JPH11231599A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the occurrence of positional deviation among respective color image on the toner image carrier, even when the load fluctuation with respect to the toner image carrier occurs, with respect to the image forming device provided with the toner image carrier in a belt shape. SOLUTION: Relating to this image forming device provided with detecting means 18 and 19 for detecting phase differential between the toner image carrier 1a and disposing means 2, and a correcting means 20 for correcting the above phase differential by increasing/reducing rotary speed of the toner image carrier 1a based on the detection result, the device is provided with recognizing means 21 for recognizing the differential of rotary cycle between a case of the presence and the case of the absence of load fluctuation with respect to the toner image carrier 1a, and a correction indicating means for correcting the positional deviation of the toner image due to the above load fluctuation by indicating the increase/reduce of the above rotary speed to the correcting means 20 based on the recognizing result.

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 for forming an image by an electrophotographic system, and more particularly to an image forming apparatus for forming a color image using a belt-shaped toner image carrier. .

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus using a belt-shaped toner image carrier, for example, as shown in FIG.
A copier equipped with an intermediate transfer member belt 1a as a toner image carrier is known. In this image forming apparatus, a latent image writing unit 2 such as a laser ROS (Raster Output Scanner) is used.
When a toner image is formed on the photosensitive drum 4 by writing by the developer and development by the developing device 3, the toner image is once transferred onto the intermediate transfer belt 1a. However, in the case of a color image, the intermediate transfer belt 1a
Every rotation, Y (yellow), M (magenta), C
The toner images of each color (cyan) and K (black) are sequentially transferred to the intermediate transfer belt 1a, and the intermediate transfer belt 1a
Above, the four color toner images are combined. And then,
The toner image on the intermediate transfer belt 1a is transferred to recording paper and output.

Further, as shown in FIG. 7, for example, there is a type having a photosensitive belt 1b as a toner image carrier.
In this image forming apparatus, each time the photoreceptor belt 1b makes one rotation, the writing by the latent image writing unit 2 and the developing unit 3
, M, Y on the photoreceptor belt 1b
A toner image of each color of C and K is formed, and a photoreceptor belt 1b is formed.
After the four color toner images are synthesized, the image is transferred to recording paper.

In these image forming apparatuses, each time a toner image carrier such as the intermediate transfer belt 1a or the photoreceptor belt 1b rotates once, toner images of each color are sequentially superimposed on the toner image carrier. I have. Therefore, the rotation cycle of the toner image carrier and the writing timing of the latent image by the latent image writing unit 2 must be synchronized, and if they are not synchronized, a positional shift occurs between the toner images of each color. It will be.

However, in the latent image writing section 2 for writing a latent image, the writing timing is usually determined by the scanning cycle of a laser beam, that is, a rotating polygon mirror (polygon mirror).
, And the cycle is asynchronous with the rotation cycle of the toner image carrier. That is,
The rotation phases of the toner image carrier and the polygon mirror are asynchronous. For this purpose, an image forming apparatus using a belt-shaped toner image carrier has a function of correcting a misalignment of a toner image that may occur due to the asynchronous rotation phases (hereinafter, referred to as a polygon synchronization function). The polygon synchronization function is used to prevent the toner image from being displaced on the toner image carrier.

Here, the polygon synchronization function will be described. As the polygon synchronization function, for example, Japanese Patent Application Laid-Open No. 9-80
There is one disclosed in Japanese Patent No. 853. As shown in FIG. 8, the polygon synchronization function includes a belt drive motor 11 and a drive motor control unit 12 necessary for rotating the toner image carrier.
A reference clock generating unit 13; an image writing timing control unit 14, an image processing unit 15, and an image input unit 16 necessary for writing a latent image in the latent image writing unit 2; and a main controller 17 for controlling these units. Others,
Belt reference position detection means 18 for detecting the rotation cycle of the toner image carrier, and exposure beam scanning start timing detection means for detecting the writing timing of the latent image by the latent image writing unit 2 (rotation cycle of the polygon mirror). 1
9 and a control unit 20 for correcting the phase difference between these rotation periods.

The belt reference position detecting means 18 detects a reference position provided on the toner image carrier by a sensor or the like, and a reference position signal (hereinafter referred to as a TR0 signal) indicating the reference position every time the reference position is detected. Is output. The exposure beam scanning start timing detecting means 19 outputs a scanning start signal (hereinafter referred to as SO) every time the polygon mirror passes a predetermined position.
S signal).

The image writing timing control section 14 starts writing a latent image based on the TR0 signal and the SOS signal. Specifically, as shown in FIG.
The writing of the latent image is started after a lapse of a predetermined time from the SOS signal immediately after the output of the R0 signal. Therefore, the time from the detection of the reference position on the toner image carrier to the start of writing of the latent image is “T1 + Tsos” for the first color.
× n ”and“ T2 + Tsos × n ”for the second color.

However, since the rotation phases of the toner image carrier and the polygon mirror are asynchronous, "T1" and "T1"
"2" means that there is variation among each other. Therefore, in this state, the timing of writing the latent image also varies, and the leading end position (formation start position) of the toner image formed on the toner image carrier also varies.

The control unit 20 calculates the phase difference between the rotation cycle of the toner image carrier and the rotation cycle of the polygon mirror between the TR0 signal for each color and the writing of the latent image, and calculates the calculation result. On the basis of this, the rotational speed of the toner image carrier or the rotational speed of the polygon mirror is increased or decreased to correct the phase difference between the respective rotation periods during toner image formation.

As shown in FIG. 10, this correction is performed when the latent image is not written (in a non-image forming state) during one rotation of the toner image carrier. This is performed by changing the rotation speed or the rotation speed of the polygon mirror at a constant speed variation rate. As a result, variations in “T1” and “T2” are removed,
The tip positions of the toner image of a certain color and the toner image of the next color to be formed coincide with each other, and the displacement of the toner image on the toner image carrier does not occur.

[0012]

However, the positional deviation between the toner images of each color on the toner image carrier can also be caused by the fluctuation of the rotation speed of the toner image carrier. For example, if the rotational speed of the toner image carrier is different between the time of forming a toner image of a certain color and the time of forming a toner image of another color, misregistration occurs between these toner images, and as a result, As a result, it causes color shift and density unevenness in an output image.

One cause of the fluctuation of the rotation speed of the toner image carrier is a fluctuation in load on the toner image carrier. That is, as shown in FIG. 11A, when the load on the rotation of the toner image carrier increases,
As a result, slip and elongation of the toner image carrier occur, and the rotation speed of the toner image carrier differs depending on whether the load is increased or not.
As shown in (b), the formation position of the toner image on the toner image carrier is shifted.

Such a load change occurs for the following reasons. In general, in an image forming apparatus, the belt length of the toner image carrier corresponds to the size of a toner image that can be formed in order to reduce the size of the apparatus. Further, in order to speed up the image forming process, four colors (Y, M,
C, K) are formed, and formation of the first color (Y color) of a new toner image is started on the next circumference. on the other hand,
To transfer the toner image onto the recording paper, a transfer roll (see reference numeral 5 in FIG. 6 or FIG. 7) must be in contact with the toner image carrier at the transfer position. Further, after the transfer of the toner image, it is necessary to abut a cleaner (see reference numeral 6 in FIG. 6 or 7) to remove the residual toner from the toner image carrier. Therefore, for example, 4
Before the formation of the color toner image (K color) is completed,
The transfer of the leading end of the combined toner image is started, and the remaining toner is removed. That is, during the formation of the K color toner image, the transfer roll 6 and the cleaner 7 come into contact with each other, which increases the load on the rotation of the toner image carrier. Become.

Due to such a load variation, even if correction is made on the toner image carrier by the polygon synchronization function so that the leading end positions of the toner images of the respective colors match, for example, as shown in FIG. The rear end position between the K color and the other color toner image will be shifted.

On the other hand, for example, Japanese Patent Laid-Open No.
No. 12 discloses that a resin or an adhesive having a high friction coefficient is applied to the back surface of a belt-shaped toner image carrier or the surface of a drive roll for driving the toner image carrier,
There is disclosed an image forming apparatus capable of reducing slip due to a load on a toner image carrier. However,
This is effective for a slip due to a large load that makes the toner image carrier inoperable as shown in FIG. 13, but is small for a small slip due to a small load, for example, less than the size of one pixel. Slip which causes such a slight displacement cannot be sufficiently prevented. Further, it cannot deal with the elongation of the toner image carrier at all.

Accordingly, in order to prevent the occurrence of a slight positional shift between the toner images of the respective colors as described above, the speed fluctuation of the toner image carrier is detected, and the toner image of each color is detected based on the detection result. It is considered most effective to correct the formation position.

As a device for detecting the speed fluctuation of the toner image carrier, for example, as disclosed in JP-A-4-172376 and JP-A-4-234064,
There is a type in which an encoder is attached to a shaft of a driven roll that is driven by a toner image carrier, and the speed of the toner image carrier is calculated and recognized from an angular speed detected by the encoder.
However, these are suitable as a technique for controlling the speed fluctuation of the toner image carrier with high accuracy, but on the other hand, the speed of the toner image carrier is recognized from the detection means such as an encoder and the detection result. It is necessary to newly provide a recognition (calculation) means and the like. Therefore, the configuration of the image forming apparatus becomes complicated, which may hinder miniaturization and cost reduction of the apparatus.

Therefore, in the present invention, the use of the above-described polygon synchronizing function can be caused by a load variation on the toner image carrier without newly providing a means for detecting a speed variation of the toner image carrier. It is an object of the present invention to provide an image forming apparatus capable of reducing a displacement between toner images of respective colors.

[0020]

SUMMARY OF THE INVENTION The present invention is directed to an image forming apparatus devised to achieve the above object, comprising: a belt-shaped toner image carrier which is driven to rotate; and one rotation of the toner image carrier. Exposure means for writing a latent image for forming a toner image on the toner image carrier for each toner image, and detecting the rotation cycle of the toner image carrier and the timing of writing the latent image by the exposure means, Detecting means for detecting a phase difference therebetween, and rotation of the toner image carrier when a toner image is not formed on the toner image carrier based on a detection result by the detecting means. Correction means for correcting the phase difference by increasing or decreasing the speed or the writing speed of the latent image by the exposure means, and correcting the plurality of colors on the toner image carrier by the correction by the correction means. In a case where images are formed so as to be superimposed, when there is a load variation on the toner image carrier during a plurality of rotations of the toner image carrier required for superimposing the toner images of the plurality of colors, A recognition unit for recognizing a difference between the rotation periods when there is no toner image, and an instruction to increase or decrease the rotation speed or the writing speed to the correction unit based on the recognition result by the recognition unit. Correction instruction means for correcting a positional deviation is provided.

According to the image forming apparatus having the above configuration, the recognizing means determines whether the load on the toner image carrier changes at a predetermined time, for example, at a time prior to the formation of the toner image on the toner image carrier. Recognize the difference between the rotation cycle when there is no rotation cycle. When the recognizing unit recognizes the difference between the rotation periods, the correction instructing unit instructs the correcting unit to increase or decrease the rotational speed of the toner image carrier or the writing speed of the latent image by the exposing unit based on the recognition result. . With this, the correction unit can control the toner in a plurality of rotations of the toner image carrier required for the superposition of the toner images of the plurality of colors even if the load on the toner image carrier is changed. The rotation speed of the image carrier or the writing speed of the latent image by the exposure means is increased or decreased. Therefore, in this image forming apparatus, when forming a toner image of a plurality of colors on the toner image carrier, even if there is a load fluctuation on the toner image carrier, the toner image of each color on the toner image carrier is not changed. The displacement will be corrected.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described with reference to the drawings. Here, an example in which the present invention is applied to a copying machine having an intermediate transfer belt as a toner image carrier (see FIG. 6) will be described. However, in the present embodiment, the conventional example described above (FIG. 6)
The same reference numerals are given to the same components as those in FIG. 8), and the detailed description thereof will be omitted.

As shown in FIG. 1, the copying machine of the present embodiment has a conventional polygon synchronization function (see FIG. 8).
In addition to the above, a recognition unit 21 and a correction instruction unit 22 are provided in the control unit 20. These units are realized by the control unit 20 including a microprocessor or the like executing a predetermined program.

The recognizing means 21 detects a change in load on the intermediate transfer belt 1a during the four rotations of the intermediate transfer belt 1a necessary for superimposing toner images of four colors of Y, M, C, and K. It is to recognize the difference in the rotation cycle between a certain case and a case without this load fluctuation. Note that the recognition means 21 recognizes this recognition as described in detail later.
This is performed based on the TR0 signal from the belt reference position detecting means 18 in the dummy cycle.

The correction instructing means 22 calculates a correction value when there is a load variation on the intermediate transfer belt 1a based on the recognition result by the recognition means 21, and uses the correction value to calculate the rotation speed of the intermediate transfer belt 1a. This is for instructing an increase or decrease. In accordance with the instruction from the correction instruction means 22, the control unit 20 increases or decreases the rotation speed of the belt drive motor 11 via the reference clock generation unit 13 and the drive motor control unit 12, as in the case of the correction by the polygon synchronization function. It has become.

Next, an example of the operation of the image forming process in the copying machine configured as described above, in particular, an example of the control process in the control unit 20 will be described with reference to the flowchart of FIG.

In this copying machine, a dummy cycle is executed before image formation. At the time of this dummy cycle, the correction by the polygon synchronization function described in the conventional example (see FIG. 8) may be performed together.

The dummy cycle is performed when the apparatus is started by turning on a power supply or the like. The operations include rotation of the intermediate transfer belt 1a, output of the TR0 signal by the belt reference position detecting means 18, contact of the transfer roll 6 and the cleaner 7, and the like. Is performed in the same procedure as in actual image formation. However, at this time, actual image formation, for example, formation of a toner image on the intermediate transfer body belt 1a, and the like are not performed.

During the execution of the dummy cycle, the control section 20 recognizes the difference between the rotation periods when the load on the intermediate transfer belt 1a is changed and when the load is not changed. For example, a K (fourth color) cycle corresponds to a case where there is a load change,
Further, when there is no load fluctuation, for example, an M (second color) cycle corresponds.

Specifically, in the recognizing means 21, first, when the execution of the dummy cycle is started, the control unit 2
A timer (not shown) provided at 0 or the like is reset, and the timer is set as a counter for detecting the rotation cycle of the intermediate transfer belt 1a (step 101,
Hereinafter, the step is abbreviated as S). Thereafter, when the TR0 signal corresponding to M cycles is output from the belt reference position detecting means 18 (S102), the timer starts counting (S103). Then, when there is an output of the next TR0 signal (TR0 signal corresponding to the C cycle) (S10
4) When the counting by the timer is completed (S1)
05), the count value at that time is set to “Tm” (S10
6) The value is held in a memory or a register (not shown). This “Tm” is the value of the rotation cycle in M cycles.

When the detection of "Tm" is completed, the recognizing means 21 sets a counter again (S107),
The rotation cycle in the K cycle is detected in the same manner as described above (S108 to S111), and the result is set to “Tk” (S112). Note that the recognizing means 21 determines that Y, M,
The count value may be detected from each cycle of C and K. However, since it is sufficient to determine the difference between the rotation cycles when there is a load change and when there is no load change, two cycles of M cycle and K cycle are used. Recognition processing is speeded up by detecting only the information.

When the values of "Tm" and "Tk" are detected in this way, the recognizing means 21 determines the value of "Tk-Tm", which is the difference between them, when there is a load change and when there is no load change. Is recognized as the difference between the rotation periods.

When the recognizing means 21 recognizes the difference between the rotation periods, the correction instructing means 22 then transmits the correction signal to the intermediate transfer belt 1a.
Of the toner image forming position when there is a load change with respect to the first, third, and third colors (Y color, M color, C color)
The value of the positional deviation between the formation position of the toner image of the final color (K color) and the formation position of the toner image of the final color (K color), specifically, the value of the deviation amount at the rear end position of the toner image is calculated (S1).
13).

The value of this position shift is calculated as the expected registration shift value “R
k, the expected registration deviation value “Rk” is calculated from the value of the reference speed “V” of the intermediate transfer belt 1a by Rk = (Tk
−Tm) × V. At this time, the reference speed “V” is a predetermined value. Therefore, the recognition means 21
If the value of “Tk−Tm”, which is the recognition result by
The correction instruction means 22 can calculate the expected registration deviation value “Rk”.

The correction instructing means 22 calculates the expected registration deviation value “Rk” based on the recognition result by the recognizing means 21,
Subsequently, a correction value “ΔR” when there is a load change on the intermediate transfer belt 1a is calculated (S114).

As the correction value “ΔR”, a value for halving the expected registration deviation value “Rk” can be considered. This is because the correction using the polygon synchronization function is performed by increasing or decreasing the rotation speed of the intermediate transfer belt 1a when a toner image is not formed on the intermediate transfer belt 1a. This is because the positions of the leading ends of the images are matched, and the intermediate transfer belt 1a is caused to run at the reference speed "V" during the formation of the toner image on the intermediate transfer belt 1a. That is, the correction using the polygon synchronization function cannot completely remove the displacement of the formation position (see FIG. 12) due to the load fluctuation occurring during the formation of the toner image. Therefore, it is conceivable to reduce the expected registration deviation value “Rk” by half so that the deviation is most inconspicuous. In this case, ΔR = Rk / 2 may be set.

When the correction instructing means 22 obtains the correction value “ΔR”, next, in the copying machine, the main controller 17
Each unit starts image formation according to the instruction from. More specifically, first, the latent image writing unit 2 writes a latent image on the photosensitive drum 4 for the Y color image. Then, after the developing device 3 develops the latent image with the Y color toner, the toner image is transferred (primary transfer) onto the intermediate transfer belt 1a. Subsequently, the same processing is performed for the M color and the C color, and three color toner images are synthesized on the intermediate transfer belt 1a.
At this time, it is assumed that the formation positions of the toner images of the respective colors are corrected by the polygon synchronization function, and the respective leading end positions match.

When the synthesis of the three color toner images is completed, a K color toner image, which is the final color, is formed. However, in the case of the last color, the load on the intermediate transfer belt 1a fluctuates.
When the transfer of the toner image onto the intermediate transfer belt 1a is not performed before the formation of the color toner image, that is, before the writing of the latent image by the latent image writing unit 2 is started (hereinafter, this time region) Is referred to as a primary transfer non-image area), and an increase or decrease of the rotation speed of the intermediate transfer belt 1a is instructed by the correction value “ΔR”.

More specifically, the correction instruction means 22 adds a correction instruction based on the correction value “ΔR” to the correction instruction “
R ”, the reference clock generator 1
Give to 3. In response to the correction instruction from the correction instruction means 22, the reference clock generator 13 and the drive motor controller 1
2 increases / decreases the number of pulses given per hour to the belt drive motor 11 composed of, for example, a stepping motor. Thus, the rotation speed of the belt drive motor 11 increases and decreases. The rotation speed is increased or decreased only in the primary transfer non-image area, and when the formation of the K color toner image is started, the intermediate transfer belt 1a is moved to the reference speed “V”.
To be driven.

By the correction instructed by the correction instructing means 22, the K color toner image is formed on the intermediate transfer belt 1a in a state of being entirely shifted by an amount corresponding to the correction value “ΔR”. . That is, the tip position of the K color toner image is shifted by the correction value “ΔR” as compared with the other color toner images.

Therefore, in the intermediate transfer belt 1a,
As shown in FIG. 3, during the formation of the K color toner image, the load fluctuates due to the contact of the transfer roll 6 and the cleaner 7 and the like.
Even if a shift occurs by the expected registration shift value “Rk” at the rear end of the K color toner image, the absolute amount of the positional shift between the K color toner image and the other color toner image is “ΔR”. Becomes
Then, in this state, the toner images of the four colors of Y, M, C and K synthesized on the intermediate transfer belt 1a are transferred (secondary transfer) onto the recording paper in that state.

As described above, in the copying machine of the present embodiment, the correction instructing means 22 instructs to increase or decrease the rotation speed of the intermediate transfer belt 1a based on the recognition result by the recognizing means 21. Intermediate transfer belt 1a
In forming the toner images of the four colors Y, M, C, and K, even if the load on the intermediate transfer belt 1a fluctuates, the position between the toner images of each color that may be generated due to the load fluctuation. The correction is made so that the absolute amount of the shift becomes small. As a result, in this copying machine, the positional deviation between the toner images of the respective colors due to the load fluctuation can be made smaller than in the related art, and even if the toner image on the intermediate transfer belt 1a is secondarily transferred onto recording paper. In addition, color shift and density unevenness in the output image can be suppressed as compared with the related art.

Further, in this copying machine, the positional deviation between the toner images of each color due to the load fluctuation is reduced by utilizing the polygon synchronization function which the copying machine has conventionally had. That is, only by changing the processing control in the control unit 20 from the conventional one, there is no need to newly provide a detecting means such as an encoder or a means for performing an operation on the operation result, and the positional deviation between the toner images of each color due to a load change. Can be corrected. Therefore, in this copying machine, in order to correct the position shift due to the load fluctuation, the apparatus configuration does not become complicated, and there is no possibility that the apparatus becomes smaller and the cost is not reduced.

That is, in this copying machine, by utilizing the polygon synchronization function, the positional deviation between the toner images of each color which may be caused by the load fluctuation on the intermediate transfer belt 1a can be achieved without providing any new detecting means. Can be reduced.

It should be noted that, in the present embodiment, the invention described in claim 1, ie, the polygon synchronization function
The description has been given of the case where the rotational speed of the intermediate transfer belt 1a is increased and decreased, and the positional deviation between the toner images of the respective colors is corrected by increasing and decreasing the rotational speed of the intermediate transfer belt 1a. If the polygon synchronization function increases or decreases the rotation speed of the polygon mirror, the displacement between the color toner images may be corrected by increasing or decreasing the rotation speed of the polygon mirror.

In this embodiment, the case where the present invention is applied to a copying machine having an intermediate transfer belt 1a as a toner image carrier has been described. For example, a photoreceptor belt 1b is provided as a toner image carrier. However, the present invention can be applied to any other device (see FIG. 7).

Further, in the present embodiment, the case where the load fluctuation on the intermediate transfer belt 1a occurs only in the K cycle and the formation position of the K color toner image is corrected has been described as an example. Is not limited to this.

For example, consider a case where image output to a plurality of recording sheets is performed continuously. In this case,
In the next cycle of the K (fourth color) cycle, a Y (first color) cycle of a new toner image is started. That is, a new Y cycle is started before the contact of the transfer roll 6 or the contact of the cleaner 7 is completed. Therefore, a load change also occurs in a new Y cycle, and the Y color toner image formed in this Y cycle is changed as shown in FIG.
A position shift “Ry” as shown in FIG.
Therefore, by correcting the displacement “Ry” in the same manner as in the case of “Rk” described above, FIG.
As shown in (a), the absolute amount of displacement can be reduced. In other words, the present invention can be applied to the first and subsequent colors of the second and subsequent sheets in the case of continuously outputting images, and can reduce color shift even during continuous output.

The correction value “ΔR” at that time is not limited to ΔR = R / 2, whether it is for a K color toner image or for a Y color toner image. Absent. Intermediate transfer belt 1
When it is formed over substantially the entire surface of a, it is most effective to set ΔR = R / 2, but the toner image length actually varies. For example, as shown in FIG. 5B, the toner image length (corresponding to A4) is equal to the circumferential length (A3
If ΔR = R / 2, then the amount of color misregistration actually occurring on the recording paper is R × Lp / Lb (L
p: paper length, Lb: peripheral length), and the absolute amount of displacement is rather increased. Therefore, in such a case, ΔR is determined according to the length of the recording paper for outputting the toner image.
= R x (Lp / Lb) / 2 (the circumference "Lb" is a fixed value), and the correction instruction means 22 may calculate "? R". As a result, even when the toner image length is shorter than the circumference of the intermediate transfer belt 1a, it is possible to reduce the color shift on the recording paper as shown in FIG. 5A.

The correction of the toner image forming position for reducing the color shift is performed not on the toner image when there is a load change but on the toner image when there is no load change. Is also good. For example, if the load fluctuation on the intermediate transfer belt 1a occurs only in the K cycle, instead of the K color toner image, Y,
Even if the formation positions of the M and C color toner images are corrected, the same effect as in the above-described case can be obtained.

Further, in this embodiment, the case where the rotation cycle of the intermediate transfer belt 1a necessary for correcting the formation position of the toner image is detected by executing a dummy cycle performed at the time of starting the apparatus, for example. However, the same effect can be obtained even if the correction amount is measured in advance before the device is shipped, for example, in an adjustment process in the device manufacturing process, and the result is set in a memory or the like. Further, the processing can be speeded up at the time of starting the apparatus.

[0052]

As described above, in the image forming apparatus of the present invention, when a plurality of color toner images are superimposed on the toner image carrier, the load on the toner image carrier may fluctuate. The rotation speed of the toner image carrier or the writing speed of the latent image is increased or decreased so that the absolute amount of the positional shift between the toner images of each color which may be caused by the load fluctuation becomes small. Therefore, in this image forming apparatus, the positional deviation between the toner images of the respective colors due to the load fluctuation can be reduced as compared with the related art, and the color misregistration and the density unevenness in the output image can be suppressed as compared with the related art. Further, for this purpose, there is no need to provide a new configuration such as a detection unit such as an encoder, so that the configuration of the device is not complicated, and there is no possibility that the reduction in size and cost of the device will not be hindered. In other words, in this image forming apparatus, by utilizing the polygon synchronization function which has existed conventionally, the positional deviation between the toner images of the respective colors which may occur due to the load fluctuation on the toner image carrier without providing a new detecting means or the like. Can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a functional configuration of an example of an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a flowchart illustrating an operation example of an image forming process in the image forming apparatus of FIG. 1, particularly a control process example in a control unit.

FIG. 3 is an explanatory diagram showing a shift amount of a formation position between toner images of each color when the formation position of a K color toner image is corrected in the image forming apparatus of FIG. 1;

4A and 4B are explanatory diagrams showing shift amounts of formation positions between toner images of each color when the formation positions of Y and K toner images are corrected in the image forming apparatus of FIG. 1; FIG. 7B is a diagram illustrating a shift amount after correction, and FIG. 7B is a diagram illustrating a shift amount before correction.

FIGS. 5A and 5B are explanatory diagrams showing a shift amount of a formation position between toner images of respective colors when the formation position of the toner image of the image length and K is corrected in the image forming apparatus of FIG. 1; FIG. 7B is a diagram illustrating a shift amount after correction, and FIG. 7B is a diagram illustrating a shift amount before correction.

FIG. 6 is a cross-sectional view illustrating a schematic configuration of an example of an image forming apparatus using a belt-shaped toner image carrier.

FIG. 7 is a cross-sectional view illustrating a schematic configuration of another example of an image forming apparatus using a belt-shaped toner image carrier.

FIG. 8 is a block diagram illustrating a functional configuration for realizing a polygon synchronization function in an example of a conventional image forming apparatus.

FIG. 9 is a time chart showing operation timings of a toner image carrier and a polygon mirror in a conventional image forming apparatus.

FIG. 10 is an explanatory diagram showing a timing of correcting an image tip position by a polygon synchronization function.

11A and 11B are explanatory diagrams of a load variation on a toner image carrier, wherein FIG. 11A illustrates a state in which a rotation speed changes due to an increase in load, and FIG. 11B illustrates a state in which an image forming position is shifted due to a difference in rotation speed. FIG.

FIG. 12 is an explanatory diagram illustrating an example of a positional shift at a rear end position of a toner image caused by a load change on a toner image carrier.

FIG. 13 is an explanatory diagram showing a relationship between a change in average speed of the toner image carrier and a slip with a load change.

[Description of Signs] 1a: Intermediate transfer belt, 2: Latent image writing unit, 18 ...
Belt reference position detecting means 19 Exposure beam scanning start timing detecting means 20 Control section 21 Recognizing means 22 Correction instructing means

Claims (2)

[Claims] 1. A belt-shaped toner image carrier which is driven to rotate, and an exposure for writing a latent image for forming a toner image on the toner image carrier every one rotation of the toner image carrier Means for detecting the rotation cycle of the toner image carrier and the timing of writing the latent image by the exposing means, and detecting a phase difference between these, and based on the detection result by the detecting means, When a toner image is not formed on the toner image carrier,
Correction means for increasing or decreasing the rotational speed of the toner image carrier to correct the phase difference, wherein an image formed by superimposing a plurality of color toner images on the toner image carrier by correction by the correction means In the forming apparatus, a rotation cycle between a case where there is a load change on the toner image carrier and a case where there is no load change among a plurality of rotations of the toner image carrier required for superimposing the plurality of color toner images. And a correction instructing unit that instructs the correcting unit to increase or decrease the rotation speed based on the recognition result by the recognizing unit, and corrects a deviation of the toner image forming position due to the load change. An image forming apparatus provided. 2. A belt-shaped toner image carrier which is driven to rotate, and an exposure for writing a latent image for forming a toner image on the toner image carrier every one rotation of the toner image carrier. Means for detecting the rotation cycle of the toner image carrier and the timing of writing the latent image by the exposing means, and detecting a phase difference between these, and based on the detection result by the detecting means, When a toner image is not formed on the toner image carrier,
Correction means for increasing or decreasing the writing speed of the latent image by the exposure means to correct the phase difference, and forming a plurality of color toner images on the toner image carrier by the correction by the correction means. In the image forming apparatus, rotation among a plurality of rotations of the toner image carrier required for superimposing the toner images of the plurality of colors is performed when there is a load change on the toner image carrier and when the load does not fluctuate. Recognition means for recognizing a difference in period; correction instructing means for instructing the correction means to increase or decrease the writing speed based on a recognition result by the recognition means, and correcting a deviation of a toner image formation position due to the load change; An image forming apparatus provided with: