Metal linear expansion coefficient automatic detection platform and detection method

Abstract

The invention discloses a metal linear expansion coefficient automatic detection platform and detection method, and belongs to the technical field of expansion coefficient detection. The method comprises the steps that S101, the length L0 of metal to be detected is measured, the metal to be detected is placed in a heater, and a grating is bonded to the free end of a glass rod and placed on a glass slide; s102, the heater is heated within a preset range, the temperature is recorded, and a grating image is obtained through an image obtaining module; s103, performing image processing on the raster image to obtain a binary image with black and white stripes alternated; s104, at different temperatures, obtaining a stripe movement number according to the number of binary changes of the gray image at the detection point in the binary image; s105, fitting the temperature and the stripe movement number to obtain a stripe movement number-temperature fitting curve; and S106, the linear expansion coefficient is calculated according to the length L0, the grating constant, the magnification factor and the fringe movement number-temperature fitting curve.

Description

Technical Field

[0001] The invention belongs to the technical field of expansion coefficient detection, and particularly relates to an automatic detection platform and a detection method for metal linear expansion coefficient. Background Art

[0002] In the laboratory, the measurement of the linear expansion coefficient of metal using the steady-state method is a very important electromagnetic experiment. The existing technology can use a micrometer and an optical lever to measure the linear expansion coefficient of metal.

[0003] For example, the patent with application number CN202222606976.6 discloses a device for measuring the thermal expansion coefficient of metal, including a heating device, a temperature measuring unit, a small elongation measuring device, a temperature signal processing and display unit, and a metal tube fixing seat; a metal tube to be measured is arranged inside the heating device, and the temperature measuring unit is fixed in the middle of the metal tube to be measured; the metal tube to be measured supports the small elongation measuring device, and the small elongation measuring device is connected to the temperature signal processing and display unit.

[0004] For example, the patent with application number CN202010328363.3 discloses a device for measuring the linear expansion coefficient of metal, including: a heat equalization structure, which is composed of a quartz tube, a heating belt, and a thermal insulation layer, wherein the heating belt is wrapped around the outside of the quartz tube, and the metal rod to be measured is heated by being placed in the quartz tube and supported in the air in the quartz tube; a thermocouple temperature sensor, whose thermocouple probe is glued together with the metal rod with heat-resistant tape, and is used to measure the temperature of the metal rod in real time; and a first grating displacement sensor, which is composed of a grating ruler moving end and a fixed end, and is located at an axial end of the metal rod to be measured, and is used to measure its expansion displacement, wherein thermal insulation parts are provided at both axial ends of the metal rod to be measured, and the grating ruler moving end is in seamless contact with an axial end of the metal rod to be measured.

[0005] For example, the patent with application number CN201920161300.6 discloses a device for measuring the linear expansion coefficient of metal, which includes a heating device, a length measuring device, a thermistor module, an amplifier circuit and a single-chip microcomputer; the thermistor module is connected to the amplifier circuit, the amplifier circuit is connected to the single-chip microcomputer, and the length measuring device is connected to the single-chip microcomputer; wherein the heating device is used to change the temperature of the experimental material and the thermistor module; the length measuring device is used to measure the length expansion and contraction of the experimental material under the corresponding temperature change; the thermistor module is heated by the heating device and changes its own resistance value according to the temperature change; the amplifier circuit is used to receive the voltage across the thermistor module, and perform AD acquisition and amplification on the received voltage to obtain a digital signal; the single-chip microcomputer is used to receive the digital signal, process the digital signal, and calculate the temperature change data during the experiment; and the linear expansion coefficient of metal is obtained based on the calculated temperature change data and the length expansion and contraction of the experimental material under the corresponding temperature change.

[0006] For example, the patent application number CN201220057434.1 discloses a metal linear expansion coefficient tester, which includes a base casing, a temperature signal input end of an electric heating controller connected to a temperature sensor, an output end of the electric heating controller connected to an electric heating tube, a copper sleeve fixed to the base casing by a bracket, an insulation layer on the outside of the copper sleeve, a guide block fixed inside the copper sleeve, a material to be tested placed in the copper sleeve through the guide block, a left end cap and a right end cap fixed at both ends of the copper sleeve, a top end can be screwed and fixed to the left end cap and contact the left end of the material to be tested, and is characterized in that the electric heating tube is placed in a water tank, and the steam The lower end of the pipe is connected to the water tank, the upper end of the steam pipe is connected to the copper sleeve, the lower end of the return pipe is connected to the water tank, the upper end of the return pipe is connected to the copper sleeve, the upper end of the lever is fixed to the Hall displacement sensor, the lower end of the lever is connected to the shaft plate through the shaft, the bracket and the shaft plate are fixed on the base casing, the tension spring is installed between the bracket and the lever, the left end of the push rod is inserted into the center hole of the right end cover and contacts the right end of the material to be measured, the right end of the push rod passes through the hole of the bracket to the left side of the lever, the Hall displacement sensor is placed between the magnets, the millivoltmeter is connected to the Hall displacement sensor, and the guide block is provided with a vent.

[0007] The two existing methods have many disadvantages: First, the micrometer uses human eyes to observe the readings, which cannot guarantee the accuracy and stability of the readings. The values ​​vary greatly, resulting in large experimental errors. Second, the micrometer needs to perform multiple measurements and data analysis during the measurement process, which is relatively cumbersome. Third, the construction of the optical lever system usually requires more complex experimental settings and precise adjustments, and the operation is relatively cumbersome. Fourth, the accuracy and stability requirements of the optical instruments in the optical lever system are relatively high, which increases the cost and technical requirements of the experiment. Summary of the invention

[0008] In order to solve the above problems, the embodiments of the present invention provide a metal linear expansion coefficient automatic detection platform and detection method, which are simple to build and have high detection accuracy.

[0009] The present invention provides an automatic metal linear expansion coefficient measuring instrument that can visually observe the slight deformation of metal and the temperature state in the heating chamber, and can autonomously identify, read, record and calculate. In the process of metal thermal expansion, a CCD video system, MATLAB software, a single-chip microcomputer and a temperature sensor are used to realize the movement of a grating when the metal expands and automatically count the number of stripes of the grating movement and the temperature value read by the temperature sensor. At the same time, the grating movement image, the function image of the temperature and time, the number of grating movement stripes and the temperature and the residual graph are displayed in real time in the MATLAB GUI interface, and the measured value of the metal linear expansion coefficient and the relative error are displayed at the same time, thereby reducing the experimental error caused by the incorrect reading method, increasing the accuracy and stability of the reading, and automatically collecting a large amount of data to provide persuasiveness for the experimental results, and the experimental device is simple to operate and the measurement results are highly accurate. The technical scheme is as follows: On the one hand, an automatic detection platform for metal linear expansion coefficient provided by an embodiment of the present invention comprises a heater 1, a temperature detection module, a control module and a micro-distance detection module 2, wherein the temperature detection module is arranged in the heater 1 and is electrically connected to the control module; the micro-distance detection module 2 comprises a smooth glass rod 21, a microscope 22 next to the heater 1, a light source 23 directly below the stage of the microscope 22, an image acquisition module 24 on the eyepiece of the microscope 22, a glass slide 25 on the stage, a grating 26 on the glass slide 25 and a pressing sheet on the stage for fixing the glass slide 25; the metal to be detected is placed in the heater 1 and its inner end is against the closed end of the heater 1; the glass rod 21 is arranged horizontally, and is arranged along the direction where the heater 1 is located, and its inner end is against the metal to be detected. The outer end of the glass rod 21 is passed through the heater 1 to serve as a free end; the free end is fixedly connected to the corresponding side of the grating 26, the slit of the grating 26 is perpendicular to the glass rod 21, and the image acquisition module 24 is electrically connected to the control module; the control module is used to perform image processing on the grating image through MATLAB to obtain a binary image with alternating black and white stripes; at different temperatures, the number of stripe movements is obtained according to the number of binary changes of the grayscale image at the detection point in the binary image; the temperature and the number of stripe movements are fitted to obtain a stripe movement number-temperature fitting curve and displayed; the linear expansion coefficient is calculated according to the length L0 of the metal rod, the grating constant, the magnification and the stripe movement number-temperature fitting curve and displayed; the temperature-time fitting curve is obtained and displayed.

[0010] Specifically, the magnification of the microscope 22 in the embodiment of the present invention is 30-50 times, the image acquisition module 24 is a CCD, and the grating constant of the grating 26 is 1 / 200-1 / 400 mm.

[0011] Among them, the heater 1 in the embodiment of the present invention includes a horizontally arranged heating chamber 11 and a lifting structure 12 on the lower side thereof, wherein the heating chamber 11 is composed of an insulation layer, a glass tube, a heating wire and a copper tube from the outside to the inside, wherein the heating wire is wound around the outer wall of the copper tube, and the lifting structure 12 is fixed on the lower side of the insulation layer; one end of the heating chamber 11 away from the micro-distance detection module 2 is closed, and the other end is open and closed with a wooden plug 13; the wooden plug 13 is provided with a through hole for a glass rod 21 to pass through and slide; the metal to be detected is placed at the bottom of the heating chamber 11 and rests against the closed end of the heating chamber 11, and the glass rod 21 passes through the through hole.

[0012] On the other hand, the detection method using the aforementioned metal linear expansion coefficient automatic detection platform comprises the following steps: S101: Measure the length L0 of the metal to be detected and place it in the heater 1, adhere the grating 26 to the free end of the glass rod 21 and place it on the slide glass 25; S102: raising the temperature of the heater 1 within a predetermined range and recording the temperature, and acquiring a grating image through the image acquisition module 24; S103: performing image processing on the grating image to obtain a binary image with alternating black and white stripes; S104: obtaining the number of fringe movements according to the number of grayscale image binarization changes at the detection point in the binarized image at different temperatures; S105: fitting the temperature and the number of fringe movements to obtain a fringe movement number-temperature fitting curve; S106: Calculate the linear expansion coefficient based on the length L0, grating constant, magnification and fringe movement amount-temperature fitting curve.

[0013] Wherein, steps S103-S106 are executed by MATLAB; and the grating image, the binarized image, the temperature-time fitting curve, the fringe movement number, the fringe movement number-temperature fitting curve, the residual graph, the linear expansion coefficient and the relative error are displayed in real time in the MATLAB GUI interface.

[0014] Furthermore, step S102 also includes: a preheating stage and a detection stage; in the preheating stage: between room temperature and the starting detection temperature, the MATLAB GUI interface displays a temperature-time fitting curve, and manually or automatically determines whether the heater 1 heats evenly and increases linearly; in the detection stage: if the heater 1 heats evenly and increases linearly, a stripe movement quantity-temperature fitting curve is obtained based on the detection value between the starting detection temperature and the ending detection temperature.

[0015] Furthermore, the method provided by the embodiment of the present invention also includes: obtaining a linear uniform heating interval according to the temperature-time fitting curve, and obtaining a stripe movement quantity-temperature fitting curve according to the data of the linear uniform heating interval.

[0016] Wherein, step S103 specifically includes: S301: obtaining a raster image of the image acquisition module 24 through a videoinput function, wherein the raster image is a grayscale image; S302: Get the current raster image through the getsnapshot command and display it on the MATLAB GUI interface; S303: Binarization processing is performed on the current raster image; S304: Obtain a smooth and noise-free binary image through filtering and denoising, and display it on the MATLAB GUI interface.

[0017] Wherein, step S104 specifically includes: S401: Taking the center point of the binary image as the detection point, defining the value of the black stripe as 0 and the value of the white stripe as 1; S402: The gradient is calculated by using the grad command. According to the gradient value of the first data, the gradient value with the opposite sign is discarded. Finally, the absolute values ​​of all the gradient values ​​are added together to obtain the number of stripe movements.

[0018] Wherein, step S105 specifically includes: recording the current temperature each time the stripes of the binary image move once; performing least squares linear fitting by using the polyfit command, drawing a stripe movement number-temperature fitting curve with temperature as the horizontal coordinate and stripe movement number as the vertical coordinate, and displaying it on the MATLAB GUI interface.

[0019] The technical solution provided by the embodiment of the present invention has the following beneficial effects: 1. The present invention innovatively utilizes the movement of grating stripes to measure tiny deformations, and combines CCD and temperature sensors to achieve real-time and accurate measurement of the metal linear expansion coefficient.

[0020] 2. Compared with the manual reading of micrometer by human eyes, this experiment realizes automatic data collection and processing, and improves the accuracy and stability of readings.

[0021] 3. Compared with the traditional light amplification method, the present invention has an easy-to-adjust instrument, intuitive visualization of phenomena, and automated measurement.

[0022] 4. The system of the present invention is easy to operate, the data is intuitive, the system is open and the interface is user-friendly, and it is more efficient and practical than traditional measuring devices. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 It is a structural schematic diagram of a metal linear expansion coefficient automatic detection platform provided by an embodiment of the present invention; Figure 2 is a flow chart of a method for automatically detecting a metal linear expansion coefficient provided by an embodiment of the present invention; Figure 3 is the flowchart of step 3; Figure 4 is the flowchart for step 4; Figure 5 is a raster image; Figure 6 is a binary image; Figure 7 It is a flowchart of binarization processing; Figure 8 It is a flowchart of the method disclosed in the present invention; Fig. 9 This is a schematic diagram of the MATLAB GUI interface; Fig.10 yes Fig. 9 Schematic diagram after fitting the curve; Fig.11 is a schematic diagram of the temperature-time fitting curve; Fig.12 This is a schematic diagram of the MATLAB GUI interface for the first copper rod inspection; Fig.13 This is a schematic diagram of the MATLAB GUI interface for the second copper rod test; Fig.14 This is a schematic diagram of the MATLAB GUI interface for the third copper rod inspection.

[0023] Among them, 1 heater, 2 micro distance detection modules; 11 heating chamber, 12 lifting structure, 13 wooden plug; 21 glass rod, 22 microscope, 23 light source, 24 image acquisition module, 25 slide glass, 26 grating. DETAILED DESCRIPTION

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0025] Example 1 See also Figure 1 Embodiment 1 provides an automatic detection platform for metal linear expansion coefficient, including a heater 1, a temperature detection module, a control module and a micro-distance detection module 2. The temperature detection module is arranged in the heater 1 and is electrically connected to the control module, and can specifically include a single-chip microcomputer and a DS18B20 temperature sensor. Among them, the control module can specifically be a computer. The micro-distance detection module 2 includes a smooth glass rod 21, a microscope 22, a light source 23, an image acquisition module 24, a slide 25, a grating 26 and a pressing sheet. The microscope 22 is located next to the heater 1, and can specifically be arranged vertically with the glass rod 21. It can specifically be a biological microscope with a magnification of 30-50 times. Specifically, the model of the microscope 22 is specifically xsp-02. The light source 23 is located directly below the stage of the microscope 22, and is specifically a monochromatic light source. The image acquisition module 24 is arranged on the eyepiece of the microscope 22 (the eyepiece itself is removed), and is specifically a CCD, which is electrically connected to the control module. The glass slide 25 is placed on the stage, and is arranged horizontally. It is fixed by the pressing plate of the stage. The grating 26 is placed on the glass slide 25, and its slit is perpendicular to the glass rod 21. Its grating constant is specifically 1 / 200-1 / 400mm. The metal to be detected is placed in the heater 1 and its inner end is against the closed end of the heater 1. The glass rod 21 is arranged horizontally, and is arranged along the direction of the heater 1. Its inner end is against the outer end of the metal to be detected, and its outer end passes through the heater 1 to serve as a free end. The free end is fixedly connected to the corresponding side of the grating 26 (specifically fixed by gluing). The setting of this platform must ensure that the glass rod 21 can slide freely.

[0026] The control module is used to process the grating image through MATLAB to obtain a binary image with alternating black and white stripes. At different temperatures, the number of stripe movements is obtained according to the number of grayscale image binary changes at the detection point set in the binary image (specifically located at the center of the binary image); the temperature and the number of stripe movements are fitted to obtain the stripe movement number-temperature fitting curve and displayed; the linear expansion coefficient is calculated according to the length L0 of the metal rod, the grating constant, the magnification and the stripe movement number-temperature fitting curve and displayed; the temperature-time fitting curve is obtained and displayed.

[0027] Among them, the heater 1 in the embodiment of the present invention includes a horizontally arranged heating chamber 11 and a lifting structure 12 on the lower side thereof, etc., and the lifting structure 12 can enable the heating chamber 11 to move up and down. The heating chamber 11 is composed of an insulation layer, a glass tube, a heating wire and a copper tube from the outside to the inside, the heating wire is wound around the outer wall of the copper tube, the inner wall of the copper tube is smooth, and the lifting structure 12 is fixed on the lower side of the insulation layer. The heating chamber 11 is closed at one end away from the micro-distance detection module 2, and the other end is open and closed with a wooden plug 13 (the cover is arranged at the end of the glass tube (extending relative to the copper tube)). The wooden plug 13 is provided with a through hole for the glass rod 21 to pass through and slide (the contact part with the glass rod 21 is smooth). The metal to be detected is placed at the bottom of the heating chamber 11 and it is against the closed end of the heating chamber 11. The glass rod 21 passes through the through hole and is suspended on the wooden plug 13.

[0028] Example 2 Embodiment 1 provides an automatic detection platform for metal linear expansion coefficient, and its structure is basically the same as that of embodiment 1, except that: the magnification of the microscope 22 in this embodiment is 40 times, and the grating constant of the grating 26 is 1 / 300mm, which is easy to obtain in the laboratory.

[0029] Example 3 See also Figure 1-14 Embodiment 3 provides a method for automatically detecting a metal linear expansion coefficient, the method comprising the following steps: S101 : Measure the length L0 of the metal to be detected and place it (along the direction of the heater 1 ) in the heater 1 , adhere the grating 26 to the free end of the glass rod 21 and place it on the slide glass 25 .

[0030] S102 : raising the temperature of the heater 1 within a predetermined range (specifically, between a starting detection temperature and an ending detection temperature) and recording the temperature, and acquiring a grating image through the image acquisition module 24 .

[0031] Furthermore, the step also includes: a preheating stage and a detection stage; in the preheating stage: between room temperature and the starting detection temperature (such as about 30°C), the MATLAB GUI interface displays a temperature-time fitting curve, and manually or automatically determines whether the heater 1 heats evenly and increases linearly. In the detection stage: if the heater 1 heats evenly and increases linearly, a stripe movement quantity-temperature fitting curve is obtained based on the detection value between the starting detection temperature and the ending detection temperature (such as about 60°C).

[0032] S103: performing image processing on the grating image to obtain a binary image with alternating black and white stripes; this step specifically includes: S401: Obtain the raster image of the image acquisition module 24 through the videoinput function. The raster image is a grayscale image (the CCD itself has this function).

[0033] S402: Get the current raster image through the getsnapshot command and display it on the MATLAB GUI interface.

[0034] S403: Binarization processing is performed on the current raster image.

[0035] S404: De-noising is performed by filtering (specifically Gaussian filtering) to obtain a smooth and noise-free binary image and display it on the MATLAB GUI interface.

[0036] S104: Under different temperatures, the number of stripe movements is obtained according to the number of grayscale image binarization changes at a detection point in the binarized image (specifically located at the center of the binarized image). This step specifically includes: S501: Taking the center point of the binary image as the detection point, defining the value of the black stripe as 0 and the value of the white stripe as 1.

[0037] S502: The gradient is calculated by using the grad command. According to the gradient value of the first data, the gradient values ​​with opposite signs are discarded. Finally, the absolute values ​​of all the gradient values ​​(after discarding the gradient values ​​with opposite signs) are added together to obtain the number of stripe movements.

[0038] S105: Fitting the temperature and the number of fringe movements to obtain a fringe movement number-temperature fitting curve; Step S105 specifically includes: Each time the stripes of the binary image move, the current temperature is recorded; the least squares linear fitting is performed using the polyfit command, and a stripe movement number-temperature fitting curve is drawn with temperature as the horizontal coordinate and the stripe movement number as the vertical coordinate and displayed on the MATLAB GUI interface.

[0039] S106: Calculate the linear expansion coefficient based on the length L0, grating constant, magnification and fringe movement number-temperature fitting curve. The calculation process is well known to those skilled in the art, and a detailed description is omitted in this embodiment.

[0040] Among them, steps S103-S106 are executed through MATLAB; the raster image, the binary image, the temperature-time fitting curve, the number of fringe movements, the fringe movement number-temperature fitting curve, the residual graph, the linear expansion coefficient and the relative error, etc. are displayed in real time in the MATLAB GUI interface.

[0041] Furthermore, the method provided by the embodiment of the present invention also includes: obtaining a linear uniform heating interval according to a temperature-time fitting curve, and obtaining a stripe movement quantity-temperature fitting curve according to data of the linear uniform heating interval to improve accuracy.

[0042] Example 4 Embodiment 4 provides a method for automatically detecting the linear expansion coefficient of metal, using the automatic detection platform for the linear expansion coefficient of metal disclosed in Embodiment 1. This experimental measuring instrument mainly uses the grating 26 as the measurement standard, the microscope 22 and the CCD video system form a test imaging system, the image binarization result is input into the computer, the temperature sensor is controlled by the single chip microcomputer to measure the real-time temperature and communicate with the computer serial port, and the measured data is processed by MATLAB, and the results are all displayed in the MATLAB GUI interface. The operator observes the video generated by the CCD video system in the interactive interface of the MATLAB GUI design and processing, and the fixed point automatically counts the number of stripe movements, and then inputs the temperature data of the metal heating in real time through the temperature sensor, and can automatically follow the measurement to draw the stripe movement number-temperature fitting curve, the linear fitting residual diagram, and calculate the linear expansion coefficient of the metal and the error between the measured value and the theoretical value, and finally present it in the MATLAB GUI.

[0043] The main components are described below: 1. See Figure 1 In order to observe the grating stripes, the microscope 22 and the grating 26 are used as the basic measuring tool. The objective lens is adjusted to 40 times. The slide 25 and the grating 26 are placed on the stage in sequence. The slide 25 is gently clamped with a slide clamp. In order to see the grating image clearly, a light source 23 is placed at the position of the reflector under the stage. The light source 23 is turned on to allow light to illuminate the grating 26 through the light hole.

[0044] 2. CCD imaging system See also Figure 7-8 , remove the eyepiece of the microscope 22, and insert a CCD camera on the top of the lens barrel. CCD has a magnification function, which is equivalent to the eyepiece. The image collected in the CCD is an upright, magnified virtual image. Connect the CCD camera to the computer via a USB data cable, set the videoinput function to transfer the video recorded by the CCD to MATLAB, so that it can obtain real-time video in MATLAB (such as Figure 5 As shown in the figure), the image at the current moment is obtained through the MATLAB getsnapshot command. Since the CCD imaging has been grayscale processed, a suitable sensitivity factor is selected to binarize the image. After the image is binarized, there are still many places where "burrs" and other improper processing exist. Then, the image is denoised by Gaussian filtering, and a very smooth and almost noise-free binary image can be obtained (as shown in the figure). Figure 6 As shown in the figure, the red dots are the detection points).

[0045] At this point, a good quality binary stripe image has been obtained. After algorithm design, the center point of the image is selected as the detection point, and the value of the black stripe is set to 0 and the value of the white stripe is set to 1. When the grating stripes move, the value of the detection point will alternate between 0 and 1, so the gradient can be calculated through the grad in MATLAB. According to the gradient value of the first data, the gradient value with the opposite sign is discarded, and finally all the gradient values ​​are added up to get the number of grating stripes moving.

[0046] 3. AT89C52 single-chip temperature measurement system This patent specifically uses a temperature sensor based on a single-chip microcomputer. The temperature sensor can not only display temperature data in real time, but also has the advantages of high sensitivity and high precision. The DS18B20 digital temperature sensor is selected to measure the temperature. Its temperature measurement range is: -55℃—125℃, the highest measurement accuracy is 0.0625℃, and the lowest measurement accuracy is 0.5℃. This experiment uses a measurement accuracy of 0.1℃. The temperature data detected by the temperature sensor is connected to the computer through USB serial communication. In MATLAB, the serial function can be used to communicate with the single-chip microcomputer. After initializing and setting the relevant parameters and baud rate, the fread function is used to obtain the temperature data transmitted by the single-chip microcomputer and convert the data format. Finally, the temperature value can be encapsulated in a matrix for subsequent processing.

[0047] 4. Solid Linear Expansion Coefficient Tester See also Figure 1 , connect the test sample with a length of L0 to the temperature sensor and put it into the heater 1. The heater 1 is placed horizontally. The outer side of the heating chamber is covered with a wooden plug 13. The plug 13 has a through hole. A glass rod 21 is put in. One end of the glass rod 21 is close to the test sample, and the other end is connected to the edge of the grating 26 and fixed with glass glue. In order to reduce the friction between the grating 26 and the stage of the microscope 22 when it moves, a glass slide 25 is put between the stage and the grating 26 to reduce the sliding friction. The height of the heater 1 is adjusted so that the test sample, the glass rod 21, and the grating 26 are in the same horizontal plane.

[0048] 5. Data processing based on MATLAB GUI See also Figure 9-14 According to the matrix derivation of the univariate linear regression model in MATLAB GUI machine learning, the least squares linear fitting of the number of fringe movements and temperature can be realized in MATLAB using the polyfit command. The linear expansion coefficient and error of the metal can be obtained by substituting the slope of the fitting into the theoretical equation of the linear expansion coefficient. The residual graph, that is, the degree of deviation between the true value and the fitting curve, can also be automatically generated using relevant algorithms.

[0049] On this basis, the functions of temperature and time are added. By observing their linear correlation, the linear uniform heating range of the solid linear expansion coefficient measuring instrument can be obtained. Measuring data within this linear range can improve the accuracy of the data and correct erroneous data in time.

[0050] 6. Experimental device performance description (1) Heater 1 and power supply The heater 1 is composed of a base, a heating chamber 11 and a lifting structure 12. The heating chamber 11 is composed of a heating wire, a foam insulation layer, a glass tube and a copper tube. A copper tube with good thermal conductivity is placed in the glass tube, and its end is closed with a small wooden cover to form an approximately thermally insulating environment in the tube. The heating power supply adopts an AC voltage-regulated power supply, and the working voltage is set at 20V to 24V.

[0051] (2) Grating 26 accuracy One of the cores of this patent is that the grating 26 measures the tiny deformation of metal under the microscope 22. In this patent, the grating 22 is used as a measuring instrument like a ruler, and its minimum graduation value is 1 / 300mm. Compared with conventional measuring instruments, it has higher accuracy and can be used to measure the tiny deformation of objects and meet the measurement accuracy requirements.

[0052] (3) Microscope 22 and CCD imaging system performance The specific model of microscope 22 is xsp-02, the objective lens is x40, and the eyepiece is replaced by a CCD camera, which has magnification and image transmission functions. The resulting image has high resolution and high signal-to-noise ratio, and the image has been processed by grayscale, which is convenient for measuring the movement distance of the stripes.

[0053] (4) Temperature sensor Another core measurement of this patent is the temperature value when the metal is heated. For traditional mercury thermometers, the accuracy is low, manual reading is required, it is easily affected by the environment, and the response is very slow, and data cannot be directly transmitted. This experiment uses the DS18B20 temperature sensor, which has a temperature measurement range of -55℃—125℃, high accuracy, the highest measurement accuracy is 0.0625℃, and the lowest measurement accuracy is 0.5℃. This experiment uses a measurement accuracy of 0.1℃. Therefore, this experimental system has the advantages of fast response, small size, and can directly transmit data to the computer, which can ensure the real-time, reliability and accuracy of the experimental data.

[0054] The following is a description of the detection process: First, use a vernier caliper to measure the length L0 of the metal rod, then put the metal rod and the temperature sensor into the heater 1, close the wooden plug 13, and finally insert the glass rod 21 into the tube through the through hole on the wooden plug 13 so that one end of the glass rod is close to the metal rod. Adjust the objective lens of the microscope 22 to 40 times, stack the slide 25 and the grating 26 on the stage in sequence, gently clamp the slide 25 with the stage clamp to prevent the slide 25 from moving, turn on the light source 23, and let the light of the light source 23 illuminate the grating 26 through the light transmission hole. Open the MATLAB software, connect the USB interface of the CCD, the single-chip microcomputer and the temperature sensor USB interface at the same time, click the run button, debug the program, and make the MATLAB GUI interface run normally.

[0055] Then, adjust the coarse focusing knob and the fine focusing knob of the microscope 22 until clear alternating light and dark stripes can be observed in the computer MATLAB GUI interface, as shown in FIG. Figure 4 and Figure 5 . Adjust the position of the heater 1, coordinate with the height change of the lifting structure 12, and bring the other end of the glass rod 21 close to the edge of the grating 26. After the device is assembled and adjusted, start the subsequent measurement. Turn on the AC voltage regulating power supply, adjust it to the working voltage of the heater 1, observe the computer interface, preheating stage: observe the temperature at this time and the function graph of temperature and time. The graph shows whether the internal temperature of the heater 1 is uniform and increases linearly. When the temperature reaches about 30°C, it can be considered that the interior is linearly heated, and the system preheating is completed.

[0056] See also Figure 9-10 , when the detection point moves to the black stripe part, select the working mode (Please select the working mode), click Automatic (Automatic), click Start (Start), then just observe the measured data, each time a stripe is moved, the temperature at this time will be recorded, and these data will be presented in real time on the computer MATLAB GUI interface, and the measured data will be fitted on this interface to directly obtain the linear expansion coefficient measurement value, and compare it with the theoretical value to display the relative error. Of course, this step can also be clicked semi-automatically to manually enter the temperature value. The process is as follows Figure 8 shown.

[0057] Observe the data. Whenever the CCD monitoring point detects a stripe movement, the system automatically records the number of stripes moving through the monitoring point n and the current temperature value. The temperature range recorded is generally between 30℃ and 50℃ (copper records about 22 sets of data). Click Save Date, turn off the power, and end the experiment.

[0058] Take three samples of copper rod, iron rod and aluminum rod, and record the measurement data in Table 1, Table 2 and Table 3 according to the above measurement method and steps: T i (K) represents the metal temperature value of the i-th experiment.

[0059] (1) Measurement data and results of copper rod: Table 1 Copper rod experimental data record table

[0060] Linear fitting is performed on the data measured in Table 1, and the measurement results are as follows: the fitting function measured for the first time is y=1.0964*x-334.9, the RMSE (root mean square error) is 0.0600, and the linear expansion coefficient is α=1.7403*10 -5 , the relative error is 0.56%. The fitting function measured for the second time is y=1.1048*x-337.18, the RMSE (root mean square error) is 0.2102, and the linear expansion coefficient is α=1.7537*10 -5 , the relative error is 0.21%. The fitting function measured for the third time is y=1.1058*x-340.85, the RMSE (root mean square error) is 0.1064, and the linear expansion coefficient is α=1.7552*10 -5 , the relative error is 0.30%.

[0061] (2) Measurement data and results of iron rod: Similarly, replace the metal rod with an iron rod and repeat the above experimental steps. The experimental measurement data are recorded in Table 2.

[0062] Table 2 Iron rod experimental data record table

[0063] Linear fitting is performed on the data measured in Table 2, and the measurement results are as follows: the fitting function measured for the first time is y=0.7326*x-223.42, and the linear expansion coefficient is α=1.1587*10 -5 , the relative error is 0.97%. The fitting function measured for the second time is y=0.7500*x-224.38, and the linear expansion coefficient is α=1.1905*10 -5 , the relative error is 1.72%. The fitting function measured for the third time is y=0.7334*x-220.29, and the linear expansion coefficient is α=1.1641*10 -5 , the relative error is 0.50%.

[0064] (3) Measurement data and results of aluminum bars: Similarly, replace the metal rod with an aluminum rod and repeat the above experimental steps. The experimental measurement data are recorded in Table 3.

[0065] Table 3 Iron rod experimental data record table

[0066] Linear fitting is performed on the data measured in Table 3, and the measurement results are as follows: the fitting function measured for the first time is y=1.4839*x-464.09, the RMSE (root mean square error) is 0.1806, and the linear expansion coefficient is α=2.3554*10 -5 , the relative error is 0.74%. The fitting function measured for the second time is y=1.4806*x-462.26, the RMSE (root mean square error) is 0.0872, and the linear expansion coefficient is α=2.3436*10 -5 , the relative error is 0.24%. The fitting function measured for the third time is y=1.4837*x-463.72, the RMSE (root mean square error) is 0.1458, and the linear expansion coefficient is α=2.3524*10 -5 , the relative error is 0.62%.

[0067] Table 4 Reference data table of linear expansion coefficient of solids

[0068] Note: The linear expansion coefficient of iron varies with the carbon content and processing technology, and the linear expansion coefficient of brass varies with the composition and proportion of other metal elements added.

[0069] It can be seen from Tables 1-4 that the accuracy of the method using this patent is high, very close to the reference data and the relative error is very small. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An automatic detection platform for metal linear expansion coefficient, comprising a heater (1), a temperature detection module, a control module and a micro-distance detection module (2), wherein the temperature detection module is arranged in the heater (1) and is electrically connected to the control module; characterized in that: The micro-distance detection module (2) comprises a smooth glass rod (21), a microscope (22) next to the heater (1), a light source (23) directly below the stage of the microscope (22), an image acquisition module (24) on the eyepiece of the microscope (22), a glass slide (25) on the stage, a grating (26) on the glass slide (25), and a pressing sheet on the stage for fixing the glass slide (25); The metal to be detected is placed in the heater (1) and its inner end is against the closed end of the heater (1); the glass rod (21) is arranged horizontally and along the direction of the heater (1), its inner end is against the outer end of the metal to be detected, and its outer end passes through the heater (1) to serve as a free end; the free end is fixedly connected to the corresponding side of the grating (26), the slit of the grating (26) is perpendicular to the glass rod (21), and the image acquisition module (24) is electrically connected to the control module; The control module is used to process the grating image through MATLAB to obtain a binary image with alternating black and white stripes; at different temperatures, the number of stripe movements is obtained according to the number of binary changes of the grayscale image at the detection point set in the binary image; The temperature and the number of fringe movements are fitted to obtain the fringe movement number-temperature fitting curve and displayed; the linear expansion coefficient is calculated according to the length L0 of the metal rod, the grating constant, the magnification and the fringe movement number-temperature fitting curve and displayed; The temperature-time fitting curve is obtained and displayed.

2. The metal linear expansion coefficient automatic detection platform according to claim 1, characterized in that: The magnification of the microscope (22) is 30-50 times, the image acquisition module (24) is a CCD, and the grating constant of the grating (26) is 1 / 200-1 / 400 mm.

3. The metal linear expansion coefficient automatic detection platform according to claim 1, characterized in that: The heater (1) comprises a horizontally arranged heating chamber (11) and a lifting structure (12) at the lower side thereof; the heating chamber (11) comprises, from the outside to the inside, a heat-insulating layer, a glass tube, a heating wire and a copper tube in sequence; the heating wire is wound around the outer wall of the copper tube; and the lifting structure (12) is fixed to the lower side of the heat-insulating layer; one end of the heating chamber (11) away from the micro-distance detection module (2) is closed, and the other end is open and closed with a wooden plug (13); the wooden plug (13) is provided with a through hole for a glass rod (21) to pass through and slide; the metal to be detected is placed at the bottom of the heating chamber (11) and abuts against the closed end of the heating chamber (11), and the glass rod (21) passes through the through hole.

4. A detection method using the metal linear expansion coefficient automatic detection platform as claimed in claim 1, characterized in that: The method comprises the following steps: S101: Measure the length L0 of the metal to be detected and place it in the heater (1), bond the grating (26) to the free end of the glass rod (21) and place it on the slide glass (25); S102: raising the temperature of the heater (1) within a predetermined range and recording the temperature, and acquiring a grating image through an image acquisition module (24); S103: performing image processing on the grating image to obtain a binary image with alternating black and white stripes; S104: obtaining the number of fringe movements according to the number of grayscale image binarization changes at the detection point in the binarized image at different temperatures; S105: fitting the temperature and the number of fringe movements to obtain a fringe movement number-temperature fitting curve; S106: Calculate the linear expansion coefficient based on the length L0, grating constant, magnification and fringe movement amount-temperature fitting curve.

5. The method according to claim 4, characterized in that Execute steps S103-S106 through MATLAB; display the grating image, the binarized image, the temperature-time fitting curve, the fringe movement number, the fringe movement number-temperature fitting curve, the residual graph, the linear expansion coefficient and the relative error in real time in the MATLAB GUI interface.

6. The method according to claim 5, characterized in that Step S102 also includes: a preheating stage and a detection stage; In the preheating stage: between room temperature and the starting detection temperature, the MATLAB GUI interface displays the temperature-time fitting curve, and manually or automatically determines whether the heater (1) heats evenly and increases linearly; In the detection stage: if the heater (1) heats evenly and increases linearly, a stripe movement quantity-temperature fitting curve is obtained according to the detection value between the starting detection temperature and the ending detection temperature.

7. The method according to claim 6, characterized in that The method further comprises: obtaining a linear uniform heating interval according to a temperature-time fitting curve, and obtaining a stripe movement quantity-temperature fitting curve according to data of the linear uniform heating interval.

8. The method according to claim 7, characterized in that Step S103 specifically includes: S301: obtaining a raster image of an image acquisition module (24) through a videoinput function, wherein the raster image is a grayscale image; S302: Get the current raster image through the getsnapshot command and display it on the MATLAB GUI interface; S303: Binarization processing is performed on the current raster image; S304: Obtain a smooth and noise-free binary image through filtering and denoising, and display it on the MATLAB GUI interface.

9. The method according to claim 5, characterized in that Step S104 specifically includes: S401: Taking the center point of the binary image as the detection point, defining the value of the black stripe as 0 and the value of the white stripe as 1; S402: The gradient is calculated by using the grad command. According to the gradient value of the first data, the gradient value with the opposite sign is discarded. Finally, the absolute values ​​of all the gradient values ​​are added together to obtain the number of stripe movements.

10. The method according to claim 5, characterized in that Step S105 specifically includes: recording the current temperature each time the stripes of the binary image move once; performing least squares linear fitting by using the polyfit command, drawing a stripe movement number-temperature fitting curve with temperature as the horizontal coordinate and stripe movement number as the vertical coordinate, and displaying it on the MATLAB GUI interface.

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