JP2005349647A - Inkjet recording apparatus and ejection control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording apparatus which forms a favorable image on a medium by correcting a change in density of an image, caused by a change in viscosity of ink, and a droplet ejection control method. <P>SOLUTION: The temperature of a nozzle is set at 30°C, and a lapsed time t on the basis of a time t0, when at least a predetermined quantity of ink is ejected from each nozzle, is recorded. When the lapsed time t exceeds a time tng1 until abnormal ejection starts to occur at a nozzle temperature of 30°C, the temperature of the nozzle is set at 35°C by controlling a nozzle temperature regulating means. Additionally, a driving signal of a pressurizing means for applying an ejection force to the ink is sequentially updated in accordance with the progress of the lapsed time t. When the recording time t exceeds a time tng2 until the abnormal ejection starts to occur at a nozzle temperature of 35°C, the nozzle temperature is set at 40°C by controlling the nozzle temperature regulating means, and the driving signal is sequentially updated. When nozzle temperature control and ejection control are performed in this manner, the amount of ejection is kept constant even if the vicinity of the ink is increased, and the original density of the image can be secured. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink jet recording apparatus and an ejection control method, and more particularly to an image forming technique for expressing a gradation and color by a plurality of dots to form a preferable image.

  In recent years, ink jet recording apparatuses have become widespread as data output apparatuses for images and documents. An ink jet recording apparatus drives a recording element such as a nozzle provided in a recording head according to data, and forms data on a printing medium (recording medium) such as recording paper by ink ejected from the nozzle. it can.

  In an ink jet recording apparatus, a desired image is formed on a print medium by relatively moving a print head having a large number of nozzles and the print medium and ejecting ink droplets from the nozzles.

  In an ink jet recording apparatus, when the ink is left in a state where ink is filled in the nozzle, moisture and solvent contained in the ink are evaporated (dried), and the density of the ink is increased and the viscosity of the ink is increased. An increase in the density of ink causes a gradation failure and the like, and a thickening of ink causes a discharge failure and the like, and the gradation failure and the discharge failure significantly deteriorate the quality of the formed image.

  In general, as a method for correcting the above-described density increase, a method for controlling the temperature of the nozzle to maintain the ink density in the nozzle at a preferable density, or a method for controlling the ink discharge amount and the droplet ejection density, the ink is printed on the printing medium. There is a method of correcting the density of the image. In addition, as a method of eliminating the thickening, a method of decreasing the viscosity of the thickened ink by controlling the temperature of the nozzle, or performing spitting (purge) or suction to discharge the thickened ink in the nozzle. There are methods.

  In the ink jet recording apparatus described in Patent Document 1, an instruction input of recording density is received, and when recording, the optimum temperature of the recording head is set by detecting the outside air temperature and taking into consideration the characteristics of the recording head. By adjusting the temperature, stable and accurate recording can be performed at the instructed concentration.

In addition, in the ink jet recording head described in Patent Document 2 and the ink jet recording apparatus using the ink jet recording head, a memory having a storage area for a plurality of electrical thermal conversion elements, and image data stored in the memory are included. Accordingly, it is configured to have a gate circuit that determines the energization time of the electrical heat conversion element.
Japanese Patent Laid-Open No. 5-77424 JP-A-6-328722

  However, in the prior art, there is no method for simultaneously correcting the concentration increase and eliminating the viscosity increase. This is because when thickening occurs due to drying of the ink, this thickening affects the discharge amount of the ink and the like, and thus it is difficult to control the gradation realized by controlling the discharge amount of the ink.

  In addition, the density correction technology according to the prior art uniformly controls all nozzles in the print head. For example, since the frequency of use of the nozzles is low at the edge of the image, the density tends to increase and the color tone changes. End up. Therefore, it is necessary to control each nozzle individually according to the discharge frequency.

  The ink jet recording apparatus described in Patent Document 1 discloses density correction, but does not disclose ink viscosity increase.

  In the ink jet recording head described in Patent Document 2 and the ink jet recording apparatus using the ink jet recording head, a technique for preventing an increase in viscosity is disclosed, but density correction is not disclosed.

  The present invention has been made in view of such circumstances, and an ink jet recording apparatus and an ejection device that form a preferable image on a printing medium by correcting ink density changes and recorded image density changes due to ink viscosity changes. An object is to provide a control method.

  In order to achieve the object, the invention according to claim 1 is a print head comprising: a nozzle that ejects ink droplets onto a print medium; and a pressurizing unit that imparts ejection force to the ink droplets ejected from the nozzles. And detecting means for detecting the ink state in the nozzle, temperature variable means for changing the temperature of the ink in the nozzle, and controlling the temperature variable means in accordance with the detection result detected by the detecting means. And a control means for controlling the pressurizing means in order to obtain a predetermined discharge amount for recording a predetermined image density.

  That is, in order to detect the ink state in the nozzle and vary the temperature of the ink according to the detection result, and to obtain a predetermined discharge amount for recording a predetermined image density regardless of the ink state, Since the control is performed, it is possible to eliminate the variation in the ejection amount and the variation in the ink density due to the change in the state of the ink in the nozzle.

  The discharge head includes a full-line print head in which nozzles that discharge ink droplets are arranged over a length corresponding to the entire printable width of the print medium, and a length shorter than the length corresponding to the full width of the print medium. There is a serial type (shuttle scan type) print head that discharges ink droplets onto a print medium while scanning a short head on which nozzles for discharging ink drops are arranged in the width direction of the print medium.

  In addition, the full-line type print head is formed by staggering short heads having short nozzle rows that are less than the length corresponding to the entire printable width of the print medium, and connecting them together. It may be a length corresponding to the entire printable width.

  As the pressurizing means, a piezoelectric body (piezoelectric actuator) such as a PZT piezoelectric element may be applied, or a heater that generates bubbles by heating ink in the pressure chamber may be applied.

  In addition to the opening for ejecting ink droplets, the nozzle is formed near a pressure channel (ink chamber) for accommodating ink to be ejected from the nozzle and the opening, or in the vicinity of the opening. A thin tube (throttle) part may be included.

  The medium to be printed is a medium that receives ink droplets ejected from the print head, and it can be used regardless of paper such as cut paper, continuous paper, and seal paper, resin sheets such as OHP sheets, film, cloth, and other materials. Media.

  The print medium may include a medium called a print medium, a print medium, a recording medium, a recording medium, or an image forming medium.

  According to a second aspect of the present invention, in the first aspect of the present invention, the detection unit includes an ink viscosity detection unit that detects a viscosity of the ink, and the control unit includes an ink that is associated with an increase in the viscosity of the ink. The pressurizing unit is controlled so as to correct the variation in the discharge amount.

  That is, since it is configured to correct the variation in the ink ejection amount in accordance with the ink viscosity, the ink ejection amount can always be maintained at a constant eigenvalue.

  Generally, when moisture or ink solvent evaporates, the viscosity of the ink tends to increase. Therefore, when the detection means detects that the ink viscosity has increased, the temperature of the ink is raised and the viscosity of the ink is lowered.

  On the other hand, if the ink viscosity increases, even if a predetermined pressure is applied to the ink, the predetermined ink cannot be ejected and the ink discharge amount may decrease. Therefore, the detection means detects that the ink viscosity has increased. Then, the amount of pressure applied by the pressure means is increased, and the amount of ink discharged is corrected so that the amount of ink discharged is always constant.

  In the case of ink having a high viscosity, the amount of ink droplets actually ejected by one ejection is smaller than a predetermined ejection amount, and the dots formed on the printing medium are originally formed by the ink droplets. It becomes smaller than the size of the dot. For this reason, the proportion of dots per unit area on the print medium is reduced, and a desired recording density may not be obtained on the print medium. Therefore, for the ink having a high viscosity, the ejection amount is corrected so as to reduce the ejection amount, and the ejection amount is corrected so as to obtain a desired recording density.

  In the ejection amount correction, the amount of ink droplets ejected at one time may be increased, or the number of ejections (the number of dots formed) may be increased.

  As a mode for detecting the viscosity of the ink, there is a mode in which the ink viscosity is calculated (specified) by estimating the evaporation amount of the ink solvent using the estimation unit based on the elapsed time from the last ejection.

  According to a third aspect of the present invention, in the first aspect of the present invention, the detection unit includes an ink concentration detection unit that detects the concentration of the ink, and the control unit includes a change in ink density of the ink. The pressurizing means is controlled to correct image density fluctuations accompanying the above.

  That is, since the ink ejection amount is corrected in accordance with the ink density, the image density composed of dots formed by the ejected ink droplets can always be kept within a predetermined range.

  As an aspect of detecting the ink density, there is an aspect of calculating (specifying) the ink density by detecting the evaporation amount of the ink solvent by using the detection unit based on the elapsed time from the last ejection.

  In general, when the ink solvent evaporates from the nozzle, the ink density tends to increase, and when the ink density increases, a gradation failure may occur. Therefore, when the ink density increases, the pressure amount of the pressure means is reduced to reduce the dot size (ink droplet size), thereby obtaining an image having a predetermined density (the gradation is always set). Constant).

  On the other hand, the viscosity of the ink increases due to evaporation of the ink solvent. When the ink viscosity increases, the ink temperature can be kept within a predetermined range by increasing the ink temperature step by step, and can be discharged at normal discharge pressure, and the ink density fluctuation By correcting the ink discharge amount (pressurizing amount of the pressurizing means) to correct the dot size, the dot size can be changed to a predetermined density.

  According to a fourth aspect of the present invention, in the invention according to the second or third aspect, the detection means detects at least one of ink viscosity and ink concentration based on a pause time of the nozzle. It is characterized by doing.

  In general, when ink (a meniscus surface in a nozzle) comes into contact with air, moisture and solvent in the ink evaporate, and the viscosity of the ink and the concentration of the ink tend to increase. Further, since the viscosity of the ink tends to increase as the time during which the ink is in contact with the air, the ink viscosity and the ink concentration can be detected from the nozzle rest time.

  Counting means for counting the nozzle pause time and recording means (memory) for recording the nozzle pause time counted by the count means are provided. The counting unit and the recording unit may be combined.

  Further, the nozzle rest time may be estimated from data of an image formed on the printing medium, or the discharge history of the nozzle is recorded in a recording means, and the rest time is estimated from the discharge history ( (Calculation).

  The detecting means may detect either the ink viscosity or the ink concentration, or may detect both the ink viscosity and the ink concentration.

  According to a fifth aspect of the present invention, in the invention according to the second, third, or fourth aspect, the control means causes the temperature variable means to be instructed when a pause time of the nozzle exceeds a predetermined threshold value. And controlling to raise the temperature of the ink.

  For example, the time until the start of occurrence of satellites or splashes that split into multiple drops, or the time until the start of occurrence of an ejection abnormality in which the ink ejection amount or ejection direction differs from the original ejection amount or ejection direction, There is a mode in which these times are obtained as threshold values. With this configuration, the ink temperature can be controlled effectively according to the viscosity of the ink.

  The threshold value may be one, or a plurality of threshold values may be provided according to the setting range of the ink temperature so as to increase the temperature of the ink stepwise.

  Also, a threshold value is recorded in advance for each ink type and print head environmental temperature, and the threshold value is changed by obtaining information such as the ink type and print head environmental temperature. Also good.

  It is preferable that the upper limit of the ink temperature is set and the ink temperature is controlled so as not to exceed the upper limit. For the upper limit of the ink temperature, a mode in which the temperature of the ink does not affect other parts in the print head, a mode in which a failure (damage) does not occur in other parts in the print head, etc. Can be considered.

  Further, according to a sixth aspect of the present invention, in the invention described in any one of the first to fifth aspects, when the discharge amount of each nozzle per unit time exceeds a predetermined amount, the control unit Control is performed so that the ink temperature control state and the ink ejection control state are returned to the initial state.

  That is, since raising the temperature of the ink may promote drying of the ink, a certain amount or more of ink is ejected per unit time, and the nozzle (pressure chamber) is preferable for ejection from the ink supply system. When ink having a viscosity is supplied, the recorded elapsed time, ink temperature control, and ink discharge amount are controlled to return to the initial state. In other words, the control is performed so that the temperature of the ink is lowered and returned to the initial set temperature, the rest time count is initialized (reset), and the ejection control is initialized.

  The unit time may be an ejection cycle or an integer multiple of the ejection cycle. Further, the predetermined discharge amount may be a volume of the pressure chamber, an integral multiple of the pressure chamber volume, and an integral multiple of the discharge amount in one discharge.

  The temperature variable means may include a heating means for raising the ink temperature and a cooling means for lowering the ink temperature, or heating and cooling (natural cooling) may be controlled by turning on and off the heating means for raising the ink temperature. Good.

  Further, according to a seventh aspect of the present invention, in the invention described in any one of the first to sixth aspects, the control unit changes the drive signal applied to the pressurizing unit and is discharged from the nozzle. The ink discharge amount is changed.

  When a piezoelectric material (electromechanical transducer) such as a PZT piezoelectric element is used as the pressurizing means, increasing the peak voltage of the drive signal applied to the pressurizing means increases the amount of ink droplets ejected from the nozzles. If the peak voltage of the drive signal is reduced, the amount of ink droplets ejected from the nozzles can be reduced.

  Further, according to an eighth aspect of the present invention, in the invention described in any one of the first to seventh aspects, the print head includes a plurality of nozzles and the temperature variable means corresponding to each nozzle. The control means is characterized in that the temperature of the ink droplet is varied for each nozzle, and control is performed so as to correct the ink ejection amount for each nozzle.

  That is, since the ink temperature variable control and the droplet discharge amount correction control are performed for each nozzle, the temperature variable control and the discharge amount correction control corresponding to the status of each nozzle can be performed.

  When the number of nozzles in the print head increases, the operation rate varies depending on the nozzles. In particular, since the nozzle at the center of the print head has a higher operating rate than the nozzle at the end, it is necessary to control each nozzle according to the operating rate (frequency of use).

In order to achieve the above object, the invention described in claim 9 includes a nozzle that ejects ink droplets onto a print medium, a pressurizing unit that imparts ejection force to the ink droplets ejected from the nozzle, A discharge control method for an ink jet recording apparatus comprising: a detection step for detecting an ink state in the nozzle; and a discharge from the nozzle according to a detection result detected by the detection step. A temperature variable step of changing the ink viscosity by changing the temperature of the ink droplets to be obtained, and a predetermined discharge amount for recording a predetermined image density according to the detection result detected by the detection step A control process for controlling the pressurizing means;
It is characterized by including.

  That is, since it is possible to simultaneously control the ink density correction and the ink thickening suppression (thickening prevention) according to the state of the ink, a preferable image is formed on the printing medium.

  In this specification, the term “printing” represents not only the formation of characters, but also the concept of forming an image in a broad sense including characters, and “images” include photographs, pictures, and illustrations. In addition, characters, symbols, and the like may be included.

  According to the present invention, the ink state is detected by the detection means, the ink temperature is varied according to the detection result, the ink state is controlled, and a predetermined image density is recorded according to the detection result. Since the pressurizing unit is controlled so as to obtain a predetermined ink discharge amount for the purpose, a change in ink discharge amount and a change in ink density due to a change in the ink state are corrected, and a preferable image is formed on the print medium. be able to.

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

[Overall configuration of inkjet recording apparatus]
FIG. 1 is an overall configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. As shown in the figure, the inkjet recording apparatus 10 includes a print unit 12 having a plurality of print heads 12K, 12C, 12M, and 12Y provided for each ink color, and each print head 12K, 12C, 12M, An ink storage / loading unit 14 for storing ink to be supplied to 12Y, a paper feeding unit 18 for supplying recording paper 16, a decurling unit 20 for removing curling of the recording paper 16, and a nozzle of the printing unit 12 A suction belt transport unit 22 that is disposed to face a surface (ink ejection surface) and transports the recording paper 16 while maintaining the flatness of the recording paper 16, and a print detection unit 24 that reads a printing result by the printing unit 12, A paper discharge unit 26 that discharges printed recording paper (printed matter) to the outside.

  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. Therefore, it is preferable to automatically determine the type of paper to be used and perform ink ejection control so as to realize appropriate ink ejection according to the type of paper.

  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 greater 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. Then, the suction chamber 34 is sucked by the fan 35 to be a negative pressure, whereby the recording paper 16 on the belt 33 is sucked and held.

  When the power of a motor (not shown in FIG. 1, described as reference numeral 88 in FIG. 6) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, the belt 33 rotates in the clockwise direction in FIG. , And the recording paper 16 held on the belt 33 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.

  The printing unit 12 is a so-called full-line type head in which line-type heads having a length corresponding to the maximum paper width are arranged in a direction perpendicular to the recording paper conveyance direction (sub-scanning direction) (main scanning direction) ( (See FIG. 2). Although a detailed structural example will be described later (FIGS. 3 to 5), each of the print heads 12K, 12C, 12M, and 12Y is a recording paper of the maximum size targeted by the inkjet recording apparatus 10 as shown in FIG. The line head includes a plurality of ink discharge ports (nozzles) arranged over a length exceeding at least one side of 16.

  A print head corresponding to each color ink in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording paper 16 (hereinafter referred to as the recording paper transport direction). 12K, 12C, 12M, and 12Y are arranged. A color image can be formed on the recording paper 16 by discharging the color inks from the print heads 12K, 12C, 12M, and 12Y while the recording paper 16 is conveyed.

  As described above, according to the printing unit 12 in which the full line head that covers the entire paper width (full width of the printable region) is provided for each ink color, the recording paper 16 and the printing unit 12 are relatively moved in the sub-scanning direction. The image can be recorded on the entire surface of the recording paper 16 with only one movement (i.e., with one sub-scan). Thereby, it is possible to perform high-speed printing as compared with a shuttle type head in which the print head reciprocates in the main scanning 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 are added as necessary. May be. For example, it is possible to add a print head that discharges light ink such as light cyan and light magenta.

  Further, although the full-line type print head is applied to the print heads 12K, 12C, 12M, and 12Y mounted in the ink jet recording apparatus, the present invention can also be applied to a shuttle type head.

  As shown in FIG. 1, the ink storage / loading unit 14 has tanks that store inks of colors corresponding to the print heads 12K, 12C, 12M, and 12Y, and each tank is connected via a conduit (not shown). The print heads 12K, 12C, 12M, and 12Y communicate with each other. 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.

  The print detection unit 24 includes an image sensor for imaging the droplet ejection result of the print unit 12, and functions as a means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the image sensor.

  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 print 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.

  The print detection unit 24 reads the test pattern printed by the print heads 12K, 12C, 12M, and 12Y for each color, and detects the ejection of each head. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like. Details of discharge detection will be described later.

  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) that switches the paper discharge path so as 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.

  Next, the structure of the print head will be described. Since the structures of the print heads 12K, 12C, 12M, and 12Y provided for the respective ink colors are common, the print heads are represented by reference numeral 50 in the following.

  3A is a plan perspective view showing an example of the structure of the print head 50, FIG. 3B is a plan perspective view showing another example of the structure of the print head 50, and FIG. 4A is a plan view of the ink chamber unit. FIG. 4B is a cross-sectional view showing a three-dimensional configuration, and FIG. 4B is a plan perspective view of the ink chamber unit shown in FIG. 4A viewed from the ink ejection surface side.

  In order to increase the dot pitch printed on the recording paper surface, it is necessary to increase the nozzle pitch in the print head 50. As shown in FIGS. 3A, 3B, and 4, the print head 50 of this example includes a plurality of inks including nozzles 51 that eject ink droplets, pressure chambers 52 that correspond to the nozzles 51, and the like. The chamber units 53 have a structure in which the chamber units 53 are arranged in a staggered matrix, thereby achieving an increase in the apparent nozzle pitch density.

  That is, in the print head 50 according to the present embodiment, as shown in FIGS. 3A and 3B, a plurality of nozzles 51 that eject ink are substantially orthogonal to the conveyance direction of the print medium (in this example, the recording paper 16). This is a full line head having one or more nozzle rows arranged over a length corresponding to the entire width of the printing medium (recording paper 16) in the direction of the recording medium.

  Further, as shown in FIG. 3 (b), short two-dimensionally arranged heads 50 'may be arranged in a staggered manner and connected to form a length corresponding to the entire width of the print medium.

  Although the pressure chamber 52 provided corresponding to each nozzle 51 is not shown, its planar shape is substantially square. In this example, as shown in FIGS. 4 (a) and 4 (b), the nozzle 51 is provided at a substantially central portion of the pressure chamber 52, a supply port 54 is provided at one of the four corners of the pressure chamber 52, and each pressure chamber 52 is connected via a supply port 54 (throttle portion 54A). Are connected to the common flow channel 55.

  In addition to the embodiment shown in FIG. 4A, the supply port 54 may be provided in any one of the four sides of the pressure chamber 52, or both on the diagonal line of the pressure chamber 52. A nozzle 51 and a supply port 54 may be provided at the corner.

  An actuator 58 having an individual electrode 57 is joined to the pressure plate 56 constituting the top surface of the pressure chamber 52, and the actuator 58 is deformed by applying a driving voltage to the individual electrode 57, and the nozzle 51 Ink is ejected. When ink is ejected, new ink is supplied from the common channel 55 to the pressure chamber 52 through the supply port 54.

  As shown in FIG. 4B, a nozzle temperature adjusting heater 59 is provided on the bottom surface of the pressure chamber 52 to vary the temperature of ink in the nozzle 51 and in the vicinity of the nozzle 51. The nozzle temperature control heater 59 has an annular shape and is disposed so as to surround the periphery of the nozzle 51, and the temperature is uniform so as not to cause a distribution in the temperature of the ink in the nozzle 51 and the ink in the vicinity of the nozzle 51. To be controlled.

  The nozzle temperature adjusting heater 59 may be composed of a plurality of heaters divided in the circumferential direction as indicated by reference numeral 59 ′ indicated by a one-dot broken line. Further, in FIG. 4B, the supply port 54 and the common flow path 55 shown in FIG. 4A are omitted.

  In this example, the nozzle opening 51A may be simply referred to as the nozzle 51, and the pipe 51B that connects the nozzle opening 51A and the pressure chamber 52 and serves as a flow path for the discharged ink is referred to as a nozzle. There is. Furthermore, the nozzle opening 51A and the pipe line portion 51B may be collectively referred to as the nozzle 51.

  In the print head 50 having a large number of ink chamber units 53 having such a structure, as shown in FIG. 3A, the row direction along the main scanning direction and an oblique angle having a constant angle θ that is not orthogonal to the main scanning direction. It is a structure arranged in a grid pattern with a fixed arrangement pattern along the column direction. 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. .

  That is, 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. Hereinafter, for convenience of explanation, it is assumed that the nozzles 51 are linearly arranged at a constant interval (pitch P) along the longitudinal direction (main scanning direction) of the head.

  When the nozzles are driven by a full line head having a nozzle row corresponding to the entire width of the paper (in this example, the recording paper 16), (1) all the nozzles are driven simultaneously, (2) the nozzles are moved from one to the other. (3) The nozzle is divided into blocks, each block is sequentially driven from one side to the other, and the like in the paper width direction (direction perpendicular to the paper transport direction). The driving of the nozzle that prints a line composed of a single row of dots or a line composed of a plurality of rows of dots is defined as main scanning.

  In particular, when driving the nozzles 51 arranged in a matrix as shown in FIGS. 3A and 3B, the main scanning as described in the above (3) is preferable. That is, the 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, The nozzles 51-31,..., 51-36 are set as one block,..., And the recording paper 16 is driven by sequentially driving the nozzles 51-11, 51-12,. One line is printed in the width direction.

  On the other hand, the sub-scan is defined as the above-described full-line head and the paper are moved relative to each other to repeatedly print a line composed of one row of dots or a line composed of a plurality of rows of dots formed by the above-described main scan. To do.

  In the implementation of 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.

  FIG. 5 is a schematic diagram showing the configuration of the ink supply system in the inkjet recording apparatus 10.

  The ink supply tank 60 is a base tank for supplying ink, and is installed in the ink storage / loading unit 14 described with reference to FIG. There are two types of ink supply tank 60: a system that replenishes ink from a replenishment port (not shown) and a cartridge system that replaces the entire tank when the ink remaining amount 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 and ink temperature control are performed in accordance with the ink type. The ink supply tank 60 of FIG. 5 is equivalent to the ink storage / loading unit 14 of FIG. 1 described above.

  As shown in FIG. 5, a filter 62 is provided between the ink supply tank 60 and the print 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. 5, a configuration in which a sub tank is provided in the vicinity of the print head 50 or integrally with the print 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 nozzle surface cleaning means.

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

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

  During printing or standby, if the frequency of use of a specific nozzle 51 is reduced and ink is not ejected for a certain period of time, the ink solvent near the nozzle evaporates and the ink viscosity increases. In such a state, ink cannot be ejected from the nozzle 51 even if the actuator 58 operates.

  Before such a state is reached (within the range of the viscosity that can be discharged by the operation of the actuator 58), the actuator 58 is operated, and the cap 64 (ink near the nozzle whose viscosity has increased) is discharged. Preliminary ejection (purging, idle ejection, collar ejection, dummy ejection) is performed toward the ink receiver. In the inkjet recording apparatus 10, the preliminary ejection control is performed in conjunction with ink temperature control (details will be described later).

  Further, when air bubbles are mixed into the ink in the print head 50 (in the pressure chamber 52), the ink cannot be ejected from the nozzle even if the actuator 58 is operated. In such a case, the cap 64 is applied to the print head 50, the ink in the pressure chamber 52 (ink mixed with bubbles) is removed by suction with the suction pump 67, and the suctioned and removed ink is sent 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. Since the suction operation is performed on the entire ink in the pressure chamber 52, the amount of ink consumption increases. Therefore, it is preferable to perform preliminary ejection when the increase in ink viscosity is small.

  The cleaning blade 66 is made of an elastic member such as rubber, and can slide on the ink discharge surface (surface of the nozzle plate) of the print head 50 by a blade moving mechanism (wiper) (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. It should be noted that when the ink ejection surface is cleaned by the blade mechanism, preliminary ejection is performed in order to prevent foreign matter from being mixed into the nozzle 51 by the blade.

  FIG. 6 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, a memory 74, a motor driver 76, a heater driver 78, a print control unit 80, an image buffer memory 82, a head driver 84, 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. The 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 memory 74. The 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 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 is a control unit that controls the communication interface 70, the memory 74, the motor driver 76, the heater driver 78, and the like. The system controller 72 includes a central processing unit (CPU) and its peripheral circuits, and performs communication control with the host computer 86, read / write control of the memory 74, and the like, and controls the motor 88 and heater 89 of the transport system. A control signal to be controlled is generated.

  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 heater 89 such as the post-drying unit 42 in accordance with an instruction 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 image data in the memory 74 in accordance with the control of the system controller 72, and the generated print control. A control unit that supplies a signal (print data) to the head driver 84. Necessary signal processing is performed in the print controller 80, and the ejection amount and ejection timing of the ink droplets of the print 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. Further, the image buffer memory 82 includes setting of each nozzle such as a set temperature of each nozzle, discharge history such as discharge amount per unit time, elapsed time after discharge, maintenance history such as execution history such as purge and suction, and the like. Management data is recorded.

  In FIG. 6, the image buffer memory 82 is shown in a mode associated with the print control unit 80, but it can also be used as the memory 74. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with a single processor. Of course, a recording means for recording management data of each nozzle may be provided separately from the image buffer memory 82.

  The head driver 84 drives the actuators of the print heads 12K, 12C, 12M, and 12Y for each color based on the print data given from the print control unit 80. The head driver 84 may include a feedback control system for keeping the head driving conditions constant.

  Further, the print controller 80 sends the operation command signal for the nozzle temperature adjusting heater 59 shown in FIGS. 4A and 4B to the nozzle temperature adjusting heater driver 90 to control the nozzle temperature adjusting heater 59. . Details of the operation control of the nozzle temperature adjusting heater 59 will be described later.

  The nozzle temperature adjustment heater driver 90 controls the temperature of the nozzle temperature adjustment heater 59 according to the set value by changing the ratio of the on time and the off time according to the operation command signal sent from the print control unit 80.

  Various control programs are stored in the program storage unit 92, and the control programs are read out and executed in accordance with instructions from the system controller 72. Further, when the program is executed, the system parameters and operation parameters (setting values) recorded in the memory 74 are read as needed.

  The program storage unit 92 may use a semiconductor memory such as a ROM or an EEPROM, or may use a magnetic disk or the like. An external interface may be provided and a memory card or PC card may be used. Of course, you may provide several recording media among these recording media.

  Note that the program storage unit 92 may also be used as a recording unit for operating parameters or the like (in this example, the memory 74).

  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 80.

  The print control unit 80 performs various corrections on the print head 50 based on information obtained from the print detection unit 24 as necessary.

  In the example shown in FIG. 1, the print detection unit 24 is provided on the print surface side, and the print surface is illuminated by a light source (not shown) such as a cold cathode tube disposed in the vicinity of the line sensor. Although the configuration is such that the reflected light is read by the line sensor, other configurations may be used in the implementation of the present invention.

  6 shows a mode in which the system controller 72 and the print control unit 80 are separately provided. However, a part or all of them may be configured as a common processor (MPU, CPU), the memory 74, A part or all of recording means (storage means) such as the image buffer memory 82 may be shared.

(Discharge control)
Next, the discharge control of the inkjet recording apparatus 10 will be described in detail.

  In the inkjet recording apparatus 10, while suppressing an increase in viscosity (thickening) of the ink in the nozzle 51, a correction that occurs due to an increase in ink viscosity and a recording that occurs due to a change in ejection amount due to an increase in ink viscosity Density change is corrected.

  FIG. 7 is a timing chart showing the relationship between the elapsed time t after ejection from the nozzle 51 at the timing t 0, the temperature of the nozzle 51, and the drive signal of the actuator 58.

  As shown in FIG. 7, at the timing t0 when ink is ejected from the nozzles 51, the nozzles from the print controller 80 shown in FIG. 6 are set so that the temperature of all the nozzles (ink temperature in the nozzles) is 30.degree. An operation command is sent to the nozzle temperature adjustment heater 59 shown in FIGS. 4A and 4B via the temperature adjustment heater driver 90, and the elapsed time t is reset (t = 0 is set).

  Thereafter, an elapsed time t from the discharge time t0 is obtained and recorded in the image buffer memory 82 shown in FIG. When the elapsed time t recorded in the image buffer memory 82 becomes equal to or greater than the first threshold value tng1, the print controller 80 passes through the nozzle temperature adjustment heater driver 90 so that the temperature of the nozzle 51 becomes 35 ° C. An operation command is sent to the nozzle temperature control heater 59.

  Further, when the elapsed time t becomes equal to or greater than the second threshold value tng2, the print controller 80 operates the nozzle temperature adjustment heater 59 via the nozzle temperature adjustment heater driver 90 so that the temperature of the nozzle 51 becomes 40 ° C. When the command is sent and the elapsed time t is equal to or greater than the third threshold value tng3, an operation command is issued from the print control unit 80 to the head driver 84 so as to execute the maintenance operation (spitting, suction, etc.) of the nozzle. Sent. Further, the nozzle 51 that has undergone maintenance operations such as spitting (purge) and suction is controlled from the print controller 80 via the nozzle temperature adjustment heater driver 90 so that the temperature inside the nozzle becomes 30 ° C. An operation command is sent to the heater 59.

  The first threshold value tng1 is a time period until a discharge abnormality such as a defective ink droplet size (discharge amount abnormality) or frequent occurrence of satellites occurs at a temperature T = 30 ° C. of the nozzle 51.

  The second threshold value tng2 is the time until a discharge abnormality such as a defective ink droplet size (discharge amount abnormality) or frequent occurrence of satellites occurs at the temperature T = 35 ° C. of the nozzle 51.

  Further, the third threshold value tng3 is a time period until a discharge abnormality such as an ink droplet size defect (discharge amount abnormality) or frequent occurrence of satellites occurs at the temperature T = 40 ° C. of the nozzle 51.

  The first threshold value tng1, the second threshold value tng2, and the third threshold value tng3 described above may be changed for each ink type. Further, the temperature of the nozzle 51 may be controlled more finely to provide three or more threshold values.

  The threshold value of the elapsed time t for each ink type is recorded in advance as a data table, and when the ink type changes, the ink type (ID) is read from an information reading medium such as a barcode attached to the ink cartridge. Information may be acquired, and the threshold value of the elapsed time t may be read from the data table based on the ink type information.

  As described above, since the temperature of the ink in each nozzle 51 is controlled to increase stepwise according to the elapsed time t after ejection, the increase in the viscosity of the ink in the nozzle 51 that progresses with the elapsed time t after ejection. Can be suppressed. When the ink temperature exceeds the upper limit value (temperature exceeding 40 ° C. in this example), the maintenance operation of the nozzle is executed, and the setting of the nozzle 51 is initialized.

  As the viscosity of the ink increases, even if a predetermined pressure is applied to the ink (a predetermined drive signal is applied), the amount of ink droplets discharged from the nozzle at a time is larger than the predetermined discharge amount. May decrease.

  In order to correct such a decrease in the discharge amount, the drive signal applied to the actuator 58 shown in FIG. 4A is changed in accordance with the elapsed time t from the discharge time t0. Correction is performed so that the ejection amount of ink ejected at one time is constant regardless of the elapsed time t (regardless of the viscosity of the ink).

  FIG. 8 shows an example of changing the drive signal during discharge in the main discharge control. Note that the drive signals shown in FIG. 8 are merely examples, and do not limit the scope of application of the present invention.

  As shown in FIG. 8, a drive signal waveform 100 is a drive signal waveform in a state where no increase in the viscosity of ink occurs (initial state at t0 in FIG. 7), and its maximum voltage (peak voltage) A. Further, the corrected drive signal waveform 110 (the portion common to the drive signal waveform 100 is indicated by a solid line, and the different portion is indicated by a one-dot broken line) is the time when the elapsed time t after ejection reaches the first threshold value tng1. This is a drive signal waveform, and its maximum voltage is B. Further, the maximum voltage B of the corrected drive signal waveform 110 is approximately 102% when the maximum voltage A of the drive signal waveform 100 is used as a reference (100%). For example, if the voltage A is 10V, the voltage B is 10.2V.

  As shown in FIG. 8, the drive signal waveform 100 and the corrected drive signal waveform 110 have a common slope (voltage change amount per unit time) and a common application time, while the drive signal waveform 100 and the corrected drive signal waveform. 110 has different maximum voltages.

  8 illustrates an example in which the drive signal waveform 100 and the correction drive signal waveform 110 have a common slope, but the drive signal waveform 100 and the correction drive signal waveform 110 may have different slopes.

  The drive signal waveform shown in FIG. 7 indicates the maximum voltage (corresponding to voltage A and voltage B) of the drive signal waveform 100 and the corrected drive signal waveform 110 shown in FIG.

  As shown in FIG. 7, between the discharge timing t0 and the first threshold value tng1, the maximum voltage of the drive signal is continuously updated from the voltage A to the voltage B as the elapsed time t progresses. At a threshold value tng1 of 1, the maximum voltage of the drive signal is changed from voltage B to voltage C.

  In addition, between the first threshold value tng1 and the second threshold value tng2, the maximum voltage of the drive signal is continuously updated from the voltage C to the voltage D as the elapsed time t progresses. The maximum voltage of the drive signal is changed from the voltage D to the voltage E at the threshold value tng2.

  Further, between the second threshold value tng2 and the third threshold value tng3, the maximum voltage of the drive signal is continuously updated from the voltage E to the voltage F as the elapsed time t progresses. Of course, the control may be performed so that the maximum voltage of the drive signal is changed stepwise in each section (the maximum voltage of the drive signal is changed every predetermined time).

  Although not shown in FIG. 7, since the setting of the nozzle 51 is initialized at the third threshold value tng3, the maximum voltage of the drive signal is changed from the voltage F to the voltage A.

  Further, when the elapsed time t reaches the first threshold value tng1, the temperature control of the nozzle increases the temperature of the nozzle 51 so that the viscosity of the ink in the nozzle whose viscosity has increased is brought close to (lowered) the original viscosity. Is done. As a result, the maximum voltage of the drive waveform is adjusted within a predetermined range, and correction for obtaining the original discharge amount becomes possible.

  Further, in order to correct the gradation change corresponding to the increase in the ink density due to the evaporation and concentration of the ink solvent during the period from the discharge timing t0 to Tng1, the voltage A is changed from the voltage A to the voltage C (however, the voltage Control is performed to lower the initial maximum voltage to A> voltage C).

  Similarly, when the second threshold value tng2 is reached, control is performed to lower the initial maximum voltage from voltage C to voltage E (voltage C> voltage E). As a result, even if the ink density rises, an image can be formed with a predetermined gradation density.

  Next, the flow of the main discharge control will be described with reference to FIG. FIG. 9 is a flowchart showing a flow of the above-described discharge control.

  When the main discharge control is started (step S10), the nozzle temperature adjusting heater 59 shown in FIG. 4 is operated to preheat all the nozzles in the print head 50 (step S12). It is detected whether the nozzle temperature T is 30 ° C. (step S14).

  In step 14, when the temperature T of all the nozzles is not 30 ° C. or higher (NO determination), the process returns to step S12, and the preheating is continued until the temperature T of all the nozzles reaches 30 ° C.

  On the other hand, when the temperature T of all the nozzles reaches 30 ° C. in step S14 (YES determination), spitting is performed (step S16), and the elapsed time t is reset (step S18). In step S14, it may be detected whether the nozzle temperature T is within an error range of 30 ° C. (for example, within an error range of 5% 28.5 ° C. ≦ T ≦ 31.5 ° C.).

  When the power is turned on (when the ink jet recording apparatus 10 is started) or after being left for a long time, the initialization operation (initialization) of the ink jet recording apparatus 10 is performed. The nozzle 51 is initialized.

  When the initialization of the nozzle 51 shown in steps S10 to S18 is completed, the elapsed time t after discharge is started, and the elapsed time t after discharge is recorded for each nozzle in the image buffer memory 82 shown in FIG. (Step S20).

  When the initialization of each nozzle is completed, image recording (printing) is started (step S22), and the drive waveform is changed (updated) with the progress of the elapsed time t after ejection (step S24), and step S26. Proceed to

  Here, the update of the drive waveform includes, for example, a mode in which the maximum drive voltage is changed from the voltage A to the voltage B in the period from the discharge timing t0 to the first threshold value tng1 in FIG.

  In step S26, the end of image recording is monitored. If the image recording is not ended (NO determination), it is determined whether or not the ink discharge amount per unit time is equal to or greater than a predetermined value (step S28). . In this example, the predetermined discharge amount is set to 80 pl / 100 msec (80 pl with a unit time of 100 msec), but this value can be changed depending on the type of ink, components, environmental temperature, and the like.

  Further, it is preferable that a plurality of discharge amounts to be applied to the predetermined discharge amount are prepared in advance and can be switched depending on the type, component, environmental temperature, and the like of the ink. Examples of the predetermined discharge amount include an integer multiple of the volume of the pressure chamber 52 and an integer multiple of a single discharge amount. The unit time may be an ejection cycle or an integer multiple of the ejection cycle.

  In step S28, when the discharge amount exceeds a predetermined value (YES determination), the process proceeds to step S30, and the nozzle temperature adjusting heater 59 is controlled and recorded in FIG. 4 so that the nozzle temperature becomes 30 ° C. The elapsed time t is reset.

  On the other hand, when the discharge amount per unit time is equal to or less than the predetermined discharge amount in step S28 (NO determination), image recording, counting of elapsed time t, and recording of elapsed time t are continued, and the process proceeds to step S32. The elapsed time t is counted and the elapsed time t is reset when not only normal image recording but also purge, suction, and the like are executed.

  In step S32, it is determined whether the recorded elapsed time t is equal to or greater than the first threshold value tng1. If t <tng1 (NO determination), the process returns to step 22 to continue image recording. If t ≧ tng1 (YES determination), the process proceeds to step S34.

  In step S34, it is determined whether the recorded elapsed time t is greater than or equal to the second threshold value tng2. If t <tng2 (tng1 ≦ t <tng2) (NO determination), the nozzle temperature adjusting heater 59 is controlled to raise the temperature of the nozzle 51 to 35 ° C. (step S36), and then the process returns to step 22 to record an image. Will continue. On the other hand, if t ≧ tng2 (YES determination), the process proceeds to step S38.

  In step S38, it is determined whether the recorded elapsed time t is greater than or equal to the third threshold value tng3. If t <tng3 (tng2 ≦ t <tng3) (NO determination), the nozzle temperature adjustment heater 59 is controlled to raise the temperature of the nozzle 51 to 40 ° C. (step S40), and then the process returns to step S22 to record an image. Will continue. On the other hand, if t ≧ tng3 (YES determination), the process returns to step S12, the nozzle temperature adjusting heater 59 is controlled to lower the temperature of the nozzle 51 to 30 ° C., and the initialization of the nozzle is executed.

  Here, if the temperature of the nozzle 51 exceeds 40 ° C., the apparatus does not become abnormal, but it is expected to affect the temperature control and temperature control of other nozzles (particularly neighboring nozzles). Image recording is continued while maintaining the temperature at 40 ° C. When the image recording is completed, the above-described initialization of the nozzle 51 is executed.

  If it is determined in step S26 that the image recording is completed (YES determination), after the paper discharge process, spitting (step S42) and heating of the nozzle 51 are stopped (step S44), and the image recording end process is performed. Is executed (step S46), and image recording is terminated (step S48).

  The ink jet recording apparatus 10 includes temperature monitoring means for monitoring the temperature of the nozzle 51, and the temperature of the nozzle 51 is a device such as breakage of the actuator 58, peeling of an adhesive joint portion in the print head 50, or alteration of the adhesive. When reaching the temperature at which an abnormality occurs, image recording is immediately stopped and the nozzle temperature adjustment heater 59 is turned off.

  As described above, a nozzle cooling means (ink cooling means) using a Peltier element or the like may be provided to cope with a case where the temperature in the nozzle 51 is rapidly lowered or a case where the heating temperature is in a wide range.

  In addition, when continuous printing is performed, the nozzle 51 is also initialized when spit is executed between the sheets or in the margin.

  The numerical values such as the temperature, time, and discharge amount described above are merely examples, and may be changed as appropriate according to the type of ink, components, environmental temperature, and the like.

  In this example, the mode in which the above-described ejection control is performed by the print control unit 80 in FIG. 6 is illustrated. However, for example, part and all of the ejection control such as counting and recording of the elapsed time t is performed by the system controller 72. Also good. In the inkjet recording apparatus 10, when image recording is continuously performed on a narrow sheet having a width shorter than the printable width of the print head 50, the nozzle 51 is increased when the temperature in the nozzle 51 outside the print range (image range) is increased. There is a possibility that drying of the ink in 51 may be promoted. Therefore, the range in which the nozzle temperature is controlled from the size (width) of the recording paper 16 and the image range may be limited.

  In the nozzle that does not control the temperature described above, the temperature inside the nozzle may be gradually changed, or may be controlled so as to be a low temperature (constant temperature) that does not promote the drying of the ink.

  Even if the drive signal is controlled, the recording density on the recording paper 16 is different between when a small droplet (for example, ejection amount 2 pl) is ejected and when a large droplet (for example, ejection amount 11 pl) is ejected. However, since the recording density on the recording paper 16 is substantially the same when the small droplets are ejected and when the large droplets are ejected, the optimum driving signal for each droplet ejection size. It is preferable to record the data as a data table.

  As shown in FIG. 1, the ink jet recording apparatus 10 includes print heads 12K, 12C, 12M, and 12Y corresponding to four colors K, C, M, and Y. Since the components are different for each ink color, the ratio of the increase in viscosity and the increase in density is different for each ink color. Therefore, it is preferable to obtain an optimum drive signal for each ink color in advance and record it in a data table. The data table may be updated from the temperature change history and the discharge amount change history.

  In the inkjet recording apparatus 10 configured as described above, a discharge amount (discharge amount per unit time) is recorded for each nozzle, and an elapsed time t after a predetermined amount or more is discharged for each nozzle is recorded. Is done. Control is performed to increase the temperature of the ink in the nozzles according to the elapsed time t, and an increase in the viscosity of the ink is suppressed. On the other hand, since the drive signal is changed from the elapsed time t and the temperature of the nozzle 51 to correct the decrease in the ejection amount due to the increase in ink viscosity, the stability of the recording density of the image formed on the recording paper 16 is improved. Is expected.

  Further, since the above discharge control is performed for each nozzle, the density correction can be performed according to the situation of each nozzle, and the stability of the recording density is improved.

1 is a basic configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. FIG. 1 is a plan view of the main part around the printing of the ink jet recording apparatus shown in FIG. Plane perspective view showing structural example of print head The figure which shows the three-dimensional structure etc. of the ink chamber unit which a print head has 1 is a conceptual diagram showing the configuration of an ink supply system in an ink jet recording apparatus according to an embodiment. Main part block diagram which shows the system configuration | structure of the inkjet recording device which concerns on this embodiment. Timing chart for explaining ejection control of an ink jet recording apparatus according to an embodiment of the present invention The figure which shows the drive signal waveform of the inkjet recording device which concerns on embodiment of this invention. 1 is a flowchart showing a flow of ejection control of an ink jet recording apparatus according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 50 ... Print head, 51 ... Nozzle, 52 ... Pressure chamber, 58 ... Actuator, 59 ... Nozzle temperature control heater, 72 ... System controller, 74 ... Memory, 80 ... Print control part, 82 ... Image buffer Memory 84 ... Head driver 90 ... Nozzle temperature control heater driver 92 ... Program storage unit 100,110 ... Drive signal

Claims (9)

A print head comprising: a nozzle that ejects ink droplets onto a print medium; and a pressurizing unit that applies ejection force to the ink droplets ejected from the nozzles;
Detecting means for detecting an ink state in the nozzle;
Temperature variable means for varying the temperature of the ink in the nozzle;
Control means for controlling the temperature varying means according to the detection result detected by the detection means, and for controlling the pressurizing means to obtain a predetermined discharge amount for recording a predetermined image density;
An ink jet recording apparatus comprising: The detection means includes ink viscosity detection means for detecting the viscosity of the ink,
2. The ink jet recording apparatus according to claim 1, wherein the control unit controls the pressurizing unit so as to correct a variation in an ink discharge amount accompanying an increase in the viscosity of the ink. The detection means includes ink density detection means for detecting the density of the ink,
2. The ink jet recording apparatus according to claim 1, wherein the control unit controls the pressurizing unit in order to correct an image density variation accompanying an ink density variation of the ink.   4. The ink jet recording apparatus according to claim 2, wherein the detection unit detects at least one of ink viscosity and ink density based on a pause time of the nozzle.   4. The control unit according to claim 2, wherein when the nozzle idle time exceeds a predetermined threshold value, the control unit controls the temperature variable unit to increase the temperature of the ink. Or the inkjet recording device of 4.   The control means controls to return the ink temperature control state and the ink discharge control state to an initial state when the discharge amount of each nozzle per unit time exceeds a predetermined amount. The inkjet recording apparatus according to any one of 1 to 5.   7. The inkjet according to claim 1, wherein the control unit changes a discharge amount of ink discharged from the nozzle by changing a drive signal applied to the pressurizing unit. Recording device. The print head includes a plurality of nozzles and the temperature variable means corresponding to each nozzle.
8. The control unit according to claim 1, wherein the control unit performs control so as to vary a temperature of the ink droplet for each nozzle and to correct an ink ejection amount for each nozzle. The ink jet recording apparatus described in 1. An ejection control method for an inkjet recording apparatus, comprising: a print head having a nozzle that ejects ink droplets onto a print medium; and a pressurizing unit that imparts ejection force to the ink droplets ejected from the nozzles. ,
A detecting step of detecting an ink state in the nozzle;
A temperature variable step of changing the ink viscosity by changing the temperature of the ink droplets ejected from the nozzles according to the detection result detected by the detection step;
A control step of controlling the pressurizing means in order to obtain a predetermined discharge amount for recording a predetermined image density according to the detection result detected by the detection step;
A discharge control method comprising:

Images