Dynamic degaussing system

• US 20040042150A1
• Filed: 05/08/2003
• Published: 03/04/2004
• Est. Priority Date: 01/27/2000
• Status: Active Grant

• Current Assignee: VSSI Commercial Incorporated
• Original Assignee: VSSI Commercial Incorporated
• Inventors: Swinbanks, Malcolm A., Holford, John M., Ruckman, Christopher E.
• Granted Patent: US 7,113,384 B2
• Time in Patent Office: Days
• US Class Current: 361/144
• CPC Class Codes: B63G 9/06 for degaussing vessels demagnetising in general H01F13/00
• CPC Class Codes: B63H 21/17 by electric motor
• CPC Class Codes: F16F 15/03 using magnetic or electromagnetic means F16F9/53, F16F15/005 take precedence
• CPC Class Codes: H01F 13/006 Methods and devices for demagnetising of magnetic bodies, e.g. workpieces, sheet material for erasing of information on magnetic record carriers G11B5/00
• CPC Class Codes: H01F 7/0226 PM with variable field strength H01F7/0284 takes precedence
• CPC Class Codes: H02K 11/0094 Structural association with other electrical or electronic devices
• CPC Class Codes: H02K 11/0141 Shields associated with casings, enclosures or brackets
• CPC Class Codes: H04N 9/29 using demagnetisation or compensation of external magnetic fields

Abstract

A dynamic degaussing system includes a magnetic field sensor for generating a sensor signal in response to a sensed magnetic field. The magnetic sensor is coupled to a controller that produces an output signal based on the sensor signal. The controller may include feedforward and feedback control loops. The output signal of the controller controls a magnetic field generator which generates a magnetic field so as to attenuate the sensed magnetic field. According to one aspect of the invention, a vessel is provided with a reduced magnetic signature and a control system for controlling magnetic fields about a podded electric motor. The control system employs feed-forward and feedback control in tandem. The control system may be dynamically adapted to changing physical characteristics of the motor. Control signals are generated in response to sensed or predicted magnetic fields internal to, or external to, the motor. The control inputs may be used to modify one or more motor driving currents, or to drive one or more magnetic field generators, so as to attenuate one or more magnetic field components generated by the motor.

Claims

1. A dynamic degaussing system comprising:

a magnetic field sensor adapted to generate a sensor signal in response to a sensed magnetic field;

a controller adapted to receive said sensor signal and produce an output signal, said controller including feedforward and feedback control loops; and

a magnetic field generator adapted to receive said output signal and generate a responsive magnetic field, said responsive magnetic field adapted to attenuate said sensed magnetic field.

2. A dynamic degaussing system as defined in claim 1, wherein said controller further comprises a modal decomposition matrix.

3. A dynamic degaussing system as defined in claim 2, wherein said modal decomposition matrix comprises a partial matrix.

4. A dynamic degaussing system as defined in claim 1, wherein said controller further comprises a modal reconstitution matrix.

5. A dynamic degaussing system as defined in claim 1 wherein said sensed magnetic field is an external magnetic field of an electric motor.

6. A dynamic degaussing system as defined in claim 1 further comprising a podded electric motor of a naval vessel.

7. A dynamic degaussing system as defined in claim 6 farther comprising a shaft position sensor mechanically coupled to a shaft of said electric motor and signalingly coupled to said feedforward portion of said controller.

8. A dynamic degaussing system as defined in claim 1 wherein said control system further comprises a logic block adapted to modify a transfer function representing a motor system, said motor system being a source of said sensed magnetic field.

9. A dynamic degaussing system as defined in claim 1 wherein said magnetic field generator comprises a coil of insulated wire adapted to generate a magnetic field in response to an applied electric current.

10. A dynamic degaussing system as defined in claim 1 wherein said magnetic field generator comprises a magnetic field generating coil hermetically sealed within a polymer housing, said polymer housing coupled to an electric machine producing said sensed magnetic field.

11. A dynamic degaussing system as defined in claim 10 wherein said polymer housing also encloses said magnetic field sensor.

12. A dynamic degaussing system as defined in claim 1 wherein said controller system comprises a digital electronic control system.

13. A dynamic degaussing system as defined in claim 12 wherein said digital electronic control system comprises a digital signal processor.

14. A dynamic degaussing system as defined in claim 1 wherein said feedforward control loop of said control system comprises a processor adapted to execute a modal matrix decomposition algorithm.

15. A motor system comprising:

an electric motor;

a motor controller electrically coupled to said electric motor and adapted to supply a plurality of driving electric currents to said electric motor;

at least one sensor signallingly coupled to said motor controller and adapted to supply at least one sensor signal thereto, whereby said motor controller modifies one or more driving electric currents of said plurality of driving electric currents in response to said at least one sensor signal so as to reduce an external magnetic field generated by said electric motor.

16. A motor system as defined in claim 15 wherein said external magnetic field generated by said motor comprises a far field magnetic field mode.

17. A motor system as defined in claim 15 wherein said external magnetic field generated by said motor comprises a propagating magnetic field.

18. A motor system as defined in claim 15 wherein said motor controller further comprises a modal decomposition matrix adapted to modify respective amplitudes and waveforms of said plurality of driving electric currents.

19. A motor system as defined in claim 15 further comprising:

at least one sensor signalingly coupled to said motor controller and adapted to supply at least one sensor signal thereto, whereby said motor controller is adapted to supply one or more electrical currents to one or more respective magnetic field generators responsive to said at least one sensor signal.

20. A vehicle comprising:

an electric motor for moving said vehicle; and

a dynamic degaussing system, for dynamically degaussing said motor, said system comprising a plurality of magnetic field detectors, a plurality of electromagnets, and a control system coupled between said magnetic field detectors and said electromagnets for driving said electromagnets to attenuate an electric field detected by said magnetic field detectors.

21. A marine vessel having a podded electric motor, said podded electric motor comprising:

a plurality of magnetic transducers coupled to a control system, said transducers and control system adapted to mutually interoperate so as to mask a magnetic signature of said podded electric motor.

22. A marine vessel defined in claim 21 wherein said plurality of magnetic transducers comprises:

a plurality of magnetic sensors; and

a plurality of magnetic field generators.

23. A marine vessel as defined in claim 21 wherein said control system comprises a first computer processor and a second digital signal processor mutually coupled to produce an output signal, said output signal adapted to drive one of said transducers so as to attenuate a magnetic field produced by said podded electric motor.

24. A method of masking a magnetic signature of an electric motor, said method comprising the steps of:

predicting a respective location, magnitude and orientation of a first magnetic field vector of a first magnetic field produced by an first electric current within said motor, based in part on a magnitude of said first electric current of said motor;

supplying a second electric current to a magnetic field generator, said magnetic field generator adapted, on receipt of said electric current, to produce a second magnetic field having a second magnetic filed vector with a respective location and magnitude substantially equal to said location and magnitude of said first magnetic field vector, and having an orientation substantially opposite that of said first magnetic field vector.

25. An attenuation system for attenuating external electric fields, said system comprising:

a sensor for sensing an external magnetic field about an electric machine;

a processor for receiving a first input signal from said sensor and producing a second output signal;

a phasor maker for receiving said second output signal and producing a third output signal having a respective first magnitude and phase; and

a magnetic field transducer adapted to produce a magnetic field configured to attenuate at least a portion of said external magnetic field based on said third output signal.

26. The system as defined in claim 25 further comprising an amplifier adapted to receive said third output signal and transmit an amplified version thereof to said magnetic field transducer.

27. The system as defined in claim 26 wherein said processor further comprises a digital signal processor.

28. The system as defined in claim 26 wherein said processor further comprises a storage medium adapted to store a computer program, said computer program adapted to predict that external magnetic field at a particular time period.

29. A method of attenuating a magnetic field comprising:

disposing a permanent magnet device including two rotatably connected magnetic structures in a magnetic field region;

rotatably adjusting said connected magnetic structures to adjust a net magnetic field produced by said permanent magnet device; and

attenuating a further magnetic field within said magnetic field region by combining said net magnetic field and said further magnetic field within said magnetic field region.

30. A method of attenuating a magnetic field as defined in claim 29 wherein said further magnetic field is a static magnetic field.

31. A method of attenuating a magnetic field as defined in claim 29 wherein said further magnetic field is a dynamic magnetic field when viewed with respect to an environment of said magnetic field region.

32. A magnetic field attenuating device comprising:

first and second legs pivotingly coupled to one another;

a first magnet coupled to said first leg;

a second magnet coupled to said second leg, said first and second magnets disposed so as to produce respective magnetic fields, said respective magnetic fields being at least partially opposed to one another; and

means for fixing said first and second legs within a magnetic field region.

33. A magnetic field attenuating device as defined in claim 32 further comprising a third and a fourth magnet coupled to said first and second legs respectively.

34. A magnetic field device as defined in claim 32 wherein said first leg is adapted to pivot in relation to said second leg, whereby a net magnetic field produced by said first and second magnets is adjusted.