U.S. patent application number 12/396208 was filed with the patent office on 2009-06-25 for piezoelectric generators having an inductance circuit for munitions fuzing and the like.
This patent application is currently assigned to OMNITEK PARTNERS LLC. Invention is credited to Jahangir S. Rastegar, Thomas Spinelli.
Application Number | 20090160294 12/396208 |
Document ID | / |
Family ID | 39474891 |
Filed Date | 2009-06-25 |
United States Patent
Application |
20090160294 |
Kind Code |
A1 |
Rastegar; Jahangir S. ; et
al. |
June 25, 2009 |
Piezoelectric Generators Having an Inductance Circuit For Munitions
Fuzing and the Like
Abstract
A piezoelectric generator for generating power from an
acceleration is provided. The piezoelectric generator including: a
piezoelectric member capable of producing an output power; means
for applying a force to the piezoelectric member due to the
acceleration; means for sustaining a strain in the piezoelectric
member resulting from the applied force; and an inductor
electrically connected to the piezoelectric member for forming an
oscillating circuit.
Inventors: |
Rastegar; Jahangir S.;
(Stony Brook, NY) ; Spinelli; Thomas; (East
Northport, NY) |
Correspondence
Address: |
Thomas Spinelli, Esq.
2 Sipala Court
East Northport
NY
11731
US
|
Assignee: |
OMNITEK PARTNERS LLC
Bayshore
NY
|
Family ID: |
39474891 |
Appl. No.: |
12/396208 |
Filed: |
March 2, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11998925 |
Dec 3, 2007 |
|
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12396208 |
|
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60872248 |
Dec 2, 2006 |
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Current U.S.
Class: |
310/339 |
Current CPC
Class: |
F42C 11/008 20130101;
H02N 2/18 20130101 |
Class at
Publication: |
310/339 |
International
Class: |
H01L 41/00 20060101
H01L041/00 |
Claims
1. A piezoelectric generator for generating power from an
acceleration, the piezoelectric generator comprising: a
piezoelectric member capable of producing an output power; means
for applying a force to the piezoelectric member due to the
acceleration; means for sustaining a strain in the piezoelectric
member resulting from the applied force; and an inductor
electrically connected to the piezoelectric member for forming an
oscillating circuit.
2. The piezoelectric generator of claim 1, wherein the inductor is
electrically connected in series with the piezoelectric member.
3. The piezoelectric generator of claim 1, wherein the
piezoelectric member comprises two or more layers of piezoelectric
material.
4. The piezoelectric generator of claim 3, wherein the two or more
layers of piezoelectric material are arranged in a direction of the
acceleration.
5. The piezoelectric generator of claim 3, wherein the two or more
layers of piezoelectric material are arranged orthogonal to a
direction of the acceleration.
6. The piezoelectric generator of claim 1, wherein the means for
applying a force to the piezoelectric member comprises a mass
disposed to compress the piezoelectric member upon the
acceleration.
7. The piezoelectric generator of claim 1, further comprising an
elastic means for providing elasticity to one or more members
acting to apply the force to the piezoelectric member.
8. The piezoelectric generator of claim 1, wherein the means for
sustaining a strain in the piezoelectric member comprises
configuring two or more components to have a locking frictional tit
which is engaged upon the application of the force to the
piezoelectric member.
9. The piezoelectric generator of claim 8, wherein the two or more
components comprises: a mass disposed to compress the piezoelectric
member upon the acceleration. the piezoelectric material having at
least a first angled surface; and a locking member having at least
a second angled surface in sliding contact with the first angled
surface such that the piezoelectric member and locking member
engage to limit relative motion therebetween.
10. The piezoelectric generator of claim 1, wherein the means for
sustaining a strain in the piezoelectric member comprises
configuring two or more components to have an interference with
each other which is engaged upon the application of the force to
the piezoelectric member.
11. The piezoelectric generator of claim 10, wherein the two or
more components comprises: a mass disposed to compress the
piezoelectric member upon the acceleration; and a locking member
having a portion for engaging the mass to limit relative motion
therebetween.
12. A method for generating power from an acceleration, the method
comprising: applying a force to a piezoelectric member due to the
acceleration; sustaining a strain in the piezoelectric member
resulting from the applied force so as to increase a time of power
output from the piezoelectric member; and connecting the
piezoelectric member to a circuit to produce an oscillator)
output.
13. The method claim 12, wherein the connecting comprises including
an inductor in the circuit and electrically connected to the
piezoelectric member.
14. The method of claim 13, wherein the indictor is electrically
connected to the piezoelectric member in series.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a Continuation application of U.S.
application Ser. No. 11/998,925 filed on Dec. 3, 2007 which claims
the benefit of provisional application Ser. No. 60/872,248 filed on
Dec. 2, 2006, the contents of each of which is incorporated herein
by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to piezoelectric
generators and, more particularly, to piezoelectric generators for
munitions fuzing.
[0004] 2. Prior Art
[0005] All existing and future smart and guided gun-fired munitions
and mortars that are equipped with electronics for fuzing or other
similar purposes require electric power for their operation. The
amount of power required for proper operation of certain components
in gun-fired munitions, for example for the operation of certain
fuzing electronics, is small enough to be provided by harvesting
the electric charge generated directly from piezoelectric elements
due to the firing acceleration induced straining. The advantage of
using piezoelectric elements that can generate electric energy is
that it eliminates the need for a primary battery and its related
safety and shelf life problems. In general, such piezoelectric
generators that harvest mechanical energy during the firing
acceleration provide a very high degree of safety in munitions
since they provide electrical energy that could operate onboard
electronics only post firing. The use of reserve batteries for such
very low power requirements is not cost effective and requires the
allocation of valuable space and may face safety issues.
[0006] Current applications of piezoelectric elements of various
designs and configurations such as stacks of piezoelectric ceramic,
film layers, etc. which are loaded (strained) due to the firing
acceleration in the axial direction, in bending, etc. and which may
be equipped with appropriate inertial components to increase the
generated loads (axial, bending, torsional, etc.), or are equipped
with motion amplifying mechanisms to amplify the applied stains,
have a common shortcoming that reduces their effectiveness as
electrical energy generators and prevents efficient collection and
storage of the generated charges. This shortcoming stems from the
fact that during firing, the piezoelectric element is subjected to
a very high level of acceleration induced impact type of forces
during a very short period of time, in many cases of the order of
one-tenth of a millisecond. As a result, the window for extraction
and storage of the generated electrical charge is equally small,
making efficient harvesting of the generated charge very difficult.
The harvested charge is generally intended to be stored in a
storage device such as a capacitor or used directly or conditioned
to power a certain load.
[0007] A need therefore exists for new methods and devices that
allow the aforementioned charges generated by piezoelectric
elements due to the firing acceleration or other similar impact
forces to be harvested over significantly longer periods of time,
thereby allowing the generated charges to be harvested with
significantly higher efficiency.
[0008] In addition, a need exists for new methods and devices that
allow efficient harvesting of the aforementioned generated
charges.
SUMMARY OF THE INVENTION
[0009] An objective of the present invention is to provide new
methods for the development of devices that would allow firing
acceleration and or other similar impact force induced charges
generated in piezoelectric elements to be sustained for periods of
times that are significantly longer than the duration of the firing
acceleration or other similar impact forces.
[0010] An additional objective of the present invention is to
provide a number of devices for implementing the aforementioned
method to piezoelectric generators designed to generated charges
due to the firing acceleration in munitions and other impact
induced forces to significantly increase the amount of time
available to harvest the generated charges.
[0011] Accordingly, a piezoelectric generator for generating power
from an acceleration is provided. The piezoelectric generator
comprising: a piezoelectric member capable of producing an output
power; means for applying a force to the piezoelectric member due
to the acceleration; means for sustaining a strain in the
piezoelectric member resulting from the applied force; and an
inductor electrically connected to the piezoelectric member for
forming an oscillating circuit.
[0012] The inductor can be electrically connected in series with
the piezoelectric member.
[0013] The piezoelectric member can comprise two or more layers of
piezoelectric material. The two or more layers of piezoelectric
material can be arranged in a direction of the acceleration. The
two or more layers of piezoelectric material can be arranged
orthogonal to a direction of the acceleration.
[0014] The means for applying a force to the piezoelectric member
can comprise a mass disposed to compress the piezoelectric member
upon the acceleration.
[0015] The piezoelectric generator can further comprise an elastic
means for providing elasticity to one or more members acting to
apply the force to the piezoelectric member.
[0016] The means for sustaining a strain in the piezoelectric
member can comprise configuring two or more components to have a
locking frictional fit which is engaged upon the application of the
force to the piezoelectric member. The two or more components can
comprise: a mass disposed to compress the piezoelectric member upon
the acceleration, the piezoelectric material having at least a
first angled surface; and a locking member having at least a second
angled surface in sliding contact with the first angled surface
such that the piezoelectric member and locking member engage to
limit relative motion therebetween.
[0017] The means for sustaining a strain in the piezoelectric
member can comprise configuring two or more components to have an
interference with each other which is engaged upon the application
of the force to the piezoelectric member. The two or more
components can comprise: a mass disposed to compress the
piezoelectric member upon the acceleration; and a locking member
having a portion for engaging the mass to limit relative motion
therebetween. Also provided is a method for generating power from
an acceleration. The method comprising: applying a force to a
piezoelectric member due to the acceleration; sustaining a strain
in the piezoelectric member resulting from the applied force so as
to increase a time of power output from the piezoelectric member;
and connecting the piezoelectric member to a circuit to produce an
oscillatory output.
[0018] The connecting can comprise including an inductor in the
circuit and electrically connected to the piezoelectric member. The
indictor can be electrically connected to the piezoelectric member
in series.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] These and other features, aspects, and advantages of the
apparatus of the present invention will become better understood
with regard to the following description, appended claims, and
accompanying drawings where:
[0020] FIG. 1 illustrates an embodiment of a piezoelectric
generator of the prior art.
[0021] FIG. 2 illustrates an embodiment of a piezoelectric
generator.
[0022] FIG. 3 illustrates a variation of the piezoelectric
generator of FIG. 2
[0023] FIG. 4 illustrates another embodiment of a piezoelectric
generator.
[0024] FIG. 5 illustrates another embodiment of a piezoelectric
generator.
[0025] FIG. 6 illustrates another embodiment of a piezoelectric
generator.
[0026] FIG. 7 illustrates another embodiment of a piezoelectric
generator.
[0027] FIG. 8a illustrates a sectional view another embodiment of a
piezoelectric generator as taken along line 8a-8a in FIG. 8b.
[0028] FIG. 9 illustrates another embodiment of a piezoelectric
generator.
[0029] FIG. 10 illustrates a variation of the embodiment of the
piezoelectric generator of FIG. 9.
[0030] FIG. 11 illustrates a variation of the embodiment of the
piezoelectric generator of FIG. 1
[0031] FIG. 12 illustrates another embodiment of a piezoelectric
generator.
[0032] FIG. 13 illustrates a variation of the embodiment of the
piezoelectric generator of FIG. 12
[0033] FIG. 14 illustrates a schematic circuit having a
piezoelectric generator,
[0034] FIG. 15 illustrates an exemplary plot of voltage vs. time
for a piezoelectric generator and circuitry of FIG. 14.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0035] Although this invention is applicable to numerous and
various types of devices, it has been found particularly useful in
the environment of generating power aboard munitions due to a
firing acceleration of the munition. Therefore, without limiting
the applicability of the invention to generating power aboard
munitions due to a firing acceleration of the munition, the
invention will be described in such environment. However, those
skilled in the art will appreciate that the present methods and
devices can also be used in generating power in other devices,
including commercial electronic devices where an acceleration, such
as resulting from an induced impact (where the acceleration is
negative, i.e. a deceleration), can be used to generate the power
from the disclosed devices and methods. In this regard, co-pending
U.S. application Ser. No. 11/447,788 is incorporated herein by
reference in its entirety.
[0036] In the following, an operation of the currently available
piezoelectric generators for munitions and the like that employ the
firing acceleration or other similar impact induced forces to
generate charges that are to be harvested, and the disclosed novel
method of sustaining the generated charges is described by an
example of a piezoelectric element that is intended to be axially
loaded in compression (strained in compression). The disclosed
method is, however, readily seen to be general and applicable to
piezoelectric elements that are loaded (strained) in other modes,
such as in shear; bending; torsion, and the combination of two or
more of the above modes.
[0037] A piezoelectric element based generator 10 is shown in FIG.
1 as attached to the structure 12 of munitions, such as in its
fuzing. The piezoelectric generator 10 consists of a piezoelectric
(which can be stacked of multiple layers) block 11, which is poled
to generate a charge when subjected to a force in the direction of
the arrow 13. It is noted that in the present description and for
the sake of brevity, the term force is also intended to mean
bending moment, torque and the like.
[0038] In general, stacked piezoelectric elements with relatively
thin layers (stacked parallel to the base structure 12, hereinafter
indicated as vertically, as shown in FIG. 1) provide a given force
(pressure over the surface area of the piezoelectric stack), they
would generate lower voltage levels as they would if they were
constructed as a single block or with thick layered stacks. During
the firing, the munitions and its structure 12 is accelerated in
the direction 14, thereby generating a compressive strain on the
piezoelectric stack 11, which would in turn generate an electric
charge in the piezoelectric element which could then be harvested
using an appropriate and well known electronic or electric
circuitry (not shown). To increase the level of compressive strain
in the piezoelectric stack 11, a mass 15 is attached atop the
piezoelectric stack, which applies an additional compressive force
(compressive strain) to the piezoelectric stack 11, proportional to
the amount of mass and the magnitude of the acceleration 14.
However, since the duration of the firing acceleration is very
short, in many cases on the order of one-tenth of a millisecond or
less, the window for extraction and storage of the electrical
energy is equally small, making efficient harvesting of the
generated charge very difficult.
[0039] It is noted that in general, piezoelectric elements can be
subjected to compressive load (strain) and not tensile loads
(strains) since piezoelectric materials are generally brittle and
susceptible to cracking and are much stronger in compression than
in tension. However, one can still safely subject piezoelectric
elements to higher tensile forces (strains) by first preloading
them in compression to eliminate the net tensile loading during its
operation or reduce it to within acceptable levels.
[0040] The methods being disclosed provide the means to
indefinitely sustain the aforementioned charge generating forces
(strains) that are induced as a result of the tiring acceleration
or other similar impact forces. The sustained charges can then be
harvested over the length of time necessary for their efficient
collection or even left for direct use by the intended components
since piezoelectric elements act as capacitors and can hold the
charge for a significant length of time, which may in fact be long
enough for many munitions applications due to their short flight
time. It is, however, noted that in practice, piezoelectric
elements like any other capacitors do suffer from certain amount of
leakage depending on their quality and this issue must be
considered for each particular application. It is also noted that
as the induced charges are collected, the level of generated force
on the piezoelectric stack is reduced, since the piezoelectric
stack resistance to the applied compressive load is in part due to
the generated charges and in part due to the elasticity of the
piezoelectric material structure.
[0041] Mechanical means may be used to sustain or "lock" the
aforementioned generated force (strain) in the piezoelectric stack
11. FIG. 1, as described below. It is noted that the embodiments
selected below to describe the aforementioned mechanical means for
sustaining (locking) the generated force (stain) are chosen
primarily for the sake of simplifying the present description.
Other embodiments are provided below.
[0042] A first mechanical means functions based on friction. In
devices constructed based on friction, a friction force is used to
prevent the piezoelectric stack 11 to return to its unstrained
condition. Such a "force (stain) locking mechanism" can, for
example, be provided to the piezoelectric generator 10 by providing
small angles 16 (FIG. 2) to the sides of the top mass 15
(identified with the number 17 in FIG. 2) so that as the mass
displaces down due to the shortening of the piezoelectric stack 11
as a result of the firing acceleration in the direction 14, the
angled sides of the mass 15 are wedged against the mating sides 18
protruding from the base structure 12, thereby preventing the mass
15 from returning to its original pre-firing position following the
removal of the firing acceleration, i.e. after the munition has
exited the barrel. The aforementioned wedging angle must be small
enough such that the generated friction force is greater than a
component of the compressive force that tends to push the mass 17
out of its locking position. The allowable wedging angle is
dependent of the coefficient of friction between the contacting
surfaces and its maximum amount can be readily calculated using
well known relationships.
[0043] In practice, however, since the amount of strain in the
piezoelectric stack, i.e. the downward travel of the mass 17, is
very small and in the order of micrometers, relatively stiff
springs can be added in series with the piezoelectric stack,
thereby significantly increasing the length of travel of the mass
17. Such an arrangement is shown in FIG. 3, in which the spring 19
is added between the mass 17 and the piezoelectric stack 11 to
significantly increase the total downward travel of the mass 17 as
a result of the firing acceleration in the direction 14. As a
result, the level of compressive force that is achieved on the
piezoelectric stack 11 is more predictable and a slight movement of
the wedge mass 17 would not cause a significant portion of the
compressive force to be lost.
[0044] A second mechanical means functions as a locking mechanism
that is based on geometrical interference between appropriate parts
of the locking mechanism to prevent the piezoelectric stack 11 from
returning to its pre-firing (un-strained) configuration, thereby
sustaining the generated force (strain) that is applied to the
piezoelectric stack 11 as a result of the firing acceleration in
the direction 14 or other similar impact forces. Such a locking
mechanism is shown in the schematic of FIG. 4. In this embodiment,
the mass 20 is attached to the piezoelectric stack 11 via a spring
21 to allow a significant displacement of the mass 20 as a result
of the firing acceleration in the direction of the arrow 14 for the
reason described for the embodiment shown schematically in FIG. 3.
In its pre-tiring position, the mass 20 is in the position 25 shown
with dashed lines. At least one locking element 22 is provided and
is initially in the position 23 (not engaged with mass 20), thereby
allowing vertical motion of the mass 22 (about its position 25). It
is noted that the locking elements 22 are provided with elastic
elements that bias their locking tips 24 to move towards their
locking position 22. It is also noted that in the schematic of FIG.
4, the locking element is shown to be constructed as a single
element with bending flexibility. However, in general, the locking
mechanism may be constructed with any mechanism type that would
provide the desired movement towards the indicated locking position
with at least one elastic element (which may be an integral part of
the mechanism structure) to bias its movement towards the
aforementioned locking position. As a result of tiring, the
munitions structure 12 is accelerated in the direction 14, thereby
forcing the mass 20 to move downward towards the piezoelectric
stack 11. As the mass 20 moves down, at a desired position, i.e. at
a desired level of force being applied to the piezoelectric element
by the spring 21, the tips 24 of the locking element move into
their locking position, thereby allowing the locking elements 22 to
move from their positions 23 to the positions 22 to engage and lock
the mass 20. The mass is thereby locked in its position 20, thereby
"locking" the force applied by the spring 21 onto the piezoelectric
element 11.
[0045] The above two methods of sustaining the generated force
(strain) in the piezoelectric element 11 may also be combined. In
such embodiments, the aforementioned geometrical interference type
mechanisms provides the means to ensure that if friction forces do
not sustain the generated strain, for example due to the generally
present vibratory oscillations of the munitions platform, then a
secondary means is provided to ensure the proper operation of the
device.
[0046] One embodiment 30, based on friction forces alone to sustain
the generated force (strain) in the piezoelectric stack 31, is
shown in the schematic of FIG. 5. In this embodiment, the long axis
of the piezoelectric stack 31 is positioned perpendicular to the
direction of the firing acceleration 14. To generate a charge, the
piezoelectric stack 31 should therefore be compressed to reduce its
length 36. i.e. a compressive force has to be applied to the
piezoelectric stack in the direction perpendicular to the direction
of the firing acceleration 14. The applied force (strain) should
also be sustained post the firing event. To this end, the
piezoelectric stack 31 is fixed on one end to a support 32, which
is fixed to the structure of the munition 12. On the opposite side
of the piezoelectric stack 31, another support 33 is fixed to the
structure of the munitions 12. The side 35 of the support 33 facing
the piezoelectric stack 31 is inclined with a relatively small
angle. A matching wedging block 34 with an appropriate mass is
positioned between the piezoelectric stack 31 and the support 33.
During the firing, the firing acceleration in the direction 14 acts
on the mass of the block 34, pushing it downwards, and exerting a
compressive force on the piezoelectric stack 31. With an
appropriate wedging angle of the surface 35, the wedging block is
locked in place post firing due to the generated friction forces.
The compressive force (strain) acting on the piezoelectric stack 31
is thereby sustained. The compressive force (strain) acting on the
piezoelectric stack 31 generates an electric charge in the
piezoelectric stack layers, which can then be harvested and stored
in certain storage device such as a capacitor or used directly to
power, for example, certain electronic or electric devices. One
advantage of the present embodiment in munitions is that in
general, a relatively long piezoelectric stack 31 may be used in
the device without making the device very tall.
[0047] In an alternative embodiment of the device shown in FIG. 5,
at least one elastic element such as a spring washer (not shown)
with relatively high spring rates is positioned between the
piezoelectric stack 31 and the support 32 and/or the piezoelectric
stack 31 and the wedge 34 to increase the range of motion of the
wedge for the reasons described for the embodiment shown in FIG.
3.
[0048] Another embodiment 40 is shown in the schematic of FIG. 6.
Similar to the embodiment of FIG. 5, this embodiment is also based
on friction forces alone to sustain the generated force (strain) in
the piezoelectric stack 41, which is directed in the same direction
as the piezoelectric stack 31 relative to the direction of
acceleration 14. The blocks 44 with inclined surfaces 43 are fixed
to the piezoelectric stack 41. The inclined surfaces 43 of the
blocks 44 mate with the similarly inclined surfaces of the supports
42. The supports 42 are fixed to the structure of the munitions 12.
During the firing, the firing acceleration in the direction 14 acts
on the total mass of the piezoelectric stack 41 and the blocks 44,
pushing them downwards between the blocks 42, and thereby exerting
a compressive force on the piezoelectric stack 41. With an
appropriate wedging angle of the surfaces 43, the assembly of the
piezoelectric stack 41 and the blocks 44 is locked in place
relative to the supports 42 post firing due to the generated
friction forces between the inclined surfaces. The compressive
force (strain) acting on the piezoelectric stack 41 is thereby
sustained. The compressive force (strain) acting on the
piezoelectric stack 41 generates an electric charge in the
piezoelectric stack layers, which can then be harvested and stored
in certain storage device such as a capacitor or used directly to
power, for example, certain electronic or electric devices. It is
noted that this embodiment could have been constructed with only
one wedging element 41, leaving the opposite side (which can have a
rectangular end element--not shown) to slide down against a
straight edged support (not shown). Such an arrangement, however,
may cause the piezoelectric stack assembly to rotate (about the
direction perpendicular to the plane of the illustration) due to
the difference in the vertical component of the friction forces
acting at its two sliding surfaces. The embodiment shown in FIG. 6
can minimize the aforementioned possibility of rotation.
[0049] In an alternative embodiment shown in FIG. 6, at least one
elastic element such as spring washer (not shown) with relatively
high spring rates is positioned between the piezoelectric stack 41
and one or both of the support 42, and can be between the
piezoelectric stack 41 and one or both of the wedges 44, to
increase the range of motion of the wedge for the reasons described
for the embodiment shown in FIG. 3.
[0050] In general, the position of the traveling wedging element(s)
may be exchanged, for example, in the embodiment of FIG. 6, the
piezoelectric stack 41 (51 in FIG. 7) and its two sides wedging
elements 44 (52 in FIG. 7) may be set against the munitions
structure 12 as shown in FIG. 7. In this embodiment 50, the
supports 42 (53 in FIG. 7) are then joined together by the
relatively rigid backing 54, and positioned as shown in FIG. 7 over
the piezoelectric slack assembly. The piezoelectric stack is held
against the munitions structure surface 12, but is allowed to
expand and/or contract. As the munitions is fired, the acceleration
of the munitions in the direction of the arrow 14 would act on the
mass of the assembly of the elements 53 and the backing 54, thereby
applying a compressive force on the piezoelectric stack 1 via the
side wedges 52. With an appropriate wedging angle of the surfaces
55, the assembly of the piezoelectric stack 51 and the blocks 52 is
locked in place relative to the supports 53 post firing due to the
generated friction forces between the inclined surfaces. The
compressive force (strain) acting on the piezoelectric stack 51 is
thereby sustained. The compressive force (strain) acting on the
piezoelectric stack 51 generates an electric charge in the
piezoelectric stack layers, which can then be harvested and stored
in certain storage device such as a capacitor or used directly to
power, for example, certain electronic or electric devices.
[0051] In an alternative embodiment to the embodiment shown in FIG.
7, at least one elastic element such as spring washer (not shown)
with relatively high spring rates is positioned between the
piezoelectric stack 51 and one or both of the elements 53, which
can be between the piezoelectric stack 51 and one or both of the
wedges 52, to increase the range of motion of the wedge for the
reasons described for the embodiment shown in FIG. 3.
[0052] It is noted that even though in the embodiments shown in
FIGS. 2-7 the piezoelectric layers are stacked in planes
perpendicular to the direction of the applied compressive loads,
the compressive loads may be applied to similar layers stacked in
numerous other configurations. For example, in one embodiment 60,
the layers 66 may be stacked to form a cone segment 61, which can
have an inside hole 62 as shown in the schematic of longitudinal
cross-sectional view in FIG. 8a (shown with ring 63). The layers
are shown in the top view of piezoelectric element 61 in FIG. 8b
(without ring 63). The cone angle is indicated as 65. A ring 63
with a matching inside cone angle is used as the support element
attached to the munitions structure 12. During the firing, the
firing acceleration in the direction 14 acts on the mass of the
piezoelectric element 61, thereby wedging it inside the ring 63. An
additional mass 64 may be used to increase the generated
compressive force. With an appropriate wedging angle of the cone
surfaces 65, the piezoelectric stack 61 is locked inside the ring
63 post firing due to the generated friction forces between
generated by the radial forces compressing the contacting cone
surfaces. The compressive force (strain) acting on the
piezoelectric stack 61 is thereby sustained. The compressive force
(strain) acting on the piezoelectric stack 61 generates an electric
charge in the piezoelectric stack layers, which can then be
harvested and stored in certain storage device such as a capacitor
or used directly to power, for example, certain electronic or
electric devices.
[0053] In an alternative embodiment, the piezoelectric element 61
is composed of a single (or annular layers of) piezoelectric (cone)
element, which is poled in the radial direction such that its
radial contraction as it is edged into the support element 63 would
generate electric charge that could be harvested as described above
for the embodiment of FIGS. 8a and 8b.
[0054] The embodiments shown in FIGS. 8a and 8b, the ring 63 can
possess a certain amount of circumferential flexibility to increase
the range of downward motion of the piezoelectric element 61 for
the reasons described for the embodiment shown in FIG. 3.
[0055] In the embodiments shown in FIGS. 3-4 and the aforementioned
alternatives to the embodiments shown in FIGS. 5-7 with elastic
(spring) elements, the elasticity may be built into the structure
of one of the elements in the line of compressive loading. For
example, in the embodiment of the FIG. 3, the elasticity may be
built into the structure of either the mass element 17 (in the
direction of the compressive load) or one or both of the supports
18 (again in the direction of the compressive load). In the
embodiment of the FIG. 4, the required elasticity of the spring
element 21 may be built into the structure of the mass 20. In the
embodiment of FIG. 5, the aforementioned elasticity in the
direction of the piezoelectric slack 31 loading may be built into
the structure of the wedge 34 and/or the support 32 and/or the
support 33. In the embodiment of the FIG. 6, the aforementioned
elasticity in the direction of the piezoelectric stack 41 loading
may be built into the structure of the one or both wedges 44 and or
one or both of the supports 42. In the embodiment of the FIG. 7,
the aforementioned elasticity in the direction of the piezoelectric
stack 51 loading may be built into the structure of the one or both
wedges 52 and/or one or both of the supports 53 and/or the
connecting member 54.
[0056] In yet another embodiment 70, the schematic of which is
shown in FIG. 9, the compressive force on the piezoelectric stack
71 can be applied by a counterclockwise rotation of a cam 74, due
to the firing acceleration in the direction 14 of the munitions
platform 12 acting on the mass 77. The mass 77 may be an integral
part of the cam 74. The piezoelectric stack 71 is directed and
attached to the support 72, which is in turn fixed to the structure
of the munitions 12, similar to the embodiment of FIG. 5 (with the
piezoelectric stack and support numbered 31 and 32, respectively).
The cam 74 is attached to the munitions structure 12 by a support
76 by a rotary joint 75, which allows it free rotation about the
axis of the joint 75. The firing acceleration in the direction 14
acts on the mass 77, thereby forcing the cam 74 to rotate in the
counterclockwise direction. Due to the shape of the cam 74 profile,
this rotation causes a compressive force to be applied to the
intermediate block 73, which would in turn apply the compressive
force to the piezoelectric stack 71. The compressive force (strain)
acting on the piezoelectric stack 71 generates an electric charge
in the piezoelectric stack layers, which can then be harvested and
stored in certain storage device such as a capacitor or used
directly to power, for example, certain electronic or electric
devices.
[0057] In an alternative embodiment to that shown in FIG. 9, the
cam 74 is positioned as shown in FIG. 10. A relatively long lever
arm 77 is attached rigidly to the cam 74, to which, its far end, a
mass 79 can be attached. The firing acceleration in the direction
14 acts on the mass 78 and causes it to move downwards in the
direction of the arrow 80, thereby forcing the cam 74 to rotate in
the clockwise direction. Due to the shape and positioning of the
cam 74 profile, this rotation causes a compressive force to be
applied to the intermediate block 73, which would in turn apply the
compressive force to the piezoelectric stack 71. The compressive
force (strain) acting on the piezoelectric stack 71 generates an
electric charge in the piezoelectric stack layers, which can then
be harvested and stored in certain storage device such as a
capacitor or used directly to power, for example, certain
electronic or electric devices.
[0058] In an alternative embodiment to that shown in FIG. 9 or 10,
at least one elastic element such as spring washer (not shown) with
relatively high spring rates is positioned between the
piezoelectric stack 71 and the support 72 and/or between the
piezoelectric stack 71 and the block 73 to increase the range of
motion of the cam for the reasons described for the embodiment
shown in FIG. 3. Alternatively, as it was previously described, the
desired elasticity may be built into the structure of one or more
of the elements 72, 73 and/or the cam assembly.
[0059] In yet another embodiment, a group of one or more of the
aforementioned embodiments, e.g. the embodiments shown in FIGS.
1-8, may be used to form a single piezoelectric based generator.
For example, as shown in the schematics of FIG. 11, more than one
arrangement of piezoelectric stacks 11 may be attached to the
structure 12 of the munitions, to be compressed by a single mass
101 (in place of individual masses 15 in FIG. 1), due to the
acceleration of the munitions in the direction 14. Similarly, more
than one arrangement of the embodiments shown in FIGS. 2-8 could be
used to form a single piezoelectric based generator. For the
embodiment shown in FIG. 5 (6 or 7), the only difference would be
that the wedges 34 (44 or 54) are to be attached to the downward
moving mass 105. FIG. 11. For the embodiment shown in FIG. 8, the
only difference would be that the piezoelectric elements 61 and
when present, the masses 64 are to be attached to the downward
moving mass 105. FIG. 11.
[0060] In yet another embodiment, the aforementioned more than one
of the embodiments shown in FIGS. 2-8 may be configured in a
variety of configurations, for example in a hollow cylindrical
configuration as shown in FIG. 12. Such a configuration can be
advantageous since due to the more distant and symmetrical
distribution of the piezoelectric generators, the compressive force
(downward motion of the upper moving part 86) becomes more
uniformly distributed amount the present (preferably at least
three) individual piezoelectric based generator unit. Such a
configuration can be particularly advantageous in munitions
applications since it leaves the most useful central volume of the
munitions free for munitions specific components.
[0061] In the embodiment shown in FIG. 12, three embodiments of the
piezoelectric generators shown in FIG. 5, one of which is indicated
to be within the range 83, are shown to be positioned around a
hollow cylindrical base 82, which is in turn attached to the
munitions structure 81. Here, the piezoelectric stack layers 88 (31
in FIG. 5) are attached on one end (right side of the stack 88
within the range 83) of the support 89 (corresponding to the
support 32 in FIG. 5), which can be flat and vertically oriented,
and on the other end to the block 91. On the opposite side of the
supports 89 are constructed with the inclined surfaces 85, with
relatively small angles. The top hollow cylindrical part 86 is
constructed with extending wedges 87, with one side surface flat
and the opposite side surface inclined to mate at the inclined
surfaces 85 of the supports 89. As the munitions structure 12
accelerates during the firing in the direction of the arrow 92,
which is preferably parallel to the long axes of the cylinders 82
and 86, the firing acceleration acts on the mass of the upper
hollow cylinder 86, and thereby wedging the parts 87 between the
supports 84 and the blocks 91. As a result, compressive forces will
be applied to the piezoelectric stacks 88. The compressive force
(strain) acting on the piezoelectric stacks 88 generate electric
charge in the piezoelectric stack layers, which can then be
harvested and stored in certain storage device such as a capacitor
or used directly to power, for example, certain electronic or
electric devices.
[0062] An alternative embodiment 110 to that shown in FIG. 12 is
shown schematically in FIG. 13. A difference between the
embodiments shown in FIG. 12 and FIG. 13 is the positioning and
shape of the wedging elements on the two hollow cylindrical
elements 82 and 86. In the embodiment 110, opposing end blocks 111
and 112 (replacing blocks 91 in the embodiment of FIG. 12) are
provided with inclined surfaces 113 and 114, respectively. The
wedging element 115, which is attached to the upper hollow cylinder
86, is provided with inclined surfaces on its either sides, which
matches the inclined surface 113 and 114 as shown in FIG. 13. As
the munitions structure 12 (FIG. 12) accelerates during the firing
in the direction of the arrow 92 (FIG. 12), which is preferably
parallel to the long axes of the cylinders 82 and 86, the firing
acceleration acts on the mass of the upper hollow cylinder 86, and
thereby wedging the elements 115 between the two blocks 113 and
114. As a result, compressive forces will be applied to the
piezoelectric stacks 88 (FIG. 12). The present arrangement of the
wedging surfaces eliminates rotational motion of the upper hollow
cylinder 86 as it travels downward as is the case for the
embodiment of FIG. 12. The compressive force (strain) acting on the
piezoelectric stacks 88 generate electric charge in the
piezoelectric stack layers, which can then be harvested and stored
in certain storage device such as a capacitor or used directly to
power, for example, certain electronic or electric devices.
[0063] In an alternative embodiment to that shown in FIG. 12 or 13,
at least one elastic element such as spring washer (not shown) with
relatively high spring rates is positioned between the
piezoelectric stack 88 and the block 91 (111 and/or 112) and/or
between the piezoelectric stack 88 and the supports 116 to increase
the range of motion of the cam for the reasons described for the
embodiment shown in FIG. 3. Alternatively, as it was previously
described, the desired elasticity may be built into the structure
of one or more components, such as in elements 111, 112, 115 and
116.
[0064] In the aforementioned methods of sustaining the strain in
the piezoelectric elements due to the firing acceleration or other
similar impact forces and the related embodiments shown in FIGS.
2-13, the generated charges in the piezoelectric element(s) can
then be efficiently harvested over significantly longer periods of
time as compared to the duration of the applied impact forces.
Alternatively, noting that piezoelectric elements are capacitors
and that the charges generated by the piezoelectric elements are
stored in these capacitive elements, one may connect at least one
inductance element to these capacitor elements to form an
oscillating LC circuit as shown schematically in FIG. 14. In the
schematic of FIG. 14, the capacitor element 201 represents the
piezoelectric elements that are subjected to the aforementioned
impact forces, the element 202 represents the inductance elements
used in series with capacitors 201, and the resistance element 203
represents the unavoidable resistance of the above elements and the
circuitry. The resistance element 203 is generally desired to be as
low as possible to minimize losses in the electrical energy as the
charges oscillate back and forth in the circuitry.
[0065] Once an oscillatory circuitry similar to that shown in FIG.
14 is constructed, then as the piezoelectric (capacitance) element
201 is strained, such as in compression as previously described,
due to the firing acceleration or other similar impact forces, an
initial charge is generated in the capacitance. The resulting
charge with its corresponding voltage across the capacitance
element 201 will then oscillate in the closed circuit shown
schematically in FIG. 14. If it were possible to construct the
circuitry with elements that did not have any inherent resistance
to the follow of current, then the initiated oscillation would last
indefinitely. In reality, the circuitry would provide resistance to
the flow of current, which in the schematic of FIG. 14 is shown as
a lumped resistance element 203. As a result, during each cycle of
oscillation, certain amount of present electrical energy is
converted into heat, depending on the amount of resistance of the
element 203 and the level of current passing through the resistance
element 203. In general, inductance elements with low internal
resistance (usually the main portion of the total resistance 203)
are available and can be used. For example, using a small
piezoelectric stack element (a cylinder of about 10 mm diameter and
3 mm thick) with capacitance of C-760 nF, an inductance element
with 1 10000 .mu.H with internal resistance of R -30 m.OMEGA. will
provide an oscillatory circuitry (FIG. 14) with a frequency of
oscillation of about (.omega.) 1825 Hz. If the applied firing
acceleration or other similar impact force had generated a charge
resulting in an initial voltage of 200 Volts, which is a typical
voltage level for the above piezoelectric stack, then the resulting
voltage oscillation across the piezoelectric element were simulated
using a computer model of the circuitry, the plot of which is shown
in FIG. 15. As can be seen, the oscillations die out very slowly,
and if the charges are harvested over several hundred cycles of
oscillations (100 cycles correspond to about 55 msec), then only a
few percentage (less than 10%) of the energy is lost to heat.
[0066] In general, an energy collection circuitry (not shown in
FIG. 14, and which are well known in the art) may harvest the
electrical energy by connecting into the oscillatory circuitry of
FIG. 14 at many locations as long as it does not interfere with the
oscillatory operation of the circuitry. For example, the electrical
energy harvesting electronics may be connected to the capacitance
element to directly collect charges from this element as is well
known in the art.
[0067] It is noted that one or more piezoelectric (capacitive)
elements 201, additional capacitive and inductance elements may be
connected in different circuitry to achieve different oscillatory
circuitry as is well known in the art and the circuitry shown in
FIG. 14 is only for the purpose of describing the basic method
being disclosed.
[0068] While there has been shown and described what is considered
to be preferred embodiments of the invention, it will, of course,
be understood that various modifications and changes in form or
detail could readily be made without departing from the spirit of
the invention. It is therefore intended that the invention be not
limited to the exact forms described and illustrated, but should be
constructed to cover all modifications that may fall within the
scope of the appended claims.
* * * * *