JPH075786A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device which obtains satisfactory fixability without increasing the wattage of a heater. CONSTITUTION:Pressure rollers 4 and 5 are set so as to be in pressure-contact with a fixing roller 3, and a movable shifting member 8 is provided between the two pressure rollers. Further, a separation claw 9 is disposed so as to move while interlocking with the shifting member 8. For example, when fixing is carried out by the use of thick paper, the shifting member 8 and the separation claw 9 are moved to the position shown by a solid line, and the thick paper ejected from the pressure-contact part of the pressure roller 4 and fixing roller 3 is guided again to the pressure-contact part of the pressure roller 5 and fixing roller 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus equipped with a fixing device for thermally fixing toner.

[0002]

2. Description of the Related Art Conventionally, as a fixing device used in an image forming apparatus such as a copying machine, a pair of a fixing roller and a pressure roller are pressed against each other, and a sheet carrying unfixed toner is passed through the pressure contact portion. As a result, a heat fixing system is well known in which heat is applied to the unfixed toner on the sheet to melt the toner, and the toner is fixed on the sheet by the pressure of the roller pair pressed against the sheet.

When these fixing methods are used in a high-speed image forming apparatus having a large number of copies per unit time or in an image forming apparatus which forms an image on both sides of a sheet, it is necessary to improve the fixing property. Therefore, in the conventional image forming apparatus, the number of wattages of the heater of the fixing roller is increased to cope with the problem.

[0004]

However, according to the above-described conventional example, when the number of wattages of the heater is increased, the power supply of the main body is increased, and the power supply section of the building or office to be installed is constructed, for example, 100V. To 200V
It is necessary to change to 20A or change from 20A to 40A. In addition, when copying is performed continuously, the heat taken by the paper during copying increases, and even if the maximum current is applied to the heater, the temperature of the outer peripheral surface of the fixing roller does not rise enough to maintain the prescribed fixability. To do so, it is necessary to reduce the copy speed extremely.

Therefore, as a method of improving the fixing property without performing the above-mentioned construction or a process of extremely slowing down the copy speed, there are two pressure rollers and an image is formed only on one side of the sheet, and on both sides. USP4,526,45 has different sheet direction from the passing nip part when forming.
It has been proposed at 9 mag.

However, this method also has a problem that good fixing property cannot be obtained when a sheet having poor fixing property such as thick paper is used.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide an image forming apparatus capable of obtaining a good fixing property without significantly increasing the wattage number of the heater.

[0008]

According to the present invention, an object of the invention is to form an image having a roller pair of a fixing roller and a pressure roller, and nipping and conveying a recording material by the roller pair. In the fixing device of the apparatus, a plurality of pressure rollers are installed around the fixing roller so as to be in pressure contact with each other, and the recording material discharged from any one pressure contact portion is further pressed to the next pressure contact portion or recording material discharge portion. It is achieved by having a recording material guide means for selectively guiding to any one of the above and a control means set to switch the guide direction of the recording material guide means according to the fixing condition.

[0009]

According to the present invention, the image on the recording material which has passed through the pressure contact portion between the fixing roller and the pressure roller is given heat at a predetermined pressure or with this pressure. In the case where a sufficient fixing property cannot be obtained only by the first fixing, the control means switches the guide direction of the recording material by the recording material guide means to the pressure contact portion direction of the next pressure roller. . As a result, the recording material is guided to the pressure contact portion of the next pressure roller, and the image of the recording material that has once passed through the pressure contact portion is again given a predetermined pressure or heat together with this pressure to perform sufficient fixing. If you need more,
Similarly, the recording material is successively passed through the pressure contact portion of each pressure roller to obtain the required fixing property.

[0010]

Embodiments 1 and 2 of the present invention will be described with reference to the accompanying drawings.

<Embodiment 1> First, Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is a view best showing the features of the present invention. In FIG. 1, 2 is a fixing device,
3 is a fixing roller, 4 is a first pressure roller, 5 is a second pressure roller, 6 is a first path which is a straight path, 7 is a second path consisting of a bending path, and 8 is a pressure roller. Deflection member which doubles as a separation claw of 4 and switches the sheet to the first path 6 or the second path 7, and a fixing roller separation claw 9 which is normally in contact with the fixing roller 3 but interlocks with the deflection member 8.
Reference numeral 10 is a fixing heater, 11 is a thermistor for detecting the outer peripheral temperature of the fixing roller 3, 12 is a first nip portion, 13 is a second nip portion, 14 is a first pressure roller 4 to a second pressure roller. It is a delivery pass to 5.

Further, in FIG. 2, 1 is the main body of the image forming apparatus, 15 is a photosensitive drum, 16 is a reversing path used for double-sided or reverse ejection, and 17 is a sheet on which an image is formed on the first side during double-sided / multiplexing. An intermediate tray to be stacked, 18 is a first paper feed deck, and 19 is a second paper feed deck.

In the above structure, the sheet sent from the first paper feed deck 18 passes under the photosensitive drum 15 and the image is transferred by the known transfer means to the fixing device 2 via the transport head portion. Next, the unfixed sheet is transferred to the first nip 1
The sheet is fixed through the sheet 2 and is conveyed to the sheet discharge unit through the first path 6. At this time, the deflecting member 20 is at the position indicated by the solid line in the case of one side, and the sheet is discharged without being deflected, and the deflecting member 20 stops at the intermediate position between the alternate long and short dash line and the line in the case of double sided / multiplexing.
It is sent to the intermediate tray 17.

Further, in the present embodiment, as shown in FIG. 3, the fact that only thick paper is set in the first paper feed deck 18 is input to the operation section, or thick paper is used by the paper thickness detection sensor. If it is detected (F1),
The controller determines that the nip needs to be switched (F
3) Then, a deflecting member solenoid (not shown) for moving the deflecting member 8 is turned on (F4), and the deflecting member 8 is kept pulled up to the position shown by the solid line in FIG. Further, even if the fixing heater 10 in the fixing roller 3 is turned on by using a full electric current,
When the thermistor 11 detects that the outer peripheral temperature of the fixing roller 3 has not reached the predetermined set temperature for melting the toner (F2), the nip is switched by the control unit by the procedure of F3 and F4 as in the case of thick paper.

As described above, according to the present invention, not only in double-sided / multi-image formation, but also in thick paper and when the fixing temperature is lowered, the paper is pressed twice, so that the wattage of the heater is significantly increased. It is possible to improve the fixing property without performing the above.

Further, by bending the second path as described above, it is possible to reduce the upper curl when thick paper is used.

<Second Embodiment> Next, a second embodiment of the present invention will be described. Note that the description of the common points with the first embodiment will be omitted.

In the first embodiment, the branch point is provided after the sheet passes through one nip, but the sheet may always pass through two or more nips.

Since the first nip passes thin paper, plain paper, and slightly thick paper, the pressing force is moderate. After the second nip, the pressing force is much stronger for thick paper, and the nip length is made larger. It may be configured.

Further, the second pressure roller may be configured to be able to come into contact with and separate from the fixing roller by hydraulic power. However,
In that case, it is required to provide a residual heat means so as not to lower the surface temperature of the fixing roller when the contact is made.

[0021]

As described above, according to the present invention,
By providing a plurality of pressure rollers and providing a recording material guide means capable of switching the conveying direction of the recording material at the discharge position of each pressure roller, a sheet having poor fixing property is passed through the nip twice, By only needing once, fixing efficiency can be improved and energy saving can be realized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a fixing device according to a first exemplary embodiment of the present invention.

FIG. 2 is a sectional view showing a schematic configuration of an image forming apparatus in which the apparatus of FIG. 1 is used.

FIG. 3 is a flowchart showing a control flow in the apparatus shown in FIG.

[Explanation of symbols]

 2 fixing device 3 fixing roller 4 first pressure roller 5 second pressure roller 8 deflecting member (recording material guide means)

Claims (3)

[Claims] 1. A fixing device of an image forming apparatus having a roller pair of a fixing roller and a pressure roller, wherein a recording material is sandwiched and conveyed by the roller pair to form an image. A pressure roller is installed so as to be in pressure contact, and a recording material guide means for selectively guiding the recording material discharged from any one of the pressure contact parts to either the next pressure contact part or the recording material discharge part. An image forming apparatus comprising: a control unit configured to switch the guide direction of the recording material guide unit according to a fixing condition. 2. Two pressure rollers are installed so as to be in pressure contact with a fixing roller, and a straight first path is provided downstream of a pressure contact portion with the first pressure roller in the recording material conveyance direction. The image forming apparatus according to claim 1, wherein a bent second path is provided downstream of the pressure contact portion with the pressure roller in the recording material conveyance direction. 3. The image forming apparatus according to claim 1, wherein the pressing force of each pressure roller with respect to the fixing roller is set to be different.