JP2005215450A - Developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device in which developer fall is prevented by a simple structure even when an amount of developer, or a layer of developer to be supplied, is increased and, in addition, the followability can be ensured even when images having high density bandlike parts in the direction of paper passage are consecutively formed. <P>SOLUTION: Each magnet seal m having the shape of an almost half ring is affixed to one side of each of specific vanes 57a of a stirring screw 57. This makes it possible to attract carrier with magnetic force and enhances force with which the developer is held. Accordingly, so-called developer fall is prevented and an amount of developer, or a layer of developer to be supplied, between the stirring screw 57 and the developing roller 55 in a lower chamber 53 can be increased. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a developing device that supplies a developer to an image carrier in an image forming apparatus such as a copying machine or a printer, and more specifically, uses a two-component developer composed of toner and a magnetic carrier. The present invention relates to a developing device of a form.

  2. Description of the Related Art Conventionally, in an image forming apparatus, in order to develop an electrostatic latent image formed on a photosensitive drum as an image carrier, a developing apparatus using a two-component developer composed of toner and a magnetic carrier has been used. ing. Such an electrostatic latent image developing device includes a developing housing for containing a developer, a developing roller as developer supplying means for supplying the developer in the developing housing to the electrostatic latent image on the photosensitive drum, and a developing housing. The developer includes a stirring screw that is a developer stirring unit that stirs the developer inside and transports the developer in a required direction, and a toner replenishing unit that replenishes toner in the developing housing.

  The developer supply means supplies toner to the electrostatic latent image in the development area of the photosensitive drum. Thereby, the electrostatic latent image is developed into a toner image. When the toner in the developing housing is consumed according to the supply of toner to the electrostatic latent image, the toner is supplied by the toner supply means. The developer agitating unit agitates the developer in the developing housing to agitate the toner and the carrier, mixes the toner and the carrier, and frictionally charges the toner and the carrier, and conveys the toner in the required direction.

As a prior art satisfying the above requirements for stirring and transporting developer, a configuration in which developer pumping means is provided in a vertical stirring type developing device having first and second stirring means at the top and bottom. (For example, refer to Patent Document 1). In this way, the developer is sufficiently stirred to prevent stagnation, and the entire developing device is downsized.
JP 2001-109264 A

  However, for example, in a color tandem developing type color copying machine, the conventional developing device described above has a stirring screw that supplies developer to the developing roller with respect to the diameter of the developing roller (developer supplying means). In some cases, the diameter of (developer stirring means) is very small, and the position of the stirring screw is higher than the developing roller.

  In such a configuration, the amount of developer existing in the developer supply layer between the agitating screw and the developing roller is small, so that the toner supply amount in the developer is insufficient. For this reason, for example, when an image having a belt-like portion having a high density in the sheet direction is continuously printed, the toner supply cannot be followed. Further, as a countermeasure against this, when the amount of the developer is increased, there is a problem that the developer leaks out from the gap between the developing roller and the developing housing (developer drops).

  In view of such problems, the present invention has a simple configuration, and even when the amount of developer in the supply layer is increased, the developer does not fall off, and an image having a high density belt-shaped portion in the paper direction is continuously provided. It is an object of the present invention to provide a developing device that can ensure followability even when printing is performed.

  In order to achieve the above object, according to the present invention, a developer supply means for supplying a developer comprising toner and a carrier to an image carrier, and a developer supply means provided in the vicinity of the developer supply means for conveying the developer while stirring. And a developer stirring means for supplying the developer supplying means, and a magnetic field generating means is provided on a blade portion of the developer stirring means.

  According to the present invention, even if the developer amount in the supply layer is increased with a simple configuration, the developer does not fall off, and even if an image having a high density belt-shaped portion in the paper direction is continuously printed, In addition, it is possible to provide a developing device that can ensure followability.

  Specifically, by providing a magnetic field generating means on the blades of the developer agitating means, thereby adsorbing the magnetic carrier and increasing the holding power for holding the developer, so-called developer dropping occurs. The developer amount in the developer supply layer can be increased.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of an image forming apparatus having a developing device according to an embodiment of the present invention, and shows an example of a color copier of a quadruple tandem developing system. In the figure, 1 is a paper feeding unit, 2 is an image forming unit, 3 is a fixing unit, and 4 is a paper discharge device. In the image forming unit 2, the developing units 5a, 5b, 5c, and 5d have toners colored magenta, cyan, yellow, and black, respectively.

  Each of the photosensitive drums 7 whose surfaces are uniformly charged by the respective chargers 6 corresponding to each of them receives the light image of the original that has been color-separated into predetermined colors, and is exposed. The electrostatic latent image generated on the surface of each photosensitive drum 7 by exposure is visualized by electrostatically adsorbing toner of each color by the developing devices 5a, 5b, 5c, and 5d. .

  On the other hand, the paper fed from the paper feeding unit 1 is transported by the transport belt 8, and the toner image of each color is transferred when passing through each photosensitive drum 7. In this way, the paper on which the multicolor toner image is formed is further conveyed and passes through the fixing unit 3 where it is heated and pressed to fix the multicolor toner image. The fixed sheet is conveyed to the sheet discharge device 4 and is discharged from here to the sheet discharge unit 9 to be stocked.

  The image forming procedure will be described again. The surface of the photosensitive drum 7 is uniformly charged by the charger 6. On the other hand, image data from a document (not shown) is written on the surface of the photosensitive drum 7 by the exposure device 21, and an electrostatic latent image is formed on the surface of the photosensitive drum 7. Next, the electrostatic latent images on the photosensitive drum 7 are visualized with toners of various colors by the developing units 5a, 5b, 5c, and 5d.

  On the other hand, the paper stored in the paper feed cassette 22 is pulled out by the pickup roller 23 of the paper feed unit 1, is sandwiched between the paper feed roller 24 and the separating roller 25, and is sent to the conveyance path. Then, the paper is sent out to the image forming unit 2 by the conveyance belt 8 at the timing when the toner image on the photosensitive drum 7 reaches the image forming unit. In the image forming unit 2, the toner image on the photosensitive drum 7 moves onto the sheet while the sheet is sandwiched between the photosensitive drum 7 and the transfer roller 26 via the conveyance belt. The toner remaining on the photosensitive drum 7 without moving onto the paper is removed and collected by the cleaning roller 27.

  On the other hand, the sheet on which the toner image is placed is conveyed to the fixing roller pair 28 of the fixing unit 3. Here, the toner image is heated and pressurized by the fixing roller pair 28 and fixed on the paper. Then, the paper is discharged to the paper discharge unit 9 by the discharge roller 11 and the driven roller 13. The paper placed on the manual feed tray T is sent to the transport belt 8 by the paper feed roller 29, and thereafter passes through the same transport path as that described above.

  FIG. 2 is a side sectional view of the developing device according to the first embodiment of the present invention. Here, the main part of the above-described developing device is shown. The developing device of this embodiment includes a developing housing 51 as a whole, and is divided into a lower chamber 53 and an upper chamber 54 by a partition wall 52. In the lower chamber 53, an outwardly extending portion 53a is formed (on the photosensitive drum side), and a developing roller 55 having a magnet and having a rotatable sleeve is disposed in the protruding portion 53a. In addition, a panning blade 56 is disposed at a predetermined interval from the surface of the developing roller 55.

  The developing roller 55 fixes a magnet inside and rotates a sleeve of a non-magnetic member at the outer peripheral portion counterclockwise in the figure, and a developer magnetic brush adjusted to a constant layer thickness by a panning blade 56. To the development zone. The developing roller 55 is disposed so as to face a photosensitive drum (not shown). A main charging device and an optical system for performing image exposure are arranged on the upstream side in the rotation direction of the photosensitive drum, and then a developing device is arranged, and on the downstream side, a transfer mechanism including a transfer charger or a transfer roller. , A static elimination mechanism, and a cleaning device such as a cleaning blade are arranged.

  Then, the surface of the photosensitive drum is uniformly charged by the main charging device, an electrostatic image is formed on the surface of the photosensitive drum by image exposure by the optical system, and the developing area (the developing roller 55 and the photosensitive drum) is developed by the developing roller 55. The developer magnetic brush conveyed between the toner and the toner is rubbed against the electrostatic image, and as a result, a toner image is formed on the surface of the photosensitive drum. This toner image is transferred onto the surface of a predetermined transfer paper by a transfer mechanism.

  The transfer toner image is fixed on the transfer paper surface by a known mechanism such as heat and pressure by a fixing mechanism provided on the discharge path of the transfer paper. On the other hand, the surface of the photosensitive drum after the transfer of the toner image is neutralized by the static elimination mechanism and returned to the potential before the main charging, and further, the toner remaining on the photosensitive drum surface is removed by the cleaning mechanism, Thereby, one cycle of image formation is completed.

  A stirring screw 57 extending along the axial direction of the developing roller 55 is provided in the lower chamber 53 of the developing housing 51 at a distance from the developing roller 55. Further, the upper chamber 54 is provided with a stirring screw 58 that also extends along the axial direction of the developing roller 55. Further, a cover 59 is provided on the uppermost part of the developing housing 51, thereby closing the upper chamber 54.

  FIG. 3 is an external perspective view of the developing device according to the present embodiment. The above-described stirring screw 57 in the lower chamber 53 and the stirring screw 58 in the upper chamber 54 have their blades or rotation directions set so as to feed the developer in the opposite directions along the axial direction of the developing roller 55. ing. For example, the agitation screw 57 is set so as to agitate and feed the developer in the direction of arrow A in the figure, and the agitation screw 58 is set to agitate and feed the developer in the direction of arrow B in the figure.

  As can be seen from the figure, the protruding portion 53 a of the lower chamber 53 in which the developing roller 55 is accommodated is formed in a part of the developing housing 51 in the longitudinal direction, and both ends of the lower chamber 53 and the upper chamber 54 in the longitudinal direction. The overhanging portion 53a and hence the developing roller 55 are not disposed in the portion located at the position.

  Further, communicating portions 60 and 61 between the lower chamber 53 and the upper chamber 54 are formed at both ends in the longitudinal direction of the developing housing 51. In the communication portion 60 located at the tip of the stirring chamber 58 in the feed direction (B) in the upper chamber 54, although not shown, the partition wall 2 is not provided or the partition wall 52 has an appropriate size. The developer that has been stirred and fed by the stirring screw 58 falls from the upper chamber 54 into the lower chamber 53.

  Further, in the communicating portion 61 located at the tip of the agitating screw 57 in the feed direction (A) in the lower chamber 53, the developer in the lower chamber 53 is formed in the form of a magnetic brush in the upper chamber 54 by a magnet roller (not shown). It is configured to pump up. As described above, the developer is circulated and stirred between the lower chamber 53 and the upper chamber 54, and a part of the developer in the lower chamber 53 is supplied onto the developing roller 55 for development. .

  In addition, a toner replenishing opening 70 is provided in the upper wall 59 a of the upper chamber 54 connected to the communication part 61, and a predetermined amount of toner is replenished through the opening 70. Incidentally, FIG. 4 is an external perspective view of the developing device according to this embodiment in a state where covers are removed. Here, a state in which the cover 59 of the developing housing 51 and the cover of the projecting portion 53a are removed is illustrated. In this state, the stirring screw 58 in the upper chamber 54, the developing roller 55, and the ear cutting blade 56 are shown.

  FIG. 5 is an external perspective view of the stirring screw 57. In the present embodiment, as shown in the drawing, a known half-ring-shaped magnetic field generating means shown on the one side surface (downstream side surface in the developer conveying direction) of the predetermined blade 57a of the stirring screw 57 is known per se. The magnet seal m is pasted. As a result, the holding force for adsorbing the carrier by the magnetic force and holding the developer can be increased, and the developer supply between the stirring screw 57 and the developing roller 55 in the lower chamber 53 without causing the so-called developer dropping. The developer amount of the layer 53b (see FIG. 2) can be increased. However, the magnetic force of the magnet seal m and the amount to be pasted need to be set appropriately as described below because the developer conveying force decreases if it becomes excessive.

  FIG. 6 is an external view of the stirring screw 57. FIG. 4A is a plan view, FIG. 4B is a front view, and FIG. 4C is a bottom view. As shown in the figure, the stirring screw 57 sandwiches the shafts 57b from opposite sides so that the substantially semi-disc shaped blades 57a have a cross shape in plan view on the outer peripheral surface of the shaft 57b. It has a continuously arranged shape. The substantially semi-ring-shaped magnet seals m are alternately attached to the blades 57a every other piece together with the opposite side of the shaft. The surface to be affixed is one surface on one side in the axial direction. Further, the affixing range is a range where the stirring screw 57 faces the developing roller 55.

  The magnetic force (magnetic flux density) of the magnet seal m is 25 ± 5 mT (millitesla). Moreover, since the arrangement | positioning pitch of the axial direction of the blade | wing 57a is 12.75 mm, the sticking pitch of the magnet seal m every other sheet | seat will be 25.5 mm. However, since the magnetic seals m are alternately attached together with the opposite side of the shaft, the magnet seals m are continuously arranged in a substantially spiral shape.

  FIG. 7 is a schematic diagram showing an image for confirming the effect of this embodiment. In this embodiment, an apparatus with 26 copies per minute is used, and as shown in the figure, with respect to A4 (297 mm × 210 mm) paper P, the paper passing direction is the short side direction as shown by the arrow, Continuous paper passing was performed so that a solid band part a having a width of 25 mm formed in the vicinity of one end in the long side direction formed an image extending in the short side direction.

  As a result, when the magnetic seal m was not affixed to the stirring screw 57, when the image was visually confirmed on the solid band portion a at the time when about 10 sheets were continuously fed, a soft feeling was generated. However, although the image density was measured using a reflection densitometer RD918 manufactured by Macbeth Co., it was about 1.2 to 1.3, and there was no problem as the image density. After the magnet seal m was attached to the stirring screw 57, the image was visually confirmed even after passing 500 sheets continuously, but there was no rustiness and the image density was not a problem.

1 is a longitudinal sectional view of an image forming apparatus having a developing device according to an embodiment of the present invention. 1 is a side cross-sectional view of a developing device according to Embodiment 1 of the present invention. 1 is an external perspective view of a developing device according to the present embodiment. FIG. 3 is an external perspective view of the developing device according to the present embodiment in a state where covers are removed. The external appearance perspective view of a stirring screw. The external view of a stirring screw. The schematic diagram which shows the image for confirming the effect of a present Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Paper feed part 2 Image formation part 3 Fixing part 4 Paper discharge | emission apparatus 5a, 5b, 5c, 5d Developer 6 Charger 7 Photoconductor drum 8 Conveyance belt 9 Paper discharge part 11 Discharge roller 13 Drive roller T Manual feed tray 21 Exposure apparatus DESCRIPTION OF SYMBOLS 22 Paper feed cassette 23 Pickup roller 24 Paper feed roller 25 Rolling roller 26 Transfer roller 27 Cleaning roller 28 Fixing roller pair 29 Paper feed roller 51 Developing housing 52 Partition wall 53 Lower chamber 54 Upper chamber 55 Developing roller 56 Ear cutting blade 57 Stir screw 58 Stirring screw 59 Cover 60 Communication part 61 Communication part 71 Opening m Magnet seal

Claims (1)

  A developer supplying means for supplying a developer comprising toner and a carrier to the image carrier, and a developer provided near the developer supplying means for conveying the developer while stirring and supplying the developer to the developer supplying means A developing device comprising: a stirring unit; and a magnetic field generating unit provided on a blade portion of the developer stirring unit.

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