JPH023186B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in multi-stage magnetic brush development apparatus for electrophotography.

As a method for developing an electrostatic image, a magnetic brush developing method is conventionally known in which development is performed by forming a magnetic brush of developer using a magnet. Therefore, when performing high-speed copying using such a magnetic brush development method, a multi-stage magnetic brush development method in which a plurality of magnetic brushes are formed is employed in order to increase the developing ability.

In general, in the magnetic brush development method, the carrier acts as a close opposing electrode for the electrostatic charge image, so it is possible to develop a wide area image. Since the strength is high, the development speed in the peripheral area is high. Therefore, in the magnetic brush development method, development of thin lines, character portions, and peripheral portions of a wide-area image is completed first, and then development of the central portion of the wide-area image is slowly carried out.

Such development is often observed in multi-stage magnetic brush development methods, and is particularly noticeable when a carrier whose surface is insulated is used.

By the way, if the conditions are set to sufficiently develop a wide area area as described above, the developing conditions will be excessive for thin lines and characters, resulting in undesirable results such as thickening and crushing of thin lines and characters. Invite.

In view of these points, the present invention makes it possible to perform development under conditions that suit the portion that occupies a larger proportion of the document between thin lines and character portions and large area portions, thereby achieving good development. It is an object of the present invention to provide a multi-stage magnetic brush developing device.

The present invention will be explained below with reference to embodiments shown in the drawings.

FIG. 1 shows the case where an original document with many wide area areas is developed, and FIG. 2 shows the case where an original document with many thin lines and character areas is developed.

In FIGS. 1 and 2, the photosensitive drum 1
A developing unit housing 2 is disposed near the developing unit housing 2, and inside the developing unit housing 2, rotating shafts 4A, 4 that face the photoreceptor drum 1 with a small gap are disposed.
Rotating sleeves 3A, 3B, 3C, and 3D rotating around B, 4C, and 4D are arranged at approximately equal intervals. Each of these rotating sleeves 3A, 3B,
Developing magnets 5A and 5 are located in 3C and 3D, respectively.
B, 5C, 5D are supports 6A, 6B, 6C, 6
The magnets 5B and 5 are supported by magnets 5B and 5B and are disposed at positions facing the photoreceptor drum 1.
C and 5D are designed to be able to rotate in a direction in which the developer 7 is not attracted to the photosensitive drum 1. It is preferable that the magnets 5B, 5C, and 5D rotate by 180 degrees, but it may be within the range of 180 degrees ± 90 degrees. Also,
The support body 6A in the rotating sleeve 3A includes two developer-lifting magnets 8, 8 and a developer-transporting magnet 9.
is attached, and the rotating sleeve 3B,
A pair of conveyance magnets 9, 9 are attached to the supports 6B, 6C, and 6D in 3C and 3D, respectively, and spaced apart from each other in the diametrical direction.

Note that a rotary blade 1 is provided inside the developing unit housing 2.
0 is arranged to convey the developer 7 in the housing 2 toward the rotating sleeve 3A.

Next, the operation of the above-described embodiment will be explained.

Figure 1 shows a case where a document with many wide area parts is to be developed, and four rotating sleeves 3A, 3B, 3C,
The 3D developing magnets 5A, 5B, 5C, and 5D all face the photosensitive drum 1. Therefore, by rotating each of the rotating sleeves 3A, 3B, 3C, and 3D in the direction of the arrow, rotating the photosensitive drum 1 in the direction of the arrow, and further rotating the rotary blade 10,
The developer 7 is transferred from the rotating sleeve 3A to the rotating sleeve 3.
B, and from this rotary sleeve 3B to rotary sleeves 3C and 3D by a conveying magnet 9, and magnetic brushes 11A and 11 are provided on the photosensitive drum 1 side of each rotary sleeve 3A, 3B, 3C, and 3D.
B, 11C, and 11D are formed. The developer 7 forming the magnetic brushes 11A, 11B, 11C, and 11D is attracted to the electrostatic charge image on the photoreceptor drum 1 and developed.

In this way, in the case of a document with many large area parts, the four magnetic brushes 11A, 11B, 11C,
Since development is performed using 11D, a clear image with little edge effect can be obtained.

Next, FIG. 2 shows a case where a document with many fine lines and characters is developed, and the developing magnet 5C is rotated in the opposite direction to the photoreceptor drum 1 within the rotating sleeve 3C by operating a switch (not shown). ing. Therefore, in this case, the rotating sleeve 3
Since the magnetic brushes 11A and 11B are formed only in areas A and 3B, it is possible to achieve lighter development than in the case of FIG.

The multi-stage magnetic brush developing device according to the present invention can switch between a mode in which development is performed using all three or more rotating sleeves and a mode in which development is performed using only a limited number of the rotating sleeves. This has an excellent effect in that even if the document has many wide area areas or many thin lines and character areas, clear development can be achieved simply by switching the mode.

Note that the effects of the present invention described above will be explained by giving specific examples.

An electrostatic image was formed by a conventional method on a photoreceptor drum coated with a 50 μm layer of amorphous selenium using aluminum as a support. The manuscript at this time was a photograph and contained many large areas. Note that the potentials corresponding to the dark and bright areas of the original were +800V and +150V, respectively. When the latent image, which is an electrostatic charge image, on the photoreceptor drum was developed with a four-stage magnetic brush shown in FIG. 1, an image was formed in which a wide area with little edge effect was well filled with developer. The developer at this time was a so-called resin coat carrier, which is a 100μ iron ball coated with 2μ styrene resin, and toner for Ricoh PPC-900 at a weight ratio of 1.5.
The linear velocity of the photoreceptor drum is 400mm/sec, and the linear velocity of the rotating sleeve is 600mm/sec.
mm/sec.

Next, under the same conditions as described above, we changed the number of magnetic brushes to two as shown in Figure 2 and copied a manuscript consisting only of characters and lines, and a very clear image was obtained. .

[Brief explanation of drawings]

1 and 2 are explanatory diagrams showing the operating state of an embodiment of the multi-stage magnetic brush developing device according to the present invention. FIG. 7 is an explanatory diagram showing a case where a document containing many line parts is developed. 1... Photosensitive drum, 2... Developing unit housing, 3A, 3B, 3C, 3D... Rotating sleeve,
5A, 5B, 5C, 5D...Developing magnet, 7...
Developer, 8... Magnet for pumping up, 9... Magnet for conveyance, 11A, 11B, 11C, 11D... Magnetic brush.

Claims (1)

[Claims] 1. It has three or more rotating sleeves arranged close to the surface having an electrostatic charge image, and a plurality of magnetic brushes of developer are applied to the circumferential surface of the rotating sleeves by developing magnets arranged in each of these rotating sleeves. In a multi-stage magnetic brush developing device in which magnetic brushes are formed and development is performed using these magnetic brushes, the second and subsequent magnets from the developer pumping side are selectively moved to a position where no magnetic brush is formed depending on the type of document. A multi-stage magnetic brush developing device characterized by being rotatable.