Sheet feeding or delivering – Feeding – With means to interrupt feeding
Reexamination Certificate
2000-04-19
2003-01-28
Nguyen, Tuan N. (Department: 3653)
Sheet feeding or delivering
Feeding
With means to interrupt feeding
C271S258010, C367S125000
Reexamination Certificate
active
06511064
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to document transports and in particular, to ultrasonic detectors for multiple document feeds.
BACKGROUND OF THE INVENTION
Scanners and copiers use document feeders to transport documents into a machine. Mechanisms used for the transportation of documents, including paper or sheets of other material, have the capacity to accidentally pick up more than one document fed from a stack of documents. It is necessary to determine when more than one document is pulled into a document transport since multiple documents may jam the transport or prevent processing some documents.
There are two general methods for multiple document detection, contact and non-contact. The contact methods include measurement of small thickness changes with a contact foot or sensing arm that is in contact with the documents as they pass through the document transport. The contact foot is connected to a Linear Voltage Differential Transducer (LVDT), or a magnet, which is sensed by a Hall Effect Sensor. These sensors can detect changes in thickness of less than 1 &mgr;m (10
−6
m).
The major disadvantage to the contact method is that anything in contact with moving paper, especially thin paper or ripped paper, can cause a malfunction such as a paper jam. The contact method also requires calibration using the maximum thickness document that will be fed through the document transport. When a thickness is measured which is above the calibration value plus a threshold, typically 30%, it is determined to be a multiple document feed. This method, however, will only work when documents having a uniform thickness are processed. Using a wheel on the end of the contact foot can reduce the chances of paper jam, however, the variations in the diameter of this wheel, due to the nonconformity's in manufacturing, must be taken into account during the measurements, which further complicates the measurement.
The primary non-contact method for multiple document detection sends ultrasound signals through the document stream to determine if more than one document is present. Sending ultrasound 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. This method is independent of the thickness of the individual documents and is made without making contact with these documents.
A typical contact document scanner is able to detect about 94% of the test multiple documents. An attenuation detector that was tested was only able to detect about 86% of these same test multiple documents, thus there is an opportunity for improvement using ultrasound detection.
For detecting multiple documents by attenuation methods, the performance improves as higher frequency transmitters and receivers are used. Unfortunately, the cost of these components also increases with frequency. There is also a limited range of paper thicknesses that can be properly detected. Therefore, the attenuation method alone is not suitable for multiple document detection.
The phase shift of ultrasound signal passing through documents has been used to detect multiple document feeds. See U.S. Pat. No. 4,066,969 which is herein incorporated by reference. Unfortunately, using phase shift is not reliable since multiple documents may cause phase shifts greater than 360 degrees. For detecting multiple documents by phase methods, the performance decreases at higher frequencies because the wavelength is shorter and the method becomes more sensitive to signal variations.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved method and apparatus for multiple document detection, which is both accurate and relatively inexpensive.
An apparatus for multiple document detection in accordance with an embodiment of the present invention includes a signaling system and an analyzer. The signaling system transmits a signal to and receives the signal from a document feed which comprises one or more documents. The analyzer determines if the document feed comprises two or more of the documents in response to a phase shift and an amplitude change between the transmitted signal and the received signal.
A method for determining the presence of multiple documents in accordance with another embodiment of the present invention includes the following steps. An ultrasonic signal is transmitted through a document feed comprising one or more documents. The ultrasonic signal is received after it has passed through the document feed. A phase of the transmitted signal and a phase of the received signal are compared to provide a first information signal. An amplitude of the transmitted signal and an amplitude of the received signal are compared to provide a second information signal. The first and second information signals are analyzed to determine if the document feed comprises two or more of the documents.
An apparatus in accordance with another embodiment of the present invention includes a document processing system and a multiple document detection system. The document transports system supplies at least one document feed comprising one or more documents to the document processing system. The multiple document detection system determines if the document feed comprises two or more of the documents based on a phase shift and an amplitude change between a signal transmitted to and received from the document feed.
This invention uses both phase shift and amplitude variation of ultrasound passed through a document stream to determine the presence of multiple documents. By using both phase and the amplitude changes of the received ultrasound, the presence of multiple documents can be detected more reliably than is possible by using phase detection alone or amplitude detection alone.
Another advantage of the present invention is that the phase and amplitude changes in the received signal can be determined without physically contacting the paper. As a result, this invention will cause less document jams than direct contact methods.
Another advantage of this invention is that a transmitter and receiver that is used for phase shift and amplitude detection will be less expensive than for the same equipment used for detecting each separately. Additionally, the invention is able to use a low frequency transmitter and receiver, which is low cost, is less sensitive to variations in document thickness, and is able to detect a larger range of paper thickness.
The invention and its objects, various features, and advantages will become more apparent from the detailed description of the preferred embodiment presented below.
REFERENCES:
patent: 4066969 (1978-01-01), Pearce et al.
patent: 4368438 (1983-01-01), Stienstra
patent: 5023846 (1991-06-01), Busch-Sorensen
patent: 6145376 (2000-11-01), Elgee
patent: 6212130 (2001-04-01), Brazeal, Jr. et al.
Phinney Daniel P.
Pultorak David M.
Titus Albert H.
Eastman Kodak Company
Nelson Adrian Blish
Nguyen Tuan N.
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