JPH04174473A - Toner density controlling device - Google Patents

Abstract

PURPOSE:To perform a correct toner density control without receiving effects of rotation of a magnet roll by converting an AC signal outputted from a toner density sensor into a DC signal so as to control a toner density. CONSTITUTION:When a toner density inside a developing unit 14 is reduced corresponding to a development process, a magnetic flux of a magnet roll 15a detected by a toner density sensor 20 is also reduced. An output voltage from an amplifier circuit 20b is also reduced, and an output voltage rectified at an absolute value circuit 23 becomes a pulsating current with a reduced voltage level. A voltage value smoothed into a DC voltage by a low pass filter 24 is a voltage value lower than a predetermined voltage value (Vc). A voltage/ density converting part 25 therefore drives a compensation roll 12 through a compensation roll drive part 26 when it determines that the toner density is less than a predetermined level for compensating toner into the developing unit 14.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a toner concentration control device for a developing device that uses a two-component developer consisting of toner and carrier as a developer, and provides accurate toner concentration control without being affected by the rotation of a magnet roll. The purpose of the present invention is to provide a toner concentration control device for a developing device that performs a developing process using a developer made of toner and carrier. a toner concentration sensor provided at a predetermined position on the upstream side in the moving direction of the developer; a conversion means for converting an AC detection signal of the toner concentration detected by the toner concentration sensor into a DC signal; The toner replenishment determining means is configured to include a toner replenishment determining means for determining whether or not toner is replenished based on an output signal, and a toner replenishing means for replenishing toner into the developing device in accordance with the output of the toner replenishment determining means.

[Industrial application field]

The present invention relates to an image forming apparatus such as a laser beam printer, an LED printer, or an LCS printer that forms an image using an electrophotographic process, and more specifically, the present invention relates to an image forming apparatus such as a laser beam printer, an LED printer, or an LCS printer that forms an image using an electrophotographic process. The present invention relates to a toner density control device for a developing device.

[Conventional technology]

Image forming apparatuses such as laser beam printers and LED printers that form images using an electrophotographic process have a photoreceptor drum disposed therein as an image carrier, and a charger is installed near the circumference of the photoreceptor drum. , an exposure section, a developing device, a transfer device, and other image forming members are sequentially arranged. Then, the photoreceptor drum, whose peripheral surface is charged with a negative charge by the charger, is exposed to light in accordance with the image data, and the formed electrostatic latent image is turned into a toner image (visualized) by the developer. After the toner image is transferred onto paper by a transfer device, the toner image is thermally fixed onto the paper by a fixing device to form an image. In the image forming process as described above, a two-component development method consisting of toner and carrier is generally adopted as a development method for developing the above-mentioned electrostatic latent image formed on the circumferential surface of the photoreceptor drum.

FIG. 7 is a schematic diagram of a developing device using a two-component developing system. In the figure, the developing device 7 includes a developing roll 8, a stirring member 9, a blade 10, a toner hopper 11, and a supply roll 1.
2. Consists of a toner concentration sensor 13. The developing roll 8 has a magnet roll 8a inside and a developing sleeve 8 on the circumference.
b, the developing sleeve 8b attracts developer and rubs against a photoreceptor drum (not shown), thereby developing an electrostatic latent image on the circumferential surface of the photoreceptor drum. The stirring member 9 stirs the developer consisting of toner and carrier contained in the developing device 7, making the toner concentration in the developing device 7 uniform, and imparting a constant charge to the toner. Also, the blade l
O regulates the layer thickness of the developer adsorbed on the circumferential surface of the developing sleeve 8b, and maintains the layer thickness at a constant value.

As the developing process by the developing device 7 continues, the toner in the developing device 7 is gradually consumed, and the toner concentration sensor 13 detects a decrease in the toner concentration. Conventionally, this toner concentration measurement control has been carried out by, for example, providing a Hall element within the toner concentration sensor 13.
This is done by changing the magnetic force detected by this Hall element. Specifically, as the ratio of toner contained in the developer (toner concentration) increases, the gap between carriers increases,
The magnetic flux returning from the north pole to the south pole of the magnet roll 8a increases through the space formed by this gap, and at this time, the toner concentration sensor 13 detects a strong magnetic force. Furthermore, when the toner concentration decreases, the gap between the carriers decreases and the space formed decreases, so that the magnetic force detected by the toner concentration sensor 13 at this time becomes weak.

Based on the detection output of the toner density sensor 13 detected in this manner, the replenishment roll 12 is rotationally driven to supply toner from the toner hopper 11 to the developing device 7 .

[Problem to be solved by the invention]

In the conventional toner concentration control device as described above, since the magnet roll 8a rotates in the direction of the arrow, the positions of the N and S poles formed in the magnet roll 8a are also in the direction of the arrow with respect to the location of the toner concentration sensor 13. move in the direction. For this reason, the strength of the magnetic flux detected by the toner concentration sensor 13 also changes due to the rotation of the magnet roll 8a, making it impossible to accurately detect toner concentration, and therefore making it impossible to accurately replenish toner to the developing device 7. Therefore, reliable toner density control cannot be performed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a toner concentration control device that can accurately control toner concentration without being affected by the rotation of the magnet roll 8a.

[Means to solve the problem]

The means of the present invention are as follows.

FIG. 1 is a block diagram of the present invention. The present invention is based on the case where development processing is performed using a developer consisting of toner and carrier.

The toner concentration sensor 1 is disposed at a predetermined distance from the developer position on the upstream side in the developer movement direction with respect to the developer position in the developer unit, and detects, for example, an electrostatic latent image on the image carrier. Detects toner density before development.

The converting means 2 converts the AC detection signal of the toner concentration detected by the toner concentration sensor 1 into a DC signal.

The toner replenishment determining means 3 determines whether or not toner is replenishing from the output level of the output signal converted into a DC signal by the converting means 2.

The toner replenishing means 4 replenishes toner into the developing device according to the output of the toner replenishment determining means 3, for example, by using a replenishment roll.

[For production]

The operation of the means of the invention is as follows.

The toner concentration sensor 1 is, for example, a magnetic sensor, and detects the toner concentration in the developing device as a change in magnetic permeability. During this detection, the AC signal included in the detection signal is converted into a DC signal by the converting means 2 using the magnetic flux of the magnetic roll. Convert to The DC signal including this toner concentration information is sent to the toner replenishment determining means 3.
For example, the signal level is compared with a voltage value of a predetermined level, and if the signal level is higher than the predetermined value, the toner replenishing means 4 is driven to replenish toner to the developing device.

By controlling toner replenishment in this way, even if the signal detected by the toner density sensor contains an AC component, the toner replenished to the developer is converted into a DC signal and compared with a predetermined value. Therefore, toner concentration can be detected accurately and toner supply control can be performed reliably.

〔Example〕

One embodiment will be described below with reference to FIGS. 2 to 6.

FIG. 2 is a block diagram showing a circuit configuration of a toner concentration control device according to an embodiment, and FIG. 3 is a diagram showing a configuration of a developing device in which toner concentration is measured by a toner concentration measuring device according to an embodiment. be. First, in FIG. 3, the developing device 14 includes a developing roll 15, a stirring member 16, a toner hopper 17, a blade 18, a supply roll 19, a toner concentration sensor 20, and the like. The developing roll 15 includes a rotating shaft (not shown) to which rotational force is transmitted from a motor, a magnet roll 15a fixed to the rotating shaft, and a magnet roll 15.
The developing sleeve 15b is arranged to maintain a predetermined gap with respect to the developing sleeve 15b.

N poles and S poles are alternately arranged on the magnet roll 15a, and the developer is attracted to the circumferential surface of the developing sleeve 15b by magnetic force. Further, the developer adsorbed to the circumferential surface of the developing sleeve 15b is specifically configured such that a carrier is adsorbed to the circumferential surface of the developing sleeve 15b, and the toner stands in spikes on the carrier. Further, as the magnet roll 15a rotates, the developer on the developing sleeve 15b is conveyed in the direction of the arrow, and the layer thickness of the developer is regulated at the position where the blade 18 is disposed.

As described above, the stirring member 16 keeps the toner concentration in the developing device 14 constant, and also applies a constant electric charge to the toner by causing friction between the carrier and the toner.

The toner concentration sensor 20 is disposed upstream of the developing area 21, which is a sliding position between a photosensitive drum (not shown) and the developing sleeve 15b, with respect to the direction of movement of the developer. The toner density sensor is composed of a Hall element and an amplifier circuit, and is connected to the developer 1.
Detection of toner density within 4 is performed. A control circuit 22 shown in FIG. 2 is connected to this toner concentration sensor 20.

This control circuit 22 includes an absolute value circuit 23, a low-pass filter 24, a voltage/fi degree conversion section 25, and a replenishment roll drive section 26.
It consists of The circuit diagram in FIG. 4 specifically shows the configuration of the toner concentration sensor 20, absolute value circuit 23, and low-pass filter 24 in the above-described circuit configuration. The detection signal detected by the Hall element 20a in the toner concentration sensor 20 is amplified by the amplifier circuit 20b and output to the absolute value circuit 23. At this time, from the Hall element 20a to the amplifier circuit 2
As shown in the characteristic curve of FIG. 5, the output voltage output to the terminal 0b has a characteristic that the output voltage increases as the toner concentration within the developing device 14 increases. However, since the output voltage of the Hall element 20a is on the order of mV, the configuration is such that the output voltage of the toner concentration sensor 20 is increased to a predetermined voltage level by the amplifier circuit 20b.

The absolute value circuit 23 is made up of a bridge circuit made up of four diodes DI-DJ, and rectifies the amplified voltage (signal) output from the amplifier circuit 20b. The low-pass filter 24 is composed of a resistor R and a capacitor C, and smoothes the rectified voltage output from the absolute value circuit 23. That is, since the voltage output from the absolute value circuit 23 is specifically a so-called pulsating current voltage, it is smoothed to create a substantially direct current voltage.

The output terminals O3, 0□ of the low-pass filter 24 are output to the voltage/concentration converter 25 described above.
Then, the supply roll drive unit 2 is activated according to the supplied DC voltage value.
This configuration outputs a control signal to 6.

The operation of the toner density control device having the above configuration will be described below.

First, the toner concentration in the developer in the developing device 14 is detected by the toner concentration sensor 20, and a predetermined voltage value based on the above-mentioned FIG. 4 is output to the absolute value circuit 23 via the amplifier circuit 20b. As described above, the toner concentration sensor 20 detects changes in the magnetic flux of the magnet roll 15a detected via the developer adsorbed on the developing sleeve 15b.
As shown in FIG. 6(a), the output voltage from the amplifier circuit 20b is an alternating current voltage. Moreover, when the toner concentration in the developing device 14 is at an appropriate value, the output voltage of the amplifier circuit 20b supplied to the absolute value circuit 23 has the same AC voltage output level as shown in period A in FIG. 6(a). Become. Therefore, the output voltage rectified by the absolute value circuit 23 also becomes a pulsating current with the same level as shown in FIG. The voltage value is approximately constant and exceeds the voltage value (VC). Therefore, it is determined that the density data converted by the voltage/density conversion unit 25 is a voltage value that does not require driving the replenishment roll 19, and no drive signal is output to the replenishment roll drive unit 26.

On the other hand, when the toner concentration in the developing device 14 decreases according to the development process, the magnetic flux of the magnet roll 15a detected by the toner concentration sensor 2o also decreases.

For this reason, as shown in period B of FIG. 6(a), the amplifier circuit 20
The output voltage from b also decreases, and the output voltage rectified by the absolute value circuit 23 also becomes a pulsating current with a decreased voltage level, as shown in FIGS. Therefore, the voltage value smoothed into a DC voltage by the low-pass filter 24 becomes a voltage value lower than the predetermined voltage value (Vc) as shown in FIG. Therefore, the voltage/density conversion section 25 easily determines that the toner concentration is below a certain level, and drives the replenishment roll 12 via the replenishment roll drive section 26 to replenish toner into the developing device 14 .

As mentioned above, toner supply to the developing device 14 of this embodiment is as follows.
By converting the alternating current signal detected by the toner concentration sensor 20 into direct current using the control circuit 22, it is possible to easily detect, for example, that the direct current voltage has fallen below a certain value, and based on this detection information, Since the replenishment roll 19 is driven to replenish toner, accurate toner replenishment can be achieved.

〔Effect of the invention〕

According to the present invention, by converting the AC signal output from the toner concentration sensor into a DC signal and controlling the toner concentration, it is possible to replenish an accurate amount of toner corresponding to the consumed toner.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the present invention; FIG. 2 is a circuit block diagram of a toner concentration control device according to an embodiment; FIG. 3 is a configuration diagram of a developing device used in the toner concentration control device according to an embodiment; The figure shows a specific circuit diagram of the toner concentration sensor, absolute value circuit, and low-pass filter. Figure 5 is a characteristic diagram showing the relationship between the detection voltage value of the toner concentration sensor and the toner concentration. Figures 6 (a) to (C) 7 is a characteristic diagram of toner concentration control by a toner concentration control device according to an embodiment, and FIG. 7 is a configuration diagram of a conventional toner concentration control device. L... Toner concentration sensor, 2... Conversion means, 3... Toner replenishment determining means, 4... Toner replenishment means, 14... Developing device, 15... Developing roll, 15a... Magnet roll, 15b... Developing sleeve, 16... Stirring member, 17... Toner hopper, 18... Blade, 20... Toner concentration sensor, 20a... Hall element, 20b... Amplifying circuit , 23... Absolute value circuit, 24... Low pass filter, 25... Voltage/1 degree conversion section, 26... Replenishment roll drive section.

Claims (1)

[Scope of Claims] In a toner concentration control device for a developing device that performs development processing using a developer composed of toner and carrier, a predetermined position upstream in the direction of movement of the developer with respect to the development position in the developing device. a toner concentration sensor (1) provided in the toner concentration sensor (1); a conversion means (2) for converting an AC detection signal of the toner concentration detected by the toner concentration sensor (1) into a DC signal; toner replenishment determining means (3) for determining whether or not toner replenishment is required based on the output signal; and toner replenishing means (4) for replenishing toner into the developing device according to the output of the toner replenishment determining means (3). A toner density control device comprising: