JP2006192788A - Liquid-ejecting apparatus, image-forming apparatus and ejection-detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid-ejecting apparatus which enables a plurality of droplets ejected from a plurality of liquid droplet-ejection openings to be detected nearly simultaneously, and which can achieve shortening of a detection time and improvement of a detection precision, and to provide an image-forming apparatus and an ejection-detecting method. <P>SOLUTION: A light-emitting means and a light-receiving means for optically detecting the ejected liquid droplets are arranged. At least two ejection openings which have an ejection opening interval distance nearer than a predetermined regulation distance (L) along a light axis direction of detection light are selected as detection objects of the simultaneous detection. When a flight direction abnormality (droplet E) and a flight velocity abnormality (droplet D) take place in regard to the plurality of liquid droplets nearly simultaneously ejected from at least two ejection openings in the positional relationship, the liquid droplets (droplet D and droplet E) located behind with respect to an advance direction of the detection light come out of a shadow region 120 of the liquid droplet C located ahead. In consequence, the detection light is blocked also by the liquid droplets (droplet D and droplet E) of the flight abnormality, whereby a detection signal changes greatly. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid ejection apparatus, an image forming apparatus, and an ejection detection method, and more particularly to a liquid ejection apparatus suitable for detecting ejection failure in an inkjet head in which a large number of liquid droplet ejection ports (nozzles) are two-dimensionally arranged. The present invention relates to an image forming apparatus and a discharge detection method thereof.

  An ink jet recording apparatus forms an image on a recording medium by ejecting ink from the nozzles while relatively moving a recording head (also called a print head) in which a plurality of nozzles are arranged and a recording medium. . In this type of apparatus, ink is no longer ejected from the nozzles due to ink thickening or air bubble mixing, or the amount of ink ejected (dot size to be ejected onto the recording medium) or droplet ejection position (flying) Incorrect ejection may occur, such as inappropriate orientation.

  For this reason, conventionally, there has been known a method of detecting ink shortage or ejection failure by irradiating a droplet discharged from a recording head with light such as laser light and detecting a light amount variation due to light blockage by an optical sensor. (Patent Documents 1 and 2).

  In Patent Document 1, the discharge timing of the nozzle group is shifted in the range of the discharge cycle with respect to the discharge of the other nozzle groups, thereby simplifying the position adjustment between the optical axis and the nozzle and improving the detection speed.

On the other hand, in Patent Document 2, by detecting the timing and time when a droplet is applied to the light beam of a laser detector, or by detecting a single nozzle from a plurality of directions by a plurality of laser detection systems, A tail curve (bending in the flight direction) is detected. It also discloses that the tail bend is corrected by changing the drive waveform after detecting the tail bend.
JP-A-2003-191453 Japanese Patent Laid-Open No. 2002-361863

  However, the technique disclosed in Patent Document 1 controls the timing of droplets present in a detection light beam in a time-sharing manner, and a plurality of droplets cannot be present in the light beam at the same time. For this reason, it is necessary to discharge the nozzles one by one at different timings, and it takes a certain amount of time to finish detecting the discharged droplets for all the nozzles.

  On the other hand, since the technique disclosed in Patent Document 2 performs detection by paying attention to the passage time of a droplet passing through the detection light beam, it cannot be detected unless the amount of bending in the flight direction is relatively large. . That is, although it is possible to detect a tail bend that shows an extremely abnormal direction with reference to normal ejection, it is considered difficult to detect a bend with a small degree of bend, and the detection accuracy is not high.

  The present invention has been made in view of such circumstances, and can detect a plurality of droplets discharged from a plurality of droplet discharge ports substantially simultaneously, thereby realizing a reduction in detection time and an improvement in detection accuracy. It is an object of the present invention to provide a liquid ejection apparatus, an image forming apparatus, and an ejection detection method.

  In order to achieve the above object, a liquid discharge apparatus according to the first aspect of the present invention includes a liquid discharge head having a plurality of discharge ports for discharging droplets, and at least two of the plurality of discharge ports to be detected. Light emitting means for generating detection light that intersects the droplet flight path of the discharge port, and detection light that has passed through the droplet flight path of at least two discharge ports to be detected, and detection according to the received light amount A light receiving means for outputting a signal, and a distance between the discharge ports which is disposed on a line parallel to the optical axis of the detection light among the plurality of discharge ports, and is along a direction of the optical axis is smaller than a predetermined specified distance; A discharge port selecting unit that selects at least two discharge ports as the detection target; a discharge control unit that performs discharge driving for discharging droplets from the at least two discharge ports selected by the discharge port selecting unit substantially simultaneously; and Based on the detection signal obtained from the light receiving means when the liquid droplets ejected by the ejection drive of the ejection control means pass through the detection light, the ejection state of the liquid droplets from at least two ejection ports as detection targets is determined. And a discharge state determining means.

  According to the present invention, the light emitting means and the light receiving means for optically detecting the ejected liquid droplets are arranged, and the optical axis of the detection light from the ejection openings arranged on a line parallel to the optical axis of the detection light. At least two discharge ports having a distance between the discharge ports that is shorter than a predetermined specified distance along the direction are selected as detection targets for simultaneous detection. A plurality of droplets ejected substantially simultaneously from at least two ejection openings in such a positional relationship, when they are ejected normally, overlap each other when viewed in a cross section orthogonal to the optical axis of the detection light, In addition, since the distance between the droplets in the optical axis direction is closer than a predetermined specified distance, the droplet positioned rearward with respect to the traveling direction of the detection light enters the shadow region of the droplet positioned forward and moves backward. If the detection light does not sufficiently strike the liquid droplets.

  However, if a flying direction abnormality or a flying speed abnormality occurs in one of these two droplets related to the substantially simultaneous ejection, the relative positional relationship between the two droplets is shifted, and the rear droplet is moved away from the shadow region. Since it comes off, the detection light also hits the rear droplet. For this reason, the detection light is also blocked by the rear droplet, and the amount of light received by the light receiving means changes according to the number of droplets present in the detection light beam. That is, when the flying direction abnormality or the flying speed abnormality of the droplets ejected substantially simultaneously occurs, more light is blocked as compared with the normal case, so that the detection signal from the light receiving means changes more greatly. From this change in the detection signal, it is possible to identify whether or not ejection has been normally performed for the ejection port to be detected, that is, whether or not a flying direction abnormality or a flying speed abnormality has occurred.

  According to the present invention, since discharge detection can be performed simultaneously for a plurality of discharge ports, the time required for detection can be shortened, and the throughput can be improved. In addition, according to the present invention, detection light strikes a rear droplet even when a slight flying direction abnormality or flying speed abnormality is detected, so that highly accurate detection is possible.

  The two or more ejection ports to be detected may be selected from one-dimensionally arranged rows, may be selected from the same row (nozzle row) in the two-dimensional arrangement, or may be different rows. It may be selected from (a plurality of nozzle rows).

  In the present invention, “substantially simultaneously discharging” is the same as the application timing (drive timing) of a drive signal for driving a pressure generating means (for example, an actuator or a heating element) that generates discharge pressure. It is assumed that the droplet discharge timing is not strictly the same.

  The invention according to claim 2 relates to an aspect of the liquid ejecting apparatus according to claim 1, wherein the predetermined specified distance is a wraparound distance of diffracted light that wraps behind a droplet that blocks the detection light. And

  When the diameter of the droplet is D and the wavelength of the detection light is λ, the diffraction angle θ is approximately θ = λ / D under the condition of D> λ, and the wrapping distance L of the diffracted light is L = D / (2 × tan θ). If the distance between the droplets (for example, the distance between the centers, more preferably, the distance from the center of the front droplet to the outside of the rear droplet) is closer than the wraparound distance L, the rear droplet is the front liquid. Enter the shadow area of the drop.

  A third aspect of the invention relates to an aspect of the liquid discharge apparatus according to the first or second aspect, and further includes a detection light moving unit that moves the detection light relative to the liquid discharge head.

  By moving the detection light by the detection light moving means, discharge detection can be performed for a desired discharge port. In particular, all the discharge ports can be inspected by scanning the detection light over the entire range of the two-dimensionally arranged discharge port group.

  The detection light moving unit includes a necessary configuration among a moving mechanism for moving all or part of the optical member and the light emitting unit constituting the optical system, a driving source thereof, a driving control unit, and the like. The detection light moving means may be any means that moves the detection light relative to the liquid discharge head, and there are various types of movement such as parallel movement, rotational movement (rotation), or a combination thereof. Are included.

  The invention according to a fourth aspect relates to an aspect of the liquid ejection apparatus according to the first, second, or third aspect, wherein the ejection state determination unit is selected according to the number of ejection ports that are selected as the detection target and are simultaneously driven to be ejected. A plurality of determination threshold values are set, and based on the plurality of determination threshold values and the detection signal obtained from the light receiving means, droplets discharged from the plurality of discharge ports related to the detection target are set. It is characterized by determining the presence or absence of an abnormality in at least one of the flight direction and the flight speed.

  Since the detection signal changes according to the number of droplets that block the detection light, having a plurality of determination thresholds having different levels according to the number of droplets ejected substantially simultaneously allows a plurality of discharge targets to be detected. It is possible to identify the number of discharge ports related to the flight direction abnormality (or flight speed abnormality) among the outlets.

  Further, in the present invention, when discharge droplets are detected simultaneously for a plurality of discharge ports and a discharge abnormality is detected in the detection, the discharge detection target for the plurality of discharge ports is set to 1 in the second detection. It is also preferable to specify a discharge port related to abnormality by narrowing down the detection target to a number smaller than that at the time of the first or first inspection and performing discharge detection, or by changing the combination of discharge ports to be discharged simultaneously. .

  A fifth aspect of the present invention relates to an aspect of the liquid ejection apparatus according to any one of the first to fourth aspects, wherein the recovery unit that recovers the ejection performance of the liquid ejection head and the determination by the ejection state determination unit And recovery control means for controlling the recovery operation by the recovery means based on the result.

  A mode in which the recovery operation by the recovery unit is performed when the ejection state determination unit confirms the presence of the ejection abnormality outlet is preferable. The recovery operation includes an operation for sucking the liquid in the liquid discharge head, a preliminary discharge, and the like. Thereby, discharge failure is eliminated and good discharge can be performed.

  The invention described in claim 6 provides an image forming apparatus that achieves the object. That is, an image forming apparatus according to a sixth aspect includes the liquid ejecting apparatus according to any one of the first to fifth aspects, and forms an image on a recording medium by droplets ejected from the ejection port. Features.

  As a configuration example of the liquid ejection head in the image forming apparatus of the present invention, a full-line type inkjet head having a nozzle row in which a plurality of nozzles (ejection ports) are arranged over a length corresponding to the entire width of the recording medium is used. it can.

  In this case, a combination of a plurality of relatively short ejection head modules having a nozzle row less than the length corresponding to the entire width of the recording medium, and connecting them together, the nozzle having a length corresponding to the entire width of the recording medium as a whole There is an aspect that constitutes a column.

  A full-line type ink jet head is usually arranged along a direction orthogonal to the relative feed direction (relative transport direction) of the medium to be ejected, but with respect to a direction orthogonal to the transport direction. There may be a mode in which the inkjet head is arranged along an oblique direction with an angle.

  In the case of forming a color image, a full-line type recording head may be arranged for each color of a plurality of inks (recording liquids), or a configuration in which a plurality of colors of ink can be ejected from one recording head. Also good.

  “Recording medium” in an image forming apparatus is called a medium (recording medium, printing medium, image forming medium, recording medium, image receiving medium, etc.) that receives an image recorded by liquid ejected from a liquid ejection head (recording head). A continuous sheet, a cut sheet, a seal sheet, a resin sheet such as an OHP sheet, a film, a cloth, a printed circuit board on which a wiring pattern is formed by a droplet discharge head, an intermediate transfer medium, and other materials and shapes. Regardless, it includes various media.

  The conveying means for relatively moving the recording medium and the liquid ejection head is an aspect in which the ejection medium is conveyed with respect to the stopped (fixed) head, an aspect in which the head is moved with respect to the stopped ejection medium, or Any of the modes in which both the head and the medium to be ejected are moved is included.

  The invention according to claim 7 provides a method invention for achieving the object. That is, the discharge detection method according to claim 7 is a method for detecting the discharge state of a liquid discharge head having a plurality of discharge ports for discharging droplets, and at least two of the plurality of discharge ports to be detected. Light emitting means for generating detection light that intersects the droplet flight path of one ejection port, and detection light that has passed through the droplet flight path of at least two ejection ports that are the detection targets, and detection according to the received light amount A light receiving means for outputting a signal, arranged on a line parallel to the optical axis of the detection light among the plurality of discharge openings, and having a predetermined distance between the discharge openings along the optical axis direction of the detection light. At least two discharge ports that are smaller than a specified distance are selected as the detection targets, and discharge driving is performed to discharge droplets from the selected at least two discharge ports substantially at the same time. Said Based on the detection signal obtained from said light receiving means when passing through the light exit, and judging the discharge state of the liquid droplets from the detection target serving at least two discharge ports.

  According to the present invention, since discharge detection can be performed simultaneously for a plurality of discharge ports, the time required for detection can be shortened and productivity can be improved. In addition, according to the present invention, even a slight deviation in flight direction and flight speed can be detected, and improvement in detection accuracy can be achieved as compared with the conventional method. Furthermore, the present invention can suitably cope with ejection detection of a large number of nozzles or high density nozzles.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Overall configuration of inkjet recording apparatus]
FIG. 1 is an overall configuration diagram of an ink jet recording apparatus using a liquid ejection apparatus according to an embodiment of the present invention. As shown in the figure, the ink jet recording apparatus 10 includes a plurality of ink jet recording heads (corresponding to black (K), cyan (C), magenta (M), and yellow (Y) inks). Hereinafter, it is referred to as a head.) A printing unit 12 having 12K, 12C, 12M, and 12Y, an ink storage / loading unit 14 that stores ink to be supplied to each of the heads 12K, 12C, 12M, and 12Y, and recording as a recording medium A paper feeding unit 18 that supplies the paper 16, a decurling unit 20 that removes curling of the recording paper 16, and a nozzle surface (ink ejection surface) of the printing unit 12 are arranged to face the flatness of the recording paper 16. A suction belt transport unit (corresponding to a transport unit) 22 that transports the recording paper 16 while holding the paper, and a paper discharge unit 26 that discharges the recorded recording paper (printed matter) to the outside. Each of the heads 12K, 12C, 12M, and 12Y includes a light source (corresponding to a light emitting means) 27A and a photo sensor (optical sensor) for optically detecting flying droplets ejected from nozzles (ink ejection ports). A discharge inspection device 27 composed of 27B is provided.

  The ink storage / loading unit 14 includes tanks (ink tanks) that store inks of colors corresponding to the heads 12K, 12C, 12M, and 12Y. Each ink tank is connected to each head 12K via a pipe line (not shown). , 12C, 12M, 12Y. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. ing.

  In FIG. 1, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 18, but a plurality of magazines having different paper widths, paper quality, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  When a plurality of types of recording media can be used, an information recording body such as a bar code or a wireless tag that records the recording medium type information is attached to the magazine, and the information on the information recording body is read by a predetermined reader. Accordingly, it is preferable to automatically determine the type of recording medium (media type) to be used and perform ink ejection control so as to realize appropriate ink ejection according to the media type.

  The recording paper 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine. In order to remove this curl, heat is applied to the recording paper 16 by the heating drum 30 in the direction opposite to the curl direction of the magazine in the decurling unit 20. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  In the case of an apparatus configuration that uses roll paper, a cutter (first cutter) 28 is provided as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 28. The cutter 28 includes a fixed blade 28A having a length equal to or greater than the conveyance path width of the recording paper 16, and a round blade 28B that moves along the fixed blade 28A. The fixed blade 28A is provided on the back side of the print. The round blade 28B is disposed on the printing surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  After the decurling process, the cut recording paper 16 is sent to the suction belt conveyance unit 22. The suction belt conveyance unit 22 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and at least a portion facing the nozzle surface of the printing unit 12 forms a horizontal surface (flat surface). Has been.

  The belt 33 has a width that is wider than the width of the recording paper 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, a suction chamber 34 is provided at a position facing the nozzle surface of the printing unit 12 inside the belt 33 spanned between the rollers 31 and 32, and the suction chamber 34 is connected to the fan 35. The recording paper 16 is sucked and held on the belt 33 by suctioning to negative pressure.

  The power of the motor (reference numeral 88 in FIG. 8) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, whereby the belt 33 is driven in the clockwise direction in FIG. The held recording paper 16 is conveyed from left to right in FIG.

  Since ink adheres to the belt 33 when a borderless print or the like is printed, the belt cleaning unit 36 is provided at a predetermined position outside the belt 33 (an appropriate position other than the print area). Although details of the configuration of the belt cleaning unit 36 are not shown, for example, there are a method of niping a brush roll, a water absorbing roll, etc., an air blow method of blowing clean air, or a combination thereof. In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

  Although a mode using a roller / nip conveyance mechanism instead of the suction belt conveyance unit 22 is also conceivable, if the roller / nip conveyance is performed in the print area, the image easily spreads because the roller contacts the printing surface of the sheet immediately after printing. There is a problem. Therefore, as in this example, suction belt conveyance that does not bring the image surface into contact with each other in the print region is preferable. It is also possible to use a belt conveying means by electrostatic adsorption instead of the belt conveying means by suction adsorption.

  A heating fan 40 is provided on the upstream side of the printing unit 12 on the paper conveyance path formed by the suction belt conveyance unit 22. The heating fan 40 heats the recording paper 16 by blowing heated air onto the recording paper 16 before printing. Heating the recording paper 16 immediately before printing makes it easier for the ink to dry after landing.

  Each of the heads 12K, 12C, 12M, and 12Y of the printing unit 12 has a length corresponding to the maximum paper width of the recording paper 16 targeted by the inkjet recording apparatus 10, and the nozzle surface has a recording medium of the maximum size. This is a full-line type head in which a plurality of nozzles for ink discharge are arranged over a length exceeding at least one side (full width of the drawable range) (see FIG. 2).

  The heads 12K, 12C, 12M, and 12Y are arranged in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side in the recording paper 16 feed direction. 12K, 12C, 12M, and 12Y are fixedly installed so as to extend along a direction substantially orthogonal to the conveyance direction of the recording paper 16.

  A color image can be formed on the recording paper 16 by discharging different color inks from the heads 12K, 12C, 12M, and 12Y while transporting the recording paper 16 by the suction belt transporting section 22.

  As described above, according to the configuration in which the full-line heads 12K, 12C, 12M, and 12Y having nozzle rows that cover the entire width of the paper are provided for each color, the recording paper 16 and the printing unit in the paper feeding direction (sub-scanning direction). The image can be recorded on the entire surface of the recording paper 16 by performing the operation of moving the 12 relatively once (that is, by one sub-scan). Thereby, it is possible to perform high-speed printing as compared with a shuttle type head in which the recording head reciprocates in a direction orthogonal to the paper transport direction, and productivity can be improved.

  In this example, the configuration of KCMY standard colors (four colors) is illustrated, but the combination of ink color and number of colors is not limited to this embodiment, and light ink, dark ink, and special color ink are used as necessary. May be added. For example, it is possible to add an ink jet head that discharges light ink such as light cyan and light magenta. Also, the arrangement order of the color heads is not particularly limited.

  As shown in FIG. 1, a post-drying unit 42 is provided after the printing unit 12. The post-drying unit 42 is means for drying the printed image surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  When printing on porous paper with dye-based ink, the weather resistance of the image is improved by preventing contact with ozone or other things that cause dye molecules to break by pressurizing the paper holes with pressure. There is an effect to.

  A heating / pressurizing unit 44 is provided following the post-drying unit 42. The heating / pressurizing unit 44 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 45 having a predetermined surface uneven shape while heating the image surface to transfer the uneven shape to the image surface. To do.

  The printed matter generated in this manner is outputted from the paper output unit 26. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 10 is provided with a sorting means (not shown) for switching the paper discharge path in order to select the print product of the main image and the print product of the test print and send them to the discharge units 26A and 26B. Yes. Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by a cutter (second cutter) 48. The cutter 48 is provided immediately before the paper discharge unit 26, and cuts the main image and the test print unit when the test print is performed on the image margin. The structure of the cutter 48 is the same as that of the first cutter 28 described above, and includes a fixed blade 48A and a round blade 48B.

  Although not shown in FIG. 1, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

[Head structure]
Next, the structure of the head will be described. Since the structures of the heads 12K, 12C, 12M, and 12Y provided for each ink color are common, the head is represented by the reference numeral 50 in the following.

  FIG. 3 is a view of the head 50 as viewed from the discharge port surface (nozzle surface) side, and FIG. 4 is a cross-sectional view showing a three-dimensional configuration of one droplet discharge element (an ink chamber unit corresponding to one nozzle 51). It is. In order to increase the dot pitch printed on the recording paper 16, it is necessary to increase the nozzle pitch in the head 50. As shown in FIG. 3, the head 50 of this example includes a plurality of ink chamber units (droplet discharge elements) 53 including nozzles 51 serving as ink droplet discharge ports and pressure chambers 52 corresponding to the nozzles 51. Are arranged in a zigzag matrix (two-dimensionally), so that a substantial nozzle interval projected along the head longitudinal direction (direction perpendicular to the paper feed direction) ( High density of projection nozzle pitch) has been achieved.

  As shown by the dotted lines in FIG. 3, the pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape, and is connected to the nozzle 51 at one of the diagonal corners. An outflow port is provided, and an inflow port (supply port) 54 for supply ink is provided on the other side. The shape of the pressure chamber 52 is not limited to this example, and the planar shape may have various forms such as a quadrangle (rhombus, rectangle, etc.), a pentagon, a hexagon and other polygons, a circle, and an ellipse.

  As shown in FIG. 4, each pressure chamber 52 communicates with a common flow channel 55 through a supply port 54. The common flow channel 55 communicates with an ink tank (not shown in FIG. 4; described as reference numeral 60 in FIG. 7) as an ink supply source, and the ink supplied from the ink tank 60 passes through the common flow channel 55 in FIG. Then, it is distributed and supplied to each pressure chamber 52.

  An actuator 58 having an individual electrode 57 is joined to a pressure plate (vibrating plate also serving as a common electrode) 56 constituting a part of the pressure chamber 52 (the top surface in FIG. 4). By applying a drive voltage between the individual electrode 57 and the common electrode, the actuator 58 is deformed and the volume of the pressure chamber 52 is changed, and ink is ejected from the nozzle 51 due to the pressure change accompanying this. The actuator 58 is preferably a piezoelectric element using a piezoelectric material such as lead zirconate titanate or barium titanate. After the ink is ejected, when the displacement of the actuator 58 is restored, new ink is supplied from the common channel 55 through the supply port 54 to the pressure chamber 52.

  As shown in FIG. 5, the ink chamber units 53 having the above-described structure are arranged in a fixed arrangement pattern along the row direction along the main scanning direction and the oblique column direction having a constant angle α not orthogonal to the main scanning direction. The high-density nozzle head of this example is realized by arranging a large number in a lattice pattern.

  That is, with a structure in which a plurality of nozzles 51 are arranged at a constant pitch d along the direction of an angle α with respect to the main scanning direction, the pitch P of the nozzles projected so as to be aligned in the main scanning direction is d × cos α. With respect to the main scanning direction, each nozzle 51 can be handled equivalently as a linear array with a constant pitch P. With such a configuration, it is possible to realize a high-density nozzle configuration in which 2400 nozzle rows are projected per inch (2400 nozzles / inch) so as to be aligned in the main scanning direction.

  When the nozzles are driven by a full line head having a nozzle row having a length corresponding to the entire printable width, (1) all the nozzles are driven simultaneously, (2) the nozzles are sequentially moved from one side to the other. (3) The nozzles are divided into blocks, and the nozzles are sequentially driven from one side to the other for each block, etc., and one line (1 in the width direction of the paper (direction perpendicular to the paper conveyance direction)) Driving a nozzle that prints a line of dots in a row or a line consisting of dots in a plurality of rows is defined as main scanning.

  In particular, when driving the nozzles 51 arranged in a matrix as shown in FIG. 5, the main scanning as described in (3) above is preferable. That is, nozzles 51-11, 51-12, 51-13, 51-14, 51-15, 51-16 are made into one block (other nozzles 51-21,..., 51-26 are made into one block, Nozzles 51-31,..., 51-36 as one block,...), And the nozzles 51-11, 51-12,. One line is printed in 16 width directions.

  On the other hand, by relatively moving the above-mentioned full line head and the paper, printing of one line (a line formed by one line of dots or a line composed of a plurality of lines) formed by the above-described main scanning is repeatedly performed. This is defined as sub-scanning.

  The direction indicated by one line (or the longitudinal direction of the belt-like region) recorded by the main scanning is referred to as a main scanning direction, and the direction in which the sub scanning is performed is referred to as a sub scanning direction. In other words, in the present embodiment, the conveyance direction of the recording paper 16 is the sub-scanning direction, and the direction orthogonal to it is the main scanning direction.

  The structure of the head 50 and the form of the nozzle arrangement are not limited to the examples described with reference to FIGS. For example, as shown in FIG. 6, a nozzle array having a length corresponding to the entire width of the recording paper 16 is obtained by arranging short head modules 50 ′ in which a plurality of nozzles 51 are two-dimensionally arranged in a staggered manner. You may comprise the full line head which has.

  As described with reference to FIG. 4, in this embodiment, a method of ejecting ink droplets by deformation of an actuator 58 typified by a piezo element (piezoelectric element) is adopted. There are no particular limitations on the method used, and instead of the piezo jet method, various methods such as a thermal jet method in which ink is heated by a heating element such as a heater to generate bubbles and ink droplets are ejected by the pressure can be applied.

[Configuration of ink supply system]
FIG. 7 is a schematic diagram showing the configuration of the ink supply system in the inkjet recording apparatus 10. The ink tank 60 is a base tank that supplies ink to the head 50 and is installed in the ink storage / loading unit 14 described with reference to FIG. In the form of the ink tank 60, there are a system that replenishes ink from a replenishing port (not shown) and a cartridge system that replaces the entire tank when the remaining amount of ink is low. A cartridge system is suitable for changing the ink type according to the intended use. In this case, it is preferable that the ink type information is identified by a barcode or the like, and ejection control is performed according to the ink type. The ink tank 60 of FIG. 7 is equivalent to the ink storage / loading unit 14 of FIG. 1 described above.

  As shown in FIG. 7, a filter 62 is provided between the ink tank 60 and the head 50 in order to remove foreign substances and bubbles. The filter mesh size is preferably equal to or smaller than the nozzle diameter (generally about 20 μm).

  Although not shown in FIG. 7, a configuration in which a sub tank is provided in the vicinity of the head 50 or integrally with the head 50 is also preferable. The sub-tank has a function of improving a damper effect and refill that prevents fluctuations in the internal pressure of the head.

  Further, the inkjet recording apparatus 10 is provided with a cap 64 as a means for preventing the nozzle 51 from drying or preventing an increase in ink viscosity near the nozzle, and a cleaning blade 66 as a means for cleaning the nozzle surface 50A. .

  The maintenance unit including the cap 64 and the cleaning blade 66 can be moved relative to the head 50 by a moving mechanism (not shown), and is moved from a predetermined retracted position to a maintenance position below the head 50 as necessary.

  The cap 64 is displaced up and down relatively with respect to the head 50 by an elevator mechanism (not shown). The cap 64 is lifted to a predetermined raised position when the power is turned off or during printing standby, and is brought into close contact with the head 50, thereby covering the nozzle surface 50 </ b> A with the cap 64.

  The cleaning blade 66 is made of an elastic member such as rubber, and can slide on the ink discharge surface (nozzle plate surface) of the head 50 by a blade moving mechanism (not shown). When ink droplets or foreign substances adhere to the nozzle plate, the nozzle plate surface is wiped by sliding the cleaning blade 66 on the nozzle plate to clean the nozzle plate surface.

  During printing or standby, when a specific nozzle is used less frequently and the ink viscosity in the vicinity of the nozzle increases, preliminary discharge is performed toward the cap 64 to discharge the deteriorated ink.

  Further, when bubbles are mixed in the ink (pressure chamber) in the head 50, the cap 64 is applied to the head 50, and the ink (ink in which the bubbles are mixed) is removed by suction with the suction pump 67, and is removed by suction. Ink is fed to the collection tank 68. In this suction operation, the deteriorated ink with increased viscosity (solidified) is sucked out when the ink is initially loaded into the head or when the ink is used after being stopped for a long time.

  If the head 50 is not ejected for a certain period of time, the ink solvent near the nozzles evaporates and the viscosity of the ink near the nozzles increases. Will not discharge. Therefore, before this state is reached (within the viscosity range in which ink can be discharged by the operation of the actuator 58), the actuator is operated toward the ink receiver to discharge ink in the vicinity of the nozzle whose viscosity has increased. "Preliminary discharge" is performed. In order to prevent foreign matter from being mixed into the nozzle 51 by the wiper rubbing operation after the dirt on the nozzle plate surface is cleaned by a wiper such as a cleaning blade 66 provided as a nozzle surface cleaning means. Preliminary discharge is performed. Note that the preliminary discharge may be referred to as “empty discharge”, “purge”, “spitting”, or the like.

  In addition, if bubbles are mixed into the nozzle 51 or the pressure chamber 52 or if the viscosity increase of the ink in the nozzle 51 exceeds a certain level, ink cannot be ejected by the preliminary ejection, and the suction operation described below is performed.

  That is, when bubbles are mixed in the ink in the nozzle 51 or the pressure chamber 52, or when the ink viscosity in the nozzle 51 rises to a certain level or more, the ink can be ejected from the nozzle 51 even if the actuator 58 is operated. Disappear. In such a case, a suction means for sucking ink in the pressure chamber 52 with a pump or the like is brought into contact with the nozzle surface of the head 50 to suck ink mixed with bubbles or thickened ink.

  However, since the above suction operation is performed on the entire ink in the pressure chamber 52, the ink consumption is large. Therefore, when the increase in viscosity is small, it is preferable to perform preliminary discharge as much as possible. The cap 64 described with reference to FIG. 7 functions as a suction unit and can also function as a preliminary discharge ink receiver. The above suction operation is also performed when the ink is initially loaded into the head 50 or when use is started after a long stop.

[Explanation of control system]
Next, the control system of the inkjet recording apparatus 10 will be described.

  FIG. 8 is a principal block diagram showing the system configuration of the inkjet recording apparatus 10. The inkjet recording apparatus 10 includes a communication interface 70, a system controller 72, an image memory 74, a motor driver 76, a heater driver 78, a print control unit 80, an image buffer memory 82, a head driver 84, an ejection detection control unit 85, and the like. .

  The communication interface 70 is an interface unit that receives image data sent from the host computer 86. As the communication interface 70, a serial interface such as USB, IEEE 1394, Ethernet, and wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  Image data sent from the host computer 86 is taken into the inkjet recording apparatus 10 via the communication interface 70 and temporarily stored in the image memory 74. The image memory 74 is a storage unit that temporarily stores an image input via the communication interface 70, and data is read and written through the system controller 72. The image memory 74 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 72 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 10 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 72 controls the communication interface 70, the image memory 74, the motor driver 76, the heater driver 78, and the like, and performs communication control with the host computer 86, read / write control of the image memory 74 and the ROM 75, and the like. At the same time, a control signal for controlling the motor 88 and the heater 89 of the transport system is generated.

  The ROM 75 stores programs executed by the CPU of the system controller 72 and various data necessary for control. The ROM 75 may be a non-rewritable storage means, or may be a rewritable storage means such as an EEPROM. The image memory 74 is used as a temporary storage area for image data, and is also used as a program development area and a calculation work area for the CPU.

  The motor driver 76 is a driver (drive circuit) that drives the motor 88 in accordance with an instruction from the system controller 72. The heater driver 78 is a driver that drives the heaters 89 of the post-drying unit 42 and other units in accordance with instructions from the system controller 72.

  The print control unit 80 has a signal processing function for performing various processing and correction processing for generating a print control signal from the image data in the image memory 74 according to the control of the system controller 72, and the generated print A control unit that supplies a control signal (dot data) to the head driver 84. Necessary signal processing is performed in the print control unit 80, and the ejection amount and ejection timing of the ink droplets of the head 50 are controlled via the head driver 84 based on the image data. Thereby, a desired dot size and dot arrangement are realized.

  The print control unit 80 includes an image buffer memory 82, and image data, parameters, and other data are temporarily stored in the image buffer memory 82 when image data is processed in the print control unit 80. In FIG. 8, the image buffer memory 82 is shown in a mode accompanying the print control unit 80, but it can also be used as the image memory 74. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with one processor.

  An overview of the flow of processing from image input to print output is as follows. Image data to be printed is input from the outside via the communication interface 70 and stored in the image memory 74. At this stage, for example, RGB image data is stored in the image memory 74.

  In the ink jet recording apparatus 10, a pseudo continuous tone image is formed by changing the droplet ejection density and dot size of fine dots with ink (coloring material) to the human eye. It is necessary to convert to a dot pattern that reproduces the gradation (shading of the image) as faithfully as possible. Therefore, the original image (RGB) data stored in the image memory 74 is sent to the print control unit 80 via the system controller 72, and the print control unit 80 uses a halftoning technique such as a dither method or an error diffusion method. Is converted into dot data for each ink color.

  That is, the print control unit 80 performs processing for converting the input RGB image data into dot data of four colors K, C, M, and Y. Thus, the dot data generated by the print control unit 80 is stored in the image buffer memory 82.

  The head driver 84 generates a drive signal for driving the actuator 58 corresponding to each nozzle 51 of the head 50 based on print data (that is, dot data stored in the image buffer memory 82) given from the print control unit 80. Output. The head driver 84 may include a feedback control system for keeping the head driving conditions constant.

  When a drive signal output from the head driver 84 is applied to the head 50, ink is ejected from the corresponding nozzle 51. An image is formed on the recording paper 16 by controlling the ink ejection from the head 50 in synchronization with the conveyance speed of the recording paper 16.

  As described above, the ejection amount and ejection timing of ink droplets from each nozzle are controlled via the head driver 84 based on the dot data generated through the required signal processing in the print controller 80. Thereby, a desired dot size and dot arrangement are realized.

  The discharge detection control unit 85 includes a light source control circuit that controls lighting (ON) / extinguishment (OFF) of the light source 27A for discharge detection and a light emission amount at the time of lighting, a driving circuit for the photosensor 27B, and a photosensor 27B. And a signal processing circuit for processing the detection signal. The ejection detection control unit 85 controls the operation of the light source 27A and the photosensor 27B according to a command from the print control unit 80, and provides the detection result obtained from the photosensor 27B to the print control unit 80.

  Based on the detection information obtained through the discharge detection control unit 85, the print control unit 80 determines the discharge state of the nozzle 51 (discharge / non-discharge, flight direction / presence of speed abnormality, etc.), and an abnormal nozzle is detected. In such a case, control for performing a predetermined coping operation (such as a recovery operation) is performed. That is, the print control unit 80 functions as an ejection port selection unit, an ejection control unit, and an ejection state determination unit of the present invention.

[Discharge detection method]
FIG. 9 is a schematic configuration diagram of means for detecting flying droplets. As shown in the figure, the ejection inspection apparatus 27 mainly includes a light source 27A such as a laser diode and a photosensor 27B, an optical system 90 for shaping light emitted from the light source 27A into a light beam having a predetermined shape, and a photosensor 27B. The discharge detection means 92 etc. which detect the discharge state in response to the detection signal obtained from is comprised.

  The optical path from the light source 27A to the photosensor 27B does not necessarily have a straight line configuration, and a variety of optical path forms are made using known optical members (folding means) such as folding mirrors and prisms, optical fibers, and the like. Is possible.

  In implementing the present invention, the type of the light source 27A is not particularly limited, but it is preferable to use a coherence light source having a relatively uniform wavelength, such as a laser diode (LD) or a light emitting diode (LED).

  The optical system 90 includes a collimator lens 90A and a cylindrical lens 90B that use light from the light source 27A as first parallel light 93, which is substantially parallel light having a first beam width, and the first parallel light 93 as the first parallel light 93. And a beam converter 90C for converting the second parallel light 94, which is substantially parallel light having a second beam width different from the first beam width. The beam converter 90C changes the cross-sectional shape of the beam (such as the vertical beam width and the horizontal beam width) by narrowing or spreading the light beam.

  An optical system that makes these parallel lights parallel lights of different widths, makes the width of the parallel lights variable, and switches the width of the parallel lights will be described later.

  The second parallel light 94 is formed in the droplet flight space between the nozzle surface 50 </ b> A of the head 50 and the recording paper 16, and the optical axis direction of the second parallel light 94 is the ink ejected from the head 50. The droplet (droplet) 96 is perpendicular to the flight direction.

  This second parallel light (hereinafter referred to as “detection light beam”) 94 is condensed by a condensing lens 98 and is received by the photosensor 27B at a substantially condensing position. The photosensor 27B is a photoelectric conversion element that outputs an electrical signal corresponding to the amount of received light, and the amount of received light changes depending on the number of droplets present in the detection light beam 94, and the output signal (detection signal) changes.

  The detection signal of the photosensor 27B is input to the discharge detection means 92, and based on the detection signal, the presence / absence (discharge / non-discharge) of the flying liquid droplet, the flight direction shift, the flight speed shift, etc., that is, the discharge state of the nozzle 51 Is to be detected. Details of this discharge detection method will be described later.

  In addition to the above-described configuration, the ejection inspection apparatus 27 includes a changing unit 100 that changes the cross-sectional shape of the detected light beam 94, a scanning unit 102 that scans the detected light beam 94 with respect to the droplet 96 ejected from the head 50, and a photosensor. A droplet speed calculating means 104 for calculating the flying speed of the droplet 96 based on the detection signal 27B, and a discharge timing control means 106 for controlling the discharge timing when the droplet 96 is discharged into the detected light beam 94. Yes.

  The changing unit 100 includes a member configuration that changes the optical configuration by changing the arrangement of the optical members in the optical system 90 and the optical physical properties (refractive index, etc.), and a drive control circuit thereof. The scanning means (corresponding to detection light moving means) 102 includes a moving mechanism that moves part or all of the light source 27A and the optical system 90, a member configuration such as a motor, and a drive control circuit thereof. The discharge detection unit 92, the droplet velocity calculation unit 104, and the discharge timing control unit 106 are units realized by a combination of the system controller 72, the print control unit 80, and the discharge detection control unit 85 described in FIG. Calculation and control are performed based on a predetermined program.

[Principle of discharge detection]
Here, the principle of ejection detection will be described.

  FIG. 10 is a schematic diagram of a detection system. An optical system is formed which guides light from a light source (here, LD is used) 27A shown in the left side of the figure to parallel light and guided to the photosensor 27B side. Among the nozzle groups provided in the head 50, two nozzles (detection target nozzles [1] and [1] corresponding to positions indicated by [1] in FIG. 10) arranged on a line parallel to the optical axis of the detection light beam 94 are arranged. , [2] corresponding to the position indicated by [2] is selected, and these two nozzles are simultaneously driven, so that two droplets 96-1 and 96-2 are formed in the detected light beam 94. Make it exist at the same time. The distance between these two droplets (approximately the distance in the optical axis direction between the two nozzles [1] and [2]) should be considered to be able to detect the two droplets.

  In general, even if there is an obstacle that blocks light that goes straight, the light travels from the edge of the obstacle to the shadow side (diffraction phenomenon), so the obstacle is separated by a distance behind the obstacle. Light also enters the back side area of the object.

  Although the intensity distribution of light is seen at a distance close to the obstacle due to the influence of “interference”, the phenomenon of “diffraction” will be examined with the main point being “light quantity”.

  FIG. 11 is a schematic diagram depicting a state in which a droplet (an obstacle that blocks light) exists in the detected light beam. When collimated light (wavelength λ) is irradiated from the left in the drawing to the droplet 110 having a diameter φD, light wrap around at an angle θ occurs due to furanpher diffraction. As a result, an area where light does not reach (hereinafter referred to as a “shadow area”), such as a substantially triangular area behind the droplet 110 indicated by a slanted line in the drawing (actually a substantially conical area since it is symmetrical with respect to the axis center). ) 120 occurs.

The diffraction angle θ is approximately θ = λ / D under the condition of D> λ. Therefore, when the distance from the center of the droplet 110 to the apex of the shadow region 120 (the diffracted light wraparound distance) is L, the following equation L = D / (2 × tan θ)
It is represented by Specifically, when the droplet diameter φD = 30 μm (equivalent to 14 pl) and the wavelength λ = 800 nm, L = 0.56 mm.

  Light hardly reaches the shadow region 120 defined by the distance L, and conversely, the detection light reaches a region farther than the defined distance L. Therefore, as in the case of the droplets A and C shown in FIG. 12, when the distance in the optical axis direction of the two droplets A and C ejected at the same time is smaller than the specified distance L, light is emitted to the rear droplet A. It does not reach sufficiently, and it is difficult to detect the droplet A.

  On the other hand, when the distance in the optical axis direction of the two droplets B and C is larger than the specified distance L as in the case of the droplets B and C in FIG. Droplet B can be detected.

  For this reason, when detecting non-ejection (presence / absence of ejection) for a plurality of nozzles, when the distance between the centers of two droplets (that is, the distance between the centers of the nozzles) is Pn, the condition of Pn> L is satisfied. Two nozzles are selected as inspection targets (see FIG. 12).

  In this way, when detecting a non-ejection by simultaneously ejecting a plurality of droplets, the distance (interval) in the optical axis direction is made larger than a prescribed value calculated from the droplet size and the light source wavelength. , Accurate detection is possible.

  FIG. 13A is a diagram showing the positional relationship between the cross section of the detection light beam 94 (light reception cross section viewed from the photosensor 27B) and the droplet 96, and FIG. 13B shows the change in the detection signal due to the passage of the droplet. FIG. 13C shows a signal obtained by extracting the change amount of the detection signal shown in FIG. 13B (a signal indicating the amount of change, hereinafter referred to as “change extraction signal”). FIG.

  As shown in these drawings, when a droplet (one droplet) 96 enters the detection light beam 94, a part of the detection light beam 94 is blocked by the droplet 96, and the amount of light incident on the photosensor 27B decreases. . Along with this, the sensor output of the photosensor 27B decreases. When the liquid droplet 96 finishes passing through the detection light beam 94 and no liquid droplet 96 exists in the detection light beam 94, the output of the photosensor 27B returns to the original reference level.

  As shown in FIG. 13 (c), by setting a threshold value (Th1) for determining a droplet, the change output signal of the sensor output is compared with the threshold value (Th1) to detect the detected light beam 94. It is possible to determine the presence or absence of a droplet in the inside.

  14 and 15 are diagrams showing examples of sensor output change extraction signals obtained when two droplets are detected simultaneously. In these drawings, the vertical axis represents signal amplitude (for example, voltage value), and the horizontal axis represents time.

  FIG. 14 is an example of a change extraction signal obtained when two droplets having the positional relationship between the droplets B and C described in FIG. 12 pass through the detected light beam. In this case, since the two droplets are at a position farther than the specified distance L, the light also travels to the second droplet (rear) droplet B to irradiate the droplet B and blocks the light accordingly. Therefore, a large signal change is obtained as shown in FIG. Since the light shielding area by these two droplets is about twice that of one droplet (FIG. 13), as shown in FIG. 14, the amount of change in the sensor output change extraction signal is as shown in FIG. About twice as much.

  For this reason, as shown in FIG. 14, the first threshold value (Th1) for determining the passage of only one drop and the second threshold value (Th2) for determining the passage of two drops; By setting (Th1 <Th2), it is possible to compare the sensor output change extraction signal with the threshold values (Th1, Th2) to determine the number of droplets in the detection light beam 94. .

  If the change extraction signal exceeds the second threshold Th2, it can be determined that the two nozzles have normally discharged, and the change extraction signal exceeds the first threshold Th1 and the second threshold Th1. If it is less than Th2, it can be determined that one of the nozzles is normal and the other is abnormal. When the change extraction signal is below the first threshold Th1, it is determined that both nozzles are abnormal.

  In contrast, in the case of the two droplets having the relationship between the droplets A and C described in FIG. 12, the distance between the droplets is smaller than the specified distance L, so that the second droplet A is exposed to light. Difficult (behind the shadow of the previous droplet C). Therefore, even if the two nozzles discharge normally, the output of the detection signal is small, and the change amount of the change extraction signal is small as shown by the solid line in FIG. That is, the signal is substantially the same level as the signal for one drop described in FIG. 13C, and the output does not exceed the threshold value Th2. For this reason, it cannot be determined from the change extraction signal described in FIG. 15 and FIG. 13C whether two drops have passed or only one drop has passed.

  From the above, when simultaneous detection (non-ejection detection) of two droplets is performed, the detection target nozzle is controlled so that the distance between the detection target droplets is controlled and the distance between the two droplets is larger than the specified distance L. It is necessary to choose. Here, although two droplets have been described as an example, it is possible to detect n droplets (n is a number of 2 or more) arranged on the same line on the same principle. In this case, the n nozzles arranged on the optical axis direction line are simultaneously driven, and the threshold values are set in n stages (Thj; j = 1, 2,..., N), thereby being discharged substantially simultaneously. The number of droplets can be determined.

  As described above, by setting a plurality of determination thresholds according to the number of droplets to be detected at the same time, it is possible to grasp the number of normal nozzles (or the number of abnormal nozzles) among a plurality of nozzles to be detected. Can do. In an actual apparatus, the detection signal processing circuit or control software has the above-described determination threshold value, and discharge determination is performed.

  When an ejection abnormality is detected, control for performing a predetermined recovery operation, droplet ejection correction, and the like is performed. If an abnormality is detected by the discharge detection, the second detection is performed for the plurality of nozzles, and one nozzle or a smaller number of nozzles are discharged at the second detection. Alternatively, there is an aspect in which abnormal nozzles are specified by performing ejection by changing the combination of nozzles to be detected.

  In addition, a mode in which maintenance operations such as suction and preliminary discharge are performed only for the nozzle group in which the discharge abnormality is detected is also preferable. In this case, for example, the inside of the cap 64 is divided into a plurality of areas corresponding to the nozzle groups by a partition wall, and each of the partitioned areas can be selectively sucked by a selector or the like.

  The detection process described above can be performed by scanning the detection light beam 94 with respect to the head 50 during the printing operation. Of course, the ejection detection is not limited to the mode performed during the printing operation, and it is also possible to perform the ejection detection by performing the ejection operation during maintenance during non-printing (for example, during preliminary ejection).

[Principle of detection of flight direction abnormality and flight speed abnormality]
Next, the detection principle of the flying direction abnormality and the flying speed abnormality using the shadow region 120 due to the diffraction phenomenon described in FIGS. 11 and 12 will be described.

  FIG. 16A is a view of the liquid droplets simultaneously ejected from the two nozzles as viewed from the optical axis direction of the detection light. It is assumed that the detection light travels from the front side to the back side of the page. Moreover, FIG.16 (b) is a side view of Fig.16 (a), and light shall be irradiated from the left of FIG.16 (b).

  When two droplets are simultaneously present in the detection light beam 94 by simultaneously driving two nozzles arranged on a line parallel to the optical axis of the detection light, the distance between these two droplets (ie, two nozzles). The distance in the optical axis direction) is shorter than the specified distance L as shown in FIG. That is, when two nozzles are normally ejected, the position where the rear (downstream) droplet A passes through the shadow region 120 of the front (upstream) droplet C with respect to the traveling direction of the detected light beam. Two nozzles of interest are selected.

  If the two selected nozzles perform normal ejection (normal (normal) droplet flight in both ejection direction and ejection speed), detection is performed as A droplet and C droplet shown in FIG. Since both droplets overlap in the cross section of the light beam, and the rear A droplet is not sufficiently irradiated with light, the amount of change in the output waveform from the photosensor 27B (that is, the waveform amplitude of the change extraction signal) is small (FIG. 17). (Refer to the waveform shown by the broken line.)

  On the other hand, when an abnormality occurs in the flying speed (discharge speed) of the droplets and a speed shift occurs between the two droplets, for example, the D droplets shown in FIGS. It becomes a state like this. The flying speed of the D droplet is slower than that of the preceding droplet C. Since the flight speed is slower than the reference (C drop), the D drop is drawn on the C drop in FIG.

  In addition, when an abnormality occurs in the flight direction (discharge direction) of a droplet and a shift in the discharge direction occurs between the two droplets, a state such as an E droplet is obtained. The flying direction of the E droplet is shifted to the right in FIG. Although the E drop is not deviated from the rear position of the C drop in the side view of FIG. 16B, it is shifted in the cross-sectional direction as shown in FIG.

  When viewed from the direction of the cross section of the optical axis, if it is deviated from the standard C drop, such as D drop and E drop, not only the C drop but also the D drop and E drop are exposed to light and detected by the D drop and E drop. Since the light is blocked, the detection signal of the photosensor 27B becomes small. That is, since the waveform amplitude of the change extraction signal increases (see the waveform shown by the solid line in FIG. 17), an abnormality can be detected.

  FIG. 17 shows the difference between the change extraction signals as described above. If the two droplets originally discharge in the same manner (normal discharge), like the A and C droplets in FIG. 16A, the two droplets substantially overlap in the optical axis cross section, and the specified distance L Since it is closer, the output is as shown by the broken line in FIG. That is, although two droplets are ejected, an output with a small degree of change in detection and a small difference in waveform is obtained (refer to the solid line waveform in FIG. 15 for comparison).

  On the other hand, the area that blocks the detection light increases when the position becomes the D drop or E drop in FIG. 16A due to the flying speed abnormality or the flying direction abnormality, so the output waveform as shown by the solid line in FIG. become.

  As described above, when two nozzles having a distance shorter than the specified distance L are ejected substantially simultaneously, it is assumed that ejection is performed from each nozzle (not ejection), but from the photosensor 27B. If the output is small (if only one drop of waveform is output), it can be determined that the flight direction and the flight speed are normal. Other than that, it can be determined that the flight direction or the flight speed is abnormal (the flight direction and the speed are not uniform). That is, as shown in FIG. 17, when the threshold value Th1 and Th2 are provided for the change extraction signal and the threshold value Th2 is exceeded or falls below the threshold value Th1, it can be determined that an ejection failure has occurred.

  As described above, when detecting the flying direction and velocity abnormality for a plurality of nozzles, when the distance between the centers of two droplets (that is, the distance between the centers of the nozzles) is Pn, the condition of Pn ≦ L is satisfied. Two nozzles that satisfy the conditions are selected as inspection targets (see FIG. 12).

  Although two droplets have been described as an example here, n (n is a number of 2 or more) droplets can be detected simultaneously on the same principle. In this case, the n nozzles arranged on the optical axis direction line are simultaneously driven, and the threshold values are set in n stages (Thj; j = 1, 2,..., N), thereby being discharged substantially simultaneously. It is possible to discriminate the number of droplets that are abnormal in flight.

  As described above, by setting a plurality of determination thresholds according to the number of droplets to be ejected substantially simultaneously, the number of normal nozzles (or the number of abnormal nozzles) among the plurality of nozzles to be detected is grasped. be able to. In an actual apparatus, the detection signal processing circuit or control software has the above-described determination threshold value, and discharge determination is performed.

  When an ejection abnormality is detected, control for performing a predetermined recovery operation, droplet ejection correction, and the like is performed. If an abnormality is detected by the discharge detection, the second detection is performed for the plurality of nozzles, and one nozzle or a smaller number of nozzles are discharged at the second detection. Alternatively, there is also an aspect in which abnormal nozzles are specified by changing the combination of nozzles that are driven simultaneously.

  In addition, a mode in which maintenance operations such as suction and preliminary discharge are performed only for the nozzle group in which the discharge abnormality is detected is also preferable. In this case, for example, the inside of the cap 64 is divided into a plurality of areas corresponding to the nozzle groups by a partition wall, and each of the partitioned areas can be selectively sucked by a selector or the like.

  The detection process described above can be performed by scanning the detection light beam 94 with respect to the head 50 during the printing operation. Of course, the ejection detection is not limited to the mode performed during the printing operation, and it is also possible to perform the ejection detection by performing the ejection operation during maintenance during non-printing (for example, during preliminary ejection).

  Here, with reference to FIGS. 18 to 20, an example of the relationship between the nozzle 51 to be detected and the optical axis of the detected light beam 94 will be described.

  FIG. 18 is a schematic plan view illustrating an example in which two nozzles to be detected are selected from a two-dimensionally arranged nozzle row. FIG. 18 is a view as seen from the nozzle surface side of the head (the same applies to FIGS. 19 and 20). In the example shown in FIG. 18, the arrangement direction of the nozzles 51 arranged along the oblique column direction at an angle α with respect to the longitudinal direction of the head 50 (lateral direction in FIG. 18) and the optical axis of the detection light beam 94 are an angle. A plurality of nozzles 51 that constitute ψ (ψ> 0) and are to be detected are arranged on a line parallel to the optical axis of the detected light beam 94 having the beam width W1. A detection optical system that forms such a detection light beam 94 is configured.

  That is, nozzles 51-A and 51-B indicated by black circles in FIG. 18 are to be detected, and droplets are ejected substantially simultaneously from the nozzles 51-A and 51-B in these different nozzle rows. Here, “substantially simultaneously discharging” means that the drive signals are applied simultaneously to the discharge driving actuators corresponding to the nozzles 51-A and 51-B. Does not require simultaneity.

  The detection target is changed by moving the detection light beam 94 of FIG. 18 relative to the nozzle array by the scanning unit 102 described in FIG.

  FIG. 19 is a schematic plan view showing another example of selecting two nozzles to be detected from a two-dimensionally arranged nozzle row. In the example shown in the figure, the arrangement direction of the nozzles 51 arranged along the oblique row direction at an angle α with respect to the longitudinal direction of the head 50 (lateral direction in FIG. 19) and the optical axis of the detection light beam 94 are parallel. The detection optical system is configured so that the droplets ejected from the plurality of nozzles 51 to be detected pass through substantially the same position in the cross section of the detection light beam 94 having the beam width W2.

  That is, in FIG. 19, nozzles 51-C and 51-D indicated by black circles are detection targets, and droplets are ejected substantially simultaneously from the nozzles 51-C and 51-D in the same nozzle row. When non-ejection is detected based on the detection principle described with reference to FIGS. 12 to 15, nozzles whose distance between the nozzles is greater than the specified distance L are selected. On the other hand, when detecting the flying direction and speed abnormality by the detection principle described with reference to FIGS. 16 and 17, the nozzles whose distance between the nozzles is shorter than the specified distance L are selected.

  Further, the nozzle row to be detected can be changed by moving the detection light beam 94 of FIG. 19 by the scanning means 102 described in FIG.

  FIG. 20 is a schematic plan view showing still another example of selecting two nozzles to be detected from two-dimensionally arranged nozzle rows. In the example shown in the figure, the optical axis of the detection light beam 94 is arranged in parallel with the nozzle row arranged along the main scanning direction of the full-line head, and droplets ejected from the plurality of nozzles 51 to be detected are discharged. The detection optical system is configured to pass through substantially the same position in the cross section of the detection light beam 94 having the beam width W3.

  That is, in FIG. 20, nozzles 51-E and 51-F indicated by black circles are detection targets, and droplets are ejected substantially simultaneously from the nozzles 51-E and 51-F in the same nozzle row. When non-ejection is detected based on the detection principle described with reference to FIGS. 12 to 15, nozzles whose distance between the nozzles is greater than the specified distance L are selected. On the other hand, when detecting the flying direction and speed abnormality by the detection principle described with reference to FIGS. 16 and 17, the nozzles whose distance between the nozzles is shorter than the specified distance L are selected.

  Further, by moving the detection light beam 94 of FIG. 20 by the scanning means 102 described in FIG. 9, the nozzle row to be detected can be changed.

  The cross-sectional shape (cross-sectional shape and cross-sectional area) of the detection light beam 94 is appropriately set in consideration of the number of droplets to be detected at the same time, the arrangement relationship of the nozzles 51 that are discharge detection targets, the time difference in discharge timing, and the like. For example, when realizing a resolution of 2400 dpi, the dot pitch is about 10 μm, and the diameter of a flying droplet (spherical liquid) is about 15 μm. When the cross-sectional area of the detection light beam 94 is increased, the ratio of the shielding area by the ejected liquid droplets is reduced, so that the SN is deteriorated. Therefore, it is preferable to use a beam as thin as possible so that a plurality of droplets to be detected do not overlap in space and time.

  More preferably, the beam shape is made variable, and control is performed to automatically switch the beam shape to an appropriate shape according to the situation. By optimizing the beam shape and increasing the droplet blocking rate with respect to the beam cross-sectional area, highly accurate detection with good SN can be realized. Means for changing the beam shape of the detection light will be described later.

[Control flow]
Next, a discharge detection procedure in the inkjet recording apparatus 10 of the present embodiment will be described.

  FIG. 21 is a flowchart illustrating a non-ejection detection control example. When the non-ejection detection sequence is started (step S110), first, two nozzles having a positional relationship in which the inter-nozzle distance Pn is larger than the specified distance L among the nozzle rows arranged on a straight line parallel to the optical axis of the detection light. (2 nozzles satisfying the relationship of Pn> L) is selected (step S112). Information on the specified distance L is stored in a storage means such as the ROM 75 described with reference to FIG. Further, the optical axis position of the detection light is grasped based on the control information of the scanning means 102 described in FIG. 9 or the detection information from the position detection means.

  In this way, both actuators are simultaneously driven for the two nozzles selected satisfying the above conditions (step S114), and droplets are ejected substantially simultaneously from the two nozzles. The amount of light received by the photosensor accompanying this ejection operation is measured (step S116), and the change extraction signal of the detection signal obtained from the photosensor is compared with the threshold value Th2 (step S118). If the change extraction signal of the detection signal is greater than or equal to the predetermined threshold value Th2 in step S118, it is determined that ejection is normally performed (step S120). On the other hand, if the change extraction signal of the detection signal is less than the predetermined threshold value Th2 in step S118, it is determined that there is a discharge abnormality for at least one of the two nozzles (step S122).

  In this case, the process proceeds to the abnormal nozzle identification process flow (FIG. 22). As shown in FIG. 22, when the abnormal nozzle specifying process is started (step S210), first, the change extraction signal of the detection signal and the threshold value Th1 are compared (step S212). If the change extraction signal of the detection signal is equal to or less than the threshold value Th1, it is determined that both nozzles are not ejecting (step S214).

  If the threshold value Th1 is exceeded in step S212, one of the two nozzles is non-ejection, and the ejection timing of the two nozzles is shifted in order to specify which nozzle is non-ejection. Are sequentially driven (step S216).

  The amount of received light is measured in synchronization with the drive timing of each nozzle (step S218), and a change extraction signal of a detection signal is obtained for the ejection operation of each nozzle. The obtained change detection signal is compared with the threshold value Th1, and it is determined that the nozzle that is equal to or lower than the threshold value Th1 is an abnormal nozzle (step S220). If an abnormal nozzle is specified in step S210 or S214, the process returns to the flowchart of FIG. 21 and proceeds to step S126.

  In step S126 of FIG. 21, processing for storing the position of the identified abnormal nozzle and the number of abnormal nozzles is performed. The means for storing the information may be a memory inside the apparatus, or may be an external storage device (removable medium) that is removable.

  Next, it is determined whether or not to end the detection (step S128). This determination is made as to whether or not the inspection of all nozzles of the head has been completed, whether or not the inspection has been completed for nozzles to be inspected (a part of the nozzle group) set in advance, or stored in step S126. This is determined from the viewpoint of whether or not the number of abnormal nozzles has reached a specified value.

  If the detection is not terminated in step S128, the process returns to step S112, the inspection target nozzle is changed, another two nozzles are selected, and the processes in steps S112 to S128 are repeated.

  If it is determined in step S128 that the detection is to be terminated, the process proceeds to step S130. In step S130, it is determined what type of response processing is to be performed according to the detection result. Table data defining the association between the detection result and the corresponding process is stored in advance in a memory (preferably a non-volatile storage unit) in the apparatus, and the processing content is determined according to this table.

  For example, when the ratio of abnormal nozzles to the total number of nozzles exceeds a specified value, ejection is stopped and recovery processing such as nozzle suction is performed (step S132). Alternatively, when the number of abnormal nozzles is relatively small and the cover on the image can be covered by substitute droplets from adjacent nozzles, recovery by adjacent nozzles (substitute droplets on the image by neighboring nozzles of undischarge nozzles) I do. Alternatively, there is also an aspect in which processing such as error display is performed instead of or in combination with the recovery processing (step S132) and the recovery processing (step S134). If no abnormal nozzle is detected, it is determined that the process is unnecessary, and the present process is terminated without performing the corresponding process (step S136).

  According to the method described in FIG. 21 and FIG. 22, since the nozzles located at a position away from the fixed distance in the optical axis direction are selected as the targets for simultaneous detection, a plurality of droplets can be detected simultaneously, and the detection time Can be shortened. As a result, the total printing throughput can be improved. In addition, when an abnormal nozzle is detected, the recovery process and the corresponding process such as recovery are performed, so that the print quality can be improved.

  In the above description, when an abnormal nozzle is detected, the abnormal nozzle is identified by sequentially discharging the nozzles discharged simultaneously (FIG. 22), but the abnormal nozzle is changed by changing the combination of the nozzles to be discharged. It is also possible to specify.

  Next, a case where an abnormality in the flight direction and speed is detected will be described.

  FIG. 23 is a flowchart illustrating an example of control for detecting an abnormality in the flight direction and speed. When the flight direction and speed abnormality detection sequence is started (step S310), first, among nozzles arranged on a straight line parallel to the optical axis of the detection light, the inter-nozzle distance Pn has a positional relationship of 2 or less. Two nozzles (two nozzles satisfying the relationship Pn ≦ L) are selected (step S312).

  The actuators of these two selected nozzles are simultaneously driven (step S314), and droplets are ejected from the two nozzles substantially simultaneously. The amount of light received by the photosensor accompanying this ejection operation is measured (step S316), and the change amount extraction signal is compared with the threshold values Th1 and Th2 (step S318). When the change extraction signal is not less than the first threshold value Th1 and not more than the second threshold value Th2, it is determined that the ejection of the two nozzles is normal.

  On the other hand, if the change amount extraction signal of the detection signal is less than the first threshold value Th1 or exceeds the second threshold value Th2 in step S318, of the ejection direction and the ejection speed. It is determined that there is an abnormality in at least one (step S322).

  After step S322 or step S320, the process proceeds to step S328 to determine whether or not to end the detection. This determination (step S328) is based on whether or not the inspection of all nozzles of the head has been completed, or whether or not the inspection has been completed for preset inspection target nozzles (partial nozzle group), or abnormal. Judgment is made from the viewpoint of whether or not a nozzle has been detected.

  If the detection is not terminated in step S328, the process returns to step S312 to change the nozzle to be inspected, select another two nozzles, and repeat the processes in steps S312 to S328.

  If it is determined in step S328 that the detection is to be terminated, the process proceeds to step S330. In step S330, it is determined what type of response processing is performed according to the detection result. Table data defining the association between the detection result and the corresponding process is stored in advance in a memory (preferably a non-volatile storage unit) in the apparatus, and the processing content is determined according to this table.

  For example, when an abnormal nozzle is detected, ejection is stopped and recovery processing such as nozzle suction is performed (step S332). Alternatively, even if an abnormal nozzle is detected, if it is possible to cover the image with the substitute ejection by the adjacent nozzle, recovery by the adjacent nozzle (substitute ejection on the image by the neighboring nozzle of the non-ejection nozzle) is performed. This is performed (step S334). There is also an aspect in which processing such as error display is performed instead of or in combination with the recovery processing (step S332) and the recovery processing (step S334). If no abnormal nozzle is detected, it is determined that the process is not necessary, and this sequence is terminated without performing the corresponding process (step S336).

  Note that when an abnormal nozzle is detected, the abnormal nozzle can be identified by sequentially discharging the simultaneously ejected nozzles or changing the combination of the ejected nozzles, as in the example described in FIG. is there.

  According to the method described with reference to FIG. 23, it is possible to detect a flying direction abnormality and a flying speed abnormality with high accuracy. In addition, when an abnormal nozzle is detected, the recovery process and the corresponding process such as recovery are performed, so that the print quality can be improved.

  In the above description, the example in which the non-ejection detection sequence (FIGS. 21 and 22) and the ejection direction and ejection speed abnormality detection sequence (FIG. 23) are performed independently has been described. Is also possible.

  FIG. 24 is a flowchart showing a detection procedure in which a non-ejection detection sequence and a flight direction and speed abnormality detection sequence are combined.

  In the figure, the same or similar steps as those in the flowcharts described in FIGS. 21 to 23 are denoted by the same step numbers, and the description thereof is omitted.

  In the flowchart of FIG. 24, the determination in step S129 is added compared to FIG. This determination is processing for determining whether or not to detect an abnormality in the ejection direction and ejection speed following the detection of non-ejection. The determination may be made based on a detection mode designated by a user via a predetermined input device (such as a user interface), or may be automatically determined by a program based on time management or other predetermined conditions such as a timer. Good.

  If it is determined in step S129 that the abnormality in the ejection direction and the ejection speed is not detected, the process proceeds to step S130, and the recovery process and recovery are performed based on the non-ejection detection result as described below with reference to FIG. Processing such as processing and error display is performed (steps S130 to S136).

  On the other hand, if it is determined in step S129 that an abnormality in the flight direction and speed is to be detected, the process proceeds to step S140. In step S140, the presence or absence of a non-ejection nozzle is determined based on the non-ejection detection result. When a non-ejection nozzle has been detected, recovery processing (step S142) is performed, and after non-ejection is resolved, the process proceeds to a flight direction and speed abnormality detection process (explained in FIG. 23) (FIG. 23). 24 step S144).

  If no ejection nozzle is detected in step S140, the recovery process (step S142) is omitted, and the process proceeds to the flight direction and speed abnormality detection sequence (described in FIG. 23) (FIG. 24). Step S144).

  This is based on the premise that the nozzle to be inspected is not non-ejection in the flight direction and speed abnormality detection sequence described with reference to FIG. When non-ejection is detected in the preceding non-ejection detection sequence, recovery processing such as nozzle suction is performed, and after non-ejection nozzles are eliminated, the process proceeds to an abnormality detection sequence for the ejection direction and ejection speed in the latter stage.

  When the nozzles fail to discharge, an abnormality in the flight direction and speed will occur at first, and then discharge will not occur. Therefore, after detecting the abnormality in the flight direction and speed first, A procedure of detecting discharge is also possible.

[Means for changing the beam shape of the detection light]
Here, a configuration for controlling the cross-sectional shape of the detection light beam 94 will be described. A lens system that converts parallel light of a certain width into parallel light of a different width is generally configured as an optical system similar to a “telescope”. When the telescope is viewed at infinity, the incident light becomes parallel light, and the outgoing light from the eyepiece also becomes parallel light. When light is incident on the telescope optical system from the “eyepiece side”, the telescope optical system functions as a beam expander. An example of the basic configuration of such an optical system is shown below.

  FIG. 25 shows a first example of a basic configuration of an optical system that converts parallel light having a certain width into parallel light having a different width. FIG. 25A is a plan view of the optical system as viewed from above. FIG. 2B shows the optical system as viewed from the side (front). In other words, views viewed from two directions orthogonal to the optical axis are shown as (a) and (b), respectively. In these figures, it is assumed that light is incident from the left (hereinafter, the relations (a) and (b) in FIGS. 26 to 31 and the incident light incident direction are the same as those in FIG. 25). .

  The configuration shown in FIG. 25 is a Galileo type beam expander optical system, and the lens 200a diverges light in two directions orthogonal to the optical axis, particularly in one direction shown in FIG. It is a concave lens, and the lens 200b is a convex lens, and functions as a beam expander that converts the beam width from d1 to d2. In addition, as shown in FIG. 25A, a cylindrical type beam expander having no optical power is provided in another direction orthogonal to the optical axis. Thereby, rectangular parallel light having different vertical and horizontal sizes can be formed.

  FIG. 26 is a second example showing a basic configuration of an optical system that converts parallel light with a certain width into parallel light with a different width. The second example is a Kepler type beam expander optical system, and both the lens 202a and the lens 202b are convex lenses in two axes orthogonal to the optical axis, particularly in the direction shown in FIG. It functions as a beam expander and converts the beam width. Further, as shown in FIG. 26 (a), a cylindrical type beam expander having no optical power is provided in another direction orthogonal to the optical axis.

  Any of the optical systems shown in FIGS. 25 and 26 described above can be used as a beam expander.

  A third example of the basic configuration shown in FIG. 27 is an example in which two Galileo type beam expanders having different focal lengths in the type shown in FIG. 25 are connected in series and connected in series. That is, in the direction shown in FIG. 27A, the parallel light width is narrowed by the beam expander including the convex lens 204a and the concave lens 204b in the preceding stage of the incident light, and in the direction shown in FIG. A beam expander including a concave lens 204c and a convex lens 204d widens the parallel light width.

  FIG. 28 shows a fourth example of the basic configuration. An example of this is a beam expander using an anamorphic prism pair. As shown in the figure, the width of the emitted light can be continuously changed according to the incident angle of the parallel light by using the rectangular prisms 206a and 206b having a trapezoidal cross section (see FIG. 31). . By using two pairs of the prisms 206a and 206b and placing them in an appropriate positional relationship, the incident optical axis and the outgoing optical axis can be made parallel (but not coincident). Further, by using two of these prisms 206a and 206b, the range in which the width of the parallel light can be changed becomes large.

  Further, in FIG. 28, a plane mirror (mirror) 206c is placed after these prisms 206a and 206b, and the position of the mirror 206c is adjusted so that the optical axis after converting the width of the parallel light is made constant. ing. In this case, the optical axis after passing through the prisms 206a and 206b does not need to be parallel to the incident light, and by adjusting the position and angle of the mirror 206c at the same time, the outgoing light always reflected by the mirror 206c The optical axis can be made constant.

  Next, a configuration example of an optical system in which the width of parallel light is variable, that is, the relationship between the width of incident light and outgoing light is variable will be described.

  First, in the system using the lens as shown in FIG. 25 or FIG. 26 described above, generally known zoom optics is used for one or both of the left-side incident side lens and the right-side exit side lens in these drawings. By using the system and making the focal length variable, the relationship between the width of the incident light and the outgoing light can be made continuously variable. In this case, the zoom optical system uses a cylindrical lens as shown in FIGS.

  FIG. 29 shows a first configuration example in which the parallel light width is variable. This example is an optical system similar to that shown in FIG. 25, a lens 208a that is a concave lens in one direction orthogonal to the optical axis, a cylindrical lens in the other direction, a convex lens in one direction, and the like. In this direction, the lens 208b is a cylindrical lens. In particular, the focal length of the exit-side lens 208b is shorter than that in the example of FIG.

  That is, the relationship between the incident light width d3 and the outgoing light width d4 can be changed by changing the focal length of the outgoing lens 208b shown in FIG. A plurality of optical systems having different emission widths as shown in FIG. 25 or FIG. 29 are prepared and switched, and parallel light having a necessary width can be obtained.

  FIG. 30 is a diagram illustrating a second configuration example in which the parallel light width is variable. This configuration is an example in which a movable aperture that changes the width of parallel light is arranged on the emission side. As shown in FIGS. 30A and 30B, the basic lens configuration of this example is the same as that shown in FIG. 25. The incident-side lens 210a is a concave lens in one direction orthogonal to the optical axis, and the like. The exit lens 210d is a convex lens in one direction orthogonal to the optical axis, and is a cylindrical lens in the other direction. Furthermore, in this example, a movable aperture 212 for changing the width of parallel light is provided behind the lens 210d on the emission side. The aperture 212 is driven as indicated by an arrow in FIG. 30B, and the gap is adjusted to make the width of the parallel light variable.

  Also, in this example, the aberration is favorably corrected by combining a plurality of lenses 210b and 210c with respect to the exit-side lens 210d. As described above, the use of the aberration-corrected optical system provides a configuration suitable for use for the purpose of allowing parallel light to pass through a relatively long distance, such as that used for detecting ink droplets.

  FIG. 31 shows a third example in which the parallel light width is variable. This shows a configuration similar to that in FIG. 28, in which the positional relationship between the prisms 206a and 206b is changed to change the width of the parallel light.

  Next, beam shaping means for switching between the case where the cross-sectional shape of the parallel light is long in the flying direction of the ink droplet and the case where it is long in the direction orthogonal thereto will be described.

  One method for switching the vertical and horizontal directions of the parallel light width is to rotate the optical system around the optical axis. That is, in any of the optical systems shown in FIGS. 25 to 31 described above, the influence on the incident parallel light is different in two directions orthogonal to the optical axis. If the optical system is rotated 90 degrees around the optical axis except for the one shown in FIG. 31, the parallel light of the longitudinal section can be switched to the parallel light of the lateral section. In the case of FIGS. 28 and 31, the parallel light width can be similarly switched by rotating the prism portion 90 degrees around the outgoing optical axis. In these cases, the changing means 100 described with reference to FIG. 9 includes a drive system that mechanically rotates the components (lenses or prisms) of the optical system 90.

  As another method for switching the vertical and horizontal directions of the parallel light width, two beam expanders having variable parallel light widths shown in FIGS. 29 to 31 are connected in series, and each of them is orthogonal to the optical axis. A method of using the parallel light so that the width of the parallel light independently changes in one direction can be considered.

  In FIG. 27, two beam expanders connected in series are shown. However, two of the beam expanders shown in FIGS. 28 to 31 are connected in series in this way, and each is connected to the optical axis. By using the parallel light so that the width of the parallel light changes independently in two orthogonal directions, the parallel light of the vertically long cross section can be converted into the parallel light of the horizontally long cross section.

  At this time, in particular, by using a zoom lens, a pair of anamorphic prisms, or the like that can change the width of parallel light continuously, the beam shape can be continuously changed.

[Other Embodiments]
FIG. 32 shows another embodiment of the present invention. As shown in the figure, it is also possible to generate a plurality of detection light beams 244 and 245 using a plurality of light sources 241 and 242 and perform discharge detection using these plurality of detection light beams 244 and 245 at the same time. It is. In this case, a condensing lens 250 common to a plurality of detection light beams 244 and 245 is used in the light receiving system, and the light is guided to a smaller number (one in FIG. 32) of photosensors 252 than the number of light sources. Can do. In FIG. 32, two light sources 241 and 242 are shown, but a larger number of light sources may be used.

  According to such a configuration, the ejection states of a larger number of nozzles 51 can be detected at the same time, and the detection time can be further shortened.

  Further, as shown in FIG. 33, a configuration in which a light guide path 256 is disposed on the light receiving side and a photosensor 258 is disposed at an end of the light guide path 256 is also possible. The detected light beams 244 and 245 emitted from the light sources 241 and 242 are received by the light guide path 256 and guided to the photosensor 258 through the light guide path 256.

  Even in such a configuration, the number of photosensors can be smaller than the number of light sources. 33 does not require a moving mechanism of the light receiving system, and the plurality of light sources 241 and 242 can be moved independently.

  In the above description, the inkjet recording apparatus 10 has been exemplified, but the scope of application of the present invention is not limited to this. For example, the liquid ejection apparatus of the present invention can be applied to a photographic image forming apparatus provided with a liquid ejection head that applies a developing solution or the like to a photographic paper in a non-contact manner. The scope of application of the present invention is not limited to an image forming apparatus, and various apparatuses (a coating apparatus, a coating apparatus, a wiring drawing apparatus) that eject a processing liquid and other various liquids toward a discharge medium using a liquid discharge head. Etc.) can be applied.

1 is an overall configuration diagram of an ink jet recording apparatus using a liquid ejection apparatus according to an embodiment of the present invention. FIG. 1 is a plan view of a main part around a printing unit of the ink jet recording apparatus shown in FIG. Top view when the head is viewed from the ejection surface (nozzle surface) side Sectional drawing which shows the three-dimensional structure of one discharge element in a head FIG. 3 is an enlarged view showing the nozzle arrangement of the print head shown in FIG. Plane perspective view showing another configuration example of the head Schematic diagram showing the configuration of an ink supply system in an ink jet recording apparatus Main block diagram showing the system configuration of the inkjet recording apparatus of this example Configuration diagram including a partial block showing the schematic configuration of the discharge inspection device Schematic diagram showing an example of detecting droplets discharged simultaneously from multiple detection target nozzles Schematic diagram for explaining light wraparound due to diffraction phenomenon Schematic diagram showing the relationship between the distance between two droplets and the light wraparound distance It is a figure for demonstrating the principle of discharge detection, (a) is a figure which showed the cross section of the detected light beam seen from the photosensor, and the positional relationship of an ink drop, (b) is a change of the detection signal by passage of a droplet. (C) is a waveform diagram of a signal obtained by extracting a change amount of the detection signal. The figure which showed the example of the change extraction signal of the sensor output in the case of detecting two discharge droplets simultaneously The figure which showed the other example of the change extraction signal of the sensor output in the case of detecting two discharge droplets simultaneously. Schematic diagram used to explain the detection principle of flight direction abnormality and flight speed abnormality The figure which showed the example of the change extraction signal of the sensor output obtained at the time of detection of a flight direction and speed abnormality A diagram showing an example of the relationship between the nozzle to be detected and the detected light beam The figure which showed the other example of a relationship between the nozzle used as a detection object, and a detection light beam The figure which showed the other example of a relationship between the nozzle used as a detection object, and a detection light beam Flow chart showing non-ejection detection control procedure Flow chart showing the procedure of abnormal nozzle identification processing Flow chart showing control procedure for detection of abnormality in flight direction and speed Flow chart showing a detection control procedure combining non-ejection detection and flight direction / velocity abnormality detection It is a block diagram which shows the 1st example of the basic composition of the optical system which converts parallel light into parallel light of different width, (a) is a top view, (b) is a side view It is a block diagram which shows the 2nd example of the basic composition of the optical system which converts parallel light into parallel light of different width, (a) is a top view, (b) is a side view It is a block diagram which shows the 3rd example of the basic composition of the optical system which converts parallel light into parallel light of different width, (a) is a top view, (b) is a side view It is a block diagram which shows the 4th example of the basic composition of the optical system which converts parallel light into parallel light of different width, (a) is a top view, (b) is a side view It is a block diagram which shows the 1st example of the optical system which makes a parallel light width variable, (a) is a top view, (b) is a side view. It is a block diagram which shows the 2nd example of the optical system which makes a parallel light width variable, (a) is a top view, (b) is a side view. It is a block diagram which shows the 3rd example of the optical system which makes a parallel light width variable, (a) is a top view, (b) is a side view. The block diagram of the discharge inspection apparatus which shows other embodiment of this invention. The block diagram of the discharge inspection apparatus which shows other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12 ... Printing part, 12K, 12C, 12M, 12Y ... Print head, 14 ... Ink storage / loading part, 16 ... Recording paper, 22 ... Adsorption belt conveyance part, 27 ... Discharge inspection apparatus, 27A ... Light source, 27B ... photo sensor, 50 ... print head, 51 ... nozzle, 52 ... pressure chamber, 57 ... individual electrode, 58 ... actuator, 72 ... system controller, 80 ... print controller, 84 ... head driver, 85 ... discharge detection Control unit 90 ... Optical system 94 ... Detection light beam 96 ... Ink droplet (droplet) 241,242 ... Light source 244,245 ... Detection light beam 252 ... Photo sensor 256 ... Light guide path 258 ... Photo sensor

Claims (7)

A liquid ejection head having a plurality of ejection openings for ejecting droplets;
A light emitting means for generating detection light that intersects a droplet flight path of at least two discharge ports to be detected among the plurality of discharge ports;
A light receiving means for receiving detection light that has passed through a droplet flight path of at least two discharge ports to be detected, and outputting a detection signal corresponding to the amount of received light;
Among the plurality of ejection openings, at least two ejection openings arranged on a line parallel to the optical axis of the detection light and having a distance between the ejection openings along the direction of the optical axis being smaller than a predetermined specified distance are detected. A discharge port selecting means for selecting as a target;
Discharge control means for performing discharge driving for discharging droplets from at least two discharge ports selected by the discharge port selection means substantially simultaneously;
Based on the detection signal obtained from the light receiving means when the liquid droplets ejected by the ejection drive of the ejection control means pass through the detection light, the ejection state of the liquid droplets from at least two ejection ports as the detection targets is determined. A discharge state determining means for determining;
A liquid ejection apparatus comprising:   The liquid ejection apparatus according to claim 1, wherein the predetermined specified distance is a wraparound distance of diffracted light that wraps behind a droplet that blocks the detection light.   The liquid ejection apparatus according to claim 1, further comprising detection light moving means for moving the detection light relative to the liquid ejection head.   The discharge state determination means is set with a plurality of determination threshold values corresponding to the number of discharge ports that are selected as the detection target and are driven to discharge simultaneously. The plurality of determination threshold values and the light receiving means The presence / absence of abnormality of at least one of the flight direction and the flight speed of the droplets discharged from the plurality of discharge ports related to the detection target is determined based on a detection signal obtained from Or the liquid discharge apparatus of 3. Recovery means for recovering the discharge performance of the liquid discharge head;
A recovery control means for controlling a recovery operation by the recovery means based on a determination result by the discharge state determination means;
The liquid ejection apparatus according to claim 1, further comprising:   An image forming apparatus comprising the liquid ejection device according to claim 1, wherein an image is formed on a recording medium by droplets ejected from the ejection port. A method for detecting a discharge state of a liquid discharge head having a plurality of discharge ports for discharging droplets,
Light emitting means for generating detection light that intersects the droplet flight path of at least two ejection ports to be detected among the plurality of ejection ports, and the droplet flight path of at least two ejection ports to be detected A light receiving means for receiving detection light and outputting a detection signal corresponding to the amount of received light; and
Among the plurality of ejection openings, at least two ejection openings arranged on a line parallel to the optical axis of the detection light and having a distance between the ejection openings along the optical axis direction of the detection light smaller than a predetermined specified distance Select as the detection target,
Performing ejection driving for ejecting droplets from the at least two selected ejection ports substantially simultaneously,
Determining a discharge state of liquid droplets from at least two discharge ports to be detected based on a detection signal obtained from the light receiving unit when the liquid droplets discharged by the discharge driving pass the detection light. Discharge detection method characterized.

Images