JP3353572B2 - Induction heating 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 used in an image forming apparatus such as an electrophotographic copying machine, a printer and a facsimile, and more particularly, to fixing a toner image to a recording medium using induction heating. 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. The fixing device includes, for example, a fixing roller also referred to as a heating roller that thermally melts toner on a sheet, and a pressure roller that presses against the fixing roller to sandwich the sheet. The fixing roller is formed in a hollow shape, and a heating element is held on a central axis of the fixing roller by holding means. The heating element is formed of, for example, a tubular heating heater such as a halogen lamp, and generates heat when a predetermined voltage is applied. Since this halogen lamp is located on the center axis of the fixing roller, the heat generated from the halogen lamp is uniformly radiated to the inner wall of the fixing roller,
The temperature distribution on the outer wall of the fixing roller becomes uniform in the circumferential direction. The outer wall of the fixing roller is heated until its temperature reaches a temperature suitable for fixing (for example, 150 to 200 ° C.). In this state, the fixing roller and the pressure roller rotate in mutually opposite directions while slidingly contacting each other, and sandwich the sheet to which the toner has adhered. At a sliding contact portion (hereinafter, 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 to the sheet by the pressure applied from both rollers. After the toner is fixed, the sheet is conveyed by a paper discharge roller and discharged onto a paper discharge tray as the fixing roller and the pressure roller rotate.

In the fixing device having a heating element composed of a halogen lamp or the like, after the power is turned on,
It took a relatively long time for the temperature of the fixing roller to reach a predetermined temperature suitable for fixing (hereinafter, referred to as "preheating time"). During that time, the user cannot use the copier, and there is a problem that the user has 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 preheating time and improve the operability of the user, the power consumption in the fixing device increases, which is a problem against energy saving. . Therefore, in order to increase the value of products such as copying machines, attention and emphasis has been placed on achieving both energy saving (low power consumption) of the fixing device and improvement in user operability (quick print) of the fixing device. Have been.

Japanese Patent Application Laid-Open No. Sho 5
As shown in 4-39645 and JP-A-59-33477, high-frequency induction is used as a heating source,
There has been proposed an induction heating type fixing device in which the electric-heat conversion efficiency is improved and the preheating time is shortened.
In this induction heating fixing device, a coil is arranged concentrically inside a hollow fixing roller made of a metal conductor, and an induced eddy current is generated in the fixing roller by a high-frequency magnetic field generated by applying a high-frequency current to this coil. The fixing roller itself generates Joule heat by the skin resistance of the fixing roller itself.

[0005]

There is an induction heating fixing device in which a winding is wound around a core forming a magnetic path to form an induction coil. However, the distance between the core and the fixing roller is limited. The following relationship exists between the heating efficiency of the fixing roller (energy transmission efficiency). In other words, if the distance between the core and the fixing roller is reduced, the magnetic coupling becomes stronger, so that the heating efficiency is improved and the amount of heat generated in the fixing roller is increased. Conversely, if the distance is increased, the magnetic coupling is reduced. Since it becomes weak, the heating efficiency deteriorates and the calorific value decreases.

Further, it is necessary to ensure sufficient electrical insulation between the fixing roller and the core in order to eliminate the possibility of short circuit in order to prevent damage to the fixing device. For similar reasons, electrical insulation between the fuser roller and the coil is also required.

In order to ensure sufficient electrical insulation, the distance between the fixing roller and the core may be increased, but with such a configuration, sufficient heating efficiency can be obtained as described above. Disappears. In such a case, in order to obtain a predetermined amount of heat generated by the fixing roller, it is necessary to supply more current to the coil. However, the amount of heat generated by the copper loss of the coil increases, and the temperature of the coil itself exceeds 200 ° C. .
For this reason, a holder that supports the core or coil, or
As the material of the coil, an expensive material that can withstand the above-mentioned temperature must be used, which not only causes an increase in cost, but also results in energy saving.

The inventors of the present invention have conducted intensive studies to achieve both energy saving of the fixing device and improvement of operability for the user, and as a result, the distance between the core and the hollow metal body to be heated has been determined. It has been found that when the size is within the range described above, the heating efficiency can be improved while ensuring sufficient electrical insulation between the hollow metal body and the core, and the present invention has been completed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an induction heating fixing device capable of sufficiently securing electrical insulation between a hollow metal roller and a core and improving the heating efficiency.

[0010]

SUMMARY OF THE INVENTION The present invention as set forth in claim 1 for achieving the above object, is rotatably held, the hollow gold Shokuro over La to be heated, a core made of a magnetic material, An induction coil that is formed by winding a winding around an insulating portion around the core and induces an induction current in the hollow metal roller to heat it, and is formed in a substantially cylindrical shape from an electrically insulating material,
In the induction heat fixing apparatus having a holding member of the non-rotating housed at a gap against the inner surface of the hollow metal roller to support the core and the induction coil within said hollow metal roller, wherein the induction coil Is the holding member
The core is wound so that it does not exceed the outer peripheral surface,
An induction heating fixing device, which is connected to the outer peripheral surface of the holding member and is arranged such that a distance between the holding member and the hollow metal roller is 0.5 mm or more and 4 mm or less.

With this configuration, the temperature of the coil can be suppressed to a temperature lower than the temperature at which expensive materials must be used, thereby suppressing an increase in cost. Can contribute. Further, electrical insulation between the hollow metal body and the core is secured, and the induction heating fixing device does not hinder the rotation of the hollow metal roller. Ma
Also, the end face of the core is connected to the outer peripheral face of the holding member.
This makes it easier to bring the core closer to the inner surface of the hollow metal roller,
It becomes easier to achieve an improvement in heating efficiency.

[0012]

[0013]

It is preferable that at least a portion of the core and the induction coil exposed to the outside from the holding member is covered with a thin electric insulator having heat resistance.

With this configuration, even if the core is brought closer to the inner surface of the hollow metal roller, electrical insulation between the hollow metal roller, the core, and the induction coil becomes more reliable. Even in the case where the fixing device is broken due to temperature or the like, it is possible to secure electrical insulation and prevent the entire fixing device from being broken.

Further, the holding member, the insulating portion for insulating the induction coil and prior SL core characterized in that it is formed integrally.

[0017] By integrating the holding member thus insulating portion, Ru can ensure a sufficient mechanical strength.

[0018]

[0019]

[0020]

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

[0021] Figure 1 "shape state implementation" is a cross-sectional view showing an induction heating fixing device according to the shape condition of the present invention schematically.

As shown in FIG. 1, the induction heating fixing device incorporated in a printer or the like is provided with a heating roller or a fixing roller 10 rotatably driven in the direction of an arrow a, and in pressure contact with the fixing roller 10. And a pressure roller 11 that rotates following the rotation of the fixing roller 10.

The fixing roller 10 is a conductive hollow pipe, and has a coil assembly 12 for generating an induced current (eddy current) in the fixing roller 10 therein.
Are arranged. The coil assembly 12 is held by a holder 24 and constitutes a holder unit 13 as a whole. The fixing roller 1 generates heat due to the induced current.
0, and the fixing roller 10 corresponds to a hollow metal roller as a hollow metal body. Further, the holder 24 corresponds to a holding member.

The fixing roller 10 has sliding bearings formed at both ends thereof, and is rotatably attached to a fixing unit frame (not shown). Further, the fixing roller 10
A drive gear (not shown) is fixed to one end thereof, and is rotatably driven by a drive source (not shown) such as a motor connected to the drive gear. The holder 24 is fixed to the fixing unit frame and is non-rotatable. The holder 24 is housed inside the roller 10 with a predetermined gap between the holder 24 and the inner peripheral surface of the fixing roller 10.

The toner carrier, that is, the sheet 14 to which the unfixed toner image has been transferred is conveyed from the left as indicated by an arrow b in FIG.
Is sent toward the nip between the two. Sheet 14
Is the heat of the heated fixing roller 10 and the two rollers 10,
The nip portion is conveyed while the pressure acting from 11 is applied. As a result, the unfixed toner is fixed,
A fixed toner image is formed on the sheet 14. The sheet 14 that has passed through the nip portion is naturally separated from the fixing roller 10 by the curvature of the fixing roller 10, or is provided such that the leading end thereof is in sliding contact with the surface of the fixing roller 10 as shown in FIG. The fixing roller 10
And is conveyed rightward in FIG. The sheet 14 is conveyed by a discharge roller (not shown) and discharged onto a discharge tray.

Above the fixing roller 10, a temperature sensor 16 for detecting the temperature of the fixing roller 10 is provided. The temperature sensor 16 is in pressure contact with the surface of the fixing roller 10 so as to face the induction coil 22 with the fixing roller 10 therebetween. The temperature sensor 16 includes, for example, a thermistor, and the fixing roller 1 is
While detecting the temperature of 0, energization of the induction coil 22 is controlled so that the temperature of the fixing roller 10 becomes the optimum temperature.

A thermostat 17 is provided above the fixing roller 10 as a safety mechanism in the event of abnormal temperature rise. This thermostat 17 is used for the fixing roller 1.
When the temperature reaches a preset temperature, the contact is opened to cut off the power supply to the induction coil 22, thereby preventing the fixing roller 10 from reaching a predetermined temperature or higher.

The fixing roller 10 is formed of a conductive member such as an iron, stainless steel alloy tube, nickel, carbon steel tube, or aluminum alloy tube, and its outer peripheral surface is coated with a fluororesin. Are formed. More preferably, the fixing roller 10 is formed from a conductive magnetic member. A silicone rubber layer 19 which is a surface-releasable heat-resistant rubber layer is formed around a shaft core 18 of the pressure roller 11. In addition, a sliding bearing or a separation claw 15
Is made of heat-resistant slidable engineering plastic or the like.

As shown in FIG. 2, the holder unit 13
Is composed of the coil assembly 12 and the holder 24 as described above. The coil assembly 12 is formed by winding a copper wire 21 around a core 23 made of a magnetic material and an insulating portion around the core 23. And an induction coil 22 that is formed and heats the fixing roller 10 by inducing an induction current. The core 23 and the induction coil 22 are supported by a holder 24.

[0030] In particular, in the form status of the present embodiment, the holder 2
Reference numeral 4 denotes a substantially cylindrical shape made of an electrically insulating material, and an insulating portion for insulating the core 23 and the induction coil 22 integrally formed. The core 23 has an end surface 38 connected to the outer peripheral surface 33 of the holder 24. Is formed.

More specifically, as shown in FIG.
The holder 24 has a holder body 30 formed in a substantially cylindrical shape.
And openings 31 provided at both axial ends of the holder body 30.
And an end plug 32 that closes the end plug. The holder main body 30 further includes an arc portion 34 which is located vertically above and below in the drawing and has an arc-shaped outer peripheral surface 33, and a rectangular bobbin portion 35 which extends in the axial direction and connects the two arc portions 34, 34. A through hole 36 for inserting the core 23 is formed in the arc portion 3.
4, 34 are formed. The holder main body 30 and the end plug 32 are both formed of heat-resistant insulating engineering plastic, and the holder main body 30 has both arc portions 34 and bobbin portions 35 integrally formed.
Further, each end plug 32 is provided with a protrusion 37 for fixing to the fixing unit frame. The induction coil 22 is formed by winding the copper wire 21 around the bobbin portion 35 a plurality of times in one direction.
Are formed, but the four wall surfaces of the bobbin portion 35 function as the insulating portions formed integrally with the holder 24.

The core 23 has a relatively long plate shape,
4A, the end face 38 along the opening direction of the through hole 36 has the same radius of curvature as the arc-shaped outer peripheral surface 33 of the arc portion 34, and when inserted and fixed into the through hole 36, as shown in FIG. The end face 38 is smoothly connected to the arc-shaped outer peripheral face 33. The core 23 is made of, for example, a ferrite core or a laminated core.
1 to form a magnetic path.

FIG. 3 shows an embodiment in which the end plug 32 is attached to the opening 31 of the holder body 30 after the induction coil 22 is formed. However, the end plug 32 is not an essential member constituting the holder 24, Opening 31 on fixing unit frame side
May be provided to hold the holder main body 30. Further, as the coil 22, it is preferable to use a single or litz copper wire having a fusion layer and an insulating layer on the surface. The copper wire 21 is wound so as not to exceed the outer peripheral surface of the holder.

Furthermore in the form status of the present embodiment, as shown by a chain line in FIG. 4 (A), Aru wrapped in thin electrical insulator 40 having heat resistance across the holder 24. This thin electric insulator 40 is, for example, polyimide, polyamideimide,
An insulating film or tube made of fluororesin or the like and having a thickness of about 30 μm to 100 μm.
However, the electric insulator 40 is not limited to the tube shape, and may be in any form as long as it can cover at least a portion of the core 23 and the induction coil 22 that is exposed to the outside from the holder 24. For example, an electric insulator having a sheet shape is attached to or coated on the arc portion 34 of the holder body 30 so as to partially cover the end surface 38 of the core 23 and the side surface of the induction coil 22 instead of the entire holder 24. Is also good.

Then, with the holder 24 accommodated in the fixing roller 10 in a non-rotating manner, the core 23 is removed from the fixing roller 10.
Distance d of gap (hereinafter, also referred to as gap) between inner surface
Are arranged to have a size of 0.5 mm or more and 4 mm or less.

The reason why the size of the gap is defined as described above is as follows.

Since the holder 24 holds the coil 22 and the core 23 and is housed in the fixing roller 10 and is fixed at both ends to the fixing unit frame, a certain amount of bending occurs due to the weight of the coil 22 and the core 23. . Also,
There are variations in parts such as dimensional fluctuation of the inner diameter of the fixing roller 10 and dimensional fluctuation of the outer diameter of the holder 24. In consideration of these, it is necessary to keep the gap at 0.5 mm or more. Although the amount of deflection of the holder 24 depends on its length, if the gap is at most 4 mm, the core 23 and the fixing roller 10 do not come into contact with each other, including variations in component dimensions.

On the other hand, as the size of the gap becomes longer, the heating efficiency becomes worse, and it is necessary to supply more current to the coil. FIG. 5 is a graph showing the relationship between the distance between the fixing roller and the core and the coil temperature. When the gap exceeds 4 mm, the amount of heat generated by the copper loss of the coil increases considerably. At 160 ° C., the temperature of the coil itself exceeds 200 ° C. The applied power at this time was 160 W for a roller having an outer diameter of 20 mm, and 30 W for the outer diameter.
300 mm with a roller of 70 mm and 70 with a roller with an outer diameter of 40 mm
0W. If the temperature of the coil itself exceeds 200 ° C,
It is necessary to use an expensive material that can withstand the above-mentioned temperature as a material of the holder for supporting the core or the coil or the material of the coil, which not only causes an increase in cost, but also results in energy saving.

From the above points, by setting the gap to 4 mm or less, the coil temperature can be suppressed to within 200 ° C., and by setting the gap to 0.5 mm or more, the core does not contact the fixing roller, and It can be rotated without hindrance.

[0040] Therefore, according to the induction heating fixing device in the form status of this embodiment which defines the gap following dimensions 4 mm,
It can suppress the rise in cost and contribute to energy saving.
Since the size is specified to be 0.5 mm or more, the fixing roller 10
Smooth rotation of the core 23 and the fixing roller 10.
And electrical insulation between them. Further, since the entire holder 24 is wrapped with the insulating film or the insulating tube 40, the electrical insulation between the core 23 and the fixing roller 10 and between the induction coil 22 and the fixing roller 10 is further ensured. Even if the coating of the induction coil 22 is broken due to excessive temperature rise or the like, electrical insulation can be ensured and the entire fixing device can be prevented from being broken.

Generally, in a fixing device of a copying machine or a printer, a fixing roller having an outer diameter in a range of about 16 mm to 60 mm is used. Further, as the number of print pages per unit time increases, that is, as the printing speed increases, the outer diameter of the fixing roller needs to be increased in order to secure a sufficient nip width for heating the paper. If the outer diameter of the fixing roller is large, the coil assembly of the holder unit can be made large. However, since the required power becomes large, the situation of the rise of the coil temperature is as shown in FIG.
It is almost the same regardless of the roller outer diameter. That is, it is understood that the rise in the coil temperature is largely affected by the dimension of the gap rather than the outer diameter of the roller. For this reason, in a fixing device using a fixing roller having the above outer diameter range, it is necessary to set the gap to a size of 4 mm or less regardless of the outer diameter of the fixing roller. From other measurement results, it has been found that even if the material of the fixing roller is different, the dimension of the gap has a greater effect on the rise of the coil temperature than the difference in the material.

As shown in FIG. 4B, in the case where the holder unit 45 in which the entire core 43 and the coil 42 are surrounded by the holder 44 is housed in the fixing roller 46, the outer peripheral surface of the holder 44 and the fixing roller the distance between the inner 46 circumference is to be the same on purpose form of this embodiment, the holder 4
The core 43 is moved away from the inner surface of the fixing roller 46 by an amount corresponding to the thickness of 4. Make the holder 44 thinner and make the core 4
It is conceivable to bring the holder unit 3 closer to the inner surface of the fixing roller 46, but this would result in insufficient mechanical strength for fixing the holder unit 45 to the fixing unit frame.

[0043] In contrast, in the form status of the present embodiment, to ensure a sufficient mechanical strength as a whole holder 24 by integrating the bobbin portion 35 to the holder main body 30, the holder 30 the end face 38 of the core 23 The core 23 can be made as close as possible to the inner surface of the fixing roller 10 by connecting to the arc-shaped outer peripheral surface 33 of the main body. Moreover, since the entire holder 24 is wrapped by the thin insulating film or insulating tube 40, sufficient electrical insulation can be obtained even when the core 23 is brought closer to the inner surface of the fixing roller 10.

[0044]

[0045]

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

As described above, according to the first aspect of the present invention, the core is arranged so that the distance between the core and the hollow metal roller is 0.5 mm or more and 4 mm or less. Therefore, the temperature of the coil can be kept below the temperature at which expensive materials must be used to suppress the rise in cost, and the deterioration of the heating efficiency can be suppressed, contributing to energy saving. The hollow metal roller can be smoothly rotated while ensuring sufficient electrical insulation between the core and the core. Also, the end face of the core is
The core is connected to the hollow metal roller
It is easier to get closer to the inner surface, and it is easier to achieve improved heating efficiency.
You.

[0054]

According to the second aspect of the present invention,
Since the portion of the core and the induction coil that is exposed to the outside from at least the holding member was covered with a thin electric insulator,
Even if the core is brought closer to the inner surface of the hollow metal roller, electrical insulation between the hollow metal roller, the core, and the induction coil can be more reliably ensured. Even if the fixing is performed, it is possible to secure electrical insulation and prevent the entire fixing device from being destroyed.

According to the third aspect of the present invention,
Because the core and the induction coil is integrated in the holding member an insulating portion for insulating, Ru can ensure a sufficient mechanical strength as a whole holding member.

[0057]

[Brief description of the drawings]

[1] The induction heat fixing apparatus according to the shape condition of the present invention is a cross-sectional view showing schematically.

FIG. 2 is an external perspective view of the holder unit shown in FIG.

FIG. 3 is an exploded perspective view showing a core and a holder of the holder unit.

[4] FIG. 4 (A), enlarged cross-sectional view showing the main part of the induction heat fixing apparatus according to the shape condition of the embodiment, FIG. (B), the induction heating fixing device using a holder unit of the comparative example is an enlarged sectional view showing the principal.

FIG. 5 is a graph showing a relationship between a distance between a fixing roller and a core and a coil temperature.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Fixing roller (hollow metal roller) 1 1 ... Pressure roller 2 2 ... Induction coil 23 3 ... Core 24 ... Holder (holding member) 33 ... Arc-shaped outer peripheral surface (outer peripheral surface of holding member) 35 ... Bobbin part ( Insulating part) 38: End face of core 40: Insulating film or insulating tube (electric insulator)

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-8-220912 (JP, A) JP-A-9-73245 (JP, A) JP-A-8-16005 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G03G 13/20 G03G 15/20 H05B 6/00-6/44

Claims (3)

(57) [Claims] 1. A hollow metal rotatably held and heated.
And Shokuro over La, a core made of a magnetic material, an induction coil around the core is formed by winding a winding wire through the insulating portion is heated by inducing an induction current in the hollow metal roller, electrically insulating A non-rotating holding member that is formed in a substantially cylindrical shape from a material , supports the core and the induction coil, and is housed in the hollow metal roller with a gap with respect to an inner surface of the hollow metal roller. In the induction heating fixing device, the induction coil may be arranged so as not to exceed an outer peripheral surface of the holding member.
And the end surface of the core is continuous with the outer peripheral surface of the holding member.
Ri, the distance between the hollow metal roller 0.5mm or more, the induction heat fixing apparatus, characterized in that arranged so that the following dimensions 4 mm. 2. A portion of the core and the induction coil which is exposed to the outside from at least the holding member,
2. The induction heating fixing device according to claim 1, wherein the device is covered with a thin heat insulator having heat resistance. Wherein said retaining member includes an insulating portion for insulating the induction coil and prior SL core induction heat fixing apparatus according to claim 1, characterized in that it is formed integrally.