Stripper blade assembly

Information

  • Patent Grant
  • 6293545
  • Patent Number
    6,293,545
  • Date Filed
    Wednesday, December 15, 1999
    25 years ago
  • Date Issued
    Tuesday, September 25, 2001
    23 years ago
Abstract
A stripper blade assembly for an ink jet offset printer has a thin blade fixedly mounted on a top surface of a blade holder. The blade holder includes at a trailing edge flexible eyelet portions that extend downwards to snap over protuberances on mechanical connectors overmolded onto a rotatable shaft in order to secure the blade holder to the shaft. The thin blade engages the surface of an offset drum of the ink jet offset printer along the width of the drum at an appropriate point in the print process to strip the leading edge of a print medium from the offset drum surface, minimizing damage to the offset drum surface and to the printed image on the print medium while also minimizing the risk of a jam.
Description




BACKGROUND OF THE INVENTION




The present invention relates to ink jet offset printers, and more particularly to a stripper blade assembly for removing a print medium from the surface of an offset drum in an ink jet offset printer.




In an offset print process an intermediate image is printed onto a print surface of a drum, the print surface generally being a release agent coated on the surface of the drum. The intermediate image is then transferred from the print surface onto a print medium, such as paper or transparency material, in a transfer fusing process. Such a transfer fusing process causes the print medium to tend to adhere to the surface of the drum. Typically in the industry the print medium is stripped from the drum with multiple, spring loaded, plastic fingers that are presented to the drum and print medium at a specified time in the print process. If there is any damage to the print medium, such as a bent comer, a bent leading edge, a cut medium, etc., or any other error in the print process at this critical juncture, the result is a serious jam that is difficult to clear and requires an expensive service call. Also the plastic fingers may damage the drum and cause damage to the printed image on the print medium due to the point loading.




What is desired is a stripper assembly that removes a print medium from an offset drum of an ink jet offset printer without damage to the printed image on the print medium or to the drum and without risk of a serious jam.




BRIEF SUMMARY OF THE INVENTION




Accordingly the present invention provides a stripper blade assembly for removal of a print medium from an offset drum of an ink jet offset printer that uses a thin, durable, flexible blade. The stripper blade assembly may be easily removable and installable by a customer. The blade, that extends the width of the drum, is mounted on a blade holder. The blade holder is detachably mounted on a shaft having an overmolded connector. The entire assembly rotates or otherwise moves to present the thin edge of the blade to the drum along the axial length of the drum in order to strip the leading edge of the print medium from the drum at the appropriate point in the print process.




The objects, advantages and other novel features of the present invention are apparent from the following detailed description when read in conjunction with the appended claims and attached drawing.











BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING





FIG. 1

is a partial sectional view of a stripper blade assembly according to the present invention.





FIG. 2

is a bottom side perspective view of a stripper blade assembly according to the present invention.





FIG. 3

is a top side perspective view of a stripper blade assembly according to the present invention.





FIGS. 4A

,


4


B and


4


C are respective back, bottom and side plan views of a blade holder for the stripper blade assembly according to the present invention.





FIGS. 5A

,


5


B and


5


C are respective bottom, top and end plan views of a shaft with connectors for the stripper blade assembly according to the present invention.











DETAILED DESCRIPTION OF THE INVENTION




Referring now to

FIGS. 1-5

an offset drum


12


is shown with a transfer roller


14


which together form a nip


16


through which a print medium, such as paper or transparency material, passes along a medium path


18


. A stripper blade assembly


20


includes a thin blade


22


fixedly mounted on a blade holder


24


. The blade holder


24


may be detachedly mounted on a shaft


26


via connectors


28


that are fixedly mounted on the shaft, such as by an overmolding process. The blade holder


24


has guide ribs


30


with slots that fit over the shaft


26


. The blade holder


24


also has a flexible eyelet portion


32


that engages a protuberance


34


on the connectors


28


to secure the blade holder to the shaft


26


.




The blade holder


24


has a main body


36


with a top surface


38


and a bottom surface


40


. The thin blade


22


is fixedly attached to the top surface


38


via a suitable adhesive


44


that is compatible with the materials of both the blade holder


24


and the thin blade. A leading edge


46


of the thin blade


22


extends beyond a leading edge


42


of the top surface


38


of the blade holder


24


. The adhesive


44


may be in the form of a double-sided sticky tape. The top surface


38


also includes a longitudinal ledge


48


. The thin blade


22


includes a corresponding longitudinal bend


50


that overhangs the ledge


48


to provide a smooth transition of the medium path


18


over the top of the blade holder


24


. For detachability the flexible eyelet portion


32


extends down from the bottom surface


40


at the trailing edge


52


to engage the protuberance


34


on the connector


28


mounted on the shaft


26


. Also on the bottom surface


40


are a pair of opposing guide rails


54


that guide the blade holder


24


into alignment longitudinally such that the flexible eyelet portions


32


engage the connector protuberances


34


. The bottom surface


40


also includes guide posts


56


adjacent the flexible eyelet portions


32


that fit into a recess


58


in the connectors


28


. Alternatively the blade holder


24


may be fixedly attached to the shaft


26


by suitable means.




In operation the guide ribs


30


of the blade holder


24


engage the shaft


26


via the slots, and the blade holder is rotated until the flexible eyelet portions


32


snap over the protuberances


34


of the connectors


28


to secure the blade holder to the shaft. The stripper blade assembly


20


is generally kept clear of the drum


12


, but when the print medium passes through the transfer nip


16


, the shaft


26


rotates to bring the thin blade


22


in contact with the drum


12


along the width of the drum to detach the leading edge of the print medium from the drum. Alternatively the entire assembly


20


may be moved linearly to bring the thin blade


22


in contact with the drum


12


. Once the leading edge of the print medium is detached from the drum


12


, the stripper blade assembly


20


then moves away from the drum and the print medium passes over the blade holder


24


to exit the printer along the medium path


18


. In the detachable configuration to remove the blade holder


24


from the shaft


26


, the flexible eyelet portions


32


are lifted from the protuberances


34


and the body


36


is rotated to clear the connectors


28


. The blade holder


24


is then pulled back from the shaft


26


, disengaging the guide ribs


30


from the shaft, to complete the removal.




The material of the thin blade


22


needs to be flexible, but durable; needs to be compatible with the ink chemistry of the printer, as vapor from the ink is present; and needs to be heat resistant. One such material includes a Mylar/polyester material. The thickness of the material may be 0.005″ to 0.020″. The length of the material is sufficient to engage the entire leading edge of the final print medium, such as 8.75″ for A and A4 size printers. The bend


50


in the thin blade material is formed thermally to provide a smooth bend in order to avoid any sharp edges that might scrape the ink surface of the print medium. Likewise the material of blade holder


24


, which may be a plastic molding, needs to have dimensional stability and be moldable; needs to be compatible with the ink chemistry of the printer; and needs to be heat resistant. Finally the materials of the thin blade


22


and the blade holder


24


need to be compatible with the adhesive


44


used to assure a secure attachment of the thin blade to the blade holder.




Because a continuous surface in the form of the thin blade


22


is presented to the print medium, any resulting load against the printed image is more evenly distributed than with the prior art fingers, and damage to the printed image is minimized. Also due to the continuous surface being laid down on the surface of the drum


12


, the stripper blade assembly


20


is capable of stripping print medium that has been severely damaged. Further because the stripping edge of the thin blade


22


distributes the load along the long edge instead of point loading by small fingers, the damage to the drum


12


is minimal and acceptable. In the unlikely event of a jam, the jam will be easier to clear and will not be as serious as is the case with individual fingers which may shred the medium. Finally the detachability of the blade holder


24


makes access to any jams easier.




Thus the present invention provides a stripper blade assembly


20


for an ink jet offset printer that has a thin blade


22


fixedly attached to a blade holder


24


that in turn may be removably attached to a shaft


26


, which at the appropriate point in the print process engages the drum


12


along its axial length to strip the leading edge of the print medium from the surface of the drum while minimizing damage to the drum or medium and reducing the risk of jams.



Claims
  • 1. A stripper blade assembly for an ink jet printer having an offset drum comprising:a rotatable shaft; and a mechanical connector fixedly attached to the rotatable shaft; a blade holder including a body having a top surface, a bottom surface, and means fixedly mounted to the bottom surface for detachably attaching the body to the mechanical connector; and a thin blade fixedly mounted to the top surface of said body such that, when contacted to the drum at an appropriate point in a print process, the thin blade engages an entire leading edge of a print medium on the offset drum to strip the print medium therefrom; wherein the body further comprises a plurality of ribs, each having a slot, fixedly mounted on the bottom surface for interacting with the rotatable shaft when the body is attached thereto.
  • 2. The stripper blade assembly as recited in claim 1 wherein the body further comprises guide means fixedly attached to the bottom surface to guide the detachably attaching means to interact with the mechanical connector to secure the body on the rotatable shaft.
  • 3. The stripper blade assembly as recited in claim 1 further comprising means for fixedly attaching the thin blade to the top surface of the body.
  • 4. The stripper blade assembly as recited in claim 3 wherein the fixedly attaching means comprises a double sided, sticky tape.
  • 5. The stripper blade assembly as recited in claim 1 wherein the material of the thin blade comprises a Mylar/polyester material.
  • 6. The stripper blade assembly as recited in claim 1 wherein an edge of the thin blade has a thickness between 0.005 and 0.020 inches.
  • 7. The stripper blade assembly as recited in claim 1 wherein the mechanical connector is overmolded onto the rotatable shaft to fixedly attach the mechanical connector to the rotatable shaft.
  • 8. The stripper blade assembly as recited in claim 1 wherein the mechanical connector has a protuberance and the detachably attaching means has a flexible eyelet that snaps over the protuberance to attach the body to the rotatable shaft.
  • 9. The stripper blade assembly as recited in claim 1 wherein the thin blade comprises a thin, rectangular piece of flexible material having a longitudinal leading edge and having a longitudinal bend toward a rear edge opposite the leading edge.
  • 10. The stripper blade assembly as recited in claim 9 wherein the body has a longitudinal ledge corresponding to the longitudinal bend in the thin, rectangular piece of flexible material such that, when the thin, rectangular piece of flexible material is fixedly mounted on the body, the rear edge overhangs the longitudinal ledge to guide the print medium smoothly from the offset drum along a print medium path in the printer.
US Referenced Citations (6)
Number Name Date Kind
4000694 Schroder Jan 1977
4119308 Hamaker Oct 1978
4387981 Cormier Jun 1983
5570775 Kleinhans et al. Nov 1996
5676054 Lubke et al. Oct 1997
5996900 Kawashima Dec 1999