JPS58105172A - Color copying machine - Google Patents

Abstract

PURPOSE:To realize color copying operation which improves color balance and shortens the time of sequence control by forming a latent image for every color- separated light component in a revolving shaft direction of a photoreceptor and controlling the surface potential of every color with a detecting means for every latent image potential. CONSTITUTION:Cyan (C), magenta (M), and yellow (Y) are made different mutually as shown in the 1st quadrant and the picture density of M is assumed to be a center to make the ratio C to M is 1.5:1-1:1, preferably about 1.2:1, and the ratio of M to Y is 1:0.9-0.6, preferably 1:0.8. The respective picture density of C and Y is allowed to extend to low through high range centering around the center value. To adapt to variations in an advance of development, desired values of potentials of a photoreceptor surfaces set for respective color- separated exposed light components are shifted bit by bit to be red>green> blue; for example, the desired potentials of the dark part VDD, intermediate density part VWLO and light part VSLO of a full color are set as shown in the table.

Description

[Detailed description of the invention] The present invention relates to a color copying apparatus.

In conventional color copying devices, the surface potential on the photoreceptor on which the latent image is formed changes over time, making it difficult to obtain a stable and color-balanced copy image over a long period of time. . This problem will be explained below using the gradation reproduction characteristics of color copying shown in FIG. In the figure, DO is the original image density, Dp is the print image density, and E
Let v8 represent the exposure amount and v8 the surface potential on the photoreceptor. Here, the first quadrant is the tone reproduction characteristic when a grayscale original is used. ,C,M.

Y represents the single colors cyan, magenta, and yellow, respectively, and C1M+Y represents the tone reproduction characteristics of a copied image obtained by superimposing these three colors. The second quadrant when viewed clockwise is D
The exposure characteristics of n-E (common logarithm) are shown. The third quadrant shows the color separation latent image characteristics of red (R), green (G), and blue (B) on the photoreceptor.

The fourth quadrant shows the development characteristics of cyan (C), magenta (M), and yellow (Y) toners.

In the characteristics of the first quadrant, cyan, magenta.

The reason why the yellow print image density Dp is different for the same original image density Do is to correct unnecessary light absorption of each toner and maintain color balance. Currently, color balance is gray balance, so 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, and the three colors of cyan, magenta and yellow are superimposed. Balances the colors in the image. Therefore, 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, cyan.

There are differences in the development characteristics of 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 was extremely difficult in the past. The reason for this is due to environmental changes such as temperature and humidity or deterioration of the photoreceptor.
The latent image characteristics varied from 1 to 1. In addition, jJ! of each cyan, magenta and yellow developer (toner)! ! ! It is necessary to correct variations in development characteristics from one lot to another or variations in development characteristics due to changes in developer over time.

To this end, conventionally, the color separation latent image characteristics of red, green, and blue were intentionally made different from the nearly uniform state shown in the third quadrant, and the characteristics were selected to achieve an appropriate relationship. Ta.

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 was virtually impossible for general users to make adjustments.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a color copying apparatus that eliminates the above-mentioned drawbacks, has good color balance, and can perform sequence control in a short time.

The present invention will be described 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 10 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 scan the original in synchronization with the rotation of the drum 1, and mirrors 7 and 9 scan the original in synchronization with the rotation of the drum 1.
, and move to the position 9/, and the illumination lamp 5 also turns 5.
’ move to the position. The optical image of the scanned document is captured by lens 11. Through the mirror 131 color separator 15 and mirror 17 (7, and through the secondary charger 19 for simultaneous charge removal during IC exposure)
7, an image is formed on the surface of the photoreceptor of the photoreceptor drum 1. A latent image is formed by such exposure means. Here, the color separator 15 includes a blue filter 15B according to each color separation.

It consists of a green filter 15G, a red filter 15R, and an ND filter 15N, and these filters are rotated to perform color separation of light.

The surface of the photoconductor of the photoconductor drum 1 is preliminarily coated with a blade cleaner 31.
The pre-exposure lamp 33 and the pre-static eliminator 3
51C, the influence of the previous latent image is removed. Next, the photoreceptor surface is uniformly charged by a primary charger 37 to have a uniform potential. The charged photoreceptor surface is neutralized together with the original light image by the secondary charger 19, and then the entire surface is uniformly exposed by the entire surface exposure lamp 39, so that a high-contrast static latent image is formed on the photoreceptor surface. It is formed. An electrometer globe 43 disposed near the surface of the drum 1 between the full-surface exposure lamp 39 and the developing device 41 detects the intensity of the static frost 1 along the image, that is, the electrostatic potential (5).

The developing devices 41 include a yellow developing device 41Y, a magenta developing device 41M, a cyan developing device 41C, and a black developing device 41.
B, and develops by supplying developer (toner) of each color. The transfer paper 51 placed in the cassette is sent to the transfer section 55K by the delivery roller 53. In the transfer section 55, first, the gripper 57 grips the leading edge of the transfer paper 51. A transfer corona discharger 59 transfers the developed image on the surface of the photoreceptor of the photosensitive drum 1 to the held transfer paper 51 by corona discharge from the back side of the paper.

In the case of monochrome copying, the transfer paper 51 is separated from the transfer unit 55 by the operation of the separation claw 63 immediately after the separation static eliminator 61 removes the electricity. In the case of multicolor copying, the gripper 5 of the transfer unit 55 is
Transfer paper 5 without opening 7 or operating separation claw 63.
Keep 1. When the transfer is completed, the transfer paper 51 is separated from the transfer section 55 by the operation of the separation claw 63, and is sent to the heating roller fixing device 67 by the conveyor belt 65, where the image is fixed. The transfer paper 51 at the end of the fixing process is discharged onto the tray 69 .

(6) After the transfer is completed, the toner remaining on the surface of the photosensitive drum 10 is cleaned by the blade cleaner 31 in preparation for the next copying cycle.

FIG. 4 is a cross-sectional view showing the schematic structure of the secondary container 19 shown in FIG. As shown in the figure, the secondary band '11f,
Groups of wires are arranged near and along the surface V of the photosensitive drum 1 in the openings on the side of the photosensitive drum 1 of the container 19. Each group of wires is connected to a negative grid 191 .
A zero grid 193 and a positive grid 195 are assumed. These grid biases are negative grid 191. Zero grid 193. Positive grid 195 is -50 to -30 respectively
0V, OV (ground), +50 to +200V. .

Color here? The color balance of photo images will be explained. As shown in the first quadrant of Figure 1, image density of cyan, magenta and yellow (color filter rotation)
Let's make them 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 magenta should be set to medium lb, and the image density of cyan and yellow should be taken into consideration.

For color balance, the image density ratio of cyan to magenta is in the range of 1.5:1 to 1:1, preferably at t2:. Image density ratio of magenta to yellow is 1:0
The ratio is in the range of 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 suitable for color balance is 1.44, and the allowable range is between 1.8 and 1.32. Further, the maximum image density of yellow is 096, and the allowable range is between 1.08 and 0720. 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 the colors are red, green, and blue. For example, in the third quadrant of FIG. 1, the potential of the non-exposed part of the latent image (dark part potential) Vn
But red, green.

In blue it is approximately 380 (V). For example, 400 (V), 380 (V), 360 (
V) A different type of cell is effective in overcoming problems such as fluctuations in development characteristics or problems with stacking capacity in automatic control of surface potential.

In the apparatus according to the embodiment of the present invention, for example, the temporary dark area (illumination lamp 5 is turned off), intermediate density area (lamp 5 is turned on at an intermediate voltage), and bright S (lamp 5 is turned on at the maximum rated voltage) during full color copying. The target value potential is voo, respectively.
VWLO and V8 LO are set as shown in Table 1 below.

Table 1 (9) 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 10 outputs a drum clock pulse 105 corresponding to the rotation angle from a photointerrupter 103. This clock pulse 105 is counted by the main sequence controller 107 of the copying apparatus, and controls information signals necessary for copying, such as the set number of copies. A controller 107 sends timing signals necessary for switching high voltage and halogen light intensity to a microcomputer 109 for potential control, a dark area potential VD, and an intermediate density area potential VWL.
and a measurement timing signal for the bright area potential V8L. The latent image potential detected by the surface electrometer globe 43 is measured as a potential of 1/300 of the surface potential by a surface potential measuring circuit 111, converted into digital data by an A-D converter 113, and then supplied to a computer 109. The computer 109 performs calculations according to the control formula so that the measured potential value converges to the target value selected by the switch board 115.

The signal of the calculation barrier is passed through the path line 117 to the D-A
Comparator (10) Data 119 K is supplied for analog conversion. Each analog-converted signal is sent to high voltage control circuits 121 and 123.

125 and mix circuit 127. The computer 109 also sends a control signal 131 to the analog multiplexer 129 to switch the image fine adjustment signal 135 from the fine adjustment board 133 and supply it to one of the high voltage control circuits 121 to 125 and the mix circuit 127. Analog 4 obtained by high voltage control circuits 121, 123, 125
@No. 1371.137G, 137V and image fine adjustment signal 1
Addition voltage signal 1391.139G with 35, 139
V+! , high-voltage transformers 141 , 143 , and 145 , respectively, and then a negative charger 37 . Negative grid 191° of the secondary charger is supplied to the secondary charger 19, respectively. As a result, a negative charging current ■1. Negative grid voltage VG- and secondary charging voltage V are controlled. In addition, the analog signal 137H and the image fine adjustment signal 1 from the mix circuit 127 are
The mixed signal 139H with
is supplied to control the halogen voltage VH1 applied to the illumination (halogen) lamp 5. Also computer 109
provides a digital signal to I10 driver 161 via pass line 117. This I10 driver 161 performs digit scanning of the 7-segment, 8-digit display 163, and converts the display signal 165 from the computer 109 to the BCD.
-7 segment driver 167, and its output signal 169 is used to display the photosensitive drum surface potential on display 163. Further, the diode switch board 171 is scan-controlled via the Z10 driver 161 to sequentially select the target values set on the switch board 115 1, and the voltage signal of the selected target value is sent to the computer 109. and individual control formulas (described later) [therefore, calculations are performed to converge to their target values.

The signals based on the target values converged by these computers 109 are converted into analog signals by the 11-A converter 119 1-1 The analog-converted voltage signals are supplied to each of the high voltage control circuits 121 to 125 and the mix circuit 127 .

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 device to "5" (standard). Next, the target value is set using a target value setting changeover switch (connected to the switch board 115) provided outside the copying machine.

After performing such 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 (step 40).
1). Next, potential cleaning is performed by pre-rotating the photosensitive drum l (step 403). In this state, the document illumination lamp 5 is turned on with the voltage VH1 set to the maximum rated voltage, and the amount of light emitted by this lamp 50 is maximized. The original image light with such maximum light intensity is transmitted to the ND filter 15N of the color separator 15.
This color separator 15 is set as a filter so that Q is transmitted. The photosensitive drum 1 is rotated once to expose the surface of the photosensitive member. The electrometer probe 43 detects the bright area potential V8L on the surface of the photoreceptor of the photosensitive drum l, and supplies the detected value to the potential measuring circuit 111 to obtain the bright area potential VSt.

is measured (step 405). This measured brightness (1
3) Difference between the part potential VSL and the target value VS LO of the bright part potential (l
Vst.

-V8LOl) is within the allowable error (C,) (step 407). If the determination is negative, the secondary charging voltage of the secondary charger 19 is also controlled by the control formula Δ■, -δΔV8.
Control is performed according to L (step 409). Then, the process returns to step 405 and repeats the operation. Step 40
Steps 405 and 40 until the bright area potential VSt, obtained again by the secondary charging voltage controlled by 9, falls within the tolerance C8 and converges to its target value vsLo.
The operations at 7 and 409 are repeated.

If the error is within the allowable error CI and an affirmative determination is made in step 4'07, the color separator 15 is rotated and the blue filter 15B is set so that the original image light passes therethrough (step 411). Note that in this step you can change the filter to green, red,
The colors are switched in the order of ND, green, and red. The illumination lamp 5 is turned off and the photosensitive drum 1 is rotated once without any original light. Since the surface potential of the photoconductor surface of the photoconductor drum 1 is the dark potential VD, this dark potential VD? 'Detected and measured by electrometer globe 43 (step 41
3). This measurement (14) determines whether the difference between the determined dark potential VD and its target value VDO is within the tolerance C3 (step 415).
,, If this determination is negative, the flow of the one-component band *: of the charger 37 is controlled according to the restriction type 1 JI, -α7jvDVc (step 417). After that, the process returns to step 413 and the operation is repeated. When the dark potential VD converges to its target value VDO within the tolerance C6, step 41
The judgment in step 5 is affirmative, the loop is removed, and the next operation is started.

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 to make the surface of the photosensitive member bright and dark. In this state, the bright area potential vsL, which is a surface potential, is detected and measured by the electrometer probe 43 (step 419).

M (l VSL - VSLOl) between the measured light st position VSL and its target value vst, o is the allowable dμ difference C
It is determined whether the value is within s (step 421). (If the judgment is negative, the negative grid voltage VC- of the negative grid 191 in the secondary charger 19 is set by the control formula Δ"Q-"""β+ΔVD
+βrJVsL&C therefore controls (step 423
). Then, the process returns to step 419 to repeat the loop operation. The bright area potential VSL has a tolerance C to its target value VSLO.
If it converges within 1, an affirmative determination is made in step 421, and the loop is exited.

The illumination lamp 5 is turned on at a norogen voltage vH which is an intermediate voltage, and the exposure amount of the original 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 potential VWL, and this potential VWL is measured by the electrometer probe 43 and the potential measuring circuit 111 (step 425). This measured intermediate concentration portion potential VWt.

It is determined whether the difference between the target value and the target value (l VWL VWLOI ) is within the tolerance C4 (step 42
7).

If the determination is negative, the halogen voltage Vml for lighting the illumination lamp 5 is controlled according to the control formula tVH1=r, fVyLK (step 429). Then step 4
Return to step 25 and repeat the loop operation. Intermediate concentration potential VWL
If converges to its target value VWLO within the tolerance C1, then
An affirmative determination is made in step 427, and the loop is removed.

Through such an operating procedure, steps 411 to 427
Based on, the primary charging current 1 in the blue filter 15B
1. Negative grid voltage VG- and negative grid voltage VH1
is controlled and set. Next, it is determined whether the set filter in the color separator 15 is the last one (step 431).
. In this case, since the determination is negative, the process returns to step 411. Step 411: The IC rotates the color separator 15 in the order of blue → green → red → ND → green → red to switch and set the filter. Each time the filter is set, steps 413 to 429 are performed, and the single band tt flow in that filter is determined.11. Negative grid voltage vG- and halogen voltage VHI are controlled and set.

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 step 431, and the control operation of the control circuit is completed. In this way, the trichromatic colors blue and green.

The voltage relationship is set at 5 to set the surface potentials based on red, black and white, and the two colors magenta and black to predetermined values. Then, under the set control voltage relationship, the image of the original placed on the original table glass 3 is transferred in color to the transfer paper 511C.

(17) For example, a changeover switch may be provided outside the copying device so that the three colors, blue, green, red, and black and white, and the two colors, magenta and black, can be set individually in, for example, three levels. Good too. Each surface potential converges to the target value set in this manner.

Note that in steps 405, 419, and 425, the bright area potential vsL and intermediate density area potential vwL are measured by scanning the original at the same speed as in normal copying with the transfer paper placed on the original platen glass 3. This is done after forming a potential. In addition, the coefficients γ, δ, α,
β1 and β indicate the slope of the function based on each relational expression.

As shown in the flowchart of FIG.
- The reason for controlling it beforehand will be explained. Refer to the configuration of the secondary charger 19 in FIG. 4.

The distance between the wires of the grids 191 to 195 and the surface of the photosensitive drum 1 is usually 1.0±0.1 . Within this distance tolerance, for example, the voltage applied to the discharge wire of the secondary charger 19 is -8.5KV, which is 191,1
93.

(18) 19517) The applied voltages are -120V, OV,
When set to 100V, the bright area potential V8L is 1120±3
Varies within the range of 0V. Therefore, the secondary charging voltage level is first controlled so as to offset variations between devices and obtain a constant bright area potential V8L with a constant grid bias voltage. Thereafter, a negative grid voltage vG-, which is the bias voltage of the negative grid 191, is applied to adjust the bright area potential based on the gradation control method introduced in the specification of JP-A-54-142371 Electrophotography Method and Apparatus. VSt,
It controls the

As explained in accordance with the flowchart of FIG. 5, in the present invention, when performing automatic potential control of a color separation latent image, color separation filters are switched differently from the normal copying sequence. That is, as soon as a desired surface potential is obtained in one color separation filter, the next color separation filter is switched to, and potential control is performed so as to obtain the desired surface potential in that filter. This minimizes the time required to control the potential of each color separated latent image, increasing processing efficiency.

After the potential is controlled in this manner, by placing the original to be copied on the original table glass 3 and copying, a color image with appropriate color balance can be obtained on the transfer paper 51. By the way, it takes time to perform such potential control for each color separation filter. Therefore, the photosensitive drum 1 is divided in the axial direction according to the number of separated color lights, and a color separation filter 650 is provided so as to irradiate each divided area with the separated light.
If 7 and 19 are divided into a large number of parts corresponding to each other and the latent image measurement described above can be performed at the same time, the control time can be reduced to 1/3.

FIG. 6 shows the arrangement of the charger and probe. The light reflected from the original is reflected by the red light section 650R and the green light section 650.
Color separation filter 65 consisting of G and blue light sections 650B
0, red light LR, green light LG and blue light LB
IC color separation. These three colors LR.

LG and LB irradiate the photosensitive drum 1 through corresponding secondary chargers 19C, 19M, and 19Y for cyan, magenta, and yellow, respectively. The potential of the electrostatic latent image formed by each separated color light is detected separately by the corresponding cyan sensor 43C, magenta sensor 43M, and yellow sensor 43Y. −
The respective voltages of the wide chargers 37C, 37M, 37Y and the secondary chargers 19C, 19M, 19Y are 5th
It is controlled according to the scheme described above in connection with the figures. Detection values and primary values by sensors 43C, 43M and 43Y,
The secondary charging voltage is stored in a microcomputer (not shown). After this, when normal copying is started, each charger performs charging at the same charging voltage as if there were only three or one charger. 1- That is, the color separation filter 650 repeats exposure three times in the order of B→G-+R. ．． Each of the three divided chargers is operated in the same way as a single charger, with a charging voltage according to the filter, and image retention with optimal color balance is achieved. In addition, if it is not possible to maintain the potential between the ends of the charger divided into three parts, it is recommended to install a separate charger that is not divided into three parts at the time of copying.

As described in detail above, according to the present invention, it is possible to realize a color copying apparatus with good color balance and short copying time.

[Brief explanation of the drawing]

(21) FIG. 1 is a diagram showing the gradation reproduction characteristics of color copying, FIG. 2 is a device configuration diagram showing an embodiment of the color copying apparatus according to the present invention, and FIG. 3 is a diagram showing the control in the device shown in FIG. 2. A block diagram of the circuit, Fig. 4 is a schematic diagram of the secondary charger, Fig. 5 is a flowchart showing the operation of Fig. 3, and Fig. 6 is a configuration showing the corresponding positional relationship of the color separation filter, charger, and sensor. It is a diagram. 1... Photosensitive drum, 3... Document glass, 5
...Lighting rung, 15...Color separator, 19
, 19C, t9M, 19Y...Secondary charger, 37
, 37C, 37M, 37Y...-wide charger, 4
1...Developer, 43...Electrometer probe, 43C, 43M, 43Y...Sensor, 51...
- Transfer paper, 55... Transfer unit, 59... Transfer corona discharger, 67... Heating roller fixing device, 101... Chopper disk, 107... Main sequence controller, 109...
...Microcomputer, 111...Surface tQ, measurement circuit, 991 115...Switch board, 133...Fine adjustment board, 161...I10 driver, 163...Display device, 171...Diode switch Board, 650...
・Color separation filter. Patent applicant Canon Co., Ltd. (23) Figure 1 Figure 2 Figure 4 Figure 3 to 5) I Anti-bv Figure 5 Figure 6/qY) 3Y

Claims (1)

[Claims] In a color copying apparatus that separates the reflected light from an original into colors, forms a latent image for each color on a photoreceptor, develops it, and reproduces a color image by overlapping the images onto the same transfer material. The rotary axis direction VC is configured such that a latent image is formed for each of the color-separated lights, a means is provided for detecting the potential of each latent image, and the surface potential of the photoreceptor is controlled for each color. Characteristic color copying device.