JP2002311690A - Electrifier, process cartridge and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrifier by which the occurrence of the halftone lateral stripe image of an electrifying roller cycle due to leaving pressing/ abutting is prevented with an inexpensive configuration without separately providing an abutment/estrangement driving device for an electrifying roller. SOLUTION: In the electrifier to electrifying the surface of a photoreceptor drum 101 at a fixed potential by applying voltage to the electrifying roller 102 in contact with a photoreceptor drum (an image carrier) 101, an electrifying roller abutting/estranging member 120 to make the electrifying roller 102 abut and estrange on/from the photoreceptor drum 10 by linking with the rotating driving of the photoreceptor drum 101 is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device, a process cartridge having the same, and an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, a corona charger has been used as a charging device for electrophotography. In recent years, however, a contact charging device has been put into practical use instead of a corona charger. This is intended for low ozone and low power, and among them, a roller charging method using a conductive roller as a charging member is particularly widely used because it is preferable in terms of charging stability.

[0003] In the roller charging method, a conductive elastic roller is brought into pressure contact with a double charged body, and a voltage is applied thereto to charge the charged body by discharging. Specifically, a DC voltage obtained by adding the required photoconductor surface potential Vd to the discharge start voltage (about 550 V when the charging roller is pressed against the OPC photoconductor) is applied. DC charging method in which charging is performed by a DC voltage having a peak-to-peak voltage that is at least twice the discharge start voltage in a DC voltage corresponding to the photoconductor surface potential Vd required for the purpose of improving fluctuations in potential due to environmental and endurance fluctuations. There is an AC charging method in which charging is performed by applying a voltage on which an AC component is superimposed to a contact charging member.

However, even in this contact roller charging method, the elastic roller functions when the image forming apparatus is not operating because the elastic roller functions while being brought into contact with and pressed against the photosensitive drum which is the charged object. If it is left in contact with the drum and pressurized, and more strictly, if the left environment is a high-temperature and high-humidity environment, the contact part of the elastic roller will be distorted, causing shape deformation and increase in resistance. In some cases, a horizontal stripe image having a roller cycle is generated in a halftone image or the like.

Heretofore, with respect to the generation of the charging roller cyclic horizontal stripe image, measures have been taken such as improving the charging roller and minimizing the pressure applied to the charging roller while maintaining the balance with the floating of the charging roller.

[0006]

However, in response to recent demands for higher image quality and higher speed in the market, multi-gradation images in which charging unevenness is more easily picked up are frequently used, and the charging ability of the charging roller is required to increase the speed. When it became impossible to catch up, a horizontal streak appeared on the image even with the same level of contact and pressure. On the other hand, as shown in FIG. 8, a contact / separation driving device 140 for the charging roller 102 is separately provided, and the charging roller 102 is separated from the photosensitive drum 101 by the contact / separation driving device 140 during non-image formation. The contact / separation driving device 140 causes the charging roller 102 to move the charging roller 102
There is a countermeasure example of contacting the contact.

However, even in the above countermeasures, the contact / separation drive device 140 is required separately in addition to the rotation drive device of the photosensitive drum 101 and the paper conveyance drive device, which increases the cost. In addition, there is a problem that it is difficult to mount the charging roller 102 and the photosensitive drum 101 and the like in a process cartridge which is housed integrally and is detachable from the image forming apparatus.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide a charging roller contact / separation driving apparatus which does not separately provide a charging roller contact / separation driving device. An object of the present invention is to provide a charging device, a process cartridge, and an image forming apparatus that can prevent the generation of a halftone horizontal stripe image with an inexpensive configuration.

[0009]

In order to achieve the above object, according to the first aspect of the present invention, the surface of the image bearing member is charged to a constant potential by applying a voltage to a charging roller contacting the image bearing member. The charging device is characterized in that a mechanism is provided for turning ON / OFF or abutting / separating pressing of the charging roller against the image carrier in conjunction with rotation driving of the image carrier.

According to a second aspect of the present invention, in the first aspect of the invention, the image bearing member is rotated at a predetermined timing to separate the charging roller.

According to a third aspect of the present invention, in the second aspect of the present invention, the charging roller is turned on or abutted on the image carrier during normal rotation of the image carrier to rotate the image carrier. It is characterized in that the charging roller is pressed off or separated from the image carrier at the time of reverse rotation of the rotation of the body.

According to a fourth aspect of the present invention, in the second or third aspect of the present invention, the timing at which the image bearing member is rotationally driven to turn off or separate the charging roller is turned off when the power is turned off or when the power is turned off. After a certain period of time.

According to a fifth aspect of the present invention, in the second or third aspect of the present invention, the timing for rotating the image bearing member to turn off or separate the charging roller by a predetermined time after the image forming operation is performed. It is characterized by having.

According to a sixth aspect of the present invention, in the second or third aspect of the present invention, the timing at which the image bearing member is rotationally driven to turn off or separate the charging roller is shifted to a sleep mode or a sleep mode. It is characterized by being a certain time after the transition.

According to a seventh aspect of the present invention, in the second or third aspect of the present invention, the timing at which the image bearing member is rotationally driven to turn off or separate the charging roller is determined when a jam occurs or when a jam occurs. After a certain period of time.

According to an eighth aspect of the present invention, in the second or third aspect of the present invention, the timing at which the image carrier is rotationally driven to turn off or separate the charging roller from the time when a user's instruction is issued is set. It is characterized by having done.

According to a ninth aspect of the present invention, in accordance with the second or third aspect of the present invention, the timing at which the image bearing member is rotationally driven to turn off or separate the pressure of the charging roller is determined by the timing of the charging from the image forming apparatus. It is characterized by taking out the device.

According to a tenth aspect of the present invention, there is provided a charging device for charging a surface of an image carrier to a constant potential by applying a voltage to a charging roller contacting the image carrier. Pressing the charging roller against the image carrier or contacting the charging roller during rotation, and pressing off the charging roller against the image carrier during reverse rotation of the image carrier.
Alternatively, a mechanism for performing separation is provided.

According to an eleventh aspect of the present invention, there is provided a process cartridge comprising: the charging device according to any one of the first to ninth aspects;
It is characterized in that at least the image carrier is integrally accommodated and is configured to be detachable from the image forming apparatus main body.

According to a twelfth aspect of the present invention, the process cartridge houses the charging device of the tenth aspect and at least the image carrier integrally, and is configured to be detachable from the image forming apparatus main body. And

According to a thirteenth aspect of the present invention, there is provided a charging device for charging a surface of an image bearing member to a constant potential by applying a voltage to an image bearing member and a charging roller contacting the image bearing member. In an image forming apparatus having an exposure unit that records an electrostatic latent image on an image carrier, and a developing unit that develops the electrostatic latent image on the image carrier with a developer, the charging roller applies a charge to the image carrier. A feature is provided in which a mechanism for turning ON / OFF or contacting / separating the pressurization in conjunction with the rotational driving of the image carrier is provided.

According to a fourteenth aspect of the present invention, there is provided a charging device for charging a surface of an image bearing member to a constant potential by applying a voltage to an image bearing member and a charging roller contacting the image bearing member. In an image forming apparatus having an exposure unit that records an electrostatic latent image on an image carrier and a developing unit that develops the electrostatic latent image on the image carrier with a developer, the rotation of the image carrier is positive. A mechanism is provided that turns on or abuts the charging roller against the image carrier during rotation, and turns off or separates the pressure of the charging roller against the image carrier during reverse rotation of the rotation of the image carrier. It is characterized by the following.

According to a fifteenth aspect of the present invention, there is provided a charging device for charging a surface of an image carrier to a constant potential by applying a voltage to an image carrier and a charging roller in contact with the image carrier. An exposure unit for recording an electrostatic latent image on the image carrier, and a developing unit for developing the electrostatic latent image on the image carrier with a developer. ON / OFF of pressure or contact /
A mechanism is provided to perform the separation in conjunction with the rotation drive of the image carrier,
The image bearing member is rotated at a predetermined timing to turn off or separate the pressure of the charging roller.

According to a sixteenth aspect of the present invention, in the invention according to the fifteenth or sixteenth aspect, the charging roller is pressurized on or abutted on the image carrier at the time of forward rotation of the image carrier. It is characterized in that the charging roller is pressed off or separated from the image carrier at the time of reverse rotation of the rotation of the image carrier.

According to a seventeenth aspect of the present invention, in the invention according to the fifteenth or sixteenth aspect, the timing at which the image carrier is rotationally driven to turn off or separate the charging roller is turned off when the power is turned off or when the power is turned off. After a certain period of time.

According to an eighteenth aspect of the present invention, in the invention of the fifteenth or sixteenth aspect, the timing at which the image bearing member is driven to rotate to turn off or separate the charging roller is fixed for a predetermined time after the image forming operation. It is characterized by having.

According to a nineteenth aspect of the present invention, in the invention according to the fifteenth or sixteenth aspect, the timing for rotating the image carrier to turn off or separate the charging roller by pressing the sleep mode is changed to a sleep mode or a sleep mode. It is characterized by being a certain time after the transition.

According to a twentieth aspect of the present invention, in the invention according to the fifteenth or sixteenth aspect, the timing at which the image carrier is rotationally driven to turn off or separate the charging roller is pressurized or jammed. It is characterized by being a certain time after the time.

According to a twenty-first aspect of the present invention, in the invention of the fifteenth or sixteenth aspect, the timing at which the image carrier is rotationally driven to turn off or separate the pressure of the charging roller is determined when a user's instruction is issued. It is characterized by having done.

According to a twenty-second aspect of the present invention, in the invention according to the fifteenth or sixteenth aspect, the timing at which the image bearing member is rotationally driven to turn off or separate the pressure of the charging roller is determined by the image forming apparatus. It is characterized by taking out the charging device.

[0031]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIG. 1 is a schematic sectional view of a laser printer as an image forming apparatus according to the present invention, and FIG. 2 is an enlarged view of a charging roller portion of the laser printer.

The image forming apparatus (laser printer) according to the present embodiment is connected to a host such as a personal computer or a workstation (not shown), and receives an image via a video interface in response to a print request from the host. Receive data. Based on this image data, the image forming apparatus according to the present embodiment uses image data separated into four colors of yellow (Y), magenta (M), cyan (C), and black (K) in the same manner as in the related art. A toner image of each color is sequentially formed, and the toner images are superimposed on an intermediate transfer member and collectively transferred to a transfer material 107 such as paper to obtain a full-color image.

In FIG. 1, reference numeral 101 denotes a predetermined peripheral speed (8
0 mm / s) is a photosensitive drum (a photosensitive layer formed of an organic photosensitive material on an aluminum cylinder having an outer diameter of 100 mm) as a first image carrier that is driven to rotate in the direction of arrow A at 0 mm / s). The surface is a charging roller 10 serving as charging means.
2 is uniformly charged to about -600 V.

Next, scanning is performed by the exposure unit 103, which is ON / OFF controlled in accordance with the image data of the first color (Y), and an electrostatic latent image of the first color is formed on the photosensitive drum 101. (The exposed portion potential is about -100 V). The first-color electrostatic latent image is developed by the first developing unit 104a including the first-color Y toner (polarity-), and is visualized as a first toner image.

Then, the visualized first toner image is
A second image that is pressed against the photosensitive drum 101 as the first image carrier with a predetermined pressing force and is driven to rotate in the direction of arrow B at a speed (80 mm / s) substantially equal to the peripheral speed of the photosensitive drum 101. The intermediate transfer member 105 serving as a support member (a surface layer of a conductive elastic layer made of NBR rubber or the like formed on an aluminum cylinder having a releasable surface layer made of urethane resin in which carbon, fluorine resin, etc. is dispersed, and having a resistance value of 10 ⁵ ~
^The transfer is performed (primary transfer) on the surface of the intermediate transfer member 105 at a nip portion of about ¹⁰ Ω · cm and an outer diameter of 153 mm. At this time, a voltage V1tr (+100 V) uniquely set in advance and having a polarity opposite to the toner charging polarity (−) is applied to the intermediate transfer member 105. 1
The toner remaining on the photosensitive drum 101 without being transferred at the time of the next transfer is scraped off by a cleaning blade 108, which is a cleaning unit pressed against the photosensitive drum 101, and collected in a waste toner container 109.

Thus, the above steps are performed for the remaining three colors (M,
C, K) is repeated in the same manner, and each time, the second
Are electrostatically transferred to the surface of the intermediate transfer member 105 and sequentially laminated by toner images of developers of different colors included in the developing unit 104b, the third developing unit 104c, and the fourth developing unit 104d. A color image is formed. A nip of the color image is formed between an intermediate transfer member 105 and a transfer roller 106 serving as a detachable transfer unit that is pressed against the intermediate transfer member 105 at a predetermined timing and rotated at a speed substantially equal to the peripheral speed of the intermediate transfer member 105. The transfer is performed collectively (secondary transfer) on the surface of the transfer material 107 conveyed from the paper supply unit. At this time, the transfer roller 106 is
A voltage Vtr (+1000 V) uniquely set in advance with a polarity opposite to the charging polarity of the toner is applied.

Thereafter, the transfer material 107 is conveyed to the fixing means 112, and the four color toner images are permanently fixed to the transfer material 107, and the transfer material 107 on which the toner images are fixed is discharged out of the apparatus from the paper discharge unit. A desired print image is obtained.

The toner remaining on the intermediate transfer member 105 without being transferred at the time of the secondary transfer is subjected to charge polarity control by a toner charge control member (not shown).
5 and the photosensitive drum 101 due to a potential difference between the photosensitive drum 10 and the photosensitive drum 101.
The toner is returned to the first side, is scraped off by a cleaning blade 108 disposed on the photosensitive drum 101, and is collected in a waste toner container 109.

The photosensitive drum 101 and the charging roller 10
2. Cleaning blade 108, waste toner container 109
In addition, a charging roller contacting / separating member 120 described later is a single process cartridge (photosensitive drum cartridge) 110.
Is configured to be detachable from the image forming apparatus main body. Each of the yellow (Y), magenta (M), cyan (C), and black (K) developing means 104 (104
a, 104b, 104c, and 104d) can be separately replaced as one process cartridge (developing cartridge) depending on the degree of consumption.

As shown in detail in FIG. 2, the charging roller 102 includes a metal shaft 102a and a base layer 1 made of a sponge material.
02b and the surface high resistance layer 102c, and the bearing member 1
The photosensitive drum 101 is pressed against the photosensitive drum 101 via a pressing spring 124 via the reference numeral 23. The pressurizing spring 124 is connected to the charging roller 1.
02 is adjusted so that the total contact pressure against the photosensitive drum 101 becomes 1.0 kgf. Also, the charging roller shaft 102a
A charging roller contacting / separating member 120 for contacting / separating the charging roller 102 is rotatably attached to the charging roller shaft 102a. At the tip of the charging roller contacting / separating member 120, a projection 121 that meshes with gear portions 122 provided at both longitudinal ends of the photosensitive drum 101.
Is provided.

Next, the contact / separation operation of the charging roller 102 in conjunction with the rotation drive of the photosensitive drum 101 by the charging roller contact / separation member 120 constituting the gist of the present invention is shown in FIG.
It will be described based on.

When the rotation of the photosensitive drum 101 is stopped at the time of non-image formation or the like, the charging roller contact / separation member 120 is moved to the position shown in FIG.
As shown in (a), the charging roller 102 is arranged in parallel with the pressing direction of the charging roller 102 (home position). At this time, since the charging roller 102 is pressed in the direction opposite to the pressing direction, it is approximately They are separated by an interval of 0.5 mm.

At the time of image formation or the like, the photosensitive drum 101
When driven in the direction, the gear 1 of the photosensitive drum 101 and the protrusion 1
21, the charging roller contact / separation member 12
0 is the axis 10 of the charging roller 102 as shown in FIG.
It rotates around arrow 2a in the direction of arrow A '. Then, the influence of the charging roller contacting / separating member 120 supporting the shaft 102a of the charging roller 102 is eliminated, and the charging roller 10
2 is pressed against the photosensitive drum 101 with a predetermined amount of pressing force by a pressing spring 124.

The photosensitive drum 101 at the end of image formation or the like
When the rotation of the photosensitive drum 101 is stopped, the image forming apparatus reversely rotates the photosensitive drum 101 in the direction of arrow B in FIG. 3C by a predetermined amount, and the gear 122 of the photosensitive drum 101 and the protrusion at the tip of the charging roller contact / separation member 120. Due to the engagement of 121, the charging roller contacting / separating member 120 is rotated in the direction of arrow B 'in the drawing to return to the home position, and a state is created in which the charging roller 102 is separated from the photosensitive drum 101 by about 0.5 mm.

According to the above configuration, the charging roller 102 does not come into contact with the photosensitive drum 101 except when the photosensitive drum 101 needs to be charged, so that a halftone horizontal stripe image of the charging roller cycle caused by leaving is generated. Can be prevented.

In addition to the conventional structure in which the contact and separation of the charging roller 102 are not performed, the photosensitive drum 1
01 and the charging roller contact / separation member 120
Therefore, the configuration can be made very inexpensive and simple as compared with the case where a contact / separation drive device for the charging roller is separately provided, and introduction into the process cartridge 110 having such a configuration is also easy.

Second Embodiment Next, a second embodiment of the present invention will be described.

FIG. 4 is an enlarged view of a charging roller portion of the laser printer according to the present embodiment. Note that the image forming process of the laser printer according to the present embodiment is the same as that of the first embodiment, and the description thereof will not be repeated.

Also, as in the first embodiment, the photosensitive drum 1
01, charging roller 102, cleaning blade 10
8. Waste toner container 109 and charging roller pressurization described later ON
The / OFF member 125 is detachably configured as one process cartridge (photosensitive drum cartridge) 110 with respect to the image forming apparatus.

In the first embodiment, the contact and separation operations of the charging roller 102 are performed in conjunction with the rotation of the photosensitive drum 101. In the present embodiment, the charging roller 1
In the same manner, a mechanism for turning ON / OFF (increase / decrease of pressurizing force) 02 pressurization in conjunction with the rotation driving of the photosensitive drum 101 is provided.

As in the first embodiment, the charging roller 102 has a metal shaft 102a and a base layer 102 made of a sponge material.
b and the surface high-resistance layer 102c.
, And is pressed against the photosensitive drum 101 by a pressure spring 124. The pressure spring 124 is supported by a pressure spring support member 127.
Reference numeral 27 denotes a cam 1 of the charging roller pressing ON / OFF member 125.
28, the charging roller 102 is controlled to the pressure ON position or the pressure OFF position, and the total contact pressure of the charging roller 102 against the photosensitive drum 101 is 1.0 kgf at the pressure ON position and 0.5 kg at the pressure OFF position.
It is adjusted to be 3 kgf or less.

The charging roller pressure ON / OFF member 125 for turning ON / OFF the pressure of the charging roller 102 is rotatably mounted on the photosensitive drum cartridge frame. This charging roller pressing ON / OFF member 125
A protrusion 126 is provided at the end of the photosensitive drum 101 so as to mesh with the gear portions 122 provided at both longitudinal ends of the photosensitive drum 101. The position of the pressure spring support member 127 is set on the rotation axis of the charging roller pressure ON / OFF member 125. A controlling cam 128 is provided. Reference numeral 129 denotes a positioning member that determines the home position of the charging roller pressing ON / OFF member 125. The positioning member 129 causes the charging roller pressing ON / OFF member 125 to be unnecessarily upstream due to the reaction force of the pressing spring 124. Prevents side rotation.

Next, the pressing ON / OF of the charging roller 102 in conjunction with the rotation driving of the photosensitive drum 101 by the charging roller pressing ON / OFF member 125 constituting the gist of the present invention.
The F operation will be described with reference to FIG.

When the rotation of the photosensitive drum 101 is stopped during non-image formation or the like, the charging roller pressurizing ON / OFF member 125 moves in the rotation direction of the photosensitive drum 101 (direction of arrow A) as shown in FIG. It is arranged (home position) on the upstream side of the charging roller 102, and at this time, the pressing spring support member 127 is
5 is controlled to the pressure OFF position by the cam 128, and the total contact pressure of the charging roller 102 with the photosensitive drum 101 is 0.3 kgf or less.

On the other hand, when the photosensitive drum 101 is driven to rotate in the direction of arrow A during image formation or the like, the gear portion 122 of the photosensitive drum 101 and the charging roller pressing ON / OFF member 125
Due to the engagement of the protrusion 126 at the tip, the charging roller pressure O
As shown in FIG. 5B, the N / OFF member 125 rotates in the direction of the arrow A ″ downstream of the charging roller 102 with respect to the rotation direction of the photosensitive drum 101 (the direction of the arrow A).
The pressure spring support member 127 is a charging roller pressure ON / OFF.
The pressure is turned on by the cam 128 of the member 125, and the total contact pressure of the charging roller 102 against the photosensitive drum 101 is increased to 1.0 kgf.

The photosensitive drum 101 at the end of image formation or the like
When the rotation of the photosensitive drum 101 is stopped, the image forming apparatus reversely rotates the photosensitive drum 101 by a predetermined amount, and the gear unit 1 of the photosensitive drum 101 is rotated.
22 and the charging roller pressing ON / OFF member 125 engage with the projection 126 at the tip thereof, so that the charging roller pressing ON / OFF
The F member 125 is rotated to the upstream side with respect to the rotation direction of the photosensitive drum 101 (direction of arrow A) to return to the home position, the charging roller 102 is pressed off the photosensitive drum 101, and the total contact pressure is zero. A state of contact at 3 kgf or less is created.

With the above configuration, the charging roller 102 contacts the photosensitive drum 101 with an extremely light pressure that does not affect the contacting and leaving of the photosensitive drum 101 except when the photosensitive drum 101 needs to be charged. It is possible to prevent the occurrence of the halftone horizontal stripe image of the charging roller cycle due to the occurrence.

In addition to the conventional structure in which the contact and separation of the charging roller 102 are not performed, the photosensitive drum 1
01, the charging roller 122, the charging roller pressing ON / OFF member 125, and the pressing spring support member 127. Therefore, the configuration is very inexpensive and simple as compared with a separate device for driving the contact and separation of the charging roller. The introduction into the process cartridge 110 having such a configuration is also easy.

<Third Embodiment> Next, a third embodiment of the present invention will be described.

FIG. 6 is an enlarged view of the charging roller portion of the laser printer according to the present embodiment. Note that the image forming process of the laser printer according to the present embodiment is the same as that of the first embodiment, and the description thereof will not be repeated.

In the second embodiment, the operation of turning off the pressure of the charging roller 102 is performed by the reverse rotation of the photosensitive drum 101, whereas in the present embodiment, the rotation of the photosensitive drum 101 is automatically stopped when the rotation of the photosensitive drum 101 is stopped. A mechanism for turning off the pressure is provided.

As in the first embodiment, the charging roller 102 has a metal shaft 102a and a base layer 102 made of a sponge material.
b and the surface high resistance layer 102c, and is supported by the charging roller guide 134 so as to be movable in the normal direction of the photosensitive drum 101. In the vicinity of the charging roller 102, a planetary gear 130 supported by a gear shaft guide 133 movably in a tangential direction of the photosensitive drum 101 and a fixed shaft 132 rotatably supported are arranged. The shaft 130a of the gear 130 and the shaft 10 of the charging roller 102
2a and the fixed shaft 132 are pulled inward by the tension of the elastic belt 131, and the shafts 130a, 1
The rotation driving force is transmitted by friction between the elastic belts 02a and 132 and the inside of the elastic belt 131. In the present embodiment, the outer diameter of the shaft 102a of the charging roller 102 and the outer diameter of the shaft 130a of the planetary gear 130 are equal to 6 mm, the outer diameter of the charging roller 102 is set to 14 mm, and the outer diameter of the planetary gear 130 is set to 10 mm.

Next, the planetary gear 130 which is a feature of the present invention is described.
The pressurizing ON / OFF operation of the charging roller 102 in conjunction with the rotation of the photosensitive drum 101 by the elastic belt 131 will be described with reference to FIG.

When the rotation of the photosensitive drum 101 is stopped during non-image formation or the like, the planetary gear 130 is moved with respect to the rotation direction (the direction of arrow A) of the photosensitive drum 101 by the tension of the elastic belt 131 as shown in FIG. It is in a state of being moved to the upstream side (the side close to the charging roller 102) of the gear shaft guide 133. At this time, the tension of the elastic belt 131 is loose, the force in the normal direction of the photosensitive drum 101 for pressing the charging roller 102 against the photosensitive drum 101 is weakened, and the total contact pressure of the charging roller 102 with the photosensitive drum 101 is reduced to 0.1. 3kgf
It is as follows.

On the other hand, when the photosensitive drum 101 is driven to rotate in the direction of arrow A during image formation or the like, the charging roller 102 receives drive from the surface of the photosensitive drum 101 as shown in FIG. The planetary gear 130
Rotates in the A ″ ″ direction due to engagement with the gear portion 122 of the photosensitive drum 101. At this time, the surface speed of the charging roller 102 and the surface speed of the planetary gear 130 are substantially the same, but since their outer diameters are different, their respective rotational speeds are different. As a result, the shafts 102a, 102e, 1
The surface speed 30a of the shaft 130a of the planetary gear 130 is larger than that of the shaft 102a of the charging roller 102.

However, since the rotational drive of the shafts 102a and 130a is transmitted by friction with the elastic belt 131, the shaft 130a of the planetary gear 130 rotates under the influence of the shaft 102a of the charging roller 102 having a low rotational speed. The force is applied in the direction opposite to the direction A "". Therefore, the planetary gear 13
0 is hard to rotate, and is moved to the downstream side (far side from the charging roller 102) of the gear shaft guide 133 with respect to the rotation direction of the photosensitive drum 101 (direction of arrow A) in a form dragged by the rotation of the photosensitive drum 101. As a result, the elastic belt 131 is stretched, and the tension is applied to the charging belt 102.
Receives a force in the normal direction of the photosensitive drum 101 along the charging roller guide 134 and is pressed against the photosensitive drum 101.
At this time, the elasticity of the elastic belt 131, the movable amount of the planetary gear 130, and the like are adjusted such that the total pressure of the charging roller 102 abutting on the photosensitive drum 101 becomes 1.0 kgf.

Thereafter, at the end of image formation or the like, the photosensitive drum 1
When the rotation of the planetary gear 01 stops, the planetary gear 130 again
As shown in (a), the elastic belt 131 moves the photosensitive drum 101 toward the upstream side (the side closer to the charging roller 102) of the gear shaft guide 133 with respect to the rotation direction (the direction of the arrow A) of the photosensitive drum 101. Roller 102 to photosensitive drum 1
The force applied to the photosensitive drum 101 in the normal direction of the photosensitive drum 101 is also weakened, and the pressing of the charging roller 102 on the photosensitive drum 101 is automatically released.

With the above configuration, the charging roller 102 comes into contact with the photosensitive drum 101 with an extremely light pressure that does not have an effect of being left in contact with the photosensitive drum 101 except when the photosensitive drum 101 needs to be charged. In the same manner as in the second embodiment, it is possible to prevent the occurrence of a halftone horizontal stripe image of the charging roller cycle due to leaving.

Similarly, it is not necessary to separately provide a contact / separation drive device for the charging roller, and it is necessary to reversely drive the photosensitive drum 101 to release the pressure of the charging roller 102 as in the second embodiment. Therefore, the present invention is effective for an image forming apparatus in which the reverse rotation driving mechanism of the photosensitive drum is omitted for simplifying the drive system of the photosensitive drum.

<Fourth Embodiment> Next, a fourth embodiment of the present invention will be described.

Since the configuration of the charging device according to the present embodiment is the same as that of the first embodiment, the following description will be made with reference to FIGS. 2 and 3.

The charging roller 102 interlocked with the rotation driving of the photosensitive drum 101 by the charging roller contact / separation member 120
Will be described. First, when the photosensitive drum cartridge 110 is mounted, the charging roller contact / separation member 120 is moved to the charging roller 10 as shown in FIG.
2, the charging roller 102 is pressed in a direction opposite to the pressing direction, so that the charging roller 102 is
Are separated from each other at an interval of about 0.5 mm. afterwards,
When the photosensitive drum 101 is driven to rotate in the direction of arrow A during an initial sequence, image formation, or the like, the gear portion 122 of the photosensitive drum 101 engages with the projection 121 at the tip of the charging roller contacting / separating member 120 to cause the charging roller contact. The contact / separation member 120 rotates in the direction of arrow A 'about the axis 102a of the charging roller 102 as shown in FIG. Then, the effect of the charging roller contact / separation member 120 supporting the shaft 102a of the charging roller 102 is eliminated, and the charging roller 102 is pressed against the photosensitive drum 101 by the pressing spring 124 with a predetermined amount of pressing force. And is in a state suitable for the charging operation.

After the end of the image forming operation, the image forming apparatus starts counting the elapsed time after the image formation by the time counting means, and the print request by the user is not made for a certain time or more (set to one hour in the present embodiment). Then, the photosensitive drum 101 is reversely rotated by a predetermined amount in the direction of arrow B in FIG. 3C, and the gear portion 122 of the photosensitive drum 101 and the protrusion 121 at the tip of the charging roller contacting / separating member 120 engage with the charging roller. The contact / separation member 120 is rotated in the direction of arrow B ′ in the figure to return to the home position,
02 creates a state separated from the photosensitive drum 101 by about 0.5 mm.

In the present embodiment, after the image forming operation is completed, the operation timing for bringing the charging roller 102 into a state of being separated from the photosensitive drum 101 is not limited to a time after a predetermined time has elapsed since the image forming operation is completed. (When the power switch of the image forming apparatus main body is turned off, the image forming apparatus rotates the photosensitive drum 101 by a predetermined rotational speed,
When the power supply of the image forming apparatus is completely turned off, when a jam occurs (when a jam occurs, the image forming apparatus
1 is rotated counterclockwise after a predetermined rotation, the process proceeds to a jam processing standby state). When the photosensitive drum cartridge 110 is removed (when the user presses the photosensitive drum cartridge replacement door access switch to remove the photosensitive drum cartridge 110, image formation is performed). The apparatus rotates the photosensitive drum 101 by a predetermined number of times and then reversely rotates the photosensitive drum cartridge, and then opens and closes a photosensitive drum cartridge replacement door. When an instruction is issued by a user (the operation panel of the image forming apparatus displays the charging roller And a switch for performing the separation are provided).

With the above configuration, when the photosensitive drum 101 needs to be charged, the charging roller 1 is automatically rotated.
No. 02 is in a state suitable for the charging process operation.
In a case where the charging roller 102 is left in pressure contact with the photosensitive drum 101 for a long time, for example, the charging roller 102 does not contact the photosensitive drum 101. Can be prevented.

Further, as an additional member, a photosensitive drum 1
01 and the charging roller contact / separation member 120
Therefore, the configuration can be made very inexpensive and simple as compared with the case where a contact / separation drive device for the charging roller is separately provided, and introduction into the process cartridge 110 having such a configuration is also easy.

<Fifth Embodiment> Next, a fifth embodiment of the present invention will be described.

The configuration of the charging device according to the present embodiment is the same as that of the charging device according to the second embodiment, and will be described below with reference to FIGS.

The charging roller pressurization ON /
The pressurization ON / OFF operation of the charging roller 102 in conjunction with the rotation driving of the photosensitive drum 101 by the OFF member 125 will be described with reference to FIG.

First, when the photosensitive drum cartridge 101 is mounted, the charging roller pressurizing ON / OFF member 125 moves upstream of the charging roller 102 with respect to the rotating direction of the photosensitive drum 101 (direction of arrow A) as shown in FIG. Side (home position), the pressure spring support member 127 is controlled to the pressure OFF position by the cam 128 of the charging roller pressure ON / OFF member 125, and the photosensitive drum 101 of the charging roller 102. The total contact pressure is 0.
It is less than 3 kgf.

Thereafter, when the photosensitive drum 101 is driven to rotate in the direction of arrow A during an initial sequence or image formation, the gear portion 122 of the photosensitive drum 101 and the protrusion 126 at the tip of the charging roller pressing ON / OFF member 125 are formed. Due to the engagement, the charging roller pressing ON / OFF member 125 rotates in the A ″ direction downstream of the charging roller 102 with respect to the rotation direction of the photosensitive drum 101 (the direction of arrow A) as shown in FIG. Then, the pressing spring supporting member 127 is controlled to the pressing ON position by the cam 128 of the charging roller pressing ON / OFF member 125, and the total contact pressure of the charging roller 102 with the photosensitive drum 101 is increased to 1.0 kgf. As a result, the state becomes suitable for the charging operation.

After the end of the image forming operation, the image forming apparatus starts counting the elapsed time after the image formation by the time counting means, and the print request from the user is not made for a certain time or more (set to one hour in the present embodiment). Then, the image forming apparatus enters a sleep mode (power consumption saving mode) such as turning off the temperature control of the fixing device, and after a certain period of time (15 minutes as an initial setting in the present embodiment). The cooling fan is stopped, the photosensitive drum 101 is rotated in the reverse direction by a predetermined amount, and the gear portion 122 of the photosensitive drum 101 engages with the protrusion 126 at the tip of the charging roller pressing ON / OFF member 125 to turn on / off the charging roller.
The FF member 125 is moved in the rotation direction of the photosensitive drum 101 (arrow A).
Direction) to return to the home position, and as a result, the charging roller 102
Is turned off, and a contact state is created with a total contact pressure of 0.3 kgf or less.

Also, in the present embodiment, similarly to the fourth embodiment, the operation timing for turning off the charging roller 102 with respect to the photosensitive drum 101 under pressure is different from the operation timing when the power of the image forming apparatus is turned off. When a jam occurs, when the photosensitive drum cartridge 110 is removed, when an instruction is issued by a user, and the like are set.

Further, in the image forming apparatus according to the present embodiment, after the cooling fan is rotated for a certain period of time after the power is turned off, the power is turned off when the image forming apparatus is completely off. Pressurizing OF of the charging roller 102 when a cooling fan stops after a certain time has elapsed
The F operation may be performed to simplify the control program. Conversely, the same applies to the operation of pressing off the charging roller 102 in conjunction with the transition to the sleep mode.

With the above configuration, when the photosensitive drum 101 needs to be charged, the charging roller 10 is automatically rotated.
Reference numeral 2 denotes a state suitable for the charging operation, in which the charging roller 102 is in contact with the photosensitive drum 101 with an extremely light pressure such that the contact roller 102 does not have an effect of being left in contact with the photosensitive drum 101, such as when shifting to a sleep mode or when the power is turned off. For this reason, it is possible to prevent the occurrence of a halftone horizontal stripe image of the charging roller cycle due to the pressure contact and standing.

In addition to the conventional structure in which the contact and separation of the charging roller 102 are not performed, the photosensitive drum 1
01, the charging roller 122, the charging roller pressing ON / OFF member 125, and the pressing spring support member 127. Therefore, the configuration is very inexpensive and simple as compared with a separate device for driving the contact and separation of the charging roller. The introduction into the process cartridge 110 having such a configuration is also easy.

[0088]

As is apparent from the above description, according to the present invention, the charging roller contact / separation drive device is not separately provided, and the halftone horizontal rotation of the charging roller cycle caused by the pressure contact is left. The effect is obtained that the generation of a streak image can be prevented by an inexpensive configuration.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a laser printer which is an image forming apparatus according to the present invention.

FIG. 2 is an enlarged view of a charging roller portion of the laser printer according to Embodiments 1 and 4 of the present invention.

FIG. 3 is a diagram illustrating contact / separation operations of charging rollers of the laser printer according to Embodiments 1 and 4 of the present invention.

FIG. 4 is an enlarged view of a charging roller portion of the laser printer according to Embodiments 2 and 5 of the present invention.

FIG. 5 is a diagram illustrating a pressure ON / OFF operation of a charging roller of the laser printer according to Embodiments 2 and 5 of the present invention.

FIG. 6 is an enlarged view of a charging roller portion of a laser printer according to Embodiment 3 of the present invention.

FIG. 7 is a diagram illustrating a pressure ON / OFF operation of a charging roller of the laser printer according to Embodiment 3 of the present invention.

FIG. 8 is an enlarged view of a charging roller portion of a conventional image forming apparatus.

[Explanation of symbols]

 Reference Signs List 101 photosensitive drum (image carrier) 102 charging roller 103 exposing means 104 developing means 120 charging roller contacting / separating member 121 projection 122 gear portion 123 bearing member 124 pressure spring 125 charging roller pressing ON / OFF member 126 projection 127 Compression spring support member 128 Cam 129 Positioning member 130 Planetary gear 131 Elastic belt 132 Fixed shaft 133 Gear shaft guide

Continued on the front page F-term (reference) 2H027 DA29 DA32 DA38 DC14 DE07 DE09 EC06 ED02 ED03 EE02 EE05 EF06 EF12 EF16 EF17 EF18 JB20 ZA01 2H071 BA03 BA13 BA15 BA20 BA27 CA05 DA13 DA15 DA31 EA16 2H200 FA16 GA10 HA23 GA34 HB33 HB43 HB46 HB47 JC02 LA03 LA17 LA24 MA03 MB05 PA03 PA10 PA18 PB21

Claims (22)

[Claims] 1. A charging device for charging a surface of an image carrier to a constant potential by applying a voltage to a charging roller in contact with the image carrier, wherein ON / OFF of pressing of the charging roller to the image carrier. Alternatively, the charging device is provided with a mechanism for performing contact / separation in conjunction with rotation driving of the image carrier. 2. A charging device according to claim 1, wherein said image bearing member is rotated at a predetermined timing to separate said charging roller. 3. The pressure roller turns on or abuts on the image carrier when the image carrier is rotated forward when the image carrier is rotated.
3. The charging device according to claim 2, wherein the charging roller is turned off or separated from the image carrier when the image carrier is rotated in a reverse direction to the rotation of the image carrier. 4. A power supply OF which rotates the image carrier and turns off or separates the pressure of the charging roller.
The charging device according to claim 2, wherein the charging device is set at a predetermined time after the start of the operation or when the power is turned off. 5. The charging device according to claim 2, wherein the timing at which the image bearing member is rotationally driven to turn off or separate the charging roller is a predetermined time after the image forming operation. . 6. The apparatus according to claim 2, wherein the timing at which the image bearing member is rotationally driven to turn off or separate the pressure of the charging roller is set to a sleep mode transition or a fixed time after the sleep mode transition. Or the charging device according to 3. 7. The apparatus according to claim 2, wherein the timing at which the image bearing member is rotationally driven to turn off or separate the charging roller is pressurized when a jam occurs or a predetermined time after the jam occurs. The charging device as described in the above. 8. The charging device according to claim 2, wherein the timing for turning off the image bearing member and pressing off or separating the charging roller is performed when an instruction is issued from a user. 9. The image forming apparatus according to claim 2, wherein the timing at which the charging roller is pressed off or separated by rotating the image bearing member is taken out of the image forming apparatus. The charging device as described in the above. 10. A charging device for charging a surface of an image carrier to a constant potential by applying a voltage to a charging roller in contact with the image carrier, comprising: Pressing ON or contacting the image bearing member, and pressing the charging roller against the image bearing member at the time of reverse rotation of the rotation of the image bearing member.
A charging device provided with a mechanism for performing FF or separation. 11. A process characterized by accommodating the charging device according to claim 1 and at least an image carrier integrally and detachably mounted on an image forming apparatus main body. cartridge. 12. A process cartridge accommodating the charging device according to claim 10 and at least an image carrier, and being detachably attached to an image forming apparatus main body. 13. A charging device for charging a surface of an image bearing member to a constant potential by applying a voltage to an image bearing member and a charging roller in contact with the image bearing member. In an image forming apparatus having an exposure unit that records an electrostatic latent image and a developing unit that develops an electrostatic latent image on an image carrier with a developer, ON / OFF of pressing of the charging roller to the image carrier is performed. Alternatively, an image forming apparatus provided with a mechanism for performing contact / separation in conjunction with rotation driving of the image carrier. 14. A charging device for charging a surface of an image carrier to a constant potential by applying a voltage to an image carrier, a charging roller in contact with the image carrier, and a statically charged image carrier. In an image forming apparatus having an exposure unit that records an electrostatic latent image and a developing unit that develops an electrostatic latent image on an image carrier with a developer, the image forming apparatus includes a charging roller that rotates when the image carrier is rotated forward. Pressing ON or contacting the image bearing member, and pressing the charging roller against the image bearing member at the time of reverse rotation of the rotation of the image bearing member.
An image forming apparatus provided with a mechanism for performing FF or separation. 15. A charging device for charging a surface of an image carrier to a constant potential by applying a voltage to an image carrier, a charging roller in contact with the image carrier, and a statically charged image carrier. An image forming apparatus comprising: an exposure unit for recording an electrostatic latent image; and a developing unit for developing an electrostatic latent image on an image carrier with a developer. Alternatively, a mechanism for performing contact / separation in conjunction with rotation driving of the image carrier is provided, and the image carrier is rotationally driven at a predetermined timing to turn off or separate the pressure of the charging roller. Image forming device. 16. The image forming apparatus according to claim 1, wherein the charging roller is turned on or in contact with the image carrier when the image carrier is rotated forward, and the charging roller is rotated when the image carrier is rotated in reverse. The image forming apparatus according to claim 15, wherein pressurization is turned off or separated. 17. A timing for turning off the image bearing member and pressing off or separating the charging roller by a power supply O
The image forming apparatus according to claim 15, wherein the predetermined time has elapsed after the FF or when the power was turned off. 18. The image forming apparatus according to claim 15, wherein the timing at which the image bearing member is rotationally driven to turn off or separate the pressure of the charging roller is a predetermined time after the image forming operation.
Or the image forming apparatus according to 16. 19. The apparatus according to claim 15, wherein the timing at which the charging roller is pressed off or separated by rotating the image carrier is shifted to a sleep mode or a predetermined time after the shift to the sleep mode. Or the image forming apparatus according to 16. 20. The apparatus according to claim 15, wherein the timing at which the image carrier is rotationally driven to turn off or separate the pressure of the charging roller is at the time of occurrence of a jam or a predetermined time after the occurrence of the jam. 17. The image forming apparatus according to item 16. 21. The timing of turning off the image bearing member and pressing off or separating the charging roller by rotating the image carrier when an instruction from a user occurs.
Or the image forming apparatus according to 16. 22. The image forming apparatus according to claim 15, wherein the timing at which the image bearing member is rotationally driven to turn off or separate the pressure of the charging roller is when the charging device is taken out of the image forming apparatus. 17. The image forming apparatus according to item 16.