JP5088685B2 - Image forming apparatus and position detection method - Google Patents

Description

  The present invention relates to an image forming apparatus and a position detection method for detecting a relative position between a head and a medium.

In an ink jet printer that forms an image by ejecting ink as droplets while alternately repeating conveyance of a recording medium such as paper and main scanning for moving the carriage in a direction perpendicular to the conveyance direction, a preset feed is set. Based on the amount, the recording medium is moved between the main scanning and the next main scanning by sub-scanning that drives a motor for transporting the recording medium. In this sub-scanning, if there is a deviation amount between a preset feed amount and the feed amount in which the recording medium is actually conveyed, white streaks and color unevenness occur in an image formed on the recording medium.
For example, the friction between the recording medium and the roller that conveys the recording medium differs depending on the recording medium material. May occur.
In addition, for example, in an inkjet printer that forms an image by ejecting droplets on a large-sized recording medium having a paper size of A1, a nozzle row having a long length in the transport direction is formed in order to increase the printing speed. A predetermined feed amount to be moved for each sub-scan is increased using the head. If the predetermined feed amount is increased and an image is formed by repeating sub-scanning, there may be a large deviation in the feed amount of the recording medium in the transport direction.
Thus, for example, in Patent Document 1, ink is ejected from one of the two nozzles arranged in the transport direction on the upstream side to form a first image, and only the distance in the transport direction between the two nozzles is formed. After the recording medium is moved in the transport direction, ink is ejected from the other nozzle on the downstream side to form a second image, and the amount of deviation between the position of the first image and the position of the second image is set. There has been proposed a method of correcting a feed amount that is detected by reading with a scanner.

JP 2001-146051 A

However, before printing a desired image, it is necessary to detect the shift amount of the feed amount in advance and correct the relative movement amount in the sub-scanning direction. Therefore, in addition to the recording medium for printing a desired image, a recording medium to be printed in advance is required in order to detect the shift amount of the feed amount. In addition to the time for operating the image forming apparatus to print a desired image, the user needs work time for operating the image forming apparatus in order to detect and correct the shift amount of the feed amount in advance. There is a problem of doing.
Furthermore, there is a problem that the shift amount in the distance between dots formed in the main scanning direction cannot be corrected.

  SUMMARY An advantage of some aspects of the invention is to solve some of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1] By repeating relative movement between a head that forms dots with a basic resolution period in the first direction, an imaging unit that images the dots formed on the medium, and the head and the medium, An image forming apparatus comprising: an image forming unit that forms an image composed of the dots on a medium; and A step of forming a dot image composed of the dots on the medium based on predetermined image data. And B step for performing the one relative movement after the A step, C step for capturing the dot image with the imaging unit after the B step, and the captured dot image with respect to the first direction. D step for generating distribution data of the dots, and Fourier transform of the distribution data to detect a phase value for the first direction related to the basic resolution periodic component E step and the difference between the detected phase value and the ideal phase value when the one relative movement is ideally performed, the relative of the head and the medium after the one relative movement And an F-step for detecting a position.
Further, the head in which the nozzles are formed in the first direction at the basic resolution cycle and the medium are relatively moved, and dots are formed on the medium by the head based on predetermined image data. Forming a dot image to be formed on the medium; capturing the dot image with an imaging unit; and generating distribution data of the dots in the first direction based on the captured dot image data Performing a Fourier transform on the distribution data to detect a phase value in the first direction related to the basic resolution period; the detected phase value; and the first of the relative movements. Based on the difference from the ideal phase value when the relative movement in the direction is ideally made, the phase between the head and the medium in the first direction It may be an image forming apparatus and executes a step of detecting a position.

  According to such a configuration, the distribution data is generated from the captured dot image, and the relative position between the head and the medium is determined from the difference between the phase value detected by Fourier transforming the generated distribution data and the ideal phase value. To detect. Thereby, the distance between dots in the main scanning direction and the sub-scanning direction can be detected. Therefore, apart from the recording medium for printing a desired image, a recording medium to be printed in advance for detecting the shift amount is not necessary. In addition to the time for operating the liquid ejecting apparatus to print a desired image, the user does not need the work time for operating the image forming apparatus in order to detect the shift amount in advance.

Application Example 2 In the image forming apparatus, the intensity value of the distribution data is an integrated intensity value of the dots formed along a direction orthogonal to the first direction.
According to such a configuration, since integration is performed, it is possible to suppress a decrease in relative position detection accuracy even if the number of dots formed along the direction orthogonal to the first direction is small.

  Application Example 3 In the case where the image forming unit forms an image with a resolution corresponding to an integral fraction of the basic resolution period in the first direction by the interlace method, the single scan is performed. The image forming apparatus, wherein the distribution data is generated for a dot image.

  According to such a configuration, since the distribution data is generated for the dot image related to a single scan, the periodicity is detected in the distribution data, and the phase value related to the basic resolution period corresponding to the nozzle pitch is detected. It becomes possible to do. Accordingly, the relative position detection accuracy is improved.

Application Example 4 The image forming apparatus, wherein the imaging unit includes an optical filter that selects a wavelength range.
According to such a configuration, distribution data can be generated from a dot image in which one ink color such as yellow, magenta, cyan, and black is selected, so that the relative position detection accuracy is improved.

Application Example 5 In the image forming apparatus, the image forming unit corrects a relative position between the head and the medium based on the detected relative position.
According to such a configuration, it is possible to suppress the occurrence of color unevenness and white stripes in an image formed on a medium.

Application Example 6 By repeating relative movement between a head that forms dots with a basic resolution period in the first direction, an imaging unit that images the dots formed on the medium, and the head and the medium, An image forming apparatus comprising: an image forming unit that forms an image composed of the dots on a medium; and A step of forming a dot image composed of the dots on the medium based on predetermined image data. And B step for performing the one relative movement after the A step, C step for capturing the dot image with the imaging unit after the B step, and the captured dot image with respect to the first direction. A D step for generating the dot distribution data, and an E step for Fourier-transforming the distribution data to detect a phase value for the first direction related to a low-order period component. And F step of Fourier transforming the dot image based on the image data to simulate a phase value for the first direction according to a low-order period component; and the detected phase value and the simulated An image forming apparatus comprising: a G step of detecting a relative position between the head and the medium after the one relative movement based on a difference from a phase value.
Further, the head in which the nozzles are formed in the first direction at the basic resolution cycle and the medium are relatively moved, and dots are formed on the medium by the head based on predetermined image data. Forming a dot image to be formed on the medium; capturing the dot image with an imaging unit; and generating distribution data of the dots in the first direction based on the captured dot image data A step of Fourier transforming the distribution data to detect a phase value in the first direction related to a low-order period component; and a Fourier transform of a dot image based on the image data to obtain a low-order period component. Simulating a phase value for the first direction, the detected phase value, and the simulated phase value. Based on the difference may be an image forming apparatus and executes a step of detecting a relative position between the head and the medium in the first direction.

  According to such a configuration, the dot image based on the image data is Fourier transformed to simulate the phase value for the first direction related to the low-order period component, and the detected phase value and the simulated phase value are Based on the difference, the relative position between the head and the medium after one relative movement is detected. Thereby, since the low-order period component can be detected by Fourier transform, the detection accuracy of the deviation amount is improved.

Application Example 7 An image that includes a head that forms dots at a basic resolution period in the first direction, and that repeats relative movement between the head and the medium to form an image composed of the dots on the medium In the forming apparatus, there is provided a position detecting method for detecting a relative position between the head and the medium, wherein an A step for forming a dot image composed of the dots on the medium based on predetermined image data, and the A step Later, one B step for performing the relative movement, C step for capturing the dot image after the B step, and D for generating distribution data of the dots in the first direction for the captured dot image. And E step of detecting a phase value for the first direction related to the basic resolution periodic component by Fourier transforming the distribution data, Based on the serial detected phase value, a position detecting method characterized by having a F detecting the relative position between the head and the medium after the moving one relative.
Further, the head in which the nozzles are formed in the first direction at the basic resolution cycle and the medium are relatively moved, and dots are formed on the medium by the head based on predetermined image data. Forming a configured dot image on the medium; capturing the dot image; and generating distribution data of the dots in the first direction based on the captured dot image data; , Performing a Fourier transform on the distribution data to detect a phase value in the first direction related to the basic resolution period; and detecting a relative value in the first direction among the detected phase value and the relative movement. Based on the difference from the ideal phase value when the movement is ideal, the relative position between the head and the medium in the first direction is calculated. It may be a position detecting method characterized by a step of leaving.

Hereinafter, the present embodiment will be described with reference to the drawings.
<First embodiment>
FIG. 1 is an external perspective view of an ink jet printer 1 as a liquid ejecting apparatus according to the present embodiment. The inkjet printer 1 includes a roll paper 3 as a recording medium covered with an upper cover 2, and a cut paper (not shown) as a recording medium can be fed from the paper guide 4. From the opening provided in the lower part of the inkjet printer 1, the paper S, which is the roll paper 3 or the cut paper, can be discharged in the transport direction D1.

  A side surface of the ink jet printer 1 is provided with a removable ink cartridge 12 filled with ink (yellow, magenta, cyan, black), and a head (not shown) in which ink is provided inside the main body cover 11 by a tube. ).

  On the front side of the inkjet printer 1, camera units 5 and 6 as imaging units are provided at positions for capturing images formed on both ends of the paper S in the paper width direction.

FIG. 2 is a view for explaining the internal appearance with the upper cover 2 and the main body cover 11 removed.
The carriage 25 is connected to a timing belt (not shown) that rotates in accordance with the rotation of a carriage drive motor (not shown), and along the slide shaft 24, the conveyance direction of the paper S (hereinafter referred to as the conveyance direction). Reciprocates in a perpendicular direction. The carriage 25 is provided with a head 26. As the carriage 25 reciprocates, the head 26 reciprocates in a direction perpendicular to the transport direction. The movement of the head 26 in one direction in the direction perpendicular to the conveyance direction is called main scanning, and the direction perpendicular to the conveyance direction is called main scanning direction.

  The roll paper 3 is rotatably supported by the rotation shafts 22 and 23 provided in the left and right cases 20 and 21. On the upstream side in the transport direction of the head 26, a paper feed roller (not shown) driven by a paper feed motor (not shown) and a rotatable free driven roller (not shown) are provided so as to sandwich the paper S, A sheet S is fed. On the downstream side in the transport direction of the head 26, a paper discharge roller (not shown) that rotates in conjunction with the driving of the paper feed motor and a rotatable free driven roller are provided so as to sandwich the paper S, and the paper S is discharged. Paper.

  The carriage 25 includes a linear encoder (not shown) that outputs a pulse signal corresponding to the amount of movement in the main scanning direction, and can control the position of the head 26 in the main scanning direction. The paper feed motor is provided with a rotary encoder (not shown) that outputs a pulse signal corresponding to the rotation amount. The feed amount of the paper S in the transport direction can be controlled by the rotary encoder. Moving the paper S in the transport direction by a predetermined feed amount is called sub-scanning, and the transport direction is called sub-scanning direction.

  As described above, the housing 21 on the right side of the drawing is provided with the ink cartridge 12, and ink is supplied to the head 26. The head 26 is formed with a nozzle row composed of a plurality of nozzles that respectively eject yellow, magenta, cyan, and black inks in the sub-scanning direction. The ink jet printer 1 ejects ink from nozzles formed on the head 26 while repeating main scanning for moving the head 26 in the direction perpendicular to the sub-scanning direction and sub-scanning for moving the paper S in the sub-scanning direction. An image can be formed on the paper S. The head 26 can form dots on the paper S with a basic resolution period of, for example, 1/360 inch or 1/720 inch in the main scanning direction and the sub-scanning direction.

  FIG. 3 is a block diagram illustrating an electrical configuration of the inkjet printer 1. The ink jet printer 1 is schematically configured by a printer controller 113, a print engine 114, and an imaging unit 111.

  The printer controller 113 includes an external interface (I / F) 101 to which print data from the host computer 200 as an external device is input, a RAM 102 for storing various data, a control routine for various data processing, and the like. Stored ROM 103, control unit 107 including a CPU, oscillation circuit 104, drive signal generation circuit 106 that generates a drive signal to be supplied to the head 26, and print obtained by developing print data for each dot An internal interface (I / F) 105 for outputting data, drive signals, and the like to the print engine 114 is provided.

  FIG. 4 is a diagram showing the waveform of the drive signal generated by the drive signal generation circuit 106 in this embodiment. A unit signal having pulse signals P1, P2, and P3 in a period T2 (also referred to as a segment in which the carriage 25 crosses one pixel interval) for printing an image corresponding to one pixel by the drive signal generation circuit 106. Is repeatedly generated.

  Further, the control unit 107 selects the dot size formed on the paper S by selecting a pulse from the pulse signals P1, P2, and P3 based on the print data obtained by developing each dot. can do. The pulse signals P1, P2, and P3 cause each ink droplet to be ejected from the nozzle. Small dots are formed on the paper S with only the pulse signal P1, medium-sized dots with the pulse signals P1 and P2, and large-sized dots with the pulse signals P1, P2, and P3.

  T1 in FIG. 4 indicates a start time from the start point in the period T2 until the pulse signal P1 is generated. For example, when dots are formed by the pulse signals P1, P2, and P3, if the start time T1 is changed, the timing at which ink is ejected is changed by the pulse signals P1, P2, and P3, and the inter-dot distance in the main scanning direction is changed. Is changed.

  The control unit 107 controls the ejection of ink by the head 26 while controlling the movement of the carriage 25 (head 26) in the main scanning direction by the carriage moving unit 109 and the conveyance of the paper S in the sub-scanning direction by the conveyance unit 110. .

  The control unit 107 can detect a phase value from image data stored in the RAM 102 by reading and executing a Fourier transform program from the ROM 103.

  Further, the control unit 107 can obtain a basic resolution period component such as 1/360 inch or 1/720 inch from the image data received from the host computer 200.

  The print engine 114 includes a head unit 108, a carriage moving unit 109, and a transport unit 110. The carriage moving unit 109 includes a carriage drive motor and a linear encoder. The transport unit 110 includes a paper feed motor, a rotary encoder, and a detector (not shown) that detects paper S feeding and paper ejection.

  FIG. 5 is a diagram of the head unit 108 including the piezo actuator 60 that moves the head 26 in the sub-scanning direction. The head 26 having the nozzle rows YL, ML, CL, and BL can slide in the sub-scanning direction indicated by the arrow D2 inside the support member 61 fixed to the carriage 25. The head 26 is in contact with the piezo actuator 60, and a pressing force is exerted by the springs 62 and 63 in the lower direction of the drawing.

  The control unit 107 in FIG. 3 applies a voltage to the piezo actuator 60 and displaces the length of the piezo actuator 60 in the sub-scanning direction. Then, the head 26 in contact with the piezo actuator 60 moves in the sub-scanning direction, and the relative position in the sub-scanning direction between the nozzle row formed on the head 26 and the paper S is adjusted.

  The image forming unit according to the present exemplary embodiment includes a printer controller 113 and a print engine 114. As described above, the image forming unit repeats relative movement between the head 26 and the paper S, which are composed of main scanning and sub-scanning, and forms an image composed of dots on the paper S.

  FIG. 6 is a cross-sectional view illustrating the camera units 5 and 6. On the paper S, a dot image 35 composed of dots is formed by ejecting ink. The dot image 35 is a part of an image formed on the entire printable area of the paper S. Light reflected from the imaging range of the camera units 5 and 6 in the dot image 35 passes through the lens 33, the lens 32, and the optical filter 34 and enters the CCD 31. By passing through the optical filter 34, in this embodiment, light in the yellow wavelength region enters the CCD 31. Light incident on the CCD 31 is converted into an electrical signal by the CCD 31. The converted electric signal is converted into image data by the control unit 107.

  By passing through the optical filter 34, the reflected light from the dot image 35 formed with only yellow dots enters the CCD 31. As the image data converted by the CCD 31, image data converted only from yellow dots is obtained. This image data is composed of a row of pixels arranged in the main scanning direction and a row of pixels arranged in the sub-scanning direction.

  Pipes 72 and 73 for injecting a gas such as air supplied from an air pressure generating unit (not shown) constituted by a fan or the like to the surface of the lens 33 are provided around the lens 33 at the lower part of the housing 30. ing. By injecting the gas from the pipes 72 and 73 as shown by the arrows, it is possible to prevent the ink mist and paper dust from the paper S from adhering to the surface of the lens 33. The pipes 72 and 73 indicate the tip portions of the respective pipes, and the portions of the pipes connected to the air pressure generating unit side are not shown.

  FIG. 7 is a diagram for explaining the dot arrangement in a part of the dot image 35 composed of dots on the paper S. FIG. For ease of explanation, the case where the dot image 35 is formed by ejecting only black ink will be described. One black circle represents one dot, and the vertical column on the left side of FIG. L1 indicates a distance between dots in the sub-scanning direction.

  FIG. 8 is a diagram of a waveform W1 of distribution data in the sub-scanning direction of the integrated intensity value obtained by integrating pixels in the main scanning direction with respect to the converted image data. The image data is converted into image data in which pixels are arranged in the main scanning direction and the sub-scanning direction so as to correspond to the dot arrangement of FIG. The integrated intensity value is calculated by adding the black pixels in the row of pixels lined up in the main scanning direction. Then, the integrated intensity value is calculated continuously in the sub-scanning direction for a plurality of columns of pixels arranged in the main scanning direction. A waveform W1 in FIG. 8 is a waveform of distribution data in the sub-scanning direction of the integrated intensity value obtained by calculating in this way. The horizontal axis in the horizontal direction in FIG. 8 indicates the pixel position in the sub-scanning direction, and the vertical axis in the vertical direction in the drawing indicates the integrated intensity value.

  The control unit 107 performs a Fourier transform on the distribution data indicated by the waveform W1 to detect a phase value related to the basic resolution period component in the sub-scanning direction.

  FIG. 9 shows a phase value and distribution data related to a basic resolution period component when it is assumed that a dot image formed by performing sub-scanning with an ideal feed amount is image-transformed and Fourier-transformed. It is a schematic diagram for comparing the phase value which concerns on the basic-resolution period component obtained by Fourier-transforming. Here, it is assumed that the feed amount in the sub-scanning direction is set to a length obtained by adding one inter-nozzle distance to the length of the nozzle row in FIG. .

  In the upper part of FIG. 9, two nozzles 41 and 42 included in the nozzle row BL of FIG. 5 and arranged in the sub-scanning direction are shown. C1 indicates the center position in the sub-scanning direction of the range captured by the camera units 5 and 6. C2 indicates the position of the nozzle 42 in the sub-scanning direction. A waveform W2 is a waveform diagram of a basic resolution period when it is assumed that a dot image formed by performing sub-scanning with an ideal feed amount is image-transformed and Fourier-transformed. The basic resolution period L3 of the waveform W2 is the same as the nozzle pitch. The waveform W2 is extended upstream in the sub-scanning direction, and the phase value of the waveform W2 at the intersection C3 with the position C2 of the nozzle 42 in the sub-scanning direction is zero.

  The control unit 107 calculates the ideal phase value a based on the distance L2 between the center position C1 and the nozzle 42, the set feed amount, and the basic resolution period L3. As described above, the control unit 107 performs the ideal conveyance in the sub-scanning direction and the distance between the position of the nozzle row formed on the head 26 and the position of the range of the sheet S imaged by the camera units 5 and 6. The ideal phase value a related to the basic resolution period is calculated on the basis of the feed amount and the resolution of the image formed on the paper S.

  A waveform W3 is a waveform of the basic resolution period L1 in the sub-scanning direction detected by Fourier transforming the distribution data shown in the waveform W1. The basic resolution period L1 is the same as the nozzle pitch. The phase value b related to the basic resolution periodic component is detected by Fourier transform.

  The control unit 107 calculates the difference between the ideal phase value a and the detected phase value b, and calculates the relative position in the sub-scanning direction.

  The control unit 107 corrects the relative position in the sub-scanning direction by moving the head 26 in FIG. 5 in the sub-scanning direction based on the detected relative position.

FIG. 10 is a flowchart of processing in the first embodiment. In step S300,
Image data to be printed on the paper S is received from the host computer 200. In step S310, the relative movement between the main scanning and the sub scanning is repeated to form the dot image 35 on the paper S. In step S320, sub-scanning is performed as one relative movement.

  In step S330, the dot images 35 formed on the paper S are imaged using the camera units 5 and 6. In step S340, an integrated intensity value obtained by integrating the pixels aligned in the main scanning direction orthogonal to the sub-scanning direction is calculated for the captured dot image 35. Then, the integrated intensity value is continuously calculated in the sub-scanning direction, and the integrated intensity value is generated as distribution data in the sub-scanning direction.

  In step S350, the generated distribution data is Fourier transformed to calculate a phase value in the basic resolution period in the sub-scanning direction. In step S360, as described with reference to FIG. 9, the distance between the position of the nozzle row formed on the head 26 and the position of the sheet S imaged by the camera units 5 and 6, and the ideal conveyance in the sub-scanning direction. The ideal phase value a related to the basic resolution period L <b> 1 is calculated based on the feed amount when performing the above and the resolution of the image formed on the paper S.

  In step S370, the generated distribution data is detected by Fourier transform, and the phase value b related to the basic resolution period in the sub-scanning direction and the basic resolution period L1 when transported with an ideal feed amount in the sub-scanning direction. The difference is calculated from the ideal phase value a related to.

  In step S380, a relative position in one relative movement is detected based on the calculated difference. In step S390, the relative position in the sub-scanning direction is corrected by adjusting the position of the head 26 in the sub-scanning direction based on the detected relative position.

  Next, a method for detecting the relative position in the main scanning direction and correcting the relative position will be described. As described above, in the main scanning in which the head 26 is moved in the main scanning direction while ejecting ink, the timing at which the ink is ejected from the head 26 is controlled by the printer controller 113, and the image on the paper S with the resolution in the main scanning direction. Is formed. At this time, when the sheet S is skewed during the sub-scanning and deviates in the main scanning direction, the relative position between the position where the head starts ejection and the position where the dots are formed shifts in the main scanning direction.

  The dot images 35 are picked up by the camera units 5 and 6, and distribution data continuous in the main scanning direction is generated from the converted image data using the integrated value in the sub-scanning direction as an integrated intensity value.

  A Fourier transform is performed from the calculated distribution data, and a phase value related to the basic resolution period based on the resolution in the main scanning direction is detected.

  In the main scanning direction, the control unit 107 ejects ink at a distance from the position where the head starts ejection from the position where the camera units 5 and 6 image the paper S and the ideal ejection timing from the head 26. The ideal phase value related to the basic resolution period is calculated based on the dot pitch at that time.

  The control unit 107 calculates a difference based on the phase value detected by Fourier transform of the distribution data and the ideal phase value when main scanning is performed at the ideal ejection timing. Based on this difference, the control unit 107 detects the relative position of the paper S and the head 26 in the main scanning direction.

  Based on the detected relative position in the main scanning direction, the control unit 107 adjusts the ink ejection timing and adjusts the relative position in the main scanning direction by adjusting the start time T1 in the drive waveform of FIG.

  As described above in the first embodiment, the inkjet printer 1 captures images of dots formed on the paper S as a medium and the head 26 that forms dots with a basic resolution period in the first direction. An image forming apparatus including: camera units 5 and 6 as units; and an image forming unit that forms an image composed of dots on the paper S by repeating relative movement between the head 26 and the paper S. Based on the predetermined image data, the A step for forming a dot image composed of dots on the paper S, the B step for performing one relative movement after the A step, and the dots at the camera units 5 and 6 after the B step. A C step for capturing an image, a D step for generating dot distribution data in the first direction for the captured dot image, and Fourier transforming the distribution data Based on the difference between the E step for detecting the phase value with respect to the first direction related to the image period component and the ideal phase value when the detected relative value and the relative movement are ideally made, F step for detecting the relative position between the head 26 and the paper S after the movement is executed.

  According to such a configuration, the distribution data is generated from the captured dot image, and the difference between the phase value detected by Fourier transforming the generated distribution data and the ideal phase value is determined between the head 26 and the paper S. Detect relative position. Thereby, the distance between dots in the main scanning direction and the sub-scanning direction can be detected. Therefore, apart from the recording medium for printing a desired image, a recording medium to be printed in advance for detecting the shift amount is not necessary. In addition to the time for operating the image forming apparatus to print a desired image, the user does not need the work time for operating the image forming apparatus in order to detect the shift amount in advance.

  The intensity value of the distribution data is an integrated intensity value of dots formed along a direction orthogonal to the first direction. In this way, since integration is performed, it is possible to suppress a decrease in detection accuracy of the relative position, that is, the shift amount, even if the number of dots formed along the direction orthogonal to the first direction is small.

In addition, the camera units 5 and 6 as imaging units include an optical filter 34 that selects a wavelength range.
According to such a configuration, distribution data can be generated from a dot image in which one ink color such as yellow, magenta, cyan, or black is selected. An image picked up without the optical filter 34 has a high density of picked up pixels and becomes image data having no periodicity, and even if Fourier transform is performed, the basic resolution period may not be detected. In such a case, if the image captured using the optical filter 34 is Fourier-transformed, the basic resolution period can be detected, so that the relative position detection accuracy is improved.

  Further, since the camera units 5 and 6 can capture dot images formed at both ends of the paper S in the paper width direction, the relative positions of the head and the paper S at both ends of the paper S in the paper width direction are detected. can do. Therefore, the inclination of the paper S can be detected.

Further, the image forming unit corrects the relative position between the head 26 and the paper S based on the detected relative position.
According to such a configuration, it is possible to suppress the occurrence of color unevenness and white stripes in the image formed on the paper S.

<Second embodiment>
In the second embodiment, a method of detecting the relative position by forming the dot image 35 formed on the paper S in FIG. 6 using the interlace method will be described. In the interlace method, an image is formed with a resolution corresponding to an integral fraction of the basic resolution period. The inkjet printer of the second embodiment has the same configuration as the inkjet printer 1 described in the first embodiment.

  Here, the interlace system in the present embodiment will be described. In the interlace method, a recording head having a nozzle row in which N nozzles are arranged in the sub-scanning direction at a pitch corresponding to k times the k-dot pitch, with a recording (printing) resolution pitch as a unit. As the nozzle pitch k, when the number of nozzles to be used is N, an integer equal to or smaller than N that is relatively prime to N is selected. Then, every time the head 26 completes the main scanning once, the sub-scanning, that is, the paper feeding is performed by a certain distance corresponding to the N dot pitch.

  FIG. 11 is a diagram for explaining printing by the interlace method in the present embodiment. M1, M2, and M3 in FIG. 11 indicate the relative positions of the sheet S and the nozzle row when the head 26 performs sub-scanning by a fixed distance corresponding to the N dot pitch every time the head 26 completes one main scanning pass. The black circle indicates the position of the nozzle in the nozzle row. Here, a recording head having a nozzle row in which 20 nozzles are arranged in the sub-scanning direction at a nozzle pitch L5 corresponding to a three-dot pitch that is three times the recording resolution pitch L4 will be described. The nozzle row located at the relative position M1 moves in the sub-scanning direction by a distance L6 of 20 dots by one sub-scan, and performs one main scan at the relative position M2. Next, the nozzle row located at the relative position M2 moves in the transport direction by a distance L6 of 20 dots by one sub-scan, and performs one main scan at the relative position M3. When main scanning is performed at each of the relative positions M1, M2, and M3, ink is ejected from the head 26 onto the paper S.

  K1, K2, and K3 in FIG. 11 indicate images formed on the paper S by ejecting ink from the nozzles by the interlace method. For the sake of explanation, FIG. 11 is based on image data that forms an image by ejecting ink from all nozzles. An image K1 shows an image formed by three main scans, an image K2 shows an image formed by two main scans, and an image K3 shows an image formed by one main scan. ing. In the image K1, dots for three dots in the sub-scanning direction are continuously formed in the carriage moving direction, and in the image K2, dots for two dots in the sub-scanning direction are continuously formed in the carriage moving direction, In the image K3, one dot in the sub-scanning direction is formed continuously in the carriage movement direction. When such printing is performed, a striped pattern is formed in the range A1 in the sub-scanning direction in which dots arranged in two dots in the sub-scanning direction are continuously formed in the carriage movement direction. In the range A2, a striped pattern in which dots for one dot are continuously formed in the moving direction of the carriage is formed.

  The basic resolution period of the head 26 is a 3-dot pitch indicated by the nozzle pitch L5. The dot image formed on the paper S is formed at a 1-dot pitch indicated by the recording resolution pitch L4. Therefore, when an image is formed on the paper S by the interlace method, the image is formed with a resolution corresponding to an integral fraction of the basic resolution period.

  FIG. 12 is a diagram illustrating a case where the dot image 35 formed on the paper S described with reference to FIG. 11 is printed using an interlace method. The vertical column on the left side of FIG. In FIG. 12, when dots are formed by the interlace method, dots are formed in one dot row, and dots are formed in two adjacent dot rows, similarly to the range indicated by A2 in FIG. The case where is not formed is shown. As shown in FIG. 12, dots are formed in the dot rows 3, 6, 9, 12, and 15, and there are portions where dots are not formed in the other dot rows. L7 indicates the distance between dots formed at this time. The control unit 107 generates distribution data in which the integrated intensity value integrated in the main scanning direction is continuous in the sub-scanning direction from the image data converted by the CCD 31.

  Next, the control unit 107 performs Fourier transform based on the calculated distribution data, and calculates a phase value related to the basic resolution period. The control unit 107 calculates a phase value related to the basic resolution period based on the distance between the head 26 and the position of the sheet S imaged by the camera units 5 and 6 and the feed amount in ideal conveyance. .

  Then, the control unit 107 calculates a difference from the phase value detected by Fourier transform based on the distribution data and the ideal phase value related to the basic resolution period when transporting with an ideal feed amount. The control unit 107 detects the relative position in the sub-scanning direction between the paper S and the head 26 based on this difference.

  The control unit 107 corrects the relative position in the sub-scanning direction by moving the head 26 in FIG. 5 in the sub-scanning direction based on the detected relative position.

  The dot image formed in the range A2 in FIG. 11 has been described above. However, the image data obtained by capturing the dot image formed in the range A1 in FIG. .

  When the formed dot density is high, the dot image 35 formed without using the interlace method is captured, and Fourier transform is performed based on the distribution data of the integrated intensity value of the converted image data. In some cases, the periodicity of the period may not be detected. In such a case, if the dot image 35 in which dots are formed at the interval of the nozzle pitch as the basic resolution period is imaged using the interlace method, and the converted image data is Fourier transformed, the interval at the nozzle pitch is obtained. The basic resolution period based on the formed dot pitch is detected as periodicity, and the probability of detecting the phase value related to the basic resolution period corresponding to the nozzle pitch is improved.

  As described above in the second embodiment, when the image forming unit forms an image with a resolution corresponding to an integral fraction of the basic resolution period in the first direction by the interlace method, a single scan is performed. Distribution data is generated for the dot image according to the above.

  According to such a configuration, since the distribution data is generated for the dot image related to a single scan, the periodicity is detected in the distribution data, and the phase value related to the basic resolution period corresponding to the nozzle pitch is detected. It becomes possible to do. Accordingly, the relative position detection accuracy is improved. When the dot image 35 formed without using the interlace method is captured and Fourier-transformed based on the distribution data of the integrated intensity value of the converted image data, the periodicity may not be detected. In such a case, if the dot image 35 in which dots are formed at the interval of the nozzle pitch as the basic resolution period is imaged using the interlace method, and the converted image data is Fourier transformed, the interval at the nozzle pitch is obtained. Periodicity is detected from the formed dot pitch, and a phase value related to the basic resolution period corresponding to the nozzle pitch can be detected.

<Third embodiment>
In the first embodiment and the second embodiment, the ideal phase value when the dot image 35 is to be formed is used, but in the third embodiment, the phase value that simulates the image data received from the host computer 200. The case of using will be described. The ink jet printer in the third embodiment has the same configuration as that of the ink jet printer 1 described in the first embodiment.

  In the third embodiment, in order to form the dot image 35 on the paper S, the inkjet printer 1 receives image data from the host computer 200 and stores it in the RAM 102. The stored image data is subjected to Fourier transform to simulate a phase value related to a low-order period component in the main scanning direction or the sub-scanning direction.

  As described in the first embodiment and the second embodiment, dot images captured using the camera units 5 and 6 are converted into image data, and distribution data of integrated intensity values is generated from the converted image data. . A phase value related to a low-order period component is detected from the generated distribution data by Fourier transform.

  The difference between the phase value detected from the distribution data and the phase value obtained by simulating the image data received from the host computer 200 is calculated, the relative position between the head 26 and the paper S is detected, and the relative position is determined. to correct.

  FIG. 13 is a flowchart for explaining processing in the third embodiment. The flowchart of FIG. 13 is obtained by deleting steps S360 and S370 and adding steps S351 and S352 from the flowchart of FIG. 10 described in the first embodiment.

  Steps S300 to S340 in FIG. 13 in the third embodiment are the same as the processing contents from steps S300 to S340 in the flowchart in FIG. 10 in the first embodiment.

  In step S350 of FIG. 10 of the first embodiment, the phase value in the basic resolution period is calculated. However, in step S350 of FIG. 13 of the third embodiment, the analysis data is Fourier-transformed and the phase of the low-order period component is calculated. Calculate the value.

  In step S351, the phase value related to the low-order period component detected by Fourier transforming the image data received from the host computer 200 is simulated. In step S352, the difference between the phase value related to the low-order period component calculated from the distribution data and the phase value obtained by simulating the image data received from the host computer 200 is calculated.

  The process from step S380 to the end of the process is the same as the process from step S380 to the end of the process in the flowchart of FIG. 10 in the first embodiment.

  As described above in the third embodiment, the ink jet printer 1 in the third embodiment includes a head that forms dots at a basic resolution period in the first direction of the main scanning direction or the sub-scanning direction, and a medium as a medium. By repeating relative movement between the camera units 5 and 6 as imaging units for imaging dots formed on the paper S and the head 26 and the paper S as main scanning and sub-scanning, an image composed of dots is printed on the paper. An image forming apparatus comprising: an image forming unit formed on S; a step of forming a dot image composed of dots on paper S based on predetermined image data; For the B step for performing main scanning or sub-scanning as relative movement, the C step for capturing a dot image with the camera units 5 and 6 after the B step, D step for generating dot distribution data for the direction, E step for detecting the phase value for the first direction related to the low-order period component by Fourier transforming the distribution data, and Fourier transform for the dot image based on the image data Then, based on the difference between the F step for simulating the phase value in the first direction related to the low-order period component and the detected phase value and the simulated phase value, G step of detecting a relative position with respect to the sheet S is executed.

  Since the dot image 35 picked up by the camera units 5 and 6 has few dots formed by ejecting ink, even if Fourier transform is performed, the basic resolution period corresponding to the resolution for forming the image and the nozzle pitch In some cases, it is not possible to detect the basic resolution period corresponding to. For example, in the case where the formed dots are scattered in the entire print area of the paper S, since the dots included in the dot image 35 are few, based on the resolution and nozzle pitch from the generated distribution data. In some cases, the basic resolution period component cannot be detected.

  In such a case, as in this embodiment, the dot image based on the image data is Fourier transformed to simulate the phase value for the first direction in the main scanning direction or the main scanning direction according to the low-order period component, Based on the difference between the detected phase value and the simulated phase value, the relative position between the head 26 and the paper S after one relative movement is detected. Thereby, since the low-order period component can be detected by Fourier transform, the detection accuracy of the relative position, that is, the shift amount is improved.

<Fourth embodiment>
In the fourth embodiment, a head unit 108a in which a function of rotating the head 26 is further added to the head unit 108 used in the first to third embodiments will be described.

  FIG. 14 is a diagram of a head unit 108a in which a function for rotating the head 26 is added to the head unit 108 described in the second embodiment. The head 26 having a nozzle row (not shown) in the sub-scanning direction is fixed to a head fixing plate 85. A pin 86 is fixed to the bottom surface of a box-shaped head receiving box 83 having an opening at the front of the drawing, and the head fixing plate 85 freely rotates as shown in the rotation direction R with the pin 86 as a fulcrum. be able to. A piezo actuator 82 is in contact with the head fixing plate 85 via a spherical member 81. The spring 80 is provided so as to be sandwiched between the head fixing plate 85 and the head receiving box 83, and a pressing force is applied to the head fixing plate 85 and the head receiving box 83 by the spring 80.

  When a voltage is applied to the piezo actuator 82 by the control unit 107 in FIG. 3, the head fixing plate 85 that contacts the head 26 rotates about the pin 86 as a fulcrum due to the mechanical displacement of the piezo actuator 82. The head 26 fixed to the head also rotates as shown in the rotation direction R.

  A piezo actuator 60 and springs 62 and 63 are provided outside the head receiving box 83, and a force pushing the head receiving box 83 by the springs 62 and 63 always acts. The head receiving box 83 can slide in the sub-scanning direction along the inside of the support member 84.

  By doing in this way, the nozzle row formed in the head 26 can be inclined with respect to the sub-scanning direction. Thereby, the nozzle pitch in the sub-scanning direction can be changed. Accordingly, it is possible to suppress the occurrence of white streaks and color unevenness while forming an image by ejecting ink.

  The technique described above can also be applied to the case where bubbles are generated in the nozzle using a heating element and the liquid is ejected by the bubbles.

  Further, the present invention can be applied to various industrial apparatuses other than a printing apparatus that performs printing by ejecting ink onto paper or the like. Mainly dispersed or dissolved materials such as color filters, textile printing devices for patterning fabrics, liquid crystal displays and organic EL (Electro Luminescence) displays. And a liquid state device for injecting a liquid material contained in

1 is an external perspective view of an inkjet printer. The figure explaining the internal appearance which removed the upper cover and the main body cover. The block diagram which shows an electrical structure. The figure which shows the waveform of the drive signal which a drive signal generation circuit produces | generates. The figure of the head unit provided with the piezoelectric actuator which moves a head to a subscanning direction. Sectional drawing explaining a camera part. The figure explaining the dot image comprised by the dot. The figure of the waveform W1 of the distribution data in the subscanning direction of the integrated intensity value which integrated the pixel in the main scanning direction. Schematic diagram for comparing the phase value related to the basic resolution period component when sub-scanning is performed with the ideal feed amount and the phase value related to the basic resolution period component obtained by Fourier transform of the distribution data . The flowchart of the process in 1st Example. The figure explaining the printing by an interlace system. The figure explaining the case where a dot image is printed using an interlace system. The flowchart explaining the process in 3rd Example. The figure of the head unit which added the function to rotate a head.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Inkjet printer, 5,6 ... Camera part, 26 ... Head, 34 ... Optical filter, 35 ... Dot image, 101 ... External interface (I / F), 102 ... RAM, 103 ... ROM, 104 ... Oscillator circuit, 105 DESCRIPTION OF SYMBOLS Internal interface (I / F) 106 Drive signal generating circuit 107 Control unit 108 Head unit 109 Carriage moving unit 110 Transport unit 111 Imaging unit 113 Printer controller 114 Print Engine, S ... paper.

Claims (7)

The head is configured with the dots by performing relative movement between the head in which nozzles are formed in the first direction at a basic resolution period and the medium, and forming dots on the medium by the head based on predetermined image data. a step for the dot image is formed on the medium that,
A step of imaging the dot image in the imaging unit,
A step which, based on the data of the dot image obtained by the imaging, and generates the distribution data of the dots definitive in the first direction,
It said distribution data to Fourier transform, and step for detecting a phase value of the first direction according to the basic resolution period,
Said detected phase value, relative movement in the first direction of said relative movement based on a difference between the ideal phase value when the has been made ideally, the said head in the first direction medium image forming apparatus and executes a step for detecting the relative position between. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the intensity value of the distribution data is an integrated intensity value of the dots formed along a direction orthogonal to the first direction. The image forming apparatus according to claim 1, wherein:
In the case of forming an image at a resolution corresponding to one integer fraction of Oite the basic resolution period in the first direction by an interlace method,
The image forming apparatus, wherein the distribution data is generated for the dot image related to a single scan. The image forming apparatus according to any one of claims 1 to 3,
The image forming apparatus, wherein the imaging unit includes an optical filter that selects a wavelength range. An image forming apparatus according to any one of claims 1 to 4,
The image forming apparatus further comprises a step of correcting a relative position between the head and the medium based on the detected relative position. The head is configured with the dots by performing relative movement between the head in which nozzles are formed in the first direction at a basic resolution period and the medium, and forming dots on the medium by the head based on predetermined image data. a step for the dot image is formed on the medium that,
A step of imaging the dot image in the imaging unit,
A step which, based on the data of the dot image obtained by the imaging, and generates the distribution data of the dots definitive in the first direction,
It said distribution data to Fourier transform, and step for detecting a phase value of the first direction according to the low order periodic component,
The Fourier transform of the dot image based on the image data, a step of simulating a phase value for said first direction according to the low order periodic component,
Said detected phase values, on the basis of the difference between the simulated phase values, and executes the step of detecting the relative position between the head and the medium in the first direction Image forming apparatus. The head is configured with the dots by performing relative movement between the head in which nozzles are formed in the first direction at a basic resolution period and the medium, and forming dots on the medium by the head based on predetermined image data. a step for the dot image is formed on the medium that,
And the step of imaging the dot image,
A step which, based on the data of the dot image obtained by the imaging, and generates the distribution data of the dots definitive in the first direction,
The distribution data by Fourier transform, and step for detecting a phase value of the first direction according to the basic resolution period,
Said detected phase value, relative movement in the first direction of said relative movement based on a difference between the ideal phase value when the has been made ideally, the said head in the first direction medium position detecting method characterized by comprising the steps of detecting the relative position of the.

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