Position encoder calibration method and system for print substrate printing

Abstract

The application discloses a position encoder calibration method and system for printing of a printing substrate, the method comprising: setting a plurality of reference distance intervals divided by a plurality of photoelectric detectors on a conveying path of the printing substrate; in response to a first photoelectric detector being triggered by a front end edge of the printing substrate, clearing the encoder and printing based on the first photoelectric detector; in response to a subsequent photoelectric detector being triggered by the front end edge of the printing substrate, obtaining a cumulative count value of the encoder and calculating a position error of a previous interval; during the printing substrate passing through the current interval, converting the position error into a number of compensation pulses and inserting or skipping a corresponding number of count cells in an expected natural count sequence of the encoder to complete compensation. The application effectively eliminates the accumulated deviation caused by long-distance conveying of a large-size printing substrate by segmenting the measurement error and uniformly distributing the pulses in the next interval for compensation, and realizes high-precision printing without surface marking.

Description

Technical Field

[0001] This application relates to the field of industrial printing, and in particular to a method and system for calibrating a position encoder for printing on substrates. Background Technology

[0002] In the field of industrial printing, it is sometimes necessary to pre-print cutting outlines on the surface of large steel plates using printing equipment to facilitate subsequent precision cutting processes. These steel plates are huge (often tens of meters in length) and heavy. Due to the influence of rolling or storage processes, their surfaces inevitably have local unevenness and deformation, resulting in inconsistent flatness in different sections of the plate.

[0003] Existing material handling systems primarily rely on the coordinated drive of multiple drive shafts. However, due to the uneven deformation of the steel plate surface, the contact pressure distribution between each drive shaft and the steel plate is uneven, causing some drive shafts to slip relative to the steel plate in local sections due to insufficient friction. This slippage results in a deviation between the rotation of the drive shaft and the actual displacement of the steel plate, making it impossible for the position encoder mounted on the transmission mechanism to accurately reflect the actual distance the steel plate has moved.

[0004] The aforementioned displacement deviations have a cumulative effect during the conveying process. For large steel plates tens of meters long, the cumulative positional deviation throughout the entire conveying process can reach several millimeters or even more than ten millimeters. However, in the actual cutting process, the positional accuracy requirements for the pre-printed contour are extremely high (usually needing to be controlled within ±1 millimeter). The current level of cumulative error far exceeds this tolerance requirement, causing subsequent cutting to deviate from the target contour and severely reducing the forming accuracy of the parts.

[0005] To eliminate such accumulated errors, existing technologies have attempted the following two solutions: The first approach is to add reference marks to the surface of the steel plate and use sensors or image recognition for real-time coordinate correction. However, since large steel plates weigh over a ton and are in continuous motion on the production line, there is a serious safety risk of manual marking being jammed by the equipment or crushed by the steel plate. If automated equipment is introduced for marking, additional marking stations and equipment are required, which not only increases equipment costs and occupies too much factory space, but also reduces the overall conveyor efficiency of the production line.

[0006] The second approach is to introduce a high-precision vision measurement system to monitor the displacement of the steel plate in real time. However, industrial printing sites typically contain large amounts of metal dust and oil, making it difficult to maintain the cleanliness of optical components and resulting in poor system reliability. Furthermore, adding a vision system requires a large-scale reconstruction of existing hardware and software, which is too costly and difficult to promote on a large scale in industry. Summary of the Invention

[0007] In order to achieve accurate calibration of the position encoder without contacting the steel plate surface or adding any auxiliary marks, and to control the position error of large-size steel plates within a strict tolerance range during long-distance transmission, this application provides a position encoder calibration method and system for printing on substrates.

[0008] Firstly, this application provides a method for calibrating a position encoder for printing on a substrate, which adopts the following technical solution: A method for calibrating a position encoder for printing on a substrate includes: S1. Install N+1 photodetectors along the conveyor belt travel direction to divide the conveyor belt travel into N intervals. The length of each interval is a preset reference distance D. Fix the print head at the first photodetector. N is a positive integer greater than 1. S2. In response to the triggering of the first photodetector at the leading edge of the substrate, the encoder is zeroed, and the print head begins printing on the substrate with the encoder count value as a position reference; S3. In response to each triggering of the (k+1)th photodetector at the front edge of the substrate, obtain the cumulative count value of the encoder since it has been cleared, convert the cumulative count value into a cumulative measurement distance, and determine the position error of the kth interval based on the difference between the reference cumulative distance between the first photodetector and the (k+1)th photodetector and the cumulative measurement distance, where k is a positive integer and k is less than N; S4. During the (k+1)th interval of the substrate passing through the print head, the absolute value of the position error of the kth interval is converted into the number of compensation pulses. In response to the position error being greater than zero, the number of additional counting cells of the compensation pulses is uniformly inserted into the counting sequence of the encoder. In response to the position error being less than zero, the number of natural counting cells of the compensation pulses is uniformly skipped in the counting sequence of the encoder until the compensation is completed.

[0009] Optionally, the displacement corresponding to each counting cell of the encoder is no greater than one-tenth of the printing accuracy of the print head.

[0010] Optionally, in S3, the event that triggers the (k+1)th photodetector by the front edge of the substrate is based on the first light-blocking signal of the (k+1)th photodetector by the front edge of the substrate. Changes in the optical path state during the period when the substrate continuously blocks the (k+1)th photodetector are not recognized as triggering events.

[0011] Optionally, in S1, the N+1 photodetectors are installed on the ground, with their installation positions arranged along the conveyor belt travel, and the support structure of the N+1 photodetectors is independent of the conveyor belt equipment body.

[0012] Optional, also includes: S5. In response to the trailing edge of the substrate passing the print head, the encoder is zeroed to re-execute S2 to S4 for the next substrate.

[0013] Optionally, the number of intervals N in S1 satisfies the following condition: the maximum position error generated by the encoder within a single interval does not exceed the allowable tolerance of the printing accuracy of the substrate.

[0014] Optionally, in response to the position error of the k-th interval being greater than zero, step S4 includes the following sub-steps: S41. Determine the expected number of natural pulses corresponding to the (k+1)th interval based on the preset reference distance D and the displacement resolution of the encoder; S42. Determine the insertion interval between two adjacent additional counter insertion operations based on the ratio of the expected natural pulse number to the compensated pulse number; S43. In the counting sequence of the encoder, an additional counting cell is inserted after each natural counting cell of the insertion interval, until all the additional counting cells of the compensation pulse are inserted.

[0015] Optionally, in response to the position error of the k-th interval being less than zero, step S4 includes the following sub-steps: S41. Determine the expected number of natural pulses corresponding to the (k+1)th interval based on the preset reference distance D and the displacement resolution of the encoder; S42. Determine the skip interval between two adjacent natural count skip operations based on the ratio of the expected natural pulse number to the compensated pulse number; S43. In the counting sequence of the encoder, after accumulating the skip interval of natural count cells, one natural count cell is skipped, until all natural count cells of the compensation pulse have been skipped.

[0016] Optionally, the printhead prints on the substrate using a theoretical measurement code as a position reference. The theoretical measurement code is determined based on the actual measurement code, the estimated compensation code, and the accurate compensation code. The actual measurement code is the real-time count value output by the encoder as the substrate moves. The estimated compensation code is a pre-compensation count value extracted from the historical statistical error data of the substrate. The historical statistical error data includes the mean error of the previous interval of the same substrate, the mean error of the same batch of substrates, or the average error trend line of the same batch of substrates. The accurate compensation code is a fine-tuning compensation value calculated based on the position error of the k-th interval.

[0017] Secondly, the position encoder calibration system for printing on a substrate provided in this application adopts the following technical solution: A position encoder calibration system for printing on a substrate includes: The photodetector array includes N+1 photodetectors installed along the conveyor belt travel direction, dividing the conveyor belt travel into N intervals, the length of each interval being a preset reference distance D, where N is a positive integer greater than 1; An encoder, fixed above the conveyor belt relative to the ground and used to contact the substrate, is configured to output a counting sequence as the substrate moves. A printhead, fixedly mounted at the first photodetector, is configured to print on the substrate using the encoder's count value as a position reference; and The calibration control module is configured to perform the position encoder calibration method described above for printing on substrates.

[0018] In summary, this application includes at least one of the following beneficial technical effects: 1. This application divides a long travel distance into multiple preset reference distance intervals using a photodetector array, calculates the position error for each interval, and completes compensation in the next interval. This mechanism cuts off the error transmission chain, ensuring that the printing position deviation of the current interval is determined only by the newly added error within that interval, avoiding the amplification of errors from previous intervals. This strictly compresses the overall printing error to the order of magnitude of a single interval error, perfectly solving the problem of precision deviation caused by transmission slippage in large-size steel plates.

[0019] 2. This application employs a method of converting positional errors into compensation pulse counts and uniformly inserting or skipping counting cells in the encoder counting sequence based on the ratio of natural pulse counts to compensation pulse counts for correction. Combined with the setting that the displacement of a single encoder cell does not exceed one-tenth of the printing accuracy, the displacement compensation action is finely distributed throughout the entire physical range, effectively avoiding abrupt positional changes caused by concentrated compensation and ensuring that the compensation process has no visible interference with the quality of the final printed pattern.

[0020] 3. At the logic triggering level, the system only recognizes the first light-blocking signal at the front edge of the substrate, shielding against false triggering caused by light path jitter due to surface deformation or notches. At the hardware structure level, the photodetector adopts an independent support structure that is mechanically decoupled from the conveyor belt equipment body (such as being directly installed on the ground), eliminating the periodic interference of equipment operation vibration on the detector spacing and ensuring the absolute stability and accuracy of the ranging reference.

[0021] 4. This application sets up an encoder reset after the printhead passes the edge of the substrate, ensuring that the calibration process for each sheet is independent and does not interfere with each other. This isolation mechanism allows the system to seamlessly connect to the processing of the next sheet without stopping for calibration, which is highly suitable for assembly line operations where metal sheets pass through continuously. Attached Figure Description

[0022] Figure 1 A flowchart of a position encoder calibration method for substrate printing according to some embodiments of this application is shown.

[0023] Figure 2 A schematic diagram of the mounting layout of a photodetector array and a printhead according to some embodiments of this application is shown. Detailed Implementation

[0024] The present application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the application and are not intended to limit the scope of the application.

[0025] In the following description, numerous specific details are set forth for purposes of explanation in order to provide a thorough understanding of the inventive concept. As part of this specification, some of the accompanying drawings of this disclosure are block diagrams illustrating structures and devices to avoid complicating the disclosed principles. For clarity, not all features of the actual embodiment need to be described. Furthermore, the language used in this disclosure has been primarily chosen for readability and instructional purposes and may not have been chosen to define or limit the subject matter of the invention, thus requiring the necessary claims to determine such inventive subject matter. References to “an embodiment” or “an embodiment” in this disclosure mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment, and multiple references to “an embodiment” or “an embodiment” should not be construed as necessarily referring to the same embodiment.

[0026] Unless explicitly defined, the terms “a,” “an,” and “the” are not intended to refer to a singular entity, but rather to include a general category whose specific examples can be used for illustration. Therefore, the use of the terms “a” or “an” can mean any number of at least one, including “a,” “one or more,” “at least one,” and “one or more.” The term “or” means any of the options and any combination of the options, including all options unless explicitly indicated that the options are mutually exclusive. The phrase “at least one of” when combined with a list of items refers to a single item in the list or any combination of items in the list. The phrase does not require all items listed unless explicitly defined as such.

[0027] This application discloses a position encoder calibration method for printing on substrates. Before describing the embodiments of this application in detail, some terms will be explained first.

[0028] The substrate refers to an object that is conveyed by a conveyor belt and printed by a print head. As an example, the substrate can be a large-sized metal steel plate that needs to be pre-printed with a cut outline pattern. For example, the substrate can be a steel plate with a length of 20 meters and a slightly uneven surface, which will be used as an example below, but this application is not limited to this. The substrate can also be other large-sized plates that need to be precisely positioned and printed on the surface.

[0029] The preset reference distance D is the installation spacing between two adjacent photodetectors. This spacing is determined after precise measurement during the equipment installation phase and serves as the absolute reference for the actual displacement in the calibration calculation. No restrictions are imposed here.

[0030] Position error refers to the deviation between the measured distance calculated from the cumulative count value of the encoder within a certain interval and the actual displacement within that interval. A positive position error indicates that the encoder is under-counting, while a negative position error indicates that the encoder is over-counting.

[0031] The number of compensation pulses is the value after the position error is converted into the number of encoder counts, and it is used to determine the number of counts that need to be inserted or skipped in the next interval.

[0032] Figure 1 A flowchart of a position encoder calibration method for substrate printing according to some embodiments of this application is shown. Figure 2 A schematic diagram illustrating the mounting layout of a photodetector array and a printhead according to some embodiments of this application is shown. Figure 2 As shown, 21 photodetectors are installed along the conveyor belt travel direction, dividing the conveyor belt travel into 20 intervals. The length of each interval is a preset reference distance D, i.e., 1 meter. The print head is fixedly installed at the first photodetector and its position remains unchanged throughout the printing process. The laser triggering timing is driven by the real-time count value of the encoder. Of course, in other embodiments, the print head can also be flexibly installed in other positions. In fact, these 20 intervals are divided along the conveyor belt travel as needed. Depending on the different division and positioning, the relative position of the print head in these intervals will also be different, but this does not substantially affect the inventive concept of this application.

[0033] In response to the first photodetector being triggered by the leading edge of the substrate, the encoder is zeroed, and the printhead begins printing on the substrate using the encoder count as a position reference. The triggering event is based on the first light-blocking signal from the leading edge of the substrate to the first photodetector. During transport, the substrate continuously covers the detectors it has already passed; therefore, changes in the optical path during this continuous blocking period are not recognized as triggering events, thus avoiding false triggering caused by optical path jitter due to uneven substrate surfaces. Furthermore, if the leading edge of the substrate has chamfers or other edge notches, the initial light-blocking signal is based on the portion of the leading edge that first blocks the optical path; subsequent brief restoration of the optical path due to the notch does not reset the trigger state.

[0034] The second photodetector is triggered by the leading edge of the substrate to acquire the cumulative count value of the encoder since it was zeroed. Since the actual distance between the first and second detectors is 1 meter, and the encoder experiences counting deviation due to slippage between the encoder and the substrate, the difference between the two is the positional error within the first interval. For example, if the cumulative encoder count is converted to 0.998 meters, then the positional error in the first interval is 1.000 - 0.998 = 0.002 meters, or 2 millimeters, indicating undercounting by the encoder.

[0035] After the positional error in the first interval is determined, during the second interval when the substrate passes the print head, this positional error is converted into a number of compensation pulses, and a corresponding number of additional counting cells are evenly inserted into the encoder's counting sequence until compensation is complete. Here, the positional error generated in the previous interval is distributed and compensated within the current interval, ensuring that the displacement sensed by the printing module matches the actual displacement of the substrate, thereby eliminating the influence of previous interval errors on the current interval's printing position. Therefore, the printing position deviation in the current interval is determined only by the error generated by the current interval itself, and is not affected by the cumulative errors of previous intervals.

[0036] Specifically, let N be the expected number of natural pulses corresponding to the second interval, and m be the number of pulses to be compensated. The insertion interval between two adjacent extra counting operations is determined by the ratio of N to m. That is, one extra counting cell is inserted after every N / m natural count, until all m cells are inserted. For example, if the encoder's displacement resolution is 0.01 mm per division, the expected number of natural pulses corresponding to a 1-meter interval is 100,000. The position error of the first interval is 2 mm, which translates to 200 compensation pulses. The insertion interval is 100,000 ÷ 200 = 500 divisions, meaning one extra counting cell is inserted after every 500 natural counts by the encoder, for a total of 200 times, until compensation is complete. The total count sensed by the printing module is 100,000 + 200 = 100,200 divisions, corresponding to 1.002 meters, which precisely compensates for the 2 mm undercount deviation.

[0037] The above describes the compensation method when the position error is greater than zero, i.e., uniform interpolation. In other embodiments, the position error can also be less than zero, i.e., the encoder overcounts, in which case the cumulative distance recorded by the encoder is greater than the actual displacement of the steel plate. For example, when the front end of the substrate triggers the third photodetector, the cumulative encoder count is converted to 2.003 meters, while the actual cumulative distance is 2.000 meters. Then the position error of the second interval is 2.000 - 2.003 = -0.003 meters, or -3 millimeters. In this case, the compensation direction is reversed. During the third interval of the substrate passing through the print head, the corresponding number of natural count intervals are uniformly skipped in the encoder's counting sequence. The skip interval is calculated in the same way as the interpolation, i.e., the expected number of natural pulses is divided by the number of compensated pulses to obtain the skip interval. Taking the above scenario as an example, 300 frames need to be skipped. The skipping interval is approximately 333 frames (100000 ÷ 300 ≈ 333 frames). That is, the encoder skips one frame after every 333 natural counts until a total of 300 frames are skipped. This reduces the total count sensed by the printing module by 300 frames, corresponding to a shortening of 0.003 meters, thus eliminating the forward shift deviation in printing position caused by over-counting. Both frame insertion and frame skipping are compensation operations that uniformly correct the encoder counting sequence. Their triggering conditions are opposite, but both determine the operation interval based on the ratio of the expected natural pulse count to the compensation pulse count. They both belong to the implementation method of uniformly distributing and compensating for position errors within an interval in this application.

[0038] In some embodiments, the displacement corresponding to each encoder cell is no greater than one-tenth of the printhead's printing accuracy. This is because the compensation operation uses a single cell as the smallest granularity. If the cell size is too large, the impact of each cell insertion or skipping operation on the print position will exceed the acceptable range of printing accuracy, causing visible print position jitter to be introduced into the compensation process itself. For example, if the printing accuracy is 0.1 mm, the displacement corresponding to each encoder cell is no greater than 0.01 mm, ensuring that the impact of each cell insertion or skipping operation on the print position does not exceed 0.01 mm, which is far less than the printing accuracy requirement, thus guaranteeing that the compensation process has no visible impact on print quality.

[0039] In response to each triggering of a new photodetector at the leading edge of the substrate, the above error measurement and compensation process is repeated. Taking the triggering of the (k+1)th detector at the leading edge of the substrate as an example, the cumulative count value of the encoder since zeroing is obtained. This cumulative count value is converted into a cumulative measurement distance. Based on the difference between the reference cumulative distance k×D between the 1st and (k+1)th detectors and the cumulative measurement distance, the position error of the kth interval is determined, and compensation is completed during the (k+1)th interval of the substrate passing through the print head. Since the errors of the 1st to (k-1)th intervals have been compensated one by one in their respective subsequent intervals, the position error of the kth interval essentially only reflects the new deviation generated in the transmission process of that interval itself. For example, when the leading edge of the substrate triggers the 10th photodetector, the encoder's cumulative count value is converted to 8.991 meters, the reference cumulative distance is 9.000 meters, and the position error is 0.009 meters, or 9 millimeters. The errors of the first 8 intervals have all been compensated in their respective subsequent intervals, so this 9 millimeters is only the new deviation generated in the 9th interval itself. During the 10th interval of the substrate as it passes the printhead, 9 mm is converted into 900 grids. 900 additional counting grids are then evenly inserted at an insertion interval of 100000÷900≈111 grids to compensate for the error in the 9th interval.

[0040] In some embodiments, based on fixed-point position sampling provided by the photodetector array, in addition to single-time compensation for hysteresis position errors generated in previous intervals, a pre-compensation mechanism can be introduced. To clearly describe the logic of the pre-compensation mechanism, estimated compensation code, accurate compensation code, actual measurement code, and theoretical measurement code are introduced. The actual measurement code is the measured count value directly output by the encoder as the substrate moves. The estimated compensation code is the pre-compensation count value extracted based on the statistical error data of the previous few intervals or batches of the substrate. The accurate compensation code is the compensation value converted from the hysteresis position error of the interval, that is, the difference between the reference cumulative distance of the photodetector and the cumulative measurement distance of the encoder since zeroing. The theoretical measurement code is obtained by combining the actual measurement code, estimated compensation code, and accurate compensation code. The theoretical measurement code is used as a position reference to guide the print head to print on the substrate.

[0041] As a first implementation of the estimated compensation code, the estimated compensation code can be obtained based on the average value of multiple intervals preceding the same substrate. For example, when the same steel plate passes through the first, second, and third intervals, the compensation grids corresponding to the measured errors are 200, 180, and 220 grids respectively. Before the substrate passes through the fourth interval, the average value of the first three intervals (i.e., 200 grids) is obtained as the estimated compensation code. During the transfer of the fourth interval, the system evenly inserts 200 grids of estimated compensation code based on the actual measured code. When the fifth photodetector is triggered at the front end of the substrate, if the actual total deficit in the fourth interval is measured to be 210 grids, since 200 grids have already been pre-compensated through the estimated compensation code, the accurate compensation code for the fourth interval is only the remaining 10 grids. During the fifth interval as it passes the printhead, these 10 accurate compensation grids are superimposed onto the generated sequence of the theoretical measured code.

[0042] As a second implementation of the estimated compensation code, the estimated compensation code can be obtained based on the average value of the same batch of substrates. For example, the system records the positional error of the first 5 steel plates in the first batch as they pass through all 20 intervals, calculating the average error per interval as 150 counts of under-count. When the 6th steel plate in the same batch begins printing, the system directly uses 150 counts as the estimated compensation code during the transfer process through all 20 intervals, evenly inserting this estimated compensation code into the actual measurement code. The additional true deviation measured by each photodetector at the end of each interval is then converted into an accurate compensation code, used to fine-tune the theoretical measurement code in the next interval.

[0043] As a third implementation of the estimated compensation code, the estimated compensation code can be obtained based on the average trend line of the error of the same batch of substrates. Due to wear of the transmission mechanism or the gradual change of the steel plate thickness in the rolling direction, the error may exhibit a linear increase or decrease. For example, the system performs polynomial fitting on the data of multiple preceding steel plates to obtain the average trend line function of the error of the batch of steel plates as a function of interval number k (e.g., error grid number = 100 + 5 × k). When the current steel plate passes through the 10th interval, k equals 10 and is substituted into the average trend line function to calculate an estimated compensation code of 150 grids, which is then evenly inserted into the actual measurement code of that interval. By introducing the average trend line, the pre-compensation amount of the theoretical measurement code dynamically adapts to the changing law of the error.

[0044] After introducing the estimated compensation code, due to the deviation between the estimated value and the actual value, the actual applied pre-compensation amount may exceed the true error, i.e., overcompensation occurs. The system detects overcompensation and executes a remedial scheme when the next photodetector is triggered at the front end of the substrate. For example, the estimated compensation code applied in the 6th interval is to uniformly insert 150 additional count squares (estimated deficit of 150 squares). When the front end of the substrate triggers the 7th photodetector, the reference distance is compared with the converted cumulative distance, and the actual total deficit in the 6th interval is measured to be only 100 squares. At this time, the applied estimated compensation code exceeds the actual total deficit, and the excess of 50 squares is the overcompensation. As a remedial scheme, the system converts this 50-square overcompensation into a negative accurate compensation code. During the 7th interval of the substrate passing through the printhead, the system cancels the overcompensation of the 6th interval by uniformly skipping 50 natural count squares in the generation sequence of the theoretical measurement code, so that the theoretical measurement code is re-aligned with the actual displacement of the substrate.

[0045] In some embodiments, the selection of the number of intervals N satisfies the following condition: the maximum positional error generated by the encoder within a single interval does not exceed the allowable tolerance of the printing accuracy of the substrate. Since the printing deviation of each interval is only affected by the error of that interval itself, if the error generated in a certain interval due to severe transmission slippage exceeds the allowable tolerance, it is necessary to increase the number of segments to shorten the length of each interval, thereby reducing the accumulation of error within a single interval. For example, when divided into 20 segments, the maximum error of a single segment is approximately 0.5 mm, meeting the tolerance requirement of ±1 mm; if the error of a certain segment is found to reach 1.5 mm in actual testing, the number of segments can be increased to 40 segments, and the length of each segment can be shortened to 0.5 meters, correspondingly compressing the maximum error of a single segment to within 0.75 mm, thus restoring the accuracy requirement.

[0046] In some embodiments, the process further includes a step of zeroing the encoder after the trailing edge of the substrate passes the printhead, so as to restart the error measurement and compensation process for the next substrate. In operation scenarios where multiple substrates pass through sequentially, the status information of the previous substrate should not be carried over to the printing process of the next substrate. By resetting the encoder after each printing, the calibration process of each substrate is made independent and does not interfere with each other. For example, after the trailing edge of the first steel plate leaves the sensor coverage area, the encoder is zeroed. When the front end of the second steel plate triggers the first photodetector, the printing and calibration process is restarted, completely isolated from the cumulative counting history of the first steel plate.

[0047] In some embodiments, the 21 photodetectors are mounted on the ground, with the support structure independent of the conveyor belt equipment body. This is because the conveyor belt experiences mechanical vibration during operation. If the detectors were mounted on the frame of the conveyor belt equipment body, the vibration would cause the actual mounting position of the detectors to periodically jitter, deviating the actual distance between adjacent detectors from a preset reference distance D, introducing a systematic reference error. By mounting the detectors on the ground and structurally decoupling them from the conveyor belt equipment body, the influence of equipment vibration on the reference distance can be eliminated. In other embodiments, the photodetectors can also be mounted on independent supports rigidly connected to the ground, as long as there is no mechanical coupling between the support structure and the conveyor belt equipment body. This also falls under the category of isolating the detector mounting position from the vibration source of the conveyor belt equipment body.

[0048] This application also discloses a position encoder calibration system for printing on substrates. The system includes a photodetector array, an encoder, a printhead, and a calibration control module. The photodetector array comprises 21 photodetectors mounted on the ground along the conveyor direction, dividing the conveyor belt travel into 20 intervals, each interval being 1 meter in length. The encoder is fixedly mounted above the conveyor belt relative to the ground and is used to contact the substrate, outputting a counting sequence as the substrate moves. The printhead is fixedly mounted at the first photodetector and prints on the substrate using the encoder's count value as a position reference.

[0049] The calibration control module is configured to: zero the encoder in response to the triggering of the first photodetector at the leading edge of the substrate; acquire the cumulative count value of the encoder and calculate the position error of the kth interval in response to the triggering of the (k+1)th photodetector at the leading edge of the substrate; and uniformly insert or skip a corresponding number of counting cells in the encoder's counting sequence according to the sign of the position error during the (k+1)th interval of the substrate passing through the print head, until compensation is completed.

[0050] Therefore, the printing position deviation of each interval on each substrate in the system is determined only by the error generated by that interval itself, and is not affected by the cumulative error of the preceding intervals, thus compressing the overall printing error to the level of a single interval error.

[0051] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is used as an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above.

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for calibrating a position encoder for printing on a substrate, characterized in that, include: S1. Install N+1 photodetectors along the conveyor belt travel direction to divide the conveyor belt travel into N intervals. The length of each interval is a preset reference distance D. Fix the print head at the first photodetector. N is a positive integer greater than 1. S2. In response to the triggering of the first photodetector at the leading edge of the substrate, the encoder is zeroed, and the print head begins printing on the substrate with the encoder count value as a position reference; S3. In response to each triggering of the (k+1)th photodetector at the front edge of the substrate, obtain the cumulative count value of the encoder since it has been cleared, convert the cumulative count value into a cumulative measurement distance, and determine the position error of the kth interval based on the difference between the reference cumulative distance between the first photodetector and the (k+1)th photodetector and the cumulative measurement distance, where k is a positive integer and k is less than N; S4. During the (k+1)th interval of the substrate passing through the print head, the absolute value of the position error of the kth interval is converted into the number of compensation pulses. In response to the position error being greater than zero, the number of additional counting cells of the compensation pulses is uniformly inserted into the counting sequence of the encoder. In response to the position error being less than zero, the number of natural counting cells of the compensation pulses is uniformly skipped in the counting sequence of the encoder until the compensation is completed.

2. The position encoder calibration method for printing on substrates according to claim 1, characterized in that, The displacement corresponding to each counting cell of the encoder is no greater than one-tenth of the printing accuracy of the print head.

3. The method for calibrating a position encoder for printing on a substrate according to claim 1, characterized in that, In S3, the event that triggers the (k+1)th photodetector by the front edge of the substrate is based on the first light-blocking signal of the (k+1)th photodetector by the front edge of the substrate. Changes in the optical path state during the period when the substrate continuously blocks the (k+1)th photodetector are not recognized as triggering events.

4. The method for calibrating a position encoder for printing on a substrate according to claim 1, characterized in that, In S1, N+1 photodetectors are installed on the ground, with their installation positions arranged along the conveyor belt travel, and the support structure of the N+1 photodetectors is independent of the conveyor belt equipment body.

5. The method for calibrating a position encoder for printing on a substrate according to claim 1, characterized in that, Also includes: S5. In response to the trailing edge of the substrate passing the print head, the encoder is zeroed to re-execute S2 to S4 for the next substrate.

6. The method for calibrating a position encoder for printing on a substrate according to claim 1, characterized in that, The number of intervals N in S1 satisfies the following condition: the maximum position error generated by the encoder within a single interval does not exceed the allowable tolerance of the printing accuracy of the substrate.

7. The method for calibrating a position encoder for printing on a substrate according to claim 1, characterized in that, In response to the position error in the k-th interval being greater than zero, step S4 includes the following sub-steps: S41. Determine the expected number of natural pulses corresponding to the (k+1)th interval based on the preset reference distance D and the displacement resolution of the encoder; S42. Determine the insertion interval between two adjacent additional counter insertion operations based on the ratio of the expected natural pulse number to the compensated pulse number; S43. In the counting sequence of the encoder, an additional counting cell is inserted after each natural counting cell of the insertion interval, until all the additional counting cells of the compensation pulse are inserted.

8. The method for calibrating a position encoder for printing on a substrate according to claim 1, characterized in that, In response to the position error in the k-th interval being less than zero, step S4 includes the following sub-steps: S41. Determine the expected number of natural pulses corresponding to the (k+1)th interval based on the preset reference distance D and the displacement resolution of the encoder; S42. Determine the skip interval between two adjacent natural count skip operations based on the ratio of the expected natural pulse number to the compensated pulse number; S43. In the counting sequence of the encoder, after accumulating the skip interval of natural count cells, one natural count cell is skipped, until all natural count cells of the compensation pulse have been skipped.

9. The method for calibrating a position encoder for printing on a substrate according to claim 1, characterized in that, The printhead prints onto the substrate using a theoretical measurement code as a position reference. The theoretical measurement code is determined based on the actual measurement code, the estimated compensation code, and the accurate compensation code. The actual measurement code is the real-time count value output by the encoder as the substrate moves. The estimated compensation code is a pre-compensation count value extracted from the historical statistical error data of the substrate. The historical statistical error data of the substrate includes the mean error of the previous interval of the same substrate, the mean error of the same batch of substrates, or the average error trend line of the same batch of substrates. The accurate compensation code is a fine-tuning compensation value calculated based on the position error of the k-th interval.

10. A position encoder calibration system for printing on substrates, characterized in that, include: The photodetector array includes N+1 photodetectors installed along the conveyor belt travel direction, dividing the conveyor belt travel into N intervals, the length of each interval being a preset reference distance D, where N is a positive integer greater than 1; An encoder, fixed above the conveyor belt relative to the ground and used to contact the substrate, is configured to output a counting sequence as the substrate moves. The printhead, fixedly mounted at the first photodetector, is configured to print on the substrate using the encoder's count value as a position reference; as well as The calibration control module is configured to perform the position encoder calibration method for printing on substrates as described in any one of claims 1-9.

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