JPH0267578A - Image forming device - Google Patents

Abstract

PURPOSE:To continuously reproduce developed pictures with a large portion of image area at a sufficient density level by making the quantity of developer contained in a developing device positioned upstream of the moving direction of an electrostatic latent image carrier large than the quantity of developer contained in a developing device positioned downstream of the former developing device. CONSTITUTION:The quantity of the developer contained in the developing device 1 positioned upstream of the moving direction (a) of the electrostatic latent image carrier 100 is made larger than the quantity of the developer contained in the developing device 2 positioned downstream of the developing device 1. As a result, the developer in the upstream developing device 1 aiming reproducibility of a picture with some density is more used than in the downstream developing device 2. By increasing the developer in the upstream developing device 1 rather than the developer in the downstream developing device 2, sufficiently electrified toner can be supplied for development in response to the consumption of the developer. Consequently, even if images with a large portion of image areas are continuously developed, they can be reproduced at a sufficient density level.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus in which a plurality of magnetic brush type developing devices are arranged on the side of an electrostatic latent image carrier.

(Background of the Invention) In general, in an image forming apparatus having a magnetic brush type developing device, the image quality is affected by the developer filling rate, toner content ratio, charging potential of the toner, etc. in the opposing portion between the electrostatic latent image carrier and the developing sleeve. For example, increasing the developer filling rate tends to improve density reproducibility, and conversely, decreasing the developer filling rate tends to improve thin line reproducibility. However, the density reproducibility and fine line reproducibility are in a contradictory relationship, and it has not been possible to simultaneously satisfy the requirements for density reproducibility and fine line reproducibility with a second developing device.

Therefore, as a result of studies to obtain images with excellent density reproducibility and fine line reproducibility using a magnetic brush type developer, the applicant found that, for example,
In the specification of the present invention, a developing device which has a high developer filling rate in which the development order takes priority with respect to the electrostatic latent image carrier, and is located downstream of the developing device with respect to the moving direction of the electrostatic latent image carrier. By lowering the developer filling rate and simultaneously driving multiple developers set to different conditions to develop the same electrostatic latent image multiple times, it is possible to develop the same electrostatic latent image multiple times. It was disclosed that sufficient image density is ensured and reproducibility of fine lines is ensured in the subsequent developing device.

However, in the image forming apparatus, the amount of toner consumed by the developing device intended for density reproducibility is significantly greater than that of the developing device intended for fine line reproducibility.

For this reason, it is unreasonable to design these developing units to have the same developer storage capacity, and it is necessary to prepare a large amount of developer for the developing unit that consumes a large amount.

(Structure of the Invention) The present invention has been made based on the above considerations, and will be explained with reference to FIG. 1 showing one embodiment.
A plurality of magnetic brush type developers (1) for the same electrostatic latent image formed on the surface of the magnetic brush type developer (100).

(2) In an image forming apparatus that supplies toner of the same color from the direction of movement of the electrostatic latent image carrier (100) [arrow (
a) The amount of developer contained in the developing device (1) located upstream with respect to the direction] is set to be larger than the amount of developer contained in the developing device (2) located downstream of the developing device (1). This is what I did.

(Function) According to the above configuration, the upstream developing device (1), which aims at reproducibility of image density, consumes more developer than the downstream developing device (2).

Therefore, the amount of developer accommodated in the upstream developer (1) is larger than that of the downstream developer (2), making it possible to keep up with the consumption of developer and provide sufficiently charged toner for development. Therefore, even if a large number of images are continuously formed, the density of these images can be maintained at a required value.

(Example) Hereinafter, an example of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows the main parts of an image forming apparatus that employs an electrophotographic copying process, such as a copying machine, a printer, etc.
) is a photoreceptor drum with a photoreceptor layer on the outer periphery, and the arrow (
It is designed to rotate in the direction shown in a), and (1)
, (2) is a developing device that uses a two-component developer consisting of toner and carrier to supply toner to the electrostatic latent image formed on the surface of the photoreceptor drum (100).

The housing of the first developer (1) is the bottom casing (3)
, an upper casing (4), and a cover (5), and in the space constituted by these, from the photoreceptor drum (100) side, a developing section (6), a conveyance path (7), (8
) is formed, and the transport paths (7) and (8) are separated by a partition wall (9). Note that this partition wall (9) has passages (10a) and (10b) on the back and front sides (front and back sides of the page).
(see Fig. 2) are formed respectively, and conveyance paths (7) and (8
) have been contacted.

A developing sleeve (11) is disposed in the developing section (6), and this developing sleeve (11) is connected to the photoreceptor drum (100).
) and are opposed to each other with a minute development gap (Ds+).

Further, a brush height regulating portion (13) formed in the upper casing (4) is opposed to the upper outer circumferential surface of the developing sleeve (11) with a small spike height regulating gap (Db,).

Furthermore, there is a magnet (12) inside the developing sleeve (11).
is accommodated, and a developing sleeve (
11) is designed to rotate. In addition, the magnet body (12
) A plurality of magnetic poles are arranged on the outer periphery of the transport path (
7) S with the same polarity in the opposite part.

The south poles are adjacent.

A packet roller (14) is arranged on the conveyance path (7), and this packet roller (14) carries a plurality of packets (17) on support plates (16), (16) provided on both sides of the shaft (15). ), and a plurality of blade members (1
8). Further, a screw (19) is arranged in the conveyance path (8), and this screw (1
9) is one in which a shaft (20) is provided with a plurality of blade members (21).

A magnetic sensor (22) is provided at the bottom of the conveyance path (7) to measure changes in magnetic permeability of the developer present in the conveyance path (7).

On the other hand, the developing device (1) is equipped with a toner replenishing device (23), and the toner replenishing tank (2) of the toner replenishing device (23) is attached to the developing device (1).
A groove-shaped conveyance path (25) connected to the conveyance path (8) is formed at the bottom of the toner replenishment tank (24), stirring members (26), (27), and a conveyance path (25) are formed at the bottom of the toner replenishment tank (24). ) is provided with a screw (28).

The second developing device (2) has almost the same configuration as the first developing device (1), with (33) a bottom casing, (34) an upper casing, (35) a cover, (36) a developing section,
(37), (38) are conveyance paths, (39) are bulkheads, (4
0a), (40b) are passages (see Figure 2), (41) is a developing sleeve, (42) is a magnet, (43) is a height regulating section, (44) is a packet roller, (45) is a shaft, (46
) is the support plate, (47) is the packet, (48) is the blade member, (49) is the screw, (50) is the shaft, (51) is the blade member, (52) is the magnetic sensor, and (53) is the toner supply. device, (54 is a toner supply tank, (55) is a conveyance path, (5
6), (57) is a stirring blade, and (58) is a screw.

In the second developing device (2) having the above configuration, the transport paths (37), (38) and the packet roller (44) and screw (49) housed in each are different in size and rotation speed. It is smaller than the transport paths (7), (8), packet roller (44), and screw (19) of the corresponding first developing device (1).

In this way, the first developing device (1) is larger than the second developing device (2), and the amount of developer stored in the first developing device (1) is larger than that of the second developing device (2). It's more than that. Similarly, the toner replenishing device (53) also has the first developing device (
The size of each part is smaller than that of the toner replenishing device (23) of 1), and the first developing device (1) has a second developing device (1) corresponding to the amount of developer stored in the second developing device (1). 2) The amount of toner replenishment per unit time is larger than that of 2). however,
The developing sleeve (11) of the first developing device (1) and the developing sleeve (41) of the second developing device (2) are of the same size,
It is made to rotate at the same speed.

Further, the developing gap (DS2) of the second developing device (2) is made larger than the developing gap (DS l) of the first developing device (1), and the height regulating gap (DS2) of the second developing device (2) is made larger than that of the first developing device (1).
D b 2) is the height regulation gap (
D b +).

Therefore, the developer filling rate (P, D) in the developing area (X,) is larger in the first developing area (Xl) than in the second developing device (X2).

Furthermore, in the first developing device (1) and the second developing device (2),
As shown in FIG. 2, a packet roller (14).

The interval (Ll) between the blade member (18) of (44) and (48)
), but the first developing device (1) is narrower, and the blade members (21), (51) of the screws (20), (50) are narrower.
) is similarly narrower in the first developing device (1).

The image forming operation using the developing devices (1) and (2) will be described below.

Note that the developing devices (1) and (2) have transport paths (7) and (8).
), (37), and (38) accommodate two-component developers consisting of toner and carrier of the same color, respectively.

This developer is released by the rotation of the packet rollers (14) and (44) in the directions of arrows (c) and (f) and by the screw (19).
, (49) in the directions of arrows (d) and (g), transport paths (7) and (8) and (37) and (38) are connected to both end passages of partition walls (9) and (39). (10a), (l O
b).

(40a) and (40b).

That is, as shown in FIG. 2, the developer in the transport paths (7), (37) is transported by the packet rollers (14), (44) in the direction of the arrow (Pl) from the back side to the front side. At the front end there is a passageway (lob), (40b
) is conveyed in the direction of arrow (P2) to conveyance paths (8) and (3).
8). Further, the developer in the conveyance paths (8) and (38) is conveyed from the front side to the back side in the direction of arrow (P3) by the screws (19) and (49), and at the end of the back side, the developer is conveyed to the path (10a), (40a) is conveyed in the direction of arrow (P4) and sent into conveyance paths (7) and (37).

Note that between the first developing device (1) and the second developing device (2), the distances (Lt) and (L2) between the blade members (18) and (21) of the first developing device (1) are the same as those of the first developing device (1) and the second developing device (2). It is narrower than that of the blade members (48) and (51) in the second developing device (2).

Therefore, the developer transportability of the first developing device (1) is lower than that of the second developing device (1).
better than that of the developer (2), even if the first developer (1)
Even if the amount of developer in the second developer (2) is larger than that in the second developer (2), the developer conveyance speed in the conveyance paths (7) and (8) of the first developer (1) is lower than that in the second developer (2). 2) conveyance path (37), (
This is almost the same as the developer transport speed in 38).

As the developer is transported in this manner, the toner and carrier that constitute it come into frictional contact with each other and are charged to different polarities.

Furthermore, the developer transported through the transport paths (7) and (37) is
The developing sleeve (l l) is conveyed as described above based on the rotation of the packet rollers (14) and (44),
(41), and the magnets (12), (42
) is held on the outer periphery of the developing sleeve (l l), (41) which is rotating in the directions of arrows (b) and (e).

The developer held on the outer periphery of the developing sleeves (11) and (41) is conveyed in the directions of arrows (b) and (e) based on the rotation of the developing sleeves (11) and (41), and It is regulated by the opposing parts of the regulating parts (13) and (43).

Then, the hot height regulation gap (D b +), (D b
The developer that has passed through the arrow (b) forms a magnetic brush along the lines of magnetic force formed by the plurality of magnetic poles.
a developing area (x+) where the developing sleeves (11), (41) and the photosensitive drum (100) face each other;
(xi).

On the other hand, the surface of the photoreceptor drum (100) is charged with an electric charge in a charging area (not shown) and then exposed to image light in an exposure area to form an electrostatic latent image.

When this electrostatic latent image passes through the development area (Xυ, (XI)), it comes into contact with the developer held on the surface of the development sleeve (11), (41), and the toner is electrostatically removed. It is supplied and visualized as a toner image.

Note that the operation of making the electrostatic latent image into a visible image will be explained in detail later.

This toner image is then conveyed to a transfer area (not shown), where it is transferred to a copy sheet and then heat-fixed.

On the other hand, the developer on the developing sleeve whose toner concentration has decreased due to the consumption of toner in the developing areas (XI) and (XI) continues to be transported in the direction of arrow (b) and reaches the part facing the transport path (7). and is released from the binding force of the magnet body (11) due to the repulsive magnetic field formed by the adjacent S and S magnetic poles,
It separates from the surface of the developing sleeve (10) and enters the conveyance path (7).
to fall.

The developer that has fallen onto the conveyance path (7) is transferred to the packet roller (1).
3) is taken into the developer being mixed and conveyed.

Next, the developing operation in the developing area (Xυ, (XI)) will be explained.

In the first development area (Xυ), the development gap (DS) is set narrower than the development gap (Dsx) of the developer (2), so here the electrostatic latent image comes into contact with the developer more frequently. Sufficient toner is supplied to the electrostatic latent image.

However, there is a high probability that the toner attached to the thin line electrostatic latent image will be scraped off by the magnetic brush, and the amount of toner attached to the thin line electrostatic latent image that has passed through the development area (X,) is small. However, the electrostatic latent image to which the toner adheres and is subsequently scraped off still retains a charge.

Next, the electrostatic latent image conveyed to the developing area (X,) is again supplied with toner from the second developing device (2), and is transferred onto the toner image formed in the developing area (XI). Further toner is supplied.

Furthermore, toner is again supplied to the fine line electrostatic latent image that has been scraped off by the magnetic brush in the first development area (XI).

However, since the developer filling rate here is small, the toner adhering to the electrostatic latent image is rarely scraped off by the magnetic brush, making it difficult to visualize even thin electrostatic latent images. It passes through the development area (X,) with sufficient toner attached.

Therefore, normal character images and area images are reproduced with sufficient density, and fine lines are also reproduced in a state where they are sufficiently visualized.

In this way, since the density reproducibility of the image is ensured in the first developing device (1), the toner consumption amount of the first developing device (1) is reduced to the second developing device (1).
It exceeds that of the developing device (2).

However, in the first developing device (1), the capacity of the conveying paths (7), (8) is reduced to the capacity of the conveying paths (37), (38) of the second developing device (2).
In addition to increasing the developer transport speed there, the mixing and stirring performance of the developer in both developing devices (1) and (2) is made almost the same, so that the toner in the first developing device (1) is increased. Even if a large amount is consumed, it can sufficiently supplement it and maintain good concentration reproducibility.

The amount of developer contained in the first developing device (1) and the second developing device (2) will be discussed below.

Figure 3 shows a case where an image is formed by driving the first developing device (1) and a second developing device (2) each independently, and a case where an image is formed by driving these two developing devices (1) and (2) simultaneously. The copy density of the area image when the same electrostatic latent image is developed twice, and the 50μ
This shows the limit density at which a thin line can be reproduced.

Note that in the first developing device (1), the developing gap (Dsl)
is 0.4mm, and the height regulation gear 'yp (Db+) is 0.5
mm, and in the second developing device (2), the developing gap (
D S 2) is 1.2 mm, and the height regulation gap (Db+
) was set to 0 and 5 mm.

As shown in this figure, when the first developing device (1) was driven alone, the copy image density of the area image was 1.4, and the thin line reproduction limit density was 0.9 to 1.2. When the second developing device (2) was driven alone, the density of the copied image of the area image was 0.8, and the thin line reproduction limit density was 0.4 to 0.6.

Further, when the first developing device (1) and the second developing device (2) are driven simultaneously, the copy image density is 1.4, the fine line reproduction limit density is 0.4 to 0.6, and the area image is Developer (1)
It can be seen that the fine lines are developed by the second developing device (2).

Here, the relationship between the copy image density and the toner adhesion amount is shown in FIG. 4, and the copy image density: 1. The amount of toner adhesion for the image with D=1.4°0.8 is approximately 1.4.0.35mg/cm2
It is.

Therefore, if an image to be copied includes a portion copied by the first developing device (1) and a portion copied by the second developing device (2) in approximately the same proportion, the first developing device (1) In this case, about four times as much toner as in the second developing device (2) is consumed.

Therefore, when setting as described above, the first developing device (
The volume, developer amount, toner amount, and developer conveyance capacity of the conveyance paths (7) and (8) in 1) are approximately 4 in the conveyance paths (37) and (38) of the second developing device (2). Double it.

In this way, even if the developer (1) is replenished with four times as much toner as the toner supplied to the developer (2), the amount of toner and carrier in both the developer units (1) and (2) will be reduced. The contact probabilities become the same, and the toner charge characteristics become the same.

(Effects of the Invention) As is clear from the above description, in the image forming apparatus according to the present invention, a plurality of toners of the same color are supplied in a superimposed manner to an electrostatic latent image on an electrostatic latent image carrier. Among the developing devices, the developer capacity of the developing device located upstream and using a large amount of developer is made larger than that of the developing device located downstream thereof.

Therefore, even if an image having a large proportion of area images is continuously developed, it can be reproduced with sufficient density.

[Brief explanation of the drawing]

Figure 1 is a longitudinal cross-sectional view of the developing device, Figure 2 is a cross-sectional view of the developing device, Figure 3 is a diagram showing the development characteristics of the developing device, and Figure 4 is a diagram showing the relationship between toner adhesion amount and image density. It is a diagram. 1.2... Developing device, 7, 8, 37. 38... Conveyance path, X, ,... Development area, 100... Photosensitive drum. Figure 3

Claims (1)

[Scope of Claims] [1] An image forming apparatus in which toner of the same color is supplied from a plurality of magnetic brush developing devices to the same electrostatic latent image formed on the surface of an electrostatic latent image carrier, The developer capacity of the developing unit located upstream with respect to the moving direction of the electrostatic latent image carrier is larger than the developer capacity of the developing unit located downstream of the developing unit. image forming device.