JP5176285B2 - Image recording device - Google Patents

Description

  The present invention relates to an image recording apparatus, for example, an image recording apparatus including a recording head such as a droplet discharge head having a plurality of nozzles each discharging a droplet for image recording.

  Conventionally, a pressure generating chamber filled with ink is volume-changed (expanded / contracted) using an actuator such as a piezoelectric element, and a nozzle formed in communication with the pressure generating chamber by a change in internal pressure due to this volume change. 2. Related Art An ink jet recording apparatus (so-called ink jet printer) including an ink jet recording head that discharges ink droplets from the tip is known.

  In recent years, inkjet recording apparatuses have been increasingly miniaturized and printing speeds are increasing. For this reason, an inkjet recording head that can form an image in a wider area in a shorter time is used by elongating the inkjet recording head, increasing the number of nozzles per inkjet recording head, and arranging them in a straight line. It has become like this.

  In this ink jet recording apparatus, a plurality of transport rolls are arranged along a transport direction (transport path) and each is driven to rotate to transport a recording medium, and a transport belt is wound around drive rolls at both ends, A belt conveyance system that conveys a conveyance medium by moving a conveyance belt by rotating a driving roll is adopted.

  However, in the roll conveyance method, the conveyance speed of the recording medium varies due to the variation in the rotation speed of each conveyance roll. In the belt conveyance method, the conveyance speed of the recording medium varies due to component accuracy such as uneven thickness of the conveyance belt and roundness of the drive roll. As a result, the recording medium that is conveyed with the conveyance speed fluctuating also fluctuates at the position of the recording head, and the image formed by the droplets ejected by the recording head at a predetermined timing is deformed. For example, part or all of the image in the transport direction is enlarged or reduced, or the density is uneven. Also, in the case of a color image in which a plurality of color images are superimposed, secondary color unevenness (color change) occurs due to deviation between color images and density unevenness in the same color image, and the image quality of the color image decreases. .

In order to eliminate this point, a sensor is provided in the vicinity of each print head for recording a color image on a recording medium to detect the belt surface speed, or the distance between the print heads matches the circumference of the drive roll. A technique for adjusting the printing timing by detecting the belt surface speed by separating them by a distance (see, for example, Patent Document 1) is known.
Japanese Patent Laid-Open No. 2-80269

  However, in the above technique, a sensor is provided in the vicinity of each print head for recording a color image on a recording medium to detect the belt surface speed, or the distance between the print heads matches the circumference of the drive roll. Because it is necessary to detect the belt surface speed by separating them only, there are problems such as an increase in the number of sensors, an increase in sensor contamination due to the arrangement near the head, and an increase in the size of the device by increasing the head interval. there were.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an image recording apparatus that can be miniaturized without degrading image quality.

In order to achieve the above object, an image recording apparatus of the present invention includes a plurality of long recording heads that are provided along a predetermined transport direction and are long in a direction perpendicular to the transport direction, and the recording head. A transport unit that transports a sheet as a recording medium, a detection unit that detects a transport speed of the sheet transported by the transport unit, and a reference position when the sheet is transported by the transport unit A reference position detecting means for detecting, a leading edge position detecting means for detecting a leading edge position of the sheet conveyed by the conveying means, a conveyance speed detected by the detecting means, and the reference position detecting means based on the reference position, as the fluctuation width of the conveying speed becomes equal correction amount when within a predetermined range, based on the conveying speed with a periodicity of the sheet conveyed by said conveying means When generating the correct print clock and generating the image recording timing by the plurality of print heads based on the print clock, the plurality of print heads are arranged from a predetermined position for each of the plurality of print heads. The image recording start timing is determined based on the distance to the position and the distance from the leading end position when the leading end position of the sheet is detected by the leading end position detecting unit to the arrangement positions of the plurality of recording heads. Control means for setting each of the plurality of recording heads.

  The image recording apparatus of the present invention is provided with a recording head along a predetermined conveying direction, and the recording medium is conveyed to the recording head by the conveying means. The conveyance speed of the recording medium conveyed by the conveyance means is detected by the detection means. The conveyance speed may fluctuate, and in order to eliminate image deformation or the like due to the fluctuation in the conveyance speed, the control unit performs control so that image recording is performed at a predetermined conveyance speed based on the conveyance speed. Variations in the conveyance speed often occur constantly due to deformation or eccentricity of parts provided in the image recording apparatus, such as drive rolls. Therefore, the control means includes storage means for storing the correction amount of the print clock for the conveyance speed of the recording medium conveyed by the conveyance means based on the conveyance speed detected by the detection means. Then, the control means generates a print clock based on the correction amount stored in the storage means corresponding to the transport speed detected by the detection means. As a result, even when the conveyance speed fluctuates, image recording that can suppress image deformation and density unevenness can be performed. Further, since the correction amount of the printing clock with respect to the conveyance speed of the recording medium is stored in advance, it is only necessary to refer to this, and the processing load can be reduced.

  The control means generates the print clock of the recording head from a predetermined reference clock in the print clock generation unit, and the print timing generation unit generates the image recording timing based on the generated print clock. You may do it.

The present invention further includes a reference position detecting means for detecting a reference position when the recording medium is conveyed by the conveying means, and the control means generates a print clock based on the detected reference position and the conveying speed. you generate. When the conveyance speed fluctuates periodically, a conveyance speed corresponding to one of the increasing conveyance speed and the decreasing conveyance speed can be taken. Therefore, a predetermined reference position (for example, a rotation reference position of the drive roll) when the recording medium is conveyed by the conveying unit is detected, and a print clock is generated based on the conveyance speed from the reference position. Thereby, in the case of the conveyance speed fluctuation having periodicity, it can be accurately adjusted from the reference position.

Further, in the present invention, when the control means generates the image recording timing by the recording head based on the printing clock, the image recording is performed based on an arrangement position from a predetermined position for each of the plurality of recording heads. to set the start timing. Even if fluctuations in the conveyance speed are suppressed, there may be a case where a deviation between a plurality of recording heads remains. Therefore, by setting the image recording start timing for each of the plurality of recording heads based on the arrangement positions from the predetermined positions, the position difference of the recording heads is canceled and the image recording start timing by each recording head is matched. For example, color images can be superimposed without color misregistration.

Further, the present invention further includes a leading end position detecting unit that detects a leading end position of the recording medium conveyed by the conveying unit, and the control unit generates an image recording timing by the recording head based on the printing clock. If, upon detecting the tip position, to set the image recording start timing on the basis of the distance to the installation position of the recording head from the tip position. When recording an image, it is preferable to align the position on the recording medium on which the image is recorded. Therefore, by setting the image recording start timing based on the distance from the leading end position to the installation position of the recording head with reference to the leading end position of the recording medium, the image recording start timing by the recording head based on the leading end position of the recording medium is set. Can be set, and the image recording area of the recording medium can be freely set. When a plurality of recording heads are provided, the position of the recording heads can be offset by using the leading end position of the recording medium as a reference, and the image recording start timing by each recording head can be matched. It is possible to superimpose without deviation.

In the image recording apparatus, the control means, a timing generator configured to generate the image recording timing, the Ru can be provided to each recording head. In many cases, a plurality of recording heads are individually controlled for recording. Therefore, by providing a timing generation unit included in the control unit in each recording head, the recording head can be individually adjusted and a plurality of recording heads can be adjusted in parallel.

In the image recording apparatus , the recording head includes a unit structure having a nozzle group in which a plurality of nozzles each ejecting droplets for image recording are linearly arranged at the same interval in a predetermined direction. wherein Ru can be a predetermined direction droplet ejection heads which are arrayed in a direction intersecting with. As described above, in order to suppress the recording deviation due to the fluctuation in the conveyance speed, the image recording is performed at a predetermined conveyance speed so as to cancel the fluctuation in the conveyance speed, for example, by detecting the conveyance speed and controlling the image recording timing. Is made. Accordingly, the present invention can be easily applied to a droplet discharge head having nozzles in which recording heads are two-dimensionally arranged. By applying the present invention to this droplet discharge head, the image recording apparatus can be further miniaturized.

  As described above, according to the image recording apparatus of the present invention, the print clock correction amount corresponding to the detected conveyance speed is set so that the conveyance speed is detected and image recording is performed at a predetermined conveyance speed. Since the print clock is generated based on this, an excellent effect can be obtained that image recording that can suppress image deformation and density unevenness can be performed even when the conveyance speed fluctuates.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, the case where the present invention is applied to an ink jet recording apparatus that records an image by ejecting ink droplets will be described.

  In the first embodiment, printing for generating image recording timing using a reference position signal of a driving roll for transporting paper P in order to eliminate (at least suppress) print density unevenness caused by transport speed fluctuations. The present invention is applied to an inkjet recording apparatus that starts generation of a clock.

  FIG. 1 shows an ink jet recording apparatus 12 according to the present embodiment. A paper feed tray 16 is provided in the lower part of the casing 14 of the ink jet recording apparatus 12, and the sheets P stacked in the paper feed tray 16 can be taken out one by one by a pickup roll 18. The taken paper P is transported by a plurality of transport roller pairs 20 constituting a predetermined transport path 22. Hereinafter, the “conveying direction” simply refers to the conveying direction of the paper P that is a recording medium, and the “upstream” and “downstream” refer to upstream and downstream in the conveying direction, respectively.

  Above the sheet feed tray 16, an endless transport belt 28 stretched around a drive roll 24 and a driven roll 26 as a transport means is disposed. A recording head array 30 is disposed above the conveyor belt 28 and faces the flat portion 28F of the conveyor belt 28. This opposed area is an ejection area SE where ink droplets are ejected from the recording head array 30. The sheet P transported along the transport path 22 is held by the transport belt 28 and reaches the discharge area SE, and ink droplets corresponding to image information are attached from the recording head array 30 in a state of facing the recording head array 30. The

  Then, by transporting the paper P while being held by the transport belt 28, image recording can be performed by passing the paper P into the ejection region SE. In addition, by rotating the paper P while being held by the conveyance belt 28, it is possible to perform image recording by so-called multi-pass by allowing the paper P to pass through the ejection region SE a plurality of times.

  The means for conveying the paper P, which is a recording medium, to the recording head array 30 is not limited to the conveyance belt 28. For example, the recording medium (paper P) may be sucked and held on the outer periphery of a conveyance roller formed in a cylindrical shape or a columnar shape and rotated. However, since the flat portion 28F is formed when the transport belt 28 is used as in the present embodiment, the recording head array 30 can be arranged corresponding to the flat portion 28F, which is preferable.

  In this embodiment, the recording head array 30 has a long shape in which the effective recording area is equal to or larger than the width of the paper P (the length in the direction orthogonal to the transport direction), and is yellow (Y) and magenta (M). , Cyan (C), and black (K), four ink jet recording heads 32 corresponding to each of the four colors are arranged along the transport direction, and a full color image can be recorded. The method for ejecting ink droplets in each inkjet recording head 32 is not particularly limited, and a known method such as a so-called thermal method or piezoelectric method can be applied.

  The operation of each inkjet recording head 32 is controlled by a recording head controller 78 (see FIG. 4) described later. For example, the recording head controller 78 determines the ink droplet ejection timing and the ink ejection port (nozzle) to be used according to the image information, and sends a drive signal to the inkjet recording head 32. The recording head array 30 may be fixed in a direction orthogonal to the transport direction. However, if the recording head array 30 is configured to move as necessary, an image with higher resolution can be obtained by multi-pass image recording. Or failure of the ink jet recording head 32 is not reflected in the recording result.

  Although not shown in the drawing, in the vicinity of the recording head array 30 (at least one of the upstream side and the vulcanization side in the transport direction), the head moves to the gap between the recording head array 30 and the transport belt 28 to perform predetermined maintenance. A maintenance unit for performing operations (vacuum, dummy jet, wiping, capping, etc.) is arranged.

  On the other hand, on the downstream side of the recording head array 30, a line sensor 84 composed of a CCD is arranged so that an image recorded on the paper P by the recording head array 30 can be taken. In the present embodiment, the line sensor 84 has a long shape in which the effective imaging area is equal to or greater than the width of the paper P (the length in the direction orthogonal to the transport direction), and can read a full-color image. . Note that the line sensor 84 according to the present embodiment is applied so that the resolution of the captured image is about four times the image recording resolution of the inkjet recording head 32 (about twice the nozzle resolution). . Although a CCD line sensor is applied as the line sensor 84, the present invention is not limited to this, and other solid-state imaging devices such as a CMOS image sensor can also be applied. The operation of the line sensor 84 is controlled by a sensor controller 86 (see FIG. 7) described later.

  Although not shown, a charging roll connected to a power source is disposed on the upstream side of the recording head array 30. The charging roll is driven between the driving roll 24 while sandwiching the conveyance belt 28 and the paper P, and is movable between a pressing position for pressing the paper P against the conveyance belt 28 and a separation position separated from the conveyance belt 28. It is said that. At the pressing position, the sheet P is charged and electrostatically attracted to the transport belt 28.

  A separation plate 40 formed of an aluminum plate or the like is disposed on the downstream side of the line sensor 84 of the recording head array 30, and the sheet P can be separated from the transport belt 28. The peeled paper P is transported by a plurality of discharge roller pairs 42 that constitute a discharge path 44 on the downstream side of the peeling plate 40, and is discharged to a paper discharge tray 46 provided on the top of the housing 14.

  Below the peeling plate 40, a cleaning roll 48 capable of sandwiching the conveying belt 28 with the driving roll 24 is disposed, and the surface of the conveying belt 28 is cleaned.

  A reversing path 52 composed of a plurality of reversing roller pairs 50 is provided between the paper feed tray 16 and the conveying belt 28, and the sheet P on which an image is recorded on one side is reversed and held on the conveying belt 28. By doing so, it is possible to easily record images on both sides of the paper P.

  Between the conveyance belt 28 and the paper discharge tray 46, an ink tank 54 for storing each of the four color inks is provided. The ink in the ink tank 54 is supplied to the recording head array 30 through an ink supply pipe (not shown). As the ink, various known inks such as water-based ink, oil-based ink, and solvent-based ink can be used.

  Next, the configuration of the ink jet recording head 32 according to the present embodiment will be described.

  As shown in FIG. 2, in each color ink jet recording head 32, a plurality of nozzles N that eject ink droplets for image recording are arranged in the same interval (pitch) S linearly in a predetermined direction. It consists of a nozzle group G. The ink jet recording heads 32 are arranged so as to have an inclination angle θ with respect to the transport direction. Note that the spacing S, the inclination angle θ, and the number of nozzles are exemplified for description, and the numbers are not limited to those in the drawing.

  In this embodiment, in order to adjust the image recording timing as will be described in detail below, an ink jet recording head 32 having a two-dimensional array of nozzles N shown in FIG. 3 can be attached. As shown in FIG. 3, the inkjet recording head 32 includes a plurality (three in FIG. 3) of nozzle groups G arranged in a straight line as shown in FIG. The That is, a plurality of head units 32A, 32B, and 32C having a nozzle group G in which a plurality of nozzles N are linearly arranged at the same interval (pitch) S with respect to a predetermined direction are arranged in adjacent head units. The nozzle groups G are arranged so as not to overlap with the conveying direction H of the nozzle group G. The head units 32A to 32C have the same specifications, but in the following description, when describing individual head units, the ink jet recording head 32 is distinguished and described as one of the head units 32A to 32C for convenience. There is a case.

  Next, with reference to FIG. 4, the configuration of the main part of the electrical system of the inkjet recording apparatus 12 according to the present embodiment will be described.

  As shown in FIG. 4, the inkjet recording apparatus 12 according to the present embodiment includes a CPU (central processing unit) 70 that controls the operation of the entire apparatus, a RAM 72 that is used as a work area when various programs are executed, A ROM 74 in which various programs and parameter information are stored in advance, and a nonvolatile and rewritable memory 76 are provided. The ink jet recording apparatus 12 includes a recording head controller 78 that controls the operation of the ink jet recording head 32, and a plurality of motors (not shown) that rotationally drive each part such as the pickup roll 18, the transport roller pair 20, and the drive roll 24. A motor controller 80 for controlling the operation of the sensor, a sensor controller 86 for controlling the operation of the line sensor 84, and an external interface 88 for electrically and mechanically connecting an external device such as a personal computer. The sensor controller 86 also includes a paper detection sensor 34 for detecting the leading edge position of the paper P, a surface speed detection sensor 36 for detecting the surface speed of the paper P, and a reference position for detecting the reference position of the drive roll 24. An encoder 39 for detecting the rotational position of the detection sensor 38 and the drive roll 24 is also connected. These sheet detection sensor 34, surface speed detection sensor 36, reference position detection sensor 38, and encoder 39 can be directly connected to the recording head controller 78.

  The CPU 70, RAM 72, ROM 74, memory 76, print head controller 78, motor controller 80, sensor controller 86, and external interface 88 are electrically connected to each other via a system bus BUS. Therefore, the CPU 70 controls access to the RAM 72, ROM 74, and memory 76, controls the operation of the print head controller 78, motor controller 80, and sensor controller 86, acquires output signals from sensors such as the line sensor 84, and the like. Various types of information can be exchanged with an external device via the interface 88. In addition to the above configuration, the inkjet recording apparatus 12 according to the present embodiment includes a number of electrical components such as a power supply device that applies a voltage to the charging roll. Therefore, detailed description is omitted.

  In the ink jet recording apparatus 12 of the present embodiment having the above configuration, the paper P taken out from the paper feed tray 16 is transported and reaches the transport belt 28. Then, it is pressed against the conveyance belt 28 by the charging roll, and is held by adhering (adhering) to the conveyance belt 28 by the voltage applied from the charging roll. In this state, while the paper P passes through the ejection area SE by circulation of the transport belt, ink droplets are ejected from the recording head array 30 and an image is recorded on the paper P. The image-recorded paper P is peeled off from the transport belt 28 by the peeling plate 40, transported by the discharge roller pair 42, and discharged to the paper discharge tray 46.

  Here, the speed unevenness of the paper feed speed has periodicity. This includes, for example, eccentricity of the drive roll, gear back crash, non-uniformity of the thickness of the circulating belt, and the like. Therefore, it has been concluded that the print density unevenness can be eliminated (at least suppressed) by correcting the image recording timing (print timing) with the position of each inkjet recording head 32 and the cycle of the conveyance speed fluctuation (speed unevenness).

  FIG. 5 shows the positional relationship between the conveyance speed fluctuation (speed irregularity) of the conveyance belt 28 by the eccentric drive roll and the inkjet recording head 32. The vertical axis represents the normalization of the conveyance speed fluctuation (speed unevenness), and the horizontal axis represents the distance from the reference position of the drive roll 24. As understood from the figure, the characteristic of the conveyance speed fluctuation at the head position of each inkjet recording head 32 has periodicity, and the characteristic curve shapes match. Therefore, the conveyance speed fluctuation need only be corrected for one cycle with respect to the reference characteristic, and can be corrected continuously.

  From this, in this embodiment, when a plurality of recording heads (inkjet recording heads 32) are mounted in an image recording apparatus (inkjet recording apparatus 12) that transports the paper P using a belt or drum having a closed loop, As will be described in detail below, a mechanism for detecting a reference position of a drive roll such as a belt or a drum, a mechanism for detecting a conveyance speed (surface speed of the belt or drum), and an image recording timing correction from the reference position of the belt or drum ( The basic structure of the image recording apparatus (inkjet recording apparatus 12) is to have a mechanism for performing (print timing correction).

  Using these configurations, timing correction data is generated with respect to the reference position of the drive roll (or drum), phase correction with respect to the position of the inkjet recording head 32 is performed, and then the recording timing (printing) of each inkjet recording head 32 is printed. Timing) and control.

  It should be noted that the phase shift of the conveyance speed variation accompanying the position of the ink jet recording head 32 is corrected at the same time if the speed unevenness correction of the print timing is performed.

  Next, the details of the electric recording head controller 78 in the ink jet recording apparatus 12 according to the present embodiment, which eliminates (at least suppresses) the printing density unevenness caused by the conveyance speed fluctuation, will be described with reference to the drawings.

  As shown in FIG. 6, the recording head controller 78 includes an image recording timing control mechanism 60 and a print driving device 66, and the output side of the printing drive device 66 is connected to the inkjet recording head 32 of the corresponding color. It is connected. The image recording timing control mechanism 60 performs inkjet recording so as to cancel (or at least suppress) fluctuations in the conveyance speed of the paper P in order to correct print density unevenness caused by fluctuations in the printing density due to fluctuations in the conveyance speed of the paper P. The image recording timing (printing timing) in the head 32 is controlled. The print drive device 66 generates a drive signal obtained by combining the controlled image recording timing signal and the image data, and sends the drive signal to the inkjet recording head 32.

  The image recording timing control mechanism 60 includes a corrected printing clock generation mechanism 62 and a printing timing generation mechanism 64 provided for each color. The image recording timing control mechanism 60 is connected to the line sensor 84 and receives a signal from the line sensor 84. In addition, a surface velocity detection sensor 36, a reference position detection sensor 38, and an encoder 39 are connected to the corrected print clock generation mechanism 62.

  The correction print clock generation mechanism 62 includes a surface speed data signal of the paper P or the conveyor belt 28 by the surface speed detection sensor 36, a reference position signal of the drive roll 24 by the reference position detection sensor 38, and a rotational position of the drive roll 24 by the encoder 39. Based on these signals, a print clock signal is generated based on these signals and output to each of the print timing generation mechanisms 64. A paper detection sensor 34 is connected to each of the print timing generation mechanisms 64 and a leading edge position detection signal of the paper P is input. The print timing generation mechanism 64 generates a print timing signal based on the print clock signal from the corrected print clock generation mechanism 62 and the leading edge position detection signal from the paper detection sensor 34 and outputs the print timing signal to the print drive device 66.

  In the present embodiment, the rotational position signal input of the drive roll 24 by the encoder 39 is not essential, and can be omitted.

  Here, in the inkjet recording apparatus 12 according to the present embodiment, generation of a print clock is started using the reference position signal of the drive roll 24 by the reference position detection sensor 38.

  As shown in FIG. 7, the correction print clock generation mechanism 62 includes a correction data generation unit 100, a correction data storage memory 102, a correction clock generation unit 104, and an address control unit 106. The correction data generation unit 100 starts from the drive roll reference position signal obtained from the reference position detection sensor 38 based on the surface speed data obtained from the surface speed detection sensor 36 for one period (one rotation of the drive roll 24). This is for generating correction data and storing it in the correction data storage memory 102.

  The correction data storage memory 102 is a memory for storing correction data. For example, the correction data is stored in order from the correction data corresponding to the drive roll reference position at address 0. The address control unit 106 generates an address for accessing the correction data storage memory 102. In the correction data storage memory 102, the address is incremented by 1 according to the correction data request signal output from the correction clock generation unit 104. However, after reading the last data, it returns to address 0 which is the drive roll reference position. The correction clock generation unit 104 generates a correction print clock signal based on the correction data using the drive roll reference position signal as a trigger.

  FIG. 8 shows the relationship between the fluctuation characteristic 110 and the correction amount, in which the maximum value is normalized to “1” for the surface velocity data signal output from the surface velocity detection sensor 36 starting from the drive roll reference position. The correction data generation unit 100 converts the surface velocity data signal into digital data (surface velocity data), and sets the same correction amount when the fluctuation range of the surface velocity data is within a predetermined range. That is, the fluctuation within the corresponding time is treated so that the surface velocity data whose fluctuation range is within the predetermined range is treated as a predetermined value (average value, maximum value or minimum value; the average value is adopted in FIG. 8) within the predetermined fluctuation range. A region 112 is obtained in which the amount is repeated R times with the printing frequency in a unit time in which a correction amount D corresponding to a predetermined value within the predetermined fluctuation range is obtained as one unit. At this time, the correction amount D and the repetition count R are obtained. The correction amount D and the number of repetitions R are small when the change in the fluctuation characteristic 110 is steep, and the number of repetitions R is large when the change is slow. Therefore, fine data setting according to the speed fluctuation is possible.

  When the drive roll 24 is not decentered or the like and the surface velocity data signal does not vary, the image recording timing signal can be generated with a print clock generated at the basic print frequency F (for example, 18 kHz). When the surface speed data varies as in the variation characteristic 110, it is necessary to add only the correction amount D to the basic printing frequency F. Therefore, as shown in FIG. 9, the correction data generation unit 100 uses the speed data V (= F + D) obtained by adding the correction amount D (correction frequency) to the basic printing frequency F and the number of repetitions R as correction data as correction data. Store in the storage memory 102. The correction data storage memory 102 stores correction data for one cycle (one rotation of the drive roll 24) starting from the drive roll reference position, that is, the address “0”. For this reason, the hour counter of the number of repetitions R corresponds to one period of time. By sequentially reading the correction data (speed data V and the number of repetitions R in FIG. 9) in the correction data storage memory 102 from the address “0”, one period of correction data can be extracted.

  In the above description, the generation of the correction data stored in the correction data storage memory 102 has been described using the variation characteristic 110 based on the surface velocity data signal obtained by the surface velocity detection sensor 36. However, the variation related to the generation of the correction data is described. The detection of the characteristic 110 is not limited to this. For example, the test printing shown in FIG. 10 may be performed, and this may be measured and obtained.

  When the ink jet recording head 32 of each color is a one-dimensional nozzle composed of a single nozzle group G (see FIG. 2), as shown in FIG. 10A, a gray pattern or ladder pattern is printed for each color and tested. Create a chart. When the conveyance speed varies, the printed gray pattern or ladder pattern appears as light and shade in the conveyance direction. Therefore, by measuring the density distribution in the transport direction, the periodic density distribution corresponds to the fluctuation characteristic 110.

  Further, in the case of the ink jet recording head 32 having the two-dimensional array of nozzles N (see FIG. 3), it is impossible to measure by printing a gray pattern or the like as described above. For this reason, as shown in FIG. 10B, printing is performed at regular intervals (dot pitches) with the nozzles N at the same position in the main scanning direction that intersects the transport direction. By measuring the printed dot interval, line interval unevenness due to the test pattern (dot) corresponding to the conveyance speed fluctuation is detected. That is, when there is a variation in the conveyance speed, the printed dot interval appears as a periodic length in the conveyance direction. For this reason, by measuring the distance distribution of the intervals in the transport direction, the periodic distance distribution corresponds to the fluctuation characteristic 110. Therefore, the fluctuation characteristic 110 and the phase of each head can be detected by measuring the dot interval of one dot line printed by the nozzle N for each color and detecting the conveyance speed fluctuation.

  As shown in FIG. 11, the correction clock generation unit 104 included in the correction print clock generation mechanism 62 (FIG. 7) includes a speed data register 120, a repetition number counter 122, a correction data request unit 124, and a clock generation unit 126. And. The correction clock generation unit 104 is for generating a correction print clock signal based on the correction data from the correction data storage memory 102 using the drive roll reference position signal from the reference position detection sensor 38 as a trigger.

  The speed data register 120 is a register for storing the speed data V of the correction data, temporarily stores the speed data V output from the correction data storage memory 102, and outputs it to the clock generator 126. Using this speed data V, the clock generator 126 generates and outputs a corrected print clock signal. The repetition number counter 122 counts down the repetition number R of the correction data, and the counter value becomes “0” after setting the repetition number R output from the correction data storage memory 102 to the initial counter value. The counter value is output to the correction data request unit 124. Since this counter value is output to the correction data requesting unit 124 until the counter value becomes “0”, it can be considered as a remaining signal indicating that the number of repetitions remains.

  The correction data request unit 124 generates a correction data request signal based on the drive roll reference position signal from the reference position detection sensor 38 and the counter value of the repetition number counter 122. That is, when the counter value becomes “0”, a correction data request signal is generated and output. As a result, the correction data request unit 124 sequentially generates correction data request signals representing the correction data output requests from the correction data storage memory 102 for the number of addresses in the correction data storage memory 102, starting from the drive roll reference position. And output to the address control unit 106.

  In the correction clock generation unit 104 configured as described above, the correction data request unit 124 first generates and outputs a correction data request signal to the address control unit 106 based on the drive roll reference position signal from the reference position detection sensor 38. In response to this, correction data (speed data V and number of repetitions R) is output from the correction data storage memory 102. The speed data V is stored in the speed data register 120, and a corrected print clock signal is generated and output by the clock generator 126. At this time, generation of the corrected print clock signal is repeated by the number of repetitions R. When the repetition is completed, the correction data request unit 124 acquires the next correction data based on the correction data request signal. By repeating this for the number of addresses, it is possible to generate a corrected print clock signal of one cycle.

  As shown in FIG. 6, the print timing generation mechanism 64 for each color includes a delay circuit 64A. The delay time of the delay circuit 64A is set to a phase time in which the same image is recorded at the same position when the paper P is conveyed, depending on the installation position of the ink jet recording head 32 for each color. The print timing generation mechanism 64 delays the corrected print clock signal from the correction print clock generation mechanism 62 after a predetermined time has elapsed from the detection of the paper P, that is, by the delay time of the delay circuit 64A. It is designed to output as a signal.

  Thus, the print timing generation mechanism 64 generates a corrected print clock signal using the drive roll reference position signal from the reference position detection sensor 38 as a trigger. The corrected print clock signal does not output the print timing signal for each ink jet recording head 32 by the head position delay after the paper detection signal indicating the front end of the paper detected by the paper detection sensor 34 is input. The print timing generation mechanism 64 outputs a predetermined number of print clock signals delayed by a predetermined time as a print timing signal. The predetermined number of print clock signals is the number of clocks corresponding to one rotation of the drive roll 24, that is, one cycle.

  FIG. 12 shows a timing chart in the corrected print clock generation mechanism 62 and the print timing generation mechanism 64. The corrected print clock generation mechanism 62 generates a corrected print clock signal based on the drive roll reference position signal from the reference position detection sensor 38. The corrected print clock signal is output to the print timing generation mechanism 64. In each of the print timing generation mechanisms 64, a print timing signal is generated after being delayed by a time corresponding to the distance of the installation position of the inkjet recording head 32. In FIG. 12, each of the print timing signals for which the delay time becomes longer in the order of colors in the transport direction, that is, in the order of each color of YMCK, for each inkjet recording head 32 is shown in time series. The print timing generation mechanism 64 outputs a predetermined number of print clock signals corresponding to one rotation of the drive roll 24, that is, one cycle, as a print timing signal.

  As shown in FIG. 6, an image recording timing control mechanism 60, specifically, a printing timing generation mechanism 64 for each color, is connected to the input side of each color print driving device 66 so that image data is input. Connected. The output side is connected to the ink jet recording head 32 for each color. In the print drive device 66, a drive signal (here, each of the print timing signals (image recording timing signals) output from the image recording timing control mechanism 60 and the image data) is used to record a predetermined image on the paper P. A signal for discharging a droplet for each nozzle is generated and output to the ink jet recording head 32.

  Next, the operation of the inkjet recording apparatus 12 that eliminates (or at least suppresses) the print density unevenness caused by the conveyance speed fluctuation will be described.

  In the inkjet recording apparatus 12 of the present embodiment, the paper P taken out from the paper feed tray 16 is transported and reaches the transport belt 28. Then, it is pressed against the conveyance belt 28 by the charging roll, and is held by adhering (adhering) to the conveyance belt 28 by the voltage applied from the charging roll. In this state, while the paper P passes through the ejection area SE by circulation of the transport belt, ink droplets are ejected from the recording head array 30 and an image is recorded on the paper P. At the time of this image recording, the image recording timing is adjusted according to the conveyance speed fluctuation of the paper P. When recording an image in only one pass, the paper P is peeled from the transport belt 28 by the peeling plate 40, transported by the discharge roller pair 42, and discharged to the paper discharge tray 46. On the other hand, when performing multi-pass image recording, the paper P is circulated until it reaches the required number of times and passed through the ejection region SE, and then the paper P is peeled off from the transport belt 28 by the peeling plate 40 and discharged. The paper is conveyed in pairs 42 and discharged to a paper discharge tray 46.

  At the time of image recording, the image recording timing adjustment according to the conveyance speed fluctuation of the paper P is executed by the image recording timing control mechanism 60 of the recording head controller 78.

  The image recording timing control mechanism 60 generates a print clock signal corrected by the corrected print clock generation mechanism 62 in accordance with the change in the conveyance speed, and outputs the print clock signal to each of the print timing generation mechanisms 64. The correction data storage memory 102 of the correction print clock generation mechanism 62 corrects one period (one rotation of the drive roll 24), which is obtained or measured in advance by the correction data generation unit 100, starting from the drive roll reference position. Data is stored. The correction clock generation unit 104 generates a correction print clock signal based on the correction data using the drive roll reference position signal of the reference position detection sensor 38 as a trigger, and outputs the correction print clock signal to the print timing generation mechanism 64. The correction data is composed of speed data V and the number of repetitions R. The clock generation unit 126 generates a correction print clock signal based on the speed data V output from the correction data storage memory 102 and outputs the correction data R by the number of repetitions R. When the speed data V is output by the number of repetitions R, a correction data request signal is output from the correction data request unit 124, and correction data is sequentially output from the correction data storage memory 102. As a result, it is possible to output a corrected print clock signal that is generated starting from the drive roll reference position. The print timing generation mechanism 64 generates a corrected print clock signal using the drive roll reference position signal from the reference position detection sensor 38 as a trigger, and outputs it to the inkjet recording head 32.

  As described above in detail, in the image recording timing control mechanism 60 included in the inkjet recording apparatus 12 according to the present embodiment, the conveyance speed fluctuation having periodicity caused by the eccentricity of the drive roll 24 is stored in advance as correction data. In addition, since the image recording timing is controlled from the drive roll reference position using the correction data, it is possible to provide the ink jet recording apparatus 12 that eliminates (at least suppresses) the printing density unevenness caused by the conveyance speed fluctuation.

  Further, according to the present embodiment, it is possible to eliminate the deviation of the image recording timing caused by the fluctuation in the conveyance speed, and there is no restriction on the interval between the ink jet recording heads 32 of each color, so that the apparatus can be miniaturized.

  Further, when the ink jet recording head 32 is a two-dimensional head, even if the head interval is arranged at a 2πr interval of the drive roll, the printing position deviation for each nozzle occurs. The print position can be corrected regardless of the nozzle arrangement. For this reason, the interval between the ink jet recording heads 32 can be reduced, and the apparatus can be miniaturized.

  Note that in the case of a conventional apparatus in which the head interval is an integral multiple of the drive roll circumference, if the head interval is shortened, it is necessary to reduce the drive roll diameter, and it is difficult to ensure the driving force. In the recording apparatus 12, the driving roll diameter can be determined from the surface of the belt driving force independently of the head interval.

  The surface speed detection sensor 36 of the present embodiment corresponds to the detection means of the present invention. The recording head controller 78 and the image recording timing control mechanism 60 of the present embodiment correspond to the control means of the present invention. The corrected print clock generation mechanism 62 corresponds to the print clock generation means of the present invention, and the print timing generation mechanism 64 corresponds to the print timing generation means. The correction data storage memory 102 corresponds to the storage means of the present invention, and the paper detection sensor 34 corresponds to the tip position detection means of the present invention. The reference position detection sensor 38 corresponds to an example of a reference position detection unit of the present invention.

  Next, a second embodiment of the present invention will be described. In the second embodiment, in order to eliminate (or at least suppress) the print density unevenness caused by the fluctuation in the conveyance speed, the image recording timing is set using the encoder signal of the encoder 39 attached to the drive roll 24 for conveying the paper P. Generation of a print clock for generation is started. In addition, since this Embodiment is a structure substantially the same as the said embodiment, the same code | symbol is attached | subjected to the same part and detailed description is abbreviate | omitted.

  As shown in FIG. 13, the corrected print clock generation mechanism 63 of this embodiment includes an encoder reference position signal generation unit 130 to which an encoder signal output from the encoder 39 is input. The output side of the encoder reference position signal generation unit 130 is connected to the correction data generation unit 100 and the correction clock generation unit 104. The difference between the corrected print clock generating mechanism 63 in FIG. 13 and the corrected print clock generating mechanism 62 in FIG. 7 is that the corrected print clock generating mechanism 62 converts the drive roll reference position signal from the reference position detection sensor 38 to the correction data generating unit 100 and the correction. The correction print clock generation mechanism 63 is added with an encoder reference position signal generation unit 130 for generating a reference position signal from the encoder signal, while being directly input to the clock generation unit 104. The encoder reference position signal generation unit 130 is a functional unit that detects a predetermined reference position and outputs it as an encoder reference position signal when the encoder signal from the encoder 39 periodically varies in speed. The encoder 39 and the encoder reference position signal generation unit 130 correspond to an example of a reference position detection unit of the present invention.

  Note that the encoder 39 is eccentric with respect to the central axis of the drive roll 24 due to an attachment error. Thereby, the signal output from the encoder 39 becomes a signal having periodicity according to the amount of eccentricity, as shown in FIG.

  As shown in FIG. 14, the encoder reference position signal generation unit 130 includes a designated value register 132, a designated value comparison unit 134, an encoder signal sampling unit 136, a first register 138, a second register 140, and a sampling value. A comparison unit 142 and an integration unit 144 such as an AND circuit are provided.

  The designated value register 132 is a memory for storing designated value data for designating the encoder reference position, and the designated value data is stored by inputting a predetermined value.

  The encoder signal sampling unit 136 samples the encoder signal for a predetermined time with a system clock (for example, 40 MHz). The sampling value is stored in the first register 138. At the same time, the sampling value of the first register 138 is stored in the second register 140. This sampling value varies according to the rotational position of the encoder 39, and has a periodicity that increases or decreases during one rotation of the encoder 39. The sampling value of the first register 138 is stored in the second register 140 in order to delay by the system clock. That is, the current sampling value is stored in the first register 138 and the previous sampling value is stored in the second register 140.

  The sampling value comparison unit 142 compares the sampling values stored in the first register 138 and the second register 140. For example, it is determined if the sampling value is increasing (the sampling value of the first register 138> the sampling value of the second register 140). Although the number of comparisons may be one, it is preferable to execute a designated number (for example, 10 times) for noise countermeasures.

  The specified value comparison unit 134 compares the specified value stored in the specified value register 132 with the sampling value stored in the first register 138. For example, it is determined whether or not the value of the first register 138 exceeds the specified value (specified value <the value of the first register 138). Although the number of comparisons may be one, it is preferable to execute a designated number (for example, 10 times) for noise countermeasures.

  The integration unit 144 is a signal generation unit that outputs an encoder reference position signal when both the comparison result of the designated value comparison unit 134 and the comparison result of the sampling value comparison unit 142 are affirmed.

  The operation of the encoder reference position signal generation unit 130 configured as described above will be described with reference to FIG. First, the encoder signal sampling unit 136 samples the encoder signal, and stores the sampling values in the first register 138 and the second register 140 (step 150). Next, the sampling value comparison unit 142 compares the sampling values to determine whether or not they are increased (step 152). In the case of a decrease, negative determination is made and sampling is continued (return to step 150 as it is). On the other hand, in the case of an increase, as a positive determination, a sampling comparison result signal is output to the integrating unit 144. When the sampling value is increased, the specified value comparing unit 134 compares the specified value with the current sampling value, and determines whether or not the sampling value exceeds the specified value (step 154). If the sampling value is less than or equal to the specified value, negative sampling is made and sampling is continued (return to step 150 as it is). On the other hand, if the sampling value exceeds the specified value, the accumulating unit 144 generates and outputs an encoder reference position signal as an affirmative determination (step 156).

  In this manner, in this embodiment, the encoder reference position signal generated using the encoder signal from the encoder 39 can be used instead of the drive roll reference position signal without providing the reference position detection sensor 38. .

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various changes or improvements can be added to the above-described embodiment without departing from the gist of the invention, and embodiments to which such changes or improvements are added are also included in the technical scope of the present invention.

  Further, the above-described embodiments do not limit the invention according to the claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention. The embodiments described above include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. Even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, as long as an effect is obtained, a configuration from which these some constituent requirements are deleted can be extracted as an invention.

  For example, in the above-described embodiment, the case where correction data is stored in the correction data storage memory 102 provided in the correction print clock generation mechanism 62 is performed in advance, for example, before shipment of the inkjet recording apparatus 12 from the factory. The invention is not limited to this, for example, a mode that is automatically performed at predetermined intervals, a mode that is performed at any timing when an execution instruction is given by the user, and a mode that is performed at other timings. You can also Also in this case, the same effect as the above embodiment can be obtained.

  In addition, the configurations of the inkjet recording apparatus 12, the inkjet recording head 32, and the recording head controller 78 described in the above embodiment are merely examples, and it goes without saying that they can be appropriately changed without departing from the gist of the present invention.

  In the above embodiment, the case where ink is used as the droplet of the present invention has been described as an example. However, the present invention is not limited to this, and for example, a reaction liquid can be used instead of ink. . Specifically, since the image quality is further improved by mixing the ink droplets and the reaction droplets on the recording medium, the present invention can be applied in the same manner as described above when the reaction droplets are ejected by the nozzles. . In addition, the present invention can be applied to the application of the alignment film forming material of the liquid crystal display element, the application of the flux, the application of the adhesive, the application of the wiring material of the printed circuit board, and the like by the inkjet method.

It is a front sectional view showing the configuration of the ink jet recording apparatus according to the embodiment in the image recording state. It is a bottom view which shows the structure of the inkjet recording head of the one-dimensional arrangement | sequence which concerns on embodiment. It is a bottom view which shows the structure of the inkjet recording head of the two-dimensional arrangement which concerns on embodiment. 1 is a block diagram illustrating a main configuration of an electric system of an ink jet recording apparatus according to an embodiment. FIG. 4 is a diagram illustrating a conveyance speed variation (speed unevenness) and a phase relationship between each inkjet recording head in the inkjet recording apparatus according to the embodiment. FIG. 2 is a block diagram illustrating a configuration of a main part around an electric recording head controller of the ink jet recording apparatus according to the embodiment. It is a block diagram which shows schematic structure of the correction | amendment print clock generation mechanism which concerns on 1st Embodiment. It is explanatory drawing about operation | movement of the correction data generation part which concerns on embodiment. It is an image figure which shows the content of the correction data stored in the correction data storage memory which concerns on embodiment. It is explanatory drawing of measuring and obtaining | requiring test printing about (A) 1-dimensional head and (B) 2-dimensional head about the production | generation of the correction data stored in the correction data storage memory which concerns on embodiment. It is a block diagram which shows schematic structure of the correction | amendment clock generation part which concerns on embodiment. 6 is a timing chart in a corrected print clock generation mechanism and a print timing generation mechanism according to the embodiment. It is a block diagram which shows schematic structure of the correction | amendment print clock generation mechanism which concerns on 2nd Embodiment. It is a block diagram which shows schematic structure of the encoder reference position signal generation part which concerns on 2nd Embodiment. It is a diagram which shows the signal waveform output from the encoder which concerns on 2nd Embodiment. It is a flowchart which shows the flow of a process in an encoder reference position signal generation part.

Explanation of symbols

12 Inkjet recording device 32 Inkjet recording head (recording head)
32A, 32B, 32C Head unit (unit structure)
34 Paper Detection Sensor 36 Surface Speed Detection Sensor 38 Reference Position Detection Sensor 60 Image Recording Timing Control Mechanism 62 Correction Print Clock Generation Mechanism 64 Print Timing Generation Mechanism 70 CPU
76 Memory 78 Recording head controller G Nozzle group N Nozzle P Paper (recording medium)

Claims (3)

A plurality of long recording heads that are long in a direction orthogonal to the transport direction provided along a predetermined transport direction;
Conveying means for conveying a sheet as a recording medium to the recording head;
Detecting means for detecting a conveying speed of the sheet conveyed by the conveying means;
A reference position detecting means for detecting a reference position when the sheet is conveyed by the conveying means;
Tip position detecting means for detecting the tip position of the sheet conveyed by the conveying means;
Based on the conveyance speed detected by the detection means and the reference position detected by the reference position detection means, the conveyance means is set so that the same correction amount is obtained when the fluctuation range of the conveyance speed is within a predetermined range. When generating a print clock corrected based on the conveyance speed having the periodicity of the sheet conveyed by the above, and generating image recording timing by the plurality of recording heads based on the print clock, A plurality of recordings from the front end position when the front end position of the sheet is detected by the front end position detecting unit by the distance from the predetermined position determined for each recording head to the arrangement position of the plurality of recording heads and the front end position detecting unit. Control means for setting the image recording start timing for each of the plurality of recording heads based on the distance to the head disposition position;
An image recording apparatus comprising:   The image recording apparatus according to claim 1, wherein the control unit includes a timing generation unit that generates the image recording timing in each of the recording heads.   The recording head includes a unit structure having a nozzle group in which a plurality of nozzles each ejecting droplets for image recording are linearly arranged at the same interval with respect to a predetermined direction in a direction intersecting the predetermined direction. The image recording apparatus according to claim 1, wherein the image recording apparatus is a plurality of droplet discharge heads.

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