JP2011046074A - Liquid ejection failure detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect the ejection failure of each liquid drop with high accuracy even when the liquid drops are continuously ejected. <P>SOLUTION: This liquid ejection failure detector includes a camera for imaging the flying liquid drops ejected from a nozzle, from the ejected direction of the liquid drops; a coordinate computing section 112 computing the coordinates of the liquid drops in a predetermined coordinate system on the picked-up image; a difference computing section 113 computing the difference between the computed coordinates and the coordinates of the liquid drops in the coordinate system when normally ejected; and a determining section 114 comparing the difference with a predetermined threshold and determining the occurrence of an ejection failure of the liquid drop by the nozzle when the difference is larger than the threshold. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a liquid ejection failure detection apparatus for inspecting liquid droplets ejected from an inkjet head or the like.

  The ink jet recording apparatus includes an ink jet head of each color for ejecting minute ink droplets from minute nozzles, and ejects ink droplets while moving the ink jet head with respect to a recording medium such as paper. Perform image formation. In order to form an image with high accuracy, it is necessary to perform control so that ink droplets are ejected in a normal direction.

  For this reason, a recording head inspection apparatus that performs an inspection for confirming the deviation of the landing positions of droplets (ink droplets) before factory shipment is used (for example, Patent Document 1). In the method of Patent Document 1, droplets are landed on a recording medium that is located away from the ejection surface, and the droplets that have landed on the ejection port surface and the recording medium are recognized by an image processing camera disposed below the recording medium. Image processing. Then, the horizontal distance and the vertical distance between them are calculated from the landed droplet and the coordinates of the ejection port.

JP 2000-062158

  However, in the method of Patent Document 1, for example, when a plurality of liquid droplets are ejected continuously from the same nozzle, a plurality of liquid droplets overlap and land on the recording medium. There was a problem that could not.

  The present invention has been made in view of the above, and provides a liquid discharge failure detection device that can detect discharge failure of each droplet with high accuracy even when droplets are continuously discharged. For the purpose.

  In order to solve the above-described problems and achieve the object, the present invention is preliminarily determined on an imaged means for imaging a droplet ejected from a nozzle and flying from the ejection direction of the droplet. Coordinate calculation means for calculating the coordinates of the droplet in a coordinate system, and difference calculation for calculating a difference between the calculated coordinates and the coordinates of the droplet in the coordinate system when ejected normally And a determination unit that compares the difference with a predetermined threshold value and determines that the ejection failure of the droplet by the nozzle has occurred when the difference is greater than the threshold value. To do.

  According to the present invention, even when droplets are ejected continuously, it is possible to detect the ejection failure of each droplet with high accuracy.

FIG. 1 is a side view of the liquid ejection failure detection apparatus according to this embodiment. FIG. 2 is a diagram illustrating an example of an image in which ink droplets are captured among images captured by a camera. FIG. 3 is a functional block diagram of the liquid ejection failure detection device. FIG. 4 is a diagram illustrating an example of an image obtained by combining a plurality of images. FIG. 5 is a diagram illustrating an example in which the pitch is calculated based on the ink droplet Bn. FIG. 6 is a diagram illustrating an example of the difference between the nozzle position and the position of the imaged ink droplet with respect to the nozzle position. FIG. 7 is a diagram showing an example of a jig used in such a configuration. FIG. 8 is a diagram illustrating an example of the ink droplet group and the variation range. FIG. 9 is a diagram illustrating an example of the coordinates of the center obtained from the variation range as illustrated in FIG. FIG. 10 is a diagram illustrating the positional relationship between the lens of the camera and the ink droplets.

  Exemplary embodiments of a liquid ejection failure detection apparatus according to the present invention will be explained below in detail with reference to the accompanying drawings.

  FIG. 1 is a side view of a liquid ejection failure detection apparatus 100 according to this embodiment. As shown in FIG. 1, the liquid discharge failure detection device 100 includes a pedestal 1, a head fixing shaft 2, stages 3 a and 3 b, a head fixing jig 4, a rail 5, an automatic stage 6, and a camera 7. And a glass plate 8.

  The head fixing shaft 2 is fixed to the base 1. The stage 3a is fixed to the head fixing shaft 2 and holds the stage 3b. The stage 3b is held so as to be movable in the vertical direction with respect to the stage 3a. The head fixing jig 4 is connected to the head fixing shaft 2 via the stages 3a and 3b.

  The stages 3 a and 3 b function as changing means for changing the distance from the focal position of the camera 7 to the nozzles of the head 200.

The rail 5 is fixed to the base 1. The automatic stage 6 is held on the rail 5 so that it can move along the rail 5. A camera 7 that functions as an imaging unit is mounted on an automatic stage 6. The automatic stage 6 has an ink droplet (ink droplets B _n−1 , B _n , B _{n + 1 in} FIG. 1) by a movement control unit (not shown). Hereinafter, an ink droplet discharged from the nozzle N _n may be referred to as an ink droplet B _n. ) Is controlled to move according to the discharge position. Thereby, for example, the camera 7 can be moved so that the ink droplets from the nozzles from which the ink droplets are ejected in the nozzle row of the head 200 can be imaged. Thus, the automatic stage 6 functions as a moving unit that moves the camera 7. For automatic stage 6, a program or the like, it becomes possible to automatically align the nozzle N _n is.

  Instead of the automatic stage 6 controlled by the movement control unit, a manual stage for manually controlling movement may be used. Moreover, you may comprise so that both the control mechanism by a movement control part and the manual control mechanism may be provided.

  The camera 7 includes a lens 7a for capturing an image (video) of ink droplets ejected from each nozzle of the head 200 installed above. It is desirable to select an appropriate magnification for the lens 7a in accordance with the interval between nozzles (inter-nozzle pitch) and the diameter of the ink droplets to be ejected.

  In this embodiment, a high-speed camera is used as the camera 7. Thereby, it is possible to image the ink droplets flying at high speed. Since the speed of the ink droplet is about 10 m / s, the number of frames of the camera 7 (timing for releasing the shutter) is preferably about 30,000 frames / s or more.

  The glass plate 8 is disposed on the top of the camera 7 in order to protect the camera 7 from ink stains. Since the focal position SH of the camera 7 is out of the glass plate 8, the influence of ink droplets attached to the glass plate 8 on the image captured by the camera 7 is small. By tilting the glass plate 8 and disposing the waste liquid tank downward, or by providing a mechanism to move the unclean glass surface to the camera 7 part, the illuminance drops due to ink stains even during long-term ejection. You may comprise so that it may decrease.

The head 200 is installed on the head fixing jig 4. A plurality of nozzles N _n (1 ≦ n ≦ N (N is a natural number)) for ejecting ink droplets are arranged on the head nozzle surface 201 of the head 200. The camera 7 is disposed below the head 200 (ink droplet ejection direction).

  The head fixing jig 4 on which the head 200 is installed is connected to the stage 3b that can move in the vertical direction (ink droplet ejection direction) as described above. For this reason, the head 200 can freely change the position in the height direction (ink droplet ejection direction). Hereinafter, the head height HH representing the height of the head 200 is defined as the distance from the focal position SH of the camera 7 to the head nozzle surface 201.

  When observing the ejection state of the ink droplets, the head height HH is a predetermined reference distance (the transport of the recording medium) that represents the distance from the head 200 to the recording medium transported when the head 200 is mounted on the ink jet recording apparatus. The height is set to be substantially the same. Thereby, the actual printing state can be reproduced. The head height HH may be configured to be larger than the transport height. In this case, since the bending is enlarged, it is possible to accurately detect the ejection failure.

  Thus, in this embodiment, instead of observing ink droplets that have landed on a transparent member or paper, the ink droplets are ejected and the ink droplets passing through the focal position SH of the camera 7 are observed. In other words, not the ink droplets after landing but the ink droplets ejected and flying are observed.

FIG. 2 is a diagram illustrating an example of an image in which ink droplets are captured among videos captured by the camera 7. FIG. 2 shows an example of an image 51 including ink droplets B _n−1 , B _n , and B _{n + 1} ejected from nozzles N _n−1 , N _n , and N _{n + 1} . As shown in FIG. 2, may be when ejecting ink droplets simultaneously, observing the ink droplet B _n corresponding to the nozzles N _n. Then, by extracting the image 51 including ink droplets from the captured image and performing image processing, it is possible to determine ejection failure (bending or missing). Details of the ejection failure determination process will be described later.

  In this embodiment, since observation is performed at the focal position SH, satellites (satellite Bs in FIG. 1) that cannot be observed by landing on a transparent body or paper can also be observed. As a result, it becomes possible to detect imprinting defects by satellites. Although satellites have a small liquid diameter, they have a liquid shape, so that imprinting defects can be detected by the same method as ink droplets (see FIGS. 3 to 6). Since the satellite passes through the focal position after the ink droplet, for example, a method of capturing only the satellite by delaying the imaging timing can be used. At this time, if no satellite is displayed in the video within a predetermined time, it can be determined that no satellite is generated.

  Next, the functional configuration of the liquid ejection defect detection device 100 will be described with reference to FIG. FIG. 3 is a functional block diagram of the liquid ejection defect detection device 100. As shown in FIG. 3, the liquid ejection failure detection apparatus 100 includes an image processing unit 111, a coordinate calculation unit 112, a difference calculation unit 113, and a determination unit 114 as main functional configurations.

  The image processing unit 111 performs image processing on the image captured by the camera 7. For example, the image processing unit 111 extracts an image in which ink droplets are captured from continuous frames (images). As a method for extracting an image, any conventionally used method such as a method of collating with a predetermined ink droplet image pattern can be applied.

  The coordinate calculation unit 112 calculates ink droplet coordinates in a predetermined coordinate system on the image. For example, as shown in FIG. 2, the origin CG is set at an arbitrary position in the image, the X axis is taken from the origin CG in the nozzle arrangement direction (nozzle row direction), and the Y axis is taken in the direction perpendicular to the nozzle arrangement direction. Other coordinate systems can be used. The coordinate calculation unit 112 calculates the distance in the X direction (X coordinate) and the distance in the Y direction (Y coordinate) with respect to the origin CG of each ink droplet in the image from the image as shown in FIG. The position of each ink drop in the image can be specified at the same time as the extraction of the image including the ink drop, for example.

  The difference calculation unit 113 calculates a difference between the calculated coordinates of each ink droplet and the coordinates of the ink droplet in the coordinate system when ejected normally. The determination unit 114 compares the calculated difference with a predetermined threshold value, and determines that an ink droplet ejection failure has occurred when the difference is greater than the threshold value.

  In addition, the liquid ejection failure detection device 100 may include an imaging control unit that controls imaging by the camera 7, the above-described movement control unit, and the like, which are omitted in FIG.

  Details of the ejection failure determination process will be described below.

First, the coordinate calculation unit 112 measures the coordinates of each ink droplet (B _{n−1 to} B _{n + 1} ) from the image shown in FIG. 2 extracted by the image processing unit 111.

Here, the ink droplets are simultaneously ejected from each nozzle (N _{n−1 to} N _{n + 1} ) and imaged. If a large bend occurs, it may not be possible to determine which ink droplets (B _{n−1 to} B _{n + 1} ) are ejected from which nozzles (N _{n−1 to} N _{n + 1} ). In view of this, a configuration may be adopted in which imaging is performed by sequentially ejecting ink droplets from the respective nozzles (N _{n−1 to} N _{n + 1} ). Thus, it is possible to identify the nozzle N _n corresponding to the ink droplet B _n.

Moreover, large number of nozzles N _n, if not fit in a single screen, by the automatic stage 6, a camera 7 is moved in an arbitrary pitch, ejecting sequentially ink droplets from the nozzle N _n corresponding to the moved position And may be configured to take an image.

In this case, the nozzle row direction of the head 200 and the traveling direction of the automatic stage 6 are made parallel. Then, the plurality of images picked up according to the movement are integrated into one image based on the coordinate system of each image, the moving speed of the automatic stage 6 and the like. FIG. 4 is a diagram illustrating an example of an image obtained by combining a plurality of images. FIG. 4 shows an example of a composite image 52 represented by a coordinate system obtained by integrating the coordinate systems of a plurality of images with the virtual origin CKG as the origin. The coordinate calculation unit 112 can calculate the coordinates of each ink droplet (B _{n−5 to} B _{n + 5} ) from the combined image. With such a configuration, it is possible to cope with a long head such as a line head.

  After calculating the coordinates of each ink droplet, a defective nozzle is detected based on the calculated coordinates. First, the difference calculation unit 113 identifies the position (nozzle position) of each nozzle. Below, an example of the identification method of the nozzle position of a X direction is demonstrated.

The difference calculation unit 113 calculates a pitch representing a difference from another coordinate (X coordinate) with respect to the reference, based on the coordinate (X coordinate) of any one of the calculated ink droplet coordinates. To do. FIG. 4 shows an example in which the pitches ( _{Pn-5 / n-4 to Pn-5 / n + 5} ) are calculated based on the ink droplet Bn-5. Note that the pitch P _{k / l} represents the distance in the X direction to the ink droplet B ₁ when the ink droplet B _k is used as a reference.

That is, for example, as shown in FIG. 4, the difference calculation unit 113 uses the ink droplet B _n-5 as a reference, and the pitch P _{n-5 / n-4} from the ink droplet B _{n- 5} to the ink droplet B _n-4. Ask for. Next, the difference calculation unit 113 obtains a pitch P _{n−5 / n−3} from the ink droplet B _n−5 to the ink droplet B _n−3 . The difference calculation unit 113 repeats such processing, and finally obtains the pitch P _{n−5 / n−5} from the ink droplet B _{n −5} to the ink droplet B _{n + 5} .

The difference calculation unit 113 selects a different ink droplet as a reference, and repeats the same processing. That is, the difference calculation unit 113 calculates the pitch to the other ink droplets with respect to the reference with the coordinates of the remaining ink droplets (B _{n−4 to} B _{n + 5} ) as the reference. FIG. 5 is a diagram illustrating an example in which the pitch (P _{n / n−5 to} P _{n / n + 5} ) is calculated based on the ink droplet Bn.

Next, the difference calculation unit 113 compares the predetermined value of the inter-nozzle pitch with the pitch based on the coordinates of the obtained ink droplets (B _{n−5 to} B _{n + 5} ). Then, the difference calculation unit 113 determines the ink droplet pitch is often match, and an ink droplet discharged from the nozzle N _n that normal ejection. Whether there are many matching pitches may be determined, for example, based on whether the number of matches is greater than a predetermined threshold (number threshold) or the ratio of the number of matches to the number of ink droplets is a predetermined threshold (ratio threshold). It may be determined by whether or not it is larger.

Then, the difference calculating unit 113 calculates from the position and the specified value of the nozzle pitch of the nozzles N _n are normally ejected, the position of the other nozzle (nozzle position), respectively. For example, the difference calculation unit 113 can calculate a position that is an integer multiple of the specified value of the pitch between nozzles from the position of the nozzle Nn that normally discharges as the nozzle position of the other nozzles. The calculated nozzle position represents the coordinates (X coordinate) of the ink droplet imaged when ejected normally.

  FIG. 6 is a diagram illustrating an example of the difference between the nozzle position and the position of the imaged ink droplet with respect to the nozzle position. In FIG. 6, the broken line represents the calculated nozzle position.

Next, the difference calculation unit 113 calculates the difference between the calculated nozzle position and the X coordinate of each ink droplet. In FIG. 6, Px _n-4 , Px _n−1 , Px _{n + 1} , Px _{n + 3} , and Px _{n + 5} are for ink drops B _n−4 , B _n−1 , B _{n + 1} , B _{n + 3} , and B _{n + 5} , respectively. It represents the calculated difference. Then, the determination unit 114 compares the calculated difference with a predetermined difference threshold, and determines that an ink droplet ejection failure has occurred when the difference is greater than the threshold.

  Note that a two-dimensional nozzle position can be specified by performing the same processing in the Y direction. Further, by comparing a difference in the Y direction and a predetermined threshold with respect to the difference in the Y direction, it is possible to detect an ejection failure of the ink droplet.

  In the above description, the nozzle position is calculated from the captured image. On the other hand, by moving the head 200 up and down to focus on the head nozzle surface 201 and specifying the nozzle position, the ink droplets may be ejected by returning to a prescribed head height.

  Further, as a method for specifying the nozzle position without changing the head height, a target capable of specifying the head nozzle position is arranged at the focal position of the camera 7 and an image at the time of ink ejection is taken together with the target. You may do it. This target may be an object or an optical one.

  FIG. 7 is a diagram showing an example of a jig used in such a configuration. First, the reference line 632 of the head clamping jig 601 and the reference line 631 connecting the centers 612 and 622 of the targets 611 and 621 are configured to be at right angles.

  Then, the head 200 is sandwiched by the head sandwiching jig 601 in this state. When sandwiched, the reference line 632 and the head nozzle row 602 are perpendicular to each other. Then, the head clamping jig 601 is moved so that the centers 612 and 622 of the targets 611 and 612 are positioned on the extended line of the head nozzle row 602.

  With these operations, the direction of the head nozzle row 602 and the direction of the line connecting the centers 612 and 622 of the targets 611 and 621 can be matched. In this state, when ink droplets are ejected from each nozzle of the head nozzle row and imaged by the camera 7, an image including the target arranged at the focal position together with each ink droplet can be imaged. Therefore, the nozzle position can be specified by specifying the positions of the targets 611 and 621 in the captured image. Further, the amount of variation from the head nozzle row 602 can be easily measured.

  Here, when the head 200 is a head for a serial printer, the X direction is the nozzle row direction, which is the paper transport direction. Further, the Y direction is a direction perpendicular to the nozzle row and is a direction in which the head 200 is scanned.

  Among the image defects, defects that can be recognized remarkably include bending in the nozzle row direction (X direction). Therefore, when performing ejection failure detection, the threshold value (array direction threshold value) for comparing with the distance (difference) in the X direction is smaller than the threshold value (right angle direction threshold value) for comparing with the distance (difference) in the Y direction. May be. As a result, it is possible to efficiently detect an ejection failure that is an image failure.

Previously, it had done determination of ejection failure by ejecting ink droplets of one drop from the nozzles N _n. However, it has been confirmed that the ejection failure includes normal ejection at the beginning, but there is a case where a bending or a defect occurs in the middle or a case where the bending direction is not constant.

Accordingly, ejecting ink droplets B _n in succession from the nozzles N _n the same configuration as described above, configured and to detect the discharge failure by using the coordinates calculated for each ink droplet (the ink droplet group BG) Also good.

First, the coordinate calculation unit 112 obtains the coordinates of each ink droplet (ink droplet group BG _{n−1 to} BG _{n + 1} ) ejected continuously, and the distribution of the obtained coordinates (variation range BT _{n−1 to} BT _{n + 1} ). Is calculated. The variation range is calculated, for example, as a minimum rectangle including each coordinate. FIG. 8 is a diagram illustrating an example of the ink droplet group and the variation range.

Next, the coordinate calculation unit 112 obtains the coordinates BC _{n−1 to} BC _{n + 1} of the centers of the variation ranges BT _{n−1 to} BT _{n + 1} . FIG. 9 is a diagram illustrating an example of the coordinates of the center obtained from the variation range as illustrated in FIG. Next, the coordinate calculation unit 112 calculates the nozzle position by the same method as described above, using the obtained center coordinates BC _{n−1 to} BC _{n + 1} as the coordinates of the ink droplets discharged from each nozzle, and determines a discharge failure. To do. Thereby, it becomes possible to determine the ejection failure with higher accuracy. In addition, as a simple ejection failure determination method, a method of comparing the variation range may be used. For example, when the area of the variation range is larger than a predetermined threshold, it may be determined that a discharge failure has occurred in the corresponding nozzle.

  Next, a method for efficiently observing the ink droplet B with the camera 7 will be described with reference to FIG. FIG. 10 is a diagram showing the positional relationship between the lens 7a of the camera 7 and the ink droplets. Since the ink droplets fly at a speed of about 10 m / s, even if a high-speed camera is used, the ink droplets may not be properly observed depending on the characteristics of the lens 7a used.

  As one of the characteristics of the lens 7a, there is a characteristic called depth of field that means a length in which an object is in focus. If the depth of field is small, there is a possibility that ink droplets flying at high speed cannot be properly imaged. Therefore, the camera 7 is provided with a lens 7a having a depth of field HS equal to or greater than the ink droplet flight distance calculated from the ink droplet flight speed and the shutter speed of the camera 7 (time interval for storing images). This makes it possible to catch ink droplets ejected at high speed.

Assuming that the shutter speed of the camera 7 is T (s) and the flying speed of the ink droplet is V (m / s), the ink droplet advances by a distance K = T × V (m). In FIG. 10, the intervals between the ink droplets B _m−1 , B _m , and B _{m + 1} flying at the times T _m−1 , T _m , and T _{m + 1} correspond to the distance K.

  Therefore, if the lens 7a having the depth of field HS equal to or greater than the distance K is used, it is possible to image the focused ink droplet in one frame (one image) of the video. In addition, since an accurate ink droplet diameter can be calculated from a focused image, it is possible to detect a discharge amount abnormality or a shape abnormality.

  As described above, in the present embodiment, ink droplets flying on the focal position of the camera are observed instead of observing ink droplets that have landed on a transparent member or paper. For this reason, even when droplets are continuously ejected, it is possible to detect ejection failure of each droplet with high accuracy.

DESCRIPTION OF SYMBOLS 1 Base 2 Head fixing shaft 3a, 3b Stage 4 Head fixing jig 5 Rail 6 Automatic stage 7 Camera 7a Lens 8 Glass plate 100 Liquid discharge defect detection apparatus 111 Image processing part 112 Coordinate calculation part 113 Difference calculation part 114 Determination part 200 Head 201 Head nozzle surface

Claims (9)

An imaging means for imaging a droplet ejected from a nozzle and flying from the ejection direction of the droplet;
Coordinate calculating means for calculating the coordinates of the droplet in a predetermined coordinate system on the captured image;
Difference calculating means for calculating a difference between the calculated coordinates and the coordinates of the droplet in the coordinate system when ejected normally;
A determination unit that compares the difference with a predetermined threshold, and determines that a discharge failure of the liquid droplets by the nozzle has occurred when the difference is greater than the threshold;
A liquid discharge defect detection device comprising: The nozzle can be mounted on an ink head of an ink jet recording apparatus that forms an image on a recording medium,
In the imaging means, the distance from the nozzle to the focal position of the imaging means is substantially the same as a predetermined reference distance representing the distance from the nozzle to the recording medium when mounted on the ink head. ,
The liquid discharge defect detection device according to claim 1. Further comprising changing means for changing the distance from the focal position to the nozzle;
The liquid discharge defect detection device according to claim 2. The imaging means images the plurality of droplets that are ejected continuously from the nozzle and fly,
The coordinate calculation means calculates the coordinates of each of the plurality of droplets to obtain a distribution of the plurality of coordinates, calculates the coordinates of the approximate center of the obtained distribution,
The difference calculating means calculates a difference between the coordinates of the substantially center and the coordinates of the droplet in the coordinate system when ejected normally;
The liquid discharge defect detection device according to claim 1. The imaging means images the plurality of droplets ejected from each of the plurality of nozzles arranged in a predetermined arrangement direction and flying,
The difference calculation means calculates the difference for each of the arrangement direction and a direction perpendicular to the arrangement direction,
The determination unit compares the difference in the arrangement direction with a predetermined arrangement direction threshold value with respect to the arrangement direction, and a difference between the difference in the right angle direction and a right angle direction threshold value predetermined with respect to the right angle direction. And when the difference in the arrangement direction is larger than the arrangement direction threshold value, or when the difference in the perpendicular direction is larger than the perpendicular direction threshold value, the ejection failure of the droplets by the nozzle has occurred. Judging,
The liquid discharge defect detection device according to claim 1. The arrangement direction threshold is smaller than the right-angle threshold;
The liquid discharge defect detection device according to claim 5. The imaging means images the plurality of droplets ejected from each of the plurality of nozzles arranged in a predetermined arrangement direction and flying,
Further comprising moving means for moving the imaging means in the arrangement direction;
The liquid discharge defect detection device according to claim 1. The imaging means is a high-speed camera capable of capturing more than 30,000 images per second;
The liquid discharge defect detection device according to claim 1. The imaging means has a depth of field greater than the product of the shutter speed and the droplet flight speed;
The liquid discharge defect detection device according to claim 1.

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