FR2692017A1 - Active vibration suppressor using piezoelectric sensor and actuator - has microprocessor to calculate cancelling signal from digitalised sensor signal for analogue conversion to supply actuator - Google Patents

Abstract

The suppressor is used in a machine (1) to separate it from the base (2). The force sensor comprises a piezoelectric layer (3) between a first metal sheet (5), connected to an amplifier, and a second sheet which also screens the signal. Further screening is provided by a box (9) around the amplifier and another metal sheet (4) separated from the first by an insulator (7). The amplified signal passes to an A-to-D converter (10) and the microprocessor (11) which monitors the phase, frequency and amplitude and produces the cancelling signal to a certain threshold amplitude. A D-to-A converter (13) and amplifier (14) send the cancelling signal to an impedance matching transformer (15). The transformer output is connected to a plate between two piezoelectric sheets (20, 21) in inverse polarisation and the entire section is completely screened (16, 18, 19). USE - Naval vibrations, pointing and aiming equipment, passenger transport.

Description

 There are known devices for reducing the transmission of vibrations from machines or objects subjected to vibratory movements, such as damping pads made of blocks of elastomers or other elastic materials with high internal dissipation. The effectiveness of these devices is insufficient when the propagation of vibrations must be low, for example to ensure the acoustic discretion of submarines or surface boats, the stability of targeting systems, or even improve the comfort of passengers of leisure, cruise ships, cars, trains or planes. The invention provides a significant improvement in reducing the propagation of vibrations, which can reduce the transmission of residual vibrations after a first reduction by a conventional device, by a factor of 10 to 100. It thus considerably reduces the costs of the machines, no longer requires the use of heavy, bulky and expensive vibration isolation methods, and improves existing suspensions.

 According to the invention, when the vibration to be reduced propagates along a single axis, the device ensuring the reduction of vibrations consists of 2 sets of piezoelectric plates, the piezoelectric effect of which is manifested according to the thickness, that is to say perpendicular to the largest dimension, stacked on top of each other.

 According to the invention, the first set of piezoelectric plates which we will call hereinafter the transmitter is excited by an oscillatory voltage and expands and contracts along the axis parallel to the thickness.

 According to the invention, the second set of piezoelectric plates which we will call receiver whose axis of symmetry is coincident with that of the transmitter delivers a voltage proportional to the force which is applied to it along the axis parallel to the thickness .

 According to the invention, these 2 bonded assemblies are separated by a metal sheet forming an electric screen and are sandwiched between the fulcrum of the vibrating machine or more generally the vibration generator and the ground or the structure which must not not be subjected to unwanted vibrations.

 According to the invention, the receiver is combined with an electronic signal amplifier filtering the low frequencies and the high frequencies and which amplifies only the annoying vibrational frequencies.

 According to the invention, the voltage thus suitably amplified is converted into digital data by means of an appropriate converter.

 According to the invention, this data is delivered to a specialized processor programmed to perform the following sequences.

First sequence: All of the above digital data is filtered again as soon as it is converted using a very stiff edge bandpass digital filter, in order to reduce frequencies by more than - 80 dB outside the frequency reduction range annoying vibration desired. The vibration reduction is then carried out according to the sequence cycles below
Second sequence: According to the invention, the above processor dedicated to controlling the operation memorizes the filtered voltage in digital form coming from the transmitter and which is the faithful translation of the vibratory force transmitted by the vibrating machine to the structure of support.

 Third sequence: According to the invention, the processor then searches for the recurrence time of the vibratory signal to be neutralized, time separating 2 identical repetitive waveforms.

 Fourth sequence: According to the invention, the processor stores a cycle of the recurrent vibratory signal identified in the previous sequence, at points calculated by interpolation or measured in large numbers. When this sequence is completed, the actual regulation begins.

 Fifth sequence: According to the invention, the processor injects this signal continuously and by reproducing it at each cycle, to a digital analog converter, the latter driving the input of a power amplifier, the output of which is coupled to a transformer voltage booster, intended to adapt the output impedances of the amplifier to the transmitter described above, in order to ensure the latter an oscillatory movement according to its thickness. Simultaneously, the processor filters the voltage emitted by the receiver, and measures its amplitude averaged over a number of cycles greater than the delay caused by the filtering.

 Sixth sequence: According to the invention, by successive approximations and for a determined duration, the processor searches for the best coefficient to be applied to the amplitude of the injected signal and the best time shift of the points of the cycle of the injected signal such as the measured force be minimal. At the end of the determined duration, if the signal which is a direct reflection of the transmitted force is not less than a set threshold value, the processor returns to the first sequence, if not, it continues the operations of the fifth sequence .

Thus, the device behaves, in the useful frequency band, as an extremely flexible elastic suspension, since it ensures very low force transmission, while maintaining the vibratory level of the vibrating object.

 According to the invention, during a variation in frequency or amplitude of the vibrations of the machine, exceeding the predetermined threshold value causes the cycle to switch to the first sequence, and the complete cycle is resumed. Thus, the device automatically adapts to changes in the vibration source.

 According to the invention, the mechanical and electrical assembly of the elements described above forms a single-axis vibration reduction module. Several modules are necessary when the axis of vibratory movement is not known or is fluctuating: they can be of a simple or complex structure depending on the desired use, the modules of the first type will be called simple modules hereinafter, the second indifferent modules. A preferred non-limiting description is shown in Figures 1, 2 and 3.

 FIG. 1 represents a section of the mechanical structure and the diagram of the electronic and computer elements ensuring the regulation, the assembly of which constitutes a simple single-axis vibration reduction module.

 The mass (1) represents the frame of the vibrating machine or of the vibration generator, this can also be the bearing end of an anti-vibration pad whose effect is thus reinforced. The mass (2) shows schematically the structure on which the machine rests, by means of the device which is the subject of the invention. The invention comprises a force sensor, consisting of the following elements: a piezoelectric ceramic plate (3) converting the forces coming from the machine (1) into an electrical signal, this signal being conveyed by a sheet of metal (5) to a amplifier (8). According to the invention, the metal sheet (5) and the amplifier (8) are protected from electrostatic and magnetic radiation by the 2 metal sheets (4) and (6) and a shielding box (9), the sheets of metal (3), (4) and (5) of very small thickness having a very high flexibility along the vibration axis so as not to disturb the operation of the force sensor.

 The invention also includes a vibratory displacement generator consisting of a power amplifier (14) whose output voltage is amplified by the adapter transformer (15), whose output is connected to the common point of the 2 piezoelectric plates (20) and (21), mounted in such a way that their polarizations are opposite and their displacements add up. The 2 remaining faces of the 2 plates (20) and (21) are connected to the housing (16) by metal sheets (18), (19), the assembly (16), (18), (19) forming a high quality electrostatic screen, which with the shields (4), (6) and (9), make the crosstalk between the high voltage emission signals of vibration of the generator and the extremely tenuous signals received by the amplifier ( 8) negligible. As for the connections (4) and (6), the connections (18) and (19) consist of very thin and very flexible metal sheets.

According to the invention, the stacking of the above elements is separated by a rigid plate (22) of which one face is in the form of a spherical, concave cap, and by a second rigid plate (23) of which one face is in the form of convex spherical cap, the 2 spherical faces
being in contact with each other in order to keep a great measure of effort
fidelity, by removing parasitic moments.

According to the invention, a sheet of insulating material (7) isolates the conductor (5) from the
armor sheet (6).

According to the invention, the ball joint formed by the 2 spherical surfaces can be placed in
other places, for example between the support (1) and the sheet (19) or between the mass (2) and the
sheet (3).

According to the invention, the output of the amplifier (8) is connected to the converter
analog digital (10), itself in connection with the microprocessor (11) and the memory
(12). The digital information delivered by the microprocessor is then
reconverted into analog data by the digital analog converter (13).

This module can be used when a permanent static force is applied in
a direction parallel to the vibration and of direction such as it maintains the whole of the parts
contiguous. However, it cannot be used in other cases.

FIG. 2 represents a single-axis vibration reduction module indifferent to the
application force, the shape of the stirrups (26) and (27) is schematic: According to the invention, they
can take different constructive forms. In addition to the building blocks
described previously in Figure 1, this module called indifferent includes another set of
piezoelectric plates (24) and (25) generating vibration and operating
opposite the assembly (20) and (21) FIG. 1. Thus when the assembly (20) and (21) expands,
the assembly (24) and (25) contracts by the same displacement value. The screen
electrostatic consists of the sheets (28) and (29) and the supply of electrical energy
performed by the driver (30). The detail in figure 2 represents the connection of the assembly
to the adapter transformer (15).

Figures 3, 4, 5 and 6 represent an assembly of 3 modules associated with 2 studs
antivibration which according to the invention provide a very triaxial vibration attenuation
large and identical in size to the size of an anti-vibration pad
conventional: this arrangement, which according to the invention is not limiting, provides a means
for replacing the suspensions of existing machines, for example during recasting
existing military boats at the lowest cost, ensuring their performance
equivalent or superior to new constructions. The 3 areas of mitigation
vibratory can be orthogonal and the modules can be identical.

Figure 3 shows a section of the assembly of 2 indifferent modules and a
simple module, associated to provide a triaxial antivibration support ensuring a stable mechanical connection as necessary for the suspensions intended for the boats of
surfaces, subject to roll and pitch, and must therefore transmit forces
considerable static.

 FIG. 4 represents a fictitious section made in line with the 2 indifferent modules.

 FIG. 5 represents a fictitious section made in line with the horizontal bars and the simple module.

 FIG. 6 represents a section similar to the section of FIG. 3 but made in a plane orthogonal to the first section plane.

 Figure 7 schematically explains the regulations adopted on the one hand for a provision corresponding to Figure 1, and on the other hand for the regulation corresponding to the design described in Figures 3, 4 and following.

According to the invention, the non-limiting structure forming a triaxial antivibration support consists, between the mass of the vibrating machine (1) and the structure shown diagrammatically by the mass (2), of a set of 2 elastic studs of known design (31 ), linked together by known means on the one hand to the support plate (40) and on the other hand to the stirrup (32). This stirrup (32) is crossed by the cylindrical rod (33) which suspends it from the cylindrical plate (34) while remaining guided laterally by the 2 recesses of the rod (33) with the plate (34) and the frame (35 ). This stiff rod along the OZ axis is flexible along the OX axes and
OY. The cylindrical frame (35) has at the bottom of its upper part 2 openings allowing the movement of the stirrup (32) and its mounting. The stirrup (32) is immobilized laterally along the 2 axes OX and OY by 2 indifferent modules (36) and (42) which cancel any lateral movement of the frame (35), according to a process which will be described later. In the lower part of the frame (35) a cell is provided for inserting a simple module (39) between the frame (35) and the base (38). The frame (35) and the base (38) are secured in movement in the directions OX and OY by 3 to 4 flexible bending bars (37) along the axis OZ fixed to the frame (35) and to the base (38) by a known means such as soldering. The module (39) cancels the vertical movement of the base (38) in the same way as the modules (36) and (42) cancel the lateral movements. The bending moments, if they exist, transmit, according to the invention, the forces by means of the bending bars (33) and (37) which reduce their amplitude by their great inherent flexibility. The attenuation of the vibrations due to the moments is therefore less than the attenuation of the forces, which is of minor importance, a machine being always supported by several points of support very widely spaced from each other, and the moments therefore still very unimportant.

 According to the invention, the fifth sequence described above and of control of the vibratory force to a minimum value is modified to take account of the constructive particularity which establishes a continuous link for transmitting the vibrations placed in derivation of each module, and constituted rods (36) and (37). This modification consists in slaving the amplitude of the compensation excitation until the phase between the emission and the force measurement is reversed, which is manifested when the vibratory forces derived by the parasitic links are strictly compensated. by the forces generated by the vibratory displacement of each module, operation controlled by the microprocessor (11).

 According to the invention, the bending rods are made of materials ensuring a high resonance factor, a necessary condition for the realization of the control claimed above.

 FIG. 7 represents a simplified schematic flowchart of the control ensuring the attenuation of the transmission of vibrations in the case of a suspension using only one module and in the case of a suspension with bending bars such as cides sus.

Claims (9)

 1) Device intended for reducing the transmission of vibrations, characterized in that it comprises, by axis of transmission of the vibrations to be attenuated, a set of piezoelectric plates generating displacement (20), (21), (24), ( 25) and a piezoelectric measurement plate (3) of the forces joined together and with the axes of symmetry combined.  2) Device according to claim 1 characterized in that the method comprises an amplifier (8) with bandpass filter and an analog digital converter (10), a control processor (11), a digital analog converter (13), a power amplifier (14) and an impedance converter transformer (15).  3) Device according to claim 2 characterized in that the reduction of vibrations is obtained by measuring the vibratory force which controls the vibratory displacement caused by the piezoelectric plates generating displacement (20), (21), (24), (25 ).  4) Device according to claim 3 characterized in that this reduction of vibrations is effected by a sequence of measurement phases, then search for the vibration cycle and use of this vibration cycle, phase and suitable amplitude, for generating the vibratory displacement canceling the vibratory force, provided by a microprocessor (11).  5) Device according to claim 2 characterized in that each module for reducing the transmission of vibrations comprises, stacked along a single axis, a set of piezoelectric plates generating displacement, at least one piezoelectric plate for measuring force separated by sheets metallic (18, 19, 3, 7, 28 and 29) flexible forming shields, and associated with 2 plates of hard material with bearing surface in the form of spherical caps (22) and (23).  6) Device as actuated in that the attenuation of vibrations along 3 orthogonal axes is effected by 3 identical modules according to claim 5.  7) Device for reducing triaxial vibrations according to any one of the preceding claims, characterized in that it can include rods (33) and (37) ensuring the transmission of static forces.  8) Device according to claim 7 characterized in that it can comprise 2 elastic studs (31).  9) Device according to claim 7 characterized in that it comprises 2 indifferent modules each comprising a piezoelectric measurement plate (3) and 2 sets of piezoelectric plates generating opposite vibrations (20) and (21) and (24) and ( 25), and a simple module comprising only a set of piezoelectric vibration generator plates (20) and (21) and a piezoelectric measurement plate (3).