JPH026979A - Image forming device - Google Patents

Abstract

PURPOSE:To control toner concentration in a desired condition by altering a reference level for controlling toner concentration, depending on whether developing devices whose toner concentrations are not controlled but which affect values detected by toner concentration sensor, when toner concentration is controlled. CONSTITUTION:Developing units 8, 10 and 12 include parts 9, 11 and 13 identifying color of internal toner and the presence or absence of the developing units. The developing device identifying parts 9, 11 and 13 input the color of toner to a microcomputer 31 with the aid of a code of three bits and can identify the color of toner and the presence or absence of the developing units by a combination of high and low signals from the computer. The comparison reference level for controlling toner concentration in the developing units currently used is altered, depending on whether the developing units currently not used, which affect the values detected by the toner concentration sensors 40, 41 and 42, are present or not. Thus, toner concentration in the developing units currently used can be controlled in a desired manner.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is applicable to image forming apparatuses such as copying machines and printers [Prior Art] In image forming apparatuses such as electrophotographic copying machines and printers, toner and A two-component developing device using a carrier is used. When such a developing device is employed, the ratio of toner and carrier must always be kept constant in order to obtain stable image density. This ratio of toner to carrier (the weight ratio of toner to the total weight of toner and carrier) is called the T/C ratio. This T
A typical method of keeping the /C ratio constant is to adjust the iJ of the developer.
There is a method using a toner concentration sensor that converts the fff rate into voltage and detects the voltage as the T/C ratio.

In this sensor, for example, as shown in FIG. 151 It is usually attached to the bottom of the developing tank 80 of the developing device. In the illustrated example, it is fitted into a hole 801 provided at the bottom of the developer tank 80.

An oscillation circuit C1 is connected to the oscillation coil Ll, and
The concentration detection coil L2 and the comparison coil L3 are connected in series so that their phases are opposite to each other, and their output voltage is guided to a phase detection circuit C2, where a voltage is determined based on the phase difference between the output voltages of the coils L2 and L3. is created and output.

To explain further, this sensor detects the change in the concentration of the developer TC as a change in the inductance of the concentration detection coil L2, and utilizes the phase difference or level difference between the output voltages of both the coil L2 and the comparison coil L3. It is.

That is, when the developer concentration in the developer tank 8 increases, in other words, when the ratio of toner in the developer increases and the ratio of carrier decreases, the toner concentration sensor detects the coil L.
2's inductance becomes smaller. If it is reversed, coil L
The inductance of 2 becomes large.

In this way, changes in developer concentration are detected by the concentration detection coil L2.
By detecting the change in inductance of
The phase difference with the comparison coil L3 is extracted as a voltage change by the phase detection circuit C2. The output value here is, for example, the value shown in FIG. 17.

The sensor output value or detection value obtained in this way is compared with a predetermined reference level value, and based on the comparison result, the amount of toner replenishment in the developing device is controlled, and the T/C ratio remains constant. .

[Problem to be solved by the invention]

However, in recent years, as image forming apparatuses such as copying machines and printers have become smaller and more color-oriented, small and compact image forming apparatuses that are or can be equipped with a plurality of developing units have been put into practical use.

In such an image forming apparatus, the space per developing device is small, the interval between developing devices is narrow, and the N1 type toner concentration sensor installed in one developing device is adjacent to another developing device. may be placed very close together. In such devices, some of the multiple developing units may be used without being installed, so
For example, when the above-mentioned sensor is provided at the bottom of the developing device, the inductance of the comparison coil L3 of the sensor changes depending on the presence or absence of the developing device that is placed close to it, and accordingly, the sensor output There is a problem that d changes (see Figure 18. In Figure 18, d
is the distance between the sensor and the upper aluminum lid of another developing device that approaches below). Especially the part of the lower developer that approaches (
For example, when the material of the lid is made of metal such as aluminum or iron, the influence on the comparison coil L3 becomes large, so the detected value of the toner concentration sensor becomes thick (varies) depending on the presence or absence of the lower developing device. Even if the upper material of the lower developing device is not metal, if there is a sufficient amount of developer in the developing device and there is almost no dead space in the developing device (especially when the developing device is downsized), The same inconvenience occurs.

When using a toner density centimeter that measures magnetic permeability in this way, the output value of the toner density sensor depends on whether or not another developing device is placed within the range that affects the output value or detected value of the sensor. There is a problem in that the detected value fluctuates and the toner density cannot be accurately controlled.

Therefore, in the present invention, a two-component developing type developing device using toner and carrier is adopted, and the toner concentration in the developing device is set to a predetermined reference level based on the detection value of a toner concentration sensor provided in the developing device. In an image forming apparatus that is controlled by comparing the toner replenishment amount with a value, even when a plurality of developing devices are provided, the toner concentration in the developing device used is determined by a toner concentration sensor installed in the developing device. Is there any other toner density side that affects the detected value? ″l
It is an object of the present invention to provide an image forming apparatus that can control the density to a desired state regardless of whether there is a non-target developer.

[Means for Solving the Problems] According to the above object, the present invention employs a two-component developing device using toner and carrier, and the toner concentration in the developing device is lower than that of the toner installed in the developing device. In an image forming apparatus that is controlled by comparing a detected density centimeter value with a predetermined reference level value and controlling the amount of toner replenishment, it is possible to include a plurality of developing devices of the two-component developing method. In addition, in controlling the toner concentration, the reference level value for toner concentration control is determined depending on the presence or absence of a developing device not subject to toner concentration control that affects a detected value of a toner concentration sensor of a developing device subject to toner concentration control. An image forming apparatus characterized by comprising a means for changing the image.

(Function) According to the image forming apparatus of the present invention, the specific aperture reference level value for controlling the toner concentration in the developing device used is determined by the specific aperture reference level value for controlling the toner concentration in the developing device used. It changes depending on the presence or absence of.

〔Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic cross section of a copying machine to which the present invention is applied. According to this copying machine, a photoconductor L is provided approximately at the center inside the copying machine, and chargers 6 and L are provided around the photoconductor L.
An ED array 7, an upper developing device 8, a middle developing device IO1, a lower developing device 12, a transfer charger 2, a separation charger 3, a cleaning device 4, and a main eraser lamp 5 are arranged in this order.

The original on the original table glass is scanned while being irradiated with light by the scanner 26 of the optical system 25, and the photoreceptor 1 is exposed to light in accordance with the original image on the downstream side of the charger 6. Paper is fed from an upper paper feed cassette 14 by a paper feed roller 16 via an intermediate roller 18, or from a lower paper feed cassette 15 by a paper feed roller 17.

The paper thus supplied advances along the guide 19 and advances to the transfer charger 2 via the timing roller 20. On the downstream side of the chargers 2 and 3, there is a transport section 21.
, fixing roller 22, paper ejection roller 23, and paper ejection tray 24
is provided.

A main motor 27 is provided inside the copying machine, and the motor operates the photoreceptor 1, paper feed rollers 16 and 17, intermediate roller 18, timing roller 20, conveyance section 21, fixing roller 22, paper ejection roller 23, and developing roller. The developing sleeve rollers 81, 101, 121 and the developer agitating general feed bodies such as bucket rollers in the container are each rotationally driven.

The paper feed roller, intermediate roller, timing roller, sleeve roller, etc. are configured to be driven via an electromagnetic clutch so as to be rotated as necessary.

Each developer 8.10.12 is provided with a portion 9.11.13 for identifying the color of the internal toner and the presence or absence of the developer. The developer identification section inputs the toner color as a 3-bit code to a microcomputer 51 (described later), and uses the combination of the signals 1 "high" and 1 "1-1" to identify the toner color and the presence or absence of the developer. It is something that can be identified.

Further, each of the developing units 8.1O112 is provided with a toner concentration sensor (ATL) C sensor) 40,41,42. Each ATDC sensor is of the type shown in FIGS. 15 and 16 for measuring magnetic permeability, and is fitted into a hole provided at the bottom of the developer tank case.

Further, the copying machine is provided with an operation panel P shown in FIG. 2 on its surface, and is also provided with an operation panel 28 shown in FIG. 3 at an easily accessible position inside. The operation panel P has a print switch Kl for starting the copy operation, as well as 2 for the numeric key group, 3 for the clear key, 4 for the interrupt key, 5 for the paper selection key group, and for displaying the selected paper size. It is equipped with an LED group D3, a developer selection key group 6, and an LEv group D4 for displaying the selected developer, and also includes an exposure amount display section DI, a sheet number display section []2, etc. There is.

The operation panel 28 in the copying machine shown in FIG.
A key 29 for entering the adjustment mode and a light emitting diode (LED) 30 for monitoring the output adjustment are provided.

This copying machine is controlled and operated by a control circuit schematically shown in FIG.

In the control circuit block diagram of FIG. 4, 51 is a microcomputer (hereinafter referred to as 1.1 microcomputer),
The input port is connected to the developer identification unit 9.11.13, the developer A'r v c sensor 40.41.42, and the print switch 1 on the operation panel P and the 1 on the operation panel 28. An ATDC sensor adjustment mode setting key 29 is connected. Further, to the output boat of the microcomputer 51, drive circuits for toner replenishment motors m1, m2, and m3 (not shown in FIG. 1) provided in each of the developing units 8.1O112 are connected, and the operation panel 28 The upper ATDC sensor adjustment monitor LED 30 is connected. In addition, the microcomputer 51 has an operation panel P.
Other input/output loads including the above human power means are also connected.

The toner replenishing motors m1, m2, and m3 of the developing device are motors for driving a toner replenishing mechanism (not shown) provided in the developing device to replenish toner from the toner hoppers H1, H2, and H3 to the developing tank.

To explain the general operation of such a copying machine, the photoreceptor l is rotated counterclockwise in the figure, and after being uniformly charged by the charger 6, it is exposed by the optical system 25 according to the added image. The electrostatic latent image formed by the exposure is applied with toner and developed by a developing device 8.10 or 12. The toner image is transferred onto the paper sent from the timing roller 20 by the charger 2 with its leading edge aligned with this.
Transcribed by. The paper is then separated from the photoreceptor l by the separation charger 3, passes through the conveyance section 21, reaches the fixing roller 22, where the toner is fixed, and is then ejected by the paper ejection roller 23. It will be done.

The developing unit of the copying machine in this example initially had a 'l''/C density of 8.
% developer, but the toner density decreases as the developer is used. This toner density is detected as a voltage value by the ATLJC sensor installed in each developing device.
It is input to the microcomputer 51.

The microcomputer 51 stores in advance a comparison reference level value for determining whether or not toner should be replenished from the toner hopper. Then, the level value TI for use when the lower developing device is close to each of the sensors 40 and 41, that is, when the developing device immediately below is installed, and Two types of level value T2 are available for use when a developer is not installed in the
Depending on whether there is a developing device immediately below, one of the level values TI and ]2 is used. A level value of 1゛2 is set for the sensor 42 of the developing device 12 at the lowest stage, and the level value T1 is set.
is set slightly higher than the level value T2. Figure 20 shows the relationship between the toner concentration in the developer and the sensor output. In the figure, curve A is the sensor output when the first developing device is installed, and curve B is the one immediately below the developing device. This is the sensor output when there is no device. In this embodiment, when the toner concentration drops to 6%, toner is replenished, so as shown in the figure, TI and T2 are each 3. OV, set to 2.3V. For example, when the developing device 8 is used and the developing device 10 is installed, if the toner concentration detected by the sensor 40 becomes higher than ]l, toner is replenished to return the toner concentration to the specified concentration. Toner is replenished by operating the motor ml.

When the developer IO is not installed, the detected value of the sensor 42 is compared with Leher 1'2, and the sensor detected value is T2.
(Then, the motor ml is operated so as to return the toner concentration to a predetermined concentration, and toner is replenished. In this way, the toner concentration (T/C ratio) in the developing device used is maintained at the desired state.

By the way, if the output of the toner density sensor is supposed to change like a curve in FIG. 19, for example,
In reality, due to variations in the developer, variations in developer manufacturing loft (the particle size of the carrier is the main cause of variation), and variations in output adjustment at the sensor manufacturing stage, it is difficult to actually use the sensor in an actual machine. If attached to
With respect to the target sensitivity curve A shown in FIG. 19, the sensor sensitivity curve varies as shown by a or a'.

Therefore, for each developing device at the beginning of operation of the image forming apparatus, and when using new developer, it is necessary to adjust the sensor output to bring the characteristics to the target curve A in FIG. 19.

Therefore, when you insert a starter into the developing device when using the copying machine for the first time, or when you start using a new developer after replacing the developer due to its lifespan, the ATDC sensor on the operation panel 28 inside the copying machine Adjustment mode setting key 29
Press to set the adjustment mode. In this example, when adjusting the sensor output, a developer whose T/C ratio (8%) is known in advance is used.

The adjustment mode is one of the function modes,
This mode is for operating the developing device during image formation. After a predetermined time has elapsed since the developer is activated by turning on the key 29, adjustment can be performed for a predetermined time by turning on the print switch Kl. The predetermined time after the key 29 is turned on is a time for stabilizing the flow of the developer, and may be set appropriately, but in this example, it is about 5 to 10 minutes. Further, the fixed time for the adjustment is usually set to about 3 minutes, and the adjustment is performed while checking the lighting state of the monitor LED 30 on the operation panel 28 during this period. If the adjustment is not completed during this time, press the print switch Kl again to continue the adjustment. To make this adjustment, insert the driver DR through the hole 32 provided at the bottom of the sensor, as shown in FIG.
Turn to change its position and set this to L E l) 30
Continue until it turns on. Note that the core 31 is screwed into a female screw hole 34 in the bobbin 33.

When the output value of the sensor falls between the predetermined upper limit level and the upper limit level, the monitor LEIJ 30 lights up and the adjustment is completed. Two types of upper limit level and lower limit level are prepared and stored in the microcomputer. That is, one is for use when the developing device below is in close proximity, and the other is for use when there is no other developing device within the range covered by the sensor output.

In this example, since the sensor output level is determined by the ripple due to fluctuations due to the flow of the developer, the LED 30 is turned on when all the ripples are within the range from the upper limit level to the lower limit level, as shown in FIG. 3A. let

In this example, one monitor Lbv is used, but the monitor LED
Two lights may be provided, one for the upper limit and the other for the lower limit, and the lights may be turned on depending on the set level.

Note that the sensor output adjustment mode is canceled by turning on the key 29 again.

Next, the operation of the microcomputer 51 will be explained with reference to FIGS. 5 to 14, focusing on the toner concentration control of the developer and the ATDC sensor adjustment control.

FIG. 5 shows a schematic flowchart of the main routine of the operation of the microcomputer 51. In this main routine, first, initial settings are performed in step SO, and a toner density state counter, various flanks, etc., which will be described later, are initialized here.

In the following description, each step is represented by the letter S followed by a number.

Next, an internal timer built into the microcomputer 51 and whose value is previously set as an initial setting is started at St.

After that, each subroutine is called in sequence from 32(1) to Sll, and when all subroutine processing is completed, S12
Wait for the end of the internal timer that was first set in
End the routine and return to St. The length of this l routine is used to count the various timers that appear in the subroutine.

S 2 (1) is a subroutine that reads data input to the microcomputer input port, S 2 (2) is a subroutine that outputs data for turning on and off each load from the microcomputer output port, and S 3 is a subroutine that reads data input to the microcomputer output port. This is a subroutine that controls the operation of 10.12. Also, S4 is the paper feeding operation, S5 is the operation of photoconductor l and its surrounding f+j'R,
S6 is a subroutine that mainly controls the operations of the optical systems.

S7 is a toner density control subroutine, S8 is a toner replenishment control subroutine, S9 is an ATD C (= sensor adjustment control subroutine), SIO is a subroutine for controlling the temperature of the fixing roller 22, and Sll is a subroutine for controlling the temperature of the exposure lamp in the scanner 26. This is a subroutine that performs control.

Next, toner density control will be explained with reference to FIGS. 6 to 12. This toner density control subroutine is executed for any developing device 8, 10, 12 when that developing device is selected. In this subroutine, first, in step S70, a toner density state counter is checked.

This counter is initialized in the RAM on the microcomputer 51 at step SO in the main routine. Jumps from ■ to ■ depending on the value of this counter.

First, the process advances to 5711, where it is determined whether copying is in progress. If 1 is pressed on the print switch on the operation panel P described above, it is determined that copying is in progress. If it is determined that copying is in progress, it is determined in step 3712 whether or not the developing device is being used, and if it is being used, it is checked in step 3713 whether or not the sleeve roller in the developing device is rotating. The reason for checking whether this sleeve roller is rotating is that it is installed in the developing device.
This is because the sleeve roller is configured in such a way that stable output is obtained and no holes occur unless the sleeve roller is rotating.

If the developing sleeve roller is rotating in S713, S'
The process advances to 714, where the toner density status counter is updated and the process returns to the main routine.
Proceed to step 15. Note that if the answer in each of steps 5711 to 5713 is 1-no J, the process immediately returns to the main routine, and in the next routine proceeds to 5711 again.

In S715, it is checked whether the scanner 26 including the exposure lamp has reached the leading edge of the document on the document table. The reason for making such a judgment here is to perform toner density control for each copy operation.If 5715 is 1 or no, the process returns to the main routine, but if 5715 is 1 or 2, the process returns to the main routine.
T L) Set the C senna detection start timer to seven seconds], 3
In step 717, the toner density state counter is updated and the process returns to the main routine, and in the next routine, the process proceeds to step 371B.

The reason why the ΔT' DC sensor detection start timer is set in step 5716 is to wait for the rise time until the sensor output becomes stable. In addition, this timer is microcomputer 51.
This is set in the internal RAM. Also, this A'
l'L) Is the human power from C sensor 1? It is read at any time in step 52(1) of the main routine in Chapter I. Also,
1 detection start in 5716, 1 means to compare and judge the input value from the ATDC sensor with the reference level value.

In 5718, the timer set in 5716 is counted, and if the timer has not ended, the process returns to the main routine, but if the timer has ended, detection is started in 3719.
The program then proceeds to step 5720, sets the AT'DC sensor detection time timer, updates the toner status counter in step 3720, returns to the main routine, and advances to step 5721 in the next routine.

The reason why the ATDC sensor detection time timer is set in step 5719 is to set the same number to compare and judge the sensor detection value with the reference level value. That is, since the length of the main routine is constant, the total number of detections is obtained by dividing the time set by this timer by the length of one routine. Note that if it is not yet the detection start time after 371 days, the process immediately returns to the main routine, and returns to 371B (4t) in the next routine.

At step 5721, it is determined which detection time timer has expired or not, and if it has not yet expired, the toner concentration is judged at steps 727 to 730. In other words, 371
3 until the detection time timer set in step 9 ends.
The density judgment is repeated from 727 to 730.

In step 5727, it is determined whether there is another developing device below the developing device to be controlled for toner concentration.If yes, it is determined in step 5728 whether or not the sensor detection value is greater than the reference level value T1, and if it is, the toner concentration is determined. is low, so the counter ('a degree'' low degree detection counter) for detecting low density is incremented at 3730 and the process returns to the main routine.If there is no other developer below, the sensor is detected at 5729. It is determined whether the detected value is greater than the reference level value] 2, and if it is, the toner concentration is low, so the counter is updated in 5730 to replenish toner and the process returns to the main routine. 57
If the ATDC sensor detection value is less than the level value at 28 or 5729, the process immediately returns to the main routine.

The counter 5730 is also stored in the RAM of the microcomputer 51. In this way, the reference level value to be compared with the ATL) C sensor detection value is set to be different depending on whether there is another developing device below, thereby eliminating detection errors.

When all the detections are completed, it is determined in 5722 whether the concentration "low" detection counter in 5730 has counted a predetermined number of times or more. In this case, a majority vote is taken based on the total number of detections. If the number of low degrees detected is greater than the predetermined number, the toner replenishment time timer when the toner density is low is set to 7 increments in step 5723.

When the number of detections is less than the predetermined number, a shorter toner replenishment time timer is set in step 5724.

Next, the toner density status counter is updated at 8725, and 87
At 26, the toner concentration "low °° detection counter is reset and the process returns to the main routine. In the next routine, 573 is set.
Go to 1.

At step 5731, it is determined whether or not the operation of the optical system 25 has been completed, and if it has been completed, the toner density state counter is updated at step 8732, and the process returns to the main routine, and the process advances to step 5733 in the next routine. If the optical system operation has not been completed at step 5731, the process immediately returns to the main routine, and returns to step 5731 in the next routine.

At 5733, it is checked whether the next optical system operation has been started, and if it has been started, at 5734 the toner density state counter is set to 1", and the process returns to the main routine.
Repeat the same action.

If the next optical system operation has not been started in 5733, it is determined in 5735 whether or not copying has ended, and when it has ended, the toner density state counter is set to "0" in 3736, and toner density control is ended. Further, if the copying is not completed yet, the process returns to the main routine.

Next, the toner replenishment control subroutine will be explained with reference to FIG. This subroutine is executed for the developing device in use.

First, in S80, it is determined whether the main motor 27 in the copying machine is rotating. This is because the sleeve roller of the developing device is driven by the main motor, and if the sleeve roller is stopped, the developer will not be generally fed.

In S81, it is determined whether the toner replenishment timer is set. The value of this timer is set in step 5723 or 724 in the toner density control subroutine.

If this timer is not set or if the 1-toner replenishment has already ended, the toner replenishment motor is stopped in S87. If the toner replenishment timer has been set, it is determined in S82 whether or not the timer has expired, and if the timer has expired, the toner replenishment motor is stopped in S83, but if it has not yet been set, the developing sleeve roller is turned off once again in S84. Determine whether it is rotating or not. If the sleeve roller is rotating in S84, the toner supply motor is turned on in S85, and if it is stopped, the toner supply motor is stopped in S87. As a result, while the toner replenishment timer is set, as long as the main motor 27 does not stop, and while the developing sleeve roller is rotating, developer is replenished from the hopper to the developer tank by the rotation of the toner replenishment motor. Toner concentration is maintained constant.

Next, the ATDC sensor adjustment control routine will be explained with reference to FIG.

This routine is a subroutine executed for the selectively used developing device.

In the sensor adjustment mode, each subroutine in the main routine shown in FIG. 5 performs its own operation that is different from the copy operation. For example, in S3, the developing sleeve roller of the selected developing device rotates, and in S5, the main motor 27 rotates.

Now, in step 390, it is determined whether the ATDC sensor adjustment mode is set, and if it is set, in step 391, it is determined whether or not the developing device equipped with the sensor to be adjusted is being operated, that is, the developing sleeve roller of the developing device is checked. It is determined whether or not the developing device is rotating, and if it is, it is determined in S92 whether there is another developing device below the developing device, and if there is, in S93 and S94, the developing device is Lower limit level L1 and upper limit level U predetermined for a certain case
It is determined whether or not there is an ATL)C sensor detection value between 1 and 1.

If it is determined in step 392 that there is no developing device below, then in steps S97 and 398, A is set between the predetermined lower limit level L2 and upper limit level U2 in case there is no developing device below.
Check whether the TDC sensor detection value is included.

ATD in S93 and S94 or in S97 and 39B
When the C sensor detection value is between the lower limit and upper limit level, the A1 DC sensor adjustment monitor LED 30 is turned on in S95 or S99, otherwise, the monitor LED 30 is turned off in S96 or 5100, and the main routine is executed. Return to. It should be noted that if the determination result in 390 and S91 is negative, the monitor LED is turned off and the process returns to the main routine.

〔Effect of the invention〕

According to the present invention, a two-component developing type developing device using toner and carrier is employed, and the toner concentration in the developing device is set to a predetermined reference level based on a detection value of a toner concentration sensor provided in the developing device. Even if the image forming apparatus is controlled by comparing the toner replenishment amount with the toner supply amount and is equipped with a plurality of developing devices, the toner concentration in the developing device used is compared with the toner concentration installed in the developing device. This has the effect of providing an image forming apparatus that can control toner density to a desired state regardless of whether or not there are other developing devices not subject to toner density control that affect the detected value of the senna.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of a copying machine which is an embodiment of the present invention;
Figure 2 shows a portion of the operation panel on the surface of the copying machine omitted.
Figures 1 and 3 are perspective views of the operation panel inside the copying machine, and Figure 3A.
The figure shows toner density sensor output and sensor output adjustment monitor LE.
FIG. 4 is a schematic block diagram of the copying machine control circuit, FIGS. 5 to 14 are flowcharts showing the operation of the microcomputer that controls the copying machine operation, and FIG. 6 to 12 are flowcharts of the toner concentration control subroutine, FIG. 13 is a flowchart of the toner replenishment control subroutine, and FIG. 14 is a flowchart of the ATI) C sensor adjustment control subroutine. Fig. 15 is a cross-sectional view of an example of a toner concentration sensor, Fig. 16 is a circuit 1 of the sensor, Fig. 17 is a graph showing an example of an output value of the toner density sensor, and Fig. 18 is a toner density control target. FIG. 19 is a graph showing the state in which the detected value of the toner density sensor on the developing device is affected by other developing devices. FIG. 20 is a graph showing the relationship between the toner concentration in the developer and the sensor output when there is and is not another developing device near the toner concentration sensor that affects its output. 8, l0112=-Developer, 40.41.42... Toner concentration sensor, TC=) Toner and carrier, TI, '2... Reference level value for toner density control, Ll, L2...・Upper limit level value for sensor adjustment, Ul
, U2... Upper limit level value for sensor adjustment, 30... Monitor LED for sensor adjustment. 29...Sensor adjustment mode setting key Kl...Print switch. Applicant: Minolta Camera Co., Ltd.

Claims (1)

[Claims] (1) A two-component development type developing device using toner and carrier is adopted, and the toner concentration in the developing device is determined by the detection value of the toner concentration sensor installed in the developing device being a predetermined reference level value. The image forming apparatus, which is controlled by comparing the toner replenishment amount and controlling the toner supply amount, is configured to be able to include a plurality of developing devices of the two-component developing method, and in controlling the toner concentration, the toner concentration is Image formation characterized by comprising means for changing the reference level value for toner density control depending on the presence or absence of a developing device that is not subject to toner density control and which affects the detected value of a toner density sensor of a developing device that is subject to control 1. Device.