Method and device for weighing an object based on laser speckle interferometry

Abstract

The present application relates to a kind of object weighing method and device based on laser speckle interference, comprising: the measured object is placed on elastomer;The speckle image of the measuring surface of the elastomer before and after the measured object is placed is collected;Based on the principle of laser speckle interference, the speckle image is analyzed and processed, the speckle graph difference value before and after the deformation of the measuring surface is obtained, phase fringe diagram is formed, and the phase reflecting the change of optical path difference caused by the deformation of measuring surface is obtained by phase unwrapping;Calibration method is used to establish the corresponding relationship between the phase and object weight;Based on the corresponding relationship, the weight of the measured object is solved;The measuring surface is not the surface of the elastomer for supporting the measured object.The present application solves the technical problems that the existing weight detection scheme has precision, stability and environmental adaptability limitations, and it is difficult to realize non-contact, high-precision measurement in extreme environment or special occasions such as high temperature and high humidity environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of weight measurement, in particular to a method and device for weighing an object based on laser speckle interference. BACKGROUND

[0002] The existing weighing measurement method mainly relies on sensing technology such as resistance strain gauge, and adopts a contact type weight measurement method, which has bottlenecks in precision, stability and environmental adaptability.

[0003] The laser speckle interference technology is an optical measurement technology based on laser speckle phenomenon, which uses the high coherence and monochromaticity of laser to analyze the change of speckle pattern formed by scattered light on the surface of an object, so as to obtain physical quantity information such as displacement, strain and vibration of the object surface. Laser speckle interference is a high-sensitivity, non-contact and full-field measurement technology, which can detect sub-micron / nanometer sensitivity of micro deformation / strain without direct contact with the measured object.

[0004] Currently, there is no report on non-contact weighing measurement using laser speckle interference technology. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a method and device for weighing an object based on laser speckle interference, which solves the technical problems of the existing weight detection scheme, such as precision, stability and environmental adaptability limitations, and difficulty in realizing non-contact and high-precision measurement in extreme environments or special occasions such as high temperature and high humidity environments.

[0006] The technical solution adopted by the present application is as follows:

[0007] The present application provides a method for weighing an object based on laser speckle interference, comprising:

[0008] Placing the measured object on an elastic body;

[0009] Collecting speckle images of the measurement surface of the elastic body before and after placing the measured object;

[0010] Based on the principle of laser speckle interference, analyzing and processing the speckle images to obtain the difference value of the speckle images before and after the deformation of the measurement surface, forming a phase fringe pattern, and obtaining the phase reflecting the change of optical path difference caused by the deformation of the measurement surface through phase unwrapping;

[0011] Establishing the corresponding relationship between the phase and the weight of the object by calibration method;

[0012] Solving the weight of the measured object based on the corresponding relationship;

[0013] The measurement surface is not the surface of the elastic body used to support the measured object.

[0014] Further technical solutions are provided.

[0015] The mapping relationship between the phase and the weight of the object is established by using a calibration method, and the mapping relationship includes:

[0016] A loading platform is placed on the elastic body, and standard weights with different weights are placed on the loading platform;

[0017] Speckle images of the measuring surface of the elastic body are collected before and after each standard weight is placed, respectively;

[0018] Based on the principle of laser speckle interference, the phase is obtained according to the speckle images;

[0019] The phase is mapped with the weight of the corresponding standard weight.

[0020] The mapping relationship between the phase and the weight of the corresponding standard weight includes: a mapping relationship function is obtained by using a fitting algorithm.

[0021] The elastic body is a metal beam or column structure.

[0022] The measuring surface is perpendicular to the surface of the elastic body supporting the measured object.

[0023] The environmental temperature during the weighing process ranges from 0 to 100 DEG C.

[0024] The environmental humidity during the weighing process ranges from 30 %RH to 70 %RH.

[0025] The measured object is placed on the elastic body, and the method includes:

[0026] A loading platform is placed on the elastic body, and the measured object is placed on the loading platform.

[0027] The application also provides a weighing device using the object weighing method based on laser speckle interference, which includes a measuring module and a calculation module.

[0028] The measuring module includes an elastic body, a loading platform, a laser, a light splitting device, a mirror one, a mirror two and a camera, the light splitting device is used for splitting the laser emitted by the laser into two beams of object light, the two beams of object light are respectively irradiated to the measuring surface of the elastic body through the mirror one and the mirror two, the two beams of object light have the same angle between the normal line of the measuring surface as the symmetry axis and the normal line; the measuring surface scatters the two beams of object light, the scattered light interferes at the target surface of the camera, and the speckle image is collected by the camera;

[0029] The computing module is used for obtaining the phase according to speckle images of the measuring surface before and after the placement of the measured object collected by the camera, and solving the weight of the measured object according to the corresponding relationship between the phase and the weight of the object.

[0030] The measuring surface is in an XY plane, and the camera lens axis is consistent with a Z axis.

[0031] The present application has the following advantages:

[0032] (1) The present application is based on laser speckle interference technology, and uses the characteristics of non-contact measurement, high precision and high resolution, full-field measurement and real-time, to realize remote, maintenance-free and high-resolution weight detection, and break through the bottleneck of traditional contact type weight measurement technology in terms of precision, stability and environmental adaptability. It also provides a new precise measurement scheme for extreme environments or special occasions such as high temperature and high humidity environments.

[0033] (2) The present application establishes the corresponding relationship between the phase reflecting the change of optical path difference caused by the deformation of the measuring surface and the weight of the measured object through a calibration method. After the phase is obtained by using the laser speckle interference technology, the corresponding gravity measurement value is obtained directly through the corresponding mapping function relationship, and the calculation efficiency is high.

[0034] (3) The present application measures weight by means of laser interference method, and is based on non-contact measurement method, which eliminates the influence of environmental factors on weight measurement.

[0035] Other features and advantages of the present application will be described in the subsequent specification, or will be understood by implementing the present application. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 It is a flowchart of the second embodiment of the present application.

[0037] Figure 2 It is a schematic diagram of the laser speckle interference measurement principle of the weighing device of the first embodiment of the present application.

[0038] Figure 3 It is a schematic diagram of the placement structure of the measured object of the first embodiment of the present application.

[0039] Figure 4 It is a phase change relationship with weight in the calibration fitting in the example of the second embodiment of the present application.

[0040] Figure 5 It is a processing result of the phase fringe pattern of the measured object in the example of the second embodiment of the present application.

[0041] In the figure: 1, elastomer; 2, laser; 3, light splitting device; 4, mirror one; 5, mirror two; 6, camera; 7, measured object; 8, object table; 101, measuring surface. DETAILED DESCRIPTION

[0042] The specific embodiments of the present application are described below with reference to the accompanying drawings. Embodiment one:

[0043] Referring to Figure 2 and Figure 3 The object weighing device based on laser speckle interference of the embodiment comprises a measuring module and a calculation module.

[0044] The measuring module comprises an elastic body 1, a carrier table 8, a laser 2, a light splitting device 3, a mirror one 4, a mirror two 5, and a camera 6. The carrier table 8 is placed on the upper surface of the elastic body 1, and the measured object 7 is placed on the upper surface of the carrier table 8. The light splitting device 3 is used for splitting the laser emitted by the laser 2 into two beams of object light, and the two beams of object light are respectively irradiated to the measuring surface 101 of the elastic body 1 through the mirror one 4 and the mirror two 5. The two beams of object light are symmetrical about the normal line of the measuring surface 101, and the included angle between the two beams of object light and the normal line is α The same. The measuring surface 101 scatters the two beams of object light, and the scattered light interferes at the target surface of the camera 6 to form a speckle image which is collected by the camera 6.

[0045] The calculation module is used for obtaining the in-plane strain field of the measuring surface 101 according to the speckle images of the measuring surface 101 before and after the measured object 7 is placed, and solving the weight of the measured object 7.

[0046] As a preferred mode, the measuring surface is in the XY plane, and the camera lens axis is consistent with the Z axis.

[0047] The elastic body is an elastic element in the existing weighing sensor, which is the skeleton of the sensor, commonly made of high-strength alloy steel or aluminum alloy, and designed in the shape of S, cantilever beam or disc structure. The core capability is “micro deformation under stress”. When the object is pressed, the elastic body will produce extremely fine deformation (usually only a few microns) like a spring. This design can accurately conduct pressure direction and avoid lateral force interference data. The elastic body of the embodiment is preferably a metal beam or column structure.

[0048] The weighing device of the embodiment is based on the laser speckle interference technology, uses the characteristics of non-contact measurement, high precision and high resolution, full-field measurement and real-time, realizes long-distance, maintenance-free and high-resolution weight detection, and breaks through the bottleneck of traditional contact type weighing technology in terms of precision, stability and environmental adaptability. It also provides a new measurement scheme for extreme environments or special occasions such as high temperature and high humidity environments.

[0049] Embodiment two:

[0050] Referring to Figure 1 The object weighing method of the embodiment uses the weighing device of embodiment one, which comprises:

[0051] S1. placing a measured object on an elastic body;

[0052] S2. collecting speckle images of a measurement surface of the elastic body before and after placing the measured object;

[0053] S3. based on the principle of laser speckle interference, analyzing and processing the speckle images to obtain the difference between the speckle images before and after the deformation of the measurement surface, forming a phase fringe pattern, and obtaining the phase reflecting the change of the optical path difference caused by the deformation of the measurement surface through phase unwrapping;

[0054] S4. establishing a corresponding relationship between the phase and the weight of the object by calibration;

[0055] S5. based on the corresponding relationship, solving the weight of the measured object;

[0056] The measurement surface is not the surface of the elastic body used to support the measured object.

[0057] As a preferred mode, during the weighing process, the environmental temperature is preferably 0-100 ℃, and the environmental humidity is preferably 30 %RH-70 %RH.

[0058] Specifically, the weight range of the measured object is from gram level to ton level, that is, the weighing method of the embodiment can realize a wide range of measurement.

[0059] As a specific mode, in S1, a sample holder is placed on the elastic body, and the measured object is placed on the sample holder. A suitable elastic body material is selected, and a reasonable elastic body structure is designed to make the elastic body have good elastic performance and stability. When in use, the elastic body is placed on a stable support platform.

[0060] As a specific mode, in S2, a laser assembly and a camera are arranged at a suitable position around the elastic body, and the wavelength, power and other parameters of the laser are adjusted to make it uniformly irradiate the measurement surface of the elastic body. The position of the laser assembly and the camera, and the parameter setting of the laser light source should be optimized according to the material of the elastic body and the weighing requirement.

[0061] The measured object is placed on the elastic body, and the measurement surface of the elastic body deforms in-plane, causing the surface speckle field to change. The speckle images before and after the in-plane deformation of the measurement surface are collected by the camera. The camera collects the changed speckle images in real time, and transmits the image data to the computer. The collected image data should have sufficient resolution and clarity for subsequent image processing and analysis.

[0062] As a specific mode, in S3, based on the principle of laser speckle interference, the speckle images are analyzed and processed to obtain the difference between the speckle images before and after the deformation of the measurement surface, form a phase fringe pattern, and obtain the phase through phase unwrapping, which is based on the following principles:

[0063] 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 These are the light intensity distributions of the two object beams, respectively. φ The phase difference between the two beams;

[0064] After the object to be measured is placed, the surface to be 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 object beams caused by the deformation of the measurement surface, respectively.

[0065] 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:

[0066]

[0067] 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.

[0068] Therefore, the phase difference Δ depends only on the horizontal deformation u within the measurement plane, and we can obtain:

[0069]

[0070] 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:

[0071]

[0072] In the formula, v The amount of vertical deformation within the measurement plane.

[0073] Therefore, the phase difference Δ is only related to the vertical deformation within the measurement plane. v Regarding this, we can obtain:

[0074]

[0075] Based on the above two phase difference △, the phase reflecting the change of optical path difference caused by the measured deformation is obtained.

[0076] Specifically, the phase map can be solved by using digital processing technology:

[0077] Real-time subtraction or addition processing is performed by a computer to enhance the contrast of interference fringes;

[0078] The wrapped phase (range [0, 2π)) is extracted from the fringe pattern, and then unwrapped to continuous phase by least squares method or quality map guided algorithm.

[0079] As a preferred mode, in S4, the mapping relationship between the phase and the weight of the object is established by using the calibration method, comprising:

[0080] S41. Placing a standard weight with different weights on the stage on the elastic body;

[0081] S42. Respectively collecting speckle images of the measuring surface of the elastic body before and after placing each standard weight;

[0082] S43. Based on the principle of laser speckle interference, the phase fringe pattern is obtained according to the speckle images, and then the phase is obtained;

[0083] S44. Mapping relationship between the phase and the corresponding weight of the weight is established, and the mapping relationship function is obtained by using the fitting algorithm.

[0084] The different weights of the measured object cause different in-plane deformations of the elastic body, so that the to-be-measured weight can be calculated from the phase.

[0085] In order to further illustrate the beneficial effects of the present scheme, the weighing method of the present embodiment will be further described in combination with specific examples.

[0086] In this example, the material of the elastic body is aluminum alloy, and the corresponding relationship between the phase of the measuring surface of the elastic body before and after deformation and the weight of the object is calibrated. During calibration, the measuring surface of the elastic body is in XY plane, and the camera is in Z axis. The mapping relationship function is obtained by using the fitting algorithm, the corresponding relationship is as shown in Figure 4 , and the expression is as follows:

[0087]

[0088] In the formula, x is the weight, f ( x ) is the phase, and the fitting R value is 0.9999. The linear relationship is very consistent, which verifies the effectiveness of the speckle interference weight measurement.

[0089] Taking the mass of 20g standard weight as the measured object, first, in the process of processing the phase fringe pattern of the measured object, the fringe area in the figure is intercepted for processing, and the phase fringe pattern obtained after interception is shown in (a) of Figure 5 ; the cosine mean filtering method is used for filtering, and the filtered phase fringe pattern is shown in (b) of Figure 5 ; the unwrapping algorithm is used to obtain the unwrapped phase, as shown in (c) of Figure 5 ; according to the aforementioned phase and weight mapping relationship function, the weight of 20.0001g is obtained by solving the unwrapped phase. Finally, the weight of the measured object obtained by the traditional weighing sensor (or other ways) is 20.002g. It can be seen that the weight precision obtained by the weighing method of the application is higher.

[0090] Those skilled in the art can understand that the above only describes the preferred embodiments of the present application and is not used to limit the present application, although the present application has been described in detail with reference to the foregoing embodiments, and those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or make equivalent replacement for part of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method of object weighing based on laser speckle interferometry, characterized in that, The method comprises the following steps: placing an object to be measured on an elastic body; collecting speckle images of a measurement surface of the elastic body before and after placing the object to be measured; analyzing and processing the speckle images based on the principle of laser speckle interference to obtain a difference value of speckle patterns before and after deformation of the measurement surface, form a phase fringe pattern, and obtain a phase reflecting a change in optical path difference caused by deformation of the measurement surface through phase unwrapping; establishing a corresponding relationship between the phase and the weight of the object by calibration; solving the weight of the object to be measured based on the corresponding relationship; the measurement surface is perpendicular to the surface of the elastic body supporting the object to be measured; the step of establishing the corresponding relationship between the phase and the weight of the object by calibration comprises the following steps: placing a stage on the elastic body and placing standard weights with different weights on the stage; collecting speckle images of the measurement surface of the elastic body before and after placing each standard weight; obtaining the phase based on the principle of laser speckle interference according to the speckle images; establishing a mapping relationship between the phase and the weight of the corresponding standard weight, which comprises: obtaining a mapping relationship function by using a fitting algorithm; the weighing method uses a weighing device comprising: a measurement module and a calculation module; the measurement module comprises an elastic body, a stage, a laser, a light splitting device, a mirror one, a mirror two, and a camera, the light splitting device is used to split the laser emitted by the laser into two beams of object light, the two beams of object light are respectively irradiated to the measurement surface of the elastic body through the mirror one and the mirror two, the two beams of object light have the same angle with the normal line of the measurement surface as the symmetric axis; the measurement surface scatters the two beams of object light, the scattered light interferes at the target surface of the camera to form a speckle image which is collected by the camera; the calculation module is used to obtain the phase according to the speckle images of the measurement surface collected by the camera before and after placing the object to be measured, and solve the weight of the object to be measured according to the corresponding relationship between the phase and the weight of the object.

2. 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.

3. The method of object weighing based on laser speckle interferometry according to claim 1, characterized in that, The environmental temperature during the weighing process ranges from 0 to 100 ℃.

4. The object weighing method based on laser speckle interferometry according to claim 1, characterized in that, The environmental humidity during the weighing process ranges from 30 %RH to 70 %RH.

5. The method of object weighing based on laser speckle interferometry according to claim 1, characterized in that, The step of placing the object to be measured on the elastic body comprises the following steps: placing a stage on the elastic body and placing the object to be measured on the stage.

6. The object weighing method based on laser speckle interference according to claim 1, wherein the measurement surface is in the XY plane, and the camera lens axis is consistent with the Z axis.

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