Fixing device having temperature detecting member and image forming apparatus using said fixing device

Information

  • Patent Grant
  • 6636709
  • Patent Number
    6,636,709
  • Date Filed
    Thursday, June 28, 2001
    23 years ago
  • Date Issued
    Tuesday, October 21, 2003
    21 years ago
Abstract
A fixing device for fixing a toner image on a recording medium includes a heating roller, a fixing roller, an endless fixing belt extended around at least the heating roller and the fixing roller and configured to be heated by the heating roller, a pressing roller disposed opposite to the fixing roller via the fixing belt, a temperature detecting member configured to detect a surface temperature of the heating roller, and a control device configured to control a surface temperature of the fixing belt at a predetermined temperature based on a surface temperature of the heating roller detected by the temperature detecting member. The temperature detecting member contacts a circumferential surface of the heating roller where the fixing belt is not extended around, such that the temperature detecting member is held in a low frictional relation to the circumferential surface of the heating roller.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates to a fixing device for use in an image forming apparatus such as a printer, a facsimile machine, a photocopier, etc., and more particularly to a temperature detecting structure for a heating mechanism in a fixing device.




2. Discussion of the Background




Generally, in an image forming apparatus such as a photocopier, a facsimile machine, a printer, etc, an unfixed toner image carried on a recording medium, for example a sheet, is fixed onto the recording medium by a fixing device. Then the recording medium having a fixed toner image thereon is discharged from the image forming apparatus as a copy sheet or a printed sheet.




A known fixing device employs a structure in which a pair of rollers are opposed to each other. One roller is a heating roller, and another roller is a pressing roller which press-contacts the heating roller. In this type of fixing device, a recording medium carrying an unfixed toner image is passed through a nip part between the heating roller and the pressing roller. While the recording medium passes through the nip part, a toner image on the recording medium is fused and fixed on the recording medium by heat and pressure.




Another type of fixing device employs a structure having a combination of rollers and a belt. In this structure, for example, a fixing belt is extended and stretched around a heating roller and a fixing roller. In addition, a pressing roller is arranged opposite to the fixing roller via the fixing belt.




The heating roller and the pressing roller include heat sources to heat back and front surfaces of the fixing belt, respectively.




Because the volume and the thermal capacity of the fixing belt are smaller than those of the roller, the temperature of the fixing belt can be increased in a short period of time. For this reason, the fixing belt has an advantage in that heating-up is quick upon start of the fixing device compared to the above-described structure of the fixing device having a heating roller and a pressing roller without a fixing belt. Further, the provision of the heat source in the pressing roller results in the acceleration of heating-up at both front and back surfaces of the fixing belt.




The above-described fixing belt has a two-layer structure. When each roller is made of aluminum having high thermal conductivity, the fixing belt includes a base member which contacts the surfaces of the rollers and is made of a conductive metallic member of high heat capacity such as stainless steel, etc. The fixing belt further includes a releasing layer made of silicone rubber or fluororesin on the surface of the base member.




In a background fixing device, the surface temperature of such a fixing belt is controlled to be at a predetermined value by detecting the surface temperature of the fixing belt with a temperature detecting member arranged in a non-contacting relation to the front surface of the fixing belt. Because the temperature detecting member is held in a non-contacting relation to the front surface of the fixing belt, the surface temperature of the fixing belt may not be detected with accuracy.




If the temperature detecting member is arranged in a contacting relation to the front surface of the fixing belt, the front surface of the fixing belt may be damaged by the temperature detecting member, thereby resulting in deterioration of image quality.




For the above-described reasons, as an alternative configuration, the temperature detecting member can be arranged in a contacting relation to the back surface of the fixing belt. However, the fixing belt is configured to be rotated during the rotations of the heating roller and the pressing roller, by frictional contact pressure between the fixing belt and the heating/pressing rollers. At the time of rotation start and stop of the heating/pressing rollers, the fixing belt may move by itself due to its inertia. Therefore, the contact surfaces of the fixing belt and the heating/pressing rollers, which have a smaller hardness than that of the other contact surfaces, may abrade due to frictional resistance. As a result, abrasion powder is typically produced between the contact surfaces of the fixing belt and the heating/pressing rollers.




When the temperature detecting member contacts the back surface of the fixing belt so as to detect the surface temperature of the fixing belt, the above-described abrasion powder may enter a space around the contact surface of a temperature detecting portion of the temperature detecting member and the fixing belt. Due to the entry of the abrasion powder, the temperature detecting portion typically abrades.




In addition, the abrasion of the temperature detecting portion is typically caused by friction between the temperature detecting portion and the fixing belt.




The abrasion of the temperature detecting portion may cause the contact condition of the temperature detecting member and the fixing belt to be unstable. As a result, the temperature detecting member cannot detect the surface temperature of the fixing belt with accuracy, so that the surface temperature of the fixing belt may not be controlled properly. Moreover, when the surface temperature of the fixing belt is not controlled with accuracy, heat is not adequately supplied to an unfixed toner image carried on a recording medium. This results in deterioration of image quality.




SUMMARY OF THE INVENTION




According to one aspect of the present invention, a fixing device for fixing a toner image on a recording medium includes a heating roller including a heat source, a fixing roller, an endless fixing belt extended around at least the heating roller and the fixing roller and configured to be heated by the heating roller to fuse a toner image on the recording medium, a pressing roller disposed opposite to the fixing roller via the fixing belt and configured to press the recording medium against the fixing roller, a temperature detecting member configured to detect a surface temperature of the heating roller, and a control device configured to control a surface temperature of the fixing belt at a predetermined temperature based on a surface temperature of the heating roller detected by the temperature detecting member. The temperature detecting member contacts a circumferential surface of the heating roller where the fixing belt is not extended around, such that the temperature detecting member is held in a low frictional relation to the circumferential surface of the heating roller.




According to another aspect of the present invention, a diameter of a circumferential surface of the heating roller where the temperature detecting member contacts is smaller than a diameter of the other circumferential surface of the heating roller.











BRIEF DESCRIPTION OF THE DRAWINGS




A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:





FIG. 1

is a schematic view of an image forming apparatus including a fixing device according to an embodiment of the present invention;





FIG. 2A

is a schematic view of the fixing device of

FIG. 1

, and





FIG. 2B

is an enlarged view of a part of a fixing belt of

FIG. 2A

;





FIG. 3

is a perspective view of a heating roller and a temperature detecting member of the present invention;





FIG. 4

is a perspective view of a heating roller having a low coefficient of friction member, and the temperature detecting member according to another example of the present invention;





FIG. 5

is a sectional view of the fixing belt and the heating roller of the present invention; and





FIG. 6

is a sectional view of the fixing belt and the heating roller according to another example of the present invention.











DESCRIPTION OF THE PREFERRED EMBODIMENTS




Preferred embodiments of the present invention are described in detail referring to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views.





FIG. 1

is a schematic view of an image forming apparatus including a fixing device according to an embodiment of the present invention. The image forming apparatus


20


illustrated in

FIG. 1

is a full color copier or printer. In addition, the image forming apparatus


20


may be a facsimile machine which forms an image in accordance with received image signals by an image forming process similar to that of a copier or printer. The image forming apparatus


20


of

FIG. 1

is not limited to a full color image forming apparatus, but may instead be a single color image forming apparatus.




In the image forming apparatus


20


, color toner images by separated colors are consecutively transferred and superimposed onto an intermediate transfer member. Upon completion of formation of the superimposed color toner images of a multi-color original image on the intermediate transfer member, the superimposed color toner images are transferred from the intermediate transfer member to a sheet-like recording medium (hereinafter simply referred to as a recording medium).




Referring to

FIG. 1

, the image forming apparatus


20


includes image forming units


21


C,


21


Y,


21


M, and


21


Bk which form respective color toner images of a multi-color original image, and a transfer device


22


arranged opposite to the image forming units


21


C,


21


Y,


21


M, and


21


Bk.




The image forming apparatus


20


further includes a manual sheet tray


23


and sheet feeding cassettes


24


serving as a recording medium feeding device which feeds various kinds of recording media to a transfer station between the respective image forming units


21


C,


21


Y,


21


M, and


21


Bk and the transfer device


22


.




The image forming apparatus


20


further includes a pair of registration rollers


30


which rotate to feed the recording medium fed from the manual sheet tray


23


or the sheet feeding cassettes


24


to the transfer station at a time of image forming by the image forming units


21


C,


21


Y,


21


M, and


21


Bk.




In addition, the image forming apparatus


20


further includes a fixing device


1


which fixes the transferred color toner image onto the recording medium.




The image forming apparatus


20


uses a sheet-like recording medium such as a plain paper generally used in a copier, or a special sheet having larger thermal capacity than that of the plain paper such as an overhead transparency film sheet, a card, a postcard, a thick paper having a basis weight of about 100 g/m2 or greater or an envelope.




The image forming units


21


C,


21


Y,


21


M, and


21


Bk form cyan, yellow, magenta, and black toner images, respectively, and their configurations are substantially the same except for the color of their toner. For this reason, the configuration of the image forming unit


21


C will be described hereinafter as being representative.




The image forming unit


21


C includes a drum-shaped photoreceptor


25


C serving as an electrostatic latent image bearing member. Arranged around the photoreceptor


25


C are a charging device


27


C, a developing device


26


C and a cleaning device


28


C, in the order of the rotational direction of the photoreceptor


25


C. The surface of the photoreceptor


25


C is exposed to a light


29


C between the charging device


27


C and the developing device


26


C. As an alternative electrostatic latent image bearing member, a belt-shaped photoreceptor may be employed instead of the drum-shaped photoreceptor


25


C. Respective color toner images are formed by a known electrophotographic image forming process, and the description of the electrophotographic image forming process is omitted here.




Referring now to

FIG. 2A

, the configuration of the fixing device


1


of

FIG. 1

will be described. The fixing device


1


includes an endless fixing belt


2


(fusing means) for fusing a toner image carried on a recording medium, a heating roller


3


(heating means) and a fixing roller


4


(fixing means) around which the fixing belt


2


is extended and stretched. The fixing belt


2


is driven by the rotations of the heating roller


3


and the fixing roller


4


. The heating roller


3


includes a heater


6


to heat the fixing belt


2


.




The fixing device


1


further includes a pressing roller


5


(pressing means) arranged opposite to the fixing roller


4


via the fixing belt


2


to press a recording medium against the fixing roller, a heater


7


provided inside the pressing roller


5


, a temperature detecting member


8


(temperature detecting means) such as a thermistor which detects the surface temperature of the heating roller


3


, and a control device


15


(control means) which controls a surface temperature of the fixing belt


2


at a predetermined temperature based on a surface temperature of the heating roller


3


detected by the temperature detecting member


8


. The configuration of the temperature detecting member


8


will be described later.




Although the fixing belt


2


is extended around the heating roller


3


and the fixing roller


4


in this embodiment, the fixing belt


2


may be extended around three rollers or more.




In order to give a predetermined suitable tension on the fixing belt


2


, the heating roller


3


is biased in a direction away from the fixing roller


4


, indicated by arrow P


1


, by a resilient member (not shown) such as a spring.




The fixing roller


4


includes a core


9


, a heat-resistant and porous elastic layer


10


which covers the core


9


and an end shaft


11


. The end shaft


11


is driven to rotate by a driving device (not shown), thereby driving the core


9


to rotate. The heating roller


3


is driven to rotate by the fixing roller


4


, thereby driving the fixing belt


2


.




The pressing roller


5


is biased in a direction of press-contacting the fixing roller


4


, indicated by arrow P


2


, by a resilient member (not shown) such as a spring. The pressing roller


5


is press-contacted to the fixing roller


4


such that an angle formed between a line connecting the shaft centers of the fixing roller


4


and the heating roller


3


and a line connecting the shaft centers of the heating roller


4


and the pressing roller


5


is an acute angle.




With these arrangements of the heating roller


3


, the fixing roller


4


, and the pressing roller


5


, as illustrated in

FIG. 2A

, two fixing areas A and B are formed in a fixing station where a toner image is fixed on a recording medium. In the first fixing area A, the pressing roller


5


does not contact the fixing roller


4


but contacts the fixing belt


2


. In the second fixing area B, the pressing roller


5


press-contacts the fixing roller


4


via the fixing belt


2


.




The reference numeral


12


in

FIG. 2A

designates a guide plate which directs a recording medium to the first fixing area A.




As illustrated in

FIG. 2B

, the fixing belt


2


includes a base member


13


of about 50 μm through 100 μm in thickness made of a metallic member such as nickel and stainless steel, and a releasing layer


14


of about 200 μm in thickness made of an elastic member such as silicone rubber and layered on the base member


13


. With this structure, the fixing belt


2


has low thermal capacity and a suitable thermoresponse.




As an alternative to the above-described metallic member, the base member


13


may be made of resin such as polyimide. In this case, the thickness of the base member


13


may be in a range of about 30 μm to 150 μm in consideration of its flexibility.




When silicone rubber is employed for the releasing layer


14


, the thickness of the releasing layer


14


is preferably in a range of about 50 μm to 300 μm. When fluororesin is employed for the releasing layer


14


, the thickness of the releasing layer


14


is preferably in a range of about 10 μm to 50 μm.




The surface roughness (Rmax) of the contact surface of the fixing belt


2


with the heating roller


3


is set to about 6 μm. Rmax is a maximum height from a reference surface, which is prescribed in JIS (Japanese Industrial Standards). In this condition, the contact surface of the fixing belt


2


with the heating roller


3


is almost uniform.




The releasing layer


14


may have an alternative structure in which fluororesin is layered on silicone rubber. The fixing belt


2


is required to have a property such that the fixing belt


2


is quickly heated up and the surface of the fixing belt


2


is self-cooled in the fixing station without causing a hot offset condition in which a part of a fused toner image adheres to the fixing belt


2


.




On the other hand, the fixing belt


2


is required to have a thermal capacity necessary for fusing and fixing a toner image on a recording medium in the fixing station. The above-described material and thickness of the fixing belt


2


meet such required conditions.




By biasing the heating roller


3


in the direction indicated by arrow P


1


, a tension of about 6 kgf acts on the fixing belt


2


. The tension on the fixing belt


2


is adjustable by changing the biasing force in the direction indicated by arrow P


1


. The tension on the fixing belt


2


may be preferably set in a range of about 2 kgf (19.6 N) to 6 kgf (58.8 N) for a proper toner image fixing process.




The heating roller


3


and the pressing roller


5


respectively include hollow cylindrical core metals, aimed at providing a low thermal capacity.




The diameter of the core metal of the heating roller


3


preferably ranges from about 20 mm to 30 mm, and the thickness of the core metal thereof preferably ranges from about 0.3 mm to 2.0 mm. Further, the surface roughness (Rmax) of the heating roller


3


is set to be smaller than 100 μm for smooth contact with the fixing belt


2


.




The diameter of the core metal of the pressing roller


5


preferably ranges from about 30 mm to 50 mm, and the thickness of the core metal thereof preferably ranges from about 0.3 mm to 1.5 mm.




The thermal capacity of the heating roller


3


is set to 26 cal/° C. or less, and the thermal capacity of the pressing roller


5


is set to 36 cal/° C. or less.




Specifically, in this embodiment, the core metal of the heating roller


3


is made of iron, and has a diameter of 20 mm and a thickness of 0.7 mm. The material of the core metal preferably has low specific heat and high thermal conductivity. As alternatives to iron, metals such as aluminum, copper, stainless, etc. may be employed.




For example, when the diameter of an iron core metal of the heating roller


3


is 20 mm, the thickness of the core metal may be set in a range of about 0.7 mm to 1.4 mm. When the diameter of an iron-made core metal of the heating roller


3


is 30 mm, the thickness of the core metal may be set in a range of about 0.3 mm to 0.9 mm. Further, when the diameter of an aluminum core metal of the heating roller


3


is 30 mm, the thickness of the core metal may be set in a range of about 0.6 mm to 1.4 mm. The reason why the thickness of the core metal is made smaller as the diameter thereof is increased is that the distortion of the heating roller


3


in the axial direction thereof is obviated.




As illustrated in

FIG. 2A

, a temperature detecting member


8


is provided at the left side of the heating roller


3


. Specifically, the temperature detecting member


8


is provided such that it opposes the circumferential surface of the heating roller


3


where the fixing belt


2


is not extended around in the circumferential direction of the heating roller


3


. Further, the temperature detecting member


8


press-contacts the circumferential surface of the heating member


3


in the vicinity of a position where the fixing belt


2


starts to be extended around the heating roller


3


in a rotational direction of the heating roller


3


, indicated by arrow C.




In the fixing device


1


, the surface temperature of the fixing belt


2


is controlled to be at a predetermined temperature by detecting the surface temperature of the heating roller


3


with the temperature detecting member


8


. Specifically, the control device


15


controls the heat of the heater


6


of the heating roller


3


based on the surface temperature of the heating roller


3


detected by the temperature detecting member


8


, thereby controlling the surface temperature of the fixing belt


2


to be a predetermined temperature.




As illustrated in

FIG. 2A

, the temperature detecting member


8


includes a temperature detecting portion


8


A, a low frictional resistance member


8


B and a cantilever swing arm


8


C. The temperature detecting portion


8


A is provided at one end of the swing arm


8


C at a location to detect the surface temperature of the heating roller


3


. The swing arm


8


C extends in a direction almost parallel to the tangential direction of the circumferential surface of the heating roller


3


.




As illustrated in

FIG. 2A

, the temperature detecting portion


8


A is positioned above the horizontal rotation centerline of the heating roller


3


. With this arrangement of the temperature detecting portion


8


A, the temperature detecting member


8


can be provided within a space between the upper and lower runs of the horizontally extended fixing belt


2


.




Further, because the temperature detecting portion


8


A is provided at one end of the tangentially extending swing arm


8


C positioned above the rotation center of the heating roller


3


, the pressing force of the temperature detecting member


8


against the heating roller


3


can be made relatively small as compared to the pressing force of a temperature detecting portion


8


A which press-contacts the circumferential surface of the heating roller


3


on the horizontal rotation center line. This is because, even though the pressing force of the temperature detecting member


8


against the heating roller


3


is made relatively small, the contact pressure between the temperature detecting member


8


and the heating roller


3


is adequately maintained without causing a temperature detecting error, owing to the turning moment of the swing arm


8


C. Because the pressing force of the temperature detecting member


8


against the heating roller


3


is relatively small, the contact resistance at the contact position of the temperature detecting portion


8


A and the heating roller


3


can be reduced. In this embodiment, the pressing force of the temperature detecting member


8


against the heating roller


3


is set to 0.2 N. On the other hand, if the temperature detecting portion


8


A were to press-contact the circumferential surface of the heating roller


3


on the horizontal rotation centerline, the swing arm


8


C would be bent to a large extent. Consequently, a large moment would be produced in the swing arm


8


C, thereby causing the pressing force of the temperature detecting member


8


against the heating roller


3


to be relatively large.




The temperature detecting member


8


is configured to be held in a low frictional relation to the circumferential surface of the heating roller


3


. As illustrated in

FIGS. 3 and 4

, the temperature detecting portion


8


A contacts the surface of the heating roller


3


via the low frictional resistance member


8


B in order to reduce the friction between the temperature detecting portion


8


A and the heating roller


3


.




In this embodiment, the low frictional resistance member


8


B is made of heat resistant fluororesin tape having a thickness which does not affect thermoresponse, or made of a fluororesin tape such as a Teflon (trademark) tape. The Teflon is also used to coat the surface of the temperature detecting portion


8


A. Alternatively, a film made of polyimide resin may be employed as the low frictional resistance member


8


B.




As another configuration which can reduce the contact resistance of the temperature detecting portion


8


A against the circumferential surface of the heating roller


3


, it may be possible to polish an area of the circumferential surface of the heating roller


3


where the temperature detecting portion


8


A press-contacts.




Specifically, as illustrated in

FIG. 3

, the area of the circumferential surface of the heating roller


3


indicated by a double-headed arrow L is polished by brushing using a buffer or the like. In this case, the circumferential surface of the heating roller


3


is smoothly finished by polishing such that the surface roughness (Rmax) thereof is about 100 μm or less, more preferably to about 30 μm or less.




Moreover, in order to reduce the friction between the heating roller


3


and the temperature detecting portion


8


A, in addition to the low frictional resistance member


8


B of the temperature detecting member


8


, a low coefficient of friction member


8


D may be provided on an area of the circumferential surface of the heating roller


3


where the temperature detecting portion


8


A press-contacts.




Specifically, as illustrated in

FIG. 4

, the low coefficient of friction member


8


D is provided on the area of the circumferential surface of the heating roller


3


indicated by double-headed arrow L. The low coefficient of friction member


8


D may be made of fluororesin such as Teflon, polyimide, etc.




As described above, the temperature detecting member


8


is held in a low frictional relation to the circumferential surface of the heating roller


3


employing the low frictional resistance member


8


B. Therefore, the abrasion of the temperature detecting portion


8


A is suppressed and the durability of the temperature detecting portion


8


A is increased.




In addition, contact resistance of the temperature detecting portion


8


A against the circumferential surface of the heating roller


3


is not likely to be produced because the surface of the heating roller


3


which the temperature detecting portion


8


A contacts is smoothly finished by polishing or is provided with the low coefficient of friction member


8


D.




With this configuration, the abrasion of the temperature detecting portion


8


A is suppressed, thereby extending the useful life of the temperature detecting portion


8


A, and detecting the surface temperature of the heating roller


3


with accuracy. As a result, the temperature of the fixing belt


2


is adequately controlled, so that the deterioration of the image is prevented.




The surface temperature of the heating roller


3


is detected by the temperature detecting member


8


, not only in the fixing operation but also during the starting of the image forming apparatus


20


. At the start of the image forming apparatus


20


, the heating roller


3


is heated up, with the fixing belt


2


stopped. With the above-described configuration of the fixing device


1


, because the temperature of the fixing belt


2


is controlled by way of detecting the surface temperature of the heating roller


3


with the temperature detecting member


8


, the rising temperature of the fixing belt


2


at the start of the image forming apparatus


20


is also controlled adequately.




Next, a description will be made as to how the abrasion powder produced due to the contact of the fixing belt


2


and the heating roller


3


is prevented from entering the contact position of the temperature detecting portion


8


A of the temperature detecting member


8


and the heating roller


3


.





FIG. 5

is a sectional view of the fixing belt


2


and the heating roller


3


, seen from the left in FIG.


2


A. Referring to

FIG. 5

, the temperature detecting portion


8


A is press-contacted onto the heating roller


3


at substantially a center portion thereof in the axial direction.




Further, the diameter of the circumferential surface of the heating roller


3


where the temperature detecting portion


8


A contacts, and its vicinity, is made smaller than that of the remainder of the circumferential surface of the heating roller


3


. In

FIG. 5

, a small diameter portion of the heating roller


3


is indicated by a reference character


3


A. With this configuration, a space is formed between the circumferential surface of the small diameter portion


3


A of the heating roller


3


and the back surface of the fixing belt


2


.




Because the fixing belt


2


does not contact the circumferential surface of the heating roller


3


at the small diameter portion


3


A, abrasion powder is not produced therebetween. As a result, the abrasion of the temperature detecting portion


8


A due to the abrasion powder is obviated.




Referring further to

FIG. 6

, in addition to the small diameter portion


3


A of

FIG. 5

, grooves


3


B may be provided at both end portions of the small diameter portion


3


A in the axial direction of the heating roller


3


, that is, in the vicinity of the circumferential surface of the heating roller


3


where the temperature detecting portion


8


A does not press-contact in the axial direction thereof. With this configuration, even if the abrasion powder produced at the contact position of the fixing belt


2


and the heating roller


3


enters the small diameter portion


3


A, the grooves


3


B serve to block the abrasion powder from moving to the contact position of the temperature detecting portion


8


A and the circumferential surface of the heating roller


3


. Because the abrasion of the temperature detecting portion


8


A due to the abrasion powder is prevented, the useful life of the temperature detecting member


8


is extended and the surface temperature of the heating roller


3


is detected with accuracy.




Numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.




This document claims priority and contains subject matter related to Japanese Patent Application No. 2000-199044 filed in the Japanese Patent Office on Jun. 30, 2000, and Japanese Patent Application No. 2001-173573 filed in the Japanese Patent Office on Jun. 8, 2001, the entire contents of which are hereby incorporated by reference.



Claims
  • 1. A fixing device for fixing a toner image on a recording medium, comprising:a heating roller; a fixing roller; an endless fixing belt extended around at least the heating roller and the fixing roller and configured to be heated by the heating roller to fuse a toner image on a recording medium; a pressing roller disposed opposite to the fixing roller via the fixing belt and configured to press the recording medium against the fixing roller; a temperature detecting member configured to detect a surface temperature of the heating roller; and a control device configured to control a surface temperature of the fixing belt to be a predetermined temperature based on a surface temperature of the heating roller detected by the temperature detecting member at least during a fixing operation, wherein the temperature detecting member contacts a circumferential surface of the heating roller where the fixing belt is not extended around, such that the temperature detecting member is held in a low frictional relation to the circumferential surface of the heating roller, and the circumferential surface of the heating roller which the temperature detecting member contacts includes a polished surface.
  • 2. The fixing device according to claim 1, wherein the temperature detecting member contacts the circumferential surface of the heating roller via a low frictional resistance member.
  • 3. The fixing device according to claim 2, wherein the low frictional resistance member is made of polyimide resin film.
  • 4. The fixing device according to claim 1, wherein the temperature detecting member includes a cantilever swing arm which extends in a direction almost parallel to the tangent direction of the circumferential surface of the heating roller, and a temperature detecting portion provided at one end of the swing arm to detect the surface temperature of the heating roller, and wherein the temperature detecting portion is press-contacted with the circumferential surface of the heating roller by a turning moment of the swing arm.
  • 5. The fixing device according to claim 4, wherein a pressing force of the temperature detecting member against the heating roller is set to 0.2 N.
  • 6. The fixing device according to claim 1, wherein a surface roughness (Rmax) of the circumferential surface of the heating roller which the temperature detecting member contacts is 100 μm or less.
  • 7. The fixing device according to claim 1, wherein a low coefficient of friction member is provided on the circumferential surface of the heating roller which the temperature detecting member contacts.
  • 8. The fixing device according to claim 7, wherein the low coefficient of friction member is made of fluororesin.
  • 9. A fixing device for fixing a toner image on a recording medium, comprising:a heating roller; a fixing roller; an endless fixing belt extended around at least the heating roller and the fixing roller and configured to be heated by the heating roller to fuse a toner image on a recording medium; a pressing roller disposed opposite to the fixing roller via the fixing belt and configured to press the recording medium against the fixing roller; a temperature detecting member configured to detect a surface temperature of the heating roller; and a control device configured to control a surface temperature of the fixing belt to be a predetermined temperature based on a surface temperature of the heating roller detected by the temperature detecting member, wherein the temperature detecting member contacts a circumferential surface of the heating roller via a low frictional resistance member, and wherein the circumferential surface of the heating roller which the temperature detecting member contacts is a polished surface.
  • 10. A fixing device for fixing a toner image on a recording medium, comprising:a heating roller having a low coefficient of friction member provided on a circumferential surface of the heating roller; a fixing roller; an endless fixing belt extended around at least the heating roller and the fixing roller and configured to be heated by the heating roller to fuse a toner image on a recording medium; a pressing roller disposed opposite to the fixing roller via the fixing belt and configured to press the recording medium against the fixing roller; a temperature detecting member configured to detect a surface temperature of the heating roller and including a low frictional resistance member configured to contact the low coefficient of friction member of the heating roller; and a control device configured to control a surface temperature of the fixing belt to be a predetermined temperature based on a surface temperature of the heating roller detected by the temperature detecting member at least during a fixing operation.
  • 11. A fixing device for fixing a toner image on a recording medium, comprising:a heating roller; a fixing roller; an endless fixing belt extended around at least the heating roller and the fixing roller and configured to be heated by the heating roller to fuse a toner image on a recording medium; a pressing roller disposed opposite to the fixing roller via the fixing belt and configured to press the recording medium against the fixing roller; a temperature detecting member configured to detect a surface temperature of the heating roller; and a control device configured to control a surface temperature of the fixing belt to be a predetermined temperature based on a surface temperature of the heating roller detected by the temperature detecting member, wherein a diameter of a circumferential surface of the heating roller at a small diameter portion of the heating roller where the temperature detecting member contacts is smaller than a diameter of a remainder of the circumferential surface of the heating roller.
  • 12. The fixing device according to claim 11, wherein grooves are provided at both end portions of the small diameter portion of the heating roller in an axial direction thereof.
  • 13. An image forming apparatus comprising:a fixing device for fixing a toner image on a recording medium including, a heating roller; a fixing roller; an endless fixing belt extended around at least the heating roller and the fixing roller and configured to be heated by the heating roller to fuse a toner image on a recording medium; a pressing roller disposed opposite to the fixing roller via the fixing belt and configured to press the recording medium against the fixing roller; a temperature detecting member configured to detect a surface temperature of the heating roller; and a control device configured to control a surface temperature of the fixing belt to be a predetermined temperature based on a surface temperature of the heating roller detected by the temperature detecting member at least during a fixing operation, wherein the temperature detecting member contacts a circumferential surface of the heating roller where the fixing belt is not extended around, such that the temperature detecting member is held in a low frictional relation to the circumferential surface of the heating roller, and the circumferential surface of the heating roller which the temperature detecting member contacts includes a polished surface.
  • 14. The image forming apparatus according to claim 13, wherein the temperature detecting member contacts the circumferential surface of the heating roller via a low frictional resistance member.
  • 15. The image forming apparatus according to claim 14, wherein the low frictional resistance member is made of polyimide resin film.
  • 16. The image forming apparatus according to claim 13, wherein the temperature detecting member includes a cantilever swing arm which extends in a direction almost parallel to the tangent direction of the circumferential surface of the heating roller, and a temperature detecting portion provided at one end of the swing arm to detect the surface temperature of the heating roller, and wherein the temperature detecting portion is press-contacted with the circumferential surface of the heating roller by a turning moment of the swing arm.
  • 17. The image forming apparatus according to claim 16, wherein a pressing force of the temperature detecting member against the heating roller is set to 0.2 N.
  • 18. The image forming apparatus according to claim 13, wherein a surface roughness (Rmax) of the circumferential surface of the heating roller which the temperature detecting member contacts is 100 μm or less.
  • 19. The image forming apparatus according to claim 13, wherein a low coefficient of friction member is provided on the circumferential surface of the heating roller which the temperature detecting member contacts.
  • 20. The image forming apparatus according to claim 19, wherein the low coefficient of friction member is made of fluororesin.
  • 21. The image forming apparatus according to claim 13, wherein the control device is configured to cause the temperature detecting member to detect the surface temperature of the heating roller with the fixing belt stopped for a predetermined time, at a start of the fixing device.
  • 22. An image forming apparatus comprising:a fixing device for fixing a toner image on a recording medium including, a heating roller; a fixing roller; an endless fixing belt extended around at least the heating roller and the fixing roller and configured to be heated by the heating roller to fuse a toner image on a recording medium; a pressing roller disposed opposite to the fixing roller via the fixing belt and configured to press the recording medium against the fixing roller; a temperature detecting member configured to detect a surface temperature of the heating roller; and a control device configured to control a surface temperature of the fixing belt to be a predetermined temperature based on a surface temperature of the heating roller detected by the temperature detecting member, wherein the temperature detecting member contacts a circumferential surface of the heating roller via a low frictional resistance member, and wherein the circumferential surface of the heating roller which the temperature detecting member contacts is a polished surface.
  • 23. An image forming apparatus comprising:a fixing device for fixing a toner image on a recording medium including, a heating roller having a low coefficient of friction member provided on a circumferential surface of the heating roller; a fixing roller; an endless fixing belt extended around at least the heating roller and the fixing roller and configured to be heated by the heating roller to fuse a toner image on a recording medium; a pressing roller disposed opposite to the fixing roller via the fixing belt and configured to press the recording medium against the fixing roller; a temperature detecting member configured to detect a surface temperature of the heating roller and including a low frictional resistance member configured to contact the low coefficient of friction member of the heating roller; and a control device configured to control a surface temperature of the fixing belt to be a predetermined temperature based on a surface temperature of the heating roller detected by the temperature detecting member at least during a fixing operation.
  • 24. An image forming apparatus comprising:a fixing device for fixing a toner image on a recording medium including, a heating roller; a fixing roller; an endless fixing belt extended around at least the heating roller and the fixing roller and configured to be heated by the heating roller to fuse a toner image on a recording medium; a pressing roller disposed opposite to the fixing roller via the fixing belt and configured to press the recording medium against the fixing roller; a temperature detecting member configured to detect a surface temperature of the heating roller; and a control device configured to control a surface temperature of the fixing belt to be a predetermined temperature based on a surface temperature of the heating roller detected by the temperature detecting member, wherein a diameter of a circumferential surface of the heating roller at a small diameter portion of the heating roller where the temperature detecting member contacts is smaller than a diameter of a remainder of the circumferential surface of the heating roller.
  • 25. The image forming apparatus according to claim 24, wherein grooves are provided at both end portions of the small diameter portion of the heating roller in an axial direction thereof.
  • 26. The image forming apparatus according to claim 24, wherein the control device is configured to cause the temperature detecting member to detect the surface temperature of the heating roller with the fixing belt stopped for a predetermined time, at a start of the fixing device.
  • 27. A fixing device for fixing a toner image on a recording medium, comprising:fusing means for fusing a toner image on a recording medium; heating means for heating the fusing means; and fixing means for fixing a toner image on a recording medium, wherein the fusing means is extended around at least the heating means and the fixing means, the fixing device further comprising, pressing means for pressing the recording medium against the fixing means, the pressing means being disposed opposite to the fixing means via the fusing means; temperature detecting means for detecting a surface temperature of the heating means; and control means for controlling a surface temperature of the fusing means at a predetermined temperature based on a surface temperature of the heating means detected by the detecting means at least during a fixing operation, wherein the detecting means contacts a circumferential surface of the heating means where the fusing means is not extended around such that the detecting means is held in a low frictional relation to the circumferential surface of the heating means, and the circumferential surface of the heating means which the temperature detecting means contacts includes a polished surface.
  • 28. A fixing device for fixing a toner image on a recording medium, comprising:fusing means for fusing a toner image on a recording medium; heating means for heating the fusing means; and fixing means for fixing a toner image on a recording medium, wherein the fusing means is extended around at least the heating means and the fixing means, the fixing device further comprising, pressing means for pressing the recording medium against the fixing means, the pressing means being disposed opposite to the fixing means via the fusing means; temperature detecting means for detecting a surface temperature of the heating means; and control means for controlling a surface temperature of the fusing means to be a predetermined temperature based on a surface temperature of the heating means detected by the detecting means, wherein the detecting means contacts a circumferential surface of the heating means via a low frictional resistance member, and wherein the circumferential surface of the heating means which the detecting means contacts is a polished surface.
  • 29. A fixing device for fixing a toner image on a recording medium, comprising:fusing means for fusing a toner image on a recording medium; heating means for heating the fusing means, the heating means having a low coefficient of friction member; and fixing means for fixing a toner image on a recording medium, wherein the fusing means is extended around at least the heating means and the fixing means, the fixing device further comprising, pressing means for pressing the recording medium against the fixing means, the pressing means being disposed opposite to the fixing means via the fusing means; temperature detecting means for detecting a surface temperature of the heating means and including a low frictional resistance member configured to contact the low coefficient of friction member of the heating means; and control means for controlling a surface temperature of the fusing means to be a predetermined temperature based on a surface temperature of the heating means detected by the detecting means at least during a fixing operation[, wherein the detecting means contacts a circumferential surface of the heating means via a low frictional resistance member, and wherein a low coefficient of friction member is provided on the circumferential surface of the heating means which the detecting means contacts.
  • 30. A fixing device for fixing a toner image on a recording medium, comprising:fusing means for fusing a toner image on a recording medium; heating means for heating the fusing means; and fixing means for fixing a toner image on a recording medium, wherein the fusing means is extended around at least the heating means and the fixing means, the fixing device further comprising, pressing means for pressing the recording medium against the fixing means, the pressing means being disposed opposite to the fixing means via the fusing means; temperature detecting means for detecting a surface temperature of the heating means; and control means for controlling a surface temperature of the fusing means to be a predetermined temperature based on a surface temperature of the heating means detected by the detecting means, wherein a diameter of a circumferential surface of the heating means where the detecting means contacts is smaller than a diameter of a remainder of the circumferential surface of the heating means.
  • 31. A method of making a fixing device for fixing a toner image on a recording medium, comprising the steps of:providing a heating roller; providing a fixing roller; extending an endless fixing belt around at least the heating roller and the fixing roller so as to be heated by the heating roller to fuse a toner image on a recording medium; providing a pressing roller opposite to the fixing roller via the fixing belt to press the recording medium against the fixing roller; positioning a temperature detecting member in contact with a circumferential surface of the heating roller where the fixing belt is not extended around to detect a surface temperature of the heating roller; providing a control device to control a surface temperature of the fixing belt to be a predetermined temperature based on a surface temperature of the heating roller detected by the temperature detecting member at least during a fixing operation; and holding the temperature detecting member in a low frictional relation to the circumferential surface of the heating roller, wherein the step of holding the temperature detecting member includes polishing the circumferential surface of the heating roller which the temperature detecting member contacts.
  • 32. The method according to claim 31, wherein the step of holding the temperature detecting member includes contacting the temperature detecting member with the circumferential surface of the heating roller via a low frictional resistance member.
  • 33. The method according to claim 31, wherein the step of holding the temperature detecting member includes providing a low friction coefficient member on the circumferential surface of the heating roller which the temperature detecting member contacts.
  • 34. A method of making a fixing device for fixing a toner image on a recording medium, comprising the steps of:providing a heating roller; providing a fixing roller; extending an endless fixing belt around at least the heating roller and the fixing roller so as to be heated by the heating roller to fuse a toner image on a recording medium; providing a pressing roller opposite to the fixing roller via the fixing belt to press the recording medium against the fixing roller; positioning a temperature detecting member in contact with a circumferential surface of the heating roller where the fixing belt is not extended around to detect a surface temperature of the heating roller; providing a control device to control a surface temperature of the fixing belt to be a predetermined temperature based on a surface temperature of the heating roller detected by the temperature detecting member; and making a diameter of a circumferential surface of a small diameter portion of the heating roller where the temperature detecting member contacts smaller than a diameter of a remainder of the circumferential surface of the heating roller.
  • 35. The method according to claim 34 further comprising the step of providing grooves at both end portions of the small diameter portion of the heating roller in an axial direction thereof.
  • 36. A fixing device for fixing a toner image on a recording medium, comprising:a heating roller having a circumferential surface having a low friction part and a high friction part; a fixing roller; an endless fixing belt extended around at least the heating roller and the fixing roller and configured to be heated by the heating roller to fuse a toner image on a recording medium; a pressing roller disposed opposite to the fixing roller via the fixing belt and configured to press the recording medium against the fixing roller; a temperature detecting member configured to detect a surface temperature of the heating roller; and a control device configured to control a surface temperature of the fixing belt to be a predetermined temperature based on a surface temperature of the heating roller detected by the temperature detecting member at least during a fixing operation, wherein the temperature detecting member contacts the low friction part of the circumferential surface of the heating roller where the fixing belt is not extended around, such that the temperature detecting member is held in a low frictional relation to the circumferential surface of the heating roller, and the circumferential surface of the heating roller which the temperature detecting member contacts includes a polished surface.
Priority Claims (2)
Number Date Country Kind
2000-199044 Jun 2000 JP
2001-173573 Jun 2001 JP
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