A composite hose gradient color flexographic printing process and color control method

Abstract

The present application relates to the technical field of composite hose printing, and discloses a composite hose gradient color flexographic printing process and a color control method. The process comprises the following steps: collecting the color distribution sequence of the surface of the composite hose along the circumference of the tube body after the tube body is separated from the impression cylinder; extracting the color uniformity characteristic value; inverting the pressure distribution curve along the circumference of the impression cylinder; and adjusting the axial feed amount of the impression cylinder by taking the pressure distribution curve as the feedback amount. The present application also discloses a composite hose gradient color control method. The present application converts the color distribution of the tube body into a pressure distribution sensing signal from the printing result, and realizes closed-loop adjustment of the contact pressure in the flexographic printing process.

Description

Technical Field

[0001] This invention relates to the field of composite tube printing technology, and in particular to a composite tube gradient color flexographic printing process and color control method. Background Technology

[0002] Composite flexible tubes, due to their lightweight, foldable, and corrosion-resistant properties, are widely used in packaging for industries such as daily chemicals, pharmaceuticals, and food. With the increasing demands of the consumer market for packaging appearance quality, the gradient color printing quality on the surface of composite flexible tubes has become a crucial factor influencing product competitiveness. In the flexographic printing process of composite flexible tubes, the contact pressure between the impression cylinder and the composite flexible tube is a core process parameter determining the ink transfer volume and color uniformity. Currently, flexographic printing pressure adjustment mainly relies on operators manually adjusting the bearing positions at both ends of the impression cylinder using feeler gauges or based on experience while the equipment is stopped. The inherent problem with this adjustment method is that the pressure adjustment is based on static measurement results, while in actual printing processes, tube wall thickness errors (approximately 0.02-0.05 mm) and flexible deformation of the tube body cause the contact pressure to exhibit a dynamic, non-uniform distribution in the circumferential and axial directions of the impression cylinder. Static adjustment cannot capture and compensate for this dynamic change.

[0003] However, existing technologies lack an effective means to sense the contact pressure distribution between the impression cylinder and the composite hose online. Directly installing pressure sensors on the impression cylinder surface would compromise its geometric accuracy and surface hardness; attaching sensors to the composite hose surface would affect normal printing and hose transport. This technological blind spot has resulted in flexographic pressure control remaining in an open-loop state of "setting based on experience at startup, undetectable during production, and only discovered after defective products are produced." The fundamental reason is that existing technologies limit "pressure sensing" to the framework of "direct measurement with installed sensors," failing to recognize that the color distribution on the hose after printing is itself a "spatial mapping record" of the contact pressure on the hose—areas with high pressure have more ink transfer and darker colors, while areas with low pressure have less ink transfer and lighter colors. Therefore, this invention reconstructs the "pressure distribution sensing" problem into a "circumferential color distribution analysis" problem. By collecting the color distribution of the composite hose after it detaches from the impression cylinder, the contact pressure distribution between the impression cylinder and the composite hose is inverted, thus achieving online sensing and closed-loop control of flexographic pressure without installing any pressure sensors.

[0004] Therefore, this invention proposes a composite flexible tube gradient color flexographic printing process and color control method. Summary of the Invention

[0005] This invention provides a composite flexible tube gradient color flexographic printing process and color control method. By converting the color distribution of the tube body from the printing result into a pressure sensing signal, it realizes online closed-loop adjustment of flexographic printing pressure, fundamentally solving the technical problem that flexographic printing pressure cannot be sensed and controlled online.

[0006] This invention provides a composite flexible tube gradient color flexographic printing process, comprising: Downstream of the contact surface between the impression cylinder and the composite tube in the flexographic printing unit, the circumferential color distribution sequence of the composite tube surface after it leaves the impression cylinder is collected. Extract color uniformity feature values ​​from the circumferential color distribution sequence of the tube; Based on the color uniformity characteristic value, the pressure distribution curve of the contact pressure between the impression cylinder and the composite hose in the circumferential direction of the impression cylinder is derived. Using the pressure distribution curve as feedback, the axial feed of the impression cylinder is adjusted so that the color uniformity characteristic value of the circumferential color distribution sequence of the tube approaches the preset target value.

[0007] Furthermore, the circumferential color distribution sequence of the composite tube surface after it detaches from the impression cylinder is collected, including: A first image is acquired by illuminating the surface of the composite hose with a first ray at an acute angle to the axis of the composite hose. A second image is acquired by illuminating the surface of the composite hose with a second ray at an obtuse angle to the axis of the composite hose. Based on the grayscale gradient changes on the surface of the composite hose in the first and second images, the three-dimensional morphological contour of the composite hose surface is reconstructed. The color values ​​of each position on the surface of the composite hose in the circumferential angular coordinates are extracted from the three-dimensional morphological contour. The color values ​​of all positions on the circumferential angular coordinates are arranged in circumferential order to form the circumferential color distribution sequence of the hose body.

[0008] Furthermore, when extracting the color values ​​of each position on the surface of the composite tube in circumferential angular coordinates from the three-dimensional morphological contour, the foot of the perpendicular line between the common perpendicular line of the composite tube axis and the imprint cylinder axis on the surface of the composite tube is taken as the mapping origin. The coordinates of each pixel in the three-dimensional morphological contour are transformed into the circumferential angular coordinate system with the mapping origin as the starting point, and the circumferential angular coordinate value of each pixel is obtained. The average color value of all pixels with the same circumferential angular coordinate value in the three-dimensional morphological contour is taken as the average color value corresponding to the circumferential angular coordinate value. The average color values ​​corresponding to all circumferential angular coordinate values ​​are arranged in circumferential order to form the circumferential color distribution sequence of the tube body.

[0009] Furthermore, color uniformity feature values ​​are extracted from the circumferential color distribution sequence of the tube, including: Starting from the first element of the circumferential color distribution sequence of the tube, accumulate elements one by one forward from the current element. For each accumulated element, calculate the average of the absolute values ​​of the color differences between adjacent elements in the current accumulated sequence as the local color fluctuation amplitude of the current accumulated sequence. When the change in local color fluctuation amplitude relative to the local color fluctuation amplitude of the previous accumulated position exceeds the preset change threshold for the first time, the end point of the current accumulated sequence is used as the boundary of the first sub-interval. The operation is repeated in the remaining sequence until all sub-intervals are divided to obtain a sub-interval sequence of unequal length. For each unequal-length subinterval, with the median of all element color values ​​in that subinterval as the center, calculate the cumulative distribution function value of the absolute deviation between the color values ​​of all elements in that subinterval and the median. Sum the cumulative distribution function values ​​of all subintervals and divide by the number of subintervals to obtain the color uniformity characteristic value.

[0010] Furthermore, when calculating the cumulative distribution function value of the absolute deviation of all element color values ​​in the sub-interval from the median, the absolute deviations of all element color values ​​in the sub-interval from the median are arranged in ascending order to form a deviation sequence. The ratio of the sum of the first k deviation values ​​in the deviation sequence to the sum of all deviation values ​​is taken as the cumulative distribution function value of the kth deviation value, where k is a positive integer from 1 to the length of the deviation sequence.

[0011] Furthermore, the preset change threshold is 10% of the local color fluctuation amplitude of the previous cumulative position.

[0012] Furthermore, based on the color uniformity characteristic value, the pressure distribution curve of the contact pressure between the impression cylinder and the composite hose in the circumferential direction of the impression cylinder is derived, including: The absolute value of the difference between the color value corresponding to each circumferential angle coordinate value and the color uniformity characteristic value in the circumferential color distribution sequence of the tube body is taken as the color deviation of that circumferential angle coordinate value. The color deviation of all circumferential angle coordinate values ​​are arranged in circumferential order to form a color deviation sequence. Perform a second-order difference operation on the color deviation sequence to obtain the color deviation curvature sequence; The peak and valley positions of curvature are extracted from the color deviation curvature sequence. The difference in color deviation between the peak and valley positions is used as the pressure deviation characterization of the pair. The pressure deviation characterizations of all positions are arranged in circumferential order to form a pressure distribution curve.

[0013] Furthermore, when extracting the peak and valley positions of curvature from the color deviation curvature sequence, the local maxima in the color deviation curvature sequence are used as the peak positions of curvature, the local minima in the color deviation curvature sequence are used as the valley positions of curvature, and the difference in color deviation between the peak and valley positions of curvature is used as the pressure deviation characterization quantity of the paired positions.

[0014] Furthermore, using the pressure distribution curve as feedback, the axial feed of the impression cylinder is adjusted, including: Extract the locations of pressure peaks and valleys from the pressure distribution curve; Calculate the pressure difference between the pressure peak location and the pressure trough location; When the pressure difference exceeds the preset pressure difference threshold, the axial feed of the first and second ends of the impression cylinder is adjusted to reduce the pressure difference as the control objective, so that the axial feed corresponding to the pressure peak position is reduced and the axial feed corresponding to the pressure valley position is increased.

[0015] This invention provides a method for controlling the gradient color of a composite flexible tube, comprising: Collect the circumferential color distribution sequence of the composite tube surface after it is removed from the impression cylinder; Extract color uniformity feature values ​​from the circumferential color distribution sequence of the tube; Based on the color uniformity characteristic value, the pressure distribution curve of the contact pressure between the impression cylinder and the composite hose in the circumferential direction of the impression cylinder is derived. Using the pressure distribution curve as feedback, the axial feed of the impression cylinder is adjusted so that the color uniformity characteristic value of the circumferential color distribution sequence of the tube approaches the preset target value.

[0016] The beneficial effects of this invention compared to existing technologies are as follows: Existing flexographic printing pressure regulation relies on operators manually adjusting the pressure based on static measurements or experience while the equipment is stopped. This fails to detect and compensate for the dynamic non-uniform distribution of contact pressure in the circumferential direction of the impression cylinder caused by tube wall thickness errors and flexible deformation during printing, resulting in uncontrolled color uniformity, high scrap rates, and the inability to intervene online. This invention, by collecting the circumferential color distribution sequence of the composite flexible tube after it detaches from the impression cylinder, extracts color uniformity feature values, and reconstructs the pressure distribution curve in the circumferential direction of the impression cylinder. This curve is then used as feedback to adjust the axial feed of the impression cylinder in real time. This achieves online sensing and closed-loop control of flexographic printing pressure without installing any pressure sensors, ensuring that the color uniformity feature values ​​continuously approach the preset target value. This fundamentally solves the technical problem of flexographic printing pressure being "unable to be sensed online and can only operate in an open-loop manner."

[0017] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in this application.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart illustrating the overall data processing of the composite flexible tube gradient color flexographic printing process in an embodiment of the present invention. Figure 2 This is a flowchart of the circumferential color distribution sequence acquisition process in an embodiment of the present invention; Figure 3 This is a flowchart illustrating the pressure distribution curve inversion in an embodiment of the present invention. Detailed Implementation

[0020] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0021] refer to Figure 1 This invention provides an embodiment of a composite flexible tube gradient color flexographic printing process, comprising: Downstream of the contact surface between the impression cylinder and the composite tube in the flexographic printing unit, the circumferential color distribution sequence of the composite tube surface after it leaves the impression cylinder is collected. Extract color uniformity feature values ​​from the circumferential color distribution sequence of the tube; Based on the color uniformity characteristic value, the pressure distribution curve of the contact pressure between the impression cylinder and the composite hose in the circumferential direction of the impression cylinder is derived. Using the pressure distribution curve as feedback, the axial feed of the impression cylinder is adjusted so that the color uniformity characteristic value of the circumferential color distribution sequence of the tube approaches the preset target value.

[0022] In this embodiment, the downstream side of the contact surface between the impression cylinder and the composite hose in the flexographic printing unit refers to the area after the composite hose has completed contact with and detached from the impression cylinder. Collecting the tube's color distribution at this location reflects the actual printing effect after the impression cylinder applies contact pressure to the composite hose, while avoiding interference with the normal printing process due to the collection location being within the contact area of ​​the impression cylinder. The circumferential color distribution sequence is a one-dimensional sequence of data formed by extracting the color values ​​at various circumferential angles on the surface of the composite hose and arranging them in circumferential order. This sequence comprehensively reflects the color distribution state of the composite hose at various circumferential angles.

[0023] In this embodiment, the color uniformity feature value is used to quantify the consistency of color distribution at various circumferential angles of the composite hose body. When the contact pressure between the impression cylinder and the composite hose is uniformly distributed in the circumferential direction of the impression cylinder, the amount of ink transferred at each position in the circumferential direction of the hose body is consistent, the numerical differences of each element in the circumferential color distribution sequence of the hose body are small, and the color uniformity feature value is high. When the contact pressure distribution is uneven, the numerical differences of each element in the circumferential color distribution sequence of the hose body are large, and the color uniformity feature value is low.

[0024] In this embodiment, the pressure distribution curve of the contact pressure between the impression cylinder and the composite hose in the circumferential direction of the impression cylinder is derived by inverse calculation based on the color uniformity characteristic value. This means that the physical correspondence between the color uniformity characteristic value and the contact pressure is used for reverse calculation. The physical correspondence is that the magnitude of the contact pressure directly affects the amount of ink transferred, and the magnitude of the amount of ink transferred further determines the color depth of the composite hose surface. That is, the greater the contact pressure, the greater the amount of ink transferred and the darker the color at that position, and the smaller the contact pressure, the smaller the amount of ink transferred and the lighter the color at that position.

[0025] In this embodiment, the axial feed of the impression cylinder refers to the displacement of the impression cylinder along its own axis. Adjusting the axial feed of the impression cylinder can change the contact pressure distribution between the two ends of the impression cylinder and the composite hose. When the axial feed of the first end of the impression cylinder increases, the contact pressure between the first end of the impression cylinder and the composite hose increases; when the axial feed of the second end of the impression cylinder increases, the contact pressure between the second end of the impression cylinder and the composite hose increases. The preset target value is the expected value of the color uniformity characteristic value of the circumferential color distribution sequence of the tube body, which is determined by statistically analyzing the color uniformity characteristic values ​​of multiple qualified printed samples. Using the pressure distribution curve as feedback, the axial feed of the impression cylinder is adjusted so that the color uniformity characteristic value of the circumferential color distribution sequence of the tube body approaches the preset target value, thus forming a closed-loop control with the pressure distribution curve as feedback signal.

[0026] refer to Figure 2In another embodiment of the present invention, collecting the circumferential color distribution sequence of the composite tube surface after it leaves the impression cylinder includes: A first image is acquired by illuminating the surface of the composite hose with a first ray at an acute angle to the axis of the composite hose. A second image is acquired by illuminating the surface of the composite hose with a second light beam at an obtuse angle to the axis of the composite hose. Based on the grayscale gradient changes on the surface of the composite hose in the first and second images, the three-dimensional morphological contour of the composite hose surface is reconstructed. The color values ​​of each position on the surface of the composite hose in the circumferential angular coordinates are extracted from the three-dimensional morphological contour. The color values ​​of all positions on the circumferential angular coordinates are arranged in circumferential order to form the circumferential color distribution sequence of the hose body.

[0027] In this embodiment, illuminating the surface of the composite hose with a first light ray at an acute angle to the axial direction of the composite hose means that the angle between the direction of the light emitted by the first light source and the axial direction of the composite hose is an acute angle, that is, the first light source illuminates the surface of the composite hose from above. Illuminating the surface of the composite hose with a second light ray at an obtuse angle to the axial direction of the composite hose means that the angle between the direction of the light emitted by the second light source and the axial direction of the composite hose is an obtuse angle, that is, the second light source illuminates the surface of the composite hose from below.

[0028] In this embodiment, the first image is an image of the surface of the composite hose acquired under the first light illumination condition, and the second image is an image of the same composite hose surface acquired under the second light illumination condition. The illumination angles of the two light sources are different, so that the same position on the surface of the composite hose exhibits different grayscale responses under the illumination of the two light sources.

[0029] In this embodiment, the three-dimensional shape contour of the composite hose surface is reconstructed based on the gray-level gradient changes on the surface of the composite hose in the first and second images. Specifically, the gray-level gradient change refers to the difference in gray-level values ​​between corresponding pixels at various locations on the composite hose surface in the first and second images. This difference in gray-level values ​​is related to the unevenness of the composite hose surface. The deformation circumferential decomposition unit extracts the gray-level value of each pixel in the first image and the corresponding pixel in the second image, and calculates the difference between the two gray-level values. Assuming that the composite hose surface satisfies the Lambertian reflection model, there is a proportional relationship between this difference value and the normal direction of the composite hose surface, determined by the light source direction. The deformation circumferential decomposition unit solves for the surface normal direction corresponding to each pixel based on this proportional relationship, and then integrates along the surface normal direction to calculate the height value of the composite hose surface position corresponding to that pixel along the acquisition direction. After performing the above calculation on all pixels, the height distribution data of each position on the composite hose surface in three-dimensional space is obtained, and this height distribution data is the three-dimensional shape contour.

[0030] In this embodiment, extracting the color values ​​of each position on the surface of the composite hose in circumferential angular coordinates from the three-dimensional morphological contour means converting the position coordinates of each pixel in the three-dimensional morphological contour into circumferential angular coordinates with the axis of the composite hose as a reference, and associating the color value corresponding to each pixel with the circumferential angular coordinate of that pixel; the color values ​​on all circumferential angular coordinates are arranged in ascending order of circumferential angle, and the obtained one-dimensional sequence data is the circumferential color distribution sequence of the hose body.

[0031] In this embodiment, the direction of the light source is obtained in advance by calibration plate.

[0032] In another embodiment of the present invention, when extracting the color values ​​of each position on the surface of the composite tube in circumferential angular coordinates from the three-dimensional morphological contour, the origin of the mapping is taken as the foot of the perpendicular line between the common perpendicular line of the composite tube axis and the imprint cylinder axis on the surface of the composite tube. The coordinates of each pixel in the three-dimensional morphological contour are transformed into the circumferential angular coordinate system with the mapping origin as the starting point, and the circumferential angular coordinate value of each pixel is obtained. The average color value of all pixels with the same circumferential angular coordinate value in the three-dimensional morphological contour is taken as the average color value corresponding to the circumferential angular coordinate value. The average color values ​​corresponding to all circumferential angular coordinate values ​​are arranged in circumferential order to form the circumferential color distribution sequence of the tube body.

[0033] In this embodiment, the common perpendicular line between the composite tube axis and the impression cylinder axis refers to a straight line that is perpendicular to both the composite tube axis and the impression cylinder axis. The foot of the perpendicular line on the surface of the composite tube is the mapping origin. The mapping origin is used as the starting reference point for establishing the circumferential angle coordinate system. That is, starting from the origin, the coordinate system is expanded along the circumference of the composite tube to determine the circumferential angle position of each pixel point relative to the origin.

[0034] In this embodiment, transforming the coordinates of each pixel in the three-dimensional shape contour to a circumferential angular coordinate system starting from the mapping origin means that for each pixel in the three-dimensional shape contour, the projection direction of the line connecting the pixel and the axis of the composite hose on a plane perpendicular to the axis of the composite hose is calculated, and then the angle between the projection direction and the reference direction corresponding to the mapping origin is calculated. This angle is the circumferential angular coordinate value of the pixel.

[0035] In this embodiment, the average color value of all pixels with the same circumferential angle coordinate value in the three-dimensional shape contour is taken. This means that multiple pixels in the three-dimensional shape contour that are located at the same circumferential angle position but at different positions along the axis of the composite hose each correspond to a color value. The color values ​​of these multiple pixels are added together and divided by the number of pixels. The quotient obtained is used as the average color value corresponding to the circumferential angle coordinate value. This average value can represent the overall color level of the tube at the circumferential angle position, thereby eliminating the interference caused by local color fluctuations along the axis direction on the circumferential color analysis.

[0036] In this embodiment, the average color values ​​corresponding to all circumferential angle coordinate values ​​are arranged in circumferential order, which means that all circumferential angle coordinate values ​​are arranged in ascending order, and each circumferential angle coordinate value corresponds to an average color value. The one-dimensional sequence data obtained after the arrangement is the circumferential color distribution sequence of the tube body.

[0037] In this embodiment, the preset target gradient color distribution is a pre-defined sequence of desired color values ​​at various circumferential angles on the surface of the composite tube. This sequence of desired color values ​​is determined based on the gradient color target values ​​in the printing design file. The color deviation refers to the degree of deviation between the measured color value corresponding to each circumferential angle coordinate value in the tube's circumferential color distribution sequence and the desired color value corresponding to the same circumferential angle coordinate value in the preset target gradient color distribution. This deviation is caused by the contact pressure between the impression cylinder and the composite tube deviating from the target pressure.

[0038] In another embodiment of the present invention, extracting color uniformity feature values ​​from the circumferential color distribution sequence of the tube body includes: Starting from the first element of the circumferential color distribution sequence of the tube, accumulate elements one by one forward from the current element. For each accumulated element, calculate the average of the absolute values ​​of the color differences between adjacent elements in the current accumulated sequence as the local color fluctuation amplitude of the current accumulated sequence. When the change in local color fluctuation amplitude relative to the local color fluctuation amplitude of the previous accumulated position exceeds the preset change threshold for the first time, the end point of the current accumulated sequence is used as the boundary of the first sub-interval. The operation is repeated in the remaining sequence until all sub-intervals are divided to obtain a sub-interval sequence of unequal length. For each unequal-length subinterval, with the median of all element color values ​​in that subinterval as the center, calculate the cumulative distribution function value of the absolute deviation between the color values ​​of all elements in that subinterval and the median. Sum the cumulative distribution function values ​​of all subintervals and divide by the number of subintervals to obtain the color uniformity characteristic value.

[0039] In this embodiment, starting from the first element of the circumferential color distribution sequence of the tube body, elements are accumulated one by one in advance. This means that starting from the first element of the circumferential color distribution sequence of the tube body, the first element is used as the initial accumulation sequence. Then the second element is added to the accumulation sequence to form a new accumulation sequence. Then the third element is added to the accumulation sequence to form an updated accumulation sequence, and so on, gradually expanding the range of the accumulation sequence.

[0040] In this embodiment, for each accumulated element, the average absolute value of the color difference between adjacent elements in the current accumulated sequence is calculated. For any pair of adjacent elements in the current accumulated sequence, the deformation entropy construction unit calculates the difference between the color value of the next element and the color value of the previous element, and then takes the absolute value of the difference as the absolute value of the color difference between the pair of adjacent elements; the average absolute value of the color difference between all pairs of adjacent elements in the current accumulated sequence is the local color fluctuation amplitude.

[0041] In this embodiment, the preset change threshold is a pre-defined value used to determine the boundary of the sub-interval, and this threshold is related to the local color fluctuation amplitude of the previous accumulation position. The deformation entropy construction unit subtracts the local color fluctuation amplitude of the previous accumulation position from the local color fluctuation amplitude of the current accumulation position to obtain the change amount; when the change amount first exceeds the preset proportion of the local color fluctuation amplitude of the previous accumulation position, the deformation entropy construction unit uses the end point of the current accumulation sequence as the boundary of the first sub-interval.

[0042] In this embodiment, after completing the division of the first sub-interval, the deformation entropy construction unit starts from the first element of the remaining sequence, that is, from the next element immediately following the boundary of the previous sub-interval in the circumferential color distribution sequence of the tube body, and repeatedly performs the complete process of accumulating elements one by one from the first element, calculating the local color fluctuation amplitude, calculating the change amount and comparing it with the preset change amount threshold, until the change amount first exceeds the preset change amount threshold. Then, the end point of the current accumulated sequence is used as the boundary of the next sub-interval. The deformation entropy construction unit continuously repeats the above operation until all elements of the circumferential color distribution sequence of the tube body are assigned to a certain sub-interval, obtaining an unequal length sub-interval sequence. Each element in the unequal length sub-interval sequence is a sub-interval, and the number of elements contained in each sub-interval is different.

[0043] In this embodiment, for each unequal-length sub-interval, the deformation entropy construction unit sorts the color values ​​of all elements in the sub-interval in ascending order and takes the value of the middle position as the median; the deformation entropy construction unit calculates the difference between the color value of each element in the sub-interval and the median and takes the absolute value to obtain the absolute deviation value corresponding to each element; the deformation entropy construction unit sorts all absolute deviation values ​​in ascending order to form an absolute deviation sequence, and takes the ratio of the sum of the first k deviation values ​​in the absolute deviation sequence to the sum of all deviation values ​​as the cumulative distribution function value of the kth deviation value in the deviation sequence; the deformation entropy construction unit adds the cumulative distribution function values ​​corresponding to all absolute deviation values ​​in the sub-interval to obtain the sum of the cumulative distribution function values ​​of the sub-interval; the deformation entropy construction unit adds the sum of the cumulative distribution function values ​​of all sub-intervals and divides it by the number of sub-intervals to obtain the quotient value as the color uniformity feature value.

[0044] In another embodiment of the present invention, when calculating the cumulative distribution function value of the absolute deviation of all element color values ​​in the sub-interval from the median, the absolute deviations of all element color values ​​in the sub-interval from the median are arranged in ascending order to form a deviation sequence. The ratio of the sum of the first k deviation values ​​in the deviation sequence to the sum of all deviation values ​​is used as the cumulative distribution function value of the kth deviation value, where k is a positive integer from 1 to the length of the deviation sequence.

[0045] In this embodiment, the absolute deviations of all element color values ​​within the sub-interval from the median are arranged in ascending order to form a deviation sequence. This means that the deformation entropy construction unit obtains the color value of each element within the sub-interval, calculates the difference between each color value and the median of the sub-interval, and takes the absolute value to obtain the absolute deviation value corresponding to each element within the sub-interval. All absolute deviation values ​​are arranged in ascending order of value, and the resulting one-dimensional sequence is the deviation sequence. The first element in the deviation sequence is the smallest absolute deviation value within the sub-interval, and the last element in the deviation sequence is the largest absolute deviation value within the sub-interval.

[0046] In this embodiment, the ratio of the sum of the first k deviation values ​​in the deviation sequence to the sum of all deviation values ​​is used as the cumulative distribution function value of the kth deviation value. k is a positive integer from 1 to the length of the deviation sequence. This means that the deformation entropy construction unit adds all deviation values ​​from the 1st to the kth deviation value in the deviation sequence to obtain the sum of the first k deviation values; adds all deviation values ​​in the deviation sequence to obtain the sum of all deviation values; and divides the sum of the first k deviation values ​​by the sum of all deviation values ​​to obtain the quotient value, which is the cumulative distribution function value of the kth deviation value. When all deviation values ​​in the deviation sequence are zero, the sum of all deviation values ​​is set to 1, making the cumulative distribution function value of each deviation value zero. This cumulative distribution function value reflects the relative proportion of the degree of deviation of the color value from the median within the sub-interval to the overall deviation level.

[0047] In another embodiment of the present invention, the preset change threshold is 10% of the local color fluctuation amplitude of the previous cumulative position.

[0048] In this embodiment, the preset change threshold is 10% of the local color fluctuation amplitude of the previous accumulated position. Specifically, the deformation entropy construction unit calculates the difference between the local color fluctuation amplitude of the current accumulated position and that of the previous accumulated position as the change, and compares this change with one-tenth of the local color fluctuation amplitude of the previous accumulated position. When the change first exceeds one-tenth of the local color fluctuation amplitude of the previous accumulated position, the deformation entropy construction unit determines the endpoint of the current accumulated sequence as the sub-interval boundary. This threshold setting method makes the sub-interval division sensitive to changes in local color fluctuation amplitude. When the color fluctuation amplitude of the accumulated sequence increases by more than 10% compared to the previous position, boundary determination is triggered, thereby enabling the identification of locations in the circumferential color distribution sequence of the tube body where the color fluctuation pattern changes significantly as sub-interval boundaries.

[0049] refer to Figure 3 In another embodiment of the present invention, the pressure distribution curve of the contact pressure between the impression cylinder and the composite hose in the circumferential direction of the impression cylinder is derived based on the color uniformity characteristic value, including: The absolute value of the difference between the color value corresponding to each circumferential angle coordinate value and the color uniformity characteristic value in the circumferential color distribution sequence of the tube body is taken as the color deviation of that circumferential angle coordinate value. The color deviation of all circumferential angle coordinate values ​​are arranged in circumferential order to form a color deviation sequence. Perform a second-order difference operation on the color deviation sequence to obtain the color deviation curvature sequence; The peak and valley positions of curvature are extracted from the color deviation curvature sequence. The difference in color deviation between the peak and valley positions is used as the pressure deviation characterization of the pair. The pressure deviation characterizations of all positions are arranged in circumferential order to form a pressure distribution curve.

[0050] In this embodiment, the color deviation refers to the degree of deviation of the color value corresponding to each circumferential angular coordinate value in the circumferential color distribution sequence of the pipe body from the color uniformity feature value. The deformation entropy construction unit subtracts the color uniformity feature value from the color value corresponding to each circumferential angular coordinate value to obtain the difference, and then takes the absolute value of the difference as the color deviation of the circumferential angular coordinate value; the larger the color deviation, the greater the degree of deviation of the color from the uniform state at that circumferential angular position, that is, the greater the degree of deviation of the contact pressure corresponding to that position from the ideal pressure value.

[0051] In this embodiment, the color deviation of all circumferential angle coordinate values ​​is arranged in circumferential order to form a color deviation sequence. This means that all circumferential angle coordinate values ​​are arranged in ascending order, and each circumferential angle coordinate value corresponds to a color deviation. The one-dimensional sequence data obtained after the arrangement is the color deviation sequence.

[0052] In this embodiment, a second-order difference operation is performed on the color deviation sequence to obtain a color deviation curvature sequence. Specifically, the deformation entropy construction unit calculates the difference between every two adjacent elements in the color deviation sequence to obtain a first-order difference sequence; the deformation entropy construction unit then calculates the difference between every two adjacent elements in the first-order difference sequence to obtain a second-order difference sequence, which is the color deviation curvature sequence. Each element in the color deviation curvature sequence reflects the acceleration of the color deviation sequence at that position. A positive value indicates that the rate of increase of the color deviation at that position is accelerating, and a negative value indicates that the rate of increase of the color deviation at that position is slowing down.

[0053] In this embodiment, extracting the peak and valley positions of curvature from the color deviation curvature sequence means that the deformation entropy construction unit traverses each element in the color deviation curvature sequence. When the value of an element is greater than the values ​​of its immediate and adjacent elements, the position of that element is marked as the peak curvature position; when the value of an element is less than the values ​​of its immediate and adjacent elements, the position of that element is marked as the valley curvature position. The peak curvature position corresponds to the turning point where the growth rate of the color deviation changes from positive to negative, and the valley curvature position corresponds to the turning point where the growth rate of the color deviation changes from negative to positive.

[0054] In this embodiment, the difference in color deviation between the peak and valley positions of curvature is used as the pressure deviation representation for that pair of positions. This means that the deformation entropy construction unit extracts the color deviation values ​​corresponding to the peak and valley positions of curvature from the color deviation sequence, calculates the difference between these values, and this difference is the pressure deviation representation for that position. This pressure deviation representation indicates the deviation between the actual pressure on the tube body at that circumferential angle position and the uniform pressure. After calculating the corresponding pressure deviation representation for all peak and valley positions of curvature, the deformation entropy construction unit arranges the pressure deviation representations for all positions according to their order along the circumferential direction of the impression cylinder, obtaining a one-dimensional sequence of data, which is the pressure distribution curve.

[0055] In another embodiment of the present invention, when extracting the peak curvature position and the valley curvature position from the color deviation curvature sequence, the local maximum point in the color deviation curvature sequence is used as the peak curvature position, the local minimum point in the color deviation curvature sequence is used as the valley curvature position, and the difference in color deviation between the peak curvature position and the valley curvature position is used as the pressure deviation characterization quantity of the paired position.

[0056] In this embodiment, a local maximum point refers to the position in the color deviation curvature sequence where the value of an element is greater than the values ​​of its immediate and adjacent elements. This position corresponds to the peak of the growth rate of the color deviation within that local region, i.e., the turning point where the growth rate of the color deviation changes from accelerating to slowing down. A local minimum point refers to the position in the color deviation curvature sequence where the value of an element is less than the values ​​of its immediate and adjacent elements. This position corresponds to the trough of the growth rate of the color deviation within that local region, i.e., the turning point where the growth rate of the color deviation changes from slowing down to accelerating again.

[0057] In this embodiment, the deformation entropy construction unit uses all local maxima in the color deviation curvature sequence as curvature peak positions and all local minima as curvature valley positions. The deformation entropy construction unit extracts the color deviation amount corresponding to each curvature peak position and each curvature valley position in the color deviation sequence, and calculates the color deviation difference between paired curvature peak positions and curvature valley positions. This difference is the pressure deviation characterization quantity at that position. Paired curvature peak positions and curvature valley positions refer to local maxima and local minima that alternate sequentially in a circumferential order in the color deviation curvature sequence. Each curvature peak position and its adjacent subsequent curvature valley position form a pair, and each curvature valley position and its adjacent subsequent curvature peak position form a pair.

[0058] In another embodiment of the present invention, the axial feed of the impression cylinder is adjusted using the pressure distribution curve as feedback, including: Extract the locations of pressure peaks and valleys from the pressure distribution curve; Calculate the pressure difference between the pressure peak location and the pressure trough location; When the pressure difference exceeds the preset pressure difference threshold, the axial feed of the first and second ends of the impression cylinder is adjusted to reduce the pressure difference as the control objective, so that the axial feed corresponding to the pressure peak position is reduced and the axial feed corresponding to the pressure valley position is increased.

[0059] In this embodiment, the pressure peak position refers to the circumferential angle position corresponding to the element with the largest pressure deviation in the pressure distribution curve. This position represents that the contact pressure between the impression cylinder and the composite hose reaches its maximum value at this circumferential angle. The pressure valley position refers to the circumferential angle position corresponding to the element with the smallest pressure deviation in the pressure distribution curve. This position represents that the contact pressure between the impression cylinder and the composite hose reaches its minimum value at this circumferential angle.

[0060] In this embodiment, the pressure difference between the pressure peak position and the pressure valley position is the difference obtained by subtracting the pressure deviation characterization value corresponding to the pressure valley position from the pressure deviation characterization value corresponding to the pressure peak position. This difference reflects the maximum deviation of the contact pressure between the impression cylinder and the composite hose in the circumferential direction.

[0061] In this embodiment, the preset pressure difference threshold is a pre-defined numerical boundary used to determine whether the unevenness of pressure distribution exceeds the allowable range. When the pressure difference exceeds the preset pressure difference threshold, it indicates that the unevenness of the contact pressure between the impression cylinder and the composite hose in the circumferential direction has exceeded the allowable range, and the axial feed of the impression cylinder needs to be adjusted.

[0062] In this embodiment, the control objective is to reduce the pressure difference. The axial feed of the first and second ends of the impression cylinder is adjusted to decrease the axial feed corresponding to the pressure peak position and increase the axial feed corresponding to the pressure trough position. Specifically, the first and second ends of the impression cylinder correspond to the two ends of the circumferential angle position in the pressure distribution curve, respectively. Adjusting the axial feed of the first and second ends of the impression cylinder changes the contact pressure between the two ends of the impression cylinder and the composite hose. When the pressure peak position is close to the first end of the impression cylinder, the axial feed of the first end of the impression cylinder is reduced to decrease the contact pressure at that end, while the axial feed of the second end of the impression cylinder is increased to increase the contact pressure at that end. When the pressure peak position is close to the second end of the impression cylinder, the axial feed of the second end of the impression cylinder is reduced to decrease the contact pressure at that end, while the axial feed of the first end of the impression cylinder is increased to increase the contact pressure at that end. Through the above reverse adjustment operation, the contact pressure at the pressure peak position is reduced and the contact pressure at the pressure trough position is increased, the pressure difference is reduced, and the color uniformity characteristic value of the circumferential color distribution sequence of the tube body approaches the preset target value.

[0063] In this embodiment, the correspondence between the circumferential angular position of the impression cylinder and the axial position of the first and second ends of the impression cylinder is as follows: the circumferential angular position of the impression cylinder is mapped to the axial position of the impression cylinder along the axial direction of the impression cylinder, wherein the 0° circumferential angular position of the impression cylinder corresponds to the axial position of the first end of the impression cylinder, and the 180° circumferential angular position of the impression cylinder corresponds to the axial position of the second end of the impression cylinder; the remaining circumferential angular positions are linearly interpolated between the first and second ends of the impression cylinder. The pressure peak position and pressure valley position in the pressure distribution curve each have a corresponding circumferential angular coordinate value. Based on the circumferential angular coordinate value, the corresponding axial position is determined in the linear interpolation correspondence, thereby determining whether the pressure peak or pressure valley is closer to the first end or closer to the second end of the impression cylinder in the axial direction, and thus determining whether to adjust the axial feed amount of the first or second end of the impression cylinder accordingly.

[0064] This invention provides an embodiment of a method for controlling gradient colors in composite flexible tubes, comprising: Collect the circumferential color distribution sequence of the composite tube surface after it is removed from the impression cylinder; Extract color uniformity feature values ​​from the circumferential color distribution sequence of the tube; Based on the color uniformity characteristic value, the pressure distribution curve of the contact pressure between the impression cylinder and the composite hose in the circumferential direction of the impression cylinder is derived. Using the pressure distribution curve as feedback, the axial feed of the impression cylinder is adjusted so that the color uniformity characteristic value of the circumferential color distribution sequence of the tube approaches the preset target value.

[0065] In this embodiment, the difference between the composite tube gradient color control method and the aforementioned composite tube gradient color flexographic printing process lies in that the control method focuses on a closed-loop control logic from color perception to pressure inversion and then to execution adjustment, while the flexographic printing process focuses on a complete printing process flow that includes this control logic. The composite tube gradient color control method uses the circumferential color distribution sequence of the tube body as the input signal for the control process, the axial feed amount of the impression cylinder as the output execution amount of the control process, and the convergence target of the control process being that the color uniformity feature value of the circumferential color distribution sequence approaches a preset target value. The specific implementation methods for acquiring the circumferential color distribution sequence of the tube body, extracting the color uniformity feature value, inverting the pressure distribution curve, and adjusting the axial feed amount of the impression cylinder are the same as the implementation methods of the corresponding steps in the aforementioned composite tube gradient color flexographic printing process.

[0066] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of this invention and its equivalents, this invention also intends to include these modifications and variations.

Claims

1. A composite flexible tube gradient color flexographic printing process, characterized in that, include: Downstream of the contact surface between the impression cylinder and the composite tube in the flexographic printing unit, the circumferential color distribution sequence of the composite tube surface after it leaves the impression cylinder is collected. Extract color uniformity feature values ​​from the circumferential color distribution sequence of the tube; Based on the color uniformity characteristic value, the pressure distribution curve of the contact pressure between the impression cylinder and the composite hose in the circumferential direction of the impression cylinder is derived. Using the pressure distribution curve as feedback, the axial feed of the impression cylinder is adjusted so that the color uniformity characteristic value of the circumferential color distribution sequence of the tube approaches the preset target value.

2. The composite flexible tube gradient color flexographic printing process according to claim 1, characterized in that, The circumferential color distribution sequence of the composite tube surface after it leaves the impression cylinder is collected, including: A first image is acquired by illuminating the surface of the composite hose with a first ray at an acute angle to the axis of the composite hose. A second image is acquired by illuminating the surface of the composite hose with a second light beam at an obtuse angle to the axis of the composite hose. Based on the grayscale gradient changes on the surface of the composite hose in the first and second images, the three-dimensional morphological contour of the composite hose surface is reconstructed. The color values ​​of each position on the surface of the composite hose in the circumferential angular coordinates are extracted from the three-dimensional morphological contour. The color values ​​of all positions on the circumferential angular coordinates are arranged in circumferential order to form the circumferential color distribution sequence of the hose body.

3. The composite flexible tube gradient color flexographic printing process according to claim 2, characterized in that, When extracting the color values ​​of each position on the surface of the composite tube in circumferential angular coordinates from the three-dimensional morphological contour, the origin of the mapping is taken as the foot of the perpendicular line between the common perpendicular line of the composite tube axis and the imprint cylinder axis on the surface of the composite tube. The coordinates of each pixel in the three-dimensional morphological contour are transformed into the circumferential angular coordinate system starting from the mapping origin to obtain the circumferential angular coordinate value of each pixel. The average color value of all pixels with the same circumferential angular coordinate value in the three-dimensional morphological contour is taken as the average color value corresponding to that circumferential angular coordinate value. The average color values ​​corresponding to all circumferential angular coordinate values ​​are arranged in circumferential order to form the circumferential color distribution sequence of the tube body.

4. The composite flexible tube gradient color flexographic printing process according to claim 1, characterized in that, Color uniformity feature values ​​are extracted from the circumferential color distribution sequence of the tube, including: Starting from the first element of the circumferential color distribution sequence of the tube, accumulate elements one by one forward from the current element. For each accumulated element, calculate the average of the absolute values ​​of the color differences between adjacent elements in the current accumulated sequence as the local color fluctuation amplitude of the current accumulated sequence. When the change in local color fluctuation amplitude relative to the local color fluctuation amplitude of the previous accumulated position exceeds the preset change threshold for the first time, the end point of the current accumulated sequence is used as the boundary of the first sub-interval. The operation is repeated in the remaining sequence until all sub-intervals are divided to obtain a sub-interval sequence of unequal length. For each unequal-length subinterval, with the median of all element color values ​​in that subinterval as the center, calculate the cumulative distribution function value of the absolute deviation between the color values ​​of all elements in that subinterval and the median. Sum the cumulative distribution function values ​​of all subintervals and divide by the number of subintervals to obtain the color uniformity characteristic value.

5. The composite flexible tube gradient color flexographic printing process according to claim 4, characterized in that, When calculating the cumulative distribution function value of the absolute deviation of all element color values ​​in the sub-interval from the median, the absolute deviations of all element color values ​​in the sub-interval from the median are arranged in ascending order to form a deviation sequence. The ratio of the sum of the first k deviation values ​​in the deviation sequence to the sum of all deviation values ​​is taken as the cumulative distribution function value of the kth deviation value, where k is a positive integer from 1 to the length of the deviation sequence.

6. The composite flexible tube gradient color flexographic printing process according to claim 4, characterized in that, The preset change threshold is 10% of the local color fluctuation amplitude of the previous cumulative position.

7. The composite flexible tube gradient color flexographic printing process according to claim 1, characterized in that, Based on the color uniformity characteristic value, the pressure distribution curve of the contact pressure between the impression cylinder and the composite hose in the circumferential direction of the impression cylinder is derived, including: The absolute value of the difference between the color value corresponding to each circumferential angle coordinate value and the color uniformity characteristic value in the circumferential color distribution sequence of the tube body is taken as the color deviation of that circumferential angle coordinate value. The color deviation of all circumferential angle coordinate values ​​are arranged in circumferential order to form a color deviation sequence. Perform a second-order difference operation on the color deviation sequence to obtain the color deviation curvature sequence; The peak and valley positions of curvature are extracted from the color deviation curvature sequence. The difference in color deviation between the peak and valley positions is used as the pressure deviation characterization of the pair. The pressure deviation characterizations of all positions are arranged in circumferential order to form a pressure distribution curve.

8. The composite flexible tube gradient color flexographic printing process according to claim 7, characterized in that, When extracting the peak and valley positions of curvature from the color deviation curvature sequence, the local maxima in the color deviation curvature sequence are used as the peak positions of curvature, the local minima in the color deviation curvature sequence are used as the valley positions of curvature, and the difference in color deviation between the peak and valley positions of curvature is used as the pressure deviation characterization quantity of the paired positions.

9. The composite flexible tube gradient color flexographic printing process according to claim 1, characterized in that, Using the pressure distribution curve as feedback, the axial feed of the impression cylinder is adjusted, including: Extract the locations of pressure peaks and valleys from the pressure distribution curve; Calculate the pressure difference between the pressure peak location and the pressure trough location; When the pressure difference exceeds the preset pressure difference threshold, the axial feed of the first and second ends of the impression cylinder is adjusted to reduce the pressure difference as the control objective, so that the axial feed corresponding to the pressure peak position is reduced and the axial feed corresponding to the pressure valley position is increased.

10. A method for controlling the gradient color of a composite flexible tube, characterized in that, include: Collect the circumferential color distribution sequence of the composite tube surface after it is removed from the impression cylinder; Extract color uniformity feature values ​​from the circumferential color distribution sequence of the tube; Based on the color uniformity characteristic value, the pressure distribution curve of the contact pressure between the impression cylinder and the composite hose in the circumferential direction of the impression cylinder is derived. Using the pressure distribution curve as feedback, the axial feed of the impression cylinder is adjusted so that the color uniformity characteristic value of the circumferential color distribution sequence of the tube approaches the preset target value.

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