JPH10133490A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively reduce color slurring caused by the oblique advancing of a transfer medium by setting the distance between transfer positions from the transfer position of an image carrier for a 1st color to the transfer position of an image carrier for a final color equal to or under the distance between both supporting points for supporting a transfer medium carrying device. SOLUTION: The respective image carriers are arranged so that the distance L between the transfer positions from the transfer position of the image carrier 1a for the 1st color to the transfer position of the image carrier 1d for the final color may be equal to or under the distance W between both supporting points for supporting the transfer medium carrying device 9 in a direction crossing with the moving direction of the transfer medium 5. Thus, the degree of the color slurring is within an allowable level. By shortening the traveling distance of the transfer medium at the time of transferring the toner image of each color to the transfer medium 5, the color slurring caused by the oblique advancing of the transfer medium 5 is effectively reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus used for an electrophotographic color printer, a color copying machine, a color facsimile and the like.

[0002]

2. Description of the Related Art Conventionally, various types of electrophotographic color image forming apparatuses have been proposed, but roughly classified into two types: a multi-developing type and a multi-transfer type. The multiple development type (for example, JP-A-1-195774)
Although it has the feature that color misregistration is unlikely to occur, there are many problems to be solved because charging, exposure and development are repeatedly performed from the top of the toner image in image formation for the second and subsequent colors, and it is difficult to obtain stable color formation. On the other hand, the multi-transfer type can be further divided into two types, a four-cycle type and a one-cycle type. In either type, although it is necessary to prevent color misregistration when performing superimposed transfer, a single color type is used. There is an advantage that the quality of image quality can be used as it is.
In particular, the four-cycle system has a disadvantage that the recording speed is slow, but the problem of color misregistration is relatively easy to overcome, and therefore many products adopt this system. On the other hand, a color image forming apparatus of a one-cycle type (for example, JP-A-61-79658) has a great advantage that the recording speed is faster than that of a four-cycle type, but easily causes color misregistration and solves it. Therefore, it is used only for some expensive products because it requires a large-scale and precise control device.

FIG. 6 is a plan view showing a schematic configuration of a conventional one-cycle type multi-transfer type color image forming apparatus, and FIG. 7 is a side view thereof. As shown in FIGS. 6 and 7, the color image forming apparatus includes four sets of electrophotographic process units 2a, 2b, 2c, and 2d corresponding to cyan, magenta, yellow, and black, respectively. Corresponding four transfer devices 8a, 8b, 8c, 8d
And a transfer medium transport device 9 for transporting the transfer medium 5. Further, a transfer medium supply roll 10 for supplying the transfer medium 5 to the color image forming apparatus is provided at a front stage of the color image forming apparatus, and a transfer medium supply roll 10 for transferring the transfer medium 5 to the color image forming apparatus at a rear stage. A fixing device 14 for fixing the toner image is provided.

Electrophotographic process units 2a, 2b, 2
c, 2d are image carriers 1a, 1b, 1 that rotate in the direction of the arrow and carry a toner image on the surface and correspond to each of the above colors.
c, 1d; scanning exposure devices 21a, 21b, 21c, 21d for forming electrostatic latent images corresponding to the respective colors on the image carriers 1a, 1b, 1c, 1d; and developing these electrostatic latent images. Developing devices 22a and 22 for forming toner images
b, 22c, 22d, four charging devices (not shown), four cleaning devices (not shown), and the like. These four electrophotographic process units 2a, 2
b, 2c and 2d are transfer positions 26a and 26, respectively.
b, 26c and 26d, the unit mounting side plates 7a and 7 are arranged in parallel with each other along the conveyor belt 6 so that toner images of respective colors can be sequentially transferred onto the transfer medium 5.
b.

The electrophotographic process units 2a, 2b, 2c, 2d in the present embodiment correspond to the image carrier and the toner image forming means according to the present invention.
The transfer medium transport device 9 is provided with the image carriers 1a, 1b, 1
A transfer belt 6 for sequentially transferring a transfer medium 5 for receiving the transfer of the toner image on the transfer rollers c and 1d to respective predetermined transfer positions of the image carriers 1a, 1b, 1c and 1d, and a belt tension roll 3a for stretching the transfer belt 6 , 3b, belt tension roll 3a,
Roller supporting side plates 4a and 4b for supporting the shaft 3b, a driving device (not shown) for driving the conveyor belt 6 in the direction of arrow A, and the like.

The transfer medium 5 in the color image forming apparatus shown in FIGS. 6 and 7 is generally plain paper, high quality paper,
An OHP sheet or the like is used. The transfer medium 5 is placed on or adsorbed on the transfer belt 6 of the transfer medium transfer device 9 and the electrophotographic process units 2a, 2b, 2c, 2
d, the transfer positions 26a, 26b, 26c, 26d are sequentially moved to the respective transfer positions 26a, 26b, 26c, 26d.
In step d, the color toner images formed on the image carriers 1a, 1b, 1c, and 1d are sequentially transferred onto the transfer medium 5 in a superimposed manner.

At this time, each of the image carriers 1a, 1b, 1c,
It is extremely important for each color toner image formed on 1d to be accurately superimposed on a predetermined position on the transfer medium 5 in order to obtain a high-quality color image without color shift. The factors causing the color shift include the scanning exposure devices 21a, 21b, 2
The displacement of the latent image writing position on the image carriers 1a, 1b, 1c, 1d due to 1c, 21d and the deviation of the scanning / exposure timing, the deviation of the parallelism among the four image carriers 1a, 1b, 1c, 1d. Eccentricity of the image carriers 1a, 1b, 1c, 1d, fluctuations in the rotational angular velocity, fluctuations in the transport speed of the transfer medium 5, meandering or skew, and thermal expansion due to temperature changes in the color image forming apparatus. There are many factors such as dimensional changes.

The movement (meandering and skew) of the transfer medium 5 in the main scanning direction (both the axial direction of the image carrier and the axial direction of the belt tension roll) is undesirable for image formation. Above all, the skew of the transfer medium 5 has a particularly large adverse effect on color misregistration. FIG. 8 is a graph schematically showing the meandering and skew of the transfer medium.

As shown in FIG. 8A, the meandering of the transfer medium 5 (see FIG. 6) indicates a periodic change with the progress of the time t. This is mainly due to the transfer medium transfer device 9. Is generated when the direction of the speed v in the main scanning direction is reversed within one rotation cycle of the belt stretching rolls 3a, 3b due to the eccentricity of the belt stretching rolls 3a, 3b. When viewed on a time scale longer than the rotation cycle of 3b, the position y of the transfer medium 5 in the main scanning direction only vibrates periodically within a certain range. As described above, since the meandering of the transfer medium stays within a certain range and the displacement is not accumulated, the influence on the color shift is smaller than the skew described below. Also, the belt tension roll rows 3a, 3
b, the transfer medium 5 is controlled by the image carriers 1a, 1b, 1
There has been conventionally known a method of making the color shift due to the meandering of the transfer medium 5 inconspicuous by setting the interval G between c and 1d (see FIG. 6) to be an integral fraction of the moving time.

On the other hand, the skew of the transfer medium is caused by the image carriers 1a,
1B, 1C, and 1D (see FIG. 6), the alignment direction of the scanning exposure devices 21a, 21b, 21c, and 21d, and the transport direction of the transfer medium transport device 9 are different from each other. As shown in FIG. 8B, the position y of the transfer medium 5 in the main scanning direction shifts in only one direction,
Since the deviation is accumulated with the passage of time t,
The transfer medium 5 is located at the transfer position 26a of the image carrier 1a for the first color.
A large displacement occurs during the transfer of the transfer position distance L (see FIG. 6) from the transfer position to the transfer position 26d of the image carrier 1d for the final color, and the first color on the transfer medium 5 transferred at the transfer position 26a. A large color shift occurs between the toner image of the fourth color and the toner image of the fourth color transferred at the transfer position 26d.

Next, color misregistration due to skew of the transfer medium will be schematically described with reference to FIGS. 9, 10 and 11. FIG. FIG. 9 is a schematic diagram illustrating a state in which the transfer medium is transported without skew and a transfer image is formed normally. In the color image forming apparatus shown in FIG. 9, the image carriers 1a, 1b, 1c, 1
d and the scanning exposure devices 21a, 21b, 21
c, 21d, scanning exposure images 25a, 25b, 25c,
The three directions of the arrangement direction s of 25d and the conveyance direction t of the transfer medium conveyance device 9 (that is, the arrangement direction of the belt stretching rolls 3a and 3b) are parallel to each other. At this time, the scanning exposure images 25a, 25 on the image carriers 1a, 1b, 1c, 1d
b, 25c and 25d are visualized by a developing device (not shown) to form toner images on the image carriers 1a, 1b, 1c and 1d, respectively, as the image carriers 1a, 1b, 1c and 1d rotate. Transfer positions 26a, 26b, 2
6c and 26d, the image is transferred onto the transfer medium 5 conveyed by the belt tension rolls 3a and 3b at an appropriate timing. In this transfer, first, the transfer image 28a of the first color is transferred at the first transfer position 26a, and then the second transfer image 26a is transferred onto the transfer image 28a of the first color at the second transfer position 26b.
The transfer image 28b of the color is transferred, and the third
The transfer image 28c of the third color and the transfer image 28d of the fourth color at the transfer position 26c and the fourth transfer position 26d
Is transferred.

As shown in FIG. 9, the transfer medium transport device 9
Of the image carriers 1a, 1b, 1c, 1d and the scanning exposure images 25a, 25b, 25c, 25
When the arrangement direction d coincides with the arrangement direction s, the transfer images 28a, 28b, 28c, 28 of the respective colors on the transfer medium 5 'after the transfer.
No color shift in the main scanning direction occurs between d.

[0013]

However, unlike the color image forming apparatus described below, the transport direction of the transfer medium transport device, the arrangement direction of the image carriers, and the arrangement direction of the scanning exposure images are not parallel to each other. In this case, a color shift occurs in the main scanning direction between the transfer images of the respective colors. FIG. 10 is a schematic diagram illustrating a state in which color misregistration occurs when the transfer direction of the transfer medium transfer device does not match the arrangement direction p of the image carriers and the arrangement direction s of the scanning exposure images.

FIG. 10 shows that the transfer direction t of the transfer medium transfer device 9 is at an angle with respect to the arrangement direction p of the image carriers 1a, 1b, 1c, 1d and the arrangement direction s of the scan exposure images 25a, 25b, 25c, 25d. If it is shifted by error theta _1, in which the transferred image 29a of the respective colors, 29b, 29c, the main scanning direction color misregistration between 29d shows how the resulting. In FIG. 10, the scanning exposure image 25a on the image carrier 1a for the first color is shown.
To the scanning exposure image 25d on the image carrier 1d for the fourth color are formed at normal exposure positions, respectively, and formed on the image carriers by developing devices (not shown). Although the toner image is also formed at a normal position on each image carrier, the transfer medium 5 is skewed when sequentially transferred onto the transfer medium 5, so that the toner image is transferred onto the transfer medium 5 'after the transfer. The images are transferred while being shifted in the main scanning direction like images 29a, 29b, 29c, and 29d. In this case, the largest color shift occurs between the transfer image 29a of the first color and the transfer image 29 of the fourth color.
d, the transfer position 2 of the image carrier 1a for the first color.
Assuming that the distance between the transfer positions from the transfer position 6a to the transfer position 26d of the final color image carrier 1d is L, the size of the color shift δ ₁
Can be expressed as δ ₁ = L · tan θ ₁ (1)

From equation (1), it can be seen that the smaller the distance L between the transfer positions, the smaller the size δ _{1 of the} color misregistration. But,
In the case of a conventional one-cycle type multi-transfer type color image forming apparatus, the distance L between transfer positions is, for example, about 400 to 600.
mm, the size of the color shift δ caused by the inclination of the transfer direction t even when the transfer direction t of the transfer medium transfer device 9 is sufficiently adjusted at the time of assembling the color image forming apparatus. _It is the best to reduce ₁ to about 0.2 to 0.3 mm. Therefore, for example, it is necessary to take measures such as performing color misregistration correction control using a complicated optical element inclination correction device provided in the scanning exposure apparatus while detecting the actual color misregistration during operation.

The reason why such color misregistration occurs is that the belt tension rolls 3a and 3b of the transfer medium transport device 9 are attached to be displaced from their proper attachment positions. That is, in FIG. 10, the image carrier 1d for the final color and the belt stretching roll 3b on the transfer medium outlet side are originally a regular distance d.
Must be maintained in parallel with each other, but a regular distance d is provided between the belt tension roll bearing portion 4b 'of the upper roll supporting side plate 4b and the axis of the image carrier 1d as viewed in the drawing. the distance d _r is the error from the normal of the distance d between the belt stretching roller bearing portion 4a of the lower roll supporting side plate 4a toward the drawing while being kept 'and the axis of the image bearing member 1d to only e ₁ short. That is, the belt tension roll 3b is attached to be inclined leftward as viewed in the drawing. At this time, assuming that the center-to-center distance between the two roll supporting side plates 4a and 4b supporting the belt tension rolls 3a and 3b is W, the direction p in which the image carrier row 1 is arranged and the transport direction of the belt tension roll row 3 An angle θ ₁ formed with t can be expressed as tan θ ₁ = e ₁ / W (2).

Strictly speaking, W should be expressed as a distance between both fulcrums which substantially support the belt tension roll 3b, but here, for convenience, both roll supporting side plates 4a, 4b.
Is used as W. Here, from the above equations (1) and (2), the color shift magnitude δ ₁ can be expressed as δ ₁ = e ₁ × L / W (3)

Instead of expressing the mounting position of the belt tension roll 3b as a relative relationship with the image carrier (that is, the distance d or the distance d + L), the distance between the belt tension roll 3a and the belt tension roll 3a on the transfer medium entrance side is used. When expressed in D,
Instead of using the dimensional errors e ₁ to the image bearing member 1d of the belt tension roller 3b, both belt stretching rolls 3a, 3b
The size of the color misregistration can also be expressed using the dimensional error e ₂ between them (that is, the difference between the regular distance D and the actual distance _Dr ).

By the way, as shown in Table 1 of JIS-B0405 "Normal tolerance-Part 1", the standard size is 6 m.
The tolerance for the length dimension in the case of about m to 400 mm is defined as "fine" in the range of ± 0.1 to 0.2 mm.
On the other hand, the size of the color shift allowed in the color reproduction of a color image in the field of printing is set at 0.1 in consideration of the sensitivity of human eyes.
It is said to be 1 to 0.15 mm or less. Therefore, if the distance error e ₁ in the above equation (3) is the lower limit value (0.1 mm) of the tolerance of the JIS standard, when the value of L / W is almost 1, the allowable color shift is large. The height is equal to the lower limit (0.1 mm) in the field of printing. That is, the distance L between the transfer positions from the image carrier 1a for the first color to the image carrier 1d for the fourth color and the distance W between the centers of both the roll supporting side plates 4a and 4b of the belt tension roll 4a are substantially equal. When they are equal, the color shift falls within the allowable level, but in the conventional image forming apparatus, since the value of L / W greatly exceeds 1, the magnitude of the color shift must exceed the allowable level. Absent.

Next, the case where the transfer medium skews when the arrangement direction of the scanning exposure device does not match the conveyance direction of the transfer medium conveyance device and the arrangement direction of the image carrier belt will be described. FIG. 11 is a schematic diagram showing a state in which color misregistration occurs when the arrangement direction of the scanning exposure devices does not match the conveyance direction of the transfer medium conveyance device and the arrangement direction of the image carrier belt.

In the color image forming apparatus shown in FIG. 11, scanning exposure images 25a and 25
The arrangement direction s of b, 25c and 25d is the transport direction t of the transfer medium transport device 9 and the image carriers 1a, 1b, 1c and 1d.
Are shifted by an angle θ _{2 with} respect to the arrangement direction p. That is, the transfer direction t of the transfer medium transfer device 9 and the image carrier 1a,
The arrangement direction p of 1b, 1c, and 1d matches.

In such a color image forming apparatus, the first
The color scanning exposure image 25a is formed at an angle θ _{2 with} respect to the rotation axis of the first color image carrier 1a, and the first color toner image is rotated while the image carrier 1a rotates. Then, the toner image is conveyed and developed by a developing device (not shown) to form a toner image. Then, the toner image is transferred to the transfer position 27a and is transferred onto the transfer medium 5. However, the regular transfer position 26a is the position shown in the figure, and the actual transfer position 27a and the regular transfer position 26a are not shown.
and a. Similarly, the toner images of the second, third, and fourth colors are sequentially transferred onto the transfer medium 5 at transfer positions 27b, 27c, and 27d shifted from the normal transfer positions 26b, 26c, and 26d, and are transferred onto the transfer medium 5 'after transfer. Causes a color shift in the main scanning direction as in the transfer images 29a, 29b, 29c, and 29d. Also in this case, the largest color shift is the first.
This is the color shift between the transfer image 29a of the color and the transfer image 29d of the fourth color, and the magnitude of the color shift δ ₂ is δ ₂ = L · tan θ ₂ as in the above equation (1). 4) can be expressed as

That is, as shown in FIG. 11, when the arrangement direction s of the scanning exposure apparatus is shifted by an angle θ _{2 with} respect to the conveyance direction t of the transfer medium conveyance device 9 and the arrangement direction p of the image carrier, as shown in FIG. The transfer direction t of the transfer medium transfer device 9 as shown in FIG.
Is shifted by an angle θ _{1 with} respect to the arrangement direction p of the image carrier and the arrangement direction s of the scanning exposure device, it can be seen that the same color shift occurs.

The present invention has been made in view of the above circumstances, and has as its object to provide a color image forming apparatus capable of forming a color image with little color shift without complicated control.

[0025]

A color image forming apparatus according to the present invention that achieves the above object rotates in a predetermined direction.
A plurality of image carriers that carry a toner image on the surface, and a toner image forming unit that is provided on each of the plurality of image carriers and forms toner images of different colors on each image carrier based on image data, A predetermined transfer medium for receiving the transfer of the toner image on the plurality of image carriers is sequentially moved to each predetermined transfer position of the plurality of image carriers, and both ends of the transfer medium in a direction intersecting the moving direction are supported. Transfer device for transferring the toner image on the image carrier to the transfer medium at each of the transfer positions, the transfer unit corresponding to the image carrier, and the image carrier on the transfer medium. In a color image forming apparatus for forming a color image fixed on a predetermined image recording medium through a process of sequentially superimposing and transferring the toner images on the body from the first color to the final color, Carrying The distance between the transfer positions of the image carrier for the first color and the transfer position of the image carrier for the final color among the above intersects the moving direction of the transfer medium that supports the transfer medium transport device. The plurality of image carriers are arranged so as to be equal to or less than the distance between the two fulcrums in the direction.

Here, it is preferable that the plurality of image carriers are arranged such that the distance between the transfer positions is equal to or less than half of the distance between the two fulcrums. Further, the plurality of image carriers and the transfer medium transport device,
It is also a preferred embodiment that the shaft is supported by a pair of common side plates. In the present invention, the transfer medium and the image recording medium may be the same medium, or the transfer medium may transfer the toner image after receiving the transfer of the toner image on the image carrier. An intermediate transfer medium for transferring to the image recording medium may be used.

[0027]

Embodiments of the present invention will be described below. FIG. 1 shows a first embodiment of the color image forming apparatus of the present invention.
It is a schematic diagram showing an embodiment. The color image forming apparatus shown in FIG. 1 has a configuration similar to that of the conventional one-cycle type multiple transfer type color image forming apparatus shown in FIGS. 6 and 7, and performs almost the same image forming process. Therefore, only the differences will be described below.

In the embodiment shown in FIG. 1, each image carrier is located between the transfer position 26a of the image carrier 1a for the first color and the transfer position 26d of the image carrier 1d for the final color. The distance L is set to be equal to or less than the distance W between the two fulcrums in the direction intersecting the moving direction of the transfer medium 5 that supports the transfer medium transport device 9. Further, the scanning exposure device 11a for each color is set within the distance G between the transfer positions of the adjacent image carriers.
11b, 11c, 11d and developing devices 12a, 12
b, 12c, and 12d are configured to fit. However, the distance G between the image carriers of each color does not necessarily have to be the same distance, and the distance G is suitable for forming the toner image of each color, and the toner image of each color is correctly formed on the transfer medium according to the distance. What is necessary is just to set the writing timing of each color of the scanning exposure apparatus so as to be superimposed.

Further, the image carriers 1a, 1b, 1c, 1d
Are the belt tension rolls 3a, 3b of the transfer medium transport device 9.
Are rotatably supported by roll supporting side plates 15a and 15b which are rotatably supported. Thus, the image carriers 1a, 1b, 1c, 1
d and the belt tension rolls 3a, 3b are supported by the common roll supporting side plates 15a, 15b, so that the deviation in the angle between the transport direction of the transfer medium transport device and the direction in which the image carriers are arranged is reduced. can do. As described above, this angle shift is caused by an error in the mounting position of each image carrier on the roll supporting side plate, and each image carrier and the transfer medium transport device are provided on separate supporting side plates. If they are attached, it is necessary to perform alignment of the two, and since this alignment error is added to the error of the distance on each supporting side plate, the angle shift becomes large.
Therefore, in order to avoid an angle shift due to this alignment error, the image carriers 1a, 1b, 1c, 1d and the belt stretching rolls 3a, 3b are shared by the roll supporting side plates 15a, 1b.
5b. Further, the image carriers 1a, 1b, 1 are provided on the roll supporting side plates 15a, 15b.
scanning exposure devices 11a, 11b, 11c,
Related devices constituting the electrophotographic process unit such as 11d and developing devices 12a, 12b, 12c and 12d are fixed.

The developing rolls 12a, 12b, 12
Reference numerals c and 12d denote conductive rubber rolls that carry and transport the toner. Developing rolls 12a, 12b, 12c, 12
d is not limited to only the conductive rubber roll,
It may be a magnetic roll for transporting a two-component magnetic developer. Around each of the image carriers 1a, 1b, 1c, and 1d, four charging devices (not shown), a transfer device, and a cleaning device are arranged. The charging device is composed of, for example, a rubber blade or a rubber roll, and is applied with a voltage necessary for charging the photoconductor layer on the surface of the image carrier. The cleaning device includes a rubber blade, a rubber roll, and the like, and may apply a voltage for separating the toner from the photoconductor as needed. The charging device, the cleaning device, and the like may be omitted depending on a process to be applied, or a plurality of functions may be combined into one shared device.

Next, the magnitude of color misregistration in the color image forming apparatus of the present embodiment will be described. FIG. 2 shows the first
FIG. 8 is a schematic diagram illustrating the occurrence of color misregistration in the embodiment. FIG. 2A is a plan view of an ideal color image forming apparatus in which a scanning exposure apparatus, an image carrier, and a transfer medium transport apparatus are manufactured and assembled without errors. The image carriers 1a, 1b, 1c, and 1d, the belt tension rolls 3a and 3b, and all the scanning exposure images 25a, 25b, 25c, and 25d from four scanning exposure devices (not shown) of this color image forming apparatus are mutually attached. Since they are arranged in parallel, in such an ideal color image forming apparatus, the transfer images 28a, 28 of the respective colors formed on the transfer medium 5 'after transfer.
No color shift in the sub-scanning direction exists in b, 28c, and 28d. However, in reality, occurrence of an error in manufacturing and assembling the color image forming apparatus is unavoidable, and it is almost impossible to obtain such an ideal color image forming apparatus. For example,
In the case of an actual color image forming apparatus, as shown in FIG. 2B, the transfer direction t of the transfer medium transfer device 9 and the image carrier 1
The arrangement direction p of a, 1b, 1c, and 1d may be displaced from the arrangement direction p by an error angle θ ₃ . However, in this case, for the sake of explanation, it is assumed that there is no error angle between the arrangement direction p of the image carriers 1a, 1b, 1c, 1d and the arrangement direction s of the scanning exposure apparatus. The difference between the angles will be described later.

In FIG. 2B, as in FIG. 2A, the scanning exposure images 25a, 25b, 25c, 25d
Are formed at regular positions on the image carriers 1a, 1b, 1c and 1d, respectively, and the toner images of each color are also transported to the regular transfer positions 26a, 26b, 26c and 26d. However, the transfer direction t of the transfer medium transfer device 9 is
Since the toner image is transferred onto the transfer medium 5 because the toner image is transferred on the transfer medium 5 by an angle θ _{3 with} respect to the arrangement direction p of the lines a, 1b, 1c, and 1d, the transfer images 29a, 29
Color shift occurs in the main scanning direction as shown in FIG. The color shift between the transfer image 28a of the first color and the transfer image 28d of the fourth color indicates the largest color shift, and the color shift between the transfer position 26a of the image carrier 1a for the first color and the fourth color.
Assuming that the distance between the transfer positions of the color image carrier 1d to the transfer position 26d is L, the magnitude of the color shift δ ₃ is δ ₃ = L ·
It is represented as tan θ ₃ . The error angle θ ₃ can also be expressed as tan θ ₃ = e ₁ / W or tan θ ₃ = e ₂ / W using the dimensional error e ₁ or e ₂ . here,
The size of e ₁ or e ₂ is such that the reference dimension d or D is about 10
Since it is about 300 mm, it is about 0.1 to 0.2 mm. Since the distance W between both fulcrums supporting the transfer medium transporting device 9 (in the drawing, represented as the distance between the centers of both the roll supporting side plates 15a and 15b) is about 300 mm,
tan θ is 0.00033 to 0.00067, that is, θ ₃ is ± 1 ′ to 2 ′. In the present embodiment shown in FIG. 2B, the distance L between transfer positions is set to, for example, 60 to 220.
mm, the size of the color shift δ ₃
(= L · tan θ ₃ ) is 0.04 or more even if it is largely estimated.
0.15 mm, which is within the allowable range. This figure 2
(B) is compared with a conventional example (see FIG. 10) in which the transfer direction t of the transfer medium transfer device 9 is similarly shifted from the arrangement direction p of the image carriers 1a, 1b, 1c, 1d. By setting the value of W to 1 or less, the color misregistration of about 0.2 to 0.3 mm (δ ₁ in FIG. 10) is reduced to the state shown in FIG.
It can be seen that δ ₃ shown in FIG.

As described above, in the color image forming apparatus of this embodiment, the transfer position 26 of the image carrier 1a for the first color is changed.
By setting the distance L between the transfer positions from the position a to the transfer position 26d of the image carrier 1d for the fourth color to be shorter than the distance W between the two fulcrums supporting the transfer medium transport device 9, the magnitude of the color shift δ
₃ can be kept below the acceptable level. That is, it is possible to effectively reduce the color shift caused by the skew of the transfer medium 5 by shortening the travel distance of the transfer medium when each color toner image is transferred onto the transfer medium 5. It is shown that. As described above, the effect of reducing the color misregistration is caused not only when the transfer medium 5 is skewed due to the misalignment of the transfer medium conveyance device 9 in the conveyance direction t, but also because the misalignment of the image carrier p is caused. The same applies to the case where the transfer medium 5 is skewed due to the deviation of the arrangement s of the scanning exposure apparatus even when the medium 5 is skewed.

If the cause of the color misregistration is one of the above-mentioned causes, the distance L between the transfer positions is made smaller than the distance W between the two fulcrums as described above, so that the color misregistration is kept below an allowable level. However, there are generally a plurality of causes of color misregistration other than the above-mentioned causes. Color misregistration can be roughly classified by these causes into: regular color misregistration in the main scanning direction, periodic color misregistration in the main scanning direction, constant color misregistration in the sub-scanning direction, and periodic color misregistration in the sub-scanning direction. The color shift due to the skew of the transfer medium is one of the steady color shifts in the main scanning direction. As described above, when a plurality of error factors δ _n operate independently, the combined error δ is represented by the square root of the sum of squares from the additive property of variance, and δ = √ (δ ₁ ² + δ ₂ ² + δ ₃ ² + δ ₄ ² ). Since the magnitude of the color misregistration in the main scanning direction and the color misregistration in the sub-scanning direction can also be expressed by the square root of the sum of squares from the calculation of the geometric distance, each color misregistration should be treated in this way. Can be. When each cause to cause a color shift is assumed to cause the substantially the same size as the color shift, [delta] = a √ (4δ ₁ ²⁾ That δ ₁ = δ / 2. Therefore, assuming that there are a plurality of causes of color misregistration, for example, four particularly large causes, the error due to each cause must be one half of the combined error. Accordingly, in the present invention, the distance L between the transfer positions from the transfer position of the image carrier for the first color to the transfer position of the image carrier for the final color (that is, the transfer medium travel distance from the start of the transfer to the end of the transfer) is determined. It is preferable that the distance between the two fulcrums supporting the transfer medium transport device be equal to or less than one half of the distance W, so that the color misregistration can be maintained at an allowable level regardless of other similar causes of color misregistration. The following can be included.

Next, the second embodiment of the color image forming apparatus of the present invention will be described.
An embodiment will be described. FIG. 3 is a schematic diagram illustrating the occurrence of color misregistration in the second embodiment. FIG. 3 shows a color image forming apparatus in which the arrangement direction s of the scanning exposure apparatus has an angle error θ ₄ with respect to the conveyance direction t of the transfer medium conveyance device and the arrangement direction p of the image carrier. Accordingly, in this embodiment, the transfer direction t of the transfer medium transfer device and the arrangement direction p of the image carriers are the same.

In this color image forming apparatus, the first color scanning exposure image 25a is formed at an angle θ _{4 with} respect to the rotation axis of the first color image carrier 1a, and the first color toner image is formed. accompanied by the rotation of the left image bearing member 1a in a state where the angle theta ₄ inclined by with respect to the axis of rotation is conveyed, the transfer medium 5 on the flow proceeds to a transfer position 27a After a toner image is developed by an unillustrated developing device Is transferred to However, the normal transfer position 26a of the toner image and the actual transfer position 27a are shifted as shown in the drawing, and similarly, the toner images of the second, third, and fourth colors are also shifted from the normal transfer positions 26b, 26c, and 26d. Are sequentially transferred onto the transfer medium 5 at the transfer positions 27b, 27c, 27d, and the transfer images 29a, 29
Color shifts in the main scanning direction occur as shown by b, 29c and 29d.

As described above, in the color image forming apparatus according to the present embodiment, color misregistration in the main scanning direction similar to the above-described conventional example (see FIG. 11) occurs.
Is set to be small, the magnitude of the color shift is extremely small as compared with the case of FIG. That is, in the present embodiment, the distance L between the transfer positions from the transfer position 26a of the image carrier 1a for the first color to the transfer position 26d of the image carrier 1d for the fourth color is equal to the distance between the transfer media supporting the transfer medium. It is configured to be shorter than the fulcrum distance W. Also in the present embodiment, the largest color shift is the color shift between the transfer image 29a of the first color and the transfer image 29d of the fourth color, and the magnitude of the color shift δ ₄ is the same as in the above equation (1). Δ ₄ = L ・
tan θ ₄ . Color shift magnitude θ
₄ is ± 1 ′ to 2 ′ as described above, and in the embodiment shown in FIG. 3, the distance L between the transfer positions is shorter than the distance W between both fulcrums of about 300 mm, for example, from the range of 60 to 260 mm. By selecting, the magnitude of the color shift δ ₄ is
0.03 to 0.15 mm, which is below the allowable level.
On the other hand, the distance L between the transfer positions with respect to the distance W between the two fulcrums
Conventional example in which the ratio of the above is not taken into account (see FIG. 11)
In this case, the magnitude of the color shift δ ₂ is 0.2 to 0.3 mm, which indicates that the effect of the present invention is great.

Next, the third embodiment of the color image forming apparatus of the present invention will be described.
An embodiment will be described. FIG. 4 is a schematic diagram illustrating the occurrence of color misregistration in the third embodiment. FIG. 4 shows a color image forming apparatus similar to the color image forming apparatus of the first embodiment shown in FIG. In the color image forming apparatus shown in FIG. 4, the distance L between the transfer positions from the transfer position 26a of the image carrier 1a for the first color to the transfer position 26d of the image carrier 1d for the fourth color is determined by the transfer medium transport device. 9
, Which is half the distance W between the two fulcrums in the direction intersecting the moving direction of the transfer medium 5. That is, in the embodiment shown in FIG.
An example in the case where L is set to 120 mm as a distance L between transfer positions that is equal to or less than half of the distance W between both fulcrums with respect to 0 mm is shown below. Here, the image carrier 1 having a diameter of 16 mm
a, 1b, 1c, 1d are the distances between the respective axes 40 mm
And are supported by the roll supporting side plates 15a and 15b in parallel with each other.

Around the image carriers 1a, 1b, 1c, 1d, charging devices 53a, 53b, 53c, 53d, developing rolls 51a, 51b, 51c, 51d, a transfer device and a cleaning device (not shown) are arranged, respectively. ing. The charging devices 53a, 53b, 53c, 53d are constituted by, for example, rubber blades or rubber rolls having a diameter of 10 mm or less. The cleaning device is constituted by a rubber blade or a rubber roll having a diameter of 10 mm or less. The charging device, the cleaning device, and the like may be omitted depending on a process to be applied, or a plurality of functions may be combined into one shared device. Developing roll 5
Each of 1a, 51b, 51c, and 51d is formed of a conductive rubber roll having a diameter of 10 mm to shorten the distance L between transfer positions. Developing rolls 51a, 51b, 51c, 51d
Is not limited to only the conductive rubber roll, but may be any material having a diameter of about 10 mm.
A magnetic roll for transporting the component magnetic developer may be used.

When the magnitude of the color shift in the third embodiment is determined according to the above-described calculation example, it is about 0.06 mm, and the magnitude of the color shift δ ₄ : 0. This indicates that it is possible to further reduce the color misregistration as compared with the case of 03 to 0.15 mm. next,
A fourth embodiment of the color image forming apparatus of the present invention will be described.

Each of the above embodiments is an example of the color image forming apparatus of the present invention in which the distance L between transfer positions is shorter than the normal distance W between both fulcrums. An example for outputting a wide drawing will be described as a color image forming apparatus of the present embodiment in which the distance W between both fulcrums is wider than the distance L between positions. A2 size (420mm × 59
4mm) or A1 size (594mm x 840mm)
In the color image forming apparatus for paper output described above, the magnitude of the color shift is determined when the distance W between both fulcrums is 450 mm and 630 mm, and the distance L between the transfer positions is 300 mm. As described above, the magnitude of the color shift can be represented by δ = e × L / W, and L = 300 mm
Is e = 0.1 to 0.2 mm with respect to the color image forming apparatus for A2 size.
13 mm, and in the case of an A1 size color image forming apparatus, δ = 0.05 to 0.1 mm. Therefore, even in the case of a color image forming apparatus for outputting a wide drawing such as A2 size or A1 size, the color misregistration can be reduced to a sufficiently allowable level by the color image forming apparatus of the present invention.

Next, as an example in which the color misregistration cannot be reduced to an allowable level or less by simply shortening the distance L between the transfer positions, that is, the transfer medium travel distance from the start of the transfer to the end of the transfer, a postcard, a photograph, a card, etc. The case of the small-size dedicated color image forming apparatus will be described. Now, A6
The distance W between both fulcrums of the transfer medium transport device of the color image forming apparatus using the paper of size (74 mm × 105 mm) is set to 1
00 mm. Even if the distance L between the transfer positions is set to L = 120 mm as in the third embodiment, since the distance L between the transfer positions is longer than the distance W between the two fulcrums, the magnitude δ of the color misregistration becomes 3) From the formula, δ = 0.12 to 0.24 mm
And exceeds the allowable level. When the distance W between the two fulcrums is narrow as described above, according to the present invention, if the distance L between the transfer positions is shorter than the distance W between the two fulcrums, for example, 60 to 100 mm, it is possible to realize a color shift below an allowable level. Can not.

In each of the above embodiments, the transfer medium that receives the transfer of the toner images on the plurality of image carriers is plain paper, high-quality paper, an OHP sheet, or the like. Although a color image forming apparatus of a type in which a toner image is transferred and fixed and finally becomes an image recording medium on which a color image is recorded has been described, the present invention is such that the transfer medium and the image recording medium are the same. The intermediate transfer medium is not limited to a color image forming apparatus of the type described above, and is not limited to a color image forming apparatus. Can be applied to a color image forming apparatus.

Further, in each of the above embodiments, an example was described in which the transfer medium conveying device was an endless belt type conveying device. However, the present invention is not limited to this type of transfer medium conveying device. The present invention can also be used in the case of other types of transfer devices such as a member, a drum member, and a gripper member. Further, in each of the above embodiments, only an example in which a plurality of image carriers are arranged in a straight line has been described. However, the present invention is not limited to such an embodiment. The present invention can be applied to a case where the bodies are arranged on an arc or other curved lines. FIG. 5 is a schematic diagram showing a fifth embodiment of the color image forming apparatus of the present invention.

As shown in FIG. 5, this color image forming apparatus includes an intermediate transfer medium drum 1 rotating in the direction of arrow A.
3. four sets of electrophotographic process units 20a, 20b, 20c, 20d surrounding the intermediate transfer medium drum 13, a power supply 16 for applying a transfer voltage to the intermediate transfer medium drum 13,
A secondary transfer device 18 for transferring the toner image formed on the intermediate transfer medium drum 13 onto the transfer medium 5, and a transfer medium 5 at a nip portion between the intermediate transfer medium drum 13 and the secondary transfer device 16.
Is provided.

Electrophotographic process units 20a, 20
b, 20c and 20d denote image carriers 1a, 1b, 1c and 1d for cyan, magenta, yellow and black, respectively.
And irradiating the image carriers 1a, 1b, 1c, 1d with exposure light 11a, 11b, 11c, 11d corresponding to the image information, and electrostatically irradiating the photoconductor layers on the surfaces of the image carriers 1a, 1b, 1c, 1d. Four sets of scanning exposure devices (not shown) for forming latent images, and image carriers 1a, 1b, 1c, 1
Four developing devices 12a, 12b, 12c, and 12d for forming toner images corresponding to the respective colors on the photoconductor layer on the surface d.
, Four charging devices (not shown), and four cleaning devices (not shown). These four sets of electrophotographic process units 20a, 20b, 20c,
Reference numeral 20d is attached to the unit attachment side plate 17 so that toner images of each color can be sequentially transferred onto the intermediate transfer medium drum 13 at respective predetermined transfer positions.

As described above, in this embodiment, the image carrier 1
The toner images corresponding to the respective colors formed on the photoreceptor layers on the surfaces a, 1b, 1c, and 1d are primary-transferred onto the intermediate transfer medium drum 13 in a superimposed manner, and then primary-transferred onto the intermediate transfer medium drum 13 in multiple layers. The transferred color toner image is transferred to the secondary transfer device 16.
Is secondary-transferred onto the transfer medium 5. Therefore, in the present embodiment, the four image carriers 1a, 1b, 1c, 1d are arranged side by side on an arc on the outer periphery of the intermediate transfer medium drum 13.

In the present embodiment, the intermediate transfer medium drum 13 corresponds to the transfer medium according to the present invention, and the image carriers 1a, 1b, 1c and 1d correspond to the image carrier 1a for the first color. The transfer distance L (i.e., the transfer medium travel distance) from the transfer position of the first color to the transfer position of the image carrier 1d for the final color is determined by the transfer medium transport device (the intermediate transfer medium drum 1).
The image forming apparatus is arranged such that the distance between the two fulcrums supporting 3) is equal to or less than the distance (corresponding to W in FIG. 1). In this case, the distance L between the transfer positions from the transfer position of the image carrier 1a for the first color to the transfer position of the image carrier 1d for the final color, that is, the transfer medium travel distance is equal to the outer circumference of the intermediate transfer medium drum 13. A value measured along the line may be used. Note that the distance G between the transfer positions of each image carrier does not necessarily have to be the same distance, but a distance suitable for forming each toner image. What is necessary is just to set the writing timing of each color of the scanning exposure apparatus so as to be correctly superimposed.

In each of the embodiments described above, an example is shown in which the electrophotographic process unit is provided for four colors. However, the present invention is not limited to the formation of an image of four colors, but uses a plurality of colors of two or more colors. The present invention can be applied to a case where a multicolor image is formed.

[0050]

As described above, according to the color image forming apparatus of the present invention, the distance between the transfer positions from the transfer position of the image carrier for the first color to the transfer position of the image carrier for the final color. Is less than or equal to the distance between the two fulcrums supporting the transfer medium transport device, it is possible to effectively reduce the color shift caused by the skew of the transfer medium. This effect is the same even when the skew of the transfer medium is caused by any of a shift in the transfer direction of the transfer medium transfer device, a shift in the arrangement direction of the image carriers, and a shift in the alignment direction of the scanning exposure device. is there.

Further, according to the present invention, a control device for detecting and correcting color misregistration is not required, and an inexpensive and compact color image forming apparatus can be realized. Further, the distance between the transfer positions of the image carrier for the first color and the transfer position of the image carrier for the final color is set to be not more than half of the distance between the two fulcrums supporting the transfer medium transport device. Thus, even when other causes of color misregistration exist, the color misregistration can be suppressed to an allowable level or less, and a higher quality color image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a first embodiment of a color image forming apparatus of the present invention.

FIG. 2 is a schematic diagram illustrating occurrence of color misregistration in the first embodiment.

FIG. 3 is a schematic diagram illustrating the occurrence of color misregistration in a second embodiment.

FIG. 4 is a schematic diagram illustrating the occurrence of color misregistration in a third embodiment.

FIG. 5 is a schematic view showing a fifth embodiment of the color image forming apparatus of the present invention.

FIG. 6 is a plan view showing a schematic configuration of a conventional one-cycle type multiple transfer color image forming apparatus.

FIG. 7 is a side view showing a schematic configuration of a conventional one-cycle type multiple transfer color image forming apparatus.

FIG. 8 is a graph schematically showing the meandering and skew of the transfer medium.

FIG. 9 is a schematic diagram illustrating a state in which a transfer medium is conveyed without skew and a transfer image is formed normally.

FIG. 10 is a schematic diagram illustrating a state in which color misregistration occurs when the transfer direction of the transfer medium transfer device does not match the arrangement direction p of the image carriers and the arrangement direction s of the scanning exposure images.

FIG. 11 is a schematic diagram illustrating a state in which color misregistration occurs when the arrangement direction of the scanning exposure device does not match the conveyance direction of the transfer medium conveyance device and the arrangement direction of the image carrier belt.

[Explanation of symbols]

1a, 1b, 1c, 1d Image carrier 2a, 2b, 2c, 2d Electrophotographic process unit 3a, 3b Belt stretching roll 4a, 4b Roll supporting side plate 5 Transfer medium 6 Transport belt 7a, 7b Unit mounting side plate 8 Transfer Apparatus 9 Transfer medium transport device 10 Transfer medium supply roll 11a, 11b, 11c, 11d Scanning exposure device 12a, 12b, 12c, 12d Developing device 14 Fixing device 15a, 15b Roll supporting side plate 16 Power supply 17 Unit mounting side plate 18 Secondary Transfer device 21a, 21b, 21c, 21d Scanning exposure device 22a, 22b, 22c, 22d Developing device 25a, 25b, 25c, 25d Scanning exposure image 26a, 26b, 26c, 26d Transfer position 27a, 27b, 27c, 27d Transfer position 28a , 28b, 28c, 28d, 29a, 29 , 2
9c, 29d Transfer image

Claims (5)

[Claims] 1. A plurality of image carriers that rotate in a predetermined direction and carry a toner image on a surface, and different colors are provided on each image carrier based on image data provided on each of the plurality of image carriers. A toner image forming means for forming a toner image, and a transfer medium for receiving a transfer of the toner image on the plurality of image carriers is sequentially moved to each predetermined transfer position of the plurality of image carriers. A transfer medium transport device having both ends supported in a direction intersecting the moving direction of the medium; and a transfer corresponding to each image carrier, which transfers a toner image on the image carrier to the transfer medium at each transfer position. Means, the toner image on the image carrier on the transfer medium through a process of sequentially overlapping and transferring from the first color to the final color,
Finally, in a color image forming apparatus for forming a color image fixed on a predetermined image recording medium, a transfer position of a first color image carrier among the plurality of image carriers is transferred to a final color image carrier. The plurality of image carriers are arranged such that a distance between transfer positions of the image carriers to a transfer position is equal to or less than a distance between two fulcrums in a direction intersecting a moving direction of the transfer medium, which supports the transfer medium transport device. A color image forming apparatus, which is arranged. 2. The color according to claim 1, wherein the plurality of image carriers are arranged such that the distance between the transfer positions is equal to or less than half of the distance between the two fulcrums. Image forming device. 3. The color image forming apparatus according to claim 1, wherein the plurality of image carriers and the transfer medium transport device are pivotally supported by a set of common side plates. 4. The color image forming apparatus according to claim 1, wherein the transfer medium and the image recording medium are the same medium. 5. The image forming apparatus according to claim 1, wherein the transfer medium is an intermediate transfer medium that transfers the toner image to the image recording medium after receiving the transfer of the toner image on the image carrier.
The color image forming apparatus as described in the above.