EP0434468A2

EP0434468A2 - Vibration control system

Info

Publication number: EP0434468A2
Application number: EP90314217A
Authority: EP
Inventors: Toshihiro Miyazaki; Keiichiro Mizuno; Kazuyoshi Iida; Kazutomo Murakami
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 1989-12-22
Filing date: 1990-12-21
Publication date: 1991-06-26
Also published as: EP0434468A3

Abstract

A vibration control system comprises at least one original vibration detecting means (7) located on or close to each of at least one vibration source (2) for detecting an original vibration or noise from the vibration source, at least one controlled vibration applying actuator (6) provided on an acoustic radiator (5) which is vibrated by the original vibration or noise, and controlling means for receiving a signal from the original vibration detecting means and outputting a control signal to the controlled vibration applying actuator, the controlling means including a digital filter (8) which produces a control signal for actuating the vibration applying actuator (6) so as to generate a controlled vibration wave having an inverse waveform which is of an opposite sign to the original vibration, thereby offsetting the original vibration with the controlled vibration to reduce the original vibration of the acoustic radiator and effectively isolate noise of a random vibration.

Description

The present invention relates to a vibration control system for significantly reducing a radiate sound at a desired location by actively reducing vibration of an acoustic radiator which is acoustically vibrated by an original vibration which is directly transmitted through a solid body or acoustically transmitted from a vibration or noise source.
There is a prior art in order to isolate vibration or noise by actively reducing vibration of an acoustic radiator by use of a vibration applying actuator as disclosed in Japanese Patent Application Publication No. 55-29304.
A conventional vibration control system disclosed in the aforementioned publication is arranged as shown in Fig. 21 for preventing noise at a vibration wave generating source O2 in a factory building O1 from transmitting to a house O3.
To this end, a sidewall O4 of the building is provided with a plurality of vibration applying actuators O5, a microphone O6 is located closely to the sidewall O4 at the inside of the factory building O1, and the microphone O6 is connected to each of the vibration applying actuators through a controller O7.
The controller O7 controls the vibration applying actuators O5 so as to simultaneously apply compulsory vibration force to the sidewall O4, which vibration force has an inverse phase opposite to an original vibration force transmitted to the sidewall O4 by an acoustic wave from the vibration wave generating source O2.
The original vibration force transmitted from the vibration wave generating source O2 to the sidewall O4 is affect by the forced vibration force having an inverse phase applied by the vibration applying actuators to reduce vibration of the sidewall O4 and prevent vibration from transmitting to the house O3.
The aforementioned convenience vibration control system can effectively reduce the original vibration by applying a compulsory vibration having an inverse phase shifted by the controller O7 to the sidewall O4 when the original sound wave from the vibration wave generating source O2 has a cyclic characteristic.
However, when the original sound wave from the vibration generating source 20 is a random vibration rather than a cyclic vibration, it is difficult to determine the phase of the original sound wave so that even if the compulsory vibration is applied to the sidewall, the random vibration could not be effectively reduced.
Actually, the original vibration is generally a random vibration and consequently the conventional vibration control system is limited in applicable conditions.
It is an object of the present invention to provide an improved vibration control system which makes it effectively possible to reduce noise of the random vibration by offsetting an original vibration with a controlled vibration having an inverse waveform.
According to the present invention, there is provided a vibration control system comprising at least one original vibration detecting mans located on or closely to each of at least one vibration source for detecting an original vibration or noise from the vibration source, at least one controlled vibration applying actuator provided on an acoustic radiator which is vibrated by the original vibration or noise, and controlling means for receiving a signal from the original vibration detecting means and outputting a control signal to the controlled vibration applying actuator, the controlling means being a digital filter which produces a control signal for actuating the vibration applying actuator so as to generate a controlled vibration wave having an inverse waveform which is of an opposite sign to the original vibration.
The digital filter outputs a control signal to the controlled vibration applying actuator which generates a controlled vibration wave having an inverse waveform which is of an opposite sign to the original vibration transmitted to the acoustic radiator so that the original vibration is offset by the controlled vibration to significantly reduce the original vibration and effectively isolate the noise of random vibration.
The system according to the present invention advantageously comprises at least one controlled vibration detecting means located for detecting controlled vibration or noise of the acoustic radiator, and the controlling means further includes a coefficient renewal algorithm which is arranged to be input the original vibration signal from the original vibration detecting means and the controlled vibration signal from the controlled vibration detecting means, and output a filtering coefficient renewing signal to the digital filter.
The present invention will become more apparent in the following description and the accompanying drawings.

Fig. 1 is a diagrammatic view showing a first embodiment of vibration control system according to the present invention;
Fig. 2 is a diagrammatic plan view showing an arrangement of a vibrator shown in Fig. 1;
Figs. 3 and 4 are graphs showing test results of the vibration control system of Fig. 1;
Fig. 5 is a diagrammatic view showing a second embodiment of vibration controlling system according to the present invention;
Fig. 6 is a diagrammatic plan view illustrating an arrangement of vibration control system applied for an automobile according to a third embodiment;
Fig. 7 is a diagrammatic side view of Fig. 6;
Fig. 8 is a sectional view of a window in the third embodiment;
Fig. 9 is a block diagram showing a control system in the third embodiment;
Figs. 10 and 11 are graphs showing test results of the third embodiment;
Fig. 12 is a diagrammatic plan view illustrating an arrangement of vibration control system applied for an automobile according to a fourth embodiment;
Fig. 13 is a diagrammatic side view of Fig. 12;
Fig. 14 is a block diagram showing the control system of the fourth embodiment;
Fig. 15 is a diagrammatic view showing a fifth embodiment of vibration control system according to the present invention;
Figs. 16 and 17 are graphs showing test results of the vibration control system of the fifth embodiment;
Fig. 18 is a diagrammatic view showing a sixth embodiment of vibration control system;
Fig. 19 is a diagrammatic view showing a seventh embodiment of vibration control system;
Fig. 20 is a diagrammatic view showing an eighth embodiment of vibration control system; and
Fig. 21 is a diagrammatic view of a prior art vibration control system.

Referring to Figs. 1-4 showing the first embodiment of vibration control system according to the present invention for experimental use, Fig. 1 shows a general arrangement of the vibration control system which comprises a sound isolating box 1 of a cube having an open top. A noise source such as a speaker 2 is positioned closely to a bottom wall 1a within the sound isolating box.
The speaker 2 is connected to a noise generator 3 through a power amplifier 4 to receive a signal of a random vibration wave output from the noise generator and amplified through the amplifier and generate a noise.
The open top of the sound isolating box 1 is closed by a sound isolating plate 5 which is acoustic radiator and a vibration applying actuator or vibrator 6 is adhered to the outer surface of the sound isolating plate 5 at the center thereof.
The vibration applying actuator may be an electric actuator such as a piezoelectric oscillator.
A microphone 7 is located closely to the speaker 2 in the inside of the sound isolating box 1 to instantly detect a noise generated from the speaker 2. The detected noise signal is input to a digital filter 8 and a coefficient renewal algorithm 9.
A microphone 10 is located opposedly to the sound insulating plate 5 at the outside of the sound insulating box 1 to detect a noise at this location. A noise signal detected by the microphone 10 is input to the coefficient renewal algorithm. Thus the coefficient renewal algorithm 9 receives the noise signals detected by the microphones 7 and 10 to renew the filtering coefficient (characteristic) of the digital filter 8 so as to maintain it most appropriate.
The digital filter 8 operates the noise signal input from the microphone 7 on the base of a filtering coefficient determined by the coefficient renewal algorithm 9 to output a control signal for actuating the vibration applying actuator 6. The control signal is amplified by an amplifier 11 to a voltage sufficient to actuate the vibration applying actuator 6 and then applied to the vibration applying actuator 6.
A multi-channel digital filter having multiple inputs (including single input) and multiple outputs (including single output) may be used as the digital filter. In this case, the coefficient renewal algorithm renews the coefficient so as to minimize each of square means errors of input error signals according to the least means square method.
The digital filter 8 outputs a control signal to the vibration applying actuator to forcedly generate a controlled vibration having an inverse waveform which is of an opposite sign to the original vibration of the sound insulating plate 5 generated by the noise propagated from the speaker 2. Thus the original vibration of the sound insulating plate 5 is offset by the controlled vibration having the inverse waveform to reduce the vibration of the sound insulating plate 5 and as the result the noise at the microphone 10 is reduced.
As mentioned above, since the vibration of the sound insulating plate 5 is reduced by the controlled vibration having the inverse waveform, a cyclic vibration as well as any random vibration in a wide band are effectively reduced so that the applicable range is greatly extended.
Referring to Fig. 21, a conventional vibration control system of prior art comprises a microphone O6 which is located closely to a sidewall O4 at the inside of a building O1 to detect a vibration wave propagated from a vibration generating source O2. The sidewall O4 is provided with a plurality of vibrators which are actuated to generate a vibration with a shifted phase, thereby reducing a vibration of the sidewall O4. Such a conventional vibration control system is applicable only for a cyclic vibration, but not for any random vibration.
On the contrary, according to the present invention, the original vibration from the speaker 2 which is a vibration source is detected by the microphone 7 located closely to the speaker 2 and a controlled vibration having an inverse waveform of an opposite sign to the original vibration is applied to the vibration insulating plate 5 before the original vibration wave reaches to the vibration insulating plate 5 from the speaker 2, thereby reducing the vibration of the vibration insulating plate. Consequently, the arrangement of the vibration control system according to the present invention is different from the conventional vibration control system and is effective for the cyclic vibration as well as any random vibration to greatly reduce such a vibration.
Test results of the aforementioned first embodiment are shown in Figs. 3 and 4.
Fig. 3 is a graph showing the frequency characteristics of the sound pressure spectrum, in which a broken line shows a non-control case and a solid line shows a controlled case.
In the non-control case, the sound pressure varies over a range of 50 dB ± 10 dB and the peak sound pressure of 80 dB occurs about 200 Hz.
On the other hand, in the controlled case, the sound pressure varies in a range of 50 dB ± 5 dB and is apparently reduced.
Fig. 4 is a graph showing time characteristics of output voltage of the microphone 10, in which a broken line is a non-control case, and a solid line is a controlled case.
It is seen from Fig. 4 that in the controlled case, the output voltage greatly decreases and the noise at the location near the microphone 10 is greatly reduced.
Referring to Fig. 5 showing the second embodiment, the sound insulating plate 5 is provided with an acceleration pickup 15 in place of the microphone 10 in the first embodiment shown in Fig. 1 and an output of the acceleration pickup 15 is connected to the coefficient renewal algorithm 9.
According to this embodiment, the coefficient renewal algorithm also operates in an adaptive type mode so as to minimize the vibration of the vibration insulating plate and test results similar to those shown in Figs. 3 and 4 corresponding to the first embodiment were obtained.
The first and second embodiments use the adaptive digital filter. Accordingly, even if the characteristics of the microphone and sound insulating plate change with the passage of time, the vibration of the sound insulating plate can be effectively reduced.
However, if the change of characteristics of the microphone and sound insulating plate is sufficiently small, a conventional time invariant or fixed digital filter may be used in place of the adaptive digital filter. In such a case, either of the microphone 10 in Fig. 1 or the acceleration pickup 15 in Fig. 5 is not required and a circuit of the digital filter becomes smaller and further the vibration control system can be simplified as the whole.
Furthermore, in the first and second embodiments, a piezoelectric actuator 6 is put on the sound isolating plate at the center thereof (Fig. 2), but the actuator 6 should be selectively arranged in an adequate number, dimension, form and location corresponding to the purpose of application.
Referring to Figs. 6-11, a third embodiment will be described.
This embodiment is applied for an automobile 20 in order to prevent a noise generated in an engine 21 from transmitting to a car room 22 through a dashboard 23.
Fig. 6 is a plan view illustrating an arrangement of vibration control system in the automobile 20 (a roof and windows are not shown), and Fig. 7 is a side elevational view of Fig. 6.
A piezoelectric acceleration pickup 24 is fixed to a cylinder head of the engine 21 to directly detect vibration of the engine 21 and piezoelectric acceleration pickups 25 are fixed to lower portions of suspension springs for wheels, respectively, to detect vibration from the wheels.
In case of automobiles, the whole of a body is a sound radiator, so that a number of vibration applying actuators 26 are arranged round the car room 22.
That is there are three actuators on the dashboard 23, one actuator on each door panel, one actuator on the roof panel, three actuators on a rear seatback panel, and one actuator on a rear shelf panel.
Furthermore, transparent high molecular piezoelectric actuators 27 are included in front, rear and side windows 28. Referring to Fig. 8 illustrating a cross section of the window 28, the high molecular piezoelectric actuator 27 is sandwiched by glass layers integrally molded in the form of a laminate.
In the inside of the car room 22, microphones 30 are fixed to head rests of the front and rear seats, respectively.
Referring to Fig. 9, in this embodiment, a control circuit comprises a multi-channel digital filter 31 and a coefficient renewal algorithm 32. The multi-channel digital filter 31 is a digital filter having multiple inputs and multiple outputs, and is arranged to input vibration detect signals from acceleration pickups 24 and 25 and output driving signals to the vibration applying actuators 26 and high molecular piezoelectric actuators 27 through amplifiers, respectively.
The coefficient renewal algorithm 32 is arranged to input the vibration detect signals from the acceleration pickups 24 and 25 and signals as error signals from the microphones 30 at the front right and left and rear right and left seats and calculates renewal values of filtering coefficients with the vibration detect signals and the error signals to renew successively the filtering coefficients.
The multi-channel digital filter 31 operates according to successively renewed filtering coefficients to output driving signals to the vibration applying actuators 26 and the high molecular piezoelectric actuators 27.
Thus, the vibration applying actuators 26 and the high molecular piezoelectrical actuators 27 arranged round the car room 22 generate most adequate vibration, respectively, to offset a vibration directly transmitted through a solid body from the engine 21 and an acoustic vibration by a controlled vibration having an inverse waveform, thereby reducing the vibration of the body round the car room 22 and decreasing the output voltage of the microphones 30 and 31. That is the noise which is took by persons sit on the front and rear seats can be reduced by the vibration control systems of the third embodiment.
Figs. 10 and 11 are graphs showing a sound pressure spectrum and output voltage of microphone 30 located at the right front seat in the third embodiment.
It can be seen from these graphs, in a controlled case which is shown by a solid line, the amplitude of the sound pressure and output voltage are greatly reduced.
Figs. 12-14 show a fourth embodiment in which an acceleration pickup 35 is located closely to each of vibration applying actuators 26 on each panel. As shown in Fig. 14, the acceleration pickups 35 are connected to a multi-channel digital filter 31 and a coefficient renewal algorithm 32 to obtain a similar noise reducing effect in the same manner as that of the second embodiment shown in Fig. 5.
In the third and fourth embodiment, even if the coefficient renewal is stopped after the coefficient renewal algorithm is focused and stabilized, the noise reducing effect is maintained so that a coefficient fixed multi-channel type of digital filter can be used in place of the adaptive digital filter in order to simplify the vibration control system.
The test results at the rear seat were substantially the same as those of the front seat.
Referring to Figs. 15-17, in a fifth embodiment which is applied to a partition in a house, two rooms 41 and 42 are separated by a thin panel wall 40 which is provided with vibration applying actuators 43.
One of the rooms 41 is provided with a speaker 44 of an imitation vibration source and a microphone 45 is located closely to the speaker 44.
Another room 42 is provided with a microphone 46 at a place at which noise is to be reduced.
A multi-channel digital filter 47 and a coefficient renewal algorithm 48 in a control circuit are input with signals detected by the microphone 45 located closely to the speaker 44 and the coefficient renewal algorithm 48 is additionally input with a signal detected by the microphone 46 located in the room 42 as an error signal.
As in the aforementioned embodiments, the filtering coefficient is successively renewed by the coefficient renewal algorithm 48, and the multi-channel digital filter 47 outputs a control signal on the base of the renewal coefficient to actuate the vibration applying actuator 43 through an amplifier 49, thereby vibrating the panel 40.
As the aforementioned embodiments, a vibration generated in the panel 40 by a sound pressure caused by the speaker 44 is forced into a vibration having an inverse waveform in order to reduce the noise.
Figs. 16 and 17 are graphs showing a sound pressure spectrum and an output voltage of microphone 46, respectively. It can be seen from these graphs that the amplitude of the sound pressure and output voltage are greatly reduced in the same manner as described in the aforementioned embodiment of the present invention. Referring to Fig. 18 showing a sixth embodiment, acceleration pickups 55 may be fixed to the panel 40 in place of the microphones 46 as shown in the fifth embodiment to obtain the similar noise reducing effect.
Referring to Fig. 19 showing a seventh embodiment of the present invention, a prefabricated house 60 is provided with a vibration applying actuator 62 put on an outer wall 61 and is provided with two vibration sources 63 and 64 such as vibrating motors arranged in the inside of the house 60. Each of the vibration sources 63 and 64 is provided with a vibration sensor 65 and 65. Microphones 67 are arranged at two different places in the outside of the prefabricated house 60 in order to detect noise reducing effect.
In this embodiment, a multi-channel digital filter 68 and a coefficient renewal algorithm 69 are used and signals detected by the vibration sensors 65 and 66 are separately input to the multi-channel digital filter 68 and the coefficient renewal algorithm 69, respectively, and signals detected by the microphone 67 are input to the coefficient renewal algorithm 69.
The multi-channel digital filter 68 outputs an actuating signal to the vibration applying actuator though an amplifier 70.
In this embodiment thus arranged mentioned above, signals detected from two vibration sources 63 and 64 form a control signal for minimizing error signals by each of the multi-channel digital filter 68 and make it an actuating signal for actuating the vibration applying actuators 62 through the amplifier 70 to restrict vibration of the sidewall 61, thereby significantly reducing noise at two locations of the microphones 67.
In the eighth embodiment shown in Fig. 20, acceleration pickups 75 are fixed to the outer wall 61 in place of the microphones 67 in the seventh embodiment to output signals to the coefficient renewal algorithm 69, thereby obtaining similar noise reducing effect to the embodiments mentioned above.
Furthermore, in case of more than two vibration sources, similar noise reducing effect can be obtained by the similar arrangement of the vibration control system so that a wide application range is assured.
In any cases, an electromotive type inertia mass actuator may be used as the vibration applying actuator.
As mentioned above, the vibration control system according to the present invention is capable of reducing any random vibration as well as cyclic vibration and also any vibration acoustically transmitted or directly transmitted though a solid body from a vibration or noise source or sources.

Claims

A vibration control system comprising at least one original vibration detecting means (7) located on or close to each of at least one vibration source (2) for detecting an original vibration or noise from the vibration source, at least one controlled vibration applying actuator (6) provided on an acoustic radiator (5) which is vibrated by the original vibration or noise, and controlling means for receiving a signal from the original vibration detecting means and outputting a control signal to the controlled vibration applying actuator, the controlling means including a digital filter (8) which produces the control signal for actuating the vibration applying actuator (6) so as to generate a controlled vibration wave having an inverse waveform which is of an opposite sign to the original vibration.
A system as claimed in claim 1, characterized in that the digital filter is an adaptive digital filter.
A system as claimed in claim 1, characterized in that the digital filter is a multi-channel digital filter.
A system as claimed in any of claims 1 to 3, characterized in that the original vibration detecting means is a microphone (7) located close to the vibration source.
A system as claimed in any of claims 1 to 3, characterized in that the original vibration detecting means is a piezoelectric acceleration pickup located on the vibration source.
A system as claimed in any of claims 1 to 5, characterized in that the controlled vibration applying actuator is an electric actuator such as a piezoelectric oscillator.
A system as claimed in any of claims 1 to 5, characterized in that the controlled vibration applying actuator is a transparent high molecular piezoelectric actuator.
A system as claimed in any of claims 1 to 7, characterized by further comprising at least one controlled vibration detecting means (10, 15) located on or close to the acoustic radiator (5) for detecting controlled vibration or noise of the acoustic radiator, and in that the controlling means further includes a coefficient renewal algorithm (9) which is arranged to input the original vibration signal from the original vibration detecting means and the controlled vibration signal from the controlled vibration detecting means, and output a filtering coefficient renewing signal to the digital filter (8).
A system as claimed in claim 8, characterized in that the controlled vibration detecting means is a microphone (10) located close to the acoustic radiator.
A system as claimed in claim 8, characterized in that the controlled vibration detecting means is an acceleration pickup (15) located on the acoustic radiator.