JPH10177283A - Monochrome/color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple method whereby monochrome-image formation productivity is substantially improved in comparison to color image formation productivity without causing a degradation in monochrome image quality as much as possible. SOLUTION: A monochrome/color image forming device 1 reads the image of an original document by means of an image reader, and forms a color image in the case of a color mode by repeating the processes of electrification, exposure, and development several times on a photoreceptor 7 and then transferring to recording paper and also forms a monochrome image in the case of a monochrome mode by performing the processes of electrification, exposure, and development one time on the photoreceptor 7 and then transferring to recording paper. In the monochrome/color image forming device, a monochrome image storage device 6 is provided for storing, in the monochrome mode, monochrome image data corresponding to the monochrome image to be outputted, and a processing-speed switching means is also provided for making the speed of the image formation process in the monochrome image higher than that in the color mode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for developing an electrostatic latent image formed on an electrostatic latent image carrier such as a photoreceptor by using a powder developer to form a toner image on the electrostatic latent image carrier. The present invention relates to a black-and-white color image forming apparatus for forming a toner image and transferring and fixing the toner image on a recording medium such as paper.

[0002]

2. Description of the Related Art As is well known, in a color image forming apparatus, in a color mode, a color image is formed by fixing a toner image obtained by superimposing a plurality of developed images on a recording medium, and in a black and white mode. Discloses that a black-and-white image is obtained by fixing a black single-color toner image on a recording medium.

Although there are various types of color image forming apparatuses, a single electrostatic latent image carrier is used in common for each color, and toner images of each color sequentially formed on the electrostatic latent image carrier are formed. In a color image forming apparatus of a type in which a transfer is performed while being superimposed on a recording material wound around a transfer drum, the process speed for forming a black-and-white image and the process speed for forming a color image are the same. For example,
In the case of a color image forming apparatus that performs four-color development, the productivity of a black-and-white image has increased only four times the productivity of a color image.

Further, for a high quality color image, the control accuracy of the entire system must be increased, and the process speed cannot be increased significantly.

A tandem type color image forming apparatus in which a plurality of image forming apparatuses are arranged in parallel in order to increase the color copying speed and image formation of each color is processed in parallel is also known. Also in the color image forming apparatus, the process speed in the monochrome mode is the same as the process speed in the color mode, and the productivity of monochrome image formation is determined by the limitations of the color image forming apparatus.

[0006]

In order to greatly increase the productivity of monochrome image formation relative to the productivity of color image formation, it is necessary to increase the process speed at a level at which there is no problem with black and white image quality. However, in a conventional full-color copying machine, the process speed is the same for black and white and color in order to guarantee the positional deviation accuracy due to the repetitive operation of the scanning carriage of the image reading device and to prevent the image quality from deteriorating due to vibration or the like. In addition, a full-color copying machine generally reproduces an image using a four-color plate of black, yellow, magenta, and cyan. Therefore, unless a four-color memory for one A3-size sheet is provided, one full-color copying machine is used. 4 manuscripts
It is necessary to scan twice, and the copy speed is limited due to the speed limit of the image reading device.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a simple method for greatly improving the productivity of monochrome image formation with respect to the productivity of color image formation without deteriorating monochrome image quality as much as possible.

[0008]

According to the present invention, an image of a document is read by an image reading apparatus, and in a case of a color mode, a plurality of steps of charging, exposure and development are performed on an electrostatic latent image carrier. A color image is formed by transferring the image onto a recording sheet after repeating the process, and in the case of a black and white mode, each of the charging, exposure and development steps is performed once on the electrostatic latent image carrier, and then the recording sheet is formed. A black-and-white color image forming apparatus that forms a black-and-white image by transferring the image to a black-and-white image storage device that stores black-and-white image data corresponding to the black-and-white image to be output in the black-and-white mode; A process speed switching means capable of making the speed higher than that in the color mode.

In the black and white color image forming apparatus of the present invention, in the black and white mode, the original is read only once and the black and white image data is stored in the black and white image storage device. When a monochrome image is formed, the monochrome image data is repeatedly read from the monochrome image storage device, and a required number of monochrome images are output. Also, in the black and white mode,
The image forming process speed is made faster than in the color mode.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

<First Embodiment> FIG. 1 is a schematic view showing a principle configuration of a first embodiment of a monochrome / color image forming apparatus according to the present invention.

The monochrome / color image forming apparatus 1 is roughly divided into an image reading section 2 for reading an image of a document and converting the image into an image signal, and performs predetermined signal processing on the image signal from the image reading section 2. It comprises a signal processing unit 3 to be applied and an image forming unit 4 for forming an image on a sheet based on an image signal from the signal processing unit 3.

The image reading section 2 has a scanning carriage 2b which moves along the lower surface of a platen glass 2a on which a document D is placed, and is attached to the scanning carriage 2b to convert an image of the document into an electric image signal. And a color image sensor 2c.

A signal processing section 3 stores an image processing circuit 5 for performing color correction and gradation correction on an image signal from the color image sensor 2c of the image reading section 2, and stores monochrome image data in a monochrome mode. Black and white image storage device 6 for performing
Etc. are provided. It is assumed that the monochrome image storage device 6 has a through function or a bypass function for directly outputting input data.

The image forming section 4 includes a drum-shaped photosensitive member 7 serving as an electrostatic latent image carrier, and a charging device 8 such as a corotron or a scorotron for uniformly charging the surface of the photosensitive member 7.
An exposure device 9 for exposing the surface of the photoconductor 7 according to an image signal to form an electrostatic latent image on the surface of the photoconductor 7;
A rotary type multicolor developing device 10 that is arranged in close proximity to the photosensitive member 7 and sequentially develops the electrostatic latent images formed on the surface of the photoconductor 7 with toners of different colors to form toner images of the respective colors;
A drum-shaped transfer member 11 which is arranged close to the photoreceptor 7 and rotates in a state in which a sheet is wrapped around the photoreceptor 7; a paper tray 12 for storing sheets on which an image is to be formed; A transfer device 13 for transferring the toner image formed on the surface of the photoconductor 7 to the surface of the paper around which the transfer body 11 is wound, and a paper for separating the paper from the surface of the transfer body 11 , A fixing device 14 having a heating roll 14a and a pressure roll 14b for performing a fixing process on the transferred paper separated from the transfer body 11, and a photoconductor 7 after the transfer. And a cleaning device 15 for removing the toner remaining on the surface.

The rotary type multicolor developing device 10 includes color developing units 10a, 10b, 10c, 1 arranged in a ring.
The developing device using the toner of the color to be developed is controlled so as to face the surface of the photoconductor 7 by rotating about the shaft 10e. Each color developing device includes a toner cartridge containing a toner of a different color, a rotating sleeve disposed at a position facing the surface of the photoreceptor 7, and an auger (toner) for supplying the toner in the toner cartridge to the developing sleeve. (Not shown).

FIG. 2 is a principle block diagram showing an electric signal system of the monochrome / color image forming apparatus shown in FIG.

The color image sensor 2c of the image reading section 2
Are supplied to the image processing circuit 5 and subjected to image processing such as color correction and gradation correction, and then supplied to the memory 6a of the monochrome image storage device 6. The memory 6a stores monochrome image data in the monochrome mode. Memory 6
The content of a is read out in synchronization with the video clock and supplied to the exposure device 9.

The exposure device 9 includes a laser modulation circuit 9a to which the output of the memory 6a is supplied, and a laser to which the output of the laser modulation circuit 9a is supplied in synchronization with the video clock and emits a laser beam modulated with image data. 9b and laser 9b
A rotating polygon mirror 9c for reflecting the laser beam from the mirror to scan the surface of the photoconductor 7, and a motor 9d for rotating the rotating polygon mirror 9c.

The memory 6a and the laser modulation circuit 9a are provided with a clock generation circuit 1 for determining the timing of writing / reading to / from the memory 6a and for determining the timing of modulation in the laser modulation circuit 9a.
6 generates a video clock.

The frequency of the video clock from the clock generation circuit 16 is controlled by a control circuit 17. The control circuit 17 includes a high-voltage control circuit 18 for controlling the voltage applied to the charging device 8, a high-voltage control circuit 19 for controlling the voltage applied to the transfer device 13, and a motor 9d of the exposure device 9. , A motor drive circuit 22 for controlling a motor 21 for rotationally driving the photoconductor 7, a scan control circuit 23 for controlling a scanning operation in the image reading section 2, a monochrome / black / white combination An operation panel 24 for inputting various instructions to the color image forming apparatus 1 and displaying an operation state of the image forming apparatus;
A high-voltage control circuit 32 for controlling the voltage applied to the static eliminator 31 and the like are connected.

Next, the operation in the color mode in the black-and-white color image forming apparatus 1 will be described.

When a document is placed on the platen glass 2a and a color mode is designated from the operation panel 24, and then a start button is pressed, the same document is scanned four times repeatedly for the same document. Each time, the image processing circuit 5 performs image processing in the order of black, yellow, magenta, and cyan, for example. At this time, the memory 6a is in a through state, the output of the image processing circuit 5 is supplied to the exposure device 9 as it is, and an electrostatic latent image corresponding to each color image is sequentially formed on the surface of the photoreceptor 7. Is done. Further, a video clock having a frequency f1 is supplied to the laser modulation circuit 9a.

In the first document scanning, image data corresponding to a black image is output from the image processing circuit 5, and an electrostatic latent image corresponding to the black image is formed on the surface of the photoconductor 7. At this time, the black developing device of the rotary type multicolor developing device 10 faces the photoreceptor 7, and the electrostatic latent image is developed with black toner to form a black toner image. At the time of development, toner in a toner cartridge (not shown) is supplied to a rotating sleeve (not shown) by an auger (not shown) and adheres to the outer peripheral surface of the rotating sleeve. And is sent in the direction of the photoconductor 7 to develop the electrostatic latent image on the photoconductor 7.

On the other hand, the paper fed from the paper tray 12 is wound around the transfer member 11 and rotates together with the transfer member 11, and the black toner image on the photoreceptor 7 is wound around the transfer member 11. Is transferred to the printed sheet. The black toner remaining on the photoconductor 7 is removed by the cleaning device 15.

In the second original scanning, image data corresponding to the yellow image is output from the image processing circuit 5, and an electrostatic latent image corresponding to the yellow image is formed on the surface of the photoconductor 7. At this time, the rotary type multicolor developing device 10 is rotated so that the yellow developing device is opposed to the photoconductor 7, and the electrostatic latent image is developed with yellow toner to form a yellow toner image.

The yellow toner image on the photoreceptor 7 is transferred on the paper on which the black toner image is already formed, which is wound around the transfer member 11. The yellow toner remaining on the photoconductor 7 is removed by the cleaning device 15.

Similar processing is performed for magenta and cyan, and black, yellow, magenta, and cyan toner images are transferred onto the paper wound around the transfer body 11 in a superimposed manner, and a full-color image is formed. It is formed.

Next, the paper on which the full-color image has been formed is peeled off from the transfer body 11 by the charge removing device 31, sent to the fixing device 14 and subjected to a fixing process, and a copy of the full-color image is completed.

In the case of the second and subsequent copies, similarly to the above-described operation, the original is scanned four times to output the second and subsequent color copies.

In the case of a color copier, an image is generally read at 400 dots / inch and 256 gradations in order to obtain high image quality. The read digital data is read by an image processing circuit 5 using an image processing circuit 5. The signal is converted to a signal that matches the characteristics. Reads originals with such high image quality, and
There is a limit to the speed of image processing, and there is a limit to increasing the copy speed while maintaining high image quality.

In the present invention, the black-and-white image data is stored in a storage device in advance, and the operation of the image reading device is not performed at the time of the black-and-white copy, so that the black-and-white copy speed is increased. I have.

Next, the operation in the black-and-white mode in the above-described black-and-white color image forming apparatus will be described.

When a document is placed on the platen glass 2a and the black and white mode is designated from the operation panel 24 and the start button is pressed, the document is scanned only once by the document, and the image processing circuit 5 Performs black image processing. The output of the image processing circuit 5 is stored in the memory 6a of the black-and-white image storage device 6 and then supplied to the laser modulation circuit 9a of the exposure device 9, where the surface of the photoconductor 7 has an electrostatic latent image corresponding to a black image. Is formed. At this time, the clock generation circuit 16 is controlled by the control circuit 17, and the frequency of the video clock supplied to the memory 6a and the laser modulation circuit 9a is set to f2 higher than f1.

In the monochrome mode, the image data corresponding to the black image is stored in the memory 6a of the monochrome image storage device 6 at the frequency f2.
, And an electrostatic latent image corresponding to a black image is formed on the surface of the photoconductor 7. At this time, the black developing device of the rotary type multicolor developing device 10 faces the photoreceptor 7, and the electrostatic latent image is developed with black toner to form a black toner image.

On the other hand, the paper fed from the paper tray 12 is wound around the transfer
, And the black toner image on the photoconductor 7 is transferred to the paper wound around the transfer body 11. The black toner remaining on the photoconductor 7 is removed by the cleaning device 15.
To be removed.

The paper on which the black-and-white image is formed is peeled off from the transfer body 11 and sent to a fixing device 14 to undergo a fixing process.
The copy of the black and white image is completed.

In the case of the second copy, scanning of the original is not performed, and monochrome image data from the memory 6a of the monochrome image storage device 6 is synchronized with the video clock of frequency f2 supplied from the clock generation circuit 16. The readout is supplied to the exposure device 9 and a copy of a black and white image is output by the same operation as that described above.

In the case of the second and subsequent copies, since the original is not scanned, the time required for copying is reduced by the time required for scanning the original. As a result, the copy speed in the monochrome mode can be made higher than four times the copy speed in the color mode.

Further, in the case of the monochrome mode, it is not necessary to consider the color shift as in the case of the color mode, so that the positional accuracy of image formation can be made lower than in the case of the color mode, and the process speed itself can be reduced. Can be faster.
That is, even if the process speed in the black-and-white mode is higher than that in the color mode, the image quality of the black-and-white image is not substantially reduced.

In order to increase the process speed, the photosensitive member 7
It is necessary to increase the rotation speed of the rotating polygon mirror 9c. Further, it is necessary to increase the frequency of the video clock supplied to the memory 6a of the monochrome image storage device 6 and the laser modulation circuit 9a in proportion to the increase in the rotation speed of the rotary polygon mirror 9c.

Therefore, in the present embodiment, when the monochrome mode is designated from the operation panel 24, the control circuit 1
7, the rotation speed of the motor 21 is increased through the motor drive circuit 22 to increase the rotation speed of the photosensitive member 7, and the rotation speed of the motor 9d is increased through the motor drive circuit 20 to rotate the rotating polygon mirror 9c. Speeding up. Further, the frequency of the video clock of the clock generation circuit 16 is increased by the control circuit 17. Further, by the control circuit 17,
The operating speed of the fixing device 14 is increased.

Further, various control parameters are controlled with the increase in the process speed. In the present embodiment, as described below, the control was changed for the charging condition, the exposure condition, the developing condition, the transfer condition, and the fixing condition.

[Charging Condition] In the black-and-white mode, the corona generation amount is increased as compared with the color mode. Specifically, the voltage applied to the discharge wire of the corotron discharge device or the scorotron discharge device constituting the charging device 8 is adjusted so that the surface potential of the electrostatic latent image carrier, that is, the photoconductor 7 is held at the target. I raised it. This is because, when only the process speed is increased, the amount of ions sprinkled onto the surface of the photoconductor 7 per unit surface area per unit time decreases, and the surface potential of the photoconductor 7 decreases.

Also, a method other than corona discharge, for example,
In the case of roll contact charging, brush contact charging, and the like, control may be performed to increase the charge amount.

[Exposure Conditions] In the monochrome mode, the latent image writing speed is increased and the exposure light amount is increased as compared with the color mode. Specifically, the frequency of the video clock is increased in proportion to the increase in the process speed, and the rotation speed of the rotary polygon mirror 9c is increased. Further, since the photoreceptor 7 has a characteristic of forming a latent image in response to the light amount, the laser modulation circuit 9a is controlled so that the light amount per unit area is the same in the monochrome mode and the color mode. Increase the amount of exposure light.

[Developing Conditions] In the black-and-white mode, the developer supply speed to the surface of the photosensitive member 7 is increased as compared with the color mode. Specifically, as the process speed increases, the number of rotations of the rotating sleeve of the developing device in operation in the rotary multicolor developing device 10 increases. In addition, the auger transport amount increases with an increase in the sleeve rotation speed. This is because if the process speed increases, the amount of toner consumed per unit time increases, so that it is necessary to increase the toner supply rate.

[Transfer Conditions] In the monochrome mode, the transfer current is increased as compared with the color mode. Specifically, as the process speed increases, the high-voltage control circuit 19 is controlled to increase the transfer current in the transfer device 13. this is,
When the process speed increases, the transfer area per unit time increases, so that the transfer current per unit area is made equal so as not to lower the transfer efficiency.

[Electrification Elimination Conditions] In the monochrome mode, the static elimination current is increased as compared with the color mode. Specifically, as the process speed increases, the high-voltage control circuit 32 is controlled to control the high-voltage control circuit 32 so that the corona discharge current in the corona discharge device constituting the neutralization device 31, that is, the amount of electric charge discharged to the paper becomes the target neutralization current. Increase the current. This is because if the process speed is increased, the static elimination area per unit time is increased, so that the static elimination current per unit area is made equal so as not to lower the static elimination efficiency.

[Fixing Condition] In the monochrome mode, the amount of fixing heat is increased as compared with the color mode. In particular,
The amount of heat generated by the heating roll 14a of the fixing device 14 is increased. This is because the amount of heat supplied to the fixing device 14 per unit time is increased, so that the amount of heat applied to the recording paper is kept constant even when the paper passing speed increases. Further, as the paper passing speed increases, the supply amount of the fixing oil supplied to the heating roll 14a increases.

As described above, in the monochrome mode, the process speed is made faster than in the color mode, and various control parameters contributing to image formation are changed with the increase in the process speed. The productivity of black-and-white images can be increased without lowering the image quality.

<Embodiment 2> FIG. 3 is a schematic view showing the principle configuration of a second embodiment of a black-and-white color image forming apparatus according to the present invention. FIG. 4 is a principle block diagram showing electric signals of the monochrome / color image forming apparatus shown in FIG. The members corresponding to those of the first embodiment are denoted by the same reference numerals.

In the second embodiment, a black-and-white image forming exposure device 25 and a color image forming exposure device 26 are separately provided.

The exposure device 25 for forming a black-and-white image, like the exposure device 9 of the first embodiment, includes a laser modulation circuit 25a, a laser 25b, a rotary polygon mirror 25c, a motor 25d, and the like. The output of 6 is supplied to the laser modulation circuit 25a. However, unlike the first embodiment, the laser modulation circuit 25 of the black-and-white image forming exposure device 25 is different from the first embodiment.
The frequency of the video clock supplied to a is a constant frequency f2 higher than the frequency f1 of the video clock in the color mode. Further, the video clock having a constant frequency f2 higher than the frequency f1 of the video clock in the color mode is also supplied to the monochrome image storage device 6.

The exposure device 26 for forming a color image also has a laser modulation circuit 26 similar to the exposure device 25 for forming a black and white image.
a, a laser 26b, a rotary polygon mirror 26c, a motor 26d, and the like. The output of the image processing circuit 5 is directly supplied to the laser modulation circuit 26a of the exposure device 26 for color image formation. The frequency of the video clock supplied to the laser modulation circuit 26a is a constant frequency f1 that is lower than the frequency f2 of the video clock in the black and white mode.

The motor 25d of the black-and-white image forming exposure device 25 and the motor 26d of the color image forming exposure device 26
d denotes a motor 25 of the black-and-white image forming exposure device 25 to which respective motor drive circuits 27 and 28 are connected.
The rotation speed of d is independently controlled so as to be higher than the rotation speed of the motor 26d of the color image forming exposure device 26. Further, the laser 25 of the exposure device 25 for black and white image formation is used.
The laser modulation circuits 26a and 26b are set so that the exposure amount by b becomes larger than the exposure amount by the laser 26b of the color image forming exposure device 26.

FIG. 5 is a flowchart showing a schematic flow of an image forming operation in the second embodiment.

When the start button provided on the operation panel 24 of the monochrome / color image forming apparatus 1 is pressed (step 101), the image reading apparatus 2 first performs a preliminary scanning of the document (step 102). This preliminary scanning is performed for the purpose of detecting the size of the document, determining the type of the document (photo / text, black / white / color), and the like. Next, it is determined whether the operation mode of the image forming apparatus is the monochrome mode or the color mode (step 103). The determination of the mode is performed based on the information on the type of the document obtained by the above-described preliminary scanning, or based on the operation mode set in advance from the operation panel 24.

If the mode is not the monochrome mode, that is, if the mode is the color mode, the image reading device 2 performs the main scanning of the original (step 104), and the image of the original is converted into an image signal by the image sensor 2c. The predetermined image processing is performed by the image processing circuit 5 (step 10).
5), it is supplied to the color image forming exposure device 26 (step 106). The processing of steps 104 to 106 is performed once for each color of yellow, magenta, cyan, and black.
(Step 107), and the image forming section 4 outputs one color copy (Step 108). The processes of steps 104 to 108 are repeated for the set number of copies (step 109). By the above-described processes of 104 to 109, a set number of color copies are output.

If it is determined in step 103 that the mode is the monochrome mode, the main scanning of the original is performed (step 1).
10) The image of the document is converted into an image signal by the image sensor 2c, undergoes predetermined image processing by the image processing circuit 5 (step 111), and is stored in the monochrome image storage device 6 (step 112). Next, the monochrome image data is read out from the monochrome image storage device 6 in synchronization with the video clock having a higher frequency than in the color mode (step 1).
12), the exposure speed of the color image forming exposure device 26
It is supplied to the exposure device 25 for forming a black and white image which has been made faster (step 113). Thus, one black-and-white copy is output in the image forming section 4 (step 114).
The processing of steps 113 to 114 is repeated for the set number of copies (step 115). By the above processing, the set number of monochrome copies is output at high speed.

In the second embodiment, since the black-and-white image forming exposure device 25 and the color image forming exposure device 26 are separately provided, the frequency of the video clock supplied to the laser modulation circuit can be switched. In addition, there is no need to switch the rotation speed of the motor for rotating and driving the rotary polygon mirror.

<Embodiment 3> In the third embodiment, a platen cover sensor 29 for detecting the opening / closing operation of the platen cover is provided as shown by a broken line in FIG.
When the opening / closing operation of the platen cover 30 (see FIG. 1) is detected, the document image is read and stored in the monochrome image storage device 6 before the start button is pressed. Or,
The operation panel 24 is provided with a dedicated monochrome priority button for selecting the monochrome image formation speed priority mode. When the monochrome priority button is pressed, the original image is read before the start button is pressed, and the monochrome image storage device is read. Is stored.

FIG. 6 is a flowchart showing a schematic flow of an image forming operation in the third embodiment. Steps corresponding to those in the flowchart shown in FIG. 5 are denoted by the same reference numerals.

The flowchart shown in FIG. 6 has steps similar to those of the flowchart shown in FIG. 5, but a step 201 for detecting the opening / closing operation of the platen cover is inserted at the beginning of the processing. Steps 202 and 203 for detecting that the start button is pressed are inserted between steps 103 and 104 and between steps 112 and 113, respectively, and step 101 is deleted. If a monochrome priority button is provided, it is determined in step 201 whether the monochrome priority button has been pressed.

In the third embodiment, when the opening / closing operation of the platen cover is detected, or when the monochrome priority button is pressed (step 201), the image forming mode is determined (step 103), and the color mode is set. If there is, in step 202, the process waits until the start button is pressed. The operation after the start button is pressed is the same as in the flowchart shown in FIG.

When the mode is the monochrome mode, the main scanning of the original (step 110), image processing (step 111), and storage in the monochrome image storage device 6 are performed (step 11).
2) Wait for the start button to be pressed in step 203. The operation after the start button is pressed is the same as in the flowchart shown in FIG.

As described above, in the third embodiment,
Since the original image is read in advance and stored in the black-and-white image storage device 6, it is possible to shorten the time when the copy is actually discharged after the start button is pressed. Also,
In particular, when detecting the opening and closing operation of the platen cover,
Even if the original is once placed on the platen glass 2a and then replaced with another original, each time the platen cover 30 is opened and closed, the image of the original is overwritten and saved in the monochrome image storage device 6. You. Thus, even if the document is replaced before the start button is pressed, a black-and-white copy with the latest image data can always be output.

<Embodiment 4> In the fourth embodiment, step 10 of the document preliminary scanning of the flowchart shown in FIG.
In step 2, the type of the document is determined by identifying the content of the image of the document, and the mode is set to either the monochrome mode or the color mode. In step 103, the mode is automatically switched. The operation after step 103 is the same as in the previous embodiment.

Here, if the image read in the original preliminary scanning is a black-and-white image and a character image, the monochrome mode is set, and if not, the color mode is set. That is, in the present embodiment, the monochrome copy speed priority mode is set only for text and monochrome documents. Thereby, the operation of selecting the mode by the operator can be omitted, and the burden can be reduced.

[0070]

By adding an image storage device for one color to the conventional structure and increasing the process speed only in the black and white mode, the black and white productivity capability, which is a drawback of the black and white color image forming apparatus, is improved. In addition to this, the cost of only the storage device for one color can be increased.

When the image forming apparatus is driven by one main motor, the process speed of the entire image forming apparatus can be easily increased by increasing the rotation of the main motor. The process speed can be increased without performing.

If the black and white image data is fetched before pressing the start button, the time from when the start button is pressed until the first copy is obtained can be shortened.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of a black-and-white color image forming apparatus of the present invention.
It is a schematic diagram which shows the principle structure of Example of this.

FIG. 2 is a basic block diagram showing electric signals of the monochrome / color image forming apparatus shown in FIG.

FIG. 3 shows a second embodiment of the black-and-white color image forming apparatus of the present invention.
It is a schematic diagram which shows the principle structure of Example of this.

4 is a basic block diagram showing electric signals of the monochrome / color image forming apparatus shown in FIG. 3;

FIG. 5 is a flowchart showing a schematic flow of an image forming operation in a second embodiment.

FIG. 6 is a flowchart showing a schematic flow of an image forming operation in a third embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Black-and-white color image forming apparatus 2 ... Image reading part 2
c ... color image sensor, 3 ... signal processing unit, 4 ... image forming unit, 5 ... image processing circuit, 6 ... black and white image storage device, 7
... Photoconductor, 8 ... Charging device, 9 ... Exposure device, 10 ... Rotary multicolor developing device, 11 ... Transfer body, 12 ... Paper tray, 13 ... Transfer device, 14 ... Fixing device, 15 ... Cleaning device, 16 ... Clock generation circuit, 17 ... control circuit,
18 high voltage control circuit, 19 high voltage control circuit, 20 motor drive circuit, 21 motor, 22 motor drive circuit, 2
3 ... Scan control circuit, 24 ... Operation panel, 25 ... Exposure device for black and white image formation, 26 ... Exposure device for color image formation, 2
7, 28: motor drive circuit, 29: platen cover sensor, 30: platen cover, 31: static eliminator, 32: high voltage control circuit

Claims (8)

[Claims] 1. An image reading apparatus reads an image of an original by an image reading apparatus, and in a case of a color mode, repeats charging, exposing, and developing processes on an electrostatic latent image carrier a plurality of times, and then transfers the image onto a recording sheet. In the black-and-white mode, a charging, exposure, and development process is performed once on the electrostatic latent image carrier, and then transferred to a recording sheet to form a black-and-white image. A black-and-white color image forming apparatus for forming, in a black-and-white mode, a black-and-white image storage device for storing black-and-white image data corresponding to a black-and-white image to be output; A black-and-white color image forming apparatus, comprising: 2. A raster output scanner for performing the exposure step, the raster output scanner being at least a laser modulation circuit operating in synchronization with a video clock, and being driven by the laser modulation circuit. A laser that emits a laser beam modulated by image data, and a rotary polygon mirror that reflects the laser beam from the laser to irradiate the electrostatic latent image carrier with the laser beam. 2. A black-and-white color image forming apparatus according to claim 1, wherein said color image forming apparatus is provided at a stage preceding said raster output scanner. 3. In the black and white mode, a black and white normal mode and a black and white image forming speed priority mode can be selected. Only when the black and white image forming speed priority mode is selected, the image forming process speed is made faster than the color mode. 3. An image forming apparatus according to claim 1, wherein said image forming apparatus is a black-and-white image forming apparatus. 4. The black and white color image forming apparatus according to claim 3, wherein the image reading apparatus starts reading in advance when the monochrome image forming speed priority mode is selected. 5. The monochrome image forming apparatus according to claim 3, further comprising a dedicated button for selecting a monochrome image forming speed priority mode. 6. An automatic mode setting means for judging the contents of an image read by the image reading device and setting an operation mode to a monochrome image forming speed priority mode when the image is a character image and a monochrome image. 5. The black-and-white color image forming apparatus according to claim 3, wherein the color image forming apparatus is provided. 7. The process speed switching means changes a frequency of a video clock supplied to a laser modulation circuit of the raster output scanner, a rotation speed of the rotary polygon mirror, and a light amount of the laser between a monochrome mode and a color mode. 3. The black-and-white color image forming apparatus according to claim 2, wherein the color image forming apparatus is different. 8. The monochrome / color image forming apparatus according to claim 2, wherein said raster output scanner comprises a raster output scanner for monochrome image formation and a raster output scanner for color image formation.