JPH03192382A - Fixing device - Google Patents

Abstract

PURPOSE:To keep the conveying speed of a paper constant on right and left sides and to prevent the wrinkle of the copying paper and the irregularities in fixing by providing a mechanism for adjusting the nip pressure between a heating roller and a pressurizing roller in accordance with a temperature difference in an axial direction. CONSTITUTION:The heating roller 58 of a fixing device 57 is constituted of cylindrical metal and a fixing lamp 61 functioning as a heat source is arranged inside the roller 58. Both ends of the pressurizing roller 59 are pressurized by the heating roller 58 with the specified nip pressure F and G. Between the nip pressure F and G, the nip pressure F on a driving mechanism part 62 side can be adjusted by a pressurization adjusting part such as a screw or a spring. The nip width of the roller 59 is in proportion to the magnitude of the nip pressure. Therefore, the nip width of the roller 59 is adjusted by adjusting the nip pressure by the pressurization adjusting part. The nip pressure F on the driving mechanism part 62 side is adjusted to be larger than the nip pressure G on the other side by the pressurization adjusting part.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention relates to a fixing device that fixes a toner image transferred from a photoreceptor such as a photoreceptor belt or a photoreceptor drum to a sheet of paper, and particularly relates to a fixing device that fixes a toner image transferred to paper from a photoreceptor such as a photoreceptor belt or a photoreceptor drum. The present invention relates to a fixing device that performs thermal fixing using a pressure roller that is pressed against a roller.

"Prior Art" For example, in electrostatic copying machines, facsimile machines, printers, etc., it is necessary to heat a toner image formed on a sheet of paper to a predetermined temperature to fix it. As a device for this purpose, a fixing device using a heating roller is generally used in a copying machine because it has high thermal efficiency and excellent fixing performance.

FIG. 12 shows a schematic configuration of a conventionally used copying machine.

A charge corotron 2 disposed around the photosensitive drum 1 of this copying machine uniformly charges the drum surface. The charges on the surface of the photoreceptor drum 1 are selectively eliminated by exposure of an optical system such as a lens 3, and an electrostatic latent image is formed on the drum surface. This electrostatic latent image is developed by the developing device 4, and a toner image is formed on the surface of the photoreceptor drum 1. This toner image is transferred to the copy paper 6 by the action of the transfer corotron 50.
transcribed into. The copy paper 6 on which the toner image has been transferred is conveyed to a fixing device, is thermally fixed to a heating roller 7 while being pressed by a pressure roller 8, and is discharged outside the machine. After the toner image is transferred to the copy paper 6, the toner remaining on the surface of the photoreceptor drum 10 is removed by a cleaning brush 9.
is removed.

FIG. 13 shows a schematic configuration of a fixing device conventionally used in such a copying machine.

A fixing lamp (not shown) serving as a heat source is disposed inside the heating roller 7 of the fixing device.

A drive mechanism section 10 including a sprocket or the like is provided on one side of the rotating shaft of the heating roller 7, and applies rotational force to the heating roller rough. On the other hand, the pressure roller 8 has an outer circumferential portion made of silicone rubber, for example, and is pressed against the heating roller 7 by receiving a pressure force D1E indicated by an arrow at both ends thereof. In order to keep the conveyance of the copy paper 6 constant, a pressure force E is equally applied to the pressure roller 8.

Before starting copying, the heating roller 7 is heated by a fixing lamp (not shown) to a temperature at which the toner image is sufficiently fixed on the copy paper 6, for example, to a surface temperature of about 160° C. to 220° C. The pressure roller 8 is also sufficiently heated by the heating roller rough. When the heating roller 7 is sufficiently heated, copying starts. When the copy paper 6 on which the toner image has been transferred is supplied to the pressure contact portion between the heating roller 7 and the pressure roller 8, the toner image is heated under pressure by both rollers 7.8 and fixed onto the copy paper 6. Ru.

"Problems to be Solved by the Invention" However, even if the heating roller 7 is sufficiently heated, the heat distribution is not actually uniform in the axial direction of the roller, and the temperature on the drive mechanism section 10 side is generally low.

This is because the heat of the heating roller is transferred to the frame and other parts of the device via the sprocket and transmission roller chain (not shown) of the drive mechanism section 100. Additionally, an exhaust duct is generally installed near the fixing device to prevent temperature rise inside the copying machine, and if the exhaust is uneven in the axial direction of the heating roller ruff, this will also affect the temperature distribution. Ta.

When the heating roller 7 generates a temperature difference in the axial direction in this way,
This also affects the amount of expansion of the pressure roller 8, which is heated in contact with the pressure roller 8. That is, since the silicone rubber of the pressure roller 8 is heated and expands thermally, the outer diameter of the roller in the high temperature section becomes larger than that in the low temperature section.

For this reason, the conveyance speed of the copy paper 6 becomes faster on the high temperature side, and the paper may be conveyed bent toward the low temperature side where the drive mechanism section 10 is located. In such a case, there is a possibility that the copy paper 6 may be wrinkled or the toner image after fixing may be disturbed. This is especially likely when the copy paper 6 is a continuous paper or a long copy paper such as Japanese Industrial Standard A-column 1-size paper.

In order to solve these problems,
No. 796 proposes a fixing device using a fixing lamp with a special structure.

In this fixing lamp, the density of a filament, which is a heating element, is changed in the axial direction according to the heat distribution of the heating roller 7. That is, in the fixing lamp, the density of the filament on the drive mechanism section 10 side, where heat dissipation is large, is increased so that the temperature is higher than that on the other side. With this structure, the surface temperature of the heating roller 7 is constant in the axial direction, and the copy paper 6 is conveyed straight without being bent by the fixing device. Therefore, wrinkles in the copy paper 16 and disturbances in fixing can be prevented.

However, changing the density of the filament complicates the structure of the fuser lamp and makes it expensive. In addition, since the left and right sides of the fixing lamp are defined by the high and low filament density sides, the operation of attaching the fixing lamp to the heating roller 7 becomes troublesome. Furthermore, when the fixing lamp is installed in a temperature control device, there is a problem in that the temperature cannot be adjusted unless the fixing lamp is replaced with another fixing lamp with a different filament density distribution.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a fixing device that can easily prevent paper wrinkles and fixing irregularities.

"Means for Solving the Problems" The fixing device of the present invention includes (i> a heated cylindrical heating roller, (ii) a pressure roller that is in rolling contact with the heating roller, and (iii) a toner image. a nip pressure adjustment mechanism that adjusts the nip pressure between the heating roller and the pressure roller so that the nip pressure on the side where the outer circumferential temperature is lower at both ends of the heating roller is greater than the nip pressure on the other side during fixing; Equipped with:

That is, in the fixing device of the present invention, the nip pressure between the heating roller and the pressure roller is adjusted according to the temperature difference in the axial direction.

"Example" Hereinafter, the present invention will be described in detail with reference to Examples.

Overview of Copying Machine FIG. 2 shows the external appearance of a copying machine according to an embodiment of the present invention.

This copying machine 11 has a copying machine main body 1 that is horizontally elongated and box-shaped.
The configuration is such that a similarly long and narrow box-shaped document transport section 13 is placed on the upper back side of the document transfer section 2. This document conveyance section 13 is detachable and can be replaced with other parts in a predetermined case, such as when making a copy of a book document.

A manual feed shelf 14 that can be opened and closed is arranged on the front side of the copying machine main body 12. The front portion of the upper surface of the copying machine main body 12 constitutes a document shelf 15, in which a document guide 17 for positioning a document to be inserted is slidably arranged. An operation panel 21 is attached to the side plate 18 disposed on both sides of the copying machine main body 12.The operation panel 21 is attached to the shoulder on the right side in FIG. Also, on the side of this side plate 19, there is a power switch 2 for turning the power on and off.
2 is placed. A document guide 23 is attached to the rear of the copying machine 11 for folding back the document that has passed through the document transport section 13 toward the front side of the apparatus.

FIG. 3 shows an example of the state in which copies are made with this copying machine. When making a copy, the copy paper 31 is manually fed from the copy paper insertion slot 32 with the manual feed shelf 14 tilted forward.

Next, the leading edge of the original 33 is inserted along the original shelf 15 into the original insertion opening 34 between the copying machine main body 12 and the original transport section 130. As a result, the copy paper 31 and the original document 33 begin to be carried into the apparatus at the same speed. At this time, manuscript 3
3 passes under the document transport unit 13 and is sequentially exposed.
The document is guided by a document guide 23 located behind the copying machine main body 12 and is ejected. For copy paper 31, copy machine main body 12
The course of the sheet is changed approximately 180 degrees inside the sheet, and after the image is transferred and fixed, it is discharged from the copy sheet discharge port 36.

FIG. 4 shows an outline of the internal configuration of this copying machine. A photosensitive drum 41 for forming an electrostatic latent image is arranged inside the copying machine main body 12 . Around the photosensitive drum 41, there is a charge corotron 42 for uniformly charging the document 33, a collective optical system 43 for forming an image of the image information on the document 33 on the drum surface in the form of a slit, and A fluorescent lamp 45 for exposure, a developing device 46 for developing the electrostatic latent image on the drum surface, a transfer corotron 47 for transferring the toner image obtained by development onto the copy paper 31, and a peeling of the copy paper 31. A helping butt corotron 48, a cleaning corotron 49 to neutralize any charge left on the drum, and a blade 51 to remove toner particles from the drum surface are arranged in this order.

The copy paper 31 inserted from the copy paper insertion slot 32 is transported by a transport roll 53 to a location of an arcuate guide 55, where the transport direction is changed by approximately 180 degrees by the transport force of a feed roller 56. Then, it passes between the transfer corotron 47 and the transfer corotron 48 and the photosensitive drum 41, and the toner image is transferred thereto. The copy paper 31 after the transfer passes between the heating roller 58 and the pressure roller 59 of the fixing device 57, is thermally fixed, and is then discharged from the copy paper discharge port 36 to the outside of the machine.

Description of Fixing Device FIG. 1 shows the principle of the fixing device of this embodiment.

The heating roller 58 of the fixing device 57 is made of cylindrical metal, and a fixing lamp 61 as a heat source is disposed inside it. The fixing lamp 61 uses a filament wound evenly in the axial direction. A drive mechanism section 62 consisting of a sprocket, a transmission roller chain, etc. is provided on one side of the rotating shaft of the heating roller 58, and applies rotational force to the roller.

On the other hand, the pressure roller 59 is pressed against the heating roller 58 at a predetermined nip pressure FSG at both ends thereof. Of the nip pressures, the nip pressure F on the drive mechanism H62 side can be adjusted by, for example, a pressure adjustment unit such as a screw or a spring (not shown). The nip width of the pressure roller 59 is proportional to the magnitude of this nip pressure.

Therefore, the nip width of the pressure roller 59 is adjusted by adjusting the nip pressure with this pressure adjustment section. The nip pressure F on the drive mechanism section 62 side is adjusted to be larger than the nip pressure G on the other side by the pressure adjustment section.

Adjustment of Nip Pressure FIG. 5 shows a radial cross section of the pressure roller.

The pressure roller 59 includes a cylindrical iron core 63 and an elastic body 64 made of silicone rubber. In this embodiment, the thickness of the elastic body 64 is 3 mm.

The entire pressure roller 59 has a diameter of 66 mm.

FIG. 6 shows a state in which the pressure roller is pressed against the heating roller.

When the outer circumferential speed of the pressure roller 59 is Vp, the thickness of the elastic body 64 is hl, and the amount of collapse is Δh, the conveyance speed V of the copy paper 31 is expressed by the following equation (1).

v=Vpx (1+ (Δh/h))−・−・・−(1
) Now, in equation (1), the outer peripheral speed Vp is 50 mm/s
Assuming that the S thickness h is gmm and the amount of crushing Δh is 0.5 mm, the speed V of the copy paper 31 at the nip portion is 5
3.125 mm/s (provided that the temperature is 20°C and the pressure roller diameter is 50 mm).

7 to 9 show the shape of the nip portion in the rotational axis direction in each state of the pressure roller.

71st! I shows the state of the nip portion when the nifb pressure FSG, pressure roller diameter, and temperature in FIG. 1 are the same in the axial direction. As shown in FIG. 7, the X point side where the drive mechanism section 62 of the pressure roller 59 is
On the Y point side where there is no 2, the shape of the nip portion is left-right symmetrical. Therefore, the conveyance speed of the copy paper 31 on the X point side and the Y point side becomes equal, and problems such as paper wrinkles and image shift do not occur.

However, the thickness of the elastic body 64 of the pressure roller 59 is h =
3 (mm), approximately 3% per 1°C temperature rise
．． Experiments have revealed that the increase in thickness is 5 μm. Therefore, the temperature on the X point side where the drive mechanism section 62 of the pressure roller 59 is located rises from the normal temperature of 20 degrees Celsius by 80 degrees Celsius to 100 degrees Celsius, and the temperature on the Y point side where the blade drive mechanism section 62 is not located is higher. Become,
For example, assume that the temperature has risen to 110°C. In this case, the thickness of the elastic body 64 on the X point side is 35 μm on the Y point side.
m becomes thicker, h ma = 8. 315 (rnm). Also, the amount of crushing on the X point side is 0.5 + 0.28 = 0.
78 (mm), whereas on the Y point side it is 0.5+0°315=0. It becomes 815 (mm). For this reason, X
Conveying speed V of the copy paper 31 on the point side and the Y point side,
When SVma is calculated from equation (1), v, =50.56 x (1+(0,78/8.
28) ) =55J23(mm/s)
...(2) V, =50.
63 x (1+(0,815/ 8.315)]
=55.593(mm/s)
...self... (3), and the Y point side becomes faster. The shape of the nip portion at this time is as shown in FIG.

If there is a temperature distribution in the axial direction as described above, a difference will occur in the paper conveyance speed. Therefore, the transport speed VX on the X point side
In order to make Δχ equal to the conveyance speed V on the Y point side, which is 55.593 mm/s, let Δχ be the amount of crushing of the pressure roller 59 on the X point side. .82
It may be 4 mm.

50.56 X (1+Δχ/8.28) ) =5
5.593 (mm/s) (4) In other words, the nip pressure F on the side of point X where the temperature is lower (Fig. 1)
is made larger than the nip pressure G on the Y point side, and when the amount of crushing on the X point side becomes 0.824 mm with the pressure roller heated, the conveyance speeds of the left and right copy sheets 31 become equal. FIG. 9 shows the state of the nip portion when the nip pressure is set as described above. In this way, by increasing the nip pressure G on the X point side where the amount of heat from the heating roller 58 is low, wrinkles in the copy paper 31 and image disturbance are prevented from occurring. Furthermore, since the nip pressure is higher on the X point side where the temperature is lower, it is possible to prevent a difference in the degree of fixing of the toner image between the X point side and the Y point side.

FIGS. 10 and 11 show the adjustment state of the nip pressure and the conveyance state of copy paper.

The nip pressures F and G, the amount of crushing of the pressure roller 790, the nip pressure correction value, etc. are determined by the heating roller 58 and the pressure roller 59.
It varies depending on the outer diameter, length, hardness, etc. However, in order to adjust the nip pressure FSG and check the left-right balance of the paper transport speed at the nip portion, it is sufficient to check the bending of the paper immediately after the fixing device 57. That is, if the nip pressure F (FIG. 1) on the X point side is too low, the copy paper 31 will bend toward the X point as shown in FIG. On the other hand, if the nip pressure F on the X point side is too high, the copy paper 31 will bend toward the Y point as shown in FIG. The optimum nip pressure is when the paper is conveyed almost straight.When adjusting the nip pressure, it is necessary to perform the adjustment while heating the paper with the heating roller 58 in the same way as in a normal copying state. Also, make adjustments using relatively long copy paper.

In the embodiment described above, the nip pressure on the drive mechanism side is adjusted, but the present invention is also applicable to a structure in which the nip width on the drive mechanism side can be adjusted to be wider than the nip width on the other side. For example, the pressure adjusting section may be arranged on both the drive mechanism side and the other side of the pressure roller. Also,
Apply nip pressure from the heating roller side toward the pressure roller,
It is also possible to have a configuration that can adjust this.

In addition, in the embodiments described above, the case where the temperature on the drive mechanism side is low has been explained, but for example, depending on the placement location of the heat dissipation fan, the temperature on the opposite side may be lower than the drive mechanism side due to air flow. There is. In such a case, the pressure adjustment section is adjusted so that the nip pressure on the side opposite to the drive mechanism section is increased. That is, in the present invention, the nip pressure on the lower temperature side is made larger than on the higher temperature side, and it does not matter what causes the temperature to decrease or on which side the temperature decreases.

"Effects of the Invention" As described above, according to the present invention, since a mechanism is provided to adjust the nip pressure between the heating roller and the pressure roller according to the temperature difference in the axial direction, the paper conveyance speed can be kept constant on the left and right sides. I can do it. Therefore, it is possible to prevent wrinkles in copy paper and disturbances in fixing.

[Brief explanation of drawings]

Figures 1 to 11 are for explaining one embodiment of the present invention, of which Figure 1 is a principle diagram showing the pressure principle of the fixing device, and Figure 2 is a diagram showing the fixing device of this embodiment. FIG. 3 is a perspective view showing the appearance of the copying machine used, FIG. 3 is a perspective view showing copy paper and originals set in this copying machine, and FIG. 4 is a schematic diagram showing an overview of the internal configuration of this copying machine. Configuration diagram, 5th
The figure is a sectional view showing the radial cross section of the pressure roller, Figure 6 is a sectional view showing the pressure roller in pressure contact with the heating roller, and Figure 7 is the axial nip pressure of the pressure roller, and the roller An explanatory diagram showing the state of the nip part when the diameter and temperature are equal,
Fig. 8 is an explanatory diagram showing the state of the nip portion when the temperature is high on the side without the drive mechanism of the pressure roller, and Fig. 9 is an explanatory diagram showing the state of the nip portion when the temperature in the axial direction of the pressure roller is equal and on the side with the drive mechanism. Fig. 10 is an explanatory diagram showing the state of the nip portion when the nip pressure is increased. Fig. 11 is a principle diagram showing the conveyance state of copy paper when the nip pressure on the side where the pressure roller does not have the drive mechanism is too high; Fig. 12 is a schematic diagram of a conventional copying machine; and Fig. 13 +riA is FIG. 2 is a principle diagram showing the pressure principle of a conventional fixing device. 31... Copy paper, 57... Fixing device, 58... Heat roller, 59... Pressure roller, 61... Fixing lamp , 62...
...Drive mechanism section.

Claims (1)

[Scope of Claims] A heated cylindrical heating roller, a pressure roller that is in rolling contact with the heating roller, and a nip on the side where the temperature of the outer periphery at both ends of the heating roller is lower when a toner image is fixed. A fixing device comprising: a nip pressure adjustment mechanism that adjusts the nip pressure between the heating roller and the pressure roller so that the nip pressure on the other side is greater than the nip pressure on the other side.