JPH04308876A - Toner concentration control method for image recorder - Google Patents

Abstract

PURPOSE:To accurately maintain the toner concentration of the image recorder even when carrier of two component developer is changed with a lapse of time or when there is variation in sensitivity of the toner concentration sensor. CONSTITUTION:A compensation value m of sensitivity so that the variation quantity of the output voltage Vo of a toner concentration sensor against the variation quantity of control voltage Vc of a toner concentration sensor 28 is made equivalent to a value set beforehand and a compensation value Vc against variation due to the lapse of time are calculated and read in. Everytime a sumed up recorded pieces of paper n is increased by a specified number of pieces, control voltage Vc is varied based on the compensation value m and Vc.

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 determine the toner concentration. A detection method has been proposed.

[0005]

[Problems to be Solved by the Invention] Generally, when recording on recording paper using a two-component developer, the amount of toner decreases as the number of recording sheets increases, and the amount of charge Q/M per unit mass of toner decreases, for example. It decreases from 15 μC/g to 12 μC/g (here, Q is the charge amount of the toner, and M is the mass of the toner). This also reduces the repulsive force between the toners, increasing the number of carriers per unit volume of developer. 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. It will be detected.

FIG. 4 shows the toner concentration sensor control voltage (voltage that controls the strength of the magnetic field generated from the toner concentration sensor) Vc when it is constant (6.75V, 7.0V, 7.25V). The relationship between the output voltage Vo of the toner concentration sensor and the detected toner concentration Td with respect to the actual toner concentration Tc is shown. 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. In the figure, the diagonal dotted line indicates the control voltage Vc is 6.75V, and the diagonal solid line (MEAN) indicates the control voltage Vc is 7.0V (Q/M = 15μC at start)
The diagonal broken line indicates the relationship between the actual toner concentration Tc, the output voltage Vo of the toner concentration sensor, and the detected toner concentration Td when the control voltage Vc is 7.25V. As shown in the figure, when the control voltage Vc increases from 7.0V to 7.25V, the solid line (MEAN) shifts parallel to the position of the broken line, so when the actual toner concentration Tc is, for example, 6.0%, the detected toner concentration Td is 5. .0%. On the contrary, when the control voltage Vc decreases from 7.0V to 6.75V, the solid line (M
EAN) shifts parallel to the position of the dotted line, so when the actual toner concentration Tc is, for example, 6.0%, the detected toner concentration T
Since d is 7.0%, the actual toner concentration Tc and the detected toner concentration Td no longer match.

Furthermore, the toner density sensor used in this type of image recording apparatus has variations in the amount of change in output voltage with respect to the amount of change in toner density, that is, the sensitivity, and the toner density sensor differs from the actual change in toner density. - Changes in concentration may be detected.

FIG. 5 shows the control voltage V when the actual toner concentration Tc of the developer is constant (5.0%, 6.0%, 7.0%).
3 is a graph showing the relationship between the detected toner concentration Td and the output voltage Vo of the toner concentration sensor with respect to c. In the figure, each straight line represents the characteristics when the actual toner concentration Tc is 5.0%, 6.0%, and 7.0%, respectively. For example, when the actual toner concentration Tc is 6.0%, the control voltage Vc is 7.0%.
When the voltage is 0V, the output voltage Vo is 1.6V, and the detected toner
Since the density Td is 6.0%, the detected toner density Td matches the actual toner density Tc. The relationship between the output voltage Vo of the toner concentration sensor and the control voltage Vc of the toner concentration sensor is that at the start (Q/M=15 μC/g), the toner concentration T
There is a linear relationship in which the straight line c follows the 6.0% straight line, but as the number of recorded sheets n increases, the final (Q/M = 12 μC/
In g), the straight line of the toner concentration Tc shifts to the 5.0% straight line, so if the control voltage Vc remains at 7.0V, the output voltage Vo increases to 2.1V, and as a result, the detected toner concentration Tc shifts to the 5.0% straight line. The density Td becomes 5.0%, and the detected toner density Td and the actual toner density Tc no longer match.

The toner concentration sensor is connected to a CPU, which will be described later, and the relationship between the output voltage Vo and the actual toner concentration Tc shows a negative characteristic as shown in FIG. 4, so the output voltage Vo is high. Then, the detected toner concentration Td becomes low, and since toner is replenished, the actual toner concentration Tc increases. In other words, although the control voltage Vc is actually constant and the actual toner concentration Tc does not decrease as shown in FIG. 5, the detected toner concentration Td obtained from the toner concentration sensor apparently decreases and toner is replenished. As a result, the actual toner concentration Tc increases, resulting in the disadvantage that the toner concentration deviates from an appropriate range.

Furthermore, as shown in FIG. 4, the actual toner concentration T
When the relationship between c and output voltage Vo is shown by a solid line (MEAN in the figure), the actual toner concentration Tc and the detected toner concentration Td
matches. However, when the relationship between the actual toner concentration Tc and the output voltage Vo becomes as shown by the two-dot chain line, that is, when the sensitivity of the toner concentration sensor is low (MIN in the figure), the detected toner concentration Td is in a region lower than 6.0%. , the toner concentration sensor outputs a signal indicating that the detected toner concentration Td is lower than the actual toner concentration Tc, and the detected toner concentration Td is 6.
．． In a region higher than 0%, the toner concentration sensor outputs a signal indicating that the detected toner concentration Td is higher than the actual toner concentration Tc.

On the contrary, when the relationship between the actual toner concentration Tc and the output voltage Vo is as shown by the chain double-dashed line (MA
X), that is, when the sensitivity of the toner concentration sensor is high, the toner concentration sensor generates a signal indicating that the detected toner concentration Td is higher than the actual toner concentration Tc in a region where the detected toner concentration Td is lower than 6.0%. The detected toner density Td is 6.
．． In a region higher than 0%, the toner concentration sensor outputs a signal indicating that the detected toner concentration Td is lower than the actual toner concentration Tc, so the actual toner concentration Tc and the detected toner concentration
There is a drawback that the density Td does not match.

The present invention has been made in view of the above-mentioned drawbacks, and its purpose is to prevent the carrier of the two-component developer from changing over time and the sensitivity of the toner concentration sensor from varying. Another object of the present invention is to provide a toner density control method for an image recording apparatus that can accurately maintain toner density.

[0013]

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 a change in magnetic permeability of the developer. 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 method comprising: A correction value is calculated and stored so that the amount of change in the output voltage of the toner concentration sensor with respect to the amount of change in the control voltage for controlling the strength of the magnetic field is equal to a predetermined value, and the correction value is formed on the photoreceptor. This is achieved by changing the control voltage based on a stored correction value each time the number of sheets of recording paper on which an electrostatic latent image is developed with a two-component developer and subsequently recorded increases by a predetermined number. .

[0014]

[Operation] In the toner concentration control method of the present invention, the amount of change in the output voltage of the toner concentration sensor with respect to the amount of change in the control voltage for controlling the intensity of the magnetic field generated by the toner concentration sensor is set to a predetermined value. A correction value is calculated and stored so that the electrostatic latent image formed on the photoconductor is developed with a two-component developer, and each time the number of recording sheets on which the electrostatic latent image formed on the photoreceptor is recorded increases by a predetermined number, By changing the control voltage based on the stored correction value, the relationship between the control voltage of the toner density sensor and the output voltage is corrected to the state at the start of recording, so that the toner density sensor outputs a correct signal. A visible image is recorded on recording paper at an appropriate density.

[0015]

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. 6 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 this visible image onto the copy paper 12 fed from the paper feed cassette 11 through the path shown by the two-dot chain line, and the copy paper 12 to which the visible image has been transferred. A separation electrode 14 for separating the toner from the drum 8, a static elimination electrode 15 for removing the charge remaining on the photoconductor, and a cleaning device 16 for removing toner remaining on the photoconductor after static elimination. are arranged respectively. After transfer, the copy paper 12 is separated from the drum 8 through the path shown by the two-dot chain line.
is conveyed to a fixing device 18 by a conveyance roller 17, where the toner on the copy paper 12 is thermally melted and fixed to the copy paper 12, and then discharged onto a paper discharge tray 19.

FIG. 7 is a block diagram of the developing device and control circuit of the electrophotographic copying machine shown in FIG.

Two rotatable ladder wheels 21a and 21b are provided diagonally below and in front of the toner cartridge 20 containing a two-component developer consisting of toner and carrier. two rudder wheels 21a, 2
A ladder chain 22 is attached to 1b. A conveying plate 24 for scooping up developer 23 is attached to the ladder chain 22. lower rudder wheel
A remaining toner amount sensor 25 for detecting the remaining amount of developer 23 is provided near the wheel 21b. upper rudder
A replenishment roller 26 is rotatably mounted diagonally below the front side of the wheel 21a, and an auxiliary stirring plate 27 for stirring the developer 23 is rotatably mounted below the replenishment roller 26. It is set in. Supply roller 26 and auxiliary stirring plate 2
7, there is a toner for detecting the concentration of the developer 23.
A concentration sensor 28 is arranged. 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 31 is arranged adjacent to the drum 30 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 23 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 23 between the replenishment roller 26 and the auxiliary stirring plate 27, and a coil for generating a magnetic field for the developer 23 by 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 CP
The signal is input to a replenishment determination circuit 34 and an arithmetic circuit 35 via an amplifier circuit 33 in U32.

The replenishment determination circuit 34 is connected to the motor M1 and the motor
The motor M2 is connected to a drive circuit 36 for driving the motor M2, and drives the motors M1 and M2 in accordance with the output voltage Vo from the toner concentration sensor 28. That is, when the output voltage Vo becomes higher than the initially set voltage value, for example 1.6V, the detected toner concentration Td becomes low and the motor
A signal instructing to drive the motors M1 and M2 is sent to the drive circuit 36. As a result, these motors M1 and M2 are driven and toner is replenished. On the other hand, the output voltage Vo from the toner concentration sensor 28 is lower than the set voltage 1.6V.
When the detected toner concentration Td is obtained, the detected toner concentration Td becomes high and the motor
A signal instructing to stop the motors M1 and M2 is sent to the drive circuit 36. As a result, these motors M1 and M2 are stopped, and toner replenishment is stopped.

The arithmetic circuit 35 calculates the sensitivity S (SH, SL) of the toner concentration sensor 28 and the correction value ΔV of the control voltage Vc.
Correction value m (mH, mL
) (≧0) and adds the product of the correction value ΔVc and the correction value m to the control voltage Vc. This allows accurate toner density correction. Calculations for obtaining such a correction value m are performed as follows. That is, the detected toner density Td is the standard toner.
Toner concentration sensor 28 when the concentration is higher than (6.0%)
The sensitivity SH can be found using equation 1,

[0022]

[Equation 1] SH = (Vo2-Vo1)/(Vc=7.0-Vc=
6.5 )=(Vo2-Vo1)/0.5=2(Vo2-Vo1) Sensitivity SL when the detected toner concentration Td is lower than the standard toner concentration can be found by Equation 2.

[0023]

[Formula 2] SL = (Vo3-Vo2)/(Vc=7.5-Vc=
7.0)=2(Vo3-Vo2) Here, Vo1 is the output voltage of the toner concentration sensor 28 when the control voltage Vc is 6.5V, and Vo2 is the output voltage of the toner concentration sensor 28 when the control voltage Vc is 7.0V. The output voltage and Vo3 respectively indicate the output voltage when the control voltage Vc is 7.5V.

The correction value m is the standard value of the output voltage Vo of the toner concentration sensor 28 (Vo10 = 1.1V, Vo20 =
1.6V), which is a correction value for the detected toner concentration Td
The correction value mH when is higher than the standard toner density can be found using equation 3,

[0025]

[Math. 3] mH = 2(Vo2-Vo1)/2(Vo20-Vo1
0 )=2(Vo2-Vo1)/2×0.5=2(Vo2-Vo1) The correction value mL when the detected toner concentration Td is lower than the standard toner concentration can be obtained using Equation 4.

[0026]

[Equation 4] mL = 2 (Vo3-Vo2) The calculation circuit 35 controls the control voltage Vc applied to the toner concentration sensor 28 via the control voltage generation circuit 37, and sends each calculated value to the nonvolatile memory 38. and store it.

Table 1 below shows five sensors (sensor numbers 1 to 5).
) shows the variation in sensitivity for the toner concentration sensor.

[0028]

[Table 1] However, Vc=7 means that Vc is around 7V (6.75V to 7.
25V), and Tc=6.0% means Tc is 6.0%.
Represents the neighborhood (5.0% to 7.0%).

When the distribution of variations in the numerical values (x and y) of the toner concentration sensor 28 is examined, it becomes a normal distribution as shown in FIGS. 8 and 9. Figure 8 shows the distribution of x, x
The average value of is 0.5, and the 3σ (sigma) is 0.1. Figure 9 shows the distribution of y, where the average value of y is 2.0 and 3σ is 0.
It is 4.

When the correlation between the x and y values shown in Table 1 is taken, the correlation coefficient γ is approximately equal to 1, so it can be determined that there is a linear correlation. Therefore, the relationship between the sensitivity (y) of the toner concentration sensor to the toner concentration and the sensitivity (x) of the toner concentration sensor to the control voltage Vo can be expressed by Equation 5 as shown in FIG. FIG. 10 is a graph showing the relationship between x at which the distribution in FIG. 8 is the maximum and y at which the distribution in FIG. 9 is at the maximum.

[0031]

[Formula 5] y=0.25x In Figure 11, x in the equation expressed by Equation 5 is changed from 1.6 to 2.4.
This data is stored in the nonvolatile memory 38.

The nonvolatile memory 38 is composed of, for example, a RAM (random access memory), and stores standard toner.
Data representing the relationship between the density, the control voltage Vc of the toner density sensor 28 and the output voltage Vo, data of the step value and correction value ΔVc for the number of recorded sheets n as shown in Table 2, each calculated value and the current It stores the number of sheets to be recorded and sends the calculated value to the control voltage calculation circuit 39.

[0033]

[Table 2] In Table 2, the step value is CP from non-volatile memory 38.
This is instruction data transferred to U32, and is stored in non-volatile memory 3.
A correction value ΔVc of the control voltage corresponding to this step value is sent from 8 to the CPU 32. In addition, in Table 2, when the number of recorded sheets is 30,000 or more, the step value is saturated at "-7" because the developer has a durability of 30,000 times, so correction is not performed when the total number of recorded sheets n is 30,000 or more. This is because there is no The data representing the relationship between the control voltage Vc and the output voltage Vo of the toner concentration sensor 28 can be obtained by increasing the control voltage Vc by a predetermined voltage in advance (for example, when loading developer into a copying machine). It is obtained by measuring the output voltage Vc. The values of these voltages Vc and Vo are stored in nonvolatile memory 38.

The control voltage calculation circuit 39 uses the nonvolatile memory 3
Sensitivity SH, SL and correction values mH, m stored in 8
A control voltage Vc is calculated from L, and the control voltage generation circuit 37
A signal is sent to generate the control voltage Vc.

On the other hand, a paper ejection sensor 40 is provided at the copy paper ejection section of the copying machine, and when the recorded copy paper 12 passes this paper ejection sensor 40, a signal indicating the passage counts the number of recorded sheets n. It is output to the counter 41. counter 4
1 sends a signal representing the number of recording sheets to the control voltage calculation circuit 39.

Next, the operation of the electrophotographic copying machine having the above structure will be explained based on the flowcharts shown in FIGS. 1 to 3. FIG. 1 shows a main routine for explaining the operation of an embodiment of toner concentration control of the present invention, FIG. 2 shows a sensitivity estimation routine, and FIG. 3 shows a specific example of sensitivity calculation and correction value calculation. The contents of the flowchart are shown. (1) Operations before copying First, before copying, load developer into the copying machine for the first time,
When the power switch is turned on at the time of starting, such as when replacing, the CPU 32 measures the relationship between the control voltage of the toner concentration sensor 28 and the output voltage in advance, and stores it in the nonvolatile memory 3.
The sensitivity of the toner concentration sensor 28 is estimated from the data stored in the memory 8 and measured, the amount of correction is calculated, and the obtained data is transferred to the nonvolatile memory 38.

In FIG. 2, the CPU 32 controls the control voltage Vc
Input the output voltage Vo1 obtained by setting the control voltage Vc to 6.5V (T-1), input the output voltage Vo2 obtained by setting the control voltage Vc to 7.0V (T-2), and input the output voltage Vo1 obtained by setting the control voltage Vc to 7.0V. The output voltage Vo3 obtained by setting the voltage to 7.5V is input (T-3). The sensitivity S to the control voltage Vc is calculated from the obtained data (T-4) and transferred to the nonvolatile memory 38 (T-6). A correction value for the standard value (for example, control voltage Vc=7.0V, output voltage Vo=1.6V) is calculated (T-5) and transferred to the nonvolatile memory 38 (T-6). Step (T-4) and (T-
The calculation of 5) is shown in the flowchart of FIG. Steps (U-1) to (U-5) correspond to step (T-4), and step (U-6) corresponds to step (T-5).

In FIG. 3, in step (U-1), the control voltage Vc is set so that the output voltage Vo becomes 1.6V. This is to set the median value when the actual toner concentration Tc is 6.0%, and the toner concentration sensor 28
In a standard product (an average product that takes the above standard value), the control voltage Vc is 7.0V. Next step (U-2
), when the control voltage Vc is 7.1V, the output voltage Vo is 1.
6V, and when the control voltage Vc is 7.1+0.25V, the output voltage Vo is 2.0V (U-3). This is to create a state in which the actual toner concentration Tc is 5% in a pseudo manner by increasing the control voltage Vc by 0.25V. Note that the output voltage Vc of the standard toner concentration sensor 28 is 2.1V.

In step (U-4), the sensitivity x of the control voltage Vc is calculated as shown in Equation 6.

[0040]

[Equation 6]x=(2.0-1.6)/0.25=1.6 In step (U-5), the actual toner when Find the sensitivity of the concentration Tc. Note that for the standard toner concentration sensor 28, x=2.0 and y=0.5 from Equation 7.

[0041]

[Equation 7] x = (2.1-1.6)/0.25 Next, toner
When the sensitivity correction value m is calculated when the sensitivity of the standard product of the concentration sensor 28 is set to 1, the correction value m is 0.4 divided by 0.5 and becomes 0.8 (U-6). The sensitivity and correction value thus determined are stored in the nonvolatile memory 38. As a result, for example, the slope of the characteristic line shown by the dashed line (MIN) or the dashed double dotted line (MAX) in FIG.
The slope can be corrected to the slope shown in N).

In FIG. 7, when the sensitivity and correction values are stored in the non-volatile memory 38, the CPU 32 uses the standard control voltages stored in the non-volatile memory 38 (for example, the output voltage Vo value of the toner density sensor is 1.6 V, the toner density sensor is The control voltage Vc value of the sensor (7.00 V) is read out (S-1). (2) Operation during copying When the copy button is turned on, the copying machine starts a recording operation, and the counter 41 counts the total number of recorded sheets n every time a copy is made thereafter (S-2). By counting the total number of recorded sheets n, the usage status of the copying machine body and developer can be known, and the timing of inspection and maintenance can be determined.

Next, it is determined whether the total number of recorded sheets n exceeds 5000 sheets (S-3). As a result of the determination, if the total number of recorded sheets n is less than 5000 sheets, the CPU 32 sends the step value "0" to the nonvolatile memory 38, and the nonvolatile memory 38 sends the correction value ΔVc "0" of the control voltage Vc to the CPU 32.
Send to. Since the correction value ΔVc is “0V”, CP
U32 is the control voltage Vc read from the nonvolatile memory 38
(for example, +7V) is directly applied to the toner concentration sensor 28 (S-4). That is, when the number of recorded sheets n is less than 5000 sheets, the control voltage Vc is not corrected and the CPU
32 is, for example, +1.5V from the toner concentration sensor 28.
The value of the output voltage Vo is written into the nonvolatile memory 38. When the recording operation is completed, it is counted that the number of recording sheets n has increased by one, and the contents of the counter 41 are incremented by one.

As a result of the determination in step (S-3), if the number of recorded sheets n is 5000 or more, the next step (S-3) is performed.
In step 5), it is determined whether the number of recorded sheets n exceeds 10,000 sheets. As a result of the determination, if the number of recorded sheets n is less than 10,000 sheets, the CPU 32 stores the step value "
-2'', and the nonvolatile memory 38 sends out the correction value ΔVc``-2''.
0.10V" to the CPU 32 (S-6). In the next step (S-14), the CPU 32 reads a sensitivity correction value m, which will be described later, from the nonvolatile memory 38, and calculates the sensitivity correction value m from the nonvolatile memory 38.

0
045]

[Formula 8] Substitute Vc=Vc+ΔVc×m to calculate the control voltage Vc, and calculate the control voltage Vc for the toner concentration sensor 2.
8 (S-15).

As a result of the determination in step (S-5), if the number of recorded sheets n is 10,000 or more, the next step (S-5) is performed.
-7), it is determined whether the number of recorded sheets n exceeds 15,000 sheets. As a result of the determination, the number of recorded sheets n is 1500.
When the number of sheets is less than 0, the CPU 32 sends a step value "-4" to the nonvolatile memory 38, and the nonvolatile memory 38
The correction value ΔVc “-0.20V” is sent to 32 (S-
8). In step (S-14), the CPU 32 reads the sensitivity correction value m from the nonvolatile memory 38, substitutes it into Equation 6 to calculate the control voltage Vc, and applies it to the toner concentration sensor 28 (S-15).

If the result of the determination in step (S-7) is that the number of recorded sheets n is 15,000 or more, the process proceeds to step (S-9), where it is determined whether or not the number of recorded sheets n exceeds 20,000. As a result of the determination, if the number of recorded sheets n is less than 20,000 sheets, the CPU 32 stores the step “
-5'', and the nonvolatile memory 38 sends a correction value ΔVc of ``-0.25V'' to the CPU 32 (S-10). The CPU 32 stores the non-volatile memory 38 in step (S-14).
The sensitivity correction value m is read from , and substituted into Equation 8 to calculate the control voltage Vc, which is applied to the toner concentration sensor 28 (S
-15).

[0048] Similarly, if the result of the determination in step (S-9) is that the number of recorded sheets n is 20,000 or more, the process advances to step (S-11) and it is determined whether or not the number of recorded sheets n exceeds 25,000 sheets. If the number of recorded sheets n is less than 25,000 sheets, the non-volatile memory 38 sends a correction value ΔVc to the CPU 32.
The CPU 32 sends "-0.30V" (S-12), reads the sensitivity correction value m from the nonvolatile memory 38 in step (S-14), calculates the control voltage Vc, and applies it to the toner concentration sensor 28. (S-15).

As a result of the determination in step (S-11), if the number of recorded sheets n is 25,000 or more, the nonvolatile memory 38
sends the correction value ΔVc "-0.35V" to the CPU 32 (S-13), and the CPU 32 reads the sensitivity correction value m from the nonvolatile memory 38 in step (S-14), calculates the control voltage Vc, and sets the toner. - applied to the concentration sensor 28 (S
-15).

Through these series of operations, the correct control voltage Vc is applied to the toner density sensor 28 based on the number of recording sheets n and the correction value m of the sensitivity S of the toner density sensor 28, so that the recording density is normalized. In other words, for example, in FIGS. 4 and 5, the characteristic straight line shown by the dotted line (actual toner concentration Tc 5.0%) or the broken line (actual toner concentration Tc 7.0%) is a solid line (actual toner concentration Tc 6.0%). It is corrected to

As described above, according to this embodiment, the control voltage V for controlling the intensity of the magnetic field generated by the toner concentration sensor is
Output voltage V of the toner concentration sensor 28 with respect to the amount of change in c
After calculating the correction value (mH, mL) of the sensitivity S so that the amount of change in o is equal to a predetermined value, and calculating the correction value ΔVc of the control voltage Vc corresponding to the change over time of the toner, the non-volatile The electrostatic latent image stored in the memory 38 and formed on the photoreceptor is developed with a two-component developer, and each time the number n of recording sheets recorded thereafter increases by 5000 sheets, the correction value ΔVc is corrected. By controlling the toner concentration sensor using the voltage obtained by adding the product of the value m to the control voltage Vc as the control voltage, the relationship between the control voltage Vc of the toner concentration sensor 28 and the output voltage Vo is corrected to the state at the start of recording. The detected toner density Td and the actual toner density Tc match, and the increase in the detected toner density Td due to deterioration of the developer carrier is corrected in the direction of decrease. As a result, the correct output voltage Vo is output from the toner concentration sensor 28 to the CPU 32,
The actual toner concentration Tc is accurately maintained. In this embodiment, the control voltage is corrected every time the total number of sheets recorded is 5000, but the invention is not limited to this.

[0052]

As explained above, in the present invention, a magnetic field is generated, applied to a two-component developer consisting of toner and carrier, and a change in the magnetic permeability of the developer is detected. 1. A toner density control method for an image recording apparatus that uses a toner density sensor that detects toner density and controls toner density based on the output of the toner density sensor, the method comprising:
A correction value is calculated and stored so that the amount of change in the output voltage of the toner concentration sensor with respect to the amount of change in the control voltage for controlling the strength of the magnetic field generated by the toner concentration sensor is equal to a predetermined value. , the control voltage is adjusted based on the stored correction value every time the number of recording sheets on which the electrostatic latent image formed on the photoconductor is developed with a two-component developer and recorded increases by a predetermined number. Therefore, it is possible to minimize the influence on the output of the toner concentration sensor due to changes in the developer carrier over time and variations in the characteristics of the toner concentration sensor, thereby making it possible to accurately control the toner concentration.

[Brief explanation of drawings]

FIG. 1 is a flowchart for explaining a toner density control method for an image recording apparatus according to the present invention.

FIG. 2 is a subroutine of the flowchart of FIG. 1;

FIG. 3 is a subroutine of the flowchart of FIG. 2;

FIG. 4 is a graph showing the relationship between the output voltage of the toner density sensor and the detected toner density with respect to the actual toner density of the developer when the control voltage of the toner density sensor is kept constant.

FIG. 5 is a graph showing the relationship between the control voltage of the toner concentration sensor, the detected toner concentration of the developer, and the output voltage of the toner concentration sensor when the actual toner concentration is constant.

FIG. 6 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.

7 is a block diagram of a developing device and a control circuit of the electronic copying machine shown in FIG. 6. FIG.

FIG. 8 is a distribution diagram showing changes in output voltage of a toner concentration sensor with respect to changes in toner concentration.

FIG. 9 is a distribution diagram showing changes in output voltage with respect to control voltage of a toner concentration sensor.

FIG. 10 is a graph showing the relationship between x at which the distribution in FIG. 8 is the maximum and y at which the distribution in FIG. 9 is at the maximum.

FIG. 11 is part of data representing the value of y when x in the graph of FIG. 10 increases by 0.01 from 1.6 to 2.4.

[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 35 Arithmetic circuit 37 Control voltage generation circuit 38 Non-volatile memory 39 Control voltage calculation circuit

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. A toner density control method for an image recording apparatus that uses a density sensor and controls toner density based on the output of the toner density sensor, the method comprising: a control voltage for controlling the intensity of a magnetic field generated by the toner density sensor; The amount of change in the toner
A correction value that makes the amount of change in the output voltage of the density sensor equal to a predetermined value is calculated and stored, and the electrostatic latent image formed on the photoreceptor is developed with a two-component developer and then recorded. 1. A toner density control method for an image recording apparatus, characterized in that the control voltage is changed based on the stored correction value every time the number of recording sheets increases by a predetermined number.