JPH04322275A - Toner concentration controller - Google Patents

Abstract

PURPOSE:To reduce the number of times and a frequency that a reference image for controlling the concentration of toner is formed and to stably keep the various kinds of image quality for a long time. CONSTITUTION:First of all, the density voltage VSG of an area on a photosensitive body 9 where there is not a toner image is detected and the density voltage VSP1 of the reference image of a solid image and the density voltage VSP2 of the dot-like or line-like reference image are detected, next. In the case that it is not in course of toner replenishment, the ratio VSP1/VSG and a reference value R1 for judging the start of the toner replenishment are compared. Then, since the density of the reference image of the solid image is normal when the ratio VSP1/VSG> the reference value R1 is not attained, processing is finished. On the other hand, the toner is replenished with the ratio VSP1/VSG> the reference value R1 is attained. Besides, in the case that it is in course of the toner replenishment, the ratio VSP2/VSG and the reference value R2 are compared. Then, when the ratio VSP2/VSG> the reference value R2 is attained, the toner is continuously replenished. When the ratio VSP2/VSG> the reference value R2 is not attained, the toner is stopped being replenished.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner density control device for an electrophotographic image forming apparatus.

0002

2. Description of the Related Art Generally, in an electrophotographic image forming apparatus, it is necessary to control the toner density of a developer in order to keep the image density constant. Therefore, various inventions related to toner density control have been proposed and put into practical use. As one method, for example,
As shown in Japanese Patent No. 9-30269, a method is known in which a reference image for controlling toner density is formed outside the image forming area of a document on an image carrier, and the optical density is detected to control the toner density. ing.

0003

[Problems to be Solved by the Invention] However, although the conventional toner density control method described above is excellent in keeping the image density constant, it also forms a reference image outside the image forming area of the original on the image carrier. Therefore, there are various problems. The first point is that toner for the reference image is wasted. The second point is that it is necessary to prevent the toner for the reference image on the image carrier from being transferred to the transfer paper. In this case, since this toner image also needs to be cleaned, a correspondingly high cleaning performance is required. In general, increasing the cleaning performance is not preferable because it wears out the surface layer of the photoreceptor, which is an image carrier, and shortens the life of the photoreceptor. In particular, when toner with a particle size of 10 μm or less is used due to the recent demand for higher image quality, it is technically difficult to achieve both cleaning performance and photoreceptor life.

Third, since a series of electrophotographic processes such as charging, exposure, and development are performed separately from the original image formation, the life of each component is shortened, and in particular, ozone, NOx, etc. are generated due to the charger. In addition, scattering of toner from the developer increases. Furthermore, these problems become more noticeable as the number of times and frequency of formation of the reference image increases. Here, from the point of view of toner density control, it is preferable to form the reference image as many times as possible and as frequently as possible.
In terms of image quality, the greater the number of times the reference image is formed and the more frequently it is formed, the more detailed the control can be, which is preferable, but on the other hand, even if there is a slight deviation from the reference value, the quality of the image does not necessarily deteriorate sharply. , there is a practical tolerance range in actual machines.

FIG. 5 shows the relationship between the toner density in the developer and the density depending on the original image. There is no problem with the density of solid images as long as the toner density is above a relatively low value.
When the toner concentration falls below this value, it decreases. On the other hand, the density of dot images is, unless the toner density is extremely low,
There is no problem when the value is below a relatively high value, but only when the toner concentration is excessive there is a tendency for the toner to become thicker, and toner dust around the dots becomes noticeable. As a result, the density of the dot image increases, causing problems such as a decrease in resolution and deterioration in sharpness. Note that the relationship shown in FIG. 5 is based on the usage state of the developer,
Naturally, it changes depending on the environmental conditions, the potential of the photoreceptor, and the development conditions other than the toner concentration.

In view of the above conventional problems, the present invention is capable of reducing the number and frequency of formation of a reference image for toner density control, and also stably maintaining the quality of various different images for a long period of time. An object of the present invention is to provide a toner density control device that can control the toner concentration.

[0007]

[Means for Solving the Problems] In order to achieve the above object, a first means includes a latent image forming means for forming a reference latent image on an image bearing member by an optical writing system; a developing means for developing the formed latent image; a toner replenishing means for replenishing toner to the developing means; an optical detecting means for detecting the density of the developed reference image; In a toner concentration control device comprising a toner replenishment amount control means for controlling the amount of toner supplied from the toner replenishment means to a developing means according to a detection output, conditions for generating a toner replenishment start signal of the toner replenishment amount control means and toner replenishment amount control means are provided. The conditions for generating the replenishment stop signal are set to different conditions.

Further, in order to achieve the above object, the second means forms first and second reference images by the latent image forming means and the developing means in the first means, and defines a lower limit of toner concentration. The condition for generating the toner replenishment start signal is set based on the result of detecting the density of the first reference image by the optical detection means, defines an upper limit of toner density, and generates the toner replenishment stop signal. The conditions for determining the density of the second reference image are set based on the result of detecting the density of the second reference image by the optical detection means.

Furthermore, in order to achieve the above object, a third
In the above method, the first reference image was formed as a solid image, and the second reference image was formed as either a dot image or a line image.

In addition, in order to achieve the above object, a fourth
In this method, the first reference image was formed by an image with an image area ratio of 80% or more, and the second reference image was formed by a dot or line image with an image area ratio of 60% or less.

[0011] In addition, in order to achieve the above object,
In the fifth means, the first means further includes display control means for causing a warning display to be displayed when a condition for generating the toner replenishment start signal and a condition for generating the toner replenishment stop signal overlap. We are prepared.

0012

[Operation] According to the first means, the conditions for generating the toner replenishment start signal and the conditions for generating the toner replenishment stop signal are different. Appropriate reference images are formed according to the conditions that restrict the upper limit, the density of these reference images is detected by an optical detection means, and toner replenishment is started and toner replenishment is performed according to the detection output and the two conditions. Performs stop control. At that time, conditions that restrict the lower limit of toner concentration,
Since the conditions that restrict the upper limit of toner density have a relatively wide allowable range, if the toner replenishment start condition and toner replenishment stop condition are different, the number of times a reference image for controlling toner density is formed can be reduced to the necessary minimum. However, it is possible to prevent fluctuations in image density and large fluctuations in toner density.

According to the second means, the condition for generating the toner replenishment start signal is set by the output of the density of the first reference image detected by the optical detection means, and the condition for generating the toner replenishment stop signal is set by the first reference image. By detecting the density of the reference image No. 2 by the optical detection means and setting it by output, the toner replenishment control means can start and stop toner replenishment according to the type of the reference image and the density conversion of the reference image. Take control.

According to the third means, the first reference image is formed as a solid image, and the second reference image is formed as a dot or line image, thereby adjusting the conditions for restricting the lower limit of toner density and toner density. The conditions under which the upper limit of the density is restricted are made clear, and since the width between the two is wide, it becomes possible to sufficiently control the toner density with the minimum number of times the reference image is formed.

According to the fourth means, the first reference image is formed by an image with an image area ratio of 80% or more, and the second reference image is formed by an image with an image area ratio of 60% or less. , like the third means, the conditions under which the lower limit of toner density is restricted and the conditions under which the upper limit of toner density is restricted are clarified, and similarly to the third means, the toner concentration can be sufficiently achieved with the minimum number of times of formation of the reference image. It becomes possible to perform control.

According to the fifth means, a warning is issued when the toner concentration is detected abnormally, and therefore, by displaying a warning display to call a serviceman, etc., it is possible to take immediate action against abnormal control. can.

[0017]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a toner density control device according to the present invention, FIG. 2 is a sectional view showing an image forming apparatus equipped with the toner density control device of FIG. 1, and FIG. 3 is a toner density control device of FIG. 1. FIG. 4 is an explanatory diagram showing a reference image used by the apparatus. FIG. 4 is a flowchart for explaining the operation of the toner density control apparatus of FIG.

First, the configuration and operation of the image forming apparatus will be explained with reference to FIG. For example, this image forming apparatus uses a negatively charged organic photoreceptor 9 as an image carrier, and uses a two-component developer containing negatively charged toner as a developer to reversely develop an electrostatic latent image. . The original image is illuminated by a light source 1, reflected by mirrors 2 to 4, and photoelectrically converted by an image reading unit 6 via a lens 5. After this read signal is electrically processed, a laser beam 7 corresponding to the image signal is emitted by a laser diode (not shown), and is scanned by a polygon mirror 8 in the main scanning direction (direction orthogonal to the drawing). The image is corrected so that it is scanned at a constant speed.

The photoreceptor 9 rotates in the clockwise direction (sub-scanning direction) in the figure, and its surface is charged to a uniform potential by a charger 10, and an electrostatic latent image is formed on the surface of the photoreceptor 9 by the laser beam 7. be done. This electrostatic latent image is visualized by applying toner by a developing device 11, and the toner image is transferred onto a sheet of paper by a transfer charger 12. The remaining toner on the photoreceptor 9 is removed by the cleaning unit 13, and the remaining charge is removed by the neutralizing lamp 14, and the above steps are repeated again.

In this case, the laser beam 7 for creating a reference image for toner density control is emitted outside the image forming area of the original image on the photoreceptor 9, and the electrostatic latent image is similarly developed by the developing device 11. Toner is applied and visualized, and its density is detected (described later). The toner image of the reference image is removed by the cleaning unit 13 without being transferred to the paper. Note that the paper is set in the cassette 15 on the right side of the figure and is conveyed to the transfer charger 12 by paper feed rollers 15a etc. After the toner image is transferred, the paper is transferred to the separation charger 1.
The toner image is separated from the photoreceptor 9 by a fixing unit 17 and then discharged.

Next, the structure and operation of the toner density control device will be explained with reference to FIG. The toner is agitated within the toner cartridge 111 by an agitator 112, and the amount thereof is controlled by a toner replenishing roller 113 to be replenished into a toner tank 114. Toner tank 11
The toner in 4 is agitated by an agitation roller 115 and transferred to a developing roller 117 by a conveyance screw 116.
The electrostatic latent image area of the photoreceptor 9 is adhered by the developing roller 117. The toner replenishment roller 113 is rotated by the drive device 23, and therefore, by controlling the toner replenishment roller 113, the amount of toner replenishment can be controlled.

Here, as described above, the toner image of the reference image for toner density control is formed by the laser beam 7 outside the image forming area of the original image on the photoreceptor 9. A (first) reference image in the form of a solid image and a (second) reference image in the form of dots or lines are formed as shown in FIGS. 3(a) to 3(d). The formation conditions for the reference image for the solid image are the same as for the original image.
For example, the dark area potential is -800V and the exposed area potential is -100V.
The toner is applied at a concentration of about 0.3 to 0.7 mg/cm to the photoreceptor 9 due to the potential difference with the developing bias of -450V.
Attach it on top. On the other hand, when forming a relatively coarse dot-like reference image as shown in FIG. 3(b), -450
The toner is attached by the potential difference with the developing bias of V,
Area ratio is approximately 25%, dot interval d2 = approximately 63.5 μm
A toner image is formed. Note that it is desirable that the reference image of a solid image has a toner image area ratio of 80% or more, and that the dot-shaped or line-shaped reference image has a toner image area ratio of 60% or more.
% or less, the intervals d1, d2, d3,
It is desirable that d4 is 30 to 300 μm.

In FIG. 1, the reflective density sensor 20 is composed of a light source for illuminating the photoreceptor 9 and an optical sensor that receives the reflected light and outputs a voltage V according to the intensity of the reflected light. There is. This voltage V is converted into a digital value by the A/D converter 21 and taken into the arithmetic unit 22,
As shown in FIG. 4, the computing device 22 controls the toner replenishing roller 113 via the drive device 23 based on this value,
Warn about abnormal conditions.

In FIG. 4, first, the density voltage VSG of the area where there is no toner image on the photoreceptor 9 is detected (step 1-
1) Next, it is determined whether this concentration is appropriate. If it is not appropriate, there is a high possibility that the density sensor 20 or photoreceptor 9 is abnormal, so the process branches to step 1-3 to display the abnormal state. If appropriate, the process proceeds to step 1-4 and subsequent steps, and the density voltage VSP1 of the solid image reference image and the density voltage VSP2 of the dot-shaped or line-shaped reference image are detected.

Next, it is determined whether or not toner is being replenished (steps 1-5), and if the determination is negative, step 1 is executed.
-6 and below, and in the case of an affirmative determination, the process branches to step 1-13 and below. In step 1-6, the ratio VSP1 /V
SG is compared with a reference value R1 that defines the lower limit of toner concentration for determining the start of toner replenishment, and if the ratio VSP1/VSG>reference value R1, the process proceeds to step 1-7. ratio VSP
If 1/VSG>reference value R1 is not satisfied, the density of the reference image of the solid image is normal, and thus the process ends. In step 1-7, the ratio VSP2 /VSG and the reference value R2 (<R
1), and the ratio VSP2 /VSG>Reference value R2
If not, the toner replenishment start condition and toner replenishment stop condition occur simultaneously, so the process branches to step 1-8 and an abnormal state is displayed. In the subsequent step 1-9, a transition is made to another replenishment mode, a quantitative toner replenishment mode.

In step 1-7, the ratio VSP2 /V
If SG>reference value R2, the process proceeds to step 1-10, and it is determined whether the remaining amount of toner is sufficient. If the remaining amount of toner is sufficient, the process proceeds to step 1-11 and the toner replenishing roller 1 is activated via the drive device 23 to replenish toner.
13, and if the remaining amount of toner is not sufficient, the process branches to step 1-12, and a message to that effect (toner end) is displayed.

If it is determined in step 1-5 that toner is being replenished, the ratio VS is determined in step 1-13.
Compare P2 /VSG and reference value R2, and find the ratio VSP2
/VSG>Reference value R2, the process branches to step 1-10 and continues toner replenishment. Ratio VSP2 /VS
If G>reference value R2 is not satisfied, a toner replenishment stop condition occurs, and after stopping toner replenishment in step 1-14, the process ends.

Therefore, according to the above embodiment, as shown in FIG. 5, toner replenishment is started based on the reference image and the reference value R1 of the solid image, which is adversely affected when the toner density becomes low, so that the formation of the reference image is prevented. Even if the number of times and frequency is reduced, the density of the image can be maintained. In addition, since toner replenishment is stopped based on the dot-like or line-like reference image and the reference value R2, which have an adverse effect when the toner density increases, the resolution and sharpness of the image can be improved even if the number and frequency of reference image formation is reduced. can be ensured. Therefore, the number of times a reference image is formed for toner density control,
The frequency can be reduced, and the quality of various images can be maintained stably for a long time.

Next, a second embodiment will be explained. Figure 6 is
7 is a flowchart for explaining the operation of the arithmetic device of the second embodiment, and in this embodiment, one type of reference image is used, and when the toner concentration becomes low, toner replenishment is started when the toner density becomes low. The replenishment start condition and the toner replenishment stop condition for stopping toner replenishment when a high toner concentration has an adverse effect are controlled to be different.

First, the density voltage VSG of the area where there is no toner image on the photoreceptor 9 is detected (step 2-1), and then,
It is determined whether this concentration is appropriate. If it is not appropriate, there is a high possibility that the density sensor 20 or photoreceptor 9 is abnormal, so the process branches to step 2-3 and an abnormal state is displayed. If it is appropriate, the process proceeds to step 2-4 and subsequent steps, and the density voltage VSP of one type of reference image is detected.

Next, it is determined whether or not toner is being replenished (step 2-5), and if the determination is negative, step 2 is executed.
The process proceeds to -6, and if the determination is affirmative, the process branches to step 2-10. In step 2-6, the ratio VSP/VSG is compared with the reference value R1 (>R2), and if the ratio VSP/VSG>reference value R1, the process proceeds to step 2-7. On the other hand, ratio VS
If P/VSG>reference value R1, the density of the reference image is normal, and the process ends. Step 2-7
Then, it is determined whether or not the remaining amount of toner is sufficient. If the remaining amount of toner is sufficient, the process proceeds to step 2-8 and the toner replenishing roller 11 is activated via the drive device 23 to replenish toner.
Control 3. If the remaining amount of toner is not sufficient, the process branches to step 2-9, and a message to that effect (toner end) is displayed.

[0032] Also, in step 2-10, the ratio VSP/V
Compare SG with a relatively high reference value R2, and calculate the ratio VSP/V
If SG>reference value R2, the process branches to step 2-7 to continue toner replenishment. On the other hand, the ratio VSP/VSG>
If it is not the reference value R2, a toner replenishment stop condition occurs, and the toner replenishment is stopped in step 2-11, and the post-processing is ended.

[0033] Therefore, in this embodiment as well,
In the case where a low toner density has an adverse effect, in other words, toner replenishment is started at the reference value R1 that defines the lower limit of toner density, so the number of times the reference image is formed,
Even if the formation frequency is reduced, image density can be maintained. Furthermore, in cases where high toner density has an adverse effect, in other words, toner replenishment is stopped at the reference value R2 that defines the upper limit of toner density, so even if the number and frequency of reference image formation is reduced, the image resolution remains and sharpness can be ensured. Therefore, it is possible to reduce the number and frequency of formation of reference images for toner density control, and it is also possible to stably maintain the quality of various images for a long time.

Note that step 2-6 and step 2 in FIG.
-7, the processes of steps 1-7 and 1-8 in FIG. 4 may be added to issue a warning when the toner replenishment start condition and toner replenishment stop condition occur simultaneously.

[0035]

As explained above, the invention according to claim 1, wherein the conditions for generating the toner replenishment start signal and the conditions for generating the toner replenishment stop signal of the toner replenishment amount control means are set to different conditions. According to the method, appropriate reference images are formed according to conditions that restrict the lower limit of toner density and conditions that restrict the upper limit of toner density, and the densities of these reference images are detected by optical detection means. , toner replenishment start and replenishment stop control can be performed according to the detection output and two conditions, so if the toner replenishment start condition and toner replenishment stop condition are different, the toner replenishment start and toner replenishment stop conditions can be controlled. The tolerance range for toner density control has been increased, making it possible to prevent fluctuations in image density and large fluctuations in toner density while minimizing the number of times a reference image is formed for toner density control. Quality can be maintained for a long time.

[0036] The latent image forming means and the developing means
The conditions for forming a second reference image, defining the lower limit of toner density, and generating a toner replenishment start signal are set based on the result of detecting the density of the first reference image by the optical detection means, and According to the invention according to claim 2, the condition for defining the upper limit of the density and generating the toner replenishment stop signal is set based on the result of detecting the density of the second reference image by the optical detection means. Since the toner replenishment control means controls the start and stop of toner replenishment according to the type and the density change of the reference image, stable quality can be maintained for a long time for various images.

[0037] The first reference image is converted into a second reference image by a solid image.
According to the invention as set forth in claim 3, wherein the reference image is formed by a dot image or a line image, the conditions for restricting the lower limit of toner density and the conditions for restricting the upper limit of toner density are made clear, and the conditions for restricting the upper limit of toner density are clarified. Since the width is large, it is possible to sufficiently control toner density with a minimum number of times of formation of the reference image, and stable quality can be maintained for a long time for various images.

The first reference image is an image with an image area ratio of 80% or more, and the second reference image is an image with an image area ratio of 60%.
According to the invention according to claim 4, in which the following images are respectively formed, the conditions under which the lower limit of toner density is restricted and the conditions under which the upper limit of toner density is restricted are clarified, and
Since the width between the two is large, it becomes possible to sufficiently control the toner density with a minimum number of times of forming the reference image, and it is possible to maintain stable quality for various images for a long time.

Conditions for generating a toner replenishment start signal;
Claim 5 further comprising display control means for displaying a warning when the conditions for generating the toner supply stop signal overlap.
According to the described invention, since a warning is issued when an abnormality occurs, it is possible to promptly deal with the abnormality that has occurred based on the display content displayed by the warning display means.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a toner density control device according to the present invention.

FIG. 2 is a sectional view showing an image forming apparatus equipped with the toner density control device of FIG. 1;

FIG. 3 is an explanatory diagram showing a reference image used by the toner density control device of FIG. 1;

FIG. 4 is a flowchart for explaining the operation of the toner density control device in FIG. 1;

FIG. 5 is a graph showing the relationship between the toner concentration in the developer and the density depending on the original image.

FIG. 6 is a flowchart for explaining the operation of a second embodiment of the toner density control device according to the present invention.

[Explanation of symbols]

7 Laser beam 9 Photosensitive drum 11 Developing device 20 Concentration sensor 22 Arithmetic device 113 Toner supply roller

Claims (5)

[Claims] 1. A latent image forming means for forming a reference latent image on an image bearing member by an optical writing system, a developing means for developing the latent image formed on the image bearing member, and a toner for the developing means. a toner replenishing means for replenishing the toner, an optical detecting means for detecting the density of the developed reference image, and controlling the amount of toner supplied from the toner replenishing means to the developing means according to the detection output detected by the optical detecting means In a toner concentration control device having a toner replenishment amount control means, a condition for generating a toner replenishment start signal and a condition for generating a toner replenishment stop signal of the toner replenishment amount control means are set to different conditions. A toner density control device characterized by: 2. Conditions for forming first and second reference images by the latent image forming means and developing means, defining a lower limit of toner concentration, and generating the toner replenishment start signal are based on the first reference image. The condition is set based on the result of detecting the density of the image by the optical detection means, defines the upper limit of the toner density, and generates the toner replenishment stop signal. 2. The toner concentration control device according to claim 1, wherein the toner concentration control device is set based on a result detected by. 3. The toner density control device according to claim 2, wherein the first reference image is a solid image, and the second reference image is one of a dot image and a line image. 4. The first reference image is an image with an image area ratio of 80% or more, and the second reference image is an image with an image area ratio of 60% or less. 2. The toner density control device according to 2. 5. The apparatus further comprises display control means for displaying a warning when the condition for generating the toner replenishment start signal and the condition for generating the toner replenishment stop signal overlap. The toner concentration control device according to claim 1.