JP2719147B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus including a plurality of developing devices arranged to face a photoconductor on which an electrostatic latent image is formed. .

(Prior Art) In recent various image forming apparatuses such as a color copying machine, a plurality of developing devices are arranged in parallel with a photoconductor, or a plurality of replaceable developing devices are selectively mounted and used. Various types of image forming apparatuses including a plurality of developing devices for one main body device, such as those described above, have been developed and put into practical use. For example, in a full-color copying machine, four or three developing devices are arranged in parallel to one photosensitive drum, and colors such as black, cyan, magenta, and yellow are arranged in each developing device. Different developers are accommodated respectively. In a twin-color copying machine, a developing device for containing a color developer is provided in addition to a developing device for containing a black developer. It can be replaced arbitrarily.

A plurality of developing devices used in such an image forming apparatus have different capacities depending on the frequency of use. Generally, since there are more black images than color images, the black developing device is set to have the largest capacity, and the color developing device is set to be smaller than the black developing device.

However, if the sizes of the respective developing devices are different from each other as described above, there is a problem that a difference occurs in the developer supply capability between the respective developing devices. In other words, in a small-sized developing device, the size of the developing sleeve that transports the developer to the developing area while holding the developer is also reduced, and accordingly, the size, characteristics, or shape of the magnet installed in the developing sleeve is restricted. As a result, the ability to hold the developer, that is, the ability to transport the developer is reduced. For this reason, a state in which the toner density is excessive in a small-sized developing device may cause a problem such as background contamination or toner scattering. Further, there is a case where a difference occurs in the developer conveying ability depending on a position where each developing device is arranged, which causes the same problem.

(Object) Accordingly, an object of the present invention is to provide an image forming apparatus capable of reliably correcting a difference in developer supply capability among a plurality of developing devices with a simple configuration.

(Structure) In order to achieve the above object, the present invention comprises a plurality of developing devices arranged to face a photoreceptor, and in each of the developing devices, a developer is conveyed while being held on a surface. In an image forming apparatus provided with a developing sleeve for supplying toner to the electrostatic latent image formed on the photoconductor, the diameter of the developing sleeve provided in each of the developing devices is different, and each of the developing devices is The surface shape of the developing sleeve having a smaller diameter is formed so as to have a greater developer holding force than the surface shape of the developing sleeve having a larger diameter so as to have substantially the same developer supply capacity. It has a configuration.

In the image forming apparatus having such a configuration, the surface shape of the developing sleeve provided in each developing device has a different developer holding force, that is, a different developer holding force corresponding to the capacity and arrangement position of the developing device and the diameter of the developing sleeve. It will be set to have different developer transport capacity, respectively,
As a result, the amount of toner supplied from each developing device is made substantially the same.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 3 shows an example of a twin-color copying machine to which the present invention is applied. Around the photoconductor drum 1, a charging charger 2 for uniformly charging the surface of the photoconductor drum 1 along the rotation direction of the photoconductor drum 1, and a predetermined light image is formed on the charged surface of the photoconductor drum 1. An exposure optical system 3 for irradiating and exposing to form an electrostatic latent image, an eraser 4 for removing electricity from non-image areas, a first developing device D1 and a second developing device D2 for developing and visualizing the electrostatic latent image, Charger 5 for transferring the toner visible image obtained by
A separation charger 6 for peeling off the transferred recording paper from the photosensitive drum 1 and a cleaning device 7 for removing toner remaining on the surface of the photosensitive drum after the transfer are arranged. Further, at a transfer section where the transfer charger 5 is arranged, a transport belt 9 for sending and sending the recording paper to and from the transfer section is arranged.

The first developing device D1 is a color developing device that uses a color toner, and the second developing device D2 is a black developing device that uses a black toner. The color developing device D1 has a larger capacity than the color developing device D1 which is used less frequently. In each of the developing casings D11 and D21 of the first developing device D1 and the second developing device D2, the developer is transported to a developing area formed in a portion facing the photosensitive drum 1 while holding the developer. Developing sleeves D12 and D22 are provided, respectively, and stirring rollers D13, D14 and D23, D24 for pumping up the developer stored in the developing casings D11 and D21 to the developing sleeves D12 and D22 respectively are provided in the respective developing casings. It is provided in D11 and D21, respectively. At the rear ends of the developing casings D11 and D21, cartridges D15 and D25 for storing new toner are respectively provided in series.

Further, each of the developing sleeves D12 and D22 is formed in the surface shape shown in FIGS. 1 (a) and 1 (b). That is, in the developing sleeve D12, as shown in FIG. 1 (a), a plurality of grooves D12a having a U-shaped cross section are provided on the outer peripheral portion of a cylindrical body having an outer diameter of 25φ. Each of the grooves D12a has a radial groove depth of 0.2 mm, a circumferential groove width angle of 6 °, and a groove D12a having a pitch of 12 mm.
It is formed to be adjacent with 隣接. In the convex portions formed between the respective groove portions D12a, the convex width angle toward the circumferential direction is 6 °, and therefore, the concave portion in which the groove portion D12a is formed and the convex portion are formed. Are alternately arranged at equal intervals. The upper groove D12a has a groove depth of 0.2 mm for the carrier particles (particle diameter 7
5 to 100 μm), which are set from dimensions corresponding to the thickness of two or three layers, and the groove width angle 6 ° is:
10 to 30 times (1.0 to 1.5 m) of the carrier particle diameter (75 to 100 μm)
It is set from the dimensions corresponding to m).

On the other hand, in the developing sleeve D22, as shown in FIG. 1 (b), a cross section V
A plurality of U-shaped grooves D22a are provided. Each of the grooves D22a has a groove depth in the radial direction of 0.2 mm and a pitch of 7.2.
゜ is formed. The groove depth of the groove D22a is 0.2 m.
m is a carrier particle (particle size 75
100100 μm) corresponding to the thickness of two or three layers.

FIG. 2 shows the developer supply amount (vertical axis) with respect to the doctor blade developing sleeve interval (horizontal axis) in the case of using the developing sleeves D12 and D22 in such an embodiment. In this figure, the diagram shows the developer supply amount characteristics of the developing sleeve D22 in the second developing device D2, and the diagram ′ shows the developer supply amount characteristics of the developing sleeve D12 in the first developing device D1. Is shown. As can be seen, the developer supply capability of the developing sleeve D22 and the developer supply capability of the developing sleeve D12 are almost the same. Also, in the figure, the line ′ shows the developer supply amount characteristics when the surface shape of the developing sleeve D22 in the second developing device D2 is the surface shape of the developing sleeve D12 in the first developing device D1. In this case, the developing sleeve D22
It can be seen that the developer supply capacity becomes too large. Further, the diagram shows a developer supply amount characteristic when the surface shape of the developing sleeve D12 in the first developing device D1 is the surface shape of the developing sleeve D22 in the second developing device D2. In this case, it can be seen that the developer supply capacity of the developing sleeve D12 is significantly reduced.

As described above, by making the respective surface shapes of the respective developing sleeves D12 and D22 provided in the respective developing devices D1 and D2 different from each other, the respective developing sleeves D12 and D2 are formed.
The developer holding power, that is, the developer conveying ability in 2, is adjusted, and as a result, the supply amount of the toner supplied from each of the developing devices D1 and D2 is made substantially equal. That is, the developer holding capacity of each of the developing sleeves D12 and D22 is determined by the cross-sectional area, the groove width, the groove depth, and the like of the groove formed on each surface. The developer holding ability, that is, the developer conveying ability can be increased. The developing sleeve having the increased developer holding ability is reduced to a small size in which the size, characteristics or shape of the magnet installed in the developing sleeve is restricted, and the developer carrying ability is originally reduced. By applying the present invention to the developing device, the developer supply capability of the small-sized developing device as in the above-described embodiment can be made substantially equal to the developer supplying capability of the large-sized developing device.

In order to increase the developer carrying capacity of the developing sleeve, it is conceivable to increase the distance between the doctor blade and the developing sleeve as shown in FIG. It is not preferable to strictly regulate the distance to adjust the developer supply amount in the distance between.

(Effects) As described above, in the image forming apparatus according to the present invention, even when the capacities, arrangement positions, and sleeve diameters of the plurality of developing devices are different, the developer supply amounts of the respective developing devices are substantially the same. As described above, the surface shape of the developing sleeve having the smaller diameter is formed so as to increase the developer holding force compared to the surface shape of the developing sleeve having the larger diameter. Despite having a developing sleeve, it is possible to reliably correct the difference in developer supply capacity among a plurality of developing devices with a simple configuration, stabilize the developing action, and achieve background contamination or toner scattering. And the like can be satisfactorily avoided.

[Brief description of the drawings]

1 (a) and 1 (b) are partially enlarged cross-sectional views showing the surface shape of a developing sleeve in one embodiment of the present invention, FIG. 2 is a diagram showing the developer supply capability of each developing sleeve, and FIG. FIG. 3 is a schematic side view illustrating a twin-color copying machine as an example of an image forming apparatus to which the present invention is applied. 1. Photoconductor drum, D1, D2 Developing device, D12, D22
Developing sleeve, D12a, D22a ... groove.

Claims (1)

(57) [Claims] An image forming apparatus includes a plurality of developing devices arranged opposite to a photoreceptor. In each of the developing devices, a developer is conveyed while holding a developer on a surface, and formed on the photoreceptor. In an image forming apparatus provided with a developing sleeve for supplying toner to the electrostatic latent image, the diameter of the developing sleeve provided in each of the developing devices is different, and each of the developing devices is
The surface shape of the developing sleeve having the smaller diameter is formed so as to increase the developer holding force more than the surface shape of the developing sleeve having the larger diameter so as to have substantially the same developer supply capacity. An image forming apparatus comprising: