Method and Apparatus for Document Identification

Other objects and advantages of the invention will become apparent upon reading the following detailed description in conjunction with the drawings in which:

FIG. 1 is a functional block diagram illustrating a currency discriminating system having a single scanhead;

FIG. 2A is a diagrammatic perspective illustration of the successive areas scanned during the traversing movement of a single bill across an optical sensor according to a preferred embodiment of the present invention;

FIG. 2B is a perspective view of a bill and a preferred area to be optically scanned on the bill;

FIG. 2C is a diagrammatic side elevation view of the scan area to be optically scanned on a bill according to a preferred embodiment of the present invention;

FIG. 3A is a block diagram illustrating a preferred circuit arrangement for processing and correlating reflectance data according to the optical sensing and counting technique of this invention;

FIG. 3B is a block diagram illustrating a circuit arrangement for producing a reset signal;

FIG. 4 is a top view of a bill and size determining sensors according to a preferred embodiment of the present invention;

FIG. 5 is a top view of a bill illustrating multiple areas to be optically scanned on a bill according to a preferred embodiment of the present invention;

FIG. 6A is a graph illustrating a scanned pattern which is offset from a corresponding master pattern;

FIG. 6B is a graph illustrating the same patterns of FIG. 6A after the scanned pattern is shifted relative to the master pattern;

FIG. 7 is a side elevation of a multiple scanhead arrangement according to a preferred embodiment of the present invention;

FIG. 8 is a side elevation of a multiple scanhead arrangement according to another preferred embodiment of the present invention;

FIG. 9 is a side elevation of a multiple scanhead arrangement according to another preferred embodiment of the present invention;

FIG. 10 is a side elevation of a multiple scanhead arrangement according to another preferred embodiment of the present invention;

FIG. 11 is a top view of a staggered scanhead arrangement according to a preferred embodiment of the present invention;

FIG. 12A is a top view of a linear array scanhead according to a preferred embodiment of the present invention illustrating a bill being fed in a centered fashion;

FIG. 12B is a side view of a linear array scanhead according to a preferred embodiment of the present invention illustrating a bill being fed in a centered fashion;

FIG. 13 is a top view of a linear array scanhead according to another preferred embodiment of the present invention illustrating a bill being fed in a non-centered fashion;

FIG. 14 is a top view of a linear array scanhead according to another preferred embodiment of the present invention illustrating a bill being fed in a skewed fashion; and

FIGS. 15A and 15B are a flowchart of the operation of a currency discrimination system according to a preferred embodiment of the present invention.

According to a preferred embodiment of the present invention, multiple scanheads per side are used to scan a bill. Nonetheless, before explaining such a multiple head scanner, the operation of a scanner having a single scanhead is first described. In particular, a currency discrimination system adapted to U.S. currency is described in connection with FIGS. 1-3. Subsequently, modifications to such a discrimination system will be described in obtaining a currency discrimination system in accordance with the present invention. Furthermore, while the preferred embodiments below entail the scanning of currency bills, the system of the present invention is applicable to other documents as well. For example, the system of the present invention may be employed in conjunction with stock certificates, bonds, and postage and food stamps.

Referring now to FIG. 1, there is shown a functional block diagram illustrating a currency discriminating system having a single scanhead. The system 10 includes a bill accepting station 12 where stacks of currency bills that need to be identified and counted are positioned. Accepted bills are acted upon by a bill separating station 14 which functions to pick out or separate one bill at a time for being sequentially relayed by a bill transport mechanism 16, according to a precisely predetermined transport path, across scanhead 18 where the currency denomination of the bill is scanned and identified. Scanhead 18 is an optical scanhead that scans for characteristic information from a scanned bill 17 which is used to identify the denomination of the bill. The scanned bill 17 is then transported to a bill stacking station 20 where bills so processed are stacked for subsequent removal.

The optical scanhead 18 of FIG. 1 comprises at least one light source 22 directing a beam of coherent light downwardly onto the bill transport path so as to illuminate a substantially rectangular light strip 24 upon a currency bill 17 positioned on the transport path below the scanhead 18. Light reflected off the illuminated strip 24 is sensed by a photodetector 26 positioned directly above the strip. The analog output of photodetector 26 is converted into a digital signal by means of an analog-to-digital (ADC) convertor unit 28 whose output is fed as a digital input to a central processing unit (CPU) 30.

While scanhead 18 of FIG. 1 is an optical scanhead, it should be understood that it may be designed to detect a variety of characteristic information from currency bills. Additionally, the scanhead may employ a variety of detection means such as magnetic, optical, electrical conductivity, and capacitive sensors. Use of such sensors is discussed in more detail U.S. patent application Ser. No. 08/219,093 filed on Mar. 29, 1994 for a "Currency Discriminator and Authenticator", now abandoned and incorporated herein by reference.

Referring again to FIG. 1, the bill transport path is defined in such a way that the transport mechanism 16 moves currency bills with the narrow dimension of the bills being parallel to the transport path and the scan direction. Alternatively, the system 10 may be designed to scan bills along their long dimension or along a skewed dimension. As a bill 17 moves on the transport path on the scanhead 18, the coherent light strip 24 effectively scans the bill across the narrow dimension of the bill. As depicted, the transport path is so arranged that a currency bill 17 is scanned by scanhead 18 approximately about the central section of the bill along its narrow dimension, as shown in FIG. 1. The scanhead 18 functions to detect light reflected from the bill as it moves across the illuminated light strip 24 and to provide an analog representation of the variation in light so reflected which, in turn, represents the variation in the dark and light content of the printed pattern or indicia on the surface of the bill. This variation in light reflected from the narrow dimension scanning of the bills serves as a measure for distinguishing, with a high degree of confidence, among a plurality of currency denominations which the system of this invention is programmed to handle.

A series of such detected reflectance signals are obtained across the narrow dimension of the bill, or across a selected segment thereof, and the resulting analog signals are digitized under control of the CPU 30 to yield a fixed number of digital reflectance data samples. The data samples are then subjected to a digitizing process which includes a normalizing routine for processing the sampled data for improved correlation and for smoothing out variations due to contrast fluctuations in the printed pattern existing on the bill surface. The normalized reflectance data so digitized represents a characteristic pattern that is fairly unique for a given bill denomination and provides sufficient distinguishing features among characteristic patterns for different currency denominations. This process is more fully explained in U.S. patent application Ser. No. 07/885,648, filed on May 19, 1992, now issued as U.S. Pat. No. 5,295,196 for a "Method and Apparatus for Currency Discrimination and Counting," which is incorporated herein by reference in its entirety.

In order to ensure strict correspondence between reflectance samples obtained by narrow dimension scanning of successive bills, the initiation of the reflectance sampling process is preferably controlled through the CPU 30 by means of an optical encoder 32 which is linked to the bill transport mechanism 16 and precisely tracks the physical movement of the bill 17 across the scanhead 18. More specifically, the optical encoder 32 is linked to the rotary motion of the drive motor which generates the movement imparted to the bill as it is relayed along the transport path. In addition, the mechanics of the feed mechanism (not shown, see U.S. Pat. No. 5,295,196 referred to above) ensure that positive contact is maintained between the bill and the transport path, particularly when the bill is being scanned by scanhead 18. Under these conditions, the optical encoder 32 is capable of precisely tracking the movement of the bill 17 relative to the light strip 24 generated by the scanhead 18 by monitoring the rotary motion of the drive motor.

The output of photodetector 26 is monitored by the CPU 30 to initially detect the presence of the bill underneath the scanhead 18 and, subsequently, to detect the starting point of the printed pattern on the bill, as represented by the thin borderline 17A which typically encloses the printed indicia on currency bills. Once the borderline 17A has been detected, the optical encoder 32 is used to control the timing and number of reflectance samples that are obtained from the output of the photodetector 26 as the bill 17 moves across the scanhead 18 and is scanned along its narrow dimension.

The use of the optical encoder 32 for controlling the sampling process relative to the physical movement of a bill 17 across the scanhead 18 is also advantageous in that the encoder 32 can be used to provide a predetermined delay following detection of the borderline prior to initiation of samples. The encoder delay can be adjusted in such a way that the bill 17 is scanned only across those segments along its narrow dimension which contain the most distinguishable printed indicia relative to the different currency denominations.

In the case of U.S. currency, for instance, it has been determined that the central, approximately two-inch (approximately 5 cm) portion of currency bills, as scanned across the central section of the narrow dimension of the bill, provides sufficient data for distinguishing among the various U.S. currency denominations on the basis of the correlation technique disclosed in U.S. Pat. No. 5,295,196 referred to above. Accordingly, the optical encoder can be used to control the scanning process so that reflectance samples are taken for a set period of time and only after a certain period of time has elapsed since the borderline 17A has been detected, thereby restricting the scanning to the desired central portion of the narrow dimension of the bill.

FIGS. 2A-2C illustrate the scanning process of scanhead 20 in more detail. Referring to FIG. 2B, as a bill 17 is advanced in a direction parallel to the narrow edges of the bill, scanning via a wide slit in the scanhead 18 is effected along a segment S of the central portion of the bill 17. This segment S begins a fixed distance D inboard of the borderline 17A. As the bill 17 traverses the scanhead 18, a strip s of the segment S is always illuminated, and the photodetector 26 produces a continuous output signal which is proportional to the intensity of the light reflected from the illuminated strip s at any given instant. This output is sampled at intervals controlled by the encoder, so that the sampling intervals are precisely synchronized with the movement of the bill across the scanhead 18.

As illustrated in FIGS. 2A and 2C, it is preferred that the sampling intervals be selected so that the strips s that are illuminated for successive samples overlap one another. The odd-numbered and even-numbered sample strips have been separated in FIGS. 2A and 2C to more clearly illustrate this overlap. For example, the first and second strips s1 and s2 overlap each other, the second and third strips s2 and s3 overlap each other, and so on. Each adjacent pair of strips overlap each other. For U.S. currency, this is accomplished by sampling strips that are 0.050 inch (0.127 cm) wide at 0.029 inch (0.074 cm) intervals, along a segment S that is 1.83 inch (4.65 cm) long (64 samples).

The optical sensing and correlation technique is based upon using the above process to generate a series of stored intensity signal patterns using genuine bills for each denomination of currency that is to be detected. According to a preferred embodiment, two or four sets of master intensity signal samples are generated and stored within system memory, preferably in the form of an EPROM 34 (see FIG. 1), for each detectable currency denomination. The sets of master intensity signal samples for each bill are generated from optical scans, performed on the green surface of the bill and taken along both the "forward" and "reverse" directions relative to the pattern printed on the bill. Alternatively, the optical scanning may be performed on the black side of U.S. currency bills or on either surface of bills from other countries. Additionally, the optical scanning may be performed on both sides of a bill, for example, by placing a scanhead on each side of the bill transport path as described in more detail in co-pending U.S. patent application Ser. No. 08/207,592 filed Mar. 8, 1994, now U.S. Pat. No. 5,467,407, for a "Method and Apparatus for Currency Discrimination" and incorporated herein by reference.

In adapting this technique to U.S. currency, for example, sets of stored intensity signal samples are generated and stored for seven different denominations of U.S. currency, i.e., $1, $2, $5, $10, $20, $50 and $100. For bills which produce significant pattern changes when shifted slightly to the left or right, such as the $2 and the $10 bill in U.S. currency, it is preferred to store two patterns for each of the "forward" and "reverse" directions, each pair of patterns for the same direction represent two scan areas that are slightly displaced from each other along the long dimension of the bill. Accordingly, a set of 18 different master characteristic patterns is stored within the system memory for subsequent correlation purposes (four master patterns for the $2 and the $10 bill and two master patterns for each of the other denominations). Once the master patterns have been stored, the pattern generated by scanning a bill under test is compared by the CPU 30 with each of the 18 master patterns of stored intensity signal samples to generate, for each comparison, a correlation number representing the extent of correlation, i.e., similarity between corresponding ones of the plurality of data samples, for the sets of data being compared.

The CPU 30 is programmed to identify the denomination of the scanned bill as corresponding to the set of stored intensity signal samples for which the correlation number resulting from pattern comparison is found to be the highest. In order to preclude the possibility of mischaracterizing the denomination of a scanned bill, as well as to reduce the possibility of spurious notes being identified as belonging to a valid denomination, a bi-level threshold of correlation is used as the basis for making a "positive" call. Such a method is disclosed in U.S. Pat. No. 5,295,196 referred to above. If a "positive" call can not be made for a scanned bill, an error signal is generated.

Using the above sensing and correlation approach, the CPU 30 is programmed to count the number of bills belonging to a particular currency denomination as part of a given set of bills that have been scanned for a given scan batch, and to determine the aggregate total of the currency amount represented by the bills scanned during a scan batch. The CPU 30 is also linked to an output unit 36 (FIG. 1) which is adapted to provide a display of the number of bills counted, the breakdown of the bills in terms of currency denomination, and the aggregate total of the currency value represented by counted bills. The output unit 36 can also be adapted to provide a print-out of the displayed information in a desired format.

Referring now to FIG. 3A, there is shown a representation, in block diagram form, of a preferred circuit arrangement for processing and correlating reflectance data according to the system of this invention. As shown therein, the CPU 30 accepts and processes a variety of input signals including those from the optical encoder 32, the photodetector 26 and a memory unit 38, which can be an erasable programmable read only memory (EPROM). The memory unit 38 has stored within it the correlation program on the basis of which patterns are generated and test patterns compared with stored master programs in order to identify the denomination of test currency. A crystal 40 serves as the time base for the CPU 30, which is also provided with an external reference voltage V.sub.REF on the basis of which peak detection of sensed reflectance data is performed.

The CPU 30 also accepts a timer reset signal from a reset unit 44 which, as shown in FIG. 3B, accepts the output voltage from the photodetector 26 and compares it, by means of a threshold detector 44A, relative to a pre-set voltage threshold, typically 5.0 volts, to provide a reset signal which goes "high" when a reflectance value corresponding to the presence of paper is sensed. More specifically, reflectance sampling is based on the premise that no portion of the illuminated light strip (24 in FIG. 1) is reflected to the photodetector in the absence of a bill positioned below the scanhead. Under these conditions, the output of the photodetector represents a "dark" or "zero" level reading. The photodetector output changes to a "white" reading, typically set to have a value of about 5.0 volts, when the edge of a bill first becomes positioned below the scanhead and falls under the light strip 24. When this occurs, the reset unit 44 provides a "high" signal to the CPU 30 and marks the initiation of the scanning procedure.

The machine-direction dimension, that is, the dimension parallel to the direction of bill movement, of the illuminated strip of light produced by the light sources within the scanhead is set to be relatively small for the initial stage of the scan when the thin borderline is being detected. The use of the narrow slit increases the sensitivity with which the reflected light is detected and allows minute variations in the "gray" level reflected off the bill surface to be sensed. This is important in ensuring that the thin borderline of the pattern, i.e., the starting point of the printed pattern on the bill, is accurately detected. Once the borderline has been detected, subsequent reflectance sampling is performed on the basis of a relatively wider light strip in order to completely scan across the narrow dimension of the bill and obtain the desired number of samples, at a rapid rate. The use of a wider slit for the actual sampling also smooths out the output characteristics of the photodetector and realizes the relatively large magnitude of analog voltage which is essential for accurate representation and processing of the detected reflectance values.

Returning to FIG. 3A, the CPU 30 processes the output of photodetector 26 through a peak detector 50 which essentially functions to sample the photodetector output voltage and hold the highest, i.e., peak, voltage value encountered after the detector has been enabled. For U.S. currency, the peak detector is also adapted to define a scaled voltage on the basis of which the pattern borderline on bills is detected. The output of the peak detector 50 is fed to a voltage divider 54 which lowers the peak voltage down to a scaled voltage V.sub.s representing a predefined percentage of this peak value. The voltage V.sub.s is based upon the percentage drop in output voltage of the peak detector as it reflects the transition from the "high" reflectance value resulting from the scanning of the unprinted edge portions of a currency bill to the relatively lower "gray" reflectance value resulting when the thin borderline is encountered. Preferably, the scaled voltage V.sub.s is set to be about 70-80 percent of the peak voltage.

The scaled voltage V.sub.s is supplied to a line detector 56 which is also provided with the incoming instantaneous output of the photodetector 26. The line detector 56 compares the two voltages at its input side and generates a signal L.sub.DET which normally stays "low" and goes "high" when the edge of the bill is scanned. The signal LDET goes "low" when the incoming photodetector output reaches the predefined percentage of the peak photodetector output up to that point, as represented by the voltage V.sub.s. Thus, when the signal L.sub.DET goes "low", it is an indication that the borderline of the bill pattern has been detected. At this point, the CPU 30 initiates the actual reflectance sampling under control of the encoder 32 (see FIG. 3A) and the desired fixed number of reflectance samples are obtained as the currency bill moves across the illuminated light strip and is scanned along the central section of its narrow dimension.

When master characteristic patterns are being generated, the reflectance samples resulting from the scanning of one or more genuine bills for each denomination are loaded into corresponding designated sections within a system memory 60, which is preferably an EPROM. The loading of samples is accomplished through a buffered address latch 58, if necessary. During currency discrimination, the reflectance values resulting from the scanning of a test bill are sequentially compared, under control of the correlation program stored within the memory unit 38, with each of the corresponding master characteristic patterns stored within the EPROM 60, again through the address latch 58. The procedure for scanning bills and generating characteristic patterns is described in U.S. Pat. No. 5,295,196 referred to above and incorporated by reference in its entirety and co-pending U.S. patent application Ser. No. 08/243,807, filed on May 16, 1994 and entitled "Method and Apparatus for Currency Discrimination."

The optical sensing and correlation technique described in U.S. Pat. No. 5,295,196 permits identification of pre-programmed currency denominations with a high degree of accuracy and is based upon a relatively short processing time for digitizing sampled reflectance values and comparing them to the master characteristic patterns. The approach is used to scan currency bills, normalize the scanned data and generate master patterns in such a way that bill scans during operation have a direct correspondence between compared sample points in portions of the bills which possess the most distinguishable printed indicia. A relatively low number of reflectance samples is required in order to be able to adequately distinguish among several currency denominations.

Now that a single scanhead currency scanner has been described in connection with scanning U.S. currency, the currency discrimination system of the present invention will be described.

First of all, because currencies come in a variety of sizes, sensors are added to determine the size of a bill to be scanned. These sensors are placed upstream of the scanheads to be described below. A preferred embodiment of size determining sensors is illustrated in FIG. 4. Two leading/trailing edge sensors 62 detect the leading and trailing edges of a bill 64 as it passing along the transport path. These sensors in conjunction with the encoder 32 (FIG. 1) may be used to determine the dimension of the bill along a direction parallel to the scan direction which in FIG. 4 is the narrow dimension (or width) of the bill 64. Additionally, two side edge sensors 66 am used to detect the dimension of a bill 64 transverse to the scan direction which in FIG. 4 is the wide dimension (or length) of the bill 64. While the sensors 62 and 66 of FIG. 4 are optical sensors, any means of determining the size of a bill may be employed.

Once the size of a bill is determined, the potential identity of the bill is limited to those bills having the same size. Accordingly, the area to be scanned can be tailored to the area or areas best suited for identifying the denomination and country of origin of a bill having the measured dimensions.

Secondly, while the printed indicia on U.S. currency is enclosed within a thin borderline, the sensing of which may serve as a trigger to begin scanning using a wider slit, most currencies of other currency systems such as those from other countries do not have such a borderline. Thus the system described above may be modified to begin scanning relative to the edge of a bill for currencies lacking such a borderline. Referring to FIG. 5, two leading edge detectors 68 are shown. The detection of the leading edge 69 of a bill 70 by leading edge sensors 68 triggers scanning in an area a given distance away from the leading edge of the bill 70, e.g., D.sub.1 or D.sub.2, which may vary depending upon the preliminary indication of the identity of a bill based on the dimensions of a bill. Alternatively, the leading edge 69 of a bill may be detected by one or more of the scanheads (to be described below) in a similar manner as that described with respect to FIGS. 3A and 3B. Alternatively, the beginning of scanning may be triggered by positional information provided by the encoder 32 of FIG. 1, for example, in conjunction with the signals provided by sensors 62 of FIG. 4, thus eliminating the need for leading edge sensors 68.

However, when the initiation of scanning is triggered by the detection of the leading edge of a bill, the chance that a scanned pattern will be offset relative to a corresponding master pattern increases. Offsets can result from the existence of manufacturing tolerances which permit the location of printed indicia of a document to vary relative to the edges of the document. For example, the printed indicia on U.S. bills may vary relative to the leading edge of a bill by as much as 50 mils which is 0.05 inches (1.27 mm). Thus when scanning is triggered relative to the edge of a bill (rather than the detection of a certain part of the printed indicia itself, such as the printed borderline of U.S. bills), a scanned pattern can be offset from a corresponding master pattern by one or more samples. Such offsets can lead to erroneous rejections of genuine bills due to poor correlation between scanned and master patterns. To compensate, overall scanned patterns and master patterns can be shifted relative to each other as illustrated in FIGS. 6A and 6B. More particularly, FIG. 6A illustrates a scanned pattern which is offset from a corresponding master pattern. FIG. 6B illustrates the same patterns after the scanned pattern is shifted relative to the master pattern, thereby increasing the correlation between the two patterns. Alternatively, instead of shifting either scanned patterns or master patterns, master patterns may be stored in memory corresponding to different offset amounts.

Thirdly, while it has been determined that the scanning of the central area on the green side of a U.S. bill (see segment S of FIG. 2B) provides sufficiently distinct patterns to enable discrimination among the plurality of U.S. denominations, the central area may not be suitable for bills originating in other countries. For example, for bills originating from Country 1, it may be determined that segment S.sub.1 (FIG. 5) provides a more preferable area to be scanned, while segment S.sub.2 (FIG. 5) is more preferable for bills originating from Country 2. Alternatively, in order to sufficiently discriminate among a given set of bills, it may be necessary to scan bills which are potentially from such set along more than one segment, e.g., scanning a single bill along both S.sub.1 and S.sub.2.

To accommodate scanning in areas other than the central portion of a bill, multiple scanheads may be positioned next to each other. A preferred embodiment of such a multiple scanhead system is depicted in FIG. 7. Multiple scanheads 72a-c and 72d-f are positioned next to each other along a direction lateral to the direction of bill movement. Such a system permits a bill 74 to be scanned along different segments. Multiple scanheads 72a-f are arranged on each side of the transport path, thus permitting both sides of a bill 74 to be scanned.

Two-sided scanning may be used to permit bills to be fed into a currency discrimination system according to the present invention with either side face up. An example of a two-sided scanhead arrangement is disclosed in co-pending U.S. patent application Ser. No. 08/207,592 filed on Mar. 8, 1994, now U.S. Pat. No. 5,467,406, and incorporated herein by reference. Master patterns generated by scanning genuine bills may be stored for segments on one or both sides. In the case where master patterns are stored from the scanning of only one side of a genuine bill, the patterns retrieved by scanning both sides of a bill under test may be compared to a master set of single-sided master patterns. In such a case, a pattern retrieved from one side of a bill under test should match one of the stored master patterns, while a pattern retrieved from the other side of the bill under test should not match one of the master patterns. Alternatively, master patterns may be stored for both sides of genuine bills. In such a two-sided system, a pattern retrieved by scanning one side of a bill under test should match with one of the master patterns of one side (Match 1) and a pattern retrieved from scanning the opposite side of a bill under test should match the master pattern associated with the opposite side of a genuine bill identified by Match 1.

Alternatively, in situations where the face orientation of a bill (i.e., whether a bill is "face up" or "face down") may be determined prior to or during characteristic pattern scanning, the number of comparisons may be reduced by limiting comparisons to patterns corresponding to the same side of a bill. That is, for example, when it is known that a bill is "face up", scanned patterns associated with scanheads above the transport path need only be compared to master patterns generated by scanning the "face" of genuine bills. By "face" of a bill it is meant a side which is designated as the front surface of the bill. For example, the front or "face" of a U.S. bill may be designated as the "black" surface while the back of a U.S. bill may be designated as the "green" surface. The face orientation may be determinable in some situations by sensing the color of the surfaces of a bill. An alternative method of determining the face orientation of U.S. bills by detecting the borderline on each side of a bill is disclosed in co-pending U.S. patent application Ser. No. 08/207,592 filed on Mar. 8, 1994, now U.S. Pat. No. 5,467,406. The implementation of color sensing is discussed in more detailed below.

According to the embodiment of FIG. 7, the bill transport mechanism operates in such a fashion that the central area C of a bill 74 is transported between central scanheads 72b and 72e. Scanheads 72a and 72c and likewise scanheads 72d and 72f are displaced the same distance from central scanheads 72b and 72e, respectively. By symmetrically arranging the scanheads about the central region of a bill, a bill may be scanned in either direction, e.g., top edge first (forward direction) or bottom edge first (reverse direction). As described above with respect to FIGS. 1-3, master patterns are stored from the scanning of genuine bills in both the forward and reverse directions. While a symmetrical arrangement is preferred, it is not essential provided appropriate master patterns are stored for a non-symmetrical system.

While FIG. 7 illustrates a system having three scanheads per side, any number of scanheads per side may be utilized. Likewise, it is not necessary that there be a scanhead positioned over the central region of a bill. For example, FIG. 8 illustrates another preferred embodiment of the present invention capable of scanning the segments S.sub.1 and S.sub.2 of FIG. 5. Scanheads 76a, 76d, 76e, and 76h scan a bill 78 along segment S.sub.1 while scanheads 76b, 76c, 76f, and 76g scan segment S.sub.2.

FIG. 9 depicts another preferred embodiment of a scanning system according to the present invention having laterally moveable scanheads 80a-b. Similar scanheads may be positioned on the opposite side of the transport path. Moveable scanheads 80a-b may provide more flexibility that may be desirable in certain scanning situations. Upon the determination of the dimensions of a bill as described in connection with FIG. 4, a preliminary determination of the identity of a bill may be made. Based on this preliminary determination, the moveable scanheads 80a-b may be positioned over the area of the bill which is most appropriate for retrieving discrimination information. For example, if based on the size of a scanned bill, it is preliminarily determined that the bill is a Japanese 5000 Yen bill-type, and if it has been determined that a suitable characteristic pattern for a 5000 Yen bill-type is obtained by scanning a segment 2.0 cm to the left of center of the bill fed in the forward direction, scanheads 80a and 80b may be appropriately positioned for scanning such a segment, e.g., scanhead 80a positioned 2.0 cm left of center and scanhead 80b positioned 2.0 cm right of center. Such positioning permits proper discrimination regardless of the whether the scanned bill is being fed in the forward or reverse direction. Likewise scanheads on the opposite side of the transport path (not shown) could be appropriately positioned. Alternatively, a single moveable scanhead may be used on one or both sides of the transport path. In such a system, size and color information (to be described in more detail below) may be used to properly position a single laterally moveable scanhead, especially where the orientation of a bill may be determined before scanning.

FIG. 9, depicts a system in which the transport mechanism is designed to deliver a bill 82 to be scanned centered within the area in which scanheads 80a-b are located. Accordingly, scanheads 80a-b are designed to move relative to the center of the transport path with scanhead 80a being moveable within the range R.sub.1 and scanhead 80b being moveable within range R.sub.2.

FIG. 10 depicts another preferred embodiment of a scanning system according to the present invention wherein bills to be scanned are transported in a left justified manner along the transport path, that is wherein the left edge L of a bill 84 is positioned in the same lateral location relative to the transport path. Based on the dimensions of the bill, the position of the center of the bill may be determined and the scanheads 86a-b may in turn be positioned accordingly. As depicted in FIG. 10, scanhead 86a has a range of motion R.sub.3 and scanhead 86b has a range of motion R.sub.4. The ranges of motion of scanheads 86a-b may be influenced by the range of dimensions of bills which the discrimination system is designed to accommodate. Similar scanheads may be positioned on the opposite side of the transport path.

Alternatively, the transport mechanism may be designed such that scanned bills are not necessarily centered or justified along the lateral dimension of the transport path. Rather the design of the transport mechanism may permit the position of bills to vary left and right within the lateral dimension of the transport path. In such a case, the edge sensors 66 of FIG. 4 may be used to locate the edges and center of a bill, and thus provide positional information in a moveable scanhead system and selection criteria in a stationary scanhead system.

In addition to the stationary scanhead and moveable scanhead systems described above, a hybrid system having both stationary and moveable scanheads may be used. Likewise, it should be noted that the laterally displaced scanheads described above need not lie along the same lateral axis. That is, the scanheads may be, for example, staggered upstream and downstream from each other. FIG. 11 is a top view of a staggered scanhead arrangement according to a preferred embodiment of the present invention. As illustrated in FIG. 11, a bill 130 is transported in a centered manner along the transport path 132 so that the center 134 of the bill 130 is aligned with the center 136 of the transport path 132. Scanheads 140a-h are arranged in a staggered manner so as to permit scanning of the entire width of the transport path 132. The areas illuminated by each scanhead are illustrated by strips 142a, 142b, 142e, and 142f for scanheads 140a, 140b, 140e, and 140f, respectively. Based on size determination sensors, scanheads 140a and 140h may either not be activated or their output ignored.

In general, if prior to scanning a document, preliminary information about a document can be obtained, such as its size or color, appropriately positioned stationary scanheads may be activated or laterally moveable scanheads may be appropriately positioned provided the preliminary information provides some indication as to the potential identity of the document. Alternatively, especially in systems having scanheads positioned over a significant portion of the transport path, many or all of the scanheads of a system may be activated to scan a document. Then subsequently, after some preliminary determination as to a document's identity has been made, only the output or derivations thereof of appropriately located scanheads may be used to generate scanned patterns. Derivations of output signals include, for example, data samples stored in memory generated by sampling output signals. Under such an alternative embodiment, information enabling a preliminary determination as to a document's identity may be obtained by analyzing information either from sensors separate from the scanheads or from one or more of the scanheads themselves. An advantage of such preliminary determinations is that the number of scanned patterns which have to be generated or compared to a set of master patterns is reduced. Likewise the number of master patterns to which scanned patterns must be compared may also be reduced.

While the scanheads 140a-h of FIG. 11 are arranged in a non-overlapping manner, they may alternatively be arranged in an overlapping manner. By providing additional lateral positions, an overlapping scanhead arrangement may provide greater selectivity in the segments to be scanned. This increase in scanable segments may be beneficial in compensating for currency manufacturing tolerances which result in positional variances of the printed indicia on bills relative to their edges. Additionally, in a preferred embodiment, scanheads positioned above the transport path are positioned upstream relative to their corresponding scanheads positioned below the transport path.

FIGS. 12A and 12B illustrate another preferred embodiment of the present in invention wherein a plurality of analog sensors 150 such as photodetectors are laterally displaced from each other and are arranged in a linear array within a single scanhead 152. FIG. 12A is a top view while FIG. 12B is a side elevation view of such a linear array embodiment. The output of individual sensors 150 are connected to analog-to-digital converters (not shown) through the use of graded index fibers, such as a "lens array" manufactured by MSG America, Inc., part number SLA20A1675702A3, and subsequently to a CPU (not shown) in a manner similar to that depicted in FIGS. 1 and 3A. As depicted in FIGS. 12A and 12B, a bill 154 is transported past the linear array scanhead 152 in a centered fashion. A preferred length for the linear array scanhead is about 6-7 inches (15 cm-17 cm).

In a manner similar to that described above, based on the determination of the size of a bill, appropriate sensors may be activated and their output used to generate scanned patterns. Alternatively many or all of the sensors may be activated with only the output or derivations thereof of appropriately located sensors being used to generate scanned patterns. Derivations of output signals include, for example, data samples stored in memory generated by sampling output signals. As a result, a discriminating system incorporating a linear array scanhead according the present invention would be capable of accommodating a wide variety of bill-types. Additionally, a linear array scanhead provides a great deal of flexibility in how information may be read and processed with respect to various bills. In addition to the ability to generate scanned patterns along segments in a direction parallel to the direction of bill movement, by appropriately processing scanned samples, scanned patterns may be "generated" or approximated in a direction perpendicular to the direction of bill movement. For example, if the linear array scanhead 152 comprises one hundred and sixty (160) sensors 150 over a length of 7 inches (17.78 cm) instead of taking samples for 64 encoder pulses from say 30 sensors, samples may be taken for 5 encoder pulses from all 160 cells (or all those positioned over the bill 154). Alternatively, 160 scanned patterns (or selected ones thereof) of 5 data samples each may be used for pattern comparisons. Accordingly, it can be seen that the data acquisition time is significantly reduced from 64 encoder pulses to only 5 encoder pulses. The time saved in acquiring data can be used to permit more time to be spent processing data and/or to reduce the total scanning time per bill thus enabling increased throughput of the identification system. Additionally, the linear array scanhead permits a great deal of flexibility in tailoring the areas to be scanned. For example, it has been found that the leading edge of Canadian bills contain valuable graphic information. Accordingly, when it is determined that a test bill may be a Canadian bill (or when the identification system is set to a Canadian currency setting), the scanning area can be limited to the leading edge area of bills, for example, by activating many laterally displaced sensors for a relatively few number of encoder pulses.

FIG. 13 is a top view of another preferred embodiment of a linear array scanhead 170 having a plurality of analog sensors 172 such as photodetectors wherein a bill 174 is transported past the scanhead 170 in a non-centered manner. As discussed above, positional information from size determining sensors may be used to select appropriate sensors. Alternatively, the linear array scanhead itself may be employed to determine the size of a bill, thus eliminating the need for separate size determining sensors. For example, all sensors may be activated, data samples derived from sensors located on the ends of the linear array scanhead may be preliminarily processed to determine the lateral position and the length of a bill. The width of a bill may be determined either by employing separate leading/trailing edge sensors or pre-processing data samples derived from initial and ending cycle encoder pulses. Once size information is obtained about a bill under test, only the data samples retrieved from appropriate areas of a bill need be further processed.

FIG. 14 is a top view of another preferred embodiment of a linear scanhead 180 according to the present invention illustrating the ability to compensate for skewing of bills. Scanhead 180 has a plurality of analog sensors 182 and a bill 184 is transported past scanhead 180 in a skewed manner. Once the skew of a bill has been determined, for example through the use of leading edge sensors, readings from sensors 182 along the scanhead 180 may be appropriately delayed. For example, suppose it is determined that a bill is being fed past scanhead 180 so that the left front corner of the bill reaches the scanhead five encoder pulses before the right front corner of the bill. In such a case, sensor readings along the right edge of the bill can be delayed for 5 encoder pulses to compensate for the skew. Where scanned patterns are to be generated over only a few encoder pulses, the bill may be treated as being fed in a non-skewed manner since the amount of lateral deviation between a scan along a skewed angle and a scan along a non-skewed angle is minimal for a scan of only a few encoder pulses. However, where it is desired to obtain a scan over a large number of encoder pulses, a single scanned pattern may be generated from the outputs of more than one sensor. For example, a scanned pattern may be generated by taking data samples from sensor 186a for a given number of encoder pulses, then taking data samples from sensor 186b for a next given number of encoder pulses, and then taking data samples from sensor 186c for a next given number of encoder pulses. The number of given encoder pulses for which data samples may be taken from the same sensor is influenced by the degree of skew, the greater the degree of skew of the bill, the fewer the number of data samples which may be obtained before switching to the next sensor. Alternatively, master patterns may be generated and stored for various degrees of skew, thus permitting a single sensor to generate a scanned pattern from a bill under test.

With regards to FIGS. 12-14, while only a single linear array scanhead is shown, another linear array scanhead may be positioned on the opposite side of the transport path to permit scanning of either or both sides of a bill. Likewise, the benefits of using a linear array scanhead may also be obtainable using a multiple scanhead arrangement which is configured appropriately, for example such as depicted in FIG. 11 or a linear arrangement of multiple scanheads.

In addition to size and scanned characteristic patterns, color may also be used to discriminate bills. For example, while all U.S. bills are printed in the same colors, e.g., a green side and a black side, bills from other countries often vary in color with the denomination of the bill. For example, a German 50 deutsche mark bill-type is brown in color while a German 100 deutsche mark bill-type is blue in color. Alternatively, color detection may be used to determine the face orientation of a bill, such as where the color of each side of a bill varies. For example, color detection may be used to determine the face orientation of U.S. bills by detecting whether or not the "green" side of a U.S. bill is facing upwards. Separate color sensors may be added upstream of the scanheads described above. According to such an embodiment, color information may be used in addition to size information to preliminarily identify a bill. Likewise, color information may be used to determine the face orientation of a bill which determination may be used to select upper or lower scanheads for scanning a bill accordingly or compare scanned patterns retrieved from upper scanheads with a set of master patterns generated by scanning a corresponding face while the scanned patterns retrieved from the lower scanheads are compared with a set of master patterns generated by scanning an opposing face. Alternatively, color sensing may be incorporated into the scanheads described above. Such color sensing may be achieved by, for example, incorporating color filters, colored light sources, and/or dichroic beamsplitters into the currency discrimination system of the present invention. Color information acquisition is described in more detail in co-pending U.S. application Ser. No. 08/219,093 filed Mar. 29, 1994, now abandoned for a "Currency Discriminator and Authenticator" incorporated herein by reference. Various color information acquisition techniques are described in U.S. Pat. Nos. 4,841,358; 4,658,289; 4,716,456; 4,825,246; and 4,992,860.

The operation of a currency discriminator according to a preferred embodiment of the present invention may be further understood by referring to the flowchart of FIGS. 15A and 15B. In the process beginning at step 100, a bill is fed along a transport path (step 102) past sensors which measure the length and width of the bill (step 104). These size determining sensors may be, for example, those illustrated in FIG. 4. Next at step 106, it is determined whether the measured dimensions of the bill match the dimensions of at least one bill stored in memory, such as EPROM 60 of FIG. 3. If no match is found, an appropriate error is generated at step 108. If a match is found, the color of the bill is scanned for at step 110. At step 112, it is determined whether the color of the bill matches a color associated with a genuine bill having the dimensions measured at step 104. An error is generated at step 114 if no such match is found. However, if a match is found, a preliminary set of potentially matching bills is generated at step 116. Often, only one possible identity will exist for a bill having a given color and dimensions. However, the preliminary set of step 116 is not limited to the identification of a single bill-type, that is, a specific denomination of a specific currency system; but rather, the preliminary set may comprise a number of potential bill-types. For example, all U.S. bills have the same size and color. Therefore, the preliminary set generated by scanning a U.S. $5 bill would include U.S. bills of all denominations.

Based on the preliminary set (step 116), selected scanheads in a stationary scanhead system may be activated (step 118). For example, if the preliminary identification indicates that a bill being scanned has the color and dimensions of a German 100 deutsche mark, the scanheads over regions associated with the scanning of an appropriate segment for a German 100 deutsche mark may be activated. Then upon detection of the leading edge of the bill by sensors 68 of FIG. 5, the appropriate segment may be scanned. Alternatively, all scanheads may be active with only the scanning information from selected scanheads being processed. Alternatively, based on the preliminary identification of a bill (step 116), moveable scanheads may be appropriately positioned (step 118).

Subsequently, the bill is scanned for a characteristic pattern (step 120). At step 122, the scanned patterns produced by the scanheads are compared with the stored master patterns associated with genuine bills as dictated by the preliminary set. By only making comparisons with master patterns of bills within the preliminary set, processing time may be reduced. Thus for example, if the preliminary set indicated that the scanned bill could only possibly be a German 100 deutsche mark, then only the master pattern or patterns associated with a German 100 deutsche mark need be compared to the scanned patterns. If no match is found, an appropriate error is generated (step 124). If a scanned pattern does match an appropriate master pattern, the identity of the bill is accordingly indicated (step 126) and the process is ended (step 128).

While some of the preferred embodiments discussed above entailed a system capable of identifying a plurality of bill-types, the system may be adapted to identify a bill under test as either belonging to a specific bill-type or not. For example, the system may be adapted to store master information associated with only a single bill-type such as a United Kingdom 5 pound bill. Such a system would identify bills under test which were United Kingdom 5 pound bills and would reject all other bill-types.

The scanheads of the present invention may be incorporated into a document identification system capable of identifying a variety of documents. For example, the system may be designed to accommodate a number of currencies from different countries. Such a system may be designed to permit operation in a number of modes. For example, the system may be designed to permit an operator to select one or more of a plurality of bill-types which the system is designed to accommodate. Such a selection may be used to limit the number of master patterns with which scanned patterns are to be compared. Likewise, the operator may be permitted to select the manner in which bills will be fed, such as all bills face up, all bills top edge first, random face orientation, and/or random top edge orientation. Additionally, the system may be designed to permit output information to be displayed in a variety of formats to a variety of peripherals, such as a monitor, LCD display, or printer. For example, the system may be designed to count the number of each specific bill-types identified and to tabulate the total amount of currency counted for each of a plurality of currency systems. For example, a stack of bills could be placed in the bill accepting station 12 of FIG. 1, and the output unit 36 of FIG. 1 may indicate that a total of 370 British pounds and 650 German marks were counted. Alternatively, the output from scanning the same batch of bills may provide more detailed information about the specific denominations counted, for example one 100 pound bill, five 50 pound bills, and one 20 pound bill and thirteen 50 deutsche mark bills.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and herein described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.