Boots – shoes – and leggings
Patent
1995-06-02
1997-11-25
Elmore, Reba I.
Boots, shoes, and leggings
381 71, 381 93, 370 321, 379406, 379409, G05B 1302
Patent
active
056918933
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an adaptive control system and method for reducing undesired primary signals generated by a primary source of signals.
The basic principle of adaptive control is to monitor the primary signals and produce a cancelling signal which interferes destructively with the primary signals in order to reduce them. The degree of success in cancelling the primary signals is measured to adapt the cancelling signal to increase the reduction in the undesired primary signals.
This idea is thus applicable to any signals such as electrical signals within an electrical circuit in which undesired noise is produced. One particular area which uses such adaptive control is in the reduction of unwanted acoustic vibrations in a region.
It is to be understood that the term "acoustic vibration" applies to any acoustic vibration including sound.
There has been much work performed in this area with a view to providing a control system which can adapt quickly to changes in amplitude and frequency of vibrations from a primary source. Such a system is disclosed in WO88/02912. In this document a controller is disclosed which is implemented as a digital adaptive finite impulse response (FIR) filter. Such a filter adapts its coefficients based on the degree of success in cancelling the undesired vibrations. In order to be able to do so however it must be provided with a model of the acoustic response of the system, i.e. the response of the residual vibration sensors to the output from the secondary vibration sources. In the arrangement disclosed in WO88/02912, the acoustic response of the system is modelled by a matrix of transfer functions termed C. This can either be a prestored model or the arrangement disclosed in WO88/02912 can adaptively modify the matrix entries denoting changes in the transfer functions due to changes in the acoustic properties within the enclosure in which noise cancellation is taking place. Such adaptive learning of the transfer functions is performed in the time domain.
It is therefore an object of the present invention to adaptively determine in the frequency domain the transfer functions between the drive signals generated to cancel the noise and the detected residual signals.
SUMMARY OF THE INVENTION
The present invention provides an adaptive control system for reducing undesired signals comprising a process or adapted to provide at least one secondary signal to interfere with the undesired signals; and a circuit to provide for said processor at least one residual signal indicative of the interference between said undesired and secondary signals; wherein said processor 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; characterized by a noise generator adapted to add at least one low level noise signal to the at least one secondary signal and provide the at least low level noise signal to the processor; said processor being adapted to transform the at least one low level noise signal and the at least one residual signal to provide the amplitude and phase of spectral components of the signals, and to modify the at least one secondary signal using said spectral components of said signals.
Preferably the system includes a circuit to provide at least one first signal indicative of at least selected undesired signals; the processor comprising an adaptive response filter having first filter coefficients to model the response of the at least one secondary signal to the at least one residual signal, and second filter coefficients adaptable in response to the at least one residual signal; the adaptive response filter being adapted to adjust the at least one secondary signal using the first and second filter coefficients to reduce the at least one residual signal.
Preferably at least one cross spectral estimate is formed by using the transforms of the said signals and said at least one cross spectral estimate is used to modify said first filter coefficients.
In one embodi
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Academic Press, "Active Control of Sound", by P.A. Nelson et al., 1992, pp. 113-115.
Elmore Reba I.
Lotus Cars Limited
Marc McDieunel
LandOfFree
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