JPS6289081A - Developing device - Google Patents

Abstract

PURPOSE:To maintain toner concentration to a proper value even when the thickness of the layer of a magnetic brush is changed by adjusting a doctor blade by providing a very thin toner concentration sensor inside of the doctor blade. CONSTITUTION:A toner concentration sensor 11a is provided on the side of a doctor blade 10 that faces developer 2. The sensor 11a is provided with coils 13, 14 near the center of a non-magnetic substrate 12, and the coils are connected mutually to form a primary coil. A detecting coil 15 is provided on one face of the substrate 12, and a reference coil 16 is provided on another face, and an adjusting member 17 that regulates the degree of coupling is provided between the two coils. The detecting coil 15 and reference coil 16 are connected to become opposite phase to form a secondary coil, and a differential transformer is formed as a primary coil. When toner concentration became less by consumption, induced voltage of the detecting coil 15 becomes large, and a replenishing roll 3 is driven, and toner 4 is replenished to a developer tank 1. Thus, toner concentration of developer 2 is maintained to a proper value.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a developing device, for example, an electronic copying machine, which uses a fine powder developer, and particularly relates to a developing device equipped with a means for detecting the concentration of the developer. This relates to improvements in equipment.

[Conventional technology]

In electrostatic recording and developing devices such as electronic copying machines, facsimile machines, and electrostatic printers, an electrostatic latent image recorded on the surface of a photosensitive drum, etc., which is an image carrier, is processed by a magnetic brush method using a magnetic developer. It is developed and fixed by heat or pressure means to obtain the final visible image. In this case, in order to obtain a stable image, in a developing device that uses a two-component developer, it is necessary to monitor the mixing ratio of 1 ferromagnetic carrier and toner powder with high precision and maintain it at an appropriate concentration. A developing device equipped with a measuring means has been put into practical use.

FIG. 5 is a sectional view of essential parts of a developing device using a two-component developer. In the figure, reference numeral 1 denotes a developer tank which stores a developer 2 and is connected to an upper part via a supply roll 3 to a toner tank 5 which stores toner 4. As shown in FIG. A magnet roll 6 having a cylindrical shape and having a plurality of magnetic poles arranged on its surface and a hollow cylindrical sleeve 7 made of a non-magnetic material are provided in the developer tank 1 so as to be mutually rotatable. to face. Note that developer tank 1 contains developer 2.
A rotary blade 9 is provided in parallel with the magnet roll 6 to stir the toner 4 and frictionally charge the toner 4. then 10
is Doctor Blade.

It is provided at the end of the developer tank 1 facing the photosensitive drum 8, and the gap between it and the sleeve 7 is adjustable. Reference numeral 11 is a toner concentration sensor, and a detection portion thereof is provided above the developer tank 1 so as to be in contact with the developer 2.

With the above configuration, due to the relative rotation of the magnet roll 6 and the sleeve 7, the developer 2 on the sleeve 7 moves in the direction of the arrow, forms a magnetic brush on the sleeve 7, and rubs the surface of the photosensitive drum 8. , the electrostatic latent image formed on the photosensitive drum 8 can be developed. The developer 2 is further moved in the direction of the arrow by the sleeve 7 and returns to the developer tank 1.
After returning to the interior, the toner is stirred by a two-rotation blade 9 together with the toner 4 replenished from the toner tank 5 via the replenishment roll 3.

The image is then subjected to development again. The toner concentration sensor 11 provided in contact with the developer 2 measures the toner concentration in the developer 2 and outputs an external signal to maintain the toner concentration of the developer 2 according to the measured concentration.

The replenishment roll 3 is driven via an appropriate driving means (not shown), and the toner 4 is controlled to be replenished from the toner tank 5.

[Problem that the invention seeks to solve]

In the conventional developing device as described above, the toner/3 degree sensor 11 is provided above the sleeve 7 as shown in FIG. When provided below, the number is limited to approximately three locations. That is, the main reason for this is that the toner concentration sensor 11 is larger in size than the developer tank 1, as shown in FIG.

It is difficult to install in locations other than those mentioned above due to interference with other members, and the degree of freedom in the location of installation is extremely small. Therefore, the optimum location W for measuring the toner concentration of the developer 2 cannot be selected, and the measured result may not necessarily represent the true toner concentration of the developer 2. Also, due to environmental conditions and other changes, the doctor blade 10
The height of the magnetic brush formed on the sleeve 7 may be adjusted by adjusting the height of the magnetic brush formed on the sleeve 7, but in this case, the layer thickness of the developer 2 in contact with the toner concentration sensor 11 changes, so the measured value of the toner concentration changes. may occur, making it impossible to determine the true toner density. When variations or errors occur in the toner quadrature measurement value as described above, it becomes difficult to properly control and maintain the toner concentration of the developer, making it impossible to develop a high-quality image. The present invention solves the problems that exist in conventional developing devices as described above, and provides a developing device that can accurately detect and measure the toner concentration of the developer without variation, maintain it at an appropriate concentration, and develop high-quality images. The purpose is to provide a device.

[Means for solving problems]

In order to achieve the above objects, two aspects of the present invention include a developing device having a developer concentration measuring means and a proper agricultural degree maintaining means, in which the concentration measuring means is constructed as follows. Namely.

(1) Coils are provided concentrically on the front and back sides of the board to form a primary coil.

(2) A detection coil is provided on one surface of the substrate, and a reference coil is provided on the other surface of the substrate via a degree-of-coupling adjustment means with the primary coil.

(3) The detection coil and the reference coil are connected to have opposite phases to each other to form a secondary coil.

(4) The primary coil and the secondary coil form a differential transformer.

(5) The substrate is mounted on a doctor blade with the detection coil side facing the developer.

〔Example〕

FIG. 1 is a sectional view of a developing device showing an embodiment of the present invention, and the same components are designated by the same reference numerals as in FIG. 5. In the figure, lla is a toner concentration sensor, which is provided on the side of the doctor blade 10 facing the developer 2. FIGS. 2 and 3 are an enlarged side view and a front view of the main part of the toner concentration sensor 11a. In both figures, 12 is a substrate, which is made of a non-magnetic material and is formed into approximately 10 ma x 50 cranes x 2 dragons.

Coils 13 and 14 are provided concentrically on the front and back sides of the substrate 12 at approximately the center thereof, and are connected to each other to form a primary coil.

The coils 13 and 14 are formed flat and thin, for example, by sheet coils. Next, a detection coil 15 is provided on one surface of the substrate 12, and a base coil I6 is provided on the other surface. An adjusting member 17 is provided between the coil 14 forming the primary coil and the reference coil 16 to adjust the degree of coupling between the two coils. The adjusting member 17 is made of a magnetic material such as rough 1-ferrite, or a conductive material such as copper, and is provided on the substrate 12 so as to be adjustable at a position 311.

Note that the detection coil 15 and the reference coil 16 are connected in opposite phases to form a secondary coil, and together with the primary coil, a differential transformer is formed. After configuring as above, the doctor blade 1 is installed as shown in Figure 1.
The first detection coil 15 is fixed to the side of the developer 2 so as to be in contact with the developer 2 at a distance 3.

FIG. 4 is a diagram showing the winding structure and circuit blocks of the toner concentration sensor shown in FIGS. 1 to 3, and the same parts are designated by the same reference numerals as in FIGS. 2 and 3. Fourth
In the figure, 18 is an oscillator, which together with coils 13 and 14 constitutes an oscillation circuit. Next, an amplifier 19 is connected to the detection coil 15 forming the secondary coil, and a phase detector 20 is further connected to the secondary coil to form a phase detection circuit.

A comparator 21 connects the 3-phase detector 20 and the DC power source 23, and the 5 output side connects the drive output circuit 22. With the above configuration, the first oscillator 18 and the primary coil 13
．． The oscillation signal of the oscillation circuit 14 is transmitted in opposite phases to a detection coil 15 and a reference coil 16, which constitute a secondary coil.

In this case, since the developer is in contact with the upper part of the substrate 12 in FIG. If the magnetic resistances in the magnetic circuits of the adjustment member 17 and the reference coil 16 are the same, the differential voltage between the induced voltages in the detection coil 15 and the reference coil 16 forming the secondary coil will be:

After being amplified by the amplifier 19, the oscillation voltage on the primary coil side is detected and output by the phase detector 20, and a predetermined voltage value is output. However, developer 2 shown in FIG.
When the toner is consumed by repeated development, the toner concentration becomes thinner and the effective magnetic permeability of the developer 2 increases.
The induced voltage of the detection coil 15 becomes large, and the detection output also becomes large. Therefore, the output of the comparator 21 becomes high level, and the drive output circuit 22 is activated to drive the replenishment roll 3 shown in FIG. 1, and the toner 4 is replenished into the developer tank 1. On the other hand, when toner continues to be replenished and reaches a proper toner concentration, the induced voltage in the detection coil 15 becomes small.

Since the detection output also becomes small, the output of the comparator 21 becomes low level, and as a result, the operation of the drive output circuit 22 is stopped. In this way, by turning off the supply roll 3, the toner 4
The toner concentration of the developer 2 is maintained at an appropriate value.

In this embodiment, an example is shown in which the toner concentration sensor 11a is fixed to the developer 2 side of the doctor blade 10, but the substrate 12 shown in FIGS. Good too. Alternatively, the center portion of the doctor blade 10 may be hollowed out to match the dimensions of the substrate 12, and the substrate 12 may be fitted therein.

〔Effect of the invention〕

Since the developing device of the present invention has the structure and operation as described above, it has the following effects.

(1) Since the toner concentration sensor is provided inside the doctor blade, the developer is in the most dense state, and detection accuracy is good and reliability is high.

(2) Since the toner concentration sensor is formed extremely thin, there is no interference with other members constituting the developing device, and there is a high degree of freedom in selecting the mounting position.

(3) Even if the layer thickness of the magnetic brush is changed by adjusting the circumference of the doctor blade, the conditions of the developer in a portion of the density sensor remain unchanged, so there is no change in the measured value.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part showing an embodiment of the present invention, FIGS. 2 and 3 are an enlarged side view and front view of a main part of the toner concentration sensor shown in FIG. 1, and FIG. 4 is a toner density sensor. FIG. 5 is an explanatory diagram showing a winding structure and a circuit block, and FIG. 5 is a sectional view of a main part showing an example of a conventional developing device. 1: Developer tank 13: Supply roll, 6: Magnet roll 17: Sleeve, 10: Doctor plate, 11. ll
a: toner concentration sensor, 12: substrate, 13.14: coil, 15: detection coin b. 16: Reference coil.

Claims (4)

[Claims] (1) A density measuring means for measuring changes in the density of the developer by changes in magnetic permeability, a means for maintaining the developer at an appropriate density according to the measurement results by the density measuring means, and an image-bearing means for carrying the developer at an appropriate density. In a developing device equipped with a developing means for developing a latent image on an image carrier by conveying it to a body, coils are provided concentrically on the front and back sides of a substrate to form a primary coil, and a detection coil is provided on one side of the substrate. A reference coil is provided on the other side of the coil via the primary coil and coupling degree adjusting means, and the detection coil and the reference coil are connected in opposite phases to each other to form a secondary coil, A developing device characterized in that a differential transformer is formed by a coil and a secondary coil, and the substrate is provided on a doctor blade with the detection coil side facing the developer to constitute a density measuring means. (2) The developing device according to claim 1, wherein the substrate is integrated with the doctor blade. (3) Claim 1 in which the coil is a sheet coil
Developing device according to item 1 or 2. (4) The coupling degree adjustment means between the primary coil and the reference coil is a magnetic material or a conductive material.
Developing device according to any one of item 3.