U.S. patent number RE33,618 [Application Number 07/360,225] was granted by the patent office on 1991-06-25 for method for initially polarizing and centering a piezoelectric ceramic switching device.
This patent grant is currently assigned to General Electric Company. Invention is credited to John D. Harnden, Jr., William P. Kornrumpf.
United States Patent |
RE33,618 |
Harnden, Jr. , et
al. |
June 25, 1991 |
Method for initially polarizing and centering a piezoelectric
ceramic switching device
Abstract
Improved piezoelectric ceramic switching devices are described
along with their .[.method.]. .Iadd.methods .Iaddend.of
fabrication. In addition to the devices themselves, novel electric
circuits are described for the energization as well as the use of
such devices as switching elements in electrical systems. Parts of
both the energization circuits and/or utilization circuits
employing the piezo ceramic switching device are physically mounted
on and supported by non-polarized parts of the piezoelectric
ceramic plate elements comprising the switching devices so that
lightweight compact construction is achieved along with substantial
reduction of stray inductance intercoupling.
Inventors: |
Harnden, Jr.; John D.
(Schenectady, NY), Kornrumpf; William P. (Albany, NY) |
Assignee: |
General Electric Company (Fort
Wayne, IN)
|
Family
ID: |
27000813 |
Appl.
No.: |
07/360,225 |
Filed: |
June 1, 1989 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
685109 |
Dec 21, 1984 |
4670682 |
|
|
Reissue of: |
835830 |
Mar 3, 1986 |
04669160 |
Jun 2, 1987 |
|
|
Current U.S.
Class: |
29/25.35;
264/430; 264/435 |
Current CPC
Class: |
H01H
57/00 (20130101); H01H 11/00 (20130101); H01H
49/00 (20130101); Y10T 29/42 (20150115) |
Current International
Class: |
H01H
57/00 (20060101); H01L 41/09 (20060101); H01L
41/00 (20060101); H01L 41/04 (20060101); H01L
41/24 (20060101); H01H 11/00 (20060101); H01H
49/00 (20060101); H01L 041/22 () |
Field of
Search: |
;29/25.35 ;264/22
;310/330-332,317,319,357-359,367,368,340,344 |
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 |
|
961606 |
|
Jun 1964 |
|
GB |
|
Other References
Guntersdorfer, M. et al., "Application of Piezoceramics in Relays",
Electrocomponent Science and Technology, vol. 3, 1976, pp. 1-11.
.
Electronic Engineering, by P. Kleinschmidt, "A Piezoelectric
Ceramic Touch-Operated Button", Aug. 1975, pp. 9 and 11..
|
Primary Examiner: Hall; Carl E.
Attorney, Agent or Firm: Krisher, Jr.; Ralph E.
Parent Case Text
This is a division, of copending application Ser. No. 685,109,
filed Dec. 21, 1984 now .[.abandoned.]. .Iadd.U.S. Pat. No.
4,670,682.Iaddend..
Claims
What is claimed is:
1. The method of prepolarizing and centering the movable
piezoceramic bender member of a piezoceramic bender-type switching
device which comprises substantially completing the fabrication
assembly of all of the major components of the piezoceramic
switching device into a unitary structure and thereafter applying a
relatively high value prepolarization potential to the respective
piezoceramic plate elements of the bender member while maintaining
the plate elements near their Curie temperature to achieve dipole
alignment of the dipoles of the piezoceramic material and
thereafter simultaneously adjusting the relative magnitudes of the
prepolarizing potential applied to the respective piezoceramic
plate elements of the bender member to cause it to be precisely
positioned relative to the load current fixed switch contacts of
the switching device.
2. The method of prepolarizing and centering the movable
piezoceramic bender member of a piezoceramic bender-type switching
device which comprises substantially completing the fabrication
assembly of all of the major components of the piezoceramic
switching device into a unitary structure and thereafter applying a
relatively high value prepolarization potential to the respective
piezoceramic plate elements of the bender member to achieve dipole
alignment of the dipoles of the piezoceramic material and
thereafter simultaneously adjusting the relative magnitudes of the
prepolarizing potential applied to the respective piezoceramic
plate elements of the bender member to cause it to be precisely
positioned relative to the load current fixed switch contacts of
the switching device. .Iadd.
3. A method for initially polarizing and controlling the movement
of a piezoceramic bender-type switching device having a movable
piezoceramic bender member comprised by at least two planar
piezoceramic plate elements, the piezoceramic bender-type switching
device including at least one set of coacting electrical switch
contacts opened and closed by the movable bender member of the
piezoceramic switching device, and clamping means securing the
piezoceramic plate elements together and mechanically supporting
the movable bender member in a cantilever manner for opening and
closing the set of coacting electrical switch contacts comprising
the steps of:
(a) connecting the piezoceramic bender-type switching device to a
power source with selectively operable electrical excitation
circuit means, whereby a direct current energizing potential is
selectively applied to each piezoceramic plate element, causing
initial polarization of the plate elements,
(b) thereafter adjusting the relative magnitudes of the initial
polarization potentials applied to the respective plate elements to
cause the bender member to be precisely positioned relative to the
switch contacts, and
(c) subsequently applying direct current energizing potential from
the power source to the polarized piezoceramic plate elements only
in the same direction employed to initially polarize the respective
plate elements. .Iaddend. .Iadd.4. The method of claim 3 wherein
the initial polarization in each piezoceramic plate element is
produced at an energizing potential level exceeding the energizing
potential level of the power source. .Iaddend. .Iadd.5. The method
of claim 3 wherein an end portion of each polarized piezoceramic
plate element remains unpolarized. .Iaddend.
.Iadd. . A method of initially polarizing and centering the movable
piezoceramic bender member of a piezoceramic bender-type switching
device, comprising:
substantially completing the assembly of all of the major
components of the piezoceramic switching device into a unitary
structure;
applying a relatively high value initial polarization potential to
the respective piezoceramic plate elements of the bender member to
achieve dipole alignment of the piezoceramic material; and
simultaneously adjusting the relative magnitudes of the initial
polarizing potential applied to the respective piezoceramic plate
elements of the bender member to cause it to be precisely
positioned relative to the load
current fixed switch contacts of the switching device. .Iaddend.
.Iadd.7. The method of claim 7 wherein the bender member further
includes two sets of coacting electrical switch contacts disposed
on opposite sides of the bender member, further including the step
of applying the energizing potential in a manner which enables make
or break connection of electric current to at least two separate
electrically conductive paths extending through the respective sets
of contacts. .Iaddend. .Iadd.8. The method of claim 3 further
including preventing excess arcing across the coacting electrical
contacts when opened to interrupt electrical current being applied
through a load. .Iaddend. .Iadd.9. The method of claim 3 further
including causing the set of coacting electrical switch contacts to
close upon the application of the direct current energizing
potential. .Iaddend. .Iadd.10. The method of claim 9 further
including causing the set of switch contacts to open upon the
removal of the energizing potential. .Iaddend.
Description
TECHNICAL FIELD
This invention relates to improved piezoelectric ceramic switching
devices and to novel electrical systems for the energization,
control and utilization of such devices.
More particularly, the invention relates to improved piezoelectric
ceramic switching devices, their fabrication, and to novel
electrical circuits for the energization as well as use of such
improved devices as switching elements in electrical systems, some
parts of which may by physically mounted on and supported by the
improved piezoelectric ceramic switching devices themselves.
BACKGROUND PRIOR ART PROBLEM
In conventional electrical circuits, electrical relays and switches
are employed at points in such circuits where it is desired either
to initiate or interrupt (or both) electric current flow through
the circuit. In the past, electromagnetic solenoid operated
switches and relays have been employed to either close or open the
contacts of a power switch or relay in response to a small control
signal (low voltage, low current) which initiates either closure or
opening of the contact of a larger power rated switch that
thereafter controls current flow through the contacts to a circuit
being supplied via the switch contacts.
Relays and switches which use piezoelectric drive elements have a
number of advantages over their electromagnetic counterparts. For
example, a piezoelectric driven relay or switch requires
substantially lower current and dissipates very little power during
operation to open or close a set of contacts in comparison to an
electromagnetic driven device of the same rating. Additionally,
piezoelectric driven switching devices have very low mass and
therefore require less space and introduce less weight into circuit
systems with which they are used. Additionally, piezoelectric
driven switching devices possess very short actuation times. Thus,
fast acting switching is possible with smaller and lower weight
devices that dissipate less power and hence can operate with lower
temperature rises if piezoelectric ceramic switching devices are
used.
Piezoelectric plate elements may be fabricated from a number of
different polycrystalline ceramic materials such as barium
titanate, lead zirconate titanate, lead metaniobate and the like
which are precast and fired in a desired shape, such as a
rectangular-shaped plate. Electrically conducting surfaces in the
form of .[.metalized.]. .Iadd.metallized .Iaddend.electrodes
usually are deposited on the surface of the plates which then are
used to apply a polarizing voltage across the piezoceramic plate in
order to make them piezoelectric in a chosen polar direction by a
prepoling treatment which involves exposing the ceramic plates to a
high electric field applied across the metalized electrode while
the plates are held at a temperature not far below their Curie
point. As a result of this prepolarizing treatment, the plate
elongates in the same direction as the applied field. After cooling
of the plates and removal of the prepoling field, the dipoles
within the ceramic plate which were aligned as a result of the
prepoling treatment, cannot easily be returned to their original
position and therefore possess what is known as .[.remanant.].
.Iadd.remanent .Iaddend.polarization. Thus, the ceramic plates are
made permanently piezoelectric whereby the dipoles are permanently
enhanced and can convert mechanical energy into electrical energy,
and vice versa. The piezoelectric effect is described more fully in
a booklet entitled "The Piezoelectric Effect in Ceramic Materials"
edited by J. Van Randeraat & R. E. Setterington and published
by Philips Golilampenfabriken of Eindhoven, The Netherlands, second
edition, dated January 1924.
In piezoelectric ceramic materials, the direction of the electrical
and mechanical dipole axes depends upon the direction of the
original unidirectional prepolarizing high voltage field. During
the prepoling process the ceramic plate element experiences a
permanent increase in dimension between the poling electrodes and a
permanent decrease in dimension parallel to the electrodes. When a
DC excitation voltage of the same polarity as the prepoling
voltage, but of smaller magnitude, subsequently is applied between
the poling electrodes, the element experiences further but
temporary expansion in the poling direction and contraction
parallel to the electrodes. Conversely, when a DC excitation
voltage of opposite polarity is applied to the plate element
electrodes, the plate contracts in the poling direction and expands
parallel to the electrodes. In either case, the piezoelectric
ceramic plate element returns to its original prepolarized
dimensions when the later applied excitation voltage is removed
from the electrodes.
A number of different piezoelectric ceramic switching devices have
been offered for sale in the past having a variety of different
configurations. One of the more popular, if not the prevailing
structural approach employed in the past, is known as a bimorph
bender-type piezoelectric ceramic switch which employs two adjacent
piezoelectric plate elements mounted side by side having conductive
electrodes coating their outer surfaces and sharing a common
conductive inner surface to form a bimorph .[.bender-tye.].
.Iadd.bender-type .Iaddend.device. A known commercially available
bimorph bender-type piezoelectric ceramic switch is described in an
application note copyrighted in 1978 and published by the Piezo
Products Division of Gulton Industries.[.,.]. Inc. located in
Metuchen, N.J. and Fullerton, Calif. If one end of such a
piezoelectric ceramic bimorph bender is clamped cantilever fashion,
the bender can be made to bend in either direction from its central
neutral unenergized condition by application of an energizing
potential of either polarity but lower than the prepolarizing
potential to one of its conductive outer electrodes. If a suitable
value energizing potential of either polarity is applied across
only one of the piezoelectric ceramic plate elements of the bender,
it enhances dipole alignment of that particular plate element
resulting in a shortening and thickening of the plate element. This
in turn results in bending of the overall bimorph bender device due
to the fact that the two piezoelectric plate elements are
physically secured together. By suitable design, the bending action
can result in the closing of two switch contacts or other similar
effect.
Unfortunately, prior art attempts to provide piezoelectrically
driven switch devices have resulted in devices having poor
electrical and mechanical performance characteristics. In the case
of prior art bimorph bender-type switching devices as described
briefly above, they possess severe performance limitations which
are founded in the trade-offs between contact force, contact
separation, depolarization, retentivity and reliability in service
and the .[.uncertainity.]. .Iadd.uncertainty .Iaddend.of contact
position due to creep and temperature effects which build up over a
period of continued device usage. One such prior art switching
device employing a piezoelectric bender-type drive member is
described in U.S. Pat. No. 2,166,763 issued July 18, 1939 for a
"Piezoelectric Apparatus and Circuits". The piezoelectric
bender-type drive member described in U.S. Pat. No. 2,166,763 is
comprised by two juxtaposed piezoelectric plate elements having
electrodes as described biefly above, and is energized in such a
manner that one of the piezoelectric plate elements has the
energizing potential applied to it in the same direction as the
direction of the prepoling electric field; however, the other
piezoelectric plate element has an energizing signal applied
thereto of opposite polarity from that of its prepolarizing
electric field. As a consequence, the device of U.S. Pat. No.
2,166,763 undergoes long term depolarization of either one or both
of the piezoelectric plate elements after a period of usage due to
the depolarizing effect of the repeated application of a wrong
polarity (out of phase anti-poling direction) energizing signal.
The deleterious effect on dipole enhancement of operation in this
mode greatly restricts the applied voltage stress and thus the
useful work output obtainable with such devices. In addition, the
device of this prior art patent possesses a number of other
weaknesses sought to be overcome by the present invention. The same
objectional characteristics are present in a number of different
prior art piezoelectric driven bender-type switches and/or relay
devices such as the following U.S. Pat. No. 2,182,340--issued Dec.
5, 1939 for "Signaling System"; U.S. Pat. No. 2,203,332--issued
June 4, 1950 for "Piezoelectric Device"; U.S. Pat. No.
2,227,268--Dec. 31, 1940 for "Piezoelectric Apparatus"; U.S. Pat.
No. 2,365,738--issued Dec. 26, 1944 for "Relay"; U.S. Pat. No.
2,714,642--issued Aug. 2, 1955 for "High Speed Relay of
Electromechanical Transducer Material"; U.S. Pat. No.
4,093,883--issued June 6, 1978 for " Piezoelectric Multimorph
Switches"; U.S. Pat. No. 4,395,651--issued July 26, 1983 for "Low
Energy Relay Using Piezoelectric Bender Elements"; and U.S. Pat.
No. 4,403,166--issued Sept. 6, 1983 for "Piezoelectric Relay with
Oppositely Bending Bimorphs". In addition to the above prior art
patented piezoelectric bender-type switching devices, the textbook
"Manual of Electromechanical Devices" by Douglas C. Greenwood
published by McGraw-Hill Book Company and copyrighted in 1965
discloses a somewhat similar piezo ceramic switching device on page
64 thereof.
In order to overcome the shortcomings of the known prior art
piezoelectric ceramic driven relays and switches such as those
listed above, the present invention was devised.
SUMMARY OF INVENTION
It is therefore a primary object of the present inventon to provide
new and improved piezoelectric ceramic switching devices of novel
construction having better operating characteristics than those of
comparable prior art devices of the same general nature.
Another object of the invention is to provide improved energization
circuit designs for use with piezo ceramic switching devices which
provide improved longevity and greater reliability in operation to
such piezo ceramic switching devices over extended periods of
service requiring substantial numbers of switching operations.
Still another object of the invention is to provide improved
piezoelectric ceramic switching devices and circuits therefor
having the above-listed characteristics wherein many of the
components employed in either the energization and/or utilization
circuits employing such devices are formed or otherwise supported
on an inactive unpolarized portion of the piezoelectric ceramic
switching device thereby reducing to a minimum stray inductance of
the circuits and enhances miniaturization and batch processing.
A still further object of the invention is to provide improved
piezoelectric ceramic switching devices which themselves carry and
selectively close or open power rated switch contacts for
controlling current flow therethrough or, alternatively, provide a
sufficient electric discharge current to the control gate of a gate
turn-on/turn-off semiconductor power switch such as an SCR, triac
or transistor to cause it to turn on and conduct current or to turn
off and block current flow selectively.
In practicing the invention, a novel piezoelectric ceramic
switching circuit and bender-type piezoelectric ceramic switching
device is provided wherein the piezoelectric ceramic switching
device comprises at least two prepolarized piezoelectric plate
elements having respective outer conductive surfaces and disposed
on opposite sides of at least one central conductive surface
sandwich fashion to which they are physically and electrically
bonded. The piezo ceramic switching device coacts with a set of
make and break electrical contacts to close or open such contacts
and thereby make or break an electrically conductive path extending
through the contacts. Selectively operable electric excitation
circuit means are connected to the bender-type piezoelectric
ceramic switching device for selectively and respectively exciting
each piezoelectric plate element thereof with a direct current
excitation electric field which is polarized and applied always in
the same direction as the prepolarizing electric field enhancing
dipole alignment previously permanently induced in the
piezoelectric plate element whereby no depolarization of the
piezoelectric plate element occurs during successive operations of
the switch in order to close or open the make and break contacts.
Further, continuous energization is not deleterious with the
contacts opening the instant that charge is reduced in the
bender.
The selectively operable electric excitation circuit means
comprises respective switch energization circuit means connected in
circuit relationship across respective ones of prepolarized
piezoelectric plate elements of the piezo ceramic bender-type
switching device for selectively closing or opening respective ones
of the set of coacting electrical switch contacts for controlling
electric current supplied through a load by opening and closing the
contacts. Each switch energization circuit means selectively
connects the .[.bender.]. .Iadd.bender-type .Iaddend.switching
device across a source of bender energization potential, a normally
open low power rated user operated electric switch, a current
limiting resistor and diode rectifier circuit means poled to
provide an electric energization potential having the same polarity
as the polarity of the prepolarizing potential used to polarize the
prepoled dipole enhanced piezoelectric plate element of the
piezoelectric bender-type switching device. The series electric
circuit thus comprised is connected in series circuit relationship
across a respective one of the prepoled piezoelectric plate
elements of the bender-type switch so that upon closure of the
normally open low power rated user's switch, the respective
prepolarized piezoelectric plate element of the bender-type
piezoelectric switch selectively and respectively is excited with a
direct current excitation field which always has the same polarity
as the polarity of the prepoling electric field dipole enhanced
alignment previously permanently induced in the respective
piezoelectric plate element and no depolarization of the
piezoelectric plate elements .[.occur.]. .Iadd.occurs
.Iaddend.during continued or successive operation of the
piezoelectric bender-type switch device for closing and/or opening
the load current controlling electric switch contacts.
The improved piezoelectric ceramic switching device comprises at
least one piezoelectric bender-type switching device having two
planar piezoelectric plate elements secured in opposed parallel
relationship sandwich fashion on opposite sides of at least one
central conductive surface and having respective outer conductive
surfaces that are insulated from each other and the central
conductive surface by the respective intervening piezoelectric
plate element material thicknesses. The bender-type piezoelectric
switching device further includes at least one set of coacting
electrical switch contacts which are opened or closed by a
prepolarized movable bender-portion of the piezoelectric ceramic
switching device. The improved device further includes clamping
means secured to a different portion of the bender-type
piezoelectric ceramic switching device adjacent to and mechanically
supporting the prepoled movable bender portion of the device
cantilever fashion with the different portion of the piezoelectric
ceramic plate elements comprising the bender-type device disposed
under the clamping means being unpoled and electrically
neutral.
In addition to being unpoled and electrically neutral, the
different portion of the piezoelectric ceramic plate elements
disposed under the clamping means have the outer conductive
surfaces thereof removed from that portion which is disposed under
the clamping means. In addition, a conformal electrically
insulating protective coating covers at least some of the outer
surfaces of the prepolarized movable portion of the bender-type
piezoelectric device with the conformal electrically insulating
protective coating comprising a polyimide siloxane copolymer.
In preferred embodiments of the invention, the conformal
electrically insulating coating extends over and covers the outer
planar conductive surfaces and the edges of the prepoled planar
piezoelectric ceramic plate elements, and further extends over and
covers the side edges of the piezoelectric ceramic plate
.[.element.]. .Iadd.elements .Iaddend.and their outer conductive
surfaces and the outer edges of the central conductive surface
sandwiched therebetween at least over the prepolarized portions of
the device. Further, the conformal insulating coating covering the
outer planar conductive surfaces of the prepolarized portions of
the piezoelectric ceramic plate .[.element.]. .Iadd.elements
.Iaddend.also extends down to and covers the portions of the
piezoelectric ceramic plate elements exposed by any removal of the
outer conductive surfaces thereon as well as the edge portions of
such outer conductive surfaces exposed by such removal.
BRIEF DESCRIPTION OF DRAWINGS
These and other objects, features and many of the attendant
advantages of this invention will be appreciated more readily as
the same becomes better understood by a reading of the following
detailed description, when considered in connection 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 top elevational view of a new and improved
piezoelectric ceramic bender-type switching device constructed
according to the invention;
FIG. 1A is a cross sectional view of the device shown in FIG. 1
taken through plane 1A--1A;
FIG. 1B is a schematic circuit diagram of a novel energization
circuit employed in operating the switching device of FIG. 1;
FIG. 1C is a cross sectional view of the device shown in FIG. 1
taken through plane 1C--1C;
FIG. 1D is a top planar view of the movable bender end of the
switching device shown in FIG. 1 in an unfinished condition during
the manufacture thereof, and illustrates the manner of forming
electric load current carrying contacts at the movable end of the
bender-type piezo ceramic switching device;
FIG. 1E is a perspective end view of the same portion of the device
shown in FIG. 1D at .[.the.]. .Iadd.a .Iaddend.moment later in time
during the manufacture thereof following the stage shown in FIG.
1D;
FIG. 1F is a partial side end view of the finished device showing
the manner of fabrication of the end contacts when viewed in
conjunction with FIG. 1D and FIG. 1E;
FIG. 2 is a longitudinal sectional view of a different embodiment
of improved piezoelectric ceramic switching device constructed in
accordance with the invention and illustrates the device mounted on
a separate insulating base member;
FIG. 2A is a schematic circuit diagram illustrating a utilization
circuit controlled by the device of FIG. 2 and which is fabricated
on the device;
FIG. 3 is a partial top planar view of an unpolarized, electrically
neutral end of the bender-type piezoelectric ceramic switching
device illustrating an electric fuse element deposited on a portion
of such unpolarized piezoelectric ceramic;
FIG. 4 is a longitudinal sectional view of still a different
embodiment of the invention showing active circuit components
mounted on a non-polarized portion of a bender-type .[.switch.].
.Iadd.switching .Iaddend.device constructed according to the
invention with the active components comprising diode rectifier
elements interconnected with discrete wired connectors to effect a
desired excitation circuit design for the device shown in FIG.
4;
FIGS. 4A, 4B and 4C comprise schematic circuit diagrams of three
different embodiments of a diode rectifier doubler circuit
configuration suitable for use as an excitation circuit with the
piezoelectric ceramic switching device shown in FIG. 4, with the
circuit arrangement of FIG. 4B corresponding to the physical
illustration of the circuit elements depicted in FIG. 4 and
physically supported on unpoled portions of the bender-type
switching device;
FIG. 5 is a top-side perspective view of a different form of
piezoelectric ceramic switching device constructed in accordance
with the invention showing how the device would be fabricated for
use with a voltage tripler energization circuit shown schematically
in FIG. 5A of the drawings;
FIG. 6 is top-side elevational-partial perspective view of still
another form of switching device according to the invention which
employs a diode rectifier quadrupling circuit illustrated
schematically in FIG. 6A of the drawings;
FIG. 7 is a side elevational view of still another form of improved
piezoelectric ceramic bender-type switching device according to the
invention to provide H-type double acting switching operations on
each of the opposite sides of the neutral position of the bender
element of the device;
FIG. 7A is a schematic circuit diagram of one embodiment of a
utilization load circuit which could be operated with the device of
FIG. 7;
FIG. 7B is a schematic circuit diagram of a second type of
utilization load circuit which could be controlled by the
bidirectional acting piezoelectric ceramic switching device of FIG.
7 wherein the device is employed to directly apply gating current
to the gates of higher power rated, gated power semiconductor
switches triggered by the device;
FIG. 7C is a schematic circuit diagram of a mirror image of the
circuit shown in FIG. 7B and illustrates how inverse polarity
voltages can be obtained to provide negative polarity gating
currents for use with gated power semiconductor switches of the
turn-off type;
FIG. 8 is a longitudinal sectional view of a preferred embodiment
of piezoelectric ceramic bender-type switching device according to
the invention wherein a conformal coating is provided over the
active polarized movable bender portions of the device;
FIG. 8A is a cross sectional view of the device shown in FIG. 8
taken through plane 8A--8A;
FIG. 8B illustrates a cross sectional view taken through a device
such as FIG. 8 but which has been provided with an alternative
coating arrangement which covers the entire planar exterior
surfaces of the polarized active movable bender portions of the
device;
FIG. 8C is a partial cross sectional view of the device of FIG. 8
taken through that part of the device under the clamping means in
order to better illustrate how the conformal coating is caused to
cover any exposed parts or edges of the active, polarized portions
of the piezoelectric ceramic plate elements;
FIG. 8D shows a number of characteristic curves plotting bender
force versus time and illustrates the operating characteristics of
a number of different piezoelectric ceramic bender-type switching
devices constructed according to the prior art with or without some
form of protective coating as well as the operating characteristics
of preferred forms of the invention illustrating their force versus
time operating characteristics over a period of time;
FIG. 9 is a longitudinal sectional view of an embodiment of the
invention similar to that shown in FIG. 8 and illustrates the
manner in which load current carrying contacts can be formed on the
free movable bender portion of the device; and
FIGS. 10 and 11 are perspective views of different techniques
employed in order to obtain terminal tabs for application of
energization potential to or providing electric load current flow
through the electrically conductive surfaces formed on the
piezoelectric plate elements of the devices shown in FIGS. 8 and
9.
BEST MODE OF PRACTICING INVENTION
FIG. 1 illustrates a piezoelectric ceramic switching device
constructed according to the invention and comprises at least one
piezoelectric bender-type switching device 11 having at least two
planar piezoelectric plate elements formed by an upper plate 12 and
a lower plate 13 .[.best.]. .Iadd.better .Iaddend.seen in .[.FIG.
1A.]. .Iadd.FIGS. 1A-1F .Iaddend.of the drawings. The piezoelectric
ceramic plate elements 12 and 13 are secured in opposed parallel
relationship sandwich fashion on opposite sides of at least one
central conductive surface 14 and have respective outer conductive
surfaces 15 and 16 that are insulated from each other and the
central conductive surface 14 by the respective intervening
piezoelectric ceramic plate element thicknesses. The piezoelectric
ceramic plates 12 and 13 may be formed from lead zirconate
titanate, lead metaniobate, barium titanite or other known
piezoelectric ceramic materials and, if desired, could even
comprise naturally .[.occuring.]. .Iadd.occurring
.Iaddend.piezoelectric materials such as quartz. The conductive
surfaces 14, 14A, 14B, 15 and 16 may be formed by nickle, silver or
other like .[.conductor.]. .Iadd.conductors .Iaddend.deposited or
otherwise secured to the plate elements 12 and 13.
The bender-type piezoelectric switching device further includes at
least one set of coacting fixed electrical switch contacts 17 and
18 mounted on relatively right arms which may be sufficiently
flexible to absorb impact .Iadd.and .Iaddend.which .[.ae.].
.Iadd.are .Iaddend.opened and closed by movement of a prepolarized
movable bender portion comprised by the piezoelectric ceramic plate
elements 12A and 13A of the bender-type switching device. The
contacts 17 and 18 coact respectively with contacts 19 and 21
formed on the movable end of the bender device 12A, 13A in a manner
to be described more fully hereafter with relation to FIGS. 1D, 1E
and 1F.
The movable bender portions 12A, 13A of the piezoelectric ceramic
switching device 11 are physically supported in a cantilever manner
by clamping means shown at 22 and 23 which both serve to physically
hold and clamp together the piezoelectric ceramic plates 12 and 13
with the central conductive surface 14 sandwiched therebetween. The
clamping means 22 and 23 is illustrated better in FIG. 1C of the
drawings where it can be seen that it is comprised by two elongated
substantially rigid electrically insulating bars 22 and 23 whose
ends extend beyond the side edges of the piezoelectric ceramic
plate elements 12 and 13. Threaded set screws shown at 24 serve to
clamp the two insulating bar members 22 and 23 together along with
the interposed ceramic plate elements 12 and 13 and central
conductive surface 14. Other forms of suitably clamping and holding
the piezoelectric ceramic plate members 12 and 13 together in
assembled relation will be suggested to those skilled in the
art.
As best shown in FIG. 1A, the clamping means 22 and 23 are disposed
over portions 12B and 13B of the piezoelectric ceramic plate
elements 12 and 13 which have not been prepolarized and therefore
are unpoled and electrically neutral as opposed to the prepolarized
active movable bender portions 12A and 13A of the plate elements on
which the contacts 19 and 21 are formed. Preferably, the clamping
means 22 and 23 are disposed over the ends of the non-polarized or
unpoled portions 12B and 13B which are immediately adjacent to and
physically integrated with the end of the prepolarized active
movable bender portion comprised by plate element portions 12A and
13A which have been prepolarized and therefore are indicated as
poled. It has been discovered that by mounting the piezoelectric
ceramic plate elements in this manner, the number of failures due
to fracturing of the piezoceramic plates at their support points is
greatly reduced.
With the bender-type piezoelectric ceramic switching device shown
in FIGS. 1 and 1A, it is possible to prepolarize the plate portions
12A and 13A in-situ after fabrication of the device in the manner
shown in these drawings. This is achieved by applying suitable
value prepolarizing potentials of the same polarity to the
terminals T3 and T4 respectively, while concurrently holding the
common terminal Tc at the opposite polarity. Simultaneously the
temperature of the device may be elevated in an oven or otherwise
to a temperature just under the Curie temperature of the
piezoelectric ceramic plate elements 12 and 13. The temperature to
which the devices will be elevated and the value of the
prepolarizing potentials will vary dependent upon the particular
piezoelectric ceramic material employed to form the plate elements
12 and 13 as is known to those skilled in the art of
.[.peizoceramic.]. .Iadd.piezoceramic .Iaddend.fabrication. Ambient
temperature polarization also is possible if the polarizating
potential is sufficiently high. During the prepolarization
operation, and in order to separate the peizoelectric ceramic plate
elements 12 and 13 into the two separate poled portions 12A and 13A
and the unpoled portions 12B and 13B, it is necessary to
electrically isolate the two portions so that the prepolarizing
potential is not applied across the unpoled portion 12B and 13B and
the common conductive surface 14. For this purpose, suitable gaps
shown at 15A and 16A are deliberately formed across the width of
the exterior conductive surfaces 15 and 16, respectively, whereby
an electric potential applied between either of the terminals T3 or
T4 and the common terminal Tc connected to the central conductive
surface 14, will not appear across the piezoceramic plate portions
12B and 13B which are to remain unpoled. It .[.sould.].
.Iadd.should .Iaddend.be noted that the portions of the
piezoelectric ceramic plate elements disposed under the clamping
bars 22 and 23 have their outer conductive surfaces removed so that
the portions 12B and 13B under the clamping means and immediately
adjacent and physically integrated with the prepolarized plate
portions 12A and 13A remain unpoled and electrically neutral.
As a result of fabrication in this manner, during operation of the
bender-type switching device, energizing potentials may be
selectively and respectively applied either to terminal T3 or
terminal T4 relative to Tc to cause the polarized active movable
bender plate portions 12A or 13A to bend and close their respective
contacts 19 or 21 on either of the coacting contacts 17 or 18,
respectively. As noted in the brief discussion earlier in the
specification, prepolarization of the active movable portions 12A
and 13A of the piezoelectric ceramic plate elements will leave
these portions permanently altered in physical dimensions relative
to what they were prior to prepolarization and relative to the
unpoled portions 12B and 13B of the piezoelectric ceramic plates 13
and 14. This alternation will be in the form of a permanent
increase in dimension of the plate portions 12A and 13A between the
poling electrodes 15-14 and 16-14 and also will induce a permanent
decrease in dimension parallel to the electrodes (i.e. along the
longitudinal dimension of the device as shown in FIG. 1A). When a
DC voltage of the same polarity as the prepolarizing voltage, but
of smaller magnitude, subsequently is applied as an energizing
potential between the poling electrodes, the plate element portions
12A and 13A experience a further temporary expansion in the poling
direction and contraction parallel to the electrodes. When the
energizing DC potential is removed, this temporary expansion in the
poling direction and contraction parallel to the electrode is
relaxed, and the plate element portions 12A and 13A return to their
normal, at rest unenergized condition established by the
prepolarization voltage effects only. Thus, it will be appreciated
that the movable bender plate element portions 12A and 13A
automatically return to their original prepolarized dimensions so
that the bender moves back to its central, at rest, unenergized
condition with contacts 19 and 21 .Iadd.being .Iaddend.opened when
the DC energizing voltage is removed from across the electrodes
T3-Tc or T4-Tc
A key feature of the present invention is the provision of
piezoelectric ceramic bender-type switch energization and/or
utilization circuit means which are built directly onto an unused
portion of the piezoceramic plate elements 12 and 13 of the
bender-type piezoelectric ceramic switching device 11 as will be
described hereinafter. Where thus constructed, circuit stray
inductance is reduced to an absolute minimum since circuit
interconnecting conductor runs formed on such unused piezoceramic
plate portions require only minimum lengths. The energization
circuits thus formed serve to supply a direct current energizing
potential selectively and respectively to each piezoelectric plate
element portion 12A or 13A which energization potential always is
poled in the same direction as the prepolarizing electric field
previously permanently induced in the piezoelectric plate element
portions 12A and 13A whereby no depolarization of the piezoelectric
plate element portions occur during continued or successive
operations of the switch to close or open the make and break
contacts 17, 19 or 18, 21. It will be appreciated therefor that an
improved piezoceramic switching device according to the invention
such as that shown in FIGS. 1 and 1A can be operated as either a
normally-open or a normally-closed switch without detriment to the
long term stability and reliability characteristics of the switch.
This is explained as follows.
Assume that the outer conductive surfaces 15 and 16 over
.[.peizoelectric.]. .Iadd.piezoelectric .Iaddend.ceramic plate
portions 12A and 13A are maintained positive while the central
conductive surface 14 is maintained negative during the
prepolarization of the plate portions 12A and 13A as described
briefly above. The prepolarization of these plate elements then
will cause a permanent increase in dimension between the poling
electrodes and a permanent decrease in dimensions parallel to the
electrodes (i.e. the plate portions 12A and 13A will become thicker
and shorter). Since both plate element portions 12A and 13A are
prepolarized substantially simultaneously, this permanent change in
dimension will not effect the centering position of the active
movable bender comprised by plate portions 12A, 13A relative to the
coacting contacts 17 and 18. However, in the event that some
off-centering does occur, then the magnitude of the prepolarizing
potential applied across either one or the other of the plate
element portions 12A or 13A can be adjusted so as .Iadd.to
.Iaddend.precisely center the bender contacts 19, 21 between the
coacting contacts 17, 18. This ability to precisely center the
bender element in an easily applied and readily adjusted manner is
attributable to the fact that .[.th.]. .Iadd.the .Iaddend.bender
plate elements 12A and 13A can be prepolarized in-situ and is of
extreme importance during manufacture in order to assure proper
operation of the bender switch at relatively low cost since there
are fewer fabrication and process steps involved. Thereafter,
during operation, DC energizing potential selectively and
respectively can be applied either to terminals T3 or T4 and such
energizing potentials always are poled in the same direction as the
polarity of the prepolarizing potential. Since it was assumed that
the prepolarizing potential applied to conductive surfaces 15 and
16 was positive relative to the potential of the central conductive
surface 14 which therefore is negative relative to 15 and 16, the
applied energizing DC potential required to operate the switch
would have corresponding polarities. That is, DC energizing
potential applied either through T3 or T4 would be positive
relative to the potential applied to Tc. This is the proper
polarity relation where the bender-type switch is designed for use
with PNP bipolar transistors or P-type FET transistors. Where the
switching circuit is to be used with NPN bipolar transistors or
N-type FET transistors, then the polarities would be reversed both
with respect to the high voltage value prepolarizing potential and
the later applied operating energizing potentials so as to preserve
the proper dipole enhancement of the prepolarized portions of the
piezoelectric ceramic plate elements 12A, 13A. That is to say,
negative polarity energizing potentials would be selectively
applied to either terminal T3 or T4 and a politive polarity
energizing potential applied to terminal Tc.
As noted earlier, during operation the application of the further
DC energizing potential which is of smaller magnitude than the
prepolarizing potential, but of the same polarity, results in a
further thickening and shortening of one or the other of the plate
element portions 12A or 13A. This thickening and shortening of one
of the plates consequently will result in physically bending the
free movable end of the active bender portion 12A, 13A sufficiently
to selectively close either the contact 19 on its coacting contact
17 (in the event T3 is energized), or, alternatively, selectively
close contact 21 on its coacting contact 18 (if T4 has been
energized). The closure thus achieved will remain for so long as
the DC energizing potential is applied to the respective contacts
T3 or T4. This can be for an indefinite period of time. Thus the
bender-type switching device 11 shown in FIGS. 1 and 1A, by
appropriate energization and utilization circuit design, can be
used either as a normally-open or a normally-closed switching
device. This capability is achieved because of three principal
characteristics of the switching device. First, the piezoelectric
ceramic plate elements 12 and 13 essentially are high quality
capacitors having little or no losses when charged (energized).
Secondly, any losses that do occur over extended periods of being
energized are supplanted immediately and continuously by the
continually applied energization potential. Lastly, because the
energization potential always is applied with the same polarity as
the prepolarization potential used to initially prepole and enhance
the dipole orientation of the piezoelectric ceramic plate portions
12A and 12B, there is no possibility of long term depolarizing
effects rendering the device unstable in operation.
Upon removal of the DC energizing potential to either T3 or T4, the
active movable bender portion 12A, 13A returns to its center
neutral unenergized position thereby opening which ever set of
contacts 17, 19 or 18, 21 was closed. It should be noted at this
point in the description, that prepolarization and subsequent
operation with DC energizing potentials of positive polarity
applied to the respective outer conductive surfaces 15 and 16 via
terminals T3 and T4 while the center conductive surface 14 is
maintained negative, is cited as exemplary only. The device could
be fabricated and operated equally well with negative polarity
prepolarizing potentials applied to the terminals T3 and T4 while
the central conductive surface 14 terminal Tc is maintained
positive. If thus prepolarized, the device of course subsequently
would have to be operated using only DC energizing signals applied
to the terminals T3 and T4 which are negative relative to the
potential applied to the central conductive surface 14 via terminal
Tc. FIGS. 7B and 7C to be described hereinafter illustrate this
capability.
With reference again to FIGS. 1 and 1A, it will be seen that there
are two unpoled piezoelectric plate element portions 12B and 13B
which extend beyond the clamped portion of the piezoelectric plates
12 and 13 in a direction opposite from the prepoled active movable
bender portions 12A, 13A. These unpoled plate element portions 12B
and 13B may be provided with exterior conductive surfaces such as
shown at 15B and 16B which are separated from the conductive
surfaces 15 and 16 overlying the polarized piezoceramic plate
portions 12A and 13A by the gaps 15A and 16A under clamping bars 22
and 23, respectively, together with the central conductive surface
14 sandwiched therebetween to form two separate, relatively large
(i.e. 1 microfarad) capacitors. In the embodiment of the invention
shown in FIG. 1A, the conductive surface 14 extends throughout the
length of the piezoceramic plate elements 12 and 13 so that a
continuous central electrically conductive path 14 extends between
the free movable bender .Iadd.portions .Iaddend.12A, 13A of the
device and the end thereof connected to the common terminal Tc. If
required for particular circuit design purposes, the central
conductive path 14 provided through conductive surface 14 may be
interrupted along a line under the clamping bars 22 and 23, or at a
number of points, and the space therein filled with a suitable
insulating adhesive for the purpose of electrically isolating
portions of the central conductor 14 under non-poled plate portions
12B and 13B and/or to electrically isolate the central conductor
portion 14 under the prepoled plate .[.portion.]. .Iadd.portions
.Iaddend.12A and 13A from that under non-poled portions 12B, 13B.
In either form of construction, the unpoled plate portions 12B and
13B form two capacitors which in effect readily can be connected in
either a series or parallel circuit relationship via the central
conductor surface 14 thereunder and terminal Tc. The capacitors
thus formed by appropriate design and fabrication of the outer
conductive surfaces 15B and 16B may be provided with capacitance
values required for particular circuit designs. The size of the
capacitors and their capacitance values are related to the power
rating of the circuit and bender size. For example, up to a
capacitance of about a tenth of a microfarad would be provided for
switching devices constructed in the manner described having bender
member dimensions of about one inch wide by three inches long and
with piezoelectric ceramic plate element thicknesses of about 3-10
milli-inches with the conductive surfaces being extremely thin. It
should be understood that if a number of different size capacitors
are desired in any particular circuit arrangement, they can be
formed by appropriately subdividing the outer conductive surfaces
15B or 16B into the desired number and size capacitors. The
multiplicity of capacitors thus formed could all use the common
central conducting surface 14 as a common electrode via terminal
Tc.
In addition to .Iadd.the .Iaddend.capacitors formed in the above
briefly described manner, other electrical circuit components
comprising either active semiconductor devices or passive circuit
elements fabricated either in discrete, hybrid or monolithic
integrated circuit form physically can be formed on or supported by
the unpoled piezoelectric plate element portions 12B or 13B. In
such devices the conductive surfaces 15B and 16B could be shaped to
provide conductive paths (runs) between the various components to
interconnect them into desired circuit relationship in accordance
with known printed circuit and integrated circuit fabrication
techniques as described in the textbook "Microelectronics" edited
by Max Fogiel and published by Research and Education Association,
copyrighted 1968, and others such as "Handbook of Electronics
Packaging", Charles A. Harper, editor, published by McGraw-Hill
Book Company and copyrighted 1969 and "Handbook of Components for
Electronics", Charles A. Harper, editor, published by McGraw-Hill
Book Company, copyrighted 1977.
In FIG. 1A, relatively large hybrid integrated resistors are shown
at 25 and 26 which are surface mounted on the respective conductive
surface portions 15B and 16B of the unpoled electrically neutral
piezoelectric ceramic plate portions 12B and 13B,
respectively.Iadd., .Iaddend.and may be formed either by surface
deposition, bonding or screening. This structure results in two
series connected resistor and capacitor elements which are designed
to form a snubber circuit connected across the terminals T1-Tc and
T2-Tc, respectively. By interconnecting the two snubber
capacitances in parallel, the total capacitance of the snubber
circuit can be doubled
FIG. 1B of the drawings is a schematic circuit diagram of the novel
piezoelectric ceramic switching device and related energization and
utilization circuit shown physically in FIGS. 1 and 1A of the
drawings. In FIG. 1B the terminals T1 and T2 are connected to a
suitable source of alternating current or direct current of the
correct polarity. Terminal T1 is connected through the switch S1
formed by contacts 17 and 19 via the central conductive surface 14
to the common terminal Tc. Terminal T2 is connected through the
switch S2 formed by the coacting contacts 18 and 21 via central
conductive surface 14 to common terminal Tc. The snubber circuit
formed by the series connected resistor 25 and capacitor C12B is
connected in parallel across switch S1 and the snubber circuit
formed by the series connected resistor 26 and capacitor C13B is
connected in parallel circuit relationship across the switch S2.
The snubber circuits R25, C12B and R26, C13B are provided to
prevent excessive arcing across the contacts 17, 19 or 18, 21,
respectively, as the contacts are opened in order to interrupt
current flow through the respective switches and result in reducing
the rate of rise of reapplied forward potential across the contacts
as they open. The inclusion of the snubber circuit thus provided is
referred to as a dv/dt protection circuit for the switch S1 and S2
contacts and can greatly increase their operating life, and reduce
electrical noise effects.
User operated energization circuit means are provided for
selectively and respectively closing or opening the switches S1 and
S2. The energization circuits are comprised by either a negative
polarity source of direct current potential or an alternating
current source of potential connected in series circuit
relationship through a normally open user operated switch 27, a
limiting resistor 28, and diode rectifier circuit means 29 across
the prepolarized portion 12A or 13A of the piezoelectric ceramic
switching device 11 and the common central conducting surface 14 to
the common terminal Tc that is connected to the positive polarity
terminal of the direct current source or an alternating current
source, which ever is used. In preferred embodiments, the normally
open user operated switch 27 either is electrically or mechanically
interconnected with a normally-closed switch 31 that is connected
in series circuit relationship with a limiting resistor 32 with the
series circuit thus comprised being connected in parallel circuit
relationship across the respective prepolarized upper and lower
piezoelectric ceramic plate elements 12A and 13A, respectively,
which are indicated as capacitors C12A and C13A. The energization
circuit comprised by elements 27-32 have not been illustrated in
their physical form in FIGS. 1 and 1A in order not to unduly
complicate these drawings; however, it is believed obvious to one
of ordinary skill in the electronic art as to how these components
would be physically implemented and interconnected to the piezo
ceramic switching device 11 shown in FIGS. 1 and 1A in the light of
the teachings of this application.
In operation, the normally closed contacts 31 will maintain the
prepolarized upper and lower piezoelectric ceramic plate elements
12A and 13A in an uncharged condition so that the bender device 11
is maintained at its central neutral position with neither switch
S1 .[.of.]. .Iadd.or .Iaddend.S2 .Iadd.being .Iaddend.closed. If it
is desired to close switch S1 comprised by contacts 17 and 19, for
example, in order to supply load current to a load device
controlled by switch S1, the user operated, normally open switch
contact 27 is closed. This results in charging the upper
piezoelectric ceramic plate element 12A via the limiting resistor
28, diode rectifier circuit means 29 and the source of electric
potential connected across the energization circuit input terminal
and common terminal Tc. Concurrently with this action, the
normally-closed contact 31 automatically opens so that
piezoelectric ceramic plate element 12A can be charged thereby
causing it to physically deform in the manner described earlier and
close switch S1 by closing contact 19 on coacting switch contact 17
to provide load current supply to a load (not shown). After a
desired period of operation of unlimited duration, and at the
user's option, the electrical load current flow being supplied via
switch S1 contacts 17, 19 can be interrupted by merely opening the
normally-open switch contacts 27 thereby automatically closing
normally-closed contacts 31 and discharging the piezoelectric
ceramic plate element 12A. This results in deenergizing the upper
plate element 12 and allows the bender device 11 to return to its
normally quiescent, neutral central position whereby neither of the
switch contacts S1 or S2 are closed. Operation of the device to
close the switch S2 comprised by contacts 18 and 21 is entirely
similar to that described with relation to the switch S1 so that it
need not be described here in detail. Further, it should be noted
that reversal of polarity of the excitation voltage supplied to the
prepolarized, movable bender plate portions 12A and 13A readily can
be accomplished by reversal of the polarity of connection of the
diode rectifiers 29 should that be desired for a given utilization
circuit application. Additionally, in alternative embodiments of
the FIG. 1B circuit, the normally closed .[.contact.]. .Iadd.switch
.Iaddend.31 is eliminated and the resistance value of resistor 32
increased to about ten times the value of resistor 28.
One of the difficulties encountered with bender-type piezoelectric
ceramic switching devices of the same general type as that
illustrated in FIGS. 1 and 1A of the drawings is a tendency for the
movable bender .Iadd.portions .Iaddend.12A, 13A at the free movable
end thereof to which the contacts 19 and 21 are secured tending to
curl during continued energization. As a result of this tendency to
curl at the free movable .[.end.]. .Iadd.ends .Iaddend.while being
energized, the available contact area for doing work is reduced
.[.and increases.]. .Iadd.with increased .Iaddend.heating, the
contact force with which the contacts close is reduced and the
spacing of the contacts and the timing of their closure cannot be
precisely controlled thus rendering the device unstable and
unreliable in operation. To avoid this difficulty, the present
invention provides a relatively thin inflexible stiffening member
35 secured widthwise across the extreme free movable end of the
prepolarized movable bender portions of the respective upper and
lower piezoelectric ceramic plate elements 12B and 13B as best seen
in FIGS. 1 and 1A of the drawings. The inclusion of the stiffening
member 35 assures that the mass of the extreme free end of the
bender portion moves as a unit thereby summing the available forces
and remains rigidly straight so that it is not allowed to curl or
bend during energization .[.detrimentally.]. .Iadd.detrimental
.Iaddend.to the operation of the switching device 11. By
appropriate design, the mass of the stiffening members 35 can be
tailored to cause the overall bender operation to more nearly
approach mechanical resonance during movement of the bender portion
of the device should this be desired.
FIGS. 1D, 1E and 1F of the drawings illustrate a preferred form of
fabricating the electrical contacts 19 and 21 secured to the free
movable ends of the respective piezoelectric ceramic bender plate
portions 12A and 13A. As best seen in FIG. 1D, the central
conductive surface 14 at the free movable end of the bender device
is fabricated in the form of a foil having two halves 14A and 14B
separated by a slit 14C cut lengthwise through the extended portion
of the conductive foil. As shown in FIG. 1E, the two conductive
foil halves 14A and 14B are bent upwardly and downwardly so as to
extend over and cover about half of the length of the upper and
lower exposed surfaces of the respective stiffening members 35
secured to the ends of the upper and lower piezo ceramic plate
element portions 12B and 13B, respectively. The folded over
conductive foil portions 14A and 14B then may be extended by
additional foil (not shown) along the full lengths of the outer
upper and lower surfaces of the stiffening members 35 to provide
balance to the bender and then secured to the stiffening members 35
by flat headed conductive rivets 19 or 21, respectively, located
centrally on the stiffening member as best seen in FIGS. .[.1.].
.Iadd.1A .Iaddend.and 1F of the drawings. Since the respective
conductive foil halves 14A and 14B and their extension together
with the flat headed rivets 19 and 21 provide good electrically
conductive connections to the central conductive surface 14, the
problem of supplying relatively large load current flow through
these bender end mounted contacts and down to the anchored end of
the bender without unduly dampening movement of the bovable bender
plate portions 12A, 13A is made possible.
FIG. 2 is a side elevational view of a second embodiment of an
improved piezoelectric ceramic switching device constructed
according to the invention. In FIG. 2 a piezoelectric switching
device 11 constructed as described with relation to FIG. 1 is
secured to and supported by an insulating base member 41. Base 41
holds switching device 11 with the .[.the.]. movable contacts 19
and 21 on the free movable end of bender portions 13A and 12A in
juxtaposed switching relationship to sets of fixed contact
terminals T5 and T6 mounted on the insulating base member 41 and
terminals T5' and T6' mounted on a mirror image of the base member
41' (not shown in full). The insulating base member 41 has a number
of conductive runs formed in a known manner on the exposed surfaces
thereof for interconnecting the various components of an electrical
control circuit including an active power semiconductor device 42
as shown in FIG. 2A of the drawings. The active power semiconductor
device 42 preferably comprises a power rated triac such as those
manufactured and sold commercially by the General Electric Company
Semiconductor Products Department, secured to an extended mounting
surface of base member 41 and on which the power semiconductor
device 42 is supported together with the conductive runs required
to interconnect triac 42 with the several elements of the circuit
shown in FIG. 2A.
The piezoceramic switching device 11 of FIG. 2 is constructed and
operates in a manner similar to that shown and described with
relation to FIGS. 1 and 1A of the drawings with the exception that
the extended portions 14A and 14B of the central conductive surface
14 foil are eliminated so that contacts 19 and 21 are electrically
isolated from surface 14. In FIG. 2, only the lower portion of the
complete switching device is disclosed since the upper portion of
the device would constitute a mirror image of the lower portion and
has not been shown for the sake of simplicity. The circuit
illustrated in FIG. 2A, including power triac 42, would be
controlled by the lower contact 21 of the bender switching device
11 and a similar circuit (not shown) would be controlled by the
mirror image portion of the structure shown in FIG. 2 actuated
through the upper contact 19 of the bender device. The following
description will be with relation to only the illustrated lower
portion of the structure and the upper portion would be constructed
and operate in a similar manner.
In the circuit of FIG. 2A the contact points T5 and T6 which are
closed by movable contact 21 on the lower portion of the
piezoelectric ceramic bender-type switching device 11 constitute a
switch S3 which controls power to an electrical load (not shown)
from an alternating current source connected via terminals T1 and
Tc and switch S3 ine series with the load. The circuit of FIG. 2
constitutes a unique assisted commutation circuit wherein electric
current flow through the switch contacts of bender operated switch
S3 is interrupted with the assistance of the power triac 42 which
is connected in parallel circuit relationship with the switch S3
via a fuse element 43 formed either on the insulating base member
or an unpoled portion of one of the piezoelectric ceramic plate
elements as shown in FIG. 3. Connected in parallel circuit
relationship with the triac 42 are two snubber circuits formed by
series connected resistor R25 and capacitor C12B and series
connected resistor R26 and capacitor C13B, fabricated and mounted
in the manner described with relation to FIGS. 1 and 1A of the
drawings, and connected in parallel circuit relationship across
each triac 42 and fuse 30. Energization potentials are applied
across the respective upper and lower polarized movable bender
plate elements 12A and 13A indicated by the .[.capacitor.].
.Iadd.capacitors .Iaddend.C12A and C13A, respectively, via
respective energization circuits including user operated switches
such as 27, 31 (not shown) similar to those illustrated in FIG. 1B
via terminals T3 and T4, respectively.Iadd.. .Iaddend.
In operation, a suitable gating signal source (not shown) applies a
gating on signal to the triac 42 at a desired point in the phase of
the applied alternating current operating potential to be supplied
to the load via switch S3. At this point, the triac 42 turns on and
carries the load current for only a short period of time before
energization of the bender switch 11 results in closure of the
contacts S3. Closure of the S3 switch contacts under these
conditions is substantially without arcing since the potential
across the switch during closure has been reduced substantially due
to conduction through the triac 42. After closure of the hard
switch contact S3 by the piezoelectric ceramic switching device 11,
conduction through triac 42 terminates due to the shunting of the
operating current through the closed contacts T5 and T6 of switch
S3. The turn-on signal supplied to triac 42 through terminal T7 by
the gating signal source (not shown) then can be removed. Supply of
operating current to the load through the closed bender switch
contact S3 then can be maintained for so long as the user desires
by maintaining the energizing potential applied to the lower
piezoelectric ceramic plate element 13A via energizing signal input
terminal T4 in the manner described with relation to the FIG. 1
embodiment of the invention.Iadd.. .Iaddend.
When it is desired to interrupt the current flow through the bender
switch S3 contacts T5 and T6, the triac 42 again is gated on by the
gating signal source (not shown) at any point in the operating
cycle of the operating alternating current source before
.[.de-energizaton.]. .Iadd.de-energization .Iaddend.of the
piezoelectric ceramic bender-type .[.switch.]. .Iadd.switching
.Iaddend.device 11. Hence as the S3 contacts start to open, current
will be diverted from the contacts T5 and T6 and load current flow
will take place through the now conducting triac 42. By thus
diverting current flow from across the partially open contacts T5,
T6 and 21 in this manner, the triac 42 assists commutation off
(opening) of the bender switch contacts T5, T6 with little or no
arcing taking place. The triac itself then is turned off by removal
of its gate turn-on signal at or before the next current zero of
the load current supply source. Turn-off of the triac 42 at this
point is supported through action of the snubber circuits R25, C12B
and R26, C13B which cushion or soften the rate of rise of reapplied
voltage across the triac 42 as it turns off to avoid its
unintentional turn-on and reconduction resulting from steep a rate
of rise of reapplied potential. It will be appreciated therefore
that the structure of FIG. 2 provides a fast acting precision
synchronous operating relay which allows the power rating of the
structure to be greatly enhanced due to the very high surge current
rating of the power semiconductor device 42 when operated over such
short operating periods, and yet the low on-state resistance of the
load current carrying bender operated switch contacts T5-21-T6 of
the piezoceramic bender switch device 11 allows the device to be
operated indefinitely without substantial heating in its load
current carrying condition. Further, the novel switching circuits
eliminate the bulk, weight, slow and variable response and heat
producing characteristics of traditional electromagnetic relay
structures and the stray inductive loops normally encountered with
such structures are substantially eliminated .[.and.]. .Iadd.or
.Iaddend.reduced to an absolute minimum by the short
interconnecting electrical paths formed on the switch component
itself. Lastly, it should be understood that polyphase circuit
configurations as well as single pole, double throw, center-off
systems are within the .[.teaching.]. .Iadd.teachings .Iaddend.of
the disclosure as indicated by the phantom lines in FIG. 2.
FIG. 4 of the drawings illustrates still another embodiment of the
invention intended for use with low voltage energization sources.
The embodiment of the invention shown in FIG. 4 is fabricated and
operates in substantially the same manner as the FIG. 1, 1A
embodiment with the exception that it has voltage doubler
.[.cicuits.]. .Iadd.circuits .Iaddend.formed on the unpoled
.[.portion.]. .Iadd.portions .Iaddend.12B and 13B of the
piezoelectric ceramic plate elements comprising the bender
switching device 11. In FIG. 4, active semiconductor devices in the
form of sets of surface mounted semiconductor diodes D1 and D2 are
secured on the conductive surface portions 15B', 15B" and 16B',
16B", respectively. Each of the conductive surfaces 15B and 16B
have been separated into two separate surfaces 15B', 15B" and 16B',
16B" by a suitable insulating gap in each of the conductive
surfaces to form two separate capacitor elements from each of the
unpoled piezo ceramic plate portions 12B and 13B thereunder.
Additionally, a break in conductive surface 14 is provided at 20 by
an insulating land (gap filled adhesive) in the central conductive
surface 14. Gap 20 insulates and electrically isolates the portions
of conductive surface 14 under the prepolarized portions 12A, 13A
from unpoled portions 12B, 13B of the piezoceramic plate elements
12 and 13. The components formed as described above are
electrically interconnected by hard wire insulated conductors
interconnected in the manner shown in FIG. 4 between the several
components to form the electrical circuit illustrated schematically
in FIG. 4B of the drawings. A somewhat different arrangement of
either the circuit of FIG. 4A or FIG. 4C could be fabricated in a
similar manner using discrete or hardward interconnections or
printed conductive paths as described earlier. Each of the circuits
shown in FIG. 4A, 4B and 4C are classical, known diode voltage
doubler circuits wherein the value of the AC voltage supplied to
the input of the energization circuits for the bender switching
device 11 is double across their output to terminals T3 and T4,
respectively. Thus, if the piezoceramic switching device 11 shown
in FIG. 4 has available only say a 115 volt residential alternating
current supply with which it is to be used, the switching device
shown in FIGS. 4 and 4B could be employed to double the
energization potential being applied to input terminals T3 and T4
of the piezoelectric ceramic switching device 11 and still be able
to selectively open and close its load current carrying switch
contacts 17, 19 and 18, 21 as described earlier with relation to
FIGS. 1 and 1A. In other respects, the device operates and is
constructed similarly to the switching device shown in FIGS. 1 and
1A of the drawings.
FIG. 5 is a top perspective view of still another embodiment of the
invention fabricated in accordance with the techniques and
structural features discussed with relation to FIGS. 1-4, and FIG.
5A is a schematic circuit diagram of the energization drive circuit
formed on the unpolarized electrically neutral piezoceramic plate
portions 12B and 13B. In FIG. 5 (as well as FIG. 6), the clamping
means 22, 23 has been eliminated in order to simplify the
illustration, however the gap 15A, 16A in the outer conductive
surfaces 15 and 16 is shown clearly. FIG. 5 physically illustrates
a printed circuit design for forming a voltage tripler circuit
illustrated schematically in FIG. 5A whereby a lower voltage
alternating current can be converted to three times its original
voltage value for application to the prepolarized piezoceramic
bender plate portions 12A and 13A as an energization potential for
moving the bender plates.
FIG. 6 of the drawings is similar to FIG. 5 but illustrates a
piezoelectric ceramic switching device 11 fabricated to provide a
voltage quadrupling energization circuit illustrated schematically
in FIG. 6A of the drawings formed on each outer surface of the
unpoled, electrically neutral piezoceramic plate portions 12B, 13B.
The voltage quadruple circuit of FIG. 6A and the tripler circuit of
FIG. 5A are of known construction and operation and therefore need
not be described further. It should be noted, however that the
capacitors shown in these electrical circuit diagrams correspond in
numbering C1, C2, etc., to the numbering of the diodes D1, D2,
etc., which are supported on the capacitors as shown in FIGS. 5 and
6. The manner in which the islands of conductive surface 15B are
formed on the unpoled electrically neutral piezoceramic plate
portions 12B and 13B, in the FIG. 5 and FIG. 6 devices is similar
to that described with relation to FIG. 1 using known conventional
photo-resist screening deposition and etching techniques. In this
.[.manneer.]. .Iadd.manner .Iaddend.desired size capacitor
neutralized electrodes 15B1, 15B2.Iadd., .Iaddend..[.and.].
15B3.Iadd. , etc. .Iaddend.in FIG. 5 in 15B1, 15B2, 15B3.Iadd.,
.Iaddend..[.and.]. 15B4 .Iadd., etc. in FIG. 6 .Iaddend.are formed
together with the appropriate size interconnecting conductive runs
between the several electrodes. Semiconductor diodes D1-D3 in FIG.
5 or D1-D4 in FIG. 6 are supported on the respective
.[.metalized.]. .Iadd.metallized .Iaddend.electrode surfaces. A
practical way to implement the FIG. 5 and FIG. 6 devices would be
to employ discrete semiconductor diode devices prepared for surface
mounting directly to the conductive surface of the metallized
electrodes 15B1, .[.15B2.]. .Iadd.16B1 .Iaddend., etc. by
soldering, ultrasonic bonding techniques and/or by a suitable
conductive adhesive or the like. These fabrication steps will have
been carried out after prepolarization of the active, movable
prepolarized portions 12A, 13A of the piezoelectric ceramic
bender-type device to prevent possible damage to the components by
the high prepolarizing potential. Alternatively, the capacitor
electrode areas .[.15B.]. .Iadd.15B1, 16B1, etc. .Iaddend.and
diodes D1-D3 or D1-D4 could be formed by integrated circuit
fabrication techniques such as those described in the above
referenced textbook entitled "Microelectronics" by Max Fogiel
published by Research Education Associates of New York, N.Y.,
copyrighted 1968. Similar techniques could of course be employed in
forming corresponding capacitor electrodes and conductive runs
employed in the FIG. 1, 1A and FIG. 2 embodiments of the invention
described earlier.
FIG. 7 and 7A of the drawings illustrate still another embodiment
of the invention wherein a piezoceramic bender switching device 11
is employed to close a circuit selectively either through switch
contact 19 or switch contact 21 to supply a gating-on-signal
current to the control gate of a respective associated gated power
switch such as an SCR, power transistor or triac 42, 42' as
illustrated in FIG. 7A. Conductive runs are formed out of the
portion of the interior conductive surface 14 of the bender
switching device 11 to provide electrical interconnections to
limiting resistors 25 and 26 formed on the unpoled electrically
neutral portions 12B and 13B of the bender device as described with
relation to the FIG. 1, 1A embodiment of the invention. The current
limiting resistors 25 and 26 are connected intermediate the
piezoceramic bender switch contacts 19 and 21, respectively, and
the control gates of the respective triac devices 4 associated with
the respective bender actuated switch contacts 19 and 21.
In operation, turn-on of either one or the other of the gate
controlled power switching devices 42 is achieved by energizing the
appropriate prepolarized piezoceramic plate element of switching
device 11 to cause either contact 19 or contact 21 to close on the
gate input terminal of its associated power triac 42 .Iadd.or
42'.Iaddend.. The stored electrical charge in the prepolarized
piezoceramic plate element then discharges into the gate of the
triac and provides adequate turn-on current to the triac to cause
it to turn-on and conduct current. Upon turn-on of the triac 42 or
42', either load 51 or load 52 will be supplied with alternating
current load current via the conducting power triac switch 42.
Turn-off of the conducting triac power switch 42 is achieved by
merely de-energizing the respective previously energized
prepolarized, active movable piezoceramic plate portion (either 12A
or 13A) of the bender switch device 11 at an appropriate point in
the cycle of the supply alternating current. If desired, suitable
snubbing circuits as described with relation to FIG. 1B may be
provided across the gate controlled power switching devices 42
.Iadd., 42' .Iaddend.to assist these devices in withstanding the
reapplied forward load voltage after turn-off by suitable
fabrication of the switching device 11 shown in FIG. 7 as described
earlier with respect to FIG. 1.
FIG. 7B illustrates an alternative form of power circuit gating
arrangement using a novel piezoceramic bender-type switch 11
constructed according to the invention and wherein the electric
energy stored in the piezoceramic plate elements of the bender-type
switch 11 is employed as a source of gating current for a gated
power semiconductor switch such as an SCR, power transistor or
triac 42 supplying a load 51 or 52 as shown in FIG. 7B. The circuit
arrangement of FIG. 7B is for use with those types of gated power
semiconductor switches which require a positive polarity turn-on
gating current supplied to the gate measured relative to the
cathode polarity. In this arrangement, an energization circuit
.[.comprised by.]. .Iadd.includes .Iaddend.a diode rectifier 29P
havings its anode connected to the positive terminal of a direct
current supply or an alternating current supply. The cathode of
diode 29P is connected through a limiting resistor 28 across a set
of normally open contacts of either one of a set of normally-open
user operated switches 27A or 27B to the outer conductive surface
15 or 16 of the prepolarized active movable piezoelectric ceramic
plate elements 12A or .[.12B.]. .Iadd.13A .Iaddend.of bender device
11. The outer conductive surfaces 15 or 16 are not excited normally
and are shorted to the negative terminal of the DC or AC supply by
the normally-closed contacts of either one of normally-closed
switches 31A or 31B. The two sets of switches 27 and 31 are either
electrically or mechanically interconnected so that when 27 is
open, 31 is closed and vice versa. The bender actuated contacts 19
and 21 on the free movable bender end of device 11 .[.is.].
.Iadd.are .Iaddend.designed to close on a coacting contact which is
connected through either limiting resistor 25 or 26 to the gated
power semiconductor switch device 42' or 42 supplying either load
51 or 52.
In operation, upon closure of the normally open contacts 27A (for
example) by a user of the circuit, the piezoelectric ceramic plate
element 12A of bender switching device 11 will be charged via
rectifier 29P, limiting resistor 28 and the closed contacts of
normally open switch 27A. Normally closed switch 31A automatically
will have opened so that charging of the plate element 12A is made
possible. In the short time which is required to charge plate
element 12A sufficiently to cause bender device 11 to close contact
19 on its coacting fixed contact connected through resistor 25 to
the gate of the gated power switch 42', sufficient electrical
energy will have been stored in the piezoelectric ceramic plate
element 12A to supply adequate gate current to turn-on the gated
power switching device 42'. This gate turn-on current is supplied
via contact 19 which has been modified to have its contact surface
connected to the outer conductive surface 15 of piezoelectric
ceramic plate element 12A as opposed to the inner conductive
surface 14. The modification to the contacts 19 as well as 21 to
provide such connection is believed obvious in the light of the
teachings of FIG. 1B, FIG. 1E and 1F. The gate turn-on current thus
supplied to the gate of power switch 42' will be adequate to gate
on the semiconductor power switch 42' and maintain it conducting
for so long as the user operated switch 27A is maintained closed on
its contacts and load 51 will be supplied with load current via the
conducting gated power semiconductor switch device 42'. If it is
desired to turn-on the opposite gated power switch 42 supplying the
load 52, the normally open switch 27A supplying piezo ceramic plate
element 12A is returned to its normally-open condition and the
opposite normally open switch 27B supplying piezo ceramic plate
element 31A is closed to thereby turn-on the gated power switch 42
supplying load 52 in the same manner described with relation to
excitation of load 51.
FIG. 7C of the drawings shows an oppositely poled connection of the
bender switch device 11 so that it is arranged to provide negative
polarity gate turn-off signals to the control gate of certain types
of gated semiconductor power switches 42 .Iadd.or 42'
.Iaddend.which are designed to provide turn-off of the load current
supplied through either the load 51 or 52 by means of a negative
polarity gate turn-off signal applied to its gate. For these types
of devices, it is anticipated that two separate energization
(de-energization) circuits will be provided, one such as FIG. 7B
supplying a positive polarity gate turn-on signal to the gate for
turn-on purposes, and the other supplying a negative polarity gate
turn-off signal with the circuit arrangement shown in FIG. 7C to
effect turn-off of the load current.
FIGS. 8, 8A, 8B and 9 all illustrate still further embodiments of
the invention wherein two separate central conductive surfaces 14U
and 14L are employed in place of a single central conductive
surface 14 as shown in the embodiments of the invention heretofore
described. In FIG. 8, the two central conductive surfaces 14U and
14L extend throughout the full length of the piezoelectric ceramic
plate elements 12 and 13 over the surfaces of both the prepolarized
portions 12A and 13A as well as the unpoled electrically neutral
portions 12B and 13B. To form the contacts 19 and 21 on the active
movable prepolarized end portions 12A and 13A, the entire width of
the central conductive surface 14U is folded up and over the
inflexible stiffening member 35, secured widthwise across the upper
surface of the free end of the bender member 12A and centrally
riveted in a manner similar to that shown and described with
relation to FIGS. 1B, 1E and 1F. The difference in the FIGS. 1-7
embodiments being primarily that the single central conductive
surface 14 of FIG. 1 has its extended portions 14A and 14B cut by a
slit with one half being folded up and over and the other half
being folded down and over. In the case of the FIGS. 8 and 9
embodiments, the central conductive surfaces 14U and 14L do not
have to be split but instead have the entire width of the extended
portion of the surface 14UA is folded up and over the rigid
insulating stiffening member 35 and secured by a central flat
headed rivet 19 in the manner shown. In the case of the lower
conductive surface 14L its extended portion 14UL has its entire
width folded down and over the insulating stiffening member 35 and
secured by the flat headed rivet 21 in the manner shown.
The two central conductive surfaces 14U and 14L are secured rigidly
to an exposed lower surface of the entire .[.piezelectric.].
.Iadd.piezoelectric .Iaddend.ceramic plate member 12 and exposed
upper surface of the lower piezoelectric ceramic plate member 13
with the two central conductive surfaces 14U and 14L being secured
together to form the bender device 11 by a thin adhesive layer 61.
In preferred forms of the FIG. 8 embodiment of the invention, the
adhesive layer 61 will be insulating so that the respective inner
conductive surfaces 14U and 14L can be maintained at different
electric potentials during energization of the bender switch device
11 to cause it to bend in one direction or the other. In other
forms, it may be desirable to use an electrically conductive
adhesive 61 to secure the two plate elements 12 and 13 together in
order that both inner conductive surfaces 14U and 14L are
maintained at the same electric potential. The adhesives employed
for this purpose and used in any of the embodiments of the
invention described in this application are of the type that can
take any high temperature that might be required during in-situ
prepolarization treatment as described earlier or in bake-out of
vacuum mounted devices without undue out gassing. Typical adhesive
systems which could be used for all of the embodiments of the
invention herein disclosed include GEMID (imide ether), PIQ
(polyimide isoindroquinzolianedione), PEK (polyethereeketon), ULTIM
(polyetholyulpem) or ULTEM .[.(polyethermide).].
(.Iadd.polyetherimide).Iaddend.. Such adhesives normally are
insulating in nature but that conductive granules of a very fine
nature may be added to an adhesive layer such as 61 in order to
make it suitably conductive where it is desired that the two inner
conductive surfaces 14U and 14L be maintained at the same electric
potential during operation. However, it is important that the
adhesive layer 61 be pinhole free so that in such situations it may
be more advisable to interconnect surfaces 14U and 14L externally
of the bender member.
Known bender piezoelectric ceramics such as those listed earlier in
this application are of such high density that they will provide
long service life if correctly formulated, cast and fired. In the
present invention it is proposed to extend the operating life of
such piezoelectric ceramic bender members through the use of
selective electrode formations so as to provide longer creepage
paths to avoid surface breakdown .[.and.]. .Iadd.with .Iaddend.the
use of a variety of passivating protective coatings and adhesives
such as those listed in the previous paragraph. The embodiment of
the invention shown in FIG. 8 of the drawings illustrates the use
of a passivating protective coating 62 formed over the exterior
(particularly the exterior side) surfaces of the prepolarized,
active movable bender portions 12A and 13A of the piezoelectric
ceramic bender device 11. The preferred passivating protective
coating 62 is a polyimide siloxane copolymer which forms an
excellent thin pinhole-free conformal surface passivating
protective coating in that it readily flexes to allow movement of
the bender device without undue damping effects and is
substantially pinhole free. The combination of the selective bender
prepoling to provide a separate movable prepolarized bender portion
12A, 13A different from the unpoled clamped portion 12B, 13B
together with properly shaped surfaces 14U, 14L, 15 and 16 to
recess their edges back away from the side edges of the
prepolarized piezoceramic plate elements 12A, 13A as best shown in
FIGS. 8A and 8B and a properly composed and applied passivating
protective coating to provide a pinhole-free protective surface
which encompasses all of the active (movable) areas of the bender
while not being subjected to the sharp bending action that takes
place at the clamped end of the piezo ceramic bender, provides the
utmost in stability, repeatability of operation, and voltage
withstand capability together with good service longevity in a
piezo ceramic bender-type switching device. These features also
show the use of much higher prepolarization potentials than were
possible with previously known bender switching devices and hence
result in piezoceramic bender-type switching devices capable of
greater work output than previously known devices of comparable
size.
With reference to FIG. 8D, a number of curves A-D are shown wherein
the characteristics of a number of different piezoelectric ceramic
bender-type devices are shown. In FIG. 8D, the bending force
developed by the bender device is plotted as the ordinate and time
as the abcissa. Curve A shows that the force versus time
characteristics of a piezoceramic switching device fabricated as
described in this application and then mounted in a properly
baked-out vacuum or gas sealed enclosure, provides substantially
constant bending force over an indefinite period of time. A
piezoceramic bender-type switching device according to the
invention having a pinhole-free passivating protective coating of
polyimide siloxane copolymer fabricated as described above with
relation to FIGS. 8 and 9 and operated in air will have essentially
constant force that drops slowly with time as shown in curve B as
energization charge bleeds from the piezoceramic bender plate
element capacitor. In contrast, a prior art protectively coated
piezoelectric ceramic bender switch device bender .[.for.].
.Iadd.exhibits .Iaddend.a force versus time operating
characteristic .[.is.]. .Iadd.are .Iaddend.shown in curve C under
conditions where the device is operated in air with low humidity.
Curve C' illustrates force-time characteristics of the same prior
art device operated under high humidity conditions. From Curve C'
it can be seen that the bender force of the protectively coated
prior art device drops off drastically with time while thus
operated under high humidity conditions. Curve D illustrates the
force versus time characteristics of known prior art piezo ceramic
bender devices which are provided with no protective coating. From
these curves it will be appreciated that significant bender force
changes can occur if the impedance of the piezo ceramic bender is
not maintained at a high value so that leakage current across and
around the piezoceramic cannot increase with time or increasing
humidity thereby reducing the ability to apply high energization
voltage and obtain stability of operation of the device in
service.
FIGS. 8A, 8B and 8C all illustrate fabrication techniques whereby
the sealing effects of the passivating protective coating 62 can be
improved and a force-time operating characteristic curve such as
that shown in B in FIG. 8, or nearly approaching the idealized
curve A, can be obtained. In FIG. 8A, a particular coating is
provided as shown at 62 which extends to a considerable depth over
the exposed side edges of the prepolarized, movable bender plate
element portions 12A and 13A and may or may not leave exposed or
only thinly cover the central planar areas of the outer conductive
surfaces 15 and 16. In this embodiment, the outer side edges of the
inner conductive surfaces 14U and 14L are shown as being shortened
widthwise so that a considerable portion of the passivating
protective coating projects into the space and covers area which
otherwise might be occupied by the exposed side edge portions of
the inner conductive surfaces. Experience has shown that when
current creepage and voltage breakdown occur, it is normally at the
side edges between the upper and inner conductive surfaces. To
avoid such voltage breakdown and current creepage while the devices
are under excitation, fabrication as shown in FIG. 8A is provided.
Needless to say, if only a single central conductive surface 14 is
used as in the embodiment of the invention shown in FIG. 1, for
example, similar techniques would be used in avoiding undue current
leakage between the side edges.
FIG. 8B of the drawings illustrates an embodiment of the invention
wherein the entire prepolarized movable bender portion 12A, 13A,
the side edges thereof, and their associated inner and outer
conductive surfaces 15 and 16 are completely enclosed and
encompassed by the passivating protective coating 62. In addition
FIG. 8B .[.shown.]. .Iadd.shows .Iaddend.the manner in which
different side tabs shown at 63 and 64 can be brought out from the
bender device package for use as terminal connections to the inner
conductive surfaces 14U and 14L, respectively. In the event that
the adhesive system used to bond the bender together in a unitary
structure is insulating in nature, then it will be appreciated that
the upper and lower inner conductive members 14U and 14L can be
maintained at separate potentials. Alternatively, if the bonding
adhesive is conducting in nature, either terminal 63 or 64 could be
employed as an output terminal for the device or otherwise.
FIG. 10 of the drawings illustrates an embodiment of the invention
wherein the side tab terminals 63 and 64 are placed at different
locations along the longitudinal axis of the bender switching
device. FIG. 10 illustrates a device having only a single, common
conductive surface 14 which has been separated into two parts by an
insulating gap shown at 71 longitudinally aligned under the gaps
15A and 16A in the outer conductive surfaces 15 and 16 where the
bender device is clamped by a suitable clamping means (not shown).
With this arrangement it will be appreciated that side tab 63
provides terminal access to the portion of the central conductive
surface 14 disposed under the prepolarized movable active bender
portions 12A, 13A of the piezoelectric ceramic switching device and
the side tab 64 provides access to the central conductive surface
portion 14 under the unpoled portions 12B and 13B of the
piezoceramic plate members of the device.
FIG. 8C is a partial sectional view through a piezo ceramic bender
device constructed according to FIGS. 8, 8A and 8B but which has
been exaggerated somewhat in order to clearly illustrate the extent
to which one should go in assuring that the conformal passivating
protective coating 62 .[.extend.]. .Iadd.extends .Iaddend.down into
and .[.cover.]. .Iadd.covers .Iaddend.any exposed surfaces of the
prepolarized piezo ceramic plate elements 12A or 13A as shown at
62A. It is this type of area made, for example, by formation of the
gaps 15A and 16A in the outer conductive surfaces 15 and 16 during
fabrication in order to accommodate the clamping members 22, 23
where current creepage and voltage breakdown can occur particularly
between the exposed cut, etched or otherwise formed side edges of
the outer conductive surfaces. To insure against such
.[.undersirable.]. .Iadd.undesirable .Iaddend.effects, particular
care must be taken to see that the conformal passivating protective
coating 62 (as shown at 62A) extends over and covers the outer
planar exposed conductive surfaces and their side edges of the
prepoled movable bender portion of the device, the side edges of
the prepoled planar piezoelectric plate elements, the recessed side
edges of the central conductive surface or surfaces sandwiched
therebetween and down to and cover any portions of the prepolarized
piezoelectric ceramic plate elements exposed by the removal of the
outer conductive surfaces 15 and 16 as well as the edge portions of
the recessed selectively metallized outer conductive surfaces
exposed by such removal.
FIG. 9 illustrates another embodiment of the invention illustrating
a different are of the piezoceramic bender device 11 where the
prospect of voltage breakdown and current leakage is quite high and
with respect to which caution and care should be taken to assure
proper fabrication of the device. This area is at the free movable
end of the switching device where the outer conductive surfaces 15
and 16 extend up to or near the elongated insulating stiffening
members 35 over which the contacts 19 and 21 are formed in
conjunction with the portion 14UA and 14LA of the inner conductive
surface. At these intersections, it is desirable to remove by
cutting, etching or otherwise the portion of the conductive
surfaces 15 and 16 abutting stiffening members 35 and filling the
spaces thus formed with additional passivating protective coating
62B.
The embodiment of the invention shown in FIG. 9 further illustrates
a bender device 11 wherein the portions of the central conductive
surfaces 14U and 14L underlying the prepoled and unpoled portions
of the device are electrically isolated from each other by an
insulating segment of adhesive 63 in the area underlying the
clamping means 22-23. As a consequence, that portion of the central
conductive surfaces 14U and 14L underlying the prepolarized piezo
ceramic plate element portions 12A and 13A will be electrically
isolated from the portion of the central conductors underlying the
unpoled piezoceramic plate element portions 12B and 13B.
FIG. 11 is a partial perspective view similar to FIG. 10 of the
unpoled plate portion of a piezoelectric ceramic bender-type
switching device according to the invention, and illustrates still
different techniques of construction for providing terminal tabs
with which to make electrical connection to either of the inner
conductive surfaces 14U or 14L of a device such as that illustrated
in FIGS. 8 and 9 of the drawings. As shown in FIG. 11, one corner
of each of the upper and lower unpoled piezo ceramic plate element
portions 12B and 13B, respectively is ground away so as to expose
for access the underlying inner conductive surface 14U secured to
the upper plate element portion 12B and the overlying conductive
surface portion 14L secured to the lower plate portion 13B. The
exposed conductive surfaces thus obtained then may have hard wire
connectors or other terminal tabs secured to their surface for
application of electric potentials and currents therethrough. For
those devices which have only a single central conductive surface
14 or alternatively where the two separate central conductive
surfaces 14U and 14L are electrically interconnected by reason of
the use of an electrically conductive adhesive, a central tab shown
at 65 may be provided at the end of the structure in order to
obtain electrical connection to the central conducting
surfaces.
As noted earlier in the specification, it is anticipated that
complete piezoelectric ceramic bender-type switching devices 11
will be completely fabricated with most if not all of the
above-listed and discussed features prior to polarization of the
active movable polarized piezoceramic plate portions of the device.
Prepolarization in-situ after completion of the device rather than
an earlier prepolarization in oil as is normally used with prior
art piezo ceramic plate elements is necessary in order to assure
good stability of the device in operation. In the absence of an
assured 100% dense piezoceramic material, sealing prior to
prepolarization is desirable if not essential in order to avoid any
possible permeation or breakdown of the piezoceramic plate elements
during the high voltage prepolarization operation. However, it
should be noted that the degree of hermetic packaging provided in
the manner described above necessarily will depend upon the degree
of absolute stability required for each switching device
application. Thus, for certain switching devices, absolute hermetic
packaging (or an attempt at such packaging) may not be required due
to more relaxed operating specifications for the device. Further,
the selective electroding and shaping of conductive surfaces 15,
16, 14 or 14U, 14L provides for increased protection voltage
creepage around side edges and operating stress ends and also
reduces potential life-cycle problems which might otherwise limit
performance of the piezo ceramic bender-type devices resulting from
microscopic edge cracking that otherwise .[.are.]. .Iadd.is
.Iaddend.produced if conventional cutting and fabrication
processing techniques are used.
From the foregoing description, it will be appreciated that the
invention provides improved piezoelectric ceramic switching devices
together with improved fabrication techniques for such devices as
well as novel energization and utilization electrical circuits for
the energization as well as use of such improved piezoceramic
switching devices. The improved structure provides for the
inclusion of parts of either the energization circuit or
utilization circuits or both which are physically mounted on and
supported by non-prepoled portions of the piezoelectric ceramic
plates which comprise the piezoceramic switching devices. By such
fabrication, the size, weight and bulk of the switching devices is
greatly reduced so that their compactness and .[.usefullness.].
.Iadd.usefulness .Iaddend.with .[.minaturized.]. .Iadd.miniaturized
.Iaddend.circuit components is greatly improved. Further, because
the circuit components with which the devices are used can be
mounted right on a portion of the devices themselves, stray circuit
inductance is greatly reduced thereby improving the circuit noise
immunity characteristics during operation of the devices
The piezoelectric ceramic switching devices fabricated in
accordance with the invention are of greatly improved construction
and opeating characteristics than the comparable prior art devices
of the same general nature. The improved piezoceramic switching
devices consequently operate with greater stability, reliability
and longetivity in service over extended periods of operation
requiring substantial numbers of switching operations.
INDUSTRIAL APPLICABILITY
Improved piezoelectric ceramic switching devices and systems having
the features of construction made available by the invention are
useful in a wide number of residential, commercial and heavy
industrial electrical systems for use as switching devices in
controlling current flow to widely different types of electrical
loads having different power ratings. Because of their novel
construction, the devices are of lighter weight, less bulk and
lower cost than comparable electromagnetically operated switching
devices currently being used and have much faster response
times.
Having described several embodiments of new and improved
piezoelectric ceramic switching devices and systems using the same
and their methods of manufacture 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.
* * * * *