JP3425036B2 - 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 image forming apparatuses such as printers, copiers and facsimiles.
In particular, it belongs to the technical field of an electrophotographic image forming apparatus that cleans a photosensitive drum by a cleanerless system.

[0002]

2. Description of the Related Art Conventionally, in this type of electrophotographic image forming apparatus, a photosensitive drum on which an electrostatic latent image is formed by charging and exposure is developed by using toner charged negatively or positively. Is common. The toner image formed on the photosensitive drum by this development is transferred to the recording paper by the transfer roller, but is not transferred to the photosensitive drum portion after the transfer depending on the density of the formed toner image. Toner remains. When the process of charging, electrostatic latent image formation, development, and transfer is performed on the photosensitive drum portion where the residual toner remains in the next cycle, a portion contaminated by the residual toner is formed on the recording paper, which lowers the quality of the formed image. Will be invited. Therefore, conventionally, a cleaner such as a blade that scrapes off the residual toner on the photosensitive drum after transfer is provided to clean the photosensitive drum, or the residual toner is returned to the developing device without using such a cleaner. The residual toner is collected by a cleanerless method.

In this cleanerless system, a leveling means including a cleaning roller and a cleaning brush for electrically sucking and discharging the residual toner is arranged downstream of the transfer roller in the rotating direction of the photosensitive drum. The leveling means sucks the residual toner from the photosensitive drum by an electric suction force while the image formation is being performed on the photosensitive drum, and the discharging mode while the image formation is not being performed. Thus, the residual toner is discharged to the photosensitive drum, and the smoothed toner can be returned to the developing device on the rotating photosensitive drum. Therefore, in the suction mode,
A first power source for generating a potential difference from the photosensitive drum for sucking the residual toner from the photosensitive drum and a second power source for generating a potential difference with the photosensitive drum for discharging the attracted toner to the photosensitive drum are connected via a switch. It is configured to be selectively connected. For example, if the surface potential of the photosensitive drum that has been charged and then undergoes the steps of electrostatic latent image formation, development, and transfer is +50 V (volts), the first power source for the suction mode of the leveling means is -300 V. And
The second power supply for the discharge mode is + 400V.

According to the cleanerless system using the so-called leveling means, it is possible to prevent the residual toner left on the photosensitive drum after the transfer from deteriorating the image quality of the formed image in the subsequent cycle, and to prevent the residual toner. Is very advantageous because it can be recovered and used again for development.

[0005]

However, according to the above-mentioned cleanerless system, it is necessary to supply different voltages to the cleaning means such as the cleaning roller in the two modes of the suction mode and the discharge mode. There is a problem in that two power sources are required for the equalizing means, which leads to an increase in size, complexity, and cost of the device. Further, according to the above-described method of developing by contacting the developing roller and the photosensitive drum, when the power of the image forming apparatus is turned on, the surface potential of the photosensitive drum and the surface potential of the developing roller are the same (both 0 V). Therefore, by the time the surface potential of the photosensitive drum reaches a predetermined bias value, development is performed with toner on the portion of the photosensitive drum where no latent image is formed, and the transfer roller is contaminated with this toner. There were also problems.

The present invention has been made in view of the above-mentioned problems, and an image formation capable of reducing the image quality deterioration due to useless development when the power supply for the leveling means is sufficient and only one power supply is turned on. An object is to provide a device.

[0007]

In order to solve the above-mentioned problems, an image forming apparatus according to a first aspect of the present invention includes a photoconductor and a charging for charging the photoconductor to a predetermined voltage so that an electrostatic latent image can be formed on the photoconductor. And a latent image forming means for forming an electrostatic latent image on the photoconductor, and the electrostatic latent image is developed by a developer charged to a predetermined polarity in an operating state to form an image on the photoconductor. , A developing means for collecting the developer leveled on the photoconductor in a non-operating state, a transfer means for transferring the image onto a recording medium, and a developer remaining on the photoconductor after transfer in the suction mode. In the discharge mode, the developer is sucked due to the potential difference from the photoconductor, and the attracted developer is discharged onto the photoconductor due to the potential difference from the photoconductor, and the leveling means is different from the ground potential. A first power supply for supplying a voltage, and the photosensitive material Wherein a ground potential and the current-voltage converting element for supplying a second different voltage from said first voltage to,
A voltage difference from the second voltage supplied to the photoconductor is used as a developing bias voltage, and a third voltage for developing the electrostatic latent image on the photoconductor by the developing unit is supplied to the developing unit during development. Switching to the suction mode by connecting a third power source and the leveling means to one of the ground and the first power source, and connecting the leveling means to the other of the ground and the first power source causes the discharge And a switching means for switching to the mode.

According to the image forming apparatus of the first aspect,
First, the latent image forming means forms an electrostatic latent image on the photoconductor. Next, the developing means develops the electrostatic latent image with a developer charged to a predetermined polarity to form an image on the photoconductor. Next, the image is transferred onto the recording medium by the transfer means. Then, in the suction mode, the developer remaining on the photoconductor after the transfer is attracted by the leveling means due to the potential difference with the photoconductor, and in the discharge mode, the attracted developer is exposed due to the potential difference with the photoconductor. It is spit out on the body and is made smooth. At this time, the leveling means is switched to the suction mode by connecting the leveling means to one of the ground and the first power source by the switching means (for example, supplying 0V as a ground voltage to the leveling means). By connecting the charging means to the other of the ground and the first power supply (for example, +700 V is supplied as the first voltage), the discharge mode is switched. Here, the photoconductor has a second voltage different from the ground potential and the first voltage due to the current-voltage conversion element.
Since the voltage (for example, + 300V) is supplied, in the suction mode, the voltage difference (for example, 0V− () between the ground and the first power source and the current-voltage conversion element and the electrostatic latent image potential (for example, 50V). 300V + 50V) =-350V)
As a result, the developer remaining on the photoconductor after the transfer is sucked into the leveling means. In the discharge mode, the voltage difference between the other of the ground and the first power source and the current-voltage conversion element and the electrostatic latent image potential (for example, 700V- (300V + 50V)).
= + 350 V), the sucked developer is discharged onto the photoconductor from the leveling means. Finally, the developer leveled on the photoconductor is collected by the non-operating developing means. In this way, the cleanerless cleaning is performed by supplying only one power source (that is, the first power source) to the leveling means.

Further, since the second voltage is supplied to the photosensitive member by the current-voltage converting element, the image forming apparatus is powered on until the surface potential of the developing roller reaches a predetermined bias value. In addition, the developer is not attached to the photoconductor from the developing unit due to the potential difference between the developing unit and the photoconductor, and therefore wasteful development is not performed. Also, since it has a current-voltage conversion element, it supplies the second voltage.
The power supply to be supplied can be constructed at low cost. Further, according to the image forming apparatus of the first aspect, since the third voltage different from the ground potential is supplied to the developing unit by the third power source during the development, the third power source and the photoconductor are supplied. Second Den
The electrostatic latent image on the photoconductor is developed by the developing unit in the normal operating state, using the voltage difference from the pressure as the developing bias voltage.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the developing means is discharged to the photoconductor from the leveling means in a non-operating state in which the developing means is grounded. The developer is recovered.

According to the image forming apparatus of the second aspect,
Since the developing unit collects the developer discharged to the photoconductor from the leveling unit in a non-operating state where it is grounded, the developer is not attached to the photoconductor from the developing unit and wasteful development is performed. Is never done.

[0012]

[0013]

An image forming apparatus according to a third aspect is the image forming apparatus according to the above-mentioned first or second aspect,
The smoothing unit includes one of a cleaning roller and a cleaning brush arranged to face the photoconductor.

According to the image forming apparatus of claim 3,
The developer remaining on the photoconductor is suitably leveled by the leveling means provided with either one of the cleaning roller and the cleaning brush disposed opposite to the photoconductor.

The operation and other advantages of the present invention will be apparent from the embodiments described below.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION 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 image formation, and an image forming unit. A photosensitive drum 20 as an example of a photoconductor in which the steps of charging, exposing, developing, transferring, collecting, etc. are sequentially performed, and a fixing unit for fixing the transfer image transferred from the photosensitive drum 20 to the paper P to the paper P. 70 and a paper discharge tray 77 for discharging the paper P on which the image is fixed along the transport path PP.
And is configured.

The laser beam printer 1 is also provided with a driving means (not shown) for rotating the photosensitive drum 20, and on the photosensitive drum 20 rotated by the driving means 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 surface of the photosensitive drum 20, and a toner image as an example of a developer for developing the electrostatic latent image formed on the photosensitive drum 20. 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 that transfers the toner image developed on the photosensitive drum 20 onto the sheet P, and after transfer by the transfer roller 60. In order to return the residual toner remaining on the photosensitive drum 20 to the developing unit 50 using the photosensitive drum 20 at a predetermined timing, the residual toner is temporarily absorbed. Cleaning roller 42 as an example of the smoothing means for discharging and smoothing, a discharging lamp 41 for removing the residual potential left on the photosensitive drum 20 after transfer, and an electrostatic latent image for the photosensitive drum 20 after discharging. And a charging device 40 for charging so that an image can be formed.

Next, the respective constituent elements of the laser beam printer 1 will be described in detail with reference to FIGS. 1 to 3. In FIG. 1, the feeder unit 10 includes a sheet pressing plate 11 having a width dimension substantially the same as that of the sheet P, which is disposed in the upper feeder section case 3 located at the rear end of the main body case 2. The paper pressing plate 11 is swingably supported at its rear end. A compression spring 12 is provided at the front end of the paper pressing plate 11, and the paper pressing plate 11 is elastically biased upward by the compression spring 12.
The paper pressing plate 11 includes a paper feed roller 13 extending in the left-right direction.
However, it is rotatably supported. The paper feed roller 13 is configured to be rotationally driven at a paper feed timing by a drive system (not shown). In the feeder unit 10, a paper feed cassette 14 capable of accommodating a plurality of sheets P of standard cut paper is detachably mounted in an inclined manner in the feeder case 3, and by rotation of the paper feed roller 13, Among the paper P stored in the paper feed cassette 14, the upper paper P is fed one by one. Further, the feeder unit 10 is provided with a separating member 15 below the paper feeding roller 13 in order to prevent double feeding of the paper P, and the separating member 15 is elastically attached to the paper 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 pivoted downstream of the paper feed roller 13 in the conveying direction (from the rear to the front in FIG. 1). There is.

In FIG. 1 and FIG. 2, the photosensitive drum 20
Is composed of a positively chargeable material, for example, an organic photoreceptor having a positively chargeable polycarbonate as a main component. More specifically, as shown in FIG. 2, the photosensitive drum 20 is, for example, a cylindrical cylindrical sleeve 21 made of aluminum.
The main body of which has a predetermined thickness (for example, about 20 μm) in which a photoconductive resin is dispersed in polycarbonate on the outer peripheral portion thereof.
The photoconductive layer 22 is formed into a hollow drum, and is rotatably supported by the main body case 2 with the cylindrical sleeve 21 grounded. That is, the photosensitive drum 2
The toner 53 charged in the positive polarity is developed by the reversal development method with respect to the electrostatic latent image formed in the positive polarity (positive charge). The photosensitive drum 20 is
The drive means is configured to rotate and drive clockwise in a side view.

In FIG. 1, the laser scanner unit 3
Reference numeral 0 denotes a laser generator 31 disposed below the photosensitive drum 20, which generates a laser beam L for forming an electrostatic latent image on the photosensitive drum 20, and a polygon mirror (a pentahedron) driven to rotate. Mirror 32, a pair of lenses 33 and 34, and a pair of reflection mirrors 35 and 36.

The charger 40 is composed of, for example, a scorotron type charger for positive charging, which generates corona discharge from a charging wire made of tungsten or the like. In the present embodiment, a cleanerless system is adopted, but the charger 40 is arranged so as to face the photosensitive drum 20 in a non-contact manner so that the residual toner on the photosensitive drum 20 does not adhere to the charger 40. ing.

The charge eliminating lamp 41 is constituted by including a light source such as an LED (laser light emitting diode), an EL (Electro Luminescence), a fluorescent lamp or the like, and removes the electric charge remaining on the photosensitive drum 20 after the transfer (eliminating the charge). ), The residual charge affects the next electrostatic latent image,
It finally functions to prevent the image from appearing on the sheet P.

By changing the bias voltage, the cleaning roller 42 once absorbs the residual toner 53 remaining on the photosensitive drum 20 after the transfer by the transfer roller 60 in the suction mode, and in the discharge mode,
The absorbed residual toner 53 at a timing that does not interfere with the next exposure, development, transfer, etc. performed on the photosensitive drum 20.
The residual toner 53 is returned from the photosensitive drum 20 to the developing unit 50 by discharging the residual toner 53 onto the photosensitive drum 20.

Specifically, as shown in FIG. 3, the cleaning roller 42 is provided with a first power supply 101 and a switch SW1 for supplying a cleaning voltage Vc as an example of the first voltage. By switching the switch SW1, the voltage Vc of the first power supply 101 is supplied or connected to the ground. The switching of the switch SW1 is controlled by a microcomputer (not shown). In the suction mode, the switch SW1 is switched to the ground side, and the potential of the cleaning roller 42 is set to "0". 1
The potential of the cleaning roller 42 is switched to the side of the power supply 101 so that the potential of the cleaning roller 42 becomes "Vc".

Further, as shown in FIG. 3, the photosensitive drum 20
A second power supply 102 for supplying a drum offset voltage Va as an example of a second voltage is connected to the. Therefore, the potential of the photosensitive drum 20 is always "Va". Here, the second power supply 102 is composed of a current-voltage conversion element such as a varistor.

Further, as shown in FIG. 3, the developing roller 56
Is provided with a third power supply 103 and a switch SW2 for supplying a developing voltage Vb as an example of a third voltage, and the voltage Vb of the third power supply 103 is supplied by switching the switch SW2. Or configured to be connected to ground. The switching of the switch SW2 is controlled by a microcomputer (not shown). In a non-operating state in which the toner cleaned by the cleaning roller 42 is to be collected, the switch SW2 is switched to the ground side and the potential of the developing roller 56 is changed. On the other hand, in the operating state in which development is to be performed, on the other hand, the potential of the developing roller 56 is set to "Vb" by switching to the side of the third power source 103, and a developing bias is generated.

The cleaning roller 42 is made of, for example, a conductive foamed elastic body made of silicon rubber or urethane rubber to which a bias voltage can be applied.
Incidentally, as the recovery of the residual toner 53 by the developing roller 56 is efficiently, but the cleaning roller 42 is provided, even out residual toner 53 on the surface of the place of, or in addition the photosensitive drum 20 of the cleaning roller 42 A cleaning brush may be provided for this purpose.

1 and 2, the developing unit 50
Includes a double-cylindrical toner box 51 detachably mounted in the developing unit case 4. The toner box 51 accommodates an agitator 52 that is driven to rotate and a positively charging toner 53 that has electrical insulation. In front of the toner box 51, a toner storage chamber 54 for storing the toner 53 supplied by the rotation of the agitator 52 through the toner supply port 51a formed in the toner box 51.
Are formed. In the toner storage chamber 54, a supply roller 55 is horizontally arranged in the longitudinal direction and is rotatably supported. Further, a developing roller 56 is horizontally arranged in the longitudinal direction and is rotatably supported 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.

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

Further, the developing roller 56 constitutes a nip portion N by contacting the photosensitive drum 20 as shown in FIG. 2, and is a conductive rigid roller made of silicone rubber or urethane rubber. . In the present embodiment, for example, the photosensitive drum 20 formed of an organic photoconductor whose main components are positively chargeable toner and positively chargeable polycarbonate.
Therefore, 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 peripheral nip portion 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 rotationally driven clockwise by a drive mechanism.

The developing roller 56 develops on the photosensitive drum 20 by using the positively charged toner 53 in the operating state where the developing voltage Vb is applied, and in the non-operating state in which it is grounded, the developing roller 56 is driven by the cleaning roller 42. 20 is configured to collect the residual toner 53 returned onto the surface 20.

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

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

The bent portion 57a formed at the lower end 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 be supplied to the developing roller 56.
The layer thickness of the toner 53 attached to the surface of the toner 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 supported, and is composed of a conductive foamed elastic body made of silicon rubber or urethane rubber. The resistance value at the contact portion of the transfer roller 60 with the photosensitive drum 20 is about 1 × 10 ⁶ to 1 ×.
It is set to 10 ¹⁰ Ω. That is, the transfer roller 60 is
Since it is in contact with the surface of the photosensitive drum 20, its resistance value is increased so that the photoconductive layer 22 formed on the photosensitive drum 20 is not destroyed by the voltage applied to the transfer roller 60. The toner image on the photosensitive drum 20 is configured to be reliably transferred to the paper P.

The fixing unit 70 is provided on the downstream side of the photosensitive drum 20 in the conveying direction, and is composed of a heating roller 71 and a pressing roller 72 having a well-known halogen lamp built therein, and the toner image transferred to the lower surface of the paper P. Is pressed while being heated and fixed on the paper P.

A pair of transport rollers 75 and a paper discharge tray 77 for transporting the paper are respectively provided on the downstream side of the fixing unit 70 in the transport direction. 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 discharge tray 77 are separated from the paper feed cassette 14 along a conveyance 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 of a positively chargeable type, and is, for example, a pulverized toner or a non-magnetic one-component toner made of a polymerized toner such as styrene-acryl having a nearly spherical shape. , And contains silica as an external additive (fluidity imparting agent) added to the base toner. As a result, toner 5
Most of 3 is rubbed by the developing roller 56, the photosensitive drum 20 and the like and charged to a positive polarity.

Next, the operation of the laser beam printer 1 configured as described above will be described with reference to FIGS. 1 to 5. In FIG. 1, the photosensitive drum 20 is rotationally driven clockwise in a side view by a driving unit, and is supplied to the supply roller 55.
The developing roller 56 is rotationally driven in the clockwise direction.

As a result, as shown in FIG.
Of the particles of the developing roller 5 of the developing roller 5 of the layer thickness regulating plate 57 by rubbing between the supply roller 55 and the developing roller 56.
The toner 53, which is positively charged due to the pressure friction against 6, is rubbed and charged by the developing roller 56 and the photosensitive drum 20, and is formed on the photosensitive drum 20 by the laser light L. The toner is attached to the electrostatic latent image and developed.

Here, the charge amount of the toner 53 changes from about 25 μC / g to 20 μC / g depending on the temperature and humidity. Therefore, when the developing roller 56 is driven in the same rotation direction as the photosensitive drum 20, the predetermined developing toner amount (for example, about 0.78 mg / cm ² ), the effective developing bias voltage of the developing roller 56 (the electrostatic latent image potential V1 of the photosensitive drum 20 and the potential Vb of the developing roller 56) is obtained.
Potential difference) is set to "about 200 V".

Here, the drum offset voltage Va of the photosensitive drum 20 is set to, for example, about 300 V, and the electrostatic latent image voltage V1 which is the voltage of the electrostatic latent image formed on the photosensitive drum 20 is, for example, Since it will be about 350V,
The voltage Vb of the developing power source 103 applied to the developing roller 56.
Is set to, for example, "about 550V" so that the effective developing bias voltage becomes 200V, and the cleaning roller 42
The voltage Vc of the first power source is set to, for example, "about 700 V" so that the residual toner 53 can be discharged onto the photosensitive drum 20.

As a result of the voltage setting of each part, the cleaning roller 42 is switched to the switch S in the suction mode.
Grounded by W1, for example, "0V-350V =-
Due to the potential difference of “350 V”, the residual toner 53 charged in the positive polarity can be sucked from the surface of the photosensitive drum 20. On the other hand, in the discharge mode, the switch SW
1 is connected to the first power supply 101, for example, "700
The residual toner can be discharged onto the surface of the photosensitive drum 20 due to the potential difference of “V−350V = + 350V”.

When the image forming process is started under the voltage setting as described above, the charge eliminating lamp 41 first causes the photosensitive drum 20 to move.
After the residual charge on the upper side is wiped out, the surface of the photosensitive drum 20 is, for example, as shown in FIG.
As shown in (4), it is uniformly charged to V0 (for example, 800V + 300V). Then, in this state, the laser generator 3
The laser beam L emitted from No. 1 is irradiated onto the photosensitive drum 20 through the lenses 33 and 34 and the reflecting mirrors 35 and 36 while being main-scanned by the polygon mirror 32, and an electrostatic latent image is formed on the photosensitive drum 20. To be done. At this time, the voltage of the portion corresponding to the electrostatic latent image on the photosensitive drum 20 is lowered to V1 (for example, 350 V) by the irradiation of the laser light L, as shown in FIG. 5A, for example. To the surface of the developing roller 56, when a developing bias voltage of, for example, Vb (for example, 550V) is applied as shown in FIG. 5A, the toner 53 has a charging voltage V0 higher than its own voltage. (Electrical potential of unexposed area, eg 800V
However, the toner 53 on the developing roller 56 is attracted to the electrostatic latent image voltage V1 (for example, 350 V) lower than the electrostatic latent image voltage V1 (+300 V).
0 is attached and developed only on the electrostatic latent image formed on the surface.

The toner image of the electrostatic latent image developed with the toner 53 is transferred onto the paper P by the transfer roller 60,
The fixing processing is performed by the fixing unit 70 and the sheet is discharged to the sheet discharge tray 77.

At this time, the transport path PP for transporting the paper P fed from the paper feed cassette 14 is formed in a substantially linear shape,
Since the image is formed on the paper P while being conveyed by the substantially linear conveyance path PP, even if a thick paper such as a postcard or an envelope or an OHP film is used as the paper P, the paper P can be neatly and reliably formed. An image can be formed on.

On the other hand, in FIG. 1, the residual toner 53 remaining on the photosensitive drum 20 without being transferred to the paper P when passing through the transfer roller 60 is obtained by connecting the cleaning roller 42 to the ground by the switch SW1. 5
As shown in (b), the cleaning roller 42 in the suction mode is once absorbed by the potential difference of −350V. Then, by connecting the cleaning roller 42 to the first power source 101 by the switch SW1 at a timing that does not interfere with the next exposure, development, transfer, etc. performed on the photosensitive drum 20, it is once absorbed by the potential difference of + 350V. The residual toner 53 is discharged onto the photosensitive drum 20 from the cleaning roller 42 in the discharge mode and is smoothed.

The residual toner 53 is transferred to the developing unit 5
Returning to 0, the developing roller 56 in the non-operating state, which is connected to the ground by the switch SW2, causes the photosensitive drum 20
The upper residual toner 53 is collected.

The toner 53 may be collected in the discharge mode described above by periodically stopping the image forming operation so that it does not interfere with the image forming operation at the corresponding timing between the sheets P. Alternatively, the image forming operations may be sewn in between.

As described above, according to the laser beam printer 1 of the present embodiment, the cleanerless cleaning is performed by supplying only one power source (that is, the first power source 101) to the cleaning roller 42. Be seen. Further, since the second voltage is supplied to the photosensitive drum 20 by the second power source 102, when the power source of the laser beam printer 1 is turned on, the developing roller 56 is 0V,
Since the potential is lower than the potential of the photosensitive drum 20 (Va: +300 V, for example), the toner 53 is not attached to the photosensitive drum 20 from the developing roller 56 due to this potential difference, and therefore wasteful development is not performed. As a result, the transfer roller 60 is not contaminated by the toner 53 when the power of the laser printer 1 is turned on, and it is possible to prevent printing defects due to such contamination and form a high-quality image. .

According to the above-mentioned embodiments, only the formation of a monochrome image has been described, but the present invention effectively functions also when forming a color image. Further, although the photoconductor is composed of the photoconductor drum, it may be a belt-shaped photoconductor, and the relative moving directions of the photoconductor drum and the developing roller may be opposite or the same. Furthermore, although the laser beam printer has been described in the present embodiment, the present invention is applicable to copying, facsimile and the like as in the case of the present embodiment as long as it is an electrophotographic image forming apparatus using toner. It works effectively.

Further, according to the present embodiment, the second power source 1
02 includes a current-voltage conversion element such as a varistor, so that the second power supply 102 can be configured at low cost.

[0055]

According to the image forming apparatus of the first aspect, the cleanerless cleaning can be performed by supplying only one power source (that is, the first power source) to the leveling means, The size, simplification and cost of the device can be reduced. No wasteful development is performed until the surface potential of the photosensitive drum reaches a predetermined bias value when the power of the image forming apparatus is turned on, and at this time, the transfer unit is contaminated with the developer. In addition, it is possible to prevent defective printing due to such stains, and it is possible to form a high-quality image. Further, since the current-voltage converting element is provided, the cost can be reduced, and the cost of the image forming apparatus can be reduced.

According to the image forming apparatus of the first aspect,
By using the voltage difference between the third power source and the second voltage supplied to the photosensitive member as the developing bias voltage, the developing unit in the normal operating state can appropriately develop the electrostatic latent image on the photosensitive member.

According to the image forming apparatus of the second aspect,
The developer is prevented from adhering to the photoconductor from the developing means, and unnecessary development is not performed.

According to the image forming apparatus of claim 3,
The developer remaining on the photoconductor can be appropriately smoothed by the cleaning roller or the cleaning brush. As a result, according to the present invention, a relatively low cost image forming apparatus capable of forming a high quality image can be realized.

[Brief description of 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 respective power supplies and switches of the laser beam printer of FIG.

FIG. 4 is an enlarged side view of a developing unit of the laser beam printer of FIG.

5 is an explanatory diagram showing the potential of each portion in the developing process and the cleaning process performed by the laser beam printer of FIG.

[Explanation of symbols]

1 ... Laser beam printer 10 ... Feeder unit 13 ... Paper feed roller 14 ... Paper feed cassette 20 ... Photosensitive drum 30 ... Laser scanner unit 42 ... Cleaning roller 50 ... Development unit 53 ... Toner 55 ... Supply roller 56 ... Developing roller 57 ... Layer thickness control blade 60 ... Transfer roller 70: fixing unit 77 ... Paper ejection tray 101 ... 1st power supply 102 ... Second power source 103 ... Third power source SW1 ... switch SW2 ... switch

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) G03G 21/00 G03G 21/10-21/12 G03G 15/08-15/08 507 G03G 21/00 370-540 G03G 21 /14

Claims (3)

(57) [Claims] 1. A photosensitive member, a charger for charging the photosensitive member to a predetermined voltage so as to form an electrostatic latent image, a latent image forming means for forming an electrostatic latent image on the photosensitive member, and an operating state. Developing means for developing the electrostatic latent image with a developer charged to a predetermined polarity to form an image on the photoconductor, and collecting the developer leveled on the photoconductor in a non-operating state; A transfer means for transferring the image to a recording medium; in the suction mode, the developer remaining on the photoconductor after the transfer is attracted by a potential difference from the photoconductor, and in the discharge mode, the attracted developer is transferred to the photoconductor. Means for discharging and smoothing the light on the photoconductor by the potential difference between the first and second power supplies, and a first power supply for supplying a first voltage different from the ground potential to the smoothing means; and the ground potential and the first voltage for the photoconductor. A current that supplies a second voltage that is different from the voltage Wherein the pressure transducer, the voltage difference between the second voltage supplied to the photosensitive member as the developing bias voltage, during the development of the third voltage causes the developer for electrostatic latent image of the photosensitive member by said developing means By connecting the third power source to the developing means and the leveling means to one of the ground and the first power source, the suction mode is switched to, and the leveling means is connected to the other of the ground and the first power source. An image forming apparatus comprising: a switching unit that switches to the discharge mode by doing so. 2. The image forming apparatus according to claim 1, wherein the developing unit collects the developer discharged from the photoconductor from the leveling unit in a non-operating state of being grounded. 3. The image according to claim 1, wherein the leveling unit includes one of a cleaning roller and a cleaning brush that are arranged to face the photoconductor. Forming equipment.