JPH0731447B2 - Image forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a color image forming apparatus, and in particular, a plurality of image forming media such as electrophotographic photoconductors are juxtaposed and electrophotographic is performed on these photoconductors. An image forming process is performed to obtain a developed image of each color, and the developed image is sequentially transferred to a transfer material carried and conveyed by a transfer material conveying device, or an image carrier such as an intermediate transfer body or continuous paper to obtain a color image. The present invention relates to such a multicolor electrophotographic image forming apparatus. The present invention can be embodied not only in an electrophotographic color copying apparatus, but also in various color printers and the like. In the present specification, a laser beam printer to which electrophotography is applied will be described. Further, the image forming medium used in the present invention may have any form such as a belt or a drum as long as it is an image forming medium which moves endlessly, but in the present specification, it is described as a drum. To do.

2. Description of the Related Art Conventionally, some methods have been proposed as laser beam printers based on electrophotography. One of the typical methods among them is schematically shown in FIG.

According to the full-color laser beam printer of FIG. 7, three image forming units Pa, Pb, Pc are arranged, and each image forming unit has its own photosensitive drums 1a, 1b, 1c, and its surroundings, respectively. Image forming process means (not shown except for laser beam exposure means 3a, 3b, 3c, for example, charging section, exposure section, developing section, transfer section,
(A cleaning unit etc.) is arranged. Photosensitive drums 1a, 1b,
1c indicates that the rotational driving force of the drive motors 13a, 13b, 13c is the gear 1
It is driven by being transmitted to the photosensitive drum via 2a, 12b, 12c and 11a, 11b, 11c. On the other hand, photosensitive drum 1
Below the a, 1b, and 1c, a transfer material is equipped with a movable body, that is, an endless belt 7 that is suspended by the drums 5 and 6 and rotates in the direction of the arrow while penetrating the image forming units Pa, Pb, and Pc. Means 4 are arranged to transfer the transfer material 9 fed by a paper feeding device (not shown) to the transfer position 18 of each image forming unit Pa, Pb, Pc.
It is configured to be conveyed in the direction of the arrow through a, 18b, 18c.

In such a structure, first, the first image forming unit
A visible image of yellow toner is formed at Pa, and the yellow toner image is transferred to the transfer material 9 conveyed by the transfer material conveying means 4 at the transfer portion, that is, at the transfer position 18a. On the other hand, while the yellow image is being transferred to the transfer material 9, a toner image with magenta toner is obtained in the second image forming unit Pb, and the transfer material 9 that has been transferred in the first image forming unit Pa is When the two-image forming unit Pb is carried into the transfer position 18b, the magenta toner image is transferred to a predetermined position on the transfer material P.

Thereafter, an image is formed in the same manner for cyan and, if desired, black, and when the superimposing of the toner images of three or four colors on the transfer material 9 is completed, the transfer material 9 is fixed on a fixing portion (not shown). Then, a multicolor (full color) image is obtained on the transfer material 9.

After the transfer, each photosensitive drum is cleaned of residual toner by cleaning means (not shown) to prepare for the next latent image formation.

Such a full-color image forming apparatus has an image forming unit for each color, which is advantageous for speeding up.

Since the transfer path can be configured linearly, it is adaptable to transfer materials such as thick paper and transparent film.

However, one of the biggest drawbacks is that it has a great problem in how to properly perform the resist registration of each color image formed by different image forming units.

The deviation (registration) of the image forming positions of the three or four colors transferred onto the transfer material finally appears as a color deviation or a hue change. One of the causes of this misregistration is that the start position of image transfer to the transfer material is deviated between the photosensitive drums due to uneven rotation of the photosensitive drums.
That is, as shown in FIG. 8, for example, the color misregistration in the paper feeding direction between the yellow image (Y) and the magenta image (C) transferred to the transfer material 9 by the image forming units Pa and Pb is the gear 11a, Occurring randomly due to the eccentricity of 11b, 11c, 12a, 12b, 12c and the eccentricity of the photosensitive drums 1a, 1b, 1c (8th
(Figure A). In the worst case, as shown in FIG. 8B, the yellow image (Y) and the magenta image (C) have completely opposite phases.

In order to solve such a problem, it is necessary to make the manufacturing error of the photosensitive drum, the gear, etc. severe, and the manufacturing cost of the image forming apparatus becomes high. Further, the present applicant has proposed a method of connecting a rotary encoder to the photosensitive drums to accurately control the rotation of each photosensitive drum. The method was able to obtain good results, but the structure and control mode were complicated, and the cost of the image forming apparatus was consequently high.

As a result of researching a driving method and a controlling method of a photosensitive drum to solve such a problem, the present inventors have found that all the image forming media such as the photosensitive drum of the image forming apparatus are manufactured by the same manufacturing method, and the eccentricity of gears It is noted that the amount is approximately the same and that the expansion and contraction of the image due to these values is reproduced in a cycle of one rotation of the photosensitive drum. For example, the expanded portion (reduction of the image) of the photosensitive drum located on the upstream side is reduced. The phase (phase angle) between the photosensitive drums is set so that the expanded portion (reduced portion) of the image on the photosensitive drum located on the downstream side is transferred to the transfer material on which Thus, it has been found that it is possible to obtain a multicolor image that is substantially free of color misregistration, that is, inconspicuous color misregistration, while allowing eccentricity of the photosensitive drum and gears.

Focusing on such phase matching, there are proposals such as JP-A-61-156158 and 61-156159, but since this proposal is composed of a spur gear train, the following drawbacks are encountered. Have.

As the drive source is transmitted from the upstream side to the downstream side, the accumulated pitch errors for the number of gear meshing stages are added. That is, the wow fratter becomes larger on the downstream side.

Since the backlash increases by the number of gear meshing steps, the backlash increases and the image is likely to be adversely affected.

Pitch unevenness caused by the gears also increases by the number of gear meshing steps and increases on the downstream side, resulting in poor image quality.

Accordingly, an object of the present invention is to set a phase angle between image forming media without using a continuous gear train, thereby deviating an image from each image forming medium to an image carrier, That is, it is an object of the present invention to provide an image forming apparatus that can obtain a high-quality color image without color misregistration.

Another object of the present invention is to provide an image forming apparatus capable of obtaining a high-quality color image with a simple structure by eliminating the image transfer deviation from each image forming medium to the image carrier, that is, the color deviation. Is.

Means for Solving Problems The above object is achieved by the image forming apparatus according to the present invention.
In summary, the present invention relates to a plurality of image forming media, a plurality of driving means for independently rotating and driving each of the image forming media, an image forming means for forming an image on each of the image forming media, and An image forming apparatus that has a moving body that moves a transfer position of an image forming medium, and that transfers the image to the moving body or a transfer material carried on the moving body. The phase state detecting means for detecting the phase state of each of the image forming media, and the driving means detects the phase state detecting means so as to align the phases of the image forming media with respect to the moving body. The image forming apparatus is characterized in that the rotation speed of each image forming medium is controlled based on the result.

Embodiment Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

1 to 3 show a first embodiment of the present invention. Since the present invention is embodied in the conventional image forming apparatus described above with reference to FIG. 7 in this embodiment, the same or equivalent members and parts as those in the conventional example are designated by the same reference numerals. Detailed description is omitted.

The principle of the present invention will be described with reference to FIGS. 1 and 2.

As described above, it is usual that the image forming medium manufactured by the same manufacturing method, the photosensitive drum in this embodiment, the gear of the driving means, and the like have substantially the same shape and error. For example, in the case of a photosensitive drum, since the shape of the master die is transferred as it is by an extrusion molding method, a deep drawing molding method, etc., the eccentricity amount becomes a value approximate to each other. Further, regarding gears, it has been found that gears manufactured by the same processing machine also show similar eccentricity between gears even in hobbing, molding, etc.

According to the research and experiment conducted by the present inventors, in the image forming apparatus formed by using the photosensitive drum, the gear and the like having such an approximate shape and eccentricity, as shown in FIG. Expansion and contraction of the color images Y, M, and C formed by the forming units Pa, Pb, and Pc show the same tendency, have substantially the same maximum expansion and contraction amounts 15a, 15b, and 15c, and are reproduced in a constant cycle. Found.

In FIG. 1, the phase 15a of the photosensitive drum 1a showing the maximum image expansion amount of the photosensitive drum 1a of the image forming unit Pa is
At the transfer position 18a, the phase 15b of the photosensitive drum 1b indicating the maximum image extension amount of the photosensitive drum 1b of the image forming unit Pb adjacent to the image forming unit Pa is the transfer position 18b.
It is assumed that the position is from (360 degrees −θ ₁ ). Here, the transfer position 18a of the image forming unit Pa and the image forming unit Pb
If the distance from the transfer position 18b of the photosensitive drum 1 to S ₁ is S ₁ , the expansion and contraction phase of the photosensitive drums 1a and 1b is set so that S ₁ = r ₁ × θ ₁
Both a and 15b are set, and both photosensitive drums are maintained while maintaining the phase relationship.
By rotating 1a and 1b, when the transfer material 9 passes through the transfer position 18a, for example, if the extended portion of the image is transferred, when the next transfer position 18b is passed, the extended portion of the image on the photosensitive drum 1b is changed. It will be transcribed. As a result, both images are transferred to the transfer material without any color shift. Of course, θ ₁ is 2π
The value is not limited to (360 degrees), and a value of 2π or more can be adopted depending on the value of S ₁ .

Regarding the relationship between the image forming units Pb and Pc, it will be understood that both images are transferred onto the transfer paper in the same manner as described above without causing color shift.

Referring to FIG. 3, in this embodiment, the photosensitive drums 1a, 1a
b and 1c are driven by independent drive means having drive motors 13a, 13b and 13c, respectively. Each photosensitive drum 1a, 1b, 1c
Is the gear 1 meshed with the output gears 12a, 12b, 12c of the drive motor
1a, 11b, 11c, the gears 11a, 11b, 11c are provided with phase marks (reflection marks) 14a, 14b, 14c, and photo sensors 15a, 15b as phase detection means for detecting the reflection marks, 15c is provided in the main body of the device.

A control circuit known as a PLL (phase locked loop) method is connected between the sensors 15a, 15b, 15c and the motors 13a, 13b, 13c, and a reference signal generator 16 using a crystal oscillator and an amplifier are built in. Phase comparison circuits 17a, 17b, 17c are provided.

Explaining how to match the phases with reference to FIG.
Indicates a pulse of the reference signal generator 16. This generates a pulse train at intervals of one rotation in the steady rotation of the drum. The pulse 19 is, for example, a pulse train of the reflection mark 14a detected by the sensor 15a.

The pulse 20 indicates the amount of electric power supplied to the motor 13a. This energy rises in the pulse train 18 and
Disappears.

The pulse 21 is also a pulse train of the reflection mark 14b detected by the sensor 15b, for example.

The pulse 22 indicates the amount of electric power supplied to the motor 13b. The pulse 22 also rises by the pulse train 18 and disappears in the pulse train 21.

When the print start signal is generated, the phase of each reflection mark varies, so that the electric power 20a, 22a is supplied to each motor according to the delay amount from the reference clock 18.

Here, the power pulse 22a is longer than the power pulse 20a because the motor 13b rotates faster than the motor 13a and is controlled so as to catch up with the reference clock.

Finally, as shown in power amounts 20b and 22b, the respective reflection marks converge to a state delayed by a specific amount from the reference pulse 18, and at this time, the power amounts 20b and 22b become equal. That is, the reflection mark 14
The phases of a and 14b rotate together. As described above, in the present embodiment, it is possible to correct from the state where the phase of each image forming medium with respect to the moving body is shifted to the state where the phase of each image forming medium with respect to the moving body is aligned. Although both phase control and wow-flutter control are necessary for rotation control, the latter PLL control is well known, so only phase control is shown here.

More specifically, as described above, according to the present invention, when the photosensitive drums 1a, 1b, and 1c are driven in the above-described configuration, the image is transferred onto the transfer material 9 in the extended position at the transfer position 18a of the photosensitive drum 1. When transferred, the transfer material 9 is transferred to the next photosensitive drum 1c even at the transfer position 18b of the next photosensitive drum 1b.
Even at the transfer position 18c, the image on each photosensitive drum is transferred onto the transfer material 9 in an expanded state, and the transfer deviation at each image station is eliminated. On the other hand, the image is transferred onto the transfer material 9 in the contracted state at the transfer position 18c of the photosensitive drum 1a.
Even when the image is transferred to the transfer material, the image is transferred to the transfer material 9 in a contracted state at each photosensitive drum transfer position as described above, and thus the image is transferred onto the transfer material without causing transfer deviation. .

The reflection marks 14a, 14b, 14c do not necessarily have to show the peak of the expansion / contraction phase, and may be provided anywhere as long as the phase in the manufacturing process of the photosensitive drum or the gear can be specified.

Further, the gears 12a to 12c can have any number of teeth,
Especially for gears 11a to 11c, select the number of teeth with an integer ratio relationship,
The gears 12a to 12c may also be provided with phase marks in the manufacturing process so that the gear pairs 12a and 11a, 12b and 11b, and 12c and 11c have the same phase relationship. In this case gears 12a-1
The wow flatter of 2c repeats the same phase, so there is no color misregistration.

The above-described embodiment is a multi-color electrophotographic laser beam printer in which a developed image is sequentially transferred to a transfer material conveying means 4 having a belt, that is, a transfer material 9 carried and conveyed by a moving body to obtain a color image. Was described in connection with
The present invention can also be embodied in a multicolor electrophotographic image forming apparatus that sequentially transfers a developed image to an image carrier such as an intermediate transfer body or continuous paper to obtain a color image. Another embodiment of the present invention is illustrated in FIGS.

FIG. 5 shows that in the present invention, the image formed on the photosensitive drums 1a, 1b and 1c is temporarily transferred to the intermediate transfer body 40, and thereafter, the visible image on the intermediate transfer body 40 as the moving body is transferred onto the transfer material 9. 1 shows an aspect realized in an image forming apparatus of a transfer type.

According to this embodiment, the endless belt-shaped intermediate transfer member 40 is arranged below the photosensitive drums 1a, 1b, 1c. The driving structure of the intermediate transfer member is substantially the same as that of the transfer material transfer means 4 described with reference to FIGS. 1 and 3, and instead of the transfer belt 7, a belt-shaped intermediate transfer member 40, For example, the only difference is that a belt-shaped polyester film, polyimide film, silicone rubber, urethane rubber or the like is used. Further, in the present embodiment, in order to further transfer the visible image once transferred to the intermediate transfer member 40 onto the transfer material 9, the transfer material 9 fed from a paper feeding device (not shown) is transferred to the intermediate transfer member 40.
In order to press the transfer rollers 40a and 40b instead of the suspension drum 6 in FIG.

In the present embodiment, gear reduction is performed by a two-stage gear pair 24a and 23a,
Although it is configured by 12a and 11a, it is not necessary that all the gear trains have an integer ratio relationship, and the low speed side gear pair 12a and 11a may have an integer ratio relationship. The color superposition shift due to the wow flatter of the high speed side gear pair 24a and 23a becomes relatively small as a result of the deceleration and becomes inconspicuous.

In this embodiment, the same effect as that of the embodiment shown in FIG. 3 can be obtained.

FIG. 6 shows a multicolor electronic device according to the present invention, in which images formed on the photosensitive drums 1a, 1b and 1c are sequentially transferred to an image carrier such as a continuous paper 9a as a moving body to obtain a color image. The mode realized in the photographic image forming apparatus is shown. According to this embodiment, the continuous transfer paper 9a fed from the transfer roll paper is arranged below the photosensitive drums 1a, 1b and 1c, and the image on the photosensitive drum is directly transferred to the roll paper. That is, in this embodiment, the continuous paper 9 is provided instead of the conveyor belt 7 in the transfer material conveying means described with reference to FIG.

In the case of this embodiment, direct drive motors are used as the motors 41a to 41c, and they have rotary encoders 42a to 42c, respectively.

The zero phase signal of the rotary encoder (referred to as Z signal) and the increment signal pulse of the encoder used for phase matching in FIG. 4 are used for wow and flatter control.

Also in this embodiment, the same effect as that of the first embodiment can be obtained.

Although the present invention has been described with respect to the electrophotographic method in the above-mentioned embodiments, the present invention is not limited to this and can be applied to, for example, an ink jet method, a heat-sensitive method, a general printing technique and the like.

Effects of the Invention The image forming apparatus according to the present invention configured as described above is
By detecting the phase state of each image forming medium being rotationally driven by each driving means and changing the rotational speed of each image forming medium based on the detection result by this phase state detecting means to drive the moving body, Since the phases of the respective image forming media are aligned with respect to each other, in the transfer of the image from the respective image forming media to the moving body or the transfer material carried on the moving body, the transfer deviation due to the phase variation of the image forming medium is prevented. It becomes possible. Furthermore, since the phase of each image forming medium with respect to the moving body is aligned based on the detection result by the phase state detecting means, it is not necessary to align the phase when mounting each image forming medium in the apparatus, and when the driving means starts driving. Even if the phase of each image forming medium with respect to the moving body is deviated due to uneven driving or the like when the driving is stopped, this can be corrected.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for explaining the principle of the image forming apparatus according to the present invention. FIG. 2 is a graph showing the cyclic variation of expansion and contraction of each color image. FIG. 3 is a perspective view of an embodiment of the image forming apparatus according to the present invention. FIG. 4 is a control pulse diagram according to the present invention. FIG. 5 is a perspective view of a second embodiment of the image forming apparatus according to the present invention. FIG. 6 is a perspective view of a third embodiment of the image forming apparatus according to the present invention. FIG. 7 is a perspective view of a conventional image forming apparatus. FIG. 8 is a graph showing a periodic variation in the expansion / contraction amount of a color image in the conventional image forming apparatus. 1a, 1b, 1c: Image forming medium 4: Transfer material conveying means 9, 9a: Transfer material 18a to c: Transfer position 40: Intermediate transfer member

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Claims (1)

[Claims] 1. A plurality of image forming media, a plurality of driving means for independently rotating and driving each of the image forming media, an image forming means for forming an image on each of the image forming media, and each of the image forming means. An image forming apparatus that has a moving body that moves a transfer position of a medium, and that transfers the image to the moving body or a transfer material carried on the moving body, and is rotationally driven by each of the driving units. A phase state detecting means for detecting a phase state of each of the image forming media, each driving means is provided with a detection result by the phase state detecting means so as to align the phase of each of the image forming media with respect to the moving body. An image forming apparatus, wherein the rotation speed of each image forming medium is controlled based on the above.