Note: Descriptions are shown in the official language in which they were submitted.
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FERROELECTRIC PUMP
Cross Reference to Related Cases
This application is related to co-pending, commonly owned Patent
Cooperation Treaty application Serial No. . , filed , 1998,
entitled "Ferroelectric Fluid Flow Control Valve."
Origin of the Invention
The invention described herein was made by employees of the United
States Government and may be manufactured and used by the government
for governmental purposes without the payment of any royalties thereon or
therefor.
Background of the Invention
Field of the Invention
This invention relates to pumps for both liquids and gases, and more
particularly to ferroelectric pumps utilizing one or more dome shaped
internally prestressed ferroelectric actuators having a curvature and a dome
height that varies with an electric voltage applied between an inside and
outside surface of the actuators.
Description of the Related Art
Conventional pumps generally fall into two classes; positive
displacement and force. Force pumps force a material along through a
mechanical moving part, thereby creating a pressure on the material.
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Positive displacement pumps work on the principal of compression of the
material. Examples include a reciprocating pump and a bellows pump.
Reciprocating pumps normally use a piston in a cylinder and an external
power source is used to provide the needed mechanical motion of the piston.
A bellows pump normally consists of a pumping volume that is formed by two
nondeforming externally driven end plates with a deformable membrane
between the end plates.
The heat loss associated with copper windings and magnetic Losses
from eddy currents contribute to the reduction in the efficiency of
conventional pumps using moving mechanical parts. It would be
advantageous to have a pump which can meet the flow rate and pressure
capabilities of conventional pumps but which suffers less heat loss. A
reduction is size and construction complexity is also desired so that the cost
of manufacturing can be reduced. In addition, a reduction in the number of
moving mechanical parts would reduce wear and contamination and increase
reliability.
Numerous pumps currently exist which utilize piezoelectric devices
rather than the conventional pistons, bellows, etc. The opposing action of
two piezoelectric materials is disclosed in U.S. Pat. Nos. 3,963,380 and
4,842,493. U.S. Pat. No. 3,963,380 to Thomas et al. discloses a micro pump
having a variable volume chamber consisting of one or two commercially
available disk benders fixed to a mounting ring. The disk benders consist of
a thin wafer of piezoelectric material bonded with an epoxy cement to a
slightly larger disk of brass shim stock. When a voltage is applied, the
piezoelectric wafer expands or shrinks in diameter within the plane of the
wafer. Because the circumference of the wafer cannot change diameter due
to the bonding to the brass disk, the resulting motion is that of bulging in
the
center to form a spherical surface. U.S. Pat. No. 4,842,493 to Nilsson
disctoses a piezoelectric pump wherein piezoceramic parts are arranged in a
manner such that the changes in length, width, and height all combine in
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concert to produce the desired pump volume displacement. Since
conventional, small displacement piezoelectric elements are used, a
relatively long pumping channel is needed to provide an adequate pumping
volume which requires a complex assembly of component parts.
It is believed that the concept disclosed in U.S. Pat. No. 4,939,405 to
Okuyama et al. is useful only for pumping against a small fluid pressure
head, i.e., for pumping against very small back-pressure of the fluid to be
pumped. The concept rests on increasing the piezoelectric wafer's modest
amplitude by suspending it on a springy membrane and driving the wafer at
the resonant frequency. The drawback is the small force and hence small
fluid-head capability associated with such a resonant system. The concept
also requires an intricate assembly of component parts.
U.S. Pat. Nos. 4,944,659 and 5,094,594 each use piezoelectric disks
as a deforming means coupled to a deformable chamber wall of the pump.
U.S. Pat. No. 4,944,659 to Abbe et al. is believed to pertain to an
implantable
pump with remotely commendable control logic which delivers relatively small
quantities of fluid against a small fluid pressure head. Pumping action is
provided by a piezoelectric disk affixed to a membrane to curve the
piezoelectric disk. U.S. Pat. No. 5,094,594 to Brennan is believed to pertain
to a pump for use in combination with an electrophoresis unit to supply
accurate highly repeatable picoliter quantities of fluid. The variable volume
chamber contains a thin wafer of piezoelectric material affixed to a larger
disk
of shim stock. The circumference of the wafer cannot change diameter
because it is fixed to the disk; therefore, when a voltage is applied the
resulting motion is that of bulging in the center.
The drawbacks of the existing piezoelectric pumps are their small flow
rate and pressure capabilities. In addition, they usually require an assembly
of bonded component parts. Therefore, a need exists for a new piezoelectric
pump design which produces higher flow rates and higher pressures than
existing piezoelectric pump devices while maintaining reliability, efficiency,
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small size, and low cost. There is also a need for piezoelectric pumps which
do not require an assembly of bonded components. Many markets could
benefit from such pumps. They may have applications in the military and
biomedical areas as well as in ink jet printers and in titration processes.
They
may also be useful as fuel pumps and small feed pumps.
Statemgr~t of the Invention
Accordingly, one object of the invention is to provide a pump which is
smaller in size than existing piezoelectric pumps and which can maintain
equal or greater flow rate and pressure capabilities than existing
piezoelectric
pumps of the same size.
Another object is to provide a pump without moving mechanical parts.
Another object of the invention is to provide a pump which does not
require a complex assembly of bonded components.
A further object of the invention is to provide a pump utilizing one or
more dome shaped internally prestressed ferroelectric actuators, each
actuator having a curvature and a Borne height that varies with an electric
voltage applied between an inside and outside surface of the actuators.
Another object is to provide a pump utilizing one or more dome shaped
internally prestressed ferroelectric actuators, each actuator having a
curvature and a dome height that varies with an electric voltage applied
between an inside and outside surface of the actuator, where each actuator
has a mounting configuration which isolates the ferroelectric actuator from
the pumped medium, supplies a path for voltage to be applied to the
ferroelectric actuator, and positively contains the ferroelectric actuator
while
allowing displacement of the entire ferroelectric actuator in response to the
applied voltage.
Another object of the invention is to provide unidirectional continuous
pumping of both liquids and gases.
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Yet another object is to provide a pump which is capable of cyclical
compression of gases.
Additional objects and advantages of the present invention are
apparent from the drawings and specification which follow.
Summary of the Invention
According to the present invention, the foregoing and other objects
and advantages are attained by providing a ferroelectric pump which utilizes
one or more dome shaped internally prestressed ferroelectric actuators, each
actuator having a curvature and a dome height that varies with electric
voltages applied between an inside and outside surface of the actuator. The
present pump embodies the recognition that ferroelectric devices, which in
the past, were regarded as being only transducers of electrical power into
mechanical motion, can additionally be an integral and in fact principal part
of
the fluid pumping mechanism. The present invention differs from
reciprocating pumps in that the ferroelectric actuator itself performs both
the
functions of piston and cylinder. In addition, the motive mechanical force to
the 'piston', rather than supplied externally, is integrally generated inside
the
ferroelectric device. The present pump also differs from bellows type pumps
in that the end plates as well as the deforming membrane and the mechanical
mover all reside in a single simple part, i.e., the ferroelectric actuator.
The present pump has one or more variable volume pumping
chambers internal to a housing. Each chamber has at least one wall
comprising a dome shaped internally prestressed ferroelectric actuator
having a curvature and a dome height that varies with an electric voltage
applied between an inside and outside surface of the actuator. A pumped
medium flows into and out of each pumping chamber in response to
displacement of the ferroelectric actuator. The ferroelectric actuator is
mounted within each wall and isolates each ferroelectric actuator from the
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pumped medium, supplies a path for voltage to be applied to each
ferroelectric actuator, and provides for positive containment of each
ferroelectric actuator while allowing displacement of the entirety of each
ferroelectric actuator in response to the applied voltage.
Brief Description of the Drawings
A more complete appreciation of the invention and the many of the
attendant advantages thereof will be readily attained as the same becomes
better understood by reference to the following detailed description when
considered in connection with the accompanying drawings, wherein:
FIG. 1 is a diagram of an embodiment of the pump having three
pumping chambers.
FIG. 2 is a single chamber pump with valves.
FIG. 3 is a single chamber pump with a fluidic valve.
FIG. 4 is a diagram representing suitable electronic circuitry for
providing a sinusoidally varying voltage waveform.
FIG. 5 is a diagram representing suitable electronic circuitry for
providing a sinusoidaliy varying voltage waveform at a fixed frequency.
FIG. 6 is an exploded view of the ferroelectric actuator mounting.
FIG. 7 is an electrical contact ring.
Detailed Description of the PreferLed Embodiments
A first embodiment of the invention is illustrated in FIG. 1, which is a
diagram of a three-chamber pump. The pump housing 30 encloses three
pumping chambers 32, 34, and 36. As many pumping chambers as desired
and as few as one may be used. Each pumping chamber has at least one
wall 38 comprising a dome shaped internally prestressed ferroelectric
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actuator 40 having a curvature and a dome height that varies with an electric
voltage applied between an inside and outside surface of the actuator.
Examples of such actuators are shown in U.S. Patent No. 5,471,721, "Method
for Making Monolithic Prestressed Ceramic Devices," hereby incorporated by
reference, and commonly available from Aura Ceramics, and in U.S. Patent
No. 5,632,841, "Thin Layer Composite Unimorph Ferroelectric Driver and
Sensor," also hereby incorporated by reference. Application of an electric
voltage to the ferroelectric actuator causes an electric field between the
faces
of the actuator, and in response the shape of the actuator changes. The
actuator will either flatten or heighten depending on the polarity of the
applied
electric field. This type of ferroelectric actuator inherently exhibits a
favorable
balance between the range of mechanical motion and the range of force it
outputs. The choice of ferroelectric actuator size, along with the applied
voltage and frequency, determines the specific amount of motion and force
produced. This ferroelectric actuator can have strains up to several hundred
percent and can sustain loads of at least ten pounds. The work capacity of
the pump can be increased by using multiple ferroelectric actuators mounted
on a common manifold. Twice as large excursions can be obtained from a
pair of actuators stacked rim against rim in clamshell fashion. Several such
clamshell assemblies can be cascaded if still larger excursions are needed.
Such arrangements are described in U.S. Patent No. 5,471,721, "Method for
Making Monolithic Prestressed Ceramic Devices," and in U.S. Patent No.
5,632,841, "Thin Layer Composite Unimorph Ferroelectric Driver and
Sensor."
The actuator drive voltage can be any waveform, although sinusoidal
is preferable. During positive half-cycle of sinusoidal drive voltage, the
actuators move toward each other. Valves 44 and 46 open and valves 42 and
48 close. Liquid flows into sections 32 and 36 and exits section 34. During
negative half-cycle of sinusoidal drive voltage, the actuators move away from
each other. Valves 44 and 46 now close and valves 42 and 48 open. Liquid
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flows into section 34 and exits sections 32 and 36. The pumped medium
flows from the pumped medium source 54 to each chamber by means of inlet
flow lines 50. One pumped medium supply inlet 52 is connected to the
pumped medium source 54. The chamber supply inlets 50 located at the
entrance to each chamber are interfaced to the supply inlet 52. The pumped
medium exits the chambers by means of outlet flow lines 56. One-way flow
valves 42 and 44 positioned between the supply inlet 52 and chamber inlets
50 allow the pumped medium to enter each pumping chamber in response to
the actuators and also prevent back-flow of the pumped medium. The outlet
is configured similarly to the inlet with chamber discharge outlets 56, a
medium discharge outlet 58 and one-way flow valves 46 and 48. In the
configuration depicted in FIG. 1, the volumes of chambers 32 and 36 are
shown in their decreased state, thus forcing the pumped medium out. Valve
44 prevents back-flow of the medium when the volume of chambers 32 and
36 are being reduced and valve 48 allows the flow from the decreased
chamber volume to exit. The volume of chamber 34 is shown as being
increased, thus bringing flow into the chamber. Valve 42 opens to allow the
pumped medium to enter chamber 34 and valve 46 closes to prevent back-
flow of the pumped medium. There are numerous possible configurations of
pumping chambers and flow valve and pipe arrangements. FIG. 1 is meant
only to be one example of the pump configuration. A single chamber can be
used or multiple chambers greater than three can be used. Either
conventional valves or ferroelectric valves, such as that described in
"Ferroelectric Fluid Flow Control Valve," Patent Cooperation Treaty
application Serial No. , filed April -, 1998, which patent
application is hereby incorporated by reference, can be used. Also, the
valves can be of any suitable configuration; e.g., the inlet and outlet valves
can be located on opposite ends of the chambers or at a single end of the
chambers. A simple single chamber pump is shown in FIG. 2, the operation
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of which generally follows the above three-chamber discussion. The pumped
medium enters at inlet 60 through valve 62 and exits at outlet 70 through
valve 72. Pumping chamber 64 is formed by two ferroelectric actuators 66.
Seals 68 and valves 62 and 72 can be of any suitable configuration. An
orifice 74 can be provided to prevent back pressure on the moving actuators
66. FIG. 3 also shows a single chamber embodiment; however, this
embodiment uses a fluidic valve configuration 76, thereby avoiding any
moving parts. The diameter of port 77 is less than the diameter of valve
outlet 78. Volume 79 is cylindrically shaped. The pumped medium enters
through inlet 75 and then flows into pump chamber 54 through port 77. The
flow of the pumped medium from port 77 out of outlet 78 has a velocity vector
due to entrainment of the flow. Such a velocity vector and entrainment of flow
is not present at inlet 75.
The displacement of each actuator occurs when voltage is supplied to
the actuator. By controlling the amplitude and frequency of this varying
voltage, pumping action and thereby pump flow rates are controlled. Flow
rates can be adjusted over the range of a few per cent of maximum flow to full
flow with great precision. FIG. 4 is a block diagram of suitable electronic
logic for providing a sinusoidally varying voltage waveform. In consists of a
waveform generator 80 which generates the sinusoidal wave shape for pump
operation, a voltage amplifier 82 which raises the voltage and current to
levels required by the actuators and a do power supply 84 which provides do
voltages for the waveform generator 80 and voltage amplifier 82. This circuit
is capable of providing an output sine wave of up to 1000 volts peak-to-peak
in amplitude at 1 Hz to 20 kHz frequency range and several hundred
milliamperes of current. For the waveform generator 80, a dedicated function
generator integrated circuit chip, such as XR2206, with the addition of a few
resistors, capacitors and potentiometers will produce the desired sinusoidal
wave shape which is variable in amplitude from 0 to 6 volts peak-to-peak and
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from 1 Hz to 20 kHz in frequency. This low level sine wave signal is
connected to the input of the fixed gain voltage amplifier 82 which can
provide up to times 200 increase in voltage amplitude. One practical
amplifier design uses two high voltage operational amplifiers connected in a
push-pull configuration which will provide twice the output of a single opamp.
A wide selection of high voltage opamps is available to tailor the circuit for
high voltage output capability at moderate levels of output current or to
provide moderate levels of output voltage at higher output current capability.
The actual requirements of the particular actuator will determine the
selection
of the high voltage opamp. A suitable configuration of a push-pull circuit
using two Apex PA89 opamps, manufactured by Apex Microtechnology
Corporation, with a few external components was easily configured to provide
the required voltage and current to drive the actuators. The do power supply
provides do voltages to the waveform generator 80 and amplifier circuit 82.
The modular power supply provides 12 Vdc to the waveform generator and
amplifier circuit. Two dc-to-do converters step the 12 Vdc to up to +500 and -
500 Vdc which is required by the high voltage opamps in the amplifier circuit.
Another suitable electronic circuit for providing a sinusoidally varying
voltage at a fixed 60 Hz frequency is shown in FIG. 5. It consists of a
variable transformer 90 whose input is connected to any standard 117 vac
wall outlet. The output of the variable transformer 90 is connected to a 1:1
turns ratio isolation transformer 92 for operator safety. The output of the
transformer 92 connects to the remaining two sections of the power supply.
One section is a full wave bridge rectifier 94 containing a filter capacitor
96
for providing a positive do bias at the electronic circuit output. The other
section is a voltage step-up transformer 98 for providing the higher voltage
levels required by the actuators. The output of the step-up transformer 98 is
connected in series with the positive do bias voltage. Through proper
selection of the voltage step-up transformer 98 and by adjustment of the
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variable transformer 90 control, the output voltage of this circuit can
pravide
from 0 to 1000 volts peak-to-peak amplitude. Due to the positive do bias, the
typical maximum output voltage is +600 volts peak and -400 volts peak. It is
an inherent property of the actuators to respond to higher levels of positive
voltage than negative voltage. Thus, for maximum displacement of the
actuators to occur, the positive do bias is utilized.
The actuators are mounted such that the mounting configuration
isolates each actuator from the pumped medium, supplies a path for voltage
to be applied to each actuator, and provides for positive containment of each
actuator while allowing displacement of the entirety of each actuator in
response to an applied voltage. FIG. 6 is an exploded view of one
embodiment of the housing and pump chambers. A nonconductive pump
housing 100 encloses the three pumping chambers 102, 104, and 106. A
wall assembly forms a partition between each chamber. Each wall is formed
by two nonconductive sealing gaskets 108, two electrical insulators 110, two
electrical contact rings 112, an actuator spacer 114, and an actuator 116. It
is preferred that the spacer 114 has the same thickness as the actuator 116.
The actuator 116 is positioned within the spacer 114 such that the
circumference of the actuator 116 is contiguous with the inner circumference
of the spacer 114. An electrical contact ring 112 is positioned contiguous to
each side of the spacers 112 and provides voltage contact to the actuator
116. An electrical insulator 110 is positioned contiguous to the outside
surface of each contact ring 112 and concentric with the actuator 116. The
insulator 110 should be compatible with the pumped medium and possess
some elasticity; e.g. latex. A nonconductive fluid, such as a silicon fluid,
is
used between the insulator 110 and the actuator 116. The fluid should be
chemically stable with the other materials and be of a suitable viscosity to
hold the insulator 110 and actuator 116 together. This eliminates air pockets
which increases efficiency and capability. A sealing gasket 108 having a
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hole concentric with the contact ring 112 hole is positioned contiguous to
each insulator 110. The sealing gasket 108 is made from a nonconductive
material such as rubber. The wall assembly is contained between sections of
the housing by a fastening means such as set screws. The fastening force
required is only the minimum force required to adequately maintain the
assembly. No prestress is required.
The design is not limited to any certain number, thickness or size of
actuators. Each particular application should be considered to design
component parameters; e.g.. amount of actuator displacement and actuator
force capability.
A voltage lead 118 is positioned in the housing 100 via a drilled hole in
the housing 100. The lead 118 contacts a set screw spring 120 positioned in
the housing 100. The set screw 120 contacts the electrical contact ring 112
to provide the applied voltage to the ring 112. The contact ring 112 overlaps
a portion of both the spacer and the actuator. As shown in FIG. 7, the
contact ring 112 has a portion 130 overlapping the actuator which is an
electrical conductor such as aluminum foil. The outer portion 132 of the ring
that is in contact with the actuator is a nonconductive material which has a
conductive portion 134 which contacts the set screw spring. Masking tape is
one example of a suitable nonconductive material. Although circular
actuators and associated circular shaped mounting components are
preferred, other shapes can be utilized.
The positive and negative voltage levels applied to the actuator will
vary with its thickness, with arc over resulting from too much voltage.
The efficiency and capacity of the pump can be improved by using
valves capable of high frequency response. The fluid flow capability will be
several times better if ferroelectric valves, such as described in
"Ferroelectric
Fluid Flow Control Valve," Patent Cooperation Treaty application Serial No.
filed April ~, 1998, which patent application is hereby
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incorporated by reference, are utilized.
In comparison to conventional displacement pumps, the present pump
has improved reliability and lower cost due to the lack of mechanicai moving
parts. The present pump also has improved efficiency over conventional
pumps. The heat loss associated with copper windings as well as magnetic
losses from eddy currents suffered by existing devices is completely absent.
There is also improved reliability, lower cost, less complexity, and smaller
size with respect to existing piezoelectric pumps due the lack of
bonding/assembly of multiple piezoelectric disks. The same force and
displacement can be obtained as is presently possible only with an assembly
of piezoelectric disks. In addition, the mounting configuration allows
displacement of the entirety of each actuator in response the applied voltage.
Obviously, numerous additional modifications and variations of the
present invention are possible in light of above teachings. It is therefore to
be understood that within the scope of the appended claims, the invention
may be practiced otherwise than is specifically described herein.
What is claimed is:
