Paper gravure press hot air adjusting device and method based on machine vision

Abstract

The invention discloses a paper gravure press hot air adjusting device based on machine vision, which comprises an unwinding unit, a printing stock is wound on the unwinding unit, the printing stock sequentially passes through a plurality of overprinting drying units, and the plurality of overprinting drying units are electrically connected with a controller. The controller is connected with an upper computer, and the printing stock winding and rolling units of the multiple overprinting and drying units are used for recycling and rolling. The invention further discloses a paper gravure press hot air adjusting method based on machine vision, through real-time monitoring and rapid adjustment, accurate control over the hot air amount is achieved, and the problems that due to improper drying or excessive drying, printing stock deformation is caused, accurate adjustment cannot be achieved, and then the overprinting precision is affected are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of printing and packaging equipment, and in particular relates to a hot air regulating device of a paper-type gravure printing machine based on machine vision, and also relates to a hot air regulating method of a paper-type gravure printing machine based on machine vision. Background Art

[0002] As a traditional printing process, gravure printing is widely used in packaging, labels, decorative materials and other fields with its high-precision and high-quality printing effects. There are many types of gravure printing machines. Taking the applicable materials as an example, there are mainly paper gravure printing machines, plastic film gravure printing machines, composite material gravure printing machines, etc., which transfer ink to the surface of the substrate through the gravure cylinder. In paper gravure printing, various types of paper can be selected, such as wood grain paper, powder paper, coated paper, special art paper, etc. Among them, wood grain paper simulates the texture of natural wood and is used in furniture, floor and other decorative industries; powder paper is favored by publications such as books and picture albums for its delicate feel and rich colors; coated paper and special art paper are often used in the production of high-end printed products and artworks because of their special texture and visual effects. However, in the gravure printing process, these substrates are easily affected by the moisture in the ink and the width will increase. This width increase cannot be eliminated when the drying is insufficient, and excessive air volume during the drying process will also cause it to shrink excessively, thereby affecting the registration accuracy of the printing.

[0003] The basic process of gravure printing covers plate making, inking, printing, drying and other links. Among them, registration refers to the accurate overlap of various ink patterns on the substrate during the gravure printing process, which is crucial to ensure the printing quality during the gravure printing process. In recent years, with the application of advanced technologies such as machine vision, machine learning, and artificial intelligence, it has provided an important foundation for improving the registration accuracy of gravure printing machines.

[0004] However, for paper-based gravure printing machines, registration still faces many difficulties. For example, in the process of printing substrates, due to the extremely high printing speed of gravure printing machines, once the registration is deviated, not only will batches of waste products be produced, resulting in waste of substrates, materials, inks and other materials, but also additional environmental pollution; secondly, due to the high added value and large output of gravure printing products, inaccurate registration will seriously affect the quality of batch products, resulting in the failure of printed products to meet demand, causing large economic losses, and improper drying or excessive drying will cause deformation of the substrate, thereby affecting the axial (lateral) registration accuracy. Therefore, how to effectively adjust the hot air drying device to avoid deformation of the substrate while ensuring the printing speed has become a problem that needs to be solved in the development and improvement of registration technology for paper-based gravure printing machines. Summary of the invention

[0005] An object of the present invention is to provide a hot air regulating device for a paper-based gravure printing machine based on machine vision, which solves the problem that the printing material is deformed due to improper drying or excessive drying, and cannot be accurately adjusted, thereby affecting the overprinting accuracy.

[0006] Another object of the present invention is to provide a hot air regulating method for a paper gravure printing machine based on machine vision.

[0007] A technical solution adopted by the present invention is a hot air regulating device for a paper-based gravure printing machine based on machine vision, including an unwinding unit, on which a substrate is wound, and the substrate passes through a plurality of overprint drying units in sequence, and the plurality of overprint drying units are electrically connected to a controller, and the controller is connected to a host computer, and the substrates of the plurality of overprint drying units are wound around a reeling unit for recovery into a roll.

[0008] The present invention is also characterized in that The unwinding unit includes an unwinding motor, a reference camera is arranged above the unwinding motor, and the reference camera is used to determine the standard position of the substrate. The rewinding unit includes a rewinding motor, and under the driving action of the rewinding motor, the substrate coils on multiple overprinting and drying units are recovered into rolls; each overprinting and drying unit includes a gravure printing unit, the substrate is wound around a guide roller through the gravure printing unit, a steering roller a is arranged vertically above the guide roller, an oven is arranged between the guide roller and the steering roller a, an air outlet fan is arranged at one end of the oven close to the guide roller, an air inlet fan is arranged at one end of the oven close to the steering roller a, a steering roller b is arranged on the horizontal side of the steering roller a, a guide roller is arranged vertically below the steering roller b, a gravure printing unit is arranged on one side of the guide roller, two guide rollers located between the two gravure printing units are on the same horizontal straight line, a monitoring camera is arranged on the guide roller located at the rear of each overprinting and drying unit, the reference camera and the monitoring camera are both connected to the host computer, the air inlet fan and the air outlet fan are both connected to the fan frequency converter, and the fan frequency converter is connected to the controller.

[0009] The two guide rollers, steering roller a and steering roller b located between the two gravure printing units are responsible for carrying the substrate and guiding the substrate to run along a specific trajectory. The guide roller includes a guide roller body. The guide roller bodies are basically similar and are all cylindrical. A guide roller head is arranged in the axial direction of the guide roller body. The guide roller head adopts a multi-stage shoulder, and the end of the guide roller head is installed in the mechanical wall panel.

[0010] The projection lines of the two ends of the guide roller body on the horizontal ground are the guide roller boundaries, and each projection line is set inwardly and parallel to the detection area boundary. The area between the guide roller boundary on each side and the detection area boundary forms an image acquisition area. The width between the guide roller boundary on each side and the detection area boundary is 35mm to 45mm. The guide roller boundary is the projection of the planes at both ends of the guide roller body cylinder, which is used to determine the other side boundary of the image acquisition area; the image acquisition area is a rectangular area, and the detection area boundary and the guide roller boundary together determine the width of the image acquisition area. The length of the image acquisition area is equal to any value between 30% and 50% of the width of the substrate; each image acquisition area has only one side image of a group of guide rollers for acquiring the substrate image.

[0011] Two substrate fluctuation boundaries are set in parallel inside each image acquisition area, and a substrate position line is set in parallel between the two substrate fluctuation boundaries. The substrate fluctuation boundary reflects the fluctuation range in substrate printing, and the substrate position line reflects the coordinate point where most of the substrate boundary information is concentrated. The distance between the substrate position line and the guide roller boundary is the spacing.

[0012] Both the reference camera and the monitoring camera are linear array industrial cameras.

[0013] Another technical solution adopted by the present invention is: The hot air regulating method of a paper-type gravure printing machine based on machine vision adopts a hot air regulating device of a paper-type gravure printing machine based on machine vision, and is specifically implemented according to the following steps: S1, the printing material is fed through the unwinding unit, guide roller and winding unit working together to realize the moving feeding of the printing material; S2, the reference camera collects the initial image and calculates and determines the initial width of the substrate; S3, the substrate arrives at multiple overprinting and drying units for gravure printing, and after printing, the paper substrate is dried; S4. The monitoring camera collects secondary images of the dried substrate and calculates the change in deformation of the dried substrate before and after printing. According to the change in width of the substrate before and after printing, the controller adjusts the air inlet and outlet of the oven, and the substrate continues to move forward for subsequent printing or material collection operations.

[0014] The present invention is also characterized in that the specific process of S2 is: S21, the reference camera is installed before the substrate enters the printing area, and the reference camera is used to collect the original image of the substrate before printing; S22, graying the original image captured by the reference camera; converting the original image into a grayscale image, with a pixel grayscale level of 0 to 255; S23, binarizing the grayscale image; selecting a threshold to perform image binary segmentation calculation according to the color difference between the substrate background color and the substrate edge; when the substrate is white, the binarization threshold is set to 50 to 100, and when the substrate is gray, the binarization threshold is set to 20 to 50; a value greater than the threshold is assigned a value of 1, and a value less than the threshold is assigned a value of 0; S24, along the forward direction of the substrate, the binarized pixels are projected and calculated; before the binary image is projected, a negative calculation is first performed to set the points with pixel values ​​of 0 to 1, and the points with pixel values ​​of 1 to 0; then the projection calculation is performed, the projection direction is the direction parallel to the axial direction of each guide roller body as the reference line, all pixels are projected onto it, the sum of the corresponding pixel values ​​at each position on the reference line is counted, and a projection curve is obtained according to the projection result as the pixel projection, the projection curve reflects the total number of points with pixel values ​​of 1 at each position in the horizontal direction, and the points with pixel values ​​of 1 correspond to the darker color area, that is, the boundary information of the substrate; S25. Calculate the position of the initial substrate position line according to the projection calculation result; Draw a projection coordinate diagram, with the intersection of the baseline and the guide roller boundary as the origin and the baseline as the horizontal axis coordinate, count the number of projected pixels at each position above the baseline, and obtain the number distribution of projected pixels on the baseline, divide the number of projected pixels by the total number of pixels to obtain a probability density function, where the horizontal axis of the corresponding probability density function represents the position and the vertical axis represents the pixel density, and construct a probability distribution function based on the probability density function calculation: (1) In the formula, is the probability distribution function, t is the independent variable of the probability distribution function, is the probability density function, x is the horizontal coordinate value of the pixel after projection, which is 0 at the origin; dx is the integral variable, by calculating The corresponding solution t 0.5 , which is the coordinate value corresponding to the probability distribution function value of 0.5, and the corresponding coordinate position is the position of the identified substrate position line; S26. Calculate the initial width of the substrate based on the initial position of the substrate position line; the spacing is the distance between the substrate position line and the edge of the guide roller, and the spacing is calculated and summed on both sides of the guide roller; calculate the sum of the spacings on both sides of the substrate at the monitoring camera after printing by the gravure printing unit, and compare it with the sum of the spacings on both sides of the substrate calculated by the initial reference camera; when the sum of the spacings on both sides from the substrate position line to the edge of the guide roller decreases, the substrate becomes wider; when the sum of the spacings on both sides increases, the substrate becomes narrower.

[0015] The specific process of S4 is: S41, using a monitoring camera to collect images of the printed and dried substrate; S42, graying the substrate image captured by the monitoring camera; converting the substrate image into a grayscale image, with a pixel grayscale level of 0 to 255; S43, binarizing the grayscale processed image; selecting a threshold to perform image binary segmentation calculation according to the color difference between the substrate background color and the substrate edge, wherein the binarization threshold is set to 50 to 100 when the substrate is white, and the binarization threshold is set to 20 to 50 when the substrate is gray; S44, along the forward direction of the substrate, the binarized pixels are projected and calculated; before the binary image is projected, a negative calculation is first performed to set the points with pixel values ​​of 0 to 1, and the points with pixel values ​​of 1 to 0; then the projection calculation is performed, the projection direction is the direction parallel to the axial direction of each guide roller body as the reference line, all the pixels are projected onto it, the sum of the corresponding pixel values ​​at each position on the reference line is counted, and a projection curve is obtained according to the projection result as the pixel projection, the projection curve reflects the total number of points with pixel values ​​of 1 at each position in the horizontal direction, and the points with pixel values ​​of 1 correspond to the darker color area, that is, the boundary information of the substrate; S45. Calculate the position of the current substrate position line according to the projection calculation result; draw a projection coordinate diagram, take the intersection of the baseline and the guide roller boundary as the origin, take the baseline as the horizontal axis coordinate, count the number of pixels projected at each position above the baseline, obtain the number distribution of the projected pixels on the baseline, and then divide it by the total number of pixels to obtain the corresponding probability density function; the horizontal axis of the corresponding probability density function represents the position, and the vertical axis represents the pixel density; solve the probability distribution function corresponding to the corresponding pixel probability density function, and find the coordinate value corresponding to the probability distribution function value of 0.5, and the corresponding coordinate position is the identified substrate position line; S46. Calculate the change in substrate width according to the current substrate position line position.

[0016] The specific process of S46 is: S461, the spacing is the distance between the substrate position line and the guide roller boundary, and the spacing is calculated and summed on both sides of the guide roller; S462, comparing the sum of the spacings of the corresponding monitoring cameras after printing of each gravure printing unit with the sum of the spacings calculated by the initial reference camera; S463, converting the error generated by the printing and drying of the substrate according to the difference between the current length of the substrate and the initial length in S26; S464, calculating the deformation amount of the substrate after printing and drying according to the current substrate width and the initial substrate width; When the sum of the distances on both sides from the substrate position line to the guide roller boundary decreases, the substrate becomes wider and the substrate humidity increases, and the controller controls the oven and fan inverter to increase the drying air volume; when the sum of the distances on both sides increases, the substrate becomes narrower, and the controller controls the oven and fan inverter to reduce the drying air volume; when the error change of the sum of the distances on both sides at the corresponding monitoring camera of each group of ovens is less than 2%, it is considered that the oven effect is reasonable and no adjustment is required.

[0017] The beneficial effects of the present invention are as follows: the hot air regulating device of the paper gravure printing machine based on machine vision of the present invention monitors the state of the substrate in real time through machine learning and image processing, dynamically adjusts the hot air volume parameters according to the actual printing situation, realizes the precise control of the drying air volume, ensures that the substrate is dried under suitable temperature and humidity conditions, thereby avoiding the shrinkage of the substrate caused by excessive drying, and finally causing the overprinting failure, thereby ensuring the overprinting accuracy in the printing process, and further improving the printing quality and production efficiency. It improves the energy utilization efficiency, reduces the overall energy consumption of the gravure printing equipment, reduces the scrap rate and production cost, and significantly improves the printing quality and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of a hot air regulating device of a paper gravure printing machine based on machine vision of the present invention; Figure 2 is a schematic diagram of the image acquisition area of ​​the present invention; Figure 3 It is a principle diagram of the image acquisition area of ​​the present invention; Figure 4 (a) is a schematic diagram of the guide roller structure of the present invention; Figure 4 (b) is a schematic diagram of the multipolar shoulder structure of the guide roller of the present invention; Figure 5 It is a flow chart of a hot air regulating method of a paper gravure printing machine based on machine vision of the present invention; Figure 6 is a calculation flow chart for determining the initial width of a substrate according to the present invention; Figure 7 It is a calculation flow chart for determining the current width of the substrate of the present invention.

[0019] In the figure, 1. unwinding unit, 2. substrate, 3. gravure printing unit, 4. guide roller, 401. guide roller body, 402. guide roller shaft head, 5. oven, 6. air inlet fan, 7. air outlet fan, 8. rewinding unit, 9. reference camera, 10. monitoring camera, 11. host computer, 12. controller, 13. fan inverter, 14. image acquisition area, 15. reference line, 16. pixel projection, 17. detection area boundary, 18. guide roller boundary, 19. substrate fluctuation boundary, 20. substrate position line, 21. spacing. DETAILED DESCRIPTION

[0020] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] Example 1 The invention discloses a hot air regulating device for a paper gravure printing machine based on machine vision, the structure of which is as follows: Figure 1 and Figure 2 As shown, it includes an unwinding unit 1, on which a printing material 2 is wound. The printing material 2 passes through a plurality of overprinting and drying units in sequence. The plurality of overprinting and drying units are electrically connected to a controller 12. The controller 12 is connected to a host computer 11. The printing material 2 passing through the plurality of overprinting and drying units is wound around a reeling unit 8 and is recovered into a roll.

[0022] Example 2 On the basis of Example 1, in this embodiment, the unwinding unit 1 is used as a feeding mechanism of the gravure printing machine, and the unwinding unit 1 includes an unwinding motor, and a reference camera 9 is arranged above the unwinding motor. The reference camera 9 is used to determine the standard position of the substrate 2, and the substrate 2 is continuously output in the form of a paper roll under the action of the unwinding motor. The rewinding unit 8 includes a rewinding motor, and under the driving action of the rewinding motor, the substrate 2 rolls on multiple overprinting and drying units are recovered into rolls.

[0023] Each overprint drying unit includes a gravure printing unit 3, the substrate 2 is wound around the guide roller 4 through the gravure printing unit 3, a steering roller a is arranged vertically above the guide roller 4, an oven 5 is arranged between the guide roller 4 and the steering roller a, an air outlet fan 7 is arranged at one end of the oven 5 near the guide roller 4, an air inlet fan 6 is arranged at one end of the oven 5 near the steering roller a, a steering roller b is arranged on the horizontal side of the steering roller a, a guide roller 4 is arranged vertically directly below the steering roller b, a gravure printing unit 3 is arranged on one side of the guide roller 4, and two guide rollers 4 located between the two gravure printing units 3 are on the same horizontal straight line. A monitoring camera 10 is arranged on the guide roller 4 located at the rear of each overprint drying unit, and the reference camera 9 and the monitoring camera 10 are connected to the host computer 11. The oven 5 dries the ink on the substrate 2, and the air inlet fan 6 and the air outlet fan 7 are responsible for the entry and extraction of hot air inside the oven 5. The substrate 2 is dried inside the oven 5 after printing. The air inlet fan 6 and the air outlet fan 7 are both connected to the fan frequency converter 13 , and the fan frequency converter 13 is connected to the controller 12 .

[0024] Example 3 On the basis of Example 2, the gravure printing unit 3 in this embodiment includes a plate cylinder, an impression cylinder and a scraper. A concave pattern is engraved on the plate cylinder. The concave pattern is filled with ink, and the ink is transferred to the substrate 2 under the action of the impression cylinder. The scraper is used to remove excess ink on the surface of the plate cylinder to ensure that only the ink of the concave pattern can be transferred to the paper. The substrate 2 is the main material for printing. In this embodiment, it refers to various types of roll paper substrates, including but not limited to coated paper, offset paper, newsprint, and special paper. Since the water absorption in the printing of paper substrates causes large deformation, the hot air regulating device of the paper gravure printing machine based on machine vision of the present invention can not only be used for various types of roll paper gravure printing machines, but also be applicable to other types of gravure printing machines.

[0025] The reference camera 9 and the monitoring camera 10 are both linear array industrial cameras, which are used to monitor the width and position of the substrate 2 in real time. The monitoring camera 10 in each overprint drying unit is used to detect the position change of the substrate 2 during the printing process in real time. The initial substrate width is obtained through the reference camera 9, and the current substrate 2 width is grasped through the monitoring camera 10. The air intake of the oven 5 is controlled according to the width change, thereby preventing excessive width deformation, thereby improving overprinting accuracy and ensuring printing quality.

[0026] The host computer 11 is the control center of the entire system, responsible for processing the data from the reference camera 9 and the monitoring camera 10, calculating the width and position changes of the substrate, and then analyzing these data through algorithms and sending corresponding instructions to the controller 12. The controller 12 receives instructions from the host computer 11, controls the fan inverter 13 according to the width change, and the fan inverter 13 changes the fan speed, and finally changes the air intake and drying efficiency of the oven 5. The fan inverter 13 adjusts the speed of the air intake fan 6 and the air outlet fan 7 according to the instructions of the controller 12, and adjusts the drying efficiency by increasing or decreasing the air intake and outlet volume per unit time. Larger air intake and air outlet volumes also correspond to larger energy consumption.

[0027] Example 4 On the basis of Example 3, in this embodiment, the two guide rollers 4, the steering roller a, and the steering roller b located between the two gravure printing units 3 are responsible for carrying the substrate 2 and guiding the substrate 2 to run along a specific trajectory. The guide roller 4 includes a guide roller body 401, which is basically similar and is a cylinder, such as Figure 4 As shown in (a), a guide roller shaft head 402 is provided in the axial direction of the guide roller body 401. Figure 4 As shown in (b), the guide roller shaft head 402 uses a multi-level shoulder, and the end of the guide roller shaft head 402 is installed in the mechanical wall panel. Figure 3As shown, the projection lines of the two ends of the guide roller body 401 on the horizontal ground are the guide roller boundaries 18, and each projection line is parallel to the detection area boundary 17 set inwardly. The projection line on each side and the detection area boundary 17 must cover the non-printing area of ​​at least 5mm at the edge of the substrate, and the projection line on each side and the detection area boundary must cover the guide roller boundary line. The area between the guide roller boundary 18 and the detection area boundary 17 on each side forms the image acquisition area 14, and the width between the guide roller boundary 18 and the detection area boundary 17 on each side is 35mm to 45mm. The guide roller boundary 18 is the projection of the plane at both ends of the cylinder of the guide roller body 401, which is used to determine the other side boundary of the image acquisition area 14; the image acquisition area 14 is a rectangular area, and the detection area boundary 17 and the guide roller boundary 18 together determine the width of the image acquisition area 14. The length of the image acquisition area 14 is equal to any value between 30% and 50% of the width of the substrate 2; each image acquisition area 14 has only one side image of a group of guide rollers 4 inside, which is used to collect the image of the substrate 2. Two substrate fluctuation boundaries 19 are arranged in parallel inside each image acquisition area 14, and a substrate position line 20 is arranged in parallel between the two substrate fluctuation boundaries 19. The substrate fluctuation boundary 19 reflects the fluctuation range in substrate printing, and the substrate position line 20 reflects the coordinate point where most of the substrate boundary information is concentrated, which is the direct basis for substrate positioning. At this position of the substrate position line 20, the probability distribution of pixels on the left and right sides is the same, reflecting the center position of the substrate boundary. The distance between the substrate position line 20 and the guide roller boundary 18 is the spacing 21.

[0028] The hot air regulating device of a paper gravure printing machine based on machine vision of the present invention can monitor the state of the printing material and the drying degree in real time, and accurately adjust the air volume according to the actual situation, which can effectively avoid the problem of deterioration of the quality of printed products due to insufficient drying. The adjustment process is short in time and fast in speed, which can avoid problems in large quantities of products, reduce material loss and save energy, avoid unnecessary energy waste, reduce environmental pollution, achieve energy conservation and emission reduction, and improve production efficiency and product quality.

[0029] Example 5 The present invention is a method for adjusting hot air of a paper gravure printing machine based on machine vision, which adopts the hot air adjusting device of the paper gravure printing machine based on machine vision. The flow chart is as follows: Figure 5 As shown, the implementation is carried out according to the following steps: S1, the printing material 2 is fed, and the unwinding unit 1, the guide roller 4, and the winding unit 8 work together to realize the movement and feeding of the printing material 2; S2, the reference camera 9 captures an initial image and calculates and determines the initial width of the substrate 2; S3, the printing substrate 2 arrives at multiple overprinting and drying units for gravure printing, and after printing is completed, the paper-type printing substrate 2 is dried; S4. The monitoring camera 10 performs secondary image acquisition on the dried printing substrate 2, calculates the change in deformation of the dried printing substrate 2 before and after printing, and according to the change in width of the printing substrate 2 before and after printing, the controller 12 adjusts the air intake and air outlet of the oven 5, and the printing substrate 2 continues to move forward for subsequent printing or material collection operations.

[0030] Example 6 The hot air regulating method of a paper gravure printing machine based on machine vision of the present invention adopts the hot air regulating device of a paper gravure printing machine based on machine vision, and is specifically implemented according to the following steps: S1, the printing material 2 is fed, and the unwinding unit 1, the guide roller 4, and the winding unit 8 work together to realize the movement and feeding of the printing material 2; The unwinding unit 1 unwinds the rolled substrate 2 and transports the substrate 2 to the printing area via the guide roller 4. During the transportation process, the guide roller 4 ensures that the substrate 2 is flat and stable to prevent deviation or wrinkles. After printing is completed, the winding unit 8 rewinds the substrate 2 to complete the entire feeding and winding process.

[0031] S2, the reference camera 9 captures an initial image and calculates and determines the initial width of the substrate 2; like Figure 6 As shown, the specific process of S2 is: S21, the reference camera 9 is installed before the substrate 2 enters the printing area, and the reference camera 9 is used to collect the original image of the substrate 2 before printing; S22, grayscale processing is performed on the original image captured by the reference camera 9; the original image is converted into a grayscale image, with pixel grayscale levels ranging from 0 to 255. The grayscale processing reduces the amount of data and improves the processing speed.

[0032] S23, performing binarization processing on the grayscale processed image; According to the color difference between the background color of substrate 2 and the edge of substrate 2, a threshold is selected for image binary segmentation calculation. When the substrate is white, the binarization threshold is set to 50 to 100, and when the substrate is gray, the binarization threshold is set to 20 to 50; when the value is greater than the threshold, the binarization value is assigned to 1, and when the value is less than the threshold, the binarization value is assigned to 0.

[0033] S24, performing projection calculation on the binarized pixels along the forward direction of the substrate 2; Before projecting the binary image, a negative calculation is performed first, and the points with pixel values ​​of 0 are set to 1, and the points with pixel values ​​of 1 are set to 0; then a projection calculation is performed, and the projection direction is the axial parallel direction of each guide roller body 401 as the reference line 15, all pixels are projected onto it, and the sum of the corresponding pixel values ​​at each position on the reference line 15 is counted. According to the projection result, a projection curve is obtained as the pixel projection 16. The projection curve reflects the total number of points with pixel values ​​of 1 at each position in the horizontal direction, and the points with pixel values ​​of 1 correspond to darker areas, that is, the boundary information of the substrate 2.

[0034] S25, calculating the position of the initial substrate position line 20 according to the projection calculation result; The baseline 15 is used as an image processing reference line to determine the direction and position of image acquisition. The pixel projection 16 performs projection calculation on the binarized pixels along the forward direction of the substrate 2 during the image processing process. By drawing a projection coordinate diagram, the distribution of the number of projected pixels is obtained.

[0035] Draw a projection coordinate diagram, with the intersection of the reference line 15 and the guide roller boundary 18 as the origin and the reference line 15 as the horizontal axis coordinate. Count the number of pixels projected at each position above the reference line 15 to obtain the number distribution of projected pixels on the reference line 15. Divide the number of projected pixels by the total number of pixels to obtain a probability density function. The horizontal axis of the corresponding probability density function represents the position, and the vertical axis represents the pixel density. Based on the probability density function calculation, a probability distribution function is constructed: (1) In the formula, is the probability distribution function, t is the independent variable of the probability distribution function, is the probability density function, x is the horizontal coordinate value of the pixel after projection, which is 0 at the origin; dx is the integration variable.

[0036] By calculation The corresponding solution t 0.5 , which is the coordinate value corresponding to the probability distribution function value of 0.5, and the corresponding coordinate position is the position of the identified substrate position line 20.

[0037] S26, calculating the initial width of the printing substrate 2 according to the initial position of the printing substrate position line 20.

[0038] The spacing 21 is the distance between the substrate position line 20 and the guide roller boundary 18. The spacing 21 is calculated and summed on both sides of the guide roller 4 at the same time; the sum of the spacings 21 on both sides of the substrate 2 at the monitoring camera 10 after printing by the gravure printing unit 3 is calculated, and compared with the sum of the spacings 21 on both sides of the substrate 2 calculated by the initial reference camera 9; when the sum of the spacings on both sides from the substrate position line 20 to the guide roller boundary 18 decreases, the substrate 2 becomes wider; when the sum of the spacings on both sides increases, the substrate 2 becomes narrower.

[0039] S3, the printing substrate 2 arrives at multiple overprinting and drying units for gravure printing, and after printing is completed, the paper-type printing substrate 2 is dried; S4. The monitoring camera 10 performs secondary image acquisition on the dried printing substrate 2, calculates the change in deformation of the dried printing substrate 2 before and after printing, and according to the change in width of the printing substrate 2 before and after printing, the controller 12 adjusts the air intake and air outlet of the oven 5, and the printing substrate 2 continues to move forward for subsequent printing or material collection operations.

[0040] Each overprint drying unit is responsible for printing one color to ensure the precise overlap of multi-color printing. The substrate 2 enters the gravure printing unit 3 for gravure printing. After printing, the substrate 2 enters the oven 5, and the hot air from the oven 5 dries the ink on the substrate 2 to ensure that the ink adheres to the surface of the substrate 2. The controller 12 controls the fan inverter 13 according to the deformation data provided by the monitoring camera 10. The fan inverter 13 changes the frequency and voltage of the AC power supplied to the motor to control the speed of the air inlet fan 6 and the air outlet fan 7, thereby changing the air intake and drying efficiency of the oven 5. The dried substrate 2 enters the subsequent printing process to complete the printing operation or directly enters the winding unit 8 to rewind the dried substrate 2 to complete the entire printing process.

[0041] like Figure 7 As shown, the specific process of S4 is: S41, using the monitoring camera 10 to collect an image of the printed material 2 after printing and drying; S42, graying the image of the substrate 2 captured by the monitoring camera 10; Convert the substrate 2 image to a grayscale image, with pixel gray levels ranging from 0 to 255. Grayscale processing reduces the amount of data and increases processing speed.

[0042] S43, performing binarization processing on the grayscale processed image; According to the color difference between the background color of substrate 2 and the edge of substrate 2, a threshold is selected for image binary segmentation calculation. When the substrate is white, the binarization threshold is set to 50 to 100, and when the substrate is gray, the binarization threshold is set to 20 to 50.

[0043] S44, performing projection calculation on the binarized pixels along the forward direction of the substrate 2; Before projecting the binary image, a negative calculation is performed first, and the points with pixel values ​​of 0 are set to 1, and the points with pixel values ​​of 1 are set to 0; then a projection calculation is performed, and the projection direction is the axial parallel direction of each guide roller body 401 as the reference line 15, all pixels are projected onto it, and the sum of the corresponding pixel values ​​at each position on the reference line 15 is counted. According to the projection result, a projection curve is obtained as the pixel projection 16. The projection curve reflects the total number of points with pixel values ​​of 1 at each position in the horizontal direction, and the points with pixel values ​​of 1 correspond to darker areas, that is, the boundary information of the substrate 2.

[0044] S45, calculating the position of the current substrate position line 20 according to the projection calculation result; Draw a projection coordinate diagram, with the intersection of the baseline 15 and the guide roller boundary 18 as the origin and the baseline 15 as the horizontal axis coordinate, and count the number of pixels projected at each position above the baseline 15 to obtain the number distribution of projected pixels on the baseline 15, and then divide it by the total number of pixels to obtain the corresponding probability density function; the horizontal axis of the corresponding probability density function represents the position, and the vertical axis represents the pixel density; solve the probability distribution function corresponding to the corresponding pixel probability density function, and find the coordinate value corresponding to the probability distribution function value of 0.5, and the corresponding coordinate position is the identified substrate position line 20.

[0045] S46, calculating the change in substrate width according to the current position of the substrate position line 20.

[0046] S461, the spacing 21 is the distance between the substrate position line 20 and the guide roller boundary 18, and the spacing 21 is calculated and summed on both sides of the guide roller 4; S462, comparing the sum of the spacings 21 of the corresponding monitoring cameras 10 after printing of each gravure printing unit 3 with the sum of the spacings 21 calculated by the initial reference camera 9; S463, converting the error generated by the printing and drying of the substrate according to the difference between the current length of the substrate and the initial length in S26; S464. Calculate the deformation amount of the substrate 2 after printing and drying according to the current width of the substrate 2 and the initial width of the substrate 2.

[0047] When the sum of the two-side spacings 21 from the substrate position line 20 to the guide roller boundary 18 decreases, the substrate 2 becomes wider, the humidity of the substrate 2 increases, and the controller 12 controls the oven 5 and the fan inverter 13 to increase the drying air volume; when the sum of the two-side spacings 21 increases, the substrate 2 becomes narrower, and the controller 12 controls the oven 5 and the fan inverter 13 to reduce the drying air volume; when the error change of the sum of the two-side spacings 21 at the corresponding monitoring camera 10 of each group of ovens 5 is less than 2%, it is considered that the effect of the oven 5 is reasonable and no adjustment is required.

[0048] The present invention is based on the machine vision of the paper type gravure printing machine hot air regulating method, before the substrate 2 is printed, the reference camera 9 collects the grayscale image of the initial state, after the substrate 2 is printed and dried, the monitoring camera 10 collects the image again at the specified position, and the upper computer 11 receives and processes the two sets of image data, and calculates the width change of the substrate 2 before and after printing through graying, binarization, and pixel projection processing, and then according to the calculation result, the upper computer 11 generates a hot air regulating instruction, and drives the frequency converter 13 through the controller 12 to adjust the speed of the air inlet fan 6 and the air outlet fan 7, so as to ensure that the substrate 2 remains stable during the drying process and avoids deformation. The present invention is based on the machine vision of the paper type gravure printing machine hot air regulating method, from the perspective of image pixels, adopts the strategy of indirectly measuring the width change of the substrate, simplifies the actual size conversion process between the substrate and the image, greatly reduces the amount of calculation, improves the equipment operation efficiency, reduces the manufacturing cost, and can match the high-speed printing of the gravure printing machine. The determination of the position of the substrate uses pixel probability density function and probability distribution function, which is highly efficient in calculation: by introducing machine vision algorithms, the air volume adjustment strategy can be automatically optimized based on real-time monitoring data feedback, which greatly reduces human intervention, improves the accuracy and response speed of adjustment, enhances adaptability, and improves the overall intelligence level and production efficiency of the equipment. Improve the level of equipment automation.

Claims

1. A hot air regulating device for a paper gravure printing machine based on machine vision, characterized in that: The invention comprises an unwinding unit (1), a printing substrate (2) is wound around the unwinding unit (1), the printing substrate (2) passes through a plurality of overprinting and drying units in sequence, the plurality of overprinting and drying units are electrically connected to a controller (12), the controller (12) is connected to a host computer (11), and the printing substrate (2) passing through the plurality of overprinting and drying units is wound around a reeling unit (8) to be recovered into a roll.

2. The hot air regulating device for a paper gravure printing machine based on machine vision according to claim 1, characterized in that: The unwinding unit (1) comprises an unwinding motor, a reference camera (9) is arranged above the unwinding motor, and the reference camera (9) is used to determine the standard position of the substrate (2). The rewinding unit (8) comprises a rewinding motor, and under the driving action of the rewinding motor, the substrate (2) on multiple overprinting and drying units is recovered into a roll; each overprinting and drying unit comprises a gravure printing unit (3), the substrate (2) is wound around a guide roller (4) through the gravure printing unit (3), a steering roller a is arranged vertically above the guide roller (4), a drying oven (5) is arranged between the guide roller (4) and the steering roller a, and an air outlet fan (7) is arranged at one end of the drying oven (5) close to the guide roller (4). An air inlet fan (6) is arranged near one end of the box (5) near the steering roller a, a steering roller b is arranged on the horizontal side of the steering roller a, a guide roller (4) is arranged vertically directly below the steering roller b, a gravure printing unit (3) is arranged on one side of the guide roller (4), two guide rollers (4) located between the two gravure printing units (3) are located on the same horizontal straight line, a monitoring camera (10) is arranged on the guide roller (4) located at the rear of each overprint drying unit, the reference camera (9) and the monitoring camera (10) are both connected to the host computer (11), the air inlet fan (6) and the air outlet fan (7) are both connected to the fan frequency converter (13), and the fan frequency converter (13) is connected to the controller (12).

3. The hot air regulating device for a paper gravure printing machine based on machine vision according to claim 2, characterized in that: The two guide rollers (4), steering roller a and steering roller b located between the two gravure printing units (3) are responsible for carrying the printing material (2) and guiding the printing material (2) to run along a specific track. The guide roller (4) comprises a guide roller body (401). The guide roller bodies (401) are basically similar and are all cylindrical. A guide roller shaft head (402) is arranged in the axial direction of the guide roller body (401). The guide roller shaft head (402) uses a multi-stage shaft shoulder. The end of the guide roller shaft head (402) is installed in the mechanical wall panel.

4. The hot air regulating device for a paper gravure printing machine based on machine vision according to claim 3, characterized in that: The projection lines of the two ends of the guide roller body (401) on the horizontal ground are the guide roller boundaries (18), and each projection line is parallel to the detection area boundary (17) set inwardly. The area between the guide roller boundary (18) and the detection area boundary (17) on each side forms an image acquisition area (14). The width between the guide roller boundary (18) and the detection area boundary (17) on each side is 35 mm to 45 mm. The guide roller boundary (18) is the projection of the plane at both ends of the cylinder of the guide roller body (401), which is used to determine the other side boundary of the image acquisition area (14); the image acquisition area (14) is a rectangular area, and the detection area boundary (17) and the guide roller boundary (18) together determine the width of the image acquisition area (14). The length of the image acquisition area (14) is equal to any value between 30% and 50% of the width of the substrate (2); each image acquisition area (14) has only one side image of a group of guide rollers (4) inside, which is used to acquire the image of the substrate (2).

5. The hot air regulating device for a paper gravure printing machine based on machine vision according to claim 4, characterized in that: Two substrate fluctuation boundaries (19) are arranged in parallel inside each image acquisition area (14), and a substrate position line (20) is arranged in parallel between the two substrate fluctuation boundaries (19). The substrate fluctuation boundary (19) reflects the fluctuation range of the substrate during printing, and the substrate position line (20) reflects the coordinate point where most of the substrate boundary information is concentrated. The distance between the substrate position line (20) and the guide roller boundary (18) is the spacing (21).

6. The hot air regulating device for a paper gravure printing machine based on machine vision according to claim 5, characterized in that: The reference camera (9) and the monitoring camera (10) are both linear array industrial cameras.

7. A hot air adjustment method for a paper gravure printing machine based on machine vision, characterized in that: The hot air regulating device for a paper gravure printing machine based on machine vision according to claim 6 is implemented specifically according to the following steps: S1, the printing substrate (2) is fed, and the unwinding unit (1), the guide roller (4), and the rewinding unit (8) work together to realize the moving feeding of the printing substrate (2); S2, the reference camera (9) captures an initial image and calculates and determines the initial width of the substrate (2); S3, the printing substrate (2) arrives at a plurality of overprinting and drying units for gravure printing, and after printing is completed, the paper-type printing substrate (2) is dried; S4, the monitoring camera (10) performs secondary image acquisition on the dried printing substrate (2), calculates the change in deformation of the dried printing substrate (2) before and after printing, and according to the change in width of the printing substrate (2) before and after printing, the controller (12) adjusts the air inlet and outlet of the drying oven (5), and the printing substrate (2) continues to move forward to perform subsequent printing or material collection operations.

8. The hot air regulating method for a paper gravure printing machine based on machine vision according to claim 7, characterized in that: The specific process of S2 is: S21, the reference camera (9) is installed before the substrate (2) enters the printing area, and the reference camera (9) is used to capture an original image of the substrate (2) before printing; S22, graying the original image captured by the reference camera (9); converting the original image into a grayscale image, with a pixel grayscale level of 0 to 255; S23, binarizing the grayscale processed image; selecting a threshold to perform image binary segmentation calculation according to the color difference between the background color of the substrate (2) and the edge of the substrate (2); when the substrate is white, the binarization threshold is set to 50 to 100, and when the substrate is gray, the binarization threshold is set to 20 to 50; If the value is greater than the threshold, it is assigned a value of 1; if the value is less than the threshold, it is assigned a value of 0. S24, along the forward direction of the substrate (2), projection calculation is performed on the binarized pixels; before the binary image is projected, a negative calculation is performed to set the points with pixel values ​​of 0 to 1 and the points with pixel values ​​of 1 to 0; then projection calculation is performed, the projection direction is the axial direction parallel to each guide roller body (401) as the reference line (15), all pixels are projected onto it, the sum of the corresponding pixel values ​​at each position on the reference line (15) is counted, and a projection curve is obtained according to the projection result as the pixel projection (16), the projection curve reflects the total number of points with pixel values ​​of 1 at each position in the horizontal direction, and the points with pixel values ​​of 1 correspond to the darker color area, that is, the boundary information of the substrate (2); S25. Calculate the position of the initial substrate position line (20) according to the projection calculation result; Draw a projection coordinate diagram, with the intersection of the reference line (15) and the guide roller boundary (18) as the origin and the reference line (15) as the horizontal axis coordinate, count the number of projected pixels at each position above the reference line (15), obtain the number distribution of projected pixels on the reference line (15), divide the number of projected pixels by the total number of pixels, and obtain a probability density function. The horizontal axis of the corresponding probability density function represents the position, and the vertical axis represents the pixel density. Based on the probability density function calculation, a probability distribution function is constructed: （1） In the formula, is the probability distribution function, t is the independent variable of the probability distribution function, is the probability density function, x is the horizontal coordinate value of the pixel after projection, which is 0 at the origin; dx is the integral variable, by calculating The corresponding solution t 0.5 , which is the coordinate value corresponding to the probability distribution function value of 0.5, and the corresponding coordinate position is the position of the identified substrate position line (20); S26, calculating the initial width of the printing substrate (2) according to the initial position of the printing substrate position line (20); The spacing (21) is the distance between the substrate position line (20) and the guide roller boundary (18), and the spacing (21) is calculated and summed on both sides of the guide roller (4); the sum of the spacings (21) on both sides of the substrate (2) at the monitoring camera (10) after printing of the gravure printing unit (3) is calculated, and compared with the sum of the spacings (21) on both sides of the substrate (2) calculated by the initial reference camera (9); when the sum of the spacings on both sides from the substrate position line (20) to the guide roller boundary (18) decreases, the substrate (2) becomes wider; when the sum of the spacings on both sides increases, the substrate (2) becomes narrower.

9. The hot air regulating method for a paper gravure printing machine based on machine vision according to claim 8, characterized in that: The specific process of S4 is: S41, using a monitoring camera (10) to collect an image of the printed material (2) after printing and drying; S42, graying the image of the substrate (2) captured by the monitoring camera (10); converting the image of the substrate (2) into a grayscale image, with a pixel grayscale level of 0 to 255; S43, binarizing the grayscale processed image; selecting a threshold value to perform image binary segmentation calculation according to the color difference between the background color of the substrate (2) and the edge of the substrate (2); when the substrate is white, the binarization threshold value is set to 50 to 100, and when the substrate is gray, the binarization threshold value is set to 20 to 50; S44, along the forward direction of the substrate (2), projection calculation is performed on the binarized pixels; before the binary image is projected, a negative calculation is performed to set the points with pixel values ​​of 0 to 1 and the points with pixel values ​​of 1 to 0; then projection calculation is performed, the projection direction is the axial direction parallel to each guide roller body (401) as the reference line (15), all pixels are projected onto it, the sum of the corresponding pixel values ​​at each position on the reference line (15) is counted, and a projection curve is obtained according to the projection result as the pixel projection (16), the projection curve reflects the total number of points with pixel values ​​of 1 at each position in the horizontal direction, and the points with pixel values ​​of 1 correspond to the darker color area, that is, the boundary information of the substrate (2); S45, calculating the position of the current substrate position line (20) according to the projection calculation result; drawing a projection coordinate diagram, taking the intersection of the reference line (15) and the guide roller boundary (18) as the origin and the reference line (15) as the horizontal axis coordinate, counting the number of pixels projected at each position above the reference line (15), obtaining the number distribution of the projected pixels on the reference line (15), and then dividing by the total number of pixels to obtain a corresponding probability density function; the horizontal axis of the corresponding probability density function represents the position, and the vertical axis represents the pixel density; solving the probability distribution function corresponding to the corresponding pixel probability density function, and finding the coordinate value corresponding to the probability distribution function value of 0.5, the corresponding coordinate position is the identified substrate position line (20); S46, calculating the change in substrate width according to the current position of the substrate position line (20).

10. The hot air regulating method for a paper gravure printing machine based on machine vision according to claim 9, characterized in that: The specific process of S46 is: S461, the spacing (21) is the distance between the substrate position line (20) and the guide roller boundary (18), and the spacing (21) is calculated and summed on both sides of the guide roller (4); S462, comparing the sum of the spacings (21) of the corresponding monitoring cameras (10) after printing of each gravure printing unit (3) with the sum of the spacings (21) calculated by the initial reference camera (9); S463, converting the error generated by the printing and drying of the substrate according to the difference between the current length of the substrate and the initial length in S26; S464, calculating the deformation amount of the substrate (2) after printing and drying according to the current width of the substrate (2) and the initial width of the substrate (2); When the sum of the two side spacings (21) from the substrate position line (20) to the guide roller boundary (18) decreases, the substrate (2) becomes wider, the humidity of the substrate (2) increases, and the controller (12) controls the oven (5) and the fan inverter (13) to increase the drying air volume; when the sum of the two side spacings (21) increases, the substrate (2) becomes narrower, and the controller (12) controls the oven (5) and the fan inverter (13) to reduce the drying air volume; when the error of the sum of the two side spacings (21) at the monitoring camera (10) corresponding to each group of ovens (5) is less than 2%, it is considered that the effect of the oven (5) is reasonable and no adjustment is required.

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