US2387108A - Piezoelectric apparatus - Google Patents

Description

Oct. 16, 1945. J. P. ARNDT, JR., ETAL. 2,387,108

PIEZOELECTRIC APPARATUS Filed March 18, 1942 Patented Oet. 16,v 1945 UNITED .STATES PATENT ori-ICE PIEZOELECTRIC APPARATUS John P. Arndt, Jr., Euclid, and Walter J. Brown and Alfred L. W. Williams, Cleveland Heights, Ohio, assignors to The Brush Development Company, Cleveland, Ohio, a corporation ot Ohio Application March 1s, 1942, serial No. 435194 (ci. 1v1-321)' Claims.

This invention relates to .piezoelectric apparatus and more particularly to relays or the like wherein the actuating member is similar to the piezoelectric `motor element disclosed in the lSawyer Reissue Patent 20,213.

Piezoelectric crystal elements of the sodiumpotassium tartrate type have many advantages a relay, actuated by a piezoelectric element, that shall not depend upon critical contact spacing and one that is substantially unaifected by temperature changes.

Another object of the invention is to provide a relay, actuated by a piezoelectric element, that shall be rapid in action, inexpensive to manufacture, yet extremely rugged. y

Another object of the invention is to provide a relay or tle like, actuated by a piezoelectric element, wherein alteration of the shape of the element, from natural causes, or at very low veloclty, does not interfere with reliability.

istiil further object of the invention is to provide a reiay or the like, actuated bya multipiate flexing piezoelectric element, wherein set or sag thereof shall be compensated automatically.

.In accordance with the invention, a piezoelectric element, preferably a multiplate fiexing element of the type disclosed in the Sawyer patent, is so supported in operative relation to an instru'- mentality having a movable part such, for example, as a snap-action switch, that slow changes inthe shape of the element,` at low velocity or from natural causes, are continuously compensated, whereas movements thereof at .high

pivot, the free upper end being operatively connectedwith the switch. The system is in stable equilibrium and, if the resistance offered by the switch to movement by the free end of the element is properly adjusted. slow bending of the element is compensatedby rotary movement o! the weight about its pivot. the free end of the element being effectively decoupled" from the switch. When, however, potential is applied to the electrodes of the element such as to cause it to bend with high velocity, the inertia of the weight is such ,that it serves the purpose of a fixed mounting, causing operation of the'switch. Another way of explaining thea'ction is by analogy to a high pass `illter, the movable part of the switch corresponding to the output terminals thereof, and the weight corresponding to a shunt,- ing inductor.

The novel features of the invention are set forth with particularity in the appended claims. The inventionqitself, however, both as to its organization and its method of operation, together withl further objects and advantages thereof, will best be understood from a consideration of the following description of certain specific embodiments taken in connection withthe accompanying drawing in which:

Fig. i is a diagrammatic elevational view of one embodiment of the invention, also showing an operating circuit therefor.

Fig. 2 is a conventionalized side elevational view of a modification of the device shown in Fis. 1.

velocity are transmitted to the said instrumerztality. To obtain such action, a piezoelectric element of either' the "bender or the "twister type may be utilized, one portion of which is operatively engaged with the switch at all times while another portion is permitted to move slowly, as the element "setsj without disturbing the engage- .ment with the, switch. Such elements are disclosed in the Sawyer Reissue Patent 20,213, and

they are now well known to those skilled in `the f art. For example, a bender element may be mounted' upright upon a horizontally pivoted weight, tc/flex in a yplane at right angles to the Fig. 3 is a conventionalized sectional view of an alternative embodiment of the invention.

Fig. 4 is a conventional view,=pai'tly` in' vertical section and partly in elevation, -of another embodiment of the invention.

Fig. 5 is a fragmentary view in perspective showing an alternative einbodunent oi.' the invention exemplified by Fig. 4.

Fig. 6 is a view in perspectiveoi an actual relay constructed according to thevinvention, part of the apparatus being broken away in order to disclose more clearly the details thereof.

In all figures of the drawing, identical elements are similarly designated.

Referring now to Fig. 1 of the. drawing, an' embodiment of the invention may comprise a weight i rotatably supported upon a horizontal pivot I on the upper surface of which is'vertically mounted a piezoelectric crystal element 5 of the multiplate bender type, the crystal sections constituting the element being disposed in planes parallel to the plane of the weight-supporting pivot 3. The upper end of the piezoelectric element is pi a- .nois.

vided with means such as a plurality of ilngers 1 1, or the like, which engage the movable part t of a snap-action switch ll, or the like, of the type that requires only a short throw for actuation.

As is well known to those skilled in the art, snap-action switches usually require a certain denite amount o f force to throw them from one position past dead center to the other position. This action may be secured by a small spring so mounted with respect to the movable part of the switch-or similar device that it is placed under tension as the said movable part moves through dead j center, the tension being relaxed at either of the rest positions. There is also another well known short .throw switch on the market known as a micro switch, manufactured under United States Patent 1,960,0 by the .Micro Switch VCorporation of Freeport, Illi- The latter switch requires a short throw for operation to the closed position, after which it tends, because of its construction, toreturn to;A

the open position. A slight modification of this invention is necessary for the operation of a micro switch or switches of that general type,

as hereinafter will be explained in connection v with other ligures of the drawing.

For the purpose of causing the multiplate dexing elementi to bend to either one side or the other, a source of potential is provided for application to .the inner an'd outer electrodes thereof. The source may, if desired, be unidirectional and a reversing switch (not shown) may be utilized or it may be constituted, as shown in Fig. 1, by a battery I3, a central tap I5 which is connected to the interior electrode I1 -of the multiplate flexing element, a three-point switch I9 be- Y ing so connected to the outer electrodes 2I-2I of the multiplate flexing element that eitherthe positive or negative terminal of the battery I3 may .be connected thereto.' A bleeding resistor 23 having a resistance usually of the order of 116 to 10 megohms is connected across the electrodes of the multiplate flexing element for the purpose of dissipating the charge thereon afteractuation thereof and after opening' of the switch.

The weight I is so chosen and the position of the pivot 3 is so fixed that the system constituted bythe piezoelectric element 5 and the weight is in a state of 'stable equilibrium. Furthermore, the inertia of the weight is so related to the force required to throw-the snap-action .switch past dead center that when the crystal element 5 tends to slowly sag or set or to change its shape because of temperature changes, the switch il is not actuated but the weight l is so moved in a small arc around the pivot 3 as to compensate for changes in crystal lelement conguration.

.However, if potential is applied to the electrodes,

ture eiects, and to the eiects of set or sag, re-` sponding, to actuate the switchfonly to potentials such that the crystal is caused to ilex suddenly@ Obviously, the apparatus will be immune to very low frequency alternating potentials if the frequency thereof is below the natural `flexing period of the crystal and weight assembly, and the apparatus, accordingly,.may be utilized to discriminate between high and low alternating freitA , as Viscoloidf' aestgios a dierent frequency, ii the potential is suiiip ciently high.

There are a number of modified embodiments of the invention analogous to the device shown' in Fig. 1. For example, referring to Fig. 2 of the drawing, the piezoelectric element 5 may be sup- -ported horizontally upon the weight l as shown in full lines in Fig.' 2, or vertically below the pivot 3. In such event, the vertically suspended clement would function in exactly the same manner 'as hereinbefore described in connection with Fig. l. A jfmicro switch" 25 may be associatedwith the horizontally positioned piezoelectric element provided a resilient adjustment device 21 is supplied for maintaining adenite pressure upon the free end of the element to balance the tendency 'of the movable portion 29 of the micro switch to return toits open position. The action of the adjusting device 21 will be explained in more detail in connection with Figs. 3 and 6 of the drawing. f'

Inasmuch as the spirit of the invention resides A in the-provision of means whereby slow movement itself being relied upon to secure snapaction. Such alternative embodiment of the invention is exempliiied by Fig. 3 of the drawing wherein one end ofA the crystal element is embedded in a mass 3| of deformable material such The free end of the crystal element,`still referring to Fig. 3, rests upon the movable portion 29 of a snap-action switch 25, such as the micro switch previously referred to, and` is held against it by an adjusting device 21 shown partly in section and partly in elevation. .The adjusting device 21 is constituted by a small plunger 33' that telescopes within a hollow screw 35 having a knurledhead 31 and is resilently urged 'against the upper `face of the multiplate exing element by a small spring 39 interposed between the inner end ,of the hollow screw and f the top of the plunger. The pressure exerted by the spring upon the plunger and ultimately upon Y the crystal element is determined by adjustmentA of the hollow screw in a yoke di such as is shown more clearlyl in Fig. 6. The pressure is made just slightly to overbalance the tendency of the I switch knob 29 to return to the openposition but 4it is'insulcient to cause any appreciable movement of the crystal element'such as would actuate the switch 25.

Il. in use, the crystal element 5 shown in Fig. 3

tends to sag or set or otherwise to'change its configuration, such change is permitted t a. slow rate by the semi-resilient*mounting 3i, the unscribed alternative embodiment of the invention.

A still further embodiment of the invention is exemplified by Fig. 4 of the drawing, wherein a snap-action switch Il is operatively connected by a rod 43, or the like, to the mid-portion of a piezoelectric crystal element I5 of the multiplate bender type, the ends of which are fixed in a yoke 41,v which is in turn supported from the piston I9 of a. dash-pot 5I. No attempt hasbeen made in the drawing to show the details of an i actual dash-pot, the essential feature of` which is the provision of a very small passageway 53 between the cylinder in which the piston carrying the yoke moves, and a storage reservoir 55.

, Should lthe bender type element shown in Fig. 4 tend slowly to deform, only relatively slight resistance is offered to the flow of fluid through the interconnecting passageway 53, and the piston moves to compensate the changes in shape of the crystal while permitting the switch arm 9 to remain in position. When, however, potential is applied to the bender element, it tends to flex at l high velocity and in such event the passageway 53 o'ers extremely high resistance to movement of the fluid againstwhich the piston presses with the result that the yoke 41 carrying the piezo- 'mounting means 3| shown in Fig. 3 in that after the crystal has slowly deformed by reason of y natural causes, no restoring force is applied to it other than the difference in level between the fluid in the cylinder of the dash-pot and in the StOrage chamber.

lcal planes.

As will be apparent from an inspectionof the drawing, the pairs of corner-clamping devices 65-61 are such as to permit a limited rocking movement of the piezo-electric element while re-u straining any movement of the corners in verti- Accordingly, as the element sets or sags or changes its shape because of temperature changesfno force is applied to the switch arm, the free end of the element being permitted to move slowly to compensate` such changes. However, when potential is applied to the electrodes as described in connection with Fig. 1, the free corner 68 and the corner 1| -in contact with the switch arm tend to move with high velocity. Because of the construction of a twister type piezoelectric element, the free corner and the corner in contact with the switch tend to move downwardly While the clamped corners tend to move upwardly or vice versa, depending upon the polarity of the applied potential. If it is assumed that the momentarily applied potential is such as to cause the free corner to move downwardly at a high velocity whilethe corner in contact with the switch arm also tends to move downward, the tendency to movement of the said free corner introduces a reaction into the system that is the same in kind as the reaction that would be introduced were the said free corner to be provided' with a weight. This effect, together with the actual inertia of the free corner, causes the crystal to flex around an axis 'interconnecting the clamped corners with the result that the switch is moved to the closed position where it is held by lthe resilient adjusting device until such time as a potential of opposite polarity is applied.

It will, accordingly. be apparent from a consideration of the foregoing description of several modifications of the invention, that it offers advantages heretofore unobtainable. The invention is mainly advantageous in that it obviates all need for exact and meticulous contact spacing and in that a device constructed in accordance Referring to Fig.- 5, if a twister element -51 is utilized in the embodiment exemplified by Fig.

4, a plurality of yokes 41 are utilized and they are connected, respectively, to pairs of opposite corners of the element.

Perhaps the simplest embodiment of the invention is one wherein resilient mountings, weights, and the like, are dispensed with and the inertia of the crystal element itself is relied upon to cause a switch to be thrown when the said element is energized. Such a device is shown in Fig. 6 of the drawing. It preferably comprises a base 59 having two uprights Si, the said uprights, respectively, serving to ,hold the opposite corners of a piezoelectric element 51 of the torque or twister type. For clamping purposes, each upright may be provided with a slot or niche 63 having a vertically extending abutment 65 on which a corner of the crystal rests and against which the corner is held by a clamping screw 61'. One corner B8 of the crystal is left perfectly free while the diagonally opposite corner 1i rests upon the upwardly extending movable operating arm 29 of a switch 25 such as a micro switch. The last-mentioned corner of the crystal is resilientiy held against the operating arm of the micro switch by an adjusting device of the type shown in section in Fig. 3 that is mounted in a yoke 4I which extends over the said corner. By turning the knurled head 31 of the adjusting device, the pressure upon the' switch arm 29 may be maintained just suiiiclent to hold it in the closed position after actuation by the piezoelectric element.

natural causes.

therewith is` free from the troublesome disturbance of contact spacing introduced by setf or sag or by changes in crystal element configuration resulting from temperature changes or from other Operative engagement between the crystal element and the switch arm is maintained throughout the useful life of the device and it has proven to be very rugged and reliable in operation.

p Further advantages of the invention as well as further embodiments thereof willlbe apparent to those skilled in the art to which it pertains. For example, any other device, capable of being actuated by a relatively small movement of an element thereof, may be substituted for the switches shown. The invention, therefore, is not to be limited except insofar as is necessitated by the prior art and by the spirit of the following claims.

What is claimed is:

' 1, In combination, a piezoelectric element adapted to flex rapidly in response to an electrical potential applied thereto, a, switch having a movable part biased into operative engagement with said element and yieldable mounting means for said element permitting it to move slowly while maintaining engagement with said movable part.

2. The invention set forth in claim 1, further characterized in that the switch is of the snapaction type.

3. In combination, a piezoelectric element adapted to flex at high velocity in response to an electrical potential applied thereto, a switch having a movable 'part biased into operative en gagernent with said element, and yieldable mounting means for said element, the mounting means permitting the element to move slowly While maintaining a substantially fixed relation to said movable part.

t. The invention set forth in claim 3, further characterized in that the switch is of the snap-1V action type.

5. in cornbii'iation, a piezoelectric element, a switch having a movable part operatively associated with said element for actuation thereby at high velocity and a yieldable support for the element against which it reacts during actuation o the movable part, said support permitting the element to move slowly While nriaintaining operative association with the movable part.

6. The invention set forth in claimt, further characterized in that the switch is of the snapaction type.

7., In combination, a. piezoelectric element, an instrumentality of the snap-action type having a movable part in operative engagement with a portion oi the element, and a support for the element againstwhich it reacts during operation of the instrumentality, the support oiering a largel opposing force to movements of the crystal at high velocity and relativeif/- small opposing force to movements thereof at low velocity, whereby only movement at high velocity is imparted to the said movable part.

8. in combination, a piezoelectric element, a carrier therefor including a weight, means supporting the weight for rotary movement around anv ams adiacent to its center of gravity, the entire movable system being so constructed and arranged that it vis in stable equilibrium.

d. 1in combination a piezoelectric element, an instrumentality oi' the snap-action type having a movable member, means 'for establishing and maintaining operative engagement between said movablemember and one portion of the piezo-v electric element, and mounting means for holding another portion of said element in semi-fixed position, the said mounting means substantially impeding rapid motions of the portion of the element supported thereby while permitting slow movements thereof.

lo. The invention set forth in claim 9, further characterized in that the said mounting means incl'udes la. material having high internal viscosity,

1l.` The invention set forth in claim 9, further characterized in that the of the multiplate flexing t i2. In combination, a piezoeltric element and a carrier therefor constituted at least in part by a dash-pot.

piezoelectric elementis/ acentos i3. in combination, a piezoelectric elementand a carrier therefor comprising a dash-pot and means connecting the element to the dash=pot.

1i. In combination, a piezoelectric element, means of the snap-action type having a movable part inoperative engagement with a movable portion of the element, said movable part exerting a first'orce against the movement of the element which upon said torce being overcome actuates said snap-action means, means associated with said element for exerting a second force against movement of said element, said force er.. erted by said associated means due to set or sag or" said piezoelectric element being insuiiicient to overcome said rst force and cause actuation oi said snap-action means, and said force exerted by said associated means due to operation of said piezoelectric element being sufcient to overcome said iirst force and cause actuation of said snapaction means.

15. The invention as set forth in claim l, rar ther characterizedby means for adjusting the force of the bias.

` 16. In combination, a piezoelectric element adapted to flex rapidly in resnonseto an electrical potential applied thereto, a switch having a movable part biased into operative engagement with. said piezoelectric element, and movable mounting means for said piezoelectric element permitting said element to move slowly while maintaining engagement with the said movable part of said switch without actuating said switch, the resistance of said mounting means-to move ment when said element le'xes rapidly causing said switch to be actuated.

l7. The invention as set forth in claim i6, further characterized in this: that said movable mounting means comprises a mass of deformable material vvithin which a portion of said piezoelectric element is embedded.

18. The invention as set forth in claim lo, further characterized in this: that said movable mounting means comprises pivotably mounted inertia means to which a portion of said piezoelectric element is connected.

19. nThe invention as set forthin claim 5, further characterized in this: that said yieldable support comprises deformable material within which a portion of said piezoelectric element is embedded.

20. The invention as set forth in claim 5, iurther characterized in this: that said yieldable' support comprises pivotably mounted inertia means to which a portion of said piezoelectric element is connected.

- JOHN P. ARNDT, Jn.

WALTER J. BROWN. ALFR L. W. wl

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