Electrophotography – Document handling – Copy
Reexamination Certificate
2002-07-23
2003-12-23
Chen, Sophia S. (Department: 2852)
Electrophotography
Document handling
Copy
C399S390000, C162S197000, C162S270000, C250S559010, C356S445000
Reexamination Certificate
active
06668155
ABSTRACT:
Disclosed is a relatively low cost, simple, and non-contacting system for detecting or measuring either or both lead edge and trail edge curl of sheets, especially, print media sheets moving in a conventional paper transport path, which is easily mounted to conventional such sheet transport paths, and is fast enough in operation to provide “real time” measurement data which may be used to provide “on line” automatic control of various automatic sheet decurling systems.
Disclosed in the embodiment herein is an improved system for measuring the amount of curl of an edge of a print media sheet moving through a printer or other media handling system. The disclosed system provides a novel optical reflectivity sensing system for providing an electrical output signal responsive to the curl of the paper or other sheet passing a relatively simple optical sensor in a sheet transport path with relatively uncritical confinement of the sheet being measured.
The disclosed sheet curl sensing system embodiment is thus particularly suitable for the implementation of a “closed loop” curl detection plus curl correction system, by providing a more accurate curl detection signal in a high speed, on line manner, and without needing to contact the paper. Furthermore, this may be accomplished even though there is ink, toner, or other imaging material on the curled edge of the sheet, or with different color sheets. Further disclosed in the embodiment herein are displacement insensitive optics for this measurement, to render less critical the position of the sheet relative to the sensor, and thus allow more accurate sheet curl measurements to be made in various different normal, relatively unconfined, sheet transport paths.
In addition to the optional use of the curl detection signal of the disclosed sheet curl detector to control an automatic, (e.g., variable penetration roller depth) mechanical sheet decurler, the curl detection signal may also be optionally used additionally or separately to control an automatic remoisturizer in the same paper path, such as between the fuser and the output tray, to remoisturize the sheet and thereby automatically additionally or alternatively reduce detected sheet curl.
The curling of print media sheets is a particular problem in the printing industry. It is exacerbated by high-density images and plural color printing. However, sheet curling can occur even for unprinted sheets of paper with changes in the ambient humidity or moisture content of the paper. Sheet curl can interfere with proper sheet feeding, causing sheet feeding jams or delays. If sheet curl is present in the output it can interfere with proper stacking or other finishing operations of the sheets. For example, if printed sheets with curl do not lie flat when stacked together in sets, such as in the pages of booklets, an objectionable distortion of the booklet may result.
Furthermore, the amount of moisture in the sheet of paper can drastically change from the printing process itself, to cause or exacerbate curl. In particular, from water-based ink jet printing or the thermal fusing operation for toners in xerographic printing, and particular from high density image printing near the edges of a sheet. There is a further sheet curl problem in duplex printing, where the sheets are re-fed or recirculated for printing imaging material on their second sides, especially if that involves a second pass of the sheet through a thermal fuser and/or higher density images on one side than the other.
It is known to use decurlers with adjustable amounts of sheet decurling in the output of printers to at least partially correct or compensate for sheet curl. Some examples of automatic or manually adjusted sheet decurling systems include Xerox Corporation U.S. Pat. Nos.: 5,392,106; 5,515,152; 5,519,481; 5,539,511; 5,565,971; 5,848,347; 6,003,864; and 6,314,268. Note that while, for example, said U.S. Pat. No. 5,539,511 does not explicitly identify a control signal, it describes variable position decurling rollers with a position controlled by solenoid, screw drive, etc., according to the amount of expected sheet curl.
Sheet remoisturizing systems are another alternative or additional known means for reducing sheet curl. Some examples of Xerox Corporation Patents on sheet remoisturizing or wetting systems include U.S. Pat. Nos.: 5,264,899; 5,850,589; 5,920,751; and 6,094,560 (the later also including decurling).
It would be particularly desirable to provide a more automatic, rather than manual, control of the appropriate amount of decurling force or deformation and/or remoisturizing of individual sheets as they are being outputted, for better sheet flattening before the sheet output, for improved stacking and/or finishing. The disclosed embodiment, as illustrated, can provide an electrical output control signal proportional to the amount of detected curl of individual sheets upstream of an automatic sheet decurler and/or remoisturizer to provide such a control thereof.
However, the disclosed exemplary sheet curl detection system is not limited to that particular application. Other applications will be apparent to those skilled in the printing or other sheet handling arts. For example, a system of automatically diverting (with a sheet path gate to a “purge” tray output) a sheet detected as having an amount of curl above a safe sheet feeding level, in order to avoid Is potential sheet jams in downstream sheet transport paths, imaging stations or finishing operations.
Of particular interest as to the disclosed sheet displacement insensitive optics of the embodiment herein is Xerox Corporation U.S. Pat. No. 6,384,918 B1 issued May 7, 2002 to Fred F. Hubble, III, et al., and the related disclosure in Xerox Corporation U.S. Pat. No. 6,351,308 B1 issued Feb. 26, 2002 to L. K. Mestha, and pending Xerox Corporation U.S. application Ser. No. 09/862,945, filed May 22, 2001 by the same Fred F. Hubble, III, et al.
The present system should be distinguished from previous systems for detecting the position of the edge of a document with optical detectors and angled illumination to form edge shadows, such as Xerox Corporation U.S. Pat. Nos. 5,847,405 and 5,859,440. Likewise, the present system should be distinguished from photoelectric transmissive paper basis weight thickness or density measurement devices, such as Xerox Corporation U.S. Pat. No. 5,138,178.
A specific feature of the specific embodiment disclosed herein is to provide a sheet curl sensing system for sensing the curl of a sheet moving in a movement direction in a sheet transport path, comprising an unobstructing non-contacting optical sheet curl sensor having a first sheet illuminator mounted to illuminate a portion of the moving sheet at an angle in a direction substantially parallel to said movement direction, a second sheet illuminator mounted to illuminate a portion of the moving sheet at an angle in a direction substantially transverse to said movement direction, and a photodetector system positioned to sense said illumination of the moving sheet by both said first and second sheet illuminators as said illumination is reflected approximately perpendicularly from said illuminated portion of the moving sheet and to provide variable output control signals in response to said sensed reflected illumination level.
Further specific features disclosed in the embodiment herein, individually or in combination, include those wherein said variable output control signals in response to said sensed reflected illumination are a ratio of the output control signals from said photodetector system produced by said first and second sheet illuminators; and/or an automatic sheet decurling system comprising a variable sheet decurler and/or re-moisturizer controlled by output control signals from an unobstructing non-contacting optical sheet curl sensor sensing the curl of a sheet moving in a movement direction in a sheet transport path towards said decurler and/or re-moisturizer, said optical sheet curl sensor comprising an unobstructing non-contacting optical sheet curl sensor having a
Hubble, III Fred F.
Love Tonya L.
Robbins Daniel A.
Wallace Stanley J.
Chen Sophia S.
Xerox Corporation
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