JP2020146947A - Liquid discharge device - Google Patents

Abstract

To provide a liquid discharge device which detects a defective nozzle accurately in less processing time and memory area.SOLUTION: A liquid discharge device includes a conveyance part which conveys a recording medium, a liquid discharge head which is provided with nozzles for discharging liquid to the recording medium conveyed by the conveyance part in a line-shape, a scanner installed so as to cause a main scanning direction to coincide with a nozzle array direction of the liquid discharge head, a chart preparation part for preparing a chart for defective nozzle detection in which a line of a sub-scanning direction corresponding to each nozzle of the liquid discharge head is arranged and a position detection part which performs interpolation processing with respect to a pixel value of a circumferential plurality of pixels on a line position detected from the pixel value of reading data of the chart for defective nozzle detection read by the scanner and detects a position which becomes 0 by differentiating an interpolation function lead out by the interpolation processing as a line position.SELECTED DRAWING: Figure 7

Description

The present invention relates to a liquid discharge device.

Conventionally, in a line head type liquid discharge device, a technique for detecting a defective nozzle is known in order to prevent deterioration of image quality due to non-discharge / discharge bending of the liquid.

In Patent Document 1, each of the reading data of the detection chart read by the scanner and the entire ideal data are converted to high resolution by interpolation processing, and the read data and the ideal data are binarized to correspond to a plurality of nozzles. A technique for determining defective nozzles by comparing line spacing is disclosed. As a result, according to the technique disclosed in Patent Document 1, it is possible to detect ejection bending with high accuracy even with a scanner having a resolution lower than that of printing.

However, according to the technique disclosed in Patent Document 1, a large amount of memory and processing time required for detection are required in order to increase the resolution of the read data of the detection chart read by the scanner and the entire ideal data by interpolation processing. There was a problem that it would end up.

Further, since the defective nozzle is determined by comparing with the ideal data, there is a problem that it cannot be detected accurately when there is a disturbance such as a magnification or skew or vibration of the read data.

The present invention has been made in view of the above, and an object of the present invention is to detect defective nozzles with high accuracy in a short processing time and a memory area.

In order to solve the above-mentioned problems and achieve the object, the liquid discharge device of the present invention has a line of a conveying unit for conveying a recording medium and a nozzle for discharging liquid to the recording medium conveyed by the conveying unit. A defective nozzle in which a liquid discharge head provided in a shape, a scanner installed so that the main scanning direction is aligned with the nozzle row direction of the liquid discharge head, and a line in the sub-scanning direction corresponding to each nozzle of the liquid discharge head are arranged. The chart generation unit that generates the detection chart and the pixel values of a plurality of pixels around the line position detected from the pixel values of the read data of the defective nozzle detection chart read by the scanner are subjected to interpolation processing, and the above-mentioned It is characterized by including a position detection unit that differentiates the interpolation function derived by the interpolation process and detects a position where the position becomes 0 as a line position.

According to the present invention, by limiting the range in which the interpolation processing is performed on the data, it is possible to accurately detect the defective nozzle with a small processing time and a memory area.

FIG. 1 is a schematic diagram showing a schematic configuration of an inkjet recording device according to an embodiment. FIG. 2 is a diagram showing an arrangement example of two scanners. FIG. 3 is a block diagram showing a control configuration of an inkjet recording device. FIG. 4 is a functional block diagram showing a function related to the defective nozzle detection process. FIG. 5 is a diagram showing an example of a defective nozzle detection chart. FIG. 6 is a diagram illustrating a process for detecting a defective nozzle. FIG. 7 is a diagram illustrating an interpolation process. FIG. 8 is a diagram for explaining the omission / bending determination process. FIG. 9 is a flowchart schematically showing the flow of the defective nozzle detection process. FIG. 10 is a flowchart showing the flow of the omission / bending detection process for one step in step S4. FIG. 11 is a flowchart showing the flow of the line coordinate detection process in step S12. FIG. 12 is a flowchart showing the flow of the median / average value calculation process in step S13. FIG. 13 is a flowchart showing the flow of the omission / bending detection process in step S15. FIG. 14 is a schematic diagram showing a schematic configuration of another inkjet recording device according to the embodiment.

Hereinafter, embodiments of the liquid discharge device will be described in detail with reference to the accompanying drawings. In this embodiment, an inkjet recording device of an inkjet method is applied as a liquid ejection device.

FIG. 1 is a schematic diagram showing a schematic configuration of an inkjet recording device 1 according to an embodiment. As shown in FIG. 1, the inkjet recording device 1 mainly includes a paper feeding unit 100, an image forming unit 200, a drying unit 300, and a paper ejection unit 400. The inkjet recording device 1 forms an image on the paper P, which is a recording medium as a sheet material to be fed from the paper feeding unit 100, by the image forming unit 200 with ink which is a liquid for forming an image. Then, the inkjet recording device 1 dries the ink adhering to the paper P in the drying unit 300, and then discharges the paper P from the paper ejection unit 400.

First, the paper feed unit 100 will be described.

The paper feed unit 100 mainly includes a paper feed tray 110 on which a plurality of paper Ps are loaded, a feeding device 120 that separates and feeds the paper P one by one from the paper feed tray 110, and an image forming unit for the paper P. It includes a resist roller pair 130 that feeds to 200.

As the feeding device 120, any feeding device such as a device using rollers and rollers and a device using air suction can be used.

The paper feeding unit 100 drives the resist roller pair 130 at a predetermined timing after the tip of the paper P fed from the paper feed tray 110 by the feeding device 120 reaches the resist roller pair 130. As a result, the paper P is fed to the image forming unit 200.

In the present embodiment, the paper feeding unit 100 is not limited in its configuration as long as it feeds the paper P to the image forming unit 200.

Next, the image forming unit 200 will be described.

The image forming unit 200 mainly includes a receiving cylinder 201, a paper-supporting drum 210, an ink ejection unit 220, and a delivery cylinder 202. The receiving cylinder 201 receives the fed paper P. The paper-supporting drum 210 that functions as a transport unit carries the paper P that has been transported by the receiving cylinder 201 on the outer peripheral surface. The ink ejection unit 220 ejects ink toward the paper P supported on the paper-supporting drum 210. The delivery cylinder 202 delivers the paper P conveyed by the paper-carrying drum 210 to the drying unit 300.

The tip of the paper P transported from the paper feeding unit 100 to the image forming unit 200 is gripped by a paper gripper provided on the surface of the receiving cylinder 201, and is conveyed as the surface of the receiving cylinder 201 moves. The paper P conveyed by the receiving cylinder 201 is delivered to the paper-carrying drum 210 at a position facing the paper-carrying drum 210.

A paper gripper is also provided on the surface of the paper-carrying drum 210, and the tip of the paper P is gripped by the paper gripper. Further, a plurality of suction holes are dispersedly formed on the surface of the paper-supporting drum 210, and a suction airflow toward the inside of the paper-supporting drum 210 is generated in each suction hole by the suction device 211.

The tip of the paper P delivered from the receiving cylinder 201 to the paper-carrying drum 210 is gripped by the paper gripper and is adsorbed on the surface of the paper-carrying drum 210 by the suction airflow, and the surface of the paper-carrying drum 210 moves. Is transported.

The ink ejection unit 220 of the present embodiment is a line head that ejects four colors of ink, C (cyan), M (magenta), Y (yellow), and K (black) to form an image, and for each ink. It includes individual liquid discharge heads 220C, 220M, 220Y, 220K.

The liquid discharge heads 220C, 220M, 220Y, 220K are not limited in their configuration as long as they discharge liquid, and any configuration can be adopted. If necessary, a liquid ejection head that ejects a special ink such as white, gold, or silver may be provided, or a liquid ejection head that ejects a liquid that does not form an image, such as a surface coating liquid, may be provided.

The liquid ejection heads 220C, 220M, 220Y, 220K of the ink ejection unit 220 are respectively controlled to eject operations by a drive signal corresponding to the image information. When the paper P supported on the paper-carrying drum 210 passes through the region facing the ink ejection portion 220, each color ink is ejected from the liquid ejection heads 220C, 220M, 220Y, 220K, and an image corresponding to the image information is displayed. It is formed.

In the present embodiment, the image forming unit 200 is not limited in its configuration as long as the liquid is adhered to the paper P to form an image.

In addition, as shown in FIG. 1, the image forming unit 200 includes two scanners 231,232, which are line scanners, on the downstream side of the paper P in the transport direction with respect to the ink ejection unit 220. The two scanners 231 and 232 read the defective nozzle detection chart C (see FIG. 5). The resolutions of the two scanners 231,232 are lower than the print resolution of the image forming unit 200.

Immediately after the image forming unit 200 prints the defective nozzle detection chart C by the ink ejection unit 220 in a state where the tip of the paper P is gripped by the paper gripper and sucked and conveyed on the surface of the paper carrying drum 210. The defective nozzle detection chart C is read by two scanners 231,232.

Here, FIG. 2 is a diagram showing an arrangement example of two scanners 231,232. As shown in FIG. 2, the two scanners (Front) 231 and the scanner (Rear) 232 are arranged in a staggered pattern to read the entire surface of the paper P. More specifically, the two scanners 231,232 have an area (overlap area) in which the reading ranges overlap (overlap) in the main scanning direction. Further, the two scanners 231,232 are arranged so as to be offset in the sub-scanning direction.

In the present embodiment, two scanners 231 and 232 are arranged, but the present invention is not limited to this, and one scanner can be used as long as the reading range in the main scanning direction can be secured. It may be a combination of three or more scanners.

Next, the drying unit 300 will be described.

The drying unit 300 mainly includes a drying mechanism 301 for drying the ink adhering on the paper P in the image forming unit 200, and a conveying mechanism 302 for conveying the paper P conveyed from the image forming unit 200. I have.

The drying unit 300 receives the paper P conveyed from the image forming unit 200 by the conveying mechanism 302, then conveys the paper P so as to pass through the drying mechanism 301, and delivers the paper P to the paper ejection unit 400. When the paper P passes through the drying mechanism 301, the drying unit 300 performs a drying process on the ink on the paper P. As a result, liquids such as water in the ink evaporate, the ink adheres to the paper P, and curling of the paper P is suppressed.

Next, the paper ejection unit 400 will be described.

The paper ejection unit 400 mainly includes a paper ejection tray 410 on which a plurality of sheets P are loaded. The paper ejection unit 400 sequentially stacks and holds the paper P conveyed from the drying unit 300 on the paper ejection tray 410.

In the present embodiment, the paper ejection unit 400 is not limited in its configuration as long as it ejects the paper P.

Next, other functional parts will be described.

The inkjet recording device 1 of the present embodiment includes a paper feeding unit 100, an image forming unit 200, a drying unit 300, and a paper ejection unit 400, but other functional units may be added as appropriate. For example, after adding a pre-processing unit that performs pre-processing of image formation between the paper feeding unit 100 and the image forming unit 200, or after performing post-processing of image formation between the drying unit 300 and the paper discharging unit 400. A processing unit can be added.

Examples of the pretreatment unit include a treatment liquid coating process for applying a treatment liquid to the paper P to react with the ink to suppress bleeding, but the content of the pretreatment is not particularly limited. .. Further, as the post-processing unit, for example, a paper reversal transfer process for inverting the paper P on which the image is formed by the image forming unit 200 and sending it to the image forming unit 200 again to form an image on both sides of the paper P is performed. , A process of binding a plurality of sheets of paper P on which an image is formed, a correction mechanism for correcting deformation of the paper P, a cooling mechanism for cooling the paper P, and the like, but the content of post-processing is not particularly limited. ..

Subsequently, the control configuration of the inkjet recording device 1 will be described.

Here, FIG. 3 is a block diagram showing a control configuration of the inkjet recording device 1. As shown in FIG. 3, the inkjet recording device 1 includes a control unit 10 that controls the entire device. The control unit 10 comprises a CPU (Central Processing Unit) 11 as a control main body, a ROM (Read Only Memory) 12, a RAM (Random Access Memory) 13, a memory 14, and an ASIC (Application Specific Integrated Circuit) 15. I have. The ROM 12 stores a computer program executed by the CPU 11 and other fixed data. The RAM 13 temporarily stores image data and the like. The memory 14 is a rewritable non-volatile memory for holding data even while the power supply of the inkjet recording device 1 is cut off. The ASIC 15 executes image processing for performing various signal processing and rearranging on image data, and other input / output signal processing for controlling the entire device.

Further, as shown in FIG. 3, the control unit 10 includes a host interface (I / F) 16, a head drive control unit 17, a motor control unit 18, an I / O 19, and a scanner control unit 8. ing.

The host I / F 16 transmits and receives image data (print data) and control signals to and from the host side via a cable or a network. Examples of the host connected to the inkjet recording device 1 include an information processing device such as a personal computer, an image reading device such as an image scanner, and an imaging device such as a digital camera.

The I / O 19 connects various sensors 25 such as a humidity sensor, a temperature sensor and other sensors. The I / O 19 inputs detection signals from various sensors 25.

The head drive control unit 17 drives and controls the ink ejection unit 220, and includes data transfer means. More specifically, the head drive control unit 17 transfers the image data as serial data. Further, the head drive control unit 17 generates a transfer clock and a latch signal necessary for transferring image data and confirming the transfer, and a drive waveform used when ejecting liquid drops from the ink ejection unit 220. Then, the head drive control unit 17 inputs the generated drive waveform and the like to the drive circuit inside the ink ejection unit 220.

The motor control unit 18 drives the motor M that rotates the receiving cylinder 201, the paper-supporting drum 210, the delivering cylinder 202, and the like.

The scanner control unit 8 controls two scanners 231,232.

In addition, the control unit 10 connects an operation panel 60 for inputting and displaying necessary information to the inkjet recording device 1.

The control unit 10 comprehensively controls each unit by expanding the computer program read from the ROM 12 (or the memory 14) by the CPU 11 into the RAM 13 and executing the computer program. More specifically, the CPU 11 reads the control contents set for each print mode from the ROM 12 (or the memory 14) based on the print mode set from the operation panel 60. Then, the CPU 11 executes the control described later by controlling each unit based on the control content read from the ROM 12 (or the memory 14).

The computer program executed by the inkjet recording apparatus 1 of the present embodiment is a file in an installable format or an executable format, and is a CD-ROM, a flexible disk (FD), a CD-R, or a DVD (Digital Versatile Disk). It is recorded and provided on a computer-readable recording medium such as.

Further, the computer program executed by the inkjet recording device 1 of the present embodiment may be stored on a computer connected to a network such as the Internet and provided by downloading via the network. Further, the computer program executed by the inkjet recording device 1 of the present embodiment may be configured to be provided or distributed via a network such as the Internet.

Further, the computer program executed by the inkjet recording device 1 of the present embodiment may be configured to be provided by incorporating it into a ROM or the like in advance.

Next, the function related to the defective nozzle detection process executed by the control unit 10 of the inkjet recording device 1 will be described.

Here, FIG. 4 is a functional block diagram showing a function related to the defective nozzle detection process. As shown in FIG. 4, the control unit 10 functions as a chart generation unit 101 and a defective nozzle detection unit 102.

The chart generation unit 101 generates a defective nozzle detection chart C (see FIG. 5) in which lines in the sub-scanning direction corresponding to the nozzles of the liquid discharge heads 220C, 220M, 220Y, and 220K are arranged in a stepped manner.

Here, FIG. 5 is a diagram showing an example of a defective nozzle detection chart C. As shown in FIG. 5, in the defective nozzle detection chart C, nozzle check lines L for detecting defective nozzles corresponding to the nozzles of the liquid discharge heads 220C, 220M, 220Y, and 220K are arranged in a stepped manner. The number and length of the nozzle check line L are variable.

In addition, as shown in FIG. 5, the defective nozzle detection chart C has a start mark M1 for specifying a position to start defective nozzle detection and an end mark M2 for specifying a position to end defective nozzle detection. And have.

As shown in FIG. 5, in the defective nozzle detection chart C, the line length in the sub-scanning (paper transport) direction corresponding to each nozzle is lengthened, the data is averaged in the sub-scanning direction, or the data in the main scanning direction is read. The sub-scanning direction resolution is lower than the resolution to lengthen the reading sampling period. As a result, the line position can be detected with high accuracy even when there is vibration or skew, and by determining a defective nozzle from the difference in pitch with the adjacent line, nozzle bending can be detected even when there is a reading magnification error.

More specifically, the line length of the defective nozzle detection chart C is the relative vibration between the liquid discharge heads 220C, 220M, 220Y, 220K or two scanners 231,232 and the paper-supporting drum 210 that functions as a transport unit. Of these, the length shall be two cycles or more of the longer frequency. This has the effect of reducing the influence of relative vibration between the paper P and the scanners 231,232.

Returning to FIG. 4, the defective nozzle detection unit 102 interpolates with the pixel values of a plurality of pixels around the line position detected from the pixel values of the read data of the defective nozzle detection chart C read by the two scanners 231,232. In addition to performing the processing, it functions as a position detection unit that differentiates the interpolation function derived by the interpolation processing and detects the position where it becomes 0 as the line position, and determines a defective nozzle from the difference in pitch with the adjacent line.

Here, FIG. 6 is a diagram illustrating a process for detecting a defective nozzle. As shown in FIG. 6, the defective nozzle detection unit 102 first detects from the image the main scanning positions of the start mark M1 for starting the defective nozzle detection and the end mark M2 for specifying the position for ending the defective nozzle detection. , The defective nozzle detection range X is determined. The defective nozzle detection unit 102 performs the detection process of the nozzle check line L with respect to Nm pixels (liquid discharge head 220C, 220M, 220Y, 220K or scanners 231,232 and the paper-supporting drum 210) in the sub-scanning direction. Of the vibrations, the value obtained by averaging the pixels having a length of two cycles or more of the longer frequency is used. This has the effect of reducing the influence of relative vibration between the paper P and the scanners 231,232.

As shown in FIG. 6, the defective nozzle detection unit 102 has a nozzle check line from the start position (start mark M1) of the first stage of the nozzle check line L to the position of the end mark M2 or the image end in the detection direction. The L coordinate detection process is performed.

The defective nozzle detection unit 102 compares the pixel value one pixel at a time with the nozzle detection threshold value T, and if the value is larger than the nozzle detection threshold value T, determines the position of the nozzle check line L.

Next, the defective nozzle detection unit 102 executes the interpolation process. FIG. 7 is a diagram illustrating an interpolation process.

As shown in FIG. 7, the defective nozzle detection unit 102 performs tertiary spline interpolation on the pixel values of S pixels before and after the main scanning direction of the coordinates determined to be the nozzle check line L, and obtains a spline function. As a result, even a low-resolution scanner can detect with high accuracy.

The defective nozzle detection unit 102 differentiates the spline function to obtain the X coordinate whose value becomes 0, converts the X coordinate into mm units based on the main scanning reading resolution of the X coordinate, and holds it as the nozzle position.

The defective nozzle detection unit 102 calculates the nozzle coordinates for all the lines of one step of the nozzle check line L, then calculates the difference in pitch between the adjacent lines, and calculates the pitch difference of one step of the nozzle check line L. Calculate the median difference. The defective nozzle detection unit 102 uses the calculated median value to determine whether the nozzle is missing or bent. This has the effect of being able to accurately detect even if the reading magnification fluctuates.

The median value does not have to be the median value of all the lines for one stage of the nozzle check line L, and may be the median value among several lines around the line of interest. This has the effect of accurately detecting even if there is a deviation (aberration) in the reading magnification.

Next, the defective nozzle detection unit 102 determines whether the nozzle is missing or bent. FIG. 8 is a diagram for explaining the omission / bending determination process. FIG. 8A shows the omission determination process, and FIG. 8B shows the bend determination process.

As shown in FIG. 8A, the defective nozzle detection unit 102 has an absolute pitch difference between the pitch difference between the adjacent lines and the median pitch difference of one step of the nozzle check line L. It is determined that there are several nozzle omissions immediately before the nozzle check line L whose value is more than half of the median value. That is, when the spaces between adjacent lines are represented as D _n , D _{n + 1} , D _{n + 2,} ..., It is determined that there is nozzle omission when the following conditions are satisfied.
｜ D _n − D _{n + 1} ｜ ≧ Median / 2

In addition, as shown in FIG. 8B, the defective nozzle detection unit 102 excludes the nozzles determined to have nozzle omission immediately before, and obtains the average value of the pitch differences between all the adjacent lines.

Then, the defective nozzle detection unit 102 obtains the number of missing nozzles by the distance between the nozzle check line L ÷ the average value rounded to the nearest whole number, and holds the defective nozzle number.

When the absolute value of the difference between the difference between the adjacent nozzles and the average value is equal to or greater than the bending determination threshold value Tm, the defective nozzle detecting unit 102 determines that the nozzle is bent and holds it as the defective nozzle number. That is, when the following conditions are satisfied, it is determined that the nozzle is a bent nozzle.
｜ D _{n −} Mean ｜ ≧ Tm

Subsequently, the flow of the defective nozzle detection process will be described.

Here, FIG. 9 is a flowchart schematically showing the flow of the defective nozzle detection process. As shown in FIG. 9, the defective nozzle detection unit 102 repeats the defective nozzle detection process for the number of stages in order from the first stage of the nozzle check line L of the defective nozzle detection chart C, and detects defective nozzles for all stages. Do. It will be described in detail below.

The defective nozzle detection unit 102 first detects the position of the start mark M1 on the defective nozzle detection chart C in order to specify the position where the defective nozzle detection is started (step S1).

Next, the defective nozzle detection unit 102 detects the position of the end mark M2 on the defective nozzle detection chart C in order to specify the position where the defective nozzle detection ends (step S2).

Subsequently, the defective nozzle detection unit 102 detects the start nozzle position of each stage of the nozzle check line L between the start mark M1 and the end mark M2 (step S3).

Then, the defective nozzle detection unit 102 executes a process of detecting nozzle omission / bending for the number of stages of the nozzle check line L (step S4).

Here, FIG. 10 is a flowchart showing the flow of the omission / bending detection process for one step in step S4. As shown in FIG. 10, the defective nozzle detection unit 102 sets the total width of the nozzle check line L as a value obtained by averaging Nm pixels in the sub-scanning direction (step S11).

Next, the defective nozzle detection unit 102 sets the coordinates of the nozzle check line L from the start position of the nozzle check line L (start mark M1) to the position of the end mark M2 or the image end in the detection direction for all stages. The detection process is performed (step S12).

Here, FIG. 11 is a flowchart showing the flow of the line coordinate detection process in step S12. As shown in FIG. 11, first, the defective nozzle detection unit 102 acquires the next pixel (step S21), and determines whether the acquired pixel is the position of the end mark M2 or the image edge (step S22).

When the defective nozzle detection unit 102 determines that the acquired pixel is the position of the end mark M2 or the image edge (Yes in step S22), the process ends.

On the other hand, when the defective nozzle detection unit 102 determines that the acquired pixel is not the position of the end mark M2 or the image edge (No in step S22), the defective nozzle detection unit 102 determines whether the acquired pixel value is equal to or higher than the nozzle detection threshold T (No). Step S23).

When the defective nozzle detection unit 102 determines that the acquired pixel value is not equal to or higher than the nozzle detection threshold value T (No in step S23), the line detection in-progress flag is turned off (step S24), and the process ends.

On the other hand, when the defective nozzle detection unit 102 determines that the acquired pixel value is equal to or higher than the nozzle detection threshold value T (Yes in step S23), it determines that it is the position of the nozzle check line L, and the line detection flag is ON. It is determined whether or not there is (step S25).

When the defective nozzle detection unit 102 determines that the line detection in-progress flag is ON (Yes in step S25), the defective nozzle detection unit 102 ends the process.

On the other hand, when the defective nozzle detection unit 102 determines that the line detection flag is not ON (No in step S25), the defective nozzle detection unit 102 turns the line detection flag ON (step S26), and the main coordinates determined to be the nozzle check line L. A third-order spline interpolation is performed on the pixel values of S pixels before and after the scanning direction to obtain a spline function (step S27).

Next, the defective nozzle detection unit 102 differentiates the spline function (step S28), calculates the X coordinate at which the value becomes 0 (step S29), and converts it into mm units based on the main scanning reading resolution of the X coordinate. The position is held as the nozzle position (step S30), and the process ends.

The defective nozzle detection unit 102 calculates the nozzle coordinates for all the lines of one step of the nozzle check line L by repeating the process of the above step S12 from the start mark M1 to the position of the end mark M2 or the image edge. To do.

Returning to FIG. 10, when the line coordinate detection process is completed, the defective nozzle detection unit 102 proceeds to step S13 to execute the median / average value calculation process.

Here, FIG. 12 is a flowchart showing the flow of the median / average value calculation process in step S13. As shown in FIG. 12, first, the defective nozzle detection unit 102 calculates the difference in pitch between the adjacent lines (step S41), and calculates the average value of the difference in pitch for one step of the nozzle check line L. (Step S42), the median value of the pitch difference for one step of the nozzle check line L is calculated (step S43).

Next, in the defective nozzle detection unit 102, the absolute value of the pitch difference between the pitch difference between the adjacent lines and the median pitch difference of one step of the nozzle check line L is half of the median value. If there is more than that (Yes in step S44), it is determined that there are several nozzle omissions immediately before the nozzle check line L, and the coordinates are held as the missing coordinates (step S45). The defective nozzle detection unit 102 repeats the processes of steps S44 and S45 for the number of lines.

Subsequently, the defective nozzle detection unit 102 excludes the nozzles held as the missing coordinates, obtains the average value of the pitch differences between all the adjacent lines (step S46), and obtains the pitch between all the adjacent lines. The median value of the difference between the two is obtained (step S47).

The defective nozzle detection unit 102 ends the median / average value calculation process in step S13.

Returning to FIG. 10, when the above median / average value calculation process is completed, the defective nozzle detection unit 102 proceeds to step S14.
Start nozzle number of each stage = Start mark Nozzle number + Number of stages -1
And.

Next, the defective nozzle detection unit 102 executes a missing / bending detection process (step S15).

Here, FIG. 13 is a flowchart showing the flow of the omission / bending detection process in step S15. As shown in FIG. 13, first, when there is a nozzle held as the missing coordinates (Yes in step S51), the defective nozzle detection unit 102 determines the number of missing nozzles by the distance between the nozzle check lines L ÷ average value. Rounded to the nearest whole number (step S52). The defective nozzle detection unit 102 proceeds to step S56 when there is no nozzle held as the missing coordinates (No in step S51).

Next, the defective nozzle detection unit 102 holds the defective nozzle number (step S53) and repeats the process of incrementing the nozzle number (step S54) for the number of omissions.

After that, the defective nozzle detection unit 102 subtracts (the number of missing nozzles × the average value) from the inter-line distance value of the nozzle check line L (step S55).

Next, when the absolute value of the difference between the difference between the adjacent nozzles and the average value is equal to or greater than the bending determination threshold value Tm (Yes in step S56), the defective nozzle detection unit 102 determines that the nozzle is a curved nozzle and holds it as a defective nozzle number. (Step S57), and the nozzle number is incremented (step S58).

The defective nozzle detection unit 102 detects nozzle omission / bending by repeating the process of step S15 for the number of lines.

As a result, the process of detecting the omission / bending of the number of steps of the nozzle check line L in step S4 shown in FIG. 9 is completed.

The defective nozzle detection unit 102 executes the process of detecting nozzle omission / bending in step S4 for the number of stages, and ends the process.

As described above, according to the present embodiment, a plurality of pixels around the line position detected from the pixel values of the read data of the defective nozzle detection chart C read by the two scanners 231 and 232 whose resolution is lower than the print resolution. The difference in pitch from the adjacent line is not the line position obtained by binarization but the position where the interpolation function derived by the interpolation process is differentiated and becomes 0 as the line position. Determine the defective nozzle from. Therefore, interpolation processing is performed on the pixel values of several pixels around the line position detected from the pixel values of the read data of the defective nozzle detection chart C read by two scanners 231 and 232 having a resolution lower than the print resolution. Therefore, defective nozzles can be detected accurately with a small processing time and a memory area.

Further, in the defective nozzle detection chart C, the line length in the sub-scanning (paper transport) direction corresponding to each nozzle is lengthened, and the sampling period for averaging or reading data in the sub-scanning direction is lengthened. This makes it possible to accurately detect the line position even when there is vibration or skew, and by determining a defective nozzle from the difference in pitch with the adjacent line, it is possible to detect nozzle bending even when there is a reading magnification error. ..

In this embodiment, an example of application to the inkjet recording device 1 as a liquid discharging device is described. However, the “liquid discharging device” is a liquid discharging head that discharges a liquid toward a surface to be dried of a recording medium. The liquid is not limited to the one in which a significant image such as a character or a figure is visualized by the discharged liquid, and includes, for example, a pattern having no meaning in itself.

The recording medium is not limited to any material, and may be any material such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, ceramics, etc., to which a liquid can adhere even temporarily. For example, it may be used for film products, cloth products for clothing, building materials such as wallpaper and flooring, and leather products.

Further, the "liquid discharge device" can also include means related to feeding, transporting, and discharging paper to which a liquid can be attached, a pretreatment device, a posttreatment device, and the like.

The "liquid" may have a viscosity and surface tension that can be discharged from the head, and is not particularly limited, but has a viscosity of 30 mPa · s or less at room temperature, under normal pressure, or by heating or cooling. It is preferable to have. More specifically, solvents such as water and organic solvents, colorants such as dyes and pigments, polymerizable compounds, resins, functionalizing materials such as surfactants, biocompatible materials such as DNA, amino acids and proteins, and calcium. , Solvents, suspensions, emulsions and the like containing edible materials such as natural pigments, and the like, and these can be used in applications such as inks for inkjets and surface treatment liquids.

Further, the "liquid discharge device" includes a device in which the liquid discharge head and the recording medium move relative to each other, but the present invention is not limited to this. Specific examples include a serial type device that moves the liquid discharge head, a line type device that does not move the liquid discharge head, and the like.

The "liquid discharge head" is a functional component that discharges and ejects liquid from a discharge hole (nozzle). As an energy generation source for discharging liquid, a piezoelectric actuator (laminated piezoelectric element and thin-film piezoelectric element), a thermal actuator using an electrothermal conversion element such as a heat generating resistor, and an electrostatic actuator composed of a vibrating plate and a counter electrode are discharged. Although energy generating means can be used, the discharge energy generating means to be used is not limited.

In the present embodiment, the liquid ejection device is described as an example of application to the inkjet recording device 1, but the present invention is not limited to this, and application to a so-called continuous book machine is also possible.

Here, FIG. 14 is a schematic view showing a schematic configuration of another inkjet recording device 1a. As shown in FIG. 14, the inkjet recording apparatus 1a includes a paper feeding unit 100a having a roll around which a recording medium Pa which is a long paper is wound, an image forming unit 200a, a drying unit 300a for drying the recording medium Pa, and a drying unit 300a. It is composed of a paper ejection unit 400a on which the image-formed recording medium Pa is wound. A scanner 500 that scans the recording medium Pa after the image forming step is arranged after the image forming unit 200a.

The recording medium Pa is continuous paper (roll paper) wound in a roll shape, and the recording medium Pa is unwound from the paper feed unit 100a by a transfer roller and conveyed on the platen 600 of the image forming unit 200a to discharge the paper. It is wound up by the part 400a.

In addition, the inkjet recording apparatus 1a may have a pretreatment step unit for applying the pretreatment liquid to the recording medium Pa, and a pretreatment drying unit for drying the recording medium Pa coated with the pretreatment liquid.

When the recording medium Pa, which is such a long paper, is conveyed, the paper tension varies in the direction orthogonal to the conveying direction (main scanning direction), and the paper is biased due to the parallelism of the conveying rollers. Orthogonal. These cause meandering. The control for correcting this meandering is performed by providing a sensor for detecting the paper edge in the transport path, detecting the amount of offset of the paper, and tilting the transport roller according to the detected amount. This correction may cause the paper to meander. This meandering is detected as low frequency (several hertz) vibrations.

1, 1a Liquid discharge device 101 Chart generator 102 Position detection unit 210 Conveyance unit 220C, 220M, 220Y, 220K Liquid discharge head 231,232,500 Scanner C Defective nozzle detection chart

Japanese Patent No. 4684801

Claims (8)

A transport unit that transports recording media and
A liquid discharge head provided with a line of nozzles for discharging liquid to a recording medium conveyed by the transfer unit, and
A scanner installed with the main scanning direction aligned with the nozzle row direction of the liquid discharge head,
A chart generation unit that generates a chart for detecting defective nozzles in which lines in the sub-scanning direction corresponding to each nozzle of the liquid discharge head are arranged.
Interpolation processing is performed on the pixel values of a plurality of pixels around the line position detected from the pixel values of the reading data of the defective nozzle detection chart read by the scanner, and the interpolation function derived by the interpolation processing is differentiated. A position detection unit that detects the position where it becomes 0 as a line position,
A liquid discharge device characterized by comprising. The chart generation unit arranges lines in the sub-scanning direction in a stepped manner.
The liquid discharge device according to claim 1. The line length of the defective nozzle detection chart shall be a length of two cycles or more of the longer frequency of the relative vibrations of the liquid discharge head or the scanner and the transport unit.
The liquid discharge device according to claim 1 or 2. The position detection unit uses a value obtained by averaging pixels whose sub-scanning directions correspond to a length of two or more cycles of the frequency in the line detection process of the defective nozzle detection chart.
The liquid discharge device according to claim 3. The scanner has a lower resolution in the sub-scanning direction than a reading resolution in the main scanning direction by lengthening the sampling period.
The liquid discharge device according to claim 1 or 2. The position detection unit performs spline interpolation as the interpolation processing.
The liquid discharge device according to claim 1 or 2. The position detection unit is defective when the difference between the average value or the median value of the pitch calculated based on the pitch of one step of the line and the pitch difference between the line of interest and the adjacent line is equal to or more than a predetermined value. Judge as a nozzle,
The liquid discharge device according to any one of claims 1 to 6, wherein the liquid discharge device is characterized. When the difference between the average value or the median of the pitches calculated based on the pitches of several lines around the line of interest and the pitches of the line of interest and its adjacent lines is greater than or equal to a predetermined value in the position detection unit. Judge as a defective nozzle,
The liquid discharge device according to any one of claims 1 to 6, wherein the liquid discharge device is characterized.

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