JPH09138598A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device applicable to a high-speed image forming device. SOLUTION: A heat-resistant belt 10 is supported by plural rollers 4 and 6 and a pressure roller 12 is brought into press-contact with these rollers 4 and 6 with the belt 10. Further, the rollers 4 and 6 are connected to a driving motor 14 and a braking motor 22 respectively. Therefore, a belt part 10a supported between the rollers 4 and 6 is pulled in a moving direction (the direction of the arrow 18) and a direction opposite to it, to be closely stuck to the outer periphery of the pressure roller 12, without any gap. Thus, even if the moving speed of the belt 10 is increased, a sheet 26 and a developer 24 which are carried to the gap between the belt 10 and the pressure roller 12 coming into contact therewith are uniformly heated by heat transmitted to the belt 10 from a heater 20, to be melt-fixed.

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 such as an electrophotographic copying machine, a printer, and a facsimile which heats a developer adhering to a sheet to fix it. is there.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, a fixing device is used to heat and fix a developer image formed on a sheet. As the fixing device, a fixing device having a heating roller having a heat source and a pressure roller arranged in parallel with and in contact with the heating roller is widely used.
However, in this heat roller type fixing device, since the circumferential contact length (nip length) of the contact portion (nip portion) of the two rollers cannot be sufficiently obtained, it is necessary to provide the developer with the heat amount required for the melt fixing. There was no choice but to slow down the peripheral speed of the roller, which hindered the speeding up of the image forming apparatus. Further, if an attempt is made to improve the melt fixing property of the developer by increasing the pressure applied by the pressure roller, there is a problem that the image is crushed and the image quality is deteriorated.

[0003]

On the other hand, a belt type fixing device has been proposed as a means for solving the problems of the above heat roller type fixing device. Since this belt type fixing device also requires a certain amount of pressure in the nip portion, the belt in the nip portion may float if a structure in which the pressure roller and a plurality of rollers in pressure contact with the pressure roller are sandwiched.
Then, when the belt floats, uniform pressure is not applied to the sheet, and uneven fixing occurs. Particularly, in the case where the toner is in contact with the belt, there is a problem that the toner image is displaced.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a fixing device capable of coping with speeding up of an image forming apparatus and having an excellent melt fixing performance of a developer. Two supporting rollers, a heat-resistant belt wound around these supporting rollers, a pressure roller that is pressed against at least two supporting rollers via the belts, a heating unit that heats the belts, and one of the belts. And a braking means for applying a tension in a direction opposite to the belt moving direction to the belt portion in contact with the pressure roller.

[0005]

In the fixing device described above, the heat resistant belt is supported by at least two supporting rollers, and the belt portion supported by the at least two supporting rollers contacts the pressure roller and is supported by the outer peripheral surface thereof. To be done. Further, the belt is driven in one direction by the driving means, and the belt portion in contact with the pressure roller is given a tension in the direction opposite to the moving direction by the braking means.
Therefore, the portion of the belt that comes into contact with the pressure roller comes into close contact with the outer peripheral surface of the pressure roller without any gap. Therefore, even if the moving speed of the belt is increased so that it can be applied to a high-speed image forming apparatus, the sheet conveyed between the pressure roller and the belt heated by the heating unit and the developer supported by the sheet are conveyed. It is evenly heated and evenly fixed on the sheet.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a first embodiment of the present invention. In this figure, the fixing device 2 includes rollers 4, 6,
And 8 and a heat resistant belt 10 is wound around these three rollers 4, 6, 8. Further, the pressure roller 12 is pressed against the rollers 4 and 6 via the belt 10, and the belt portion 10 a between the rollers 4 and 6 is in contact with the outer peripheral surface of the pressure roller 12.

Of the above three rollers, the roller 4 is connected to the drive motor 14, and the roller 4 rotates in the direction of arrow 16 based on the drive of the motor 14 and the belt 10 rotates based on the rotation of the roller 4. Moves in the direction of arrow 18. The roller 6 is provided with a heater 20 inside, and transfers heat to the belt portion that contacts the outer peripheral surface of the roller 6. The roller 6 is connected to the braking motor 22, and the rotational speed (roller peripheral speed) transmitted from the braking motor 22 to the roller 6 is smaller than the rotational speed (roller peripheral speed) transmitted from the drive motor 14 to the roller 4. It is made small. The roller 8 is biased from the inside of the belt 10 toward the outside by a spring or the like (not shown), and applies a constant tension to the belt 10.

The heat-resistant belt 10 has a thickness of 30 to, for example.
100 μm polyimide, polyamideimide, polyetherimide, polyethersulfone, or polyetherketone sheet, or nickel, stainless steel, or copper metal sheet coated with a material having excellent releasability such as silicon resin or fluorine resin What was done is used suitably.

The operation of the fixing device 2 will be described. In the fixing device 2, when the drive motor 14 is driven to rotate the roller 4 in the arrow 16 direction, the belt 10 moves in the arrow 18 direction by the contact frictional force with the roller 4. Further, the braking motor 22 is driven and the rotational force is transmitted to the roller 6. However, the peripheral speed of the roller 6 is slightly lower than that of the roller 4. Therefore, the belt portion 10a supported between the rollers 4 and 6 is pulled in the moving direction (the direction of the arrow 18) by the rotation of the roller 4 and the roller 6
Is pulled in the direction opposite to the moving direction. Therefore, the belt portion 10a closely contacts the outer peripheral surface of the pressure roller 12 without any gap. Further, the heat of the heater 20 is transferred to the belt 10 via the roller 6.

Therefore, when the sheet 26 having the developer 24 on the surface facing the belt is conveyed to the contact portion (nip portion) between the belt 10 and the pressure roller 12, the sheet 26 is passed through the nip portion. The heat of the belt 10 uniformly heats and melts the developer. In addition, the pressure roller 12
The melted developer 24 is fixed to the sheet 26 by the pressure contact force between the roller 4 and 6 and the pressure contact force between the belt 10 and the pressure roller 12.

FIG. 2 shows a fixing device of the second embodiment, and this fixing device 30 is a modification of the fixing device 2 of the first embodiment. Therefore, the fixing device 30 corresponds to the fixing device 2 of FIG.
And many common components, and these same components function in the same manner, the same reference numerals are given and description thereof is omitted. A new roller 32 for supporting the belt 10 is added to the fixing device 30, and a braking motor 34 is connected to the roller 32. Therefore, the fixing device 3
Also at 0, the belt portion 10a supported between the rollers 4 and 6 is pulled in the moving direction and the opposite direction, and tightly adheres to the outer peripheral surface of the pressure roller 12 without a gap. Therefore, the developer 24 held on the belt-opposing surface of the sheet 26 is supplied with heat from the belt 10 while passing through the nip portion, melted and fixed on the sheet 26.

FIG. 3 shows a fixing device of the third embodiment, and this fixing device 40 is a modification of the fixing device 30 of the second embodiment. Therefore, the fixing device 40 has many common components with the fixing device 30 of FIG. 2, and since these same components function in the same manner, the same reference numerals are given and description thereof is omitted. A new roller 42 for supporting the belt 10 is added to the fixing device 40.
A drive motor 44 is connected to the drive motor 2. This fixing device 4
Even at 0, the belt portion 10a is in close contact with the outer peripheral surface of the pressure roller 12 without a gap, and the developer held on the belt facing surface is heated and melted and fixed on the sheet while passing through the nip portion.

FIG. 4 shows a fixing device according to the fourth embodiment. The fixing device 50 includes four rollers 52, 54, 56 and 58, and a belt 60 is supported by these rollers 52 to 58. The roller 52 is connected to the drive motor 62, and the roller 56 is connected to the braking motor 64. The rotation amounts of the two motors 62 and 64 are such that the peripheral speed of the roller 52 is slightly faster than the peripheral speed of the roller 56. Is set to. The fixing device 50 also includes a pressure / heating roller 6
6 is provided. The pressure / heating roller 66 is provided with a heater 68 therein, and the belt 52 is attached to the rollers 52 and 54.
Is pressed through.

In the fixing device 50, the drive motor 62 causes the roller 52 to rotate in the direction of arrow 70. As a result, the belt 60 moves in the direction of the arrow 72 at the same speed as the peripheral speed of the roller 52, the rollers 54 and 58 are driven to rotate, and the pressure roller 66 rotates in the direction of the arrow 74. In addition, the braking motor 64 causes the roller 56 to rotate in the direction of arrow 76. However, since the peripheral speed of the roller 56 is slightly slower than the peripheral speed of the roller 52 and the moving speed of the belt 60, the belt portion 60a between the rollers 52 and 54 and in contact with the pressure roller 66 is It is pulled in the direction opposite to the moving direction. Therefore, the sheet conveyed from the direction of the arrow 78 to the contact area between the belt 60 and the pressure / heating roller 66 and the developer held on the surface facing the pressure roller are in close contact with the pressure / heating roller 66 and the belt 60 without a gap. To do. Therefore, the developer is uniformly heated by the heat transmitted from the heater 68, melted, and fixed on the sheet.

FIG. 5 shows a fixing device of the fifth embodiment, and this fixing device 80 is a simplification of the fixing device 50 of the fourth embodiment. Therefore, the fixing device 80 has many common components with the fixing device 50 of FIG. 4, and since these same components function in the same manner, the same reference numerals are given and description thereof is omitted. In the fixing device 80, the roller 54 is connected to the braking motor 82, and the roller 54 is rotated at a speed slightly lower than that of the roller 52. Therefore, as in the above-described embodiment, the belt portion 60a is pulled in the moving direction and the opposite direction to be in close contact with the pressure / heating roller 66, whereby the pressure / heating roller 66 and the belt 60 remove the sheet. Heat is evenly transferred to the developer held on the surface facing the pressure roller.

In the above embodiment, the roller selected from the rollers supporting the belt is connected to the drive motor, the belt is moved by the rotational force, and the pressure roller or the pressure / heating roller is further connected. It is assumed that it is driven to rotate.
However, a pressure roller or a pressure / heating roller may be connected to the drive motor, so that the belt and further the roller are driven to rotate. In this case, the pressure contact force to the roller in contact with the pressure roller or the pressure / heating roller on the downstream side in the belt moving direction is smaller than the pressure contact force to the roller in contact with the pressure roller or the pressure / heating roller on the upstream side. It is preferable to increase the size so that the belt portion on the downstream side is pulled in the moving direction by the roller on the downstream side.

Further, in the above description, the braking motor is used as the braking means, but any means capable of applying tension to the belt portion contacting the pressure roller in the direction opposite to the moving direction of the belt portion. Alternatively, it may be a means for controlling the rotation torque such as a torque limiter. Also,
The number of rollers in pressure contact with the pressure roller, the arrangement of the drive motor and the control motor (that is, which roller is used as the drive roller), and whether the toner surface is the belt side or the pressure roller side are the configurations of the above-described embodiment. However, various combinations are possible.

[Brief description of the drawings]

FIG. 1 is a side view of a fixing device according to a first embodiment.

FIG. 2 is a side view of a fixing device according to a second embodiment.

FIG. 3 is a side view of a fixing device according to a third embodiment.

FIG. 4 is a side view of a fixing device according to a fourth embodiment.

FIG. 5 is a side view of a fixing device according to a fifth embodiment.

[Explanation of symbols]

2 ... Fixing device, 4, 6, 8 ... Roller, 10 ... Belt, 1
2 ... Pressure roller, 14 ... Drive motor, 20 ... Heater, 2
2 ... Braking motor.

Claims (1)

[Claims] 1. At least two supporting rollers, a heat-resistant belt wound around these supporting rollers, and at least two.
A pressure roller that comes into pressure contact with one support roller via the belt, a heating means that heats the belt, a driving means that moves the belt in one direction, and a belt moving direction at a belt portion that is in contact with the pressure roller. Is a fixing device having a braking means for applying tension in the opposite direction.