Patent Grant
7025348
This invention relates in general to using multiple detectors for sensing multiple document feeds or small documents overlapped with larger documents.
Scanners and copiers use document feeders to transport documents into the 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. In many cases, the documents fed into the scanner are different sizes. Some smaller documents may be located on one side of a document feed path and not pass under a single position sensor.
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 μm (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 in manufacturing, must be taken into account during the measurements.
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 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.
There are currently ultrasonic detection system available, which use high frequency sensors to sense multiple zones within a local area. This approach works because the sensors are directional, and the signal from one sensor does not interfere with the signal from other sensors. However, these sensors are also more expensive. Low cost sensors have a wide angle of energy emitted, and if used, the sensors can interfere with each other (cross-talk). The interference often causes the design to fail. The problem cannot be solved by multiplexing individual pulses to the emitters, because not enough energy will be sent by the detector and the time phasing of the signal is not stable.
U.S. Pat. No. 6,212,130 uses a tilted ultrasonic sensor. This could be used in multiple locations but the cost would be significant, using the more expensive directional high frequency sensors.
The present invention provides an improved method and apparatus for multiple document detection, which is both accurate and relatively inexpensive, over a wide area. The interference between the sensors is limited by allowing only one transmitter and receiver pair to be on at once.
Briefly, according to one aspect of the present invention an apparatus for detection of multiple documents in a document transport system comprises a first transmitter emitting a first signal at a first interval through a document feed path. A first sensor detects the first signal from the first transmitter. A second transmitter emits a second signal at a second interval through the document feed path. A second sensor detects the second signal from the second transmitter.
An aspect of the present invention is maintaining the phase signal from the sensors stable when being turned on and off by applying multiple cycles to the transmitter. In one embodiment of the invention, 100 cycles of the emitting frequency creates almost the same amount of energy as a continuously operational sensor. By transmitting multiple cycles of the transmitter and then multiplexing those times between sensors, multiple sensors may be used to reliably sense documents. Signal from the active sensor can then be sampled at specific times, when the other sensors are turned off. Therefore, these sensors may be multiplexed reliably and used to sense multiple zones for multiple document detection.
The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below.
The present invention will be directed in particular to elements forming part of, or in cooperation more directly with the apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.
Referring now to
The ultrasonic receiver 16 converts the received ultrasonic signal into an electrical signal. The electronic signal is sent to a demultiplexer 19 and then supplied to an input to a phase comparator 20 wherein the phase difference between the drive signal and the electronic signal is determined. An information signal 50 which represents the determined phase difference is fed from phase comparator 20 to a microprocessor 21.
The microprocessor 21 checks the appropriate information signal, after about 100 cycles, to determine if multiple documents are present based on the resulting phase shift or difference between the drive signal and the electronic signal. The microprocessor 21 switches to a different set of transmitters and receivers, for example transmitter 17 and receiver 18, and repeats the process continuously between the sets. In a similar fashion, the microprocessor 21 checks for double document feed between transmitter 13 and receiver 14. In this embodiment only one set of transmitters and receivers are energized at any particular time, although other sequencing schemes are possible.
Although a microprocessor 21 is shown, other types of processors or programmable devices can also be used. Additionally, although in this particular example, an ultrasonic signal is used in this apparatus, other types of signals can also be used.
Referring now to
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.
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