Heating apparatus with mechanical attachment

In accordance with an aspect of the present invention, an image heating apparatus is provided for fusing an unfixed toner image to a substrate including a housing base for supporting a heater, and a thin film or belt extending around the housing base and heater. The heater is held to the housing base by a fastener structure that may include a pair of retainer clips having opposing ends attached to the housing base and having a central portion extending across the heater for retaining the heater in position. The clips may include outwardly extending walls for engaging edges of the belt to maintain the lateral position of the belt.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrophotographic image forming apparatus, and more particularly to a heater attachment structure for use in a fusing system of such an apparatus.

2. Description of Related Art

In an electrophotographic image forming apparatus, such as a printer or copier, a latent image is formed on a light sensitive drum and developed with toner. The toner image is then transferred onto media, such as a sheet of paper, and is subsequently passed through a fuser assembly where heat and pressure are applied to melt and adhere the unfused toner to the surface of the media. There are a variety of devices to apply heat and pressure to the media such as radiant fusing, convection fusing, and contact fusing. Contact fusing is the typical approach of choice for a variety of reasons including cost, speed and reliability. Contact fusing systems themselves can be implemented in a variety of manners. For example, a roll fusing system consists of a fuser roll and a backup roll in contact with one another so as to form a nip therebetween, which is under a specified pressure. A heat source may be associated with the fuser roll, backup roll, or both rolls in order to raise the temperature of the rolls to a temperature capable of adhering unfixed toner to a medium. As the medium passes through the nip, the toner is adhered to the medium via the pressure between the rolls and the heat resident in the fusing region (nip).

As an alternative to the roll fusing system, a belt fusing system can be used. In one configuration of a belt fusing system, a heater, such as a ceramic heater may be supported on a supporting member, and a pressure roll may be pressed against the heating element with a thin film belt member therebetween. Heat from the heat source may pass through the thin film to heat and adhere unfixed toner to a medium as the medium is passed between the pressure roll and the belt.

In a known construction of a belt fusing system, a ceramic heater may be attached to a supporting member with an adhesive, such as a silicone adhesive. Assembly of the heater to the supporting member using adhesive generally requires a significant investment in processing equipment, as well as a relatively long “cycle time,” such as twenty-four hours, to allow the adhesive to cure. The adhesive bond may limit thermal expansion of the heater relative to the supporting member where the heater and supporting member have different coefficients of thermal expansion, and thus may cause a structural failure of the heater due to thermally induced stresses. Also, it has been observed that many “late” to “end of life” heater assembly failures have occurred as a result of a failure of the bond formed by the adhesive between the heater and the supporting member. This failure of the adhesive bond may allow the heater to move on the supporting member in an uncontrolled manner in the process direction. With the heater no longer fixed, the thin film belt may track uncontrollably side-to-side in the nip area, which can eventually lead to a failure of the belt and require fuser replacement.

U.S. Pat. No. 5,828,035 discloses a heating apparatus in which a heater is movably supported on a support member without requiring an adhesive to attach the heater. During operation of the heating apparatus, the heater is allowed to move in the process direction within a space defined in a heater holder structure. The disclosed structure permits movement of the heater relative to the nip location, and it is believed that this may adversely affect belt tracking and may lead to additional belt wear and inconsistent print quality as compared to a heater that is precisely fixed in an immovable position.

Further, a wear condition has been observed to occur at certain contact points between the thin film belt and the heater of belt fusing systems incorporating ceramic heaters. In particular, a wear pattern on a glass layer of the ceramic heater contacting the belt has been observed to occur at a location that generally matches up with the ends or outer edges of the belt.

Accordingly, alternative designs of image heating apparatus comprising a thin film belt passing over a heater are desired.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, an image heating apparatus is provided comprising a heater having opposing first and second sides, and a support member in engagement with the second side of the heater. A movable member extends around the support member and contacts the first side of the heater. The apparatus further includes a fastener structure extending around the heater for positioning the heater on the support member.

In accordance with another aspect of the invention, an image heating apparatus is provided comprising a ceramic heater having opposing first and second sides, and a support member in engagement with the second side of the heater. A movable member extends around the support member and contacts the first side of the heater. The apparatus further includes a fastener structure comprising first and second fastener elements. The fastener elements are attached to the support member and extend around the heater for positioning the heater on the support member.

DETAILED DESCRIPTION

FIG. 1depicts a representative electrophotographic image forming apparatus, such as a color laser printer, which is indicated generally by the numeral10. An image to be printed is electronically transmitted to a print engine controller or processor12by an external device (not shown) or may comprise an image stored in a memory of the processor12. The processor12includes system memory, one or more processors, and other logic necessary to control the functions of electrophotographic imaging.

In performing a printing operation, the processor12initiates an imaging operation where a top substrate14of a stack of media is picked up from a media tray16by a pick mechanism18and is delivered to a media transport belt20. The media transport belt20carries the substrate14past each of four image forming stations22,24,26,28, which apply toner to the substrate14. The image forming station22includes a photoconductive drum22K that delivers black toner to the substrate14in a pattern corresponding to a black image plane of the image being printed. The image forming station24includes a photoconductive drum24M that delivers magenta toner to the substrate14in a pattern corresponding to the magenta image plane of the image being printed. The image forming station26includes a photoconductive drum26C that delivers cyan toner to the substrate14in a pattern corresponding to the cyan image plane of the image being printed. The image forming station28includes a photoconductive drum28Y that delivers yellow toner to the substrate14in a pattern corresponding to the yellow image plane of the image being printed. The processor12regulates the speed of the media transport belt20, media pick timing and the timing of the image forming stations22,24,26,28to effect proper registration and alignment of the different image planes to the substrate14.

The media transport belt20then carries the substrate14with the unfused toner image superposed thereon to an image heating apparatus or fuser assembly30, which applies heat and pressure to the substrate14so as to promote adhesion of the toner thereto. Upon exiting the fuser assembly30, the substrate14is either fed into a duplexing path32for performing a duplex printing operation on a second surface of the substrate14, or the substrate14is conveyed from the apparatus10to an output tray34.

To effect the imaging operation, the processor12manipulates and converts data defining each of the KMCY image planes into separate corresponding laser pulse video signals, and the video signals are then communicated to a printhead36. The printhead36may include four laser light sources (not shown) and a single polygonal mirror38supported for rotation about a rotational axis37, and post-scan optical systems39A and39B receiving the light beams emitted from the laser light sources. Each laser of the laser light sources emits a respective laser beam42K,44M,46C,48Y, each of which is reflected off the rotating polygonal mirror38and is directed towards a corresponding one of the photoconductive drums22K,24M,26C and28Y by select lenses and mirrors in the post-scan optical systems39A,39B.

Referring toFIG. 2, the fuser assembly30in the illustrated embodiment includes a heater assembly50and a pressure roller52cooperating with the heater assembly50to define a nip for conveying substrates14therebetween. The pressure roller52may comprise a hollow core54covered with an elastomeric layer56, such as silicone rubber, and a fluororesin outer layer (not shown), such as may be formed, for example, by a spray coated PFA (polyperfluoroalkoxy-tetrafluoroethylene) layer or a PTFE (polytetrafluoroethylene) sleeve. The pressure roller52has an outer diameter of about 30 mm. The pressure roller52may be driven by a fuser drive train (not shown) to convey substrates14through the fuser30.

The heater assembly50may comprise a housing structure58defining a support member, a heater59supported on the housing structure58, and an endless belt60positioned about the housing structure58. The belt60may comprise a thin film, and preferably comprises a stainless steel tube having a thickness of approximately 35-50 μm and covered with an elastomeric layer, such as a silicone rubber layer, having a thickness of approximately 250-350 μm. The elastomeric layer is formed on the outer surface of the stainless steel tube so as to contact substrates14passing between the heater assembly50and the pressure roller52.

Referring toFIG. 3, the housing structure58may comprise a housing base62, a frame member64and first and second end caps66,68. The housing base62may be formed of a polymeric material such as a liquid crystal polymer (LCP). The housing base62comprises a central portion63defining a top or upper portion70. The upper portion70includes first and second longitudinal walls72,74defining a central recess76therebetween. The central recess76is formed to receive the heater59therein, as will be described further below.

Referring additionally toFIGS. 4 and 5, a lower portion78of the housing base62includes inner walls80,82extending from the central portion63that comprise respective engagement wall surfaces84,86. In addition, a plurality of curved wing portions88,90extend from either side of the central portion63and are located outwardly from the wall surfaces84,86.

Referring toFIG. 3, the heater frame64is formed from a metal, such as steel, and comprises opposing leg parts64A and64B, and a base part64C joining lower edges of the leg parts64A,64B so as to define a generally U-shaped member. The housing base62defines a space92between the wall surface84and the wing portion88, and defines a space94between the wall surface86and the wing portion90, seeFIGS. 4 and 5. The heater frame is positioned in the lower portion78of the housing base62with the leg parts64A,64B positioned in the spaces92,94, to located inner surfaces of the leg parts64A,64B adjacent to the engagement wall surfaces84,86, respectively.

Referring toFIGS. 6 and 7, the end caps66,68are described with reference to the end cap66, wherein it should be understood that the other end cap68is formed with a substantially identical construction. The end cap66may be formed from a polymeric material, such as a liquid crystal polymer (LCP). The end cap66is provided with a first outer slot100for receiving an end164A of the heater frame leg part64A, and a second outer slot102for receiving an end164B of the heater frame leg part64B, seeFIG. 3. A center slot104is provided between the outer slots100,102for receiving portions of the inner walls82,84extending longitudinally outwardly from the housing base62. The end cap66further includes opposing outer mounting walls106,108for engaging with a wall of a fuser frame (not shown). In particular, the outer mounting wall106,108may slide between edges of slots in the fuser frame to position the heater assembly50within the fuser30.

Referring toFIG. 3, the heater59includes a connection end110. The connection end110of the heater59may extend onto a connector extension112of the housing base62when the heater59is positioned in the recess76. A power connector114is provided for engagement with the connector extension112such that it is located in engagement with exposed contacts130,132of the heater59. The power connector114is formed with a recess116, see alsoFIG. 8, that receives the connector extension112. The connector extension112includes a guide rib118extending widthwise across the connector extension112, and a latch tab120located adjacent one edge of the connector extension112. The power connector114includes a guide groove122for receiving the guide rib118in sliding engagement, and further includes a resilient latch member124for engaging the latch tab120to maintain the power connector114in position on the connector extension112. The power connector114further includes contacts126,128that extend toward the recess116to engage the exposed contacts130,132on the heater59to thereby provide power to the heater59.

It should be noted that the connector extension112and connector114are located longitudinally outwardly from the end cap68when the end cap68is attached to the housing base62. Accordingly, when the heater assembly50is mounted within a fuser frame (not shown), the connector114will be located outside of the fuser frame.

The heater59preferably comprises a ceramic heater, and in the illustrated embodiment it comprises a ceramic heater having a heating element defined by a single trace on a first, heating surface133of the heater59, facing outwardly from the housing base62. The heating surface133is preferably covered by a layer of glass to provide a contact surface that protects the heater element.

Referring toFIGS. 2 and 3, the heater59is held in position on the housing base62by a fastener structure comprising first and second fastener elements or retainer clips134,136.FIGS. 9 and 10illustrate the retainer clip136wherein it should be understood that the retainer clip134is formed with a substantially similar construction. Each retainer clip134,136includes a clip body138that is preferably formed of a material that provides a coefficient of thermal expansion substantially similar to the coefficient of expansion of the housing base62. In the described embodiment, the clip body138may be formed of a liquid crystal polymer (LCP).

The clip body138includes a central portion140and arm portions142,144located at opposing ends of the central portion140. Each of the arm portions142,144supports a respective latch tooth portion146,148, each latch tooth portion146,148including a respective generally convex engagement face150,152facing inwardly toward the central portion140. A biasing element comprising a laterally extending rib154extends from the central portion140and is located proximal to the arm portion142.

As seen inFIG. 2, the retainer clips134,136are positioned on the housing base62with the latch tooth portions146,148located within respective recesses156,158formed on outer sides160,162of the housing base62. The engagement faces150,152seat within respective generally concave areas166,168of the recesses156,158to latch the retainer clips134,136onto the housing base62with an inner face170of the central portion140extending across the heating surface133of the heater59and biasing a second surface172of the heater59toward engagement within the recess76(FIG. 3). In addition, the rib154is located between a leading or upstream edge174of the heater59, as viewed in the process direction, and the first longitudinal wall72to bias a trailing or downstream edge176of the heater59toward the second longitudinal wall74.

The retainer clips134,136wrap around a portion of the housing base62to provide a biasing force toward the housing base62to prevent the heater59from lifting from the recess76, without requiring an adhesive attachment of the heater59to the housing base62. In addition, the biasing elements defined by the ribs154bias the heater59against a longitudinal wall, i.e., against the second longitudinal wall74, to prevent or limit movement of the heater59in the process direction, and substantially positively defines the location of the heater59in the process direction.

It should be understood that the construction of the retainer clips134,136is not limited to the particular embodiment illustrated herein, and they may be provided with an additional rib, similar to the rib154, to engage the downstream edge176of the heater59for further locating the heater59relative to the housing base62. Alternatively, the rib154may be located on the central portion140, proximal to the arm portion144, to engage the downstream edge176instead of the upstream edge174of the heater59, to bias the heater59toward engagement with the first longitudinal wall72.

The retainer clips134,136may additionally be formed with a guide wall178extending from an outer surface180of the central portion140, seeFIGS. 3,9and10. The guide wall178defines a guide surface182oriented generally perpendicular to the heating surface133, where the guide surfaces182of the pair of retainer clips134,136face inwardly toward each other to form lateral guides to engage the edges186,188(FIG. 3) of the belt60and guide or limit lateral movement of the belt60.

The heater assembly50is assembled by mounting the heater59in the recess76of the housing base62with an end edge190of the heater59against an end wall192of the recess76, attaching at least one of the retainer clips134,136, such as retainer clip136, to the housing base62, positioning the heater frame64in engagement with the lower portion78of the housing base62, slipping the belt60over the combined housing base62, heater59and heater frame64, and attaching the remaining clip134to the housing base62. The ends caps66,68may then be attached to the ends of the base housing62. When the heater assembly50is assembled into the fuser frame (not shown), the slots in the fuser frame receive the outer mounting walls106,108of the end caps66,68to maintain the end caps66,68, housing base62and heater frame64assembled together. It may be noted that the end194(FIG. 3) of the recess76opposite the end wall192is not provided with an end wall in order to allow room for lengthwise thermal expansion of the heater59at the end194.

The retainer clips134,136are spaced from each other along the length of the housing base62a distance that positions the outer surfaces180of the retainer clips134,136in engagement with an inner surface184(FIG. 3) of the belt60, adjacent the outer edges186,188of the belt60. The surfaces180extend substantially parallel to the heating surface133of the heater59and act as wear surfaces preventing or reducing the wear that may occur on the glass layer of the heating surface133in the area of the outer edges186,188of the belt60. Further, movement of the belt across the heater59may be facilitated by application of a grease to the heater59or to the inner surface184of the belt60during assembly of the heater assembly50to lubricate the contact area between the belt59and the heater60. An example of a commercially available grease that may be applied is DEMNUM L200 grease, a product of Daikin Industries, Ltd., of Japan.

The pressure roller52rotatably engages the belt60, and friction between the pressure roller52and the belt60, or between a medium14passing through the fuser30between the pressure roller52and the belt60, drives the belt60such that it rotates with the pressure roller52. The belt is guided in a generally circular path around the wings88,90of the housing base62and past the heater59.

The described construction for retaining the heater59to the housing base62acts to retain the heater59in a predetermined position on the housing base62without requiring use of an adhesive. In addition to locating the heater59in position, the fastener structure described herein permits differential thermal movement of the heater59relative to heater base62, to alleviate thermal stresses that may otherwise occur if a more rigid connection is provided for holding the heater59in position. Also, the retainer clips134,136provide a fastener structure that may be efficiently applied during assembly of the heater assembly50, thus substantially reducing the assembly time that may be required when adhesives are applied.