Low cost controller

Details Low cost controller Low cost controller

1995-03-01

1997-05-06

Ruggiero, Joseph

Boots, shoes, and leggings

364176, 3647242, 381 71, G05B 1302, G06F 1700

Patent

active

056277466

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a low cost active noise cancellation system. It was designed by the need for very low cost electronics in using active noise cancellation for quieting small fans, refrigerators and other extremely cost sensitive applications. The instant invention has the ability to cancel stationary random noise such as that encountered on a rangehood fan or tonal noise. The "plant" of the operation, i.e., the speakers, enclosure, microphone and the configuration itself has to be of a certain design so as to minimize delays which interfere with the plants ability to produce a cancellation signal. These delays are the result of the response of the loudspeaker, its cabinet and the transit time between speaker and microphone. While repetitive compensating techniques can be used in repetitive noise, they don't work with random noise. This invention contemplates employing strict design criteria in designing the "plant" and using equalizing filters. The equalization filter allows for a relaxation of the strict time delay requirements. A filter is used to produce an estimate of the noise by subtracting the predicted effects of the cancellation signal from the residual signal. For tonal cancellation the equalization filter is used to add additional delays at frequencies where needed, for instance where the plant delay is too long to meet the requirements for random cancellation, in order to meet an earlier cycle of the tonal noise. For random cancellation the equalization filter minimizes the mean-square error resulting from twin delays in the system.
The DVE (digital virtual earth) system disclosed in U.S. Pat. No. 5,105,377 can, with a dozen or so taps, cancel band limited random noise if plant delays are small enough. This has been done by canceling random noise limited between 150 Hz to 450 Hz shown in the charts of FIGS. 12 and 13 herein. The adaptive FIR filter of DVE can be replaced by a single inverting amplifier with adjustable gain under appropriate plant criteria. Thus a small, low cost canceller consists of a single filter to predict the effects of the cancellation signal on the residual signal enabling the feedback to be electronically subtracted. An inverting amplifier with adjustable gain is used and, possibly, an equalization circuit is used to compensate for delays in the plant that are too long for random cancellation when applying the device to tonal cancellation. The DVE feedback filter can be replaced with a simple delay resulting in a cancellation system including equalization that requires only a single filter.
Accordingly it is an object of this invention to provide an active noise cancellation plant system that can cancel band limited random noise.
Another object of this invention is to provide a low cost active noise cancellation system.
A further object of this invention is to provide an active noise cancellation system that can cancel tonal noise.
These and other objects will become apparent when reference is had to the accompanying description and drawings in which
FIG. 1 shows a circuit diagram of a basic standard controller set.
FIG. 2 shows a circuit of a basic controller simplified per this invention.
FIG. 3 is a circuit diagram showing a basic/weight optimum filter circuit.
FIG. 4 is a circuit diagram showing a weight optimum filter with an equalizer.
FIG. 5 is illustrative of a circuit showing equalizer training position.
FIG. 6 is a diagram showing an alternate equalizer position.
FIG. 7 shows a canceller with plant equalization.
FIG. 8 shows a diagram of a basic low cost canceller.
FIG. 9 shows a single filter low cost canceller with equalization.
FIG. 10 shows a plot of random noise cancellation in a SAAB twin prop.
FIG. 11 shows the plot of random noise cancellation in a Grumman Tiger single prop.
FIGS. 12 and 13 show the results of fan noise cancellation with DVE cancellation On and Off.
FIGS. 14 and 15 shows the amount of cancellation without equalization plotted for various frequencies and time delays.
FIG. 16 shows the value of Aopt without equalization for vari

REFERENCES:
patent: 4566118 (1986-01-01), Chaplin et al.
patent: 4649505 (1987-03-01), Zinser, Jr. et al.
patent: 4878188 (1989-10-01), Ziegler, Jr.
patent: 5105377 (1992-04-01), Ziegler, Jr.
patent: 5219037 (1993-06-01), Smith et al.

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