JPH04318569A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the delicate change of a color between respective images formed to cause the same change of the color on all the images that are respectively transferred to plural transfer materials from getting very conspicuous. CONSTITUTION:The transfer material 15 is consecutively fed by setting the distance L1 between the transfer materials so that L1 L3.N-L2 (N is a natural number) may be satisfied in the case of assuming that a distance between the transfer materials 15 consecutively fed is L1, the length in the feeding direction of the transfer material is L2, and the circumferential length of photosensitive drums 18a-18d where a visible image is formed is L3. Even when the very small change of the color caused by the fluctuation of the speed of the surface of the photosensitive drum or the partial unevenness of characteristic or the difference of characteristic is caused, all the images respectively formed on the plural transfer materials have the same color partially as well as wholly, so that the change of the color is prevented from getting very conspicuous.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to image forming apparatuses such as copying machines and printers using electrophotography or electrostatic recording.
In particular, but not limited to, images using a multi-transfer method that includes a plurality of image forming means and in which visible images formed by each image forming means are sequentially superimposed and transferred onto a transfer material to obtain a desired color image. The present invention relates to a forming device.

0002

2. Description of the Related Art Conventionally, a plurality of image forming means, for example, four image forming means, are arranged side by side, and each of these image forming means uses a photoreceptor drum as an image bearing member, and each photoreceptor drum has yellow, magenta, and cyan. , a black visible image, that is, a toner image, is formed separately, and the toner images of each color are sequentially superimposed and transferred onto a transfer material held and conveyed on a transfer material conveying device made of, for example, a dielectric belt, A multi-transfer type color image forming apparatus is known in which a desired full-color image or multi-color image is obtained by heating and fixing the multi-toner image on the transfer material using a fixing device.

[0003] Such a color image forming apparatus is advantageous in increasing speed because it has its own image forming means for each color, and it can be used with various materials such as cardboard and transparent recording paper because the transfer path can be configured in a straight line. Although it has advantages such as being adaptable to the thickness and material of the transfer material, it is difficult to achieve good registration (position matching) of each color toner image formed by separate image forming means. It had a serious drawback in that it had many problems in terms of.

[0004] Misalignment in the formation positions of the four colors of images transferred onto the transfer material (registration misalignment) ultimately appears as color misregistration or a change in hue. In order to prevent this registration shift, measures such as (1) matching the rotational speeds of the four photosensitive drums, and (2) keeping the moving speed of the transfer material constant are required.

For this reason, in the past, encoders were directly connected to the drive motors of the photosensitive drum and transfer material conveying means, and these drive motors were controlled to rotate at a constant speed by PLL (phase locked loop) control.

[0006]

By controlling the drive motor in this manner, large color misregistration is prevented, and becomes almost non-problematic when forming a single color image. However, when a number of identical color images are continuously formed, color misregistration becomes noticeable, and the above-mentioned conventional control method does not sufficiently solve the problem of color misregistration.

That is, minute speed fluctuations occur on the surface of the photoreceptor drum due to eccentricity of the photoreceptor drum or eccentric components due to misalignment of the axes between the photoreceptor drum and the photoreceptor drum driver, and this causes a difference of about several tens of μm on the image. A color shift occurs. It is difficult to distinguish this when forming a single color image, and therefore, this color shift does not pose a problem. However, when the same color images are continuously formed, the created color images are compared. A color shift of several tens of micrometers is then noticeable as a minute change in color tone in a halftone area (particularly gray), and there still remains the problem that the color tone appears different from image to image.

[0008] Furthermore, a photosensitive drum having a photosensitive layer has slightly different photosensitive characteristics depending on its surface. For this purpose, if images are formed continuously and photoconductor drums are used randomly, the same problem as mentioned above arises in that each image looks different in color, and as the image quality improves, , this is becoming a big problem.

Therefore, an object of the present invention is to transport the transfer material so that the same change in color tone occurs in all the images transferred to a plurality of sheets of transfer material that are continuously transported. To provide an image forming apparatus in which subtle changes in color between colors are not particularly noticeable.

0010

Means for Solving the Problems The above objects are achieved by an image forming apparatus according to the present invention. In summary, the present invention forms visible images of different colors on a plurality of image carriers,
In an image forming apparatus that obtains a color image by sequentially transferring visible images formed on each of the image carriers onto a continuously conveyed transfer material, an interval between the continuously conveyed transfer materials is defined as L1. , when the length of this transfer material in the conveying direction is L2 and the circumferential length of the image carrier is L3, L1 ≈L3 ・N − L2
(N is a natural number)
This is an image forming apparatus characterized by setting.

[0011] In another aspect of the present invention, the invention further includes means for separately setting the distance L1 between the transfer materials independently of the above relational expression, and the means can shorten the distance L1 between the transfer materials as necessary. By setting this, it is possible to speed up image formation for images that do not require high image quality such as multicolor images.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, an example of an image forming apparatus to which the present invention can be applied will be described with reference to FIG. Although the image forming apparatus shown in FIG. 3 is an electrophotographic color copying machine, the present invention is equally applicable to various image forming apparatuses such as electrophotographic and electrostatic recording methods. This color copying machine has a configuration in which four image forming means Pa, Pb, Pc, and Pd are linearly arranged, and each image forming means has a dedicated photosensitive drum 18a, 18b, 18c as an image carrier. and 18d, and these photoreceptor drums 18a to 18d.
Around 18d, there are dedicated image forming process means, such as chargers 8a, 8b, 8c, 8d, developing section 9a,
9b, 9c, 9d, transfer section 19a, 19b, 19c, 1
9d, cleaning parts 10a, 10b, 10c, 10d
and forming the image information as a latent image on the photoreceptor drum.
For example, laser scanner exposure means 1a, 1b, 1c, 1d
etc. are arranged.

On the other hand, a transfer material conveying section 7 equipped with an endless transfer belt 4 is disposed below the photosensitive drums 1a to 1d so as to pass through each image forming means Pa to Pd, and a transfer material 15 is provided to the right of the transfer material conveying section 7. A paper feed device 30 including a paper feed cassette 15a containing a paper feed cassette 15a is arranged. Further, a pair of rollers 16 for feeding the transfer material 15 in a timely manner is arranged between the paper feeding device 30 and the transfer material conveyance section 7, and the transfer material 15 is transferred from the paper feeding device 30 to the pair of rollers. 16 to the image forming means Pa to Pd.

In the above-described structure, first, the transfer material 15 sent out by the paper feeding device 30 is transferred to the roller pair 16.
Stop once when the tip is slightly pinched by the first
The transfer material is sent to the transfer material conveyance section 7 in synchronization with the image forming process of the image forming means Pa, and is electrostatically attracted onto the transfer belt 4 by an attraction means (not shown). In the first image forming means Pa, a laser scanner exposure means 1a scans image information on a photoreceptor drum 18a uniformly charged by a charger 8a to form an electrostatic latent image. A visible image of yellow toner is then formed in the developing section 9a.

On the other hand, the transfer material 15 is conveyed while being electrostatically attracted and held on the transfer belt 4, and is transferred onto the photoreceptor drum 18a by the action of the transfer charger of the transfer section 19a in the lower transfer area of the photoreceptor drum 18a. The formed yellow visible image, ie, the toner image, is transferred onto the transfer material 15. Thereafter, toner images of magenta, cyan, and black colors are sequentially formed in the second, third, and fourth image forming means Pb, Pc, and Pd in the same manner as in the first image forming means Pa, and the transfer belt These toner images are sequentially and multiple-transferred onto the transfer material 15 conveyed by the transfer member 4. When the transfer process is completed, the transfer material 15 is separated from the transfer material conveying section 7 and sent to the fixing device 14, where it is fixed all at once to obtain a desired full-color image. Further, the photosensitive drums 18a to 18 of each image forming means Pa to Pd after the transfer has been completed.
At d, residual toner is removed by cleaning sections 10a to 10d in preparation for the next latent image formation to be performed subsequently.

Next, an embodiment of the present invention applied to the image forming apparatus having the above configuration will be described in detail with reference to FIGS. 1 and 2.

FIG. 1 is a timing chart for explaining a first embodiment of the present invention, in which the same image is continuously formed on a plurality of transfer materials shorter than the circumference of the photoreceptor drums 18a to 18d. photoreceptor drum (a typical example is photoreceptor drum 1)
8a) shows the relationship between the surface positional deviation amount Δl and a plurality of sheets of transfer material that are continuously conveyed. Positional deviation amount Δ
l indicates the amount by which the image writing position by the exposure means deviates from the normal rotating position due to speed fluctuations on the surface of the photoreceptor drum, and since this amount and phase differ between each photoreceptor drum, the image writing position on the transfer material A slight color shift (change in color tone) occurs in the image formed.

In this embodiment, the circumferential length of the photosensitive drum is L3.
, the length of the transfer material in the advancing direction is L2, and the interval between continuously conveyed transfer materials is L1, then the interval L1 of the transfer materials is set to satisfy the following equation. L1 ≒ L3 ・N − L2
(N=1) (As a specific example, if the photoreceptor drum diameter is 80 mm and the transfer material is A4 horizontally fed (L2 = 210 mm), L1 ≒ 80π - 210 = 41.33 mm.) In this way, the transfer material When the interval L1 is set, the plurality of transfer materials are continuously conveyed at the timing shown in FIG. Further, in this embodiment, image formation on one sheet of transfer material is completed with one rotation of the photoreceptor drum. At this time, the distance L1 between the transfer materials is controlled by the timing at which the roller pair 16 is fed out. Furthermore, the above-mentioned positional deviation amount Δ
Since l is caused by eccentricity of the photoreceptor drum, eccentricity due to axis misalignment between the photoreceptor drum and the photoreceptor drum driver, etc., Δl is the period of one rotation of the photoreceptor drum, as shown in FIG. Becomes a function.

Therefore, as in this embodiment, the distance L between the transfer materials is
When 1 is set, the above-mentioned positional deviation occurs in the same way for a plurality of sheets of transfer material that are continuously conveyed, in other words, for a plurality of images to be formed. This also holds true for the photoreceptor drums 18b to 18d of the other three image forming means, so even if a subtle change in color occurs due to the above-mentioned positional deviation, it is possible to The plurality of images formed respectively have the same color tone. Thus, according to the present invention, subtle changes in color are not particularly noticeable.

Furthermore, even if there is a local unevenness or difference in the photosensitive characteristics of the photosensitive drum, according to the present invention, for the same reason as mentioned above, there is no difference in the photosensitive characteristics of the photosensitive drum. Even if a partial change in color occurs in each of the plurality of images formed, it is not particularly noticeable because it is the same for all images.

FIG. 2 is a timing chart for explaining a second embodiment of the present invention, in which the same image is continuously formed on a plurality of transfer materials longer than the circumferential length of the photoreceptor drums 18a to 18d. The relationship between the amount of positional deviation Δl on the surface of the photoreceptor drum (the photoreceptor drum 18a is shown as a typical example) and a plurality of sheets of transfer material that are continuously conveyed is shown. In this embodiment as well, the circumferential length of the photosensitive drum is L3, the length of the transfer material in the advancing direction is L2, and the interval between continuously conveyed transfer materials is L1.
, the distance L between the transfer materials satisfies the following formula:
1. L1 ≒ L3 ・N − L2
(N=2) (As a specific example, if the photoreceptor drum diameter is 80 mm and the transfer material is A3 vertically fed (L2 = 420 mm), L1 ≒ 80π x 2 - 420 = 82.65 mm.) Transfer in this way When the material interval L1 is set, the plurality of transfer materials are continuously conveyed at the timing shown in FIG. Further, in this embodiment, image formation on one sheet of transfer material is completed by two rotations of the photoreceptor drum. The distance L1 between the transfer materials is the same as in the first embodiment described above.
It is controlled by the sending timing of step 6.

Obviously, in this embodiment as well, the images formed on the plurality of sheets of transfer material that are continuously conveyed have the same color both partially and as a whole. Changes in color are no longer particularly noticeable, and the above-mentioned drawbacks of the conventional technology can be completely eliminated.

Note that the length of the transfer material in the conveying direction is various, and the distance L1 between the plurality of transfer materials that continuously form images is
If L1 is set as in the above embodiment, the circumferential length of the photosensitive drum is uniquely determined by the apparatus, so the interval L1 between the transfer materials may be sufficiently large. In this case, although deterioration in image quality due to differences in color can be prevented, there is a slight disadvantage in terms of image forming speed. On the other hand, the images to be formed have a wide range of needs, from gravure-like pictorial color images to graph-like multicolor images, and the requirements for image quality also vary.

Therefore, in addition to being able to set the distance L1 between the transfer materials using the above-mentioned relational expression as in each of the above embodiments, it is also possible to set the distance L1 between the transfer materials independently of the formula.
Further, a means for setting is provided. That is, since the distance L1 between the transfer materials is determined by the feeding timing of the pair of rollers 16, for example, a mode is set in which the timing is electrically changed to reduce the distance L1 between the transfer materials. When forming a multicolor image or the like that does not require high image quality, it is convenient to perform image formation in this mode because it can speed up the image formation.

Furthermore, even if the transfer material is shorter than the circumference of the photosensitive drum, it is not necessary to limit the condition to L1 ≒L3 - L2, but to the condition L1 ≒L3 ・N-L2 (N is a natural number). It goes without saying that it is a good thing if the conditions are met (the biggest drawback, deterioration in image quality due to differences in color tone, can be completely prevented).

In the above embodiments, the present invention is applied to an image forming apparatus using a drum-shaped photoreceptor, but the present invention is not limited to this. For example, a belt-shaped endlessly moving photoreceptor may be used. Furthermore, the number of image forming means may be plural, and is not limited to four as in this embodiment. Further, in each of the above embodiments, the present invention is applied to an electrophotographic color copying machine, but the present invention can be applied to various copying machines, printers, etc. using electrophotography, electrostatic recording, etc. other than the embodiments. It is equally applicable to the following image forming apparatuses. Further, as described above, it goes without saying that various modifications and changes can be made to the members, elements, etc. constituting the image forming apparatus as necessary.

[0028]

As explained above, in the image forming apparatus according to the present invention, when the circumferential length of the image carrier is L3, the interval between the transfer materials is L1, and the length of the transfer material in the transport direction is L2, L1 ≒ L3 ・N − L2
(N is a natural number)
can be set, so even if slight changes in color occur due to speed fluctuations on the surface of the image carrier, all continuously formed images will have the same color and will not be particularly noticeable. . Furthermore, even if a slight change in color occurs due to unevenness or difference in the characteristics of the image carrier, all continuously formed images will have the same color and will not be particularly noticeable. This has a remarkable effect.

Furthermore, if a means for setting L1 separately from L1 determined by the above-mentioned relational expression is provided, and if necessary, this setting means is used to shorten the interval between the transfer materials, thereby producing a multicolor image. This also has the effect of speeding up image formation for images that do not require high image quality.

[Brief explanation of the drawing]

FIG. 1 is a timing chart for explaining a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a timing chart for explaining a second embodiment of the image forming apparatus according to the present invention.

FIG. 3 is a schematic cross-sectional view showing an example of an image forming apparatus to which the present invention is applicable.

[Explanation of symbols]

4 Transfer belt 7
Transfer material conveyance section 15
Transfer material 16
Roller pairs 18a to 18d Photosensitive drum

Claims (2)

[Claims] 1. Visible images of different colors are formed on a plurality of image carriers, and the visible images formed on each of the image carriers are sequentially transferred onto a transfer material that is continuously conveyed. In an image forming apparatus that obtains an image, when the interval between the continuously conveyed transfer materials is L1, the length of the transfer material in the conveyance direction is L2, and the circumference of the image carrier is L3,
L1 ≒ L3 ・N − L2
(N is a natural number)
An image forming apparatus characterized by setting. 2. The image according to claim 1, further comprising means for separately setting the distance L1 between the transfer materials, and the distance L1 between the transfer materials can be set by the means as necessary. Forming device.