JP2001150722A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus in which the amount of color shift can be minimized over the entire image region. SOLUTION: Assuming the maximum scan width (width in the main scanning direction printable at an imaging section, 297 mm for A3 size) is 1.0, resist mark detectors 48 are located symmetrically to the center (central part of scan width) at an interval of about 0.9 (about ±130 mm with respect to the center position). More specifically, the resist mark detectors 48 are located symmetrically to the center at an interval of 0.9×L, where L is the maximum width of image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus which forms an image by exposing an image bearing member using an electrophotographic system such as a copying machine, a printer, a facsimile, etc. The present invention relates to an image forming apparatus for forming a multiplex and multi-color image using the image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, in order to speed up color image formation, each color (K: black,
C: cyan, Y: yellow, M: magenta image forming units 102 (102C, 1
02M, 102Y, and 102K) to form a color image. In the image forming apparatus 100, an optical signal obtained by reading an original by the image reading apparatus 104 is separated into signals of R, G, and B by a filter, and this is photoelectrically converted to form an image signal of each color. I do. Each color image signal is sent to the control unit 1
The control unit 106 outputs these image signals to the laser scanning device (ROS unit) 108 of each image forming unit 102 at a predetermined timing. As shown in FIG. 24, each laser scanning device 108 includes a laser light source 110 for emitting a laser beam, and a laser light source 11
A collimator lens 112 for shaping the laser beam emitted from the laser beam into a parallel beam, a rotary polygon mirror 114 for deflecting the parallel beam, and an fθ lens 11 for scanning speed correction
6 and folding mirrors 118 and 12 for guiding the beam passing through the fθ lens 116 onto the photosensitive drum 124.
0, 122, and a start position detection sensor 126 for detecting an image signal write start signal (SOS signal) in the main scanning direction on the photosensitive drum 124. Timing is determined by the image write start signal. While forming a latent image on the photosensitive drum 124.

Next, as shown in FIG. 23, a toner image obtained by depositing a color toner on a latent image by a developing device 128 is transferred to a paper 132 which is sequentially conveyed by a transfer belt 130, and the color image is transferred. The image is fixed by a fixing device (not shown) provided downstream of the image forming apparatus 100 in the conveyance direction. As described above, when the transfer image position in the image forming apparatus having a plurality of image forming units deviates from the ideal position, in the case of a multicolor image, the image intervals of different colors are shifted or overlapped, and in the case of a color image, In
When the difference in the color tone and the degree of the color change become more severe, a color shift appears and the image quality is remarkably deteriorated. These color shifts are caused by a combination of shifts in the sub-scanning direction and the main scanning direction. The color shifts in the main scanning direction are caused by component tolerances of the optical scanning device (for example, flatness of optical components, thickness of lenses, curvature, It occurs due to a component mounting accuracy, a wavelength difference between light sources, a positional shift between the photoconductor and the optical scanning device, and the like.

In FIG. 25, a case where there is no part manufacturing error is shown by a solid line, and a case where a part manufacturing error occurs is shown by a broken line. Originally, the two lines should overlap, but it can be seen that they are shifted due to a part manufacturing error. FIG. 26 shows, as an example, a shift amount when the flatness of a mirror as an optical system varies in manufacturing. Here, the solid line shows the case where the mirror was manufactured as designed, and the broken line shows the manufacturing error and the mirror is on an arc of 8λ per 76.2 mm (3 inches) (143326 mm in r conversion).
, And a color shift of 0.43 mm at the maximum occurs.

To cope with such a problem, Japanese Unexamined Patent Publication No.
According to the technique described in Japanese Patent Application Laid-Open No. 3-66578, a latent image obtained by irradiating a photoreceptor with a light beam at the time of adjusting the apparatus is developed.
A test pattern image is formed on the transfer belt, the deviation of the test pattern position from the specified line is detected, and the time from when the photoconductor detects the light beam to when the image is written out is adjusted based on the deviation. There has been proposed a color image forming apparatus that corrects a transfer deviation by performing the correction. In addition, special fair 05
In the technology described in Japanese Patent Application No. -70149, an image forming apparatus that reads a reference mark after transfer and adjusts an image position and an image width is proposed.

[0006]

However, in the techniques described in JP-A-63-66578 and JP-B05-70149, even if the image writing position and the image recording width are adjusted, the entire image area is not adjusted. This does not mean that the color shift is eliminated. For example, as shown in FIG. 27, when the magnification is corrected at both ends of the image area and the video clock is changed, the position shift does not occur at both ends but the inner position shift remains. FIG. 27 shows each image height position (main scanning direction position) when correcting by changing the video clock in correcting the color shift occurring due to the component tolerance as described above.
FIG. 6 is a diagram showing a difference between misregistrations in a case where there is no part manufacturing error and a case where a manufacturing error occurs, that is, a color misregistration. In this example, the image area is 297 mm of the A3 paper width, and the amount of displacement is 0 mm from the edge in the main scanning direction (image height-1 in FIG. 27).
48.5 mm) and a distance of 297 mm from the end in the main scanning direction (FIG. 2).
7, the image writing position and the magnification are adjusted in accordance with the detected shift amount. Although the occurrence of color misregistration is 0 at both ends of the image, FIG.
Image height of about -90 mm and about 3 in the vicinity of about 90 mm
A color shift of 5 μm has occurred. It should be noted that the color misregistration tends to be suddenly noticeable visually when it exceeds a certain amount, and the above-described color misregistration becomes a serious problem for an image.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and has as its object to provide an image forming apparatus capable of minimizing the amount of color misregistration over the entire image area.

[0008]

According to a first aspect of the present invention, there is provided an image forming apparatus for forming an image on the basis of image data representing an image, and a main scan by the image forming means. A pair of detection means for detecting the positional deviation in the direction, based on the detection result of the detection means, magnification correction and writing position correction at the time of image formation, and image correction including left and right magnification correction and writing position correction, A correction unit that performs at least one image correction, wherein the correction result by the correction unit is the largest in the main scanning direction with respect to the maximum image width that can be formed by the image forming unit. It is characterized in that the detection means is arranged at a position where the size is reduced.

As in the conventional image forming apparatus, when detecting means are arranged at both ends of the maximum image area where an image is formed, and image correction such as magnification correction or left / right magnification correction during image formation is performed, detection is performed. Since the image correction is performed based on the position where the means is arranged, the position shift at the positions at both ends of the maximum image area is corrected, but the position shift in the area inside the area cannot be suppressed. Therefore, according to the first aspect of the present invention, the position where the detecting unit is arranged is set to the position where the positional deviation in the main scanning direction in the correction result by the correcting unit is minimized with respect to the maximum image width. The displacement can be minimized over the entire area. That is, the amount of color misregistration can be minimized over the entire image area.

The image forming apparatus only needs to have a detecting means for detecting a positional shift in the main scanning direction, and can be applied to, for example, a printer or a copying machine for recording an image by optical scanning. It is.

According to a second aspect of the present invention, in the first aspect, the image forming means comprises a scanning optical device for forming an image using a plurality of light beams.

According to the invention described in claim 2, according to claim 1,
In the invention described in (1), the image forming unit can be applied to a scanning optical device that forms an image by optically exposing a photosensitive member or the like using a plurality of light beams.

According to a third aspect of the present invention, in the first or the second aspect of the present invention, an interval between the pair of detecting means is substantially 0.9, where 1 is the maximum image width. It is characterized by being equally distributed based on the center of the maximum image width.

According to the invention described in claim 3, according to claim 1 of the present invention,
Alternatively, in the invention according to claim 2, the interval between the pair of detecting means is a ratio of about 0.9, where the maximum image width is 1, and the detection means are equally distributed based on the center of the maximum image width. Accordingly, it is possible to minimize the displacement in the main scanning direction with respect to the entire image width region. It is more preferable to arrange a pair of detection means at a position where the ratio is 0.84 to 0.95.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the correcting means changes a scanning magnification by changing an optical path length in the image forming means. Is changed.

According to the invention described in claim 4, according to claim 1 of the present invention,
4. The apparatus according to claim 3, wherein the correction unit changes an optical path length in the image forming unit (for example, a distance to a recording medium such as a photoconductor on which light is scanned) to perform main scanning. You can change the magnification. For example, in the case of an image forming apparatus that forms an image by scanning light from a light source with a rotating polygon mirror and irradiating the photosensitive member through a reflecting mirror, the optical path length to the photosensitive member by moving the reflecting mirror or the like. Is adjusted, it is possible to change the main scanning magnification.

According to a fifth aspect of the present invention, in the first aspect of the present invention, the correction means changes a clock frequency used when performing image formation. Features.

If the frequency of the clock (image clock) used for image formation is reduced (the period is increased),
As the image recording width increases and the frequency of the image clock increases (the period decreases), the image recording width decreases. Therefore, according to the invention described in claim 5, in the invention described in any one of claims 1 to 3, the correction unit changes the frequency of the image clock according to the detection result of the detection unit. Thus, the main scanning magnification can be changed.

According to a sixth aspect of the present invention, in the first aspect of the present invention, the correction means changes the clock frequency during one-line scanning. It is characterized in that the right and left magnification correction is carried out by means of.

According to the invention of claim 6, according to claim 1,
In the invention according to any one of claims 3 to 3, the correction means changes the image clock frequency in the course of one-line scanning, thereby, for example, detecting a difference between left and right magnifications centered on the center of one line. Can be corrected.

According to a seventh aspect of the present invention, in the first aspect of the present invention, there is provided an image processing apparatus comprising: a plurality of the detecting means; The image processing apparatus further includes a width detection unit, wherein a detection unit to be used is selected from the plurality of detection units according to a detection result of the image region width detection unit.

According to the invention of claim 7, according to claim 1,
According to the present invention, the width of image recording, for example, the width of a sheet to be output is detected by the image area width detecting means, and the width of the plurality of detecting means is used in accordance with the detection result. By selecting the detection means, it is possible to always perform image correction using the detection means arranged at the position of about 0.9 according to the image area width. Therefore, the color shift amount can be minimized over the entire image area.

According to an eighth aspect of the present invention, in the first aspect of the present invention, there is provided a moving means for moving a position of the detecting means, and an image area width for detecting an image area width for forming an image. The image processing apparatus further includes a detecting unit, wherein the position of the detecting unit is moved by the moving unit in accordance with a detection result of the image area width detecting unit.

According to the invention described in claim 8, according to claim 1,
7. The image forming apparatus according to claim 6, wherein the image area width detecting means detects a width at which the image is recorded, for example, a width of a sheet to be output, and moves the moving means according to the detection result. According to the area width, the above-mentioned value of approximately 0.1.
9, the detection means can be moved. Therefore,
The color shift amount can be minimized over the entire image area.

According to a ninth aspect of the present invention, there is provided an image forming means for forming an image based on image data representing an image, a detecting means for detecting a displacement in the main scanning direction by the image forming means, A correction unit that performs at least one image correction among image correction including magnification correction and writing position correction at the time of image formation and right and left magnification correction and writing position correction based on the detection result of the unit. A forming apparatus, based on a detection result by the detection unit,
Calculating means for calculating a clock frequency when forming an image so that the positional deviation in the main scanning direction is minimized over the entire image width for recording the image; and forming the image in accordance with the calculation result of the calculating means. And determining means for determining the timing of the operation.

As described above, the position where the detecting means is arranged is set to a position where the maximum image width (for example, the image recording width in the main scanning direction) is 1, and the ratio is about 0.9 at the center distribution. Although the amount of color misregistration can be minimized over the entire image area, there is a case where the detecting means cannot be arranged at a position having the ratio of about 0.9 due to the structure of the apparatus. Therefore, according to the ninth aspect of the present invention, the calculating means calculates the clock (image clock) frequency at the time of forming an image so that the displacement in the main scanning direction is minimized over the entire image width. For example, a correction value is calculated in advance when it is assumed that the detection unit is located at a position having a ratio of about 0.9 when the maximum image width (for example, the image recording width in the main scanning direction) is set to 1 at the center distribution. By calculating the image clock from the correction value, it is possible to obtain an image clock for performing the same image correction as the one arranged at the position having the ratio of about 0.9. Further, the deciding means decides the timing of forming an image in accordance with the image clock frequency obtained by the calculating means, so that the same image correction as the one arranged at the position of the ratio of about 0.9 can be performed. it can. Therefore, the color shift amount can be minimized over the entire image area.

In other words, according to the ninth aspect of the present invention, the image area width varies depending on the paper size or the like when the detection means cannot be arranged at the position having the ratio of about 0.9 due to the structure of the apparatus. In this case, the same image correction can be performed as when the detection unit is arranged at a position having a ratio of about 0.9.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. In this embodiment, the present invention is applied to a tandem type color image forming apparatus.

FIG. 1 is a perspective view schematically showing a color image forming apparatus 10 according to a first embodiment of the present invention.

The color image forming apparatus 10 includes an image forming section 12 (12C, 12C, 12C) for each color provided with a developer (toner) of each color of cyan (C), magenta (M), yellow (Y), and black (K). 12M, 12Y, and 12K), and the image forming unit 12 includes a photosensitive drum 14 for each color.
(14C, 14M, 14Y, 14K) are provided. Around this photosensitive drum 14, a primary charger (not shown) for uniformly charging, and a scanning optical device (scanning optical system) as an image writing means (latent image forming means).
16 (16C, 16M, 16Y, 16K), a developing device (not shown) for visualizing the latent image with toner, a cleaner, and a transfer charger are provided.

The scanning optical device 16 is, as shown in FIG.
A laser light source 24 for emitting a laser beam is provided, which comprises a semiconductor laser 18, a collimator lens 20, and a stop 22, and a condensing lens for condensing the laser beam emitted from the laser light source 24 on the emission side of the laser light source 24. 26, a cylindrical lens 28 for condensing the laser beam in a predetermined direction and a reflection mirror 30 are sequentially arranged. On the light reflection side of the reflection mirror 30, there is provided a rotary polygon mirror 32 that deflects the laser beam by rotating in the direction of arrow R in FIG. 2 around the rotation axis 0. The deflected laser beam is deflected. The laser beam is incident on an fθ lens 34 provided to make the scanning speed of the laser beam substantially constant. The fθ lens 34 includes two lenses 34A,
34B.

The laser beam transmitted through the fθ lens 34 is irradiated onto the photosensitive drum 14 via two reflecting mirrors 36 and 38 and a cylindrical mirror 40,
Light is scanned in the direction of arrow Q in FIG. 2 by the rotation of the rotary polygon mirror 32. A latent image is formed on the photosensitive drum 14 by rotating the photosensitive drum 14 in the direction of arrow S in FIG.

The surface formed by the trajectory of the laser beam reflected and deflected by the rotary polygon mirror 32 is the main scanning surface, and the direction in which the main scanning surface and the photosensitive drum 14 intersect is the main scanning direction. A direction that intersects (especially orthogonal) with the main scanning plane is defined as a sub-scanning direction.

A reflection mirror 42 is provided on the scanning start side between the cylindrical mirror 40 and the photosensitive drum 14, and the writing position is fixed on the light reflection side of the reflection mirror 42 for each line (main scanning direction). The start position detection sensor 44 detects that the laser beam has reached a specific position in the pre-scanning stage of image recording and outputs a detection signal.
Is provided.

Image writing is started after a predetermined time elapses with reference to the detection signal of the start position detection sensor 44. By changing the predetermined time, the image writing position can be changed. FIG. 3 shows a start position detection sensor 44.
5A and 5B are diagrams showing the relationship between the output signal of FIG. 5 and the image writing start timing, wherein FIG. 6A shows the output signal from the start position detection sensor 44, and FIG. 6B shows the output obtained by delaying the output signal of FIG. (C) shows an image clock synchronized with (B), and (D) shows an image writing timing signal. The image writing timing signal is generated after counting the image clock (cycle s) n times (after T time) after the output signal of (B). The image is a point A on the photosensitive drum 14.
Recorded. The image writing point A can be changed by changing the count number n of the image clock and the above-mentioned delay time t.

The scanning optical device 16 includes an actuator 4 composed of, for example, a linear stepping motor.
6 (see FIG. 1), the scanning optical device 16 is moved in the vertical direction (up and down direction in FIG. 1) in accordance with the detection timing of the registration mark image detected by the registration mark detector 48 described later, It is configured so that the magnification error of the scanning line can be adjusted.

Below the photosensitive drum 14, a conveyor belt 50 constituting a conveyor is provided.
No. 0 is wound around the drive roller 52 and the driven roll 54 with a predetermined tension. The drive roller 50 is provided with a belt drive motor 56, and the transfer belt 50 is transferred at a constant speed P (mm / sec) in the direction of arrow B in FIG. Note that the transport body is not limited to the transport belt 50, and may be, for example, an intermediate transfer body, roll paper, cut paper, or the like.

Further, on the downstream side of the final image forming section (the image forming section for K color in the present embodiment) 12K in the conveying direction of the conveying belt 50, an image reading sensor generally used in a facsimile or the like is similar. Charge coupled device 5 such as CCD
8, a registration mark detector 48 composed of a lens 60 and a lamp 62 for irradiating light is provided. The registration mark detector 48 sets the maximum scanning width (the width in the main scanning direction in which printing can be performed by the image forming unit 12, in the present embodiment, 297 mm of A3 size) to 1.0, and sorts the center (the center of the scanning width). Approximately 0.9 (approximately ± 13 to center position
0 mm) (hereinafter, approximately 0.9 mm of the maximum scanning width).
). That is, as shown in FIG.
It is arranged at a position of 9 × L.

The registration mark detector 48 uses a ramp to display the registration mark transferred by each photosensitive drum 14 between the transfer papers of the transfer paper P on the conveyor belt 50 (between each image area). The registration mark is detected by receiving, via the lens 60, the reflected light of the light emitted from 62 to the conveyor belt 50. The registration mark image formed by each image forming unit 12 constituting the registration mark is transferred to the conveyance belt 50 as shown in FIG.
It is transferred substantially parallel to the transport direction and at a predetermined interval.
Further, the registration mark image is transferred between the transfer papers P of the transfer paper P continuously transported on the transport belt 50, or with high precision as needed. Further, the registration mark detector 48 is configured to output image data corresponding to each detected registration mark image to a displacement correction processing circuit 66 described later.

The registration mark transferred to the conveyor belt 50 is configured to be collected by the cleaner member 64.

Next, the position shift correction processing circuit 66 will be described with reference to FIG.

The position shift correction processing circuit 66 includes a start position detection sensor 44 and a registration mark
8 is connected. The above-described actuator 46 for moving the scanning optical device 16 via a driver 70 is connected to the CPU 68, and the start position detection sensor 4
The laser light source 24 is connected via a delay circuit 72 for delaying the output signal of the device No. 4 for a time t, a synchronization circuit 74 for generating an image writing timing signal, and a driver 76 for driving the laser light source 24.

Next, the operation of the color image forming apparatus 10 configured as described above will be described.

First, the registration mark formed by the image forming unit 12 for each color is registered with the registration mark detector 4.
The image data detected by the registration mark detector 8 and obtained by the registration mark detector 48 is output to the displacement correction processing circuit 66. In the misregistration correction processing circuit 66, the misregistration amount of the registration mark for each color is calculated by the CPU 68, and the movement amount of the scanning optical device 16 of the image forming unit 12 is calculated based on the calculation result. Then, a signal for driving the actuator 46 according to the calculated movement amount is output to the driver 70, and the driver 46 drives the actuator 46 to move the scanning optical device 16. The distance of the body drum 14 is adjusted, and the magnification in the main scanning direction at the time of writing an image is corrected.

In the image forming units 12 for each color, the laser beam is detected by the start position detection sensor 44 and a detection signal is output to the CPU 68. The CPU 68 generates a delay time t for generating the image writing timing signal based on the detection signal output from the start position detection sensor 44 of each color, and a signal obtained by delaying the detection signal of the start position detection sensor 44 by t time. Is calculated, and an image writing timing signal is generated based on the calculation result. Then, the driving of the laser light source 24 is controlled by the driver 76 based on the image writing timing signal, so that the image writing position in the main scanning direction at the time of writing the image is adjusted. Note that the order of performing the magnification correction and the adjustment of the image writing position may be reversed,
The magnification correction may be performed again, such as magnification correction, image writing position adjustment, and magnification correction.

When the registration mark detectors 48 are provided at both ends of the image area as in the prior art, the color shift is corrected based on both ends of the image area. Although no shift occurs, a color shift occurs due to a position shift in a region inside the shift. Therefore, in the present embodiment, the registration mark detector 48 is arranged at a position of about 0.9 of the maximum scanning width (maximum image area width), and the color misregistration is corrected based on this position.
The color shift is minimized in the entire image area.

As for the color misregistration, the image height position (the position of the image area in the main scanning direction) where the color misregistration is maximum differs depending on the location where the registration mark detector 48 is arranged. 48 is the maximum scanning width (A3 paper width of 297 mm) of 1.0 (0 mm and 1 mm from the terminal in the image area).
48.5mm), 0.94 (8.5mm and 288.5mm from the end of the image area), 0.88 (18.5mm and 278.5mm from the end of the image area), 0.7
1 shows the measurement results of the color misregistration amounts at the positions of 1 (43.5 mm and 253.5 mm from the terminal in the image area), but the image height position at which the color misregistration is maximum differs. You can see that.

Each of the registration mark detectors 4
FIG. 7 is a plot of the amount of color misregistration at both ends (end sides) of the scanning width and the largest amount of color misregistration at the center (center) in the scanning width region at the arrangement position 8. Show. FIG. 7 shows that when the registration mark detector 48 is arranged at the position of 0.87 of the maximum scanning width and the color misregistration is corrected based on the position, the color misregistration amount becomes small over the entire scanning width. Table 1 shows an outline of optical data after the rotating polygon mirror at this time.

[0049]

[Table 1]

As described above, by disposing the registration mark detector 48 at a position of about 0.9 of the maximum scanning width, the displacement in the main scanning direction in the entire main scanning direction can be minimized. .

[Second Embodiment] The color image forming apparatus 10 according to the first embodiment corrects the magnification in the main scanning direction by moving the scanning optical device 16. The image forming apparatus 11 corrects the magnification by changing the frequency of the image clock. Therefore, the color image forming apparatus 1 of the first embodiment
Actuator 46 provided in the scanning optical device 16
Since the scanning optical device 16 is fixed and the only difference is the misalignment correction processing circuit 66, and the other configuration is the same, the description is omitted. Note that the registration mark detector 48 of the color image forming apparatus 11 of the second embodiment is also disposed at a position of about 0.9 of the maximum scanning width similarly to the first embodiment.

Next, a misregistration correction processing circuit 67 in the color image forming apparatus 11 of the second embodiment will be described with reference to FIG.
This will be described with reference to FIG.

The misregistration correction processing circuit 67 of the second embodiment
As in the first embodiment, the start position detection sensor 44 and the registration mark detector 48 are connected to the CPU 68. The CPU 68 has a delay circuit 72 for delaying the output signal of the start position detection sensor 44 for a time t, a synchronization circuit 74 for generating an image writing timing signal, and a laser light source 2 via a driver 76 for driving the laser light source 24.
4 is connected, and an image clock frequency changing circuit 78 is connected. The image clock frequency change circuit 78 is connected to the driver 76 and is configured to adjust the frequency of the image clock for writing an image.

Next, the operation of the second embodiment will be described.

The registration mark formed by the image forming section 12 for each color is detected by the registration mark detector 48, and the image data obtained by the registration mark detector 48 is output to the misregistration correction processing circuit 67. In the misregistration correction processing circuit 67, the misregistration amount of the registration mark for each color is calculated by the CPU 68, and the image clock frequency at the time of image writing is calculated based on the calculation result. Then, the image clock frequency is changed by the image clock frequency changing circuit 78 according to the calculated image clock frequency, and the driving of the laser light source 24 is controlled by the driver 76, so that the image clock at the time of writing the image is changed. Thus, the magnification in the main scanning direction is corrected. That is, when the image clock frequency changing circuit 78 increases the frequency S of the image clock shown in FIG. 3B (decreases the frequency), the image recording width increases, and conversely, when the frequency S decreases, the image recording width decreases. Therefore, the magnification can be changed by changing the frequency according to the amount of displacement.

In the image forming units 12 for each color, the laser beam is detected by the start position detecting sensor 44 and a detection signal is output to the CPU 68. The CPU 68 calculates the delay time t described in the first embodiment for generating the image writing timing signal and the detection signal of the start position detection sensor 44 based on the detection signal output from the start position detection sensor 44 of each color. The count number n of the signal synchronized with the signal delayed by the time t is calculated, and the image writing timing signal is generated based on the calculation result. Then, the driving of the laser light source 24 is controlled by the driver 76 based on the image writing timing signal, so that the image writing position in the main scanning direction at the time of writing the image is adjusted.
Note that the order of performing the magnification correction and the adjustment of the image writing position may be reversed, or the magnification correction may be performed again such as the magnification correction, the image writing position adjustment, and the magnification correction.

Here, in the color image forming apparatus 11 according to the second embodiment, when the magnification correction and the adjustment of the image writing position are performed, the amount of color shift at both ends of the scanning width and the color at the center in the scanning width area. FIG. 9 shows a plot of the color shift amount where the shift amount is the largest as in FIG. In the second embodiment, it can be seen from FIG. 9 that when the registration mark detector 48 is arranged at the position of 0.88 of the maximum scanning width, the color misregistration amount becomes small over the entire scanning width.

That is, also in the second embodiment, the registration mark detector 48 is arranged at a position of about 0.9 of the maximum scanning width, similarly to the first embodiment, so that the color shift is determined by the scanning width (image area width). ) It can be minimized over the whole area.
Further, in the second embodiment, since magnification correction can be performed without moving the scanning optical device 16 or the mirror, the other optical performance (for example, focus position, lead registration, tilt correction performance, etc.) is not changed. , The color shift can be minimized over the entire scanning width.

Subsequently, when the magnification correction and the image writing position are adjusted by another scanning optical device (a scanning optical device having different optical data), the detection position ratio-color obtained in the same manner as in FIGS. The characteristics of the shift amount are shown in FIGS.
Tables 2 and 3 show the optical data after the rotating polygon mirror at that time.
Shown in Note that the scanning optical device shown in FIG.
This shows a configuration in which the number of folding mirrors is one less.

[0060]

[Table 2]

[0061]

[Table 3]

In the case of another scanning optical device, as shown in FIGS. 10 and 11, when the registration mark detector 48 is arranged at the position of 0.88 (approximately 0.9) of the maximum scanning width, the amount of color misregistration is reduced. It can be seen that it becomes smaller over the entire scanning width. Therefore, as in the first embodiment and the second embodiment, the registration mark detector 48 is set to a maximum scanning width of about 0.9, preferably,
By arranging them at the positions of 0.84 to 0.94, the color shift amount can be minimized over the entire scanning area. The results of FIGS.
, The thickness of the fθ lens 34 (34A, 34B),
This includes the component error of the positional deviation of the fθ lens 34 (34A, 34B), and the relationship between the detection position ratio and the amount of color deviation for each component error is as shown in Tables 4 to 9, and FIG. It looks like 14.

[0063]

[Table 4]

[0064]

[Table 5]

In Tables 4 and 5, when the cylindrical mirror 40 has a tolerance of r = 143326 mm, the mirror 38 has a tolerance of r = 143326 mm, and the mirror 36 has r = 143326 mm. When the thickness of the lens 34A has a tolerance of 0.3 mm, when the thickness of the lens 34B has a tolerance of 0.3 mm, the position error of the lens 34A When the tolerance of 0.3 mm is set, it indicates when the tolerance of the position error of the lens 34B is 0.3 mm, and Tables 4 and 5 are shown in FIG.

[0066]

[Table 6]

[0067]

[Table 7]

Tables 6 and 7 show when the mirror has a tolerance, when the cylindrical mirror 40 has a tolerance, when the thickness of the lens 34A has a tolerance, and when the lens 34B has a tolerance. When there is a tolerance on the thickness of
When the position error of A has a tolerance, the position error of the lens 34B has a tolerance, and Tables 6 and 7 are shown in FIG.
Shown in

[0069]

[Table 8]

[0070]

[Table 9]

Tables 8 and 9 show that the mirror 36 has a tolerance, the cylindrical mirror 40 has a tolerance, the mirror 38 has a tolerance, and the thickness of the lens 34A. When there is a tolerance, there is a tolerance on the thickness of the lens 34B, when there is a tolerance on the position error of the lens 34A, and when there is a tolerance on the position error of the lens 34B. And Tables 8 and 9 are shown in FIG.

[Third Embodiment] In the second embodiment, the registration mark detector 48 is arranged at a position of about 0.9 in the image area. However, in the third embodiment, the color mark of the second embodiment is used. In the image forming apparatus 10, the configuration is arranged at both ends (1.0) of the image area, and the other configuration is the same as that of the second embodiment.

In the third embodiment, even if the magnification correction and the adjustment of the image writing position are performed in this state, the color shift remains large.

If the period of the image clock obtained for adjusting the magnification in the case where the component tolerance is included (specifically, when a manufacturing error of R = 143326 mm occurs in the final mirror) is assumed to be T1, the registration mark Set the detector 48 to the maximum scan width of 0.94 (8.5 mm and 288.5 mm), 0.88
(18.5mm and 278.5mm), 0.71 (43.5mm
And 253.5 mm), the image clock frequency in that case is 0.94, 0.8 of the maximum image area.
The image clock frequencies of 8, 0.71 are T2, T1, respectively.
3, and T4, T2 = 0.9995 × T1, T3 =
0.9988 × T1, T4 = 0.9969 × T1. The values are almost the same even when other component tolerances occur.

Therefore, in the third embodiment, although the registration mark detector 48 is not located at a position of about 0.9 of the maximum scanning width,
The CPU 68 calculates the image clock frequency by multiplying the detection result at other positions (in this embodiment, both ends of the image area) by a predetermined coefficient, and thereby the registration mark is placed at the position of 0.9 of the maximum scanning width. The same correction as when the detector 48 is arranged is performed. Therefore, by calculating a predetermined coefficient for multiplying the image clock frequency in advance, the same effect as in the second embodiment can be obtained.

In the present embodiment, a plurality of coefficients (coefficients obtained by assuming that the registration mark detector 48 is arranged at a ratio to a plurality of maximum widths) are used as predetermined coefficients for multiplying the image clock frequency in advance. Is stored, it is possible to perform color misregistration correction according to the sheet width.

In the first to third embodiments, the registration mark detector 48 is arranged at a position of about 0.9 of the maximum scanning width. That is, the two registration mark detectors 48
Is arranged, but by further arranging one registration mark detector 48 at the center of the scanning width,
Detecting a position shift at the center of the scanning width, and detecting one position in the main scanning direction.
A configuration in which the frequency of the image clock is varied while scanning the line to correct the difference in left and right magnification (for example, Japanese Patent Application No. 10-62).
The image forming apparatus described in Japanese Patent Publication No. 700) may be used. The measurement result of the detection position ratio-color shift amount at this time is shown in FIG.
To 17 are shown. FIGS. 15 to 17 show the case where the same mirror tilt and fθ lens tilt component error as in FIGS.

The registration mark detector 4 is shown in FIGS.
8 are arranged at 0.92, 0.94, and 0.93 positions to correct the difference between the right and left magnifications, thereby reducing the amount of color shift caused by the difference between the right and left magnifications over the entire scanning area in the main scanning direction. Can be minimized. The results in FIGS. 15 to 17 include the component errors of the mirror flatness, the thickness of the fθ lens, and the positional deviation of the fθ lens. The relationship between the detection position ratio and the color deviation amount for each component error is as follows. The results are as shown in Tables 10 to 15, and as shown in FIGS.

[0079]

[Table 10]

[0080]

[Table 11] Tables 10 and 11 show that when the mirror 36 has a tolerance of 0.2 °, the mirror 38 has a tolerance of 0.2 °, and the mirror 38 has a tolerance of 0.2 °. When there is a tolerance, when the lens 34A has a tolerance of 0.1 °, when the lens 34B has a tolerance of 0.1 °, there is a tolerance on the optical system in front of the rotary polygon mirror. 18 and Tables 10 and 11 are shown in FIG.

[0081]

[Table 12]

[0082]

[Table 13] Tables 12 and 13 show when the inclination of the mirror 36 has a tolerance, when the inclination of the mirror 38 has a tolerance,
Is when there is a tolerance on the tilt of the cylindrical mirror 40,
Indicates a time when the inclination of the lens 34A has a tolerance, a time when a tolerance has occurred on the inclination of the lens 34B, and a time when the optical system in front of the rotary polygon mirror has a tolerance. Tables 12 and 13 Is shown in FIG.

[0083]

[Table 14]

[0084]

[Table 15]

Tables 14 and 15 show the mirror 36.
When the tolerance of the inclination of the cylinder mirror 40 has a tolerance, there is a tolerance on the inclination of the lens 34A. When the tolerance of the inclination of the lens 34B has a tolerance,
Indicates when the optical system in front of the rotating polygon mirror has a tolerance,
Table 14 and Table 15 are shown in FIG. FIG. 20 (Table 1)
4 and Table 15) show a configuration having one less folding mirror.

In the above description, the registration mark detector 4
The description has been given of the image forming apparatus in which two magnification corrections are provided to correct the magnification, or the three correction marks are used to correct the difference between the right and left magnifications. More than one may be provided. For example, when the registration mark detector 48 is 15.5 mm, 34.5 mm, 54.5 mm, 148.
7 of 5mm, 242.5mm, 262.5mm, 281.5mm
In addition to the above arrangement, there is provided a detecting means for detecting a different image area width depending on the paper size or the like (see FIG. 21).
Then, the size of the output paper or the like selected by the color image forming apparatus (the image area width detected by the detection unit)
The registration mark detector 48 to be used may be selectively used according to the above. Specifically, when a sheet of A3 width is selected, the registration mark detector 48 arranged at 15.5 mm, 281.5 mm, or 15.5 mm, 148.5 mm, or 281.5 mm is used. And B
If a sheet of width 4 is selected, 34.5 mm, 26
2.5mm, or 34.5mm, 148.5mm, 26
The registration mark detector 48 arranged at 2.5 mm is used, and when A4 width paper is selected, 5
4.5mm, 242.5mm, or 54.5mm, 14
The magnification correction and the image writing position correction are performed using the registration mark detectors 48 arranged at 8.5 mm and 242.5 mm. By using the registration mark detector 48 arranged at a position where the width of the paper to be output is approximately 0.9 as described above,
By performing magnification correction and image writing position correction,
Regardless of the paper size or the like, the amount of color misregistration can be minimized over the entire scanning area.

Further, the two registration mark detectors 48 may be provided with a moving mechanism provided with two registration mark detectors 48 so as to be movable in accordance with the size of the sheet. For example, as shown in FIG. 22, the moving mechanism 80 is provided with a pinion gear 84 on a rotating shaft 82A of a motor 82, a rack gear 86A corresponding to the pinion gear 84, and a member 86 on which the registration mark detector 48 is arranged. It is arranged to be movable in the main scanning direction. Then, the moving mechanism 80
Is arranged so that the motor 82 rotation shaft 82A is located at the center of the image recording area, or is arranged such that the registration mark detector 48 moves around the center of the image recording area, and according to the size of the paper or the like. By rotating the motor 82, the member 86 is moved to an arbitrary target position around the image area by rotation of the pinion gear 84, and the registration mark detector 48 is set to the maximum image area according to the paper size or the like. Can be moved to a position of about 0.9.

[0088]

As described above, according to the present invention, the detecting means for detecting the displacement in the main scanning direction is arranged at the position where the displacement in the main scanning direction is the smallest with respect to the maximum image width. In addition, there is an effect that an image forming apparatus capable of minimizing the amount of color misregistration over the entire image area can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view illustrating a schematic configuration of a scanning optical device.

3A shows an output signal from a start position detection sensor, FIG. 3B shows an output signal obtained by delaying the output signal of FIG. 3A by t time, and FIG. 3C shows a signal synchronized with FIG. 5D shows an image clock, and FIG. 5D shows an image writing timing signal.

FIG. 4 is a diagram showing an arrangement of a registration mark detector.

FIG. 5 is a block diagram illustrating a schematic configuration of a misregistration correction processing circuit according to the first embodiment.

FIG. 6 is a diagram showing that the amount of color misregistration varies depending on where the registration mark detector is arranged.

FIG. 7 is a diagram illustrating a registration mark detector position and a color shift amount according to the first embodiment.

FIG. 8 is a block diagram illustrating a schematic configuration of a misregistration correction processing circuit according to a second embodiment.

FIG. 9 is a diagram illustrating a registration mark detector position and a color shift amount according to the second embodiment.

FIG. 10 is a diagram illustrating a registration mark detector position and a color shift amount in another scanning optical device (optical data scanning optical device in Table 2).

FIG. 11 is a diagram showing a registration mark detector position and a color shift amount in another scanning optical device (optical data scanning optical device in Table 3).

FIG. 12 is a diagram showing the position of a registration mark detector and the amount of color misregistration (Tables 4 and 5) for each component having a tolerance in the second embodiment.

FIG. 13 is a diagram showing a position of a registration mark detector and a color shift amount (Tables 6 and 7) for each component having a tolerance.

FIG. 14 is a diagram showing a position of a registration mark detector and a color shift amount (Tables 8 and 9) for each component having a tolerance.

FIG. 15 is a diagram illustrating the position of a registration mark detector and the amount of color misregistration for each component having a tolerance shown in Table 1 in the image forming apparatus that corrects the horizontal magnification.

FIG. 16 is a diagram showing the position of a registration mark detector and the amount of color misregistration for each component having a tolerance shown in Table 2 in the image forming apparatus for correcting the horizontal magnification.

FIG. 17 is a diagram illustrating the position of the registration mark detector and the amount of color misregistration for each component having the tolerance shown in Table 3 in the image forming apparatus that corrects the horizontal magnification.

FIG. 18 is a diagram illustrating a position of a registration mark detector and an amount of color misregistration (Table 10 and Table 11) for each component having a tolerance in the image forming apparatus that corrects the lateral magnification.

FIG. 19 is a diagram illustrating a position of a registration mark detector and an amount of color misregistration (Tables 12 and 13) for each component having a tolerance in the image forming apparatus that corrects the horizontal magnification.

FIG. 20 is a diagram illustrating a position of a registration mark detector and an amount of color misregistration (Table 14 and Table 15) for each component having a tolerance in the image forming apparatus that corrects the lateral magnification.

FIG. 21 is a diagram showing an arrangement example when a plurality of registration mark detectors are arranged.

FIG. 22 is a diagram illustrating an example of a moving mechanism.

FIG. 23 is a schematic view of an image forming apparatus for explaining a conventional technique.

FIG. 24 is a schematic view of a laser scanning device for explaining a conventional technique.

FIG. 25 is a schematic diagram for explaining color misregistration in the main scanning direction.

FIG. 26 is a diagram illustrating a positional shift amount in the main scanning direction when there is no component tolerance and when there is a component tolerance;

FIG. 27 is a diagram illustrating the amount of color misregistration in the main scanning direction when a component tolerance is present.

[Explanation of symbols]

 Reference Signs List 10 color image forming apparatus 11 color image forming apparatus 12 image forming section 16 scanning optical apparatus 46 actuator 48 registration mark detector 66 misregistration correction processing circuit 67 misregistration correction processing circuit 78 image clock frequency change circuit 80 moving mechanism

 ────────────────────────────────────────────────── ─── Continued on the front page F-term (reference) 2C362 AA10 BA04 BA50 BA52 BA69 CA22 CA39 2H030 AA01 AB02 AD12 2H045 AA01 BA02 BA22 BA34 CA88 CA97 DA02 5C072 AA03 BA17 BA19 HA02 HA06 HA13 HB08 HB11 HB20 QA14 QA17 RA01 A03 AB BB CC22 DD08 DD15 EE04 HH02 HH04

Claims (9)

[Claims] 1. An image forming means for forming an image based on image data representing an image, a pair of detecting means for detecting a displacement in a main scanning direction by the image forming means, and a detecting result of the detecting means. A correction unit that performs at least one image correction among magnification correction and writing position correction at the time of image formation, and image correction including right and left magnification correction and writing position correction based on the image formation. An image forming apparatus, wherein the detection unit is arranged at a position where the positional deviation in the main scanning direction is smallest with respect to a maximum image width that can be formed by the image forming unit as a result of the correction by the correction unit. 2. The image forming apparatus according to claim 1, wherein the image forming unit includes a scanning optical device that forms an image using a plurality of light beams. 3. A distance between said pair of detecting means is substantially 0.9, wherein said maximum image width is 1, and said detection means are equally distributed based on a center of said maximum image width. The image forming apparatus according to claim 1 or 2, wherein 4. The image forming apparatus according to claim 1, wherein the correcting unit changes a scanning magnification by changing an optical path length in the image forming unit. apparatus. 5. The image according to claim 1, wherein the correction unit performs magnification correction by changing a clock frequency used when forming an image. Forming equipment. 6. The image according to claim 1, wherein the correction unit corrects the right and left magnification by changing the clock frequency during one-line scanning. Forming equipment. 7. The image processing apparatus according to claim 1, further comprising: a plurality of said detecting means, further comprising an image area width detecting means for detecting an image area width for forming an image, wherein said plurality of detecting means are provided in accordance with a detection result of said image area width detecting means. The image forming apparatus according to claim 1, wherein a detection unit to be used is selected. 8. An image forming apparatus according to claim 1, further comprising a moving unit for moving a position of said detecting unit, and an image region width detecting unit for detecting an image region width for forming an image. The image forming apparatus according to claim 1, wherein a position of the detection unit is moved by a movement unit. 9. An image forming means for forming an image based on image data representing an image, a detecting means for detecting a displacement in the main scanning direction by the image forming means, and a detecting means for detecting a positional deviation in the main scanning direction. A correction unit for performing at least one image correction among image correction including magnification correction and writing position correction at the time of image formation, and right and left magnification correction and writing position correction. Calculating means for calculating a clock frequency at the time of forming an image based on a detection result by the detecting means so as to minimize the positional deviation in the main scanning direction over the entire image width in which an image is recorded; and An image forming apparatus comprising: a determination unit that determines a timing at which image formation is performed according to a calculation result.