US2222056A - Piezoelectric device - Google Patents

Description

Nov. 19, 1940. A. L. WILLIAMS 2,222,056

PIEZOELECTRIC DEVICE Filed April 22, 1958 5 37 fief@ i7 2,956/

L 255 7 29 i@ 56 37 @fw/5 429 TTOPIVEX Patented Nov. 19, 1940 UNITED STATES PATENT OFFICE PIEZOELECTRIC DEVICE Application April 22, 1938, Serial No. 203,488

8 Claims.

This invention relates to piezoelectric devices and in particular to improved supporting and housing means for piezoelectric crystal units of the flexing type.

Two types of such flexing crystal units are now in general use. In operation, one type flexes torsionally about a longitudinal axis and the other type bends in double curvature or saddle like form on its two major dimensions. Rigid sealed housings are commonly provided for such units to protect them from mechanical injury, moisture and dehydration; and supports of yieldable material are usually provided in order to avoid undesired stresses on the unit.

A unit may be supported in various Ways depending on the operating characteristics desired. For example, in some types of devices a unit of the torsional type is clamped at three corners between pads or blocks of yieldable material, such as rubber, held in compression by the rigid wall sections of the housing. In operation the fourth corner moves in a direction normal to the faces of the unit. To this corner is connected a driving or driven member, such as a phonograph stylus or an acoustic diaphragm. In other cases a unit of the bending type is supported at two ends of the unit and driven by pressure applied at the center or throughout its unsupported area. Devices embodying such mountings are disclosed in United States Letters Patent 2,105,011. United States Letters Patent; 2,081,862 disclosed a unit of the torsional type supported at one end between pads of soft material held in compression by wall sections of the surrounding case and connected at the other end to a torsional shaft.

In some applications of crystal units the exact location of the supports and the pressure applied thereto have considerable effect on the performance of the device, and consequently great care is required in assembling the parts to obtain uniform results. Furthermore, difilculties may be encountered in clamping the crystal unit between its supports, due to variations in the thickness of the material from which the supporting blocks or pads are formed.

An object of this invention is to provide improved supporting and housing means for piezoelectric units adapted to rapid and accurate assembly.

Another object of this invention is to provide improved supporting vand housing means for piezoelectric units in which the 'clamping pressure on the units may readily be held within close tolerances despite normal variations in thickness of the material used.

A further object of this invention is to provide an improved terminal arrangement for piezoelectric devices.

Another object of the invention is to reduce the production costs of piezoelectric devices of the kind under consideration.

Another object of this invention is to provide improved piezoelectric motor and generator devices.

Still other objects of the invention, more or less incidental or ancillary to the foregoing, will be apparent from the further explanation of the invention which follows.

With the foregoing objects in view, the invention consists in certain features of construction and combinations of parts hereinafter explained and defined.

The invention, in some at least of its aspects, is applicable to a wide variety of uses, among which may be mentioned loud-speakers, microphones, phonograph pickups, phonograph record cutters and oscillographs. For purposes of explanation, the accompanying drawing shows the invention embodied in an enclosed piezoelectric motor or generator device adapted to various uses such as in loud-speakers, microphones, and oscillographs, and also shows the invention embodied in a phonograph pickup.

In the drawing, Fig. 1 is a plan view of a piezoelectric motor or generator device in which a crystal unit is hermetically enclosed and supported according to this invention and which is adapted to actuate or to be actuated by an acoustic diaphragm or other device.

Fig. 2 is an edge view of the device shown in Fig. 1.

Fig. 3 is a vertical section on the line 3-3 of Fig. 1 with the piezoelectric unit in edge elevation.

Fig. 4 is an expanded perspective view of the device shown in Figs. 1 and 2.

Fig. 5 is an enlarged, expanded edge view of the piezoelectric unit shown in Fig. 3.

Fig. 6 is a vertical sectional view of a piezoelectric device of the same general character as that of Figs. 1 and 5 but showing an alternative construction of the supporting and housing parts with part of the piezoelectric unit shown in elevation, the section corresponding to one taken at right angles to section line 3-3 of Fig. 1.

' Figs. 'I and 8 are vertical sectional views of enclosed piezoelectric devices of the same genat right angles to section line 3 3 of Fig. 1.

Fig. 9 is a plan view of a phonograph pickup device embodying the invention shown with some of the parts broken away to illustrate interior construction.-

Fig. 10 is a vertical section on the line Il--III of Fig. 9 but with the piezoelectric unit in edge elevation.

Referring first to the construction illustrated in Figs. l, 2, 3 and 4, I is a piezoelectric unit of the multiple plate flexing type which in operation iiexes torsionally. The piezoelectric unit as illustrated is square in outline and comprises two plates Ia, Ia, of Rochelle salt crystalA or the like, each plate having a thin electrode Ib attached to each of its faces and the two electroded plates being ilrmly cemented together. In Fig. the unit is shown diagrammatically with the plates and electrodes expanded or separated to better show the construction. The plates Ia, Ia have their-faces cut perpendicular to the electrical or a axis of the crystal from which they are formed and their edges parallel to the b and c axes. With the crystalline plates thus oriented, the unit which they constitute ilexes in torsion about a longitudinal axis when the plates are subjected to electrostatic ilelds caused by electromotive forces of proper polarity applied to their electrodes and, vice versa, when the unit is flexed in torsion electromotive forces are generated at its electrodes. Piezoelectric units of this character are now well known and reference may be made to United States Letters Patent Reissue No. 20,680 for a detailed description oi' such units. The specific construction oi the unit shown is presented for the purpose of illustration and it will be understood that known alternative constructions may be employed.

The unit I is enclosed in a housing andsupporting structure comprising a plate-shaped member or wall section 2 having an aperture 2a within which the unit is disposed. The section 2 has substantially the same thickness as the unit I and is formed of rigid material such as Bakelite or compressed ber or the like.

'I'he housing and supporting structure cornprises further two plate-shaped wall sections I, 3 formed oi' yieldable material such as rubber and having openings la, 3a which correspond to opening 2a in wall section 2 except that at three corners of the opening the material is not cut away, leaving inward projections or portions 3b, 3b that overlap the adjacent corner areas of the faces of the piezoelectric unit. 'Ihe fourth corner of the unit is not contacted by the sections 3, 3 and to this corner is secured a drive rod 4 of still.' wire or the like.

Metal cover or wall plates 5, 5 complete the housing structure. 'Ihey are'disposed adjacent the sections 3, 3 and the assembly is held together under pressure by rivets 6, 6.

Electrical terminals for the device may be mounted on one of the wall sections of the housing structure and if they are mounted on one of the intermediate sections 2 or 3, such section is formed with a peripheral extension for the purpose. Preferably the section 2 is provided with such an extension 2b and terminals 1, I are secured thereto, as by rivets 8, t. To the terminals are soldered the leads Ic, Ic of unit I.

'I'he drive rod l projects through opening 5a in one of the metal plates. The hole is sealed by ilexible material such as a plug of gum rubber 9. 'I'he pressure applied to the assembly by the rivets holds the unit I iirmly between the supi and iit snugly around the leads.

` The housing part 2 serves as a spacer between the yielding or gasket sections l, 3 and consequently the thickness of the -part 2 in relation to the thickness of the crystal unit I determines the amount of pressure applied to the unit by the supporting portions of gaskets 3. 3. v

When an electromotive force is applied between terminals l, 1, the unit tends to ilex torsionally and since three corners are held by the casing structure the remaining corner is displaced in a direction perpendicular to the faces of the unit giving the drive rod l an endwise movement. An alternating electromotive force applied to the terminals results in vibratory endwise motion of the drive rod. Due to the reversible action of piezoelectric units, an endwise motion applied to drive rod 4 produces a corresponding electromotive force at the terminals The device of Figs. 1, 2, 3 and 4 may be used for various purposes such as to actuate 4a loudspeaker diaphragm (partially shown in dotted line in Fig. 3), record cutting stylus or other mechanism in response to alternate voltages applied to terminals 1, 1, or to generate an alternating voltage corresponding to vibrations applied to drive rod by a diaphragm, phonograph pickup stylus or other vibratory mechanism.

In prior enclosed unit devices such as disclosed in United States Letters Patents 2,081,862 and 2,105,011, the crystal unit was supported between a number of pairs of pads or blocks of yieldable material held in compression. To obtain uniform results it was necessary to accurately locate the crystal unit in the case and properly position as many as six separate supporting pads. In the construction provided by the present invention the combination, in one yieldable body, oi' supports for the crystal unit with a wall section of the housing makes the parts of the device practically self-aligning, because each of the wall sections of the housing is die formed so as to be of uniform size and proper alignment of the piezoelectric unit in relation to one of the wall sections insures the proper location and area of contact at each of the three supported corners. This result in greater uniformity, together with a marked reduction in the time and skill required in assembly. Naturally, a corresponding reduction of production cost also is attained.

Since the terminals are carried by one of the wall sections, the leads of the crystal unit are made very short and are well protected from mechanical injury and the extra parts and operations necessary for a separate terminal block are eliminated.

In prior types of construction such as disclosed 76 l in Patent 2,105,011, even though the yieldability ofthe material of the supporting pads may be uniform from one piece to another, variations in thickness of various pieces are often encountered and such variations have a marked effect in the clamping pressure of the crystal unit. Variations in the mechanical characteristics of the material further tend to reduce uniformity. In constructions such as illustrated in Patent 2,081,862 the pressure on the crystal unit depends, for materials of uniform mechanical characteristics, on the thicknesses of the supporting pads relative to the thicknesses of the gaskets. It is difilcult to maintain these relative thicknesses to close tolerances. However, in the present construction the pressure applied to the crystal unit depends chiefly on the total pressure applied by the outer plates and on the relative thicknesses of the spacing member and the crystal unit. These parts may be made to accurate dimensions so that uniform clamping pressure may be obtained. Furthermore, the clamping pressure may be controlled in design by altering the relative thickness of the crystal unit and spacer. For example, the spacer may be made slightly thicker than the crystal unit so that a large pressure may be applied to the gaskets to insure an air-tight enclosure without applying excessive pressure to the crystal unit. In such cases the yieldability of the gasket material is of more or less consequence depending on the diiferenc in thickness of spacer and crystal unit.

In Fig. 6 is shown a modied construction in which a piezoelectric unit I0, which may be of either the bending or twisting type, is enclosed in a housing comprising a recessed wall section I I, a cover section I2, and a yieldable section I3.

In this construction portions I3a, I3a of the yieldable section engage peripheral areas on one face of the unit and pressure is applied thereto by the cover I2 held in place by screws I4, I4. At the other face of the unit, directly opposite the above mentioned areas rigid supports for the unit are provided. These supports comprise metal plates I5, I5 cemented to the crystal unit and having semi-spherical bosses I5a, I5a bearing against insulating blocks I6, I6. The pressure applied to the yieldable wall section holds the bosses of plates I5 in firm contact with blocks I6. The supports formed by plates I5 and blocks I6 are advantageous in certain applications where especially accurate location of supports is required or where considerable mechanical power is to be delivered by the crystal unit. In the latter case the metal supports prevent or reduce lost motion that might occur with wholly yieldable supports, but introduce a minimum of restraint to the flexing action of the unit.

As in the first described construction, the construction of Fig. 6 permits automatic and accurate alignment of the yieldable portions of the supports, and the dimensions of the box and rigid portions of the mountings are readily held to close tolerances so that the desired clamping pressure is readily and uniformly obtained.

In Fig. '7 is shown another modified mounting in which a piezoelectric unit I1, which may be of either the bending or twisting type, is enclosed in a housing comprising cover plates I8, I8 and wall sections I9, I9 of yieldable material. In this construction the rigid spacer member has been omitted and the wall sections I9 are formed entirely ofyieldable material, such as rubber, and have inward projections I9a, I9a of reduced thickness to embrace the parts of the crystal unit to be clamped. The assembly is held together by rivets 20, 2li.4

The construction shown in Fig. 8 is like that in Fig. '7 as to the unit I1', cover plate sections I8', I8 and rivets 20' but the yieldable parts comprise sections 2I, 2I with unit-engaging inward projections 2Ia, 2Ia and a spacing section 22.

'Ihe constructions of Figs. '7 and 8 provide an air-tight enclosure for the crystal unit and are adapted to rapid assembly and accurate align-4 ment'of crystal supports since the crystal supports are combined with bodies forming wall sections of the housing,

Figs. 9 and 10 show the invention as it may be embodied in a phonograph pickup of the type disclosed in United States Letters Patent No. 2,081,862.

The piezoelectric unit is of the same genera1 type as unit I of Fig. 4. The plates 25a, 25a are of trapezoidal shape and formed from a Rochelle salt crystal with their faces perpendicular to the electrical or a axis and with their parallel edges parallel to the b or c axis of the crystal. In operation the unit flexes torsionally about its longitudinal axis. It is disposed within an opening 26a in spacer wall section 26 which is made of Bakelite, fiber or the like. Leads 27, 27 connect the electrodes 25h, 25b of the unit to terminals 28, 28 which are carried by the spacer 26. The crystal unit is clamped along one end between flat gasket wall sections 29, 29 of yieldable material which are held in compression between plates 3l, 3|. The remaining portion of crystal unit 25 is left free to flex by provision of opening 29a in gaskets 29.

A flexible torsional shaft 32 is secured to the end of the crystal unit by a clamp 33. The shaft 32 may be in the form of a thin wire of beryllium bronze or other suitable material. A stylus arm 34 is secured to the torsional shaft and carries a stylus 35.

In order to seal in the crystal unit, gaskets 36, 36 of yieldable material are disposed between the inner wall of the spacer 26 and the periphery of crystal unit 25, the torsion shaft 32 being disposed between said gaskets 36, 36 and the gasket sections 36, as well as sections 29, being formed with rectangular apertures to provide space for the stylus arm 34. Before assembly in the pickup, the combined thickness of gaskets 36, 36 is somewhat greater than the thickness of spacer 26, so that when said gaskets are pressed between gaskets 29, 29 by screws 37, 31 they form an air-tight seal around the crystal unit, ratio of the thickness of the unit to the thickness of the spacer 26 largely determines the relative pressures on the spacer and the unit. This ratio is near unity so that the clamping pressure is independent of minor variations in gasket thickness and yieldability.

In operation the pickup is supported over a rotating phonograph record with the stylus engaging the recorded groove. Lateral undulations of the groove are translated into corresponding torsional vibrations of shaft 32 by the stylus 35 and arm 34. These torsional vibrations are transmitted to the unsupported end of crystal unit 25 with resultant vibratory flexing of the unit. Such flexing of the unit causes a corresponding alternating voltage to appear between terminals 28, 28 and this voltage may be utilized to actuate loud-speakers or other devices in well known manner. By suitable modification of the stylus arm 34, the device may be adapted to operate The with vertically cut or hill-and-dale records. Further, the device may be adapted to record-cutting applications by use of a rigid shaft in place of wire 32 and the substitution of a suitable cutting stylus.

From the foregoing specification it will be apparent that the invention providesA improved mounting means applicable to both bending and twisting types of flexing units which may be supported according to various principles and embodied in variety of devices. The combination of a plurality of yieldable supporting members in one body improves the uniformity of results and greatly simplifies assembly, The combination of the crystal unit supports with bodies forming part of the housing further simplifies assembly and adds to the accuracy and uniformity of results obtained. Furthermore, the provision of the spacer member of the same or nearly the same thickness as the crystal unit improves the uniformity of results by insuring proper crystal clamping pressure. The use of the spacer member for terminal supports further simplifies the construction and provides mechanical protection for the crystal unit leads.

It will be understood that the invention is not limited to specic forms of construction herein illustrated and described and that the various features of the invention may take various other forms within the scope of the appended claims.'

What I claim is: I

l. In a piezoelectric device, the combination of a flexing type piezoelectric unit, and a housing for enclosing and supporting said unit comprising a body of yieldable material constituting an outer wall section of the housing and having a portion disposed to engage a part of said unit, and means for pressing such portion of said body against said unit to hold the engaged part of the unit substantially fixed relative to the housing.

2. In a piezoelectric device. a combination as claimed in claim 1 in which the yieldable wall section and the means for pressing it against the piezoelectric unit are formed to engage and apply clamping pressure to a plurality of separate surface areas of the piezoelectric unit.

3. In a piezoelectric device, the combination of a plate-shaped flexing type piezoelectric unit and a structure for supporting and housing said unit comprising a wall section of rigid material having a face substantially flush with a face of said unit, a wall section of yieldable material contacting said face of the rigid section and an area of said face of said unit, and means for pressing the mutually engaging faces of the wall sections and the unit together.

4. In a piezoelectric device, the combination of a plate-shaped piezoelectric unit of the flexing,

type and a structure for supporting and housing said unit comprising an apertured plate-shaped wall section of rigid material having the said unit disposed within its aperture with the faces of the wall section and unit substantially flush with each other, plate-shaped wall sections of yieldable material engaging the two faces of the rigid wall section and predetermined areas of the two faces of the piezoelectric unit, cover plate wall sections engaging the yieldable sections, and means for clamping the several wall sections together in predetermined relation to each other and to the piezoelectric unit.

6. In a piezoelectric device, the combination of a plate-shaped piezoelectric unit of the ilexing type and a structure for supporting and housing said unit comprising an apertured plate-shaped wall section of rigid material having the said unit disposed within its aperture with the faces of the wall section and unit substantially flush with each other, plate-shaped wall sections of yieldable material engaging the two faces of the rigid wall section and predetermined areas of the' two faces of the crystal unit, cover plate wall sections engaging the yieldable sections, and means for clamping the several wall sections together in predetermined relation to each other and to the piezoelectric unit, one of the wall sections of the housing structure being formed of non-conducting material, and electric terminals for the piezoelectric unit mounted on the nonconducting section of the housing.

7. In a piezoelectric device, a combination as claimed in claim 6 in which the rigid wall section has a projecting part upon which the electric terminals are mounted.

8. In a piezoelectric device, the combination of a flexing type piezoelectric unit, and a housing for enclosing and supporting said unit comprising a body of yieldable material constituting an outer wall section of the housing and having portions thereof disposed to engage a plurality of separate surface areas of the piezoelectric unit, and means for pressing such portions of said body against said unit to hold the latter in position.

ALFRED L. W. WILLIAMS.

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