JPH0850491A - Active silencer - Google Patents

Abstract

PURPOSE:To decrease a calculation quantity by decreasing the number of transformations of Fourier transform at the time of forming antinoise signals. CONSTITUTION:This active silencer has plural band-pass filters 22 which separate the primary noise signals from a primary noise detecting microphone 9 to frequency components desired to be decreased, a Fourier transform processing section 25 which subjects the digital residual noise signals of an A/D conversion section 24 to Fourier transform and extracts amplitude values and phase values in the respective frequency-components of the residual noise signals and an antinoise signal forming section 26 which forms the antinoise signals in accordance with the primary noise signals of every frequency-component from a multiplexer A/D conversion section 23 and the residual noise signals subjected to a frequency decomposition by the Fourier transform. This antinoise signal forming section 26 forms the antinoise signals in a time region without making Fourier transform of the primary noise signals and, therefore, the number of times of the Fourier transform is necessitated to be just one time of the residual noise signals to be executed by the Fourier transform processing section 25. The calculation quantity is thus decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an active silencer,
More specifically, the present invention relates to an active silencer that silences noise from a noise source.

[0002]

2. Description of the Related Art As a method of silencing noise from a noise source such as an engine, a method of disposing a silencing material around the noise source has been conventionally known. In recent years, an active muffling device has been put into practical use as a method of muffling noise in a low frequency range (near 100 Hz to 500 Hz) that is difficult to muffle with a muffling material. As an example of this active silencer, Japanese Patent Publication No. 3-25
No. 679, special table 1-501344, special table 3-50
No. 1317, Japanese Patent Publication No. 2-503219, Japanese Patent Laid-Open No. 3-2
There is a device and method as disclosed in 04354.

Among these, the device disclosed in Japanese Patent Application Laid-Open No. 3-204354 is a device for reducing the muffled sound in the interior of an automobile, and is a microphone for detecting a residual sound provided in the engine rotation signal and the interior of the automobile. The anti-noise signal that is in anti-phase with the noise is generated based on the signal from, and the canceling sound is generated from the speaker provided at the predetermined position inside the vehicle interior to muffle the muffled sound inside the vehicle interior. ing. In this active silencer, an engine rotation signal and a residual noise signal are transformed into a frequency domain by a fast Fourier transform, and an adaptive algorithm (eg, LM) in the frequency domain is used.
S algorithm) is used to change the filter coefficient of the digital filter so as to reduce the residual noise, and then the inverse fast Fourier transform is performed to return to the time domain to generate an anti-noise signal.

[0004]

However, according to the active muffler having the above structure, it is necessary to Fourier transform both the engine rotation signal and the residual sound signal, and
Since an inverse Fourier transform that returns the frequency domain to the time domain is also necessary, the Fourier transform processing is performed three times in total. For this reason, the device configuration becomes complicated, and a very large amount of calculation needs to be performed in a short time, so that a high-speed and high-performance dedicated signal processor is indispensable, and the device becomes expensive.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an active silencer capable of reducing the number of calculations and processing by a general-purpose processor.

[0006]

In order to achieve the above object, an active noise suppressor according to claim 1 is a reference signal detecting means for detecting a reference signal related to noise, and a canceling sound for noise is converted into an anti-noise signal. Based on the canceling sound generating means, a residual noise detecting means for detecting residual noise remaining due to the interference of the noise and the canceling sound, a filter means for separating the reference signal for each frequency component targeted for noise reduction, The residual noise signal detected by the noise detecting means is Fourier-transformed, and the residual noise amplitude / phase extracting means for extracting the amplitude value and the phase value of the residual noise for each frequency component decomposed by the Fourier transform is separated by the filter means. Amplitude value of each frequency component, phase value and extracted amplitude value,
Anti-noise signal generating means for generating an anti-noise signal by performing amplitude increase / decrease processing and phase advance / retard processing for each frequency component based on the phase value.

As a method of obtaining a reference signal relating to noise, a method of detecting primary noise of a noise source with a sound collecting microphone or the like and using it as a reference signal, a signal having a correlation with noise such as an engine rotation signal, etc. A method of generating a reference signal based on

According to another aspect of the active muffler of the present invention, a code discriminating means for discriminating the sign of the real number data and the imaginary number data of each frequency component obtained by Fourier transform, and the imaginary number data and the real number data of the residual noise signal are used. , A lookup table storing the phase value of the residual noise signal given by a predetermined function.

[0009]

According to the active muffler of the present invention, the filter means separates the reference signal for each frequency component to be subjected to noise reduction, and the residual noise amplitude / phase extracting means detects the residual noise detected by the residual noise detecting means. The noise signal is Fourier-transformed, and the amplitude value and the phase value of the residual noise are extracted for each frequency component decomposed by the Fourier transform. Then, the anti-noise signal generation means performs amplitude increase / decrease processing and phase advance / retard processing for each frequency component based on the amplitude value, phase value and extracted amplitude value and phase value of each frequency component separated by the filter means. To generate an anti-noise signal.

In this operation, the Fourier transform and inverse Fourier transform of the reference signal are not performed, but only the residual noise signal is Fourier transformed. Therefore, the number of calculations can be reduced because the Fourier transform processing is performed only once, and it is not necessary to process a large number of calculations in a short time as in the conventional configuration, so that a general-purpose processor can sufficiently process.

According to the active muffler of the second aspect, the residual noise signal is identified by identifying the corresponding area in the Fourier-transformed complex plane by the code discrimination by the code discriminating means and referring to the look-up table in the area. Find the phase value of. By using the code discriminating means and the look-up table in this way, it is possible to perform processing at a much higher speed than directly calculating the phase by calculation.

[0012]

Embodiments will be described in detail below with reference to the accompanying drawings showing embodiments. FIG. 1 is a schematic perspective view showing a vehicle silencer as an embodiment of the active silencer of the present invention. This vehicle interior silencer is used to muffle the muffled noise in the cabins of construction machinery and agricultural machinery. FIG. 2 is a block diagram of the vehicle silencer. In FIG. 1, a vehicle body 2a of the construction machine 2
A 4-cylinder diesel engine 4 as an internal combustion engine is mounted behind the vehicle, and a seat 5 in which a worker sits is provided in a vehicle compartment 3 in front of the engine 4.

The vehicle interior silencer 1 includes a primary noise detection microphone 9 for detecting primary noise from the engine 4, and an engine rotation signal detector 10 for detecting a rotation signal of the engine 4.
An active noise controller (hereinafter referred to as an ANC controller) 11, a canceling sound generating speaker 12 provided at a predetermined position below the seat 5 in the vehicle compartment 3, and a residual provided at a predetermined position on the vehicle compartment ceiling. It has a noise detection microphone 13.

The primary noise detection microphone 9 detects the noise transmitted from the engine 4 to the vehicle compartment 3 near the engine 4. As shown in FIG. 2, the ANC controller 11 includes a sampling pulse generator 21 that generates a sampling pulse based on an engine rotation signal, and a plurality of units that separate the primary noise signal from the primary noise detection microphone 9 into frequency components for reduction. Band pass filter 22 and multiplexer A for converting the separated frequency components into digital signals
An A / D converter 23, an A / D converter 24 for A / D converting the residual noise signal from the residual noise detecting microphone 13, and an A / D converter.
A fast Fourier transform is performed on the digital residual noise signal of the transforming unit 24, and a Fourier transform processing unit 25 that performs an extracting process described later, a primary noise signal for each frequency component from the multiplexer A / D converting unit 23, and a frequency decomposition by Fourier transform are performed. It has an anti-noise signal generation unit 26 that generates an anti-noise signal based on the generated residual noise signal, and a D / A conversion unit 27 that converts the generated anti-noise signal into an analog signal.

FIG. 3 is a block diagram showing the details of the Fourier transform processing section 25 and the anti-noise signal generating section 26. The Fourier transform processing unit 25 has a Fourier transform unit 31 and an amplitude / phase extraction unit 32. The anti-noise signal generation unit 26 includes a comparison / difference calculation unit 35 that calculates an amplitude increase / decrease amount Δa and a phase advance / retard amount Δp, and an increase / decrease / advance processing unit 36 that performs an increase / decrease process and an advance / retard process for each frequency component. It has an adder 37.

The operation of the main part of the vehicle interior silencer configured as above will be described with reference to the flow chart shown in FIG. First, in step SP1, the primary noise signal is separated by the bandpass filter 22 (BPF1 to BPFn) for each frequency component for noise reduction, and in step SP2, the primary noise signal and the residual noise detecting microphone 13 are separated.
The residual noise signal from the A / D conversion unit 23, the sampling pulse from the sampling pulse generation unit 21,
24 performs A / D conversion, the Fourier transform unit 31 Fourier transforms the residual noise signal in step SP3, and decomposes it into frequencies. In step SP4, the amplitude / phase extraction unit 32 performs amplitude A and phase P for each frequency component. (Indicated by f ₁ (A ₁ , P ₁ ), ..., F _n (A _n , P _n ) in FIG. 3)
To extract.

Then, in step SP5, the comparison / difference calculation section 35 causes the amplitude a and the phase p (f ₁ of each frequency component of the primary noise signal separated by the bandpass filter 22 to be separated.
(A ₁ , p ₁ ), ..., F _n ( _denoted by a _n , _pn )) and the extracted amplitude A and phase P are compared, and the amplitude increase / decrease amount Δa that minimizes the residual noise. , The phase advance / retard amount Δp is calculated, and in step SP7, the increase / decrease / advance processing unit 36 performs the amplitude increase / decrease process and the phase advance / retard process on each frequency component separated based on the amplitude increase / decrease amount Δa and the phase advance / retard amount Δp. In step SP8, the addition unit 37 combines the frequency components to generate a digital anti-noise signal, and in step SP9, the D / A conversion unit 37 converts the digital anti-noise signal into an analog signal and ends the series of processes. To do.

The operation of this main part will be further described with reference to FIG. The residual noise signal is the Fourier transform unit 3
1, the frequency is decomposed, and the information on the amplitude A and the phase P is extracted. Here, sinB and sinC waves (however, B
= Ωt, C = (ωt + θ))

[0019]

[Equation 1]

Therefore, the superposition of the noise and the anti-noise wave corresponding to the frequency is calculated from the equation 1 and the amplitude A = 2cos
The wave is formed by (−θ / 2) and the phase P = θ / 2. On the other hand, when paying attention to the frequency, as shown in FIG. 5, it is converted into Q point (r ₁ , i ₁ ) by Fourier transform,
Due to the r ₁ and i ₁ , the amplitude A is A = (r ₁ ² + i ₁ ² ) ^1/2
And the phase P can be calculated by P = tan ⁻¹ (i ₁ / r ₁ ). Using the information of A and P, the amplitude a and the phase p of each frequency component obtained by the band pass filter 22 are respectively increased / decreased and advanced / decreased and output as an anti-noise signal.

According to the vehicle interior muffler of this embodiment, the Fourier transform needs to be performed only once in the residual noise signal, and the Fourier transform of the reference signal can be omitted. Therefore, there is an advantage that the configuration can be simplified and the amount of calculation can be reduced, and processing can be performed by a general-purpose processor.

[0022]

Second Embodiment Next, a second embodiment of the present invention will be described. FIG. 6 is a block diagram showing a main configuration of a vehicle interior sound deadening system according to the second embodiment, which corresponds to FIG.
This embodiment is different from the first embodiment only in that the Fourier transform processing section 25 has a code discrimination section 41 and the anti-noise signal generation section 27 has a lookup table 42.

As shown in FIG. 5, Q is obtained by Fourier transform.
The phase P of the residual noise signal converted into points is P = tan
Obtained by ^{_{-1 (i 1 / r 1)}} . Here, as shown in FIG. 7, the range of the phase shift amount from the clock signal (0 ° to 3
60 °), the sign of the real number data r _{1 and} the sign of the imaginary number data i ₁ change. Therefore, at least ta
The values in the range of 90 ° to 180 ° and 180 ° to 270 ° of n ^-1 φ are held in the form of a lookup table, and the sign of the real number data r _{1 and} the sign of the imaginary number data i ₁ are discriminated. The phase can be obtained by specifying I to IV and referring to the lookup table 42 using (i ₁ / r ₁ ) as an argument.

With this structure, the processing is much simpler than the calculation of the phase, and the active silencer is composed of a general-purpose processor which is slower and cheaper in combination with the effect of the first embodiment. become able to.

[0025]

Third Embodiment Next, a third embodiment of the present invention will be described. FIG. 8 is a block diagram showing the configuration of the vehicle interior silencer of the third embodiment. The difference of this embodiment from the first embodiment is that the primary noise signal detecting microphone is omitted, and a reference signal generator 51 for generating a noise reference signal based on the engine rotation signal is provided. The only difference is that the output is input to the bandpass filter 22.

With respect to noise from a noise source having a periodicity such as an engine, the cause of the noise can be identified, so that a reference signal is generated from the signal of the noise source itself (for example, a drive signal) correlated with the periodicity. be able to. in this case,
Since periodic noise is easier to control than random noise, the signal processor can sufficiently cope with low-speed noise as compared with the case of controlling random noise. According to this embodiment, there is an advantage that the device configuration can be simplified and a signal processor having a lower speed can be applied.

The present invention is not limited to the above-mentioned embodiments, and various design changes can be made within the scope of the present invention. Hereinafter, such an embodiment will be described. (1) In the above embodiment, the case where the engine is the noise source having frequency periodicity in the generation of noise has been described.
As such a periodic noise source, other than the engine,
A motor, a compressor, etc. can be illustrated.

(2) In the third embodiment, the engine rotation signal is adopted as the reference signal having a correlation with the noise of the noise source. However, other than that, the noise is substantially correlated with the rotation phase reference. The reference signal is not particularly limited as long as it can be specified. (3) In the above-described embodiments, the case of the vehicle compartment is described as an example, but the present invention can be applied to an engine generator having an engine and a generator housed in a muffler case, an engine exhaust pipe, and the like.

[0029]

As described above, according to the invention of claim 1, since only the residual noise signal needs to be Fourier transformed,
Since the Fourier transform processing only needs to be performed once, the number of calculations can be reduced, and since it is not necessary to process a large number of calculations in a short time as in the conventional configuration, a general-purpose processor can sufficiently deal with There is a unique effect that the cost of the static muffling device can be reduced.

In addition to the effect of the invention of claim 1, the invention of claim 2 can further reduce the amount of arithmetic processing, improve the followability, and can be sufficiently applied to a general-purpose processor having a relatively low speed. Produce the effect of.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing a case where a vehicle interior sound deadening device according to an embodiment of the present invention is applied to muffle muffled sound in a vehicle interior of a construction work vehicle.

FIG. 2 is a block diagram of a muffler for a passenger compartment showing an embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a main part of the vehicle interior silencer.

FIG. 4 is a flowchart showing the operation of the vehicle interior silencer.

FIG. 5 is a diagram showing a wave subjected to Fourier transform on a complex plane.

FIG. 6 is a block diagram showing a second embodiment of the present invention.

FIG. 7 is a diagram for explaining the operation of the second embodiment.

FIG. 8 is a block diagram showing a third embodiment of the present invention.

[Explanation of symbols]

9 ... Microphone for primary noise detection, 10 ... Engine rotation signal detection unit, 12 ... Speaker for canceling noise generation, 13 ... Microphone for residual noise detection, 22 ... Multiple bandpass filters,
25 ... Fourier transform processing unit, 26 ... Anti-noise signal generation unit, 41 ... Code discrimination unit, 42 ... Look-up table, 51 ... Reference signal generation unit.

Claims (2)

[Claims] 1. A reference signal detecting means (9) (10) (51) for detecting a reference signal relating to noise, a canceling sound generating means (12) for generating a canceling sound for noise based on an anti-noise signal, and noise. Noise detection means (13) for detecting residual noise remaining due to the interference of the canceling sound with each other, filter means (22) for separating the reference signal for each frequency component to be subjected to noise reduction, and residual noise detection means (13). ) Residual noise amplitude / phase extraction means (25) for performing Fourier transform on the residual noise signal detected by (1) and extracting the amplitude value and the phase value of the residual noise for each frequency component decomposed by the Fourier transform, and the filter means (22). The amplitude value of each frequency component separated by, the phase value and the extracted amplitude value,
An active noise suppressor comprising: an anti-noise signal generating means (26) for generating an anti-noise signal by performing an amplitude increase / decrease process and a phase advance / retard process for each frequency component based on the phase value. 2. A code discriminating means (41) for discriminating the sign of real number data and imaginary number data of each frequency component obtained by Fourier transform, and a predetermined function based on the imaginary number data and real number data of the residual noise signal. And a look-up table (42) for storing the phase value of the residual noise signal stored therein.