JP2007101868A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus achieving prevention of deterioration in image quality. <P>SOLUTION: The apparatus includes; a cleaning member cleaning a member by moving while in contact with at least one of the members of a charge applying member and an electrifying control member provided in a charging apparatus, a cleaning control part making the cleaning member clean at least one of the members, a temperature sensor detecting the temperature, a fixing apparatus heating a toner image transferred on a recording medium and fixing it to the recording medium, a temperature sensor detecting the temperature of the fixing apparatus, and a cleaning action permitting part. The cleaning action permitting part; forbids the action of the cleaning member when the detected result by a humidity sensor indicates humidity which is a given value or more and the detected result by the temperature sensor indicates temperature which is less than a given value and permits the action of the cleaning member when the detected result by the humidity sensor indicates humidity which is less than the given value or the detected result by the temperature sensor indicates the temperature which is the given value or more. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is arranged opposite to an image carrier and generates a charge imparted to the image carrier, and is disposed between the image carrier and the charge imparting member. The present invention relates to an image forming apparatus including a charger having a charge control member that controls charging of an image carrier.

  Conventionally, an electrostatic latent image formed on the surface of an image carrier on which an electrostatic latent image is formed by being charged and exposed while moving in a predetermined direction is developed with toner to obtain a toner image. An image forming apparatus is known that forms an image composed of a fixed toner image on a recording medium by finally transferring and fixing the image onto the recording medium.

  In such an image forming apparatus, a charge imparting member that is disposed opposite to the image carrier and generates a charge to be imparted to the image carrier, and disposed between the image carrier and the charge imparting member. In addition, there is a charger that includes a charging control member that controls charging of the image carrier by the charge imparting member, and the surface of the image carrier is charged by the charger.

  As for the image forming apparatus including the charger as described above, a proposal has been made to clean these constituent members every time the number of printed sheets reaches a certain value (for example, see Patent Document 1).

By the way, in an image forming apparatus in which a long time has passed with the power off, there is a high possibility that rust and discharge products are attached to each component of the charger. It can be considered that these members have been cleaned.
Japanese Patent Laid-Open No. 3-274667

  However, since the discharge product has a characteristic of easily containing moisture, if this cleaning is performed under high humidity, the discharge product dropped on the photoconductor by this cleaning becomes low resistance by containing moisture. Therefore, the toner image of that portion is not transferred onto the recording paper at the time of transfer, so that so-called white spots may occur and the image quality may deteriorate.

  On the other hand, if the image forming apparatus is placed in a low humidity environment, even if these members are cleaned before the start of the job, However, it has been reported that streaks that appear to be caused by charging failure appear in the image as the operating time becomes longer, although no white spots are observed.

  In view of the above circumstances, an object of the present invention is to provide an image forming apparatus in which deterioration of image quality is suppressed.

In order to achieve the above object, the first image forming apparatus of the image forming apparatus of the present invention comprises:
The electrostatic latent image formed on the surface of the image carrier on which the electrostatic latent image is formed by being charged and exposed while moving in a predetermined direction is developed with toner to obtain a toner image. In an image forming apparatus for forming an image composed of a fixed toner image on a recording medium by transferring and fixing to the recording medium,
A charge imparting member disposed opposite to the image carrier and generating a charge imparted to the image carrier, and disposed between the image carrier and the charge imparting member. A charger having a charge control member for controlling charging of the carrier;
A cleaning member that moves in contact with at least one of the charge imparting member and the charge control member to clean the member;
A cleaning control unit that moves the cleaning member and causes the cleaning member to clean the at least one member;
Humidity sensor to detect humidity,
A fixing device for heating and fixing the toner image transferred onto the recording medium onto the recording medium;
A temperature sensor that detects the temperature of the fixing device; and a detection result by the humidity sensor indicates a humidity that is equal to or higher than a predetermined value, and a detection result by the temperature sensor indicates a temperature that is lower than a predetermined value. The operation of the cleaning member is prohibited when the operation of the cleaning member is prohibited and the detection result by the humidity sensor indicates a humidity less than a predetermined value, or the detection result by the temperature sensor indicates a temperature not less than the predetermined value. And a cleaning operation permission / rejection section that permits the cleaning.

  In the first image forming apparatus of the present invention, since the time has not passed since the apparatus was turned on, it is highly possible that the dehumidifying effect due to the increase in the apparatus internal temperature due to the turning on of the apparatus is not yet expected. Is less than the predetermined value and is currently in a humidity environment that is equal to or higher than the predetermined value, a large amount of discharge products containing a large amount of moisture have been obtained after the device has been turned off for a long time. Assuming that the discharge product does not fall on the surface of the image carrier by performing cleaning, it is considered that cleaning is prohibited and the water content of the discharge product is low. When the humidity is lower than a predetermined value, or when the temperature of the fixing device is higher than a predetermined value where a dehumidifying effect can be expected due to an increase in the temperature inside the apparatus when the power is turned on, cleaning is permitted. Therefore, according to the first image forming apparatus of the present invention, it is possible to suppress the occurrence of so-called white spots due to the discharge product containing a large amount of water falling on the surface of the image carrier and to suppress the deterioration of the image quality. it can.

To achieve the above object, the second image forming apparatus of the image forming apparatus of the present invention comprises:
The electrostatic latent image formed on the surface of the image carrier on which the electrostatic latent image is formed by being charged and exposed while moving in a predetermined direction is developed with toner to obtain a toner image. In an image forming apparatus for forming an image composed of a fixed toner image on a recording medium by transferring and fixing to the recording medium,
A charge imparting member disposed opposite to the image carrier and generating a charge imparted to the image carrier, and disposed between the image carrier and the charge imparting member. A charger having a charge control member for controlling charging of the carrier;
A cleaning member that moves in contact with at least one of the charge imparting member and the charge control member to clean the member;
A cleaning control unit that moves the cleaning member and causes the cleaning member to clean the at least one member;
Humidity sensor to detect humidity,
A timer that counts the time elapsed since the power is turned on to the image forming apparatus, and the detection result by the humidity sensor indicates a humidity equal to or higher than a predetermined value, and the timing result by the timer indicates a time within a predetermined time. Prohibits the operation of the cleaning member, and the operation of the cleaning member is performed when the detection result by the humidity sensor represents a humidity less than a predetermined value, or when the time measurement result by the timer is other than the predetermined time. And a cleaning operation permission / rejection section that permits the cleaning.

  In the second image forming apparatus of the present invention, there is a high possibility that the dehumidifying effect due to the increase in the temperature inside the apparatus due to power-on is not yet expected. If the device is in a humidity environment, it is assumed that a large amount of discharge products containing a large amount of moisture have adhered to the charger after a long power-off period. Implementation of cleaning is prohibited so that these discharge products do not fall on the surface of the image carrier, and the moisture content of the discharge products is considered to be low. When the dehumidifying effect accompanying the rise in the internal temperature can be expected and the time from power-on is a predetermined time or more, the cleaning is permitted. Therefore, according to the second image forming apparatus of the present invention, it is possible to suppress the occurrence of so-called white spots due to the discharge product containing a large amount of moisture falling on the surface of the image carrier and to suppress the deterioration of the image quality. it can.

In order to achieve the above object, a third image forming apparatus of the image forming apparatus of the present invention includes:
The electrostatic latent image formed on the surface of the image carrier on which the electrostatic latent image is formed by being charged and exposed while moving in a predetermined direction is developed with toner to obtain a toner image. In an image forming apparatus for forming an image composed of a fixed toner image on a recording medium by transferring and fixing to the recording medium,
A charge imparting member disposed opposite to the image carrier and generating a charge imparted to the image carrier, and disposed between the image carrier and the charge imparting member. A charger having a charge control member for controlling charging of the carrier;
A cleaning member that moves in contact with at least one of the charge imparting member and the charge control member to clean the member;
A cleaning control unit that moves the cleaning member and causes the cleaning member to clean the at least one member; and a humidity sensor that detects humidity;
The cleaning control unit increases the frequency of movement of the cleaning member by the cleaning member when the detection result by the humidity sensor indicates a humidity less than a predetermined value, compared to when the detection result indicates a humidity of a predetermined value or more. It is characterized by being.

  Since the resistance value of the image carrier becomes higher as the humidity becomes lower, it is necessary to increase the output of the charger in order to impart a predetermined amount of charge to the image carrier. The higher the output of the charger, the easier it is for the discharge product to be generated and it will be more likely to adhere to the charger. Therefore, in the third image forming apparatus of the present invention, the movement frequency of the cleaning member when the humidity is less than the predetermined value is increased as compared with the case where the humidity is equal to or higher than the predetermined value. Therefore, according to the third image forming apparatus of the present invention, it is possible to suppress the charging failure due to the discharge product adhering to the charger and to suppress the deterioration of the image quality.

  According to the image forming apparatus of the present invention, it is possible to suppress deterioration in image quality.

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is a schematic view showing an embodiment of the first image forming apparatus of the present invention.

  The printer 1 of the present embodiment shown in FIG. 1 is based on image data transmitted to the surface of a photoconductor 10 that has been given a predetermined charge by a charger 11 and rotates in the direction of arrow A. The electrostatic latent image is formed by irradiating the exposure light generated in 12, the formed electrostatic latent image is developed with toner stored in the developing device 13, and the toner image obtained by this development is converted into a paper tray 16. Is a monochrome image dedicated machine that forms an image on a recording sheet by transferring it by a transfer unit 14 onto a recording sheet that has been pulled out by the sheet conveying unit 16a and conveyed in the direction of arrow B, and fixing by a fixing unit 15. .

  In FIG. 1, a tungsten wire 111 plated with gold and generating a charge to be applied to the photoconductor 10, which is a component of the charger 11, is disposed between the photoconductor 10 and the tungsten wire 111. A stainless steel mesh 112 for controlling charging of the photosensitive member 10 by the wire 111, a cover 113, a first cleaner 111a for tungsten wire, and a second cleaner 112a for mesh are shown.

  FIG. 1 shows a state in which a temperature sensor 151 for detecting the temperature of the fixing device 151 is disposed in the fixing device 15. Since the photosensitive member 10 is a member extending from the far side to the near side in FIG. 1, the tungsten wire 111, the mesh 112, and the cover 113 are also placed from the far side to the near side in FIG. It is extended.

  2 and 3 are schematic configuration diagrams of the charger shown in FIG.

  As shown in FIG. 2, in addition to the components shown in FIG. 1, the charger 11 includes a first cleaner 111 a fixed via a first arm 1141 and a second cleaner 112 a fixed via a second arm 1142. A frame 114, a motor 115 having a rotating shaft 115a attached to the frame 114, and a pinion 1151 attached to the rotating shaft 115a of the motor 115 are arranged on the upper surface of the cover of the charger 11. The rack 116 is a constituent element. 2 also shows a humidity sensor 17 that is disposed on the frame 114 and detects the humidity around the charger, and an electric cord 115b of the motor 115.

  FIG. 3 shows a case where the frame 114 is viewed in the direction of the arrow C shown in FIG. 2, where the first cleaner 111 a and the second cleaner 112 a are fixed by the rotation of the motor 115. 3 shows that the rack 116 is engaged with the pinion 115a attached to the rotating shaft 115a of the motor 115 so that the frame 114 can move in the left-right direction in FIG.

  In this printer 1, by rotating the motor 115, the frame 114 to which the first cleaner 111 a and the second cleaner 112 a are fixed moves in the left-right direction in FIG. 3, so that the discharge adhered to the tungsten wire 111 and the mesh 112. Products and the like can be cleaned. In FIG. 3, the cover 113 is not shown in order to avoid complexity. Further, the frame 114 is sandwiched between guide members (not shown), so that the frame 114 can be smoothly moved in the left-right direction in FIG.

  FIG. 4 is a control block diagram of the printer of this embodiment.

  In FIG. 4, a control unit 20 that controls the entire printer 1, a counter 21 that counts the total number of prints in the printer 1, and a motor control unit 22 that controls the rotation of a motor 115 that is a component of the charger 15. A humidity sensor 17 for detecting the humidity around the charger 11 and a temperature sensor 151 for detecting the temperature of the fixing device 15 are shown. 4 shows an electric cord 115b that connects the motor control unit 22 and a motor 115 (not shown).

  In the printer 1 of the present embodiment, when the detection result by the humidity sensor 17 represents a humidity having a relative humidity (RH) of 65% or more and the detection result by the temperature sensor 151 represents a temperature of less than 50 ° C. The operation instruction to the motor 15 is not made. This is because it is highly likely that the dehumidifying effect due to the rise in printer temperature due to power-on has not yet been expected since the time has not elapsed since the printer was turned on, and the temperature of the fixing device 15 is less than 50 ° C. Currently, when the device is in a humidity environment of RH 65% or more, a large amount of discharge product containing a large amount of water adheres to the charger because the device has been subjected to a long power-off period. When the cleaning is prohibited so that these discharge products do not fall on the surface of the photosensitive member by cleaning, the moisture content of the discharge products is considered to be low, and the humidity is less than RH 65%. Alternatively, if the temperature of the fixing unit 15 is 50 ° C. or higher where a dehumidifying effect can be expected due to an increase in the temperature in the printer when the power is turned on, cleaning is permitted. Therefore, according to the printer 1 of the present embodiment, it is possible to suppress the occurrence of so-called white spots due to the discharge product containing a large amount of moisture falling on the photoreceptor, and to suppress the deterioration of the image quality.

  FIG. 5 is a flowchart of a routine executed when the power is turned on in the control unit of the printer according to the present embodiment.

  In step S1 shown in FIG. 5, it is determined whether or not the detection result by the humidity sensor 17 is 65% RH or more. If it is determined that the detection result is 65% RH or more, the process proceeds to step S2, and in step S2, the detection by the temperature sensor 151 is performed. It is determined whether the result is 50 ° C. or higher. If it is determined in step S1 that it is less than 65% RH, the process proceeds to step S3. If it is determined in step S2 that the temperature is less than 50 ° C., the process returns to step S1. If it is determined that the temperature is 50 ° C. or more, the process proceeds to step S3, and whether or not the number of prints since the previous cleaning has exceeded 100 is determined. Determine. If it is determined in step S3 that the number is less than 100, the process returns to step S1, and if it is 100 or more, the process proceeds to step S4 to perform cleaning, and then returns to step S1.

  In the embodiment described above, since the time has not passed since the printer was turned on, the fixing device temperature is considered to have a high possibility that the dehumidification effect due to the increase in the printer internal temperature due to the power supply is not yet expected. Although an example in which the humidity contained in the discharge product is set to 65% RH or higher with the amount of water that reduces the image quality being set to less than 50 ° C. has been described, the present invention has not so much time elapsed since the printer was turned on. If the fixing device temperature is such that it is highly likely that the dehumidification effect due to the rise in printer temperature due to power-on is still not expected, the temperature is not limited to less than 50 ° C, and the amount of moisture that lowers the image quality is discharged. If contained in the product, the humidity is not limited to 65% RH or more.

  Next, an embodiment of the second image forming apparatus of the present invention will be described.

  The difference between the printer of this embodiment and the printer 1 which is an embodiment of the first image forming apparatus is that, in the printer 1, the detection result by the humidity sensor 17 is a relative humidity (RH) of 65% or more. In the printer according to the present embodiment, the humidity is indicated and the operation instruction to the motor 15 is not given when the detection result by the temperature sensor 151 indicates a temperature lower than 50 ° C. When the detection result of 17 indicates that the relative humidity (RH) is 65% or more and the elapsed time from turning on the power measured by the timer is less than the predetermined time, the operation instruction to the motor 15 is not made. The schematic configuration diagram of the printer according to the present embodiment and the schematic configuration diagram of the charger provided in the printer according to the present embodiment are shown in FIGS. It is shown and described since the same figure is omitted.

  FIG. 6 is a control block diagram of the printer of this embodiment.

  The difference between the control block diagram of the printer of the present embodiment shown in FIG. 6 and the control block diagram of the printer 1 shown in FIG. 4 is that the temperature sensor 151 shown in FIG. It is a point that has been replaced.

  In the printer according to the present embodiment, the timer 23 measures the elapsed time since the power is turned on, and is currently in a humidity environment of 65% RH or more and is dehumidified due to an increase in the printer internal temperature due to the power being turned on. If it is less than 10 minutes after power-on, there is a high possibility that the effect has not yet been expected. This printer has gone through a long power-off period, so that a large amount of discharge products containing a large amount of moisture are charged. Assuming that the discharge product does not fall on the surface of the photosensitive member by cleaning, the cleaning is prohibited and the moisture content of the discharge product is considered to be low. If it is less than% RH, or if the dehumidifying effect can be expected as the printer temperature rises when the power is turned on, and the time from turning on the power is more than 10 minutes, To allow. Therefore, according to the printer of this embodiment, it is possible to suppress the occurrence of so-called white spots due to the discharge product containing a large amount of moisture falling on the surface of the photoreceptor, and to suppress the deterioration of the image quality.

  FIG. 7 is a flowchart of a routine executed when the power is turned on in the control unit of the printer according to the present embodiment.

  In step S11 shown in FIG. 7, it is determined whether or not the detection result by the humidity sensor 17 is 65% RH or more. If it is determined that the detection result is 65% RH or more, the process proceeds to step S12. It is determined whether or not is 10 minutes or more. If it is determined in step S11 that it is less than 65% RH, the process proceeds to step S13. If it is determined in step S12 that it is less than 10 minutes, the process returns to step S11, and if it is determined that it is 10 minutes or more, the process proceeds to step S13, and whether or not the number of prints since the previous cleaning has exceeded 100 is determined. Determine. If it is determined in step S13 that the number is less than 100, the process returns to step S11, and if it is 100 or more, the process proceeds to step S4, cleaning is performed, and then the process returns to step S11.

  In the embodiment described above, the timer time for which there is a high possibility that the dehumidifying effect due to the rise in the printer internal temperature due to power-on is still not expected is set to less than 10 minutes, and the amount of moisture that reduces the image quality is set to the discharge product. Although the present invention has been described with reference to an example in which the humidity included is 65% RH or more, the present invention can be used as long as it is possible to determine that there is a high possibility that the dehumidifying effect due to the increase in printer temperature due to power-on is not yet expected. It is not limited to less than 10 minutes, and the humidity is not limited to 65% RH or more as long as the discharge product contains a water content that reduces image quality.

  Finally, an embodiment of the third image forming apparatus of the present invention will be described.

  The schematic configuration diagram of the printer of the present embodiment, the schematic configuration diagram of the charger provided in the printer of the present embodiment, and the control block diagram of the printer of the present embodiment are shown in FIGS. Since it becomes the same figure as FIG. 4, illustration and description of these are omitted.

  Since the resistance value of the photoconductor becomes higher as the humidity becomes lower, in order to give a predetermined charge to the surface of the photoconductor, it is necessary to increase the output of the charger as compared to when the humidity is high. The higher the output of the charger, the easier it is to generate and the easier it is to adhere to the charger.

  In the printer according to the present embodiment, the cleaning frequency when the humidity is less than 40% RH is increased as compared with the case where the humidity is 40% RH or more. To suppress image quality degradation.

  FIG. 8 is a flowchart of a routine that is executed when the printer of this embodiment is turned on.

  In step S21 shown in FIG. 8, it is determined whether or not the detection result by the humidity sensor 17 is less than 40% RH. If it is determined in step S21 that it is less than 40% RH, the process proceeds to step S22 and the previous cleaning is performed. It is determined whether or not the number of prints since the execution has exceeded 50. If it is determined in step S21 that it is 40% RH or more, the process proceeds to step S23, and it is determined whether or not the number of prints since the previous cleaning has exceeded 100. If it is determined in step S22 that the number of prints has not exceeded 50, the process returns to step S21. If it is determined that the number of prints has exceeded 50, the process proceeds to step S24 to instruct execution of cleaning. Then, it returns to step S21. If it is determined in step S23 that the number of printed sheets does not exceed 100, the process returns to step S21. If it is determined that the number of printed sheets exceeds 100, the process proceeds to step S24.

  In the embodiment described above, an example is given in which the resistance value of the image carrier is less than 40% RH, which imposes an output on the charger that causes discharge organisms to adhere to the charger so as to degrade the image quality. As described above, the present invention is not limited to this as long as the humidity imposes an output on the charger, which causes discharge organisms that deteriorate image quality to adhere to the charger.

1 is a schematic view showing an embodiment of a first image forming apparatus of the present invention. It is a schematic block diagram of the charger shown in FIG. It is a schematic block diagram of the charger shown in FIG. It is a control block diagram of the printer of this embodiment. 4 is a flowchart of a routine that is executed when power is turned on in the control unit of the printer according to the embodiment. It is a control block diagram of the printer of this embodiment. 4 is a flowchart of a routine that is executed when power is turned on in the control unit of the printer according to the embodiment. 4 is a flowchart of a routine that is executed when power is turned on to the printer of the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer 11 Charger 111 Tungsten wire 111a 1st cleaner 112 Mesh 112a 2nd cleaner 113 Cover 114 Frame 115 Motor 1151 Pinion 115a Rotating shaft 115b Electric cord 116 Rack 15 Fixing device 151 Temperature sensor 17 Humidity sensor 20 Control part 21 Counter 22 Motor Control unit 23 Timer

Claims (3)

The electrostatic latent image formed on the surface of the image carrier on which the electrostatic latent image is formed by being charged and exposed while moving in a predetermined direction is developed with toner to obtain a toner image. In an image forming apparatus for forming an image composed of a fixed toner image on a recording medium by transferring and fixing to the recording medium,
A charge-providing member that is disposed opposite to the image carrier and generates a charge to be imparted to the image carrier, and is disposed between the image carrier and the charge-providing member, and the image by the charge-giving member A charger having a charge control member for controlling charging of the carrier;
A cleaning member that moves in contact with at least one of the charge imparting member and the charge control member to clean the member;
A cleaning control unit that moves the cleaning member to cause the cleaning member to clean the at least one member;
Humidity sensor to detect humidity,
A fixing device for heating and fixing the toner image transferred on the recording medium onto the recording medium;
A temperature sensor that detects a temperature of the fixing device; and a detection result by the humidity sensor indicates a humidity that is a predetermined value or more, and a detection result by the temperature sensor indicates a temperature that is less than a predetermined value. The operation of the cleaning member is prohibited when the operation of the cleaning member is prohibited and the detection result by the humidity sensor represents a humidity less than a predetermined value, or the detection result by the temperature sensor represents a temperature of the predetermined value or more. An image forming apparatus comprising a cleaning operation permission / rejection unit that permits The electrostatic latent image formed on the surface of the image carrier on which the electrostatic latent image is formed by being charged and exposed while moving in a predetermined direction is developed with toner to obtain a toner image. In an image forming apparatus for forming an image composed of a fixed toner image on a recording medium by transferring and fixing to the recording medium,
A charge-providing member that is disposed opposite to the image carrier and generates a charge to be imparted to the image carrier, and is disposed between the image carrier and the charge-providing member, and the image by the charge-giving member A charger having a charge control member for controlling charging of the carrier;
A cleaning member that moves in contact with at least one of the charge imparting member and the charge control member to clean the member;
A cleaning control unit that moves the cleaning member to cause the cleaning member to clean the at least one member;
Humidity sensor to detect humidity,
A timer that counts the elapsed time from power-on to the image forming apparatus, and a detection result by the humidity sensor indicates a humidity that is equal to or greater than a predetermined value, and a timing result by the timer indicates a time within a predetermined time. Prohibits the operation of the cleaning member, and if the detection result by the humidity sensor represents a humidity less than a predetermined value, or the time measurement result by the timer is other than the predetermined time, the operation of the cleaning member An image forming apparatus comprising a cleaning operation permission / rejection unit that permits The electrostatic latent image formed on the surface of the image carrier on which the electrostatic latent image is formed by being charged and exposed while moving in a predetermined direction is developed with toner to obtain a toner image. In an image forming apparatus for forming an image composed of a fixed toner image on a recording medium by transferring and fixing to the recording medium,
A charge-providing member that is disposed opposite to the image carrier and generates a charge imparted to the image carrier, and is disposed between the image carrier and the charge-providing member, and the image formed by the charge-providing member. A charger having a charge control member for controlling charging of the carrier;
A cleaning member that moves in contact with at least one of the charge imparting member and the charge control member to clean the member;
A cleaning control unit that moves the cleaning member to cause the cleaning member to clean the at least one member, and a humidity sensor that detects humidity;
The cleaning control unit increases the frequency of movement of the cleaning member by the cleaning member when the detection result by the humidity sensor indicates a humidity less than a predetermined value than when the detection result indicates a humidity by a predetermined value or more. What is claimed is: 1. An image forming apparatus comprising:

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