JPH09211943A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To almost uniformly press a cleaning member against the surface of an electrifying roller over all areas with proper pressurizing force. SOLUTION: At the time of executing the cleaning mode of the electrifying roller 2, a cleaning pad 25 is brought into contact with the electrifying roller 2 with the pressurizing force generated by the gravity of the cleaning pad 25 and a cleaning pad holder 27 for integrally holding the cleaning pad 25. Thus, the pressurizing force is set by the weight of the cleaning member 25 and the cleaning pad holder 27, so that the pressurizing force can be made more even than that when the cleaning member 25 is energized by using an elastic member such as a spring and the proper pressurizing force can be easily obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus provided with a charging roller that can be brought into contact with and separated from a photosensitive member, and a cleaning member that cleans the surface of the charging roller.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus having a charging device provided with a charging roller which can be brought into contact with and separated from a photosensitive member and a cleaning member for cleaning the charging roller,
For example, there is one described in JP-A-5-333670. In this image forming apparatus, a photoconductor (image carrier) is attached to a process cartridge that can be attached to and detached from the apparatus main body.
A charging roller for charging the surface thereof, a developing device, and a cleaning device for cleaning the surface of the photoconductor integrally formed, and a direction in which the core metal of the charging roller approaches and separates from the surface of the photoconductor. It is movably held in the cartridge frame.

When this process cartridge is mounted at a predetermined position on the main body of the apparatus, it is formed of a foam material such as polyurethane fixed to a projecting seat formed on the main body of the apparatus so as to correspond to the charging roller. An elastic body that also functions as a cleaning member that cleans the surface of the roller contacts the surface of the charging roller and presses it toward the photoconductor, and presses the charging roller against the surface of the photoconductor, and the charging roller rotates with the photoconductor. (Driven rotation). There is also a cleaning member that cleans the surface of the charging roller by rotating the charging roller while the pressing member is pressed against the surface of the charging roller by the urging force of a spring.

[0004]

However, when the process cartridge is mounted in the predetermined position of the apparatus body in this way, the cleaning member made of foam is compressed,
When the cleaning member is pressed against the surface of the charging roller by the reaction force generated at that time or the cleaning member is pressed against the surface of the charging roller by the urging force of the spring, the cleaning member is pressed against the charging roller. The pressure was sometimes too strong.

If the applied pressure is too strong, the minute toner that has passed through the cleaning blade of the main body cleaning device while adhering to the surface of the photoconductor adheres to the surface of the charging roller that rotates while contacting therewith, The toner is strongly rubbed against the surface of the charging roller by the cleaning member. In such a case, the toner adheres to the surface of the charging roller in a filming state, so that a charging failure occurs corresponding to the portion where the toner adheres.

On the other hand, if the cleaning member is eliminated, the surface of the charging roller becomes soiled with toner, resulting in uneven charging. Further, it is preferable that the pressing force of the cleaning member with respect to the charging roller is uniform at all positions of the cleaning member that are in contact with the charging roller, and if it is not uniform, uneven charging is likely to occur. was there.

The present invention has been made in view of the above problems, and the cleaning member can be pressed against the surface of the charging roller with an appropriate pressing force, and the pressing force is applied to the entire area of the cleaning member. The object is to make it possible to make them substantially uniform so that abnormal images such as uneven charging do not occur.

[0008]

In order to achieve the above object, the present invention provides a charging roller, a cleaning member that cleans the surface of the charging roller, and a charging roller that is brought into contact with and separated from the photosensitive member and the cleaning member. A contacting / separating mechanism, a charging mode in which the charging roller is brought into contact with the photosensitive member, a cleaning mode in which the cleaning member is brought into contact with the surface of the charging roller, and a mode in which the charging roller is separated from the photosensitive member and the cleaning member. In the image forming apparatus having the above, the cleaning member is brought into contact with the surface of the charging roller by its own weight in the cleaning mode.

By doing so, the cleaning member comes into contact with the surface of the charging roller by its own weight, and the pressure applied to the charging roller by the cleaning member is determined by the weight of the cleaning member and the member holding the cleaning member. The variation in the applied pressure (contact pressure) can be made smaller than the applied pressure when the member is biased by using an elastic member such as a spring.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of a charging portion of an image forming apparatus according to an embodiment of the present invention.
3 is a schematic diagram showing each of the two modes, FIG. 2 is a schematic configuration diagram showing the vicinity of the image forming unit of the image forming apparatus, and FIG.
Is a perspective view of the same, and FIG. 4 is a perspective view showing the vicinity of the photoconductor and the charging roller, which are also provided in the image forming unit.
In this image forming apparatus, the image forming unit is formed in a cartridge shape as shown in FIG. 2, and the image forming unit can be detachably attached to the apparatus main body (not shown).

The cartridge comprises a photosensitive member 1 and a charging roller 2 constituting a charging device in a case 6 (see FIG. 3).
The developing device 3, the cleaning device 4, and the recycle transport unit 5 for sending the residual toner collected by the cleaning device 4 to the developing device 3 are arranged so that they can be integrally removed from the main body of the device in a cartridge state. ing. As shown in FIG. 2, this cartridge allows the photosensitive member 1 to rotate in the direction of arrow A by a drive source (not shown) in a state where the cartridge is mounted at a predetermined position on the apparatus main body.

In this image forming apparatus, when the image forming operation is started, the surface of the photosensitive member 1 is discharged by discharging light L1 from the discharging lamp 49, and the surface potential is 0 to -150V. It is averaged to the reference potential. Next, a high voltage is applied to the charging roller 2 that is in contact with the surface of the photoconductor 1 to charge the photoconductor 1, and the surface potential of the photoconductor 1 is -1.
Set to around 100V. Then, the charged potential surface is irradiated with exposure L2 from the exposure section to form a latent image portion having an image surface potential of 0 to -290V.

When the latent image portion moves to the position of the developing sleeve 13 of the developing device 3 due to the rotation of the photosensitive member 1 in the direction of arrow A, the latent image portion is biased at about -800V. The toner held on the surface of the developing sleeve 13 adheres. Therefore, the latent image portion is developed into a toner image (visible image).

On the other hand, the transfer paper P is fed from a paper feed section (not shown), and the front end of the transfer paper P and the front end of the toner image on the photoconductor 1 are aligned at the position of the transfer roller 8. The timing is adjusted by the registration roller pair 7, and the photoconductor 1
The upper toner image is transferred onto the transfer paper P by the transfer roller 8. The transfer paper P is conveyed between rollers of a fixing unit (not shown), where the toner is fused to the transfer paper P by heat and pressure, and the toner is discharged to a discharge tray or the like outside the machine.

Then, the residual toner remaining on the photosensitive member 1 after the image transfer is scraped off by the cleaning blade 10 of the cleaning device 4, and the surface of the photosensitive member 1 is almost free of toner. Move to the image forming process. Further, the residual toner collected by the cleaning device 4 is transported to the recycling transport unit 5 by the toner transport coil 11, and then transported to the developer stirring unit of the developing device 3 by the recycling belt 12 to be collected and recycled. To be done. The above is the basic operation of the image forming apparatus.

The photosensitive member 1 is, for example, a laminated drum-shaped photosensitive member, and has a charge generation layer (CGL) 10 to 10 having a thickness of 0.1 to 1 μm on a conductive substrate. A charge transfer layer having a thickness of 30 μm (Carrier transport layer hereinafter abbreviated as CTL) is laminated. The light incident on the surface of the photoconductor 1 passes through the CTL having a light-transmitting property, and
Is absorbed by. In the CGL, carriers are generated by this excitation energy. The generated carriers are injected into the CTL by an external force, move in the CTL, reach the surface, and neutralize the surface charge.

As shown in FIG. 4, the charging device includes a charging roller 2, bearings 14 and 15 for supporting the charging roller 2, and bearing 1 thereof.
Pressure springs 18 and 18 before and after pressurizing 4, 15
, Charging roller drive gear 19, and cleaning pad 2
5 and a cleaning pad holder 27 for holding it
The electrode terminal 22 and the charging roller case 16 are integrally formed as a unit. The charging roller 2 includes a metal cored bar 2a and a conductive rubber 2b mounted on the outer periphery of the metal cored bar 2a. When the surface of the conductive rubber 2b is in contact with the surface of the photoconductor 1, the charging roller 2 has a high pressure. By applying a voltage, the surface of the photoconductor 1 is uniformly charged.

This image forming apparatus employs such a contact type charging roller 2 so that the amount of ozone generated is 1/100 to 1/1 as compared with the case where a conventional corona charger is used.
It can be 1000. Both ends of the cored bar 2a of the charging roller 2 are rotatably held by bearings 14 and 15, and each of the bearings 14 and 15 has vertically elongated projections 14a on both left and right sides as shown in FIG. 14a and 15a, 15a are formed, and the respective protrusions are slidably fitted in the vertically elongated guide grooves 16a respectively formed in the charging roller case 16 so as to be movable in the vertical direction. ing.

The bearings 14 and 15 and the charging roller case 1
As shown in FIG. 4, a pressure spring 18 is interposed between the inner surface 16c of the charging roller 2 and the inner surface 16c of the charging roller 2, and the charging roller 2 is pressed by the urging force of the charging roller 18 to the photoconductor 1 through the bearings 14 and 15. It can be pressed with.

The core metal 2a of the charging roller 2 is a bearing 14
The outer diameter of the portion located inside the is larger than that of the portion fitted into the bearing 14, and a part of the outer periphery thereof is processed into a flat surface to form a portion having a D-shaped cross section, A charging roller drive gear 19 having a center hole corresponding to the shape of the D-shaped portion is fitted and fixed integrally. The charging roller driving gear 19 is exposed to the photoreceptor front gear 21 fixed to one end other than the photosensitive surface of the photoreceptor 1 whose both ends are rotatably supported on the front and rear surfaces of the case 6, by which the charging roller 2 is exposed. It is adapted to engage when in contact with the surface of the body 1.

Therefore, when the photoconductor 1 rotates in the arrow A direction, the charging roller drive gear 19 rotates in the arrow B direction by the photoconductor front gear 21 rotating in the same direction, and the charge roller 2 moves in the arrow B direction. To force to rotate. In addition, the electrode terminal 22 is, when the charging device is in a predetermined set state,
It contacts the electrode terminal (not shown) of the main body side receptacle. Then, in this state, a charging voltage is applied to the electrode terminal 22 from a high voltage power source (not shown).

The electrode terminal 22 is electrically connected to the bearing 15 via the pressure spring 18 on the rear side. Since the bearing 15 is made of a conductive material,
The voltage from the high voltage power supply is applied to the charging roller 2.
On the inner surface 16 c side of the charging roller case 16, a cleaning pad 25, which is a cleaning member for cleaning the surface of the charging roller 2, is provided.
It is held so as to be movable toward and away from the photoconductor 1 while being held by 7.

That is, as shown in FIGS. 1A to 1C, the cleaning pad 25 is fixed to the lower surface of the cleaning pad holder 27 with double-sided tape or the like, and the tongue pieces 27a are provided on both side edges of the cleaning pad holder 27. , 27
As shown in FIG. 4, b are formed in two places (three or more places) at intervals along the longitudinal direction. Then, as shown in FIG. 1, the tongues 27a and 27b are fitted in the guide holes 16f and 16g formed in the charging roller case 16 so as to be vertically movable so as to correspond to the tongues 27a and 27b, respectively. Let the cleaning pad 2
The cleaning pad holder 27 and the cleaning pad holder 27 are in contact with each other by their own weight so as to come into contact with the surface of the charging roller 2.

Since the surface of the charging roller 2 can be cleaned by bringing the cleaning pad 25 into contact with the surface of the charging roller 2 as described above, the charging roller 2 is kept in contact with the photoconductor 1 during the charging operation. Body 1
The surface of the charging roller 2 is easily soiled by the minute toner adhering to the surface of the charging roller, causing uneven charging. However, by pressing the cleaning pad 25 against the surface, the surface can be cleaned to remove the toner. It is possible to prevent uneven charging caused by stains on the surface.

Further, as shown in FIG. 4, push-up springs 26, 26 are provided between both ends in the longitudinal direction of the inner surface 16c of the charging roller case 16 and spring receivers 6a, 6a formed on the front and rear surfaces of the case 6, respectively. And the charging roller case 16 is biased upward by the biasing forces. When the charging roller 2 is attached to the case 6 in the unit state described above, the left and right surfaces 16d and 16e of the charging roller case 16 are attached to the front and rear surfaces of the case 6.
To the groove portions 6b and 6c formed corresponding to
The front and rear ends of the left and right surfaces 16d and 16e of the charging roller case 16 are respectively dropped.

If the charging roller case 16 is simply dropped into the groove portions 6b and 6c of the case 6, the charging roller case 16 pushes the springs 26 and 26 forward and backward.
As a result, it is pushed upward and becomes free in the upward direction, so a stopper is required to push it from the upper side to a predetermined position suitable for charging. Therefore, in this embodiment, the role of the stopper is shown in FIG.
9 doubles. The upper cover 29 regulates the amount of upward movement of the charging roller 2 integrated with the charging roller case 16 in the unit state in the figure.

The upper cover 29 is snap-fitted (patchon stop) by fitting, for example, elastic claws formed on the case 6 (FIG. 3) into corresponding recesses formed on the upper cover 29 side. It is fixed by the fixing means. Therefore, the upper cover 29 can be operated only by hand without using any tool or the like.
It can be attached to and detached from. Therefore, when replacing the charging roller 2 in the unit state, the charging roller 2 can be removed from the case 6 together with the charging roller case 16 and the upper cover 29 by hand without using any tool or the like.

Since the charging roller case 16 has the left and right surfaces 16d and 16e only dropped into the groove portions 6b and 6c formed on the front and rear surfaces of the case 6, as described with reference to FIG. , It can be taken out from the case 6 simply by lifting it. Further, each push-up spring 26 has a spring receiver 6a on the case 6 side.
Alternatively, if a circular convex portion is formed on at least one side of the inner surface 16c on the side of the charging roller case 16 and press-fitted into the circular convex portion, the push-up spring 26 is removed when the charging roller 2 is detached as a unit. It can be prevented.

Next, the applied voltage control for changing the applied voltage applied to the charging roller 2 according to the surface temperature of the charging roller 2 will be described. In the case of performing constant voltage control in which the voltage applied to the charging roller 2 is constant, if the environmental temperature in which the charging roller 2 is placed changes, the resistance value of the charging roller 2 changes accordingly. Therefore, the surface potential of the photoconductor 1 changes.

In order to prevent this, the temperature of the surface of the charging roller 2 (or in the vicinity thereof) is detected, and a voltage corresponding to the temperature change from the reference temperature preset according to the detected temperature is applied. It is necessary to apply the corrected correction applied voltage to the charging roller 2. As a means for detecting the temperature of the surface of the charging roller 2, in this embodiment, a thermistor 31 as shown in FIG. 10 is integrally attached to the inner surface of the upper cover 29 to detect the temperature of the surface (or the vicinity) of the charging roller 2. I am able to do it.

With the thermistor 31 as described above, the charging roller 2
In the case of detecting the surface temperature of the thermistor 31, when the voltage is applied to the charging roller 2 while the thermistor 31 is in contact with the surface of the charging roller 2, the thermistor 31 and a detection circuit to which the thermistor 31 is connected (Fig. (Not shown) may be destroyed by the applied high voltage.

Therefore, in this image forming apparatus, by fixing the thermistor 31 integrally to the upper cover 29 as shown in FIG. 7, the charging roller 2 is separated from the photoconductor 1 and a voltage is applied to the charging roller 2. The thermistor 31 contacts the surface of the charging roller 2 when not in contact, and the thermistor 3 when the charging roller 2 contacts the photoreceptor 1 as shown in FIG.
1 is separated from the surface of the charging roller 2.

The thermistor 31 is adapted to come into contact with the surface of the charging roller 2 in a portion outside the maximum sheet passing width of the sheet usable in the image forming apparatus. By doing so, even if the surface of the charging roller 2 is slidably contacted by the thermistor 31 to deteriorate the surface, the image can be prevented from being affected. In addition, since the thermistor 31 is integrally fixed to the upper cover 29 as described above, the cost can be reduced because the bracket or the screw for attaching the thermistor 31 to the upper cover 29 is not required. Assembly man-hours can be reduced.

Next, the contact / separation mechanism 40 for contacting / separating the charging roller 2 with respect to the photosensitive member 1 will be described. Generally, when the charging roller is in contact with the same portion of the photoconductor for a long time in a state where the image forming operation is stopped, the contact portion of the photoconductor becomes dirty and an abnormal image is likely to occur. Therefore, when the charging roller and the photoconductor are left for a long time in this state, the charging roller needs to be separated from the photoconductor.

Therefore, in this image forming apparatus, as shown in FIG. 7, in the standby state in which the image forming operation is stopped, the charging roller case 16 is pushed up by the pushing-up spring 26 in the direction away from the photoconductor 1, and the charging roller 2 is pushed. Are separated from the photoconductor 1. Then, when the image forming operation is started, as shown in FIG.
Is brought into contact with the surface of the photoconductor 1 from the separated state, and the charging operation is performed in that state. When the predetermined image formation is completed, as shown in FIG. 6, the cleaning pad 25 is pressed against the surface of the charging roller 2 to clean the surface, and after the cleaning, the charging roller 2 is separated from the photoconductor 1.

Hereinafter, the charging roller 2 is attached to the photosensitive member 1 in this manner.
The contact / separation mechanism 40 for contacting / separating with respect to will be described. In FIG. 4, reference numeral 41 is a first pressure arm, and 42 is a second pressure arm, both of which press the upper surface of the charging roller case 16 at one end side.

The first pressure arm 41 and the second pressure arm 42 are fixed to the arm holding shaft 43 with a space therebetween at the same phase in the rotating direction, and the arm holding shaft 43 has both ends. Main body front side plate 23 and main body rear side plate 24 of the image forming apparatus
Is rotatably supported by bearings and the like. Therefore, when the arm holding shaft 43 is rotated clockwise or counterclockwise in the figure, the first and second pressing arms 4 are rotated.
1, 42 simultaneously rotate in the same direction and by the same amount.

The second pressing arm 42 has a cam contact portion 42a extending from the end opposite to the side contacting the charging roller case 16, and the lower surface of the second pressure arm 42 has an eccentric charging roller contact surface which is clearly shown in FIG. The separation cam 44 is contacted. And the second
On the upper surface of the cam contact portion 42a of the pressure arm 42, an arm pressure spring 47 is interposed between a spring holder 46 fixed to the apparatus main body and the arm pressure spring 4
The cam contact portion 42a is pressed against the charging roller contact / separation cam 44 by the biasing force of 7.

With this structure, when the charging roller contact / separation cam 44 is rotated, from the position where the charging roller contact / separation cam 44 contacts the second pressure arm 42 to the center of the shaft 45 integrally supporting the cam. The second pressure arm 42 swings in the arrow C direction along with the arm holding shaft 43 according to the distance Lc as shown in FIG. 4 fixed to the arm holding shaft 43. The first pressure arm 41 also swings in the same direction as the second pressure arm 42 by the same amount. Therefore, the first and second pressure arms 41, 4
By the swing of 2, the charging roller case 16 moves up and down.

The charging roller contact / separation cam 44 rotates 120 ° by one operation. The electromagnetic spring clutch 4 shown in FIG.
It is directly connected to the rotating shaft of 8. The electromagnetic spring clutch 48 is a clutch that uses a known magnetic force and rotates by 120 °. Briefly, a rotor is integrally fixed on a rotary shaft, and a gear is arranged in the axial direction of the same rotary shaft. It is mounted rotatably next to each other. Teeth capable of meshing are formed on the surfaces of the rotor and the gear which are opposed to each other, and when these mesh with each other, the rotor is rotated together with the rotating shaft by the gear.

A plurality of springs are interposed between the rotor and the gear, and normally the urging force causes the rotor to separate from the gear so that only the gear idles with respect to the rotating shaft. Further, a yoke is provided in the rotor, and three holes are formed in the yoke at 120 ° intervals in the rotation direction of the rotor, and pins corresponding to the holes are provided on the rotor side so as to project. ing. The pin is fitted into the hole of the yoke when the rotor is pressed toward the hole of the yoke by the urging force of the spring.

The rotor moves to the gear side by an armature that moves when the coil is excited. At the time of the movement, the pin comes out from the hole of the yoke, and the tooth portion meshes with the gear tooth. It is rotated with the rotating shaft. After that, the excitation of the coil is stopped, and the rotor rotates while the tip of the pin is pressed against the yoke surface by the spring, and at the position rotated by 120 °, the pin moves in the direction away from the gear by entering the next hole.
As a result, the meshing of the teeth that meshed with the gear of the rotor is released, and the rotor stops.

With such a structure, the rotary shaft of the electromagnetic spring clutch 48 rotates by 120 °. Therefore, the charging roller contact / separation cam 44 is rotated by 120 ° by the electromagnetic spring clutch 48 and selectively stopped at three positions during one rotation. Thereby,
The position where the charging roller case 16 is pushed down can be selected in three stages by the first and second pressure arms 41 and 42.

Specifically, the three positions are such that the cleaning pad 25 shown in FIG. 5 is separated from the surface of the charging roller 2 and the charging roller 2 is brought into contact with the photosensitive member 1 so that the photosensitive member 1 can be charged. 6 to expose the charging roller 2 shown in FIG. 9 to the first position, and the second position to make the surface of the charging roller 2 cleanable by pressing the cleaning pad 25 onto the surface of the charging roller 2 shown in FIG. It is a third position in which both the body 1 and the cleaning pad 25 are separated from each other. The shape of the charging roller contact / separation cam 44 (the cam distance Lc so as to be in each of the above three positions) so that each of the first, second and third positions can be selected.
Is set.

In this embodiment, as shown in FIG. 4, a static elimination lamp 49 is arranged so as to straddle between the first pressure arm 41 and the second pressure arm 42, and each end of the static elimination lamp 49 is made to be the first. The first pressure arm 41 and the second pressure arm 42 are integrally fixed to each other. A voltage is applied to the static elimination lamp 49 from a power source (not shown), and the static elimination lamp 49 is turned on.

As described above, in this embodiment, since the static elimination lamp 49 is directly attached to the first pressure arm 41 and the second pressure arm 42, the static elimination lamp 49 for the static elimination lamp 49 is attached to the main body of the apparatus or the like. Since it is not necessary to provide a lamp holder, the cost can be reduced accordingly. In addition,
The drive means for rotating the charging roller contact / separation cam 44 by 120 ° is not limited to the electromagnetic spring clutch 48 of the above-described embodiment, but a stepping motor is used to connect its rotation shaft to the shaft 45, and the shaft 45 is connected. The stepping motor may be rotated by the number of steps for rotating by 120 °.

Next, the operation of each part during the charging operation, the cleaning of the charging roller and the separation of the charging roller will be described respectively. <Regarding Charging Operation> In this image forming apparatus, when the apparatus main body is in a stopped state in which the image forming operation and all other operations are stopped, the charging roller 2 pushes the biasing force of the spring 26 as shown in FIG. As the charging roller case 16 is pushed up by the above, the charging roller case 16 is separated from the surface of the photoconductor 1 as shown in the figure.

At this time, the cleaning pad 25 has the cleaning pad holder 27 holding the cleaning pad 25 pushed up as shown in FIG.
Each of the tongue pieces 27a,
27b are lifted to the position shown in the figure in a state of being in contact with each other, so that they are separated from the surface of the charging roller 2.

When a copy start button (not shown) is pressed in this state, an ON signal is sent to the electromagnetic spring clutch 48 shown in FIG. 9 almost simultaneously with the pressing of the button or after a certain time has passed. The electromagnetic spring clutch 48 causes the charging roller contact / separation cam 44 to move.
Is rotated about the axis 45 in the direction of arrow E by 120 °. Also, almost at the same time as the copy start button is pressed, or after a lapse of a predetermined time, the photoconductor 1 starts rotating in the clockwise direction in the figure.

As a result, the charging roller contact / separation cam 44
Rotates 120 ° from the position of FIG. 9 to the position shown in FIG. Therefore, a portion of the charging roller contact / separation cam 44 having a distance Lc larger than that at the position in FIG. 9 comes into contact with the cam contact portion 42a of the second pressure arm 42, so that the second pressure arm 42 is moved. The arm holding shaft 43 is swung in the arrow F direction.

At this time, the second pressure arm 42 is integrated with the first pressure arm 41 via the arm holding shaft 43 as described with reference to FIG. The same amount as the pressure arm 42 is swung in the arrow F direction. As a result, the charging roller case 16 is pushed down by the ends of the first and second pressure arms 41, 42, and the front and rear bearings 14, 1 are driven by the biasing forces of the front and rear pressure springs 18.
The charging roller 2 is brought into pressure contact with the photoconductor 1 with a constant contact pressure via 5.

The charging operation is performed by applying a charging voltage to the charging roller 2 from the high voltage power source at a certain timing while the charging roller 2 is pressed against the surface of the photoreceptor 1. The surface of the photoconductor 1 is uniformly charged. At this time, since the charging roller drive gear 19 and the photoconductor front gear 21 are in mesh with each other, the charging roller 2
Is forcibly rotated in the direction of arrow B, which rotates with the photoconductor 1. Therefore, when the charging roller 2 is driven and rotated only by the frictional force received at the contact portion with the photoconductor 1, the charging roller 2 slips between the photoconductor 1 and a part thereof, and local wear occurs. By doing so, a problem such as deterioration of charging performance may occur, but such a problem can be prevented by this image forming apparatus.

During such a charging operation, as shown in FIG. 1A, the charging roller case 16 is pushed down to press the charging roller 2 against the photosensitive member 1. Since the pressing amount is small, the tongue pieces 27a, 2 of the cleaning pad holder 27 are
7b is each guide hole 16f, 16 of the charging roller case 16.
The cleaning pad 25 is still in contact with the lower edge of g, and the cleaning pad 25 is still separated from the charging roller 2. Further, as shown in FIG. 8, the thermistor 31 is located away from the surface of the charging roller 2.

<At Charging Roller Cleaning> The trailing edge of the transfer sheet when making a copy of one sheet, and the trailing edge of the transfer sheet that is conveyed last when making a copy of a plurality of sheets are at the transfer area (photoreceptor 1 in FIG. 2). Of the charging roller contact / separation cam 44 is detected by the ON signal sent to the electromagnetic spring clutch 48 shown in FIG. With the cam position at the time of the charging operation shown as a reference, the cam position is rotated by 120 ° in the direction of arrow E from that position to the position shown in FIG.

In the position of FIG. 6, the charging roller contact / separation cam 44 has a portion in which the distance Lc is larger than that in the position of FIG. 5 contacts the cam contact portion 42a of the second pressure arm 42. Therefore, the second pressure arm 42 swings further in the arrow F direction around the arm holding shaft 43,
The pressure arm 41 also swings in the F direction indicated by the arrow by the same amount. As a result, the charging roller case 16 is further pushed down from the position shown in FIG. 5 by a fixed amount corresponding to the change in the distance Lc of the charging roller contact / separation cam 44. Therefore, FIG.
As shown in FIG.
Is pressed against the surface of.

At this time, the lower surface of the cleaning pad 25 comes into contact with the surface of the charging roller 2 when the charging roller case 16 is largely pushed down, and at that time, as shown in FIG.
As shown in (b) of FIG.
The tongues 27a and 27b of the charging roller case 16 are spaced apart from the lower end edges of the guide holes 16f and 16g of the charging roller case 16 and are in a position where they are raised. Therefore, the cleaning pad 2
5 comes into contact with the surface of the charging roller 2 by a pressing force (contact pressure) generated only by its own weight plus the own weight of the cleaning pad holder 27 holding it.

Thus, in this image forming apparatus, when the charging roller 2 is in the cleaning mode, the cleaning pad 25 has its own weight and the cleaning pad 2 has its own weight.
Since the charging roller 2 is brought into contact with the charging roller 2 only by its own weight including the own weight of the cleaning pad holder 27 that holds 5, the contact pressure is more uneven than when the cleaning pad 25 is pressed by using an elastic member such as a spring. Can be very small.

That is, since the self-weights of the cleaning pad 25 and the cleaning pad holder 27 are determined by their size and thickness, it is only necessary to control the size and thickness so that they are within the predetermined manufacturing tolerances. It is possible to prevent large variations in weight from occurring. Therefore, generally, a cleaning member (pad or the like) that cleans the surface of the charging roller does not press the toner adhering to the surface of the charging roller onto the surface of the charging roller without fixing the toner in a filming state. A contact pressure with a very high accuracy (narrow tolerance width) that can be leveled uniformly and uniformity of the contact pressure at each position are required. As in this embodiment, the cleaning pad 25 and the cleaning pad holder are required. By applying a pressing force (contact pressure) with the own weight of 27, the required specifications can be sufficiently satisfied.

Specifically, in the case where the cleaning pad 25 has a pad length of 30 cm, the cleaning pad 25 and the cleaning pad 25 are uniformly cleaned over the entire area of the cleaning pad 25. The total weight of the pad holders 27 is 300-
By using a material of 900 gf, the contact pressure per unit length can be made uniform over the entire area.

Further, the variation in the density of the material forming the cleaning pad 25 and the cleaning pad holder 27 can be kept within 5%. Therefore, according to this image forming apparatus, the variation width of the contact pressure is remarkably higher than that in the case where the conventional spring or the like is used to press the cleaning member such as the cleaning pad to obtain the contact pressure with respect to the charging roller. The cleaning pad 25 can be uniformly pressed with an appropriate pressure, so that the cleaning property is improved.

During this cleaning, the charging roller drive gear 19 and the photoconductor front gear 21 shown in FIG. 4 are still in mesh with each other, so that the rotational driving force of the photoconductor 1 is forcibly transmitted to the charging roller 2. Therefore, when the cleaning pad 25 is pressed against the surface of the charging roller 2 in this way, it acts as a load on the rotation of the charging roller 2, so that the charging roller 2 has a frictional force between the photoconductor 1 and the contact portion. In the case where the charging roller 2 is rotated only by itself, the charging roller 2 may not rotate due to the load received from the cleaning pad 25 and cleaning may not be performed. However, according to this embodiment, the rotational driving force is applied to the charging roller 2. Is forcibly given, so that such a problem can be prevented.

Further, the mode for cleaning the surface of the charging roller 2 by bringing the cleaning pad 25 into pressure contact with the charging roller 2 is provided separately from the charging operation (the cleaning pad 25 is not in pressure contact). It is possible to prevent the occurrence of abnormalities such as uneven charging due to the surface of No. 2 being damaged by the cleaning pad 25.

That is, in the case where the cleaning pad 25 is in pressure contact with the charging roller 2 even during the charging operation, the cleaning pad 25 is in sliding contact while being in pressure contact with the charging roller 2 for a long time during continuous sheet feeding or the like. Since the state is continued, the surface of the charging roller 2 is easily scratched and abnormalities such as charging unevenness are likely to occur, but charging is prevented by not contacting the cleaning pad 25 with the charging roller 2 during the charging operation. It is possible to prevent uneven charging due to scratches on the surface of the roller 2.

The detection of the timing when the trailing edge of the transfer paper passes through the transfer area is performed by placing a paper detection sensor near the registration roller pair 7 shown in FIG. The timing is detected after a predetermined time after the trailing edge reaches the transfer area from the time when the trailing edge is detected.

<When the charging roller is separated> After the charging roller cleaning mode is finished, an ON signal is sent to the electromagnetic spring clutch 48 shown in FIG. 9, and the charging roller contact / separation cam 44 is moved from the position shown in FIG. At the position shown in
Further rotate 120 ° in the direction of arrow E. In this position,
The charging roller contact / separation cam 44 comes into contact with the cam contact portion 42a of the second pressure arm 42 at a portion where the distance Lc is smaller than the position during the charging operation described with reference to FIG. The pressure arm 42 swings around the arm holding shaft 43 in the direction G indicated by the arrow opposite to the above, and accordingly, the first pressure arm 41 shown in FIG. 4 also swings by the same amount in the same direction. .

As a result, the first and second pressing arms 4
9, portions of the charging roller cases 16 and 42 that come into contact with the upper surface of the charging roller case 16 are lifted, so that the charging roller case 16 is lifted upward in the figure by the urging force of the pushing springs 26, 26 on both sides shown in FIG. Therefore,
The charging roller 2 attached to the charging roller case 16 via the bearings 14 and 15 is lifted up, and is separated from the photoconductor 1 as shown in FIG.

As described above, in this image forming apparatus, when the image forming operation is stopped and the machine is stopped, the charging roller 2 is separated from the photoconductor 1 as described above. Even if the charging roller 2 is left for a long time, the surface of the photoreceptor 1 is not contaminated by the charging roller 2, unlike when the charging roller 2 is left pressed against the photoreceptor 1 for a long time.

When the charging roller 2 is separated from the photoconductor 1, the charging roller 2 and the cleaning pad 25 are also separated from each other, as is apparent from FIGS. 1C and 9. . Therefore, when the cleaning pad 25 is left in contact with the charging roller 2 in a high temperature and high humidity environment for a long time, the cleaning pad 2
Abnormal charging may occur due to the toner adhering to the toner 5 sticking to the charging roller 2, which can be prevented according to the present embodiment.

Further, when the charging roller 2 is separated from the photosensitive member 1, the thermistor 31 comes into contact with the surface of the charging roller 2 as shown in FIG. 7, so that the temperature of the surface can be detected. Become. In this state, the high voltage for charging is not applied to the charging roller 2, so in this state, the thermistor 31 and the temperature detection circuit for detecting the temperature by the signal from the thermistor 31 are applied to the charging roller 2. It is not destroyed by high voltage. As described above, in this image forming apparatus, the charging roller 2 can be brought into contact with the photoconductor 1 while the cleaning pad 25 is separated from the charging roller 2, and even if the charging roller 2 is brought into contact with the photoconductor 1, cleaning is performed. Pad 25
Can be kept separated from the charging roller 2.

[0070]

[Equation 1]

[0071]

[Equation 2]

Next, the charging model formula will be described. If the applied voltage is Va, the voltage applied to the charging roller is VR, the discharge start voltage in the air gap is VG, and the photoconductor surface potential is VD, then Va = VR + VG + VD. Here, the voltage VR applied to the charging roller is VR = IR, where R is the resistance value of the charging roller and I is the flowing current value. Further, the discharge start voltage VG in the above-mentioned air gap is
When the relative permittivity of the photoconductor is KD, it is expressed by Equation 1. The surface potential VD of the photoconductor is VD = Q / C, where Q is the charge supplied to the photoconductor and C is the capacitance. Here, the peripheral speed Vp of the photoconductor, the width L of the charging roller, and the dielectric constant Ko
Then, Q and C become (1) and (2) of the equation 2,
VD becomes (3) of Equation 2 and the charging model equation of (4) of Equation 2 is obtained.

Next, the case where the charging control method is the constant voltage control method and the constant current control method will be described. <When the charge control method is a constant voltage control method> This charge control method is a control method in which Va in the above formula is constant. In the case of this control method, Va = VR + V described above
It is the term of VD that is actually used as the charging potential of the photoconductor in the expression of G + VD. Therefore, changes in VR and VG will affect VD.

Looking at each term, the resistance value of the charging roller is a variation factor in the term VR. Therefore, if the resistance value of the charging roller increases due to environmental changes, VR
The value goes up and VD goes down. Therefore, in order to suppress this influence, it is necessary to provide a temperature detecting means and correct Va. Further, since the resistance value of the charging roller increases remarkably at low temperature and humidity, it is necessary to prevent the temperature of the charging roller from falling below a certain temperature by providing a heater or the like.

Next, in terms of VG, the photoconductor film thickness d
It is affected by D, but by actually substituting a numerical value, initial dD =
28 μm, 4 μm decrease over time, and KD = 3.2, VG (28) = 626, VG (24)
= 599, and the difference is about 27V, which is considered to have a small effect on the charging potential (usually 800 to 1000V). Since the value of the current flowing when the resistance value of the charging roller varies is small, it is possible to reduce the effect on VD by suppressing the resistance value of the charging roller to a low value (for example, 10 ⁷ Ω or less).

<When the charging control method is the constant current control method> This constant current method is a control method in which I is constant in the equation (4) of Equation 2, and the influence of the term of VR and the term of VG is I do not receive it. However, the influence of the change of the photoconductor film thickness dD in the term of VD has a direct influence on VD and the initial 28 μm shown in the above example.
And, when it changes by 4 μm with time, VD becomes VD × 2 with time.
The value becomes 4/28, and if VD is 850V in the initial stage, it becomes 728V with time and drops by 100V or more, and there is a possibility that the charging performance cannot be guaranteed.

In order to prevent this, the change in the film thickness of the photoconductor may be detected and corrected, but as a practical problem, the detection mechanism is expensive and cannot be mounted at all. Therefore, it is difficult to take measures at present except for increasing the hardness of the surface of the photoconductor and using a photoconductor that does not wear. As described above, the charging roller control method requires the applied voltage correction for the resistance fluctuation of the charging roller at present, but the constant voltage control method is adopted.

[0078]

As described above, according to the present invention, the cleaning member is not charged by an elastic member such as a spring that causes a large variation in biasing force, but the charging member itself is charged by its own weight. Since it is made to contact the surface of the charging roller, it is possible to reduce the variation of the contact pressure with respect to the charging roller and easily obtain an appropriate contact pressure. It can be uniformly cleaned. Therefore, the cleaning property of the cleaning member is improved, and thereby the occurrence of an abnormal image can be prevented.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating the vicinity of a charging unit of an image forming apparatus in three different modes for explaining an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing the vicinity of an image forming unit of the image forming apparatus.

FIG. 3 is a perspective view of the same.

FIG. 4 is a perspective view showing the vicinity of a photoconductor and a charging roller, which are also provided in the image forming unit.

FIG. 5 is a schematic view showing a state in which the photoconductor, the charging roller, and the cleaning pad are in the first position.

FIG. 6 is a schematic view showing a state in which the photoconductor, the charging roller, and the cleaning pad are also in the second position.

FIG. 7 is a schematic diagram showing a state in which the thermistor 31 is in contact with the charging roller and its surface temperature can be detected when the photosensitive member, the charging roller, and the cleaning pad are in the third position.

FIG. 8 is a schematic view showing how the thermistor 31 is separated from the surface of the charging roller at the first position.

FIG. 9 is a schematic view showing a state in which the photoconductor, the charging roller, and the cleaning pad are in the third position.

FIG. 10 is a perspective view showing a state in which the thermistor 31 is attached to the upper cover.

[Explanation of symbols]

 1: Photosensitive member 2: Charging roller 25: Cleaning pad (cleaning member) 27: Cleaning pad holder 40: Contact / separation mechanism

Claims (1)

[Claims] 1. A charging roller, a cleaning member for cleaning a surface of the charging roller, and a contacting / separating mechanism for contacting / separating the charging roller with respect to a photoconductor and the cleaning member. A mode in which the charging operation is performed by contacting with the body, and a cleaning mode in which the cleaning member is brought into contact with the surface of the charging roller,
In an image forming apparatus having a mode in which the charging roller is separated from both the photoconductor and the cleaning member, the cleaning member is in contact with the surface of the charging roller by its own weight in the cleaning mode. Image forming apparatus.