JPS5876865A - Toner density controller - Google Patents

Abstract

PURPOSE:To control the amount of toner supplemented to a developer by winding a coil in an E-sectioned material with high magnetic permeability, and detecting variation in the toner density of the developer in the form of variation in the inductance of the coil. CONSTITUTION:An E-sectioned ferritic core 11 made of a magnetic material with high magnetic permeability is wound with a coil 12 at the center part. According to an increase in the rate of carriers, the inductance of the coil increases, and an oscillation frequency (f) is as shown by the expression where L is inductance and C1 and C2 are capacitor capacities. The oscillation frequency (f) is in inverse proportion to the square root of the value L varying with the rate of carriers, and a PLL circuit outputs a DC signal proportional to the (f). When the signal voltage outputted from the PLL circuit drops below a preset value, a cpmparing circuit judges that the toner density in a developer decreases, and then outputs a toner supplementation signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a toner concentration control device in an electrostatic recording device or the like that uses a two-component developer consisting of toner and a magnetic carrier.

In an electrostatic recording device using a two-component developer, the carrier serves to triboelectrically charge the toner to a predetermined polarity, adsorb the toner, and transport the toner to a developing position on the latent image carrier. Of the toner and the carrier, only the toner actually develops the electrostatic latent image, and as development is repeated, the toner in the developer is gradually consumed, the toner density decreases, and the density of the developed image also decreases.

In order to keep the density of the developed image constant, it is necessary to keep the toner density constant by sequentially replenishing the developer with an amount of toner corresponding to the consumed amount. As a device for keeping this toner concentration constant, a device that utilizes changes in the inductance of a coil is known.

Furthermore, the specification of Japanese Patent Publication No. 53-135644 proposes a device that uses an iron core with a U-shaped cross section around which a coil is wound, and detects the toner concentration of the developer by changing the inductance of the coil. ing. In the above proposal, both legs of the U-shaped iron core are buried in the developer, and a steady flow of developer flows in parallel to the recess formed by the legs. In addition, it was necessary for the iron core to protrude into the developer.

The present inventors have studied how to reduce the size of the detection unit and improve its performance without protruding the iron core into the developer. In order to increase the detection ability of a detection sensor, the following conditions are required for the detection sensor.

(1) A magnetic circuit is formed using a material with high magnetic permeability and a developer, and at this time, the area where the material with high magnetic permeability comes into contact with the developer is increased.

(2) Increase the number of turns of the coil.

(3) Make the magnetic permeability of the material around which the coil is wound as high as possible.

An object of the present invention is to provide a toner concentration control device having a small-sized detection sensor with high detection ability.
The above object is to provide a toner concentration control device which winds a coil around a material with high magnetic permeability, detects a change in toner concentration of a developer as a change in inductance of the coil, and thereby controls the amount of toner supplied to the developer. This is achieved by a toner concentration control device characterized in that the cross-sectional shape of a material with a high magnetic permeability is a white character shape.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Figure 1 shows the shape of the sensor section.
) is a perspective view of the core 11, which uses a mountain-shaped material with high magnetic permeability and a ferrite core. Figure 1+b) is a detection diagram in which the coil 12 is wound around the center of the ferrite core 11. It shows a cross-sectional view of Senna.

FIG. 2 is a cross-sectional view showing the detection sensor shown in FIG. 1(b) attached to the resin plate 2 of the developer container and in contact with developer solution. By arranging the sensor relative to the developer layer in this way, the area in contact with the developer increases compared to the U-shaped sensor described above, and also when winding the coil, the sensor is placed in the center of the chevron shape. By winding the coil,
This provides a compact sensor with high sensitivity and no waste of space.

/ FIG. 3 shows a block diagram of a detection circuit using a stamp sensor according to the present invention, and the principle of operation will be explained.

When the toner concentration decreases, the proportion of magnetic carrier (iron powder) in the developer increases, thereby increasing the inductance of the coil.

At the oscillation frequency of the Colpitts oscillation circuit, if the inductance of the coil is L1 and the capacitance of each capacitor is C1, C (shown in FIG. 3), it is given by the following equation.

, 1 is inversely proportional to the square root of the value of the inductance L that changes.

The PLL (Phase Locked Loop) circuit thus outputs a DC signal proportional to the input oscillation frequency f.

In the next comparison circuit, when the signal voltage output from the PLL circuit becomes less than a predetermined value, it is assumed that the toner concentration in the developer has decreased, and a toner replenishment signal is output.

FIG. 4 shows the present invention applied to a magnetic brush developing device for an electrostatic recording device. A magnetic sleeve 3 is located inside the developer container 2.
And a stirring screw 4 is rotatably provided. A developer mixture consisting of toner and magnetic carrier in the developing container 2 is stirred by a stirring screw 4, and the toner and magnetic carrier adhere to each other due to frictional electrification. The mutually attached developer ← is attracted to the circumferential surface of the magnetic sleeve 3, is conveyed as the sleeve 3 rotates counterclockwise, and comes into contact with the electrostatic latent image on the rotating photoreceptor 5 at a predetermined position. , the toner is attracted to the electrostatic latent image and development is performed. Therefore, the constantly stirred developer is conveyed to a predetermined position and development is performed, but if toner T is not replenished from the toner replenishment tank 6, the proportion of carrier in the developer gradually increases.

Detection sensors 11 and 12 according to the present invention are attached to the wall surface of the developer container 2 made of resin. The agitated developer always comes into contact with the wall surface of the developer container where the detection sensor is attached, and if the proportion of carrier in the developer increases, the third
As explained in the drawings, the electromagnetic valve or toner replenishing roller provided at the lower opening of the toner replenishing tank 6 is controlled to replenish the required amount of toner into the developer container and maintain a constant toner concentration.

As explained above, the toner production control device according to the present invention has a small sensor with high detection ability and a high-performance detection ability by attaching a detection sensor to the wall surface of the developer container and using the electric circuit described in the embodiment. This enables highly accurate developer management.

[Brief explanation of drawings]

FIG. 1 shows the shape of the sensor section according to an embodiment of the present invention, FIG. 1(a) shows a perspective view of the core, and FIG.
b) shows a sectional view of the cell. FIG. 2 is a sectional view showing how the sensor of the present invention is installed, FIG. 3 is a block diagram of a detection circuit, and FIG. 4 is a sectional view of the present invention applied to a developing device. 2・φ・Resin plate 11... Ferrite core 1
2・■ Coil River, ... Developer T ... Toner agent Yoshimi Kuwabara 1 Kasumi (α) (b) Yu 2 Fig.

Claims (3)

[Claims] (1) In a toner concentration control device, a coil is wound around a material with high magnetic permeability, and a change in the toner concentration of the developer is detected as a change in the inductance of the coil, thereby controlling the amount of toner supplied to the developer. A toner concentration control device characterized in that the cross-sectional shape of a highly magnetic substance is a white letter shape. (2) The toner concentration control device according to claim 1, characterized in that ferrite is used as the material with high magnetic permeability. (3) Forming a Colpitts oscillation circuit including the above-mentioned coil as a means for detecting changes in inductance of the coil,
The toner concentration control device according to claim 1, wherein a change in oscillation frequency due to a change in inductance of a coil of the oscillation circuit is detected using a PLL circuit, and the amount of toner supplied to the developer is controlled. .