JP2013059877A - Method for detecting discharge defects of inkjet nozzle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for detecting discharge defects of inkjet nozzle for detecting defects such as clogging of the nozzle and defects of ink splashing of an inkjet recording device, and position gap of an ink dot, etc, by inspecting a discharge state based on a test pattern recorded on a predetermined inspection sheet.SOLUTION: In the method, whether ink discharge is normal or abnormal is detected by reading a test pattern of the ink dot recorded on the inspection sheet by an inkjet recording head. The method for detecting discharge defect of inkjet nozzle includes a process for previously reading an image data (A) of the inspection sheet at a position which a test pattern is recorded on, a process for inkjet-recording the test pattern on the pre-read position of inspection sheet, a process for reading an image data (B) of the inspection sheet which the test pattern has been recorded on, a process for obtaining an image data (C) by subtracting the image data (A) from the image data (B), which has been read, and a process for analyzing the image data (C), which has been obtained.

Description

  The present invention relates to an inkjet nozzle that detects defects such as nozzle clogging, ink skipping, and ink dot misalignment by inspecting the ejection state based on a test pattern recorded on a predetermined inspection sheet. The present invention relates to a discharge failure detection method.

  In an inkjet recording apparatus, it is possible to form an image by ejecting minute ink droplets from a nozzle of a recording head toward a recording medium such as paper and attaching the ink droplets to the recording medium. When an image is formed with such an ink jet recording apparatus, a good image may not be output due to clogging of ink in the nozzles of the recording head. For this reason, it is necessary to periodically check the ink discharge state of the nozzles of the recording head and recover the ink discharge state when there is a defect.

  For example, in Patent Document 1, a predetermined pattern is recorded on a recording material dedicated to a monitor by a recording head, and the recorded pattern is read by a sensor. The point that an abnormality such as non-ejection of the recording head is determined is described. Further, in Patent Document 2, a test pattern is printed on a test recording medium by a print head, a group of ink dot columns in the pattern is imaged by sensor means, and the average area and edge position of ink dots are obtained by image processing. In addition, it is described that the normal interval and the abnormal state of the ink discharge are determined by obtaining the center interval.

JP-A-5-301426 JP 2000-94655 A

  However, in the methods of Patent Document 1 and Patent Document 2, an inspection sheet such as paper is required for each test pattern recording, and if dust or the like is attached to the inspection sheet, the sensor also detects the dust. In some cases, reading may occur and accurate inspection may not be possible. Although this problem can be solved to some extent by using an expensive inspection sheet with less dust and impurities, the dust may adhere to the inspection sheet after opening. Since this is performed regularly and relatively frequently, a large amount of inspection sheet is consumed, so that the use of an expensive inspection sheet is costly, and some other solution is required.

  The present invention has been made to solve the above-described problems, and by inspecting the discharge state based on a test pattern recorded on a predetermined inspection sheet, nozzle clogging and ink in an ink jet recording apparatus are performed. An object of the present invention is to provide a method for detecting an ejection failure of an inkjet nozzle that detects a defect such as a skipping defect or a misalignment of ink dots.

  That is, the ejection failure detection method for an inkjet nozzle according to the present invention is a method for detecting normal or abnormal ink ejection by reading a test pattern of ink dots recorded on an inspection sheet by an inkjet recording head. A step of reading the image data (A) of the inspection sheet at the position to be scanned, a step of inkjet recording the test pattern at the position of the read inspection sheet, and a step of reading the image data (B) of the inspection sheet on which the test pattern is recorded. The image data (A) is subtracted from the read image data (B) to obtain the image data (C), and the obtained image data (C) is analyzed. Is.

In the step of analyzing the image data (C), it is preferable to measure the area of the ink dots, the length in the X direction, and the length in the Y direction.
Further, it is preferable that the image data (A) and the image data (B) are read by a CCD image sensor.

  By having the above-described configuration, it is possible to detect problems such as nozzle clogging, ink skipping, and ink dot misalignment in an ink jet recording apparatus.

It is a schematic block diagram of the inkjet recording device of this invention. It is a processing flow for inspecting the recording state of the recording head. It is a figure which shows an example of the read test | inspection sheet. It is a figure which shows an example of the read test | inspection sheet. It is a figure which shows the image data obtained by making a difference. It is a figure which shows the detection method of the shape of an ink dot. It is a figure which shows the calculation method of the area of an ink dot. It is a figure which shows the determination method of the position shift of the X direction of an ink dot. It is a figure which shows the determination method of the position shift of the Y direction of an ink dot.

  Embodiments of the present invention will be described below. The embodiments described below are preferable specific examples for carrying out the present invention, and thus various technical limitations are made. However, the present invention particularly limits the present invention in the following description. Unless explicitly stated, the present invention is not limited to these forms.

  FIG. 1 is a schematic configuration diagram of an ink jet recording apparatus. The inkjet recording head 1 is mounted and fixed on a carriage 2, and the carriage 2 is fixed to an endless drive belt 3. The driving belt 3 is stretched between the driving pulley 4 and the driven pulley 5, and the conveying belt 3 is moved by the rotational driving of the driving pulley 4, so that the carriage 2 reciprocates in the main scanning direction X. Further, an inspection mechanism 20 for inspecting the ink discharge state of the nozzles of the recording head is disposed outside the recording range in the main scanning direction. In FIG. 1, a serial type ink jet recording apparatus is described as an example. However, the present invention is not particularly limited to a serial type, and may be a line type ink jet recording apparatus.

  The sheet-like recording medium 6 is fed from the feed roll 7 and recorded so as to be wound around the take-up roll 8, and the recording medium 6 is transported by the transport roll 9 so as to face the ink jet recording head 1. A path is set and conveyed in the sub-scanning direction Y.

  The surface of the ink jet recording head 1 facing the recording medium 6 is a nozzle surface on which a plurality of nozzles for ejecting ink are formed. Ink is supplied into the head from an ink supply device (not shown) and connected to the nozzles. The ink is introduced into the ink flow path, and pressure fluctuation is applied to the ink by pressure fluctuation means such as a piezoelectric element disposed in the ink flow path, so that the ink is ejected from the nozzle. As such an ink jet recording head, a known one can be used.

  When a recording operation is performed on the recording medium 6, the inkjet recording head is driven and controlled based on the recording signal while moving the inkjet recording head in the main scanning direction, and ink is ejected along the scanning line to perform line recording. When the scanning line recording is completed, the recording medium is transported in the sub-scanning direction, and transport control is performed so that the next scanning line faces the ink jet recording head. In this way, image recording is performed on the surface of the recording medium 6 by alternately repeating recording control in the main scanning direction and conveyance control in the sub-scanning direction.

  The drive pulley 4 and the driven pulley 5 that stretch the drive belt 3 are attached to a frame (not shown) and mounted and fixed on the upper surface of the base 10 via the frame, and both ends of the base 10 are paired with each other. It is supported by the support frame 11. A rail portion (not shown) is formed on the upper surface of the support frame 11 toward the recording medium 6 on the joint surface between the base 10 and the support frame 11, and the lower surface of the base 10 is fitted to the rail portion. A matching notch is formed. Therefore, the base 10 is movably attached so as to move forward and backward with respect to the recording medium 6. A spacing adjustment screw 12 is threadedly engaged with the attachment portion 13 and passes through the upper portion of the support frame 11, and a distal end portion of the spacing adjustment screw 12 is rotatably fixed to the attachment hole of the base 10. Therefore, the base 10 moves forward and backward with respect to the recording medium 6 by rotating the interval adjusting screw 12, and the interval between the recording medium 6 and the nozzle surface of the inkjet recording head 1 can be adjusted. In addition, when moving the base 10 and adjusting a space | interval, you may use the means to electrically control movement, such as a motor.

  The inspection mechanism 20 is fixedly attached to an apparatus frame (not shown), and the ink jet recording head 1 is moved to a position facing the inspection mechanism 20 during a recording operation or at the start of recording to inspect the ink ejection state. When the ink ejection abnormality is determined by the inspection mechanism 20, the suction recovery operation is performed by capping the nozzle surface by moving to a discharge recovery mechanism (not shown).

  The inspection mechanism 20 includes a strip-shaped inspection sheet 21 that receives ink ejected from the nozzles of the ink jet recording head, and the inspection sheet 21 is fed from a feed roll 22 and is recorded with a predetermined pattern for inspection. The conveyance path of the inspection sheet 21 is set so as to face the inkjet recording head 1 by the conveyance roll 24 and is conveyed in the sub-scanning direction Y. The material of the inspection sheet 21 is described by taking paper as an example in this specific example. However, other than paper, a fabric, a plastic film, or the like may be used, or the same material as that of the recording medium 6 may be used. It is not particularly limited. Further, the shape of the inspection sheet 21 is not particularly limited, and may be not only a roll shape but also a plate shape.

  The predetermined pattern recorded on the inspection sheet 21 is conveyed to a position facing the image sensor 25. The image sensor 25 detects the origin, and then captures an image in units of groups consisting of rows of ink dots in a predetermined pattern recorded by scanning in the X and Z directions. As the image sensor 25, a CCD image sensor or the like is used, and a scanning unit of the image sensor 25 is not shown in the figure, but is a drive mechanism including a pulse motor and a ball screw that are usually used. Then, the presence or absence of ink ejection abnormality is determined from the captured image.

  A pressing member 26 is disposed as a positioning means on the side opposite to the ink jet recording head 1 at a position facing the ink jet recording head 1 of the inspection sheet 21, and the contact surface of the pressing member 26 with the inspection sheet 21. Is formed so as to be flat and substantially parallel to the nozzle surface of the inkjet recording head 1.

  The pushing member 26 is fixedly attached to the upper end portion of the arm member 27, and an air cylinder is attached to the lower end portion of the arm member 27 as driving means. The air cylinder is attached and fixed to the base 10, and the pushing member 26 moves in conjunction with the inkjet recording head 1. By driving and controlling the air cylinder, the arm member 27 is moved to move the pushing member 26 forward and backward with respect to the ink jet recording head 1.

  FIG. 2 is a processing flow for inspecting the recording state of the ink jet recording head. First, it is checked whether an inspection record signal is input during the recording operation or at the start of recording (S100). When the inspection record signal is input, the image sensor 25 reads the inspection sheet 21 (image data A). (S101). FIG. 3A shows a case where the dust 100 is attached to the read inspection sheet 21. FIG. 3B shows the acquired image data, and the dust 100 is attached. There is a reaction at the position.

  Next, the test pattern data is read (S102), the recording head 1 is moved to the inspection position (the recording head position indicated by the broken line in FIG. 1) facing the inspection mechanism 20 (S103), and positioned. In step S101, the portion of the inspection sheet that has been read is fed to the inspection position (S104) and positioned, and a test pattern is recorded (S105).

  Next, when the test pattern recording is completed, the recording head 1 is moved to the retracted position (S106), the inspection sheet 21 is conveyed, and the test pattern recording portion is moved to a position facing the image sensor 25 (S107). The test pattern recorded by the image sensor 25 is read (image data B) (S108). FIG. 4A shows the read test pattern. In this example, one dust 100, one abnormal ink dot 210, and four normal ink dots 200 are shown. FIG. 4B shows the acquired image data, and two of the five peaks are larger than the others.

  Next, the image data C read in S101 is differentiated from the image data B read in S108 to create image data C (S109). Then, the created image data C is analyzed (S110). That is, the difference between the image data A before the binarization process and the image data B before the binarization process is obtained to obtain the image data C, the binarization process is performed on the image data C, and the data Analyze. FIG. 5A shows image data C obtained by subtracting image data A from image data B, and dust 100 is removed. FIG. 5B shows the image data, and the peak of the position where the ink dot abnormality is recognized is larger than the other peaks. Since the difference is made, the unevenness of the graph is reversed. By performing the process of S109, the abnormality due to the adhering of dust or the like is eliminated, so that it is possible to extract the case where the ink dot is truly abnormal. When analyzing image data, image processing is performed to calculate an RGB value for each pixel, and a threshold value for binarization processing of a captured image is determined based on the calculated RGB value. Then, the captured image is binarized based on the threshold value, and the items such as the area S of the recording pattern of each nozzle subjected to the binarization process, the length Lx in the X direction, and the length Ly in the Y direction are measured.

  Next, the measured value of each item is compared with a preset reference value to determine whether or not there is a discharge abnormality (S111). For example, when the measured value is out of the allowable range of the reference value, it is determined that a nozzle ejection abnormality has occurred. If it is within the allowable range, the recording operation is continued as it is (S112), and if it is determined to be abnormal, the ink jet recording head is moved to a position facing the ejection recovery mechanism (S113), and the nozzle of the ink jet recording head Capping is performed so as to cover the surface, and a recovery operation such as cleaning of the nozzle surface and suction of the nozzle is performed (S114). After completion of the recovery operation, the process returns to step S101, and the recording state is inspected again.

  Whether the test pattern recorded on the inspection sheet 21 is correct / incorrect can be determined by the following method described in Patent Document 2.

[Understanding the shape of ink dots]
As shown in FIG. 6, reading is performed while scanning the image sensor 25 in the X direction at intervals of δ μm, and the shape of each ink dot 200 is grasped by the binarization processing of the image. Although an image processing means is not shown, a known device is connected to the image sensor 25 with a cable and performs processing based on an output signal. The shape of each ink dot 200 can be grasped by such a method.

[Calculation of ink dot area and average area]
After grasping the shape of the ink dot 200, each area Si (i = 1, 2,... N) and its average area Save are obtained. First, the area Si of the ink dot 200 is obtained as follows. The size of the ink dot 200 is about 80 to 100 μm, and sampling is performed at intervals of δ as shown in FIG. 7, and the dot widths W0, W1, W2,. That is, Si = W0 + W1 + W2 + ... + Wn. Since the sampling interval δ is minute, the above equation is integrated. Next, the average area Save of the ink dots 200 is obtained by dividing the total sum of Si by the number of ink dots 200 existing in one group. That is,
Save = ΣSi / N
N is the number of ink dots 200.

[Set judgment value, judgment]
In order to set an allowable range for determination, α% of the average area Save determined above is set as a determination value SA. Therefore, the judgment value SA is
SA = Save * [alpha] / 100. α is about 80%.
The area Si of the individual ink dots 200 determined above is compared with the determination value SA. As a result, if there is a set number of ink dots 200 equal to or greater than the determination value SA, OK (normal ink discharge) is determined, and if even one dot does not satisfy the determination value SA, it is determined NG (ink discharge abnormality). Thereby, the non-ejection of the ink dots 200 existing in the group or a state close thereto, that is, clogging of the nozzles can be detected by relative comparison. In addition, this makes it possible to identify the nozzle that has been clogged, and to inform the operator who is working on which nozzle has the problem.

[Presence or absence of misalignment of ink dots in X direction]
Whether or not the ink dots 200 are displaced in the X direction will be described with reference to FIG.
The position of one end edge (for example, the start end position) can be found from the shape of each ink dot 200 obtained above. That is, when the shape of the ink dot 200 is grasped as described above, the start end position of the ink dot 200 can be determined by storing the position where the dot width of λ μm or more appears first. Note that the value of λ may be set as appropriate in consideration of the dot width of the ink dots 200. Next, the start end position is searched for each ink dot 200, and the difference ΔX between the maximum value and the minimum value is obtained.
Then, the difference ΔX is compared with the set determination value β, and if ΔX is less than β, it is determined OK (no misalignment), and if not, NG (position misalignment) is determined. Accordingly, it is possible to detect the presence or absence of positional deviation in the X direction of the ink dots 200 existing in the group by relative comparison.

[Presence / absence of misalignment of ink dots in the Y direction]
Whether or not the ink dots 200 are misaligned in the Y direction will be described with reference to FIG.
The position of the edge in the Y direction can be found from the shape of each ink dot 200 determined above. That is, when grasping the shape of the ink dot 200 as described above, the upper and lower end positions of the ink dot 200 can be determined by storing the position where the dot width of λ μm or more appears first. Then, the upper and lower end positions of each ink dot 200 are searched, and the center of gravity (center) position can be calculated by obtaining half of the sum of the Y coordinate values of the upper and lower ends. Thus, the center distance d between two adjacent ink dots is obtained. Among them, the difference ΔY between the maximum value dmax and the minimum value dmin is obtained.
Then, the difference ΔY is compared with the set determination value γ, and if ΔY is less than γ, it is determined OK (no misalignment), and if not, NG (position misalignment) is determined. As a result, the positional deviation in the Y direction of the ink dots 200 existing in the group, that is, the width of the center interval can be detected by relative comparison.

DESCRIPTION OF SYMBOLS 1 Inkjet recording head 2 Carriage 6 Recording medium 20 Inspection mechanism 21 Inspection sheet 22 Delivery roll 23 Winding roll 25 Image sensor 100 Garbage 200 Ink dot 210 Abnormal ink dot

Claims (3)

In a method of detecting normal or abnormal ink discharge by reading a test pattern of ink dots recorded on an inspection sheet by an inkjet recording head,
Reading image data (A) of an inspection sheet at a position where a test pattern is recorded in advance;
A step of inkjet recording a test pattern at the position of the read inspection sheet;
Reading image data (B) of an inspection sheet on which a test pattern is recorded;
Obtaining image data (C) by subtracting the image data (A) from the read image data (B);
And a step of analyzing the obtained image data (C). An ejection failure detection method for an inkjet nozzle, comprising:   The method of detecting an ejection failure of an inkjet nozzle according to claim 1, wherein in the step of analyzing the image data (C), the area of the ink dot, the length in the X direction, and the length in the Y direction are measured. .   3. The method for detecting an ejection failure of an inkjet nozzle according to claim 1, wherein the image data (A) and the image data (B) are read by a CCD image sensor.