JP2821166B2 - Method for controlling toner density in color image forming apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a toner density of a developer of an image forming apparatus capable of developing with a plurality of types of developers.

2. Description of the Related Art Conventionally, in a color copying machine, which is one of image forming apparatuses, a color image mode in which at least three types of toner images such as cyan, magenta, and yellow are transferred in an overlapping manner, and a black image mode in which black toner alone is used. Is known to be switchable.

Efforts have been made to increase the image forming speed of copiers as much as possible, but in the color image mode where development is carried out using a plurality of color developers, a large amount of power is supplied to the original illuminating device and fixing device. Need
In the case of the black image mode by the development of the black toner alone, the copying linear speed is increased, and in the case of the color image mode, the copying linear speed is switched to a low speed to save labor.

In a copier, in order to maintain good image quality, toner density is detected by a toner density detecting unit for each color developer, and when the density decreases, toner is supplied to maintain a constant toner density. I have.

As the toner density detecting means, a toner density sensor for magnetically detecting the passing toner and measuring the density is used. This toner density sensor has the property that the output characteristics change when the speed of the developer flowing near it changes.Therefore, in an image forming apparatus that changes the image forming speed, when the image forming speed is changed, the characteristics of the toner density sensor change. Therefore, the detection result from the toner density sensor also changes. That is, even when the toner density of the developer in the developing device has not changed, when the image forming speed changes, it is detected that the toner density has decreased or that the toner density has increased. This means that if toner supply is performed according to the output of the toner density sensor without considering that the development speed, that is, the copy speed has changed,
If it is determined that the toner concentration is insufficient but sufficient,
There is a problem that it is determined that the toner is insufficient but insufficient, and that the toner supply is not performed correctly.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and provides a toner density control method for a color development forming apparatus capable of always replenishing toner properly even when an image forming speed is switched and maintaining a constant toner density. That is the task.

[Means for solving the problem]

SUMMARY OF THE INVENTION The present invention is directed to a color image forming apparatus for forming an image using a plurality of types of developers, wherein the image forming speed can be switched according to a black image mode / color image mode. In the toner density control method, the toner density control is changed according to the image forming speed,
The problem has been solved by a toner density control method characterized in that at least at a certain image forming speed, the toner replenishment amount is controlled in accordance with the output value of the toner density detecting means.

[Action]

According to the present invention, the toner density control of the color developer used in both the black image mode and the color image mode can be performed, for example, in the case of high-low speed two-stage switching, a high-speed image which is a frequently used black single development black image mode. At the time of formation, the output from the toner density sensor is compared with a target value, and if the comparison value is determined to be lower than the target value and the density is insufficient, an amount preset in a stepwise manner according to the deviation from the target value. Replenish the toner. Also, during low-speed image formation in the color image mode, the output from the toner density sensor is not input to the control device, or even if input, the arithmetic processing is not performed, and the output is not involved in toner supply control. In this case, the normal amount of toner supply among the toner supply amounts set in stages during high-speed image formation is supplied. Further, the toner supply may be switched according to the characteristic curve of the sensor output at the time of low-speed image formation.

According to the present invention, even if the characteristic curve changes in the output of the toner density sensor due to the speed switching, the change in the characteristic curve due to the speed switching does not affect the toner replenishment control, and the toner can be stably supplied.

〔Example〕

 The details of the present invention will be described based on an embodiment shown in the drawings.

In a color copying machine as an example of an image forming apparatus to which the present invention is applied, for example, as shown in FIG. 1, as a toner density detecting means, a toner density sensor 1 for magnetically detecting passing toner to measure the density. Is disposed between the stirring paddle 2 for stirring the toner and the developing roller 3, and detects the toner density of the developer passing near the toner density sensor 1. A developing unit 4B for black developing having a stirring paddle 2 and a developing roller 3, a developing unit 4C for cyan developing, a developing unit 4M for magenta developing, a developing unit 4Y for yellow developing, and an electrostatic latent image developed by these developing units. A photosensitive drum 5 as an image carrier for carrying an image; a charger 6 and an image exposure unit 7 for forming an electrostatic latent image on the photosensitive drum 5; Transfer charger 11
And a transfer drum 8 carrying transfer paper.

In the developing device 4B, the toner is automatically supplied from the supply tantalum 9 by the supply roller 10 in response to the supply command.

The developing devices 4C, 4M, and 4Y for storing the color developer can be formed in the same manner, but since the consumption is usually small, the worker supplies the toner near end or the toner end display. The toner density sensor 1 is connected to each of the developing devices 4B and 4
C, 4M, and 4Y are arranged at positions where the flow of the developer is good between the developing roller 3 and the stirring paddle 2.

Development with black toner is developed by a combination of the development units 4C, 4M, and 4Y, as in a black image in the case of color transfer, and in the case of development with the development unit 4B alone, as in a normal black-white copy In some cases, development with black toner is added on the toner image.

When developing with black toner in normal black-and-white copying, power is not required for exposure, fixing, and the like as compared with the case of color development, so that the speed is increased as much as possible. Therefore, in the case of black toner single development, high-speed copying is performed at a line connection of, for example, 226 mn / sec.
Low-speed copying is performed at a linear speed of m / sec. In copying, the copying speed is automatically switched by selecting a copying mode.

The toner concentration sensor 1 serving as a toner concentration detecting means
It has the property that the output characteristics change when the speed of the developer flowing near it changes. When copying speed is changed, the toner flow rate through the toner density sensor 1 is changed, the output of the toner density sensor 1 in the high speed S _1, for example, characteristic curve shown by the curve B of FIG. 2 is obtained, about 2 minutes Of 1
Characteristic curve shown by the curve A is obtained in the low-speed S _2.
Setting the constant toner density D _0, with respect to the output of the toner density sensor to maintain the toner concentration constant target value V ₂ the curve A is the target value V ₁ the curve B is obtained. In the figure, the vertical axis indicates the output of the toner density sensor, and the horizontal axis indicates the toner density.

Now the output V ₁ in the curve B of FIG. 2 as the target value, when it indicates that the output is that it requires a high and becomes low concentration replenishment, even at the same predetermined density, low development rates S ₂ will be output resulting in determined that the toner density despite a proper density because it is smaller than V ₂ becomes output V ₁ too dark when. Conversely, when the sensor output curve at a low developing speed is used as a reference, a signal is output indicating that toner supply is necessary despite proper density, and excessive toner supply is performed. Means

Since the color developer is generally used at a low speed and is not used at a high speed, the developing units 4C, 4M, and 4Y may be controlled so as to replenish the toner density according to the curve A.

When the black developer is developed by switching the speed between normal black-and-white development (black image mode) and color copying (color mode), the characteristic curve at high speed of the frequently used black image mode is used. If toner replenishment control is performed in accordance with B and toner density control is not performed depending on the output from the low-speed toner density sensor 1 that is used less frequently, it is possible to avoid a difference in toner density. In this case, the toner density control at the time of low-speed copying is fixed to the replenishment control based on the toner replenishing amount at the normal stage among the toner replenishing amounts that are different in steps in the toner density control at the time of high-speed copying. It is convenient.

The toner supply control is performed based on, for example, a flowchart shown in FIG.

That is, the speed of the developing unit S ₁ or to check, if it is S ₁ in high-speed copying detects the toner density data V ₀ is the output of the toner density sensor, the upper limit value V determined in advance with respect to the target V ₁ ′ _{2 and} this V _1, the toner is replenished for the toner replenishment time T ₂ as a normal level replenishment amount, and V ′
₁ or more when the density reduction is great in output replenished by the toner replenishment time T ₁ as makeup large becomes stage of replenishing amount, the output is
Because when the V ₁ below a predetermined concentration is reserved toner supply time is set to 0.

If the speed of the developing device is S ₂ instead of S ₁ is may be a toner supply time 0, similarly toner supply and replenishment of normal stages in the case in order to prevent the toner density loss rate S ₁ is it is convenient to the toner supply only time T _2.

When the copying speed is switched, the control of the present invention can be controlled as shown in the control flowchart of FIG. That the toner density data V ₀ is sampled from the toner density sensor 1, the speed of the developing device is checked whether it is S _1, if the speed S ₁ is the toner density than the characteristic curve B which correspond to the high and reduced When it is large, the toner is replenished. When the toner concentration exceeds a predetermined amount and V ₀ <V ₁ , the toner replenishment is turned off.

When the speed of the developing device is in a low speed S _2, the toner density data
It is checked whether V ₀ is greater than the target value V ₂ set from the characteristic curve A, and if V ₀ <V ₂ due to a decrease in toner density, the toner supply is turned off.

In the control shown in FIG. 4, low-speed and high-speed toner density output target values are stored in the control device in advance, and when a corresponding copying speed is selected by selecting an image mode, the target level corresponding to the copying speed is set. The comparison target of the toner density data is shifted.

〔effect〕

According to the present invention, even in a color image forming apparatus in which the image forming speed is switched, the characteristics of the toner density sensor in the case of a frequently used high-speed image forming speed are used only during the high-speed image forming, and other speeds, that is, other speeds, that is, Since another control is performed at the time of low-speed image formation, occurrence of an abnormal toner supply state is eliminated.

[Brief description of the drawings]

1 is a schematic diagram of an image forming section of a color copying machine as an example of an image forming apparatus utilizing the present invention, FIG. 2 is a diagram showing a change in a toner density output characteristic curve depending on the speed of a developing device, and FIG. FIG. 4 is a flowchart showing another toner supply control according to the present invention, and FIG. 4 is a flowchart showing another toner supply control when the speed of the developing device can be switched. DESCRIPTION OF SYMBOLS 1 ... Toner density sensor 2 ... Stirring paddle 3 ... Developing roller 4B, 4C, 4M, 4Y ... Developing device 5 ... Image carrier

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ identification symbol FI G03G 21/00 384 G03G 21/00 384 21/14 372 (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 15 / 00 303 G03G 21/00 370-540 G03G 13/01 G03G 15/01 G03G 13/08 G03G 15/08

Claims (1)

(57) [Claims] 1. A color image forming apparatus for forming an image with a plurality of types of developers, wherein the toner density control of the color image forming apparatus is capable of switching the image forming speed according to a black image mode / color image mode. In the method, the toner density control is changed according to the image forming speed, and at least at a certain image forming speed, the toner replenishment amount is controlled according to the output value of the toner density detecting means. Control method.