METAL DETECTOR

• US 20090021252A1
• Filed: 07/19/2007
• Published: 01/22/2009
• Est. Priority Date: 07/19/2007
• Status: Active Grant

• Current Assignee: Carnes Company, Inc.
• Original Assignee: Carnes Company, Inc.
• Inventors: Simon, Joseph S.
• Granted Patent: US 7,791,337 B2
• Time in Patent Office: Days
• US Class Current: 324/236
• CPC Class Codes: G01V 3/104 using several coupled or uncoupled coils G01V3/101 takes precedence

Abstract

A vibration canceling circuit for a metal detector. The metal detector includes a transmit coil, first and second receive coils, a differential circuit coupled to the first and second receive coils, a controller coupled to the differential circuit, and a vibration canceling circuit coupled to the controller. The controller uses a signal provided by the vibration canceling circuit to remove a vibration component from a metal detection signal.

Claims

1. A metal detector comprising:

a transmit coil;

first and second receive coils inductively coupled to the transmit coil;

a differential circuit coupled to the first and second receive coils;

a controller coupled to the differential circuit; and

a vibration canceling circuit coupled to the controller.

2. The metal detector of claim 1, wherein the first and second receive coils are positioned substantially equidistantly on opposite sides of the transmit coil

3. The metal detector of claim 1, wherein the vibration canceling circuit includes a vibration detection circuit providing a signal indicative of motion on an axis.

4. The metal detector of claim 3, wherein the vibration detection circuit provides signals indicative motion on two or more axes, wherein each axis is orthogonal to the other axes.

5. The metal detector of claim 3, wherein the vibration canceling circuit includes a filter and an amplifier.

6. The metal detector of claim 1, wherein the vibration canceling circuit includes a vibration detection circuit providing a plurality of signals, each signal indicative of motion on an axis.

7. The metal detector of claim 6, wherein the plurality of signals are filtered and combined, and the combined signal is amplified and provided to the controller.

8. The metal detector of claim 6, wherein the signals are generated by an accelerometer.

9. The metal detector of claim 8, wherein the accelerometer is coupled to a passageway, the accelerometer detecting vibration of the passageway.

10. The metal detector of claim 1, wherein the controller modifies a signal received from the differential circuit using a signal received from the vibration canceling circuit to obtain a metal detection signal with a vibration component substantially removed.

11. The metal detector of claim 10, wherein the signal received from the vibration canceling circuit is converted to a digital value before being provided to the controller.

12. A method of reducing a vibration component of a detection signal in a metal detector, the method comprising:

detecting movement of the metal detector on a first axis;

generating a first signal indicative of the movement on the first axis; and

modifying a detection signal based at least on the first signal.

13. The method of claim 12, further comprising

detecting movement of the metal detector on a second axis orthogonal to the first axis;

generating a second signal indicative of the movement on the second axis; and

combining the first and second signals to create a combined signal;

wherein the modifying of the detection signal is based on the combined signal.

14. The method of claim 13, further comprising

detecting movement of the metal detector on a third axis orthogonal to the first and second axes;

generating a third signal indicative of the movement on the third axis; and

combining the first, second, and third signals to create the combined signal.

16. The method of claim 12, further comprising amplifying the first signal, to create an amplified signal, before modifying the detection signal.

17. The method of claim 16, further comprising converting the amplified signal to a digital value and providing the digital value to a controller.

18. The method of claim 12, wherein the detection signal is modified by scaling and/or a subtraction.

15. The method of clam 14, further comprising filtering the first, second, and third signals before combining.

19. A vibration detection circuit, comprising:

an accelerometer configured to generate a one or more signals, each signal indicative of movement along an axis;

a combining filter configured to filter a component of the one or more signals not associated with movement and to combine the components of the one or more signals indicative of movement to create a combined signal;

an amplifier configured to amplify the combined signal and create an amplified signal; and

an analog to digital converter configured to convert the amplified signal into a digital value.

20. The vibration detection circuit of claim 19, wherein the one or more signals include a first signal indicative of movement on a first axis and a second signal indicative of movement on a second axis orthogonal to the first axis.

21. The vibration detection circuit of claim 20, wherein the one or more signals include a third signal indicative of movement on a third axis, the third axis orthogonal to the first and second axes.