JPH09160427A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent image quality independently of the density of an image to be formed. SOLUTION: This device is provided with a transfer means 3 for consecutively transferring toner images onto orienting papers P traveling on a carrying path R, a heating roller 5a for heating toner T on the printing papers P, a pressure roller 5b in contact with the heating roller 5a, a power source 9 for supplying power to the heating roller 5a and a main control part 7 for adjusting a current from the power source 9 to the heating roller 5a and transmitting image information to the transfer means 3. At this time, the main control part 7 is provided with a current varying control function for controlling the supplying of the current to the heating roller 5a, in accordance with the density of an image obtained from the image information.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus using toner as a medium such as a printer, a copying machine or a facsimile.

[0002]

2. Description of the Related Art Conventionally, there have been the following electrophotographic image forming apparatuses. That is, the image forming apparatus includes a transfer unit that transfers a toner image onto a print sheet, a fixing unit that heat-fixes the toner on the print sheet, and a power supply that supplies a current to a heating roller provided in the fixing unit. Is equipped with.

The power switch of the image forming apparatus is turned off.
When set to N, a predetermined current is supplied from the power source to the heating roller, and the heating element inside the heating roller generates heat. This allows
Ready for heat fixing. However, at this stage, the heating roller is preheated as a preparation for thermal fixing.

Subsequently, when the image forming process is started, a larger amount of electric current is supplied to the heating element in the heating roller to generate heat necessary for heat fixing. Then, the printing paper that has traveled on the conveyance path is sandwiched between the heating roller and the pressure roller that constitute the fixing device, receives predetermined heat and pressure, the toner is melted, and the printing paper is pressed against the printing paper. To be done.
This completes a series of steps.

[0005]

However, the above-mentioned conventional example has the following inconveniences. That is, in the conventional image forming apparatus, the fixing is always performed at a constant temperature regardless of the density of the image to be formed. Here, when the image density is high, that is, in an image with a large amount of toner on the printing paper, the heat capacity is correspondingly increased, and a large amount of heat is required for fixing. Therefore, if fixing is performed at a constant temperature, there is a problem that fixing failure occurs.

On the other hand, since an image having a low image density has a small heat capacity, when fixing at a constant temperature as described above,
This gives an excessive amount of heat, which also causes curling and wrinkling of the printing paper. Further, since the amount of heat suitable for the heat capacity is not given, there is a disadvantage that it is inefficient in terms of power consumption.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of improving the disadvantages of the conventional example and, in particular, providing good image quality without depending on the density of the image to be formed. , And its purpose.

[0008]

In order to achieve the above-mentioned object, according to the invention of claim 1, a transfer means for continuously transferring a toner image onto a print sheet running on a conveying path, and a print sheet. A heating roller that heats the upper toner, a pressure roller that is in contact with the heating roller, a power supply that supplies power to the heating roller, a current from the power supply to the heating roller is adjusted, and image information is transmitted to the transfer unit. In the image forming apparatus including the main control unit, the main control unit has a variable current control function for controlling the supply of current to the heating roller according to the density of the image obtained from the image information. There is.

With the above configuration, first, the image density of the image formed by the main controller is determined. And
A fixing temperature corresponding to the determined image density is selected. At this time, a temperature sensor is arranged on the surface of the heating roller, and the temperature information is always transmitted to the main controller.

From the above, if the actual temperature of the heating roller is lower than the selected reference temperature value, the main controller controls to supply a large amount of electric power from the power source. On the other hand, when the actual temperature is higher than the reference value, the current supply is reduced or stopped to control the temperature appropriately.

According to the second aspect of the present invention, the transfer means for continuously transferring the toner image onto the printing paper running on the conveying path, the heating roller for heating the toner on the printing paper, and the heating roller. In the image forming apparatus, a pressure roller in contact with the heating roller, a power source for supplying electric power to the heating roller, and a main control section for adjusting the current from the power source to the heating roller and transmitting image information to the transfer means are provided. An image density detecting means for detecting the image density of the toner image on the printing paper is provided on the upstream side of the heating roller in the path, and the main control section controls the current to the heating roller based on the detection value of the image density detecting means. It has a configuration that has a variable current control function for controlling supply.

Further, in the invention described in claim 3, when the image density is large, the main controller controls the increase of the current supplied to the heating roller, and the other structure is defined in claim 1 or 2. It is similar to the invention.

[0013]

An embodiment of the present invention will be described with reference to the drawings.

First, in FIG. 1, the image forming apparatus 1 is
A transfer unit 3 for continuously transferring a toner image onto the print paper P traveling on the transport path R, and a toner T on the print paper P.
A heating roller 5a for heating the heating roller 5a, a pressure roller 5b in contact with the heating roller 5a, a power source 9 for supplying electric power to the heating roller 5a, a current from the power source 9 to the heating roller 5a, and a transfer unit 3 for controlling the current. And a main control unit 7 for transmitting image information. Then, the main controller 7 has a current variable control function of controlling the supply of current to the heating roller 5a according to the density of the image obtained from the image information.

To explain the above in detail, as shown in FIG. 1, the transfer means 3 is arranged in the upper region of the substantially central portion of the image forming apparatus main body 1a. And this transfer means 3
A toner storage chamber 11 that stores the toner T and a developing roller 13 that receives the toner T from the toner storage chamber 11 and transmits the toner T to a developing unit are provided. Furthermore,
A photoconductor 15 is arranged near the developing roller 13.

A predetermined charger (not shown) is provided near the surface of the photoconductor 15. This charger is for uniformly charging the entire surface of the photoconductor 15. Therefore, the length of the photosensitive member 15 is substantially the same as the length of the cylindrical photosensitive member 15. In addition, a predetermined blade (not shown) is provided in the vicinity of the photoconductor 15 in contact with the surface of the photoconductor 15. This blade is for photoreceptor 1
It is for scraping off the toner that has not been used and remains on the surface of No. 5, and is set to generate a predetermined contact pressure.

A predetermined exposure device (not shown) is arranged above the transfer means 3. This exposure device is for forming an electrostatic latent image on the surface of the photoconductor 15, and is adapted to generate laser light according to the image to be formed.

On the other hand, the photosensitive member 15 in the lower region of the transfer means 3
A transfer roller 23, which is in contact with the surface of the photoconductor 15, is disposed at a position opposed to. The transfer roller 23 is for applying a predetermined pressure to transfer the toner T onto the surface of the conveyed printing paper P, and is also formed in a cylindrical shape. The space between the photoconductor 15 and the transfer roller 23 is configured as a part of the conveyance path R of the print paper P.

In the vicinity of the transfer means 3 (on the left side in FIG. 1),
A predetermined fixing device 5 is arranged in a height region approximately the same as the photoconductor 15 and the transfer roller 23. The fixing device 5 is for fixing the toner image transferred onto the printing paper P on the printing paper P by heat and pressure, and is composed of a heating roller 5a and a pressure roller 5b. And
The print sheet conveyance path R is provided between the rollers 5a and 5b.
It is formed as.

Here, the heating roller 5a is formed to have a length substantially the same as that of the photoconductor 15 and the transfer roller 23, and the halogen lamp 5c is provided therein. The halogen lamp 5c is for heating the heating roller 5a from the inside, and is connected to a power source 9 described later. However, the heat source is not limited to the halogen lamp 5c, and may be a heating wire or a ceramic heater.

The heating roller 5a will be described in more detail. The heating roller 5a is made of a cylindrical aluminum material, and the outer peripheral surface of the heating roller 5a is coated with a fluororesin. This is to prevent the melted toner from adhering to the surface when the toner T is melted.

Further, a rotary shaft (not shown) is provided at both ends of the heating roller 5a in the longitudinal direction, and the rotary shaft is supported by a bearing portion (not shown) of the image forming apparatus main body 1a. Thus, the heating roller 5a is adapted to rotate.

Inside the heating roller 5a, the predetermined halogen lamp 5c is arranged as described above. The halogen lamp 5c is connected to the power source 9 and emits light when power is supplied to heat the heating roller 5a from the inside. Then, this heat melts the toner T. Further, a predetermined temperature sensor 17 is arranged near the heating roller 5a. This temperature sensor 17
This is for detecting the surface temperature of the heating roller 5a.

Further, the above-mentioned predetermined power source 9 is provided inside the apparatus main body 1a. The power source 9 is connected to the halogen lamp 5c described above, and supplies a necessary current each time in response to a command signal from the main controller 7. Further, the main control unit 7 receives the temperature information from the temperature sensor 17 and simultaneously outputs a desired image signal to the transfer unit 3. Here, the image signal is information of an image to be transferred onto the printing paper P, and
It is created by the main control unit 7 based on a signal from a host machine (not shown).

On the other hand, the pressure roller 5b is for pressing the printing paper P as described above, but to be exact,
The pressure is generated in cooperation with the heating roller 5a. The pressure roller 5b is made of a heat resistant material so that its properties and strength are not changed by the heat of the heating roller 5a.

Further, as shown in FIG. 1, the image forming apparatus 1
A predetermined opening 25 is provided at one end (the right end in the drawing) of
Is formed and communicates with a paper stocker that stores printing paper P before printing. In addition, a pick roller for taking the print paper P into the print paper transport path R of the apparatus main body 1a is disposed in the opening 25. On the other hand, a predetermined opening 29 is formed at the other end of the image forming apparatus 1 (the left end in the figure), and a paper stacker for storing the printed paper is arranged outside the opening 29.

The operation and function of the image forming apparatus 1 configured as described above will be described. The photoconductor 15 in the transfer means 3 described above rotates clockwise with the start of printing operation. Then, the surface is uniformly charged by the charger,
An electrostatic latent image corresponding to the image formed by the exposure device is formed.

Here, the electrostatic latent image is created by the main controller 7 in response to a command from the host machine as described above. For this reason,
The main controller 7 can recognize the density of the image to be formed. That is, it is possible to judge how much toner is transferred onto the printing paper P. Thereby, the main control unit 7 variably controls the amount of current supplied from the power supply 9 to the halogen lamp 5c depending on the size of the image density.

Explaining a concrete control method, the main control section 7 stores a plurality of reference values of the image density. In this embodiment, three reference values are stored. Then, the value of the supplied power corresponding to each image density is also stored. If the image density is high, the power supply is increased, while if the image density is low, the power supply is reduced. Therefore, when the density of the image created by the signal from the host machine is high, that is, when a large amount of toner is transferred to the printing paper P, a correspondingly large current is supplied to the halogen lamp 5c. On the other hand, when the image density is low, less electric power is supplied to the halogen lamp 5c.

In parallel with the above, the predetermined opening 2
The printing paper P is taken into the image forming apparatus main body 1 a from the sheet 9. Then, the photosensitive member 1 is moved along the print sheet conveyance path R.
Come to position 5. The printing paper P that has reached the photoconductor 15 is
The toner image on the surface of the photoconductor 15 is transferred onto the printing paper P by being sandwiched between the photoconductor 15 and the transfer roller 23. And
As the photoconductor 15 rotates, the toner image is transferred onto the entire surface of the print paper P, and subsequently, is transferred to the fixing device 5 disposed on the downstream side of the print paper transfer path R. At this time, the photoconductor 15 after the toner T is transferred is
The toner that remains slightly above is cleaned by the blade 19.

The printing paper P conveyed to the fixing device 5 is heated by a heating roller 5a and a pressure roller 5b which applies a predetermined pressure to the printing paper P in cooperation with the heating roller 5a.
Sandwiched between each other. Then, the heat of the heating roller 5a melts the toner on the printing paper P, and the pressure roller 5b makes the toner adhere to the printing paper P closely.

At this time, the main control section 7 transmits the necessary power to the halogen lamp 5c according to the density of each image.
There is no inconvenience such as unfixed toner or supply of a large amount of unnecessary current.

Next, another embodiment will be described with reference to FIG. 2. An image forming apparatus 21 according to this embodiment will be described.
Are common to the above-mentioned image forming apparatus 1 and its basic constituent elements. However, in the present embodiment, the image forming apparatus 21 is equipped with the image density detecting means 19 for detecting the image density of the toner image on the printing paper P on the upstream side of the heating roller 5a in the transport path R, and Main control unit 7
However, the supply of electric current to the heating roller 5a is controlled based on the detection value of the image density detecting means 19.

To explain the above in detail, as shown in FIG. 2, on the downstream side of the transfer means 3 on the conveying path R and at the fixing device 5.
A predetermined image density detecting means 19 is disposed on the upstream side of the. The image density detecting means 19 includes a light emitting means (not shown) for irradiating the surface of the printing paper P with the light L, and a light receiving means for receiving the light reflected from the printing paper P.

When the image forming process is started, the light emitting means irradiates the printing paper P with the light L. Then, the light receiving means detects the reflected light to detect the image density. That is, when the image density is high, the surface of the printing paper P is covered with the toner, so the amount of reflected light is small. On the other hand, when the image density is low, a lot of white background is left on the surface, and a lot of light is reflected. This makes it possible to determine the size of the image density.

In the present embodiment, the main controller 7 controls the print paper P
Is also monitored, and electric power to the halogen lamp 5c is controlled with a delay of a predetermined time from the detection of the image density detecting means 19. This is the image density detection means 19
This is because it takes a predetermined time to detect the surface of the printing paper P and actually reach the position of the heating roller 5a of the fixing device 5. As a result, the fixing temperature is flexibly controlled according to the change in the image density even on one sheet of printing paper P.

[0037]

As described above, according to the present invention, the current supply to the heating roller is variably controlled according to the size of the image density. Therefore, when the image density is high, sufficient current is supplied to the heating roller, and sufficient fixing strength can be maintained even in high-density images. On the other hand, when the image density is small, the supply of the electric current is suppressed to the required amount, so that the curl or wrinkle is not generated in the printing device. Further, there is also an excellent effect that the power consumption can be suppressed while fixing is surely performed.

Further, since the image density of each part on the printing paper can be detected at all times and the temperature of the heating roller can be optimally controlled for each part, the fixing quality of the image can be improved and at the same time, further power consumption is reduced. The excellent effect that suppression can be realized is produced.

[Brief description of the drawings]

FIG. 1 is a side sectional view with a part omitted showing an embodiment of the present invention.

FIG. 2 is a partially omitted side sectional view showing another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming apparatus 1a Image forming apparatus main body 3 Transfer means 5 Fixing device 5a Heating roller 5b Pressure roller 7 Main controller 9 Power supply 19 Image density detecting means R Printing paper transport path T Toner

Claims (3)

[Claims] 1. A transfer unit for continuously transferring a toner image onto a print sheet running on a conveying path, a heating roller for heating the toner on the print sheet, and a pressure roller in contact with the heating roller. An image forming apparatus comprising: a power supply for supplying electric power to the heating roller; and a main control section for adjusting a current from the power supply to the heating roller and transmitting image information to the transfer means. However, the image forming apparatus has a current variable control function of controlling the supply of current to the heating roller according to the density of the image obtained from the image information. 2. A transfer means for continuously transferring a toner image onto a print sheet running on a conveying path, a heating roller for heating the toner on the print sheet, and a pressure roller in contact with the heating roller. In the image forming apparatus, a power supply for supplying electric power to the heating roller and a main control unit for adjusting current from the power supply to the heating roller and transmitting image information to the transfer unit are provided. An image density detecting means for detecting the image density of the toner image on the printing paper is provided on the upstream side of the heating roller, and the main control section controls the current to the heating roller based on the detection value of the image density detecting means. An image forming apparatus characterized by having a variable current control function for controlling the supply of electricity. 3. The image forming apparatus according to claim 1, wherein when the image density is high, the main controller controls to increase the supply current to the heating roller.