JPS6139060A - Formation method of polychromic picture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Chiku supervisor division The present invention relates to a multicolor image forming method.

14 In the conventional multicolor image forming method, one latent image carrier is rotated multiple times to obtain a visible image of a predetermined color each time, or a plurality of latent image carriers are used, and a predetermined image is formed on each of the latent image carriers. A common method is to obtain visible color images and sequentially transfer them onto the same transfer paper. However, if the latent image carrier is rotated multiple times, it takes time to complete one image forming process, and conversely, if a plurality of latent image carriers are used, the cost of the device increases and the structure becomes larger. Not immune to shortcomings.

A so-called one-shot copying method has also been proposed in which a multicolor image is obtained by rotating one latent image carrier once, but it is difficult to obtain a high-quality image with this conventional method.

- The present invention has been made based on the above recognition, and its purpose is to provide a multicolor image forming method that allows a high quality multicolor image to be obtained by rotating one latent image carrier once. It is.

The present invention includes a step of determining the color of each document read by a color scanner and obtaining color information, a step of forming an electrostatic latent image corresponding to the document image on a latent image carrier, and a step of forming an electrostatic latent image on a latent image carrier based on the color information. The above objects are achieved by a multicolor image forming method that includes the step of developing an electrostatic latent image in each color designated unit with toner of one or more colors.

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

FIG. 1 shows a copying machine as an example of an image forming apparatus implementing the method according to the invention. In the illustrated copying machine, the latent image carrier is constructed as a photoreceptor 1 formed in the shape of an endless belt, and this photoreceptor 1 is wound around three rollers 2, 3, and 4 and driven in six directions of arrows. Ru. Such a photoreceptor 1 has, for example, panchromatic spectral sensitivity. PC
(Organic photoconductor) can be used as appropriate.

A contact glass 5 is fixedly installed in the upper part of the copying machine, and an original 6 to be copied is placed on the contact glass 5.

In this example, for convenience of explanation, first, as shown in FIG. 2(a), a red image R1, a green image G, a blue image B, and a black image BL are
A case will be described in which a document 6 having a white background W is to be copied.

During the copying operation, the light source 7 located below the contact glass 5 illuminates the original 6 while scanning, as in a normal copying machine, and the reflected light is reflected from the mirrors 8, 9, 9, 7, 9, 7, 9, 7, 9, 9, 9, 10, 10, 10, 10, 10, 10, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
10, passes through an imaging lens 11, is reflected by another mirror 12, reaches the photoreceptor 1, and forms a document image thereon.

At this time, the photoreceptor 1 is driven in the direction of arrow A and is uniformly charged to a predetermined polarity by the charger 13, so that an electrostatic latent image corresponding to the original image is formed on the photoreceptor 1 by the exposure. (In this example, the charging polarity of the photoreceptor 1 is negative, and the surface potential after being charged by the charger 13 is about 1,700 V).

The electrostatic latent images formed on the photoreceptor 1 are images R and G on the original 6, as schematically shown in FIG. 2(c).

B, red latent image R1, green latent image G1, and blue latent image B corresponding to BL
1, and the Kuroshio statue BLI.

On the other hand, there is a half mirror in the optical path from the original 6 to the photoreceptor 1.
14 is interposed, and as described above, the light reaching the photoreceptor 1 is transmitted through the half mirror 14, but the light reflected there passes through another imaging lens 15 and reaches the color scanner 16. As a result, the original image is formed on the color scanner 16, and each color of the original image is determined.

As the color scanner 16, an appropriate type of scanner known per se can be used, but in the illustrated example, a CCD 17 having a large number of light receiving sections arranged in a direction perpendicular to the plane of the paper of FIG. Three types of filters: red filter, green filter, and blue filter superimposed on each light receiving section 1
7a, the filters are arranged alternately in the order described above. Manuscript 6 and CCD
2 (a), (b), (
C) is schematically shown. A color scanner that uses three CODs and superimposes red, green, and blue filters on the light-receiving part of each CCD, a scanner that uses a 1x sensor instead of a CCD, etc. may be used, and a 1x sensor may be used. In some cases, the imaging lens 15 may be omitted.

When light from the document 6 enters the color scanner 16 described above, the light selectively passes through red, green, and blue filters depending on its properties, and the output from the CCD 17 is sent to the CPU.
18 (FIG. 2(b)), the document 6 can be divided into minute portions (reading units) and the color of each can be determined in a manner known per se. This color information is stored in the memory 19 (FIG. 2(b)). The reading unit of the above-mentioned original is an appropriate size, for example, 0.5 n.
wn2 is set, and the document is divided into areas of this reading unit and its color is determined.

On the other hand, as shown in FIG. 1, two or more (four in this example, four) developing units 20, 20a, 20b, and 20c are located around the photoreceptor 1 on the downstream side of the exposure position. It is located in The developing device shown here is manufactured by Japanese Patent Application Laid-Open No. 1986-
This is an application of the so-called LIST type developer disclosed in Japanese Patent Laid-Open No. 84955 or Japanese Patent Laid-Open No. 58-66954, and each developer is placed opposite to the photoreceptor 1 and rotated counterclockwise. Donor rollers 21, 21 a, 2
lb, 2 IC, doctors 22° 22a, 22b, 22e and multi-styli 23° 23a, 23b, 23c placed opposite each donor roller.

Further, in this example, the red toner RT is in the hopper of the first developing device 20, and the green toner G is in the hopper of the second developing device 20a.
T is blue toner BT in the hopper of the third developing device 20b.
However, black toner BLT is stored in the hopper of the fourth and final developing device 20C. A positioning plate 25 is disposed on the opposite side of the donor roller across the photoreceptor 1, and thereby the photoreceptor 1 and each donor roller 21, 21a, 2
The relative positions of 1b and 21c are regulated.

Each donor roller is, for example, a conductive rubber roller with a diameter of 36 mm, and each multi-stylus 23, 23a, 23b
, 23c are a large number of electrode needles 26 made of, for example, nickel plates, arranged in a staggered manner in a direction transverse to the rotational direction of the donor roller or the running direction A of the photoreceptor 1, as shown in FIGS. 3 and 4. and a fixing material 27 made of, for example, epoxy resin to fix this.

FIG. 2(d) schematically shows the relationship between each electrode needle 26 and the donor roller 21 of the first developing device 20, but the relationship is exactly the same for the other developing devices.

A voltage of, for example, -100 cm, which has the same polarity as the charged polarity of the photoreceptor 1, is applied to the doctor rollers 22, 22a, 22b+ 22c.
A negative charge is injected into the toner carried by 1b and 21c and sent out from each hopper, and the toner becomes, for example, -
It is charged to about 10 to -20 μc/g. The doctor also serves to regulate the thickness of a layer of toner on the donor roller fed from the hopper to a predetermined thickness of, for example, 3'θμ (toner particle size is about 10μ).

After the toner layer on each donor roller is charged as described above, an electrostatic latent image is formed by the electrode needles of each multi-stylus 23, 23a, 23b, and 23c to which a pulse voltage of, for example, +200V is applied, as described below. A charge having a polarity opposite to that of the latent image, that is, a positive polarity, is injected only into the portion of the toner to which the toner should be attached, more precisely, the portion of the toner layer that includes the portion corresponding to the latent image, and the charge polarity is exactly +10, for example.
It is converted to about +200v or g. In the example shown, the electrostatic latent image on the photoreceptor l first passes through the first developing device 20, so
The state at this time will be clarified. First, color scanner 1
The red image information of the color information read by the memory 19
Based on this, a positive pulse voltage of <+200 V is selectively applied to the electrode needle 26 of the first developing device 20 via the driver 28 (FIG. 2(d)). Therefore, the amount of charge of the red toner passing under the electrode needle to which voltage is applied is converted to positive polarity, and here, the amount of charge is +15 μc/g.
As shown in FIG. 3, the charge polarity of the toner layer becomes positive in l or a plurality of units (these are called color designation units) determined by the width W of the electrode needle 26 (FIG. 3), and corresponds to red image information. A charge pattern is formed (Fig. 2(d)).
. In this example, for convenience of explanation, 126
It is assumed that a pulse voltage is applied to the two electrode needles marked with , and the four color designation units CUI of the toner layer passing under the electrode needle 126 are reversed to positive polarity. The other toner layers remain negative and do not reverse.

A layer of toner that is positively or negatively charged as described above.

As the donor roller 21 rotates, it faces the photoreceptor 1,
It comes into sliding contact with or approaches the surface of the photoreceptor. At this time, the positively charged toner layer corresponds to the red latent image R1, and the toner on the donor roller charged to the opposite polarity to this latent image electrostatically transfers to the latent image R1, and the latent image R1 becomes red. The toner transforms it into a red visible image R2 (FIG. 2(e)). In other words, if we explain the correspondence between the color designation unit and the latent image, as shown by the dashed line in FIG. A pulse voltage is applied in advance to each electrode needle 126 based on the red image information so that only the one layer of toner that includes the image R1 and is the smallest color designated unit has positive polarity. Also, there may be color difference during development.

Toner other than constant unit CUI remains negatively charged, so
This toner does not adhere to the latent images Gl, Bl, BLI, which should not be visualized, and the background area, which have the same polarity, and development is performed by the cooperative action of the positive toner and negative latent image. Therefore, among the positively charged toner within the color designated unit, the toner in the portion that does not match the latent image R1 does not adhere to the photoreceptor. In this way, the red latent image R1 is visualized for each color specified unit of a predetermined size, and only the red visible image R2 is formed on the photoreceptor 1 after passing through the first developing device 20.

Since the toner on the donor roller 21 is positively charged by the electrode needles in each color designated unit, the size of one color designated unit is determined by the width W of the electrode needle 26, the pulse width of the pulse voltage, etc. , the size of the unit is, for example, 0.
It is set to an appropriate size such as 5 or 3.

The recorded image information is retrieved in exactly the same manner, and as shown in FIG. 2(f), a pulse voltage is applied selectively to the electrode needles of the second developing device 20a (in the example shown, 226 electrode needles), and a line latent image is generated. G
For example, the charge polarity of the toner layer of the color specified unit (in the example shown, one unit CU2) that can visualize 1 is set to +15μc/
g, and an amount of green toner GT determined by the surface potential of the latent image 61 and the amount of charge of the toner is attached to the latent image 61. As a result, a green visible image G2 (FIG. 2(g)) is formed on the photoreceptor 1. Thereafter, in the same manner, the blue latent image B1 is visualized using the blue toner BT in the third developing device 20b.

Next, in the fourth developing device 20e, the black latent image BLI is developed with black toner BLT, and images R1G, B, B of the original 6 are developed.
A multicolor image that is the same as or similar to L is obtained. This multicolor image is printed on a transfer paper 30 fed from a paper feed section 29 (FIG. 1).
Then, the images are transferred all at once by the discharge action of the transfer charger 31. After the transfer paper 30 is separated from the photoreceptor 1, it is sent to a fixing device 32, where the multicolor image is fixed thereon, and the paper is discharged outside the machine. After the visible image has been transferred, the photoreceptor portion is subjected to a static neutralizing action by a static neutralizing charger 33, and is then moved to a cleaning device 34.
The remaining toner is removed by

The method described above reads the original image in predetermined reading units, selectively applies voltage to the electrode needles based on the color information, and develops the electrostatic latent image in each predetermined color designated unit. , it is possible to obtain a multicolor image with one rotation of the photoreceptor. Moreover, since development is performed by the cooperation of the toner charge and the electrostatic latent image of the opposite polarity, a charge pattern corresponding to the visible image can be formed using only the multi-stylus, and a visible image can be created using only the toner charge. The width W of the electrode needle can be made larger, for example, about 0.5 m, compared to the method of obtaining the stylus, thereby reducing the cost of the multi-stylus and increasing the image forming speed. For example, 100 V15A
High-speed copying of approximately 30 to 50 copies per minute is possible using a power source of 30 to 50 copies per minute.

When a chromatic original image has a blackish tinge, this is determined in advance, and when the latent image corresponding to that image passes through the fourth developing device 20c, a small amount of black toner is applied to these latent images as well. By attaching , the original image can be reproduced more faithfully.

It goes without saying that images of colors other than those shown in FIG. 2(a) can also be reproduced in the same manner. If you increase the number of toner colors used for development, the number of colors in the visible image that can be obtained will also increase, but if the number of toner colors is less than the number of colors in the original, the toner color that uses the JI draft color will increase. It is also possible to form a visible image using toner of a predetermined color according to the classification, or it is also possible to use toner of another color and form a visible image by overlapping toner of different colors, as shown below. In the second embodiment, each developing device 2
Yellow toner Y at 0,20at 20b,20c
T, magenta toner MT, cyan toner CT, and black toner BLT are used, respectively. In this case as well, if the document 6 having the four-color image shown in FIG. 5(a), which is the same as that in FIG. 2(a), is to be copied, the image will be copied as shown in FIG. Electrostatic latent image R corresponding to the original image
1, G1, Bl, and BLI are formed on photoreceptor l. Further, the color scanner 16 scans the original image, for example, 0.
5. It is read in 2 units and its color is determined. At that time, when visualizing the electrostatic latent image (described later), what proportion of toner of each color is applied to the electrostatic latent image portion corresponding to each color specified unit? The CPU 18 calculates whether the original image can be reproduced by attaching the image, and this information is stored in the memory 19. At this time, it is advantageous to simultaneously perform color correction (masking) and background processing (UCR) to improve the quality of the reproduced image.

In this example, the red latent image R1 formed on the photoreceptor 1 is visualized in red by the yellow toner YT of the first developer 20 and the magenta toner MT of the second developer 20a, and the line latent image G1
is the yellow toner YT of the first developer 20 and the third developer 2.
Visualized in green by cyan toner CT of 0b,
Similarly, the blue latent image B1 is the cyan toner C of the third developing device 20b.
T and the magenta toner MT of the second developing device 20a make it visible in blue, and finally the black latent image BLI becomes the 4'IIt
It is visualized by the black toner BLT of the imager 20c, but in this case as well, if we consider the first developer 2o,
First, the yellow information regarding which part of the latent image the yellow toner YT of the first developing device 20 should be attached to and in what ratio with respect to toners of other colors is retrieved, and a positive pulse voltage based on this is first applied. The charge is selectively applied to the electrode needle of the first developing device 2o via the driver 28, and the charge is injected into a single layer of toner on the donor roller 21 to form a charge distribution (FIG. 5(d)). In this example, 12
A pulse voltage is applied to two electrode needles marked with 6 and one electrode needle also marked with 226, and the four color designation units CUI of the toner layer passing under the electrode needle 126 and the one of the electrode needles 226 are similarly applied. One color specification unit CU2 of one layer of toner passing below
is reversed to positive polarity, and the amount of charge is approximately +10 μc/g.

When the charged toner layer slides into contact with or approaches the surface of the photoreceptor as described above, the positively charged toner layer forms a mackerel latent image R1 and a line latent image G! Correspondingly, the toner on the donor roller charged to the opposite polarity to these latent images electrostatically transfers to these latent images,
The latent images R1 and Gl are visualized with yellow toner (5th vR(e)). Other than that, the red tide image visualization operation is the same as in the previous embodiment.

Call up the magenta information in exactly the same way as shown in Figure 5(f).
As shown in FIG. 2, a pulse voltage is selectively applied to the electrode needles of the second developing device 20a (in this case, electrode needles 126 and 326),
The toner layer of the four color designation units CUI that can visualize the red tide image R1 is charged to, for example, +15 μc/g, and the toner layer of the three color designation units CU3 that can visualize the blue latent image B1 is charged to, for example, +10 μC/g. Then, magenta toner MT is attached to both temperature images R1 and Bl in an amount determined by the surface potential thereof and the amount of charge of the toner. As a result, the previous yellow toner YT and the current magenta toner MT adhere to the red tide image R1, forming a red visible image R2 (Fig. 5 (g)).
) - In the same manner, the cyan toner CT is applied to the line latent image G1 and the blue latent image Bl by the third developing device 20b over the yellow toner and magenta toner that have already adhered, respectively, to form a visible green color. 1. Then, in the fourth developing device 20C, black toner BLT is attached to the black latent image BLI to form a multicolor image that is the same as or similar to the images R, G, B, and BL of the original 6. obtain. This multicolor image is also transferred and fixed onto the transfer paper 30 as in the previous embodiment. The density and color tone of the resulting multicolor image are determined by the amount of toner that adheres to the latent image during development, and this amount of adhesion depends on the amount of charge of the toner on the donor roller. By controlling the amount of charge, it is possible to reproduce an image that is faithful to the original image. FIG. 6 is a graph showing an example of the relationship between the amount of charge of the toner on the donor roller and the density of the visible image using the surface potential (-100V to -700V) of the electrostatic latent image as a parameter. From this, it can be clearly understood that the visible image density is determined by the surface potential of the latent image and the amount of charge of the toner, and when the surface type is the same, the density is determined by the amount of charge of the toner.

In the second embodiment, cyan, magenta, yellow,
Since black toner is used, it is possible to obtain full-color multicolor images not only when the images of each color R, G, B, and BL are independent as shown in FIG. 5(a), but also from an original such as a photograph. In this case as well, the reproduced color is determined by the blending ratio of each toner, and the density is determined by the surface potential of the photoreceptor. Although cyan, magenta, and yellow toners may be superimposed to obtain a black visible image without using black toner, it is advantageous to use separate black toners because different color images can be made clearer. be.

When the latent image is visualized in multiple stages using multiple developers,
If the development conditions are the same, the development efficiency of the later development device may be lower, but in such cases, this situation can be dealt with by controlling the development bias for the donor roller and the amount of charge on the toner. be able to.

Furthermore, when using the developing device shown in Figure 1, the circumferential speeds of the donor roller and the photoreceptor are set to be the same so that the visible image already formed on the photoreceptor is not disturbed. The bodies may be brought into light contact via the toner, or it is advantageous to space the donor roller and the photoreceptor slightly apart to perform non-contact development. In addition, the development itself is carried out by contact development, and at that time, instead of forming a single layer of toner on the entire surface of the donor roller, toner is applied only to the necessary area (corresponding to the single layer of positively charged toner in the illustrated embodiment). A developing device configured to send out a film may also be used. For example, the donor roller itself can be charged by a multi-stylus to which a pulsed voltage is applied to form the required toner layer thereon. In short, any suitable developing device other than the LIST system may be used as long as it is capable of developing the latent image on the photoreceptor in designated units of each color. Further, the electrostatic latent image formed on the photoreceptor may not be formed analogously as shown in the embodiments, but may be formed using a laser, an LED array, or an electrostatic recording method.

Normally, the electrode needles of the multi-stylus in each developing device are located on the same plane along the direction of movement of the photoreceptor, but by appropriately shifting their positions slightly, the highlight part of the image can be smoothed. It becomes possible to finish it.

The size of the image reading unit by the color scanner 16,
Based on this, the size of the color specification unit for injecting charge into one layer of toner does not necessarily have to be the same; for example, the size of the color specification unit can be a multiple of the reading unit.
In addition, the sizes of these units are 0 and 5 m as shown in the example above.
It is also possible to set the width W of each electrode needle to an appropriate size other than "0.2 mm to 1.0 mm +", and the size of one color designation unit is determined based on this. Of course, the color specification unit should be smaller than this, for example 0.2mm2.
It may be possible to increase the sharpness of the completed visible image by making the unit smaller than , but normally the resolving power of the human eye for color is not very high, so even if the unit for specifying one color is made too small, it will not be as effective. It is normal for it not to rise. However, when different color images on a document are close to each other or in contact with each other, latent images that should be visualized with different color toners may coexist in one color specification unit. If it is large, the sharpness of the finished visible image may be significantly reduced. This is because toners of different colors cannot be attached to each latent image within the same color specification unit, and the color of the visible image within one color specification unit is constant. For example, as shown in FIG. 7(a), a document portion 6a in which a round red image R is formed on a yellow background, that is, a yellow image Y.
When copying, the electrostatic latent image on the photoreceptor l obtained from this portion 6a becomes as shown in FIG. 7(b), and the red image R
The surface potential of the red latent image R1 corresponding to the yellow image Y is higher than that of the yellow latent image Y1 corresponding to the yellow image Y. Now, it is assumed that each of the 16 equal parts divided by the solid line in FIG. 7(b) is an individual color designation unit, and the individual units are determined as shown in FIG. 7(C). Y indicates that it is determined to be yellow, and R indicates that it is determined to be red. When a yellow latent image Yl and a red latent image R1 coexist in the same color designated unit, it is determined that the color is orange as indicated by O. In accordance with this color determination and the level of surface potential of the latent image, the latent image is visualized for each color designated unit, and a visible image as shown in FIG. 7(d) is obtained. In this case, this visible image consists of a yellow part Y2 indicated by the coarsest diagonal lines, a light orange part 02 indicated by the next coarsest diagonal lines, a dark orange part 022 indicated by the finest diagonal lines, and a double diagonal line. It consists of a red portion R2 shown by , and is the same color within each color designation unit. Therefore, the size PXQ of the color specification unit is, for example, P as shown in the previous embodiment.
If it is relatively large, such as =Q=0.5■, the outline of the visible image shown in FIG. 7(d) becomes unclear, resulting in an image with low sharpness.

To eliminate the above drawback, the size of the color specification unit should be made smaller, for example, P = Q = 0.125 m1.
The above-mentioned defects become less noticeable, and it is possible to obtain a natural-looking visible image. However, if the size of the color specification unit is made smaller in this way, the size of each electrode needle must also be made smaller, which increases the time required for the electrode needles to apply a predetermined amount of charge to the toner. This results in a disadvantage of reduced performance.

For example, consider the case where one multi-stylus is divided into eight parts n1 to n8 in the axial direction of the donor roller as schematically shown in FIG. Electrode needle 2 schematically shown only
If the total number of 6's is 424 (2/rttn),
The number of electrode needles in each segment is 53). When the multi-stylus is divided in this way, for example, 2. actuating the third division;
Finally, after the eighth actuation, the first divided portion n1 is actuated again, and such operations are performed continuously. Now, both the width W of each electrode needle 26 and the length D in the circumferential direction of the donor roller (Fig. 3) are set to relatively large values so that the size of the color specification unit is 0.5 n1n x 0.5 mn. 0.5 +nm
and the peripheral speed V of the donor roller and therefore the photoreceptor 1 is 2.
If set to 00 TIn/sec, 1 divided portion n
The time required to perform operations from 1 to n8 (operation time for 1 line) is 0.5 am÷200 mm/qec
= 2.5 m5 ec, and the time during which a voltage can be applied to each divided portion, in other words, the time during which charge is injected into the toner per line is approximately 0.31 m5 ec, which is 1/8 of that time. However, since the time for each electrode needle to contact the toner per line is D+v, it is 2.5 m5ec.

Each electrode needle was 0.5 nwnXo, 5 rr as described above.
If you make it as large as rn, you can use the same operating mode as a normal multi-stylus and increase the photoreceptor to 200 +nm/se.
It can be operated at a high speed of c, for example 30 sheets/m
It is possible to achieve a copying speed of approximately 1.5 in. However, when using such an electrode needle, the size of each color designation unit is also 0.5 mm
0.5 m, which may reduce the sharpness of the completed image.

Therefore, we reduced the size of one color specified unit, and this became 0.1
25 + a Xo, 125 + nm, the total number of electrode needles is 1680, and the number of electrode needles in each divided part is 210.
Multi-stylus for books (hereinafter referred to as the second stylus)
(In this case, the color scanner 17 uses a CCD having a resolution of, for example, 8 lines/mm.) The width W of each electrode needle is 0.125 nwa, and the length D is also reduced accordingly, so if this is set to 0.125 nyn, the toner can be reliably charged positively and given a predetermined amount of charge. This requires the same time as the aforementioned 2/m multi-stylus (hereinafter referred to as the first stylus), that is, 2.5 m5ec, so the peripheral speed V of the donor roller or photoreceptor is 0.125 ÷2.
5 msec=50 mm/see, the circumferential speed of the photoreceptor must be reduced to 1/4 compared to the previous example, and the copying speed is significantly reduced to about 7 sheets/min.

From the above-mentioned viewpoint, in the third embodiment of the present invention,
Each developing device 20, 20a, 20b, 20
In c, two or more multi-styli having different resolving powers, such as the first and second styluses described above, are used, and these are configured to be able to be used selectively. For example, as shown in FIG.
1, a first stylus 23a and a second stylus 23b
When the distance between different color images on the original is large, for example 0.5 wta or more, the first two low-resolution lines/circle are
High-speed copying is possible using the stylus 23a. If the different color image spacing is large, the quality of the finished visible image will not be degraded even when multiple styluses with low resolution are used. On the other hand, when the distance between different color images of the document is small, for example less than 0.5 an, the second stylus 23b with a high resolution of 8 stylus/an is used. As a result, although the copying speed becomes slow, a high-quality copied image can be obtained.

The second to fourth developing units have exactly the same configuration.

The operator may decide which multi-stylus to use each time and switch by operating a switch (not shown) attached to the copying machine. ), the document 6 is placed on top of the scanner, and this is prescanned, and the color scanner 16 determines whether the interval between different color images is 0.5 m or more or less than 0.5 m in this example, and automatically switches the multi-stylus to be used. You may also do so.

Also, using only the high-resolution second stylus 23b,
The circumferential speed of the donor roller is set to a low speed, for example, 50 mm/se.
e, and a first mode in which a voltage can be applied independently to each electrode needle, and a first mode in which a plurality of adjacent electrode needles, for example, four, are electrically connected together. The electrode needle can be used as a single electrode needle, and the circumferential speed of the donor roller can be increased to a high speed, for example, 2.
00 m/sec may be selected. In the second mode, the multi-stylus functions as a low resolution stylus. Therefore, when priority should be given to copying speed, the second mode is selected, and conversely, when priority is given to image quality, the first mode is selected. In this case, in the second mode, the time during which each small electrode needle with length D = 0.1251 m1 is in contact with the toner on the donor roller is 0.125 m÷200 m/5ec = 0.625
wsec, and 2.5 tssec in the first mode
The voltage applied to the electrode needle should be increased.

This prevents the inconvenience of insufficient toner charge (see FIG. 10).

The selection of the first and second modes or switching between the first and second stylus is set for each document, and one document is processed in its entirety using either mode or stylus. However, by prescanning the original image, the original is read by a color scanner, and it is determined in advance in which parts of the original the distance between different color images is large or small, and the necessary parts,
In other words, for example, where the distance between different color images is less than 0.5 na, or an appropriate area including this area, the image is created using the second stylus 23b or the first mode, and for other areas, the image is created using the first stylus 23b. 23a or the second mode to enable high-quality and high-speed copying. In this case, as the stylus or mode is switched, the temperature, etc. of the electrostatic charger 13, light source 7, transfer charger 31, and fixing device 32 shown in FIG. Make it possible to obtain a duplicate image.

Even when using a high-resolution multi-stylus or selecting the first mode, if the same color specified unit contains latent images that should be visualized with different color toners, the color It is advantageous in improving image quality to visualize a latent image within a designated unit using toners of a plurality of colors to obtain a visible image of an intermediate color.

As described above, when using the second stylus 23b with high resolution or executing the first mode, the copying speed decreases, but it is possible to prevent the speed decrease by taking the following measures. be.

As shown in FIG. 8(a), images of different colors, for example, a red image R and a blue image B, approach or come into contact with each other.

When copying original documents 6 whose distance is less than 0.5 m, for example, the second stylus 23b with high resolution is used.

In this case, when the second stylus 23b is divided into eight equal parts as shown in FIG. 8(b), in the previous embodiment, the stylus operates sequentially from the first divided part n1 to the eighth divided part n8. do.

However, the image formed in the original is only a part as shown in FIG. 8(a), and this is, for example, the seventh divided part n7.
, it is wasteful to activate the first to sixth and eighth divisions. Therefore, in this embodiment, the operation of unnecessary divided parts is stopped, in other words, the operation of the first divided part is stopped.
The sixth divided portions n1 to n6 are skipped, only the seventh divided portion n7 is operated, and the eighth divided portion n8 is also skipped. In this way, image formation can be performed without reducing the circumferential speed of the donor roller, maintaining a high speed of 200 m/see in this example. Again, to explain with specific numerical values, in the previous example, the length of each electrode needle 26 was D=0.12.
5 m), the donor roller was rotated at a speed of 50 m+/see, and the first to eighth divisions were sequentially operated, and the time each electrode needle was in contact with the toner per line was 2.5 m5ec. , the time for applying voltage to the electrode needles of each divided part is 2.5 tssec÷8 = 0.31m5e
c, but in this example, only the seventh divided portion n7 is operated, so the peripheral speed of the donor roller or photoreceptor is set to 200.
m/see, the time the electrode needle is in contact with the toner is 0.125 rm÷200■/5ec=0.625
m+sec, and a pulse voltage can be applied to the electrode needle of the seventh divided portion for a time of the same length as in the previous example (0.31 m5ec) or up to 0.625 l1sec.

In this way, high-speed and high-resolution copied images can be obtained.

Even when the original image corresponds to a plurality of divided parts, and therefore the number of divided parts to be activated is plural, as long as the total number of times for applying voltage to these parts is less than the time for each electrode needle to contact the toner per line. The above configuration can be adopted. That is, when the number of divided parts to be operated is n, the time for applying voltage to the electrode needle of one divided part is t, and the time for which the electrode needle is in contact with the toner is T, then if nXt≦T is satisfied, the number n is There may be more than one, in the above example t = 0.3
Since 1m5ec, T=0.625 m5ec,
Up to n=2 is possible.

Judgments such as the form in which the original image is formed and which divided portions should be activated based on this form can be made not only visually by the operator, but also automatically by pre-scanning. . Additionally, this configuration is not limited to selectively using multiple styluses;
It goes without saying that the present invention can also be applied to cases where a plurality of modes are selectively used as described above.

When using a high-resolution stylus, including when switching modes, the height of the pulse voltage applied to each electrode needle can be increased without reducing the copying speed.
Naturally, a predetermined amount of charge may be injected into the toner. For reference, FIG. 1θ shows an example of the relationship between the height of the pulse voltage applied to the electrode needle and the amount of charge of the toner, using the width (time) of the pulse voltage as a parameter.

The configuration shown in connection with FIGS. 8 to 10 is as follows.

Not only when forming an electrostatic latent image on a photoreceptor in an analog manner, but also when forming a latent image digitally using a laser, an LED array, etc. based on an image signal on a latent image carrier including a photoreceptor or a dielectric material. It can also be applied to

According to the present invention, it is possible to produce multicolor images at higher speed and higher quality than before.
It is possible to obtain it with a device of compact construction.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing an example of a copying machine that implements the method according to the present invention, and FIGS. 2 (a) to (g) schematically illustrate the procedure for obtaining a multicolor image by the method according to the present invention. The explanatory diagram shown in FIG. 3 is a bottom view showing an example of a multi-stylus.
FIG. 4 is a side view thereof, FIGS. 5(a) to (g) are explanatory diagrams similar to FIG. 2 in other embodiments, and FIG. 6 is the relationship between the amount of charge of the toner and the density of the visible image. Graphs showing an example, Figures 7 (a) to (d) are explanatory diagrams showing the copying operation when different color images on the original are in contact with each other, and Figure 8 (a) is an illustration of the copying operation when the images are skewed. An example of the manuscript is shown in Figure 8 (b
) is a schematic diagram showing a multi-stylus divided into eight parts, No. 9
The figure is a perspective view showing a part of the first developing device in another embodiment, and FIG. 10 is a graph showing an example of the relationship between the voltage applied to the electrode needle and the amount of charge of toner. 6... Original 16... Color scanner CUI, C1J2... Color specification unit R1, Gl, Bl, BLI... Latent image RT, GT, BT, BLT, YT, MT, CT... Toner number Figure 1 Figure 2 Figure 3 Figure 5 (a

Claims (1)

[Claims] A process of determining the color of each document read by a color scanner and obtaining color information, a process of forming an electrostatic latent image corresponding to the document image on a latent image carrier, and a process of specifying a color based on the color information. A multicolor image forming method comprising the step of developing an electrostatic latent image unit by unit with toner of one or more colors.