RU2230615C1 - Sonic energy rod transducer - Google Patents

Abstract

FIELD: ultrasonic equipment, applicable in ultrasonic devices of industrial equipment for metal working, equipment for realization of other production processes.

SUBSTANCE: the transducer has a piezoelectric element in the form of a set of longitudinally polarized washers of piezoelectric ceramics, rod waveguide, front cover plate, concentrator and a back cover plate connected to the end surfaces of the piezoelectric element, and reinforced by the waveguide between each other. The back cover plate is made with a bulge and a central hole, exceeding the waveguide diameter. The waveguide has a mount on the supporting end, which is mechanically linked with the mount end. The fastening end of the waveguide is connected to the concentrator. The front cover plate and the concentrator are made integral. The cover plates are made of material with an acoustic resistance commensurable with the acoustic resistance of the piezoelectric ceramics with a difference up to 20%. The bulge height is determined by relation:

where:

- the resonance resistance of the sonic rod transducer, Hz;

- the thickness of the back cover plate, m; h - the height of the bulge on the back cover m;

- the velocity of the longitudinal wave in the material of the back cover plate, m/s;

- the velocity of the longitudinal wave in the waveguide material, m/s; n - the number of piezoelectric washers in the piezoelectric element, pc;

- the thickness of one piezoelectric washer, m;

- the velocity of the longitudinal wave in the piezoelectric ceramics, ms; The bulge of the back cover plate may be made in form of a truncated cone, whose diameter of the lesser base equals the diameter of the waveguide mount, and diameter of the larger base equals the outside diameter of the back cover plate. A washer of metal with a low velocity of the longitudinal wave is inlaid in the end of the bulge. A contracting cavity in the form of a truncated cone is made in the front cover plate and in the concentrator, its larger diameter is close to the inside diameter of the washers made of piezoelectric ceramics. The waveguide is made of metal with a level of the internal mechanical resistance lower than that of the cover plates.

EFFECT: enhanced electroacoustic efficiency.

5 cl, 3 dwg

Description

The invention relates to ultrasonic technology and can be used in ultrasonic devices of industrial equipment for processing materials, in equipment for cleaning and implementing other technological processes.

Known acoustic rod transducer [1], containing a piezoelectric package, on one side of which there is a front plate with a hub fixed to it, and on the other, a back plate compressed between each other by a stud and a nut.

The disadvantage of this device is its low efficiency.

Known rod magnetostrictive emitter containing a core of magnetostrictive material, to the front end of which is attached a hub [2].

The disadvantage of this device is the low electro-acoustic efficiency due to large electrical losses in the core.

A well-known acoustic rod transducer containing a piezoelectric element, a back (back) plate, a front plate made in the form of a quarter-wave concentrator, a waveguide, one end of which is rigidly attached to the working end of the concentrator, and the other using a sound-conducting compound, to the side surface of the piezoelectric element, is the ratio of lengths the waveguide and the hub is 1.5-2.5, and the waveguide is made in the form of three series-connected rods embedded one into the other, two of which are hollow [3] (prototype).

The disadvantages of the prototype are as follows:

- the rear end of the waveguide is attached to the lateral surface of the piezoelectric element that performs transverse vibrations, the amplitude of which is about 3 times less (the Poisson's ratio of piezoceramics is on average 0.3 [4]) than the amplitude of the longitudinal vibrations if the waveguide were connected to the rear overlay oscillating along the longitudinal axis. This significantly reduces the electro-acoustic efficiency of the device;

- the front plate and the waveguide are made composite, which leads to large oscillatory losses and, consequently, to a significant decrease in the electro-acoustic efficiency of the device;

- the ratio of the waveguide and hub lengths is 1.5-2.5. From the description of the prototype it is impossible to determine exactly what exactly the waveguide length should be so that the vibrations of the elements of the device would be accurately phased, and thus the highest electro-acoustic efficiency is obtained. If you practically use the specified ratio, then you can not get the maximum efficiency of the Converter.

The problem to which the invention is directed, is to increase the electro-acoustic efficiency of the transducer.

This problem is solved by the fact that in an acoustic rod transducer containing a piezoelectric element in the form of a set of longitudinally polarized washers made of piezoceramics, a rod waveguide, a front plate, a concentrator and a back plate connected to the end surfaces of the piezoelectric element, and the back plate reinforced with a waveguide according to the invention made with a protrusion and a Central hole larger than the diameter of the waveguide, the latter at the supporting end has a head, which is mechanically connected to the end face of the protrusion, and the mounting end of the waveguide is connected to the hub, the front plate and the hub being made as a whole, the plates are made of a material with acoustic resistance comparable with the acoustic resistance of piezoceramics with a difference of up to 20%, and the height of the protrusion is determined by the ratio:

where f _r is the resonant frequency of the acoustic transducer, Hz;

t ₁ - the thickness of the back lining, m;

h is the height of the protrusion on the back pad, m;

c ₁ is the propagation velocity of the longitudinal wave in the material of the back lining, m / s;

c ₂ — longitudinal wave propagation velocity in the waveguide material, m / s;

n is the number of piezo washers in the piezoelectric element, pcs;

t ₂ is the thickness of one piezo washer, m;

with ₃ - the propagation velocity of a longitudinal wave in piezoceramics, m / s.

In addition, the protrusion of the back lining can be made in the form of a truncated cone, the diameter of the smaller base of which is equal to the diameter of the head of the waveguide, and the diameter of the larger base is equal to the outer diameter of the back lining; a washer of metal is inlaid at the upper end of the protrusion with a low longitudinal wave propagation velocity; in the front plate and in the hub, a tapering cavity is made in the form of a truncated cone, the larger diameter of which is close to the inner diameter of the piezoceramic washers, while the waveguide is made of a material with an internal mechanical resistance level lower than that of the plates.

The invention is illustrated by drawings, in which Fig. 1 shows a general view of a transducer, a longitudinal section, Fig. 2 is a longitudinal section of a general view of a transducer presented taking into account particular cases of its implementation according to claims 2, 3, 4 of the claims; figure 3 - diagram of the calculated model of the Converter based on the method of electromechanical analogy (hereinafter - the diagram).

The acoustic rod transducer contains a half-wave concentrator 1, a waveguide 2 connected to it by a thread 3 with a head 3 in the form of a reinforcing rod for phasing, a piezoelectric element 4, formed by a set of washers made of piezoceramics, electrical contacts 5 of the connection of the washers of the piezoelectric element 4 in series or in parallel, the back 6 overlay with the protrusion 7 , the height of which is equal to h, the front 8 pad, made at the same time with the hub 1, terminals 9 and 10 for connecting an ultrasonic generator (not shown in Figs. 1 and 2). The waveguide 2 is made of a material with a low level of internal mechanical resistance, for example, of a titanium alloy. The conical surface of the hub 1 smoothly passes into the cylindrical surface of the front 8 lining. The end surface of the front pads 8 with glue connected with the front surface of the piezoelectric element 4.

At the node of the distribution function of the standing wave of vibrational displacements, a flange 11 can be placed in the converter (Fig. 2), intended for fastening the given converter to technological equipment.

The back 6 of the piezoelectric element 4 is glued to the opposite end face of the piezoelectric element 4 with a protrusion 7. It is supported by its head 3 on the end surface of the protrusion 7 and the supporting end of the waveguide 2 is glued to it. To reduce the height of the protrusion 7, a washer 12 can be inlaid at its end (figure 2) from a material having a low velocity of propagation of a longitudinal elastic wave, for example, from lead.

For some extension of the frequency bandwidth of the converter, the protrusion 7 on the back 6 of the plate can be made in the form of a truncated cone (figure 2), the smaller diameter of which is equal to the diameter of the head 3 of the waveguide 2, and the larger diameter is equal to the diameter of the rear 6 of the plate. The height of the truncated cone is h. In addition to expanding the passband, such a protrusion makes it possible to increase the dynamic stability of the longitudinal waveform with the exception of bending displacements.

The whole structure is reinforced (compressed) by a constant force, which is fixed using a waveguide 2, which increases the strength and power of the rod acoustic transducer. In the front 8 overlay and hub 1, a cavity 13 (FIG. 2) can be made in the form of a truncated cone, the larger diameter of which is close to the diameter of the hole in the piezoelectric element washer 4.

The diagram (figure 3) shows the following model elements:

14 - reduced to the output of the ultrasonic generator (terminals 9 and 10) the active resistance of the transducer that occurs when it is connected to the tool and then to the technological object, which are not shown in figure 3;

15 - electric capacity of the piezoelectric element;

16 - transformer equivalent to a piezoelectric element, converting electrical energy into mechanical energy;

17 - the primary winding and 18, 19 - the secondary windings of the equivalent transformer 16, the outputs of which are included in antiphase;

20 - electric capacitance corresponding to the elasticity of the back of the transducer;

21 - active resistance corresponding to the resistance of mechanical losses in the back plate of the Converter;

22, 23, 24 — inductances corresponding to the masses of the back plate, protrusion and the reinforcing waveguide;

25 - active resistance corresponding to the resistance of mechanical losses during the propagation of a longitudinal wave along the waveguide;

26 is an electric capacitance corresponding to the elasticity of the front plate, hub and piezoelectric element;

27 - active resistance corresponding to the resistance of mechanical losses in the front plate, hub and piezoelectric element;

28 and 29 — inductances corresponding to the masses of the front plate and the hub, respectively;

30 - a time delay element corresponding to the protrusion 7 of the back lining;

31 - electric transformer, equivalent to the hub 1, as a transformer of vibrational velocity;

32 and 33 - the primary and secondary windings of the transformer 31, respectively;

34 - complex (in the general case) the load resistance corresponding mechanical transducer load a process tool, and object processing zone therebetween, where P is dissipated power _and acoustic.

If K _ea is the electro-acoustic efficiency, and P _e is the electric excitation power supplied to terminals 9 and 10, then

When operating at the resonant frequency of the converter, all reactive elements from the circuit (Fig. 3) disappear, except for the electric capacitance 15. The remaining resistances 21, 25, 27 and 34, which are active elements, form a mechanical resistance R _m

R _m = R ₂₁ + R ₂₅ + R ₂₇ + R $\genfrac{}{}{0ex}{}{\text{/}}{\text{34}}$

R $\genfrac{}{}{0ex}{}{\text{/}}{\text{34}}$ = R ₃₄ (D ₁ : D ₂ ) ^1/2 ,

where r $\genfrac{}{}{0ex}{}{\text{/}}{\text{34}}$ -reduced to the mechanical side of the circuit (Fig.3) load resistance;

D ₁ - the larger diameter of the hub 1;

D ₂ is the small diameter of the hub 1;

Reduced to the electrical side of the circuit (figure 3) resistance

R ₁₄ = k ² R _m ,

where k is the coefficient of electromechanical coupling of the piezoceramics of which the piezoelectric element is made.

In this type of converter design, a longitudinal piezoelectric effect is used, which allows to obtain the maximum energy effect. When using the resonant mode of operation, the input electrical resistance R _{14 of the} Converter tends to the value of the resistance of internal losses.

The proposed acoustic rod transducer operates as follows. When applying to the terminals 9 and 10 of the exciting voltage from the ultrasonic frequency generator, not shown in FIGS. 1, 2, 3, the piezoelectric element 4 increases or decreases its longitudinal dimensions. Half-wave concentrator 1 increases the vibrational velocity. If the concentrator 1 has an exponential, exponential, or catenoid law of change in the external horn profile, then the coefficient of increase in the vibrational velocity will be calculated accordingly and approximately equal to (D ₁ / D ₂ ) ^1/2 . In the diagram (figure 3) this is reflected in the form of a step-up transformer 31. Since the plate 8 and the hub 1 are made at the same time, this eliminates the mechanical losses that occur in the prototype device [3], and therefore, increased K _ea . When the piezoelectric element 4 is excited, the outer ends of the plates perform oscillations along the longitudinal axis that differ in phase by 180 °.

In the prototype device, it was not possible to fully realize the maximum possible K _ea due to the complex design of the phasing waveguide, the presence of many gaps in it and the connection of one of the ends with the side surface of the piezoelectric element using an adhesive compound. The oscillations of the lateral surfaces of the piezoelectric element in amplitude make up only 30% of the amplitude of oscillations along the longitudinal axis, i.e. the fraction of mechanical power transmitted by waveguide 2 (if the proposed device were to be so done) would be only 9% with ideal phasing of the oscillations. This is clearly not enough to solve the task. In accordance with the fact that the back 6 and front 8 plates are made of a material whose acoustic impedance is close to or commensurate with the acoustic resistance of piezoceramics, the plates do not perform a reflective function and develop the maximum possible vibrational velocity, and therefore, they allow to realize the maximum mechanical power of the converter.

To perform the function of reinforcing the piezoelectric element 4 and the simultaneous transfer of mechanical energy from the back 6 of the lining to the hub 1 for the waveguide 2 (Figs. 1 and 2), a material with low mechanical losses was used. The magnitude of the delay in the oscillations of the back 6 of the lining, sent to the hub 1, corresponds to one half-cycle of oscillations at the resonant frequency f _r or phase shift of 180 °.

To obtain such a time delay, depending on the linear parameters of the transducer elements, a relation is obtained for determining the height of the protrusion 7:

where f _r is the resonant frequency of the Converter, Hz;

t ₁ - the thickness of the back lining, m;

h is the height of the protrusion on the back pad, m;

c ₁ is the propagation velocity of the longitudinal wave in the material of the back lining, m / s;

c ₂ — longitudinal wave propagation velocity in the waveguide material, m / s;

n is the number of washers in the piezoelectric element, pieces;

t ₂ is the thickness of one piezo washer, m;

with ₃ - the propagation velocity of a longitudinal wave in a piezoceramic washer, m / s.

The calculation according to the proposed relation (1) allows us to exclude the out-of-phase oscillations at the resonant frequency and to obtain the maximum possible value of K _ea .

Obtaining the desired phase shift by 180 ° is structurally achieved due to the fact that the longitudinal vibrations propagating along the material of the back 6 of the lining, and then along the protrusion 7 through the head 3, made on the supporting end of the waveguide 2, change their direction towards the hub 1 and thus a phase difference of 180 ° occurs or a time delay T = (2f _r ) ^-1 .

If the cylindrical shape of the protrusion 7 of the back 6 pads is changed to conical (claim 2 of the claims), then the frequency bandwidth of the transducer will expand, which creates favorable conditions for operation, since when the ultrasonic generator feeds the transducer, the value of K _ea and the amplitude of the oscillations change less.

The protrusion 7 on the back 6 pad may be partially made of metal with a low speed of sound, for example, in the form of a washer 12 made of lead inlaid at the end of the protrusion 7. In this case, as follows from the consideration of the scheme (Fig. 3), the protrusion will have smaller dimensions, losses in it will decrease, which will increase the quality factor of the system, the height of the peak of the amplitude-frequency characteristic will increase, and therefore, an increase in K _ea will be realized.

The front plate 8 and the hub 1 may contain a cavity 13 in the form of a truncated cone, the diameter of the base of which is close to the diameter of the hole in the piezoelectric element of the piezoelectric element 4, while improving the matching of the wave impedances of the elements and reducing the mass of the front 8 plate and concentrator 1, as follows from the consideration of the scheme (figure 3) should lead to an increase in the amplitude of oscillations in the load 34.

With electrical excitation of the piezoelectric element, the oscillations of the ends of the latter along the longitudinal axis are directed in opposite directions from the middle of the piezoelectric element. This is reflected in the diagram (figure 3) in the form of two independent windings 18 and 19 of the transformer 16. As follows from the consideration of the circuit, a signal with an oscillating speed from the outputs of these windings propagates through the elements connected in series 20, 21, 22, 23, 24, 25 , 30 on the one hand and for elements 26, 27, 28, 29 on the other. At the primary winding 32 of the transformer 31 (equivalent to the hub 1), the in-phase addition of two oscillations occurs, which leads to an increase in the amplitude of the oscillations at the output of the transformer 31 (winding 33) connected to the mechanical load 34.

The effectiveness of the proposed device is illustrated by an example of a converter design similar to the well-known commercially available magnetostrictive rod converter ПМС-15 for technological purposes, rated operating frequency, rated impedance, load. For commercially available piezoceramic rings with dimensions of 100 × 70 × 7 mm, pad material D16T, waveguide material VT 8, with a height of the waveguide head 10 mm, for the operating frequency of 18 kHz, the calculated protrusion was 42 mm.

The problem has been solved: at the operating frequency of 18 kHz, the developed converter has K _ea at the level of 80-85% versus 35% for the PMS-15.

Literature

1. G.A.Kardashev and P.E. Mikhailov, Heat and mass transfer acoustic processes and apparatuses, M., Mechanical Engineering, 1973, p. 100, Fig. 43.

2. D. A. Gershgal and V. M. Fridman, Ultrasonic Technological Equipment, ed. 3rd, rev. and add., M., Energy, 1976, p.143.

3. V.N. Nosov, B.C. Yamshchikov, V.L. Shkuratnik, M.D. Vigdorchik, A.S. USSR No. 1050754, Acoustic rod transducer, 09/06/1982, B 06 V 1/06, H 04 R 17/00 (prototype).

4. Piezoceramic transducers, reference book, ed. S.I. Pugacheva, L., Shipbuilding, 1984, p. 256.

Claims (5)

1. An acoustic rod transducer containing a piezoelectric element in the form of a set of longitudinally polarized washers made of piezoceramics, a rod waveguide, a front plate, a concentrator and a back plate connected to the end surfaces of the piezoelectric element and reinforced by a waveguide, characterized in that the back plate is made with a protrusion and a central hole larger than the diameter of the waveguide, the latter at the supporting end has a head that is mechanically connected to the end face of the protrusion, and the mounting end of the waveguide is connected with a concentrator, the front plate and the concentrator being made as a whole, the plates are made of a material with acoustic resistance comparable with the acoustic resistance of piezoceramics with a difference of up to 20%, and the height of the protrusion is determined by the ratio 2f _r ((t ₁ + h) / c ₁ + (t ₁ + h) / c ₂ ) + nt ₂ / c ₂ -nt ₂ / c ₃ ) = 1, where f _r is the resonant frequency of the acoustic rod transducer, Hz; t ₁ - the thickness of the back lining, m; h is the height of the protrusion on the back pad, m; c ₁ is the propagation velocity of the longitudinal wave in the material of the back lining, m / s; c ₂ — longitudinal wave propagation velocity in the waveguide material, m / s; n is the number of piezo washers in the piezoelectric element, pcs .; t ₂ is the thickness of one piezo washer, m; c ₃ is the longitudinal wave propagation velocity in piezoceramics, m / s. 2. The acoustic rod transducer according to claim 1, characterized in that the protrusion of the back lining is made in the form of a truncated cone, the diameter of the smaller base of which is equal to the diameter of the head of the waveguide, and the diameter of the larger base is equal to the outer diameter of the back lining. 3. An acoustic rod transducer according to any one of claims 1 and 2, characterized in that a metal washer is encrusted at the end of the protrusion with a low longitudinal wave propagation velocity. 4. An acoustic rod transducer according to any one of claims 1 to 3, characterized in that the front cover and the hub have a tapering cavity in the form of a truncated cone, the larger diameter of which is close to the inner diameter of the piezoceramic washers. 5. An acoustic rod transducer according to any one of claims 1 to 4, characterized in that the waveguide is made of a material with a level of internal mechanical resistance lower than that of the overlays.

Images