JPH0359580A - Toner concentration controller - Google Patents

Abstract

PURPOSE:To accurately control toner concentration with simple constitution by selecting the output of a sensor part provided every developing unit and providing a signal processing part for processing the selected output. CONSTITUTION:In a developing device where two-component developer is used, a detection means for detecting the toner concentration of the developer with which plural developing units 2 is filled in accordance with the change of magnetic permeability is constituted of the sensor part 8 provided every developing unit 2, a selection means for selecting the output of the sensor part 8 and the signal processing part for processing the output of the sensor part selected by the selection means. The toner is replenished in accordance with the difference between the detection value of the detection means and a reference value previously measured. Thus, the toner concentration is accurately controlled at low cost.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a toner density control device for an electrophotographic recording device such as a copying machine or a printer, which performs development using a dual-function developer using a plurality of developing units. Regarding.

(Prior art) Conventionally, in a developing device using a two-part developer,
The toner concentration in the developer is detected and controlled so that the value is kept constant. Conventional toner concentration detection methods include forming a toner image of an appropriate size on an image support, measuring the reflectance of the image, and determining the toner concentration from the change; L detection method that captures the mixing ratio with toner, which is a non-magnetic material, as a change in magnetic permeability;
Furthermore, a method that utilizes the change in the volume fraction of toner is known.

Among these methods, the L detection method is characterized by its superior detection ability for changes in toner concentration compared to other methods.

In the conventional L detection method, a magnetic sensor section consisting of a coil and an amplifier section for amplifying the output from the coil are integrally configured and attached to a developing device. This method may also be applied to a recording device having multiple developing devices, such as a color electrophotographic device.

A combination of the above-mentioned sensor section and amplifier section was attached to each developing device. Therefore, it is necessary to provide as many sensors and amplifiers as there are developing devices (for example, four sets), which increases the number of components and increases costs.

Furthermore, each sensor has variations, which must be adjusted individually, making the adjustment complicated.

(Objects and Structure of the Invention) The present invention has been made in view of the above points, and is a toner concentration control device that performs development with a plurality of developing units using a two-component developer. The purpose is to achieve a toner concentration Mll of
In order to achieve this purpose, a sensor section provided in each developing device is used to detect the toner concentration of each developer loaded in the plurality of developing devices according to changes in its magnetic permeability.
It is constituted by a selection means for selecting the output of this sensor section, and a signal processing section for processing the output of the sensor section selected by this selection means, and the difference between the detected value of this detection means and a preset reference value. Toner is refilled accordingly.

(Example) The present invention will be explained below based on the drawings.

FIG. 1 is a block diagram showing the main parts of a color laser printer incorporating a toner density control device according to the present invention.

In the figure, 1 is a photosensitive drum, and 2 is a developing device. As developing devices, there are four developing devices numbered 1 to 4 for color toner and black toner along the outer periphery of the photosensitive drum l. In Figure 0, only the first developing device is shown. However, the second to fourth developing units have exactly the same configuration.

The first developing device 2 includes a developing roller 4 installed in a housing 3, a stirring screw 5.6, a hopper 7 for toner replenishment, and a toner concentration sensor 8 placed under the stirring screw 5. It is configured.

The sensor 8 is composed of a coil 8a and an oscillation circuit 8b. An alternating current of a predetermined frequency is supplied from the oscillation circuit 8a to the coil 8a, and the magnetic flux generated by the current flowing through the coil 8a moves the developer in the housing 3. It is now passable. When the toner in the developer is consumed, the density of the magnetic material changes, and therefore the magnetic permeability of the developer changes, causing the inductance of the coil 8a to change. When the inductance of the coil 8a changes, the phase of the current flowing through it changes, so by detecting the change in phase, the toner concentration can be detected.

The output from each sensor 8 is sent to an analog multiplexer 9, which in turn is sent to a microcomputer 10.
The output of one of the four sensors 8 is sent to the PLL circuit 11 in response to a selection signal from the sensor. The PLL circuit 11 detects the phase difference between the output current of the sensor 8 and the reference current in the PLL, converts it into a voltage value, and outputs it to the operational amplifier 12. This voltage value is amplified by an amplifier 12 and then sent to an A/D converter 13.
After being converted into a digital value, it is output to the microcomputer IO. The PLL circuit 11 and the operational amplifier 12 constitute an amplifier section 20.

In this embodiment, the detection means detects the toner concentration of the developer using four sensors 8 provided for each developer, a multiplexer 9 for selecting the output of the sensor, a PLL circuit 11, and an operational amplifier 12. It consists of

FIG. 2 is a waveform diagram of the output voltage of the amplifier 12, and the output voltages are V, □ and V wa i. It changes periodically between This is due to the influence of the magnetic permeability of the rotating stirring screw 5 (although these V□ and V w
a i n changes almost linearly in response to changes in toner concentration (see FIG. 3). Among these, the influence from the stirring screw 5 is relatively small.

is sampled in synchronization with the rotation of the stirring screw 5,
The toner density is detected from this value of V sa j n.

Returning to FIG. 1, 14 is a developing motor that drives the developing roller 4 and stirring screws 5 and 6; 15 is a driver that drives the developing motor 14 in response to a signal from the microcomputer 10;
16 is a motor that rotates the conveyance screw 7a of the hopper 7, 17 is a driver that drives the motor 16, and 18 is an initial setting switch as an operating means for initially setting a reference value that is a reference for toner replenishment. The switch 18 is replaced by, for example, a numeric keypad on the printer operation section.

Before this device is actually used as an output device, a reference value serving as a reference for toner replenishment is initially set during the manufacturing process or by the user. This reference value is set by installing unused developer or standard developer in the developing device. However, the present invention is not limited to this, and each sensor 8 may be attached to each developing device 2 in a state in which a reference magnetic permeability is given to each sensor.

Next, the initial setting operation of a reference value that is a reference for toner replenishment will be explained based on the flowchart of FIG.

First, when switch 18 is turned on by manual operation (F-
1) The developing motor 14 of the first developing device 2 is malfunctioning.
-2) The developing roller 4 and stirring screws 5 and 6 rotate. Furthermore, the multiplexer 9 is switched so as to receive only the output signal from the sensor 8 of the first developing device (
F-3), based on the output signal from the first sensor 8,
The above-mentioned V min is sampled for a predetermined period of time (F-4), and the value is stored as a first reference value in, for example, a non-volatile memory (F-5). Then, the first developing motor is stopped (F-6), and then the second to fourth developing units are also stopped in steps (F-2) to F-5.
) to obtain and memorize the second to fourth reference values for each developer in sequence (F-7).
, the reference value initialization operation ends.

During the actual developing operation of the printer, the output of the sensor 8 of each developing unit is monitored in turn and compared with the reference value preset at the time of the initial setting. If the toner concentration changes by more than a predetermined amount from the reference value, it is assumed that the toner concentration has decreased, and the motor 16 rotates the conveying screw 7a to replenish toner from the hopper 7.

In the above embodiment, a change in the magnetic permeability of the developer is detected as a change in the inductance of the coil, and detected as a change in the phase of the current flowing through the coil. However, other known methods may be used. Good too. For example, a change in magnetic permeability of the developer may be detected based on a change in resonance frequency, a change in current value, or a change in Q. Further, the sensor is not limited to a coil, and a Hall element or the like can also be used.

(Effects of the Invention) In a conventional electrophotographic recording apparatus that uses a two-component developer and performs development using a plurality of developing units.

In order to accurately control toner density, multiple sensors are required, and their adjustment and control become complicated.
Therefore, there was a problem that the cost was high, but according to the present invention, the toner concentration can be controlled with high precision at low cost with a simple configuration.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the main parts of a color laser printer incorporating the toner density control device according to the present invention, Fig. 2 is a waveform diagram of the output voltage of the operational amplifier, and Fig. 3 is a diagram showing the relationship between the output voltage of the operational amplifier and the toner density. FIG. 4 is a flowchart illustrating the initial setting operation of a reference value that is a reference for toner replenishment. l...Photosensitive drum, 2...Developer, 7...Hopper, 8...Toner density sensor,

Claims (1)

[Claims] In a toner concentration control device for an electrophotographic recording device that performs development using a two-component developer using multiple developing devices, the toner concentration of each developer loaded in each developing device is controlled according to changes in its magnetic permeability. an operating means for initially setting a reference value that is a reference for toner replenishment, and when this operating means is operated, a detection value of the detection means is used as the reference value for each developer. a storage means for storing, and a detection value of the detection means and the reference value stored in the storage means are compared for each developer during an actual developing operation, and toner is replenished for each developer according to the difference. The detection means includes a sensor unit provided for each developing device, a selection unit that selects the output of the sensor unit, and a signal that processes the output of the sensor unit selected by the selection unit. 1. A toner concentration control device comprising: a processing section;