JP3426061B2 - Fixing device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device,
More specifically, the present invention relates to a fixing device in an image forming apparatus such as a copying machine, a printer, and a FAX that uses an electrophotographic process.

[0002]

2. Description of the Related Art In a copying machine, a printer, a fax machine or the like using an electrophotographic process, an unfixed toner image is formed by a heat roller heated to a desired temperature and a pressure roller having an elastic layer. 2. Description of the Related Art A fixing device that performs thermal fixing while nipping and conveying a recording sheet is well known. When a recording sheet having a size smaller than the width of the heat roller is continuously subjected to the heat fixing operation by using this fixing device, a roller portion (sheet passing portion) with which the recording sheet contacts and a roller portion (non-contact) (Paper passing section)
There is a difference in heat dissipation. That is, the surface temperature of the heat roller becomes higher in the area where the recording paper does not pass than in the area where the recording paper passes. This is a phenomenon conventionally called “temperature rise in non-sheet passing portion”.

When the size of the recording paper is switched to a larger one at the time when the temperature rise of the non-sheet passing portion occurs, the surface of the heat roller corresponding to the portion which was not in contact with the recording paper of the small size processed before the switching. The temperature may be too high and so-called high temperature offset may occur. Furthermore, if a partial excessive temperature rise occurs on the surface of the heating element (heating roller), the following problems occur. -Non-uniform heat is applied to the recording paper, resulting in non-uniform fixability, poor fixability, and wrinkles. -Parts such as the pressure roller around the temperature rising part of the non-sheet passing part are thermally damaged, resulting in a shortened life of the parts. -The defective running occurs due to the external shape change due to the thermal expansion of the pressure roller.

As a means for solving the above problems,
Various proposals have been made in the past. Specific examples are as follows: 1) The energization range of the heating element is changed according to the size of the recording paper. (See Japanese Patent Laid-Open No. 05-027645) 2) A heating element having a temperature resistance coefficient of PTC (Positive Temperature Coefficient) characteristics is used. (Japanese Patent Laid-Open No. 06-06
Reference No. -0278840) 3) A plurality of heaters are used for the heating element, and switching / combining is performed according to the recording paper size. (JP-A-02-2621
No. 77 publication, reference) etc. have been proposed. However, these methods have the following problems. That is, the configuration / temperature control of the heating element, various sensors and their control circuits are complicated, and the cost is high. Further, since heating control is performed depending on the paper size, the temperature of the end portion of the heat roller actually increases. If it does, control to lower the end temperature is not performed.

Therefore, as means for cooling the heated roller end portion, 4) air is blown to the heat roller through a window provided in a casing covering the periphery of the heat roller. (See Japanese Patent Application Laid-Open No. 03-139682) 5) A cover that covers the heat roller is provided with a plurality of windows, and a guide device for allowing cooling air to flow along the non-sheet passing shaft is opened and closed vertically from there. Performed according to the size of the paper to be passed. (See Japanese Patent Laid-Open No. 05-181382). However, all of those using the blower require a fan and a drive circuit for the fan, which causes problems in layout and space of the entire device. Also,
With regard to the above 5), since the guide device is opened vertically, an additional problem occurs in the layout and the space of the entire device.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the prior art. It eliminates the need for air blowing means, solves the space-related problem, and provides a heat roller cover. Efficient heat dissipation from the holes provided eliminates the temperature rise in the non-sheet passing area, eliminates high-temperature offset and abnormal images, is simpler, more economical, and saves energy compared to conventional heat rollers. It is an object of the present invention to provide a fixing device capable of uniform temperature.

[0007]

[0008]

According to a first aspect of the present invention, in a fixing device having a heat roller for thermally fixing an image formed on a recording paper to the recording paper, an end cover for covering an end of the heat roller. A member and a cover member that covers a portion other than the end portion of the heat roller, and moves the end cover member in the heat roller axial direction to expose the end portion of the heat roller,
The amount of heat released from the exposed portion is adjusted.

[0009] invention of claim 2 is the invention of claim 1, at the time of heating start-up of the heat roller, covering the whole of the heat roller, and thereafter, the width size of the recording paper, before <br/> Symbol The amount of movement of the end cover member is controllable, and heat is radiated only to the portion where the temperature rises abnormally.

According to a third aspect of the invention, in the first aspect of the invention, when the heating of the heating roller is started, the entire heating roller is covered, and thereafter, the temperature of the end portion of the heating roller is changed by
And you can control the amount of movement of the front Kitan cover member, in which so as to heat dissipation only the end abnormal temperature Nukutoki.

According to a fourth aspect of the present invention, in a fixing device having a heat roller for thermally fixing an image formed on a recording paper to the recording paper, the end of the cover covering the periphery of the heat roller is provided with the end of the heat roller. An amount of heat released through the hole by moving the cover member in the rotation direction of the heat roller and having a cover member that has a hole for radiating the heat of the portion to the outside of the cover and that closes the hole. Is adjusted so that the heat at the end of the heat roller is radiated while keeping the heat at the center of the heat roller.

According to a fifth aspect of the invention, in the invention of the fourth aspect , the amount of movement of the cover member that closes the hole can be controlled by the temperature of the end portion of the heat roller, and heat is radiated only when the end portion has an abnormal temperature rise. It was done like this.

According to a sixth aspect of the present invention, in the fourth aspect of the invention, the movement amount of the cover member that closes the hole can be controlled by the width size of the recording paper, and heat is radiated only to an abnormally heated portion. It is the one.

[0014]

PREFERRED EMBODIMENTS FIG. 1 (A) ~ FIG 1 (C) is present onset
FIG. 1 is a schematic diagram illustrating one form of a fixing device to which light is applied ,
1A is a side view of FIG. 1B, FIG. 1B is a schematic view when the slide cover 2 is closed, and FIG. 1C is a schematic view when the slide cover 2 is open. Is.

The heat roller 10 may be one using a commonly used halogen lamp, but for example, a substrate (thickness 0.1 mm to 2.0 mm) on a cylindrical body such as glass, ceramic or heat resistant plastic is used. There is a type in which a heating resistance layer is formed and surface heat is generated by applying electricity. Among them, especially in the case of a small heat capacity aiming at high-speed temperature rise, such as a film heating method for fixing from a heating element through a heat-resistant film, the temperature rise in the non-sheet passing part is particularly severe . Any of the inventions can be effectively applied.

As the pressure roller 11, a roller generally used in a heat fixing device of an electrophotographic recording apparatus can be used, and a roller provided with a rubber layer having good releasability and heat resistance such as silicone rubber is desirable. . Then, the recording paper 12 on which the unfixed toner image is formed is nipped and conveyed by the heat roller 10 and the pressure roller 11. As the heat insulating cover 1 covering the periphery of the heat roller 10, a material having excellent heat resistance / heat insulating property is preferable,
Heat-resistant non-conductive plastic, PET (polyethylene terephthalate), fluororesin, or the like is used.
There are holes C above both ends of the heat insulating cover 1 in the axial direction of the heat roller. The slide cover 2 is located above both ends of the heat insulating cover 1 in the axial direction of the heat roller, forms a part of the heat insulating cover 1, has a size capable of covering the hole C, and can be moved (slide) in the heat roller axial direction. It is formed on.

FIG. 2 is a diagram showing an example of a slide driving means of the slide cover 2, which utilizes a motor 3 and a gear 4 (a rack and a pinion). Further, when a material whose shape changes with temperature, for example, a heat-sensitive deformable material such as a shape memory alloy or a bimetal is used for the slide drive mechanism of the slide cover 2, the temperature detection means and the drive means are not necessary and the abnormality automatically occurs. The slide cover 2 slides as the temperature rises.

Then, for example, when the recording paper 12 having a size smaller than the maximum paper passing width is continuously (for example, 10 sheets) passed, the slide cover 2 slides in the axial direction of the heat roller to keep the heat insulating cover 1. The heat of the end portion of the heat roller can be radiated through the hole C provided in the.

FIGS. 3A to 3F show the heat insulating cover 1
3A is an example of the shape of the hole C provided in FIG. 3, FIG. 3A is an example of one large hole shown in FIG. 1, and FIGS. 3B to 3F are examples in which a large number of holes are provided. Various heat radiation effects can be selected depending on the size, shape, and interval.

[0020]

[Experimental Example] The structure is as shown in FIG. 1 and 50 small size (A4 width) recording sheets are continuously fed under the following conditions.・ Width of fixing roller heating part ………… 305mm ・ Fixing roller heat source power supply …… 700W ・ Recording paper ………………………… Ricoh type 6200 paper (A4) ・ Recording paper feed speed ………… … 90mm / s ・ Fixing roller set temperature Tc …… 180 ℃ ・ Slide cover ……………… Always open

FIG. 4 (A), (B) is a graph showing the non-sheet passing portion temperature rise, FIG. 4 (A) non-sheet-passing portion in the form state in Fig. 1 under the conditions of Experimental Example Graph showing temperature rise, FIG.
(B) is a graph showing the temperature rise in the non-sheet passing portion when no hole for radiating heat to the outside of the cover is provided under the conditions of the experimental example . As is clear from FIGS. 4 (A) and 4 (B), the temperature rise of the non-sheet passing portion when the small size paper is continuously fed by providing the hole for radiating heat to the outside of the cover is Compared to the case where there is no, the difference from the setting temperature of the fixing roller (the temperature of the sheet passing portion in the central portion) is small.
Immediately after 50 sheets were continuously fed, A3 size paper on which a toner image was formed was passed, and the fixed image was evaluated. As a result, when the hole is not provided, a high temperature offset occurs at the edge of the recording paper. In contrast, in this embodiment, a good fixed image without high temperature offset was obtained.

[Embodiment of the Invention of Claim 1 ] FIGS. 5A to 5C are schematic views for explaining an embodiment of the invention of Claim 1 , and FIG. 5B is a side view, FIG. 5B is a schematic view when the slide cover 5 is closed, and FIG. 5C is a schematic view when the slide cover 5 is open. The structure of FIG. 5 has a slide cover 2 provided at a part above the end of the cover 1 of the structure shown in FIG.
There is no hole C and the end cover member (slide cover 5) that covers the end of the heat roller 10 is configured to move (slide). Then, when recording paper of a size smaller than the maximum paper passing width is continuously (for example, 10 sheets) passed, the slide cover 5 slides in the roller axial direction to expose the end of the heat roller, Dissipates the heat of the roller ends. Part that radiates the heat (exposed part)
Is larger than (hole C) shown in FIG. 1 , the heat dissipation effect is increased, and the temperature rise at the end is efficiently reduced.

[0023]

Example 1 The structure is as shown in FIG. 5, and 50 small size (A4 width) recording sheets were continuously fed under the following conditions.・ Width of fixing roller heating part ………… 305mm ・ Fixing roller heat source power supply …… 700W ・ Recording paper ………………………… Ricoh type 6200 paper (A4) ・ Recording paper feed speed ………… … 90mm / s ・ Fixing roller set temperature Tc …… 180 ℃ ・ Slide cover ……………… Always open

FIG. 6 is a graph showing the temperature rise of the non-sheet passing portion under the conditions of the first embodiment. Clearly comparing the graphs of FIG. 6 and FIG. 4 (A), the temperature rise of the non-sheet passing portion is further reduced as compared with the temperature rise result of the end portion in the experimental example . A toner image was formed immediately after 50 sheets were continuously fed.
After passing through 3 size paper and evaluating the fixed image,
In this embodiment, a good fixed image without high temperature offset was obtained.

[0025] The description of the embodiments of the Embodiment of the invention of claim 2 invention of claim 2. In this embodiment, in the embodiment of claim 1 , the cover member (slide cover 2) above the end of the cover that covers the periphery of the heat roller 10 or the end of the heat roller is covered. The end cover member (slide cover 5) moves (slides) in the roller axis direction in accordance with the width of the recording paper to effectively radiate heat according to the size of the recording paper.

FIG. 7 is a sequence diagram for explaining the operation of this embodiment. This embodiment will be described with reference to FIG. 7. First, the user sets a paper size to be used (or is automatically selected from the apparatus main body side) to perform mode setting (S1). When the recording paper having the maximum paper passing width is designated (S2), normal printing is started (S9). However, if a recording paper of which the paper size is smaller than the maximum paper passing width is designated (S2), the counter for counting the number of passed paper is reset (S3), and the number of prints from the start of printing is started (S).
4). At the same time, when a small size recording paper is designated (S2), the set paper width information of the small size paper is set (S5), and the corresponding slide amount is determined (S2).
6). A predetermined number C ₀ (for example, 10
Is set, and when the actual number of printed sheets Cn exceeds the predetermined number C ₀ , a signal for sliding the slide cover 2 (or the slide cover 5) is output (S
7) Slide to the paper width portion (S8), and radiate heat from the non-sheet passing portion from the hole C. Therefore, when the set number of sheets is not exceeded (when the heating of the heating roller is started, etc.), the slide cover 2 and the like are always closed, and the entire heating roller is covered and kept warm. When the initially set number of prints is completed, the slide cover 2 and the like are closed and the entire sequence is completed. Here, the form in which the user specifies and controls the width size of the recording paper has been shown, but the width size of the recording paper may be automatically controlled using a paper size signal on the apparatus main body side.

[0027] describing the embodiments of the invention [Claim EMBODIMENT 3] according to claim 3. In this embodiment, in the embodiment of claim 1 , the cover member (slide cover 2) above the end portion of the cover that covers the periphery of the heat roller 10 or the end portion of the heat roller 10 is covered. The end cover member (slide cover 5) moves (slides) in the roller axis direction in accordance with the temperature of the end of the heat roller to effectively dissipate the excessive temperature rise heat of the end. An example of the operation will be described below.

When the detection value detected by the temperature detecting element (for example, thermistor) installed at the end of the heat roller exceeds a preset temperature T ₀ (for example, 190 ° C.), the slide cover 2 ( Alternatively, the slide cover 5) is started to slide, and when the end temperature becomes lower than T ₀ , the slide cover 2 and the like are closed to end the operation. In addition, in order to prevent the sliding operation in a temporary high temperature state such as overshoot at the time of heating the heating roller, do not perform the sliding operation for several seconds t ₁ (for example, 10 seconds) after heating the heating roller. Control. Therefore, when the heat roller is heated and started, the slide cover 2 and the like are always closed, the heat roller 10 is entirely covered, and the heat roller 10 is kept warm to shorten the time required for raising the heat roller 10 to the set temperature.

[Embodiment of the Invention of Claim 4 ] FIGS. 8 (A) to 8 (C) are schematic diagrams for explaining an embodiment of the invention of Claim 4 , and FIG. 8B is a side view, FIG. 8B is a schematic view when the slide cover 2 is closed, and FIG. 8C is a schematic view when the slide cover 2 is open.

The configuration of this embodiment is such that the slide cover 2 shown in FIG. 1 is slid in the roller rotation direction instead of the roller axis direction. Further, in this configuration, the shape memory alloy 6 is used for the slide mechanism. Then, for example, when the recording paper 12 having a size smaller than the maximum paper passing width is continuously (for example, 10 sheets) passed, the slide cover 2 is provided in the heat insulating cover 1 by sliding in the rotation direction of the heat roller. The heat at the end of the heat roller is radiated from the hole C. Sliding the slide cover 2 in the roller rotation direction allows effective heat dissipation from the excessive temperature rise portion even if the slide amount is small. This is because the size (width) of the recording paper determines the part where the temperature of the heat roller rises. Therefore, when sliding in the axial direction, it is necessary to slide to the part where the temperature rises abnormally according to the width of the recording paper. By sliding in the roller rotation direction, even if the sliding amount is small, a hole is formed near the upper part of the abnormal temperature rising portion, so that heat can be radiated. Further, since the size of the hole can be changed depending on the sliding amount, the heat radiation amount in a part in the axial direction of the heat roller can be adjusted. That is, the heat radiation amount can be adjusted without wasteful heat radiation depending on the degree of abnormal temperature rise.

[0031] describing the embodiments of the invention Embodiment of the invention of claim 5 according to claim 5. In this embodiment, in the embodiment of claim 4 , the cover member (slide cover 2) above the end of the cover that covers the periphery of the heat roller 10 is a roller depending on the temperature of the end of the heat roller. It moves (slides) in the rotation direction to effectively dissipate the excessive temperature rise heat at the end.

FIG. 9 is a sequence diagram for explaining the operation of this embodiment. This embodiment will be described with reference to FIG. 9. First, when the power of the fixing device is turned on, the heater is turned on to bring the heat roller 10 to the set temperature, and a timer for measuring the heater energization time t is started (S11). ). When the temperature T based on the detection value detected by the temperature detection element (for example, a thermistor) installed at the end of the heat roller becomes equal to or higher than the preset predetermined temperature T ₀ (for example, 190 ° C.) (S12), slide the slide. Start (S1
4). It should be noted that, in order to prevent the sliding operation in a temporary high temperature state such as an overshoot at the time of heating the heating roller, a few seconds after the heating of the heating roller t ₁ (for example, 1
At 0 seconds, control is performed so that the slide operation is not performed (S
13). Therefore, when the heat roller is heated and started up, the slide cover 2 is always closed, the heat roller is entirely covered, and the time required for keeping the heat and raising the temperature to the set temperature is shortened.
As a result of sliding the slide cover 2, if the temperature T at the end of the heat roller is T ≧ T ₀ (S15), the slide amount is further increased (S14), and the area of the hole C not covered by the slide cover 2 is increased. Grow bigger. And T <T ₀
(S15), the slide amount is gradually returned (S16), and the area of the hole C not covered by the slide cover 2 is reduced.

FIG. 10 shows the cover end temperature T and the predetermined temperature T.
FIG. 6 is a relationship diagram between a detection result of ₀ and a slide amount S of the slide cover 2. As described above, the end portion temperature adjustment is performed by increasing or decreasing the slide amount S of the slide cover 2 depending on the end portion temperature detection result. Then, when the slide cover 2 is completely closed (that is, when the temperature rise at the end is eliminated) (S17), the operation of the slide cover 2 is ended.

As a slider mechanism of the slide cover 2,
A material whose shape changes with temperature, for example, a heat-sensitive deformable material such as shape memory alloy or bimetal, is used for the slide drive mechanism of the slide cover 2 and does not require temperature detection means or drive means, and automatically responds to abnormal temperature rise. Then slide cover 2
May be controlled to open and close.

[0035] describing the embodiments of the invention Embodiment of the invention of claim 6 according to claim 6. In this embodiment, in the embodiment of claim 4 , the cover member (slide cover 2) above the end portion of the cover that covers the periphery of the heat roller is moved in the roller rotation direction according to the width of the recording paper. It moves (slides) and effectively radiates heat depending on the size of the recording paper. In the operation, first, the user specifies the paper size to be used (or is automatically selected from the apparatus main body side). At this time, when a recording paper having a paper size smaller than the maximum paper passing width is designated, the counter for counting the number of passed paper sheets is reset, and the number of printed sheets from the start of printing is started. A predetermined number C ₀ (for example, 10) is preset in the counter,
When the actual number of printed sheets Cn exceeds the predetermined number of sheets C ₀ , the slide cover 2 is slid in the roller rotation direction, and the heat of the non-sheet passing portion is radiated from the hole C. Therefore, when the set number of sheets is not exceeded (for example, when the heating of the heating roller is started up), the slide cover 2 is always closed and the entire heating roller is covered and kept warm. When the initially set number of prints is completed, the slide cover 2 is closed and the entire sequence is completed. Here, the form in which the user specifies and controls the width size of the recording paper has been shown, but the width size of the recording paper may be automatically controlled using a paper size signal on the apparatus main body side.

[0036]

[0037]

Effects of the Invention corresponds to claim 1 Effect: By the end cover member covering an end portion of the heat roller (the sliding cover 5) slides in the axial direction of the roller, the thermal effect release increases, the end abnormal temperature The temperature can be suppressed more.

Effect corresponding to claim 2 : Since the slide amount of the slide cover 2 and the like can be controlled according to the paper size, heat can be dissipated only in the portion where the temperature rises abnormally and the surface of the heat roller can be used for various small size papers. A uniform temperature can be achieved. Further, when the set number of sheets is not exceeded (for example, when the heat roller is heated and started up), the slide cover 2 and the like are always closed to cover the entire heat roller and keep the temperature high. The set temperature can be reached quickly) and energy saving can be achieved.

Effect corresponding to claim 3 : Since the temperature of the end portion of the heat roller is actually detected, heat can be dissipated only when the end portion has an abnormal temperature rise. Further, when the heat roller is heated and started up, the slide cover 2 and the like are always closed, and the heat roller is entirely covered and kept warm, so that the temperature rising characteristic is excellent (the set temperature of the heat roller is quickly reached), and Energy saving can be achieved.

Effect corresponding to claim 4 : Since the slide cover 2 is slid in the roller rotation axis direction, effective heat dissipation can be performed even if the slide amount is small. Further, it is possible to finely adjust the heat radiation amount in the same width (non-sheet passing portion).

Effect corresponding to claim 5 : Since the temperature of the end portion of the heat roller is actually detected, heat can be dissipated only when the temperature of the end portion is abnormally increased, and the slide amount of the slide cover 2 is changed to the end portion. Since the temperature can be adjusted, more efficient and accurate temperature control becomes possible.

Effect corresponding to claim 6 : Since the slide amount of the slide cover 2 can be set according to the paper size,
Heat can be dissipated only in the unnecessary temperature rise parts, and the surface temperature of the heat roller can be made uniform for various types of small size paper. Also, when the set number is not exceeded (when heating the heat roller, etc.),
Since the slide cover 2 is always closed and covers the entire heat roller and keeps it warm, the temperature rise characteristic is excellent (the set temperature of the heat roller is reached quickly), and energy saving can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating one form of a fixing device to which the present invention is applied .

FIG. 2 is an example of a slide driving means of a slide cover 2 in FIG.

FIG. 3 is an example of the shape of a hole C provided in the heat insulating cover 1 in FIG.

FIG. 4 is a graph showing the temperature rise of the non-sheet passing portion under the conditions of the experimental example in FIG. 1.

FIG. 5 is a schematic diagram illustrating an embodiment of the invention of claim 1 .

FIG. 6 is a graph showing the temperature rise of the non-sheet passing portion under the conditions of Example 1 in FIG.

FIG. 7 is a sequence diagram for explaining the operation of the embodiment of the invention of claim 2 ;

FIG. 8 is a schematic diagram illustrating an embodiment of the invention of claim 4 ;

FIG. 9 is a sequence diagram for explaining the operation of the embodiment of the invention of claim 5 ;

FIG. 10 is a relationship diagram between a detection result of a cover end temperature T and a predetermined temperature T ₀ and a slide amount S of the slide cover 2 in the embodiment of the invention of claim 5 ;

[Explanation of symbols]

1 ... Insulating cover, 2 ... Slide cover, 3 ... Motor, 4
… Gear, 5… Slide cover, 6… Shape memory alloy, 10
... heat roller, 11 ... pressure roller, 12 ... recording paper.

─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Takao Inoue 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Shuji Motomura 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd. (56) Reference JP-A-4-234778 (JP, A) JP-A-3-139682 (JP, A) Actual Kaihei 1-85856 (JP, U) (58) Fields investigated ( Int.Cl. ⁷ , DB name) G03G 13/20 G03G 15/20

Claims (6)

(57) [Claims] 1. A fixing device having a heat roller for thermally fixing an image formed on a recording paper to the recording paper, and an end cover member for covering an end of the heat roller, and a portion other than the end of the heat roller. A cover member for covering, and moving the end cover member in the axial direction of the heat roller to expose the end portion of the heat roller so that the amount of heat released from the exposed portion can be adjusted. Fixing device characterized by. To 2. During the heating startup of the heat roller is to cover the entire of the heat roller, and thereafter, the width size of the recording sheet, and characterized in that a controllable movement amount before Kitan cover member The fixing device according to claim 1. The wherein the time of heating start-up of the heat roller, characterized in that to cover the entire of the heat roller, thereafter, the temperature of the heat roller end was possible to control the amount of movement of the front Kitan cover member The fixing device according to claim 1. 4. A fixing device having a heat roller for thermally fixing an image formed on a recording paper to the recording paper, wherein the end of the cover covering the periphery of the heat roller covers the heat of the end of the heat roller. It has a hole for radiating heat to the outside and a cover member for closing the hole, and the cover member is moved in the rotation direction of the heat roller, so that the amount of heat released through the hole can be adjusted. A fixing device characterized by the above. 5. The fixing device according to claim 4, wherein the movement amount of the cover member closing the hole can be controlled by the temperature of the end portion of the heat roller. 6. The fixing device according to claim 4, wherein the movement amount of the cover member closing the hole can be controlled by the width size of the recording paper.