JPS5885470A - Fixing device - Google Patents

Abstract

PURPOSE:To obtain always a constant roller linear speed independently of the rise of the temperature of the roller, by providing a driving member which rotates a fixing roller and a pressure roller with a frictional force while allowing them to follow up. CONSTITUTION:Neither of a fixing roller 23 and a pressure roller 21 are used as driving sources, and the rotatory force of these rollers is obtained from a driving roller 26 pressed to the pressure roller 21. The driving roller 26 is not affected too much by the heat of the fixing roller 23, and the linear speed of the roller 26 is always constant approximately independently of the temperature of the fixing roller 23.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fixing device that includes a fixing roller and a pressure roller that are in pressure contact with each other and at least one of which is heated.

In the fixing device of the above type, a device is known in which either the fixing roller or the pressure roller is used as a driving source, and the other is driven to rotate by the friction force between their surfaces. For example, as shown in FIG. 1, a pressure roller 1 made of an elastic member such as silicone rubber is brought into pressure contact with a fixing roller 3 made of Teflon or the like having a heater 2 inside, and the fixing roller is rotated counterclockwise in the figure. It is like being driven to. In this case, the toner image 5 on the transfer paper 4 is fixed while passing through a pressure contact surface (hereinafter referred to as a fixing section) between the driven fixing roller 3 and the driven rotating pressure roller 1. however,
When this fixing roller 6 is used as a driving source, it is necessary to extend the axis of the roller and attach a transmission member such as a sprocket or gear to it in order to obtain power, which may result in poor roller temperature distribution or It is also necessary to increase the length of the heater 2. Furthermore, since the heat capacity increases due to the attachment of the above-mentioned transmission member, the temperature rise time becomes slow (and heat is easily dissipated), and the thermal efficiency is generally not good.Furthermore, if the fixing roller 3 is thin and has low strength, for,
A disadvantage also arises in that the driven fuser roller creates torsional stresses.

On the other hand, when the pressure roller 1 is used as the driving source, there is no problem with the ridges described above, but on the other hand, the pressure roller 1 receives heat from the fixing roller 3 and thermally expands, resulting in a linear velocity of the roller. or faster. Regarding the heat and lucidity mentioned above, for example, the diameter is 45 m.
a. Rubber layer 8.5 myO If the i-knit temperature of the roller increases by 100°C, the calculated diameter will expand to 47 m.

When the linear speed of the roller increases, for example, a difference occurs between the linear speed of the photosensitive drum (not shown) for transferring the toner image 5 onto the transfer paper 4, and the distance between the fixing section and the drum increases. If the value is small, normal transfer will not be performed during transfer, resulting in image deletion. Also, normally, a pair of paper ejection rollers (not shown) that rotate independently at a constant linear velocity are arranged downstream of the fixing device (right position in the figure). If the speed of the rollers increases, the transfer paper will sag at the discharge roller section, and the final copy paper will be wavy.

In addition to the fixing device of the above type, as shown in FIG. 2, a pair of pressure rollers 11a and 11b each having heaters 12a and 12b are provided above and below the fixing roller 13, which has an elastic body such as silicone rubber on its outer periphery. There is also known an apparatus in which the pressure rollers 11a and 11b are driven at the same linear velocity, thereby heating and fixing the toner image 5 on the transfer paper 4' while the fixing roller 1 is driven by friction. This fixing device includes pressure rollers 1 L-'a, 1 lb
Although it is intended to prevent slip between the fixing roller 13 and the fixing roller 13 and eliminate the cliff speed difference between the two, it has the following drawbacks.

First, since at least two pressure rollers and heaters are required, the cost is high. Second, since the surface of the fixing roller 13 is heated by the pressure rollers 11a and 11b, thermal efficiency is poor. Sixth, it is unavoidable that variations in diameter occur between the upper and lower pressure rollers i1a and Ilb, and therefore it is actually difficult to rotate the fixing roller 16 without slipping. Fourth, as shown in FIG. 3, when the amount of penetration of the upper and lower pressure rollers 11a, 11b into the fixing roller 13 is not constant, a difference in slow speed also occurs.

As mentioned above, in the conventional fixing device, either the fixing roller or the pressure roller is used as the driving source, so the linear speed of the roller changes as the roller temperature rises. In order to prevent changes in linear velocity, a complicated structure is required, which also has the disadvantage of decreasing heating efficiency.

In view of the above drawbacks, the present invention has a simple configuration, and
It is an object of the present invention to provide a fixing device that can always obtain a constant roller linear speed regardless of the rise in roller temperature.

Hereinafter, the present invention will be explained based on drawings showing embodiments thereof.

FIG. 4 is a partial plan view of a fixing device showing a first embodiment of the present invention. In the figure, a machine frame 20 (() is a fixing roller 23 and a pressure roller 21 that are in pressure contact with each other are both rotatably attached, and paper conveyance paths 24 and 25 are installed before and after the pressure contact portions of these rollers, respectively. The transfer paper 4 having the toner image 5 is sent into the fixing device from the conveyance path 24 as shown in the figure, and a drive roller 26 is arranged on the paper introduction side of the pressure roller 21. The drive roller 26 receives power from a drive source (not shown) through a sprocket 27 attached to the end of the shaft 26a and a chain meshing with the sprocket 27, and rotates in the direction of the hour hand in the figure. and pressure roller 2
16 are in contact with each other under appropriate pressure, so the rotation of the drive roller 26 is transmitted to the edge pressure roller 21 by frictional force, thereby causing the roller 21 to rotate counterclockwise. The drive roller 26 is desirably made of a material with low thermal expansion and has a rough surface.

The rotational force of the driven rotating pressure roller 21 is
It is transmitted to the fixing roller 23 which is in pressure contact with the fixing roller 1.

Therefore, the fixing roller 26 rotates in a clockwise direction.

The transfer paper 4 conveyed through the conveyance path 24 is transferred to the fixing roller 26
As the pressure roller 21 rotates, the fixing roller 21 passes through a pressure contact portion between the two, and is heated by heat from a heater 22 provided in the fixing roller 2 filter.

Thus, the toner image 5 is fixed on the transfer paper 4.

After the transfer paper has been fixed, it passes through the conveyance path 25 and then passes through a pair of paper ejection rollers 29 arranged in front of the conveyance path 25.
The paper is ejected by 50.

In this way, in this embodiment, neither the fixing roller 23 nor the pressure roller 21 is used as a driving source, and the rotational force of these rollers is obtained from the drive roller 26 that is in pressure contact with the pressure roller 21. Here, the drive roller 26 is the fixing roller 23
For example, if the surface temperature of the fixing roller 23 is 190°C, the temperature of the pressure roller 21 will rise to 100 to 110°C in a stable state, but the temperature of the drive roller 26 will rise to 50 to 110°C. The temperature only rises to about 60°C. Therefore, the linear velocity of the drive roller 26 is always approximately constant regardless of the temperature of the fixing roller 26, and as a result, the pressure roller 21, which is driven by the drive roller 26 due to frictional force, may have an outer diameter that decreases due to thermal expansion. Grew up 1
′, it always rotates at a nearly constant linear speed. In FIG. 4, the transfer paper 4 is separated from the photosensitive drum (not shown), but in this embodiment, the linear speed of the fixing roller 23 and the pressure roller 21 is always almost constant as described above, so the photosensitive drum 4 is separated from the photosensitive drum (not shown). In particular, the transfer paper 4 separated from the body drum can be directly sent to the fixing device without passing through the conveyance section, and in this case, the entire device can be made smaller.

Further, since the fixing roller 25 is not used as a driving source, it is naturally unnecessary to attach a driving system to the roller 23, and therefore the fixing roller 23 can be made symmetrical, compact, and lightweight. Therefore, the efficiency of the heater 22 is improved and the start-up time is shortened.

Further, in order to drive the fixing roller 23 and the pressure roller 21, it is sufficient to adopt a very simple configuration in which the drive roller 26 is brought into pressure contact with the pressure roller 21, and the cost is low.

Further, the drive roller 26 not only rotates the pressure roller 21 but also serves as a cleaning roller for cleaning the roller 21.

FIG. 5 shows a second embodiment of the invention, in which:
The pressure roller 21 is driven on its end surface by a belt 35 with little expansion and contraction that meshes with the driving sprocket 3B.

The fixing operation by the fixing roller 2'5 and the pressure roller 21 is the same as in the first embodiment described above, but in this embodiment, since there is less contact surface between the drive source and the pressure roller 21, the temperature of the drive source does not rise. (Also, there is a unique effect that the heat dissipation of the pressure roller 21 is reduced.

FIG. 6 shows a third embodiment of the invention. In this example,
A drive roller 46 is arranged on the paper output side of the pressure roller 21, and this drive roller 46 is in pressure contact with the pressure roller 21 and also with the paper discharge roller 30 at the same time. Therefore, the pressure roller 21, the fixing roller 26, and the paper ejection roller pair 29, 30 are driven by one driving source, which is very economical and structurally advantageous. Furthermore, since the pair of paper ejection rollers 29 and 30 are driven by the surface frictional force with the drive roller 46, even if the operator tries to pick up the stocked transfer paper, the pair of paper ejection rollers 29 and 30 are not forced to be driven. There is less risk of injury.

[Brief explanation of drawings]

FIG. 1 is a side view showing the main parts of one example of a conventional fixing device, FIG. 2 is a side view showing another example of the conventional fixing device, and FIG. 6 is a pressure roller 11a in FIG. 11b is embedded in the fixing roller 13, FIG. 4 is a side sectional view showing the first embodiment of the present invention, FIG. 5 is a perspective view showing the second embodiment of the present invention, and FIG. Third aspect of the present invention
It is a side sectional view showing an example. 3.13.23...Fixing roller 1.11a, 11b, 21=-pressure roller 26.46.
... Drive roller 35... Drive belt No. 1 Fig. Rod 2 is l Fig. 3 Fig. 4 □ ' 20 92223 2524 '' ~, - 3oO- Intertwined 5 Mouth j 482-

Claims (3)

[Claims] (1) In a fixing device that includes a fixing roller and a pressure roller that are in pressure contact with each other and at least one of which is heated, one of the rollers has a drive member that rotates one of the rollers driven by frictional force. A fixing device comprising: (2) The fixing device according to claim 1, wherein the drive member is a drive roller that comes into contact with the outer peripheral surface of the pressure roller. (3) The fixing device according to claim 1, wherein the drive member is a drive belt that is passed around the outer peripheral surface of the pressure roller.