JP2974082B2 - Developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention stirs a two-component developer obtained by mixing a toner and a carrier, and supplies a triboelectrically charged toner to a photosensitive drum via a developing sleeve. To a developing device.

(Prior Art) Recently, a two-component developer obtained by mixing a toner and a carrier tends to be frequently used as a developer for an electrophotographic copying machine. The developing step using the developer is performed by supplying the toner in the developer to the electrostatic latent image on the photosensitive drum.

Therefore, as the number of copies increases, the toner in the developer stored in the housing of the developing device gradually decreases,
The toner density decreases. If this state is left unchecked, the image density decreases and the image quality deteriorates.

Therefore, the toner concentration of the developer is detected by a toner sensor including a magnetic sensor composed of a coil and an oscillator,
A configuration is adopted in which toner is supplied into the housing in accordance with the detection result to maintain the toner concentration of the developer within a predetermined range. The detection principle of the toner sensor is as follows. That is, the toner density is detected based on a phenomenon that the inductance of the coil changes due to a change in the toner density (more specifically, the amount of the carrier in the developer) in the developer contacting the energized coil. .

By the way, according to such a toner sensor, when the copying machine in the stable standby state in which the copying operation is stopped is restarted, the output of the toner sensor immediately after the restart is remarkably transiently larger than the output in the steady state thereafter. There is a problem of becoming larger. This is presumably because the coil of the toner sensor is energized during the stable standby, so that the magnetization of the carrier adhering to the sensor sensor is promoted, and the sensor output at the time of copying restart is increased. If the toner density is controlled based on the detection output of the toner sensor which becomes transiently large, the toner is unnecessarily replenished, so that accurate toner density control cannot be performed and the image quality deteriorates. Further, there is a possibility that the toner empty may be erroneously displayed.

For this reason, Japanese Patent Application Laid-Open No.
In the prior art disclosed in Japanese Patent Publication No. 56 (hereinafter referred to as first prior art), when the flow of the developer is not stable immediately after re-starting after the stabilization standby, the toner concentration is detected, that is, the toner sensor is detected. The output of the toner sensor at the time when the flow of the developer is stopped, which is the time when the flow of the developer is most stabilized, is read without reading the output, and the toner density is controlled.

Further, in the prior art disclosed in Japanese Patent Application Laid-Open No. 59-202474 (hereinafter referred to as a second prior art), the developer remaining near the toner sensor during stable standby is discharged, and new developer is discharged. At the time of the flow, the output of the toner sensor is read to control the toner density.

(Problems to be Solved by the Invention) However, according to the first prior art, the copying operation ends before the flow of the developer is stabilized, and
There is a disadvantage that the toner density may not be substantially controlled.

Further, the second prior art also has a disadvantage that accurate toner density control cannot be performed immediately after re-driving.

The present invention has been made to solve the problems of the related art, and even when the image forming operation is resumed after the stable standby,
It is an object of the present invention to provide a developing device capable of controlling the toner density and consequently improving the image quality.

The developing device of the present invention is a developing device that stirs a two-component developer obtained by mixing a toner and a carrier, and supplies a triboelectrically charged toner to a photosensitive drum via a developing sleeve. A toner sensor for detecting the toner concentration of the developer based on a change in the inductance of the coil; and turning on the power to the coil during the image forming operation until the temporarily stopped image forming operation is restarted. And energization control means for keeping the energization of the coil turned off during the standby time, thereby achieving the above object.

(Operation) As described above, if the power supply to the coil of the toner sensor is turned off during the stable standby, the carrier staying at the position of the toner sensor during the stable standby does not adhere to the sensor sensor of the toner sensor. . Therefore, the magnetization of the carrier is not promoted. Therefore, a transient phenomenon in which the sensor output abnormally increases when copying is restarted does not occur, and the toner density can be controlled immediately after re-driving.

(Example) An example of the present invention will be described below.

FIG. 1 shows a developing device of a copying machine according to an embodiment of the present invention. A developer 7 in which a toner and a carrier are mixed is accommodated in a housing 2 having a container shape of the developing device.
The developer 7 is conveyed to the position of the stirring rotor 21 by the rotationally driven developing spiral 20, and is stirred by the stirring rotor 21. The agitated developer 7 is attracted to a developing sleeve 22 in which a developing magnet roller is concentrically fixed and arranged inside, and is conveyed on the developing sleeve 22 in the same direction by the rotation of the developing sleeve 22 in the direction of arrow A. Is done.

A doctor blade 25 for making the layer thickness of the developer 7 uniform is disposed in the rotation region of the developing sleeve 22, and the developer 7 that has passed through the doctor blade 25 is conveyed to the left end opening of the housing 2, The toner is supplied to the photosensitive drum 1 through the opening, and the developing process is performed.

On the other hand, the excess developer 7 removed from the developing sleeve 22 by the doctor blade 25 is collected at the position of the developing spiral 20 via the partition plate 23 disposed above the stirring rotor 21.

The toner in the housing 2 is consumed with the progress of the above-described development process, and the toner concentration in the developer 7 decreases.
In order to compensate for this and to control the toner concentration in the developer 7 to be within a predetermined range, the supply toner 9 is supplied into the housing 2 in accordance with the consumption of the toner.

The supply of the replenishment toner 9, that is, the control of the toner concentration is performed by a toner sensor disposed near the doctor blade 25.
This is performed based on 24 detection outputs. The toner sensor 24 is
The output of the toner sensor 24 is provided to the CPU 20. The magnetic sensor includes a coil and an oscillator. Then, the CPU 20 determines whether toner replenishment is necessary based on the output of the toner sensor 24, and when it determines that toner replenishment is necessary, drives the toner replenishing roller 3 disposed in the toner cassette 8 disposed on the upper part of the housing 2. I do. As a result, the replenishing toner 9 in the toner cassette 8 falls into the housing 2 by a predetermined amount, and the toner is replenished.

A known toner sensor 24 composed of a magnetic sensor having a coil and an oscillator is disposed above the toner sensor 24. The toner sensor 24 detects the toner concentration of the developer 7 based on a change in the inductance of the coil. Based on the output signal from the toner sensor 24, the toner supply mechanism 3
And the toner concentration of the developer 7 is set in a predetermined range.

The coil of the toner sensor 24 is connected to a power supply 10 via a switching circuit 11, and the switching circuit 11
When turned on and off, the power supply from the power supply 10 to the coil is turned on and off. ON / OFF of switching circuit 11
Is controlled by the CPU 12. That is, when it is confirmed that the copying operation has been completed and the copying machine has entered a stable standby state by a command signal from a switch provided on the operation panel of the copying machine, the CPU 12 turns off the switching circuit 11 and energizes the coil. Turn off. Then, when it is confirmed that the copy switch on the operation panel is turned on and the copy operation is restarted, the switching circuit 11 is turned on, and the energization to the coil is restarted.

FIG. 2 shows the results of an experiment performed using the developing device of the present invention. Of these, FIG. 2 (a) shows the timing of energizing the coil of the toner sensor 24, and FIG. 3 shows the detection output. Where the toner sensor
A state where the detection output of 24 is 0 indicates a stable standby state.

As can be seen from the figure, the toner sensor 24
When the drive of the copying machine is restarted from this state, the transient phenomenon in which the detection output of the toner sensor 24 becomes abnormally large for a predetermined time from the restart point as shown by C10 to C13 in this case. Occur.

On the other hand, when the energization of the coil is turned off in the stable standby state, as shown by C1 to C9, the transient output described above does not occur, and the detection output of the toner sensor 24 immediately settles to a steady state. I understand. This causes a problem that if the power to the coil of the toner sensor 24 is turned off during the stable standby, the carrier does not adhere to the sensor sensing unit, and the magnetization of the carrier is promoted, and the detection output of the toner sensor 24 becomes abnormally large. It is presumed that they do not.

The present invention is not limited to a copying machine, but can be applied to other image forming apparatuses such as a printer.

(Effects of the Invention) According to the present invention described above, it is possible to effectively prevent the occurrence of a transient phenomenon in which the detection output of the toner sensor becomes abnormally large at the time of re-driving after a stable standby, and a steady state in which the detection output is immediately stabilized. Since the state is settled, the detection output of the toner sensor is read immediately after the re-driving to control the toner density.
Therefore, it is possible to improve the image quality and to prevent a problem such as an erroneous display of the toner empty.

[Brief description of the drawings]

FIG. 1 is a drawing showing a developing device of a copying machine according to an embodiment of the present invention, and FIG. 2 is a drawing showing experimental results of the present invention. DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum, 7 ... Developer, 9 ... Reinforcement toner, 11 ... Switching circuit, 12 ... CPU, 24 ... Toner sensor.

Claims (1)

(57) [Claims] 1. A developing device for stirring a two-component developer obtained by mixing a toner and a carrier, and supplying a triboelectrically charged toner to a photosensitive drum via a developing sleeve, comprising: a coil and an oscillator. A toner sensor for detecting the toner concentration of the developer based on the change in the inductance of the coil; and turning on the power to the coil during the image forming operation and waiting until the temporarily stopped image forming operation is restarted. And a power supply control means for keeping power supply to the coil turned off.