CN113029042B - Dynamic measuring device and method for surface morphology of high-temperature molten metal - Google Patents
Dynamic measuring device and method for surface morphology of high-temperature molten metal Download PDFInfo
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Abstract
The invention discloses a dynamic measuring device and a method for the surface appearance of high-temperature molten metal, wherein the method comprises the following steps: acquiring a modulation image on the surface of a measured object in real time; performing three-dimensional Fourier transform on the modulation image, filtering according to the fundamental frequency spectrum information corresponding to the modulation image to obtain a surface shape modulation spectrum of the object, and acquiring truncated phase data of the modulation image through three-dimensional inverse Fourier transform; then, based on the truncated phase data of the modulation image, performing phase expansion on the subsequent truncated phase by using the continuity relation of the phase on the time axis to obtain the phase data of the measured object; and finally, acquiring height data according to the phase data of the object to be measured by utilizing a pre-established object phase-height mapping relation to obtain point cloud data of the surface of the object to be measured. Therefore, the invention can intuitively acquire the shape, the geometric dimension state and the structure quality condition of the current state of the surface of the measured object in the laser processing process.
Description
Technical Field
The invention belongs to the technical field of laser processing process detection, and particularly relates to a dynamic measurement device and method for the surface morphology of high-temperature molten metal in laser welding, laser cladding, laser additive manufacturing and other processes.
Background
With the development of laser processing technology, especially in recent years, the development of laser welding and material-increasing and material-decreasing manufacturing technology, the quality real-time detection technology of high-precision laser processing process is highly emphasized, and especially when continuous processing and large-size component manufacturing are carried out, the stability and control of the process are the key points of batch application. At present, the detection of laser thermal processing process at home and abroad includes CCD image detection (molten pool monitoring), infrared thermal imaging, X-ray and other technologies. Quality inspection and control techniques for additive manufacturing processes have been a global research hotspot since 2018, which also promoted the development of quality control for laser additive manufacturing processes. However, in these detection methods, there are two main ways, one is to detect the gap where the laser operation is stopped, and the other is to detect after the formation or between layers; the technologies such as in-situ X-ray and the like can be used for on-line detection, but the use cost, the field requirement, the applicability of a detection object and the like are high, and the method is not suitable for the actual complex structure manufacturing process or the industrial production field; the infrared thermal imaging and other technologies are difficult to obtain the actual geometric dimension of the fine defect on the surface of a metal object (the object state is a high-temperature molten state) in laser processing, more than a macroscopic angle is used for comprehensive judgment, and online detection cannot be realized; in the traditional CCD molten pool monitoring and temperature monitoring technology, the macroscopic judgment of the length width and the local quality of the molten pool is more concentrated, and the defect detection and quantitative judgment of the surface appearance of the molten pool are difficult to realize; the method is expected to realize high-precision process quality judgment and monitoring of a specific material under certain equipment, but a large number of tests and a fixed learning model frame are required in the establishing process, so once the state of the material or the equipment is changed, the established training model and control model can reduce the precision or become invalid.
Therefore, there is a need to provide a technical solution that can perform three-dimensional topography measurement on line during laser processing and obtain corresponding quality defects directly through the topography features of the object.
Disclosure of Invention
The invention aims to overcome the problem that the shape defect of a metal object (the object state is high-temperature molten state) in the laser processing process cannot be obtained in the prior art, and provides a dynamic measuring device and a dynamic measuring method for the surface shape of the high-temperature molten state metal.
In order to achieve the above purpose, the invention provides the following technical scheme:
a dynamic measurement method for the surface topography of high-temperature molten metal comprises the following steps:
s1: projecting a standard stripe image to the surface of a measured object by adopting an illumination projection system based on ultraviolet illumination, and acquiring a modulation image on the surface of the measured object in real time;
s2: performing three-dimensional Fourier transform on the modulation image, filtering according to the fundamental frequency spectrum information corresponding to the modulation image to obtain a surface shape modulation spectrum of the object, and acquiring truncated phase data of the modulation image through three-dimensional inverse Fourier transform;
s3: based on the truncated phase data of the modulation image and based on the initial value state of space phase expansion, performing phase expansion on the subsequent truncated phase by using the continuity relation of the phase on the time axis to obtain the phase data of the measured object;
s4: and acquiring the height data of the measured object according to the phase data of the measured object by utilizing the pre-established object phase-height mapping relation, thereby obtaining the point cloud data of the surface of the measured object.
By selecting the wave band of the light source (projecting and imaging the object to be measured by adopting an illumination projection system based on an ultraviolet light source), the high-temperature molten object in the laser process can be accurately imaged to obtain a modulation image of the surface of the object; and then modulating and demodulating the modulated image to obtain a truncated phase of the measured object, obtaining phase information of the measured object with small error by adopting a phase expansion method along a time axis, obtaining complete phase information of the measured object by adopting the phase expansion method along the time axis, obtaining height data of the measured object according to the phase data of the measured object by utilizing a pre-established phase-height mapping relation, and obtaining three-dimensional point cloud data of the surface of the measured object, so that the appearance geometric dimension state and the structural quality condition of the current state of the surface of the measured object can be intuitively obtained in the laser processing process.
According to a specific embodiment, in step S3, let it be assumed that the t-th measured modulation image is at a point
At a truncated phase of
For the same point
Calculating the phase difference of two adjacent modulation images
Multiple of (2):
wherein,
as described in paragraph t-1Modulating the image at the point
The phase of the truncation of (a) is,
the phase difference of two adjacent modulation images is obtained;
is a multiple; if the phase difference of the front and rear two modulated images
If < 1, the phase unwrapping process at the next moment in space truncation cannot be differed
To reliably spread the phase points, or vice versa, if
And if the sum of the sums of the sum of the sums of the sum of the sums of the sum of the sums of the sum of the sums.
According to a specific implementation manner, the object phase-height mapping relationship is established according to calibration parameters, and the object phase-height mapping relationship is as follows:
wherein,
is the coordinates of the image of the camera,
representing the difference in height of a point on a plane corresponding to each pixel point in the image at a known location in measurement space relative to a reference plane,
is the phase difference of the corresponding point, wherein,
the method is used for calibrating parameters and is used for representing the mapping coefficient between the phase difference and the height difference of each point on the reference plane relative to the reference plane.
According to a specific embodiment, the ultraviolet light source based illumination projection system is a Kovar illumination projection system configured with an ultraviolet light source.
According to a specific embodiment, the koala illumination projection system further comprises: and the light homogenizing rod structure is connected with the ultraviolet light source, and the brightness of the ultraviolet light source is increased through the light homogenizing rod structure.
According to a specific embodiment, the Kolla illumination projection system employs a grating of 4 lines per millimeter.
According to a specific embodiment, the Kovar illumination projection system employs an illumination source with a central wavelength of 320 nm.
In a further embodiment of the present invention, there is also provided a dynamic measurement apparatus for surface topography of a high temperature molten metal, comprising:
the illumination projection system based on the ultraviolet light source is used for projecting a standard stripe image to the surface of a measured object;
the imaging camera is used for shooting a modulation image formed on the surface of the measured object;
the data processing module is used for carrying out three-dimensional Fourier transform on the modulation image, filtering according to the base frequency spectrum information corresponding to the modulation image to obtain a surface shape modulation spectrum of the object, and obtaining truncation phase data of the modulation image through three-dimensional inverse Fourier transform; based on the truncated phase data of the modulation image and based on the initial value state of space phase expansion, performing phase expansion on the subsequent truncated phase by using the continuity relation of the phase on the time axis to obtain the phase data of the measured object; and acquiring the height data of the measured object according to the phase data of the measured object by utilizing the pre-established object phase-height mapping relation, thereby obtaining the point cloud data of the surface of the measured object.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the invention, through selecting the wave band of the light source (adopting an illumination projection system based on an ultraviolet light source to carry out projection imaging on the object to be measured), the high-temperature molten object can be accurately imaged in the laser process, and after a modulated image of the surface of the object is obtained, the modulated image is modulated and demodulated to obtain the truncation phase information of the object to be measured; the method comprises the steps of obtaining phase information of a measured object with small error by adopting a phase expansion method along a time axis, obtaining height data of the measured object according to the phase data of the measured object by utilizing a pre-established phase-height mapping relation, and obtaining three-dimensional point cloud data of the surface of the measured object, so that the morphology and geometric dimension state and the structure quality condition of the current state of the surface of the measured object can be visually obtained in the laser processing process.
2. An even light rod structure is arranged at an ultraviolet light source in the Korea illumination projection system, so that the illumination brightness of the light source is improved, and the imaging precision of a measured object is further ensured.
3. The Kolla illumination projection system of the ultraviolet illumination light source provided by the invention adopts the grating with 4 lines per millimeter, and the measurement stability is improved while the measurement precision is ensured.
Drawings
FIG. 1 is a flow chart of the dynamic measurement method for the surface topography of a high-temperature molten metal according to the present invention;
FIG. 2 is a schematic diagram of the dynamic measuring apparatus for the surface topography of the high-temperature molten metal according to the present invention (data processing module not shown);
FIG. 3a shows an ultraviolet LED source (LED array) in accordance with an exemplary embodiment of the present invention;
FIG. 3b shows a schematic view of the position of an LED array and a light bar according to an exemplary embodiment of the present invention;
FIG. 3c shows a schematic ray propagation of an LED array in an integrator rod according to an exemplary embodiment of the present invention;
FIG. 3d is a schematic diagram showing a simulation of the intensity of an LED array on a dodging rod according to an exemplary embodiment of the present invention;
FIG. 4 is a schematic diagram of the truncated phase calculation process of the modulation image according to the present invention;
FIG. 5 is a schematic diagram of using spatial phase unwrapping;
fig. 6 is a schematic diagram employing phase unwrapping along the time axis.
Detailed Description
The present invention will be described in further detail with reference to test examples and specific embodiments. It should be understood that the scope of the above-described subject matter is not limited to the following examples, and any techniques implemented based on the disclosure of the present invention are within the scope of the present invention.
Example 1
FIG. 1 shows a dynamic measurement method of the surface topography of a high-temperature molten metal according to an exemplary embodiment of the present invention, which comprises the following steps:
s1: projecting a standard stripe image to the surface of a measured object by adopting an illumination projection system based on an ultraviolet light source, and acquiring a modulation image on the surface of the measured object in real time;
s2: performing three-dimensional Fourier transform on the modulation image, filtering according to the fundamental frequency spectrum information corresponding to the modulation image to obtain a surface shape modulation spectrum of the object, and acquiring truncated phase data of the modulation image through three-dimensional inverse Fourier transform;
s3: based on the truncated phase data of the modulation image and based on the initial value state of space phase expansion, performing phase expansion on the subsequent truncated phase by using the continuity relation of the phase on the time axis to obtain the phase data of the measured object;
s4: and acquiring the height data of the measured object according to the phase data of the measured object by utilizing the pre-established object phase-height mapping relation, thereby obtaining the point cloud data of the surface of the measured object.
Specifically, as shown in fig. 1 and 2, the dynamic measurement method for the surface topography of the high-temperature molten metal provided by the invention projects a standard fringe image to the surface of a measured object by using a kovar illumination projection system equipped with an ultraviolet light source, and shoots a modulation image formed on the surface of the measured object by using an imaging camera. Koala lighting is an imaging system that becomes parallel light through a point source and then focuses through a grating, and when the focus position coincides with the focal point of a lens, the lens projects the image of the grating into space. In the implementation, the point light source of the ultraviolet light illumination in the Korea illumination projection system can be an LED light source, a laser light source or other ultraviolet light generators generating point illumination, in the embodiment, a 320nm central wavelength illumination light source is adopted, wherein the laser light source is arranged on the heat dissipation sheet, and the fixation and natural heat dissipation of the light source are realized; the collimating lens converts a point light source into parallel light, and aims to realize vertical illumination on the grating sheet and realize the irradiation of single light on each point of the grating surface, thereby obtaining a clear grating image; the grating is a line etched on the glass, the line is uniformly distributed on the glass, the grating lines adopt different frequencies according to projection requirements, such as 2 lines per millimeter, 4 lines per millimeter, 6 lines per millimeter and the like, the denser the grating lines are, the higher the resolution of projection optical information on the surface of a measured object is, the higher the measurement precision is realized, but meanwhile, the denser the grating lines are, the worse the signal-to-noise ratio under the same noise condition is, the measurement stability is reduced, and the implementation scheme preferably adopts a 4-line grating per millimeter; the imaging lens aims to project a grating image in a reverse direction through an optical system, and a virtual image is changed into an actual shadow on the surface of an object, so that the object surface is modulated through the image of a uniform grating.
Furthermore, in actual measurement, due to the influence of ambient light and the like, the independent LED light source structure adopted by the koala lighting projection system has the defect of insufficient brightness, and if a plurality of LED lamp beads are adopted for direct lighting, the requirement of a point light source of koala lighting imaging can not be met. Therefore, the LED array is increased in intensity by the dodging bar (in this embodiment, the size of the dodging bar is 50mm x 150 mm) through continuous reflection and refraction, and the final high-brightness point light source is obtained. Fig. 3a shows an ultraviolet LED source (preferably an LED array consisting of 55 LED lamps according to the brightness simulation test result) according to an exemplary embodiment of the present invention, fig. 3b shows a schematic diagram of the LED array and the position of the light-homogenizing rod according to an exemplary embodiment of the present invention, fig. 3c shows a schematic diagram of the light propagation of the LED array according to an exemplary embodiment of the present invention in the light-homogenizing rod, and further, fig. 3d shows a schematic diagram of the light intensity simulation of the LED array according to an exemplary embodiment of the present invention in the light-homogenizing rod (the ordinate is the light intensity, the abscissa is the distance, and the distance unit is mm).
As shown in fig. 4, in step S2, the method for dynamically measuring the surface topography of a high-temperature molten metal according to the present invention performs three-dimensional fourier transform on a dynamic deformation fringe image acquired by an imaging camera in real time, filters fundamental frequency spectrum information corresponding to a deformation fringe caused by the height of the surface of an object to be measured, and removes other spectrum information except the fundamental frequency, thereby obtaining a modulation spectrum of the surface topography of the object, and then obtains truncated phase data of a sequence image through three-dimensional inverse fourier transform for phase expansion in step S3.
The invention relates to a dynamic measuring method for the surface topography of high-temperature molten metal, in step S3, because the phase value obtained by the inverse tangent operation of the truncated phase obtained after the inverse Fourier transform is truncated
In this way, the phase unwrapping must be performed to obtain a true continuous phase value, so that the unique phase value corresponding to the three-dimensional geometric data calculation can be realized.
As shown in FIG. 5 (the abscissa is the number of stripes and the ordinate is the phase value), wherein (a) in FIG. 5 is a diagram of periodic truncated phases, the truncated phase of each period is truncated from- π to- π due to the arctan function
However, the phase unwrapping algorithm cannot be periodic, so the phase unwrapping is performed by adding the truncated phase of the first period
Or subtract from
To obtain the firstThe phase of the cycle, and thus the corresponding spatial phase development (b) in fig. 5. The spatial phase expansion is to compare the truncated phase values of two adjacent pixel points one by one along the row direction or the column direction of the phase data matrix, if the difference value between the two is greater than
Then the phase value of the latter point is decreased
(ii) a If the difference is less than
Then the phase value of the next point is added
So that the phase difference between adjacent points is in
Within.
In contrast, as shown in fig. 6, in the three-dimensional space-time truncated phase development, a set of phase maps along the time axis forms a phase distribution in a three-dimensional space. When no noise and boundary exist, the correct continuous phase can be obtained by spreading along any three-dimensional path; when noise and boundary exist, the phase expansion along the time axis (such as P to P') is obviously better than the spatial phase expansion method, because the error propagation problem (such as P to Q) caused by jump, boundary and noise can be avoided.
Therefore, aiming at the high noise condition of the welding environment of the molten pool, a space-time combination phase expansion method of three-dimensional space-time combination is adopted, and the phase expansion of the subsequent truncation phase is carried out by utilizing the continuity relation of the phase on the time axis on the basis of the initial value state of the space phase expansion. Namely:
assuming a truncated phase for each of the modulated images after measurement
At the same point
The phase difference of two time-adjacent modulation images and
multiple of
；
If the time before and after
Less than 1, the phase difference in the space truncation phase unwrapping process at the later moment cannot be obtained
Otherwise, deleting the point as an unreliable unwrapped phase point.
The invention discloses a dynamic measurement method for the surface morphology of a high-temperature molten metal, which comprises the following steps of obtaining an implicit phase-height mapping method based on the geometric imaging principle after phase expansion in step S4, establishing an object phase-height mapping relation with higher precision according to calibration parameters, wherein the height-phase mapping relation based on quadratic fitting is as follows:
wherein,
is the coordinates of the image of the camera,
planes representing known positions in the measurement space corresponding to each pixel point on the imageThe height difference of the point above with respect to the reference plane,
is the phase difference of the corresponding point,
and reflecting the mapping coefficient between the phase difference and the height difference of each point on the reference plane relative to the reference plane for calibrating the parameters.
FIG. 2 shows a high-temperature molten metal surface topography dynamic measurement apparatus according to an exemplary embodiment of the present invention, which comprises:
the Korea illumination projection system is used for projecting a standard fringe image to the surface of a measured object;
the imaging camera is used for shooting a modulation image formed on the surface of the measured object;
the data processing module is used for carrying out three-dimensional Fourier transform on the modulation image, filtering according to the base frequency spectrum information corresponding to the modulation image to obtain an object surface shape modulation spectrum, and obtaining truncated phase data of the modulation image through three-dimensional inverse Fourier transform; based on the truncated phase data of the modulation image and based on the initial value state of space phase expansion, performing phase expansion on the subsequent truncated phase by using the continuity relation of the phase on the time axis; and establishing a height-phase mapping relation of the surface of the measured object according to the calibration parameters, and acquiring point cloud data of the surface of the measured object according to the height-phase mapping relation.
In another aspect of the present invention, a computer storage medium is further provided, wherein the computer storage medium stores program instructions, and the program instructions are executed to implement the method for dynamically measuring the surface topography of a high-temperature molten metal according to the present invention.
It should be understood that the disclosed system may be implemented in other ways. For example, the division of the modules into only one logical function may be implemented in another way, for example, multiple units or components may be combined or integrated into another system, or some features may be omitted, or not implemented. In addition, the communication connection between the modules may be an indirect coupling or communication connection through some interfaces, devices or units, and may be electrical or in other forms.
In addition, functional modules in the embodiments of the present invention may be integrated into one processing unit, or each module may exist alone physically, or two or more modules are integrated into one processing unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.
The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a removable hard disk, a magnetic or optical disk, and other various media capable of storing program codes.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (7)
1. A dynamic measurement method for the surface topography of high-temperature molten metal is characterized by comprising the following steps:
s1: projecting a standard stripe image to the surface of a measured object by adopting an illumination projection system based on an ultraviolet light source, and acquiring a modulation image on the surface of the measured object in real time;
s2: performing three-dimensional Fourier transform on the modulation image, filtering according to the fundamental frequency spectrum information corresponding to the modulation image to obtain a surface shape modulation spectrum of the object, and acquiring truncated phase data of the modulation image through three-dimensional inverse Fourier transform;
s3: based on the truncated phase data of the modulation image and based on the initial value state of space phase expansion, performing phase expansion on the subsequent truncated phase by using the continuity relation of the phase on the time axis to obtain the phase data of the measured object;
s4: acquiring height data of the measured object according to the phase data of the measured object by using a pre-established object phase-height mapping relation, thereby obtaining point cloud data of the surface of the measured object;
wherein, in the step S3, the coordinate of the t-th modulation image after measurement is set
At a truncated phase of
For the same coordinate
Calculating the phase difference of two adjacent modulation images
Multiple of (2):
wherein,
for the t-1 th modulation image in coordinates
The phase of the truncation of (a) is,
the phase difference of two adjacent modulation images is obtained;
is a multiple; if the phase difference of the front and rear two modulated images
If < 1, the phase unwrapping process at the next moment in space truncation cannot be differed
To reliably spread the phase points, or vice versa, if
And if the sum of the sums of the sum of the sums of the sum of the sums of the sum of the sums of the sum of the sums.
2. The method according to claim 1, wherein the object phase-height mapping relationship is established according to different calibration parameters, and is:
wherein,
is the coordinates of the image of the camera,
point phases on a plane representing known positions in the measurement space corresponding to each pixel point on the imageAs for the height difference of the reference plane,
is the phase difference of the corresponding point, wherein,
the method is used for calibrating parameters and is used for representing the mapping coefficient between the phase difference and the height difference of each point on the reference plane relative to the reference plane.
3. The method for dynamically measuring the surface topography of a high temperature molten metal according to claim 1 or 2, wherein said uv light source based illumination projection system is a kola illumination projection system configured with a uv light source.
4. The method of claim 3, wherein said Kovar illumination projection system further comprises: and the light homogenizing rod structure is connected with the ultraviolet light source.
5. A method as claimed in claim 3, wherein said kovar illumination projection system uses a grating of 4 lines per mm.
6. The method of claim 3, wherein said Kovar illumination projection system employs an illumination source with a central wavelength of 320 nm.
7. A dynamic measuring device for the surface topography of high-temperature molten metal is characterized by comprising:
the illumination projection system based on the ultraviolet light source is used for projecting a standard stripe image to the surface of a measured object;
the imaging camera is used for shooting a modulation image formed on the surface of the measured object;
the data processing module is used for carrying out three-dimensional Fourier transform on the modulation image, filtering according to the base frequency spectrum information corresponding to the modulation image to obtain a surface shape modulation spectrum of the object, and obtaining truncation phase data of the modulation image through three-dimensional inverse Fourier transform; based on the truncated phase data of the modulation image and based on the initial value state of space phase expansion, performing phase expansion on the subsequent truncated phase by using the continuity relation of the phase on the time axis to obtain the phase data of the measured object; acquiring height data of the measured object according to the phase data of the measured object by utilizing a pre-established object phase-height mapping relation, thereby obtaining point cloud data of the surface of the measured object;
wherein, the phase unwrapping of the subsequent truncated phases using the continuity of the phases on the time axis comprises: setting the coordinate of the measured t-th modulation image
At a truncated phase of
For the same coordinate
Calculating the phase difference of two adjacent modulation images
Multiple of (2):
wherein,
for the t-1 th modulation image in coordinates
The phase of the truncation of (a) is,
the phase difference of two adjacent modulation images is obtained;
is a multiple; if the phase difference of the front and rear two modulated images
If < 1, the phase unwrapping process at the next moment in space truncation cannot be differed
To reliably spread the phase points, or vice versa, if
And if the sum of the sums of the sum of the sums of the sum of the sums of the sum of the sums of the sum of the sums.
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