JP2007069428A - Ink jet recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink jet recorder for recording images of different colors on a recording sheet in which printing is performed with excellent image quality by injecting ink of each color to an accurate position with good precision without using an unnecessary mark excepting an image being recorded on a recording medium. <P>SOLUTION: The ink jet recorder records images sequentially by carrying a recording medium such as a sheet in a predetermined carrying direction and ejecting ink drops from recording heads of a plurality of colors toward the recording medium wherein the absolute position of the recording medium is detected by means of a sesor located on the upstream side of the recording head of each color and ejection timing of ink drop of each color is adjusted thus performing printing at an accurate position. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet recording apparatus that records images of different colors on recording paper.

  In an inkjet recording apparatus that sequentially records images of different colors on recording paper, for example, a fixed head such as a line head may be used. The fixed head has a nozzle row that can be ejected over the width of the recording medium, and ejects ink onto the recording paper while conveying the recording paper with the nozzle rows facing each other to perform image recording.

  The line head may have a single-row nozzle configuration, or may have a configuration in which a plurality of heads are connected in the paper width direction and finished into a single line head. One line head is composed of one color, and different colors such as Black (hereinafter denoted by K), Cyan (hereinafter denoted by C), Magenta (hereinafter denoted by M), Yellow (hereinafter denoted by Y). The image forming unit is composed of four color line heads. The four color line heads are arranged in parallel along the paper transport direction.

  In such a recording apparatus, an image is formed on a recording medium conveyed by ink ejection from heads of different colors arranged at a predetermined distance, and therefore the ink ejection timing of each color and the position of the recording medium And the correlation is taken. Ideally, when the conveyance speed of the recording medium is constant, a high-quality image can be obtained without ink landing deviation due to ink ejection timings that are equally spaced in time.

  However, the conveyance speed is not necessarily constant due to various electrical or mechanical factors in the conveyance path, and even if the ink is ejected at regular intervals in time, color unevenness and image distortion occur. In addition, the conveyance speed of the recording medium is not uniform at all points on the surface of the recording medium due to the influence of the meandering in the conveyance direction and the floating of the recording medium, and the nonuniformity of the conveyance speed is a cause of color misregistration and image distortion. Become. In order to solve these problems, it is necessary to correct the ink ejection timing according to the transport state of the recording medium being transported.

  In the invention described in Patent Document 1, a plurality of photosensors for detecting the leading edge of the recording medium are provided for each line head, a rotary encoder for detecting the moving distance of the recording medium is provided, and the leading edge of the recording medium is The position of the recording medium is calculated for each line head by detecting with the photo sensor and integrating the moving distance therefrom with a rotary encoder, and ink is ejected from the recording head of each line according to the calculated position.

The invention described in Patent Document 2 proposes means for accurately detecting the position of the recording medium by marking the recording medium for detection. Since this method can directly detect the position of the paper, the error can be reduced and printing deviation can be reduced.
JP 2005-131929 A JP-A-10-35021

  In the invention of Patent Document 1, after the leading end position of the recording medium is detected, the printing position on the recording medium is calculated by the rotary encoder, and printing is performed at the printing position from the recording head. For this reason, an error occurs in the actual print position due to conveyance unevenness of the conveyance unit, slippage between the recording medium and the conveyance unit, and the like. That is, the leading edge of the recording medium is detected by a sensor provided in the vicinity of the recording head, and accurate position detection is performed when the leading edge of the recording medium passes immediately below the recording head. However, the moving distance of the recording medium after passing through the leading edge is measured by a single rotary encoder regardless of the positions of the plurality of recording heads, and the conveyance speed of the recording medium is assumed to be uniform at every position on the recording medium. Thus, an error occurs in the actual printing position due to uneven conveyance of the conveying means, slippage between the recording medium and the conveying means, and the ink of each color cannot be printed at an accurate position.

On the other hand, in the invention of Patent Document 2, position detection can be performed accurately as described above, but it is necessary to use a recording medium with a mark.
Therefore, the present invention accurately discharges ink droplets of each color to accurate positions to perform image recording with excellent quality and does not use unnecessary marks other than an image to be recorded on a recording medium. An object is to provide an apparatus.

  In order to solve the above-described problems, an ink jet recording apparatus according to the present invention includes a transport unit that transports a recording medium in a predetermined transport direction, and an ink droplet that is disposed along the predetermined transport direction from a plurality of nozzles toward the recording medium. In an ink jet recording apparatus having a plurality of recording heads that sequentially eject images and detect the amount of movement of the recording medium being conveyed in a unit time in a non-contact manner at an arbitrary position on the surface of the recording medium A plurality of sensor units, and a control unit that adjusts the ejection timing of the ink droplets from the recording head according to the outputs of the plurality of sensor units.

  According to the present invention, the ejection timing of the ink droplets from the plurality of recording heads is adjusted by the control unit that adjusts the ejection timing of the ink droplets according to the output from the plurality of sensor units that detect the movement amount of the recording medium, respectively. Controlled.

  According to the present invention, the absolute position of the transported recording medium is detected directly and in a non-contact manner, and the printing position is corrected, so that the timing of the ink droplets can be adjusted with accuracy, resulting in color unevenness and image distortion. It is possible to record a high quality image without causing it to occur.

  Further, since the position adjustment of each line head unit can be performed independently for each color, even when the transport speed of the paper 10 is uneven, the ink droplet ejection timing can be adjusted for each color. . Further, it is not necessary to process signals from sensors at a distance from each other in the same circuit, and wiring can be simplified. Furthermore, it is possible to reduce the risk of erroneous detection caused by detecting a speckle pattern at the same position by a plurality of sensors.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 2 is a schematic sectional view of the ink jet recording apparatus according to the first embodiment.
In FIG. 1, an ink jet recording apparatus 1 includes a paper feeding unit 2, an image forming unit 3, an ink bottle 4, a waste oil tank 5, a paper discharge tray 6, and the like. A sub tank 22a, a pressure pump 22b, and a suction pump 22c are also provided below the image forming unit 3. A discharge roller 6 a is provided immediately before the paper discharge tray 6, and the paper 10 on which the printing process has been performed is discharged to the paper discharge tray 6.

  The sheet feeding unit 2 includes a sheet feeding table 7, a sheet feeding roller 8, and a registration roller 9, and a sheet 10 is placed on the sheet feeding table 7. One sheet located on the uppermost portion of the paper 10 placed on the paper feed table 7 is in contact with the paper feed roller 8 at the top end of the paper 10 and is fed into the main body according to the rotation of the paper feed roller 8. At this time, the leading edge of the sheet 10 is abutted against the registration roller 9, and after the posture is corrected, the sheet 10 is supplied into the main body at the same timing.

  The image forming unit 3 includes a platen unit and a line head unit. FIG. 3 is a diagram illustrating the configuration of the platen unit. The platen unit 11 includes a case 13 in which a suction fan 16 is housed, a platen 14, and a belt conveyance mechanism 15. The case 13 is composed of a box-shaped sheet metal, and a discharge port 17 for exhausting the suction fan 16 is provided on one side of the case 13. The platen 14 is made of, for example, an aluminum plate having a thickness of 5 mm, and is provided with a plurality of through holes.

  The belt conveyance mechanism 15 is configured by a belt 20 being stretched over a driving roller 18 driven by a motor (not shown) and a passive roller 19 that freely rotates. The belt 20 is applied with a predetermined pressure by a tension roller 21. ing. Further, the belt 20 is provided with a plurality of holes, and the sheet 10 is conveyed in a contact state without being lifted from the belt 20 while being sucked by the suction fan 16 from below.

  On the other hand, the line head unit 12 is provided above the platen unit 11 as shown in FIG. 2, and is provided at a position facing the platen unit 11. The line head unit 12 includes four color line head units 12K, 12C, 12M, and 12Y of K (black), C (cyan), M (magenta), and Y (yellow), and sequentially in the conveyance direction of the paper 10. They are arranged at equal intervals.

  FIG. 4 is a perspective view for explaining the configuration of the line head unit 12. Of the four color line heads, a K (black) line head unit will be described as a representative. As shown in the figure, the line head unit 12K has a configuration in which six single heads 12a to 12f are arranged in a staggered manner, and each has, for example, about 636 nozzles at a density of 300 dpi. These 636 nozzles are arranged so as to be perpendicular to the paper transport direction.

  Further, the head spacing between adjacent single heads, for example, the single heads 12a and 12b, is overlapped in the paper transport direction or arranged with a predetermined gap, and the predetermined gap is substantially in the paper transport direction. It is adjusted so as to have a 300 dpi lattice (that is, 84.6 μm) interval in the orthogonal direction.

  With this arrangement, the six single heads 12a to 12f are apparently handled as if they were one head with a nozzle pitch of 300 dpi and the number of nozzles of about 3816. Also, it is possible to adjust the timing of ejecting ink for each single head. The single heads 12 a to 12 f are supplied with ink from a distributor 45 through a pipe 44, and further supplied with ink of a corresponding color from the ink bottle 4 through the pipe 46. The other color line head units 12C, 12M, and 12Y have the same configuration as the line head unit 12K.

  On the other hand, a sensor unit 23 for detecting a speckle pattern, which will be described later, is attached to the side surface of the single head 12f shown in FIG. The sensor unit 23 is attached to the upstream side in the conveyance direction of the paper 10. FIG. 5 is a diagram illustrating the configuration of the sensor unit 23.

  The sensor unit 23 includes a laser diode 24, a lens 25, and an area sensor 26, and the sheet 10 is conveyed in the direction of the arrow below the sensor unit 23. Laser light from the laser diode 24 is applied to the upper surface of the paper 10, and the reflected light passes through the lens 25 and enters the area sensor 26. The area sensor 26 detects the speckle pattern of the portion irradiated with the laser light, converts the speckle pattern into an electrical signal, and outputs it as a speckle pattern signal to a control unit described later.

  FIG. 6 is a schematic diagram of the image forming unit 3 including the sensor unit 23. In the drawing, four sensor units 23K, 23C, 23M, and 23Y have the configuration shown in FIG. 5 and are provided upstream of the corresponding line head units 12K, 12C, 12M, and 12Y in the sheet conveyance direction. . For example, the sensor unit 23 </ b> K is provided on the upstream side of the line head unit 12 </ b> K and on the upper side end of the paper 10 that becomes a margin. Similarly, the sensor unit 23C is provided on the upstream side of the line head unit 12C and on the upper side edge of the paper 10 that becomes a margin, and the sensor units 23M and 23Y are also upstream of the corresponding line head unit 12M or 12Y, respectively. , Provided at the upper part of the side edge of the paper 10 which becomes a margin.

  The speckle pattern signals 27K, 27C, 27M, and 27Y generated by the sensor units 23K to 23Y are supplied to the control unit 28 that controls the ink ejection timing. The control unit 28 calculates the paper position based on the supplied speckle pattern signals 27K, 27C, 27M, and 27Y, and print pulses 29K, 29C, 29M, and 29Y for discharging ink in accordance with the position of the paper 10. Is output to the corresponding line head units 12K, 12C, 12M, and 12Y.

  FIG. 1 is a diagram for explaining the circuit configuration of the control unit 28. The control unit 28 includes the sensor units 23K, 23C, 23M, and 23Y, and the line head units 12K, 12C, 12M, and 12Y. The control unit 28 includes a comparator 30, delay circuits 31a, 31c, 31e, position error detection circuits 32C, 32M, 32Y, a print pulse generation circuit 33, delay circuits 34b, 34d, 34f, a delay circuit 35, and a timing correction circuit 36C. 36M and 36Y. Further, the control unit 28 is provided with a memory 37 and an edge detection circuit 38.

  The edge detection circuit 38 is a circuit that detects the leading end position of the paper 10 conveyed through the image forming unit 3. The delay circuits 31a, 31c, and 31e are circuits for delaying a speckle pattern signal 27K detected by the sensor unit 23K for a time Td described later, and the delay circuits 34b, 34d, and 34f are output from the print pulse generation circuit 33. This is a circuit for delaying the pulse signal to be delayed by time Td.

The delay circuit 35 is a circuit that delays the pulse signal output from the print pulse generation circuit 33 by a time Ta. This time Ta corresponds to an ideal paper conveyance time between the sensor unit and the line head unit. Further, the timing correction circuits 36C, 36M, 36Y are circuits for correcting the ideal transport time Ta between the sensor unit and the line head unit and the error value ΔT detected by the corresponding position error detection circuits 32C, 32M, 32Y. It is. The time Ta is set to two types of time because the line head unit is configured by arranging the single heads 12a to 12f in a staggered manner in this example.

Next, the processing operation in the inkjet recording apparatus 1 having the above configuration will be described.

  As described above, the sheet 10 placed on the sheet feed table 7 is conveyed into the main body according to the rotation of the sheet feed roller 8 and reaches the image forming unit 3. First, the leading end of the paper 10 is detected by the sensor unit 23K located at the uppermost stream. In this process, a signal detected by the sensor unit 23K is sent to the edge detection circuit 38, and the edge detection circuit 38 detects the leading edge of the paper 10 based on the color contrast difference between the paper 10 and the belt 20.

  Thereafter, the speckle pattern of the paper 10 is detected by the sensor unit 23K. FIG. 7 shows an example of this speckle pattern. This speckle pattern is sampled at a time interval of 100 μs, for example. The accuracy of the area sensor 26 described above is, for example, 1600 dpi, that is, one pixel has a resolution of about 16 μm.

  The comparator 30 compares the received speckle pattern signal 27K with the previously sampled speckle pattern signal 27K (hereinafter referred to as the speckle pattern signal 27K0), and obtains the sheet movement distance between 100 μs. The speckle pattern signal 27K0 detected last time is stored in the memory 37, and the comparator 30 reads the speckle pattern signal 27K0 from the memory 37 and compares it.

  Here, if the conveyance speed of the paper 10 is 600 mm / s, for example, the moving distance of the paper 10 at a sample interval of 100 μs is 60 μm, and information of about 4 pixels (60/16) is detected by the comparator 30. The Note that the printing accuracy of the inkjet recording apparatus 1 of the present example is 300 dpi, for example, and the dot interval is 85 μm (about 5 pixels).

  The print pulse generation circuit 33 outputs a pulse (reference print pulse) for each unit distance according to the movement distance detected by the comparator 30. For example, if one pulse is output for each dot printed, a pulse signal corrected with a resolution of one pixel (16 μm) is output at an average interval of five pixels. During this time, if the conveyance speed of the paper 10 is uneven, the reference print pulse is generated at regular intervals according to the movement distance.

  The reference print pulse 40 is supplied to the delay circuit 35, delayed by time Ta by the delay circuit 35, and output to the line head unit 12K as the print pulse 29K. This time Ta is the time necessary for the sheet 10 to move in the ideal state over the distance between the sensor unit 23K and the line head unit 12K as described above, and is delayed by the delay circuit 35 by this time Ta, and the printing pulse 29K. Is output to the line head unit 12K. As described above, in this example, since the line head unit 12 is configured by arranging the single heads 12a to 12f in a staggered manner, two types of delay times Ta are used.

  8 and 9 are time charts for explaining the above processing, and FIG. 9 is an enlarged time chart showing a portion A of FIG. As described above, the speckle pattern signal 27K detected by the sensor unit 23K at the most upstream in the paper transport direction is the speckle pattern signal of one sample (100 μs) before recorded in the memory 37 by the comparator 30. Compared with 27K0, the difference in the position of the image formed by the speckle pattern is output as the transport distance of the paper 10 in units of the number of pixels. The print pulse generation circuit 33 outputs the reference print pulse 40 based on the information output from the comparator 30, and the delay circuit 35 performs a delay process for the time Ta.

  This time Ta is the time required when the paper 10 is transported from the sensor unit 23 to the line head unit 12 when the sensor unit 23K and the line head unit 12K are provided at a position separated by 30 mm, for example. /600=0.05 s, and other delay times Ta are set in the same manner. Therefore, the reference print pulse 40 is delayed by the time Ta by the delay circuit 35, and is output to the line head unit 12K as the print pulse 29K.

  Thereafter, when the paper 10 is conveyed and reaches the sensor unit 23C, the sensor unit 23C detects the speckle pattern of the paper 10 and outputs it to the position error detection circuit 32C. On the other hand, the position error detection circuit 32C is also supplied with the speckle pattern signal 27K (hereinafter referred to as 27K1) delayed by Td by the delay circuit 31a. The delay time Td is a time required when it is assumed that the paper 10 is conveyed in an ideal state from a position immediately below the sensor unit 23K to a position immediately below the sensor unit 23C. For example, assuming that the head interval (= sensor interval) is 100 mm, Td = 100/600 = 0.17 s if the conveyance speed of the paper 10 is 600 mm / s.

  Therefore, the speckle pattern signal 27C is output from the sensor unit 23C, and the position error detection circuit 32C detects an error between both speckle patterns. Then, the position error detection circuit 32C generates a correction signal ΔT1 based on the error value and outputs it to the timing correction circuit 36C. That is, as shown in FIG. 8, the speckle pattern signal 27K1 delayed by time Td (0, 17s) and the speckle pattern signal 27C are compared by the position error detection circuit 32C, and the correction signal ΔT1 according to the error value is obtained. This is output to the timing correction circuit 36C.

  The timing correction circuit 36C is also supplied with a pulse 41 obtained by delaying the reference print pulse 40 by the delay circuit 34d for a time Td, and the timing correction circuit 36C corrects both signals.

  In an ideal case where there is no unevenness in the conveyance speed of the paper 10, ΔT1b = 0 as shown in (2) of FIG. However, when the conveyance speed of the paper 10 is uneven, for example, when the paper conveyance speed is slower than the printing speed of black (K), the speckle pattern signal 27C is output by ΔT1a as shown in (1) of FIG. Be late. On the other hand, when the paper transport speed is faster than the black (K) printing speed, the speckle pattern signal 27C is accelerated by ΔT1c as shown in (3) of FIG.

  For example, the example shown in FIG. 7 shows a case where there is an error of two pixels. That is, a shown in the figure indicates a base image, and b indicates a target image. The base image a shows the speckle pattern 27K1 detected by the sensor unit 23K and supplied to the position error detection circuit 32C with a delay of the above-described time Td, and the target image b is detected by the sensor unit 23C, and the position error detection circuit The speckle pattern 27C supplied to 32C is shown. In this case, two pixels excluding the common part of both speckle patterns are error amounts, and are output as ΔT1 to the timing correction circuit 36C, where the correction including the time Ta (0.05 s) described above is performed, and the print pulse 29C. Is output to the line head unit 12C. Therefore, the print pulse 29C output to the line head unit 12C at this time is a print pulse that is actually corrected to match the same speckle pattern of the paper 10, and the discharge position of the cyan ink droplet is set to the black ink droplet. It is possible to accurately match the discharge position.

  Next, when the paper 10 is further conveyed and reaches the sensor unit 23M, the sensor unit 23M detects the speckle pattern of the paper 10 and outputs it to the position error detection circuit 32M as described above. On the other hand, the speckle pattern signal 27K2 further delayed by the time Td by the delay circuit 31c is also supplied to the position error detection circuit 32M.

  Therefore, as described above, the position error detection circuit 32M detects the error value of both speckle pattern signals, generates the correction signal ΔT2, and outputs it to the timing correction circuit 36M. The timing correction circuit 36M corrects the timing for the pulse 42 in accordance with the correction signal ΔT2, further corrects the time Ta, and outputs the print pulse 29M to the line head unit 12M. Also in this case, the print pulse 29M supplied to the line head unit 12M is a print pulse that is actually corrected to match the same speckle pattern of the paper 10, and the discharge position of the magenta ink droplet is set to the black or cyan ink. It is possible to accurately match the droplet discharge position.

  Further, when the paper 10 is conveyed and reaches the sensor unit 23Y, the sensor unit 23Y detects the speckle pattern of the paper 10 and outputs it to the position error detection circuit 32Y. On the other hand, the speckle pattern signal 27K3 further delayed by the time Td by the delay circuit 31e is also supplied to the position error detection circuit 32Y, and the position error detection circuit 32Y generates a correction signal ΔT3 for the error and corrects the timing. Output to circuit 36M. Therefore, the timing correction circuit 36Y corrects the timing of the pulse 43 according to the correction signal ΔT3, further corrects the time Ta, and outputs the print pulse 29Y to the line head unit 12Y.

  Also in this case, the print pulse 29Y supplied to the line head unit 12Y is a print pulse that is actually corrected to match the same speckle pattern of the paper 10, and the discharge position of the yellow ink droplet is set to black, cyan, magenta. It is possible to accurately match the ink droplet ejection position.

  As described above, according to the first embodiment, the absolute position of the conveyed paper 10 is detected directly and non-contacted as a speckle pattern signal, and the timing of ink droplets by the line head unit is controlled using the signal. Therefore, there is no color unevenness and image distortion, and a high-quality image can be recorded. Further, it is not necessary to use a sheet with an unnecessary mark as in the prior art.

  In the above embodiment, the KCMY four-color line head unit is used and one sensor unit is provided for each color head unit. However, for example, only the KM two-color recording head has a sensor unit. The CY may be a print pulse obtained by performing a certain delay process on the signal pulse from the KM sensor unit. The present invention can be similarly applied to recording heads of at least two colors.

Further, in the above embodiment, the CMY three-color ink ejection timing is adjusted by comparison with the speckle pattern signal 27K of the most upstream sensor unit 23K, but C is K, M is C, and Y is M, respectively. The ink discharge timing may be adjusted by comparison with the sensor unit upstream.

Next, a second embodiment of the present invention will be described.

In the description of the second embodiment, components common to those in the first embodiment are denoted by the same reference numerals, and descriptions of operations and effects common to those in the first embodiment are omitted. .
In the present embodiment, the ejection timing of ink droplets by each line head unit is controlled by four independent control units. This will be specifically described below.

  FIG. 10 is a diagram for explaining the configuration of the control unit of this example. FIG. 10A shows an example of the configuration of the black (K) control unit. Similarly, FIG. 10B shows cyan (C). FIG. 3C shows an example of the configuration of the magenta (M) control unit, and FIG. 3D shows an example of the configuration of the yellow (Y) control unit.

  First, in FIG. 2A, the control unit 50K is provided with a memory 51K, a comparator 52K, an edge detection circuit 53K, a print pulse generation circuit 54K, and a delay circuit 55K. The speckle pattern signal 27K detected by the sensor unit 23K is supplied to the comparator 52K. Similarly to the above, the memory 51K is a memory that records the previous speckle pattern signal 27K0 detected by the sensor unit 23K, and the comparator 52K is the speckle pattern signal 27K0 recorded in the memory 51K and the spec detected by the sensor unit 23K. The pattern signal 27K is compared.

  Control units other than black (K), that is, the control unit 50C shown in FIG. 5B, the control unit 50M shown in FIG. 5C, and the control unit 50Y shown in FIG. The corresponding configuration is denoted by the corresponding number, and the description on the configuration is omitted.

  As described above, when the leading edge of the sheet is detected by the sensor unit 23K located at the most upstream in the sheet conveying direction, the sensor unit 23K causes a sudden change in contrast based on the color difference between the belt 20 and the sheet 10. The leading edge of the paper 10 is detected by the edge detection circuit 53K.

  Next, the speckle pattern of the paper 10 is detected by the sensor unit 23K, the first speckle pattern signal 27K is recorded in the memory 51K, and thereafter the speckle pattern is sampled at intervals of 100 μs. The comparator 52K compares the speckle pattern signal 27K sent sequentially with the speckle pattern signal 27K0 sampled one time before, and obtains the sheet movement distance in 100 μs.

  The print pulse generation circuit 54K outputs a reference print pulse according to the movement distance detected by the comparator 52K while the paper 10 passes just below the sensor unit 23K. At this time, even when the conveyance speed of the paper 10 is uneven, the reference print pulses are generated at equal intervals according to the movement distance.

  Next, as described above, the reference print pulse is delayed by the delay circuit 55K by the time Ta necessary for the sheet 10 to move in the ideal state over the distance between the sensor unit 23K and the line head unit 12K. It is output to the unit 12K.

  Similarly, the sensor units 23C, 23M, and 23Y that follow on the downstream side with respect to the paper transport direction sequentially output speckle pattern signals 27C, 27M, and 27Y, generate a reference print pulse according to the movement distance, and further perform reference printing. The pulse is delayed by the delay circuit 55K for the time Ta, and sequentially output to the corresponding line head units 12C, 12M, and 12Y as print pulses 29C, 29M, and 29Y. The line head units 12K, 12C, 12M, and 12Y discharge ink droplets according to the printing pulses 29K, 29C, 29M, and 29Y, and form an image on the conveyed paper 10.

  As described above, according to the second embodiment, the absolute position of the sheet 10 immediately below each sensor unit can be detected, and control can be performed independently for each color, compared to the first embodiment. Therefore, even when the conveyance speed of the paper 10 is uneven, the ink droplet ejection timing can be corrected in accordance with the absolute position of the paper for each color.

  Further, it is not necessary to process sensor signals at a distance from each other by the same circuit, and wiring can be simplified. Furthermore, it is possible to reduce the risk of erroneous detection caused by detecting a speckle pattern at the same position by a plurality of sensors.

  In the above-described embodiment, the KCMY four-color line head unit is used and one sensor unit is provided for each color head unit. However, for example, only the KM two-color recording head is used. The CY may be configured to include a sensor unit, and each CY may use a print pulse obtained by performing a certain delay process on the signal pulse from the KM sensor unit. The present invention can be similarly applied to recording heads of at least two colors.

  In the above embodiment, the CMY three-color ink ejection timing is adjusted by comparison with the speckle pattern signal 27K of the most upstream sensor unit 23K. However, C is K, M is C, and Y is 1 each. The ink discharge timing may be adjusted by comparison with the sensor unit upstream.

It is a figure explaining the circuit structure of a control unit. It is a schematic sectional drawing of this embodiment. It is a figure which shows the structure of a platen unit. It is a perspective view explaining the structure of a line head unit. It is a figure explaining the structure of a sensor unit. It is a figure explaining the image formation part containing the structure of a sensor unit. It is a figure explaining a speckle pattern signal. It is a time chart explaining the process of this embodiment. It is a figure which expands and shows a part of time chart of FIG. (A)-(d) is a figure explaining 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Inkjet recording device 2 ... Paper feed part 3 ... Image formation part 4 ... Ink bottle 5 ... Waste oil tank 6 ... Paper discharge tray 6a ... Discharge roller 7 ... Feeding base 8 ... feeding roller 9 ... registration roller 10 ... paper 11 ... platen unit 12, 12K, 12C, 12M, 12Y ... line head unit 12a to 12f ... single head 13 ... case 14 .. Platen 15... Belt transport mechanism 16 .. suction fan 17 .. discharge port 18 .. drive roller 19 .. passive roller 20 .. belt 21 .. tension roller 22 a .. sub tank 22 b. 22c ··· Suction pump 23, 23K, 23C, 23M, 23Y ··· Sensor unit 24 · · Laser diode 25 · · Lens 26 · · Eliasn 27K, 27C, 27M, 27Y ... Speckle pattern signal 28 ... Control unit 29K, 29C, 29M, 29Y ... Print pulse 30 ... Comparator 31a, 31c, 31e ... Delay circuit 32C, 32M, 32Y ... Position error detection circuit 33..Print pulse generation circuit 34b, 34d, 34f..Delay circuit 35..Delay circuit 36C, 36M, 36Y..Timing correction circuit 37..Memory 38..Edge detection circuit 40..Reference print Pulses 44, 46 ··· Pipe 45 ··· Distributor 50K, 50C, 50M, 50Y · · Control unit 51K, 51C, 51M, 51Y · · · Memory 52K, 52C, 52M, 52Y · · · Comparator 53K, 53C, 53M, 53Y .. edge detection circuit 54K, 54C, 54M, 54Y .. print pulse generation circuit 55 , 55C, 55M, 55Y ·· delay circuit

Claims (10)

A transport unit that transports the recording medium in a predetermined transport direction, and a plurality of recording head arrays that are arranged along the predetermined transport direction and that sequentially record images by ejecting ink droplets from the plurality of nozzles toward the recording medium. In an inkjet recording apparatus having:
A plurality of sensor units for detecting the absolute position of the surface of the recording medium being conveyed;
A controller that adjusts the ejection timing of the ink droplets from the recording head array based on the outputs of the plurality of sensor units;
An ink jet recording apparatus comprising:   2. The ink jet recording apparatus according to claim 1, wherein the absolute position of the surface of the recording medium is a non-printing portion of the recording medium.   2. The ink jet recording apparatus according to claim 1, wherein the plurality of sensor units are arranged on the upstream side of each of the recording head arrays with respect to the predetermined transport direction.   The plurality of recording head arrays eject ink droplets of a plurality of colors, and the plurality of sensor units are provided at least one for each color of the plurality of ink droplets, and the plurality of sensor units are arranged in the predetermined transport direction. 2. The ink jet recording apparatus according to claim 1, wherein the ink jet recording apparatus is disposed on an upstream side of the recording head row provided for each color of the color ink droplets. The plurality of sensor units have two sensor units on the upstream side and the downstream side at least with respect to the predetermined transport direction, and the control unit outputs a first position output from the upstream sensor unit. A print pulse generating circuit for accumulating information signals and generating a print pulse signal each time the recording medium is transported a certain distance;
A sensor signal delay circuit that delays the first position information signal from the upstream sensor unit to the downstream sensor unit by a time required for the recording medium to move in an ideal state;
A position error detection circuit that outputs an error correction signal by comparing the second position information signal output from the downstream sensor unit and the first position information signal delayed by the signal delay circuit;
A pulse signal delay circuit for delaying the print pulse by a time required when the recording medium moves in an ideal state from the upstream sensor unit to the downstream sensor unit;
A timing correction circuit for correcting the print pulse signal delayed by the pulse signal delay circuit with the error correction signal;
The inkjet recording apparatus according to claim 1, comprising: The controller is
A tip detection circuit for detecting the tip of the recording medium conveyed from the output of the sensor unit;
A print pulse generating circuit that integrates position information signals output from the sensor unit and generates a print pulse signal every time the recording medium is conveyed a certain distance;
The inkjet recording apparatus according to claim 1, comprising:   The inkjet recording apparatus according to claim 1, wherein the sensor unit is an optical sensor that detects a speckle pattern on the recording medium. The controller is
The speckle pattern detected by the sensor unit is sampled at fixed time intervals, and the sampled speckle pattern is compared with the speckle pattern sampled a predetermined number of times before the unit time within the unit time. A moving distance detection circuit for detecting the moving distance of the recording medium;
A print timing control circuit for generating a signal for controlling ink ejection according to the absolute position of the recording medium based on the output of the movement distance detection circuit;
The ink jet recording apparatus according to claim 7, comprising: The controller is
A tip detection circuit for detecting the tip of the recording medium conveyed from the output of the sensor unit;
The position information signal detected by the sensor unit is sampled every predetermined time, and the sampled position information signal is compared with the position information signal sampled a predetermined number of times before the unit information within the unit time. A moving distance detection circuit for detecting the moving distance of the recording medium;
A print pulse generating circuit for accumulating the moving distance of the recording medium and generating a print pulse signal every time the recording medium is conveyed by a certain distance;
A print pulse signal delay circuit for delaying the recording medium from the sensor unit to the recording head row by a necessary time when moving in an ideal state;
The inkjet recording apparatus according to claim 1, comprising: The inkjet recording apparatus according to claim 9, wherein the control unit is provided for each of at least two recording head arrays.