U.S. patent application number 11/747450 was filed with the patent office on 2007-11-22 for compressor and compression using motion amplification.
This patent application is currently assigned to PAR TECHNOLOGIES, LLC.. Invention is credited to David D. Wright.
Application Number | 20070267940 11/747450 |
Document ID | / |
Family ID | 39736955 |
Filed Date | 2007-11-22 |
United States Patent
Application |
20070267940 |
Kind Code |
A1 |
Wright; David D. |
November 22, 2007 |
COMPRESSOR AND COMPRESSION USING MOTION AMPLIFICATION
Abstract
A compressor system (20, 20', 20'') comprises a motion amplifier
(22) which acts through a compressor head or piston (46) to
compress fluid in a variable compression chamber (52). The motion
amplifier (22) comprises a piezoelectric diaphragm (30) and drive
electronics (26) for applying a drive signal to the piezoelectric
diaphragm. The drive signal is generated to maintain the motion
amplifier resonant at a predetermined frequency. The motion
amplifier preferably comprises (in addition to the piezoelectric
diaphragm) a reaction mass (34) connected to the piezoelectric
diaphragm; a reacted mass (40) connected to the piezoelectric
diaphragm; and, a reacted mass spring (50, 270) for resiliently
carrying the reacted mass. The structure of the motion amplifier
carried by the reacted mass spring (e.g., the piezoelectric
diaphragm, the reaction mass, and the reacted mass) has a resonant
frequency f2. The resonant frequency f2 is related to a spring
constant K2 of the reacted mass spring and a sum of masses of the
reaction mass and the reacted mass. Preferably the predetermined
frequency is f2, which means that the drive signal is generated to
maintain the motion amplifier resonant at a frequency f2, e.g., the
drive signal is generated to urge the motion amplifier to the
frequency f2 as its operational frequency. Driving the motion
amplifier (22) at the frequency f2 achieves peak amplitude
displacement of the motion amplifier, and thus peak displacement of
the compressor head acting in the compression chamber.
Inventors: |
Wright; David D.; (Vershire,
VT) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
PAR TECHNOLOGIES, LLC.
Hampton
VA
|
Family ID: |
39736955 |
Appl. No.: |
11/747450 |
Filed: |
May 11, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60747286 |
May 15, 2006 |
|
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|
60747287 |
May 15, 2006 |
|
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|
60747289 |
May 15, 2006 |
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Current U.S.
Class: |
310/311 ;
310/328 |
Current CPC
Class: |
F04B 45/047 20130101;
F04B 43/046 20130101; H01L 41/0973 20130101; H04R 17/00
20130101 |
Class at
Publication: |
310/311 ;
310/328 |
International
Class: |
H01L 41/00 20060101
H01L041/00 |
Claims
1. A fluid compressor assembly comprising: a motion amplifier
comprising: a piezoelectric diaphragm; a reaction mass connected to
the piezoelectric diaphragm; a reacted mass connected to the
piezoelectric diaphragm, the reacted mass forming a compression
head; a reacted mass spring for resiliently carrying the reacted
mass; an amplifier base for at least partially defining a
compression chamber into which fluid is selectively admitted and
exhausted; drive electronics for driving the piezoelectric
diaphragm and thereby displacing the compression head for
compressing fluid in the compression chamber; an inlet valve and an
outlet valve for respectively admitting and exhausting fluid
relative to the compression chamber.
2. The apparatus of claim 1, wherein the drive electronics
generates and applies the drive signal to the piezoelectric
diaphragm so as to maintain the motion amplifier resonant at a
predetermined frequency.
3. The apparatus of claim 2, wherein structure of the motion
amplifier carried by the reacted mass spring has a resonant
frequency f2, wherein the predetermined frequency is f2, and
wherein the drive signal is generated to urge the motion amplifier
to the frequency f2 as its operational frequency.
4. The apparatus of 3, wherein the resonant frequency f2 is related
to a spring constant K2 of the reacted mass spring and a sum of
masses of the reaction mass and the reacted mass.
5. The apparatus of 1, wherein the drive electronics generates the
drive signal to maintain a predetermined phase angle between the
drive signal and a signal indicative of displacement of the motion
amplifier.
6. The apparatus of claim 5, wherein the drive electronics
comprises a sensor for sensing displacement of the motion amplifier
and for generating the signal indicative of displacement of the
motion amplifier.
7. The apparatus of 1, wherein a periphery of the piezoelectric
diaphragm is held and carried by the reacted mass.
8. The apparatus of 1, wherein the piezoelectric diaphragm is
mounted to and carried by the reacted mass; wherein the reacted
mass comprises a reacted mass cup which defines a reacted mass
cavity, and wherein the reaction mass is suspended from the
piezoelectric diaphragm in the reacted mass cavity.
9. The apparatus of claim 1, further comprising an amplifier base
for at least partially defining a compression chamber, wherein the
reacted mass spring also at least partially defines the compression
chamber, and further comprising means for resiliently mounting the
amplifier base relative to the outside world.
10. The apparatus of claim 9, wherein the amplifier base carries
the piezoelectric diaphragm, the reaction mass, the reacted mass,
and the reacted mass spring.
11. The apparatus of 1, further comprising an amplifier base for at
least partially defining a compression chamber, wherein the reacted
mass spring comprises a diaphragm which also at least partially
defines and covers the compression chamber, the amplifier base
having an inlet and an outlet for respectively intaking and
exhausting fluid in accordance with displacement of the reacted
mass.
12. The apparatus of claim 11, wherein the diaphragm comprising the
reacted mass spring is a corrugated diaphragm.
13. The apparatus of claim 11, further comprising means for
resiliently mounting the amplifier base relative to the outside
world.
14. The apparatus of 1, further comprising a bellows assembly, and
wherein the bellows assembly comprises a sidewall for defining a
compression chamber, the sidewall comprising the reacted mass
spring.
15. The apparatus of claim 14, wherein the bellows assembly further
comprises an amplifier base for defining a valve assembly cavity,
the valve assembly cavity and the compression chamber being sized
to accommodate a valve assembly through which fluid is introduced
into the compression chamber and compressed in the compression
chamber by displacement of the motion amplifier.
16. The apparatus of claim 14, wherein the bellows assembly further
comprises an amplifier base, and further comprising means for
resiliently mounting the amplifier base relative to the outside
world.
17. The apparatus of claim 1, wherein the natural frequency of the
inlet valve and the natural frequency of the outlet valve are
greater than an operating frequency of the motion amplifier.
18. The apparatus of claim 17, wherein the natural frequency of
each of the inlet valve and the outlet valve is at least twice the
operating frequency of the motion amplifier.
19. A method of operating a compressor assembly for compressing a
fluid comprising: displacing a motion amplifier having a compressor
head in a compressor chamber, the motion amplifier comprising a
piezoelectric diaphragm, a reaction mass connected to the
piezoelectric diaphragm, a reacted mass connected to the
piezoelectric diaphragm, and a reacted mass spring for resiliently
carrying the reacted mass; selectively admitting and exhausting
fluid from the compressor chamber in accordance with displacement
of the motion amplifier; wherein the displacing the motion
amplifier comprises generating and applying a drive signal to the
piezoelectric diaphragm, the drive signal being generated to
maintain the motion amplifier resonant at a predetermined
frequency.
20. The method of claim 19, wherein structure of the motion
amplifier carried by the reacted mass spring has a resonant
frequency f2, wherein the predetermined frequency is f2, and
further comprising generating the drive signal to urge the motion
amplifier to the frequency f2 as its operational frequency.
21. The method of claim 20, wherein the resonant frequency f2 is
related to a spring constant K2 of the reacted mass spring and a
sum of masses of the reaction mass and the reacted mass.
22. The method of claim 19, further comprising generating the drive
signal to maintain a predetermined phase angle between the drive
signal and a signal indicative of displacement of the motion
amplifier.
23. The method of claim 22, further comprising sensing displacement
of the motion amplifier and generating the signal indicative of
displacement of the motion amplifier.
24. The method of claim 19, wherein the compressor assembly further
comprises an amplifier base for at least partially defining the
compression chamber, and further comprising resiliently mounting
the amplifier base relative to the outside world.
25. The method of claim 24, mounting the piezoelectric diaphragm,
the reaction mass, the reacted mass, and the reacted mass spring on
the amplifier base.
Description
[0001] This application claims the benefit and priority of the
following U.S. provisional patent applications, all of which are
incorporated herein by reference in their entirety: U.S.
Provisional Patent application 60/747,286, entitled "COMPRESSOR AND
COMPRESSION USING MOTION AMPLIFICATION"; U.S. Provisional Patent
application 60/747,287, entitled "MOTION AMPLIFICATION USING
PIEZOELECTRIC ELEMENT"; and U.S. Provisional Patent application
60/747,289, entitled "VIBRATION AMPLIFICATION SYSTEM FOR
PIEZOELECTRIC ACTUATORS AND DEVICES USING THE SAME". This
application is related to the following simultaneously-filed U.S.
patent applications, both of which are incorporated herein by
reference: U.S. patent application Ser. No. 11/______, (attorney
docket 4209-160), entitled "MOTION AMPLIFICATION USING
PIEZOELECTRIC ELEMENT" and U.S. patent application Ser. No.
11/______, (attorney docket 4209-162), entitled "VIBRATION
AMPLIFICATION SYSTEM FOR PIEZOELECTRIC ACTUATORS AND DEVICES USING
THE SAME".
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention pertains to amplification of motion
such as vibration motion, and particularly to amplification of
motion caused by a piezoelectric diaphragm or the like.
[0004] 2. Related Art and Other Considerations
[0005] Piezoelectric diaphragms have been employed in various types
of pumps and actuators. As is well known, a piezoelectric material
is polarized and will produce an electric field when the material
changes dimensions as a result of an imposed mechanical force. This
phenomenon is known as the piezoelectric effect. Conversely, an
applied electric field can cause a piezoelectric material to change
dimensions.
[0006] One exemplary piezoelectric diaphragm, known as a ruggedized
laminated piezoelectric or RLP.TM., has a central piezoelectric
wafer which is laminated to a stainless steel substrate and
preferably also has an aluminum cover laminated thereover. Examples
of such RLP.TM. elements, and in some instances pumps employing the
same, are illustrated and described in one or more of the
following: PCT Patent Application PCT/US01/28947, filed 14 Sep.
2001; U.S. patent application Ser. No. 10/380,547, filed Mar. 17,
2003, entitled "Piezoelectric Actuator and Pump Using Same"; U.S.
patent application Ser. No. 10/380,589, filed Mar. 17, 2003,
entitled "Piezoelectric Actuator and Pump Using Same", and U.S.
patent application Ser. No. 11/279,647 filed Apr. 13, 2006,
entitled "PIEZOELECTRIC DIAPHRAGM ASSEMBLY WITH CONDUCTORS ON
FLEXIBLE FILM", all of which are incorporated herein by
reference.
[0007] The displacement of a ruggedized laminated piezoelectric,
while large compared to other piezoelectric devices, is still small
in relation to the diameter of a pumping chamber in which it can be
employed. Hence, compression ratios are still small, e.g., in a
range on the order of 1.1 to 1.0, for example. An increased stroke
for the piezoelectric diaphragm would facilitate an increased
compression ratio.
[0008] What is needed, therefore, and an object of the present
invention, are apparatus, method, and technique for achieving
motion amplification of a piezoelectric element.
BRIEF SUMMARY
[0009] A compressor system comprises a motion amplifier which acts
through a compressor head or piston to compress fluid in a variable
compression chamber. The motion amplifier comprises a piezoelectric
diaphragm and drive electronics for applying a drive signal to the
piezoelectric diaphragm. The drive signal is generated to maintain
the motion amplifier resonant at a predetermined frequency.
[0010] The motion amplifier preferably comprises a piezoelectric
diaphragm and drive electronics for applying a drive signal to the
piezoelectric diaphragm; a reaction mass connected to the
piezoelectric diaphragm; a reacted mass connected to the
piezoelectric diaphragm; and, a reacted mass spring for resiliently
carrying the reacted mass. The reacted mass either forms or is
connected to an actuator portion or actuator surface which, in
turn, either forms or is connected to an actuator element. For
example, the actuator portion or surface can serve as a piston head
or a cylinder head, or as a surface or portion to which a further
element such as an actuator shaft of the like can be connected.
[0011] The structure of the motion amplifier carried by the reacted
mass spring (e.g., the piezoelectric diaphragm, the reaction mass,
and the reacted mass) has a resonant frequency f2. The resonant
frequency f2 is related to a spring constant K2 of the reacted mass
spring and a spring constant of any load upon which the reacted
mass acts, as well as a sum of masses of the reaction mass and the
reacted mass. Preferably the predetermined frequency is f2, which
means that the drive signal is generated to maintain the motion
amplifier resonant at a frequency f2, e.g., the drive signal is
generated to urge the motion amplifier to the frequency f2 as its
operational frequency. Driving the motion amplifier 22 at the
frequency f2 achieves peak amplitude displacement of the motion
amplifier, and thus peak displacement of the compressor head acting
in the compression chamber.
[0012] The drive electronics generates a drive signal to maintain
the motion amplifier resonant at a predetermined frequency. In
particular, in an example illustrated embodiment the drive
electronics generates the drive signal to maintain a predetermined
phase angle between the drive signal and a signal indicative of
displacement of the motion amplifier system. To this end, the drive
electronics comprises a sensor for sensing displacement of the
motion amplifier and for generating the signal indicative of
displacement of the motion amplifier.
[0013] In one example embodiment, the piezoelectric diaphragm is
mounted to and carried by the reacted mass. The reacted mass
comprises a reacted mass cup which defines a reacted mass cavity.
In one example implementation of this embodiment, a periphery of
the piezoelectric element is held by the reacted mass cup while the
center of the piezoelectric diaphragm is free to vibrate. The
reaction mass is preferably centrally suspended from the
piezoelectric diaphragm in the reacted mass cavity.
[0014] Compressor assemblies of differing embodiments can
incorporate the embodiments of motion amplifiers. The compressor
assembly can include an amplifier base which carries the
piezoelectric diaphragm, the reaction mass, the reacted mass, and
the reacted mass spring. The amplifier base at least partially
defines the compression chamber. The reacted mass spring can also
at least partially defines the compression chamber. As one aspect
of the technology, means are provided for resiliently mounting the
amplifier base relative to the outside world, and thereby
mitigating any damping caused by the outside world.
[0015] In one example embodiment of a motion amplifier, the reacted
mass spring comprises a diaphragm which also at least partially
defines and covers the compression chamber. The diaphragm
comprising the reacted mass spring is a preferably a corrugated
diaphragm. Corrugation of the diaphragm provides increased motion
for the motion amplifier. In an embodiment of a compressor assembly
incorporating a diaphragm-type reacted mass spring, the amplifier
base can have an inlet and an outlet for respectively intaking and
exhausting fluid in accordance with displacement of the reacted
mass (the reacted mass serving as the compression or piston head in
the compression chamber).
[0016] Another example embodiment of a motion amplifier comprises a
bellows assembly. The bellows assembly has a sidewall for at least
partially defining the compression chamber. The sidewall comprises
and serves as the reacted mass spring. The bellows assembly further
comprises an amplifier base for defining a valve assembly cavity.
The valve assembly cavity and the compression chamber are sized to
accommodate a valve assembly through which fluid is introduced into
the compression chamber and compressed in the compression chamber
by displacement of the motion amplifier.
[0017] The technology also includes a method of operating a
compressor assembly for compressing a fluid. The method includes
displacing a motion amplifier having a compressor head in a
compressor chamber, the motion amplifier comprising a piezoelectric
diaphragm, a reaction mass connected to the piezoelectric
diaphragm, a reacted mass connected to the piezoelectric diaphragm,
and a reacted mass spring for resiliently carrying the reacted
mass. The method further includes selectively admitting and
exhausting fluid from the compressor chamber in accordance with
displacement of the motion amplifier. The step of displacing the
motion amplifier comprises generating and applying a drive signal
to the piezoelectric diaphragm, the drive signal being generated to
maintain the motion amplifier resonant at a predetermined
frequency. Preferably, the method includes generating the drive
signal to urge the motion amplifier to the frequency f2 as its
operational frequency.
[0018] A further aspect of the method includes resiliently mounting
the compressor assembly (e.g., an amplifier base) relative to the
outside world.
[0019] The compressor assembly includes an inlet valve and an
outlet valve for respectively admitting and exhausting fluid
relative to the compression chamber. As another aspect of the
technology, the natural frequency of the inlet valve and the
natural frequency of the outlet valve are each greater than an
operating frequency of the motion amplifier. For example, in an
example embodiment, the natural frequency of each of the inlet
valve and the outlet valve is at least twice the operating
frequency of the motion amplifier.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The foregoing and other objects, features, and advantages of
the invention will be apparent from the following more particular
description of preferred embodiments as illustrated in the
accompanying drawings in which reference characters refer to the
same parts throughout the various views. The drawings are not
necessarily to scale, emphasis instead being placed upon
illustrating the principles of the invention.
[0021] FIG. 1 is a front perspective view of an example embodiment
of a compressor assembly which includes an example embodiment of a
motion amplifier.
[0022] FIG. 2 is an exploded view of the compressor assembly of
FIG. 1.
[0023] FIG. 3 is top view of the compressor assembly of FIG. 1.
[0024] FIG. 4 is a front view of the compressor assembly of FIG.
1.
[0025] FIG. 5 is a bottom view of the compressor assembly of FIG.
1.
[0026] FIG. 6 is a right side view of the compressor assembly of
FIG. 1.
[0027] FIG. 7 is a sectioned view of portions of the compressor
assembly of FIG. 1, showing the compressor assembly without a valve
assembly.
[0028] FIG. 8A is a sectioned view showing portions of a motion
amplifier and an alternate way of retaining the motion amplifier in
place.
[0029] FIG. 8B is a sectioned view showing portions of a motion
amplifier and another alternate way of retaining the motion
amplifier in place.
[0030] FIG. 9 is schematic view of a drive model for the compressor
assembly of FIG. 1 combined with a sectioned view of the compressor
assembly of FIG. 1.
[0031] FIG. 10 is a front perspective view of an example embodiment
of a valve assembly for the compressor assembly of FIG. 1.
[0032] FIG. 11 is an exploded view of the valve assembly of FIG.
10.
[0033] FIG. 12 is a top view of the valve assembly of FIG. 10.
[0034] FIG. 13 is a front view of the valve assembly of FIG.
10.
[0035] FIG. 14 is a bottom view of the valve assembly of FIG.
10.
[0036] FIG. 15 is a right side view of the valve assembly of FIG.
10.
[0037] FIG. 16 is a front perspective of a exhaust valve housing of
the valve assembly of FIG. 10.
[0038] FIG. 17 is a front perspective of an intake valve housing of
the valve assembly of FIG. 10.
[0039] FIG. 18A is a cross sectional view showing an example
embodiment of a compressor housing and a first mode of resiliently
mounting a compressor assembly in the compressor housing.
[0040] FIG. 18B is a cross sectional view showing another example
embodiment of a compressor housing and a second mode of resiliently
mounting a compressor assembly in the compressor housing.
[0041] FIG. 19A is a partial cross sectional view showing an
example technique for mounting a sensor system for a motion
amplifier.
[0042] FIG. 19B is a partial cross sectional view showing another
example technique for mounting a sensor system for a motion
amplifier.
[0043] FIG. 20 is a schematic view of a generic, example sensing
system for a motion amplifier.
[0044] FIG. 21 is a schematic view of control circuit for the
compressor assembly of FIG. 1.
[0045] FIG. 22 is a graph showing frequencies of a system which
includes a motion amplifier
[0046] FIG. 23 is a graph showing a plot of amplitude verses phase
angle.
[0047] FIG. 24 is a graph showing a plot of a sense position signal
(in voltage) as a function of position.
[0048] FIG. 25 is a schematic sectioned view of portions of a
compressor assembly according to another example embodiment.
[0049] FIG. 26 is a schematic sectioned view of portions of a
compressor assembly according to yet another example embodiment,
and particularly comprising plural motion initiator elements.
DETAILED DESCRIPTION OF THE DRAWINGS
[0050] In the following description, for purposes of explanation
and not limitation, specific details are set forth such as
particular architectures, interfaces, techniques, etc. in order to
provide a thorough understanding of the present invention. However,
it will be apparent to those skilled in the art that the present
invention may be practiced in other embodiments that depart from
these specific details. That is, those skilled in the art will be
able to devise various arrangements which, although not explicitly
described or shown herein, embody the principles of the invention
and are included within its spirit and scope. In some instances,
detailed descriptions of well-known devices, circuits, and methods
are omitted so as not to obscure the description of the present
invention with unnecessary detail. All statements herein reciting
principles, aspects, and embodiments of the invention, as well as
specific examples thereof, are intended to encompass both
structural and functional equivalents thereof. Additionally, it is
intended that such equivalents include both currently known
equivalents as well as equivalents developed in the future, i.e.,
any elements developed that perform the same function, regardless
of structure.
[0051] Thus, for example, it will be appreciated by those skilled
in the art that block diagrams herein can represent conceptual
views of illustrative circuitry embodying the principles of the
technology. The functions of the various elements including
functional blocks labeled as "processors" or "controllers" may be
provided through the use of dedicated hardware as well as hardware
capable of executing software in association with appropriate
software. When provided by a processor, the functions may be
provided by a single dedicated processor, by a single shared
processor, or by a plurality of individual processors, some of
which may be shared or distributed. Moreover, explicit use of the
term "processor" or "controller" should not be construed to refer
exclusively to hardware capable of executing software, and may
include, without limitation, digital signal processor (DSP)
hardware, read only memory (ROM) for storing software, random
access memory (RAM), and non-volatile storage.
[0052] FIG. 1-FIG. 7 illustrate an example, non-limiting embodiment
of a compressor assembly 20. As seen in FIG. 2, compressor assembly
20 comprises a motion amplifier 22 and valve assembly 24. The
motion amplifier 22 can serve as a driver for compressor assembly
20. The valve assembly 24 is further illustrated by FIG. 10-FIG.
17. Also included in compressor assembly 20 is a sensor and control
system, an example embodiment of which is illustrated as sensor and
control system 26 illustrated in FIG. 20. As used herein, "drive
electronics" encompasses one or more elements of sensor and control
system 26.
[0053] The motion amplifier 22 comprises an actuator or motion
initiator element which, in the illustrated example embodiment,
takes the form of a piezoelectric diaphragm 30. The piezoelectric
diaphragm 30 is mounted (such as by example ways described
hereinafter) preferably with its peripheral edge constrained and in
a manner to permit its central portion to move, displace, or
deflect through a range of positions in accordance with a drive
signal applied to piezoelectric diaphragm 30 by sensor and control
system 26. For example, when a zero volt signal is applied to
piezoelectric diaphragm 30, the piezoelectric diaphragm 30 has a
slightly domed configuration with respect to an axial direction 31.
On the other hand, upon application of a non-zero voltage
piezoelectric the central region of diaphragm 30 may displace or
dome more significantly. In the illustrated embodiment, the drive
signal is applied to motion initiator element 30 by radially
extending electrodes 32.
[0054] The piezoelectric diaphragm 30, serving as the motion
initiator element, has a reaction mass 34 mounted or adhered to an
underside of its central region. Although shown in the illustrated
embodiment as being a disc, reaction mass 34 can take a variety of
other shapes.
[0055] The piezoelectric diaphragm 30 is mounted to and carried by
a reacted mass which includes a reacted mass cup 40. The reacted
mass cup 40 is preferably cylindrical in shape, having a
cylindrical sidewall 42 which is surmounted by a relatively thinner
or sharp crown or "knife edge" 44 (see FIG. 2 and FIG. 7). The
reacted mass cup 40 has an essentially flat bottom wall 46 (see
FIG. 7) which also serves essentially as a piston head or cylinder
head or compressor head. A reacted mass cup cavity 48 is formed
interior to the cylindrical side wall 42. The reacted mass cup
cavity 48 is sized so that reaction mass 34, suspended on the
underside of piezoelectric diaphragm 30, is accommodated in reacted
mass cup cavity 48. The perimeter of piezoelectric diaphragm 30
sits on reacted mass cup crown edge 44. Thus, in the example
implementation shown in FIG. 2, a periphery of the piezoelectric
element 30 is held by the reacted mass cup 48 while the center of
the piezoelectric diaphragm 30 is free to vibrate. The reacted mass
need not take the form of a cup, but can have other configurations.
The reaction mass 34 is preferably centrally suspended from the
piezoelectric diaphragm 30 in the reacted mass cup cavity 48.
[0056] The reacted mass 40 either forms or is connected to an
actuator portion or actuator surface, such as the essentially flat
bottom wall 46 described above. The actuator portion or actuator
surface can, in turn, either form or be connected to an actuator
element. For example, the actuator portion or surface can serve as
a piston head or a cylinder head, or as a surface or portion to
which a further element such as an actuator shaft of the like can
be connected.
[0057] Suspended in axial direction 31 from reacted mass cup 40 is
a bellows assembly 50. As shown in FIG. 7, bellows assembly 50 has
an essentially inverted-cup shape for defining a compression
chamber 52. The compression chamber 52 is partially bounded by
flexible interior cylindrical wall 54 and interior upper wall 56 of
bellows assembly 50. The interior cylindrical wall 54 is sealed to
an interior of rigid amplifier base 58 by bellows seal 59. The
amplifier base 58 also has a shape of an inverted cup to define
valve assembly cavity 60, and has a cylindrical sidewall having a
slightly larger diameter than elements carried or mounted
thereover. The amplifier base 58 also has a radial channel, port,
or slot 61 formed in its cylindrical sidewall thereof to
accommodate portions of valve assembly 24 as herein after
described.
[0058] The bellows assembly 50 further comprises a resilient and
flexible exterior cylindrical sidewall 62. The bellows exterior
sidewall 62 can be pleated in resilient fashion or, more
preferably, has a coiled spring 64 or other elastic member embedded
therein or carried thereon. A bottom of bellows exterior sidewall
62 is mounted to a top of amplifier base 58; a top of bellows
exterior sidewall 62 is sealingly connected to an underside of
reacted mass cup bottom wall 46. As shown in FIG. 7, a compression
space 66 is defined between bellows interior cylindrical wall 54
and bellows exterior sidewall 62.
[0059] In the example embodiment illustrated in FIG. 1 and FIG. 2,
motion amplifier 22 has one or more amplifier sleeve sections 70
which at least partially surround piezoelectric diaphragm 30,
reacted mass cup 40, and the flexible portion of bellows assembly
50. The amplifier sleeve 70 can be a single hollow cylindrical
member which essentially completely encloses these interior
elements, or two or sections (which, when positioned, define a
cylindrical cavity) as shown in FIG. 2. In the illustrated
embodiment, the amplifier sleeve section(s) 70 can be affixed or
fastened to a top surface of amplifier base 58, as evidenced by
aligned fastener holes 72 and 74 formed in amplifier sleeve
sections 70 and amplifier base 58, respectively. In addition, the
motion amplifier 22 is covered by a ceiling board 76 which is
mounted, affixed, or fastened to amplifier sleeve section(s) 70.
For example, ceiling board 76 can be fastened to amplifier sleeve
section(s) 70 as evidenced by aligned fastener holes 77 and 78
formed in ceiling board 76 and amplifier sleeve section(s) 70,
respectively. As explained subsequently, ceiling board 76 can carry
some or all portions of sensor and control system 26.
[0060] As mentioned above, and as shown in FIG. 7, piezoelectric
diaphragm 30 is carried on reacted mass cup crown edge 44. The
peripheral edge of piezoelectric diaphragm 30 can be constrained by
any of several mounting methods. For example, a bead of an adhesive
or the like can be applied circumferentially underneath
piezoelectric diaphragm 30 and around reacted mass cup crown edge
44 in the region 80 illustrated in FIG. 7. Such adhesive should
preferably be sufficiently sticky but also allow shear movement
between layers of the piezoelectric diaphragm 30. One example of
such adhesive is a 467MP adhesive supplied by Minnesota Mining
& Manufacturing.
[0061] As another example, illustrated in FIG. 8A, an intermediate
clamping sleeve 82 can be arranged circumferentially around
piezoelectric diaphragm 30 and reacted mass cup 40. The
intermediate clamping sleeve 82 has an overhanging rim section 84
which has a distal depending contact foot 86. A (rubber) gasket 88
or the like is interposed between contact foot 86 and an upper
circumferential edge of piezoelectric diaphragm 30, to apply a
retaining force on the top periphery of piezoelectric diaphragm 30.
The intermediate clamping sleeve 82 is retained in position by
affixation to the exterior sidewall of reacted mass cup 40 by,
e.g., fasteners or the like such as fastener 90 illustrated in FIG.
8A.
[0062] In a yet further alternate implementation, rather than or in
addition to having fastener 90, intermediate clamping sleeve 82 has
a bottom rim 92. In the FIG. 8B embodiment, piezoelectric diaphragm
30 and reacted mass cup 40 are securely clamped between overhanging
rim section 84 and bottom rim 92 of intermediate clamping sleeve
82.
[0063] As shown in FIG. 1-6, valve assembly 24 fits internally into
bellows assembly 50, occupying at least a portion of compression
chamber 52 and valve assembly cavity 60. FIG. 10-FIG. 17 illustrate
valve assembly 24 or portions thereof in more detail. For example,
FIG. 11 shows (in exploded fashion) valve assembly 24 as comprising
exhaust valve housing 102 and intake valve housing 104. Both
exhaust valve housing 102 and intake valve housing 104 comprise two
essentially half-cylindrical sections, with a lower of the two
cylindrical sections having a larger diameter than an upper
section. The exhaust valve housing 102 has an intake port 106 and
an exhaust port 108, which communicate with an intake chamber 110
and an exhaust chamber 112, respectively, of exhaust valve housing
102 as shown in FIG. 16. The intake valve housing 104 has a ramped
intake chamber 116 and a smaller ramped exhaust chamber 118. The
ramped intake chamber 116 of intake valve housing 104 communicates
through a compression chamber intake port 120 formed on a top
surface of intake valve housing 104 for admitting fluid into
compression chamber 52 (see FIG. 7). Similarly, exhaust chamber 118
communicates through a compression chamber exhaust port 122 formed
on the top surface of intake valve housing 104 for exhausting fluid
from compression chamber 52.
[0064] A valve seat 130 is interposed between exhaust valve housing
102 and intake valve housing 104. The valve seat 130 has valve seat
intake port 132 and valve seat exhaust port 134. An exhaust tape
seal 136 is interposed between exhaust valve housing 102 and valve
seat 130; an intake tape seal 138 is interposed between intake
valve housing 104 and valve seat 130. The exhaust tape seal 138 is
profiled for insertion between exhaust valve housing 102 and valve
seat 130, and has apertures or cutouts corresponding in position
and size to intake chamber 110 and exhaust chamber 112 of exhaust
valve housing 102. Similarly, intake tape seal 136 is profiled for
insertion between intake valve housing 104 and valve seat 130, and
has apertures or cutouts corresponding in position and size to
ramped intake chamber 116 and exhaust chamber 118 of intake valve
housing 104. An exhaust reed valve 140 is retained in cantilever
fashion between intake tape seal 138 and valve seat 130, a base or
proximal end of exhaust reed valve 140 being held in position
between intake tape seal 138 and valve seat 130 by laser weld
retainer 142 while a distal or upper end of exhaust reed valve 140
selectively covers valve seat exhaust port 134 of valve seat 130.
In similar fashion, intake reed valve 144 is retained in cantilever
fashion between exhaust tape seal 136 and valve seat 130, a base or
proximal end of intake reed valve 144 being held in position
between exhaust tape seal 136 and valve seat 130 by laser weld
retainer 146 while a distal or upper end of intake reed valve 144
selectively covers valve seat intake port 132. The exhaust valve
housing 102, intake tape seal 138, valve seat 130, exhaust tape
seal 136, and intake valve housing 104 are held in alignment by a
pair of alignment pins 147 which extend through corresponding
apertures in each of the elements aligned thereby. When exhaust
valve housing 102 and intake valve housing 104 are joined together
with each of intake tape seal 138, valve seat 130, and exhaust tape
seal 136 aligned therebetween by the alignment pins 147, and with
the exhaust reed valve 140 and intake reed valve 144 properly
positioned, a valve assembly gasket 148 is fit over the top
sections of both exhaust valve housing 102 and intake valve housing
104. Interface tubes 149 are then inserted into intake port 106 and
exhaust port 108 for providing a conduit for fluid to enter and
exit from valve assembly 24.
[0065] The compressor assembly 20 is resiliently mounted with
respect to the outside world. Resilient mounting of compressor
assembly 20 can be accomplished in several ways. As a first
example, FIG. 18A shows compressor assembly 20 as being located at
least partially within a compressor housing 150. The compressor
housing 150 comprises a housing base 152; one or more housing
sidewall(s) 154; and housing cover 156. The housing base 152 can
have a plurality of short mounting pedestals 158 extending upwardly
therefrom, with the mounting pedestals 158 being positioned in a
pattern or arrangement adapted for support of compressor assembly
20. However, compressor assembly 20 does not rest on mounting
pedestals 158 directly. Rather, the mounting pedestals 158 have
proximal ends of resilient beams 160 mounted thereto in cantilever
fashion. The compressor assembly 20 is situated on distal or second
ends of the resilient beams 160. For example, an underside of
amplifier base 58 can be fixedly mounted to upper surfaces of
resilient beams 160. The resilient beams 160 can be, for example, a
springy or resilient metallic material. Thus, in the implementation
of FIG. 18A, the compressor assembly 20 is mounted on a series of
radially extending (with respect to axial direction 31) resilient
cantilever beams 160 which resemble diving boards.
[0066] Alternatively, as shown in FIG. 18B, compressor assembly 20
can be resiliently mounted on coiled springs 162. The coiled
springs 162 can be circularly mounted, for example, on housing base
152, and have one end connected to a top surface of housing base
152 and another end connected to an underside of amplifier base
58.
[0067] The compressor assembly 20 thus comprises both motion
amplifier 22 and valve assembly 24. In an illustrated embodiment of
FIG. 1, motion amplifier 22 has a peripheral edge of its
piezoelectric diaphragm 30 attached or secured (e.g., with a
flexible epoxy) to reacted mass cup crown edge 44 so that the
periphery of piezoelectric diaphragm 30 is constrained while the
piezoelectric diaphragm 30 is otherwise free to flex. The
piezoelectric diaphragm 30 flexes as a voltage is applied from
sensor and control system 26 via electrodes 32. The reaction mass
34 is carried by piezoelectric diaphragm 30 to increase its
inertia. The flexing of piezoelectric diaphragm 30 reciprocates
reaction mass 34. By Newton's Third Law, the moving mass produces a
force on reacted mass cup 40. Thus, the energy input is transformed
first to a force and ultimately to motion of reacted mass cup 40
and of reacted mass cup bottom wall 46, which serves as a
compression head or piston head. The reacted mass cup 40 vibrates
and deflects into the compression chamber 52 defined partially by
the bellows assembly 50 that carries reacted mass cup 40. As
explained subsequently, large deflections are produced when the
piezoelectric diaphragm 30 is driven/operated at the resonant
frequency of the piston head assembly, e.g., the assembly carried
by bellows assembly 50. The maximum stroke of the piston head is
limited only by structural damping. In an example implementation,
such damping is on the order of 3%-6% of critical damping, so the
maximum stroke can be ten to thirty times the stroke or
displacement of the piezoelectric diaphragm 30 itself.
[0068] There is an energy cost to operating at resonance. The work
done against the internal losses is not useful work and it
increases with stroke. Fortunately, this component of the total
work is manageable. In fact, this work term is masked by the
capacitor-like nature of the piezoelectric diaphragm 30 with a
conventional drive circuit. The pumping work is equivalent to a
damping term. For incompressible flow and as an approximation to
compressors at low pressure ratio, pumping work is simply the
product of pressure rise and flow rate. This work must be supplied
each cycle. The work provides useful compression of the fluid.
[0069] The motion amplifier 22 thus can be used, when employed
within a compressor context, to create a variable volume in
compression chamber 52. Fluid is admitted into and exhausted from
compression chamber 52 by valve assembly 24. As the volume in
compression chamber 52 increases, fluid is drawn in through the
intake valve of valve assembly 24. As the volume decreases, fluid
is expelled or exhausted through the exhaust valve of valve
assembly 24.
[0070] The motion amplification created by motion amplifier 22 is
particularly useful when working with gases because the large
motion makes it easy to achieve a large ratio of maximum to minimum
volume (e.g., the so-called compression ratio), which is necessary
for achieving a large output pressure. The large motion may also
facilitate producing a large swept volume and hence flow rate.
Producing both a high pressure and a large flow rate simultaneously
depends on having adequate input power.
[0071] Preferably motion amplifier 22 works in conjunction with a
motion sensing system. In one non-limiting example embodiment, such
a motion sensing system can include an optical emitter 170 and an
optical sensor 172 (e.g., phototransistor). The optical emitter 170
is positioned to direct an electromagnetic (e.g., optical) beam
onto a top surface of piezoelectric diaphragm 30. The optical
sensor 172 is situated and positioned to detect reflection of the
beam from piezoelectric diaphragm 30.
[0072] FIG. 19A shows a first example technique for mounting
optical emitter 170 and optical sensor 172. In the technique of
FIG. 19A, optical emitter 170 and optical sensor 172 are both
mounted on an underside of a sensor system cantilever support
member 174. The sensor system cantilever support member 174 is held
aloft above compressor housing 150. The housing cover 156 of
compressor housing 150 has a cover aperture 176 which is preferably
centrally located above a center portion of piezoelectric diaphragm
30. The optical emitter 170 and optical sensor 172 are held by
sensor system cantilever support member 174 so that optical emitter
170 directs a beam 178 toward the (preferably shiny) top surface of
piezoelectric diaphragm 30, and so that optical sensor 172 receives
the beam as reflected by piezoelectric diaphragm 30. If desired,
the aforementioned sensor and control system 26 can also be mounted
on sensor system cantilever support member 174, e.g., on an
underside of sensor system cantilever support member 174.
[0073] FIG. 19B shows another example technique for mounting
optical emitter 170 and optical sensor 172. The FIG. 19B technique
is useful for an embodiment of a compressor assembly which has one
or more amplifier sleeve sections 70 such as illustrated in FIG. 1
and FIG. 8A and FIG. 8B, with a ceiling board 76 which fits over
amplifier sleeve sections 70. In the FIG. 19B technique, the
optical emitter 170 and sensor system cantilever support member 174
are mounted on the underside of ceiling board 76. Again, if
desired, the sensor and control system 26 can also be mounted as a
circuit board on the underside of ceiling board 76.
[0074] FIG. 20 illustrates that sensor and control system 26
includes the optical emitter 170 and optical sensor 172 described
above. In accordance with the amplitude of the beam reflected from
the piezoelectric diaphragm 30, optical sensor 172 generates a
sense position signal which is applied to control circuit 200. The
value of the sense position signal indicates the degree of motion
(displacement, deflection) of the entire motion amplifier. The
control circuit 200, described in more detail along with other
elements with reference to FIG. 21, resembles a phase locked loop
voltage control output circuit. An output signal of control circuit
200 is applied to power amplifier 202, which generates the drive
signal which is applied by electrodes 32 to piezoelectric diaphragm
30.
[0075] An example embodiment of control circuit 200 is illustrated
in FIG. 21. In one sense, the control circuit 200 resembles a phase
lock loop. However, control circuit 200 differs from a conventional
phase locked loop in that the drive signal applied by control
circuit 200 to piezoelectric diaphragm 30 is a sine wave (rather
than a square wave) and the output of sensor and control system 26
depends on the amplitude of motion, which decreases greatly for off
resonant conditions.
[0076] The control circuit 200 of FIG. 21 includes an optical
sensor 206 which includes both the optical emitter 170 and optical
sensor 172. A buffer 208 buffers the signal generated by optical
sensor 206. The signal is amplified (two stages of amplification)
by amplifier 210 and amplifier 220. The amplified signal OPT is
applied to phase detector 222. The phase detector 222 detects the
phase output from optical sensor 206 relative to phase output from
variable frequency oscillator 223. The output from phase detector
222 is applied to low pass filter 224 to produce a phase angle
signal PHAZ. The phase angle of phase angle signal PHAZ is compared
to a reference by phase error amplifier 226. The compared signal is
inverted by inverter 228. A frequency range selector 230 selects a
frequency range, which goes to the control line for controlling the
frequency. The sine wave output SINE is applied to power amplifier
202, as well as to a squaring circuit 234 which squares it and
feeds it back phase detector 222.
[0077] As understood from the foregoing, a motion amplifier
comprises a piezoelectric diaphragm, a reaction mass carried or
attached to the piezoelectric diaphragm; drive electronics for
driving the piezoelectric diaphragm; a reacted mass; and, a reacted
mass spring. Preferably the motion amplifier, and any compressor
assembly comprised by the same, is resiliently mounted on yet
another spring. These aspects of a motion amplifier can be
implemented in many ways, including but not limited to the
embodiments already described with reference to previously
described figures. FIG. 9 shows that a generic system encompassed
hereby includes a first mass M1 corresponding to the reaction mass;
a first spring constant K1 corresponding to the spring constant or
resilience of the piezoelectric diaphragm; a second mass M2
corresponding to a reacted mass of the system; a second spring
constant K2 corresponding to the reacted mass spring any load acted
upon by the reacted mass; a third mass M3 corresponding to a base
of the system; and, a third spring constant K3 corresponding to the
system resilient mounting spring.
[0078] More particularly, FIG. 9 further illustrates mapping of the
model of the general system to structure of the example embodiments
already described. In accordance with such mapping, the first mass
M1 corresponding to the reaction mass is the mass of reaction mass
34 carried by piezoelectric diaphragm 30. The first spring constant
K1 is the spring constant or resilience of piezoelectric diaphragm
30, and affords a first degree of freedom. The second mass M2
corresponds to a reacted mass is the mass of reacted mass cup 40.
The second spring constant K2 corresponds to the reacted mass
spring and any load upon which the reacted mass acts, and affords a
second degree of freedom. Thus, the second spring constant K2 is
the spring constant of bellows assembly 50 and any load acted upon
by bellows assembly 50, e.g., any load acted upon by piston head
46. The load acted upon by the reacted mass may be, for example,
fluid (gas or liquid) being compressed or acted upon by piston head
46. The third mass M3 corresponding to a base of the system is the
mass of bellows assembly 58; and, the third spring constant K3
corresponding to the system resilient mounting spring is the spring
constant of the resilient means which resiliently mounts the entire
foregoing structure relative to the outside world, e.g., either
resilient beams 160 (in FIG. 18A) or coiled springs 162 (in FIG.
18B). The third spring constant K3 affords a third degree of
freedom. C1, C2, and C3 are damping coefficients, and as shown in
FIG. 9 correspond to intrinsic damping (and, the case of C3, work
done on the fluid).
[0079] The use of the third spring, as represented by third spring
constant K3 and implemented, for example, by resilient beams 160
(in FIG. 18A) or coiled springs 162 (in FIG. 18B), thus affords or
invokes a third degree of freedom. Unless the compressor assembly
20 is firmly clamped to a rigid base (in which case it transmits
vibration force, but no energy) or is free (in which case it
transmits vibration displacement but also no energy), the vibration
will be damped. Therefore, the third spring constant provides a
resilient mounting of the compressor assembly 20 within compressor
housing 150. An alternative configuration would be to place two
well matched units back to back to cancel vibration.
[0080] While specific embodiments have been described, the scope
hereof is not so limited. For example, the reaction mass can be
added or carried elsewhere than on a central underside of the
piezoelectric diaphragm. What is preferred is that one of the
reaction mass and the reacted mass be at the center of the
piezoelectric diaphragm, and the other carried or attached at the
periphery of the piezoelectric diaphragm. The reacted mass spring
contributes to the spring constant K2 preferably has a first end
attached to the reacted mass and a second end attached to a base or
housing which serves as the third mass M3. In the particular
embodiment that has a third spring, such third spring serves for
resiliently mounting the entire system (relative to the rest of the
world) and preferably has a first end connected to the amplifier
base and a second end connected to a system housing. Alternatively,
if there is no such third spring (e.g., no resilient mounting), the
amplifier base is rigidly fixed (e.g., to earth) or allowed to
float freely.
[0081] The springs (having spring constants K1, K2, and K3) and
masses M1, M2, and M3 of the system are selected such that the
desired operating frequency is at a strategic natural frequency of
the system. The reaction mass, the working stroke, and the
frequency combine to define the load on the piezoelectric
diaphragm. In order to maximize the power transfer from the
piezoelectric diaphragm, the load on the piezoelectric diaphragm
should lie at half of the blocked force. The blocked force is the
force produced by a piezoelectric actuator when "blocked" from
moving. In other words, the static force that it can impart on an
immovable object. The power transferred is then twenty five percent
of the product of blocked force, free displacement, and
frequency.
[0082] In the FIG. 9 depiction, since there are three masses (M1,
M2, and M3) and three degrees of freedom, there are also three
natural or resonant frequencies f1, f2, and f3. These three
resonant frequencies correspond to the three peaks labeled as f1,
f2, and f3 in FIG. 22. In FIG. 22, the first peak is frequency f1
which is the resonant frequency of the entire mounting (the natural
frequency of everything that is bouncing on K3, e.g., all the
structure carried by the resilient beams 160, for example). This
first resonant frequency f1 is low and serves to isolate the
vibrations of the system from its housing. The third frequency is
essentially mass M1 (e.g., reaction mass 34) bouncing on spring K1
(e.g., piezoelectric diaphragm 30). The second resonant frequency
is the resonant frequency of the structure carried by spring K2
(e.g., the resonant frequency of the structure carried by the
reacted spring mass (the reacted spring mass being reacted mass cup
40 in the illustrated embodiments)). It is this second resonant
frequency, f2, which is chosen as the desired operational frequency
of the motion amplifier 22. Both first resonant frequency f1 and
third resonant frequency f3 are kept reasonably far from the
operating frequency f2.
[0083] As an aside, in addition to the three resonant frequencies
of the system, there are also three partial frequencies
.OMEGA..sub.1, .OMEGA..sub.2, and .OMEGA..sub.3, thus making a
total of six frequencies. The three partial frequencies are
.OMEGA..sub.1=K1/M1, .OMEGA..sub.2=K2/M2, and .OMEGA..sub.3=K3/M3,
respectively. Preferably the first partial frequency
.OMEGA..sub.1=K1/M1 is made to be a high frequency; the second
partial frequency .OMEGA..sub.2=K2/M2 is made equal to about the
operating frequency (an intermediate frequency), and the third
partial frequency .OMEGA..sub.3=K3/M3 is make to be a fairly low
frequency (if operating frequency is about 250 Hz, K3/M3 is made
about 40 Hz).
[0084] As mentioned above, the motion amplifier 22 is preferably
operated at the second resonance frequency (f2). This second
resonance frequency is essentially the square root of the quantity
K2 divided by the sum of the masses M1 and M2. Because the first
spring constant K1 is stiff, mass M1 does essentially the same
thing as mass M2 does. So these two masses M1 and M2 bounce on the
spring having spring constant K2, and this bouncing is what
determines the peak at frequency f2. Advantageously, the
displacement amplitude of the motion amplifier increases
considerably at the frequency f2, as shown in FIG. 22. For example,
operating at the resonant frequency f2 may provide as much as a
twenty five fold in displacement amplitude. That is, the amplitude
of the displacement of the motion amplifier is twenty five times
the amplitude of the displacement of the piezoelectric diaphragm by
itself.
[0085] Thus, frequency f2 is the operating frequency which produces
a greatly amplified motion of the cylinder head (e.g., of flat
bottom wall 46 of reacted mass cup 40). Energy is required to drive
this large amplitude displacement. There is also a differential
motion between mass M1 and mass M2, but such differential motion is
not a concern because stresses of the piezoelectric diaphragm are
set by the total motion of mass M1 rather than the differential
motion.
[0086] Of interest also is the phase angle between the motion of
the piezoelectric diaphragm and the voltage driving the
piezoelectric diaphragm. Line 250 of FIG. 22 shows phase angle as a
function of frequency. For a sharply resonant peak like the
amplitude peak that occurs for resonant frequency f2, the phase
angle goes through a ninety degree phase shift at the resonant
frequency and is fairly steep. As FIG. 22 shows, there is almost no
phase shift until approaching the resonant frequency f2, and then
right after the resonant frequency the phase shift is one hundred
eighty degrees. FIG. 23 shows a graph of amplitude verses phase
angle, which results in a fairly broad curve. The particular curve
shown in FIG. 23 is for a particular damping ratio. The lower the
damping ratio, the higher the relative response. So operating on
the curve of FIG. 23 provides a fairly broad phase angle change for
a fairly small change in amplitude. Accordingly, if the phase angle
between the displacement of the system and the drive voltage
applied to the piezoelectric diaphragm is maintained to, e.g., 10
degrees of the 90 degree resonant frequency f2, the displacement
amplitude will be at its peak amplitude almost exactly.
[0087] The displacement of the system here is superposition of the
displacements X1, X2, and X3 in FIG. 9. Thus, the displacement of
the system includes the motion of the piezoelectric diaphragm 30.
But since the piezoelectric diaphragm 30 is attached to other
masses (actually two masses M1 [reaction mass 34] and M2 [reacted
mass 40]) that is moving with the bellows, the displacement of the
system is a superposition of the motion of the piezoelectric
diaphragm 30 and the other structure attached thereto. Of course,
peak amplitude is desired in order to obtain maximum motion
amplification, and thus the greatest possible compression ratio
when the motion amplifier is used in a compressor assembly.
[0088] The sensor and control system 26 thus controls the phase
angle between the displacement of the system and the drive voltage
applied to the piezoelectric diaphragm 30 to be within a
predetermined neighborhood of the second resonant frequency (e.g.,
within ten degrees of ninety degrees), in order to achieve peak
amplitude of displacement of motion amplifier 22. In this regard,
sensor and control system 26 employs optical emitter 170 and
optical sensor 172 to measure the displacement of the top surface
of piezoelectric diaphragm 30. The optical sensor senses
displacement of the motion amplifier 22 relative to bellows base
58.
[0089] Thus, the sensor and control system 26 measures displacement
of piezoelectric diaphragm as well, and thus in actuality measures
both displacement of the entire motion amplifier 22 (displacement
X1) and the displacement of piezoelectric diaphragm 30
(displacement X2), relative to a fixed position (X3), e.g., on
bellows base 58. But as a practical matter, displacement X1 of the
piezoelectric diaphragm 30 is fairly small, and displacement X2 is
much larger.
[0090] The optical sensor comprising optical emitter 170 and
optical sensor 172 measures the displacement by reflection (using a
simple type of sensor similar that detects whether door is open or
closed). The optical sensor is biased into the linear region. As
the distance separating the optical sensor 172 and the
piezoelectric diaphragm 30 changes, so does the response as
indicated by the sense position signal (see FIG. 20). FIG. 24 is a
voltage verses distance graph showing an example response signal
(e.g., sense position signal). Operating close to the second
resonant frequency, e.g., at point x.sub.0, give a high voltage for
the sense position signal, but moving away from the second resonant
frequency causes the sense position signal voltage to decrease.
[0091] The motion amplifier is operated by phase control feedback,
as implemented by sensor and control system 26, to lock the system
to the second resonant frequency f2 in spite of variations in the
load, system non-linearity, and the like. The sensor and control
system 26 thus includes a feedback loop to lock the frequency of
the drive signal to the piezoelectric diaphragm 30 to produce a
fixed value of the phase. The operation of the feedback loop to
lock the frequency of the drive signal is understood with reference
to control circuit 200 of FIG. 21.
[0092] Other aspects of the example control circuit 200 of FIG. 21
will now be described. It should be understood again that the
structure and operation of example control circuit 200 of FIG. 21
are merely illustrative, and that other forms of control circuitry
(e.g., primarily digital circuitry) may instead be implemented.
[0093] The motion of the motion amplifier is sensed by a miniature
reflective photointerrupter (e.g., optical sensor 172) of example
control circuit 200 of FIG. 21. The photointerrupter is
electrically biased to provide a monotonic response with position.
The signal from the position detector is buffered by U1B of buffer
208. The series resistance to the optical sensor 172 is set by
potentiometer P6 so that, at the nominal position of the
piezoelectric diaphragm 30 (about 0.070 inch to the front of the
sensor 172), the signal at testpoint 2 is four volts. During
operation, the signal is sinusoidal with an amplitude of about two
volts peak to peak about the nominal test point of four volts. The
buffered signal is ground referenced by C3. The ground referenced
peak to peak signal is available at test point 3 as an output. The
ground referenced signal is then amplified by the two stage
squaring amplifier 210 and 220 comprising U2B and U2A,
respectively, until it becomes a square wave.
[0094] The optical sensor is phase detected relative to the drive
signal. The drive signal is converted to a square wave by
amplifying the sine wave used to drive the piezoelectric diaphragm
30 until it saturates the amplifier. The phase angle is detected by
the flip flop circuit U4 of phase detector 222. The two square
waves are first differentiated by capacitors C5 and C6 to produce
spikes which turn the flip flop U4 on and then off with each cycle
of the square waves. While the flip flop U4 is on, a voltage is
produced at the output Q. The DC level of this voltage is detected
by the low pass filter 224 (in U1A). This voltage is proportional
to the phase difference between the optical response and the drive
voltage.
[0095] The phase angle is used to control frequency as follows. The
difference between the measured phase angle and a fixed "set point"
voltage set by potentiometer P2 is integrated by capacitor C28. The
integrator output is inverted by U3A and amplified relative to a
frequency set point in U3B. In principle, both inverter 228 and the
center frequency setpoint amplifier, U3B and U3A, could be omitted.
However, they may be useful because, by shorting capacitor C28, the
frequency can be adjusted by potentiometer P8 to sweep over a wide
range. The output of U3B drives a voltage variable frequency. This
sine wave is offset, buffered, and amplified by U6A, U6B, and U7B.
The conditioned sine wave is fed to the high voltage amplifier
which drives piezoelectric diaphragm 30. The U8A amplifies the sine
wave to produce the square wave needed for the phase detector.
[0096] Thus, feedback control is based on the phase angle between
the motion of the piezoelectric diaphragm and the drive voltage
applied to piezoelectric diaphragm. As explained above, if the
phase angle is kept between sixty and one hundred twenty degrees,
the motion amplitude will be within 5% of the second resonant
frequency peak. Such a relatively broad range in phase space is due
to the sharpness of the resonance.
[0097] As in the preceding example, the motion sensor may typically
detect position. Other types of detection are also possible, such
as velocity or acceleration, for example. The currently preferred
embodiment is to use an optical sensor comprised of an LED (as
optical emitter 170) and phototransistor (as optical sensor 172)
where the transconductance depends on position in a relatively
linear fashion. Such a sensor provides the additional function of
limiting the stroke of the compressor in order to prevent the drive
from impacting the cylinder head.
[0098] The example compressor assembly embodiment 20 of FIG. 1
includes bellows assembly 50, which can be desirable because the
compression chamber at least partially defined thereby can be
smaller (e.g., in diameter) than the piezoelectric diaphragm 30 and
because stock bellows are available for reasonable cost. In the
bellows embodiment, the second spring constant K2 corresponds in
part to the reacted mass spring and thus includes the spring
constant of bellows assembly 50 (as well as the spring constant of
any load acted upon by the reacted mass, e.g., the actuator portion
of surface).
[0099] FIG. 25 illustrates another example embodiment of a
compressor assembly, particularly compressor assembly 20'. The
compressor assembly 20' includes many of the like-referenced
elements of the first embodiment compressor assembly 20 of FIG. 7,
including piezoelectric diaphragm 30 which carries reaction mass
34, the piezoelectric diaphragm 30 and reaction mass 34 in turn
being carried within reacted mass cup cavity 48 by reacted mass cup
40. The bottom of reacted mass cup 40 (e.g., reacted mass cup
bottom wall 46) provides or serves as a compression head or piston,
e.g., as the actuator portion or surface of the motion
amplifier.
[0100] The compressor assembly 20' of FIG. 25 differs in the form
of the second spring K2 which carries the reacted mass cup 40. In
particular, the second spring having spring constant K2 of the FIG.
25 embodiment comprises corrugated diaphragm 270. A rim or
periphery of corrugated diaphragm 270 is attached to an amplifier
base 58'. Corrugations in the diaphragm 270 enhance motion of the
entire motion amplifier structure. Amplifier base 58' at least
partially defines a crater-type cavity which serves as compression
chamber 52'. The crater-type cavity formed by amplifier base 58'
may itself have an undulating surface to accommodate corrugations
in the diaphragm 270. The corrugated diaphragm 270 also at least
partially defines the compression chamber 52' by serving as a cover
therefore (in addition to serving to support the reacted mass cup
40). An intake or inlet valve 272 is provided in amplifier base
58', as is an outlet or exhaust valve 274.
[0101] The corrugated diaphragm 270 can be provided in the form of
an essentially solid member upon which the reacted mass cup 40 is
situated. In this implementation, the corrugated diaphragm 270 can
have reacted mass cup 40 adhered or otherwise secured
thereover.
[0102] Alternatively, the corrugated diaphragm 270 can have a
central aperture or the like through which the bottom (e.g., the
compression head) of reacted mass cup 40 protrudes. The reacted
mass cup 40 is, in this implementation, securely engaged by
corrugated diaphragm 270 in its central aperture.
[0103] The corrugated diaphragm 270 may be fabricated from a
flexible material such as elastomer, or of a rigid material such as
nickel, silver, or steel. In the size ranges of commercial
interest, a flat rigid diaphragm would have a very non-linear
deflection curve which might create a challenge for maintaining
resonant operation. Therefore, a corrugated diaphragm is
recommended. The end wall of the amplifier base 58' may be
contoured to provide minimum dead volume.
[0104] Other embodiments and ways of employing a motion amplifier
in a compressor assembly are also possible. For example, a motion
amplifier reciprocate in a base defining a compression chamber,
with sliding seals provided between the motion amplifier and the
base. Alternatively, a rubber-edged disk or bellofram may be
utilized. As another alternative, a Peek diaphragm or electroformed
bellows may be employed.
[0105] Whatever embodiment the motion amplifier 22 takes, including
the embodiment of FIG. 25 described above and the embodiment of
FIG. 26 described hereinafter, providing a third degree of freedom
eliminates or mitigates any dampening imposed or caused by the
outside world. To this end, coiled springs 162 are shown in FIG. 25
as providing the spring constant K3 and thus the third degree of
freedom. Other resilient mounting structure or techniques can be
employed, such as (by way of non-limiting example) the resilient
beams hereinbefore described.
[0106] As mentioned above, the drive signal can be applied to
motion initiator element 30 by radially extending electrodes or
leads 32. Flexures can be arranged in these leads or electrodes to
pass electricity to the motion initiator element 30 since the
motion initiator element 30 moves with respect to the housing in
which the power supply may be fixed. Moreover attachment points of
the flexing leads, one being on the motion initiator element 30 and
the other being fixed in space, may lie directly over each other as
to form a hairpin shape, which is efficient with respect to bending
stresses on the attachment points.
[0107] FIG. 26 illustrates another embodiment of a compressor
assembly 20'' wherein the motion amplifier comprises plural motion
initiator elements, e.g., plural piezoelectric diaphragms 30. In
the illustrated example of FIG. 26, a second piezoelectric
diaphragm 30-2 is positioned by mounting member 180 above the first
piezoelectric diaphragm 30. The mounting member 180 can take the
form of pedestals or a ring. More than one auxiliary piezoelectric
diaphragm 30 can be provided, e.g., in stacking arrangement, in
similar manner, not only for the illustrated embodiment having a
corrugated diaphragm, but for the bellows embodiment and other
embodiments as well.
[0108] In whatever embodiment of compressor assembly is utilized,
the valves employed in the compressor assembly should open and
close efficiently at the operating frequency, and will in fact do
so if the valves have a sufficiently high natural frequency. Since
valve pressure drop and bending stress increase with the valve
natural frequency, the valves will ultimately set an upper
operating limit on the compressor. To help limit the stress and
improve the time response of the valves, as one example technique
stops can be utilized to limit the travel of the valves. FIG. 25
illustrates stop 276 for inlet valve 272 and stop 278 for exhaust
valve 274. These stops should reasonably conform to the shape of
the deflected element (e.g., to the reed for a reed valve), and
also allow some clearance. Without a technique such as stops, the
blast of fluid forces the valves open too far (dynamically), and
the valves then shut and reopen several times during the cycle,
which does not improve the fluid flow.
[0109] In an example embodiment, valve natural frequency is
selected and set at 650 Hz and the operating frequency at 250 Hz.
The equivalent mass is about 20% of the mass of the reed (rather
than about 33% as expected for a regular spring). If the natural
frequency of the valves (e.g., the reeds of the valves) is at least
twice the operating frequency, the valves do not have timing issues
at some of the larger backpressure levels.
[0110] In a preferred embodiment and mode of operation,
piezoelectric diaphragm 30 more particularly takes the form of a
ruggedized laminated piezoelectric member. Examples of such
ruggedized laminated piezoelectric members are provided in PCT
Patent Application PCT/US01/28947, filed 14 Sep. 2001; U.S. patent
application Ser. No. 10/380,547, filed Mar. 17, 2003, entitled
"Piezoelectric Actuator and Pump Using Same"; U.S. patent
application Ser. No. 10/380,589, filed Mar. 17, 2003, entitled
"Piezoelectric Actuator and Pump Using Same", and U.S. patent
application Ser. No. 11/279,647 filed Apr. 13, 2006, entitled
"PIEZOELECTRIC DIAPHRAGM ASSEMBLY WITH CONDUCTORS ON FLEXIBLE
FILM", all of which are incorporated herein by reference.
[0111] The motion amplifier 22 uses the displacement/motion of
piezoelectric diaphragm 30 (such displacement being on the order of
0.1 mm for an example embodiment) to drive an actuator region or
surface (e.g., compressor head) to large displacements. In
illustrated embodiment, the actuator surface (also known as a
cylinder head or piston head) may take the form of flat bottom wall
46 of reacted mass cup 40.
[0112] For example, a displacement of 2 mm (e.g., strokes of 2 mm)
is possible in motion amplifier 22 having a 25 mm piezoelectric
diaphragm 30 operating at 400 volts peak to peak. Such a drive
voltage would only produce a 0.16 mm stroke if applied directly to
the piezoelectric diaphragm 30 alone. Since the motion of the
piezoelectric diaphragm 30 in the motion amplifier 22 is at most
half of this 0.16, or only 0.08 mm, a "gain" of 25 is achieved.
This gain occurs at the operating frequency which is a resonant
condition. This resonant condition (frequency and gain) change with
load and system nonlinearities, such as a hardening spring (typical
of diaphragms and gas springs).
[0113] In addition to large amplitude, an advantage of the motion
amplifiers described herein are their ability to impedance match to
a variable load. When the motion amplifier is used in compressor
assembly 20 or 20', for example, the load impedance changes as the
flow rate and pressure rise of the compressor change. Over wide
ranges the piezoelectric diaphragm can still drive the load
efficiently because of the flexibility afforded by the resonant
drive of the sensor and control system. Thus, at low flow rates,
pressures up to the limit imposed by the maximum achievable
compression can be reached. Work is not expended until the valves
open to allow fluid to escape the compression chamber. With no flow
(and also with no pressure rise), no energy is lost from the
system. At low pressures, the flow is only limited by the maximum
possible displacement. Intermediate operating points tend to fall
on a hyperbolic operating curve representing constant input power.
By way of contrast, centrifugal and axial compressors have very
little tolerance to changes in load.
[0114] The described embodiments are particularly suitable, but not
limited to, compressors for air or other fluid which are generally
in a flow range of from 0.01 to 10 liters per minute, and pressure
ratios up to 2:1 with weights in the 50 gram range and power
efficiencies up to about 30%.
[0115] Although the description above contains many specificities,
these should not be construed as limiting the scope of the
invention but as merely providing illustrations of some of the
presently preferred embodiments of this invention. Thus the scope
of this invention should be determined by the appended claims and
their legal equivalents. Therefore, it will be appreciated that the
scope of the present invention fully encompasses other embodiments
which may become obvious to those skilled in the art, and that the
scope of the present invention is accordingly to be limited by
nothing other than the appended claims, in which reference to an
element in the singular is not intended to mean "one and only one"
unless explicitly so stated, but rather "one or more." All
structural, chemical, and functional equivalents to the elements of
the above-described preferred embodiment that are known to those of
ordinary skill in the art are expressly incorporated herein by
reference and are intended to be encompassed by the present claims.
Moreover, it is not necessary for a device or method to address
each and every problem sought to be solved by the present
invention, for it to be encompassed by the present claims.
Furthermore, no element, component, or method step in the present
disclosure is intended to be dedicated to the public regardless of
whether the element, component, or method step is explicitly
recited in the claims. No claim element herein is to be construed
under the provisions of 35 U.S.C. 112, sixth paragraph, unless the
element is expressly recited using the phrase "means for."
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