Adaptive passive acoustic attenuation system

• US 6,295,363 B1
• Filed: 03/20/1997
• Issued: 09/25/2001
• Est. Priority Date: 03/20/1997
• Status: Expired due to Term

• Current Assignee: Nelson Industries Incorporated (Cummins Incorporated), Digisonix Incorporated
• Original Assignee: Nelson Industries Incorporated (Cummins Incorporated), Digisonix Incorporated
• Inventors: Laak, Trevor A. Jr., Kapsos, David W. Jr.
• Primary Examiner(s): Nguyen, Duc
• Application Number:
  US08/821,110
• Time in Patent Office: 1,650 Days
• Field of Search: 381/71.5, 381/71.13, 381/71.1, 381/71.8, 381/71-1-, 381/94.1, 381/94-- 9, 181/206, 181/250, 181/276
• US Class Current: 381/94.1
• CPC Class Codes: G10K 11/161 in systems with fluid flow G10K11/162 takes precedence; gas flow silencers or exhaust apparatus for machines or engines in general or for internal combustion engine F01N, noise absorbers in pipes or pipe systems F16L55/02; noise absorption in air conditioning and ventilation F24F13/24; silencing exhaust or propulsion jets in aircraft B64D33/06

Abstract

An adaptive passive acoustic attenuation system implements control techniques to facilitate practical use of adaptive passive acoustic attenuation in industrial and commercial applications. The system includes multiple banks of multiple adjustable tuners that are used to passively attenuate an acoustic disturbance (e.g. a tone) propagating through an acoustic plant. All of the tuners in one of the banks are contemporaneously adjusted during an adaptation scan while the tuners in the other banks remain stationary. The process is then carried out for the other banks of adjustable tuners. The number of adjustable tuners per bank is chosen so that adaptation scans of the tuners in the respective bank create observable changes in acoustic levels to enable adaptation. Multiple sets of multiple banks of adjustable tuners can be provided to attenuate multiple disturbances propagating through the acoustic plant. Signals from error sensors are filtered and processed to account for acoustic energy in the plane wave mode as well as higher order modes. Adaptation accuracy is improved by a double scan technique, and by accounting for time-varying acoustic disturbances. Mechanical malfunctioning of the adjustable tuners is reduced by an exercising technique, and the control model implements a lock-out scheme for mechanically malfunctioning tuners.

Claims

1. An adaptive passive acoustic attenuation system that attenuates an acoustic disturbance in an acoustic plant comprising:

multiple banks of adjustable tuners communicating acoustically with the acoustic plant, each adjustable tuner having passive acoustical characteristics determined in accordance with passive parameter settings;

an error sensor that senses an acoustic disturbance in the acoustic plant and generates an error signal in response thereto;

an electronic controller that receives the error signal from the error sensor and outputs correction signals to selectively adjust the passive parameter settings of the adjustable tuners;

means for adapting the system which comprises contemporaneously adjusting the passive parameter settings for all of the tuners in one of the banks to vary the acoustic disturbance sensed by the error sensor while the tuners in the other banks remain stationary;

means for determining whether each adjustable tuner is fully operational; and

means for deactivating adjustment of any adjustable tuner in the system that is not fully operational.

2. An adaptive passive acoustic attenuation system that attenuates an acoustic disturbance in an acoustic plant comprising:

multiple banks of adjustable tuners communicating acoustically with the acoustic plant, each adjustable tuner having passive acoustical characteristics determined in accordance with passive parameter settings;

an error sensor that senses an acoustic disturbance in the acoustic plant and generates an error signal in response thereto;

an electronic controller that receives the error signal from the error sensor and outputs correction signals to selectively adjust the passive parameter settings of the adjustable tuners;

means for adapting the system which comprises contemporaneously adjusting the passive parameter settings for all of the tuners in one of the banks to vary the acoustic disturbance sensed by the error sensor while the tuners in the other banks remain stationary;

each adjustable tuner is a quarter wavelength resonator having a selectively positionable plunger and a stepper motor dedicated to each tuner that moves the respective plunger in response to the respective correction signal from the electronic controller;

the adjustable tuner comprises a first end stop switch that indicates when the plunger is at a fully closed position and a second end cap stop switch that indicates when the plunger is at a fully open position; and

the electronic controller contains means for estimating the position of the plunger in the quarter wavelength resonator in accordance with the respective correction signals transmitted to the respective stepper motor.

3. A method of passively attenuating acoustic disturbances in an acoustic plant, the method comprising the steps of:

a) sensing an acoustic disturbance in an acoustic plant and generating an error signal in response thereto;

b) providing multiple banks of adjustable tuners that communicate acoustically with the acoustic plant;

c) determining an optimal setting for the adjustable tuners by contemporaneously adjusting all of the tuners in one of the banks to vary the acoustic disturbance in the acoustic plant while the tuners in the other banks remain stationary;

d) setting the adjustable tuners in the respective bank in unison so that the acoustic disturbance sensed in the acoustic plant is minimized; and

e) repeating steps c) and d) for all of the tuners in each respective bank.

4. A method as recited in claim 3 further comprising the steps of repeating steps c) through e) listed in claim 3.

5. A method as recited in claim 3 further comprising the step of:

sensing the acoustic disturbance in the acoustic plant at several distinct physical locations to generate a plurality of error signals;

separately filtering each of the plurality of error signals to generate separate processed error signals representing the energy of the acoustic disturbance within a frequency bandwidth containing the disturbance of interest;

summing the plurality of separate processed error signals to generate a group processed error signal; and

setting all of the adjustable tuners in each respective bank in unison so that the group processed error signal is minimized.

6. A method as recited in claim 5 wherein the acoustic plant has a plant inlet receiving acoustic input and the method further comprises:

sensing the acoustic disturbance with an input sensor at a location closer to the plant inlet than any of the adjustable tuners, and generating an input characteristic signal in response thereto; and

using the input characteristic signal to adjust the determination of the optimal setting for the adjustable tuners.

7. A method as recited in claim 3 wherein the banks of adjustable tuners are defined by software within an electronic controller so that each adjustable tuner is assigned to a particular bank and the system is capable of reassigning adjustable tuners to other banks within the system.

8. A method as recited in claim 3 further comprising the steps of:

determining whether each adjustable tuner is fully operational on an intermittent basis; and

deactivating adjustment of any adjustable tuner in the system that is not fully operational.

9. A method as recited in claim 3 wherein each adjustable tuner is a quarter wavelength resonator having a selectively positionable plunger and a stepper motor dedicated to each tuner that moves the respective plunger in response to a correction signal from an electronic controller, and wherein each adjustable tuner comprises a first end stop switch that indicates when the plunger is at a fully closed position and a second end stop switch that indicates when the plunger is at a fully open position;

and the method further comprises the steps of;

estimating the position of the plunger in the quarter wavelength resonator in accordance with the respective correction signals transmitted from the stepper motor;

intermittently determining whether each adjustable tuner is fully operational by comparing the estimated position of the plunger in the quarter wavelength resonator as the plunger moves between a fully closed position and a fully open position or vice-versa; and

deactivating adjustment of any adjustable tuner in the system that is not fully operational.

10. An adaptive passive acoustic attenuation system that attenuates an acoustic disturbance in an acoustic plant comprising:

an adjustable tuner communicating acoustically with the acoustic plant, the adjustable tuner having passive acoustic characteristics determined in accordance with passive parameter settings;

a group of error sensors, each error sensor sensing an acoustic disturbance in the acoustic plant and generating an error signal in response thereto; and

an electronic controller that receives the error signals from the error sensors and outputs correction signals to selectively adjust the passive parameter settings of the adjustable tuner, the electronic controller having;

a narrow band filtering and processing element that receives the error signals from the error sensors and for each error signal outputs a processed error signal representing the magnitude of the acoustic disturbance within a frequency bandwidth containing the disturbance desired to be attenuated, and

a summer that inputs the separate processed error signals and outputs a group processed error signal that is used when the electronic controller adapts the passive parameter settings for the adjustable tuner,

wherein the narrow band filtering and processing element includes;

a frequency-shifting multiplier that receives the error signal from each error sensor and for each error signal outputs a frequency-shifted error signal; and

a fixed narrow bandpass filter that inputs the frequency-shifted error signals.

11. An adaptive passive acoustic attenuation system as recited in claim 10 wherein the fixed narrow bandpass filter outputs a plurality of filtered disturbance signals and the narrow band filtering and processing element further includes a multiplier that multiplies each of the filtered disturbance signals by itself to output respective squared disturbance signals, and a time averager that inputs the squared disturbance signals and outputs the plurality of separate processed error signals.

12. An adaptive passive acoustic attenuation system as recited in claim 10 further comprising a broad bandpass filter that inputs the error signals from the error sensors and outputs a plurality of pre-filtered error signals to the frequency shifting multiplier.

13. A method of passively attenuating acoustic disturbances in an acoustic plant, the method comprising the steps of:

providing at least one adjustable tuner that communicates acoustically with an acoustic plant;

sensing a disturbance in the acoustic plant at a plurality of several distinct physical locations within the acoustic plant to generate a plurality of error signals;

frequency-shifting the error signals from the error sensor by multiplying each error signal by a heterodyning tone signal to generate a plurality of frequency-shifted error signals;

filtering the frequency-shifted error signals through a fixed narrow bandpass filter to generate a plurality of filtered disturbance signals;

estimating the energy of the plurality of filtered disturbance signals; and

setting the adjustable tuner so that the sum of estimated energy is minimized.

14. The method as recited in claim 13 further comprising the step of:

pre-filtering the plurality of error signals through a broad bandpass filter before frequency-shifting the error signals from the error sensors.

15. A method as recited in claim 13 wherein the step of estimating the energy of the plurality of filtered disturbance signals is accomplished in accordance with the following expression:

16. A method as recited in claim 13 wherein the heterodyning tone signal is determined by tracking the frequency of the undesired disturbance in the acoustic plant and selecting the heterodyne tone signal so that the disturbance being attenuated is represented in the frequency-shifted filtered disturbance signals such that the disturbance lies within the frequency range of the fixed narrow bandpass filter.

17. A method as recited in claim 13 wherein the frequency of the disturbance within the acoustic plant is tracked by one of the error sensors.

18. A method as recited in claim 13 wherein the frequency of the disturbance within the acoustic plant is tracked by a tachometer monitoring a source of the disturbance.

19. A method as recited in claim 13 wherein the frequency of the disturbance within the acoustic plant is tracked by an input sensor located closer to a source of the disturbance than any of the adjustable tuners communicating acoustically with the acoustic plant.

20. A method of passively attenuating a first narrow band acoustic disturbance in an acoustic plant and a second distinct narrow band acoustic disturbance in the acoustic plant, the method comprising the steps of:

providing at least one first adjustable tuner communicating acoustically with the acoustic plant to attenuate the first narrow band disturbance;

providing at least one second adjustable tuner communicating acoustically with the acoustic plant to attenuate the second narrow band disturbance;

sensing disturbances in the acoustic plant at a plurality of several distinct physical locations within the acoustic plant to generate a plurality of error signals;

frequency-shifting the error signals from the error sensors by multiplying each error signal by a first heterodyning tone signal to generate a plurality of first frequency-shifted error signals;

filtering the first frequency-shifted error signals through a fixed narrow bandpass filter to generate a plurality of first filtered disturbance signals;

estimating the energy of the plurality of first filtered disturbance signals;

setting the at least one first adjustable tuner so that the sum of the estimated total energy represented by the first filtered disturbance signals is minimized;

frequency-shifting the error signals from the error sensors by multiplying each error signal by a second heterodyning tone signal to generate a plurality of second frequency-shifted error signals;

filtering the second frequency-shifted error signals through the fixed narrow bandpass filter to generate a plurality of second filtered disturbance signals;

estimating the energy of the second plurality of filtered disturbance signals; and

setting the at least one second adjustable tuner so that the sum of the estimated total energy represented by the second filtered disturbance signals is minimized.

21. A method as recited in claim 20 wherein the at least one first adjustable tuner is one of a first plurality of adjustable tuners and the at least one second adjustable tuner is one of a second plurality of adjustable tuners, and the first plurality of adjustable tuners consists of a set of multiple banks of adjustable tuners and the second plurality of adjustable tuners consists of a second set of multiple banks of adjustable tuners, each adjustable tuner having passive acoustical characteristics determined in accordance with passive parameter settings;

and

wherein adapting the system comprises contemporaneously adjusting the passive parameter settings for all of the tuners in one of the banks to vary the acoustic disturbance sensed by the error sensors while the tuners in the other banks remain stationary.

22. A method of passively attenuating a plurality of narrow band acoustic disturbances in an acoustic plant, the method comprising the steps of:

providing a plurality of adjustable tuners communicating acoustically with the acoustic plant to attenuate a plurality of narrow band acoustic disturbances;

sensing disturbances in the acoustic plant at a plurality of several distinct physical locations within the acoustic plant to generate a plurality of error signals;

frequency-shifting the error signals from the error sensors by multiplying each eerror signal by a respective heterodyning tone signal to generate a plurality of corresponding frequency-shifted error signals;

filtering each of the corresponding frequency-shifted error signals through a fixed narrow bandpass filter to generate a plurality of corresponding filtered disturbance signals;

estimating the energy of the plurality of corresponding filtered disturbance signals for each respective narrow band acoustic disturbance;

assigning at least one adjustable tuner to attenuate each respective narrow band acoustic disturbance; and

setting each respective adjustable tuner so that the sum of the estimated total energy represented by the filtered disturbance signals corresponding to the respective narrow band acoustic disturbance is minimized.