WO2023031901A1

WO2023031901A1 - Paper sheet thickness detector

Info

Publication number: WO2023031901A1
Application number: PCT/IL2021/051081
Authority: WO
Inventors: Edward Slepyan
Original assignee: Dv Uvirma Ltd.
Priority date: 2021-09-02
Filing date: 2021-09-02
Publication date: 2023-03-09

Abstract

A paper sheet detector includes a rotating reference roller, mounted in a fixed housing and a detection unit, mounted in an openable housing, which is openable from the fixed housing. The detection unit includes a detection roller opposite the reference roller, a fulcrum shaft fixed with respect to the openable housing, a lever arm to rock around the fixed fulcrum shaft and moving within the openable housing as at least a paper sheet moves between the reference roller and the detection roller, and a displacement sensor to sense a motion of the detection roller in the presence of at least the paper sheet. The fixed housing, the openable housing and the detection unit have positioning elements which coincide with each other when the detection roller and the reference roller become aligned and touch each other at least during manufacture.

Description

TITLE OF THE INVENTION

PAPER SHEET THICKNESS DETECTOR

FIELD OF THE INVENTION

[0001] The present invention relates to paper sheet thickness detectors generally and to such detectors for banknote thickness in particular.

BACKGROUND OF THE INVENTION

[0002] Devices which handle banknotes, such as banknote sorting machines, cash deposit machines and cash recycling machines, typically include banknote recognition units. These units recognize value, authenticity and fitness of the banknotes including but not limited to whether or not the banknotes they are receiving have been altered in some way, such as by tape, paper or the like.

[0003] Banknote fitness is usually defined as whether or not the banknote is suitable for circulation in the market or should be withdrawn from the circulation and destroyed by the Central Bank. Fitness criteria are regulated by Central Banks and typically include detection of the presence of adhesive tapes on the banknotes. This may include determining if the banknotes are altered (i.e. they are genuine banknotes composed of different parts of the same genuine banknote, such as might happen when someone repairs a tom banknote, or different parts of different banknotes combined together) . Alternatively, this may include determining if the banknotes are composed counterfeit notes, such as a geniuine banknote where some parts of it are substituted by counterfeit parts.

[0004] Fig. 1, to which reference is now briefly made, shows a pile of banknotes 10 where some of them have adhesive tape 12 thereon. Banknote recognition units need to detect tape 12, due to the banking regulations and in order to prevent jamming of the banknotes inside cash handling equipment such as cash dispensers, ATMs and the like). So banknote sorters, cash deposit machines and cash recyclers are equipped with a tape detection unit. Such tape detection units may measure the differing thicknesses between banknotes with and without adhesive tape, may detect the attenuation of ultrasonic waves which pass through or are being reflected from the bankinote, which is different for the paper with and without adhesive tape, may optically detect bright reflection from tape, and may measure the differing electrical capacity of the banknote with and without adhesive tape .

[0005] A typical paper thickness detector 20 is shown in Fig. 2, to which reference is now made.

[0006] Detector 20 has a pair of rollers 22A and 22B, where roller 22A, the “detection roller” moves away against an elastic element, such as a spring, while roller 22B, the “reference roller”, stays fixed. Paper or banknotes can be moved through rollers 22 by an external force and their movement will cause rollers 22A and 22B to turn. Sensor 24 gauges the displacement of detection roller 22A as a banknote passes between rollers 22A and 22B. There may be a single pair or multiple pairs of rollers 22, as required for the width of the paper or banknote.

[0007] US 8,496,246 to Muranaka et al. describes another paper thickness detector whose detection roller moves around a fulcrum shaft, rather than moving up as in Fig. 2, and in the process, moves an element whose displacement is measured by a displacement detection unit. The entire detection block is floating relative to a baseplate holding a reference shaft for the reference rollers. SUMMARY OF THE PRESENT INVENTION

[0008] There is provided, in accordance with a preferred embodiment of the present invention, a paper sheet detector which includes a rotating reference roller, mounted in a fixed housing and a detection unit, mounted in an openable housing, which is openable from the fixed housing. The detection unit includes a detection roller opposite the reference roller, a fulcrum shaft fixed with respect to the openable housing, a lever arm to rock around the fixed fulcrum shaft and moving within the openable housing as at least a paper sheet moves between the reference roller and the detection roller, and a displacement sensor to sense a motion of the detection roller in the presence of at least the paper sheet. The fixed housing, the openable housing and the detection unit have positioning elements which coincide with each other when the detection roller and the reference roller become aligned and touch each other at least during manufacture.

[0009] Moreover, in accordance with a preferred embodiment of the present invention, the lever arm provides a mechanical amplification of the motion.

[0010] Further, in accordance with a preferred embodiment of the present invention, the paper sheet detector includes means to provide a high signal to noise ratio to an output of the displacement sensor. The means to provide includes at least a plurality of means to dampen vibrations to at least a critical damping level, and the displacement sensor generates a nonproportional response to the motion.

[0011] Still further, in accordance with a preferred embodiment of the present invention, one of the means to dampen includes a shock absorber mounted between a moving part of the paper sheet detector and a non-moving part of the paper sheet detector.

[0012] Moreover, in accordance with a preferred embodiment of the present invention, the shock absorber is formed with dry or viscous friction, which can be resistive oil, silicone or rubber. [0013] Further, in accordance with a preferred embodiment of the present invention, one of the means to dampen includes a coating of the reference roller with a shock absorbing material, which can be polyurethane.

[0014] Moreover, in accordance with a preferred embodiment of the present invention, the displacement sensor includes a magnet housed in one of the lever arm and the openable housing, and a magnetic sensor housed in the other of the lever arm and the openable housing. A distance between the magnet and the magnetic sensor is small enough for the magnetic sensor to operate in a non-linear region.

[0015] Further, in accordance with a preferred embodiment of the present invention, the lever arm has a first portion connecting the detection roller to the fulcrum shaft and a second portion connecting the fulcrum shaft to at least one element of the displacement sensor. The second portion is larger than the first portion thereby to amplify the motion of the detection roller.

[0016] Still further, in accordance with a preferred embodiment of the present invention, the means to provide includes a gap between the detection roller and the reference roller, wherein the gap is no more than an expected thickness of the paper sheet.

[0017] Moreover, in accordance with a preferred embodiment of the present invention, the positioning elements are positioning indentations on the detection unit, enlarged holes on the openable housing, and holes on the fixed housing.

[0018] There is also provided, in accordance with a preferred embodiment of the present invention, a paper sheet detection apparatus including a housing having an openable housing element, a reference shaft mounted on the housing and integrally formed with a plurality of reference rollers, and a detection unit fixedly mounted to the openable housing element. The detection unit includes a fulcrum shaft fixed with respect to the openable housing, a plurality of lever arms rotatably mounted on the fixed fulcrum shaft, a plurality of detection rollers, each one mounted on one of the lever arms opposite an associated one of the reference rollers, and a plurality of displacement sensors, each to sense a motion of an associated one of the detection rollers in the presence of at least the paper sheet. The housing, the openable housing element and the detection unit have positioning elements which coincide with each other when the plurality of detection rollers and the plurality of reference rollers become aligned and touch each other at least during manufacture.

[0019] Moreover, in accordance with a preferred embodiment of the present invention, the paper sheet detection apparatus includes means to provide a high signal to noise ratio to outputs of the displacement sensors. The means to provide includes at least a plurality of means to dampen vibrations to at least a critical damping level, and the displacement sensor generates a nonproportional response to the motion.

[0020] Further, in accordance with a preferred embodiment of the present invention, the means to provide includes at least one pair of support rollers for the reference shaft.

[0021] Still further, in accordance with a preferred embodiment of the present invention, at least one lever arm of the plurality of lever arms provides a mechanical amplification of the motion.

[0022] Moreover, in accordance with a preferred embodiment of the present invention, one of the means to dampen includes a shock absorber located between at least the lever arm and the openable housing.

[0023] Further, in accordance with a preferred embodiment of the present invention, the shock absorber is formed with a dry or viscous coating, which can be resistive oil, silicone or rubber.

[0024] Still further, in accordance with a preferred embodiment of the present invention, one of the means to dampen includes a coating of at least one the reference roller with a shock absorbing material, which can be polyurethane. [0025] Moreover, in accordance with a preferred embodiment of the present invention, at least one of the displacement sensors includes a magnet mounted on one lever arm of the plurality of lever arms and the openable housing element, and a magnetic sensor housed in the other of the one lever arm and the openable housing element. A distance between the magnet and the magnetic sensor is small enough for the magnetic sensor to operate in a non-linear region.

[0026] Further, in accordance with a preferred embodiment of the present invention, the at least one lever arm has a first portion connecting the detection roller to the fulcrum shaft and a second portion connecting the fulcrum shaft to at least one element of the displacement sensor. The second portion is larger than the first portion thereby to amplify the motion of the detection roller.

[0027] Finally, in accordance with a preferred embodiment of the present invention, the means to provide includes a gap between the detection rollers and the reference rollers, wherein the gap is no more than an expected thickness of the paper sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

[0029] Fig. 1 is an illustration of a pile of banknotes;

[0030] Fig. 2 is a schematic illustration of a typical prior art paper thickness detector;

[0031] Fig. 3 is a schematic illustration of an improved paper sheet thickness detector, constructed and operative in accordance with a preferred embodiment of the present invention;

[0032] Fig. 4 is a graphical illustration of an exemplary magnetic sensor signal, generated by the detector of Fig. 3;

[0033] Figs. 5A and 5B are schematic illustrations of a portion of a detection apparatus comprising multiple detectors of Fig. 3;

[0034] Fig. 5C is a schematic illustration of the portion of the detection apparatus shown in Fig. 5 A connected to an opened housing element;

[0035] Fig. 6 A is a schematic illustration of a portion of a lever arm, forming part of the detector of Fig. 3; and

[0036] Figs. 6B and 6C are graphical illustrations of sensor signals for the detector of Fig. 3 without and with shock absorbers.

[0037] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0038] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.

[0039] Applicant has realized that measurement of the displacement of the detection roller of a paper thickness detector is affected by the vibrations of the detection roller, the precision of the reference roller and of the detection roller and by overall vibrations of the mechanism.

[0040] Moreover, Applicant has realized that the measurement is affected by the alignment of the reference roller with the detection rollers and that the alignment is difficult to maintain after the machine is opened (e.g., to enable a user to remove a paper jam or to perform maintenance). Applicant has realized that this alignment can be fixedly set during manufacture, such that neither floating nor self-adjustment are required during operation of the thickness detector.

[0041] Reference is now made to Fig. 3, which illustrates an improved paper sheet thickness detector 30. Detector 30 comprises a reference roller 32, rotating with a shaft 31, and a detection unit 34 which includes a lever arm 40 that may rock slightly around a fixed fulcrum shaft 36 when a paper moves between reference roller 32 and a detection roller 38 forming part of detection unit 34 and located opposite reference roller 32. Detection roller 38 may rotate around an axis 39.

[0042] Detection unit 34 comprises, in addition to detection roller 38 and lever arm 40, an openable housing 41 which may have a lower portion 42 and an upper portion 44. Lever arm 40 may rock back and forth between lower portion 42 and upper portion 44, around fulcrum shaft 36 as a paper 46 moves between rollers 32 and 38. [0043] Detection unit 34 additionally comprises an elastic element 48, shown here as a spring, connected between upper portion 44 and lever arm 40, a magnet 50, housed in lever arm 40, and a magnetic sensor 52, housed in lower portion 42. Elastic element 48 may be operative to push lever arm 40 against reference roller 32 and may be implemented in any suitable way. For example, elastic element 48 may be formed of a spring, of two mutually repulsive magnets, of a piece of rubber, of silicone or of another elastic material. Moreover, a friction or viscous type shock absorber maybe combined together with the elastic element 48. Magnetic sensor 52 may, for example, be a Hall effect sensor.

[0044] Rollers 32 and 38 may continually rotate. When paper 46 may move between rollers 32 and 38, paper 46 may cause lever arm 40 to rock slightly around fulcrum 36, as indicated by arrow 55, squeezing elastic element 48 against upper portion 44 and causing magnet 50 to move away from magnetic sensor 52. When paper 46 may finish moving through rollers 32 and 38, elastic element 48 may return lever arm 40 to its initial location, bringing magnet 50 closer to magnetic sensor 52.

[0045] Applicant has realized that, by placing magnet 50 and magnetic sensor 52 relatively far, by a distance R, from fulcrum shaft 36, the curvature (indicated by curve 53) of the rotation of lever arm 40 around fulcrum shaft 36 is relatively flat. Thus, the slight motion of magnet 50 may be relatively linear, as indicated by arrow 54, with respect to magnetic sensor 52.

[0046] Similarly, Applicant has realized that it is difficult to measure the displacement of detection roller 38 since it may be a function of the thicknesses of paper 36 and tape 47 and the total thickness is only about 0.1 - 0.2mm. Applicant has realized that detection is improved when the displacement of detection roller 38 is amplified. In the present invention, this may be achieved with at least one lever arm, such as the lever arm produced by setting distance R to be larger than a distance D between fulcrum shaft 36 and the location where rollers 32 and 38 meet. [0047] Applicant has realized that there is a region, close to the surface of the magnet, in which the magnetic field of the magnet changes rapidly and non-linearly . Outside of this region, there is a quasi-linear region where the magnetic field decays almost linearly with the distance. Prior art detection systems operate in the quasi-linear region and, as a result, see only a slight change (no more than a 30% increase) in the sensor signal in the presence of the tape.

[0048] Applicant has realized that, by keeping magnet 50 close to magnetic sensor 52 (within a distance comparable to the radius of the magnet if the magnet is round), detector 30 may operate in the non-linear region, such that the signal from the tape may be a non-proportional response compared to that of the banknote. For example, the signal from the area where the tape is stuck to the banknote may be significantly higher than the signal from the banknote without tape, although the thickness of the tape is just 20%-30% of the thickness of a banknote. Thus, magnetic sensor 52 may be mounted close to an upper edge of lower portion 42 of housing 41, and magnet 50 may be mounted close to a lower edge of lever arm 40 which may be aligned, at manufacture, close to magnetic sensor 52.

[0049] For example, in the non-linear region, a displacement of magnet 50 by just 0.1mm may create a small change in the magnetic field (and a corresponding small change of the sensor output) but a further displacement of 0.03mm (such as in the presence of tape 47) may cause much higher changes in the signals. This may provide a high signal to noise ratio which may enable detector 30 to detect tape 47 very reliably.

[0050] Fig. 4, to which reference is now made, illustrates an exemplary magnetic sensor signal 60, from magnetic sensor 52, as paper 46 with adhesive tape 47 moves through detector 30, and an exemplary voltage change signal 62 in magnetic field as a function of the distance of magnet 50 from magnetic detector 52. Note that sensor signal 60 is low when no banknote is present

(arrow 70 on sensor signal 60, coinciding with dot 71 at voltage change level vcl on voltage change signal 62) and increases to a first level 72 in the presence of just paper 46 (coinciding with a jump in voltage change level to vc2, noted by dot 73).

[0051] Voltage change signal 62 increases even more (to voltage change level vc3, noted by dot 75) as adhesive tape 47 moves between rollers 32 and 38. This can also be seen in sensor signal 60, which is at a higher level 74 in the presence of adhesive tape 47. Note that the changes in voltage change signal 62 from no banknote to banknote (vcl to vc2) and from banknote to banknote with tape (vc2 to vc3) are about the same size, even though adhesive tape 47 only adds an additional 0.03mm of thickness to the 0.1mm thickness of paper 46. Thus, there is a significant difference in signal between the two, providing a large signal to noise ratio in the present invention.

[0052] Note, however, that sensor signal 60 has significant jumps 76a and 76b as first paper 46 and then adhesive tape 47 first touch rollers 32 and 38, after which signal 60 settles down to vibrate around lower level 72 or 74, respectively. This may be due to the impact of paper 46 and then adhesive tape 47 hitting rollers 32 and 38.

[0053] In an alternative embodiment, alternative displacement sensors may be utilized, such as optical sensors, capacitance sensors, encoders and the like. Moreover, either of the two elements needed for sensing (e.g., the magnet and the magnetic sensor) may be located on lever arm 40.

[0054] Applicant has realized that, in general, a single detector 30 is not sufficient to check a piece of paper or a bank note. Therefore, a typical paper thickness detector comprises multiple detectors 30 in a single apparatus. However, in such an apparatus, in order to provide generally the same output for the same amount of displacement, the distances between all reference rollers 32 and fulcrum 36 should be equal and all detection units 30 should press paper 46 with more or less equal force. [0055] Reference is now made to Figs. 5A, 5B and 5C, which illustrate, in expanded view, a detection apparatus 100 comprising multiple detectors 30 in a row, capable of handling variable width pieces of paper or banknotes and detecting adhesive tapes anywhere along their width. It will be appreciated that not all detectors 30 have to be located all on the same shaft; there may be multiple groups of detectors, each group on a shorter fulcrum shaft. This may reduce the bending or impact related displacement of the fulcrum and reference shafts as well as the bending and/or displacement of the entire frame of the detector.

[0056] Multiple reference rollers 32 may be formed as a single rotating shaft 31 which may be rotatably connected, during manufacture, to external plates 102 (only one is shown in Fig. 5A) of a fixed housing of apparatus 100. This may maintain reference rollers 32 in place. Similarly, fulcrum shafts 36 may be formed as a single fulcrum shaft 36’ connecting multiple detectors 30 together into a detection block 103 having plate 101 on each side (only one is shown in Fig. 5A). Detection block 103 may be connected to an openable housing element 105, which may open (as shown in Fig. 5C) to give a user access to detection block 103, such as to clear a paper jam or to perform maintenance operations.

[0057] Plates 101 of detection block 103, external plates 102 of the fixed housing, and openable housing element 105 may have positioning elements thereon. The positioning elements may be positioning indentations 107 on plates 101 of detection block 103, enlarged holes 109 of openable housing element 105, and holes 110 of external plates 102. In accordance with a preferred embodiment of the present invention, these positioning elements may coincide with each other when detection roller and reference roller first become aligned and touch each other, after detection block 103 may be placed within openable housing element 105 and openable housing element 105 may be closed against the fixed housing of external plates 102. [0058] At this point, the alignment may be affixed by extending positioning pins 104 (three are shown in Fig. 5A) through holes 110 in external plates 102 and through the relevant portion of enlarged holes 109 into positioning indentations 107 on detection block 103. With positioning pins 104 in place, screws 106 may be placed through enlarged holes 109 to affix detection block 103 to openable housing element 105. After assembly, positioning pins 104 may be removed, leaving detection block 103 permanently aligned with respect to reference shaft 31.

[0059] It will be appreciated that only holes 109 in openable housing element 105 need to be enlarged to compensate for any manufacturing tolerance errors and to enable precise alignment of detection block 103 to reference shaft 31.

[0060] When, during operation, openable housing element 105 may be opened, as is shown schematically in Fig. 5C, detection block 103 may be moved away from rotation rollers 32. However, since detection block 103 may now be fixed with respect to openable housing element 105, when openable housing element 105 may later be closed, detection block 103 may be returned to its position, aligned with reference rollers 32.

[0061] In a further embodiment, as shown in Fig. 5B, reference shaft 31 may be supported by support rollers 108 in at least one location along reference shaft 31, so as to maintain reference shaft 31 straight.

[0062] It will be appreciated that, by supporting reference shaft 31, reference shaft 31 may be thinner and may also handle more rollers per shaft than otherwise.

[0063] Applicant has further realized that other means may be utilized to improve the signal to noise ratio. In one embodiment, the signal to noise ratio may be further improved by reducing the amount of vibration in each detector 30 and ideally, to dampen vibrations to at least a critical damping level, where the critical damping level is just sufficient to prevent oscillations. [0064] In particular, Applicant has realized that vibrations may be caused by the impact of the edge of paper 46 kicking the detection roller 38. Applicant has realized that the latter may be reduced by adding shock absorbers 111, as shown in Fig. 6A to which reference is now made, to a portion of lever arm 40 near detection rollers 38. Such shock absorbers 111 may absorb many of the vibrations in lever arm 40, and particularly those which occur when paper 46 and/or adhesive tape 47 begin to move through rollers 32 and 38. Shock absorbers 111 may be formed of any viscous material, such as rubber, resistive oils and/or silicone. Shock absorbers 111 may also include a dry friction component in order to suppress the vibrations.

[0065] Vibrations may be further reduced by inserting a shock absorber inside spring 48 and/or into other locations between moving lever 40 and fixed housing 42.

[0066] Figs. 6B and 6C, to which reference is now briefly made, show sensor signals 62’ and 62’ ’ for detectors 30 without and with shock absorbers 111, respectively. Note that the impact of paper 46 on measuring roller 38, due to the entrance of paper 46, may cause vibrations. These vibrations are high and wide in signal 112 and lower and narrower in signal 114, indicating that the vibration is absorbed immediately by shock absorbers 111. Moreover, the vibrations are kept at a low level such that the oscillation of signal 114 while paper 46 moves through detectors 30 is much lower than that of signal 112.

[0067] In another embodiment, the signal to noise ratio may be improved by coating either reference roller 32 or detection roller 38 with a shock absorbing material. This may further increase shock absorption and may also significantly reduce the acoustic noise of the apparatus. The coating may be of polyurethane or any elastic material that does not change shape significantly due to the pressure of the banknote (or measuring roller) but still absorbs the energy caused by the impact of the banknotes (and, at the same time, reduces noise). The uncoated shaft may be formed of a hard material, such as stainless steel or specially hardened and polished steel. [0068] Applicant has further realized that having a gap of less than thickness of paper 46 between rollers may further reduce the noise. For example, the gap may be of between 50% - 70% of the typical thickness of the banknotes. Such a gap may reduce the impact on rollers 32 and 38 when paper 46 begins to move through detector 30. However, tape 47 may still impact rollers 32 and 38 and this may make a larger distinction between the presence of paper 46 and tape 47.

[0069] Referring back to Fig. 3, each detector 30 may provide output to a signal processor 200 which may process signals 114 to identify the presence of tape 47. In one embodiment, signal processor 200 may detect abnormal jumps in signal 114 other than the initial jump that occurs when paper 46 enters rollers 32 and 38 and/or voltage levels above a threshold level defining the presence of paper only.

[0070] In a further embodiment, signal processing unit 200 may implement a self-learning neural network or other deep learning method to distinguish between the banknotes with the tape and those without tape.

[0071 ] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

CLAIMS What is claimed is:

1. A paper sheet detector comprising: a rotating reference roller, mounted in a fixed housing; and a detection unit, mounted in an openable housing, which is openable from said fixed housing, said detection unit comprising: a detection roller opposite said reference roller; a fulcrum shaft fixed with respect to said openable housing; a lever arm to rock around said fixed fulcrum shaft and moving within said openable housing as at least a paper sheet moves between said reference roller and said detection roller; and a displacement sensor to sense a motion of said detection roller in the presence of at least said paper sheet, wherein said fixed housing, said openable housing and said detection unit have positioning elements which coincide with each other when said detection roller and said reference roller become aligned and touch each other at least during manufacture.

2. The paper sheet detector according to claim 1 and wherein said lever arm provides a mechanical amplification of said motion.

3. The paper sheet detector according to claim 1 and also comprising: means to provide a high signal to noise ratio to an output of said displacement sensor, said means to provide comprising at least: a plurality of means to dampen vibrations to at least a critical damping level; and said displacement sensor to generate a non-proportional response to said motion.

4. The paper sheet detector according to claim 3 and wherein one of said means to dampen comprises a shock absorber mounted between a moving part of said paper sheet detector and a non-moving part of said paper sheet detector.

5. The paper sheet detector according to claim 4 and wherein said shock absorber is formed with dry or viscous friction.

6. The paper sheet detector according to claim 5 and wherein said dry or viscous friction is one of: resistive oil, silicone and rubber.

7. The paper sheet detector according to claim 3 and wherein one of said means to dampen comprises a coating of said reference roller with a shock absorbing material.

8. The paper sheet detector according to claim 7 and wherein said shock absorbing material is polyurethane.

9. The paper sheet detector according to claim 3 and wherein said displacement sensor comprises: a magnet housed in one of said lever arm and said openable housing; and a magnetic sensor housed in the other of said lever arm and said openable housing, wherein a distance between said magnet and said magnetic sensor is small enough for said magnetic sensor to operate in a non-linear region.

10. The paper sheet detector according to claim 2 and wherein said lever arm has a first portion connecting said detection roller to said fulcrum shaft and a second portion connecting said fulcrum shaft to at least one element of said displacement sensor, wherein said second portion is larger than said first portion thereby to amplify said motion of said detection roller.

11. The paper sheet detector according to claim 3 and wherein said means to provide comprises a gap between said detection roller and said reference roller, wherein said gap is no more than an expected thickness of said paper sheet.

12. The paper sheet detector according to claim 1 and wherein said positioning elements are positioning indentations on said detection unit, enlarged holes on said openable housing, and holes on said fixed housing.

13. A paper sheet detection apparatus comprising: a housing having an openable housing element; a reference shaft mounted on said housing and integrally formed with a plurality of reference rollers; and a detection unit fixedly mounted to said openable housing element, said unit comprising: a fulcrum shaft fixed with respect to said openable housing; a plurality of lever arms rotatably mounted on said fixed fulcrum shaft; a plurality of detection rollers, each one mounted on one of said lever arms opposite an associated one of said reference rollers; and a plurality of displacement sensors, each to sense a motion of an associated one of said detection rollers in the presence of at least said paper sheet,

19 wherein said housing, said openable housing element and said detection unit have positioning elements which coincide with each other when said plurality of detection rollers and said plurality of reference rollers become aligned and touch each other at least during manufacture.

14. The paper sheet detection apparatus according to claim 13 and also comprising: means to provide a high signal to noise ratio to outputs of said displacement sensors, said means to provide comprising at least: a plurality of means to dampen vibrations to at least a critical damping level; and said displacement sensor to generate a non-proportional response to said motion.

15. The paper sheet detection apparatus according to claim 14 and wherein said means to provide comprises at least one pair of support rollers for said reference shaft.

16. The paper sheet detection apparatus according to claim 13 and wherein at least one lever arm of said plurality of lever arms provides a mechanical amplification of said motion.

17. The paper sheet detection apparatus according to claim 14 and wherein one of said means to dampen comprises a shock absorber located between at least one said lever arm and said openable housing.

18. The paper sheet detection apparatus according to claim 17 and wherein said shock absorber is formed with a dry or viscous coating.

19. The paper sheet detection apparatus according to claim 18 and wherein said dry or viscous coating is one of: resistive oil, silicone and rubber.

20

20. The paper sheet detection apparatus according to claim 14 and wherein one of said means to dampen comprises a coating of at least one said reference roller with a shock absorbing material.

21. The paper sheet detection apparatus according to claim 20 and wherein said shock absorbing material is polyurethane.

22. The paper sheet detection apparatus according to claim 13 and wherein at least one said displacement sensor comprises: a magnet mounted on one lever arm of said plurality of lever arms and said openable housing element; and a magnetic sensor housed in the other of said one lever arm and said openable housing element, wherein a distance between said magnet and said magnetic sensor is small enough for said magnetic sensor to operate in a non-linear region.

23. The paper sheet detection apparatus according to claim 16 and wherein said at least one lever arm has a first portion connecting said detection roller to said fulcrum shaft and a second portion connecting said fulcrum shaft to at least one element of said displacement sensor, wherein said second portion is larger than said first portion thereby to amplify said motion of said detection roller.

24. The paper sheet detection apparatus according to claim 14 and wherein said means to provide comprises a gap between said detection rollers and said reference rollers, wherein said gap is no more than an expected thickness of said paper sheet.

21