JPH03179481A - Fixing device - Google Patents

Abstract

PURPOSE:To eliminate a defect in fixation right after printing operation is started by pressing a fixing roller and a pressure roller against each other with a 1st press- contacting force when printing operation is performed or with a 2nd press-contacting force when not, and making the 2nd press-contacting force less than the 1st press- contacting force. CONSTITUTION:When the printing operation is performed, a cam 6 rotates to press up a movable plate 10 which is rotatable around a fixed shaft 9, so a spring 8 extended between the movable plate 10 and a holding member 4 has specific extension and a force which lifting the holding member 4 operates. A spring 7, on the other hand, is extended between a fixed hook part 11 which is added to a frame, etc., and the holding member 4 and a force which lifts the holding member 4 operates as well as the spring 8. When the printing operation is not performed, the spring 8 enters a free state wherein there is no extension as the cam 6 rotates. The spring 7, however, generates the same spring force as that in the printing operation even when the printing operation is not performed irrelevantly to the rotation of the cam 6. Consequently, the fixing roller and pressure roller are held in a light press-contacting state when the printing operation is not performed and stable fixation strength is obtained right after the printing operation is started.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a fixing device such as a printing mechanism using an electrophotographic method.

[Background of the invention]

A fixing device using a heat fixing method heats and melts the toner image and fixes it on the paper by passing the paper to which the toner image is attached by electrostatic force or the like through a nip between a fixing roller and a pressure roller. be. Normally, at least one of the fixing roller and the pressure roller is made of an elastic material such as silicone rubber, and when the fixing roller and the pressure roller are in pressure contact with each other under a predetermined load, the elastic material deforms, so-called " A “nip” is formed. This nip width greatly affects the fixing performance, and although it varies depending on the printing speed of mounting and the properties of the toner used, it is generally required to be about 3 mm to 15 mm. In order to ensure a nip width of about 3-15 an, it is necessary to press the fixing roller and the pressure roller with a high load. It goes without saying that the specific value of the load is determined by various conditions, but for example, if the diameters of the fixing roller and the pressure roller are each φ
50, and if the necessary nip width is about 8 nn, then a load of about 100 kg is required.

As mentioned above, the fixing roller and the pressure roller are pressed together under a high load during printing (when the roller is rotating), but they are also pressed under the same high load when not printing (when the roller is stopped). If this condition continues, local permanent deformation will occur in the elastic body, such as silicone rubber, provided on at least one of the fixing roller and the pressure roller. If local permanent deformation occurs in the elastic body, uneven rotation will occur when the fixing roller and pressure roller rotate, leading to serious problems such as poor paper conveyance and poor printing. To solve this problem, when printing (when the roller rotates)
In this method, the fixing roller and the pressure roller are brought into pressure contact with each other under a predetermined load, while at the time of non-printing (when the rollers are stopped), the load between the rollers is released by a load release mechanism, and the fixing roller and the pressure roller are pressed together. The method of asking difficult questions is commonly used. However, this method has the following problems.

Usually, the fixing roller, which comes into direct contact with the unfixed toner image, has a heat source such as a lamp inside it, and its surface temperature is kept within a predetermined range by an external temperature control means. Generally, the pressure roller does not have a heat source, and its surface temperature is not controlled in any way.

From the above, when the fixing roller and the pressure roller are in pressure contact, the pressure roller receives heat from the fixing roller, so the pressure roller can maintain a certain level of surface temperature. However, when the fixing roller and the pressure roller are separated from each other, the surface temperature of the pressure roller decreases. Therefore, when the fixing roll and the pressure roller are separated from each other for a long time and then change to the pressure contact state again, the surface temperature of the pressure roller is low, so a large amount of heat is transferred from the fixing roller to the pressure roller. flows into the fuser roller, and for a while the surface temperature of the fixing roller is
This results in a situation where the temperature becomes lower than a predetermined temperature.

That is, the first problem with the prior art is that if the fixing roller and the pressure roller are separated from each other during printing, there is a possibility that a fixing failure may occur due to a decrease in the surface temperature of the fixing roller immediately after printing starts.

Next, the second problem of the prior art will be explained. In the conventional fixing device, the fixing roller and the pressure roller are separated from each other when printing is stopped, so that if a paper jam occurs, the paper can be easily pulled out. However, unfixed toner adheres to a portion of paper that is jammed in the fixing device that is located upstream in the paper conveyance direction from the nip between the fixing roller and the pressure roller. When the paper is pulled out from the nip portion downstream in the paper transport direction, the unfixed toner is rubbed against the fixing roller, causing a problem in that a large amount of toner adheres to the fixing roller.

Usually, a cleaning member such as felt is in contact with the fixing roll, and this is for cleaning a minute amount of toner that adheres to the fixing roller when the paper passes normally. As mentioned above, if a large amount of toner adheres to the fixing roller at one time, cleaning will be insufficient.
This results in contamination of the next sheet of paper and the pressure roller.

[Purpose of the invention]

An object of the present invention is to provide a fixing device that solves the above-mentioned drawbacks of the prior art.

[Summary of the invention]

The present invention focuses on the problem that occurs when the fixing roller and the pressure roller are separated from each other during non-printing, as described in the explanation of the prior art. The roller pressure mechanism has been devised to maintain the pressure contact state.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to the drawings. FIGS. 1 and 2 are side views and FIG. 3 is a perspective view of a fixing device according to the present invention.

In the figure, a fixing roller 1 is rotatably fixed to frames on both sides (not shown), and a pressure roller 2 is held by a holding member 4 that is rotatable around a fixed shaft 5. It shows the state at the time. The cam 6 is rotated by a drive means (not shown) and is fixed at the position shown in FIG. 1 during printing. Since the movable plate 10, which is rotatable around the fixed shaft 9, is pushed up by the cam 6, the spring 8, which is hooked between the movable plate 10 and the holding member 4, is stretched to a predetermined extent, and the holding member A force acts to lift 4 upward. On the other hand, the spring 7 is a fixed spring hook attached to a frame (not shown), etc., and is passed between the holding member 4 and the fixed spring hook portion 11, and similarly to the spring 8, it provides a force for lifting the holding member 4 upward. do. In other words, the fixing roller 1 required during printing
The pressing force P1 of the pressing roller 2 is provided by the springs 7 and 8 described above.

FIGS. 2 and 3 show the state during non-printing. The cam 6 is fixed at the position shown in the drawing by a driving means (not shown). As the cam 6 rotates, the movable plate 10 descends counterclockwise, and the spring 8 is in a free state with no stretch. On the other hand, the panel 7 provides the same spring force during non-printing as it does during printing, regardless of the rotation of the cam 6. That is, the pressing force P2 between the fixing roller 1 and the pressing roller 2 during non-printing is provided only by the spring 7 described above.

The pressing force P2 is a small force that does not cause permanent deformation of the elastic body provided on at least one of the fixing roller 1 and the pressing roller 2 even if left for a long time;
It goes without saying that two conditions must be met: and when either one of the pressure rollers 2 is driven, the remaining roller must have sufficient force to rotate as a driven roller without slipping.

In FIG. 3, the knob 14 is connected to the shaft 16 and the gear 1819.2.
0, and when the knob 14 is turned, the fixing roller 1 and the pressure roller 2 pressed thereto rotate. That is, when a paper jam occurs, the paper can be removed by turning the knob 14. If the paper cannot be removed by using the knob 14, turning the lever 13 connected to the cam 12 will cause the cam 12 to push down the holding member 4 and separate the fixing roller 1 and pressure roller 2. can be easily taken out.

During printing standby, the fixing roll 1 and the pressing roll 2, which are pressed together by the pressing force P2 as described above, are rotated continuously at a slower speed than during printing or rotated intermittently by a driving mechanism (not shown). . This stabilizes the surface temperature of the pressure roller, so that stable fixing strength can be obtained even immediately after printing starts.

1. In the example, two types of springs are used to obtain the pressure contact force P during printing and the pressure contact force P2 during non-printing. The same effect can be obtained even if predetermined Pl and P2 are obtained by changing the amount of elongation. A specific example is shown in FIG. During printing, the cam 22 is fixed at a first position as shown in FIG. 5 by a drive device (not shown), and the pressure contact force between the fixing roller 1 and the pressure roller 2 necessary during printing is maintained by a predetermined extension of the spring 8. P, is provided. Similarly, during non-printing, the cam 22 provides a pressing force P2 with the second position as shown in FIG. In the unlikely event that the fixing roller 1 and the pressure roller 2 are fixed due to a paper jam or the like and it becomes necessary to separate the fixing roller 1 and the pressure roller 2, manually rotate a knob, etc. (not shown) connected to the cam 22. This switches the cam 22 to the third position as shown in FIG. At this time, since the spring 8 is in a free state, the holding member 4 is held against the shaft 5 by its own weight.
Rotate counterclockwise around . The pressure roller 2 is
Following the movement of the holding member 4, the fixing roller 1 and the pressure roller 2 are separated from each other as shown in FIG.

〔Effect of the invention〕

According to the present invention, since the fixing roller and the pressure roller are in pressure contact even during non-printing, the temperature of the pressure roller does not decrease, and it is possible to prevent fixing failure immediately after printing starts. Further, when a paper jam occurs, the paper can be removed while the fixing roller and the pressure roller are in pressure contact, so the fixing roller and the paper do not rub against each other, and the fixing roller can be prevented from being stained with toner. Also, since it is equipped with a mechanism to mrlJ the fixing roller and pressure roller, even if a paper jam occurs that cannot be repaired if the fixing roller and pressure roller remain in pressure contact, it can be easily repaired. I can do it.

[Brief explanation of drawings]

1 and 2 are side views showing one embodiment of the fixing device according to the present invention, and FIG. 3 is a perspective view. FIG. 4, FIG. 5, and FIG. 6 are side views showing application examples. In the figure, 1 is a fixing roller, 2 is a pressure roller, 3 is a heater lamp, 4 is a holding member, 5 is a shaft, 6 is a cam, 7.8 is a spring, 9 is a shaft, 10 is a movable plate, and 11 is a spring hook. Part 1
2 is a cam, 13 is a lever 14 is a knob, 15.16.17
indicates a shaft, 18, 19, 20 indicates a gear, and 21 indicates a bearing. )2 days

Claims (1)

[Claims] 1. A fixing device such as an electrophotographic device that fixes the toner image on the paper by passing the paper having the toner image between a fixing roller and a pressure roller that is in pressure contact with the fixing roller. In the above, the fixing roller and the pressure roller are pressed against each other by a first pressure force during printing, and are pressed against each other by a second pressure force when not printing, and the second pressure contact force is equal to the first pressure contact force. A fixing device characterized by being smaller than. 2. The fixing device according to claim 1, further comprising a knob for manually rotating the fixing roller and the pressure roller. 3. The fixing device according to claim 1, further comprising a mechanism for separating the fixing roller and the pressure roller. 4. The fixing device according to claim 1, wherein the fixing roller and the pressure roller rotate when the fixing device is not printing (standby for printing).