JP2004054144A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus that highly accurately corrects color slurring. <P>SOLUTION: At the start of image forming operation, the detection temperature of a belt drive roller temperature sensor and that of an environment sensor are stored in a memory 16. Subsequently, it is determined whether or not an amount of change in the detection temperature of the belt drive roller temperature sensor is equal to or beyond ±1°C during a period from a color slurring correction operation to the subsequent color slurring correction operation. If it is not equal to or beyond ±1°C, the temperature is serially detected by the belt drive roller temperature sensor until it exceeds ±1°C. Conversely, if it is equal to or beyond ±1°C, ±REF1 and an amount of change in the detection temperature of the environment sensor is compared. If the amount of change does not exceed ±REF1, the speed of the belt drive motor is corrected with an amount of speed correction which corresponds to the amount of temperature change. Conversely, if it exceeds ±REF1, the speed of the belt drive motor is corrected with an amount of speed correction which is smaller than the value which corresponds to the temperature change. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrophotographic color image forming apparatus.
[0002]
[Prior art]
In an electrophotographic color image forming apparatus, various methods have been proposed which have a plurality of image forming units for speeding up and sequentially transfer images of different colors onto a recording material held on a transport belt. I have.
[0003]
Meanwhile, as a problem of the apparatus having a plurality of image forming units, there is a change in the diameter of the driving roller of the transport belt due to a rise in temperature in the image forming apparatus. The conveyor belt is suspended by rollers whose surfaces are covered with a thin rubber layer such as a conveyor belt drive roller and a conveyor belt driven roller, and when the temperature inside the apparatus rises, the rubber layer on the surface of each roller thermally expands, The thickness of the rubber layer increases. As the thickness of the rubber layer increases, the diameter of the driving roller increases, and the speed of the belt increases, resulting in color misregistration.
[0004]
FIG. 11 shows an example of color misregistration. Reference numeral 20 denotes an original image position, and reference numeral 21 denotes an image position when a color shift occurs. FIGS. 7B and 7C show cases where there is a color shift in the main scanning direction. For the sake of explanation, two lines are drawn apart in the transport direction.
(A) shows the inclination shift of the main scanning line, which occurs when there is an inclination between the optical unit and the photosensitive drum. For example, correction is made in the direction of the arrow by adjusting the positions of the optical unit, the photosensitive drum, and the lens.
2B shows a color shift due to a variation in the width of the main scanning line, which is caused by a difference in a distance between the optical unit and the photosensitive drum. This is likely to occur when the optical unit is a laser scanner. For example, by adjusting the positions of the optical unit, the photosensitive drum, and the lens, or finely adjusting the image frequency (if the scanning width is long, increase the frequency), and changing the length of the scanning line, the direction of the arrow is changed. Fix it.
(C) shows a writing start position error in the main scanning direction. For example, if the optical unit is a laser scanner, the correction is made in the direction of the arrow by adjusting the writing start timing from the beam detection position.
(D) shows the writing position error in the paper transport direction. For example, the correction is made in the direction of the arrow by adjusting the writing start timing of each color from the detection of the leading edge of the sheet.
[0005]
To correct these color shifts, a pattern for color shift detection is formed on the transport belt for each color, and detected by a pair of optical sensors provided on both sides of the downstream portion of the transport belt, and the detected shift amount Various adjustments as described above are performed according to the above.
[0006]
The color shift due to the temperature rise is provided by providing a temperature sensor on the transport belt drive roller, calculating the diameter of the drive roller from the temperature detected by the temperature sensor, and controlling the speed of the transport belt.
[0007]
[Problems to be solved by the invention]
However, the above conventional example has the following problems.
In the speed control of the transport belt based on the temperature detected by only one transport belt drive roller temperature sensor, appropriate control is not performed on the transport belt because the amount of color shift variation varies depending on the ambient temperature.
[0008]
Further, the color misregistration caused by the above factors can be reduced by executing the color misregistration correction. However, the color misregistration correction operation requires a certain amount of downtime (print operation interruption time). In order to reduce the downtime, the color shift correction operation is not performed until a certain amount of color shift variation occurs. Therefore, appropriate color misregistration correction has not always been performed for color misregistration occurring between the operation of color misregistration correction and the next operation.
[0009]
Therefore, the present invention solves the above-described problems, and provides a color image forming apparatus capable of correcting a high-accuracy color shift with respect to a color shift occurring between a color shift correction operation and the next color shift correction operation. The purpose is to provide.
[0010]
[Means for Solving the Problems]
The invention according to claim 1, wherein a plurality of image forming units, and a transfer means provided corresponding to the plurality of image forming units, wherein the endless belt or the endless belt sequentially passing through the plurality of image forming units A first temperature detecting means for detecting a temperature of a first heat source in the color image forming apparatus having a transfer means for transferring onto a recording material conveyed while being held on a belt. A second temperature detecting means for detecting a temperature of a second heat source different from the first heat source, and a speed adjustment amount corresponding to the detected temperatures of the first and second temperature detecting means. Speed control means for controlling a moving speed of the endless belt based on the speed.
[0011]
In claim 1, the first heat source may be any one of an image forming unit during image formation, a conveying unit for conveying an endless belt, and an endless belt driving roller.
[0012]
3. The rotational speed of the endless belt driving roller according to claim 2, wherein the speed control means reduces the correction amount when the difference between the detected temperature fluctuations of the first and second temperature detecting means is large as compared with the case where the difference is small. Can be controlled.
[0013]
The invention according to claim 4, wherein the plurality of image forming units and transfer means provided corresponding to the plurality of image forming units, wherein the endless belt or the endless belt sequentially passing through the plurality of image forming units A first temperature detecting means for detecting a temperature of a first heat source in the color image forming apparatus having a transfer means for transferring onto a recording material conveyed while being held on a belt. A second temperature detecting means for detecting a temperature of a second heat source different from the first heat source, and detecting a temperature of the first and second temperature detecting means at the time of color misregistration correction. Speed control means for controlling a moving speed of the endless belt based on a corresponding speed adjustment amount.
[0014]
5. A means for forming a pattern for detecting a displacement on an endless belt according to claim 4, a detecting means for detecting a pattern for detecting a displacement formed on the endless belt by the forming means, Calculating means for calculating a positional shift amount of the detected color with respect to the reference color from a detection result of the pattern for detecting the positional shift by the means.
[0015]
In claim 4, the first heat source may be any one of an image forming unit during image formation, a conveying unit for conveying an endless belt, and an endless belt driving roller.
[0016]
7. The endless belt driving roller according to claim 6, wherein the speed control means reduces the correction amount when the difference between the detected temperatures of the first and second temperature detecting means at the time of color misregistration correction is smaller than when the difference is large. Rotation speed can be controlled.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0018]
<First embodiment>
FIG. 1 shows a first embodiment of the present invention. This is an example of a color image forming apparatus having image forming means for four colors, that is, yellow (Y), magenta (M), cyan (C), and black (K), and the structure is shown in FIG. .
[0019]
Referring to FIG. In FIG. 2, reference numeral 1 denotes a photosensitive drum for forming an electrostatic latent image (a, b, c, and d indicate Y, M, C, and K, respectively); and 2, a photosensitive drum that performs exposure according to an image signal Reference numeral 1 denotes a laser scanner for forming an electrostatic latent image, 3 denotes an intermediate transfer belt for sequentially transferring and conveying the toner image formed on the photosensitive drum 1, and 4 denotes an intermediate transfer belt which is connected to driving means (not shown) including a motor and gears. A belt driving roller 5 for driving the transfer belt 3 is rotated by the movement of the intermediate transfer belt 3, and a belt driven roller for applying a constant tension to the intermediate transfer belt 3. , A paper cassette, 8 a fixing unit for melting and fixing the toner image transferred on the paper by heat, and 9 a double-sided surface for reversing the front and back of the paper for printing on both sides of the paper. unit Reference numeral 10 denotes a flapper for switching a transport path when a sheet is sent to the duplex unit 9. Reference numeral 11 denotes a pair of lights provided on both sides of the intermediate transfer belt for detecting a color misregistration detection pattern formed on the intermediate transfer belt 3. A sensor 12a is a belt drive roller temperature sensor that detects the surface temperature of the drive roller 4, and 13a is an environment sensor that detects the temperature inside the printer. Arrows indicate the flow of sheet conveyance.
[0020]
Referring to FIG. In FIG. 1, reference numerals 12a and 13a denote the same parts as in FIG. 14 is a CPU that controls and manages the entire apparatus, 15 is a host I / F unit that controls communication between the printer and the PC, 16 is a memory that stores print data, various parameters, various information, and the like, and 17 is sent from the PC to the printer. An image control unit for converting the print data into data suitable for the printer engine system, a sensor control unit for detecting the state of each unit of the printer, and a drive control for actuators, laser, high voltage power supply and the like of the printer engine. A drive control unit 101 is an interface unit for connecting the belt drive roller temperature sensor 12a and the environment sensor 13a to the CPU 14. When print data is sent from the PC to the printer through the host I / F unit 15, the image control unit 17 completes data conversion suitable for the printer engine system, and the data is held in the memory 16 and becomes ready for printing. The drive control unit 19 starts driving the photosensitive drum 1 and the intermediate transfer belt 3 connected to driving means including a motor and gears (not shown). Next, the image signal of each color is sent to the laser scanner 2 of each color, an electrostatic latent image is formed on the photosensitive drum 1, the toner is developed by a developing unit (not shown), and the image is transferred onto the intermediate transfer belt 3 by a transfer unit (not shown). Is transferred to In FIG. 2, images are sequentially formed in the order of Y, M, C, and K. At the same time, the paper is supplied from the paper cassette 7 to the secondary transfer roller 6 in synchronization with the image position on the intermediate transfer belt 3 and the toner image is transferred onto the paper. It is fixed on the top and discharged outside. The inside of the apparatus is monitored by the sensor control unit 18, and the whole is controlled by the CPU 14.
[0021]
FIG. 3 shows an example of the relationship between time and the amount of temperature fluctuation. In FIG. 3, reference numeral 22a denotes a relationship between time and a detected temperature fluctuation amount of the belt driving roller temperature sensor 12a, and reference numeral 22b denotes a relation between time and a detected temperature fluctuation amount of the environment sensor 13a.
[0022]
FIG. 4 shows an example of the relationship between time and the amount of color shift. The relationship between time and the amount of color shift is not necessarily linear. However, since the present invention can be applied regardless of whether it is linear or not, this embodiment will be described on the assumption that the relationship between time and the amount of color shift is linear.
[0023]
FIG. 5 shows an example of the relationship between the temperature and the amount of color misregistration. As a result of the image forming operation, the temperature inside the apparatus rises due to the operation of the fixing device 8 and motors, circuits, and the like (not shown) (inside temperature rise). When the intermediate transfer belt 3 is warmed by the fixing device 8, the temperature of the belt driving roller 4, the belt driven roller 5, and the secondary transfer roller 6 around which the intermediate transfer belt 3 is suspended rises. Since the belt drive roller temperature sensor 12a detects the surface temperature of the belt drive roller 4, the temperature rise immediately after the start of the image forming operation is rapid (fast), and thereafter shows a gradual rise (FIG. 3, 22a). ). The surface of each roller is covered with a thin rubber layer, and the thickness of the rubber layer increases as the temperature rises. When the diameter of the belt driving roller 4 increases, the speed of the intermediate transfer belt 3 increases, and color misregistration occurs. In order to reduce the color shift due to the temperature fluctuation, it is necessary to add an appropriate speed correction amount corresponding to the temperature fluctuation of the belt driving roller to the speed of the belt driving motor (not shown) as the speed correction. On the other hand, the environment sensor 13a is separated from the intermediate transfer belt 3, the optical unit 2, a driving unit having a motor (not shown), and a driving circuit, and the temperature rise is slow (slow) during the image forming operation (FIG. 3, 22b).
[0024]
When the temperature rise is rapid, a time lag occurs before the color shift varies due to the heat capacity (thermal time constant) of the belt drive roller 4, and the color shift corresponding to the temperature detected by the belt drive roller temperature sensor 12 a is reduced. A small amount of color shift occurs. If the temperature rise is gradual, there is no time lag until the color misregistration changes, so that a color misregistration amount corresponding to the temperatures detected by the belt drive roller temperature sensor 12a and the environment sensor 13a is generated.
[0025]
Further, even in the same image forming operation, the relationship between the amount of temperature fluctuation and the amount of color shift fluctuation differs depending on the installation environment of the apparatus. When the temperature of the device installation environment is high (high temperature environment), the temperature of the device at the start of the image forming operation is high, so the temperature rise inside the device is small (slow), and when the temperature of the device installation environment is low (low temperature environment), the image formation is performed. Since the temperature of the device at the start of operation is low, the temperature inside the machine rises greatly (fast).
[0026]
Next, the speed correction of the belt driving roller will be described with reference to FIG. T1 is the current temperature detected by the belt driving roller temperature sensor 12a, T1old is the temperature detected by the previous belt driving roller temperature sensor 12a, T2 is the current temperature detected by the environment sensor 13a, and T2old is the temperature detected by the previous environment sensor 13a. It is held in the memory 16. REF1 indicates a threshold for determining whether the temperature of the environment sensor 13a rises rapidly or slowly. The detection of the temperature and the determination of the threshold are executed by the CPU 14 via the sensor control unit 18.
[0027]
At the start of the image forming operation, the detected temperature T1old of the belt drive roller temperature sensor 12a and the detected temperature T2old of the environment sensor 13a are stored in the memory 16 (S601). Thereafter, the detection temperature T1 of the belt driving roller temperature sensor 12a and the detection temperature T2 of the environment sensor 12b are sequentially detected, and the detection of the belt driving roller temperature sensor 12a is performed between the color misregistration correction operation and the next color misregistration correction operation. It is determined whether or not the temperature fluctuation amount T1-T1old of the temperature T1 is ± 1 ° C. or more (S602).
[0028]
If T1-T1old does not exceed ± 1 ° C., the detection temperature T1 of the belt drive roller temperature sensor 12a is successively detected until it exceeds ± 1 ° C. On the other hand, when T1-T1old exceeds ± 1 ° C., ± REF1 is compared with the temperature fluctuation amount T2-T2old of the detected temperature T2 of the environment sensor 13a (S603).
[0029]
If T2−T2old does not exceed ± REF1, it is determined that the increase in the temperature detected by the belt drive roller temperature sensor 12a with respect to the temperature detected by the environment sensor 13a is gradual, and the temperature of the temperature detected by the belt drive roller temperature sensor 12a is determined. A speed correction of a belt drive motor (not shown) is executed using the speed correction amount f1 (T1-T1old) corresponding to the fluctuation (S604, S605, S606).
[0030]
On the other hand, if T2−T2old exceeds ± REF1, it is determined that the temperature detected by the belt drive roller temperature sensor 12a rises sharply with respect to the temperature detected by the environment sensor 13a, and the time lag of color shift variation due to heat capacity is taken into consideration. Then, the speed of the belt drive motor (not shown) is corrected using the speed correction amount 0.5 * f1 (T1-T1old) smaller than the value corresponding to the temperature fluctuation of the temperature detected by the belt drive roller temperature sensor 12a (S607, S605 and S606).
[0031]
By repeating the above determination, it is possible to correct the color misregistration with high accuracy for the color misregistration occurring between the color misregistration correction operation and the next color misregistration correction operation.
[0032]
<Second embodiment>
The color misregistration correction operation is executed at the start of the image forming operation and every time the image forming operation time elapses a predetermined time. The cause of the color shift that occurs after the color shift correction operation is not limited to the belt drive roller, but also includes some other factors, and the total thereof is generated as a color shift. The color misregistration variation occurring due to factors other than the belt driving roller after the color misregistration correction operation does not indicate the same color misregistration direction with respect to time but indicates a different variation.
[0033]
FIG. 7 shows the relationship between time and the amount of color misregistration caused by factors other than the belt driving roller. The color shift fluctuation caused by factors other than the belt driving roller differs depending on the installation state of the apparatus. FIG. 8 shows the relationship between the time and the amount of color shift including factors other than the belt driving roller.
[0034]
Therefore, the color shift variation including the factor of the belt driving roller after the color shift correction operation does not always indicate the same color shift variation direction until the temperature rises to a certain temperature, but occurs in the opposite direction (FIG. 7). ).
[0035]
At this time, if the speed of the belt driving roller is corrected in either the positive or negative color misregistration direction, when the color misregistration direction is opposite, the color misregistration amount further increases, and it cannot be said that the optimal compensation has been performed.
[0036]
Therefore, taking into account the direction of color misregistration caused by factors other than the belt driving roller, the speed of the belt driving roller is determined by the temperature difference between the temperature detected by the belt driving roller temperature sensor 12a and the temperature detected by the environment sensor 13a during color misregistration correction. By setting the correction amount to 0, optimal color shift correction is achieved.
[0037]
Next, the speed control of the belt driving roller from the color misregistration correction operation to the next color misregistration correction operation in the present embodiment will be described with reference to FIG. T1 (0) is the temperature detected by the belt drive roller temperature sensor 12a during the color misregistration correction operation, and T2 (0) is the temperature detected by the environment sensor 13a during the color misregistration correction operation, and is stored in the memory 16 (S901, S902). REF2 is a threshold value for determining the magnitude of the difference between the detected temperature T1 (0) of the belt drive roller temperature sensor 12a during the color misregistration correction operation and the detection temperature T2 (0) of the environment sensor 13a during the color misregistration correction operation. REF3 is a threshold value for determining the magnitude of the temperature rise of the temperature detected by the belt drive roller temperature sensor 12a.
[0038]
When the color misregistration correction operation is performed, the magnitude of T1 (0) -T2 (0) and ± REF2 is detected at the detected temperature T1 (0) of the belt drive roller temperature sensor 12a and the detected temperature T2 (0) of the environment sensor 13a. A comparison is made (S903). If T1 (0) -T2 (0) does not exceed ± REF2, it is determined that the image forming apparatus is in a state shortly after startup, and the temperature fluctuation T1-T1 (of the detected temperature of the belt drive roller temperature sensor 12a is determined. Until 0) exceeds ± REF3, the speed correction amount of the belt driving roller is set to 0 (S904 to S906). On the other hand, when T1 (0) -T2 (0) exceeds ± REF2, the same comparison as in the first embodiment is performed, and the speed correction amount corresponding to the temperature fluctuation of the temperature detected by the belt drive roller temperature sensor 12a is obtained. The speed of the belt drive motor (not shown) is corrected using (S601 to S607).
[0039]
<Third embodiment>
FIG. 10 shows a third embodiment of the present invention. This embodiment is different from the first and second embodiments in that, instead of the belt drive roller temperature sensor 12a and the environment sensor 13a of the first and second embodiments, each of the optical units 2 The difference is that an optical unit temperature sensor 12b for detecting the ambient temperature of the paper cassette 7 and an environment sensor 13b (different from 13a) for detecting the temperature near the paper cassette 7 are used.
[0040]
The temperature around the optical section 2 during the image forming operation is large (fast) due to the driving operation of a laser, a polygon motor, and the like (not shown). Further, when an optical component such as a lens (not shown) of the optical unit 2 is deformed due to the temperature rise, the laser irradiation position of the photosensitive drum 1 fluctuates, and a color shift occurs. Therefore, the optical section temperature sensor 12b has the same function as the belt drive roller temperature sensor 12a of the first and second embodiments.
[0041]
On the other hand, the vicinity of the paper cassette 7 is at a position where it is hard to be affected by the internal temperature rise due to the image forming operation, and the temperature rise during the image forming operation is small (slow). Therefore, the environment sensor 13b has the same function as the environment sensor 13a of the first and second embodiments. In addition, the position of the temperature sensor in the machine is not limited to the position described in the above embodiment.
[0042]
The drive roller speed correction amount based on the detected temperature difference between the two temperature sensors or the detected temperature difference fluctuation amount is not limited to the one described in the above embodiment. For example, the detected temperature fluctuation amount and the detected temperature difference or the detected temperature difference fluctuation amount may be divided into a plurality of levels, and a table value may be held.
[0043]
Further, the drive roller speed correction amount based on the detected temperature fluctuation amount of the temperature sensor is not limited to that described in the above embodiment. For example, if the detected temperature difference or the detected temperature difference fluctuation amount is large, the drive roller speed correction amount is determined according to the detected temperature fluctuation amount of one of the temperature sensors, and if the detected temperature difference or the detected temperature difference fluctuation amount is small, Alternatively, the drive roller speed correction amount may be determined according to the detected temperature fluctuation amount of the other temperature sensor.
[0044]
【The invention's effect】
As described above, according to the present invention, since the configuration is as described above, it is possible to always adjust the speed of the endless belt with a variable speed adjustment amount to adjust the color misregistration with high accuracy.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of the present invention.
FIG. 2 is a cross-sectional view illustrating a structure of the color image forming apparatus of FIG.
FIG. 3 is a diagram illustrating an example of a relationship between time and a temperature fluctuation amount.
FIG. 4 is a diagram illustrating an example of a relationship between time and a color shift amount.
FIG. 5 is a diagram illustrating an example of a relationship between a temperature and a color shift amount.
FIG. 6 is a flowchart illustrating a procedure for correcting the speed of a belt driving roller.
FIG. 7 is a diagram illustrating an example of a relationship between time and a color shift amount generated from a factor other than a belt driving roller.
FIG. 8 is a diagram illustrating an example of a relationship between a time and a color shift amount including a factor other than a belt driving roller.
FIG. 9 is a flowchart illustrating a belt drive roller speed control procedure from a color misregistration correction operation to a next color misregistration correction operation.
FIG. 10 is a block diagram showing a third embodiment of the present invention.
FIG. 11 is an explanatory diagram for explaining color misregistration.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 photosensitive drum 2 laser scanner 3 intermediate transfer belt 4 belt drive roller 6 secondary transfer roller 7 paper cassette 8 fixing device 9 double-sided unit 11 color misregistration detection sensor 12a belt drive roller temperature sensor 12b optical unit temperature sensors 13a, 13b environment sensor 101 Interface section

Claims (7)

A plurality of image forming units, and a transfer unit provided corresponding to the plurality of image forming units, wherein the transfer unit is provided on an endless belt sequentially passing through the plurality of image forming units, or while being held on the endless belt. A color image forming apparatus having a transfer unit for transferring onto a conveyed recording material,
First temperature detecting means for detecting a temperature of a first heat source in the apparatus;
A second temperature detecting means for detecting a temperature of a second heat source, which is a second heat source in the apparatus and is different from the first heat source,
A color control unit configured to control a moving speed of the endless belt based on a speed adjustment amount corresponding to a temperature detected by the first and second temperature detecting units. 2. The color image according to claim 1, wherein the first heat source is any one of the image forming unit during image formation, a conveying unit that conveys the endless belt, or the endless belt driving roller. Forming equipment. 3. The endless belt driving roller according to claim 2, wherein the speed control unit reduces the correction amount when the difference between the detected temperature fluctuations of the first and second temperature detecting units is large as compared with when the difference is small. A color image forming apparatus, wherein the rotation speed of the color image is controlled. A plurality of image forming units, and a transfer unit provided corresponding to the plurality of image forming units, wherein the transfer unit is provided on an endless belt sequentially passing through the plurality of image forming units, or while being held on the endless belt. A color image forming apparatus having a transfer unit for transferring onto a conveyed recording material,
First temperature detecting means for detecting a temperature of a first heat source in the apparatus;
A second temperature detecting means for detecting a temperature of a second heat source, which is a second heat source in the apparatus and is different from the first heat source,
A speed control unit for controlling a moving speed of the endless belt based on a speed adjustment amount corresponding to a detected temperature of the first and second temperature detecting units at the time of color misregistration correction. Forming equipment. 5. The forming means according to claim 4, wherein a pattern for detecting a displacement is formed on the endless belt.
Detecting means for detecting a pattern for detecting a displacement formed on the endless belt by the forming means;
Calculating means for calculating a positional shift amount of the detected color with respect to a reference color from a detection result of the position shift detecting pattern by the detecting means. 5. The color image according to claim 4, wherein the first heat source is any one of the image forming unit during image formation, a conveying unit that conveys the endless belt, or the endless belt driving roller. Forming equipment. 7. The endless printer according to claim 6, wherein the speed control means reduces the correction amount when the difference between the detected temperatures of the first and second temperature detecting means during color misregistration correction is smaller than when the difference is large. A color image forming apparatus for controlling a rotation speed of a belt driving roller.

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