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Piezoelectric ceramic switching devices and systems and method of making the same |
| RE33691 |
Piezoelectric ceramic switching devices and systems and method of making the same
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| Patent Drawings: | |
| Inventor: |
Harnden, Jr., et al. |
| Date Issued: |
September 17, 1991 |
| Application: |
07/361,843 |
| Filed: |
June 1, 1989 |
| Inventors: |
Harnden, Jr.; John D. (Schenectady, NY)
Kornrumpf; William P. (Albany, NY)
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| Assignee: |
General Electric Company (Fort Wayne, IN) |
| Primary Examiner: |
Budd; Mark O. |
| Assistant Examiner: |
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| Attorney Or Agent: |
Krisher, Jr.; Ralph E. |
| U.S. Class: |
200/181; 310/317; 310/319; 310/332; 310/358; 310/366 |
| Field Of Search: |
; 310/330; 310/331; 310/332; 310/340; 310/344; 310/357; 310/358; 310/359; 310/367; 310/368; 200/181 |
| International Class: |
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| U.S Patent Documents: |
2166763; 2471967; 2479926; 2633543; 2714642; 3500451; 3622815; 3794410; 4093883; 4237399; 4392074; 4443729; 4538087; 4553061; 4654553 |
| Foreign Patent Documents: |
273157; 970817; 2537760; 2852795; 69545; 32456; 0175777; 0222976; 961606 |
| Other References: |
Electronic Engineering, by P. Kleinschmidt, "A Piezoelectric Ceramic Touch-Operated Button", Aug. 1975, pp. 9 and 11..
Guntersdorfer, M. et al., "Application for Piezoceramics in Relays" Electrocomponent Science and Technology, vol. 3, 1976, pp. 1-11.. |
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| Abstract: |
Improved piezoelectric ceramic switching devices are described along with their .[.method.]. .Iadd.methods .Iaddend.of fabrication. In addition to the devices themselves, novel electric circuits are described for the energization as well as the use of such devices as switching elements in electrical systems. Parts of both the energization circuits and/or utilization circuits employing the piezo ceramic switching device are physically mounted on and supported by non-polarized parts of the piezoelectric ceramic plate elements comprising the switching devices so that lightweight compact construction is achieved along with substantial reduction of stray inductance intercoupling. |
| Claim: |
What is claimed is:
1. A piezoelectric ceramic switching device being operated as a normally-open three-position switch including in combination at least one piezoelectric ceramic bender-typeswitching device having movable contacts that is positioned between a pair of fixed contacts to close one of said fixed contacts upon selective energization of said bender-type switching device producing movement in the direction of said fixed.[.contact.]. .Iadd.contacts .Iaddend.whereas the other of said fixed contacts is closed upon successive selective energization of said bender-type switching device causing movement in the opposite direction toward said other fixed .[.contact.]. .Iadd.contacts .Iaddend.and with both of said fixed contacts being opened by return movement of said bender-type switching device to its original unenergized position when energization of said bender-type switching device is discontinued, saidpiezoelectric ceramic bender-type switching device having a piezoceramic bender member comprised by at least two .[.planer.]. .Iadd.planar .Iaddend.selectively prepoled piezoelectric plate elements secured in opposed parallel relationship sandwichfashion on opposite sides of at least one central conductive surface and having respective outer conductive surfaces that are insulated from each other and the central conductive surface by the respective intervening piezoelectric plate element.[.thickness.]. .Iadd.thicknesses, .Iaddend.said piezoceramic bender member further including movable contacts which coact with the fixed contacts to open and close the electrical switch contacts of said piezoelectric ceramic switching device, clampingmeans securing a different non-poled portion of the piezoelectric ceramic plate elements adjacent to and mechanically supporting the selectively prepoled movable bender portion in a cantilever manner for opening and closing said coacting fixed contacts,the different non-poled portion of the piezoelectric ceramic plate elements disposed under said clamping means remaining non-movable as being mechanically unstrained and electrically neutral, and switch energization circuit means operatively associatedwith said piezoelectric ceramic bender-type switching device which selectively applies a source of bender energization potential to the prepoled .[.moveable.]. .Iadd.movable .Iaddend.bender portion of each prepoled piezoelectric plate element in asuccessive manner and having the same polarity as the polarity of the prepoled electric field previously permanently induced in said prepoled movable bender portions so that no depolarization of the piezoelectric plate elements occurs during successiveoperations of the piezoelectric ceramic bender-type switching device.
2. A piezoelectric ceramic switching device according to claim 1 wherein the different portions of the piezoelectric ceramic plate elements disposed under said clamping means have the outer conductive surfaces thereof removed from the portionsdisposed under the clamping means and wherein said central and outer conductive surfaces are selectively formed following fabrication of the planar piezoelectric plate elements to desired size with the side edges of the conductive surfaces being recessedrelative to the side edges of the piezoelectric ceramic plate elements to thereby provide increased voltage stress withstandability around the side edges of the piezoceramic bender member.
3. A piezoelectric ceramic switching device according to claim 1 further including a conformal electrically insulating protective coating covering at least some of the outer surfaces of the prepoled movable portion of the bender-typepiezoelectric device.
4. A piezoelectric ceramic switching device according to claim 3 wherein the conformal electrically insulating protective coating comprises a polyimide siloxane copolymer.
5. A piezoelectric ceramic switching device according to either of claims 3 or 4 wherein the conformal electrically insulating coating extends over and covers the outer planar conductive surfaces and .[.their.]. .Iadd.the .Iaddend.edges of theprepoled planar piezoelectric ceramic plate elements, and further extends over and covers the side edges of the piezoelectric plate elements and the central conductive surface sandwiched therebetween at least over the prepoled portions of the device.
6. A piezoelectric ceramic switching device according to claim 2 further including a conformal electrically insulating coating .Iadd.which .Iaddend.extends over and covers the outer planar conductive surfaces and .[.their.]. .Iadd.the.Iaddend.edges of the prepoled planar piezoelectric ceramic plate elements, and further extends over and covers the side edges of the piezoelectric plate elements and the central conductive surface sandwiched therebetween at least over the prepolarizedportions of the device and wherein the conformal insulating coating covering the outer planar conductive surfaces of the prepoled portions of the piezoelectric plate elements also extends down to and covers the portions of the piezoelectric plateelements exposed by the removal of the outer conductive surfaces thereon as well as the edge portions of the outer conductive surfaces exposed by such removal.
7. A piezoelectric ceramic switching circuit employing a piezoelectric ceramic switching device according to claim 1 and further including respective switch energization circuit means connected in circuit relationship across respective ones ofthe prepolarized piezoelectric plate elements of the piezoelectric bender-type switching device for selectively closing or opening respective ones of sets of coacting electrical switch contacts for controlling electric current supplied to a load withopening and closing of the contacts, said switch energization circuit means comprising a source of bender energization potential, normally open low power rated user operated electric switch means, current limiting resistor means and diode rectifiercircuit means poled to provide an electric energization potential having the same polarity as the polarity of the prepoling potential used to polarize the prepoled piezoelectric plate elements of the bender-type piezoelectric switching device, allconnected in series circuit relation with a respective one of the prepoled piezoelectric plate elements of the bender-type piezoelectric switch upon closure of the normally open low power rated user's switch, whereby the respective prepolarizedpiezoelectric plate element of the bender-type piezoelectric switch selectively and respectively can be excited with a direct current excitation field which always has the same polarity as the prepoling electric field previously permanently induced inthe respective piezoelectric plate element and no depolarization of the piezoelectric plate element occurs during successive operations of the piezoelectric bender-type switching device to close or open the load current controlling electric switchcontacts.
8. A piezoelectric ceramic switching circuit according to claim 7 further including normally-closed electric switch means connected in parallel circuit relationship with a respective piezoelectric plate element for electrically discharging thesame and means interconnecting the normally-closed electric switch means with the normally-open low power rated user operated electric switch means for energizing the respective piezoelectric plate element whereby upon closure of the normally-open useroperated switch means the interconnected normally-closed electric switch means connected in parallel with the respective piezoelectric plate element to be energized automatically is opened to allow energization of the respective piezoelectric plateelement.
9. A piezoelectric ceramic switching circuit employing a piezoelectric ceramic switching device according to claim 1 and further including respective switch energization circuit means connected in circuit relationship across respective ones ofthe prepolarized piezoelectric plate elements of the piezoelectric bender-type switching device for selectively closing or opening respective ones of sets of coacting electrical switch contacts for controlling electric current supplied to a load withopening and closing of the contacts, said switch energization circuit means comprising a source of bender energization potential, normally open low power rated user operated electric switch means, current limiting resistor means and diode rectifiercircuit means poled to provide an electric energization potential having the same polarity as the polarity of the prepoling potential used to polarize the prepoled piezoelectric plate elements of the piezoelectric bender-type switching device, allconnected in series circuit relation across a respective one of the prepoled piezoelectric plate elements of the bender-type switch upon closure of the normally open low power rated user's switch, whereby the respective prepolarized piezoelectric plateelement of the bender-type piezoelectric switch selectively and respectively can be excited with a direct current excitation field which always has the same polarity as the prepoling electric field previously permanently induced in the respectivepiezoelectric plate element and no depolarization of the piezoelectric plate element occurs during successive operations of the piezoelectric bender-type device to close or open the load current controlling electric switch contacts.Iadd., .Iaddend.andsnubber circuit means comprising a series connected resistor and capacitor connected in parallel circuit relationship across the load current controlling electrical switch contacts opened and closed by the bender-type piezoelectric switching device uponenergization of a respective prepolarized piezoelectric plate element, and snubber circuit means being formed by a passive resistor element mounted on an unpolarized piezoelectric plate element portion of the bender-type piezoelectric switching deviceand electrically interconnected with a capacitor formed by at least a part of such unpolarized piezoelectric plate element portion.
10. A piezoelectric ceramic switching circuit employing a piezoelectric ceramic switching device according to claim 6 and further including respective switch energization circuit means connected in circuit relationship across respective ones ofthe prepolarized piezoelectric plate elements of the piezoelectric bender-type switching device for selectively closing or opening respective ones of sets of coacting electrical switch contacts for controlling electric current supplied to a load withopening and closing of the contacts, said switch energization circuit means comprising a source of bender energization potential, normally open low power rated user operated electric switch means, current limiting resistor means and diode rectifiercircuit means poled to provide an electric energization potential having the same polarity as the polarity of the prepoling potential used to polarize the prepoled piezoelectric plate elements of the piezoelectric bender-type switching device, allconnected in series circuit relation across a respective one of the prepoled piezoelectric plate elements of the bender switch upon closure of the normally open low power rated user's switch, whereby the respective prepolarized piezoelectric plateelement of the bender-type piezoelectric switch selectively and respectively can be excited with a direct current excitation field which always has the same polarity as the prepoling electric field previously permanently induced in the respectivepiezoelectric plate element and no depolarization of the piezoelectric plate element occurs during successive operations of the piezoelectric bender device to close or open the load current controlling electric switch contacts.
11. A piezoelectric ceramic switching circuit according to claim 10 further including normally-closed electric switch means connected in parallel circuit relationship with a respective piezoelectric plate element for electrically discharging thesame and means interconnecting the normally-closed electric switch means with the normally-open low power rated user operated electric switch means for energizing the respective piezoelectric plate element whereby upon closure of the normally-open useroperated switch means the interconnected normally-closed electric switch means connected in parallel with the respective piezoelectric plate element to be energized automatically is opened to allow energization of the respective piezoelectric plateelement.
12. A piezoelectric ceramic switching circuit according to claim 11 further including snubber circuit means comprising a series connected resistor and capacitor connected in parallel circuit relationship across the load current controllingelectric switch contacts opened and closed by the bender-type piezoelectric switching device upon energization of a respective prepolarized piezoelectric plate element, said snubber circuit means being formed by a passive resistor element mounted on anunpolarized piezoelectric plate element portion of the bender-type piezoelectric switching device and electrically interconnected with a capacitor formed by at least a part of such unpolarized piezoelectric plate element portion.
13. A piezoelectric ceramic switching circuit according to claim 7 wherein said diode rectifier circuit means also comprises multiplier circuit means for increasing the value of the energization voltage to a level suitable for actuating thepiezoelectric bender type switching device.
14. A piezoelectric ceramic switching circuit according to claim 12 wherein said diode rectifier circuit means also comprises multiplier circuit means for increasing the value of the energization voltage to a level suitable for actuating thepiezoelectric bender-type switching device.
15. A piezoelectric ceramic switching circuit according to claim 7 wherein said sets of coacting electrical switch contacts each comprise a first electrical contact means electrically connected to and supplied with electric charge stored in arespective piezoelectric plate element also acting as a capacitor and second electrical contact means connected to and supplying gate current to a gated power semiconductor switch such as an SCR, triac or transistor whereby upon selective energization ofthe respective piezoelectric plate element, the prepoled movable bender portion of the switching device closes the first and second electrical contact means momentarily and a sufficient electric current pulse is discharged from the respectivepiezoelectric plate element into the gate of the gated power semiconductor switch to cause it to .[.turn-on.]. .Iadd.turn on. .Iaddend.
16. A piezoelectric ceramic switching circuit according to claim 12 wherein said sets of coacting electrical switch contacts each comprise a first electrical contact means electrically connected to and supplied with electric charge stored in arespective piezoelectric plate element acting also as a capacitor and second electrical contact means connected to and supplying gate current to a gated power semiconductor switch such as an SCR, triac or transistor whereby upon selective energization ofthe respective piezoelectric plate element, the prepoled movable bender portion of the switching device closes the first and second electrical contact means momentarily and a sufficient electric current pulse is discharged from the respectivepiezoelectric plate element into the gate of the gated power semiconductor switch to cause it to .[.turn-on.]. .Iadd.turn on. .Iaddend.
17. A piezoelectric ceramic switching circuit according to claim 14 wherein said sets of coacting electrical switch contacts each comprise a first electrical contact means electrically connected to and supplied with electric charge stored in arespective piezoelectric plate element acting also as a capacitor and second electrical contact means connected to and supplying gate current to a gated power semiconductor switch such as an SCR, triac or transistor whereby upon selective energization ofthe respective piezoelectric plate element, the prepoled movable bender portion of the switching device closes the first and second electrical contact means momentarily and a sufficient electric current pulse is discharged from the respectivepiezoelectric plate element into the gate of the gated power semiconductor switch to cause it to .[.turn-on.]. .Iadd.turn on. .Iaddend.
18. A piezoelectric ceramic switching device according to claim 1 wherein the central conductive surface comprises two separate adjacent inner conductive metal foil elements each separately secured to a respective one of the planar piezoelectricplate elements with the planar piezoelectric plate elements being physically secured together by a thin adhesive layer disposed between the adjacent inner conductive surfaces of said foil elements.
19. A piezoelectric ceramic switching device according to claim 18 wherein the thin adhesive layer is electrically insulating and separate terminal tabs are provided to respective ones of the adjacent inner conductive surfaces.
20. A piezoelectric ceramic switching device according to claim 18 wherein the thin adhesive layer is electrically conductive and the inner adjacent conductive surfaces share a common terminal tab.
21. A piezoelectric ceramic switching device according to claim 8 wherein the different portion of the piezoelectric plate elements disposed under said clamping means have the outer conductive surfaces removed from the portion disposed under theclamping means.
22. A piezoelectric ceramic switching device according to claim 21 further including a conformal electrically insulating protective coating covering at least some of the outer surfaces of the prepoled bender member movable portion of thepiezoelectric ceramic bender-type switching device and wherein the conformal electrically insulating protective coating comprises a polyimide siloxane copolymer.
23. A piezoelectric ceramic switching device according to claim 22 wherein the conformal electrically insulating coating extends over and covers the outer planar conductive surfaces and the side edges of the prepoled planar piezoelectric plateelements, and further extends over and covers the side edges of the piezoelectric plate elements and the central conductive surface sandwiched therebetween at least over the prepoled portions portion of the device and wherein the conformal insulatingcoating covering the outer planar conductive surfaces of the prepoled portions of the piezoelectric plate elements also extends down to and covers the portions of the piezoelectric plate elements exposed by the removal of the outer conductive surfacesthereon as well as the edge portions of the outer conductive surfaces exposed by such removal.
24. A piezoelectric ceramic switching device according to claim 23 wherein the device further includes unpoled piezoelectric plate element portions extending beyond the clamped portion thereof in a direction opposite from the prepoled movablebender portion and wherein the further unpoled piezoelectric plate element portions between the respective outer conductive surfaces and the central conductive surface form capacitors having any desired capacitance value in the range of tenths of amicrofarad dependent on power rating and .[.useable.]. .Iadd.usable .Iaddend.as circuit components in an electrical circuit for controlling operation of the piezoelectric bender-type switching device or otherwise.
25. A piezoelectric ceramic switching device according to claim 24 further including additional electrical circuit components comprising either active semiconductor devices or passive circuit elements or both fabricated either in discrete,hybrid or monolithic integrated circuit form physically formed on and/or supported by the unpoled piezoelectric plate element portions extending beyond the clamping means and also including preformed conductive pathways selectively formed by appropriatefabrication of the conductive surfaces on the unpoled piezoelectric plate element portions to interconnect the active devices and/or passive circuit elements.
26. A piezoelectric ceramic switching device according to claim .[.25.]. .Iadd.1 .Iaddend.further including a relatively thin inflexible stiffening member secured widthwise across the free movable end of the prepoled movable bender portion ofthe bender-type piezoelectric switching device.
27. A piezoelectric ceramic switching device according to either of claims 1 6, 18, 22 or 26 wherein the set of coacting electrical switch contacts opened and closed by the movable bender member are fabricated from a copper-vanadium alloy.
28. A piezoelectric ceramic switching circuit according to either of claims 1, 6, 18, 22 or 26 wherein the bender-type piezoelectric drive member can be made to operate to either side of a center position normally assumed with the bender memberin an unexcited condition whereby the bender member can coact with two different sets of make and break electrical contacts disposed on opposite sides of the bender member for selectively making or breaking at least two different and separateelectrically conductive paths extending through the respective sets of contacts.
29. A piezoelectric ceramic switching circuit according to either of .[.claim.]. .Iadd.claims .Iaddend.1, 6, 18, 22 or 26 wherein the bender type piezoelectric drive member can coact with two different sets of .[.moveable.]. .Iadd.movable.Iaddend.make and break electrical contacts disposed on opposite sides of the bender member for selectively making or breaking at least two different and separate electrically conductive paths extending through the respective sets of movable and fixedcontacts, wherein each set of coacting movable and fixed contacts opened and closed by the movable bender member are fabricated from a copper-vanadium alloy.
30. A piezoelectric ceramic switching device according to either of .[.claim.]. .Iadd.claims .Iaddend.1, 6, 18, 22 or 26 wherein the piezoelectric plate element portions comprising the prepolarized movable bender member portion of the deviceare prepolarized in place after assemblage of the switching device into a complete structure.
31. A piezoelectric ceramic switching circuit according to claim 1 wherein the bender-type piezoelectric drive member can coact with two different sets of movable make and break electrical contacts .[.desposed.]. .Iadd.disposed .Iaddend.onopposite sides of the bender member for selectively making or breaking at least two different and separate electrically conductive paths extending through the .[.repective.]. .Iadd.respective .Iaddend.sets of movable and fixed contacts wherein each setof coacting movable and fixed contacts opened and closed by the movable bender member are fabricated from a copper-vanadium alloy, and wherein the piezoelectric plate element portions comprising the prepolarized movable bender member portion of thedevice are prepolarized in place after assemblage of the switching device into a complete structure.
32. A piezoelectric ceramic switching circuit according to claim 26 wherein the bender-type piezoelectric drive member can be made to operate to either side of a center position normally assumed with the bender member in an unexcited conditionwhereby the bender member can coact with two different sets of make and break electrical contacts disposed on opposite sides of the bender member for selectively making or breaking at least two different and separate electrically conductive pathsextending through the respective sets of contacts, wherein the set of coacting electrical switch contacts opened and closed by the movable bender member are fabricated from a copper-vanadium alloy, and wherein the piezoelectric plate element portionscomprising the prepolarized movable bender member portion of the device are prepolarized in place after assemblage of the switching device into a complete structure.
33. A piezoelectric ceramic switching circuit according to claim 1 wherein the selectively operable electric excitation circuit means comprises respective switch energization circuit means connected in circuit relationship across respective onesof the selectively prepolarized piezoelectric plate element of the piezoelectric ceramic bender-type switching device for .[.selectively.]. .Iadd.selectrively .Iaddend.closing or opening respective ones of sets of coacting movable and fixed contacts forcontrolling electric current supplied to a load with opening and closing of the contacts, said switch energization circuit means comprising a source of bender energization potential, normally open low power rated user operated electric switch means,current limiting resistor means and diode rectifier circuit means poled to provide an electric energization potential having the same polarity as the polarity of the prepoling potential used to selectively polarize the prepoled piezoelectric plateelements of the piezoelectric bender-type switching device, all connected in series circuit relationship with a respective one of the selectively prepoled piezoelectric plate elements of the bender-type switch upon closure of the normally open low powerrated user's switch whereby the respective prepolarized piezoelectric plate element of the bender-type piezoelectric switch selectively and respectively can be excited with a direct current excitation field to close or open the load current controllingelectric switch contacts.
34. A piezoelectric ceramic switching circuit according to claim 33 further including normally-closed electric switch means connected in parallel circuit relationship with a respective piezoelectric plate element for electrically discharging thesame and means interconnecting the normally-closed electric switch means with the normally-open low power rated user operated electric switch means for energizing the respective piezoelectric plate element whereby upon closure of the normally-open useroperated switch means the interconnected normally-closed electric switch means connected in parallel with the respective piezoelectric plate element to be energized automatically is opened to allow energization of the respective piezoelectric plateelement.
35. A piezoelectric ceramic switching circuit according to claim 34 further including snubber circuit means comprising a series connected resistor and capacitor connected in parallel circuit relationship across the load current controllingelectrical switch contacts opened and closed by the bender-type piezoelectric switching device upon energization of a respective prepolarized piezoelectric plate element, said snubber circuit means being formed by a passive resistor element mounted on anunpolarized piezoelectric plate element portion of the bender-type piezoelectric switching device and electrically interconnected with a capacitor formed by at least a part of such unpolarized piezoelectric plate element portion.
36. A piezoelectric ceramic switching device according to claim 35 wherein said diode rectifier circuit means also comprises multiplier circuit means for increasing the value of the energization voltage to a level suitable for actuating thepiezoelectric bimorph bender switching device.
37. A piezoelectric ceramic switching circuit according to claim 35 wherein said sets of coacting electrical switch contacts each comprise a first electrical contact means electrically connected to and supplied with electric charge stored in arespective piezoelectric plate element also acting as a capacitor and second electrical contact means connected to and supplying gate current to a gated power semiconductor switch such as an SCR, triac or transistor whereby upon selective energization ofthe respective piezoelectric plate element, the prepoled movable bender portion of the switching device closes the first and second electrical contact means momentarily and a sufficient electric current pulse is discharged from the respectivepiezoelectric plate element into the gate of the gated power semiconductor switch to .[.caus.]. .Iadd.cause .Iaddend.it to .[.turn-on.]. .Iadd.turn on. .Iaddend.
38. A piezoelectric ceramic switching .[.circuit.]. .Iadd.device .Iaddend.according to claim .[.35.]. .Iadd.36 .Iaddend.wherein said sets of coacting electrical switch contacts each comprise a first electrical contact means electricallyconnected to and supplied with electric charge stored in a respective piezoelectric plate element also acting as a capacitor and second electrical contact means connected to and supplying gate current to a gated power semiconductor switch such as an SCR,triac or transistor whereby upon selective energization of the respective piezoelectric plate element, the prepoled movable bender portion of the switching device closes the first and second electrical contact means momentarily and a sufficient electriccurrent pulse is discharged from the respective piezoelectric plate element into the gate of the gated power semiconductor switch to cause it to .[.turn-on.]. .Iadd.turn on. .Iaddend.
39. A piezoelectric ceramic switching device according to claim 36 further including a conformal electrically insulating protective coating covering at least some of the outer surfaces of the prepoled bender member movable portion of thepiezoelectric ceramic bender-type switch device with the conformal electrically insulating protective coating comprising a polyimide siloxane copolymer, and wherein the conformal electrically insulating coating extends over the side edges of the prepoledplanar piezoelectric plate elements, and further extends over and covers the side edges of the piezoelectric plate elements and the central conductive surface sandwiched therebetween at least over the prepoled portions portion of the device and whereinthe conformal insulating coating covering the outer planar conductive surfaces of the prepoled portions of the piezoelectric plate elements also extends down to and covers the portions of the piezoelectric plate elements exposed by the removal of theouter conductive surfaces thereon as well as the edge portions of the outer conductive surfaces exposed by such removal.
40. A piezoelectric ceramic switching device including in combination at least one piezoelectric ceramic bender-type switching device having a piezoceramic bender member comprised by at least two planar prepoled piezoelectric plate elementssecured in opposed parallel relationship sandwich fashion on opposite sides of at least one central conductive surface and having respective outer conductive surfaces that are insulated from each other and the central conductive surface by the respectiveintervening piezoelectric plate element thicknesses, said bender-type piezoelectric switching device further including at least one set of coacting electrical switch contacts opened and closed by a prepolarized movable bender member of the piezoelectricceramic switching device, and a conformal electrically insulating protective coating covering at least some of the outer surfaces of the prepoled bender member movable portion of the piezoelectric ceramic bender-type switching device, the conformalelectrically insulating protective coating comprising a polyimide siloxane copolymer, and extending over and covering the outer planar conductive surfaces and the side edges of the prepoled planar piezoelectric plate elements, and further extending overand covering the side edges of the prepoled piezoelectric plate elements and the central conductive surface sandwiched therebetween at least over the prepoled portions of the bender member and also extending down to and covering the portions of theprepoled piezoelectric plate elements exposed by the removal of the outer conductive surfaces thereon as well as the edge portions of the outer conductive surfaces exposed by such removal. .Iadd.
41. Electrical switching apparatus comprising
(a) at least one piezoelectric ceramic bender-type switching device having a movable piezoceramic bender member, said bender member having at least two planar piezoceramic plate elements secured in opposed parallel relationship sandwich fashionon opposite sides of at least one central conductive surface and having respective outer conductive surfaces that are insulated from each other and the central conductive surface by the respective intervening piezoceramic plate element thicknesses,
(b) said piezoelectric ceramic bender-type switching device further including at least one set of coacting electrical switch contacts opened and closed by the movable bender member of the piezoelectric ceramic switching device,
(c) clamping means securing the piezoceramic plate elements together and mechanically supporting the movable bender member in a cantilever manner for opening and closing said set of coacting electrical contacts, and
(d) selectively operable electric excitation circuit means connected to the piezoelectric ceramic bender-type switching device for selectively and respectively actuating each piezoceramic plate element thereof with a direct current energizingpotential which is applied in the same direction employed to produce initial polarization in the respective plate elements,
(e) the electric excitation circuit means being connected in circuit relationship across the respective ones of the piezoceramic plate elements of the piezoelectric ceramic bender-type switching device for selectively closing or opening the setof coacting electrical switch contacts to control electric current being supplied through a load by the opening and closing of the switch contacts. .Iaddend. .Iadd.42. The piezoceramic switching means of claim 41 wherein the movable bender memberincludes coacting electrical switch contacts disposed on opposite sides to selectively make or break at least two separate electrically conductive paths extending through the respective sets of contacts. .Iaddend. .Iadd.43. The piezoceramic switchingmeans of claim 41 wherein the electrical excitation circuit means includes multiplier circuit means for increasing the value of the direct current energizing potential to a level suitable for actuating the piezoelectric ceramic bender-type switchingdevice. .Iaddend. .Iadd.44. The piezoceramic switching means of claim 41 which further includes circuit means to prevent excess arcing across the coacting electrical contacts when opened to interrupt the electrical
current being supplied through a load. .Iaddend. .Iadd.45. A switching device operable as a normally-open three-position switch comprising:
at least one movable piezoelectric bender member having two planar piezoelectric plate elements secured in sandwich fashion on opposite sides of at least one central conductive surface;
an outer conductive surface extending at least over a movable bender portion of said bender member and secured to each of said plate elements so that said outer conductive surfaces are insulated from each other and said central conductive surfaceby said plate elements, each said outer conductive surface having at least one movable contact means operatively secured thereto;
clamping means for clamping a non-bending portion of said bender member located adjacent to and mechanically supporting said bender portion in a cantilever manner;
said non-bending portion disposed under said clamping means remaining non-movable and being electrically isolated from said conductive surfaces;
a first fixed contact secured adjacent one planar side of said bender portion for contact with said movable contact means when one of said plate elements is energized, and a second fixed contact secured adjacent the other planar side of saidbender portion for contact with said movable contact means when the other of said plate elements is energized; and
switch energization circuit means operatively associated with said bender member for selectively applying a direct current potential to a selected one of said plate elements on said bender portion, each successive energization of said respectiveplate elements having the same polarity so that no depolarization of said plate elements occurs during successive energizations of said plate elements;
whereby sufficient energization of one of said plate elements causes movement of said bender portion toward said first fixed contact for contacting said first fixed contact, and sufficient energization of said other plate element and sufficientdeenergization of said first plate element causes movement of said bender portion toward said second fixed contact for contacting said second fixed contact, and upon deenergization of both of said plates, said bender member is positioned so that both of
said fixed contacts are open. .Iaddend. .Iadd.46. The device of claim 45 wherein said non-bending portions of said bender member disposed under said clamping means have said outer conductive surfaces removed from the portion disposed undersaid clamping means, and wherein said central and outer conductive surfaces are selectively formed following fabrication of said plate elements to desired size, with said conductive surfaces being recessed from the side edges of said plate elements tothereby provide increased voltage stress withstandability of said bender member. .Iaddend.
.Iadd.47. The device of claim 45 further including a conformal electrically insulating protective coating covering at least some of the outer surfaces of said movable bender portion. .Iaddend. .Iadd.48. The device of claim 47 wherein saidcoating comprises a polyimide siloxane copolymer. .Iaddend. .Iadd.49. The device of either of claims 47 or 48 wherein said coating extends over and covers all of the outer surfaces of said movable bender portion. .Iaddend. .Iadd.50. The device ofclaim 46 further including a conformal electrically insulating coating which extends over all of the outer surfaces of said movable bender portion, including portions of said plate elements exposed where said outer conductive surfaces are recessed. .Iaddend. .Iadd.51. The device of claim 45 wherein
said switch energization circuit means are connected in circuit relationship across at least one of said plate elements for selectively closing or opening said first fixed contact and said movable contact means for controlling electric currentsupplied to a load with opening and closing of said first fixed contact and said movable contact means,
said switch energization circuit means including a source of bender energization potential, normally-open, low power rated, user-operated electric switch means, current limiting resistor means and diode rectifier circuit means oriented to providea selected direct current electric energization potential, all connected in series circuit relation with said plate element upon closure of said user-operated switch,
whereby said plate element can be selectively excited with a direct current excitation field which always has the same polarity, and no depolarization of said plate element occurs during successive operations of said bender
member. .Iaddend. .Iadd.52. The device of claim 51 further including
normally-closed electric switch means connected in parallel circuit relationship across said plate element for electrically discharging said plate element, and
means interconnecting said normally-closed switch means with said normally-open switch means,
whereby upon closure of said normally-open switch means said normally-closed switch means is opened to allow energization of said plate element. .Iaddend. .Iadd.53. The device of claim 45 wherein
said switch energization circuit means are connected in circuit relationship across at least one of said plate elements for selectively closing or opening said first fixed contact and said movable contact means for controlling electric currentsupplied to a load with opening and closing of said first fixed contact and said movable contact means,
said switch energization circuit means comprising a source of bender energization potential, normally-open, low power rated, user-operated electric switch means, current limiting resistor means and diode rectifier circuit means oriented toprovide a selected direct current electric energization potential, all connected in series circuit relation with said plate element upon closure of said normally-open switch,
whereby said plate element can be selectively excited with a direct current excitation field which always has the same polarity, and no depolarization of said plate element occurs during successive operations of said bender member, and
snubber circuit means including a series-connected resistor and capacitor connected in parallel circuit relationship across said first fixed contact and said movable contact means,
said snubber circuit means being formed by a passive resistor element mounted on said non-bending portion and being electrically interconnected with a capacitor formed by at least a part of one of said plate elements.
.Iaddend. .Iadd.54. The device of claim 50 wherein
said switch energization circuit means are connected in circuit relationship across at least one of said plate elements for selectively closing or opening said first fixed contact and said movable contact means for controlling electric currentsupplied to a load with opening and closing of said first fixed contact and said movable contact means,
said switch energization circuit means comprising a source of bender energization potential, normally-open, low power rated, user-.Iadd.operated electric switch means, current limiting resistor means and diode rectifier circuit means oriented toprovide a selected direct current electric energization potential, all connected in series circuit relation with said plate element upon closure of the normally-open switch,
whereby said plate element can be selectively excited with a direct current excitation field which always has the same polarity, and no depolarization of said plate element occurs during successive operations of said bender member. .Iaddend. .Iadd.55. The device of claim 54 further including
normally-closed electric switch means connected in parallel circuit relationship across said plate element for electrically discharging said plate element, and
means interconnecting said normally-closed switch means with said normally-open switch means,
whereby upon closure of said normally-opened switch means said normally-closed switch means is opened to allow energization of said plate element. .Iaddend. .Iadd.56. The device of claim 55 further comprising snubber circuit means including aseries-connected resistor and capacitor connected in parallel circuit relationship across said first fixed contact and said movable contact means, said snubber circuit means being formed by a passive resistor element mounted of said non-bending portionand being electrically interconnected with a capacitor formed by at least a part of one of said plate elements. .Iaddend. .Iadd.57. The device of claim 51 wherein said diode rectifier circuit means also comprises multiplier circuit means forincreasing the value of said energization potential to a level suitable for actuating said bender member. .Iaddend. .Iadd.58. The device of claim 56 wherein said diode rectifier circuit means also includes multiplier circuit means for increasing thevalue of the energization potential to a level suitable for actuating said bender
member. .Iaddend. .Iadd.59. The device of claim 51 further comprising
first electrical contact means electrically connected to and supplied with electric charge stored in a selected plate element also acting as a capacitor, and
second electrical contact means connected to and supplying gate current to a power semiconductor switch having a gate, such as an SCR, triac or transistor,
whereby upon selective energization of said plate element, said bender portion closes said first and second electrical contact means momentarily, and a sufficient electric current pulse is discharged from said plate element into said gate to turnon said gated switch. .Iaddend. .Iadd.60. The device of claim 56 further comprising
first electrical contact means electrically connected to and supplied with electric charge stored in both of said plate elements acting also as capacitors, and
second electrical contact means separately connected to and supplying gate current to a power semiconductor switch having a gate, such as an SCR, triac or transistor,
whereby upon selective energization of said plate elements, said bender portion closes said first and second electrical contact means momentarily, and a sufficient electric current pulse is discharged from said respective plate elements into saidgates to turn on said gated switches. .Iaddend.
.Iadd.61. The device of claim 58 further comprising
first electrical contact means electrically connected to and supplied with electric charge stored in a selected plate element acting also as a capacitor, and
second electrical contact means connected to and supplying gate current to a power semiconductor switch having a gate, such as an SCR, triac or transistor,
whereby upon selective energization of said plate element, said bender portion closes said first and second contact means momentarily, and a sufficient electric current pulse is discharged from said plate element into said gate to turn on saidgated switch. .Iaddend. .Iadd.62. The device of claim 45 wherein said central conductive surface includes two separate adjacent inner conductive metal foil elements, each separately secured to a respective one of said plate elements, with said plateelements being physically secured together by a thin adhesive layer disposed between said adjacent inner conductive elements. .Iaddend. .Iadd.63. The device of claim 62 wherein said adhesive layer is electrically insulating, and separate terminal tabsare provided to respective ones of said adjacent inner conductive elements. .Iaddend. .Iadd.64. The device of claim 62 wherein said thin adhesive layer is electrically conductive and said adjacent inner conductive elements share a common terminal tab. .Iaddend. .Iadd.65. The device of claim 52 wherein said non-bending portion of said bender member disposed under said clamping means has said outer conductive surfaces removed from said portion disposed under said clamping means. .Iaddend. .Iadd.66. The device of claim 65 further including a conformal electrically insulating protective coating covering at least some of the outer surfaces of said bender member and wherein said coating includes a polyimide siloxane copolymer. .Iaddend. .Iadd.67. The device of claim 66 wherein said coating extends over and covers all of the outer surfaces of said movable bender portion, including portions of said plate elements exposed where said outer conductive surfaces are recessed. .Iaddend. .Iadd.68. Thedevice of claim 67 further including third plate element portions extending beyond said clamped portion thereof in a direction opposite from said movable bender portion, and wherein said third plate element portions are located between said respectiveouter conductive surfaces and said central conductive surface, said third plate element portions forming capacitors having any desired capacitance value in the range of tenths of a microfarad dependent on power rating and being usable as circuitcomponents in an electrical circuit for controlling operation of the device. .Iaddend. .Iadd.69. The device of claim 68 further including additional electrical circuit components including either active semiconductor devices or passive circuitelements, or both, fabricated either in discrete, hybrid or monolithic integrated circuit form, physically formed on and/or supported by said third plate element portions which extend beyond said clamping means, and also including preformed conductivepathways selectively formed by appropriate fabrication of said conductive surfaces on said third plate element portions to interconnect said active devices and/or passive circuit elements. .Iaddend. .Iadd.70. The device of claim 45 further including arelatively thin inflexible stiffening member secured widthwise across said movable end of said movable bender portion. .Iaddend. .Iadd.71. The device of any of claims 45, 50, 62, 66 or 70 wherein said bender member can be made to operate to eitherside of a center position normally assumed with said bender portion in an unexcited condition, whereby said bender portion can coact with two different sets of make and break electrical contacts disposed on opposite sides of said bender portion forselectively making or breaking at least two different and separate electrically conductive paths extending through said respective sets of contacts. .Iaddend. .Iadd.72. The device of any of claims 45, 50, 62, 66 or 70 wherein said plate elementportions including said movable bender portion are initially polarized in place after assembly of the device. .Iaddend. .Iadd.73. The device of claim 45 wherein said bender member can coact with two different sets of movable make and break electricalcontacts disposed on opposite sides of said bender portion for selectively making or breaking at least two different and separate electrically conductive paths extending through said respective sets of movable and fixed contacts, wherein each set ofcoacting movable and fixed contacts opened and closed by said bender portion are fabricated from a copper-vanadium alloy, and wherein said plate element portions comprising said movable bender portion are initially polarized in place after assembly ofthe device. .Iaddend. .Iadd.74. The device of claim 70 wherein said bender member can be made to operate to either side of a center position normally assumed with said bender portion in an unexcited condition, whereby said bender portion can coactwith two different sets of make and break electrical contacts disposed on opposite sides of said bender portion for selectively making or breaking at least two different and separate electrically conductive paths extending through the respective sets ofcontacts, wherein said set of coacting electrical switch contacts opened and closed by said bender portion are fabricated from a copper-vanadium alloy, and wherein said plate element portions comprising said movable bender portion are initially polarizedin place after assembly of the device. .Iaddend. .Iadd.75. A piezoelectric switching device comprising:
at least one bender member including at least two planar piezoelectric plate elements secured in sandwich fashion on opposite sides of at least one central conductive surface;
an outer conductive surface secured to each of said plate elements so that said outer conductive surfaces are insulated from each other and said central conductive surface by said plate elements;
said bender member further including at least one set of coacting electrical switch contacts opened and closed by said bender member; and
a conformal electrically insulating protective coating covering at least some of the outer surfaces of said bender member, said coating including a
polyimide siloxane copolymer. .Iaddend. .Iadd.76. A piezoelectric switching device comprising:
at least one movable piezoelectric bender member having two planar piezoelectric plate elements secured in sandwich fashion on opposite sides of at least one central conductive surface;
an outer conductive surface extending at least over a movable bender portion of said bender member and secured to each of said plate elements so that said outer conductive surfaces are insulated from each other and said central conductive surfaceby said plate elements, each said outer conductive surface having at least one movable contact means operatively secured thereto;
clamping means for clamping a non-bending portion of said bender member located adjacent to and mechanically supporting said bender portion in a cantilever manner;
said non-bending portion disposed under said clamping means remaining non-movable and being electrically isolated from said conductive surfaces;
a fixed contact secured adjacent said bender portion for contact with said movable contact means when a selected one of said plate elements is energized; and
switch energization circuit means operatively associated with said bender member for selectively applying a direct current potential to said selected plate element, each successive energization of said selected plate element having the samepolarity so that no depolarization of said plate element occurs during successive energizations of said plate element;
whereby sufficient energization of said selected plate element causes movement of said bender portion toward said fixed contact for contacting said movable contact, and upon deenergization of said plate, said bender member is positioned so thatsaid fixed contacts is open. .Iaddend.
.Iadd. 7. The device of claim 76 wherein said non-bending portions of said bender member disposed under said clamping means have said outer conductive surfaces removed from the portion disposed under said clamping means, and wherein saidcentral and outer conductive surfaces are selectively formed following fabrication of said plate elements to desired size, with said conductive surfaces being recessed from the side edges of said plate elements to thereby provide increased voltage stress
withstandability of said bender member. .Iaddend. .Iadd.78. The device of claim 76 further including a conformal electrically insulating protective coating covering at least some of the outer surfaces of said movable bender portion. .Iaddend. .Iadd.79. The device of claim 78 wherein said coating comprises a polyimide siloxane copolymer. .Iaddend. .Iadd.80. The device of either of claims 78 or 79 wherein said coating extends over and covers all of the outer surfaces of saidmovable bender portion. .Iaddend. .Iadd.81. The device of claim 77 further including a conformal electrically insulating coating which extends over all of the outer surfaces of said movable bender portion, including portions of said plate elementsexposed where said outer conductive surfaces are recessed. .Iaddend. .Iadd.82. The device of claim 76 wherein
said switch energization circuit means are connected in circuit relationship across said selected plate element for selectively closing or opening said fixed contact and said movable contact means for controlling electric current supplied to aload with opening and closing of said fixed contact and said movable contact means,
said switch energization circuit means including a source of bender energization potential, normally-open, low power rated, user-operated electric switch means, current limiting resistor means and diode rectifier circuit means oriented to providea selected direct current electric energization potential, all connected in series circuit relation with said plate element upon closure of said user-operated switch,
whereby said plate element can be selectively excited with a direct current excitation field which always has the same polarity, and no depolarization of said plate element occurs during successive operations of said bender
member. .Iaddend. .Iadd.83. The device of claim 82 further including
normally-closed electric switch means connected in parallel circuit relationship across said plate element for electrically discharging said plate element, and
means interconnecting said normally-closed switch means with said normally-open switch means,
whereby upon closure of said normally-open switch means said normally-closed switch means is opened to allow energization of said plate element. .Iaddend. .Iadd.84. The device of claim 76 wherein
said switch energization circuit means are connected in circuit relationship across at least one of said plate elements for selectively closing or opening said fixed contact and said movable contact means for controlling electric current suppliedto a load with opening and closing of said fixed contact and said movable contact means,
said switch energization circuit means comprising a source of bender energization potential, normally-open, low power rated, user-operated electric switch means, current limiting resistor means and diode rectifier circuit means oriented toprovide a selected direct current electric energization potential, all connected in series circuit relation with said plate element upon closure of said normally-open switch,
whereby said plate element can be selectively excited with a direct current excitation field which always has the same polarity, and no depolarization of said plate element occurs during successive operations of said bender member, and
snubber circuit means including a series-connected resistor and capacitor connected in parallel circuit relationship across said fixed contact and said movable contact means,
said snubber circuit means being formed by a passive resistor element mounted on said non-bending portion and being electrically interconnected with a capacitor formed by at least a part of one of said plate elements.
.Iaddend. .Iadd.85. The device of claim 81 wherein
said switch energization circuit means are connected in circuit relationship across at least one of said plate elements for selectively closing or opening said fixed contact and said movable contact means for controlling electric current suppliedto a load with opening and closing of said fixed contact and said movable contact means,
said switch energization circuit means comprising a source of bender energization potential, normally-open, low power rated, user-operated electric switch means, current limiting resistor means and diode rectifier circuit means oriented toprovide a selected direct current electric energization potential, all connected in series circuit relation with said plate element upon closure of the normally-open switch,
whereby said plate element can be selectively excited with a direct current excitation field which always has the same polarity, and no depolarization of said plate element occurs during successive operations of said bender member. .Iaddend. .Iadd.86. The device of claim 85 further including
normally-closed electric switch means connected in parallel circuit relationship across said plate element for electrically discharging said plate element, and
means interconnecting said normally-closed switch means with said normally-open switch means,
whereby upon closure of said normally-opened switch means said normally-closed switch means is opened to allow energization of said plate element. .Iaddend. .Iadd.87. The device of claim 86 further comprising snubber circuit means including aseries-connected resistor and capacitor connected in parallel circuit relationship across said fixed contact and said movable contact means, said snubber circuit means being formed by a passive resistor element mounted on said non-bending portion andbeing electrically interconnected with a capacitor formed by at least a part of one of said plate elements. .Iaddend. .Iadd.88. The device of claim 82 wherein said diode rectifier circuit means also comprises multiplier circuit means for increasingthe value of said energization potential to a level suitable for actuating said bender member. .Iaddend. .Iadd.89. The device of claim 87 wherein said diode rectifier circuit means also includes multiplier circuit means for increasing the value ofsaid energization potential to a level suitable for actuating said bender
member. .Iaddend. .Iadd.90. The device of claim 82 further comprising
first electrical contact means electrically connected to and supplied with electric charge stored in a second selected plate element also acting as a capacitor, and
second electrical contact means connected to and supplying gate current to a power semiconductor switch having a gate, such as an SCR, triac or transistor,
whereby upon selective energization of said selected plate element, said bender portion closes said first and second electrical contact means momentarily, and a sufficient electric current pulse is discharged from said selected plate element intosaid gate to turn on said gated switch. .Iaddend. .Iadd.91. The device of claim 87 further comprising
first electrical contact means electrically connected to and supplied with electric charge stored in both of said plate elements acting also as capacitors, and
second electrical contact means separately connected to and supplying gate current to a power semiconductor switch having a gate, such as an SCR, triac or transistor,
whereby upon selective energization of said selected plate element, said bender portion closes said first and second electrical contact means momentarily, and a sufficient electric current pulse is discharged from said respective plate elementsinto said gates to turn on said gated
switches. .Iaddend. .Iadd.92. The device of claim 89 further comprising
first electrical contact means electrically connected to and supplied with electric charge stored in a second selected plate element acting also as a capacitor, and
second electrical contact means connected to and supplying gate current to a power semiconductor switch having a gate, such as an SCR, triac or transistor,
whereby upon selective energization of said second selected plate element, said bender portion closes said first and second contact means momentarily, and a sufficient electric current pulse is discharged from said plate element into said gate toturn on said gated switch. .Iaddend. .Iadd.93. The device of claim 76 wherein said central conductive surface includes two separate adjacent inner conductive metal foil elements, each separately secured to a respective one of said plate elements, withsaid plate elements being physically secured together by a thin adhesive layer disposed between said adjacent inner conductive elements. .Iaddend. .Iadd.94. The device of claim 93 wherein said adhesive layer is electrically insulating, and separateterminal tabs are provided to respective ones of said adjacent inner conductive elements. .Iaddend. .Iadd.95. The device of claim 93 wherein said thin adhesive layer is electrically conductive and said adjacent inner conductive elements share a commonterminal tab. .Iaddend. .Iadd.96. The device of claim 83 wherein said non-bending portion of said bender member disposed under said clamping means has said outer conductive surfaces removed from said portion disposed under said clamping means. .Iaddend. .Iadd.97. The device of claim 96 further including a conformal electrically insulating protective coating covering at least some of the outer surfaces of said bender and wherein said coating includes a polyimide siloxane copolymer. .Iaddend. .Iadd.98. The device of claim 97 wherein said coating extends over and covers all of the outer surfaces of said movable bender portion, including portions of said plate elements exposed where said outer conductive surfaces are recessed. .Iaddend. .Iadd.99. The device of claim 98 further including third plate element portions extending beyond said clamped portion thereof in a direction opposite from said movable bender portion, and wherein said third plate element portions are located betweensaid respective outer conductive surfaces and said central conductive surface, said third plate element portions forming capacitors having any desired capacitance value in the range of tenths of a microfarad dependent on power rating and being usable ascircuit components in an electrical circuit for controlling operation of the device. .Iaddend. .Iadd.100. The device of claim 99 further including additional electrical circuit components including either active semiconductor devices or passivecircuit elements, or both, fabricated either in discrete, hybrid or monolithic integrated circuit form, physically formed on and/or supported by said third plate element portions which extend beyond said clamping means, and also including preformedconductive pathways selectively formed by appropriate fabrication of said conductive surfaces on said third plate element portions to interconnect said active devices and/or passive circuit elements. .Iaddend. .Iadd.101. The device of claim 76 furtherincluding a relatively thin inflexible stiffening member secured widthwise across said movable end of said movable bender portion. .Iaddend. .Iadd.102. The device of any of claims 76, 81, 93, 97 or 101 wherein said plate element portions includingsaid movable bender portion are initially polarized in place after assembly of the device. .Iaddend. |
| Description: |
TECHNICAL FIELD
This invention relates to improved piezoelectric ceramic switching devices and to novel electrical systems for the energization, control and utilization of such devices.
More particularly, the invention relates to improved piezoelectric ceramic switching devices, their fabrication, and to novel electrical circuits for the energization as well as use of such improved devices as switching elements in electricalsystems, some parts of which may be physically mounted on and supported by the improved piezoelectric ceramic switching devices themselves.
BACKGROUND PRIOR ART PROBLEM
In conventional electrical circuits, electrical relays and switches are employed at points in such circuits where it is desired either to initiate or interrupt (or both) electric current flow through the circuit. In the past, electromagneticsolenoid operated switches and relays have been employed to either close or open the contacts of a power switch or relay in response to a small control signal (low voltage, low current) which initiates either closure or opening of the .[.contact.]. .Iadd.contacts .Iaddend.of a larger power rated switch that thereafter controls current flow through the contacts to a circuit being supplied via the switch contacts.
Relays and switches which are piezoelectric drive elements have a number of advantages over their electromagnetic counterparts. For example, a piezoelectric driven relay or switch requires substantially lower current and dissipates very littlepower during operation to open or close a set of contacts in comparison to an electromagnetic driven device of the same rating. Additionally, piezoelectric driven switching devices have very low mass and therefore require less space and introduce lessweight into circuit systems with which they are used. Additionally, piezoelectric driven switching devices possess very short actuation times. Thus, fast acting switching is possible with smaller and lower weight devices that dissipate less power andhence can operate with lower temperature rises if piezoelectric ceramic switching devices are used.
Piezoelectric plate elements may be fabricated from a number of different polycrystalline ceramic materials such as barium titanate, lead zirconate titanate, lead metaniobate and the like which are precast and fired in a desired shape, such as arectangular-shaped plate. Electrically conducting surfaces in the form of .[.metalized.]. .Iadd.metallized .Iaddend.electrodes usually are deposited on the surface of the plates which then are used to apply a polarizing voltage across the piezoceramicplate in order to make them piezoelectric in a chosen polar direction by a prepoling treatment which involves exposing the ceramic plates to a high electric field applied across the metalized electrode while the plates are held at a temperature not farbelow their Curie point. As a result of this prepolarizing treatment, the plate elongates in the same direction as the applied field. After cooling of the plates and removal of the prepoling field, the dipoles within the ceramic plate which werealigned as a result of the prepoling treatment, cannot easily be returned to their original position and therefore possess what is known as .[.remanent.]. .Iadd.remanent .Iaddend.polarization. Thus, the ceramic plates are made permanently piezoelectricwhereby the dipoles are permanently enhanced and can convert mechanical energy into electrical energy, and vice versa. The piezoelectric effect is described more fully in a booklet entitled "The Piezoelectric Effect in Ceramic Materials" edited by J.Van Randeraat & R. E. Setterington and published by Philips Gloeilampenfabrieken of Eindhoven, The Netherlands, second edition, dated January 1924.
In piezoelectric ceramic materials, the direction of the electrical and mechanical dipole axes depends upon the direction of the original unidirectional prepolarizing high voltage field. During the prepoling process the ceramic plate elementexperiences a permanent increase in dimension between the poling electrodes and a permanent decrease in dimension parallel to the electrodes. When a DC excitation voltage of the same polarity as the prepoling voltage, but of smaller magnitude,subsequently is applied between the poling electrodes, the element experiences further but temporary expansion in the poling direction and contraction parallel to the electrodes. Conversely, when a DC excitation voltage of opposite polarity is appliedto the plate element electrodes, the plate contracts in the poling direction and expands parallel to the electrodes. In either case, the piezoelectric ceramic plate element returns to its original prepolarized dimensions when the later appliedexcitation voltage is removed from the electrodes.
A number of different piezoelectric ceramic switching devices have been offered for sale in the past having a variety of different configurations. One of the more popular, if not the prevailing structural approach employed in the past, is knownas a bimorph bender-type piezoelectric ceramic switch which employs two adjacent piezoelectric plate elements mounted side by side having conductive electrodes.[.,.]. coating their outer surfaces and sharing a common conductive inner surface to form abimorph .[.bender-typ.]. .Iadd.bender-type .Iaddend.device. A known commercially available bimorph bender-type piezoelectric ceramic switch is described in an application note copyrighted in 1978 and published by the Piezo Products Division of GultonIndustries.[.,.]. Inc. located in Metuchen, N.J. and Fullerton, Calif. If one end of such a piezoelectric ceramic bimorph bender is clamped cantilever fashion, the bender can be made to bend in either direction from its central neutral unenergizedcondition by application of an energizing potential of either polarity but lower than the prepolarizing potential to one of its conductive outer electrodes. If a suitable value energizing potential of either polarity is applied across only one of thepiezoelectric ceramic plate elements of the bender, it enhances dipole alignment of that particular plate element resulting in a shortening and thickening of the plate element. This in turn results in bending of the overall bimorph bender device due tothe fact that the two piezoelectric plate elements are physically secured together. By suitable design, the bending action can result in the closing of two switch contacts or other similar effect.
Unfortunately, prior art attempts to provide piezoelectrically driven switch devices have resulted in devices having poor electrical and mechanical performance characteristics. In the case of prior art bimorph bender-type switching devices asdescribed briefly above, they possess severe performance limitations which are founded in the trade-offs between contact force, contact separation, depolarization, retentivity and reliability in service and the .[.uncertainity.]. .Iadd.uncertainty.Iaddend.of contact position due to creep and temperature effects which build up over a period of continued device usage. One such prior art switching device employing a piezoelectric bender-type drive member is described in U.S. Pat. No. 2,166,763issued July 18, 1939 for a "Piezoelectric Apparatus and Circuits". The piezoelectric bender-type drive member described in U.S. Pat. No. 2,166,763 is comprised by two juxtaposed piezoelectric plate elements having electrodes as described brieflyabove, and is energized in such a manner that one of the piezoelectric plate elements has the energizing potential applied to it in the same direction as the direction of the prepoling electric field; however, the other piezoelectric plate element has anenergizing signal applied thereto of opposite polarity from that of its prepolarizing electric field. As a consequence, the device of U.S. Pat. No. 2,166,763 undergoes long term depolarization of either one or both of the piezoelectric plate elementsafter a period of usage due to the depolarizing effect of the repeated application of a wrong polarity (out of phase anti-poling direction) energizing signal. The deleterious effect on dipole enhancement of operation in this mode greatly restricts theapplied voltage stress and thus the useful work output obtainable with such devices. In addition, the device of this prior art patent possesses a number of other weaknesses sought to be overcome by the present invention. The same objectionablecharacteristics are present in a number of different prior art piezoelectric driven bender-type switches and/or relay devices such as the following: U.S. Pat. No. .[.2,1682,340.]. .Iadd.2,182,340.Iaddend.--issued Dec. 5, 1939 for "Signaling System";U.S. Pat. No. 2,203,332--issued June 4, 1950 for "Piezoelectric Device"; U.S. Pat. No. 2,227,268--issued Dec. 31, 1940 for "Piezoelectric Apparatus"; U.S. Pat. No. 2,365,738--issued Dec. 26, 1944 for "Relay"; U.S. Pat. No. 2,714,642--issuedAug. 2, 1955 for "High Speed Relay of Electromechanical Transducer Material"; U.S. Pat. No. 4,093,883--issued June 6, 1978 for "Piezoelectric Multimorph Switches"; U.S. Pat. No. 4,395,651--issued July 26, 1983 for "Low Energy Relay UsingPiezoelectric Bender Elements"; and U.S. Pat. No. 4,403,166--issued Sept. 6, 1983 for "Piezoelectric Relay with Oppositely Bending Bimorphs". In addition to the above prior art patented piezoelectric bender-type switching devices, the textbook"Manual of Electromechanical Devices" by Douglas C. Greenwood published by McGraw-Hill Book Company and copyrighted in 1965 discloses a somewhat similar piezo ceramic switching device on page 64 thereof.
In order to overcome the shortcomings of the known prior art piezoelectric ceramic driven relays and switches such as those listed above, the present invention was devised.
SUMMARY OF INVENTION
It is therefore a primary object of the present invention to provide new and improved piezoelectric ceramic switching devices of novel construction having better operating characteristics than those of comparable prior art devices of the samegeneral nature.
Another object of the invention is to provide improved energization circuit designs for use with piezo ceramic switching devices which provide improved longevity and greater reliability in operation to such piezo ceramic switching devices overextended periods of service requiring substantial numbers of switching operations.
Still another object of the invention is to provide improved piezoelectric ceramic switching devices and circuits therefor having the above-listed characteristics wherein many of the components employed in either the energization and/orutilization circuits employing such devices are formed or otherwise supported on an inactive unpolarized portion of the piezoelectric ceramic switching device thereby reducing to a minimum stray inductance of the circuits and enhancing miniaturizationand batch processing.
A still further object of the invention is to provide improved piezoelectric ceramic switching devices which themselves carry and selectively close or open power rated switch contacts for controlling current flow therethrough or, alternatively,provide a sufficient electric discharge current to the control gate of a gate turn-on/turn-off semiconductor power switch such as an SCR, triac or transistor to cause it to turn on and conduct current or to turn off and block current flow selectively.
In practicing the invention, a novel piezoelectric ceramic switching circuit and bender-type piezoelectric ceramic switching device is provided wherein the piezoelectric ceramic switching device comprises at least two prepolarized piezoelectricplate elements having respective outer conductive surfaces and disposed on opposite sides of at least one central conductive surface sandwich fashion to which they are physically and electrically bonded. The piezo ceramic switching device coacts with aset of make and break electrical contacts to close or open such contacts and thereby make or break an electrically conductive path extending through the contacts. Selectively operable electric excitation circuit means are connected to the bender-typepiezoelectric ceramic switching device for selectively and respectively exciting each piezoelectric plate element thereof with a direct current excitation electric field which is polarized and applied always in the same direction as the prepolarizingelectric field enhancing dipole alignment previously permanently induced in the piezoelectric plate element whereby no depolarization of the piezoelectric plate element occurs during successive operations of the switch in order to close or open the makeand break contacts. Further, continuous energization is not deleterious with the contacts opening the instant that charge is reduced in the bender.
The selectively operable electric excitation circuit means comprises respective switch energization circuit means connected in circuit relationship across respective ones of prepolarized piezoelectric plate elements of the piezo ceramicbender-type switching device for selectively closing or opening respective ones of the set of coacting electrical switch contacts for controlling electric current supplied through a load by opening and closing the contacts. Each switch energizationcircuit means selectively connects the bender-.Iadd.type .Iaddend.switching device across a source of bender energization potential, a normally open low power rated user operated electric switch, a current limiting resistor and diode rectifier circuitmeans poled to provide an electric energization potential having the same polarity as the polarity of the prepolarizing potential used to polarize the prepoled dipole enhanced piezoelectric plate element of the piezoelectric bender-type switching device. The series electric circuit thus comprised is connected in series circuit relationship across a respective one of the prepoled piezoelectric plate elements of the bender-type switch so that upon closure of the normally open low power rated user's switch,the respective prepolarized piezoelectric plate element of the bender-type piezoelectric switch selectively and respectively is excited with a direct current excitation field which always has the same polarity as the polarity of the prepoling electricfield dipole enhanced alignment previously permanently induced in the respective piezoelectric plate element and no depolarization of the piezoelectric plate elements .[.occur.]. .Iadd.occurs .Iaddend.during continued or successive operation of thepiezoelectric bender-type switch device for closing and/or opening the load current controlling electric switch contacts.
The improved piezoelectric ceramic switching device comprises at least one piezoelectric bender-type switching device having two planar piezoelectric plate elements secured in opposed parallel relationship sandwich fashion on opposite sides of atleast one central conductive surface and having respective outer conductive surfaces that are insulated from each other and the central conductive surface by the respective intervening piezoelectric plate element material thicknesses. The bender-typepiezoelectric switching device further includes at least one set of coacting electrical switch contacts which are opened or closed by a prepolarized movable bender-portion of the piezoelectric ceramic switching device. The improved device furtherincludes clamping means secured to a different portion of the bender-type piezoelectric ceramic switching device adjacent to and mechanically supporting the prepoled movable bender portion of the device cantilever fashion with the different portion ofthe piezoelectric ceramic plate elements comprising the bender-type device disposed under the clamping means being unpoled and electrically neutral.
In addition to being unpoled and electrically neutral, the different portion of the piezoelectric ceramic plate elements disposed under the clamping means have the outer conductive surfaces thereof removed from that portion which is disposedunder the clamping means. In addition, a conformal electrically insulating protective coating covers at least some of the outer surfaces of the prepolarized movable portion of the bender-type piezoelectric device with the conformal electricallyinsulating protective coating comprising a polyimide siloxane copolymer.
In preferred embodiments of the invention, the conformal electrically insulating coating extends over and covers the outer planar conductive surfaces and the edges of the prepoled planar piezoelectric ceramic plate elements, and further extendsover and covers the side edges of the piezoelectric ceramic plate .[.element.]. .Iadd.elements .Iaddend.and their outer conductive surfaces and the outer edges of the central conductive surface sandwiched therebetween at least over the prepolarizedportions of the device. Further, the conformal insulating coating covering the outer planar conductive surfaces of the prepolarized portions of the piezoelectric ceramic plate .[.element.]. .Iadd.elements .Iaddend.also extends down to and covers theportions of the piezoelectric ceramic plate elements exposed by any removal of the outer conductive surfaces thereon as well as the edge portions of such outer conductive surfaces exposed by such removal.
BRIEF DESCRIPTION OF DRAWINGS
These and other objects, features and many of the attendant advantages of this invention will be appreciated more readily as the same becomes better understood by a reading of the following detailed description, when considered in connection withthe accompanying drawings, wherein like parts in each of the several figures are identified by the same reference .[.char.]. .Iadd.character .Iaddend.and wherein:
FIG. 1 is a top elevational view of a new and improved piezoelectric ceramic bender-type switching device constructed according to the invention;
FIG. 1A is cross sectional view of the device shown in FIG. 1 taken through plane 1A--1A;
FIG. 1B is a schematic circuit diagram of a novel energization circuit employed in operating the switching device of FIG. 1;
FIG. 1C is a cross sectional view of the device shown in FIG. 1 taken through plane 1C--1C;
FIG. 1D is a top planar view of the movable bender end of the switching device shown in FIG. 1 in an unfinished condition during the manufacture thereof, and illustrates the manner of forming electric load current carrying contacts at the movableend of the bender-type piezo ceramic switching device;
FIG. 1E is a perspective end view of the same portion of the device shown in FIG. 1D at .[.the.]. .Iadd.a .Iaddend.moment later in time during the manufacture thereof following the stage shown in FIG. 1D;
FIG. 1F is a partial side end view of the finished device showing the manner of fabrication of the end contacts when viewed in conjunction with FIG. 1D and FIG. 1E;
FIG. 2 is a longitudinal sectional view of a different embodiment of improved piezoelectric ceramic switching device constructed in accordance with the invention and illustrates the device mounted on a separate insulating base member;
FIG. 2A is a schematic circuit diagram illustrating a utilization circuit controlled by the device of FIG. 2 and which is fabricated on the device;
FIG. 3 is a partial top planar view of an unpolarized, electrically neutral end of the bender-type piezoelectric ceramic switching device illustrating an electric fuse element deposited on a portion of unpolarized piezoelectric ceramic;
FIG. 4 is a longitudinal sectional view of still a different embodiment of the invention showing active circuit components mounted on a non-polarized portion of a bender-type .[.switch.]. .Iadd.switching .Iaddend.device constructed according tothe invention with the active components comprising diode rectifier elements interconnected with discrete wired connectors to effect a desired excitation circuit design for the device shown in FIG. 4;
FIGS. 4A, 4B and 4C comprise schematic circuit diagrams of three different embodiments of a diode rectifier doubler circuit configuration suitable for use as an excitation circuit with the piezoelectric ceramic switching device shown in FIG. 4,with the circuit arrangement of FIG. 4B corresponding to the physical illustration of the circuit elements depicted in FIG. 4 and physically supported on unpoled portions of the bender-type switching device;
FIG. 5 is a top-side perspective view of a different form .[.or.]. .Iadd.of .Iaddend.piezoelectric ceramic switching device constructed in accordance with the invention showing how the device would be fabricated for use with a voltage triplerenergization circuit shown schematically in FIG. 5A of the drawings.
FIG. 6 is top-side elevational-partial perspective view of still another form of switching device according to the invention which employs a diode rectifier quadrupling circuit illustrated schematically in FIG. 6A .Iadd.of .Iaddend.the drawings:
FIG. 7 is a side elevational view of still another form of improved piezoelectric ceramic bender-type switching device according to the invention to provide H-type double acting switching operations on each of the opposite sides of the neutralposition of the bender element of the device;
FIG. 7A is a schematic circuit diagram of one embodiment of a utilization load circuit which could be operated .[.w h.]. .Iadd.with .Iaddend.the device of FIG. 7;
FIG. 7B is a schematic circuit diagram of a second type of utilization load circuit which could be controlled by the bidirectional acting piezoelectric ceramic switching device of FIG. 7 wherein the device is employed to directly apply gatingcurrent to the gates of higher power rated, gated power semiconductor switches triggered by the device;
FIG. 7C is a schematic circuit diagram of a mirror image of the circuit shown in FIG. 7B and illustrates how inverse polarity voltages can be obtained to provide negative polarity gating currents for use with gated power semiconductor switches ofthe turn-off type;
FIG. 8 is a longitudinal sectional view of a preferred embodiment of piezoelectric ceramic bender-type switching device according to the invention wherein a conformal coating is provided over the active polarized movable bender portions of thedevice;
FIG. 8A is a cross sectional view of the device shown in FIG. 8 taken through plane 8A--8A;
FIG. 8B illustrates a cross sectional view taken through a device such as FIG. 8 but which has been provided with an alternative coating arrangement which covers the entire planar exterior surfaces of the polarized active movable bender portionsof the device;
FIG. 8C is a partial cross sectional view of the device of FIG. 8 taken through that part of the device under the clamping means in order to better illustrate how the conformal coating is caused to cover any exposed parts or edges of the active,polarized portions of the piezoelectric ceramic plate elements;
FIG. 8D shows a number of characteristic curves plotting bender force versus time and illustrates the operating characteristics of a number of different piezoelectric ceramic bender-type switching devices constructed according to the prior artwith or without some form of protective coating as well as the operating characteristics of preferred forms of the invention illustrating their force versus time operating characteristics over a period of time.
FIG. 9 is a longitudinal sectional view of an embodiment of the invention similar to that shown in FIG. 8 and illustrates the manner in which load current carrying contacts can be formed on the free movable bender portion of the device; and
FIG. 10 and 11 are perspective views of different techniques employed in order to obtain terminal tabs for application of energization potential to or providing electric load current flow through the electrically conductive surfaces formed on thepiezoelectric plate elements of the devices shown in FIGS. 8 and 9.
BEST MODE OF PRACTICING INVENTION
FIG. 1 illustrates a piezoelectric ceramic switching device constructed according to the invention and comprises at least one piezoelectric bender-type switching device 11 having at least two planar piezoelectric plate elements formed by an upperplate 12 and a lower plate 13 .[.best.]. .Iadd.better .Iaddend.seen in .[.FIG..]. .Iadd.FIGS. .Iaddend.1A.Iadd.-1F .Iaddend.of the drawings. The piezoelectric ceramic plate elements 12 and 13 are secured in opposed parallel relationship sandwichfashion on opposite sides of at least one central conductive surface 14 and have respective outer conductive surfaces 15 and 16 that are insulated from each other and the central conductive surface 14 by the respective intervening piezoelectric ceramicplate element thicknesses. The piezoelectric ceramic plates 12 and 13 may be formed from lead zirconate titanate, lead metaniobate, barium titanate or other known piezoelectric ceramic materials and, if desired, could even comprise naturally.[.occuring.]. .Iadd.occurring .Iaddend.piezoelectric materials such as quartz. The conductive surfaces 14, 14A, 14B, 15 and 16 may be formed by nickel, silver or other like .[.conductor.]. .Iadd.conductors .Iaddend.deposited or otherwise secured tothe plate elements 12 and 13.
The bender-type piezoelectric switching device further includes at least one set of coacting fixed electrical switch contacts 17 and 18 mounted on relatively rigid support arms which may be sufficiently flexible to absorb impact .Iadd.and whichare opened .Iaddend.and closed by movement of a prepolarized movable bender portion comprised by the piezoelectric ceramic plate elements 12A and 13A of the bender-type switching device. The contacts 17 and 18 coact respectively with contacts 19 and 21formed on the movable end of the bender device 12A, 13A in a manner to be described more fully hereafter with relation to FIG. 1D, 1E and 1F.
The movable bender portions 12A, 13A of the piezoelectric ceramic switching device 11 are physically supported in a cantilever manner by clamping means shown at 22 and 23 which both serve to physically hold and clamp together the piezoelectricceramic plates 12 and 13 with the central conductive surface 14 sandwiched therebetween. The clamping means 22 and 23 is illustrated better in FIG. 1C of the drawings where it can be seen that it is comprised by two elongated substantially rigidelectrically insulating bars 22 and 23 whose ends extend beyond the side edges of the piezoelectric ceramic plate elements 12 and 13. Threaded set screws shown at 24 serve to clamp the two insulating bar members 22 and 23 together along with theinterposed ceramic plate elements 12 and 13 and central conductive surface 14. Other forms of suitably clamping and holding the piezoelectric ceramic plate members 12 and 13 together in assembled relation will be suggested to those skilled in the art.
As best shown in FIG. 1A, the clamping means 22 and 23 are disposed over portions 12B and 13B of the piezoelectric ceramic plate elements 12 and 13 which have not been prepolarized and therefore are unpoled and electrically neutral as opposed tothe prepolarized active movable bender portions 12A and 13A of the plate elements on which the contacts 19 and 21 are formed. Preferably, the clamping means 22 and 23 are disposed over the ends of the non-polarized or unpoled portions 12B and 13B whichare immediately adjacent to and physically integrated with the end of the prepolarized active movable bender portion comprised by plate element portions 12A and 13A which have been prepolarized and therefore are indicated as poled. It has beendiscovered that by mounting the piezoelectric ceramic plate elements in this manner, the number of failures due to fracturing of the piezoelectric plates at their support points is greatly reduced.
With the bender-type piezoelectric ceramic switching device shown in FIGS. 1 and 1A, it is possible to prepolarize the plate portions 12A and 13A in-situ after fabrication of the device in the manner shown in these drawings. This is achieved byapplying suitable value prepolarizing potentials of the same polarity to the terminals T3 and T4 respectively, while concurrently holding the common terminal Tc at the opposite polarity. Simultaneously the temperature of the device may be elevated in anoven or otherwise to a temperature just under the Curie temperature of the piezoelectric ceramic plate elements 12 and 13. The temperature to which the devices will be elevated and the value of the prepolarizing potentials will vary dependent upon theparticular piezoelectric ceramic material employed to form the plate elements 12 and 13 as is known to those skilled in the art of .[.peizoceramic.]. .Iadd.piezoceramic .Iaddend.fabrication. Ambient temperature polarization also is possible if thepolarizing potential is sufficiently high. During the prepolarization operation, and in order to separate the piezoelectric ceramic plate elements 12 and 13 into the two separate poled portions 12A and 13A and the unpoled portions 12B and 13B, it isnecessary to electrically isolate the two portions so that the prepolarizing potential is not applied across the unpoled portions 12B and 13B and the common conductive surface 14. For this purpose, suitable gaps shown at 15A and 16A are deliberatelyformed across the width of the exterior conductive surfaces 15 and 16, respectively, whereby an electric potential applied between either of the terminals T3 or T4 and the common terminal Tc connected to the central conductive surface 14, will not appearacross the piezoceramic plate portions 12B and 13B which are to remain unpoled. It .[.sould.]. .Iadd.should .Iaddend.be noted that the portions of the piezoelectric ceramic plate elements disposed under the clamping bars 22 and 23 have their outerconductive surfaces removed so that the portions 12B and 13B under the clamping means and immediately adjacent and physically integrated with the prepolarized plate portions 12A and 13A remain unpoled and electrically neutral.
As a result of fabrication in this manner, during operation of the bender-type switching device, energizing potentials may be selectively and respectively applied either to terminal T3 or terminal T4 relative to Tc to cause the polarized activemovable bender plate portions 12A or 13A to bend and close their respective contacts 19 or 21 on either of the coacting contacts 17 or 18, respectively. As noted in the brief discussion earlier in the specification, prepolarization of the active movableportions 12A and 13A of the piezoelectric ceramic plate elements will leave these portions permanently altered in physical dimensions relative to what they were prior to prepolarization and relative to the unpoled portions 12B and 13B of thepiezoelectric ceramic plates 12 and 13. This alteration will be in the form of a permanent increase in dimension of the plate portions 12A and 13A between the poling electrodes 15-14 and 16-14 and also will induce a permanent decrease in dimensionparallel to the electrodes (i.e. along the longitudinal dimension of the device as shown in FIG. 1A). When a DC voltage of the same polarity as the prepolarizing voltage, but of smaller magnitude, subsequently is applied as an energizing potentialbetween the poling electrodes, the plate element portions 12A and 13A experience a further temporary expansion in the poling direction and contraction parallel to the electrodes. When the energizing DC potential is removed, this temporary expansion inthe poling direction and contraction parallel to the electrode is released, and the plate element portions 12A and 13A return to their normal, at rest unenergized condition established by the prepolarization, voltage effects only. Thus, it will beappreciated that the movable bender plate element portions 12A and 13A automatically return to their original prepolarized dimensions so that the bender moves back to its central, at rest, unenergized condition with contacts 19 and 21 .Iadd.being.Iaddend.opened when the DC energizing voltage is removed from across the electrodes T3-Tc or T4-Tc.
A key feature of the present invention is the provision of piezoelectric ceramic bender-type switch energization and/or utilization circuit means which are built directly onto an unused portion of the piezoceramic plate elements 12 and 13 of thebender-type piezoelectric ceramic switching device 11 as will be described hereinafter. When thus constructed, circuit stray inductance is reduced to an absolute minimum since circuit interconnecting conductor runs formed on such unused piezoceramicplate portions require only minimum lengths. The energization circuits thus formed serve to supply a direct current energizing potential selectively and respectively to each piezoelectric plate element portion 12A or 13A which energization potentialalways is poled in the same direction as the prepolarizing electric field previously permanently induced in the piezoelectric plate element portions 12A and 13A whereby no depolarization of the piezoelectric plate element portions occurs during continuedor successive operations of the switch to close or open the make and break contacts 17, 19 or 18, 21. It will be appreciated therefore than an improved piezoceramic switching device according to the invention such as that shown in FIGS. 1 and 1A can beoperated as either a normally-open or a normally-closed switch without detriment to the long term stability and reliability characteristics of the switch. This is explained as follows.
Assume that the outer conductive surfaces 15 and 16 over .[.peizoelectric.]. .Iadd.piezoelectric .Iaddend.ceramic plate portions 12A and 13A are maintained positive while the central conductive surface 14 is maintained negative during theprepolarization of the plate portions 12A and 13A as described briefly above. The prepolarization of these plate elements then will cause a permanent increase in dimension between the poling electrodes and a permanent decrease in dimensions parallel tothe electrodes (i.e. the plate portions 12A and 13A will become thicker and shorter). Since both plate element portions 12A and 13A are prepolarized substantially simultaneously, this permanent change in dimension will not effect the centering positionof the active movable bender comprised by plate portions 12A, 13A relative to the coacting contacts 17 and 18. However, in the event that some off-centering does occur, then the magnitude of the prepolarizing potential applied across either one or theother of the plate element portions 12A or 13A can be adjusted so as .Iadd.to .Iaddend.precisely center the bender contacts 19, 21 between the coacting contacts 17, 18. This ability to precisely center the bender element in an easily applied and readilyadjusted manner is attributable to the fact that the bender plate elements 12A and 13A can be prepolarized in-situ and is of extreme importance during manufacture in order to assure proper operation of the bender switch at relatively low cost since thereare fewer fabrication and process steps involved. Thereafter, during operation, DC energizing potential selectively and respectively can be applied either to terminals T3 or T4 and such energizing potentials always are poled in the same direction as thepolarity of the prepolarizing potential. Since it was assumed that the prepolarizing potential applied to conductive surfaces 15 and 16 was positive relative to the potential of the central conductive surface 14 which therefore is negative relative to15 and 16, the applied energizing DC potential required to operate the switch would have corresponding polarities. That is, DC energizing potential applied either through T3 or T4 would be positive relative to the potential applied to Tc. This is theproper polarity relation where the bender-type switch is designed for use with PNP bipolar transistors or P-type FET transistors. Where the switching circuit is to be used with NPN bipolar transistors or N-type FET transistors, then the polarities wouldbe reversed both with respect to the high voltage value prepolarizing potential and the later applied operating energizing potentials so as to preserve the proper dipole enhancement of the prepolarized portions of the piezoelectric ceramic plate elements12A, 13A. That is to say, negative polarity energizing potentials would be selectively applied to either terminal T3 or T4 and a positive polarity energizing potential applied to terminal Tc.
As noted earlier, during operation the application of the further DC energizing potential which is of smaller magnitude than the prepolarizing potential, but of the same polarity, results in a further thickening and shortening of one or the otherof the plate element portions 12A or 13A. This thickening and shortening of one of the plates consequently will result in physically bending the free movable end of the active bender portion 12A, 13A sufficiently to selectively close either the contact19 on its coacting contact 17 (in the event T3 is energized), or, alternatively, selectively close contact 21 on its coacting contact 18 (if T4 has been energized). The closure thus achieved will remain for so long as the DC energizing potential isapplied to the respective contacts T3 or T4. This can be for an indefinite period of time. Thus the bender-type switching device 11 shown in FIGS. 1 and 1A, by appropriate energization and utilization circuit design, can be used either as anormally-open or a normally-closed switching device. This capability is achieved because of three principal characteristics of the switching device. First, the piezoelectric ceramic plate elements 12 and 13 essentially are high quality capacitorshaving little or no losses when charged (energized). Secondly, any losses that do occur over extended periods of being energized are supplanted immediately and continuously by the continually applied energization potential. Lastly, because theenergization potential always is applied with the same polarity as the prepolarization potential used to initially prepole and enhance the dipole orientation of the piezoelectric ceramic plate portions 12A and 13A, there is no possibility of long termdepolarizing effects rendering the device unstable in operation.
Upon removal of the DC energizing potential to either T3 or T4, the active movable bender portion 12A, 13A returns to its center neutral unenergized position thereby opening which ever set of contacts 17, 19 or 18, 21 was closed. It should benoted at this point in the description, that prepolarization and subsequent operation with DC energizing potentials of positive polarity applied to the respective outer conductive surfaces 15 and 16 via terminals T3 and T4 while the center conductivesurface 14 is maintained negative, is cited as exemplary only. The device could be fabricated and operated equally well with negative polarity prepolarizing potentials applied to the terminals T3 and T4 while the central conductive surface 14 terminalTc is maintained positive. If thus prepolarized, the device of course subsequently would have to be operated using only DC energizing signals applied to the terminals T3 and T4 which are negative relative to the potential applied to the centralconductive surface 14 via terminal Tc. FIGS. 7B and 7C to be described hereinafter illustrate this capability.
With reference again to FIGS. 1 and 1A, it will be seen that there are two unpoled piezoelectric plate element portions 12B and 13B which extend beyond the clamped portion of the piezoceramic plates 12 and 13 in a direction opposite from theprepoled active movable bender portions 12A, 13A. These unpoled plate element portion 12B and 13B may be provided with exterior conductive surfaces such as shown at 15B and 16B which are separated from the conductive surfaces 15 and 16 overlying thepolarized piezoceramic plate portions 12A and 13A by the gaps 15A and 16A under clamping bars 22 and 23, respectively, together with the central conductive surface 14 sandwiched therebetween to form two separate, relatively large (i.e. 1 microfarad)capacitors. In the embodiment of the invention shown in FIG. 1A, the conductive surface 14 extends throughout the length of the piezoceramic plate elements 12 and 13 so that a continuous central electrically conductive path 14 extends between the freemovable bender .Iadd.portions .Iaddend.12A, 13A of the device and the end thereof connected to the common terminal Tc. If required for particular circuit design purposes, the central conductive path 14 provided through conductive surface 14 may beinterrupted along a line under the clamping bars 22 and 23, or at a number of points, and the space therein filled with a suitable insulating adhesive for the purpose of electrically isolating portions of the central conductor 14 under non-poled plateportions 12B and 13B, and/or to electrically isolate the central conductor portion 14 under the prepoled plate .[.portion.]. .Iadd.portions .Iaddend.12A and 13A from that under non-poled portions 12B, 13B. In either form of construction, the unpoledplate portions 12B and 13B form two capacitors which in effect readily can be connected in either a series or parallel circuit relationship via the central conductor surface 14 thereunder and terminal Tc. The capacitors thus formed by appropriate designand fabrication of the outer conductive surfaces 15B and 16B may be provided with capacitance values required for particular circuit designs. The size of the capacitors and their capacitance values are related to the power rating of the circuit andbender size. For example, up to a capacitance of about a tenth of a microfarad would be provided for switching devices constructed in the manner described having bender member dimensions of about one inch wide by three inches long and with piezoelectricceramic plate element thicknesses of about 3-10 milli-inches with the conductive surfaces being extremely thin. It should be understood that if a number of different size capacitors are desired in any particular circuit arrangement, they can be formedby appropriately subdividing the outer conductive surfaces 15B or 16B into the desired number and size capacitors. The multiplicity of capacitors thus formed could all use the common central conducting surface 14 as a common electrode via terminal Tc.
In addition to .Iadd.the .Iaddend.capacitors formed in the above briefly described manner, other electrical circuit components comprising either active semiconductor devices or passive circuit elements fabricated either in discrete, hybrid ormonolithic integrated circuit form physically can be formed on or supported by the unpoled piezoelectric plate element portions 12B or 13B. In such devices the conductive surfaces 15B and 16B could be shaped to provide conductive paths (runs) betweenthe various components to interconnect them into desired circuit relationship in accordance with known printed circuit and integrated circuit fabrication techniques as described in the textbook "Microelectronics" edited by Max Fogiel and published byResearch and Education Association, copyrighted 1968, and others such as "Handbook of Electronics Packaging", Charles A. Harper, editor, published by McGraw-Hill Book Company and copyrighted 1969 and "Handbook of Components for Electronics", Charles A.Harper, editor, published by McGraw-Hill Book Company, copyrighted 1977.
In FIG. 1A, relatively large hybrid integrated resistors are shown at 25 and 26 which are surface mounted on the respective conductive surface portions 15B and 16B of the unpoled electrically neutral piezoelectric ceramic plate portions 12B and13B, respectively.Iadd., .Iaddend.and may be formed either by surface deposition, bonding or screening. This structure results in two series connected resistor and capacitor elements which are designed to form a snubber circuit connected across theterminals T1-Tc and T2-Tc, respectively. By interconnecting the two snubber capacitances in parallel, the total capacitance of the snubber circuit can be doubled.
FIG. 1B of the drawings is a schematic circuit diagram of the novel piezoelectric ceramic switching device and related energization and utilization circuit shown physically in FIGS. 1 and 1A of the drawings. In FIG. 1B the terminals T1 and T2are connected to a suitable source of alternating current or direct current of the correct polarity. Terminal T1 is connected through the switch S1 formed by contacts 17 and 19 via the central conductive surface 14 to the common terminal Tc. TerminalT2 is connected through the switch S2 formed by the coacting contacts 18 and 21 via central conductive surface 14 to common terminal Tc. The snubber circuit formed by the series connected resistor R25 and capacitor C12B is connected in parallel acrossswitch S1 and the snubber circuit formed by the series connected resistor R26 and capacitor C13B is connected in parallel circuit relationship across the switch S2. The snubber circuits R25, C12B and R26, C13B are provided to prevent excessive arcingacross the contacts 17, 19 or 18, 21, respectively, as the contacts are opened in order to interrupt current flow through the respective switches and result in reducing the rate of rise of reapplied forward potential across the contacts as they open. The inclusion of the snubber circuit thus provided is referred to as a dv/dt protection circuit for the switch S1 and S2 contacts and can greatly increase their operating life, and reduce electrical noise effects.
User operated energization circuit means are provided for selectively and respectively closing or opening the switches S1 and S2. The energization circuits are comprised by either a negative polarity source of direct current potential or analternating current source of potential connected in series circuit relationship through a normally open user operated switch 27, a limiting resistor 28, and diode rectifier circuit means 29 across the prepolarized portion 12A or 13A of the piezoelectricceramic switching device 11 and the common central conducting surface 14 to the common terminal Tc that is connected to the positive polarity terminal of the direct current source or an alternating current source, which ever is used. In preferredembodiments, the normally open user operated switch 27 either is electrically or mechanically interconnected with a normally-closed switch 31 that is connected in series circuit relationship with a limiting resistor 32 with the series circuit thuscomprised being connected in parallel circuit relationship across the respective prepolarized upper and lower piezoelectric ceramic plate elements 12A and 13A, respectively, which are indicated as capacitors C12A and C13A. The energization circuitcomprised by elements 27-32 have not been illustrated in their physical form in FIGS. 1 and 1A in order not to unduly complicate these drawings; however, it is believed obvious to one of ordinary skill in the electronic art as to how these componentswould be physically implemented and interconnected to the piezo ceramic switching device 11 shown in FIGS. 1 and 1A in the light of the teachings of this application.
In operation, the normally closed switch contacts 31 will maintain the prepolarized upper and lower piezoelectric ceramic plate elements 12A and 13A in an uncharged condition so that the bender device 11 is maintained at its central neutralposition with neither switch S1 or S2 .Iadd.being .Iaddend.closed. If it is desired to close switch S1 comprised by contacts 17 and 19, for example, in order to supply load current to a load device controlled by switch S1, the user operated, normallyopen switch contacts 27 are closed. This results in charging the upper piezoelectric ceramic plate element 12A via the limiting resistor 28, diode rectifier circuit means 29 and the source of electric potential connected across the energization circuitinput terminal and common terminal Tc. Concurrently with this action, the normally-closed switch contacts 31 automatically open so that piezoelectric ceramic plate element 12A can be charged thereby causing it to physically deform in the mannerdescribed earlier and close switch S1 by closing contact 19 on coacting switch contact 17 to provide load current supply to a load (not shown). After a desired period of operation of unlimited duration, and at the user's option, the electrical loadcurrent flow being supplied via switch S1 contacts 17, 19 can be interrupted by merely opening the normally-open switch contacts 27 thereby automatically closing normally-closed contacts 31 and discharging the piezoelectric ceramic plate element 12A. This results in de-energizing the upper plate element 12 and allows the bender device 11 to return to its normally quiescent, neutral central position whereby neither of the switch contacts S1 or S2 are closed. Operation of the device to close theswitch S2 comprised by contacts 18 and 21 is entirely similar to that described with relation to the switch S1 so that it need not be described here in detail. Further, it should be noted that reversal of polarity of the excitation voltage supplied tothe prepolarized, movable bender plate portions 12A and 13A readily can be accomplished by reversal of the polarity of connection of the diode rectifiers 29 should that be desired for a given utilization circuit application. Additionally, in alternativeembodiments of the FIG. 1B circuit, the normally closed .[.contact.]. .Iadd.switch .Iaddend.31 is eliminated and the resistance value of resistor 32 increased to about ten times the value of resistor 28.
One of the difficulties encountered with bender-type piezoelectric ceramic switching devices of the same general type as that illustrated in FIGS. 1 and 1A of the drawings is a tendency for the movable bender .Iadd.portions .Iaddend.12A, 13A atthe free movable end thereof to which the contacts 19 and 21 are secured tending to curl during continued energization. As a result of this tendency to curl at the free movable .[.ends.]. .Iadd.end .Iaddend.while being energized, the available contactarea for doing work is reduced .[.and increases.]. .Iadd.with increased .Iaddend.heating, the contact force with which the contacts close is reduced and the spacing of the contacts and the timing of their closure cannot be precisely controlled thusrendering the device unstable and unreliable in operation. To avoid this difficulty, the present invention provides a relatively thin inflexible stiffening member 35 secured widthwise | | | |
