Fixing device having flexible fusing member

A fixing device includes a tubular flexible fusing member, a heater, a nip member, a backup member, and a restricting member. The fusing member is rotatable about a rotational axis defining an axial direction and has an inner peripheral surface defining an internal space. The heater is disposed in the internal space. The nip member is disposed in the internal space for receiving radiant heat from the heater. The nip member is in sliding contact with the inner peripheral surface. The backup member nips the fusing member in cooperation with the nip member. The restricting member restricts displacement of the fusing member in the axial direction and is tiltable about a fulcrum portion.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2010-287935 filed Dec. 24, 2010. The entire content of this priority application is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a fixing device mounted in an electrophotographic type image forming device.

BACKGROUND

A conventional fixing device includes a cylindrical fusing film, a heater provided in an internal space of the fusing film, a pressure roller disposed opposite to the heater with respect to the fusing film, and a circular flange member for restricting a displacement of the fusing film in an axial direction thereof. A sheet carrying a toner image is passed through a nip portion defined between the circular film and the pressure roller, so that the toner image can be thermally fixed onto the sheet.

The circular flange member has a regulation portion to which an axial end portion of the fusing film is abutted for regulating axial displacement of the film. The circular flange member also has a guide portion integral with the regulation portion and in sliding contact with an inner peripheral surface of the film for guiding rotation of the film. The regulation portion extends in a direction perpendicular to a rotation axis of the cylindrical film. Such conventional fixing device is disclosed in Japanese Patent Application Publication No. 2009-237089.

SUMMARY

The present inventors have found drawbacks in such a conventional fixing device, such that only a portion of the axial end portion of the circular film is brought into abutment with the regulation portion, if the axial end of the film is not orthogonal to the rotational axis of the film due to production error or assembling error or unwanted displacement of the film in association with the rotation of the film. The axially displacing force of the circular film is only received by the portion of the axial end portion contacting the regulation portion. Therefore, the portion of the axial end portion may be buckled or degraded.

Even if the axial end portion of the film is orthogonal to the rotation axis, such partial contact of the axial end portion of the circular film may also occur due to production error or assembling error of the circular flange member in which the regulation surface of the flange member is not directed in a direction perpendicular to the rotation axis.

In view of the foregoing, it is an object of the invention to provide a fixing device capable of suppressing deformation and degradation of the fusing film.

In order to attain the above and other objects, the present invention provides a fixing device. The fixing device includes a tubular flexible member, a heater, a nip member, a backup member, and a restricting member. The fusing member is rotatable about a rotational axis defining an axial direction and has an inner peripheral surface defining an internal space. The heater is disposed in the internal space. The nip member is disposed in the internal space for receiving radiant heat from the heater. The nip member is in sliding contact with the inner peripheral surface. The backup member nips the fusing member in cooperation with the nip member. The restricting member restricts displacement of the fusing member in the axial direction and is tiltable about a fulcrum portion.

According to another aspect, the present invention provides a fixing device. The fixing device includes a tubular flexible fusing member, a nip member, a backup member, and a restricting member. The fusing member is rotatable about a rotational axis defining an axial direction and has an inner peripheral surface defining an internal space. The nip member is disposed in the internal space. The nip member is configured to be in sliding contact with the inner peripheral surface. The backup member is configured to nip the fusing member in cooperation with the nip member. The restricting member is configured to restrict displacement of the fusing member in the axial direction and is tiltable about a fulcrum portion.

According to still another aspect, the present invention provides a fixing device. The fixing device includes a tubular film, a nip plate, a backup roller and a restricting member. The tubular film is rotatable about a rotational axis defining an axial direction and has an inner peripheral surface defining an internal space. The nip plate is disposed in the internal space. The nip plate is configured to be in sliding contact with the inner peripheral surface. The backup roller is configured to nip the film in cooperation with the nip plate. The restricting member is configured to restrict displacement of the film in the axial direction and is tiltable about a fulcrum portion.

DETAILED DESCRIPTION

Next, a general structure of a laser printer as an image forming device according to an embodiment of the present invention will be described with reference to accompany drawings. The laser printer1shown inFIG. 1is provided with a fixing device100according to the embodiment of the present invention. A detailed structure of the fixing device100will be described later.

<General Structure of Laser Printer>

As shown inFIG. 1, the laser printer1includes a main frame2with a movable front cover21. Within the main frame2, a sheet supply unit3for supplying a sheet P, an exposure unit4, a process cartridge5for transferring a toner image (developing agent image) on the sheet P, and the fixing device100for thermally fixing the toner image onto the sheet P are provided.

Throughout the specification, the terms “above”, “below”, “right”, “left”, “front”, “rear” and the like will be used assuming that the laser printer1is disposed in an orientation in which it is intended to be used. More specifically, inFIG. 1, a left side and a right side are a rear side and a front side, respectively.

The main frame2has a lower portion where the sheet supply unit3is disposed. The sheet supply unit3includes a sheet supply tray31for accommodating the sheet P, a lifter plate32for lifting up a front side of the sheet P, a sheet supply roller33, a sheet supply pad34, paper dust removing rollers35,36, and registration rollers37. Each sheet P accommodated in the sheet supply tray31is directed upward to the sheet supply roller33by the lifter plate32, separated by the sheet supply roller33and the sheet supply pad34, and conveyed toward the process cartridge5passing through the paper dust removing rollers35,36, and the registration rollers37.

The main frame2has an upper portion where exposure unit4is disposed. The exposure unit4includes a laser emission unit (not shown), a polygon mirror41, lenses42,43, and reflection mirrors44,45,46. In the exposure unit4, the laser emission unit is adapted to project a laser beam (indicated by a chain line inFIG. 1) based on image data so that the laser beam is deflected by or passes through the polygon mirror41, the lens42, the reflection mirrors44,45, the lens43, and the reflection mirror46in this order. A surface of a photosensitive drum61is subjected to high speed scan of the laser beam.

The process cartridge5is disposed below the exposure unit4. The process cartridge5is detachable or attachable relative to the main frame2through a front opening defined by the front cover21at an open position. The process cartridge5includes a drum unit6and a developing unit7.

The drum unit6includes the photosensitive drum61, a charger62, and a transfer roller63. The developing unit7is detachably mounted to the drum unit6. The developing unit7includes a developing roller71, a toner supply roller72, a regulation blade73, and a toner accommodating portion74in which toner (developing agent) is accommodated.

In the process cartridge5, after the surface of the photosensitive drum61has been uniformly charged by the charger62, the surface is subjected to high speed scan of the laser beam from the exposure unit4. An electrostatic latent image based on the image data is thereby formed on the surface of the photosensitive drum61. The toner accommodated in the toner accommodating portion74is supplied to the developing roller71via the toner supply roller72. The toner is conveyed between the developing roller71and the regulation blade73so as to be deposited on the developing roller71as a thin layer having a uniform thickness.

The toner deposited on the developing roller71is supplied to the electrostatic latent image formed on the photosensitive drum61. Hence, a visible toner image corresponding to the electrostatic latent image is formed on the photosensitive drum61. Then, the sheet P is conveyed between the photosensitive drum61and the transfer roller63, so that the toner image formed on the photosensitive drum61is transferred onto the sheet P.

The fixing device100is disposed rearward of the process cartridge5. The toner image (toner) transferred onto the sheet P is thermally fixed on the sheet P while the sheet P passes through the fixing device100. The sheet P on which the toner image is thermally fixed is conveyed by conveying rollers23and24so as to be discharged on a discharge tray22.

<Detailed Structure of Fixing Device>

As shown inFIG. 2, the fixing device100includes a flexible tubular fusing member such as a tube or film110, a halogen lamp120, a nip plate130, a reflection plate140, a pressure roller150, and a stay160.

The fusing film110is of a tubular configuration having heat resistivity and flexibility. The fusing film110has an internal space for accommodating the halogen lamp120, the nip plate130, the reflection plate140, and the stay160. The rotation of the fusing film110is guided by a guide assembly170described later at its width ends.

The halogen lamp120is a heater to heat the nip plate130and the fusing film110for heating toner on the sheet P. The halogen lamp120is positioned at the internal space of the fusing film110. The fusing film110and the nip plate130respectively have an inner surface spaced away from the halogen lamp120by a predetermined distance. As shown inFIG. 3, electrical terminals121are provided at each longitudinal end portion of the halogen lamp120

The nip plate130has a plate shape and contacts with the inner surface of the fusing film110. The nip plate130is adapted for receiving resident heat from the halogen lamp120and for transmitting resident heat to the toner on the sheet P through the fusing film110.

The nip plate130has a generally U-shaped cross-section made from a material such as aluminum having a thermal conductivity higher than that of the stay160(described later) made from steel. More specifically, for fabricating the nip plate130, an aluminum plate is bent into U-shape to provide a base portion131and upwardly folded portions132.

The base portion131may be painted with black color or provided with a heat absorbing member. With this configuration, the nip plate130effectively receives resident heat from the halogen lamp120.

As shown inFIG. 3, the nip plate130has a right end portion provided with an insertion portion133extending flat, and a left end portion provided with an engagement portion134. The engagement portion134has U-shaped configuration as viewed from a left side and includes side wall portions134A extending upward and formed with engagement holes134B.

The reflection plate140is adapted to reflect radiant heat radiating in the front-to-rear direction and the upper direction from the halogen lamp120toward the nip plate130(toward the inner surface of the base portion131). As shown inFIG. 2, the reflection plate140is positioned within the fusing film110and surrounds the halogen lamp120, with a predetermined distance therefrom. Thus, radiant heat from the halogen lamp120can be efficiently concentrated onto the nip plate130to promptly heat the nip plate130and the fusing film110.

The reflection plate140is configured into U-shape in cross-section and is made from a material such as aluminum having high reflection ratio regarding infrared ray and far infrared ray. The reflection plate140has a U-shaped reflection portion141and a flange portion142extending from each end portion of the reflection portion141in the front-to-rear direction. A mirror surface finishing is available on the surface of the aluminum reflection plate140for specular reflection in order to enhance heat reflection ratio.

As shown inFIG. 3, two engagement sections143are provided at each widthwise end of the reflection plate140. Each engagement section143is positioned higher than the flange portion142. As a result of assembly of the nip plate130together with the reflection plate140and the stay160as shown inFIG. 4, comb-like contact portions163of the stay160described later are nipped between the right and left engagement sections143. That is, the right engagement section143is in contact with the rightmost contact portion163A, and the left engagement section143is in contact with the leftmost contact portion163A.

As a result, displacement of the reflection plate140in the right-to-left direction due to vibration caused by operation of the fixing device100can be restrained by the engagement between the engagement sections143and the comb-like contact portions163A.

As shown inFIG. 2, the pressure roller150is elastically deformable and is positioned below the nip plate130. The deformed pressure roller150nips the fusing film110in cooperation with the nip plate130to provide a nip region for nipping the sheet P between the pressure roller150and the fusing film110. To provide the nip region, a biasing member such as a spring urges one of the nip plate130and the pressure roller150toward the other.

The pressure roller150is rotationally driven by a drive motor (not shown) disposed in the main frame2. By the rotation of the pressure roller150, the fusing film110is circularly moved along the nip plate130because of a friction force generated therebetween or between the sheet P and the fusing film110. A toner image on the sheet P can be thermally fixed thereto by heat and pressure during passage of the sheet P at the nip region between the pressure roller150and the fusing film110.

The stay160is adapted to support the end portions131B of the nip plate130via the flange portion142of the reflection plate140for maintaining rigidity of the nip plate130. The stay160has a U-shape configuration in conformity with the outer shape of the reflection portion141covering the reflection plate140. For fabricating the stay160, a highly rigid member such as a steel plate is folded into U-shape to have a top wall166, a front wall161and a rear wall162. As shown inFIG. 3, each of the front wall161and the rear wall162has a lower end portion provided with comb-like contact portions163.

The front and rear walls161,162have right end portions provided with L shaped engagement legs165each extending downward and then leftward. The top wall166has a left end portion provided with a retainer167having U-shaped configuration. The retainer167has a pair of retaining walls167A whose inner surfaces are provided with engagement bosses167B protruding inward.

As shown inFIGS. 2 and 3, each width end portion of each of the front wall161and the rear wall162has an inner surface provided with two abutment bosses168protruding inward in abutment with front and rear side walls of the reflection plate140in the front-to-rear direction. Therefore, displacement of the reflection plate140in the front-to-rear direction due to vibration caused by operation of the fixing device100can be restrained because of the abutment of the reflection portion141with the bosses168.

Assembling procedure of the reflection plate140and the nip plate130to the stay160will be described. First, the reflection plate140is temporarily assembled to the stay160by the abutment of the outer surface of the reflection portion141on the abutment bosses168. In this case, the engagement sections143are in contact with the widthwise endmost contact portions163A.

Then, as shown inFIG. 4, the insertion portion133is inserted between the engagement legs165and165, so that the base portion131can be brought into engagement with the engagement legs165. Thereafter, the engagement bosses167B are engaged with the engagement holes134B.

The end portion131B of the base portion131is supported on the engagement legs165and the engagement portion134is supported on the retainer167. Each flange portion142is sandwiched between the nip plate130and the stay160. Thus, the nip plate130and the reflection plate140are held to the stay160.

Vertical displacement of the reflection plate140due to vibration caused by operation of the fixing device100can be restrained, since the flange portions142are held between the nip plate130and the stay160as shown inFIG. 2. Thus, position of the reflection plate140relative to the nip plate130can be fixed.

Incidentally, the stay160holding the nip plate130and the reflection plate140and the halogen lamp120are directly held to the guide assembly170as shown inFIGS. 5 and 6. That is, the guide assembly170integrally supports the fusing film110, the halogen lamp120, the nip plate130, the reflection plate140, and the stay160.

The guide assembly170is made from insulating member such as resin and is disposed at each axial end portion of the fusing film110. The guide assembly170is in abutment with each axial end of the fusing film110in order to restrict displacement of the fusing film110in the right-to-left direction (axial direction). Specifically, the guide assembly170includes an inner guide member171for guiding the rotation of the fusing film110and a restricting member175for restricting displacement of the fusing film110in the right-to-left direction. The restricting member175is tiltably movably mounted on the inner guide member171.

The inner guide member171mainly includes a main body172, an inner guide173provided on the main body172at a side of the film110, and a support portion174for holding widthwise end of the stay160.

The main body172is of rectangular shape and fixed to the main frame2of the laser printer1. The main body172has side surfaces172A in the front-to-rear direction each provided with a pair of protrusions172B and a lateral surface172C opposed to the inner guide173. Specifically, as shown inFIG. 7B, the fixing device100further includes a wall portion105serving as a casing to which the pair of protrusions172B of the main body172is fixed. The lateral surface172C has a center region formed with a spherical receiving portion172D for tiltably supporting the restricting member175and a bottom portion provided with an extending portion172E for supporting the inner guide173.

The inner guide173is in the form of a rib in sliding contact with the inner surface of the fusing film110to guide the rotation thereof and is of C-shape having cutout part in the bottom. As shown inFIGS. 6 and 7A, the inner guide173includes an upper wall173A, a support portion173B, a front edge173C, a rear edge173D, a side wall173G, and a connecting portion173H that provides connection of the upper wall173A with the extending portion172E. The inner guide173is inserted into the internal space of the fusing film110to restrain radially inward deformation of the fusing film110. The stay160is fittingly inserted into the support portion174through the cutout part of the inner guide173.

Two support portions173B are integrally with the upper wall173A for supporting an upper surface of the stay160. The support portion173B is a rib protruding downward from the upper wall173A and extending in the right-to-left direction. One of the support portions173B is spaced away from remaining support portion173B in order to evenly support the stay160at a front and rear portion thereof.

The front edge173C is positioned higher than the rear edge173D in a vertical direction, as shown inFIG. 5. A space is defined immediately below the front edge173C to accommodate a thermometer180adapted to detect a temperature of the nip plate130. That is, the space is provided for preventing the interference between the inner guide173and the thermometer180.

The support portion174has a groove-like shape with its bottom portion open for holding the stay160in the front-to-rear direction. The support portion174includes a fixing portion (not shown) for fixing the terminal121of the halogen lamp120(FIG. 3).

The restricting member175is configured to restrict a displacement of the fusing film110in the right-to-left direction and is tiltable in a gimbal fashion (like a universal joint) about a fixed fulcrum point or portion with respect to the inner guide member171. The restricting member175includes a restricting portion176in abutment with the axial end of the fusing film110, an outer guide177extending from the restricting portion176toward the fusing film110, and a protruding portion178protruding from the restricting portion176toward the main body172.

The restricting portion176is a semicircular shaped wall disposed between the inner guide member171of the main body172and the inner guide173. The restricting portion176has a radially outer portion176A located outside of the inner guide173in the radial direction as viewed from right-to-left direction, and has a concave portion176B for preventing interference with the extending portion172E of the inner guide member171. The radially outer portion176A is abuttable against the axial end of the fusing film110. The radially outer portion176A functions as a restricting plane for restricting a displacement of the fusing film110in the right-to-left direction (axial direction). As shown inFIGS. 7A and 7B, gaps are formed between the restricting portion176and the main body172, between the restricting portion176and the inner guide173, and between the restricting portion176and the extending portion172E in order to permit the restricting member175to be tiltably movable.

The outer guide177shaped like a letter C with an opening downward is a rib for guiding an outer surface of the fusing film110. The outer guide177is positioned outside of the fusing film110in the radial direction to restrain radially outward deformation of the fusing film110. A gap is formed between the outer guide177and the inner guide173. The gap is larger than the thickness of the fusing film110. The opening of the outer guide177is adapted for positioning the inner guide173within the space of the outer guide177and for permitting the stay160to be held to the support portion174in cooperation with the bottom opening of the inner guide173. The outer guide177has lower edge portions177B positioned lower than the inner guide member171.

The protruding portion178and the spherical receiving portion172D function as the fulcrum point or fulcrum portion when the restricting member175tilts. The protruding portion178has a distal end provided with a spherical portion178A. The spherical portion178A is pivotally supported to the spherical receiving portion172D of the main body172. The spherical portion178A has a diameter substantially equal to that of the spherical receiving portion172D. Consequently, the restricting member175is smoothly tiltable in all directions in a gimbal fashion or like a universal joint on a virtual plane perpendicular to the right-to-left direction. In this embodiment, the protruding portion178and the spherical receiving portion172D are positioned in alignment with the internal space and located on an extension of an axial center of the fusing film110.

With this configuration, the above-mentioned embodiment can attain advantageous effects as follows. The guide assembly170includes the inner guide member171and the restricting member175tiltable about the fulcrum point configured of the protruding portion178and the spherical receiving portion172D. When the axial end of the fusing film110is in abutment with the restricting member175, i.e., the restricting member175is pressed by the axial end of the fusing film110, the restricting member175can tilt in all directions in the gimbal fashion on the virtual plane about the fulcrum point. Thus, even if the axial end of the fusing film110slants relative to the virtual plane, the restricting member175tilts along with the fusing film110so that entire axial end of the fusing film110is in abutment with the restricting member175. This configuration prevents the axial end of the fusing film110from being partially and strongly pushed by the restricting member175. Thus, deformation and degradation of the axial end portion can be obviated.

The protruding portion178protrudes toward the main body172, and the spherical receiving portion172D is formed on the lateral surface172C. Even if the axial end of the fusing film110presses the restricting member175rightward, the fulcrum point configured of the protruding portion178and the spherical receiving portion172D is immovable in the right-to-left direction (The main body172is held stationarily by the wall105). That is, since a position of the fulcrum point in the right-to-left direction is fixedly provided, the restricting member175can stably tilt about the fulcrum point.

In the embodiment, the restricting member175is tiltably mounted on the inner guide member171. Thus, the inner guide member171restricts the radially inward displacement of the fusing film110, and simultaneously the restricting member175is tiltable in accordance with the slant of the axial end face of the fusing film110.

The supporting portion is configured of the spherical portion178A of the protruding portion178and the spherical receiving portion172D of the main body172. Thus, the restricting member175can tilt in all directions in the gimbal fashion on the virtual plane. Even if the axial end of the fusing film110slants in any directions, the restricting member175can tilt in conformance with the slanting direction of the axial end face of the fusing film110. Thus any damage to the axial end portion of the fusing film110can be prevented. Additionally, the tilt of the restricting member175is achieved by the spherical portion178A and the spherical receiving portion172D without an urging member such as a spring. The restricting member175can tilt even by a slight pushing force of the fusing film110. Therefore, axial position of the fusing film110can be properly regulated without any damage to the end portion thereof.

In the embodiment, the protruding portion178and the spherical receiving portion172D are positioned in alignment with the internal space, and more specifically, are located on an extension of the axial center of the fusing film110. Therefore, a distance between the fulcrum point and any point on the axial end of the fusing film110can be substantially uniform, and accordingly, stabilized tilting motion of the restricting member175can be realized.

Various modifications are conceivable. A first modification to the above-described embodiment will be described with reference toFIGS. 8A and 8B. In the first modification, like parts and components are designated by the same reference numerals added with 100 as those shown inFIGS. 1 through 7to avoid duplicating description.

Description is given to a configuration different from that of the embodiment. As shown inFIGS. 8A and 8B, a guide assembly270includes an inner guide member271and a restricting member275. The restricting member275includes a restricting portion276facing a connecting portion273H of the inner guide member271and provided with a protruding portion278protruding toward the connecting portion273H. The connecting portion273H is formed with a spherical receiving portion273D. The inner guide member271includes an inner guide273, and the restricting member275includes an outer guide277.

As shown inFIG. 8B, the spherical receiving portion273D is formed with an opening having a diameter D1smaller than a diameter D2of a spherical portion278A receiving a distal end portion of the protruding portion278. When the spherical portion278A is pressingly fitted into the spherical receiving portion273D, the spherical portion278A is caught by the spherical receiving portion273D by a resilient deformation of the connecting portion273H, and accordingly, the restricting member275is held on the inner guide member271. The protruding portion278includes a base portion having a diameter D3smaller than the diameter D1. With this configuration, the restricting member275is tiltable about a fulcrum point but immovable in the right-to-left direction. Further, since the spherical receiving portion273D is provided in the connecting portion273H rather than a main body272of the inner guide member271, the main body272can be downsized. Incidentally, according to the above-described embodiment, pressing force from the fusing film110is exerted on a bottom surface of the spherical receiving portion172D. Therefore, separation of the spherical portion178A from the spherical receiving portion172D can be effectively avoided when compared with the first modification.

Next, a second modification will be described with reference toFIGS. 9A and 9Bin which like parts and components are designated by the same reference numerals but added with 200 as those shown in the above-described embodiment. A guide assembly370according to the second modification includes an inner guide member371and a restricting member375. The restricting member375is not supported as a pivot support but supported as a pin support using a shaft and a bearing. The inner guide member371includes an inner guide373, and the restricting member375includes an outer guide377.

A main body372of the inner guide member371has an upper surface372A provided with a cylindrical pin372B. The restricting member375includes a restricting portion376having a side surface376B provided with an annular portion378engaged with the pin372B and rotatable relative to the pin372B. With this configuration, the restricting member375can be tiltable in a horizontal direction. Since the restricting member375can tilt about a vertical axis of the pin371B in accordance with the slant of the axial end face of the fusing film110. Accordingly, the deformation and the damage to the fusing film110can be restrained in comparison with a configuration in which the restricting member is fixedly provided.

In the above-described embodiment and the first modification, the restricting member175and275is tiltable in all direction in a gimbal fashion in a virtual plane perpendicular to the right-to-left direction by the employment of the spherical portion178A,278A and the spherical receiving portion172D,273D. Instead of the above-described structure, a universal joint is available.

While the invention has been described in detail and with reference to the specific and modified embodiments thereof, it would be apparent to those skilled in the art that various changes and modification is available without departing from the scope of the invention.