JP2005271389A - Droplet ejection device, droplet ejecting method, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a droplet ejection device and a droplet ejection method for controlling the internal pressure of an ejection head so as to suppress a fluctuation in ejection quantity, to thereby satisfy necessary ejection conditions, and to provide an image forming device which prevents degradation in printing quality and recording speed by using the droplet ejection device. <P>SOLUTION: According to the configuration of the droplet ejection device, an internal pressure detecting means (90) is arranged in the ejection head (50), and a head internal pressure adjusting means (80) is arranged in a liquid supply system to the ejection head (50). During printing (during ejection action), the head internal pressure is measured and the internal pressure adjusting means (80) is controlled so as to maintain the head internal pressure in a predetermined range. It is preferred that the internal pressure adjusting means (80) is formed of a mechanism that can vary a pumped height h between a liquid surface (85) of a liquid tank (60) and a nozzle surface (50A) of the ejection head (50). Further if the ejection head (50) has a plurality of common channels, it is preferred that both the internal pressure detecting means (90) and the internal pressure adjusting means (80) are provided for each of the common channels. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a droplet discharge apparatus and method, and more particularly to a droplet discharge apparatus and method suitable for use in an image forming apparatus such as an inkjet recording apparatus that discharges droplets from a nozzle to form an image on a recording medium.

  An ink jet recording apparatus ejects ink from a recording head according to a print signal while moving the recording medium such as recording paper relative to a recording head having an ink ejection nozzle on the recording medium. An ink droplet is landed and an image is formed by the ink dot.

  When a long recording head having a length corresponding to the entire width of the recording medium (a so-called full-line type head) is used, the nozzles are arranged with high density, so that the ink flow path in the head becomes narrower, and the ink As a result, the amount of ink consumed becomes very large as a whole, and there is a possibility that the ink supply to the liquid chamber in the head may not be in time when printing is performed with a high duty.

  For this reason, there is a problem that the size of the ejected droplet is reduced and an appropriate image is not printed. For example, since the print density decreases as the droplet size decreases, a density change occurs in one print, and the required maximum density (Dmax) cannot be obtained at the trailing edge of the image. In addition, when a plurality of sheets are printed, if the required ink supply is not in time during the ejection suspension period between sheets and the next print is started before the head internal pressure recovers to a predetermined value, the plurality of sheets are printed. Concentration differences also occur between the two.

  Furthermore, if the delay in ink supply becomes more significant, the meniscus shape of the nozzle will eventually collapse, and ink cannot be supplied to the tip of the nozzle, making it impossible to discharge. In particular, in the case of a thermal ink jet in which ink is rapidly heated by the heat energy of a heating element (heater) and the ink is ejected by the force of bubbles due to film boiling, the meniscus collapses and there is no ink in the heater section If this continues, there is a problem that the heater burns out.

In response to such a problem, Patent Document 1 detects the head internal pressure and changes the recording speed so that the print pressure does not deteriorate when the continuous recording is performed with a high duty. ) To propose.
Japanese Patent Laid-Open No. 2002-355953

  However, the technique disclosed in Patent Document 1 has a drawback in that print productivity is deteriorated because the recording speed decreases instead of maintaining the print quality.

  The present invention has been made in view of such circumstances, and provides a droplet discharge apparatus and method capable of managing the head internal pressure to suppress fluctuations in the discharge amount and maintaining the required discharge conditions. Objective. In addition, an object of the present invention is to provide an image forming apparatus capable of preventing a decrease in print quality and a decrease in recording speed by using such a droplet discharge device.

  In order to achieve the above object, a droplet discharge device according to a first aspect of the present invention includes a discharge head in which a nozzle for discharging a droplet and a flow path communicating with the nozzle are formed, and a discharge head for discharging to the discharge head. Liquid supply means for supplying the liquid, internal pressure detection means for detecting the internal pressure of the discharge head, internal pressure adjustment means for adjusting the internal pressure of the discharge head, and detection information obtained from the internal pressure detection means during the discharge operation. And a control means for controlling the internal pressure adjusting means so as to keep the internal pressure of the ejection head within a predetermined range.

  According to the present invention, the liquid supplied from the liquid supply means to the discharge head is discharged from the nozzle through the flow path in the head. Although it is conceivable that the internal pressure of the discharge head decreases with the discharge operation, in the present invention, the internal pressure of the head is detected by the internal pressure detection means during discharge, and pressurization / depressurization by the internal pressure adjustment means is controlled according to the detection result. Thus, the internal pressure of the discharge head is maintained within a predetermined range. As a result, the internal pressure fluctuation of the discharge head can be suppressed within a certain range during the discharge operation, and the required discharge conditions can be maintained.

  The “predetermined range” that defines the permissible range of the internal pressure fluctuation is appropriately designed according to the actual apparatus configuration. For example, the permissible range is set from the viewpoint of suppressing the variation in the ejected droplet amount due to the internal pressure variation within a certain range.

  The invention according to claim 2 relates to an aspect of the droplet discharge device according to claim 1, further comprising reference value setting means for determining a determination reference value for internal pressure control by the control means, wherein the control means includes the internal pressure. Control is performed to increase the internal pressure of the ejection head when the internal pressure value detected by the detecting means is lower than the determination reference value.

  The determination reference value set by the reference value setting means is compared with the internal pressure value of the ejection head obtained from the internal pressure detection means during the discharge operation. If the head internal pressure is below the determination reference value, the internal pressure The internal pressure adjusting means is controlled in the pressurizing direction to compensate for the decrease. Thus, the internal pressure fluctuation is corrected and maintained within a predetermined range.

  For example, as the reference value setting means, there is a mode in which the determination reference value is determined based on the measurement result of the head internal pressure in the non-ejection state (the state before the ejection operation).

  A third aspect of the present invention relates to an aspect of the droplet discharge device according to the first or second aspect, wherein the discharge head is provided corresponding to each nozzle and discharges from each nozzle. A plurality of liquid chambers for storing liquid, and at least one common flow path that communicates with at least some of the plurality of liquid chambers and supplies the liquid to each of the liquid chambers, The internal pressure detecting means and the internal pressure adjusting means are provided independently for each of the common flow paths.

  In the case of a discharge head having a flow path structure in which liquid is supplied to each liquid chamber via an individual supply path branched from the common flow path toward each liquid chamber, the internal pressure detection means and the internal pressure adjustment in units of the common flow path It is preferable that a means is provided to independently detect the internal pressure and control the internal pressure adjustment according to the detection result for each common flow path.

  In particular, in a long ejection head, since the flow path becomes long and locality of the supply flow path resistance is likely to occur, the locality of the supply flow path resistance can be eliminated by providing a plurality of common flow paths. In this case, the locality of the discharge conditions can be eliminated by providing independent internal pressure detecting means and internal pressure adjusting means corresponding to each common flow path.

  The “common flow path” here refers to any aspect of the main flow (main flow path portion) directly connected to the liquid supply port for introducing the liquid from the liquid supply means to the discharge head, or the branch flow branched from the main flow. included. Further, it is desirable that there is no locality of internal pressure in one common flow path (it is a level that can be substantially ignored), and it is desirable to realize this by designing the flow path shape and cross-sectional area of the common flow path.

  The invention according to claim 4 relates to an aspect of the droplet discharge device according to claim 1, 2, or 3, wherein the internal pressure adjusting means is negative depending on a water head difference between the liquid tank communicating with the discharge head and the discharge head. It is configured to generate pressure, and includes a mechanism that moves at least one of the liquid tank and the discharge head to vary the water head difference.

  Although a mode in which a pump is used as the internal pressure adjusting means and the head internal pressure is adjusted by pressurization / depressurization of the pump is possible, a mode using water head pressure is more preferable as shown in claim 4. By changing the relative height (pumping height) from the liquid surface in the liquid tank to the nozzle surface of the discharge head, by changing the internal pressure of the discharge head, subtle pressure control becomes possible. Internal pressure adjustment with higher accuracy than control can be realized.

  The invention according to claim 5 provides an image forming apparatus that achieves the object. That is, an image forming apparatus according to a fifth aspect includes the liquid droplet ejection apparatus according to any one of the first to fourth aspects, and forms an image on a recording medium by the liquid droplets ejected from the nozzle. Features.

  For example, an ejection head applied to the image forming apparatus includes pressure generating means for causing a pressure change in the liquid in the liquid chamber communicating with the nozzle to eject liquid droplets from the nozzle, and based on the image data, A desired dot arrangement is realized by controlling the pressure generating means.

  According to the image forming apparatus of the present invention, the internal pressure of the head is detected during printing, and the internal pressure is controlled within the predetermined range by controlling the internal pressure adjusting means according to the detection result. It is possible to suppress fluctuations in the amount of ejected droplets accompanying this. As a result, it is possible to maintain a substantially constant discharge condition (within a predetermined allowable range) at all times, irrespective of the print duty high / low, and to maintain the print quality and prevent the recording speed from being lowered. it can. “Duty” refers to the ratio of the number of nozzles that are actually driven to the total number of nozzles in the ejection head. In the case of an image forming apparatus, the duty can be predicted (calculated) based on image data to be printed.

  As a configuration example of the ejection head, a full-line type inkjet head having a nozzle row in which a plurality of nozzles for ejecting ink are arranged over a length corresponding to the entire width of the recording medium can be used.

  In this case, a plurality of relatively short ejection head blocks having nozzle rows that are less than the length corresponding to the full width of the recording medium are combined and connected to form a nozzle row corresponding to the full width of the recording medium as a whole. There is a mode to do. In such a configuration, it is preferable that the internal pressure detecting means and the internal pressure adjusting means are provided independently for each ejection head block.

  A full-line type inkjet head is usually arranged along a direction perpendicular to the relative feeding direction (relative conveyance direction) of the recording medium, but at a certain angle with respect to the direction perpendicular to the conveyance direction. There may also be a mode in which the ink jet is arranged along an oblique direction with the.

  A “recording medium” is a medium that can record an image by the action of an ejection head (a medium that can be called an ejection medium, a printing medium, an image forming medium, a recording medium, an image receiving medium, etc.), continuous paper, cut paper It includes various media regardless of materials and shapes, such as a sealing 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 an ejection head, an intermediate transfer medium, and the like.

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

  The invention according to claim 6 provides a method invention for achieving the object. That is, a droplet discharge method according to a sixth aspect includes a liquid supply step of supplying a discharge liquid to a discharge head having a nozzle for discharging a droplet and a flow path communicating with the nozzle, and a flow path of the discharge head. A discharge process for generating a pressure change in the liquid inside and discharging a droplet from the nozzle; an internal pressure detection process for detecting an internal pressure of the discharge head during the discharge operation; and detection information obtained by the internal pressure detection process. And an internal pressure control step of controlling the internal pressure of the discharge head so as to keep the internal pressure of the discharge head within a predetermined range.

  According to the present invention, the internal pressure of the head is measured during the discharge operation, and the internal pressure adjusting means is controlled to correct the pressure so as to keep the internal pressure within a predetermined range based on the detection result. The internal pressure fluctuation is suppressed, and the required discharge conditions can be maintained.

  In addition, according to the image forming apparatus using the droplet discharge device according to the present invention, it is possible to maintain the print quality within one print and between a plurality of prints, and avoid a decrease in recording speed. The

  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 droplet discharge device 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 heads (hereinafter referred to as “ink jet heads”) corresponding to black (K), cyan (C), magenta (M), and yellow (Y) inks. 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 a recording sheet as a recording medium 16 is disposed opposite to the decurling unit 20 for removing the curl of the recording paper 16 and the nozzle surface (ink ejection surface) of the printing unit 12 to improve the flatness of the recording paper 16. A suction belt conveyance unit 22 that conveys the recording paper 16 while holding it, a print detection unit 24 that reads a printing result by the printing unit 12, and a discharge that discharges the printed recording paper (printed matter) to the outside. And parts 26, and a.

  The ink storage / loading unit 14 has an ink tank that stores ink of a color corresponding to each of the heads 12K, 12C, 12M, and 12Y, and each tank has a head 12K, 12C, 12M, and 12Y through a required pipe line. Communicated with. 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 multiple types of recording paper are used, an information recording body such as a barcode or wireless tag that records paper type information is attached to the magazine, and the information on the information recording body is read by a predetermined reader. Thus, 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 portions facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 24 are horizontal ( Flat surface).

  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 print unit 12 and the sensor surface of the print detection unit 24 inside the belt 33 spanned between the rollers 31 and 32. The recording paper 16 is sucked and held on the belt 33 by sucking the suction chamber 34 with a fan 35 to a negative pressure.

  The power of the motor (reference numeral 118 in FIG. 8) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, so that 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.

  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 colors and the number of colors is not limited to this embodiment, and light ink and dark ink may be added as necessary. Good. 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.

  The print detection unit 24 shown in FIG. 1 includes an image sensor for imaging the droplet ejection result of the printing unit 12, and means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the image sensor. Function as.

  The print detection unit 24 of this example is composed of a line sensor having a light receiving element array that is wider than at least the ink ejection width (image recording width) by the heads 12K, 12C, 12M, and 12Y. The line sensor includes an R sensor row in which photoelectric conversion elements (pixels) provided with red (R) color filters are arranged in a line, a G sensor row provided with green (G) color filters, The color separation line CCD sensor is composed of a B sensor array provided with a blue (B) color filter. Instead of the line sensor, an area sensor in which the light receiving elements are two-dimensionally arranged can be used.

  A test pattern or practical image printed by the heads 12K, 12C, 12M, and 12Y of each color is read by the print detection unit 24, and ejection determination of each head is performed. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like.

  A post-drying unit 42 is provided following the print detection unit 24. 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 substances 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 respective heads 12K, 12C, 12M, and 12Y for each color are common, the heads are represented by the reference numeral 50 in the following.

  FIG. 3A is a plan perspective view showing an example of the structure of the head 50, and FIG. 3B is an enlarged view of a part thereof. 3C is a plan perspective view showing another structure example of the head 50, 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). FIG. 4 is a sectional view taken along line 4-4 in FIG.

  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 FIGS. 3A and 3B, the head 50 of this example includes a plurality of ink chamber units including nozzles 51 serving as ink droplet ejection openings, pressure chambers 52 corresponding to the nozzles 51, and the like. It has a structure in which (droplet discharge elements) 53 are arranged in a zigzag matrix (two-dimensionally), and is thereby projected so as to be arranged along the head longitudinal direction (direction perpendicular to the paper feed direction). High density of substantial nozzle interval (projection nozzle pitch) is achieved.

  The configuration in which one or more nozzle rows are configured over a length corresponding to the entire width of the recording paper 16 in a direction substantially orthogonal to the feeding direction of the recording paper 16 is not limited to this example. For example, instead of the configuration of FIG. 3 (a), short head blocks 50 ′ in which a plurality of nozzles 51 are two-dimensionally arranged are arranged in a staggered manner and connected as shown in FIG. 3 (c). A line head having a nozzle row having a length corresponding to the entire width of the recording paper 16 may be configured.

  The pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape (see FIGS. 3 (a) and 3 (b)), and is connected to the nozzle 51 at both corners on a diagonal line. An outlet and an inlet (supply port) 54 for supply ink are provided.

  As shown in FIG. 4, each pressure chamber 52 communicates with a common flow channel 55 through a supply port 54. The common channel 55 communicates with an ink tank (not shown in FIG. 4, not shown in FIG. 6 and indicated by reference numeral 60) serving as an ink supply source, and the ink supplied from the ink tank 60 passes through the common 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 that also serves as a common electrode) 56 that forms the top surface of the pressure chamber 52. By applying a driving voltage to the individual electrode 57, the actuator 58 is deformed to change the volume of the pressure chamber 52, and ink is ejected from the nozzle 51 due to the pressure change accompanying this. For the actuator 58, a piezoelectric body such as a piezoelectric element is preferably used. After ink discharge, new ink is supplied from the common channel 55 to the pressure chamber 52 through the supply port 54.

  As shown in FIG. 5, the ink chamber unit 53 having such a structure is latticed in a fixed arrangement pattern along a row direction along the main scanning direction and an oblique column direction having a constant angle θ not orthogonal to the main scanning direction. The high-density nozzle head of this example is realized by arranging a large number in the shape.

  That is, with a structure in which a plurality of ink chamber units 53 are arranged at a constant pitch d along a certain angle θ 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 θ. Thus, in the main scanning direction, each nozzle 51 can be handled equivalently as a linear arrangement 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 each block is sequentially driven from one side to the other, etc., and one line or one in the sheet width direction (direction perpendicular to the sheet conveyance direction) Nozzle driving for printing individual strips 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, repetitively moving the above-described full line head and the paper to repeatedly perform one line or one band-like printing formed by the above-described main scanning is defined as sub-scanning.

  In implementing the present invention, the nozzle arrangement structure is not limited to the illustrated example. In the present embodiment, a method of ejecting ink droplets by deformation of an actuator 58 typified by a piezo element (piezoelectric element) is adopted. However, in the practice of the present invention, the method of ejecting ink is not particularly limited. 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. 6 is a schematic diagram showing the configuration of the ink supply system in the inkjet recording apparatus 10. As shown in the figure, 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. 6, 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.

  When air bubbles are mixed in the ink in the head 50 (in the pressure chamber 52), the cap 64 is applied to the head 50, and the ink in the pressure chamber 52 (ink in which the air bubbles are mixed) is removed by suction with the suction pump 67. Then, the sucked and removed ink is sent to the collection tank 68. In this suction operation, the deteriorated ink that has increased in viscosity (solidified) is sucked out when the ink is initially loaded into the head 50 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 58 is operated toward the ink receiver to discharge ink in the vicinity of the nozzle whose viscosity has increased. “Preliminary discharge” is performed. In addition, after the dirt on the surface of the nozzle plate is cleaned by a wiper such as a cleaning blade 66 provided as a cleaning means for the nozzle surface 50A, the foreign matter is prevented from entering the nozzle 51 by the wiper rubbing operation. Also, 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 50A of the head 50, and an operation of sucking ink mixed with bubbles or thickened ink is performed.

  However, since the above suction operation is performed on the entire ink in the pressure chamber 52, the amount of ink consumption is large. Therefore, when the increase in viscosity is small, it is preferable to perform preliminary discharge as much as possible.

[Description of head internal pressure adjusting means]
FIG. 7 is a configuration diagram of the internal pressure adjusting means of the head 50 in the inkjet recording apparatus 10 of the present example. In the figure, reference numeral 69 denotes a sub tank. Ink is supplied from the ink tank 60 to the sub tank 69 via the conduit 70, and ink is supplied from the sub tank 69 to the ejection head 50 via the conduit 72. The sub tank 69 is provided with an air release valve 74. By opening the air release valve 74 as necessary, the inside of the tank can be set to atmospheric pressure.

  In the figure, an example in which the sub tank 69 and the discharge head 50 are communicated with each other via the pipe line 72 is shown, but a form in which the sub tank 69 is integrated with the discharge head 50 in the practice of the present invention is also possible. In some cases, the conduit 72 is substantially omitted.

  The ink tank 60 is provided with a tank vertical movement device 80 as a pumping height adjusting means. The tank vertical movement device 80 includes a rail member 81, an eccentric cam 82, and a pulse motor 83. A guide protrusion (for example, a roller) 84 provided on the side surface of the ink tank 60 is in contact with the rail member 81, and the ink tank 60 is moved up and down along the rail member 81.

  The eccentric cam 82 is in contact with the bottom surface of the ink tank 60, and is rotated by a pulse motor 83. The pumping height h from the ink liquid level 85 in the ink tank 60 to the nozzle surface 50A of the head 50 is adjusted by moving the ink tank 60 up and down by the rotation of the eccentric cam 82 around the rotation shaft 82A.

  On the upper surface of the ink tank 60, a replenishing port 86 that enables ink replenishment is provided. The replenishing port 86 is also used as an air hole for allowing the ink tank 60 to communicate with the atmosphere, and the pressure applied to the ink liquid level 85 in the ink tank 60 is always atmospheric pressure. Further, a liquid level detection sensor 87 for detecting the position of the ink liquid level 85 is attached inside the ink tank 60. As the liquid level detection sensor 87, an electrode type sensor using a change in electrical resistance, a float switch, or the like can be used.

  An internal pressure detection sensor 90 for detecting the internal pressure is provided in the common flow path 55 (not shown in FIG. 7) of the head 50, and the detection signal is sent to the system controller 92. As the internal pressure detection sensor 90, for example, a sensor (a so-called pressure sensor) that uses a strain gauge and converts the displacement of the diaphragm into an electrical signal and outputs it can be used.

  The system controller 92 is a control unit that controls the entire inkjet recording apparatus 10 according to a predetermined program, and functions as an internal pressure control unit of the ejection head 50. Further, the system controller 92 functions as a calculation unit that performs various calculations.

  That is, the system controller 92 selects a desired signal based on a detection signal from the internal pressure detection sensor 90, a detection signal from the liquid level detection sensor 87, a detection signal from an atmospheric pressure detection sensor not shown in FIG. The pumping height h for realizing the head internal pressure is calculated, and the drive pulse applied to the pulse motor 83 is controlled according to the calculation result. In calculating the pumping height h, a table stored in a non-volatile storage means such as an EEPROM may be used, or an arithmetic process using a predetermined arithmetic expression may be performed.

[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 100, a system controller 92, an image memory 104, a motor driver 106, a heater driver 108, a print control unit 110, an image buffer memory 112, a head driver 114, and the like.

  The communication interface 100 is an interface unit that receives image data sent from the host computer 116. As the communication interface 100, a serial interface such as USB, IEEE 1394, Ethernet, and wireless network, and 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 116 is taken into the inkjet recording apparatus 10 via the communication interface 100 and temporarily stored in the image memory 104. The image memory 104 is a storage unit that temporarily stores an image input via the communication interface 100, and data is read and written through the system controller 92. The image memory 104 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 92 is a control unit that controls the communication interface 100, the image memory 104, the motor driver 106, the heater driver 108, the tank vertical movement device 80, and the like. The system controller 92 includes a central processing unit (CPU) and its peripheral circuits, and performs communication control with the host computer 116, read / write control of the image memory 104, and the like, as well as a transport system motor 118 and heater 119. In addition, a control signal for controlling the pulse motor 83 and the like of the tank vertical movement device 80 is generated.

  The motor driver 106 is a driver (drive circuit) that drives the motor 118 in accordance with instructions from the system controller 92. The heater driver 108 is a driver that drives the heaters 119 of the post-drying unit 42 and other units in accordance with instructions from the system controller 92.

  The print control unit 110 has a signal processing function for performing various processes and corrections for generating a print control signal from the image data in the image memory 104 according to the control of the system controller 92. A control unit that supplies a control signal (dot data) to the head driver 114. Necessary signal processing is performed in the print control unit 110, and the ink droplet ejection amount and ejection timing of the head 50 are controlled via the head driver 114 based on the image data. Thereby, a desired dot size and dot arrangement are realized.

  The print control unit 110 includes an image buffer memory 112, and image data, parameters, and other data are temporarily stored in the image buffer memory 112 when image data is processed in the print control unit 110. In FIG. 8, the image buffer memory 112 is shown in a form associated with the print control unit 110, but it can also be used as the image memory 104. Also possible is an aspect in which the print controller 110 and the system controller 92 are integrated and configured with one processor.

  The head driver 114 drives the ejection driving actuator 58 of the head 50 for each color based on the print data given from the print controller 110. The head driver 114 may include a feedback control system for keeping the head driving conditions constant.

  Data of an image to be printed is input from the outside via the communication interface 100 and stored in the image memory 104. At this stage, for example, RGB image data is stored in the image memory 104. The image data stored in the image memory 104 is sent to the print control unit 110 via the system controller 92. The print control unit 110 converts the data into dot data for each ink color using a known dither method, error diffusion method, or the like. Converted.

  In this way, the head 50 is driven and controlled based on the dot data generated by the print controller 110, and ink is ejected from the head 50. 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 with reference to FIG. 1, the print detection unit 24 is a block including a line sensor, reads an image printed on the recording paper 16, performs necessary signal processing, and the like to perform a print status (whether ejection is performed, droplet ejection And the detection result is provided to the print control unit 110. The reading start timing of the line sensor is determined from the distance between the sensor and the nozzle and the conveyance speed of the recording paper 16.

  The print control unit 110 performs various corrections on the head 50 based on information obtained from the print detection unit 24 as necessary. Further, the print control unit 110 determines whether or not the nozzle 51 is ejected based on the detection information obtained through the print detection unit 24, and performs a predetermined recovery operation when a non-ejection nozzle is detected. I do.

  In addition, the inkjet recording apparatus 10 includes an atmospheric pressure detection sensor 122 for measuring atmospheric pressure, and an ink physical property information reading unit 124 that reads physical property information of ink, and information obtained from the information is a system controller. 92.

  The installation location of the atmospheric pressure detection sensor 122 is not particularly limited, and various modes such as the ink tank 60 or the vicinity thereof, the sub tank 69 or the vicinity thereof are possible.

  As a means for obtaining the ink physical property information, for example, the ink physical property information is obtained from the shape of the cartridge of the ink tank 60 (a specific shape capable of identifying the ink type) or a barcode or IC chip incorporated in the cartridge. Reading means can be used. In addition, the operator may input necessary information using a user interface. The physical property information of the ink includes viscosity, density, surface tension, date of manufacture, and the like.

  The system controller 92 includes measurement information obtained from the atmospheric pressure detection sensor 122, ink physical property information obtained from the ink physical property information reading unit 124, a liquid level detection sensor 87 in the ink tank 60, and an internal pressure detection sensor 90 in the head 50. Based on this detection signal, a control target value of the pumping height h is obtained, and the tank vertical movement device 80 is controlled according to the calculation result.

  FIG. 9 is a graph illustrating a change in the internal pressure of the head accompanying a high-duty printing operation, where the horizontal axis indicates time and the vertical axis indicates pressure. This graph shows a general tendency when the head internal pressure control technique according to the present invention is not applied. As shown in the drawing, the head internal pressure at the time of non-recording (t <t1) before the start of printing is an optimum pressure P0 (negative pressure). When high duty printing is started at time t1, ink supply to the head is not in time, and the internal pressure of the head decreases (t1≤t≤t2). When printing is completed at time t2, the head internal pressure gradually recovers by supplying ink (t2 <t <t3), and eventually returns to the initial pressure P0 at time t3.

  In order to avoid a decrease in print quality due to a decrease in internal pressure during printing (t 1 ≦ t ≦ t 2), the ink jet recording apparatus 10 according to the embodiment of the present invention drives the tank vertical movement device 80 according to the internal pressure measurement result of the head 50. By doing so, the internal pressure of the head 50 is controlled to be kept within a certain range.

  FIG. 10 is an explanatory diagram showing the action of head internal pressure control in the inkjet recording apparatus 10 of this example. FIG. 10A is a graph showing a change in the internal pressure of the head detected by the internal pressure detection sensor 90 when the internal pressure correction is not performed. As described with reference to FIG. 9, the pressure decreases after the print start time t1.

  FIG. 10B is a graph of the pressure correction value calculated for the pressure fluctuation in FIG. The pressure correction value is determined so as to complement the internal pressure decrease measured in FIG. Then, the pulse motor 83 of the tank vertical movement device 80 is controlled according to this pressure correction value, and the height position of the ink tank 60 is changed by the eccentric cam 82. In this manner, the height position of the ink liquid surface 85 in the ink tank 60 (that is, the pumping height h described with reference to FIG. 7) is adjusted, and a pressure corresponding to the pumping height h is generated.

  As a result, as shown in FIG. 10C, the internal pressure of the head 50 is kept substantially constant. Since it is difficult to keep the internal pressure constant in a strict sense, the internal pressure is adjusted to fall within a certain range (allowable range). Thereby, the discharge amount is stabilized, and a constant print quality can be maintained.

  Although not shown in FIG. 10, when the printing is finished, the internal pressure of the head 50 naturally recovers. Accordingly, the tank vertical movement device 80 is operated (operated in the pressure reducing direction) accordingly, and the nozzle 51 Prevent liquid leakage from the water.

  The target value of the negative pressure in the internal pressure control of the head 50 is appropriately designed according to the actual device. For example, it is set to a range of −0.2 to −4 kPa with respect to the atmospheric pressure, and more preferably to the atmospheric pressure. On the other hand, it is good to set it as -0.4--1.5kPa.

  Also, the internal pressure detection sensors 90 described with reference to FIGS. 7 and 8 are provided at least for the number of ink supply ports of the head 50 or the number of the common flow passages 55, and the independent ink tank 60 and tank vertical movement device 80 corresponding to each of them are provided. An embodiment in which is provided is preferable. The ink supply port of the head 50 here means a basic supply port to which an ink supply system is connected.

  FIG. 11 shows an arrangement configuration example of the common flow channel 55 in the head 50. 11A to 11C, reference numerals 141 to 144 denote ink supply ports, and reference numerals 151 and 152 denote common flow paths (corresponding to reference numeral 55 in FIG. 4).

  In the example of FIGS. 11A and 11B, two common flow channel main streams 151A and 152A are formed in parallel along the longitudinal direction of the head, and each main stream is inclined in the nozzle arrangement direction with respect to the short direction of the head. A plurality of common channel tributaries 151B and 152B are communicated with each other. Ink supply ports 141 and 143 communicate with both ends of the common channel main stream 151A, and similarly, ink supply ports 142 and 144 communicate with both ends of the common channel main stream 152A. In this way, by providing a plurality of ink supply ports for one common flow path, simultaneous supply or circulation supply from a plurality of ports is possible. Of course, a configuration in which one ink supply port is provided for one common flow path is also possible. In this case, for example, the ink supply ports 143 and 144 are omitted.

  In the head 50 shown in FIGS. 11A and 11B, the internal pressure detection sensor 90 is provided in each of the common flow paths 151 and 152, and the internal pressure adjusting means described in FIG. Embodiments are preferred. The installation location of the internal pressure detection sensor 90 may be in the common channel main flow 151A, 152A, or in the common channel tributaries 151B, 152B.

  In the example of FIG. 11C, the formation region of the common flow paths 151 and 152 is divided in the longitudinal direction of the head. That is, in the drawing, the common flow path 151 formed in the left partition region of the head 50 includes two common flow path main streams 151A-1 and 151A-2 parallel to the longitudinal direction of the head. The ink supply ports 141 and 142 communicate with the ends of the common flow channel main streams 151A-1 and 151A-2, respectively.

  Similarly, the common flow path 152 formed in the right partition region of the head 50 in the figure has a structure in which two common flow path main streams 152A-1 and 152A-2 are connected in a ladder shape by a common flow path tributary 152B. The ink supply ports 143 and 144 communicate with the ends of the common channel main streams 152A-1 and 152A-2, respectively. Of course, a configuration in which one ink supply port is provided for one common flow path is also possible. In this case, for example, the ink supply ports 142 and 144 are omitted.

  In the head 50 shown in FIG. 11C, it is preferable that the internal pressure detection sensor 90 is provided in each of the common flow paths 151 and 152, and the internal pressure adjusting means described in FIG. The installation location of the internal pressure detection sensor 90 may be in the common channel main flow 151A-1, 151A-2, 152A-1, 152A-2, or in the common channel tributaries 151B, 152B.

  In FIG. 11, the example in which the two common flow paths 151 and 152 are formed in the head 50 has been described. However, the number and arrangement of the common flow paths formed in the head are not particularly limited, and the common flow paths are not limited. N (N is an integer of 1 or more) independent internal pressure detecting means and internal pressure adjusting means are provided in accordance with the number of.

  Next, an internal pressure control procedure in the inkjet recording apparatus 10 configured as described above will be described. Here, it is assumed that N internal pressure detecting means and N internal pressure adjusting means are provided.

  FIG. 12 is a flowchart showing an internal pressure control procedure of the head 50 in the inkjet recording apparatus 10 of the present example.

  When a print instruction is given to the inkjet recording apparatus 10 of this example (step S10), first, the internal pressures of the heads 50 are respectively measured by the N internal pressure detection sensors 90, and a determination reference value is set based on the measured values. (Step S12). This determination reference value indicates, for example, a lower limit value and an upper limit value of an internal pressure allowable range that is a control target.

  After setting the determination reference value, a printing operation (printing operation) based on the print data is started (step S14), and head internal pressures are measured (internal pressure monitoring) by the N internal pressure detection sensors 90 (step S16). ). The measured value of each internal pressure detection sensor 90 is compared with the determination reference value, and it is determined whether or not the measured internal pressure value is lower than the determination reference value (here, the allowable lower limit value) (step S18). When the measured internal pressure value exceeds the determination reference value, the pumping height h required for correcting the internal pressure is calculated (step S20), and the tank vertical movement device 80 of the corresponding ink supply system is calculated based on the calculation result. Is driven to change the pumping height h (step S22). Thereby, the pressure according to the pumping height h is added.

  After step S22, the process returns to step S16 to continue monitoring the head internal pressure. If it is determined in step S18 that the internal pressure measurement value does not exceed the determination reference value (is within the allowable fluctuation range), the process proceeds to step S24, and it is determined whether or not the printing operation is completed. Do. Here, “end of printing operation” may be a print job for each sheet or a plurality of continuous print jobs (for example, in order units).

  If the printing operation is continuing, the process returns to step S16 and the above processing step S is repeated. If it is confirmed in step S24 that printing has ended, the process proceeds to step S26. In step S26, it is determined whether the head internal pressure has returned to the determination reference value. Here, since the head internal pressure gradually increases with the ink supply after the printing is completed, it is determined whether or not the internal pressure measurement value exceeds the allowable upper limit value.

  When it is detected that the internal pressure of the head exceeds the allowable upper limit due to the recovery of the internal pressure due to the end of printing, the pulse motor 83 of the tank vertical movement device 80 is driven to keep the pumping height h in order to keep the internal pressure within the allowable range. Change (step S28). At this time, the pumping height h may be gradually changed according to the measurement value of the internal pressure detection sensor 90, or control may be performed so as to return to the initial position before the start of printing.

  After adjusting the pumping height h in step S28, the process returns to step S26. If it is confirmed in step S26 that the internal pressure of the head 50 has returned to the determination reference value, the present control sequence is terminated (step S30).

  In the flowchart of FIG. 12, when another print instruction is input before the internal pressure returns to the original value in step S26, the following two modes can be considered. The first is a method of setting a reference value for internal pressure control based on a time point when a print instruction is newly given. The second method is to use a reference value at the time of previous printing. The latter can be said to be a more preferable control mode because it can suppress variations in the quality of the total print.

  In addition, if the internal pressure has fallen beyond the adjustable range of the internal pressure of the tank vertical movement device 80 (internal pressure adjusting means), the printing operation is temporarily stopped, and after waiting for the internal pressure to recover, printing is performed again. It is preferable to control so as to perform.

[Modification]
In FIG. 7, the example in which the pumping height is controlled by using the eccentric cam 82 and the pulse motor 83 to control the pumping height is described. However, the mechanism for moving the ink tank up and down is not limited to this example. In FIG. 7, the ink tank 60 is moved up and down. However, any structure that can change the relative height relationship between the ink liquid surface of the ink tank 60 and the nozzle surface of the head 50 may be used. You may comprise as both, and you may comprise both as a movable part. Of course, the power source is not limited to the pulse motor 83, and other actuators may be used.

  In the above description, an inkjet recording apparatus has been illustrated as an example of an image forming apparatus, but the scope of application of the present invention is not limited to this. For example, the droplet discharge device of the present invention can also be applied to a photographic image forming apparatus that applies a developing solution to a photographic paper in a non-contact manner. In addition, the application range of the droplet discharge device according to the present invention is not limited to the image forming apparatus, and various devices (coating device, coating device) that eject processing liquid and other various liquids toward the discharge medium using the discharge head. The present invention can be applied to apparatuses, wiring drawing apparatuses, and the like.

1 is an overall configuration diagram of an ink jet recording apparatus using a droplet discharge device 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. Plane perspective view showing the configuration of the head Enlarged view of the main part of Fig. 3 (a) Plane perspective view showing another configuration example of a full-line head Sectional view along line 4-4 in Fig. 3 (a) Enlarged view showing the nozzle arrangement of the head shown in FIG. Schematic diagram showing the configuration of the ink supply system in the inkjet recording apparatus of this example Configuration diagram of the internal pressure adjusting means of the head in the ink jet recording apparatus of this example Main block diagram showing the system configuration of the inkjet recording apparatus of this example A graph illustrating the change in the internal pressure of the head during high duty printing Explanatory drawing which shows the effect | action of the head internal pressure control in the inkjet recording device of this example. Plane perspective view schematically showing an example of the arrangement of common channels formed in the head Flow chart of the internal pressure control procedure of the head in the ink jet recording apparatus of this example

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12 ... Printing part, 12K, 12C, 12M, 12Y ... Head, 14 ... Ink storage / loading part, 16 ... Recording paper, 18 ... Paper feed part, 22 ... Adsorption belt conveyance part, 50 ... Head 50A ... Nozzle surface, 51 ... Nozzle, 52 ... Pressure chamber, 55 ... Common flow path, 58 ... Actuator, 60 ... Ink tank, 69 ... Sub tank, 80 ... Tank vertical movement device, 82 ... Eccentric cam, 83 ... Pulse Motor, 85 ... ink level, 87 ... liquid level detection sensor, 90 ... internal pressure detection sensor, 92 ... system controller, 110 ... print control unit, 141, 142, 143, 144 ... ink supply port, 151, 152 ... common flow Road, 151A, 152A ... Common flow channel main flow, 151B, 152B ... Common flow channel tributary

Claims (6)

A discharge head in which a nozzle for discharging droplets and a flow path communicating with the nozzle are formed;
A liquid supply means for supplying a liquid for discharge to the discharge head;
An internal pressure detecting means for detecting an internal pressure of the ejection head;
An internal pressure adjusting means for adjusting an internal pressure of the ejection head;
Control means for controlling the internal pressure adjusting means so as to keep the internal pressure of the discharge head within a predetermined range based on detection information obtained from the internal pressure detecting means during a discharge operation;
A droplet discharge apparatus comprising: Comprising reference value setting means for determining a determination reference value for internal pressure control by the control means;
2. The droplet discharge according to claim 1, wherein the control unit controls to increase the internal pressure of the discharge head when an internal pressure value detected by the internal pressure detection unit is lower than the determination reference value. apparatus. The discharge head includes a plurality of nozzles, a plurality of liquid chambers that are provided corresponding to the nozzles and store liquid discharged from the nozzles, and at least some of the plurality of liquid chambers. And at least one common flow path for supplying a liquid to each of the liquid chambers,
3. The liquid droplet ejection apparatus according to claim 1, wherein the internal pressure detecting means and the internal pressure adjusting means are provided independently for each of the common flow paths.   The internal pressure adjusting means generates a negative pressure due to a water head difference between the liquid tank communicating with the discharge head and the discharge head, and moves at least one of the liquid tank and the discharge head to vary the water head difference. The droplet discharge device according to claim 1, wherein the droplet discharge device is configured to include a mechanism for performing the operation.   An image forming apparatus comprising the droplet discharge device according to claim 1, wherein an image is formed on a recording medium by droplets discharged from the nozzle. A liquid supply step of supplying a liquid for discharge to a discharge head having a nozzle for discharging liquid droplets and a flow path communicating with the nozzle;
A discharge step of generating a pressure change in the liquid in the flow path of the discharge head and discharging a droplet from the nozzle;
An internal pressure detection step of detecting an internal pressure of the discharge head during a discharge operation;
An internal pressure control step of controlling the internal pressure of the discharge head so as to keep the internal pressure of the discharge head within a predetermined range based on detection information obtained by the internal pressure detection step;
A droplet discharge method comprising:

Images