JPH0670726B2 - Color image forming device - Google Patents

Description

Description: TECHNICAL FIELD The present invention provides a high quality copy image when a latent image formed on a photoconductor is provided with a plurality of developing devices as in a color electrophotographic copying apparatus. And a color image forming apparatus.

[Prior art]

In an image forming apparatus such as a conventional color electrophotographic copying apparatus, it is difficult to adjust charging and exposure conditions for obtaining good color balance, and the electric resistance of the surface of the photoconductor on which a latent image is formed changes. Therefore, it is difficult to obtain a copied image that satisfies a stable color balance over a long period of time. The reason for this is due to environmental changes such as temperature and humidity or sensitivity deterioration of the photoconductor, and is caused by variations in latent image characteristics. Further, in order to obtain a good color balance, variations in physical properties of the developer due to manufacturing lots of cyan, magenta, and yellow developers (toners), or changes in properties due to deterioration of these developers over time, etc. It needs to be corrected. Therefore, conventionally,
The latent image forming conditions have been selected so that the latent image characteristics obtained by color separation into red, green, and blue have an appropriate relationship.

Figure 1 shows the indirect electronic copying system (hereinafter referred to as NP system).
It is a diagram showing latent image characteristics a for blue (B) light immediately after performing the above potential control using the CDS photosensitive drum and latent image characteristics b after repeating copying, where Do on the horizontal axis is the original. , And Vs on the vertical axis represents the surface potential of the photosensitive drum. The smaller Do is, the whiter it is, and the larger it is, the closer it is to black (darker), and the surface potential of the photosensitive drum changes in the white portion (Do is 0 to 0.5) of the document as shown in the figure when the copying is repeated. In this way, the potential of the part corresponding to the white part of the original changes, but the development of this change (decreased sensitivity) differs depending on the wavelength, and thus in a color copying machine that performs color separation exposure. However, there is a problem that the color balance changes with the fogging of the copied image.

The phenomenon in which the latent image potential changes will be described in detail.

FIG. 2 is a partially enlarged view showing the structure of the photoconductor applied to the above-mentioned NP system. C is a conductive substrate, D is a photoconductive layer such as CDS, and E is an insulating layer. In this configuration, direct current (DC)
When the primary charging is performed by the power source, the charges injected from the conductive substrate c remain at the boundary portion / adhesive portion between the photoconductive layer d and the insulating layer e. Then, when the secondary discharge simultaneous exposure by DC or AC (AC) having a polarity opposite to that of the primary charging in the next step is performed, the charges in the photoconductive layer D are released and flow to the conductive substrate C. At that time, the electric charge is gradually released according to the time constant corresponding to the resistance and the capacitance of the adhesive layer between the insulating layer E and the photoconductive layer D, and is propagated through the layer D by light to reach the conductive substrate C. Flow to. As described above, in the NP method, there is a phenomenon in which the surface potential gradually rises, and this potential shift may reach about 60 V 2 seconds after 2 seconds immediately after the whole surface exposure step. Therefore, the potential of the latent image formed on the photoreceptor is the passage of time,
That is, it gradually changes as the photoconductor rotates. Therefore, even if the potential after the latent image formation is the same, the potential at the development differs depending on whether the development position is near or far from the latent image formation position. If the sensitivity decrease due to the potential change described above is taken as a short-term sensitivity decrease, it is expected that a long-term sensitivity decrease will occur. That is, the short-term decrease in sensitivity occurs within a short time reaching each developing device under the same charging conditions, whereas the decrease in sensitivity caused by repeated copying is a long-term decrease in sensitivity. Is considered as follows. In the case of a short-term decrease in sensitivity, electric charges enter the adhesive part between the photoconductive layer d and the insulating layer e and are discharged with a certain time constant.
From the photoconductive property of the photosensitive layer, it can be seen as an impurity that traps charges. In the case of the NP method, the charges that have entered the adhesive portion, which is an impurity, are released by the simultaneous secondary charging exposure, and most of them are discharged according to a certain number with the above-mentioned short-term sensitivity decrease. The electric charge is strongly trapped by the bond as an impurity and becomes immobile. In other words, as the copying process was repeated, the number of items that were strongly trapped by the impurities and had a very long discharge time constant increased.
It is considered that long-term sensitivity deterioration occurs. In addition, some impurities are also contained in the photoconductive layer d forming the photosensitive layer, and the charges trapped by the impurities in the photoconductive layer d are also absorbed in the photoconductive layer d by the electric field of the charges themselves. It is believed that this affects the movement of moving electric charges, resulting in a decrease in sensitivity. Such a phenomenon of sensitivity decrease similarly occurs in a photoconductor such as OPC in which the photoconductor also has a layer structure.

As described above, when continuous copying is performed in the NP system, the surface potential rises from a to b in the white part of the document, and the rise may be about 30 V, as shown in FIG. . The latent image potential formed on the photoconductor gradually changes with the passage of time, particularly during continuous copying, even if the exposure amount and the charge amount, which are latent image forming conditions, are the same.

Therefore, even if a means for detecting the latent image potential is provided and the potential is controlled as described above, and the potential is controlled to an appropriate potential so that a copy image with good color balance can be obtained, the potential changes with the passage of time. Therefore, there is a problem that a proper development result cannot be obtained. Here, if the increase in the potential of the white portion of the original for each color separation light used in the color copying machine is the same amount, it is possible to predict the value and set the potential control condition in advance. The rate of decrease in sensitivity varies depending on the type of photoconductor used, and it also varies depending on the environment and other conditions, so it is difficult to predict the potential change, and therefore, there is the problem that a proper copy image cannot be obtained. is there.

[Object of the Invention]

The present invention has been made to solve the above problems, and an object of the present invention is to provide a color image forming apparatus that can obtain an optimum target potential and developing conditions regardless of the position of the developing unit for each color of the photoconductor. .

In detail, a photosensitive member on which latent images corresponding to respective color images are sequentially formed, a plurality of developing units corresponding to respective colors sequentially arranged in the moving direction of the photosensitive member, and a latent image of each color are formed. Latent image forming means for uniformly charging the photoconductor and removing charges on the photoconductor after charging by image light; and latent image forming means provided near the upstream side of the plurality of developing means in the moving direction, respectively. A plurality of potential detecting means for detecting the potential of the photoconductor, and the operating conditions of the latent image forming means are set so as to obtain different target potentials for each color, and according to each output of the plurality of potential detecting means. A potential control unit that controls the operating condition for each corresponding color, and the detection unit that respectively corresponds to the developing bias of the developing unit when forming the color corresponding to the developing unit on the downstream side immediately adjacent to the potential detecting unit. Bias controlled based on the output of It is intended to provide a color image forming apparatus and a control means.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

The layer structure of the photoconductor of the present invention may be a combination of the conductive substrate C and the photoconductive layer D shown in FIG. 2, or may be one having an insulating layer on the photoconductive layer D. In addition, if it has a characteristic that the potential changes, it also works effectively on a photoconductor having another layer structure.

Furthermore, as a structure for endless movement, a drum type or an endless belt type is generally used. Further, as a latent image forming means for forming a latent image on such a photoreceptor, a conventional electrophotographic method such as a corona discharger or an exposure optical system for forming an original image on the photoreceptor is used. Means available. As the developing means formed on the photoreceptor, the soft developing method and the wet developing method can be applied. On the other hand, the latent image potential control unit controls the operation of the latent image forming unit based on the potential of the photoconductor detected by the latent image potential detection unit.
For example, the amount of exposure is changed, or the voltage applied to the charger is changed.

In the present invention, among the plurality of developing devices, a latent image having a predetermined potential is formed on the photoconductor in consideration of the position of the developing device to be used, and as in the conventional case, regardless of the number of developing devices, There is no adverse effect caused by a change in the latent image potential caused by the position of the developing device, which occurs when the potential is set based on a single potential detecting means. In other words, considering the position of the developing device used, the latent image can be formed in a state in which the potential change of the latent image up to this position is corrected. Therefore, the latent image formed from the same original should be well developed. Is possible. Further, during continuous copying, the latent image potential due to the standard density document provided in front of the document table is detected by the latent image potential detecting means arranged adjacent to each developing device and compared with the latent image potential during potential control. ,
Comparison correction means is provided for applying a bias potential corresponding to the potential difference to the developing device. As a result, it is possible to suppress the gentle fluctuation of the latent image potential that appears during continuous copying. For this purpose, the potential detecting means should be arranged upstream of the developing device in the moving direction of the photoconductor. It is preferable to detect the latent image potential due to the standard density original document provided at the front end of the original table and compare the potential with the potential at the time of potential control to apply a bias potential to the developing device. This is because it is preferable to arrange it on the upstream side.

Further, if the present invention is applied to a color electrophotographic copying machine,
Since the latent image for each color can be developed under the most preferable conditions by the developing device for each color, the color balance of the final color image can be improved. Further, even in a black-and-white copying apparatus having a developing device for halftone and a developing device for obtaining an edge effect such as characters, the latent image potential is set based on the potential in the vicinity of the selected developing device. It is possible to maintain high image quality.

Hereinafter, the present invention will be described in more detail with an example of a color electrophotographic copying apparatus using the NP process.

FIG. 3 is a structural explanatory view of a color electrophotographic apparatus to which the present invention is applied.

In the figure, the photosensitive drum 1 rotating in the a direction is composed of a conductive layer, a CDS photoconductive layer and a surface insulating layer. A document to be copied is placed on the platen glass 3, and the document is illuminated by an illumination lamp 4. The scanning mirrors 5 and 6 for scanning the original scan the original in synchronism with the rotation of the drum 1, and the mirrors 5 and 6 respectively move to the chain line position, and at the same time, the illumination lamp 4 also moves to the chain line position. An optical image of the scanned original is imaged on the surface of the photosensitive drum 1 via the lens 7, the mirror 8, the color separation device 9 and the mirror 10, and further via the secondary charger 11 for simultaneous exposure and neutralization. Here, the color separation device 9 of the optical system uses a blue filter according to each color separation color.
It consists of 9B, green filter 9G, red filter 9R and ND filter 9N. These filters are sequentially rotated and switched to perform color separation of light respectively.

The surface of the photoconductor of the photosensitive drum 1 is previously cleaned by a cleaning device 13 using a blade plate, and a pre-exposure lamp 14 and a pre-electrification device 15 remove the influence of the previous latent image.
Next, the primary charger 16 uniformly charges the surface of the photoconductor to a uniform potential. The charged surface of the photoconductor is neutralized by the secondary charger 11 together with the light image of the original, and then uniformly exposed by the lamp 12 for full-surface exposure, so that the surface of the photoconductor has a high contrast. A latent image is formed.

The color-separated latent images sequentially formed on the photosensitive drum are
It is developed by a developing device corresponding to each latent image. The developing devices 17 sequentially arranged on the downstream side of the lamp 12 are yellow developing devices 17
It consists of Y, magenta developing unit 17M, cyan developing unit 17C and black developing unit 17B, and supplies each color developer (toner) to develop the latent image on the drum 1.

On the other hand, the transfer paper 18 placed in the cassette is sent out by the delivery roller 19
And send in the direction of the transfer section 20. In the transfer section 20, the grip 22 on the drum 21 first grips the front end of the transfer paper 18. The developed image on the photosensitive drum 1 is transferred to the gripped transfer paper by the electric field of the transfer corona discharger 23.

Separate static eliminator for single-color copying by each of the above developing devices
Immediately after the charge is removed by 24, the transfer paper is separated from the transfer drum 21 by the operation of the separation claw 25. In the case of multicolor (color) copying, the gripper 22 of the transfer drum 21 is not opened until the transfer of the developed image of the two or three colors to be reproduced is completed, and the separation claw is used.
The transfer paper 18 is held without operating 25. When the transfer is completed, the transfer paper is separated from the transfer drum 21 by the operation of the separation claw 25, and the transfer belt 26 sends the transfer paper to the heating roller fixing device 27 to fix the transfer image. The transfer paper after the fixing is discharged to the tray 28.

In the above copying apparatus to which the present invention is applied, the photosensitive drum 1
In order to form a latent image of a predetermined potential on the top, a potential sensor 29, which is a potential detecting means, is arranged on the upstream side in the moving direction of the photoconductor of each developing device. That is, a sensor 29Y is provided for the yellow developing device 17Y, a sensor 29C is provided for the cyan developing device 17C, a sensor 29M is provided for the magenta developing device 17M, and a sensor 29B is provided for the black developing device 17B. Thus, for example, in order to control the latent image developed by the yellow developing device to a predetermined potential, it is determined based on the detection result by the sensor 29Y, and the latent image to be developed by the black developing device is determined based on the detection result by the sensor 29B. .

As described above, even when developing with a developing device located at a different position from the latent image completion position, the potential control can be performed in consideration of changes in the latent image potential up to each developing device. Potential control becomes possible.

Specific examples of potential control will be described below with reference to the drawings.

In the apparatus of the embodiment of the present invention, the dark portion (lighting lamp 4 is turned off), the intermediate density portion (lamp 4 is turned on at an intermediate voltage), and the bright portion (lamp 4 is maximum) at the time of full-color copying for three potential setting levels The target value potential of lighting at the rated voltage) is set as V _DO , V _WLO, and V _SLO , respectively, as shown in Table 1 below.

FIG. 4a is a block diagram of a potential control circuit according to an embodiment of the present invention. In the figure, the photo-interleaver 31 outputs a drum clock pulse according to the rotation angle by the rotation disk 30 for detecting the rotation angle of the photosensitive drum 1. This clock pulse is counted by the main sequence controller 32 of this copying machine, and the information necessary for copying,
For example, an information signal such as the set number of sheets is controlled. With this sequence controller 32, the timing signal necessary for switching the high voltage and the halogen light amount to the potential controlling micro computer 33, the measurement timing of the dark potential V _D , the intermediate density potential V _WL and the bright potential V _SL are measured. Supply a signal.

The latent image potential detected by each sensor 29, which is each surface electrometer probe, is measured as a potential of 1/300 of the surface potential by the surface potential measuring circuit 34, digitally converted by the AD converter 35, and then Supplied to computer 33. The computer 33 performs calculation according to a control formula so that the measured potential value converges to the target value selected by the switch board 36.

The signal of the calculation result is supplied to the DA converter 38 via the bus line 37 and converted into an analog signal. The analog-converted signals are supplied to the high-voltage control circuits 39, 40, 41 and the mix circuit 42. Further, the computer 33 sends a control signal to the analog multiplexer 43 to switch the image fine adjustment signal from the fine adjustment board 44 and supply it to any or all of the high voltage control circuits 39 to 41 and the mix circuit 42. In the high-voltage control bottleneck 39 to 41, the added voltage signal of the analog signals I, G, V obtained from the D / A converter 38 and the image fine adjustment signal
I, G, and V are boosted through high-voltage transformers 45, 46, 47, respectively, and then the primary charger 16, the negative grid of the secondary charger, and the secondary charger 11
Is supplied to each.

As a result, the primary charging current I ₁ , the negative grid voltage V _G-, and the secondary charging voltage V ₂ are controlled. In addition, the mix circuit 42
In, the mixed signal of the analog signal H from the D / A converter 38 and the image fine adjustment signal is supplied to the halogen control circuit 48 to control the halogen voltage V _H1 applied to the illumination (halogen) lamp 4. In addition, computer 3 is bus line 3
A digital signal is supplied to the I / O driver 49 via 7. With this I / O driver 49, 7 segment 8 digit display 50
Scanning the digit and displaying the display signal from the computer 33 to BCD.
It is input to the -7 segment driver 51, and the display unit 50 displays the surface potential of the photosensitive drum by the output signal. Also,
The diode switch board 52 is scan-controlled via the I / O driver 49, and the target values set in the switch board 36 are sequentially and individually selected. The voltage signal of the target value that has been selected and set is sent to the computer 33, an operation is performed according to each control formula (described later), and the target value is converged.

The signal according to the target value converged by these computer 33 is converted into an analog signal by the D / A converter 38,
The analog-converted voltage signals are converted into high-voltage control circuits 39, 4
0, 41 and the mix circuit 42, respectively.

The control sequence of the control circuit shown in FIG. 4a will be described below. Before operating the control circuit, the operator of the copying machine performs the following operations. First, a blank sheet (transfer sheet) is placed on the platen glass 3. Set the aperture on the copying machine to "5" (standard), which is the number at the center of the scale. Next, it is connected to the switch board 36, and the operation unit (not shown) of the copying machine.
The target value is set by the changeover switch for setting the target value provided in. After performing such an operation, a control button (not shown) is pressed to activate the control circuit.

The control operation is performed according to the flow chart shown in FIG.

First, the power supply of the potential control circuit is turned on (block 53).
Next, during the pre-rotation of the photosensitive drum 1, the drum surface is uniformly charged by the charger 15 to perform potential cleaning (block 5).
Four).

In this state, the illumination lamp 4 for the original is turned on with the voltage V _H1 as the maximum rated voltage, and the amount of light emitted from the lamp 4 is maximized. The color separation unit 9 is set to a filter so that the original image light having such a maximum light amount passes through the red filter 9R of the color separation unit 9. Here, the secondary charging voltage V ₂ is changed according to the block diagrams 54 to 56 of the block diagram of FIG.
Grid bias voltage _G- of the secondary charger 11 determined by 4,65
The reason for controlling prior to the decision of is described.

In the configuration of the secondary charger 11 of FIG. 4b, the grids 11a, 11
The distance between the wire b and the surface of the photosensitive drum 1 is usually 1.0 ± 0.
It is 1 mm. Within the tolerance of this distance, for example, the secondary charger 1
The discharge wire applied voltage of 1 is -8.5KV, and the grid 11a, 11
When the applied voltage of b is −120V and 0V respectively, the bright part potential
V _SL changes within the range of −120V ± 30V.

Therefore, the secondary charging voltage V ₂ is controlled so as to cancel the variation between the devices and obtain a constant bright portion potential V _SL with a constant grid bias voltage. Also at this time,
The red filter 9R is used because the CDS of the photoconductor used in the embodiment of the present invention has the least sensitivity to red, so that the red potential V _SL can be taken even for this red. The secondary charging voltage V ₂ is determined using the filter 9R.

While exposing the photosensitive drum 1 with the reflected light of the white original that has passed through the set filter, this drum is rotated once to form a latent image. At this time, the potential sensor 29C detects the bright portion potential V _SL on the surface of the photoconductor of the photosensitive drum 1 and supplies the detection signal to the potential measuring circuit 34 to measure the bright portion potential V _SL (block 55). This measured bright part potential V _SL
It is determined whether the difference (| V _SL −V _SLO |) between the light _source potential and the target value V _SLO is within the allowable error (C ₁ ) (block 56).
If the determination is negative, the secondary charging voltage V ₂ of the secondary charger (the connected high-voltage transformer has a constant voltage characteristic) 11 is controlled according to the control formula ΔV ₂ = δΔV _SL (block 57).
Then, the operation returns to the block 55 and the operation is repeated. Blocks 55, 56 and 57 are adjusted until the bright portion potential V _SL obtained again by the secondary charging voltage V ₂ controlled by the block 57 falls within the tolerance C ₁ and converges to its target value V _SLO. Repeat the circulating operation. If the result of block 56 is affirmative because the error is within the allowable error C ₁ , the color separator 9R is rotated to set the blue filter 9B so that the original image light of the set light amount is transmitted. (Block 58).

At this time, since the developing device 17Y is used for the latent image on the photosensitive drum,
The potential sensor to measure the latent image of this drum is from 29C to 2
Switch to 9Y.

FIG. 6 shows one means for switching the detection sensor, and is an enlarged view of a part of FIG. 4a.

Each sensor 29Y, 29M, 29C, 29B has a potential measurement circuit 3
One potential measuring circuit is composed of 4Y, 34M, 34C and 34B and A / D converters 35Y, 35M, 35C and 35B which receive the level-adjusted analog output in this circuit and convert it into a digital signal. The digital output of the A / D converter 35 is connected to different ports 59 of the multiplexer. The potential control microcomputer 33 can output a control signal for designating each port from the signal line A and take in the output of the potential sensor corresponding to each filter as data. For example, when the blue separation filter 9B is set, the sensor is linked with this setting signal.
The port 59Y to which the output of 29Y is connected is specified, and its digital output is input to the potential control microcomputer 33. And when the filter 9B is converted to 9G,
Similarly, sensor 29M is designated for potential detection (block 60).

In this way, it is possible to specify the potential sensor 29 corresponding to the color of the filter set in the optical path and read the measurement result by the specified specific sensor. Similarly, the above control is continued for the filters 9G and 9B.

That is, the potential sensor corresponding to the color of the filter is configured to measure the surface potential of the photosensitive drum 1, and thus the potential of the bright portion can be measured corresponding to the color of the filter. And the filter 9R is a sensor
It corresponds to 29C, 9G corresponds to sensor 29M, and 9B corresponds to 29Y. That is, the color complementary to the color of the filter becomes the color of the developing device.

Next, the setting of the target value of the dark portion will be described. The lamp 4 is extinguished, and the photosensitive drum 1 is rotated once without exposing the original image to form a latent image. The surface potential of the photoreceptor surface of the photosensitive drum 1 from the dark potential V _D, measured by'm connexion detect this dark portion potential V _D to the potential sensor 29Y (block 6
1). It is determined whether or not the difference between the measured dark area potential V _D and its target value V _DO is within the allowable error C ₂ (block 6
2). If this determination is negative, the primary charging current I ₁ of the primary charger (the connected high voltage transformer has a constant current characteristic) 16 is controlled according to the control formula ΔI ₁ = αΔV _D (block 63). Then, the operation is repeated by returning to block 61. When the dark area potential V _D converges to the target value V _DO within the allowable error C ₂ , the determination at block 62 becomes affirmative and the loop is exited to move to the next operation.

The illumination lamp 4 emits light at the maximum rated voltage to maximize the document exposure amount. The photosensitive drum 1 is rotated to expose the surface of the photosensitive member with the maximum amount of light. In that state, the light sensor voltage V _SL, which is the surface potential, is detected and measured by the potential sensor 29Y (block 64). It is determined whether or not the difference (| V _SL −V _SLO |) between the measured bright portion potential V _SL and its target value V _SLO is within the allowable error C ₃ (block 65). If If a negative decision, negative grids voltage V _G-the negative grids in the secondary charger 11 (the transformer is connected with the constant voltage characteristics), controlled _{ΔV G- = β 1 Δ D +} β 2 ΔV SL Control (block 66). Then, the process returns to the block 64 and the above loop operation is repeated. The light portion potential V _SL has a tolerance C _{3 of} its target value V _SLO.
If it converges within, a positive determination is made at block 65 and the loop is exited.

Turn on the illumination lamp 4 with the intermediate voltage halogen voltage V _H l,
The exposure amount of the original is 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 photoconductor becomes V _WL , which is the intermediate density portion.
_WL is measured by the potential sensor 29Y and the potential measuring circuit 34 (block 67). It is determined whether or not the difference (| V _WL −V _WLO |) between the measured intermediate concentration portion potential V _WL and its target value is within the allowable error C ₄ (block 68). If a negative determination is made, the halogen voltage V _H1 for lighting the illumination lamp 4 is controlled according to the control formula ΔV _H1 = γΔV _WL (block 69). Then, the process returns to block 68 and the above loop operation is repeated. If the intermediate density portion potential V _WL converges to the target value V _WLO within the allowable error C ₄ , a positive determination is made at block 68 and the loop is exited. Thus, according to the operating procedure, the primary charging current I ₁ , the negative grid voltage V _G−, and the halogen voltage V _H1 in the blue filter 9B are controlled and set based on the blocks 58 to 68.
Next, it is determined whether or not the set filter in the color separator 9 is the last one (block 70). In this case, since the determination is negative, the process returns to block 58. At block 58, the color separator 9 is rotated in the order of blue → green → red → ND to switch and set the filters. Blocks 61 to 69 are operated each time the filter is set, and the primary charging current I ₁ , the negative grid voltage V _G-, and the halogen voltage V _H1 in the filter are controlled and set.

When such a loop operation is repeated and the control of each voltage is completed for the last filter as well, an affirmative determination is made at block 70, and the control operation of the control circuit is completed.

In this way, the voltage relationship is set so that the surface potentials based on the three colors of blue, green, red, black and white and the two colors of magenta and black are set to predetermined values. Then, the image of the document placed on the document table glass 3 is color-copied onto the transfer paper 18 under the set control voltage relationship.

It should be noted that, for example, a switching switch may be provided outside the copying apparatus so that three colors of blue, green, red, black and white, and two colors of magenta and black can be individually set in, for example, three stages. In the case of the device of this example, as shown in Table 1, it is possible to switch and set in three stages. The electric potentials converge to the target values thus set.

The light potential V _SL and the intermediate density potential V _WL of the blocks 55, 64, and 67 were measured at the same speed as a normal copy with a white transfer paper placed on the platen glass 3. This is performed after scanning and potential formation. Further, the coefficients δ, α, β ₁ and β ₂ γ of each control equation indicate the slope of the function according to each relational expression.

In this way, by setting the surface potential on the surface of the photoconductor of the photosensitive drum 1 for each color separation exposure with the transfer paper or the like placed on the platen glass 3, an appropriate color balance is automatically obtained. .

After that, if the original to be copied is placed on the original platen glass 3 and copied, a copied image can be obtained on the transfer paper 18 under an appropriate color balance.

Next, the photoreceptor 1 during continuous copying, which is a feature of the present invention,
The control for correcting the decrease in sensitivity will be described in detail.

The latent image potential of the standard density document provided on the front edge of the document table is detected prior to development for each color, and this potential is compared with the potential during potential control, and the potential corresponding to the potential difference is used as the bias potential for the developing device. In addition. Explaining FIGS. 3 and 4 (a), first, when the copy start button (not shown) is pressed, the document is placed on the front edge of the document table prior to the color separation exposure of the three colors B, G and R of the document. The white plate as a standard density original document provided is exposed. The latent image on the photosensitive drum 1 corresponding to the exposure of the white plate is located at the tip of the color separation latent image of the document.
Then, as the photosensitive drum 1 rotates, when passing through a surface electrometer (sensor 29) arranged upstream of the developing device for each color, the electrometer is switched for each color and the surface potential is read. Further, after the surface potential is automatically controlled, the latent image potential of the white plate is stored in the memory in the potential control microcomputer 33 at the first copy. After that, copying is repeated, but the potential control microcomputer
33 reads the latent image potential of the white plate portion during each color separation exposure while sequentially switching the potential measuring circuit 34, and compares the value of this potential with the value recorded in the potential control microcomputer 33. , The potential difference is the D / A converter 100
Then, via each potential control unit 101Y, 101M, 101C, 101B, it is applied as a bias potential to each developing unit 29.

FIG. 7 is a flow chart of potential control during copying.

In FIG. 7, copying is started at 71, and the primary charging output is judged at 72. If it is the primary charging output, the block 73 outputs the primary charging control value, and if not, the primary charging output is turned off (block 74). Regarding the secondary charging output,
The same operation is performed on blocks 75, 76 and 77, and then the output of the light amount is determined on block 78. That is, the presence or absence of the primary charging output command is judged at 72, and if there is a command, the primary charging is
Turns on at 73, and turns off at 74 if there is no command. Similarly, at 75, the presence / absence of the secondary charging output command is determined, and at 78, the presence / absence of the light amount output command is determined. That is, the primary and secondary charging and the lamp are simply turned on while there is an instruction. Then, when to output the light amount, the exposure for each color in the block 79 (the light amount control value × F _{R, G, R)} to output. here,
F _B , _G , and _R are 1.2 to 1.3.

If the light amount is not output, the block 81 turns off. Then, it is judged whether or not it is the first copy of the potential control by the block 102, and if it is the first copy, the latent image potential of the white plate at the front end of the document table is stored (block 103). And when copying,
The potential of the white plate is read every time, the difference is compared with the stored value, and the difference is output as the developing device bias (block 104, block 104,
105,106). In this way, a good quality copy image can always be obtained. Subsequently, it is judged whether or not the copy is completed (block 82). If the copy is not completed, blocks 72 and below are repeated. If the copy is completed, the block 83 is reached, and the copy is completed.

〔The invention's effect〕

As described above, according to the present invention, the potential detecting means is provided in the vicinity of each developing means, and the latent image forming condition and the developing bias are provided for each color corresponding to the developing means in the vicinity by the output of each potential detecting means. Therefore, it is possible to optimally control the latent image forming conditions and developing conditions for each color regardless of the developing position of each color developing unit, and it is possible to obtain a high-quality color image with good color balance. The effect is that you can do it.

[Brief description of drawings]

FIG. 1 is a latent image potential characteristic diagram in the NP system, FIG. 2 is a partially enlarged view showing the structure of a photoconductor in the NP system, FIG. 3 is an overall configuration diagram of a copying machine to which the present invention is applicable, and FIG. FIG. 4 (a) is a block diagram showing the overall configuration of the embodiment of the present invention, FIG. 4 (b) is a configuration diagram of the secondary charger, and FIG. 5 is a potential control flow chart. , FIG. 6 is the fourth
FIG. 7A is a block diagram showing sensor switching of the potential measuring unit in FIG. 7A, and FIG. 7 is a flow chart of potential control during copying. 1 ... Photosensitive drum 17 ... Developing device 29 ... Sensor 33 ... Microcomputer for potential control Note that the same reference numerals in the drawings indicate the same parts.

Continuation of the front page (56) References JP-A-57-100449 (JP, A) JP-A-57-100448 (JP, A) JP-A-57-102675 (JP, A) JP-A-57-102672 (JP , A) JP-A-57-102671 (JP, A) JP-A-57-102673 (JP, A) JP-A-58-132247 (JP, A) JP-A-54-130134 (JP, A) JP-B 59-2897 (JP, B2) JP 59-2898 (JP, B2) JP 55-36144 (JP, B2)

Claims (1)

[Claims] 1. A photosensitive member on which a latent image corresponding to each color image is sequentially formed, a plurality of developing means corresponding to each color sequentially arranged in the moving direction of the photosensitive member, and for forming a latent image of each color. Latent image forming means for uniformly charging the photoconductor and removing charges on the photoconductor after charging by image light; and latent image forming means provided near the upstream side of the plurality of developing means in the moving direction, respectively. A plurality of potential detecting means for detecting the potential of the photoconductor, and the operating conditions of the latent image forming means are set so as to obtain different target potentials for each color, and according to each output of the plurality of potential detecting means. A potential control unit that controls the operating condition for each corresponding color, and the detection unit that respectively corresponds to the developing bias of the developing unit when forming the color corresponding to the developing unit on the downstream side immediately adjacent to the potential detecting unit. Bias control that is controlled based on the output of Color image forming apparatus characterized by a means.