JP3400542B2 - Toner density control device for image forming apparatus - Google Patents

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 image forming apparatus, and more particularly to an image forming apparatus having a developing device for electrostatically adhering toner onto a photoconductor using a developer containing toner. The present invention relates to a toner concentration control device.

[0002]

2. Description of the Related Art For example, an image forming apparatus such as a copying machine is provided with a developing device for adhering toner to an electrostatic latent image formed on the surface of a photosensitive drum to visualize the electrostatic latent image.
As a developer used in a developing device, a two-component developer including a toner and a magnetic carrier has been widely used. In such an apparatus, the mixing ratio of the toner and the carrier (toner concentration) is an important factor from the viewpoint of developing effect. That is, when the toner density is below the proper value, the image density becomes low, and when the toner density is above the proper value, so-called fog occurs.

Therefore, in order to obtain a good image, it is necessary to accurately detect the toner density and control the toner density to an appropriate value. As a structure for detecting the toner concentration, a magnetic sensor for detecting a change in magnetic permeability in the developer has been conventionally used. This magnetic sensor is provided on the inner surface of the container having the toner supply port, detects the magnetic force in the developer flowing out, and outputs a detection signal as a toner concentration value. Toner replenishment is controlled so that the detection signal of the magnetic sensor reaches a predetermined value, and the toner concentration in the developer is controlled.

[0004]

Since the output characteristics of the magnetic sensor as described above change depending on the humidity, it is necessary to correct the detected toner density value based on the humidity inside the image forming apparatus. In the conventional image forming apparatus, the toner density of the developing device is not controlled based on the humidity inside the machine, and there is a problem that the density of the image formed on the paper cannot be properly maintained due to the change in humidity. It was

An object of the present invention is to set the toner concentration in the developer to an appropriate value based on the internal humidity in the image forming apparatus.

[0006]

A toner density control device for an image forming apparatus according to the present invention comprises a humidity detection means and a toner control means. The humidity detecting means detects the humidity inside the image forming apparatus. The toner control unit controls the toner concentration in the developer of the developing device based on the humidity in the image forming apparatus.

Here, the toner control means includes a toner density detecting means for detecting a toner density contained in the developer and outputting a toner density detecting signal, and the toner in the developer is based on the toner density detecting signal. It can be configured to control the concentration. Further, the toner control means is provided with a humidity control table based on the humidity detected by the humidity detection means, and the toner concentration in the developer can be controlled according to the humidity control table.

Further, the image forming apparatus includes a fixing section for heating and fixing the toner image formed on the sheet onto the sheet, the humidity detecting section detects the temperature of the fixing section, and the first temperature detecting section, and the image forming apparatus. Second temperature detecting means for detecting a temperature other than that of the fixing portion, and the second temperature detection and the temperature difference of the fixing portion before and after the sheet passes through the fixing portion, which is obtained by the first temperature detecting means. The humidity may be calculated based on the temperature detected by the means.

[0009]

In the toner density control device of the image forming apparatus according to the present invention, the humidity inside the image forming apparatus is detected by the humidity detecting means. The toner control unit controls the toner concentration in the developer of the developing device based on the humidity inside the image forming apparatus detected by the humidity detecting unit.

When the toner control means includes a toner density detecting means and is configured to control the toner density in the developer based on the toner density detecting signal output from the toner density detecting means, the above-mentioned image forming apparatus is used. It is possible to correct the toner concentration detection signal based on the internal humidity and appropriately control the toner concentration in the developer. If the toner control means has a humidity control table and is configured to control the toner concentration in the developer according to this humidity control table, it is possible to quickly respond to changes in humidity inside the image forming apparatus. It is possible to maintain the toner concentration in the developer at an appropriate value at all times.

The humidity detecting means comprises a first temperature detecting means for detecting the temperature of the fixing portion of the image forming apparatus and a second temperature detecting means for detecting the temperature of the portion other than the fixing portion. When the humidity is calculated based on the temperature difference of the fixing unit before and after the sheet passes through the fixing unit and the temperature detected by the second temperature detecting unit,
It is possible to accurately detect the humidity inside the image forming apparatus, and it is possible to use a temperature detecting means such as a thermistor provided to maintain the fixing unit at an appropriate temperature, and to reduce the number of parts. Therefore, the manufacturing cost can be reduced.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a copying machine in which a toner density control device is adopted as an embodiment of the present invention. In FIG. 1, a document table 2 is fixed to the upper surface of a copying machine body 1, and a document holder 3 is provided on the document table 2 so as to be openable and closable. On the right side of the copying machine main body 1 in the drawing, the paper feed cassette 4,
5 is detachably attached. On the left side of the copying machine main body 1 in the drawing, a paper discharge tray 6 for discharging copied paper is mounted.

An exposure device 7 for reading a document is provided in the upper part of the inside of the copying machine main body 1.
The exposure device 7 is composed of a light source, a mirror, a lens and the like. A photoconductor drum 8 on the surface of which an electrostatic latent image is formed is arranged in the center of the copying machine body 1.
Around the photosensitive drum 8, a charging device 9 and a developing device 1 are provided.
0, the transfer device 11, the paper separating device 12, and the cleaning device 13 are arranged in this order.

Between the paper feed cassettes 4 and 5 and the image forming portion constituted by the photoconductor drum 8 and the like, a paper feed transport path 14 for feeding paper is provided. Further, between the image forming unit and the paper discharge tray 6, a paper discharge conveyance path 15, a fixing device 16 for fixing the transfer image on the paper, and a discharge roller 17 are arranged. The fixing device 16 includes a heat roller 31 having a heater 32 therein and a pressure roller 33 that can be pressed against the heat roller 31. Further, a thermistor 34 is provided adjacent to the heat roller 31, by which the surface temperature of the heat roller 31 is measured.

FIG. 2 is a diagram showing details of the developing device 10 and the toner density control device thereof. In the developing container 20 that constitutes the developing device 10, a developer including toner and carrier is stored. The toner and the carrier are frictionally charged by being agitated with each other, and have charges of opposite polarities. In this example, the toner has a negative charge,
The carrier has a + charge. As the carrier, a carrier having a high resistance such as a resin-coated ferrite carrier or a binder-based carrier made of a resin is used, so that counter charge (+ charge remaining in the carrier after toner development) is difficult to flow. ing.

Further, inside the developing container 20, a developing sleeve 21 facing the surface of the photosensitive drum 8 with a predetermined gap, a stirring roller 22 for conveying the developer to the developing sleeve 21, and a developing device A spiral 23 for stirring and mixing the developer in the container 20 is arranged. Inside the developing sleeve 21, a magnet roller 36 for raising the carrier is provided. Above the developing sleeve 21, a doctor blade 24 that regulates the height of the surface of the developing sleeve 21 is provided. A partition plate 25 for guiding the developer scraped off by the doctor blade 24 onto the spiral 23 is provided above the stirring roller 22.

A hopper 26 containing replenishment toner is fixed to the upper portion of the developing container 20. At the bottom of the hopper 26, a toner replenishing roller 27 for replenishing the developing container 20 with toner is mounted. A stepping motor 28 is connected to the toner supply roller 27. A detection unit 29 for detecting the toner concentration is provided in the developing container 20. The detection unit 29 is
It is composed of a magnetic sensor and the like, for example, the photosensitive drum 8
The photosensitive drum 8 is provided directly below the portion where the developing roller 21 and the developing roller 21 face each other.
It is provided at a position where the developer at the contact portion with passes through. The detection unit 29 outputs a detection signal as a toner density value based on the charge amount of the toner consumed in a certain time.

Further, the copying machine main body 1 is provided with a control section 40 shown in FIG. The control unit 40 includes a CPU,
It is composed of a microcomputer system including RAM, ROM, various drivers and various IOs. The control unit 40 has a ROM 41 in which a control program, a reference table, etc. are stored, and RA in which various operation data are temporarily stored.
M42 is connected. A thermistor 34 that measures the surface temperature of the heat roller 31 is connected to the control unit 40. The heater driver 43 connected to the control unit 40 is
The heater 32 is controlled according to the temperature data input from the thermistor 34.

The control section 40 is further connected to a toner concentration detecting section 29 provided in the developing container 20 and a stepping motor 28 for supplying toner into the developing container 20. In addition, the controller 40 includes a second thermistor 44 mounted on the substrate on which the controller 40 is placed.
Are connected. The second thermistor 44 is the fixing device 3.
The temperature inside the image forming apparatus other than 1 is measured.

Next, the operation of this embodiment will be described with reference to the flow chart shown in FIG. In step S1, various parameters are initialized. In step S2, it is determined whether the print key has been operated. If the print key is operated, the process proceeds to step S3. In step S3, the toner from the developing device 10 is attached to the electrostatic latent image formed on the photosensitive drum 8. In step S4, the toner density flowing out from the developing device 10 is detected by the toner density detecting unit 29, and control is performed so that the toner density becomes appropriate. Generally, the optimum toner density is about 3%. Assuming that the internal humidity in the copying machine main body 1 is normal (70%), the detection signal (v) of the toner density detecting unit 29 used here and the toner density (T / D%) in the developing container 20 are used. The relationship is as shown in FIG. Therefore, by controlling the stepping motor 28 so that the detection signal of the toner concentration detecting section 29 becomes 2.5V, the toner concentration in the developing container 20 can be maintained at 3%.

In step S5, the paper is fed from one of the paper feed cassettes 4 and 5 and is fed to the photosensitive drum 8 side. At step S6, at this time
The temperature (before passing 6) is taken in from the thermistor 34 and stored in the RAM 42 as the temperature before passing T ₁ . In step S7, a toner image is formed on the sheet by the transfer device 11, and the formed toner image is heated and fixed by the fixing device 16. Further, in step S8, the discharge roller 17 discharges the paper to the paper discharge tray 6. At this time in step S9 (after the sheet passes through the fixing device 16)
Temperature is taken in from the thermistor 34, and the temperature T after passing
₂ is stored in the RAM 42. In step S10, the difference between the temperature T ₁ before passing and the temperature T ₂ after passing is calculated. In step S11, the temperature of the second thermistor 43 is read as the in-machine temperature T ₃ of the image forming apparatus, and the humidity is calculated. In step S12, the humidity control table stored in the ROM 41 is referred to based on the calculation result in step S11. In step S13, the toner concentration control based on the detection signal of the toner concentration detecting unit 29 is corrected based on the humidity control table referenced in step S12.
After this, the process returns to step S2. If the print key is not operated in step S2, another process is executed in step S14 and the process proceeds to step S2.

The humidity calculation in step S11 of FIG. 4 can be obtained from the table shown in FIG. 7 shows an example of the humidity control table referred to in step S12. That is, the control value of the toner density detecting unit 29 is corrected according to the humidity (%) obtained from the table of FIG. The output characteristic of the toner density detecting unit 29 used here changes as shown in FIG. 5 depending on the level of humidity. That is, from the one with the highest humidity to the one shown in FIG.
It changes in the order of (B), (C), and (D). Therefore, by correcting the control value of the toner concentration detecting unit 29 as shown in FIG. 7 based on the obtained humidity in the machine, an appropriate toner concentration value (in this case, 3%) can be maintained. [Other Embodiments] It is also possible to provide a humidity sensor in the copying machine main body 1 and control the toner density according to the output of the humidity sensor.

[0023]

In the toner concentration control device of the image forming apparatus according to the present invention, the toner control means controls the toner concentration in the developer of the developing device based on the humidity detected by the humidity detecting means. Variation in image density due to humidity inside the forming apparatus is eliminated. In addition, it becomes possible to quickly respond to changes in humidity inside the image forming apparatus.

When the toner control means includes a toner density detecting means and is configured to control the toner density in the developer based on the toner density detecting signal output from the toner density detecting means, this toner density detecting signal The toner concentration in the developer can be properly controlled by correcting the toner concentration control based on the value based on the humidity inside the image forming apparatus. When the toner control unit has a humidity control table based on the humidity detected by the humidity detection unit, and is configured to control the toner concentration in the developer according to this humidity control table, the toner control unit in the image forming apparatus is It is possible to quickly respond to changes in humidity, and it is possible to always maintain the toner concentration in the developer at an appropriate value.

Further, when the humidity is calculated by using the first temperature detecting means for detecting the temperature of the fixing portion and the second temperature detecting means for detecting the temperature other than the fixing portion, the inside of the image forming apparatus is Humidity can be detected accurately, the number of parts can be reduced, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a copying machine to which an embodiment of the present invention is applied.

FIG. 2 is a configuration diagram of the developing device.

FIG. 3 is a control block diagram thereof.

FIG. 4 is a control flowchart thereof.

FIG. 5 is an output characteristic diagram of a toner density detection unit.

FIG. 6 is a diagram showing an example of a humidity table.

FIG. 7 is a diagram showing an example of a humidity control table.

[Explanation of symbols]

10 Development device 16 Fixing device 27 Toner supply roller 28 Stepping motor 29 Detector 31 heat roller 32 heater 33 Pressure roller 34 Thermistor

Claims (3)

(57) [Claims] 1. A toner concentration control device for an image forming apparatus, comprising a developing device for electrostatically adhering the toner onto a photoconductor using a developer containing toner, wherein the humidity in the image forming device is controlled. Humidity detecting means for detecting, toner control means for controlling the toner concentration in the developer of the developing device based on the humidity inside the image forming apparatus , and fixing for heating and fixing the toner image formed on the paper on the paper.
Comprising a part, the said humidity detecting means, second detecting a temperature of the fixing unit 1
Temperature detecting means and temperature other than the fixing portion of the image forming apparatus
And a second temperature detecting means for detecting
Before the paper passes through the fixing unit, which is obtained by the output means
And the temperature difference of the fixing unit after passing and the second temperature detection
A toner concentration control device for an image forming apparatus , which calculates humidity based on the temperature detected by the means . 2. The toner control means includes a toner density detecting means for detecting a toner density contained in the developer and outputting a toner density detecting signal, and the toner density detecting means outputs the toner density detecting signal based on the toner density detecting signal. The toner concentration control device for an image forming apparatus according to claim 1, wherein the toner concentration control device controls the toner concentration. 3. The toner control means has a humidity control table based on the humidity detected by the humidity detection means, and controls the toner concentration in the developer according to the humidity control table. Toner density control device for image forming apparatus.