JPS62112182A - Device for controlling toner concentration of developer - Google Patents

Abstract

PURPOSE:To reduce the size and thickness of a sensor by providing plural pieces of magnetoresistance elements to one face of a base plate consisting of a nonmagnetic material and magnetic field generating means to the other face, and detecting the output voltage when the electric resistance of the magnetoresistance elements changes in accordance with the toner concn. of a developer. CONSTITUTION:Variable resistances r1, r2 change and therefore, the output voltage V corresponding to the toner concn. is obtd. if the variable resistors r1, r2 corresponding to the magnetoresistance element 13 and external fixed resister R are connected and the input voltage V is impressed thereto. Since the output voltage is weak, the voltage is impressed via an amplifier circuit to a smoothing circuit, then the voltage is compared with a preset reference voltage by a comparator. An external signal for maintaining the toner concn. of the developer is outputted to make such control as to drive a replenishing roll or stop the driving thereof via a proper driving means to replenish the toner from a toner tank or to stop the replenishment.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a developer toner quadrature control device in a developing device of, for example, an electronic copying machine, which uses a fine powder developer.

[Conventional technology]

In electrostatic recording and developing devices such as electronic copying machines, facsimiles, and electrostatic printers, an electrostatic latent image recorded on the surface of a photosensitive drum, etc., which is an image carrier, is processed using 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. 3 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 a toner tank 5 which stores toner 4 through a replenishment roll 3 on the other side. In the developer tank 1, 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 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 denotes a toner concentration control device, and a detection section is provided above the developer tank 1 and 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 inside and stirring with the toner 4 supplied from the toner tank 5 via the supply roll 3 by the two-rotation blade 9.

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]

As described in, for example, Japanese Patent Laid-Open Nos. 53-49437 and 54-159233, the toner density control device as described above includes a part of the magnetic circuit of a detection coil made up of the developer itself.

The most common method is to detect the concentration of toner in the developer by changing the inductance of a detection coil. However, with devices like this that use electric coils for the detection part,
This is because the device is relatively large.

There are restrictions on the mounting locations within the developing device, making it difficult to install at the optimum position, and the detection accuracy and reliability are not necessarily sufficient.
The method described in Publication No. 75 is a so-called magnetic bridge method, which compares the output signals of two magnetic circuits.

While it is not affected by environmental changes and has high reliability,
Since this method uses an electric coil for the detection section, it does not satisfy the demand for miniaturization of the entire device. Furthermore, the method described in Japanese Patent Application Laid-open No. 51-111047 detects leakage magnetic flux from the developer by using a Hall element as a detection means. This method is
Although it is possible to downsize and has good detection accuracy,
Since it is easily affected by environmental changes, it is still insufficient in terms of reliability and has not yet been put into practical use.

The present invention eliminates the drawbacks of conventional devices as described above.
．． It is an object of the present invention to realize miniaturization and thinning of sensors, which have recently been particularly in demand, and to provide a toner concentration control device having high precision and high reliability.

[Means for solving problems]

In order to achieve the above object, in the present invention, a plurality of magnetoresistive elements are provided on one surface of a substrate made of a non-magnetic material, and a magnetic field generating means is provided on the other surface.

A means for detecting an output voltage when the electric resistance of the magnetoresistive element changes in accordance with a toner concentration of the developer, arranged so that the magnetic field generating means extends to the magnetoresistive element; Toner compared to reference voltage? ; a means for generating an electric signal corresponding to a change in temperature, and the replenishment of toner is controlled by this electric signal.

〔Example〕

FIG. 1 is a longitudinal sectional view of a main part showing an embodiment of the present invention. In the figure, 12 is a substrate, which is made of a nonmagnetic material. On one side of the substrate 12.

A plurality of magnetoresistive elements 13 are placed on the other side, and a permanent magnet 1 is placed on the other side.
4 are respectively arranged so that the lines of magnetic force caused by the permanent magnets 14 reach the magnetoresistive element 13. Reference numeral 15 is a case for preventing the magnetic field produced by the permanent magnet 14 from being influenced by an external magnetic field.

Formed from magnetic material. Although it is configured as described above and is fixed to the developer tank 1 containing the developer 2, the magnetoresistive element 13 is disposed on the developer 2 side.

The first-order effect will be described using the above configuration.

As shown in FIG. 1, the flow of magnetic flux caused by the permanent magnet 14 extends to the magnetoresistive element 13 and the developer 2. As shown in FIG. When the toner concentration in the developer 2 changes, the magnetic permeability of the developer 2 changes, and therefore the magnetic flux in the vicinity of the magnetoresistive element 13 changes. When such a state occurs, the magnetoresistive element 13
As the resistance value changes, the output power also changes.

That is, a voltage corresponding to the toner concentration in the developer is output. Therefore, compare this output voltage with the reference voltage.

It outputs a signal according to the toner density.

FIG. 2 is a diagram showing an equivalent circuit corresponding to the embodiment of the present invention, in which the variable resistor rl+'2 corresponding to the magnetoresistive element 13 shown in FIG. 1 and the external fixed resistor R are arranged as shown in FIG. If the input voltage ■ is applied, the variable resistor r1+'Z changes in accordance with the change in the toner concentration of the developer as described above, so an output voltage V corresponding to the toner concentration is obtained. .

Since this output voltage is weak, it is applied to a smoothing circuit via an amplifier circuit as shown in FIG. 2, and then compared with a preset reference voltage using a comparator. Then, an external signal for maintaining the toner concentration of the developer is outputted via an appropriate driving means.

For example, control is performed such as driving or stopping the replenishment roll 3 shown in FIG. 3, replenishing the toner 4 from the toner tank 5, or stopping the replenishment.

In this embodiment, an example is shown in which a permanent magnet is used as the magnetic field generating means, but the same effect can be obtained by using an electromagnet. The thickness of the substrate also depends on its constituent materials and the magnetic force of the magnetic field generating means.

It is appropriately selected and determined so that the generated magnetic flux has the optimum density and direction.

C Effects of the Invention Since the developer toner concentration control device of the present invention has the structure and operation as described above, it can achieve the following effects.

(1) Since the detection section constituting the control device can be made extremely small and thin, the installation location in the developing device can be freely selected, and the optimal detection location can be selected.

(2) It has a structure that is not affected by external magnetic fields.

In connection with the above (1), both detection accuracy and reliability can be greatly improved.

(3) The entire device can be made smaller or thinner.

This not only increases the number of types of developing devices that can be used, but also has an extremely economical effect because it can be manufactured at a low cost.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a main part showing an embodiment of the present invention. FIG. 2 is a diagram showing an equivalent circuit of the same embodiment, and FIG. 3 is a sectional view of essential parts of the developing device. 1: Developer tank, 2: Developer, 12: Substrate, 13: Magnetoresistive element, 14: Permanent magnet.

Claims (2)

[Claims] (1) A plurality of magnetoresistive elements are provided on one surface of a substrate made of a non-magnetic material, and magnetic field generation means are provided on the other surface, and the magnetic field generation means are arranged so that the lines of magnetic force from the magnetic field generation means reach the magnetoresistive elements. , means for detecting an output voltage when the electrical resistance of the magnetoresistive element changes in accordance with the toner concentration of the developer;
A toner concentration control device for a developer, comprising means for comparing the output voltage with a reference voltage to generate an electric signal corresponding to a change in toner concentration, and controlling toner replenishment based on the electric signal. (2) The developer toner concentration control device according to claim 1, wherein the magnetic field generating means is a permanent magnet.