JP2006264074A - Droplet ejector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eject a droplet from a recording head with appropriate timing by feeding back a carrying speed caused by a recording medium or a carrying passage for carrying the recording medium, and a deviation from the direction of an interval dimension from the recording head. <P>SOLUTION: The misregistration of an arrival of ink is eliminated by correcting the timing of ejection from a nozzle 40 of the recording head 36 depending on unevenness capable of occurring on a carrying belt 12 and recording paper P, so that a malfunction such as a color shift can be avoided. In double-sided printing, even if unevenness is caused by the appearance of wrinkles on the recording paper P due to moisture, included in ink, after one-side printing, the unevenness of the recording paper P etc. after the one-side printing can be canceled because a gap sensor 103 is provided in a part (except an arrangement position of a head unit 37) of the carrying belt 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention includes a recording head that ejects liquid droplets from nozzles by applying a drive signal based on image data, and the liquid ejection surface of the recording head is arranged at a predetermined interval with respect to the conveyance path of the recording paper. The present invention relates to a droplet discharge device that forms an image on the recording sheet by discharging droplets at a predetermined discharge timing.

  2. Description of the Related Art Conventionally, in an image recording apparatus, for example, an ink jet printer, a loaded recording sheet (recording sheet) is closely fixed to a conveyance path constituted by a conveyance belt or the like, and the conveyance belt is driven by a driving force, whereby a predetermined one is obtained. Transport at a constant speed in the direction.

  A recording head in which recording elements are arranged in a direction orthogonal to the one direction is disposed in the transport direction of the transport path. In this recording head, an ink ejection surface provided with nozzles is opposed to the transport path at a predetermined interval.

  When the recording paper reaches the position where the recording head is disposed, this is detected by a paper detection sensor, and recording by the recording head is started with the leading edge detection by this paper detection sensor as a trigger.

  Ink droplets are ejected from the nozzles of the recording head at a predetermined timing and land on the recording paper at a predetermined speed, whereby an image is recorded on the recording paper.

  In general, the distance between the nozzle and the recording paper is 1.5 mm, the conveyance speed of the conveyance belt is 300 mm / sec, and the ink ejection speed is 10 m / sec. Naturally, if any of the above parameters has an error, the landing position on the recording paper will be shifted.

  For example, if the transport speed of the transport belt is uneven (speed deviation) or irregularities occur on the recording paper, the landing position of the ink droplets shifts according to the gap size error due to the uneven speed. Will be reduced.

  Here, in Patent Document 1, the speed of the conveyance belt that conveys the recording material is detected by an encoder attached to a dry roll, and the drive timing (discharge timing) of the recording head is controlled according to the speed deviation of the conveyance belt. Is disclosed.

In Patent Document 2, surface undulations (joints) on the conveyor belt are detected and drive control of the conveyor belt is performed according to the surface state.
JP-A-2-187355 JP-A-5-092632

  However, in the above-mentioned Patent Document 1, it is not possible to cope with the unevenness of the recording paper itself and the wrinkles of the conveyance belt. Note that the unevenness of the recording paper is generated by containing moisture by image recording, and the wrinkles of the conveying belt are often generated by expansion and contraction due to the environment such as a joint.

  Further, Patent Document 2 relates to drive control of the conveyor belt, and does not correspond to the unevenness of the recording paper itself as in Patent Document 1.

  In addition, there are various types of recording paper, and if the paper thickness dimension differs due to the difference in type, there may be a gap in the distance between the recording head. In such a case, the recording paper Even if there is flatness, it may be different from the calculated ink landing position.

  In consideration of the above-mentioned fact, the present invention feeds back a conveyance speed and a deviation in a gap dimension direction from the recording head due to a recording medium or a conveyance path for conveying the recording medium, and drops droplets from the recording head at an appropriate timing. It is an object to obtain a droplet discharge device that can be discharged.

  According to a first aspect of the present invention, a recording head is provided that ejects droplets from nozzles by applying a drive signal based on image data, and a liquid ejection surface of the recording head is set to a predetermined path with respect to the conveyance path of the recording paper. A droplet discharge device that forms an image on the recording sheet by discharging droplets at a predetermined discharge timing, facing each other at an interval, and upstream of the recording head in the conveyance direction of the recording sheet in the conveyance path A first interval measuring device that is provided on the side and measures the interval to the recording sheet, an interval measured by the first interval measuring device, and a predetermined interval between the recording head and the recording sheet. Comparing means for comparing, and droplet timing correcting means for correcting the discharge timing of the droplets based on the comparison result of the comparing means.

  According to the first aspect of the present invention, in order to correct the ejection timing based on the result of comparing the interval measured by the first interval measuring device with the predetermined interval between the recording head and the recording sheet, the droplet recording sheet is used. The landing position on is not shifted.

  In the first aspect of the invention, the conveyance path is provided with a reversing mechanism for reversing the front and back surfaces of the recording paper, and after reversing the recording head, the image is formed on the front and back surfaces of the recording material. A second interval measurement that is arranged on a conveyance path after recording an image on one side of the recording sheet and before recording an image on the other side and that measures the distance to the recording sheet. It further has an apparatus.

  Due to the image recording on one side, the recording paper may absorb moisture by droplets and cause wrinkles or the like. At this time, it is possible to prevent the landing position from being shifted by detecting the state of the recording paper after image recording on one side by the second interval measuring device.

  Furthermore, in the first invention, a determination unit for determining the type classified by the thickness of the recording material, and a predetermined discharge timing as a reference are set according to the type of the recording material determined by the determination unit. And a reference discharge timing setting means.

  Since the paper thickness dimension may differ depending on the type of recording paper, the ejection timing can be set with high accuracy by setting and correcting the reference ejection timing according to the difference in the paper thickness dimension.

  In the first invention, a first interval measuring device is attached to the recording head.

  When the recording head is displaced, the recording head moves following the recording head, so that the relative positional relationship between the recording head and the first interval measuring device does not shift.

  Furthermore, in the first invention, a plurality of recording heads are provided, and the first interval measuring device is attached to each of the plurality of recording heads.

  When the recording paper is conveyed, the intervals between the recording heads are not necessarily equal. For this reason, a highly accurate interval can be obtained by providing the first interval measuring device for each of the plurality of recording heads.

  According to a second aspect of the present invention, a recording head that discharges droplets from nozzles by applying a drive signal based on image data is provided, and a liquid discharge surface of the recording head is set to a predetermined path with respect to the conveyance path of the recording paper. A liquid droplet ejection apparatus that forms an image on the recording paper by ejecting liquid droplets at a predetermined ejection timing, facing each other at intervals, and based on the image data, between the recording head and the recording paper Computation means for computing the interval, and droplet timing correction means for controlling the discharge timing of the recording head based on the computation result of the computation means.

  The second invention is characterized in that the type data of the recording paper is used as information for calculating the interval between the recording head and the recording paper.

  Further, the second invention is characterized in that the interval is calculated based on image information recorded by a relatively upstream recording head having a plurality of recording heads.

  According to the second invention, the interval is predicted from the image data or the like without having the first interval measuring means which is essential in the first invention. The discharge timing is controlled based on the predicted interval.

  Here, for example, in the case of a single recording head, it can be applied to double-sided printing or divided printing (multipass printing). In the case of having a plurality of recording heads, in addition to the above double-sided printing and divided printing, the paper is deformed by the droplets ejected by the upstream recording head in the same pass, thereby changing the TD (Throw Distance). It is applicable to control when doing. Note that TD refers to the interval between the nozzle and the recording paper.

  As described above, according to the present invention, the conveyance speed caused by the recording medium or the conveyance path for conveying this recording medium and the deviation in the gap dimension direction from the recording head are fed back, and droplets are ejected from the recording head at an appropriate timing. It has an excellent effect of being able to be made.

(First embodiment)
FIG. 1 shows a schematic configuration diagram of an FWA (Full Width Array) type ink jet printer 10 as a droplet discharge device according to the first embodiment.

  In the center of the apparatus, a conveyor belt 12 that circulates along a predetermined locus is wound around a plurality of (four in the first embodiment) rollers 14, 16, and 18.

  A part of the rollers 14, 16, 18 includes a driving roller that rotates by receiving a driving force of a driving unit (not shown), and the driving belt 12 causes the conveyor belt 12 to move to the arrow A in FIG. 1. Circulate in the direction.

  A pulse encoder 19 is attached to one of the three rollers 14, 16, 18 (for example, the roller 18), and a pulse signal (pulse encoder signal) corresponding to the rotation of the roller 18 is generated. It is sent to the recording head controller 100.

  The upper part of the circular locus of the conveyor belt 12 is a substantially horizontal plane, and the conveyor belt 12 is linearly conveyed. This pulse encoder signal is applied as a so-called print clock signal and serves as a reference for the timing of image recording for each color.

  A head unit 37 composed of a plurality of recording heads 36 whose driving is controlled by the recording head controller 100 is disposed along the conveying direction above the conveying belt 12 that is linearly conveyed.

  The recording head 36 is used for discharging reaction liquid, discharging C color ink, discharging Y color ink, discharging M color ink, and discharging K color ink in order from the upstream side in the transport direction.

  In each recording head 36, nozzles 40 (see FIG. 2) to be described later are arranged over the entire region (main scanning direction) orthogonal to the conveying direction of the conveying belt 12.

  A paper feed tray 20 is disposed on the lower left side of the transport belt 12 in FIG. A plurality of recording papers P are stacked on the paper feed tray 20.

  A paper feed conveyance path 22 is provided between the paper feed tray 20 and a position where the conveyance belt 12 is wound around the leftmost roller 14.

  The uppermost recording paper P is taken out from the paper feed tray 20, and the taken-out recording paper P is guided to the paper feeding / conveying path 22, and the recording head for the reaction liquid on the uppermost stream side. It is sent out onto the conveyor belt 12 from the upstream side of the arrangement position of 36.

  The conveyance belt 12 has a function of closely holding the recording paper P, and the recording paper P that is in close contact with the conveyance belt 12 is supplied with reaction liquid, C color ink, Y color ink, Liquid droplets are ejected in the order of M color ink and K color ink, and a full color image is formed.

  The reaction liquid has a function of promoting the permeability of the recording paper P of each color ink of CMYK, and is a so-called pre-processing in which droplet discharge is performed on all print dots regardless of image data. Although it is positioned, it is not essential for image formation.

  Each recording head 36 corresponds to an ink cartridge (not shown), and an appropriate amount of ink or reaction liquid (hereinafter collectively referred to as “ink or the like” if necessary) is an ink tank 41 ( (See FIG. 2).

  Each recording head 36 is driven in synchronization with a print start signal (timing signal) from the recording head controller 100, and ink droplets of each color are ejected based on image data.

  Further, a scraper 26 is provided corresponding to the roller 16 positioned at the right end of the transport belt 12, and the recording paper P on which image recording has been completed is peeled off from the transport belt 12, and the paper discharge tray 30 is disposed via the discharge path 28. It is structured to send out to

  The discharge path 28 and the discharge tray 30 also serve as a reversing mechanism. That is, when the trailing end in the conveyance direction of the recording paper P sent from the conveyance belt 12 to the discharge path 28 passes between the upper and middle rollers of the triple roller 28A provided in the discharge path 28, the guide plate 28B is shown by a solid line. By moving from the position to the chain line position, it passes between the middle and lower rollers of the triple roller 28A and is returned to the conveying belt 12 again. As a result, the recording paper P is held in close contact with the conveyor belt 12 with the front and back sides reversed, and reaches the head unit 37.

  The reversing mechanism is not limited to the above structure, and may be provided as a dedicated reversing mechanism at another position of the transport belt 12.

  As shown in FIG. 2, the recording head 36 includes an ink tank 41, a supply path 44, a pressure chamber 46, a nozzle 40, and a piezoelectric element 42.

  The ink tank 41 stores ink and the like from the ink cartridge 24 (see FIG. 1). The ink tank 41 communicates with the pressure chamber 46 through the supply path 44, and the pressure chamber 46 further includes the nozzle 40. It communicates with the outside through.

  A part of the wall surface (the lower surface in FIG. 2) of the pressure chamber 46 is made of a vibration plate 46A, and a piezoelectric element 42 is attached to the vibration plate 46A. A pressure wave is generated in the ink in the chamber 46. That is, ink or the like stored in the ink tank 41 is ejected from the nozzle 40 via the supply path 44 and the pressure chamber 46 by a pressure wave generated by vibration of the piezoelectric element 42.

  Here, in the first embodiment, the gap sensor 102 is attached to the upstream side of the recording head 36 for each color provided in the head unit 37.

  As shown in FIG. 3, the gap sensor 102 is a photoelectric sensor including a light projecting unit and a light receiving unit (PSD), and light emitted from the light projecting unit is reflected on the recording paper P on the transport belt 12. Light is received at any position on the PSD. The electrical signal corresponding to the light receiving position is sent to the recording head controller 100 so that the recording head controller 100 calculates the distance (interval size) between the gap sensor 102 and the recording paper P on the conveying belt 12. It has become.

  This sensor is not limited to PSD, and any type of sensor can be used as long as it measures a distance to an object such as a laser displacement meter, an ultrasonic sensor, or a reflected light amount sensor. Although a contact type may be used, the non-contact type is more preferable when measuring the distance immediately after printing.

  In addition, this sensor may measure one location in the center of the paper, but finer control is possible by measuring multiple locations in the width direction.

  The sensor is preferably attached directly to each recording head 36. The recording head 36 moves from the printing position and may be attached to the maintenance unit or the cap at the time of jam removal, maintenance or standby, and may be attached to the cap. Relative position may vary.

  Further, when the machine installation state (floor distortion or installation location) changes, the machine main body is distorted, and the positional relationship between the recording head and the conveyance belt also changes. Therefore, the correct gap can always be measured by attaching the sensor at a position integrated with the change of the recording head.

  In addition, a UI (user interface) 104 is connected to the recording head controller 100, and it is possible to specify a print instruction, the type and size of the recording paper P, and notify the recording head controller 100. ing.

  The gap sensors 102 have the same height as the ejection surface of the nozzle 40 of the corresponding recording head 36, and the calculation result can be said to be a distance dimension between the tip of the nozzle 40 and the recording paper P ( Reference interval dimension GAP0). If there is an offset between the gap sensor 102 and the tip of the nozzle 40, this offset amount may be registered in advance as a correction value.

  Here, a reversing gap sensor 103 having the same function as the gap sensor 102 is provided at a position other than the facing position of the head unit 37 on the conveyor belt 12 (between the roller 16 and the roller 18 in the first embodiment). It is arranged. This position serves to detect the distance between the recording paper P and the recording paper P when the recording paper P is reversed.

  In the ink jet printer 10 having the above-described configuration, the recording head controller 100 discharges ink from each recording head 36 based on the gap (distance between the surface of the recording paper P and the tip of the nozzle 40) detected by the gap sensor 102. I am trying to correct.

  That is, when the conveying belt 12 or the recording paper P is lifted (convex) (“+ ΔGAP” when the reference shown in FIG. 4 is 0), the recording paper P maintains flatness. The ink ejected from the nozzle 40 lands faster than the projection. On the other hand, when a dent (concave shape) is generated (“−ΔGAP” when the reference shown in FIG. 4 is 0), the recording paper P has a concave portion and a nozzle as compared with the case where the recording paper P maintains flatness. The ink ejected from 40 lands slowly.

  Therefore, in order to eliminate this landing timing error, the discharge timing is delayed when a convex shape occurs, and the discharge timing is advanced when a concave shape occurs.

  FIG. 5 is a block diagram functionally showing the control for correcting the ink ejection timing in the recording head controller 100.

  The gap sensor 102 provided corresponding to each recording head 36 and the gap sensor 103 arranged to face a part of the conveying belt 12 are connected to the selector 106, respectively. The selector 106 sequentially selects the gap sensors 102 and 103 and receives signals from the selected gap sensors 102 and 103. The received signal is sent to the gap calculation unit 108, calculates the interval dimension from the actual tip of the nozzle 40 of the recording head 36 to the surface of the recording paper P, and sends it to the comparison unit 110 described later. .

  The selector 106 is connected to an ejection target recording head selection unit 112, and the ejection target recording head selection unit 112 transports the gap sensor 102 corresponding to the recording head 36 selected based on a selection signal to be described later or at the end of inversion. The selector 106 is instructed to select the gap sensor 103 facing the part of the belt 12.

  An ink ejection drive signal generation unit 114 is connected to the ejection target recording head selection unit 112. Image data is input to the ink ejection drive signal generation unit 114, and a drive signal for each color is generated based on the image data.

  A selection signal is output to the ejection target recording head selection unit 112 in synchronization with the output timing of the generated drive signals for each color (actually slightly earlier than the ejection timing).

  The ink ejection drive signal generation unit 114 is connected to the ejection control unit 116, and the drive of the piezoelectric element 42 of each recording head 36 is controlled based on the generated drive signal to eject ink.

  On the other hand, the UI 104 is connected to a recording sheet determination unit 118 and a sheet correction mode state determination unit 120.

(Regarding the sheet correction mode state determination unit 120)
This sheet correction mode state determination 120 is not essential, but is advantageous when the deformation of the recording sheet P is large. That is, when the deformation of the recording paper P is large (an image with a high printing rate of the recording paper P that is easily deformed), the paper may not be transported, the paper may be jammed, or the output quality may be significantly deteriorated.

  In such a case, an apparatus for correcting the deformation of the recording paper P after single-sided printing may already be obtained after single-sided printing. This apparatus may be a method of correcting the deformation of the recording paper P by passing the recording paper P through a roll pair, or a method of correcting the deformation by speeding up the recording paper P in a flat state. It is more effective when combined with heat.

  For example, when heat is applied to the discharge path 28 in FIG. 1, the recording paper can be corrected. Separately, a recording sheet correction device may be provided on the conveyance path. It is preferable to have a recording sheet correction mode that can selectively execute such recording sheet correction.

  The recording paper discriminating unit 118 discriminates the type of the recording paper P input to the UI 104, and based on the discrimination result, the paper thickness dimension reading unit 122 determines the type of the recording paper P from the recording paper-paper thickness dimension map 124. The paper thickness dimension corresponding to is read out. For example, the paper thickness dimension varies depending on the paper type, such as plain paper (thick paper, thin paper), OHP paper, and the like.

  The read paper thickness dimension is sent to the reference gap setting unit 126.

  A nozzle-belt default gap memory 128 is connected to the reference gap setting unit 126. The nozzle-belt default gap memory 128 stores in advance a gap dimension (gap) between the tip of the nozzle 40 of the recording head 36 and the conveying belt 12.

  A value obtained by subtracting the read paper thickness dimension from the stored interval dimension becomes a reference gap (GAP0 shown in FIG. 3), and is sent to the comparison unit 110.

  The comparison unit 110 is inputted with a gap dimension from the gap calculation unit 108 to the tip of the nozzle 40 of the actual recording head 36 and the surface of the recording paper P. Compared with the reference gap GAP0, the difference ΔGAP (FIG. 3). Browse).

  The comparison result (difference ΔGAP) in the comparison unit 110 is sent to the ejection timing correction unit 130. A ΔGAP-discharge timing correction value map 132 is connected to the discharge timing correction unit 130.

  The ΔGAP-discharge timing correction value map 132 basically has discharge timing correction data registered according to the characteristics shown in FIG. 4, but when the sheet correction mode is in operation. Since the correction needs to be canceled out, the correction value is adjusted based on the selection signal from the correction mode selection unit 134 set by the determination result of the sheet correction mode state determination unit 120 (characteristic diagram of FIG. 4). There is also a change in the inclination of

  The correction value obtained by the ejection timing correction unit 130 is sent to the ejection control unit 116, and becomes a reference ejection timing (ejection timing on the assumption that the recording paper P is flat) in each storage head 36. Correction is added to the discharge control.

  The operation of the first embodiment will be described below.

  When printing is instructed, the recording paper P fed one by one from the paper feed tray 20 is brought into close contact with the transport belt 12 and transported in the sub-scanning direction at a predetermined pitch or continuously at a constant speed, and the recording head 36 Ink droplets are selectively ejected from the nozzles 40 to the recording paper P based on the image data.

  Ink ejection is controlled by a drive signal of the piezoelectric element 42 based on the image data. This drive signal is a continuous trapezoidal wave and is output at a period of 14 μsec to vibrate the piezoelectric element. This vibration is transmitted to the vibration plate 46A of the pressure chamber 46, and the vibration plate 46A vibrates to generate a pressure wave in the ink in the pressure chamber 46. By this pressure wave, the ink stored in the ink tank 41 is ejected from the nozzle 40 through the supply path 44 and the pressure chamber 46.

  When the recording of the entire image based on the image data is completed on the recording paper P, the recording paper P is peeled off from the transport belt 12 by the scraper 26 provided corresponding to the roller 16 positioned at the right end of the transport belt 12, It is sent out to the paper discharge tray 30 via the discharge path 28.

  In the case of double-sided printing, after passing through the triple roller 28A of the discharge path 28, the transport direction is changed by 180 ° and returned to the transport belt 12 again. As a result, the recording paper P whose front and back are determined is held tightly on the conveyor belt 12.

  Here, in order to take ink ejection timing when an image is recorded on the recording paper P, the recording head controller 100 performs ejection timing correction control based on a detection signal from the gap sensor 102.

  Hereinafter, the discharge timing correction control procedure will be described with reference to the flowcharts of FIGS.

  FIG. 6 is a basic setting routine for setting a reference gap. When it is determined in step 150 that there is a print instruction (affirmative determination), the process proceeds to step 152 and a recording sheet based on an input from the UI 104. The type of P is determined.

  In the next step 154, the paper thickness dimension is read according to the determined type of the recording paper P. For example, a numerical value set for each type of recording paper P is read, such as X1 mm for plain paper, X2 mm for thin paper, X3 mm for OHP paper, and so on.

  In the next step 156, a reference gap (GAP0 in FIG. 3) is set based on the read paper thickness dimension. That is, since the interval dimension from the tip of the nozzle 40 of the recording head 36 to the conveying belt 12 is determined in advance as a default value, the reference gap is set by subtracting the paper thickness dimension of the recording sheet 12 from this default value. Can do.

  The difference between the reference gap and the actually measured gap includes an error including the unevenness of the recording paper P and the unevenness of the transport belt 12.

  FIG. 7 is a discharge timing correction routine. In step 160, it is determined whether image data has been input. If the determination is negative, this routine ends.

  If an affirmative determination is made in step 160 (image data is input), the process proceeds to step 162 to generate a drive signal.

  In the next step 164, the gap sensors 102 and 103 are selected, and then the actual gap is calculated based on the detection signals from the gap sensors 102 and 103 selected in step 166.

  In the next step 168, a difference ΔGAP between the actual gap and the reference gap (set in step 156 in FIG. 6) is obtained, and the process proceeds to step 170.

  In step 170, a correction map is selected based on the paper correction mode (for example, the inclination of ΔGAP-discharge timing correction value map without correction mode in FIG. 4 is changed), and then the process proceeds to step 172 to discharge based on ΔGAP. Read the timing correction value.

  In the next step 174, the discharge timing is set by adding the discharge timing correction value to the read reference discharge timing (discharge timing when the recording paper P or the like maintains flatness). In step 176, ink is ejected from the recording head 36, and the flow advances to step 178.

  In the next step 178, it is determined whether or not the next color is ejected. If the determination is affirmative, the process returns to step 164 and the above steps are repeated. If the determination in step 178 is negative, this routine ends.

  By the way, the recording paper P after printing generates paper wrinkles deformed by ink. The sheet deformation due to this wrinkle lowers the output quality, or in the case of printing the next color or back side continuously, the second color or later or the back side print quality.

  Therefore, by providing the gap sensor 102 immediately before each color recording head, printing can be performed without the influence of paper deformation (wrinkle) caused by each printing (printing).

  Note that the gap sensor 103 is disposed on the inverted recording paper P so as to cope with wrinkles caused by the moisture content that occurs after single-sided printing during double-sided printing.

  Thus, by providing the gap sensors 102 and 103 immediately after printing or immediately after printing, it is possible to correct the ejection timing in real time with respect to the gap variation due to deformation (皺) of the recording paper P, and obtain a good image. be able to.

  Also, in multi-pass, since an image is formed by a plurality of rounds of printing, an appropriate ejection timing can be obtained for each round of recording paper P containing ink (moisture) for the first and subsequent rounds. Can do.

(Modification)
FIG. 8 is a block diagram according to a modified example of the control for correcting the ink discharge timing in the recording head controller 100 shown in FIG.

  In the control based on FIG. 5 described above, the default discharge timing is stored in advance, and the control is performed to correct the discharge timing based on the difference from the gap when the default discharge timing is determined. In the control No. 8, the discharge timing is determined each time based on the simply detected gap.

  As shown in FIG. 8, the gap calculation unit 108 is connected to the ejection timing determination unit 136. A gap-discharge timing map memory 137 is connected to the discharge timing determination unit 136, and when gap data is input to the discharge timing determination unit 136, an appropriate discharge is generated from the gap-discharge timing map 137 based on the gap data. Select timing. In this gap-discharge timing map, the reference shown in FIG. 4 is eliminated, and the horizontal axis is gap data (the left end in FIG. 4 has a small gap and the right end has a large gap).

  As described above, in the first embodiment, the deviation of the ink landing position is corrected by correcting the ejection timing from the nozzle 40 of the recording head 36 according to the unevenness that may occur on the transport belt 12 or the recording paper P. This eliminates problems such as color misregistration. In addition, even when the recording paper P is wrinkled due to moisture contained in the ink after single-sided printing and has irregularities during double-sided printing, a part of the conveying belt 12 (other than the position where the head unit 37 is disposed) is formed. Since the gap sensor 103 is provided, the unevenness of the recording paper P or the like after the single-sided printing can be canceled out.

(Second Embodiment)
The second embodiment of the present invention will be described below. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description of the configuration is omitted.

  The feature of the second embodiment is that the gap is not directly measured (that is, the gap sensor (the gap sensor 102 or 103 shown in the first embodiment is not provided)). The gap is predicted based on the type of the recording paper P and information on the print image (see FIG. 8).

  That is, the deformation and wrinkle are determined (predicted) by the ease with which the recording paper P is deformed and the print discharge amount of ink.

  Therefore, the sheet deformation calculation unit 139 is obtained from the type information of the recording sheet P and the ejection information (corresponding to the image data) of the front color or the back side printing stored in the front color (front surface) ejection information memory 138. Thus, the deformation amount of the recording paper is calculated.

  Note that this relationship is often complicated (non-linear), and it is preferable to measure the relationship between the two in advance and form a table such as a lookup table.

  Thereafter, the recording sheet deformation amount data is sent to the gap calculation unit 108, the gap calculation unit 108 calculates the gap, and the ejection timing control is executed. This eliminates the need for a gap sensor at all, reduces the number of parts, reduces the size of the apparatus, and enables fine control in the transport direction of the recording paper P.

  In the first and second embodiments, the single recording head 36 can be applied to double-sided printing or divided printing (multi-pass printing).

  When a plurality of recording heads 36 are provided, the recording paper P is deformed by the ink ejected by the upstream recording head 36 in the same pass in addition to the above-described double-sided printing and divided printing. Applicable to control when) changes.

1 is a schematic configuration diagram of an FWA type inkjet printer according to a first embodiment. FIG. 2 is a cross-sectional view showing an internal structure of the recording head according to the first embodiment. FIG. 4 is a side view for explaining a gap between the recording head and the conveyance belt according to the first embodiment. FIG. 6 is a characteristic diagram illustrating a discharge timing correction value for a gap difference due to unevenness of a recording sheet or the like according to the first embodiment. FIG. 3 is a block diagram functionally illustrating control for ink ejection timing correction in the recording head controller according to the first embodiment. It is a control flowchart for setting the reference gap according to the first embodiment. It is a control flowchart for correct | amending the discharge timing which concerns on 1st Embodiment. FIG. 9 is a block diagram functionally illustrating control for ink ejection timing correction in a print head controller according to a modification of the first embodiment. FIG. 9 is a block diagram functionally illustrating control for ink ejection timing correction in a recording head controller according to a second embodiment.

Explanation of symbols

P Recording paper 10 FWA type inkjet printer (image recording device)
12 Conveying belt 14, 16, 18 Roller 28A Triple roller (reversing mechanism)
28B Guide (Reversing mechanism)
36 recording head 37 head unit 40 nozzle 100 recording head controller 102 gap sensor (first interval measuring device)
103 Gap sensor (second interval measuring device)
104 UI
106 selector 108 gap calculation unit (droplet timing correction means)
110 Comparison part (comparison means)
DESCRIPTION OF SYMBOLS 112 Ejection target recording head selection part 114 Ink ejection drive signal generation part 116 Ejection control part 118 Recording paper discrimination | determination part 120 Paper correction mode state discrimination part 122 Paper thickness dimension reading part 124 Recording paper-paper thickness dimension map 126 Reference | standard gap setting part 128 Nozzle-belt default gap memory 130 Discharge timing correction unit (droplet timing correction means)
132 ΔGAP-Discharge timing correction value map (droplet timing correction means)
134 Correction mode selection section

Claims (8)

By providing a drive signal based on the image data, a recording head for discharging droplets from the nozzles is provided, and the liquid discharge surface of the recording head is opposed to the recording paper conveyance path at a predetermined interval, A droplet discharge device that forms an image on the recording paper by discharging droplets at a discharge timing of
A first interval measuring device that is provided upstream of the recording head in the conveying direction of the recording paper in the conveying path and measures an interval to the recording paper;
Comparing means for comparing the interval measured by the first interval measuring device with a predetermined interval between the recording head and the recording paper;
Droplet timing correction means for correcting the discharge timing of the droplet based on the comparison result of the comparison means;
A droplet discharge device having The transport path is provided with a reversing mechanism for reversing the front and back surfaces of the recording paper, and by reversing the recording head after reversing, image recording on the front and back surfaces of the recording material is enabled.
The image forming apparatus further includes a second interval measuring device that is disposed on a conveyance path after image recording on one side of the recording sheet and before image recording on the other side, and that measures an interval to the recording sheet. The droplet discharge device according to claim 1. Discriminating means for discriminating the type classified by the thickness of the recording material;
Reference discharge timing setting means for setting a predetermined discharge timing as a reference according to the type of the recording material determined by the determination means;
The droplet discharge device according to claim 1, further comprising:   The liquid droplet ejection apparatus according to claim 1, wherein a first interval measuring device is attached to the recording head.   4. The droplet discharge device according to claim 1, further comprising a plurality of recording heads, wherein the first interval measuring device is attached to each of the plurality of recording heads. 5. By providing a drive signal based on the image data, a recording head for discharging droplets from the nozzles is provided, and the liquid discharge surface of the recording head is opposed to the recording paper conveyance path at a predetermined interval, A droplet discharge device that forms an image on the recording paper by discharging droplets at a discharge timing of
An arithmetic means for calculating an interval between the recording head and the recording paper based on the image data;
Droplet timing correction means for controlling the discharge timing of the recording head based on the calculation result of the calculation means;
A droplet discharge device having   7. The liquid droplet ejection apparatus according to claim 6, wherein type information of the recording paper is used as information for calculating an interval between the recording head and the recording paper.   8. The droplet discharge apparatus according to claim 6, wherein the interval is calculated based on image information recorded by a relatively upstream recording head having a plurality of recording heads.

Images