JP2608302B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Use Range> The present invention relates to an image forming apparatus that forms image information on a recording medium using an electrophotographic method or the like, and more particularly, to a method for forming a plurality of images on the same recording medium. The present invention relates to a multiplex image forming apparatus (copier, facsimile, printer, etc.) for multiplexing. In this specification, a description will be given below by taking a four-drum laser printer as an example.

<Prior Art> Conventionally, a laser beam printer having a plurality of optical scanning means has a laser device as a light source, a rotating polygon mirror for scanning the laser device, and fθ for condensing a scanning beam on a generatrix on the surface of a photosensitive drum. It comprises a lens, a reflecting mirror for deflecting a light beam, and a beam detecting device for detecting a specific position of the scanning beam.

A conventional image forming apparatus having a plurality of optical scanning means as described above is known as shown in FIG. Third
FIG. 1 is a schematic diagram showing a first conventional example of a four-drum full-color printer. In FIG. 1, reference numeral 1 denotes a photosensitive drum serving as an image forming medium, and the photosensitive drum 1 rotates in the direction of an arrow, and the periphery thereof is charged. A device 2, a scanning optical device (optical scanning means) 3, a developing device 4, and a cleaner 5 are provided.
The photosensitive drum 1, the charger 2, the scanning optical device 3, the developing device 4, and the cleaner 5 include yellow, magenta, cyan,
It is arranged for each black color station. The transfer section 6 as a moving body has a transfer belt 6a and a transfer charger 6b, and a full-color image is formed on the transfer belt 6a.
It is formed by sequentially transferring color toner on a transfer material supported above. This transfer material is supplied from the paper supply cassette 7 and the transfer material after the transfer process is separated is separated and reaches the tray 9 via the fixing device 8.

The most important problem in such an apparatus having a plurality of image forming stations is to prevent the transfer positions of the colors to be transferred and transferred from the ideal positions, which are transferred onto the transfer material in each image forming station, from each other. . This appears as a gap or overlap between colors in the case of multi-color images, and in the case of full-color images,
Differences in color and, if severe, a color shift appears, which significantly degrades image quality. FIG. 5 shows the types of this color shift. In the figure, it is assumed that the solid line is, for example, a magenta image, and the dotted line is another color, for example, a cyan image. The color shift on the transfer material is a shift (a) in a direction perpendicular to the direction of conveyance by the transfer belt 6a (arrow A in the figure).
(Top margin), parallel displacement (b) (left margin), and oblique displacement (c). In an actual image, these displacements (a), (b), and (c) are superimposed. Things appear. Of these, the color shift (top margin) in (a) is mainly caused by a shift in the writing start timing of the image of each image forming station shown in FIG. 3 of the transfer material. Can be prevented by making it electrically variable. The color shift (left margin) in (b) mainly occurs because the beam detection position of the photodetector 27 shown in FIG. 4 is slightly different between the four colors. Can be prevented by adjusting the delay time from the detection of the laser beam to the generation of the recording signal start signal for each color. Regarding the displacement (c), that is, the displacement in the oblique direction, it is possible that the scanning lines of the respective laser scanning optical systems are not scanned in parallel between the colors, and the rotation axis of each photosensitive drum is not parallel between the colors. It is possible. Further, in most cases, both of these usually occur at the same time. FIGS. 6 and 7 show how these color shifts occur.

In FIG. 6, the rotation axes of the photosensitive drums 1Y to 1BK are parallel, for example, the scanning lines 31Y, 31M, and 31BK of yellow, magenta, and black are parallel, and only the scanning line 31c of cyan is the other scanning line. 2 shows a case where the angle is inclined by an angle θ. The transfer material is sent in the direction of arrow A in the figure. (A) is where the latent image is written on each photosensitive drum by the scanning lines 31Y, 31M, 31C, 31BK. There is a delay in the time of writing on each of the photosensitive drums 1Y to 1BK by the time during which the transfer material is transported. From this state (a), each image carrier is rotated by 180 °, and the latent images are visualized by the developing device 4 into images 31Y 'to 31BK'.
(B) when the image is at the position to be transferred to the transfer material. At this time, the image 31C 'is inclined by the angle θ in the opposite direction to the latent image written by the scanning line 31C. As a result, in the transfer material, only the cyan image becomes an image output (c) with a color shift inclined by the angle θ in the same direction as in FIG.

FIG. 7 shows a case where the scanning lines 31M to 31BK are parallel, and the rotation axis of the photosensitive drum is only the cyan photosensitive drum 1C as an example, and is inclined by an angle θ with respect to the parallel lines with the rotation axes of the other photosensitive drums. Is shown. The transfer material is fed in the direction of arrow A in the figure. As in FIG. 6, (a) shows the state where the latent image is written,
(B) shows the state of transfer to the transfer material, and (c) shows the color shift on the image. In this figure, the rotating shaft support on the front side (lower side in the figure) of the photosensitive drum 1C is not at the ideal position, and the rotating shaft is inclined by an angle θ with respect to the ideal position. In this case, as is apparent from the drawing, in the image output on the transfer material, the angle 2θ inclination color shift amount is increased.

Here, comparing the case where the scanning line is inclined (FIG. 6) and the case where the rotation axis of the photosensitive drum is inclined (FIG. 7), the same angle is obtained when the rotation axis of the photosensitive drum is inclined. Even if it is only tilted, the effect is exaggerated and appears on the image.

The color shift in the oblique direction as described above can be temporarily prevented, for example, by performing adjustment / assembly using a jig at the time of assembly.However, for example, the photosensitive drum is frequently replaced, and At the time of replacement, it is common to remove the rotating shaft support member, and thus the replacement of the rotating shaft support member deteriorates the positioning accuracy, causing the inclination in FIG. 7 (a). In addition, similar color misregistration occurs due to replacement of the scanning optical device. Also, especially when the image forming stations are each unitized,
After positioning the rotation axis of the photosensitive drum in the unit, it is usual to position the unit with respect to the main body. Therefore, high accuracy is required for positioning the rotation axis in the unit, and when the unit is replaced. It is extremely difficult to maintain the parallelism of the rotation axes of the respective photosensitive drums, and the color shift as shown in FIG. 7 (c) could not be prevented.

Conventionally, in consideration of this point, a means for inclining each scanning line, for example, a means for moving the scanning optical device itself, or changing the light beam from the scanning optical device on the photosensitive drum is provided. Means for moving the reflection mirror for forming an image on the surface, and means for tilting each writing position, for example,
The operation of matching the scanning lines of each color is performed by using the movement of the bearing portion of the photosensitive drum. However, according to this method, for example, in a four-drum printer as in this example, it is necessary to provide scanning line inclination adjusting means for all four colors, and since there are also four adjustment methods,
It is complicated and extremely difficult.

<Problems to be Solved by the Invention> However, as described above, in an image superimposed by a plurality of image forming stations, the problem of the misalignment of the formed image position is serious, and (a) Displacement (top margin), (b) Displacement in the direction parallel to the transport direction (left margin), and (c) Displacement in the oblique direction. Each image is described above in (a), (b), and (c).
It is necessary to make adjustments while looking at the image.In addition to the difficulty of each adjustment, since each image exists for each image, it causes a lot of confusion and requires much effort. In addition, since each image is provided with each adjustment mechanism, cost increases cannot be avoided.

Therefore, the present invention has been made in order to solve the above-described problems of the conventional example, and an object of the present invention is to solve the above-described problems by simplifying the upper position adjustment and performing it at low cost. It is an object of the present invention to provide an image forming apparatus capable of performing the above.

<Means for Solving the Problems> In order to achieve the above object, in the present invention, images formed by a plurality of image forming means are multiplexed on the same recording medium conveyed by a conveyance body. An image formed by a predetermined image forming unit of the plurality of image forming units and an image formed by another image forming unit other than the predetermined image forming unit. Correction means for correcting the positional deviation of the image forming means, and the correction means is provided only for the other one of the plurality of image forming means.

<Embodiment> The present invention will be described below with reference to the illustrated embodiment. FIG. 1 is a schematic view showing an embodiment in which the present invention is applied to a four-drum color printer, and FIG. FIG. 1B is a schematic diagram of a case where a conveyance belt is used as a recording material of a registration mark, FIG. 1B is an intermediate transfer body, and FIG. In the figure, reference numerals 1Y, 1M, 1C, and 1BK denote photosensitive drums arranged for each of the yellow, magenta, cyan, and black stations as latent image carriers. These photosensitive drums 1Y, 1M, 1C, and 1BK are indicated by arrows. Around the photosensitive drums 1Y, 1M, 1C, and 1BK, corresponding to the chargers 2Y, 2M,
2C, 2BK, scanning optical devices 3Y, 3M as image writing means,
3C, 3BK, developing devices 4Y, 4M, 4C, 4BK, cleaners 5Y, 5M, 5C, 5BK
Are arranged. The transfer unit 6 includes a transfer belt 6a and a transfer charger 6b, and a full-color image is formed on the transfer belt 6a.
The toner is formed by sequentially transferring the toners of the respective colors on a transfer material supported on 6a. The transfer material is supplied from a paper supply cassette 7, and the transfer material having undergone the transfer process is separated and reaches a tray 9 via a fixing device 8. In FIG. 1 (b)
Reference numeral 16 denotes an intermediate transfer member as a transfer medium transport member. An image formed on the photosensitive drum is first transferred to the intermediate transfer member 16 and then transferred to a transfer material. FIG. 1 (c) is a schematic view of a case where roll paper is used as a transfer material, and a transfer material 17 wound in a roll as a transfer medium is sequentially conveyed. In the first embodiment, the scanning optical devices 3Y, 3M, 3C, 3
Of the BK, the scanning optical device of 3Y, that is, the yellow station, is positioned and fixed to the main body housing. This fixing method is performed by, for example, fitting with the main body stay 26 or fixing with a jig or the like, and does not include a position adjusting means on the main body. For the scanning optical devices 3M, 3C, and 3BK in the stations other than yellow,
Each scanning optical device has a position adjusting means as shown in FIG. In this figure, 20 is an fθ lens, 21 is a polygon, 22
Denotes a laser light source, and 23 denotes an optical box for integrally fixing the fθ lens, polygon and laser. The position of the optical box 23 can be moved and adjusted in the directions a and b in the figure with respect to the main body housing. This adjusts the color shift (registration) from other colors. For example, by moving in the direction a, the scanning line m can be inclined like m '. Also, the magnification in the main scanning direction can be adjusted by moving the scanning line m to m "by moving in the direction b. In this way, by moving the optical box 23, each of the scanning optical devices 3Y, 3M, 3C, and 3BK can adjust the magnification. It is possible to transfer the formed image without misalignment of each color.

Next, regarding the adjustment method, as described above, the scanning optical device 3Y has its position accuracy, that is, the photosensitive drum to the reflection mirror to
The relationship between the optical boxes is maintained at a high accuracy by, for example, an assembling method using a jig or a tool or mechanical accuracy. 3M, 3
As described above, since C and 3BK have the position adjusting means, their position accuracy on the main body may be relatively low.

For example, when correcting color misregistration of a four-color full-color image, the first reference which is positioned on the main body with high accuracy is used.
The color shift may be adjusted for each color of the station, for example, the yellow station. That is,
First, the deviation of the magenta image from the yellow image is read, and the deviation is adjusted by the optical box moving means described above. Thus, after the color shift between the yellow and the magenta images is completed, the shift of the cyan image with respect to the yellow is adjusted next. Then, the color shift of the black image with respect to the yellow image is adjusted. That is, these are a certain reference scanning optical device which is positioned with high precision with respect to the main body housing. In this case, the color shift is adjusted by moving and adjusting a scanning optical device of another color with respect to the image formed by yellow. It is to match.

FIG. 2 (b) shows a second embodiment of the present invention. In the figure, reference numeral 24 denotes a reflection mirror for turning a good beam from the scanning optical device 3 and forming an image on the photosensitive drum. Other numbers are the same as in the first embodiment. Reflection mirror 24
Are supported at three points with respect to the main body housing. In this embodiment, the color misregistration is adjusted by moving the reflection mirror 24, and the three points are simultaneously moved in the same direction, that is, the optical path length is changed by the parallel movement (direction a) of the reflection mirror. The scanning line m can be made to be like m ″ and the magnification can be corrected. Also, by moving only one side of the support point, the scanning line m can be tilted (in the direction b) and moved like m ′. As for the adjustment method, as described in the first embodiment, a certain position which is positioned with high accuracy.
A color shift is corrected by moving a reflection mirror of another color with respect to an image formed by one scanning optical device.

As described above, according to the image forming apparatus of the present embodiment,
Of the plurality of scanning optical devices arranged, only one scanning optical device is positioned with respect to the main body housing with high precision by mechanical precision or assembling with a jig, and the other with respect to the image formed by the scanning optical device. By correcting the color image shift, color shift adjustment can be performed reliably and easily.

As another embodiment, an example in which the present invention is applied to a shaft support device of an image carrier of the multiple image forming apparatus will be described.

FIG. 8 (a) is a schematic diagram showing an apparatus to which the present invention is applied. 101M ~ BK are magenta, cyan,
Image carrier corresponding to yellow and black, 4 is a transport unit,
103M to BK are flanges fixed to the image carrier. For example, the magenta flange 103M is supported by a bearing 6M fixed to a support member 7M, and each of them except for the magenta flange 103M is shown in FIG. 1 (b). The supporting devices 6M to BK are supported, and the supporting devices are fixed to supporting members 7C to BK corresponding to the respective image carriers.

In addition, a power source M is connected to the inner side of the flange of each image carrier via a transmission mechanism (not shown). Although one power source M is arranged for each image carrier in the figure, it may be connected to a single power source. The support members 7M to BK are attached to the main body B by, for example, pins 70 or the like.

8 (b) and 8 (c) are detailed views of the shaft support device 6. FIG.
In this figure, the shaft of each flange 103 is supported by a bearing 601. The bearing 601 is supported by the inner case 604 so as to be movable in the direction of arrow A by a guide groove (not shown), and is urged by a spring 602 by an adjusting screw 603. The inner case 604 is also supported by the outer case 607 by a guide groove (not shown) so as to be movable in the direction of arrow B perpendicular to the arrow A, and is urged by the spring 605 by the adjusting screw 606.

When the shaft support device 6 is mounted with the direction A in the horizontal direction and the direction B in the vertical direction as shown in FIG. 8 (a), for example, the color shift in FIG. The adjustment can eliminate color shift due to the inclination of the scanning line. In such a configuration, if you use an M3 screw with a pitch of 0.5 mm, for example, you can adjust the position by 0.1 mm by turning the 1/5 turn screw. Can be.

FIG. 9 shows another embodiment. In this example, FIG.
2 shows a case where the support members 7M and BK are integrated support members 7. This method has an advantage that the shaft supporting devices 6C to BK are easily arranged with substantially the same pitch, and the amount of adjustment in the direction A in the figure is reduced.

Further, the outer case 607 in FIGS.
And a plurality of inner cases 604 may be attached thereto.

Further, in the present description, the image carrier for magenta in the first station is fixedly supported, but it is needless to say that the image carrier in any other station can be fixedly supported.

In this way, even in a plurality of rotation shaft adjustment mechanisms, if a certain arbitrary rotation shaft support is fixed and the position of another rotation shaft is adjusted based on this, the method of adjustment itself becomes easy. You will be able to make accurate adjustments.

In the present embodiment, as the color misregistration adjustment method, the adjustment method by moving the optical box and the movement of the reflection mirror and the drum support moving method are separately described, but by combining them, a more efficient adjustment method can be realized. . or,
In the present embodiment, an image forming apparatus for superimposing images of four colors has been described. However, for the purpose of the present invention in which one reference color is fixedly positioned and the other colors are adjusted and positioned, for example, two colors are used. Naturally, the present invention can be applied to a three-color copying machine or the like and to the multiplexing of two or more images other than color images.

In the present embodiment, the yellow image station is described as a reference image forming station. However, as a color misregistration correction operation performed by a machine operator, the reference color has a visual sensitivity such as cyan black. The higher the color, the easier the adjustment work is.

<Effects of the Invention> The image forming apparatus according to the present invention has the above configuration and operation, and has the following effects.

(1) By positioning only one of the plurality of image forming units with high accuracy, positioning of other image forming units is not required to be accurate.

(2) Since the position of another image is adjusted with respect to the reference image, the adjustment work is facilitated.

(3) Since the adjustment mechanism is not required for all images, the cost is reduced.

As described above, the registration can be adjusted by a simple method.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a), (b) and (c) are perspective views of a four-drum color printer, FIGS. 2 (a) and (b) are diagrams showing a method of adjusting a recording position, Fig. 3 is a perspective view of a conventional four-drum color printer, Fig. 4 is a perspective view of an optical scanning device, Figs. 5 (a), (b), (c), Figs.
(B), (c) and FIGS. 7 (a), (b), (c) are explanatory diagrams of positional deviation, FIGS. 8 (a), (b), (c) are explanatory diagrams of axis adjustment, FIG. 9 is an explanatory diagram of another axis adjustment.

Continuing on the front page (72) Inventor Setsu Uchida 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Kunihiko Matsuzawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc.

Claims (4)

(57) [Claims] 1. An apparatus for obtaining an image by multiplexing images formed by a plurality of image forming means on the same recording medium conveyed by a conveying body, wherein a predetermined one of the plurality of image forming means is provided. A correcting unit that corrects a positional shift between an image formed by the image forming unit and an image formed by another image forming unit other than the predetermined image forming unit; An image forming apparatus provided only for the other image forming unit among the forming units. 2. The image forming apparatus according to claim 1, wherein each of the plurality of image forming units has an image carrier and an optical system for irradiating the image carrier with a light beam. An image forming apparatus according to any one of the preceding claims. 3. An image forming apparatus according to claim 2, wherein said correcting means includes an adjusting means for adjusting a position of said optical system. 4. The apparatus according to claim 1, wherein said correcting means corrects a tilt shift between an image formed by said predetermined image forming means and an image formed by said another image forming means. The image forming apparatus according to item (1).