A 3D-DIC measurement system and method for low-temperature deformation measurement

Abstract

The present invention discloses a 3D-DIC measurement system and method for low-temperature deformation measurement, which relates to the field of full-field displacement measurement technology. The system includes a vacuum container, a vacuum and temperature control system, a mounting bracket for the object to be measured, a window assembly, a DIC measuring instrument, a rotary table, and a control and recording computer. First, during pre-test operations, a speckle pattern of the measured surface is prepared, and the 3D-DIC measurement system is installed to complete the measurement environment preparation. During the measurement test, the field of view and exposure of the DIC measuring instrument are adjusted, the DIC measuring instrument is calibrated, and the test conditions are adjusted. The speckle patterns of the measured surface are collected under different working conditions. During data processing, the displacement of each point on the measured surface is calculated based on the speckle pattern, and the rigid body displacement is obtained by fitting, ultimately obtaining the low-temperature deformation value. The present invention has the advantages of full-field measurement and avoids calibration of complex structures in a vacuum environment.

Description

Technical Field

[0001] The present invention relates to the technical field of full-field displacement measurement, and in particular to a 3D-DIC measurement system and method for low-temperature deformation measurement. Background Art

[0002] Complex optomechanical structures experience extreme temperature fluctuations in space. Thermal deformation and interactions between components cause relative displacement of key components, impacting the optomechanical structure's imaging performance. The rigid-body component of this relative displacement is known as cryogenic deformation, and this relative displacement must be measured during ground-based testing.

[0003] Traditional point measurement methods require the extensometer to contact the surface being measured, which can affect the results of small displacement measurements. Laser displacement sensors are also difficult to place within complex optomechanical structures. Among full-field measurement methods, holographic interferometry and speckle interferometry have extremely demanding requirements for the measurement test environment. Digital Image Correlation (DIC) has lower environmental requirements. However, in a vacuum environment, DIC measurement faces challenges with ambient temperature and heat dissipation, requiring the installation of protective devices. Furthermore, measuring complex structures requires multiple calibrations and repetitive movement of the measured object, which increases testing costs. Furthermore, existing infrared remote sensing measurement technologies face numerous challenges when applied to complex optomechanical structures. First, inconsistent pixel sizes, differences in projection and coordinate systems, and sensor distortion can lead to pixel mismatch. Second, atmospheric influences, varying target characteristics, and sensor performance limitations can lead to measurement inaccuracies. Furthermore, difficulties in data fusion, processing, and analysis complicate application. These issues lead to difficulties in pixel matching and reduced measurement accuracy, which in turn impacts the quality and application value of infrared remote sensing data.

[0004] Therefore, a 3D-DIC full-field displacement measurement system and method for low-temperature deformation measurement is needed to conveniently and accurately measure the low-temperature deformation of complex optomechanical structures. Summary of the Invention

[0005] In order to solve the problem that existing devices and methods cannot further meet the requirements of low-temperature deformation measurement, the present invention provides a 3D-DIC measurement system and method for low-temperature deformation measurement.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A 3D-DIC measurement system for low-temperature deformation measurement includes a vacuum container, a vacuum and temperature control system, a mounting bracket for a measured object, a window assembly, a DIC measuring instrument, a support device, and a control and recording computer. Measurements are performed outside the vacuum container where the measured object is placed. The vacuum and temperature control system controls the vacuum container to create a vacuum and low-temperature environment, simulating a space environment, and controls the temperature of the measured object, placing the measured object in different working conditions. The DIC measuring instrument observes a measured surface on the measured object through the window assembly, and when the measured object is in different working conditions, it collects speckle images of the measured surface and records them in the control and recording computer. The control and recording computer processes the speckle images, obtains the full-field displacement of the measured object based on correlation between images, obtains the displacement of the measured surface based on fitting of the displacement data at multiple points, and further obtains the low-temperature deformation. The measured surfaces are multiple sets of non-coplanar planes. DIC stands for digital image correlation.

[0008] Furthermore, the vacuum container provides a low-temperature radiation background under the control of a vacuum and temperature control system.

[0009] Furthermore, the vacuum and temperature control system includes a vacuum pump, a liquid nitrogen storage device, an electric heater, and a temperature sensor. The vacuum and temperature control system creates a vacuum environment in the vacuum container by turning on the vacuum pump; creates a low-temperature radiation background in the vacuum container by turning on the liquid nitrogen storage device; and controls the temperature of the object under test by the electric heater, so that the object under test forms and maintains different temperature conditions.

[0010] Furthermore, the object to be measured is set on the object to be measured mounting bracket, which is mounted on the vacuum container and is used to connect the vacuum container and the object to be measured; the object to be measured mounting bracket is provided with an opening at the measured surface of the object to be measured for installing a window assembly.

[0011] Furthermore, the DIC measuring instrument includes a left camera, a right camera, a light source, a left polarizer, a right polarizer, and a fixing fixture;

[0012] The left camera and the right camera adjust the focus, aperture and shutter, observe the measured surface of the measured object through the window assembly, and transmit the collected images to the control and recording computer;

[0013] The light source is controlled by the control and recording computer and illuminates the measured surface of the measured object through the window assembly when turned on;

[0014] The left polarizer and the right polarizer filter the reflected light by rotating the angle;

[0015] The fixing fixture is used to install the left camera, the right camera, the light source, the left polarizer and the right polarizer.

[0016] Furthermore, the control and recording computer is used to turn on and off the left camera, the right camera and the light source, adjust the shutter of the left camera and the right camera, control the left camera and the right camera to acquire images, calibrate the left camera and the right camera according to the DIC algorithm and the acquired images, calculate the displacement field according to the DIC algorithm and the acquired images, store the calibration results and the calculation results, and visualize the calculation results.

[0017] The present invention also provides a measurement method for the above-mentioned 3D-DIC measurement system for low-temperature deformation measurement, comprising the following steps:

[0018] Step 1: Prepare the speckle pattern of the measured surface, install and calibrate the DIC measuring instrument;

[0019] Step 2: Assemble the 3D-DIC measurement system for low-temperature deformation measurement, adjust the test conditions, and collect the speckle pattern of the measured surface;

[0020] Step 3: Calculate the displacement of each point on the measured surface according to the speckle pattern, fit the rigid body displacement, and finally obtain the low-temperature deformation value.

[0021] Furthermore, the step 1 includes:

[0022] Prepare a speckle pattern on the surface of the measured surface, and install the measured surface on the measured object;

[0023] Install the window assembly on the outside of the mounting bracket of the object to be measured; install the object to be measured on the inside of the mounting bracket of the object to be measured; install the mounting bracket of the object to be measured on the vacuum container;

[0024] Connect the vacuum and temperature control system, the object to be measured, and the vacuum container, and make the vacuum container enter a vacuum environment through the vacuum and temperature control system; and make the object to be measured enter a heating condition through the vacuum and temperature control system.

[0025] Furthermore, the step 2 includes:

[0026] Install the DIC measuring instrument on the rotary table, adjust the field of view and focus, and adjust the light source;

[0027] The working conditions of the measured object are adjusted by a vacuum and temperature control system, and the working conditions include normal temperature process, low temperature process, cooling process and heating process, and the speckle images of the measured surface are collected under different working conditions.

[0028] Furthermore, the step 3 includes:

[0029] Using a control and recording computer, the displacement of each point on the measured surface under different working conditions relative to the initial working condition is calculated based on the speckle pattern of the measured surface;

[0030] The expression of the displacement corresponding plane relative to the initial operating point is obtained by fitting, and the fitting adopts the least square method, including:

[0031] The coordinates of the working point under low temperature conditions are , let the fitting plane equation be , z represents the position, a, b, c represent the coefficients, and the Z-axis position vector is recorded , plane parameter vector , the superscript T represents the transpose of the matrix, then:

[0032] ;

[0033] in, is the Jacobian matrix;

[0034] According to the fitted plane equation and the coordinates of the plane center point, the translation angle and deflection angle of the measured surface under different working conditions relative to the initial working condition are calculated;

[0035] According to the translation angle and deflection angle of each measured surface, the translation component and rotation component of low-temperature deformation are calculated.

[0036] Beneficial effects:

[0037] (1) In order to simultaneously measure the translational and rotational components of low-temperature deformation with high precision, the present invention uses a DIC measuring instrument to construct a full-field measurement device. The measurement is performed outside the vacuum container where the object to be measured is placed. The positions of multiple measured surfaces are measured simultaneously, and the displacement and low-temperature deformation are calculated. It can perform multi-point measurement and full-field measurement, which overcomes the shortcomings of sensor point measurement and is more suitable for low-temperature deformation measurement of multiple measured surfaces.

[0038] (2) Compared with the existing DIC measurement in high and low temperature environments, the use of a rotary table and a fixed fixture can realize the calibration and measurement of the measured surface inside the complex structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the structure of a 3D-DIC measurement system for low-temperature deformation measurement according to the present invention;

[0040] Figure 2 This is a flow chart of a 3D-DIC measurement method for low-temperature deformation measurement according to the present invention;

[0041] Among them, the figure numbers are: 1. object to be measured; 2. surface to be measured; 3. vacuum container; 4. mounting bracket for the object to be measured; 5. window assembly; 6. DIC measuring instrument; 7. left camera; 8. right camera; 9. light source; 10. fixing fixture; 11. control and recording computer; 12. rotary table; 13. vacuum and temperature control system; 14. supplementary light source. DETAILED DESCRIPTION

[0042] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0043] An embodiment of the present invention provides a 3D-DIC measurement system and method for low-temperature deformation measurement. In this embodiment, a W-shaped radiation cooler is selected as the measured object, and its multiple sets of non-coplanar measured surfaces are planes on the outer shell and inside the cold optical channel.

[0044] like Figure 1 As shown, an embodiment of the present invention provides a 3D-DIC measurement system for low-temperature deformation measurement, including a measured object 1 in this embodiment and a W-type radiation cooler, wherein only the planes on the outer shell and the interior of the cold optical channel are replaced by a measured surface 2 with a speckle pattern. The measured object 1 is mounted on a measured object mounting bracket 4, which is mounted on a vacuum vessel 3 as part of the vacuum vessel, and a window assembly 5 is mounted on the measured object mounting bracket 4; a DIC measuring instrument 6 is fixedly mounted on a rotary worktable 12, and a control and recording computer 11 is connected to the DIC measuring instrument 6 via a data cable; and a vacuum and temperature control system 13 is connected to the measured object 1 and the vacuum vessel 3.

[0045] The vacuum and temperature control system 13 controls the vacuum container 3 to create a vacuum and low-temperature environment, simulating a space environment, and controlling the temperature of the measured object 1 to place it in different operating conditions. The DIC measuring instrument 6 observes the measured surface 2 of the measured object 1 through the window assembly 5. When the measured object 1 is in different operating conditions, it collects speckle images of the measured surface 2 and records them in the control and recording computer 11. The control and recording computer 11 processes the speckle images and, based on the correlation between the images, obtains the full-field displacement of the measured object. It then fits the displacement data at multiple points to obtain the displacement of the measured surface, and further obtains the low-temperature deformation.

[0046] Figure 1 In the table, LN2 represents liquid nitrogen.

[0047] Preferably, the vacuum container 3 has a certain volume for mounting the object to be measured 1; the vacuum container 3, the object to be measured mounting bracket 4, and the window assembly 5 form a closed environment, which can provide a vacuum environment under the control of the vacuum and temperature control system 13; the vacuum container 3 has a heat sink and a cold screen, which can provide a low-temperature radiation background under the control of the vacuum and temperature control system 13.

[0048] Preferably, the vacuum and temperature control system 13 includes:

[0049] A vacuum pump connected to the vacuum container 3 via a pipeline;

[0050] A liquid nitrogen storage device connected to a heat sink and a cold shield of the vacuum vessel 3 via a pipeline;

[0051] an electric heater mounted on the object under test 1;

[0052] Temperature sensors installed on the object to be measured 1 and the vacuum container 3;

[0053] Connected to the control computer of the vacuum and temperature control system 13 via cables.

[0054] The vacuum and temperature control system 13 creates a vacuum environment in the vacuum container 3 by turning on the vacuum pump; creates a low-temperature radiation background in the vacuum container 3 by turning on the liquid nitrogen storage; and controls the temperature of the object 1 by the electric heater, so that the object 1 forms and maintains different temperature conditions.

[0055] Preferably, the object mounting bracket 4 is divided into two sides, with threaded holes on the inner side for mounting the object 1 and threaded holes on the outer side for mounting the window assembly 5. The object mounting bracket 4 is provided with an opening, which together with the window assembly 5 forms an observation window, through which the measured surface 2 of the object 1 at different positions can be observed.

[0056] Preferably, the DIC measuring instrument 6 includes a left camera 7, a right camera 8, a light source 9, and a fixing fixture 10. The fixing fixture 10 is fixedly connected to a rotary table 12. The left camera 7, the right camera 8, and the light source 9 are mounted on the fixing fixture 10 and fixed by threaded fasteners. A control and recording computer 11 is connected to the left camera 7, the right camera 8, and the light source 9 via a data cable.

[0057] Preferably, the left camera 7 and the right camera 8 observe the measured object 1 and the measured surface 2 through the window assembly 5, and transmit the collected images to the control and recording computer 11 through a data line.

[0058] Preferably, the left camera 7 and the right camera 8 can adjust the focus, aperture, exposure time, and shooting frame number: the focus adjustment rings and aperture adjustment rings of the left camera 7 and the right camera 8 are provided with threaded fasteners, which are fixed by tightening the bolts after adjusting the focus and aperture; the exposure time and shooting frame number of the left camera 7 and the right camera 8 are adjusted by the control and recording computer 11.

[0059] Preferably, the light source 9 is controlled by a control and recording computer 11 , and when turned on, it illuminates the object 1 and the surface 2 through the window assembly 5 , ensuring that the left camera 7 and the right camera 8 can capture bright images.

[0060] Preferably, in order to capture images with high contrast and no overexposure, a supplementary light source 14 is arranged near the rotary table 12 to provide lighting with various angles and brightness.

[0061] Preferably, a polarizing plate is placed in front of the left camera 7 and the right camera 8 respectively. The polarizing plate can filter the reflected light by rotating the angle to reduce the influence of the reflected light from other areas illuminated by the light source on the left camera 7 and the right camera 8.

[0062] Preferably, the fixing fixture 10 has a closed structural shell to protect the left camera 7 , the right camera 8 , and the light source 9 .

[0063] Preferably, the fixing fixture 10 can be used to install polarizing plates in front of the left camera 7 and the right camera 8 to maintain the angle of the polarizing plates through static friction.

[0064] Preferably, the control and recording computer 11 is used to:

[0065] Turn on / off the left camera 7, the right camera 8, and the light source 9;

[0066] Adjust the exposure time and shooting frame number of the left camera 7 and the right camera 8;

[0067] Control the left camera 7 and the right camera 8 to capture images;

[0068] Calibrate the left camera 7 and the right camera 8 according to the DIC algorithm and the acquired images;

[0069] Calculate the displacement field based on the acquired images using the DIC algorithm;

[0070] Store calibration results and calculation results;

[0071] Visualize the calculation results.

[0072] Preferably, the rotary table 12 includes:

[0073] a platform for mounting a DIC measuring instrument 6;

[0074] The displacement mechanism can make the platform translate and rotate.

[0075] Preferably, the rotary workbench 12 has an electronic display system that can display the position coordinates and angle information of the platform.

[0076] like Figure 2 As shown, taking a W-type radiation cooler as an example, an embodiment of the present invention further provides a measurement method of a 3D-DIC measurement system for low-temperature deformation measurement, comprising the following steps:

[0077] Step 1: Pre-test operations, including:

[0078] Step 1.1: According to the technical requirements of 3D-DIC measurement, prepare test surface 2 using a part on test object 1 that corresponds to test surface 2 as a template, prepare a test surface speckle pattern on the surface of test surface 2, and mount test surface 2 with the speckle pattern on test object 1;

[0079] Step 1.2: Mount the window assembly 5 on the outside of the test object mounting bracket 4 by bolting; mount the test object 1 with the test surface 2 mounted thereon on the inside of the test object mounting bracket 4 by bolting; and mount the test object mounting bracket 4 with the window assembly 5 and the test object 1 mounted thereon on the vacuum container 3;

[0080] Step 1.3: Connect the vacuum and temperature control system 13, the object to be measured 1, and the vacuum container 3, and place the vacuum container 3 in a vacuum environment through the vacuum and temperature control system 13; and place the object to be measured 1 in a heating state through the vacuum and temperature control system 13;

[0081] Step 2: Measurement test operation, including:

[0082] Step 2.1: Securely mount the DIC measuring instrument 6 on the rotary table 12. The fixture 10 is fixedly connected to the rotary table 12. The left camera 7, right camera 8, and light source 9 are mounted on the fixture 10 and secured with threaded fasteners. The control and recording computer 11 is connected to the left camera 7, right camera 8, and light source 9 via a data cable.

[0083] Preferably, before the test begins, the left camera 7, the right camera 8, and the light source 9 are fixedly mounted on the fixing fixture 10 in advance;

[0084] Move the platform of the rotary table 12 to adjust the field of view of the DIC measuring instrument 6, with the goal of seeing all the measured surfaces 2 on the housing, and the measured surfaces 2 on the housing being perpendicular to the DIC measuring instrument 6;

[0085] Preferably, the vertical refers to that the normal vector of the measured surface 2 is parallel to the angle bisector vector of the axis of the left camera 7 and the right camera 8;

[0086] Step 2.2: Set the aperture of the left camera 7 and the right camera 8 to maximum, and adjust the focus rings of the left camera 7 and the right camera 8 to control and record the grayscale gradient of the speckle image of the measured surface 2 on the housing obtained in the computer 11 to reach the maximum. Secure the focus rings of the left camera 7 and the right camera 8 by tightening the bolts. Record the position reading of the rotary table 12 at this time as the corresponding position of the measured surface 2 on the housing.

[0087] The platform of the rotary table 12 is moved to control and record the grayscale gradient of the speckle image of the measured surface 2 inside the cold optical channel obtained by the computer 11 to reach the maximum, and the measured surface 2 inside the cold optical channel is perpendicular to the DIC measuring instrument 6; the position reading of the rotary table 12 at this time is recorded as the corresponding position of the measured surface 2 inside the cold optical channel;

[0088] Preferably, before the test, the aperture of the left camera 7 and the right camera 8 are adjusted to the maximum and fixed;

[0089] Step 2.3: Turn on the left camera 7 and the right camera 8 on the control and recording computer 11 to capture images. The image brightness is adjusted by turning on and off the light source 9 and adjusting the aperture and exposure time of the left and right cameras 7 and 8. The goal is to ensure that the speckle image obtained by the control and recording computer 11 has high contrast and no overexposure.

[0090] Fix the apertures of the left camera 7 and the right camera 8 by tightening the bolts; move the rotary table 12 to obtain space for placing and moving the calibration plate, and complete the calibration using the calibration plate; move the rotary table 12 back to the corresponding position of the measured surface 2 on the measurement housing;

[0091] Preferably, in order to capture images with high contrast and no overexposure, a supplementary light source 14 is arranged near the rotary table 12 to provide lighting with various angles and brightness;

[0092] Preferably, the angles of the polarizers installed in front of the left camera 7 and the right camera 8 are adjusted to reduce the overexposed area;

[0093] Preferably, different light sources 9 and supplementary light sources 14 are provided for illumination according to the recorded position indications of the rotary table 12, i.e., for measuring the corresponding position of the measured surface 2 on the housing and for measuring the corresponding position of the measured surface 2 inside the cold optical channel;

[0094] Step 2.4 controls the temperature of the radiation cooler of the object under test 1 to obtain different working conditions of the object under test 1, including:

[0095] The heat sink and cold shield in the vacuum container 3 are cooled by the liquid nitrogen storage in the vacuum and temperature control system 13. At this time, the electric heater is controlled by the vacuum and temperature control system 13 to maintain the temperature of the test object 1 at 293 K. This is called the normal temperature working condition of the test object 1. The test object 1, acting as a radiation cooler, radiates heat to the vacuum container 3 through the vacuum and temperature control system 13 and stabilizes at different lower temperatures in stages. This is called the low temperature working condition (below 293 K) of the test object 1.

[0096] The process of the measured object 1 changing from normal temperature to low temperature is called the cooling process of the measured object 1; the process of changing from low temperature to normal temperature is called the heating process of the measured object 1.

[0097] Step 2.5: When the object 1 is in a normal temperature condition, a low temperature condition, a cooling process, or a heating process, the control and recording computer 11 controls the left camera 7 and the right camera 8 to collect speckle images of the surface 2;

[0098] Preferably, the acquired speckle image of the measured surface 2 on the housing and the acquired speckle image of the measured surface 2 inside the cold optical channel are stored in different acquisition items on the control and recording computer 11;

[0099] Preferably, images can be collected multiple times in a process of normal temperature working condition - cooling process - low temperature working condition - heating process - normal temperature working condition;

[0100] A preferred measurement process is as follows: the object 1 is first subjected to a process of normal temperature operation, cooling process, low temperature operation, heating process, and normal temperature operation. During this process, the rotary table 12 is fixed at a corresponding position of the measured surface 2 on the measurement housing, and the left camera 7 and the right camera 8 are used on the control and recording computer 11 to collect speckle images of the measured surface 2 on the housing multiple times.

[0101] The object 1 undergoes a second cycle of normal temperature, cooling, low temperature, heating, and normal temperature. During this cycle, the rotary table 12 is fixed at a position corresponding to the surface 2 to be measured within the cold optical channel. The control and recording computer 11 uses the left camera 7 and the right camera 8 to capture speckle images of the surface 2 within the cold optical channel multiple times.

[0102] Another preferred measurement process is: by moving the platform of the rotary table 12, multiple images are collected in a process of normal temperature working condition - cooling process - low temperature working condition - heating process - normal temperature working condition, and the speckle images of the measured surface 2 on the housing and the measured surface 2 inside the cold optical channel are collected almost simultaneously in one acquisition, wherein:

[0103] First, the platform of the rotary table 12 is moved to the corresponding position of the measured surface 2 on the measuring shell, and the left camera 7 and the right camera 8 are used on the control and recording computer 11 to collect the speckle image of the measured surface 2 on the measuring shell, and record it in the collection item corresponding to the measured surface 2 on the measuring shell;

[0104] Switch to the acquisition project corresponding to the measured surface 2 inside the cold optical channel; move the platform of the rotary table 12 to the corresponding position for measuring the measured surface 2 inside the cold optical channel; use the left camera 7 and the right camera 8 on the control and recording computer 11 to acquire a speckle image of the measured surface 2 inside the cold optical channel; and record the image in the acquisition project corresponding to the measured surface 2 inside the cold optical channel;

[0105] Step 3: Post-test data processing, including:

[0106] Step 3.1. Using the DIC measurement software on the control and recording computer 11, calculate the full-field displacement nephogram of each point on the measured surface 2 relative to the initial image based on the speckle image of the measured surface 2. Select multiple points in the full-field displacement nephogram, denoted as points 1 to n. Output and record the following information based on the XYZ coordinate system provided by the DIC measurement software when calculating the full-field displacement nephogram:

[0107] Position of selection point under normal temperature conditions and the displacement relative to the initial stage , i represents the serial number of the point, x, y, z represent the coordinates of the point, and the superscript (0) represents the normal temperature condition; the position of the selected point under low temperature conditions and the displacement relative to the initial stage ;

[0108] Preferably, the initial stage generally corresponds to the normal temperature condition of the object under test 1;

[0109] Preferably, the positions of all stages of the shooting can be output and displacement , the superscript (t) is the number of stages of image acquisition;

[0110] Preferably, when selecting multiple points in the full-field displacement cloud map, one should select the geometric center of the measured surface and multiple points around it;

[0111] Step 3.2 uses the least squares method to fit the low temperature working plane relative to the normal temperature working plane to obtain the expression:

[0112] Assume the position of the first to nth points output in stage t The fitting plane equation is , z represents the position, a, b, c represent the coefficients, and the Z-axis position vector of each point is recorded , plane parameter vector , then:

[0113] ;

[0114] in, is the Jacobian matrix, and the superscript T indicates the transpose of the matrix.

[0115] Step 3.3: Based on the fitted plane equation and the coordinates of the plane center point, calculate the translation and rotation of the measured surface 2 from the normal temperature working condition to the low temperature working condition;

[0116] Taking the measured surface 2 on the shell as an example, the center point position of the measured surface 2 on the shell at normal temperature is , fitting plane normal vector , where the superscript (0) indicates the normal temperature condition, and the subscript 0 indicates the measured surface 2 on the shell; the center point position of the low temperature condition , fitting plane normal vector ; Then the translation of the measured surface 2 on the housing is:

[0117] ;

[0118] Preferably, in the initial stage, corresponding to the calculation result of the normal temperature working condition of the measured object 1, the translation of the measured surface 2 is the displacement of the center point of the low temperature working condition relative to the initial stage;

[0119] Preferably, the rotation of the measured surface 2 is described by the attitude matrix A: the coordinate system X given when the full-field displacement cloud map is calculated by the DIC measurement software r Y r Z r As the reference coordinate system, construct the posture coordinate system of the measured surface 2 at stage t:

[0120] Taking the measured surface 2 on the shell as an example, the normal vector of the fitted plane is Normalized to the Z-axis unit vector ; Select two points P and Q in the plane multi-point, and the selection standard is the initial stage vector With reference coordinate system Y r The axis angle is small, points P and Q do not change with the stage t, and then the vector The component perpendicular to the Z axis is normalized to Y r Axis unit vector ; The X axis is right-handedly perpendicular to the Y and Z axes, and the X axis unit vector ;

[0121] Therefore, the normal temperature working condition attitude coordinate system of the measured surface 2 on the shell is obtained and the low temperature working condition attitude coordinate system X0Y0Z0; the low temperature working condition attitude coordinate system X0Y0Z0 of the measured surface 2 on the shell and the normal temperature working condition attitude coordinate system The relationship is:

[0122] ;

[0123] in, represents the coordinates of the low temperature working attitude coordinate system X0Y0Z0, A is the attitude matrix, ~ represents direction cosines, such as , and so on;

[0124] Preferably, the rotation of the measured surface 2 is represented by yaw, roll and pitch angles:

[0125] Get the normal temperature working condition attitude coordinate system of the measured surface 2 on the shell After calculating the attitude matrix A of the low temperature working condition attitude coordinate system X0Y0Z0, calculate the low temperature working condition attitude coordinate system X0Y0Z0 relative to the normal temperature working condition attitude coordinate system Yaw angle ;

[0126] Roll angle ;

[0127] Pitch angle ;

[0128] Step 3.4 calculates the translation and rotation components of the low-temperature deformation based on the translation and rotation of each measured surface 2. For example, take the displacement of the measured surface 2 inside the cold optical channel relative to the measured surface 2 on the shell as an example of low-temperature deformation, where the translation of the measured surface 2 on the shell is , the attitude matrix is ​​A0; the translation of the measured surface 2 inside the cold optical channel is , the attitude matrix is ​​A1; where the subscript 1 of the translation and attitude matrix represents the measured surface 2 inside the cold optical channel;

[0129] Then the low-temperature deformation translation component of the measured surface 2 inside the cold optical channel relative to the measured surface 2 on the outer shell is: ;

[0130] Taking the attitude of the measured surface 2 inside the cold optical channel and the measured surface 2 on the shell under normal temperature conditions as the initial attitude, the attitude matrix of the low-temperature deformation rotation component is ;

[0131] Preferably, the posture matrix A of the low-temperature deformation rotation component is obtained 10 Then, the corresponding yaw, roll, and pitch angles can be obtained:

[0132] Corresponding yaw angle ;

[0133] Corresponding roll angle ;

[0134] Corresponding pitch angle ;

[0135] in, The parameters representing the brackets are selected from the attitude matrix A of the low temperature deformation rotation component 10 .

[0136] The above is only an embodiment of the present invention, and common knowledge such as the specific technical solutions or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect and practicality of the implementation of the present invention. The scope of protection required by the present invention shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A 3D-DIC measurement system for low-temperature deformation measurement, characterized in that: The system comprises a vacuum container, a vacuum and temperature control system, a mounting bracket for the object to be measured, a window assembly, a DIC measuring instrument, a support device, and a control and recording computer. Measurements are performed outside the vacuum container where the object to be measured is placed. The vacuum and temperature control system controls the vacuum container to form a vacuum and low-temperature environment, simulates a space environment, and controls the temperature of the object to be measured, placing the object to be measured in different working conditions. The DIC measuring instrument observes the measured surface of the object to be measured through the window assembly, and when the object to be measured is in different working conditions, it collects speckle images of the measured surface and records them in the control and recording computer. The control and recording computer processes the speckle images, obtains the full-field displacement of the object to be measured based on the correlation between the images, obtains the displacement of the measured surface based on the multi-point displacement data fitting, and further obtains the low-temperature deformation. The measured surfaces are multiple sets of non-coplanar planes, including planes on the housing and inside the cold optical channel. DIC stands for digital image correlation. The vacuum container provides a low-temperature radiation background under the control of a vacuum and temperature control system; The object to be measured is set on the object to be measured mounting bracket, which is mounted on the vacuum container and is used to connect the vacuum container and the object to be measured; the object to be measured mounting bracket is provided with an opening at the measured surface of the object to be measured for mounting the window assembly; Using a control and recording computer, the displacement of each point on the measured surface under different working conditions relative to the initial working condition is calculated based on the speckle pattern of the measured surface; An expression for a displacement corresponding plane relative to an initial operating point is obtained by fitting, wherein the fitting adopts a least square method; According to the fitted plane equation and the coordinates of the plane center point, the translation angle and deflection angle of the measured surface under different working conditions relative to the initial working condition are calculated; According to the translation angle and deflection angle of each measured surface, the translation component and rotation component of low-temperature deformation are calculated.

2. The 3D-DIC measurement system for low-temperature deformation measurement according to claim 1, characterized in that: The vacuum and temperature control system includes a vacuum pump, a liquid nitrogen storage device, an electric heater, and a temperature sensor. The vacuum and temperature control system creates a vacuum environment in the vacuum container by turning on the vacuum pump; creates a low-temperature radiation background in the vacuum container by turning on the liquid nitrogen storage device; and controls the temperature of the object being measured by the electric heater, so that the object being measured forms and maintains different temperature conditions.

3. The 3D-DIC measurement system for low-temperature deformation measurement according to claim 1, characterized in that: The DIC measuring instrument includes a left camera, a right camera, a light source, a left polarizer, a right polarizer and a fixing fixture; The left camera and the right camera adjust the focus, aperture and shutter, observe the measured surface of the measured object through the window assembly, and transmit the collected images to the control and recording computer; The light source is controlled by the control and recording computer and illuminates the measured surface of the measured object through the window assembly when turned on; The left polarizer and the right polarizer filter the reflected light by rotating the angle; The fixing fixture is used to install the left camera, the right camera, the light source, the left polarizer and the right polarizer.

4. The 3D-DIC measurement system for low-temperature deformation measurement according to claim 1, characterized in that: The control and recording computer is used to turn on and off the left camera, right camera and light source, adjust the shutter of the left camera and right camera, control the left camera and right camera to collect images, calibrate the left camera and right camera according to the DIC algorithm and the collected images, calculate the displacement field according to the DIC algorithm and the collected images, store the calibration results and calculation results, and visualize the calculation results.

5. A measurement method applied to a 3D-DIC measurement system for low-temperature deformation measurement according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Prepare the speckle pattern of the measured surface, install and calibrate the DIC measuring instrument; Step 2: Assemble the 3D-DIC measurement system for low-temperature deformation measurement, adjust the test conditions, and collect the speckle pattern of the measured surface; Step 3: Calculate the displacement of each point on the measured surface according to the speckle pattern, fit the rigid body displacement, and finally obtain the low-temperature deformation value, including: Using a control and recording computer, the displacement of each point on the measured surface under different working conditions relative to the initial working condition is calculated based on the speckle pattern of the measured surface; The expression of the displacement corresponding plane relative to the initial operating point is obtained by fitting, and the fitting adopts the least square method, including: The coordinates of the working point under low temperature conditions are , let the fitting plane equation be , z represents the position, a, b, c represent the coefficients, and the Z-axis position vector is recorded , plane parameter vector , the superscript T represents the transpose of the matrix, then: ； in, is the Jacobian matrix; According to the fitted plane equation and the coordinates of the plane center point, the translation angle and deflection angle of the measured surface under different working conditions relative to the initial working condition are calculated; According to the translation angle and deflection angle of each measured surface, the translation component and rotation component of low-temperature deformation are calculated.

6. The measuring method according to claim 5, characterized in that The step 1 comprises: Prepare a speckle pattern on the surface of the measured surface, and install the measured surface on the measured object; Install the window assembly on the outside of the mounting bracket of the object to be measured; install the object to be measured on the inside of the mounting bracket of the object to be measured; install the mounting bracket of the object to be measured on the vacuum container; Connect the vacuum and temperature control system, the object to be measured, and the vacuum container, and make the vacuum container enter a vacuum environment through the vacuum and temperature control system; and make the object to be measured enter a heating condition through the vacuum and temperature control system.

7. The measuring method according to claim 6, characterized in that The step 2 includes: Install the DIC measuring instrument on the rotary table, adjust the field of view and focus, and adjust the light source; The working conditions of the measured object are adjusted by a vacuum and temperature control system, and the working conditions include normal temperature process, low temperature process, cooling process and heating process, and the speckle images of the measured surface are collected under different working conditions.

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