JPH0158505B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a color image forming apparatus. In particular, the present invention relates to a color copying apparatus that maintains good color balance and obtains a color copy image that is faithful to the original. In conventional image forming apparatuses, such as color copying apparatuses, the surface potential on the photoreceptor on which the latent image is formed changes over time, making it difficult to obtain copied images with stable color balance over a long period of time. It was difficult. This problem will be explained below with reference to the gradation reproduction characteristics of color copying shown in FIG. In the figure, Do represents the original image density, Dp represents the print image density, E represents the exposure amount, and Vs represents the surface potential on the photoreceptor. Here, the first quadrant is the tone reproduction characteristic when a grayscale original is used. C, M, and Y represent the single colors of cyan, magenta, and yellow, respectively, and C+M+Y represents the tone reproduction characteristics of a copied image obtained by superimposing these three colors. The second quadrant when viewed clockwise is Do-E.
(common logarithm) exposure characteristics. The third quadrant shows the color separation latent image characteristics of red (R), green (G), and blue (B) on the photoreceptor. The fourth quadrant is cyan (C),
The development characteristics of magenta (M) and yellow (Y) toners are shown. In the characteristics of the first quadrant, cyan, magenta,
The reason why the yellow print image density Dp is different from the same original image density Do is to correct unnecessary light absorption of each toner and maintain color balance. Since the current color balance is gray balance, the unnecessary light absorption of blue and green in the cyan toner and the unnecessary light absorption of blue in the magenta toner are corrected to create a superimposed image of the three colors of cyan, magenta, and yellow. The colors are balanced. For this reason, as shown in the third quadrant, the color separation latent image characteristics of red, green, and blue are almost the same, and as shown in the fourth quadrant, differences are provided in the development characteristics of cyan, magenta, and yellow. Incidentally, in order to obtain a copied image with good color balance, it is necessary to keep the red, green, and blue color separation latent image characteristics of the photoreceptor constant for a long time. However, as mentioned above, this has been extremely difficult in the past. The cause of this was due to environmental changes such as temperature and humidity, deterioration of the photoreceptor, etc., and the latent image characteristics varied. Further, it is necessary to correct variations in development characteristics due to production lots of cyan, magenta, and yellow developers (toners), or variations in development characteristics due to changes in these developers over time.
To this end, in the past, the characteristics of the red, green, and blue color separation latent images were intentionally made different from the nearly uniform state shown in the third quadrant, and the characteristics were selected so as to have an appropriate relationship. However, it is extremely difficult to adjust the latent image characteristics of each color separation appropriately, and strictly speaking, it is necessary to carefully adjust the charger output, exposure amount, etc. of the color copying machine for each color using a surface electrometer and a recorder. It was necessary for the person to make adjustments. Therefore, it has been practically impossible for general users to make adjustments. The purpose of the present invention is to eliminate the above-mentioned drawbacks, make it possible to obtain a color image that always maintains good color balance regardless of environmental changes, changes over time, etc., and furthermore, to make it possible to obtain color images with a good color balance according to the user's preference. An object of the present invention is to provide a color image forming apparatus capable of obtaining images. That is, the present invention provides an electrophotographic means for forming a color image on a recording material by performing an image forming process for each color multiple times on a photoconductive photoreceptor, and a dark area surface potential on the photoreceptor after being charged. or a potential detection means for detecting the bright area surface potential on the photoreceptor after static elimination, an A/D conversion means for converting an analog value output from the potential detection means into a digital value, and an output from the A/D conversion means. A predetermined value is set for the digital value in order to set the operating conditions for each color of the electrophotographic means so that the digital value corresponding to the dark area surface potential or the bright area surface potential to be applied becomes a value corresponding to the target potential for each color. A control means for calculating a control value according to a control formula and determining a control value according to the result of the calculation, a D/A conversion means for converting the control value obtained by the control means into an analog value, and an output from the D/A conversion means. a driving means for driving the electrophotographic means based on an analog value of the electrophotographic means; and an adjusting means capable of independently adjusting operating conditions of the electrophotographic means set by the control means for each color. An image forming apparatus is provided. The present invention will be explained in detail below based on the drawings. FIG. 2 is a block diagram of an apparatus according to an embodiment of the present invention.
In the figure, a photosensitive member composed of a conductive layer, a CdS photoconductive layer, and an insulating layer is formed on the surface of a photosensitive drum 1 rotating in the direction a. A document to be copied is placed on document table glass 3 and illuminated by illumination lamp 5 . Scanning mirrors 7 and 9 that scan the original scan the original in synchronization with the rotation of the drum 1, and the mirrors 7 and 9 move to positions 7' and 9', respectively, and the illumination lamp 5 also moves to the position 5'. Move up to. The optical image of the scanned original is captured by lens 1
1, mirror 13, color separator 15 and mirror 17
The image is formed on the surface of the photoreceptor of the photoreceptor drum 1 through a secondary charger 19 for static neutralization at the same time as exposure. A latent image is formed by such an exposure means. Here, the color separator 15 includes a blue filter 15B, a green filter 15G, and a red filter 1 according to each color separation.
It consists of 5R and ND filter 15N, and these filters are rotated to separate the colors of light. The surface of the photosensitive drum 1 is cleaned in advance by a blade cleaner 31, and the influence of the previous latent image is removed by a pre-exposure lamp 33 and a pre-static eliminator 35. Next, the photoreceptor surface is uniformly charged by a primary charger 37 to have a uniform potential. This charged photoreceptor surface is transferred to a secondary charger 1 along with the optical image of the original.
The static electricity is removed by 9, and then the entire surface exposure lamp 3
9, the entire surface is uniformly exposed, and a high contrast electrostatic latent image is formed on the surface of the photoreceptor. The drum 1 is placed between the entire surface exposure lamp 39 and the developing device 41.
The intensity of the electrostatic latent image, that is, the electrostatic potential, is detected by an electrometer probe 43 placed near the surface of the electrostatic latent image. The developing device 41 consists of a yellow developing device 41Y, a magenta developing device 41M, a cyan developing device 41C, and a black developing device 41B, and each color developer (toner) is
is supplied for development. Transfer paper 51 placed in a cassette is sent to a transfer section 55 by a delivery roller 53.
In the transfer section 55, first, the gripper 57 grips the leading edge of the transfer paper 51. Transfer paper 51 held
Then, the developed image on the photoreceptor surface of the photoreceptor drum 1 is transferred by the transfer corona discharger 59 from the back side of the paper by corona discharge. In the case of monochrome copying, the separation claw 63 is activated immediately after the static electricity is removed by the separation static eliminator 61.
The transfer paper 51 is separated from the transfer section 55. In the case of multi-color copying, the grippers 57 of the transfer section 55 are not released and the separation claws 63 are not operated until the transfer paper 5 is completely transferred.
Keep 1. After the transfer is completed, release the separation claw 63
The transfer sheet 51 is separated from the transfer section 55 by the operation of the transfer sheet 51, and is sent to the heating roller fixing device 67 by the conveyor belt 65, where the image is fixed. Transfer paper 51 after fixing
is discharged onto the tray 69. After the transfer is completed, the toner remaining on the surface of the photosensitive drum 1 is cleaned by a blade cleaner 31 in preparation for the next copying cycle. FIG. 4 is a sectional view showing a schematic configuration of the secondary charger 19 shown in FIG. 2. FIG. As shown in the figure, groups of wires are arranged in the openings of the secondary charger 19 on the photosensitive drum 1 side, close to the surface of the photosensitive drum 1 and hidden therein. The respective wire groups are designated as negative grid 191, zero grid 193, and positive grid 195. These grid biases are negative grid 191, zero grid 193,
Positive grid 195 is -50 to -300V, respectively.
0V (ground), +50 to +200V. Here, the color balance of a color copy image will be explained. As shown in the first quadrant of Figure 1,
It is assumed that the image densities (color filter densities) of cyan, magenta, and yellow are made different from each other. The image density of magenta should be located between cyan and yellow, and in terms of color balance, the image density of cyan and yellow must be considered with the image density of magenta as the center. For color balance, the image density ratio of cyan to magenta should be in the range of 1.5: to 1:1, preferably
The ratio is around 1.2:1. The magenta to yellow image density ratio is in the range of 1:0.9 to 1:0.6, preferably around 1:0.8. For example, if the maximum image density of magenta is 1.2, the maximum image density of cyan that is suitable for color balance is 1.44, and the allowable range is
It is between 1.8 and 1.32. The maximum image density for yellow is 0.96, and the allowable range is between 1.08 and 0.72.
In this way, the tolerance range for cyan image density is higher than the center value, and the tolerance range for yellow image density is lower than the center value. Therefore,
Even if the initial development characteristics are ideal as shown in the fourth quadrant of FIG. It is convenient to shift them slightly so that >green >blue. For example, in the third quadrant of FIG. 1, the potential of the non-exposed portion of the latent image (dark potential) V _D is approximately 380 (V) in red, green, and blue. For example, 400 (V),
If the voltages are made different such as 380 (V) and 360 (V), it is effective to overcome problems such as fluctuations in development characteristics or problems with accuracy in automatic control of surface potential. In the apparatus according to the embodiment of the present invention, there are three potential setting levels: dark areas during full color copying (illumination lamp 5 is turned off), intermediate density areas (lamp 5 is turned on at an intermediate voltage), and bright areas (lamp 5 is set to the maximum rating). V DO and V _DO , respectively.
Set V _WLO and V _SLO as shown in Table 1 below.

[Table] FIG. 3 is a block diagram of a circuit that controls the potential. In the figure, a chopper disk 101 for detecting the rotation angle of the photosensitive drum 1 outputs a drum clock pulse 105 corresponding to the rotation angle from a photo interrupter 103. This clock pulse 105 is counted by the main sequence controller 107 of the present copying apparatus, and controls information signals necessary for copying, such as the set number of copies. The controller 107 supplies the potential control microcomputer 109 with timing signals necessary for switching high voltage and halogen light intensity, and measurement timing signals of the dark potential V _D , intermediate density potential V _WL , and light potential V _SL . . The latent image potential detected by the surface electrometer probe 43 is measured by the surface potential measurement circuit 111 as a potential of 1/300 of the surface potential, and
After being digitally converted by the converter 113, the signal is supplied to the computer 109. computer 109
performs calculations according to a control formula so that the measured potential value converges to the target value selected by the switch board 115. The signal resulting from the calculation is supplied to the DA converter 119 via the bus line 117 and converted into analog. Each analog-converted signal is supplied to high voltage control circuits 121, 123, 125 and mix circuit 127. Also computer 10
9 is the control signal 1 to the analog multiplexer 129
31 and switches the image fine adjustment signal 135 from the fine adjustment board 133 to the high voltage control circuits 121 to 125.
and mix circuit 127. Analog signals 137I, 137G, 137V obtained from high voltage control circuits 121, 123, 125
Addition voltage signal 139 of and image fine adjustment signal 135
I, 139G, 139V is high voltage transformer 14
1, 143, and 145, respectively, and then supplied to the primary charger 37, the negative grid 191 of the secondary charger, and the secondary charger 19, respectively. Thereby, the primary charging current I ₁ , the negative grid voltage V _G- and the secondary charging voltage V ₂ are controlled. Also, mix circuit 1
A mixed signal 139H of an analog signal 137H based on 27 and an image fine adjustment signal 135 is supplied to a halogen control circuit 155 to control the halogen voltage V _Hl applied to the illumination (halogen) lamp 5. Also,
Computer 109 supplies digital signals to I/D driver 161 via bus line 117. This I/O driver 161 performs digit scanning of the 7-segment, 8-digit display 163, and converts the display signal 165 from the computer 109 into a BCD-
The signal is input to a 7-segment driver 167, and the output signal 169 is used to display the surface potential of the photosensitive drum on the display 163. Further, the diode switch board 171 is scan-controlled via the I/O driver 161 to sequentially and individually select the target values set on the switch board 115. The voltage signal of the selected target value is sent to the computer 109, and calculations are performed according to individual control formulas (described later) to converge to these target values. The signals based on the target values converged by these computers 109 are converted into analog signals by the D/A converter 119, and each of the analog-converted voltage signals is sent to each of the high voltage control circuits 121 to 125 and the mixer circuit 127. Supplied. Let's look at the control sequence of the control circuit shown in FIG. Before activating this control circuit, the operator of the copying machine performs the following operations. Place a blank sheet of paper (transfer paper) on the document table glass 3. Set the aperture on the copying machine to “5”
(Standard). Next, a target value is set using a target value setting initial switch (connected to the switch board 115) provided outside the copying machine. After performing these operations, a control button (not shown) is pressed to activate the control circuit. The control operation is performed according to the flowchart shown in FIG. First, the power to the potential control circuit is turned on (block 401). Next, potential cleaning is performed by pre-rotating the photosensitive drum 1 (block 403).
In this state, the document illumination lamp 5 is turned on with the potential V _Hl set to the maximum rated voltage, and the amount of light emitted from this lamp 5 is maximized. The color separator 15 is set as a filter so that the original image light having the maximum amount of light passes through the ND filter 15N of the color separator 15. The photosensitive drum 1 is rotated once to expose the surface of the photosensitive member. With the electrometer probe 43, the photosensitive drum 1
Detecting the bright area potential V _SL on the surface of the photoreceptor,
The detection signal is supplied to the potential measuring circuit 111 to measure the bright area potential _VSL (block 405).
This measured light area potential V _SL and the target value of the light area potential
The difference from V _SLO (|V _SL V _SLO |) is the tolerance (C ₁ )
It is determined whether it is within (block 407). If the determination is negative, the secondary charging voltage of the secondary charger 19
V ₂ is controlled according to the control equation ΔV ₂ =δΔV _SL (block 409). Then, the process returns to block 405 and repeats the operation. Blocks 405 and 40 are continued until the bright area potential V _SL obtained again by the secondary charging voltage V ₂ controlled by block 409 falls within the tolerance C ₁ and converges to its target value V _SLO .
The operations at 7 and 409 are repeated. If the error is _within the tolerance C1 and a positive determination is made in block 407, the color separator 15 is rotated and the blue filter 15B is set so that the original image light passes therethrough (block 411). In this step, the filter is switched in the order of green, red, ND, green, and red. The illumination lamp 5 is turned off and the photosensitive drum 1 is rotated once without exposing the original. The surface potential of the photoconductor surface of photoconductor drum 1 is the dark area potential V _D
Therefore, this dark potential V _D is detected and measured by the electrometer probe 43 (block 41
3). This measured dark potential V _D and its target value
It is determined whether the difference from _VDO is within the tolerance _C2 (block 415). If this judgment is negative,
The primary charging current I ₁ of the primary charger 37 is controlled by the control formula △I ₁
= αΔV _D (block 417).
Thereafter, the process returns to block 413 and repeats the operation. When the dark potential V _D converges to its target value V _DO within the tolerance C ₂ , the determination at block 415 becomes affirmative, exiting the loop and proceeding to the next operation. The illumination lamp 5 is emitted at the maximum rated voltage to maximize the exposure amount of the original. The photosensitive drum 1 is rotated and the surface of the photosensitive drum 1 is exposed to the maximum amount of light. In this state, the bright area potential _VSL , which is a surface potential, is detected and measured by the electrometer probe 43 (block 419). The difference between the measured bright area potential V _SL and its target value V _SLO (|V _SL − V _SLO |) is the tolerance C ₃
It is determined whether it is within the range (block 421). If the determination is negative, the negative grid voltage V _G- of the negative grid 191 in the secondary charger 19 is set using the control formula △V _G- =
Control according to β ₁ △V _D + β ₂ △V _SL (block 4
23). The process then returns to block 419 to repeat the loop. If the bright area potential V _SL converges to its target value V _SLO within the tolerance C ₃ , an affirmative determination is made in block 421 and the loop exits. The illumination lamp 5 is turned on with an intermediate halogen voltage V _Hl , and the original exposure amount is set to the standard light amount. Under such an amount of light, the photosensitive drum 1 is rotated to expose the surface of the photosensitive member. The potential on the surface of the photoreceptor becomes the intermediate density region V _WL , and this potential V _WL is measured by the electrometer probe 43 and the potential measuring circuit 111 (block 425). This measured intermediate concentration potential
The difference between V _WL and its target value (|V _WL − V _WLO |) is
It is determined whether the error is within the tolerance _C4 (block 427). If the judgment is negative, the halogen voltage V _Hl for lighting the illumination lamp 5 is controlled by the control formula △V _Hl = γ△
V _WL (block 429). The process then returns to block 425 to repeat the loop.
The intermediate concentration potential V _WL has a tolerance to its target value V _WLO .
If it converges within _C4 , an affirmative determination is made in block 427 and the loop exits. Through such an operating procedure, the primary charging current I ₁ , the negative grid voltage V _G- and the halogen voltage V _Hl in the blue filter 15B are controlled and set based on blocks 411 to 427. Next, it is determined whether the set filter in the color separator 15 is the last one (block 43).
1). In this case, since the judgment is negative, block 4
Return to 11. At block 411, blue → green → red →
The color separator 15 is rotated in the order of ND → green → red to switch and set the filter. Each time a filter is set, operations in blocks 413 to 429 are performed to control and set the primary charging current I ₁ , negative grid voltage V _G- and halogen voltage V _Hl in that filter. Such a loop operation is repeated, and when the control of each voltage for the last filter is completed, an affirmative determination is made in block 431, and the control operation of the control circuit is completed. In this way, the three colors blue, green, red,
The voltage relationship is set so that the surface potentials based on black and white and two colors of magenta and black are set to predetermined values. And under the set control voltage relationship,
The image of the original placed on the original table glass 3 is copied in color onto the transfer paper 51. Further, it is preferable to provide, for example, a changeover switch outside the copying apparatus so that the three colors of blue, green, red, black and white, and the two colors of magenta and black can be individually set to several levels. In the case of this example device, the first
As shown in the table, it is possible to switch settings in three stages. Each potential converges to the target value set in this manner. Note that the measurement of the bright area potential _SL and intermediate density area potential V _WL in blocks 405, 419, and 425 is as follows.
This is performed after the transfer paper is placed on the document table glass 3 and the document is scanned at the same speed as in normal copying to form a potential. Further, the coefficients γ, δ, α, β ₁ and β ₂ of each control equation shown in FIG. 5 indicate the slope of the function based on each relational equation. As shown in the flowchart in Figure 5, the secondary charging voltage
The reason why V ₂ is controlled prior to the grid 19 voltage V _G-, which is the grid bias voltage of the secondary charger 19, will be described. Refer to the configuration of the secondary charger 19 in FIG. 4. The distance between the wires of grids 191 to 195 and the surface of photosensitive drum 1 is usually 1.0±0.1mm.
It is. Within this distance tolerance, for example, if the voltage applied to the discharge wire of the secondary charger 19 is -8.5KV, and the voltages applied to the grids 191, 193, and 195 are -120V, 0V, and 100V, respectively, the bright area potential
V _SL varies within the range of -120±30V. Therefore, the secondary charging voltage V ₂ is first controlled so as to offset variations between devices and obtain a constant bright area potential V _SL with a constant grid bias voltage. Thereafter, a negative grid voltage V _G- , which is a bias voltage of the negative grid 191, is applied to perform the gradation control method proposed by the present applicant in the specification of ``Electrophotography Method and Apparatus'' in Japanese Patent Application Laid-Open No. 54-14237. Based on light potential
This controls _VSL . As described above, the target values set on the switch board 115 are set in stages (three stages in the above example). Therefore, there are steps between the target values, and it is impossible to set the target values to a value intermediate between them. To make this possible, the fine adjustment board 133
has been established. The fine adjustment board 133 is provided with a volume corresponding to each of the three colors, blue, green, red, and black and white, which are linked with knobs so that they can be adjusted from the outside of the device. These fine adjustment boards 13
The image fine adjustment signal 135, which is a voltage signal adjusted with a volume of 3, controls the output of the high voltage control circuits 121 to 125 or the mixer circuit 127 by switching the multiplexer 129. In response to this fine adjustment signal 135, the halogen voltage V _Hl , the primary charging current I ₁ , the negative grid voltage V _G- , the secondary charging voltage V ₂ , and even the positive grid voltage (supplied to the positive grid 195 shown in FIG. 4) voltage (although its supply and control system are not shown). It should be noted that potential-related control that takes into account the fine adjustment to the target value is also performed by the operation shown in the flowchart shown in Figure 5. That is, the light area potential V _SL and the intermediate density potential are set at the switch board 115.
Each target value V _SLO of V _WL and dark potential V _D ,
V _WDO and V _DO are set, and the operations of blocks 405, 407 and 409 shown in FIG. Next, the fine adjustment signal 135 is sent to the high voltage control circuit 123.
The operations of blocks 413, 415, and 417 are executed with the current supplied. In addition, the fine adjustment signal 13
5 is supplied to the high voltage control circuit 121, the operations of blocks 419, 421 and 423 are as follows:
Then, while the fine adjustment signal 135 is being supplied to the mix circuit 127, the operations of blocks 425, 427 and 429 are executed, respectively. In this way, the secondary charging voltage V ₂ , the primary charging current I ₁ , the negative grid voltage V _G- and the halogen voltage V _Hl can be set under the desired target value + fine adjustment surface potential relationship. Therefore, by setting the volume of the fine adjustment board 133, the potential relationship can be set and controlled linearly even between target values. Further, since the operation shown in FIG. 5 is performed for each color, fine adjustments can be made individually for each color.
Thereby, it is possible to look at the original and copy an image with each color emphasized according to preference. Referring again to FIG. 3, when the mode changeover switch 203 is turned to the contact F side to set the fully automatic mode, the surface potential is automatically set to the desired value including fine adjustment as described above. When the switch 203 is turned to the contact S side, a mode selection signal 205 is supplied to the computer 109,
Set the potential control circuit to semi-automatic mode. In this mode, first, target values of surface potential (V _DO , V _WLO , V _SLO ) are set in stages on the switch board 115.
Then, the voltage relationship is determined according to the flowchart shown in FIG. However, automatic control with addition of fine adjustment is not performed. Next, the control signal 131 is sent to the multiplexer 1.
A voltage fine adjustment signal 135, which is individually manually adjusted by the volume of the fine adjustment board 133, is switched and supplied to the high voltage control circuits 121 to 125 and the mix circuit. Then, the analog signals 137I, 137G, 137V when the previous target value converged
And fine adjustment signal 135 by manual setting to 137H
The voltages V G- , V 2 , V Hl and the current I ₁ are determined in the state where the voltages V _G- , V ₂ , V _Hl and the current I 1 are added. By placing an original to be copied on the original table glass 3 and copying it, a color image with appropriate color balance can be obtained on the transfer paper 51. You can adjust the strength of a particular color to your liking, and especially in semi-automatic mode, you can freely adjust the strength of a particular color even when copying by adjusting the fine adjustment volume. As described above, according to the present invention, the operating conditions of the image forming process are set for each color according to the surface potential of the dark or bright part of the photoreceptor after charging or neutralization and the target potential for each color. Since the set operating conditions can be adjusted independently for each color, it is possible to compensate for environmental fluctuations, photoreceptor deterioration, etc., and to obtain color images with proper color balance at all times. It is also possible to obtain a color image in which the strength of each color is adjusted according to preference.

[Brief explanation of drawings]

Figure 1 is a diagram showing the gradation reproduction characteristics of color copying.
FIG. 2 is a device configuration diagram showing an embodiment of an image forming apparatus according to the present invention, FIG. 3 is a block diagram of a control circuit in the device shown in FIG. 2, and FIG. 4 is a schematic configuration diagram of a secondary charger. FIG. 5 is a flowchart showing the operation of FIG. 3. 1...Photosensitive drum, 3...Original table glass, 5...
...Illumination lamp, 15...Color separator, 19...Secondary charger, 41...Developer, 43...Electrometer probe, 51...Transfer paper, 55...Transfer section, 59...
Transfer corona discharger, 67...Heating roller fixing device,
101... Chippad disk, 107... Main sequence controller, 109... Microcomputer, 111... Surface potential measurement circuit, 11
5...Switch board, 133...Fine adjustment board,
161...I/O driver, 163...display device,
171...Diode switch board, 203...
...Mode changeover switch.

Claims (1)

[Scope of Claims] 1. An electrophotographic means for forming a color image on a recording material by performing an image forming process for each color multiple times on a photoconductive photoreceptor, a dark area on the photoreceptor after being charged. Potential detection means for detecting a surface potential or a bright area surface potential on the photoreceptor after neutralization; A/D conversion means for converting an analog value output from the potential detection means into a digital value; and the A/D conversion means. The operating conditions for each color of the electrophotographic means are set so that the digital value corresponding to the dark area surface potential or the bright area surface potential outputted from the unit becomes a value corresponding to the target potential for each color. A control means that performs calculation according to a predetermined control formula and obtains a control value according to the result of the calculation; D/A conversion means that converts the control value obtained by the control means into an analog value; and the D/A conversion means. The image forming apparatus is characterized by comprising: a driving means for driving the electrophotographic means based on an analog value output from the electrophotographic means; and an adjusting means capable of independently adjusting the operating conditions of the electrophotographic means set by the control means for each color. color image forming device.