JPH11231754A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly detect, in the case of using an endless belt, a change in the speed of the endless belt in the position of the transfer of a toner image in order to exert feedback control accurately for the change of the speed of the endless belt. SOLUTION: The device is equipped with the endless belt 1 that carries a toner image on it, a drive roll 3 that drives this, a tension roll 4 that moves following the endless belt 1, and an image forming means 2 that forms an image on the endless belt 1. The device is also equipped with a speed detection means 5 that detects the speed of the movement of the endless belt 1 on the side of the image forming means 2, between the drive roll 3 and tension roll 4. Here, rotary drive by the drive roll 3 is controlled based on the result of the detection by the speed detection means 5.

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 method.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses such as copiers and printers use an endless belt to carry a toner image or to convey a medium for outputting a toner image in order to cope with the formation of a color image. Widely used.

As an image forming apparatus using an endless belt, for example, as disclosed in JP-A-4-44071, an intermediate transfer belt is provided as an endless belt.
In some image forming apparatuses, a plurality of color toner images are stacked and transferred from a photosensitive drum onto an intermediate transfer belt and then collectively transferred onto a medium such as recording paper to form a color image. In this image forming apparatus, when forming a full-color image, the intermediate transfer member belt is composed of Y (yellow), M (magenta), C (cyan), and K (black).
The four color toner images are carried.

Further, as an image forming apparatus using an endless belt, in addition to the above-described one, for example, a photosensitive belt is provided as an endless belt, and writing and developing of a toner image of a plurality of colors are performed on the photosensitive belt. In some cases, a color image is formed by performing a batch transfer onto a medium after the transfer. Furthermore, a color image is provided by transporting the medium under a plurality of photosensitive drums arranged at a predetermined pitch, and sequentially transferring the toner images onto the medium, provided with a transport belt that transports the medium as an endless belt. Some also form

In these image forming apparatuses, the endless belt is driven by rotating a driving roll connected to a driving means such as a motor. Therefore, if the drive roll is eccentric, the moving speed of the endless belt fluctuates in accordance with the rotation frequency of the drive roll even if the rotational angular speed of the drive roll is constant. Such a change in the moving speed causes a shift in the formation position between the toner images of each color, and as a result, there is a possibility that a color shift or density unevenness in an output image may be caused.

However, it is very difficult to completely remove the eccentricity of the drive roll from the viewpoint of manufacturing technology or equipment cost. For this reason, various techniques have been conventionally proposed in order to suppress the fluctuation of the moving speed on the endless belt even when the drive roll is eccentric. For example, Japanese Patent Application Laid-Open No. 2-1271 / 1990 discloses an apparatus in which the outer diameter of a drive roll is set to a fraction of the circumference of an endless belt to minimize the influence of eccentricity of the drive roll on speed fluctuation. I have. Further, Japanese Patent Application Laid-Open No. Hei 6-13373 discloses an apparatus in which the outer peripheral length of a driving roll is set to be a fraction of the installation pitch of the photosensitive drums to minimize the influence on speed fluctuation.

However, even with these techniques, it is difficult to completely suppress fluctuations in the moving speed on the endless belt due to variations in the accuracy of the components of the endless belt and the drive roll, etc., and a slight displacement (for example, several tens of (approximately μm) cannot prevent color shift and density unevenness. Therefore, for example, Japanese Patent Application Laid-Open Nos. 4-172376 and 4-234.
No. 064 discloses a rotary encoder provided on a shaft of a driven roll driven by an endless belt to detect a rotational angular velocity of the driven roll, and a rotation of a motor for rotating a driving roll based on a detection result by the rotary encoder. An apparatus for controlling speed is disclosed. in this way,
If the speed detection means comprising a driven roll and a rotary encoder is provided, and the speed detection means obtains the moving speed of the endless belt and performs feedback control on the motor, the moving speed of the endless belt is kept constant, and the position of the endless belt can be reduced. Color shift and density unevenness can be prevented.

[0008]

However, in the image forming apparatus using the endless belt as described above, even if the feedback control based on the detection result by the speed detecting means is performed, a slight positional deviation occurs due to the following reason. There is a possibility that color shift and density unevenness due to the image cannot be completely prevented.

Usually, in an image forming apparatus using an endless belt, when eccentricity occurs in a driving roll, a belt winding side (hereinafter, referred to as an entrance side) and a belt feeding side (hereinafter, an exit side) of the driving roll. ) Causes a difference in the moving speed. Therefore, depending on the position where the moving speed of the endless belt is detected, the detection result may have a different value.

More specifically, as shown in FIG. 6, for example, as shown in FIG. 6, an endless belt 11 such as an intermediate transfer member belt, a driving roll 12 for driving the endless belt 11, a driven roller 11 and a predetermined direction. When the rotation center of the drive roll 12 is eccentric by (R1−R2) / 2, the drive roll 12 is moved in the direction of the arrow in the figure. When rotated in the (counterclockwise) direction, the moving speed of the endless belt 11 on the outlet side of the drive roll 12 is V1 = R1 × ω (ω is the angular speed of the drive roll 12), and the moving speed of the endless belt 11 on the inlet side. Is V2
= R2 × ω, and a speed difference is generated by the difference between the radii R1 and R2 of the drive roll 12. Note that V at this time
The speed difference between 1 and V2 is absorbed by the position of the tension roll 13 moving in the feed direction of the endless belt 11.

Further, these moving speeds V1 and V2 always fluctuate periodically due to the eccentric rotation of the drive roll 12. For example, on the exit side of the drive roll 12 (point a in FIG. 6), as shown in FIG. 7A, the moving speed V1 fluctuates at a predetermined cycle in synchronization with the rotation frequency of the drive roll 12. On the other hand, on the entrance side (point d in FIG. 6) of the drive roll 12, as shown in FIG. 7B, the moving speed V2 differs from the moving speed V1 by 180.
It fluctuates at a phase shifted by degrees. That is, the phase of the speed fluctuation is completely different between the exit side and the entrance side of the drive roll 12.

Therefore, as shown in FIG.
The image transfer position e of the toner image onto the
Is located on the exit side (between a and b in the figure) and the speed detecting means 14 composed of the driven roll and the rotary encoder is on the entrance side of the drive roll 12 (between cd in the figure). The speed fluctuation at e
Even in the state shown in FIG. 7A, the speed detecting means 14 detects the state shown in FIG. 7B (a state in which the phase is shifted by 180 degrees). Therefore, the speed detecting means 14
Even if feedback control is performed based on the detection result by
The speed fluctuation at the image transfer position e cannot be suppressed, and the speed fluctuation is rather amplified.

The endless belt 11 is usually formed by adhering the belt ends to each other to form an endless (ring) shape. However, the end-to-end adhering portion (hereinafter referred to as a seam portion) is formed. The thickness is different from other parts. Therefore, the difference in the moving speed (surface speed) of the endless belt 11 between the case where the seam portion passes through the entrance side of the drive roll 12 and the case where it passes through the exit side becomes even more remarkable than in the case described above. I will.

That is, in the conventional image forming apparatus as described above, even if the feedback control based on the detection result of the speed detecting means 14 is performed, the moving speed of the endless belt 11 is kept constant and the color due to the slight positional shift is changed. There is a possibility that the shift and the density unevenness cannot be prevented.

Accordingly, the present invention provides an image forming apparatus capable of accurately detecting a speed variation at a transfer position of a toner image in order to accurately perform feedback control and to prevent color shift and density unevenness due to a minute position shift. The purpose is to provide.

[0016]

SUMMARY OF THE INVENTION The present invention is directed to an image forming apparatus devised to achieve the above object, comprising: an endless belt for carrying a toner image or conveying a medium for outputting a toner image; A drive roll for driving a belt, and a tension roll that follows the endless belt and applies tension to the endless belt by urging in a predetermined direction,
An image forming unit that forms an image on the endless belt or a medium conveyed to the endless belt on the endless belt on one side between the drive roll and the tension roll; and an image forming unit that is driven by the drive roll. Speed detecting means for detecting the moving speed of the endless belt, and drive control means for controlling the driving of the endless belt by the driving roll based on the detection result of the speed detecting means, The detecting means detects the moving speed of the endless belt on a side between the driving roll and the tension roll where the image forming means is provided.

According to the image forming apparatus having the above structure, the speed detecting means detects the moving speed of the endless belt on the side where the image forming means is provided between the driving roll and the tension roll. ing. Therefore, even if the moving speed of the endless belt is different between the inlet side and the outlet side of the driving roll due to, for example, the eccentricity of the driving roll, the speed detecting unit detects the moving speed of the endless belt on the side where the image forming unit forms an image. Will be detected.

Further, in the image forming apparatus of the present invention, the speed detecting means detects the moving speed of the endless belt between the driving roll and the tension roll on the side where the image forming means is not provided, Drive control means corrects the phase of the detection result by the speed detection means in accordance with the wrap angle between the endless belt and the drive roll, and drives the endless belt by the drive roll based on the corrected detection result. Is controlled.

According to such an image forming apparatus, even if the speed detecting means detects the moving speed of the endless belt on the side where the image forming means is not provided, the drive control means controls the wrap between the endless belt and the drive roll. The phase of the detection result by the speed detecting means is corrected in accordance with the angle, that is, the angle at which they overlap. Therefore, even if the moving speed of the endless belt is different between the entrance side and the exit side of the driving roll due to, for example, the eccentricity of the driving roll, the image forming unit provides the driving control unit with the detection result of the moving speed by the speed detecting unit. After the correction that is the same as the phase of the moving speed of the endless belt on the side of the endless belt, the driving of the endless belt by the driving roll is controlled.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described with reference to the drawings. However, here,
An example in which the present invention is applied to an image forming apparatus provided with an intermediate transfer belt as an endless belt will be described.

[First Embodiment] Here, an image forming apparatus according to the first, third and fourth aspects of the present invention will be described. The image forming apparatus according to the present embodiment
As shown in FIG. 1, in addition to an intermediate transfer belt 1 that carries a toner image, a photosensitive drum 2 and an intermediate transfer belt 1
And four rolls (a driving roll 3, a tension roll 4, a driven roll 5, and a transfer roll 6) that engage with the roller.

The photosensitive drum 2 is provided with a laser RO (not shown).
A toner image to be transferred onto the intermediate transfer belt 1 is formed by writing a latent image by S (Raster Output Scanner) or the like and developing by a developing device (not shown). That is, the photosensitive drum 2 functions as an image forming unit in the present invention.

The driving roll 3 is connected to driving means such as a motor (not shown) and drives the intermediate transfer belt 1. The tension roll 4 is driven by the intermediate transfer body belt 1 and applies tension to the intermediate transfer body belt 1 by urging in a predetermined direction.

The driven roll 5 is driven by the intermediate transfer belt 1 on the side where the photosensitive drum 2 is provided between the driving roll 3 and the tension roll 4, and is driven from the photosensitive drum 2 to the intermediate transfer body. This is for maintaining the image transfer position E to the belt 1 constant. Further, the driven roll 5 is provided with a rotary encoder (not shown) on the axis thereof, and the rotary encoder detects the rotational angular velocity of the driven roll 5. That is, the driven roll 5 provided with the rotary encoder functions as a speed detecting unit in the present invention. The detection result of the rotational angular velocity of the driven roll 5 by the rotary encoder is used for feedback control of the drive unit of the drive roll 3 by a drive control unit (not shown).

Further, the driven roller 5 has an outer diameter different from the outer diameter of the driving roll 3 and an outer peripheral length of the driven roll 5 is an integral number of the peripheral length of the intermediate transfer belt 1 for a reason described later in detail. It is assumed that

The transfer roll 6 is driven by the intermediate transfer belt 1 on the side between the drive roll 3 and the tension roll 4 where the photosensitive drum 2 is not provided. This is for keeping the transfer position of the toner image on the medium such as the above constant.

In the image forming apparatus configured as described above,
When performing image output on media such as recording paper,
First, a toner image is formed on the photosensitive drum 2. Then, the toner image formed on the photosensitive drum 2 is transferred to the intermediate transfer belt 1 at the image transfer position E. At this time, if a full-color image is to be formed, each time the intermediate transfer belt 1 makes one rotation, the toner images of each of the colors Y, M, C, and K are sequentially stacked and transferred. After that, the toner image on the intermediate transfer belt 1 is transferred onto the medium at the installation position D of the transfer roll 6. In this way, the image forming apparatus outputs an image on a medium.

When the above-described image output is performed, the main cause of the positional deviation between the toner images of the respective colors due to the eccentricity of the driving roll 3 is that the intermediate transfer belt 1 moves from the photosensitive drum 2 to the intermediate transfer belt 1. Transfer position E where image transfer is performed
Of the moving speed of the intermediate transfer belt 1 at the time of printing.

If the drive roll 3 is eccentric, the moving speed of the intermediate transfer belt 1 is different between the entrance side A1 and the exit side A2 of the drive roll 3, as described above. Therefore, in order to prevent the misregistration between the toner images of each color, the moving speed of the intermediate transfer belt 1 at the image transfer position E, that is, the distance between the driving roll 3 and the tension roll 4 at the exit side A2 of the driving roll 3 It is necessary to detect the moving speed of the intermediate transfer belt 1 (between A2 to B to C in the figure) and perform feedback control based on the detection result.

On the other hand, in this image forming apparatus, the driven roll 5 exists on the side where the photosensitive drum 2 is provided between the drive roll 3 and the tension roll 4, and the driven roll 5 A rotary encoder provided on the shaft detects the rotational angular velocity of the driven roll 5. That is, the moving speed (moving speed at the image transfer position E) of the intermediate transfer belt 1 at the outlet side A2 of the driving roll 3 is detected by the driven roll 5 and the rotary encoder. Therefore, if the feedback control is performed based on the detection result of the rotation angular velocity of the driven roll 5 by the rotary encoder, even if the moving speed of the intermediate transfer belt 1 is different between the entrance side A1 and the exit side A2 of the driving roll 3, The moving speed of the intermediate transfer belt 1 at the image transfer position E can be kept constant.

As described above, in the image forming apparatus according to the present embodiment, the intermediate transfer belt 1 is provided between the drive roll 3 and the tension roll 4 on the side where the photosensitive drum 2 is provided.
Is detected, and feedback control is performed based on the detection result. Accordingly, in this image forming apparatus, even if the drive roll 3 is eccentric, the moving speed of the intermediate transfer belt 1 at the image transfer position E can be accurately grasped, and furthermore, the fluctuation of the moving speed can be detected. It is also possible to suppress the color shift and the density unevenness due to the minute positional shift. This is because the intermediate transfer belt 1 has a seam portion, and the difference in the moving speed (surface speed) of the intermediate transfer belt 1 between the entrance side A1 and the exit side A2 of the drive roll 3 due to the seam portion. Is also effective in cases where is more noticeable.

Further, in the image forming apparatus of the present embodiment,
The moving speed of the intermediate transfer belt 1 at the image transfer position E is detected by detecting the rotational angular velocity of the driven roll 5 with a rotary encoder. That is, the moving speed of the intermediate transfer belt 1 is detected by using the existing driven roll 5 for maintaining the image transfer position E at a constant value. Therefore, no special means for detecting the moving speed, for example, addition of a new roll or the like is not required, so that the apparatus configuration is not complicated and the apparatus cost is not increased. Further, since the wrap angle (overlap angle) between the intermediate transfer belt 1 and the driven roll 5 is sufficiently ensured, a good result is obtained even with respect to the slip between the intermediate transfer belt 1 and the driven roll 5 and accurate. It is possible to realize detection of a moving speed.

In the image forming apparatus according to the present embodiment,
The outer diameter of the driven roll 5 is different from the outer diameter of the drive roll 3,
In addition, the outer peripheral length is an integral fraction of the peripheral length of the intermediate transfer belt 1. Therefore, in this image forming apparatus,
Even if the driven roll 5 is eccentric, the influence can be removed, and the moving speed of the intermediate transfer belt 1 at the image transfer position E can be accurately detected.

More specifically, for example, when the outer diameter of the driven roll 5 to which the rotary encoder is attached is equal to the outer diameter of the driving roll 3, if the driven roll 5 is eccentric, The eccentricity component and the eccentricity component of the drive roll 3 may coincide with each other, making it impossible to grasp the influence of the eccentricity on the drive roll 3. On the other hand, when the outer diameter of the driven roll 5 and the outer diameter of the drive roll 3 are made different, the frequency range in which both influences occur can be changed.

Therefore, if the outer diameter of the driven roll 5 is made different from the outer diameter of the driving roll 3 and the frequency range in which the influence of the eccentricity of the driven roll 5 is affected is cut by a digital filter or the like, the eccentricity of the driven roll 5 can be reduced. By removing the influence, the influence of the eccentricity on the drive roll 3 can be correctly grasped. However, since the influence of the eccentricity of the driven roll 5 remains to some extent even after being cut by a digital filter or the like, the outer circumference of the driven roll 5 is set to be an integral length of the circumference of the intermediate transfer belt 1 to further ensure the reliability. The effect of the eccentricity of the driven roll 5 can be suppressed.

That is, if the outer diameter of the driven roll 5 is different from the outer diameter of the driving roll 3 and the outer circumference thereof is set to an integral fraction of the circumference of the intermediate transfer belt 1, the driven roll 5 Even if eccentricity has occurred, it is possible to remove the influence of the eccentricity. As a result, the moving speed of the intermediate transfer belt 1 at the image transfer position E can be more accurately detected.

[Second Embodiment] Next, an image forming apparatus according to the second aspect of the present invention will be described. However, here, only the differences from the above-described first embodiment will be described.

In the first embodiment, the rotary encoder is provided on the shaft of the driven roll 5 and the intermediate transfer belt is provided between the drive roll 3 and the tension roll 4 on the side where the photosensitive drum 2 is provided. Although the case of detecting the moving speed of No. 1 has been described, the moving speed of the photosensitive drum 2 may not be detected depending on the device configuration. In the present embodiment, even in such a case, the fluctuation of the moving speed of the intermediate transfer belt 1 at the image transfer position E is suppressed, and the color shift and the density unevenness due to a minute position shift are also prevented. It is.

In the image forming apparatus of this embodiment, unlike the first embodiment, a rotary encoder is provided on the axis of the transfer roll 6 due to restrictions on the structure of the apparatus. That is, the intermediate transfer belt 1 is located on the side where the photosensitive drum 2 is not provided between the drive roll 3 and the tension roll 4 (the entrance side A1 of the drive roll 3).
The moving speed of the object is detected.

However, by merely detecting the moving speed of the intermediate transfer belt 1 at the entrance side A1 of the drive roll 3, the speed fluctuation of the intermediate transfer belt 1 at the image transfer position E can be accurately grasped as described above. Can not do it. More specifically, for example, as shown in FIG.
When the drive roll 3 and the drive roll 3 overlap at a wrap angle (∠A1-OA2) θ, the wrap angle between the speed fluctuation detected by the rotary encoder on the axis of the transfer roll 6 and the speed fluctuation at the image transfer position E is determined. The phase is shifted by an amount corresponding to θ.

Therefore, in the image forming apparatus of the present embodiment, the drive control means including a microprocessor or the like for performing feedback control corresponds to the wrap angle θ between the intermediate transfer belt 1 and the drive roll 3, The phase of the detection result by the rotary encoder on the axis of the transfer roll 6 is corrected, and feedback control is performed based on the corrected detection result.

More specifically, when the intermediate transfer belt 1 and the driving roll 3 overlap at the lap angle θ, the influence of the eccentricity of the driving roll 3 is more affected by the entrance side A1 than the exit side A2.
Appears earlier by an amount corresponding to the lap angle θ. Therefore, the speed fluctuation of the intermediate transfer belt 1 detected by the rotary encoder on the axis of the transfer roll 6 (see FIG. 3A) is the actual speed fluctuation of the intermediate transfer belt 1 at the image transfer position E (FIG. 3). (See (b))), the phase is shifted forward by an amount corresponding to the lap angle θ. Therefore, the drive control means corrects the phase of the result of detection by the rotary encoder so as to be delayed in accordance with the wrap angle θ (see FIG. 3C), so that the actual intermediate transfer belt 1 at the image transfer position E is changed. The speed fluctuation of the vehicle is grasped in a pseudo manner.

As described above, in the image forming apparatus of the present embodiment, the moving speed of the intermediate transfer belt 1 is detected on the side where the photosensitive drum 2 is not provided between the driving roll 3 and the tension roll 4. In addition, the drive control means corrects the phase of the detection result corresponding to the lap angle θ, and performs feedback control based on the corrected detection result. Therefore, in this image forming apparatus, even when the moving speed of the intermediate transfer belt 1 is detected on the side where the photoconductor drum 2 is not provided, the image forming apparatus can detect the moving speed of the intermediate transfer belt 1 on the side where the photoconductor drum 2 is provided. The moving speed of the intermediate transfer belt 1 can be accurately grasped, and furthermore, the fluctuation of the moving speed can be suppressed to prevent color misregistration and density unevenness due to minute displacement.

[Third Embodiment] Next, an image forming apparatus according to a fifth aspect of the present invention will be described. However, also here, only the differences from the above-described first embodiment will be described.

As shown in FIG. 4, the image forming apparatus according to the present embodiment has a so-called four photosensitive drums 2a to 2d corresponding to respective colors of Y, M, C and K provided at a predetermined pitch P. It is a tandem type. In this image forming apparatus, when outputting an image on a medium, first, a toner image is formed on each of the photosensitive drums 2a to 2d. Then, after the toner images formed on the respective photosensitive drums 2a to 2d are sequentially stacked and transferred onto the intermediate transfer belt 1, the toner images synthesized by the stacked transfer are collectively transferred onto a medium. In this way, the image forming apparatus outputs an image on a medium.

Incidentally, also in the image forming apparatus having such a configuration, the driving roll 3 and the tension roll 4 are provided by the rotary encoder provided on the shaft of the driven roll 5.
In the case of the first embodiment, if the moving speed of the intermediate transfer belt 1 is detected on the side where the photosensitive drums 2a to 2d are provided and feedback control is performed based on the detection result, Similarly to the above, even if the drive roll 3 is eccentric, the moving speed of the intermediate transfer belt 1 can be suppressed to prevent color shift and density unevenness due to slight positional shift.

Further, in this image processing apparatus, the outer diameter of the driven roll 5 is different from the outer diameter of the drive roll 3, and the outer peripheral length thereof is an integral number of the pitch P between the photosensitive drums 2a to 2d. It is one. Therefore, in this image forming apparatus as well, it is possible to remove the influence of the eccentricity of the driven roll 5 and detect the moving speed of the intermediate transfer belt 1 more accurately, as in the first embodiment. It becomes possible.

In the first to third embodiments, the case where the present invention is applied to an image forming apparatus having the intermediate transfer belt 1 as an endless belt has been described.
The present invention is not limited to this, and can be similarly applied to a device having a photosensitive belt as an endless belt or a device having a transport belt as an endless belt.

For example, as shown in FIG. 5, even in a tandem-type image forming apparatus having a transport belt 7 as an endless belt, a tension is applied to the drive roll 3 for rotating the transport belt 7 and the transport belt 7. On the side where the photosensitive drums 2a to 2d are provided between the transfer belt 7 and the roll 4, the driven belt 5 and the rotary encoder
Of the moving speed of the photosensitive drums 2a to 2
If the moving speed is detected on the side where 2d is not provided, and the result is corrected according to the wrap angle between the driving roll 3 and the transport belt 7, the same effect as in the case described above can be obtained.

In the first to third embodiments described above, the case where the moving speed of the intermediate transfer belt 1 is detected by the driven roll 5 and the rotary encoder has been described. However, the present invention is not limited to this. Not something. For example, the moving speed of the intermediate transfer belt 1 may be detected using a speed detecting means such as a laser Doppler speed detecting device using a Doppler shift of a laser beam. By detecting the moving speed on the photosensitive drum 2 side between the tension roll 4 and the
The same effect as in the case described above can be obtained.

[0051]

As described above, the image forming apparatus of the present invention accurately grasps the moving speed of the endless belt at the image transfer position even when the drive roll for driving the endless belt is eccentric. Therefore, it is possible to reliably suppress the fluctuation of the moving speed, and as a result, it is possible to prevent the occurrence of minute color shift and density unevenness in the output image.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram showing a wrap angle between an intermediate transfer member belt and a driving roll for driving the belt.

FIGS. 3A and 3B are explanatory diagrams showing a speed change of an endless belt (intermediate transfer belt) in an image forming apparatus according to a second embodiment of the present invention; FIG. FIG. 3B is a diagram illustrating a detection result of the speed fluctuation, and FIG. 3C is a diagram illustrating a detection result of the speed fluctuation after the correction.

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

FIG. 5 is a schematic configuration diagram illustrating a main part of another example of the image forming apparatus according to the present invention.

FIG. 6 is a schematic configuration diagram illustrating a main part of an example of a conventional image forming apparatus.

FIG. 7 is an explanatory diagram showing speed fluctuation of an endless belt (intermediate transfer belt) in a conventional image forming apparatus;
(A) is a diagram showing the speed fluctuation on the exit side of the driving roll,
(B) is a figure which shows the speed fluctuation at the entrance side of a drive roll.

[Explanation of symbols]

1. Intermediate transfer belt, 2, 2a, 2b, 2c, 2d ...
Photoreceptor drum, 3 ... drive roll, 4 ... tension roll, 5 ... driven roll, 6 ... transfer roll

Claims (5)

[Claims] An endless belt that carries a toner image or conveys a medium that outputs a toner image; a drive roll that drives the endless belt; and an endless belt that is driven by the endless belt and biased in a predetermined direction. An image is formed on the endless belt or a medium conveyed to the endless belt on a tension roll that applies tension to the endless belt, and on the endless belt on one side between the driving roll and the tension roll. Image forming means; speed detecting means for detecting a moving speed of the endless belt driven by the driving roll; driving for controlling driving of the endless belt by the driving roll based on a detection result by the speed detecting means. Control means, wherein the speed detecting means is provided between the drive roll and the tension roll. The moving speed of the endless belt is detected on the side where the image forming means is provided. 2. An endless belt that carries a toner image or conveys a medium that outputs a toner image, a drive roll that drives the endless belt, and is driven by the endless belt, and is energized in a predetermined direction. An image is formed on the endless belt or a medium conveyed to the endless belt on a tension roll that applies tension to the endless belt, and on the endless belt on one side between the driving roll and the tension roll. Image forming means; speed detecting means for detecting a moving speed of the endless belt driven by the driving roll; driving for controlling driving of the endless belt by the driving roll based on a detection result by the speed detecting means. Control means, wherein the speed detecting means is provided between the drive roll and the tension roll. Detecting the moving speed of the endless belt on the side where the image forming means is not provided, wherein the drive control means detects the speed corresponding to a wrap angle between the endless belt and the drive roll. An image forming apparatus that corrects a phase of a detection result by the means, and controls driving of the endless belt by the driving roll based on the corrected detection result. 3. The apparatus according to claim 2, wherein the speed detecting means includes a driven roll that follows the endless belt, and an encoder that detects a moving speed of the endless belt from a rotational angular velocity of the driven roll. Item 3. The image forming apparatus according to Item 1 or 2. 4. When only one image forming means is provided on the endless belt, the driven roll has an outer diameter different from the outer diameter of the drive roll, and has an outer peripheral length. 4. The image forming apparatus according to claim 3, wherein the endless belt is formed so as to be an integral fraction of the circumference of the endless belt. 5. When the plurality of image forming means are provided on the endless belt at a predetermined pitch, the driven roll has an outer diameter different from the outer diameter of the drive roll,
4. The image forming apparatus according to claim 3, wherein the outer peripheral length is formed to be an integral fraction of the pitch.