System and method for monitoring whether inkjet ink droplet is normally discharged by using image matching accuracy

Abstract

The present invention relates to a system and method for monitoring whether an inkjet ink droplet is normally discharged by using an image matching accuracy, wherein: an ink droplet image of an inkjet print head, which is discharging an ink droplet normally, is acquired by using a wide-field 1D line scan camera or 2D area scan camera, and saved as a reference ink droplet image; an ink droplet discharge image of an inkjet print head to be tested is acquired by using a 1D line scan camera or 2D area scan camera of a test system; a matching accuracy between the reference ink droplet image and the ink droplet discharge image to be tested is calculated; and it is determined as an abnormal inkjet print head nozzle if the matching accuracy is less than a set matching accuracy and determined as a normal inkjet print head nozzle if the matching accuracy is greater than or equal to the set matching accuracy.

Description

Inkjet ink droplet normal ejection monitoring system and method using image alignment

[0001] The present invention relates to a system and method for monitoring whether an inkjet ink droplet is being ejected normally using an image alignment degree. In particular, the invention relates to a system and method for monitoring whether an inkjet ink droplet is being ejected normally using an image alignment degree, wherein an image of an inkjet print head that is ejecting an ink droplet normally is acquired by a wide-width 1D line scan camera or a 2D area scan camera and stored as a reference ink droplet image, an image of an inkjet print head to be inspected is acquired by a 1D line scan camera or a 2D area scan camera of an inspection system, an alignment degree is calculated between the reference ink droplet image and the ink droplet ejection image to be inspected, and if the alignment degree is less than a set alignment degree, it is determined to be an abnormal inkjet print head nozzle, while if the alignment degree is greater than or equal to the set alignment degree, it is determined to be a normal inkjet print head nozzle.

[0002] A conventional method for configuring subpixels of a display panel involves manufacturing a color filter by repeatedly applying a color resist of one of three colors (red, green, or blue) to the top surface of the display panel and then using a photolithography process to leave the color resist of the desired color only on the desired subpixels.

[0003] However, manufacturing in this manner not only results in significant material waste but also presents a problem in that photolithography is difficult to apply to expensive materials such as OLEDs (Organic Light-Emitting Diodes) and QDs (Quantum Dots), which are susceptible to post-processing involving chemicals and high temperatures. Consequently, patterning technologies capable of applying a desired amount of ink to specific areas, such as inkjet printing, have attracted the attention of the display industry.

[0004] During the manufacturing of display panels, there was a need to rapidly inspect for ejection defects or abnormalities in ink droplets falling from the inkjet printer head. Conventionally, laser phase Doppler measurement or vision inspection methods were used to monitor the shape, volume, velocity, and ejection angle of the ink droplets from the nozzle.

[0005] However, laser phase Doppler measurement has a problem in that it cannot measure the shape of ink droplets, and especially when the ink droplets contain particles capable of scattering the laser, it is impossible to measure the volume, velocity, ejection angle, etc. of the ink droplets due to scattering noise.

[0006] Furthermore, the method for measuring ink droplet volume using vision inspection had several problems: accurate contour detection was difficult because the outlines were blurred by moving ink droplets; multiple exposures were often used because the image was too dark when exposed with a single light per camera frame, but accurate contour detection became even more difficult due to the blurring of the ink droplet outlines during multiple exposures; and accurate volume calculation was difficult because the size of the ink droplets appeared to vary depending on the light intensity.

[0007] Accordingly, the present invention has been made to solve the above-mentioned problems, and the objective of the present invention is to provide a system and method for monitoring the normal ejection of inkjet ink droplets using image alignment, which can quickly determine whether there is a nozzle defect in an inkjet print head by not using complex image processing such as contour extraction for calculating the volume of the ink droplet.

[0008] To achieve the above objective, an inkjet ink droplet normal ejection monitoring system using image matching according to an embodiment of the present invention comprises: one or more optical strobes configured to irradiate light onto an ink droplet falling from an inkjet print head installed in a system to be inspected and a reference system for acquiring reference image data; a reference image data acquisition unit configured to acquire ink droplet image data by photographing an ink droplet of an inkjet print head that is normally ejecting at a set period, positioned opposite to the optical strobes; an inspection image data acquisition unit configured to acquire comparative ink droplet ejection image data by photographing an ink droplet ejected from an inkjet print head to be inspected at a set period, positioned opposite to the optical strobes; and a first control unit configured to perform a calibration operation of the reference image data acquisition unit and to store the ink droplet image data of the inkjet print head that is normally ejecting, acquired by the reference image data acquisition unit, as reference ink droplet image data.A calibration operation is performed on the above-mentioned inspection image data acquisition unit, and comparison ink droplet ejection image data of the inkjet print head to be inspected, acquired by the above-mentioned inspection image data acquisition unit, is collected and stored. If the overall alignment value between the reference ink droplet image data and the comparison ink droplet ejection image data of the inkjet print head to be inspected is less than a set value, the brightness, size, angle, and up / down / left / right position of the comparison ink droplet ejection image data of the inkjet print head to be inspected are corrected using a calibration tool to increase the alignment value between the comparison ink droplet ejection image data of the inkjet print head to be inspected and the reference ink droplet image data. If the alignment value is greater than or equal to the set value after a calibration operation within a set number of times, a local comparison operation is performed between the comparison ink droplet ejection image data of the inkjet print head to be inspected and the image data within the set ROI (Region Of Interest) for each nozzle on the reference ink droplet image data to determine whether the ink droplet ejection is normal or abnormal. At this time, if the alignment value is greater than or equal to the set alignment value, it is determined to be a normal inkjet print head nozzle, and the above It is characterized by including a second control unit configured to determine an abnormal inkjet print head nozzle if the alignment degree is less than the set alignment degree.

[0009] In the inkjet ink droplet normal ejection monitoring system using image matching according to the above embodiment, the reference image data acquisition unit and the inspection image data acquisition unit are wide-width 1D line scan cameras, and ink droplet image data can be acquired through multiple exposures per frame of the camera, and more preferably, ink droplet image data can be acquired using one exposure per frame of the camera.

[0010] In the inkjet ink droplet normal ejection monitoring system using image matching according to the above embodiment, the reference image data acquisition unit and the inspection image data acquisition unit are 2D area scan cameras, and ink droplet image data can be acquired through multiple exposures per frame of the camera, and more preferably, ink droplet image data can be acquired using one exposure per frame of the camera.

[0011] The inkjet ink droplet normal ejection monitoring system using image alignment according to the above embodiment may further include a display unit configured to display the normal or abnormal result for the inkjet print head nozzle determined by the second control unit, and the alignment degree between the reference ink droplet image data and the ink droplet ejection image data of the inkjet print head to be inspected.

[0012] In a monitoring system for determining whether an inkjet ink droplet is normally ejected using image alignment according to the above embodiment, the second control unit may be further configured such that when the overall alignment value between the reference ink droplet image data and the ink droplet ejection image data of the inkjet print head to be inspected is less than a set value, the second control unit performs a correction operation within a set number of times using a correction tool to make the comparison ink droplet ejection image data of the inkjet print head to be inspected match the reference ink droplet image data as much as possible in terms of brightness, size, angle, and position, and calculates the alignment value between the reference ink droplet image data and the ink droplet ejection image data of the inkjet print head to be inspected.

[0013] In an inkjet ink droplet normal ejection monitoring system using image matching according to the above embodiment, the matching is quantified by a matching tool, and the matching tool may use any one of a feature-based technique, a brightness-based technique, and a non-rigid matching technique, and may use various matching calculation techniques capable of calculating the matching of a reference and a comparison image.

[0014] To achieve the above objective, a method for monitoring whether an inkjet ink droplet is being ejected normally according to another embodiment of the present invention comprises: a step in which a first control unit of a reference system for acquiring reference image data performs a calibration operation of a reference image data acquisition unit; a step in which the first control unit collects ink droplet image data of an inkjet print head being ejected normally captured by the reference image data acquisition unit and stores the collected ink droplet image data of the inkjet print head being ejected normally as reference ink droplet image data; a step in which a second control unit of a system to be inspected performs a calibration operation of an inspection image data acquisition unit; a step in which the second control unit collects comparison ink droplet image data of an inkjet print head to be inspected captured by the inspection image data acquisition unit and stores the collected ink droplet image data of the inkjet print head being ejected as comparison ink droplet image data; A step in which the second control unit quantifies the overall alignment status of the reference ink droplet image data and the comparison ink droplet image data of the inkjet print head to be inspected, and determines whether the quantified alignment value is greater than or equal to a set value; and a step in which, in the step of determining whether it is greater than or equal to a set value, if the alignment value is less than the set value, the second control unit improves the alignment between the comparison ink droplet ejection image data of the inkjet print head to be inspected and the reference ink droplet image data by correcting the brightness, size, angle, and up / down / left / right position of the comparison ink droplet ejection image data of the inkjet print head to be inspected using a correction tool.In the step of determining whether the alignment value is greater than or equal to the set value, if the alignment value is greater than or equal to the set value, the second control unit performs a local comparison operation of image data within a Region of Interest (ROI) set for each nozzle on the reference ink droplet image data and the comparison ink droplet ejection image data of the inkjet print head to be inspected; if the alignment value is greater than or equal to the set alignment value in the step of performing the local comparison operation, the second control unit determines it as a normal inkjet print head nozzle, while if the alignment value is less than the set alignment value, the second control unit determines it as an abnormal inkjet print head nozzle; and the result determined in the determination step and the alignment value are displayed through a display unit; characterized by comprising:

[0015] According to the system and method for monitoring whether an inkjet ink droplet is being ejected normally using image alignment according to an embodiment of the present invention, a calibration operation is performed on a reference image data acquisition unit, ink droplet image data of an inkjet print head being ejected normally captured by the reference image data acquisition unit is collected, the collected ink droplet image data of the inkjet print head being ejected normally is stored as reference ink droplet image data, comparison ink droplet image data of an inkjet print head to be inspected is collected by an inspection image data acquisition unit, the overall alignment value of the reference ink droplet image data and the comparison ink droplet image data of the inkjet print head to be inspected is checked, and if it is less than a set value, a calibration tool is used to perform a calibration operation on the brightness, size, angle, and up / down / left / right position of the comparison ink droplet image data within a set number of times to match the brightness, size, angle, and up / down / left / right position of the reference ink droplet image data, and the overall alignment value of the reference ink droplet image data and the comparison ink droplet image data of the inkjet print head to be inspected If the alignment value is greater than the set alignment value, a local comparison operation is performed using the alignment value of ink droplets within the ROI set for each nozzle to determine whether the ink droplet ejection is normal or abnormal; additionally, if the alignment value of the reference ink droplet image and the comparison ink droplet image data within the ROI set for each nozzle is less than the set alignment value, it is determined to be an abnormal inkjet print head nozzle. This configuration provides the excellent effect of rapidly determining whether an inkjet print head nozzle is defective without using complex image processing.

[0016] FIG. 1 is a block diagram of an inkjet ink droplet normal ejection monitoring system using image matching according to an embodiment of the present invention.

[0017] FIG. 2 is a flowchart for explaining a method for monitoring whether an inkjet ink droplet is normally ejected using an image matching diagram according to an embodiment of the present invention.

[0018] FIG. 3 is a diagram showing that when the reference image data acquisition unit or the inspection image data acquisition unit of FIG. 1 is a wide-width 1D line scan camera, the Flat Field Correction (FFC) function is used to make the uneven background lighting as uniform as possible through a calibration process.

[0019] FIG. 4 is a diagram showing that ink droplet image data is acquired using one exposure per camera frame when the reference image data acquisition unit or the inspection image data acquisition unit of FIG. 1 is a 1D line scan camera.

[0020] FIG. 5 is a diagram showing that when the reference image data acquisition unit or the inspection image data acquisition unit of FIG. 1 is a 2D area scan camera, ink droplet image data is acquired using one exposure per camera frame.

[0021] FIG. 6 is a diagram showing that the first control unit of FIG. 1 collects ink droplet image data of an inkjet print head in normal ejection, captured by a reference image data acquisition unit, and stores it as reference ink droplet image data.

[0022] FIG. 7 is a diagram showing that the second control unit of FIG. 1 collects ink droplet ejection image data of an inkjet print head to be inspected, captured by an inspection image data acquisition unit, and stores it as comparison ink droplet image data.

[0023] Figure 8 is an example of ink droplet ejection image data (comparison ink droplet image data) of an inkjet print head to be inspected and matched with reference ink droplet image data.

[0024] Figure 9 is a diagram illustrating the process of correcting the brightness of the comparison ink droplet image data to be the same as the reference ink droplet image data by adjusting the brightness of the comparison ink droplet image data using a correction tool when the brightness of the reference ink droplet image data and the comparison ink droplet image data are different.

[0025] Figure 10 is a diagram illustrating the process of correcting the comparison ink droplet image data to be the same size as the reference ink droplet image data by reducing or enlarging the comparison ink droplet image data when the sizes of the reference ink droplet image data and the comparison ink droplet image data are different.

[0026] Figure 11 is a diagram illustrating a correction process that horizontally aligns the comparison ink droplet image data with the reference ink droplet image data by rotating the comparison ink droplet image data when the angles of the reference ink droplet image data and the comparison ink droplet image data are different.

[0027] Figure 12 is a diagram illustrating a correction process that aligns comparison image data with reference ink droplet image data through horizontal or vertical movement.

[0028] FIG. 13 is a diagram illustrating a situation where the degree of alignment between the reference ink droplet image data and the comparison image data is greater than the set degree of alignment, and thus they are well superimposed, when the reference image acquisition unit or the inspection image acquisition unit is a wide 1D line scan camera.

[0029] FIG. 14 is a diagram showing a situation where, when a reference image acquisition unit or an inspection image acquisition unit is a wide 1D line scan camera, the degree of alignment between the reference ink droplet image data and the comparison image data is less than the set degree of alignment and thus does not overlap well.

[0030] FIG. 15 is a diagram showing reference ink droplet image data and comparison image data when the reference image acquisition unit or the inspection image acquisition unit is a 2D area scan camera.

[0031] FIG. 16 is a diagram showing a situation in which comparison ink droplet image data and reference ink droplet image data are superimposed after brightness, size, angle, and up / down / left / right position correction work is completed, when the reference image acquisition unit or inspection image acquisition unit is a 2D area scan camera.

[0032] Figure 17 is a diagram showing a case where the degree of alignment between the reference ink droplet image data and the comparison image data is well aligned, with the degree of alignment value being 99.5%, which is close to 100%.

[0033] Figure 18 is a diagram showing the case where the degree of alignment between the reference ink droplet image data and the comparison image data is 82%.

[0034] Figure 19 is a diagram quantifying the ink droplet image alignment for each corresponding ROI after setting the ROI (Region Of Interest) for each nozzle of an inkjet print head.

[0035] FIG. 20 is a drawing illustrating a case in which a single or multiple ROI setting per nozzle of an inkjet print head and the shape of one or more ink droplets within the ROI are included.

[0036] In describing the embodiments of the present invention, if it is determined that a detailed description of known technology related to the present invention may unnecessarily obscure the essence of the present invention, such detailed description will be omitted. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intentions or practices of the user or operator. Therefore, such definitions should be based on the content throughout this specification. Terms used in the detailed description are intended merely to describe the embodiments of the present invention and should not be interpreted restrictively. Unless explicitly stated otherwise, expressions in the singular form include the meaning of the plural form. In this description, expressions such as "include" or "comprise" are intended to refer to certain characteristics, numbers, steps, actions, elements, parts thereof, or combinations thereof, and should not be interpreted as excluding the existence or possibility of one or more other characteristics, numbers, steps, actions, elements, parts thereof, or combinations thereof other than those described.

[0037] In each system illustrated in the drawings, elements in some cases may have the same or different reference numbers, suggesting that the represented elements may be different or similar. However, elements may have different implementations and may operate with some or all of the systems shown or described herein. The various elements illustrated in the drawings may be the same or different. It is optional which is referred to as the first element and which is referred to as the second element.

[0038] In this specification, the phrase “transmits,” “delives,” or “provides” data or signals from one component to another component includes not only the direct transmission of data or signals from one component to another component, but also the transmission of data or signals to another component through at least one other component.

[0039] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0040] FIG. 1 is a block diagram of an inkjet ink droplet normal ejection monitoring system using image matching according to an embodiment of the present invention, FIG. 3 is a diagram showing that when the reference image data acquisition unit or inspection image data acquisition unit of FIG. 1 is a wide-width 1D line scan camera, the uneven background lighting is made as uniform as possible through a correction process using the Flat Field Correction (FFC) function, FIG. 4 is a diagram showing that when the reference image data acquisition unit or inspection image data acquisition unit of FIG. 1 is a 1D line scan camera, ink droplet image data is acquired using one exposure per camera frame, and FIG. 5 is a diagram showing that when the reference image data acquisition unit or inspection image data acquisition unit of FIG. 1 is a 2D area scan camera, ink droplet image data is acquired using one exposure per camera frame.

[0041] An inkjet ink droplet normal ejection monitoring system using image matching according to an embodiment of the present invention includes, as illustrated in FIGS. 1, 3 to 5, a light strobe (L), a reference image data acquisition unit (100), a first control unit (200), an inspection image data acquisition unit (101), a second control unit (201), and a display unit (300).

[0042] The optical strobe (L) serves to irradiate light onto an ink droplet falling from an inkjet print head (H) installed in a reference system (a system used to acquire reference image data) and a system to be inspected. For example, as shown in FIGS. 4 and 5, the optical strobe (L) is positioned below and behind the inkjet print head (H) to irradiate light onto the ink droplet, thereby enabling the reference image data acquisition unit (100) or inspection image data acquisition unit (101) facing the optical strobe (L) to capture a 1D image or 2D image of the ink droplet falling from the inkjet print head (H).

[0043] The light strobe (L) can be composed of a cluster of one or more high-brightness LEDs or a laser-excited phosphor (LEP), and can be overdriven at a current higher than the normal operating current to provide very high brightness for a very short flashing time.

[0044] A reference image data acquisition unit (100) or an inspection image data acquisition unit (101) is positioned opposite a light strobe (L) and serves to photograph an ink droplet at a set interval and acquire ink droplet image data. A wide-width 1D line scan camera or a 2D area scan camera may be used for the reference image data acquisition unit (100) or the inspection image data acquisition unit (101). Here, the reference image data acquisition unit (100) is used for acquiring reference image data, and the inspection image data acquisition unit (101) is installed in a system to be inspected and used for acquiring image data to be inspected, but a single image data acquisition unit may be used for acquiring both reference image data and image data to be inspected.

[0045] A wide-width 1D line scan camera is positioned opposite a light strobe (L) through a lens and barrel for the wide-width 1D line scan camera and serves to acquire 1D high-resolution ink droplet image data by capturing ink droplets at a set interval. When the wide-width 1D line scan camera is used, an ultra-high brightness light strobe must be used to supply sufficient light to the camera's image sensor even at sub-microseconds, more preferably at ultra-short pulses (light strobe illumination time) of 500 ns or less, in order to acquire ink droplet image data of a falling ink droplet using one exposure per frame of the camera. It is desirable to use an ultra-high brightness LED or LED cluster capable of operating at a current higher than the normal operating current, i.e., overdriving, or a light strobe using LEP (laser excited phosphor), or a combination thereof.

[0046] A wide 1D line scan camera can simultaneously measure ink droplets ejected from many more nozzles at high speed than a 2D area scan camera. Unlike a 2D area scan camera that captures a 2D image of length and width at a specific viewpoint, a wide 1D line scan camera measures how the width of an ink droplet changes according to a set time period, and using the information obtained from this image, it is possible to make a precise relative comparison of ink droplets ejected from nozzles.

[0047] A 2D area scan camera serves to acquire shape image data of an ink droplet at a specific time. The 2D area scan camera can capture an ink droplet by receiving light through a lens designed for the 2D area scan camera. The 2D area scan camera can acquire ink droplet image data by using one exposure per frame of the camera. Likewise, it is preferable for the 2D area scan camera to use an ultra-high brightness optical strobe at ultra-short pulses of 500 ns or less.

[0048] Shape image data of an ink droplet at a specific viewpoint acquired by a 2D area scan camera is information about a two-dimensional plane of length and width.

[0049] The first control unit (200) performs calibration work such as the degree of brightness, illumination uniformity, magnification, focus, scaling between image pixels and physical length, nozzle position and angle of the inkjet print head (H), etc. of the reference image data acquisition unit (100), collects ink droplet image data of the inkjet print head (H) in normal ejection captured by the reference image data acquisition unit (100), stores the collected ink droplet image data of the inkjet print head (H) in normal ejection as reference ink droplet image data, and provides it to the second control unit (201).

[0050] The second control unit (201) is a microcomputer that controls all components and performs calibration work such as the degree of brightness, illumination uniformity, magnification, focus, scaling between image pixels and physical length of the inspection image data acquisition unit (101), and the nozzle position and angle of the inkjet print head (H). It collects comparison ink droplet ejection image data of the inkjet print head (H) to be inspected, which is captured by the inspection image data acquisition unit (101). If the overall degree of alignment between the reference ink droplet image data provided by the first control unit (200) and the comparison ink droplet ejection image data of the inkjet print head (H) to be inspected is less than a set value, it can prioritize calibration within a set number of times using a calibration tool (a generally used processing tool may be used) to ensure that the comparison ink droplet ejection image data of the inkjet print head (H) to be inspected matches the reference ink droplet image data as much as possible in terms of brightness, size, angle, and position. The second control unit (201) determines whether the ink droplet ejection is normal or abnormal by performing a local comparison operation between the image data within the Region of Interest (ROI) set for each nozzle on the comparison ink droplet ejection image data of the inkjet print head (H) to be inspected and the image data within the Region of Interest (ROI) set for each nozzle on the reference ink droplet image data, if the alignment degree after calibration is greater than or equal to the set value.

[0051] The second control unit (201) uses a matching tool (for example, if MATLAB is used as the matching tool, any one of a feature-based technique, a contrast-based technique, and a non-rigid matching technique may be used, and a method capable of calculating and quantifying the difference between two images and other tools that apply this may be used) to quantify the degree of matching between the stored reference ink droplet image data and the comparison ink droplet ejection image data (comparison ink droplet image data) of the inkjet print head (H) to be inspected, and if the degree of matching value is greater than or equal to a set value, it determines that it is a normal inkjet print head nozzle, while if the degree of matching value is less than the set degree of matching, it determines that it is an abnormal inkjet print head nozzle.

[0052] The display unit (300) serves to display the normal or abnormal result for the inkjet print head nozzle determined by the second control unit (201), and the degree of alignment between the reference ink droplet image data and the comparison ink droplet ejection image data of the inkjet print head to be inspected.

[0053] A method for monitoring the normal ejection of an inkjet ink droplet using an inkjet ink droplet normal ejection monitoring system utilizing image matching according to an embodiment of the present invention configured as above will be described.

[0054] FIG. 2 is a flowchart for explaining a method for monitoring whether an inkjet ink droplet is normally ejected using an image matching diagram according to an embodiment of the present invention, where S means a step.

[0055] First, the first control unit (200) performs a calibration operation of the reference image data acquisition unit (100) (S10). FIG. 3 is a diagram showing a calibration operation in which the uneven background lighting is made as uniform as possible through a calibration operation using the Flat Field Correction (FFC) function when the reference image data acquisition unit (100) or the inspection image data acquisition unit (101) of FIG. 1 is a wide-width 1D line scan camera. The calibration operation may include adjusting the brightness level, magnification, focus, scaling between image pixels and physical length of the reference image data acquisition unit (100) or the inspection image data acquisition unit (101), and the nozzle position and angle of the inkjet print head (H).

[0056] Next, the first control unit (200) collects ink droplet image data of the inkjet print head (H) that is being normally ejected, which is captured by the reference image data acquisition unit (100) (S20), and stores the collected ink droplet image data of the inkjet print head (H) that is being normally ejected as reference ink droplet image data (S30).

[0057] FIG. 4 is a diagram showing that when the reference image data acquisition unit (100) or inspection image data acquisition unit (101) of FIG. 1 is a 1D line scan camera, after the inspection calibration work is performed by the first control unit (200) or the second control unit (201), ink droplet image data is acquired using one exposure per camera frame.

[0058] FIG. 5 is a diagram showing the acquisition of ink droplet image data when the reference image data acquisition unit (100) or inspection image data acquisition unit (101) of FIG. 1 is a 2D area scan camera.

[0059] FIG. 6 is a diagram showing that the first control unit (200) of FIG. 1 collects ink droplet image data of an inkjet print head (H) that is being normally ejected, which is captured by the reference image data acquisition unit (100), and stores it as reference ink droplet image data.

[0060] The second control unit (201) of the system to be inspected can perform a calibration operation of the inspection image data acquisition unit (101) (S11). Next, the second control unit (201) of the system to be inspected collects comparison ink droplet ejection image data of the inkjet print head (H) to be inspected, which is captured by the inspection image data acquisition unit (101) (S21).

[0061] FIG. 7 is a diagram showing that the second control unit (201) of the system to be inspected in FIG. 1 collects ink droplet image data of an inkjet print head (H) captured by an inspection image data acquisition unit (101) and stores it as comparison ink droplet image data (S31).

[0062] FIG. 8 is a comparison diagram of reference ink droplet image data stored by the first control unit (200) of the reference system and comparison ink droplet ejection image data (comparison ink droplet image data) of the inkjet print head (H) to be inspected, which is captured by the image data acquisition unit (101) of the second control unit (201) of the system to be inspected.

[0063] Next, the second control unit (201) of the system to be inspected quantifies the alignment status of the reference ink droplet image data and the ink droplet ejection image data of the inkjet print head (H) to be inspected (S40), and determines whether the quantified alignment value is greater than or equal to a set value (S50).

[0064] In the above step (S50), if the alignment value is less than the set value (N), the second control unit (201) of the system to be inspected may perform a correction operation on the comparison ink droplet ejection image data so that the reference ink droplet image data and the comparison ink droplet ejection image data of the inkjet print head (H) to be inspected match as much as possible (S60). That is, if the brightness, size, angle, and position of the comparison ink droplet image data differ from the reference ink droplet image data due to differences in the system and shooting conditions between the inspection image data acquisition unit (101) that acquired the comparison ink droplet image data of the inkjet print head (H) to be inspected and the reference image data acquisition unit (100) that acquired the reference ink droplet image data, the comparison ink droplet image data of the inkjet print head (H) to be inspected may be corrected within a set number of times using a correction tool to be suitable for the subsequent alignment calculation operation.

[0065] FIG. 9 is an example of a process for correcting the brightness of the comparison ink droplet ejection image data (comparison ink droplet image data) of the inkjet print head (H) to be inspected, stored by the second control unit (201) of the system to be inspected, so that it is as similar as possible to the brightness of the reference ink droplet image data.

[0066] FIG. 10 is a diagram illustrating the process of correcting the size of the comparison ink droplet ejection image data of the inkjet print head (H) to be inspected by the second control unit (201) of the system to be inspected, so that it matches the size of the reference ink droplet image data through image enlargement or reduction. At this time, it is desirable to match not only the size of the image but also the number of horizontal and vertical pixels constituting the image.

[0067] FIG. 11 is a diagram showing the process of horizontally aligning the comparison ink droplet ejection image data of the inkjet print head (H) to be inspected with the reference ink droplet image data through rotation by the second control unit (201) of the system to be inspected.

[0068] FIG. 12 is a diagram showing the process of aligning the comparison ink droplet ejection image data of the inkjet print head (H) to be inspected with the reference ink droplet image data through horizontal or vertical movement by the second control unit (201) of the system to be inspected.

[0069] FIG. 13 is a diagram showing a situation (overlapping situation) in which the degree of alignment between the reference ink droplet image data and the comparison image data is greater than or equal to the set degree of alignment when the reference image acquisition unit (100) or the inspection image acquisition unit (101) is a wide 1D line scan camera.

[0070] FIG. 14 is a diagram showing a situation in which the degree of alignment between the reference ink droplet image data and the comparison image data is less than the set degree of alignment, so they do not overlap well (a situation in which they do not overlap well), when the reference image acquisition unit (100) or the inspection image acquisition unit (101) is a wide 1D line scan camera.

[0071] FIG. 15 is a drawing showing reference ink droplet image data when the reference image acquisition unit (100) or inspection image acquisition unit (101) is a 2D area scan camera, and comparison ink droplet image data after performing position correction work through brightness, size, angle and horizontal / vertical movement, similar to the case of a wide 1D line scan camera.

[0072] FIG. 16 is a diagram showing a situation where the reference ink droplet image data and the comparison image data do not overlap well even after performing a correction operation through brightness, size, angle, and horizontal / vertical movement, when the reference image acquisition unit (100) or the inspection image acquisition unit (101) is a 2D area scan camera.

[0073] Through a calibration operation by the second control unit (201) of the system to be inspected, the reference ink droplet image data and the comparison ink droplet ejection image data of the inkjet print head (H) to be inspected are calibrated within a set number of times. If, even after performing the calibration operation, the degree of alignment between the reference ink droplet image and the comparison ink droplet image is less than the set value, a determination of misalignment is made and subsequent operations are stopped. The cause of the misalignment at this stage may be differences in image acquisition systems, significant differences in shooting conditions, or significant abnormal ejection of ink droplets.

[0074] Meanwhile, in the above step (S50), if the degree of alignment between the reference ink droplet image data and the ink droplet ejection image data of the inkjet print head (H) to be inspected is greater than or equal to a set value (Y), the process proceeds to the above step (S70).

[0075] In step (S70), the second control unit (201) calculates the degree of alignment of ink droplets by nozzle by performing a local comparison operation between the image data within the ROI set for each nozzle on the reference ink droplet image data and the image data within the ROI set for each nozzle on the comparison ink droplet image data of the inkjet print head (H) to be inspected. Instead of comparing the degree of alignment using the entire images of the reference ink droplet image data and the comparison ink droplet image data, by performing a local comparison operation within the ROI set for each nozzle, not only can the image processing time be reduced, but the difference between the ink droplets can also be quantified more accurately. At this time, one ROI is generally set for each nozzle, but multiple ROIs can be set as needed.

[0076] Next, the second control unit (201) of the system to be inspected determines whether the alignment degree calculated in step (S70) is greater than or equal to the set alignment degree (S80). In step (S80), if the alignment degree is greater than or equal to the set alignment degree (Y), the second control unit (201) of the system to be inspected determines that it is a normal inkjet print head nozzle (S1090), while if the alignment degree is less than the set alignment degree (N), the second control unit (201) of the system to be inspected determines that it is an abnormal inkjet print head nozzle (S1200).

[0077] Next, the result of the second control unit (201) of the system to be inspected determining a normal inkjet print head nozzle in step (S90) or determining an abnormal inkjet print head in step (S100), the alignment value, reference droplet image data, and comparison ink droplet image data, etc., are displayed through the display unit (301) of the system to be inspected (S110).

[0078] Meanwhile, in carrying out the present invention, the calibration step (S10 and S11) for the reference image acquisition unit (100) and the inspection image acquisition unit (101), the step of quantifying the overall alignment degree of the comparison ink droplet image data of the inkjet print head (H) to be inspected with the reference ink droplet image data (S40), the step of comparing the alignment degree with a set value (S50), and the calibration step (S60) for the comparison ink droplet image data of the inkjet print head (H) to be inspected may be omitted if not necessary.

[0079] Figure 17 is a diagram illustrating a case where the degree of alignment between reference ink droplet image data and comparison image data is 99.5%.

[0080] Figure 18 is a diagram illustrating a case where the degree of alignment between reference ink droplet image data and comparison image data is 82%.

[0081] FIG. 19 is a diagram illustrating the numerical matching degree of reference and comparison ink droplet image data for each corresponding ROI after setting the Region Of Interest (ROI) for each nozzle of an inkjet print head (H).

[0082] Here, since image processing is performed to conduct a local comparison within the ROI set for each nozzle rather than performing a matching inspection on the entire reference ink droplet image and the comparison ink droplet image, the time required to calculate the matching value can be reduced. Additionally, when a matching inspection is performed on the entire reference ink droplet image and the comparison ink droplet image, the margins occupying a significant portion of the image are judged to have high matching, so the final matching value may be high even if the shapes of the reference ink droplet image and the comparison ink droplet image are different. On the other hand, when a local comparison is performed within the ROI set for each nozzle, the influence of margins on the matching value can be minimized, thereby increasing the accuracy of reading normal and abnormal nozzles. In this case, one ROI is generally set per nozzle, but as shown in FIG. 20, multiple ROIs can be set as needed, and one or more ink droplets may be included within a single ROI. When there are multiple ROIs per nozzle, the matching value of the ink droplet may be the average of the matching values ​​of each ROI for each nozzle.

[0083] If the alignment is, for example, less than 82%, it may be read as an abnormal nozzle.

[0084] According to the system and method for monitoring whether an inkjet ink droplet is being ejected normally using image alignment according to an embodiment of the present invention, a calibration operation is performed on a reference image data acquisition unit, ink droplet image data of an inkjet print head being ejected normally captured by the reference image data acquisition unit is collected, the collected ink droplet image data of the inkjet print head being ejected normally is stored as reference ink droplet image data, comparison ink droplet image data of an inkjet print head to be inspected is collected by an inspection image data acquisition unit, the overall alignment value of the reference ink droplet image data and the comparison ink droplet image data of the inkjet print head to be inspected is checked, and if it is less than a set value, a calibration tool is used to perform a calibration operation on the brightness, size, angle, and up / down / left / right position of the comparison ink droplet image data within a set number of times to match the brightness, size, angle, and up / down / left / right position of the reference ink droplet image data, and the overall alignment value of the reference ink droplet image data and the comparison ink droplet image data of the inkjet print head to be inspected is set If the alignment degree is greater than the set alignment degree, a local comparison operation is performed using the alignment degree values ​​of ink droplets within the ROI set for each nozzle to determine whether the ink droplet ejection is normal or abnormal; and if the alignment degree of the reference ink droplet image and the comparison ink droplet image data within the ROI set for each nozzle is less than the set alignment degree, it is determined to be an abnormal inkjet print head nozzle, thereby enabling rapid determination of whether the inkjet print head nozzle is defective without using complex image processing.

[0085] Optimal embodiments have been disclosed in the drawings and specification, and specific terms have been used, but these are used only for the purpose of describing embodiments of the invention and are not intended to limit the meaning or the scope of the invention as described in the claims. Therefore, those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the true technical scope of protection of the invention should be determined by the technical spirit of the appended claims.

[0086] [Explanation of the symbol]

[0087] H: Inkjet print head

[0088] L: Light strobe composed of LED or LEP

[0089] 100: Reference image data acquisition unit

[0090] 101: Inspection image data acquisition unit

[0091] 200: First control unit

[0092] 201: Second control unit

[0093] 300: Display unit

[0094] The present invention is applicable to the field of monitoring the normal ejection of inkjet ink droplets, which can rapidly determine whether an inkjet print head nozzle is defective by utilizing image matching without using complex image processing such as contour extraction for calculating the volume of the ink droplet.

Claims

1. One or more optical strobes (L) configured to irradiate light onto ink droplets falling from an inkjet print head (H) installed in a reference system for acquiring reference image data and a system to be inspected; A reference image data acquisition unit (100) configured to acquire ink droplet image data by photographing an ink droplet of an inkjet print head that is normally ejected at a set period and positioned opposite the above-mentioned optical strobe; An inspection image data acquisition unit (101) configured to be positioned opposite the light strobe and configured to photograph an ink droplet ejected from an inkjet print head to be inspected at a set period to acquire comparison ink droplet ejection image data; A first control unit (200) configured to perform a calibration operation of the reference image data acquisition unit and to store the ink droplet image data of the inkjet print head currently being ejected normally, acquired by the reference image data acquisition unit, as reference ink droplet image data; A calibration operation is performed on the above-mentioned inspection image data acquisition unit, and comparison ink droplet ejection image data of the inkjet print head to be inspected, acquired by the above-mentioned inspection image data acquisition unit, is collected and stored. If the overall alignment value between the reference ink droplet image data and the comparison ink droplet ejection image data of the inkjet print head to be inspected is less than a set value, the brightness, size, angle, and up / down / left / right position of the comparison ink droplet ejection image data of the inkjet print head to be inspected are corrected using a calibration tool to increase the alignment value between the comparison ink droplet ejection image data of the inkjet print head to be inspected and the reference ink droplet image data. If the alignment value is greater than or equal to the set value after a calibration operation within a set number of times, a local comparison operation is performed between the comparison ink droplet ejection image data of the inkjet print head to be inspected and the image data within the set ROI (Region Of Interest) for each nozzle on the reference ink droplet image data to determine whether the ink droplet ejection is normal or abnormal. At this time, if the alignment value is greater than or equal to the set alignment value, it is determined to be a normal inkjet print head nozzle, and the above A monitoring system for normal inkjet ink droplet ejection using image alignment, comprising: a second control unit (201) configured to determine an abnormal inkjet print head nozzle if the alignment is less than the set alignment.

2. In Paragraph 1, The above reference image data acquisition unit (100) and inspection image data acquisition unit (101) It is a wide 1D line scan camera, and An inkjet ink droplet normal ejection monitoring system using image matching, which acquires ink droplet image data using one exposure per frame of a camera.

3. In Paragraph 1, The above reference image data acquisition unit (100) and inspection image data acquisition unit (101) It is a 2D area scan camera, and An inkjet ink droplet normal ejection monitoring system using image matching, which acquires ink droplet image data using one exposure per frame of a camera.

4. In Paragraph 1, The above reference image data acquisition unit (100) and inspection image data acquisition unit (101) It is a 2D area scan camera, and An inkjet ink droplet normal ejection monitoring system using image matching, which acquires ink droplet image data using multiple exposures per frame of a camera.

5. In Paragraph 1, A monitoring system for normal ink droplet discharge using image alignment, further comprising a display unit (300) configured to display the normal or abnormal result for an inkjet print head nozzle determined by the second control unit (201), and the degree of alignment between the reference ink droplet image data and the comparison ink droplet discharge image data of the inkjet print head to be inspected.

6. In Paragraph 1, The above second control unit (201) is A monitoring system for normal inkjet ink droplet ejection using image alignment, further configured such that when the overall alignment value between the reference ink droplet image data and the ink droplet ejection image data of the inkjet print head to be inspected is less than a set value, the second control unit (201) performs a correction operation within a set number of times using a correction tool to match the reference ink droplet image data and the comparison ink droplet ejection image data of the inkjet print head to be inspected as closely as possible in brightness, size, angle, and position, and calculates the alignment value between the reference ink droplet image data and the ink droplet ejection image data of the inkjet print head to be inspected.

7. In Paragraph 6, The above alignment is quantified by an alignment tool, and The above-mentioned alignment tool is an inkjet ink droplet normal ejection monitoring system using image alignment, which uses any one of feature-based techniques, brightness-based techniques, and non-rigid alignment techniques.

8. A method for monitoring the normal ejection of an inkjet ink droplet using an inkjet ink droplet normal ejection monitoring system using image alignment, A first control unit (200) of a reference system for acquiring reference image data performs a calibration operation of a reference image data acquisition unit (100); The first control unit collects ink droplet image data of an inkjet print head (H) in normal ejection captured by the reference image data acquisition unit, and stores the collected ink droplet image data of the inkjet print head in normal ejection as reference ink droplet image data; A step in which the second control unit of the system to be inspected performs a calibration operation of the inspection image data acquisition unit; The second control unit collects comparison ink droplet image data of an inkjet print head to be inspected, captured by an inspection image data acquisition unit, and stores the collected ink droplet image data of the inkjet print head being ejected as comparison ink droplet image data; The second control unit quantifies the overall alignment status of the reference ink droplet image data and the comparison ink droplet image data of the inkjet print head to be inspected, and determines whether the quantified alignment value is greater than or equal to a set value; In the step of determining whether the above-mentioned setting value is greater than or equal to the above-mentioned value, if the above-mentioned alignment value is less than the above-mentioned value, the second control unit improves the alignment between the above-mentioned comparison ink droplet ejection image data of the inkjet print head to be inspected and the above-mentioned reference ink droplet image data by correcting the brightness, size, angle, and up / down / left / right position of the comparison ink droplet ejection image data of the inkjet print head to be inspected using a correction tool; In the step of determining whether the above-mentioned set value is greater than or equal to the set value, if the above-mentioned alignment value is greater than or equal to the set value, the second control unit performs a step of performing a local comparison of image data within a Region of Interest (ROI) set for each nozzle on the reference ink droplet image data and the comparison ink droplet ejection image data of the inkjet print head to be inspected; A step in which, in the step of performing the local comparison operation above, if the alignment degree is greater than or equal to the set alignment degree, the second control unit determines it to be a normal inkjet print head nozzle, while if the alignment degree is less than the set alignment degree, the second control unit determines it to be an abnormal inkjet print head nozzle; and A method for monitoring whether an inkjet ink droplet is normally ejected, comprising the step of displaying the result determined in the above determination step and the degree of alignment through a display unit (300).

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