JP2016093949A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a discharge failure of a nozzle without a wasteful resource consumption.SOLUTION: An image forming device includes: a head 110 having the nozzle for discharging an ink droplet; a line sensor 121 disposed in a position facing a nozzle face of the head 110; and image comparison means 103 comparing an image of the read nozzle face to the nozzle face in normal state to determine the state of the nozzle face based on the comparison result.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus, and more particularly, to abnormality detection of a droplet discharge surface.

  In an ink jet printer, the nozzles of the head correspond to one pixel of the printed material, which may directly affect the image quality. If a nozzle causes a discharge failure, the image quality will be deteriorated unless the pixels that the nozzle is responsible for are corrected in some way. Therefore, it is an important technique to grasp the nozzle discharge failure.

  Also, in line type printers (hereinafter referred to as “line printers”) that increase the speed by arranging a plurality of heads, the head drive frequency is lower than that of a serial machine. However, since the head is not scanned with respect to the printing paper during printing, the nozzle of each head directly affects the image of the printed matter. For this reason, it is necessary not to cause a discharge failure of the nozzle, and maintenance of the nozzle is indispensable.

  Japanese Patent Application Laid-Open No. 2004-228561 discloses that a read image signal is obtained by driving a head and reading a line-shaped test pattern recorded on paper for the purpose of determining ejection failure of a nozzle. However, the detection of nozzle discharge failure by this method has a problem that ink and paper are consumed wastefully because an image printed on the described paper is read.

  In the prior art, as a nozzle maintenance means, a technique for detecting a nozzle ejection failure by reading a paper printed in a test mode is already known.

  However, the method of detecting the nozzle discharge failure by reading the paper printed in the test mode so far can surely detect the nozzle discharge failure, but there is a problem of wasteful consumption of ink and paper. there were.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to detect nozzle ejection defects without wasting resources.

  In order to achieve the above object, an apparatus according to the present invention includes a head having a nozzle for ejecting ink droplets, an image reading unit disposed at a position facing the nozzle surface of the head, and the image reading unit reading. Image comparison means for comparing an image of the nozzle surface of the head with an image of the nozzle surface of the head in a normal state and determining the state of the nozzle surface based on the comparison result is provided.

  According to the present invention, it is possible to detect nozzle ejection defects without wasting resources.

It is a figure showing roughly the whole composition of an embodiment. It is a figure which shows the structure of the discharge head of the line printer of embodiment. It is a figure which shows the external appearance structure of the discharge defect detection part 10 of embodiment. It is a figure which shows the function structure of the discharge defect detection part 10 of embodiment. FIG. 6 is a diagram (part 1) illustrating operations of the head 110, the line sensor 121, and the light source 122 during an ejection detection operation in the embodiment. FIG. 6 is a diagram (part 2) illustrating operations of the head 110, the line sensor 121, and the light source 122 during an ejection detection operation in the embodiment. It is a flowchart of the discharge detection operation in the embodiment. It is a figure which shows the state of the head 110, the line sensor 121, and the light source 122 when there exists abnormality at the time of the discharge detection operation in embodiment. It is a figure which shows the state of the head 110, the line sensor 121, and the light source 122 when there exists abnormality by a bubble etc. at the time of the discharge detection operation in embodiment. FIG. 6 is a diagram for describing a configuration for performing an ejection detection operation on a plurality of heads 110 in the embodiment. It is FIG. (1) for demonstrating the structure 1 for improving discharge detection precision in embodiment. It is FIG. (2) for demonstrating the structure 1 for improving discharge detection precision in embodiment. It is FIG. (1) for demonstrating the structure 2 for improving discharge detection precision in embodiment. It is FIG. (2) for demonstrating the structure 2 for improving discharge detection precision in embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

In the present specification, the “main scanning direction” refers to a direction orthogonal to the paper transport direction. The line printer usually scans mainly in the paper transport direction. However, in this specification, the description is simplified when compared with the serial printer, and therefore, the direction orthogonal to the paper transport direction is referred to as “main scan. Direction. In addition, the paper transport direction is referred to as “sub-scanning direction”.
Further, in this specification, “printing”, “printing”, and “image formation” are used with substantially the same meaning.

<Example of overall configuration>
An ink jet printer according to an embodiment of the present invention includes an apparatus main body, a paper feed tray for loading paper that is a recording medium attached to the apparatus main body, and a paper on which an image is recorded (formed) attached to the apparatus main body. A paper discharge tray for stocking, and further, a cartridge loading portion protruding from the front surface to the front side and lower than the upper surface is provided at one end of the front surface of the apparatus main body. The upper surface of the cartridge loading portion Are equipped with operation units such as operation keys and indicators.

  As a paper feeding unit for feeding the paper stacked on the paper stacking unit (pressure plate) of the paper feed tray, a half-moon roller (paper feeding roller) and a paper feeding roller for separating and feeding the paper one by one from the paper stacking unit Is provided with a separation pad made of a material having a large friction coefficient, and this separation pad is urged toward the sheet feeding roller.

  As a transport unit for transporting paper fed from the paper feed unit below the recording head, a transport belt for electrostatically attracting and transporting the paper and a guide from the paper feed unit A counter roller for transporting the paper to be transported sandwiched between the transport belt, a transport guide for changing the paper transported vertically upward by 90 ° and following the transport belt, and transported by a pressing member A tip pressing roller urged toward the belt side. In addition, a charging roller that is a charging unit for charging the surface of the conveying belt is provided.

  Here, the conveyance belt is an endless belt, and is configured to wrap around the conveyance roller and the tension roller and circulate in the belt conveyance direction. The charging roller is arranged so as to come into contact with the surface layer of the conveyor belt and to rotate by the rotation of the conveyor belt, and applies 2.5 N to both ends of the shaft as a pressing force.

  In addition, a guide member is disposed on the back side of the conveyance belt so as to correspond to the printing area by the recording head. The upper surface of the guide member protrudes closer to the recording head than the tangent line of two rollers (conveyance roller and tension roller) that support the conveyance belt. As a result, the conveyance belt is pushed up and guided by the upper surface of the guide member in the printing region, so that highly accurate flatness is maintained.

  Furthermore, a plurality of grooves are formed in the main scanning direction, that is, in a direction orthogonal to the conveying direction, on the surface side of the guide member that contacts the back surface of the conveying belt to reduce the contact area with the conveying belt. Can smoothly move along the surface of the guide member.

  Further, as a paper discharge unit for discharging the paper recorded by the recording head, a separation claw for separating the paper from the conveyance belt, a paper discharge roller, and a paper discharge roller are provided below the paper discharge roller. A paper discharge tray is provided. Here, the height from the space between the paper discharge roller and the paper discharge roller to the paper discharge tray is increased to some extent in order to increase the amount that can be stored in the paper discharge tray.

  In addition, a double-sided paper feeding unit is detachably attached to the back surface of the apparatus main body. This double-sided paper feeding unit takes in the paper returned by the reverse rotation of the transport belt, reverses it, and feeds it again between the counter roller and the transport belt. In addition, a manual sheet feeding unit is provided on the upper surface of the duplex feeding unit.

<Configuration example of line printer>
FIG. 2 shows an example of the arrangement of the ejection heads of the line printer of this embodiment.
In the line printer, as shown in FIG. 2, a plurality of heads are arranged side by side in the main scanning direction. In a serial printer with one head, the head moves in the main scanning direction for printing, but in a line printer, printing is performed by ejecting ink on the spot without moving a plurality of heads arranged in the main scanning direction. .

  In a serial printer, one head prints the entire print portion, but in a line printer, since the print portion per head is smaller than that of a serial printer, the drive frequency of the head is also reduced. For this reason, the printing speed can be increased. However, since the head is not scanned with respect to the printing paper during printing, the nozzles of each head directly affect the image of the printed matter. For this reason, it is necessary not to cause a discharge failure of the nozzle, and maintenance of the nozzle is indispensable.

Hereinafter, a configuration for detecting a discharge failure will be described. The present embodiment has the following features when detecting discharge from a line inkjet printer.
That is, unlike the prior art, the state of the meniscus is changed by finely driving the nozzle with respect to the meniscus generated at the time of ejection detection, and the image around the nozzle opening at that time is a sensor such as a CCD. Get in. In the present embodiment, whether or not ejection is possible is determined based on the difference in shading of the image, and therefore, it is possible to reduce consumption of ink and paper in ejection detection in the line printer as compared with the prior art.

<Discharge failure detection unit>
FIG. 3 shows an external configuration of a configuration (hereinafter referred to as a discharge failure detection unit 10) for detecting a discharge failure of an ink nozzle of the line-type ink jet printer shown in FIG. The illustrated external configuration is an example, and various modifications can be made. In the present embodiment, as shown in FIG. 3, a line sensor 121 is disposed below the head 110 with respect to the head 110 on which ink nozzles are mounted, and a light source is also disposed below the head 110 for acquiring image data of the line sensor 121. 122 is arranged. The head 110, the line sensor 121, and the light source 122 are connected to an engine control board 100, which is a control board for controlling them, by wires such as a harness.

  FIG. 4 shows a functional configuration of the ejection failure detection unit 10. As shown in the figure, a CPU (Central Processing Unit) 101, a memory 102, and a non-volatile memory 107 containing a program (not shown) are mounted on the engine control board 100. The engine control board 100 also includes a drive control unit 106 that controls an ink ejection function 111 that is a function of ejecting ink from the ink nozzles of the head 110. Further, the engine control board 100 is equipped with an image capturing unit 104 and an image comparison unit 103 for the line sensor 121 and a light source control unit 105 for the light source 122 with respect to the discharge detection unit 120. The drive control unit 106 may be configured to be mounted on the head 110.

  Further, the ejection failure detection unit 10 includes a cleaning unit 130 that is driven under the control of the engine control board 100. In the present embodiment, the cleaning unit 130 is a plate-like cleaning device called a cleaning blade. When an abnormality is recognized on the nozzle surface of the head 110, it has a function of removing foreign matters such as dust and ink residue that are considered to be attached to the nozzle surface.

<Discharge detection operation>
Hereinafter, the discharge detection operation by the discharge failure detection unit 10 will be described with reference to FIGS. 5, 6, and 7. 5 and 6 show operations of the head 110, the line sensor 121, and the light source 122 when the discharge detection unit 120 performs discharge detection.

  As shown in FIGS. 5 and 6, the ink forms a droplet film called a meniscus with respect to an ink nozzle (hereinafter, nozzle) in the head 110. Since the nozzle is composed of an actuator that expands and contracts by applying a potential such as a piezoelectric element, a droplet is ejected by applying a potential to eject an ink droplet from the nozzle to the actuator.

Further, it is possible to vibrate the meniscus film by applying an electric potential to the actuator within a range where the droplets are not ejected. This operation is called fine drive, and the case where the meniscus vibrates toward the outside of the nozzle as shown in FIG. 5 is called fine drive 1, and the meniscus vibrates toward the inside of the nozzle as shown in FIG. This case is referred to as fine drive 2.

  The above control is controlled by the drive control unit 106 in the engine control board 100. However, when the drive control unit 106 is mounted on the head 110, since the drive control unit 106 performs control, the control can also be performed by the head 110, and the drive control by the engine control board 100 is possible. The control of the unit 106 will be described as an example. In addition, it is assumed that the resolution of the line sensor 121 is sufficiently high with respect to the nozzles, and here, it is assumed that image acquisition is performed with an image resolution of 4 pixels per nozzle.

FIG. 7 is a flowchart of the discharge detection operation.
The discharge detection operation based on meniscus vibration is not performed frequently, but is performed after a predetermined time has elapsed since the previous printing (S101). When performing ejection detection, a control signal for fine drive 1 is transmitted from the drive control unit 106 to the ink ejection mechanism 111 (S102). The ink ejection mechanism 111 performs an operation corresponding to the fine driving 1 for the nozzle, and vibrates the ink meniscus of the nozzle opening outward. In synchronization with the timing at which the fine drive 1 control signal is transmitted from the drive control unit 106, the light source control unit 105 transmits a signal for turning on the light source 122 to light the light source 122 (S103). The image capturing unit 104 is also operated to capture information on nozzle image data input from the line sensor 121 (S104), and the nozzle image data is stored in the memory 102 (S105).

  The nozzle image data stored in the memory 102 is read by the image comparison unit 103 together with the correct image data stored in the nonvolatile memory 107 (S107), and the correct image data and the nozzle image data are compared. Perform (S108).

  When the drive control unit 106 transmits the fine drive 2 control signal, the reverse is true, the ink meniscus at the nozzle opening vibrates inward, and the light source control unit 105 and the image capturing unit 104 have the same timing. It works with. The nozzle image data will be described here as being stored as 8-bit gradation data when the line sensor 121 is monochrome.

  The nozzle image data is converted into 8-bit gradation data by the line sensor 121. At that time, due to the reflection of light from the light source 122, the value is close to “0x0” in the bright case, and close to “0xFF” in the dark state. As shown in FIG. 5, when the meniscus vibrates outward by the fine driving 1, the reflection from the light source is large and a bright image is obtained. On the other hand, when the meniscus vibrates inward by the fine driving 2, the reflection of light from the light source becomes small, resulting in a dark image (FIG. 6). The nozzle image data acquired as described above is stored in the memory 102.

  The image comparison unit 103 compares the nozzle image data stored in the memory 102 and the image data stored in the nonvolatile memory 107, and determines that the ejection detection is normal when there is no difference between the comparison results ( S109). Conversely, if there is a difference in the compared data, it is determined that there is an abnormality, and abnormal nozzle information is notified to the CPU 101 (S110). Information on abnormal nozzles at this time is information for diagnosing failures such as nozzle positions (numbers when numbered), degree of data difference, past abnormality history, and the like. By combining the information, the failure level of the nozzle is determined. Information for diagnosing these failures (the above information) is stored in the memory 102 (S111).

<If there is an abnormality>
FIG. 8 shows the state of ejection detection when a foreign object adheres to the nozzle.
The discharge detection operation as described with reference to FIG. 7 is performed. At that time, normal image data is compared with the nozzle image data acquired by the image capturing unit 104. If the difference between the image data is more than twice, foreign matter is attached to the nozzle opening. Therefore, the cleaning unit 130 cleans the nozzle opening of the head.

  Note that foreign matter adhesion is determined when the difference between the image data is doubled or more, but when the difference is more than a certain threshold or when the value is an extreme value such as “0xFF” or “0x0”, etc. It can be changed according to the foreign object to be detected.

FIG. 9 shows the state of discharge detection due to bubbles or the like.
The discharge detection operation as described with reference to FIG. 7 is performed. At that time, normal image data is compared with the nozzle image data acquired by the image capturing unit 104, and if it is determined that the difference in image data is abnormal N times or more in succession, the meniscus of the nozzle It is determined that the amount of displacement is small for some reason, the nozzles are ejected idle, and the ink supply state is made normal. At that time, the ejection detection unit 120 such as the line sensor 121 is retracted from below the head 110 so that the line sensor 121 and the light source 122 are not contaminated by ink.

  The above-mentioned N times can be changed depending on the number of pixels corresponding to the line sensor 121 with respect to the nozzles. In this description, since detection is performed with four line sensor pixels for one nozzle, N = 4.

<Multi-row head>
Next, a configuration for performing an ejection detection operation on the plurality of rows of heads 110 will be described. FIG. 10 shows the state of ejection detection for a plurality of rows of ink heads.
The discharge detection operation described with reference to FIG. 7 is performed on the nozzles of each ink head. Here, the case of black / yellow / red / blue four-color ink heads as a plurality of rows of ink heads will be described.

  For each ink head, the ejection detection unit 120 on which the line sensor 121 and the light source 122 are mounted is moved in parallel to the nozzle surface using a driving source such as a motor. Fine driving 1 is performed on the nozzles of each ink head, and the line sensor 121 reads the nozzle image data while sequentially moving from the right side (blue side of the nozzle) to the left in FIG. The read nozzle image data is stored in the memory 102, the nozzle image data of each nozzle is extracted from the moving speed of the ejection detection unit 120, and the presence or absence of abnormality is detected by comparing with normal image data.

  Next, fine driving 2 is performed on the nozzles of each ink head, and the line sensor 121 reads the nozzle image data while sequentially moving from the left side (black side of the nozzle) to the right in FIG. The read nozzle image data is stored in the memory 102 in the same manner as in the fine driving 1, and compared with normal image data. Note that the movement direction of the ejection detection unit 120 may be reversed with respect to the movement direction described above, and there is no problem even if the movement is from the front to the back of the page.

<Improved discharge detection accuracy>
In order to improve the accuracy of detecting the ejection abnormality, it is preferable to further include the following configuration in addition to the configuration of the above-described embodiment.

  FIG. 11 and FIG. 12 show Configuration 1 for improving the discharge detection accuracy when the line sensor 121 is used. 11 shows the state of fine drive 1 and FIG. 12 shows the state of fine drive 2. As shown in the figure, the line sensor 121 drives a pendulum so as to scan the nozzle surface. By this driving, the line sensor 121 reads the image of the nozzle surface over a wide range in a plane.

  By acquiring the nozzle surface as plane image data in this way, the meniscus image data is stored in the memory 102 as a plane. By comparing the nozzle plane image data with the normal image data, it is possible to detect the case where there is a foreign substance other than the portion where the line sensor 121 is fixed, and the cleaning can be performed more accurately.

  The significance of this configuration is to read the nozzle surface of the head 110 in a plane, so that the line sensor 121 is not moved and the head 110 is swung or translated with respect to the image acquisition surface of the line sensor 121. Also good. Alternatively, the nozzle surface may be scanned two-dimensionally by moving both the head 110 and the line sensor 121.

  FIGS. 13 and 14 show a configuration 2 for improving the discharge detection accuracy when the line sensor 121 is used. 13 shows the state of fine drive 1 and FIG. 14 shows the state of fine drive 2. As shown in the figure, by installing the line sensor 121 at a certain angle with respect to the nozzle from below the head 110, the meniscus displacement is viewed as light reflection, so the meniscus displacement is acquired as image data. Since it is possible to more clearly acquire the magnitude of the displacement amount at the time of carrying out, it is possible to reliably perform the idle discharge against the abnormality due to bubbles or the like.

  In the present embodiment described above, fine driving is performed in which the meniscus of the ink droplet at the nozzle tip is slightly raised and depressed, and the state of the nozzle tip during the fine driving is imaged by optical means. An abnormality is detected by comparing the captured image with a normal image. Therefore, according to the above-described embodiment, unlike the configuration of the prior art that determines whether there is an abnormality by ejecting ink droplets onto a sheet or the like, it does not involve consumption of resources such as a sheet. According to the above-described embodiment, it is possible to detect nozzle ejection defects without wasting resources.

The optical means is an image reading means, and a CMOS sensor or a CCD sensor can be used.
In addition, according to the present embodiment, by providing the cleaning unit 130, it is possible to perform an optimum maintenance that suppresses ink consumption in accordance with the abnormality of the nozzle surface.
Further, according to the present embodiment, by providing the configuration 1 that improves the discharge detection accuracy, the image of the nozzle surface can be read over a wide range, and the foreign matter detection of the nozzle surface can be performed more accurately.
In addition, according to the present embodiment, by providing the configuration 2 that improves the discharge detection accuracy, the displacement amount of the meniscus is viewed as reflection of light, and therefore the displacement amount when acquiring the displacement amount of the meniscus as image data. Since it is possible to acquire the size more clearly, abnormality detection can be performed more accurately with respect to abnormality caused by bubbles or the like.

DESCRIPTION OF SYMBOLS 10 Discharge defect detection part 100 Engine control board 101 CPU
DESCRIPTION OF SYMBOLS 102 Memory 103 Image comparison part 104 Image taking part 105 Light source control part 106 Drive control part 107 Nonvolatile memory 110 Head 111 Ink ejection function 120 Discharge detection part 121 Line sensor 122 Light source 130 Cleaning part

Japanese Patent No. 5296825

Claims (5)

A head having a nozzle for discharging ink droplets;
Image reading means disposed at a position facing the nozzle surface of the head;
An image comparison unit that compares the image of the nozzle surface of the head read by the image reading unit with an image of the nozzle surface of the head in a normal state, and determines the state of the nozzle surface based on a comparison result;
An image forming apparatus comprising: With light emitting means,
The image forming apparatus according to claim 1, wherein the light emitting unit is arranged at a position where emitted light illuminates a nozzle surface of the head.   The image forming apparatus according to claim 1, further comprising: a cleaning unit that removes foreign matter on the nozzle surface when the image comparison unit determines that the nozzle surface is abnormal. Means for driving at least one of the head and the image reading means;
The image forming apparatus according to claim 1, wherein the image reading unit scans the nozzle surface of the head two-dimensionally.   6. The image forming apparatus according to claim 1, wherein the image reading unit is installed with a predetermined angle with respect to a nozzle surface of the head.

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