JPS6250777A - Control method for developing device of image forming device - Google Patents

Abstract

PURPOSE:To prevent image density from decreasing and toner from being wasted by applying a developing bias to the developing electrode of an unselected developing device in such a direction that toner is hard to develop. CONSTITUTION:When the unselected developing device is a normal developing device 20, a developing sleeve 21 is put away from a development area Yb and a developing bias nearly equal to the potential of an electrostatic latent image is applied to the developing electrode 22. In this case, the toner in the developing device 20 is triboelectrified to the opposite polarity from the electrostatic latent image potential, but the developing bias is substantially zero V, so no toner sticks on an electrostatic latent image carrier. Further, when the unselected developing device is a reversal developing device 10, a developing bias nearly equal to the earth potential is applied to the developing electrode 11. In this case, the toner in the developing device 10 is triboelectrified to the same polarity as the electrostatic latent image potential, but the electrode 11 is grounded, so no toner sticks on the electrostatic latent image carrier. Thus, a decrease in image density and a waste of toner at the time of a change in developing mode are eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling a developing device in an image forming apparatus capable of obtaining a copy image in an electrophotographic process or the like.

Prior art and its problems In recent years, image forming devices such as electrophotographic copying machines and reader printers have been equipped with a developing device for reversal development (developing a negative original into a positive image) and a regular one around the electrostatic latent image carrier. A developing device for developing (developing a positive original into a positive image) is arranged, and each developing device is selectively switched to perform reversal development or regular development on electrostatic latent images of the same polarity. is provided.

In this case, it is necessary to separate the non-selected developing device from the developing area in order to prevent development by the non-selected developing device and to prevent image holes in the electrostatic latent image.

Such a contact/separation mechanism is disclosed in Japanese Utility Model Publication No. 55-31557 as a means for coping with color copying. However, even if one non-selective developing device is separated from the developing area, in the current situation where it is not possible to provide a very large separation space between the developing devices, especially for small ones, the gap between the developing device and the surface of the electrostatic latent image carrier is 2.S mm. It is difficult to prevent toner from adhering to the surface of the electrostatic latent image carrier from non-selective developing devices.

Therefore, the inventors of the present invention have devised a method of separating the non-selected developing device from the developing area and applying a potential approximately equal to the developing bias applied to the developing electrode of the selected developing device to the developing electrode of the non-selected developing device. I tried the lesson. Application of such a developing bias to the non-selective developing device results in application of the developing bias in a direction where toner is less likely to adhere than when used for development, but it still causes toner to adhere to the non-selective developing device slightly. confirmed. For example, if you continue copying about 1,000 sheets using reversal development and then switch the development mode to regular development and copy, the toner concentration of the developer on the developing sleeve of the switched regular developer will change from the unnecessary toner adhesion. Since the toner density has decreased in the 2000s, the image density has decreased. Toner adhesion from the non-selective developer to the surface of the electrostatic latent image carrier not only reduces the image density when switching the development mode, but also consumes unnecessary toner and is uneconomical, as well as requiring a cleaning device to remove residual toner. This is not a desirable phenomenon as it places an excessive burden on the public.

In order to solve the problem more than just a means to solve the problem, the method for controlling a developing device according to the present invention is as follows: In an image forming apparatus, the developing device is arranged such that each developing device is selectively switched to apply reversal development or regular development to an electrostatic latent image of the same polarity. (c) At the time of reversal development, electrostatic charge is applied to the developing electrode of the regular developing device that is not selected. Applying a developing bias with a potential substantially equal to the potential of the latent image; (C) Applying a developing bias with a potential substantially equal to the ground potential to the developing electrode of the reversal developing device that is not selected during normal development; vf symptoms.

In other words, in the above control method, the developing sleeve of the unselected developing device is separated from the developing area, and if the unselected developing device is a regular developing device, the developing sleeve is moved away from the developing electrode of the unselected developing device. A developing bias having a potential substantially equal to the potential of the electrostatic latent image is applied. In this case, the toner in the regular developing device is frictionally charged to a polarity opposite to the potential of the electrostatic latent image, but since the developing potential is substantially o■, it will not adhere to the electrostatic latent image carrier. do not have.

Further, when the non-selected developing device is a reversal developing device, a developing bias having a potential substantially equal to the ground potential is applied to the developing electrode thereof. In this case, the toner in the reversal developing device is frictionally charged to the same polarity as the potential of the electrostatic latent image, and because the developing electrode is grounded, it does not adhere to the electrostatic latent image carrier.

Of course, it goes without saying that a developing bias of a necessary potential is applied to the developing electrode of the developing device selected to carry out development, and a developed image is formed using toner.

Figures 1 through 7a and 7b show the main parts of a reader printer for carrying out the method for controlling a developing unit according to the present invention, and the developing units (10) and (20) are arranged in two stages. A ram (
Each of the electrostatic latent images formed on the surface of 1) can be developed. Note that the photoreceptor V-ram (1) is used here as an example of an electrostatic latent image carrier.

The developing devices (10) and (20) are both magnetic brush type and have the same configuration, the developing device (10) is for performing reversal development, and the developing device (20) is for performing normal development. First, we will explain its internal structure.

Each developing device (10), (20) has a developing sleeve (1 l), (21), which also functions as a developing electrode, facing the photoreceptor drum (1), and the developing sleeve (1
1), (21) have built-in magnetic rollers (12), (22) with N and S poles magnetized on the outer periphery, and the developer is distributed magnetically on the outer periphery of the developing sleeves (11), (21). roller(
While being attracted like a brush by the magnetic force of 12) and (22), it moves on the outer peripheral surface of the developing sleeves (11) and (21) based on the rotation of the developing sleeves (11) and (21) in the direction of arrow (b). It is transported in the direction of arrow (b). Note that the amount of conveyance is regulated when the developer passes through the height regulating plates (13) and (23).

On the other hand, behind the developing sleeves (i 1), (21), developer circulation passages (14a), (1
4b), (24a), (24b) are formed, and the passageway (1
4a), (24a) have screw rollers (15), (
The passageway (14) is rotatably driven in the direction of the arrow (C).
b), (24b) include Baceratolla (16), (
26) is installed so as to be rotatably driven in the direction of arrow (d), and the developer flows through the passage (
14a), (14b) and (24a).

(24b) is circulated.

Toner is stored in a toner bottle (not shown) for each of the developing devices (10) and (20), and is replenished to the front side of the passages (14a) and (24a) based on a toner replenishment signal. The replenished toner is mixed with the developer, mixed and agitated by the rotation of the screw rollers (15) and (25), and conveyed to the inner side through the passages (14a) and (24a), and is charged during this conveyance. The developer passes through the passage (14a) = (24
The adjacent developing sleeves (11) go around the passages (14b) and (24b) on the back side of a) and are conveyed to the front side by bucket rollers (16) and (26).

On the other hand, each developing device (10), (20) is supplied to the outer peripheral surface of the frame (30).
.

(31), is pressed to the right by a cam plate (33) that presses against the frame (30), and is regulated in position by the frame (32) coming into contact with the cam plate (35). ing. This cam plate (35) can be rotated by a switching motor (39), which will be explained below, and has two positions: a position where the small diameter part contacts the frame (32) (see Figure 1), and a position where the large diameter part contacts the frame (32). The contact position (see FIG. 2) can be taken. Also, a developing device (10).

(20) is rotatably supported in the vertical direction about the support shaft (34) of the cam plate (33), and when the small diameter portion of the cam plate (35) abuts the frame (32), the developing device (10) .

(20) is located approximately horizontally, the developing sleeve (11) is located in the developing area (Ya), and the developing sleeve (21) is located in the developing area (Ya).
) is separated from the development area (Yb). On the contrary, the cam plate (3
When the large diameter portion of 5) comes into contact with the frame (32), the developing devices (10), (20) rotate slightly upward about the support shaft (34), and the developing sleeve (21) moves into the developing area. (
Yb), and the developing sleeve (11) is separated from the developing area (Ya).

Then, as shown in Figure 3, the cam plates (35), (35)
is fixed to a support shaft (36), and a gear (37) fixed to the support shaft (36) is connected to an output gear (40) of a switching motor (39) via an idle gear (38).

Further, a position detection plate (41) is fixed to one end of the support shaft (36), and a transmission type position detection sensor (42) is arranged around it.
), (43) are installed. The sensor (42) is for reversal development, and when the cam plates (35), (35) are rotated by the drive of the switching motor (39) and their small diameter portions abut against the frame (33), the sensor (42) is at the above position. Detection plate (41
) is detected, and the switching motor (3) is detected.
9) Stops the drive.

The other sensor (43) is for regular development, and is driven by the switching motor (39) to the cam plate (35).

(35) rotates and its large portion comes into contact with the frame (33), the position detection plate (41) is
1a) and stops driving the switching motor (39).

Next, the drive mechanism of the developing devices (10) and (20) will be explained with reference to FIGS. 5, 6, 7a, and 7b.

A gear (44) connected to the output shaft of the developing motor is connected to a drive gear (46) via a developing clutch (45).
This drive gear (46) is connected to the developing sleeves (11) and (21).
) can be meshed with the gears (51) and (61) fixed to the end of the spindle, and when the reversal developing device (10) is selected, it can mesh with the gear (51) (see Figure 7b) , and gears (51) in mesh with the gear (61) when the regular developing device (20) is selected (see FIG. 7a).

(61) is rotated in the direction of arrow (b). Further, the gear (44) is connected to the gear (48) via the idle gears (47a) and (47b), and the drive gear (49) fixed coaxially with this gear (48) is connected to the bucket roller (16).
), a gear (52) fixed to the end of the spindle of (26).

(62), each gear (52), (62) is aligned with the arrow (
d) rotationally driven in the direction. In addition, the screw roller (
Pulley (54) fixed to the end of the spindle of 15L (25).

(64) is the gear <52), pulleys (53), (63) provided integrally with (62) and belts (55), (65).
), and are each driven to rotate in the direction of arrow (C).

Switching between the developing devices (10) and (20) used for development is performed by operating a developing mode selection switch on a processing panel (not shown), and the switching motor (39) is started based on this selection signal. When the cam plate (35) rotates and the reversal development mode, that is, the reversal developer (10) is selected, the cam plate (35) rotates as shown in FIG.
The small diameter part of the developing sleeve (
11) is brought close to the photosensitive drum (1). When the regular development mode, that is, the regular developer (20) is selected, as shown in FIG. body drum (1). In addition, in the developing device (10) or (20) that is not used for development, a screw roller (15) or (25), a bucket roller (16)
Or (26) is rotationally driven to continue the circulation of the developer, but the rotation of the developing sleeve (11) or (21) is caused by the gear (46) and the gear (51) or (61) being disengaged. It is stopped by being

On the other hand, the developer used in the developing devices (10) and (20) is made of a mixture of a magnetic carrier and a toner, specifically a mixture of a small-diameter binder-type magnetic carrier and a non-magnetic insulating donor, and is made of a mixture of a magnetic carrier and a toner. In the developer filled in the reversal developing device (10) by charging, the magnetic carrier is positively charged and the toner is negatively charged, and in the developer filled in the regular developing device (20), the magnetic carrier is negatively charged. The toner is positively charged.

Here, the developing operation will be explained with reference to the time chart shown in FIG.

As for the image forming device itself, as shown in the upper part of Fig. 8, when the print switch is turned on, the main motor starts and the photosensitive drum (1) starts rotating in the direction of the arrow (,), and the developing The motor starts and the developing units (10) and (20)
screw roller (15) inside.

(25), bucket rollers (16) and (26) start rotating in the directions of arrows (C) and (d), respectively. Further, an illumination lamp of an optical system (not shown) is turned on and off, the optical system is scanned, and a charger is turned on and off at predetermined timings.

In reversal development, the reversal developing device (10) is selected and the developing devices (10) and (20) are in the state shown in FIG. 16
A charge of 00V is applied, and a negative image is exposed to light to form a negative electrostatic latent image, which is developed with a developing bias of -440V applied to the developing sleeve (11) of the reversal developing device (10). do. At this time, negatively charged toner adheres to the image area of the electrostatic latent image (low potential area of the electrostatic latent image), and a positive developed image is formed. The image is transferred onto the copy paper by the charger's positive discharge. Mainly, the developing sleeve (21) of the regular developing device (20) is separated from the developing area, and is equal to the charging potential of the photoreceptor drum (1), that is, the potential of the electrostatic latent image)-6
A developing bias of 00V is applied to prevent positively charged toner from adhering to the photoreceptor drum (1).

On the other hand, in regular development, the regular developer (20) is selected and the developers (10) and (20> are in the state shown in FIG. 2 described above, and the surface of the photoreceptor drum (1) is Similar to reversal development, a charge of 1,600 μm is applied, and a positive image is exposed to form a positive electrostatic latent image, which is then transferred to a regular developer (2
Developing is performed with a developing bias of -x95v applied to the developing sleeve (21) of No. 0). When printing, positively charged toner adheres to the image area of the electrostatic latent image (high potential area of the electrostatic latent image), forming a positive developed image, which is transferred onto the copy paper by the negative discharge of the transfer charger. transcribed. Further, the developing sleeve (11) of the reversal developing device (10) is separated from the developing area, and the developing bias is lowered to the ground potential, so that negatively charged toner adheres to the photoreceptor drum (1'). This will be prevented.

In addition, in this example, other conditions of the experiment conducted by the present inventors are as follows: Developing sleeve (11).

The rotation speed of (21) is 160 rpm, and the screw roller (
15), (25) and packet rollers (16), (26
) is 1100 rpm. Developing sleeve (11
) and (21) to prevent unnecessary toner consumption.
Only the selected one is rotationally driven only when the developing clutch (45) is turned on, and the unselected one remains stopped. The gap between development areas (Ya) and (Yb) is 0.7
mm, and the separation gap of the developing sleeve (IIL (21) is 2.51 mm. Also, in the reversal development mode shown in the middle row of Fig. 8, the exposure shutter is turned on before and after the image forming section passes through. In order to prevent the surface of the photoreceptor drum (1) before and after the image creation section from becoming ○V, the light from the optical system is blocked from reaching the display on the photoreceptor drum (1), and unnecessary toner consumption is avoided. Furthermore, in the regular development mode shown in the lower part of Figure 8, the inter-image eraser is turned on before and after the image forming section passes through the photosensitive drum (1) before and after the image forming section. This is to erase the surface potential of the toner to ○V and prevent unnecessary consumption of toner.

When the present inventors performed continuous copying of 1000 sheets at a time by switching between reversal development and regular development under the above development conditions and control method, the photoreceptor drum (1) was transferred from the non-selected developer (20) or (10) to There was almost no toner adhesion to the surface, and no decrease in image density was observed even immediately after switching to the non-selective developing device (20) or (10).

Note that the method for controlling a developing device according to the present invention is not limited to the method of the above-mentioned embodiments, and can be variously modified within the scope of its essential parts. For example, the developing sleeve (11)
, (21) are rotated with some margin before and after passing through the image area, in order to prevent unnecessary consumption of toner from the selected developer (10) or (20), it is necessary to In the development mode, as shown by the dotted line in the middle part of Fig. 8, 1440
In addition to turning on and off the developing bias (2), a developing bias of +200 ■, which has the opposite polarity to the electrostatic latent image, is applied to the developing sleeve ( 11) may be applied.

On the other hand, in the regular development mode, as shown by the dotted line in the lower part of Fig. 8, while the photosensitive drum (1) is rotating, a development bias of -195■ is applied to the development sleeve (21). It's okay.

Effects of the Invention As is clear from the above description, according to the present invention, the developing sleeve of the developing device selected to perform development is located in the developing area, and the developing sleeves of other developing devices are separated from the developing area. Then, during reversal development, a developing bias having a potential approximately equal to the potential of the electrostatic latent image is applied to the developing electrode of the unselected regular developing device, and during regular development, a developing bias of a potential approximately equal to the potential of the electrostatic latent image is applied to the developing electrode of the unselected reversing developing device. By applying a developing bias with a potential approximately equal to the ground potential, that is,
A developing bias in a direction in which the toner is less likely to be developed is applied to the developing electrode of the unselected developing device, and the toner from the unselected developing device is prevented from adhering to the electrostatic latent image carrier. This prevents a decrease in image density when switching, and also prevents unnecessary toner consumption.

[Brief explanation of drawings]

1 to 7a and 7b show the main parts of a reader printer for implementing the developing device control method according to the present invention, and FIGS. 1 and 2 are sectional views of the developing device portion, and FIG. 3 is a sectional view of the developing device switching means, FIG. 4 is a front view of FIG. 3, FIG. 5 is a front view of the developing device driving means, FIG. 6 is a plan view of FIG. 5, FIG. 7a, and FIG. Figure 7b is an explanatory diagram of the developing sleeve drive. FIG. 8 is a time chart showing the control method. (1)...Photosensitive drum, (10)...Reversal developer, (20)...Regular developer, (11), (21).
・Developing sleeve (developing electrode), (12), (22
)...Magnetic roller, (33)...Pressure cam plate, (
35)...Positioning cam plate, (39)...Switching motor, (Ya), (Yb) -Development area.

Claims (1)

[Claims] 1. A developer for reversal development and a developer for regular development are arranged around the electrostatic latent image carrier, and each developer is selected for an electrostatic latent image of the same polarity. In an image forming apparatus that performs reversal development or regular development by switching between the two, the developing sleeve of the developing device selected to perform development is positioned in the developing area, and the developing sleeves of other developing devices are moved from the developing area. A developing bias having a potential approximately equal to the potential of the electrostatic latent image is applied to the developing electrode of the regular developing device that is not selected during reverse development, and a developing bias of a potential approximately equal to the potential of the electrostatic latent image is applied to the developing electrode of the reverse developing device that is not selected during regular development. A method for controlling a developing device, comprising: applying a developing bias having a potential substantially equal to a ground potential to the developing device.