JP3293371B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus capable of forming a color visible image or the like at a high speed by using a plurality of belt-shaped photoconductors, and more particularly, to the position of an image even when the belt-shaped photoconductor has a speed fluctuation. The present invention relates to a technique capable of preventing occurrence of a shift or the like.

[0002]

2. Description of the Related Art Conventionally, in a color image forming apparatus using an electrophotographic system or the like, a full-color image is generally formed by superimposing a single color image of three colors of cyan, magenta and yellow, or four colors including black. It is configured to be. For this reason, in the case of the color image forming apparatus, a single-color image of three colors of cyan, magenta, and yellow, or four colors including black is sequentially formed, and the single-color images are overlapped with each other to form a full-color image. Therefore, the productivity of the image is reduced to about 1/3 or 1/4 as compared with a black and white image forming apparatus.

In order to obtain the same productivity as that of the monochrome image forming apparatus in the above color image forming apparatus, a technique of using a plurality of image forming units and superimposing the single color images created by each image forming unit sequentially to form a full color image is described. A so-called tandem type color image forming apparatus has been proposed. In this tandem-type color image forming apparatus, since it is necessary to provide a plurality of image forming units, there is a drawback that the apparatus is increased in size, and in order to solve such a drawback and reduce the size of the apparatus, a belt-shaped photoconductor is required. It is effective to use In such a color image forming apparatus, the eccentricity of the roll over which the belt-shaped photoconductor is stretched causes fluctuations in the angular velocity of other rolls and the surface speed of the belt-shaped photoconductor. Due to the inconsistency of the amounts, there has been a problem that positional shifts of the respective color images transferred in a superimposed state, so-called color shifts and color unevenness, occur, thereby deteriorating the image quality.

In order to solve this problem, Japanese Patent Application Laid-Open No.
The techniques disclosed in 129873, Japanese Utility Model Laid-Open No. 1-85739, Japanese Utility Model Application Laid-Open No. 63-82256 and the like have already been proposed. The color recording apparatus according to Japanese Patent Application Laid-Open No. 62-129873 discloses a method in which a plurality of belt photoconductors are
Each color-separated light image is formed, visualized by a corresponding color toner, and sequentially superimposedly transferred onto a transfer sheet. The distance from the image exposure position to the transfer position is set to 1 / integer, and the effect of speed fluctuation due to the eccentricity of the drive roll and the rotation accuracy of the drive roll shaft is to be minimized.

Next, the principle of the color recording apparatus according to the above proposal will be briefly described with reference to FIG. Now, due to the eccentricity of the driving roll that rotationally drives the belt-shaped photoconductor, FIG.
As shown in FIG. 3A, it is assumed that a sinusoidal variation in the surface velocity having a period T and an amplitude a has occurred in the belt-shaped photosensitive member. The period T of the surface speed fluctuation of the belt-shaped photoconductor is equal to a value obtained by dividing the circumference of the driving roll by the process speed. In this case, the fluctuation of the image position at the time of exposure to the image exposure performed on the surface of the belt-shaped photoreceptor at regular intervals,
It is obtained by integrating the speed fluctuation waveform of the belt-shaped photoconductor from the exposure start point as shown in FIG. Here, when the speed of the belt-shaped photoconductor is higher than a predetermined speed, the exposed image is delayed with respect to the reference position. Conversely, when the speed of the belt-shaped photoconductor is lower than the predetermined speed, the exposed image is Since the image moves forward with respect to the reference position, the image position at the time of exposure changes as shown in FIG. 13B in which the positive and negative of the waveform obtained by integrating the speed fluctuation waveform of the belt-shaped photoconductor are inverted.

On the other hand, image position fluctuations at the time of transfer with respect to the exposure images formed on the belt-shaped photoreceptor at regular intervals are as shown in FIG. 13C. In the case of a transfer image transferred from the belt-shaped photoconductor, if the speed of the belt-shaped photoconductor is high, the transferred image advances to the reference position, and if the speed of the belt-shaped photoconductor is low, the transferred image is Since the waveform is delayed with respect to the reference position, the waveform shown in FIG. 13C becomes the waveform obtained by integrating the speed fluctuation.

As described above, the sum of the position fluctuation at the time of exposure and the position fluctuation at the time of transfer appears as an image position fluctuation on an actual transfer medium. In FIG. 13, the distance between the exposure position and the transfer position is set to an integral multiple of the circumference of the driving roll (in this example, 1), so that the phase of the position change at the time of exposure and the position change at the time of transfer are shifted by exactly π. Therefore, when the position fluctuation at the time of exposure and the position fluctuation at the time of transfer are added, the fluctuation is canceled out, and the position fluctuation on the transfer medium is not observed. Therefore, the above-described color shift does not occur and the image does not deteriorate. Further, the speed fluctuation caused by the driving roll also occurs due to a periodic rotation speed fluctuation of the driving motor, a mechanical error of the transmission system, and the like. Also in these cases, by configuring the rotation number of the transmission system to rotate an integer number of times with respect to one rotation of the driving roll, it is possible to cancel the fluctuation as shown in FIG.

The color image forming apparatus disclosed in Japanese Utility Model Laid-Open Publication No. 1-85739 forms color-separated light images on a plurality of photoreceptor belts, and visualizes them with color toners corresponding to the respective light images. In a color image forming apparatus of the type in which the color toner image is sequentially transferred from each photoconductor belt onto a transfer material conveyed onto a transfer belt, a distance between an exposure position and a transfer position on each photoconductor belt, The distance between the transfer positions is set to be an integral multiple of the diameter of the drive roller of each photoreceptor belt and the transfer belt, the material and shape of the drive rollers are the same, and the linear expansion coefficient in the diameter direction of each drive roller is made equal. It was done.

Further, the belt photoreceptor driving apparatus in a color copying machine or the like according to Japanese Utility Model Application Laid-Open No. 63-82256 discloses a method in which color-separated light images are formed on a plurality of belt photoreceptors, respectively. In a color copier or the like that visualizes each color toner image of the plurality of belt photoconductors on a transfer sheet and transfers the images, the eccentricity of a driving roller provided at a transfer position of each belt photoconductor is developed. Are mounted in such a manner that their phases are matched.

[0010]

However, the prior art described above has the following problems. That is, in the case of the color image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 62-129873, it is possible to prevent image displacement from occurring as long as a specific condition is satisfied with respect to speed fluctuation due to eccentricity of the driving roll. However, the configuration of a normal color image forming apparatus has a problem in that image displacement cannot be prevented. for that reason,
There is a problem that conditions for designing the color image forming apparatus are very limited, and the degree of freedom in designing is very small. In particular, in a color image forming apparatus using a belt-shaped photoconductor as described above, as disclosed in Japanese Patent Application Laid-Open Nos. 61-80276 and 62-238587, a plurality of image forming apparatuses are used. By setting the distance between the exposure position and the transfer position of the belt-like photoconductor of the unit so as to satisfy a specific relationship, a large-capacity memory is not required for an image processing apparatus or the like that processes an image of a read original. ,
A technique for reducing the cost of a color image forming apparatus is known. In the above-described color image forming apparatus, in order to apply such a technology, it is necessary to design the distance between the exposure position and the transfer position of the belt-shaped photoreceptor of the plurality of image forming units to a certain degree of freedom. Is limited, there is a new problem that the above-described cost reduction technique cannot be applied effectively.

Next, the above-mentioned Japanese Patent Application Laid-Open No. 62-129873 is described.
The problems of the color image forming apparatus according to Japanese Patent Application Laid-Open Publication No. H10-26095 will be described in further detail. Now, as shown in FIG. 14, the belt-shaped photoreceptor 100 is
Suppose that the belt-shaped photoconductor 100 is stretched by two rolls 02 and circulates at a predetermined rotational speed in the direction of the arrow. After the surface of the belt-shaped photoconductor 100 is charged to a predetermined potential by the primary charger 103, image exposure is performed at the exposure position A by the image exposure unit 104, and an electrostatic latent image is formed.
The electrostatic latent image formed on the surface of the belt-shaped photoreceptor 100 is developed by a developing unit 105 to become a visible image, and this developed image is transferred onto a transfer sheet (not shown) held on a transfer belt 106 at a transfer position. Transcribed. Such a process is sequentially performed on the belt-shaped photoconductor 100 corresponding to each color, and a developed image of a predetermined number of colors is transferred onto a transfer paper (not shown) held on the transfer belt 106 in a state where the developed images are superimposed on each other.

In order to consider the influence of the eccentricity of the drive roll 101, it is assumed that the eccentric drive roll 101 is rotating at a constant angular velocity. The belt-shaped photoreceptor 10
The surface speed of 0 is given by the product ω · r of the angular velocity ω of the drive roll 101 and the radius of rotation r, and when there is eccentricity, the radius of rotation r changes periodically.
00, as in the case described above, FIG.
It changes periodically as shown in FIG. Now, an image is exposed on a belt span (hereinafter, this belt span is referred to as “span 1”) from the drive roll to the tension roll among the spans between the drive roll and the tension roll of the belt-shaped photoconductor, When an image is transferred on the same span 1 of the belt-shaped photoconductor, the distance between the exposure position and the transfer position is set to an integral multiple of the circumference of the drive roll (1 in this example).
15), the speed variation in span 1 is exactly the same at both the exposure position and the transfer position as shown in FIG. 15A, and as described with reference to FIG. It is possible to offset the fluctuation.

However, a belt span (hereinafter, referred to as a belt span) from the tension roll of the belt-shaped photosensitive member to the drive roll is referred to as a belt span.
In this belt span is referred to as “span 2”, the surface speed fluctuation of the belt-shaped photoconductor due to the eccentricity is shown in FIG.
As shown in FIG. 15A, the speed fluctuation of span 1 is shown in FIG.
Is shifted in phase by π. Therefore, when the exposure point is in the span 1 that fluctuates as shown in FIG. 15A and the transfer point is in the span 2 that fluctuates as shown in FIG. Even if the distance is an integral multiple of the circumference of the driving roll, the variation in the exposure position is as shown in FIG. 15C as described above, and the phase in the variation in the transfer position is the same as shown in FIG. 15D. Therefore, the fluctuation of the sum of these fluctuations has a problem that the amplitude is 2a, that is, the fluctuation is twice as large as the fluctuation originally occurring, and the positional displacement of the image is increased.

Further, in the case of the configuration shown in FIG. 14, since the transfer position is directly below the drive roll 101, the exposed image passes not only on the belt span but also on the drive roll 101 until the transfer is performed. Will do. Therefore, in the case of the above configuration, when the image moves on the driving roll 101, another phenomenon occurs. That is, as described above, when the exposure position and the transfer position of the image are on the span of the belt-shaped photoconductor 100, if the exposure position and the transfer position are on the same span, as described above, the speed fluctuation of the belt-shaped photoconductor 100 is changed. In some cases. However, on the drive roll 101, the drive roll 1
The phase of the speed fluctuation waveform due to the eccentricity of 01 is different. For example, in FIG. 14, the speed fluctuation at the position of point B and the speed change at point C
Is shifted by π / 4, which is the angle between the points B and C. Therefore, the speed at which the image passes through point B and the speed at which the image reaches point C are determined by the point B image on the drive roll corresponding to the radius r as the drive roll rotates. Exactly equal to move to C. That is, considering the position fluctuation of the image, the period, the amplitude, and the phase at the points B and C are the same. Considering the exposure at the point A and the transfer at the point C in FIG. 14, when the distance between the exposure and the transfer is set to an integral multiple of the circumference of the driving roll, the speed fluctuation of the span 1 is as shown in FIG. For example, the change in the position of the image exposed at the point A is as shown in FIG. 16C, and the change in the transfer position at the point C when the speed change at the span 2 or the point B is as shown in FIG. FIG. 16D shows a state where the phase is shifted by T / 4. Therefore, also in this case, if the distance between the exposure and the transfer is set to an integral multiple of the circumference of the drive roll, the position fluctuation at the time of the exposure and the position fluctuation at the time of the transfer cannot be offset, and the image is displaced. There is a problem.

Further, in the case of the apparatus disclosed in Japanese Patent Application Laid-Open No. 62-129873, the effect of eccentricity of a tension roll other than the driving roll has no improvement effect.

On the other hand, the apparatus according to Japanese Utility Model Laid-Open No. 1-85739 is a technique similar to the apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 62-129873, and by improving the material and shape of the driving roll, Although improvement in temperature fluctuation can be expected, as described above, there is a problem that image displacement can be prevented only in a very limited specific case with respect to the eccentricity of the driving roll.

Further, as a technique aimed at reducing the influence of the eccentricity of the driving roll, Japanese Utility Model Application Laid-Open No. 63-822 is disclosed.
There is one disclosed in Japanese Patent Application Publication No. 56-56. 63-
As described above, the technique disclosed in Japanese Patent Application Laid-Open No. 82256 is intended to reduce the color shift between a plurality of belt photoconductors, not the fluctuation of the driving roll, and to set the phase of the eccentricity of the driving roll. It is characterized in that all the belt photoconductors are aligned. With such a configuration, the phase of the position fluctuation generated in the image formed by each belt photoconductor is adjusted to reduce the color shift on the transfer medium.

However, in the case of the technique disclosed in Japanese Utility Model Laid-Open Publication No. 63-82256, if the amplitudes of the positional fluctuations generated in the respective belt photoconductors do not coincide with each other, the fluctuations are directly generated as color shifts. There is a problem that it appears. In addition, in order to match the eccentric phases of the driving rolls with each other, it is necessary to measure the eccentric phase of the driving roll to be used in advance or to adjust the phase when the driving roll is mounted. Measurement and adjustment are complicated, and the manufacturing cost is increased due to an increase in man-hours.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to cause all rolls on which a belt-shaped photosensitive member is stretched to be caused by eccentricity. Reduce the fluctuation of the image forming position,
Accordingly, it is an object of the present invention to provide an inexpensive and highly productive image forming apparatus that can output a high-quality color image by eliminating color misregistration and color unevenness between color images.

[0020]

An image forming apparatus according to a first aspect of the present invention stretches a belt-shaped photosensitive member by a plurality of rolls including a driving roll, and forms image information on the belt-shaped photosensitive member. In the image forming apparatus that forms an image by performing scanning exposure according to and transferring an image formed on the belt-shaped photoconductor to a transfer medium, the image forming apparatus is configured to perform the scanning exposure from the exposure position on the belt-shaped photoconductor to the transfer position. Let L be the distance,
The exposure position and the transfer position are set such that the distance obtained by subtracting the distance L from the distance corresponding to the phase difference of the belt fluctuation caused by the belt photoconductor being stretched by the plurality of rolls becomes an integral multiple of the drive roll circumference. It is configured to set a position.

In the image forming apparatus according to a second aspect of the present invention, the belt-shaped photoconductor is stretched by a plurality of rolls including a driving roll and a tension roll, and image information is formed on the belt-shaped photoconductor. In an image forming apparatus that forms an image by performing scanning exposure in accordance with and transferring an image formed on the belt-shaped photoconductor to a transfer medium, a distance from an exposure position on the belt-shaped photoconductor to a transfer position Is L, the length of the belt wrap portion of the drive roll in the path where the image moves from the exposure position to the transfer position on the belt-shaped photoreceptor is l _dw , the length of the non-belt wrap portion of the drive roll is l _dn , The length of the belt wrap portion of the tension roll, l _tw ^′ , and the length of the belt wrap portion of the tension roll, l _{t, in} the path through which the image moves from the exposure position to the transfer position of the belt-shaped photoreceptor _w , L− ｛I _dw + (I _tw ^′ /
The exposure position and the transfer position are set so that I _tw ) × I _dn } becomes an integral multiple of the circumference of the driving roll.

Further, according to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the number of rotations of the drive system for driving the driving roll per one rotation of the driving roll is determined. n, the circumferential length of the drive roll is l _d , and the length of the belt wrap portion of the drive roll in the path along which the image moves from the exposure position to the transfer position on the belt-shaped photoconductor is l.
_dw , the length of the non-belt wrap portion of the driving roll is l _dn , the length of the belt wrap portion of the tension roll in the path where the image moves from the exposure position to the transfer position of the belt-like photoreceptor is l _tw ^′ , the tension roll when the length of the belt wrapped portion was _{l tw, l dw / (l} d / n), or {(I _{tw
^{'/ I tw) × I dn}} } / (l d / n) is configured to be an integer. An image forming apparatus according to a fourth aspect of the present invention is the image forming apparatus according to any one of the first to third aspects, further comprising: The exposure and transfer positions are arranged between the belt wrap start points of the roll immediately after the drive roll.

The belt-shaped photoreceptor is stretched by, for example, three rolls of a drive roll, a tension roll, and an idler roll.
Four or more rolls can be used, and the arrangement of the drive roll, the tension roll, and the idler roll can be freely set.

Further, the present invention is applied, for example, to the configuration of a belt-shaped photoconductor in a color image forming apparatus, but is also applicable to a belt-shaped photoconductor in a black-and-white image forming apparatus. That is, there is an effect that the expansion and contraction of the image can be reduced.

[0025]

In the image forming apparatus according to the first aspect of the present invention, the distance from the exposure position on the belt-shaped photosensitive member to the transfer position is defined as L, and the belt L is moved from the distance L by a plurality of rolls. Since the exposure position and the transfer position are set so that the distance obtained by subtracting the distance corresponding to the phase difference caused by the stretching is an integral multiple of the drive roll circumference, the belt-shaped photoconductor is used. Even if there is eccentricity in the drive roll that rotationally drives the belt, it occurs from the exposure position on the belt-shaped photoconductor to the transfer position in consideration of the phase difference caused by the belt photoconductor being stretched by multiple rolls. Which can offset image position variations,
It is possible to prevent the occurrence of a positional shift in the image.

In the image forming apparatus according to the second aspect of the present invention, L- {I _dw + (I _tw ^' / I _tw ) × I _dn }
Is the exposure position so that it is an integral multiple of the circumference of the drive roll,
Since the transfer position is configured to be set, by setting each parameter so as to satisfy this relationship, it is possible to prevent the image from being misaligned.

Furthermore, the image forming apparatus according to claim 3 wherein the _{invention, l dw / (l d /} n), or {(I _tw ^'/
Since _{I tw) × I dn} /} (l d / n) is configured to be an integral, even if there is rotational fluctuation corresponding to the period of the driving system for driving the drive roll, satisfies the above relationship By setting the parameters as described above, it is possible to prevent the image from being misaligned. Further, in the image forming apparatus according to claim 4 of the present invention, the exposure and transfer positions are arranged between the end point of the belt wrap of the roll immediately before the drive roll and the start point of the belt wrap of the roll immediately after the drive roll. As a result, the influence of eccentricity of rolls other than the drive roll can be prevented.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the illustrated embodiment.

FIG. 2 is a schematic structural view of an electrophotographic color image forming apparatus showing one embodiment of the present invention.

In FIG. 2, reference numeral 1 denotes a main body of the color image forming apparatus.
An image reading device 3 for reading an image of the document 4 is disposed above the image reading device. The image reading device 3 illuminates a document 4 placed on a platen glass 3 with a light source 5 and reflects reflected light images from the document 4 on first and second scanning mirrors 6 and 7.
And scans and exposes the color CCD sensor 9 via the imaging lens 8, and the color CCD sensor 9 scans the original 4.
Is read as an RGB analog image signal. The RGB analog image signal read by the color CCD sensor 9 is converted into a YMCK image signal by the image processing device 10.
The image data is temporarily stored in a memory provided inside the image processing apparatus 10 as needed.

In the color image forming apparatus main body 1, four image forming units 11 for yellow (Y), magenta (M), cyan (C), and black (K) are provided.
a, 11b, 11c, and 11d, and a paper transport belt unit 20 that is installed to face the four image forming units 11a, 11b, 11c, and 11d. Each of the image forming units 11a, 11b, 11c,
11d is a belt-shaped photoconductor 12a, 12b, respectively.
12c and 12d.
a, 12b, 12c, and 12d are stretched by a drive roll 13, a tension roll 14, and an idler roll 15. The belt-shaped photoconductors 12a, 12b, 1
2c and 12d are primary chargers 16a, 16b, 16c,
After being uniformly charged to a predetermined potential by 16d, images of each color are exposed by laser beam scanning devices 17a, 17b, 17c, and 17d to form an electrostatic latent image.
The laser beam scanning devices 17a, 17b, 17c,
17d scans a laser beam according to image data of each color of yellow (Y), magenta (M), cyan (C), and black (K) sequentially output from the image processing apparatus 10 to perform image exposure. It has become. The electrostatic latent images formed on the belt-shaped photoconductors 12a, 12b, 12c, and 12d are developed by developing units 18a, 18b, 18c, and 18d.
Respectively, yellow (Y), magenta (M),
The toner image is developed as a toner image of each color of cyan (C) and black (K).

Each of the belt-shaped photoconductors 12a, 12b, 1
The recording paper 19 for recording the toner images of each color formed on 2c and 12d is fed from a paper feed cassette 21 to a feeding roll 22.
And is conveyed to the sheet conveying belt unit 20 by the registration roll 23 at a predetermined timing. The paper transport belt unit 20 includes a paper transport belt 24, and the paper transport belt 24 is stretched by a drive roll 25, a tension roll 26, and an idler roll 27. Paper transport belt 2
The recording sheet 19 sent out onto the sheet 4 is conveyed while being electrostatically adsorbed on the sheet conveying belt 24 by the charging of the attraction charger 28.

The leading end of the recording paper 19 transported by the paper transport belt 24 and the first image forming unit 11
The paper feed timing and the image writing timing are determined such that the leading end of the yellow image on the belt-shaped photoconductor 12a formed by the a coincides with the lowest transfer point of the belt-shaped photoconductor 12a. I have. The visible image on the belt-shaped photoconductor 12a is transferred to the recording paper 19 that has reached the transfer point by the transfer charger 29a.
Further, the transfer point reaches a transfer point immediately below the belt-shaped photoconductor 12b. On the recording paper 19 that has reached the transfer immediately below the belt-shaped photoconductor 12b, a visible image on the belt-shaped photoconductor 12b is transferred in the same manner as the transfer on the belt-shaped photoconductor 12a. Similarly, the recording paper 19 on which all the transfer is completed is further transported by the paper transport belt 24, and when the recording paper 19 reaches the vicinity of the tension roll 26, the recording paper 19 is separated from the transfer transport belt 24 by the discharging charger 30. Thereafter, the recording paper 19 to which the four color toner images have been transferred is fixed by heat and pressure by the fixing device 31 and is discharged onto the discharge tray 32, thereby completing the color image forming process.

The belt-shaped photoconductors 12a, 12b, 12c, and 12d after the transfer of the visible image are removed of the residual developer and the like by the cleaning devices 33a, 33b, 33c, and 33d. Prepare for.

The paper transport belt 24 from which the recording paper 19 has been peeled is neutralized by a neutralizing charger 34 to prepare for the next image forming step.

In this embodiment, the distance from the exposure position on the belt-shaped photosensitive member to the transfer position is defined as L, and the phase difference caused by the belt photosensitive member being stretched by a plurality of rolls from this distance L. The exposure position and the transfer position are set so that the distance obtained by subtracting the distance corresponding to the above becomes an integral multiple of the drive roll circumference.

The distance corresponding to the phase difference of the belt fluctuation caused by the belt photoconductor being stretched by a plurality of rolls is the distance along the path where the image moves from the exposure position to the transfer position on the belt photoconductor. The length of the belt wrap portion of the drive roll is l _dw , the length of the non-belt wrap portion of the drive roll is l _dn , and the belt of the tension roll in the path where the image of the belt-shaped photoreceptor moves from the exposure position to the transfer position When the length of the wrap portion is l _tw ^′ and the length of the belt wrap portion of the tension roll is l _tw , it is given by I _dw + (I _tw ^′ / I _tw ) × I _dn (1).

FIG. 1 is an enlarged view showing the structure of each image forming unit.

Each of the belt-shaped photoconductors 12a, 12b, 1
2c and 12d are, as shown in FIG.
It is stretched by the tension roll 14 and the idler roll 15, and circulates at a predetermined speed in the direction of the arrow. The drive roll 13 is for transmitting a drive force transmitted from a drive motor (not shown) via a timing belt or the like to the belt-shaped photoconductor 12. The tension roll 14 is supported by a spring 35 having one end fixed so as to be able to translate. The irradiation position A of the belt-shaped photoreceptor 12 for image exposure by the laser beam scanning device 17 is set to the span between the tension roll 14 and the drive roll 13 located immediately before the drive roll 13, and the image transfer position Is set to a point C immediately below the driving roll 13. Further, taking the lap start point of the drive roll 13 as a point B, the exposure transfer distance L which is the sum of the distance l _AB between the exposure point A and the lap start point B and the distance l _BC between the point B and the point C.
(= L _AB + l _BC ), L−l _BC = l _AB is set to be an integral multiple of the circumference of the drive roll 13.

That is, in the above equation (1), l _dw corresponds to l _BC , and the tension roller 14 moves the belt-shaped photosensitive member 12 along the path where the image moves from the exposure position to the transfer position.
Since there is no belt wrap portion, this corresponds to the case where l _tw ^′ = 0.

In the above-described configuration, the color image forming apparatus according to the present embodiment prevents the image from being misaligned as follows. That is,
In the above-described color image forming apparatus, as shown in FIG. 2, in each of the image forming units 11a, 11b, 11c, and 11d, the yellow, yellow, and yellow processes are performed by charging, exposing, and developing the belt-shaped photoconductors 12a, 12b, 12c, and 12d. (Y), magenta (M), cyan (C), and black (K) monochromatic images of the belt-shaped photoconductors 12a, 12b, 12c, and 1
It is formed on 2d. The belt-shaped photoconductors 12a, 12
b, 12c, and 12d are stretched and supported by a drive roll 13, a tension roll 14, and an idler roll 15, and the drive roll 13 transmits a driving force transmitted from a drive motor (not shown) via a timing belt or the like to the belt. To the photoconductor 12. The tension roll 14 applies a predetermined tension to the belt-shaped photoconductor 12 so that the surface of the belt-shaped photoconductor 12 is flat and the driving force from the driving roll 13 is transmitted to the belt-shaped photoconductor 12 without loss. This is for applying to the belt-shaped photoconductor 12 by the operation of 35. Further, the idler roll 15 is mainly used for increasing the inner volume of the belt-shaped photoconductor 12 and for setting the surface position of the belt-shaped photoconductor 12 to a desired position. On the other hand, in the paper transport belt unit 20, the recording paper 19 is electrostatically attracted onto the paper transport belt 24 by the action of the attraction charger 28, and the image forming units 11a, 11b, 11c, 11
It is conveyed to the transfer part of d. Then, the images formed on the belt-shaped photoconductor 12 are transferred to the transfer chargers 29a, 29b, 29.
By the action of c and 29d, the image is electrostatically transferred to the recording sheet 19 on the sheet conveying belt 24. The function of each roll of the paper transport belt unit 20 is the same as that of the roll of the belt-shaped photoconductor 12. Further, the cleaning devices 33a, 3
3b, 33c and 33d are belt-shaped photoconductors 12 after transfer.
Unnecessary images remaining on a, 12b, 12c, and 12d are cleaned to prepare for the next image forming step. Furthermore, the static eliminator 3
4 removes the electric charge on the paper transport belt 24 applied in the suction transfer process.

By the way, how the exposure point A and the transfer point C set as shown in FIG. 1 operate will be described below. First, the effect when the three rolls 13, 14, and 15 that stretch the belt-shaped photoconductor 12 have eccentricity will be considered. When the driving roll 13 is eccentric, the belt span between the point E and the point H of the belt-shaped photoconductor 12 (hereinafter, this belt span is referred to as “span EH”) due to the fluctuation of the rotation radius r of the driving roll 13. ) And a belt span between points G and B (hereinafter, referred to as a belt span).
This belt span is referred to as “span GB”), and a speed fluctuation occurs. The speed fluctuations occurring in the span EH and the span GB of the belt-shaped photoconductor 12 have the same amplitude and frequency, but the phase of each speed fluctuation is the same as that of the belt-shaped photoconductor 1.
2 differs by an angle φ between the spans BE wound around the drive roll 13. In the belt span between the point I and the point F of the belt-shaped photoconductor 12 (hereinafter, this belt span is referred to as “span IF”), the idler roll 1
5 merely changes the moving direction of the belt-shaped photoreceptor 12, the speed fluctuation of the same amplitude, the same frequency and the same phase as the span EH occurs. The fluctuation of the speed of the belt-shaped photoconductor 12 is the same in the wrap between the point H and the point I on the idler roll 15 (hereinafter, this wrap is referred to as “wrap HI”). On the other hand, the tension roll 14 absorbs a difference in speed fluctuation between the span IF and the span GB.
Translational displacement and rotational speed fluctuations occur. The amplitude of the translational displacement motion and the rotational speed fluctuation generated in the tension roll 14 depends on the speed difference between the span IF and the span GB, the translation displacement direction of the tension roll, and the wrap angle.

Next, when the tension roll 14 is eccentric, there is no fluctuation due to the rotation radius r of the drive roll 13, so that the span EH and the span G
Speed fluctuation does not occur in any of B, span FI, and lap HI. In this case, the tension roll 14 generates a velocity distribution on the surface due to its own eccentricity. However, in order to keep the velocity of the span IF and the span GB constant,
The tension roll 14 undergoes a translational displacement motion and a rotational speed fluctuation. The amplitude of the translational displacement motion and the rotational speed fluctuation generated in the tension roll 14 depends on the amount of eccentricity of the tension roll 14, the translation displacement direction, and the wrap angle.

Finally, consider the case where the idler roll 15 has eccentricity. Since there is no change in the rotation radius in the drive roll 13, no change occurs in the spans EH and GB. On the other hand, since the rotation radius of the idler roll 15 at the lap point H and the point I fluctuates due to the eccentricity of the idler roll 15, the fluctuation of the rotation angular velocity of the idler roll 15 depending on the fluctuation of the rotation radius at the point H, and the change of the idler roll 15 The surface speed of the span IF varies depending on the lap angle of the span. The tension roll 14 absorbs the speed difference between the span IF and the span GB.
Translational and rotational displacement movements occur. The amplitude of the translational displacement motion and the rotation speed fluctuation generated in the tension roll 14 depends on the speed difference between the span IF and the span GB, the translation displacement direction of the tension roll 14, and the wrap angle.

As a result, the exposure position and the transfer position change due to the eccentricity of each of the rolls 13, 14, and 15. However, by setting the exposure point and the transfer point between the point G and the point H, the tension roll is changed. The effect of the eccentricity of the idler roll 14 and the idler roll 15 disappears.

Regarding the eccentricity of the drive roll 13, the speed fluctuations in the span EH and the span GB have the same amplitude and frequency and the same phase as shown in FIGS. 3 (a) and 3 (b), respectively. 13 is shifted by the wrap angle φ at which the belt-shaped photoconductor 12 wraps. At this time, as shown in FIG. 1, it is assumed that image exposure is performed on the belt-shaped photoconductor 12 at the exposure position A, and the image exposure is started at (A) in FIG. In this case, since l _AB given by equation (1) is an integral multiple of the circumference of the driving roll 13 (in this case, 1), the time at which the image passes point B in FIG. It becomes (b) of (b). Since the same speed when this image passes through point B and the speed when the image reaches transfer point C are the same, the speed fluctuation waveform at point B and the speed fluctuation waveform at transfer point C become the same. . As a result, FIG.
As shown in FIG. 3C, the position change of the exposure image started at
The position fluctuation of the transferred image becomes as shown in FIG. 3D, and the position fluctuation on the recording paper 19 to which these are added is canceled to be zero.

Therefore, it is possible to reduce the fluctuation of the image forming position due to the eccentricity of all the rolls 13, 14, 15 on which the belt-shaped photosensitive member 12 is stretched. An inexpensive and highly productive color image forming apparatus capable of eliminating color unevenness and outputting a high-quality color image can be provided.

Embodiment 2 FIG. 4 shows Embodiment 2 of the present invention. The same parts as those in the above embodiment are denoted by the same reference numerals. The image exposure position is set to a belt span between the drive roll and the idler roll.

In this embodiment, as shown in FIG.
The lap end point of roll 13 is point E, tension roll 1
The lap start point and the lap end point of No. 4 are respectively set to the F point and the lap point.
As point G, distance l between points D and F_DFAnd points F and G
Distance l between_FG, And the distance l between points G and A_GAEtc.
Then, the distance L between exposure and transfer is L = l_DF+ L_FG+ L _GA
+ L_AB+ L_BCAnd L- ｛l_BC+ (L_FG/ L_FG) × l
_EB｝ = L-1_BC−l_EB= L_DF+ L_FG+ L_GA+ L_AB−l_EB
Is an integral multiple of the circumference of the drive roll 13
A point D indicating an exposure position is set. That is,
In equation (1), l_dwIs l_BCEquivalent to tension low
The length l passing over the le 14_tw ^'Is l_FGPlace that became equal to
It corresponds to the case. Where l_EBIs the non-rack of the drive roll 13.
Is the length of the loop part.

In this embodiment, since the image exposure is performed at the point D in FIG. 4, the speed fluctuations of the belt-shaped photosensitive member 12 in the span EH and the span GB are the same as those in FIGS. Assuming that the images are as shown in FIGS. 5A and 5B, the time at which the image exposed in FIG. (A). This is because in FIG. 4, the exposure transfer distance L is L = I _DF + I _FG + I _AG + I _AB + I _BC and L−I
{I _BC + (I _FG / I _FG ) × I _EB } = L−I _BC −I _EB = I
_{DF + I FG + I AG +} I AB -I EB is the point D to be an integral multiple of the circumferential length of the driving roll 13 is because has been set.
In other words, if I _DF + I _FG + I _AG + I _AB is an integral multiple of the circumference of the drive roll 13, the time when passing point B is as shown in FIG.
It should be (c) in (b), but since it is set shorter by l _EB, it is the time in (b). Since the speed fluctuation waveform at the transfer point C is the same as the speed fluctuation waveform at the point B, the exposure position fluctuation and the transfer position fluctuation are respectively shown in FIG.
(C) and (d), in which case the recording paper 1
Position shifts on 9 cancel out to zero.

As described above, the exposure point and the transfer point are set between the lap end point G of the tension roll 14 of FIG. 4 through the points A, B, C, and E, and the lap start point H of the idler roll 15. In either case, and in the case of the belt-shaped photoconductor 12 stretched by four or more rolls as shown in FIG. It is possible to do.

Further, the exposure point and the transfer point in FIG. 4 are not limited to the above case, and the wrap start point H of the idler roll passes through the points A, B, C and E from the wrap end point G of the tension roll. In any case, the distance between the exposure and the transfer and the circumference of the driving roll are set so as to satisfy the relationship described in the equation (1).

Third Embodiment FIG. 7 is a schematic structural view of a color image forming apparatus showing a third embodiment according to the present invention. In this embodiment, an intermediate transfer belt unit 40 using an intermediate transfer belt 41 is provided instead of the sheet transport belt unit in the embodiment of FIG. Until the image is transferred to the intermediate transfer belt 41,
The configuration and operation are exactly the same as those of the embodiment shown in FIG.
The image transferred on the intermediate transfer belt 41 is transferred to the backup roll 42 on the recording paper 19 by the secondary transfer position.
Is transferred collectively by the pressing force of
Thereafter, a fixing process is performed by a fixing device (not shown). The situation of the speed fluctuation in the belt-shaped photoconductor 12 and the situation of the position fluctuation on the recording paper 19 caused by the speed fluctuation are the same as those in the embodiment in FIG. Other configurations and operations are the same as those of the above-described embodiment, and a description thereof will be omitted.

Experimental Example Next, the inventor made a prototype of the image forming unit 11 as shown in FIG. 1 and conducted an experiment for examining the state of occurrence of image displacement. Note that the numerical values are displayed after being appropriately rounded or the like, but in reality, the relationship shown in Expression (1) is strictly satisfied.

Each image forming unit 11a, 11b, 11
In c and 11d, as shown in FIG. 1, a driving roll 13 having a radius of 14 mm, a tension roll 14 having a radius of 14 mm,
The belt-shaped photoconductor 12 is stretched and supported by an idler roll 15 having a radius of 14 mm, and the drive roll 13 is rotated by a driving force transmitted from a drive motor (not shown) via a timing belt or the like. Subject to the action of a given electrophotographic process. The tension roll 14 applies a tension of about 5 kgf to the belt-shaped photoconductor 12 via a spring 35, whereby the surface of the belt-shaped photoconductor 12 is maintained flat, and the driving roll 1
3 is transmitted without loss. The center distance between the drive roll 13 and the tension roll 14 is about 275 mm, and the rotation center of the idler roll 15 is located at a point about 93 mm above the center of the drive roll 13 and about 54 mm to the left. In addition, each roll 13, 14,
Reference numerals 15 each have an eccentricity of about 1 mm.

The primary charger 1 is placed on the belt-shaped photosensitive member 12.
6, a uniform charge is applied, and the laser beam scanning device 17 performs a scanning exposure in accordance with predetermined image information at a position A shown in the figure to form an electrostatic latent image. The electrostatic latent image is then converted into a monochromatic visible image of a predetermined color by the operation of the developing device 18 and is conveyed to a transfer area. Each of the four image forming units 11a, 11b, 11c, and 11d forms a single-color image of yellow, magenta, cyan, and black, respectively, and each image is a transfer charger 29a, 29b,
The images are electrostatically transferred to the same position on the recording paper 19 by 29c and 29d to obtain a full-color image. After the transfer, the residual image on the belt-shaped photoconductor 12 is removed by the cleaning device 33a.
The image is scraped off by 33b, 33c and 33d, and the next image formation becomes possible.

The exposure point A is located at a position about 176 mm from the lap start point B of the drive roll 13 on the belt span between the tension roll 14 and the drive roll 13 (l _AB = 1 in FIG. 1).
76 mm). Distance between exposure and transfer is about 19
Since the length of the wrap portion of the drive roll 13 in the image moving path is about 22 mm and the length of the wrap portion of the tension roll 14 in the image moving path is zero,
−22 = 28 × π × 2, which satisfies the relationship of Expression (1).

The paper transport belt 24 in the paper transport belt unit 20 is made of, for example, a PET film having a thickness of 75 μm, is stretched by a tension roll 14 at a tension of about 5 kgf, and driven by a drive roll 13. The sheet conveying belt 24 electrostatically adsorbs the recording sheet 19 on its surface by an adsorbing device 28, and the image forming units 11a,
The sheet is conveyed to transfer portions 11b, 11c, and 11d. The charge removing device 34 removes the electric charge on the sheet conveying belt 24 supplied in the suction transfer process.

A full-color image is formed at a high speed according to the above-described procedure. Here, a description will be given of a situation in which a position change occurs in a belt-shaped photosensitive member which causes color misregistration on a sheet.

The driving roll 13, the tension roll 14,
The eccentricity of each idler roll 15 causes a speed fluctuation of each roll shaft and a speed fluctuation of the surface of the belt-shaped photoconductor 12. The frequency of fluctuation drives the process speed
3, which is the same for each roll. The phase differs depending on the phase of the eccentricity of each roll and the measurement location. The amplitude of the fluctuation also depends on the measurement location,
Each is as shown in FIG. Here, D / R means a drive roll, T / R means a tension roll, and I / R means an idler roll. The span EH and the like are as shown in FIG.

The exposure point A is located on the span GB as described above.
Since the transfer point C is set immediately below the drive roll 13, no fluctuation occurs due to the eccentricity of the tension roll 14 and the idler roll 15. FIG. 9 shows the result of examining the image position fluctuation on the recording paper 19 by moving the exposure point before and after the point A in order to confirm that the fluctuation due to the eccentricity of the driving roll 13 is canceled. It was confirmed that the amount of fluctuation caused by the distance between exposure and transfer changed, and the fluctuation at the position of point A was zero.

In this embodiment, the exposure point is additionally shown in FIG.
The position can be set as shown in FIG. Both equations (1)
And the image on the recording paper 19 does not fluctuate. Further, another configuration in which the transfer position is changed can be adopted.

Fourth Embodiment FIG. 11 shows an embodiment of the image forming apparatus according to the third aspect of the present invention, and the same parts as those of the first embodiment of the present invention are the same. Explaining with reference numerals, the configuration of the entire apparatus is the same as that shown in FIG. 1, FIG. 2 or FIG. In the case of the embodiment of the first aspect of the present invention, an improvement effect may not be obtained in some cases with respect to the fluctuation of the rotational angular velocity in the rotary drive system of the drive roll 13. Then
Even when there is a change in the rotational angular velocity in the rotation drive system of the drive roll, it is possible to prevent the occurrence of positional deviation in the image. Therefore, in this embodiment, the number n of rotations of the power transmission system from the drive motor of the belt-shaped photoreceptor to the drive roll per rotation of the drive roll n, the circumference l _{d of the} drive roll
To one in which _{l dw / (l d / n} ) (2) or ^{_{{(l tw '/ l tw}} ) × l dn} / (l d / n) (3) is constructed to be an integral .

FIG. 11 is an enlarged view of the drive and drive transmission portion of the drive roll. A gear 52 is attached to a rotation shaft 51 of the drive motor 50, and the gear 52 and the gear 53 are connected by a timing belt 54.
Further, the gear 53 and the driving roll 13 are connected to a shaft 55
Are connected by For the rotation speed n of the drive motor 50 and the gear 51 and the circumference l _d of the drive roll 13, l _dw / (l
_d / n) is an integer.

It should be noted that the drive system is not limited to this configuration, and a multi-stage speed reduction mechanism may be used, and other speed reduction / transmission means such as a gear instead of a timing belt may be used. In any case, the rotation speed of the transmission system is configured to satisfy the above-described relationship.

The same applies to the case of a belt-shaped photoconductor composed of four or more rolls. For example, in the case of FIG. 6, the transfer point is set between point H and point A on the drive roll. The exposure point can be set anywhere on the belt-shaped photoreceptor, and the distance between exposure and transfer is set so that the relationship with the circumference of the driving roll satisfies the relationship described in the above equation (1).
The distance from to the transfer point is set so as to satisfy the relationship described in Expression (2) or (3).

Next, the rotation fluctuation of the driving roll 13 will be described.
Think about it. As shown in FIG. 12, the rotational speed n of the drive transmission system (this
Here, if a periodic speed fluctuation corresponding to 3) is occurring
I do. If the exposure is started in FIG.
Position where the shooting start time is exactly in phase with (a) as in (a)
Can be offset by setting
It is understood from the explanation. 1, 2, 4, and 11 will be described.
L-l_BCOr L- ｛I_BC+ (I_FG
/ I_FG) × I_EB｝ = LI_BC-I_EB= I_DF+ I _FG+ I_AG
+ I_AB-I_EBBecomes an integral multiple of the circumference of the drive roll 13
Is set to_BC, (I_FG/ I_FG) × I_EBHato
It is an integral multiple of the length obtained by dividing the circumference of the drive roll 13 by n.
It is set to be. That is, the distance between exposure and transfer
L means that the fluctuation cycle T / 3 in FIG. 12 is repeated an integer number of times.
The exposure is started in FIG.
In this case, the transfer start time is set as shown in FIG.
The position is exactly the same as that in FIG. Therefore, at the time of exposure
And the fluctuation at the time of transfer are offset to zero.

EXPERIMENTAL EXAMPLE Next, the present inventor made a prototype of an image forming unit as shown in FIGS. 1 and 11, and conducted an experiment for examining the state of occurrence of image displacement. The numerical values are appropriately rounded or the like.

Each image forming unit 11a, 11b, 11
In c and 11d, as shown in FIG. 1, a driving roll 13 having a radius of 14 mm, a tension roll 14 having a radius of 14 mm,
The belt-shaped photoconductor 12 is stretched and supported by an idler roll 15 having a radius of 14 mm, and the driving roll 13 rotates the belt photoconductor 12 by a driving force transmitted from a driving motor 50 via a timing belt 54 to a predetermined position. Under the action of the electrophotographic process. The drive motor 50 rotates four times per rotation of the drive roll 13 as shown in FIG. The tension roll 14
5 kgf applied to the belt-shaped photoreceptor 12 via the spring 35
To the belt-like photoreceptor 1
2 is kept flat, and the driving force from the driving roll 13 is transmitted without loss. The center distance between the drive roll 13 and the tension roll 14 is about 275 mm, and the rotation center of the idler roll 15 is located at a point about 93 mm above the center of the drive roll 13 and about 54 mm to the left. Each of the rolls 13, 14, 15 has an eccentricity of about 1 mm.

As shown in FIG. 1, a uniform charge is applied to the belt-shaped photoreceptor 12 by a primary charger 16 and a laser beam scanning device 17 performs scanning exposure according to predetermined image information at a position shown in the figure. By performing the process at A, an electrostatic latent image is formed. The electrostatic latent image is then converted into a monochromatic visible image of a predetermined color by the operation of the developing device 18 and is conveyed to a transfer area. 4
Image forming units 11a, 11b, 11c, 11d
Respectively, a single-color image of yellow, magenta, cyan, and black is formed, and each image is electrostatically transferred to the same position on the recording paper 19 by a transfer charger 29 in a transfer area to obtain a full-color image. After the transfer, the residual image on the belt-shaped photoconductor 12 is scraped off by the cleaning device 33, so that the next image formation can be performed.

The exposure point is located on the belt span between the tension roll 14 and the drive roll 13 at a position approximately 176 mm from the lap start point of the drive roll 13 (l _AB = 176 in FIG. 1).
mm). Distance between exposure and transfer is about 198m
m, the length of the wrap portion of the drive roll 13 in the image movement path is about 22 mm, and the length of the wrap portion of the tension roll 14 in the image movement path is zero.
2 = 28 × π × 2, which satisfies the relationship of the above equation (1). Also, the circumference 88 mm of the driving roll 13 is
When the number of rotations of the drive motor 50 per one rotation of the drive roll 13 is divided by four, the result is 22 mm, which satisfies the relationship of Expression (2).

The paper transport belt 24 in the paper transport belt unit 20 is made of, for example, a PET film having a thickness of 75 μm, is stretched by a tension roll 14 at a tension of about 5 kgf, and driven by a drive roll 13. The sheet conveying belt 24 electrostatically adsorbs the recording sheet 19 on its surface by an adsorbing device 28, and the image forming units 11a,
The sheet is conveyed to transfer portions 11b, 11c, and 11d. The charge removing device 30 removes the electric charge on the sheet conveying belt 24 supplied in the suction transfer process.

A full-color image is formed at high speed according to the above-described procedure. Here, a description will be given of a situation in which the position of the belt-shaped photosensitive member 12 causes a color shift on a sheet, which causes a color shift.

The eccentricity of the driving roll 13 causes a speed fluctuation of each roll shaft and a speed fluctuation of the surface of the belt-shaped photosensitive member 12. The frequency of the fluctuation is obtained by dividing the process speed by the circumference of the driving roll 13, and is the same for each roll. The phase differs depending on the phase of the eccentricity of each roll and the measurement location. The amplitude of the fluctuation also differs depending on the measurement location, and is as shown in FIG. Here, D / R means a drive roll, T / R means a tension roll, and I / R means an idler roll. The span EH and the like are as shown in FIG. Further, a fluctuation occurs in synchronization with the rotation speed of the drive motor 50, and this fluctuation has the same amplitude, the same period, and the same phase at any position on the belt-shaped photosensitive member.

FIG. 9 shows the result of examining the change in the image position on the paper by moving the exposure point before and after the point A in order to confirm that the fluctuation due to the eccentricity of the driving roll 13 is offset. The amount of fluctuation that occurs due to the distance between exposure and transfer changes,
It was confirmed that the fluctuation was zero at the position of point A.

The fluctuation synchronized with the rotation speed of the drive motor 50 is 198 mm / mm from the exposure time to the transfer time.
(88 mm / 4) = 9 changes are repeated, and a speed change of the same phase occurs at the time of exposure and at the time of transfer. Therefore, the position change on the recording paper 19 is canceled and becomes zero.

In this embodiment, the exposure point is additionally shown in FIG.
The position can be set as shown in FIG. Both equations (1)
(2) The relationship of (3) is satisfied, and no fluctuation occurs on the recording paper. Further, another configuration in which the transfer position is changed can be adopted.

In the present invention, as shown in FIG.
The same applies to the case where an intermediate transfer member is used.

[0079]

The present invention has the above-described structure and operation, and can reduce the fluctuation of the image forming position due to the eccentricity of all the rolls on which the belt-shaped photosensitive member is stretched. Accordingly, it is possible to provide an inexpensive and highly productive color image forming apparatus capable of eliminating color shift and color unevenness between color images and outputting a high-quality color image.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram showing a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a color image forming apparatus according to one embodiment of the present invention.

FIGS. 3A to 3D are graphs each showing an operation of the color image forming apparatus according to the embodiment.

FIG. 4 is a main part configuration diagram showing a color image forming apparatus according to another embodiment of the present invention.

FIGS. 5A to 5D are graphs respectively showing the operation of the color image forming apparatus according to the embodiment.

FIG. 6 is a main part configuration diagram showing a modification of the color image forming apparatus according to the embodiment.

FIG. 7 is a main part configuration diagram showing a color image forming apparatus according to still another embodiment of the present invention.

FIGS. 8A to 8C are graphs each showing an operation of the color image forming apparatus according to the experimental example.

FIG. 9 is a graph illustrating an operation of the color image forming apparatus according to the experimental example.

FIG. 10 is a main part configuration diagram showing a color image forming apparatus according to a modification of the present invention.

FIG. 11 is a main part configuration diagram showing a color image forming apparatus according to an embodiment of claim 3 of the present invention.

FIG. 12 is a graph showing an operation of the color image forming apparatus according to the embodiment.

FIGS. 13A to 13C are graphs showing the operation of a conventional color image forming apparatus, respectively.

FIG. 14 is a main part configuration diagram showing a conventional color image forming apparatus.

FIGS. 15A to 15D are graphs showing operations of a conventional color image forming apparatus.

FIGS. 16A to 16D are graphs showing the operation of a conventional color image forming apparatus, respectively.

[Explanation of symbols]

12 belt-shaped photoreceptor, 13 drive roll, 14 tension roll, 15 idler roll, A exposure point, B
Lapping start point of drive roll, C transfer point, distance between L exposure transfer, l _AB distance between points A and B l _AB , l _BC distance between points B and C.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-129873 (JP, A) JP-A-61-80276 (JP, A) JP-A-62-238587 (JP, A) 274077 (JP, A) JP-A-6-266175 (JP, A) JP-A-1-85739 (JP, U) JP-A-63-82256 (JP, U) (58) Fields investigated (Int. Cl. ^7, DB name) G03G 15/00 550 G03G 15/01 G03G 21/00 370 G03G 21/14 - 21/16

Claims (4)

(57) [Claims] 1. A belt-shaped photoconductor is stretched by a plurality of rolls including a driving roll, and scanning exposure is performed on the belt-shaped photoconductor in accordance with image information to form an image formed on the belt-shaped photoconductor. In the image forming apparatus that forms an image by transferring the image to a transfer medium, a distance from the exposure position on the belt-shaped photoconductor to the transfer position is L, and the belt L is used to stretch the belt photoconductor by a plurality of rolls. An image forming apparatus, wherein an exposure position and a transfer position are set such that a distance obtained by subtracting a distance corresponding to a phase difference of belt fluctuation caused by being stretched becomes an integral multiple of a drive roll circumference. 2. A belt-shaped photoconductor is stretched by a plurality of rolls including a driving roll and a tension roll, and scanning exposure is performed on the belt-shaped photoconductor in accordance with image information to form on the belt-shaped photoconductor. In the image forming apparatus for forming an image by transferring the formed image to a transfer medium, the distance from the exposure position on the belt-shaped photoconductor to the transfer position is L, and the distance from the exposure position on the belt-shaped photoconductor to the transfer position is The length of the belt wrap portion of the drive roll in the path along which the image moves is l _dw , the length of the non-belt wrap portion of the drive roll is l _dn , and the image moves from the exposure position to the transfer position on the belt-shaped photoconductor. When the length of the belt wrap portion of the tension roll in the path is l _tw ^′ and the length of the belt wrap portion of the tension roll is l _tw , L− _{ＬI dw} + (I _tw ^′)
/ I _tw ) × I _dn } is set to an exposure position and a transfer position so as to be an integral multiple of the circumference of the driving roll. 3. The image forming apparatus according to claim 2, wherein
And the driving system for driving the driving roll is one driving roll.
The number of rotations per roll is n and the circumference of the drive roll is l_d,
The image moves from the exposure position to the transfer position on the photoconductor
The length of the belt wrap portion of the drive roll in the path
_dwAnd the length of the non-belt wrap portion of the drive roll is l_dn,
The image moves from the exposure position to the transfer position
Length of the belt wrap of the tension roll in the path
To l_tw ^', Length of belt wrap part of tension roll
To l_twAnd l_dw/ (L_d/ N) or ｛(I_tw
^'/ I_tw) × I_dn｝ / (L_d/ N) is an integer
An image forming apparatus comprising: 4. An exposure and transfer position is arranged between a belt wrap end point of a roll immediately before the drive roll and a belt wrap start point of a roll immediately after the drive roll. 4. The image forming apparatus according to claim 3.