Object weighing method and device based on laser speckle interference

Abstract

The invention relates to an object weighing method and device based on laser speckle interference. The method comprises the following steps: placing a measured object on an elastic body; speckle images of the measuring surface of the elastomer before and after the measured object is placed are collected; based on a laser speckle interference principle, analyzing and processing the speckle image to obtain a speckle image difference value before and after the deformation of the measurement surface, forming a phase fringe pattern, and obtaining a phase reflecting the optical path difference change caused by the deformation of the measurement surface through phase unwrapping; establishing a corresponding relation between the phase and the weight of the object by adopting a calibration method; solving the weight of the measured object based on the corresponding relation; and the measuring surface is not the surface of the elastic body for supporting the measured object. The technical problems that an existing weight detection scheme is limited in precision, stability and environmental adaptability, and non-contact and high-precision measurement in extreme environments or special occasions such as high-temperature and high-humidity environments is difficult to achieve are solved.

Description

Technical Field

[0001] This invention relates to the field of weight measurement technology, and in particular to a method and apparatus for weighing objects based on laser speckle interferometry. Background Technology

[0002] Existing weighing measurement methods mainly rely on sensing technologies such as resistance strain gauges and adopt contact weighing methods, which have bottlenecks in terms of accuracy, stability and environmental adaptability.

[0003] Laser speckle interferometry is an optical measurement technique based on the laser speckle phenomenon. It utilizes the high coherence and monochromaticity of laser light to analyze changes in the speckle pattern formed by scattered light from an object's surface, thereby obtaining information about physical quantities such as displacement, strain, and vibration. Laser speckle interferometry is a highly sensitive, non-contact, full-field measurement technique that can detect minute deformations / strains with sub-micron / nanometer sensitivity without direct contact with the object being measured.

[0004] There are currently no reports of using laser speckle interferometry for non-contact weighing measurement. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method and apparatus for weighing objects based on laser speckle interferometry, which solves the technical problems of existing weight detection schemes having limitations in accuracy, stability, and environmental adaptability, making it difficult to achieve non-contact, high-precision measurement in extreme environments or special occasions such as high temperature and high humidity environments.

[0006] The technical solution adopted in this invention is as follows: This invention provides a method for weighing objects based on laser speckle interferometry, comprising: Place the object to be tested on an elastic body; Acquire speckle images of the measurement surface of the elastic body before and after placing the object under test; Based on the principle of laser speckle interferometry, the speckle image is analyzed and processed to obtain the difference in speckle patterns before and after the deformation of the measurement surface, forming a phase fringe pattern. The phase reflecting the change in optical path difference caused by the deformation of the measurement surface is obtained by unwrapping the phase. The correspondence between the phase and the object weight is established using a calibration method; Based on the aforementioned correspondence, the weight of the object being measured is determined. The measuring surface is not the surface of the elastic body used to support the object being measured.

[0007] The further technical solution is as follows: The step of establishing the correspondence between the phase and the object weight using a calibration method includes: A stage is placed on the elastomer, and standard weights of different weights are placed on the stage. Speckle images of the measurement surface of the elastomer were collected before and after each standard weight was placed. Based on the principle of laser speckle interference, the phase is obtained from the speckle image; Establish a mapping relationship between the phase and the corresponding standard weight.

[0008] The step of establishing a mapping relationship between the phase and the corresponding standard weight includes: obtaining a mapping relationship function using a fitting algorithm.

[0009] The elastic body is a metal beam or column structure.

[0010] The measuring surface is perpendicular to the surface of the elastic body that supports the object being measured.

[0011] The ambient temperature range during the weighing process is 0~100℃.

[0012] The ambient humidity range during the weighing process is 30%RH~70%RH.

[0013] Placing the object to be tested on the elastic body includes: A stage is placed on the elastomer, and the object to be tested is placed on the stage.

[0014] The present invention also provides a weighing device utilizing the aforementioned object weighing method based on laser speckle interferometry, comprising a measurement module and a calculation module; The measurement module includes an elastic body, a stage, a laser, a beam splitter, a first reflector, a second reflector, and a camera. The beam splitter splits the laser emitted by the laser into two object beams. The two object beams are respectively illuminated onto the measurement surface of the elastic body by the first and second reflectors. The two object beams are symmetrical about the normal to the measurement surface, and the angles between them and the normal are the same. The measurement surface scatters the two object beams, and the scattered light interferes at the target surface of the camera, forming a speckle image that is captured by the camera. The calculation module is used to obtain the phase based on the speckle images of the measurement surface before and after the object is placed, captured by the camera, and to calculate the weight of the object based on the correspondence between the phase and the object's weight.

[0015] The measuring surface is located in the XY plane, and the camera lens axis is aligned with the Z-axis.

[0016] The beneficial effects of this invention are as follows: (1) Based on laser speckle interferometry, this invention utilizes the characteristics of non-contact measurement, high precision and high resolution, full-field measurement and real-time performance to achieve long-distance, maintenance-free, high-resolution weight detection, breaking through the bottlenecks of traditional contact weighing technology in terms of accuracy, stability and environmental adaptability. It also provides a brand-new precise measurement solution for extreme environments or special occasions such as high temperature and high humidity environments.

[0017] (2) The present invention establishes the correspondence between the phase reflecting the change of optical path difference caused by the deformation of the measuring surface and the weight of the object being measured by a calibration method. After obtaining the phase by using laser speckle interferometry, the corresponding gravity measurement value is obtained by directly solving the corresponding mapping function relationship, which has high calculation efficiency.

[0018] (3) The present invention uses laser interferometry to measure weight, which is a non-contact measurement method and eliminates the influence of environmental factors in weight measurement.

[0019] Other features and advantages of the invention will be set forth in the following description or may be learned by practicing the invention. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating Embodiment 2 of the present invention.

[0021] Figure 2 This is a schematic diagram of the laser speckle interferometry measurement principle of the weighing device in Embodiment 1 of the present invention.

[0022] Figure 3 This is a schematic diagram of the placement structure of the object under test in Embodiment 1 of the present invention.

[0023] Figure 4 This is the phase variation relationship with weight in the calibration and fitting example of Embodiment 2 of the present invention.

[0024] Figure 5 This is the processing result of the phase fringe pattern of the measured object in the second example of the present invention.

[0025] In the diagram: 1. Elastic body; 2. Laser; 3. Beam splitter; 4. Mirror 1; 5. Mirror 2; 6. Camera; 7. Object under test; 8. Stage; 101. Measuring surface. Detailed Implementation

[0026] The specific embodiments of the present invention are described below with reference to the accompanying drawings. Embodiment 1:

[0027] See Figure 2 and Figure 3 This embodiment of an object weighing device based on laser speckle interferometry includes a measurement module and a calculation module; The measurement module includes an elastic body 1, a stage 8, a laser 2, a beam splitter 3, a first reflector 4, a second reflector 5, and a camera 6. The stage 8 is placed on the upper surface of the elastic body 1, and the object to be measured 7 is placed on the upper surface of the stage 8. The beam splitter 3 splits the laser emitted from the laser 2 into two beams. The two beams are respectively reflected by the first reflector 4 and the second reflector 5 onto the measurement surface 101 of the elastic body 1. The two beams are symmetrical about the normal to the measurement surface 101, and the angle between the two beams and the normal is... α The same applies; the measuring surface 101 scatters the two beams of object light, and the scattered light interferes at the target surface of the camera 6, forming a speckle image that is captured by the camera 6. The calculation module is used to obtain the in-plane strain field of the measurement surface 101 based on the speckle images of the measurement surface 101 before and after the object under test 7 is placed, acquired by the camera 6, and to calculate the weight of the object under test 7.

[0028] As a preferred method, the measurement surface is located in the XY plane, and the camera lens axis is aligned with the Z-axis.

[0029] The elastomer, a common elastic element in existing weighing sensors, forms the sensor's framework and is typically made of high-strength alloy steel or aluminum alloy, with an S-shaped, cantilever beam, or disc-like structure. Its core capability is "micro-deformation under force"; when an object is pressed down, the elastomer undergoes extremely minute deformation (usually only a few micrometers) like a spring. This design accurately transmits the direction of pressure, avoiding interference from lateral forces on the data. In this embodiment, the elastomer is preferably a metal beam or column structure.

[0030] The weighing device in this embodiment, based on laser speckle interferometry, utilizes non-contact measurement, high precision and high resolution, full-field measurement, and real-time capabilities to achieve long-distance, maintenance-free, high-resolution weight detection, overcoming the bottlenecks of traditional contact weighing technology in terms of accuracy, stability, and environmental adaptability. It also provides a novel measurement solution for extreme environments or special occasions such as high-temperature and high-humidity environments.

[0031] Example 2:

[0032] See Figure 1 This embodiment of the method for weighing an object using the weighing device described in Embodiment 1 includes: S1. Place the object to be tested on the elastic body; S2. Acquire speckle images of the measurement surface of the elastic body before and after placing the object under test; S3. Based on the principle of laser speckle interferometry, the speckle image is analyzed and processed to obtain the difference in speckle patterns before and after the deformation of the measurement surface, forming a phase fringe pattern. The phase reflecting the change in optical path difference caused by the deformation of the measurement surface is obtained by unwrapping the phase. S4. Establish the correspondence between the phase and the object weight using a calibration method; S5. Based on the aforementioned correspondence, calculate the weight of the object being measured; The measuring surface is not the surface of the elastic body used to support the object being measured.

[0033] As a preferred method, during the weighing process in this embodiment, the ambient temperature is preferably 0~100 ℃; the ambient humidity is preferably 30 %RH~70 %RH.

[0034] Specifically, the weight range of the object being measured is from grams to tons, meaning that the weighing method in this embodiment can achieve a wide range of measurements.

[0035] Specifically, in step S1, a stage is placed on the elastomer, and the object to be tested is placed on the stage. A suitable elastomer material is selected, and a reasonable elastomer structure is designed to give the elastomer good elastic properties and stability. During use, the elastomer is placed on a stable support platform.

[0036] Specifically, in S2, a laser assembly and camera are positioned at appropriate locations around the elastomer, and the wavelength, power, and other parameters of the laser are adjusted to ensure uniform illumination of the elastomer's measurement surface. The positions of the laser assembly and camera, as well as the parameter settings of the laser source, should be optimized based on the elastomer material and weighing requirements.

[0037] The object under test is placed on an elastic body, causing in-plane deformation of the measurement surface and resulting in a change in the surface speckle field. A camera acquires speckle images of the measurement surface before and after the in-plane deformation. The camera then acquires the changed speckle images in real time and transmits the image data to a computer. The acquired image data should have sufficient resolution and sharpness for subsequent image processing and analysis.

[0038] Specifically, in S3, based on the principle of laser speckle interferometry, the speckle image is analyzed and processed to obtain the difference in speckle patterns before and after the deformation of the measurement surface, forming a phase fringe pattern. The phase is obtained by unwrapping the phase, based on the following principle: The speckle image of the light intensity distribution of the measured surface is acquired before the object is placed on it, i.e., before the surface deforms. I 1( x , y )for: In the formula, x , y These are the coordinates of the camera target surface in the x and y directions, respectively. I o1 , I o2 The light intensity distributions of the two beams are shown below. φ The phase difference between the two beams; After the object to be measured is placed, the surface being measured deforms, and a speckle image of the light intensity distribution on the measured surface is acquired. I 2( x , y )for: In the formula, the phase difference Δ = Δ1 - Δ2, where Δ1 and Δ2 are the phase changes of the two beams of object light caused by the deformation of the measurement surface, respectively. When the measurement surface is in the XY plane, the laser source is in the XZ plane, and the camera is on the Z-axis, the calculation formulas for △1 and △2 are as follows:

[0039] in, α like Figure 2 As shown, this represents the angle between the object beam and the camera's viewing direction. λ Represents the laser wavelength. w Represents the out-of-plane direction of the measurement surface. u The amount of horizontal deformation within the measurement plane.

[0040] Therefore, the phase difference Δ depends only on the horizontal deformation u within the measurement plane, and we can obtain:

[0041] Similarly, when the measuring surface is in the XY plane, the laser source is in the YZ plane, and the camera is on the Z-axis, the formulas for calculating △1 and △2 are as follows:

[0042] In the formula, v The amount of vertical deformation within the measurement plane.

[0043] Therefore, the phase difference Δ is only related to the vertical deformation within the measurement plane. v Regarding this, we can obtain:

[0044] Based on the two phase differences Δ mentioned above, the phase that reflects the change in optical path difference caused by the measured deformation is obtained.

[0045] Specifically, digital processing techniques can be used to solve the phase diagram: The contrast of interference fringes is enhanced by real-time subtraction or addition processing using a computer. Extract the wrapped phase (range [0, 2π)) from the stripe pattern, and then expand it into a continuous phase using the least squares method or the quality map guided algorithm.

[0046] As a preferred embodiment, in step S4, establishing the correspondence between the phase and the object weight using a calibration method includes: S41. Place a stage on the elastic body, and place standard weights of different weights on the stage; S42. Collect speckle images of the measuring surface of the elastic body before and after each standard weight is placed; S43. Based on the principle of laser speckle interference, a phase fringe pattern is obtained from the speckle image, and then the phase is obtained; S44. Establish a mapping relationship between the phase and the corresponding weight of the weight, preferably by using a fitting algorithm to obtain the mapping relationship function.

[0047] Different weights of the object being measured cause different in-plane deformations of the elastic body, and the weight to be measured can be calculated from the phase.

[0048] To further illustrate the beneficial effects of this solution, the weighing method of this embodiment will be further explained below with specific examples.

[0049] In this example, the elastomer is made of aluminum alloy. The calibration establishes the correspondence between the phase of the elastomer's measurement surface before and after deformation and the object's weight. During calibration, the elastomer's measurement surface is located in the XY plane, and the camera is positioned along the Z-axis. A fitting algorithm is used to obtain the mapping function, and the correspondence is as follows: Figure 4 As shown, the expression is as follows:

[0050] In the formula, x For weight, f ( x ( ) represents the phase, and the fitted R value is 0.9999. This linear relationship is a very good match, verifying the effectiveness of speckle interferometry for weight measurement.

[0051] Using a 20g standard weight as the object to be measured, firstly, during the processing of the phase fringe pattern of the object, the fringe area in the pattern is cropped for further processing. The resulting phase fringe pattern is shown below. Figure 5 As shown in (a); the sine and cosine mean filtering method is used to obtain the following result. Figure 5 The filtered phase fringe pattern is shown in (b); the unwrapped phase is obtained using an unwrapping algorithm, as shown in (b). Figure 5 As shown in (c), based on the aforementioned phase-weight mapping function, the weight is calculated to be 20.0001g by determining the phase after unwrapping. Finally, the weight of the object being measured is obtained as 20.002g using a conventional weighing sensor (or other methods). It can be seen that the weighing method used in this application yields a higher accuracy.

[0052] It will be understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for weighing objects based on laser speckle interferometry, characterized in that, include: Place the object to be tested on an elastic body; Acquire speckle images of the measurement surface of the elastomer before and after placing the object under test; Based on the principle of laser speckle interferometry, the speckle image is analyzed and processed to obtain the difference in speckle patterns before and after the deformation of the measurement surface, forming a phase fringe pattern. The phase reflecting the change in optical path difference caused by the deformation of the measurement surface is obtained by unwrapping the phase. The correspondence between the phase and the object weight is established using a calibration method; Based on the aforementioned correspondence, the weight of the object being measured is determined. The measuring surface is not the surface of the elastic body used to support the object being measured.

2. The object weighing method based on laser speckle interferometry according to claim 1, characterized in that, The step of establishing the correspondence between the phase and the object weight using a calibration method includes: A stage is placed on the elastomer, and standard weights of different weights are placed on the stage. Speckle images of the measurement surface of the elastomer were collected before and after each standard weight was placed. Based on the principle of laser speckle interference, the phase is obtained from the speckle image; Establish a mapping relationship between the phase and the corresponding standard weight.

3. The object weighing method based on laser speckle interferometry according to claim 2, characterized in that, The step of establishing a mapping relationship between the phase and the corresponding standard weight includes: obtaining a mapping relationship function using a fitting algorithm.

4. The object weighing method based on laser speckle interferometry according to claim 1, characterized in that, The elastic body is a metal beam or column structure.

5. The object weighing method based on laser speckle interferometry according to claim 1, characterized in that, The measuring surface is perpendicular to the surface of the elastic body that supports the object being measured.

6. The object weighing method based on laser speckle interferometry according to claim 1, characterized in that, The ambient temperature range during the weighing process is 0~100℃.

7. The object weighing method based on laser speckle interferometry according to claim 1, characterized in that, The ambient humidity range during the weighing process is 30%RH ~ 70%RH.

8. The object weighing method based on laser speckle interferometry according to claim 1, characterized in that, Placing the object to be tested on the elastic body includes: A stage is placed on the elastomer, and the object to be tested is placed on the stage.

9. A weighing device utilizing the object weighing method based on laser speckle interferometry as described in any one of claims 1 to 8, characterized in that, Includes a measurement module and a calculation module; The measurement module includes an elastic body, a stage, a laser, a beam splitter, a first reflector, a second reflector, and a camera. The beam splitter splits the laser emitted by the laser into two object beams. The two object beams are respectively illuminated onto the measurement surface of the elastic body by the first and second reflectors. The two object beams are symmetrical about the normal to the measurement surface, and the angles between them and the normal are the same. The measurement surface scatters the two object beams, and the scattered light interferes at the target surface of the camera, forming a speckle image that is captured by the camera. The calculation module is used to obtain the phase based on the speckle images of the measurement surface before and after the object is placed, captured by the camera, and to calculate the weight of the object based on the correspondence between the phase and the object's weight.

10. The weighing device according to claim 9, characterized in that, The measuring surface is located in the XY plane, and the camera lens axis is aligned with the Z-axis.

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