JPH05197253A - Color electrophotographic device - Google Patents

Abstract

PURPOSE:To prevent color balance from being damaged caused by that the appropriate quantity of color toner is not imparted at the time of successively laying the color toner to overlap each other on a photosensitive body and developing. CONSTITUTION:Noticing that each color toner has different light transmittivity and electrifying quantity, and considering the difference of these transmittivity and electrostatic charging quantity, the quantity of the toner to be imparted to the photosensitive body 1 is adjusted in the following process. In the case of adjusting the quantity of the toner to be imparted, the adjustment is performed by controlling exposure. Thus, the accuracy of the color toner imparting quantity is improved, so that a full color image of well-balanced in color and of high quality can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor image forming apparatus such as a copying machine, a printer or the like of an electrophotographic system or an electrostatic recording system which can form a multicolor image of full color, multicolor or the like. ..

[0002]

2. Description of the Related Art In recent years, a plurality of developing devices for accommodating developers (toners) of different colors are provided, and the steps of charging, exposing, and developing are sequentially performed by using an electrophotographic method. A multicolor image forming apparatus that forms a visible multicolor image on a photosensitive drum, which is an image carrier, in a recording cycle, transfers the multicolor image to a recording material at a time, and fixes it to obtain a desired multicolor image. Although actively proposed, an example of such a multicolor image forming apparatus, for example, a schematic configuration example of a color laser beam printer is shown in FIG.

This color laser beam printer has a photosensitive drum 1 in which a photoconductive layer is coated on a drum-shaped conductive substrate, and the photosensitive drum 1 rotates steadily in the direction of the arrow shown in the drawing. Along with, a charger 2 for uniformly charging the photosensitive drum 1 and developers (toners) of different colors for developing the latent image after exposure are contained in the first to first parts.
Fourth developing units 31 to 34 for magenta, cyan, yellow, and black, a transfer unit 4 for transferring the developed toner image onto a recording material (paper), and a cleaner 5 for removing the residual toner on the photosensitive drum 1. A static elimination lamp 8 which is a static eliminator for static erasing the surface of the photosensitive drum 1 is provided.

At the time of forming a multicolor image, the photosensitive drum 1 is uniformly charged by the charger 2 and image exposure is performed based on an image signal of a specific color to form a latent image. By repeating the process of developing with a developing device accommodating color toner corresponding to a color to form a visible image in a predetermined order for each image signal of each of a plurality of preset colors, the photosensitive drum 1 is formed. A multiple multicolor toner image is formed, and this multicolor toner image is collectively transferred onto a recording material by the transfer means 4 and passed through a fixing device (not shown) to form a permanent image.

The color laser beam printer is characterized in that toner images of respective colors are formed on the photosensitive drum 1 in a superimposed manner to obtain a multicolor toner image. Therefore, as a developing method, the toner image is first formed on the photosensitive drum 1. Since it is necessary that the toner image is not destroyed when developing latent images of different colors later and is not mixed in the developing device in which toners of different colors are accommodated, it does not contact the photosensitive drum 1. Developing method is required. As a light source for image exposure, a semiconductor laser is typically used. For example, as shown
The semiconductor laser 6 is driven according to the color-separated image data input from the reader unit 10, the photoconductor drum 1 is scanned with the light emitted from the semiconductor laser 6, and the electrostatic latent image according to the image signal of the specific color is scanned. Forming an image.

[0006]

However, in the above-mentioned conventional example, since the first color irradiates the image exposure directly on the photosensitive drum 1, the latent image can be formed correctly, but when the second and subsequent colors are processed. Since the image exposure has to be applied from above the toner image, the amount of image exposure reaching the photosensitive drum 1 is different between the portion with toner and the portion without toner, and proper latent image formation can be performed. Absent.
Therefore, the color image produced by this process has poor color reproducibility.

Further, according to the color image forming method of such a system, when developing characters or lines on the toner image, the characters or lines tend to be thin. The cause will be described with reference to FIG.

FIG. 11 is a diagram showing changes in the surface potential of the image carrier in the process of forming a multicolor image in such an apparatus. In the figure, the polarity is positive for the sake of explanation. Hereinafter, they will be sequentially described.

(1) The image carrier is uniformly charged by the charger to have a constant positive surface potential E. (Fig. 11
See (A). (2) The first image is exposed by an exposure source such as a semiconductor laser, and the potential of the first exposed portion drops to E '. (See FIG. 11B.) (3) The electrostatic latent image thus formed is developed by a developing device to which a positive bias close to the surface potential E of the unexposed portion is applied. As a result, the positively charged toner adheres to the first exposed portion having a relatively low electric potential, and a first toner image is formed. (Refer to FIG. 11C.) (4) By removing the electric charge by the pre-exposure lamp (charge eliminating lamp) or the like, the surface potential of the unexposed portion is eliminated, and the electric charge of the toner adhering portion is equal to the electric potential T ₁ due to the toner charge. Get higher (See FIG. 11D.) This static elimination step is performed to prevent the unexposed portion from being overcharged. (5) The surface of the image carrier on which the first toner image is formed is again uniformly charged by the charger, and as a result, the surface potential E becomes substantially uniform regardless of the presence or absence of toner. At this time, the charge amount of the toner is increased and the toner potential (potential due to the toner charge) is also increased because recharging is performed on the formed toner image (T ₁ → T ₁ ′). Therefore, even if the surface potential E on the image carrier is uniform, the potential on the surface of the photoconductive layer (below the toner layer) is the toner potential T.
_{It is} lowered by ₁ ', resulting in ET ₁ '. (Fig. 11
See (E). (6) If the second image exposure is performed on the surface of the image bearing member with the same light amount as the light amount of the first image exposure, the image exposure is performed from the top of the first toner image. Since the potential on the surface is as low as ET ₁ ′ and the amount of image exposure light is attenuated by the toner image, the surface potential of the image bearing member becomes E ″ at the exposed portion, which is higher than that in the case of no toner. (See FIG. 11F.) (7) Here, similarly to (3) above, the positively charged toner of a color different from that of the first toner is developed to form a multiple toner image. Even when the first toner image and the second toner image are superposed by the image exposure with the same exposure amount as in the above (6), the latent image contrast for the second toner image becomes smaller, It can be seen that the second toner image has less toner adhesion amount. That. (Fig. 11
See (G). (8) It is known that this phenomenon becomes even more prominent when the charge is removed thereafter (see FIG. 11 (H)) and the third and fourth toner images are further developed.

An object of the present invention is to provide an image processing apparatus capable of obtaining a good color image when carrying out multiple development.

Another object of the present invention is to solve the above problems, improve color reproducibility, and form a multicolor image capable of clearly reproducing fine portions such as characters and lines of an image. It is to provide a device.

[0012]

SUMMARY OF THE INVENTION The present invention which achieves the above object is a color electrophotographic apparatus for forming color toners on an electrophotographic photosensitive member, which is an endlessly moving electrophotographic photosensitive member. A charging unit disposed to face the body; a scanning optical unit that scans the charged photoconductor with information light based on a color signal; a control unit that controls the exposure amount of the scanning optical unit to the photoconductor; And a transfer unit for collectively transferring the toner images formed on top of each other onto a transfer material, and the control unit for controlling the exposure amount is a scanning optical device in consideration of the transmittance of the toner which varies depending on the light wavelength. It controls the amount of exposure emitted by the means.

Further, one pixel in the present invention indicates a minimum recording unit of image information, and in binary, multi-valued, pseudo gradation, etc., one pixel means the minimum in the present invention. Shows the recording unit of.

[0014]

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

FIG. 1 is a schematic configuration diagram showing a main part of a first embodiment in which the present invention is applied to an electrophotographic color laser beam printer. This color laser beam printer makes hard copies based on image data transferred from various types of image data output devices such as an image data forming device, an image storage device, an image reading device, an image processing device, and an image display device. Printer. In addition,
Parts, members and the like corresponding to the conventional color laser beam printer shown in FIG. 5 described above are denoted by the same reference numerals and the description thereof will be omitted unless necessary. Of course, the present invention is a multicolor image forming apparatus such as a color printer and a color copying machine having various electrophotographic system configurations, or a multicolor image forming apparatus such as a color printer and a color copying machine having various configurations other than the electrophotographic system. It can also be applied to a device.

The printer of this embodiment also has a photosensitive drum 1 having a photoconductive layer deposited on a drum-shaped conductive substrate. The photosensitive drum 1 rotates steadily in the direction of the arrow shown in the drawing. Along the line, a charger 2 for uniformly charging the photosensitive drum 1 and developers (toners) of different colors for developing the latent image after exposure, for example, yellow, magenta, cyan, and black toners are contained. First to fourth developing devices 31 to 34, a transfer unit 4 that transfers the developed toner image onto a recording material (paper), a cleaner 5 that removes residual toner on the photosensitive drum 1, and a photosensitive drum 1. A static elimination lamp 8 which is a static eliminator for static erasing the surface is provided. A semiconductor laser 6 is used as a light source for image exposure.

The semiconductor laser 6 is driven according to the color-separated image data input from the reader section 10.

In the present embodiment, the color separated image data output from the reader unit 10 is pulse width modulated (PWM).
It is supplied to the circuit 9, where the image exposure time per pixel is changed. That is, the pulse width modulation circuit 9 is a correction unit for color separated image data, and corrects the color separated image data supplied from the reader unit 10 in accordance with the toner amount of each color estimated from the data, and 1 pixel The image exposure time per hit is changed according to the toner amount. The semiconductor laser 6 is driven by the corrected drive signal from the pulse width modulation circuit 9, the photosensitive drum 1 is scanned by the light emitted from the semiconductor laser 6, and the electrostatic latent image corresponding to the image signal of the specific color is detected. It forms an image.

Next, the circuit configuration and operation of the pulse width modulation circuit 9 for changing the image exposure time per pixel will be described.

FIG. 9 is a circuit diagram showing an example of the pulse width modulation (PWM) circuit 9 used in this embodiment, and FIG. 8 is FIG.
FIG. 10 is a circuit diagram showing an example of the laser driver circuit of FIG. 10, and FIG. 10 is a timing chart showing the operation of the pulse width modulation circuit of FIG.

In FIG. 9, the 8-bit digital image signal which is the color separation image data from the reader unit 10 is TT.
It is input to the L latch circuit 401 and latched. A pixel clock signal f is supplied to the latch circuit 401 from a clock signal oscillator 406 that generates a clock signal 2f through a 1/2 frequency divider 408. In synchronization with the pixel clock signal f, the latch circuit 401 outputs a TTL logic signal. The level signal is supplied to the first level converter 402. The first level converter 402 converts a TTL logic level signal into a high-speed ECL logic level signal and supplies it to a digital-analog converter (D / A converter) 403 to convert the ECL logic level signal into an analog signal. To do. The converted analog signal is supplied to one input of the ECL comparator 404 and pulse width modulation (PWM) of the ECL logic level is performed by the ECL triangular wave signal d from the triangular wave generator 407 supplied to the other input of the comparator 404. Generate a signal. The PWM signal from the comparator 404 is the second
Of the TTL logic level by the level converter 405 of
It is converted into a signal and supplied to the laser driver circuit 500. It should be noted that the triangular wave generator 407 uses the clock signal 2f.
Generates an almost ideal triangular wave signal in synchronization with. Also,
The ½ frequency divider 408 divides the clock signal 2f by ½ to generate the pixel clock signal f. Therefore, the clock signal 2f has a cycle twice that of the pixel clock signal f. In addition, in order to operate the circuit at high speed, EC everywhere
An L logic circuit is arranged.

The operation of the pulse width modulation circuit 9 having the above configuration will be described with reference to the timing chart of FIG. The clock signal 2f and the pixel clock signal f having a doubled cycle are related as shown in the figure. Also, the triangular wave generator 4
07 is the duty ratio of the generated triangular wave signal is 50%
In order to maintain the above, the clock signal 2f is internally divided by 1/2 to generate the triangular wave signal c, and the triangular wave signal c is further converted into the ECL level (0 to -1V) to generate the ECL triangular wave signal d. Occur.

On the other hand, the image signal e is 00H (white) to FFH.
It changes in 256 gradation levels up to (black). The symbol "H" indicates hexadecimal notation. In FIG. 10, the image signal e is shown at the ECL voltage level obtained by D / A converting some image signal values. For example, the first
The pixel indicates a black pixel level FFH, the second pixel indicates a halftone level 80H, the third pixel indicates a halftone level 40H, and the fourth pixel indicates a halftone level 20H. The comparator 404 compares the ECL triangular wave signal d and the image signal e to generate a PWM signal having a pulse width T, t ₂ , t ₃ , t ₄ or the like according to the pixel density to be formed. Then, this PWM signal is converted into a TTL level signal of 0V or 5V to become a PWM signal f, which is input to the laser driver circuit 500.

Next, the configuration of the laser driver circuit 500 will be described with reference to FIG. This laser driver circuit 500 is a constant current type laser driver circuit, and uses a semiconductor laser element 501 as a light emission source. This semiconductor laser device 501 is a switching transistor 502.
When the switching transistor 502 is turned off, the laser light is emitted when the switching transistor 502 is turned on. This switching transistor 50
Reference numeral 2 forms a current switch circuit together with the transistor 504 which forms a pair with the transistor 504, and controls the on / off (commutation) of the current to flow to the semiconductor laser element 501 in accordance with the input TTL PWM signal f. This laser device 501
The current flowing through is controlled to be constant by the transistor 505. Moreover, this constant current value is
It becomes variable by changing the base potential of 05. That is, the input 8-bit laser power value is digitally
The analog converter 503 converts the voltage into an analog voltage, and the voltage value obtained by comparing this voltage with the reference voltage is transferred to the transistor 505.
By inputting into the base of, the laser drive current value corresponding to the laser power value is determined.

Using such a pulse width modulation circuit 9, P
By performing WM exposure, 256 gradations can be obtained in one pixel.

The toner used in this embodiment is a polyester type toner having a particle size of 8 μm, and the image exposure light source has a wavelength of 78.
A semiconductor laser 6 of 0 nm is used. FIG. 6 shows the measured laser transmittances of the magenta, yellow, cyan, and black toners having the particle diameter of 8 μm. The measurement method of this data is the transmittance when the unfixed toner is placed on the transparent film when the laser spot light in the vicinity of the photosensitive drum 1 is transmitted through the transparent film and measured by the sensor to be 100%. Is what [%] becomes.

An approximate expression for the toner of each color was prepared for the relationship between the toner amount and the laser transmittance. The toner amount was X, and the maximum toner amount was Xmax = 255 (256 gradations of laser PWM exposure for image exposure. .), The laser transmittance F (X) [%] can be expressed as follows.

Yellow Fy (Xy) = 4.9 × 10 ⁻⁴ × X ² -2.
7 × 10 ⁻¹ × X + 100 (1) Magenta Fm (Xm) = 4.4 × 10 ⁻⁴ × X ² −2.
7 × 10 ⁻¹ × X + 100 (2) Cyan Fc (Xc) = 4.3 × 10 ⁻⁴ × X ² −3.4
× 10 ⁻¹ × X + 100 (3) Black Fbk (Xbk) = 5.9 × 10 ⁻⁴ × X ² −
4.0 × 10 ⁻¹ × X + 100 (4)

The present invention utilizes these equations in FIG.
As in (B), the amount of attenuation of the laser light amount (image exposure amount) is corrected so that the amount of light reaching the photosensitive drum 1 is the same as when there is no toner. In the present embodiment, color superposition is performed in the order of yellow, magenta, cyan, and black, but the order of color superposition is not limited to this. A non-contact developing method is used as a developing method so as not to disturb the toner image formed in the previous stage.

Here, by changing the output of the semiconductor laser 6,
A method of correcting the light amount of the above attenuation will be described using the configuration of the laser driver in FIG. The output during continuous oscillation is determined by the current value flowing through the laser element 501. The current flowing through the laser element 501 is the transistor 505.
It is variable by changing the base potential of the transistor 505.

That is, the input 8-bit laser power value is converted into an analog voltage by the digital-analog converter 503, and the voltage value obtained by comparing this voltage with the reference voltage is input to the base of the transistor 503. Determine the laser drive current. In the present embodiment, the output of the semiconductor laser 6 is changed by changing the value of the current flowing through the laser element 501 according to the correction formula described later by such means.

Next, assuming that the laser output is B [mW] and the laser power value is A [0-255], B [mW] = 0.05 in the semiconductor laser 6 used in this embodiment.
Since there is a relationship of × (A-160), the photosensitive drum 1
The correction method for the attenuation of the laser light due to the toner image above is as follows: When the corrected laser power value A ″ and the corrected laser output are B ″ [mW] and F (X) [%], B ″ = 0.
05 × (A ″ −160), B = [{F (X)} / 10
Since 0] × B ″, the laser power value correction equation for image exposure correction can be expressed as follows: A ″ = INT [[10
0 / {F (X)}] × (A−160) +160] Here, the correction term is [100 / {F (X)}] and the following G
It is represented by (X). In this example, the laser power value was corrected as follows.

First color Yellow A ″ m = A Second color magenta A ″ y = INT [Gy (Xy) ×
(A-160) +160] Third color cyan A ″ c = INT [Gy (Xy) × Gm
(Xm) × (A−160) +160] Fourth color black A ″ bk = INT [Gy (Xy) ×
Gm (Xm) × Gc (Xc) × (A-160) +16
0] Here, INT is a symbol representing the smallest integer in [], and the reason why integer conversion is performed is that the laser power value must be an integer.

Further, the PWM signal value (the laser P of 256 gradations
When the signal [0-255]) read from the scanner unit for WM exposure is P, P and the toner amount X have the same value when the correction can be performed correctly, and therefore the correction formula can be expressed as follows.

First color Yellow A ″ y = A Second color magenta A ″ m = INT [Gy (Py) ×
(A-160) +160] Third color cyan A ″ c = INT [Gy (Py) × Gm
(Pm) × (A−160) +160] Fourth color black A ″ bk = INT [Gy (Py) ×
Gm (Pm) × Gc (Pc) × (A-160) +16
0]

In the present embodiment, the laser power value before correction was temporarily set to 180 (exposure intensity about 1 mn), so the above correction formula can be expressed as follows. 1st color yellow latent image A ″ y = 180 2nd color magenta latent image A ″ m = INT [Gy (Py) × 20 + 160] 3rd color cyan latent image A ″ c = INT [Gy (Py) × Gm (Pm) ) × 20 +
160] Fourth color black latent image A ″ bk = INT [Gy (Py) × Gm (Pm) × Gc
(Pc) × 20 + 160]

Next, a correction method using the above correction formula will be described. As shown in FIG. 3, the R (red), G (green), and B (blue) component signals obtained by reading the original image with the CCD sensor 31 are converted into digital signals of R, G, and B by the A / D converter 32. To be converted. And
The image processing unit 33 performs processing such as logarithmic conversion, masking, and UCR on the digital signals of the R, G, and B components, and sequentially outputs pixel data in the order of the magenta component. Then, similarly, data is output in the order of the yellow component, the cyan component, and the black component.

The printer unit 3 for the obtained pixel data
In step 4, the following correction processing is performed.

Now, the processing and correction method when the signals of the yellow component, the magenta component, the black component and the cyan component are input will be described.

First, when the signal Py of the yellow component is input, the laser power value is set to A and a latent image is written on the photosensitive drum 1. At the same time, a correction term Gy (Py) for magenta of the next color is input to the image memory for each pixel.

Next, when the magenta component signal Pm is input, the laser power value is set to A ″ m = INT [Gy (Py) using the correction term Gy (Py) read from the image memory.
y) × 20 + 160] for each pixel to perform correction and form a latent image. At the same time, the value multiplied by Gm (Pm), that is, the correction term Gy (Py) × Gm (Pm) for cyan is rewritten and input to each pixel in the image memory.

Next, when the cyan component signal Pc is input, the correction term Gy (Py) × read from the image memory.
The laser power value is A ″ c = I using Gm (Pm).
NT [Gy (Py) × Gm (Pm) × 20 + 160] is changed for each pixel to correct and form a latent image.

At the same time, Gc (P
value multiplied by c), that is, the correction term Gy for black
(Py) × Gm (Pm) × Gc (Pc) is rewritten and input for each pixel. When the black component signal Pbk is finally input, the laser power value is set to A ″ bk = INT [using the correction terms Gy (Py) × Gm (Pm) × Gc (Pc) read from the image memory. Gy (P
y) × Gm (Pm) × Gc (Pc) × 20 + 160] for each pixel to perform correction to form a latent image.

(Embodiment 2) A description will be given of a case where the LED array 7 is used as the exposing means in the same correction method as in the first embodiment. The process when the LED array 7 is used is shown in FIG. The toner used in this example is a polyester-based toner having a particle size of 8 μm as in Example 1, the LED array 7 having a wavelength of 665 nm is used as the image exposure light source, and the non-contact developing method is used as the developing method. ..

In this embodiment, a color image is formed by a multiple development method in which toners of three colors, yellow, magenta, and cyan in this order, are superposed on the photosensitive drum 1. Here, the order of colors is yellow, magenta, and cyan, because the transmittance of the toner at the emission wavelength of the LED array 7 used in this study is compared with that of the semiconductor laser 6, and yellow toner and magenta toner are This is because the cyan toner showed almost the same transmittance, but the cyan toner hardly penetrated.

In this embodiment, an LED array is used as the image exposing means to output 17 gradations by a 4 pixel × 4 pixel dither method. Therefore, when considered in pixel units, a binary toner image is obtained. Therefore, the correction method according to the present embodiment is also a binary correction of a portion with toner and a portion without toner in pixel units.

Next, assuming that the exposure output is B [mW] and the current value for LED light emission is A [mA], in the LED array 7 used in this embodiment, B [mW] =
The relationship is 1.2 × 10 ⁻³ × A. Here, the transmittance [%] of a portion having toner is set to Hm, Hy, and
When Hc is set to (constant), the following correction is required in order to make the exposure amount that passes through the toner and reaches the photosensitive drum the same as when there is no toner. Assuming that the corrected exposure output is B ″ and the corrected current value for LED emission is A ″, in order to perform the above correction, when Q = 1 (when toner is present), B ″ = ( 100 / H) × B, Q = 0
When there is no toner, the correction B ″ = B must be performed. Therefore, B ″ = [1− (1-100 /
A correction formula of (H) × Q] × B can be created. From this correction formula, the correction formula by the current value for LED light emission is A ″ = [1-
(1-100 / H) × Q] × A.

First color yellow A "y = A Second color magenta A" m = [1- (1-100 / H
y) × Qy] × A Third color cyan A ″ c = [1− (1-100 / Hy)
X Qy] x [1- (1-100 / Hm) x Qm] x A

Next, a correction method using the above correction formula will be described. As shown in FIG. 3, the R, G, and B component signals read from the image by the CCD sensor are converted into digital signals by the A / D converter. Then, the yellow component is read for each pixel from the digital signals of the R, G, and B components in a known image processing.
Then, similarly, the magenta component and the cyan component are extracted and read in this order. Then, when the respective signals of the yellow component, magenta component, and cyan component are input,
The processing and correction method will be described.

First, the yellow component signal Qy (1or
When 0) is input, the current value for LED light emission is set to A and a latent image is written on the photosensitive drum 1. At the same time, the correction term for the next color magenta [1- (1-1
00 / Hy) × Qy] is input for each pixel.

Next, the magenta component signal Qm (1 or 0)
When the input is, the correction term read from the image memory [1
− (1-100 / Hy) × Qy], the current value for LED emission is A ″ m = [1− (1-100 / Hy)
× Qy] × A is changed for each pixel to correct and form a latent image. At the same time, the image memory is multiplied by [1- (1-100 / Hm) × Qm], that is, the correction term for cyan [1- (1-100 / Hy)]
× Qy] × [1- (1-100 / Hm) × Qm] is rewritten and input for each pixel.

Finally, the cyan component signal Qc (1o
When r0) is input, the correction term read from the image memory [1- (1-100 / Hy) × Qy] × [1- (1-
100 / Hm) × Qm], and the current value for LED emission is A ″ c = [1− (1-100 / Hy) × Qy]
× [1- (1-100 / Hm) × Qm] × A is changed for each pixel to perform correction to form a latent image.

(Example 3) Yellow in Example 2,
The wavelength of 665 was used for the three colors of magenta and cyan.
This is because the cyan and black toners hardly pass through image exposure in the LED array of nm. Therefore, in order to carry out multiple development in four-color superposition, the wavelength of the LED array may be set to 780 nm or more like the semiconductor laser. Therefore, in the present embodiment, the same correction as that of the second embodiment is performed using the LED array having the wavelength of 780 nm, and as a result, the correction in the four-color overlapping multiple development using the LED array becomes possible.

Further, the numerical values in these embodiments are determined by the toner, the photosensitive member, the exposing means, etc., and if these elements are changed, the numerical values also need to correspond.

As described above, the attenuation of the exposure amount due to the developer such as the toner on the photosensitive member is corrected by the current value of the exposure means (semiconductor laser 6, LED 7) and the exposure output is increased, so that FIG. As described above, the amount of light reaching the photoconductor is equal in the portion with the developer and the portion without the developer, and normal latent image formation can be performed. Therefore,
Compared with the conventional multiple development process, the color reproducibility is remarkably improved, and a high quality image can be obtained.

(Embodiment 4) A process diagram in this embodiment is the same as that in FIG. 1 of the first embodiment.

In this embodiment, the attenuation amount of the image exposure amount is corrected by using the above equations (1) to (4), and the amount of light reaching the photosensitive drum 1 is the same as when there is no toner. ..

In this embodiment, color superposition is performed in the order of yellow, magenta, cyan and black. Also,
As the developing method, a non-contact developing method was used so that the toner image formed in the previous stage was not scraped. Next, as a correction method in the present invention for the attenuation of the laser light due to the toner, as shown in FIG. 7B, the PWM exposure time is lengthened by the amount by which the laser output is attenuated so that the exposure amount reaching the photosensitive drum can be adjusted. It is the same in a part and a part. (Exposure amount = laser output x
PWM exposure time) As an actual correction formula, let P be the PWM input signal (the signal [0-255] read from the scanner unit for laser PWM exposure of 256 gradations) and P
When the WM output signal (corrected signal) is R, the laser transmitted light amount F (X) for the toner image on the photosensitive drum
When [%] is used, it is represented by the formula R = [100 / {F (X)}] × P. Here, the correction term is [100 / {F
(X)}], and is represented by G (X) below. However, R = G
In the correction method of (X) × P, P = 255 (P
The WM exposure time maximum value) cannot be corrected in the vicinity of the PWM exposure time. This is the PWM value MA
This is because X is 255. Therefore, the following examples will be described in consideration of this fact.

(Embodiment 5) In the present embodiment, the output during continuous oscillation is set as high as 3 mw and kept constant. And P
The development conditions are set by setting the WM exposure time to 40% of the normal time. As described above, by setting the PWM exposure time to 40% of the normal time, it becomes possible to correct the laser transmitted light amount to 40% or more.

Here, the correction in the present embodiment is performed with the transmitted light amount 4
The reason for setting it to 0% or more is that in the apparatus and toner of this embodiment, when forming a latent image for developing the maximum amount of monochromatic toner, the amount of transmitted light at the maximum amount of toner on the photosensitive drum 1 is 40% or more. Is. The correction formula in this embodiment is as follows.

First color Yellow Output during continuous oscillation 3
mw Ry = INT [0.4 × Py] Second color magenta Output during continuous oscillation 3 mw Rm = INT [0.4 × Gy (Xy) × Pm] Third color Cyan Output during continuous oscillation 3 mw Rc = INT [0. 4 x Gy (Xy) x Gm (Xm) x
Pc] Fourth color black output during continuous oscillation 3 mw Rbk = INT [0.4 × Gy (Xy) × Gm (Xm)
X Gc (Xc) x Pbk]

Here, INT is a symbol representing the smallest integer in [], and the reason why integer conversion is performed is that the PWM exposure signal value must be an integer. Also P
When X and X are corrected correctly, they have the same value, so the correction equation can be expressed as follows.

First color Yellow Output during continuous oscillation 3
mw Ry = INT [0.4 × Py] 2nd color magenta output during continuous oscillation 3 mw Rm = INT [0.4 × Gy (Py) × Pm] 3rd color cyan output during continuous oscillation 3mw Rc = INT [0. 4 x Gy (Py) x Gm (Pm) x
Pc] Fourth color black output during continuous oscillation 3 mw Rbk = INT [0.4 × Gy (Py) × Gm (Pm)
X Gc (Pc) x Pbk]

A correction method using the above correction formula will be described below. As shown in FIG. 2, the R, G, B, and component signals read by the CCD sensor 31 from the image are
It is converted into a digital signal by the A / D converter 32.
Then, the image processing unit 33 reads the yellow component for each pixel from the digital signals of the R, G, and B components. Similarly, the magenta component, the cyan component, and the black component are read in this order.

Next, the processing method in the printer unit 34 when the signals of the yellow component, the magenta component, the cyan component and the black component are input will be described.

First, when the yellow component signal Py is input, Ry = 0.4 × Py is output as an output signal, and the latent image is written on the photosensitive drum 1 by the semiconductor laser. At the same time, the correction term Gy for the next color magenta is stored in the image memory.
(Py) is input for each pixel. Next, when the magenta component signal Pm is input, correction is performed using the correction term Gy (Py) read from the image memory, and Rm =
The latent image is written on the photosensitive drum 1 by the semiconductor laser which is output by the signal INT [0.4 × Gy (Py) Pm]. At the same time, the image memory is multiplied by Gm (Pm), that is, the correction term Gy (Py) × for cyan.
Gm (Pm) is rewritten and input for each pixel.

Next, when the cyan component signal Pc is input, the correction term Gy (Py) × read from the image memory.
Correction is performed using Gm (Pm) and Rc = INT [0.
4 × Gy (Py) × Gm (Pm) × Pc], and a latent image is written on the photosensitive drum 1 by the semiconductor laser. At the same time, Gc (P
value multiplied by c), that is, the correction term Gy for black
(Py) × Gm (Pm) × Gc (Pc) is rewritten and input for each pixel.

Finally, when the black component signal Pbk is input, the correction term Gy read from the image memory.
Correction using (Py) × Gm (Pm) × Gc (Pc) is performed and Rbk = INT [0.4 × Gy (Py) × Gm
(Pm) × Gc (Pc) × Pbk], and a semiconductor laser writes a latent image on the photosensitive drum 1.

(Embodiment 6) In this embodiment, the first color-
For the fourth color, the output during continuous oscillation of the semiconductor laser 6 was changed to 1 mw, 2 mw, 3 mw, 3 mw, and the following correction was performed.

First color Yellow Output during continuous oscillation 1
mw Ry = Py 2nd color magenta output during continuous oscillation 2mw Rm = INT [(1/2) × Gy (Py) × Pm] 3rd color cyan output during continuous oscillation 3mw Rc = INT [(1/3) × Gy (Py) × Gm (P
m) × Pc] 4th color black output during continuous oscillation 3 mw Rbk = INT [(1/3) × Gy (Py) × Gm (P
m) × Gc (Pc) × Pbk] This method increases the laser output as color superposition progresses and shortens the exposure time (shortens the PWM exposure time) to obtain the exposure amount (laser output × PWM exposure time). ), The range in which the PWM exposure amount correction can be performed is widened.

Next, a correction method using the above correction formula will be described. As shown in FIG. 2, from the image, the CCD sensor 3
The signals of the R, G, and B components read by 1 are A /
The digital signal is converted by the D converter 32. Then, from the digital signals of the R, G, and B components, the image processing unit 3
In 3, the yellow component is read for each pixel. Similarly, reading is performed in the order of magenta component, cyan component, and black component. Now, the processing and correction method in the printer unit 34 when the signals of the yellow component, the magenta component, the black component, and the cyan component are input will be described.

First, when the yellow component signal Py is input, Ry = Py is output as an output signal, and a latent image is written on the photosensitive drum 1 by the semiconductor laser. At the same time, the correction term Gy (Ay) for the next color magenta is stored in the image memory.
Is input for each pixel.

Next, when the magenta component signal Pm is input, correction is performed using the correction term Gy (Py) read from the image memory, and Ry = INT [(1/2) × Gy (P
y) × Pm], and a latent image is written on the photosensitive drum 1 by the semiconductor laser. At the same time, a value multiplied by Gm (Pm), that is, a correction term Gy (Py) × Gm (Pm) for cyan is rewritten and input to each pixel in the image memory.

Next, when the signal Ac of the cyan component is input, the correction term Gy (Py) × Gm read from the image memory.
Correction using (Pm) is performed and Rc = INT [(1 /
3) × Gy (Py) × Gm (Pm) × Pc], and a latent image is written on the photosensitive drum 1 by the semiconductor laser. At the same time, Gc (P
value multiplied by c), that is, the correction term Gy for black
(Py) × Gm (Pm) × Gc (Pc) is rewritten and input for each pixel.

Finally, when the black component signal Pbk is input, the correction term Gy read from the image memory.
Correction using (Py) × Gm (Pm) × Gc (Pc) is performed and Rbk = INT [(1/3) × Gy (Pm) × G
y (Py) × Gc (Pc) × Pbk] is output and a latent image is written on the photosensitive drum 1 by the semiconductor laser.

(Embodiment 7) In this embodiment, an LED having a wavelength of 665 nm was used as an exposing means to carry out multiple development by superimposing three colors of yellow, magenta and cyan.

Further, in this embodiment, PWM exposure is performed by controlling the light emission time of the LED. Then, as a correction method, similarly to the first embodiment, the output during continuous light emission is set to be high and constant, the PWM exposure time is set to 40% of the normal time, and the developing condition is set, and then the PWM correction is performed.

(Embodiment 8) By using the same LED as in Embodiment 6, PWM exposure is performed, and as a correction method, the output at the time of continuous light emission is strengthened sequentially for each color as in Embodiment 5, and the light emission time is shortened. After widening the correction range, PWM correction was performed and exposure was performed.

(Embodiment 9) In Embodiments 6 and 7, three colors of yellow, magenta, and cyan were superposed, and in the LED array having a wavelength of 665 nm, cyan and black toners could almost pass through image exposure. Because there is no. Therefore, in order to perform multiple development in four-color superimposition, the wavelength of the LED array is set to 78 as in the semiconductor laser.
It may be 0 nm or more. Therefore, in this embodiment, the same correction as in Embodiments 6 and 7 was performed using the LED array having the wavelength of 780 nm, and as a result, the correction in the four-color overlapping development using the LED array became possible.

Further, the numerical values in these embodiments are determined by the toner, the photosensitive member, the exposure means, etc., and if these elements are changed, the numerical values need to correspond.

As described above, the attenuation of the exposure amount due to the developer such as toner on the photoconductor is corrected by the PWM exposure time and the exposure time is lengthened to increase the exposure amount reaching the photoconductor as shown in FIG. However, the area where the developer is present is equal to the area where the developer is absent, and normal latent image formation can be performed. Therefore, the color reproducibility is remarkably improved as compared with the conventional multiple development process.

According to the above-described first to ninth embodiments, as shown in FIG. 4A, when the image exposure is performed from the developer such as the toner, the image exposure amount is attenuated. By correcting the image exposure output (current value) as shown in FIG. 4 (B), the image exposure amount reaching the photosensitive drum 1 becomes equal to that in the case where no developer is used. A color image forming apparatus capable of outputting an image with improved color reproducibility is possible in a multiple development process.

Further, as shown in FIG. 7 (A), when the image exposure is attenuated by performing image exposure from the developer such as toner, as shown in FIG. 7 (B). As the output is attenuated, by increasing the PWM exposure time, the image exposure amount reaching the photosensitive drum 1 becomes equal in the toner-containing portion and the toner-free portion, so that the color reproducibility is improved as compared with the conventional case. A color image forming apparatus capable of outputting an image becomes possible in a multiple development process.

In the next embodiment, in addition to the problem caused by the difference in the light transmittance of the toner depending on the wavelength of the light, the problem due to the charging potential of the toner described in FIG. 11 is solved at the same time. is there.

(Embodiment 10) In this embodiment, the same apparatus as that shown in FIG. 1 is used, and the toner used therein is the same series as the toner used in the first embodiment, and the particle size is 8
A semiconductor laser 6 having a wavelength of 780 nm was used as the image exposure light source. The toner amount of each of the yellow, magenta, cyan, and black toners having the particle diameter of 8 μm (PWM signal value “0 (00H) to 255 (FF
H) ”corresponding to the toner amount.
5 ”) and the laser transmittance are shown in FIG. As a measuring method, a light quantity measuring device (detector) is fixed inside an image carrier having a transparent conductive substrate, and exposure is performed with a semiconductor laser. Then, when the amount of light when there is no toner on the image carrier is 100%, the transmittance is measured when the toner amount of each color toner is changed on the image carrier. Further, the potential due to the amount of toner and the electric charge of the toner (the surface potential after recharging and pre-exposure with the toner placed on the grounded image bearing member, that is, the grounded photoconductor drum. 12) is a measurement of the relationship
Is. The relationship between the number of times of charging and the toner potential of the toner used in this embodiment is as shown in FIG. FIG.
As shown in, when a polyester-based toner is used,
When the grid bias of the primary charger was 500 V to 700 V, the toner potential was saturated and almost constant by one recharge. Therefore, in the correction in this embodiment, as shown in FIG. 12, the toner potential is uniquely determined with respect to the toner amount. By the way, in this embodiment, no difference in toner potential was found between the toners of different colors.

Next, in order to investigate the influence of the toner potential, in order to remove the influence of the light shielding by the toner, an image carrier having a transparent conductive substrate is used, and an LED array is used from the inside of the image carrier. The experiment was conducted by a backside exposure method in which image exposure was performed. Toner potential 100
The surface potential decay curve (charging potential 700V) when the amount of toner corresponding to V (indicated by the one-dot chain line D) is placed on the image carrier is the curve (C) in FIG. The surface potential decay curve (charging potential 7) when toner is not applied
00V) is the curve (B) in FIG. The difference between the curves (C) and (B) is the influence of the toner potential.

Here, the following is considered as the cause of this deviation. When the toner is on the image carrier, even if the surface potential is 700 V as in the toner-free portion, it is lower by the toner potential on the surface of the photoconductive layer.
It is considered to be 0V. Therefore, the surface potential decay curve (charge potential 700) when toner is placed on the image carrier
V) is obtained by adding the toner potential 100V (D) to the surface potential decay curve (charging potential 600V) (C ') of the image carrier as in the above curve (C). As described above, even if the toner is not shielded from light, as long as the toner charge is present, the surface potential decay curve is deviated between the portion with toner and the portion without toner.

In the above experiment, an image carrier using a transparent conductive substrate was used in order to eliminate the effect of light shielding by the toner.
Image exposure was performed with a semiconductor laser using a PC photosensitive drum. The surface potential decay curve in this case is shown in FIG. In FIG. 17, a curve (A) in FIG. 17 is a surface potential decay curve (charging potential 700 V) when the image carrier is loaded with toner in an amount such that the toner potential becomes 100 V. The surface potential decay curve (charge potential 700V) when no toner is applied is curve (B) in FIG. Here, the surface potential decay curve (charging potential 600V) on the photoconductive layer when the toner potential is 100V is (C '), and the toner potential 100V (D) is added to this to obtain the toner It can be seen that the surface potential decay curve (charging potential 700V) in the case where there is no light amount decay due to (the effect only due to the toner potential) is shown in FIG. 17C. In FIG. 17, (A)-(C) (curve (A) minus curve (B)) is the amount of light attenuation, and similarly (C)-(B) is due to the influence of the toner potential. This is the gap.

As is apparent from the above description, when a toner image is present on the image carrier and a latent image is formed on the toner image,
It is necessary to correct the influence of the light amount attenuation and the influence of the toner potential. The correction method in this embodiment will be described below.

As shown in FIG. 19, first, in the reader unit 10 of the apparatus of FIG. 1, an image to be printed is read by, for example, a CCD sensor, decomposed into R, G, B component signals, and an analog-digital converter. (A / D converter)
And convert it to a digital signal. And this R,
The digital signals of the G and B components are subjected to known image processing in the image processing section to be decomposed into yellow component, magenta component, cyan component and black component for each pixel. The yellow, magenta, cyan, and black PWM signal values “0 to 255” P _Y , P thus obtained
_M , P _C and P _BK are output from the reader unit 10 at each scan.

Therefore, first, the correction term for the light amount attenuation will be described. _Assuming that the toner amounts of yellow, magenta, cyan, and black (indicated by PWM signal values) “0 to 255” are P _Y , P _M , P _C , and P _BK , respectively, from FIG.
Laser transmittance (%) is F (P _Y ), F (P _M ), F (P
_C ) and F (P _BK ) can be expressed as a function of the toner amount. The correction term for the light amount attenuation used in the present embodiment is 1 because there is no toner on the photosensitive drum 1 at the time of the latent image of yellow. Next, at the time of a magenta latent image, since the yellow toner is on the photosensitive drum 1, the correction term is G (P _Y ) (where G (P) = 100 / F (P) ( (See FIG. 15)). Then, at the time of the latent image of cyan, since the exposure is performed from the superposition of the yellow toner and the magenta toner, the correction term is G (P _Y ) × G (P _M ). Finally,
At the time of a black latent image, since the exposure is performed on the magenta toner, the yellow toner, and the cyan toner, the correction term is G (P _Y ) × G (P _M ) × G (P _C ).

Next, how to obtain the correction term for the toner potential will be described. As described above, the deviation due to the toner potential is obtained by subtracting the curve (B) from the curve (C) of FIG. 7 ((C)-(B)). In order to correct this deviation, the output signal values P _Y , P _M , P from the reader unit 10
It is necessary to multiply _C and P _BK by the correction term K (P) (where K (P) ≧ 1 and P represents the cumulative value of the input signal values up to the previous color). Here, this correction term K (P)
Is a function with respect to the toner potential D (P) as shown in FIG. 18 under the experimental conditions of this time. this,
In terms of the correction term for each color, 1 for yellow latent image, K (P _Y ) for magenta latent image, and K for cyan latent image.
(P _Y + P _M ), K (P _Y + P _M + P) for black latent image
_C ). By applying such correction to the toner potential, the toner potential shown in FIG.
The deviation as shown in (B) can be almost eliminated in this embodiment.

The correction term G (P) for the light amount attenuation and the correction term K for the toner potential thus obtained are given.
(P) is used to actually generate yellow, magenta, cyan,
Colors were layered in black order. Further, as a developing method, a non-contact developing method was used to prevent scraping of the toner image formed in the previous stage. Here, a correction term G (P) for the light amount attenuation and a correction term K for the toner potential
If the correction term G (P) × K (P) multiplied by (P) is simply used, the PWM exposure time cannot be corrected in the vicinity of P = 255 (the maximum value of the PWM exposure time). (Because the maximum PWM value is 255
Because it is. Therefore, in this embodiment, the correction is performed in consideration of this fact.

(Embodiment 11) In this embodiment, FIG.
The output during continuous oscillation of the semiconductor laser 6 was set to a high value of 4 mW and kept constant. Then, the developing conditions were set by setting the PWM exposure time to 25% of the normal time. (When the PWM exposure time is 25%, the density is set to be the same as that in the normal time.) By thus setting the PWM exposure time to 25% of the normal time, the correction term G (P) × K (P)
= 4 can be corrected. Here, the reason why the correction in this embodiment is up to G (P) × K (P) = 4 is that G (P) × K (P This is because almost all color images can be corrected by the correction up to 4).

The correction formula in this embodiment is as follows. (The signal value output from the reader unit 10 is P _Y , P
_M, P _C, and P _BK, the signal value of the corrected R _Y, R _M, R
_C and R _BK . ) First color yellow output when continuous oscillation _{4mW R Y = INT [0.25 ×} P Y] 2 color output when magenta continuous oscillation _{4mW R M = INT [0.25 ×} G Y (P Y) × K (P _Y ) ×
P _M] 3 during color cyan continuous oscillation output _{4mW R C = INT [0.25 ×} G Y (P Y) × G M (P M) ×
_{K (P Y + P M)} × P C] 4 -color black during continuous oscillation output _{4mW R BK = INT [0.25 ×} G Y (P Y) × G M (P M) ×
G _C (P _C ) × K (P _Y + P _M + P _C ) × P _BK ] Here, INT is a symbol representing the smallest integer in [], and the reason why integer conversion is performed is that the signal of PWM exposure is used. This is because the value needs to be an integer.

Although the output during continuous oscillation of the semiconductor laser 6 is constant at 4 mW in the above embodiment, the present invention is not limited to this.

For example, the output during continuous oscillation of the semiconductor laser 6 is 1 mW, 2.5 mW, and 4 m for the first to fourth colors.
The correction formulas in the second embodiment of the present invention which are changed to W and 4 mW are shown below.

Output of the first color yellow continuous oscillation
1mW R _Y = P _Y 2nd color magenta Output during continuous oscillation 2.5mW R _M = INT [0.4 × G _Y (P _Y ) × K (P _Y ) × P _M
] Third color cyan output during continuous oscillation 4 mW _RC = INT [0.25 x G _Y (P _Y ) x G _M (P _M ) x
_{K (P Y + P M)} × P C] 4 -color black during continuous oscillation output _{4mW R BK = INT [0.25 ×} G Y (P Y) × G M (P M) ×
G _C (P _C ) × K (P _Y + P _M + P _C ) × P _BK ]

In this embodiment, the amount of exposure (laser output × PWM) is increased by increasing the laser output and shortening the exposure time (shortening the PWM exposure time) as color superposition progresses.
The range in which the PWM exposure amount can be corrected without changing the exposure time) is widened.

(Embodiment 12) An LED (light emitting diode) array 7 having a wavelength of 665 nm is used as an exposing means by using the same apparatus structure as in FIG. 2, and a polyester-based particle diameter is used as in the first embodiment. Three developing units 31, 32, and 33 for yellow, magenta, and cyan containing 8 μm toner
The present invention is applied to a color laser beam printer of the electrophotographic system for sequentially forming three-color toner images on the photosensitive drum 1 by a non-contact developing method to obtain a multicolor image.

In this embodiment, PWM exposure is performed by controlling the light emission time of the LED array 7.
Then, as a correction method, as in the ninth embodiment,
Set the output for continuous light emission to a high value and make it a constant output.
The PWM correction was performed after setting the development conditions with the WM exposure time set to 25% of the normal time. As a result, the same effect as that of the ninth embodiment was obtained.

(Embodiment 13) In the above eleventh embodiment, L
Although the output of the ED array 7 during continuous light emission is constant at 4 mW, in the twelfth embodiment of the present invention, the output during continuous light emission of the LED array 7 is strengthened sequentially for each color as in the tenth embodiment. , By shortening the light emission time, the correction range that can correct the PWM exposure amount without changing the exposure amount is expanded,
After that, PWM correction was performed and exposure was performed. As a result, the same effect as that of the tenth embodiment was obtained.

(Embodiment 14) In the eleventh and twelfth embodiments, the three-color toner image is developed in the order of yellow, magenta and cyan in the L wavelength of 665 nm.
This is because the cyan and black toners hardly transmit image exposure light in the ED array 7. Therefore,
In order to form a multi-color image by superimposing four-color toner images, the wavelength of the LED array 7 is set to 780 nm so that cyan toner can be transmitted, similarly to the semiconductor lasers 6 of the ninth and tenth embodiments. All you have to do is do the above. Therefore, in the thirteenth embodiment of the present invention, a wavelength of 780n
As a result of performing the same correction as that of the eleventh and twelfth embodiments using the LED array of m, good results were obtained.
It has become possible to make corrections in four-color overlapping multiple development using an LED array as an exposure source.

The numerical values in each of the above-mentioned embodiments are appropriately determined depending on the toner used, the image carrier, the exposing means, etc., and it is necessary to correspond the numerical values if these elements change. At present, it has been known that the lower the charge amount of the developer such as toner, the lower the toner potential, which is advantageous for correction, and the number of gradations of the output image can be increased. It is desirable to use a toner in which the toner charge amount is 20 μc / g or less after recharging and the toner potential is 70 to 80 V or less in the maximum toner amount in a single color.

In each of the above-described embodiments, the color separation image data input from the reader unit 10 is corrected in accordance with the toner amount of each color estimated from the data, so that the image exposure time per pixel can be adjusted. The color-separated image data input from the reader unit 10 is changed according to the amount of toner, according to the toner amount of each color estimated from the data.
By performing the correction, the exposure intensity of image exposure per pixel may be changed according to the toner amount.

Next, the exposure intensity of image exposure per pixel is changed according to the amount of toner.
Example 6 will be described. Each of the embodiments described below is applied to the multicolor image forming apparatus having the configuration shown in FIG. 1 or 2, and the pulse shown in FIG. 9 is used to change the exposure intensity of image exposure. Since the width modulation circuit and the laser driver circuit 500 shown in FIG. 8 are used and the reader has the structure shown in FIG. 19, description thereof will be omitted. In addition, the toner is polyester type, particle size 8μ
m toner, and as an image exposure light source, a semiconductor laser having the same wavelength of 780 nm as the ninth and tenth embodiments in the fourteenth embodiment, and the eleventh and first lasers in the fifteenth embodiment.
LED array with the same wavelength of 665 nm as in the second embodiment, first
In the sixth embodiment, the same wavelength 780n as in the thirteenth embodiment is used.
m LED array was used. Therefore, FIG. 12, FIG.
The relationship between the toner amount and the electric potential due to the electric charge of the toner described above with reference to FIGS. 14 to 18, the relationship between the number of times the toner is charged and the toner potential, the relationship between the toner amount and the laser transmittance, and the toner amount and the transmitted light amount correction ratio. The relationship, correction of the influence of the light amount attenuation, the correction of the influence of the toner potential, and the like are the same as those in each of the above-described embodiments, and therefore their description will be omitted unless necessary.

(Fifteenth Embodiment) First, a fourteenth embodiment of the present invention is applied to a multicolor image forming apparatus having the structure shown in FIG. 1, and by correcting the 8-bit laser power value described above, The exposure intensity of the image exposure was corrected by changing the value of the current flowing through the semiconductor laser 6. Also in this embodiment, the correction term G (P) for the light amount attenuation and the correction term K for the toner potential, which are obtained as described above, are also obtained.
(P) is used to actually generate yellow, magenta, cyan,
A multicolor image was formed by overlapping colors in the order of black.
As a developing method, a non-contact developing method was used so that the toner image formed in the previous stage was not scraped.

Next, assuming that the laser output value is B (mW) and the laser power value is A "0 to 255", the semiconductor laser 6 used in this embodiment has the output characteristics as shown in FIG. If this is expressed by an equation, B = 0.05 (A-16
The relationship is 0). Therefore, the correction of the light amount attenuation and the influence of the toner potential caused by the toner image on the image carrier is performed as follows.

When the corrected laser power value is A ″ and the corrected laser output value is B ″ (mW), the correction term G (P) for the light amount attenuation and the correction term K (P) for the toner potential are given.
When G (P) × K (P) obtained by multiplying by and is used as a correction term, B ″ = G (P) × K (P) × B, and therefore the correction formula of the laser power value is A ″ = It can be expressed as G (P) × K (P) × (A−160) +160.

In this example, the laser power value was corrected for each pixel as follows.

First color yellow latent image A ″ _Y = A Second color magenta latent image A ″ _M = INT [G (P _Y ) × K (P _Y ) × (A-16
0) +160] third color cyan latent image A ″ _C = INT [G (P _Y ) × G (P _M ) × K (P _Y +
P _M ) × (A−160) +160] 4th color black latent image A ″ _BK = INT [G (P _Y ) × G (P _M ) × G (P _C ).
× K (P _Y + P _M + P _C ) × (A-160) +160]

Here, INT is a symbol that represents the smallest integer in [], and the reason why integer conversion is performed is that the laser power value must be an integer.

In this embodiment, the laser power value before correction is 1
Since it was temporarily set to 80 (exposure intensity of about 1 mW), the above correction equation can be expressed as follows.

First color yellow latent image A ″ _Y = 180 Second color magenta latent image A ″ _M = INT [G (P _Y ) × K (P _Y ) × 20 + 16
0] Third color cyan latent image A ″ _C = INT [G (P _Y ) × G (P _M ) × K (P _Y +
P _M ) × 20 + 160] 4th color black latent image A ″ _BK = INT [G (P _Y ) × G (P _M ) × G (P _C ).
× K (P _Y + P _M + P _C ) × 20 + 160]

By performing the above image exposure intensity correction for each pixel, a proper latent image could be formed regardless of the presence or absence of toner.

(Embodiment 16) Next, a fifteenth embodiment of the present invention is applied to the multicolor image forming apparatus having the above construction shown in FIG. 2, and the eleventh and twelfth embodiments are used as image exposure light sources. Using the same LED array having a wavelength of 665 nm as in the example, and similarly to the eleventh and twelfth examples, three developing units 31, 32 for yellow, magenta, and cyan containing a polyester-based toner having a particle size of 8 μm are stored. No. 33, a toner image of three colors was sequentially formed on the photosensitive drum 1 by a non-contact developing method to obtain a multicolor image. Where yellow,
The three-color toner image was developed in the order of magenta and cyan because the toner transmittance at the emission wavelength of the LED array with a wavelength of 665 nm was almost the same for the yellow toner and the magenta toner as compared with the case of the semiconductor laser. This is because the cyan toner hardly penetrated. Therefore, in this embodiment, an LED array was used as the image exposure means, and 17 gradations were output by the 4 pixel × 4 pixel dither method. Therefore, when it is considered in pixel units, it is a binary toner image. Therefore, the correction method in the present embodiment is also a binary correction of the portion with toner and the portion without toner in pixel units. Next, the exposure output is B (m
W), and the current value for LED emission is A (mW), B (m) in the LED array used in this example.
W) = 1.2 × 10 ⁻³ × A. here,
The input signal Q from the scanner unit for each pixel is set to 1 in the exposed pixel and 0 in the non-exposed pixel.

As described above, since a binary toner image is formed in a pixel unit, the transmittance of each color is constant in the portion where toner is present. In this example, the transmittance H of each color was as follows.

Yellow H _Y = 0.85 (85%) Magenta H _M = 0.80 (80%) Cyan H _C = 0.10 (10%)

Therefore, the correction term for the attenuation of the light quantity is 1 because the toner does not exist on the image carrier at the time of the latent image of yellow. Next, when a magenta latent image has a yellow toner image on the image bearing member, the correction term is [1- (1-1 / 0.85) Q _Y ], and the value in () is calculated. (1 + 0.176Q _Y )
Is the correction term (Q _Y is 1 or 0). Since the yellow and magenta toner images are on the latent image of cyan, the correction term is (1 + 0.176Q _Y ) × (1 + 0.25Q _M ).

Next, the correction term for the influence of the toner potential will be described. When a multicolor image is formed by superimposing three colors of yellow, magenta, and cyan on a binary image, it is necessary to correct when yellow toner is on the magenta latent image or when yellow toner and magenta are on the cyan latent image. This is the case where either one or both of the toners are carried. Here, as described above, since the difference in toner potential due to the color difference was not seen, there are only two types of determination methods for the correction item, one with one color toner and one with two color toners. Good. It has been found that the following correction is necessary under the conditions of the toner, LED, etc. used in this embodiment. That is, the correction term when the toner of one color is on was 1.6, and the correction term when the toner of two colors was on was 2.2.

Therefore, the input signals Q _Y and Q at the time of each color latent image are obtained.
_M, expressed using a Q _C, since at the time of the yellow latent image is not the toner is present on the image carrier, correction term is 1.
Next, when a magenta latent image has a yellow toner image on the image carrier, the correction term is (1 + 0.6Q _Y ).
(1 when Q _Y = 0, 1.6 when Q _Y = 1).
Since the yellow and magenta toner images are on the latent image of cyan, the correction term is [1 + 0.6 (Q _Y +
Q _M )] (1 when Q _Y + Q _M = 0, Q _Y + Q _M
1.6 when = 1 and 2.2 when Q _Y + Q _M = 2).

By using the correction term for the light amount attenuation and the correction term for the toner potential thus obtained, the colors are actually superimposed in the order of yellow, magenta, and cyan to form a three-color multiplexed multicolor image.

Next, the exposure intensity of the LED array is set to B (m
W) and the value of the current flowing through the LED array is A (mW), as described above, B (mW) = 1.2 × 10 ⁻³ × A
There is a proportional relationship. Therefore, the exposure intensity B can be corrected with the same correction ratio as that for correcting the current value A flowing through the LED. In the present embodiment, the value of the current flowing through the LED is corrected for each pixel as follows. However,
A ″ is the corrected current value.

First color yellow latent image A ″ _Y = A Second color magenta latent image A ″ _M = (1 + 0.176Q _Y ) × (1 + 0.6Q _Y )
× A 3rd color cyan latent image A ″ _C = (1 + 0.176Q _Y ) × (1 + 0.25Q
_M ) × [1 + 0.6 (Q _Y + Q _M )] × A

By performing the above image exposure intensity correction for each pixel, a proper latent image could be formed regardless of the presence or absence of toner.

(Embodiment 17) In the above-mentioned fifteenth embodiment, three-color toner images are overdeveloped in the order of yellow, magenta and cyan, in the LED array having a wavelength of 665 nm, cyan and black toners are This is because almost no image exposure light is transmitted. Therefore, in order to form a multi-color image by superimposing four-color toner images, it is possible to transmit cyan toner in the same manner as the semiconductor laser L.
The wavelength of the ED array should be 780 nm or more.
Therefore, in the sixteenth embodiment of the present invention, the wavelength 78
A correction value was determined by using the 0 nm LED array in the same manner as in the fifteenth embodiment, and a good result was obtained as a result of correction using this correction value.
The correction in the four-color multi-development development using the array became possible.

The numerical values in each of the above-mentioned embodiments are appropriately determined depending on the toner used, the image bearing member, the exposing means, etc., and it is needless to say that the numerical values need to correspond if these elements change. .. The present invention also illustrates
Not only the multi-color image forming apparatus having the above-described configuration, but also various color printers of electrophotographic type, multi-color image forming apparatuses such as color copying machines, or color printers of various types other than electrophotographic type It can also be applied to a multicolor image forming apparatus such as a color copying machine. Further, it goes without saying that the configurations of the pulse width modulation circuit, the laser driver circuit, etc., the circuit elements, parts, etc. used can be variously changed as necessary.

As described above, in the multicolor image forming apparatuses according to the ninth to sixteenth embodiments, the influence of the light exposure of the developer such as the toner on the image carrier against the light shielding of the image exposure and the charge of the developer. For the deviation of the surface potential decay curve due to the presence or absence of the developer due to the influence of the amount, the input color separation image data is corrected for the exposure time according to the toner amount of each color estimated from the data. Since the exposure time for each pixel is changed, or the exposure intensity for image exposure is corrected and the exposure intensity for each pixel is changed, compared with the conventional multiple development process. The color reproducibility is remarkably improved, and there is a remarkable effect that fine parts such as characters and lines of an image can be clearly reproduced.

[0129]

As described above, when the color toners are superposed and developed, the difference in the light transmittance of each color toner is taken into consideration, or further the difference in the electrostatic amount of each color toner is taken into consideration, and the amount of toner to be superposed next is determined. By adjusting the color balance, it became possible to further improve the color balance accuracy compared to the conventional one.

[Brief description of drawings]

FIG. 1 is a diagram showing a process according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a process of Example 2 of the present invention.

FIG. 3 is a block diagram of an image processing unit.

FIG. 4 is a model diagram of a correction process of the present invention.

FIG. 5 is a conventional example showing a multiple development process.

FIG. 6 is a diagram showing a relationship between a toner amount and a transmitted light amount.

FIG. 7 is a model diagram showing a correction process of the present invention.

FIG. 8 shows a laser driver circuit.

FIG. 9 is a block diagram of a PWM circuit.

FIG. 10 is a timing chart showing the operation of the PWM circuit.

FIG. 11 is an explanatory diagram showing changes in surface potential on an image carrier in a conventional multicolor image forming apparatus.

FIG. 12 is a diagram showing a relationship between a toner amount and a toner potential.

FIG. 13 is a diagram showing the relationship between the number of times toner is charged and the toner potential.

FIG. 14 is a diagram showing a relationship between a toner amount and a laser transmittance.

FIG. 15 is a diagram showing a relationship between a toner amount and a transmitted light amount correction ratio.

FIG. 16 is a diagram showing a state where the potential on the image carrier is attenuated when image exposure is performed from the inner surface of the image carrier.

FIG. 17 is a diagram showing a potential decay state in a normal OPC photosensitive drum.

FIG. 18 is a diagram showing a relationship between a toner amount (integrated value) and a toner potential correction ratio.

FIG. 19 is a circuit configuration diagram showing an example of a reader unit used in the multicolor image forming apparatus of the present invention.

FIG. 20 is a diagram showing the output characteristic of the semiconductor laser used in the sixth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 4 Transfer means 6 Semiconductor laser 7 LED array 10 Leader part 31 Yellow developing device 32 Magenta developing device 33 Cyan developing device 34 Black developing device

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04N 1/29 G 9186-5C

Claims (2)

[Claims] 1. A color electrophotographic apparatus for forming color toners on an electrophotographic photosensitive member, the electrophotographic photosensitive member being endlessly moving, and a charging unit arranged to face the photosensitive member.
A scanning optical unit that scans the charged photoconductor with information light based on a color signal, a control unit that controls the exposure amount of the scanning optical unit to the photoconductor, and a toner image that is formed on the photoconductor in an overlapping manner. In a color electrophotographic apparatus having a transfer means for collectively transferring the above to a transfer material, the control means for controlling the exposure amount is such that the exposure amount emitted by the scanning optical means is taken into consideration in consideration of the transmittance of toner which varies depending on the light wavelength. A color electrophotographic apparatus characterized by controlling the. 2. A color electrophotographic apparatus for forming color toners on an electrophotographic photosensitive member, wherein the electrophotographic photosensitive member is moved endlessly, and a charging unit is arranged to face the photosensitive member.
A scanning optical unit that scans the charged photoconductor with information light based on a color signal, a control unit that controls the exposure amount of the scanning optical unit to the photoconductor, and a toner image that is formed on the photoconductor in an overlapping manner. In a color electrophotographic apparatus having a transfer unit for collectively transferring the toner to a transfer material, the control unit for controlling the exposure amount considers the transmittance of the toner which differs depending on the light wavelength and the charge amount of the toner, A color electrophotographic apparatus characterized by controlling an exposure amount emitted by a scanning optical means.