JP3420436B2 - 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 for fixing an unfixed image by heating a cylindrical member by electromagnetic induction.

[0002]

2. Description of the Related Art Many printers, copiers and the like form an image by an electrophotographic recording method. In this electrophotographic recording method, a toner image is transferred onto a recording medium and heat and pressure are applied to the recording medium. Is applied to fix the toner image.

As a fixing device for fixing the toner image, a heat roller fixing device having a halogen heater therein, a film fixing device for contacting a ceramic heater with a polyimide-based cylindrical film from the inner surface, and the like have hitherto been used. Although known, in recent years, a fixing device by electromagnetic induction heating using a high frequency current has been proposed from the viewpoint of power saving.

In the fixing device based on the electromagnetic induction heating, an exciting coil is arranged in a cylindrical member (film or roller) made of a high resistance material, and an eddy current generated by applying a high frequency current to the exciting coil is used to make the cylindrical member. The member is caused to generate heat, and the heat fixes the image.

[0005]

Since the fixing device is heated by a heater or the like, temperature detecting means such as a thermoswitch or a temperature fuse is provided so as not to excessively heat the fixing device.

However, in the above-mentioned fixing device using electromagnetic induction heating, the heat generation portion varies depending on the position of the exciting coil, and the heat is nonuniform on the circumference of the cylindrical member. For this reason,
Depending on the arrangement position of the temperature detecting means, there is a possibility that only a temperature lower than the exothermic peak temperature can be detected or the temperature detecting element itself generates heat.

The present invention is to solve the above problems,
The purpose thereof is to provide a highly reliable fixing device that enables accurate temperature detection in the fixing unit.

[0008]

A typical structure according to the present invention for achieving the above object is a rotatable cylindrical member made of a magnetic material and a recording medium sandwiched between the cylindrical member. A rotating member for imparting a conveying force to the core member, a core having a high magnetic permeability provided inside the cylindrical member along the longitudinal direction of the cylindrical member, and an exciting coil wound around the core, The tubular member generates heat due to the eddy current generated in the tubular member by the action of the magnetic field generated by energizing the exciting coil,
In the fixing device for heating and fixing the unfixed toner image on the recording medium passing through the nip portion between the tubular member and the rotating member by this heat, the exciting coil is arranged along the tubular member around the longitudinal direction of the core. It is characterized in that a temperature detecting means for preventing abnormal temperature rise is provided at a position corresponding to a region along the tubular member of the exciting coil on the outer peripheral surface side of the tubular member.

In the above arrangement, since the temperature is detected at the position facing the exciting coil, the peak temperature of the tubular member can be detected more reliably, and overheating can be prevented reliably.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of an image forming apparatus using a fixing device according to the present invention will be described with reference to the drawings.

First Embodiment FIGS. 1 to 3 show a first embodiment, FIG. 1 is an explanatory view of the configuration of a fixing device, and FIG. 2 shows the positions of an exciting coil and a temperature detecting means. FIG. 3 is an explanatory diagram of the overall configuration of an image forming apparatus using the fixing device.

As the order of description, the overall structure of the image forming apparatus will be described first, and then the structure of the fixing device will be described.

{Overall Structure of Image Forming Apparatus} This image forming apparatus (laser beam printer) A, as shown in FIG. 3, produces a drum-shaped image of information light (laser light) based on image information from the optical means 1. The latent image is formed on the electrophotographic photosensitive member by irradiating the electrophotographic photosensitive member, which is a carrier, and the latent image is developed to form a toner image. Then, in synchronization with the formation of the toner image, the recording medium P, which is a recording medium, is conveyed by the conveying means, and an image is formed on the recording medium P by the image forming means.

In the present embodiment, the electrophotographic system is used as the image forming means, and the photosensitive drum 2 which is an electrophotographic photosensitive member, the charging means, the developing means, and the cleaning means (not shown) are made into a cartridge, and this process is performed. The cartridge 3 can be attached to and detached from the apparatus body. The image forming means uniformly charges the surface of the rotating photosensitive drum 2 by the charging means, forms a latent image on the photosensitive drum 2 by the light irradiation from the optical means 1, and the latent image is developed by the developing means. Toner is developed to form a visible image. Then, the toner image is transferred onto the recording medium P conveyed by the transfer means 4, and the transferred image is fixed by the fixing means 5 which is a fixing device.

On the other hand, the sheet conveying means for conveying the recording medium P separates and feeds one by one from the recording medium cassette 6 mounted on the bottom of the apparatus main body by the pickup roller 7 and the separating claw 6a, and also the conveying roller. 8 and a pinch roller 9 that is pressed against the pin 8 and is driven to rotate, conveys a U-turn to the image transfer portion.

By applying a voltage to the transfer roller 4 constituting the transfer means, the recording medium P on which the toner image formed on the photosensitive drum 2 is transferred is guided by the driving rotation of the conveying roller 8 and the transfer roller 4. The sheet is conveyed along the conveyance guide member 10 constituting the means and reaches the fixing means 5. Further, the recording medium P on which the transfer toner image is fixed by applying heat and pressure by the fixing means 5 is ejected by the pair of discharge rollers 11 and 12.
It is configured to be transported by and discharged to the discharge section 13 at the upper part of the apparatus main body.

{Structure of Fixing Device} Next, the structure of the fixing means (fixing device) 5 for fixing the toner image transferred to the recording medium P will be described.

The fixing means 5 according to the present embodiment heats the recording medium P by electromagnetic induction heating to fix the toner image. As shown in FIG. 1, the fixing upper roller unit 14 which is an electromagnetic induction heating section. And a lower fixing roller 15 that is a rotating member that is driven and rotated by a motor (not shown), and applies heat and pressure when passing the recording medium P on which the toner image is transferred.

The upper fixing roller unit 14 is a cylindrical member made of a magnetic material having a length equal to or larger than the width of the recording medium P (the length of the recording medium in the direction orthogonal to the conveying direction). A fixing film 14a made of a cylindrical film of nickel material is rotatably supported by a film guide 14b. Inside the fixing film 14a, a core 14c made of a high magnetic permeability material and having a rectangular rod shape extending in the longitudinal direction of the fixing film 14a is held by a core holder 14d.
The core holder 14d and the film guide 14b are fixed by a holder stay 14e. Also,
An exciting coil 14f is wound around the core 14c in the longitudinal direction of the fixing film 14a.

When a high-frequency current is passed through the exciting coil 14f, an eddy current is generated around the exciting coil 14f, and the flow of this eddy current intersects with the fixing film 14a made of a high resistance material, so that the film 14a is removed. It generates heat due to its own internal resistance.

On the other hand, below the upper fixing roller unit 14, there is provided a lower fixing roller 15 which is a rotating body driven and rotated in the direction of arrow a in FIG. 1 by a motor (not shown). The lower fixing roller 15 is formed by forming silicon rubber on the outer periphery of an aluminum cored bar, has a length equal to or larger than the width of the recording medium P, and can rotate the both end axial portions in the lower fixing frame 16 by bearings. Supported by.

Further, the spring hook portion 17a of the upper fixing frame 17 for supporting the upper fixing roller unit 14 and the holder stay.
A compression type pressure spring 18 is attached between the spring hook portions 14e1 of 14e, and a nip portion is formed by pressing the upper fixing roller unit 14 against the lower fixing roller 15.

In FIG. 1, reference numeral 19 denotes an entrance guide, which functions as a guide for directing the recording medium P on which the toner image is not fixed to the nip portion formed by the upper fixing roller unit 14 and the lower fixing roller 15. A fixing discharge lower guide 20 is rotatably supported by the lower fixing frame 16 with a hinge portion and is biased in the direction of arrow b by a spring (not shown).

In the above structure, the recording medium P on which the toner image is transferred by the image forming means is nipped by the entrance guide 19 in the nip portion between the upper fixing roller unit 14 and the lower fixing roller 15 and pressure is applied, Further, by passing a high frequency current through the exciting coil 14f, the unfixed toner image is fixed by being heated by the fixing film 14a which is heated by the eddy current as described above, and is discharged by the discharge roller pair 11.

Further, the fixing means 5 automatically shuts off the current to the exciting coil 14f when the heat of the fixing film 14a exceeds a certain temperature so that the fixing means 5 does not rise in temperature any more. I have to.

Therefore, a temperature detecting sensor (thermo switch, temperature fuse, etc.) 21 serving as a temperature detecting means is located at a position facing the exciting coil 14f with the fixing film 14a interposed therebetween, and a minute gap from the surface of the fixing film 14a. Are separated from each other. When the temperature detection sensor 21 is arranged, it is necessary to arrange it at a position where the exothermic peak temperature can be accurately detected. Next, suitable positions for disposing the temperature detection sensor 21 will be described.

In the fixing means for heating the recording medium P by electromagnetic induction heating as in this embodiment, unlike the case where the conventional halogen heater is used, only the portion close to the exciting coil 14f generates heat. , Temperature detection sensor 21
When it is provided at a position facing the exciting coil 14f with the fixing film 14a interposed therebetween, it is preferable to be provided on the downstream side in the recording medium conveyance direction where the heat generation temperature rises (downstream side in the rotating direction of the fixing film 14a).

Next, regarding the position in the longitudinal direction of the fixing film 14a, the preferable position for disposing the temperature detecting sensor 21 differs depending on the winding method of the exciting coil 14f.

That is, as shown in FIG. 2 (a), the exciting coil
When the folded-back portion R of the fixing film 14f is outside the longitudinal end portion of the fixing film 14a, the heat generation temperature becomes uniform over the entire longitudinal direction of the fixing film 14a.
Is preferably arranged in the central portion in the longitudinal direction of the fixing film 14a which is less affected by heat loss such as heat radiation.

On the other hand, as shown in FIG. 2 (b), the exciting coil
When the folded-back portion R of 14f is located inside the end portion of the fixing film 14a in the longitudinal direction, it is preferably arranged between the center C of the folded-back portion R and the apex T of the folded-back portion R.
This is because the magnetic flux density at the folded-back end portion R becomes high, and the heat generation temperature at that portion becomes higher than that at other portions.

By disposing the temperature detecting sensor 21 as described above, it becomes possible to detect the peak temperature of the fixing film 14a which generates heat more accurately, and by controlling the heat generation according to the peak temperature, the fixing means 5 It is possible to reliably prevent overheating. This makes it possible to obtain the highly reliable fixing unit 5.

In the fixing means, a temperature detection sensor
It is preferable to magnetically shield 21 with a shield member that reflects magnetic flux such as aluminum because it is possible to prevent the temperature detection sensor 21 itself from generating heat due to electromagnetic induction.

[0033]

Since the present invention is constructed as described above,
Since the temperature is detected at the position facing the exciting coil, the peak temperature of the tubular member can be detected more reliably, and overheating can be reliably prevented.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the configuration of a fixing device.

FIG. 2 is an explanatory diagram showing the positions of an exciting coil and a temperature detecting means.

FIG. 3 is a diagram illustrating the overall configuration of an image forming apparatus using a fixing device.

[Explanation of symbols]

P ... recording medium 1 ... Optical means 2 ... Photosensitive drum 3 ... Process cartridge 4 ... Transferring means 5 ... Fixing means 6 ... Recording paper cassette 6a ... Separation claw 7 ... Pickup roller 8 ... Conveyor roller 9 ... Pinch roller 10 ... Transportation guide member 11… Ejection roller pair 12… Ejection roller pair 13 ... Discharge part 14… Fixing upper roller unit 14a ... Fixing film 14b ... Film guide 14c ... core 14d ... Core holder 14e… Holder stay 14e1 ... Spring hook 14f… Excitation coil 15… Lower fixing roller 16… Fixed lower frame 17… Fixing top frame 17a ... Spring hook 18 ... Pressure spring 19… Entrance Guide 20… Fixing and discharging guide 21… Temperature detection sensor

Continuation of the front page (72) Inventor Akiko Ishiguro 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP-A-8-30139 (JP, A) JP-A-8-129313 ( JP, A) JP 8-16009 (JP, A) JP 57-128373 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 13/20 G03G 15/20 H05B 6/00-6/44

Claims (3)

(57) [Claims] 1. A rotatable cylindrical member made of a magnetic material, a rotary member for imparting a conveying force to a recording medium sandwiched between the cylindrical member, and a longitudinal direction of the cylindrical member inside the cylindrical member. An eddy current generated in the tubular member by the action of a magnetic field generated by energizing the exciting coil, which has a high-permeability core provided along the direction and an exciting coil wound around the core. In the fixing device that heats and fixes the unfixed toner image on the recording medium passing through the nip portion between the tubular member and the rotating member by the heat, the exciting coil is provided around the longitudinal direction of the core. A temperature detecting means for preventing abnormal temperature rise is provided so as to be wound along the tubular member, and at a position corresponding to a region along the tubular member of the exciting coil on the outer peripheral surface side of the tubular member. Fixing device characterized by. 2. The folded portion of the exciting coil is located outside both ends in the longitudinal direction of the tubular member, and the temperature detecting means is on the outer peripheral surface side of the tubular member along the tubular member of the exciting coil. 2. The fixing device according to claim 1, wherein the fixing device is disposed at a position corresponding to, and is disposed at a substantially central portion in the longitudinal direction of the tubular member. 3. The folded portion of the exciting coil is inside both ends in the longitudinal direction of the tubular member, and the temperature detecting means is an area on the outer peripheral surface side of the tubular member along the tubular member of the exciting coil. 2. The fixing device according to claim 1, wherein the fixing device is arranged at a position corresponding to the above position and is arranged in the vicinity of the folded portion.