JP2012106379A - Method and device for inspecting inkjet recording head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and device for inspecting an inkjet recording head that set a proper driving condition to an individual substrate without increasing man hour and process load.SOLUTION: A correction value when a limited pulse is estimated is updated with each recording inspection process of an individual recording head. A limited pulse width is thereby determined from a record of a limited number of test patterns and an image processing, and the process load and expended hours relating to an inspection process are reduced more than ever before.

Description

  The present invention relates to an ink jet recording head that ejects ink droplets from ejection openings using thermal energy, and forms an inspection image on a recording material such as recording paper, and an ink jet that evaluates the characteristics of the head from the inspection image. The present invention relates to a recording head inspection method and apparatus.

  In general, an inkjet recording head (hereinafter simply referred to as a recording head) that includes an electrothermal conversion element and ejects ink using thermal energy is manufactured by a process similar to that of a semiconductor. In other words, the ink jet recording head has a wiring board forming process for forming electrothermal conversion elements and wiring on a substrate, a nozzle forming process for forming an ink flow path on the wiring board, mounting of driving elements on the board and other components. It is manufactured through an assembly process for assembling. Further, a recording inspection process is performed on the completed recording head in order to confirm the recording quality and ejection performance of the recording head and to set parameters specific to each recording head.

  In general, in such a recording inspection process, first, a predetermined pattern is recorded while stepwise changing the voltage or pulse width when driving the ink jet recording head. Next, the recording state of each recording element is observed from the recorded image, and the limit value of the drive voltage or pulse width that can be discharged is measured. Then, a margin value obtained by a separate experiment is added to the measured limit value, and the value (voltage or pulse width) obtained in this way is set as the optimum driving condition for the ink jet recording head.

  It is known that the optimum driving conditions, that is, the optimum driving voltage and pulse width, are influenced by various variations between recording heads (strictly, between substrates), and there are individual differences between substrates. Therefore, in the inspection process as described above, a plurality of patterns are recorded while gradually changing the driving conditions in a range that can be a limit value for deriving the optimum driving conditions, that is, a range of variations in the substrate after manufacture. It is necessary to confirm the recording state for each driving condition. However, since the range of driving conditions that can be the limit value is sufficiently wide, the number of patterns to be recorded has increased in the past, and much man-hours and time have been spent for the inspection process.

  However, although there are certainly individual differences for each substrate regarding the optimum driving conditions and limit values, the resistance value of the electrothermal conversion element provided on the substrate and the thickness of the protective film for protecting the substrate are mainly used. It is known that the influence by is large. Therefore, it is possible to preliminarily measure the resistance value of the electrothermal conversion element for each substrate, and to estimate a suitable driving condition to some extent from the obtained resistance value. Patent Document 1 discloses a method of measuring the film pressure of the protective film together with the resistance value of the electrothermal transducer in the recording inspection process of the recording head, and setting an optimum driving condition based on these two types of values. Is disclosed.

Japanese Patent Laid-Open No. 06-320729

  However, when the resistance value of the electrothermal transducer is measured for each substrate and the appropriate drive condition is estimated from only the resistance value, the protection is between the estimated optimum drive condition and the actually optimum drive condition. There was a case where a shift due to the variation of the film occurred. In such a case, in actual use, the recording head cannot be used under optimum driving conditions.

  Moreover, when measuring the film pressure of the protective film of the substrate together with the resistance value of the electrothermal conversion element as in Patent Document 1, a man-hour and a measurement mechanism for measuring the film pressure are necessary, and the process load increases rather. Will be.

  The present invention has been made to solve the above problems. Therefore, an object of the present invention is to provide an ink jet recording head inspection method and inspection apparatus capable of setting appropriate driving conditions for individual substrates without increasing the man-hours and the process load.

  Therefore, the present invention is an inspection method for an ink jet recording head that ejects ink by applying a voltage pulse to an electrothermal transducer that generates thermal energy, and measuring the resistance value of the electrothermal transducer And a voltage pulse necessary for generating the minimum energy from which the ink jet recording head can eject ink from the electrothermal transducer based on the resistance value obtained in the measuring step and the measuring step. A prediction step of predicting a limit pulse width corresponding to a pulse width; and a recording step of recording a test pattern for each of a plurality of pulse widths obtained by increasing or decreasing the pulse width stepwise from the limit pulse width predicted in the prediction step; A determination step of reading an image of the test pattern and determining the limit pulse width, and a determination step before the determination step A limit pulse; a step of obtaining a difference between the limit pulses predicted in the prediction step; and a step of setting a correction value for predicting the limit pulse in the prediction step based on the difference. And

  An inspection apparatus for an ink jet recording head that discharges ink by applying a voltage pulse to an electrothermal conversion element that generates thermal energy, the measuring unit measuring the resistance value of the electrothermal conversion element, Corresponding to the pulse width of the voltage pulse necessary for generating the minimum energy that the ink jet recording head can eject ink from the electrothermal transducer based on the resistance value obtained by the measuring means Predicting means for predicting a limit pulse width to be recorded, recording means for recording a test pattern for each of a plurality of pulse widths obtained by gradually increasing or decreasing the pulse width from the limit pulse width predicted by the predicting means, and the test pattern Determination means for reading the image of the image and determining the limit pulse width; and the limit pulse determined by the determination means; Means for calculating a difference between said limit pulse predicted by said predicting means, on the basis of the difference, characterized in that it comprises means for setting a correction value for predicting limited pulses in said predicting means.

  According to the present invention, the correction value at the time of predicting the limit pulse is updated at each recording inspection process of each recording head. Thereby, it becomes possible to determine the limit pulse width from the recording and image processing of a limited number of test patterns, and the process load and consumption time related to the inspection process can be suppressed as compared with the conventional case.

It is a figure which shows the structure of the inspection apparatus of an inkjet recording head. It is a flowchart for demonstrating the recording test process of an inkjet recording head. It is a figure which shows a 1st test pattern. It is a figure which shows a 2nd test pattern. FIG. 10 is a diagram illustrating an example of a second test pattern according to the second embodiment. FIG. 10 is a diagram illustrating an example of a second test pattern according to the second embodiment.

[Example 1]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration of an inspection apparatus when performing a recording inspection process for an inkjet recording head before shipment. In FIG. 1, reference numeral 101 denotes a control computer. A VGA board 103 for display output is built in the control computer 101 and controls image display on the monitor 102. Further, the head driver 104, the image processing board 105, the motor control board 106, and the arithmetic processing unit 107 are also built in the control computer 101 so that the control computer 101 performs each process of the recording scanning process to be described later. It has become. Here, the head driver 104 is a circuit for outputting a signal for driving the inkjet recording head 110. The image processing unit 105 is a circuit for processing image data read by the CCD camera 115. The motor control board 106 is a circuit for moving the paper stage 117 in order to move the recording material 118 on which recording is performed by the recording head 110 relative to the recording head 110. Further, the arithmetic processing unit 107 is a circuit for executing high-speed arithmetic processing on the image data obtained from the image processing unit 105.

  The recording signal output from the head driver 104 is converted into a driving signal for ejecting ink from the inkjet recording head 110 in the recording signal conversion substrate 108 connected thereto. Such a drive signal is transmitted to the ink jet recording head 110 through a contact probe unit (not shown) installed on the carriage 109 for mounting the ink jet recording head 110. In response to the drive signal, a predetermined voltage pulse is applied to the electrothermal conversion elements provided in the individual recording elements of the inkjet recording head 110, and thermal energy is generated in the individual recording elements. 111 is discharged. The ejected ink droplets 111 land on the recording material 118, and dots are formed on the recording material 118.

  The recording material 118 is laid on the paper stage 117 and is attracted to the paper stage 117 by vacuum or the like. Thereby, the position of the recording material 118 on the paper stage 117 is fixed, and the distance from the ejection port surface of the recording head 110 is also kept constant. On the other hand, the paper stage 117 is provided with an encoder for acquiring stage position information. The stage controller 116 moves the paper stage 117 based on information obtained from the encoder in accordance with instructions from the motor control board 106, and controls the position of the recording material 118 relative to the recording head 110 and the CCD camera 115. Note that the recording material 118 used here is an inkjet-dedicated paper whose surface is coated with a discharge material, and the landed ink droplets 111 are absorbed almost uniformly and are circular dots that are relatively well-balanced. Is to be formed.

  The surface of the recording material 118 that can be photographed within the angle of view of the CCD camera 115 is irradiated with light by an illumination 114 connected to a power source 113. The illumination 114 in this embodiment is an LED illumination that can ensure durability and light quantity stability, and irradiates light having wavelengths of RGB. The CCD camera 115 used in the present embodiment is a line sensor type CCD camera, and an image of a predetermined area on the recording material 118 is acquired by photographing a plurality of times while moving the paper stage 117. It has become. However, if the processing capability of the image processing unit 105 is sufficiently high and high-speed processing is possible, an area sensor type CCD camera can be used. In the configuration as described above, the image processing controller 112 irradiates the test pattern recorded on the recording material 118 while controlling the amounts of light of RGB, and the image processing unit converts the image data photographed by the CCD camera 115. It transmits to 105.

  FIG. 2 is a flowchart for explaining the recording inspection process of the ink jet recording head in this embodiment. When this process is started, the control computer 101 first performs a contact check between the recording head 110 and the carriage 109 provided in the recording inspection apparatus in step S401 to confirm the electrical connection between them. .

  Next, in step S402, resistance measurement of the electrothermal transducer provided in the recording head is performed. The resistance may be measured by actually measuring the resistance value of the electrothermal conversion element used for ink ejection, but the pseudo electrothermal conversion element manufactured by the same manufacturing method as the electrothermal conversion element used for ejection It is possible to replace it with resistance measurement.

  In the subsequent step S403, the pulse width of the drive pulse used when recording the test pattern is set based on the resistance value measured in step S402. For this purpose, the control computer 101 first calculates a pulse width (hereinafter referred to as a limit pulse width) necessary to generate the minimum energy that is considered necessary for ejection of the recording head from the obtained resistance value. . Then, a value obtained by adding a predetermined margin to the limit pulse width is temporarily set as an appropriate pulse width of the recording head. In this example, it is assumed that the predicted limit pulse width is 0.90 μsec.

  In this embodiment, in order to avoid tact loss, the voltage value of the voltage pulse used for recording is fixed to a constant value in any recording head. Therefore, the variation in energy required for ejection of individual recording heads is adjusted by the pulse width of the drive pulse in this way.

  In step S404, the first test pattern is recorded based on the appropriate pulse width set in step S403.

  FIG. 3 is a diagram showing a first test pattern. In the figure, the x direction coincides with the arrangement direction of a plurality of recording elements in the recording head 110. A dot pattern as shown in FIG. 3 is obtained by moving the recording material 118 in the y direction while ejecting the recording elements at predetermined intervals. In such a pattern, the plurality of dots 114 are sufficiently separated and each dot can be associated with each recording element. That is, from the first test pattern, it is possible to confirm whether or not each recording element is normally ejected, and whether or not the dot size and ejection direction are within a normal range. The moving speed of the paper stage 117 on which the recording material 118 is placed may be adjusted according to the ejection frequency of the recording head and a suitable distance between dots. For example, in this embodiment, it is 25 inches / sec.

  In step S405, the second test pattern is recorded based on the limit pulse width predicted in step S403.

  FIG. 4 is a diagram showing a second test pattern. As in FIG. 3, the recording elements are arranged in the x direction, and the recording material 118 is conveyed in the y direction. In the second test pattern, one recording element continuously discharges five times, and a pattern 119 in which five dots are continuous is recorded for each recording element. In this embodiment, a pattern 119 corresponding to all the recording elements is recorded with a pulse width of 9 steps. The pattern for each pulse width is shown in FIG. 19-No. 11.

  The nine-stage pulse width referred to here indicates the nine-stage pulse width obtained by increasing or decreasing the pulse width in steps of 0.02 μsec centering on the limit pulse width (0.90) predicted in step S403. Specifically, No. 2 in FIG. The pulse width of the drive pulse used at 15 corresponds to the predicted limit pulse and is 0.90 μsec. And No. 16 is 0.92 μsec. No. 17 is 0.94 μsec. 18 is 0.96 μsec. In 19, each pattern is recorded with a pulse width of 0.98 μsec. As the pulse width is shortened, the energy given to the electrothermal conversion element is reduced, so that the discharge amount and the discharge stability are gradually lowered, and the discharge is not performed. In FIG. Up to 17, thin discharge is performed. 16 shows a state in which the ejection is not performed completely. From such a second test pattern, the actual limit pulse width can be determined.

  The plurality of pulse widths used for recording the second test pattern are actually No. 1-No. More pulse widths such as 30 are prepared and stored in the memory of the control computer 101 in advance. However, as in this embodiment, if the limit pulse width is predicted to some extent from the resistance value of the electrothermal transducer obtained in step S402, in step S405, the limit pulse width is used as a reference, not for all the above-described pulse widths. The pattern may be recorded for the pulse widths of several stages. In this embodiment, as described above, the man-hour and the process load for the recording inspection process and the time are reduced by limiting the prediction range of the limit pulse width based on the resistance value of the electrothermal conversion element measured in advance.

  In the subsequent step S406, the image of the first test pattern recorded in step S404 is read. At this time, the control computer 101 first moves the paper stage 117 until the top of the first test pattern recorded on the recording material 118 is located in the measurement area of the CCD camera 115. Then, the paper stage 117 is moved so that the first test pattern moves in the direction intersecting the CCD arrangement direction in accordance with the CCD reading cycle. The moving speed of the paper stage 117 may be adjusted according to the reading period of each CCD and the processing speed of the image processing controller, but in this embodiment, it is set to 25 inches / sec, for example.

  In step S407, the second test pattern recorded in step S405 is read. The reading method is the same as in the case of the first test pattern described in step S406.

  In step S408, predetermined image processing is performed on the image read in steps S406 and S407, and image determination is performed. Specifically, first, image processing such as shading correction, binarization processing, and noise removal is performed on the read image. The above processing is the same for the first test pattern and the second test pattern.

  Thereafter, for the first test pattern, the centroid position on the xy coordinates for each dot 114 formed on the recording material 118 is obtained, and the ideal of each dot is obtained from the centroid position of the plurality of dots by the least square method. Obtain xy coordinates. Then, the deviation amount of the actual recording position with respect to the ideal position is calculated for each dot (that is, each recording element), and compared with a predetermined deviation amount threshold value. Further, the diameter of each dot is obtained from the area of each dot and is also compared with a predetermined threshold value.

  In this embodiment, the threshold value of the deviation amount is 34 μm in both the x and y directions. If there is a dot whose displacement is larger than this, the recording head is out of specification. Further, the threshold for the dot diameter is 20 μm, and the recording head is out of the standard even when a dot smaller than this is present.

  On the other hand, for the second test pattern, referring to FIG. 4 again, the sum of the area S1 occupied by the test pattern recorded with the same type of pulse width and the area of the test pattern 119 recorded by each recording element. S2 is obtained, and dot coverage S3 = S2 / S1 is calculated for each pulse width. Then, such dot coverage is set for nine pulse widths. 11-No. 19 is determined. In this embodiment, the threshold value of the dot coverage S3 is 1.0%. For example, the dot coverage S3 exceeds 1.0%. 17-No. 19, the dot coverage S3 is less than 1.0%. 11-No. No.16, no. 16 is determined as the limit pulse width of the recording head.

  Further, it is determined whether or not the determined limit pulse matches the limit pulse predicted in step S403. If they do not match, the difference between the two is obtained. In the case of the above example, the limit pulse predicted in step 403 is 0.90 μsec, but the limit pulse actually determined in step S408 is 0.92 μsec, so the difference is 0.02 μsec (one table number). )

  As described above, when there is a deviation between the limit pulse predicted in step S403 and the limit pulse actually determined, the process proceeds to step S410. Then, a correction value is set such that the limit pulse width set from the resistance value measured in step S402 is shifted by the above difference from the current value. In this way, in the inspection process for the next recording head, even if the same resistance value as in this example is measured in step S402, No. is used in the second test pattern. 12-No. No. 20 like Nine patterns centering on 16 are recorded.

  In subsequent step S409, the determination result in step S408 is written in the ROM of the recording head. Specifically, whether or not the head is within the standard at the recording position and the dot diameter, the limit pulse width determined in step S408, and an appropriate characteristic specific to the recording head obtained by adding a predetermined margin to the limit pulse width. Stores pulse width, etc. In addition, the recording head ID, date of manufacture, and the like are also stored.

  In this embodiment, the correction value for predicting the limit pulse is updated every time the recording inspection process of each recording head is performed. Thereby, in the nine patterns recorded by the second test pattern, the limit pulse pattern is always arranged near the center. As a result, the limit pulse width pattern is prevented from protruding from the second test pattern, and in any recording head recording inspection process, nine patterns are recorded in the second test pattern of the recording inspection process. It becomes possible to judge the limit pulse only by doing.

[Example 2]
Also in this embodiment, the recording inspection process of the recording head is executed according to the flowchart shown in FIG. In the present embodiment, a case where the limit pulse width cannot be determined in the second test pattern recorded in step S405 will be described.

  FIG. 5 is a diagram showing an example of the second test pattern recorded in step S405 of the present embodiment. Here, an example is shown in which the dot coverage S3 exceeds 1.0% in all nine recorded patterns. In such a case, in this embodiment, the dot coverage S3 is No. which is closest to 1.0%. Nine patterns continuous to No. 11, namely No. 11; 2-No. The second test pattern is recorded again for 10 and the limit pulse width is determined. Then, from the difference between the obtained limit pulse width and the limit pulse predicted in step S403, a correction value that shifts the limit pulse width set from the resistance value by the above difference from the current value, as in the first embodiment. Set.

  On the other hand, FIG. 6 is a diagram showing another example of the second test pattern recorded in step S405 of the present embodiment. Here, an example is shown in which the dot coverage S3 is below 1.0% in all nine recorded patterns. In such a case, in this embodiment, the dot coverage S3 is No. which is closest to 1.0%. Nine patterns continuous to No. 19, namely No. 19 20-No. The second test pattern is recorded again for 18, and the minimum dischargeable pulse is determined. The minimum number of pulses that can be ejected is set to No. And No. In the same manner as in the first embodiment, a correction value that shifts the limit pulse width set from the resistance value by the above difference from the current value is set from the deviation amount from 15.

  According to the present embodiment, when the limit pulse width cannot be determined by the second test pattern for the print head currently being inspected, an additional nine patterns are formed for the second test pattern. Recording and image processing must be performed. However, in the next recording head inspection process, it is possible to increase the possibility of arranging the minimum dischargeable drive pulse pattern at the center of the nine patterns. Thereby, it is possible to suppress the process load and the consumption time in the entire inspection process for a large number of recording heads.

101 Control computer
104 Head driver
105 Image processing unit
107 arithmetic processing unit
110 Inkjet recording head
112 Image processing controller
114 dots
115 CCD camera
118 Recording material
119 5-dot continuous pattern

Claims (6)

An inspection method of an ink jet recording head that discharges ink by applying a voltage pulse to an electrothermal transducer that generates thermal energy,
A measuring step for measuring a resistance value of the electrothermal transducer;
Based on the resistance value obtained by the measurement step, the pulse width of the voltage pulse necessary for generating the minimum energy from which the ink jet recording head can eject ink from the electrothermal transducer is set. A prediction process for predicting the corresponding critical pulse width;
A recording step of recording a test pattern for each of a plurality of pulse widths obtained by gradually increasing or decreasing the pulse width from the limit pulse width predicted in the prediction step;
A determination step of reading the image of the test pattern and determining the limit pulse width;
Obtaining a difference between the limit pulse determined in the determination step and the limit pulse predicted in the prediction step;
And a step of setting a correction value for predicting a limit pulse in the prediction step based on the difference. In the determination step, when it is determined that the limit pulse width cannot be determined from the test pattern, the plurality of pulse widths different from the plurality of pulse widths used in the recording step are used again. Recording the test pattern, re-reading the image of the test pattern, and determining the limit pulse width,
2. The ink jet recording head inspection method according to claim 1, further comprising: Recording a pattern different from the test pattern using a pulse width obtained by adding a predetermined margin to the limit pulse predicted by the prediction step;
The method for inspecting an ink jet recording head according to claim 1, further comprising a step of determining whether or not the ink jet recording head is out of standard by reading an image of the pattern.   4. The method according to claim 1, further comprising a step of storing in the memory of the ink jet recording head information on the limit pulse width or a pulse width obtained by adding a predetermined margin to the limit pulse width. Inkjet recording head inspection method.   5. The determination step according to claim 1, wherein the determination step determines the limit pulse width according to a dot coverage obtained for each of a plurality of patterns corresponding to each of a plurality of pulse widths in the test pattern. A method for inspecting an ink jet recording head according to the description. An inkjet recording head inspection apparatus that ejects ink by applying a voltage pulse to an electrothermal transducer that generates thermal energy,
Measuring means for measuring the resistance value of the electrothermal transducer;
Based on the resistance value obtained by the measuring means, the pulse width of the voltage pulse necessary to generate the minimum energy from which the ink jet recording head can eject ink from the electrothermal transducer is set. A predicting means for predicting the corresponding limit pulse width;
Recording means for recording a test pattern for each of a plurality of pulse widths obtained by gradually increasing or decreasing the pulse width from the limit pulse width predicted by the prediction means;
Determination means for reading the image of the test pattern and determining the limit pulse width;
Means for obtaining a difference between the limit pulse determined by the determination means and the limit pulse predicted by the prediction means;
An inspection apparatus for an ink jet recording head, comprising: means for setting a correction value for predicting a limit pulse by the prediction means based on the difference.

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