JP2001066837A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make both toner density and the image density possible to be maintained in a specific range. SOLUTION: This image forming device controls the image forming condition giving an influence to an image being formed by comparing the density measurement result of a reference patch by an optical sensor with a reference patch target value for toner replenishment controlling, controlling the toner replenishment to a developing device 23 (developing unit 23K or the like), and comparing the density measurement result of the reference patch by the optical sensor with the reference patch target value for controlling gradation. At the time, the device changes only the toner replenishment controlling reference patch target value, in accordance with the measurement result by a counter 74a counting the number of developer adopting print sheets.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus used for an electrophotographic copying machine, a printer, and the like.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, toner supply conditions are controlled by measuring the density of a reference patch with an optical sensor. In such an image forming apparatus, when the density of the reference patch measured by the optical sensor is low, toner supply is performed, and when the density of the reference patch is high, the toner supply is stopped to maintain the reference patch density at a constant level. You.

[0003]

However, in the above-described image forming apparatus, the toner density in the developing device is not directly controlled. In some cases, the toner concentration may fluctuate due to changes in the developer characteristics or the difference between the solids in the apparatus. In such a case, if the toner concentration is too high or too low, image defects such as background fog and carrier development may occur. There's a problem.

FIG. 22 is a diagram for explaining how an image defect occurs due to a change in toner density.

FIG. 22A shows the number of prints (1 KPV).
= 1000 sheets) and FIG.
FIG. 22B shows a reference patch density (target density) with respect to the number of prints, and FIG. 22C shows a toner density with respect to the number of prints.

As shown in FIG. 22A, as the number of prints increases, the chargeability of the toner decreases and the toner is easily developed. Therefore, as shown by a solid line in FIG. When a constant reference patch density is maintained, the toner density gradually decreases as shown by the solid line in FIG. When the value is below a certain reference value, image defects such as image blurring and carrier development occur. Japanese Patent Application Laid-Open No. 04-66986 proposes a technique for preventing a decrease in the toner density by changing the target value of the reference patch density to a higher value based on the usage time of the developer. However, in this publication, although a decrease in the toner density can be prevented by preventing a decrease in the toner density, the target value of the reference patch density is changed to a higher value. Therefore, the density of the image portion having the same density as that of the reference patch also increases. The dotted lines shown in FIGS. 22 (b) and 22 (c) explain this problem. By increasing the reference patch density as the number of copies advances as shown by the dotted lines in FIG. 22 (b),
Although the toner density is prevented from lowering as indicated by the dotted line in FIG. 22C, the reference patch density, that is, the image density increases accordingly.

[0007] A similar problem also occurs when the toner charging property changes due to the environment. In general, the toner charging property is reduced under high humidity, so that the toner density decreases when a constant reference patch density is maintained. On the other hand, the toner charging property increases under low humidity, so that the toner charging property is maintained when a constant reference patch density is maintained. The concentration will increase.

If the accuracy of the reference patch density measurement by the optical sensor fluctuates, the reference patch density itself changes and the toner density also changes.
Therefore, a technique has been proposed to prevent this problem by changing the target value of the reference patch density in the same manner as described above. For example, Japanese Patent Application Laid-Open No. 07-168436 discloses a method for preventing the reference patch density itself from being properly maintained due to a flaw in an image due to temperature or humidity and a decrease in the measurement accuracy of the optical sensor. A technique for changing the target value has been proposed. Further, when the charging potential of the photoconductor is changed, the relationship between the reference patch density and the output of the optical sensor changes. Therefore, a technique of changing the target value of the reference patch density according to the setting of the charging potential of the photoconductor has been proposed. In these techniques, the toner density can be suppressed within a certain range, but since the target value of the reference patch density is changed, there is a problem that the image density fluctuates as a result.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an image forming apparatus capable of maintaining both the toner density and the image density within a predetermined range.

[0010]

According to the present invention, there is provided an image forming apparatus comprising: a photosensitive member having a surface charged to a predetermined charging potential and exposed to an image signal to form an electrostatic latent image; And a two-component developer composed of a carrier and a toner. The electrostatic latent image formed on the surface of the photoreceptor is charged in a state where a predetermined developing bias voltage is applied to the photoreceptor. A developing device for developing with the toner in the developer to form a toner image on the photoconductor, and finally transferring and fixing the toner image formed on the photoconductor on a predetermined image recording material In the image forming apparatus that forms an image on the image recording material, an electrostatic latent image for a reference patch is formed on the photoconductor, and the electrostatic latent image is developed by the developing device. , With a specified concentration as the target A reference patch forming means for forming the reference patch thus formed, and a first patch for measuring the density of the reference patch formed on the photoreceptor or the reference patch after being transferred from the photoreceptor onto a predetermined transfer receiving body. Comparing the density measurement result of the reference patch by the first measurement means with a predetermined first target value, and controlling the toner supply to the developing device according to the comparison result The control unit compares the measurement result of the density of the reference patch by the first measurement unit with a predetermined second target value, and according to the comparison result, excludes the toner supply to the developing unit and forms the toner. Image forming condition control means for controlling at least one image forming condition affecting an image, second measuring means for measuring one of the factors affecting image density, and measurement results by the second measuring means In response to the First to change individually and independently the first target value and the second target value
And changing means.

Here, the image forming condition control means includes a charging potential of the photosensitive member, an exposure light amount, a developing bias voltage of the developing device, and an image signal before being converted into exposure light for exposing the photosensitive member. Controlling the at least one of the two to correct the gradation of the formed image,
It is preferable that the first changing means changes only the first target value among the first target value and the second target value.

It is preferable that the second measuring means measures the concentration of the toner with respect to the carrier in the developing device.

Further, it is a preferable embodiment that the second measuring means measures the use time of the developer in the developing device.

Further, the second measuring means may measure an environmental condition.

Further, the density of the formed image and the first
A third measuring means for measuring a factor affecting a relationship with the measurement result by the measuring means, and the first target value and the second target value according to the measurement result by the third measuring means. And second changing means for changing both of them together.

The reference patch forming means may form different reference patches for toner supply control and for image formation condition control other than toner supply.

[0017]

Embodiments of the present invention will be described below.

FIG. 1 is a schematic configuration diagram for explaining a first embodiment to a fifth embodiment of a color copying machine to which the image forming apparatus of the present invention is applied.

As shown in FIG. 1, the color copying machine 1 includes a photosensitive drum 20 on which a surface is charged to a predetermined charging potential and which is exposed according to an image signal to form an electrostatic latent image. A charging corotron 21 for pre-charging the surface of the photosensitive drum 20, a scanner unit 22 for reading image information of a document 222, and a raster scanning device for writing an electrostatic latent image on the photosensitive drum 20 charged by the charging corotron 21 2
28 (hereinafter abbreviated as ROS), the electrostatic latent image is developed with a carrier and a developer composed of toners of different colors to form black (K), cyan (C),
Four developing units 23K, 23C, 23M, 2 for forming toner images of four colors of magenta (M) and yellow (Y)
A developing unit 23 made of 3Y, a cleaner 25 for removing residual toner on the photosensitive drum 20, and an erase lamp 26 for removing residual charge on the photosensitive drum 20 are provided. The developing unit 23 includes the above-described four developing units 23K, in which toners of K, C, M, and Y are stored.
23C, 23M, and 23Y are rotatably provided, and the four developing units 23K, 23C, 23M,
A predetermined developing unit of the photosensitive drum 20
It is configured to be able to be set at a developing position facing the image forming apparatus.

The above-described scanner unit 22 includes a platen 22
An exposure lamp 223 for irradiating the original 222 set on the original 1 with a light beam, and the exposure lamp 223
A carriage 224 for moving over the area, a reflection mirror 225 for guiding a beam from the surface of the document 222 by the exposure lamp 223 along a predetermined path, and a CCD for converting the beam from the surface of the document 222 to a digital signal for each color component The sensor 226 includes an image forming lens 227 that forms a beam from the surface of the document 222 on the CCD sensor 226. The ROS 228 is connected to the CCD sensor 22.
6. A semiconductor laser 228a that irradiates a laser beam based on the image data of each color component captured in step 6, a polygon mirror 228b that divides and deflects the beam from the semiconductor laser 228a in the main scanning direction of the photosensitive drum 20, and a semiconductor laser 228a. Lens 228 that forms an image of the beam along the main scanning direction line of the photosensitive drum 20
c and a reflection mirror 228d for regulating the beam path.

The photosensitive drum 20 is located between the writing position of the electrostatic latent image on the photosensitive drum 20 and the developing position.
An electrometer 27 for measuring the charging potential of the photosensitive drum 20 is provided, and an optical sensor 28 for measuring the density of a reference patch formed on the photosensitive drum 20 between the developing position and the transfer position (the first sensor in the present invention). (Corresponding to one measuring means). The optical sensor 28 is a reflective optical sensor that irradiates the photosensitive drum 20 with an LED and measures the amount of reflected light with a photodiode. Further, each of the developing units 23 described above
K, 23C, 23M, and 23Y have respective developing units 23.
Each of the toner concentration sensors 10 for measuring the toner concentration of the developer in K, 23C, 23M, and 23Y is provided. Further, the color copying machine 1 is provided with a hygrometer 9 for measuring the relative humidity in the machine.

The color copying machine 1 is provided with a transfer drum 31 on which a recording sheet 30 is wrapped and held on a peripheral surface, and on which the color component toner images on the photosensitive drum 20 are sequentially and multiplex-transferred. ing. This transfer drum 31
The adsorbing corotron 41 that charges the recording sheet 30 and adsorbs it onto the transfer drum 31 when the recording sheet 30 is held
And a transfer corotron 42 for transferring the toner image on the photosensitive drum 20 to the recording sheet 30, and a charge removing corotron 43 for removing charge from the recording sheet 30 after the final color transfer step is completed.
A cleaning neutralizing corotron 44 for removing charges on the recording sheet 30 after the final color transfer step has been completed; a cleaning brush 45 for cleaning paper dust and the like adhering to the recording sheet 30 after the final color transfer step has completed; Recording sheet 3
When the recording sheet 30 is peeled from the transfer drum 31, the recording sheet 30 is pushed up from the inside,
A peeling finger 47 for peeling off 0 from the transfer drum 31;
A sheet transport system 48 that transports the recording sheet 30 supplied from a sheet feeding cassette (not shown) to the suction corotron 41 at a predetermined timing according to each mode is provided.

Further, the recording sheet 30 having undergone the transfer process is passed through the color copying machine 1,
A fixing device 50 includes a heating roller 51 having a built-in heater therein for fixing an unfixed toner image on the fixing roller 50, and a pressing roller 52 disposed in pressure contact with the heating roller 51. The recording sheet 30 from 31 is conveyed to the fixing device 50 via the guide plate 53. Further, a fuser exit roll 54 that conveys the recording sheet 30 that has passed through the fixing device 50, a fuser exit switch 55 for detecting the rear end of the recording sheet 30 that has passed through the fixing device 50, and a discharge in which the fixed recording sheet 30 is stored. The recording sheet 30 is transferred to the tray 56 and the discharge tray 56.
Is provided with an outlet roll 57 for sending out.

In the color copying machine 1 constructed as described above, first, when the user operates a copy start switch (not shown), scanning of the original 222 is started,
An electrostatic latent image corresponding to black K is written on the photosensitive drum 20. On the other hand, in the developing device 23, the black developing unit 23K is set at a position facing the photosensitive drum 20, and the electrostatic latent image is stored in the black developing unit 2K.
By 3K, development is performed with a slight delay from the writing timing. The black K toner image thus formed on the photosensitive drum 20 is transferred to the recording sheet 30 held on the transfer drum 31. When the developing process by the black developing unit 23K is completed, the developing unit is replaced before the transfer drum 31 completes one rotation cycle. That is, the developing device 23 is set at 90 °
By rotating the yellow developing unit 23Y, the yellow developing unit 23Y is set at a position facing the photosensitive drum 20.

Thereafter, these operations are repeated for each rotation cycle of the transfer drum 31, and each time, the yellow Y, magenta M and cyan C toner images are transferred to the photosensitive drum 20.
Is transferred to the recording sheet 30 held on the transfer drum 31, and a superimposed toner image of four color toner images is formed on the recording sheet 30. And the final color cyan C
After the transfer of the toner image is completed, the recording sheet 30 is separated from the transfer drum 31 and discharged to the discharge tray 56 via the fixing device 50.

FIG. 2 is a block diagram of a control system in the color copying machine shown in FIG.

FIG. 2 shows a scanner unit 22 and an image processing unit 1 constituting the control system 11 of the color copying machine 1 shown in FIG.
2, a block diagram of the optical unit 13 and the image forming unit 14 is shown.

In the scanner section 22, the CCD sensor 226
Is amplified to an appropriate level by an amplifier 60, is converted into an 8-bit digital signal by an A / D converter 61, and after shading correction and gaff correction, reflectance data is converted by a density converter 62. Is converted into density data and sent to the image processing unit 12.

The image data sent to the image processing unit 12 is
First, the color conversion unit 63 performs basic image processing as the color copying machine 1, that is, color signal conversion, black reproduction (UCR), MT
The image data is converted into image data of black K, yellow Y, cyan C, and magenta M by performing F processing and the like. Next, the image data of each color is sent to the first gamma correction 64,
The color gradation is corrected according to the gradation characteristic unique to the ROS 228 and the image forming unit 14 of each copying machine.

Next, the image data is sent to the second gamma correction 65. Here, in order to prevent the image density from fluctuating due to a change in environmental factors, the input / output of the image data is corrected. A plurality of input / output correction tables are stored in the correction table section 66.
Is controlled by the first selector 67 to select an optimum table from the correction table section 66 and apply the selected table to the second gamma correction 65.

FIG. 3 is a graph showing three input / output correction tables stored in the correction table section shown in FIG. 2, and FIG. 4 is a graph showing the relationship between the input image density and the output image density in the color copying machine shown in FIG. It is a graph which shows tonality.

FIG. 3 shows a standard density table 1, a high density table 2, and a low density table 3, and FIG. A graph 2 showing the gradation at high density and a graph 3 showing the gradation at low density are shown. For example, when the gradation of the output image density indicates the gradation of low density (graph 3 shown in FIG. 4), the input / output ratio of the image data is corrected based on the low density table 3 shown in FIG. Then, the gradation of the output image substantially matches the gradation at the standard time.

The image data which has been subjected to the second gamma correction 65 in this manner is converted into analog data by a D / A converter 68, and then sent to a comparator 69 via a second selector 73, where the data is converted. Is compared with a signal of a predetermined cycle transmitted from the triangular wave generator 70, and is converted into binary image data by pulse width modulation.

FIG. 5 is an explanatory diagram of the binarization processing of the image data by the comparator shown in FIG.

As shown in FIG. 5, the input analog image data A is compared with the triangular wave T generated by the triangular wave generator 70 (see FIG. 2). , The image data is binarized with the small portion as “1”. The binary image data B thus obtained is sent to the laser driver 71 of the optical unit 13 (see FIG. 2), and when the image data is "0", the semiconductor laser 228a of the ROS 228 is turned off and the image data is changed to "1". "
Is turned on at this time, an electrostatic latent image is formed on the photosensitive drum 20.

The image processing section 12 is provided with a patch signal generating means 72 for generating an image signal when a reference patch is formed on the photosensitive drum 20. The reference signal having an image area ratio of 50% is provided. Generate data. The analog image data and the reference patch data are input to the second selector 73 controlled by the controller 74,
Only one of the data is compared with the triangular wave by the comparator 69 and binarized.

On the other hand, an electrometer 27,
A controller 74 for controlling the density of the toner image formed on the photosensitive drum 20 based on the optical sensor 28 and the detection signal of the hygrometer 9, and the controller 7.
4 charger controller 75 for changing the grid voltage V _G of the charger 21 in response to a control signal, likewise the developing unit of the developing unit 23 in response to the control signal of the controller 74 23C,
Developing bias voltage V applied to 23M, 23Y, 23K
A developing bias control unit 76 for changing _B is provided. Each of the developing units 23C and 23 of the developing device 23
A toner supply device 77 is connected to M, 23Y, and 23K, and supplies toner to each of the developing units 23C, 23M, 23Y, and 23K in accordance with a control signal from the controller 74. Further, the controller 74 also sends out a control signal to the laser light amount control unit 78 of the optical unit 13, and outputs the R signal via the laser driver 71.
The light emission amount of the semiconductor laser 228a of the OS 228 is adjusted. The controller 74 has a counter 74 for measuring the usage time of the developer in the developing device 23.
a (an example of a second measuring means according to the present invention) is provided.

Here, the conventional image density control will be described with reference to the components of the color copying machine 1, and then the image density control in the first embodiment will be described using this image density control. explain.

In the conventional image density control, the photosensitive drum 20
The density of the reference patch formed above is measured by the optical sensor 28, the toner supply amount to the developing device 23 is corrected based on the measurement result, and an input / output correction table to be applied to the second gamma correction 65 is selected. This is performed as described below.

FIG. 6 is a flowchart of a conventional routine for forming a reference patch on a photosensitive drum.

When the power of the color copying machine 1 is turned on and a start button (not shown) is pressed, this routine is executed. First, in step S11, it is determined whether a copy job has started. If it is determined that the copy job has not started, step S11 is repeatedly executed until the copy job starts. On the other hand, if it is determined that the copy job has started, the process proceeds to step S12. In step S12, the count value CNT of the counter for counting the number of copies is "0" (immediately after turning on the power of the color copier 1 and when reset) or "10" (after copying 10 sheets), or Is determined. If it is determined that the count value CNT is “0” or “10”, the process proceeds to step S14, where the controller 74 requests the patch signal generation means 72 to generate reference patch data, and then sends the second selector 73 Request the selection of the reference patch data. As a result, the reference patch data is binarized and supplied to the laser driver 71, and the photosensitive drum 2 is processed in the same manner as in the normal image forming process described above.
Reference patches of each color are sequentially formed on 0. Next, in step S15, the count value CNT is reset to "0", and the process proceeds to step S16. On the other hand, when it is determined in step S12 that the count value CNT is other than “0” or “10”, the process proceeds to step S13, where the count value CNT is counted up and the process proceeds to step S16.

In step S16, it is determined whether all jobs have been completed. If it is determined that all the jobs have not been completed, the process returns to step S12 to execute the above-described steps, while if it is determined that all the jobs have been completed, this routine ends. In this way,
Form a reference patch.

FIG. 7 is a flowchart of a conventional routine for controlling toner supply based on the density of a reference patch.

This routine is performed subsequent to the above-described routine for forming a reference patch in FIG. First, in step S21, the optical sensor 28 measures the density R_ADC of the formed reference patch. Next, in step S22, the controller 74 subtracts the target value S_ADC from the density R_ADC of the reference patch to obtain a difference ΔADC, and proceeds to step S23. Step S2
In 3, it is determined whether the difference ΔADC is larger than “0”. If it is determined that the difference ΔADC is larger than “0”, the process proceeds to step S25 because the density of the reference patch is higher than the target density. In step S25, the toner supply time DISP_TIME is set to "0", and the process proceeds to step S26. In step S26, the toner supply time D
Since ISP_TIME is “0”, the controller 74 instructs the toner supply for the “0” time, that is, the stop of the toner supply to the toner supply device 77, whereby the toner density in the developing device 23 is reduced. On the other hand, step S23
In the case where it is determined that the difference ΔADC is less than “0”, since the density of the reference patch is lower than the target density,
Proceed to step S24. In step S24, the difference ΔA
DC is multiplied by constant K, and toner supply time DISP_TIM
E is obtained, and the process proceeds to step S26. In step S26,
An instruction to supply toner to the toner supply device 77 for the toner supply time DISP_TIME is sent from the controller 74.
And the toner concentration in the developing device 23 is increased. In this way, the image density approaches the target density.

FIG. 8 is a flowchart of a conventional routine for selecting an input / output correction table to be applied to the second gamma correction and correcting the image density.

Since it takes time for the change in toner density in the developing unit 23 to be reflected on the image density, the input / output of image data is corrected using the second gamma correction 65 here. First, in step S31, the reference patch density R
Measure _ADC. Next, in step S32, the difference Δ between the reference patch density R_ADC and the target value S_ADC
ADC is calculated, and the process proceeds to step S33. Step S3
At 3, the controller 74 sends a control signal to the first selector 67 and outputs the control signal stored in the correction table 66.
From the two input / output correction tables (standard density table 1, high density table 2, low density table 3 shown in FIG. 3), the table which is most suitable for bringing the density of the reference patch closer to the target density is selected. I do. That is, the reference patch density R
_ADC is thinner than the target value S_ADC (ΔADC
> 30) proceeds to step S36, selects the low density table 3 shown in FIG. 3, and sets the reference patch density R_ADC.
Is higher than the target value S_ADC (ΔADC <−30)
Goes to step S34, selects the high density table 2 shown in FIG. 3, and furthermore, when the reference patch density R_ADC is close to the target value S_ADC (−30 ≦ ΔADC ≦ 3
0) proceeds to step S35, selects the standard density table 1 shown in FIG. 3, and changes the correction content in the second gamma correction 65. As a result, the image density is quickly corrected, and the defect of the density correction due to the change in the toner density can be compensated.

Next, the color copying machine 1 according to the first embodiment will be described. The color copying machine 1 of the first embodiment forms a predetermined density by toner by forming an electrostatic latent image for a reference patch on the photosensitive drum 20 and developing the electrostatic latent image by the developing device 23. A reference patch forming means for forming a reference patch formed as a target; a reference patch formed on the photosensitive drum 20;
A first measurement unit (optical sensor 28) for measuring the density of the reference patch after being transferred from 0 to a predetermined transfer target body; And a toner replenishment control means for controlling toner replenishment to the developing device 23 in accordance with the comparison result, and a density measurement result of the reference patch by the first measurement means is converted into a predetermined second target value. Image forming condition control means for controlling at least one image forming condition which affects the image to be formed, excluding toner supply to the developing device 23, in accordance with the comparison result, Second measuring means for measuring one of the influencing factors (counter 74a)
And first changing means for changing only the first target value of the first target value and the second target value in accordance with a result of measurement by the second measuring means. The counter 74a, which is the second measuring means, is a counter for counting the number of prints using the developer, which is provided in the controller 74 and measures the usage time of the developer in the developing device 23. The details will be described below.

In the first embodiment, the reference patch density target value is changed according to the usage time (number of used sheets) of the developer. Here, as described with reference to FIG. 22, by changing the target value of the reference patch density to a higher value during the usage time of the developer, the toner density can be prevented from lowering, but the density near the reference patch increases. . The same problem occurs when image forming conditions such as gradation control are controlled in addition to toner replenishment based on the reference patch density measurement result in the conventional image density control described above. This is because after the reference patch density target is changed as shown in FIG. 22B, the actual reference patch density is controlled to substantially the same value as the target by the toner supply control of FIG. as a result,
In the gradation control of FIG. 8, since ΔADC, which is the difference between the reference patch density and the target value, is almost “0”, the standard density table 1 (see FIG. 3) is always selected. The standard density table 1 is a table selected when the density matches the target, and is a table in which the density is not actually changed. Therefore, the standard patch density target value is changed to a higher value as described above. The problem that the density near the patch increases remains as it is.

Therefore, in the first embodiment, the controller 74 shown in FIG. 2 is provided with a reference patch density target value changing means corresponding to the first changing means according to the present invention. Control is performed so as to maintain both of the concentrations within a predetermined range.

FIG. 9 is a flowchart of a routine for controlling toner supply based on the density of the reference patch according to the first embodiment.

First, in step S41, the count value Dave_CNT of the counter 73a is set to 25 (25, 0
(00 sheets). Count value De
If it is determined that ve_CNT does not exceed 25, the process proceeds to step S42. In step S42, the set value ΔS_A set as the difference between the reference patch density and the target value
DC is set to “0”, and the process proceeds to step S46 described later. On the other hand, in step S41, the count value Dave_C
If it is determined that NT is less than 25, step S4
3 and multiplying the value obtained by subtracting 25 from the count value Dave_CNT by the offset value α to set the value ΔS_ADC
And proceeds to step S44. In step S44,
The set value ΔS_ADC is the maximum set value ΔS_ADC_Max
Is determined. When it is determined that the set value ΔS_ADC does not exceed the maximum set value ΔS_ADC_Max, the process proceeds to step S46. On the other hand, the set value ΔS_
If it is determined that the ADC has exceeded the maximum set value ΔS_ADC_Max, the process proceeds to step S45, where the set value ΔS_A
DC is set as the maximum set value ΔS_ADC_Max, and the process proceeds to step S46.

In step S46, the set value ΔS_ADC is subtracted from the reference patch target value initial value S_ADC_INIT, and the reference patch target value S_ADC for toner replenishment control is obtained.
_DISP (corresponding to the first target value according to the present invention), thereby obtaining a reference patch target value initial value S_ADC_I
The developer use number is individually counted from NIT by the counter DEV_
Calculate according to CNT. Further, the reference patch target value S_ADC_TRC (corresponding to the second target value in the present invention) for the tone control is used as the reference patch target value initial value S_ADC_INIT.
And That is, the target value of the gradation control is not changed. Next, the process proceeds to step S47. In step S47, the obtained toner supply control reference patch target value S_AD
The C_DISP is used in the above-described toner supply control routine shown in FIG. 7, and the gradation control reference patch target value S_
The control is performed by using the ADC_TRC in the above-described gradation control routine shown in FIG. 8 (here, a smaller optical sensor output value corresponds to a higher density).

FIG. 10 is a diagram for explaining the effect of the first embodiment.

As shown in FIG. 10A, the toner charge amount decreases as the number of prints increases. Here, FIG.
As shown in (b), the toner supply control reference patch target value S_ADC_DISP changes in a darker direction (vertical axis direction) in order to prevent a decrease in toner density as the number of prints increases. Then, the actual reference patch density is controlled by the toner supply control in substantially the same manner as the target, as indicated by the dotted line in FIG. 10C. Also, as shown by the solid line in FIG. 10C, the reference patch target value S_ADC_
Since the DISP is constant, the reference patch density gradually becomes higher than the gradation control reference patch target value S_ADC_DISP. Then, the gradation control routine shown in FIG.
As shown in FIG. 10D, the standard density table 1 in the correction table shown in FIG. 3 is initially selected, but the density table is reduced when the density becomes higher than a certain level. 2 is selected, and this results in FIG.
As shown in (e), an increase in density after gradation correction can be prevented. At this time, the toner replenishment control reference patch target value S_ADC_DISP is also changed according to the number of prints, so that it can be maintained within a predetermined range.

Here, the number of correction tables shown in FIG. 3 has been described using three examples for the sake of simplicity.
The number is not limited to this. For example, by having seven tables, density fluctuation and density jump at the time of table change can be made smaller, so that control can be performed with higher accuracy. As described above, in the first embodiment, even when the toner charge amount changes with the number of prints, both the toner density and the image density can be maintained within a predetermined range.

Next, a second embodiment will be described with reference to the color copying machine 1 shown in FIG.

The second embodiment is an example characterized in that the second measuring means measures environmental conditions. Specifically, the second measuring means measures the humidity of the hygrometer 9 (see FIGS. 1 and 2). The reference patch density target value is changed in accordance with.

FIG. 11 is a graph showing the relationship between humidity and toner charge amount, and FIG. 12 is a graph showing the relationship between humidity and toner concentration.

As shown in FIG. 11, when the humidity increases, the charge amount of the toner decreases. Therefore, as shown in FIG.
The toner density required to develop the same amount of toner decreases. Therefore, if the reference patch density is kept constant when the humidity changes, there arises a problem that the toner density changes. If the reference patch density target is changed as in the prior art, the toner density can be maintained constant. There is a problem that the image density changes.

Therefore, in the second embodiment, as shown in FIGS. 1 and 2, the hygrometer 9 is provided in the vicinity of the developing unit 23, and as described below, both the toner density and the image density are set to predetermined values. Keep within range.

FIG. 13 is a flowchart of a routine for controlling toner supply based on humidity according to the second embodiment.

This routine is started by the reference patch density target value changing means of the controller 74 shown in FIG. 2 at the time when the power is turned on and every predetermined time.

First, in step S51, the hygrometer 9
To measure the humidity Hum, and then proceed to step S52. In Step S52, when it is determined that the humidity Hum is less than 40%, the process proceeds to Step S53. In a step S53, the constant K2 is set to a value obtained by subtracting “40” from the humidity Hum.
Is multiplied to obtain a set value ΔS_ADC set as a difference between the reference patch density and the target value.
Proceed to. If it is determined in step S52 that the humidity Hum has exceeded 60%, the process proceeds to step S55. In step S55, a value obtained by subtracting “60” from the humidity Hum is multiplied by a constant K1 to obtain a set value ΔS_ADC, and the process proceeds to step S56. Further, when it is determined in step S52 that the humidity Hum is within the range of −40 ≦ Hum ≦ 60, the process proceeds to step S54. In step S54, the set value ΔS_ADC is set to “0”, and the process proceeds to step S56.

In step S56, the reference patch target value initial value S_AD is obtained by subtracting the set value ΔS_ADC from the reference patch target value initial value S_ADC_INIT.
Toner replenishment control reference patch target value S_ADC_D corresponding to humidity Hum from hygrometer 9 individually from C_INIT
Calculate the ISP. Further, the reference patch target value S for gradation control
_ADC_TRC as a reference patch target value initial value S_ADC
_INIT. By doing so, the target value of the gradation control is not changed. Next, the process proceeds to step S57. In step S57, the obtained toner replenishment control reference patch target value S_ADC_DISP is used in the above-described routine of the toner replenishment control shown in FIG. 7, and the gradation control reference patch target value S_ADC_TRC is used in the above-described gradation shown in FIG. The control is performed using the control routine (the smaller the optical sensor output value is, the higher the density is).

As a result, as described with reference to FIG. 10 in the first embodiment, changing the target value of the toner supply control reference patch changes the reference patch density. The variation is corrected by the gradation control table by maintaining the target value of the gradation control reference patch constant. Even if the toner charge amount changes as in the first embodiment, both the toner density and the image density are reduced. It can be maintained within a predetermined range.

Next, a third embodiment will be described.

The third embodiment is characterized in that the second measuring means measures the toner concentration with respect to the carrier in the developing unit, instead of predicting the toner concentration change from the number of used developer and humidity. Specifically, the toner density sensor 10 measures the toner density of each color of each print. Then, the reference patch density target value changing means of the controller 74 shown in FIG. 2 maintains both the toner density and the image density within a predetermined range as described below.

FIG. 14 is a flowchart of a routine for controlling toner supply based on toner density according to the third embodiment.

First, in step S61, the toner density TC_OUT is measured by the toner density sensor 10, and the flow advances to step S62. In step S62, the toner density T
If it is determined that C_OUT is less than 6%, the process proceeds to step S63. In step S63, a value obtained by subtracting the toner density TC_OUT from “6” is multiplied by a constant K4 to obtain a set value ΔS_ADC set as the difference between the reference patch density and the target value, and the flow proceeds to step S66 described below.
In step S62, the toner concentration TC_OU
When it is determined that T exceeds 10%, step S65 is performed.
Proceed to. In step S65, a value obtained by subtracting the toner concentration TC_OUT from “10” is multiplied by a constant K3 to obtain a set value ΔS_ADC, and the process proceeds to step S66. further,
In step S62, the toner concentration TC_OUT becomes 0
If it is determined that it is within the range of ≦ TC_OUT ≦ 10, the process proceeds to step S64. In step S64, the set value ΔS_ADC is set to “0”, and the process proceeds to step S66.

In step S66, the reference patch target value initial value S_ADC is obtained by subtracting the set value ΔS_ADC from the reference patch target value initial value S_ADC_INIT.
From _INIT, a toner supply control reference patch target value S_ADC_DISP corresponding to the toner density TC_OUT from the toner density sensor 10 is calculated individually. Also, the gradation control reference patch target value S_ADC_TRC is set as a reference patch target value initial value S_ADC_INIT. Thus, the target value of the gradation control is not changed. Next, the process proceeds to step S67. In step S67, the determined toner supply control reference patch target value S_ADC_DISP
Are used in the above-described routine of the replenishment control shown in FIG. 7, and the reference patch target value S_ADC_TR for gradation control is used.
The control is performed by using C in the above-described gradation control routine shown in FIG. 8 (where the smaller the optical sensor output value is, the higher the density is).

As a result, the reference patch density is changed by changing the toner supply control reference patch target value in the same manner as shown in FIG. By keeping the control reference patch target value constant, it is corrected by the gradation control table,
As in the first embodiment, even when the toner charge amount changes, both the toner density and the image density can be maintained within a predetermined range.

In the first, second and third embodiments, the gradation control reference patch target value S_ADC_TRC is not changed. However, in actuality, the toner supply control reference value is adjusted in accordance with the gradation characteristics of the image forming apparatus. Patch target value S_ADC_D
It may be changed separately from the ISP.

Specifically, in the first embodiment, FIG.
As described with reference to, the reference patch density changes as a result of changing the toner replenishment control reference patch target value to maintain the toner density within a predetermined range. FIG. 15 shows the result of the correction by the gradation control while maintaining the values in FIG.

FIG. 15 is a graph showing the gradation of the output image density with respect to the input image density. FIG. 16 is a flowchart of a routine for controlling toner supply based on the density of the reference patch. Note that the flowchart shown in FIG. 16 is the same as the flowchart shown in FIG.
Since this is the same as the flowchart shown in FIG. 7, only step S46 'will be described here, and redundant description will be omitted.

As shown in FIG. 15A, the target gradation A is changed by changing the toner supply control reference patch target value and keeping the toner density in a predetermined range. As a result of maintaining the target value of the reference patch for gradation control constant as in the first embodiment and matching the density of the correction reference patch portion by gradation control, the gradation shape as shown in gradation C is obtained. Due to the difference, the other density portions, especially the low density portions that are highly sensitive to human eyes, do not match. Therefore, as shown in step S46 'of FIG.
By changing _ADC_TRC by ΔS_ADC_TRC, which is a correction amount different from the correction amount ΔS_ADC of the toner supply control reference patch target value S_ADC_DISP,
As shown in the gradation D in FIG. 15B, the change in gradation can be minimized as a whole.

Although the gradation control has been described using an example using a gradation correction table, the present invention is not limited to the charging potential of the photosensitive member, the amount of exposure light, the developing bias voltage of the developing device, and the exposure light for exposing the photosensitive member. At least one of the image signals before being transformed
Any control may be used as long as it can correct the gradation of the formed image.

Next, a fourth embodiment will be described.

In the fourth embodiment, the third measuring means for measuring a factor affecting the relationship between the density of the image to be formed and the result of measurement by the first measuring means (optical sensor) is provided. The first target value (toner replenishment control reference patch target value S_ADC)
_DISP) and the second target value (gradation control reference patch target value S_ADC_TRC).
And changing means. That is, the factor that affects the image density is not the toner density itself or the factor that changes the toner density as in the first, second, and third embodiments described above, but the factor of the optical sensor 28 that measures the reference patch density. The reference patch density target value is changed in accordance with the potential setting of the color copying machine 1, which is a factor affecting accuracy.

First, referring to FIGS. 17, 18 and 19, the accuracy of the optical sensor 28 for measuring the reference patch density by setting the potential of the color copying machine 1, that is, the relationship between the optical sensor output and the reference patch density is shown. Explain that it changes.

FIG. 17 is a diagram showing a cross section of a toner image formed on a photosensitive drum, FIG. 18 is a diagram showing a relationship between copy density and an optical sensor output based on the toner image shown in FIG. 17, and FIG. FIG. 4 is a diagram illustrating a relationship between contrast potential and density.

The optical sensor 28 detects the density of the development patch based on the amount of light reflected from the photosensitive drum 20. That is, when the density is low (when the amount of toner is small), the amount of reflected light is large due to specular reflection on the surface of the photoconductor drum 20, but when the density is high (when the amount of toner is large), the photosensitive drum 2
Since the surface 0 is covered with the toner, the amount of reflected light is reduced. Therefore, the density of the development patch can be detected based on the amount of reflected light from the photosensitive drum 20. However, when the cross section of the toner image is stacked in the height direction indicated by the dotted line 5 from the reference state indicated by the two-dot chain line 4 in FIG. After the development of one layer, the change in the amount of reflected light is small even if the toner is further laminated. On the other hand, when the toner spreads in the horizontal direction indicated by the solid line 6 with the increase in the toner amount, the area of the toner image portion changes, and the change in the amount of reflected light is large. Therefore, when a non-solid development patch such as a halftone dot pattern is used, unlike the solid development patch, there is room for the toner image portion to spread around each halftone dot or line, so that the optical sensor 28 18 has a high sensitivity to the spread of the developed image in the horizontal direction, as shown by the dashed line 7 in FIG. 18, but has a low sensitivity as shown by the solid line 8 in the height direction. However, the developed image shown by the dotted line 5 in FIG.
It is assumed that the toner amounts of the developed images indicated by are equal. FIG.
8, E4 is the density output of the optical sensor 28 when the developed image in the reference state shown by the two-dot chain line 4 in FIG. 17 is measured, and E5 is
The density output of the optical sensor 28 when the developed image shown by the dotted line 5 extends in the height direction, and E6 is the density output of the optical sensor 28 when the developed image shown by the solid line 6 extends in the horizontal direction. Dotted line 5
Since the toner amount of the developed image indicated by is equal to the toner amount of the developed image indicated by the solid line 6, there is a difference in the density output of the optical sensor 28 although the density after fixing on the recording sheet 30 is equal.

For this reason, the density of the development patch is
8, the toner supply amount is controlled so that the detected density becomes a constant reference value. In the case of a pattern having a high contrast potential, the developed image spreads in the horizontal direction and becomes thick. Becomes darker than the actual copy density, and operates so as to match the output of the optical sensor 28 by lowering the density. As a result, the density of the output image becomes lower. Conversely, in the case of a low contrast potential,
The density of the output image increases. FIG. 19 shows the relationship between the contrast potential and the output image density. However, the output of the optical sensor 28 is constant.

As described above, if the contrast potential of the electrostatic latent image is different, the automatic density adjusting mechanism does not operate properly and the density of the output image changes.

As described above, for a halftone or linear reference patch, the accuracy of the optical sensor 28 for measuring the reference patch density changes depending on the potential setting of the color copying machine 1. Therefore, in order to correct this deterioration in accuracy, in the fourth embodiment,
The reference patch density target value is changed in accordance with the potential setting of the color copying machine 1 in combination with the first, second, or third embodiment (each using a tone correction table). Here, the conventional control of the contrast potential and the developing bias potential of the electrostatic latent image formed on the photosensitive drum will be described, and then the potential control in the fourth embodiment will be described using this potential control.

FIG. 20 is a flowchart of a conventional routine for controlling a contrast potential and a developing bias potential of an electrostatic latent image formed on a photosensitive drum.

The image density is controlled by executing the routine shown in FIG. In this routine, the surface potential of the photosensitive drum 20 is measured by the control electrometer 27 shown in FIG. 1, and the grid potential V _GS of the charger 21 and the ROSS2 are measured.
This is performed by determining a laser light amount L _DS and a developing bias potential V _B of 28. The measurement of the surface potential is performed immediately after the power of the color copying machine 1 is turned on and before the start of copying, and thereafter after 30 minutes and before the start of copying. Of course, the photosensitive drum 2 to be used
Depending on the sensitivity variation characteristic of 0, the measurement may be performed in a shorter or longer span.

[0087] Dark advance the target to the controller 74 potential V _HS, target exposed portion potential V _LS, the target dark potential V _HS from the developing bias potential V _B up antifoggants potential V _c of are stored, said based on this The potentials V _GS , L _DS and V _B are determined. First, in step S71, the controller 74 sends a control signal to the charger control unit 75 to change the different grid voltages V _G1 , V _G
G2 charges the photosensitive drum. Further, the dark potentials V _H1 and V _H2 at that time are measured by using the electrometer 27, and step S7 is performed.
Proceed to 2. In step S72, the grid potential V _GS required to obtain the target dark potential V _HS is calculated by the following equation.

[0088]

(Equation 1)

Next, in step S73, the photosensitive drum 20 is charged by using the obtained grid potential V _GS , while the controller 74 sends a control signal to the laser light amount control unit 78, and the two types of laser light amount The photoconductor drum 20 is exposed to the ROS 228 using L _D1 and L _D2 .
Further, the process proceeds to step S74 to measure the exposed portion V _L1, V _L2 for each exposure site using electrometer 27. At step S74, the calculating the amount of laser light L _DS required to obtain the target exposed portion potential V _LS by the following equation.

[0090]

(Equation 2)

Further, in step S75, the developing bias potential V _B is calculated using the target dark potential V _HS and the fog prevention potential difference V _c , and then in step S76, the calculated grid potential V _{GS is applied} to the charger controller 75. to, the amount of laser light L _DS to the laser light quantity control unit 78 sets each of which terminates this routine development bias potential V _B to a developing bias control unit 76.

Further, as for specific image density control, a reference patch is applied to the photosensitive drum 2 as in the first embodiment.
0, and the concentration is measured by the optical sensor 28. At this time, the controller 74 selects an offset value α to be added to the target exposure portion potential _VLS based on the detection signal of the optical sensor 28. When the reference patch density is low, the offset value α is a negative value, and when the reference patch density is high, the offset value α is a positive value.

In the fourth embodiment, when the power of the color copying machine 1 is turned on and at predetermined time intervals, the humidity is measured, the offset value α is obtained according to the measured humidity, and the above routine is executed. In executing the above routine, VLS ′ = VLS
VLS ′ is calculated using + α, and step S74 shown in FIG.
In obtains the amount of laser light L _DS using VLS 'instead of VLS.

In this manner, the potential control of the photosensitive drum 20 is performed after the routine shown in the flowchart of FIG. 20 is completed. If the offset value α is a negative value, the target exposure portion potential _VLS becomes small. On the other hand, the new laser light amount L _DS ′ obtained by calculation increases, and the image portion potential decreases. For this reason, the difference between the image portion potential and the developing bias potential increases, and the image density increases.

Conversely, if the offset value α is a positive value,
While the target exposure portion potential V _LS increases, the new laser light amount L _DS ′ obtained by calculation decreases, and the image portion potential increases. For this reason, the difference between the image portion potential and the developing bias potential is reduced, and the image density is reduced.

FIG. 21 is a flowchart of a routine for controlling toner supply based on an offset value obtained according to humidity according to the fourth embodiment.

First, if it is determined in step S81 that the offset value α is less than -30, the flow proceeds to step S82. In step S82, the process proceeds to step S85, which will be described later, with the setting value ΔS_ADC_α = −30 corresponding to the offset value α. If it is determined in step S81 that the offset value α has exceeded +30, the process proceeds to step S84. In step S84, the process proceeds to step S85 with the set value ΔS_ADC_α = + 30. Further, in step S81, the offset value α
Is within the range of −30 ≦ α ≦ + 30, the process proceeds to step S83. In step S83, the set value ΔS_ADC_α = 0 is set, and the process proceeds to step S85.

In step S85, the set value ΔS_ADC is subtracted from the reference patch target value initial value S_ADC_INIT, and the set value ΔS_AD corresponding to the offset value α is obtained.
C_α is added to obtain a toner replenishment control reference patch target value S_ADC_DISP, and a set value ΔS_ADC_α is added to a reference patch target value initial value S_ADC_INIT to obtain a tone control reference patch target value S_ADC_T.
Ask for RC. That is, the set value Δ corresponding to the offset value α
S_ADC_α is a toner supply control reference patch target value S_ADC_DISP and a gradation control reference patch target value S
_ADC_TRC, and the same set value ΔS_ADC as in the first, second, and third embodiments is applied only to the toner supply control reference patch target value S_ADC_DISP.

Further, in step S86, the reference patch target value S_ADC_DIS for toner replenishment control obtained.
P is used in the above-described routine of the replenishment control shown in FIG. 7, and the reference patch target value S_ADC_TR for gradation control is used.
The control is performed by using C in the above-described gradation control routine shown in FIG. 8 (where the smaller the optical sensor output value is, the higher the density is).

As described above, the color copier 1 which is a factor affecting the accuracy of the optical sensor for measuring the density of the reference patch is described.
Is applied to both the toner supply control reference patch target value S_ADC_DISP and the gradation control reference patch target value S_ADC_TRC, and the toner density itself as in the first, second, and third embodiments is applied. Alternatively, since the factor due to the factor that changes the toner density is applied only to the target patch target value for toner replenishment control S_ADC_DISP, the factor that changes the target patch density target S_ADC_D depends on the factor that changes the target patch density target.
ISP and gradation control reference patch target value S_ADC_TR
C can be changed individually, and even if the toner charge amount changes and the reference patch density sensor accuracy is affected,
Both the toner density and the image density can be maintained within a predetermined range.

Next, a fifth embodiment will be described.

In the fifth embodiment, the reference patch forming means
It is characterized in that different reference patches are formed for toner supply control and for image forming condition control excluding toner supply. In the first to fourth embodiments, a common reference patch is used for toner replenishment and gradation control, and the initial value S_ADC_ of the reference patch density target value of both is used.
INIT is also common. On the other hand, in the fifth embodiment, in order to improve the accuracy of gradation control by using a plurality of reference patches having different densities for gradation control, for example, toner supply is the same as in the first, second, and third embodiments. S_ADC_30, S_ADC_30, S_ADC_30
_ADC_50, S_ADC_60, S_ADC_70
The same result can be obtained by correcting the initial value of each reference patch density target by the reference patch density target value changing means of the controller of the first to fourth embodiments.

The color copying machines of the first to fifth embodiments described above use the reference patch density measurement results to
This is a device for controlling image forming conditions such as gradation control in addition to toner replenishment. The gradation control uses gamma correction as in the first embodiment, but the photoconductor charging potential as in the second embodiment. May be used. The measurement of the reference patch density in the color copying machine may be either measurement on the photoreceptor or measurement of the reference patch density after the transfer of an intermediate transfer member or a paper conveyance belt which is generally performed.

[0104]

As described above, according to the image forming apparatus of the present invention, both the toner density and the image density can be maintained within a predetermined range.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram for explaining a first embodiment to a fifth embodiment of a color copying machine to which the image forming apparatus of the present invention is applied.

FIG. 2 is a block diagram of a control system in the color copying machine shown in FIG.

FIG. 3 is a table 3 stored in a correction table unit shown in FIG. 2;
9 is a graph showing two input / output correction tables.

4 is a graph showing the gradation of an output image density with respect to an input image density in the color copying machine shown in FIG. 1;

FIG. 5 is an explanatory diagram of binarization processing of image data by the comparator shown in FIG. 2;

FIG. 6 is a flowchart of a conventional routine for forming a reference patch on a photosensitive drum.

FIG. 7 is a flowchart of a conventional routine for controlling toner supply based on the density of a reference patch.

FIG. 8 is a flowchart of a conventional routine for selecting an input / output correction table to be applied to the second gamma correction and correcting the image density.

FIG. 9 is a flowchart of a routine for controlling toner supply based on the density of a reference patch according to the first embodiment.

FIG. 10 is a diagram illustrating an effect of the first embodiment.

FIG. 11 is a graph showing the relationship between humidity and toner charge.

FIG. 12 is a graph showing a relationship between humidity and toner density.

FIG. 13 is a flowchart of a routine for controlling toner supply based on humidity according to the second embodiment.

FIG. 14 is a flowchart of a routine for controlling toner supply based on toner density according to the third embodiment.

FIG. 15 is a graph showing the gradation of the output image density with respect to the input image density.

FIG. 16 is a flowchart of a routine for controlling toner supply based on the density of a reference patch.

FIG. 17 is a diagram illustrating a cross section of a toner image formed on a photosensitive drum.

18 is a diagram illustrating a relationship between a copy density and an optical sensor output based on the toner image illustrated in FIG. 17;

FIG. 19 is a diagram showing a relationship between contrast potential and density.

FIG. 20 is a flowchart of a conventional routine for controlling a contrast potential and a developing bias potential of an electrostatic latent image formed on a photosensitive drum.

FIG. 21 is a flowchart of a routine for controlling toner supply based on an offset value obtained according to humidity according to the fourth embodiment.

FIG. 22 is a diagram illustrating a state where an image defect occurs due to a change in toner density.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Color copier 9 Hygrometer 10 Toner density sensor 11 Control system 12 Image processing unit 13 Optical unit 14 Image forming unit 20 Photoconductor drum 21 Charging corotron 22 Scanner unit 23 Developing units 23K, 23C, 23M, 23Y Developing unit 25 Cleaner 26 Erase lamp 27 Electrometer 28 Optical sensor 30 Recording sheet 31 Transfer drum 41 Adsorption corotron 42 Transfer corotron 43 Static elimination corotron 44 Cleaning static elimination corotron 45 Cleaning brush 46 Internal press roll 47 Peeling finger 48 Sheet transport system 50 Fixing device 51 Heating roll 52 Pressurization Roll 53 guide plate 54 fuser outlet roll 55 fuser outlet switch 56 discharge tray 57 outlet roll 60 amplifier 61 A / D converter 62 density converter 63 color converter 64 first gas Mamma correction 65 Second gamma correction 66 Correction table section 67 First selector 68 D / A converter 69 Comparator 70 Triangular wave generator 71 Laser driver 72 Patch signal generation means 73 Second selector 74 Controller 74a Counter 75 Charger controller 76 Developing bias controller 77 Toner supply device 78 Laser light amount controller 80 Screen 81a, 81b, 82a, 82b, 83a, 83b Button 84 Execute button 221 Platen 222 Original 223 Exposure lamp 224 Carriage 225 Reflection mirror 226 CCD sensor 227 Imaging lens 228 Raster scanning device (ROS) 228a Semiconductor laser 228b Polygon mirror 228c Imaging lens 228d Reflection mirror

Continued on front page F-term (reference) 2H027 DA02 DA10 DA14 DA39 DA45 DD07 DE02 DE07 EA01 EA02 EA05 EB03 EB04 EC03 EC06 EC20 ED03 ED06 ED09 EE06 EF01 EF09 ZA07 2H077 AD35 DA04 DA05 DA10 DA12 DA22 DA47 DA63 DB82 DB83

Claims (7)

[Claims] 1. A photoreceptor having a surface charged to a predetermined charging potential and exposed to light according to an image signal to form an electrostatic latent image, and a two-component developer comprising a carrier and a toner. Developing the electrostatic latent image formed on the surface of the photoreceptor with toner in a developer while a predetermined developing bias voltage is applied between the photoreceptor and the toner image on the photoreceptor; An image forming apparatus that includes a developing device that forms an image on the image recording material by finally transferring and fixing the toner image formed on the photoconductor onto a predetermined image recording material, A reference patch for forming a reference patch formed of toner with a target of a predetermined density by forming an electrostatic latent image for a reference patch on the photoconductor and developing the electrostatic latent image with the developing device Forming means; and the photoconductor First measuring means for measuring the density of the reference patch formed on the photoreceptor, or the density of the reference patch after being transferred from the photoreceptor onto a predetermined object; and measuring the density of the reference patch by the first measuring means Comparing the result with a predetermined first target value, and in accordance with the comparison result, controlling a toner supply to the developing device; a toner supply control unit; and a density measurement result of the reference patch by the first measurement unit. Is compared with a predetermined second target value, and in accordance with the comparison result, at least one image forming condition that affects a formed image, excluding toner supply to the developing device, is controlled. Control means; second measuring means for measuring one of the factors affecting image density; and the first measuring means according to a measurement result by the second measuring means.
An image forming apparatus comprising: a first changing unit configured to independently and independently change the target value and the second target value. 2. The image forming condition control means includes: a charging potential of the photoconductor, an exposure light amount, a developing bias voltage of the developing device, and an image signal before being converted into exposure light for exposing the photoconductor. Controlling the at least one to correct the gradation of an image to be formed, wherein the first changing means includes the first target value and the second target value. 2. The image forming apparatus according to claim 1, wherein only one target value is changed. 3. An image forming apparatus according to claim 1, wherein said second measuring means measures the concentration of toner with respect to a carrier in said developing device. 4. The image forming apparatus according to claim 1, wherein said second measuring means measures a use time of a developer in a developing device. 5. An image forming apparatus according to claim 1, wherein said second measuring means measures an environmental condition. 6. A third measuring means for measuring a factor which influences a relationship between a density of an image to be formed and a measurement result by said first measuring means, and according to a measurement result by said third measuring means. The apparatus according to any one of claims 1 to 5, further comprising a second changing unit configured to change both the first target value and the second target value together. Image forming apparatus. 7. A method according to claim 1, wherein said reference patch forming means forms different reference patches for toner supply control and for image forming condition control excluding toner supply. The image forming apparatus according to claim 1.