EP0103256B1 - Method and apparatus to eliminate both acoustical and mechanical vibrational effects - Google Patents

Description

The subject of the present invention is a device for eliminating the effects of acoustic or mechanical vibrations, in particular with a view to creating a zone of silence with respect to one or more sources of noise or preventing the transmission of mechanical vibrations produced by one or more sources of undesirable mechanical vibrations.

The attenuation of unwanted acoustic or mechanical vibrations is conventionally carried out using sound or mechanical damping devices which are inserted between the source or sources producing these vibrations and the environment which one wishes to protect. These dampers absorb vibrations and therefore act as notch filters for the frequency band where the vibrations to be eliminated occur.

In practice, damping vibrations is often difficult to achieve insofar as it is possible to stifle a known pure frequency vibration emitted by a well-defined source, it is much more difficult to stifle a set of vibrations whose the characteristics are only known globally.

However, there are many cases where one wishes either to create a zone of silence in an environment made noisy by the existence of more or less localized or known sources, such as for example a room made noisy by machines or a workstation. control, or even eliminate the vibrations transmitted by a machine to its environment.

It is known from European patent application EP-A-0043,565 to use, to reduce the noises coming from an electrical apparatus, a device in which a single sensor placed on this apparatus collects these noises which are then digitized and then applied to a digital signal generating device adapted to reduce noise; these digital signals are converted into analog signals which are applied to a transducer placed on the equipment, the noise of which can be reduced. To control the necessary analog / digital and digital / analog converters, it is possible to use either a signal obtained from the noise sensor, or a signal obtained from a second sensor which only serves to deliver this synchronization signal. The signal generation device comprises two inverse Fourier transform calculators and a control device which operates by comparing the same signal obtained from the single sensor at successive instants by memorizing this signal in two memories supplied in series. The information obtained under these conditions is necessarily quite poor and in particular includes only amplitude information without phase information, which only allows very average results to be obtained.

The present invention relates to a device according to claim 1. Its characteristics and advantages are specified in the following description and in relation to the figures below referenced.

FIG. 1 presents a diagram of a device for canceling the effects of acoustic or mechanical vibrations in connection with the sources causing them.

FIG. 2 shows the diagram of a correlation module for a device according to the invention.

FIG. 3 presents the diagram of the principle of cancellation according to the invention in digital form.

The cancellation device according to the invention is essentially intended to eliminate the effects of unwanted acoustic or mechanical vibrations, from the signals obtained from at least two sensors referenced 1 and 2 in FIG. 1 in the case of elimination of vibrations. acoustic and 1 'and 2' in the case of elimination of mechanical vibrations. It therefore aims to create a zone z protected from the noise created by an AP source in the first hypothesis and to avoid the transmission of mechanical vibrations from an AP 'apparatus to its environment via the EL links which connect it to the latter. , in particular its base or its support points, in the second hypothesis.

In the first case, a sensor 1 is placed upstream of a zone z which one wishes to protect in space Z where the source AP exhibits its annoying acoustic effects and a sensor 2 is placed against on or near from the AP source so as to capture the noise emissions.

The sensors 1 and 2 are for example microphones, the sensor 1 is possibly a room microphone and the microphone 2 a directional microphone, or even an accelerometer if the noises are of mechanical origin.

In the second case, a sensor 1 ′ is placed on or against the connection (s) EL by which the mechanical vibrations created by the apparatus AP ′ are capable of being transmitted to its environment, not shown. A sensor 2 'is placed against or on the apparatus AP', it being understood that at least one servo-controlled damper AM is inserted between each link EL and the apparatus AP 'to avoid transmissions of mechanical vibrations.

The sensors 1 ′ and 2 ′ are then for example accelerometers, the damper AM is for example a damper 11 controlled by electrical control and it is inserted for example between the frame of the apparatus AP ′ and the base serving as a support which then forms the EL bond.

Of course the number of sensors 1 and 2 or l 'and 2' can vary according to the existing constraints, however insofar as the principle remains the same, a single sensor 1 and a single sensor 2, or a single sensor 1 'and a single sensor 2 ′ is taken into account in the following description.

According to the invention or uses the signals b '(t) generated by the sensor 2, or 2' as the case may be and the signals b (t) generated by the sensor 1, or possibly 1 ', to produce a signal in opposition to phase with signal b (t) so to inject it either into at least one loudspeaker HP placed downstream of the sensor 1 relative to the apparatus AP so as to create downstream of this loudspeaker the zone z protected from noise, or in the control circuit not shown of the AM shock absorber.

For this purpose, the signal b '(t) of the duly amplified sensor 2 is applied to a plurality of narrow-band filters 3a to 3n, called line filters, which are individually centered on different frequencies distributed in the auditory disturbing spectrum.

Each line filter 3 provides a reference b '(f) representing the energy spectral density of the noise received by the sensor 2 for the frequency considered as b' (fa) for the line filter 3a centered on the frequency fa. Each filter 3 is connected to an input of a correlation module 4 which is specific to it and which has a second input connected to the output of the sensor 1 from which it therefore receives the signal b (t).

The correlation modules 4 are for example of the type described in French patent 2215005 of the Applicant and presented in FIG. 2.

• - d'un circuit de normalisation 48 de type usuel assurant la normalisation en puissance du signal fourni par la sortie du filtre de raie 3 associé,
• - d'un déphaseur 40 relié à la sortie du circuit de normalisation 48 auquel il est associé et dont il reçoit un signal b' (fa),
• - de deux multiplicateurs d'entrée 41, 42 dont l'un 41 a ses entrées respectivement reliées au capteur 1 et à la sortie du filtre 3a, alors que l'autre a ses entrées respectivement reliées au capteur 1 et à la sortie du déphaseur 40,
• - de deux intégrateurs 43 et 44 respectivement insérés en sortie des multiplicateurs d'entrée 41 et 42,
• - de deux multiplicateurs de sortie 45 et 46, dont l'un 45 a ses entrées respectivement reliées en sortie de l'intégrateur 43 et du filtre 3a alors que l'autre 46 à ses entrées respectivement reliées en sortie du capteur 1 et en sortie du déphaseur 40,
• - un additionneur 47 relié par ses entrées aux sorties des multiplicateurs de sortie 45 et 46 de manière à fournir un signal de sortie b(fa) qui correspond à la correction à apporter au signal b(t) pour éliminer la composante du bruit pour la fréquence fa sur laquelle est entrée le filtre de raie 3a considéré.

Each correlation module 4, such as 4a, is then composed:

• a normalization circuit 48 of the usual type ensuring the power normalization of the signal supplied by the output of the associated line filter 3,
• a phase shifter 40 connected to the output of the normalization circuit 48 with which it is associated and from which it receives a signal b ′ (fa),
• - two input multipliers 41, 42 one of which has its inputs respectively connected to the sensor 1 and to the output of the filter 3a, while the other has its inputs respectively connected to the sensor 1 and to the output of the phase shifter 40,
• - two integrators 43 and 44 respectively inserted at the output of the input multipliers 41 and 42,
• - two output multipliers 45 and 46, one of which 45 has its inputs respectively connected to the output of the integrator 43 and of the filter 3a while the other 46 to its inputs respectively connected at the output of the sensor 1 and at the output of the phase shifter 40,
• - an adder 47 connected by its inputs to the outputs of the output multipliers 45 and 46 so as to provide an output signal b (fa) which corresponds to the correction to be made to the signal b (t) to eliminate the noise component for the frequency fa on which the line filter 3a considered is entered.

The assembly 8 constituting the attenuation device according to the invention which therefore comprises the filters 3, the correlation modules 4 further comprises an adder 5 to the inputs of which the correlation modules 4 are connected so as to add the correction signals b (fa), b (fb), ... b (fn) obtained from these modules to generate a signal S (t) to be transmitted either to the transducer HP here symbolized by a loudspeaker, or to the damper AM.

The application of the signal S (t) to the acoustic transducer HP causes the emission by the latter of signals in phase opposition with those coming from the noise source AP in the zone z where this transducer is effective.

The application of the signal S (t) to the control circuit, not shown, of the controlled damper AM causes the creation in this damper of mechanical vibrations in phase opposition with the mechanical vibrations coming from the apparatus AP ', which are thus thus canceled at the level of the EL connection, for example at the level of the base carrying the apparatus.

Of course in practice the number of line filters 3 is necessarily limited as long as one does not use a signal conversion in digital form and it is therefore the filter adjustment possibilities which make it possible to select the lines intended to make the object of correction, since in the most general case, only the energy of certain lines is to be taken into account, the others being either negligible or nonexistent.

An attenuation device applying the method according to the invention can advantageously be implemented after conversion of the signals produced by the sensors from an analog form to a digital form, taking advantage of the advantages brought by the Fourier transformations and more particularly the fast Fourier transformations (FFT).

Indeed, it is then possible to obtain the equivalent of a large number of line filters distributed in the useful band, for example the equivalent of a thousand line filters using a thousand point transform, which in the digital example proposed above makes it possible to correct all of the whole frequencies of the useful band.

As shown in FIG. 2, each sensor 1 or 2 is connected to an appropriate analog-digital converter 7 and each converter supplies the results of its conversions to a set 8 ′ constituted by a computer capable of calculating a fast double Fourier transform FFT1 , FFT2 from the signals received from each of the converters to deduce therefrom a signal summing the correlated corrections made by each line at the transform point.

This sum signal is then the subject of a fast inverse Fourier transformation, the result of which is applied to the loudspeaker HP or to the damper AM via a digital-analog converter (9) and of possible amplifiers in order to obtain the previously mentioned effects.

Claims (4)

1. A device for eliminating the effects of acoustic or mechanical vibrations on a zone to be protected, these vibrations coming from a source, the device comprising a first probe for receiving the vibrations to be eliminated, a second probe located on the source, a narrow filter connected to the output of the second probe, a transducer for generating vibrations which oppose themselves to the vibrations to be eliminated, and processing means for receiving the output signals of the first probe and of the filter, characterized in that the first probe (1, 1') is located upstream of the zone to be protected with respect to the source (AP, AP'), and that the processing means (8) include a group of narrow filters (3a to 3n) connected to the output of the second probe (2, 2'), a group of complex correlators (4a to 4n) for correlating the output signals of the first probe with the signals of each of the narrow filters respectively, and an adder (5) for adding the output signals of the correlators and for delivering the signal for controlling the transducer (HP, AM).

2. A device for eliminating the effects of acoustic or mechanical vibrations on a zone to be protected, these vibrations coming from a source, the device comprising a first probe for receiving the vibrations to be eliminated, a second probe located on the source, a narrow filter connected to the output of the second probe, a transducer for generating vibrations which oppose themselves to the vibrations to be eliminated, and processing means for receiving the output signals of the first probe and of the filter, characterized in that the first probe (1, 1') is located upstream of the zone to be protected with respect to the source (AP, AP'), that the device further includes analog to digital conversion means (7, 7') for converting the output signals of the probes into digital ones, and that the processing means include a calculator (8') capable of effecting the fast Fourier transforms (FFT1, FFT2) of the digitalized probe signals, the correlation [b (fa) to b(fn)] of these fast Fourier transforms and the inverted fast Fourier transform (FFT1-') of the result of this correlation, the digital signals representing this inverted fast Fourier transform being applied to digital to analog conversion means (9) for controlling the transducer (HP, AM).

3. A device according to any one of claims 1 and 2, characterized in that the probes (1,2) are microphones and that the transducer (HP) is a loudspeaker.

4. A device according to any one of claims 1 and 2, characterized in that the probes (1', 2') are accelerometers and that the transducer (AM) is a regulated damper.

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