Detecting device having spaced transmitting and receiving coils for detecting a metal strip embedded in paper money

• US 4,536,709 A
• Filed: 08/29/1984
• Issued: 08/20/1985
• Est. Priority Date: 01/12/1981
• Status: Expired due to Fees

• Current Assignee: Tokyo Shibaura Denki Kabushiki Kaisha
• Original Assignee: Tokyo Shibaura Denki Kabushiki Kaisha
• Inventors: Ishida, Tsuyoshi
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US06/645,533
• Time in Patent Office: 356 Days
• Field of Search: 324/233, 324/234, 324/239-243, 324/329, 194/100 R, 194/100 A, 235/449, 235/450, 235/493, 340/675, 340/676, 340/551, 209/534, 209/567, 209/569
• US Class Current: 324/239
• CPC Class Codes: G07D 7/04 Testing magnetic properties of the materials thereof, e.g. by detection of magnetic imprint G07D7/01 takes precedence
• CPC Class Codes: H03K 17/954 controlled by an oscillatory signal

Abstract

The metal detecting device includes first and second coils provided on both sides of a passageway for paper money. This metal detecting device is designed for use in detecting a metal strip embedded in the paper money in order to determine whether the paper money is genuine or counterfeit. The first coil is connected to a high frequency AC source to generate an AC magnetic field. The second coil is connected to a capacitor to form a resonance circuit which resonates at the same frequency as the AC current. The variation of the Q factor of the resonance circuit due to eddy-current losses produced in the metal strip of the paper money is used by a detecting circuit to determine whether the paper money passing through the space between the first and second coils is genuine.

Claims

1. A detecting device for detecting a sheet of genuine paper money having a longer dimension and a shorter dimension, the sheet including an embedded metal strip having a length substantially equal to the shorter dimension of the sheet and a predetermined width, the strip being oriented within the sheet so that its length is substantially parallel to the shorter dimension of the sheet, said detecting device comprising:

transporting means for rapidly transporting the sheet in the direction of its longer dimension along a transportation path;

an electric transmitting coil adjacent one side of the transportation path having a long and narrow shaped plane and having a width larger than the predetermined width of the strip, the long dimension of said long and narrow shaped plane being oriented substantially parallel to the shorter dimension of the sheet as the sheet is transported along the transportation path;

an electric receiving coil adjacent the transportation path directly opposite said transmitting coil having a long and narrow shaped plane and positioned in spaced parallel relationship to said transmitting coil along the transportation path, said receiving coil having a width larger than the predetermined width of the strip, wherein the sheet is transported between said transmitting coil and said receiving coil with the surface of the sheet being parallel to the shaped planes of said coils;

AC current supply means for supplying AC current to said electric transmitting coil to generate a magnetic field;

a capacitor connected to said electric receiving coil in a resonance circuit which generates a resonance signal; and

detecting means connected to said resonance circuit for detecting variations in the resonance signal of said resonance circuit caused by eddy current losses in said metal strip when said metal strip passes between said transmitting and receiving coils.

2. A detecting device as claimed in claim 1 wherein the length of said transmitting and receiving coils is greater than the width of the sheet moving on the transportation path.

3. A detecting device as claimed in claim 1 wherein said AC current supply means is a sine wave oscillator for generating a high frequency AC signal.

4. A detecting device as claimed in claim 1 wherein said resonance circuit is a parallel resonance circuit.

5. A detecting device as claimed in claim 1 wherein said detecting means comprises a detecting circuit for detecting the resonance signal, a clamp circuit for clamping the output of said detecting circuit at a fixed potential and a comparator for converting the output of said clamp circuit into a binary signal.

6. A detecting device for detecting a sheet of genuine paper money having a longer dimension and a shorter dimension, the sheet including an embedded metal strip having a length substantially equal to the shorter dimension of the sheet and a predetermined width, the strip being oriented within the sheet so that its length is substantially parallel to the shorter dimension of the sheet, said detecting device comprising:

transporting means for rapidly transporting the sheet in the direction of its longer dimension along a transportation path;

electric transmitting coil means adjacent one side of the transportation path having a long and narrow shaped plane and having a width larger than the predetermined width of the strip, the long dimension of said long and narrow shaped plane being oriented substantially parallel to the shorter dimension of the sheet as the sheet is transported along the transportation path;

a plurality of electric receiving coil means adjacent the transportation path directly opposite said electric transmitting coil means having long and narrow shaped planes and positioned in spaced parallel relationship with said electric transmitting coil means along the transportation path, said electric receiving coil means having a width larger than the predetermined width of the strip, wherein the sheet is transported between said electric transmitting coil means and said plurality of electric receiving coil means with the surface of the sheet being parallel to the shaped planes of said coil means;

AC current means for supplying AC current to said transmitting coil means to generate a magnetic field;

a resonance element connected to each of said electric receiving coil means to form a resonance circuit which generates a resonance signal; and

detecting means connected to said resonance circuits and responsive to said metal strip for generating a detecting signal, said detecting means detecting a variation in the resonance signal in each of said resonane circuits caused by eddy current losses in said metal strip when said metal strip passes between said electric transmitting coil means and said plurality of electric receiving coil means.

7. A detecting device as claimed in claim 6 wherein said electric transmitting coil means is a single electric coil.

8. A detecting device as claimed in claim 7 wherein the length of said single electric transmitting coil is greater than the shorter dimension of the sheet moving on the transportation path.

9. A detecting device as claimed in claim 6 wherein said electric transmitting coil means is formed by a plurality of electric coils.

10. A detecting device as claimed in claim 6 wherein said AC current supply means is a sine wave oscillator for generating a sine wave high frequency signal.

11. A detecting device as claimed in claim 6 wherein each of said resonance circuits is a parallel resonance circuit.

12. A detecting device as claimed in claim 6 wherein said detecting means comprises a detecting circuit for detecting each resonance signal, a clamping circuit connected to each of said detecting circuits for clamping the output of each detecting circuit to a fixed potential, a comparator connected to each of said clamping circuits for converting the output of each clamping circuit to a binary signal and a logical circuit for generating an output detecting signal by combination of a predetermined number of the outputs of each of said comparators.

13. A detecting device as claimed in claim 6 wherein said detecting means comprises a detecting circuit connected to each of said resonance circuits for detecting each resonance signal, an adding circuit connected to said detecting circuits for adding the outputs of said detecting circuits, a clamping circuit connected to said adding circuit for claming the output of said adding circuit to a fixed potential and a comparator connected to said clamping circuit for converting the output of said clamping circuit into a binary signal.