Patent Application
20080317522
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1. Field of the Invention
The present invention relates to electrophotographic imaging devices, and, more particularly, to a fuser assembly having oil retention features.
2. Description of the Related Art
An electrophotographic imaging apparatus, such as a laser printer, forms a latent image on a surface of a photoconductive material by selectively exposing an area of the surface to light. The latent electrostatic image is developed into a visible image by electrostatic toners which contain pigment components and thermoplastic components. The photoconductor may be either positively or negatively charged, and the toner system similarly may contain negatively or positively charged particles. A print medium (e.g., a sheet of paper) or intermediate transfer medium is given an electrostatic charge opposite that of the toner and then passed close to a surface of the photoconductor, pulling the toner from the photoconductor onto the paper or immediate medium in the pattern of the image developed from the photoconductor. After the image is transferred to the print medium, the print medium is processed through a fuser assembly where it is heated and pressed. The fuser assembly may include a fuser belt, subjected to heat, which melts and fixes the toner to the print medium surface thereby producing the printed image.
An axial location of the fuser belt is controlled by an end cap attached to each end of a heater housing. The fuser belt may be, for example, a polyimide tube having a Teflon® coating. The fuser belt is rotated by paper moving through a nip produced by a backup roller being pressed against the fuser belt. A ceramic heater mounted by the heater housing is positioned in the interior of the fuser belt. As the fuser belt is rotated, an interior surface of the fuser belt slides on the heater surface. The sliding contact between the belt and the heater surface can cause a high friction force.
To reduce this friction force, grease and oil have been commonly used as lubricants between the fuser belt and the heater. Greases normally have higher viscosity than oil, and can form a thicker film on the belt and heater surface than oil. However, the higher viscosity of grease can cause a higher friction force and driving torque, and a thicker film thickness, and in turn can cause a lower fusing grade/quality. On the other hand, oil as lubricant has a lower viscosity than grease and can form a thinner film, resulting in lower driving torque and better fusing grade/quality. However, the lower viscosity of oil causes the oil to flow easily, and the oil may leak out from the two ends of the belt, especially at high fusing temperatures. As the oil leaks out, the lubrication condition between the fuser belt and the heater becomes increasingly worse, leading to higher driving torque, higher belt wear, and sometimes to the destruction of the fuser belt.
The present invention provides a fuser assembly having oil retention features in the form of ribs that engage an interior surface of a fuser belt.
The terms “first” and “second” preceding an element name, e.g., first side edge, second side edge, first end cap, second end cap, etc., are used for identification purposes to distinguish between similar elements, and are not intended to necessarily imply order, nor are the terms “first” and “second” intended to preclude the inclusion of additional similar elements.
The invention, in one form thereof, is directed to a fuser assembly configured to fix a toner image to a sheet of print media moving in a sheet feed direction through a nip. The fuser assembly includes a first end cap, and a second end cap spaced apart from the first end cap along an axis that is orthogonal to the sheet feed direction. A fuser belt has a first side edge, a second side edge spaced apart from the first side edge, an exterior surface, an interior surface, and a hollow interior defined by the interior surface. The fuser belt is positioned between and supported by the first end cap and the second end cap, with the axis passing through the hollow interior, to rotate around the axis in a belt moving direction at the nip corresponding to the sheet feed direction. A heater assembly is located in the hollow interior of the fuser belt. The heater assembly includes a heater housing and a heater body coupled to the heater housing. The heater body is positioned to contact the interior surface of the fuser belt. A plurality of ribs is positioned to contact the interior surface of the fuser belt. A first rib of the plurality of ribs is connected to one of the first end cap and the heater assembly. A second rib of the plurality of ribs is connected to one of the second end cap and the heater assembly. Each of the plurality of ribs is oriented to longitudinally extend at an acute angle with respect to the belt moving direction.
The invention, in another form thereof, is directed to a fuser assembly configured to fix a toner image to a sheet of print media moving in a sheet feed direction through a nip. The fuser assembly includes a first end cap, and a second end cap spaced apart from the first end cap along an axis that is orthogonal to the sheet feed direction. A plurality of ribs is positioned to contact the interior surface of the fuser belt, wherein a first rib of the plurality of ribs is connected to the first end cap and a second rib of the plurality of ribs is connected to the second end cap. The first rib and the second rib are oriented to be symmetrical.
The invention, in another form thereof, is directed to a fuser assembly configured to fix a toner image to a sheet of prim media moving in a sheet feed direction through a nip. The fuser assembly includes a heater assembly located in the hollow interior of a fuser belt. The heater assembly includes a heater housing and a heater body coupled to the heater housing. A plurality of ribs is positioned to contact the interior surface of the fuser belt, wherein a first rib of the plurality of ribs is connected to the heater body of the heater assembly, and a second rib of the plurality of ribs is connected to the heater body of the heater assembly. The first rib and the second rib are arranged to be symmetrical with respect to a centerline extending in the belt moving direction midway between the first side edge and second side edge of the fuser belt.
The invention, in another form thereof, is directed to an imaging apparatus for forming a toner image on a sheet of print media. A media feed section feeds the sheet of print media along a media feed path in a sheet feed direction. A laser scanning device is configured to produce a scanned light beam. An image-forming device having a photosensitive body is configured to use the scanned light beam to form a latent image on the photosensitive body and develop the latent image to form a toner image that is transferred to the sheet of print media. A fuser assembly includes a first end cap, and a second end cap spaced apart from the first end cap along an axis that is orthogonal to the sheet feed direction. A fuser belt has a first side edge, a second side edge spaced apart from the first side edge, an exterior surface, an interior surface, and a hollow interior defined by the interior surface. The fuser belt contacts a backup roller to form a nip. The fuser belt defines a belt moving direction at the nip corresponding to the sheet feed direction. A heater assembly is located in the hollow interior of the fuser belt. The heater assembly includes a heater housing and a heater body coupled to the heater housing. The heater body is positioned to contact the interior surface of the fuser belt. A plurality of ribs is positioned to contact the interior surface of the fuser belt, wherein a first rib of the plurality of ribs is connected to one of the first end cap and the heater assembly, and a second rib of the plurality of ribs is connected to one of the second end cap and the heater assembly. Each of the plurality of ribs is oriented to longitudinally extend at an acute angle with respect to the belt moving direction.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring now to the drawings and particularly to
Media feed section 12 sequentially transports a sheet of print media (e.g., paper) 20-1 from a stack of sheets of print media 20 to image-forming device 14. Each sheet of print media 20-1 moves along a media feed path 22 in a sheet feed direction 22-1. Image-forming device 14 transfers a toner image to the transported sheet of print media 20-1. Fuser assembly 18 fixes the toner image to the sheet of print media 20-1 sent from image-forming device 14. Thereafter, the sheet of print media 20-1 is ejected out of imaging apparatus 10 by media transport rollers 24, 26 and into output tray 28.
In the exemplary imaging apparatus 10, the media feed section 12 includes a feed tray 30, a feed roller 32, a media separating friction plate 34, a pressure spring 36, a media detection actuator 38, a media detection sensor 40, and a control circuit 42. Upon receiving a print instruction, the sheets of print media 20 which have been placed in media feed tray 30 are fed one-by-one by operation of feed roller 32, media separating friction plate 34 and pressure spring 36. As the fed sheet of print media 20-1 pushes down media detection actuator 38, media detection sensor 40 outputs an electrical signal instructing commencement of printing of the image. Control circuit 42, started by operation of media detection actuator 38, transmits an image signal to a laser diode light-emitting unit 44 of laser scanning device 16 so as to control the ON/OFF condition of its associated light-emitting diode.
Laser scanning device 16 includes laser diode light-emitting unit 44, a scanning mirror 46, a scanning mirror motor 48, and reflecting mirrors 50, 52, and 54. Scanning mirror 46 is rotated at a constant high speed by scanning mirror motor 48 such that laser light beam 56 scans in a vertical direction to the print media surface. The laser light beam 56 radiated by laser diode light-scanning unit 44 is reflected by reflecting mirrors 50, 52, and 54 so as to be applied to a photosensitive body 58 of image-forming device 14. When the laser light beam 56 is applied to photosensitive body 58, photosensitive body 58 is selectively exposed to the laser light beam 56 in accordance with ON/OFF information from control circuit 42.
In addition to photosensitive body 58, image-forming device 14 includes a transfer roller 60, a charging member 62, and a developer, including a developing roller 64, a developing unit 66, and a cleaning unit 68. The surface charge of photosensitive body 58, charged in advance by charging member 62, is selectively discharged by the laser light beam 56. An electrostatic latent image is thus formed on the surface of photosensitive body 58. The electrostatic latent image is visualized by developing roller 64, and developing unit 66. Specifically, the toner supplied from developing unit 66 is adhered to the electrostatic latent image on photosensitive body 58 by developing roller 64 so as to form the toner image.
Toner used for development is stored in developing unit 66. The toner contains coloring components (such as carbon black for black toner) and thermoplastic components. The toner, charged by being appropriately stirred in developing unit 66, adheres to the above-mentioned electrostatic latent image by an interaction of the developing bias voltage applied to developing roller 64 and an electric field generated by the surface potential of photosensitive body 58, and thus conforms to the latent image, forming a visual toner image on photosensitive body 58. The toner typically has a negative charge when it is applied to the latent image, forming the visual toner image.
The sheet of print media 20-1 transported from media feed section 12 is transported downstream while being pinched by photosensitive body 58 and transfer roller 60. The sheet of print media 20-1 arrives at the transfer nip in timed coordination with the toned image on the photosensitive body 58. As the sheet of print media 20-1 is transported downstream, the toner image formed on photosensitive body 58 is electrically attracted and transferred to the sheet of print media 20-1 by an interaction with the electrostatic field generated by transfer voltage applied to transfer roller 60. Any toner that still remains on photosensitive body 58, not having been transferred to the sheet of print media 20-1, is collected by cleaning unit 68. Thereafter, the sheet of print media 20-1 is transported to fuser assembly 18.
Referring also to
The backup (i.e., pressure) roller 70 may be generally cylindrical in shape. Backup roller 70 may be made from, or is coated with, a material that has good release and transport properties for the sheet of print media 20-1. Backup roller 70 may be sufficiently soft so as to allow if to be rotated against fuser belt 72 to form fuser nip 80 through which the printed sheets of print media 20 travel. As a printed sheet of print media 20-1 passes through fuser nip 80, the sheet is placed under pressure, and the combined effects of this pressure, the time the sheet is in fuser nip 80, and the heat from fuser belt 72 acts to fix the toner onto the sheet of print media 20-1. Typically, the pressure between fuser belt 72 and backup roller 70 at fuser nip 80 is from about 5 pound per square inch (psi) to 30 psi.
Backup roller 70 may be formed, for example, from silicone rubber. Backup roller 70 may have an aluminum core with a silicone rubber layer molded or adhesively bonded onto its surface. Backup roller 70 may also have a fluoropolymer, e.g., Teflon, (R) sleeve or coating. Backup roller 70 may be essentially hollow, having a metallic core, an outer metallic shell surrounding and essentially concentric with the core, and ribs between the core and the outer shell.
Fuser belt 72 is an endless belt having a first side edge 72-1, a second side edge 72-2, an exterior surface 72-3, an interior surface 72-4, and a hollow interior 72-5 that is defined by interior surface 72-4. Second side edge 72-2 is spaced apart from first side edge 72-1, with both exterior surface 72-3 and interior surface 72-4 extending therebetween. Fuser belt 72 is formed from a highly heat resistive and durable material having good parting properties and may have a thickness about 75 microns or less. Fuser belt 72 may be formed, for example, from a polyimide film or metal. Fuser belt 72 may have an outer coating of, for example, a fluororesin or Teflon® material to optimize release properties of the fixed toner. Fuser belt 72 may be shaped, for example, as a tube. Fuser belt 72 is positioned between and supported by end cap 74 and end cap 76. Additional support for fuser belt 72 is provided by heater assembly 78.
As illustrated in
Heater assembly 78 applies an appropriate temperature and pressure to fuser belt 72 while the sheet of print media 20-1 is moving through fuser nip 80 formed by backup roller 70 and fuser belt 72. The thermoplastic components of the toner on the sheet of print media 20-1 are melted by fuser belt 72 and fixed to the sheet of print media 20-1 to form the fixed image. The sheet of print media 20-1 is then transported and ejected out of the printer by media transport rollers 24, 26 and into output tray 28 where it may be stacked, one sheet upon another.
As illustrated in
In accordance with the present invention, features in the form of a plurality of ribs located on heater assembly 78 and/or the two end caps 74, 76 are positioned to contact interior surface 72-4 of fuser belt 72, and are oriented to reduce the possibility of the oil in fuser assembly 18 leaking out, so as maintain an effective lubrication condition between fuser belt 72 and heater assembly 78.
In
Each of the plurality of ribs 92 is oriented to longitudinally extend at an acute angle with respect to belt moving direction 88. For example, first rib 92-1 is oriented at a first angle 100-1 with respect to belt moving direction 88. Second rib 92-2 is oriented at a second angle 100-2 with respect to belt moving direction 88. In the present embodiment, first angle 100-1 and second angle 100-2 may be symmetrical acute angles. Each of first angle 100-1 and second angle 100-2 is in a range of 10 degrees to 80 degrees, with a preferred angle in one embodiment being 45 degrees. In the present embodiment, a height 102 of each of the plurality of ribs 92 is one millimeter or less, with a preferred height in one embodiment being between 0.05 and 0.1 millimeters.
With the orientation of ribs 92-1, 92-2 as illustrated in the embodiment of
Each of the plurality of ribs 112 is oriented to longitudinally extend at an acute angle with respect to belt moving direction 88. For example, first rib 112-1 is oriented at a first angle 114-1 with respect to a plane of rotational direction 84, and in the view of
As illustrated diagrammatically in
In the embodiment of
Each of the plurality of ribs 116 is oriented to longitudinally extend at an acute angle, e.g., in a range of 10 degrees to 80 degrees, with respect to belt moving direction 88 and the plane of rotational direction 84. Rib 116-1 and rib 116-2 may be oriented, for example, to be symmetrical, i.e., are mirror images of one another, with respect to a central region of the fuser assembly along axis 90. In the present embodiment, a height of each of the plurality of ribs 116 is one millimeter or less, with a preferred height in one embodiment being between 0.05 and 0.1 millimeters.
As illustrated diagrammatically in
In the embodiments described above (see, for example,
As an exemplary benefit of the present invention, it is possible to use a much lower viscosity lubricant, e.g., oil, than is possible in the absence of the present invention, since as fuser belt 72 is rotated the lubricant is moved toward the central region of fuser belt 72 and away from side edges 72-1, 72-2. Using a lower viscosity lubricant in turn not only leads to lower torque and lower wear associated with fuser belt 72, but also to better fuse grade/fusing quality by yielding in a thinner oil film thickness and/or lower contact resistance between heater assembly 78 and fuser belt 72.
While this invention has been described with respect to embodiments of the invention, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
