JPS6038710B2 - Toner density control device for dry developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a toner concentration control device for a dry developing device that develops an electrostatic image on a photoreceptor with a two-component developer containing a magnetic carrier and toner.

In the above-described dry developing device, of the toner and magnetic carrier that make up the developer, only the toner is consumed during development.
Therefore, when copying is repeated, the toner concentration in the developer decreases. Such a decrease in toner density causes a decrease in image quality. On the other hand, if the toner density increases too much, it may cause image fogging or toner scattering. Therefore, it is necessary to maintain the toner concentration at a constant level. For this reason,
A toner that allows a portion of the developer to pass through a coil and detects the density of the developer as a change in inductance, thereby supplying the missing toner and controlling the ratio of magnetic carrier to toner to be constant. Concentration control devices have already been proposed.

While this device normally works well, proper operation is not guaranteed with fresh developer or developer that has been out of service for an extended period of time. The reason for this is that with new developer or developer that has been stopped for a long time, the density of the developer is higher than during operation due to a decrease in the amount of charge. This is because the signal from the detection coil indicates a toner shortage even though it is appropriate. As a result, toner is replenished, causing an excess of toner in the developer. The present invention aims to eliminate the above-mentioned drawbacks in the toner concentration control device proposed above.

Embodiments of the invention will be described below with reference to the accompanying drawings. In the figure, a developing device 2 is arranged around the photosensitive drum.

In the developing device 2, a sleeve 15 having a permanent magnet therein is disposed at a position facing the toner hopper 3, clear impeller 4, and photosensitive drum. The developing sleeve 5 forms a developer brush in contact with the photoreceptor drum 1 by the action of the permanent magnet, and in this case, the amount of developer forming the brush is controlled by the doctor blade 6. A scraper 7 is disposed to be inclined downward from the upper part of the developing sleeve 5, and guides the developer after development to the fly azure blade 4. Sekiguchi 7A is provided in a part of the scraper 7, and this opening □7
A detection coil 8 is arranged below A. Reference numeral 9 denotes a toner supply adjustment member provided at the lower end outlet of the toner hopper 3, and is driven by the toner supply motor 10. A portion of the developer that completes the developing action and is guided by the scraper 7 and returned to the developer tank always passes through the entrance 7A and falls within the detection coil 8 to reach the developer tank. Changes in the density of the developer passing through it are extracted as changes in inductance.

Oscillator 11 using the above detection coil and capacitor
Accordingly, the above-mentioned change in inductance is treated as a change in frequency, and this change in frequency is detected by the converter 12 and extracted as a voltage change. The voltage level thus taken out is applied to the comparator circuit 13 and compared with a reference voltage, and if it is below the set value, an on signal is generated, and if it is above the set value, an off signal is generated. The switching circuit 14 amplifies this signal to drive the toner replenishment motor 0, and supplies toner from the toner hopper 3 to the developer tank of the developing device via the toner supply adjustment member 9. Conventionally, the developer having the above-mentioned structure was constantly monitored, and if the detected value was below a set value, the toner supply adjustment member 9 was rotated by the motor 10' to replenish toner.

As described above, as a result, erroneous detection and associated excessive toner supply occur for new developer or developer after a long period of rest. In contrast, in the present invention, a delay timer circuit 15 is provided, and this delay timer circuit is activated when the developing device 2 starts operating.

While the delay timer circuit is in operation, the comparator circuit 13 stops its operation in response to a strobe signal, so that the toner concentration control device also does not operate, and toner is not replenished from the toner hopper 3. After a predetermined time set in the delay timer circuit 15, the delay timer circuit stops operating;
The comparison circuit 13 and therefore the toner concentration control device start operating. In this case, for example, by using a capacitor, the predetermined time set in the delay timer circuit 15 is lengthened or shortened in accordance with the rest time of the developer before operation of the developing device.

In this way, the operation of the toner concentration control device can be more conveniently adapted to the respective developer conditions. As described above, the toner density control device according to the present invention prevents abnormal toner replenishment at the initial stage of operation of the developing device.

[Brief explanation of the drawing]

The figure is a sectional view of a dry developing device equipped with a toner density control device according to the present invention. 1... Photosensitive drum, 2... Developing device, 3... Toner hopper, 8... Detection coil, 9... Toner supply Adjustment member, 10...
... Toner replenishment motor, 11 ... Oscillator,
12...Converter, 13...Comparison circuit, 14...
...Switching circuit, 15...Delay timer circuit.

Claims (1)

[Claims] 1 In a dry developing device that develops an electrostatic latent image on a photoreceptor with a two-component developer having a magnetic carrier and toner, a portion of the developer is passed through a coil to change the density of the developer by inductance. In a toner concentration control device that detects the amount of water and replenishes toner so that the ratio of magnetic carrier and toner is constant, a period control operation corresponding to the rest time of the developer is performed at the beginning of the operation of the developing device. A toner density control device comprising means for stopping the toner concentration.