JPH04306670A - Image formation device - Google Patents

Abstract

PURPOSE:To easily select desired image density by providing a switch for selecting a desired gamma curve from a group of gamma curves on an operational panel. CONSTITUTION:The density of an imaging pattern 10 is detected by a reflective optical sensor 13 which is composed of an emitting device 11 and a light receiving device 12, that are arranged in an opposed way, and which is arranged in the proximity of a photosensitive drum 1, and image density is controlled by the output. In this case, two kinds of gamma curve groups are determined, and a desired gamma curve is selected from respective gamma curve groups by an operation switch 14 which is provided on an operation panel, and which is composed of notch and switch and so on, and the image density is controlled according to a gamma curve characteristic thus selected. Namely, when toner concentration(T.C.) is to be changed, by changing developing potential of the imaging pattern 10 while output ratio of the optical sensor 13 is put on a good accuracy point, the T.C. is changed into an aimed level, in such a way that the toner adhesion on the pattern is unchanged while the aimed toner concentration is changed.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an image forming apparatus using an electrophotographic method, and in particular, in an image forming apparatus using a two-component developer, image density is controlled by changing the γ curve. The present invention relates to an image forming apparatus.

0002

BACKGROUND OF THE INVENTION Conventionally, among image forming apparatuses using electrophotography, image forming apparatuses using two-component developers are
There are three ways to control image density:

(1) A user selects a threshold value for the reading density of a document from within a preset range using, for example, a notch.

(2) The density of the developed pattern is detected by an optical sensor, and toner is replenished so as to keep the output ratio constant.

(3) Regardless of the type of image to be formed, the density of a fixed developed pattern such as a solid image is detected by an optical sensor, and toner is replenished so as to keep the output ratio constant. .

In the case of (1) above, as shown in FIG. 7, the desired reading density is determined from a seven-level characteristic diagram showing the relationship between the original reading density (OD) and the image density (ID). The notch selects the one that provides the threshold value, and in the case of (2) above, as shown in Figure 9, when you want to increase the image density in the range indicated by the arrow, you want to lower the output ratio and make it lighter. Sometimes, toner is replenished to keep the output ratio high, and in the case of (3) above, toner is replenished so that a solid pattern image has a certain image density. .

[0007]

[Problem to be solved by the invention] However, the above (
In the case of 1), it is often not possible to obtain a satisfactory image with the seven-step selection, especially when it comes to the maximum image density, as shown in Figure 7.
As you can see, there was a problem in that it remained almost constant even if the selection was changed.

In the case of (2), since the development potential of the developed pattern is kept constant and the amount of toner adhering to the pattern is varied, the image density (that is, toner density; hereinafter referred to as this) The range of fluctuation of the optical sensor (referred to as T. If it falls below the range,
Even if the amount of toner adhesion on the P (photo) sensor pattern (visual image pattern of the reference image) changes, the output ratio of the sensor hardly changes. In the worst case, T.C cannot be detected. C may not be able to be controlled and may go out of control. Furthermore, when the amount exceeds the range A, the amount of toner adhering to the pattern is small and the sensitivity of the sensor to the amount of toner adhering becomes high, so a small change in the amount of toner adhering to the pattern will greatly change the output ratio of the sensor.
There was a problem that a stable sensor output ratio could not be obtained compared to controlling within the range of A.

Furthermore, in the case of (3), when copying text originals, for example, there is a problem that the desired image density or desired resolution cannot be obtained because the development method is different from that of solid images. The dot was hot.

The present invention was devised to solve these problems, and an object of the present invention is to provide an image forming apparatus that can obtain high-quality images by performing optimal image density control. shall be.

[0011]

[Means for Solving the Problems] The above object is to provide an image forming apparatus that detects the density of a developed pattern using an optical sensor and controls the image density based on the output of the sensor.
Achieved by the first means of setting two types of γ-curve groups, selecting a desired γ-curve from each γ-curve group using an operation switch, and controlling the image density according to the selected γ-curve characteristics. be done.

The above object is also achieved by a second means in which one of the γ curve groups is a γ curve group in which the toner density is changed by changing the development potential of the developed pattern.

Furthermore, the above object is achieved by a third means in which the type of the developing pattern is changed depending on the type of mode, and the image control is performed using the changed developing pattern.

[0014]

[Operation] According to the first means, by installing an operation switch such as a notch or switch on the operation panel for selecting a desired γ curve from the γ curve group, the user can easily set the desired image density. You can choose.

According to the second means, the toner concentration (T.C.
), as shown in Fig. 10, by changing the development potential of the developed pattern while keeping the output ratio of the optical sensor at the highly accurate point A, the amount of toner adhering on the pattern can be changed. Even if the target toner density changes, the target T. Even if C is changed, T. C control can be performed.

According to the third means, optimum image density control according to the copy mode is achieved by using a developed pattern resembling an actual image, such as a solid pattern, a dot, or a line, depending on the type of the mode. It can be performed.

[0017]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings.

FIG. 1 is a block diagram of the main parts of an image forming apparatus using the present invention.

In this configuration, a reversal development system is used in which a (-) charged organic photoreceptor is used as a photoreceptor and a two-component developer containing (-) charged toner is used as a developer. The photoreceptor drum 1, which is rotationally driven by a motor, is uniformly charged by a charger 2, and then the photoreceptor drum 1 is charged by a laser beam 3 that changes in accordance with image information.
The image is scanned and exposed in a direction perpendicular to the direction of rotation. As a result, the electrostatic latent image formed on the photoreceptor drum 1 is transferred to the developing device 4.
It is visualized by. The visible toner image formed on the photoreceptor drum 1 is transferred to a transfer paper 6 by a transfer charger 5, and then transferred from the photoreceptor drum 1 to the transfer paper 6 by a separation charger 7.
is peeled off. The visible toner image transferred to the transfer paper 6 is fixed by a fixing device, and the toner remaining on the photosensitive drum 1 after the transfer is removed and cleaned by a cleaning device 8. After that, the charge remaining on the photoreceptor drum 1 is
The charge is removed by the charge removal light from the lamp 9, and the above steps are repeated again. When forming an electrostatic latent image, the surface potential of the photoreceptor drum 1 has a background potential (dark potential) VD of approximately -
800V, the image area potential (bright area potential) VL is set to approximately -50V, and the developing bias potential VB is approximately -600V.
It is developed by the potential difference between the two.

By the way, in the present invention, as shown in FIG. 2, a developed pattern 10 of a reference image for image density control is formed on the photosensitive drum 1 outside the image forming area, and this developed pattern is similar to the one shown in FIG. The normal skin potential (
The dark area potential) VD is set to about -800V, the image area potential (light area potential) VL is set to about -250V, and development is performed with a potential difference from the developing bias potential VB of about -600V. Further, as shown in FIG. 2, a reflective optical sensor 13 consisting of a light-emitting element 11 and a light-receiving element 12 arranged opposite to each other is arranged close to the photoreceptor drum 1. A detection signal voltage VSP corresponding to the reflectance and a detection signal voltage VSG of the photoreceptor surface without a reference image are output. This reference image is usually a solid pattern as shown in FIG. /VSG(A) by replenishing toner until the value becomes smaller than T.VSG(A). Approximately 2% C
to adjust the image density to the standard state. The user not only selects the notch, but also selects the T. If you want to change the image density by changing T.C, use the switch 14 on the operation panel as shown in FIG. C can be changed. Specifically, when the user presses the <high> switch 14a, for example, the reference image for image density control formed on the photoreceptor drum 1 outside the image forming area changes to the image area potential (
Bright area potential) VL was changed to approximately -310V,
As in the normal case, the detected ratio VSP/VSG is set at the preset image density control level VSP/VSG point (A
) By replenishing toner until it becomes smaller, the toner density is made approximately 2.5%, and the image density is adjusted to be slightly higher as shown by curve a in FIG. Here, the development potential of the developed pattern is the target T.I. Point A shown in FIG. 10 in the range of C from 1.5 to 2.5%
and the objective T. Determined by C. That is, the desired T.I. The development potential of the development pattern 10 corresponding to C (arrow b shown in FIG.
(range), the amount of toner adhering to the developed pattern 10 is always kept constant, the influence of the characteristics of the optical sensor 13 is greatly reduced, and highly accurate image density control is possible. This is not only a black agent but also a color agent.
When you want to control the image density to a high level even though it does not absorb much light and the output ratio of the optical sensor 13 is easily saturated (especially when
It is also effective when copying HP, etc.).

Next, when the user presses the <Low> switch 14b when the user wants to lower the maximum image density or increase the gradation, the image density formed on the photoreceptor drum 1 outside the image forming area is reduced. The reference image for control is changed so that the image part potential (bright part potential) VL is about -100V, and the detected ratio VSP/VSG is set in advance to the image density control level VSP as in the normal case. /Stop toner replenishment until the VSG point (A) is exceeded, and then
/VSG point (A) by replenishing toner so that the T. By setting C to about 1.5%, the image density can be adjusted to be slightly lower as shown by curve b in FIG. Of course, the user T. After changing C, the image density can be finely adjusted by changing the notch as usual. Thus, in this example,
T. By being able to change C, the range of image density that can be adjusted by the user is greatly expanded.

FIG. 4 shows T. C mode, pattern part potential,
Development potential, target T. This is a diagram showing the relationship between C and the above operations. The development pattern 10 is usually a solid black pattern, and the exposure amount of the pattern is adjusted so that the development potential becomes the target potential. will be changed to something like The effect is also shown in Figure 5, but when a solid image is used for the developed pattern, control is performed to obtain a certain image density for the solid image. Become. Therefore, this method is effective in cases such as photographic originals where image density (ID) is an important aspect of image quality. For this reason, for example, when copying a text original, it is necessary to perform control for the text mode, since the development method and objective evaluation are different from that of a solid copy. Normally, when comparing a solid image and a character image, the edge effect occurs during development and more toner is consumed for the character, so the I.I. Although D is rarely a problem, a decrease in resolution becomes a major problem. Conventionally, in order to solve this problem, writing in character mode was
However, since the image density control was based on a solid image, the desired resolution could not be obtained depending on the environment.

Therefore, in this embodiment, when the character mode is selected, the developed pattern is automatically changed to a binary line pattern, thereby performing optimal image density control for characters. . This binary line pattern has areas that are developed and areas that are not developed, so T. If the C exceeds a certain level, resulting in excessive development and a decrease in resolution, which is extremely important for character quality, the optical sensor 13 will detect toner that has adhered to areas that should not be developed. makes a response. This effect is similar even when a dot pattern is used. Detection of such a decrease in resolution is impossible in a solid pattern. Incidentally, there are already known methods using dots or lines as the visualization pattern 10 based on the same concept, but these methods are not applicable to all modes, and it is necessary to use a pattern suitable for each copying mode. It is something that

FIG. 6 is a flowchart showing image density control in the present invention.

First, in step S1, it is determined whether the copy mode is normal or not. If it is not normal, the developed pattern 10 is changed to a character line pattern in step S2, and the process moves to a copy standby state in step S7. let

In step S1, if the copy mode is normal, the process proceeds to step S3, where it is determined whether or not the switch (TC adjustment key) 14 is pressed. If the switch 14 is pressed, In step S4, it is determined whether or not it is the <high> switch 14a. If it is the <high> switch 14a, the potential VL of the imaged pattern area is changed to -310V in step S5, and the potential VL for the pattern is changed to -310V. Output ratio of optical sensor 13 (VSP/
Toner replenishment and pattern image formation are repeated until VSG) reaches point A. In step S4, if the <high> switch 14a is not pressed, that is, if the <low> switch 14b is pressed, the potential VL of the developed pattern portion is changed to -100V in step S6. And step S
5. After step S6, the process moves to step S7.

[0027]

According to the invention as claimed in claim 1, by installing a switch on the operation panel for selecting a desired γ curve from the γ curve group, the user can easily set the desired image density. You can choose.

According to the second aspect of the invention, when it is desired to change the toner concentration (TC), the development potential of the developed pattern is changed while keeping the output ratio of the optical sensor at the highly accurate point A. In particular, the amount of toner deposited on the pattern is made constant even if the target toner concentration changes, and the target T.I. T with good accuracy by changing C
．． C control can be performed.

According to the third aspect of the invention, by using a visualization pattern similar to an actual image, such as a solid pattern, a dot, or a line, depending on the type of the copy mode, an optimal image according to the copy mode is created. Concentration control can be performed.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of main parts of an image forming apparatus used in the present invention.

FIG. 2 is a layout diagram of a sensor that detects a reference image pattern.

[Figure 3] T. It is a block diagram of the switch for C adjustment.

[Figure 4] T. It is a chart showing various data according to C mode.

FIG. 5 is an explanatory diagram showing the contents of normal mode and character mode.

FIG. 6 is a flowchart showing control of image density according to the present invention.

FIG. 7 is a first group of γ curves showing the threshold value of the reading density of a document.

FIG. 8 is a second γ curve group used in the present invention.

FIG. 9 is a characteristic diagram showing the relationship between the amount of toner adhesion on the P sensor pattern and the development potential in a conventional example.

FIG. 10 is a characteristic diagram showing the relationship between the amount of toner adhering to the P sensor pattern and the development potential according to the present invention.

[Explanation of symbols]

1 Photoreceptor drum 4 Developing device 10 Visualization pattern 13 Optical sensor 14 Switch

Claims (3)

[Claims] Claim 1: In an image forming apparatus that detects the density of a developed pattern using an optical sensor and controls the image density based on the output of the sensor, two types of γ curve groups are set, and each γ curve group is set using an operation switch. An image forming apparatus characterized by selecting a desired γ curve from a group of curves and controlling image density according to the selected γ curve characteristics. 2. The image forming apparatus according to claim 1, wherein one of the γ curve groups is a γ curve group in which the toner density is changed by changing the development potential of the developed pattern. . 3. The type of developing pattern is changed according to the type of mode, and the image density is controlled by the changed developing pattern.
2. The image forming apparatus according to 2.