JPH03181974A - Image forming device - Google Patents

Abstract

PURPOSE:To protect a toner sensor from magnetic field by providing the toner sensor so that it may be covered from the magnetic roller side of a developing device and preventing the effect of the magnetic field caused by two magnetic rollers on the toner sensor. CONSTITUTION:When the N pole 7b of the magnetic roller 5 and the S pole 13a of the magnetic roller 11 approach to each other, the line of magnetic force M which turns from the magnetic roller 5 of a sub developing device 2 to the magnetic roller 11 of a main developing device 3 is generated so as to extend over the toner sensor 15. However, the line of magnetic force M to the toner sensor 15 is conducted inside 'Permalloy(R)' 30 by forming a space in which the line of magnetic force easily flows by the 'Permalloy(R)' 30, then it is branched to the lines of magnetic force M1 and M2. Thus, the line of magnetic force M is prevented from passing in the toner sensor 5.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to an image forming apparatus, and more particularly to an improved structure of a plurality of developing units provided in an image forming apparatus such as a multicolor electronic copying machine. .

(B) Prior art In a conventional copying machine of this type, as shown in FIG. It has been proposed that a main developing device 3, which is provided adjacent to the lower side of the developing device 2, contains a developer made of toner and carrier for black copying.

That is, a sub-developing roller 4 as a developing body is provided in the sub-developing device 2, and the sub-developing roller 4 is composed of a magnet roller 5 and a developing sleeve 6 that fits around the magnetic roller 5. The magnet roller 5 has first to fifth magnetic pole parts 7a to 7e, and has first to fifth magnetic pole parts 7a to 7e. Third. Fourth magnetic pole part 7
a, 7c, 7d are S poles, 2nd. Fifth magnetic pole portions 7b, 7c
is the N pole.

Further, a main developing roller 10 as a developing body is provided in the main developing device 3, and this main developing roller 10 also includes a magnet roller 11 and a developing sleeve 1 that fits around the magnetic roller 11.
It is composed of 2. The magnet roller 11 has first to fifth magnetic pole parts 13a to 13e, and has first to fifth magnetic pole parts 13a to 13e. Third. The fourth magnetic pole parts 13a, +3c, 13d are S poles, the second
, the fifth magnetic pole portions +3b and 13e are N poles. The developing sleeve 6 of the sub-developing roller 4 rotates counterclockwise, and the developing sleeve 12 of the main developing roller 10 also rotates counterclockwise to convey the respective developers, thereby performing two types of development. It will be done.

Furthermore, toner sensors 4 and 15 are provided in the sub and main developing units 2 and 3, respectively, in order to maintain a constant toner concentration. This toner sensor 14.1
The detection unit 5 electromagnetically detects the mixture ratio of toner and carrier when a certain amount of toner passes through.

(c) Problems to be Solved by the Invention However, magnetic poles of different polarities face each other between the magnetic pole portions of the magnet roller 5 of the sub-developing device 2 and the magnetic roller 11 of the main developing device 3, producing an external magnetic field. There is. That is, the magnetic pole part 7b of the N pole and the magnetic pole part 13a of the S3- pole may be adjacent to each other, thereby generating a magnetic field between the two magnetic pole parts, which passes through the inside of the toner sensor 15, and this causes the toner to be absorbed. There is a risk that the output of the sensor 15 will be abnormal.

An object of the present invention is to provide an image forming apparatus that can protect a toner sensor from magnetic fields.

(d) Means and operation for solving the problem This invention includes:
A plurality of developing devices provided around the photoreceptor along the direction of movement of the photoreceptor, and two magnetic rollers each provided in a pair of adjacent developing devices among these developing devices, and at least one of the developing devices a toner sensor for detecting the toner concentration in the developing device; and a toner sensor made of a ferromagnetic material having high magnetic permeability, and provided to cover the toner sensor from the magnet roller side of the other developing device; The image forming apparatus includes a magnetic shielding member that can prevent the influence of a magnetic field generated by two magnet rollers on a toner sensor.

That is, the present invention provides a plurality of developing devices around the photoreceptor along the direction of movement of the photoreceptor, and a toner sensor located in at least one of a pair of adjacent developing devices is provided with a specific magnetic shield. The member covers the magnetic roller side of the other developing device, thereby cutting off at least the magnetic field to the toner sensor generated between the magnetic pole portions of different polarities that are closest to each other (adjacent and opposite to each other) of the image-type magnetic rollers. This eliminates the adverse effect on the toner sensor, allows normal toner control, allows for good developer transport, and makes it possible to obtain high-quality multicolor images.

The magnetic shielding member in this invention has a relative magnetic permeability of 3
A diamagnetic member having a high magnetic permeability of 000 to 10,000 is preferable, and permalloy is the most preferable example.

Generally, between the magnet rollers, the magnetic field generated between magnetic parts of different polarities that are adjacent to each other (closest and opposite to each other) is 10 to 1000 Gauss. However, when the toner sensor 15 of one developing device 3 is covered from the magnet roller side of the other developing device 2 with a diamagnetic member having the above-mentioned relative magnetic permeability, the magnetic shielding member 30 blocks the magnetic field as shown in FIG. A space is formed in which the lines of magnetic force M can easily flow, and the lines of magnetic force M can be guided into the magnetic shielding member (hereinafter referred to as a diamagnetic member).

For example, the lines of magnetic force M are branched into a first line of magnetic force Ml in one direction and a second line of magnetic force M in the other direction within the diamagnetic member, so that the lines of magnetic force of the toner sensor 15 can be cut.

If the magnetic field generated between magnetic pole parts of different polarities that closely face each other between the magnet rollers is, for example, about 100 Gauss, it is better to use permalloy having a relative permeability of about 5000 as the diamagnetic member. preferable.

(e) Examples The present invention will be described in detail below based on embodiments shown in the figures.

Note that this invention is not limited by this.

FIG. 1 shows an embodiment of the present invention, and the same parts as those shown in FIG. 3 are given the same reference numerals. In FIG. Two pieces are provided along the movement direction (arrow direction shown in figure A),
Magnet rollers 5 and 1 having different magnetic poles around them
1, a toner sensor 15 located between each of the magnetic rollers of the image forming type 2.3, and detecting the toner concentration in the main developing device 3; It is made of a material with relative magnetic permeability, and is provided so as to cover the surface of the toner sensor 5 from the side of the magnet roller 5 of the sub-developing device 2, so that lines of magnetic force from the magnet roller 5 of the sub-developing device 2 to the toner sensor 15 are It mainly includes a permalloy (magnetic shielding member) 30 that can prevent the intrusion of M (see FIG. 2).

Furthermore, a sub-developing roller 4 as a developing body is provided in the sub-developing device 2, and the sub-developing roller 4 is composed of a magnet roller 5 and a developing sleeve 6 that fits around the magnetic roller 5. The magnet roller 5 has first to fifth magnetic pole parts 7a to 7e, and has first to fifth magnetic pole parts 7a to 7e. 3rd: fourth magnetic pole part 7a,
7c and 7d are S poles, 2nd. The fifth magnetic pole parts 7b and 7e are N
It is extreme. The sub-developing device 2 contains two types of developer consisting of toner and carrier for red copying.

Further, a main developing roller 10 as a developing body is provided in the main developing device 3, and this main developing roller 10 also includes a magnet roller 11 and a developing sleeve 1 that fits around the magnetic roller 11.
2. The magnet roller 11 has the first to fifth magnetic pole parts 13a=I3e, and the first to fifth magnetic pole parts 13a=I3e. Third. The fourth magnetic pole parts +3a, 13c, +3d are S poles, the second
, the fifth magnetic pole portions 13b and 13e are N poles. The main developing device 3 contains a two-component developer consisting of toner and carrier for black copying.

The developing sleeve 5 of the sub-developing roller 4 rotates counterclockwise (in the direction of the arrow B in the figure), and the developing sleeve 12 of the main developing roller 10 rotates counterclockwise (in the direction of the arrow C in the figure). Each conveys developer.

8 In addition, 31.32 are the sub and main stirring rotors, respectively, 33.34 are the sub and main development spirals, respectively, 35.36 are the sub and main development partition plates, respectively, 14 is the sub toner sensor, 37; 38 are the toner hoppers and This is a toner cartridge housing section.

Although FIG. 1 shows the developing state by the main developing device 3, the switching mechanism between the main developing and sub-developing will be briefly explained below.

The main developing device 3 and the sub-developing device 2 are installed so as to be able to come into contact with and separate from the photoreceptor drum 1. First, when the toner color selection key is pressed, the sub-developing is switched to the main developing. The selected main developing device 3 is pressed by a switching lever (not shown), approaches the photosensitive drum 1, and is fixed (see FIG. 1). Control is provided by a developer switching solenoid (DEVSOL) and a developer switching assembly. Here, the main and sub-developers 3 and 2 each have sliding switching plates (
(not shown).

Next, when sub-developing unit 2 is selected and a copy operation is started, the developer switching solenoid (DEVSOL) is turned ON, the developer switching clutch is released, the switching shaft of sub-developing unit 2 rotates, and sub-developing unit 2 is selected. Ru.

After copying is completed, the development switching solenoid is turned off, switching to the main development device 3 and stopping the operation. Color development is performed in this manner.

Since this embodiment has the above configuration, for example, the N pole 7b of the magnet roller 5 and the magnet roller 11
For example, when the S pole 13a is in close proximity (see Figure 1)
At this time, lines of magnetic force M from the magnet roller 5 of the sub-developing device 2 toward the magnet roller 11 of the main developing device 3 are generated so as to straddle the toner sensor i5. However, toner sensor 15! The permalloy 30 creates a space where the lines of force M can easily flow through the permalloy 30.
can be guided into the interior of the magnetic field, and can be branched into magnetic lines of force M and M. As a result, the lines of magnetic force M can be prevented from passing through the inside of the toner sensor 5.

Note that in the above embodiment, the permalloy 30 covers the surface of the toner sensor 15, but it is configured to cover only the detection part of the toner sensor 15 so that the lines of magnetic force M can be applied to the toner sensor 1.
5 may be prevented from having an adverse effect.

(F) Effects of the Invention As described above, according to the present invention, a plurality of developing devices are provided around the photoreceptor along the moving direction thereof, and at least one of a pair of adjacent developing devices is provided around the photoreceptor. The toner sensor located in the developing device is covered with a specific magnetic shielding member from the magnetic roller side of the other developing device, thereby at least the toner sensor generated between the magnetic pole portions of different polarities closest to each other of each of the image type magnet rollers. It is possible to cut the magnetic field to the toner sensor, thereby eliminating any negative effects on the toner sensor, ensuring normal toner control and good developer transport, and the ability to obtain high-quality multicolor images. be.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the main part configuration showing an embodiment of the present invention, Fig. 2 is a principle diagram for explaining the operation in the above embodiment, and Fig. 3 is an explanatory diagram of the main part configuration without showing the conventional ρ1. be. 1...Photosensitive drum, 2...Sub developing device (other developing device), 3...
...Main developer (one developer) 5.11...
・Magnet roller, 15... Toner sensor, 30... Permalloy (magnetic shielding member) Fig. 1 Fig. 3

Claims (1)

[Claims] 1. Located between a plurality of developing devices provided around the photoreceptor along the direction of movement of the photoreceptor, and two magnetic rollers respectively provided in an adjacent pair of developing devices among these developing devices, and a toner sensor configured to detect the toner concentration in at least one developing device; and a toner sensor made of a ferromagnetic material having high magnetic permeability, and provided to cover the toner sensor from the magnetic roller side of the other developing device; An image forming apparatus comprising: a magnetic shielding member capable of preventing a magnetic field generated by the two magnet rollers from affecting a toner sensor.