Method and system for sliding door pattern cancellation in metal detection

1. A method of reducing the signal interference effects of metal doors in a metal detection system, the method comprising:

recording a pattern of signals representing electromagnetic field disturbances over time caused by a pattern of movement of the metal doors in a detection region when a transitory metallic object is not present;

receiving instantaneous signals representing electromagnetic field disturbances during operation of the metal detection system, the instantaneous signals including electromagnetic field disturbances attributed to the movement of the metal doors, the movement of the metal doors during operation of the metal detection system being substantially the same as the pattern of movement of the metal doors during the recording of the pattern of signals; and

determining a resulting waveform, the resulting waveform representing a difference between the instantaneous signals received during operation of the metal detection system and the recorded pattern of signals.

2. The method of claim 1 , wherein the recorded pattern of signals obtained when a transitory metallic object is not present is sampled and recorded over time as the metal doors move from a substantially closed position to a substantially open position.

3. The method of claim 1 , further comprising sensing a relative position of the metal doors as the doors move from a substantially closed position to a substantially open position.

4. The method of claim 1 , further comprising determining an existence of signal drift in the pattern of signals representing electromagnetic field disturbances over time caused by the pattern of movement of the metal doors in a detection region when a transitory metallic object is not present.

5. The method of claim 4 , further comprising determining if the signal drift is within a predetermined range.

6. The method of claim 5 , further comprising determining if the signal drift represents actual signal drift.

7. The method of claim 6 , further comprising revising the recorded pattern of signals obtained when a transitory metallic object is not present if it is determined that actual signal drift is within a predetermined range.

8. A metal detection system comprising:

a transmitter operable to transmit an interrogation signal, the interrogation signal establishing a detection region and being used to detect transitory metal objects within the detection region;

a receiver operable to receive instantaneous signals in response to the interrogation signal, the instantaneous signals representing electromagnetic field disturbances during operation of the metal detection system, the instantaneous signals including electromagnetic field disturbances attributed to the movement of metal doors; and

a metal detection module operable to:

determining a resulting waveform, the resulting waveform representing a difference between the instantaneous signals received during operation of the metal detection system and a recorded pattern of signals representing electromagnetic field disturbances over time caused by a pattern of movement of the metal doors in the detection region when a transitory metallic object is not present, the movement of the metal doors during operation of the metal detection system being substantially the same as the pattern of movement of the metal doors during the recording of the pattern of signals; and

determine if a metal object is present in the detection region based on the resulting waveform.

9. The system of claim 8 , wherein the recorded pattern of signals obtained when a transitory metallic object is not present is sampled and recorded over time as the metal doors move from a substantially closed position to a substantially open position.

10. The system of claim 8 , further comprising at least one motion sensor positioned proximate the metal doors, the at least one motion sensor in communication with the metal detection module and operable to sense a relative position of the metal doors as the doors move from a substantially closed position to a substantially open position.

11. The system of claim 8 , further comprising a module for determining an existence of signal drift in the recorded pattern of signals caused by a pattern of movement of the metal doors in a detection region when a transitory metallic object is not present.

12. The system of claim 11 , wherein the module for determining the existence of signal drift further determines if the signal drift is within a predetermined range.

13. The system of claim 12 , wherein the module for determining an existence of signal drift further determines if the signal drift represents actual signal drift.

14. The system of claim 13 , wherein the module revises the recorded pattern of signals obtained when a transitory metallic object is not present if it is determined that actual signal drift is within a predetermined range.

15. An integrated EAS/metal detection system comprising:

a transmitter operable to transmit an interrogation signal, the interrogation signal establishing an interrogation zone and being used to detect EAS markers and transitory metal objects within the interrogation zone;

a receiver operable to receive instantaneous signals in response to the interrogation signal, the instantaneous signals representing electromagnetic field disturbances during operation of the metal detection system, the instantaneous signals including electromagnetic field disturbances attributed to the movement of metal doors; and

a metal detection module operable to:

determining a resulting waveform, the resulting waveform representing a difference between the instantaneous signals received during operation of the metal detection system and a recorded pattern of signals representing electromagnetic field disturbances over time caused by a pattern of movement of the metal doors in the detection region when a transitory metallic object is not present, the movement of the metal doors during operation of the metal detection system being substantially the same as the pattern of movement of the metal doors during the recording of the pattern of signals; and

determine if a metal object is present in the detection region based on the resulting waveform.

16. The integrated EAS/metal detection system of claim 15 , wherein the recorded pattern of signals obtained when a transitory metallic object is not present is sampled and recorded over time as the metal doors move from a substantially closed position to a substantially open position.

17. The integrated EAS/metal detection system of claim 15 , further comprising at least one motion sensor positioned proximate the metal doors, the at least one motion sensor in communication with the metal detection module and operable to sense a relative position of the metal doors as the doors move from a substantially closed position to a substantially open position.

18. The integrated EAS/metal detection system of claim 15 , further comprising a module for determining an existence of signal drift in the recorded pattern of signals caused by a pattern of movement of the metal doors in a detection region when a transitory metallic object is not present.

19. The integrated EAS/metal detection system of claim 18 , wherein the module for determining the existence of signal drift further determines if the signal drift is within a predetermined range.

20. The integrated EAS/metal detection system of claim 19 , wherein the module revises the recorded pattern of signals obtained when a transitory metallic object is not present if it is determined that signal drift is within a predetermined range.