Phase shift in-situ calibration method and system for speckle interference technology

Abstract

The invention relates to a phase shift in-situ calibration method and system for a speckle interference technology. The speckle interference system is built based on the speckle interference technology, and the system extracts the phase through the phase shift technology. A reference speckle interferogram is collected through the system, the input value of a phase shifter in the system is changed, different phase shifts are introduced step by step, and a plurality of speckle interferograms after phase shift are collected. And performing subtraction operation on the plurality of phase-shifted speckle interferograms and the reference speckle interferogram to obtain a plurality of speckle interference fringe patterns. And according to the relative movement distance between the fringe skeletons of the plurality of speckle interferograms, determining the respective corresponding phase shift amount. And according to the relationship between the input values of the phase shifters and the corresponding phase shift amounts, phase shift in-situ calibration is realized.

Description

Technical Field

[0001] The present disclosure relates to the field of full-field non-contact optical measurement, and in particular to a phase shift in-situ calibration method and system for speckle interferometry technology. Background Art

[0002] Digital speckle interferometry is a full-field non-contact optical measurement technology. When combined with time phase shift technology, the measurement accuracy of this technology is significantly improved. Therefore, it is widely used in precision measurement application scenarios of small deformations and strains in aviation, aerospace, automobiles, machinery, materials and other fields.

[0003] Phase shifter is the core device in time phase shifting technology. Due to the piezoelectric effect of piezoelectric ceramic materials, when voltage is loaded on piezoelectric ceramics, piezoelectric ceramics will stretch and cause the optical elements attached to them to produce micro-displacement, thereby changing the optical path difference of the optical path and causing interference phase changes. Therefore, in digital speckle interferometry technology, piezoelectric ceramics are usually the core component of phase shifters. Piezoelectric ceramic materials also have nonlinear, hysteresis and bias characteristics, which will affect the accuracy of controlling phase shift and introduce phase shift errors. Therefore, before using the phase shifter, it is an essential process to calibrate it. Due to changes in temperature, environment and other factors, the calibrated data may become invalid, so the calibration data needs to be updated at any time to determine the relationship between the introduced phase amount and the driving voltage.

[0004] At present, there are many methods for phase shifter calibration, which can be divided into two categories: in-situ and ex-situ. The ex-situ method requires the phase shifter to be taken out of the measurement optical path for calibration. New errors may be introduced in the process of putting it back, and it is not suitable for integrated instruments. The in-situ method refers to calibration in the original measurement optical path without moving the phase shifter. This type of method can be divided into software and hardware. The hardware method refers to adding a calibration optical path on the basis of the measurement optical path, which makes the overall measurement system complicated. The software method refers to calibration through algorithms. Currently, there are frequency domain method, maximum correlation method, and mean square difference method. These methods have certain limitations: they are applicable to some regular or special stripes, but not to all types of stripes; the calibration is most accurate when it is an integer multiple of the phase period, and the calibration of any phase requires linear fitting for estimation, which is not applicable to nonlinear materials such as piezoelectric ceramics. Summary of the invention

[0005] In view of this, the present disclosure proposes a phase shift in-situ calibration method and system for speckle interferometry technology.

[0006] According to one aspect of the present disclosure, the phase shift in-situ calibration method for speckle interferometry technology includes:

[0007] Building a speckle interferometry system, wherein the speckle interferometry system uses a phase shifting technique to extract a phase;

[0008] According to the speckle interferometry system, collecting a reference speckle interferogram;

[0009] Changing the input value of the phase shifter in the speckle interferometer system, gradually introducing different phase shifts, and collecting multiple speckle interferograms after phase shifting;

[0010] Subtracting the multiple phase-shifted speckle interference patterns from a reference speckle interference pattern to obtain multiple speckle interference fringe patterns;

[0011] Determining the phase shift amounts corresponding to the respective ones according to the relative movement distances between the fringe skeletons of the plurality of speckle interference patterns;

[0012] According to the relationship between the input value of the phase shifter and the corresponding phase shift amount, the phase shift in-situ calibration is realized.

[0013] Optionally, the speckle interferometry system includes: a phase-shifting digital speckle interferometry system and a phase-shifting shearing speckle interferometry system.

[0014] Optionally, the phase shifter includes, but is not limited to, a device using piezoelectric ceramics as an actuator.

[0015] Optionally, performing a subtraction operation on the multiple phase-shifted speckle interferograms and a reference speckle interferogram comprises:

[0016] performing a direct subtraction operation on the plurality of phase-shifted speckle interferograms and a reference speckle interferogram;

[0017] or, performing a subtraction operation on the multiple phase-shifted speckle interferograms and a reference speckle interferogram, and then performing an absolute value operation;

[0018] Or, a subtraction operation is performed on the multiple phase-shifted speckle interferograms and a reference speckle interferogram, and then a square operation is performed.

[0019] Optionally, the relative movement distances between the fringe skeletons of the plurality of speckle interference patterns are used to determine the phase shifts corresponding to the respective ones, including:

[0020] Performing noise reduction processing on the multiple speckle interference fringe patterns to obtain multiple smooth speckle interference fringe patterns;

[0021] The noise reduction processing method includes but is not limited to frequency domain filtering, spatial domain filtering and other image processing methods that have the function of reducing speckle noise;

[0022] Performing image segmentation processing on the plurality of smoothed speckle interference fringe images to obtain a plurality of interference fringe binary images;

[0023] The image segmentation method includes but is not limited to the maximum inter-class variance, peak value, clustering and other image processing methods that have the function of segmenting the image into a binary image;

[0024] Performing skeleton extraction processing on the multiple interference fringe binary images to obtain multiple fringe skeleton images;

[0025] The skeleton extraction method includes but is not limited to deep learning, Zhang-Suen algorithm and other image processing methods that have the function of thinning stripes into single-pixel center lines;

[0026] Among the multiple fringe skeleton images, determining a fringe skeleton of any one of the fringe skeleton images as an initial fringe skeleton, and determining a fringe movement period and a starting position of the fringe skeleton according to the initial fringe skeleton;

[0027] The method of determining the stripe movement period is to select the distance between two adjacent stripe skeleton lines as the stripe movement period;

[0028] Comparing the stripe skeletons in the plurality of stripe skeleton images with the initial stripe skeleton, and determining the movement distance of the stripe skeletons in the plurality of stripe skeleton images relative to the initial stripe skeleton;

[0029] According to one aspect of the present disclosure, a phase shift in-situ calibration system for speckle interferometry technology comprises:

[0030] A fringe acquisition module is used to process the acquired speckle interference pattern to obtain a speckle interference fringe pattern;

[0031] A fringe filtering module, used for filtering and denoising the speckle interference fringe pattern to obtain a smooth speckle interference fringe pattern;

[0032] A fringe segmentation module is used to perform image segmentation processing on the smoothed speckle interference fringe pattern to obtain a binary interference fringe image;

[0033] A fringe skeleton extraction module is used to perform skeleton extraction processing on the interference fringe binary image to obtain a fringe skeleton image;

[0034] The phase shift calibration module is used to determine the relationship between the fringe movement distance and the phase shifter input value.

[0035] Other features and aspects of the present disclosure will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Various exemplary embodiments, features and aspects of the present disclosure will be described in detail below with reference to the accompanying drawings. The same reference numerals in the accompanying drawings represent elements with the same or similar functions. Although various aspects of the embodiments are shown in the accompanying drawings, the drawings need not be drawn to scale unless otherwise specified. The special word "exemplary" here means "used as an example, embodiment or illustrative". Any embodiment described here as "exemplary" is not necessarily interpreted as being superior to or better than other embodiments. In addition, in order to better illustrate the present disclosure, numerous specific details are given in the specific embodiments below. Those skilled in the art should understand that the present disclosure can also be implemented without certain specific details. In some instances, methods, means, components and circuits well known to those skilled in the art are not described in detail in order to highlight the main purpose of the present disclosure.

[0037] Figure 1 is a flow chart of a calibration method according to an embodiment of the present disclosure;

[0038] Figure 2 This is a phase-shifted shearing speckle interferometry optical path diagram of an embodiment of the present disclosure;

[0039] Figure 3 is a flow chart of the calibration steps of an embodiment of the present disclosure;

[0040] Figure 4 A module diagram of a calibration system according to an embodiment of the present disclosure;

[0041] The technical solution of the embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. DETAILED DESCRIPTION

[0042] Hereinafter, exemplary embodiments of the present application will be described in detail in conjunction with the accompanying drawings. For the sake of clarity and conciseness, not all features of the actual implementation are described in the specification. However, it should be understood that many implementation-specific decisions must be made in the process of developing any such actual implementation in order to achieve the developer's specific goals, such as meeting those constraints related to the system and business, and these constraints may vary from implementation to implementation. In addition, it should be understood that although the development work may be very complex and time-consuming, it is only a routine task for those skilled in the art who benefit from the present disclosure.

[0043] It is also necessary to explain here that, in order to avoid obscuring the present application due to unnecessary details, only the device structure and / or processing steps closely related to the scheme according to the present application are described in the drawings and descriptions, while the representation and description of components and processes that are not closely related to the present application and are known to ordinary technicians in the field are omitted.

[0044] The specific implementation methods of the present application are further described in detail below in conjunction with the accompanying drawings (the same reference numerals in several drawings represent the same elements) and embodiments. The following embodiments are used to illustrate the present application, but are not used to limit the scope of the present application.

[0045] Those skilled in the art will understand that the terms "first" and "second" in this application are only used to distinguish different steps, devices or modules, etc., and do not represent any specific technical meanings, nor do they indicate the necessary logical order between them.

[0046] The technical solutions of exemplary embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0047] Figure 1 The flowchart of a phase shift in-situ calibration method for speckle interferometry technology is a specific implementation example of the present disclosure. Figure 1 As shown, the phase shift in-situ calibration method for speckle interferometry technology provided in the embodiment of the present application includes:

[0048] S101: Building a speckle interferometry system, wherein the speckle interferometry system uses a phase shifting technique to extract a phase;

[0049] S102: collecting a reference speckle interferogram according to the speckle interferometry system;

[0050] S103: changing the input value of the phase shifter in the speckle interferometry system, gradually introducing different phase shifts, and collecting multiple speckle interferograms after phase shifting;

[0051] S104: performing a subtraction operation on the multiple phase-shifted speckle interferograms and a reference speckle interferogram to obtain multiple speckle interferograms;

[0052] S105: determining the corresponding phase shift amounts according to the relative movement distances between the fringe skeletons of the plurality of speckle interferograms;

[0053] S106: Implementing in-situ phase shift calibration according to the relationship between the input value of the phase shifter and the corresponding phase shift amount.

[0054] The theoretical basis and specific exemplary methods of a phase shift in-situ calibration method for speckle interferometry technology of the present application are further described below.

[0055] Figure 2 An optional example of a phase shift in-situ calibration method for speckle interferometry technology is provided for a specific implementation example of the present disclosure. Figure 2 In the optical path shown, 1 is a light source, 2 is a beam expander, 3 is an object to be measured, 4 is a plane mirror 1, 5 is a piezoelectric ceramic, 6 is a plane mirror 2, 7 is a beam splitter prism, 8 is an imaging lens, and 9 is a camera, where:

[0056] The beam expander expands the light emitted by the light source and irradiates it onto the surface of the object to be measured;

[0057] The light diffusely reflected from the surface of the object being measured is split by a beam splitter prism, and after being reflected by plane mirror 1 and plane mirror 2 respectively, it is converged into an imaging lens;

[0058] The image formed by the imaging lens and received by the camera is a speckle interference pattern;

[0059] The piezoelectric ceramic and the plane mirror 2 form a phase shifter device. The piezoelectric ceramic is driven by voltage to deform, which drives the plane mirror 2 to produce a micro displacement to introduce a phase.

[0060] The object under test is loaded to produce a micro deformation on its surface to introduce a phase.

[0061] Optionally, the speckle interferometry system includes: a phase-shift digital speckle interferometry system and a phase-shift shearing speckle interferometry system; wherein the phase-shift shearing speckle interferometry system is adopted in this example.

[0062] Optionally, the phase shifter includes but is not limited to: a device using piezoelectric ceramics as an actuator; wherein, in this example, a device using piezoelectric ceramics as an actuator is used. Figure 2 It is composed of 5 and 6.

[0063] according to Figure 2 In the middle optical path, the light intensity of the superposition of the two images on the image plane is:

[0064] I(x,y)=A(x,y){1+K(x,y)cos[φ x (x, y)]}

[0065] Where I is the light intensity of the two superimposed images, A is the background light intensity, K is the contrast, φ x The phase difference of the interference in the x direction is generated by driving the phase shifter or loading the object to be measured to produce a phase change Δφ x , and its speckle interference intensity is:

[0066] I′(x,y)=A(x,y){1+K(x,y)cos[φ x (x,y)+Δφ x (x, y)]}

[0067] Figure 3 Optional examples of calibration method steps provided in the embodiments of the present application include:

[0068] S301: performing a subtraction operation on the multiple phase-shifted speckle interferograms and a reference speckle interferogram to obtain multiple speckle interferograms;

[0069] Optionally, the subtraction operation includes: performing a direct subtraction operation on the multiple phase-shifted speckle interferograms and a reference speckle interferogram; or performing a subtraction operation on the multiple phase-shifted speckle interferograms and a reference speckle interferogram, and then performing an absolute value operation; or performing a subtraction operation on the multiple phase-shifted speckle interferograms and a reference speckle interferogram, and then performing a square operation;

[0070] In this embodiment, a subtraction operation is performed on the multiple phase-shifted speckle interferograms and the reference speckle interferogram, and then an absolute value operation is performed to obtain multiple speckle interferograms. The subtraction operation formula of this embodiment is as follows:

[0071]

[0072] S302: performing noise reduction processing on the multiple speckle interference fringe patterns to obtain multiple smooth speckle interference fringe patterns; optionally, the noise reduction processing method includes but is not limited to: image processing methods such as frequency domain filtering and spatial domain filtering that have the function of reducing speckle noise;

[0073] The noise reduction method used in this embodiment is the Butterworth low-pass filtering method in the frequency domain filtering.

[0074] The Butterworth filter has a smooth filter band, which can reduce the image blurring caused by the ideal filter. Speckle noise is a high-frequency noise. Therefore, in order to weaken the speckle noise and retain the clear boundaries of the stripes, this example uses a Butterworth low-pass filter with a better effect. Its transfer function is:

[0075]

[0076] in, represents the distance from the point (u, v) to the origin, D0 represents the distance from the cutoff frequency to the origin, and n represents the order of the filter. This example uses n as 3.

[0077] S303: performing image segmentation processing on the plurality of smoothed speckle interference fringe images to obtain a plurality of interference fringe binary images; optionally, the image segmentation method is an image processing method including but not limited to maximum inter-class variance, peak value, clustering, etc., which has the function of segmenting an image into a binary image;

[0078] In this embodiment, the maximum inter-class variance method is used to select the adaptive threshold and segment the image. The basic principle of the maximum inter-class variance method is as follows:

[0079] Assume that the number of image pixels is N, the grayscale value range is [0, L-1], and the number of pixels at each grayscale level i is n i , then the probability of each gray level is:

[0080]

[0081] Taking a certain gray value as the threshold T, the image is divided into two categories C0 and C1, where the gray value of the pixels in C0 is between [0, T], and the gray value of the pixels in C1 is between [T+1, L-1]. The mean value of the image is:

[0082]

[0083] The means of C0 and C1 are:

[0084]

[0085] in:

[0086]

[0087] The between-class variance is defined as:

[0088] σ 2 =w0(u0-u T ) 2 +w1(u1-u T ) 2

[0089] =w1w0(u0-u1) 2

[0090] Traverse T in [0, L-1] so that σ 2 When it is the largest, T is the optimal threshold, and then T is used as the threshold for image segmentation.

[0091] S304: Perform skeleton extraction processing on the multiple interference fringe binary images to obtain multiple fringe skeleton images; optionally, the skeleton extraction method is an image processing method including but not limited to deep learning, Zhang-Suen algorithm, etc., which has the function of refining fringes into single-pixel center lines.

[0092] Among them, the skeleton extraction method used in this embodiment is Zhang - Suen algorithm, the basic idea of ​​this method is to traverse all target pixels (value 1), and delete or retain them according to the conditions, and iterate repeatedly until all target pixels meet the retention conditions, so that the retained pixels constitute the skeleton line of the stripe. The conditions for deleting pixels are:

[0093]

[0094] and

[0095]

[0096] Where P1 is the pixel value of the target pixel (0 or 1), P2-P9 are the pixel values ​​of the eight neighboring pixels of the target pixel (0 or 1), A(P1) is the number of times it jumps from 0 to 1 on the route of traversing the neighboring points in a clockwise direction starting from P2. B(P1) is the number of pixels with a pixel value of 1 in the eight neighborhoods.

[0097] S305: Determine, among the multiple stripe skeleton images, a stripe skeleton of any one of the stripe skeleton images as an initial stripe skeleton, and determine a stripe movement period and a starting position of the stripe skeleton based on the initial stripe skeleton; wherein the stripe movement period is determined by selecting a distance between two adjacent stripe skeleton lines as the stripe movement period.

[0098] S306: Compare the stripe skeletons in the multiple stripe skeleton images with the initial stripe skeleton, determine the movement distance of the stripe skeletons in the multiple stripe skeleton images relative to the initial stripe skeleton, and obtain the stripe movement distance l and the phase change Δφ by the formula x Relationship:

[0099]

[0100] Among them, L T is the period of stripe movement.

[0101] Figure 4 Optional examples of the calibration system provided in the embodiments of the present application include:

[0102] The fringe acquisition module 401 is used to process the acquired speckle interference pattern, implement subtraction operation, and obtain the speckle interference fringe pattern;

[0103] The fringe filtering module 402 is used to filter and denoise the speckle interference fringe pattern to obtain a smooth speckle interference fringe pattern;

[0104] The fringe segmentation module 403 is used to perform image segmentation processing on the smoothed speckle interference fringe pattern to obtain an interference fringe binary image;

[0105] The fringe skeleton extraction module 404 is used to perform skeleton extraction processing on the interference fringe binary image to obtain a fringe skeleton image;

[0106] The phase shift calibration module 405 is used to determine the relationship between the fringe movement distance and the phase shifter input value.

[0107] The embodiment of the present disclosure also provides a computer-readable storage medium on which computer program instructions are stored, and the computer program instructions implement the above method when executed by a processor. The computer-readable storage medium can be a volatile or non-volatile computer-readable storage medium.

[0108] An embodiment of the present disclosure further proposes an electronic device, comprising: a processor; and a memory for storing instructions executable by the processor; wherein the processor is configured to implement the above method when executing the instructions stored in the memory.

[0109] The embodiments of the present disclosure also provide a computer program product, including a computer-readable code, or a non-volatile computer-readable storage medium carrying the computer-readable code. When the computer-readable code runs in a processor of an electronic device, the processor in the electronic device executes the above method.

[0110] The specific implementation of the present disclosure has been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A phase shift in-situ calibration method for speckle interferometry technology, characterized in that: include: Building a speckle interferometry system, wherein the speckle interferometry system uses a phase shifting technique to extract a phase; According to the speckle interferometry system, collecting a reference speckle interferogram; Changing the input value of the phase shifter in the speckle interferometer system, gradually introducing different phase shifts, and collecting multiple speckle interferograms after phase shifting; Subtracting the multiple phase-shifted speckle interference patterns from a reference speckle interference pattern to obtain multiple speckle interference fringe patterns; Determining the phase shift amounts corresponding to the respective ones according to the relative movement distances between the fringe skeletons of the plurality of speckle interference patterns; According to the relationship between the input value of the phase shifter and the corresponding phase shift amount, the phase shift in-situ calibration is realized.

2. The method according to claim 1, characterized in that The speckle interferometry system includes: a phase-shift digital speckle interferometry system and a phase-shift shearing speckle interferometry system.

3. The method according to claim 1, characterized in that The phase shifter includes, but is not limited to, a device using piezoelectric ceramics as an actuator.

4. The method according to claim 1, characterized in that The subtracting operation of the plurality of phase-shifted speckle interferograms from a reference speckle interferogram comprises: performing a direct subtraction operation on the plurality of phase-shifted speckle interferograms and a reference speckle interferogram; or, performing a subtraction operation on the multiple phase-shifted speckle interferograms and a reference speckle interferogram, and then performing an absolute value operation; Or, a subtraction operation is performed on the multiple phase-shifted speckle interferograms and a reference speckle interferogram, and then a square operation is performed.

5. The method according to claim 1, characterized in that include: Performing noise reduction processing on the multiple speckle interference fringe patterns to obtain multiple smooth speckle interference fringe patterns; Performing image segmentation processing on the plurality of smoothed speckle interference fringe images to obtain a plurality of interference fringe binary images; Performing skeleton extraction processing on the multiple interference fringe binary images to obtain multiple fringe skeleton images; In the multiple stripe skeleton images, the stripe skeleton of any one of the stripe skeleton images is determined to be the initial stripe skeleton, and the stripe movement period and the starting position of the stripe skeleton are determined based on the initial stripe skeleton; the stripe skeletons in the multiple stripe skeleton images are compared with the initial stripe skeleton to determine the movement distance of the stripe skeletons in the multiple stripe skeleton images relative to the initial stripe skeleton.

6. The method according to claim 5, characterized in that The noise reduction processing method includes but is not limited to frequency domain filtering, spatial domain filtering and other image processing methods that have the function of reducing speckle noise.

7. The method according to claim 5, characterized in that The image segmentation method includes but is not limited to the maximum inter-class variance, peak value, clustering and other image processing methods that have the function of segmenting the image into a binary image.

8. The method according to claim 5, characterized in that The skeleton extraction method includes but is not limited to deep learning, Zhang-Suen algorithm and other image processing methods that have the function of refining stripes into single-pixel center lines.

9. The method according to claim 5, characterized in that The method of determining the stripe movement period is to select the distance between two adjacent stripe skeleton lines as the stripe movement period.

10. A phase shift in-situ calibration system for speckle interferometry technology, characterized in that: The system comprises: A fringe acquisition module is used to process the acquired speckle interference pattern to obtain a speckle interference fringe pattern; A fringe filtering module, used for filtering and denoising the speckle interference fringe pattern to obtain a smooth speckle interference fringe pattern; A fringe segmentation module is used to perform image segmentation processing on the smoothed speckle interference fringe pattern to obtain a binary interference fringe image; A fringe skeleton extraction module is used to perform skeleton extraction processing on the interference fringe binary image to obtain a fringe skeleton image; The phase shift calibration module is used to determine the relationship between the fringe movement distance and the phase shifter input value.

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