JPS63106763A - Image density correcting device for color image recorder - Google Patents

Abstract

PURPOSE:To automatically keep a color balance to obtain good color images by detecting the extent of deviation between a preliminarily set target density value and an actual density and automatically changing the extent of electrification and exposure, and a developing bias voltage in each of high, low, and middle density parts to correct the density. CONSTITUTION:A density deviation detecting means consisting of a ROM 7 and a CPU 6 detects the extent of deviation between the density of each density part of each reference pattern image, which is detected by a density detecting means consisting of a sensor 1, an amplifier 4, and an A/D converter 5, and a corresponding target density value. A correcting means consisting of the ROM 7, a RAM 7A, the CPU 6, and drivers 81-83 corrects the density in accordance with detected extents DELTAV1-DELTAV3 of density deviation, and the exposure, the developing bias voltage, and the extent of electrification are changed in accordance with the extent DELTAV1 of density deviation for the low density, the extent DELTAV2 of density deviation for the middle density, and the extent DELTAV3 of density deviation for the high density respectively to correct the density.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an image density correction method in a color image recording apparatus. .

(Prior Art) Color image recording devices are well known as color copying machines, electrostatic color optical printers, and the like.

It is well known that color parannu is a problem when recording color images. In order to achieve good color balance, multiple color images that make up a color image,
For example, in each of a yellow image, magenta image, and cyan image, at each density of high density, medium density, and low density,
Good concentrations must be achieved quickly. Otherwise, for example, yellow will be emphasized in low-density areas of the color image and magenta will be emphasized in high-density areas, resulting in an unnatural and unpleasant color image.

Conventionally, in color image recording devices, as a method for adjusting color balance, a color image of a reference pattern is created,
Comparing the color image obtained by K in this way with the reference pattern, the density correction for high density areas is done by the charge amount, the density correction for the low density areas is done by the exposure amount, and the overall density is adjusted by the development bias voltage. This method is used in color copying machines. but.

This adjustment method requires manual operation by the color copier operator, which requires skill and also has the problem of being influenced by the operator's color sense, mood, and other subjective factors. .

(Objective) The present invention has been made in view of the above-mentioned circumstances, and its object is to record a plurality of color images constituting a color image in a color image recording device such as a color copying machine or a color optical printer. In each color image, high, low,
An object of the present invention is to provide a novel image density correction device that can automatically correct each density in the image.

(composition) One aspect of the present invention will be explained below.

The image density correction device of the present invention is used in color image recording devices such as color copying machines and electrostatic color source printers.

The image density correction device of the present invention includes a pattern forming means, a density detection means, a density deviation detection means, and a correction means.

The pattern forming means forms an electrostatic pattern on the photoconductive photoreceptor. In the case of a color image recording apparatus that forms electrostatic images to be developed on separate photoreceptors depending on the color of toner, an electrostatic pattern is formed on each photoreceptor.

Electrostatic patterns are formed corresponding to low, medium, and high concentrations. Further, the number of electrostatic patterns equal to the number of toner types N is formed. These Na! The electrostatic patterns may be formed under the same conditions.

Formation conditions may vary depending on the type. When a single photoreceptor is used in a color image recording device, the N types of electrostatic patterns may be formed sequentially at different times or at different locations on the photoreceptor. They may be formed coexisting.

Each type of electrostatic pattern is developed with a different color of toner. Therefore, N types of visible patterns are obtained, and these visible patterns are referred to as reference pattern images.

The density detection means is provided in each of the two reference putter images.

The density (corresponding to the amount of toner adhered) is detected on the photoreceptor. That is, the densities of low, medium, and high density areas in each reference pattern image are detected on the photoreceptor.

In this way, it is detected how much toner is applied to each of the low, medium, and high density areas of each electrostatic pattern to make it visible.

The electrostatic pattern provides a reference for low, medium, and high name densities, so that when developed with toner of the corresponding color, the reference pattern corresponding to each density will be used to achieve the ideal color balance. The density of an image can be determined experimentally in advance. This ideal density is called a target density value.

The density deviation detection means was detected by the above-mentioned density detection means. It is detected how much the density of each density portion of each reference pattern image deviates from the corresponding target density value.

The correction means were detected as described above. Density correction is performed according to the amount of density deviation.The exposure amount is adjusted depending on the amount of density deviation at low density, the development bias voltage is adjusted depending on the amount of density deviation at medium density, and the development bias voltage is adjusted depending on the amount of density deviation at high density. Accordingly, correction is performed by varying the amount of charge.

In this way, the image density correction device of the present invention detects the amount of deviation between the preset target density value and the actual density, and adjusts the high, low, and medium density areas based on this amount of deviation. Each time, the charge amount, exposure amount, and development bias voltage are automatically changed to perform density correction.

Hereinafter, description will be given based on specific examples.

As an example, a case where the present invention is applied to a well-known color optical printer as shown in FIG. 2 will be described.

In FIG. 2, numeral 12 is an optical writing device using laser light, numeral 13 is a photoconductive photoreceptor, and numeral 14 is
Charger, 15 is a developing device, 16 is a transfer drum, 17 is a static eliminator, 18 is a cleaner, 19 is a transfer device, 20 is transfer paper, 21
The symbol 22 is a cassette.

The paper feed roller, reference numeral 23, is a registration roller.

Reference numeral 25 is a clamp claw, reference numeral 26 is a separator 1, and reference numeral 2 is a separator.
Reference numeral 7 indicates a one-separation claw, and reference numeral 28 indicates a fixing device.

Next, a color image recording process using this color optical printer will be briefly explained.

Color image recording processes for obtaining one color image mainly include magenta process, cyan process,
It has yellow process, black process, and separation fixing process.

The magenta, yellow, cyan, and black color processes may be performed in any order, but here, they are performed in the above order.

Each of the above color processes includes the steps of charging the photoreceptor, writing with an optical writing device, developing an electrostatic latent image formed by writing, transferring a visible image, removing static from the photoreceptor, and cleaning. . These steps are performed in the above order.

First, to explain the magenta process, the photoreceptor 13
rotates in the direction of the arrow, and the charger 14 uniformly charges its peripheral surface. Subsequent writing by the optical writing device 12 is performed to form an electrostatic latent image to be developed with magenta toner.

This electrostatic latent image is transferred to the developing unit 15MK of the developing device 15.
The image is developed with a cyan toner to form a magenta visible image on the photoreceptor 13.

During this time, the transfer paper 20 is fed from the cassette 21 by the paper feed roller 22, and is delivered to the transfer drum 16 by the registration roller 23 at the appropriate timing. The transfer drum 16 locks the leading end of the transfer paper 20 with a clamp claw 25 and rotates in the direction of the arrow.

The K-width transfer paper 20 is held so as to wrap around the circumferential surface of the transfer drum 16, and comes into contact with the magenta visible image at the transfer section, and the magenta visible image is transferred by the action of the transfer device 19. transcribed.

After the magenta visible image has been transferred, the photoreceptor 13 is charged with electricity removed by a charge remover 17, and the cyan toner is removed by a cleaner 18.

Note that the transfer paper 20 is held on the transfer drum 16 until the black visible image is transferred in the black process.

A cyan process is then performed. In this process, writing] forms an electrostatic latent image to be developed with a cyan toner, this electrostatic latent image is developed with a cyan toner by a developer unit 15C, and the resulting cyan visible image is transferred to a transfer device. 19, the image is transferred onto the transfer paper 20 on the transfer drum 16.

In the next yellow process, an electrostatic latent image to be developed with yellow toner is formed. 20.

Further, in the black process, the formed electrostatic latent image is developed with black toner in a developing unit (15BK).

When the black visible image is transferred, the transfer paper 20 is separated from the transfer drum 16 by the action of the separator 26 and the separation claw 27.
In the fixing device 28, each color image is fixed and outputted as a color print to the outside of the device.

It goes without saying that the color images transferred onto the same transfer paper are aligned with each other during transfer. A color image is expressed by the superposition of visible images of four colors.

The above is an overview of the color image recording process.

Hereinafter, how to implement the present invention in this color optical printer will be explained.

The image density correction according to the present invention is performed prior to the color image recording process, but it may be performed prior to each color image recording process, or once every few times in the color image recording process. It may be carried out every day, or it may be carried out every day when the color optical printer is started, or it may be carried out as needed.

FIG. 1 shows the main parts of an embodiment in which the present invention is applied to the color optical printer shown in FIG.

In FIG. 1, first, a pattern forming means is used. Formation of an electrostatic pattern will be explained.

The electrostatic pattern is formed by rotating the photoreceptor 13 in the direction of the arrow, charging the photoreceptor 13 with the charger 14, and then charging the photoreceptor 13 with the optical writing device 12, which corresponds to low, medium, and high densities. This is done by writing a pattern.

First, when forming this electrostatic pattern, the CPU 6 controls the driver 8 according to the reference charging potential stored in the ROM 7.
2, the charging power pack 10 is controlled via the photoreceptor 1.
3 to charge the surface of the photoreceptor.

In addition, the ROM 7 stores information on gradation steps corresponding to low density, medium density, and high density, which should serve as a reference when forming an electrostatic pattern. The laser output power source 11 is controlled to optically write patterns corresponding to the respective densities.

Therefore, ROM 7, CPU 6, driver 81.82, i
Power pack for t10. Laser output power supply 11° charger 14. The optical writing device 12 constitutes a pattern forming means.

The electrostatic pattern formed as described above is shown in FIG. 3 as an explanatory diagram. Of course, since the electrostatic pattern is an electrical pattern, it cannot itself be seen. FIG. 3 is an explanatory diagram.

Now, the electrostatic pattern shown above depends on the type of toner.
Formed sequentially. In the example currently being explained, there are four types of toner: magenta toner, yellow toner, cyan toner, and black toner, so four types of electrostatic patterns are formed, and each electrostatic pattern is of a different color. Developed with toner. Here, electrostatic latent images formed sequentially are applied to each developing unit, magenta toner, cyan toner,
It is assumed that the image is developed in a river of yellow toner and black toner.

Through this development, four reference pattern images are sequentially formed using magenta, yellow, cyan, and black toners.

The low, medium, and high densities of these reference pattern images are photoelectrically detected by the density detection means 9.

In this embodiment, the concentration detection means includes a sensor 1;
It consists of an amplifier 4 and an A/D converter 5.

The sensor 1 is as shown in FIGS. 1 and 2.

It is arranged between the developing unit 15BK and the transfer drum 16 so as to be close to the photoreceptor 13. As shown in FIG. 4, this sensor 1 has a light source 2 and a light receiving section 3, and irradiates the light from the light source 2 onto a reference pattern image, that is, a pattern made by visualizing an electrostatic pattern using toner of each color. , the reflected light is received by the light receiving section 3 and photoelectrically converted.

In addition, the low, medium, and high concentration parts of the electrostatic pattern.

The toner adhesion amount when visualized is 054my/cr11 or less in the low density area and 0.4 to 0.8 in the medium density area.
It is desirable to form the film so that m9/cd and 0.8 to/cIi in the high concentration area.

The photoelectric conversion signal obtained from the reference pattern image is.

The signal is amplified by the amplifier 4, digitized by the A/D converter 5, and input to the CPU 6K.

The photoelectric conversion signal Vsp has the reference pattern image.
It changes in a stepwise manner depending on the concentration of low, medium, and high, generally as shown in FIG.

Figure 6 (a), ΦL ((ri) and (d) are yellow, respectively.

An example of a change in the photoelectric conversion signal VSP obtained from each reference pattern image formed using magenta, cyan, and black toners is shown.

In this way, by photoelectrically detecting the density of each reference pattern image, V1', V2'*v3'.

V1"* v2"t V3"e Vl"', V2"
' g V3"#VII"eV2"".

Information regarding the concentration V3//// will be obtained.

These photoelectric conversion signals v5', etc. will be hereinafter referred to as concentrations v1', etc. for convenience of explanation.

Now, the ROM 7 also stores ideal values for the target density values, that is, the density V1/ to density v3''. For ROM 7, of course.

Programs to be executed by the CPU 6 are also stored.

FIG. 7 shows the relationship between the density in each of the reference pattern images and the corresponding target density value V (given as corresponding to the photoelectric conversion signal). Y, M
, C, and BK correspond to standard pattern images formed using yellow, magenta, cyan, and black toners, respectively. In this way, the target density value differs depending on the color and density of the toner.

Now, by applying these target density values to the reference pattern image using yellow toner, Vly l V2Y evs
y, V1y1m for those with magenta toner
v2M, VaM, vs. cyan toner
lc.

v2c, v3c, and those with black toner
Let m V2B mV3B. Suffix 1, 2.
3 corresponds to low, medium, and high concentrations, respectively.

These target density values are compared with each corresponding density in the CPU 6, and the difference is detected as the amount of density deviation.

Therefore, the ROM 7 and the CPU 6 constitute density deviation detection means.

In FIG. 8, the density VB', v2'l V3' (marked 0) of the reference pattern image completely formed with magenta toner,
Density deviation amount ΔVl from the corresponding target density value (black circle)
eΔV2. Δv3 is illustrated. In addition, Δvl.

Δv2. The sign of Δv3 corresponds to the sign of the value obtained by subtracting the density from the target density value. That is, the density deviation amount, such as ΔV, is defined as the target density value minus the corresponding density.

In this manner, the density deviation amount Δv1. Δv2°Δv3 is determined.

Therefore, the image density is corrected by the correction means, but since the density deviation amount ΔV is a deviation in the low density area, the exposure amount is corrected according to the density deviation amount Δvx,
In accordance with the density deviation ΔV2tΔV3 in the medium density and high density areas, the developing bias voltage and charge amount are corrected, respectively.
K is adjusted to obtain the optimum image density distribution for each electrostatic latent image.

As shown in Figure 9, the objects of correction differ from the exposure amount, charge amount, and developing bias voltage depending on whether the density is low, high, or medium, depending on the correspondence between the original density and the recorded image density. The so-called γ characteristic that determines the relationship is sensitive to changes in the amount of charge in high-density areas (Figure 9(b)), and sensitive to changes in exposure level in low-density areas (Figure 9(a)). This is because medium density areas are sensitive to changes in the developing bias voltage (FIG. 9(C)).

In Figure 9 (b), when exposure is performed using a lamp with a charge amount of 600 V and a developing bias voltage of 300 V, the lamp power is 9
00, 1000. 1100W (in the figure), the exposure amount is iooow, the developing bias voltage is 300V, and the charge amount is 550V, 600V, 65
When the change is 0V and the charge is 600V, the same figure (C) shows that the charge amount is 600V.
, exposure amount 1000W, development bias voltage 250V
, 300V, and 350V are shown. At this time, the peripheral speed of the photoreceptor 13 was 120/S. Further, the concentration was measured using a Macbeth reflection type densitometer.

Returning to FIG. 1, each correction is performed by the CPU 6 according to ΔV.
The exposure amount is corrected through the yoshitri bar 81, and △v2
This is done by correcting the developing bias voltage by the CPU 6 via the transfer bar 83 in accordance with Δv3, and by correcting the charge amount by the CPU 6 via the transfer bar 82 in accordance with Δv3. The specific procedure for correction and how to determine the correction value are stored in the ROM 7 in advance. Furthermore, since specific corrections are made when forming each electrostatic latent image, information regarding the charge amount, exposure amount, and developing bias voltage set by the above corrections will not be available until the correction is actually performed. , stored in RAM 7A.

Therefore, in the embodiment shown in FIG. 1, ROM 7, ram 7A, and C
PU 6 and each driver 81.82. 83 constitutes the correction means.

FIG. 10 shows density deviation amounts ΔVl, Δv2. An example of the relationship between Δv3, exposure amount, developing bias voltage, and charge amount is shown.

Further, FIG. 11 shows a color copying machine in which a pattern original 31 having basic densities of low, medium, and high is provided near the original glass 32, irradiated with a lamp 29, and printed by the exposure optical system 30. An example will be shown in which an electrostatic pattern is formed by introducing light onto a photoreceptor and exposing it. This has been explained with reference to FIG. Is the exposure amount corrected by the lamp 29? I explained the case.

12 and below are flowcharts showing the procedure of image density correction carried out by the image density correction apparatus of the present invention. 1st
2 and 13 are overall flowcharts, and color balance adjustment corresponds to the process of calculating the correction amount of image density correction in the present invention. Furthermore, the printing operation refers to the operation of performing the color image recording process described with reference to FIG. 2, for example. During this printing operation, each time six latent images are formed, the exposure amount, charge amount, and development bias voltage are set according to the correction amount calculated in the above color balance adjustment.

In the example shown in FIG. 12, regardless of the print operation.

Color balance adjustment is automatically performed based on signals from external manual operation, hourly, number of recorded images, etc. Based on the results, exposure amount, charge amount, etc. are adjusted until the next color balance adjustment is made. The developing bias voltage is set.

In the example shown in FIG. 13, when a printing operation is performed, color balance adjustment and charge amount, exposure amount,
The developing bias voltage is corrected.

FIG. 14 shows a flowchart of a subroutine program for color balance adjustment, that is, image density correction, shown in FIGS. 12 and 13. In this example, the electrostatic pattern is
Yellow ω, magenta toner, cyan 0, and black toner are visualized in this order.

ΔV1～ΔVs 'e Vs'～V3"" *
Vs Y −Vs B are the six quantities already explained.

Also, regarding W, the suffixes are Y, M, and C.

B is the color of the toner, namely yellow.

Indicates magenta, cyan, and black.
tWB is the amount of exposure when forming an electrostatic latent image to be developed with toner of a corresponding color. Generally, Y, M, C, and B in the suffix portion indicate the color of the toner as described above.

Wyo + Wyto e WCo e WBo indicates the standard exposure amount when forming an electrostatic latent image developed with toner of the corresponding color, and the value corrected by ΔV1 is the above-mentioned Wy * WM t Wc @ WB.

Similarly, Vnyo −VDMo e VDCD #
vDne is the development bias voltage when developing the electrostatic latent image to be developed with the toner of the color specified by the suffix, and the value corrected by △v2 is VDY#VD
MIVDCw VDB, which is the developing bias voltage during actual development.

Also, Vcyos Vcuo * Vccos V
CB (1 is the amount of charge when forming an electrostatic latent image to be developed with the toner of the color specified by
*V (B is the actual charge amount when forming each electrostatic latent image.

αt, α′, α/I, α″′, β, β′
, β71. β///, 1, r/.

r// and r/// are correction coefficients, which are experimentally determined in advance to achieve appropriate color balance.

It goes without saying that in the above explanation, the exposure amount refers to the light intensity of the laser in the laser optical writing device in the color source printer shown in FIG.

Note that the color balance adjustment may be performed by selecting only an arbitrary color instead of adjusting all four colors.

By the way, as is clear from FIG. 9(C).

When correcting the developing bias voltage according to Δv2,
The effect of the correction extends not only to the medium density area but also to the low density and high density areas. Therefore, if the fluctuation of Δv2 is large, if the developing bias voltage is corrected, even if the exposure amount and charge amount are corrected, the corrected values of exposure amount and charge amount themselves will be
There may be a large deviation due to the influence of correction of the developing bias voltage.

In such a case, in order to correct secondary deviations in exposure amount and charge amount due to correction of the developing bias voltage,
The amount of correction of the exposure amount and the amount of charge may be corrected in accordance with the density deviation amount Δv2 at the medium density.

FIG. 15 shows a flowchart of color balance adjustment in such a case.

For example, for an electrostatic latent image to be developed with yellow toner, the exposure amount, development bias voltage, and charge amount set by image density correction are each WY.

Voy I vcy. The amount of exposure and the amount of charge are Δv1. It is corrected by Δv2 and modified according to the value of Δv2. g, , /, sIl, , //
/, δ, δ・I, δI/.

δ″′ is a coefficient for correction, and is experimentally determined in advance so that an appropriate color balance is achieved.

(Effects) As described above, according to the present invention, an image density correction device for a color image recording device can be provided.

Since this apparatus is constructed as described above, it is possible to automatically achieve color balance, which was conventionally achieved by manual operation, and to obtain a good color image.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, and FIG. 2 is a diagram showing one embodiment of the present invention.
A diagram showing a color optical printer to which the embodiment of the diagram is applied;
3 to 10 are diagrams for explaining the above embodiment, and FIG. 11 is a diagram showing only the main parts of another embodiment of the present invention.
12 to 15 are diagrams showing examples of flow diagrams related to implementation of the present invention. DESCRIPTION OF SYMBOLS 1...Sensor, 13...Photoreceptor, 14...Charger, 12...Optical writing device, 15...Developing device. Fig. 4 Fig. 5 Fig. 6 (C) (D copper 7 Fig. δ Fig. 2 Fig. 44

Claims (1)

[Scope of Claims] 1. In a color image recording apparatus, a pattern forming means for forming electrostatic patterns corresponding to low, medium, and high densities on a photoconductive photoreceptor, and a developing device, the electrostatic a density detection means for photoelectrically detecting the density of N types of reference pattern images (N is the type of toner) obtained by developing the pattern; , a density deviation detection means that determines the deviation from the target density value for each of low, medium, and high densities; and a density deviation detection means that corrects the exposure amount according to the density deviation amount at low density, An image density correction apparatus comprising: a correction means for correcting a developing bias voltage in accordance with the amount of density deviation at a high density, and correcting an amount of charge in accordance with the amount of density deviation at a high density. 2. An image density correction device according to claim 1, wherein the amount of correction of the amount of charge and the amount of exposure in the correction means is corrected in accordance with the amount of density deviation at a medium density.