System for computationally efficient active control of tonal sound or vibration

• US 7,224,807 B2
• Filed: 02/27/2002
• Issued: 05/29/2007
• Est. Priority Date: 02/27/2001
• Status: Active Grant

• Current Assignee: Sikorsky Aircraft Corporation (Martin Marietta Corporation)
• Original Assignee: Sikorsky Aircraft Corporation (Martin Marietta Corporation)
• Inventors: Finn, Alan M., Welsh, William Arthur, MacMartin, Douglas G.
• Primary Examiner(s): Chin; Vivian
• Assistant Examiner(s): KURR, JASON RICHARD
• Application Number:
  US10/083,773
• Publication Number:
  US 20020118844A1
• Time in Patent Office: 1,917 Days
• Field of Search: 702/56, 381/94.2, 381/94.3, 381/71.8, 700/280, 341/143, 341/122, 244/173.2
• US Class Current: 381/71.8
• CPC Class Codes: G05B 21/02 electric
• CPC Class Codes: G05B 5/01 electric
• CPC Class Codes: G10K 11/17823 Reference signals, e.g. ambient acoustic environment
• CPC Class Codes: G10K 11/17853 of the filter
• CPC Class Codes: G10K 11/17855 for improving speed or power requirements
• CPC Class Codes: G10K 11/17873 using a reference signal without an error signal, e.g. pure feedforward
• CPC Class Codes: G10K 2210/121 Rotating machines, e.g. engines, turbines, motors; Periodic or quasi-periodic signals in general
• CPC Class Codes: G10K 2210/1281 Aircraft, e.g. spacecraft, airplane or helicopter
• CPC Class Codes: G10K 2210/3012 Algorithms
• CPC Class Codes: G10K 2210/3032 Harmonics or sub-harmonics
• CPC Class Codes: G10K 2210/3051 Sampling, e.g. variable rate, synchronous, decimated or interpolated
• CPC Class Codes: G10K 2210/3053 Speeding up computation or convergence, or decreasing the computational load
• CPC Class Codes: G10K 2210/321 Physical

Abstract

A noise or vibration control system reduces a sampling rate and reduces a control rate to improve computation efficiency. The present invention permits the use of a sample frequency (f_s) that is less than twice the frequency of interest (f_d). The sensed signals are filtered to extract a particular frequency range with a lower bound given by (2n−1)*f_s/2 and an upper bound given by (2n+1)*f_s/2, where n is an integer chosen so that the frequency of interest (f_d) is within the extracted frequency range. The control commands are also calculated at a reduced rate, which is dependent upon the bandwidth of the tone, rather than the absolute frequency of the tone. Rather than updating the control signals directly on the sampled sensor data y_k as it enters the computer, the control computations are done on the harmonic components a_k and b_k, or equivalently on the magnitude and phase.

Claims

1. A method for controlling a physical variable at a frequency of interest (f_d) including the steps of:

a) sampling the physical variable at a sample frequency less than twice the frequency of interest (f_d);

b) calculating at least one control command based upon the sampling of the physical variable;

c) generating a force for controlling the physical variable based upon the control command;

wherein the physical variable is sound or vibration, and

wherein the force is sound or vibration.

2. The method of claim 1, further including the steps of:

bandpass filtering the physical variable prior to said step a).

3. The method of claim 2 wherein said bandpass filter extracts a frequency range with a lower bound generally given by (2n−

1)*f_s/2 and an upper bound generally given by (2n+1)*f_s/2, where n is an integer chosen so that the frequency of interest (f_d) is within the extracted frequency range.

4. The method of claim 1 wherein said physical variable includes information within a bandwidth including said frequency of interest and wherein said sampling frequency is at least twice the bandwidth of this information.

5. The method of claim 1 further including the step of generating the at least one control command at a rate less than twice the frequency of interest.

6. The method of claim 1 wherein the force generated in said step c) reduces the amplitude of the physical variable.

7. The method of claim 6 wherein the force is generated in said step c) by an actuator, the actuator generating the force based upon the control command.

8. A method for computing control commands at a reduced rate in a noise or vibration control system including the steps of:

a) sensing a physical variable;

b) identifying harmonic components (a_k, b_k) of the physical variable at a frequency of interest (f_d);

c) down-sampling the harmonic components (a_k, b_k) to a lower update frequency (f_u);

d) performing control computations on the harmonic components(a_k, b_k) at the lower update frequency (f_u); and

e) generating control commands based upon the control computations.

9. The method of claim 8 further including the step of:

f) generating harmonic components of the control commands in said step e).

10. The method of claim 9, further including the step of:

g) generating a control output at a frequency higher than the lower update frequency.

11. The method of claim 8 further comprising:

low-pass anti-aliasing filtering to prevent aliasing in sampling at a lower update frequency (f_u).

12. The method of claim 8, further comprising:

obtaining estimates of the harmonic components by computing a fast-Fourier transform of the physical variable; and

extracting the result corresponding to the frequency of interest (f_d).

13. The method of claim 8, wherein said physical variable comprises a plurality of physical variables, said method further including the steps of:

f) generating a sensed signal as a function of each of said plurality of physical variables; and

g) computing harmonic estimates Z_k for each sensed signal y_k at each sample time t_k according to Z_k=Z_k-1+ρ

H(y_k-H^TZ_k-1), where;

H=[1 cos(f_dt_k) sin(f_dt_k) cos(f_Xt_k) sin(f_Xt_k), . . . ]^T and where;

f_dt_k=desired frequency;

f_xt_k=frequency of unwanted information in y_k;

Z_k=estimates of harmonic content of y_k at time k;

Z_k-1=estimates of harmonic content at time k−

1;

ρ

=a variable gain that determines the corner frequency of the first order low-pass anti-aliasing filter;

y_k=sensed signal vector at time k;

(·

)^T=transpose of a vector or matrix.

14. The method of claim 13, further comprising

utilizing every N^th harmonic estimator output Z_Nk where N is the ratio of the sampling frequency and the update frequency (f_s/f_u).

15. The method of claim 13, further comprising:

generating separate control commands for each of multiple tones;

adding control commands for each tone; and

outputting a sum of the control commands for each tone to one or more force generators.

16. A method for analyzing a physical variable having a first frequency of interest f₁ and a second frequency of interest f₂ in a noise or vibration control system, including the steps of:

a) identifying first harmonic components a_k1, b_k1 of the first frequency of interest f₁;

b) down-sampling the harmonic components a_k1, b_k1 at an intermediate frequency f_u1;

c) identifying second harmonic components a_k2, b_k2 of a difference between the first frequency of interest f₁ and the second frequency of interest f₂;

d) down-sampling the harmonic components a_k2, b_k2 at an update frequency f_u2; and

e) analyzing information at the first frequency of interest f₁ and the second frequency of interest f₂ based upon said harmonic components a_k1, b_k1 and a_k2, b_k2.

17. The method of claim 16 wherein the intermediate frequency f_u1 is higher than the update frequency f_u2.

18. The method of claim 16 further including the steps of:

f) generating control signals at the update frequency f_u2 based upon said step e).

19. An apparatus for sensing physical variables at a reduced rate in a noise or vibration control system comprising:

a sensor adapted to sense physical variables at a sample frequency (f_s) less than twice a frequency of interest (f_d), and to generate a sensed signal as a function of the sensed physical variable; and

a control circuit adapted to establish the frequency of interest (f_d), and to establish the sample frequency (f_s),

wherein the control circuit filters the sensed signals to extract a frequency range with a lower bound given by (2n−

1)* f_s/2 and an upper bound given by (2n+1)* f_s/2, where n is an integer chosen so that the frequency of interest (f_d) is within the extracted frequency range,

wherein the control circuit generates a control command based upon the sensed signal to control the physical variable.

20. The apparatus of claim 19, wherein the control circuit attenuates the filtered sensed signal at a frequency less than the frequency of interest (f_d) by high-pass anti-aliasing to produce a resultant signal.

21. The apparatus of claim 19 wherein the control circuit aliases the filtered sensed signal to a lower frequency when there is no information present at the lower frequency in the sensed signal and the control circuit extracts desired information.