US2278966A - Piezoelectric apparatus - Google Patents

Description

April 7, 1942- A. L. w. WILLIAMS PIEZOELECTRIC APPARATUS Filed Nov. 14, 1938 Fla. 3.

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Patented Apr. 7, 1942 'PIEZOELECTRIC APPARATUS Alfred r). w. Williams, Cleveland Heights, out, assignor to The Brush Development Company, Cleveland, Ohio, a corporation of Ohio.

Application November 14, 1938, Serial No. 240,261

- 8 Claims. (Cl.171:-327) This invention relates to piezo-electric apparatus and more particularly to means for .supporting flexing type-piezo-electric units.

An object of this invention is to provide means for supporting piezo-electric units which means permits a high degree of freedom for. flexure of the unit while preventing motion of the supported portions of the unit normal to its faces.

Pie'zo-electric units of the flexing type are now well known in the art. Briefly they comprise a plurality of plates of piezo-electric material such as Rochelle salt crystal cemented together face to face and so oriented that the assembly either bends or twists an-application of a difierence of potential between its electrodes and conversely develops a difference of potential between its electrodes when it is bent or twisted. The one type is called a bending unit and the other type a twisting or torque unit. For a detailed description of such units reference may be made to the following United States Patents: Re. 20,213 and Re. 20,680 issued December 22, 1936, and March 29, 1938, respectively, to C. B. Sawyer, and 2,105,011.1ssued January 11, 1938, to A. L. W. Williams.

Piezo-electric units are used as electro-mechanical energy converters in a variety of de-' vices such as microphones, loud speaker's, oscillographs and vibration measuring devices.

When the forces applied to or delivered by the piezo-electric unit are not great, the ,unit is commonly supported at a plurality of points between yielding pads of! material such as rubber. Such supports permit flexing of the unit without serious lost motionofthe supported portions in a direction perpendicular to the faces of the unit. When relatively great forces are involved.

the yielding pads have been replaced by metal plates cemented to the unit and each having a.

hemispherical projection engaging a flat surface of the crystal unit housing. This form of mounting holds the supported parts of the unit rigidly against movement normal to the faces of the unit. Both of the above types of supports are fully described in United States Patent 2,105,011.

It has been found that in some devices involving large forces the above "rigid type of mounting is unsatisfactory. When the unit flexes the projecting partsof the metal plate The friction at these points introduces undesirable effects. For example,- in the direct ink writing oscillograph described in United States Patent No.'2,149,216 issued February 28, 1939 to Charles K. Gravley, the pen point 'does' not always return to its normal position after an actuating charge has been removed from the crystal unit.

the crystal unit has'cemented to a a fiat hardened metal plate at each point of support. Opposite each such plate and parallel thereto is disposed a similar plate supported on a rigid base or frame. Each pair of plates is spaced apart by a metal ball. Pressure members are provided to hold the plates and ball in contact with a pressure greater than the greatest reactionary force on the supports. This arrangement holds the supported areas of the unit rigidly against motion normal to the faces of the unit while permitting a high degree of freedom for flexure of the unit. -A yi'eldingretaining ring is provided to hold the ballin place between the hardened plates. It is convenient to assemble separate supportlng'units .each comprising a retaining ring, -a ball and a pair of metal plates and then embody the required number of such supporting units in each device. 20

For this purpose the supporting uriits may be held together by a small amount of, cement at the junction of retaining ring and ,izietal plates. The number of support units used ina piezoelectric device will, of course,'depend on the type of unit and the mounting required for the I desired results.

For the purpose of further illustration the invention will now be described with reference to the accompanying drawing which illustrates such a support unit and a piezo-electric motor or generator device embodying three units. In the drawing, v

Fig. 1 is a front elevation of an enclosed piezoelectric motor or generator device with some of the'parts broken away to show interior construction.

Fig. 2 is a sectional view on the line 2, 2, of Fig. 1.

Fig. 3 is a sectional view on the line .3, 3, of Fig. 1.

Fig. 4 is an enlarged sectional view corresponding to the right hand portion of Fig. 3.

Fig. 5 is anenlarged plan view of the improved supporting unit with a portion of the surface broken away to show the interior construction.

displaced to an exaggerated degree to illustrate their operation.

Fig. 10 is a sectional view of aunodiflcation I wherein the ring of elastic material engages and is secured to only one bearing plate.

This gives rise to false records 0f the applied 4 electrical waves. v 1 in the preferred form of the present invention Fig. 11 is a'sectional view of another modification wherein the elastic member is omitted.

In Figs. 1', 2 and 3 a square torsion piezoelectric unit I of the type disclosed in United such support 0 Fig. 6 is anenlarged sectional view of the unit, and

, their edges parallel-to the b and c axes.

States Patent 2,105,011 is enclosed and supported in a metal housing comprising a cast box I, cover plate I and gaskets u. The box assembly is held together by screws 5,5.

The piezo-electric unit comprises four plates.

la, lb, lo and ld-of crystalline material-such as Rochelle salt. The plates are cut with their faces perpendicular to the electrical axis and The plates are secured together face to face with appropriate orientation and are provided with electrodes'ta (in Fig. 4) which are connected to leads 6.. A difference of potential applied between leads 0,. causes the unit to twist and conversely twisting forces applied to the unit cause a difference of potential to appear between leads I... The unit is clamped at three corners by supporting means to be described below. To the fourth corner is secured a drive pin I which extends through an opening is in cover I. The opening is sealed with a plug of gum rubber .8. Due to the three corner mounting of the unit an endwise force applied to drive rod 1 causes twisting of the unit with resultant appearance of a potential difference between leads OJ; conversely, a potential difference applied between leads 8,! causes the unit to twist with resultant endwise displacement of the drive I.

crystal unit supports and it is important to Dre-- vent lost motion of the supported parts of the unit in a direction normal to its faces. Furthermore. it is desirable that the unit r'emainentirely free to flex. The above requirements are met by the supports provided by this invention- In the motor generator device illustrated, three supporting units... are disposed at three corners on one side of the unit. These units are highly resistant to compression forces but offer very little resistance to flexing or shearing forces.

as will be described below. Adjacent the other asvacco ports and therefore the unit is effectively rigidly supported insofar as forces normal to the faces of the unit are concerned.

Due to the construction of the support units 9 the crystal unit is free to flex. Figs. 8 and 9 are sectional views illustrating the manner in which the support units i may distort under the flexing action of the crystal unit. Fig. 8 illustrates the result of a shearing force tending to move the two discs in opposite directions parallel to the planes of the discs. Fig. 9 illustrates a rocking or flexing action. Both illustrations are greatly exaggerated, Actually the support units may partake of a complex motion which is a combination of the motions illustrated in Figs. 8 and 9. and these effects may take place in more than one direction in the same plane. The opening in retaining ring "may be larger than the ball to permit maximum freedom of motion. However, it has been found that a close flt makes assembly somewhat easier and does not interfere with the action of the support. This is probably due to the very small motions involved and the yielding nature of the ring. Moreover, the retaining ring may be slightly thicker than the diameter of the ball, since it will be compressed when mounted until the two bearing plates contact the ball.

Obviously the present invention may be modifled in various other ways. For example, the retaining ring need not be cemented to the metal discs, the frictional engagement between the parts being relied upon to hold them in place. i

Alternatively, the retaining'ring may be somewhat thinner than the diameter of the ball and may be cemented at one face only to oneof the metal discs. This latter construction is illustrated in Fig. 10, in which a pair of metal discs face of the unit and opposite the three supports i are disposed resilient members III," which are held under compression by the metal housing..

- Referring now to Figs. 5. 6 and 7. each support unit I comprises a pair of hardened metal discs ll,li spaced apart by a ball of suitable material. preferably metal. Retaining ring it of soft rubber or the like is provided tohold the ball approximately at the center of the assembly. For convenience the retaining ring'it may be cemented tothe discs ll toprovide a complete supporting unit. In the motor generator deviu illustrated. each support unit a has one metal disc ll cemented to a thin plate is of insulating material such as Bakelite which in turn is cemented to a face of thecrystal unit I. The other disc ll of each support engages the cover plate 8. A resilient member ll compressed between the element and cast box opposite each support .unit the corresponding discs Ii and ball I! incontact, while pr'essins the whole assembly flrmiy against cover 3. The

force holding these members'in contact is great 5 er than the greatest reactionary force on the supm1,- l lb, are spaced apart by a ball its and the ball 'is yieldinglyheld in position by retaining ring Ila which is cemented to metal disc Ila. The above modifications of the supporting unit will produce substantially the same results but are somewhat less convenient to assemble. In

during assembly or the metal parts may be made of steel and magnetized.

It will be realized that whens ball support of this type is used, very high local stresses may occur in the ball and in the plates which contact it. Unless the plates and ball have quite high values of hardness, deformations may occur in them during use. Naturally, if the ball becomes flattened, or a plate becomes deformed immediately under the ball, the advantages of this type of ball support are largely lost. For this reason, hardened plates are specified herein. The degree of hardness will, of course, be determined bythe stresses involved in the structure: with a given load. the stress will increase as the diameter of the ball decreases. Where a lam ball may be used'to support a small load, it will be obvious that hardened plates may not be required. Furthermore, in such instances it may then be possible and desirable to use some ma-- terials other than metal, or to omit the bearin! plates and allow theball 'to contact the moving member and the supporting case directly.

It will be seen that the supporting unit of this invention permits a freedom of movement in the crystal unit which has not heretofore been atv member is not rotated as much as 180.

i 2, I tained. Even with the rather complex motion of the supporting corners of a flexing unit such as has been illustrated above, frictional resistance of the supporting unit is reduced to a minimum with the result that a new level of coordination is achieved between the crystal unit and its cooperating elements.

As can be readily appreciated. it is not necessary that a completely spherical ball be used in the mounting here disclosed since in use the Thus, when used in devices which require only slight rotation of the member, the member could be a body of very irregular shape provided with diametrically opposed spherical surfaces. Furthermore, its spherical surfaces could be of different radii. In view of these conditions, the term ball-shaped member is used in the following claims to mean a member of any shape which is provided with two spherical surfaces normal to the same line and having a common center lying between the surfaces.

Having now disclosed the invention, what I claim is:

1. A piezo-electric device comprising a support,

a flexing type piezo-electric unit having a pair of substantially parallel faces, anti-friction means disposed between said unit and said support comprising a pair of metal plates disposed substantially in parallelism and spaced apart by a metal ball, the first of said plates engaging a face of said unit and the second of said plates engaging said base, and yielding means disposed adjacent the other face of said unit opposite said first plate and adapted to urge said unit toward said support. v

2. A piezoelectric device comprising a flexing type piezoelectric unit; 'a support therefor; a bearing member between said unit and said support; and cushioning material adapted to press said unittoward said support; said bearing member consisting of a pair of plane bearing plates disposed in substantial parallelism, a single ballshaped member disposed between said plates in rolling contact therewith, and an annular ring I of flexible material encircling the ball-shaped member and secured to a face of at least one of said plates;

3. A device having the combination which consists of: a support having a plane bearing surface a.

thereon; a flexing type piezoelectric unit having a plane bearing surface thereon disposed substantially parallel to the bearing surface of said support and substantially in register therewith, the bearing surface of saidpiezoelectric unit being subject to limited universal movement relative to the bearing surface of said support with or withwith, the bearing surface of said piezoelectric unit being subject to limited universal movement relative to the bearing surface of saidsupport with or without concurrent translational movement with respect thereto; a single ball-shaped member disposed between the said bearing surfaces;

or holding the said bearing surfaces ith said ball-shaped member. which comprises: a piezoelectric which is adapted whenin use :portion and simultaneously to n t portion; supporting means; -oned between said supportystal unit to provide antie of said portions; and d latter portion of said crystal un said bearing means; said bearing means consisting of a ball-shaped member in rolling engagement with a. first plane bearing surface on said support 'and with a second plane bearing surface on said crystal unit, and flexible retaining means encircling said ballshaped member and spaced outwardly from the portions thereof which make contact with said firstand second bearing surfaces.

6. A device which comprises: a four-cornered piezoelectric plate-like assembly which is adapted to flex when in use; supporting means; three bearing assemblies positioned between said support and said piezoelectric assembly at each of three corners of the latter; means for holding said piezoelectric assembly against said three bearing assemblies; and a drive link coupled to the fourth corner of said piezoelectric assembly and subject to movement in a direction substantially perpendicular to the plane of the piezoelectric assembly as theiatter. flexes, each of said bearing assemblies consistingof a ball-shaped member in rolling engagement with a first plane bearing surface on said support and with a second plane bearing surface on said piezoelectric ch in its inoperative state is subassembly, and flexible retaining means encir cling said ball-shaped member and spaced outwardly from the'locations thereon which engage said first and second bearing surfaces, to establish areas for free rolling movement of said ballshaped member as said piezoelectric assembly flexes.

7. A piezoelectric device comprising: a support;

a fiexing-type piezoelectric unit having a pair of substantially parallel faces; bearing means between said unit and said support in engagement with'oneof said substantially parallel faces and with said support; and cushioning means in engagement with the other of said substantially parallel faces for pressing said piezoelectric unit toward said support; said bearing means consisting of E a pair of substantially parallel plane surfaces, and a ball-shaped member disposed between said plane surfaces in rolling contact with each.

8. A magnetic antifriction bearing unit particularly adapted for use between a support and a member which is subject to limited universal rocking movement relative to said support and which may or may not be subject to concurrent translational movement parallel to said support, said unit consisting of: a pair of bodies each provided with a plane bearing surface, said bodies being composed of magnetic material and dis-'

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