EP1258841A2

EP1258841A2 - Magnetic sensor and bill validator using the same

Info

Publication number: EP1258841A2
Application number: EP02010180A
Authority: EP
Inventors: Masahiro Mizukami; Shigeru Kakimi; Yasuo Yoshioka; Kazuhiro Onaka
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp
Priority date: 2001-05-16
Filing date: 2002-05-14
Publication date: 2002-11-20
Anticipated expiration: 2022-05-14
Also published as: EP1258841B1; CN1385816A; DE60226092D1; EP1258841A3; DE60226092T2; JP3603872B2; JP2003035701A; ES2304406T3; CN1178175C

Abstract

A highly sensitive magnetic sensor and a bill validator using the magnetic sensor are disclosed. The magnetic sensor is provided with an artificial-lattice MR (magnetic resistor) element formed on a board. The artificial-lattice MR element and wiring terminals, coupled to the artificial-lattice MR element, are integrated in a housing with resin. Moreover, a magnet is mounted in a hollow at the back of the board in the housing to provide a plane of artificial-lattice MR element with an auxiliary magnetic field perpendicularly.

Description

Field of the Invention

The present invention relates to a bill validator for use in various kinds of automatic vending machines and ticket machines.

Background of the Invention

In recent years, in connection with various kinds of expensive goods sold by automatic vending machines or ticket machines. For example, a bill validator capable of using currency bills of denominations above 1000 yen has been widely used in Japan. Since Japanese government began issuing a new currency bill of 2000 yen in July 2000, vending machines capable of using larger denomination bills including 2000 yen are becoming the standard. On the other hand, due to rapid technology advance in office automation equipment such as copying machines or color printers, violation crimes using forged bills made by such sophisticated tools is also increasing. A bill validator must be improved for highly sensitive validation to prevent such crimes from being committed.
In prior art, a bill validator has used a conventional magnetic read head as a sensor to detect magnetic features of a bill. Such a magnetic read head, however, needs a direct contact to have adequate signals with high accuracy from a magnetic media. Therefore, reading of currency is more difficult to detect with high accuracy because magnetic fields exist on both the face and the back side of bill which has a certain paper thickness. The drawback is the difficulty of improvement in validation accuracy.

Summary of the Invention

A magnetic sensor and a bill validator using the magnetic sensor are disclosed. A magnetic sensor comprised of an artificial-lattice MR (magnetic resistor) element formed on a face of a board detects magnetic field features of a media passing close to the face of the board. The artificial-lattice MR element formed on the board and wiring terminals coupled to the artificial-lattice MR element are integrated in a housing with resin. Moreover, a magnet is mounted on the back of the board in the housing to provide a plane of artificial-lattice MR element with an auxiliary magnetic field perpendicularly.

Brief Description of the Drawings

Fig. 1 is a cross-sectional side view of a magnetic sensor used in the first exemplary embodiment of the present invention.
Fig. 2 is a cross-sectional view of an artificial-lattice MR element used in the first exemplary embodiment of the present invention.
Fig. 3 is a plan view of a magnetic sensor used in the first exemplary embodiment of the present invention.
Fig. 4 is a side view, partly broken away, of a magnetic-sensor-assembly covered by a case, used in the first exemplary embodiment of the present invention.
Fig. 5 is a front view, partly broken away, of magnetic-sensor-assembly covered in a case, used in the first exemplary embodiment of the present invention.
Fig. 6 is an assembling view of a magnetic-sensor-assembly, covered in a case, used in the first exemplary embodiment of the present invention.
Fig. 7 is a cross-sectional view of a bill validator equipped with a magnetic-sensor-assembly used in the first exemplary embodiment of the present invention.
Fig. 8 is a block diagram of a bill validator equipped with a magnetic sensor used in the first exemplary embodiment of the present invention.
Fig. 9 is a signal diagram from a magnetic sensor in a bill validator shown in the first exemplary embodiment of the present invention.
Fig. 10 is a signal output diagram from a sample-hold circuit of a bill validator shown in the first exemplary embodiment of the present invention.
Fig. 11 is a plan view of a magnetic sensor used in the second exemplary embodiment of the present invention.
Fig. 12 is a block diagram of a bill validator equipped with a magnetic sensor used in the second exemplary embodiment of the present invention.

Description of the Preferred Embodiments

The present invention is explained by following preferred embodiments with reference to Fig. 1 through Fig. 12.

First Exemplary Embodiment

Fig. 1 is a cross-sectional view of a magnetic sensor of the first exemplary embodiment. In Fig. 1, artificial-lattice MR (magnetic resistor) element 1 is formed on surface of ceramic board 2. As shown in Fig. 2, artificial-lattice MR element has a multi-layer structure comprising nonmagnetic Copper (Cu) layers 3, 10 to 30 Å thick, and magnetic composite of Nickel-Iron-Cobalt (NiFeCo) layers 4, 20 to 40 Å thick, sandwiched alternately. The bill validation requires necessarily more than ten-layer structure. In this first exemplary embodiment, 15 layers are formed on ceramic board 2 with surface protective finish 5.
As described above, artificial-lattice MR element 1, having a multi-layer structure of nonmagnetic layers 3 and magnetic layers 4 sandwiched alternately, shows a large change in electrical resistance of the multi-layer structure when a magnetic field is applied perpendicularly. The effect can be used for detecting a faint change in magnetic fields.
Etching the above-mentioned multi-layer artificial-lattice MR element forms a circuit configuration as shown in Fig. 3. Namely, coupling two artificial- lattice MR element 1A and 1B in series, the coupling section is connected to conductive pattern 6A, and both ends are connected to pattern 6B and 6C respectively. Patterns 6A, 6B and 6C are coupled to wiring terminals 8A, 8B and 8C (as shown in Fig. 5) via through- holes 7A, 7B and 7C respectively.
As mentioned above, a simple circuit configuration can detect changes of magnetic fields, when two artificial-lattice MR elements, 1A and 1B, are arranged so that magnetic media passes in front of each artificial-lattice MR element, sequentially in the order of 1A to 1B.
In Fig. 1, wiring terminal 8, coupled to the artificial-lattice MR element to tap off signals, is disposed on the back of board 2. Terminal 8 is coupled to artificial-lattice MR element 1 via through-hole 7. Board 2 and one end of wiring terminal 8 on board 2 are sealed with resin, forming an integration in housing 9. Magnet 11, fitting to approximately square-shaped hollow 10, opening downward, is mounted such that being embedded. Magnet 11, mounted on the back of board 2, provides artificial-lattice MR element 1 with auxiliary magnetic field perpendicularly. Strength of the auxiliary magnetic field is approximately 20 milliTesla (mT). An auxiliary magnetic field, 15 to 30 mT, increases sensitivity in detection of faint magnetic field from magnetic features printed on currency bill.
Magnet 11, composed of magnetic ferrite powder, mixed and dispersed in base material, resin or rubber, shows a nice workability. Bill 12 faces artificial-lattice MR element 1. In addition, in Fig 1, artificial-lattice MR element 1 represents 1A and 1B. Pattern 6 represents 6A, 6B and 6C. Through-hole 7 represents 7A, 7B and 7C. Wiring terminal 8 represents 8A, 8B and 8C.
Magnetic sensor 13, placed in a resin case 15, becomes magnetic-sensor-assembly 27. Fig. 4 shows a side view, partly broken away, of the magnetic-sensor-assembly and Fig. 5 shows a front view, partly broken away, of the magnetic-sensor-assembly. Fig. 6 shows an assembling view of the magnetic-sensor-assembly. As shown in Figs 4 and 5, thin resin cap 16 covers an inlet opening 15A of resin case 15 to protect artificial-lattice MR element 1. Cap 16, composed of liquid-crystal-polymer having strong mechanical properties, is strong enough in a reduced thickness of 0.15 mm, with little influence in sensitivity of magnetic-sensor-assembly 27. Since no plating is needed, like metal case, to prevent corrosion or abrasion, cap 16 can be mass-produced by injection mold system in lesser processes.
Cap 16 is secured to case 15 when hook 18, formed on case 15, is engaged with hole 17, formed on a sidewall of cap 16, by snap-fit. As both case 15 and cap 16 are composed of resin, case 15 and cap 16 are easily fixed through one-touch operation due to elastic deformation property. In addition to this, electro-static discharge is suppressed because no exposed electrical live parts exist in the vicinity of bill path way.
When hook 19, formed on case 15, is inserted through hole 21, formed on printed wiring board 20 and on opposite side of opening 15A as well, case 15 is secured to printed wiring board 20 in an elastic deformation condition. Boss 22, integrated at the back of case 15, is secured to printed wiring board 20 using screw 23. As shown in Fig. 6, convex 24, provided on the same side of hook 19 of case 15, fits concave 25, provided on printed wiring board 20, for positioning.
Air space 28 is formed between housing 9 and printed wiring board 20. An amplifier, the first circuit into which signals tapped off from artificial-lattice MR element 1 feed, is mounted in air space 28. Consequently, reduced wiring length contributes to shield strongly against external noise for faint signal level. Shorter distance from magnetic sensor to circuitry reduces influence of external noise and can contribute to a downsizing of bill validator. Wiring terminal 8 is disposed in groove 26 provided on the side of boss 22 of case 15.
In assembly drawing of Fig. 6, magnetic sensor 13 is placed in case 15 covered by cap 16. The cap functions to protect artificial-lattice MR element 1 from outer dust and mechanical impact. In addition, artificial-lattice MR element 1, highly sensitive, is little influenced on sensitivity of detection operation if covered by such a cap. Next, hook 19 is inserted through hole 21 formed on printed wiring board 20. Boss 22 is secured to printed wiring board 20 using screw 23.
As mentioned above, magnetic sensor assembly 27 disclosed in the first exemplary embodiment has a high sensitivity due to artificial-lattice MR element 1. Moreover, magnet 11, being placed on a backside of board 2, provides artificial-lattice MR element 1 with auxiliary magnetic field perpendicularly. The auxiliary magnetic field functions to increase validation ability to detect sensitively small magnetic objects included in printed ink on currency bill.
Additionally, magnet 11, being embedded and secured in hollow 10 formed in housing 9, provides magnetic field steadily without influenced by vibration.
Moreover, as housing 9 is placed in case 15, external electro-static discharge is suppressed to enter and the parts is easily maintained as well.
Moreover, wiring terminal 8, being disposed in groove 26 securely, can be easily inserted into printed wiring board 20.
Next, an operation of bill validator is described. Fig. 7 shows a cross-sectional view of a bill validator having a magnetic-sensor-assembly 27, described in Figs 4, 5, and 6 with reference to the first exemplary embodiment of the invention.
In Fig. 7, inlet opening 31 of bill 12 is coupled to bill pass-way 32. Magnetic-sensor-assembly 27 disclosed in the first exemplary embodiment is mounted on a wall of pass-way 32. In addition to this, a transportation system comprising pulley 33 and belt 34 is provided with bill pass-way 32. Roller 35 functions to press bill 12. Outlet 36 of bill 12 is provided at an end of bill pass-way 32.
Fig. 8 shows a block diagram of the bill validator using magnetic-sensor-assembly 27 disclosed in the first exemplary embodiment.
In magnetic-sensor-assembly 27 shown in Fig. 8, two artificial- lattice MR element 1A and 1B, each having almost the same sensitivity, are coupled in series on board 2, and electrically connected to power in one end and to ground in another end. Two artificial- lattice MR elements 1A and 1B are arranged to bill transportation direction in the order of 1A, 1B.
Next, pattern 6A, coupling section of artificial- lattice MR element 1A and 1B, is electrically connected to input terminal of amplifier 41. Output signals from amplifier 41 is fed into sample/hold circuit 42, then output signals from amplifier 41 is tapped off to evaluation circuit 45 in microprocessor 44 through analog/digital converter (A/D converter).
Additionally, sampling/signal circuit 46 is connected to sample/hold circuit 42 and A/D converter 43. Bill validation data and the like are stored in memory 47.
Next, an operation of aforementioned bill validator is described. First, voltage of coupling section 6A increases due to reduction in electrical resistance of artificial-lattice MR element 1A, when artificial-lattice MR element 1A senses magnetic field of magnetic features applied on bill 12. Next, both of artificial- lattice MR element 1A and 1B sense magnetic field of magnetic features applied on bill 12. Consequently, voltage of coupling section 6A decreases to half value of voltage supply 40 due to reduction in electrical resistance of both of artificial- lattice MR element 1A and 1B.
Next, only artificial-lattice MR element 1B senses magnetic field of magnetic features applied on bill 12, when bill 12 leaves away from artificial-lattice MR element 1A. Then, voltage of coupling section 6A decreases due to increase in electrical resistance of artificial-lattice MR element 1A and decrease in electrical resistance of artificial-lattice MR element 1B.
Voltage of coupling section 6A returns back to initial value (half value of voltage supply 40) due to increase in electrical resistance of both of artificial- lattice MR element 1A and 1B, when magnetic field of magnetic features applied on bill 12 leave away from artificial-lattice MR element 1B.
In the above mentioned operation, magnetic sensor assembly 27 taps off characteristic signals as shown in Fig. 9. The signal is fed to sample/hold circuit 42 after amplified in amplifier 41.
Sample/hold circuit 42 has a purpose to prevent errors in reading in A/D converter 43, as tapped off signal from magnetic sensor assembly 27 has narrow width pulsed wave-shape. Hence, A/D converter 42 can read signals correctly after peak value of the signal is held for a certain period of time in sample/hold circuit 42 as shown in Fig. 10. Sample /hold circuit 42 holds the maximum level of signal. After reading in A/D converter circuit for a certain period of time, the circuit is reset by a signal from sampling circuit 46. The certain period of time for holding the maximum peak value is necessarily longer than sampling interval of A/D converter circuit 43. In Figs. 9 and 10, horizontal axis denotes time (in ms) and vertical axis denotes level (in mV). Subsequently, A/D converter circuit 43 converts magnetic signal of bill into digital signal, and validation circuit 45 determines validity and denomination of bill 12.
As described above, in this first exemplary embodiment, the bill validator performs with high accuracy in detection due to artificial-lattice MR element 1 used in magnetic-sensor-assembly 27 of the bill validator.
The bill validator performs with high accuracy due to artificial-lattice MR element 1 formed in magnetic-sensor-assembly 27 of the bill validator. Hence, the bill validator can detect bill 12 if inserted in reversed position.
Additionally, validation circuit 45 validates bill 12 by a maximum signal value detected, for example, in adjacent to prescribed measurement area. In this case, a bill validator comprised of magnetic-sensor-assembly 27 having highly sensitive artificial-lattice MR element 1 can detect magnetic features of bill 12 with high accuracy.
Moreover, bill validation is also possible by a maximum to minimum ratio of signals detected in adjacent to a prescribed area. The validation can be free from environmental condition, since judgment depends upon the maximum to minimum ratio, a relative comparison.
Furthermore, bill validation is also possible by detecting an order of occurrence of maximum and minimum output signals from magnetic-sensor-assembly 27. In this case, utilizing relationship between time and signal level, a bill validator can detect with high accuracy.
Moreover, bill validation is also possible by detecting a difference between a peak signal level from magnetic sensor assembly 27 at a certain area on bill 12, and a signal level at a prescribed area on bill 12. In this case, data of area on bill 12 where peak signal level is shown and the peak signal level can be well utilized for bill validation.
When above mentioned methods are adopted together as appropriate. validation accuracy can be improved more.

Second Exemplary Embodiment

In this second exemplary embodiment, a magnetic sensor comprised of four artificial-lattice MR (magnetic resistor) elements is described. The description is mainly on differences between the first and the second exemplary embodiments of this invention. As to corresponding parts to the first exemplary embodiment, description is simplified by coding 100 order referring marks to corresponding parts of the first exemplary embodiment.
Fig. 11 is a plan view of a magnetic sensor used in the second exemplary embodiment of this invention.
Etching the above-mentioned multi-layer artificial-lattice MR element, described in Fig. 2 of the first exemplary embodiment, forms a circuitry shown in Fig. 11. Namely, coupling four artificial- lattice MR element 101A, 101B, 101C and 101D in series provides a series-of-MR. Subsequently, resulting four coupling-sections are coupled to conductive patterns 106A, 106B, 106C and 106D respectively. These conductive patterns are coupled to wiring terminals 108A, 108B, 108C and 108D via
through- holes 107A, 107B, 107C and 107D respectively. Namely, four artificial-lattice MR elements are disposed symmetrically on ceramic board 102 so that a bridge circuit is formed.
As clear from above, a simple circuit configuration, like shown in Fig. 11, can detect change of magnetic field with high sensitivity, when four artificial-lattice MR elements are arranged so that magnetic media passes in front of each artificial-lattice MR elements, sequentially in the order.
Referring to Fig. 1, artificial-lattice MR element 1 represents 101A, 101B, 101C and 101D. Similarly, pattern 6 represents 106A, 106B, 106C and 106D. Through-hole 7 represents 107A, 107B, 107C and 107D. Wiring terminal 8 represents 108A, 108B, 108C and 108D.
Fig. 12 shows a block diagram of a bill validator equipped with magnetic sensor assembly 127 described in the second exemplary embodiment of the present invention. Magnetic sensor assembly 127 is the same as magnetic sensor assembly 27 described in the first exemplary embodiment of the invention, except that four, not two, artificial-lattice MR elements, 101A, 101B, 101C and 101D are provided.
In magnetic-sensor-assembly 127, four artificial-lattice MR elements, 101A, 101B, 101C and 101D, each having approximately similar properties, are coupled in series on board 102. Among four resulting coupling sections, pattern 106C and 106B are electrically connected to power and ground, pattern 106A and 106D are electrically connected to input terminal of differential amplifier 141.
Four artificial- lattice MR elements 101A, 101C, 101B and 101D are arranged in this order along bill passing direction. Circuitry following differential amplifier 141 is similar to circuitry shown in Fig. 8 of the first exemplary embodiment of this invention.
Next, operation of bill validator configurated as above is described, but differences between the first and the second exemplary embodiments of this invention only. Namely, artificial-lattice MR elements detect magnetic field of magnetic features printed on bill 12, sequentially in the order of 101A, 101C, 101B and 101D. Similar to Fig. 8 of the first exemplary embodiment of this invention, voltage of coupling section 106A and 106D vary sequentially. Finally, voltage of all coupling sections return back to initial value when magnetic field of magnetic features applied on bill 12 leave away from artificial-lattice MR element 101D. Since a bill validator shown in Fig. 12 functions to detect voltage variation between coupling sections 106A and 106D, magnetic-sensor-assembly 127 is little influenced by environmental magnetic noise. Additionally, the same descriptions as the first exemplary embodiment are simplified here.
As mentioned above, magnetic sensor disclosed in this invention comprises an artificial-lattice MR element formed on a face of a board to detect magnetic field features of a media passing close to the face of the board. The artificial-lattice MR element formed on the board and wiring terminals coupled to the artificial-lattice MR element are integrated in a housing with resin. Moreover, a magnet is mounted at the back of the board in the housing to provide a plane of artificial MR element with an auxiliary magnetic field perpendicularly. The artificial-lattice MR element provided in the magnetic sensor performs with high sensitivity in bill validation. Hence, the magnetic sensor can detect magnetic ink of a bill even on the back or even if being inserted in any direction.
The magnet, adopted to provide a plane of artificial-lattice MR element with an auxiliary magnetic field perpendicularly, provides the magnetic sensor with high accuracy in validation when adopted in a bill validator.

Claims

A magnetic sensor comprising:

(a) an artificial-lattice magnetic resistor (MR) element formed on a face of a board to detect a magnetic media passing close to a face of the board;

(b) the artificial-lattice MR element and wiring terminals coupled to the artificial-lattice MR element being integrated in a housing with
resin;
and

(c) a magnet, mounted at the back of the board in the housing to provide a plane of artificial-lattice MR element with an auxiliary magnetic field perpendicularly.
The magnetic sensor of claim 1, wherein the artificial-lattice MR element has a multi-layer structure comprising not less than each ten layers of Cu layer, 10 to 30Å thick, and Ni-Fe-Co layer, 20 to 40Å thick, sandwiched alternately.
The magnetic sensor of claim 2, wherein a coupled section and both ends of series-of-MR, comprising two artificial-lattice MR element coupled in series and arranged in parallel, are coupled to the wiring terminals.
The magnet sensor of claim 1, wherein the magnet provides with magnetic flux density of 15 to 30 mT at surface of the artificial-lattice MR element.
The magnet sensor of claim 1, wherein the magnet is formed from a material composed of magnetic ferrite powder, mixed and dispersed in at least one of resin or rubber base material.
The magnet sensor of claim 1, further comprising a housing with a hollow for the magnet to be embedded.
The magnet sensor of claim 1, further comprising:

a case composed of resin to house the magnetic sensor of claim 3, wherein

the case comprises an opening against artificial-lattice MR element and grooves to dispose the wiring terminals.
The magnet sensor of claim 7, further comprising:

a resin cap to cover opening of resin case having the artificial-lattice MR element.
The magnet sensor of claim 8, wherein the cap is fitted and secured to case by elastic deformation property.
The magnet sensor of claim 8, further comprising:

a hook formed on opposite side of opening of the case to secure to outside printed wiring board in an elastic deformation property.
The magnet sensor of claim 8, further comprising:

a boss integrated on the case to secure to outside printed wiring board using a screw.
A bill validator comprising:

(d) a bill inlet opening;

(e) a bill pass-way coupled to the bill inlet opening;

(f) the magnetic sensor, described in claim 8, mounted on a wall of the bill pass-way;

(g) an amplifier electrically connected to the magnet sensor;

(h) an analog/digital converter (A/D converter) electrically connected to output of the amplifier;
and

(i) an evaluation circuit electrically connected to output of the A/D converter.
The bill validator of claim 12, further comprising:

a sample/hold circuit, having a time-constant longer than sampling cycle of the A/D converter, between the amplifier and the A/D converter.
The bill validator of claim 13, further comprising:

a printed wiring board having the magnetic sensor with an air space just below the magnetic sensor;
and

a circuit component electrically connected to the magnetic sensor disposed in the air space.
The bill validator of claim 13, wherein validation circuit validates the bill by the maximum signal value detected in adjacent to prescribed measurement area of the bill.
The bill validator of claim 13, wherein validation circuit validates the bill by the maximum to minimum ratio of signals detected in adjacent to prescribed measurement area of the bill.
The bill validator of claim 13, wherein validation circuit validates the bill by detecting an order of occurrence of maximum and minimum output signal from magnetic sensor.
The bill validator of claim 13, wherein validation circuit validates the bill by detecting with a position on the bill which outputs a peak signal level from magnetic-sensor-assembly and a difference between a peak signal level from magnetic-sensor-assembly at an area on the bill and a signal level at a prescribed area on the bill.
The magnetic sensor of claim 2, wherein four coupled sections of series-of-MR, comprising four artificial-lattice MR element coupled in series in ring-form and arranged each in parallel, are electrically connected to the respective wiring terminals.
A magnetic-sensor-assembly comprising:

the magnetic sensor described in claim 19;

a resin case having grooves to dispose the wiring terminals;
and

a resin cap to cover opening of the resin case facing the artificial-lattice MR element.
A bill validator comprising:

a bill inlet opening;

a bill pass-way coupled to the bill inlet opening;

the magnetic-sensor-assembly, described in claim 20, disclosed mounted on a wall of the bill pass-way;

a differential amplifier electrically connected to the magnetic-sensor-assembly;

an A/D converter electrically connected to output of the differential

amplifier;
and

an evaluation circuit electrically connected to output of the A/D converter.