Electrophotographic copying apparatus including transfer hold-down pump
First Claim
1. In an electrophotographic copying apparatus in which electrically charged toner of one polarity is transferred from an oppositely electrically charged surface of a photoconductive drum to the front side of a blank sheet for transforming said front side of the blank sheet into an intended copy as the back side of the blank sheet engages the surface of a transfer drum positioned adjacent said photoconductive drum, the transfer of toner occurring within a transfer nip defned by said photoconductive drum and said transfer drum, the improvement comprisinga cam rotating in a timed sequence relative to said transfer drum,a vacuum pump located adjacent said transfer drum and actuated by said cam and in communication with the surface of said transfer drum to create a vacuum at said back side of the blank sheet, whereby said paper is held to the surface of said transfer drum by ambient air pressure and said vacuum, overcoming the electrostatic attraction of the blank sheet to said photoconductive drum.
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Accused Products
Abstract
An electrophotographic copying apparatus has an electrically charged toner of one polarity which is transformed from an oppositely electrically charged surface of a photoconductive drum to the front side of a blank sheet where the front side of the blank sheet is intended to be a copy. The back side of the blank sheet engages the outer surface of a transfer drum which is positioned adjacent to the photoconductive drum. The transfer of the toner occurs within a nip defined by the photoconductive drum and the transfer drum. A cam rotates in a timed sequence relative to the transfer drum and with a vacuum pump located adjacent to the transfer drum the cam is in communication with the surface of the transfer drum so that a vacuum is created at the back side of the blank sheet resulting in the blank sheet being held to the surface of the transfer drum by ambient air pressure and the vacuum thus overcoming the electrostatic attraction of the blank sheet to the photoconductive drum.
23 Citations
14 Claims
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1. In an electrophotographic copying apparatus in which electrically charged toner of one polarity is transferred from an oppositely electrically charged surface of a photoconductive drum to the front side of a blank sheet for transforming said front side of the blank sheet into an intended copy as the back side of the blank sheet engages the surface of a transfer drum positioned adjacent said photoconductive drum, the transfer of toner occurring within a transfer nip defned by said photoconductive drum and said transfer drum, the improvement comprising
a cam rotating in a timed sequence relative to said transfer drum, a vacuum pump located adjacent said transfer drum and actuated by said cam and in communication with the surface of said transfer drum to create a vacuum at said back side of the blank sheet, whereby said paper is held to the surface of said transfer drum by ambient air pressure and said vacuum, overcoming the electrostatic attraction of the blank sheet to said photoconductive drum.
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9. In an electrophotographc copying apparatus in which electrically charged toner of one polarity is transferred from an oppositely electrically charged surface of a photoconductive drum to the front side of a blank sheet for transforming said front side of the blank sheet into an intended copy as the back side of the blank sheet engages the surface of a transfer drum positioned adjacent said photoconductive drum, the transfer of toner occurring within a transfer nip defined by the photoconductive drum and said transfer drum, the improvement comprising
vacuum means for providing a vacuum to a row of holes aligned in a row across the surface of said transfer drum substantially perpendicular to the direction of travel of the blank sheet to attract the blank sheet to said transfer drum, and timing means for controlling said vacuum means in at least three stages of operation, a first stage providing a sharply increasing vacuum, a second stage providing a slowly increasing vacuum, and a third stage for releasing said vacuum and returning said timing means to its initial position.
Specification