JPH09222776A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent from an abnormal image formation, regardless of using an electrifying roller, on a surface of which slight unevenness is present, and minute toner is liable to be heaped thereon. SOLUTION: In this device, the unevenness on the surface of the electrifying roller 2 is made set to become 10 to 50μm, while a cleaning pad 25 for cleaning its surface is made of the non woven cloth. Then, during the cleaning operation of the electrifying roller 2 by a rub of the cleaning pad 25, the cleaning is performed by reversely rotating the electrifying roller 2. As a result of the above, the heaped toner on a base part of a projection formed by the unevenness on the electrifying roller 2 can be removed by the cleaning pad 25.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer and a facsimile.

[0002]

2. Description of the Related Art Conventionally, a rotating photosensitive member, a charging roller which is a contact charging member for contacting the surface of the photosensitive member and charging the surface thereof, and a charging roller are in contact with each other while being in contact with the surface of the charging roller. As an electrophotographic image forming apparatus provided with a cleaning member for cleaning the surface by moving, there is, for example, the one described in JP-A-6-202447. The charging roller provided in this image forming apparatus generally uses an elastic body such as conductive rubber for its material in order to make uniform contact with the photoconductor.

[0003]

However, in the charging roller formed of such a conductive rubber, air bubbles appear on the surface when molding the charging roller, so that the surface has a slight unevenness, There are innumerable projections having a height of about 10 to 50 μm. These protrusions cannot be easily removed by polishing with a grindstone, and if they are polished to a state close to perfection, the cost required for them becomes enormous.

On the other hand, in the cleaning device for cleaning the surface of the photoconductor, a cleaning member (cleaning blade) such as a blade type formed of rubber or the like is rubbed on the surface of the photoconductor to cause an image. There is a cleaning device that scrapes off the remaining toner remaining after the transfer of the toner, but when cleaning by it, a small amount of toner passes through the cleaning blade, so the passed toner reaches the position of the charging roller. Occasionally, it adhered to the surface of the charging roller.

The toner adhered to the charging roller (strictly including paper powder other than toner) has, for example, a particle size of 9
If the size of the particles is as small as μm or less, even if the surface of the charging roller is cleaned by rubbing the cleaning member in one direction during cleaning, the particle size is smaller than the height of the protrusions on the surface and the particles cannot be removed. It often remains at the root of the protrusion.

In this case, the toner accumulated at the root portion appears as a black dot with a tail on the opposite side (downstream side) to the rotation direction of the charging roller, and the black dot appears on the cleaning member. Since it cannot be removed, the part locally becomes defectively charged and an abnormal image such as innumerable black spots on the image transferred to the transfer paper (black spots on a white background in the negative / positive process, white spots on a black background in the positive / positive process). ) Was generated.

The present invention has been made in view of the above problems, and uses a contact charging member in which minute toner easily accumulates on the surface due to the existence of innumerable protrusions due to minute unevenness on the surface. Also, the purpose is to prevent the occurrence of an abnormal image due to the accumulation of the toner.

[0008]

In order to achieve the above object, the present invention provides a rotating photoconductor, a contact charging member for contacting the surface of the photoconductor to charge the surface thereof, and a contact charging member for the contact charging member. An electrophotographic image forming apparatus comprising: a cleaning member that slides and cleans the surface of the contact charging member by relative movement of the contact charging member in contact with the surface. The unevenness of the surface in contact with the member is set to 10 to 50 μm, the cleaning member is formed of a non-woven fabric, and during the cleaning operation of the contact charging member by the cleaning member, the relative movement direction of the contact charging member with respect to the cleaning member is opposite. It is designed to be switched to.

With this structure, the surface is 10 to 50 μm.
By using the contact charging member having unevenness, even if a small amount of toner may be deposited on the root portion of the protrusion formed by the unevenness, the cleaning of the contact charging member by the cleaning member is performed by the cleaning. Since the relative movement direction of the contact charging member with respect to the cleaning member is switched to the opposite direction during the operation, the toner accumulated on the root portion of the protrusion can be taken out and removed when the cleaning direction is changed. It is possible to prevent the occurrence of an abnormal image due to the accumulation.

Further, in the image forming apparatus, a cleaning blade for cleaning the surface of the photoconductor by rubbing the surface of the photoconductor is provided, and the photoconductor is rotated in the opposite direction at the same time as switching of the relative movement direction of the contact charging member to the cleaning member. It is better to let them do it. By doing so, even if the toner that has adhered to the surface of the photoconductor rotates in the forward direction and adheres to the tip of the cleaning blade and remains there, rotate the photoconductor in the reverse direction. Since the toner adhering to the blade tip at that time drops from the blade tip, a good cleaning effect can be maintained for a long time. Further, since the contact charging member and the photosensitive member are controlled to rotate in reverse at the same time, the control can be simplified.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing the vicinity of an image forming unit of an image forming apparatus according to an embodiment of the present invention together with a control system, and FIG. 2 is a schematic diagram for explaining the vicinity of the image forming unit of the image forming apparatus in more detail. It is a block diagram. In this image forming apparatus, as shown in FIG. 1, an image forming unit is formed in a cartridge-shaped image forming unit 1, which can be detachably attached to an apparatus main body (not shown).

The image forming unit 1 includes a photosensitive member 9 in an image forming case 6, a charging roller 2 which is a contact charging member which constitutes a charging device, a developing device 3, and a cleaning device 4.
A recycle transport unit 5 for sending the residual toner collected by the cleaning device 4 to the developing device 3 is provided so that they can be integrally removed from the main body of the device in a unit state. As shown in FIG. 2, the image forming unit 1 allows the photoconductor 9 to rotate in the direction of arrow A by a drive source (not shown) in a state where the image forming unit 1 is mounted at a predetermined position of the apparatus main body.

In this image forming apparatus, when the image forming operation is started, the surface of the photosensitive member 9 is discharged by discharging the 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 which is in contact with the surface of the photoconductor 9 to charge the photoconductor 9, and the surface potential 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 by the rotation of the photoconductor 9 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 is attached. 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 feeding section (not shown), and the front end of the transfer paper P and the front end of the toner image on the photosensitive member 9 are aligned at the position of the transfer roller 8. The timing is adjusted by the pair of registration rollers 7, and the photosensitive member 9
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 photoconductor 9 after the image transfer is scraped off by being rubbed by the cleaning blade 10 of the cleaning device 4, and the photoconductor 9 is removed.
There is almost no toner on the surface of the
Move to the next imaging process again. Further, the residual toner collected by the cleaning device 4 is transferred to the toner carrying coil 11
Is transported to the recycling transport unit 5, where it is transported by the recycling belt 12 to the developer stirring unit of the developing device 3 and collected, and the toner is recycled. The above is the basic operation of the image forming apparatus.

As shown in FIGS. 3 and 4, the charging device includes a charging roller 2, bearings 14 and 15 that support the charging roller 2, and pressure springs 18 before and after pressing the bearings 14 and 15.
18, the charging roller drive gear 19, the cleaning pad 25 as a cleaning member, the electrode terminal 22 (FIG. 3), and the charging roller case 16 are integrally formed as a unit.

As shown in FIG. 3, the charging roller 2 comprises a metal cored bar 2a and a conductive rubber (for example, epichlorohydrin rubber) 2b mounted on the outer periphery thereof. The surface of the conductive rubber 2b is As shown in FIG. 10, there are many projections 37 (only three are shown for convenience) having a height of about 10 to 50 μm due to the unevenness formed by the bubbles at the time of molding. As shown in FIG. 3, the charging roller 2 uniformly charges the surface of the photoconductor 9 by applying a high voltage to the core metal 2a with the surface of the charging roller 2 being in contact with the surface of the photoconductor 9.

Both ends of the core metal 2a of the charging roller 2 are
The bearings 14 and 15 are rotatably held, and the bearings 14 and 15 have longitudinal projections 14a, 14a and 15a, 15a on the left and right surfaces, respectively, as shown in FIG.
The 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. As shown in FIG. 3, a pressure spring 18 is interposed between the bearing 14 and the inner surface 16c of the charging roller case 16, and the charging roller 2 is moved to the photosensitive member 9 via the bearing 14 by the urging force. It can be pressed with a predetermined pressure.

Further, the electrode terminal 22 comes into contact with the electrode terminal (not shown) of the main body side receptacle when the charging device is set at a predetermined position of the main body of the apparatus. 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 a rear pressure spring 18 for pressing the charging roller 2 against the photoconductor 9. Since the bearing 15 is formed of a conductive material, the voltage from the high-voltage power supply is applied to the charging roller 2.

One end of the core metal 2a of the charging roller 2 is
As shown in FIG. 4, a part of the outer periphery is processed into a flat shape to form a D-shaped portion 2c having a D-shaped cross-section, and the shape of the center hole is made to correspond to the D-shaped portion 2c so that it can be fitted. Further, the charging roller drive gear 19 is fitted and fixed integrally, and the E ring 35 prevents the charged roller drive gear 19 from coming off in the axial direction. As shown in FIG. 3, the charging roller drive gear 19 has a photosensitive member front side fixed to one end portion other than the photosensitive surface of the photosensitive member 9 whose both ends are rotatably supported on the front and rear surfaces of the image forming case 6. The gear 21 is engaged with the charging roller 2 when the charging roller 2 is in contact with the surface of the photoconductor 9.

Therefore, when the photoconductor 9 rotates in the direction of arrow A, the charging roller driving gear 19 is rotated in the direction of arrow B by the photoconductor front gear 21 rotating in the same direction, and the charging roller 2 moves in the direction of arrow B. To force to rotate. On the inner surface 16c of the charging roller case 16, a cleaning pad 25 for rubbing and cleaning the surface of the charging roller 2 by relative movement of the charging roller 2 in contact with the surface of the charging roller 2 is attached, for example, double-sided tape. It is attached with an agent. The cleaning pad 25 is made of, for example, a non-woven fabric (a felt material manufactured by Toray Co., Ltd., Excene E type Co., Ltd.) made of polyester ultrafine fibers and polyurethane.

Therefore, the charging roller 2 keeps in contact with the photoconductor 9 during the charging operation, so that the surface of the photoconductor 9 is easily contaminated by the minute toner adhering to the surface of the photoconductor 9, which causes uneven charging. By pressing the cleaning pad 25 against the surface of the charging roller 2, the surface of the charging roller 2 can be cleaned and the toner can be removed. Therefore, it is possible to prevent charging unevenness that occurs when the charging roller 2 is soiled.

Further, the inner surface 16c of the charging roller case 16
The push-up springs 26, 26 are respectively interposed between the both ends in the longitudinal direction of the image forming device and the spring receivers 6a, 6a (see FIG. 4) formed on the front and rear surfaces of the image forming case 6, respectively. The charging roller case 16 is biased upward in FIG. When the charging roller 2 is attached to the image forming case 6 in the unit state described above, the left and right surfaces 16 of the charging roller case 16 are attached to the front and rear surfaces of the image forming case 6.
Grooves 6 formed corresponding to d and 16e, respectively
b and 6c, the left and right surfaces 16d of the charging roller case 16,
The front and rear ends of 16e are dropped.

Then, if the charging roller case 16 is simply dropped into the grooves 6b and 6c of the image forming case 6, the charging roller case 16 causes the front and rear push-up springs 26,
Since it is pushed upward by 26 and becomes free in the upward direction, it is necessary to provide a stopper for pushing it from the upper side to a predetermined position suitable for charging. Therefore, in this embodiment, the upper cover 29 shown in FIG. 5 also serves as the stopper. And cover 29 on it
However, since it is configured as a unit, the amount of upward movement of the charging roller 2 that is driven by the movement of the charging roller case 16 in the figure is restricted (see also FIG. 2). Therefore, it is not necessary to provide a dedicated stopper mechanism for preventing the charging roller case 16 from falling out of the image forming case 6.

The upper cover 29 is for preventing the hands of an operator or a service person from coming into contact with the photoconductor 9, the charging roller 2, and the like. Then, the upper cover 29 is snap-fitted (patchon stopper) by fitting, for example, elastic claws formed on the image forming case 6 (FIG. 1) into corresponding recesses formed on the upper cover 29 side. ) Is fixed by the fixing means. Therefore, the upper cover 29 can be attached to and detached from the image forming case 6 by a manual operation without using any tool or the like. Therefore, when replacing the charging roller 2 in the unit state, the charging roller 2 can be removed from the image forming case 6 together with the charging roller case 16 and the upper cover 29 by hand without using any tool or the like. .

As described with reference to FIG. 3, the charging roller case 16 has the left and right surfaces 16d and 16e simply dropped into the grooves 6b and 6c formed on the front and rear surfaces of the image forming case 6, respectively. Since it exists, it can be easily taken out from the image forming case 6 simply by lifting it. Further, each push-up spring 26 is formed by forming a circular convex portion on at least one side of the spring receiver 6a on the image forming case 6 side or the inner surface 16c on the charging roller case 16 side and press-fitting the circular convex portion. When the charging roller 2 is detached as a unit, the push-up spring 26 can be prevented from falling off.

By the way, when constant voltage control is performed to make the voltage applied to the charging roller 2 constant,
When the environmental temperature in which the charging roller 2 is placed changes, the resistance value of the charging roller 2 changes accordingly, so that the surface potential of the photoconductor 9 changes. In order to prevent this, the temperature of the surface (or the vicinity thereof) of the charging roller 2 is detected, and the voltage corresponding to the temperature change from the reference temperature preset according to the detected temperature is corrected to correct it. It is necessary to apply the 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. 5 is integrally attached to the inner surface of the upper cover 29 so that the surface (or the vicinity) of the charging roller 2 can be covered. The temperature can be detected. When the surface temperature of the charging roller 2 is detected by such a thermistor 31, the charging roller 2 is in contact with the surface of the charging roller 2 when the thermistor 31 is in contact with the surface of the charging roller 2.
When a voltage is applied to the thermistor 31, the thermistor 31 and the detection circuit (not shown) to which it is connected may be destroyed by the applied high voltage.

Therefore, in this embodiment, by fixing the thermistor 31 integrally to the upper cover 29, the charging roller 2 is separated from the photosensitive member 9 and the charging roller 2 is separated.
When the voltage is not applied to the thermistor 31, the thermistor 31 contacts the surface of the charging roller 2, and as shown in FIG. 6, when the charging roller 2 contacts the photoconductor 9, the thermistor 31 separates from the surface of the charging roller 2. . Since the thermistor 31 is integrally fixed to the upper cover 29,
The cost can be reduced and the number of assembling steps can be reduced because the bracket or the screw for attaching the thermistor 31 to the upper cover 29 is not required.

Next, a contact / separation mechanism 30 for contacting / separating the charging roller 2 with respect to the photosensitive member 9 and the cleaning pad 25,
The control device 50 that drives and controls it will be described. Generally, when the conductive rubber portion of the charging roller is in contact with the same portion of the photoconductor for a long time with the image forming operation stopped, the softening agent (plasticizer) contained in the rubber material is used. )
Bleeds to the outside and stains the contact surface of the photoconductor, which tends to cause abnormal images. for that reason,
Thus, when the charging roller and the photoconductor are left for a long time in a stopped state, it is necessary to separate the charging roller from the photoconductor.

Therefore, this image forming apparatus is shown in FIG.
Cleaning pad 25
Is separated from the surface of the charging roller 2 and the charging roller 2 is brought into contact with the photosensitive member 9 so that the photosensitive member 9 can be charged, and a cleaning pad 25 is pressed against the surface of the charging roller 2 to charge the same. A charging roller cleaning mode in which the surface of the roller 2 can be cleaned, and the charging roller 2 is set to the photoconductor 9 and the cleaning pad 2.
It is possible to operate in three modes, that is, a charging roller separation mode in which both are separated from each other.

Then, as shown in FIG. 1, the charging roller 2 is in the charging roller separation mode except when the charging roller 2 charges the photosensitive member 9 and when the charging roller 2 is cleaned by the cleaning pad 25. The control unit 50 drives the contacting / separating mechanism 30 to control the control unit 50.

First, the contact / separation mechanism 30 will be described. In FIG. 3, reference numeral 41 denotes a first pressure arm, and 42 denotes a second pressure arm, both of which swing by pressing the upper surface of the charging roller case 16 at one end side to press the charging roller 2 toward the photoconductor 9 side. It is a possible lever member. 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 rotational direction, and both ends of the arm holding shaft 43 are formed in the image forming apparatus. The main body front side plate 23 and the main body rear side plate 24 are rotatably supported via bearings and the like. Therefore, when the arm holding shaft 43 is rotated clockwise or counterclockwise in FIG.
The first and second pressure arms 41 and 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 such a structure, when the charging roller contact / separation cam 44 is rotated, from the position of the charging roller contact / separation cam 44 in contact with the second pressure arm 42 to the center of the shaft 45 integrally supporting the cam. The second pressure arm 42 swings in the direction of arrow C along with the arm holding shaft 43 according to the distance Lc as shown in FIG. 3, which is 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. In this way, the charging roller contact / separation cam 44 engages with the second pressure arm 42 and sets the stop position of the second pressure arm 42.

The charging roller contact / separation cam 44 is directly connected via a shaft 45 to a rotating shaft of an electromagnetic spring clutch 48 which rotates 120 ° by one operation as shown in FIG. The electromagnetic spring clutch 48 is a known clutch that uses magnetic force to rotate by 120 ° as shown in FIG.

In this electromagnetic spring clutch 48, a rotor 62 is attached to a rotary shaft 61 such that the rotor 62 cannot rotate relative to the rotary shaft 61 and is movable only in the axial direction.
Gears 63 are rotatably attached side by side in the axial direction of the rotary shaft 61. The rotor 62 and the gear 6
3 includes teeth 62a and 6 which can mesh with the surfaces facing each other.
3a are respectively formed, and when they mesh with each other, the rotor 62 is rotated by the gear 63 together with the rotary shaft 61.

A spring 64 is interposed between the rotor 62 and the gear 63, and normally the spring 64 is provided.
The gear 63 is separated from the rotor 62 by the urging force of, and only the gear 63 idles with respect to the rotating shaft 61.
In addition, a yoke 65 is provided in the rotor 62,
The yoke 65 is formed with three holes 65a at 120 ° intervals in the rotation direction of the rotor 62, and each of the holes 65a is formed.
Corresponding to the above, three pins 66 are provided so as to project on the rotor 62 side.

The pin 66 is connected to the spring 64.
It is adapted to be fitted into the hole 65a by the urging force of. The rotor 62 is moved to the gear 63 side by an armature 68 that moves when the coil 67 is excited, and the pin 66 is moved through the hole 65a of the yoke 65 during the movement.
At the same time, the teeth 62a of the rotor 62 mesh with the teeth 63a of the gear 63 and rotate together with the rotary shaft 61.

When the excitation of the coil 67 is stopped, in the rotor 62, the tip of the pin 66 is applied to the surface of the yoke 65 between the hole 65a and the next hole 65a adjacent at an interval of 120 ° by the biasing force of the spring 64. It rotates while being pressed,
The pin 66 moves to the lower side in FIG. 7 by entering the next hole 65a at the position rotated by 120 °. As a result, the teeth 63a of the gear 63 and the teeth 62a of the rotor 62 are disengaged, and the rotation of the rotor 62 is stopped.

With this structure, the rotary shaft 61 of the electromagnetic spring clutch 48 rotates by 120 °. Therefore, the charging roller contact / separation cam 44 shown in FIG. 2 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 by the first and second pressure arms 41 and 42 can be selected in three stages.

Specifically, the three positions are to separate the cleaning pad 25 shown in FIG. 1 from the surface of the charging roller 2 and bring the charging roller 2 into contact with the photosensitive member 9 so that the photosensitive member 9 can be charged. 5 and a second position shown in FIG. 8 in which the cleaning pad 25 is brought into pressure contact with the surface of the charging roller 2 so that the surface of the charging roller 2 can be cleaned, and the charging roller 2 shown in FIG. It is a third position (home position) in which both the body 9 and the cleaning pad 25 are separated from each other. And this first, second
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) is set so that the third position can be selected.

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 embodiment, but a stepping motor is used to connect its rotating shaft to the shaft 45. The stepping motor may be rotated by the number of steps for rotating the shaft 45 by 120 °.

By the way, in this image forming apparatus, the charging roller 2 is removed from the photosensitive member 9 except when the charging roller 2 charges the photosensitive member 9 and when the charging roller 2 is cleaned by the cleaning pad 25 as described above. The control device 50 controls the drive of the contact / separation mechanism 30 so as to separate them. That is, when the image forming operation other than the charging operation mode and the charging roller cleaning mode described with reference to FIG. 11 is stopped, the charging roller 2 is controlled to be at the home position where it is separated from the surface of the photoconductor 9. It

Therefore, even if the image forming operation is left for a long time in a stopped state, the softening agent (plasticizer) contained in the rubber material of the charging roller 2 causes the photosensitive member to be exposed. The surface of 9 does not get dirty. The controller 5 shown in FIG. 1 for controlling the contact / separation mechanism 30.
0 is a central processing unit (C
PU), a ROM that stores each processing program including programs necessary for driving and controlling the contact / separation mechanism 30 and fixed data, a RAM that is a data memory that stores the processing data, and an input / output circuit (I / O). ) And is equipped with a microcomputer.

The control device 50 sends various signals from the thermistor 31 (FIG. 5) and various sensors provided in each part of the image forming apparatus to perform a predetermined image forming operation. In addition to the input, various signals that specify various image forming conditions set by the operator and various signals such as an image forming start signal are input. Then, various signals for driving them at predetermined timing are output to various drive systems and loads provided in the image forming apparatus, and the electromagnetic spring clutch of the contact / separation mechanism 30 is output to the driver 51. It outputs a signal to activate 48.

Hereinafter, the details of the drive control of the contact / separation mechanism 30 by the controller 50 will be described in detail in the charging operation mode, the charging roller cleaning mode, and the charging roller separation mode in order. <Charging Operation Mode> In this image forming apparatus, the charging roller 2 is driven by the biasing force of the push-up spring 26 as shown in FIG. As the charging roller case 16 is pushed up, it is at a home position separated from the surface of the photoconductor 9 as illustrated.

When a copy start button (not shown) is pressed in this state, the controller 50 causes the driver 51 (see FIG. 1 for all) to generate an electromagnetic spring almost at the same time as the button is pressed, or after a lapse of a predetermined time. An ON signal for driving the clutch 48 is sent to drive the electromagnetic spring clutch 48 to drive the charging roller contact / separation cam 4
4 is rotated about the axis 45 in the direction of arrow E by 120 °. Further, almost at the same time as the pressing of the copy start button, or after a lapse of a certain time after that, the photoconductor 9 is rotated clockwise in FIG. 9 (the photoconductor is normally rotated as shown in FIG. 13).

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 pressed against the photoconductor 9 through the photosensitive drum 9 via a constant pressure.

The charging operation is performed by applying a charging voltage from the high voltage power source to the charging roller 2 at a certain timing while the charging roller 2 is pressed against the surface of the photosensitive member 9. The surface of 9 is uniformly charged. At this time, since the charging roller drive gear 19 and the photoconductor front gear 21 shown in FIG. 3 mesh with each other, the charging roller 2 is forcibly rotated in the direction of the arrow B along with the photoconductor 9. Therefore, when the charging roller 2 is driven and rotated only by the frictional force received at the contact portion with the photoconductor 9, the charging roller 2 slips between the photoconductor 9 and a part thereof and local wear occurs. By doing so, problems such as deterioration of charging performance may occur, but according to this embodiment, such problems can be prevented. During the charging operation, the thermistor 31 is located away from the surface of the charging roller 2 as shown in FIG.

<Charging Roller Cleaning Mode> The controller 50 controls the trailing edge of the transfer sheet when one copy is made, and the trailing edge of the transfer sheet which is finally conveyed when a plurality of copies are made. After detecting that the photoconductor 9 and the transfer roller 8 of FIG.
ON for driving the electromagnetic spring clutch 48
A signal is sent, and the electromagnetic spring clutch 48 is rotated 120 ° in the direction of arrow E from the cam position of the charging roller contact / separation cam 44 during the charging operation shown in FIG. 1 to the position shown in FIG. Drive until

In the position of FIG. 8, the charging roller contact / separation cam 44 has a portion in which the distance Lc is larger than that in the position of FIG. 1 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. 1 by a fixed amount corresponding to the change in the distance Lc of the charging roller contact / separation cam 44, so that the cleaning pad 25, as shown in FIG. It is pressed against the surface of the charging roller 2.

In this state (charging roller cleaning mode), as shown in FIG. 13, the photoconductor 9 continues to rotate forward by a main motor (not shown), and the charge roller 2 rotated by the photoconductor 9 is preset. In addition, the surface of the charging roller 2 is forwardly rotated by the cleaning pad 25 which is in pressure contact therewith for a predetermined time t1. During the cleaning of the charging roller 2, the charging roller driving gear 19 and the photoconductor front gear 21 (see FIG. 3) are still in mesh with each other, so that the rotational driving force of the photoconductor 9 is forcibly transmitted to the charging roller 2. To be done.

When the constant time t1 has passed,
This time, the photoconductor 9 rotates in the reverse direction for the time t2. At that time, since the charging roller 2 is still in contact with the surface of the photoconductor 9, the charging roller 2 is rotated in the reverse direction for the time t2 in accordance with the reverse rotation of the photoconductor 9. At this time, the cleaning pad 25 is still pressed against the surface of the charging roller 2.

Therefore, during the cleaning operation of the charging roller 2 by the cleaning pad 25, the relative movement direction of the charging roller 2 with respect to the cleaning pad 25 is switched to the opposite direction (the solid line shown in the portion of the charging roller cleaning mode in FIG. 13). Switching from the arrow direction to the broken arrow direction). When the time t2 elapses, the photoconductor 9 stops rotating and the charging roller 2 also stops rotating.

By the way, most of the residual toner remaining on the photoconductor 9 after the transfer of the image is removed by the cleaning blade 10 of the cleaning device 4 described with reference to FIG. A minute toner of 9 μm or less passes through the cleaning blade 10 as it is without being removed by the cleaning blade 10 and adheres to the surface of the charging roller 2 rotating while contacting the photoconductor 9. As described above.

Then, the minute toner that gradually accumulates on the surface of the charging roller 2 is kept for a predetermined time t shown in FIG.
If only the cleaning pad 25 is rubbed against the surface of the charging roller 2 that rotates in the normal direction, the surface of the conductive rubber 2b of the charging roller 2 will be 10 to 50 as described in FIG.
Since there are innumerable projections 37 having a height of about μm, if the charging roller 2 is positively rotated in the direction of the arrow B, the projection 37 will enter the root portion on the downstream side in the rotation direction of the charging roller 2. However, it cannot completely remove the minute toner Tmi (the toner on the upstream side in the rotation direction can be removed). Therefore, the minute toner Tmi accumulates on the surface of the charging roller 2 with time.

In such a case, the accumulated fine toner Tmi becomes a black spot having a tail on the opposite side (downstream side) to the rotating direction of the charging roller 2, and this causes charging unevenness and transfer. This causes a problem that an infinite number of abnormal images such as black spot-like background stains occur on the image transferred onto the paper. The minute toner Tmi deposited on the surface of the charging roller 2 has a cleaning member of blade type, and the cleaning member is, for example, 0.3.
It can be removed by pressing the charging roller 2 with a strong load of about 9 N 2 / cm = 40 gf / cm to rotate the charging roller 2, but this may damage the surface of the charging roller 2. . In addition, doing so is disadvantageous in terms of space and cost.

However, in this embodiment, as shown in FIG.
As described in 3, the charging roller 2 is rotated forward by the cleaning pad 25 for a fixed time t1.
After the cleaning of the surface of the charging roller 2 in the normal direction, the charging roller 2 is rotated in the reverse direction for the time t2, and the surface of the charging roller 2 is again cleaned in the reverse direction. Therefore, when the charging roller 2 is rotated in the reverse direction, it is shown in FIG. Thus, the minute toner Tmi that has entered the root portion of the protrusion 37 on the surface of the charging roller 2 can be removed.

Therefore, since the surface of the charging roller 2 can be kept clean over time, it is possible to prevent uneven charging caused by toner stains and prevent the occurrence of abnormal images. When the cleaning pad 25 is used for the forward rotation cleaning and the reverse rotation cleaning of the charging roller 2, the cleaning pad 25 is made of a non-woven fabric as described above, and therefore the toner removed by wiping from the charging roller 2 is Since the toner adheres to the non-woven fabric, the toner adhered to the non-woven fabric is kept in the adhered state even during the reverse cleaning and does not drop.

Further, in this image forming apparatus, as described with reference to FIG. 2, the cleaning device 4 for cleaning the surface of the photosensitive member 9 has a blade type cleaning blade 10.
Is used. Then, the cleaning blade 10
Although not shown in detail, since it is screwed to the fixing portion of the cleaning device 4 and is not biased by pressure to the photoconductor 9 side by a spring or the like, the position between the photoconductor 9 and the position is finely adjusted. You can't do it. Therefore, in the case of such an image forming apparatus, a large amount of toner leaks between the tip of the cleaning blade 10 and the photoconductor 9 for cleaning, so that the present invention has a high cleaning effect for cleaning the surface of the charging roller 2. Target.

When the photoconductor 9 is constantly rotating in the same direction as indicated by the arrow A in FIG. 2, toner and paper dust scraped off the surface of the photoconductor 9 by the cleaning blade 10 adheres to the tip of the blade. Easy to remain. Then, if the cleaning operation is continued with the toner or the like attached to the tip of the blade, the cleaning effect deteriorates with time.

However, in this embodiment, as shown in FIG.
Since the photosensitive member 9 reversely rotates at the same time as the above-described reverse rotation of the charging roller 2 at the timing described in 3, the adhered matter (dust) accumulated on the tip portion of the cleaning blade 10
However, as the photoconductor 9 is reversed, it falls apart from the tip of the blade, and the tip of the blade becomes clean.

Therefore, by removing the deposits due to the toner and the like from the tip of the cleaning blade 10, a good cleaning effect can be maintained for a long period of time. The time t2 for rotating the photoconductor 9 and the charging roller 2 in the reverse direction may be the time for which the charging roller 2 rotates by a length equal to or less than the circumference of the charging roller 2, for example.
Specifically, the photosensitive member 9 is, for example, 5 to 6 mm in the circumferential direction.
It is time to rotate.

In the embodiment described with reference to FIG. 13,
The photoconductor 9 is reversely rotated only once in the charging roller cleaning mode once. However, after the photoconductor 9 is reversely rotated in the charging roller cleaning mode, the photoconductor 9 is reversely rotated in the charging roller separation mode (details will be described in the next section). Since the image forming operation is not performed at the time of shifting to (to be described), the toner (paper dust) or the like does not adhere (bite) to the tip of the cleaning blade 10 at that time. You only have to do this once. By doing so, process control can be simplified.

<Charging Roller Separation Mode> When the photosensitive member 9 is stopped by the end of the charging roller cleaning mode described above, transition to the charging roller separation mode is started, and the charging roller 2 is separated from the surface of the photosensitive member 9 and cleaned. The pad 25 separates from the surface of the charging roller 2 and returns to the home position. That is, the control device 5
When the charging roller cleaning mode described above is completed, 0 sends an ON signal for driving the electromagnetic spring clutch 48 to the driver 51 after that, and the charging roller contact / separation cam 44 is shown in FIG. 9 from the position shown in FIG. It is further rotated by 120 ° in the direction of arrow E to the desired position.

At this position, the charging roller contact / separation cam 44
Is a portion where the distance Lc is smaller than the position during the charging operation described in FIG. 1 is the cam contact portion 4 of the second pressure arm 42.
Since it comes into contact with 2a, the second pressure arm 42 swings around the arm holding shaft 43 in the direction of arrow G, which is the reverse of the conventional one, and accordingly the first pressure force shown in FIG. The arm 41 also swings in the same direction by the same amount.

As a result, the first and second pressing arms 4
Since the portions of 1, 1 and 42 respectively contacting the upper surface of the charging roller case 16 ascend in FIG. 9, 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, which is attached to the charging roller case 16 via bearings 14 and 15, is lifted upward and separated from the photoconductor 9 as shown in FIG.

[0071]

As described above, according to the present invention, by using the contact charging member having the projections of 10 to 50 μm due to the fine irregularities on the surface, the fine toner is deposited on the root portion of the projections. Even if this happens, at the time of cleaning the surface of the contact charging member, the relative movement direction of the contact charging member with respect to the cleaning member is switched to the opposite direction on the way to remove the toner accumulated at the root portion. Therefore, it is possible to prevent the occurrence of charging unevenness due to the accumulation of the toner and prevent an abnormal image from occurring. Then, by simply switching the relative movement direction of the contact charging member with respect to the cleaning member, it is possible to remove the minute toner accumulated on the root portion of the protrusion on the surface of the contact charging member as described above, so that a special part is added. You can do it cheaply because you don't have to do it.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing the vicinity of an image forming unit of an image forming apparatus showing an embodiment of the present invention together with a control system.

FIG. 2 is a schematic configuration diagram for explaining the vicinity of the image forming unit of the image forming apparatus in more detail.

FIG. 3 is a perspective view showing the vicinity of a photosensitive member and a charging roller which are also provided in the image forming unit.

FIG. 4 is an exploded perspective view for explaining the configuration of the charging device.

FIG. 5 is a schematic diagram showing a state in which the thermistor 31 is in contact with the charging roller and the surface temperature thereof can be detected when the photoconductor, the charging roller, and the cleaning pad are in the third position.

FIG. 6 is a schematic view showing how the thermistor 31 is separated from the surface of the charging roller at the first position.

FIG. 7 is a vertical cross-sectional view showing a configuration of an electromagnetic spring clutch that constitutes a contact / separation mechanism.

FIG. 8 is a schematic view showing a state in which the photoconductor, the charging roller, and the cleaning pad shown in FIG. 1 are in the second 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 an enlarged schematic view showing a state in which minute toner is deposited on the roots of a myriad of protrusions on the surface of the charging roller provided in the image forming unit of FIG.

FIG. 11 is an explanatory diagram for explaining three modes of the image forming apparatus in FIG.

FIG. 12 is an enlarged schematic view showing how the minute toner deposited on the root portion of the protrusion existing on the surface of the charging roller of FIG. 10 is removed by rotating the charging roller in the reverse direction.

13 is a timing chart showing rotation of a photoconductor and switching timing of each mode in the image forming apparatus of FIG.

[Explanation of symbols]

 2: Charging roller (contact charging member) 9: Photoconductor 10: Cleaning blade 25: Cleaning pad (cleaning member) 50: Control device

Claims (2)

[Claims] 1. A rotating photoconductor, a contact charging member that contacts the surface of the photoconductor to charge the surface, and the contact charging member relatively moves while being in contact with the surface of the contact charging member. In the electrophotographic image forming apparatus provided with a cleaning member for rubbing and cleaning the surface of the contact charging member, the surface roughness of the contact charging member in contact with the cleaning member is set to 10 to 50 μm. The image is characterized in that the cleaning member is formed of a non-woven fabric, and a relative movement direction of the contact charging member with respect to the cleaning member is switched to an opposite direction during a cleaning operation of the contact charging member by the cleaning member. Forming equipment. 2. The image forming apparatus according to claim 1, wherein
A cleaning blade for cleaning the surface of the photoconductor by rubbing the surface of the photoconductor is provided, and the photoconductor is rotated in the opposite direction at the same time as switching the relative movement direction of the contact charging member with respect to the cleaning member. Image forming apparatus.