JPH086375A - Toner density control device for image forming device - Google Patents

Abstract

PURPOSE:To properly maintain the toner density in a developer invariably by controlling the toner density in the developer of a developing device based on the difference between the temperatures of a fixing section before and after the paper passes through the fixing section. CONSTITUTION:The paper is fed to a fixing device from a paper feed cassette, and the temperature before the paper passes through the fixing device is received from a thermistor 34 and stored in a RAM 42 as the pre-transit temperature T1. A toner image is formed on the paper by a transfer device, and the formed toner image is heated and fixed by the fixing device. The temperature after the paper passes through the fixing device is received from the thermistor 34 and stored in the RAM 42 as the post-transit temperature T2. A controller 40 calculates the difference between the pre-transit temperature T1 and the post-transit temperature T2 and refers to a temperature control table stored in a ROM 41 based on the result. The toner density control is corrected based on the detection signal of a toner density detection section 29 according to the obtained value of the temperature control table.

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 a developing device for electrostatically adhering toner onto a photoconductor using a developer containing toner,
The present invention relates to a toner density control device of an image forming apparatus having a fixing unit that heats and fixes a toner image formed on a sheet of paper.

[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 temperature, it is necessary to correct the detected toner density value based on the temperature inside the image forming apparatus. For this purpose, it is necessary to provide a temperature sensor for detecting the temperature inside the image forming apparatus, which increases the number of parts and makes it difficult to reduce the cost.

An object of the present invention is to set the toner concentration in the developer to a proper value according to the temperature inside the machine without specially providing a temperature detecting means in order to measure the temperature inside the machine inside the image forming apparatus. It is in.

[0006]

A toner density control device for an image forming apparatus according to the present invention comprises a temperature detection means and a toner control means. The temperature detecting means detects the temperature of the fixing unit. The toner control unit controls the toner density in the developer of the developing device based on the temperature difference between the fixing unit before and after the sheet passes through the fixing unit.

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 density in the developer is based on the toner density detecting signal. Can be configured to control Further, the toner control means is provided with a temperature control table based on a temperature difference before and after the sheet passes through the fixing portion, and the toner concentration in the developer can be controlled according to the temperature control table. .

The temperature detecting means is preferably a thermistor.

[0009]

In the toner density control device of the image forming apparatus according to the present invention, the temperature of the fixing portion is detected by the temperature detecting means.
Of these, the in-machine temperature of the image forming apparatus is calculated based on the temperature difference between the fixing unit before and after the sheet passes through the fixing unit. The toner control means controls the toner concentration in the developer of the developing device based on the calculated temperature inside the image forming device.

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. The toner concentration detection signal can be corrected based on the in-machine temperature to properly control the toner concentration in the developer. The toner control unit has a temperature control table based on the temperature difference before and after the sheet passes through the fixing unit, and is configured to control the toner concentration in the developer according to this temperature control table. In addition, it is possible to quickly respond to changes in the temperature inside the image forming apparatus, and it is possible to always maintain the toner concentration in the developer at an appropriate value.

When the temperature detecting means is composed of a thermistor provided to maintain the fixing portion at an appropriate temperature, the number of parts of the image forming apparatus can be reduced and the manufacturing cost can be reduced. It will be possible.

[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, a paper discharge conveyance path 10 is provided between the image forming unit and the paper discharge tray 6.
A fixing device 16 and a discharge roller 17 for fixing the transferred image on the sheet are arranged. The fixing device 16 includes a heat roller 31 having a heater 32 therein, and the heat roller 31.
And a pressure roller 33 that can be pressed against. 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. Next, the operation of this embodiment will be described with reference to the flowchart 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 temperature inside the copying machine main body 1 is room temperature (20 ° C.), 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. In step S6, at this time (paper is fixed in the fixing device 1
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 control table stored in the ROM 41 is referred to based on the calculation result in step S10. In step S12, based on the temperature control table referenced in step S11, the toner concentration detecting unit 2
The toner density control is corrected based on the detection signal of No. 9. After this, the process returns to step S2. If the print key is not operated in step S2, another process is executed in step S13 and the process proceeds to step S2.

Reference was made in step S11 of FIG.
An example of the temperature control table is shown in FIG. Paper is fixed in the column
Temperature data of the thermistor 34 before passing through the fixing device 16
(Temperature before passage T₁), And the column indicates that the sheet is the fixing device 16
Data of the thermistor 34 after passing through the
Degree T₂). Column is temperature T before passage₁And temperature after passing T
₂Temperature difference (T₁-T₂) Is shown. Column is column
Temperature difference before and after passage (T₁-T₂), The developing device 1
To maintain the toner density within 0 properly, toner density detection
It is a control value of the detection signal of the unit 29. In this figure,
Temperature difference between before and after (T₁-T₂The smaller the value of), the copying machine
The temperature inside the main body 1 is high, and the temperature difference (T₁-T
₂It is considered that the larger the value of), the lower the temperature inside the machine. This
The toner concentration detection unit 29 used here is configured to determine the toner concentration.
The output characteristics vary depending on the temperature, as shown in Fig. 5.
Turn into. Therefore, (A), (B), shown in FIG.
In the case of (C) and (D), the control shown in each column
By setting it as a control value, the toner density in the developing device 10 can be adjusted appropriately.
It can be kept at the value (3% in this case).

[0022]

In the toner density control device of the image forming apparatus according to the present invention, the developing device is based on the temperature difference between the fixing unit before and after the sheet detected by the temperature detecting unit passes through the fixing unit. The toner concentration in the developer is controlled. Therefore, it is possible to control the toner density to an appropriate value based on the temperature inside the image forming apparatus. Further, since the temperature detecting means for detecting the temperature of the fixing portion is used,
The number of parts and cost can be reduced.

The toner control means has a temperature control table based on the temperature difference before and after the sheet passes through the fixing section, and the toner concentration in the developer is controlled according to this temperature control table. When configured, it is possible to quickly respond to changes in the temperature inside the image forming apparatus, and it is possible to always maintain the toner concentration in the developer at an appropriate value.

When the temperature detecting means is composed of a thermistor provided to maintain the fixing portion at an appropriate temperature,
The number of parts of the image forming apparatus can be reduced, and the manufacturing 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 temperature control table.

[Explanation of symbols]

 10 Developing Device 16 Fixing Device 27 Toner Replenishing Roller 28 Stepping Motor 29 Detection Unit 31 Heat Roller 32 Heater 33 Pressure Roller 34 Thermistor

Claims (4)

[Claims] 1. An image having a developing device for electrostatically adhering the toner onto a photoconductor using a developer containing toner, and a fixing portion for heating and fixing the toner image formed on the paper onto the paper. A toner concentration control device of a forming device, comprising: a temperature detecting unit that detects a temperature of the fixing unit; and a developing unit of the developing device based on a temperature difference between the fixing unit before and after the sheet passes through the fixing unit. A toner concentration control device for an image forming apparatus, comprising: a toner control unit that controls a toner concentration in a developer. 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 temperature control table based on a temperature difference before and after the sheet passes through the fixing section, and controls the toner concentration in the developer according to the temperature control table. The toner concentration control device for an image forming apparatus according to claim 2. 4. The toner density control device for an image forming apparatus according to claim 1, wherein the temperature detecting means is a thermistor.