JP2007140249A - Active type noise reducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active type noise reducing apparatus in which an operating load required for noise canceling control is reduced by minimizing a product sum operation. <P>SOLUTION: A third discrete data which is input to a first adaptive control algorithm operation section (a first coefficient update means) 12, and a fourth discrete data which is input to a second adaptive control algorithm operation section (a second coefficient update means) 13, are directly selected from a sine wave table 3 which is made discrete based on a frequency detected by a frequency detecting section (a frequency detecting means for noise to be controlled) 2, in a selection means 5. Thereby, as the product sum operation is not required when a reference sine wave signal and a reference cosine wave signal are generated, the operation load is reduced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an active noise reduction device that actively reduces vibration noise generated from a vehicle or the like.

  In a conventional active noise reduction apparatus, a method for performing feedforward adaptive control using an adaptive notch filter is known (see, for example, Patent Document 1). FIG. 7 shows a configuration equivalent to the configuration of the conventional active noise reduction device described in Patent Document 1. In FIG.

  In FIG. 7, the discrete calculation for realizing the active noise reduction device is executed in the discrete calculation processing unit 14. The engine speed detector 1 outputs the engine speed as an engine pulse p. The frequency detector 2 calculates and outputs a noise frequency f based on the engine pulse p. The reference signal generation unit 19 has a sine wave table 3 that holds a limit value of each point obtained by equally dividing one cycle of the sine wave in a memory, and selects data from the sine wave table 3 by the selection unit 5 to select a frequency. Generates and outputs a reference sine wave signal x1 [n] and a reference cosine wave signal x2 [n] equal to the noise frequency f. The reference signal generation unit 22 represents a reference sine wave signal correction value table 20 that simulates a transfer characteristic value from the speaker 10 to the microphone 11 (a reference sine wave signal correction value at a frequency k [Hz] is represented as C1 [k]. ) And the reference cosine wave signal correction value table 21 (the reference cosine wave signal correction value at the frequency k [Hz] is expressed as C2 [k]) and the reference sine wave signal r1 [n] and the reference cosine wave. A signal r2 [n] is generated and output. The first one-tap digital filter 7 filters x1 [n] with a filter coefficient W1 [n] held therein to generate a first control signal y1 [n]. The second 1-tap digital filter 8 filters the reference cosine wave signal x2 [n] with a filter coefficient W2 [n] held therein to generate a second control signal y2 [n]. The power amplifier 9 amplifies a signal obtained by adding the first control signal y1 [n] and the second control signal y2 [n]. The speaker 10 outputs the output signal from the power amplifier 9 as noise canceling sound. The microphone 11 detects sound generated as a result of interference between noise and noise canceling sound as an error signal ε [n]. Based on the reference sine wave signal r1 [n] and the error signal ε [n], the first adaptive control algorithm calculation unit 12 uses, for example, a filter coefficient W1 based on an LMS (Least Mean Square) algorithm which is a kind of steepest descent method. [N] is updated sequentially. Similarly, the second adaptive control algorithm calculation unit 13 sequentially updates the filter coefficient W2 [n] based on the reference cosine wave signal r2 [n] and the error signal ε [n]. By repeating the above-described processing at a predetermined cycle, noise can be reduced.

As prior art document information relating to this application, for example, Patent Document 1 is known.
JP 2004-361721 A

  However, in the conventional configuration, when generating the reference sine wave signal r1 [n] and the reference cosine wave signal r2 [n], the reference sine wave signal x1 [n] and the reference sine wave signal correction value C1 [k] are generated. And the product-sum operation of the reference cosine wave signal x2 [n] and the reference cosine wave signal correction value C2 [k]. As a result, there is a problem that the calculation load increases.

  An object of the present invention is to provide an active noise reduction device that reduces the calculation load necessary for noise suppression control by minimizing the execution of the product-sum operation.

  To achieve the above object, the present invention provides a control target noise frequency detecting means for detecting a frequency of noise to be controlled due to a noise source, a discretized sine wave table, a first one-tap digital filter, , A second one-tap digital filter, and an output obtained by adding the output from the first one-tap digital filter and the output from the second one-tap digital filter are input and controlled due to the noise source. Drive signal generation means for outputting a drive signal for causing interference with power noise, and an error signal resulting from interference between the drive signal output from the drive signal generation means and noise to be controlled due to the noise source. Error signal detecting means for detecting, first coefficient updating means for updating a filter coefficient of the first one-tap digital filter, and the second one-tap digital Second coefficient updating means for updating filter coefficients of the filter, first discrete data to be input to the first one-tap digital filter, second discrete data to be input to the second one-tap digital filter, and The sine wave table based on the frequency detected by the control target noise frequency detecting means for the third discrete data to be inputted to the first coefficient updating means and the fourth discrete data to be inputted to the second coefficient updating means. Selecting means for selecting each at a predetermined time from the first coefficient, and the first coefficient so as to minimize the error signal based on the error signal, the third discrete data, and the fourth discrete data. The filter coefficient is updated by the updating means and the second coefficient updating means, thereby reducing noise to be controlled due to the noise source. In particular, the third discrete data to be input to the first coefficient updating means and the fourth discrete data to be input to the second coefficient updating means are discretized based on the frequency detected by the control target noise frequency detecting means. And selecting means for directly selecting from the sine wave table.

  In the active noise reduction device of the present invention, the third discrete data to be input to the first coefficient updating unit and the fourth discrete data to be input to the second coefficient updating unit are detected by the control target noise frequency detecting unit. Since selection means for directly selecting from a sine wave table discretized based on frequency is provided, a reference sine wave signal (corresponding to third discrete data) and a reference cosine wave signal (fourth In this case, the operation load can be reduced without generating a product-sum operation.

(Embodiment 1)
Hereinafter, an active noise reduction apparatus according to Embodiment 1 of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram of an active noise reduction apparatus according to Embodiment 1 of the present invention.

  In FIG. 1, an engine speed detector 1 outputs the engine speed p as an engine pulse p as a noise source mounted on a vehicle. The frequency detection unit 2 as the control target noise frequency detection means calculates and outputs the control target noise frequency f [Hz] from the engine pulse p. The sine wave table 3 as discretized sine wave data holds a limit value of each point obtained by equally dividing one cycle of the sine wave in a memory. The phase characteristic table 4 holds a value obtained by converting a phase characteristic value of a transfer characteristic from the speaker 10 to the microphone 11 into a relative point movement amount of the sine wave table 3 for each frequency. The selection means 5 is based on the control target noise frequency f and the phase characteristic table 4 and the reference sine wave signal x1 [n] as the first discrete data and the reference cosine wave signal x2 [n] as the second discrete data. The reference sine wave signal r1 [n] as the third discrete data and the reference cosine wave signal r2 [n] as the fourth discrete data are selected from the sine wave table 3. The signal generator 6 includes a sine wave table 3, a phase characteristic table 4, and a selection unit 5. The first one-tap digital filter 7 holds the first filter coefficient W1 [n] inside, and performs the first control based on the reference sine wave signal x1 [n] and the first filter coefficient W1 [n]. The signal y1 [n] is output. The second one-tap digital filter 8 holds the second filter coefficient W2 [n] inside, and performs the second control based on the reference cosine wave signal x2 [n] and the second filter coefficient W2 [n]. The signal y2 [n] is output. The power amplifier 9 amplifies a signal obtained by adding the first control signal y1 [n] and the second control signal y2 [n]. The speaker 10 as the drive signal generating means outputs the output signal from the power amplifier 9 as noise canceling sound. The microphone 11 serving as the error signal detection means detects a sound generated as a result of interference between the control target noise generated due to engine vibration and the noise canceling sound as an error signal ε [n]. The first adaptive control algorithm computing unit 12 as the first coefficient updating unit 12 uses the filter coefficient W1 [of the first one-tap digital filter 7 based on the reference sine wave signal r1 [n] and the error signal ε [n]. n] are updated sequentially. The second adaptive control algorithm calculation unit 13 as the second coefficient updating unit 13 uses the filter coefficient W2 [of the second one-tap digital filter 8 based on the reference cosine wave signal r2 [n] and the error signal ε [n]. n] are updated sequentially. As described above, the discrete arithmetic processing unit 14 is configured by software.

  Next, a specific operation of this apparatus will be described.

  Generation of the reference sine wave signal x1 [n], generation of the reference cosine wave signal x2 [n], generation of the reference sine wave signal r1 [n], generation of the reference cosine wave signal r2 [n], first Generation of the control signal y1 [n], generation of the second control signal y2 [n], detection of the error signal ε [n], update of the filter coefficient W1 [n], and filter coefficient W2 [n] All updates are performed at the same cycle. Hereinafter, this period is described as T [seconds].

  For example, the frequency detector 2 generates an interrupt at each rising edge of the engine pulse p, measures the time between the rising edges, and calculates the frequency f of the control target noise based on the measurement result.

  The sine wave table 3 divides one cycle of the sine wave into d equal parts, and holds discrete data of sine values at each point on the memory. When an array storing sine values from the 0th point to the (d−1) th point is represented by z [m] (0 ≦ m <d), the relational expression (1) is established.

z [m] = sin (360 ° × m / d) (1)
For example, a graph and a table of z [m] when d = 3000 are shown in FIGS. 2 and 3, respectively.

  The phase characteristic table 4 is an array c [k] obtained by converting the phase characteristic value (example of graph: FIG. 4) of the transfer characteristic from the speaker 10 to the microphone 11 into the relative point movement amount of the sine wave table 3. Is stored in the memory (k is the frequency [Hz]). When the phase characteristic value at k [Hz] is θ [k] [degrees], the relational expression (2) is established.

c [k] = d × θ [k] / 360) (2)
For example, FIG. 5 shows the state of c [k] when d = 3000 and the control target noise frequency range is from 30 Hz to 100 Hz.

  The signal generation unit 6 stores the current readout position i [n] of the sine wave table 3 in the memory, and moves the current readout position every period based on the control target noise frequency f using the equation (3). .

i [n + 1] = i [n] + d × f × T (3)
However, when the calculation result on the right side of Expression (3) is equal to or greater than d, i [n + 1] is obtained by subtracting d from the calculation result on the right side of Expression (3).

  At the same time, the signal generation unit 6 generates a reference sine wave signal x1 [n] having the same frequency as the control target noise frequency f by Expressions (4) and (5).

ix1 = i [n] (4)
x1 [n] = z [ix1] (5)
However, when the calculation result of the right side of Expression (4) becomes d or more, ix1 is obtained by subtracting d from the calculation result of the right side of Expression (4).

  At the same time, the signal generation unit 6 generates a reference cosine wave signal x2 [n] having the same frequency as the control target noise frequency f and advanced by a quarter of a period from the reference sine wave signal x1 [n] as shown in Expression (6). Generated by equation (7).

ix2 = i [n] + d / 4 (6)
x2 [n] = z [ix2] (7)
However, when the calculation result of the right side of Expression (6) is equal to or greater than d, ix2 is obtained by subtracting d from the calculation result of the right side of Expression (6).

  At the same time, the signal generator 6 has the same frequency as the control target noise frequency f, and the reference cosine of which the phase difference from the reference sine wave signal x1 [n] is equal to the phase characteristic value of the transfer characteristic from the speaker 10 to the microphone 11. The wave signal r1 [n] is generated by the equations (8) and (9).

ir1 = i [n] + c [f] (8)
r1 [n] = z [ir1] (9)
However, when the calculation result on the right side of Expression (8) is equal to or greater than d, ir1 is obtained by subtracting d from the calculation result on the right side of Expression (8).

  At the same time, the signal generator 6 has the same reference cosine as the control target noise frequency f and the phase difference from the reference sine wave signal x2 [n] is equal to the phase characteristic value of the transfer characteristic from the speaker 10 to the microphone 11. The wave signal r2 [n] is generated by the equations (10) and (11).

ir2 = i [n] + d / 4 + c [f] (10)
r2 [n] = z [ir2] (11)
However, when the calculation result of the right side of Expression (10) is equal to or greater than d, ir2 is obtained by subtracting d from the calculation result of the right side of Expression (10).

  The first and second one-tap digital filters 7 and 8 generate the first and second control signals y1 [n] and y2 [n] by Expression (12) and Expression (13), respectively.

y1 [n] = W1 [n] × x1 [n] (12)
y2 [n] = W2 [n] × x2 [n] (13)
The first and second adaptive control algorithm calculation units 12 and 13 are respectively held by the first and second one-tap digital filters 7 and 8 according to an LMS (Least Mean Square) algorithm, which is a kind of steepest descent method, for example. The filter coefficients W1 [n] and W2 [n] are updated by Expression (14) and Expression (15).

W1 [n + 1] = W1 [n] −μ × ε [n] × r1 [n] (14)
W2 [n + 2] = W2 [n] −μ × ε [n] × r2 [n] (15)
Here, μ is a step size parameter and determines the convergence speed in the steepest descent method.

  Control target noise can be reduced by converging the filter coefficient W1 [n] and the filter coefficient W2 [n] by the above-described procedure.

  Here, regarding the generation method of the reference sine wave signal r1 [n] and the reference cosine wave signal r2 [n], the present invention and the method described in Patent Document 1 are compared in terms of calculation load, calculation performance, and memory usage. Compare from. In the method described in Patent Document 1, a reference sine wave signal correction value table 20 simulating a transfer characteristic value from the speaker 10 to the microphone 11 (the reference sine wave signal correction value at the frequency k [Hz] is C1 [k]. And the reference cosine wave signal correction value table 21 (the reference cosine wave signal correction value at the frequency k [Hz] is expressed as C2 [k]). And a reference sine wave signal r1 [n] and a reference cosine wave signal r2 [n], respectively.

r1 [n] = C1 [f] × x1 [n] + C2 [f] × x2 [n] (16)
r2 [n] = C1 [f] × x1 [n] −C2 [f] × x2 [n] (17)
First, while Expression (16) and Expression (17) involve multiplication, in the present invention, as described in Expression (8), Expression (9), Expression (10), and Expression (11) No multiplication is required (d is a constant, so it is not necessary to execute d / 4 operation every cycle). Therefore, compared with the method described in Patent Document 1, the present invention has an effect that calculation performance is improved and calculation load can be reduced because no digit loss occurs. In the method described in Patent Document 1, it is necessary to store the reference sine wave signal correction value C1 [k] and the reference cosine wave signal correction value C2 [k] in the memory. Then, only the value c [k] obtained by converting the phase characteristic value of the transfer characteristic from the speaker 10 to the microphone 11 into the relative point movement amount of the sine wave table 3 may be held in the memory. Therefore, the present invention has an effect that the amount of memory used can be reduced as compared with the method described in Patent Document 1.

  Note that a sine value held by the sine wave table 3 is sufficient for a quarter period. However, a sine value in the quarter cycle is also required, and a total (d / 4) +1 point sine value is required. Assuming that the arrangement of the sine wave table at this time is z ′ [x] (0 ≦ x ≦ d / 4), z [n] can be calculated by Expression (18).

z [n] = z ′ [n] (0 ≦ n <d / 4)
z ′ [d / 2−n] (d / 4 ≦ n <d / 2)
−z ′ [n−d / 2] (d / 2 ≦ n <3 × d / 4)
−z ′ [dn] (3 × d / 4 ≦ n <d)
... (18)
This method has an effect that the memory area reserved for the sine wave table 3 can be minimized.

  In the present invention, the input x2 [n] to the second one-tap digital filter is described as a reference cosine wave signal, and the input r2 [n] to the second adaptive control algorithm calculation unit is described as a reference cosine wave signal. However, the phase difference between x1 [n] and x2 [n] and the phase difference between r1 [n] and r2 [n] are not limited to 90 °, and it goes without saying that some errors are allowed. Yes.

  A plurality of first and second one-tap digital filters 7 and 8 and a plurality of first and second adaptive control algorithm computing units 12 and 13 are prepared to mute the multiple-order components of the control target noise. It is also possible to make it.

  Specifically, for example, the active noise reduction apparatus when two first and second one-tap digital filters 7 and 8 and two first and second adaptive control algorithm calculation units 12 and 13 are prepared. A block diagram is shown in FIG. 6, and different points from FIG. 1 will be described.

  In FIG. 6, the frequency detector 2 determines, for example, the frequency f1 [Hz] of the primary component and the frequency f2 [Hz] of the secondary component of the control target noise based on the engine pulse p from the engine speed detector 1. calculate. The signal generator 6 receives f1 and f2 as input, and uses the primary component of the control target noise in the same manner as the generation method of x1 [n], x2 [n], r1 [n], and r2 [n] in FIG. A reference sine wave signal x11 [n], a reference cosine wave signal x12 [n], a reference cosine wave signal r11 [n], and a reference cosine wave signal r12 [n] for control are generated, and the second order of the control target noise is generated. A reference sine wave signal x21 [n], a reference cosine wave signal x22 [n], a reference sine wave signal r21 [n], and a reference cosine wave signal r22 [n] for controlling the components are generated. The first, second, third, and fourth one-tap digital filters 7, 8, 15, and 16 have filter coefficients W11 [n], W12 [n], W21 [n], and W22 [n] inside, respectively. The control signals y11 [n], y12 [n], y21 [n], and y22 [n] are generated similarly to the operations of the first and second one-tap digital filters 7 and 8 in FIG. The power amplifier 9 amplifies the signal obtained by adding the control signals y11 [n], y12 [n], y21 [n], and y22 [n]. The first, second, third, and fourth adaptive control algorithm computing units 12, 13, 17, and 18 are respectively similar to the operations of the first and second adaptive control algorithm computing units 12 and 13 in FIG. The filter coefficients W11 [n], W12 [n], W21 [n], and W22 [n] are updated.

  As shown in FIG. 6, it can be expected that a greater silencing effect can be obtained by silencing the multiple-order components of the control target noise.

  The active noise reduction device according to the present invention can reduce the calculation load by minimizing the execution of the product-sum operation, and is useful as a practical active noise reduction device at low cost.

The block diagram for demonstrating the active noise reduction apparatus in Embodiment 1 of this invention Graph showing an example of a sine wave table in the active noise reduction device The figure showing the table | surface which shows the example of the sine wave table in the active noise reduction apparatus The graph which shows the example of the position characteristic value of the transfer characteristic from a speaker to a microphone in the active noise reduction device The figure showing the table | surface which shows the row | line | column of the arrangement | sequence which converted the position characteristic value of the transmission characteristic from a speaker in the active noise reduction apparatus into the relative point movement amount of the sine wave table Block diagram for explaining a method of silencing multiple order components of noise to be controlled in the active noise reduction apparatus Block diagram showing the configuration of a conventional active noise reduction device

Explanation of symbols

1 Engine speed detector 2 Frequency detector (Controlled noise frequency detection means)
DESCRIPTION OF SYMBOLS 3 Sine wave table 4 Phase characteristic table 5 Selection means 6 Signal generation part 7 1st 1 tap digital filter 8 2nd 1 tap digital filter 9 Power amplifier 10 Speaker (drive signal generation means)
11 Microphone (error signal detection means)
12 1st adaptive control algorithm calculating part (1st coefficient update means)
13 2nd adaptive control algorithm calculating part (2nd coefficient update means)
DESCRIPTION OF SYMBOLS 14 Discrete arithmetic processing part 15 3rd 1 tap digital filter 16 4th 1 tap digital filter 17 3rd adaptive control algorithm calculating part 18 4th adaptive control algorithm calculating part

Claims (5)

Control target noise frequency detecting means for detecting the frequency of noise to be controlled due to a noise source, a discretized sine wave table, a first one-tap digital filter, a second one-tap digital filter, The sum of the output from the first one-tap digital filter and the output from the second one-tap digital filter is input, and a drive signal for causing interference with the noise to be controlled due to the noise source is output. Drive signal generating means for detecting, error signal detecting means for detecting an error signal resulting from interference between the drive signal output from the drive signal generating means and noise to be controlled caused by the noise source, and the first First coefficient updating means for updating the filter coefficient of the one-tap digital filter, and first filter coefficient for updating the filter coefficient of the second one-tap digital filter. Coefficient updating means, first discrete data to be input to the first one-tap digital filter, second discrete data to be input to the second one-tap digital filter, and input to the first coefficient updating means. Third discrete data and fourth discrete data to be input to the second coefficient updating unit are selected from the sine wave table for each predetermined time based on the frequency detected by the control target noise frequency detecting unit. Selecting means, and based on the error signal, the third discrete data, and the fourth discrete data, the first coefficient updating means and the second coefficient updating so that the error signal is minimized. An active noise reduction device configured to reduce noise to be controlled due to the noise source by updating the filter coefficient by means. The selection unit is configured to select the first discrete data and the second discrete data based on the control target noise frequency detected by the control target noise frequency detection unit and the phase characteristic of the transfer characteristic from the drive signal generation unit to the error signal detection unit. The active noise reduction device according to claim 1, wherein the active noise reduction device is configured to select the third discrete data and the fourth discrete data. The selection means is configured so that the phase difference between the first discrete data and the second discrete data is a quarter cycle, the phase difference between the first discrete data and the third discrete data, and the second The first discrete data and the second discrete data are set such that the phase difference between the discrete data and the fourth discrete data matches the phase characteristic value of the transfer characteristic from the drive signal generating means to the error signal detecting means. The active noise reduction device according to claim 1, wherein the active noise reduction device is configured to select the third discrete data and the fourth discrete data. 2. The active noise according to claim 1, wherein at least one of the first one-tap digital filter, the second one-tap digital filter, the first coefficient updating unit, and the second coefficient updating unit is provided. Reduction device. 2. The active noise reduction device according to claim 1, wherein the discretized sine wave table has a data number corresponding to at least a quarter cycle of the sine wave.

Images