JPH07128946A - Color image forming device - Google Patents

Abstract

PURPOSE:To prevent the attaching quantity ratio of toner from being changed and to obtain average hue even when an image pattern is different by changing an adjustment value for adjusting the exposure conditions of respective colors which are superposed based on the image pattern. CONSTITUTION:Data from plane memories 509a-509c is converted to video (dot) data. Then it is detected to be the monochromatic dot data or the two- color superposed dot data (Y+M, Y+C and M+C) by a monochrome and multicolor detection circuit 554 by a selector 552. Besides, proportion occupied by the image pattern (character and graphic) on one page is discriminated by an image pattern discrimination circuit 555. Based on the discriminated result of the discrimination circuit 555, the average correction coefficient (d0) of weighting is calculated by a correction coefficient calculation circuit 557. Then, the image exposure of the first color of the color image formed by superposing two colors is changed based on the image pattern and the pulse width of the output level of laser power is modulated by a PWM modulation circuit 571.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus, and more particularly to an electrostatic system utilizing a laser beam such as a laser beam printer (LBP) used as an output device of a computer system and a digital color copying machine. The present invention relates to a color image forming apparatus.

[0002]

2. Description of the Related Art In the field of printers, the demand for high-definition color image printers based on advanced image processing has increased with the progress of computer graphics and the like. In the field of color copiers, high-accuracy gradation reproduction and
It is required to realize a clear copy in accordance with the characteristics of various copy targets such as halftone images.

For a color image, for example, a photoconductor, which is an image carrier, is scanned with a laser beam as an image exposing means to form an electrostatic latent image, and Y (yellow), M (magenta), C (cyan), It is formed by developing with a color toner such as BK (black) to form a toner image in which the color toners are superposed, and collectively transferring the toner image onto a transfer paper.

[0004]

There is no problem in forming a monochromatic toner image on the photoconductor, but in the case of forming a toner image in which two color toners are superposed, a second color electrostatic latent image is formed. Need to be formed on the portion where the toner image of the first color has already adhered. To form the electrostatic latent image of the second color on the portion to which the toner of the first color is attached, a toner that transmits infrared rays is used as the toner and a laser beam of infrared light is used as the image exposing means. . When the two color toners are overlapped in this way, there is a problem that if the adhesion amount ratios of the first color toner and the second color toner are different, the superimposed color is different from the preset color. The problem that the toner adhesion amount ratio is different depends not only on the colors to be superimposed, but also on whether the image is a line drawing, a halftone dot image, or a solid image. According to the present invention, the composition of the image pattern in one page is judged, and even if the image pattern is different, the toner adhesion amount ratio does not change,
It is an object of the present invention to provide a color image forming apparatus capable of obtaining an average hue desirably.

[0005]

The above object is to provide a plurality of developing means on the peripheral portion of the image carrier, develop the latent image formed on the image carrier by the image exposure of the image exposing means, and to develop the latent image on the toner. In a color image forming apparatus that forms a color image by transferring an image onto a transfer material, when superposing toner images of two or more colors, it has adjusting means for adjusting the image exposure conditions of each color to be superposed, and the adjustment is performed. The value is achieved by a color image forming apparatus characterized by performing adjustment processing so as to be changed according to an image pattern.

[0006]

FIG. 1 is a sectional view showing the construction of an embodiment of a color image forming apparatus of the present invention. First, the configuration and operation will be described.

In the figure, reference numeral 10 denotes a photosensitive drum which is an image bearing member, which is formed by coating an OPC photosensitive member on the drum and is grounded and driven and rotated clockwise. Reference numeral 12 denotes a scorotron charger, which applies a uniform charge of V _{H to} the peripheral surface of the photosensitive drum 10 to V _G.
It is given by a corona discharge with a grid and a corona discharge wire that are held at a potential. This scorotron charger
Prior to charging by 12, the PCL 11 using a light emitting diode or the like is exposed to eliminate the history of the photoconductor until the previous printing, and the peripheral surface of the photoconductor is neutralized.

After uniformly charging the photoreceptor, the image exposing means 13 performs image exposure based on the image signal. Image exposure means
Reference numeral 13 is a reflection mirror 1 via a polygon mirror 131 that rotates using a laser diode (not shown) as a light emitting source, an fθ lens
The optical path is bent by 32 and scanning is performed, and a latent image is formed by the rotation (sub-scanning) of the photosensitive drum 10.
In this embodiment, the character portion is exposed to form an inverted latent image in which the character portion has a lower potential V _L.

Yellow (Y)
Developers each containing a developer composed of toner such as magenta (M), cyan (C), black (K), and a carrier.
14 is provided, and first, the development of the first color is performed by the developing sleeve 141 which contains a magnet and holds the developer and rotates. The developer is a carrier in which a ferrite core is coated with an insulating resin around it, a polyester as a main material, a pigment according to the color, and a charge control agent,
The toner consists of toner to which silica, titanium oxide, etc. have been added.
The layer is regulated to a layer thickness (developer) of 00 to 600 μm and conveyed to the developing area.

The gap between the developing sleeve 141 and the photosensitive drum 10 in the developing area is 0.2 to more than the layer thickness (developer).
As 1.0mm, V _AC AC ice and V _DC D
The C bias is superimposed and applied. Since V _DC and V _H and the toner are charged with the same polarity, the toner given the opportunity to be separated from the carrier by V _AC does not adhere to the V _H portion, which has a higher potential than V _{DC, and} has a potential higher than V _DC. attached to a lower V _L portion of visualized (reversal development) is carried out.

After the visualization of the first color is completed, the process proceeds to the image forming process of the second color, uniform charging is performed again by the scorotron charger 12, and a latent image based on the image data of the second color is formed by the image exposing means 13. To be done. At this time, the charge elimination by the PCL 11 performed in the image forming process of the first color is not performed because the toner attached to the image portion of the first color scatters due to the rapid decrease in the potential around the image.

Again, V is applied over the entire surface of the photosensitive drum 10.
A latent image similar to that of the first color is formed on the portion of the photoconductor having the _H potential and the image of the first color is not developed, but development is performed again on the portion having the image of the first color. In the portion to be performed, the latent image of V _M ′ is formed due to the light shielding by the toner of the first color and the electric charge of the toner itself, and V _DC
And development is performed according to the potential difference between V _M 'and V _M '. In the overlapping portion of the images of the first color and the second color, the development of the first color is V _L
When the latent image of the first color is formed, the balance between the first color and the second color is lost, so the exposure amount of the first color is reduced and V _H > V _M ′>
The intermediate potential is _VL . This will be described later in detail.

An image forming process similar to that for the second color is performed for the third and fourth colors, and a visible image of four colors is formed on the peripheral surface of the photosensitive drum 10.

On the other hand, the recording paper carried out from the paper feed cassette 15 via the half-moon roller 16 is temporarily stopped, and when the transfer timing is adjusted, it is fed to the transfer area by the rotation operation of the paper feed roller 17.

In the transfer area, the transfer roller 18 is pressed against the peripheral surface of the photosensitive drum 10 in synchronization with the transfer timing.
The supplied recording paper is sandwiched and the multicolor image is transferred at once.

Then, the recording paper is neutralized by a separating brush 19 which is brought into a pressure contact state at almost the same time, separated by the peripheral surface of the photosensitive drum 10 and conveyed to a fixing device 20, where the heat roller 201 and the pressure roller 202 are heated and pressed. After the toner is welded by the means, it is discharged to the outside of the apparatus through the paper discharge roller 21. The transfer roller 18 and the separation brush 19 are withdrawn from the peripheral surface of the photosensitive drum 10 after the recording paper has passed and are prepared for the next toner image formation.

On the other hand, the photosensitive drum 10 from which the recording paper is separated is
Residual toner is removed and cleaned by pressing the blade 221 of the cleaning device 22. The charge is again removed by the PCL 11 and charged by the charger 12, and the next image forming process starts. The blade 221 moves immediately after cleaning the surface of the photoconductor and retracts from the peripheral surface of the photoconductor drum 10.

The features of the functions and performances of the main equipment constituting the image forming section of the above apparatus will be described below.

(Photosensitive member) The photosensitive drum 10 is stably rotated so that the OPC photosensitive member on the peripheral surface is uniformly charged by the scorotron charger 12. During charging, the grid potential is controlled to stabilize the charging potential.
The specifications of the photoconductor and the charging conditions thereof are set as follows as an example.

Photosensitizer: OPC φ120 linear velocity 100mm
/ Sec Negative charging Charging conditions: Charging wire: Platinum wire (clad or alloy) is preferably used. _VH- 850V, _VL- 50V (Image exposure) FIG. 2A shows the plane and side of the layout of the image exposure means 13, and FIG. 2B shows the semiconductor laser unit used for the image exposure means 13. It is explanatory drawing of 135.

The OPC photoconductor on the peripheral surface of the photoconductor drum 10 is negatively charged by the charger 12 and then exposed by the light emission of the semiconductor laser unit 135 of the image exposure means 13 to form an electrostatic latent image.

The image data from the formatter which decodes the printer command is sent to the laser diode (LD) modulation circuit, and when the LD of the semiconductor laser unit 135 emits light by the modulated image signal, the light beam is reflected by the mirror 1.
The scanning lines 37 are synchronized by the beam index 136 and projected onto the polygon mirror 131.

The polygon mirror 131 reflects the beam light on its polyhedron for scanning, and the scanning light is corrected in beam shape by the fθ lens 133 and the cylindrical lens 134, and then the photoconductor is exposed through the reflecting mirror 132. Main scanning is performed to form an electrostatic image.

The beam system of laser light is narrowed down to an equivalent of 600 DPI by an optical system. Therefore, in order to obtain a high quality image, it is necessary to reduce the particle size of the toner. In this embodiment, toner of 8 μm size is used for each color. But most important to the user is the black text quality,
The black toner is preferably a small particle size toner (7 μm to 11 μm).

As the image exposure optical system, for example, the one having the construction described below is used.

Polygon mirror: 6 faces, rotation speed 23600 rpm, air bearing adopted Lens focal length: f = 140 mm Dot clock: 20 MHz _Z beam diameter: Approx. 60 × 80 μm (Development) FIG. 3 shows the configuration of the developing device 14. The toner supplied from the toner box is dropped to the right end portion of the developing device, and is agitated and mixed with the carrier by a pair of agitating screws 142 rotating in opposite directions, so that a predetermined charge amount (Q / M) is obtained. Is set.

The agitated two-component developer is supplied to the supply roller 143.
Is conveyed to the developing sleeve 141 via the layer thickness regulating member 144.
Is transferred to the developing area of the photosensitive drum 10 as a thin layer, and reversal development of the electrostatic latent image is performed under the developing conditions described below.

Development gap: 0.5 mm Toner transfer amount: 20 to 30 mg / cm ² Development bias (AC): 2 KV (V _PP ), 8 KH _Z (DC): -750 V Rotation direction of development sleeve: to photoconductor drum On the other hand, normal image density adjustment: development sleeve rotation speed control or development bias control (a patch image is formed on the photoconductor by a laser beam, the reflection density is measured after development, and the image density is adjusted). Image formation of the color image forming apparatus will be described.

FIG. 4 shows a process for realizing a seven-color multi-color image from four color toners of yellow (Y), magenta (M), cyan (C) and black (BK) of this embodiment. Is.

First color Second color Overlaid color Y Y + M → Red (R) Y + C → Green (G) M M + C → Blue (B) C BK Of the above seven colors, especially in the case of a single color There is no problem, but there is a problem with the toner adhesion amount for red (R), green (G), and blue (B), which are formed by superposing two color toners.
It is necessary for the proper hue to be obtained that the toner adhesion amount of the second color and the toner adhesion amount of the second color are equal. FIG. 5 is an explanatory view showing a color image system in which two color toners are superposed to obtain a desired color image. FIG. 5 (a) shows a peripheral surface of a photosensitive drum whose back surface is grounded by a scorotron charger 12. It shows a state in which V _H is uniformly charged. Figure 5 (b)
After the photosensitive member is uniformly charged, image exposure is performed by the image exposure means 13 based on the image signal, and the image exposed portion has a charge V _H.
Are erased and the potential becomes low at V _L. FIG. 5C shows a state in which the reversal development of the first color is performed, and the toner of the first color adheres to the image-exposed portion and the development is performed. FIG. 5D shows a state in which the second charging is performed by the scorotron charger 12. FIG. 5E shows a state where the second image exposure is performed on the first color toner. In the portion where the image exposure of the second color has been performed, V _M ′ (V _H > V _M ′) due to the light shielding by the toner attached to the first color and the electric charge of the toner itself.
A latent image of> _VL ) is formed. FIG. 5F shows a state in which the reversal development of the second color is performed and the toner of the second color overlaps the toner of the first color. If the image exposure amounts of the first color and the second color are the same, the toner adhesion amount of the second color is smaller than the toner adhesion amount of the first color, and the balance between the first color and the second color is lost. The image exposure pulse width or power of the color is reduced. For red (R), green (G), and blue (B), set the exposure power of the second color to 100.
In that case, it is preferable in terms of balance that the exposure power for the first color is set to the following value, for example.

Y (30) + M (100) → RY (40) + C (100) → GM (50) + C (100) → B As described above, by reducing the pulse width or output power of the first color, The color balance is significantly improved, but still not enough, because the image pattern may have good and bad color balance, for example, good color balance in a halftone image is bad in a solid image. If the solid image has a good color balance, the halftone image is defective. In this tendency, differences in hue occur in the image pattern in the order of a solid image, thin lines (characters), and isolated dots. The reason for this is shown in FIG.

Although the laser beam for image exposure is spot exposure, it actually has a divergence. Therefore, even if image exposure is performed with the same power in a solid image and a halftone image, there is a difference in charging potential on the photoconductor. Occurs. This causes a difference in hue depending on the image pattern,
This tendency appears regardless of the toner color. The output power correction coefficient based on the image pattern is set to di (i = 1 to
In case of 5), for example, the following values were experimentally obtained as appropriate values.

Y (60) × di + M (100) → R Y (80) × di + C (100) → GM (90) × di + C (100) → B

[0034]

[Table 1]

When the image pattern of one page is a single image pattern such as a solid graphic or a character image of 9 points, a print image having a good hue can be obtained under the above setting conditions, but it is practically used. Instead of a single image pattern, a composite image pattern is often used, for example, a part of the image has solid graphics and the other has a 9-point character image. By analyzing the image information for one page, the portion determined to be solid graphics is corrected by d ₁ (40%), and the portion determined to be 9-point character is d ₄ (60%). %) To obtain the output power of the first color, it is possible to obtain a print image with a good hue even for the composite image pattern.

Further, since the image pattern of one page may be a more complex composite image pattern, by setting the following weighted average correction coefficient d ₀ for each page, it is possible to make a remarkable difference in the page. Disturbance of hue can be prevented.

Y (60) × d ₀ + M (100) → R Y (80) × d ₀ + C (100) → GM (90) × d ₀ + C (100) → B

[0038]

[Table 2]

The weighted average correction coefficient d ₀ is calculated by the following equation (1).

[0040]

[Equation 1]

FIG. 7 is a circuit diagram of a color image forming apparatus for adjusting the first image exposure amount of two colors and the second image exposure amount of two colors by an image pattern when the two color toner images are superposed. Is shown.

In this embodiment, the printer controller 503 is used.
The printer main body 505 (including the operation board 504) and the printer main body 505.

The printer controller 503 decodes image information (mainly page description language) from the host computer 502 and develops it into bitmap data, and the printer main body 50
It sends a command to the video interface 600 in 5 and recognizes the preparation status of the printer body and the host and sends a command to the host 502, the operation board 504, and the video interface 600. As components, a high-speed CPU 506, a plane memory 509 (a to c) for holding one page of data that has been bit-mapped, a RAM 510, a dot condition determination circuit 51.
It has 1 mag. Plane memories 509a, 509b, 509
c, respectively stores the dot data of each color of Y, M, C, and the data of these three memories are all "1".
In the case of, it means BK (Y + M + C).

The printer body 5 includes a CPU and a mechanical controller 516.
Video interface (controlling charging, exposure, transfer, fixing, etc.) and image data processing (generating timing for reading and writing image data, processing image data, selecting command data, etc.) One-chip gate array) 600, a timing generation circuit 515, an optical control unit 517, and a printing unit 518.

In addition to the input conversion circuit 512, the video interface 600 in charge of image signal processing includes a test pattern generator (TP) 551, a selector 552, a single color / multicolor detection circuit 554, and an image pattern discrimination. Circuit 555, hue correction circuit 556, correction coefficient calculation circuit 557, video control circuit 55
8, smoothing processing control circuit (SO) 559, and register group R
G1 to RG28 (514), OR circuit 560, laser control circuit 562, and control circuits (CPU, mechanical controller 516) for controlling the operation of these circuits, and control circuits CL1 to CLn for each circuit while exchanging information. Output) 563.

The input conversion circuit 512 outputs the video signal from the printer controller 503 to Y, M,
Converted to 4-bit signals of C and BK. The test pattern generator (TP) 551 is a ROM that enables the output of a fixed test pattern without a controller. The selector 552 selectively passes the test pattern and the regular video input signal.

The video interface 600 has an input conversion circuit 512, which converts the data from the plane memories 509a, 509b, 509c into video (dot) data and inputs it to the selector 552. FIG. 8 shows the input mechanism of this video (dot) data. In the selector 552, the single-color / multi-color detection circuit 554 detects the combined dot data (Y + M, Y + C, M + C) of the single color and the two colors. Further, the image pattern discrimination circuit 555 is (1) character as the image pattern information. (1.1) Character size (number of printing points). (2) It is graphics. (2.1) Solid, other (halftone) (3) The ratio of the above-mentioned 1 and 2 in one page, (1) to (3) are determined. The correction coefficient calculation circuit 557 calculates the weighted average correction coefficient d ₀ according to the equation (1) based on the discrimination result of the image pattern discrimination circuit 555, and inputs it to the hue correction circuit 556. In the hue correction circuit 556, by inputting from the single color / multicolor detection circuit 554 and the hue correction circuit 556, [Y (100), M
(100), C (100), KB (100)] dot data and [Y (60) × d ₀ + M (100), Y (80) × d ₀ as a combination of two colors.
+ C (100), M (90) × d ₀ + C (100)] dot data is output.

This data is judged for each dot by the video control circuit 558 and the smoothing control circuit 559 for the tint correction and the smoothing process, and the registers RG1 to RG28 storing the printing conditions for the dot are accessed. Condition data is output from the accessed register (one of RG1 to RG28), and the optical controller 517 controls the printing operation according to the data. The timing of all operations is performed in dot units with reference to an index signal (a signal indicating that the beam has reached a predetermined position near the leading edge of the image on the photoconductor) IND obtained from the printing unit 518. That is, the index signal IND is supplied to the timing generation circuit 515, based on this, the phase is the high-speed clock of dot units is synchronized (5MH _Z) is generated, the high-speed clock is sent to the printer controller 503 or the like, in which Dot data is transferred synchronously, signal processing is performed in real time, and printing is executed.

Optical control section 517 of image exposure means 13 shown in FIG.
Has a PWM modulation circuit 571, a laser on / off signal generator 572, a laser driver 573, a writing laser diode D1 and a monitoring photodiode D2, and an index signal generating photosensor 136.
Further, the printing unit 518 corresponds to the photosensitive drum 10 shown in FIG.
And a charger 12 and a developing device 14 for four colors (Y, M, C, BK)
have. The rotation of the photosensitive drum 10 is controlled by a stepping motor 583, and the number of rotations is detected by an encoder and sent to the CPU and the mechanical controller 516.

In this embodiment, the image exposure amount of the first color is changed according to the image pattern for the color image in which the two colors are superposed, and the output level of the laser power is PWM. The pulse width modulation is performed by the modulation circuit 571. 9A and 9B are explanatory diagrams of the pulse width modulation circuit 571. FIG. 9A is a circuit diagram and FIG. 9B is an operation explanatory diagram. The output level of the laser power is converted into an analog level by the D / A converter 571A, while the triangular wave output from the triangular wave generation circuit 571B as a comparison wave is compared with the write level by the comparison circuit 571C, and the resulting signal is pulsed. The PWM signal is output from the width modulation circuit 571.

In the description of the present invention, the embodiment in which the image exposure amount of the first color is changed according to the image pattern for the color image in which two colors are superposed has been described.
It is possible to change the image exposure amount of the second color without changing the image exposure amount of the color, and it is also possible to change both the first color and the second color. Included in the invention.

Although the embodiment in which the pulse width is changed to change the image exposure amount has been described, the laser power for each dot may be changed instead of the pulse width. Three
Also in the case of overlapping more than one color, the exposure conditions for each color may be set according to the pattern as in the case of two colors.

In addition to the automatic identification of the image pattern by the printer controller, the user may perform switching / adjustment by a manual switching means such as "graphics", "characters", "solid image".

As the color image forming apparatus of the present invention, an image forming system in which a toner image is superposed on an image carrier has been described. However, a system other than such a system in which a toner image is superposed on a transfer image carrier is also used. The present invention is also applied to a color image forming apparatus.

[0055]

EFFECTS OF THE INVENTION In a color image forming apparatus in which toner images of single color or two colors are superposed on an image carrier, and the formed toner images are transferred onto a transfer paper, conventionally two colors are superposed. The color tone of the combined toner image changed depending on the image pattern, and a color image with a good color tone was not always obtained. However, according to the present invention, regardless of the image pattern, a color image having a good color tone can always be obtained.

[Brief description of drawings]

FIG. 1 is a configuration cross-sectional view showing an embodiment of a color image forming apparatus.

2A is a layout of an image exposure unit, and FIG. 2B is a description of a semiconductor laser unit.

FIG. 3 is a configuration cross-sectional view of a developing device.

FIG. 4 is an explanatory diagram of combinations that realize a multicolor image of 7 colors.

FIG. 5 is an explanatory diagram of a color image system in which toners of two colors are superposed.

FIG. 6 is an explanatory diagram in which a hue difference occurs depending on an image pattern.

FIG. 7 shows an example of a circuit diagram of a color image forming apparatus of the present invention.

FIG. 8 is a diagram showing a mechanism for inputting video (dot) data from the printer controller to the printer main body.

9A and 9B are explanatory diagrams of a pulse width modulation circuit, where FIG. 9A is a circuit diagram and FIG. 9B is an operation explanatory diagram.

[Explanation of symbols]

 10 Photoconductor drum (image carrier) 12 Scorotron charger 13 Image exposure unit 14 Developer 501 Display 502 Host computer 503 Printer controller 504 Operation board 512 Input conversion circuit 517 Optical control unit 552 Selector 554 Single color / multicolor detection circuit 555 image Pattern discrimination circuit 556 Hue correction circuit 557 Correction coefficient calculation circuit 571 PWM modulation circuit

Claims (1)

[Claims] 1. A plurality of developing means are provided at the peripheral portion of the image carrier, a latent image formed on the image carrier by image exposure of the image exposing means is developed, and the toner image is transferred to a transfer material. In a color image forming apparatus for forming a color image, when toner images of two or more colors are superposed, it has an adjusting means for adjusting the image exposure condition of each color to be superposed, and the adjustment value is changed according to the image pattern. A color image forming apparatus characterized by performing adjustment processing.