JPH11170622A - Color image recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce cost of a color image recorder without lowering printing quality of a character. SOLUTION: This color image recorder comprises an image carrier body, a plurality of exposing means each exposing the image carrier body in accordance with image data and forming respective yellow, magenta, cyan, or black electrostatic latent image, a developing means for developing each of the latent images to form yellow, magenta, cyan and black toner images and a transferring means for transferring each of the toner images to a recording medium 37. The resolution of the exposing means for forming the black electrostatic latent image is higher than that of each of the other exposing means. Printing quality of a character can be improved. Since only the exposing means for black is constituted to be in the high resolution, the cost of the color image recorder can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a color image recording apparatus.

[0002]

2. Description of the Related Art Conventionally, a color image recording apparatus uses an LED formed by arranging light emitting elements in a line direction.
It has yellow, magenta, cyan, and black image forming units each having a head. Then, the recording medium is conveyed in a direction perpendicular to the line direction in a state where the recording medium is adsorbed on the carrier belt. Then, the toner image is sequentially transferred onto the same recording medium by a transfer roller to form a color toner image. Subsequently, the color toner image is fixed by a fixing device to be a color image.

[0003]

However, in the above-described conventional color image recording apparatus, when a color image in which characters and gradation images are mixed is recorded, the reproducibility of each color varies, thereby deteriorating the image quality. Resulting in. By the way, the color values of "Japan Color" established in 1993 by the domestic committee of ISO / TC130 (International Organization for Standardization Printing Technology) are as shown in Table 1.

[0004]

[Table 1]

In Table 1, cyan, magenta,
L *, a * and b * values are shown for yellow, black and white. Note that white is the color of the ground of the recording medium, the L * value is a value representing lightness, and the a * and b * values are values representing chromaticity. The L * value of yellow is 86.5, which is very close to the L * value of white of 93.0. Therefore, when yellow printing is performed on a recording medium, it is difficult to distinguish a printed portion. On the other hand, the L * value of black is 12.5, which is apart from the L * value of white of 93.0.

Therefore, when a color image in which characters and gradation images are mixed is to be recorded on a recording medium, if the resolution of each image forming means is set in correspondence with the gradation image,
Since the resolution cannot be made sufficiently high in the black image forming means, the image quality of the characters deteriorates. Further, if the resolution of each image forming means is increased, the cost of the color image recording apparatus will increase.

An object of the present invention is to solve the problems of the conventional color image recording apparatus and to provide a color image recording apparatus capable of reducing the cost without deteriorating the image quality of characters. And

[0008]

For this purpose, in a color image recording apparatus according to the present invention, an image carrier and the image carrier are exposed according to image data, and yellow, magenta,
Exposure means for forming cyan and black electrostatic latent images, developing means for developing the respective electrostatic latent images to form yellow, magenta, cyan and black toner images, and recording medium for the respective toner images And a transfer unit for transferring the image to the printer.

The resolution of the exposure means for forming the black electrostatic latent image is made higher than the resolution of each exposure means for forming the yellow, magenta and cyan electrostatic latent images.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. A color electrophotographic apparatus will be described as a color image recording apparatus. FIG. 1 is a first schematic diagram of a color electrophotographic apparatus according to the first embodiment of the present invention, and FIG. 2 is a second schematic diagram of the color electrophotographic apparatus according to the first embodiment of the present invention.

As shown in FIG.
, First to fourth printing mechanisms P1 to P4 are arranged in order from the upstream side to the downstream side in the transport direction of the recording medium 37 along the endless carrier belt 19. Each of the first to fourth printing mechanisms P1 to P4 includes an electrophotographic LED (light emitting diode) printing mechanism. The first to third printing mechanisms P1 to P3 are provided with a low resolution, for example, 300 [d] as an exposure unit for forming an electrostatic latent image in accordance with the image data of each color.
pi] LED head 13 and the image forming means 12
The transfer roller 14 serves as a transfer unit that transfers the toner image of each color formed on the recording medium 37. On the other hand, the fourth printing mechanism P4 includes an image forming unit 12, an LED head 113 having a high resolution of, for example, 600 [dpi], and a transfer roller. Although the resolution of the LED head 113 of the fourth printing mechanism P4 is set to 600 [dpi] in the present embodiment, the resolution of the LED head 13 of the first to third printing mechanisms P1 to P3 is set to 600 dpi. Any value that is an integral multiple may be used. further,
Any value larger than the resolution of the first to third printing mechanisms P1 to P3 can be used.

Each of the image forming means 12 includes a photosensitive drum 16 serving as an image carrier which is rotated about a shaft 15 in a direction of an arrow a, and a charging member for uniformly and uniformly charging the surface of the photosensitive drum 16. The toner cartridge 50 includes a roller 17 and a developing device 18 as a developing unit.
To be housed. The developing device 18 includes a developing roller 18a made of semiconductive rubber material, a developing blade 18b, and a sponge roller 1 for supplying an appropriate amount of toner to the developing blade 18b.
8c and a toner tank 18d for storing toner. The toner tank 18d is replaced when the toner runs out.

The toner in the toner tank 18d is supplied to the developing blade 18 via a sponge roller 18c.
b, is attached to the surface of the developing roller 18a in a thin layer, and reaches a developing section formed between the developing roller 18a and the photosensitive drum 16. Further, when the toner is thinned, the toner is strongly rubbed (rubbed) by the developing roller 18a and the developing blade 18b to be triboelectrically charged. In this embodiment, the toner is frictionally charged to a negative polarity.

The LED heads 13 and 113 include an LED array (not shown), a substrate 13a on which a drive IC (not shown) for driving the LED array is mounted, a rod lens array 13b for converging light from the LED array, and the like. When image data is sent from an interface unit to be described later, the LED heads 13 and 113 cause each LED element of the LED array to emit light in accordance with the image data, expose the photosensitive drum 16, and Drum 1
On the surface of No. 6, an electrostatic latent image composed of an image portion and a non-image portion is formed.

Next, toner on the surface of the developing roller 18a is adhered to the image portion of the electrostatic latent image by electrostatic force, and the electrostatic latent image becomes a toner image. And the first
Tank 18 of the developing device 18 in the printing mechanism P1 of FIG.
d, yellow toner, magenta toner in the toner tank 18d of the developing device 18 in the second printing mechanism P2, and developing device 18 in the third printing mechanism P3.
Cyan toner is stored in the fourth toner tank 18d.
Tank 18 of the developing device 18 in the printing mechanism P4
Each of d contains a black toner.

In this case, in each image forming means 12, a non-magnetic one-component toner is used so that development and toner recovery can be performed simultaneously. Further, the developing roller 18a has elasticity and conductivity, and is lightly brought into contact with the surface of the photosensitive drum 16 via the thinned toner. Then, development is performed by attaching toner to the image portion of the photosensitive drum 16, and toner remaining in the non-image portion is sucked and collected by the developing roller 18a. The collected toner is returned to a toner storage unit (not shown) of the developing device 18 and is reused.

The LED head 13 of the first printing mechanism P1 has yellow image data of the color image data, and the LED head 13 of the second printing mechanism P2 has the magenta image data of the color image data. Data is input to the LED head 13 of the third printing mechanism P3, cyan image data of the color image data, and black image data is input to the LED head 113 of the fourth printing mechanism P4.

The carrier belt 19 is made of a semiconductive plastic film having a high resistance value.
0, and is stretched between the driven roller 21 and the stretching roller 22. The resistance value is such that the recording medium 37 can be attracted to the carrier belt 19 by electrostatic force, and when the recording medium 37 is separated from the carrier belt 19, the static electricity remaining on the carrier belt 19 Is set in a range where static electricity can be naturally removed.

The drive roller 20 is connected to a motor (not shown), and is rotated in the direction of arrow b by driving the motor. Further, the tension roller 22 is urged in the direction of arrow c by a spring (not shown) to apply tension to the carrier belt 19. Then, the upper half 19a of the carrier belt 19 is caused to run between each photosensitive drum 16 and each transfer roller 14 of the first to fourth printing mechanisms P1 to P4.

A cleaning blade 23 is disposed between the driving roller 20 and the driving roller 20 with the carrier belt 19 interposed therebetween. The cleaning blade 23 is made of a flexible rubber material, a plastic material, or the like. In this way,
Since the tip of the cleaning blade 23 is pressed against the carrier belt 19, residual toner adhering to the surface of the carrier belt 19 can be scraped off and dropped into the waste toner tank 24.

Each photosensitive drum 16 and each transfer roller 14 are brought into contact with a carrier belt 19 to form each transfer section. Further, a paper feed mechanism 30 is provided on the lower right side of the color electrophotographic apparatus 11 in FIG. The paper feed mechanism 30 includes a paper storage cassette 30A, a hopping mechanism 3
0B, and first and second registration rollers 41 and 42 disposed to face each other. The paper storage cassette 30A includes a paper storage box 31, a push-up plate 32, and pressing means 33, and the hopping mechanism 30B
It comprises a discriminating means 34, a spring 35 and a paper feed roller 36.
The discriminating means 34 is provided with a paper feed roller 36 by a spring 35.
To form a discriminating portion between the sheet feed roller 36 and the sheet feed roller 36.

In the paper feed mechanism 30, first, the recording medium 37 stored in the paper storage box 31 is
By 3, the sheet is pressed against the sheet feed roller 36 via the push-up plate 32. In this state, when the motor (not shown) is driven to rotate the paper feed roller 36 in the direction of arrow e, the recording medium 37 sandwiched between the paper feed roller 36 and the discrimination means 34 is fed out of the discrimination section while being discriminated. Then, it is guided by guides 38 and 39 and reaches between the first and second registration rollers 41 and 42.

When a motor (not shown) is driven to rotate the first and second registration rollers 41 and 42 and the transport roller 81 in the directions indicated by the arrows, the recording medium 37 is rotated.
Is transported by the first and second registration rollers 41 and 42, then transported by the transport roller 81 and the second registration roller 42, guided by the medium guide 82, and placed on the carrier belt 19 on the driven roller 21 side. It is sent to half 19a. A suction roller 83 is disposed on the upper half portion 19a of the carrier belt 19 on the driven roller 21 side so as to face the carrier belt 19, and the suction roller 83 is connected to the recording medium sent from the paper feeding mechanism 30. 37, and the carrier belt 1 is charged by electrostatic force.
9 is adsorbed. The driven roller 21 is grounded to a ground (not shown), and the electrostatic force is generated by the potential difference between the driven roller 21 and the suction roller 83, and the recording medium 37 is attracted to the carrier belt 19 by the electrostatic force. The carrier belt 1 is located downstream of the suction roller 83 in the traveling direction of the carrier belt 19.
A photo sensor 70 is provided so as to face the recording medium 9, and the front end of the recording medium 37 can be detected by the photo sensor 70. The suction roller 83 is formed of a semi-conductive rubber material having a high resistance value.

In the upper half 19a of the carrier belt 19 on the drive roller 20 side, a static eliminator 43 is provided so as to face the carrier belt 19. The static eliminator 43 neutralizes the recording medium 37 adsorbed on the carrier belt 19 and conveyed in the direction of arrow d, cancels the attracted state, and facilitates separation of the recording medium 37 from the carrier belt 19. Then, the drive roller 20 in the conveyance direction of the recording medium 37 is
A photo sensor 71 for detecting the rear end of the recording medium 37 and a guide 44 for guiding the recording medium 37 separated from the carrier belt 19 are provided further downstream.

Further, a fixing device 45 is provided downstream of the photosensor 71 in the direction of transport of the recording medium 37. The fixing device 45 fixes the toner image on the recording medium 37 conveyed by the carrier belt 19. To this end, the fixing device 45 has a heat roller 46 for heating the toner on the recording medium 37 and a pressure roller 47 for pressing the recording medium 37 together with the heat roller 46.

A discharge port 48 is provided downstream of the fixing device 45 in the conveying direction of the recording medium 37, and a discharge stacker 49 is provided outside the discharge port 48.
9 is a recording medium 3 on which a color image is recorded and printing is completed.
7 is discharged. Reference numeral 84 denotes a manual tray, and the operator can manually supply the recording medium 37 along the manual tray 84 and the guide 85. Also, 86
Is a photosensor for detecting the front end of the recording medium 37 supplied manually. Recording medium 37 inserted by hand
Is transported by the transport roller 81 and the second registration roller 42, guided by the medium guide 82, and sent to the upper half 19a of the carrier belt 19 on the driven roller 21 side.

Next, the color electrophotographic apparatus 11 having the above configuration
Will be described. FIG. 3 is a block diagram of a control unit of the color electrophotographic apparatus according to the first embodiment of the present invention. In the figure, reference numeral 51 denotes a control circuit including a microprocessor or the like, and the control circuit 51 controls the entire color electrophotographic apparatus 11 (FIGS. 1 and 2). The control circuit 51 includes SP bias power supplies 52Y, 52M, 52C that apply voltages to the sponge rollers 18c of the developing units 18 of the first to fourth printing mechanisms P1 to P4, respectively.
52B is a DB bias power source 53Y, 53M, 53C, 53B for applying a voltage to each developing roller 18a of each of the first to fourth printing mechanisms P1 to P4, and is a first to fourth printing mechanism P1 to P4. Charging power supplies 54Y, 54M, 54C, 54B for applying a voltage to each of the charging rollers 17 of FIG.
Transfer power supplies 55Y and 55 for applying a voltage to each transfer roller 14 of each of the first to fourth printing mechanisms P1 to P4.
M, 55C and 55B are respectively connected.

Further, the control circuit 51 includes a suction charging power supply 56 for applying a charging voltage to the suction roller 83.
However, a static elimination power supply 57 for applying a high static elimination voltage to the static eliminator 43 is connected to each. The SP bias power supplies 52Y, 52M, 52C, and 52B, the DB bias power supplies 53Y, 53M, 53C, and 53B, and the charging power supplies 5
4Y, 54M, 54C, 54B, each transfer power supply 55Y,
55M, 55C, 55B, the power source 56 for adsorption and charging, and the power source 57 for static elimination
Controlled off.

Further, the control circuit 51 includes first to fourth
The print control circuits 58Y, 58M, 58C and 58B are connected to the print mechanisms P1 to P4, respectively. Then, the print control circuits 58Y, 58M, 58C, 58B
Represents yellow image data among the color image data from the memories 59Y, 59M, 59C and 59B,
The magenta image data, the cyan image data, and the black image data are received and transferred to each of the LED heads 13 and 113 according to an instruction from the control circuit 51, and the exposure time of each of the LED elements of the LED array (not shown) is controlled. An electrostatic latent image is formed on the surface of each photosensitive drum 16.

When the interface unit 60 receives color image data having a resolution of 600 [dpi] transmitted from a higher-level device (not shown), for example, a host computer, the interface unit 60 converts the color image data into an image (not shown). Each of the yellow image data, the magenta image data, the cyan image data, and the black image data is separated by 600 [d
pi], the yellow image data is stored in the memory 59Y, and the magenta image data is stored in the memory 59Y.
M, cyan image data is stored in the memory 59C, and black image data is stored in the memory 59B.

The control circuit 51 is connected to a fixing device driver 61, a motor drive circuit 62, a sensor receiver driver 66, and an operation panel (not shown). The fixing device driver 61 includes a heat roller 46 in the fixing device 45.
The heater (not shown) in the heat roller 46 is turned on / off so as to keep the temperature at a predetermined temperature. Further, the motor drive circuit 62 drives the motor 63 for rotating the paper feed roller 36, and transfers the transfer rollers 14, the photosensitive drums 16, the charging rollers 17, and the like of the first to fourth printing mechanisms P1 to P4. Each developing roller 18a, each sponge roller 18c,
Drive roller 20, first and second registration rollers 41, 4
2. The motor 65 for rotating the transport roller 81 and the heat roller 46 is driven.

Each of the transfer rollers 14, each photosensitive drum 16, each charging roller 17, each developing roller 18a, each sponge roller 18c rotated by the motor 65,
Drive roller 20, first and second registration rollers 41, 4
2. The transport roller 81 and the heat roller 46 are connected by a gear or a belt (not shown). Then, the sensor receiver driver 66 includes the photo sensors 70, 71,
86 is operated, and the output waveform of each photosensor 70, 71, 86 is sent to the control circuit 51 as a detection signal.

Next, the color electrophotographic apparatus 11 having the above-described configuration will be described.
Will be described. First, the color electrophotographic apparatus 1
1 is turned on, the control circuit 51
After performing a predetermined initial setting, the fixing device driver 61 is driven to warm up the heat roller 46 in the fixing device 45 until a predetermined temperature is reached, and thereafter, the temperature is maintained at the predetermined temperature.

When the temperature of the heat roller 46 reaches a predetermined temperature, the control circuit 51 drives the motor 65 via the motor drive circuit 62 to rotate the drive roller 20 so that the carrier belt 19 runs. When the carrier belt 19 is run slightly longer than one round, the residual toner, dust and the like adhering to the surface of the carrier belt 19 are scraped off by the cleaning blade 23 and dropped into the waste toner tank 24.

As described above, the color electrophotographic apparatus 11
Is completed, the interface unit 60 waits for color image data having a resolution of 600 [dpi] to be transmitted from the host computer. When the interface unit 60 receives the color image data, the control circuit 51
And an instruction to each of the memories 59Y, 59M, 59C, 59B, and based on the instruction, the image data decomposing means
The received color image data is separated for each color, and the yellow image data of the color image data is stored in the memory 59Y.
The magenta image data is stored in the memory 59M, the cyan image data is stored in the memory 59C, and the black image data is stored in the memory 59B at a resolution of 600 [dpi].

Next, the operation of recording a color image on the recording medium 37 fed from the paper feed mechanism 30 will be described. First, the control circuit 51 drives the motor 63 via the motor drive circuit 62 to rotate the paper feed roller 36.
When the paper feed roller 36 rotates, the recording medium 37 stored in the paper storage box 31 is discriminated by the discriminating means 34 and the paper feed roller 36, and only one sheet is fed out. And
The fed recording medium 37 is guided by guides 38 and 39, and the front ends thereof are first and second registration rollers 41,
It reaches between 42, after which it is further transported by a small amount.

As a result, the recording medium 37 has the first front end,
The second registration rollers 41 and 42 are slightly bent (bent) in contact with each other, and the skew of the recording medium 37 is corrected by the bending. Next, the control circuit 51 drives the motor 65 via the motor drive circuit 62 to transfer the transfer rollers 14 and the photosensitive drums 1 of the first to fourth printing mechanisms P1 to P4.
6. Each charging roller 17, each developing roller 18a, each sponge roller 18c, the driving roller 20, the first and second registration rollers 41 and 42, the transport roller 81, and the heat roller 46 are rotated. At the same time, the control circuit 5
1 turns on the suction charging power supply 56 and causes the suction roller 83
Voltage.

Therefore, the first and second registration rollers 41 and 42 are rotated in the direction of the arrow, and the recording medium 37 is rotated.
After being transported by the first and second registration rollers 41 and 42, is transported by the transport roller 81 and the second registration roller 42, guided by the medium guide 82, and the front end reaches the carrier belt 19. Then, the recording medium 37 is attracted to the carrier belt 19 by the electrostatic force generated by the attracting roller 83. further,
When the transport roller 81 is rotated in the direction of the arrow, the recording medium 37 is transported in the direction of the arrow d while being attracted to the carrier belt 19. Then, the control circuit 51 detects the front end of the recording medium 37 by the photo sensor 70 via the sensor receiver driver 66.

When the rear end of the recording medium 37 moves away from the discrimination section, the control circuit 51 stops the motor 63 via the motor drive circuit 62. The control circuit 51
When the photo sensor 70 detects the front end of the recording medium 37, in order to apply a voltage to each charging roller 17, each developing roller 18a and each sponge roller 18c, each charging power source 54Y, 54M, 54C, 54B, The DB bias power supplies 53Y, 53M, 53C, 53B and the SP bias power supplies 52Y, 52M, 52C, 52B are turned on.

Thus, in each of the first to fourth printing mechanisms P1 to P4, the surface of each photosensitive drum 16 is uniformly and uniformly charged by each charging roller 17, and each sponge roller 18c And each developing roller 18
a is charged by applying a predetermined voltage. In addition,
In the present embodiment, the charging roller 17 has −1350
The voltage of [V] is -300 [V] to the developing roller 18a.
Is applied to the sponge roller 18c, and a voltage of -450 [V] is applied to the sponge roller 18c.
The surface potential is set to 800 [V].

Next, the control circuit 51 issues an instruction to the memory 59Y, reads one line of yellow image data from the memory 59Y, and sends the yellow image data to the print control circuit 58Y. The print control circuit 58Y converts the yellow image data having a resolution of 600 [dpi] sent from the memory 59Y in accordance with an instruction from the control circuit 51 to 300 [dp] by a resolution conversion means (not shown).
i], is changed to a form that can be transferred to the LED head 13 of the first printing mechanism P1, and transferred to the LED head 13.

The LED head 13 of the first printing mechanism P1 has a LE of an LED array (not shown) corresponding to the yellow image data transferred from the print control circuit 58Y.
The D element is turned on, and an electrostatic latent image for one line corresponding to the yellow image data is formed on the charged surface of the photosensitive drum 16 at a resolution of 300 [dpi].
In this manner, an electrostatic latent image is formed on the photosensitive drum 16 in accordance with the yellow image data read from the memory 59Y line by line, and an electrostatic latent image is formed in accordance with one page of yellow image data. Then, the exposure ends. Then, the photosensitive drum 1 on which the electrostatic latent image is formed
The yellow toner adheres to the surface of the developing roller 6 by the electrostatic force of the charged developing roller 18a. Accordingly, as the photosensitive drum 16 rotates, the electrostatic latent image is sequentially developed with yellow toner to become a yellow toner image.

When the front end of the recording medium 37 reaches the transfer section of the first printing mechanism P1, the control circuit 51
The transfer power supply 55Y of the first printing mechanism P1 is turned on, and a voltage is applied to the transfer roller 14 of the first printing mechanism P1.
In this embodiment, +1 is applied to the transfer roller 14.
A voltage of 500 [V] is applied. As a result, the yellow toner image on the photosensitive drum 16 is transferred to the recording medium 37 line by line by the transfer roller 14, and the yellow toner image for one page is formed by the rotation of the photosensitive drum 16. The recording medium 37 with a resolution of [dpi]
Is transferred to

When the rear end of the recording medium 37 reaches the transfer section, the control circuit 51 sets the SP bias power supply 52
The Y and DB bias power supplies 53Y, the charging power supply 54Y, and the transfer power supply 55Y are turned off. Then, the carrier belt 19 is continuously run, and the recording medium 37 moves from the first printing mechanism P1 to the second printing mechanism P2, and then the magenta toner image is recorded in the second printing mechanism P2. The image is transferred to the medium 37.

That is, the control circuit 51 has a memory 59M
To read out one line of magenta image data from the memory 59M and send the magenta image data to the print control circuit 58M. The print control circuit 58M converts magenta image data having a resolution of 600 [dpi] sent from the memory 59M in accordance with an instruction from the control circuit 51 to 300 [dp] by a resolution conversion means (not shown).
i], converted to a form that can be transferred to the LED head 13 of the second printing mechanism P2, and transferred to the LED head 13.

The LED head 13 of the second printing mechanism P2 has a LE of an LED array (not shown) corresponding to the magenta image data transferred from the print control circuit 58M.
The D element is turned on, and an electrostatic latent image for one line corresponding to the magenta image data is formed on the charged surface of the photosensitive drum 16 at a resolution of 300 [dpi]. In this manner, the photosensitive drum 1 is read in accordance with the magenta image data read from the memory 59M line by line.
When the electrostatic latent image is formed on the image forming unit 6 and the electrostatic latent image is formed in accordance with the magenta image data for one page, the exposure is completed. Then, the photosensitive drum 16 on which the electrostatic latent image is formed
The magenta toner is attached to the surface of the developing roller 18 by the electrostatic force of the charged developing roller 18a. Therefore, as the photosensitive drum 16 rotates, the electrostatic latent image is sequentially developed with magenta toner to form a magenta toner image.

When the front end of the recording medium 37 reaches the transfer portion of the second printing mechanism P2, the control circuit 51
The transfer power supply 55M of the second printing mechanism P2 is turned on, and a voltage is applied to the transfer roller 14 of the second printing mechanism P2.
As a result, the magenta toner image on the photosensitive drum 16 is transferred line by line onto the recording medium 37 by the transfer roller 14, and with the rotation of the photosensitive drum 16,
A magenta toner image for one page is transferred over the yellow toner image on the recording medium 37 at a resolution of 300 [dpi].

When the rear end of the recording medium 37 reaches the transfer portion of the second printing mechanism P2, the control circuit 51
The SP bias power supply 52M, the DB bias power supply 53M, the charging power supply 54M, and the transfer power supply 55M are turned off. Next, the recording medium 37 is transported from the second printing mechanism P2 to the third printing mechanism P3, where the cyan toner image is transferred to the recording medium 37 at a resolution of 300 [dpi] in the third printing mechanism P3. Is done.

Then, the cyan toner image is recorded on the recording medium 37.
Is transferred to the fourth printing mechanism P4 from the third printing mechanism P3, and the recording medium 37 is transferred to the fourth printing mechanism P4.
In step 4, the black toner image is transferred to the recording medium 37 at a resolution of 600 [dpi]. That is, the control circuit 51 issues an instruction to the memory 59B, reads one line of black image data from the memory 59B, and sends the black image data to the print control circuit 58B. The printing control circuit 58B converts the black image data of 600 dpi resolution sent from the memory 59B according to the instruction from the control circuit 51 into the LED of the fourth printing mechanism P4 while maintaining the resolution of 600 dpi. The data is changed to a form that can be transferred to the head 113 and transferred to the LED head 113.

The LED head 113 of the fourth printing mechanism P4 is connected to the LED array (not shown) corresponding to the black image data transferred from the printing control circuit 58B.
The ED element is turned on, and an electrostatic latent image for one line corresponding to the black image data is formed on the charged surface of the photosensitive drum 16 at a resolution of 600 [dpi].

In this manner, the memory 5 is provided for each line.
According to the black image data read from 9B,
When an electrostatic latent image is formed on the photosensitive drum 16 and an electrostatic latent image is formed according to one page of black image data, the exposure is completed. Then, black toner is attached to the surface of the photosensitive drum 16 on which the electrostatic latent image is formed by the electrostatic force of the charged developing roller 18a. Therefore, as the photosensitive drum 16 rotates, the electrostatic latent image is sequentially developed with the black toner to become a black toner image.

When the front end of the recording medium 37 reaches the transfer portion of the fourth printing mechanism P4, the control circuit 51
The transfer power supply 55B of the fourth printing mechanism P4 is turned on, and a voltage is applied to the transfer roller 14 of the fourth printing mechanism P4.
As a result, the black toner image on the photosensitive drum 16 is transferred to the recording medium 37 line by line by the transfer roller 14, and with the rotation of the photosensitive drum 16,
One page of the black toner image is transferred to the recording medium 37 at a resolution of 600 [dpi].

In this manner, the black toner image is transferred at a resolution of 600 [dpi] onto the recording medium 37 on which the yellow, magenta and cyan toner images are transferred at a resolution of 300 [dpi]. Thus, a color toner image is formed. The resolution of the LED head 113 of the fourth printing mechanism P4 is the same as that of the first to third printing mechanisms P1 to P3.
Is made an integral multiple of the resolution of each LED head 13 of
Each of the print control circuits 58Y, 58M, 58C has a memory 59
Each of the yellow, magenta, and cyan image data sent from Y, 59M, and 59C can be easily converted to the resolution of the LED head 13 by the resolution conversion means. That is, if the resolution of the LED head 113 of the fourth printing mechanism P4 is N times the resolution of each of the LED heads 13 of the first to third printing mechanisms P1 to P3, the respective print control circuits 58Y, 58M, 58C , Memory 59Y, 59
The image data of yellow, magenta, and cyan sent from M and 59C can be converted to the resolution of the LED head 13 only by thinning it to 1 / N.

Subsequently, the recording medium 37 is the carrier belt 1
9 to the static eliminator 43. Here, the control circuit 5
In 1, the power supply 57 for static elimination is turned on, and the static eliminator 43 neutralizes the recording medium 37. As a result, the recording medium 37 is easily separated from the carrier belt 19, separated from the carrier belt 19 above the drive roller 20, and
4 and is sent to the fixing device 45. And
When the recording medium 37 is separated from the static eliminator 43, the control circuit 51 turns off the static elimination power supply 57.

In the fixing device 45, a color toner image is fixed on the recording medium 37 by a heat roller 46 which has reached a predetermined temperature at which fixing is possible, and a pressure roller 47 which is pressed against the heat roller 46. And it becomes a color image. When the fixing is completed, the recording medium 3
7 is discharged to a discharge stacker 49. The control circuit 51
When the photo sensor 71 detects the rear end of the recording medium 37, it is known that the recording medium 37 has been ejected.

When the ejection of the recording medium 37 is completed, the control circuit 51 stops the motor 65 via the motor drive circuit 62. When the transfer of the toner image of each color is completed in each of the second and third printing mechanisms P2 and P3, each of the SP bias power supplies 52M and 52C and each of the D
B bias power supplies 53M and 53C, each charging power supply 54M,
The transfer power supply 54C and the transfer power supplies 55M and 55C are turned off.

In this manner, a color image can be recorded on the recording medium 37 fed from the paper feeding mechanism 30. The recording medium 37 supplied from the manual feed tray 84
Similarly, a color image can be recorded.
In general, when a color image is recorded by printing, four-color printing is performed by adding black ink in addition to yellow, magenta, and cyan inks, unlike taking a color photograph. In this case, it is possible to increase the density of the shadow portion, which is insufficient with only the yellow, magenta, and cyan inks, and improve the sharpness of the color image. In addition, since it is not necessary to reproduce black by mixing yellow, magenta, and cyan inks, not only can the total amount of ink used be reduced, but also the feeling of stickiness can be eliminated. Furthermore, not only can it make it easier to balance gray,
The color gamut can be widened.

In the present embodiment, it is possible to record a color image by setting the resolution of yellow, magenta and cyan to 300 [dpi] and the resolution of black, which is most recognizable by human visual acuity, to 600 [dpi]. As a result, the image quality of characters can be improved. Also, only the black LED head 113 is 600
Since the structure corresponds to the resolution of [dpi], the cost of the color electrophotographic apparatus 11 can be reduced.

In this embodiment, the color image data is 600 [d] in the host computer.
pi] and a color electrophotographic apparatus 1
1 is sent. Then, each memory 59
Each of Y, 59M, and 59C contains 600 [dp] of yellow image data, magenta image data, and cyan image data for one page printed on the recording medium 37, respectively.
i] and the recording medium 3B is stored in the memory 59B.
7, one page of black image data to be printed is stored at a resolution of 600 [dpi].

Therefore, according to a second embodiment of the present invention, recording can be performed at a resolution of 600 [dpi] by an LED head 13 of 300 [dpi] in accordance with image data of a resolution of 600 [dpi]. explain. FIG. 4 is an explanatory diagram of processing of image data according to the second embodiment of the present invention. In addition, about what has the same structure as 1st Embodiment, the description is abbreviate | omitted by attaching the same code | symbol.

In this case, the black LED head 113
The resolution of FIG. 1 is 600 [dpi].
A dot is formed at a resolution of [dpi]. On the other hand, the resolution of each of the yellow, magenta and cyan LED heads 13 is 300 [dpi], but the resolution can be increased in the main scanning direction of the image data, that is, in the horizontal direction. The resolution in the sub-scanning direction, that is, the vertical direction is set to 1200 [dpi].

For this purpose, in the yellow, magenta and cyan print control circuits 58Y, 58M and 58C,
Image data generated at a resolution of 600 [dpi] is converted to image data of a resolution of 300 [dpi],
Dots are formed by the LED head 13 according to image data having a resolution of 300 [dpi]. At this time, with the conversion of the image data, dots are formed at a resolution of 600 [dpi] in a pseudo manner.

That is, a higher-level device (not shown), for example,
In the host computer, the image data indicated by ●
When generated at a resolution of 600 [dpi] and sent to the color electrophotographic apparatus 11, 300 in the main scanning direction
Regarding image data corresponding to a point where a basic line set for each [dpi] intersects with a basic line set for every 600 [dpi] in the sub-scanning direction, each LED element of the LED head 13 is left as it is. The light is turned on, and as a result, a dot indicated by ○ is formed. In this case, the light intensity when turning on each LED element is increased, and each dot is increased. Further, for image data corresponding to a point at which the sub-line set between each basic line in the main scanning direction and the basic line in the sub-scanning direction intersects, the LED head 13 is moved to the additional line. Each LED element is turned on, and as a result, two dots are formed. In this case, each L
The light intensity when the ED element is turned on is reduced, and each dot is reduced.

As described above, when two dots are formed, a dot having a center on a sub-line set between each basic line in the main scanning direction is formed. As a result, printing can be performed at a resolution of 600 [dpi] by the LED head 113 having a resolution of 300 [dpi]. Therefore, 1 recorded at 600 [dpi]
For a color image other than a special image such as a vertical dot line, image quality can be improved, and a color image without jaggedness can be recorded by a dot having a center on a sub line.

Since only the black LED head 113 has a structure corresponding to a resolution of 600 [dpi], the cost of the color electrophotographic apparatus 11 can be reduced. In each of the above embodiments, the LED heads 13 and 113 are used as exposure means for writing an electrostatic latent image on the photosensitive drum 16, but a laser, a liquid crystal shutter, or the like may be used.

In the embodiment, the first to fourth printing mechanisms P1 to P4 are arranged along the carrier belt 19 so as to transfer the toner images of each color to the recording medium 37. However, it is also possible to form a color toner image by superimposing and transferring the toner images of each color on a common transfer drum, and to transfer the color toner images to a transfer medium. Further, a color toner image can be formed by forming a toner image of each color on a common photosensitive drum and sequentially transferring the toner images of each color to a transfer medium.

The present invention is not limited to the above embodiment, but can be variously modified based on the gist of the present invention, and they are not excluded from the scope of the present invention.

[0068]

As described above in detail, according to the present invention, in a color image recording apparatus, an image carrier is exposed to light in accordance with image data, and yellow, magenta, cyan, and black are exposed. Exposure means for forming an electrostatic latent image, developing means for developing the electrostatic latent images to form yellow, magenta, cyan and black toner images, and transfer for transferring the toner images to a recording medium Means.

The resolution of the exposure means for forming the black electrostatic latent image is made higher than the resolution of each exposure means for forming the yellow, magenta and cyan electrostatic latent images. In this case, the resolution of yellow, magenta, and cyan can be reduced, and the resolution of black, which is most identifiable by human eyesight, can be increased to record a color image. Therefore, the image quality of characters can be improved.

Further, since only the black exposure means has a structure corresponding to high resolution, the cost of the color image recording apparatus can be reduced.

[Brief description of the drawings]

FIG. 1 is a first schematic diagram of a color electrophotographic apparatus according to a first embodiment of the present invention.

FIG. 2 is a second schematic diagram of the color electrophotographic apparatus according to the first embodiment of the present invention.

FIG. 3 is a block diagram of a control unit of the color electrophotographic apparatus according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of image data processing according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Color electrophotographic apparatus 13, 113 LED head 14 Transfer roller 16 Photoreceptor drum 18 Developing device 37 Recording medium 58Y, 58M, 58C Printing control circuit 60 Interface part

Claims (4)

[Claims] 1. (a) an image carrier; and (b) each exposure means for exposing the image carrier according to image data to form electrostatic latent images of yellow, magenta, cyan, and black.
(C) developing each of the electrostatic latent images to form yellow, magenta,
Developing means for forming cyan and black toner images;
(D) transfer means for transferring each of the toner images onto a recording medium, and (e) an exposure means for forming the black electrostatic latent image has a resolution of yellow, magenta and cyan electrostatic latent images. A color image recording apparatus, wherein the resolution is higher than the resolution of each exposing means to be formed. 2. The image forming apparatus according to claim 1, wherein the resolution of the exposure unit that forms the black electrostatic latent image is an integral multiple of the resolution of each of the exposure units that forms the yellow, magenta, and cyan electrostatic latent images. Color image recording device. (A) image data decomposing means for decomposing color image data received from a host device into yellow, magenta, cyan and black image data; and (b)
2. The color image recording apparatus according to claim 1, further comprising: a resolution conversion unit configured to convert yellow, magenta, and cyan image data in accordance with resolutions of respective exposure units that form yellow, magenta, and cyan electrostatic latent images. . 4. The color image recording apparatus according to claim 3, wherein said resolution conversion means makes the resolution of yellow, magenta and cyan image data pseudo the same as the resolution of black image data.