JPH04356080A - Toner concentration controlling method for image recorder - Google Patents

Abstract

PURPOSE:To provide a toner concentration controlling method by which toner concentration is accurately maintained even when the carrier of two-component type developer is changed with the lapse of time. CONSTITUTION:In an image recorder where an electrostatic latent image formed on a photosensitive drum 8 is developed with the two-component type developer 23 and then recorded on a copying paper 12, magnetic field is generated and applied to the developer 23, and the toner concentration is controlled by using a toner concentration sensor 28 for detecting the change of the magnetic permeability of the developer 23, then control voltage Vcont for controlling the intensity of the generated magnetic field to the sensor 28 is changed by specified voltage Vcont every time the recorded number of copying papers 12 is increased by specified number.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling toner density in an image recording apparatus such as an electrophotographic copying machine.

0002

[Prior Art] In image recording devices such as electrophotographic copying machines and facsimile machines, a document is irradiated with light and an electrostatic latent image is formed on a photoreceptor by the light reflected from the document, which is then converted into a visible image. 2. Description of the Related Art Recording is performed on recording paper, and electrical signals representing images from the outside are recorded on recording paper as visible images.

[0003] In this type of image recording device, toner
A visible image is formed using a two-component developer consisting of a carrier and a carrier, and is recorded on recording paper, but since the toner density affects the density of the copied image, the recorded image always has a constant density. In order to obtain this, the toner concentration is detected, and when the toner concentration decreases, toner is replenished to control the toner concentration so that it falls within an appropriate range.

Various methods for detecting toner density have been known. For example, in Japanese Patent Publication No. 64-5299, when the developer is replaced, the density control device is changed over and stopped by switching a switch, and the density control device is stopped. A method is described in which a reference value serving as a reference for control is set, the switch is switched again, and toner density control is performed based on the set reference value. Another method is to optically detect the density of a toner image formed by small pieces having a reference density. A different method is to create a magnetic field using a high-frequency voltage, apply this magnetic field to a part of the two-component developer, and detect the change in magnetic permeability per unit volume of the developer to detect the toner concentration. A method has been proposed.

[0005]

[Problems to be Solved by the Invention] Generally, when recording on recording paper using a two-component developer, as the number of sheets to be recorded increases, the amount of the two-component developer decreases and the charge retention ability of the toner deteriorates (e.g. Q/M=12μC/g). This reduces the electric charge of the toner and the repulsive force between the toner particles, thereby increasing the number of carriers per unit volume. Therefore, when toner concentration is detected using the above-mentioned toner concentration sensor that detects toner concentration by detecting changes in developer magnetic permeability, an increase in developer magnetic permeability due to an increase in carrier is treated as a decrease in toner concentration. Detect.

FIG. 1 shows the output voltage Vcon of the toner concentration sensor with respect to the actual toner concentration Tc of the developer, which is obtained by dividing the toner weight by the sum of the toner weight and the carrier weight.
7 is a graph showing the relationship between t and detected toner concentration Td. In the figure, the actual toner concentration Tc is the actual toner concentration, and the detected toner concentration Td is the apparent toner concentration obtained from the toner concentration sensor. As can be seen from the figure, the actual toner concentration Tc and the output voltage V of the toner concentration sensor
cont has a negative characteristic, for example, the control voltage that controls the magnetic field generated from the toner concentration sensor is 7.0.
When the number of sheets recorded is V and the toner charge amount Q/M (Q is the toner charge, M is the toner mass) is 15 μC/g, and the actual toner concentration TC is 6.0%, then The output voltage Vcont is 1.6V and the detected toner concentration Td is 6.
It becomes 0%.

FIG. 2 shows the output voltage Vou of the toner concentration sensor.
3 is a graph showing the relationship between t and the control voltage Vcont of the toner concentration sensor, and FIG. 3 is a graph showing the relationship between the control voltage Vcont, the actual toner concentration Tc, and the number of recording sheets n. In FIG. 2, each straight line represents the actual toner concentration T at the start.
The characteristics when c is 5.0%, 6.0%, and 7.0% are shown, respectively. For example, the toner concentration Tc is 6.0
%, when the control voltage Vcont is 7.0V, the output voltage Vo
ut becomes 1.6V (point P). The relationship between the output voltage Vout of the toner concentration sensor and the control voltage Vcont of the sensor is that at the start of recording, the toner concentration was on a curve of 6.0%, but as the number of sheets to be recorded increases, the toner concentration eventually changes. T
Since c shifts to the 5.0% curve, the control voltage Vco
If nt remains at 7.0V, the output voltage Vout increases (point Q). The toner concentration sensor is connected to a CPU, which will be described later, and the CPU is configured so that the relationship between the output voltage Vout and the toner concentration Tc has a negative characteristic as shown in FIG. As Vout increases, the detected toner concentration Td decreases, so toner must be replenished, and therefore the toner concentration Tc increases. In other words, as shown in FIG. 3, although the control voltage is constant and the toner concentration Tc does not decrease, the toner concentration Td obtained from the toner concentration sensor apparently decreases, so toner is replenished. As a result, the toner concentration Tc increases, resulting in a disadvantage that the toner concentration deviates from an appropriate range.

The present invention has been made in view of the above-mentioned drawbacks, and its object is to provide a toner density that can accurately maintain toner density even if the carrier of a two-component developer changes over time. The objective is to provide a control method.

[0009]

According to the present invention, the object is to generate a magnetic field, apply the magnetic field to a two-component developer consisting of toner and carrier, and detect changes in magnetic permeability of the developer. In a toner density control method for an image recording apparatus that uses a toner density sensor that detects the toner density of a developer and controls the toner density based on the output of the toner density sensor, The electrostatic latent image is developed by a two-component developer, and each time the number of recording sheets on which it is recorded increases by a predetermined number, the control voltage that controls the strength of the magnetic field generated by the toner concentration sensor is increased by a predetermined voltage. This is achieved by changing.

0010

[Operation] The toner concentration control method of the present invention detects toner concentration by applying a magnetic field generated by a toner concentration sensor to a two-component developer and detecting changes in magnetic permeability of the two-component developer. By changing the control voltage that controls the strength of the magnetic field generated by the toner concentration sensor by a predetermined voltage value for each number of sheets recorded, the relationship between the control voltage of the toner concentration sensor and the output voltage is always maintained at the state at the start of recording. Since the correction is made, the correct signal is output from the toner density sensor, and the visible image is recorded on the recording paper at an appropriate density.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings, and the following embodiments are examples in which the present invention is applied to toner control in an electrophotographic copying machine.

FIG. 4 shows a schematic configuration of an electrophotographic copying machine. A document M placed on a document table 1 is irradiated with an illumination lamp 2, and the reflected light 3 shown by a dashed line in the figure is reflected by a first mirror 4 and a second mirror 5, and is reflected by a first mirror 4 and a second mirror 5 through a lens 6. 3 mirror 7 and project it onto the photoreceptor drum 8.
An electrostatic latent image of the document M is formed thereon. Around the drum 8, there is a charging electrode 9 provided on the surface of the drum 8 for uniformly charging the photoreceptor, and a visible image (toner) by developing the electrostatic latent image formed on the photoreceptor. - Developing device 1 for producing (image)
0, a transfer electrode 13 for transferring the visible image onto the copy paper 12 fed from the paper feed cassette 11 through the path indicated by the two-dot chain line, and a drum for transferring the copy paper 12 to which the visible image has been transferred. 8
A separation electrode 14 for separating the toner from the toner, a static elimination electrode 15 for removing the charge remaining on the photoconductor, and a cleaning device 16 for removing the toner remaining on the photoconductor after static elimination. Arranged. After the transfer, the copy paper 12 is separated from the drum 8 through the path shown by the two-dot chain line and is conveyed to the fixing device 18 by the conveyor roller 17, where the toner on the copy paper 12 is thermally melted and the copy paper 12 is The image is fixed on the sheet, and then discharged onto the paper discharge tray 19.

FIG. 5 is a block diagram of the developing device and control circuit of the electrophotographic copying machine shown in FIG. 4.

Two rotatable ladder wheels 21a and 21b are provided obliquely in front of the toner cartridge 20 containing a two-component developer consisting of toner and carrier. Two rudder wheels 21a, 21
A ladder chain 22 is attached to b. A conveying plate 24 for scooping up developer 23 is attached to the ladder chain 22. A remaining toner amount sensor 25 for detecting the remaining amount of developer 23 is provided near the lower ladder wheel 21b. A replenishment roller 26 is rotatably mounted diagonally below the front side of the upper ladder wheel 21a, and an auxiliary stirring plate for stirring the developer 23 is provided below the replenishment roller 26. 27 is rotatably provided. Supply roller 26 and auxiliary stirring plate 27
A toner concentration sensor 28 for detecting the concentration of the developer 23 is arranged between the developer 23 and the toner concentration sensor 28 . A stirring plate 29 for further stirring the developer 23 stirred by the auxiliary stirring plate 27 is arranged adjacent to the auxiliary stirring plate 27, and a developing sleeve 30 is arranged adjacent to the drum 8 in front of the stirring plate 29. It is located.

The above-mentioned toner concentration sensor 28 includes a coil for generating a magnetic field to be applied to the developer 23a located between the supply roller 26 and the auxiliary stirring plate 27, and a coil for generating a magnetic field to apply to the developer 23a between the replenishment roller 26 and the auxiliary stirring plate 27, and a coil for generating a magnetic field for permeating the developer 23 using this magnetic field. It has a built-in coil for detecting changes in magnetic property. The output from the toner concentration sensor 28 is A
The signal is input to the toner concentration detection circuit 33 via the /D converter 31. The toner concentration detection circuit 33 is input to a motor drive circuit 34 that drives the motor MT, and is also input to a voltage control circuit 35. voltage control
The control circuit 35 controls the control voltage applied to the toner concentration sensor 28 via the D/A converter 36.

The output of a photointerrupter 37 (shown surrounded by a broken line) consisting of a light emitting diode 37a and a phototransistor 37b is input to the CPU 32 via an amplifier 38. The photo interrupter 37 is provided at the copy paper discharge section of the copying machine, and a signal is output when the recorded copy paper 12 passes through the photo interrupter 37.

The CPU 32 is connected to a non-volatile memory 40, and the memory 40a (non-volatile counter) stores the total number of copies recorded so far.
0b contains a data specifying the voltage value ΔVcont to be decreased from the control voltage Vcont when the voltage value is suitable for a specific number of copies and a voltage value of 1.6V as the control voltage to be initially set as shown in the table below. data is memorized. R.A.
A memory 40c consisting of M (random access memory) stores the data read from the memory 40b and the current control voltage V.
cont is stored in a rewritable manner. 41 is a power switch, and 42 is a copy button. In this table, the step value is from memory 40b to CPU
The sum of the voltage value Vcont corresponding to this value and the control voltage Vcont at that time is applied from the CPU 32 to the toner concentration sensor 28 as a control voltage.

Next, the operation of the electrophotographic copying machine having the above structure will be explained based on the flowcharts shown in FIGS. 6 and 7. 7 and 8 show the contents of the copy count subroutine in FIG. 6.

Now, when the power switch 41 is turned on, (F-
1), the CPU 32 reads the contents stored in the memory 40b (for example, toner concentration sensor output voltage value 1.6V, toner concentration sensor control voltage value 7V), and transfers the read data to the RAM 40c (F -2). When the copy button 42 is turned on, the copying machine starts recording operation, and the photo interrupter 3 is activated every time a copy is made.
7, the number of copies n is counted (F-4), and the process moves to the subroutine of FIG. 7, where the CPU 32 writes this counted value into the non-volatile counter 40a (P-1). Next, it is determined whether the number of copies so far n exceeds 5000 (P-2). As a result of the determination, if the number of copies to date n is less than 5000, as can be seen from the table, ΔVcon
Since t is 0, the CPU 32 directly applies the control voltage Vcont read from the memory 40c (for example, +7V control voltage Vcont) to the toner concentration sensor 28 (F-5, FIG. 6). CPU 32 is toner concentration sensor 2
For example, output voltage Vout of +1.5V from RAM
40c (F-6). When the recording operation is completed, the number of copies is counted as having increased by one, and the number of copies is stored in the non-volatile memory 4.
The content of the nonvolatile counter 40a, which is 0, is incremented by 1 and the process returns to step (F-2). Note that at this time, the control voltage Vcont and the output voltage Vout of the toner concentration sensor 28
The relationship with Tc6.0% is shown in the characteristic curve shown in Figure 2.
It corresponds to the curve of As the number of copies increases, the characteristic curve gradually shifts upward, so the control voltage Vcont must also be gradually reduced.

Then, in step (P-2) of FIG. 7 again, if it is determined that the number of copies to date exceeds 5,000, the process proceeds to the next step (P-3), and the number of copies to date is 10,000. Determine whether the limit has been exceeded. As a result of the determination, if the number of copies to date exceeds 10,000, as shown in the table, the next step is to remove the toner.
By reducing the control voltage Vcont of the concentration sensor 28 by 0.05V, the deviation of the characteristic curve is offset.

After decreasing the control voltage Vcont, the value is stored in the RAM 40c and the process returns to step (F-5) in FIG. As a result of the determination in step (P-3), if the number of copies up to that point is 10,000 or more, the process advances to step (P-7), and it is then determined whether the number of copies has exceeded 15,000. As a result, the number of copies was 15.
000 sheets or less, as shown in the table, ΔVcont
is -0.10V, so reduce the control voltage Vcont of the toner concentration sensor 28 by 0.10V (P-8).
, is stored in the RAM 40c (P-9), and the process returns to step (F-5) in FIG. 6 (F-4). On the other hand, as a result of the determination in step (P-7), the number of copies is 15.
If the number of copies exceeds 20,000, proceed to the next step and determine whether the number of copies exceeds 20,000 (P-1
0). As a result of the determination, if the number of sheets is 20,000 or less, the control voltage Vcont of the toner concentration sensor 28 is changed by 0.1.
Decrease 5V (P-11) and store it in RAM40c (
P-12), return to step (F-5) in Figure 6 (F
-4). On the other hand, as a result of the determination in step (P-10), if the number of copies exceeds 20,000, then
Proceeding to step (P-13) shown in , it is determined whether the number of copies exceeds 25,000. As a result of the determination, if the number of sheets is 25,000 or less, 0.20V is decreased from the control voltage Vcont of the toner density sensor 28 (P-14), stored in the RAM 40c (P-15), and the step in FIG. 6 (F-5) is performed. ). On the other hand, if the number of copies to date exceeds 25,000, the toner
The control voltage Vcont of the concentration sensor 28 is decreased by 0.25V (P-17), stored in the RAM 40c, and the process returns to the flowchart of FIG.

As described above, according to this embodiment, the number of copies is counted, and every time the number of copies exceeds 5000,
By decreasing the control voltage Vcont of the toner concentration sensor 28 in increments of 0.05 V according to instructions from the PU 32, the increase in toner concentration Tc due to deterioration of the developer carrier (1
%) in the direction of decreasing. As a result, the correct output voltage Vout from the toner concentration Tc sensor 28 is output to the CPU 3.
2, and the toner density is maintained accurately.

FIG. 9 shows the actual toner concentration Tc according to this embodiment.
, the number of recorded sheets n, and the control voltage V applied to the toner density sensor
It is a graph showing the relationship with cont. As shown in the figure, the control voltage Vcont decreases stepwise every time the number of recorded sheets n reaches 5000 sheets. As a result, the actual toner concentration Tc is maintained at approximately 6.0%.

Although a photointerrupter is used as a means for counting the number of copies in this embodiment, the present invention is not limited to this, and other known means such as a microswitch may be used.

[0025]

As explained above, in the present invention, a magnetic field generated by a toner density sensor is applied to a two-component developer, a change in magnetic permeability of the two-component developer is detected, and a predetermined number of recording sheets is detected. Since the control voltage applied to the toner concentration sensor is changed by a predetermined value each time, the influence of changes in the carrier over time on the output of the toner concentration sensor can be minimized and accurate toner concentration control can be achieved. Become.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the actual toner concentration of a developer, the output voltage of a toner concentration sensor, and the detected toner concentration.

FIG. 2 is a characteristic curve showing the relationship between the control voltage and output voltage of a toner concentration sensor.

FIG. 3 is a graph showing the relationship between the control voltage for controlling the magnetic field generated by the toner concentration sensor, the actual toner concentration, and the number of recording sheets.

FIG. 4 is a schematic diagram showing the configuration of an electronic copying machine to which the toner density control method of the present invention is applied.

5 is a block diagram of a developing device and a control circuit of the electronic copying machine shown in FIG. 4. FIG.

FIG. 6 is a flowchart for explaining a toner density control method according to the present invention.

FIG. 7 is a subroutine used in the flowchart shown in FIG. 6;

FIG. 8 is a part of the subroutine shown in FIG. 7.

FIG. 9 is a graph showing the relationship between the actual toner density, the number of recording sheets, and the control voltage of the toner density sensor according to the present embodiment.

[Explanation of symbols]

2 Light source 3 Reflected light 8 Photosensitive drum 9 Charged electrode 10 Developing device 13 Transfer electrode 14 Separation electrode 15 Static elimination electrode 17 Conveyance roller 18 Fixing device 28 Toner concentration sensor 32 CPU 40 Memory

Claims (1)

[Claims] 1. A toner that generates a magnetic field, applies the magnetic field to a two-component developer consisting of toner and carrier, and detects a change in the magnetic permeability of the developer to detect the toner concentration of the developer. In a toner density control method for an image recording apparatus that uses a density sensor and controls the toner density based on the output of the toner density sensor, an electrostatic latent image formed on a photoreceptor is processed by a two-component developer. A toner density control method comprising changing a control voltage for controlling the intensity of a magnetic field generated by a toner density sensor by a predetermined voltage every time the number of recording sheets to be developed and subsequently recorded increases by a predetermined number.