JP2007240956A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a developer from staying in a developing device having a developing roller, a supply roller, and an agitating member arranged vertically therein. <P>SOLUTION: The developing device for supplying the developer to a photoreceptor drum 21 includes a developing roller 221, a toner supply roller 222, a toner agitating screw 224, and an electromagnet 225. The developing roller 221 is disposed oppositely to the photoreceptor drum 21. The toner supply roller 222 is disposed in proximity to the developing roller 221 having its rotation center above the rotation center of the developing roller 221 and supplies the developer to the developing roller 221. The toner agitating screw 224 has its rotation center above the rotation center of the toner supply roller 222 and is disposed in proximity to the toner supply roller 222 and is a member for agitating the developer. The electromagnet 225 is mounted on the toner agitating screw 224 and is capable of pumping up the developer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a developing device and an image forming apparatus, and more particularly to a developing device for supplying a developer to an image carrier and an image forming apparatus provided with the developing device.

The image forming apparatus includes an image forming unit for forming an image based on image information. In the case of an electrophotographic system, the image forming unit includes an image carrier on which an electrostatic latent image is formed on the surface, and an electrostatic latent image formed on the surface of the image carrier with a developer therein. And a developing device for supplying. The developing device includes a developing roller disposed at a position facing the image carrier, a supply roller that supplies developer to the developing roller, and a stirring member that stirs the developer in the developing device. An image forming apparatus that forms a full-color image has a plurality of developing devices each having a different color developer. In such an image forming apparatus, as shown in FIG. 6, a supply roller 114 is disposed above the developing roller 113 in the developing device 111 and a stirring member 115 is disposed above the supply roller 114 in order to reduce the size. (See Patent Document 1).
Japanese Patent Laid-Open No. 2005-55840

  In the developing device 111 of such an image forming apparatus, since the developing roller 113, the supply roller 114, and the stirring member 115 are arranged vertically, there is a region A that is not stirred by the stirring member 115. In this case, the developer stays in the region A, the developer circulation becomes non-uniform, and there is a possibility that image density unevenness, image density failure, and the like occur. Further, when the developer stays, the staying developer may be stressed to promote deterioration of the developer.

  An object of the present invention is to prevent a developer from staying in a developing device in which a developing roller, a supply roller, and a stirring member are arranged vertically.

  A developing device according to a first aspect is a developing device for supplying a developer to an image carrier, and includes a developing roller, a supply roller, a stirring member, and an electromagnet. The developing roller is disposed to face the image carrier. The supply roller is disposed close to the developing roller having a rotation center above the rotation center of the developing roller, and supplies the developer to the developing roller. The stirring member has a rotation center above the rotation center of the supply roller, and is disposed in the vicinity of the supply roller, and is a member for stirring the developer. The electromagnet is attached to the stirring member and can draw up the developer.

  In this developing device, the developer in the developing device is stirred by the stirring member, and the developer on the surface of the supply roller is supplied to the developing roller. At this time, since the developer is pumped up to the stirring member side by the electromagnet mounted on the stirring member, the developer can be prevented from staying inside the developing device.

  Here, it is possible to prevent a decrease in image quality due to the deterioration of the developer due to the developer staying in the developing device for a long period of time.

  A developing device according to a second aspect is the developing device according to the first aspect, wherein the developer includes toner and a carrier, and the electromagnet pumps up the developer by generating a magnetic field.

  Here, since the developer is a two-component developer, the developer is easily pumped up by a magnetic field generated by an electromagnet.

  A developing device according to a third aspect is the developing device according to the first or second aspect, wherein the agitating member has a rotating shaft and a blade portion provided on the rotating shaft, and the electromagnet has a blade portion. It is fixed to.

  Here, the electromagnet is easily fixed and the developer is easily stirred.

  A developing device according to a fourth aspect is the developing device according to any one of the first to third aspects, wherein the electromagnet is formed in a rod shape.

  Here, the electromagnet can be easily manufactured and attached. Furthermore, manufacturing costs can be reduced.

  A developing device according to a fifth aspect is the developing device according to any one of the first to fourth aspects, further including a voltage control device that controls a voltage applied to the electromagnet during non-printing.

  Here, it is possible to prevent the toner supply amount of the supply roller from being reduced due to the influence of the developer by the electromagnet during non-printing, and the occurrence of image density unevenness.

  An image forming apparatus according to a sixth aspect includes a plurality of developing devices according to any one of the first to fifth aspects and an image carrier on which electrostatic latent images arranged corresponding to the plurality of developing devices are formed on the surface. And a plurality of developing devices and a plurality of image carriers are arranged in a tandem manner.

  In this image forming apparatus, an electrostatic latent image is formed on the surface of the image carrier, and a developer is supplied to the electrostatic latent image by the developing device.

  The present invention can prevent the developer from staying in the developing device in which the developing roller, the supply roller, and the stirring member are arranged vertically.

1. Configuration FIG. 1 shows a color printer 1 which is an image forming apparatus in which an embodiment of the present invention is adopted. FIG. 1 is a schematic diagram for showing the arrangement of each component, and details of each part are omitted.

  The color printer 1 is connected to a computer (not shown) or the like, and is a device that can print a color image on paper based on image information transmitted from an external computer or the like.

  The color printer 1 includes an image forming unit 2 that forms an image based on image information, a paper transport unit 3 that transports a paper, a fixing unit 4 that fixes an image formed by the image forming unit 2 to the paper, A paper storage unit 5 for storing paper and a discharge unit 6 for discharging the paper to the outside of the color printer 1 are provided.

  The four image forming units 2 are arranged side by side in the paper conveyance direction, and include a photosensitive drum 21 (image carrier), a developing device 22, a toner storage unit 23, an exposure device 24, and a charging device 25. have.

  The photosensitive drum 21 is a member that forms a toner image on the surface thereof, and is a cylindrical member. The photosensitive drum 21 is a rotatable member, and the rotation axis of each photosensitive drum 21 extends in a direction perpendicular to the paper surface of FIG.

  The developing device 22 is a device for supplying toner to the photosensitive drum 21 and is disposed adjacent to the photosensitive drum 21. Each of the four developing devices 22 contains a carrier and toner of different colors, and as shown in FIGS. 2 and 3, a developing roller 221, a toner supply roller 222, a voltage applying device 223, A first toner stirring screw 224 (stirring member), an electromagnet 225, a second toner stirring screw 226, and an energization control device 227 are provided. Further, a low magnetic force carrier is used as the carrier in order to improve the separation from the toner supply roller. Here, FIG. 2 is an enlarged view of the developing device 22, and FIG. 3 is a view showing the first toner stirring screw 224 and the electromagnet 225.

  The developing roller 221 is provided in the vicinity of the photosensitive drum 21. The rotating shaft of the developing roller 221 is disposed in parallel with the rotating shaft of the photosensitive drum 21.

  The toner supply roller 222 is a member that supplies toner to the developing roller 221 and is disposed in the vicinity of the developing roller 221. Further, the rotation axis (rotation center) of the toner supply roller 222 is disposed above the rotation axis (rotation center) of the developing roller 221.

  The voltage application device 223 is connected to the toner supply roller 222 and is a device for applying a voltage to the toner supply roller 222. When voltage is applied to the toner supply roller 222 by the voltage application device 223, toner and carrier spikes (magnetic brushes) are formed on the surface of the toner supply roller 222. After the magnetic brush is formed in this way, toner is supplied from the toner supply roller 222 to the developing roller 221.

  The first toner agitating screw 224 is a member for agitating the toner inside the developing device 22, and is a member having a rotating shaft 22a and a blade portion 22b. The rotation shaft 22 a (rotation center) of the first toner conveying screw 224 is disposed above the rotation shaft (rotation center) of the toner supply roller 222. The first toner stirring screw 224 is disposed at a predetermined interval from the toner supply roller 222.

The electromagnet 225 is a member that generates a magnetic field around it, and is a rod-shaped member that is formed by winding a coil around an iron core. As shown in FIG. 3, the electromagnet 225 is a member attached to the outer peripheral end of the blade portion 22 b of the first toner stirring screw 224 in parallel with the rotation shaft 22 a of the toner stirring screw 224. The surface of the electromagnet is coated with a resin so that the toner or carrier and the electromagnet 225 are not in direct contact with each other. The electromagnet 225 rotates integrally with the rotation of the first toner agitating screw 224, starts to be energized when the electromagnet 225 is at the bottom in the vertical direction, and enters a power cut-off state when the electromagnet 225 moves to the top in the vertical direction. . The magnetic force of the electromagnet 225 is 300 · 10 ⁻⁴ (T).

  The second toner stirring screw 226 is a member for stirring the toner inside the developing device 33 and is disposed in parallel with the first toner stirring screw 224. The configuration of the second toner stirring screw 226 is the same as the configuration of the first toner stirring screw 224.

  The voltage control device 227 is a device that controls the voltage applied to the electromagnet 225 to switch between the energized state and the power cut-off state of the electromagnet 225. Control application of voltage to switch. Here, FIG. 4 shows an energized state and a power cut-off state of the electromagnet 225. In FIG. 4, when the electromagnet 225 reaches the rotation direction region B, the electromagnet 225 enters the energized state, and when it exits the rotation direction region B, the power interruption state occurs. Note that the arrows in FIG. 4 indicate the rotation direction of the toner stirring screw 226.

  The toner accommodating portion 23 is a portion where four box-like members disposed above the developing device 22 are arranged side by side, and toner of a color corresponding to each developing device 22 is accommodated. .

  The charging device 24 is a device for charging the surface of the photosensitive drum 21, and is a device disposed adjacent to the photosensitive drum 21 above the photosensitive drum 21.

  The exposure device 25 is a portion that irradiates light to the photosensitive drum 21 based on image information, and is a device that is disposed above the photosensitive drum 21 and between the charging device 24 and the developing device 22. .

  The paper transport unit 3 is a part that transports the paper in the paper storage unit 5 in the order of the image forming unit 2, the fixing unit 4, and the discharge unit 6, and is disposed below the photosensitive drum 21 of the image forming unit 2. The conveyor belt 31 has a pair of rollers 32 and 33. When the paper is transported by the transport belt 31, the toner images formed on the surface of the photosensitive drum 21 are sequentially transferred onto the paper.

  The fixing unit 4 is a part for fixing the image formed on the sheet by the image forming unit 2, and includes a pressure roller 41 and a heating roller 42.

  The paper storage unit 5 is a part capable of storing various types of paper and has a plurality of paper feed cassettes 51. The paper storage unit 5 is disposed at the lower part of the color printer 1.

  The discharge unit 6 is a portion from which the sheet on which the image is fixed is discharged, and is provided on the upper portion of the color printer 1.

2. Operation Next, the operation during printing of the color printer 1 will be described.

  In the color printer 1, when image information is sent from a computer or the like connected to the outside, the surface of the photosensitive drum 21 is charged by the charging device 24. Based on this image information, the exposure device 25 irradiates the surface of the photosensitive drum 21 with light. When an electrostatic latent image is formed on the surface of the photosensitive drum 21, a voltage is applied to the toner supply roller 222 in the developing device 22 by the voltage application device 223, and a magnetic brush is formed on the surface of the toner supply roller 222. Then, toner is supplied from the toner supply roller 222 to the developing roller 221. Thereafter, the toner on the developing roller 221 is supplied to the surface of the photosensitive drum 21, and a toner image is formed on the photosensitive drum 21. At this time, the paper in the paper storage unit 5 is conveyed to the conveyance belt 31 of the paper conveyance unit 3. The paper is transported by the transport belt 31 and toner images of respective colors are sequentially transferred from the four photosensitive drums 21 to the paper. After the full color image is transferred to the paper in this way, it is conveyed to the fixing unit 4. The fixing unit 4 fixes the full-color image on the sheet, and the discharging unit 6 discharges the sheet on which the full-color image is fixed.

  Next, the operation during non-printing will be described.

  At the time of non-printing, the first toner stirring screw 224 is rotated, and the electromagnet 225 rotates about the rotation shaft 22 a of the first toner stirring screw 224 as the first toner stirring screw 224 rotates. At this time, the electromagnet 225 starts to be energized when passing through the vertical lowermost part. When the electromagnet 225 is energized, a magnetic field having a characteristic of drawing up the developer is generated. When the magnetic field is generated, the carrier is attracted to the electromagnet 225. At this time, since the first toner agitating screw 224 is located above the toner supply roller 222, the toner and carrier in a region that cannot be moved only by the rotation operation of the toner supplying roller 222 and the first toner agitating screw 224. Move. Then, when the first toner agitating screw 224 rotates and the electromagnet 225 passes through the top in the vertical direction, the electric power of the electromagnet 225 is cut off. At this time, the magnetic field generated by the electromagnet 225 disappears, and the toner and the carrier fall downward. This operation is repeated while the first toner stirring screw 224 rotates.

Here, at least a part of the toner and the carrier that cannot be moved only by the rotation operation of the toner supply roller 222 and the first toner agitating screw 224 are agitated, so that the circulation of the toner and the carrier becomes uneven. Thus, it is possible to prevent image density unevenness, image density failure, and the like. Further, it is possible to prevent deterioration phenomenon such as burying of the external additive of the toner due to the stress of the toner and the carrier.
3. Other Embodiments In the above embodiment, the electromagnet 225 has a rod shape, but the present invention is not limited to this, and the blade portion 302 of the first toner agitating screw 301 is arranged in the direction of the rotation axis 303 as shown in FIG. A plurality of small electromagnets 304 may be attached side by side. In the above embodiment, the color printer 1 has been described. However, the present invention is not limited to this and may be a copying machine, a facsimile, or the like. Furthermore, in the above embodiment, the tandem color printer 1 has been described, but the tandem color printer 1 is not limited thereto.

1 is an overall schematic sectional view of a color printer 1. FIG. FIG. 3 is an enlarged sectional view of the developing device 22 The figure showing arrangement | positioning of the 1st toner stirring screw 224 and the electromagnet 225. FIG. Sectional drawing which shows typically the time of electricity supply of the electromagnet 225, and a power interruption state. The figure of the 1st toner stirring screw 301 and electromagnet 304 of other embodiments. Sectional drawing of the conventional image development apparatus 111. FIG.

Explanation of symbols

1 Color printer (image forming device)
2 Image forming unit 21 Photosensitive drum (image carrier)
22 Developing Device 221 Developing Roller 222 Toner Supply Roller (Supply Roller)
224 First toner stirring screw (stirring member)
225 Electromagnet 227 Voltage control device 22a Rotating shaft 22b Blade portion

Claims (6)

A developing device for supplying a developer to an image carrier,
A developing roller disposed opposite to the image carrier;
A supply roller that has a rotation center above the rotation center of the developing roller, is disposed close to the developing roller, and supplies the developer to the developing roller;
An agitation member disposed in proximity to the supply roller having a rotation center above the rotation center of the supply roller, and for agitating the developer;
An electromagnet mounted on the stirring member and capable of pumping the developer;
A developing device comprising: The developer includes a toner and a carrier,
The electromagnet pumps up the developer by generating a magnetic field,
The developing device according to claim 1. The stirring member is
A rotation axis;
And a blade portion provided on the rotating shaft,
The electromagnet is fixed to the blade portion,
The developing device according to claim 1 or 2.   The developing device according to claim 1, wherein the electromagnet is formed in a rod shape.   The developing device according to claim 1, further comprising a voltage control device that controls a voltage applied to the electromagnet during non-printing. A plurality of developing devices according to any one of claims 1 to 5;
The image bearing member on which electrostatic latent images arranged corresponding to the plurality of developing devices are formed on the surface;
The plurality of developing devices and the plurality of image carriers are arranged in a tandem manner.
Image forming apparatus.

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