JPH09197850A - Induction heating fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating fixing device capable of cooling a coil by simple and inexpensive constitution and coping with a small-diameter fixing roller. SOLUTION: The induction coil 9 is arranged to be extended and projected from both ends in the axial direction of a holder 11, desirably, by >=10mm so that it may be projected to be exposed at the ends in the axial direction of the fixing device. Thus, the coil 9 is cooled from its exposed part projected to the outside. It is conceivable to internally provide a metallic member arranged to be projected from both ends in the axial direction of the holder 11 in the fixing roller 1 together with the coil 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus such as an electrophotographic copying machine, a printer and a facsimile, and more specifically, it fixes a toner image on a sheet by using induction heating. Regarding the fixing device.

[0002]

2. Description of the Related Art An electrophotographic copying machine or the like is provided with a fixing device for fixing a toner image transferred onto a sheet such as recording paper or a transfer material as a recording medium onto the sheet. This fixing device has, for example, a fixing roller as a hollow heating member, which is also referred to as a heat roller that heat-melts the toner on the sheet, and a pressure roller that presses the fixing roller to sandwich the sheet. . The fixing roller is formed in a hollow shape, and a heating element is held by a holding means on the central axis of the fixing roller. The heating element is, for example,
It is composed of a tubular heater such as a halogen lamp, and generates heat when a predetermined voltage is applied.
Since this halogen lamp is located on the central axis of the fixing roller, the heat emitted from the halogen lamp is uniformly radiated to the inner wall of the fixing roller, and the temperature distribution of the outer wall of the fixing roller becomes uniform in the circumferential direction. The outer wall of the fixing roller has a temperature suitable for fixing (for example, 150 to 200).
(° C). In this state, the fixing roller and the pressure roller rotate in opposite directions while being in pressure contact with each other to sandwich the sheet to which the toner adheres. At the pressure contact portion (hereinafter also referred to as a nip portion) between the fixing roller and the pressure roller, the toner on the sheet is melted by the heat of the fixing roller and is fixed on the sheet by the pressure applied from both rollers.

However, in the above fixing device having a heating element composed of a halogen lamp or the like, since the fixing roller is heated by utilizing the radiant heat from the halogen lamp, after the power is turned on, the temperature of the fixing roller is increased. It took a relatively long time to reach a predetermined temperature suitable for fixing (hereinafter referred to as "warm-up time"). During that time, the user cannot use the copying machine and is forced to wait for a long time. On the other hand, if a large amount of electric power is applied to the fixing roller in order to shorten the warm-up time and improve the operability for the user, the power consumption of the fixing device increases, which is against energy saving. It was Therefore, in order to increase the value of products such as copiers, it is more important and more important to achieve both energy saving (low power consumption) of the fixing device and improvement of user operability (quick print). Has been done.

As a device which meets such a demand, an induction heating type fixing device utilizing high frequency induction as a heating source has been proposed. In this induction heating fixing device, a coil is concentrically arranged inside a hollow fixing roller made of a metal body, and a high frequency magnetic field generated by applying a high frequency current to the coil causes an induction eddy current to be generated in the fixing roller. The skin resistance of the fixing roller itself causes the fixing roller itself to generate Joule heat. According to this induction heating type fixing device, the electric-heat conversion efficiency is remarkably improved, so that the warm-up time can be shortened.

By the way, in such an induction heating type fixing device, the self-heating of the coil for generating magnetic flux disposed inside the fixing roller and the heat radiation to the inner surface of the fixing roller, The temperature rise around the coil is large,
There is a risk of parts melting and burning, and in order to avoid this, materials with excellent heat resistance at high temperatures must be used as peripheral members, resulting in high costs. Also,
There is a type in which a thin metal sleeve having flexibility is used as the hollow heating member instead of the fixing roller, but the above situation is the same.

[0006] Therefore, as means for cooling the coil in order to suppress the temperature rise, for example, in Japanese Utility Model Laid-Open No. 55-2949.
As disclosed in Japanese Patent Laid-Open No. 2 (1994), a technique in which a ventilation pipe is covered so as to cover a core arranged inside a coil to be wound and a fan motor blows air into the ventilation pipe. As disclosed in Japanese Utility Model Application Laid-Open No. 55-18292, a technique has been proposed in which a heat radiation pipe for supplying air is arranged on the peripheral surface of a coil.

[0007]

However, in the above-mentioned conventional induction heating type fixing device, a ventilation pipe for covering the core, a fan motor, or a heat radiation pipe wound around the peripheral surface of the coil is used. This requires a means for sending air, which has the drawback of making the device complicated and expensive.

In the former case, since the coil is wound around the ventilation pipe to cover the core, the means for generating the magnetic flux becomes large, and a hollow heating member such as a fixing roller having a small diameter is used. When used, there is also a problem that the magnetic flux generating means cannot be installed inside.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to cope with a fixing roller having a small diameter, which can cool a coil with a simple and inexpensive structure. An object is to provide a possible induction heating fixing device.

[0010]

The present invention for achieving the above object is specified as follows for each claim. The invention according to claim 1 has an induction coil for generating a magnetic flux inside the hollow heating member, and induction heating fixing for heating the hollow heating member by electromagnetic induction by causing a high-frequency current to flow through the coil. In the apparatus, the induction coil is projected and exposed at at least one axial end portion of the fixing device. In the invention thus specified, natural cooling is performed by the external atmosphere from the exposed portion of the coil protruding to the outside. in addition,
Since the coil itself is made of copper, which has excellent heat dissipation characteristics, the cooling effect is large, and thus heat dissipation in the entire coil is promoted and the temperature rise of the coil can be suppressed.

According to a second aspect of the present invention, in the induction heating fixing device according to the first aspect, the protrusion amount of the exposed portion of the induction coil at the axial end of the fixing device is 1.
It is characterized by being 0 mm or more. In the invention thus specified, a more practically preferable cooling effect can be obtained from the viewpoint of compatibility of quality and cost considering the heat resistance of parts such as the coil coating and the holder.

The invention according to claim 3 has an induction coil for generating a magnetic flux inside the hollow heating member, and the high-frequency current is passed through the coil to heat the hollow heating member by electromagnetic induction. The induction heating fixing device is characterized in that it has a metal member that is housed inside the hollow heating member together with the induction coil and that is projected and exposed at at least one axial end of the fixing device. In the invention thus specified, the coil can be cooled simply by disposing the metal member without changing the coil shape, and the degree of cooling can be easily adjusted.

According to a fourth aspect of the present invention, in the induction heating fixing device according to the third aspect, the metal member is a metal plate formed of copper or a copper alloy. According to the invention specified in this way, the cooling effect is enhanced because the heat dissipation characteristic is excellent with an extremely simple structure.

According to a fifth aspect of the present invention, in the induction heating fixing device according to the third aspect, the metal member is a heat pipe. In the invention thus specified, the rapid movement of heat in the coil is promoted,
The invention according to claim 6 further enhances the effect of natural cooling of the coil by the outside air. In the induction heating fixing device according to claim 3, there is provided means for circulating a liquid inside the metal member. Is characterized by. In the invention thus specified, the heat accumulated in the coil is positively and quickly absorbed and transferred to the circulating liquid, and a large cooling effect of the coil is achieved.

According to a seventh aspect of the present invention, in the induction heating fixing device according to any one of the first to third aspects, a fan for cooling the inside of the main body machine is arranged near an axial end portion of the fixing device. It is characterized by According to the invention thus specified, the cooling effect of the coil is further enhanced without newly providing a cooling fan.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view of a fixing device according to the first embodiment of the present invention, FIG. 2 is a perspective view of a holder unit of the same, and FIG. 3 stores the holder unit inside a fixing roller. It is a perspective view showing a situation. The fixing device shown in FIG. 1 is an induction heating type fixing device incorporated in a printer or the like. And a pressure roller 2 that is driven by the rotation of the fixing roller 1.

The heating source is composed of a heat-resistant copper wire coil 9 wound around a heat-resistant bobbin 8 and a core 10 made of ferrite or the like, and these are collectively referred to as a coil assembly 3. The coil assembly 3 is held inside a cylindrical holder 11, and the holder 11 is fixed to a body frame (not shown).

The coil assembly 3 and the holder 11 constitute a holder unit as a whole. As shown in FIGS. 1 and 2, the bobbin 8 has a concave shape having a rectangular cross section, and the coils 9 are aligned and stacked so as to fit in the bobbin 8 and wound. In addition, in FIG. 2, the inside of the holder 11 is seen through.

This holder unit is housed inside the fixing roller 1, as shown in FIG. That is, the fixing roller 1 is a hollow pipe having a metal body, and
A holder unit including the coil assembly 3 for generating an induced current (eddy current) in the fixing roller 1 is
It is arranged so as to be spaced apart from the inner surface of the roller by a predetermined size.

The holder 11 is made of a heat resistant insulating material such as polyphenylene sulfide (PPS) or liquid crystal polymer (LCP). The holder 11 is divided into upper and lower halves as shown in FIG. 4 when viewed from the axial direction, and is composed of an upper holder 11a and a lower holder 11b which are joined by a hook-shaped engaging portion K formed in the divided portion. There is. Since the upper and lower parts are divided into two parts, they can be easily resin-molded, and the hook-shaped engaging parts K can be engaged with each other while sliding them in the axial direction, so that a strong connection can be realized. Therefore, the manufacturing is simple, the cost is low, and the strength and the rigidity are high. The hook-shaped engaging part K
Is not limited to the shape shown in FIG. 4, but can be formed into another shape such as a substantially concavo-convex shape as long as it can be coupled by sliding and engaging.

The material of the fixing roller 1 is generally
For example, magnetic metals such as iron and stainless are used. Here, the magnetic metal generally refers to one having a relative magnetic permeability of about 100 or more, and the larger the relative magnetic permeability, the higher the magnetic flux density and the more likely heat is generated. The outer surface of the fixing roller 1 is
A heat-resistant release layer is formed of a fluororesin such as polytetrafluoroethylene (PTFE) to improve the separability from the sheet S as a recording medium. Further, the fixing roller 1 has bearing portions formed at both ends thereof and is rotatably attached to the main body frame. A drive gear is fixed to one end of the fixing roller 1, and a drive source such as a motor connected to the drive gear. It is adapted to be driven to rotate by (not shown).

Further, around the shaft core 4 of the pressure roller 2,
A silicon rubber layer 5, which is a surface-releasing heat resistant rubber layer, is formed.

The sheet S to which the unfixed toner image is transferred, which is conveyed from the left side in FIG. 1, passes between the heated fixing roller 1 and the pressure roller 2 which is pressed against the fixing roller 1. As a result, heat and pressure are applied to fix the toner image on the sheet, and then the toner image is separated from the fixing roller 1 by the curvature of the separation claw 7 and the roller, and is discharged toward a discharge tray (not shown).

A temperature sensor 6 for detecting the temperature of the fixing roller 1 is provided substantially above the fixing roller 1. The temperature sensor 6 is composed of, for example, a thermistor. Is detected, the energization of the coil 9 is controlled so that the temperature of the fixing roller 1 becomes the optimum temperature. Further, substantially above the fixing roller 1,
A thermostat (not shown) is provided as a safety mechanism when the temperature rises abnormally, and when the temperature reaches a preset temperature, the contacts are opened and the coil 9 is de-energized to prevent the fixing roller 1 from reaching a temperature higher than a predetermined temperature. doing.

In the present embodiment, in particular, as shown in FIGS. 2 and 3, the induction coil 9 is exposed so as to project at at least one axial end portion of the fixing device. Here, the axial direction of the fixing device is the same as the axial direction of the fixing roller 1 and the pressure roller 2.

FIG. 5A is a perspective view showing the arrangement of coils with respect to the core of the fixing device according to the first embodiment of the present invention.
5B is a vertical cross-sectional view of a holder unit of the apparatus, FIG. 6A is a perspective view showing the arrangement of coils with respect to the core of a conventional fixing apparatus, and FIG. 6B is a holder of the apparatus. It is a longitudinal cross-sectional view of a unit. Insulators such as bobbins between the core and the coils are not shown in the drawings, and in the vertical cross-sectional view of the holder unit, only the holder is shown as a cross section so that the positional relationship with the internal coils can be clearly understood. (The same applies to subsequent FIGS. 8 to 10).

Specifically, as shown in FIG. 5B, the coil 9 has a length L (m) from both ends of the holder 11 in the axial direction.
It is arranged so as to extend by m). In this way, the coil assembly 3 including the coil 9 is held inside the cylindrical holder 11, and the length of the holder 11 is such that the fixing roller 1 and the coil 9 are electrically exposed. This is because the length is generally set to be the same as or slightly longer than the length of the fixing roller 1 in order to ensure insulation. The coil 9 may be configured to project from one axial end of the holder 11.

In this fixing device of this type, the exposed portion of the coil 9 protruding to the outside is naturally cooled by the external atmosphere. Further, as in the present embodiment, the coil 9 has a holder 11 made of a cylindrical electrically insulating material in terms of safety.
In many cases, the structure of being surrounded by the above is adopted, and in such a case, heat radiation is hindered and heat is easily collected, so that the effect of natural air cooling from the exposed portion is particularly remarkable. In addition, since the coil 9 itself is made of copper having excellent heat dissipation characteristics, the cooling effect is extremely large.

FIG. 7 is a graph showing the relationship between the coil protrusion amount and the coil temperature. According to this graph, it can be seen that the larger the coil protrusion amount is, that is, the fixing device of the present embodiment shown in FIG. 5 has a higher coil cooling effect than the conventional fixing device shown in FIG. Also, considering the heat resistance of the coil coating and parts such as the holder, the coil temperature should be 18
From the standpoint of compatibility of quality and cost, a temperature of 0 ° C. or lower is more preferable for practical use, and therefore it is generally more desirable to set the protrusion amount L of the coil to 10 mm or more.

In this way, heat dissipation from the entire coil can be promoted and the temperature rise of the coil can be suppressed. Also, because the coil is prevented from overheating,
It is not necessary to set the heat resistance of the coil peripheral parts higher than necessary, and the cost can be further reduced.

Moreover, it is sufficient to add a simple and inexpensive structure in which the coil 9 is slightly protruded from the holder 11 by using the same fixing roller 1 as the conventional one, and it is possible to cope with a fixing roller having a small diameter.

FIG. 8A is a perspective view showing a main part of the fixing device according to the second embodiment of the present invention, and FIG. 8B is a vertical sectional view of a holder unit of the same device. The same members as those shown in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted.

In the second embodiment, as shown in FIG. 8 (A), a pair of metal plates 21 are provided as metal members which are in contact with the coil 9 and are installed inside the fixing roller together with the coil 9. This metal plate 21 is shown in FIG.
As shown in (B), the holder 11 is extended and arranged so as to project from both ends in the axial direction. The metal plate 21 is made of copper or a copper alloy and has excellent heat dissipation characteristics. Further, a portion 21a having a large contact area with air for improving heat dissipation is formed at the end portion thereof. According to the second embodiment, by arranging the metal plate without changing the coil shape, it is possible to obtain the same effect as that of the above-described embodiment, and it is possible to easily adjust the cooling degree. .

The metal plate 21 may be made of another metal material having good thermal conductivity, such as aluminum or its alloy, and the number of the metal plates 21 to be installed is arbitrary. Further, instead of using a metal plate, a tubular copper tube is covered from above so as to come into contact with the coil 9, and the end portions of the copper tube are extended and arranged so as to project from both axial end portions of the holder 11. It is also possible. Further, the metal plate 21 may be arranged so as to contact not only the coil 9 but also the core 10.

FIG. 9A is a perspective view showing a main part of the fixing device according to the third embodiment of the present invention, and FIG. 9B is a vertical sectional view of a holder unit of the same. The members common to those shown in FIGS. 5 and 8 are designated by the same reference numerals,
The description is omitted.

The third embodiment is different from the second embodiment in that a heat pipe 25 is used as a metal member instead of the metal plate 21 of the second embodiment. As is well known, the heat pipe 25 encloses a working fluid in a depressurized pipe, and when one is heated, the working fluid becomes vapor and flows to the other, where it radiates heat to become a liquid, and the liquid is heated by a capillary phenomenon. It applies the principle of transmitting heat from the heating part to the heat dissipation part by repeating the action of returning to the part. Therefore, according to the third embodiment, the heat pipe 25 arranged by utilizing a small space promotes rapid movement of heat of the coil, and the effect of natural cooling of the coil by the external atmosphere is further enhanced. .

FIG. 10 (A) is a perspective view showing the main part of the fixing device according to the fourth embodiment of the present invention, and FIG. 10 (B) is a view showing the vertical cross section of the holder unit of the same device together with the cooling means. The same members as those shown in FIGS. 1 to 5, 8 and 9 are designated by the same reference numerals, and the description thereof will be omitted.

In the fourth embodiment, as shown in FIG. 10 (A), a metal pipe 31 is used as a metal member in place of the metal plate 21 of the second embodiment. This is different from the second embodiment in that a liquid having a large heat capacity is circulated in a direction indicated by an arrow in the figure. That is, in the fourth embodiment, FIG.
As shown in FIG. 5, the metal pipe 31 is penetrated into the inside of the holder 11, and a pump mechanism 33 as a means for circulating the liquid is connected to the holder 11 to form a cooling means. This is for the purpose of cooling the coil. Therefore, according to the fourth embodiment, the cooling liquid is circulated through the metal pipe 31 arranged by using a small space, so that the coil 9 is positively and promptly.
The heat accumulated in the can be absorbed and transferred to the cooling liquid, and a large cooling effect of the coil can be achieved.

FIG. 11 is a view showing the schematic arrangement of a fixing device according to the fifth embodiment of the present invention.
The same members as those shown in FIG. 10 are designated by the same reference numerals, and the description thereof will be omitted.

In the fifth embodiment, the blower fan 35 for cooling the inside of the main body machine, which is generally used in the main body machine which is an image forming apparatus such as a copying machine, is provided in the axial direction of the fixing device. It is arranged in the vicinity of the end portion, that is, in the vicinity of the exposed portion protruding to the outside of the coil 9. This blower fan 35 is mainly for cooling a power source and a fixing device (not shown) which have been conventionally installed, and if arranged as described above, a coil fan can be provided without newly providing a cooling fan. The cooling effect can be further enhanced. Here, the symbol "A" in the figure is the flow of air inside the main machine,
Reference numeral "B" indicates the flow of air exhausted outside the main machine. In order to further enhance the cooling effect, it is of course possible to additionally provide a coil cooling fan that blows air inside the fixing roller 1 in the axial direction.

The present invention is not limited to the above-described embodiments, but can be variously modified within the scope of the claims. For example, in the above-described embodiment, the fixing roller, which is a hollow pipe having a metal body, is used as the hollow heating member, but the present invention is not limited to this, and for example, a flexible thin metal wall. It can also be applied to a type using a sleeve, and in this case, the holder has a configuration in which the holder is pressed against the inner surface of the metal sleeve.

[0043]

As described above, according to the present invention, the following effects can be obtained for each claim. In the invention according to claim 1, since the induction coil is exposed by being projected at at least one axial end of the fixing device, natural cooling by the external atmosphere can be performed from the exposed portion of the coil protruding to the outside. . In addition, since the coil itself is made of copper having excellent heat dissipation characteristics, the cooling effect is extremely large.

In this way, heat dissipation from the entire coil can be promoted, and the temperature rise of the coil can be suppressed. Also, because the coil is prevented from overheating,
It is not necessary to set the heat resistance of the coil peripheral parts higher than necessary, and the cost can be further reduced.

Moreover, as compared with the conventional case, a simple and inexpensive structure in which the coil is slightly protruded in the axial direction is added, and a fixing roller having a small diameter can be supported.

According to the second aspect of the present invention, it is possible to obtain a practically more preferable cooling effect in terms of both quality and cost considering the heat resistance of the coil coating and the parts such as the holder.

According to the third aspect of the invention, the coil can be cooled by merely disposing the metal member without changing the coil shape, and the cooling degree can be easily adjusted.

In the invention described in claim 4, since the metal plate has an extremely simple structure and excellent heat dissipation characteristics, the cooling effect is enhanced.

According to the fifth aspect of the invention, the rapid movement of heat of the coil is promoted, and the effect of natural cooling of the coil by the external atmosphere is further enhanced.

According to the sixth aspect of the invention, the heat accumulated in the coil can be positively and rapidly absorbed and moved in the circulating liquid, and a large cooling effect of the coil can be achieved.

In the invention described in claim 7, the cooling effect of the coil can be further enhanced without newly providing a cooling fan.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a fixing device according to a first embodiment of the present invention.

FIG. 2 is a perspective view of a holder unit of the apparatus.

FIG. 3 is a perspective view showing a state where the holder unit is housed inside a fixing roller.

FIG. 4 is a view seen from the axial direction of the holder.

5A is a perspective view showing the arrangement of coils with respect to the core of the fixing device according to the first embodiment of the present invention; FIG.
FIG. 3 is a vertical cross-sectional view of a holder unit of the same device.

FIG. 6A is a perspective view showing the arrangement of coils with respect to the core of a conventional fixing device, and FIG. 6B is a vertical cross-sectional view of a holder unit of the same fixing device.

FIG. 7 is a graph showing the relationship between the coil protrusion amount and the coil temperature.

FIG. 8A is a perspective view showing a main part of a fixing device according to a second embodiment of the present invention, and FIG. 8B is a vertical sectional view of a holder unit of the same device.

FIG. 9A is a perspective view showing a main part of a fixing device according to a third embodiment of the invention, and FIG. 9B is a vertical sectional view of a holder unit of the same device.

FIG. 10A is a perspective view showing a main part of a fixing device according to a fourth embodiment of the present invention, and FIG. 10B is a view showing a longitudinal section of a holder unit of the device together with a cooling unit.

FIG. 11 is a diagram showing a schematic configuration of a fixing device according to a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fixing roller (hollow heating member), 2 ... Pressure roller, 3 ... Coil assembly, 8 ... Bobbin, 9 ... Coil, 10 ... Core, 11 ... Holder, 21 ... Metal plate (metal member), 25 ... Heat pipe (Metal member), 31 ... Metal pipe (metal member), 33 ... Pump mechanism (means for circulating liquid), 35 ... Fan, S ... Sheet.

Claims (7)

[Claims] 1. An induction heating fixing device having an induction coil for generating a magnetic flux inside a hollow heating member and heating the hollow heating member by electromagnetic induction by causing a high-frequency current to flow through the coil. The induction heating fixing device is characterized in that the induction coil is projected and exposed at at least one axial end of the fixing device. 2. The induction heating fixing device according to claim 1, wherein a protrusion amount of an exposed portion of the induction coil at an axial end portion of the fixing device is 10 mm or more. 3. An induction heating fixing device having an induction coil for generating a magnetic flux inside a hollow heating member and heating the hollow heating member by electromagnetic induction by causing a high frequency current to flow through the coil. It is installed in the hollow heating member together with the induction coil,
An induction heating fixing device comprising: a metal member that is projected and exposed at at least one axial end of the fixing device. 4. The induction heating fixing device according to claim 3, wherein the metal member is a metal plate made of copper or a copper alloy. 5. The induction heating fixing device according to claim 3, wherein the metal member is a heat pipe. 6. The induction heating fixing device according to claim 3, further comprising means for circulating a liquid inside the metal member. 7. The induction heating fixing device according to claim 1, wherein a fan for cooling the inside of the main body machine is arranged in the vicinity of an axial end portion of the fixing device.