JPH0810372B2 - 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 by a transfer material carrying device and carried, 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 laser beam printer for full color of FIG. 5, three image forming units Pa, Pb and Pc are arranged,
Each image forming unit has a dedicated photosensitive drum 1a, 1b, 1c, around which a dedicated image forming process means (laser beam exposure means 3a, 3b, 3c are not shown, for example, charging unit , Exposure unit, developing unit, transfer unit,
(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. Meanwhile, photosensitive drum
A transfer material transporter provided with a movable body, that is, an endless belt 7 that is suspended by drums 5 and 6 in a manner penetrating each image forming unit Pa, Pb, and Pc below 1a, 1b, and 1c, and is rotated in an arrow direction. 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, a visible image of yellow toner is formed by the first image forming unit Pa, and the transfer portion, that is, the transfer member 9 is transferred to the transfer material 9 conveyed by the transfer material conveying means 4.
The yellow toner image is transferred at the transfer position 18a. on the other hand,
While the yellow image is being transferred to the transfer material 9, the second
A toner image with magenta toner is obtained in the image forming unit Pb, and the transfer material 9 that has been transferred in the first image forming unit Pa is carried into the transfer position 18b of the second image forming unit Pb. This magenta toner image is transferred to a predetermined position on 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. 6, 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, It occurs randomly due to the eccentricity of 11b, 11c, 12a, 12b, 12c and the eccentricity of the photosensitive drums 1a, 1b, 1c (FIG. 6A). In the worst case, as shown in FIG. 6B, 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. Although the method was able to obtain good results, the structure and control aspects became complicated,
The cost of the image forming apparatus is consequently high.

The present inventors have studied the driving method and the controlling method of the photosensitive drums to solve such a problem, and as a result, all the image forming media such as the photosensitive drums of the image forming apparatus are manufactured by the same manufacturing method, and the eccentricity of the gears is increased. Focusing on the fact that the amount is approximately the same and the expansion and contraction of the image due to these are reproduced with one rotation of the photosensitive drum as a cycle, the distance between the photosensitive drums, that is, the transfer of the adjacent photosensitive drums to each other. By setting the distance between positions to be an integral multiple of the peripheral length of the photosensitive drum, for example, a transfer material to which the expanded portion (reduced portion) of the image of the photosensitive drum located on the more upstream side is transferred, By transferring the expanded portion (reduced portion) of the image on the photosensitive drum located on the downstream side, eccentricity of the photosensitive drum and gears is allowed, but there is substantially no color misregistration, that is, color superposition misregistration. Inconspicuous multicolor image It has been found that can Rukoto.

Focusing on such phase matching, there are proposals such as Japanese Patent Laid-Open Nos. 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 stages in which the gears do not mesh 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 becomes large and the image is likely to be adversely affected.

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

Object of the Invention An 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 transfer deviation of an image from each image forming medium to an image carrier, that is, color deviation. That 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 provides a plurality of image forming media having substantially the same shape, a plurality of driving means for independently rotating and driving each of the image forming media, and an image for forming an image on each of the image forming media. An image forming apparatus comprising: a forming unit and sequentially transferring the images onto the image receiving material at the transfer position of each image forming medium, the image forming apparatus including an image receiving material conveyance path between the transfer positions of the adjacent image forming media. In an image forming apparatus in which a distance along the image forming medium is an integral multiple of the circumference of the image forming medium, marks provided at the same position on the phase of each of the image forming media and the same position with respect to each of the image forming media. A plurality of mark detecting means for detecting the marks, the driving means changing the rotational speed of each image forming medium based on the detection result of the mark detecting means. Characterized by Image forming apparatus.

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

FIG. 1 illustrates 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. 5 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.

According to the present embodiment, each photosensitive drum as an image forming medium
1a, 1b, 1c are driven by independent drive means having drive motors 13a, 13b, 13c, respectively. Each photosensitive drum 1
a, 1b, 1c are provided with gears 11a, 11b, 11c meshing with output gears 12a, 12b, 12c of the drive motor, and the gears 11a, 11b, 11c
Phase marks (reflection marks) 14a, 14b, 14c are attached at the same position on the phase of the image forming medium, and a photo sensor 15 as mark detecting means for detecting the reflection marks.
a, 15b, and 15c are provided at the same position for each image forming medium.

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 16 is used.
And phase comparison circuits 17a, 17b, 17c having built-in amplifiers.

Explaining how to match the phases with reference to FIG.
Reference numeral 18 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 electric energy rises in the pulse train 18 and
It disappears by 19.

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 the pulse train 21
Disappears at.

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
This is because the motor 13b rotates faster than the motor 13a and is controlled so as to catch up with the reference clock.

Eventually, as shown by the power amounts 20b and 22b, each reflection mark converges to a state delayed by a specific amount from the reference pulse 18,
At this time, the electric power amounts 20b and 22b become equal. That is, the reflection mark
The phases of 14a and 14b rotate in unison. 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.

Here, if the transfer position intervals H ₁ and H ₂ of each drum are set to integral multiples of the drum circumferential length, the sensors 15a, 15b and 15c are assembled in the same phase with respect to the center lines of the drums 1a, 1b and 1c. Thus, the expansion / contraction phase of the image at each transfer position can be automatically adjusted.

More specifically, as described above, according to the present invention, when the photosensitive drums 1a, 1b, and 1c are driven in the above-described structure, the image is used as an image receiving material in the extended position at the transfer position 18a of the photosensitive drum 1. When the image is transferred to the transfer material 9, the image on each photosensitive drum is expanded at the transfer position 18b of the next photosensitive drum 1b and further at the transfer position 18c of the next photosensitive drum 1c. In this state, the image is transferred onto the transfer material 9, and the transfer deviation in each image station is eliminated. On the other hand, when the image is transferred to the transfer material 9 in a contracted state at the transfer position 18a of the photosensitive drum 1a, the image is transferred in the contracted state at each photosensitive drum transfer position in the same manner as described above. Then, 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 located anywhere as long as the phase can be specified in the manufacturing process of the photosensitive drum and the gear.

Further, the gears 12a to 12c may be selected with any number of teeth, but in particular, with respect to the gears 11a to 11c, the number of teeth in an integer ratio relationship is selected, and the gears 12a to 12c are also marked with phase marks in the manufacturing process. ,
It is also possible to assemble so that the gear pairs 12a and 11a, 12b and 11b, 12c and 11c have the same phase relationship. In this case, the wow and flatters of the gears 12a to 12c are not repeatedly caused to have the same phase, and thus the color overlapping shift is not caused.

The above embodiment relates to a multi-color electrophotographic laser beam printer in which a developed image is sequentially transferred to a transfer material 9 carried and carried by a transfer material carrying means 4 having a belt to obtain a color image. Although described, 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. 3 and 4 show another embodiment of the present invention.

FIG. 3 shows that the present invention temporarily transfers the image formed on the photosensitive drums 1a, 1b and 1c to the intermediate transfer body 40 as an image receiving material, and then transfers the visible image on the intermediate transfer body 40 to the transfer material 9. 1 shows a mode realized in a transfer type image forming apparatus.

According to this embodiment, the endless belt-shaped intermediate transfer member 40 is arranged below the photosensitive drums 1a, 1b, 1c. The drive structure of the intermediate transfer member is substantially the same as that of the transfer material conveying means 4 described with reference to FIGS. 1 and 5, and instead of the conveyor belt 7, a belt-shaped intermediate transfer member 40, for example, The only difference is that a belt-shaped polyester film, polyimide film, silicon 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 roller 40a, 40b instead of the suspension drum 6 in FIG.

Also in the present embodiment, the transfer position intervals H ₁ and H ₂ are configured to be integral multiples of the drum circumference, and the sensors 15a and 15b,
Since 15c is arranged in the same phase with respect to the center of the drum, the assembling work can be simplified and the sensor position fixing component (not shown) can be shared.

In the present embodiment, gear reduction is performed by a two-stage gear pair 24a and 2
3a, 12a and 11a, but it is not necessary that all the gear trains have an integer ratio relationship, and the low speed side gear pair 12a and 11a
It suffices that and have an integer ratio relationship. The reason is that the color superimposition shift caused by the wow flatter of the high speed gear pair 24a and 23a becomes relatively inconspicuous as a result of being decelerated.

Also in this embodiment, the same effect as the embodiment of FIG. 1 can be obtained.

FIG. 4 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 continuous paper 9a as an image receiving material 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. 2 are used for the wow and flatter control.

Also in this embodiment, the transfer position intervals H ₁ and H ₂ are set to integral multiples of the drum circumference. Also, the detector of the zero phase signal,
Since it is fixed to the housing of the rotary encoder 42, the rotary encoders 42a, 42b, 42c may be assembled in the same posture.

Also in this embodiment, the same effect as that of the embodiment of FIG. 1 can be obtained.

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

Advantageous Effects of Invention The image forming apparatus according to the present invention configured as described above allows expansion and contraction of an image on an image forming medium,
Therefore, it is possible to transfer images from each image forming medium to the image forming carrier with a simple structure without any transfer deviation, that is, color deviation, without the need for high-precision parts. You can obtain high quality color images.
Further, it is possible to avoid the cumulative deterioration when the spur gear trains are connected.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of the image forming apparatus according to the present invention. FIG. 2 is a control pulse diagram according to the present invention. FIG. 3 is a perspective view of a second embodiment of the image forming apparatus according to the present invention. FIG. 4 is a perspective view of a third embodiment of the image forming apparatus according to the present invention. FIG. 5 is a perspective view of a conventional image forming apparatus. FIG. 6 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: copying material conveying means 9, 9a: transfer material 13a, 13b, 13c: drive motors 18a to c: transfer position 40: intermediate transfer member

Claims (1)

[Claims] 1. A plurality of image forming media having substantially the same shape, a plurality of driving means for independently rotating and driving each of the image forming media, and an image forming means for forming an image on each of the image forming media. And an image forming apparatus that sequentially transfers the images onto the image receiving material at the transfer position of each image forming medium, the image forming apparatus being provided along an image receiving material conveying path between transfer positions of the adjacent image forming media. In an image forming apparatus in which the distance is an integral multiple of the circumference of the image forming medium, marks provided at the same position on the phase of each of the image forming media and provided at the same position with respect to each of the image forming media. A plurality of mark detecting means for detecting the marks, and each driving means changes the rotational speed of each image forming medium based on the detection result by the mark detecting means and drives the image forming medium. Image to Forming equipment.