JP2007229928A - Liquid ejector and liquid ejection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid ejector which detects remaining liquid droplets on a nozzle surface, and a liquid ejection method. <P>SOLUTION: This liquid ejector comprises: a liquid ejection head with a nozzle plate 4 in which a nozzle 5 for ejecting a liquid toward a base material K is formed; a pressure generating means for forming a meniscus in a nozzle hole 10 by making the liquid in the nozzle 5 generate pressure by applying a driving voltage; an electrostatic voltage generating means for generating an electrostatic attraction force by applying an electrostatic voltage between the liquid ejection head 2 and the base material K; a movement means 20 for relatively moving the head 2; a camera 21 which has a light-emitting means and a CCD 23 so as to image an imaging object; a mirror 26 which adjusts an optical path so that an image of the nozzle hole 10 can be formed in the camera 21 in accordance with a position of the head 2; and an image analyzing means 25 which determines the presence or absence of the remaining liquid droplets on the nozzle surface by analyzing the taken image. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid ejection apparatus and a liquid ejection method, and more particularly, to an electrostatic suction type liquid ejection apparatus and a liquid ejection method.

  In recent years, it has been required to eject highly viscous ink droplets with high accuracy as the performance of ink jet image recording apparatuses increases and the applications expand. In order to improve the accuracy of the obtained image, it is necessary to miniaturize the nozzle that ejects ink droplets. To eject ink droplets with high viscosity, the drive voltage is increased to increase the liquid ejection force. There was a need. Therefore, the liquid in the nozzle is charged, an electric field is generated between the liquid in the nozzle and the substrate on which the liquid droplets are landed, and so-called electrostatic attraction type liquid droplet ejection is performed to eject liquid droplets by electrostatic attraction force. The device is known. According to such a droplet discharge device, high viscosity ink droplets can be discharged with high accuracy.

  However, when residual ink adheres to the nozzle surface of the liquid ejection head, even the residual ink is charged by the electric field between the nozzle surface and the substrate, and the ejected ink droplets repel the residual ink. There was a problem of flying in an unexpected direction. Therefore, although the nozzle surface of the liquid discharge head is made flat and the nozzle surface is cleaned by wiping, there is a problem that it is difficult to completely remove residual ink.

  In order to prevent the residual ink from adhering to the nozzle surface, for example, a method of performing cleaning until it is confirmed that there is no residual ink while observing the nozzle surface is conceivable. As one of the methods for observing the nozzle surface, as shown in Patent Document 1, there is a method of diverting an image pickup unit that picks up an image of a flying ink droplet ejected from a recording head from the side. However, since the imaging unit focuses on the nozzle, the depth of field becomes narrower as the nozzle provided in the liquid discharge head becomes finer, and it is difficult to detect residual ink. Further, since there is observation from one direction, there may be residual ink that cannot be detected. For example, when using ink that appears in substantially the same color as the nozzle surface due to light conditions, transparent ink, or the like, it is difficult to compare the residual ink and the nozzle surface because the S / N ratio of the image obtained by the imaging means is poor, and the residual ink May not be detected.

Also, as shown in Patent Document 2, a method of observing the nozzle surface with a plurality of cameras is also known. Specifically, the image pickup means is provided in a plurality of directions with respect to the nozzle surface of one liquid discharge head, and the liquid discharge head is moved relative to these image pickup means to align the image obtained by the image pickup means. To do. Further, the position of the nozzle is confirmed by vibrating the liquid discharge head to change the ink surface at the opening end of the nozzle, and the residual ink and the ink in the nozzle are distinguished.
JP-A-5-149769 Japanese Patent Laid-Open No. 10-44399

  However, according to Patent Document 2, since it is necessary to provide a plurality of cameras, there is a problem that the apparatus becomes complicated and cost reduction is difficult. In addition, since the optical path of each imaging unit is fixed and the alignment with the object to be imaged must be performed by relative movement of the liquid ejection head, there is a problem that it is difficult to adjust the optical path of the imaging unit.

  The present invention has been made in view of the above points, and without using a plurality of cameras, the liquid discharge head that detects the remaining liquid droplets on the nozzle surface by easily aligning the liquid discharge head and the imaging means. The purpose is to provide a device.

In order to solve the above-mentioned problem, the invention according to claim 1 is a liquid ejection apparatus,
A liquid ejection head having a cavity for storing liquid ejected from the nozzle, wherein a nozzle for ejecting liquid toward the substrate is formed;
Pressure generating means for applying a driving voltage to generate pressure in the liquid stored in the cavity to form a meniscus at the open end of the nozzle;
A counter electrode supporting the substrate;
An electrostatic voltage generating means for generating an electrostatic attraction force by applying an electrostatic voltage between the liquid discharge head and the counter electrode;
Optical path adjusting means for adjusting the optical path according to the position of the liquid ejection head;
Imaging means for imaging the nozzle surface of the liquid ejection head located on the optical path;
Image analysis means for analyzing the image captured by the imaging means to determine the presence or absence of residual droplets on the nozzle surface;
It is characterized by providing.

  According to the first aspect of the present invention, since the optical path is adjusted by the optical path adjusting means even if the liquid discharge head is relatively moved, the nozzle surface is positioned on the optical path without moving the imaging means itself, and The nozzle continues to form an image on the imaging means. The imaging means continues to image the open end of the nozzle, and the obtained image is analyzed by the image analysis means to determine the presence or absence of residual droplets near the nozzle on the nozzle surface.

According to a second aspect of the present invention, in the liquid ejection device according to the first aspect,
An inclination angle changing means for changing an inclination angle of the optical path adjusting means with respect to the nozzle surface;
A focus adjusting means for adjusting the focus of the imaging means,
When the optical path adjusting unit forms an image on the imaging unit with at least two optical paths having different paths, the optical path adjusting unit has 60% or more of image data in the same region included in an image captured in each optical path. It is characterized by adjusting so that it may become.

  According to the second aspect of the present invention, since the image data of the same region included in the images continuously captured by the imaging unit is 60% or more, the image analysis unit captures the same region captured with different optical paths. By comparing these image data, a change in the shape of the remaining droplet imaged due to a change in the optical path is detected. Therefore, residual droplets can be easily detected.

According to a third aspect of the present invention, in the liquid ejection device according to the first or second aspect,
The image pickup means picks up at least one of a meniscus formed at the opening end of the nozzle and a still image and a moving image of a flying droplet when discharging a droplet.

  According to the invention described in claim 3, since at least one of the meniscus formed at the opening end of the nozzle and the still image and the moving image of the flying droplet is captured by the imaging unit when the droplet is discharged. It is possible to analyze the image obtained by the image analysis means and observe the discharge state of the droplet.

According to a fourth aspect of the present invention, in the liquid ejection device according to the second or third aspect,
The image analysis unit is characterized in that the image captured by the imaging unit is geometrically corrected according to an inclination angle of the optical path adjustment unit with respect to the nozzle surface.

  According to the invention described in claim 4, the image analysis means outputs the inclination angle of the optical path adjustment means with respect to the nozzle surface from the inclination angle changing means, and geometrically corrects the image captured in accordance with the inclination angle, The presence or absence of residual droplets is determined by analyzing the corrected image.

The invention according to claim 5 is the liquid ejection apparatus according to claim 4,
The image analysis means takes a difference value of image data of the same region included in each of the two images after the geometric correction, and determines the presence or absence of residual droplets based on the difference value.

  According to the fifth aspect of the present invention, geometric correction is performed on the images continuously captured by the imaging unit according to the inclination angle of the optical path adjustment unit, and the same region included in each of the two images after geometric correction is obtained. The image data is compared to obtain a difference value, and the residual droplet is detected based on the difference value.

According to a sixth aspect of the present invention, in the liquid ejection device according to the fourth aspect,
The image analysis means calculates a variance of pixel values of image data in the same region included in each of the three or more images after the geometric correction, and detects residual droplets based on the calculation result. .

  According to the sixth aspect of the present invention, the images continuously picked up by the image pickup means are geometrically corrected according to the inclination angle of the optical path adjusting means, and the same image included in each of the three or more images after the geometric correction. The pixel value variance is calculated by comparing the image data of the regions, and a portion where the pixel value variance is large is detected as a residual droplet.

The invention according to claim 7 is the liquid ejection apparatus according to any one of claims 1 to 6,
It is characterized in that it is provided with a stain preventing means for protecting the optical path adjusting means from being attached to the optical path adjusting means when the droplet is discharged.

  According to the seventh aspect of the present invention, the contamination preventing means prevents the droplets and dirt discharged to the optical path adjusting means from adhering.

The invention according to claim 8 is the liquid ejection apparatus according to any one of claims 1 to 7,
A removing means for removing dirt adhering to the optical path adjusting means is provided.

  According to the eighth aspect of the present invention, the dirt attached to the optical path adjusting means is removed by the removing means.

The invention according to claim 9 is the liquid ejection apparatus according to any one of claims 1 to 8,
The optical path adjusting means is a mirror.

  According to the invention described in claim 9, by using a mirror as the optical path adjusting means, the optical path of the imaging means can be adjusted with a simple configuration.

The invention according to claim 10 is the liquid ejection apparatus according to any one of claims 1 to 9,
A cleaning means for cleaning the nozzle surface;
Control means for cleaning the nozzle surface by causing the cleaning means and the liquid ejection head to face each other when residual droplets are detected by the image analysis means;
It is characterized by providing.

  According to the tenth aspect of the present invention, when a residual liquid droplet is detected in the liquid ejection device, at least one of the liquid ejection head or the cleaning unit is moved so as to face each other, and the nozzle surface is cleaned.

The invention according to claim 11
A nozzle that discharges liquid toward the substrate is formed, and a drive voltage is applied to a liquid discharge head having a cavity that stores liquid discharged from the nozzle to generate pressure in the liquid stored in the cavity. Pressure generating step of forming a meniscus at the open end of the nozzle,
An electrostatic voltage generating step of generating an electrostatic attraction force by applying an electrostatic voltage between the counter electrode supporting the substrate and the liquid ejection head;
An optical path adjusting step of adjusting the optical path according to the position of the liquid ejection head;
An imaging step of imaging the nozzle surface of the liquid ejection head located on the optical path;
An image analysis step of analyzing the image data acquired by the imaging step to determine the presence or absence of residual droplets on the nozzle surface;
It is characterized by providing.

  According to the eleventh aspect of the present invention, even if the liquid discharge head is relatively moved, the optical path is adjusted in the optical path adjustment step, and the specific nozzle continues to be positioned on the optical path without moving the imaging unit itself. Then, the opening end of the nozzle located on the optical path is imaged by the imaging process, and the obtained image data is analyzed by the image analysis process to determine the presence or absence of residual droplets near the nozzle on the nozzle surface.

The invention according to claim 12 is the liquid ejection method according to claim 11,
An inclination angle changing step of changing an inclination angle with respect to the nozzle surface of the optical path adjusting means for adjusting the optical path;
A focus adjustment step of adjusting the focus of the imaging means,
In the optical path adjustment step, when the opening end of the nozzle is imaged by at least two optical paths having different paths, the image data of the same region included in the image captured by each optical path is adjusted to be 60% or more. It is characterized by that.

  According to the twelfth aspect of the present invention, the image data of the same region included in the images continuously picked up by the image pickup process is 60% or more. Therefore, the image data of the same region picked up with different optical paths is obtained. By comparing in the image analysis step, a change in the shape of the remaining liquid droplets caused by the change in the optical path is detected. Therefore, residual droplets can be easily detected.

The invention according to claim 13 is the liquid ejection method according to claim 12,
The image analysis step is characterized in that an image captured by the imaging unit is geometrically corrected according to an inclination angle of the optical path adjusting unit with respect to the nozzle surface.

  According to the thirteenth aspect of the present invention, in the image analysis step, the image captured in accordance with the inclination angle with respect to the nozzle surface of the optical path adjustment means is geometrically corrected, and the corrected image is analyzed to analyze the residual droplets. Judgment is made.

According to a fourteenth aspect of the present invention, in the liquid ejection method according to the thirteenth aspect,
The image analysis step is characterized in that a difference value of image data in the same region included in each of the two images after the geometric correction is taken and the presence or absence of residual droplets is determined based on the difference value.

  According to the fourteenth aspect of the present invention, geometric correction is performed on the images continuously captured by the imaging unit according to the inclination angle of the optical path adjustment unit, and the same region included in each of the two images after the geometric correction is performed. The image data is compared to obtain a difference value, and the residual droplet is detected based on the difference value.

According to a fifteenth aspect of the present invention, in the liquid ejection method according to the thirteenth aspect,
The image analysis step calculates a variance of pixel values of image data in the same region included in each of the three or more images after the geometric correction, and detects residual droplets based on the calculation result. .

  According to the fifteenth aspect of the present invention, the images continuously picked up by the image pickup means are geometrically corrected according to the inclination angle of the optical path adjusting means, and the same image included in each of the three or more images after the geometric correction. The pixel value variance is calculated by comparing the image data of the regions, and a portion where the pixel value variance is large is detected as a residual droplet.

The invention according to claim 16 is the liquid ejection method according to any one of claims 11 to 15,
When discharging a droplet, the optical path adjusting means is protected from being attached to the droplet.

  According to the sixteenth aspect of the present invention, it is possible to prevent the droplets and dirt discharged to the optical path adjusting means from adhering.

The invention according to claim 17 is the liquid ejection method according to any one of claims 11 to 16,
A removal step of removing dirt adhering to the optical path adjusting means is provided.

  According to the invention described in claim 17, the dirt attached to the optical path adjusting means is removed by the removing step.

The invention according to claim 18 is the liquid ejection method according to claims 11 to 17,
The method includes a cleaning step of cleaning the nozzle surface when residual droplets are detected by the image analysis step.

  According to the invention described in claim 18, when the residual liquid droplet is detected in the image analysis step, the nozzle surface is cleaned.

  According to the invention described in claim 1 or 11, the image pickup means can easily focus on the nozzle and continue to pick up an image by the optical path adjusting means. Therefore, it is possible to determine the presence or absence of residual droplets on the nozzle surface by analyzing an image obtained by imaging the vicinity of the nozzle. Further, since it is not necessary to move the image pickup means itself and only one image pickup means is provided, the apparatus can be simplified and the cost can be reduced.

  According to the second or twelfth aspect of the present invention, the images continuously captured by the imaging means each include 60% or more of the same region of image data, so that the images captured with different optical paths by image analysis are compared. Thus, the residual droplet can be easily detected. Therefore, it is possible to easily determine the presence or absence of residual droplets on the nozzle surface. Further, since the optical path adjusting means adjusts the optical path by changing the tilt angle with respect to the nozzle surface, the apparatus can be simplified without requiring a complicated configuration.

  According to the third aspect of the present invention, it is possible to observe the discharge state of the liquid droplets by the imaging unit. Therefore, by providing one imaging means, it is possible to observe the nozzle surface and the droplet discharge state.

  According to the invention of claim 4 or 13, since the image is geometrically corrected in accordance with the inclination angle of the optical path adjusting means with respect to the nozzle surface, the change in the image due to the change in the inclination angle of the optical path adjusting means with respect to the nozzle surface is corrected. be able to. Therefore, the image can be analyzed without being affected by the change in the tilt angle with respect to the nozzle surface of the optical path adjusting means, and the presence or absence of residual droplets can be accurately determined.

  According to the invention described in claim 5 or 14, the difference is calculated in consideration of the change in the inclination angle of the optical path adjusting means by image analysis using the image data of the same region included in each of the two images after geometric correction. Since the value is obtained, the residual droplet can be detected without being affected by the change in the tilt angle of the optical path adjusting means. Further, since the change in the imaging shape of the residual droplet due to the difference in the optical path is determined based on the difference value, it is possible to detect the residual droplet easily and accurately.

  According to the invention described in claim 6 or 15, the change in the inclination angle of the optical path adjusting means is taken into account by image analysis using image data of the same region included in each of the three or more images after geometric correction. Thus, the dispersion of pixel values is obtained, so that it is possible to detect residual droplets without being affected by the change in the tilt angle of the optical path adjusting means. In addition, since the change in the imaging shape of the residual droplet due to the difference in the optical path is determined based on the dispersion of the pixel values, it is possible to detect the residual droplet easily and accurately.

  According to the invention described in claim 7 or 16, since dirt such as droplets is prevented from adhering to the optical path adjusting means, the imaging means does not capture the dirt adhering to the optical path adjusting means, and the residual It is possible to accurately determine the presence or absence of a droplet.

  According to the eighth or seventeenth aspect of the present invention, even if dirt is attached to the optical path adjusting means, it is removed, so it is possible to accurately determine the presence or absence of residual droplets.

  According to the ninth aspect of the present invention, since the optical path adjustment means has a simple configuration and the optical path of the image pickup means can be easily adjusted, it is possible to prevent the apparatus itself from becoming large and complicated. is there.

  According to the tenth or eighteenth aspect of the invention, when the residual liquid droplet is detected in the liquid ejection device, the nozzle surface is cleaned, so that the liquid droplet is discharged with the residual liquid droplet attached to the nozzle surface. It is possible to prevent the liquid from being ejected, and it is possible to land the liquid droplet at an accurate position.

  Hereinafter, an embodiment of a liquid ejection apparatus according to the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

  As shown in FIG. 1, a liquid ejection apparatus 1 according to the present embodiment ejects liquid droplets from a liquid ejection head 2 toward a substrate K. The liquid ejection apparatus 1 includes a flat counter electrode 3 that supports the base material K. The counter electrode 3 is grounded and is always maintained at the ground potential.

  As shown in FIG. 2, the liquid ejection apparatus 1 includes a liquid ejection head 2 that ejects liquid toward the substrate K in parallel with the counter electrode 3. The gap between the liquid discharge head 2 and the counter electrode 3 is adjusted within a range of about 0.1 to 3.0 mm. As the liquid discharge head 2, a so-called serial method or line method can be applied.

A resin nozzle plate 4 is provided on the substrate K side of the liquid discharge head 2. In the present embodiment, the thickness of the nozzle plate 4 is preferably 75 μm or more for stable droplet discharge. The nozzle plate 4 is made of an insulator and has a volume resistivity of 10 ¹⁵ Ωm or more.

  In the nozzle plate 4, a plurality of nozzles 5 that eject droplets D of chargeable liquid L such as ink are perforated. The nozzle 5 is formed so as to change its diameter in a tapered manner toward the base material K. The length of the opening diameter of the nozzle 5 is preferably 15 μm or less so that liquid can be stably discharged even at low electric field strength. Further, the cross-sectional shape of the nozzle 5 is not limited to the tapered shape, and can be changed as appropriate. The opening end shape of the nozzle 5 may be a polygonal shape or a star shape in addition to a circular shape.

  Further, the nozzle plate 4 is formed in a planar shape and is arranged so as to be parallel to the substrate K. Here, the planar nozzle plate 4 indicates that the nozzle 5 does not protrude from the nozzle plate 4 or the protruding amount of the nozzle 5 is about 30 μm or less. By using a flat nozzle plate, there is an advantage that the nozzle plate surface can be easily cleaned.

  On the surface of the nozzle plate facing the base material K, a liquid repellent layer 6 for suppressing the oozing of the liquid L from the nozzle 5 is provided. A nozzle hole 10 is formed at a position corresponding to the opening of the nozzle 5 in the liquid repellent layer 6. The nozzle surface in the present embodiment is a surface facing the substrate K of the liquid repellent layer 6. For the liquid repellent layer 6, for example, a material having water repellency is used if the liquid L is aqueous, and a material having oil repellency is used if the liquid L is oily. There is no restriction | limiting in particular in the material and formation method of the liquid repellent layer 6, A well-known thing can be used suitably, In order to improve the adhesiveness of the liquid repellent layer 6, you may form into a film through an intermediate | middle layer.

  On one surface of the nozzle plate 4 opposite to the liquid repellent layer 6, charging electrodes 7 for applying an electrostatic voltage to charge the liquid L are provided in layers. The charging electrode 7 is mainly made of a conductive material such as NiP. The charging electrode 7 extends to the inner peripheral surface of the nozzle 5 and is in contact with the liquid L in the nozzle 5.

  The charging electrode 7 is connected to an electrostatic voltage power supply 8 as an electrostatic voltage applying means for applying an electrostatic voltage. The electrostatic voltage power supply 8 is connected to a control means 9 to be described later, and the application operation of the electrostatic voltage is controlled. Since the counter electrode 3 is grounded, an electrostatic attraction force is generated between the liquid ejection head 2 and the counter electrode 3, particularly between the liquid L and the base material K when the liquid L is charged. It is like that. Further, when the droplet D made of the charged liquid L lands on the substrate K, the counter electrode 3 releases the electric charge by grounding.

  On the other surface side of the charging electrode 7, a body layer 13 is provided in a layered form. A substantially cylindrical cavity 14 having the same cross section as the nozzle 5 is formed at a position facing each nozzle 5 in the body layer 13. In each cavity 14, the liquid L discharged through the nozzle 5 is temporarily stored. Each cavity 14 communicates with a flow path (not shown) for supplying the liquid L from an external liquid tank (not shown).

  On the other surface side of the body layer 13, a flexible layer 15 made of a flexible metal thin plate, silicon, or the like is provided. Piezo elements 16 that are piezoelectric element actuators are provided at positions corresponding to the cavities 14 on the other surface side of the flexible layer 15. A driving voltage power source 17 that applies a driving voltage for deforming the piezo element 16 is connected to the piezo element 16. In the present embodiment, the pressure generating means includes a piezo element 16 and a drive voltage power source 17, and as shown in FIG. 3, the piezo element 16 is deformed by applying a drive voltage, and pressure is generated in the liquid L in the nozzle 5. A meniscus is formed in the opening of the nozzle 5. The drive voltage power supply 17 is connected to a control means 9 to be described later, and the drive voltage application operation is controlled. In addition to the piezoelectric element actuator as in the present embodiment, for example, an electrostatic actuator, a thermal method, or the like can be employed as the pressure generating unit.

  As shown in FIG. 1, the liquid ejection head 2 is connected to a moving unit 20 that moves the liquid ejection head 2 relative to the counter electrode 3. Control means 9 for controlling the relative movement of the liquid ejection head 2 is connected to the movement means 20, and the amount of movement of the liquid ejection head 2 is output to the control means 9 (see FIG. 9). . The moving means 20 also adjusts the gap between the liquid ejection head 2 and the counter electrode 3, and moves the liquid ejection head 2 upward so as to move away from the counter electrode 3 based on an instruction from the control means 9. It is like that.

  In the gap between the liquid discharge head 2 and the substrate K, a camera 21 is provided as an imaging means. The camera 21 includes a camera support stage 22 that supports the camera 21 while adjusting the angle of the camera 21 with respect to the liquid ejection head 2. As shown in FIG. 4, the camera 21 detects at least one of a meniscus formed in the nozzle hole 10 and a still image or moving image of the flying droplet D to detect abnormal ejection of the droplet. A known camera can be used as the camera 21 without any particular limitation, but a CCD camera is preferable because it can continuously image an object to be imaged. The camera 21 is provided with a light emitting element (not shown) that emits light. The camera 21 is provided with a CCD 23 as a photoelectric conversion element that converts the intensity of incident light reflected by the imaging object into an electric signal. Further, the camera 21 is provided with a zoom lens 24 as a focus adjusting means for adjusting the focus of the camera 21. The camera 21 is connected to an image analysis means 25 for analyzing the captured image, and the obtained image data is sequentially output.

  As shown in FIG. 5, the optical path of the camera 21 includes a mirror 26 that adjusts the path of light emitted from the camera 21 as an optical path adjusting unit. The mirror 26 reflects the light emitted from the camera 21 toward the nozzle surface, and reflects the light reflected by the nozzle surface toward the camera 21. As shown in FIG. 6, the mirror 26 is rotatably supported, and an inclination angle changing means 28 (see FIG. 7) for changing the inclination angle of the mirror 26 with respect to the nozzle surface is connected to the support portion 27. Yes. A mirror moving arm 29 for moving the mirror 26 relative to the liquid ejection head 2 is connected to the support portion 27 of the mirror 26. The control means 9 is connected to the mirror moving arm 29, and the mirror 26 is moved according to the usage status of the mirror 26.

  As shown in FIG. 7, a mirror protective cover 30 is provided on the side of the mirror 26 as a dirt preventing means for preventing the ejected ink from adhering to the mirror 26 when the mirror 26 is not used. The mirror protection cover 30 is formed in a U-shaped cross section, and the mirror 26 tilted by the tilt angle changing means 28 is moved by the mirror moving arm 29 and accommodated. The mirror protection cover 30 is provided with a mirror wiper 31 that removes dirt adhering to the mirror 26 when the mirror 26 is accommodated.

  As shown in FIG. 8, a cleaning table 32 for cleaning the nozzle surface of the liquid ejection head 2 is provided on the side of the counter electrode 3. The cleaning table 32 is provided with a nozzle wiper 33 for wiping the nozzle surface so as to face the nozzle surface when the liquid ejection head 2 is moved above the cleaning table 32. The nozzle wiper 33 is made of an elastic material, and wipes without damaging the nozzle surface while removing residual ink. In the present embodiment, the nozzle wiper 33 is used as the cleaning unit, but the cleaning unit is not particularly limited and can be appropriately changed.

  Next, the control configuration of the liquid ejection apparatus 1 will be described.

  As shown in FIG. 9, the liquid ejection apparatus 1 according to the present embodiment includes a driving voltage power source 17, an electrostatic voltage power source 8, a moving unit 20, a camera 21, a tilt angle changing unit 28, a mirror moving arm 29, a nozzle wiper 33, and A control means 9 is provided which is electrically connected to the image analysis means 25 and controls them. The control means 9 is composed of a computer configured by connecting a CPU 9a, ROM 9b, RAM 9c and the like by a BUS (not shown). The control means 9 expands the power supply control program stored in the ROM 9b on the RAM 9c and causes the CPU 9a to execute it.

  When discharging the droplet D onto the substrate K, the control means 9 controls the droplet D to be discharged while moving the liquid discharge head 2 relative to the substrate K by the moving means 20. The control means 9 applies an electrostatic voltage from the electrostatic voltage power supply 8 to generate an electric field between the liquid L and the substrate K, and generates a pressure on the liquid L by the pressure generating means to eject the droplet D. It is controlled to let you. In addition, the control unit 9 causes the camera 21 to capture at least one of a meniscus formed at the opening end of the nozzle 5 and a still image and a moving image of the flying droplet D. The obtained image data is output to the image analysis unit 25, and the control unit 9 controls the image analysis unit 25 to analyze the image data and detect abnormal ejection in order to observe the liquid ejection state.

  When determining the presence or absence of residual ink on the nozzle surface of the liquid ejection head 2, the control means 9 controls the camera 21 so that the nozzle surface is imaged and the obtained image data is analyzed by the image analysis means 25. Yes. At this time, the control unit 9 controls the tilt angle changing unit 28 to change the tilt angle of the mirror 26 with respect to the nozzle surface to adjust the optical path from the camera 21 and to cause the camera 21 to image the vicinity of the nozzle hole 10. Yes. Further, the control means 9 outputs the inclination angle with respect to the nozzle surface of the mirror 26 at the time of imaging to the image analysis means 25, and the image analysis means 25 performs analysis after geometric correction of the image data. The image analysis unit 25 outputs a determination result of the presence or absence of residual ink to the control unit 9, and the control unit 9 performs control so that maintenance of the liquid ejection apparatus 1 is performed when it is determined that residual ink exists on the nozzle surface. Yes.

  During maintenance of the liquid ejection apparatus 1, the control unit 9 controls the moving unit 20 to move the liquid ejection head 2 above the cleaning table 32 and to wipe the nozzle surface of the liquid ejection head 2 using the nozzle wiper 33. ing. The control means 9 controls the tilt 26 to be wiped by the mirror wiper 31 while the mirror 26 is tilted by the tilt angle changing means 28 and the mirror 26 is accommodated in the mirror protection cover 30 by the mirror moving arm 29. Yes.

  Next, a liquid discharge method using the liquid discharge apparatus 1 of the present embodiment will be described.

FIG. 3 is a diagram for explaining drive control of the liquid ejection head 2 by the control means 9. In the present embodiment, for example, constant electrostatic voltage V _C applied from the electrostatic voltage power source 8 to the charging electrode 7 is set to 1.5 kV, it is applied from the drive voltage supply 17 to the piezoelectric element 16 that pulsed drive voltage V _P is set to 20V.

  First, the tilt angle changing means 28 tilts the mirror 26 to an angle that can be accommodated in the mirror protection cover 30. The mirror moving arm 29 passes the mirror 26 through the opening of the mirror protection cover 30 and accommodates it.

The electrostatic voltage generating step, the electrostatic voltage power source 8, the charging electrode 7 is applied a constant electrostatic voltage V _C, an electric field is generated between each nozzle 5 and the counter electrode 3 of the liquid discharge head 2 ( (See A in FIG. 3). Further, in the pressure generation process, the drive voltage power supply 17 applies a pulsed drive voltage Vp to deform the piezoelectric element 16. Due to the deformation of the piezo element 16, the pressure of the liquid L inside the nozzle 5 increases, and a meniscus is formed in the nozzle hole 10 (see B in FIG. 3).

Thus, when a meniscus is formed in a state where an electric field is generated between the nozzle 5 and the counter electrode 3, a high electric field concentration occurs at the tip of the meniscus, and a very strong electrostatic force is applied. Stopping the application of the drive voltage V _P in this state, the meniscus is torn off the droplet D without mist or satellite occurs is discharged (see in Fig. 3 C). The discharged droplet D flies toward the substrate K, is accelerated by an electric field, and is sucked toward the counter electrode 3 (see D in FIG. 3). When the droplet D lands on the target point of the base material K supported by the counter electrode 3, the electric charge provided in the droplet D moves to the grounded portion of the counter electrode 3 and is removed (see E in FIG. 3).

  When ejecting the droplet D, the camera 21 is rotatably supported by the camera support stage 22, and captures a meniscus or a flying image of the flying droplet D formed at the opening end of the nozzle 5. The obtained image data is output to the image analysis unit 25, and the image analysis unit 25 determines whether or not the ejection state of the droplet D is normal. The determination result is output to the control means 9, and abnormal ejection of the droplet D is detected.

  Next, a residual droplet detection method using the liquid ejection apparatus 1 of the present embodiment will be described. Detection of residual liquid droplets on the nozzle surface of the liquid ejection head 2 may be performed every time a predetermined amount of liquid is ejected, or may be performed every certain time.

  In the optical path adjustment step, the control means 9 takes out the mirror 26 from the mirror protective cover 30 by the mirror moving arm 29 and moves it on the optical axis of the camera 21 and below the nozzle surface. Further, the control means 9 calculates the tilt angle of the mirror 26 based on the positional relationship between the position of the mirror 26 and the camera 21 and the nozzle hole 10. The calculated tilt angle is output to the tilt angle changing means 28, and the tilt angle of the mirror 26 is changed by the tilt angle changing means 28. The camera 21 adjusts the position of the zoom lens 24 on the optical axis and adjusts the focal point so that the nozzle hole 10 forms an image on the CCD 23.

  Subsequently, in the imaging process, the light emitting element of the camera 21 emits light rays forward. The emitted light enters the mirror 26 and is reflected toward the nozzle surface. The light beam reflected by the nozzle surface is reflected by the mirror 26, passes through the zoom lens 24, and enters the CCD 23. The CCD 23 converts the incident light beam into an electrical signal, and the camera 21 images the vicinity of the nozzle hole 10 to be imaged. The image data obtained in this way is output to the image analysis means 25.

  Thereafter, the liquid ejection head 2 is moved by the moving means 20, and the optical path adjustment process is performed by changing the tilt angle of the mirror 26 in accordance with the amount of movement of the nozzle 5 to be imaged. Based on the amount of movement of the liquid ejection head 2, the control unit 9 calculates the tilt angle of the mirror 26 that causes the imaging target nozzle hole 10 to form an image on the camera 21. At this time, the control unit 9 performs calculation so that 60% or more of the area of the nozzle surface imaged before the liquid ejection head 2 moves is imaged. The nozzle surface is imaged by the imaging process using the camera 21 after changing the tilt angle and adjusting the focal point based on the calculation result by the method described above. The obtained image data is sequentially output to the image analysis means 25.

  In this way, the control unit 9 moves the liquid ejection head 2 by a minute amount so that the image data of the same region included in continuously captured images is 60% or more, and every time it moves, the nozzle The vicinity of the hole 10 is imaged (see FIG. 6). The image captured in FIG. 6 (a) is shown in FIG. 10, the image captured in FIG. 6 (b) is shown in FIG. 11 (a), and the image captured in FIG. 6 (c) is shown in FIG. ). Further, in FIGS. 11A and 12A, the region where the same region of the nozzle surface is imaged is inside the dotted line.

Thereafter, in the image analysis step, the image analysis means 25 detects residual ink based on the obtained image data.
First, the image analysis means 25 geometrically corrects the obtained image data based on the tilt angle of the mirror 26 when imaged. After the geometric correction, the shape of the nozzle hole 10 can be obtained in a plan view, but the residual ink cannot cancel the influence of projection, and light incident on the residual ink as shown in FIGS. 11B and 12B. The effect of the angle remains in the image data.

  When there are two images to be compared, the image analysis unit 25 compares the image data of the same region after geometric correction, obtains a difference value between the pixels, and determines the presence or absence of residual ink based on the difference value. Further, when comparing three or more consecutive images, the image analysis unit 25 compares the image data of the same region after geometric correction, calculates the dispersion of pixel values, and detects the presence or absence of residual ink. In the dispersed image of the same region included in the image data after geometric correction, the residual ink is expressed as shown in FIG. 13, and its presence can be easily detected.

  The residual ink detection result by the image analysis means 25 is output to the control means 9. When there is no residual ink, the control means 9 resumes normal liquid ejection as described above. On the other hand, when the control unit 9 detects the presence of residual ink, the control unit 9 performs a cleaning process and performs maintenance of the liquid ejection apparatus 1.

  First, the control means 9 stops the application of the drive voltage and the electrostatic voltage, and once stops the liquid ejection. Then, the moving unit 20 moves the liquid ejection head 2 above the cleaning table 32 so that the nozzle surface and the nozzle wiper 33 face each other. When the nozzle surface of the liquid discharge head 2 and the nozzle wiper 33 face each other, the nozzle wiper 33 moves relative to the nozzle surface and wipes the nozzle surface. When the wiping of the nozzle surface is completed, the liquid ejection head 2 is moved again to a position facing the substrate K by the moving means 20.

  On the other hand, the control means 9 controls the mirror moving arm 29 and the tilt angle changing means 28 so that the mirror 26 is accommodated in the mirror protection cover 30. When the mirror 26 is accommodated in the mirror protection cover 30, the mirror 26 is wiped off by the mirror wiper 31. When the mirror 26 is cleaned in this way, the mirror 26 returns to the original position again.

  As described above, according to the liquid ejection apparatus 1 of the present embodiment, the camera 21 can easily focus on the nozzle hole 10 and continue to capture images by changing the tilt angle of the mirror 26. Therefore, it is possible to determine the presence or absence of residual ink on the nozzle surface by analyzing an image obtained by imaging the vicinity of the nozzle hole 10. Further, since the optical path can be easily adjusted by changing the tilt angle of the mirror 26, the camera 21 itself is not moved, and the apparatus and the control can be simplified.

  In addition, since images continuously captured by the camera 21 include 60% or more of image data in the same region, the image analysis means 25 can easily detect a change in the nozzle surface by comparing consecutive images. . Therefore, it is possible to easily determine whether there is residual ink on the nozzle surface.

  Further, the camera 21 that has been conventionally used for observing the discharge state of the liquid droplets can be used as the image pickup unit. By providing one image pickup unit, observation of the nozzle surface and observation of the liquid drop discharge state can be performed. Is possible.

  Further, since the image analysis unit 25 geometrically corrects the image according to the tilt angle of the mirror 26 with respect to the nozzle surface, the image change due to the change of the tilt angle with respect to the nozzle surface of the mirror 26 can be corrected, and the residual accurately. It is possible to determine the presence or absence of a droplet. Since the image analysis unit 25 determines the presence or absence of residual ink by obtaining a difference value or pixel dispersion value of image data, a change in the imaging shape of the residual ink due to a difference in the optical path, for example, due to an ink shadow or irregular reflection of light. A change in shape can be detected. Therefore, it is possible to detect the residual ink easily and accurately.

  Further, since the mirror protective cover 30 or the mirror wiper 31 is provided to prevent the liquid droplets from adhering to the mirror 26, the liquid droplets adhering to the optical path adjusting means are not imaged by the imaging means, and the residual liquid It is possible to accurately determine the presence or absence of drops.

  Further, since the nozzle surface is cleaned when the residual ink is detected, it is possible to prevent the droplet D from being discharged with the residual ink attached to the nozzle surface. It is possible to land on the exact position of the material K.

It is a schematic block diagram of the liquid discharge apparatus in this embodiment. It is a schematic block diagram of the liquid discharge head in this embodiment. It is explanatory drawing which shows operation control of the liquid discharge method in this embodiment. It is a figure which shows the observation of the liquid discharge state in this embodiment. It is a figure which shows observation of the nozzle surface in this embodiment. FIG. 6A is a diagram illustrating adjustment of an optical path in the present embodiment, FIG. 6A is a diagram illustrating an optical path before the liquid ejection head is moved, and FIG. 6B is a diagram in which the liquid ejection head is moved away from the camera. FIG. 6C is a diagram illustrating the optical path after adjustment when the liquid ejection head moves in a direction approaching the camera. It is a figure which shows the removal of the stain | pollution | contamination adhering to the mirror in this embodiment. It is a figure which shows the cleaning of the nozzle surface in this embodiment. It is a block diagram which shows the control structure of the liquid discharge apparatus in this embodiment. It is a figure which shows the image imaged in Fig.6 (a). FIG. 11A is an image captured in FIG. 6B, and FIG. 11B is an image after geometric correction. FIG. 12A is an image captured in FIG. 6C, and FIG. 12B is an image after geometric correction. It is the dispersion | distribution image of the pixel value of the image data of FIG. 10, the image data of FIG.11 (b), and the image data of FIG.12 (b).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid discharge apparatus 2 Liquid discharge head 3 Counter electrode 4 Nozzle plate 5 Nozzle 6 Liquid repellent layer 7 Electrode for charging 8 Electrostatic voltage power supply 9 Control means 10 Nozzle hole 16 Piezo element 17 Drive voltage power supply 20 Moving means 21 Camera 22 Camera support Stage 23 CCD
24 Zoom lens 25 Image analysis means 26 Mirror 28 Inclination angle changing means 29 Mirror moving arm 30 Mirror protective cover 31 Mirror wiper 32 Cleaning stand 33 Nozzle wiper

Claims (18)

A liquid ejection head having a cavity for storing liquid ejected from the nozzle, wherein a nozzle for ejecting liquid toward the substrate is formed;
Pressure generating means for applying a driving voltage to generate pressure in the liquid stored in the cavity to form a meniscus at the open end of the nozzle;
A counter electrode supporting the substrate;
An electrostatic voltage generating means for generating an electrostatic attraction force by applying an electrostatic voltage between the liquid discharge head and the counter electrode;
Optical path adjusting means for adjusting the optical path according to the position of the liquid ejection head;
Imaging means for imaging the nozzle surface of the liquid ejection head located on the optical path;
Image analysis means for analyzing the image captured by the imaging means to determine the presence or absence of residual droplets on the nozzle surface;
A liquid ejection apparatus comprising: An inclination angle changing means for changing an inclination angle of the optical path adjusting means with respect to the nozzle surface;
A focus adjusting means for adjusting the focus of the imaging means,
When the optical path adjusting unit forms an image on the imaging unit with at least two optical paths having different paths, the optical path adjusting unit has 60% or more of image data in the same region included in images captured by the respective optical paths. The liquid ejection device according to claim 1, wherein the liquid ejection device is adjusted as follows.   The image pickup unit picks up at least one of a meniscus formed at an opening end of the nozzle and a still image and a moving image of a flying droplet when discharging a droplet. Liquid discharge device.   The liquid ejection apparatus according to claim 2, wherein the image analysis unit geometrically corrects an image captured by the imaging unit according to an inclination angle of the optical path adjustment unit with respect to the nozzle surface.   5. The image analysis means takes a difference value of image data of the same region included in each of the two images after the geometric correction, and determines the presence or absence of residual droplets based on the difference value. The liquid discharge apparatus according to 1.   The image analysis means calculates a variance of pixel values of image data in the same region included in each of the three or more images after the geometric correction, and detects residual droplets based on the calculation result. The liquid ejection apparatus according to claim 4.   The liquid ejection apparatus according to claim 1, further comprising a dirt prevention unit that protects the optical path adjustment unit from being attached to the optical path adjusting unit when the droplet is ejected.   The liquid ejecting apparatus according to claim 1, further comprising a removing unit that removes dirt adhering to the optical path adjusting unit.   The liquid ejecting apparatus according to claim 1, wherein the optical path adjustment unit is a mirror. A cleaning means for cleaning the nozzle surface;
Control means for cleaning the nozzle surface by causing the cleaning means and the liquid ejection head to face each other when residual droplets are detected by the image analysis means;
The liquid ejecting apparatus according to claim 1, comprising: A nozzle that discharges liquid toward the substrate is formed, and a drive voltage is applied to a liquid discharge head having a cavity that stores liquid discharged from the nozzle to generate pressure in the liquid stored in the cavity. Pressure generating step of forming a meniscus at the open end of the nozzle,
An electrostatic voltage generating step of generating an electrostatic attraction force by applying an electrostatic voltage between the counter electrode supporting the substrate and the liquid ejection head;
An optical path adjusting step of adjusting the optical path according to the position of the liquid ejection head;
An imaging step of imaging the nozzle surface of the liquid ejection head located on the optical path;
An image analysis step of analyzing the image data acquired by the imaging step to determine the presence or absence of residual droplets on the nozzle surface;
A liquid ejection method comprising: An inclination angle changing step of changing an inclination angle with respect to the nozzle surface of the optical path adjusting means for adjusting the optical path;
A focus adjustment step of adjusting the focus of the imaging means,
In the optical path adjustment step, when the opening end of the nozzle is imaged by at least two optical paths having different paths, the image data of the same region included in the image captured by each optical path is adjusted to be 60% or more. The liquid discharging method according to claim 11.   The liquid ejection method according to claim 12, wherein the image analysis step geometrically corrects an image captured by the imaging unit according to an inclination angle of the optical path adjusting unit with respect to the nozzle surface.   14. The image analysis step takes a difference value of image data of the same region included in each of the two images after the geometric correction, and determines the presence or absence of residual droplets based on the difference value. The liquid discharge method described in 1.   The image analysis step calculates a variance of pixel values of image data in the same region included in each of the three or more images after the geometric correction, and detects residual droplets based on the calculation result. The liquid ejection method according to claim 13.   The liquid discharge method according to claim 11, wherein a droplet is protected from adhering to the optical path adjusting unit when the droplet is discharged.   The liquid discharging method according to any one of claims 11 to 16, further comprising a removing step of removing dirt adhered to the optical path adjusting unit.   The liquid ejection method according to claim 11, further comprising a cleaning step of cleaning the nozzle surface when residual droplets are detected by the image analysis step.

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