Adaptive control system

• US 5,691,893 A
• Filed: 06/02/1995
• Issued: 11/25/1997
• Est. Priority Date: 10/21/1992
• Status: Expired due to Term

• Current Assignee: Harman Becker Automotive Systems Manufacturing Kft (Samsung Electronics Co. Ltd.)
• Original Assignee: Lotus Cars Limited (Zhejiang Geely Holding Group Co., Ltd.)
• Inventors: Stothers, Ian MacGregor
• Primary Examiner(s): Elmore, Reba I.
• Assistant Examiner(s): Marc, McDieunel, Marc, McDieunel
• Application Number:
  US08/416,765
• Time in Patent Office: 907 Days
• Field of Search: 364/148, 364/300, 364/900, 364/572, 364/574, 381/71, 381/94, 379/388, 379/390, 379/410
• US Class Current: 700/28
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17883 the reference signal being derived from a machine operating condition, e.g. engine RPM or vehicle speed
• CPC Class Codes: G10K 2210/1082 Microphones, e.g. systems using "virtual" microphones
• CPC Class Codes: G10K 2210/3011 Single acoustic input
• CPC Class Codes: G10K 2210/3018 Correlators, e.g. convolvers or coherence calculators
• CPC Class Codes: G10K 2210/30232 Transfer functions, e.g. impulse response
• CPC Class Codes: G10K 2210/3025 Determination of spectrum characteristics, e.g. FFT
• CPC Class Codes: G10K 2210/3045 Multiple acoustic inputs, single acoustic output
• CPC Class Codes: G10K 2210/3217 Collocated sensor and cancelling actuator, e.g. "virtual earth" designs
• CPC Class Codes: G10K 2210/3229 Transducers

Abstract

An adaptive control system for reducing undesired signals comprises a processor (36) which provides secondary signals for sources (37) for interference with the undesired signals. Sensors (42) measure the residual Vibration which is indicative of the interference between the undesired and secondary signals. The processor (36) uses the residual signal to adjust the secondary signals to reduce the residual signals. Noise generation means (48) is provided to add a low level noise signal to the secondary signal and to provide a low level noise signal to the processor (36). The processor (36) is adapted to transform the low level noise signal and the residual signal from sensors (42) to provide the amplitude and phase of spectral components of the signals. The processor (36) modifies the secondary signals using these spectral components to obtain better reduction of the undesired signals.

Claims

1. An adaptive control system for reducing undesired signals comprising processing means adapted to provide at least one secondary signal to interfere with the undesired signals;

and residual means to provide for said processing means at least one residual signal indicative of the interference between said undesired and secondary signals;

wherein said processing means is adapted to use said at least one residual signal to adjust the or each secondary signal to reduce said at least one residual signal;

wherein;

noise generation means is provided which adds at least one low level noise signal to said at least one secondary signal and provides said at least one low level noise signal to said processing means;

said processing means is adapted to transform said at least one low level noise signal and said at least one residual signal to provide the amplitude and phase of spectral components of said signals;

signal means is provided which provides at least one first signal indicative of at least selected undesired signals;

said processing means filters the at least one first signal indicative of at least selected undesired signals using adaptive response filter means having first and second filter coefficients;

said processing means adapts said first filter coefficients using the spectral components of said at least one low level noise signal and said at least one residual signal;

said processing means uses the first filter coefficients to filter one of the at least first signal indicative of at least selected undesired signals and the at least one residual signal;

said processing means adapts said second filter coefficients in response to the at least first signal indicative of at least selected undesired signals and the at least one residual signal, one of said signals having been filtered using the first filter coefficients;

said processing means in producing the at least one secondary signal uses the second filter coefficients to filter the at least first signal indicative of at least selected undesired signals; and

the processing means adapts said first and second filter coefficients to reduce said at least one residual signal.

2. An adaptive control system as claimed in claim 1, wherein said processing means forms at least one cross spectral estimate using the transform of the at least one low level noise signal and the at least one residual signal and uses said at least one cross spectral estimate to adapt said first filter coefficients.

3. An adaptive control system as claimed in claim 2, wherein said processing means is adapted to form said at least one cross spectral estimate by multiplying the complex conjugate of the transform of said low level noise signal with the transform of said at least one residual signal.

4. An adaptive control system as claimed in claim 2, wherein said processing means is adapted to multiply said at least one cross spectral estimate with a convergence coefficient sufficiently small to smooth out the effect of random errors in the cross spectral estimate on the modification of the first filter coefficients.

5. An adaptive control system as claimed claim 2, wherein said fast filter coefficients are complex and said processing means is adapted to modify said complex first filter coefficients.

6. An adaptive control system as claimed in claim 2, wherein said processing means is adapted to inverse transform said at least one cross spectral estimate to form at least one cross correlation estimate, and to modify said first filter coefficients using said at least one cross correlation estimate.

7. An adaptive control system as claimed in claim 6, wherein said processing means is adapted to multiply said at least one cross correlation estimate with a convergence coefficient sufficiently small to smooth out the effect of random errors in the cross correlation estimate on the modification of said first filter coefficients.

8. An adaptive control system as claimed in claim 5, wherein said processing means is adapted to transform said at least one first signal, to form at least one second cross spectral estimate using the transform of said at least one first signal and the transform of said at least one residual signal, to inverse transform said at least one second cross spectral estimate to form at least one second cross correlation estimate, and to modify said second filter coefficients using said at least one second cross correlation estimate.

9. An adaptive control system as claimed in claim 8, wherein said processing means is adapted to form at least one second cross spectral estimate by filtering the transform of said at least one first signal using said complex first filter coefficients and multiplying the complex conjugate of the result with the transform of said at least one residual signal.

10. An adaptive control system as claimed in claim 8, wherein said processing means is adapted to form at least one second cross spectral estimate by filtering the transform of said at least one residual signal using the complex conjugate of said complex first filter coefficients and multiplying the result with the complex conjugate of the transform of said at least one first signal.

11. An adaptive control system as claimed in claim 1, for reducing selected signals of said undesired signals, wherein said processing means is adapted to only modify the first filter coefficients which do not adjust said at least one secondary signal at the frequency of said selected signals.

12. An adaptive control system as claimed in claim 1 wherein said noise generation means is adapted to generate random or pseudo-random noise.

13. An adaptive control system as claimed in claim 1 wherein said noise generation means is adapted to generate noise uncorrelated at least with selected signals of said undesired signals.

14. An adaptive control system as claimed in claim 1 wherein said processing means is adapted to modify at least one of the amplitude and phase of the spectral components of said noise signal, and to inverse transform the modified spectral components for addition to said at least one secondary signal.

15. An adaptive control system as claimed in claim 1 wherein said processing means is adapted to digitally sample said noise signal and said at least one residual signal, and to store a plurality of digits for each said signal to form noise signal and residual signal data blocks respectively, said noise signal data blocks and said residual signal data blocks being time aligned;

said processing means being further adapted to set a number of said digits at the end of each noise signal data block to zero to form a modified noise signal data block, and to transform the modified noise signal data block and the time associated residual signal data block to provide the amplitude and phase of spectral components of the digitally sampled signals.

16. An adaptive control system as claimed in claim 15, wherein said processing means is adapted to set the number of said digits at the end of each modified noise signal data block to zero in dependence on the delay between the noise signal and the contribution from the noise signal in the residual signal.

17. An adaptive control system as claimed in claim 16, wherein said processing means is adapted to select the number of digits to set to zero such that the time taken to sample said number is greater than the delay between a secondary signal and the contribution of the secondary signal in any residual signal.

18. An adaptive control system as claimed in claim 1 wherein said processing means is adapted to modify said signal filter coefficients to reduce a cost function.

19. A method as claimed in claim 18, wherein said second filter coefficients are modified to reduce a cost function.

20. An adaptive control system as claimed in claim 1, wherein the undesired signals are undesired acoustic vibrations, said system including at least one secondary vibration source adapted to receive said at least one secondary signal and generate secondary vibrations to interefere with said undesired vibrations;

said residual means comprising at least one sensor means adapted to sense the residual vibrations resulting from the interference between said secondary and undesired vibrations, and to provide said at least one residual signal.

21. A method of actively reducing undesired signals comprising the steps of:

providing at least one secondary signal which interferes with said undesired signals;

providing at least one residual signal indicative of the interference between said undesired and secondary signals;

adjusting the or each secondary signal using said at least one residual signal to reduce the or each residual signal;

generating at least one low level noise signal;

adding said at least one low level noise signal to said at least one secondary signal;

transforming said at least one low level noise signal and said at least one residual signal to provide the amplitude and phase of spectral components of said signals;

providing at least one first signal indicative of at least selected undesired signals;

filtering the at least one first signal indicative of at least selected undesired signals using adaptive response filter means having adaptable first and second filter coefficients;

adapting the first filter coefficients using said spectral components of said at least one low level noise signal and said at least one residual signal;

filtering one of said at least one first signal indicative of at least selected undesired signals and said at least one residual signal using the first filter coefficients;

adapting the second filter coefficients in response to said at least one first signal indicative of at least selected undesired signals and said at least one residual signal after having filtered one of said signals using the first filter coefficients;

filtering the at least one first signal indicative of at least selected undesired signals using the second filter coefficients in the production of the at least one secondary signal; and

adapting said first and second filter coefficients to reduce said at least one residual signal.

22. A method as claimed in claim 21, including the steps of forming at least one cross spectral estimate using the transforms of the at least one noise signal and the at least one residual signal;

and adapting said first filter coefficients using said at least one cross spectral estimate.

23. A method as claimed in claim 22, wherein said at least one cross spectral estimate is formed by multiplying the complex conjugate of the transform of said at least one noise signal with the transform of said at least one residual signal.

24. A method as claimed in claim 22, including the step of multiplying said at least one cross spectral estimate with a convergence coefficient sufficiently small to smooth out the effect of random errors in the cross spectral estimate on the modification of the first filter coefficients.

25. A method as claimed in claim 22, wherein said first filter coefficients are complex and said complex first filter coefficients are modified using said at least one cross spectral estimate.

26. A method as claimed in claim 22, including the steps of inverse transforming said at least one cross spectral estimate to form at least one cross correlation estimate, and modifying said first filter coefficients using said at least one cross correlation estimate.

27. A method as claimed in claim 26, including the step of multiplying said at least one cross correlation estimate with a convergence coefficient sufficiently small to smooth out the effect of random errors in the cross correlation estimate on the modification of said first filter coefficient.

28. A method as claimed in claim 25, including the steps of transforming said at least one first signal, forming at least one second cross spectral estimate using the transform of said at least one first signal and the transform of said at least one residual signal, inverse transforming said at least one second cross spectral estimate to form at least one second cross correlation estimate, and modifying said second filter coefficients using said at least one second cross correlation estimate.

29. A method as claimed in claim 28, wherein said at least one second cross spectral estimate is formed by filtering the transform of said at least one first signal using said complex first filter coefficients, and multiplying the complex conjugate of the result with the transform of said at least one residual signal.

30. A method as claimed in claim 28, wherein said at least one second cross spectral estimate is formed by filtering the transform of said at least one residual signal using the complex conjugate of said complex first filter coefficients, and multiplying the result with the complex conjugate of the transform of said at least one first signal.

31. A method as claimed in claim 21 for reducing selected signals of undesired signals wherein only the first filter coefficients which do not adjust said at least one secondary signal at the frequency of said selected signals are modified.

32. A method as claimed in claim 21, wherein the step of generating a low level noise signal comprises generating a low level random or pseudo-random noise signal.

33. A method as claimed in claim 21, wherein the step of generating a low level noise signal comprises generating a low level noise signal uncorrelated at least with selected signals of said undesired signals.

34. A method as claimed in claim 21, including the steps of modifying at least one of the amplitude and phase of the spectral components of said noise signal, and inverse transforming the modified spectral components for addition to said at least one secondary signal.

35. A method as claimed in claim 21, including the steps of digitally sampling said noise signal and said at least one residual signal, storing a plurality of digits for each said signal to form noise signal and residual signal data blocks respectively, said noise signal data blocks and said residual signal data blocks being time aligned;

setting a number of said digits at the end of each noise signal data block to zero to form a modified noise signal data block; and

transforming the modified noise signal data block and the time associated residual signal data block to provide the amplitude and phase of the digitally sampled signals.

36. A method as claimed in claim 35, wherein the number of digits set to zero is determined in dependence on the delay between the noise signal and the contribution from the noise signal in the residual signal.

37. A method as claimed in claim 36, wherein the number of said digits that are set to zero is determined such that the time taken to sample said number of digits is greater than the delay between a secondary signal and the contribution of the secondary signal in any residual signal.

38. A method as claimed in claim 21, wherein said undesired signals comprise undesired acoustic vibrations, the method including the steps of generating at least one secondary vibration from said at least one secondary signal, allowing said at least one secondary vibration and said undesired vibrations to interfere, and sensing residual vibrations resulting from the interference to provide said at least one residual signal.