GB1333821A - Means for testing documents - Google Patents

Abstract

1333821 Bank note validators INSTITUTET FOR MIKROVAGSTEKNIK 4 Jan 1971 [5 Jan 1970] 362/71 Heading G1A [Also in Division G4] The genuineness of documents, which term includes bank notes, is tested by a device which defines and measures the thickness of a document over an area which has substantially the same shape as a predetermined area of thickness different from that of all adjoining areas of a valid document, the device being non-contacting and non- optical and arranged to effect a test when a document is moved past it. In the embodiment described, the detecting means is an air capacitor having plates 10, 12, 13 and 26, plate 13 being shaped to conform, say, to the watermark of the note 11 being tested and plate 12 acting as a guard plate. A note 11 inserted into the device is driven forward at constant speed by rolls 27, 28 after energization of motor 29 by breaking of contact S1. Immediately prior to the watermark coming into exact vertical alignment with plate 13, contact S2 is broken by the leading edge of the note to maintain a voltage corresponding to the average thickness of the note in that position on the output side of integrator 24, Fig. 4. Subsequent variations of capacitance which represent variations of the thickness of the note under plate 13 are analyzed by unit 25 which receives signals from the output of a low-pass filter 22. Because plate 13 is shaped, the signal curve is highly dependent on the shape and thickness of the watermark and limits can thus easily be set concerning the height and width of the signal from filter 22 to produce a YES or NO signal from analyzer 25. This analyzer may comprise a Schmidt-trigger (72), Fig. 7 (not shown), which is triggered if a non- genuine note passes through the capacitor, but not otherwise, or alternatively pulses are counted by a counter (85), Fig. 8 (not shown), with a certain range of values read by a decoder (86) signifying a genuine note. In this modification, counter (85) may be set to zero when contact S2 is opened. If the watermark has areas which are thicker and areas which are thinner than the average thickness of the note, two capacitative detectors may be arranged in series with YES-signals being required from both for acceptance. In the verification of printing patterns and less well-defined watermarks a movement of the note or document in two directions may be necessary. In other embodiments the air capacitor may be replaced by a radiation transmission and detection device, e.g., using a radio-active preparation as source, or an acoustic transmitter and receiver. In modifications, contact S1 and S2 may be replaced by photo-electric elements and relays R1, R2 may be replaced by electronic logic elements.