Electrophotography – Image formation – Transfer
Reexamination Certificate
2000-09-01
2001-12-11
Royer, William J. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S316000, C399S317000
Reexamination Certificate
active
06330418
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to a color or monochrome electronic reprographic printing system, and more particularly concerns apparatus for optimizing the contact between paper or other copy media and a photoconductive surface.
In an electrophotographic printing machine, a photoconductive member (often a photoreceptor belt) is charged to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive member is thereafter selectively exposed. Exposure of the charged photoconductive member dissipates the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document being reproduced. After the electrostatic latent image is recorded on the photoconductive member, the latent image is treated with toner particles and is subsequently transferred to a copy sheet. The copy sheet is heated to permanently affix the toner image thereto in image configuration.
Multi-color electrophotographic printing is substantially identical to the foregoing process of black and white printing. However, rather than forming a single latent image on the photoconductive surface, successive latent images corresponding to different colors are recorded thereon. Each single color electrostatic latent image is developed with toner of a color complementary thereto. This process is repeated in a plurality of cycles for differently colored images and their respective complementarily colored toner. Each single color toner image is transferred to the copy sheet in superimposed registration with the prior toner image. Alternately, a plurality of images may be superimposed on the photoreceptor surface, and transferred simultaneously to the sheet. This creates a multi-layered toner image on the copy sheet. Thereafter, the multi-layered toner image is permanently affixed to the copy sheet creating a color copy. The developer material may be a liquid or a powder material.
Surface irregularities in the paper may occur prior to use or during handling. Such irregularities are often caused by exposure to moisture, mishandling, duplexing, etc and create localized deformities in the copy paper. As a result, air gaps may form between the paper and the photoreceptor belt. Such gaps result in poor transfer of toner from the belt to the paper, which may, in turn, cause deletions or distortions in the printed copy. Flipping the paper over, or discarding the old paper and adding fresh paper offer possible solutions to this problem, but require the labor of frequent monitoring. The resulting rotation of paper stock is inherently expensive in paper costs, labor, and down time. Therefore, a means for reducing the need for operator involvement and reducing the amount of paper that is wasted is needed.
A device which applies a force against the back of a sheet and flattens it against the photoreceptor belt is one possible solution to the problem. U.S. Pat. No. 5,247,335, owned by Xerox Corp., describes a machine having such a device. The device described in the '335 patent employs a cam to move a wiper blade against the copy paper to facilitate engagement of the paper and photoreceptor belt.
Another Xerox Corporation patent, U.S. Pat. No. 5,227,852, describes another embodiment of a wiper blade which uses four flexible blade segments, each of which is deflected back away from the photoreceptor belt by solenoid actuated mechanisms. One or more of the solenoids are activated by the passage of a sheet, depending on the paper size being used. Since the blades of these machines are held in a deflected-back state both during standby and between each copy, the blade may tend to take on a permanent set over time, decreasing the force applied. This may result in the degradation in performance, over time, of the blades, and the need to replace the blades frequently.
There remains a need for a device that will provide enhanced contact between a copy sheet and a photoreceptor belt that is reliable and requires little maintenance.
SUMMARY OF THE INVENTION
In the method and apparatus of this invention, a series of wiper blades are provided which are mounted on a common shaft and are spring biased against the paper in operation. The wiper blades are operated individually or in pairs by steeping motors which drive a linkage system to rotate the blades into and out of engagement with the paper. The blades pivot about a common pivot rod which is mounted transverse to the path of the paper. Each blade is equipped with an additional elastic plastic contact edge that is less rigid than the body of the supporting blade segment.
Each blade is fixed to the rod for rotation therewith through a torque spring. The torque spring allows the blade to pivot on the rod through a limited arc of motion. The pivot motion of the blades on the rod is biased by the torque spring towards engagement with the paper. The torque spring thereby provides a gradual and consistent loading of the paper to provide accurate and effective toner transfer when the blades are rotated into engagement.
The actuation mechanism of the blades involves a lever and crank assembly which applies a stepped rotation of a stepping motor to rotate the blades between two positions. All of the blades operate on the same rod and are actuated simultaneously towards and away from engagement with the paper. Depending on the size of the paper, all of the blades may not be necessary to apply uniform pressure to the paper. In order to avoid contamination of the wiper blades with toner and wear to the photoconductor element, a mechanism is needed to select the combination of blades suitable for the particular size paper in process. Accordingly, each of the blades is operatively associated with a decision stop which may be constructed as a cam sector. The cam sector engages a pawl shaped extension on the blade assembly to selectively limit movement of a selected blade against the paper. As the blade rod rotates, the cam sector holds the engaged blade assembly against the torque spring, while the rod continues to rotate to engage the unrestrained blades into contact with the paper. The blade array may consist of multiple pairs of outboard blades and a single central inboard blade to service paper in the required range of sheet widths. In a center registered configuration only the outboard blades would be associated with a stop mechanism. Alternately, the blade array may consist of a single outboard blade and a plurality of inboard blades. In this edge-registered configuration, only the inboard blades would be associated with a stop mechanism.
The cam sector is mounted on a second shaft which is driven by a second stepping motor. The second stepping motor rotates the cam sector between positions which provide the desired range of restraint to the associated blade assembly. The stop stepping motor is controlled by sensors that monitor the size of the paper as it passes through the copier. A separate control actuates the blade motor in response to a sensor which senses the leading edge of the paper prior to its arrival at the photoconductive element. The timing of the stepping motors and their motion may be determined by reference to a table of electronically stored actuation and deactuation timing values. These values are referenced to data regarding blade mechanism position which is acquired from sensors within the blade mechanism, and sheet position, which is acquired either from sensors within the blade mechanism or elsewhere in the paper path.
The invention offers the following advantages:
A large, if not limitless, number of sheet sizes may be accommodated by only two driving members (motors). Previous designs required one driving member for each size accommodated.
A flexible blade tip provides a gentle application of the load and prevents the image from being disturbed when the blade touches down.
The flexible tip also conforms to the photoreceptor belt position, thereby providing a uniform pressure t
Ahl David K.
Gross Robert A.
Kuo Youti
McKeown Douglas
Perman & Green LLP
Royer William J.
Xerox Corporation
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