US3430020A - Piezoelectric relay - Google Patents

Description

Feb- 25, 1969 R. voN roMKEwlTscl-l ETAL. 3,430,020

PIEZOELECTRIG RELAY Filed Aug. 17. 196e da mi@ ATTYS.

United States Patent 3,430,020 PIEZOELECTRIC RELAY Romuald von Tomkewitsch, Ebenhausen, and Werner Busch, Munich, Germany, assignors to y Siemens Aktiengesellschaft, a corporation of Germany Filed Aug. 17, 1966, Ser. No. 573,072 Claims priority, application 9(irrmany, Sept. 20, 1965,

U.s. c1. o- 131 1o claims 1m. c1. H01h 57/00 ABSTRACT OF THE DISCLOSURE It is known to utilize the piezoelectric effect of certain crystals in the construction of relays. If a voltage is applied to such a crystal, of plate formation, a bending throughout of the plate results, and by means thereof a contact assembly associated with such plate may be actuated. Because of this manner of operation, crystal plates of this kind are often called bending vibrators.

The advantage of relays with piezoelectric excitation consists, above all, in the fact that they possess a high electro-mechanical degree of efliciency and that the initial frequency is considerably higher than that of electromagnetic relays. Furthermore, as no electro-magnetic system is necessary for the operation of such a relay, neither an iron core nor a winding is required for the structure, and as the voltage source of a piezoelectric relay is drawn upon only in a capacitive manner only a very small power requirement is necessary for the excitation.

In spite of these qualities, particularly favorable for the construction of miniature relays, piezoelectric relays thus far have had little success in the field. This fact is attributed to the fact that the required crystal plates are, according to their nature, only suitable -for small operating travel, andr correspondingly a large mechanical leverage is required for obtaining the contact operation necessary for positive relay operation. For this reason relatively long and thin bending vibrators or appropriate lever transmission means for obtaining the necessary contact travel have been necessary. The first mentioned solution has the disadvantage that a relay of this type is not sulliciently sturdy. On the other hand, lever transmissions usually require a large number of moving parts which are bound to operate with losses which are not negligible and cannot be disregarded.

The disadvantage of known piezoelectric relays above discussed in detail, are avoided according to the invention by the feature that a bending vibrator, preferably of circular conliguration, is provided with a pressure chamber to which a metering tube enclosing a mercury drop is connected, and during excitation and resulting bending of the vibrator, the contact gap located in the metering tube may be closed by the mercury drop. In this case the power-way transformation is effected by means of the mercury located in -the metering tube almost without loss. More important, no lever transmissions are required, so that resulting mechanical losses are substantially elimi- ICC nated. If, in this case, the metering tube selected is appropriately narrow, the mercury drop to be accelerated during excitation of the relay likewise may be relatively small.

In order to achieve relay operation in a manner largely independent of position and temperature, in a particularly suitable ydevelopment of the invention there is provided the feature that the pressure chamber which encloses the bending vibrator is divided into two cooperative chambers and that metering tube or passageway, provided with the mercury drop, preferably formed by a central bore in the bending vibrator, effects a pressure compensation during excitation of the bending vibrator and therewith the bridging-over of the contact gap. In this case the divided pressure chamber is expediently filled with a liquid which is not electrically conductive, for which purpose, for example, alcohol or thin-flowing oil are suitable. Because of the division of the pressure chamber, arranged symmetrically on opposite sides of the vibrator a simple temperature compensation is assured.

If the vibrator during excitation in accordance with the operation effect a bending movement, the volume of one of the pressure chamber divisions is reduced and the volume of the other pressure chamber division is enlarged. Since the fluid compensation can take place only through the metering passageway (central bore), a mercury drop therein is shifted from one tube end to the other. The result of this movement is, for example, that one pair in the metering passageway is opened while a second contact pair is closed.

In order to increase the operating dependability of such an arrangement, it is advantageous to attach a fine mesh screen to each end of the metering passageway which, for the fluid, presents little mechanical resistance, but for the mercury drop, presents a high resistance. The mercury drop is thereby prevented from leaving the metering passageway if not too great an electrical over-excitation of the bending vibrator exists. It is even more effective to lengthen the metering passageway towards both ends in the form of capillaries whereby, due to the capillary action, the mercury cannot flow out of the metering passageway.

An especially advantageous construction for the prevention of a ow of mercury out of the metering passageway provides spherical bulges in the metering passageway at the contact gaps. The surface tension of the mercury, as is well known, is so large that in this case the mercury drop cannot leave the measuring passageway even if the relay is mounted horizontally. In order to obtain a maximum operating dependability, a further embodiment of the invention is so constructed that the metering passageway with its spherical bulges, includes a separate pressure chamber disposed at both sides of the bending vibra-tor. In this manner, the fluid pressure resulting during an overexcitation is blocked so that the mercury drop cannot leave the metering passageway and thus the contact gap. Expediently the membranes therefore are constructed as resilient members of plate-like conliguration. Such resilient members also have the effect of energy storage means and gives the relay a snap action characteristic which is effective in the achievement of an acceleration of the switching operation.

In order for the temperature compensation previously mentioned to also operate effectively, it is advantageous to provide a capillary through the bending vibrator conn ecting the two divisions of the pressure chamber, through which a gradual pressure compensation may take place at any time. The operation of the relay, with an `appropriate proportioning of the capillaries, is not operatively impaired as the supplemental capillary olers a relatively high resistance to the sudden pressure increase during excitation of the relay. In order to further improve the temperature compensation and to firmly anchor the connections to the operative contacts, the elements of the relay can be assembled into a unitary construction and such unit encased in suitable material.

Further details of the invention are evident from the subsequent description of several examples of construction and the drawings, wherein like reference characters indicate like or corresponding parts, and in which:

FIG. 1 is a sectional view, taken approximately on a central vertical line of FIG. 2, illustrating an embodiment of the invention;

FIG. 2 is a sectional view taken approximately on the line A-B of FIG. 1;

FIG. 3 is a sectional view, similar to FIG. l, illustrating a modified construction; and

FIG. 4 is a schematic figure illustrating a further modification of the invention.

FIGS. 1 and 2 schematically illustrate a piezo-electric relay, which comprises a circular bending vibrator member 1 with a central bore therein which serves as a metering passageway 3 for a drop 4 of mercury disposed therein. The bending vibrator 1 is enclosed on both sides by a pressure chamber divided into two sections or divisions 2 in which a non-conductive fluid is disposed. Because of this dual arrangement of the pressure chamber symmetrically to the vibrator 1, a large temperature compensation is assured. If the vibrator 1 bends axially during excitation, as indicated in FIG. 1 by the arrows, the volume of one chamber is reduced and the volume of the other chamber is enlarged, with the fluid compensation taking place through the metering passageway whereby the mercury drop therein is shifted from the right side to the left side. By this process, the contact gap Sa/Sb is operatively opened and the contact gap Srl/5b' is operatively closed. In order -to prevent the mercury drop 4 from being discharged from the metering passageway 3, fine mesh screens 6 are arranged at both ends of the metering passageway which offer a high resistance to the passage ofthe me-rcury.

In order to obtain an especially high security against the discharge of the mercury drop from the metering passageway, especially if the relay is overexcited, an improved relay construction may be employed, such as that illustrated schematically in FIG. 3. It should 'be particularly noted that in this embodiment the metering passageway 3 possesses spherical bulges or enlargements at the contact gaps Sa/Sb and 5a'/5b. These spherical bulges are connected with each other by only a narrow central passageway, as a result of which the mercury drop 4 cannot drop downwardly through such center passageway, even if the relay is horizontally mounted, because the drop always seeks to occupy a spherical form due to its great surface tension. Membranes 7a and 7b are additionally provided at the ends of the metering tube to also restrict the uid pressure therebehind during the occurrence of `an over actuation and excessive exing. As a result, the mercury drop 4 is restricted in the metering passageway and therewith the contact position existing under any circumstances. The membranes illustrated in this tigure are constructed as plate-like springs and since they have an energy storage eiect, they have a more or less snap action, which may be epecially advantageous if the excitation alteration, i.e., the pressure alteration involved takes a slow course since in this manner, the switch-over action is necessarily accelerated.

It has already been mentioned that due to the symmetrical arrangement of the two-section pressure chamber 2, exceptionally eilicient temperature compensation may be obtained. However, this temperature compensation approaches an optimum only when the volume of the two sections of the pressure chamber, as well as the heating and the mechanical stiffness of the closure members 9 are equal. Since such an equality may, from the standpoint of manufacturing technique, be obtained only with diiculties, a very line bore 8 is additionally provided between the two chamber sections as a compensation capillary over which pressure compensation may gradually take place.

In practice, it may occur that in order to prevent a possible inuencing of the bending vibrator, in particular where higher voltages are involved at the switch contacts, a separation of the excitation portion and the .contact portion of the piezoelectric relay is desirable. In FIG. 4 a possible form of construction is schematically illustrated, in which letters have been employed as reference characters. This embodiment comprises a bending vibrator B and a resilient metal plate M which takes the place of a second bending vibrator which would otherwise be required at this side. In this case the insulation means I which may, for example, be produced out of ceramic, serves as the contact carrier. The mercury drop Q is disposed in the metering tube in a manner similar to that illustrated in FIG. l, with the mercury drop being retained in the connection branch between the two-section pressure chamber D which is lfilled with fluid. The common contact lead is designated by the reference letter K.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

We claim:

1. A piezoelectric relay, comprising a Ibending vibrator member of a solid piezoelectric material, means `cooperable with said vibrator member for-ming a pressure chamber at each side of said vibrator member, with the latter forming a dividing wall therebetween, the volumes of which may be altered by excitation of said vibrator member, an elongated metering passageway extending through said member operatively connecting said pressure chambers, a drop mercury disposed in said passageway, contact means disposed in said metering passageway cooperable with said mercury, whereby the latter, in one position in the passageway is operable to connect said contacts, and when in another position in said passageway an inert iiuid disposed in both said chambers operative to transmit pressure changes therein, responsive to alterations in the volumes of said chambers, to said mercury drop for effecting movement of the latter in said passageway.

2. A piezoelectric relay according to claim 1, wherein said vibrator is in the form of a circular disk and said metering passageway is centered therein.

3. A piezoelectric relay according to claim 1, wherein an electrically non-conductive fluid is disposed in the respective chambers.

4. A piezoelectric relay according to claim 1, comprising in further combination, a ne mesh screen disposed at each end of said metering passageway, which, for said uid, represents an insignificant mechanical resistance, 1but a large resistance for said mercury drop, to restrict movement of the latter out of the ends of said passageway.

5. A piezoelectric relay according to claim 1, wherein the effective cross sectional area of said metering passageway, at the ends thereof, is less than at an intermediate portion of the passageway.

6. A piezoelectric relay, comprising a bending vibrator, means `cooperable with said vibrator forming a pressure chamber the volume of which may be altered by excitation of said vibrator, a metering passageway operatively connected with said pressure chamber, a drop of mercury disposed in said passageway, contact means disposed in said metering passageway cooperable with said mercury, whereby the latter, in one position in the passageway is operable to connect said contacts, and when in another position in said passageway is operable to open said contacts, and a fluid disposed in said chamber operative to transmit pressure changes therein, responsive to alterations in the volume of said chamber, to said mercury drop for eiecting movement of the latter in said passageways, said pressure chamber being divided into two sections, between which the bending vibrator is disposed, said metering passageway operatively extending between such sections for effecting a pressure compensation therebetween during excitation of the vibrator, and movement of said mercury drop as a result thereof, means for operatively separating the metering passageway and with respect to the fluid in said pressure chamber, in the form of respective membranes disposed at opposite sides of the vibrator.

7. A piezoelectric relay according to claim 1, comprising in further combination, a capillary port, formed by an opening in said vibrator, which provides a slow pressure compensation of any static pressure differential between the two pressure chambers.

8. A piezoelectric relay according to claim 1, wherein the construction components of the relay are assembled into a unitary structure, and a mass of sealing material in which said structure is encased, for promoting an improvement in temperature compensation and anchorage of the connections to said relay contacts.

9. A piezoelectric relay, comprising a bending vibrator, means cooperable with said vibrator forming a pressure chamber the volume of which may be `altered by excitation of said vibrator metering passageway operatively connected with said pressure chamber, a drop of mercury disposed in said passageway, contact means disposed in said metering passageway cooperable with said mercur-y, whereby the latter, in one position in the passageway is operable to connect said contacts, and when in another position in said passageway is operable to open said contacts, and a fluid disposed in said chamber operative to transmit pressure `changes therein, responsive to alterations in the volume of said chamber to said mercury drop for eiecting movement of the latter in said passageways said pressure chamber being divided into two sections, between which the bending vibrator is disposed, said metering passageways operatively extending between such sections for effecting a pressure compensation therebetween during excitaiton of the vibrator, and movement of said mercury drop as a result thereof, the interior of said metering passageway being provided with enlargements of spherical configuration, disposed to contain said drop of mercury when it is in its respective operative contact closing and contact opening positions.

10. A piezoelectric relay according to claim 6, wherein said membranes are constructed as spring members of plate-like formation.

References Cited UNITED STATES PATENTS 2,203,332 6/1940 Kinsley 20G-181 XR 2,851,618 9/1958 Krawinkel 200-181 XR 2,883,486 4/1959 Mason 20G-181 ROBERT K. SCHAEFER, Primary Examiner.

H. BURKS, Assistant Examiner.

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