JP4322564B2 - Pixel position specifying method, image shift correcting method, and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pixel position specifying method, an image misalignment correction method, and an image forming apparatus, and more particularly to an exposure head in an image forming apparatus that includes a plurality of exposure heads and includes a spatial modulation element in each of the exposure heads. A pixel position specifying method capable of specifying the position of the joint pixel in the exposure head with high accuracy even if the relative position between them changes, an image misalignment correcting method capable of forming a high-quality image with inconspicuous joints, and the image misalignment correction The present invention relates to an image forming apparatus that corrects an image shift between exposure heads by a method.
[0002]
[Prior art]
Conventionally, as an example of an image recording apparatus, there has been an exposure apparatus that uses a spatial light modulation element (SLM) such as a digital micromirror device (DMD) and performs image exposure with a light beam modulated according to image data. Various proposals have been made (see, for example, Non-Patent Documents 1 and 2). This DMD is configured, for example, by providing a large number of minute micromirrors on each memory cell of the SRAM, and changes the angle of the reflection surface of the micromirror by the electrostatic force caused by the charge stored in each memory cell. When actual drawing is performed, each micromirror is reset to a predetermined angle while image data is written in each SRAM, and the light reflection direction is set to a desired direction.
[0003]
One application field of the exposure apparatus is, for example, manufacturing a panel such as a liquid crystal display.
[0004]
As an exposure apparatus for manufacturing a panel, there is a multi-head exposure apparatus in which a plurality of exposure heads having the DMD are arranged along a direction intersecting a feeding direction of a photosensitive material such as the substrate for the purpose of expanding an exposure range.
[0005]
In the multi-head exposure apparatus, the relative positions between the heads are adjusted with high accuracy to such an extent that the joints do not become a practical problem.
[0006]
[Non-Patent Document 1]
Larry J. Hornbeck, Digital Light Processing and MEMS: reflecting the digital display needs of the networked society, THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING, Proceedings of SPIE Volume: 2783, 8/1996, P.2-13
[Non-Patent Document 2]
WENelson and Robit L Bhuva, .Digital micromirror device imaging bar for hard copy, THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING, Proceedings of SPIE Volume: 2413, 4/1995, P.58-65
[Patent Document 1]
Japanese Patent Laid-Open No. 10-31170
[0007]
[Problems to be solved by the invention]
However, in recent years, as the degree of integration of the substrates has increased, higher resolution has been required, so that the allowable value of the relative position shift of the image corresponding to each exposure head has decreased.
[0008]
Furthermore, in the exposure head, since many optical members and mechanism members are used from the light source to the imaging surface, the thermal expansion and contraction of each member due to temperature change, and the aging due to long-term use. Due to the accumulation of changes, there is a problem in that image quality deteriorates due to non-negligible shifts and overlaps at the joints of the image heads of the image.
[0009]
In a multi-beam exposure apparatus used for the same purpose as the multi-head exposure apparatus, the position of each beam is detected by a position detection element such as a PSD (position-sensing device) or a quadrant detector, A method for correcting a shift between images formed by a beam has been proposed (Patent Document 1).
[0010]
However, in the multi-head exposure apparatus, the interval between exposure heads is overwhelmingly larger than the interval between adjacent beams, so it is difficult to apply the method described in Patent Document 1 to the multi-head exposure apparatus.
[0011]
The present invention has been made to solve the above problem, and in an image forming apparatus such as the multi-head exposure apparatus, a pixel capable of specifying the position of a pixel corresponding to the exposure beam from the position of the exposure beam of each exposure head. It is an object of the present invention to provide a position specifying method, an image misalignment correction method and an image forming apparatus capable of extremely minimizing image misalignment and overlap at a joint portion of each exposure head.
[0012]
[Means for Solving the Problems]
In the image forming apparatus for forming an image by scanning a plurality of exposure heads capable of selectively turning on / off a plurality of pixels in a certain direction, the position of the exposure beam of each exposure head is determined. A pixel position specifying method for measuring and specifying a pixel position of a joint of the exposure head, wherein the exposure beam position is measured on a reference plane along a Y-axis direction parallel to the scanning direction. The movable beam position detecting means is used, and the first joint pixel in the vicinity of the joint of the first exposure head is turned on to detect the position of the exposure beam at the xy coordinates on the light receiving surface of the beam position detecting means. The first exposure beam position detecting step and the second joint pixel in the vicinity of the joint of the second exposure head are turned on, the beam position detecting means is moved in the Y-axis direction, and the xy position on the light receiving surface is A second exposure beam position detecting step for detecting the position of the exposure beam in the beam, a movement amount of the beam position detecting means in the Y-axis direction, and an exposure beam on the light receiving surface of the first exposure head and the second exposure head. And a connecting pixel position specifying step for specifying the positions on the reference plane of the first connecting pixel and the second connecting pixel from the position of the pixel.
[0013]
The x axis and the y axis on the light receiving surface of the beam detecting means are parallel to the X axis and the Y axis of the reference surface, respectively.
[0014]
Since the exposure beams emitted from the exposure head are parallel to each other and perpendicular to the reference plane, in the exposure head, in the first exposure beam position detection step and the second exposure beam position detection step. The detected exposure beam positions correspond to the positions of the first connection pixel and the second connection pixel, respectively.
[0015]
In the pixel position specifying method, after the exposure beam of the first exposure head is detected in the first exposure beam position detection step, the beam detection means is moved along the Y-axis direction in the second exposure beam position detection step. And the exposure beam of the second exposure head is detected.
[0016]
Therefore, the difference in the position of the exposure beam in the x-axis direction in the first exposure beam position detection step and the second exposure beam position detection step is relative to the first connection pixel and the second connection pixel in the X-axis direction. This corresponds to the difference in position.
[0017]
Then, the relative position difference in the Y-axis direction between the first joint pixel and the second joint pixel is determined in the y-axis direction of the exposure beam in the first exposure beam position detection step and the second exposure beam position detection step. This is the sum of the position difference and the amount of movement of the beam detection means in the second exposure beam position detection step.
[0018]
Therefore, according to the pixel position specifying method of the first aspect, the first connection pixel and the second connection pixel can be obtained only by measuring the irradiation position of the exposure beam between the first exposure head and the second exposure head. The relative position difference can be specified.
[0019]
Here, in order to correct the shift or overlap between the first exposure head and the second exposure head, the relative position difference between the first connection pixel and the second connection pixel can be determined. Is enough.
[0020]
Therefore, the relative position difference between the first connection pixel and the second connection pixel is specified by the pixel position specifying method, and the first exposure head is based on the specified relative position difference. If the image data input to the second exposure head is corrected, even if the first exposure head and the second exposure head are displaced from their original positions, the connection of the exposure heads caused by the displacement. It is possible to prevent the image from shifting or overlapping in the eye portion.
[0021]
According to a second aspect of the present invention, there is provided an image forming apparatus in which a plurality of pixels are formed so as to be selectively turned on / off, and an image is formed by a plurality of exposure heads arranged obliquely with respect to the scanning direction. A pixel position specifying method for measuring an exposure beam position of each exposure head to specify a pixel position of a joint of the exposure heads, wherein a Y axis parallel to the scanning direction is used to measure the position of the exposure beam The beam position detecting means that can move on the reference plane along the direction is used, pixels located near the joint of the first exposure head are sequentially turned on, and the reference plane is parallel to the scanning direction. The first pixel specifying the pixel corresponding to the exposure beam incident at the position closest to x = 0 on the xy coordinates on the light receiving surface of the beam position detecting means movable along the Y-axis direction as the first connecting pixel Ste And the first joint pixel designated in the first joint pixel designation step is turned on to move the beam position detecting means along the Y-axis direction, and the exposure beam of the first exposure head is A first beam position detecting step for detecting a first beam position which is a position on the reference plane of the beam position detecting means when the origin of the xy coordinates on the light receiving surface is irradiated, and a joint between the second exposure heads Pixels located in the vicinity are sequentially turned on, and a pixel corresponding to the exposure beam incident at a position closest to x = 0 on the xy coordinates on the light receiving surface of the beam position detecting means is used as a second connecting pixel. The second connecting pixel specified in the pixel specifying step and the second connecting pixel specifying step is turned on to move the beam position detecting means along the Y-axis direction, and the exposure beam of the second exposure head Is the light reception A second beam position detecting step for detecting a second beam position which is a position on a reference plane of the beam position detecting means when the origin of the upper xy coordinates is irradiated; and the first beam position and the second beam position. And a pixel position specifying step for specifying the positions of the first and second connection pixels on the reference plane based on the above.
[0022]
According to the pixel position specifying method, after the first beam position is detected in the first beam position detecting step, the beam position detecting means is moved in the Y-axis direction to detect the second beam position. Therefore, the first beam position and the second beam position are on the same X coordinate. Here, the first beam position and the second beam position are exposure beam irradiation positions corresponding to the first connecting pixel and the second connecting pixel, respectively. Therefore, the first beam position is specified by the pixel position specifying method. The second connection pixel and the second connection pixel are also on the same X coordinate. Then, as described above, the first joint pixel and the second joint pixel exist at the joint portions of the first exposure head and the second exposure head, respectively. Therefore, a continuous image can be formed along the X-axis direction by connecting the images with the first connecting pixel and the second connecting pixel specified by the pixel position specifying method. Further, the distance between each exposure head based on the distance between the first beam position and the second beam position, that is, the distance between the first connecting pixel and the second connecting pixel in the Y-axis direction and the scanning direction of the exposure head. By adjusting the exposure timing, it is possible to form an image with no shift or overlap along the Y-axis direction.
[0023]
According to a third aspect of the present invention, in an image forming apparatus that forms an image by scanning a plurality of exposure heads capable of selectively turning on / off a plurality of pixels in a certain direction, the exposure beam position of each exposure head is measured. A pixel position specifying method for specifying a pixel position of a joint of the exposure heads, wherein the measurement of the exposure beam includes a Y-axis direction parallel to the scanning direction and an X-axis orthogonal to the Y-axis direction. The beam position detecting means that can move on the reference plane along the axial direction is used, the first connecting pixel near the joint of the first exposure head is turned on, and the beam position detecting means is set to the X and Y axes. A first position which is a position of the beam position detecting means on the reference plane when the exposure beam is irradiated on the origin (x = 0, y = 0) on the light receiving surface of the beam position detecting means. Bee A first beam position detecting step for detecting the position (X1, Y1) and a second connecting pixel in the vicinity of the joint of the second exposure head are turned on, and the beam position detecting means is moved along the X-axis and Y-axis directions. And a second beam position (X2, Y2) which is the position of the beam position detecting means on the reference surface when the exposure beam is irradiated on the origin on the light receiving surface of the beam position detecting means. A two-beam position detecting step, and a pixel position specifying step of specifying positions of the first connecting pixel and the second connecting pixel on the reference plane based on the first beam position and the second beam position. The present invention relates to a method for specifying a pixel position.
[0024]
As described above, since the exposure beams emitted from the exposure head are parallel to each other and perpendicular to the reference plane, the first beam position and the second beam position are respectively connected to the first connection. This is the position of the pixel and the second connecting pixel on the reference plane.
[0025]
In the pixel position specifying method, beam position detection means that can move along the X-axis and Y-axis directions is used for detection of the first connection pixel and the second connection pixel. Then, the position on the XY coordinate of the beam position detection means when the exposure beam from the first connection pixel irradiates the origin of the beam position detection means is the first beam position, and exposure from the second connection pixel is performed. The position on the XY coordinates of the beam position detecting means when the beam irradiates the origin of the beam position detecting means is set as the second beam position.
[0026]
In the pixel position specifying method, the beam position detecting unit may use a small detecting element because the range in which the position of the exposure beam can be specified does not have to be so wide.
[0027]
The invention according to claim 4 relates to a pixel position specifying method in which the beam position detecting means is any one of a two-dimensional PSD, a four-division photodetector, a two-dimensional CCD, and a two-dimensional CMOS.
[0028]
The two-dimensional PSD, the four-division photodetector, the two-dimensional CCD, and the two-dimensional CMOS can all specify the position of spot light such as a pixel that is turned on and off by the exposure head in two dimensions. Therefore, it is preferable that a single element is sufficient for specifying the positions of the first and second connecting pixels in two dimensions in the beam position detecting means.
[0029]
A fifth aspect of the present invention relates to a pixel position specifying method in which the exposure head selectively turns on / off a plurality of pixels by a spatial modulation element that modulates light from a light source according to input image data.
[0030]
According to the pixel position specifying method, in an exposure head in which a plurality of pixels are selectively turned on / off by a spatial modulation element that modulates light from a light source according to input image data, the position of the connecting pixels is determined. Since it can be specified with high accuracy, even when the exposure heads deviate from their original positions for some reason, it is possible to prevent deviations between the exposure heads and occurrence of overlap.
[0031]
According to a sixth aspect of the present invention, there is provided an image forming apparatus that forms an image by scanning a plurality of exposure heads capable of selectively turning on / off a plurality of pixels in a predetermined direction. An image shift correction method for correcting overlap, wherein the first joint pixel and the second joint near the joint of the first exposure head are obtained by the pixel position specifying method according to any one of claims 1 to 5. A pixel position specifying step for specifying a position on the reference plane of a second connecting pixel in the vicinity of the joint of the exposure head; and the first connecting pixel and the second connecting pixel specified in the pixel position specifying step. An image data correction step of correcting image data input to the first exposure head and the second exposure head so that an image is connected between the first connection pixel and the second connection pixel based on the position of And have An image shift correction method comprising Rukoto.
[0032]
In the image shift correction method, in the pixel position specifying step, the first connection pixel and the second connection pixel are simply measured by measuring the exposure beam irradiation positions of the first exposure head and the second exposure head. The relative position difference is specified.
[0033]
In the image data correction step, the first connection pixel and the second connection pixel are determined based on a relative position difference between the first connection pixel and the second connection pixel specified in the pixel position specifying step. The image data input to the first exposure head and the second exposure head is corrected so that the image is connected to the connected pixels.
[0034]
Therefore, according to the pixel position specifying method, even when the first exposure head and the second exposure head are deviated from their original positions for some reason, the image at the joint portion of the exposure head caused by the deviation. It is possible to prevent the occurrence of deviation and overlap.
[0035]
According to a seventh aspect of the present invention, there is provided the pixel position specifying method according to any one of the first to fifth aspects, wherein the first joint pixel and the second exposure head near the joint of the first exposure head. A pixel position specifying step of specifying a position on the reference plane of a second connecting pixel in the vicinity of the joint; and the positions of the first connecting pixel and the second connecting pixel specified in the pixel position specifying step. And an image data correction step for correcting image data input to the first exposure head and the second exposure head so that an image is connected between the first connection pixel and the second connection pixel. In the image data correction step, regarding the shift in the Y-axis direction between the first joint pixel and the second joint pixel, between the first joint pixel and the second joint pixel. Distance in the Y-axis direction and the exposure distance The first exposure head and the second exposure head to set the exposure timing according to the scanning speed of the screen, and the first connection pixel and the second connection pixel. As for the shift in the X-axis direction, the image data is input to the first exposure head and the second exposure head so that the image data overlaps the first connecting pixel and the second pixel. The present invention relates to an image shift correction method to be removed by the above.
[0036]
In the pixel position specifying method according to any one of claims 1 to 5, since the second pixel is detected by moving the beam detection unit that detects the first connection pixel in the Y-axis direction, the first connection pixel and the The second connecting pixels have substantially the same position on the X coordinate although the positions on the Y coordinate are different.
[0037]
Therefore, when the image data is input to the first exposure head and the second exposure head so that the image data overlaps with each other in the first connection pixel and the second pixel, a shift in the Y-axis direction is caused. If the exposure timings of the first exposure head and the second exposure head are set so as not to occur, it is possible to eliminate image shift and overlap between the first joint pixel and the second pixel.
[0038]
According to an eighth aspect of the present invention, for three or more exposure heads, the position of the connection pixel in each image head on the reference plane is specified by the pixel position specifying step, and the image is connected by the connection pixel. The present invention relates to an image shift correction method for correcting image data input to each of the exposure heads based on the position of a connected pixel specified by the pixel position specifying step.
[0039]
The image shift correction method according to claim 6 or 7, wherein an image forming apparatus having a plurality of exposure heads is used to correct an image misalignment between one exposure head and another exposure head connected to the one exposure head. By correcting image misalignment and overlap, a high-quality image without misalignment or overlap between exposure heads is formed.
[0040]
An invention according to claim 9 is provided with an exposure means comprising a plurality of exposure heads capable of selectively turning on / off a plurality of pixels, and exposing the image forming surface while scanning the image forming surface in a certain direction to form an image. In the measurement of the position of the exposure beam, the position of the exposure beam of each exposure head provided in the exposure means by the beam position detection means capable of moving on the reference plane along the Y-axis direction parallel to the scanning direction. A pixel position specifying means for specifying the position of the pixel of the exposure head, and an exposure control means for controlling the exposure head based on the detection result of the pixel position in the beam position detecting means. The beam position detecting means uses the pixel position specifying method according to any one of claims 1 to 4 to perform a first joint pixel and a second exposure near a joint of the first exposure head. A position of a second joint pixel in the vicinity of the joint of the grid is specified on the reference plane, and the exposure control unit is configured to specify the first joint pixel and the second joint specified by the pixel position specifying unit. Based on pixel positions, image data input to the first exposure head and the second exposure head is corrected so that an image is connected between the first connection pixel and the second connection pixel. The present invention relates to an image forming apparatus.
[0041]
In the image forming apparatus, the relative positional relationship between the first connection pixel and the second connection pixel is specified by the pixel position specifying method according to any one of claims 1 to 5, and the relative position is determined. Based on this positional relationship, image data input to the first exposure head and the second exposure head is corrected to connect the first connecting pixel and the second connecting pixel.
[0042]
Therefore, even if the position of the exposure head is shifted for some reason, the image shift or overlap between the exposure heads is automatically corrected, so that the image shift or overlap does not occur.
[0043]
According to a tenth aspect of the present invention, in the image forming apparatus, the pixel position specifying means includes a two-dimensional PSD, a four-division photodetector, a two-dimensional CCD, and a two-dimensional CMOS pixel position detecting element as the beam position detecting means. About.
[0044]
The two-dimensional PSD, the four-division photodetector, the two-dimensional CCD, and the two-dimensional CMOS can all specify the position of spot light such as a pixel that is turned on and off by the exposure head in two dimensions. Therefore, it is preferable that a single element is sufficient for specifying the positions of the first and second connecting pixels in two dimensions in the beam position detecting means.
[0045]
In addition, since these pixel position detecting elements have high sensitivity, the relative positional relationship between the first connecting pixel and the second connecting pixel is specified to correct image misalignment and overlap between the exposure heads. In some cases, it is possible to reduce the light amount of the exposure head and to increase the light amount of the exposure head when forming an image.
[0046]
According to an eleventh aspect of the present invention, the exposure head includes a spatial light modulation element that modulates light from a light source in accordance with input image data, and a plurality of pixels are selectively turned on / off by the spatial modulation element. The present invention relates to an off-image forming apparatus.
[0047]
The image forming apparatus is an example in which a so-called SLM exposure head is used as the exposure head in the image forming apparatus according to claim 9.
[0048]
The invention according to claim 12 relates to an image forming apparatus in which the spatial modulation element has a plurality of pixels arranged to be inclined with respect to the scanning direction.
[0049]
According to the image forming apparatus, it is easy to form an image so that there is no gap between the exposure heads. In addition, the pixel position specifying method according to claims 1 to 5 can be particularly preferably applied.
[0050]
A thirteenth aspect of the present invention relates to an image forming apparatus in which pixels of the spatial modulation element are two-dimensionally arranged.
[0051]
14. The image forming apparatus according to claim 13, wherein an image forming apparatus that performs exposure using a plurality of exposure heads provided with spatial modulation elements in which pixels are arranged two-dimensionally is widely used in the manufacture of liquid crystal displays and the like. Since the image misalignment correction method of the present invention corrects the image misalignment between the exposure heads, even when a large area image is formed using a large number of exposure heads, the misalignment or overlap between the exposure heads occurs. It does not occur.
[0052]
DETAILED DESCRIPTION OF THE INVENTION
1. Embodiment 1
FIG. 1 shows the entire configuration of an example of an exposure apparatus included in the image forming apparatus of the present invention.
[0053]
The exposure apparatus according to the first embodiment is a so-called flat bed type, and includes a flat stage 152 that adsorbs and holds a sheet-like photosensitive material 150 on the surface, as shown in FIG. The surface of the stage 152 that holds the photosensitive material 150 by suction and the exposed surface of the photosensitive material 150 correspond to the image forming surface in the image forming apparatus of the present invention.
[0054]
The exposure apparatus includes a thick plate-like installation table 156 supported by four legs 154, and two guides provided on the upper surface of the installation table 156 along the stage moving direction indicated by arrows in FIG. 158. The stage 152 is arranged so that the longitudinal direction thereof faces the stage moving direction, and is supported by a guide 158 so as to be reciprocally movable. The stage 152 moves along the guide 158 by a driving device (not shown).
[0055]
A U-shaped gate 160 is provided at the center of the installation table 156 so as to straddle the movement path of the stage 152. Each end of the U-shaped gate 160 is fixed to both side surfaces of the installation table 156. A scanner 162 is provided on one side of the gate 160, and a plurality of (for example, two) detection sensors 164 for detecting the front and rear ends of the photosensitive material 150 are provided on the other side. The scanner 162 and the detection sensor 164 are respectively attached to the gate 160 and fixedly arranged above the moving path of the stage 152. Note that the scanner 162 and the detection sensor 164 are connected to the controller 100 that controls them, and are controlled so that exposure is performed at a predetermined timing when exposure is performed by the exposure head 166, as will be described later.
[0056]
A surface detector 180 that moves along the direction perpendicular to the stage moving direction by the feeding device 182, that is, the X direction to be described later, is provided at the downstream edge of the stage 152 along the stage moving direction. . The surface detector 180 is a detector that can specify the irradiation position of the exposure beam in two dimensions, and corresponds to a pixel position specifying method, an image shift correcting method, and a beam position detecting unit in the image forming apparatus according to the present invention. The surface of the stage 152 corresponds to a reference plane in the pixel position specifying method and the image shift correction method. Specifically, a PSD, a quadrant photo detector, or the like can be used as the surface detector 180. As the feeding device 182, any linear feeding device such as a belt drive mechanism using a ball screw or a linear guide can be used.
[0057]
The scanner 162 corresponds to an exposure unit in the image forming apparatus according to the present invention, and is arranged in a substantially matrix form of m rows and n columns (for example, 2 rows and 5 columns) as shown in FIG. 2 and FIG. A plurality of exposure heads 166 are provided.
[0058]
As shown in FIG. 2, the exposure area 168 that is an area exposed by the exposure head 166 has a rectangular shape with a short side along the scanning direction, and is inclined at a predetermined inclination angle θ with respect to the scanning direction. . As the stage 152 moves, a strip-shaped exposed area 170 is formed for each exposure head 166 in the photosensitive material 150. As shown in FIGS. 1 and 2, the scanning direction is opposite to the stage moving direction.
[0059]
As shown in FIGS. 3A and 3B, the exposure heads 166 are arranged in a line, and each of the strip-shaped exposed areas 170 partially overlaps the adjacent exposed areas 170. In this way, they are arranged in the arrangement direction so as to be shifted by a predetermined interval (a natural number times the long side of the exposure area, 1 time in the present embodiment). The exposure head 166 corresponds to the SLM exposure head in the image forming apparatus of the present invention.
[0060]
As shown in FIG. 1, the exposure apparatus according to the first embodiment is further connected to a controller 100 that controls the feed of the stage 152 and the exposure of each exposure head 166. The controller 100 corresponds to an exposure control unit included in the image forming apparatus according to the present invention.
[0061]
Each of the exposure heads 166A to 166J has a DMD 50 as an SLM that modulates an incident light beam for each pixel in accordance with image data, as shown in FIGS. 4 and 5A and 5B. I have. The DMD 50 is connected to a controller (not shown) that includes a data processing unit and a mirror drive control unit. The data processing unit of the controller generates a control signal for driving and controlling each micromirror in the region to be controlled by the DMD 50 for each exposure head 166 based on the input image data.
[0062]
The mirror drive control unit controls the angle of the reflection surface of each micromirror of the DMD 50 for each exposure head 166 based on the control signal generated by the image data processing unit. The control of the angle of the reflecting surface will be described later.
[0063]
On the light incident side of the DMD 50, a fiber array light source 66 including a laser emitting section in which emission ends (light emitting points) of an optical fiber are arranged in a line along a direction corresponding to the long side direction of the exposure area 168, a fiber A lens system 67 for correcting the laser light emitted from the array light source 66 and condensing it on the DMD, and a reflecting mirror 69 for reflecting the laser light transmitted through the lens system 67 toward the DMD 50 are arranged in this order.
[0064]
The lens system 67 includes a pair of combination lenses 71 that collimate the laser light emitted from the fiber array light source 66 and a pair of combination lenses that correct the light quantity distribution of the collimated laser light to be uniform. 73 and a condensing lens 75 that condenses the laser light whose light quantity distribution is corrected on the DMD. With respect to the arrangement direction of the laser emitting ends, the combination lens 73 spreads the light beam at a portion close to the optical axis of the lens and contracts the light beam at a portion away from the optical axis, and with respect to a direction orthogonal to the arrangement direction. Has a function of allowing light to pass through as it is, and corrects the laser light so that the light quantity distribution is uniform.
[0065]
Further, on the light reflection side of the DMD 50, lens systems 54 and 58 for forming an image of the laser light reflected by the DMD 50 on the scanning surface (exposed surface) 56 of the photosensitive material 150 are arranged. The lens systems 54 and 58 are arranged so that the DMD 50 and the exposed surface 56 are in a conjugate relationship.
[0066]
In the present embodiment, the laser light emitted from the fiber array light source 66 is shaped so as to uniformly irradiate the pixels on the DMD 50, and then each pixel is magnified about 5 times by these lens systems 54 and 58. Is set to
[0067]
As shown in FIG. 6, the DMD 50 is configured such that a micromirror (micromirror) 62 is supported by a support on an SRAM cell (memory cell) 60, and a large number of (pixels) (pixels) are formed. For example, it is a mirror device configured by arranging micromirrors with a pitch of 13.68 μm, 1024 × 768) in a grid pattern. Each pixel is provided with a micromirror 62 supported by a support column at the top, and a material having a high reflectance such as aluminum is deposited on the surface of the micromirror 62. The reflectance of the micromirror 62 is 90% or more. A silicon gate CMOS SRAM cell 60 manufactured in a normal semiconductor memory manufacturing line is disposed directly below the micromirror 62 via a support including a hinge and a yoke, and is entirely monolithic (integrated type). ).
[0068]
When a digital signal indicating the tilt state (modulation state) of the micromirror 60 is written in the SRAM cell 60 of the DMD 50 and further the digital signal is output from the SRAM cell 60 to the micromirror 62, the micromirror 62 supported by the support column. However, it is tilted in a range of ± α degrees (for example, ± 10 degrees) with respect to the substrate side on which the DMD 50 is disposed with the diagonal line as the center. 7A shows a state where the micromirror 62 is tilted to + α degrees when the micromirror 62 is in an on state, and FIG. 7B shows a state where the micromirror 62 is tilted to −α degrees when the micromirror 62 is in an off state. . Therefore, by controlling the inclination of the micromirror 62 in each pixel of the DMD 50 as shown in FIG. 6 according to the image signal, the light incident on the DMD 50 is reflected in the inclination direction of each micromirror 62. .
[0069]
FIG. 7 shows an example of a state in which a part of the DMD 50 is enlarged and the micromirror 62 is controlled to + α degrees or −α degrees. On / off control of each micromirror 62 is performed by a controller (not shown) connected to the DMD 50. A light absorber (not shown) is arranged in the direction in which the light beam is reflected by the micromirror 62 in the off state.
[0070]
As described above, in the scanner 162, as shown in FIGS. 3A and 3B, the exposure heads 166A to 166J have a predetermined interval (exposure area) between the first row and the second row in the column direction. The natural number is multiplied by a natural number of the long side, and is multiplied by 1 in the present embodiment).
[0071]
Therefore, for example, an unexposed portion between the exposure area 168A located on the leftmost side of the first row and the exposure area 168C located right next to the exposure area 168A is an exposure area located on the lower right side of the exposure area 168A. It is exposed by 168B. Similarly, the non-exposed portion between the exposure area 168B and the exposure area 168D adjacent to the exposure area 168B is exposed by the exposure area 168C located on the upper right side of the exposure area 168B. The same applies hereinafter. As described above, when one continuous image is formed on the surface of the photosensitive material 150 by the exposure heads 166A to 166J, it is necessary to connect the images to the exposure area located on the right side of each exposure area. Hereinafter, an example in which images are connected between the exposure area 168A and the exposure area 168B will be described with reference to FIG. Hereinafter, the conveyance direction of the photosensitive material 150 is defined as the Y-axis direction, and the direction orthogonal to the conveyance direction is defined as the X-axis direction.
[0072]
First, the stage 152 is moved so that the detector 180 is positioned in the exposure area 168 </ b> A, and the detector 180 is moved by the feeding device 82.
[0073]
Next, the pixel P1 that is formed in the exposure area 168A by the exposure beam from the exposure head 166A and is connected to the image formed in the exposure area 168B is selected and lit. The number of connecting pixels P1 may be only one, or may be two or more. The connection pixel P1 corresponds to the first connection pixel in the present invention.
[0074]
Then, the connecting pixel P1 is detected by the detector 180. This step corresponds to the first exposure beam position detecting step in the pixel position specifying method of the present invention. The position of the connection pixel P1 on the detector 180 when the connection pixel P1 is detected by the detector 180 is defined as (x1, y1).
[0075]
Next, in the exposure head 166B, the pixel P that may be connected to the exposure area 168A is selected and lit. Then, the stage 152 is moved until any one of the pixels is detected, in other words, the detector 180 is moved along the Y-axis direction. This step corresponds to the second exposure beam position detecting step in the pixel position specifying method of the present invention. The amount of movement of the stage 152 when the pixel is detected in the exposure area 168B, that is, the amount of movement of the detector 180 is Y0.
[0076]
Among the pixels P of the exposure head 166B detected by the detector 180, the pixel having the smallest distance in the X direction from the connection pixel P1 is selected as the connection pixel P2. The coordinates of the connecting pixel P2 on the detector 180 are (x2, y2).
[0077]
As described above, after detecting the connection pixel P1 (x1, y1), the detector 180 is moved in the Y-axis direction to detect the connection pixel P2 (x2, y2). Therefore, the connection pixel P1 (x1 , Y1) is detected and the X coordinate of the detector 180 is the same when the joint pixel P2 (x2, y2) is detected. Further, the x axis and the y axis on the detector are parallel to the X axis and the Y axis, respectively, as shown in FIG. Therefore, the distance in the X-axis direction between the connection pixel P1 and the connection pixel P2 is given by the position difference x2-x1 on the x coordinate. On the other hand, the distance in the X-axis direction is given by the position difference y2-y1 on the y-coordinate plus the movement distance Y0 of the detector 180 in the Y-axis direction, that is, y2-y1 + Y0.
[0078]
Therefore, the controller 100 detects the distance (x2−x1, y2−y1 + Y0) between the connection pixel P1 and the connection pixel P2 and the photosensitivity so that the image shift between the connection pixel P1 and the connection pixel P2 is minimized. The exposure timing of the exposure head 166A and the exposure head 166B is set according to the conveyance speed of the material 150, that is, the moving speed V of the stage 152, and the exposure head 166A and the exposure head 166A are exposed so that the images overlap at the connection pixel P1 and the connection pixel P2. The image data is input to the head 166B, and corrections such as image data shift, image rotation, and magnification conversion are performed on the input image data as necessary.
[0079]
FIG. 9 shows an image formed on the photosensitive material 150 when the exposure timings of the exposure head 166A and the exposure head 166B are set as described above. In FIG. 9, an image 169A is an image formed on the photosensitive material 150 by the exposure head 166A, and an image 169B is an image formed on the photosensitive material 150 by the exposure head 166B.
[0080]
As is apparent from FIG. 9, the connecting pixel P1 and the connecting pixel P2 that connect the image 169A and the image 169B have almost the same position in the X direction, and the exposure timing of the exposure head 166A and the exposure head 166B is corrected. There is no occurrence of a shift or overlap in the Y direction between the connection pixel P1 and the connection pixel P2. Therefore, the image 169A and the image 169B are joined at the joint, and are hardly displaced or overlapped.
[0081]
Next, the detector 180 is driven by the feeding device 182 and moved to the joint between the exposure head 166B and the exposure head 166C, and the image 169B and the image formed on the exposure head 166B and the exposure head 166C, respectively, in the same procedure. The connecting pixel of 169C is specified. By repeating this procedure in sequence, the connection pixels of all the exposure heads 166 of the light absorption device are specified, and image data shift and image data are input to the image data input to each exposure head 166 so that the images overlap at the connection pixels. By performing corrections such as rotation and magnification conversion, it is possible to form an image with little misalignment or overlap in the seam over the entire exposure area.
[0082]
As described above, in the exposure apparatus according to the first embodiment, the position between the exposure heads 166A to 166J changes due to the thermal expansion and contraction of each member due to a temperature change and the accumulation of temporal changes due to long-term use. Even in this case, since the shift and overlap of the images at the joints of the images 169A to 169J formed by the exposure head 166A to the exposure head 166J can be suppressed to a minimum, an image with a large area can be created. However, it is possible to obtain a high-quality image with no noticeable joints or shifts.
[0083]
Therefore, since a high-quality image can be formed even when the photosensitive material 150 has a large area, the exposure apparatus is applied to the manufacture of large-area printed wiring boards, TFTs, color filters for liquid crystal display devices, and plasma display panels. Even in this case, it is possible to effectively prevent the generation of defective products due to the image shift between the exposure heads 166.
[0084]
2. Embodiment 2
FIG. 10 shows the entire configuration of another example of the exposure apparatus included in the image forming apparatus of the present invention.
[0085]
Similarly to the exposure apparatus according to the first embodiment, the exposure apparatus according to the second embodiment is also a so-called flatbed type, and as shown in FIG. 10, a flat plate shape that adsorbs and holds the sheet-like photosensitive material 150 on the surface. Stage 152 is provided.
[0086]
However, instead of the detector 180 provided in the exposure apparatus according to the first embodiment, six surface detectors 184a to 184f are fixed along the X-axis direction at the downstream edge of the stage 152 in the stage moving direction. Has been. The surface detector 184 also corresponds to the beam position detecting means in the present invention. The surface detector 184 is the same as the surface detector 180 in the first embodiment. Further, the x axis and the y axis on the detection surface of the surface detector 184 are parallel to the X axis and the Y axis of the exposure apparatus, respectively. Therefore, the pixels of the exposure head 166 are arranged obliquely with respect to the x-axis and the y-axis of the surface detector 184.
[0087]
For other configurations, the exposure apparatus according to the second embodiment is the same as the exposure apparatus according to the first embodiment. Further, the same reference numerals as those in the first embodiment mean the same constituent elements in principle.
[0088]
Hereinafter, a procedure for selecting the connection pixel P1 and the connection pixel P2 in the exposure area 168A and the exposure area 168B will be described.
[0089]
First, the stage 152 is moved, and the surface detector 184 is positioned below the exposure area 168.
[0090]
Next, the pixels of the exposure head 166A are sequentially turned on in the exposure area 168A, and the pixels are detected by any of the surface detectors 184a to 184f as shown in FIG. Hereinafter, for the sake of simplicity, the case where the pixel is detected by the surface detector 184a will be described as an example.
[0091]
When the pixel is detected by the surface detector 184a, the pixel closest to the position x = 0 of the surface detector 184 among the pixels is connected as a pixel P1 (a, b). Note that (a, b) is the position of the connecting pixel P1 on the xy plane.
[0092]
Next, the stage 152 is moved, in other words, the surface detector 184 is moved in the Y-axis direction so that the connecting pixel P1 is positioned on the line y = 0 of the detector 184a, and the amount of movement Y1 of the stage 152 at this time is detected. . Y1 corresponds to the y coordinate b of the connection pixel P1 before the detector 184 is moved. Therefore, the xy coordinate of the connection pixel P1 is specified as (a, Y1).
[0093]
When the xy coordinates of the connection pixel P1 are set, the pixels of the exposure head 166B are sequentially turned on similarly to the case of P1, and the pixel closest to the position of x = 0 of the detector 184a in the exposure area 168B is connected. , D). Note that (c, d) is the position of the connecting pixel P2 on the xy plane.
[0094]
Next, the stage 152 is moved so that the connecting pixel P2 is positioned on the origin (0, 0) of the detector 184a, and the moving amount Y2 of the stage 152 at this time is detected. Y2 corresponds to the y coordinate d of the connecting pixel P2 before moving the detector 184a. Therefore, the xy coordinate of the connection pixel P2 is specified as (b, Y2).
[0095]
Here, since the connecting pixel P1 and the connecting pixel P2 are pixels closest to the position of x = 0 in the same surface detector 184a, the distance in the x-axis direction, that is, the distance in the X-axis direction is almost zero.
[0096]
Therefore, when the connection pixel P1 and the connection pixel P2 are selected and the xy coordinates are specified, the controller 100 determines the distance in the Y direction (Y2−Y1) between the connection pixel P1 and the connection pixel P2 and the photosensitive material 150. The exposure timings of the exposure head 166A and the exposure head 166B are set so that the images overlap in the Y-axis direction at the connecting pixel P1 and the connecting pixel P2 according to the transport speed, that is, the moving speed V of the stage 152. At the same time, in the X-axis direction, image data is input to the exposure head 166A and the exposure head 166B so that the same image is formed by the connecting pixel P1 and the connecting pixel P2.
[0097]
Thereby, as shown in FIG. 9, the shift | offset | difference and overlap between the image 169A and the image 169B can be prevented.
[0098]
In the exposure apparatus according to the second embodiment, the connection pixels P1 and P2 whose positions in the X direction are substantially equal are selected as connection pixels, and image data is converted so that the images overlap at the connection pixels P1 and P2. As a result, it is possible to form an image with less shift and overlap at the joints of the images than in the exposure apparatus according to the second embodiment.
[0099]
Next, in the same procedure, the detector 184b identifies the connecting pixel between the image 169B and the image 169C formed by the exposure head 166B and the exposure head 166C, respectively. By repeating this procedure sequentially, the connection pixels between all the exposure heads of the exposure apparatus are specified, and the image data shift and the image data are input to the image data input to each exposure head 166 so that the images overlap at the connection pixels. By performing corrections such as rotation and magnification conversion, it is possible to form an image with little misalignment or overlapping at the joints over the entire exposure region.
[0100]
Therefore, when the exposure apparatus is applied to the manufacture of large-area printed wiring boards, TFTs, color filters of liquid crystal display devices, and plasma display panels, the occurrence of defective products due to image misalignment between the exposure heads 166 is further increased. It can be effectively prevented.
[0101]
3. Embodiment 3
FIG. 12 shows the overall configuration of still another example of the exposure apparatus included in the image forming apparatus of the present invention.
[0102]
Similarly to the exposure apparatus according to the first embodiment, the exposure apparatus according to the third embodiment is also a so-called flatbed type, and as shown in FIG. 12, a flat plate shape that adsorbs and holds the sheet-like photosensitive material 150 on the surface. Stage 152 is provided.
[0103]
However, a surface detector 186 that can be moved along the X-axis direction by a high-precision feeder 187 is provided at the downstream edge of the stage 152 in the stage moving direction. As shown in FIG. 13, a groove 185 is provided across the entire width along the X-axis direction at the downstream edge of the stage 152, and the surface detector 186 slides inside the groove 185. The groove 185 is further provided with a linear encoder 188 for detecting the position of the surface detector 186 in the X-axis direction, and two feeding devices 187 for feeding the surface detector 186 are provided so as to sandwich the linear encoder 188 therebetween. As the feeding device 187, a ball screw or a linear motor can be used. When a ball screw is used as the feeding device 187, if a pulse motor is used to drive the ball screw, the surface detector 186 is calculated from the number of pulses sent to the pulse motor and the movement distance of the surface detector 186 per pulse. Can be specified, the linear encoder 188 becomes unnecessary.
[0104]
A procedure for specifying the position of the connecting pixel in the exposure apparatus according to the third embodiment will be described with reference to FIG.
[0105]
First, among the pixels of the exposure head 166A, a pixel to be connected to the exposure area 168B is selected, designated as the connection pixel P1, and lit. The number of connecting pixels P1 may be one or two or more.
[0106]
Next, the surface detector 186 is moved in the X-axis direction by the feeding device 187 and at the same time, the stage 152 is moved to move the surface detector 186 in the Y-axis direction, and the exposure beam from the connecting pixel P1 is moved to the origin ( The surface detector 186 is stopped at the point of incidence on (0, 0). From the position of the surface detector 186 detected by the linear encoder 188 at this time and the position of the stage 152 determined from the amount of movement of the stage 152, the position (X1, Y1) of the connecting pixel P1 on the XY plane is determined.
[0107]
Next, of the pixels of the exposure head 166B, the pixels to be connected to the exposure area 168A are selected and all these pixels are lit. Then, the XY coordinates of the pixel are obtained by the same procedure as described in connection pixel P1. Of the pixels, the pixel whose X coordinate is closest to the X coordinate X1 of the connection pixel P1 is defined as a connection pixel P2 (X2, Y2).
[0108]
When the connection pixel P1 (X1, Y1) in the exposure area 168A and the connection pixel P2 (X2, Y2) in the exposure area 168B are obtained, the controller 100 causes an image shift between the connection pixel P1 and the connection pixel P2. In order to minimize the exposure head 166A and the exposure according to the distance (Y2-Y1) in the Y-axis direction between the connecting pixel P1 and the connecting pixel P2 and the conveyance speed of the photosensitive material 150, that is, the moving speed V of the stage 152. The exposure timing with the head 166B is set. In addition, the exposure head 166A and the exposure head 166B perform corrections such as image data shift, image rotation, and magnification conversion as necessary to obtain an image 169A and an image 169B as shown in FIG.
[0109]
In the exposure head according to the third embodiment, the position of the connecting pixel P1 and the connecting pixel P2 is obtained by moving the surface detector 186 not only in the Y-axis direction but also in the X-axis direction.
[0110]
Therefore, even when the distance between the connection pixel P1 and the connection pixel P2 is large in the X-axis direction, the actual position on the XY plane between the connection pixel P1 and the connection pixel P2 can be specified. Then, by controlling the image signal input between the exposure head 166A and the exposure head 166B based on the actual position, it is possible to prevent the image from being shifted or overlapped between the exposure head 166A and the exposure head 166B. it can.
[0111]
Next, the detector 180 is moved to the joint between the exposure head 166B and the exposure head 166C by the feeding device 187, and an image 169B and an image 169C formed by the exposure head 166B and the exposure head 166C, respectively, according to the same procedure. The connecting pixel is specified. By repeating this procedure in sequence, the connection pixels between all the exposure heads 166 of the exposure apparatus are specified, and the image data shift and the image data are input to the image data input to the exposure head 166 so that the images overlap at the connection pixels. By performing corrections such as rotation and magnification conversion, it is possible to form an image with little misalignment or overlapping at the joints over the entire exposure region.
[0112]
As described above, when the exposure apparatus according to the third embodiment is used, even when the photosensitive material 150 having a large area is exposed by using a large number of exposure heads 166, the deviation between the exposure areas 168 on the photosensitive material 150. Continuous large images can be formed without gaps or gaps.
[0113]
Therefore, when the exposure apparatus is applied to the manufacture of large-area printed wiring boards, TFTs, color filters of liquid crystal display devices, and plasma display panels, the generation of defective products due to image misalignment between the exposure heads 166 is particularly serious. It can be effectively prevented.
[0114]
【The invention's effect】
As described above, according to the present invention, in the multi-head exposure apparatus, an image forming apparatus and an image shift correction method capable of forming a continuous large image with a very small shift between exposure areas exposed by each exposure head. Is provided.
[Brief description of the drawings]
FIG. 1 is a perspective view showing the arrangement of an exposure apparatus according to Embodiment 1. FIG.
FIG. 2 is a perspective view showing a configuration of a scanner provided in the exposure apparatus according to the first embodiment.
FIG. 3 is a plan view showing an exposed area formed on a photosensitive material, and a schematic view showing an arrangement of exposure areas by each exposure head.
FIG. 4 is a perspective view showing a schematic configuration of an exposure head provided in the exposure apparatus according to the first embodiment.
5 is a cross-sectional view in the scanning direction along the optical axis showing the configuration of the exposure head shown in FIG. 4. FIG.
6 is a partially enlarged view showing the structure of a DMD provided in the exposure head shown in FIG. 4. FIG.
FIG. 7 is an explanatory diagram showing an operation of the DMD shown in FIG. 6;
FIG. 8 is a plan view showing a procedure for selecting a connecting pixel from pixels that can be placed on an exposure head included in the exposure apparatus according to Embodiment 1 and connecting images;
FIG. 9 is a plan view showing an example of images connected by the procedure shown in FIG. 8;
FIG. 10 is a perspective view showing the arrangement of an exposure apparatus according to the second embodiment.
FIG. 11 is a plan view showing a procedure for selecting connected pixels from pixels in an exposure head included in an exposure apparatus according to Embodiment 2 and connecting images;
FIG. 12 is a perspective view showing the arrangement of an exposure apparatus according to the third embodiment.
FIG. 13 is an enlarged plan view showing details of a configuration of a surface detector provided in the exposure apparatus according to the third embodiment and its periphery.
FIG. 14 is a schematic plan view showing a procedure for specifying positions of pixels P1 and P2 connected by a surface detector.
[Explanation of symbols]
50 DMD (Digital Micromirror Device, Spatial Light Modulator)
53 Reflected light image (exposure beam)
54, 58 Lens system
56 Scanning surface (exposed surface)
64 laser module
66 Fiber array light source
68 Laser emitting part
73 Combination lens
150 Photosensitive material
152 stage (moving means)
162 Scanner
166 Exposure head
170 Exposed area
180-side detector
182 Feeder
184 face detector
186 face detector
188 linear encoder

Claims (11)

In an image forming apparatus in which a plurality of pixels are formed so as to be selectively on / off, and a plurality of exposure heads arranged obliquely with respect to the scanning direction are scanned in a fixed direction, each exposure head A pixel position specifying method for measuring the exposure beam position and specifying a pixel position of a joint of the exposure heads,
For the measurement of the position of the exposure beam, a beam position detection means capable of moving on a reference plane along the Y-axis direction parallel to the scanning direction is used.
The pixels located in the vicinity of the joint of the first exposure head are sequentially turned on, and the xy coordinates on the light receiving surface of the beam position detecting means capable of moving on the reference surface along the Y-axis direction parallel to the scanning direction. A first connecting pixel specifying step in which a pixel corresponding to the exposure beam incident on the position closest to the y-axis is a first connecting pixel;
The first joint pixel designated in the first joint pixel designation step is turned on to move the beam position detecting means along the Y-axis direction, so that the exposure beam of the first exposure head is on the light receiving surface. A first beam position detecting step of detecting a first beam position which is a position on a reference plane of the beam position detecting means when irradiating the origin of the xy coordinates of
The pixels located near the joint of the second exposure head are sequentially turned on, and the pixel corresponding to the exposure beam incident on the position closest to the y-axis on the xy coordinate on the light receiving surface of the beam position detecting means is set to the second. A second connecting pixel designating step as a connecting pixel of
The second joint pixel designated in the second joint pixel designation step is turned on to move the beam position detecting means along the Y-axis direction, so that the exposure beam of the second exposure head is on the light receiving surface. A second beam position detecting step of detecting a second beam position which is a position on a reference plane of the beam position detecting means when the origin of the xy coordinates of
A pixel position specifying step of specifying positions of the first connecting pixel and the second connecting pixel on the reference plane based on the first beam position and the second beam position; Location method. 2. The pixel position specifying method according to claim 1 , wherein the beam position detecting means is a pixel position detecting element that is one of a two-dimensional PSD, a four-division photodetector, a two-dimensional CCD, and a two-dimensional CMOS. The pixel position specifying method according to claim 1 , wherein the exposure head selectively turns on / off a plurality of pixels by a spatial modulation element that modulates light from a light source according to input image data. In an image forming apparatus that forms images by scanning a plurality of exposure heads that can selectively turn on / off a plurality of pixels in a fixed direction, an image displacement correction method that corrects image displacement and overlap between the exposure heads. There,
The pixel position specifying method according to claim 1, position on the reference surface of the second connecting pixels in the vicinity of the joint of the first connecting pixel and the second exposure head around the joint of the first exposure head A pixel position specifying step for specifying
Based on the positions of the first connection pixel and the second connection pixel specified in the pixel position specifying step, the first connection pixel and the second connection pixel are connected so that an image is connected to the first connection pixel. And an image data correction step of correcting image data input to the second exposure head and the second exposure head. The pixel position specifying method according to any one of claims 1 to 3, the second connecting pixels of the joint near the first connecting pixel and the second exposure head around the joint of the first exposure head A pixel position specifying step of specifying a position on the reference plane of
Based on the positions of the first connection pixel and the second connection pixel specified in the pixel position specifying step, the first connection pixel and the second connection pixel are connected so that an image is connected to the first connection pixel. An image data correction step for correcting image data input to the exposure head and the second exposure head, and in the image data correction step,
Regarding the displacement in the Y-axis direction between the first connection pixel and the second connection pixel, the distance in the Y-axis direction between the first connection pixel and the second connection pixel and the exposure. Removing by setting the exposure timing of the first exposure head and the second exposure head according to the scanning speed of the head,
Regarding the shift in the X-axis direction between the first joint pixel and the second joint pixel, the first exposure head is configured such that image data overlaps between the first joint pixel and the second pixel. And by inputting image data to the second exposure head
The image shift correction method according to claim 4 . For 3 or more exposure heads,
Specifying the position on the reference plane of the connecting pixels in each image head by the pixel position specifying step;
Image data input to each of the exposure heads is corrected based on the position of the connection pixel specified by the pixel position specifying step so that the image is connected by the connection pixel.
The image shift correction method according to claim 4 or 5 . An exposure unit comprising a plurality of exposure heads capable of selectively turning on / off a plurality of pixels, and exposing the image forming surface while scanning the image forming surface in a fixed direction;
For the measurement of the position of the exposure beam, a beam position detection unit capable of moving on a reference plane along a Y-axis direction parallel to the scanning direction is used. A pixel position specifying means for specifying the position of the pixel of the exposure head by measuring the position of
Exposure control means for controlling the exposure head based on the detection result of the pixel position in the beam position detection means,
The beam position detecting means uses the pixel position specifying method according to any one of claims 1 to 3 to connect a first joint pixel in the vicinity of a joint of the first exposure head and a joint of the second exposure head. Identifying the position of the second connected pixel in the vicinity on the reference plane;
The exposure control unit is configured to generate an image between the first connection pixel and the second connection pixel based on the positions of the first connection pixel and the second connection pixel specified by the pixel position specifying unit. An image forming apparatus for correcting image data input to the first exposure head and the second exposure head so as to be connected. The image forming apparatus according to claim 7 , wherein the pixel position specifying unit includes a pixel position detecting element selected from a two-dimensional PSD, a four-division photodetector, a two-dimensional CCD, and a two-dimensional CMOS as the beam position detecting unit. The exposure head according to claim 7 or 8 comprising a spatial light modulator, selectively on / off the plurality of pixels by the spatial modulation element for modulating light from a light source in accordance with input image data Image forming apparatus. The pixel forming apparatus according to claim 9 , wherein the spatial modulation element includes a plurality of pixels arranged to be inclined with respect to the scanning direction. The image forming apparatus according to claim 10 , wherein the pixels of the spatial modulation element are two-dimensionally arranged.

Images