JPS63249166A - Automatic color balancing method for color copying machine - Google Patents

Abstract

PURPOSE:To surely perform the color balancing operation with a simple device by changing a developing bias voltage in proportion to the difference between the quantity of light of a texture and the potential of the texture. CONSTITUTION:Light quantities of respective color-separated exposure luminous fluxes subjected to color separation are detected by optical sensors 38, 40, and 42. Optical sensors have spectral sensitivity characteristics practically equal to those of photosensitive bodies 16, 20, and 24. Potentials of respective color- separated latent images formed on respective photosensitive bodies are detected by potential sensors 28, 32, and 36. Outputs of optical sensors and potential sensors are subjected to A/D conversion. The difference between the quantity of light of the texture and the potential of the texture as digital signal is obtained for each photosensitive body, and developing bias voltages of developing devices 44, 46, and 48 which develop respective color-separated latent images are changed in proportion to differences between quantities of light of textures and potentials of textures. Thus, a stable and correct color balancing operation is automatically performed with the simple constitution.

Description

TECHNICAL FIELD The present invention relates to an automatic color balance method in a color copying machine.

(Conventional technology) The exposure light flux for each color obtained by color-separating the original.

Each photoreceptor is guided to a separate photoreceptor for image exposure, and the color-separated latent image formed on each photoreceptor is developed with a toner colored in a complementary color to the color of one color separation, resulting in each color toner. 2. Description of the Related Art Color copying machines that obtain color copies by superimposing and transferring images onto transfer paper are well known.

The color tone of a color copy image obtained with such a color copying machine is determined by the relative density relationship of the toner images of each color superimposed on the transfer paper, and in order to obtain a color copy image that does not look unnatural, it is necessary to It is necessary to mutually adjust the concentration relationship. This operation is known as a color balance operation or color balance operation.

Conventionally, the color balance method, that is, the method of performing color balance, has been intended to use an LCD filter to adjust the amount of light and perform color balance operation through this adjustment of the amount of light. There is a problem in that a special copying apparatus is required, which complicates the copying apparatus.

(Purpose) The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a novel color balance method that can reliably perform color balance operations with a simple device. .

(composition) The present invention will be explained below.

The present invention performs image exposure by guiding each color-separated exposure light flux obtained by color-separating an original to separate photoreceptors,
The color separation latent image formed on each photoreceptor is developed with toner colored in a complementary color to the color separation color, and the resulting toner images of each color are superimposed and transferred onto transfer paper to make a color copy. This is a method for automatically performing color balance in color copied images in a color copying machine that obtains images.

This method is carried out as follows.

The light intensity of each color-separated exposure light beam is detected by an optical sensor. The optical sensor has spectral sensitivity characteristics that are substantially equal to the spectral sensitivity characteristics of the photoreceptor.

The spectral sensitivity characteristics of the optical sensor and photoreceptor are substantially equal,
This means that the spectral sensitivity characteristics of both are completely equal or approximately equal.

Further, the potential of each color separated latent image formed on each photoreceptor is detected by a potential sensor.

The outputs of each optical sensor and each potential sensor are A/D converted.

Then, the difference between the amount of background light as a digital signal and the background potential is determined for each photoconductor, and the developing bias voltage of the developing device that develops each color separation latent image is set proportionally to the difference between the amount of background light and the background potential. change.

(Example) A specific example will be described below with reference to one drawing.

FIG. 1 schematically shows only the parts necessary for explanation of an example of a color copying machine embodying the present invention.

Reference numeral 10 indicates an imaging lens. Although the object side of the imaging lens is not shown, there is a known document illumination and scanning system on this object side, which illuminates and scans the document placed on the document placement glass.

The reflected light beam from the illumination section of the document is guided to the document illumination scanning system, enters the imaging lens 10, and becomes an image-forming exposure light beam.

The imaging exposure light flux is reflected by the mirror 12 and then enters the dichroic mirror 14. The dichroic mirror 14 selectively reflects only the back blue component of the imaging exposure light flux, so the reflected light flux is.

The blue-separated exposure light flux B forms a blue-separated original image on the photoreceptor 16.

The photoreceptor 16 is belt-shaped, rotates in the direction of the arrow during copying, and is uniformly charged by a charger 26. Therefore, when imagewise exposed by the blue-separated exposure light flux B, an electrostatic latent image corresponding to the blue-separated image of the original document, that is, a blue-separated latent image is formed on the photoreceptor 16.

The green and blue components of the imaging exposure light beam incident on the dichroic ink mirror 14 are transmitted through the same mirror 14.

A part of it is reflected by the mirror 18, and the rest enters the filter 21.

The light beam reflected by the mirror 18 is filtered by a filter 19.
The light is color-separated into green and becomes a green-separated exposure light beam G, which forms a green-separated original image on the photoreceptor 20.

In addition, the light flux incident on the filter 21 is
1, the red light is separated into a red-separated exposure light beam R, which is reflected by the mirror 22 and forms a red-separated original image on the photoreceptor 24.

Like the photoreceptor 16, the photoreceptor 20.24 is belt-shaped, and rotates in the direction of the arrow during copying, and the charger 3
0.34, each is uniformly charged.

Therefore, the green color separation exposure light flux G, the red color separation exposure light flux R
By the image exposure, a green resolved latent image and a red resolved latent image are respectively formed on the photoreceptor 20.24.

In this way, the color separation latent images formed on each photoreceptor 16, 20, 24 are developed with toner colored in a complementary color to the color of one color separation.

That is, the blue resolved latent image formed on the photoreceptor 16 is
The green and red latent images visualized by the developing device 44 using yellow toner and formed on the photoconductor 20.24 are converted into magenta toner and cyan by the developing devices 46 and 48, respectively. Visualized by toner.

In this way, the photoreceptor 16.20.24 is formed.

The yellow toner image, magenta toner image, and cyan toner image are superimposed and transferred onto the same transfer paper S by transfer devices 45, 47, and 49. At this time, the relationship between each transfer position and the image exposure position is determined so that no positional deviation occurs between the superimposed toner images of each color.

The three-color toner image superimposed and transferred onto the transfer paper S is
Next, the image is fixed by the fixing device 50, and the transfer sheet S having the color copy image fixed thereon is discharged from the device. After the toner image has been transferred, each photoconductor is charged and cleaned by a charge removing cleaning device (not shown).

The above is an overview of the color copying process.

Now, in this embodiment, the photoconductive layers of the photoreceptors 16.20.24 are of the same type, and therefore the spectral sensitivity characteristics of these photoreceptors 16.20.24 are the same.

In FIG. 3, curve 3-1 represents the photoreceptor 16.20.24.
shows the spectral sensitivity characteristics of This characteristic is defined as S(λ)(λ
:I wavelength). Moreover, in FIG. 3, track [3-2] shows the spectral transmittance characteristics of the imaging lens 10. below.

This characteristic is written as T(λ). Further, curve 3-3 is the spectral characteristic of reflection by the dichroic mirror 14, which is written as F, (λ), and curve 3-4.3-5 is
These are the spectral transmittance characteristics of the filters 19 and 21, respectively, and are written as F(, (λ), and FR(λ). Furthermore, curves 3-6 show the spectral energy characteristics of a lamp for illuminating the document (not shown). This is denoted as H(λ). Using these characteristics S(λ), T(λ), F(λ), and H(λ), the spectral reaction amount E, (
λ), EG(λ) jar(λ) are respectively.

E8cλ)=S(λ)H(λ)T(λ)FtCλ)EG
(λ)=S(λ)H(λ)T(λ)FG(λ)ER(λ
)=S(λ)l((λ)T(λ)Fdirectionλ), and the reaction amount E@tE4+Eg at photoreceptor 16.20.24 is E=/E, (λ)dλ, E:/E (λ)dλ,
E = /E, (1) dλ.

In FIG. 4, curves 4-1, 4-2, and 4-3 indicate the minute reaction amounts Eg(i), E, (i), and Eg(x), respectively, and the symbol f A(tl).

A(G) and A(R) indicate the area surrounded by the curve 4-1.4-2.4-3 and the horizontal axis. This area A(B),
A(G).

A(R) gives the above integral value, but the reaction amount E
Equal to HsE6eEz.

Now, with this invention, in order to finally achieve color balance,
The difference between the background potential of each color-separated latent image and the developing bias voltage of the developing device that develops this latent image is made to be the same value on all photoreceptors. In this way, the conditions for toner adhesion to the latent image are the same for all photoreceptors, making it possible to achieve good color balance.

If the background potential in a color-separated latent image is constant for each photoreceptor, the development bias voltage must be adjusted for each photoreceptor in order to achieve the above color balance.

The purpose can be achieved by fixing the voltage to a constant voltage higher depending on the skin potential.

However, the background potential in each color separated latent image is not necessarily constant and varies. The factors that play a major role in the variation are the background density of the single manuscript and the variation in the voltage applied to the lamp for illuminating the M manuscript.

That is, the background density of an original to be color-copied is not necessarily constant; some originals have an extremely low density, and some originals have a background density close to a medium density.

Furthermore, it is difficult to control the voltage applied to the document illumination lamp to be completely constant, and the applied voltage fluctuates due to various causes, but due to the applied voltage fluctuation, the above-mentioned reaction amounts E6, E4. The change in E is as shown in FIG.

In FIG. 5, the horizontal axis shows the ratio of the voltage applied to the document black lamp, and the vertical axis shows the photoreceptor reaction ratio, and the curves 5-B and 5-G
, 5-R indicate changes due to the blue-resolving exposure light flux, changes due to the green-resolution exposure light flux, and changes due to the red-resolution exposure light flux, respectively.

In this way, fluctuations in the voltage applied to the document illumination lamp,
Since the background potential varies from photoreceptor to photoconductor depending on the difference in density of the background part of the document, it is necessary to perform color balance in accordance with such fluctuations in the background potential.

This automatic color balance will be explained as follows based on an example.

In each color-separated exposure light flux B, G, and R.

Optical sensors 38, 40, and 42 are arranged at positions that do not interfere with image formation, and detect the amount of light of each color-separated exposure light beam.

A potential sensor 28, 32, 36 is provided between the image exposure section and the developing section of each photoconductor 16, 20, 24 to detect the potential of the color separation latent image formed on each photoconductor.

What is important here is that the spectral sensitivity characteristics of the photosensor are substantially equal to the spectral sensitivity characteristics of the photoreceptor.

In other words, the spectral sensitivity characteristics of the optical sensor 38 are the same as those of the photoreceptor 16.
The spectral sensitivity characteristics of the optical sensor 40 are substantially equal to the spectral sensitivity characteristics of the photoreceptor 20, and the spectral sensitivity characteristics of the optical sensor 42 are substantially equal to the spectral sensitivity characteristics of the photoreceptor 24. substantially equal, although in all described embodiments the photoreceptors 16, 20, 24 have identical spectral sensitivity characteristics.

The optical sensors 38, 40, 42 are identical and have the same spectral sensitivity characteristics as each photoreceptor.

Here, as an example, focusing on the relationship between the photoconductor 16 and the optical sensor 38, the photoconductor 16 and the optical sensor 38 are
Since it has substantially the same spectral sensitivity characteristics as 8,
For example, when the color separation exposure light flux has a light amount of Q, when the output of the optical sensor 38 is converted into a voltage signal, the optical detection signal is Vs (Q), and the optical attenuation voltage of the photoreceptor 16 at this time is Vp. Suppose (Q).

Between Vs(Q) and Vp(Q).

The following relationship holds true: Vs(Q)/Vp(Q)=k (constant).

In FIG. 7, curve 7-1 shows Vo-Vp(Q). vo indicates the initial charging voltage of the photoreceptor.

On the other hand, curve 7-2 in FIG. 7 shows Vs(Q).

The optical sensors 3g and 40.42 are photodiodes with amplifiers as shown in Fig. 6, but if the amplification of the optical sensor 38 is adjusted and doubled to 1/2, the curve shown in Fig. 7 will be obtained. 7-2 becomes like one curve 7-3.

The curves 7-1 and 7-3 are symmetrical with respect to the straight line Vo/2.

What has been described so far holds true not only for the optical sensor 38 and the photoreceptor 16, but also for the photoreceptor 20 and the optical sensor 40, and the photoreceptor 24 and the optical sensor 42.

Therefore, the relationship between curves 7-1 and 7-3 in FIG. 7 will be generally explained below as a relationship between a certain optical sensor and a photoreceptor corresponding to this optical sensor.

Now, a curve 7-1 in FIG. 7 defines the relationship between the latent image potential in a color-separated latent image and the exposure amount.

According to its definition, the background area is a part of a document that reflects light most strongly, and therefore corresponds to the part where the latent image potential in the formed color separation latent image is minimum. On the other hand, the background portion is detected as the maximum output value of the optical sensor for each exposure.

As mentioned above, the background potential of the photoreceptor is determined by the background density of the original, [
It varies depending on the voltage applied to the lighting lamp. This variation region is shown in FIG. 7 by reference numerals.

Then, the background potential in the color separation latent image varies according to a curve 7-1.

Therefore, in the color separation exposure light flux, if the amount of light giving the background portion is Qo as shown in FIG. 7, then the curve 7-1 in this case will be written as ① background (Qo). Further, the curve 7-3 at this time is written as V light (Qo).

At this time, this V background (Qo) is referred to as background potential.

This background potential is given as the minimum value of the output of the potential sensor, that is, the minimum output value in potential detection of one color separation latent image. Furthermore, (1) light (Qo) is called the background light amount, and is given as the maximum value (amplification factor is 17k) of the output of the photosensor in one exposure.

Now, ■ skin (Qo) and V light (QO) are curves 7-1.7-3 in Figure 7, and these curves are connected to the straight line Vo/2.
Since it is symmetrical with respect to Vo, as shown in FIG.
(Qo) = V light (Qo) -V background (Q), then -Vo+ΔV is set as the reference for the developing bias, and background potential V background (Qo), background light amount V light (Qo
), the difference between these V (Qo) = V light (Qo)
- ■ Calculate t/2V (Qo) according to the background (Qo) and set the developing bias pressure lower by -V (QO) from the reference value -V o + AV, then the actual developing The bias voltage is as follows, and is always higher than the ground potential by a predetermined constant voltage ΔV. Therefore, as described above, by changing the developing bias voltage in proportion to the difference between the amount of background light and the background potential, the difference between the developing bias voltage and the background potential can be reduced to a constant value ΔV.
It can be done.

By performing such an operation for each photoreceptor, the difference between the background potential and the developing bias voltage can be controlled to be constant for all photoreceptors, and appropriate color balance can be achieved.

The above is the principle of the present invention and examples.

This is done as follows.

That is, referring to FIG. 2, the optical sensor -38°40
．． 42. The output of potential sensor 28.32.36 is A/
The D converter 52 converts it into a digital signal, and the CPU 54
From the recorded data, the CPU 54 calculates the background potential V, front of the background, and edge of the background.

■Determine background red, background light amount V light blue, V light green, and V light red as digital signals, calculate from these, and set the developing bias voltage by these values.

The reference values are varied from V, blue, ■, green, ■, and red, and the obtained values are sent to each developing device 4 via the developing bias driver 58.
Apply on 4.46.48.

In this way, each photoreceptor 16, 20, and 24 is developed at a developing bias higher than the background potential by ΔV (set value) at t, and appropriate color bias operation is automatically performed. It will be.

Note that if it is difficult to adjust the amplification degree of the optical sensor to 1/k by adjusting the amplifier, an operation equivalent to this amplification may be performed by multiplication processing in the CPU 54.

In addition, in order to adjust the color tone by destroying the balance of one color, the amount of operation can be inputted to the CPU 54 through the operation panel 55.

(Effects) According to the present invention, a novel color balance method can be provided. Since this method has the above-described configuration, it can be implemented with a simple configuration, and stable and appropriate color bias operation can be automatically realized.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a block diagram explaining the above embodiment, and Figs. This is a diagram for B... Blue resolution exposure light flux, G... Green resolution exposure light flux, R... Red resolution exposure light flux, 16.20.24...
Photoreceptor, 28.32.36... Potential sensor, 3
8.40.42... Optical sensor-, 44, 46, 48-
...Developing device, S...Transfer paper. Figure 4 No. 4 Station Master

Claims (1)

[Scope of Claims] Each color-separated exposure light beam obtained by color-separating an original is guided to a separate photoreceptor for image exposure, and the color-separated latent image formed on each photoreceptor is converted into the color of the color separation. In a color copying machine that develops with toner colored in a complementary color, and superimposes and transfers each color toner image onto transfer paper to obtain a color copy image, the color balance operation for the color copy image is automatically performed. In this method, the amount of light of each color-separated exposure light flux is detected by an optical sensor having spectral sensitivity characteristics that are substantially equal to those of the photoreceptor, and the The potential of each color separation latent image is detected by a potential sensor, and the output of each sensor is
D conversion is performed, the difference between the amount of background light and the background potential as a digital signal is determined for each photoreceptor, and the developing bias voltage of the developing device that develops each color separated latent image is proportional to the difference between the amount of background light and the background potential. An automatic color balance method that is characterized by