JPH1124473A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent decreases in the temperatures of the ends of a fixing roller caused when a large-size sheet is inserted, and increases in the temperatures of the ends of the fixing roller caused when a small-size sheet is inserted. SOLUTION: On both ends of the fixing roller 1, bimetal caps 11 (11a, 11b) are provided. Inside the fixing roller, reinforcement rings 6 (6a-6c), through each of which a hole is made for allowing an air flow to pass along, are provided. A fin is provided on the side of each reinforcement ring, and the air flow is generated in one direction by the rotation of the fixing roller 1. When the temperatures of the ends of the fixing roller rise, the caps 11 deform to open the ends of the roller, and release heat inside the roller by the air flow generated by the actions of the fins of reinforcement rings 6. When the temperatures of the ends are low, the caps 11 close.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device in an image forming apparatus such as a copying machine, a printer, and a facsimile.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer, a facsimile or the like using an electrophotographic system, a transfer paper,
BACKGROUND ART A heat fixing device is widely used as a fixing device for fixing an unfixed image (toner image) transferred onto a recording material such as an OHP film to the recording material. Conventionally, as a heat fixing device, a heat roller system in which a pressure roller is pressed against a fixing roller heated by a heat source, and an unfixed toner image is fixed by heat and pressure while nipping and conveying the recording material between both rollers. Things are heavily used.

In the heat roller system, the fixing roller is controlled so that the surface temperature falls within a predetermined temperature range in order to provide a sufficient amount of heat necessary for melting and fixing the toner. However, since both ends of a normal fixing roller are open, the amount of heat supplied by a heat source such as a halogen heater is more likely to escape toward both ends of the roller, and the temperature distribution on the surface of the fixing roller is inevitably reduced at the roller center (axial center). Part), the both ends become lower by about 10 to 20 ° C. For this reason, even if the surface temperature in the central portion in the roller axial direction (width direction) is detected by a temperature detecting means such as a thermistor to control the surface temperature within the above-described predetermined temperature range, the surface temperature at the central portion in the roller width direction becomes lower than the predetermined value. Even if the temperature is controlled within the above range, the surface temperature of both ends of the roller becomes low. When the temperature of the fixing roller surface is lowered due to environmental fluctuations or continuous paper passing, there is a problem that a temperature drop occurs at both ends of the fixing roller during standby and when a large size paper (A4 width, A3, etc.) is passed, resulting in poor fixing. Occur. As a method of solving the temperature drop at the roller end, it is common to slightly increase the heat generation distribution (in the roller axis direction) of the heater at both ends. On the contrary, as a side effect thereof, small-size paper (B5 During continuous paper passing (vertical, etc.), heat is not removed in the non-paper passing area, so the surface temperature at both ends of the fixing roller rises as the number of continuous paper passing increases, and the Teflon layer on the roller surface becomes If the large size paper is passed after the small size continuous paper has been damaged, wrinkles may occur due to uneven temperature in the axial direction.

[0004] As a countermeasure against the rise in the temperature at the end of the roller, for example, Japanese Patent Laid-Open No. 61-55676 discloses a fan provided near the opening at both ends of the fixing roller (outside the fixing roller). There has been proposed a fixing device in which a fan is turned on / off to adjust a temperature distribution in a fixing roller longitudinal direction (axial direction).

[0005]

However, in the fixing device described in the above publication, the air inside the roller is sucked by a fan from both ends of the fixing roller when a large-size sheet is passed. In this case, there is a problem that the suction efficiency is poor and that the heat itself at both ends of the roller is deprived, which may cause a temperature drop.

Further, in the identification attachment device, the fan is stopped when a small size paper is passed. However, in general, considering that the heat generation distribution of the heater is large at both ends, the fan is stopped when the fan is stopped. There is a problem that the temperature at both ends of the roller is increased rather than when the is operated, which may cause a problem such as toner offset.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the conventional fixing device, and prevents a decrease in the temperature of the end portion of the fixing roller when large-size paper is passed and an increase in the end temperature of the fixing roller when small-size paper is passed. An object of the present invention is to provide a fixing device that can perform the fixing.

[0008]

SUMMARY OF THE INVENTION According to the present invention, there is provided a recording apparatus comprising a fixing roller which is driven to rotate, and a pressing roller which is in pressure contact with the fixing roller. In a thermal fixing device for fixing an unfixed image to a recording material by passing a material, cap members that can be selectively opened and closed at both ends of the fixing roller are provided, and a plurality of reinforcing members are provided inside the fixing roller. Provided,
The reinforcing member is solved by having an air flow hole through which air passes and fins that generate an air flow by rotating the reinforcing member.

Further, in order to solve the above-mentioned problem, the present invention is characterized in that the selectively openable / closable cap member opens the inside of the fixing roller when the end temperature of the fixing roller is higher than a predetermined temperature. It is proposed to close the inside of the fixing roller at the following times.

Further, in order to solve the above-mentioned problems, the present invention proposes that the selectively openable / closable cap member is formed of a bimetal in which two kinds of metals having different coefficients of thermal expansion are bonded to each other. I do.

According to another aspect of the present invention, there is provided a recording apparatus comprising: a fixing roller which is driven to rotate; and a pressure roller which is pressed against the fixing roller. In a thermal fixing apparatus for fixing an unfixed image to a recording material by passing a material, a plurality of reinforcing members are provided inside the fixing roller, and the reinforcing members open the air flow holes through which air passes and the air flow holes. A fin that can be selectively displaced between a position where the air flow hole is opened and a position where the air flow hole is opened. I do.

Further, the present invention proposes that the fin is formed of a shape memory alloy in order to solve the above problems.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional configuration diagram illustrating a main part of a fixing device according to an embodiment of the present invention. In this figure, a fixing roller 1 is supported by a fixing side plate 3 via a bearing (roller bearing) 2. A pressure roller 8 is pressed against the fixing roller 1 with a constant pressing force by a biasing means (not shown). The fixing roller 1 includes a halogen heater 4 as a heat source inside, and the temperature of the roller surface is detected by a thermistor 5 provided in contact with the roller surface at the central portion in the axial direction. The energization to the halogen heater 4 is controlled based on the detection output of the thermistor 5, and the surface temperature of the fixing roller is controlled to be constant. A driving gear 7 is fixed near one end (right end in the figure) of the fixing roller 1, and a driving force is transmitted to the driving gear 7 from a driving system (not shown) to be driven to rotate. In the present embodiment, the light distribution (heat generation distribution) of the halogen heater 4 is set such that a predetermined range on both ends of the roller is higher than the center.

Three reinforcing rings 6a, 6b and 6c are provided inside the fixing roller 1 to prevent the fixing roller 1 from being bent or crushed when the pressing roller 8 is pressed. As shown in FIG. 2, the reinforcing ring 6 has a plurality of holes 9 through which the halogen heater 4 penetrates.
Fins 10 are provided. The fin 10 is provided by cutting and raising a part of the side surface of the reinforcing ring 6, and an air flow hole 10 a is formed in the side surface of the reinforcing ring 6.
The fin 10 projects obliquely (before) on the air flow hole 10a. In this embodiment, only the fins of the reinforcement ring 6a at the left end in FIG. 1 are provided inside the cylinder of the reinforcement ring, and the fins of the reinforcement rings 6b and 6c at the center and the right end are outside the cylindrical side surface of the reinforcement ring. It is provided to exit.

The number and the position of the reinforcing rings 6 are determined so that the heat capacity inside the roller is not significantly increased and the reinforcing ring 6 can be effectively reinforced. In the embodiment, the axial direction of the fixing roller 1 is:
It is desirable to have a total of three places: the center in the width direction) and both end positions of the pressure roller 8, or a total of three places: the center of the pressure area and the support portions of the bearings 2 on both sides. In this embodiment, the reinforcing ring 6 is provided at the latter position (the center of the fixing roller and the bearings on both sides).
Is arranged.

Caps 11a and 11b are provided at both ends of the fixing roller 1 to close it. As shown in FIG. 3, the caps 11a and 11b are made of a bimetal in which two types of metal plates 12 and 13 having different coefficients of thermal expansion are bonded in a plane. Therefore, when the temperature rises from the normal state, the bimetallic cap 11 expands one of the metal plates 13 more than the other metal plate 12, and as shown in FIG. (Cross section) to a bowl or dish shape (arc-shaped cross section).

In the fixing device of this embodiment, the fixing roller 1
Is a size corresponding to A4 landscape or A3 size. Therefore, when a transfer sheet of A4 landscape or A3 size is passed, the transfer sheet uniformly removes heat from the surface of the fixing roller 1. Therefore, no temperature rise occurs at the end of the fixing roller 1, and the caps 11 a and 11 b maintain a planar shape without deformation, and the caps 11 a and 11 b close both end openings of the fixing roller 1 as shown in FIG. ing.

In this embodiment, the control temperature (set temperature) of the fixing roller 1 is set at 185 ° C. And A
When four horizontal or A3 size transfer papers are passed, the caps 11a and 11b usually have a temperature of about 165 to 175 ° C. At this time, the caps 11a and 11b maintain a planar shape as shown in FIG. The openings at both ends of the fixing roller 1 are closed as they are. Therefore, heat does not escape from the end of the fixing roller 1 and heat is convected inside the roller, so that a substantially uniform temperature distribution can be obtained in the longitudinal direction (axial direction) of the roller.

On the other hand, when small-size transfer paper such as A4 portrait or A5 or B5 is passed, the end temperature of the fixing roller 1 increases as the number of continuous papers increases. The temperature rise at the end of the fixing roller is determined by the number of sheets passed per unit time (C
PM) and the calorific value of the heat source (heater wattage),
It will rise to about 230-250 ° C. When the end temperature of the fixing roller 1 rises to this range, the bimetal cap 11 is deformed as shown in FIG. 5 and warps toward the roller axis (center of the cap). Therefore, a gap is generated between the openings at both ends of the fixing roller 1 and the caps 11a and 11b.

By the way, as described above, the reinforcing ring 6
Fins 10 are provided at a, b, and c. The fins 10 project obliquely from the side surface of the ring, and the fins 10 push the air to generate airflow in one direction by rotating the reinforcing ring 6 with the rotation of the fixing roller 1. Generates airflow. In the present embodiment, the fins 10 provided on each of the three reinforcing rings 6a, 6b, 6c are provided so as to generate a flow of air in the same direction. Accordingly, when the temperature of the end portion of the fixing roller 1 rises and a gap is formed between the caps 11a and 11b and the opening at both ends of the roller, as shown by an arrow in FIG. The air flows rightward inside the roller, and the fixing roller 1
Escape to the outside. As a result, the amount of heat that has caused a temperature rise at both ends of the fixing roller 1 can be effectively radiated. The driving side of the fixing roller 1 (the right side in FIGS. 1 and 5)
An exhaust fan (not shown) is provided near the outside of the end, and exhausts hot air flowing out of the fixing roller 1 to the outside of the apparatus.

When the fixing device is on standby, the temperature of the end of the fixing roller 1 does not rise so as to deform the caps 11a and 11b. The opening is closed. For this reason, heat can be prevented from escaping from the end opening of the fixing roller, and the end temperature can be prevented from lowering during standby.

As described above, according to the fixing device of the present embodiment, it is possible to prevent the temperature of the end portion of the fixing roller 1 from decreasing at the time of standby and at the time of large-size sheet passing with a simple configuration.
It is possible to prevent an end portion of the fixing roller, that is, poor fixability of an end image on a large-size sheet. At the same time, it is possible to prevent the temperature of the end portion of the fixing roller 1 from rising when the small-size paper is continuously fed, thereby preventing the fixing roller release layer (Teflon layer) from being damaged and fixing wrinkles from being generated. In addition, it is possible to prevent the offset of the image of the sheet end portion when large-size paper is passed after continuous small-size paper is passed. In the present embodiment, the light distribution of the halogen heater 4 is increased on the roller end side in order to prevent the temperature from decreasing at the end of the fixing roller. Further, by providing the reinforcing ring 6, the core metal (substrate) of the fixing roller 1 can be made thinner, so that it is possible to provide a fixing roller which is fast rising and has sufficient strength.

The present invention is not limited to this embodiment. For example, the number of reinforcing rings provided in the fixing roller can be arbitrarily set. In addition, the shape and number of the fins provided on the reinforcing ring can be arbitrarily set, and any air flow can be generated by rotation. The same applies to the structure of the caps disposed at both ends of the fixing roller. The cap is not necessarily limited to the bimetal, and the roller end is opened when the roller end temperature rises, and the roller end is closed at the normal temperature. A structure that can be selectively opened and closed can be adopted. Further, the heat source of the fixing roller is not limited to the halogen heater, and the present invention is effective regardless of the type of the heat source (heater). Further, the heat generation distribution of the heat source is not limited to this embodiment.

Next, another embodiment of the present invention will be described. The fixing device of this embodiment is the same as the above-described embodiment except that caps are not provided at both ends of the fixing roller and the configuration of a reinforcing ring provided in the fixing roller is different. Are omitted, and different parts will be mainly described.

In the fixing device shown in FIG. 6, three reinforcing rings 16a, 6b and 16c are provided inside the fixing roller 1. The reinforcing ring 6b at the center of the roller is shown in FIG.
This is the same as the reinforcing ring of the above embodiment. on the other hand,
As shown in FIG. 7, the reinforcing rings 16a and 16c at both ends are formed with a halogen heater through hole 9 and an air flow hole 17 on the side surface (in the cross-sectional direction of the roller). A fin 20 is provided adjacent to the air flow hole 17.

The fins 20 are formed of a shape memory alloy, and only one side thereof is fixed to the side surface of the reinforcing ring along one side of the air flow hole 17. As shown in FIG. 8, the shape memory alloy fin 20 is located at a position where the air flow hole 17 is closed at a normal temperature (a temperature when the temperature rise at the end of the fixing roller does not occur). When the temperature rises, it is displaced to a position where the air circulation hole 17 is opened (a position obliquely protruding in front of the air circulation hole 17) due to the temperature. Therefore, when the end temperature rises, the fin 20
Is displaced to open the air circulation hole 17, so that air can pass through the air circulation hole 17 of the reinforcing rings 16a and 16c inside the fixing roller 1.

Now, in the present embodiment, the large size (A
In the case where the sheet passes through the fixing roller 1 at the end thereof, the fins 20 close the air flow holes 17 of the reinforcing rings 16a and c as shown in FIG. It is in. Therefore, the hot air inside the fixing roller 1 is confined between the reinforcing rings 16a and 16c at both ends of the roller, and the internal heat does not escape, so that a uniform temperature distribution can be obtained in the longitudinal direction of the roller.

On the other hand, when small-size transfer paper such as A4 portrait or A5 or B5 is passed, the end temperature of the fixing roller 1 increases as the number of continuous papers increases. When the end temperature of the fixing roller 1 rises to a certain temperature, the fins 20 of the reinforcing rings 16a and 16c at both ends of the roller rise as shown in FIG.
Air circulation holes 17 provided in reinforcing rings 16a, c
Is displaced to the position where it is released. Furthermore, the fins 20 project obliquely, and together with the fins 10 of the reinforcing ring 6b at the center, the reinforcing ring 1 is rotated by the rotation of the fixing roller 1.
The fins 10 and 20 generate an airflow as the fins 6a, 6b, and 6c rotate, and as shown in FIG. 9, the air flows toward the drive gear side (from left to right in the figure) inside the fixing roller 1. Flow occurs. Accordingly, even when small-size paper is continuously passed, it is possible to effectively prevent the temperature at the end of the fixing roller 1 from rising.

In this embodiment as well, the number and positions of the reinforcing rings can be appropriately set. Further, the number of the fins 20 or 10 and the air circulation holes in the reinforcing ring, and the shape of the fins can be appropriately set.

[0030]

As described above, according to the fixing device of the present invention, cap members that can be selectively opened and closed are provided at both ends of the fixing roller, and a plurality of reinforcing members are provided inside the fixing roller. Since the reinforcing member has an air flow hole for passing air and fins for generating an air flow by rotation, heat is prevented from escaping from the roller end when the cap member closes the fixing roller end. When the cap member opens the end of the fixing roller, an air flow is generated inside the roller by the action of the fin, and the heat inside the roller can be effectively radiated. Further, since the fixing roller can be made thinner by the reinforcing member, the rising speed can be increased, and the strength of the fixing roller can be increased.

According to the second aspect of the present invention, the selectively openable / closable cap member opens the inside of the fixing roller when the end temperature of the fixing roller is equal to or higher than a predetermined temperature, and closes the inside of the fixing roller when the end temperature is equal to or lower than the predetermined temperature. Therefore, for example, at the time of passing a large-size sheet or during standby, the inside of the fixing roller is closed, so that the temperature at the end portion can be prevented from lowering and the fixing failure can be prevented. On the other hand, for example, when the small-size paper is continuously fed, the inside of the fixing roller is opened to promote heat radiation of the heat inside the fixing roller to the outside. Wrinkles and the like can be prevented.

According to the third aspect of the present invention, the cap member that can be selectively opened and closed is made of a bimetal in which two kinds of metals having different coefficients of thermal expansion are bonded to each other. it can. Further, it is possible to easily open the inside of the fixing roller when the temperature is equal to or higher than the predetermined temperature and close the inside of the fixing roller when the temperature is equal to or lower than the predetermined temperature.

According to the fourth aspect of the present invention, a plurality of reinforcing members are provided inside the fixing roller, and the reinforcing members are selectively provided in an air flow hole through which air passes, and a position where the air flow hole is opened and a position where the air flow hole is closed. And a fin that can be displaced to a position that opens the air flow hole. When the fin is displaced to a position that opens the air flow hole, an air flow is generated by rotation of the reinforcing member. Effective heat dissipation of the internal heat can be achieved.

According to the fifth aspect of the present invention, since the fin is made of a shape memory alloy, the fin can be manufactured with a simple structure. Further, the opening and closing of the air circulation hole can be easily performed at a predetermined temperature.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram illustrating a main part of a fixing device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a reinforcing ring provided inside a fixing roller of the fixing device.

FIG. 3 is an exploded perspective view showing a configuration of cap members provided at both ends of a fixing roller.

FIG. 4 is a cross-sectional view illustrating the operation of the cap member.

FIG. 5 is a cross-sectional configuration diagram showing the fixing device in a state where both ends of the fixing roller are opened.

FIG. 6 is a cross-sectional configuration diagram illustrating a main part of a fixing device according to another embodiment of the present invention.

FIG. 7 is a perspective view showing a reinforcing ring provided inside a fixing roller of the fixing device.

FIG. 8 is a partial cross-sectional view illustrating an operation of a fin provided on the reinforcing ring.

FIG. 9 is a cross-sectional configuration diagram illustrating the fixing device in a state where the fins open the air circulation holes.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing roller 4 Halogen heater 3 Heat generation layer 5 Thermistor 6a, b, c Reinforcement ring 7 Drive gear 8 Pressure roller 10, 20 Fin 10a, 17 Air flow hole 11 Cap 16a, c Reinforcement ring

Claims (5)

[Claims] A fixing roller that is driven to rotate; and a pressure roller that is pressed against the fixing roller. The recording material carrying the unfixed image is passed between the two rollers to convert the unfixed image into a recording material. In the heat fixing device for fixing, a cap member that can be selectively opened and closed is provided at both ends of the fixing roller, and a plurality of reinforcing members are provided inside the fixing roller, and the reinforcing members are air that allows air to pass therethrough. A fixing device comprising: a flow hole; and a fin that generates an airflow by rotation of the reinforcing member. 2. The fixing device according to claim 1, wherein the selectively openable and closable cap member opens the inside of the fixing roller when an end temperature of the fixing roller is higher than a predetermined temperature and closes the inside of the fixing roller when the end temperature is lower than a predetermined temperature. The fixing device according to claim 1, wherein: 3. The fixing device according to claim 1, wherein the selectively openable / closable cap member is made of a bimetal obtained by bonding two types of metals having different coefficients of thermal expansion. 4. A fixing roller which is driven to rotate, and a pressure roller which is pressed against the fixing roller, wherein a recording material carrying an unfixed image is passed between the two rollers to convert the unfixed image into a recording material. In the heat fixing device for fixing, a plurality of reinforcing members are provided inside the fixing roller, and the reinforcing members are selectively displaced to an air circulation hole through which air passes, and a position to open and close the air circulation hole. A fixing fin, wherein the fin generates an air flow by rotation of the reinforcing member when the fin is displaced to a position that opens the air flow hole. 5. The fixing device according to claim 4, wherein the fin is formed of a shape memory alloy.