detected by the focus-splitting plane type polarization detector to obtain a plurality of images with different polarization angles.
7. The three-dimensional roughness detection method based on polarization imaging as claimed in claim 6, wherein: in the step (2), according to the polarization image information obtained by the focusing plane type polarization detector, the polarization information of the light wave is calculated by using Stokes vectors, wherein the polarization information comprises the linear polarization degree P of the light wavelAnd the polarization angle ψ is as follows:
in the formula, I represents the total intensity of light waves, Q represents the light intensity difference of linearly polarized light of 0 degrees and 90 degrees, and U represents the light intensity difference of linearly polarized light of 45 degrees and 135 degrees;
estimating an incidence angle theta by using the micro-surface element emergent light polarization degree P of the surface to be measured and the target surface reflectivity information n; according to the change of the light intensity received by the detector along with the change of the angle of the polarizer, the azimuth angle is obtained by fitting the change curve
The mapping relation between the normal vector and the polarization characteristic parameter is expressed as follows:
assuming that the surface three-dimensional surface equation is z ═ f (x, y), p (x, y), and q (x, y) are the partial derivatives of the surface equation to the x and y axes, respectively, the normal vector formula is obtained as follows:
the normal vectors of different shapes and different curvature positions of the surface of the object are integrated, so that the relative depth of the object can be obtained, and the three-dimensional shape of the surface of the object is finally obtained.
8. The three-dimensional roughness detection method based on polarization imaging as claimed in claim 7, wherein: and (4) calculating three-dimensional parameters of the surface roughness, calculating a reference plane by adopting a least square plane method, extracting a surface roughness profile by taking the height of the reference plane as a standard, and taking the calculated number average value of the distances from each point on the profile to the reference plane as a three-dimensional roughness parameter value.
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