Web double-sided registration printing system

Abstract

A kind of roll double-sided alignment printing system, including printing platform, paper feed mechanism, light source, industrial camera and controller;Print as follows steps: (1) make layout file;(2) print on the first side of roll;(3) print on the second side of roll;The roll that has carried out second side printing passes between light source and industrial camera, is illuminated by light source, first alignment identification symbol and second alignment identification symbol both appear on the same side of roll;Industrial camera photographs the appearance area of first alignment identification symbol and second alignment identification symbol, after controller processes image, calculate the coordinate deviation value between first alignment identification symbol and second alignment identification symbol, compare with preset tolerance value to determine whether to adjust paper feed speed after.The invention can control the position error between the graphics and texts on the second side and the graphics and texts on the first side within the allowable error range, so that the graphics and texts on both sides are accurately aligned.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of printing technology, in particular to a double-sided printing system for a roll material. BACKGROUND

[0002] The ordinary roll material printer used in the current market of graphic and text industry, advertising industry, image industry and the like can only print on one side. However, there is a great demand for double-sided printing products in the market. In order to print graphics and texts on both sides of a roll material (i.e. a roll paper), the solution is to print graphics and texts on the first side (e.g. the front side) of the roll material first, and then print graphics and texts on the second side (e.g. the back side) of the roll material, so as to realize double-sided printing. The double-sided printing product usually requires that the graphics and texts on both sides of the roll material are accurately aligned. However, the current roll material printer has an error (about ±0.2%) in the length direction when printing. If the error is not corrected in time, a large cumulative error will be generated after printing a large length, so that the graphics and texts on the second side will have a large positional error with the graphics and texts on the first side, which will result in substandard products or waste products when the error exceeds the allowable error range. For example, a 30-meter-long roll paper is printed after being spliced. When the first side is printed, an error of about 0.2% will occur when the second side is printed. The error between the two sides is 2 mm when the first meter of the second side is printed, and the cumulative error between the two sides is 4 mm when the second meter of the second side is printed. By analogy, the cumulative error between the two sides can reach 60 mm when the last meter of the second side is printed. Therefore, in order to ensure product quality, the error should be reduced or eliminated in time when the second side is printed, so as to control the positional error within the allowable error range, so that the graphics and texts on the second side are accurately aligned with the graphics and texts on the first side.

[0003] The Chinese patent application for invention with the application publication number CN106739546A discloses a double-sided printer, which comprises a rack, a cloth feeding roller, a cloth collecting roller, a first printing platform, a visual recognition device, a second printing platform and a control box. The cloth feeding roller and the cloth collecting roller are respectively installed on the same side of the rack. The first printing platform and the second printing platform are arranged in the same direction. The first printing platform is used for printing a position coordinate pattern and a target pattern on the first side of the passing printing material, and the second printing platform is used for printing a position coordinate pattern and a target pattern on the second side of the passing printing material. The visual recognition device is arranged on the front side of the second printing platform before the cloth feeding end, and is used for detecting the position coordinate pattern, obtaining a coordinate offset and sending the coordinate offset to the control box. The control box is arranged in the rack, and is used for adjusting the printing starting position of the second printing platform according to the coordinate offset, and printing the second side of the passing printing material.

[0004] The double-sided printer works as follows: one side of the printing material is printed by the first printing platform (also referred to as the front printing platform), and the position coordinate pattern and the target pattern (also referred to as the finished picture) are printed. The visual recognition device detects the position coordinate pattern printed by the first printing platform, first judges whether the image is correct, and then, after detecting that the position coordinate pattern is correct, positions the accuracy of the initial position of the picture, acquires the coordinate offset, and sends the acquired coordinate offset to the control box. The control box is used to adjust the printing starting position of the second printing platform according to the coordinate offset, and print the second side of the passed printing material. Specifically, the printer central processing unit in the control box calculates and processes the coordinate offset, calculates the lateral and longitudinal changes of the soft material through the coordinate value, calculates the deviation value of the material on the two sides and the material elasticity, thereby understands the deformation value of the material, forms a control signal that can be recognized by the PLC controller of the second printing platform, and sends the information of the printing starting position of the second printing platform to the PLC controller to control the printing of the other side of the printing material. After each picture is printed, the visual recognition device re-reads the position of the position coordinate pattern, confirms the actual walking precision of the picture and the accuracy of the position coordinate pattern, and makes real-time adjustment, thereby ensuring the accurate alignment and printing length of the whole roll of material. The double-sided printer detects the position coordinate pattern by using the visual recognition device, acquires the coordinate offset according to the position coordinate pattern, adjusts the printing starting position of the second printing platform, and adjusts the printing starting position of the second printing platform according to the printing position of the first side and the real-time situation of the printing material, thereby ensuring the accurate alignment of the double-sided printing.

[0005] However, when the double-sided printer prints the second side of the passed printing material, the printing starting position of the second printing platform is adjusted according to the coordinate offset of the first side. This method can ensure accurate alignment of the double-sided printing when the continuous length of each target pattern picture is small, but when the continuous length of the target pattern picture is large, if the printing of the second side is performed after adjusting the printing starting position of the second printing platform, a large position deviation will occur at the rear end of the target pattern after the printing of the target pattern is completed (for example, the length of the Qingming River Map as the target pattern is about 528 cm, and a position deviation of about 10 mm will occur at the rear end of the target pattern after the printing is completed), and the larger the continuous length of the target pattern picture, the larger the position deviation at the rear end of the picture, which makes the alignment of the pictures on the two sides inaccurate. If the first printing platform prints a position coordinate pattern at a certain distance on the first side of the printing material, if the continuous length of the target pattern picture on the second side exceeds the interval distance between the two adjacent position coordinate patterns, and if the printing of the second side is performed in the above-mentioned manner, the printing starting position will be updated according to the position coordinate pattern of the first side during the printing of the target pattern, which will cause the target pattern to have a fault. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a roll material double-sided alignment printing system, which can print images and texts on the first and second surfaces of the roll material respectively, control the position error between the images and texts on the second surface and the images and texts on the first surface within an allowable error range, so as to accurately align the images and texts on the second surface and the images and texts on the first surface, and ensure product quality. The technical solution adopted is as follows:

[0007] A roll material double-sided alignment printing system comprises a printing platform, a paper feeding mechanism, an industrial camera and a controller, the industrial camera is electrically connected to the corresponding input end of the controller, characterized in that it further comprises a light source, and the controller is installed with a machine vision system.

[0008] Based on the roll material double-sided alignment printing system, the roll material double-sided alignment printing is realized by the following steps:

[0009] (1) Making a layout file: performing layout on each first target image and text to be printed on the first surface, and adding a plurality of first alignment identification symbols to form a first layout file; performing layout on each second target image and text to be printed on the second surface, and adding a plurality of second alignment identification symbols to form a second layout file;

[0010] The first alignment identification symbols in the first layout file are arranged in sequence along the paper feeding direction, and the second alignment identification symbols in the second layout file are arranged in sequence along the paper feeding direction, the number of the second alignment identification symbols is the same as that of the first alignment identification symbols, and the positions of the second alignment identification symbols correspond to those of the first alignment identification symbols one by one;

[0011] (2) The paper feeding mechanism feeds the roll material, and the printing platform prints each first target image and text and the first alignment identification symbol on the first surface of the roll material according to the first layout file;

[0012] (3) After completing the printing on the first surface of the roll material, the paper feeding mechanism feeds the roll material, and the printing platform prints each second target image and text and the second alignment identification symbol on the second surface of the roll material according to the second layout file; the roll material that has been printed on the second surface passes between the light source and the industrial camera, is irradiated by the light source, and the first alignment identification symbol and the second alignment identification symbol are both shown on the same surface of the roll material; the industrial camera takes a photo of the appearing area of the first alignment identification symbol and the second alignment identification symbol, and transmits the obtained image to the controller; after processing the image, the controller obtains the coordinates of the first alignment identification symbol and the second alignment identification symbol, calculates the coordinate deviation value between the first alignment identification symbol and the second alignment identification symbol, and compares the coordinate deviation value with a preset tolerance value;

[0013] If the coordinate deviation value exceeds the range of the preset tolerance value, the controller sends a control signal to adjust the paper feeding speed; if the coordinate deviation value is within the range of the preset tolerance value, the current paper feeding speed is maintained.

[0014] The paper feeding mechanism is used for conveying the roll material (i.e., the roll paper), and the paper feeding speed refers to the speed at which the paper feeding mechanism conveys the roll material (i.e., the roll paper).

[0015] When the roll material passes between the light source and the industrial camera, the first alignment identification symbol (or the second alignment identification symbol) on the side of the roll material facing the industrial camera can be captured by the industrial camera; the light source irradiates from one side of the roll material, and the light transmits through the roll material, so that the second alignment identification symbol (or the first alignment identification symbol) on the side of the roll material away from the industrial camera is clearly visible and can also be captured by the industrial camera. In this way, after irradiation by the light source, the first alignment identification symbol and the second alignment identification symbol are both visible on the side of the roll material facing the industrial camera, and the industrial camera can capture the first alignment identification symbol and the second alignment identification symbol at the same time (the first alignment identification symbol and the second alignment identification symbol can also be observed by the naked eye of the worker).

[0016] In the appearance area (the area captured by the industrial camera) of the first alignment identification symbol and the second alignment identification symbol, if the second alignment identification symbol lags behind the first alignment identification symbol in the paper feeding direction, it means that the paper feeding speed of the second side of the roll material at this time is relatively large relative to the printing speed of the printing platform, and when it exceeds the allowable range, the paper feeding speed should be reduced; if the second alignment identification symbol leads the first alignment identification symbol in the paper feeding direction, it means that the paper feeding speed at this time is relatively small relative to the printing speed of the printing platform, and when it exceeds the allowable range, the paper feeding speed should be increased.

[0017] The coordinate deviation value between the first alignment identification symbol and the second alignment identification symbol is positive or negative. If the coordinate deviation value is positive, it means that the paper feeding speed is too small or too large when printing the second side of the printing web. The determination should be made in combination with the paper feeding direction of the printing web at the position of the industrial camera. For example, if the paper feeding direction of the printing web at the position of the industrial camera is from top to bottom and the industrial camera is facing the appearing area of the first alignment identification symbol and the second alignment identification symbol for shooting, then the coordinate deviation value being positive means that the paper feeding speed is too small when printing the second side of the printing web (at this time, the second alignment identification symbol is on the downside of the first alignment identification symbol and leads the first alignment identification symbol in the paper feeding direction), and the coordinate deviation value being negative means that the paper feeding speed is too large when printing the second side of the printing web (at this time, the second alignment identification symbol is on the upside of the first alignment identification symbol and lags behind the first alignment identification symbol in the paper feeding direction). After adjusting the paper feeding speed, the paper feeding speed remains unchanged until the next time the coordinate deviation value exceeds the preset tolerance value. In this way, by adjusting the paper feeding speed when printing the second side of the printing web, the coordinate deviation value is controlled between the positive and negative end values of the preset tolerance value, so as to control the position error between the graphics on the second side and the graphics on the first side within the allowable error range. Since the range of the preset tolerance value is very small, the paper feeding speed is fine-tuned when adjusted, and the paper feeding speed and the printing speed are still substantially matched, the printing length of each second target graphic changes slightly, and the printing quality of each second target graphic is substantially unaffected.

[0018] Generally, the lateral direction of the printing web is limited by a mechanical structure (the lateral direction refers to the direction perpendicular to the paper feeding direction), so as to ensure that the deviation of the printing area in the lateral direction is extremely small and the lateral direction meets the requirements of alignment printing. Therefore, the problem of alignment printing in the paper feeding direction is solved, so that the graphics on the second side and the graphics on the first side are accurately aligned.

[0019] The light intensity of the light source can be adjusted generally. According to the light transmittance of the printing web, the light intensity of the light source is adjusted so that the first alignment identification symbol and the second alignment identification symbol can appear clearly on the side of the printing web facing the industrial camera, so that the industrial camera can obtain a clear image when shooting the appearing area of the first alignment identification symbol and the second alignment identification symbol. Generally, the smaller the light transmittance of the printing web, the larger the light intensity of the light source. For the printing web of the same material, the light transmittance decreases with the increase of the thickness of the printing web.

[0020] Generally, the first alignment identification symbols are arranged at equal intervals in the paper feeding direction, and the second alignment identification symbols are arranged at equal intervals in the paper feeding direction. Preferably, the interval between the two adjacent first alignment identification symbols and the interval between the two adjacent second alignment identification symbols are both 20-100 cm.

[0021] Generally, the preset tolerance range is set within ±2 mm, preferably ±0.2 mm to ±2 mm (for example, ±1 mm, ±0.5 mm, ±0.2 mm). The smaller the interval between two adjacent first alignment identification symbols (or the interval between two adjacent second alignment identification symbols), the smaller the preset tolerance range can be set.

[0022] Generally, the paper feeding speed of the paper feeding mechanism remains unchanged during the printing process of the first surface of the web on the printing platform, i.e. the paper feeding speed does not need to be adjusted.

[0023] In one specific embodiment, the same printing platform and paper feeding mechanism are used to print the first surface and the second surface of the web; after the web is installed, the paper feeding mechanism feeds the web, the printing platform prints on the first surface of the web and winds up the web; after the printing on the first surface is completed, the wound-up web is installed again, and the paper feeding mechanism feeds the web, and the printing platform prints on the second surface of the web.

[0024] In another specific embodiment, a first printing platform is used to print the first surface of the web, and a second printing platform is used to print the second surface of the web; after the web is installed, a first paper feeding mechanism feeds the web, and the first printing platform prints on the first surface of the web and winds up the web; after the printing on the first surface is completed, the wound-up web is installed again, a second paper feeding mechanism feeds the web, and the second printing platform prints on the second surface of the web.

[0025] In another specific embodiment, a first printing platform is used to print the first surface of the web, and a second printing platform is used to print the second surface of the web; after the web is installed, a first paper feeding mechanism feeds the web, and the first printing platform prints on the first surface of the web; then the paper feeding mechanism feeds the web to the second printing platform, and the second printing platform prints on the second surface of the web. Since the paper feeding speed of the web when passing through the first printing platform and the paper feeding speed of the web when passing through the second printing platform can be inconsistent, a web storage device can be arranged between the first printing platform and the second printing platform to prevent them from interfering with each other. The web storage device can refer to the storage device disclosed in the authorized announcement CN206751027U. The web passes through the web storage device after coming out of the first printing platform and is then sent to the second printing platform; when the paper feeding speed of the web when passing through the first printing platform is greater than the paper feeding speed of the web when passing through the second printing platform, the length of the web stored in the web storage device (i.e. the web wound between the movable guide rollers and the fixed guide rollers) gradually increases; when the paper feeding speed of the web when passing through the first printing platform is less than the paper feeding speed of the web when passing through the second printing platform, the length of the web stored in the web storage device (i.e. the web wound between the movable guide rollers and the fixed guide rollers) gradually decreases.

[0026] In a preferred solution, the paper feeding mechanism is electrically connected to the corresponding output of the controller; in step (3), if the coordinate deviation value exceeds the preset tolerance value, the controller sends a control signal to the paper feeding mechanism to adjust the paper feeding speed. This solution is suitable for the case where the printing platform only has printing functions.

[0027] Generally, the paper feeding mechanism includes a paper unwinding mechanism, a paper traction mechanism, and a paper winding mechanism. The paper traction mechanism is between the paper unwinding mechanism and the paper winding mechanism. The paper unwinding mechanism is used to install the paper, the paper winding mechanism is used to wind the printed paper, and the paper traction mechanism is used to pull and transport the paper. The paper traction mechanism is electrically connected to the corresponding output of the controller, and the speed at which the paper traction mechanism transports the paper is the paper feeding speed. In addition, the paper feeding mechanism can also include several guide rollers, which are between the paper unwinding mechanism and the paper winding mechanism, and are used to guide the transportation of the paper.

[0028] As a first preferred solution of the paper traction mechanism, the paper traction mechanism includes a servo motor, a driving paper feeding roller, and a pressure roller. The power output shaft of the servo motor is in transmission connection with the driving paper feeding roller. The paper passes between the pressure roller and the driving paper feeding roller. The pressure roller and the driving paper feeding roller jointly clamp the paper. When the power output shaft of the servo motor drives the driving paper feeding roller to rotate, the paper is transported. The servo motor is electrically connected to the corresponding output of the controller. By adjusting the rotating speed of the power output shaft of the servo motor, the paper feeding speed is adjusted. By fine-tuning the rotating speed of the power output shaft of the servo motor, the paper feeding speed can be fine-tuned. The power output shaft of the servo motor can be connected to one end of the driving paper feeding roller through a shaft coupling. The power output shaft of the servo motor can also be in transmission connection with one end of the driving paper feeding roller through a transmission mechanism (such as a synchronous belt or a gear set).

[0029] As a second preferred solution of the paper traction mechanism, the paper traction mechanism includes a servo motor, a driving paper feeding roller, and a plurality of pressure wheels. The power output shaft of the servo motor is in transmission connection with the driving paper feeding roller. The paper passes between the pressure wheels and the driving paper feeding roller. Each pressure wheel and the driving paper feeding roller jointly clamp the paper. When the power output shaft of the servo motor drives the driving paper feeding roller to rotate, the paper is transported. The servo motor is electrically connected to the corresponding output of the controller. By adjusting the rotating speed of the power output shaft of the servo motor, the paper feeding speed is adjusted. By fine-tuning the rotating speed of the power output shaft of the servo motor, the paper feeding speed can be fine-tuned. The power output shaft of the servo motor can be connected to one end of the driving paper feeding roller through a shaft coupling. The power output shaft of the servo motor can also be in transmission connection with one end of the driving paper feeding roller through a transmission mechanism (such as a synchronous belt or a gear set).

[0030] In another preferred solution, the printing platform adopts a printer with a self-adjustable paper feeding mechanism and a touch screen, and the speed of the self-adjustable paper feeding mechanism can be adjusted by operating the touch screen; the double-sided roll printing system further comprises a mechanical hand capable of operating the touch screen, and the mechanical hand is electrically connected to the corresponding output end of the controller; when the speed of the paper feeding needs to be adjusted, the mechanical hand operates the touch screen under the control of the controller to set the adjustment range of the speed of the paper feeding, and the touch screen transmits the setting information of the adjustment range of the speed of the paper feeding to the built-in controller of the printer, and the built-in controller of the printer sends a control signal to the self-adjustable paper feeding mechanism to adjust the speed of the paper feeding. This method is suitable for modifying the printer (such as Canon PRO-526) with a self-adjustable paper feeding mechanism to form the double-sided roll printing system of the application, which is beneficial to fully utilize the existing equipment and reduce the cost of equipment.

[0031] The machine vision system installed on the controller generally comprises an image acquisition program and an image processing program. After the controller acquires the image transmitted by the industrial camera, the image is processed to obtain image information, and the coordinates (generally X coordinate and Y coordinate, wherein the Y coordinate is the longitudinal coordinate (i.e. the coordinate in the direction of paper feeding), and the X coordinate is the transverse coordinate (i.e. the coordinate in the direction perpendicular to the direction of paper feeding)) of the first alignment identification symbol and the second alignment identification symbol are calculated. The image information generally includes the size, shape, center position, etc. of the image.

[0032] Generally, the industrial camera is directed to the display area of the first alignment identification symbol and the second alignment identification symbol when taking a picture. In order to facilitate subsequent image processing, the Y axis direction of the industrial camera is parallel to the direction of paper feeding, and the X axis direction is parallel to the surface of the display area and perpendicular to the Y axis direction.

[0033] The controller can adopt an industrial computer.

[0034] The first alignment identification symbol comprises at least one first alignment image block, and the second alignment identification symbol comprises at least one second alignment image block. The first alignment image block and the second alignment image block can be circular image blocks, rectangular image blocks, triangular image blocks or cross-shaped image blocks, or other shaped image blocks. Taking the example that the first alignment image block and the second alignment image block are both circular image blocks, the image information generally includes the size, roundness and center position of the circle, and the center position is used to determine the coordinates of the first alignment identification symbol and the second alignment identification symbol.

[0035] In one specific embodiment, the second alignment identification symbol is composed of two second alignment blocks, and the first alignment identification symbol is composed of one first alignment block. When the second alignment identification symbol is in position with the first alignment identification symbol, the two second alignment blocks are respectively on the two sides of the first alignment block. After irradiation by a light source, the first alignment block in the middle and the second alignment blocks on the left and right sides can be seen on the side of the roll material facing the industrial camera, and the industrial camera can simultaneously capture the first alignment block in the middle and the second alignment blocks on the left and right sides.

[0036] In another specific embodiment, the second alignment identification symbol is composed of one second alignment block, and the first alignment identification symbol is composed of two first alignment blocks. When the second alignment identification symbol is in position with the first alignment identification symbol, the two first alignment blocks are respectively on the two sides of the second alignment block. After irradiation by a light source, the second alignment block in the middle and the first alignment blocks on the left and right sides can be seen on the side of the roll material facing the industrial camera, and the industrial camera can simultaneously capture the second alignment block in the middle and the first alignment blocks on the left and right sides.

[0037] In the process of printing the image on the second surface, the position and deviation of the images on the two surfaces are continuously compared, and adjustments are made at any time to reduce the deviation, achieving the effect of double-side alignment. Regardless of the length of the continuous image of the target pattern, the position deviation between the image on the second surface and the image on the first surface can be kept within the allowable error range by using the scheme of the present application.

[0038] The roll material double-side alignment printing system of the present application can print images on the first surface and the second surface of the roll material respectively, continuously monitor the position deviation between the image on the second surface and the image on the first surface during the process of printing the image on the second surface, and reduce the position deviation by adjusting the paper feeding speed when the position deviation is too large. The position deviation between the image on the second surface and the image on the first surface is controlled within the allowable error range, so that the image on the second surface is accurately aligned with the image on the first surface, ensuring product quality. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is a structural schematic diagram of the roll material double-side alignment printing system in preferred embodiment 1 of the present application;

[0040] Figure 2 is a schematic diagram (partial) of the first layout file in preferred embodiment 1 of the present application;

[0041] Figure 3 is a schematic diagram (partial) of the second layout file in preferred embodiment 1 of the present application;

[0042] Figure 4This is an image obtained by taking pictures of the display areas of the first alignment identification symbol and the second alignment identification symbol by an industrial camera in the preferred embodiment of the present invention, as well as a schematic diagram of the coordinates of each alignment identification symbol.

[0043] Figure 5 This is a schematic diagram of the cooperation between the robotic arm and the touch screen in the preferred embodiment 3 of the present invention;

[0044] Figure 6 This is a schematic diagram showing the changes in the touchscreen's user interface in a preferred embodiment 3 of the present invention;

[0045] Figure 7 This is a schematic diagram of the pressing device in the preferred embodiment 3 of the present invention. Detailed Implementation

[0046] Example 1, such as Figure 1 As shown, this roll-to-roll duplex printing system includes a printing platform 1, a paper feeding mechanism 2, a light source 3, an industrial camera 4, and a controller (not shown). The industrial camera 4 is electrically connected to the corresponding input terminal of the controller, and the controller is equipped with a machine vision system. The controller uses an industrial computer.

[0047] The paper feeding mechanism 2 includes an unwinding mechanism 21, a roll traction mechanism 22, and a rewinding mechanism 23. The roll traction mechanism 22 is located between the unwinding mechanism 21 and the rewinding mechanism 23. The unwinding mechanism 21 is used to install the roll 5, the rewinding mechanism 23 is used to rewind the printed roll 5, and the roll traction mechanism 22 is used to traction and transport the roll 5. The speed at which the roll traction mechanism 22 transports the roll is the paper feeding speed. In this embodiment, the roll material traction mechanism 22 includes a servo motor 221, an active paper feed roller 222, and a pressure roller 223. The power output shaft of the servo motor 221 is connected to the active paper feed roller 222. The roll material 5 passes between the pressure roller 223 and the active paper feed roller 222, and the pressure roller 223 and the active paper feed roller 222 together clamp the roll material 5. The power output shaft of the servo motor 221 drives the active paper feed roller 222 to rotate, thus conveying the roll material. The servo motor 221 is electrically connected to the corresponding output terminal of the controller. The paper feeding speed is adjusted by regulating the rotation speed of the power output shaft of the servo motor 221. By fine-tuning the rotation speed of the power output shaft of the servo motor 221, the paper feeding speed can be fine-tuned. The power output shaft of the servo motor 221 can be connected to one end of the active paper feed roller 222 via a coupling, or it can be connected to one end of the active paper feed roller 222 via a transmission mechanism (such as a synchronous belt or gear set).

[0048] The paper feeding mechanism 2 also includes several guide rollers 24 (e.g. Figure 1 The paper feeding mechanism shown includes two guide rollers 24, each guide roller 24 being located between the unwinding mechanism 21 and the winding mechanism 23, for guiding the feeding of the roll material 5.

[0049] Based on the above-mentioned roll double-sided alignment printing system, the roll double-sided alignment printing is realized by the following steps:

[0050] (1) Making a layout file: Referring to Figure 2 , each first target graphic text 61 to be printed on the first side is laid out, and a plurality of first alignment identification symbols 62 are added to form a first layout file 6; Referring to Figure 3 , each second target graphic text 71 to be printed on the second side is laid out, and a plurality of second alignment identification symbols 72 are added to form a second layout file 7;

[0051] The first alignment identification symbols 62 in the first layout file 6 are arranged in sequence along the paper feeding direction, and the second alignment identification symbols 72 in the second layout file 7 are arranged in sequence along the paper feeding direction. The number of the second alignment identification symbols 72 is the same as that of the first alignment identification symbols 62, and the positions of the second alignment identification symbols 72 correspond to those of the first alignment identification symbols 62 one by one;

[0052] (2) The paper feeding mechanism 2 feeds the roll 5, and the printing platform 1 prints each first target graphic text 61 and first alignment identification symbol 62 on the first side of the roll according to the first layout file 6 (in the process of printing the first side of the roll 5 by the printing platform 1, the paper feeding speed of the paper feeding mechanism 2 remains unchanged, i.e. it is not necessary to adjust the paper feeding speed);

[0053] (3) After completing the printing on the first side of the roll 5, the paper feeding mechanism 2 feeds the roll 5, and the printing platform 1 prints each second target graphic text 71 and second alignment identification symbol 72 on the second side of the roll 5 according to the second layout file 7; the roll 5 that has been printed on the second side passes between the light source 3 and the industrial camera 4, and the first alignment identification symbol 62 and the second alignment identification symbol 72 are both displayed on the same side of the roll 5 after being irradiated by the light source 3; the industrial camera 4 takes a photo of the display area of the first alignment identification symbol 62 and the second alignment identification symbol 72, and transmits the obtained image to the controller; after processing the image, the controller obtains the coordinates of the first alignment identification symbol 62 and the second alignment identification symbol 72, calculates the coordinate deviation value between the second alignment identification symbol 72 and the first alignment identification symbol 62, and compares the coordinate deviation value with the preset tolerance value; if the coordinate deviation value exceeds the range of the preset tolerance value, the controller sends a control signal to adjust the paper feeding speed; if the coordinate deviation value is within the range of the preset tolerance value, the current paper feeding speed is maintained.

[0054] In this embodiment, the paper feeding mechanism 2 is electrically connected to the corresponding output end of the controller; in the step (3), if the coordinate deviation value exceeds the range of the preset tolerance value, the controller sends a control signal to the paper feeding mechanism 2 to adjust the paper feeding speed.

[0055] In this embodiment, the same printing platform 1 and paper feeding mechanism 2 are used to print the first and second sides of the web 5; after the web 5 is installed, the paper feeding mechanism 2 feeds the web 5, the printing platform 1 prints on the first side of the web 5 and winds the web 5; after the printing on the first side is completed, the wound web 5 is installed, and the paper feeding mechanism 2 feeds the web 5, and the printing platform 1 prints on the second side of the web 5.

[0056] In this embodiment, when the web 5 passes between the light source 3 and the industrial camera 4 (usually the part of the web 5 on which the second alignment identification symbol 72 is printed passes between the light source 3 and the industrial camera 4), the second side of the web 5 faces the industrial camera 4, and the first side of the web 5 faces the light source 3; the second alignment identification symbol 72 on the side of the web 5 facing the industrial camera 4 can be captured by the industrial camera 4; the light source 3 irradiates the web 5, and the light transmits through the web 5, so that the first alignment identification symbol 62 on the side of the web 5 facing away from the industrial camera 4 is also clearly visible and can be captured by the industrial camera 4. In this way, after irradiation by the light source 3, the first alignment identification symbol 62 and the second alignment identification symbol 72 are both visible on the side of the web facing the industrial camera 4, and the industrial camera 4 can capture both the first alignment identification symbol 62 and the second alignment identification symbol 72.

[0057] In this embodiment, the first alignment identification symbols 62 are arranged at equal intervals along the paper feeding direction, and the second alignment identification symbols 72 are arranged at equal intervals along the paper feeding direction. The interval between adjacent two first alignment identification symbols 62 is equal to the interval between adjacent two second alignment identification symbols 72, both being 20-100 cm (for example, 50 cm).

[0058] The first alignment identification symbol includes at least one first alignment image block, and the second alignment identification symbol includes at least one second alignment image block. The first alignment image block and the second alignment image block can be a circular image block, a rectangular image block, a triangular image block, or a cross-shaped image block, or can be an image block of other shapes. For reference Figure 2 and Figure 3In the embodiment, the second alignment identification symbol 72 is composed of two second alignment image blocks 721, and the first alignment identification symbol 62 is composed of one first alignment image block 621. The first alignment image block 621 and the two second alignment image blocks 721 are all circular image blocks (the diameters of the three circular image blocks in the imposition file are the same, for example, all 1 mm; during imposition, the two second alignment image blocks 721 have the same coordinate in the paper feeding direction). When the second alignment identification symbol 72 is in position with the first alignment identification symbol 62, the two second alignment image blocks 721 are respectively on the two sides of the first alignment image block 621. After irradiation by the light source 3, the first alignment image block 621 in the middle and the second alignment image blocks 721 on the left and right sides can be seen on the side of the web 5 facing the industrial camera 4, and the industrial camera 4 can simultaneously capture the first alignment image block 621 in the middle and the second alignment image blocks 721 on the left and right sides.

[0059] The controller-mounted machine vision system includes an image acquisition program and an image processing program. After the controller acquires the image transmitted by the industrial camera, the image is processed, image information is obtained, and the coordinates (including X coordinate and Y coordinate, wherein the Y coordinate is the longitudinal coordinate (i.e. the coordinate in the paper feeding direction), and the X coordinate is the transverse coordinate (i.e. the coordinate in the direction perpendicular to the paper feeding direction)) of the first alignment identification symbol and the second alignment identification symbol are calculated. The image information can include image size, shape, center point position, etc.

[0060] The industrial camera 4 is opposite the appearance area of the first alignment identification symbol 62 and the second alignment identification symbol 72 when taking a photo. When the industrial camera 4 takes a photo, the Y axis direction thereof is parallel to the paper feeding direction, and the X axis direction thereof is parallel to the surface of the appearance area and perpendicular to the Y axis direction. In the embodiment, at the position of the industrial camera 4, the paper feeding direction of the web 5 is from top to bottom, the industrial camera 4 takes a photo opposite the appearance area of the first alignment identification symbol 62 and the second alignment identification symbol 72, a positive coordinate deviation value represents that the paper feeding speed is too small when printing the second side of the web (at this time, the second alignment identification symbol 72 is on the lower side of the first alignment identification symbol 62 and leads the first alignment identification symbol 62 in the paper feeding direction), and a negative coordinate deviation value represents that the paper feeding speed is too large when printing the second side of the web (at this time, the second alignment identification symbol 72 is on the upper side of the first alignment identification symbol 62 and lags behind the first alignment identification symbol 62 in the paper feeding direction). After adjusting the paper feeding speed, the paper feeding speed remains unchanged until the next time the coordinate deviation value exceeds the preset tolerance value.

[0061] Reference Figure 4, the industrial camera 4 takes a picture of the appearing area of the first alignment identification symbol 62 and the second alignment identification symbol 72, and obtains an image composed of three circles, i.e., the first alignment identification symbol 62 and two second alignment identification symbols 72. In the obtained picture, there are three circles with a diameter of 1 mm, and the middle circle is the first alignment identification symbol 62 (appearing on the side of the web facing the industrial camera by the light source), and the two circles on the left and right sides together form the second alignment identification symbol 72 (the Y coordinates of the two circles on the left and right sides are the same in the layout). The controller processes the image to obtain the size, roundness, and center position of the circles, and determines the coordinates of the first alignment identification symbol 62 and the two second alignment identification symbols 72 based on the center position, and obtains the center coordinates (including the X coordinate and the Y coordinate, wherein the Y coordinate is the coordinate in the paper feeding direction, and the X coordinate is the coordinate in the direction perpendicular to the paper feeding direction) of the three circles, wherein the left point coordinate is A(x1, y1), the right point coordinate is B(x2, y2), and the middle point coordinate is P(x0, y0).

[0062] The machine vision system calculates the average value of the Y coordinates y1 and y2 of the centers of the two circles on the left and right sides, i.e., (y1+y2) / 2, and then calculates the coordinate deviation value of the Y coordinate y0 of the center of the middle circle from the average value, and compares the coordinate deviation value with the preset tolerance value; when the Y coordinate y0 of the center of the middle circle is greater than the average value, the coordinate deviation value is positive; when the Y coordinate y0 of the center of the middle circle is less than the average value, the coordinate deviation value is negative. In the case where the range of the preset tolerance value is ±1 mm, if the coordinate deviation value exceeds the range of the preset tolerance value (greater than 1 mm or less than -1 mm), a control signal is sent to the paper feeding mechanism to adjust the paper feeding speed, so as to adjust the actual printing size of the second side of the web, and realize double-sided alignment printing; if the coordinate deviation value does not exceed the preset tolerance value (i.e., -1 mm≤ coordinate deviation value≤1 mm), the paper feeding speed is not adjusted.

[0063] If the coordinate deviation value of the Y coordinate is greater than 1 mm, it means that the paper feeding speed is too small at this time, and the paper feeding speed needs to be increased; if the coordinate deviation value of the Y coordinate is less than -1 mm, it means that the real-time paper feeding speed is too large, and the paper feeding speed needs to be reduced.

[0064] In embodiment 2, the difference from embodiment 1 is that the method for calculating the coordinate deviation value is different, mainly considering that the industrial camera may be slightly tilted when taking a picture, so that the difference between the Y coordinates of the centers of the two circles on the left and right sides is slightly large.

[0065] In this embodiment, after the controller obtains the coordinates of the centers of the three circles, the machine vision system draws a straight line passing through the centers of the left and right circles, and calculates the distance d from the center of the middle circle to the straight line as the coordinate deviation value, which is compared with the preset tolerance value (for example, set to ±1 mm). If the coordinate deviation value exceeds the range of the preset tolerance value (greater than 1 mm or less than -1 mm), a control signal is sent to the paper feeding mechanism to adjust the paper feeding speed, so as to adjust the actual printing size of the second surface of the roll material, and realize double-sided alignment printing. If the center of the middle circle is on the straight line, or the coordinate deviation value does not exceed the preset tolerance value, the paper feeding speed is not adjusted. When the center of the middle circle is above the straight line (at this time, the second alignment identification symbol is ahead of the first alignment identification symbol in the paper feeding direction), the coordinate deviation value is positive; when the center of the middle circle is below the straight line (at this time, the second alignment identification symbol lags behind the first alignment identification symbol in the paper feeding direction), the coordinate deviation value is negative. In the position of the industrial camera, the paper feeding direction of the roll material is from top to bottom, if the Y coordinate deviation value is greater than 1 mm, it means that the current paper feeding speed is too small and should be increased; if the Y coordinate deviation value is less than -1 mm, it means that the real-time paper feeding speed is too large and should be reduced.

[0066] The calculation formula of the distance d from the middle point to the straight line passing through the left and right points is:

[0067] Given that the coordinates of the left point are A(x1, y1), the coordinates of the right point are B(x2, y2), and the coordinates of the middle point are P(x0, y0), the distance d from the middle point to the straight line passing through the left and right points is:

[0068]

[0069] In embodiment 3, referring to Figure 5 , the printing platform adopts a printer (such as Canon PRO-526) with a self-adjustable paper feeding mechanism and a touch screen 8. By operating the touch screen 8, the paper feeding speed of the self-adjustable paper feeding mechanism of the printer can be adjusted. The roll material double-sided alignment printing system of this embodiment further comprises a mechanical hand 9 capable of operating the touch screen. The mechanical hand 9 is electrically connected to the corresponding output end of the controller. When it is necessary to adjust the paper feeding speed, the mechanical hand 9 operates the touch screen 8 under the control of the controller to set the adjustment range of the paper feeding speed. The touch screen 8 transmits the setting information of the paper feeding speed adjustment range to the built-in controller of the printer, and the built-in controller of the printer sends a control signal to the self-adjustable paper feeding mechanism to adjust the paper feeding speed. Compared with embodiment 1, it is not necessary to additionally set the paper feeding mechanism 2, and the adjustment of the paper feeding speed is performed by the built-in controller of the printer, while the controller performs image acquisition, image processing and action control of the mechanical hand 9.

[0070] In this embodiment, the mechanical arm 9 includes four pressing devices 91, 92, 93, 94; refer to Figure 7 Each pressing device includes a pressing block 911 and a pressing block position switching mechanism 912 (which can be a pressing block position switching cylinder or a pressing block position switching electric cylinder) capable of driving the pressing block 911 to reciprocate, and the pressing block 911 is installed on the power output end of the pressing block position switching mechanism 912 (for example, on the piston rod of the pressing block position switching cylinder or on the push rod of the pressing block position switching electric cylinder). When the pressing block position switching mechanism 912 drives the pressing block 911 to reciprocate once, the pressing block 911 presses the operation interface of the touch screen 8 once.

[0071] In this embodiment, the mechanical arm 9 is set according to the characteristics of the operation interface of the touch screen of the Canon canon PRO-526 printer, and the four pressing devices 91, 92, 93, 94 correspond to the areas that need to be pressed on the operation interface of the touch screen 8, simulating the automatic pressing operation of the artificial on the operation interface of the touch screen 8. Refer to Figure 6 When the adjustment range of the paper feeding speed needs to be set (increased or decreased), the operation of the mechanical arm 9 on the touch screen 8 and the change process of the operation interface of the touch screen 8 are as follows: after the pressing device 91 clicks the "maintenance" area 811 on the first interface 81, it enters the second operation interface 82; then the pressing device 92 clicks the "paper feeding fine adjustment" area 821 on the second operation interface 82, and enters the third operation interface 83; then the pressing device 93 presses the area 831 where the upward arrow is located on the third operation interface 83, or the pressing device 94 presses the area 832 where the downward arrow is located on the third operation interface 83, to set the adjustment range of the paper feeding speed (the paper feeding speed increases by one unit every time the pressing device 93 presses the upward arrow; the paper feeding speed decreases by one unit every time the pressing device 94 presses the downward arrow).

[0072] The above mechanical arm can also use other structures, for example: the mechanical arm includes a pressing block and a pressing block position switching mechanism. The pressing block position switching mechanism includes a lifting mechanism, a lifting seat, a translation mechanism and a translation seat, the lifting mechanism is installed on a rack and can drive the lifting seat to lift, the translation mechanism is installed on the lifting seat and can drive the translation seat to translate, and the pressing block is installed on the translation seat. Alternatively, the pressing block position switching mechanism includes a translation mechanism, a translation seat, a lifting mechanism and a lifting seat, the translation mechanism is installed on a rack and can drive the translation seat to translate, the lifting mechanism is installed on the translation seat and can drive the lifting seat to lift, and the pressing block is installed on the lifting seat. Among them, the translation mechanism switches the position of the pressing block in the horizontal direction, so that the pressing block can reach the top of the corresponding position of the touch screen; the lifting mechanism can drive the pressing block to lift, realizing the action of pressing the key.

[0073] In other embodiments, the first printing platform is used to print the first side of the web, and the second printing platform is used to print the second side of the web; after the web is installed, the first paper conveying mechanism conveys the web, the first printing platform prints on the first side of the web and performs winding; after the first side printing is completed, the wound web is installed, and the second paper conveying mechanism conveys the web, and the second printing platform prints on the second side of the web. This scheme is actually the same as the way used in Embodiment 1.

[0074] In other embodiments, the first printing platform can also be used to print the first side of the web, and the second printing platform is used to print the second side of the web, and the paper conveying mechanism conveys the web to the first printing platform and the second printing platform in turn; after the web is installed, the paper conveying mechanism conveys the web, and the first printing platform prints on the first side of the web; then the paper conveying mechanism conveys the web to the second printing platform, and the second printing platform prints on the second side of the web. Since the conveying speed of the web when passing through the first printing platform and the conveying speed of the web when passing through the second printing platform can be inconsistent, a web storage device can be provided between the first printing platform and the second printing platform so that they do not interfere with each other. The web storage device can refer to the storage device disclosed in the authorized announcement CN206751027U. The web passes through the web storage device after coming out of the first printing platform, and then is sent to the second printing platform; when the conveying speed of the web when passing through the first printing platform is greater than the conveying speed of the web when passing through the second printing platform, the length of the web stored in the web storage device (i.e., the web wound between the movable guide rollers and the fixed guide rollers) gradually increases; when the conveying speed of the web when passing through the first printing platform is less than the conveying speed of the web when passing through the second printing platform, the length of the web stored in the web storage device (i.e., the web wound between the movable guide rollers and the fixed guide rollers) gradually decreases.

[0075] In other embodiments, the web traction mechanism can also include a servo motor, a driving paper conveying roller, and a plurality of paper pressing wheels. The power output shaft of the servo motor is in driving connection with the driving paper conveying roller. The web passes between the driving paper conveying roller and the paper pressing wheels. The driving paper conveying roller and the paper pressing wheels jointly clamp the web. When the power output shaft of the servo motor drives the driving paper conveying roller to rotate, the web is conveyed. The corresponding output end of the servo motor and the controller are electrically connected. The conveying speed is adjusted by adjusting the rotating speed of the power output shaft of the servo motor. The conveying speed can be finely adjusted by finely adjusting the rotating speed of the power output shaft of the servo motor. The power output shaft of the servo motor can be connected with one end of the driving paper conveying roller through a shaft coupling. The power output shaft of the servo motor can also be in driving connection with one end of the driving paper conveying roller through a transmission mechanism (such as a synchronous belt or a gear set).

Claims

1. A roll-to-roll duplex printing system, comprising a printing platform, a paper feeding mechanism, an industrial camera, and a controller, wherein the industrial camera is electrically connected to a corresponding input terminal of the controller, characterized in that... It also includes a light source, and the controller is equipped with a machine vision system; Based on the aforementioned roll-to-roll double-sided alignment printing system, roll-to-roll double-sided alignment printing is achieved according to the following steps: (1) Create the imposition file: Imposition the first target graphics and text to be printed on the first page, and add multiple first alignment identification symbols to form the first imposition file; The second target images and text to be printed on the second page are assembled, and multiple second alignment identification symbols are added to form a second assembly file; In the first imposition file, each first alignment identification symbol is arranged sequentially along the paper feeding direction. In the second imposition file, each second alignment identification symbol is arranged sequentially along the paper feeding direction. The number of second alignment identification symbols is the same as that of first alignment identification symbols, and their positions correspond one-to-one. (2) The paper feeding mechanism feeds the roll material, and the printing platform prints each first target graphic and the first alignment identification symbol on the first side of the roll material according to the first layout file; (3) After the first side of the roll is printed, the paper feeding mechanism delivers the roll, and the printing platform prints the second target graphics and the second alignment identification symbol on the second side of the roll according to the second layout file; the roll that has been printed on the second side passes between the light source and the industrial camera, and after being illuminated by the light source, the first alignment identification symbol and the second alignment identification symbol are both displayed on the same side of the roll; the industrial camera takes pictures of the display area of ​​the first alignment identification symbol and the second alignment identification symbol, and transmits the acquired image to the controller; after processing the image, the controller obtains the coordinates of the first alignment identification symbol and the second alignment identification symbol, calculates the coordinate deviation value between the first alignment identification symbol and the second alignment identification symbol, and then compares the coordinate deviation value with the preset tolerance value; If the coordinate deviation exceeds the preset tolerance value, the controller sends a control signal to adjust the paper feeding speed; if the coordinate deviation is within the preset tolerance value, the current paper feeding speed is maintained.

2. The roll-to-roll double-sided alignment printing system according to claim 1, characterized in that: The first pair of identification symbols are arranged at equal intervals along the paper feeding direction, and the second pair of identification symbols are arranged at equal intervals along the paper feeding direction.

3. The roll-to-roll double-sided alignment printing system according to claim 1 or 2, characterized in that: The spacing between two adjacent first-pair identification symbols and the spacing between two adjacent second-pair identification symbols are both 20-100 cm.

4. The roll-to-roll double-sided alignment printing system according to claim 1 or 2, characterized in that: The same printing platform and paper feeding mechanism are used to print the first and second sides of the roll material; after the roll material is installed, the paper feeding mechanism delivers the roll material, the printing platform prints on the first side of the roll material and rewinds it; after the first side is printed, the rewound roll material is installed, and then the same paper feeding mechanism delivers the roll material, and the printing platform prints on the second side of the roll material. Alternatively, the first printing platform can be used to print the first side of the roll material, and the second printing platform can be used to print the second side of the roll material; After the roll material is installed, the first paper feeding mechanism delivers the roll material, and the first printing platform prints on the first side of the roll material and rewinds it; after the first side printing is completed, the rewound roll material is installed, and then the second paper feeding mechanism delivers the roll material, and the second printing platform prints on the second side of the roll material. Alternatively, the first printing platform can be used to print the first side of the roll, and the second printing platform can be used to print the second side of the roll. The paper feeding mechanism will sequentially feed the roll to the first printing platform and the second printing platform. After the roll is installed, the paper feeding mechanism will feed the roll, and the first printing platform will print on the first side of the roll. Then the paper feeding mechanism will feed the roll to the second printing platform, and the second printing platform will print on the second side of the roll.

5. The roll-to-roll double-sided alignment printing system according to claim 1 or 2, characterized in that: The paper feeding mechanism is electrically connected to the corresponding output terminal of the controller; in step (3), if the coordinate deviation value exceeds the range of the preset tolerance value, the controller sends a control signal to the paper feeding mechanism to adjust the paper feeding speed; The paper feeding mechanism includes an unwinding mechanism, a roll traction mechanism, and a rewinding mechanism. The roll traction mechanism is located between the unwinding mechanism and the rewinding mechanism. The unwinding mechanism is used to install the roll, the rewinding mechanism is used to rewind the printed roll, and the roll traction mechanism is used to traction and transport the roll. The roll traction mechanism is electrically connected to the corresponding output terminal of the controller, and the speed at which the roll traction mechanism transports the roll is the paper feeding speed.

6. The roll-to-roll double-sided alignment printing system according to claim 5, characterized in that: The roll material traction mechanism includes a servo motor, an active paper feed roller, and a pressure roller. The power output shaft of the servo motor is connected to the active paper feed roller. The roll material passes between the pressure roller and the active paper feed roller, and the pressure roller and the active paper feed roller together clamp the roll material. The servo motor's power output shaft drives the active paper feed roller to rotate and transport the roll material. The servo motor is electrically connected to the corresponding output terminal of the controller. The paper feeding speed is adjusted by adjusting the rotation speed of the servo motor's power output shaft. Alternatively, the roll material traction mechanism includes a servo motor, an active paper feed roller, and multiple pressure rollers. The power output shaft of the servo motor is connected to the active paper feed roller. The roll material passes between the pressure rollers and the active paper feed roller. Each pressure roller and the active paper feed roller together clamp the roll material. The servo motor's power output shaft drives the active paper feed roller to rotate and transport the roll material. The servo motor is electrically connected to the corresponding output terminal of the controller. The paper feeding speed is adjusted by adjusting the rotation speed of the servo motor's power output shaft.

7. The roll-to-roll double-sided alignment printing system according to claim 1 or 2, characterized in that: The printing platform uses a printer with a built-in adjustable paper feeding mechanism and a touch screen. The paper feeding speed of the built-in paper feeding mechanism can be adjusted by operating the touch screen. The roll-to-roll duplex printing system also includes a robotic arm that can operate the touch screen. The robotic arm is electrically connected to the corresponding output terminal of the controller. When the paper feeding speed needs to be adjusted, the robotic arm operates the touch screen under the control of the controller to set the adjustment range of the paper feeding speed. The touch screen transmits the setting information of the paper feeding speed adjustment range to the printer's built-in controller, which then sends a control signal to its built-in paper feeding mechanism to adjust the paper feeding speed.

8. The roll-to-roll double-sided alignment printing system according to claim 1 or 2, characterized in that: When the industrial camera takes a picture, its Y-axis direction is parallel to the paper feeding direction, and its X-axis direction is parallel to the surface of the display area and perpendicular to the Y-axis direction.

9. The roll-to-roll double-sided alignment printing system according to claim 1 or 2, characterized in that: The first alignment identification symbol includes at least one first alignment block, and the second alignment identification symbol includes at least one second alignment block.

10. The roll-to-roll double-sided alignment printing system according to claim 9, characterized in that: The second alignment identification symbol consists of two second alignment blocks, and the first alignment identification symbol consists of one first alignment block. When the second alignment identification symbol corresponds to the first alignment identification symbol, the two second alignment blocks are respectively located on both sides of the first alignment block. Alternatively, the second alignment identification symbol consists of a second alignment block, and the first alignment identification symbol consists of two first alignment blocks. When the second alignment identification symbol corresponds to the position of the first alignment identification symbol, the two first alignment blocks are located on both sides of the second alignment block.

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