JPH0642108B2 - Image forming condition control method - Google Patents

Description

TECHNICAL FIELD The present invention corrects image forming conditions according to the degree of fatigue of a photoconductor and / or a developer, and corrects the toner replenishment amount according to the density of a reference density pattern. The present invention relates to a method for controlling image forming conditions.

(Prior Art) In a copying machine, an electrostatic latent image of a reference density pattern is continuously formed on a photoconductor, that is, each image forming operation (copying operation).
A method is known in which each image is formed once, and the potential or the density after development is detected to control the image forming conditions such as the toner replenishment amount or the developing bias voltage. However, in this method, since the detection operation is continuously performed, problems such as an increase in cost, a decrease in copying speed, and an increase in load on the exposure system and the cleaning device occur. Further, since the fatigue of the photoconductor and the like is not taken into consideration, the control of the toner replenishment amount and the like is insufficient and the quality of the copied image is poor. Also, by intermittently detecting the density of the visible image on the photoconductor,
That is, a method is generally used in which the toner supply amount and the like are detected by detecting each time a plurality of times of image forming operations. However, even in this method, since the fatigue of the photoconductor is not considered, the control is insufficient and the quality of the copied image is poor.

(Object) The present invention provides an image forming condition control method capable of improving the quality of a copied image and, at the same time, eliminating the problem caused by continuously detecting the density of a reference density pattern. The purpose is to

(Structure) The present invention will be described in detail below with reference to the drawings.

The present invention will be described with reference to FIG. 1. The present invention repeats image formation in which an electrostatic latent image is formed by charging and exposing a photoconductor, and the electrostatic latent image is developed by a developing device and transferred to a transfer material. For the image forming method performed by
Or while correcting the image forming conditions according to the degree of fatigue of the developer, charging and exposure on the photoconductor, to form a reference density pattern by development by the developing device to detect the density of this reference density pattern, An image forming condition control method for correcting the toner replenishment amount of the developing device according to the result of this detection, wherein the reference density is set when the image forming condition is not corrected according to the fatigue level of the photoconductor and / or the developer. The pattern formation and the density detection and the toner replenishment amount correction are performed every predetermined plural times of image formation, and the correction is performed when the image forming condition is corrected according to the degree of fatigue of the photoconductor and / or the developer. The formation of the reference density pattern and the density detection are performed twice or more at intervals shorter than the time, and the results of the detection of the two or more times are calculated, and the toner correction is performed based on the processing results. Correct the salary.

Therefore, since the image forming conditions are corrected according to the degree of fatigue of the photoconductor and / or the developer, it is possible to improve the control accuracy of the image forming conditions and improve the image quality. Also,
If the correction of the image forming conditions is incomplete, the density of the reference density pattern fluctuates and the toner replenishment amount fluctuates, and the fluctuation of the toner density becomes large. Since the reference density pattern is formed and the density is detected twice or more at an interval shorter than the time and the toner replenishment amount is corrected based on the processing result, the number of times the reference density pattern is formed and the density is detected is increased. The correction amount of the toner replenishment amount can be obtained more accurately based on the result of the calculation process, and the fluctuation of the toner density can be prevented. Further, when the image forming condition is not corrected according to the fatigue degree of the photoconductor and / or the developer, the reference density pattern formation, the density detection, and the toner replenishment amount correction are performed every predetermined number of image formations. So
It is possible to eliminate as much as possible the problem caused by continuously detecting the density of the reference density pattern.

FIG. 2 shows an example of a copying machine to which the present invention is applied. In this copying machine, the original 1 is placed on a transparent original table 2, and when the power is turned on by the main switch and the print switch is turned on, the photosensitive drum 3 is rotationally driven by the motor and the corona discharger 4 for charging is used. After being uniformly charged, the unnecessary charged portion is discharged by the erase lamp 27, and the slit exposure device projects the image of the original 1 to form an electrostatic latent image. This slit exposure apparatus illuminates a document 1 on a document table 2 with a light source 5 and irradiates the photosensitive drum 3 with its reflected light by an optical system, and scans the document table 2 or the light source 5 and a part of the optical system. The system is advanced to project the image of the document 1 from the front end side onto the photosensitive drum 3, and then the scanning system is returned to the home position. The electrostatic latent image on the photosensitive drum 3 is supplied with a two-component developer 7 composed of a toner and a carrier by a developing device 6 to be developed with the toner, and is transferred onto a transfer paper 8 fed from a paper feeding device (not shown). It is transferred by the transfer corona discharger 9. The transfer paper 8 is separated from the photoconductor drum 3 by the separating corona discharger 10 and is conveyed by the conveying belt 11, the toner is fixed by the fixing device, and the copy paper 8 is discharged to the external tray as a copy. The photosensitive drum 3 is cleaned by the cleaning device 12 after the transfer paper 8 is separated, and the residual potential is removed by the charge removing device 13. After the copying operation is repeated for the set number of sheets, the copying pause state is set until the next print switch is turned on.

Further, a reference density pattern 1 having a reference density of 1.8, for example, is provided outside the area of the original table 2 on which the original 1 is placed.
4 is provided, and if the erasing lamp 27 is off when the scanning system is at the home position and the scanning system starts to move forward, the image of the reference density pattern 14 is projected onto the photoconductor drum 3 and the electrostatic latent image thereof is formed. Is formed. This electrostatic latent image is developed by the developing device 6.
After the development, the density of the visible image is detected by the photo sensor 15 and then removed by the cleaning device 12, and the temperature of the photosensitive drum 3 is detected by the temperature sensitive element 16 which is a thermistor. The developing device 6 stirs the developer 7 with the stirrer 17, conveys the developer 7 to the surface of the photoconductor drum 3 by the developing sleeve 18, and develops the electrostatic latent image on the photoconductor drum 3 with the toner in the developer 7, The replenishing device 19 replenishes the internal toner 21 to the developer 7 in the developing device 6 by the rotation of the toner replenishing roller 20.
The controller 22 outputs the output signal of the thermistor 16, the copying pause time,
The developing bias voltage applied to the developing sleeve 18 also serving as the developing electrode is corrected according to the number of repeated copies, that is, the degree of fatigue of the photoconductor. When the developing bias voltage is not corrected, the control device 22 turns off the erase lamp 27 only once every 10 sheets of repeated copying to turn off the reference density pattern 14.
When the development bias voltage is corrected, the electrostatic latent image of the reference density pattern 14 is adjusted according to the degree of correction by controlling the rotation of the toner supply roller 20 by the output signal of the photosensor 15 The output signal of the photosensor 15 is calculated for each set number of times, and the rotation of the toner supply roller 20 is controlled. The continuous formation of the electrostatic latent image of the reference density pattern 14 means that the electrostatic latent image of the reference density pattern 14 is formed once for each image forming operation, as will be apparent from the description below. Means

FIG. 3 shows the developing bias controller of the controller 22.
A microcomputer is used as the bias control circuit 23, and this microcomputer is composed of a central processing unit CPU, a read only memory ROM, a random access memory RAM, and an input / output control unit IOC as shown in FIG. The central processing unit CPU sequentially reads and executes the microprogram written in the read-only memory ROM, and exchanges data with each device in this copying machine through the input / output control unit IOC and the interface circuit IF. . This data includes a start signal input when the main switch is turned on, a print signal and various timing signals from the copy sequence control unit of this copying machine, a pause time detection signal from a pause time detection circuit 24 including a timer, and a copy from a counter. An input signal such as a copy number detection signal from the number detection circuit 25, a bias correction signal to the bias power source 26, and an output signal such as a pattern image formation control signal to the erase lamp 27. Timer 24
Is set every 10 seconds after the copy operation is completed and the copy is ejected to the tray, and is set if the next copy operation is not started, and the counting of the copy pause time is started. It is reset each time it is started, and is reset when the main switch is turned on and released when the main switch is turned off. The counter 25 reads the data of the timer 24 at the start of the copying operation, judges whether or not the copying is suspended based on this data, and counts the number of continuous copies. In other words, until the timer 24 is reset after the repeated copying operation is completed, it is added up for each copying operation, and the timer 24
After is reset, cancel the previous integrated value and set 1
To add up for each copy operation. The counter 25 is released when the main switch is turned off and reset when the main switch is turned on. As shown in FIG. 5, the central processing unit CPU outputs a bias correction signal according to the contents of the timer 24 and the counter 25 (copy pause time, number of continuous copies) to the bias power supply 26 to correct the developing bias voltage. . That is, as shown in FIG. 9, the central processing unit CPU sets the content A of the timer 24 and the content B of the counter 25 to the developing bias voltage of 400V when the electrostatic latent image of the reference density pattern 14 is developed by the developing device 6. Accordingly, a bias correction signal for correcting (adding) only the voltages shown in Table 1 below is output.

As is apparent from Table 1, the developing bias voltage increases as the copying pause time increases, and the continuous copy number B
Becomes smaller, the smaller. When the electrostatic latent image of the original 1 is developed by the developing device 6, the central processing unit CPU makes 230V.
The bias correction signal is switched so as to correct (add) only the voltages shown in the following Table 2 according to the content A of the timer 24 and the content B of the counter 25 with respect to the developing bias voltage.

In this case, the correction amount of the developing bias voltage becomes large as a whole because the change in the image density is smaller than the change in the background stain due to the fatigue of the photoconductor. Bias power supply 26
When the electrostatic latent image of the reference density pattern 14 is developed by the developing device 6, the developing bias voltage is corrected according to the temperature of the photosensitive drum 3 by the output signal of the temperature sensitive element 16 as shown in FIG. When the electrostatic latent image No. 1 is developed by the developing device 6, it is corrected according to the temperature of the photosensitive drum 3 by the output signal of the temperature sensitive element 16 as shown in FIG. Further, in the toner density control section of the controller 22, as shown in FIG. 12, the density detection circuit composed of the photosensor 15 and the resistors 28 to 32 detects the density of the visible image on the photosensitive drum 3 to detect two different sizes. A density detection signal is output, and these two density detection signals are A /
The signals are input to the A ₀ and A ₁ channels of the D converter 33 and converted into digital signals. The digital signal is processed by the microcomputer 34. The microcomputer 34 turns on the toner replenishing solenoid 36 via the amplifier 35 to rotate the toner replenishing roller 20 to replenish the toner, and the decoder 37 and the driver 38. The copy density data is displayed on the display device 39 via the. In this case, the microcomputer 34 controls the toner density in connection with the correction of the developing bias voltage. However, since the correction of the developing bias voltage by the output signal of the thermistor 16 is not performed digitally, the toner density is controlled in relation to the copying pause time and the correction of the developing bias voltage depending on the number of continuous copies. That is, as shown in FIG. 10, the central processing unit CPU, when developing the electrostatic latent image of the reference density pattern 14, does not correct the developing bias voltage by the copying pause time and the number of continuous copies, so that the continuous copying of 10 sheets is performed. The erase lamp outputs the control signal for toner concentration detection only once each time
By turning off 27, an electrostatic latent image of the reference density pattern 14 is formed on the photoconductor drum 3, and at the same time the photosensor 15 detects the visible image density of the electrostatic latent image after development, and the resulting density detection signal is obtained. Based on the interrupt processing, which will be described later, a toner replenishment signal is output to control the toner replenishment on / off to control the toner density of the developer 7. Further, when the electrostatic latent image of the reference density pattern 14 is developed, if the developing bias voltage is to be corrected by 30 V depending on the copying pause time and the number of continuous copies, for example, two or more times, for example, three times in succession for each one copy. The photosensor is made to perform the latent image formation of the reference density pattern 14 and the detection of the visible image density by the photosensor 15 one by one in the same manner as described above.
The density detection signal from 15 is calculated by an interrupt process described later, for example, an average value is taken, and it is determined from the result whether toner should be replenished, and a toner replenishment signal is output to the drive unit of the toner replenishment roller 20. . Of course, the developing bias voltage is changed while the visible image density of the reference density pattern 14 is detected three times in a row.
Even if the 30V correction operation is turned off, the density of the visible image of the reference density pattern 14 is detected three times in a row. Further standard density pattern
When the electrostatic latent image of 14 is developed and the developing bias voltage is corrected by 60 V or 90 V depending on the copy pause time and the number of continuous copies, the latent image of the reference density pattern 14 is obtained every time (each copy is made). The formation and the detection of the visible image density by the photo sensor 15 are performed in the same manner as described above, and the toner replenishment is controlled based on the density detection signal from the photo sensor 15 by an interrupt process described later.

As shown in FIG. 11, the microcomputer 34 sets P = 1 as an initial setting and performs the interrupt processing. First, the display of the display device 39 is turned off, the A / D converter 33 is caused to convert the density detection signal of the A ₀ channel into a digital signal, the digital signal is read and added to the contents of the register. This is repeated 2 ⁿ (n is, for example, 4) times and the addition result of the above register is shifted to the n-bit lower-order digit to calculate the average value, and V
Store in _SG register. Here, the reference density pattern 14 is a pattern in which a white level pattern and a black level pattern are arranged adjacent to each other in the scanning direction of the scanning system, and the contents of the V _SG register are 2 ⁿ of the visible density of the white level pattern. It is detected and averaged. Next, the A / D converter 33 is caused to convert the density detection signal of the A ₁ channel into a digital signal, and this digital signal is read and compared with 2.5V. The density detection signal of the A ₁ channel becomes 2.6 V or more for the white level pattern and becomes less than 2.5 V for the black level pattern, and the A / D converter 33 detects that the density detection signal of the A ₁ channel is
If it is less than 2.5V, it will be converted to a digital signal as it is.
If it is 2.5V or higher, it is converted to a 2.5V digital signal. Therefore, by determining that the digital signal is not 2.5 V, it is detected that the image of the black level pattern has arrived at the detection position of the photo sensor 15, and the transition between the white level pattern and the black level pattern is detected. In order to avoid the visible image density detection, the A / D converter 33 is made to perform analog / digital conversion (A / D conversion) of the density detection signal m times. Then the concentration detection signal of A ₁ channel A / D converter 33 A /
D-convert, read the digital signal, and add to the contents of the register. This is repeated 2 ⁿ times and the addition result of the register is shifted to the n-bit lower digit to calculate the average value and store it in the V _SP register. The contents of the V _SP register are the averages of the visible image densities of the black level pattern detected ²ⁿ times, and are multiplied by 4 by shifting to the upper digit of 2 bits. Next, change the contents of the V _SG register to V _SP
Divide by the contents of the register, multiply by 10, and store the result in the toner register. Next, the developing bias voltage of 30 V
If there is no correction (due to the copy pause time and the number of continuous copies), the rest of the contents of the toner register is subtracted from 25. To the toner register. If the content of the toner register is not 0 or more, the process proceeds to the next routine. If the content of the toner register is 0 or more, the first toner counter is set to 0 and the content of the toner register is multiplied by 7 to the second toner counter. Set the value. In the 16-bit toner counter, the lower 8 bits are composed of the first toner counter and the upper 8 bits are composed of the second toner counter. The toner counter measures the time corresponding to the set data by counting the clock, and at this time, the toner replenishing solenoid 36 is driven to replenish the toner.
When the developing bias voltage is corrected by 30V, the contents of the toner register are added three times in another memory, and the result is added to three.
The average value is obtained by dividing by and set in the toner counter.

For example, if the repeat copying operation is started by turning on the print switch in the mode of 90 <A in Table 1,
In the case of the first copy, since the developing bias voltage is corrected by 90 V by developing the latent image of the reference density pattern 14, the latent image formation of the reference density pattern 14 and the density detection by the photo sensor 15 are performed immediately before the first copy. The central processing unit CPU outputs a toner replenishment signal corresponding to the density detection signal, and the toner replenishment roller 20 is rotationally driven by the toner replenishment signal after the completion of the first copy. In the case of the second copy, the developing bias voltage is corrected by 60 V by developing the latent image of the reference density pattern, so the latent image formation of the reference density pattern 14 and the density detection by the photosensor 15 are performed immediately before the second copy. The central processing unit CPU outputs a toner replenishment signal corresponding to the density detection signal, and the toner replenishment roller 20 is rotationally driven in response to the toner replenishment signal after the second copy is completed. In the case of the third copy, the developing bias voltage is corrected by 30 V in the development of the latent image of the reference density pattern, so that the latent image formation of the reference density pattern and the photosensor are performed immediately before each copy of the third to fifth sheets three times. The density detection is performed by 15, and the average value of each density detection signal is obtained, and the toner replenishment signal corresponding to this average value is output by the central processing unit CPU, and after the completion of the fifth copy, the toner replenishment roller 20 Rotational drive is performed according to the toner replenishment signal. That is, the rotation of the toner supply roller 20 after the completion of the third copy and after the completion of the fourth copy is performed in accordance with the toner supply signal in the toner register, and the toner supply roller 20 after the fifth copy is completed. The drive is performed according to the toner replenishment signal. In the case of the sixth copy, since the developing bias voltage is corrected by 30 V in the development of the latent image of the reference density pattern, the latent image formation and the density detection of the reference density pattern are performed three times in succession as described above, and each density The average value of the detection signals is taken, and the toner replenishment signal corresponding to this average value is 8
Output just before the first copy. Therefore, the toner replenishing roller 20 is driven according to the toner replenishing signal in the toner register after the completion of the sixth and seventh sheets of copying, and the toner replenishing roller 20 is driven after the completion of the eighth copying. It is performed in response to the supply signal. When copying the 9th sheet, the development bias voltage is set to 30 when developing the latent image of the reference density pattern.
Since only V is corrected, similarly, latent image formation and density detection of the reference density pattern are performed three times in succession, the average value of each density detection signal is taken, and the toner replenishment signal corresponding to this average value is sent for 11 sheets. Output just before the eye copying. Therefore 9
The toner supply roller 20 is driven in response to the toner supply signal in the toner register after the completion of the copying of the first and tenth sheets, and the driving of the toner supply roller 20 after the completion of the copying of the eleventh sheet becomes the toner supply signal. Will be done accordingly. In the case of the 12th copy, since the latent image of the reference density pattern is not corrected for the developing bias voltage, the latent image formation of the reference density pattern and the density detection are not performed, and the toner replenishing roller 20 after the 12th copy is completed.
Is driven in accordance with the toner replenishment signal. The same applies to copying the 13th to 20th sheets. After that, at the rate of once every 10 copies until the continuous copying is completed, that is,
When performing the 21st, 31st, 41st, etc. copying ... Immediately before the copying, latent image formation and density detection of the reference density pattern are performed and the toner replenishment signal corresponding to the density detection signal, ... is output, and the toner replenishing roller 20 is driven according to the toner replenishment signal after completion of each copy of the 21st to 30th sheets, and according to the toner replenishment signal after completion of each copy of the 31st to 40th sheets. It will be carried out.

Further, in the mode of 10 <A ≦ 90 in Table 1, when the repeat copying operation is started by turning on the print switch, the operation is performed at the timing shown in FIG.

This copying machine is not intended to correct the developing bias voltage at the time of developing the latent image of the original 1, but is intended to control the toner density to be constant, and to correct two image forming conditions. is doing. This correction is (a) when developing the latent image of the reference density pattern to detect the temperature of the photoconductor drum, the copying pause time and the number of continuous copies, and (b) to correct the development bias voltage. To detect the visible image density and correct the toner replenishment amount. (I)
Is compensated for the potential change of the latent image of the reference density pattern due to the temperature of the photosensitive drum, the copying pause time, and the number of continuous copies, and the development potential for the latent image of the reference density pattern, that is, (latent image potential)-(developing electrode (Electric potential) is properly maintained to accurately detect the toner concentration of the developer. Also
In the correction of (b), it is necessary to accurately detect the toner concentration of the developer, but this requires consideration of the incomplete correction of (a). This incompleteness means that the toner density cannot be accurately detected, and the development potential for the latent image of the reference density pattern cannot be made completely constant by the toner density detection every time. In the correction of (a), the correlation between (photoreceptor drum temperature, copy pause time, number of continuous copies) and (latent image potential of the reference density pattern) is experimentally obtained in advance, and it is determined in image formation. Pseudo-correlation factors are set by modifying within a reasonable range as control, and the developing bias voltage is corrected in analog based on the temperature of the photoconductor drum based on the pseudo-correlation factors. Have been corrected. Therefore, in the actual image formation, complete development bias voltage correction (making the development potential for the latent image of the reference density pattern constant every time) cannot be realized, and in particular, the larger the correction amount of the development bias voltage, the greater the error. Therefore, the imperfections are large.
Therefore, in order to complement the correction of (a), it is required to detect the toner density each time (for each copy of one sheet) and take the average value by the correction of (b), and from the viewpoint of the burden on the cleaning device, etc. It is required to detect the toner density as little as possible. The above copying machine satisfies both of these requirements as much as possible, and when there is a correction of (a), the toner density detection of (b) is performed in order to complement the incomplete correction of (a). The correction is performed more frequently than when the correction of (a) is not performed. Particularly, when the correction amount of (a) is large, the imperfection increases, so that the frequency of toner density detection of (b) is further increased.

In the above copying machine, the toner concentration was detected to control the toner replenishment. However, the surface potential of the photoconductor is detected to control the image forming conditions such as the exposure amount, the developing bias voltage, and the charging flow, and to control the photoconductor. The present invention can also be applied to a case where the surface potential is corrected by the temperature of the photoconductor or the like according to the degree of fatigue of the photoconductor, the developer or the like. Further, the developing bias voltage is applied to the developing electrode for the purpose of eliminating the background stain, but it is known that the developing bias voltage changes the density of the image area. Further, when the developing bias voltage is corrected by the temperature of the photosensitive drum, the copying pause time, and the number of continuously copied sheets, the fluctuations in the background stain and the image area density may not be the same. In this case, if the developing bias voltage is corrected so that the density of the image area is slightly sacrificed and the background stain is kept constant, the visible density of the reference density pattern is changed and the control of the toner density is affected. Therefore, the development bias voltage may be corrected so that the background stain is erased when the latent image of the original is developed, and the density of the image portion becomes constant when the latent image of the reference density pattern is developed.

(Effect) As described above, according to the present invention, image formation is repeated in which an electrostatic latent image is formed by charging and exposing a photoconductor, and the electrostatic latent image is developed by a developing device and transferred to a transfer material. In the image forming method, the image forming conditions are corrected according to the fatigue level of the photoconductor and / or the developer, and the reference density pattern is obtained by charging and exposing the photoconductor, and developing by the developing device. An image forming condition control method for detecting the density of this reference density pattern by correcting the toner density of the developing device and correcting the toner replenishment amount of the developing device according to the detection result. When the corresponding image forming condition is not corrected, the formation of the reference density pattern, the detection of the density, and the correction of the toner replenishment amount are performed every predetermined number of times of image formation, and the photoconductor and / or the developer is exhausted. When the image forming condition is corrected in accordance with the above, formation of the reference density pattern and density detection are performed twice or more at intervals shorter than the time when this correction is performed, and the results of the two or more detections are calculated and processed. Since the toner replenishment amount is corrected based on the processing result, by correcting the image forming condition according to the degree of fatigue of the photoconductor and / or the developer, the control accuracy of the image forming condition is improved and the image quality is improved. Can be improved. Further, when the correction of the image forming conditions is incomplete, the density of the reference density pattern fluctuates and the toner replenishment amount fluctuates and the fluctuation of the toner density becomes large. Since the reference density pattern is formed and the density is detected twice or more at intervals shorter than the correction time, and the toner replenishment amount is corrected based on the processing result, the number of times the reference density pattern is formed and the density is detected is increased. Then, the correction amount of the toner replenishment amount can be obtained more accurately based on the result of the calculation process, and the fluctuation of the toner concentration can be prevented. Further, when the image forming condition is not corrected according to the fatigue degree of the photoconductor and / or the developer, the reference density pattern formation, the density detection, and the toner replenishment amount correction are performed every predetermined number of image formations. Therefore, it is possible to eliminate the problem caused by continuously performing the density detection of the reference density pattern.

[Brief description of drawings]

FIG. 1 is a flow chart showing the present invention, FIG. 2 is a schematic view showing an example of a copying machine to which the present invention is applied, FIG. 3 is a block diagram showing a developing bias controller of the copying machine, and FIG. FIG. 5 is a block diagram showing a control microcomputer of the copying machine, FIG. 5 is a flow chart showing a developing bias control operation of the copying machine, and FIGS. 6 and 7 show a developing bias voltage and a photosensitive drum temperature in the copying machine. FIG. 8 is a characteristic diagram showing the relationship, FIG. 8 is a timing chart showing an example of toner concentration control operation of the copying machine, FIGS. 9 to 11 are flow charts showing the control contents of the microcomputer, and FIG. FIG. 3 is a block diagram showing a toner density control unit. 15 ... Photo sensor, 18 ... Developing sleeve, 19 ... Toner supply device, 22 ... Control device.

Claims (1)

[Claims] 1. An image forming method in which an electrostatic latent image is formed by charging and exposing a photoconductor, and the electrostatic latent image is developed by a developing device and transferred to a transfer material by repeating image formation. The image forming condition is corrected according to the degree of fatigue of the photoconductor and / or the developer, and a reference density pattern is formed on the photoconductor by charging and exposure and development by the developing device. The concentration of
An image forming condition control method for correcting the toner replenishment amount of the developing device according to the result of this detection, wherein the reference density is set when the image forming condition is not corrected according to the fatigue level of the photoconductor and / or the developer. The pattern formation and the density detection and the toner replenishment amount correction are performed every predetermined plural times of image formation, and the correction is performed when the image forming condition is corrected according to the degree of fatigue of the photoconductor and / or the developer. The reference density pattern is formed and the density is detected twice or more at intervals shorter than the time, and the results of the two or more times of detection are calculated and the toner replenishment amount is corrected based on the processing results. And an image forming condition control method.