JP2012016894A - Apparatus and method for forming image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which can correct the misregistration of droplets in a sub-scan direction, and to provide an image forming method.SOLUTION: The image forming apparatus 100 include: a print data memory 203 for storing print data; a conveyance belt 17 for conveying a recording medium; a driver 15 for driving the conveyance belt; a recording head 23 whose nozzles for discharging the droplets of ink onto the recording medium are arranged in a line in the main scanning direction; and a print controller 207 for controlling the ink discharging operation of the recording head according to the printing data. The image forming apparatus 100 is characterized by having: a photograph means 26 for shooting the liquid droplet landed on the recording medium; a first position information obtaining means 51 for obtaining first position information concerning the discharge position of the liquid droplet; a second position information obtaining means 52 for obtaining second position information concerning the landed position; a misregistration calculator 53 for calculating the amount of the misregistration between the discharge position and the landed position in the main scanning direction and the sub-scanning direction; and a corrector 54 for instructing the recording head to adjust the amount of the misregistration.

Description

  The present invention relates to a line-type ink jet image forming apparatus, and more particularly to an image forming apparatus and an image forming method for correcting a droplet discharge position.

  2. Description of the Related Art A line-type ink jet image forming apparatus is known in which a recording head is arranged over the entire area of a recording medium such as paper in the main scanning direction, and a recording liquid (ink) droplet is ejected from the recording head to form an image. Yes. In the line-type ink jet image forming apparatus, it is not necessary to scan the recording head in the main scanning direction, so that the printing time can be shortened.

  Such an image forming apparatus is also required to improve the image quality of the output image. However, the image quality of the inkjet image forming apparatus depends greatly on the accuracy of the position where the droplets land. If the position is shifted, not only the shape but also the color development accuracy of the color is lowered. As a technique for correcting the positional deviation or color deviation of a droplet, a technique for detecting and correcting positional deviation or color deviation by forming a predetermined pattern on a sheet and optically reading it is known (for example, Patent Documents 1 and 2).

  Patent Document 1 discloses an image forming apparatus in which a reading sensor is arranged and an approximate position of an image recording element having a recording failure is determined from a sensor output value obtained by reading the pattern recorded on the sheet and the image to be originally recorded. Is disclosed.

  In Patent Document 2, for the purpose of correcting color misregistration of an image, a dedicated pattern is printed on a conveying belt that conveys a recording medium, and an image printed on the conveying belt is photographed by a reading sensor. An image forming apparatus that corrects color misregistration by calculating the above is disclosed.

  However, when a dedicated pattern is printed on a recording medium in order to correct misregistration and color deviation as in Patent Document 1, the recording medium on which the pattern is printed cannot be used for printing a user's document or the like and is wasted. There is a problem of becoming.

  Further, as in Patent Document 2, when a pattern is formed on the transport belt, it becomes necessary to clean the transport belt, so there is a problem that a new cleaning means is required and the cost is increased.

  On the other hand, a technique that does not use a pattern for correcting misalignment has also been proposed (see, for example, Patent Document 3). Patent Document 3 compares integrated data obtained by integrating read pixel data read by a line sensor with a certain width in the recording paper conveyance direction with an integrated value of expected read data expected from an image to be ejected originally. Thus, an image forming apparatus that identifies an inappropriate nozzle is disclosed.

  However, since the image forming apparatus described in Patent Document 3 acquires only one line of read data, there is a problem that only a positional deviation in the main scanning direction can be corrected.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus and an image forming method capable of correcting a positional deviation of liquid droplets in the sub-scanning direction without wasting a recording medium and increasing the cost of a cleaning unit. .

  Print data storage means for storing print data generated from the user's document, a transport belt for attracting and transporting the recording medium, a drive unit for driving the transport belt, and ink droplets on the previous recording medium In an image forming apparatus having a recording head in which ejection nozzles are arranged in a line in a main scanning direction, and a print control unit that controls an ink ejection operation of the recording head according to the print data, a line is formed in the main scanning direction. And image pickup means for photographing a droplet landed on a recording medium, and first positional information of an ejection position at which the recording head ejects the droplet based on an end of the recording medium First position information acquisition means for acquiring the second position information acquisition means for acquiring the second position information of the landing position of the droplet with reference to the end of the recording medium, and the first position Information and the second position information are compared, a position shift calculation means for calculating the position shift amount between the ejection position and the landing position in the main scanning direction and the sub-scanning direction, and the recording head corrects the position shift amount. Correction means.

  It is possible to provide an image forming apparatus and an image forming method capable of correcting the positional deviation of the droplets in the sub-scanning direction without wasting the recording medium and increasing the cost of the cleaning unit.

It is an example of the figure which illustrates typically correction of position shift which a droplet lands. 1 is an example of a schematic side view of an image forming apparatus. It is an example of the hardware block diagram of a control part. It is an example of the figure which illustrates typically memory of initial position W. It is an example of the figure explaining memory of the first position R typically. FIG. 6 is an example of a diagram illustrating a positional deviation amount in the main scanning direction calculated from an initial position W and an initial position R. FIG. 6 is an example of a diagram for explaining a positional deviation amount in a sub-scanning direction calculated from an initial position W and an initial position R. FIG. 10 is an example of a flowchart of a procedure in which the image forming apparatus detects and corrects a deviation amount. It is an example of the flowchart figure which shows the procedure in which the initial position W memory | storage part memorize | stores the initial position W. It is an example of the flowchart figure which shows the procedure in which the initial position R memory | storage part memorize | stores the initial position R. It is an example of the hardware block diagram of a control part (Example 2). It is a flowchart figure which shows an example of the procedure in which the maximum shift amount correction | amendment part correct | amends the maximum shift amount. It is an example of the hardware block diagram of a control part (Example 3). It is an example of the figure which illustrates estimation of the calculation range of positional offset amount typically. It is an example of the figure explaining the calculation range of position shift amount. (Example 4) which is an example of the hardware block diagram of a control part. FIG. 10 is an example of a flowchart of a procedure for detecting and correcting a positional deviation amount by the image forming apparatus. FIG. 10 is an example of a flowchart of a procedure for detecting and correcting a positional deviation amount by the image forming apparatus. FIG. 10 is an example of a flowchart of a procedure for detecting and correcting a positional deviation amount by the image forming apparatus. (Example 5) which is an example of the hardware block diagram of a control part. FIG. 10 is an example of a flowchart of a procedure for detecting and correcting a positional deviation amount by the image forming apparatus.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

[Outline of misalignment correction]
FIG. 1 is an example of a diagram for schematically explaining correction of positional deviation at which a droplet lands. The image forming apparatus 100 in FIG. 1 is a full-line type ink jet image forming apparatus 100 having an ink discharge head 23 over the entire area of the conveyance belt in the main scanning direction (hereinafter simply referred to as an image forming apparatus). Further, the image forming apparatus 100 includes a line-shaped image sensor 26 that captures the entire area of the transport belt in the main scanning direction downstream of the ink discharge head 23.
(1) First, the recording medium starts to be conveyed by the conveying belt from the left side in the drawing to the right.
(2) The ink discharge head 23 discharges droplets (ink) toward a recording medium based on print data to be printed such as a user document. Thereby, for example, the letters “a” are gradually formed on the recording medium.
(3) The image forming apparatus 100 acquires, for each position in the main scanning direction, a position in the sub-scanning direction (hereinafter referred to as an initial position W) at which droplets are first discharged. As shown in the image data of the letters “A” in FIG. 1, at the position 50 in the main scanning direction, the initial position W is 2 because the liquid droplets are ejected in 2, 3, and 4 in the sub-scanning direction. In the case of the position 10 in the main scanning direction, the initial position W is 5.
(4) When the recording medium is transported in the right direction, the recording medium passes immediately below the image sensor 26, so that the image sensor 26 starts capturing an image formed from the end of the recording medium in the sub-scanning direction. Therefore, when the entire recording medium passes through the lower part of the image sensor 26, for example, the entire image of the letter “A” is captured.
(5) In the captured image, the image forming apparatus 100 uses the position in the sub-scanning direction (hereinafter, referred to as a sub-scanning direction) where droplets are first detected for each position in the main scanning direction with reference to the leading end of the recording paper in the sub-scanning direction. First position R) is stored. In the case of the letter “A” in the figure, the droplet has landed for the first time at position 2 in the sub-scanning direction with respect to position 53 in the main-scanning direction. At a position 13 in the main scanning direction, a droplet has landed for the first time at a position 5 in the sub scanning direction.
(6) In an ideal state, the print data and the captured image should have the same pixel value for each pixel, but there are often slight deviations. In the example shown in the figure, it can be seen that the landing position shift of about 3 occurs in the main scanning position when the initial position R and the initial position W are compared.
(7) The image forming apparatus 100 shifts the landing position in the main scanning direction to the left by about 3 from the next recording medium when such a positional deviation amount is determined. Thereby, it is possible to accurately correct the ejection position of the droplet in the main scanning direction.
(8) Further, the image forming apparatus 100 shifts either the initial position W or the initial position R to the left by about 3 and then calculates the difference between the initial position W and the initial position R for each corresponding position in the main scanning direction. calculate. This difference becomes a positional deviation amount in the sub-scanning direction for each position in the main scanning direction (in the example shown in the figure, the positional deviation amount in the sub-scanning direction is zero).
(9) The image forming apparatus 100 corrects the ejection position from the next recording medium also in the sub-scanning direction.

  Therefore, the image forming apparatus 100 according to the present embodiment corrects while printing the user's document without wasting the recording medium for correcting the ejection position and does not need to clean the conveyance belt. The landing position can be corrected without requiring an operation or waiting time. Further, the landing position can be corrected not only in the main scanning direction but also in the sub scanning direction.

[Configuration of Image Forming Apparatus 100]
FIG. 2 is an example of a schematic side view of the image forming apparatus 100. The image forming apparatus 100 includes a paper feeding unit 40, an image forming unit 30, and a paper discharge unit 20 from the left in the drawing, and a paper conveyance path from the paper supply unit 40 toward the paper discharge unit 20 is formed inside the apparatus. Has been. In the case of duplex printing, the recording medium is fed below the conveyance belt 17 before being discharged to the paper discharge unit 20, and the recording medium is conveyed again by the conveyance belt 17.

  The image forming apparatus 100 in FIG. 2 is for color printing, but any kind of ink may be used, such as monochrome printing or two-color printing.

  A pair of paper feed rollers 12 is provided immediately downstream of the paper feed unit 40, and a pair of registration rollers 14 is provided further downstream. The recording medium is taken out from the paper feed unit 40 one by one by the paper feed roller 12. Then, it is conveyed to the registration roller 14.

  A paper detection unit 13 is disposed between the paper feed roller 12 and the registration roller 14. The paper detection unit 13 detects the position and size of the recording medium.

  The image forming unit 30 includes two belt rollers 15 and 19, an endless transport belt 17 wound around the belt roller 15 and the belt roller 19, a recording position detection unit 22, an ink discharge head 23, and a second paper detection. Section 25, image sensor 26, and paper end detection section 27. The conveyor belt 17 rotates in a loop shape, and constitutes an upper path 17X that conveys the recording medium and a lower path 17Y that is a return path.

  A suction fan (not shown) is built in the transport belt 17 as a recording medium suction means, and the recording medium transported by the paper feed roller 12 is sucked through a suction hole provided in the transport belt 17. And adsorb and hold on the surface of the upper path 17X. The sucked and held recording medium is conveyed toward the downstream side (right side) as the reaction belt rotates by driving the belt rollers 15 and 19.

  The ink discharge head 23 is disposed at a position facing the surface of the upper path 17X, and a gap between the ink discharge head 23 and the surface of the transport belt 17 becomes the upper path 17X. The ink ejection heads 23 are arranged along the upper path 17X by the number of colors corresponding to four colors of ink (yellow Y, magenta M, cyan C, and black K).

  The ink discharge head 23 has a length corresponding to the paper width (main scanning direction) of the recording medium, and is configured as a line-type head in which the head main bodies 24 are arranged in a staggered manner in a direction perpendicular to the paper surface of FIG. ing. A head main body (shown as 24Y, 24M, 24C, and 24K for each color in FIG. 2) 24 attached to the lower surface of the ink discharge head 23 has a fineness for discharging ink toward the surface of the transport belt 17. A large number of small-diameter ejection nozzles (not shown) are arranged in the main scanning direction.

  Further, a deflection preventing member 18 made of a flat plate is disposed on the lower surface of the conveying belt 17 facing the ink ejection head 23.

  With these configurations, the recording medium transported on the surface of the transport belt 17 sequentially passes immediately below the head main body 24 in the four ink discharge heads 23, and the ink discharge heads 23 of the respective colors discharge the inks of the respective colors. Thus, a desired color image is formed.

  The deflection preventing member 18 is provided with a hole (not shown) for allowing the ink ejected from the nozzles of the head main body attached to the lower surface of the ink ejection head 23 to pass therethrough. Is provided with an empty discharge ink receiver 16 for receiving the empty discharge ink.

  The recording position detection unit 22 is a recording medium position sensor that determines the timing of ink ejection to the recording medium, and also serves to detect the trailing edge of the sheet. The second paper detection unit 25 detects the position and size of the recording medium. The paper end detection unit 27 is a sensor for determining a paper jam or a next paper supply timing.

  Further, on the downstream side of the ink discharge head 23, the image sensor 26 is disposed so as to have an optical axis perpendicular to the recording medium in the upper path 17X. The image sensor 26 may be disposed anywhere on the downstream side of the ink discharge head 23, but is preferably on the inner side of the end of the deflection preventing member 18 in the sub-scanning direction. The image sensor 26 preferably has a length corresponding to the paper width of the recording medium in the main scanning direction so as to cover the entire area of the recording medium, but includes one end of the recording medium in the main scanning direction in the imaging range. In other words, the entire recording medium need not be covered.

  Each time the recording medium passes through the lower part, the image sensor 26 captures line data for one line in the main scanning direction at each position from the leading edge in the sub scanning direction of the recording paper.

FIG. 3 shows an example of a hardware block diagram of the control unit 200 of the image forming apparatus 100. The control unit 200 includes a CPU 201 that controls the entire image forming apparatus 100, a program 240 executed by the CPU 201, a ROM 202 that stores other fixed data (such as parameters), a RAM 203 that temporarily stores print data, A rewritable non-volatile memory (NVRAM 204) for holding data while the power is cut off, and an ASIC 205 for performing various signal processing, image processing, and the like for print data are provided.
The control unit 200 also includes a host I / F 206 for transmitting and receiving data and signals to and from the host side, a print control unit 207, a motor drive unit 210 for driving the sub-scanning motor 61, and various sensors 215. I / O 213 and the like for inputting a detection signal from. The control unit 200 is connected to an operation panel 214 for inputting and displaying information necessary for the image forming apparatus 100. The sensor 215 is, for example, a paper detection unit 13, a recording position detection unit 22, a second paper detection unit 25, and a paper end detection unit 27.

The control unit 200 receives print data and the like from the host side such as an information processing device such as a personal computer, an image reading device such as an image scanner, and an imaging device such as a digital camera, via the cable or the network, by the host I / F 206. .
Then, the CPU 201 of the control unit 200 reads and analyzes the print data in the reception buffer included in the host I / F 206, performs necessary image processing in the ASIC 205, and transfers this print data to the print control unit 207. . The print data is raster data (dot pattern), and the dot pattern is generated by the printer driver on the host side or the ASIC 205.
The print control unit 207 includes a head driver (driver IC) 220. The head driver 220 extracts serial data corresponding to one line of the print data described above, generates a drive signal based on the serial data, and ejects ink. Supply to the head 23. The head driver 220 drives the head main body 24 provided on the carriage side.

  The head driver 220 includes a drive waveform generator (not shown) that generates a common drive waveform that is generated regardless of print data. The drive waveform generator generates a common drive waveform by D / A converting the drive signal pattern data stored in the ROM 202 and amplifying it. The common drive waveform is a voltage signal that increases or decreases the voltage within one cycle.

  The head driver 220 performs switching to selectively pass the common drive waveform for each period of the common drive waveform, and sets it as the drive waveform. Specifically, the head driver 220 generates an on / off signal for masking the common drive waveform based on gradation information indicating the presence or absence of dots in the print data and a droplet control signal indicating the size of the droplet. The gradation information is 2-bit information for each dot, and the droplet control signal is, for example, 2 bits (large droplet (large dot), medium droplet (medium dot), Information on small droplets (small dots). Thus, the on / off signal is determined depending on the presence and size of a dot of a certain color.

  The head driver 220 amplifies the on / off signal and supplies it to an analog switch (not shown). Therefore, the signal output from the analog switch is a signal whose on / off is controlled for each clock, and can pass the common drive waveform when on and can be cut off when off. A signal that selectively transmits the common drive waveform in this way becomes a drive signal.

  The analog switch of the head driver 220 is connected to the ink ejection head 23. Therefore, a drive signal corresponding to the print data is supplied to the ink discharge head 23, and the ink discharge head 23 can land a droplet having a specified size on the position of the recording paper specified by the print data.

  The CPU 201 also detects a speed detection value and a position detection value obtained by sampling a detection pulse from the encoder sensor 62 constituting the rotary encoder, and a speed target value and a position target value obtained from a previously stored speed / position profile. Based on the above, a drive output value (control value) for the sub-scanning motor 61 is calculated. When this control value is output to the motor drive unit 210, the motor drive unit 210 drives the sub-scanning motor 61 via the motor driver. As a result, the conveyance belt 17 conveys the recording medium at a fixed speed.

  The operation of the image forming apparatus 100 configured as described above will be described. Print data to be printed is input from a host computer (not shown) via the host I / F 206 and stored in an image memory such as the RAM 203.

  When the print data is stored in the RAM 203, the CPU 201 drives the paper feed roller 12, separates and conveys the uppermost sheet of the sheet feeding unit 40, and conveys the sheet toward the downstream registration roller 14. The CPU 201 starts driving the belt rollers 15 and 19 at substantially the same timing as the paper feed roller 12 and starts the conveying operation of the conveying belt 17.

  Next, when the sheet detection unit 13 detects the leading edge of the recording medium, the CPU 201 is notified, and after waiting for a predetermined timing, the CPU 201 drives the registration roller 14 to move the recording medium to the surface of the upper path 17X of the transport belt 17. And carry.

[First position W]
As illustrated in FIG. 3, the CPU 201 includes an initial position W storage unit 51, an initial position R storage unit 52, a positional deviation calculation unit 53, and a positional deviation correction unit 54. These are realized by the CPU 201 executing the program 240. In the present embodiment, it is assumed that the positional deviation amount is calculated in this way, but a part or the whole of the positional deviation amount may be calculated in hardware (for example, the head driver 220 or the ASIC 205).

  In the present embodiment, the initial position W storage unit 51 acquires the initial position W in the sub-scanning direction where the head driver 220 first landed the droplet for each position in the main scanning direction, and The information is stored in the RAM 203 or the like in association with the position.

  FIG. 4 shows an example of a diagram for schematically explaining storage of the initial position W. The initial position W storage unit 51 detects from the notification from the recording position detection unit 22 that the recording position detection unit 22 has detected the leading end of the recording medium. In response to this notification, the CPU 201 starts the above printing process.

The head driver 220 supplies a drive signal to the ink discharge head 23 for each ink color. The head driver 220 ejects droplets with a drive signal, and when there is a droplet ejected for the first time at each position in the main scanning direction, notifies the CPU 201 of the sub-scanning position. Taking FIG. 4 as an example,
-Black K ink was first ejected at position 2 in the main scanning direction at position 2 in the main scanning direction.-Black K ink was ejected at position 3 in the main scanning direction for the first time in the sub scanning direction. Position 3.
The black K ink was first ejected at positions 4 and 7 in the main scanning direction at position 4 in the sub-scanning direction.
The position where the black K ink is ejected for the first time at the position 6 in the main scanning direction is the position 6 in the sub-scanning direction.

  The initial position W storage unit 51 stores, in the RAM 203 and the like, the initial position W notified from the head driver 220 “the sub-scanning position at which droplets are first ejected for each position in the main scanning direction”. In FIG. 4, the initial position W is stored in association with the position in the main scanning direction. The initial position W storage unit 51 performs this for each color of ink.

  Here, the position in the main scanning direction and the position in the sub-scanning direction will be described. The resolution of the position in the main scanning direction in printing is limited by the number of nozzles in the main scanning direction, but has a resolution of at least 600 to 1200 dpi. For example, in the case of 1200 dpi, since the length in the main scanning direction is 210 mm (about 8.3 inches) on an A4 size recording medium, the position in the main scanning direction is divided into about 9920. Therefore, the initial position W storage unit 51 can store the initial position W in association with a maximum of 9920 positions. On the other hand, when correcting the positional deviation in the main scanning direction, 9920 pieces of information are not necessary, and it is only necessary that the tendency of deviation to some extent can be converted into a numerical value. For example, every 100 to 1000 positions in the main scanning direction W may be stored.

  The resolution of the image sensor 26 to be described later varies depending on the cost and applied technology, but a resolution of 600 to 1200 dpi can be obtained. In addition, if super-resolution technology is used, an image can be read at a resolution higher than that of the image sensor 26.

  When comparing the first position W and the first position R, the dot level correction becomes meaningless if the resolution of the first position R is coarser. For example, when the resolution of the initial position R is coarser, even if the positional deviation amount can be calculated, there is no guarantee that the positional deviation amount is accurate. When the resolution of the initial position W is coarser, even if the amount of positional deviation is calculated, it is difficult to correct unless the amount of positional deviation exceeds one unit of the resolution of the initial position W. Therefore, it is preferable that the resolution of the head driver 220 and the resolution of the image sensor 26 are matched.

  Note that the resolution of the position in the sub-scanning direction in printing is limited by the accuracy of position control of the transport belt 17, but has a resolution of at least 600 to 2400 dpi. Since the resolution in the sub-scanning direction is common to the ink ejection head 23 and the image sensor 26, the resolutions of the initial position W and the initial position R are the same in the sub-scanning direction.

[First position R]
The image formed on the recording medium that has passed under the ink discharge head 23 is read by the image sensor 26 downstream of the ink discharge head 23. That is, the image forming apparatus 100 simultaneously performs image formation and image reading on the same recording medium.

  FIG. 5 shows an example of a diagram for schematically explaining storage of the initial position R. The image sensor 26 starts reading an image when the second paper detection unit 25 detects the leading edge of the recording medium. The image sensor 26 sends the read line data for each line in the main scanning direction to the CPU 201 every predetermined cycle time. The line data is sequentially transmitted to the CPU 201 from the leading edge of the recording paper according to the reading resolution in the sub-scanning direction. The line data includes pixel values for each color.

When the line data includes any one of CMYK colors read for the first time, the first position R storage unit 52 associates the position of the CMYK pixels read for the first time with the position in the main scanning direction. Remember. Note that the position of the pixel of that color in the main scanning direction can be specified by counting the number of pixels from the first pixel of the line data. Taking FIG. 5 as an example,
The position 2 in the sub-scanning direction is the first time that the black K pixel value is read at position 4 in the main-scanning direction.
The black K ink was first read at position 5 in the main scanning direction at position 3 in the sub-scanning direction.
The black K ink was first read at positions 6 and 9 in the main scanning direction at position 4 in the sub-scanning direction.
The black K ink is first read at position 8 in the main scanning direction at position 6 in the sub-scanning direction.

  More specifically, the first position R storage unit 52 compares the line data with the same pixel value as that of the black K in order from the first pixel. In association with the position in the scanning direction, the position in the sub-scanning direction at that time is stored as the initial position R in the RAM 203 or the like.

  The first position R storage unit 52 performs the same processing for the next line data, but the first position R storage unit 52 corresponds to the line data corresponding to the position in the main scanning direction in which the first position R is already stored in the RAM 203. The same pixel value as that of the black K may be extracted from the pixel values of the pixels after the first pixel. In this way, the processing time can be shortened.

  Note that when the initial position W is stored for every 100 to 1000 positions in the main scanning direction, for example, the initial position R storage unit 52 is also set to every 100 to 1000 positions in the main scanning direction. The initial position R may be stored in

[Calculation of misalignment]
FIG. 6 is an example of a diagram illustrating the amount of positional deviation in the main scanning direction calculated from the initial position W and the initial position R. The first position W and the first position R need not be stored at all positions in the main scanning direction. If a certain number (for example, 100 or more) of the first position W and the first position R are stored, or If the initial position W and the initial position R are stored from a predetermined number of lines or more, the amount of positional deviation can be calculated.

  In FIG. 6, when the initial position W and the initial position R are compared for each position in the main scanning direction, the initial position W of the position 2 in the main scanning direction is “2”, whereas the initial position W of the position 2 in the main scanning direction is The initial position R is “0”. The position in the main scanning direction where the initial position R is “2” is 4. Similarly, when the correspondence between the initial position R and the initial position W is examined, it can be seen that there is a shift of two positions between the initial position W and the initial position R.

  In FIG. 6, since the number of positions in the main scanning direction is 10, the calculation of the displacement between the initial position W and the initial position R is completed in a relatively short time. For example, while the initial position W is fixed and the initial position R is shifted one by one in the main scanning direction, the difference between the initial position W and the initial position R is calculated, and the initial position R when the sum of the differences is minimized. Is a displacement amount between the initial position W and the initial position R (the initial position R may be fixed and the initial position W may be shifted). Taking FIG. 6 as an example, when the initial position R is shifted leftward by two, the total difference becomes zero.

  However, for example, when the number of positions in the main scanning direction is a large number such as 9920, the amount of calculation becomes enormous, which makes it impractical.

  Therefore, in this embodiment, the maximum shift amount that may deviate from the mechanical configuration of the image forming apparatus 100 is set. The maximum shift amount may vary depending on various factors, but may not deviate by several percent with respect to the number of 9920 positions. Therefore, for example, if the number of positions in the main scanning direction is 9920, the maximum shift amount is set to about 100 (about 1%) to 500 (about 5%).

  As for the initial position W, only the same number as the maximum shift amount may be used as a calculation target of the positional shift amount, but it can also be reduced. The larger the number, the more accurately the misregistration amount can be calculated, but it is determined in consideration of the processing load of the CPU 201.

  The positional deviation calculation unit 53 shifts the initial position R one by one, and calculates the sum of values obtained by squaring the difference between the initial position W and the initial position R for each same position in the main scanning direction.

When the shift amount is zero, the sum of values obtained by squaring the difference between the initial position W and the initial position R is
98 = (0-0) ² + (2-0) ² + (3-0) ² + (4-2) ² + (0-3) ² + (6-4) ² + (4-0) ² + (0-6) ² + (0-4) ² + (0-0) ²

When the shift amount is 1, the sum of squared differences between the initial position W and the initial position R is
78 = (0-0) ² + (2-0) ² + (3-2) ² + (4-3) ² + (0-4) ² + (6-0) ² + (4-6) ² + (0-4) ² + (0-0) ² + (0-0) ²
The eleventh first position R (not shown) is set to “0”.

When the shift amount is 2, the sum of the squared differences between the initial position W and the initial position R is
0 = (0-0) ² + (2-2) ² + (3-3) ² + (4-4) ² + (0-0) ² + (6-6) ² + (4-4) ² + (0-0) ² + (0-0) ² + (0-0) ²
The eleventh and twelfth first positions R (not shown) are set to “0”.
The positional deviation calculation unit 53 repeats this calculation until the shift amount reaches the maximum shift amount, and specifies the shift amount that minimizes the sum of the values obtained by squaring the difference between the initial position W and the initial position R. This shift amount is a positional deviation amount in the main scanning direction. By doing so, it is possible to specify the positional deviation in the main scanning direction while suppressing the calculation load.

  The misregistration calculation unit 53 calculates the misregistration amount for each ink color. Since the ink ejection head 23 is fixed, the four ink colors often exhibit substantially the same amount of misregistration, but by calculating the misregistration amount for each ink color, color misregistration and the like can be highly corrected. . Note that the misregistration of any one of the ink colors may be used instead of the misregistration of any ink color, or the average misregistration amount for each ink color may be used for the misregistration of all ink colors. May be.

[Correction of misalignment]
The positional deviation correction unit 54 notifies the positional deviation correction unit 54 of the positional deviation amount specified by the positional deviation calculation unit 53. The misregistration correction unit 54 notifies the head driver 220 of the misregistration amount and requests to shift the droplet ejection position by the misregistration amount in the main scanning direction. The head driver 220 changes the writing position of the print data in the main scanning direction according to the amount of positional deviation. As a result, the correspondence between the nozzle position in the main scanning direction and the print data (dot pattern) is shifted by a positional shift amount, so that the droplet discharge position (that is, the landing position) can be corrected.

[Sub-scan position misalignment]
If the initial position W and the initial position R are used, not only the positional deviation in the main scanning direction but also the positional deviation in the sub-scanning direction can be corrected.

  FIG. 7 is an example for explaining the amount of positional deviation in the sub-scanning direction calculated from the initial position W and the initial position R. In FIG. 7, for the sake of explanation, the initial position R is set to a different value.

  If the initial position W and the initial position R are not shifted at all in the main scanning direction, the difference between the initial position W and the initial position R between the same positions in the main scanning direction is the positional shift itself of the sub-scanning position. However, as described above, since the initial position W and the initial position R may have a positional deviation in the main scanning direction, the positional deviation calculation unit 53 first shifts the initial position R by the positional deviation amount in the main scanning direction. Let

  In FIG. 7, the initial position R of “0, 0, 0, 5, 6, 7, 0, 6, 5, 0” is shifted by two positions that are positional deviation amounts in the main scanning direction. 5, 6, 7, 0, 6, 5, 0, 0, 0 ".

  Next, the misregistration calculation unit 53 calculates the difference between the initial position W and the initial position R between the same positions in the main scanning direction, and stores the difference in the RAM 203 or the like. Thereby, the difference between the initial position W and the initial position R is obtained for each position in the main scanning direction. The positional deviation calculation unit 53 notifies the head driver 220 of all the differences. In this way, the head driver 220 can correct the droplet ejection timing by the amount of positional deviation for each nozzle position (main scanning direction).

  Since the positional deviation in the sub-scanning direction is often substantially constant in the main scanning direction unless the recording medium is in a special state such as being inclined, the positional deviation calculating unit 53 is not limited to the main scanning direction. From the difference between the initial position W and the initial position R for each position, for example, the amount of positional deviation in the sub-scanning direction may be determined by calculating an average value.

  The misregistration correction unit 54 notifies the head driver 220 of the misregistration amount and requests to shift the droplet ejection position by the misregistration amount in the sub-scanning direction. The head driver 220 changes the writing position in the sub-scanning direction for each nozzle row. As a result, the writing start position from the front end of the recording medium changes for each nozzle, so that the droplet discharge position (that is, the landing position) can be corrected. In addition, by correcting the ejection position of each ink color droplet, a shift between colors is also corrected.

[Operation procedure]
FIG. 8 is an example of a flowchart of a procedure in which the image forming apparatus 100 detects and corrects the deviation amount. The procedure of FIG. 8 starts when the image forming apparatus 100 receives print data.

  First, the initial position W storage unit 51 determines whether or not the recording position detection unit 22 has detected the leading edge of the recording medium (S10).

  When the recording position detection unit 22 detects the leading edge of the recording medium (Yes in S10), the initial position W storage unit 51 sub-scans the first droplet ejected by the head driver 220 in the main scanning direction for each ink color. Is stored in correspondence with the position in the main scanning direction (S20).

  Next, the image sensor 26 reads an image and sends the line data to the initial position R storage unit 52. When there is any color of CMYK that is first read in the main scanning direction from the line data, the initial position R storage unit 52 stores the sub-scanning position as the initial position R in association with the position in the main scanning direction. (S30).

  In both the initial position R and the initial position W, the initial position R and the initial position W are not stored in all the main scanning direction positions with only one line in the main scanning direction. I need it. For example, it is a condition that both the initial position R and the initial position W are stored in a predetermined number (predetermined ratio) or more.

  Next, the misregistration calculation unit 53 calculates the misregistration amount in the main scanning direction by the above method (S40). Further, the positional deviation calculation unit 53 calculates the positional deviation amount in the sub-scanning direction using the positional deviation amount in the main scanning direction (S50).

  However, immediately after the calculation of the misregistration amount, if the misregistration correction unit 54 immediately corrects the misregistration amount, if the ink ejection head 23 is ejecting, the ejection timing of the image that is being ejected is It will change in the middle of the scanning direction. This results in a decrease in image quality and an impression that the image is interrupted (or bulky) at a certain sub-scanning position. Wait until printing of the recording medium is completed (S60).

  When printing on one recording medium is completed, the misregistration correction unit corrects misregistration (S70). Thereby, printing can be corrected from the next recording medium.

  FIG. 9 is an example of a flowchart illustrating a procedure in which the initial position W storage unit 51 stores the initial position W. The procedure of FIG. 9 starts when the recording position detection unit 22 detects the leading edge of the recording medium.

  The initial position W storage unit 51 determines whether or not the sub-scanning position corresponding to the initial position W has been acquired from the head driver 220 (S110). The head driver 220 ejects droplets, and when there is a droplet ejected for the first time in the main scanning direction, notifies the first position W storage unit 51 of the sub-scanning position.

  When the sub-scanning position corresponding to the initial position W is acquired (Yes in S110), the initial position W storage unit 51 stores the initial position W in association with the position in the main scanning direction (S120).

  When the sub-scanning position corresponding to the initial position W is not acquired (No in S110), the initial position W storage unit 51 determines whether or not the sheet end detection unit 27 has detected the end of the sheet (S130). Thereby, for example, even if there is print data in which no droplet is ejected even once in the image, the control can be terminated when the recording medium passes under the ink ejection head 23.

  FIG. 10 is an example of a flowchart illustrating a procedure in which the initial position R storage unit 52 stores the initial position R. The procedure in FIG. 10 starts when the second paper detection unit 25 detects the leading edge of the recording medium.

  The initial position W storage unit 51 acquires line data generated by the image sensor 26 reading an image, and determines whether there is any color of CMYK read for the first time in the main scanning direction (S210). .

  When there is any color of CMYK read for the first time in the main scanning direction (Yes in S210), the initial position R storage unit 52 associates the sub-scanning position (initial position R) with the position in the main scanning direction. (S220).

  When there is no color of CMYK read for the first time in the main scanning direction (No in S210), the initial position R storage unit 52 determines whether or not the sheet end detection unit 27 has detected the end of the sheet. (S230). Thereby, for example, even if there is print data in which no droplet is ejected even once in the image, the control can be terminated when the recording medium passes under the ink ejection head 23.

  As described above, the image forming apparatus 100 according to the present exemplary embodiment does not waste the recording medium for correcting the ejection position and does not need to clean the conveyance belt 17. The droplet ejection position can be corrected.

  In the first embodiment, the maximum shift amount is set when the positional deviation calculation unit 53 calculates the positional deviation amount in the main scanning direction. The processing load on the CPU 201 can be reduced by estimating the maximum shift amount to be small.

  However, there is a concern that the maximum shift amount is affected by the temperature inside the image forming apparatus 100. Therefore, in this embodiment, the image forming apparatus 100 that corrects the maximum shift amount according to the temperature will be described.

  FIG. 11 illustrates an example of a hardware block diagram of the control unit 200 of the image forming apparatus 100 according to the present exemplary embodiment. 11, the same parts as those in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted. The image forming apparatus 100 in FIG. 11 includes a temperature sensor 217 and a maximum shift amount correction unit 55. The temperature sensor 217 is connected to the I / O 213, detects the temperature every predetermined cycle, and notifies the CPU 201 of the temperature. When the positional deviation amount is calculated, the positional deviation calculation unit 53 stores the temperature T degrees in the NVRAM 204 in association with the positional deviation amount.

  FIG. 12 is a flowchart illustrating an example of a procedure in which the maximum shift amount correction unit 55 corrects the maximum shift amount.

  The maximum shift amount correction unit 55 determines whether or not it is the timing for calculating the positional deviation amount (S310). The calculation timing of the positional deviation amount is a timing at which a sufficient number of initial positions R and initial positions W are stored.

  When it is time to calculate the amount of misalignment (Yes in S310), the maximum shift amount correction unit 55 reads the temperature T ° C. at the time of calculating the amount of misalignment from the NVRAM 204 and the current temperature detected by the temperature sensor 217. T0 is acquired (S320).

  Then, the maximum shift amount correction unit 55 determines whether or not the temperature difference | T−T0 | is larger than the threshold value (S330). For example, when there is almost no temperature difference, the amount of deviation between the initial position W and the initial position R is expected to be small, so the maximum shift amount for calculating the amount of positional deviation may be small. However, if the temperature difference is larger than the threshold value (Yes in S330), the positional shift amount is expected to be large, so the maximum shift amount correction unit 55 increases the maximum shift amount (S340). In this case, the maximum shift amount correction unit 55 preferably increases the maximum shift amount according to the temperature difference.

  After the maximum shift amount is corrected, the positional deviation calculation unit 53 calculates the positional deviation amount and stores it in the NVRAM 204 in association with the current temperature.

  Therefore, the image forming apparatus 100 according to the present exemplary embodiment can optimize the maximum shift amount according to the temperature inside the apparatus. Therefore, when the temperature difference is small, the processing load on the CPU 201 can be reduced, and when the temperature difference is large, misalignment is caused. The calculation range of the amount can be expanded, and the positional deviation amount can be calculated with high accuracy.

  A large maximum shift amount means that the calculation range of the positional deviation amount can be expanded, but it takes time to calculate the positional deviation amount.

  However, since the image forming apparatus 100 cannot correct the ejection position until the calculation of the positional deviation amount is completed, if it takes a long time to calculate the positional deviation amount, for example, the position before the printing on the next recording medium is started. It may happen that the calculation of the deviation amount is not in time. For this reason, it is preferable that the calculation time of the positional deviation amount is short rather than long.

  Therefore, in this embodiment, the image forming apparatus 100 that reduces the calculation time of the positional deviation amount will be described.

[Limit the calculation range according to the document]
FIG. 13 illustrates an example of a hardware block diagram of the control unit 200 of the image forming apparatus 100 according to the present exemplary embodiment. In FIG. 13, the same parts as those in FIG. The image forming apparatus 100 in FIG. 13 includes a calculation range estimation unit 56. The calculation range estimation unit 56 uses which part of the initial position W and the initial position R in the main scanning direction to calculate the positional deviation amount (the range between the initial position W and the initial position R used for calculating the positional deviation amount is “ The calculation range of printing misalignment amount is referred to. Note that which part of the initial position R is used for calculation is synonymous with the estimation of the maximum shift amount.

  FIG. 14 is an example of a diagram schematically illustrating estimation of a calculation range. FIG. 14A shows a document centered on characters, and FIG. 14B shows a document centered on characters. In the case of a document centered on characters, the characters are described from the left, so that characters are almost printed on the left side of the recording medium, whereas characters on the right side may not be printed due to line feeds. For this reason, in the case of a document centered on characters, it is only necessary to calculate the amount of displacement using the first position W and the first position R on the left side of the recording medium.

  The calculation range estimation unit 56 determines the type of the document, and determines that only about 10% from the left in the main scanning direction of the initial position W is used for the calculation of the positional deviation amount when the document is a document centered on the character. Further, it is determined that only about 20% from the left in the main scanning direction of the initial position R is used for the calculation of the positional deviation amount. Therefore, the maximum shift amount is 10% of the initial position R in the main scanning direction.

  Also, in the case of a document having a centered figure, the figure is often drawn at the center, so that the figure may be hardly printed on the left and right ends of the recording medium. For this reason, in the case of a document whose center is the figure, it is only necessary to calculate the amount of displacement using the first position W and the first position R near the center of the recording medium.

  The calculation range estimation unit 56 determines the type of the document, and determines that only about 10% of the center of the initial position W in the main scanning direction is used for the calculation of the misregistration amount when the figure is a center document. Further, it is determined that only about 20% including the center of the initial position R in the main scanning direction is used for the calculation of the positional deviation amount. Therefore, the maximum shift amount is 10% of the initial position R in the main scanning direction. A document centered on a photograph can be handled in the same manner as a document centered on a figure.

  Note that the document type is determined from the print quality (general document, CAD, photo, etc.) of the print conditions acquired from the printer driver. In the case of color printing, it may be determined as a photograph.

  In this way, by limiting the initial position W and the initial position R used for calculating the amount of misregistration according to the type of document, the calculation range of the amount of misregistration is optimized, and the time required for calculating the amount of misregistration is reduced. Can be suppressed.

[Narrow the calculation range of misalignment in stages]
It is also effective to narrow the calculation range of the positional deviation amount step by step.
FIG. 15 is an example of a diagram illustrating the calculation range of the positional deviation amount.
(1) First, the calculation range estimation unit 56 sets the shift amount at regular intervals or at random. In the figure, the shift amounts are set at regular intervals such as 5, 10, 15. It is assumed that the calculation range of the initial position W is fixed.
(2) The positional deviation calculation unit 53 calculates the difference between the initial position W and the initial position R with each set shift amount, and obtains the sum of the squares of the differences. In the figure, the sum of the squares of the differences when the shift amount is 5 is 50, the sum of the squares of the differences when the shift amount is 10, and the sum of the squares of the differences when the shift amount is 15 is 90.
(3) The calculation range estimation unit 56 specifies the shift amount having the smallest sum, and does not leave an interval in the shift amount before and after the shift amount (or with a sufficiently small interval), the difference is calculated in the positional deviation calculation unit 53. Request calculation. Since the shift amount is 5 and the sum of the differences is minimum, the shift range is determined to be, for example, plus or minus 50% (= about 3) with respect to 5. That is, 2 to 8 is the shift amount.
(4) The misregistration calculation unit 53 calculates the square of the difference between the initial position W and the initial position R with each shift amount by setting the shift amount to 2 to 8, and obtains the sum.

  By taking such a procedure, the calculation amount of the positional deviation calculation unit 53 can be reduced, and the calculation range of the positional deviation amount can be appropriately narrowed down.

[Change the calculation range in consideration of the recording speed]
The time required for calculating the amount of misalignment is generally until printing on the next recording medium starts. If the calculation of the positional deviation amount is completed before the printing on the next recording medium is started, the image forming apparatus 100 can correct the positional deviation for printing on the next recording medium.

  Here, since the recording speed can vary depending on the printing resolution in the sub-scanning direction and the main scanning direction, the allowable time for calculating the positional deviation amount also varies depending on the recording speed. Therefore, the calculation range estimation unit 56 changes the calculation range of the positional deviation amount according to the recording speed.

  Specifically, the calculation range estimation unit 56 acquires the recording speed from, for example, printing conditions (resolution, printing quality, etc.). The calculation range estimation unit 56 estimates which part of the initial position R and the initial position W in the main scanning direction is used for calculating the positional deviation amount according to the recording speed.

  For example, when the recording speed is V1, the calculation range estimation unit 56 determines that only about 10% from the left of the initial position W in the main scanning direction is used for calculating the positional deviation amount. Further, it is determined that only about 20% from the left in the main scanning direction of the initial position R is used for the calculation of the positional deviation amount. Therefore, the maximum shift amount is 10% of the initial position R in the main scanning direction.

  For example, when the recording speed is V2 (<V1), the calculation range estimation unit 56 determines that only about 20% from the left in the main scanning direction of the initial position W is used for calculation of the positional deviation amount. Further, it is determined that only about 40% from the left in the main scanning direction of the initial position R is used for the calculation of the positional deviation amount. Therefore, the maximum shift amount is 20% of the initial position R in the main scanning direction.

  In this way, even if the recording speed changes, it is possible to prevent the printing on the next recording medium from starting before the calculation of the positional deviation amount is completed.

  Note that the change of the misregistration amount calculation range of this embodiment can be applied to the image forming apparatus 100 together with the temperature conversion of the second embodiment. In this case, the maximum shift amount is increased according to the temperature difference.

  In the present exemplary embodiment, an image forming apparatus 100 capable of appropriately responding when a positional deviation amount is abnormally large will be described.

FIG. 16 illustrates an example of a hardware block diagram of the control unit 200 of the image forming apparatus 100 according to the present exemplary embodiment. In FIG. 16, the same parts as those in FIG. The image forming apparatus 100 in FIG. 16 has an abnormality processing unit 57. The abnormality processing unit 57 responds in the following manner when the positional deviation amount is larger than the threshold value.
(1) The image forming apparatus 100 is stopped.
(2) After the printing is stopped in the image forming apparatus 100, the same image data is printed again.
(3) The misregistration calculation unit 53 is made to recalculate the misregistration amount, and the image forming apparatus 100 is stopped.

  As described above, the abnormality processing unit 57 monitors the magnitude of the positional deviation amount, so that an appropriate response can be made even when the positional deviation amount is abnormally large.

  FIG. 17 is an example of a flowchart of a procedure in which the image forming apparatus 100 detects and corrects the misregistration amount. In FIG. 17, the description of the same step procedure as that in FIG. 8 is omitted.

  In the procedure of FIG. 17, after the amount of positional deviation is calculated in step S60, the abnormality processing unit 57 determines whether or not the amount of positional deviation is equal to or greater than a threshold value (S65). If the amount of positional deviation is not equal to or greater than the threshold (No in S65), the abnormality processing unit 57 does nothing and printing continues.

  If the amount of misalignment is equal to or greater than the threshold (Yes in S65), the abnormality processing unit 57 causes the print control unit 207 to immediately stop printing (S66). Then, the abnormality processing unit 57 causes the image forming apparatus 100 to turn on a warning lamp or display an error message so as not to accept a print request from the host side. That is, the image forming apparatus 100 is equal to the stopped state. The user can respond by calling a customer engineer.

  Thereby, when the amount of positional deviation is abnormally large, the head driver 220 can finish printing without printing all of the print data.

  FIG. 18 is an example of a flowchart of a procedure in which the image forming apparatus 100 detects and corrects the positional deviation amount. In FIG. 18, the description of the procedure of the same step as in FIG. 8 is omitted.

  In the procedure of FIG. 18, after the amount of positional deviation is calculated in step S60, the abnormality processing unit 57 determines whether the amount of positional deviation is equal to or greater than a threshold value (S65). If the amount of positional deviation is not equal to or greater than the threshold (No in S65), the abnormality processing unit 57 does nothing and printing continues.

  When the amount of misalignment is equal to or greater than the threshold (Yes in S65), the abnormality processing unit 57 causes the print control unit 207 to immediately stop printing and discharge the recording medium (S67).

  When the second paper detection unit 25 detects the discharge of the recording medium, the abnormality processing unit 57 requests the print control unit 207 to print again the print data whose amount of positional deviation is abnormally large (S68). ).

  Thereby, when the amount of positional deviation is abnormally large, the head driver 220 can finish printing without printing all of the print data, and can print again.

  FIG. 19 is an example of a flowchart of a procedure in which the image forming apparatus 100 detects and corrects the positional deviation amount. In FIG. 19, the description of the procedure of the same steps as those in FIG. 8 is omitted.

  In the procedure of FIG. 19, after the positional deviation amount is calculated in step S60, the abnormality processing unit 57 determines whether or not the positional deviation amount is equal to or greater than a threshold value (S65). If the amount of positional deviation is not equal to or greater than the threshold (No in S65), the abnormality processing unit 57 does nothing and printing continues.

  If the amount of displacement is equal to or greater than the threshold (Yes in S65), the abnormality processing unit 57 counts up the number of abnormalities (S69). The number of abnormalities is a value that is counted up when the amount of positional deviation is greater than or equal to a threshold value, and is stored in the NVRAM 204.

  Then, the abnormality processing unit 57 determines whether or not the number of abnormalities exceeds a specified value (S691). If the number of abnormalities does not exceed the specified value (No in S691), the abnormality processing unit 57 does nothing and printing continues.

  If the number of abnormalities exceeds the specified value (Yes in S691), the abnormality processing unit 57 causes the print control unit 207 to immediately stop printing (S66). Then, the abnormality processing unit 57 causes the image forming apparatus 100 to turn on a warning lamp or display an error message so as not to accept a print request from the host side. That is, the image forming apparatus 100 is equal to the stopped state. The user can respond by calling a customer engineer.

  Thereby, the image forming apparatus 100 can be stopped when an abnormally large misalignment amount is calculated many times.

  As described above, the image forming apparatus 100 according to the present exemplary embodiment can appropriately cope with a case where the amount of positional deviation is larger than the threshold value. This embodiment can be applied to all of the first to third embodiments.

  In each of the first to fourth embodiments, the image forming apparatus 100 that calculates the displacement amount and corrects the droplet discharge position has been described. However, if such a correction function is set as an option, it is possible to select whether or not to correct the positional deviation for each image forming apparatus 100, and the cost burden on the user can be reduced.

  Therefore, in this embodiment, an image forming apparatus 100 that allows a user or the like to select whether or not to correct the displacement of the ejection position will be described.

  FIG. 20 illustrates an example of a hardware block diagram of the control unit 200 of the image forming apparatus 100 according to the present exemplary embodiment. 20, the same parts as those in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted. The image forming apparatus 100 in FIG. 20 includes a switch 230 that detects the attachment / detachment of the image sensor 26. The switch 230 detects that the image sensor 26 is mounted and notifies the CPU 201 of it.

  Accordingly, only when the image sensor 26 is mounted, the image forming apparatus 100 according to the present embodiment can store the initial position W and the initial position R, calculate the positional deviation, and correct the positional deviation.

  In this way, the manufacturer can sell the image forming apparatus 100 without attaching the image sensor 26, and the cost can be reduced. Does the user purchase the image forming apparatus 100 with the image sensor 26 attached? You can determine whether or not. The image sensor 26 can be mounted on the image forming apparatus 100 by a user or a customer engineer after being shipped to the market.

  FIG. 21 is an example of a flowchart of a procedure in which the image forming apparatus 100 detects and corrects the positional deviation amount. In FIG. 21, the description of the same step procedure as in FIG. 8 is omitted.

  In the procedure of FIG. 21, prior to step S10, the switch 230 determines whether or not the image sensor 26 is mounted (S5). When the image sensor 26 is mounted (Yes in S5), the image forming apparatus 100 corrects the displacement of the ejection position as in the first to fourth embodiments.

  When the image sensor 26 is not attached (No in S5), the image forming apparatus 100 does not correct the displacement of the ejection position.

  In the image forming apparatus 100 of the present embodiment, the user can select whether to correct the displacement of the ejection position. This embodiment is applicable to all of the first to fourth embodiments.

DESCRIPTION OF SYMBOLS 11 Paper feed part 12 Paper feed roller 13 Paper detection part 14 Registration roller 15, 19 Conveyance belt roller 17 Conveyance belt 20 Paper discharge part 22 Recording position detection part 23 Ink discharge head 24 Recording head 25 2nd paper detection part 26 Image sensor 27 Paper end detection unit 30 Image forming unit 100 Image forming apparatus 200 Control unit

Japanese Patent No. 4032359 JP 2008-284808 A Japanese Patent Laid-Open No. 2006-199048

Claims (13)

Print data storage means for storing print data generated from a user's document;
A conveyance belt for adsorbing and conveying a recording medium;
A drive unit for driving the conveyor belt;
A recording head in which nozzles for discharging ink droplets on a recording medium are arranged in a line in the main scanning direction;
Print control means for controlling the ink ejection operation of the recording head according to the print data;
In an image forming apparatus having
An image pickup means that includes image pickup devices arranged in a line in the main scanning direction, and takes an image of a droplet landed on a recording medium;
First position information acquisition means for acquiring first position information of an ejection position at which the recording head ejects droplets with reference to an end of the recording medium;
Second position information acquisition means for acquiring second position information of the landing position of the droplet with respect to the end of the recording medium;
A positional deviation calculation means for comparing the first positional information and the second positional information and calculating a positional deviation amount between the ejection position and the landing position in the main scanning direction and the sub-scanning direction;
Correction means for causing the recording head to correct the displacement amount;
An image forming apparatus comprising: The positional deviation calculation means calculates the positional deviation amount between the ejection position and the landing position in the main scanning direction,
Either the first position information or the second position information is corrected for a positional deviation amount in the main scanning direction, and a positional deviation amount between the ejection position and the landing position in the sub-scanning direction is calculated. The image forming apparatus according to claim 1. The positional deviation calculation means calculates correlation information correlated with the magnitude of positional deviation while relatively shifting the correspondence between the plurality of first position information and the plurality of second position information in the main scanning direction, Determining the amount of displacement based on the correlation information;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The positional deviation calculating means relatively shifts the correspondence between the first position information and the second position information within a predetermined maximum shift range, and calculates the correlation information;
The image forming apparatus according to claim 3. Temperature detecting means for detecting the temperature in the device;
Maximum shift amount correction means for changing the maximum shift amount according to a temperature difference between the temperature at which the positional shift calculation unit last calculated the positional shift amount and the current temperature;
The image forming apparatus according to claim 4, further comprising:   According to the type of the document, the misregistration calculation unit includes a calculation range estimation unit that estimates a range of the first position information and the second position information used for calculating the correlation information. The image forming apparatus according to any one of claims 3 to 5. Based on the correlation information when the correspondence between the first position information and the second position information is discontinuously shifted in the main scanning direction, the position deviation calculation unit uses the first information used for calculating the correlation information. A calculation range estimation means for estimating a range of position information of one and the second position information;
The image forming apparatus according to claim 3, further comprising:   And a calculation range estimation unit that estimates a range of the first position information and the second position information used by the positional deviation calculation unit to calculate the correlation information in accordance with a recording speed of the recording head. The image forming apparatus according to claim 3, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 1, further comprising: an abnormality processing unit that stops the image forming apparatus and outputs a warning when the amount of positional deviation is equal to or greater than a threshold value.   9. The apparatus according to claim 1, further comprising an abnormality processing unit that stops printing on the recording medium and restarts printing of the print data when the positional deviation amount is equal to or greater than a threshold value. The image forming apparatus according to Item.   An abnormality processing unit that counts the number of times that the positional deviation amount is equal to or greater than a threshold value and stops the image forming apparatus and outputs a warning when the number of times exceeds a specified value. Item 9. The image forming apparatus according to any one of Items 1 to 8. It has a photographing means wearing detection means for detecting the wearing of the photographing means,
12. The image forming apparatus according to claim 1, wherein the positional deviation amount is calculated only when the photographing unit mounting detection unit detects the mounting of the photographing unit. Print data storage means for storing print data generated from a user's document;
A conveyance belt that adsorbs and conveys a recording medium; a drive unit that drives the conveyance belt; a recording head in which nozzles that eject ink droplets to the recording medium are arranged in a line in the main scanning direction; In an image forming method of an image forming apparatus, comprising: a print control unit that controls an ink discharge operation of the recording head according to print data.
A step of photographing a droplet landed on a recording medium by a photographing means including image sensors arranged in a line in the main scanning direction;
A first position information acquiring unit acquiring first position information of an ejection position at which the recording head ejects droplets with reference to an end of the recording medium;
A second position information acquisition unit acquires second position information of a landing position of the droplet with reference to an end of the recording medium;
A step of calculating a positional shift amount between the ejection position and the landing position in the main scanning direction and the sub-scanning direction by comparing the first position information and the second position information;
A correcting means for causing the recording head to correct the positional deviation amount;
An image forming apparatus comprising:

Images