JP3539063B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of an image forming apparatus such as a printer, a copier, and a facsimile.
In particular, it belongs to the technical field of an electrophotographic image forming apparatus for cleaning a photosensitive drum by a cleanerless method.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus of this type, a photosensitive drum on which an electrostatic latent image has been formed by charging and exposure is formed by using toner charged to a predetermined positive or negative polarity. It is common to develop. The toner image formed on the photosensitive drum by this development is transferred to a recording sheet by a transfer roller, but is not transferred to the photosensitive drum portion after the transfer in some amount according to the density of the formed toner image. Toner remains. In the next cycle, the photosensitive drum portion where the residual toner remains is charged,
When each of the exposure, development, and transfer processes is performed, a portion stained by the residual toner is formed on the recording paper, and the formed image quality is deteriorated. For this reason, conventionally, a so-called cleaning device such as a blade that scrapes off residual toner on the photosensitive drum after transfer has been provided to clean the photosensitive drum, or a method of returning residual toner to a developing device without using such a cleaner. The residual toner is collected by a cleanerless method.

In this cleanerless system, a smoothing means including a cleaning roller and a cleaning brush for electrically sucking and discharging the residual toner is disposed downstream of the transfer roller in the rotation direction of the photosensitive drum. The smoothing means suctions the residual toner from the photosensitive drum by the electric suction force while the image is being formed on the photosensitive drum, and discharges the toner while the image is not formed. Thus, the residual toner is discharged to the photosensitive drum, and the leveled toner is returned to the developing device on the rotating photosensitive drum.

According to the cleanerless system using the smoothing means structured as described above, even if the toner charged to a predetermined positive or negative polarity remains on the photosensitive drum, it can be sufficiently cleaned. This is very advantageous since it is possible to prevent the deterioration of the image quality of the formed image due to the residual toner, and to use the residual toner collected by the developing roller again for development.

[0005]

However, according to the above-described cleanerless system, even if development is performed using toner charged to a predetermined polarity such as a positive polarity, for example, the toner is actually changed to a reverse polarity such as a negative polarity. A small amount of charged toner (hereinafter referred to as “reverse polarity toner”) exists. Therefore, in the suction mode of the leveling means, actually,
The opposite polarity toner is discharged on the photosensitive drum from the leveling means in reverse due to the electrostatic force that attracts the toner charged to the predetermined polarity.

For example, if the leveling means is a cleaning roller, as shown in the timing chart of FIG.
In the cleaning process, a large amount of the opposite polarity toner is discharged particularly during the first round (time ΔT1) of the cleaning roller switched to the suction mode (discharge mode for the reverse polarity toner). As a result, the next cycle of charging, exposure, development, and the like is performed on the photosensitive drum portion where the discharged opposite polarity toner is present, and the photosensitive drum developed during the time ΔT2 due to the presence of the opposite polarity toner. There is a problem that the image quality of the image on the part is deteriorated. The timing chart in FIG. 6 is based on the photosensitive drum, and a time lag due to a difference between the cleaning position and the developing position is compensated for easy understanding.

The present invention has been made in view of the above-described problems, and an image forming apparatus that does not deteriorate image quality due to the presence of a developer such as a toner charged to the opposite polarity on a photosensitive body such as a photosensitive drum. The task is to provide

[0008]

According to another aspect of the present invention, there is provided an image forming apparatus, comprising: a rotating photosensitive member; and a latent image forming means for forming an electrostatic latent image on the photosensitive member. Developing the electrostatic latent image with a developer charged to a predetermined polarity in an operation state to form an image on the photoconductor, and collecting the developer leveled on the photoconductor in a non-operation state A developing unit, a transfer unit that transfers the image to a recording medium, and a predetermined width in a rotation direction of the photoconductor, and a predetermined leveling position downstream of the transfer unit in the rotation direction. In the suction mode, the developer charged to the predetermined polarity remaining on the photoconductor after transfer is sucked by a potential difference from the photoconductor, and in the discharge mode, the sucked developer is suctioned by the potential difference from the photoconductor. Smooth-out means on the photoreceptor A position before the photoreceptor part plan to form the image comes to a position to if the said current
At the position where the imaging means is in a non-operational state,
The stage is in the state of the discharge mode and the suction mode.
Switching means for performing switching in such a manner.

According to the image forming apparatus of the first aspect, first, an electrostatic latent image is formed on the rotating photosensitive member by the latent image forming unit. Next, an electrostatic latent image is developed by a developer charged to a predetermined polarity by a developing unit in an operating state, and an image is formed on a photoconductor. Next, the image is transferred to a recording medium by a transfer unit. Thereafter, at a predetermined leveling position downstream of the transfer unit in the rotation direction, the developer remaining on the photoconductor after transfer in the suction mode is suctioned by the leveling unit due to a potential difference from the photoconductor, and is discharged. In the mode, the sucked developer is discharged onto the photoreceptor by a potential difference from the photoreceptor, and is leveled. Then, the developer leveled on the photoreceptor by the developing unit in a non-operating state is collected. Here, the switching means switches the smoothing means to the suction mode at least before the predetermined width of the smoothing means before the photoreceptor portion on which an image is to be formed comes to the smoothing position. Therefore, a developer charged to a polarity opposite to a predetermined polarity previously attached to the leveling means (hereinafter referred to as “reverse polarity developer”)
From the switching-over to the suction mode until the photosensitive member portion on which the image is to be formed reaches the leveling position, from the smoothing means in the suction mode (discharge mode for the opposite polarity developer). It is discharged over the entire width in the rotation direction. As a result, when the photoreceptor portion on which an image is to be formed reaches the leveling unit, the leveling unit in the suction mode is set to a state in which almost no reverse polarity developer is discharged .

The image forming apparatus according to claim 2 is the image forming apparatus according to claim 1, wherein
The arranging means is arranged to face the photoconductor at the leveling position.
A cleaning roller,
The steps are as follows if the photoreceptor portion on which the image is to be formed is as described above.
Before the cleaning position and at least the cleaning
The switch is made before the distance of one round of the roller.
You.

According to the image forming apparatus of the second aspect, the photosensitive member portion on which an image is to be formed comes to the leveling position.
At least one revolution before the cleaning roller
In addition, the cleaning roller is set in the suction mode by the switching means.
Is switched to. Therefore, before that
The reverse polarity developer adhering to the roller is switched to this suction mode.
From the time of replacement, the photosensitive member portion where the image is to be formed is smoothed.
Cleaning in suction mode before reaching position
It is exhaled from the roller all around. This result
As a result, the photoreceptor portion where the image is to be formed is
When the cleaner arrives, the cleaner is already in suction mode.
The roller is in a state where it hardly discharges the opposite polarity developer.
Is done.

An image forming apparatus according to a third aspect is characterized in that
2. The image forming apparatus according to claim 1, wherein
The removing means faces the photoconductor at the leveling position
The cleaning brush is provided,
The means is such that the photoreceptor portion where the image is to be formed is
Before coming to the trash position, at least
The brush is switched before the predetermined width in the rotating direction.
And features .

[0013] According to the image forming apparatus of the third aspect, the photosensitive member portion on which an image is to be formed comes to the leveling position.
At least the width of the cleaning brush in the direction of rotation
The cleaning brush is sucked by the switching
The mode is switched to the pull mode. Therefore, before that,
The reverse polarity developer adhering to the brush is removed by the suction mode.
Photoconductor portion where the image is to be formed from the time of switching to
Until the cleaning position is reached, the
It is exhaled from the brush over its entire width. This
As a result, the photoreceptor area where the image is to be formed is cleaned.
When the brush reaches the brush, it is already in the suction mode.
Cleaning brush hardly discharges the opposite polarity developer
State.

An image forming apparatus according to claim 4 is
4. The image forming apparatus according to claim 1 , wherein the leveling unit includes the suction module.
In the mode, the current charged to the polarity opposite to the predetermined polarity is
The image agent is discharged onto the photoconductor by a potential difference from the photoconductor.
Out, and in the discharge mode, the predetermined electrode
The developer charged to the opposite polarity to the polarity of the photoreceptor
It is characterized by suction by difference.

According to the image forming apparatus of the fourth aspect, the image forming apparatus is charged to a polarity opposite to a predetermined polarity attached to the leveling unit.
Developer (hereinafter referred to as “reverse polarity developer”)
Photoreceptor section that is to form the image from the time of switching to the mode
Suction mode (reverse polarity)
(Discharge mode for developer)
Are discharged over the entire width in the rotation direction. This result
As a result, the photoreceptor portion where the image is to be formed reaches the leveling means.
When it is reached, if it is already in suction mode,
The state is such that the polar developer is hardly discharged.

[0016]

[0017]

The operation and other advantages of the present invention will become more apparent from the embodiments explained below.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a laser beam printer 1 according to an embodiment of the present invention includes a main body case 2, a feeder unit 10 for feeding a sheet P as an example of a recording medium for forming an image, and a feeder unit 10 for forming an image. Photosensitive drum 20 as an example of a photoconductor in which processes such as charging, exposure, development, transfer, and collection are sequentially performed, and a fixing unit for fixing a transfer image transferred from the photosensitive drum 20 to paper P onto paper P 70, and a paper discharge tray 77 for discharging the paper P on which the image has been fixed along the transport path PP.
It is comprised including.

The laser beam printer 1 further includes a driving unit (not shown) for rotating the photosensitive drum 20, and further on the photosensitive drum 20 rotated by the driving unit in order along the periphery of the photosensitive drum 20. A laser scanner unit 30 as an example of a latent image forming unit for forming an electrostatic latent image on the photosensitive drum 20, and a laser scanner unit 30 for developing the electrostatic latent image formed on the photosensitive drum 20 with toner as an example of a developer. A developing unit 50 as an example of a developing unit having a developing roller 56; a transfer roller 60 as an example of a transfer unit for transferring a toner image developed on the photosensitive drum 20 to a sheet P; To return the residual toner remaining on the photosensitive drum 20 to the developing unit 50 at a predetermined timing using the photosensitive drum 20, the residual toner on the photosensitive drum 20 is used. A cleaning roller 42 as an example of a smoothing means for temporarily adsorbing and discharging the residual toner, a discharging lamp 41 for removing a residual potential remaining on the photosensitive drum 20 after the transfer, and a photosensitive drum 2
And a charger 40 for charging 0 to form an electrostatic latent image.

Next, with reference to FIG. 1 to FIG. 3, each component constituting the laser beam printer 1 will be described in detail. In FIG. 1, the feeder unit 10 includes:
A paper pressing plate 11 having a width substantially the same as that of the paper P is provided in the upper feeder case 3 located at the rear end of the main body case 2. The paper pressing plate 11 is pivotally supported at its rear end so as to be swingable. Paper pressing plate 11
A compression spring 12 is provided at a front end of the sheet pressing plate 11, and the sheet pressing plate 11 is elastically urged upward by the compression spring 12. A paper feed roller 13 extending in the left-right direction is rotatably supported by the paper pressing plate 11. Paper feed roller 13
Is configured to be rotationally driven at a paper feed timing by a drive system (not shown). Feeder unit 10
Further, in the feeder unit case 3, a paper feed cassette 14 capable of accommodating a plurality of sheets P of fixed cut paper is removably mounted in an inclined manner. It is configured to feed one sheet at a time from the upper sheet P among the sheets P stored in the sheet P. Further, the feeder unit 10 is provided with a separating member 15 below the sheet feeding roller 13 to prevent double feeding of the sheet P. The separating member 15 is elastically attached to the sheet feeding roller 13 by a compression spring 16. Being energized. A pair of registration rollers 17 and 18 for aligning the leading ends of the fed paper P are rotatably supported downstream of the paper feed roller 13 in the transport direction (in FIG. 1, from the rear to the front). .

1 and 2, the photosensitive drum 20
Is made of a positively-chargeable material, for example, an organic photoreceptor mainly containing positively-charged polycarbonate. More specifically, as shown in FIG. 2, the photosensitive drum 20 is, for example, a cylindrical aluminum cylindrical sleeve 21.
With a predetermined thickness (for example, about 20 μm) obtained by dispersing a photoconductive resin in polycarbonate on the outer periphery of the main body.
, And is rotatably supported by the main body case 2 with the cylindrical sleeve 21 grounded. That is, the photosensitive drum 2
With respect to the positive polarity (positively charged) electrostatic latent image formed on 0, the toner 53 charged to the positive polarity is developed by the reversal development method. The photosensitive drum 20
The drive unit is configured to be driven to rotate clockwise in a side view.

In FIG. 1, a laser scanner unit 30 is provided below the photosensitive drum 20 and generates a laser beam L for forming an electrostatic latent image on the photosensitive drum 20. A polygon mirror (pentahedral mirror) 32 driven in rotation, a pair of lenses 33 and 34,
And a pair of reflection mirrors 35 and 36.

The charger 40 is composed of a scorotron-type charger for positive charging that generates corona discharge from a charging wire made of, for example, tungsten.
In the present embodiment, a cleaner-less system is adopted, but the charger 40 is disposed so as to be in non-contact with the photosensitive drum 20 so that residual toner on the photosensitive drum 20 does not adhere to the charger 40. ing.

The static elimination lamp 41 includes, for example, an LED (laser light emitting diode), an EL (ElectroLuminescence),
It is configured to include a light source such as a fluorescent lamp, and removes (discharges) the charge remaining on the photosensitive drum 20 after transfer by irradiating light. Thus, it is possible to prevent the remaining charge from affecting the next electrostatic latent image and finally appearing on the image formed on the sheet P.

By changing the bias voltage, the cleaning roller 42 temporarily absorbs the residual toner 53 remaining on the photosensitive drum 20 after the transfer by the transfer roller 60 in the suction mode, and on the photosensitive drum 20 in the discharge mode. By discharging the absorbed residual toner 53 onto the photosensitive drum 20 at a timing that does not hinder the next exposure, development, transfer, and the like to be performed,
The residual toner 53 is transferred from the photosensitive drum 20 to the developing unit 5.
It is configured to return to 0.

Specifically, as shown in FIG. 3, the cleaning roller 42 includes a first power supply 101 for supplying a discharge voltage Vc, a second power supply 102 for supplying a suction voltage Vs, and A changeover switch SW1 for switching between the two power supplies is provided. The changeover of the changeover switch SW1 is performed by the controller 1 composed of a microcomputer or the like.
In the suction mode, the changeover switch SW1 is switched to the side of the second power supply 102, and the potential of the cleaning roller 42 is set to the suction potential “Vs”. And the potential of the cleaning roller 42 is set to the discharge potential “Vc”. As described above, in the present embodiment, an example of a switching unit is configured by the changeover switch SW1 and the controller 105.

In this embodiment, in particular, the controller 105 switches the changeover switch SW1 so that the cleaning roller 42 is moved to a position where the portion of the photosensitive drum 20 where an image is to be formed (ie, the cleaning roller 42). The mode is switched to the suction mode at least one rotation (for example, one rotation, two rotations, three rotations, etc.) of the cleaning roller 42 before it comes to a position where the cleaning roller 42 comes into contact with the photosensitive drum 20. The photosensitive drum 2 on which this image is to be formed
The timing at which the zero portion comes to the break-in position is determined based on the detection signal Sd output from the detection unit 106 that detects the timing of image formation and the rotation state of the photosensitive drum 20.
The calculation is performed by the controller 105.

For example, the detection unit 106 detects the timing at which the paper P is transported near the registration rollers on the transport path PP, and the controller 105 calculates based on the detection signal Sd obtained at this time and the rotation state of the photosensitive drum 20. You may make it. Alternatively, the detection unit 106 may detect the image forming timing of the laser scanner unit 30, and the controller 105 may calculate based on the detection signal Sd obtained at this time and the rotation state of the photosensitive drum 20.

As described above, when the cleaning roller 42 is switched to the suction mode at a predetermined timing, the reverse polarity toner 53 (toner sucked in the discharge mode, van der Waals (For example, toner adhered by force or toner having a reverse polarity by being rubbed by the cleaning roller 42), the photosensitive drum 20 portion where the image is to be formed from the time of switching to the suction mode is moved to the leveling position. Is discharged from the cleaning roller 42 in the suction mode over the entire circumference. As a result, when the portion of the photosensitive drum 20 on which an image is to be formed reaches the leveling position, the cleaning roller 42 in the suction mode has already been in a state in which the reverse polarity toner 53 is hardly discharged.

As described above, the opposite polarity toner 53 accumulated on the cleaning roller 42 is prevented from adversely affecting the image formation, and further, the opposite polarity toner 53 is
6 is performed by a control that shifts the timing of switching from the discharge mode to the suction mode by one rotation of the cleaning roller 42, so that the present embodiment can be realized using a relatively simple configuration. .

As shown in FIG. 3, the photosensitive drum 2
0 is grounded. However, an appropriate offset voltage may be applied to the photosensitive drum 20.

A developing voltage Vb is applied to the developing roller 56.
And a changeover switch SW2 controlled by the controller 105 so as to supply the developing voltage Vb only when the developing roller 56 operates. Via this switch SW2, the developing roller 56 is connected to the third power source 103 when operating, and is grounded when not operating.

In the present embodiment, particularly, the electrostatic latent image formed on the photosensitive drum 20 where an image is to be formed is placed at a predetermined developing position (ie, a position where the developing roller 56 and the photosensitive drum 20 are in contact with each other). Until coming to the controller 1
The developing roller 56 is set in a non-operating state by the switch 05 and the changeover switch SW2. The non-operating developing roller 56 causes the positively charged toner 53 discharged from the cleaning roller 42 onto the photosensitive drum 20 in the discharging mode and suction at least over the entire periphery of the cleaning roller 42. The reverse polarity toner 53 discharged in the mode is collected.

The cleaning roller 42 is made of, for example, a conductive elastic foam made of silicon rubber or urethane rubber to which a bias voltage can be applied. The cleaning roller 42 is provided so as to efficiently collect the residual toner 53 by the developing roller 56. However, the residual toner 53 on the surface of the photosensitive drum 20 is replaced with or in addition to the cleaning roller 42. A cleaning brush for leveling may be provided. In this case, the width of the cleaning brush in the rotation direction of the photosensitive drum 20 may correspond to one rotation of the cleaning roller 42, and the timing of the above-described suction mode and discharge mode may be determined.

In FIGS. 1 and 2, the developing unit 5
Reference numeral 0 denotes a double cylindrical toner box 51 which is detachably mounted in the developing unit case 4. The toner box 51 contains an agitator 52 that is driven to rotate, and a positively charged toner 53 having electrical insulation. On the front side of the toner box 51, a toner storage chamber 5 for storing the toner 53 supplied by the rotation of the agitator 52 via a toner supply port 51a formed in the toner box 51.
4 are formed. In the toner storage chamber 54, a supply roller 55 is horizontally disposed in the longitudinal direction, and is rotatably supported. Further, a developing roller 56 is horizontally disposed in the longitudinal direction so as to partition the front side of the toner storage chamber 54 and contact the supply roller 55 and the photosensitive drum 20, respectively, and is rotatably pivoted.

The supply roller 55 is made of a conductive foamed elastic material such as silicon rubber or urethane rubber, and has a resistance value of about 5 × 10 ⁴ to 1 × 10 ^{4 at} a contact portion with the developing roller 56. It is set to ⁹ Ω.

The developing roller 56 contacts the photosensitive drum 20 as shown in FIG. 2, thereby forming a nip portion N at a developing position, and further includes a conductive rigid member made of silicon rubber or urethane rubber. Roller. In the present embodiment, for example, since the photosensitive drum 20 made of an organic photoreceptor having positively chargeable toner and positively chargeable polycarbonate as main components is used, urethane rubber is used as the material of the developing roller 56.

The resistance value from the central electrode of the developing roller 56 to which the developing bias voltage is applied to the outer nip N is set to about 5 × 10 ⁴ to 1 × 10 ⁷ Ω. The supply roller 55 and the developing roller 56 are configured to be driven to rotate clockwise by a driving mechanism.

The developing roller 56 includes a changeover switch SW2
Is developed on the photosensitive drum 20 using the positively charged toner 53 in an operation state in which the developing voltage Vb is applied via
In a non-operating state where the ground is connected via the changeover switch SW2, the residual toner 53 returned onto the photosensitive drum 20 by the cleaning roller 42 is collected.

As shown in FIG. 2, a toner storage chamber 54 is provided in the developing section case 4 of the developing unit 50. The toner storage chamber 54 is formed by providing a large upper space S above the supply roller 55. Have been.

In FIGS. 1 and 2, the developing unit case 4
, A thin plate-shaped elastic layer thickness regulating blade 57 made of stainless steel or phosphor bronze is attached downward.

A bent portion 57 a formed at a lower end portion of the layer thickness regulating blade 57 is in contact with the developing roller 56 in a pressed state, and is supplied from the supply roller 55 to the developing roller 5.
The layer thickness of the toner 53 adhered in a layer on the surface of No. 6 is regulated to a predetermined thickness (about 7 to 12 μm) by the layer thickness regulating blade 57.

The transfer roller 60 is provided so as to be in contact with the upper side of the photosensitive drum 20, is rotatably pivotally supported, and is made of a conductive elastic foam made of silicon rubber, urethane rubber, or the like. The resistance value of the transfer roller 60 at the contact portion with the photosensitive drum 20 is about 1 × 10 ⁶ to
It is set to 1 × 10 ¹⁰ Ω.

The fixing unit 70 is provided downstream of the photosensitive drum 20 in the transport direction, includes a heating roller 71 having a well-known halogen lamp, and a pressing roller 72, and transfers the toner image onto the lower surface of the sheet P. Is pressed while being heated and is fixed on the sheet P.

The pair of transport rollers 75 for paper transport and the paper discharge tray 77 are provided on the downstream side in the transport direction of the fixing unit 70, respectively. According to the present embodiment, as shown in FIG. 1, the paper feed roller 13, the photosensitive drum 20, the fixing unit 70, and the paper output tray 77 are moved from the paper feed cassette 14 along a transport path PP extending in a substantially linear shape. It is configured to convey the fed paper P.

In FIG. 1, the toner 53 in the present embodiment is a positively chargeable toner, and is, for example, a non-magnetic one-component toner made of a pulverized toner or a polymerized toner made of styrene acrylic having a nearly spherical shape. And a silica as an external additive (fluidity imparting agent) added to the elementary toner. As a result, most of the toner 53 is rubbed by the developing roller 56, the photosensitive drum 20, and the like, and is charged to a positive (positive) polarity. Then, the toner 53 is charged to a negative (negative) polarity to be a toner of the opposite polarity, albeit a small amount.

Next, the operation of the laser beam printer 1 configured as described above will be described with reference to FIGS. In FIG. 1, the photosensitive drum 20 is driven to rotate clockwise in a side view by a driving unit,
5 and the developing roller 56 are each driven to rotate clockwise.

As a result, most of the particles of the toner 53 are charged to a positive polarity by the rubbing between the supply roller 55 and the developing roller 56 and the pressing friction of the layer thickness regulating plate 57 against the developing roller 56. The toner 53 charged to a positive polarity is rubbed and charged by the developing roller 56 and the photosensitive drum 20, and adheres to the electrostatic latent image formed on the photosensitive drum 20 by the laser beam L, thereby performing development. . At this time, the reverse polarity toner 53 also adheres to the photosensitive drum 20 in a small amount by a force such as Van der Waals force.

Here, the charge amount of the toner 53 changes from about 25 μC / g to 20 μC / g according to the temperature and humidity. Therefore, when the developing roller 56 is driven in the same rotation direction as the photosensitive drum 20, the predetermined amount of developing toner (for example, about 0.78 mg / cm ² ), the effective developing bias voltage of the developing roller 56 (the potential difference between the potential of the electrostatic latent image on the photosensitive drum 20 and the potential of the developing roller 56) is set to “about 200 V”.

Therefore, as shown in FIG. 4, it is assumed that the grounded photosensitive drum 20 is charged to “about 800 V” by the charger 40, and an electrostatic latent image which is a voltage of an electrostatic latent image formed on the photosensitive drum 20 is formed. Assuming that the image voltage is, for example, “about 100 V”, the voltage Vb of the third power supply 103 for development applied to the developing roller 56 has an effective developing bias voltage of “about 20 V”.
For example, it is set to “about 300 V” so as to be “0 V”.

The voltage Vs of the second power supply of the cleaning roller 42 is set to, for example, “about −250 V (= electrostatic latent image potential) so that the residual toner 53 charged to the positive polarity can be sucked from the photosensitive drum 20 after the charge is removed. -350V) ". Also, the voltage V of the first power supply of the cleaning roller 42
c is, for example, “about 450 V (= electrostatic latent image potential +
350 V) ".

As a result of the voltage setting of each unit, in the suction mode, the cleaning roller 42 is connected to the second power supply 102 by the changeover switch SW 1, and has a potential difference of, for example, −350 V, so that the surface of the photosensitive drum 20 after the charge removal is performed. , The residual toner 53 charged to a positive polarity can be sucked.

On the other hand, in the discharge mode, the switch SW1 is connected to the first power supply 101, for example, +
The residual toner 53 can be discharged onto the surface of the photosensitive drum 20 by the potential difference of 350V.

Here, the reverse polarity toner 53 attached to the photosensitive drum 20 is attracted by the cleaning roller 42 in the discharge mode and the cleaning in the suction mode because the polarity is opposite to that of the toner 53 charged to the positive polarity. It is discharged from the roller 42.

When the image forming process is started under the above-described voltage setting, first, after the residual charge on the photosensitive drum 20 is wiped out by the charge removing lamp 41, the surface of the photosensitive drum 20 becomes positively charged. For example, as shown in FIG. 4, the charger 40 uniformly charges the battery to “800 V”. In this state, the laser beam L emitted from the laser generator 31 is irradiated on the photosensitive drum 20 via the lenses 33 and 34 and the reflection mirrors 35 and 36 while being scanned by the polygon mirror 32 in the main scanning direction. An electrostatic latent image is formed on 20. At this time, the voltage of the portion corresponding to the electrostatic latent image on the photosensitive drum 20 falls to, for example, “100 V” as shown in FIG. The toner 53 is attracted to a charging voltage (800 V) higher than its own voltage in a state where, for example, “300 V” is applied as a developing bias voltage to the surface of the developing roller 56 as shown in FIG. Is attracted to a lower electrostatic latent image voltage (100 V),
The toner 53 on the developing roller 56 adheres only to the electrostatic latent image formed on the photosensitive drum 20 and is developed.

The toner image of the electrostatic latent image developed by the toner 53 is transferred to the sheet P by the transfer roller 60, and then subjected to a fixing process by the fixing unit 70, and the sheet discharge tray 77.
Is discharged.

At this time, a transport path PP for transporting the paper P fed from the paper feed cassette 14 is formed in a substantially linear shape, and the paper P is image-formed while being transported by the substantially linear transport path PP. Therefore, even if thick paper such as a postcard or an envelope, an OHP film, or the like is used as the paper P, a clear and reliable image can be formed on the paper P.

On the other hand, in FIG. 1, the residual toner 53 remaining on the photosensitive drum 20 without being transferred to the sheet P when passing through the transfer roller 60 connects the cleaning roller 42 to the second power supply 102 by the changeover switch SW 1. Thus, the potential difference of about -350 V is temporarily absorbed by the cleaning roller 42 in the suction mode. Then, by connecting the cleaning roller 42 to the first power supply 101 by the changeover switch SW1 at a timing that does not hinder the next exposure, development, transfer, and the like performed on the photosensitive drum 20, the potential is temporarily absorbed by a potential difference of about + 350V. The discharged residual toner 53 is discharged to the photosensitive drum 20 from the cleaning roller 42 in the discharge mode, and is leveled.

When the residual toner 53 returns to the developing unit 50, it is grounded by the switch SW2,
The developing roller 56 in the non-operating state causes the photosensitive drum 2
Residual toner 53 on 0 is collected.

The toner 53 in the above-described discharge mode
The image forming operation may be periodically stopped after the image forming operation is performed. At the timing corresponding to the interval between the sheets P, the image forming operation is sewn between the image forming operations so as not to hinder the image forming operation. You may do so.

Here, as shown in the timing chart of FIG. 5, in the present embodiment, in particular, the controller 105
And the changeover switch SW1, the cleaning roller 4
2 is switched to the suction mode one revolution before the photosensitive drum 20 portion on which an image is to be formed comes to the leveling position. Therefore, the opposite polarity toner 53 that has adhered to the cleaning roller 42 before that time
Is discharged during the suction mode for one round (during the time ΔT1). Until the electrostatic latent image formed on the photosensitive drum 20 where an image is to be formed reaches the predetermined developing position, the controller 105 and the changeover switch SW2
As a result, the developing roller 56 is in a non-operating state. Accordingly, the time Δ until the developing roller 56 is brought into the operating state
During T2, no image is formed on the portion of the photosensitive drum 20 where the toner of the opposite polarity exists, and the developing roller 56 that is in the non-operating state during the time ΔT2 causes the cleaning roller 42 The discharged opposite polarity toner 53 is collected. The timing chart of FIG. 5 is based on the photosensitive drum, and a time lag due to a difference between the cleaning position and the developing position is compensated for easy understanding.

In FIG. 5, the toner 53 charged to a predetermined polarity stored in the cleaning roller 42 is discharged onto the photosensitive drum 20 during the discharge mode before switching to the suction mode, and further, the non-operation is performed. It is collected by the developing roller 56 in the state.

As described above, according to the laser beam printer 1 of the present embodiment, a large amount of ink is ejected from the cleaning roller 42 during the first round of switching to the suction mode (the ejection mode for the opposite polarity toner). The reversed polarity toner does not cause an image defect.

Although only the formation of a monochrome image has been described in the above embodiment, the present invention functions effectively also in the case of forming a color image. Further, the photoconductor is constituted by a photoconductor drum, but may be a belt-shaped photoconductor, and the relative movement directions of the photoconductor drum and the developing roller may be opposite or the same. Furthermore, in the present embodiment, a laser beam printer has been described. However, as long as the image forming apparatus is an electrophotographic image forming apparatus using toner, the present invention is applicable to copying, facsimile, and the like as in the case of the present embodiment. Works effectively.

[0066]

According to the image forming apparatus of the first aspect, the opposite polarity developer adhered to the leveling means is used for the leveling of the photosensitive member which is to form an image from the time of switching to the suction mode. Since the toner is ejected over the entire width in the rotation direction of the leveling means before it reaches the position, almost no reverse polarity developer is ejected to the photosensitive member where an image is to be formed. As a result, a high-quality image can be formed without deteriorating the image quality due to the presence of the reverse polarity developer on the photoconductor. In addition, the discharge mode of the leveling means
And the suction mode at a position where the developing means is in a non-operating state.
And move it forward according to the width of the leveling means in the direction of rotation
Because of the use of relatively simple control of the present invention it is made possible embodied by a relatively simple structure.

According to the image forming apparatus of the second aspect, the cleaning roller is a photosensitive member for forming an image.
The reverse polarity developer can be hardly discharged to the body part,
Effective with a relatively simple configuration using a cleaning roller
Reverse cleaning on the photoconductor while performing efficient cleaning
High quality without deteriorating image quality due to the presence of polar developer
A quality image can be formed.

According to the image forming apparatus of the third aspect, the cleaning brush is a photosensitive brush for forming an image.
The reverse polarity developer can be hardly discharged to the body part,
Effective with a relatively simple configuration using a cleaning brush
Reverse cleaning on the photoconductor while performing efficient cleaning
High quality without deteriorating image quality due to the presence of polar developer
A quality image can be formed.

According to the image forming apparatus of the fourth aspect, while the portion of the photoreceptor from which the opposite polarity developer is mainly discharged is at the developing position, the opposite polarity developer is removed by the developing means in a non-operation state. It can be collected and a high quality image can be formed without deteriorating the image quality due to the presence of the opposite polarity developer on the photoreceptor.

[0070]

As a result, according to the present invention, even if not only the developer charged to a predetermined polarity but also the opposite polarity developer remains,
It is possible to realize an image forming apparatus having a relatively simple configuration that can clean these by the leveling means and form a high-quality image.

[Brief description of the drawings]

FIG. 1 is a vertical sectional side view of a laser beam printer according to an embodiment of the present invention.

FIG. 2 is an enlarged side view of a developing unit and a photosensitive drum portion of the laser beam printer of FIG.

FIG. 3 is a schematic view showing power supplies and switches of the laser beam printer of FIG. 1;

FIG. 4 is an explanatory diagram showing potentials of respective portions in a developing process performed by the laser beam printer of FIG. 1;

FIG. 5 is a timing chart of a cleaning process and a developing process performed by the laser beam printer of FIG.

FIG. 6 is a timing chart of a cleaning process and a developing process performed in the related art.

[Explanation of symbols]

1. Laser beam printer 10 ... Feeder unit 13: Paper feed roller 14. Paper cassette 20 Photosensitive drum 30 ... Laser scanner unit 42 ... Cleaning roller 50: Developing unit 53 ... toner 55 ... supply roller 56 Developing roller 57 ... Layer thickness regulation blade 60 ... Transfer roller 70: Fixing unit 77 ... paper ejection tray 101: first power supply 102 ... second power supply 103: Third power supply SW1 ... Switch SW2 ... changeover switch

────────────────────────────────────────────────── ─── Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 21/14 G03G 21/00 370-540 G03G 15/08-15/08 507 G03G 21/10 G03G 21 / 00 G03G 15/22

Claims (4)

(57) [Claims] 1. A rotating photosensitive member, a latent image forming means for forming an electrostatic latent image on the photosensitive member, and developing the electrostatic latent image with a developer charged to a predetermined polarity in an operating state. Developing means for forming an image on the photoreceptor and collecting a developer leveled on the photoreceptor in a non-operating state; transfer means for transferring the image to a recording medium; rotating direction of the photoreceptor Has a predetermined width, and at a predetermined leveling position downstream of the transfer means in the rotation direction, in the suction mode, the developer charged to the predetermined polarity remaining on the photoreceptor after transfer is transferred. Suction means by a potential difference from the photoconductor, and in a discharge mode, a smoothing means for discharging the sucked developer onto the photoconductor by a potential difference from the photoconductor, and a photoconductor portion on which the image is to be formed. position der of before coming to the position to if the Te, the developing means and the non-operating state
At a certain position, the leveling means is in the discharge mode.
To switch to the suction mode and the suction mode.
An image forming apparatus characterized by comprising a switch means. 2. The apparatus according to claim 1 , wherein the leveling means is located at the leveling position.
And a cleaning roller disposed opposite to the photosensitive member.
With which it said switching means includes a photoreceptor portion plan to form the image
Before reaching the break-in position and at least
Switching before the distance of one revolution of the leaning roller
2. The image forming apparatus according to claim 1 , wherein: 3. The photoconductor according to claim 1, wherein the leveling unit includes a cleaning brush that is disposed opposite to the photoconductor at the leveling position, and the switching unit includes a photoconductor portion on which the image is to be formed.
Before reaching the break-in position and at least
Cutting the leaning brush forward by the predetermined width in the rotation direction
2. The image forming apparatus according to claim 1 , wherein the image forming apparatus is replaced . 4. The air conditioner according to claim 1 , wherein
The developer charged to the polarity opposite to the predetermined polarity
Discharging on the photoconductor due to a potential difference from the photoconductor,
In the discharge mode, the polarity is opposite to the predetermined polarity.
Polarized developer is charged by the potential difference from the photoconductor.
Claims 1 to, characterized in that aspirating 3 Noise
The image forming apparatus according to claim 1.