JPH08190298A - Fixing device - Google Patents

Abstract

PURPOSE: To obtain a stable image by keeping the carrying speed of a transfer paper constant. CONSTITUTION: This fixing device for fixing unfixed toner by a heating element with a heat resistant endless film 15 is provided with a photointerrupter (detecting means) 16 detecting the circumferential speed of the endless film 15 and a control means (microcomputer) controlling the circumferential speed of the endless film 15 based on the circumferential speed of the film 15 detected by the photointerrupter 16. The circumferential speed of the film 15 in the fixing device is controlled to a constant one, so that the carrying speed of the transfer paper in the fixing device can be kept constant and the stable image can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device (SURF fixing device) used in an image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art Conventionally, as a fixing method in a fixing device, for example, a belt fixing method described in US Pat. No. 3,578,797 is known. But,
This type of belt fixing method has a point to be improved such that it takes a long time to rise to a predetermined temperature and requires a relatively large electric power.

Therefore, the present applicant has proposed a fixing device using a thin layer belt. In this fixing device, a thin endless film is driven by tension and driving of a roller or the like, but the roller is formed by winding a rubber material around a metal shaft because of a problem of fixing property.

[0004]

However, in the fixing device according to the above-mentioned proposal, the rotation speed of the roller itself does not change, but when copying continuously, the expansion coefficient of the rubber material is large, and therefore the roller diameter is large. Is gradually increased, and therefore, the peripheral speed of the endless film is increased, and therefore, the conveyance speed of the paper in the fixing unit is also increased. For example, in the case of a pressure roller in which an aluminum shaft having a diameter of 10 mm and a thickness of 2.9 mm is wound with a silicon rubber, there is a difference of 2.5% in the paper conveyance speed between the first copy and the operation for 10 minutes. . For this reason, if the fixing paper conveyance speed when the pressure roller is cold and the paper conveyance speed before fixing are made to be approximately the same, the fixing paper conveyance speed will be increased during continuous copying. The speed became higher, the fixing device pulled the paper, and the paper rubbed the photosensitive drum, so that lines were generated in the image.

On the other hand, if the paper feeding speed for fixing when the fixing roller is warmed and the paper feeding speed before fixing are made substantially equal to each other, the diameter of the fixing roller when starting copying becomes warm. Since it is smaller than that when the paper is being held, the fixing paper conveyance speed becomes slow. Therefore, the photosensitive drum pushes the paper, and the image shrinks, or when the photosensitive drum pushes the paper, a paper loop is formed between the photosensitive drum and the fixing unit, and when the paper passes through the registration roller. The paper was pushed back toward the photosensitive drum, and the paper rubbed against the photosensitive drum, causing a line in the image.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a fixing device capable of obtaining a stable image with a constant transfer speed of the transfer paper.

[0007]

In order to achieve the above object, the invention according to claim 1 is a fixing device for fixing unfixed toner by a heating element via a heat-resistant endless film, and a peripheral speed of the endless film. And a control means for controlling the peripheral speed of the endless film based on the peripheral speed of the endless film detected by the detecting means.

According to a second aspect of the invention, in the first aspect of the invention, the detecting means also serves as a regulating member for regulating the deviation of the endless film.

According to a third aspect of the invention, in the invention of the first aspect, at least one end of the endless film is obliquely cut, and the detecting means is obliquely cut by driving the endless film. It is characterized in that the peripheral speed of the endless film is detected by detecting the presence / absence of a film portion.

According to a fourth aspect of the present invention, in the first aspect of the invention, at least one end of the endless film is subjected to a masking treatment for shielding the light of the reflection type sensor over the entire periphery. In addition, a plurality of white patterns that easily reflect light are printed thereon at equal intervals.

A fifth aspect of the present invention is characterized in that, in the first aspect of the invention, a plurality of holes are formed at equal intervals in at least one end of the endless film.

[0012]

According to the present invention, by controlling the peripheral speed of the endless film of the fixing device to be constant, the transfer paper conveying speed in the fixing device can also be made constant, and a stable image can be obtained.

[0013]

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

<First Embodiment> First, a schematic structure of an image forming apparatus having a fixing device according to the present invention will be described with reference to FIG.

A document table 1 is provided on the upper surface of the main body of the image forming apparatus shown in FIG. 2, and a photosensitive drum 4 as an image carrier is rotatably arranged in the center of the main body of the photosensitive drum 4. A charger 5, a developing device 6, a transfer discharger 9 and the like are arranged around the device. Further, in the upper part of the main body of the image forming apparatus, a short-focus small-diameter image-forming element array 2 constituting an optical system, an illumination lamp 3, etc. are arranged, and in the lower part, a cassette S containing a transfer sheet P, a feeding roller 7, A sheet feeding system including a conveying roller 8 and the like, a conveying belt 10, a fixing device 11 according to the present invention, and a sheet discharge tray 12 are arranged.

The transfer paper P on which an image is formed through a well-known process is sent to the fixing device 11 by the conveyor belt 10, and the unfixed toner image carried on the transfer paper P is fixed by the fixing device 11. It is fixed on P.

The structure of the fixing device 11 will be described with reference to FIG.

FIG. 3 is a side view showing a schematic structure of the fixing device 11. In FIG. 3, 15 is an endless film having heat resistance, and the endless film 15 is, for example, a polyimide or polyetherimide film having a thickness of about 20 μm. A release layer made of PTFE with a conductive agent added to at least the image contact surface side of a film sheet such as PES, PES, or PFA.
It is formed by coating with a thickness of 0 μm. The endless film 15 is wound around the outer periphery of the heater holder 27, and the heater holder 27 supports a low heat capacity linear heating element 18 (hereinafter referred to as a heater).
The pressure roller 14 is in contact with the heater 18 via the endless film 15.
Is composed of a rubber elastic layer having a good releasability such as silicon rubber.

Then, the heater 18 is pressed by the pressure roller 14 through the endless film 15 with a total pressure of 4 to 7 kg, and the pulse motor 13 shown in FIG. The endless film 15 is driven to rotate (counterclockwise) to move the endless film 15 in the arrow direction (clockwise) of FIG.
Follow the rotation. Then, the transfer sheet P, which is image-formed by a well-known technique and is guided to the fixing portion along the entrance guide 23, is nipped between the pressure roller 14 and the endless film 15 and conveyed in the direction of arrow e in FIG. , The transfer paper P
The toner t carried on the top is fixed.

By the way, in this embodiment, as shown in FIG. 1, a plurality of holes 1 are formed at one end of the endless film 15.
7 are formed at equal intervals, and a masking process for shielding the light of the photo interrupter 16 is applied to the entire periphery (hatched portion) of the edge of the same end. Therefore, the hole 17 of the endless film 15 is provided at the position of the photo interrupter 16.
, The photo interrupter 16 is turned on, and when the light of the photo interrupter 16 is blocked by the endless film 15, the photo interrupter 16 is turned off.
Since it is an FF, the photo interrupter 16 is repeatedly turned ON / OFF by the endless film 15 being rotationally driven in the direction of arrow a in FIG.

The ON / OFF cycle of the photo interrupter 16 changes depending on the peripheral speed of the endless film 15. The peripheral speed of the endless film 15 is detected by reading this ON / OFF cycle, and the endless film 15 is detected. The pulse motor 13 for driving the pressure roller 14 is controlled by a microcomputer (not shown) so that the peripheral speed of the same becomes the same as the peripheral speed of the photosensitive drum 4 (see FIG. 2). As a result, the conveyance speed of the transfer paper P in the fixing device 11 can be constantly kept constant, and a stable image can be supplied.

Further, in this embodiment, the endless film 1 is used.
ON / OFF of the photo interrupter 16 is optically detected depending on whether or not the hole 17 is opened in 5, so that regardless of the contamination of the endless film 15 due to the toner t or the like,
The peripheral speed of the endless film 15 can be accurately detected.

As the motor for driving the pressure roller 14, another type of motor such as a DC servo motor may be used.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. 4. FIG. 4 is a side view of the fixing device according to this embodiment.

In this embodiment, a masking process (shown by diagonal lines in the figure) for shielding the light of the reflection type sensor 20 is applied to the entire edge of the endless film 15 on one side (non-sheet passing portion). The white patterns 19 that easily reflect light are printed at equal intervals.

When the endless film 15 is rotationally driven in the direction of the arrow b in FIG. 4, the reflective sensor 20 repeats ON / OFF, and the ON / OFF thereof is performed.
Since the cycle of No. changes depending on the peripheral speed of the endless film 15, the peripheral speed of the endless film 15 is detected by reading this ON / OFF cycle, and the peripheral speed of the endless film 15 is set to the photosensitive drum 4 (see FIG. 2). The motor that drives the pressure roller 14 is controlled by a microcomputer (not shown) so that the peripheral speed becomes the same. As a result, the transport speed of the transfer paper in the fixing device 11 can always be kept constant, and a stable image can be supplied.

Further, in this embodiment, since the detection of the reflection type sensor 20 is carried out at the non-sheet passing portion of the endless film 15, the peripheral speed of the endless film 15 is accurately measured without being affected by the dirt such as toner. Can be detected.

<Third Embodiment> Next, a third embodiment of the present invention will be described with reference to FIGS.

FIG. 5 is a perspective view of the fixing device 11 according to this embodiment. In FIG. 5, 21 is the endless film 1.
5 is a photosensor for detecting the peripheral speed, and the front end 24 of the endless film 15 is provided with a masking process (shown by diagonal lines in the figure) for shielding the light of the photosensor 21 from the entire periphery. It has been applied to.

In this embodiment, the photo sensor 2
Although a photo interrupter is used as 1, the endless film 1 is used when a reflection type photo sensor is used.
It is necessary to apply a reflecting member treatment for reflecting light to the end portion 24 of No. 5. Further, in this embodiment, the masking process is applied only to the one end 24 of the endless film 15, but it goes without saying that it may be applied to the entire endless film 15.

Further, in FIG. 5, reference numeral 22 is a cleaning member, which constantly cleans the end portion of the endless film 15 to prevent erroneous reading by the photo sensor 21. Works effectively with. Although the felt is used as the cleaning member 22 in this embodiment, any type of felt may be used as long as it has a cleaning effect.

FIG. 6 shows the outer shape of the endless film 15. The diameter of the endless film 15 is φM, and one end (end on the front side) of the endless film 15 is obliquely cut, and the length of the longest part thereof is Lmax. If the length of the outermost portion is Lmin, the dimension (diagonal cut amount of film) ΔL of the obliquely cut portion (oblique cut portion) can be obtained by Lmax-Lmin.
As shown in FIG. 5, this diagonal cut portion is arranged on the front side of the main fixing device 11, and is configured so that the photosensor 21 detects the peripheral speed of the endless film 15.

FIG. 7 is a detailed view showing the positional relationship between the photo sensor 21 and the endless film 15.

In this embodiment, a transmissive photo interrupter is used as the photo sensor 21, and its detection position is shown as d in FIG. When the endless film 15 is located behind the detection position d, the photo sensor 21 is turned on, and when the film 15 is located near the detection position d, the photo sensor 2 is turned on.
1 will be turned off.

Thus, the slanted cut portion of the endless film 15 is located at the detection position d of the photo sensor 21. Therefore, when the endless film 15 is rotationally driven in the direction of arrow c in FIG. 5, the photo sensor 21 repeats ON / OFF, and the ON / OFF cycle changes depending on the peripheral speed of the endless film 15. Therefore, O of the photo sensor 21
The peripheral speed of the endless film 15 is detected by reading the N / OFF cycle, and the peripheral speed of the endless film 15 becomes the same as the peripheral speed of the photosensitive drum (not shown).
If the motor 13 that drives the pressure roller 14 is controlled by a microcomputer (not shown), the transfer paper conveyance speed in the fixing device 11 can always be kept constant, and a stable image can be supplied.

<Fourth Embodiment> Next, a fourth embodiment of the present invention will be described with reference to FIGS.

FIG. 8 is a sectional view of the fixing device 11 according to the present embodiment. In FIG. 8, 18 is a heating element, 15 is an endless film, and the endless film 15 is made of polyimide, polyetherimide, PES or the like. Composed thickness 2
A heat-resistant resin film of 0 μm is coated on one side with a release layer such as PTFE. The total thickness of the endless film 15 is generally preferably 50 μm or less.

Further, in FIG. 8, 29 is a rib provided on the outer periphery of one end (front side) of the endless film 15, and this rib 29 may be formed integrally with the same material as the film 15 or it may be slid afterwards. It is also possible to form ribs of another material having good kinematics (for example, urethane rubber or silicon rubber) by adhesion or the like.

By the way, the endless film 15 is stretched between the driving roller 30 and the tension roller 31,
This constitutes a film transport path together with the heating body 18. Then, the endless film 15 is applied to the tension roller bearings 34, 35 by the urging means 32, 33.
A predetermined tension is applied by urging the tension roller 31 in the direction indicated by the arrow A in the figure, and the driving roller 30 conveys the tension roller 31 in the direction indicated by the arrow B. Here, the driving roller 30 is configured by providing a coating layer of silicon rubber or the like on the surface of a cored bar of iron or the like in order to reliably convey the endless film 15.

Reference numeral 14 is a pressure roller, which has a rubber elastic layer having a good releasability such as silicon rubber, and presses the endless film 15 against the heating body 18 with a force necessary for fixing. Further, both ends of the pressure roller 14 are rotatably supported by bearings (not shown) so as to rotate following the endless film 15.

The heating element 18 is fixed to a stay 37 via a heat insulating member 36 made of a heat resistant resin, and the stay 37 has rigidity enough to withstand the pressure applied by the pressure roller 14. In FIG. 8, 23 is an entrance guide, 3
Reference numeral 8 is a separation guide, and 39 is a paper discharge roller. FIG. 9 shows FIG.
Is a view in the direction of arrow J, and a regulating member 40 for regulating the rib 29 is arranged inside the rib 29 (on the center side of the film 15) along the outer periphery of the drive roller 30 as shown in the drawing, and is not shown. The fixing device is fixed to the frame.

The endless film 15 is constructed so that a biasing force always acts in the direction of arrow C during transport by adjusting the biasing force of the biasing means 32, 33 and the like. When the film contacts the restriction member 40, the deviation of the film 15 is restricted. still,
At least the surface of the regulating member 40 on which the rib 29 slides is preferably made of a material such as polyacetal or fluororesin having good slidability.

FIG. 10 is a perspective view showing the relationship between the endless film 15 and the microswitch 28. As shown in the figure, the rib 29 is provided with a plurality of projections 41 at equal intervals, and the microswitch 28 has projections 41. It is installed so that it can be touched.

Thus, the endless film 15 is shown in FIG.
When it is driven to rotate in the direction of arrow f, the micro switch 2
8 is turned on by contacting the protrusion 41, and turned off when it is separated from the protrusion 41. Then, when the endless film 15 is continuously driven to rotate, the micro switch 28 is turned ON / O.
The FF is repeated, and the ON / OFF cycle changes depending on the peripheral speed of the endless film 15. Therefore, the peripheral speed of the endless film 15 is detected by reading the ON / OFF cycle of the micro switch 28, and the drive roller is adjusted so that the peripheral speed of the endless film 15 becomes the same as the peripheral speed of the photosensitive drum (not shown). If the drive of 30 is controlled by a microcomputer (not shown),
The transport speed of the transfer paper in the fixing device 11 can always be kept constant, and a stable image can be supplied.

Further, in this embodiment, if the peripheral speed of the film 15 is controlled by using the regulating member 40 for regulating the deviation of the endless film 15, the number of parts of the fixing device 11 and the cost can be reduced. be able to.

[0046]

As is apparent from the above description, according to the present invention, in the fixing device for fixing the unfixed toner by the heating element through the heat resistant endless film, the detection for detecting the peripheral speed of the endless film is performed. Means and a control means for controlling the peripheral speed of the endless film based on the peripheral speed of the endless film detected by the detection means are provided. The conveyance speed of can also be made constant, and a stable image can be obtained.

[Brief description of drawings]

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

FIG. 2 is a sectional view of the image forming apparatus.

FIG. 3 is a side view of the fixing device according to the first exemplary embodiment of the present invention.

FIG. 4 is a side view of a fixing device according to a second exemplary embodiment of the present invention.

FIG. 5 is a perspective view of a fixing device according to a third exemplary embodiment of the present invention.

FIG. 6 is a perspective view of an endless film of a fixing device according to a third exemplary embodiment of the present invention.

FIG. 7 is a detailed view showing a positional relationship between a photo sensor and an endless film of a fixing device according to a third exemplary embodiment of the present invention.

FIG. 8 is a sectional view of a fixing device according to a fourth exemplary embodiment of the present invention.

9 is a view in the direction of arrow J in FIG.

FIG. 10 is a perspective view showing a relationship between an endless film and a micro switch of a fixing device according to a fourth exemplary embodiment of the present invention.

[Explanation of symbols]

 11 Fixing Device 15 Endless Film 16 Photointerrupter (Detecting Means) 17 Hole 18 Heater (Heating Body) 19 White Pattern 20 Reflective Sensor (Detecting Means) 21 Photosensor (Detecting Means) 28 Micro Switch (Detecting Means) 40 Controlling Member

Claims (5)

[Claims] 1. A fixing device for fixing unfixed toner by a heating element through a heat-resistant endless film,
Detecting means for detecting the peripheral speed of the endless film,
A fixing device provided with control means for controlling the peripheral speed of the endless film based on the peripheral speed of the endless film detected by the detecting means. 2. The fixing device according to claim 1, wherein the detection unit also functions as a regulating member that regulates the deviation of the endless film. 3. At least one end of the endless film is obliquely cut, and the detecting means detects the presence or absence of a film portion of the endless film by driving the endless film to detect the circumference of the endless film. The fixing device according to claim 1, wherein speed is detected. 4. At least one end of the endless film is subjected to a masking process for shielding the light of a reflection type sensor over the entire periphery thereof, and a plurality of whites on which the light is easily reflected. The fixing device according to claim 1, wherein the patterns are printed at equal intervals. 5. The fixing device according to claim 1, wherein a plurality of holes are formed at equal intervals on at least one end of the endless film.