JPH03215876A - Automatic image density adjusting device for electrophotographic device - Google Patents

Abstract

PURPOSE:To prevent an image from becoming dark even if light quantity correction exceeds the limit quantity of light by adjusting the image density by correcting the quantity of light corresponding to a surface potential when the light quantity correction is less than the limit quantity of light of an exposure optical system, or correcting the surface potential based upon the limit quantity of light when the light quantity correction exceeds the limit quantity of light of the exposure optical system. CONSTITUTION:The automatic image density adjusting device adjusts the surface potential of a photosensitive body 3 where an image patch is detected and a light source lamp 2a emits light by a quantity corresponding to the surface potential. The image is therefore prevented from becoming dark owing to a rise in the surface potential and density balance can be adjusted excellently. Further, when the rise in the surface potential exceeds the limit quantity of light for the light quantity correction, the automatic image density adjusting device calculates the surface potential corresponding to the limit quantity of light inversely to control the light source lamp 2a and an electrostatic charger 7, so the image is prevented from becoming dark owing to the rise in surface potential which exceeds a fixed amount.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application in Industry] The present invention relates to an automatic image density adjustment device for an electrophotographic apparatus such as a copying machine.

[Conventional technology]

In electrophotographic devices such as copying machines, image density tends to change for the following reasons.

(1) Deterioration of the developer due to an increase in the number of copies (2) Decrease in transfer efficiency due to environmental changes (3) Decrease in the surface potential of the photoreceptor due to environmental changes (4) Changes in the characteristics of the developer due to environmental changes. Photographic devices have been devised in various ways to prevent changes in image density. In particular, in the case of full-color copying machines, the density balance between the image densities of the three colors yellow, magenta, and cyan has a significant effect on image quality, so it is necessary to maintain each image density constant in order to improve image quality. It has become something. Further, the above-mentioned density halance is very difficult to adjust, and once the density halance is disrupted, it is often impossible for the user to take measures.

Therefore, it is desirable to stabilize the image density as much as possible, and full-color copying machines are equipped with automatic image density adjustment devices that compensate for changes in photoreceptor potential and developer characteristics caused by environmental changes. It is being taken.

Conventionally, the above-mentioned automatic image density adjustment device has been designed to adjust the density difference by controlling the surface potential of the photoreceptor, and as shown in the flowchart in FIG. ), then (S
ll), the initial value stored in advance (MEMORY) is called up (INITIAI, SET). Note that this initial value is such that the surface potential of the photoreceptor 0 is equal to the surface potential A (V O =A), and the output of the detection sensor is equal to the reference value B (SENSOR OUT PUT = B
) (S12).

Then, based on the above initial value, an image batch is formed (S
13) The density of this image patch is measured by the detection sensor, and the output value C is sent to the control means manually (READ SENSOR).
OUT PUT) (S14). Next, the output value C of the detection sensor is compared with the 5 f4, t4 value B stored in advance in the control means (JUDGMENT
) is performed (S15). As a result, if the reference value B is larger than the output value C, the surface potential (■0) of the photoreceptor is set to the value obtained by adding the predetermined potential α to the surface potential (8), and S14 is executed again (S16). If the reference value B is smaller than the output value C, the surface potential ■0 of the photoconductor is set to the value obtained by subtracting the predetermined potential α from the surface potential A, and S14 is executed again (
S17). When the reference value B and the output value C match, it is assumed that the photoreceptor has reached the optimum surface potential and the photoconductor is copied (
COPY SYCLE) will be executed (S
18).

As a result, the conventional automatic image density adjustment device can optimize the density of each color.

[Problem to be solved by the invention]

However, in the above-mentioned conventional image density automatic adjustment device,
The concentration adjustment is insufficient. That is, as shown in FIG.
curves, and when these γ curves coincide at the rising point C, it is possible to achieve the best color balance. However, when the surface potential of the photoreceptor is increased, for example, the γ curve shifts in the A direction, and the rising point C of the T curve becomes different. Therefore, if only the surface potential is changed, the color balance of yellow, magenta, and cyan will be greatly disrupted.

Therefore, a recent full-color copying machine (CX-7500 manufactured by Sharp ■) is equipped with an automatic image density adjustment device that adjusts the density difference by correcting the surface potential of the photoreceptor and the amount of light of the exposure optical system.

The above image density automatic adjustment device uses a detection sensor, such as an infrared sensor, to read the amount of toner adhering to the transfer intermediate, and compares the image density obtained from this detection sensor with a pre-stored image density. It consists of a control means for adjusting the surface potential of the photoreceptor and the light amount of the exposure optical system based on the comparison results. As shown in the flowchart of FIG. 4, this control means calculates a surface potential ΔVg for each color to compensate for a decrease in copy density (S21), and further calculates a light amount correction voltage VCL required for these surface potentials ΔVg. (S22). Then, the surface potential Vg and the light amount correction voltage V are corrected by the above-mentioned surface potential ΔVg. The charger that applies a surface potential to the photoreceptor and the light source lamp of the exposure optical system are controlled based on L (S23).

As a result, when the surface potential is increased to increase image density, for example, a light amount correction is performed to increase the amount of light, and this increase in the amount of light changes the T-curve as shown in Figure 5. By shifting in direction B, a γ curve D with coincident rising points C is formed.

Therefore, this automatic image density adjustment device can prevent image darkening due to increase in surface potential, thereby making it possible to satisfactorily adjust the density balance with stable image quality.

However, the above-mentioned light amount correction has a limit due to the sensitivity of the photoreceptor and the capacity of the power source. Therefore, if the increase in surface potential exceeds the limit of light amount correction, it becomes impossible to prevent the image from darkening due to the increase in surface potential, and in the worst case, fogging will occur.

Therefore, in the present invention, by controlling the surface potential and correcting the light amount, the image density can be adjusted well, and even if the light amount correction exceeds the limit, the electrophotographic image can be prevented from darkening. The purpose is to provide an automatic image density adjustment device for the device.

[Failure to solve the problem]

The image density automatic adjustment device for an electrophotographic apparatus according to the present invention includes:
In order to solve the above problems, a detection means is a detection sensor such as an infrared sensor that detects the amount of toner adhesion, and based on this amount of toner adhesion, the surface potential of the photoreceptor is controlled and the light amount of the exposure optical system is corrected. In an automatic image density adjustment device for an electrophotographic apparatus, the control means adjusts the image density by correcting the light amount according to the surface potential when the light amount correction is less than the limit light amount of the exposure optical system. On the other hand, when the light amount correction exceeds the limit light amount of the exposure optical system, the image density is adjusted using the surface potential based on the limit light amount.

[For production]

According to the above configuration, the surface potential of the photoreceptor is controlled based on the toner adhesion amount detected by the detection means, and this control of the surface potential satisfactorily adjusts the image density. It makes it possible. At this time, the control means not only controls the image density described above, but also corrects the light amount of the exposure optical system. The light amount correction of the exposure optical system is made in accordance with the surface potential when the light amount correction is less than the limit light amount of the exposure optical system. This prevents the image from darkening that occurs when controlling the surface potential.

On the other hand, if the light amount correction exceeds the limit light amount of the exposure optical system, it becomes impossible to prevent the darkening that occurs when controlling the surface potential. By doing so, it is possible to prevent the above-mentioned darkening from occurring.

In this way, the image density automatic adjustment device adjusts the surface potential of the photoreceptor and the light amount of the exposure optical system based on the surface potential, and the surface potential based on the limit light amount, with the limit light amount of the exposure optical system as the boundary. It is designed to be controlled while switching to Therefore, this automatic image density adjustment device makes it possible to satisfactorily adjust the image density by controlling the surface potential and correcting the amount of light, and even if the amount of light correction exceeds the limit, the image will not darken. It becomes possible to prevent

〔Example〕

An embodiment of the present invention will be described below based on FIGS. 1 and 2.

As shown in FIG. 2, the automatic image density adjustment device according to this embodiment is built into a full-color copying machine, which is an electrophotographic device. This full-color copying machine has an exposure optical system 2 in the upper part, and this exposure optical system 2 has a light source lamp 2a that irradiates light onto a document 11 placed on a document table 1. .

This light source lamp 2a is connected to a regulator board whose maximum output, which is the limit light amount of the exposure optical system 2, is a limiter voltage VeLMA, and this regulator board is
It is controlled based on a light amount correction voltage VC, , by a control means to be described later.

In addition to the light source lamp 2a described above, the exposure optical system 2 also includes a plurality of reflecting mirrors 2b, which guide reflected light from the original 11 onto the photoreceptor 3, as shown by the dashed line, for example, and a plurality of reflecting mirrors 2b arranged on the optical path. It has an imaging lens 2C and a color separation filter 2d having color filters of three primary colors (red, green, blue),
The optical image reflected from the original 11 is reflected by the above-mentioned reflecting mirror 2b.
..., the image forming lens 2c and the color separation filter 2d separate the light into color components and irradiate the photoreceptor 3 with the light.

The optical body 3 is irradiated with the above-mentioned optical image, and the first roller 12
Near the top surface of the photoconductor 3 are developer tanks 4a to 4C containing developers of complementary colors (yellow, magenta, cyan) for each color filter. It is arranged in a non-contact manner. Further, a charger 7 for uniformly charging the photoreceptor 3 is disposed on the first roller 12a side of the photoreceptor 3, and the charger 7 is connected to a high-voltage substrate whose output is controlled by a control means. It is connected. Further, a cleaning mechanism 13 for removing toner remaining on the photoreceptor 3 is disposed on the lower surface of the photoreceptor 3 on the side of the first roller 12a.

On the other hand, a transfer intermediate body 5 is disposed on the second roller 12b side of the photoreceptor 3, and this transfer intermediate body 5 is rotationally driven by a first roller 14a, a second roller 14b, and a third roller 14c. It is now possible to do so. Further, on the inner peripheral side of the transfer intermediate body 5 at the portion where the second roller 12b side of the photoconductor 3 is pressed, there is a transfer charger 8a for transferring the visible image formed on the photoreceptor 3 to the transfer intermediate body 5. It is arranged. Further, below the third roller 14c of the transfer intermediate body 5, there is a transfer paper 15 conveyed from the paper feed cassettes 6a and 6b.
a transfer charger 8 for transferring the visible image of the transfer intermediate 5 to
b is provided. Then, this transfer paper is transferred to the conveyance path 1.
6 and then introduced into a fixing device 10, where the color image is fixed.

Further, in the transfer intermediate body 5, a detection sensor and a reference sensor, which are detection means (not shown) such as an infrared sensor, are arranged opposite to the transfer intermediate body 5, and the detection sensor and the reference sensor are It is designed to detect the amount of toner adhesion. The detection sensor described above is designed to detect an image patch consisting of yellow, magenta, and cyan toner patches formed on the transfer intermediate 5, while the reference sensor is designed to detect a white toner patch. It has become. These detection sensors and reference sensors are connected to a control means (not shown).

The above control means stores a control program shown in FIG. 1 that calculates and controls the surface potential and light amount of the photoreceptor 3 using the output value from the detection sensor, and the control program shown in FIG. An adjustment program is stored that controls the current 11 of the light emitting element of the detection sensor by constantly detecting . and,
This adjustment program is designed to detect the amount of toner adhesion with high accuracy by correcting changes in characteristics and temperature due to the life of the measuring section of the detection sensor so that they are similar to the initial state.

On the other hand, the control program has a reference value B with which the output value from the detection sensor is compared, and this reference value B is used to apply a toner batch of 2 cm x 3 cm to the transfer intermediate 5 at a constant surface potential of each color ( yellow, magenta, and cyan), and is set to the output value when each of these toner batches is detected by the detection sensor. This control program also includes a surface potential ΔVg that corrects changes in copy density.
It has a light amount calculation formula that calculates the light amount correction voltage VCL according to the light amount correction voltage VC obtained by this light amount calculation formula.
When the light source lamp 2a is controlled by L, the rising points of the T curve, which is a copy density curve with respect to the developed density, coincide with each other, and only the copy density is changed.

In the above configuration, the operation of the automatic image density adjustment device to adjust the surface potential of the photoreceptor 3 and the output of the light source lamp 2a when the full-color copying machine is operated will be described below.

First, the light source lamp 2a irradiates the original 11 placed on the original placing table 1 and scans it several times, and then the reflecting mirror 2b...
The optical image is separated into color components via an imaging lens 2C and a color separation filter 2d.

Optical images for each color component transmitted through each color filter of the color separation filter 2d in several scans are sequentially image-exposed to the photoreceptor 3, which is uniformly charged by the charger 7.

The latent images for each color component formed in order here are stored in the developer tank 4.
After being developed and visualized using developers of complementary colors (yellow, magenta, and cyan) of each color filter of the color separation filters 2d housed in a to 4C, they are sequentially transferred to the transfer intermediate 5 by the transfer charger 8a. . As a result, toner images for each color component are superimposed on the transfer intermediate 5 to form a completed color toner image.

The color toner image described above is transferred from one of the paper feed cassettes 6a and 6b to the transfer paper 15 that is brought into close contact with the lower surface of the transfer intermediate 5 by the transfer charger 8b. Thereafter, the transfer paper 15 is separated from the transfer intermediate 5 and introduced into the fixing device 10 via the conveyance path 16, where it is fixed as a color image.

At this time, if the temperature at which the color image is fixed is below 100° C., or if the device has been left with the power turned on for more than two hours, the control means executes the above-mentioned control program.

When this control program is executed, first, as shown in FIG. 1, the surface potential Δ
Vg is calculated from the image patch.

In addition, the measurement of the image patch is 5 mm from both ends of the image patch.
The measurement is performed on the portion excluding the inner part, and the inside of each image patch is measured every 1Qmsec, and the average of these measurements is taken as the measurement value. As a result, when measuring image patches, reading errors of the detection sensor due to variations in the amount of toner adhesion that occur at both ends due to the influence of the electric lines of force of the electrostatic latent image are reduced. Measurement fluctuations are prevented (S1).

Next, the light amount correction voltage ■ according to the above surface potential ΔVg
CL is calculated using the above-mentioned light amount calculation formula. As a result, the rising points of the γ curves of the colors yellow, magenta, and cyan coincide, making it possible to satisfactorily adjust the color harance (S2).

The above light intensity correction voltage ■. When L is calculated, this light amount correction voltage ■. L and the limiter voltage of the regulator board ■. L
MII is compared. This comparison is based on the light intensity correction voltage ■. ■ Limiter voltage from. This is done by determining whether the calculated value obtained by subtracting LMAX is positive or negative. As a result, the above calculated value becomes positive, and the light amount correction voltage V
If it is determined that CL is larger than the limiter voltage ■CLMAκ, S5 is executed, and the above calculated value becomes negative, and the light amount correction voltage ■. If it is determined that L is less than the limiter voltage V CLNAX,
S4 will be executed (S3).

16 Then, in S4, the grid voltage of the charger 7 is controlled so that the photoreceptor 3 has a surface potential Vg corrected by the above-mentioned surface potential ΔVg, and the regulator board is controlled to have the light amount correction voltages (1), 1. (S
4).

On the other hand, in S4, the light amount correction voltage VCL is changed to the limiter voltage V C
At S5, which is the jump destination determined to be a larger value than LMAX, the limiter voltage V CLMAX is substituted into the light amount correction formula, and the surface potential Vgmax based on the limiter voltage V CLMAX is calculated backwards (S5). Then, the grid voltage of the charger 7 is controlled so as to have this surface potential VgMAx, and the regulator board is controlled to the limiter voltage CLMA, which is the limit light amount (S6).

In this way, the automatic image density adjustment device adjusts the surface potential of the photoreceptor 3 by detecting image patches, and causes the light source lamp 2a to output an amount of light corresponding to this surface potential. Therefore, the image density automatic adjustment device can adjust the original density 17 while matching the rising points of the T curves of each color, making it possible to prevent image darkening due to an increase in surface potential. This makes it possible to adjust the density balance well with stable image quality.

Furthermore, in this automatic image density adjustment device, when the increase in surface potential exceeds the limit light amount for light amount correction, the surface potential is calculated backward according to the limit light amount and the light source lamp 2a and the charger 7 are controlled. It is also possible to prevent image darkening due to increase in surface potential.

〔Effect of the invention〕

The image density automatic adjustment device for an electrophotographic apparatus according to the present invention includes:
As described above, when the light amount correction is below the limit light amount of the exposure optical system, the image density is adjusted by light amount correction according to the surface potential, while when the light amount correction exceeds the limit light amount of the exposure optical system, the image density is adjusted based on the limit light amount. This configuration adjusts image density using surface potential.

This allows the surface potential of the photoreceptor and the light amount of the exposure optical system to be adjusted based on the limit light amount of the exposure optical system, and the image density is adjusted while correcting the light amount based on the surface potential and switching to the surface potential based on the limit light amount. By doing so, it becomes possible to adjust the image density well, and
Even if the light intensity correction exceeds the limit, it is possible to prevent darkening of the image.

[Brief explanation of drawings]

1 and 2 show an embodiment of the present invention. FIG. 1 is a flowchart of the control program. FIG. 2 is a schematic configuration diagram of a full-color copying machine. 3 to 5 show conventional examples. FIG. 3 is a flowchart showing the procedure for controlling the surface potential of the photoreceptor. FIG. 4 is a flowchart showing the procedure for controlling the surface potential of the photoreceptor and the amount of light of the exposure optical system. 19 FIG. 5 is an explanatory diagram showing how the T-curve changes depending on the relationship between the surface potential and the amount of light. 1 is a document mounting table, 2 is an exposure optical system, 2a is a light source lamp,
3 is a photoreceptor, 5 is a transfer intermediate, 7 is a charger, 1
0 is a fixing device, and 11 is a document. 20 r+L+-Mishuon

Claims (1)

[Claims] 1. Detection means for detecting the amount of toner adhesion, and control for adjusting image density by controlling the surface potential of the photoreceptor and correcting the light amount of the exposure optical system based on the amount of toner adhesion. In the image density automatic adjustment device for an electrophotographic apparatus, the control means adjusts the image density by light amount correction according to the surface potential when the light amount correction is less than the limit light amount of the exposure optical system; An image density automatic adjustment device for an electrophotographic apparatus, characterized in that when the limit light amount of an exposure optical system is exceeded, the image density is adjusted by a surface potential based on the limit light amount.