TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to document transports, and more particularly to a
detector for detecting multiple feed sheets.
BACKGROUND OF THE INVENTION
[0002] For efficient document processing along a document transport, a preferred method
of feeding documents into the transport is via an automated document feeder. On occasions,
however, an automated document feeder may feed more than one document at a time. In
the event that more than one document is fed, there is a need to detect that "doubles"
or multiple documents are present.
[0003] One system for detecting multiple feed documents is by measuring the thickness of
the document. However, in applications of feeding a mixture of different types of
documents, measuring the thickness of the documents is not a viable solution. Also,
a thickness detector is a contact method of sensing multiple documents and has a disadvantage
that paper jams can result. The contact method also requires calibration using the
maximum thickness document that will be fed through the document transport.
[0004] Another device for detecting multiple feed documents is utilizing a vacuum system.
In a vacuum system, detection of multiple feed documents of different thicknesses
is possible. A vacuum system is fairly reliable; however, the vacuum sensors must
be placed in close proximity to each side of the document in order to detect multiple
feed documents. A vacuum is placed on both sides of the document path. If a single
item is fed, then that item blocks only one vacuum. If two or more documents are fed
simultaneously, then both vacuums are blocked. For an open track document transport,
the use of a vacuum doubles detect system is not desirable. In an open track document
transport, a doubles detection system must not interfere with the open track design.
[0005] Another contact device for detecting sheet doubles utilizes rollers on each side
of the document path and the rotation of the rollers is monitored, such as in a magnetic
clutch and roller device. One roller, or a set of rollers is controlled by a drive
mechanism. The opposing roller or set of rollers, is connected to a mechanical clutch
and the speed of this roller set is controlled by contact with the driven rollers,
or the documents that pass between them. If a single item is passed between this type
of detector, then the opposing rollers will match the speed of the driven roller and
no multiple sheets are detected. If two or more sheets are fed simultaneously through
the device, then the magnetic brake will cause slippage between the multiple sheets,
creating a speed mis-match between the opposing rollers and the driven rollers. Detection
of doubles is then realized. However, where a chemical reaction occurs between laser
printed items and carbonless coatings, known as "sticky checks", the multiple items
are glued together, and slippage between the items is not likely to occur. Therefore,
a magnetic clutch and roller device is not itself a reliable device for detecting
doubles.
[0006] A non-contact device for multiple document detection utilizes ultrasound signals
which pass through the document to determine if more than one document is present.
Sending ultrasound waves through paper results in attenuation of the ultrasound signal.
It is possible to determine the presence of multiple documents by the change in attenuation
of the signal received. An ultrasound detector is independent of the thickness of
the individual documents and detection made without making contact with these documents.
A continuously transmitted sonic wave causes vibrations in the first sheet which is
then transmitted via the intervening air to the second sheet, which also begins to
vibrate. The receiver unit of an ultrasonic detection system is able to detect these
weakened signals via the air. While an ultrasonic multiple document detector can accurately
detect doubles even if the documents are stuck together, a disadvantage of such detectors
is that the apparatus will register a false positive when items such as envelopes
are fed. Also the presence of folded corners, sometimes known as "dog ears", will
yield a false positive.
[0007] A need has arisen for a document doubles detection system.
SUMMARY OF THE INVENTION
[0008] In accordance with the present invention, a multiple feed document detection system
for use with a document transport for detecting the presence of multiple documents
is provided. The system utilizes multiple doubles detection devices wherein each device
detects the presence of doubles. The output signals of each device are applied to
a comparator which compares the signals obtained from each device. If each device
indicates the presence of doubles, then the comparator provides an output that multiple
sheets are present. The present system thereby eliminates the reading of false doubles
by the comparison of the output signals from two or more doubles detection devices.
BRIEF DESCRIPTION OF THE DRAWING
[0009] For a more complete understanding of the present invention and for further advantages
thereof, reference is now made to the following Description of the Preferred Embodiments
taken in conjunction with the accompanying Drawing which is a block diagram of the
present system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0010] Referring to the Figure, the present multiple sheet detection system is illustrated,
and is generally identified by the numeral 10. System 10 includes an ultrasonic detection
device 12 which provides a first output signal 14 indicating the presence of multiple
sheets and a second output signal 16 indicating that no multiple sheets are detected.
Ultrasonic detection device 12 may include, for example, devices described and shown
in
U.S. Patent Nos. 4,066,969 and
6,511,064, which descriptions are hereby incorporated by reference. Signals 14 and 16 are applied
to a comparator 18 whose operation will be subsequently described.
[0011] Detection system 10 further includes a magnetic clutch and roller detection device
20. Detection device 20 generates a first signal 22 indicating the presence of multiple
documents, and a second signal 24 indicating that no multiple documents are present.
Signals 22 and 24 are applied to comparator 18. Clutch and roller detection device
20 may comprise, for example, the device described and shown in
U.S. Patent Application Serial No. 10/962,739 filed October 12, 2004, which description is hereby incorporated by reference.
[0012] Detection system 10 further includes a sheet thickness detection device 30. Detection
device 30 generates a first output signal 32 indicating the presence of multiple documents,
and a second output signal 34 indicating that no multiple documents are present. Signals
32 and 34 are applied to comparator 18. Detection device 30 may comprise, for example,
a device such as that described in
U.S. Patent No. 5,204,537, which disclosure is hereby incorporated by reference.
[0013] A fourth doubles detection device is included within detection system 10 and includes
a vacuum sheet separator detection device 40. Vacuum detection device 40 applies a
vacuum to both sides of a document transport and generates a first output signal 42
indicating the presence of multiple documents, and a second signal 44 indicating that
no document doubles are present. Signals 42 and 44 are applied to comparator 18.
[0014] Comparator 18 receives the output signals of each detection device 12, 20, 30 or
40 utilized within detection system 10. Comparator 18 functions to generate a multiple
sheet present signal 52 or a multiple sheet not present signal 54. Comparator 18 functions
to determine whether two or more first signals generated by a detection device 12,
20, 30 or 40 are present. The presence of two document doubles signals are required
in order to generate a multiple sheet present signal 52. Because detection system
10 utilizes two or more detection devices 12, 20, 30 or 40, a false doubles indication
by one detection device will not result in a multiple sheet present signal. For example,
when an envelope passes through ultrasonic detection device 12, first signal 14 will
typically be generated, but will be a false doubles indication. When utilizing detection
device 10 with a thickness detection device 30, where no doubles detection occurs
for the envelope, since the output of the thickness device 30 will produce signal
34, the output of comparator 18 will indicate that multiple sheets are not present
by generating signal 54. System 10 may utilize any combination of detection devices
12, 20, 30 or 40, so long as two or more devices are utilized in order to compare
the data output of each detection device with that of another detection device.
[0015] Other alteration and modification of the invention will likewise become apparent
to those of ordinary skill in the art upon reading the present disclosure, and it
is intended that the scope of the inventions disclosed herein be limited only by the
broadest interpretation of the appended claims to which the inventors are legally
entitled.
1. A system for detecting the presence of multiple sheets moving along a path, the system
comprising:
a first doubles detection device disposed at a first position along the path, said
first doubles detection device generating a first output signal upon detection of
multiple sheets and a second output signal upon detection of a single sheet at the
first position;
a second doubles detection device disposed at a second position along the path, said
second doubles detection device generating a first output signal upon detection of
multiple sheets and a second output signal upon the detection of a single sheet at
the second position; and
a comparator for receiving said output signals of said first and said second doubles
detection devices and for generating an output signal indicating the presence of multiple
documents along the path when said first output signal of said first doubles detection
device and said first output signal of said second doubles detection device are present.
2. The system of claim 1 wherein said first doubles detection device includes an ultrasonic
detection device.
3. The system of claim 2 wherein said second doubles detection device includes a clutch
and roller detection device.
4. The system of claim 2 wherein said second doubles detection device includes a thickness
detection device.
5. The system of claim 2 wherein said second doubles detection device includes a vacuum
detection device.
6. A system for detecting the presence of multiple sheets moving along a path, the system
comprising:
an ultrasonic detection device disposed at a first position along the path, said ultrasonic
doubles detection device generating a first output signal upon detection of multiple
sheets and a second output signal upon detection of a single sheet at the first position;
a first doubles detection device disposed at a second position along the path, said
first doubles detection device generating a first output signal upon detection of
multiple sheets and a second output signal upon detection of a single sheet at the
second position;
a second doubles detection device disposed at a third position along the path, said
second doubles detection device generating a first output signal upon detection of
multiple sheets and a second output signal upon the detection of a single sheet at
the third position; and
a comparator for receiving said output signals of said ultrasound detection device
and said first and said second doubles detection devices and for generating an output
signal indicating the presence of multiple documents along the path when said first
output signals of said doubles detection devices are present.
7. The system of claim 6 wherein said first doubles detection device includes a thickness
detection device and said second doubles detection device includes a clutch and roller
detection device.
8. The system of claim 6 wherein said first doubles detection device includes a thickness
detection device and said second doubles detection device includes a vacuum detection
device.
9. The system of claim 6 wherein said first doubles detection device includes a clutch
and roller detection device and said second doubles detection device includes a vacuum
detection device.