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DESCRIPTION JPH0850491

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DESCRIPTION JPH0850491
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
active noise reduction system, and more particularly to an active noise reduction system for
silencing noise from a noise source.
[0002]
2. Description of the Related Art As a method of muffling noise from a noise source such as an
engine, a method of arranging a muffling material around a noise source is conventionally
known. In recent years, an active noise reduction device has been put into practical use as a
method of noise reduction in a low frequency range (around 100 Hz to around 500 Hz) which is
difficult to be silenced by a noise reduction material. As an example of this active noise reduction
device, it is disclosed in Japanese Patent Publication No. 3-25679, Japanese Patent Publication
No. 1-501344, Japanese Patent Publication No. 3-501317, Japanese Patent Publication No. 2503219, and Japanese Unexamined Patent Publication No. 3-204354. There are devices and
methods that
[0003]
Among them, the device disclosed in Japanese Patent Laid-Open No. 3-204354 is a device for
reducing the muffled noise in the vehicle compartment of a car, and includes an engine rotation
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signal and a residual sound detection microphone provided in the vehicle compartment. And an
anti-noise signal that is in antiphase with the noise to generate cancellation sound from a speaker
provided at a predetermined position inside the vehicle compartment so as to mute muddy noise
in the vehicle compartment. ing. In this active noise reduction system, the rotational signal of the
engine and the residual noise signal are converted into the frequency domain by fast Fourier
transform, and the residual noise is reduced by using an adaptive algorithm (for example, LMS
algorithm) in the frequency domain. After performing arithmetic processing for changing the
filter coefficients of the digital filter, the signal is returned to the time domain by inverse fast
Fourier transform to generate an anti-noise signal.
[0004]
However, according to the active silencer of the above configuration, it is necessary to Fourier
transform both the engine rotation signal and the residual sound signal, and reverse the
frequency domain back to the time domain. Since Fourier transform is also required, a total of
three Fourier transform processes are performed. For this reason, the apparatus configuration
becomes complicated and it is necessary to perform a very large number of operations in a short
time, so a high-speed, high-performance dedicated signal processor becomes essential, and the
apparatus becomes expensive.
[0005]
SUMMARY OF THE INVENTION The present invention has been made in view of the above
problems, and it is an object of the present invention to provide an active silencer which can be
processed by a general purpose processor while reducing the number of operations.
[0006]
SUMMARY OF THE INVENTION In order to achieve the above object, an active noise reduction
system according to claim 1 comprises a reference signal detection means for detecting a
reference signal relating to noise; Cancellation sound generation means generated based on noise
signal, residual noise detection means for detecting residual noise left by interference of noise
and cancellation sound, filter means for separating reference signal for each frequency
component to be noise reduction target And residual noise amplitude phase extraction means for
performing Fourier transform on the residual noise signal detected by the residual noise
detection means and extracting the amplitude value and the phase value of the residual noise for
each frequency component resolved by the Fourier transform; Based on the amplitude value of
each separated frequency component, the phase value, the extracted amplitude value, and the
phase value, the amplitude increase / decrease processing and the position for each frequency
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component are performed. Characterized in that it comprises a anti-noise signal generating
means for generating anti-noise signal by performing Susumuoso process.
[0007]
As a method of obtaining a reference signal related to noise, there is 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 correlation with noise, such as engine rotation signal. A method
of generating a reference signal based on
[0008]
According to a second aspect of the present invention, there is provided an active noise reduction
system based on sign discriminating means for discriminating the sign of real number data and
imaginary number data of each frequency component obtained by Fourier transformation, and
imaginary number data and real number data of residual noise signal. And a look-up table storing
phase values of residual noise signals given by a predetermined function.
[0009]
In the active noise reduction system according to the first aspect of the invention, the filter
means separates the reference signal into frequency components targeted for noise reduction,
and the residual noise amplitude phase extraction means is detected by the residual noise
detection means. The residual noise signal thus obtained is subjected to Fourier transform 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 / delay processing for each frequency component based on the amplitude
value, phase value, extracted amplitude value, and phase value of each frequency component
separated by the filter means. To generate an anti-noise signal.
[0010]
In this operation, the Fourier transform or the inverse Fourier transform of the reference signal is
not performed, and only the residual noise signal is Fourier transformed.
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Therefore, the number of operations can be reduced since only one Fourier transform process is
required, and a large number of general-purpose processors can be sufficiently processed
because it is not necessary to process many operations in a short time as in the conventional
configuration.
[0011]
In the active noise reduction system according to the second aspect of the present invention, the
residual noise signal is identified by identifying the corresponding area in the complex plane
subjected to Fourier transform by the code discrimination by the code discrimination means and
referring to the lookup table in that area. Find the phase value of
By using the sign determination means and the look-up table in this way, the operation can be
processed much faster than directly calculating the phase.
[0012]
Embodiments of the present invention will be described in detail with reference to the
accompanying drawings which show the embodiments.
FIG. 1 is a schematic perspective view showing a passenger compartment silencer as one
embodiment of the active silencer according to the present invention. This cabin silencer is used
to mute the muddy noises of the cabins of construction machines and agricultural machines. FIG.
2 is a block diagram of the passenger compartment silencer. In FIG. 1, a four-cylinder diesel
engine 4 as an internal combustion engine is mounted behind a vehicle body 2 a of a
construction machine 2, and a seat 5 on which an operator sits is provided in a passenger
compartment 3 in front of the engine 4.
[0013]
The passenger compartment silencer 1 comprises a primary noise detection microphone 9 for
detecting primary noise from the engine 4, an engine rotation signal detector 10 for detecting a
rotation signal of the engine 4, and an active noise controller (hereinafter referred to as ANC
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controller 11), speaker 12 for offset sound generation provided at a predetermined lower
position of seat 5 of passenger compartment 3, and residual noise detection microphone 13
provided at a predetermined position of passenger compartment ceiling doing.
[0014]
The primary noise detection microphone 9 detects noise transmitted from the engine 4 to the
passenger compartment 3 near the engine 4.
The ANC controller 11 separates the primary noise signal from the primary noise detection
microphone 9 into a frequency component to be reduced, as shown in FIG. 2, the sampling pulse
generation unit 21 that generates sampling pulses based on the engine rotation signal. A band
pass filter 22, a multiplexer A / D converter 23 for converting separated frequency components
into a digital signal, an A / D converter 24 for A / D converting a residual noise signal from the
residual noise detection microphone 13; A Fourier transform processing unit 25 which performs
fast Fourier transform on the digital residual noise signal of the A / D conversion unit 24 and
performs extraction processing described later, a primary noise signal for each frequency
component from the multiplexer A / D conversion unit 23, Fourier Anti-noise signal generating
anti-noise signal based on residual noise signal frequency-resolved by conversion A generating
unit 26, and the generated anti-noise signal and a D / A converter 27 for converting into an
analog signal.
[0015]
FIG. 3 is a block diagram showing details of the Fourier transform processing unit 25 and the
antinoise signal generation unit 26. As shown in FIG. 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 compares and calculates an amplitude increase / decrease amount Δa
and a phase advance / delay amount Δp, and increases / decreases / advances / delays
processing unit 36 that performs increase / decrease processing and advance / delay processing
for each frequency component. And an addition unit 37.
[0016]
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The operation of the main part of the passenger compartment silencer of the above construction
will be described with reference to the flow chart shown in FIG. First, in step SP1, the primary
noise signal is separated by band pass filter 22 (BPF1 to BPFn) for each frequency component for
noise reduction, and in step SP2 these primary noise signals and residual noise signal from the
residual noise detection microphone 13 The A / D conversion units 23 and 24 respectively
perform A / D conversion with sampling pulses from the sampling pulse generation unit 21. In
step SP3, the Fourier transform unit 31 Fourier-transforms the residual noise signal and
performs frequency decomposition, In step SP4, the amplitude / phase extraction unit 32
extracts an amplitude A and a phase P (represented by f1 (A1, P1),..., Fn (An, Pn) in FIG. 3) for
each frequency component.
[0017]
At step SP5, the comparing / difference calculating unit 35 generates the amplitude a and the
phase p (f1 (a1, p1),..., Fn (an, an) of each frequency component of the primary noise signal
separated by the band pass filter 22. and the extracted amplitude A and phase P to calculate the
amplitude increase / decrease amount .DELTA.a and the phase advance / delay amount .DELTA.p
which minimize the residual noise, and at step SP7 increase / decrease / advance The processing
unit 36 performs amplitude increase / decrease processing and phase advance / delay
processing on each frequency component separated based on the amplitude increase / decrease
amount Δa and the phase advance / delay amount Δp, and the addition unit 37 combines each
frequency component in step SP8 An anti-noise signal is generated, and in step SP9, the D / A
conversion unit 37 converts the digital anti-noise signal into an analog signal to complete a series
of processing.
[0018]
The function of this main part will be further described with reference to FIG.
The residual noise signal is frequency-resolved in the Fourier transform unit 31, and information
of amplitude A and phase P is extracted. Here, considering superposition of sin B and sin C waves
(where B = ωt, C = (ωt + θ)),
[0019]
[Equation 1]
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[0020]
Thus, the superposition of the noise and the anti-noise wave corresponding to the frequency
thereof is a wave formed from the equation 1 with an amplitude A = 2 cos (-.theta./2) and a
phase P = .theta. / 2.
On the other hand, when focusing on the frequency, it is converted to point Q (r1, i1) by Fourier
transform as shown in FIG. 5, and the amplitude A can be calculated by A = (r12 + i12) 1/2 by r1,
i1. The phase P can be calculated by P = tan-1 (i1 / r1). 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 and decreased, advanced and delayed, and output as an anti-noise
signal.
[0021]
According to the passenger compartment silencer of this embodiment, the Fourier transform may
be performed only once in the residual noise signal, and the Fourier transform of the reference
signal can be omitted. Therefore, the configuration can be simplified, the amount of computation
can be reduced, and there is an advantage that processing can be performed by a generalpurpose processor.
[0022]
Embodiment 2 Next, a second embodiment of the present invention will be described. FIG. 6 is a
block diagram showing the main configuration of the passenger compartment silencer of the
second embodiment, which corresponds to FIG. The present embodiment is different from the
first embodiment only in that the Fourier transform processing unit 25 includes a sign
determination unit 41 and the anti-noise signal generation unit 27 includes a lookup table 42.
[0023]
As shown in FIG. 5, the phase P of the residual noise signal converted to the point Q by Fourier
transformation is obtained by P = tan -1 (i1 / r1). Here, as shown in FIG. 7, the sign of the real
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number data r1 and the sign of the imaginary number data i1 change according to the range (0
° to 360 °) of the phase shift amount from the clock signal. Therefore, at least values in the
range of 90 ° to 180 ° and 180 ° to 270 ° of tan-1φ are held in the form of a look-up table,
and the sign of real data r1 and the sign of imaginary data i1 are determined. The phase can be
determined by specifying the regions I to IV and referring to the lookup table 42 with (i1 / r1) as
an argument.
[0024]
By this configuration, the processing is simplified much more than calculating the phase by
calculation, and the active silencer is configured by a slower, cheaper general purpose processor
combined with the effects 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 passenger compartment silencer of
the third embodiment. This embodiment differs from the first embodiment in that the primary
noise signal detection microphone is omitted, and a reference signal generation unit 51 for
generating a noise reference signal based on an engine rotation signal is provided. The only point
is that the output is input to the band pass filter 22.
[0026]
In noise from a periodic noise source such as an engine, the cause of the noise can be identified,
so that a reference signal is generated from the signal (for example, a drive signal) of the noise
source itself correlated to the periodicity. be able to. In this case, since the periodic noise is easier
to control than the random noise, the signal processor can sufficiently cope with the low speed
noise as compared to the case where the random noise is controlled. According to this
embodiment, the device configuration can be simplified, and there is an advantage that a lower
speed signal processor can be applied.
[0027]
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The present invention is not limited to the above embodiment, and various design changes can be
made without departing from the scope of the present invention. Hereinafter, such an
embodiment will be described. (1) In the above embodiment, the case where the noise source
having periodicity in frequency is noise generation is the engine, but as the noise source having
such periodicity, in addition to the engine, a motor, a compressor, etc. Can be illustrated.
[0028]
(2) In the third embodiment, the engine rotation signal is adopted as the reference signal
correlated with the noise of the noise source, but the noise is also substantially correlated with
the noise and the rotational phase reference The reference signal is not particularly limited as
long as it can be identified. (3) In the above embodiments, the vehicle room has been described
as an example, but the present invention can be applied to an engine generator, an engine
exhaust pipe, etc. in which an engine and a generator are accommodated in a muffling case.
[0029]
As described above, according to the first aspect of the present invention, only the residual noise
signal needs to be subjected to Fourier transformation, so that only one Fourier transformation
process is required, which reduces the number of operations. And the general-purpose processor
can sufficiently cope with it because it does not need to process many operations in a short time
as in the conventional configuration, and it has a unique effect that the cost of the active silencer
can be reduced. Play.
[0030]
According to the second aspect of the present invention, in addition to the effects of the first
aspect of the present invention, the amount of arithmetic processing can be further reduced, the
followability can be improved, and a relatively low speed general purpose processor can be
sufficiently applied. Play the effect of
[0031]
Brief description of the drawings
[0032]
1 is a schematic perspective view showing a case where a room muffling device as one
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embodiment of the present invention is applied for muffling muffled noise of a case of a
construction work vehicle.
[0033]
2 is a block diagram of a passenger compartment silencer showing an embodiment of the present
invention.
[0034]
3 is a block diagram showing the configuration of the main part of the passenger compartment
silencer.
[0035]
4 is a flowchart showing the operation of the passenger compartment silencer.
[0036]
5 is a diagram showing a wave Fourier-transformed on the complex plane.
[0037]
6 is a block diagram showing a second embodiment of the present invention.
[0038]
7 is a diagram for explaining the operation of the second embodiment.
[0039]
8 is a block diagram showing a third embodiment of the present invention.
[0040]
Explanation of sign
[0041]
9: Microphone for primary noise detection, 10: Engine rotation signal detection unit, 12: Speaker
for cancellation noise generation, 13: Microphone for residual noise detection, 22: Multiple band
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pass filters, 25: Fourier transform processing unit, 26: Anti Noise signal generation unit, 41: sign
determination unit, 42: lookup table, 51: reference signal generation unit.
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