JPH0973295A - Active control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress increasing of filter operation quantity caused by increasing of sampling frequencies to the absolute minimum, in an active control device used for an adaptive digital filter. SOLUTION: In a transversal filter inputting a signal (u) (n) and outputting a control signal (y) (n), impulse response is adjusted so that impulse response (h) (n) has a value every fixed time interval and it is substantially made 0 in the other time. Therefore, each delay tap of the transversal filter is provided with a multiplication block making the product with a filter coefficient corresponding to impulse response every fixed interval. Also, updating the filter coefficient is performed every fixed time interval.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active control device for active control of noise, vibration and the like by using an adaptive digital filter composed of a microprocessor, a digital signal processor (DSP) and the like.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a system in which an active control method is applied to noise control. The noise emitted from the noise source 1 is detected by the microphone 2 and sent to the AD converter 4 via the anti-aliasing filter 3 formed of a low pass filter. The AD converter 4 sends the reference signal u (n) to the signal processing unit 5.

The DA converter 6 inputs the control signal y (n) from the signal processing unit 5, converts it into an analog signal, and outputs it to a speaker 8 which is a secondary sound source through an anti-aliasing filter 7 composed of a low pass filter. To do. Speaker 8
The sound wave output from the noise source 1 interferes with the sound wave emitted from the noise source 1, and the noise after the interference is detected by the microphone 9 as residual noise, and is input to the AD converter 11 via the anti-aliasing filter 10 composed of a low-pass filter. To be done. The AD converter 11 outputs the residual noise to the error signal e (n).
To the signal processing unit 5.

The signal processing unit 5 includes a reference signal u (n)
To the control signal y (n) and the reference signal u (n) and the error signal e.
(n) is input and the coefficient updating unit 13 is configured to sequentially update the filter coefficient a _i (n) of the adaptive digital filter 12. Here, assuming that the adaptive digital filter 12 is a finite impulse response (FIR) filter of length I, the input / output relationship is

[0005]

[Equation 1]

[0006] At this time, the impulse response h (n) of the adaptive digital filter 12 is h (n) = a _n (n = 0, ..., I-1) (2).

On the other hand, in the coefficient updating unit 13, the error signal e (n)
The filter coefficient a _i is updated by ai (n + 1) = a _i (n) −αr (n−i) e (n) (3) so as to reduce the power of A i. Here, α is a small positive value. Also, r (n) is

[0008]

[Equation 2]

Is calculated by Where c _k (k = 0, ...
.., k-1) is an impulsed response of the transfer function in the process in which the output y (n) of the adaptive digital filter 12 propagates to the coefficient updating unit 13.

In the above system, as the number of filter coefficients of the adaptive digital filter 12 increases, the calculation amount of the equations (1) and (3) increases, so that a plurality of DSPs are made to divide and process these operations. A method has been proposed.

[0011]

In active control, in the case of controlling the amount of physical phenomenon by inputting a reference signal having a correlation with the amount of physical phenomenon, performing adaptive digital signal processing of this and outputting a control signal, The time delay from the input to the output of the physical quantity for control needs to be minimized as much as possible. In particular, it becomes an important issue when the amount of physical phenomenon that is the control target changes randomly.

The main delay elements in the digital control circuit are analog low-pass filters used as the anti-aliasing filter 3 and the anti-aliasing filter 7 before AD conversion and after DA conversion, and D
It is the calculation time by SP or the like. Among these, the delay of the low-pass filter accounts for the majority.

To reduce the delay of the low-pass filter, the cutoff frequency may be shifted to the high frequency side or a low-order filter having a gentle cutoff characteristic may be used. At the same time, the sampling frequency in the digital processing is also changed accordingly. Must be high. However, if the sampling frequency is set high, it is necessary to increase the number of filter coefficients of the adaptive digital filter accordingly, which causes a problem that the amount of calculation is significantly increased.

In view of the above-mentioned problems, the present invention provides an active control device capable of executing an operation of an adaptive digital filter in active control and an operation of updating its filter coefficient with a smaller amount of operation than in the conventional case. To do.

[0015]

In order to solve the above problems, the invention of claim 1 inputs a reference signal u (n) having a correlation with a physical phenomenon amount, and applies adaptive signal processing to the reference signal u (n). In the active control device that outputs the control signal y (n) to bring the physical phenomenon amount close to a desired amount, an adaptive digital filter means for performing adaptive signal processing on the reference signal u (n). , The impulse response h (n) at the time n of the adaptive digital filter means has a value at every constant time interval x, and the impulse response h (n) is adjusted so that it becomes substantially 0 at the time between them. The configuration is such that adjustment means is provided.

According to a second aspect of the present invention, in the first aspect of the invention, the adjustment of the impulse response h (n) of the adaptive digital filter by the adjusting means is performed around the time n having the maximum absolute value. Only, the value of the physical phenomenon is made to approach a desired value without fixing the value to substantially zero.

According to the third aspect of the invention, the reference signal u (n) having a correlation with the physical phenomenon amount is input, adaptive signal processing is performed on the reference signal u (n), and the control signal y (n) is output. , In the active control device that brings the physical phenomenon amount close to a desired amount, the reference signal u
(n) is subjected to adaptive signal processing, and first and second adaptive digital filter means are adjusted so that the amount of physical phenomenon approaches a desired amount, and either the first or the second adaptive digital filter. The means is provided with an adjusting means for adjusting so that the impulse response h (n) at the time n has a value at every constant time interval x, and becomes substantially 0 at the time between them.

As described above, according to the present invention, by inputting the reference signal u (n) having a correlation with the physical phenomenon amount, performing adaptive signal processing on the reference signal u (n), and outputting the control signal y (n), In the active control device that brings the physical phenomenon amount close to a desired amount, the reference signal u
Adaptive signal processing is performed on (n) by the adaptive digital filter means, and the impulse response h (n) of the digital filter means at time n has a value at every constant time interval x, and in the time between them, the impulse response h (n) is substantially. When the impulse response h (n) is adjusted to be 0, the input / output relationship of the adaptive digital filter is

[0019]

(Equation 3)

## EQU1 ## Here, x is a positive integer of 2 or more. Also, I shall be divisible by x.

In the equation (5), when the output y (n) of the adaptive digital filter is calculated, the product-sum calculation is not performed on the filter coefficient corresponding to the impulse response of substantially 0, so the calculation amount is reduced. Is clear. Therefore, according to the present invention, the sampling frequency is set to 2
Even if the number is doubled, if x = 2, the number of filter coefficients of the adaptive digital filter does not increase, so that the increase in the amount of calculation can be suppressed to the minimum.

FIG. 5 is a conceptual diagram showing the operation of the adaptive digital filter when the sampling frequency is fs and all the filter coefficients are used, and when the sampling frequency is 2fs and x in the equation (5) is 2. . FIG.
(A) has shown the impulse response example of an adaptive digital filter. 5 (a-1) has a sampling frequency of fs, FIG. 5 (a-2) has a sampling frequency of 2fs, and x = 1, FIG. 5 (a-3) has a sampling frequency of 2fs. And x = 2,
It is an example related to the present invention.

According to the prior art, the sampling frequency is set to 2
When fs is set, as shown in FIG. 5A-2, the impulse response time interval is halved, and the number of filter coefficients to be adjusted is doubled. In the present invention, FIG.
As shown in (a-3), there is a value at every x = 2, and there is no increase in the filter coefficient to be adjusted to substantially 0 between them.

FIG. 5B is a conceptual diagram showing the difference in frequency response with respect to the difference in impulse response shown in FIG. 5A. FIG. 5 (b-1) shows the frequency response corresponding to FIG. 5 (a-1), and its processing band is fs / 2 or less. According to the conventional technique, it becomes as shown in FIG.
The frequency response is similar to the sampling frequency fs,
The processing band extends up to fs.

On the other hand, in the case of the present invention, as shown in FIG. 5B-3, a frequency response is obtained by folding the characteristic of FIG. 5B-1 to the high frequency side at the frequency of fs / 2. If the frequency band of the amount of physical phenomenon targeted for active control is fs / 2 or less, the characteristic in the frequency range of fs / 2 or more in FIG. 5B-3 does not matter. Therefore, it suffices to cut the frequency of fs / 2 or more with the low-pass filter before AD conversion and input it to the adaptive digital filter.

Further, since the processing band of the adaptive digital filter is up to the frequency fs, the low-pass filter after DA conversion has only to cut the frequency of fs or higher.
The cutoff frequency of the low-pass filter after A conversion can be raised to fs. Therefore, it is possible to reduce the delay of the low-pass filter unit after DA conversion with a minimum increase in the amount of calculation.

Further, for frequencies above fs / 2, the characteristics in the frequency range below that are folded back, so the adjustment of the filter coefficient may be performed at the sampling frequency fs. Therefore, the calculation for the successive adjustment of the filter coefficient of the adaptive digital filter can be executed at the constant time intervals x, and as a result, the calculation amount can be reduced.

By using the above-mentioned means, it is possible to suppress an increase in the amount of calculation by increasing the sampling frequency as compared with the conventional case. In this case, however, the delay can be reduced by using the low-order filter because the DA conversion is performed. It was only a low pass filter later. Therefore, in order to enable the low-pass filter before AD conversion to be handled by a lower-order filter, in the impulse response h (n) of the adaptive digital filter, the time n having the largest absolute value is used.
The value of the physical phenomenon is adjusted to be close to a desired value without fixing the value to substantially 0 only in the vicinity of.

At this time, if the desired amount is set under the condition that the physical phenomenon amount is not controlled at the frequency of fs / 2 or more in FIG. 5B, the impulse response with the fixed value of substantially 0 is released. The part of FIG.
-3) It acts to reduce the gain in the frequency band of fs / 2 or more. As a result, the order of the low-pass filter 3 before AD conversion can be reduced.

The first adaptive digital filter in which all the filter coefficients are adjusted to bring the physical phenomenon close to the desired amount and the second adaptive digital filter in the subsequent stage have the second adaptive digital filter. Next, the operation in the case where the impulse response h (n) at the time n has a value at every constant time interval x and becomes substantially 0 at the time between them will be described.

The second adaptive digital filter mentioned here has the same operation as that shown in FIGS. 5 (a-3) and 5 (b-3). The first adaptive digital filter is shown in FIG.
If the desired amount is set under the condition that the physical phenomenon amount is not controlled at the frequency of fs / 2 or more in (b), the gain of the frequency band of fs / 2 or more in FIG. 5B-3 is set. Has a reducing effect. as a result,
The order of the low-pass filter 3 before AD conversion can be reduced. When the signal processing configuration in which the connection order of the first adaptive digital filter and the second adaptive digital filter is switched is used, the same operation is performed.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram for explaining a configuration of a main part of an active noise control device according to an embodiment of the present invention. An adaptive digital filter in the active noise control device shown in FIG. The detailed configuration of the portion 12 is shown, and other configurations are the same as those in FIG. In FIG.
(C) is a configuration of an adaptive digital filter in the prior art shown for explaining the present invention by comparison with the prior art, and the sampling frequency is fs. The digital filter is composed of a plurality of unit delay blocks 14, multiplication blocks 15 and addition blocks 16, which inputs a reference signal u (n) and outputs a control signal y (n). The input / output relationship in this case is

[0033]

(Equation 4)

Is represented by a _i is a filter coefficient,
I is the filter length. Further, the delay T in the unit delay block 14 at this time is 1 / fs.

On the other hand, FIG. 1A is a block diagram of the first embodiment of the adaptive digital filter used in the present invention, and the portions corresponding to the conventional example shown in FIG. The sampling frequency in this case is 2 fs, and therefore the delay of the unit delay block 14 is T / 2. In order to maintain the same frequency resolution as in the case of the conventional example shown in FIG. 1C, a filter length of 2I is required. However, in the first embodiment of the present invention shown in FIG. By fixing every other 15 filter coefficients to 0, the corresponding multiplication block is virtually eliminated. The input / output relationship at this time is

[0036]

(Equation 5)

## EQU3 ## Therefore, the number of product-sum operations for obtaining the output y (n) from the input u (n) is the same as in the case of the conventional example shown in FIG. 1 (c) and does not increase. In this embodiment, the above-mentioned constant time interval x corresponds to 2.

The calculation regarding the update of the filter coefficient a _i is executed at the sampling frequency fs. FIG.
In the first embodiment shown in (a), the sampling frequency of the adaptive digital filter is set to 2fs, so the filter coefficient is updated once for every two samplings. The update of the filter coefficient is performed by the coefficient updating unit 13 shown in FIG. 4 using the filtered-x LMS algorithm, and a _i (n + 1) = a _i (n) -αr (ni) e (n) (8) To be done. Here, α is a small positive value. Also, r (n) is

[0039]

(Equation 6)

Is calculated by Where c _k (k = 0, ...
.., k-1) is the impulse response of the transfer function in the process in which the output y (n) of the adaptive digital filter 12 propagates to the coefficient updating unit 13 in FIG. The calculations of the equations (8) and (9) are performed once every two samplings.

FIG. 1B is a block diagram of the second embodiment of the adaptive digital filter used in the present invention, in which the sampling frequency is 3fs and the filter length is 3I. In this embodiment, the above-mentioned constant time interval x corresponds to 3. The delay of the unit delay block 14 at this time is T / 3. In the second embodiment of the present invention shown in FIG. 1B, the filter coefficient has a value every two, and the coefficient value between them is fixed to zero. The multiplication block whose filter coefficient value is substantially 0 is deleted. Therefore, the input / output relationship at this time is

[0042]

(Equation 7)

It becomes Since the calculation related to the update of the filter coefficient a _i is executed at the sampling frequency fs, the update of the filter coefficient is performed once for every three samplings.

FIG. 2 is a block diagram showing a third embodiment of the present invention. In FIG. 2, the multiplication block that has been deleted because the filter coefficient value corresponds to 0 is partially restored and used around the filter coefficient a _{k having} the largest absolute value in the configuration of FIG. . Like the other filter coefficients, the filter coefficients a _{k + 1} and a _{k + 3} in the added multiplication block are also updated by the equation (8) so as to minimize the power of the error signal e (n). Or Figure 5
It is also possible to adjust the output of the frequency band of fs / 2 or more in (b-3) to be included in the control signal y (n) so as to be minimized.

FIG. 3 is a block diagram showing a fourth embodiment of the present invention, in which the filter coefficient is fixed to 0 before the adaptive digital filter having the same configuration as the adaptive digital filter 12 shown in FIG. 1 (a). It is provided with another adaptive digital filter 17 that does not operate, and operates at a sampling frequency of 2fs.

The adaptive digital filter 17 in the preceding stage converts the signal having a frequency of fs / 2 or more in FIG.
It is provided for the purpose of removing from the control signal y (n). The high-pass filter 18 extracts a signal of fs / 2 or more from the output y (n) of the adaptive digital filter 12, and the coefficient updating unit 19 is arranged so that the extracted signal w (n) approaches 0.
At the filter coefficient b of the adaptive digital filter 17
Update _j sequentially.

At this time, the input to the high-pass filter 18 may be the output v (n) of the adaptive digital filter 17 or white noise. Further, the adaptive digital filters 12 and 17 are used by the coefficient updating unit 1.
3 also receives the update of the filter coefficient for minimizing the power of the error signal e (n). Further, the adaptive digital filters 12 and 17 may have a configuration in which the connection order is switched.

In the above embodiment, the FIR type filter is taken as an example of the adaptive digital filter, but the IIR filter can be similarly implemented by setting the filter coefficient fixed to 0.

The series of filter operations and filter coefficient update operations are processed by programming of a microprocessor or a digital signal processor or by hardware dedicated to filter operations.

[0050]

According to the present invention, a reference signal u (n) having a correlation with a physical phenomenon amount is input, adaptive signal processing is performed on the reference signal u (n), and a control signal y (n) is output.
In active control for bringing the amount of physical phenomenon closer to a desired amount, the signal processing is executed by an impulse filter at time n of the digital filter, and an impulse response h (n) at time n of the digital filter is constant time. Has a value at every interval x,
When the output y (n) of the adaptive digital filter is calculated in equation (5) by adjusting the impulse response so that it becomes substantially 0 in the time period between them,
Since the product-sum calculation regarding the filter coefficient corresponding to the impulse response of substantially 0 is not performed, the calculation amount is reduced.

Therefore, even if the sampling frequency is doubled, the number of filter coefficients of the adaptive digital filter does not increase if the constant time interval x = 2, and therefore the increase in the amount of calculation can be suppressed to the minimum. Along with D
Since the cutoff frequency of the low pass filter after A conversion can be increased, it becomes possible to reduce the delay of the low pass filter unit after DA conversion. Furthermore, the calculation for the successive adjustment of the filter coefficient of the adaptive digital filter is
It is possible to execute every fixed time interval x,
As a result, the calculation amount is reduced.

In the impulse response h (n) of the adaptive digital filter, the time n of which the absolute value is the largest is n.
By adjusting the amount of the physical phenomenon to be close to a desired amount without fixing the value to substantially 0 only in the vicinity of, the portion of the impulse response in which the fixing of substantially 0 is released is shown in FIG. Fs / in (b-3)
Since it becomes possible to perform adjustment so as to have an effect of reducing the gain in two or more frequency bands, it is possible to reduce the order of the low-pass filter 3 before AD conversion.

The first adaptive digital filter in which all the filter coefficients are adjusted so that the physical phenomenon amount approaches the desired amount, and the second adaptive digital filter in the subsequent stage are provided, and the second adaptive digital filter is provided. If the impulse response h (n) at the time n has a value at every constant time interval x and becomes substantially 0 at the time between them, the first adaptive digital filter is
If the desired amount is set under the condition that the physical phenomenon amount is not controlled at the frequency of fs / 2 or more in FIG. 5B, the gain of the frequency band of fs / 2 or more in FIG. 5B-3 is set. Has the effect of reducing As a result, the order of the low-pass filter 3 before AD conversion can be reduced. In addition, the first adaptive digital filter and the second adaptive digital filter
When the signal processing structure in which the connection order of the adaptive digital filter is changed, the same effect is obtained.

The reduction of the order of the low-pass filter or the high-frequency shift of the cutoff frequency as described above reduces the delay of the filter itself, thereby reducing the signal processing delay of the active control system. As a result, when used for active noise control as shown in FIG.
The distance can be shortened, and the whole system can be made compact.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a block diagram of a second embodiment of the present invention.

FIG. 3 is a block diagram of a third embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration when the present invention is used in an active noise control device.

FIG. 5 is a diagram illustrating the operation of the present invention.

[Explanation of symbols]

 12 ・ ・ ・ Adaptive digital filter 13 ・ ・ ・ Coefficient updating unit 14 ・ ・ ・ Unit delay block 15 ・ ・ ・ Multiplication block 16 ・ ・ ・ Adding block 17 ・ ・ ・ Adaptive digital filter 19 ・ ・ ・ Coefficient updating unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location H03H 21/00 9274-5J H03H 21/00

Claims (3)

[Claims] 1. A desired physical quantity is obtained by inputting a reference signal u (n) having a correlation with the physical quantity, subjecting it to adaptive signal processing, and outputting a control signal y (n). In an active control device for making the amount close to the quantity, an adaptive digital filter means for performing adaptive signal processing on the reference signal u (n), and an impulse response h (n) of the adaptive digital filter means at time n are constant times. An active control apparatus comprising: an adjusting unit that adjusts the impulse response h (n) so that it has a value at every interval x and becomes substantially 0 at a time interval therebetween. 2. The adjustment of the impulse response h (n) of the adaptive digital filter by the adjusting means does not fix the value to substantially 0 only around the time n having the largest absolute value, and the physical phenomenon The amount is adjusted so that the amount approaches a desired amount.
The active control device described. 3. The physical phenomenon quantity is desired by inputting a reference signal u (n) having a correlation with the physical phenomenon quantity, subjecting it to adaptive signal processing, and outputting a control signal y (n). First and second adaptive digital filter means for performing adaptive signal processing on the reference signal u (n) to adjust the physical phenomenon quantity to a desired quantity And either the first or the second adaptive digital filter means, the impulse response h (n) at the time n has a value at every constant time interval x, and becomes substantially 0 at the time between them. An active control device, characterized in that adjustment means for adjusting is provided.