JP3382403B2 - Fixing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device (SURF fixing device) used for an image forming apparatus such as a copying machine and a printer. [0002] Conventionally, as a fixing system in a fixing device, for example, a belt fixing system described in US Pat. No. 3,578,797 is known. But,
This type of belt fixing method has some points to be improved, such as a long time until the temperature is raised to a predetermined temperature and a relatively large power requirement. Accordingly, the present applicant has proposed a fixing device using a thin belt. In this fixing device, a thin endless film is driven by tension and driving of a roller or the like. However, due to a problem of fixing property, the roller is configured by winding a rubber material around a metal shaft. [0004] However, in the fixing device according to the above proposal, the rotation speed of the roller itself does not change, but the coefficient of expansion of the rubber material is large when copying is performed continuously. The roller diameter gradually increases, so that the peripheral speed of the endless film increases, and therefore, the paper conveyance speed at the fixing unit also increases. For example, in the case of a pressure roller in which a silicon rubber having a thickness of 2.9 mm is wound around an aluminum shaft having a diameter of φ10 mm, there is a difference of 2.5% in the paper conveyance speed between the first copy and the operation after 10 minutes. . For this reason, if the conveyance speed of the fixing paper when the pressure roller is cold and the conveyance speed of the paper before fixing are almost the same, the conveyance of the fixing paper during continuous copying can be performed. The speed became faster, the fixing device pulled the paper, and the paper rubbed the photosensitive drum, causing lines in the image. On the other hand, if the conveying speed of the fixing paper when the fixing roller is warmed up and the conveying speed of the paper before fixing are made substantially the same, the diameter of the fixing roller at the start of copying is increased. Therefore, the paper transport speed for fixing becomes slower. Therefore, the photosensitive drum pushes the paper, and the image shrinks or the photosensitive drum pushes the paper, thereby forming a paper loop 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 the photosensitive drum, causing lines in the image. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to form a nip with a heater.
Even if the outer diameter of the pressure roller changes, the transfer material transport speed is kept constant to prevent adverse effects of transfer and rubbing of unfixed toner images.
It is an object of the present invention to provide a fixing device that can prevent the image from being disturbed . [0007] In order to achieve the above object, the present invention provides a heater having a heating element and a heat-resistant end.
Pressed against the outer circumference of less film, a pressure roller having a rubber layer for forming a nip for nipping and conveying a transfer material having an unfixed toner image through the heater and heat-resistant endless film, driving causes rotating the pressure roller Means,
By rotating the pressure roller, it is driven
In a fixing device in which a thermal endless film rotates ,
A peripheral speed detecting means for detecting the peripheral speed of the heat-resistant endless film, a pressure roller drive means as a peripheral speed that is detected by the peripheral speed detecting means is kept constant at a predetermined speed
Yes, and the pressure roller and a control means for controlling the driving speed of
Regardless of the change in the diameter of the heat-resistant endless film.
It is characterized in that the speed is controlled to be constant . According to the present invention, the peripheral speed is detected by the peripheral speed detecting means.
That the peripheral speed is controlled by the control unit the driving speed of the drive means of the pressing roller so as to be maintained constant at a predetermined speed, pressure
Regardless of the change in roller diameter, heat-resistant endless film
Since the peripheral speed is controlled to be constant, the transfer speed of the transfer material is always kept constant even if the outer diameter of the pressure roller forming the nip with the heater changes, so that the transfer It is possible to prevent the image from being disturbed due to the adverse effect and the rubbing of the unfixed toner image, and to obtain a stable image. Embodiments of the present invention will be described below with reference to the accompanying drawings. First Embodiment First, a schematic configuration 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 serving as an image carrier is rotatably disposed at a central portion in the main body. A charger 5, a developing device 6, a transfer discharger 9, and the like are arranged around the periphery. In the upper part of the main body of the image forming apparatus, a short-focus small-diameter imaging element array 2 constituting an optical system, an illumination lamp 3 and the like are arranged, and in the lower part, a cassette S containing transfer paper P, a feeding roller 7, A paper feed system including a transport roller 8 and the like, a transport belt 10, a fixing device 11 according to the present invention, and a discharge tray 12 are arranged. The transfer paper P on which an image has been formed through a well-known process is sent to the fixing device 11 by the transport belt 10, and the unfixed toner image carried on the transfer paper P is transferred by the fixing device 11 to the transfer paper. It is fixed on P. Here, the configuration of the fixing device 11 will be described with reference to FIG. FIG. 3 is a side view showing a schematic configuration of the fixing device 11. In FIG. 3, reference numeral 15 denotes an endless film having heat resistance. The endless film 15 is, for example, polyimide or polyetherimide having a thickness of about 20 μm. , PES, PFA, etc., on a film sheet, at least on the image contacting surface side, a release layer obtained by adding a conductive agent to PTFE.
It is constituted by coating with a thickness of 0 μm. The endless film 15 is wound around an outer periphery of a heater holder 27, and the heater holder 27 supports a low heat capacity linear heating element 18 (hereinafter, referred to as a heater).
A pressure roller 14 is in contact with the heater 18 via an endless film 15.
Is configured to include a rubber elastic layer of silicon rubber or the like having good releasability. The heater 18 is pressed by the pressing roller 14 through the endless film 15 with a total pressure of 4 to 7 kg, and the pressing roller 14 is driven by the pulse motor 13 shown in FIG. The endless film 15 is rotated (clockwise) to rotate the endless film 15 in the direction of the arrow in FIG. 3 (clockwise).
Followed rotation. Then, an image is formed by a known technique, and the transfer paper P guided to the fixing unit along the entrance guide 23 is sandwiched between the pressure roller 14 and the endless film 15 and is conveyed in the direction of arrow e in FIG. , The transfer paper P
The toner t carried thereon is fixed. 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 blocking the light of the photo interrupter 16 is applied to the entire periphery of the same end portion (hatched portion). Therefore, the hole 17 of the endless film 15 is located at the position of the photo interrupter 16.
Are coincident with each other, the photointerrupter 16 is turned on. When the light of the photointerrupter 16 is cut off by the endless film 15, the photointerrupter 16 becomes O.
Since the endless film 15 is turned to the FF, the photo interrupter 16 is repeatedly turned on and off by being driven to rotate in the direction of arrow a in FIG. The ON / OFF cycle of the photointerrupter 16 changes depending on the peripheral speed of the endless film 15, and the peripheral speed of the endless film 15 is detected by reading the ON / OFF cycle. The pulse motor 13 for driving the pressure roller 14 is controlled by a microcomputer (not shown) so that the peripheral speed of the photosensitive drum 4 (see FIG. 2) becomes the same as the peripheral speed of the photosensitive drum 4. As a result, the transfer speed of the transfer paper P in the fixing device 11 can be always kept constant, and a stable image can be supplied. In this embodiment, the endless film 1
Since the ON / OFF of the photointerrupter 16 is optically detected based on whether or not the hole 17 is formed in the endless film 5, regardless of the contamination of the endless film 15 by the toner t or the like,
The peripheral speed of the endless film 15 can be accurately detected. It should be noted that another type of motor such as a DC servomotor may be used as the motor for driving the pressure roller 14. <Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a side view of the fixing device according to the present embodiment. In this embodiment, a masking process (shown by oblique lines in the figure) for shielding light from the reflection type sensor 20 is applied to one end (non-sheet passing portion) of the endless film 15 over the entire edge. A white pattern 19 that easily reflects light is printed thereon at regular intervals. When the endless film 15 is driven to rotate in the direction of the arrow b in FIG. 4, the reflection type sensor 20 repeats ON / OFF, and the ON / OFF of the reflection type sensor 20 is repeated.
Is changed by the peripheral speed of the endless film 15, the peripheral speed of the endless film 15 is detected by reading the ON / OFF period, and the peripheral speed of the endless film 15 is changed to the peripheral speed of the photosensitive drum 4 (see FIG. 2). A motor for driving the pressure roller 14 is controlled by a microcomputer (not shown) so as to be equal to the peripheral speed. As a result, the transfer speed of the transfer paper in the fixing device 11 can be always kept constant, and a stable image can be supplied. In this embodiment, since the detection of the reflection type sensor 20 is performed at the non-sheet passing portion of the endless film 15, the peripheral speed of the endless film 15 can be accurately determined without being affected by the contamination by toner or the like. 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 the present embodiment. In FIG.
5 is a photosensor for detecting the peripheral speed, and a masking process (shown by oblique lines in the figure) for shielding the light of the photosensor 21 is performed around the edge 24 on the front end 24 of the endless film 15. It is applied over. In this embodiment, the photo sensor 2
Although a photo-interrupter is used as 1, when a reflective photosensor is used, the endless film 1 is used.
It is necessary to perform a reflection member treatment for reflecting light on the end portion 24 of the fifth member 5. Further, in this embodiment, the masking process is performed only on one end 24 of the endless film 15, but it goes without saying that the masking process may be performed on the entire endless film 15. In FIG. 5, reference numeral 22 denotes a cleaning member which is for always cleaning the end of the endless film 15 to prevent erroneous reading of the photo sensor 21. It works effectively when is used. In this embodiment, a felt is used as the cleaning member 22, but any type 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, one end (front end) is obliquely cut, and the length of the longest portion is Lmax. and then, if the length of the shortest portion between Lmin, the dimensions of the part (oblique cut portion) which is obliquely cut (film oblique cutoff amount) [Delta] L is Lmax -Lmi
n. The oblique cut portion is arranged on the front side of the main fixing device 11 as shown in FIG. 5, and is configured to detect the peripheral speed of the endless film 15 by the photo sensor 21. FIG. 7 is a detailed diagram showing the positional relationship between the photo sensor 21 and the endless film 15. In this embodiment, a transmission type photo interrupter is used as the photo sensor 21, and the detection position is shown as d in FIG. When the endless film 15 is located on the back side of the detection position d, the photo sensor 21 is turned on. When the endless film 15 is located on the front side of the detection position d, the photo sensor 2 is turned on.
1 will be OFF. Thus, the oblique cut portion of the endless film 15 is configured to be located at the detection position d of the photo sensor 21. Therefore, the photosensor 21 repeats ON / OFF by rotating the endless film 15 in the direction of arrow c in FIG. 5, and the ON / OFF cycle changes according to the peripheral speed of the endless film 15. For this reason, the O
By reading the cycle of N / OFF, the peripheral speed of the endless film 15 is detected, and the peripheral speed of the endless film 15 is made equal to the peripheral speed of the photosensitive drum (not shown).
If the motor 13 for driving the pressure roller 14 is controlled by a microcomputer (not shown), the transfer speed of the transfer paper in the fixing device 11 can be always kept constant, and a stable image can be supplied. < Reference Example > Next, a reference example of the present invention will be described with reference to FIGS. FIG. 8 is a cross-sectional view of the fixing device 11 according to the present embodiment, in which 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
One side of a heat-resistant resin film of 0 μm is coated with a release layer such as PTFE. In addition, the total thickness of the endless film 15 is generally preferably 50 μm or less. In FIG. 8, reference numeral 29 denotes a rib provided on the outer periphery of one end (front side) of the endless film 15. The rib 29 may be formed integrally with the same material as the film 15 or may be slid later. A rib formed of another material having high mobility (for example, urethane rubber or silicon rubber) by bonding or the like may be used. 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 element 18. Then, the endless film 15 is biased by tensioning means 32, 33 to tension roller bearings 34, 35.
A predetermined tension is applied by urging the tension roller 31 in the direction indicated by arrow A through the arrow, and is conveyed in the direction indicated by arrow B by the drive roller 30. Here, the drive roller 30 is configured by providing a coating layer of silicon rubber or the like on the surface of a core metal such as iron in order to reliably transport the endless film 15. Reference numeral 14 denotes a pressure roller, which has a rubber elastic layer of silicon rubber or the like with good releasability, and presses the endless film 15 against the heating element 18 with a force required for fixing. Both ends of the pressure roller 14 are rotatably supported by bearings (not shown) so that the pressure roller 14 rotates 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. The stay 37 has a rigidity that can withstand the pressing force of the pressure roller 14. In FIG. 8, reference numeral 23 denotes an entrance guide,
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 (the center side of the film 15) along the outer periphery of the drive roller 30 as shown in the drawing. Is fixed to the fixing device frame. The endless film 15 is configured such that a biasing force is always exerted in the direction of arrow C during conveyance by adjusting the biasing force of the biasing means 32 and 33 or the like. Abuts on the regulating member 40 to regulate the shift of the film 15. still,
It is desirable that at least the surface of the regulating member 40 on which the rib 29 slides is made of a material such as polyacetal or fluororesin having good sliding properties. FIG. 10 is a perspective view showing the relationship between the endless film 15 and the microswitch 28. As shown, a plurality of projections 41 are provided on the rib 29 at regular intervals. It is installed so that it can be contacted. The endless film 15 shown in FIG.
When the micro switch 2 is driven to rotate in the direction of arrow f,
8 comes into contact with the projection 41 and is turned on. 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 microswitch 28, and the driving roller is driven 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 transfer 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 can be reduced and the cost can be reduced. be able to. As is apparent from the above description, according to the present invention, the peripheral speed detected by the peripheral speed detecting means is equal to the predetermined speed.
Of the driving means of the pressure roller so that it is maintained constant
The speed is controlled by the control means to change the diameter of the pressure roller.
The peripheral speed of the heat-resistant endless film is constant regardless of
Therefore, even if the outer diameter of the pressure roller that forms a nip between the heater and the heater changes, the transfer speed of the transfer material is always kept constant. Is prevented from being disturbed by the rubbing, and a stable image can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a fixing device according to a first 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 embodiment of the present invention. FIG. 4 is a side view of a fixing device according to a second embodiment of the present invention. FIG. 5 is a perspective view of a fixing device according to a third embodiment of the present invention. FIG. 6 is a perspective view of an endless film of a fixing device according to a third embodiment of the present invention. FIG. 7 is a detailed view illustrating a positional relationship between a photo sensor and an endless film of a fixing device according to a third embodiment of the present invention. FIG. 8 is a cross-sectional view of a fixing device according to a reference example of the invention. FIG. 9 is a view in the direction of arrow J in FIG. 8; FIG. 10 is a perspective view illustrating a relationship between an endless film and a micro switch of a fixing device according to a reference example of the invention. [Description of Signs] 11 Fixing device 14 Pressure roller 15 Endless film 16 Photo interrupter ( peripheral speed detecting means) 17 Hole 18 Heater ( heating element ) 19 White pattern 20 Reflective sensor ( peripheral speed detecting means) 21 Photo sensor ( peripheral ) Speed detecting means) 28 micro switch ( peripheral speed detecting means) 40 regulating member P transfer paper (transfer material)

Claims (1)

(57) [Claim 1] A heater having a heating element and a heat-resistant end
Pressed against the outer circumference of less film, a pressure roller having a rubber layer for forming a nip for nipping and conveying a transfer material having an unfixed toner image through the heater and heat-resistant endless film, driving causes rotating the pressure roller Means,
By rotating the pressure roller, it is driven
In a fixing device in which a thermal endless film rotates ,
A peripheral speed detecting means for detecting the peripheral speed of the heat-resistant endless film, a pressure roller drive means as a peripheral speed that is detected by the peripheral speed detecting means is kept constant at a predetermined speed
Yes, and the pressure roller and a control means for controlling the driving speed of
Regardless of the change in the diameter of the heat-resistant endless film.
A fixing device, wherein the fixing speed is controlled to be constant .