JPH08156332A - Image-forming device - Google Patents

Abstract

PURPOSE: To obtain an image-forming device capable of removing or relieving distortion of an image due to difference in magnification between right and left sides when a light beam polarized by a polarizing means is scanned on a photosensitive body for recording the image. CONSTITUTION: A laser beam 123Y to be jetted from a semiconductor laser 121Y is converged by an optical lens 124Y and applied to a polygon mirror 107Y. Its reflected light passes through an fγlens 125Y, passes through a right and left magnification difference correction device 126Y having a parallel plate 131Y, and arrives at a photosensitive drum 106Y. The parallel plate 131Y rotates with center at axes of rotations 132Y and 133Y. According to the angle of rotation, a difference in length (a-b) between a forward half part and a backward half part of a scanning line can be corrected.

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 such as a copying machine, a laser printer, a facsimile machine, etc., and more specifically, to correction of an unbalance between left and right of the optical image in the main scanning direction or the first half and the second half of the scanning. The present invention relates to an image forming apparatus provided with a mechanism for performing.

[0002]

2. Description of the Related Art With the colorization of printed matter and computer information in offices and homes, the demand for multicolor recording or color recording is gradually increasing in image forming apparatuses typified by copying machines. However, on the other hand, at the present time when the recording speed and resolution of an ordinary image forming apparatus that performs single-color recording is dramatically improved, when the recording method is switched to multicolor recording or color recording (hereinafter simply referred to as color recording), This leads to a decrease in recording speed and a decrease in resolution, and this is a major factor that puts a brake on the progress or spread of colorization of image forming apparatuses, especially in offices.

FIG. 11 shows a typical configuration of a conventional image forming apparatus for color recording. This image forming apparatus includes a single photosensitive drum 11 and a transfer drum 12 that is in rolling contact with the photosensitive drum 11. Around the photoconductor drum 11, a charge corotron 13 for uniformly applying an electric charge to the surface of the drum, and a black (K), a yellow (Y), a magenta (M), and a cyan (C) in that order. Four developing devices 14K, 14Y, 14M, and 14C for developing the latent image,
A transfer corotron 16 for sequentially transferring the toner image onto the sheet 15 on the transfer drum 12 and a cleaning device 17 for collecting the toner remaining on the drum surface after the transfer are arranged in this order. Here, the photosensitive drum 1
Reference numeral 1 is a diagram showing the arrangement order of these elements, and they are adapted to rotate in a clockwise direction 18 at a constant speed. Paper 15 is supplied to the transfer drum 12 from a paper feed tray (not shown) via the feed roller 21, and the paper 15 is held on at least the surface thereof until the transfer of the color image is completed. In this state, the photoconductor drum 11 rotates at a constant speed in the counterclockwise direction 22 at the same peripheral speed.

In such an image forming apparatus, black (K),
Images are formed and transferred one by one in the order of yellow (Y), magenta (M), and cyan (C). First, in the first development cycle, the laser beam irradiation position 23 on the drum surface charged by the charge corotron 13 is irradiated with the laser beam 24 modulated according to the brightness of the black image, and the static image corresponding thereto is emitted. A latent image is formed. This electrostatic latent image is a black developing device 14 containing black toner.
Developed by K, a black toner image is created on the drum surface. The toner image is transferred by the transfer corotron 16 onto the paper 15 held on the transfer drum 12. The cleaning device 17 is the photosensitive drum 11.
The surface of is cleaned, and the charge corotron 13 charges the surface again to shift to the second cycle.

In the second cycle, the laser beam 24 is applied to form a yellow image. Then, the yellow developing device 14Y containing the yellow toner
Is developed to form a yellow toner image on the drum surface. The toner image is transferred by the transfer corotron 16 while being aligned with the paper 15 held on the transfer drum 12 so as not to cause color shift. Then, the cleaning device 17 cleans the drum surface. Similarly, in the third cycle, the magenta developing device 14M transfers the magenta toner image to the same paper 15 in the third cycle, and in the fourth cycle, the cyan toner image is transferred to the same paper 15 by the cyan developing device 14C. Is transcribed to. In this way 4
When the color toner image is transferred, the paper 15 is transferred onto the transfer drum 1.
Then, the toner image is fixed by a fixing device (not shown). Then, the sheet on which the color image has been fixed is discharged to a discharge tray (not shown).

As described above, in the conventional image forming apparatus shown in FIG. 11, the toner image formation and the transfer are repeated for four cycles, and therefore, compared with the image forming apparatus for recording one black color or single color recording. The problem is that it takes many times to create an image.

FIG. 12 shows a main part of an image forming apparatus capable of recording a color image in a time substantially equal to that of monochromatic recording in order to solve such a problem. Such an apparatus is disclosed in, for example, Japanese Patent Laid-Open No. 1-142671.
It is disclosed in the publication.

This image forming apparatus is provided with a relatively long endless conveyor belt 31. The conveyor belt 31 is adapted to be conveyed at a constant speed in the direction of arrow 32 in the figure. Four photosensitive drums 34K, 34Y, 34M, and 34C are arranged at predetermined intervals on the upper planar portion of the conveyor belt 31 in a direction in which the conveyor belt 31 is conveyed at a right angle with respect to the conveyance direction. It is installed side by side. Charge corotrons 35K, 35Y, 35M, and 35 are provided around the photosensitive drums 34K, 34Y, 34M, and 34C.
C, developing devices 36K, 36Y, 36M and 36C, and transfer corotrons 37K, 37Y, 37M and 37C
And cleaning devices 38K, 38Y, 38M, 38C
Are arranged in this order. Further, a predetermined recording drum surface between the charge corotron 35K and the black developing device 36K is irradiated with a black recording laser beam 39K. Similarly, the laser beam 39Y for yellow color recording, the laser beam 39M for magenta color recording, and the laser beam 39C for cyan color recording are applied to the corresponding positions of the corresponding photosensitive drums 34Y, 34M, and 34C, respectively. Has become.

In the image forming apparatus shown in FIG. 12, the paper 42 is supplied from an unillustrated paper feed tray by a feed roller 41 to the end portion of the conveyor belt 31 on the photosensitive drum 34K side. The paper 42 is conveyed to the left in the figure along with the movement of the conveyor belt 31, and is sequentially arranged between the photosensitive drum 34K and the transfer corotron 37K, and between the photosensitive drum 34Y and the transfer corotron 37.
During Y, it passes between the photoconductor drum 34M and the transfer corotron 37M and between the photoconductor drum 34C and the transfer corotron 37C. Then, the black toner image, the yellow color toner image, the magenta color toner image, and the cyan color toner image are sequentially transferred at the respective places. In this way, the paper 4 on which the four color toner images are transferred in an overlapping manner
2 is separated from the transport belt 31 at a predetermined position thereafter, and the toner image is fixed by a fixing device (not shown),
Similarly, it will be discharged onto a discharge tray (not shown). As described above, in the image forming apparatus shown in FIG. 12, high-speed image processing can be performed as a result of performing image processing for four colors substantially in parallel in time.

By the way, generally, in an image forming apparatus for recording a color image, it is necessary to accurately align a plurality of color images on the entire surface of the paper. As described above, high-definition image quality is required not only for black-and-white images but also for color images, and prevention of color misregistration is required with extremely high accuracy. The causes of color misregistration, which is a problem in the image forming apparatus, are roughly classified into (a) image inclination (hereinafter, simply referred to as skew).
Due to the difference in the main scanning magnification,
(C) Differences in main scanning position, (d) differences in sub-scanning position, and (e) differences in image curvature.

FIG. 13 shows the state of color misregistration for two colors for each cause, for the sake of simplicity. In this figure, the horizontal axis direction is the main scanning direction, and the vertical axis direction is the sub scanning direction. FIG. 9A shows an example of color shift due to skew. The color shift due to the skew is due to the direction of the scanning line on the photoconductor being slightly deviated for each color, and the A color line 51A and the different B color line 51B have different sub-scanning directions. There is a gap. Such a color shift occurs, for example, when the tilts of the mirrors of the optical systems of the recording units for the respective colors are slightly different.

FIG. 2B shows an example of color shift due to a difference in magnification in the main scanning direction. Even if they are positioned on the same line, the length of one line differs between the A color line 52A and the different B color line 52B because the magnification in the main scanning direction is different. Therefore, in general, the color shift becomes more severe toward the end in the main scanning direction. Such color shift occurs, for example, when the two recording units have different magnifications in the optical system when scanning one line.

FIG. 3C shows an example of color shift due to a difference in main scanning position. The A-color line 53A and the B-color line 53B have the same line length, but their start points are deviated. Therefore, for example, if a line in which two colors are superimposed is recorded, each color appears as a color shift at each end. Such color shift occurs, for example, when the write start position of the image shifts.

FIG. 4D shows an example of color shift due to a difference in position in the sub-scanning direction. A color lines 54A and B
The starting point of the color line 54B is displaced in the sub-scanning direction.
Therefore, for example, if a line in which two colors are superimposed is printed, it will appear as a color shift as shown in this figure. Such color shift occurs, for example, when the positions of the two photoconductor drums are slightly different.

FIG. 5E shows an example of color shift due to image curvature. The A-color line 55A is not curved, but the B-color line 55B is curved upward in the drawing. Therefore, in this example, two lines 55A,
The color misregistration becomes prominent in the center of 55B. Such color misregistration occurs when, for example, at least one of the optical lenses of the two recording units is curved.

These color shifts are far more likely to occur in the image forming apparatus shown in FIG. 12 than in the image forming apparatus shown in FIG. In the apparatus shown in FIG. 11, the photosensitive drum 11
While the optical system of the laser beam 24 is commonly used, the recording unit for each color is independent in the apparatus shown in FIG.
It is possible that the positional relationship of 4Y, 34M, and 34C is subtly different, and the characteristics of the optical system including the rotating polygon mirror for the laser beams 39K, 39Y, 39M, and 39C, the fθ lens, and the like are completely the same. Because there is no.

FIG. 14 shows a general procedure for image correction. Here, to simplify the explanation, A
A case where the B color line 61B is aligned with the color line 61A will be described. The same figure (a) has shown the state where no correction is performed. First, B color line 61B
The skew is corrected so that the inclination of is equal to that of the A color line 61A. FIG. 6B shows a state in which the skew correction is completed. Next, the length of the B line 61B is matched with the length of the A color line 61A. FIG. 6C shows a state in which the main scanning magnification is corrected in this way.

In this state, since the image writing start position differs depending on the color, the B color line 61B is shifted in the main scanning direction so that the image writing start positions will match. FIG. 9D shows a state in which the correction in the main scanning direction is completed. Next, the B color line 61B is shifted in the sub-scanning direction so that the position where the sub-scanning is performed is the A color line
Match with A. The figure (e) shows a state in which the sub-scanning position is corrected. In addition to the above correction, FIG.
Even if the correction for the curvature of the image shown in (e) is performed, the color shift may still occur.

FIG. 15 is a diagram for explaining a color shift due to a difference in lateral magnification. Also in this figure, in order to simplify the explanation, an explanation will be given using an A-color image 62A and a B-color image 62B. These are drawn 1 at equal intervals in the main scanning direction.
It represents zero lines. Since the correction described in FIG. 14 has been performed, the images 62A ₁ and 62A _{10 at} both ends of the color A are displayed.
In the main scanning direction match the images 62B ₁ and 62B ₁₀ at both ends of B color, respectively. Originally, the sub-scanning directions also match, but for the sake of explanation, they are displayed in a shifted manner. As described above, the images at both ends in the main scanning direction are the same, but the positions of the images are different at other portions, particularly in the central portion in the main scanning direction. As a result, color misregistration occurs.

Such image distortion due to the difference in lateral magnification occurs, for example, because the surface of the photoconductor and the optical system are relatively inclined and the magnification is gradually increased or decreased depending on the position in the main scanning direction. . This also does not pose a particular problem in the image forming apparatus as shown in FIG. 11, and as shown in FIG. 12, when the optical system of each recording color is independent, the phenomenon of color misregistration occurs, which causes a problem. It will be noticeable.

Therefore, in Japanese Patent Laid-Open No. 4-119754, an optical unit for irradiating a laser beam on a photosensitive member can be rotated by a desired angle. Here, the optical unit is a light source unit for emitting a laser beam, a polygon mirror for deflecting the laser beam emitted from the unit, and a laser beam reflected by the polygon mirror is scanned at a constant speed on the photoconductor. It is composed of an fθ lens or the like for correcting so that That is, in this proposal, such an optical unit is tilted at a desired angle with respect to the photoconductor to cancel the image distortion due to the difference in lateral magnification.

[0022]

However, according to the proposed image forming apparatus, since the optical unit is movable, the optical unit is mounted on a frame or the like after adjusting the image distortion due to the difference in lateral magnification. Need to be fixed. There is a high risk of correction deviation occurring during this mounting work, and it has been difficult to perform highly accurate correction. Also,
When the optical unit is fastened and fixed with screws or the like, the optical components such as the fθ lens may be distorted, which adversely affects the optical components and hinders the formation of high-quality images. .

Therefore, an object of the present invention is to provide an image capable of removing or reducing the image distortion due to the difference in lateral magnification when the image is recorded by scanning the light beam deflected by the deflecting means on the photoconductor. To provide a forming apparatus.

[0024]

According to a first aspect of the invention, (a) a deflecting unit such as a polygon mirror for sequentially deflecting a light beam such as a laser beam modulated by image data,
(B) a photoconductor such as a photoconductor drum which is scanned by the light beam after being deflected by the deflecting means and forms an image;
(C) A transparent parallel plate made of glass or the like arranged between the deflecting means and the photoconductor so as to be orthogonal to the scanning plane of the light beam, and (d) a predetermined parallel plate parallel to the scanning plane of the light beam. An image forming apparatus is provided with a parallel plate rotating means for rotating at an angle.

That is, according to the first aspect of the invention, a parallel flat plate made of glass or the like having a predetermined refractive index is arranged between the deflecting means such as a polygon mirror and the photoconductor such as the photoconductor drum or the photoconductor belt. Is rotated to relatively change the lengths of the first half and the second half of the image formed on the photoconductor by the deflected light beam, thereby removing or reducing the image distortion due to the difference in lateral magnification. Here, when the left-right magnification difference exactly corresponds to the position of the scanning line, the image distortion can be completely removed, but even in other cases, the distortion can be greatly reduced.

According to a second aspect of the invention, (a) a light beam output means for outputting a light beam such as a laser beam,
(B) Modulating means such as a polygon mirror for modulating this light beam with image data; (c) Deflection means for sequentially deflecting the light beam modulated by this modulation means; (d) Light beam output means and deflection means. A housing which houses at least the inside thereof and emits a light beam after being deflected by the deflecting means from its opening, and (e) a photosensitive drum which forms an image by scanning with the light beam emitted from the housing. And (f) a transparent parallel plate made of glass or the like arranged on the side of the housing opening where the light beam is emitted so as to be orthogonal to the scanning plane of the light beam, and (g) this parallel plate. The image forming apparatus is provided with parallel plate rotating means for rotating the plate parallel to the scanning plane of the light beam by a predetermined angle.

That is, according to the second aspect of the invention, for example, when the semiconductor laser, the polygon mirror, or the fθ lens is added to be housed in a housing called an optical unit, the glass plate for emitting a light beam originally exists in the housing. I also decided to place a parallel plate so that it could rotate freely. As a result, it is possible to correct the difference in lateral magnification of the image without taking a space.

According to a third aspect of the invention, (a) a light beam output means for outputting a light beam such as a laser beam,
(B) Modulating means for modulating this light beam with image data, (c) Deflection means such as a polygon mirror for sequentially deflecting the light beam modulated by this modulating means, and (d) after deflection by this deflecting means. A photoconductor such as a photoconductor drum which is scanned by a light beam to form an image, and (e) a transparent parallel plate made of glass or the like which is arranged between the deflection means and the photoconductor so as to be orthogonal to the scanning plane of the light beam. A flat plate, (f) a test pattern forming means for forming a test pattern showing the central position and both ends of the image of one line on the photoconductor, and (g) a test pattern formed by the test pattern forming means To the one end and the central position and the measuring means for measuring the difference in the length from the central position to the other end, and (h) these lengths are equal according to the measurement result of this measuring means. A parallel plate rotating means for parallel predetermined angle to the scanning plane of the light beam is provided in the image forming apparatus parallel plate to so that.

That is, according to the third aspect of the invention, the difference between the horizontal magnifications is measured, and the parallel plate is rotated accordingly, so that the correction of the horizontal magnification difference of the image is automated.

According to the invention described in claim 4, (a) each has a deflecting means for a light beam such as a laser beam, and the deflected light beam is sequentially scanned on the corresponding photoconductor to form an image corresponding to these colors. From a plurality of image forming portions for forming, and (b) glass or the like arranged between the corresponding deflecting means of each of these image forming portions and the photoconductor and arranged so as to be orthogonal to the scanning surface of the corresponding light beam. And a transparent parallel plate
(C) Parallel plate rotating means for independently rotating these parallel plates parallel to the scanning plane of the light beam, and (d)
Test pattern forming means for forming a test pattern showing the center position and the end portions of the image for one line on each photoconductor, and (e) these test patterns formed by the test pattern forming means. Measuring means for measuring the difference between the length from one end to the center position and the length from the center position to the other end for each image forming part, and (f) these lengths according to the measurement result of this measuring means. Parallel plate rotating means for rotating the corresponding parallel plate parallel to the scanning plane of the light beam by a predetermined angle so that the same becomes equal to each other, and (g) after the corresponding parallel plate is rotated by the parallel plate rotating means, The image writing timing is adjusted so that the writing position of the image for one line formed on each photosensitive drum is the same in each image forming unit. To and a writing start position adjusting means for adjusting the image forming apparatus.

That is, in the fourth aspect of the invention, color misregistration that occurs in an image forming apparatus having a plurality of image forming units that use different colors is eliminated, and the difference in lateral magnification between the image forming units is eliminated. First, the difference between the lateral magnifications of the respective colors is corrected by performing the measurement and rotating the corresponding parallel plate accordingly. Next, by adjusting the writing start timings of the images of the respective colors so that the writing start positions of the images coincide with each other in the main scanning direction, the occurrence of color shift due to the difference of the writing start positions is also prevented.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

Overall Configuration of Image Forming Apparatus

FIG. 1 shows a main part of an image forming apparatus according to an embodiment of the present invention. This image forming apparatus is
It has a transparent endless transfer belt 104 that is stretched around three rollers 101, 102, 103. The transfer belt 104 is indicated by an arrow 1 in the figure by a drive motor (not shown).
It is conveyed at a constant speed in the 05 direction. On the upper surface of the transfer belt 104, four photosensitive drums 106K, 1K having drum shafts in a direction orthogonal to the conveying direction are provided.
06Y, 106M, and 106C are arranged in this order at predetermined intervals. Here, the photoconductor drum 106K is a black recording drum, the photoconductor drum 106Y is a yellow color recording drum, the photoconductor drum 106M is a magenta color recording drum, and the photoconductor drum 106C.
Is a drum for recording cyan color. Above the respective photosensitive drums 106K, 106Y, 106M and 106C, a polygon mirror 10 for recording the corresponding color is provided.
7K, 107Y, 107M, 107C and the corresponding photoconductor drum 106 for the laser beam reflected from them.
Reflecting mirrors 108K, 108Y, 108M, and 10 for irradiating K, 106Y, 106M, and 106C, respectively.
8C is arranged.

Two sets of transmissive optical sensors 111 ₁ , 111 ₂ , 112 ₁ , 112 ₂ are arranged near the left end of the upper surface of the transfer belt 104 so as to sandwich the belt surface. Of these, the optical sensors 111 ₁ and 11 on the light receiving side
Each 2 ₁ is composed of a one-dimensional image sensor such as a CCD. These optical sensors 111 ₁ , 11
2 _1, the photosensitive drums 106K, which is transferred onto the transfer belt 104 only when a test image only, 106Y, 10
The color misregistration inspection patterns 113 of 6M and 106C are detected to detect various kinds of color misregistration as described above.

When the image is not inspected, the paper (not shown) sent from the supply tray (not shown) is supplied to the third roller 103 as described with reference to FIG.
The toner image of each color is transferred to the upper surface of the transfer belt 104 from the vicinity of, and sequentially passes under the photoconductor drums 106K, 106Y, 106M, and 106C. The paper on which the toner images of the respective colors have been transferred is transferred to the transfer belt 10 near the first roller 101.
After being peeled off from the surface of No. 4 and fixed by a fixing device (not shown), it is also discharged onto a paper discharge tray (not shown). Each photoconductor drum 106K, 106Y, 106
The principle of image formation by M and 106C is based on the photoconductor drums 34K, 34Y and 34 already described in FIG.
Since it is similar to the case of M and 34C, the description thereof is omitted here.

FIG. 2 shows an outline of the configuration of an optical system for yellow color recording as one optical system of this image forming apparatus. The configurations of the other optical systems are also the same, and therefore their explanations are omitted. The yellow color recording polygon mirror 107Y is rotated at a high speed by a polygon mirror rotation motor (not shown). Laser beam 123 emitted from semiconductor laser 121Y
Y is focused by the optical lens 124Y and is incident on one surface of the polygon mirror 107Y. The reflected light on this surface is reflected by the fθ lens 125Y and the lateral magnification difference correction device 12
After 6Y, the photosensitive drum 106Y is reached and the surface thereof is repeatedly scanned in the main scanning direction. The scanning start position detection sensor 127 is provided on the path through which the laser beam passes just before the scanning start position of the photosensitive drum 106Y.
Y is arranged. In the image forming apparatus having such a configuration, the clock signal is counted after the scanning start position detection sensor 127Y detects the laser beam, and when a predetermined count value is counted, the photosensitive drum 106Y is scanned. The recording of the image of that line is started.

Description of the lateral magnification difference correction device

In this embodiment, the lateral magnification difference correction device 126Y has a single parallel plate 131Y. This parallel plate 1
A rotary shaft 132Y is vertically provided at an upper end portion near one end of 31Y, and the rotary shaft 13 is provided at a position corresponding to the lower end portion.
3Y is also installed vertically. These rotating shafts 132Y,
133Y is formed integrally with the parallel plate 131Y. The other end of the parallel plate 131Y around the rotation shafts 132Y and 133Y can be minutely rotated clockwise (CW) or counterclockwise (CCW).
Thereby, the ratio of the lengths a and b of the first half and the second half with respect to the central position of the scanning line on the photosensitive drum 106 can be adjusted.

FIG. 3 is a view for explaining the rotation mechanism of the lateral magnification difference correction device used in the yellow color recording optical system and the operation for compensating for the lateral magnification difference using the rotation mechanism.
The configurations of the other optical systems are also the same, and therefore their explanations are omitted. The rotary shaft 132Y is attached to one end of the parallel plate 131Y.
(133Y) is attached and is pivotally supported by a bearing (not shown). The parallel plate 131Y is the photosensitive drum 1
It is arranged almost parallel to the drum shaft of No. 06, and the rotary shaft 1
The vicinity of the other end to which 32Y (133Y) is attached is a U-shaped metal fitting 1 attached to an immovable member 141 such as a frame.
It is arranged in a space surrounded by both side walls 142A, 142B of 42.

The inner surface of one side wall 142A and the parallel plate 13
A spring 144 is interposed between the 1Y laser beam 123Y and the surface on the side where the laser beam 123Y is emitted.
A force is applied to rotate 31Y in the counterclockwise direction. An adjusting screw 145 is screwed into the other side wall 142B from the outer surface thereof, and the tip thereof is in contact with the surface of the parallel plate 131Y on the side on which the laser beam 123Y is incident. Therefore, when the adjusting screw 145 is rotated in the tightening direction, the parallel flat plate 131Y is slightly rotated clockwise.
Further, if it is rotated in the loosening direction, the parallel plate 131Y will be slightly rotated counterclockwise.

By the way, when the scanning of the laser beam 123Y is performed in the state before the correction work of the lateral magnification difference is performed,
It is assumed that the length of the first half of the scanning line is a ₁ and the length of the latter half is b ₁ with respect to the center position. It is assumed that the adjustment screw 145 is rotated by a predetermined amount and the parallel plate 131Y is rotated by a slight angle. In FIG. 3, an example of this rotation is shown by a broken line. Assuming that the length of the first half of the scanning line at this time is a ₂ and the length of the second half is b ₂ , the difference between the lengths of the first half and the second half before correction (a ₁ -b ₁₎ the same difference between the corrected (a ₂ -b ₂₎ is varies by the rotation angle. As shown in the example of FIG. 3, the photoconductor drum 106Y and the parallel plate 131Y are substantially parallel to each other before the correction work, and the parallel plate 13 is shown by the broken line by the correction work.
Assuming that 1Y slightly rotates counterclockwise, the difference in length after correction (a ₂ -a ₁ ) is larger than the difference in length after correction (a ₁ -b ₁ ).
-B ₂ ) becomes larger.

FIG. 4 shows a difference in lateral magnification when the parallel plate is rotated. The parallel plate 131Y has a refractive index of 1.5 and a thickness of 10 mm. In this figure, the horizontal axis represents the rotation angle when the parallel flat plate 131Y is rotated in the clockwise direction, and the vertical axis represents the image at a position 146 mm from the center of the scanning line with reference to the case where the rotation angle is zero. Difference in length (ab)
Is represented. For example, if it is rotated counterclockwise by 15 degrees, it becomes -15 degrees, so the difference in image length (ab) is 0.4 mm. That is, the first half of the scanning line is 0.4 mm larger than the latter half as compared to before correction.
Can be long.

By slightly rotating the parallel plate 131Y in this manner, the difference in lateral magnification can be corrected. The adjustment operator obtains the lateral magnification difference using a jig, and rotates the adjustment screw 145 in a desired direction by a rotation amount previously obtained from the relationship between the rotation amount of the adjustment screw 145 and the rotation angle of the parallel plate 131Y. Therefore, the correction work can be completed. The correction of the left-right magnification difference in the yellow color optical system has been described above. However, by correcting the left-right magnification difference in the other color optical systems as well, it is possible to prevent color misregistration during color recording. .

First Modification

FIG. 5 shows a main part of an image forming apparatus according to a first modification of the present invention. The same parts as those in the previous embodiment are designated by the same reference numerals, and the description thereof will be appropriately omitted. Further, although only the optical system for recording yellow color is shown as in the previous embodiment, the configuration of optical systems for other recording colors is also the same.

From the semiconductor laser 121Y to the fθ lens 12
The optical system up to 5Y, the reflection mirror 201Y, and the scanning start position detection sensor 202Y that detects the laser beam picked up by the reflection mirror 201Y are the optical unit 204Y.
And is housed in a sealed casing 205Y. This is to prevent external dust and toner particles from adversely affecting the optical system. fθ lens 1
The laser beam 123Y having passed through 25Y is a left / right magnification difference correction device 207Y provided on the front surface of the opening of the housing 205Y.
And reaches the photoconductor drum 106 via. Conventionally, a glass plate is fixed to the opening of the casing 205Y, but in the image forming apparatus of this embodiment, this dustproof glass plate is also used as the left-right magnification difference correction device 207Y.

FIG. 6 specifically shows the left-right magnification difference correction device of the first modification. In this modification, the parallel plate 211 is bonded so as to cover an opening provided in a rectangular metal plate 212, and a sponge having a predetermined thickness is further provided thereon. A frame 213 made of rubber is adhered. Further, a surface of the bearing 216 having a rectangular parallelepiped shape in which the rotary shaft 215 is protruded from the upper and lower end surfaces is fixed to one end of the plate 212, and a surface of the bearing 216 opposite to the plate 212 is fixed to the other end. It is fixed. Spring 2
A surface of the other end portion of the housing 14 opposite to the surface fixed to the plate 212 is pressed by a corresponding front wall portion of the housing 205Y, and the shaft 215 is supported by the housing 205Y by a holding member (not shown). ing.

Further, the spring 2 in the casing 205Y
The base portion 218A of the adjustment screw holding member 218 is fixed to the housing 205Y immediately adjacent to the portion to which 14 is fixed. The tip portion of the adjusting screw holding member 218 has a base portion 218A.
It is bent to the opposite side, and the adjusting screw 221 is attached to the surface as in the previous embodiment. The tip of the adjusting screw 221 is in contact with the vicinity of the end of the plate 212. Since the sponge rubber that forms the frame 213 is an elastic member, even if the plate 212 rotates a little due to the rotation of the adjusting screw 221, the end of the plate 212 remains in close contact with the front wall around the opening of the housing 205Y. ing.

Since the image forming apparatus of the first modified example has such a structure, the left-right magnification difference is measured at the time of factory assembly as in the previous embodiment, and the adjusting screw 22 is adjusted in accordance with this value.
1 may be rotated. In the image forming apparatus of this modified example, since the adjusting screw 221 is arranged outside the housing 205Y, it is possible to correct the lateral magnification difference without disassembling the optical unit 204Y.

Second Modified Example

FIG. 7 shows a main part of an image forming apparatus according to a second modification of the present invention. In this modified example, the same parts as those in the first modified example are designated by the same reference numerals, and the description thereof will be appropriately omitted. The left-right magnification difference correction device 301 of the second modified example is provided with a plate 212A that is slightly longer than the plate 212 of the first modified example, and the plate is further extended to the right side in the drawing from the portion to which the spring 214 is attached. It is extended. In this extended part, the spring 21
A plate nut 302 is fixed to the surface opposite to the surface on which No. 4 is attached, and a hole 303 having a diameter slightly larger than this is formed in the hole portion in which the female screw is engraved. In addition, the housing 20 whose one end portion 305A is shown in FIG.
A stepping motor 306 is attached to the other end of the stepping motor holding member 305 having a U-shaped cross section, which is fixed to the front wall of the 5Y.
Has been fixed.

Rotating shaft 304 of stepping motor 306
Has its tip rotatably supported by a bearing (not shown) at one end 305A. A screw is engraved in a central portion of the rotary shaft 304 over a predetermined width, and the screw is screwed into the plate nut 302. The stepping motor 306 is connected to the stepping motor drive circuit 308, and its rotation is controlled by this.

FIG. 8 is for controlling the stepping motor.
The circuit configuration of FIG. Mounted on image forming device
The CPU (Central Processing Unit) 311 currently installed is
Connected to each part of the device via a bus such as
It is designed to perform various controls such as adjustment of image color misregistration.
It Of these, the ROM 313 is a program for performing various controls.
It is a read-only memory that stores programs. R
AM314 is temporarily needed to perform these controls.
Random access memory for storing data
It The sensor input circuit 315 is a detection signal from various sensors.
Is a circuit for inputting. Figure for correction of left-right magnification difference
2 sets of transmission type optical sensors 111 shown in FIG.₁, 111
₂, 112₁, 112₂And an additional set of optical sensors 316
₁316 ₂Need to be added. Optical sensor on the light receiving side
111₁, 112₁316₁The detection signal of
It will be input to the input circuit 315.

FIG. 9 shows each optical sensor in relation to the transfer belt.
It shows the arrangement of the sa. Two optical sensors 11
1₁, 112₁Is the transfer belt 10 indicated by the arrow 105.
1 in the direction (main scanning direction) orthogonal to the transport direction of 4
The remaining optical sensors 316 are arranged on the straight line of the book.
₁Is on this straight line and both optical sensors 111₁, 112
₁It is located in the middle position. In addition, light emission
Side optical sensor 316 ₂Across the transfer belt 104
Optical sensor 316 on the light receiving side₁Placed almost symmetrically with
Have been.

Returning to FIG. 8, the description will be continued. The stepping motor drive circuit 308 is a circuit that outputs a drive pulse for controlling the drive of the stepping motor 306. The optical unit control circuit 318 is a circuit that controls the optical units 204K, 204Y, 204M, and 204C prepared for each color. The main motor drive circuit 319 is shown in FIG.
Photoreceptor drums 106K, 106Y, 106M shown in
The main motor 321 for driving the 106C, the transfer belt 104, and the like is controlled.

Now, the correction of the lateral magnification difference is made for each recording color.
Since it is performed, the case of yellow color will be described here.
At the first stage of the adjustment work, the photosensitive drum 1 shown in FIG.
Electrostatic latent image of inspection pattern corresponding to maximum paper width of 06Y
Is formed. This inspection pattern is at both ends of the scan line.
And the pixel in the center is in the printing state and the other pixels are in the non-printing state.
It is a pattern to do. This electrostatic latent image is developed,
A toner image is created. This toner image is transferred to the transfer belt 1.
Transcribed on 04. Three toner images 331 shown in FIG.
332 and 333 are created in this way.
It These toner images 331, 332, 333 correspond to each other.
Optical sensor 111₁316₁, 112 ₁Detected by
Will be. The sensor input circuit 315 detects these
The result is input, and the CPU 311 causes the toner image 331,
The left-right magnification difference is calculated from the detection positions of 332 and 333.

When the difference between the left and right magnifications is calculated, the parallel plate 21 is used based on the difference as described in FIG. 4 of the previous embodiment.
The rotation direction and the rotation angle of 1 are obtained. Based on this, the CPU 311 controls the stepping motor drive circuit 308 to rotate the stepping motor 306, and corrects the lateral magnification difference. It should be understood that the correspondence relationship between the lateral magnification difference, the rotation direction and the rotation angle may be made into a table, and the rotation control of the stepping motor 306 may be directly performed based on the table.

In the above-described embodiments and modified examples, only the correction work of the difference between the left and right magnifications has been described. However, if this work is performed, the write start position of the image in the main scanning direction may be misaligned, and this correction is usually performed. There is a need to do.

FIG. 10 is for explaining the contents of this correction work. FIG. 4A shows a state in which black (K), yellow (Y), magenta (M), and cyan (C) scan lines 401K, 401Y, 401M, and 401C are recorded in order from the right. For convenience of description, a mark 402 indicating the center position of the image is written on each of them. In the same figure (b), the scanning lines 401K, 401Y, and
It shows a state in which the lateral magnification difference between 401M and 401C is corrected. In the state where the horizontal magnification is corrected in this manner, the writing start positions of the image in the main scanning direction are different.

FIG. 6C shows a scanning line 401 for four colors.
It shows a state in which the writing positions of K, 401Y, 401M, and 401C are corrected. Such a correction is
A scan start position detection sensor 12 prepared for each recording color like the scan start position detection sensor 127Y shown in FIG.
7K, 127Y, 127M, 127C.
That is, these scanning start position detection sensors 127K,
By independently adjusting the time from the detection of the laser beam by each of 127Y, 127M, and 127C to the start of the writing of the image, the scanning lines 401K of the four colors,
The writing positions of 401Y, 401M, and 401C will be matched. Since each adjustment is generally performed as adjustment of the writing start position of the image in the main scanning direction, detailed description thereof will be omitted.

Further, although the color recording using four recording colors has been described in the embodiments and the modified examples, the present invention is also applied to the prevention of color misregistration in an image forming apparatus using two or more recording colors. be able to. In addition, even if one-color image formation requires high accuracy,
The invention is equally applicable.

Further, in the embodiment and the modified example, the parallel plate is rotated by selecting one end or the extension thereof as the center of rotation, but for example, the center of the parallel plate is selected as the center of rotation and the parallel plate is rotated. May be. Further, although the glass plate is used as a parallel plate in the embodiments, it goes without saying that other transparent materials such as plastic can also be used.

In the modification, the rotary shaft of the stepping motor is directly used for rotating the parallel plate. However, other types of motors may be used, or the parallel plate may be rotated through a transmission mechanism. It may be performed. Further, although the polygon mirror is used as the deflecting means in the embodiments and the modified examples, it goes without saying that other deflecting means can be used.

[0065]

As described above, according to the first aspect of the invention, a predetermined refractive index made of glass or the like is provided between the deflecting means such as a polygon mirror and the photoconductor such as the photoconductor drum or the photoconductor belt. It is decided that by arranging the parallel flat plates of and rotating the flat plate, the lengths of the first half and the second half of the scanning of the image formed on the photoconductor by the deflected light beam are relatively changed. With the method, it is possible to highly accurately correct the distortion due to the difference in lateral magnification of the image.

According to the second aspect of the invention, the main optical components can be housed in the housing.
Can take dustproof measures. Moreover, since the dust-proof glass plate in the opening of such a case is rotatably arranged as a parallel plate, it requires more space than the case where another parallel plate is arranged outside the case. In addition, the cost can be reduced due to the combined use of parts.
In addition, there is an advantage that the loss of the light beam on the reflecting surface is reduced as compared with the case of using two parallel flat plates such as glass plates.

Further, according to the third aspect of the present invention, since the difference between the horizontal magnification of the image is automatically measured and the adjustment of the horizontal magnification is also automated, the adjustment at the time of factory shipment becomes unnecessary as a deceleration, and the number of man-hours is reduced. Contribute to reduction. Further, as the resolution of the image forming apparatus is improved, the demand for color misregistration becomes stricter. According to the present invention, however, such as when the image forming apparatus is powered on or when the apparatus is vibrated from the outside. Since the diagnosis can be performed in a predetermined case and the color shift can be adjusted each time, there is an advantage that the apparatus can always be kept in the best state.

According to the fourth aspect of the invention, it is possible to eliminate the color misregistration caused by the difference in the lateral magnification which occurs in the image forming apparatus having a plurality of image forming units that use different colors. Further, since the writing position in the main scanning direction is further corrected after this correction is performed, the color shift can be completely eliminated by further correcting the cause of the color shift caused by the one adjustment. There is an advantage that a high quality image can be secured.

[Brief description of drawings]

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

FIG. 2 is a perspective view showing an outline of an optical system for yellow color recording of this image forming apparatus.

FIG. 3 is a schematic configuration diagram of a main part of a device showing a rotation mechanism of a lateral magnification difference correction device used in an optical system for yellow color recording and a lateral magnification difference correction operation using the rotation mechanism.

FIG. 4 is a characteristic diagram showing a lateral magnification difference when the parallel plate of this embodiment is rotated.

FIG. 5 is a plan view showing a main part of an image forming apparatus according to a first modified example of the present invention.

FIG. 6 is a perspective view specifically showing a lateral magnification difference correction device of a first modified example.

FIG. 7 is a perspective view showing a main part of an image forming apparatus according to a second modification of the present invention.

FIG. 8 is a block diagram showing a main part of a circuit configuration for controlling a stepping motor in a second modified example.

FIG. 9 is a plan view showing the arrangement of each optical sensor in relation to a transfer belt in a second modified example.

FIG. 10 is an explanatory diagram showing a state of the adjustment work of the writing position in the main scanning direction after the adjustment of the lateral magnification in the present invention.

FIG. 11 is a side view showing a main part of a conventional image forming apparatus for color recording.

FIG. 12 is a side view showing a main part of a conventional image forming apparatus capable of recording a color image at high speed.

FIG. 13 is an explanatory diagram showing the state of color misregistration for two colors for each cause.

FIG. 14 is an explanatory diagram showing a general procedure of image correction for various causes of color misregistration.

FIG. 15 is an explanatory diagram showing an example of color shift due to a difference in lateral magnification.

[Explanation of symbols]

104 ... endless belt, 106K, 106Y, 106M,
106C ... Photosensitive drum, 107, 107K, 107
Y, 107M, 107C ... Polygon mirror, 108K,
108Y, 108M, 108C ... Reflecting mirror, 111,
112, 316 ... Optical sensor, 113 ... Color shift inspection pattern, 121Y ... Semiconductor laser, 123Y ... Laser beam, 124Y ... Optical lens, 125Y ... f.theta. Lens,
126Y ... Left / right magnification difference correction device, 131Y, 211 ... Parallel plate, 132Y, 133Y, 215 ... Rotation axis, 204
Y ... Optical unit, 205Y ... Housing, 207Y, 301
... lateral magnification difference correction device, 214 ... spring, 221 ...
Adjustment screw, 302 ... Plate nut, 304 ... Rotating shaft,
306 ... Stepping motor, 311 ... CPU, 313
... ROM, 315 ... Sensor input circuit, 331-333 ...
Toner image, 401K, 401Y, 401M, 401C ...
Scan lines (of four colors)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location G03G 15/01 Y H04N 1/113 1/29 G 1/46 H04N 1/04 104 A 1/46 Z

Claims (4)

[Claims] 1. Deflection means for sequentially deflecting a light beam modulated by image data, a photoconductor for forming an image by scanning with the light beam after being deflected by the deflection means, and between the deflection means and the photoconductor. And a transparent parallel plate arranged so as to be orthogonal to the scanning plane of the light beam, and parallel plate rotating means for rotating the parallel flat plate by a predetermined angle in parallel with the scanning plane of the light beam. Image forming apparatus. 2. A light beam output means for outputting a light beam, a modulating means for modulating the light beam with image data, a deflecting means for sequentially deflecting the light beam modulated by the modulating means, and the light beam output. And a deflecting means are housed at least inside, and a casing for emitting a light beam after being deflected by the deflecting means from its opening, and a photoconductor for forming an image by scanning with the light beam emitted from the casing A transparent parallel plate disposed on the side of the housing opening where the light beam is emitted so as to be orthogonal to the scanning plane of the light beam, and the parallel plate is parallel to the scanning plane of the light beam at a predetermined angle. An image forming apparatus comprising: a parallel plate rotating means for rotating. 3. A light beam output means for outputting a light beam, a modulating means for modulating the light beam with image data, a deflecting means for sequentially deflecting the light beam modulated by the modulating means, and the deflecting means. A photoconductor for forming an image by scanning with the deflected light beam; a transparent parallel plate arranged between the deflection means and the photoconductor so as to be orthogonal to the scanning plane of the light beam; and on the photoconductor. A test pattern forming means for forming a test pattern showing the central position and both ends of the image for one line, and the length and center from the test pattern formed by the test pattern forming means to the one end and the central position. Measuring means for measuring the difference in length from the position to the other end, and the parallel plate so that these lengths become equal according to the measurement result of this measuring means. An image forming apparatus characterized by comprising a parallel plate rotating means for parallel predetermined angle to the scanning plane of the beam. 4. A plurality of image forming units each having a light beam deflecting means and sequentially scanning the deflected light beam onto a corresponding photoconductor to form images corresponding to these colors, and these image forming units. Transparent parallel flat plates arranged between the corresponding deflection means of the forming unit and the photoconductor and orthogonal to the scanning plane of the corresponding light beam, and these parallel flat plates are made parallel to the scanning plane of the light beam. Parallel plate rotating means for independently rotating, test pattern forming means for forming a test pattern indicating the center position and the end portions of the image of one line on each of the photoconductors, and the test pattern forming means Measuring the difference between the length from one end to the center position and the difference from the center position to the other end from each test pattern formed by Means, and parallel plate rotating means for rotating the corresponding parallel plates by a predetermined angle in parallel with the scanning plane of the light beam so that these lengths become equal to each other according to the measurement result of the measuring means. 1 is formed on each photosensitive drum after the corresponding parallel plates are rotated by the means 1
An image forming apparatus, comprising: a writing position adjusting unit that adjusts image writing timings so that the writing positions of the lines of images are the same in each image forming unit.