JP2002031926A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the fluctuation of the magnification accuracy of each color image even when forming two or more color images in an overlaid state. SOLUTION: Belt marks 16 showing a reference position at forming the image are arranged on an intermediate transfer belt 2 having the image carrying surface on which a toner image formed on a photoreceptor 1 can be transferred in an overlaid state plural times, and also, a mark detection sensor 3 for detecting the belt marks 16 is arranged. A measured time (ta) from the detection of one of the belt marks 16 by the mark detecting sensor 3 to the detection of the subsequent adjacent belt mark 16 while the intermediate transfer belt 2 is rotated is compared with a previously set normal time (tb), and in accordance with the comparison result, the rotating speed of a motor 11 is changed by a controller 10 so that the intermediate transfer belt 2 may be rotated at a normal rotating speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile machine, etc., provided with a toner image carrier capable of carrying a plurality of color toner images in an overlapping manner.

[0002]

2. Description of the Related Art An image forming apparatus such as a printer, a copying machine, a facsimile machine, and the like includes a photosensitive member for carrying a toner image visualized as an electrostatic latent image, and a toner image formed on the photosensitive member as an image carrying surface. And an intermediate transfer belt, which is a rotating toner image carrier that can be transferred a plurality of times in a superimposed manner, so that an image composed of two or more colors can be formed.

In such an image forming apparatus, it is necessary to carry two or more color images on the intermediate transfer belt so as not to be shifted from each other. For this purpose, for example, a mark is provided outside the area carrying the image on the intermediate transfer belt, and a mark detection sensor is provided at a position where the mark can be detected, and the mark detection sensor detects the mark and outputs the mark based on a detection signal. Thus, the timing for forming an image is set.

That is, when forming a two-color image, the intermediate transfer belt is rotated twice, three colors are rotated three times, and four colors are rotated four times. By forming an image based on a detection signal that detects the mark, a superimposed image of a plurality of colors without positional displacement is obtained. When the images of two or more colors are superimposed on the intermediate transfer belt, a belt cleaning device that cleans the image bearing surface of the intermediate transfer belt is separated from the image bearing surface of the belt, so that the belt cleaning device The toner image formed on the supporting surface is not removed.

When image formation of all colors (overlapping transfer of toner images of each color onto the intermediate transfer belt) is completed, feeding of transfer paper is started in accordance with the leading end position of the overlapped image on the intermediate transfer belt. Then, the superimposed images on the intermediate transfer belt are collectively transferred onto the transfer paper. Thereafter, the cleaning member of the belt cleaning device is brought into contact with the intermediate transfer belt, and the transfer residual toner remaining on the intermediate transfer belt is removed.

[0006]

In such an image forming apparatus, when two or more images of two or more colors are continuously formed (continuous paper passing), the first superimposed image is formed as described above. Is transferred onto the transfer paper from the intermediate transfer belt at a time, and then a cleaning member of a belt cleaning device is brought into contact with the intermediate transfer belt to remove transfer residual toner.
The first color toner image of the next image is transferred onto the image bearing surface of the cleaned belt.

Before the first color toner image reaches the position of the belt cleaning device due to the rotation of the intermediate transfer belt, the cleaning member of the belt cleaning device is separated from the image bearing surface. The load previously applied to the belt by the contact of the cleaning member is reduced.

That is, when the cleaning member is in contact with the image bearing surface of the intermediate transfer belt, the load applied to the intermediate transfer belt is large and the rotation speed of the belt is slow. By separating from the surface, the load is reduced, and the intermediate transfer belt rotates faster by that amount.

Accordingly, the first color toner image transferred onto the intermediate transfer belt when the rotation speed is slow, and the cleaning member are rotated at an increased speed by separating from the intermediate transfer belt. Since the second and subsequent color toner images transferred on the intermediate transfer belt have different image magnifications in the rotation direction (sub-scanning direction) of the intermediate transfer belt, a high-accuracy two or more-color superimposed image is formed. There was a problem that it became impossible to do.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems. Even when a superimposed image of two or more colors is formed, the rotation of the toner image carrier in the rotation direction of the first color and the images of the second and subsequent colors is performed. It is an object of the present invention to obtain a good image with no deviation between images by preventing magnification accuracy from being different.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a photoreceptor carrying a toner image in which an electrostatic latent image is visualized, and a photoreceptor which is rotated by a rotation drive system to form the photoreceptor on the photoreceptor. A toner image carrier capable of transferring the superposed toner image on the image carrier surface a plurality of times and a mark detection sensor provided on the toner image carrier for detecting a mark serving as a reference position at the time of image formation. In the image forming apparatus, a plurality of the marks are provided on the toner image carrier along a rotation direction of the toner image carrier, and one mark detection sensor is provided. The measured time from when the mark detection sensor detects one of the marks to when the next adjacent mark is detected is compared with a predetermined time set in advance, and the load is applied to the toner image carrier by the load fluctuation. time to calculate A toner image carrier rotation speed control means for driving and controlling the rotation drive system so that the toner image carrier has a regular rotation speed when the time is shifted from the specified time is provided. .

In addition, one mark is provided on the toner image carrier, and a plurality of mark detection sensors are provided along the rotation direction of the toner image carrier, and the mark detection sensor is provided when the toner image carrier rotates. The measurement time from when the sensor detects the mark to when the next adjacent mark detection sensor detects the mark is compared with a predetermined time, and the load is applied to the toner image carrier. When the measurement time is deviated from the specified time, a toner image carrier rotation speed control means for driving and controlling the rotation drive system so that the toner image carrier has a regular rotation speed is provided. An image forming apparatus is configured. The toner image carrier is preferably an intermediate transfer belt.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view showing an image forming unit of an image forming apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating an intermediate transfer belt provided in the image forming apparatus and a mark provided thereon. FIG. 3 is a perspective view showing a mark detection sensor to be used.

The image forming apparatus shown in FIG. 1 has an arrow B for carrying a toner image on the surface of which an electrostatic latent image is visualized with toner.
A is shown by a drum-shaped photosensitive member 1 rotatable in a direction and a motor 11 which is a stepping motor constituting a rotation drive system.
Transfer belt 2, which is a toner image carrier capable of transferring the toner image formed on the photoreceptor 1 onto the image carrying surface of the surface a plurality of times, and provided on the intermediate transfer belt 2. Belt mark 16 serving as a reference position during image formation
(Only two are shown in FIG. 1).

The surface of the photoreceptor 1 is charged by a charging device 4, and the charged charged surface is exposed by a laser writing device 17 using a laser diode as a light source to form an electrostatic latent image thereon. You. On the downstream side in the rotation direction of the photoconductor 1 from the exposure position by the laser writing device 17, the toner can be developed with four color toners of black (BK), cyan (C), magenta (M), and yellow (Y). Developing device 5 is provided.

The intermediate transfer belt 2 has three rollers 12,
The driving roller 12 is rotated by the motor 11 and rotates in the direction indicated by the arrow A. Reference numeral 15 denotes an intermediate transfer roller to which a voltage is applied from a power supply (not shown), and the toner image on the photoconductor 1 is electrostatically transferred onto the intermediate transfer belt 2. The surface of the intermediate transfer belt 2 is slid by a cleaning member 7 of a belt cleaning device 6 to be cleaned. The cleaning member 7 is fixed to the intermediate transfer belt 2 by a known mechanism using, for example, a solenoid. 2 can be brought into contact with and separated from the surface.

The toner image carried on the belt surface of the intermediate transfer belt 2 is fed by a paper feeding device (not shown) at a transfer position where a transfer roller 8 is provided, and is supplied at a timing adjusted by a registration roller 9. Transfer paper P to be printed
Is transferred to A fixing device 20 is disposed downstream of the transfer roller 8 in the transfer paper transport direction. The fixing device 20 heats and fixes the toner image on the transfer paper P, and transfers the transfer paper P to a discharge roller 21. To discharge to a paper discharge tray or the like.

Belt mark 16 on intermediate transfer belt 2
Are provided at one end of the image bearing surface of the intermediate transfer belt 2 outside the image forming area as shown in FIG. 2 and at a certain interval along the rotation direction of the intermediate transfer belt 2 as shown in FIG. One mark detection sensor 3 is disposed at a position where each belt mark 16 can be detected.

The mark detecting sensor 3 shown in FIG. 2 is, for example, a reflection type photo sensor, and receives a reflected light of light emitted from the light emitting element to the intermediate transfer belt 2 by a light receiving element. The belt mark 16 is detected based on the amount of reflected light that differs between a portion where the mark 16 is present and a portion where the mark 16 is not present, and a detection signal is output.
Enter.

The control device 10 includes two central processing units (CPU) having various judgment and processing functions, a ROM storing each processing program and fixed data, a RAM serving as a data memory for storing processing data, I / O circuit
(I / O).

The control device 10 controls the drive system of the entire device, and also detects the next one of the belt marks 16 when the mark detection sensor 3 detects one of the belt marks 16 when the intermediate transfer belt 2 rotates. The measurement time ta until the mark 16 is detected is compared with a preset specified time tb, and the cleaning member 7 of the belt cleaning device 6 comes into contact with or separates from the intermediate transfer belt 2 so that the intermediate transfer belt 2 The measurement time ta becomes the specified time t due to the applied load fluctuation.
When it is deviated from b, control is also performed to change the rotation speed of the motor 11 so that the intermediate transfer belt 2 has the normal rotation speed. That is, in this embodiment, the control device 10 functions as a toner image carrier rotation speed control unit.

The measurement of the measurement time ta is generally carried out by, for example, a method of reading the signal by inputting a detection signal of the mark detection sensor 3 into an interrupt of the CPU (known). And the measurement time ta
Is compared with a reference time tb serving as a reference, and the reference time tb
If it is longer than b, the rotation speed of the intermediate transfer belt 2 is reduced due to the load due to the contact of the cleaning member 7, and thus the rotation speed of the motor 11 is controlled to be increased.

Conversely, if the measurement time ta is shorter than the specified time tb, the intermediate transfer belt 2 is rotating faster than the specified time, and the rotation speed of the motor 11 is controlled to be slower. I do. Since the rotation speed of the intermediate transfer belt 2 by the motor 11 varies from machine to machine, it is preferable to turn on the power in advance to obtain the characteristics. Alternatively, if the characteristics are taken into account in adjustment at the time of factory production, the trouble can be saved.

The timing at which the load applied to the intermediate transfer belt 2 fluctuates when the cleaning member 7 of the belt cleaning device 6 comes into contact with or separates from the intermediate transfer belt 2 is known in advance. Therefore, for the sake of simplicity of explanation, if the cleaning member 7 is temporarily
When in contact with is the timing of time t ₄ shown in FIG. 4, the cleaning member 7 when separated from the intermediate transfer belt 2 is assumed to be the timing of the time t _5, the measurement of the measurement time ta, the time t ₄ , at the timing of t ₅ , the mark detection sensor 3 detects one belt mark 16.
The measurement time ta ₁ , ta ₂ between the detection of the detection of the belt mark 16 and the detection of the adjacent belt mark 16 may be measured.

Next, the image forming process performed by the microcomputer of the control device 10 will be described with reference to the flowcharts of FIGS. The first CPU of the microcomputer of the control device 10 shown in FIG. 1 inputs a start signal when an operator presses a start button provided on an operation unit (not shown). When a print request signal is input from the printer), the routine shown in FIG. 5 is started at a predetermined timing. By the input of this start signal,
The photoreceptor 1 starts rotating, and the intermediate transfer belt 2 starts rotating.

First, in step 1, it is determined by a command whether or not an image is formed in two or more colors. If an image is formed in one color (determination of NO), the toner images are superimposed on the intermediate transfer belt 2. Since there is no need to wait until the mark detection sensor 3 detects the belt mark 16,
In step 2, the belt cleaning device 6 is turned on,
The cleaning member 7 is brought into contact with the intermediate transfer belt 2 to be in a cleaning state.

Then, in the next step 3, transfer of image data is started from a reading unit (host in the case of a printer), not shown, and the laser writing device 1
After forming an electrostatic latent image by exposing the toner to a toner image, a writing process of developing the electrostatic latent image with toner to form a toner image and transferring the toner image to the intermediate transfer belt 2 is executed.
In the next step 4, the transfer paper is fed, the toner image on the intermediate transfer belt 2 is transferred to a predetermined position on the transfer paper, and after the toner image is fixed by the fixing device, it is discharged.

In step 5, it is determined whether or not the specified number of images has been formed, and if the specified number of images has not been formed, the process returns to step 3 and the processing after step 3 is performed. And the judgment is repeated. If it is determined in step 5 that the specified number of images have been formed, the process proceeds to step 6 in which the belt cleaning device 6 is turned off, and the cleaning member 7 is separated from the intermediate transfer belt 2. To end.

On the other hand, if it is determined in step 1 that the process proceeds to step 7 due to image formation of two or more colors, the second CPU is started there, and detailed description will be given later with reference to FIG. A routine for controlling the rotation speed of the intermediate transfer belt 2 by changing the rotation speed of the motor 11 according to a change in the load applied to the intermediate transfer belt 2 is started.

In the next step 8, it is determined whether or not the mark detection sensor 3 has detected one belt mark 16 which is a reference set in advance among a plurality of belt marks. In step 9, the charged photoconductor 1 is exposed by the laser writing device 17 to form an electrostatic latent image, and then the electrostatic latent image is developed with toner to form a toner image. A writing process for transferring to the transfer belt 2 is executed.

In the next step 10, until the transfer of the toner images of all the colors to the intermediate transfer belt 2 is completed, FIG.
Cleaning member 7 in order to avoid contact with the intermediate transfer belt 2, to OFF belt cleaning device 6 at the timing of time t ₅ in the belt cleaning device 6 at the timing of time it described t ₄ is turned ON . Thereafter, in step 11, it is determined whether or not the transfer of the toner images of all colors to the intermediate transfer belt 2 has been completed. If the transfer of the toner images of all colors has not yet been completed, the process returns to step 9, and The processing and the determination after step 9 are repeated again.

[0032] Then, in step 11, it is determined that the transfer to the intermediate transfer belt 2 the toner image of all the colors has been completed, and turns ON the belt cleaning device 6 at the timing of time t ₄ proceeds to Step 12 Then, the intermediate transfer belt 2 is cleaned by bringing the cleaning member 7 into contact with the intermediate transfer belt 2. In the next step 13, the transfer paper is fed, the toner image (superimposed image) on the intermediate transfer belt 2 is collectively transferred onto the transfer paper, and after the toner image is fixed by the fixing device, it is discharged.

In step 14, it is determined whether or not the specified number of images has been formed. If the specified number of images has not been formed, the process returns to step 8 to return to the next image formation. Therefore, the processing and judgment after step 9 are repeated. Then, the process proceeds to step 14, and when it is determined that the designated number of images have been formed, the process proceeds to step 6, where the belt cleaning device 6 is turned off.
Then, the cleaning member 7 is separated from the intermediate transfer belt 2, and the routine ends.

In step 7, the second CPU starts the processing shown in FIG. 6 in parallel with the processing of the first CPU for executing the routine described in FIG. That is, when the routine of FIG.
5, the time t ₄ described in FIG. 4 (in this example, the timing at which the cleaning member 7
₄ , the mark detection sensor 3 detects the belt mark 16 on the intermediate transfer belt 2 before the next belt mark 16 adjacent to it is detected. measuring the measurement time ta ₁ between until detection.

The measurement time ta ₁ is a continuous measurement time during which the mark detection sensor 3 successively detects between adjacent belt marks 16 on the intermediate transfer belt 2 during the time t _4. And measure it. Next, in step 16,
The measured time ta ₁ is either in the reference become specified time tb (set to a predetermined range having a certain width to be described later),
That is, it is determined whether or not ta ₁ = tb.

Here, as shown in FIG. 4, the cleaning member 7 of the belt cleaning device 6 has not yet contacted the intermediate transfer belt 2 at the entrance side (the left side in FIG. ₄ ) at time t4. (The load is not increased), since the intermediate transfer belt 2 is rotating at the regular rotation speed, ta ₁
= Until no longer tb, we continue to sequentially determine the respective measurement time ta ₁ was continuously measured in step 15.

[0037] Then, as shown in FIG. 4, by the cleaning member 7 of the belt cleaning device 6 becomes the middle of the time t ₄ is brought into contact with the intermediate transfer belt 2, increasing the load applied to the intermediate transfer belt 2 If the rotation speed of the intermediate transfer belt 2 becomes slow and ta ₁ = tb is not satisfied (ta ₁ > tb), the process proceeds to step 17. In step 17, the rotation speed of the motor 11 is increased, and the rotation speed of the intermediate transfer belt 2, which has been reduced by the load, is controlled so as to be the normal rotation speed.

[0038] In the next step 18, it is determined whether the time t ₄ has been completed (elapsed), returns to step 16 if still in time t _4, repeatedly executes the determination and processing of the step 16 and subsequent I do. Since in the example of FIG. 4, the second half of the time t ₄ is in the state where the cleaning member 7 of the belt cleaning device 6 is in contact with the intermediate transfer belt 2 (the load is large), normalized to the intermediate transfer belt 2 at Step 17 of was expedited so that the rotational speed of the motor 11 to the turning speed, the state as it is maintained, the process proceeds to step 19 if it is determined the end time t ₄ at step 18.

In the step 19, during the time t ₅ described in FIG. 4 (in this example, the timing at which the cleaning member 7 is separated from the intermediate transfer belt 2), the mark detection sensor 3 sets the mark on the intermediate transfer belt. after detecting the belt mark 16 on 2, to measure the measurement time ta ₂ between until detecting the next belt marks 16 adjacent thereto.

The measurement time ta ₂ is a continuous measurement time during which the mark detection sensor 3 successively detects between adjacent belt marks 16 on the intermediate transfer belt 2 during the time t _5. And measure it. In the next step 20, the specified time tb when the measured time ta ₂ is the reference
(Set in a predetermined range having a constant width described later), that is, whether or not ta ₂ <tb is satisfied.

Here, in this example, as shown in FIG.
Inlet side cleaning member 7 is an intermediate transfer belt 2 of the belt cleaning apparatus 6 (in the figure the left side) of the time t ₅
In this state, the intermediate transfer belt 2 is rotated at a regular rotation speed (ta ₂ = tb) by increasing the rotation speed of the motor 11 in step 16 while applying a load from the cleaning member 7. And then time t
Each measurement time ta to measure continuously one after another within _5
2 is maintained at the above rotation speed of the motor 11 until ta ₂ <tb.

[0042] Then, as shown in FIG. 4, by the cleaning member 7 of the belt cleaning device 6 is in the middle of the time t ₅ is separated from the intermediate transfer belt 2 Two, the load applied to the intermediate transfer belt 2 When the rotation speed of the intermediate transfer belt 2 increases and ta ₂ <tb, the process proceeds to step 21.

In step 21, the rotational speed of the motor 11 is reduced by the amount by which the rotational speed of the intermediate transfer belt 2 is increased by reducing the load, and the intermediate transfer belt 2 is returned to the normal rotational speed. I do. When it is determined the end of the time t ₅ in the next step 22, and ends the processing of this routine.

As described above, in the image forming apparatus according to the present embodiment, the load applied to the intermediate transfer belt 2 is reduced by the cleaning member 7 of the belt cleaning device 6 shown in FIG. When the rotation speed is increased or decreased, the rotation speed of the motor 11 is changed accordingly to keep the rotation speed of the intermediate transfer belt 2 at the regular rotation speed, so that two or more color images are continuously formed. Even in this case, it is possible to prevent the image magnification from being changed due to a change in the rotation speed of the intermediate transfer belt 2 in the middle of one image.

That is, in this image forming apparatus, when two or more color images are formed by continuously passing two or more sheets, steps 1 → 7 → 8 → 9 → in the flowchart of FIG.
The process proceeds from 10 → 11 → 12 → 13 → 14, and then proceeds to Steps 8 → 9 again for the second image formation to execute the writing process, and the time t during the execution of the writing process. _At the timing of ₅ , since the belt cleaning device 6 is turned off in step 10,
The load applied to the belt cleaning device 6 when the cleaning member 7 is separated from the intermediate transfer belt 2 is reduced.

However, when the load applied to the belt cleaning device 6 is reduced as described above, the image forming apparatus slows down the rotation speed of the motor 11 in accordance with the load fluctuation, thereby rotating the intermediate transfer belt 2. Since the moving speed is maintained at the regular rotation speed, the image being formed does not change in image magnification from the middle.

By the way, the specified time tb, which is a reference for comparison in steps 16 and 20 in FIG. 6, is not a single numerical value, but a value in a range specification including an allowable range such as ± 2%. That is, in the processing of the flowchart shown in FIG. 6, only when the measured time ta ₁ and ta ₂ are out of the prescribed time tb to the provisions of a predetermined allowable range, by controlling the rotational speed of the motor 11, an intermediate transfer belt The control for increasing or decreasing the rotation speed of Step 2 is performed.

Next, an example of a method for adjusting the rotation speed of the intermediate transfer belt 2 by controlling the rotation speed of the motor 11, which is a step motor, will be described with reference to FIG. In order to change the rotation speed of the motor 11, it is common to change the frequency of the motor driving clock as shown in FIG.

That is, when the rotation speed of the motor 11 rotating at a normal rotation speed is set to be lower than the clock frequency as shown in the upper part of FIG. 7, the clock frequency is lowered as shown in the middle part of FIG. Thus, the number of clocks per unit time is reduced. Conversely, when increasing the rotation speed of the motor 11, the clock frequency is increased to increase the number of clocks per unit time as shown in the lower part of FIG.

When the rotation speed of the intermediate transfer belt 2 is increased by increasing the rotation speed of the motor 11, if the rotation speed of the photosensitive member 1 is constant, the toner image transferred onto the intermediate transfer belt 2 is It extends in the direction of rotation. That is, in this case, the magnification of the image (with respect to the rotating direction of the belt) is increased.

Conversely, when the rotation speed of the intermediate transfer belt 2 is reduced, the toner image transferred onto the intermediate transfer belt 2 contracts in the rotation direction of the belt if the rotation speed of the photosensitive member 1 is constant. Become. That is, the magnification of the image decreases. In order to transfer the toner image on the intermediate transfer belt 2 onto transfer paper under optimal conditions, it is necessary to change the transfer paper transport speed in synchronization with a change in the rotation speed of the intermediate transfer belt 2.

Next, an example of a method of transferring a toner image to an accurate position on the intermediate transfer belt 2 will be described with reference to FIGS. In the image forming apparatus according to this embodiment,
When an image of only one color is formed, it is not necessary to superimpose different color toner images on the intermediate transfer belt 2, so that
Immediately, an image forming process is performed to form a toner image on the photoreceptor 1 shown in FIG. 1, and the toner image is not superimposed on the intermediate transfer belt 2 as shown in FIG. 2 is sequentially transferred along the rotation direction.

Then, each toner image Gt₁, Gt₂,
Gt₃Each tip position To₁, To₂, To₃No
The positional relationship with the default mark 16 is stored in the storage unit of the control device 10.
After the transfer paper is continuously fed,
Of the belt mark 16 and the toner image Gt stored in
₁, Gt₂, Gt₃Each tip position To₁, T
o ₂, To₃Position with each transfer paper based on the
Position, and move the intermediate position to the correct position on the transfer paper.
Toner image Gt on transfer belt 2₁, Gt₂, Gt₃In order
Next transfer.

When an image of two or more colors is to be formed, it is necessary to accurately superimpose toner images of different colors on the intermediate transfer belt 2, and therefore, as shown in FIG. Each time the intermediate transfer belt 2 rotates, a toner image of a different color is formed on the intermediate transfer belt 2 by using the belt mark 16a so that no color shift occurs. It is superimposed on an accurate position with respect to the reference (in FIG. 3, the phantom line indicates the second rotation). When the superimposed images of all colors are transferred onto the intermediate transfer belt 2, the superimposed images are collectively transferred to an accurate position on the transfer paper.

FIG. 9 is a plan view partially showing the intermediate transfer belt for explaining an embodiment in which a plurality of images are formed on the intermediate transfer belt while the intermediate transfer belt makes one rotation. In this embodiment, the mark detecting sensor 3 of one of the belt marks 16a serving as a reference (see FIG. 2) detects, then photoreceptor first color toner image Gt ₁ of the first screen of the image at a predetermined timing 1 From the intermediate transfer belt 2.

Next, if there is an image on the second screen, 1
The position of the tip of the image on the second screen is specified based on the size of the toner image on the screen, and 1
The color toner image Gt ₂ is transferred from the photoconductor 1 to the intermediate transfer belt 2.
Transfer to the top. Then, when the intermediate transfer belt 2 reaches the second rotation, and the mark detection sensor 3 detects the reference belt mark 16a again, it is reset at a predetermined timing.
The toner image of second color screen th image is transferred as superimposed in precise alignment on the first color toner image Gt ₁ of.

[0057] Similarly, the second color toner image of the second screen image is transferred as superimposed in the correct position on the second color toner image Gt _2. Thereafter, when there are toner images of the third and subsequent colors, the toner images of the third and subsequent colors are similarly superimposed on the image of the first screen and the image of the second screen, respectively. According to this embodiment, even when a plurality of images composed of two or more colors are formed, a toner image can be continuously carried on the intermediate transfer belt 2 without creating useless empty space. Therefore, printing efficiency can be improved.

FIGS. 10 and 11 show a part of an intermediate transfer belt for explaining an embodiment of an image forming apparatus in which one belt mark is provided on the intermediate transfer belt and a plurality of mark detection sensors are provided. FIG. 9 is a plan view similar to FIG. 8. In the image forming apparatus according to this embodiment, only one belt mark 16 is provided on the intermediate transfer belt 2 and the mark detection sensor 3 described with reference to FIG. Multiple (3 in this example)
A to 3F).

In FIG. 10 (the same applies to FIGS. 11 and 12 described later), the mark detection sensors 3A to 3
2, the mark detection sensors 3A to 3F are located above the belt mark 16 like the mark detection sensor 3 shown in FIG. The marks 16 are provided at positions where the marks 16 can be detected.

The measurement time ta between the time when the mark detection sensor 3 detects the belt mark 16 when the intermediate transfer belt 2 rotates and the time when the next adjacent mark detection sensor 3 detects the belt mark 16 is determined. Prescribed specified time t
b, when the measured time ta deviates from the specified time tb due to a change in load applied to the intermediate transfer belt 2, the rotation speed of the motor 11 is adjusted so that the intermediate transfer belt 2 has a regular rotation speed. There is provided a control device 10 'for performing control to speed up or slow down.

The control device 10 'is different from the control device 10 described with reference to FIG. 1 only in the contents of control. Since the configuration is the same as that of the control device 10, detailed description thereof will be omitted. In this embodiment, the control device 10 'functions as a toner image carrier rotation speed control unit.

In the image forming apparatus according to this embodiment, 1
In the case of forming an image of only colors, it is not necessary to superimpose toner images of different colors on the intermediate transfer belt 2, so that the image forming process is executed immediately upon input of the start signal, and the photosensitive member described with reference to FIG. A toner image is formed on the same photoreceptor as that of No. 1, and the toner image is sequentially transferred along the rotation direction of the intermediate transfer belt 2 without being superimposed on the intermediate transfer belt 2 as shown in FIG.

Then, each toner image Gt₁, Gt₂,
Gt₃Each tip position To₁, To₂, To₃No
The positional relationship with the tilt mark 16 is stored in the control device 10 '.
Unit, and after storing the transfer paper continuously,
Of the belt mark 16 and the toner image G stored in the
t₁, Gt₂, Gt₃Each tip position To₁, To
₂, To₃Position with each transfer paper based on the relationship
Media to the correct position on the transfer paper.
The toner image Gt on the copying belt 2₁, Gt₂, Gt ₃Sequentially
Transcribe.

When an image of two or more colors is to be formed, it is necessary to accurately superimpose toner images of different colors on the intermediate transfer belt 2, so that, for example, the same as in the embodiment described with reference to FIG. The time when the cleaning member 7 of the belt cleaning device 6 comes into contact with the intermediate transfer belt 2 is time t.
₄ is a timing when the cleaning member 7 that separates from the intermediate transfer belt 2 is to be the timing of time t ₅ measures the measuring time ta ₁ and ta ₂ in the following manner.

[0065] That is, as shown in FIG. 11, the time _{t 4}
If when the timing of the time t _5, the belt mark 16 on the intermediate transfer belt 2 moving in the direction indicated by the arrow C by using the mark detecting sensor 3A-3F, the one mark detecting sensor belt mark 16 from the detection, by the time until the mark detecting sensor adjacent the belt mark 16 is detected, to measure the measurement time ta ₁ and ta _2, respectively.

[0066] That is, at time t _4, the mark detecting sensor 3A will detect the belt mark 16, by the time until the belt mark 16 mark detecting sensor 3B detects the first measurement time ta ₁ is measured, and the next measurement time ta ₁ is measured in a time period between the time when the mark detection sensor 3B detects the belt mark 16 and the time when the mark detection sensor 3C detects the belt mark 16. In the same manner, the measurement time ta _{1 is} the time between adjacent mark detection sensors detecting the belt mark 16 in the same manner.
Is measured continuously.

[0067] Similarly, at time t _5, the mark detecting sensor 3A will detect the belt mark 16, by the time until the belt mark 16 mark detecting sensor 3B detects the first measurement time ta ₂ is measured, and the next measurement time ta ₂ is measured between the time when the mark detection sensor 3B detects the belt mark 16 and the time when the mark detection sensor 3C detects the belt mark 16. In the same manner, the measurement time ta _{2 is} the time during which the mark detection sensors adjacent to each other detect the belt mark 16.
Is measured continuously.

Then, the measured measurement time ta ₁ is
When the intermediate transfer belt 2 is longer (longer) than the reference specified time tb, the intermediate transfer belt 2 is rotated at a speed lower than the normal rotation speed due to the load applied from the belt cleaning device 6, and is shown in FIG. The rotation speed of the motor 11 is increased to set the intermediate transfer belt 2 to the reference rotation speed.

When the measured time ta ₂ is shorter (shorter) than the specified reference time tb, the time t _{5 in} FIG.
As described in the above section, while the load is applied to the intermediate transfer belt 2 from the belt cleaning device 6, the motor 11
The intermediate transfer belt 2 maintained at the regular rotation speed by increasing the rotation speed of the belt cleaning device 7 is separated from the cleaning member 7 of the belt cleaning device 6 so that the load is reduced and the intermediate transfer belt 2 is faster than the regular rotation speed. Since the rotation is performed, the rotation speed of the motor 11 is reduced to set the intermediate transfer belt 2 to the reference rotation speed.

Thereafter, each time the intermediate transfer belt 2 makes one rotation, the toner image of each color is different from the toner image of each color on the intermediate transfer belt 2 with reference to the belt mark 16, causing a color shift. After the superimposed images of all colors are transferred onto the intermediate transfer belt 2, the superimposition is performed at the correct position (the virtual line indicates the second rotation in FIG. 11). As in the case described in the embodiment, the superimposed images on the intermediate transfer belt 2 are collectively transferred to an accurate position on the transfer paper.

FIG. 12 is a partial sectional view of an intermediate transfer belt for explaining an embodiment in which a plurality of images are formed on the intermediate transfer belt provided with only one belt mark while the belt rotates once. FIG. 12 is a plan view schematically showing a portion corresponding to FIG. 11 is denoted by the same reference numeral. In this embodiment, as in the embodiment described with reference to FIG. 11, only one belt mark 16 is provided on the intermediate transfer belt 2 and a plurality of mark detection sensors 3A to 3F are connected to the intermediate transfer belt indicated by arrow C. 2 are provided along the rotation direction.

In this embodiment, when the mark detection sensor 3 (whichever of the sensors 3A to 3F may be used) detects the reference belt mark 16, one screen is displayed at a predetermined timing. The first color toner image Gt ₁ of the eye image is transferred from the photoconductor 1 (see FIG. 1) onto the intermediate transfer belt 2.

Next, if there is an image on the second screen, 1
The position of the tip of the image on the second screen is specified based on the size of the toner image on the screen, and 1
The color toner image Gt ₂ is transferred from the photoconductor 1 to the intermediate transfer belt 2.
Transfer to the top. The intermediate transfer belt 2 is 2 rotates eyes become (in which FIG. 12 the belt mark 16 and the toner image Gt ₁ in phantom), when the belt mark 16 mark detecting sensor 3 detects again, then given the toner image of the second color first screen image at the timing to transfer to be superimposed in the correct position on the first color toner image Gt ₁ of.

[0074] Similarly, the second color toner image of the second screen image is transferred as superimposed at the correct position on the second color toner image Gt ₂ of. Thereafter, when there are toner images of the third and subsequent colors, the toner images of the third and subsequent colors are similarly superimposed on the image of the first screen and the image of the second screen, respectively.

According to this embodiment, even when an image composed of two or more colors is formed, similar to the embodiment described with reference to FIG. Can continuously carry a toner image without creating a useless empty space on the intermediate transfer belt 2, so that printing efficiency can be improved.

As described above, in the image forming apparatus according to each of the embodiments described with reference to FIGS. 10, 11 and 12, only one belt mark 16 is provided on the intermediate transfer belt 2, so that a plurality of belt marks 16 are provided. Is provided on the intermediate transfer belt 2, the timing at which the toner image on the photoreceptor 1 is transferred onto the intermediate transfer belt 2 and color superimposed on which belt mark 16 is used as a reference. Although it is necessary to count and manage the number of belt marks 16 in order to determine whether or not the control is performed, the control can be simplified as much as there is no need to manage the belt marks 16.

That is, when a plurality of mark detection sensors are provided with one belt mark, a specific one of the plurality of mark detection sensors is used to transfer the toner image onto the intermediate transfer belt at the timing. By determining in advance that it will be used as a mark detection sensor for adjustment,
The transfer timing of the above-described toner image onto the intermediate transfer belt can be easily controlled based on a detection signal output by detecting and outputting the belt mark by the mark detection sensor.

The embodiments of the image forming apparatus according to the present invention have been described above. In the description of each embodiment, the cleaning member 7 of the belt cleaning device 6 described with reference to FIG. the timing of contact with the intermediate transfer belt 2 and the time t ₄ when shown in FIG. 4, but the cleaning member 7 has a timing away from the intermediate transfer belt 2 assumes that the time t _5, the cleaning member 7 is actually the intermediate transfer since it is preferable to clean the entire circumference of the belt 2, for example, a cleaning member 7 in the first rotation time t ₁ is brought into contact with the intermediate transfer belt 2 is continued until the contact time t ₁ of the two-round as It is good to

In that case, step 1 described in FIG.
When it is determined that ta ₁ = tb is not satisfied at time t ₁ of the _first round in step 6 (ta ₁ > t due to contact of the cleaning member 7).
b) In step 17, the rotation speed of the motor 11 is increased to control the rotation speed of the intermediate transfer belt 2 that has been slowed down by the load to be the normal rotation speed.

Then, in step 20 described with reference to FIG.
When it is determined that ta ₂ <tb at the time t ₁ in the _second rotation (the cleaning member 7 is separated from the intermediate transfer belt 2), the rotation speed of the motor 11 is reduced in step 21,
When the cleaning member 7 is separated from the intermediate transfer belt 2, the load applied to the intermediate transfer belt 2 is reduced, and the rotation speed of the intermediate transfer belt 2 is controlled to a normal rotation speed.

[0081]

As described above, according to the present invention, the following effects can be obtained. According to the image forming apparatus of the first aspect, when the rotation speed of the toner image carrier decreases due to an increase in the load applied to the toner image carrier,
The rotation speed is compared with a predetermined time period from the time when the mark detection sensor detects one of the marks provided on the toner image carrier to the time when the next adjacent mark is detected. According to the result, the driving of the rotation driving system is controlled so that the toner image carrier has a regular rotation speed.
Even when the load applied to the toner image carrier fluctuates in the course of forming an image of more than two colors, the rotation speed of the toner image carrier can be kept constant, so that the image of two or more colors can be formed. It is possible to prevent deviation on the toner image carrier. Therefore, the image magnification of the image of two or more colors in the rotation direction of the toner image carrier becomes equal to the reference value,
Since there is no deviation from each other, a good image without color deviation can be obtained.

According to the image forming apparatus of the present invention, since only one mark is provided on the toner image carrier, any one of the marks may be provided on the toner image carrier as in the case where a plurality of marks are provided on the toner image carrier. It is not necessary to count or manage the number of marks to transfer the toner image on the photoconductor onto the toner image carrier based on the marks. Control can be simplified as much as there is no more. According to the image forming apparatus of the third aspect, since the toner image carrier is an intermediate transfer belt, a high-quality color image can be formed by accurately overlapping toner images of two or more colors without causing color misregistration. can get.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an image forming unit of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view showing an intermediate transfer belt provided in the image forming apparatus and a mark detection sensor for detecting marks provided on the intermediate transfer belt.

FIG. 3 is a plan view partially showing an intermediate transfer belt carrying a toner image in order to explain the positional relationship on the belt of a plurality of belt marks provided on the intermediate transfer belt.

FIG. 4 is a diagram illustrating a relationship between time and a load applied to an intermediate transfer belt.

FIG. 5 is a flowchart illustrating an image forming process performed by a control device included in the image forming apparatus of FIG. 1;

FIG. 6 is a flowchart showing a process in step 7 of FIG. 5;

FIG. 7 is a diagram illustrating an example in which the frequency of a clock of a step motor is changed in order to adjust the rotation speed of the intermediate transfer belt.

FIG. 8 is a plan view illustrating a part of the intermediate transfer belt for describing an example of forming an image of only one color on the intermediate transfer belt.

FIG. 9 is a plan view partially showing an intermediate transfer belt for describing an embodiment in which a plurality of images of two or more colors are formed on the intermediate transfer belt during one rotation of the belt;

FIG. 10 shows a part of the intermediate transfer belt together with a control system to explain an embodiment of an image forming apparatus in which one belt mark is provided on the intermediate transfer belt and a plurality of mark detection sensors are provided. It is a top view similar to.

FIG. 11 is a plan view showing an example where two or more images of two or more colors are formed by the image forming apparatus.

FIG. 12 is a partial cross-sectional view of an intermediate transfer belt for explaining an embodiment in which a plurality of images are formed on an intermediate transfer belt provided with only one belt mark while the belt rotates once; FIG.

[Explanation of symbols]

1: Photoreceptor 2: Intermediate transfer belt (toner image carrier) 3: Mark detection sensor 6: Belt cleaning device 10, 10 ': Control device (toner image carrier rotational speed control means) 11: Motor (rotating system) 16: Belt mark

Claims (3)

[Claims] 1. A photoreceptor that carries a toner image visualizing an electrostatic latent image, and the toner image formed on the photoreceptor that is rotated by a rotation drive system is superimposed on an image carrying surface a plurality of times. An image forming apparatus comprising: a transferable toner image carrier; and a mark detection sensor provided on the toner image carrier to detect a mark serving as a reference position at the time of image formation. A plurality of marks are provided along the rotation direction of the toner image carrier, and one mark detection sensor is provided. When the toner image carrier rotates, the mark detection sensor detects one of the marks. When the measurement time from when the next adjacent mark is detected is compared with a predetermined specified time, and the measurement time is deviated from the specified time due to a load change applied to the toner image carrier. , Said Image forming apparatus characterized by toner image bearing member is provided with a toner image bearing member rotational speed control means for driving and controlling the rotation drive system so that the rotation speed of the normal. 2. A photoreceptor carrying a toner image visualized as an electrostatic latent image, and the toner image formed on the photoreceptor rotated by a rotation drive system is superimposed on an image carrying surface a plurality of times. An image forming apparatus comprising: a transferable toner image carrier; and a mark detection sensor provided on the toner image carrier to detect a mark serving as a reference position at the time of image formation. One mark is provided, and a plurality of the mark detection sensors are provided along the rotation direction of the toner image carrier. When the mark detection sensor detects the mark during the rotation of the toner image carrier, The measurement time until the mark detection sensor adjacent to the mark detection sensor detects the mark is compared with a predetermined time, and the measurement time is shifted from the predetermined time due to a load change applied to the toner image carrier. When you are, the image forming apparatus, wherein said toner image bearing member is provided with a toner image bearing member rotational speed control means for driving and controlling the rotation drive system so that the rotation speed of the normal. 3. The image forming apparatus according to claim 1, wherein the toner image carrier is an intermediate transfer belt.