Communications – electrical: acoustic wave systems and devices – Echo systems – Presence or movement only detection
Reexamination Certificate
1999-03-08
2001-04-03
Mullen, Thomas (Department: 2736)
Communications, electrical: acoustic wave systems and devices
Echo systems
Presence or movement only detection
C271S258010, C340S674000
Reexamination Certificate
active
06212130
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the movement of documents, for purposes of capturing an image thereof, and particularly to the detection of the presence of overlapping sheets on a transport. More specifically, this invention is directed to a sensor for detecting the presence of multiple layers of sheet material, paper bearing printed indicia for example, and especially to an acoustic device for discriminating between single and plural moving thin sheets which are in surface contact. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Related Art
In the processing of documents, for example for image capture pursuant to “machine reading”, economic considerations dictate that the indicia bearing thin sheets be serially delivered to an image capture station at a high document through-put rate. The documents to be processed are customarily stacked in a magazine and individual sheets are extracted from the stack and delivered to a transport such as a vacuum conveyor. As a result of ambient operating conditions and phenomena such as electrostatic attraction and friction, multiple documents are sometimes substantially simultaneously extracted from a magazine and deposited on the transport in partial overlapping relationship or in registration with one another. The most common type of such a delivery failure is a double document feed. If the multiple fed documents are in registration, the image of the lowermost document in the viewing direction will not be captured and, accordingly, important data will not be read and processed. If the multiple fed documents are partially overlapped, the end result is that the image of neither document will be captured, a feed failure will likely result and operator intervention will be required. Obviously, the former condition, i.e., registration of multiple documents, is the more insidious problem since it is less likely of the two feed failure modes to be noticed.
Various attempts have been made to detect the presence of multiple, i.e., overlapping, documents on a paper transport. The prior approaches to solving this long standing problem have embodied optical and capacitive measurement techniques. The prior approaches, however, have been too slow and/or lacking in sensitivity, unable to operate with invariance to sheet thickness or combinations of thickness and/or unable to operate with invariance to print color or print density.
SUMMARY OF THE INVENTION
The present invention overcomes the above briefly-discussed and other deficiencies and disadvantages of the prior art and, in so doing, provides a novel and reliable acoustic technique for detection of the presence of multiple thin sheets on a moving conveyor. This invention also encompasses a novel detector for implementing the aforementioned acoustic technique.
In accordance with the present invention, the acoustic equivalent of a Fabry-Perot interferometer is implemented. In a preferred embodiment, a pair of acoustic transducers are respectively arranged as a signal transmitter and receiver located on opposite sides of the document transport path. The transducers are oriented to define a signal transmission path, having an axis, for a short wavelength acoustic signal. The axis of this acoustic signal transmission path is oriented at a small angle (about 15° to 30°) with respect to the plane of the document transport path. The receiver transducer detects low level acoustic signals, the transmitter transducer radiating such signals as energy bursts. Received signals having a magnitude in excess of a preset threshold are commensurate with the presence of not more than a single sheet of paper disposed between the transmitter and receiver transducers. Multiple sheets disposed between the transmitter and receiver transducers will function as an acoustic interference filter and cause the magnitude of the acoustic energy incident upon the receiver transducer to fall below the threshold, i.e., the signal attenuation produced by the interference filter is much greater than the attenuation produced by one sheet multiplied by the number of sheets which are present. This large drop in acoustic signal transmittance is detected and provides a reliable indication of the occurrence of a misfeed.
REFERENCES:
patent: 4066969 (1978-01-01), Pearce et al.
patent: 4368438 (1983-01-01), Stienstra
patent: 5005192 (1991-04-01), Duss
patent: 5348286 (1994-09-01), Buck
patent: 36 20 042 A1 (1987-08-01), None
patent: 0033552 A1 (1981-12-01), None
Brazeal, Jr. Earl H.
Callahan James D.
Soussounis James M.
Stone David H.
Alix Yale & Ristas, LLP
Mullen Thomas
Scan-Optics Inc.
LandOfFree
Method and apparatus for plural document detection does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for plural document detection, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for plural document detection will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2457200