JPH0922211A - Fixing device - Google Patents

Abstract

(57) [Summary] [Purpose] The paper suction unit and preheating plate have been removed, and paper wrinkles,
To provide a fixing device that can prevent character loss and stains on the printing surface during double-sided printing and maintain stable printing quality under any printing conditions. A sheet suction unit is eliminated, and a sheet conveyance guide 20 is used, and the timing of the pressure roller 9 approaching and leaving the heating roller 7 and the swing position of the buffer 4 that absorbs the difference in sheet feeding speed, The centralized control unit 2 collectively includes the drive mechanism 18 of the heating roll 7 and the drive mechanism 10 of the pair of rotary rollers 12 that functions to draw the print paper 1 into the paper storage unit 13.
Controlled by 1 and paper feed speed in the fixing device depending on printing conditions
Change (amount).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an electrophotographic printing device.

[0002]

2. Description of the Related Art FIGS. 3, 4, and 5 show a conventional example of a fixing device in an electrophotographic printer. Normally, when two-sided printing is performed on continuous paper, two printers and a paper sheet are used. A tandem printing method using a reversing device is adopted.
FIG. 3 shows a fixing operation during double-sided printing. Printing paper 1
Being conveyed from the tractor 3, passing through the buffer 4, passing through the sheet suction unit 5, receiving heat from the heating plate 6, and being sandwiched and conveyed by the heating roll 7 and the pressure roll 9 held by the support 8. Then, the toner image 2 on the printing paper 1 is fixed on the printing paper 1. Further, the printing paper 1 has a dedicated drive mechanism 10 and control mechanism 11 provided on the paper feed,
The sheet is sent to the sheet storage unit 13 by the pair of rotating rollers 12.

Here, the rotary roller 12 has a structure that rotates so as not to have a speed difference with the printing paper 1. During printing, the drive mechanism 18 of the heating roll 7 causes the dedicated control unit 19 to swing the buffer 4 that absorbs the difference between the paper feeding speed of the tractor 3 and the paper feeding speed of the heating roll 7. Is controlled by. When the buffer 4 starts to tilt in the direction A in the figure from the position balanced with the reaction force of the paper, the control units 11 and 19 delay the paper feed speed of the heating roll 7 and the roller 12 to make the printing paper 1 loose. Return to the equilibrium position. On the contrary, when the buffer 4 starts to tilt in the direction B in the figure, the control units 11 and 19 advance the paper feed speed of the heating roll 7 and the roller 12 to apply tension to the printing paper 1 and place the buffer 4 at a balanced position. Back up.

Since the heating plate 6 efficiently applies heat to the printing paper 1 in the paper suction unit 5, the printing paper 1 is held by the mechanism (not shown) that provides an appropriate suction force according to the width of the printing paper to suppress flapping. ing. In the sheet suction unit 5, the sheet suction force acts on the printing sheet 1 from the start of printing to the end of printing to apply a restraining force to the printing sheet 1.

FIG. 4 shows a state when printing is stopped. When printing is completed, the pressure roller 9 is separated from the heating roller 7 by the restoring force of the cam 14 and the spring 15. FIG. 5 shows the fixing operation on the back surface of the printing paper during double-sided printing.
Heating plate 6 to prevent re-softening of the preset toner on the paper surface
Has a configuration in which the amount of preheating heat is set low and the shortage of the required amount of heat is wrapped around the heating roll 7 with the printing paper 1 to ensure the fixing power. The pressure roll 9 is pushed up by the rotation of the cam 14 and comes into pressure contact with the heating roll 7, and the cam 1
The maximum pressing force is generated at the top dead center of 4. At this time, the guide roller 17 also comes close to the heating roll 7 so as to be wound at a constant wrapping angle by the swinging of the support body 16, and at the same time, the roller 12 starts driving.

[0006]

In the above-mentioned fixing device of the prior art, when the printing paper is left on the preheating plate for a long time, the printing paper shrinks due to the heat from the preheating plate and is restrained by the paper suction portion. Therefore, it is in a contracted and deformed state. When printing is started in this state, wrinkles are generated in the printing paper at the nip portion between the heating roll and the pressure roll, causing a problem of missing characters (partial fixing failure). Further, at the time of printing on the back surface, the suction hole of the paper suction unit rubs against the preset toner, which causes a problem that the back surface of the printing (printed surface) is soiled. Further, since the printing paper is held by the paper suction unit, the paper feed amount due to the swinging motion of the buffer is less likely to be transmitted forward in the paper feed direction, and the paper feed amount by the heating roll is more than the paper feed amount by the tractor.
There was a shortage, and the paper transport was unstable. In order to avoid such a state, a method of adding a suction force adjusting mechanism according to the width of the printing paper is adopted, but this method requires a linear movement mechanism, an airtight structure, etc. It caused complication and cost increase.

An object of the present invention is to eliminate a paper suction portion and a preheating plate in a fixing device to prevent wrinkles, characters from the paper, and stains on the printing surface during double-sided printing, and to stabilize under any printing conditions. The stable printing quality is maintained and the stable feeding of the printing paper is secured by controlling the swing position of the buffer, the pressure roll, the heating roll and the pair of rotary rollers collectively, and an inexpensive fixing device is supplied. Especially.

[0008]

The above-mentioned object is to eliminate the paper suction mechanism and the preheating mechanism portion in front of the nip portion formed by the heating roll and the pressure roll, and eliminate the print stop timing and the buffer swing. Depending on the position, pressure roll, heating roll,
This is achieved by collectively controlling the drive timing of the rotating rolls.

[0009]

In the fixing device configured as described above, at the start of printing, the tension of the printing paper provided by the buffer that absorbs the difference between the paper feed speed between the tractor and the heating roll and the drawing of the paper into the paper storage unit. By the balance with the paper transport force by the drive of a pair of rotating rollers that play a role,
The binding force can be applied to the printing paper. Also, during printing, the tension of the printing paper given by the buffer,
Printing is performed by collectively controlling the buffer swing position, the heating roll, and the pair of rotation rollers driving time so that the printing paper can be constrained by the paper holding and conveying force of the heating roll and the pressure roll. Even if the conditions change, a constant tension can be uniformly applied to the printing paper, and stable paper feeding and fixing strength can be secured.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. The fixing device of the present invention will be described. In the state where the pressure roll 9 is separated from the heating roll 7, the paper suction unit is removed, so the binding force to the printing paper 1 is lost, and the paper conveyance force by the pair of rotating rollers 12 and the reaction force given from the buffer 4 are lost. Depends on. At this time, since the reaction force applied from the buffer 4 to the printing paper 1 is set to be larger than the paper conveyance force of the rotating roller 12, the printing paper 1 is returned backward in the paper conveyance direction, and the buffer 4 The rocking position of is the error detection position at the upper limit of the rocking range. However, at the start of the next printing, the already-printed portion always serves as the re-nip portion to prevent fixing failure.

Next, at the start of printing, the central control unit 21 does not detect an error with respect to the swing position of the buffer 4, and the heating roller 7 moves the sheet until the buffer 4 reaches the normal swing position. Raise. During printing, the paper restraining force is governed by the sandwiching and conveying force of the heating roll 7 and the pressure roll 9, so that the driving timing of the heating roll 7 and the rotating roller 12 is changed from the swing position of the buffer 4 to a predetermined value. The printing paper 1 is stably fed under the control of the centralized control unit 21 so that the buffer 4 is in the swinging position as in the prior art.

[0012]

According to the present invention, the preheating plate and the paper suction portion at the rear side in the paper transport direction from the nip point where the toner image on the printing paper is formed by the heating roll and the pressure roll are eliminated, and the buffer Depending on the swing position and the print start / stop time,
By controlling the drive timing of the heating roll and the pressure roller and the drive mechanism of the pair of rotary rollers that play a role of pulling the print paper into the paper storage unit collectively, stable paper conveyance is ensured and the print surface is rubbed, It is possible to prevent the occurrence of unfixed portions due to sheet deformation, prevent deterioration of print quality, and provide a compact and inexpensive fixing device.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing one embodiment of the present invention.

FIG. 3 is a schematic configuration diagram showing a conventional fixing device.

FIG. 4 is a schematic configuration diagram showing a conventional fixing device.

FIG. 5 is a schematic configuration diagram showing a conventional fixing device.

[Explanation of symbols]

1 is a printing paper, 2 is a toner image, 3 is a tractor, 4 is a buffer, 7 is a heating roll, 8 is a support, 9 is a pressure roll, 10 is a drive mechanism, 12 is a roller, 14 is a cam, and 15 is a cam.
Is a spring, 17 is a guide roller, 18 is a drive mechanism, 20 is a paper conveyance guide, and 21 is a centralized control unit.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Masa Sawahata 1060 Takeda Hitachinaka City, Ibaraki Prefecture, Hitachi Koki Co., Ltd. (72) Inventor Yuuo Nakajima 1060 Takeda Hitachinaka City, Ibaraki Hitachi Koki Co., Ltd. (72) ) Inventor Hiroshi Shirata 1060 Takeda, Hitachinaka City, Ibaraki Prefecture, Hitachi Koki Co., Ltd.

Claims (2)

[Claims] 1. A sandwiching / conveying mechanism composed of a heat roll and a pressure roll for heating and pressurizing an unfixed toner image on a print sheet, a guide member for winding the print sheet around the heat roll, and contacting the print sheet. The fixing roller has a rotating roller that conveys to the sheet storage section in front of the pair of rolls and conveys pressure to the heat roll during printing and retracts against the heat roll during non-printing. In the apparatus, the fixing device is characterized in that the printing paper is returned to the rear side of the sheet conveyance when the printing is stopped without using the preheating plate and the sheet suction section at the rear side of the sheet conveyance with respect to the pair of rolls. 2. A swingable buffer that absorbs a difference in sheet transport speed is provided behind the heating and pressure rolls in the sheet transport direction so that the swing position of the buffer can be detected. 2. The fixing device according to claim 1, wherein the rotating roller is driven immediately after the start of holding and conveying.