JPH0497187A - Fixing device - Google Patents

Abstract

PURPOSE:To optimumly perform fixing irrespective of the kind of a paper and also to reduce the curling of a transfer paper by making it possible to switch a roller system fixing and a belt system fixing in accordance with the kind of the transfer paper to be used. CONSTITUTION:The device is provided with a belt 27 which is laid between a pressure roller 25 and an auxiliary roller 26 and which is pressurized to the fixing roller 23 by the pressure roller 25 and a means 28 for changing the contact surface of the belt 27 with the fixing roller 23 in the length direction of the belt 27. And the fixing roller 23 and the pressure roller 25 are usually kept in a linear contact state through just only the belt 27, and the fixing is performed as in the conventional roller system. And moreover, the contact surface of the belt 27 and the fixation roller 23 is changed and the contact area of the belt 27 with reference to the fixation roller 23 and the pressure roller 25 are enlarged. Then, the nip is increased, so that the fixing can be performed as in the conventional belt system. Thus, the switching of the roller system fixing and the belt system fixing can be performed in accordance with the kind of the paper to be used, and the curling of the transfer paper can be reduced.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a fixing device in an electrophotographic recording device.

2. Description of the Related Art Conventional fixing devices include a roller type and a belt type.

FIG. 8 shows a conventional roller type fixing device, where 1 is a frame;
2 is an upper entrance guide, 3 is a lower entrance guide, 4 is a fixing roller with a built-in heater, and 5 is a pressure roller that presses the transfer paper against the fixing roller 4.

FIG. 9 shows a conventional belt-type fixing device, where 6 is a frame;
7 is a fixing roller with a built-in heater, 8 is an entrance side roller,
Reference numeral 9 denotes an 8-outlet side roller, 10 a tension shaft, and 11 a belt hooked around the inlet-side roller 8, outlet-side roller 9, and tension shaft 10.

A pressure spring 12 presses the exit roller 9 and presses the belt 11 against the fixing roller 7 .

The transfer paper is sandwiched between the fixing roller 7 and the belt 11 and conveyed from right to left.

Problem to be Solved by the Invention In the case of a conventional roller type fixing device, the fixing roller 4 and the pressure roller 5 are in line contact, and the length of the transfer paper wrapped around the roller has few lobes), which prevents curling of the transfer paper. It was sufficient to fix toner on thin paper such as plain paper because the curvature of the fixing roller 4 did not affect much. However, for transfer paper that has double, triple, or quadruple parts such as envelopes, the fixing rate is low because sufficient heat cannot be obtained in the overlapped parts, and the fixing power must be increased to increase the fixing rate. Then, there was a problem that the curl of the transfer paper became large.

On the other hand, in the case of a conventional belt-type fixing device, the fixing roller 7
Since the transfer paper and the belt 11 are in surface contact, the nip can be long and a sufficient fixing rate can be obtained even on thick paper. However, on the other hand, there is a problem in that the transfer paper is curled due to the curvature of the fixing roller rough. Furthermore, since the open area is large and the amount of heat dissipated is large, there is also a drawback that energy loss increases.

The purpose of the present invention is to make use of the advantages of roller type fixing and belt type fixing and eliminate their disadvantages, so that it is possible to switch between roller type fixing and belt type fixing depending on the transfer paper used.
That is, an object of the present invention is to provide a fixing device that can perform fixing similar to a conventional roller type when using thin paper such as plain paper, and can perform fixing similar to a conventional belt type when using thick paper such as an envelope.

SUMMARY OF THE INVENTION The present invention provides a fixing device that includes a heated fixing roller and a pressure roller that presses transfer paper against the fixing roller. The present invention is characterized by comprising: a belt that is pressed against the fixing roller by the pressure roller; and means for changing the contact surface between the belt and the fixing roller in the length direction of the belt.

Even if the means for changing the contact surface between the belt and the fixing roller is a mechanism that moves the belt around a pressure roller,
Alternatively, a mechanism for moving the fixing roller in the length direction of the belt may be used.

Function The fixing roller and the pressure roller are usually in line contact simply via a belt, and fixing is performed in the same manner as in the conventional roller type. By changing the contact surface between the belt and the fixing roller and increasing the contact area of the belt with respect to the fixing roller and the pressure roller, the nip becomes larger, so that fixing can be performed in the same manner as in the conventional belt type.

Example Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention, in which 20 is a frame;
21 is an upper entrance guide, 22 is a lower entrance guide, 23 is a fixing roller with a built-in heater 24, and 25 is the fixing roller 23.
This is a pressure roller that presses the transfer paper against the pressure roller, and these configurations are similar to those of conventional roller type fixing devices.In addition to this configuration, the fixing device according to the present invention has an auxiliary roller 26 with a small size on the exit side. A belt 27 is hooked and rotated between this and the pressure roller 25, and the following belt moving mechanism 28 is provided to move the belt 27 vertically around the pressure roller 25.

The auxiliary roller 26 is supported by a shaft 31 at one end of an arm 30 that rotates up and down about the roller shaft 29 of the pressure roller 25. The arm 30 is supported by a return spring connected to the other end. It is urged counterclockwise by a stopper 32 and is normally held in a fixed position with its counterclockwise rotation restricted by a stopper 33. At this time, belt 2
The upper part 27a of 7 is horizontal as shown in FIG.
The belt 27 is pressed against the fixing roller 23 by the pressure roller 25 in a line contact state. The other end of the arm 30 is
Spring 34 on the opposite side from return spring 32
It is connected to the plunger 36 of the electromagnet 35 via. When the electromagnet 35 is turned on and the arm 30 is rotated clockwise against the return spring 32 as shown by the chain line, the belt 27 is moved upward around the pressure roller 25.

As shown in FIG. 3, the upper portion of the belt 27 is in surface contact with the circumferential surface of the fixing roller 23 over a range of angle θ around its axis.

Therefore, when the electromagnet 35 is turned off, the fixing roller 2
3, the pressure roller 25, and the belt 27 are in the state shown in FIG.
Fixing is performed in the same manner as in the conventional roller type. When the electromagnet 35 is turned on, the state shown in FIG.
7 presses the transfer paper against the fixing roller 23 over a range of angle θ, and fixing is performed in the same manner as in the conventional belt type.

Note that since the spring 34 has a large spring constant, even if the arm 30 is rotated by turning the electromagnet 35 on and off, it hardly expands or contracts.

Furthermore, this fixing device is provided with a pressure switching mechanism 37 that switches the pressure applied by the pressure roller 25 into two levels, strong and weak, as shown in FIG. That is, the pressure arm 39 rotating around the shaft 38 is biased clockwise by the pressure spring 40 to lift the roller shaft 29 of the pressure roller 25 and press the pressure roller 25 against the fixing roller 23. ing. The pressure arm 39 is connected to a plunger 43 of a pressure switching electromagnet 42 via a spring 41 on the opposite side from the pressure spring 40 .

When fixing in the state shown in FIG. 2, the electromagnet 42 is turned off and the pressing force of the pressure roller 25 is increased, and when fixing is done in the state shown in FIG. 3, the electromagnet 42 is turned on and the pressure arm 39 is pulled down against the pressure spring 4° to weaken the pressure force of the pressure roller 25.

5 and 6 show a second embodiment of the present invention, in which the belt 27 is in a fixed position and the fixing roller 23 is moved in the length direction of the belt 27 so that the contact surface with the belt 27 can be changed. This is what I did. That is, the fixing roller 2 is attached to the arm 44 that rotates around the roller shaft 29 of the pressure roller 25.
3, and the roller shaft 45 is fitted into a long hole 47 provided in the side plate 46 of the frame 20, and the rotation of the arm 44 moves the fixing roller 23 back and forth within the range of the long hole 47. It is possible to move to Then, the arm 44 is urged clockwise by the return spring 48 so that the axis of the fixing roller 23 and the axis of the pressure roller 25 are normally located on the same vertical plane as shown by the chain line in FIG. The fixing roller 23 is held on the right side in the figure. Further, a plunger 51 of an electromagnet 50 is connected to the arm 44 via a spring 49 on the side opposite to the return spring 48 . When the electromagnet 50 is turned on and the arm 44 is rotated counterclockwise against the return spring 48, the fixing roller 23 is moved to the fifth position.
It is moved to the left as shown by the solid line in the figure, and is held at a position shifted to the left with respect to the pressure roller 25. At this time, the contact area between the belt 27 and the fixing roller 23 is larger than when the electromagnet 50 is off, so that fixing can be performed in the same manner as in the conventional belt type.

FIG. 7 is a flowchart of an example of the operation when the transfer paper is changed from plain paper to an envelope in the fixing device configured as described above. When the envelope cassette is set and the photo interrupter detects the passage of an envelope and the CPU confirms that the envelope has been passed, the electromagnet 35 or 50 and the electromagnet 42 for switching pressure force are turned on. When the CPU confirms that this is turned on, the CPU controls the heater 24 to lower the fixing temperature, and after confirming that the temperature setting is completed, the electrophotographic recording device changes to the envelope fixing mode, indicating that the preparation for envelope feeding is complete. do.

Effects of the Invention According to claim 1 of the present invention, since it is possible to switch between roller type fixing and belt type fixing depending on the transfer paper used, appropriate fixing can be performed regardless of the paper type, and curling of the transfer paper can be prevented. Since it can be reduced, transportability is also improved.

According to the second aspect, since the belt can be moved around the pressure roller to change the contact surface with the fixing roller, it is possible to prevent the belt from twisting or wrinkling.

According to claim 3, since the belt can always be kept in a fixed position to guide the transfer paper, envelopes can also be discharged in the same direction as plain paper.

[Brief explanation of drawings]

FIG. 1 is a side view of the fixing device according to the first embodiment of the present invention, FIG. 2 is a side view when fixing plain paper, FIG. 3 is a side view when fixing thick paper such as envelopes, and FIG. FIG. 4 is a side view mainly showing the pressurizing force switching mechanism of the fixing device, and FIG. 5 is a second diagram of the present invention.
FIG. 6 is a side view of the fixing device of the embodiment, FIG. 6 is a side view of the side opposite to FIG. 8 is a side view of a conventional roller type fixing device, and FIG. 9 is a side view of a conventional belt type fixing device. 23...Fixing roller 25...Pressure roller 26...Auxiliary roller 27...Belt

Claims (1)

[Claims] 1. In a fixing device equipped with a heated fixing roller and a pressure roller that presses the transfer paper against the fixing roller, the pressure roller is applied between the pressure roller and the auxiliary roller. a belt pressed against the fixing roller by a pressure roller;
A fixing device comprising means for changing the contact surface between the belt and the fixing roller in the length direction of the belt. 2. The fixing device according to claim 1, wherein the means is a mechanism for moving the belt around the pressure roller. 3. The fixing device according to claim 1, wherein the means is a mechanism for moving the fixing roller in the length direction of the belt.