JP2579043B2 - Color image forming equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a color copying machine to which electrophotography is applied.

2. Description of the Related Art In general, in order to form a color image by electrophotography, a method of forming a color image by superimposing toner images of yellow, magenta, cyan, and black is used. This method includes a method of sequentially developing toner images of respective colors on a sightseeing object which is a holder of an electrostatic image, and a method of developing a toner image on a photosensitive member.
There is a system in which each color is developed and transferred sequentially on a paper wound around a transfer drum. An example in which the former method is applied to a digital color copying machine is disclosed in, for example, JP-A-1-30774.
There is one shown in Japanese Patent Publication No.

FIG. 4 is a block diagram of a main part of the conventional digital color copying machine, and its configuration and operation will be briefly described below.

201 is a reading unit, which is mainly a document table 202 and a document illumination lamp.
It comprises a 203, a lens 204, a color line sensor 205, a drive system 206 for reciprocating these for scanning in the sub-scanning direction, and an image processing circuit (not shown). When the original is set on the platen and the copy button is pressed, first, the photoconductor 211 rotates, and the surface of the photoconductor is increased by 80 by the charger 212.
It is uniformly charged to about 0V. Further, the scanning of the reading section starts, a black image signal is calculated by the image processing circuit from the output of the color line sensor, and is input to the exposure system 213 to form a latent image pattern corresponding to the black image signal. At this time, the scanning of the reading unit and the writing by the exposure system are performed in synchronization. Next, this latent image passes through the other developing devices in a state where development is impossible, and is developed by the black developing device 217 to form a black toner image. At this time, the transfer / conveying unit 219 and the cleaner 222 are located at a position separated from the photoconductor 211, and the photoconductor surface on which the black toner image is formed is only neutralized by the neutralizer 221. The charger 212 uniformly charges the toner. Next, when the leading end of the black toner image on the photoreceptor surface comes to the exposure position, the reading unit has completed the first scanning and has returned to the start state. Then, the photoconductor 211 is exposed by the exposure system 213 from the top of the black toner image in accordance with the yellow image signal, and further developed by the yellow developing device 214. Other developing devices pass through the developing device in an undeveloped state. At this time, since the yellow development is performed in a non-contact manner with the toner image on the photoreceptor and is developed by flying with a DC bias, a new yellow toner image is formed without disturbing the black toner image. Similarly, magenta and cyan toner images are sequentially developed on a photoconductor by a magenta developing unit 215 and a cyan developing unit 216 to form a color image.
After the color image is formed, the toner image is transferred to a sheet fed from the sheet feeding unit 210 by the transfer / transport unit 219 in a transfer-enabled state. The toner remaining on the photoconductor after the transfer is cleaned by the cleaner 222 to prepare for the start of the next process.

The above is a brief description of the operation of the main part of the conventional digital color copying machine.

However, in the above configuration, there is a time interval between the end of the first reading scan by the reading unit and the preparation for the next reading start,
This greatly limits the total time for forming a color image and the size of the photoconductor. That is, since the reading scan and the writing of the latent image by the exposure unit are performed in synchronization with each other, for example, when the formation of the black latent image is completed, the reading unit has just completed the first scan, and thereafter the color sensor of the reading unit is used. And so on, and the latent image writing of the next color yellow cannot be started until the start of the next reading scan is ready. Therefore, a certain distance is required between the rear end and the front end of the image on the photoconductor, and for that purpose, the diameter of the photoconductor needs to be increased, and between the writing of one color and the writing of the next color. It takes much time, and the total time of image formation increases.

On the other hand, suppose that a photosensitive member having an outer periphery almost the same length as the maximum image length is provided, and a period in which the photosensitive member idles between the writing of the first color and the writing of the second color is waited until the reading section is ready. A method is conceivable. In this case, the photosensitive member can be small, but the total image forming time is very long.

On the other hand, the above problem can be solved by having a memory means for image information in the device,
The amount of image information memory required to obtain an image having a high resolution and a smooth gradation in image quality is enormous, which makes the device very expensive.

In view of the foregoing, the present invention provides a small, inexpensive and excellent high-speed color image forming apparatus by switching between a high-speed mode in which a color image can be formed at high speed and a normal mode in which high image quality can be obtained. The purpose is to provide.

Means for Solving the Problems In order to achieve the above object, the present invention provides a reading means for scanning a document to obtain color image information, and an image forming means for forming a color image by superimposing a plurality of color toner images. Multi-valued means for multi-leveling the output of the reading means; binarizing means for binarizing the output of the reading means with an information amount smaller than the multi-valued information amount; Image memory means for storing at least one color of the converted image information, and as the image information to be input to the image forming means, the output of the multi-level conversion means, the output of the binarization means, Alternatively, there is provided input control means capable of selecting any one of the outputs of the image memory means, and further, in the first normal mode, the input control means selects the output of the multi-value conversion means and selects the output for each color or screen. First interval specified for each In the second high-speed mode, the output of the binarizing unit and the output from the image memory stored at the same time are alternately selected in the second high-speed mode, and the output of the binarizing unit is shorter than the first interval. An object of the present invention is to provide a color image forming apparatus, which is an input control unit that operates so as to form an image at two intervals.

Operation According to the present invention, a high-resolution image having high resolution and excellent gradation can be obtained by the multi-valued image information in the normal mode with the above-described configuration.

On the other hand, in the high-speed mode, one latent image is formed based on the binarized image information at the time of reading and scanning by the reading unit, and at least the binarized image information for writing the next latent image is stored in the image memory. In addition, the input to the image forming unit is switched at the time when the previous latent image formation is completed, and the next latent image formation is performed by outputting image information from this image memory, during which the sensor of the reading unit and the like are operated. Return to prepare for the next reading start. By doing so, the latent images are formed one after another without waiting for the return time of the sensor or the like of the reading unit or preparation for picking up, so that a color image can be formed at high speed.

Also, since the next writing can be performed immediately after the writing of the previous latent image is completed, the minimum size of the image carrier is not necessary since the rear end and the front edge of the image on the image carrier need only have a minimum distance. It does not have to be large.

At this time, since the memory amount of the image memory is binary information, it is not so large.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a front view showing the overall configuration of a digital color copying machine to which the present invention is applied. The configuration and operation will be described below.

Reference numeral 1 denotes a reading section of a digital color copying machine, which is mainly a document table 2, a document illumination lamp 3, a lens 4, a color line sensor 5, a driving system 6 for moving these for scanning in the sub-scanning direction, and an image processing section 120. And

 Reference numeral 10 denotes a writing unit of the digital color copying machine.

Reference numeral 11 denotes a Se-based photoconductor whose sensitivity to laser light having a wavelength of 780 to 810 nm is sensitized and is rotatably supported in the direction of arrow A. Reference numeral 12 denotes a first charger for charging the surface of the photoconductor 11 to a predetermined positive potential, and reference numeral 26 denotes a laser beam.

Reference numeral 20 denotes a laser optical unit, and a laser beam light 26 is emitted from a laser oscillation block 21, a polygon scanner 22, and a lens system.
It is configured to scan over the photoreceptor 11 via 23, mirrors 24 and 25. A part of the scanning light of the laser beam light 26 is reflected by the mirror 27 and is irradiated on the start detection sensor 28. A developing unit 30 is provided on the right side of the photoconductor 11, and from the top along the periphery of the photoconductor 11, a Y developing unit 31 for yellow developing, an M developing unit 32 for magenta developing, and a C developing for cyan developing. A device 33 (hereinafter collectively referred to as a color developing device) and a K developing device 34 for black development are arranged. The Y developing device 31, the M developing device 32, and the C developing device 33 are non-contact developing devices using a non-magnetic one-component toner, and can perform development while flying toner in a non-contact manner with respect to the photoconductor 11. It is. K developer 34
Is a developing device that uses a two-component developer to develop while contacting the developer. Each developing device can take two positions, a position close to the photosensitive member 11 and a position away from the photosensitive member 11, and each of the eccentric cams 35 to 38 is rotated to rotate the Y developing device 31, the M developing device 32, and the C developing device. The rear portion of the developing device 33 is pushed to move horizontally to approach the photosensitive member, and the K developing device 34 is rotated counterclockwise about the shaft 39 to be in a state of approaching the photosensitive member, thereby enabling development. FIG. 1 shows a case where only the M developing device 32 is in a state capable of developing.

40 is an eccentric cam 35, 36, 37, 38 and developing units 31, 32, 33,
This is the motor that drives the 34.

Reference numeral 50 denotes a sheet feeding unit which can feed sheets one by one from each of the cassettes 51 and 52 and the manual sheet feeding unit 53. FIG. 2 shows a case where sheets 56 are fed from the cassette 51. .
The paper 56 is fed to the lower surface of the photoconductor 11 via the registration roller 54.

Reference numeral 60 denotes a transfer / conveying unit. The transfer / conveying unit 60 has two states: a state in which a semiconductive belt 63 suspended by rollers 61 and 62 is lightly pressed partially against the photoconductor 11, and a state in which the semiconductive belt 63 is separated from the photoconductor 11. It can move at the same speed as the outer peripheral surface of the photoconductor 11 in the direction of arrow B. FIG. 2 shows a state where the photosensitive member 11 is pressed against the photosensitive member 11. On the other hand, 64 is a second charger for transfer and a belt 63
The paper 56 fed between the belt 63 and the photoconductor 11 through
A negative high potential on the back surface of. Reference numeral 65 denotes a cleaning blade for cleaning the toner remaining on the belt, and a collection box 66 is disposed below the cleaning blade. 69
Is a third charger for sprinkling a negative corona when the sheet 56 is separated from the belt 63. In a fixing unit 70, a heat roller 72 heated by a fixing lamp 71 and a rubber roller 73 are rotatable while being pressed against each other, and a paper discharge roller 75 and a paper discharge tray 76 are provided at the rear thereof.

Reference numeral 80 denotes a cleaner which can take two states, that is, a state in which the fur brush 81 is lightly in contact with the photoconductor 11 and a state in which the fur brush 81 is separated from the photoconductor 11, and is rotatable in the direction of arrow D.
This figure shows a state where the photosensitive member 11 is in contact with the photosensitive member 11. Further, a collecting roller 82 is rotatably disposed while being in contact with the fur brush 81, and a negative voltage is applied to the photoconductor 11 to the fur brush 81 and the collecting roller 82, respectively. A collecting screw 83 is provided below the collecting roller 82, and a pipe 84 is connected to a front end of the collecting screw 83, and is connected to a collecting box 85 through the pipe 84. A fourth charger 86 for positively charging the toner on the photoconductor 11 and a static elimination lamp 87 for neutralizing the photoconductor 11 are disposed below the cleaner 80 at a position facing the photoconductor.

Reference numerals 91 and 92 denote cooling fans for sucking air from the lower and upper portions of the writing unit 10 and discharging the air to the outside of the apparatus.

The above is the outline of the overall configuration of the digital color copying machine to which the present invention is applied. Next, the operation will be described.

 First, the operation in the normal mode will be described.

When the document is set on the document table 2 and the copying operation is started, the document is read and scanned by the reading unit 1 and the output of the color sensor 5 is input to the image processing unit.

Hereinafter, the flow of signals in the image processing unit 120 and the operation of the image processing unit will be described with reference to FIG.

Output signals R, G, and B from the color sensor 5 are signals K, Y, M, and C corresponding to each color of black, yellow, magenta, and cyan to be formed by the writing unit 10 in the masking unit in the image processing unit 120. Is converted to These signals are output in real time when a reading scan is performed by the reading unit. These signals are signals having gradation information of 8 bits per image element.
Is input to the input switching unit 125 through the multi-level circuit 122 as a multi-level signal with 8 bits per image element. In the normal mode, the input switching unit 125 selects this signal as a signal to the writing unit 10, thereby writing image information. In this embodiment, the gradation information per one image element is multi-valued as a change in the laser lighting time to drive the laser.

In the writing section, an image is formed by a black signal by the operation described below.

First, a black signal is input to the laser oscillation block 21,
The photoreceptor 11 is irradiated with a laser beam light 26 modulated according to a black signal.

The photoreceptor 11 is uniformly charged to +850 V by the first charger 12 while rotating in the direction of arrow A, and the portion irradiated by the laser beam 26 according to the signal is discharged to about +50 V. The main scanning of the laser beam light 26 on the photoconductor 11 is performed by the polygon scanner 22, and the sub-scanning is performed by the polygon scanner 22.
To form a latent image on the photoreceptor. In the first writing of the latent image on the photoconductor, the developing unit 30 is set to a black developing state,
Only the eccentric cam 38 approaches the photoconductor 11 by the operation of the eccentric cam 38, and the other developing devices are in the separated state. Therefore, the latent image corresponding to the black signal formed by the laser beam light 26 is developed with the black toner by the K developing device 34 and passes without being affected by other developing devices. At this time, the K developing unit 34 performs the proximity operation before the photoconductor 11 is started to be exposed by the laser beam 26, and the separation / contact timing is controlled so as to separate after the development. The image developed with the black toner reaches the transfer / transport unit 60 as the photoconductor 11 rotates.
In this case, the roller 61 is at a position slightly rotated clockwise around the axis of the roller 62, the belt 63 is separated from the surface of the photoconductor 11, and the image passes without being disturbed. Further, the fur brush 81 is separated from the photoconductor 11 at a position slightly rotated counterclockwise around the axis of the collection screw 83, and the black toner image passes through the first charger again without being disturbed. Pass under 12. The portion of the photoconductor 11 where the black toner image is formed is recharged from above the toner by the first charger 12 again, and the portion without toner is charged to +850 V, and the portion with toner is apparently charged to +850 V.

The tip of the black toner image is recharged and the laser beam again
At the irradiation position 26, if the reading unit has completed the return operation and is ready to start the next reading, the Y signal from the masking unit in FIG. Is entered. At this time, the reading unit
If the first scan has just been completed and the next scan is not ready to start, the writing unit does not write the next color image and idles the photoconductor 11. For example, in the case of the image on the third row of the sheet A, the outer circumference of the photoreceptor 11 is almost large enough to allow some margin in the length of the third row of the sheet A. Required.

In this way, the yellow writing starts in accordance with the start of the next reading operation, and the laser beam light 26 is modulated according to the yellow signal and is exposed from above the black toner image on the photoconductor 11. Since the leading edge of the image is aligned and the scanning speed is constant, the black toner image and the latent image based on the yellow signal are formed so as to coincide in position. The latent image formed by the yellow signal is developed on the yellow toner only, because only the Y developing device 31 of the developing unit 30 is close to the photoconductor 11 and the other developing devices are separated. A yellow toner image is formed in addition to the black toner image. At this time, the Y developing device 31 is
Perform close proximity operation before exposure is started by the laser beam 26, and the separation / contact timing is controlled so as to be separated after development. At this time, since the yellow development is performed without contact, the previous black toner image is not disturbed. While the writing section is performing yellow writing, the reading section has already completed the return operation and is ready for the second scan start. Thereafter, in the same manner as in the case of the black signal and the yellow signal, recharging in the writing section, latent image formation by the magenta signal, magenta development, recharging, latent image formation by the cyan signal, and cyan development are repeated by the magenta signal and the cyan signal. It is.

At this time, since the yellow toner and the magenta toner transmit the laser beam, if exposed as necessary, that portion of the photoconductor is neutralized, and magenta and cyan toners are placed on the yellow toner, and cyan is placed on the magenta toner. Toner can be overlaid. After the last cyan toner image is formed, just before the leading end of the toner image reaches 60 in the transfer / conveying section,
The transfer conveyance unit 60 is lightly pressed against the photoconductor 11 and the paper 56 enters between the photoconductor 11 and the belt 63 by the registration roller 54 at the timing when the leading edge of the toner image and the leading edge of the paper 56 match. Will be fed.

While the toner image is transferred to the paper 56 by the electric field generated by the second charger 64, the paper 56 is conveyed while being adhered to the belt 63, but separates from the belt 63 because of the large curvature at the roller 62 and enters the fixing unit. I do. At this time, the paper 56 is separated from the belt by the separation electrification generated on the paper 56.
In order to prevent the toner image on 56 from being disturbed, a negative corona is sprinkled from above by a third charger. The toner image on the sheet is fixed on the sheet discharge tray 76 after being fixed by the fixing unit.

On the other hand, the untransferred toner image remaining on the photoreceptor 11 is positively charged by a fourth charger 86 which starts operating immediately before the leading end thereof approaches, and the fur brush which is brought into contact with the photoreceptor 11 almost simultaneously. The electric field applied between the fur brush 81 and the photoconductor 11 moves to the fur brush 81 while being inspected by 81. Further, the toner in the fur brush 81 is transferred to the collecting roller 82 by the electric field applied between the collecting roller 82 and the fur brush 81, dropped by the collecting screw 83, and stored in the collecting box through the pipe 84.

The surface of the photoreceptor 11 is thereby cleaned, and at the same time, the charge is removed by the charge removing lamp 87, and the photosensitive member 11 is returned to the initial state, and the preparation for the next copy is completed.

On the other hand, the toner accumulated on the belt 63 of the transfer conveyance unit 60 due to an operation error or usually minutely is cleaned by the cleaning blade 65 and dropped into the collection box 66. The above is the operation in the normal mode. In the above case, the writing of the latent image by the laser beam in the writing unit is driven by a signal which is multi-valued with 8 bits per image element, so that the image has a high resolution and a high gradation with excellent gradation. High quality image quality can be obtained.

Next, the operation in the case of A3 copy in the high-speed mode will be described.

In FIG. 2, the Y and K signals obtained in the first reading operation of the reading unit are
After 3, the K binarized signal is sent to the input switching unit 125, and the Y binarized signal is sent to the image memory and stored. In the high-speed mode, the input switching unit first selects a K signal from the halftone processor as a signal to the writing unit and sends it to the writing unit. In the writing section, a black image is written in the same manner as in the normal mode. When the writing of the black image is completed and the tip of the black image comes to the next laser writing position, the input switching unit selects the Y signal output of the image memory as a force to the writing unit. Therefore, at this time, even if the reading section has just finished the first reading operation and is in the return operation, the writing of the yellow image can be performed without any trouble.

By writing magenta and cyan images in the same manner, even in the case of the third row of sheet A, it is possible to form an image at high speed without loss of the idling time of the photoconductor. In this case, since the driving of the writing laser is a binary signal indicating that one image element is 1 or 0, if the capacity of the image memory 124 is equal to the number of bits of the number of image elements of one screen of the third row of the paper A row, Good.

In the case of the present embodiment, an error diffusion method is used as a halftone processor, and an image having a high resolution in the high-speed mode but a slightly smaller number of gradations than in the normal mode is obtained.

Other halftone processors may be used,
For example, using the dither method, in the high-speed mode as compared with the normal mode, an image having high gradation but a slightly lower resolution may be obtained.

Next, a case in which the color image of the fourth row of the paper A row is continuously copied at a high speed will be described. In the case of continuously copying a color image of A4 size paper, the same color image is formed two by two with a slight interval S on the photosensitive member as shown in FIG. In other words, in the first scanning of the reading unit, the same black signal is stored in the image memory 124 in FIG. This first
At the end of the second scan, an A4 black latent image has been written to about half of the outer circumference of the photoconductor. Then, the writing unit 1 is operated by the operation of the input switching unit 125.
The input to 0 is switched from a direct signal from the halftone processor 122 to a signal from the image memory 125, and the same black latent image as before is written in the other half of the photoconductor. During the writing, the reading unit 1 performs a return operation. When writing the next yellow to the first image is started, the reading unit 1 is already ready for the next scan. Therefore, the interval S can be made very small, and in this case, the outer peripheral length of the photoreceptor only needs to have some margin in the length of the third row of the sheet A, and further, two color images can be formed by four rotations of the photoreceptor. This allows copying of the constraints. On the other hand, when a color image of the size of A4 paper is continuously copied in the normal mode, a high-quality image with good gradation is obtained because the output of the multi-level circuit 122 is used for writing. Since a memory cannot be used, a scan must be performed every time an image is formed. However, as described above, the outer peripheral length of the photoreceptor is reduced to just the length of the A3 plate and a little margin, so that two sheets are formed including the return time of the reading unit during one rotation of the photoreceptor. Can not do. That is, one rotation of the photoconductor forms an image for one A4 screen and one color, and four rotations of the photoconductor form one color image at a time. Therefore, the normal mode is a mode in which a low-speed but high-quality image can be obtained.

As described above, in the present embodiment, it is sufficient that the maximum length of the image has some margin as the outer peripheral length of the photoconductor, and the apparatus becomes small, and in the high-speed mode, the third row of the paper A row 3 High-speed color image formation is possible because continuous writing is possible with a small memory capacity of the number of image elements of a size regardless of the return time of the reading unit. In addition, in the normal mode, since writing can be performed with gradation information for each image element, a high-quality color image with high gradation and high resolution can be obtained.

In this embodiment, the color image forming apparatus of the type in which the toner images of the respective colors are sequentially superimposed and developed on the photoreceptor which is the holding body of the electrostatic image has been described. The same effect can be obtained by a method in which the image is sequentially transferred on the paper wound around the transfer drum.

According to the present invention, with a small memory capacity, in the high-speed mode, the latent image can be continuously written irrespective of the time of the preparation operation when the reading unit is not scanned, so that a high-speed color image can be formed. Since the size of the image carrier can be a minimum size, a small and high-speed color image forming apparatus can be provided.

Further, in the normal mode, a high-quality image with high resolution and excellent gradation is obtained, so that a small-sized and inexpensive color image forming apparatus with excellent functions can be provided.

Furthermore, when the image to be created is small, the same color image can be continuously formed at small intervals on the photoconductor,
A high-speed color image forming apparatus having a very high continuous copying speed can be provided.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a digital color copying machine according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a signal flow and operation in an image processing unit, and FIG. FIG. 4 is a diagram showing a conventional example. 1 ... Reading unit, 5 ... Color sensor, 11 ... Photoconductor, 20 ... Laser optical unit, 30 ... Development unit, 50 ... Supply unit, 60 ... Transfer / convey unit, 70 ... Fix and discharge Paper section, 80 Cleaner removing section, 10 Writing section, 120 Image processing section, 1
22 Multi-valued circuit 123 Halftone processor 124
…… Image memory, 125 …… Input switching unit.

Claims (1)

(57) [Claims] A scanning means for scanning a document to obtain color image information; an image forming means for forming a color image by superimposing toner images of a plurality of colors; And binarizing the output of the reading unit with an information amount smaller than the multi-valued information amount.
A binarizing unit, and an image memory unit for storing at least one color of the binarized image information, and as image information to be input to the image forming unit, an output of the multi-valued unit, Input control means for selecting either the output of the binarization means or the output of the image memory means, and further comprising: the input control means, in a first normal mode, an output of the multi-value conversion means. To perform image formation at a predetermined first interval for each color or each screen. In the second high-speed mode, the output of the binarizing means and the output from the image memory stored simultaneously at the time of output are output. And alternately select
The color image forming apparatus is an input control unit that operates to form an image at a second interval shorter than the first interval.