Boots – shoes – and leggings
Patent
1995-06-02
1997-11-11
Elmore, Reba I.
Boots, shoes, and leggings
381 71, 381 94, G05B 1302, A61F 1106, H03B 2900
Patent
active
056870752
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 interfers 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 source. Prior art adaptive control systems either operate in the time or frequency domain on the drive signal to be output to cancel the noise. A time domain 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. In order for the filter to be adapted the filter coefficents must be modified based on the degree of success in cancelling the undesired vibrations. For such a control system disclosed in this document, where there are a large number of error signals, drive signals and reference signals, there are a large number of calculations which must be performed for each update of the coefficients. For instance, an estimate of the response of each sensor to each drive signal (the C filter) must be taken into consideration in the calculation of the update of the filter coefficients.
WO88/02912 also discloses the operation of a digital filter in the frequency domain. Such a filter has complex filter coefficients and requires the reference signal and error signals to be transformed into the frequency domain and the output drive signal from the adaptive filter to be inverse transformed back to the time domain in order to provide the drive signal. The transform which is conveniently used is the Fourier transform. In order for such a transform to be performed a number of data points within a window length are transformed and used to adapt the following window of data. Such a discrete Fourier transform provides good control if the length of the window (or number of data points) is long, but this provides a long delay in the update. A short window of data on the other hand provides for a quick adaption but poor control.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an adaptive control system which is computationally efficient compared with time domain adaptive control systems and which overcomes the problems associated with frequency domain adaptive control systems.
The present invention provides an adaptive control system for reducing undesired signals, comprising signal means to provide at least one first signal indicative of at least selected undesired signals; processing means adapted to use said at least one first signal 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 transform said at least one first signal and said at least one residual signal to provide the amplitude and phase of spectral components of said signals, to collate the transformed signals, to inverse transform of the outcome of said collation, and to adjust the or each secondary signal using the inverse transform of the outcome of the collation to reduce said at least one residual signal.
Preferably said processing means comprises a
REFERENCES:
patent: 4238746 (1980-12-01), McCool et al.
patent: 5170433 (1992-12-01), Elliot et al.
patent: 5396414 (1995-03-01), Alcone
patent: 5426704 (1995-06-01), Tamamura et al.
patent: 5473555 (1995-12-01), Potter
"Active Control of Sound", Academic Press, London, U.K., 1992, By P.A. Nelson and S.J. Elliott, pp. 113-115.
Dolan Robert J.
Elmore Reba I.
Lotus Cars Limited
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