Method for examining sheet-like objects.

p0001The invention relates to a method of inspecting sheet material for multiple transport by scanning the sheet material with radiation along a predetermined scanning path and generating a sequence of determined by properties of the sheet material sample signals whose values ​​are compared for the purpose of delivering a detection signal with stored desired values.

p0002Such a method is known from DE-PS 30 40 963 and is used for checking of documents, such as bank notes, for authenticity. For this purpose, the document is irradiated in the scanning and recovered from the reflected radiation on its surface a succession of sampling signals whose amplitude varies in the course of scanning of areas of differing reflectivity. For each test Document a predetermined amplitude profile is stored as a sequence of setpoint values, and by comparing the respective sequence of sampled signals with the associated stored sequence of setpoint values ​​can a statement be obtained if the checked document is genuine or not.

p0003The previously known method can be used, for example when entering banknotes in a cash receiving machines. Such a check for authenticity is however insufficient for a comprehensive evaluation because doing the bills need to be free of errors counted. By using the reflection principle in the generation of the scan but only an examination of surface properties, but not even a proper examination of the transport is ever Weil's only a single banknote possible. Multiple shipments of banknotes, so-called double deductions were, so far found with mechanical devices that are mostly designed as Rollenabtaster and make a thickness measurement of the transported sheet material. Such thickness measurement is susceptible but especially by contaminants and need for the proper function of a careful adjustment and maintenance. A non-contact detection of multiple transport of sheet material, in particular bank notes, is not possible according to the test methods previously known, but could replace the complex in construction and maintenance of mechanical devices advantageous.

p0004The object of the invention to provide a way for non-contact detection of multiple transport of sheet material, which operates without any moving elements which are directly involved in a measurement process.

p0005This object is starting from a method of the above-mentioned type in accordance with the invention that the scanning signals are generated depending on the radiation transparency of the sheet material and that are used as to comparative values ​​a mean value of the sampling and him similar mean of setpoints.

p0006The invention is based on the recognition that the radiation permeability of a material with the thickness of which decreases exponentially. Has eg sheet material of a predetermined thickness a particular, the radiation intensity disparaging attenuation value, thus doubling the thickness of a total attenuation becomes effective by another sheet, which is proportional to the product of the individual losses. In this way already provide for a doubling of the sheet material thickness, ie for example in a double transport of sheet material correspondingly high intensity differences of the scanning signals from the normal case, ensure a very reliable test between single and double transport of sheet material.

p0007Another advantage of generating the scanning signals with radiation that passes through the sheet material, is that this principle is very sensitive to a changing reflectance of the sheet material surface, which is caused for example by an imprint or by contamination. Such changes of the sheet material surface have, in most cases such a small thickness that the radiation permeability of the sheet material is itself relatively little affected.

p0008But to ensure a reliable determination of a multiple transport even with heavy soiling and / or larger, for example, due to printing differences in brightness, also a similar averaging the scanning signals and the setpoint values ​​is provided in the inventive process. It is thereby achieved that the comparison results are statistically reliable.

p0009Advantageously, the intensity of the radiation used for scanning for a particular type of sheet material according to a predetermined range of values ​​of the mean value of the set values ​​is set. This ensures that we constantly adjusted signals to be compared to the sensitivity range of evaluation systems with changing types of sheet material optimally.

p0010The method of the invention also leads to a reliable statement about single or multiple transport of sheet material when the transported sheets do not exactly overlie each other, but are shifted relative to each other. To be able to diagnose, even large amounts of displacement as a multi-feed, the process can be designed such further that it is determined during the scanning from the sheet material back on board and is compared to a predetermined target path for the purpose of generating a further detection signal. This ensures that accumulation of sheet material having a length which goes beyond the predetermined format length, are also detected, thereby a further criterion for the detection of the multiple transport is available.

p0011Generally provides a method according to the invention has the advantage that it can also be used in combination with a reflection method, whereby it is then possible to monitor the authenticity and the transport of individual sheets within the same evaluation device.

p0012The invention is explained below with reference to the drawing for an exemplary embodiment. They show:<ul><li>FIG. 1 shows a schematic representation of the method with reference to the interaction used therein functional units,</li><li>Fig. 2 is a flowchart of an applied calibration process in the method for determining desired values, </li><li>Fig. 3 is a control function for detecting the current with which the radiation source is to supply, and</li><li>Fig. 4 is a flowchart of an embodiment of the invention.</li></ul>

p0013In Fig. 1 is shown in block diagram an automatic teller machine in a testing device for detecting the multiple transport of banknotes. An on multiple transport test banknote 10 is passed between a controllable radiation source 12 and a radiation detector module 20th The controllable radiation source 12 comprises two light emitting diodes 14, 16, which, depending on the type used, which emit radiation in the visible range or in the infrared range. The light emitting diodes 14, 16 are connected in series and are traversed by a current I which is generated by a controllable current source eighteenth

p0014The radiation of the light emitting diodes 14, 16 penetrates into two areas, the banknote 10 and is absorbed by this partially. The light passing through the banknote 10, attenuated radiation strikes two photodetectors 22, 24, such as photodiodes, the radiation detector module 20 and is converted by this into electrical signals S. These are amplified by amplifiers 26, 28 and fed to an analog multiplexer 30th The signals S of the photodetectors 22, 24 are in the analog multiplexer 30 are alternately switched through to its output and an analog-digital converter 32 fed to its digital output is connected to the input of a microcontroller 34th This controls the analog multiplexer 30 and starts the conversion cycle of the analog-digital converter 32. The microcontroller 34 has access to a memory RAM for storing current data (signals S) and is connected via a data bus with an EPROM 38 (Erasable Programmable Read Only Memory), the serves as a program memory for the microcontroller 34, and connected to an EEPROM 40 (Electrically Erasable Programmable Read Only memory), which is used for storing banknote specific data. The microcontroller 34 controls the operation of the entire process, calculated mean values ​​and compares it, as will be described. The microcontroller 34 controls a digital-analog converter 36 whose output signal serves for adjusting the current I of the controllable current source eighteenth Further, the microcontroller 34 is connected via a data line 44 with a host computer not shown in the Fig. 1, the result of the check is notified, and sends the data for sequence control to the microcontroller 34.

p0015The on multiple transport the banknote 10 to be tested is passed over a non-illustrated conveyor device through the controllable from the radiation source 12 and the radiation receiver module 20 formed Durchlichtmeßstrecke. The distance traveled by the banknote 10 route will detected by a displacement sensor 42 and communicated by clock signals the microcontroller 34th The controllable source of radiation 12 and the radiation detector module 20 are adjustable so that the each scanned area of ​​the banknote 10 can be selected as the scanning distance. If the controllable radiation source 12 and the radiation detector module 20 as adjusted so that the tactile paths along the edges of the banknote run 10, as well as an audit of the page format or the correct position of the banknote 10 can be carried out with reference to the signals S. namely Located between the controllable radiation source 12 and the radiation detector module 20 no sheet material, as received the photoreceptor 22, 24 are not attenuated radiation of the light emitting diodes 14, 16, resulting in a significantly high level of the signals S. At this signal level occurs, the absence or misalignment of a bill may be the cause.

p0016By calibration with sample banknotes money ticket machine can be adjusted to a desired user Banknotenart. The calibration process is shown as a flow chart in Fig. 2. In a first method step 60 a defined initial state of the existing from the controllable source of radiation 12 and the radiation receiver module 20 Durchlichtmeßstrecke is generated. To this end, the Durchlichtmeßstrecke is operated without feeding a bill so that the radiation of the controllable radiation source 12 can impinge directly and undiminished on the radiation receiver module 20th The controllable radiation source 12 is adjusted via the controllable current source 18 to a base current value Io so (step 62) that the levels of the signals S of the photodetectors 22, 24 is located in the upper portion of a predetermined working range of the analog-digital converter 32, for example at 90%.

p0017In the next step 64 a pattern bill on the transport device is transported into the Durchlichtmeßstrecke and along with the position of the light-emitting diodes (LEDs) 14, 16 and the associated photoreceptor 22, sampled 24 specific scanning distance. The signals S of the photoreceptor 22, 24 are read in time division multiplex process in the RAM of the microcontroller 34 and, either during scanning or after the bill has 10 through the scanning section, the arithmetic mean value SM of the signals S formed (step 66). To obtain a higher statistical reliability of the result when calibrating, the scan process will be in accordance with the branch 67 shown in FIG. 2 with four bills which differ in their use state, performed. From the thus obtained mean values ​​SM, an arithmetic overall mean value M is calculated at step 68, which is also referred to as a target value M. This target value M is checked to the next process step 70, if he is in a predetermined range defined by a lower value of M1 and an upper value M2. The values ​​M1, M2 are permanently stored in the microcontroller 34 as digital values ​​and be using an 8-bit microcontroller for example M1 = 100, M2 = 140. If the target value M is outside this range, then in the branch shown in Fig. 2 72, 74 by an empirically determined control function which will be explained later, a differential current value .DELTA.I determined by which the basic current value Io must be changed so that the set value M at the next calibration process with a high probability within the range defined by the values ​​M1, M2 range lies.

p0018The current I, with the controllable radiation source 12 is applied after passing through the steps 72, 74, results from the sum of the base current value Io and the differential current value .DELTA.I. The calibration process is repeated with feeding the paper money according to the described process steps and comparing the target value M with the values ​​M1, M2. If the set value M, in turn, are outside the range defined by the values ​​of M1, M2 range, is calculated from the control function of the associated difference .DELTA.I current value and added to the previously determined current I. This process is repeated until the desired value M is within the specified limits M1, M2.

p0019The determined target value M and the corresponding sum of the differential current values ​​.DELTA.I characterize the sample banknotes. Using the target value M, a tolerance range with a lower limit G1 and an upper limit G2 is defined in step 76, within which the average must be SM a to be tested banknote to be regarded as belonging to this type of notes and recognized as a single bill. In practice, as the lower limit G1 0.8 times and as the upper limit G2 1.2 times the nominal value M has proven. The documents belonging to a certain type of banknote data, for example, the upper limit value G2, the lower limit value G1, the sum of the differential current values ​​.DELTA.I and an identification K of the banknotes are stored in step 78 in the EEPROM 40 and accessed in the examination of bills.

p0020In Fig. 3, the control function for detecting the difference .DELTA.I current values ​​is shown as a function from the set value M. As already explained, to stabilize M in as few iterative steps within a fixedly predetermined by the values ​​of M1, M2 range of the target value. This area also has an average value M0. By way of example 3 is shown that in the first calibration process, a target value M 'is determined, which is clearly outside the range defined by the values ​​of M1, M2 in Fig.. The curve 50 of the control function can be switched to the target value M 'associated residual current value .DELTA.I' removed, Io and corresponding control of the radiation source 12 results in addition to the basic current value to that measured in the next calibration process setpoint M with high probability within the values ​​M1 , M2 defined range. The curve 50 of the control function is to be selected so that the target value M already possible to the second calibration process within the range defined by the values ​​of M1, M2 is. It has been found in practice that the shape of the curve 50 of the control function is optimal when it progressively increases or decreases with increasing deviations of the target value M of an average value M0.

p0021In FIG. 4, the sequence of a checking operation is shown for detecting a multi-transport of banknotes on hand of a flow chart. Before a test bill is transported in the Durchlichtmeßstrecke, the basic current value Io is in the previously described manner determined (step 80). To perform the test, the microcontroller reaches 34 in the next process step 82 on the banknote specific parameters consisting of the upper limit value G2, the lower limit G1 and the differential current value .DELTA.I to that stored in the EEPROM 40th The microcontroller 34 causes via the digital-analog converter 36 and the controllable current source 18 so that the controllable radiation source 12, the current I = Io + .DELTA.I is supplied (step 84). The supplied via a conveyor of Durchlichtmeßstrecke bill 10 is scanned along the defined tactile paths and produced on the photoreceptor 22, 24 a series of sampling signals S. The digital values ​​of the scanning signals S are read into the RAM memory of the microcontroller 34 and calculated in the subsequent step 86, the arithmetic mean SM. The mean value SM is then stored with the limit values ​​G1, G2 compared (step 88). If the average SM within the tolerance range defined by the limit values ​​G1, G2, so the distance from the bank note 10 route is compared to a target path in a subsequent inspection process 90th The distance traveled is determined here by counting the clock signals of the travel sensor 42, which are ge counts as long as the photoreceptor 22, 24 receive an attenuated radiation. This type of distance measurement the correct position supplying the banknotes on the transport means or overlapping of banknotes can also be detected. Where comparison of the mean SM with the limits G1, G2 determined a limit violation or the target path is exceeded, the microcontroller 34, a detection signal is generated which indicates the multi-feed or a faulty banknote feeder (step 94). This signal is passed to the higher-level computer, which suppresses an output or incorrect evaluation of the bills at the ATM. In case of a positive test result is to step 92 branches and the computer transmits an a single transport of the banknote 10 signal characterizing.

p0022As before each bill dispenser or at certain intervals of the basic current value Io is determined in each case again, a change of the transmission behavior of Durchlichtmeßstrecke has no effect. Such changes may be caused for example by aging the light emitting diodes 14, 16, or by contamination of Durchlichtmeßstrecke. Since both before calibration and during testing each a defined initial state is set, this method of checking bank notes is virtually maintenance free.