JPH0446376A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent damage to a fixing roll surface and soiling of a recording material by holding a thermoswitch in a non-contact state with a fixing roll in a holding member, extending the holding member in a direction of rotational axis of the roll, attaching an edge part in vicinity of a bearing edge part, and making it movable in the direction of the rotational axis for length of one edge. CONSTITUTION:The thermoswitch 12 is supported by a switch plate 13 and the right side of the plate 13 is fixed by a screw 15a in the vicinity of a right side surface of an attachment frame 1 of a fixing roll bearing 14a. A round hole is provided as the attachment hole of the screw 15a. The left side of the plate 13 is supported by a stepped screw 15b through a spring washer 16 in the vicinity of a bearing 14b, a long hole 17 is provided as an attachment hole, and the plate is provided to be able to be oscillated in an axial direction of the fixing roll. Therefore, there is no camber deformation in the switch plate 13 since no stress is imparted on the switch plate 13 even if the parts are expanded by heat. The spacing between the fixing roll 3 and the thermometal cut off 12 is fixed according to the precision of the parts, and being stable, the device is also superior in its ability to be assembled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fixing device for a printer using an electrophotographic process, and particularly to a heat fixing device that fixes a developer image on a recording material using heat and pressure.

[Prior Art] A thermal fixing device generally includes a thermistor that detects mixed carbon in the fixing roller, and a thermistor that detects the temperature of the fixing roller and mechanically switches off the electricity to the heat generating heater when the temperature of the fixing roller becomes abnormally high. A thermo switch is installed to shut it off.

The thermoswitch is an essential part of the heat fixing device because the thermoswitch prevents a fire even if some trouble occurs and the heater becomes uncontrollable.

[Problems to be Solved by the Invention] However, according to the above conventional example, the thermoswitch is attached to the frame of the heat fixing device so as to come into contact with the fixing roller via a spring material, so the fixing roller may be damaged. There was a problem in that roller scratch marks appeared on the image during the fixing process. Further, there is a problem in that some developer accumulates in the contact portion, and this adheres to the recording material due to some kind of impact, staining the recording material.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a fixing device equipped with a thermoswitch that does not damage the surface of the fixing roller and does not stain the recording material.

[Means to solve the problem] According to the invention, the above objectives are achieved.

A fixing roller having a heating element inside, a pressure roller disposed in pressure contact with the fixing roller, and a thermoswitch that detects the temperature of the surface of the fixing roller and controls energization to the heating element. In the constant FI device, the thermoswitch is held by a holding member so as not to be in contact with the fixing roller, and the holding member is formed to extend in the direction of the rotation axis of the fixing roller, and has both ends attached to the fixing roller. The holding member is attached near both bearing ends of the fixing roller, and at least one end of the holding member is movable in the direction of the rotation axis.

This is achieved by

[Function] According to the present invention, a fixing roller having one heating element inside;
A pressure roller disposed in pressure contact with the fixing roller heats and presses the unfixed developer image on the recording material, thereby performing fixing. At this time, the heat of the fixing roller is also transmitted to the frame member that supports the fixing roller, and as the fixing operation continues, the frame member begins to thermally expand. However, since at least one end of the holding member of the thermoswitch attached to the frame member is movable in the direction of the rotation axis of the fixing roller, no stress is applied due to thermal expansion of the frame member. Further, since the end portion of the holding member is attached near the bearing portion of the fixing roller, the amount of expansion of the frame member around the bearing portion is small, and the end portion and the fixing roller are maintained at a predetermined distance. Thus, the thermoswitch attached to the holding member detects the surface temperature of the fixing roller while maintaining a predetermined distance from the fixing roller.

[Embodiments] First Embodiment Next, a first embodiment of the present invention will be described with reference to FIGS. 1 to 3 of the accompanying drawings.

In FIG. 1, reference numeral 1 denotes a molded fixing frame.

The fixing frame 1 is integrated with the bottom frame 2 and includes a fixing roller 3 made of aluminum and a pressure roller 4 that is pressed against the fixing roller by a spring (not shown). Furthermore, a fixing entrance guide 5 is attached to the bottom frame 2, which introduces the leading edge of the recording material into the pressure contact area of the two rollers (hereinafter referred to as the nip area), and the recording material that has entered the nip area is The fixing roller is heated and pressurized by a halogen lamp 6, which is a heating element included in the fixing roller. Thereafter, the leading end of the recording material is separated from the fixing roller 3 by the separation claw 7, and the nip portion between the paper ejection roller 8 and the paper ejection roller 9, which is pressurized by the paper ejection roller 8 with a spring (not shown). It is guided by the downward guide IO. Further, a cleaning bat 11 and a thermoswitch 12 are attached to the upper part of the fixing roller 3 for cleaning the developer attached to the fixing roller. The thermo switch 12 is supported by a switch plate 13 which is a holding member, and the right side of the switch plate 13 is located near the right side of the frame l to which the fixing roller bearing +4a is attached, as shown in FIG. It is fixed by a hissing member 15a. Category 15
The mounting hole in a is a round hole. On the other hand, the left side of the switch plate 13 is supported by a stepped screw 15h via a spring washer 16 near the fixing roller bearing +4b, and as shown in Figure $3, the mounting is done through a hole or an elongated hole 17. The fixing roller is swingable in the axial direction, that is, in the direction of arrow A. Therefore, even if the fixing device is heated from a room temperature state to an operating state and each of the components constituting the fixing device expands thermally, the switch plate 1
Since no stress is applied to 3, there is no warping of the switch plate.

The Sui-Sochi plate 13 also includes a bearing 14a of the fixing roller 3,
Since the fixing roller 3 is supported in the vicinity of b, the distance j1M between the fixing roller 3 and the support portion is manufactured without variation, and since the distance is short, an increase in the distance due to thermal expansion is so small that it can be ignored. Therefore, according to the present invention, the distance between the fixing roller and the thermoswitch is maintained at a predetermined value regardless of the temperature of the fixing device. Also, the variation in the value is determined by the dimensional accuracy of the parts,
The switch plate 13 is made of sheet metal and its dimensions are stable. Moreover, since the distance pattern in the fixing frame 1 is long or short, it is easy to produce it with a stable value because it is made of mold. Furthermore, the gap between the fixing roller 3 and the thermoswitch 12 is tight due to component accuracy and is stable, so that assembly is also excellent.

Second Embodiment Next, a second embodiment of the present invention will be described using FIG. 4. The same reference numerals are given to the same parts as in the first embodiment, and the explanation thereof will be omitted.

This embodiment differs from the first embodiment in that the position of the thermoswitch can be adjusted. In FIG. 4, reference numeral 20 denotes a switch plate that supports a thermoswitch, and its both ends are fixed to the fixing frame 1 at one end and swingable in the axial direction of the fixing roller, as in the first embodiment. The thermo switch 12 connects to the switch plate 20 via the thermo spring 21.
The direction facing the tip of the set screw 22 attached to the switch plate 20, that is, B
Always being pushed in a direction. Further, a set screw 22 is provided at a position opposite to the rear end of the set screw 22 of the fixing frame l.
An adjustment hole 23 is formed.

In this embodiment, the switch plate 20 also controls the temperature E of the fixing device.
The fixing roller 3 is always located at the same distance from the fixing roller 3 without being affected by thermal deformation caused by the fixing roller 3.

Next, a method for adjusting the gap between the thermoswitch 12 and the fixing roller 3 will be explained. Thermo spring 21 is set screw 22
Since it is pressed, the gap can be changed by rotating the set screw 22. Then, the cleaning bat 11 is taken out from the fixing device, a gap gauge (not shown) having a predetermined thickness is inserted into the gap from the direction of arrow C, and the set screw 22 is rotated to obtain a predetermined gap. Finally, the set screw 22 may be fixed to the switch plate 20 using a heat-resistant adhesive.

In this embodiment, the gap between the fixing roller and the thermoswitch can be easily adjusted, and even if the temperature of the fixing device rises and the components thermally expand after adjustment, the value of the gap is always stable. ing.

<Third Embodiment> Next, a third embodiment of the present invention will be described using FIG. 5. The same reference numerals are given to the same parts as in the first embodiment, and the explanation thereof will be omitted.

This embodiment differs from the first embodiment in that a shaft is used instead of a switch plate. In FIG. 5, reference numeral 30 denotes a cylindrical shaft installed between both sides of the fixing frame, and is prevented from being pulled out by providing E-links at both ends about lam outside the sides of the fixing frame. Furthermore, a molded thermoholter 31 to which a thermoswitch 12 is attached is press-fitted into the center of the thermostat 30. The convex portion 31' of the thermo holder 31 is engaged with a hole in the fixing frame l provided at a position facing the convex portion 31' of the thermo holder 31, thereby preventing the thermo holder 31 from rotating.

Even in this embodiment, even if the temperature of the fixing device rises and the component parts expand thermally, no stress is applied to the sensor axis.

Due to the thermal expansion of the fixing frame, the distance between the fixing roller and the sensor axis becomes slightly longer, or the thermoholter 31 also thermally expands in a direction that offsets this change, so the change due to temperature rise is also small. Therefore, the gap between the fixing roller and the thermoswitch is always at a stable value.

[Effects of the Invention] As explained above, the present invention is characterized in that both ends of the holding member of the rigid switch are attached near the bearing of the fixing roller, and at least one end is swingable in the axial direction of the fixing roller. It was movably supported. This thermoswitch was designed so that it did not come into contact with the surface of the fixing roller.

Therefore, even if the temperature of the fixing device rises and its component parts expand thermally, no stress is applied to the thermoswitch holding member. Further, since both ends of the fixing roller are supported near the bearing section, the distance from the fixing roller to the support section can be made with high precision, and thermal deformation is minimal. As a result, the gap between the thermoswitch and the surface of the fixing roller can be maintained accurately and in a stable state. Furthermore, by making the thermoswitch non-contact with the fixing roller, the surface of the fixing roller is not damaged, and developer accumulated in the thermoswitch section can be prevented from adhering to the recording material.

Furthermore, by preventing damage to the fixing roller, the life of the fixing roller can be extended, and the replacement period of the fixing device can be extended or it can be made unnecessary to replace it.

[Brief explanation of drawings]

#! Fig. 1 is a vertical sectional view of the device according to the first embodiment of the present invention, Fig. 2 is a partially broken WkWr side view of the Fig. 1s1 device, Fig. 3 is an enlarged view of a part of the device shown in Fig. 2, and Fig. 4 FIG. 5 is a vertical cross-sectional view of a device according to a second embodiment of the present invention, and FIG. 5 is a vertical cross-sectional view of a device according to a third embodiment of the present invention. 3------Fixed roller 4...Pressure roller 12...Thermo switch

Claims (1)

[Scope of Claims] A fixing roller having a heating element inside, a pressure roller disposed in pressure contact with the fixing roller, and detecting the temperature of the surface of the fixing roller to energize the heating element. A fixing device having a thermoswitch for controlling the fixing device, wherein the thermoswitch is held by a holding member so as not to contact the fixing roller, and the holding member is formed to extend in the direction of the rotation axis of the fixing roller; A fixing device, wherein both ends are attached near both bearing ends of the fixing roller, and at least one end of the holding member is movable in the direction of the rotation axis.