U.S. patent number RE33,577 [Application Number 07/383,315] was granted by the patent office on 1991-04-23 for advanced piezoceramic power switching devices employing protective gastight enclosure and method of manufacture.
This patent grant is currently assigned to General Electric Company. Invention is credited to George A. Farrall, John D. Harnden, Jr., William P. Kornrumpf.
United States Patent |
RE33,577 |
Harnden, Jr. , et
al. |
April 23, 1991 |
Advanced piezoceramic power switching devices employing protective
gastight enclosure and method of manufacture
Abstract
This application described a number of novel advanced
piezoelectric ceramic power switching devices which are mounted
within protective gastight enclosures that are either evacuated to
a high degree of vacuum or filled with an inert gas protective
atmosphere. The devices thus constructed are capable of operating
over a range of load voltages extending from about 100 volts to
5000 volts or more with corresponding currents of from a few
amperes to hundreds of amperes and wherein it is possible to
provide a number of such structures in a single common protective
gastight enclosure. For certain circuit applications the devices
thus constructed have unpoled portions on which are mounted either
passive circuit components such as resistors, capacitors and the
like or active semiconductor devices all interconnected in circuit
relationship with each other and the switching devices by using
printed circuit or integrated circuit fabrication techniques. In
these devices, stray circuit impedances whether capacitive,
inductive or resistive in nature can be reduced to an absolute
minimum by appropriate designs. Such complementary circuit
components and active semiconductor devices can be, if desired,
mounted within the common protective enclosures in close proximity
to the piezoceramic switching devices to which they are connected,
or alternatively may be mounted exteriorly of the protective
enclosures.
Inventors: |
Harnden, Jr.; John D.
(Schenectady, NY), Kornrumpf; William P. (Albany, NY),
Farrall; George A. (Rexford, NY) |
Assignee: |
General Electric Company (Fort
Wayne, IN)
|
Family
ID: |
27010134 |
Appl.
No.: |
07/383,315 |
Filed: |
July 20, 1989 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
685108 |
Dec 21, 1984 |
4714847 |
|
|
Reissue of: |
881525 |
Jun 30, 1986 |
04689517 |
Aug 25, 1987 |
|
|
Current U.S.
Class: |
310/332 |
Current CPC
Class: |
H01H
57/00 (20130101); H01H 2050/025 (20130101) |
Current International
Class: |
H01H
57/00 (20060101); H01L 41/09 (20060101); H01L
041/08 () |
Field of
Search: |
;310/330-332,340,344,357-359,367,368 ;200/181 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
273157 |
|
Jul 1964 |
|
AU |
|
970817 |
|
Jul 1975 |
|
CA |
|
69545 |
|
Jun 1975 |
|
JP |
|
32456 |
|
Jul 1982 |
|
JP |
|
421067 |
|
Aug 1974 |
|
SU |
|
961606 |
|
Jun 1964 |
|
GB |
|
Other References
Electronic Engineering, by P. Kleinschmidt, "A Piezoelectric
Ceramic Touch-Operated Button", Aug. 1975, pp. 9 and 11. .
Guntersdorfer, M. et al., "Application of Piezoceramics in Relays",
Electrocomponent Science and Technology, vol. 3, 1976, pp.
1-11..
|
Primary Examiner: Budd; Mark O.
Attorney, Agent or Firm: Krisher, Jr.; Ralph E.
Parent Case Text
This application is a division of application Ser. No. 685,108,
filed 12/21/84 .Iadd., now U.S. Pat. No. 4,714,849. .Iaddend.
Claims
What is claimed is:
1. A controlled atmosphere bender-type piezoelectric ceramic
electrical switching device comprising a gastight protective
enclosure .[.secure.]. .Iadd.secured .Iaddend.to a base member for
supporting the enclosure and sealing closed the interior of the
enclosure in a gastight manner, at least one bender-type
piezoelectric ceramic switching device having a bender member
formed by two juxtaposed selectively prepolarized piezoelectric
ceramic planar plate elements secured together sandwich fashion
with each plate element having at least inner and outer conductive
surfaces formed on the planar surfaces thereof together with
respective terminal means for selective application of energizing
electric operating potentials to the prepolarized portions of the
respective plate elements, said bender-type piezoelectric ceramic
switching device being physically supported on said base member
within said enclosure by clamping means secured on opposite sides
of the bender member at non-prepolarized portions of the respective
plate elements and physically supporting the bender member
cantilever fashion with only the prepolarized portions thereof
being freely movable whereas the non-prepolarized portions of said
piezoelectric ceramic plate elements clamped under said clamping
means remain both electrically neutral and physically unstrained,
first electric switch contact means within said gastight enclosure
moved by the free movable end of said bender member, second
electric switch contact means physically mounted within said
gastight enclosure and selectively engageable by the first electric
switch contact means upon the selective application of an
energizing electric operating potential to a respective one of the
piezoelectric plate elements for causing the bender member to bend
and close the first and second electric switch contact means to
allow electric current flow therethrough, and respective
electrically conductive lead means connected to a respective one of
said first and second electric switch contact means and extending
to respective terminal means supported by said base member outside
said protective gastight enclosure for selectively supplying
electric load current to a load outside said enclosure via said
first and second electric switch contact means, wherein the
non-prepolarized piezoelectric ceramic planar plate element
portions extend beyond the clamping means in a direction away from
the prepolarized movable member portions, and wherein the device
further includes electric circuit components in the form of passive
circuit elements and/or active semiconductor devices supported by
said non-prepolarized portions of said piezoelectric ceramic plate
elements and electrically connected in circuit relationship with
said switching device.
2. A controlled atmosphere bender-type piezoelectric ceramic
electrical switching device comprising a gastight protective
enclosure secured to a base member for supporting the enclosure and
sealing closed the interior of the enclosure in a gastight manner,
at least one bender-type piezoelectric ceramic switching device
having a bender member formed by two juxtaposed selectively
prepolarized piezoelectric ceramic planar plate elements secured
together sandwich fashion with each plate element having at least
inner and outer conductive surfaces formed on the planar surfaces
thereof together with respective terminal means for selective
application of energizing electric operating potentials to the
prepolarized portions of the respective plate elements, said
bender-type piezoelectric ceramic switching device being physically
supported on said base member within said enclosure by clamping
means secured on opposite sides of the bender member at
non-prepolarized portions of the respective plate elements and
physically supporting the bender member cantilever fashion with
only the prepolarized portions thereof being freely movable whereas
the non-prepolarized portions of said piezoelectric ceramic plate
elements clamped under said clamping means remain both electrically
neutral and physically unstrained, first electric switch contact
means within said gastight enclosure moved by the freely movable
end of said bender member, second electric switch contact means
physically mounted within said gastight enclosure and selectively
engageable by the first electric switch contact means upon the
selective application of an energizing electric operating potential
to a respective one of the piezoelectric plate elements for causing
the bender member to bend and close the first and second electric
switch contact means to allow electric current flow therethrough,
and respective electrically conductive lead means connected to a
respective one of said first and second electric switch contact
means and extending to respective terminal means supported by said
base member outside said protective gastight enclosure for
selectively supplying electric load current to a load outside said
enclosure via said first and second electric switch contact means,
wherein the non-prepolarized piezoelectric ceramic planar plate
element portions extend beyond the clamping means in a direction
away from the prepolarized movable bender portions and carry switch
energization circuit means which selectively applies a source of
bender energization potential to the prepolarized movable bender
portion of each plate element having the same polarity as the
polarity of the prepoled electric field previously permanently
induced in said prepolarized movable bender portions so that no
depolarization of the plate elements occurs during successive
operation of the piezoelectric ceramic bender-type switching
device.
3. A controlled atmosphere bender-type piezoelectric ceramic
electrical switching device as in claim 2 wherein said switch
energization .[.circuits.]. .Iadd.circuit .Iaddend.means includes
electric circuit components in the form of passive circuit elements
and/or active semiconductor devices.
4. A controlled atmosphere bender-type piezoelectric ceramic
electrical switching device as in claim 2 wherein there are a
plurality of bender-type piezoelectric ceramic switching devices
physically mounted within a single common gastight protective
enclosure with each such device being separately actuable for
controlling load current flow therethrough. .Iadd.
5. A controlled atmosphere bender-type piezoelectric ceramic
electrical switching structure comprising
(a) a gastight protective enclosure secured to a base member for
supporting the enclosure and sealing closed the interior of the
enclosure in a gastight manner,
(b) at least one bender-type piezoelectric ceramic switching device
having a bender member formed by two juxtaposed piezoelectric
ceramic planar plate elements secured together sandwich fashion
with at least a selected plate element having inner and outer
conductive surfaces formed on the planar surfaces thereof, together
with terminal means for application of energizing electric
operating potentials to the selected plate element,
(c) means connected to the terminal means for providing energizing
electric operating potentials having a single selected
polarity,
(d) the bender-type piezoelectric ceramic switching device being
physically supported on the base member within the enclosure by
clamping means secured on opposite sides of the bender member and
physically supporting the bender member cantilever fashion with one
end thereof being freely movable,
(e) first electric switch contact means within the gastight
enclosure moved by the freely movable end of the bender member,
(f) second electric switch contact means within the gastight
enclosure and selectively engageable by the first electric switch
contact means upon the selective application of the energizing
electric operating potential to the selective plate element for
causing the bender member to bend and close the first and second
electric switch contact means to allow electric current to flow
therethrough, and
(g) respective electrically conductive lead means connected to the
first and second electric switch contact means and extending to
respective terminal means supported by the base member outside the
protective gastight enclosure for selectively supplying electric
load current to a load outside the enclosure via the first and
second electric switch contact means. .Iaddend. .Iadd.
6. The switching structure of claim 5 wherein there are a plurality
of bender-type piezoelectric ceramic switching devices physically
mounted within a single common gastight protective enclosure, with
each such device being actuable for controlling electric load
current flow therethrough. .Iaddend. .Iadd.7. The switching
structure of claim 6 wherein each bender-type piezoelectric ceramic
switching device mounted within the common protective enclosure
includes its own coacting first and second electric switch contact
means and operates independently of the other switching devices
mounted within the common protective enclosure. .Iaddend. .Iadd.8.
The switching structure of claim 6 wherein the bender-type
piezoelectric ceramic switching devices mounted within the common
protective enclosure can be made to coact interdependently with
selected other switching devices mounted within the same common
protective enclosure. .Iaddend. .Iadd.9. The switching structure of
claim 5 wherein the gas-tight protective enclosure is permanently
evacuated and maintains the bender-type piezoelectric ceramic
device in a high degree of vacuum throughout is operating life.
.Iaddend. .Iadd.10. The switching structure of claim 5 wherein the
gas-tight protective enclosure is filled with an inert or high
dielectric gas atmosphere. .Iaddend. .Iadd.11. The switching
structure of claim 5 wherein the piezoelectric ceramic planar plate
elements have unpoled portions which extend beyond the clamping
means so as to remain electrically neutral and physically
unstrained. .Iaddend. .Iadd.12. The switching structure of claim 11
wherein the device further includes circuit components in the form
of passive circuit elements and/or active semiconductor devices
physically supported by the unpoled portions of the piezoelectric
ceramic plate elements and are electrically connected in circuit
relationship with the switching device. .Iaddend. .Iadd.13. The
switching structure of claim 12 wherein the unpoled portions of the
piezoelectric ceramic plate elements and any electric circuit
components supported thereby are physically located within the
gastight protective
enclosure. .Iaddend. .Iadd.14. The switching structure of claim 11
wherein there are a plurality of bender-type piezoelectric ceramic
switching devices physically mounted within a single common
gastight protective enclosure with each such device being
separately actuable for controlling load current flow therethrough.
.Iaddend. .Iadd.15. The switching structure of claim 11 wherein
there are a plurality of bender-type piezoelectric ceramic
switching devices physically mounted within a single common
gastight protective enclosure and wherein at least one of the
bender-type piezoelectric ceramic switching devices can be made to
coact interdependently with selected other bender-type
piezoelectric ceramic switching devices mounted within the same
common protective enclosure. .Iaddend. .Iadd.16. The switching
structure of claim 11 wherein the unpoled portions of the
piezoelectric ceramic plate elements and any electric circuit
components supported thereby are physically located within the
gastight protective enclosure. .Iaddend. .Iadd.17. The switching
structure of claim 11 wherein the gastight protective enclosure is
permanently evacuated and maintains the bender-type piezoelectric
ceramic device in a high degree of vacuum throughout its operating
life. .Iaddend. .Iadd.18. The switching structure of claim 11
wherein the gastight protective enclosure is filled with an inert
or high dielectric gas atmosphere. .Iaddend. .Iadd.19. A controlled
atmosphere bender-type piezoelectric ceramic switching structure
comprising
(a) a gastight protective enclosure secured to a base member for
supporting the enclosure and sealing closed the interior of the
enclosure in a gastight manner,
(b) at least one bender-type piezoelectric ceramic switching device
having a bender member formed by two juxtaposed piezoelectric
ceramic planar plate elements secured together sandwich fashion
with each plate element having inner and outer conductive surfaces
formed on the planar surfaces thereof, together with respective
terminal means for application of energizing electric operating
potentials to the respective plate elements,
(c) means connected to the terminal menas for providing energizing
electric operating potentials to each of the plate elements, the
energizing operation potential applied to each plate having a
single selected polarity,
(d) the bender-type piezoelectric ceramic switching device being
physically supported on the base member within the enclosure by
clamping means secured on opposite sides of the bender member and
physically supporting the bender member cantilever fashion with a
movable end,
(e) respective first electric switch contact means on the outer
surfaces of each of the plate elements, the first switch contact
means being within the gastight enclosure and moved by the movable
end of the bender member,
(f) second electric switch contact means opposite the respective
first switch contact means on each of the plate elements, the
second switch contact means being within the gastight enclosure and
selectively engageable by the opposing first electric switch
contact means upon the selective application of an energizing
electric operating potential to one of the piezoelectric plate
elements for causing the bender member to bend and close the
selected first and second electric switch contact means to allow
electric current to flow therethrough, and
(g) respective electrically conductive lead means connected to
respective ones of the first and second electric switch contact
means and extending to respective load terminal means supported by
the base member outside the protective gastight enclosure for
selectively supplying load current from a power source to a load
outside the enclosure via the first and second
electric switch contact means. .Iaddend. .Iadd.20. The switching
structure of claim 19 wherein there are a plurality of bender-type
piezoelectric ceramic switching devices physically mounted within a
single common gastight protective enclosure with each such device
being actuable for controlling electric current flow therethrough.
.Iaddend. .Iadd.21. The switching structure of claim 20 wherein
each bender-type piezoelectric ceramic switching device mounted
within the common protective enclosure includes its own coacting
first and second electric switch contact means and operates
independently of the other switching devices mounted within the
common enclosure. .Iaddend. .Iadd.22. The switching structure of
claim 20 wherein the bender-type piezoelectric ceramic switching
devices mounted within the common protective enclosure can be made
to coact interdependently with selected other switching devices
mounted within the same common protective enclosure. .Iaddend.
.Iadd.23. The switching structure of claim 19 wherein the gastight
protective enclosure is permanently evacuated and maintains the
piezoelectric ceramic switching device in a high degree of vacuum
throughout its operating life. .Iaddend. .Iadd.24. The switching
structure of claim 19 wherein the gastight protective enclosure is
filled with an inert or high dielectric gas
atmosphere. .Iaddend. .Iadd.25. Electrical switching apparatus
comprising:
a gastight protective enclosure secured to a base member for
supporting the enclosure,
means for sealing the interior of the enclosure in a gastight
manner,
at least one piezoelectric bender member having
a bender portion formed by two juxtaposed piezoelectric planar
plate elements secured together sandwich fashion, the bender
portion having inner and outer conductive surfaces formed on the
planar surfaces of the plate elements, and
a non-bending portion adjacent the bender portion, the non-bending
portion being electrically isolated from the conductive
surfaces,
first terminal means operatively connected to the conductive
surfaces for applying electric potentials to the respective plate
elements in the bender portion,
means for clamping the bender member within the enclosure by
securing the non-bending portion so that the bender member is
physically supported cantilever fashion with the bender portion
being movable, the non-bending portion being clamped by the
clamping means,
first electric switch contact means within the gastight enclosure
mechanically connected to the movable end of the bender
portion,
second electric switch contact means physically mounted within the
gastight enclosure and selectively engageable by the first electric
switch contact menas upon the selective application of an electric
potential to a respective one of the piezoelectric plate elements
for causing the bender member to bend and close the first and
second electric switch contact means to allow electric current flow
therethrough,
respective electrically conductive lead means connected to the
first and second electric switch contact means and extending to
respective second terminal means supported by the base member
outside the protective gastight enclosure for selectively supplying
electric load current to a load outside the enclosure via the first
and second electric switch contact means, and
electric circuit components in the form of passive circuit elements
and/or active semiconductor devices supported to said non-bending
portion of the bender member and electrically connected in circuit
relationship with the
first terminal means. .Iaddend. .Iadd.26. Electrically switching
apparatus comprising
a gastight protective enclosure secured to a base member for
supporting the enclosure,
means for sealing the interior of the enclosure in a gastight
manner,
at least one piezoelectric bender member having
a bender portion formed by two juxtaposed piezoelectric planar
plate elements secured together sandwich fashion, the bender
portion having inner and outer conductive surfaces formed on the
planar surfaces of each plate element, and
a non-bending portion adjacent the bender portion, the non-bending
portion being electrically isolated from the conductive
surfaces,
first terminal means operatively connected to the conductive
surfaces for applying electric potentials to the respective plate
elements in the bender portion,
means for clamping the bender member within the enclosure by
securing the non-bending portion so that the bender member is
physically supported cantilever fashion with the bender portion
being movable,
first electric switch contact means within the gastight enclosure
mechanically connected to the movable end of the bender
portion,
second electric switch contact means physically mounted within the
gastight enclosure and selectively engageable by the first electric
switch contact means upon the selective application of an electric
operating potential to a respective one of the piezoelectric plate
elements for causing the bender member to bend and close the first
and second electric switch contact means to allow electric current
flow therethrough,
respective electrically conductive lead means connected to the
first and second electric switch contact means and extending to
respective second terminal means supported by the base member
outside the protective gastight enclosure for selectively supplying
electric load current to a load outside the enclosure via the first
and second electric switch contact means, and
switch energization circuit means on the non-bending portion for
applying bender energization potential to a selected plate element
in the bender portion, the bender energization potential having a
selected direct current polarity so that no depolarization of the
plate elements occurs during successive operations of the bender
member. .Iaddend. .Iadd.27. The apparatus of claim 26 wherein the
switch energization circuit means comprises electric circuit
components in the form of passive circuit elements and/or active
semiconductor devices. .Iaddend. .Iadd.28. The apparatus of claim
26 comprising a plurality of bender members physically mounted
within a single common gastight protective enclosure, with each
bender member being separately actuable for controlling load
current flow therethrough. .Iaddend.
Description
TECHNICAL FIELD
This invention relates to novel advanced power rated piezoelectric
ceramic power switching devices which are mounted within protective
gastight enclosures that are either evacuated to a high degree of
vacuum or filled with an inert gas protective atmosphere.
More specifically, the invention relates to such advanced
piezoceramic power rated switching devices that are capable of
operation over a range of voltages extending from a few volts to
5000 volts (5 KV) or more with corresponding currents of from a few
amperes to hundreds of amperes, and wherein it is possible to
provide a number of such structures in a single common protective
gastight enclosure, without interaction.
BACKGROUND PRIOR ART
In the past electromagnetically actuated (EM) relays and switches
have been employed for use in higher power rated circuits having
power ratings of from a few volts to 5 KV or more and with
corresponding current ratings of from 50 amperes to several hundred
amperes or greater. These EM relays and switches while satisfactory
in many respects are bulky, heavy, slow responding and tend to
develop excessive arcing and sparking across the contacts during
operation while opening and closing due to their operation in an
ambient air atmosphere.
For a number of practical reasons, due to their bulk, weight and
out gassing properties, known EM relays and switches can only be
operated in air and cannot be enclosed within a protective gastight
enclosure that is evacuated.Iadd.. .Iaddend.Operation in air
enables prolonged arcing which is induced during opening and
closing of the contacts of such EM relays and switches. This is due
to ionization of the air gaseous medium in the space between the
contacts as they open or close so that the operating life of such
EM devices in service is severely reduced .[.and.]. .Iadd.which
.Iaddend.adds greatly to maintenance problems and expense. Further,
EM devices dissipate considerable heat and cannot be upgraded in
performance since they are not voltage (capacitor) operated.
Lastly, operation of EM device contacts in air induces oxidation of
the contact surfaces .[.and.]. .Iadd.which .Iaddend.can greatly
increase contact resistance.
Relays and switches which use piezoelectric drive elements have a
number of advantages over their electromagnetic (EM) driven
counterparts. For example, a piezoelectric driven relay or switch
requires substantially lower current and dissipates very little
power during operation to open or close a set of load current
carrying contacts in comparison to an electromagnetic driven device
of the same power rating. Additionally, piezoelectric driven
switching devices have very low mass, require less space and
introduce less weight into circuit systems with which they are
used. Lastly, piezoelectric driven switching devices may have very
short actuation times and thus respond much faster than do their EM
counterparts. Thus, fast acting switching is possible with smaller
and lower weight devices which dissipate less power and generate
less heat than does an EM relay or switch of the same power
rating.
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 and prevailing structural
approaches in these known devices.[.,.]. is referred to as a
bimorph bender-type piezoelectric ceramic switch device which
employs two adjacent piezoelectric plate elements mounted side by
side and having conductive electrodes coating their outer surfaces
and sharing a common conductive inner surface to form a bimorph
bender member. A known commercially available bimorph bender-type
piezoceramic switch is described in an application note
copy-righted in 1978 .Iadd.and .Iaddend.published by the Piezo
Products Division of Gulton Industries.[.,.]. Inc. located in
Metuchen, N.J. and Fullerton, Calif. Another such prior art
piezoceramic switching device is described in U.S. Pat. No.
2,166,763 issued July 18, 1939 for a "Piezoelectric Apparatus and
Circuits". In the intervening years since 1939, piezoceramic
bender-type switching devices have been the subject of
widely-spread efforts to improve their characteristics. This is
evidenced by a relatively large number of patents which have issued
in the intervening years such as U.S. Pat. No. 2,714,642 issued
Aug. 2, 1955 for a "High Speed Relay of Electromechanical
Transducer Material"; U.S. Pat. No. 4,093,883 issued June 6, 1978
for "Piezoelectric Multimorph Switches".Iadd.; .Iaddend.and U.S.
Pat. No. 4,403,166 - issued Sept. 6, 1983 for "Piezoelectric Relay
with Oppositely Bending Bimorph". Such piezoceramic bender-type
switching devices also have been described in a textbook entitled
"Manual of Electromechanical Devices" by .[.Douglass.]. Douglas C.
Greenwood, editor, published by McGraw-Hill Book Company and
copyrighted in 1965.
Heretofore, piezoelectric ceramic bender-type relays have been
described as being employed in a variety of circuits which involve
switching of low power rated electrical circuits (i.e., signal
level circuits with voltages less than 20 volts and corresponding
milliamp range currents). Virtually no commercially available
relays have been sold. Also, to date no serious effort has been
made to increase the power rating of piezoceramic bender-type
relays. A key requirement for a bender actuated relay is the
ability of the short gap that forms between the bender-actuated
switch contacts as they open (or close) to withstand voltages
impressed upon it by the external circuit to which the device is
connected. To increase the voltage withstandability of this gap
between the contacts after extinction of current flow, it is
advantageous to choose an ambient atmosphere such as a vacuum or an
inert gas or high dielectric strength atmosphere such as nitrogen
and argon or sulfur hexafluoride (SF.sub.6), and the like. In such
protective vacuum or inert gaseous atmospheres, the gap space
between the contacts can attain as high a dielectric as is
possible. This is an important consideration regardless of whether
the circuit to be switched operates .Iadd.at .Iaddend.a few volts
or 5000 volts since the ability of the contact gap-space to
withstand whatever voltage is required after current extinction
while the gap spacing is short, translates into a shorter time
needed to achieve that gap and consequent higher operating speeds
and capability of higher voltage operation.
Relays (which were not piezoelectric in nature) have been operated
in a vacuum according to a report in a prior publication entitled
"High Voltage Switching with Vacuum Relays" by Ronald V. Tetz and
Robert W. Hansen in a paper presented in 1965 at a relay conference
conducted by the Institute of Electrical and Electronics Engineers
(IEEE). In this publication there is no clear disclosure of the
mechanical details of construction of the switch or how it was
arranged so that contacts .[.were.]. .Iadd.could be
.Iaddend.operated in a vacuum. Further, as of the present date so
commercially practical high power vacuum relays have appeared on
the market. In addition, at a conference held in 1978 by the IEEE
and identified as the Holm Conference, a paper was presented
entitled "Electret Driven Electrical Relays" by D. Perino, G.
Dreyfus and J. Lewiner-pages 441-446 wherein an electret, not
piezoelectric, type relay device .Iadd.was .Iaddend.operated in a
vacuum enclosure .[.and suitable for use.]. at signal levels (less
than 20 volts) .[.is.]. .Iadd.as .Iaddend.disclosed on page 445.
However, electrets due to their nature are hard to bake out during
evacuation and further do not hold their charge well so that
prolonged usage would not be possible. To the knowledge of the
present inventors there has been no previous publication or use of
piezoelectric ceramic switching devices mounted and operated within
a protective gastight enclosure either in a vacuum or in a
protective inert gaseous atmosphere .[.and suitable.]. for
operation at higher power levels.
SUMMARY OF INVENTION
It is therefore a primary object of this invention to provide novel
advanced piezoelectric ceramic power switching devices designed for
operation within a vacuum or protective inert gas atmosphere
maintained within .[.the.]. .Iadd.a .Iaddend.protective gastight
enclosure containing the piezoceramic switching devices, and
wherein the piezoceramic switching devices are designed for use
with higher power rated circuits ranging from a few volts with a
corresponding current rating of 50 or so amperes up to 5 KV or more
with corresponding current ratings of several hundred amperes
.[.and also can be.]. .Iadd.as well as .Iaddend.operated at low
voltages and power in signal level circuits.
Another object of the invention is to provide such advanced
piezoceramic power switching devices wherein there are a plurality
of such switching devices mounted within a single common protective
gastight enclosure.
A further object of the invention is to provide such novel
piezoceramic power switching devices which are mounted within a
protective gastight enclosure and which employ piezoelectric plate
elements that have unpoled portions on which are mounted either
passive circuit components such as resistors, capacitors and the
like, and/or active semiconductor devices. Such circuit components
can be interconnected in circuit relationship with each other and
with the switching devices and may be constructed using discrete,
printed circuit or integrated circuit fabrication and mounting
techniques. As a result, stray circuit impedances which may be
either capacitive, inductive or resistive in nature (and which are
present in all electrical circuits) can be reduced to an absolute
minimum. In certain embodiments of the invention such circuit
components and active semiconductor devices are mounted within the
common protective gastight enclosure in close proximity to the
piezoceramic switching devices to which they are connected.
Still a further object of the invention is to provide such novel
piezoceramic power switching devices contained within protective
gastight enclosures wherein improved bender properties are provided
to the devices .[.and result in.]. .Iadd.for .Iaddend.increased
bender force and displacement, .[.the.]. optimization of
prepolarization and spacing of the bender contacts relative to
fixed contacts with which the bender contacts coact and .[.the.].
capability of .[.operation of.]. .Iadd.operating .Iaddend.of the
switch contacts at higher voltages because of the higher dielectric
of the vacuum or protective gaseous atmosphere in which they are
mounted. Because of the protective atmosphere and inherent
outgassing when the gastight enclosure is evacuated and sealed, no
protective conformal coatings or .[.enscapulation.].
.Iadd.encapsulation .Iaddend.of the piezoceramic plate elements
comprising the bender is required such as that needed with benders
designed for operation in air. It is .Iadd.also .Iaddend.possible
to employ contact materials having lower melting .[.point
materials.]. .Iadd.points .Iaddend.for establishment of stable arcs
to reduce di/dt at current extinction and which at the same time
also have high dielectric strength for improved high voltage
withstandability when the contacts open and current ceases to flow
at current extinction. Because of the higher dielectric strength
achieved while operating .[.the.]. .Iadd.such .Iaddend.improved
.[.material.]. .Iadd.contact materials .Iaddend.in a vacuum or
protective gas atmosphere, voltage withstandability of the order of
2000 volts per mil can be obtained across properly designed
contacts for such devices Further, repeatable and reliable timing
of bender-charging, contact closing, bender discharge, contact
opening and reverse bender "assist" as desirable or needed, is
optimized with the present invention. Since gap dimensions are
minimal, bounce and other .[.detremental.]. .Iadd.detrimental
.Iaddend.dynamic factors can be better controlled by suitable
design.
In practicing the invention a controlled protective atmosphere
bender-type piezoelectric ceramic switching device is provided and
comprises a gastight protective enclosure secured to a base member
for supporting the enclosure and sealing closed the interior of the
enclosure in a gastight manner. At least one bender-type
piezoelectric ceramic switching device is secured within the
gastight protective enclosure and comprises a bender member formed
by two juxtaposed prepolarized .[.peizoelectric.].
.Iadd.piezoelectric .Iaddend.ceramic planar plate elements secured
together sandwich fashion with each plate element having at least
inner and outer conductive surfaces formed on the planar surfaces
thereof together with respective terminal means for application of
energizing electric operating potentials to the respective plate
.[.element.]. .Iadd.elements.Iaddend.. The bender-type
piezoelectric ceramic switching device is physically supported on
the base member by clamping means secured on opposite sides of the
bender member and physically supporting the bender member within
the gastight enclosure cantilever fashion with one end thereof
freely movable. First movable electric switch contact means are
provided within the gastight enclosure for movement by the free
movable end of the bender member and coacts with second electrical
switch contact means also physically mounted within the gastight
enclosure. The second switch contact means are selectively
engageable by the first electric switch contact means upon
selective application of an energizing electric operating potential
to a respective one of the piezoelectric plate elements for causing
the bender member to bend and close the first and second electric
switch contact means to allow electric load current flow
therethrough. Respective electrically conductive load current lead
means are connected to respective ones of the first and second
electric switch contact means and extend to respective terminal
means supported by the base member outside the protective gastight
enclosure for selectively supplying electric load current to a load
outside the enclosure via the first and second electric switch
contact means.
In preferred embodiments of the invention, the portions of the
piezoelectric ceramic plate elements clamped under the clamping
means are non-poled and both electrically neutral and physically
unstrained.
Another feature of the invention is the provision of a plurality of
bender-type piezoelectric ceramic switching devices physically
mounted within a single common gastight protective enclosure in the
manner described above with each such device being separately
actuatable for controlling electric load current flow through its
coacting switch contacts. In certain embodiments of the invention
thus constructed, each bender-type piezoelectric ceramic switching
device mounted within the common protective enclosure operates
independently of the other switching devices mounted within the
same common protective enclosure. In still other embodiments of the
invention, a plurality of bender-type piezoelectric ceramic
switching devices mounted within a common protective enclosure
selectively can be made to coact interdependently with selected
other switching devices mounted within the same common protective
enclosure.
A further feature of the invention is the provision of novel
switching devices constructed in the above-described manner wherein
the gastight protective enclosure is permanently evacuated and
maintains the piezoceramic switching device or devices mounted
therein in a high degree of vacuum throughout the operating life of
the devices. In other embodiments of the invention the piezoceramic
switching devices mounted within a gastight enclosure are
maintained within a protective inert gas atmosphere.
Still a further feature of the invention is the provision of
improved switching devices having the above-described
characteristics wherein the piezoelectric ceramic planar plate
elements of each bender device have unpoled portions which extend
beyond the clamping means in a direction away from the prepolarized
movable bender portions thereof and which are non-polarized so as
to be electrically neutral and physically unstrained. The devices
thus constructed further include electric circuit components in the
form of passive circuit elements such as resistors, capacitors, and
the like and/or active semiconductor devices supported by said
unpoled portions of the piezoceramic plate element and electrically
connected in circuit relationship with each other and the switching
device. This in effect makes it possible to reduce stray circuit
impedances of circuits connected to the switching devices to an
absolute minimum.
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 from a reading of the following
detailed description, when considered in connection with the
accompanying drawings, wherein like parts in each of the several
figures are identified by the same reference characters, and
wherein:
FIG. 1 is a side elevational view of an advanced piezoceramic power
switching structure employing a piezoelectric ceramic bender-type
switching device mounted .[.with.]. .Iadd.within .Iaddend.an
evacuated protective gastight enclosure according to the
invention;
FIG. 2 is a fragmentary front view of the piezoceramic power
switching .[.device.]. .Iadd.strucutre .Iaddend.of FIG. 1;
FIG. 3 is an enlarged top plan view of the piezoceramic switching
device shown in FIG. 1 removed from the protective gastight
enclosure;
FIG. 4 is a vertical sectional view taken through plane 4--4 of
FIG. 3;
FIG. 5 is a longitudinal sectional view of a preferred embodiment
of the invention which provides unpoled portions of the
piezoceramic plate elements comprising the bender-type switching
device for use in mounting and clamping the bender-type switching
device within a protective gastight enclosure and for supporting
electrical circuit components thereon in close proximity to the
switching device;
FIG. 6 is an enlarged partial sectional view of the device shown in
FIG. 5 illustrating in detail how the bender-type switching device
is physically mounted and clamped cantilever fashion within the
.[.portective.]. .Iadd.protective .Iaddend.gastight enclosure shown
in FIG. 5;
FIG. 7 is a longitudinal sectional view of still a different
embodiment of the invention mounted within an all metal protective
gastight enclosure and provided with surface mounted device
terminals for ease of installation and wherein there are a
plurality of piezoceramic bender-type switching devices mounted
within a single common protective gastight enclosure;
FIG. 8 is a longitudinal sectional view of still another embodiment
of the invention wherein the protective gastight enclosure is
comprised by a glass tube secured within a metal mounting sleeve
which in turn is secured on a metal base member and wherein the
piezoceramic plate elements include unpoled plate portions for
mounting and for supporting circuit components outside the
protective gastight enclosure;
FIG. 9 is a longitudinal sectional view of still another embodiment
of the invention employing a single surrounding protective gastight
enclosure fabricated from a plastic material that is overcoated
with a conductive surface to provide electromagnetic radiation
shielding and wherein a plurality of switching devices are mounted
within the gastight enclosure; and
FIG. 10 is a longitudinal sectional view of still another
embodiment of the invention similar to that of FIG. 9 but wherein
unpoled portions of the piezoceramic plate .[.element.].
.Iadd.elements .Iaddend.are provided for use in clamping and
mounting the bender-type switching devices cantilever fashion
within the enclosure and also providing mounting surfaces on which
circuit elements comprising the switching circuit with which the
switching devices are used are all mounted within a single common
gastight enclosure and there are a plurality of switching devices
within the same protective gastight enclosure.
BEST MODE OF PRACTICING THE INVENTION
FIG. 1 is a side elevational view of a novel advanced piezoceramic
power switching device employing a protective gastight enclosure
constructed accompanying to the invention. In FIG. 1, a gastight
protective glass enclosure is shown at 11 which is in the form of
an inverted glass jar having one end supported over a glass base
member 12 for supporting the glass enclosure and sealing closed the
interior of the enclosure in a gastight manner. A nipple shown at
13 is formed on one side of the glass enclosure 11 for connection
to a suitable vacuum pumping device (not shown) for evacuating the
interior of the glass enclosure 11 to a high degree of vacuum. The
fabrication of the protective glass enclosure 11 and its securement
to the base member 12 which preferably is fabricated from glass or
an insulating non-outgassing plastic insulating material, is in
accordance with known and established electron tube manufacturing
techniques as disclosed in such prior publications as the "Handbook
of Electron Tube and Vacuum Tube Techniques" by Fred Rosbury
published by Addison-Wesley Publishing Company.[.,.]. Inc. of
Reading, Massachusetts, the textbook entitled "Fundamental of
Vacuum Tubes" by Austin B. Eastman, first edition fourth impression
published by McGraw-Hill .Iadd.Book .Iaddend.Company.[.,.]. Inc. of
New York and London in 1937 and the textbook entitled "Theory and
Applications of Electron Tubes" by Herbert J. Reich, second edition
second impression published by McGraw-Hill .Iadd.Book
.Iaddend.Company.[.,.]. Inc. of New York and London in 1944.
At least one bender-type piezoelectric ceramic switching device
shown generally at 14 is mounted within the gastight enclosure 11
and is physically supported therein by the base member 12. The
bender-type piezoelectric ceramic switching device 14 comprises a
bender member 15 which as best shown in FIG. 4 is comprised by two
juxtaposed prepolarized planar piezoelectric ceramic plate elements
15A and 15B secured together sandwich fashion to form a unitary
structure with each piezoceramic plate element having at least an
inner conductive surface 15C which they share in common and outer
conductive surfaces 15D and 15E. Respective electric terminal means
shown at 16, 16A and 16B are provided for application of energizing
electric operating potentials to the inner conductive surface 15C
and to each of the outer conductive surfaces 15D and 15E,
respectively. The bender-type piezoelectric ceramic switching
device 14 is physically mounted cantilever fashion within gastight
enclosure 11 on base member 12 by clamping means shown at 17.
Clamping means 17 comprise a set of coaching clamping members 17A
and 17B which are disposed on opposite sides of bender member 15
with the lower end of the bender member being clamped sandwich
fashion between clamping members 17A and 17B with the movable ends
thereof extending upwardly in the manner of a cantilever.
The clamping members 17A and 17B are secured to and supported by a
set of relatively rigid, upright, spaced apart, conductive contact
support members 18 and 19 with the bender member 15 .Iadd.being
.Iaddend.sandwiched therebetween cantilever fashion and the entire
structure .Iadd.being .Iaddend.held together in a relatively rigid
manner by through bolts and nuts shown at 21. The clamping members
17A and 17B are formed of electrically conductive material and have
terminal leads 16A and 16B secured therein so that they make good
electrical contact with and connection to the respective outer
conductive surfaces 15D and 15E on piezoceramic plate elements 15A,
15B for application of energizing electric potential to these
surfaces. It should be noted that since the piezoelectric ceramic
plate elements 15A and 15B are excellent electrical insulators,
they provide electrical isolation between the outer conductive
surfaces .[.15B.]. .Iadd.15D .Iaddend.and 15E and their respective
terminal lead connections provided by the clamping members 17A, 17B
and conductive leads 16A, 16B, respectively. The clamping memebrs
17A and 17B are electrically isolated from the conductive contact
supporting bars 18 and 19 by insulating surfaces 22 and 23,
respectively. For a more detailed description of a preferred form
of fabrication and operation including excitation of the
bender-type piezoelectric ceramic switching device 14 (to be
described more fully hereafter with relation to FIGS. 5 and 6),
reference is made to copending U.S. patent application Ser. No.
685,109 in the names of John D. Harnden, Jr. and William P.
Kornrumpf for Improved Piezoelectric Ceramic Switching Devices and
Systems And Method of Making Same filed concurrently with this
application, the disclosure of which hereby is incorporated into
the disclosure of this application in its entirety.
As noted in the .[.preceeding.]. .Iadd.preceding
.Iaddend.paragraph, the bender member 15 is supported cantilever
fashion within the gastight enclosure 11 by clamping means 17 in a
manner such that its movable free end is supported and centered
within the space defined between the free ends of the upright
conductive contact support bars 18 and 19. The movable free end of
bender 15 has a first electric switch contact 24 secured thereon in
the form .Iadd.of .Iaddend.an electrically conductive cap that is
electrically insulated from the outer conductive surfaces 15D and
15E by an insulating cap member 25 secured to the end of bender
member 15 under conductive cap 24. Secured to conductive cap 24
between the cap and the insulating cap 25 is a flexible braided
copper belt shown at 26 which runs down to and is secured to the
upright conductive support bar 18 about midway .Iadd.in
.Iaddend.its length for providing an electric current path between
conductive cap 24 and bar 18. A similar braided conductive belt 26
runs from the left side of the conductive cap 24 to midway the
length of upright conductive support bar 19 as shown in FIGS. 1-3
of the drawings, but has not been shown in FIG. 4 in order to
simplify the figure. The lower ends of the conductive braided belts
26 are secured to the respective upright conductive support bars 18
and 19 by respective set screw and nut fasteners 27.
To complete the bender-type switching device 14, second electric
contact means shown at 28 and 29 are secured to the free ends of
the upright, conductive contact support bars 18 and 19,
respectively, as best seen in FIG. 4. By this arrangement, it will
be seen that when the bender member 15 is caused to bend and close
the movable first contact 24 onto contact 29 on conductive bar
member 19, a closed, electrically conductive load current path is
provided through the upright bar member 19 to the closed contacts
29 and 24 and thence through the flexible braided conductor 26 and
back through upright conductive bar member 18 to the load device
(not shown) selectively being supplied current through the
piezoelectric ceramic switching device 14. Similarly, with the
movable contact 24 closed on the fixed contact 28, a closed load
current flow path will be established via the closed contacts 24
and 28, via the conductive belt 26 connected to conductive bar
member 19 (not shown in FIG. 4) and thence back across the supply
current source and load. It will be appreciated therefore that the
respective first and second electric switch contact means comprised
by movable contact 24 and fixed contacts 28, 29 are provided with
respective electrically conductive lead means 26, 18 or 26, 19
extending to respective terminal means comprised by terminal pins
.[.18.]. .Iadd.18A .Iaddend.and .[.19.]. .Iadd.19A
.Iaddend.supported by the base member outside the protective
gastight enclosure 11 for insertion in cooperating sockets (not
shown) on a circuit board or other member. Thus, electric load
current to a load selectively can be supplied outside the enclosure
via the first and second electric switch contacts 24, 28 or 24, 29,
respectively. It should be further noted that while in the
embodiment of the invention shown in FIGS. 1-4, the lead terminal
means includes a flexible conductive belt member 26, it should be
understood that the lead means need not necessarily constitute such
a flexible conductive belt but could be comprised by conductive
runs, jumper conductors or either the inner or outer conductive
surfaces such as 15C, 15D or 15E and their corresponding terminal
ends 16, 16A, 16B or the like, as described more fully in the above
referenced copending U.S. patent application Ser. No. 685,109.
FIG. 3A illustrates a modified version of a power switch contact
system usable in the switching device of FIGS. 1-4 in place of that
shown in FIG. 3. In FIG. 3A a first set of fixed contacts 28 and
28' are mounted on spaced-apart support posts (not shown, but
similar to posts 18 in FIG. 4) located on one side of the movable
switch contact system comprised by contacts 24 and 24' secured to
the end of bender member 15 and electrically interconnected by an
electrically conductive bridging member 24A also secured to the end
of bender member 15. A second set of fixed contacts 29, 29' are
secured on the opposite side of bender member 15 on posts 19 in
confronting relation to movable contacts 24, 24'. Fixed contacts 28
and 28' and 29 and 29' are physically interconnected by insulating
bar members 28A and 29A, respectively, and electrically connected
to braided conductors 26 and 26' for supply of load current from a
load current source (for example) connected through braided
conductors 26 to a load (not shown) connected to braided conductors
26'. With this contact structure, current will be supplied to the
load via contacts 29, 24, bridging conductor bar 24A and contacts
24', 29' upon the movable bender member closing movable contacts 24
and.[.,.]. 24' .[.and.]. on fixed contacts 29 and 29'. Upon
movement of the bender member in the opposite direction to close
movable contacts 24, 24' on fixed contacts 28, 28' current will be
supplied to the load via conductive bridging member 28A. Note that
in this structure, the movable bender member does not have to carry
with it any of the braided conductors 26 .Iadd.and 26'.
.Iaddend.
With the bender-type piezoelectric ceramic switching device
constructed as shown and described with relation to FIGS. 1-4 of
the drawings and mounted within a gastight evacuated enclosure, it
is possible to prepolarize the piezoceramic plate elements 15A and
15B in-situ after fabrication of the device in the manner described
above. As disclosed more fully in the above-referenced copending
U.S. application Ser. No. 685,109, permanent prepolarization of the
movable bender portions of the piezoelectric ceramic plate elements
15A and 15B is accomplished by the application of respective high
electric potential to the plates via conductive lead means 16A and
16B, respectively. The high electric prepolarizing potential can be
applied while the plates are being maintained at a temperature near
and just below their Curie point. This can be accomplished
immediately following bakeout of the evacuated gastight enclosure
11 while manufacturing commercial embodiments of bender-type
piezoceramic switching devices according to the invention.
Commercial embodiments may not include the nipple 13 for
continuously evacuating the enclosure 11, 12. The required bakeout
and evacuation techniques are described more fully in the
above-referenced vacuum tube technology textbooks. In many
embodiments of the invention it may be desirable to employ known
and established gettering techniques applied after the enclosure
has been sealed as explained in the above vacuum tube technology
texts. Flash gettering also could be used advantageously. By
combining techniques of evacuation and bake-out with gettering,
good clean-out of the vacuum-tight enclosures can be achieved less
expensively.Iadd.. .Iaddend.
Following evacuation and bakeout and while the temperature of the
piezoceramic plate elements 15A and 15B is maintained just under
the Curie temperature, high value prepolarizing potentials are
applied to conductive surfaces .[.16A.]. .Iadd.15D .Iaddend.and
.[.16B.]. .Iadd.15E, .Iaddend.respectively, while the common
conductive surface 15C and its terminal 16 is held at an opposite
polarity potential or substantially at ground potential. It should
be noted at this point that because the high value prepolarizing
potential is applied to the piezoceramic plate elements 15A and 15B
while they are being maintained in a vacuum, and due to the high
dielectric value of the vacuum, there is much less susceptibility
to breakdown and arcing across the piezoceramic plates during the
application of the high value prepolarizing potential. Further
higher value prepolarizing potentials can be employed to result in
optimized bender operating characteristics such as faster response
time and improved contact compressive force as explained hereafter.
Room temperature polarizing is also possible since the Curie
temperature can be approached in sealing and bake-out with new
bender materials that make poling at ambient .[. termpratures.].
.Iadd.temperatures .Iaddend.in situ possible and provides a whole
new technique for piezoelectric bender manufacture.
As described more fully in the above-referenced copending U.S.
patent application Ser. No. 685,109, prepolarization of the movable
bender plates 15A and 15B will leave the plates permanently altered
in physical dimensions relative to what they were prior to
prepolarization and with a .[.remnant.]. .Iadd.remanent
.Iaddend.electric charge. This alteration will be in the form of a
permanent increase in physical dimension of the ceramic plate
elements 15A and 15B between the poling electrodes 15D-15C
.[.and.]. .Iadd.or .Iaddend.15E-15C and also a permanent decrease
in physical dimension parallel to the .[.electrode.].
.Iadd.electrodes .Iaddend.(i.e., along the longitudinal dimensions
of the device as shown in FIG. 4). Thereafter, when a voltage of
the same polarity but considerably less magnitude than the
prepolarizing voltage, subsequently is supplied as an energizing
potential between the poling electrodes 15D-15C or 15E-15C, the
plate elements 15A or 15B experience a further temporary expansion
in the poling direction transverse to the electrodes and
contraction parallel to the electrodes. This causes bender member
15 to bend in one direction or the other dependent upon which plate
element is energized. When the selectively applied energizing
potential is removed, this temporary expansion in the poling
direction transverse to the electrodes and temporary contraction
parallel to the electrodes is relaxed and the bender member 15 will
return to its normal, at rest, unenergized, centered condition.
Thus, it will be appreciated that the movable bender member 15
selectively can be made to bend in one direction or the other by
application of a suitable energizing potential thereto through
dipole enhancement to selectively close either contacts 24-28 or
24-29 and thereafter, upon removal of the energizing potential,
automatically will return through internal compressive spring
forces to its original prepolarized at rest central position with
the contacts .[.25-28.]. .Iadd.24-28 .Iaddend.and .[.25-29.].
.Iadd.24-29 remaining .Iaddend.open.
It should be noted at this point in the description that a
particularly desirable feature of the invention is the ability to
precisely control centering of the bender member 15 with its
centrally located movable contact 24 so that the contact 24 is
precisely centered relative to the fixe contacts 28 and 29. This is
achieved by appropriately adjusting the magnitude of prepolarizing
potentials applied in situ across the respective plate elements 15A
and 15B during prepolarization thereof as described in the
.[.preceeding.]. .Iadd.preceding .Iaddend.paragraph all externally
of the sealed protective gastight enclosure. This novel centering
.[.techniques.]. .Iadd.technique .Iaddend.makes possible
considerable savings in device fabrication costs by combining the
prepolarization and centering manufacturing steps into one.
A suitable energization circuit for selectively energizing either
piezoceramic plate element 15A or 15B to achieve dipole enhancement
of the previously prepolarized bender member in the above briefly
described manner is disclosed in FIG. 1B of copending U.S.
application Ser. No. 685,109 and reference is made to the
description of FIG. 1B for a full disclosure of its construction
and operation. The energization circuit has not been shown in the
drawings of this application for the sake of simplicity. Briefly,
however, it can be stated that the circuit operates to provide
selective application of an energizing potential to either of the
piezoceramic plate elements 15A or 15B which is of smaller
magnitude than the prepolarizing potential, but of the same
polarity. This energization potential results in further dipole
alignment enhancement that is reflected in a temporary further
thickening and shortening of one or the other of the plate elements
15A or 15B. This temporary further thickening and shortening of one
of the plate elements consequently .[.result.]. .Iadd.results
.Iaddend.in physically bending the free movable end of the active
bender member 15 sufficiently to selective close the movable
contact 24 on either of the fixed contacts 28 or 29 thereby
resulting in establishing load current flow through either of the
fixed contacts in the manner described previously above. The load
current carrying contacts 24-28 or 24-29 will remain closed for so
long as the energizing potential continues to be applied to the
respective piezoceramic plate element 15A or 15B being selectively
energized. This can be for an indefinite period of time. Thus, the
switching device shown in FIGS. 1-4 can be used either as a
normally-open or a normally-closed switching device.
The above described characteristics are achieved by reason of three
.[.principle.]. .Iadd.principal .Iaddend.features of the switching
devices herein disclosed and by appropriate design of the
energizing circuit with which they are used. First, the
piezoceramic plate elements 15A and 15B essentially are high
quality capacitors having little or no losses when electrically
charged (energized). Secondary, any losses which do occur over
extended periods are supplanted immediately and continously by the
continuously applied energizing potential via the energizing
circuit. Thirdly, and lastly, because the energizing potential
selectively applied to the respective piezoceramic plate elements
15A and 15B always is applied with the same polarity as the
prepolarization potential used to initially prepole the
piezoelectric ceramic plate elements 15A and 15B, there is no
possibility of long term depolarizing effects rendering the device
unstable or unpredictable in operation over prolonged periods of
operation since the dipole alignment is continuously enhanced.
Upon removal of the selectively applied energizing potential to
either of the piezoceramic plate elements 15A or 15B, the active
movable bender .[.portion.]. .Iadd.member .Iaddend.15 returns to
its center, neutral, unenergized position thereby opening whichever
set of load current carrying contacts 24-28 or 24-29 was closed. It
should be noted at this point in the description that
prepolarization and subsequent operation with selectively applied
energizing potential can be achieved with either a positive
polarity or negative polarity potential measured with respect to
the outer conductive surfaces .[.15B.]. .Iadd.15D .Iaddend.or
.[.15C.]. .Iadd.15E .Iaddend.relative to the central conductive
surface 15C.
During its operating life, a power-current switching device spends
most of its life with its contacts butted firmly against each other
to conduct normal system load current. However, under conditions
where it is desired to interrupt load current flow through the
switching device, the contacts must be parted. This results in
igniting within a gap space formed between the parting contacts of
the device an arc discharge that subsequently is extinguished to
accomplish interruption or extinction of current flow between the
contacts. This phenomenon is explained more fully in a textbook
entitled "Vacuum Arcs Theory and Application" by J. M.
Lafferty.Iadd., .Iaddend.editor, and published by John Wiley &
Sons, New York, N.Y..Iadd., .Iaddend.copyrighted 1980, and in
particular in chapter 3 thereof entitled "Arc Ignition Processes"
by George A. Farrall, a co-author of the book and one of the
co-inventors of this application.Iadd.. .Iaddend.On page 81 of this
textbook it is stated that two cylindrical metal electrodes
(contacts) held with their flat faces one against the other, have
actual areas of contact much smaller than the apparent area of the
cylindrical ends of the contacts. This is a natural consequence of
the fact that the surface of a normally flat electrode (contact)
microscopically is very uneven. As the electrodes (contacts) are
pushed together, the microscopic projecting regions on the opposing
surfaces thereof make initial contact. With added compressive force
(called contact compressive force) pushing the contacts together,
the initial contact area or areas may be elastically or even
plastically deformed, allowing the bulk or the contact surfaces to
approach each other a little more closely and permitting other
.[.protuberances.]. .Iadd.protuberances .Iaddend.to supplement the
initial contact. As a consquence, the total area of contact is made
up of a number of microscopically small areas (which vary
statistically in size and number) and depend strongly on the
compressive force applied to the contacts, their microscopic
surface finish, and the elastic/plastic properties of the material
from which the contact members are fabricated. These properties
widely effect the formation of an arc within the region formed as
the contacts part while conducting load current.
For the above stated reasons, one can consider that the actual
contact area is made up of several discrete small areas
consolidated to form one large circular composite area having an
electrical resistance given by
where .pi. is the resistivity of the contact material and a is the
composite radius. Because the load current passing from one
electrode to the other is funneled through the contacting area, the
value of Rc frequently is referred to as constriction resistance or
more simply as contact resistance. It has already been stated that
the effective microscopic contact area is dependent on contact
compressive force, contact surface finish and the elastic/plastic
properties of the contact material. It therefore can be expected
that the same parameters directly influence contact resistance Rc.
It might also be noted that contact resistance can be influenced by
the formation of films such as oxide on the contact surfaces;
however, for the particular case of a vacuum enclosure or inert gas
protective atmospheres, contact electrodes are usually quite clean
so that contact resistance depends principally upon the parameters
noted in equation (1) above.
In order to provide illustration of the magnitude of effective
contact area that may be realized in a typical EM actuated vacuum
interrupter, a 15 KV vacuum interrupter whose contacts were
compressed under a load of 50-60 kilograms (KG), was determined to
dissipate no more than 14 watts with a normal load current of 600
amperes. About one third of this dissipation was considered to be
due to contact resistance. From this it can be inferred to possess
a contact resistance of less than 14 micro ohms (.mu..OMEGA.) at
room temperature. Assuming this value of contact resistance, then
the value of a is found to be 6.4.times.10.sup.-4 meters with a
corresponding contact area of 1.3.times.10.sup.-6 squaremeters.
This represents less than 1 part in 10.sup.-3 of the apparent
contact area of the contact system in question. However, since the
constriction resistance region obviously is not at room
temperature, the actual contact area realized probably is somewhat
larger.Iadd.. .Iaddend.The example, however, does show that the
actual conducting area joining two closed contacts is very much
less than might be guessed by viewing the switching device in
question.
It has been determined experimentally that the constriction
resistance Rc is found to vary with the power of the compressive
load imposed on the contacts by a factor of one half to one third.
It is important to note at this point that in addition to all of
the desirable characteristics embodied in a piezoelectric ceramic
switching device operated within a gastight vacuum enclosure, by
reason of the capability of maintaining the excitation voltages
supplied to the bender plate elements 15A and 15B continuously
after closure of the movable contact 24 on a selected one of the
fixed contacts 28 or 29 without depolarizing effects on the
piezoelectric ceramic plate elements 15A and 15B, it is possible to
continuously maintain the compressive force on the selectively
closed switch contacts indefinitely without relaxation to thereby
maintain the constriction resistance Rc at a minimum value for
indefinite periods of operation. Additionally, because of the
larger prepolarization and energizing potentials made possible by
operation in a vacuum or inert gas protective atmosphere, the
compressive force provided by the bender member can be
substantially increased beyond that of a device operated in
air.
On page 86 of the above .[.referened.]. .Iadd.referenced
.Iaddend."Vacuum Arcs Theory and Application" textbook there is
disclosed a formula
where V.sub.e is the critical velocity of separation of two contact
surfaces, K is the thermal conductivity of the contact material, I
is the load current flowing through the contacts and c is the heat
capacity of the contact system. From this equation it can be shown
that for contact electrodes separating while carrying a load
current of 100 amperes, the critical velocity for separation of a
contact system made from copper is 5 meters per second and for
stainless steel is about 10.sup.-2 meters per second. In the above
stated example for a 15 KV, 1600 ampere vacuum interrupter, the
contact parting speeds are of the order of 1 meter per second as
the contacts start to part. In the earlier part of contact
separation during formation of an arc created constriction bridge
as illustrated and defined on page 83 of the textbook, the parting
speed can be lower. The piezoelectric ceramic switching device
which is the subject of the instant application can be designed to
ideally meet this contact separating and parting speed requirement
since it is possible to design into the energization circuit for
the device the capability of applying a programmed energization
potential both to the selected and to the reverse or opposite
piezoceramic plate elements to initially assist and accelerate
.[.in.]. the initial parting action and after arc formation to
provide improved current interruption. The energization to the
opposite bender plate element thereafter can be removed within
microseconds subsequent to current extinction to avoid going beyond
the neutral center position. This important capability also can be
of considerable importance in overcoming contact welding effects if
and when they occur as described in the above referenced textbook
on pages 87-106 thereof.
In an effort to harmonize design of a contact system such as 24-28
or 24-29 with all of the characteristic effects encountered in its
operating life, it is essential to provide each contact system with
a proper L/D aspect ratio where L is equal to the area
(width.times.length) of the mating contact surfaces and D is equal
to the minimum spacing between the microscopically small
.[.projections.]. .Iadd.projection .Iaddend.regions that are formed
as protuberances on the opposed mating contact surfaces as
described in the .[.preceeding.]. .Iadd.preceding
.Iaddend.paragraph. It is also desirable to use a low melting point
material to reduce di/dt effect at "current chop" (the point where
current flow through a contact system is extinguished). It is also
desirable that the contact material have a high dielectric for high
voltage withstandability when the contacts open. A preferred switch
contact system for use with high power switching devices
constructed according to the invention employs copper-vanadium
alloys .[.and possesses.]. .Iadd.exhibiting .Iaddend.both the
desirable characteristics of relatively low melting .[.point.].
points and high voltage withstandability after current extinction.
For a more detailed disclosure of the copper-vanadium alloy contact
system, reference is made to abandoned U.S. application Ser. No.
399,669 entitled "Electrode Contacts For High Current Circuit
Interruption" filed July 19, 1982, George A. Farrall, inventor (who
is a coinventor of the present invention) and assigned to the
General Electric Company.
A particularly advantageous feature of the invention is the ability
to increase the voltage withstandability upon the contacts opening
by a factor of three or four or more by maintaining a contact
system, such as the .[.coppr.]. .Iadd.copper.Iaddend.-vanadium
alloy contact system noted above, within a gastight vacuum
enclosure or other suitable protective inert gaseous atmosphere.
For example, a contact system which has a voltage withstandability
of say 30 KV per centimeter in air after opening and extinction of
load current flow thereacross, has a comparable voltage
withstandability in vacuum of 90-100 KV per centimeter. Thus, it
will be appreciated that considerable operating advantages are
obtained with the present invention by proper selection of contact
materials and .[.the enclosure of.]. .Iadd.by enclosing
.Iaddend.the load current carrying contacts and the piezoceramic
bender operated switching devices in a protective vacuum gastight
enclosure or gastight enclosure filled with .Iadd.a
.Iaddend.protective inert or high dielectric gaseous
atmosphere.
FIG. 5 illustrates a different embodiment of the invention wherein
similar parts have been given the same reference .[.numeral.].
.Iadd.numerals .Iaddend.applied thereto in the embodiment of the
invention shown in FIGS. 1-4. In FIG. 5 a glass envelope is shown
at 11 shown seated in a cup-shaped plastic or glass base member 12
to which it is sealed in a gastight manner by suitable adhesive or
glass frit seal in the event the cup-shaped base member 12 is made
from glass.
The piezoelectric ceramic switching device 14 is supported
cantilever fashion within the glass enclosure 11 by a mounting
member 17 which is generally circular in configuration and is
sealed to the side of the glass enclosure 11 by a glass frit seal
(not shown). The clamping .[.members.]. .Iadd.member .Iaddend.17
described as comprising glass also could be formed from plastic,
but must be electrically insulating and de-gassable. The
sub-assembly composed of the glass or plastic supporting member 17
and piezoceramic switching device 14 can be assembled initially
outside of the glass enclosure 11 by inserting each of the fixed
rod supports 18 and 19 for fixed contacts 28 and 29 through
suitable openings preformed in clamping member 17 and inserting the
bender member 15 in a suitable central opening designed to
accomodate it and preformed in the clamping member. The bender
member 15 is inserted partially through the central opening of
clamping member 17 so that its lower portion extends below clamping
member 17 in the manner shown in FIG. 5. After being thus inserted
in the member 17, the bender member 15 is secured in member 17
rigidly by means of a glass frit seal shown at 30 in FIG. 6 or by a
suitable adhesive having minimal outgassing characteristics.
The piezoelectric ceramic bender member 15 used in the FIG. 5
embodiment of the invention differs from that shown in FIG. 4 in a
number of respects. The first and most important is that .[.that.].
.Iadd.a .Iaddend.portion of the piezoceramic plate .[.element.].
.Iadd.elements .Iaddend.15A and 15B which is sandwiched between the
sides of the clamping member 17, as well as a portion suspended
below clamping member 17, is not prepoled so that these portions of
the plate .[.element.]. .Iadd.elements .Iaddend.identified by
reference .[.numeral.]. .Iadd.numerals .Iaddend.15AUP and 15BUP are
unpoled and are electrically neutral and physically unstrained. The
portions of the piezoceramic plate elements identified as 15A and
15B which are located above the clamping .[.members.]. .Iadd.member
.Iaddend.17, are prepolarized and hence are electrically charged
and physically stressed in the manner described above with relation
to FIGS. 1-4.
A second significant difference in the fabrication of the bender
member 15 shown in FIG. 5 is that two central conductive surfaces
identified with the reference characters 15C1 and 15C2 are provided
for coacting with the outer conducting surfaces 15D and 15E,
respectively, for application of prepolarization and operating
energizing potentials to the piezoceramic plate element portions
15A and 15B, respectively. The two plate elements and their
adherent conductive surfaces 15C1 and 15C2 are held together in a
unitary structure by a central adhesive layer 30 which may be
either insulating in nature or conductive in nature dependent upon
design criteria and intended usage. If the central adhesive layer
is insulating in nature, than a gap is provided between the two
halves of the upper surface of the conductive cap 24 to provide
separate, electrically isolated movable contact surfaces 24A and
24B on the movable end of bender member 15. Suitable prepolarizing
electric potentials and operating energizing potentials are applied
to the respective outer conductive surfaces .[.15A.]. .Iadd.15D
.Iaddend.and .[.15B.]. .Iadd.15E .Iaddend.via jumper conductors 16A
and 16B and thin surface-mounted terminals pads identified by the
same reference numerals as the jumper conductors to which they are
connected. In a similar manner, jumper conductors identified as
16(1) and 16(2) are provided from the inner conductive surfaces
15C1 and 15C2 to the corresponding numbered terminal pins for
application of operating energizing potential and to provide a
suitable conductive path for load current flow upon closure of
either of the movable contact halves 24A or 24B on their respective
fixed contacts 28 or 29. As best seen in FIG. 6 of the drawings,
the jumper conductors 16A and 16B where they pass through the glass
or plastic clamping .[.members.]. .Iadd.member .Iaddend.17 are
provided with suitable openings through which they are sealed
firmly closed by a glass frit seal or suitable adhesive as shown at
36 in FIG. 6. This same arrangement is provided where the terminal
pins for each of the conductive leads passes through the bottom of
the base member 12, but in order to simplify the drawings, such
sealed passageways have not been illustrated in detail.
A third important feature of the present invention is made possible
by the unpoled portions 15 AUP and 15BUP of the piezoceramic plate
.[.element.]. .Iadd.elements .Iaddend.which .[.extends.].
.Iadd.extend .Iaddend.below the clamping member 17. Suitable
conductive surfaces identified as 32 and 33 are formed on these
unpoled portions of the piezoceramic plate elements so as to form
at least one capacitor in conjunction with the central conductive
surfaces 15C1 or 15C2 within the unpoled region of the piezoceramic
plate elements. If desired, more than one capacitor can be
fabricated in this manner by suitably dividing up the outer
conductive surfaces 32 or 33 or both into the desired number of
capacitors. In addition, either discrete, printed circuit or hybrid
integrated circuit resistors or other circuit components shown at
34 and .[.25.]. .Iadd.35 .Iaddend.including miniaturized
semiconductor active devices are mounted over the conductive
surfaces 32 and 33 or directly onto the unpoled portions of the
piezoceramic plate elements. Such circuit components are connected
in circuit relationship via printed conductors (not shown) or
jumper connector wires and terminal pins 32A, 33A, 34A and 35A as
desired for a particular circuit configuration in a manner
described more fully in the copending U.S. application Ser. No.
685,109 referenced above. By fabrication of the piezoelectric
ceramic switching devices in this manner to provide predetermined
unpoled portions of the plate elements for use as suitable
insulating backing members upon which discrete, hybrid, or
monolithic integrated circuit devices can be formed, it is possible
to reduce stray circuit impedances whether inductive, capacitive or
resistive in nature to an absolute minimum thereby assuring
reliable excitation and operation of the piezoceramic switching
devices.
For those devices which are intended for use in a protective
atmosphere of an inert gas such as nitrogen, argon, helium or a
high dielectric gas such as SF.sub.6 or the like, it may be
desirable to provide an outer conformal coating of a protective
material shown at 15F over the prepolarized portions of bender
member 15. By the provision of such a protective coating, the
possibility of breakdown either during prepolarization or during
subsequent operation, is further reduced. A suitable coating
material for this purpose which would not unduly damp the movement
of the bender member 15 in operation is polyimide siloxane
copolymer which provides an excellent pinhole free surface
passivating protective coating and which also can be used as an
adhesive during bender lamination, for example to secure the two
bender plate elements together as shown in FIG. 5. Other adhesive
materials which could take the high temperature bakeout required
for use in vacuum devices without undue outgassing include
GEMID(imide ether) or ULTEM .[.(polyethermide).].
.Iadd.(polyetherimide). .Iaddend.
The combination of selective bender member poling as shown in FIG.
5 together with always energizing the switch with an energizing
potential having the same polarity as the prepolarizing potential
assures continued reliable operation of the switch in service.
Further, if required for a particular device.Iadd., .Iaddend.the
protective surface coating 15F is applied to completely encompass
all of the active movable areas of the bender member 15 but is not
subjected to the sharp bending action that takes place at the
clamped portion of the piezoelectric plate elements. As a result,
greater reliability, stability and longevity in operation and
voltage withstand capability is achieved.
After fabrication of the piezoelectric ceramic switching device 14
in the above described manner and mounting of the device on the
clamping member 17, the switching device and clamping member
sub-assembly is inserted into the protective gastight envelope 11.
This assemblage is then slipped down into the cup-shaped base
member 12 to which the outer surface of the enclosure 11 then is
sealed either by a glass frit seal if base member 12 is made of
glass, or, alternatively, a suitable adhesive such as those listed
above. At this point, the interior of the gastight enclosure is
evacuated if it is designed to operate as a vacuum device, or
alternatively it is filled with an inert protective gas such as
those noted above, in a manner known to those skilled in the art of
electron tube manufacture. To assure equalization of the atmosphere
within the enclosure 11, through passageways are formed in clamping
member 17 as shown by dotted lines at 17A and 17B and are located
in an evenly distributed manner around the periphery of clamping
member 17.
FIG. 7 is a vertical sectional view of an embodiment of the
invention wherein there are a plurality of piezoelectric ceramic
switching devices 14-1, 14-2 and 14-3 mounted within a single,
gastight protective enclosure 11. In this embodiment of the
invention the gastight enclosure member 11 is fabricated from a
conductive metal which is spot welded, resistance welded, one-shot
welded or cold welded to the base member 12 in a manner such that
the piezoelectric ceramic switching devices are not exposed to any
heat while sealing the enclosure member 11 on to the base member 12
to form the required gastight seal. The individual bender members
15-1, 15-2 and 15-3 are constructed quite similar to the bender
device shown in FIGS. 1-4 in that each employs a single central
conductive surface .[.15C.]. .Iadd.15C-1, 15C-2, or 25C-3
.Iaddend.that is common to the respective piezoelectric ceramic
plate elements of each bender device. The individual bender members
15-1, 15-2 and 15-3 have the lower ends thereof individually
clamped to the top surface of the base member 12 by respective sets
of insulating clamping bars 17-1, 17-2 and 17-3 which are secured
to the base members and to the bottom ends of the bender members
.[.15.]. .Iadd.15-1, 15-2 and 15-3 .Iaddend.either by set screws
(not shown) or an adhesive or both so as to firmly clamp the lower
ends of the bender plate elements together in a unitary structure
that is secured to base member 12. In this embodiment of the
invention the portions of the piezoceramic plate elements of each
bender member which are disposed between the clamping members 17-1,
17-2 and 17-3, respectively, have no outer conductive surfaces and
are not prepoled. Consequently, the clamped portions of the
respective piezoceramic plate elements of the bender members are
electrically neutral and mechanically unstressed. Prepolarizing and
operating energizing potentials are applied to the outer conductive
surfaces 15D and 15E formed on the outer sides of the respective
upper prepoled bender member piezoelectric plate elements 15A-1,
15B-1.[.:.]. .Iadd.; .Iaddend.15A-2, 15B-2 and 15A-3, 15B-3. This
is done by means of jumper connector wires that have one end
connected to the lower end of the outer conductive surfaces of each
bender member and which extend through openings in the metal base
member 12 (such openings being sealed either by glass frit .Iadd.37
.Iaddend.or a suitable adhesive) and through an underlying
insulating layer 12I and then .[.terminate.]. .Iadd.terminated
.Iaddend.in small conductive pads identified as 16A-1, 16B-1;
16A-2, 16B-2 and 16A-3, 16B-3. The conductive pads constitute
surface mounted device terminal pads which have relatively flat
surfaces and are designed to fit over mating conductive pads formed
on a circuit board or other chassis member, and over which they are
superimposed and then permanently mated by spot or resistance
welding, conductive adhesive or other suitable conductive bonding
techniques. For a more detailed description of surface mounted
devices and their fabrication, reference is made to an article
entitled "Surface Mounting Alters the PC-Board Scene" appearing in
"Electronics"-Feb. 9, 1984 issue, pages 113-124. Similarly, the
contact support members .[.18.]. .Iadd.18-1, 18-2, 18-3
.Iaddend.and .[.19.]. .Iadd.19-1, 19-24, 19-3 .Iaddend.for the
fixed contacts of each piezoceramic switching device 14-1, 14-2 and
14-3 likewise extend through openings in the conductive base member
12 and its underlying insulating surface 12I and terminate in
surface device mounted pads for providing electrical connection to
each of the fixed contacts 28-1, 29-1; 28-2, 29-2 and 28-3, 29-3 of
the piezoceramic switching devices.
In addition to the above noted structural characteristics, each of
the bender members 15-1, 15-2 and 15-3 have their outer conductive
surfaces which cover the prepolarized movable plate element
portions of the bender provided with a conformal protective coating
15F-1, 15F-2 amd 15F-3 such as polyimide siloxane copolymer which
provides an excellent pinhole free surface passiving protective
coating for each of the respective piezoceramic bender-type
switching devices. The conformal protective coatings are not
provided.Iadd., .Iaddend.however.Iadd., .Iaddend.if a device
fabricated as shown in FIG. 7 is to be operated in a vacuum
environment since the vacuum operated devices do not require the
additional protection provided by the conformal protective coating.
However, if the device is to be filled with an inert gas
atmosphere, then it may be desirable to provide the protective
conformal coatings to the respective bender members.
During fabrication of the multiple switching device embodiment
shown in FIG. 7, each of the respective piezoceramic bender-type
switching devices 14-1, 14-2 and 14-3 initially are mounted to the
base member 12 and appropriate interconnection conductive paths,
jumper connectors and surface mounted device terminal pad
connections are provided thereto through the lower insulating
surface 12I as described above to form a complete sub-assembly that
then is inserted into the inverted bowl-shaped conductive cover
member 11. At this point, the cover member 12 is spot welded,
resistance welded, cold welded or adhesively secured to the upper
peripheral surface of the conductive base member 12 making sure not
to raise the temperature of the interior to excessive values that
could be injurious to the physical characteristics of the
piezoceramic plate elements. The interior of the resulting gastight
protective enclosure 11 then either is evacuated to a high degree
of vacuum ranging from 10.sup.-10 .[.Torrs.]. .Iadd.Torr
.Iaddend.down to 10.sup.-6 .[.Torrs.]. .Iadd.Torr, .Iaddend.or,
alternatively, filled with an inert gas atmosphere in a manner
known in the electron tube manufacturing art. Thereafter, the
device may be raised in temperature to a value just below the Curie
temperature of the piezoelectric ceramic plate elements and a high
prepolarizing potential applied to the outer conductive surfaces of
each of the bender members while a reverse polarity or ground
potential is applied to the central conductive surfaces of each
switching device 14-1, 14-2 and 14-3 in the manner described
earlier. During this prepolarization treatment, it is desirable to
separately and appropriately adjust the prepolarizing potential
across each piezoelectric ceramic plate element so that the bender
.[.member 15.]. .Iadd.members 15-1, 15-2 and 15-3 .Iaddend.formed
thereby .[.is.]. .Iadd.are .Iaddend.precisely centered between each
of .[.its.]. .Iadd.the respective .Iaddend.coacting fixed contacts
28 and 29 as depicted in the drawings. By thus initally aligning
the respective bender members .[.15.]. in a desired central
position during prepolarization, further individual adjustments to
properly align the respective bender members after completion of
manufacture of the overall assembly is not required. During
alignment, optical and capacitive means can be used to .[.guage.].
.Iadd.gauge .Iaddend.equivalent spacing which otherwise is most
difficult if not impossible to obtain using conventional
positioning techniques. A multiple piezoceramic switching device
such as shown .Iadd.in .Iaddend.FIG. 7 wherein three individual
bender-type switches are provided in a single, common gastight
enclosure protective environment is ideally suited for use in
controlling current flow through .Iadd.a .Iaddend.multi-phase
circuit arrangement, such as three phase AC system, since there is
an individual piezoceramic bender-type switching device provided
for use in connection with each phase of the three phase
circuit.
FIG. 8 illustrates still another embodiment of the invention
wherein a two part gastight enclosure is provided. The two part
enclosure of FIG. 8 is comprised by an upper inverted glass jar
member 11A having an open lower end that is designed to seat in and
be sealed to a lower metallic sleeve member 11B that in turn sits
on and is welded or otherwise secured to a metallic base member 12
by spot or resistance welding, etc. A piezoelectric ceramic
switching device 14 is mounted within the gastight enclosure 11A,
11B, 12 and is constructed in a manner similar to the piezoceramic
switching device 14 employed in the embodiment of the invention
shown in FIG. 5 and FIG. 6. Accordingly, like parts in each of the
figures have been given identical reference characters and will not
be described further except to point out differences in
construction and mounting.
In the FIG. 8 embodiment, the piezoelectric ceramic plate elements
15A and 15B include both an upper prepolarized movable bender
portion and a lower unpoled portion 15AUP and 15BUP with the upper
part of the unpoled portions of the plate .[.element.].
.Iadd.elements .Iaddend.being clamped between insulating clamping
.[.members.]. .Iadd.member .Iaddend.17 that are disposed in a
central opening in the base member 12 and secured thereto by a
suitable glass frit seal, adhesive or other similar sealant. Below
the clamped portion of the unpoled sections of the piezoceramic
elements, there are formed suitable capacitors by the conductive
surfaces 32 and 33 coacting with opposed sections of the central
conductive surfaces 15C-1 or 15C-2, respectively.Iadd., .Iaddend.in
the interposed portions of unpoled ceramic 15AUP and 15BUP. Mounted
over the capacitors thus formed are circuit components 34 and 35,
respectively, which may comprise passive circuit elements such as
discrete, .[.hybride.]. .Iadd.hybrid .Iaddend.or monolithic
integrated resistors, conductors, fuses and the like and/or active
semiconductor devices interconnected in circuit relationship by
suitable printed conductor paths. The circuits thus comprised may
be part of the energizing circuit for the prepolarized bender plate
elements 15A or 15B or may comprise part of the circuit element
interconnected with the load current switch contacts 24A, 28 or
24B, 29, or both. It should be noted that in this embodiment of the
invention, the complementary circuit elements formed on the unpoled
positions 15AUP and 15BUP of the piezoceramic plate elements extend
below the base member 12 and are not included within the protective
atmosphere within enclosure 11A, 11B and base member 12.
In the FIG. 8 embodiment of the invention, as in the FIG. 5
version, the central conductive surfaces 15C-1 and 15C-2 can be and
are in a number .Iadd.of .Iaddend.embodiments of the invention
electrically isolated from each other through the use of an
insulating adhesive 30 to secure the two bender plate elements 15A
and 15B together in a unitary structure. By thus fabricating the
bender plate elements, it is possible to reduce the inter-capacitor
coupling that otherwise occurs between capacitor elements 32 and 33
if only a single central conductive surface is employed. In this
manner, it is possible to better isolate the circuits comprised by
capacitor elements 32 and 33 together with other circuit components
such as resistors 34 and 35 and/or other circuit components so that
two circuits fabricated from such components can operate
substantially independently of each other.
During manufacture of the improved piezoceramic switching device
with protective gastight enclosure as shown in FIG. 8, the
piezoceramic switching device 14 first is fabricated in this manner
previously described in copending U.S. application Ser. No. 685,109
and then mounted on the base member 12 in the manner shown. Here
again, the fixed contact support members 18 and 19 pass through
openings in base member 12 and are suitably sealed by a glass frit
seal or a suitable adhesive such as those noted eariler in the
specification. At this point in the manufacture, or prior thereto,
the glass enclosure 11A will have been sealed to the metallic
sleeve member 11B by a suitable glass frit seal shown at 41. The
combined enclosure 11A, 11B then is seated over .[.tne.]. .Iadd.the
.Iaddend.base member 12 and the piezoceramic switching device 14
.[.subassembly.]. .Iadd.sub-assembly .Iaddend.and the rim portion
of the lower metallic member 11B is welded to the periphery of the
base member 12 by spot welding, resistance welding, cold welding or
the like in a procedure which does not allow the interior .[.of
the.]. enclosure temperature to rise to an excessive value that
could be damaging to the piezoceramic bender elements nor exceed
any Curie temperature.
The interior of the enclosure 11A, 11B, 12 then is evacuated to a
high degree of vacuum of the order of 10.sup.-10 to 10.sup.-6
.[.Torrs.]. .Iadd.Torr .Iaddend.and sealed closed in a manner known
to those skilled in the art of vacuum tube technology. Following
evacuation, the temperature of the device may be elevated to a
level just below the Curie temperature of the piezoceramic bender
plate elements 15A and 15B and a prepolarization potential applied
across the conductive surfaces 15D, 15C-1 and across 15E, 15C-2 to
prepolarize the bender plate elements in a manner previously
described. Again, as in other embodiments of the invention during
prepolarization, proper centering of the bender member 15 between
the fixed contacts 28 and 29 is achieved by manipulation of the
respective prepolarization potentials applied in the above
described manner. For convenience and in order to simplify the
drawings, the required interconnecting leads and terminals to
provide prepolarization and excitation potentials to the bender
plate elements and the circuit components 32-35 have not been
illustrated but would correspond substantially to the .[.elements
as.]. .Iadd.configurations .Iaddend.shown in the FIG. 5 embodiment
of the invention.
FIG. 9 illustrates another embodiment of the invention wherein a
plurality of individual piezoceramic bender-type switching devices
14-1, 14-2 and 14-3 are mounted within a protective gastight
enclosure formed by .[.two.]. .Iadd.mated .Iaddend.half bowl-shaped
members 11A, 11B and 11A', 11B'. In this multiple device embodiment
of the invention, however, in contrast to the embodiment shown in
FIG. 7, only a single pair of fixed contacts 28 and 29 together
with their supporting members 18 and 19 are required instead of the
three separate sets of such fixed contacts employed in the
embodiment of the invention shown in FIG. 7. Because of this
structural feature, it is possible to so program the excitation
voltages applied to the respective bender member 15-1, 15-2 and
15-3 so that the switching devices can be caused to operate
interdependently with each other. For example, in one operating
mode, bender member 15-1 can be caused to close its movable contact
24-1 on fixed contact 29 and thereafter in sequence, bender member
15-2 closes its movable contact 24-2 on movable contact 24-1
followed by actuation of bender member 15-3 to close its movable
contact 24-3 on movable contact 24-2 of bender member 15-2. When
thus programmed, it will be appreciated that closed electrical
branch circuits are provided through fixed contact 29 and its
support member 19 via movable contact 24 and the central conductive
surface 15C-1 of bender member 15-1, through movable contact 24-2
and the central conductive surface 15C-2 and through movable
contact 24-3 and the central conductive surface 15C-3 of bender
member 15-3. In another operating mode, all three bender members
15-1, 15-2 and 15-3 can be caused to close their respective movable
contacts 24-1, 24-2 and 24-3 in circuit relationship on the fixed
contact 28. Alternatively, each of the bender members 15-1, 15-2
and 15-3 can be selectively excited in a manner to close their
movable contacts on each other either separately, in pairs, or all
three together independently of the fixed contacts 28 and 29 to
form two different two branch circuit closures or a three branch
circuit closure. Thus, it will be appreciated that considerable
flexibility in switching operations is provided by a multiple
switch device structure constructed as shown in FIG. 9.
The FIG. 9 embodiment of the invention differs further from the
embodiment shown in FIG. 7 in the nature of the gastight enclosure
formed by the .[.two.]. .Iadd.mated .Iaddend.separate half
bowl-shaped members 11A, 11B and 11A', 11B'. Each half is comprised
by a first layer 11A formed of a proprietary plastic of the General
Electric Company sold under the trademark ULTEM and is fabricated
from .[.polyethermide.]. .Iadd.polyetherimide .Iaddend.material. A
characteristic of this material is that it can be readily and
inexpensively coated with a conducting surface 11B.Iadd.,
11B'.Iaddend. either before or after molding into desired shapes
such as the half bowl-shaped enclosures 11A, 11B and 11A', 11B'
depicted in FIG. 9. The lower half bowl-shaped member 11A', 11B'
includes an insulating base member 121 secured over the conductive
surface 11B' through which insulating openings are provided for
conductive leads 18, 19, 15C-1, 15C-2 and 15C-3 that are connected
to surface mounted device pads formed on the lower outer surface of
the insulating base .[.members.]. .Iadd.member .Iaddend.12I. The
additional leads and terminal pads needed to supply prepolarization
and excitation potentials to the outer conductive surfaces of the
respective piezoceramic bender members 15-1; 15-2 and 15-3 have not
been illustrated for the sake of simplicity and not to unduly
complicate the drawing. Such interconnections would be similar to
those shown and described with relation to FIG. 7.
Each of the piezoceramic bender members 15-1, 15-2 and 15-3 are
mounted within the gastight enclosure comprised by the two half
bowl-shaped members 11A, 11B and 11A', 11B' by clamping means 17-1,
17-2 and 17-3 comprised by insulating bar members that are secured
by set screws or adhesives or both, across the respective bender
members 15-1, 15-2 and 15-3 to hold them together as unitary
structures and to secure each bender member to the insulating
surface 11A' again either by set screws, adhesives or other similar
bonding devices or agents. After securement of the bender members
in this manner to the lower enclosure bowl half along with the
fixed contact rod supports 18 and 19, the lower half bowl member
assembly including the bender-type switching devices is mated with
the upper half bowl member 11A, 11B and the two bonded together
around their .[.runs.]. .Iadd.peripheral edges .Iaddend.with a
suitable adhesive to form a gastight enclosure. The enclosure
because of the conductive surfaces 11B, 11B' also prevents emission
of undesired electromagnetic interference waves (E.M.I.) produced
by the load current carrying switch contacts during switching.
With the gastight protective enclosures 11A, 11B and 11A', 11B'
sealed closed, the entire enclosure is evacuated to a high degree
of vacuum or filled with a protective inert gas. Thereafter, the
temperature within the enclosure may be raised to a level just
under the Curie temperature of the piezoelectric ceramic plate
elements and a high voltage prepolarizing potential applied across
the plate elements in the previously described manner to thereby
prepolarize the bender plate elements. Again, as in other
embodiments, during prepolarization the prepolarizing potential
values are adjusted to precisely center the bender members 15-1,
15-2 and 15-3 in the spaces allowed both with respect to each other
and with respect to the gap spacing between the movable contacts of
the end bender members 24-1.Iadd., 24-2 .Iaddend.and 24-3 and the
fixed contacts 28 and 29.
The FIG. 9 embodiment of the invention is of particular value in
illustrating the virtues of a form H contact system made available
by the invention wherein a normally centrally disposed, unenergized
bender member is precisely centered in its electrically neutral or
off condition to provide one mode of operation and then selectively
can be moved either to the right or to the left to provide two
additional modes of operation. The form H contact system is
provided in this embodiment of the invention but still alows one to
excite the piezoelectric plate elements in their prepoled direction
without applying reverse voltages on the opposite piezoelectric
plate element of the bender members. Thus, a type H system is
provided with a neutral centered off position and natural (in phase
with the prepoling direction) energization to provide flexure in
two opposite directions without the possibility of depoling
.[.of.]. the bender .[.member.]. .Iadd.members .Iaddend.over
prolonged periods of operation due to the need for application of
reverse polarity fields across one or the other piezoceramic plate
elements of the bender members. Further, because of mounting the
bender members in gastight protective enclosures which are either
evacuated to a high degree of vacuum ranging from 10.sup.-10
.[.Torrs.]. .Iadd.Torr .Iaddend.to 10.sup.-6 .[.Torrs.].
.Iadd.Torr, .Iaddend.or, alternatively, filling the gastight
enclosure with an inert protective gas such as nitrogen or argon or
a high dielectric gas such as sulfur hexaflouride (SF.sub.6),
considerably higher voltages may be used both in the prepoling
operation and in subsequent energization operations to provide much
faster switching response and .Iadd.increased .Iaddend.compressive
forces on the contacts during closure.
Additional features of the form H switching system provided by the
switching structures shown in all of the figures of the
application, are the elimination of the possibility of simultaneous
operation of two loads due to logic errors, transients or contact
welding, etc. This is in contrast to the electromagnetic relay art
where it is very difficult to balance the mechanical restoring
forces on the relay armature to provide a stable center-off
position as provided in the devices made available by the present
invention. As illustrated and described with relation to FIG. 9,
additional switching modes are available with such structures that
cannot be achieved with traditional electromagnetic actuated
switches and relays. In FIG. 9, depending upon the bender
excitation and number of individual stages provided, different
external loads selectively can be energized. Control of polyphase
circuits in an obvious application for the multi-device switches
mounted within a single protective enclosure together with all of
their attendant advantages whereby one can provide separate control
over each phase closure time independently of the closure time
required for other phases. Further, systems employing the invention
can include synchronization of switch closing or opening (or both)
to line voltage or current zeros or assisted communication modes
and makes available amazingly high performance devices for use in
high duty cycle applications.
FIG. 10 illustrates a modification to the embodiment of the
invention shown in FIG. 9 to provide for the inclusion of unpoled
portions of the piezoelectric ceramic plate elements (together with
circuit components mounted thereon) within the protective gastight
enclosure 11A, 11B and 11A', 11B'. In this modification of the
invention, the inner insulating ULTEM surface 11A' of the lower
half bowl member 11A', 11B' of the housing is provided with a
circumferential shoulder 11A" upon which is seated and secured an
insulating plastic or glass support member 51 through which are
formed a number of through passages indicated by dotted lines at 52
for maintaining the atmosphere (or evacuated spaces) on each side
of the member 51 equalized. The support member 51 has secured
thereon the respective bender members 15-1, 15-2 and 15-3 by means
of their respective sets of clamping members 17-1, 17-2 and 17-3.
These portions of the piezoelectric ceramic plate elements
comprising respective bender members 15-1, 15-2 and 15-3 which are
disposed between the clamping members and also those portions which
extend below the support member 51, are unpoled so that they are
both electrically neutral and mechanically unstressed. On these
unpoled portions of the piezoceramic plate members, respective
circuit components such as capacitors, resistors, and other passive
.[.and.]. .Iadd.and/or .Iaddend.active circuit components such as
semiconductor devices are formed as shown at 32, 33, 34 and 35 in
the same manner described with relation to the embodiment of the
invention shown in FIG. 5. In other respects, the embodiment of the
invention shown in FIG. 10 is similar to the FIG. 9 species, is
fabricated in a similar manner and operates in the same fashion. In
FIG. 10, as was done with other embodiments of the invention, all
of the required interconnected jumper conductors, printed conductor
paths, or other connections to the bender .[.plae.]. .Iadd.plate
.Iaddend.elements, circuit components and surface mounted device
terminal pads have not been illustrated in order to simplify the
drawing.
From the foregoing description, it will be appreciated that the
invention makes available novel piezoceramic power switching
devices contained within protective gastight enclosures wherein
improved bender properties are provided to the devices. These
improved properties result in increased bender force and translate
into increased contact compressive force for the switching contacts
which the benders actuate, improved bender displacement,
optimization of prepolarization voltages to achieve optimum spacing
of the bender contacts relative to the fixed contacts and the
capability of operation of the switch contacts at higher voltages
because of the higher dielectric .Iadd.characteristics .Iaddend.of
a vacuum or protective gas atmosphere in which the device are
mounted. Because of these characteristics and the protective
atmosphere provided by the gastight enclosure, plural switching
devices can be mounted in a single common enclosure and the need
for conformal coatings or .[.encapaulation.]. .Iadd.encapsulation
.Iaddend.of the prepolarized portion of the piezoceramic plate
elements is obviated. Further, it is possible to employ contact
materials such as copper-vanadium alloys having low melting points
for establishment of stable arcs to reduce di/dt at current chop
(current extinction) during switching and high voltage
withstandability. This is made possible since the protective
atmosphere in which the contacts are used provides higher voltage
withstandability upon contact opening and at current extinction
.[.and maintain.]. .Iadd.while maintaining .Iaddend.the contacts is
a non-oxidizing atmosphere such as a vacuum to protect the low
melting point contacts and prevent changes in their contact
resistance. Because of the higher dielectric strength and other
characteristics noted above .Iadd.which are .Iaddend.achieved while
operating in a vacuum or protective gas atmosphere, voltage
withstandability of at least 2000 volts per mil .[.are.]. .Iadd.is
.Iaddend.obtainable with such devices. Further, repeatability
timing of bender charging, contact closing, bender discharging,
contact opening and reverse bender assist, as needed, is
optimized.
INDUSTRIAL APPLICABILITY
The invention makes available a family of novel .[.advance.].
advanced piezoelectric ceramic power switching devices which are
mounted within protective gastight enclosures that can be either
evacuated to a high degree of vacuum of the order of
.Badd.10.sup.-10 to 10.sup.-6 .[.Torrs.]. .Iadd.Torr .Iaddend.or
filled with an inert protective gas atmosphere such as nitrogen,
argon, SF.sub.6 or the like. The switching devices thus fabricated
can be used over a wide power range for both industrial, commercial
and residential applications.
Having described several embodiments of advanced piezoceramic power
switching structures employing protective gastight enclosures and
constructed in accordance with the invention, it is believed
obvious that other modifications and variations of the invention
will be suggested to those skilled in the art in the light of the
above teachings. It is therefore to be understood that changes may
be made in the particular embodiments of the invention described
which are within the full intended scope of the invention as
defined by the appended claims.
* * * * *