U.S. patent application number 12/990300 was filed with the patent office on 2011-08-04 for pump powered by a polymer transducer.
Invention is credited to Mohamed Benslimane, Morten Kjaer Hansen, Yousef Iskandarani, Christopher Mose, Benjamin Thomsen, Michael Tryson.
Application Number | 20110189027 12/990300 |
Document ID | / |
Family ID | 40793295 |
Filed Date | 2011-08-04 |
United States Patent
Application |
20110189027 |
Kind Code |
A1 |
Hansen; Morten Kjaer ; et
al. |
August 4, 2011 |
PUMP POWERED BY A POLYMER TRANSDUCER
Abstract
The invention provides a pump with a transducer comprising a
laminate with a film of a dielectric polymer material arranged
between first and second layers of an electrically conductive
material so that it is deflectable in response to an electrical
field applied between the layers, wherein the laminate is arranged
to cause a pumping action upon deflection of the film. The
invention further provides a control system for a pump.
Inventors: |
Hansen; Morten Kjaer;
(Soenderborg, DK) ; Thomsen; Benjamin; (Aabenraa,
DK) ; Tryson; Michael; (Hanover, PA) ;
Benslimane; Mohamed; (Nordborg, DK) ; Iskandarani;
Yousef; (Grimstad, NO) ; Mose; Christopher;
(Soenderborg, DK) |
Family ID: |
40793295 |
Appl. No.: |
12/990300 |
Filed: |
April 30, 2009 |
PCT Filed: |
April 30, 2009 |
PCT NO: |
PCT/DK2009/000098 |
371 Date: |
April 26, 2011 |
Current U.S.
Class: |
417/45 ;
417/412 |
Current CPC
Class: |
F04B 43/046 20130101;
F04B 35/04 20130101; F04B 43/043 20130101; F04B 19/006
20130101 |
Class at
Publication: |
417/45 ;
417/412 |
International
Class: |
F04B 49/06 20060101
F04B049/06; F04B 43/00 20060101 F04B043/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 2008 |
DK |
PA 2008 00619 |
Claims
1-43. (canceled)
44. A fluid pump for displacing a fluid medium from an inlet to an
exit, the pump comprising a housing forming a path between the
inlet and the exit, and a transducer comprising a laminate with a
film of a dielectric polymer material arranged between first and
second layers of an electrically conductive material so that it is
deflectable in response to an electrical field applied between the
layers, wherein the laminate is arranged to cause a pumping action
upon deflection of the film.
45. The pump according to claim 44, wherein the film has a first
surface and an opposite second surface, at least the first surface
comprising a surface pattern of raised and depressed surface
portions
46. The fluid pump according to claim 45, wherein the surface
pattern comprises a super-pattern arises of repeated
sub-patterns.
47. The pump according to claim 44, wherein the laminate comprises
a multilayer structure with at least two composites, each composite
comprising: a film made of a dielectric polymer material and having
a front surface and a rear surface, the front surface comprising a
surface pattern of raised and depressed surface portions, and a
first layer of an electrically conductive material being deposited
onto the surface pattern, the electrically conductive layer having
a corrugated shape which is formed by the surface pattern of the
film.
48. The pump according to claim 47, wherein the transducer is
provided with at least three independent active portions, each
portion being arranged to enable deformation of the body at
different locations along the path.
49. The pump according to claim 44, wherein the laminate is rolled
to form an elongated transducer with axially opposite end faces and
a cylindrically shaped body portion between the end faces.
50. The pump according to claim 49, wherein the rolled laminate
defines a radius of gyration, r.sub.g, given by r g = I A ,
##EQU00003## where I is the area moment of inertia of the rolled
transducer, and r.sub.g may be within the range 5 mm to 100 mm,
such as within the range 10 mm to 75 mm, such as within the range
25 mm to 50 mm.
51. The pump according to claim 49, wherein the rolled laminate may
define a slenderness ratio, .lamda., given by .lamda.=L/r.sub.g,
where L is an axial length of the rolled laminate, and .lamda. may
be smaller than 20, such as smaller than 10.
52. The pump according to claim 44, wherein the first electrically
conductive layer is deposited onto the surface pattern and has a
shape of raised and depressed surface portions which is formed by
the surface pattern.
53. The pump according to claim 44, wherein the raised and
depressed surface portions have a shape which varies periodically
along at least one direction of the first surface.
54. The pump according to claim 44, wherein the raised and
depressed surface portions have a size which varies periodically
along at least one direction of the first surface.
55. The pump according to claim 44, wherein the first electrically
conductive layer has a modulus of elasticity being higher than a
modulus of elasticity of the film.
56. The pump according to claim 44, wherein the film has a
thickness between 90 percent and 110 percent of an average
thickness of the film.
57. The pump according to claim 44, wherein the first electrically
conductive layer has a thickness which is between 90 percent and
110 percent of an average thickness of the first electrically
conductive layer.
58. The pump according to claim 52, wherein the surface pattern
comprises waves forming troughs and crests extending in essentially
one common direction.
59. The pump according to claim 58, wherein each wave defines a
height being a shortest distance between a crest and neighbouring
troughs, an average of the heights of the waves is between 1/3 and
20 .mu.m.
60. The pump according to claim 44, wherein the film has an average
thickness being between 10 and 200 .mu.m.
61. The pump according to claim 44, wherein the first electrically
conductive layer has a thickness in the range of 0.01-0.1
.mu.m.
62. The pump according to claim 52, wherein the second surface is
substantially flat.
63. The pump according to claim 47, wherein at least two adjacent
composites are arranged with the rear surfaces towards each
other.
64. The pump according to claim 47, wherein at least two adjacent
composites are arranged with the front surfaces towards each
other.
65. The pump according to claim 47, wherein at least two adjacent
composites are arranged with the rear surface of one composite
towards the front surface of the other composite.
66. The pump according to claim 47, wherein a section of the path
is formed by a space between the composites.
67. The pump according to claim 44, comprising at least two check
valves arranged in the path to form a pumping space there
between.
68. The pump according to claim 66, wherein the valve structure is
formed by additional layers of an electrically conductive material
on the film of each composite.
69. The pump according to claim 68, wherein the transducer is
formed in such a manner that the laminate, in an unsupported state,
fulfils Euler's criteria for stability within a normal operating
range for the pump.
70. The pump according to claim 44, wherein at least a section of
the path is provided in a body of an elastically deformable
material, the transducer being arranged to deflect the body upon
deflection of the film whereby the path changes volume.
71. The pump according to claim 48, further comprising a control
system adapted to provide subsequent activation of one portion
after another in a sequence which fulfils a pumping action whereby
a fluid is pushed in the path in a flow direction.
72. The pump according to any of claim 71, wherein the body has a
build-in tension which presses the path towards a neutral
configuration from which it can be pushed against the build-in
tension towards an activated configuration by the transducer,
73. The pump according to claim 72, wherein the neutral
configuration provides a lower flow resistance in the path than the
activated configuration.
74. The pump according to claim 72, wherein the neutral
configuration provides a higher flow resistance in the path than
the activated configuration.
75. The pump according to claim 44, wherein the transducer is
arranged outside the path.
76. The pump a according to claim 44, wherein the transducer is
arranged in the path.
77. The pump according to claim 76, wherein the transducer is
arranged to cause a volumetric change of a section of the path upon
deflection of the film.
78. The pump according to claim 49, comprising at least two check
valves arranged on opposite sides of the transducer and providing a
uni-directional flow between the inlet and exit, at least one of
the valve elements being attached to, or forms part of the end
faces.
79. The pump according to claim 78, wherein the cylindrically
shaped body portion is hollow and forms part of the path.
80. The pump according to claim 78, comprising a plurality of
elongated transducers arranged with end portions of adjacent
transducers towards each other in a continuous cylindrical
chamber.
81. The pump according to claim 78, wherein the laminate is rolled
relative to a surface pattern of at least one of the layers so that
the deflection of the film causes radial expansion of the
transducer.
82. The pump according to claim 78, wherein the laminate is rolled
relative to a surface pattern of at least one of the layers so that
the deflection of the film causes axial expansion of the
transducer.
83. The pump according to claim 44, comprising a below with an
internal space, the transducer being arranged to deflect the below
and thus to provide variable volume in the space.
84. The pump according to claim 44, comprising a cylinder forming
part of the path and being provided with two check valves arranged
to cause a uni-directional flow from the inlet through the cylinder
to the exit, and a piston being movable in a cylinder, wherein the
transducer is arranged to move the piston relative to the
cylinder.
85. The pump according to claim 84, wherein the laminate of the
transducer is a plane laminate, and wherein the pump comprises a
control system adapted to drive the transformer with a frequency
corresponding to a resonance frequency of the plane laminate.
86. The pump according to claim 44, and including a control system
adapted to apply a known bias voltage between the layers and
simultaneously to determine a measure which is significant for a
capacitance of the laminate.
87. The pump according to claim 86, wherein the transducer is
arranged to provide deflection of a variable volume chamber.
88. A control system for a pump according to claim 44, the control
system being adapted to apply a known bias voltage between the
layers and simultaneously to determine a capacitance of a laminate
of the pump.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is entitled to the benefit of and
incorporates by reference essential subject matter disclosed in
International Patent Application No. PCT/DK2009/000098 filed on
Apr. 30, 2009 and Danish Patent Application No. PA 2008 00619 filed
on Apr. 30, 2008.
TECHNICAL FIELD
[0002] The present invention relates to a fluid pump for displacing
a fluid medium from an inlet of the pump to an exit of the pump,
the pump comprising a housing forming a path between the inlet and
the exit, and a transducer arranged to cause a pumping action to
move fluid through the path.
BACKGROUND OF THE INVENTION
[0003] Displacement pumps are used in many kinds of medical and
non-medical appliances for pumping and optionally compressing a
fluid medium. For example, pumps have been used to deliver all
kinds of fluid, saline etc to treatment areas etc, pumps have been
used for transporting blood from dialyses machines etc, and outside
the medical sphere, pumps play an important role in numerous
mechanical installations for transporting fluid, for mixing fluid
and not least for compressing fluid, e.g. in combination with
refrigeration systems.
[0004] In a traditional positive displacement pump, a piston is
reciprocating in a cylinder, and by opening and closing inlet and
outlet valves, alternately, a fluid is pumped and optionally
compressed by the piston. The piston and cylinder are made from
relatively inflexible metal materials, and to provide a good
efficiency and long life of the piston pump, the piston and
cylinder must be made with fine tolerances. Typically, a large
portion of the manufacturing costs of such pumps are spent on the
mechanical interaction between the piston, cylinder and other
moving parts. One problem with the traditional piston pumps is that
they may produce excessive noise, in particular if the
reciprocating movement is generated by an eccentric element on a
rotary drive shaft.
SUMMARY OF THE INVENTION
[0005] It is an object of the invention to provide a positive
displacement pump in which the pumping activity is provided in an
alternative way, and thus to provide a potentially more robust and
cost efficient pump. It is a further object to provide a
potentially more silent pump. Accordingly, the invention provides a
pump wherein the transducer comprises a laminate with a film of a
dielectric polymer material arranged between first and second
layers of an electrically conductive material so that it is
deflectable in response to an electrical field applied between the
layers, wherein the laminate is arranged to cause the pumping
action upon deflection of the film.
[0006] Since the pumping action is caused by deflection of a
polymer material, the noise and the need for fine tolerances may be
reduced considerably.
[0007] By a pumping action is meant that a fluid is moved from the
inlet to the exit by the action. Typically the action involves the
process of changing cyclically the volume of a chamber provided
with check valves or similar valves which ensures a uni-directional
flow of the fluid from the inlet to the exit through the
chamber.
[0008] By transducer is hereby meant an element which is capable of
converting electrical energy to mechanical energy and reciprocally
of converting mechanical energy to electrical energy. This enables
the use of the transducer as an actuator which works to move a
fluid through the path when provided with an electrical field
between the first and second layers of electrically conductive
material, and/or the use of the transducer as a sensor which
provides a change of an electrical characteristic, e.g. capacitance
between the layers of electrically conductive material, upon a
change in the flow conditions in the path. Accordingly, the
transducer may provide two-way communication with a control system
whereby the control system operates the transducer to work as an
actuator for moving fluid through the path, and the transducer
provides information to the control system for enabling e.g. a
close loop control based on flow resistance or other
characteristics measurable by deflection of the film of the
transducer.
[0009] The housing may be provided in any kind of material, e.g. in
a hard polymeric material, in metal such as brass or aluminium, or
even in a soft polymeric material such as silicone etc. The pump
may also include micro channels and may e.g. comprise a silicon
wafer etc.
[0010] By deflect is herein meant to bend or to deform under
influence of a pressure. In case of the film, the deflection is
triggered by the pressure from the conductive layers under a force
of attraction or repulsion from an electrical field applied between
the conductive layers.
[0011] By laminate is here meant a product made by two or more
layers of material. As an example, the laminate may comprise a
material with dielectric properties--in the following for
simplicity referred to as a dielectric material. The dielectric
material may be a non conductive polymer or elastomer material. The
electrically conductive material may form an electrode pattern on
each side of the polymer or elastomer. The at least two kinds of
material are bonded e.g. adhesively, by sintering, or simply
arranged in contact with each other.
[0012] The dielectric material could be any material that can
sustain an electric field without conducting an electric current,
such as a material having a relative permittivity, .di-elect cons.,
which is larger than or equal to 2. It could be a polymer, e.g. an
elastomer, such as a silicone elastomer, such as a weak adhesive
silicone or in general a material which has elastomer like
characteristics with respect to elastic deformation. For example,
Elastosil RT 625, Elastosil RT 622, Elastosil RT 601 all three from
Wacker-Chemie could be used as a dielectric material.
[0013] In the present context the term `dielectric material` should
be interpreted in particular but not exclusively to mean a material
having a relative permittivity, .di-elect cons..sub.r, which is
larger than or equal to 2.
[0014] In the case that a dielectric material which is not an
elastomer is used, it should be noted that the dielectric material
should have elastomer-like properties, e.g. in terms of elasticity.
Thus, the dielectric material should be deformable to such an
extent that the composite is capable of deflecting and thereby
pushing and/or pulling due to deformations of the dielectric
material.
[0015] The film and the electrically conductive layers may have a
relatively uniform thickness, e.g. with a largest thickness which
is less than 110 percent of an average thickness of the film, and a
smallest thickness which is at least 90 percent of an average
thickness of the film. Correspondingly, the first electrically
conductive layer may have a largest thickness which is less than
110 percent of an average thickness of the first electrically
conductive layer, and a smallest thickness which is at least 90
percent of an average thickness of the first electrically
conductive layer. In absolute terms, the electrically conductive
layer may have a thickness in the range of 0.01 .mu.m to 0.1 .mu.m,
such as in the range of 0.02 .mu.m to 0.09 .mu.m, such as in the
range of 0.05 .mu.m to 0.07 .mu.m. Thus, the electrically
conductive layer is preferably applied to the film in a very thin
layer. This facilitates good performance and facilitates that the
electrically conductive layer can follow the corrugated pattern of
the surface of the film upon deflection.
[0016] The film may have a thickness between 10 .mu.m and 200
.mu.m, such as between 20 .mu.m and 150 .mu.m, such as between 30
.mu.m and 100 .mu.m, such as between 40 .mu.m and 80 .mu.m. In this
context, the thickness of the film is defined as the shortest
distance from a point on one surface of the film to an intermediate
point located halfway between a crest and a trough on a corrugated
surface of the film.
[0017] The electrically conductive layer may have a resistivity
which is less than 10.sup.-2.OMEGA.cm such as less than
10.sup.-4.OMEGA.cm. By providing an electrically conductive layer
having a very low resistivity the total resistance of the
electrically conductive layer will not become excessive, even if a
very long electrically conductive layer is used. Thereby, the
response time for conversion between mechanical and electrical
energy can be maintained at an acceptable level while allowing a
large surface area of the composite, and thereby obtaining a large
actuation force in the pump. In the prior art, it has not been
possible to provide corrugated electrically conductive layers with
sufficiently low electrical resistance, mainly because it was
necessary to select the material for the prior art electrically
conductive layer with due consideration to other properties of the
material in order to provide the compliance. By the present
invention it is therefore made possible to provide compliant
electrically conductive layers from a material with a very low
resistivity. This allows a large actuation force to be obtained
while an acceptable response time of the transducer is
maintained.
[0018] The electrically conductive layer may preferably be made
from a metal or an electrically conductive alloy, e.g. from a metal
selected from a group consisting of silver, gold and nickel.
Alternatively other suitable metals or electrically conductive
alloys may be chosen. Since metals and electrically conductive
alloys normally have a very low resistivity, the advantages
mentioned above are obtained by making the electrically conductive
layer from metal or from any kind of electrically conductive
material, e.g. with a modulus of elasticity which is higher than
that of the dielectric material--i.e. the electrically conductive
layer may have a higher stiffness in the elastic range than the
dielectric material.
[0019] The dielectric material may have a resistivity which is
larger than 10.sup.10.OMEGA.cm. Preferably, the resistivity of the
dielectric material is much higher than the resistivity of the
electrically conductive layer, preferably at least
10.sup.14-10.sup.18 times higher.
[0020] To facilitate increased compliance of the transducer in one
direction, to facilitate an improved reaction time and therefore an
improved performance and controllability of the pump, or
potentially to provide an increased lifetime of the transducer, the
surface pattern may comprise corrugations which render the length
of the electrically conductive layer in a lengthwise direction
longer than the length of the composite as such in the lengthwise
direction. The corrugated shape of the electrically conductive
layer thereby facilitates that the composite can be stretched in
the lengthwise direction without having to stretch the electrically
conductive layer in that direction, but merely by evening out the
corrugated shape of the electrically conductive layer. According to
the invention, the corrugated shape of the electrically conductive
layer may be a replica of the surface pattern of the film.
[0021] The corrugated pattern may comprise waves forming crests and
troughs extending in one common direction, the waves defining an
anisotropic characteristic facilitating movement in a direction
which is perpendicular to the common direction. According to this
embodiment, the crests and troughs resemble standing waves with
essentially parallel wave fronts. However, the waves are not
necessarily sinusoidal, but could have any suitable shape as long
as crests and troughs are defined. According to this embodiment a
crest (or a trough) will define substantially linear contour-lines,
i.e. lines along a portion of the corrugation with equal height
relative to the composite in general. This at least substantially
linear line will be at least substantially parallel to similar
contour lines formed by other crest and troughs, and the directions
of the at least substantially linear lines define the common
direction. The common direction defined in this manner has the
consequence that anisotropy occurs, and that movement of the
composite in a direction perpendicular to the common direction is
facilitated, i.e. the composite, or at least an electrically
conductive layer arranged on the corrugated surface, is compliant
in a direction perpendicular to the common direction.
[0022] The variations of the raised and depressed surface portions
may be relatively macroscopic and easily detected by the naked eye
of a human being, and they may be the result of a deliberate act by
the manufacturer. The periodic variations may include marks or
imprints caused by one or more joints formed on a roller used for
manufacturing the film. Alternatively or additionally, the periodic
variations may occur on a substantially microscopic scale. In this
case, the periodic variations may be of the order of magnitude of
manufacturing tolerances of the tool, such as a roller, used during
manufacture of the film. Even if it is intended and attempted to
provide a perfect roller, having a perfect pattern, there will in
practice always be small variations in the pattern defined by the
roller due to manufacturing tolerances. Regardless of how small
such variations are, they will cause periodical variations to occur
on a film being produced by repeatedly using the roller. In this
way the film may have two kinds of periodic variations, a first
being the imprinted surface pattern of structures such as
corrugations being shaped perpendicular to the film, this could be
called the sub-pattern of variations, and further due to the
repeated imprinting of the same roller or a negative plate for
imprinting, a super-pattern arises of repeated sub-patterns.
[0023] Manufacturing the film by repeatedly using the same shape
defining element, allows the film to be manufactured in any desired
length, merely by using the shape defining element a number of
times which results in the desired length. Thereby the size of the
composite along a length direction is not limited by the dimensions
of the tools used for the manufacturing process. This is very
advantageous. The film may be produced and stored on a roll, and
afterwards, the film may be unrolled while the electrically
conductive layer or layers are applied to the film.
[0024] Each wave in the corrugated surface may define a height
being a shortest distance between a crest and neighbouring troughs.
In this case, each wave may define a largest wave having a height
of at most 110 percent of an average wave height, and/or each wave
may define a smallest wave having a height of at least 90 percent
of an average wave height. According to this embodiment, variations
in the height of the waves are very small and a very uniform
pattern is obtained.
[0025] According to one embodiment, an average wave height of the
waves may be between 1/3 .mu.m and 20 .mu.m, such as between 1
.mu.m and 15 .mu.m, such as between 2 .mu.m and 10 .mu.m, such as
between 4 .mu.m and 8 .mu.m.
[0026] Alternatively or additionally, the waves may have a
wavelength defined as the shortest distance between two crests, and
the ratio between an average height of the waves and an average
wavelength may be between 1/30 and 2, such as between 1/20 and 1.5,
such as between 1/10 and 1.
[0027] The waves may have an average wavelength in the range of 1
.mu.m to 20 .mu.m, such as in the range of 2 .mu.m to 15 .mu.m,
such as in the range of 5 .mu.m to 10 .mu.m.
[0028] A ratio between an average height of the waves and an
average thickness of the film may be between 1/50 and 1/2, such as
between 1/40 and 1/3, such as between 1/30 and 1/4, such as between
1/20 and 1/5.
[0029] The second electrically conductive layer may, like the first
layer, have a surface pattern, e.g. including a corrugated shape
which could be provided as a replica of a surface pattern of the
film. Alternatively, the second electrically conductive layer is
substantially flat. If the second electrically conductive layer is
flat, the composite will only have compliance on one of its two
surfaces while the second electrically conductive layer tends to
prevent elongation of the other surface. This provides a composite
which bends when an electrical potential is applied across the two
electrically conductive layers.
[0030] One way of making the laminate is by combining several
composites into a multilayer composite with a laminated structure.
Each composite layer may comprise: [0031] a film made of a
dielectric material and having a front surface and rear surface,
the front surface comprising a surface pattern of raised and
depressed surface portions, and [0032] a first electrically
conductive layer being deposited onto the surface pattern, the
electrically conductive layer having a corrugated shape which is
formed by the surface pattern of the film.
[0033] In this structure, an electrode group structure may be
defined, such that every second electrically conductive layer
becomes an electrode of a first group and every each intermediate
electrically conductive layer becomes an electrode of a second
group of electrodes. A potential difference between the electrodes
of the two groups will cause deformation of the film layers located
there between, and the composite is therefore electroactive. In
such a layered configuration, a last layer will remain inactive.
Accordingly, a multilayer composite with three layers comprises 2
active layers, a multilayer composite with 10 layers comprises 9
active layers, etc.
[0034] According to one embodiment, the raised and depressed
surface portions of the surface pattern of the film of each
composite layer may have a shape and/or a size which varies
periodically along at least one direction of the front surface.
This has already been explained above.
[0035] If the electrically conductive layers are deposited on front
surfaces of the films, it may be an advantage to arrange the layers
with the rear surfaces towards each other. In this way, the
multilayer composite becomes less vulnerable to faults in the film.
If the film in one layer has a defect which enables short
circuiting of electrodes on opposite surfaces thereof, it would be
very unlikely if the layer which is arranged with its rear surface
against the film in question has a defect at the same location. In
other words, at least one of the two films provides electrical
separation of the two electrically conductive layers.
[0036] The multilayer composite can be made by arranging the
composite layers in a stack and by applying an electrical potential
difference between each adjacent electrically conductive layer in
the stack so that the layers are biased towards each other while
they are simultaneously flattened out. Due to the physical or
characteristic properties of the film, the above method may bond
the layers together. As an alternative or in addition, the layers
may be bonded by an adhesive arranged between each layer. The
adhesive should preferably be selected not to dampen the compliance
of the multilayer structure. Accordingly, it may be preferred to
select the same material for the film and adhesive, or at least to
select an adhesive with a modulus of elasticity being less than the
modulus of elasticity of the film.
[0037] The composite layers in the multilayer composite should
preferably be identical to ensure a homogeneous deformation of the
multilayer composite throughout all layers, when an electrical
field is applied. Furthermore, it may be an advantage to provide
the corrugated pattern of each layer either in such a way that wave
crests of one layer are adjacent to wave crests of the adjacent
layer or in such a way that wave crests of one layer are adjacent
to troughs of the adjacent layer.
[0038] In one embodiment, the pump is based deformation and thus
volume change of a section of the path. This could e.g. be combined
with valves on opposite sides of that section of the path. As an
example, check valves such as flapper valves may be arranged to
provide uni-directional flow, i.e. flow in one direction through
the path so that repeated volume change of the section causes a
flow of fluid through the path. The section of the path may be
provided in a body of an elastically deformable material, e.g. a
hose of a silicone material, a bellow of a rubber material or in
general of a body having a flexibly deformable wall. The transducer
could be arranged to deflect the body upon deflection of the film
whereby the path changes volume. The transducer could be arranged
either outside the path, inside the path, or it may form part of
the body of an elastically deformable material.
[0039] The transducer may be provided with at least three
independent active portions which can be activated independently
and each portion being arranged to enable deformation of the body
at different locations along the path. In this way, a first portion
being upstream the flow direction may firstly be activated to
squeeze the body and close the path at an upstream first location.
Subsequently, a second portion located between the other two
portions could be activated while the first portion prevents
backflow in the path. The deformation of the body caused by the
second portion will press fluid in the path in the downstream
direction. Subsequently, the last, third, portion could be
activated to prevent backflow in the path while the first and
second portions are released. For this purpose, a control system
may be provided which is adapted to activate the portions in a
predetermined sequence.
[0040] The body may have a build-in tension which presses the path
towards a neutral configuration from which it can be pushed against
the build-in tension towards an activated configuration by the
transducer. The neutral configuration may be a configuration where
the flow resistance in the path is either lower or higher than in
the activated configuration.
[0041] Alternatively, or additionally, the shape of the body is
held by the transducer which actively moves the body between
different deformed states without any support from the body itself.
As an example, the body may comprise a bag of a flexible foil
material, e.g. a plastic bag. In one embodiment, the body is
constituted at least partly by the laminate itself. For this
purpose, the already mentioned composite layers from at least two
of which the laminate is made may form a front and a rear surface
of a bag which constitutes the body.
[0042] According to a preferred embodiment the laminate may have
been rolled to form a coiled pattern of dielectric material and
electrodes. In the following description, a transducer with a
rolled laminate is referred to as a rolled transducer. In the
present context the term `coiled pattern` should be interpreted to
mean that a cross section of the transducer exhibits a flat,
spiral-like pattern of electrodes and dielectric material. Thus,
the rolled transducer resembles a Swiss roll or part of a Swiss
roll.
[0043] According to this embodiment, the transducer is preferably
designed by rolling or spooling a laminate of potentially unlimited
length in a thick-walled column-like self-supporting structure, the
self-supporting structure being sufficiently strong to prevent
buckling during normal operation of the pump.
[0044] The laminate may be rolled around an axially extending axis
to form a transducer of an elongated shape extending in the axial
direction.
[0045] The rolled laminate may form a tubular member. This should
be understood in such a manner that the rolled laminate defines an
outer surface and an inner surface facing a hollow interior cavity
of the rolled laminate. Thus, the transducer in this case forms a
`tube`, but the `tube` may have any suitable shape.
[0046] In the case that the rolled transducer forms a tubular
member, the rolled laminate may form a member of a substantially
cylindrical or cylindrical-like shape. In the present context the
term `cylindrical-like shape` should be interpreted to mean a shape
defining a longitudinal axis, and where a cross section of the
member along a plane which is at least substantially perpendicular
to the longitudinal axis will have a size and a shape which is at
least substantially independent of the position along the
longitudinal axis. Thus, according to this embodiment the cross
section may have an at least substantially circular shape, thereby
defining a tubular member of a substantially cylindrical shape.
However, it is preferred that the cross section has a non-circular
shape, such as an elliptical shape, an oval shape, a rectangular
shape, or even an unsymmetrical shape. A non-circular shape is
preferred because it is desired to change the cross sectional area
of the transducer during operation, while maintaining an at least
substantially constant circumference of the cross section. In the
case that the cross section has a circular shape this is not
possible, since a circular shape with a constant circumference is
not able to change its area. Accordingly, a non-circular shape is
preferred.
[0047] The rolled transducer may define a cross sectional area, A,
being the area of the part of the cross section of the rolled
transducer where the material forming the rolled transducer is
positioned, and A may be within the range 10 mm.sup.2 to 20000
mm.sup.2, such as within the range 50 mm.sup.2 to 2000 mm.sup.2,
such as within the range 75 mm.sup.2 to 1500 mm.sup.2, such as
within the range 100 mm.sup.2 to 1000 mm.sup.2, such as within the
range 200 mm.sup.2 to 700 mm.sup.2. Thus, A may be regarded as the
size of the part of the total cross sectional area of the rolled
transducer, which is `occupied` by the transducer. In other words,
A is the cross sectional area which is delimited on one side by the
outer surface and on the other side by the inner surface facing the
hollow cavity of the rolled structure.
[0048] The rolled laminate may define a radius of gyration,
r.sub.g, given by
r g = I A , ##EQU00001##
where I is the area moment of inertia of the rolled transducer, and
r.sub.g may be within the range 5 mm to 100 mm, such as within the
range 10 mm to 75 mm, such as within the range 25 mm to 50 mm. The
radius of gyration, r.sub.g, reflects a distance from a centre axis
running along the longitudinal axis of the tubular member which, if
the entire cross section of the rolled transducer was located at
that distance from the centre axis, it would result in the same
moment of inertia, I.
[0049] Furthermore, the rolled laminate may define a slenderness
ratio, .lamda., given by .lamda.=L/r.sub.g, where L is an axial
length of the rolled laminate, and A may be smaller than 20, such
as smaller than 10. Thus, the slenderness ratio, .lamda., reflects
the ratio between the axial length of the rolled laminate and the
radius defined above. Accordingly, if .lamda. is high the axial
length is large as compared to the radius, and the rolled laminate
will thereby appear to be a `slender` object. On the other hand, if
.lamda. is low the length is small as compared to the radius, and
the rolled transducer will thereby appear to be a `fat` object,
hence the term `slenderness ratio`. An object having a low
slenderness ratio tends to exhibit more stiffness than an object
having a high slenderness ratio. Accordingly, in a rolled laminate
having a low slenderness ratio buckling during actuation is
avoided, or at least reduced considerably.
[0050] The rolled laminate may define a wall thickness, t, and the
ratio t/r.sub.g may be within the range 1/1000 to 2, such as within
the range 1/500-1, such as within the range 1/300-2/3. This ratio
reflects how thin or thick the wall defined by the rolled laminate
is as compared to the total size of the rolled laminate. If the
ratio is high the wall thickness is large, and the hollow cavity
defined by the rolled transducer is relatively small. On the other
hand, if the ratio is low the wall thickness is small, and the
hollow cavity defined by the rolled laminate is relatively
large.
[0051] Alternatively or additionally, the rolled laminate may have
a wall thickness, t, and may comprise a number of windings, n,
being in the range of 5 to 100 windings per mm wall thickness, such
as in the range 10 to 50 windings per mm wall thickness. The larger
this number is, the thinner the unrolled laminate has to be. A
large number of windings of a thin film allows a given actuation
force to be achieved with a lower potential difference between the
electrodes as compared to similar transducers having a smaller
number of windings of a thicker film, i.e. having the same or a
similar cross sectional area. This is a great advantage.
[0052] The mechanical and electrostatic properties of an
electroactive web are used as a basis to estimate actuator force
per unit area and stroke. Rolled laminates as described above are
made by rolling/spooling very thin composite layers, e.g. having a
thickness within the micrometers range. A typical transducer of
this type can be made of laminate which is wound in thousands of
windings.
[0053] When activated, direct/push transducers convert electrical
energy into mechanical energy. Part of this energy is stored in the
form of potential energy in the transducer material and is
available again for use when the transducer is discharged. The
remaining part of mechanical energy is effectively available for
actuation. Complete conversion of this remaining part of the
mechanical energy into actuation energy is only possible if the
transducer structure is reinforced against mechanical
instabilities, such as well known buckling due to axial
compression. This can be done by reinforcing the cross sectional
area of the transducer on one hand and then optimising the length
of the transducer according to Euler's theory.
[0054] The optimisation process starts by defining the level of
force required for a given pump. Then based on the actuator force
per unit area, it is possible to estimate the necessary cross
sectional area to reach that level of force.
[0055] Stabilisation of the transducer against any mechanical
instability requires reinforcing its cross section by increasing
its area moment of inertia of the cross section, I. Low values of I
result in less stable structures and high values of I result in
very stable structures against buckling. The design parameter for
reinforcing the structure is the radius of gyration
r g ( r g = I A ) ##EQU00002##
which relates cross section, A, and area moment of inertia, I. Low
values of r.sub.g result in less stable transducer structures and
high values of r.sub.g result in highly stable transducer
structures. After having defined optimum ranges for both area, A,
and radius of gyration, r.sub.g, it is possible to define the
optimum range for the rolled transducer wall thickness, t, with
respect to r.sub.g in the form of t/r.sub.g. Area, A, radius,
r.sub.g, and wall thickness, t, are the design parameters for
reinforcing the transducer cross section for maximum stability. Low
values of t/r.sub.g result in highly stable transducer structures
and high values of t/r.sub.g result in less stable transducer
structures.
[0056] Once the ranges of the cross section parameters have been
determined, it is necessary to estimate the maximum length, L, of
the transducer, for which buckling by axial compression does not
occur for the required level of force. Slenderness ratio, .lamda.,
as defined above, is the commonly used parameter in relation with
Euler's theory. Low values of .lamda. result in highly stable
transducer structures and high values of .lamda. result in less
stable transducer structures against buckling.
[0057] Once all design parameters for the optimum working direct
transducer have been determined, it is possible to estimate the
total number of windings that are necessary to build the transducer
based on the transducer wall thickness, t, and the number of
windings per millimeter, n, for a given electroactive web with a
specific thickness in the micrometer range.
[0058] The rolled transducer may comprise a centre rod arranged in
such a manner that the transducer is rolled around the centre rod,
the centre rod having a modulus of elasticity which is lower than a
modulus of elasticity of the dielectric material. According to this
embodiment the hollow cavity defined by the tubular member may be
filled by the centre rod, or the centre rod may be hollow, i.e. it
may have a tubular structure. The centre rod may support the rolled
transducer. However, it is important that the modulus of elasticity
of the centre rod is lower than the modulus of elasticity of the
dielectric material in order to prevent that the centre rod
inhibits the function of the transducer.
[0059] Alternatively or additionally, the rolled transducer may
comprise a centre rod arranged in such a manner that the transducer
is rolled around the centre rod, and the centre rod may have an
outer surface abutting the rolled transducer, said outer surface
having a friction which allows the rolled transducer to slide along
said outer surface during actuation of the transducer. The centre
rod could, in this case, e.g. be a spring. Since the rolled
transducer is allowed to slide along the outer surface of the
centre rod, the presence of the centre rod will not inhibit
elongation of the transducer along a longitudinal direction defined
by the centre rod, and the operation of the transducer will thereby
not be inhibited by the presence of the centre rod due to the low
friction characteristics of the centre rod.
[0060] The transducer which comprises a rolled laminate may have an
area moment of inertia of the cross section which is at least 50
times an area moment of inertia of the cross section of an
un-rolled transducer, such as at least 75 times, such as at least
100 times. According to the present invention, this increased area
moment of inertia is preferably obtained by rolling the transducer
with a sufficient number of windings to achieve the desired area
moment of inertia of the rolled structure. Thus, even though the
unrolled transducer is preferably very thin, and therefore must be
expected to have a very low area moment of inertia, a desired area
moment of inertia of the rolled transducer can be obtained simply
by rolling the transducer with a sufficient number of windings. The
area moment of inertia of the rolled transducer should preferably
be sufficient to prevent buckling of the transducer during normal
operation.
[0061] Thus, the rolled transducer may have a number of windings
sufficient to achieve an area moment of inertia of the cross
section of the rolled transducer which is at least 50 times an
average of an area moment of inertia of the cross section of an
un-rolled transducer, such as at least 75 times, such as at least
100 times.
[0062] According to one embodiment, positive and negative
electrodes may be arranged on the same surface of the dielectric
material in a pattern, and the transducer may be formed by rolling
the dielectric material having the electrodes arranged thereon in
such a manner that the rolled transducer defines layers where, in
each layer, a positive electrode is arranged opposite a negative
electrode with dielectric material there between. According to this
embodiment the transducer may preferably be manufactured by
providing a long film of dielectric material and depositing the
electrodes on one surface of the film. The electrodes may, e.g., be
arranged in an alternating manner along a longitudinal direction of
the long film. The long film may then be rolled in such a manner
that a part of the film having a positive electrode positioned
thereon will be arranged adjacent to a part of the film belonging
to an immediately previous winding and having a negative electrode
thereon. Thereby the positive and the negative electrodes will be
arranged opposite each other with a part of the dielectric film
there between. Accordingly, a transducer is formed when the film is
rolled.
[0063] The laminate may e.g. be rolled relative to a surface
pattern of at least one of the layers so that the deformation of
the film causes radial expansion of the transducer. This could be
obtained with a pattern of corrugations extending parallel to an
axis around which the laminate is rolled. Alternatively, the
laminate could be rolled relative to a surface pattern of at least
one of the layers so that the deformation of the film causes axial
expansion of the transducer and thus variable distance between
axially opposite end faces of the transducer. This could be
obtained with a pattern of corrugations extending perpendicularly
to the axis around which the laminate is rolled so that the crests
and chests of the corrugations extend circumferentially around the
transducer.
[0064] If the laminate is rolled to form a cylindrically shaped
body portion which is hollow, then the rolled laminate may itself
form at least a part of the path.
[0065] The pump may comprise at least one, and optionally a
plurality of rolled transducers provided for axial elongation and
arranged in a cylindrical chamber with end portions moving as
pistons in the chamber. If a plurality of rolled transducers is
provided in this way, they may be arranged with end faces of
adjacent transducers towards each other forming a continuous row of
transducers in a continuous cylindrical chamber.
[0066] The transducers may e.g. be fixed to the wall of the chamber
at a location between the end portions. When the transducers are
actuated, they expand axially and thus reduce volumes of spaces
provided between adjacent transducers. When the transducers
contract axially, the volumes of the spaces between adjacent
transducers increase. Additional spaces may be provided between the
end faces of each of the transducers--i.e. between an outer surface
of the rolled laminate and an inner surface of the cylindrical
chamber or in inner cavities within the rolled transducers. When
the transducers contract or expand simultaneously, the volumes of
these additional spaces increase or decrease in a reverse order
relative to the spaces between the transducers. By providing a set
of check valves or valves having a similar uni-directional function
at each end of the spaces, a pumping action may be obtained during
simultaneous actuation of all transducers in the cylinder.
[0067] In an non-rolled embodiment of the pump, the transducer
comprises a plane sheet of the laminate, and the pump comprises a
control system adapted to drive the transformer with a frequency
corresponding to a resonance frequency of the plane laminate so
that vibration of the laminate can be obtained with a relatively
large amplitude of the movement with a low energy supply. One or
more variable volume chambers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0068] Preferred embodiments of the invention will now be described
in further details with reference to the drawing in which:
[0069] FIGS. 1 and 2 illustrate two different pump structures
according to the invention;
[0070] FIG. 3 illustrates a laminate for a transducer;
[0071] FIGS. 4 and 5 illustrate rolling of the laminate for
elongation and expansion, respectively;
[0072] FIG. 6 illustrates an alternative way of making a rolled
transducer by stacking of two composite structures;
[0073] FIGS. 7-26 illustrate various alternative pumps; and
[0074] FIG. 27 illustrates an electrical diagram of a control
system for controlling the pumps.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0075] FIG. 1 illustrates a pump 1, comprising a housing 2 with an
internally arranged fixed spindle 3 with a screw thread structure
of a helix shaped fin 4 on an outer surface. The housing forms an
inlet 5 for entering fluid into the pump, and an exit 6 for exit of
the fluid from the pump. A path extends from the inlet to the exit
between an inner surface 7 of the housing and an outer surface 8 of
the spindle. The housing is made from an elastically deformable
material, and transducers 9 are attached to an outer surface to
cause deflection of the housing. FIGS. 1c and 1d illustrate two
differently deflected states of the housing, and FIGS. 1e, 1f and
1g illustrate a sequence of deflections around the fixed spindle 3.
The sequential deflection around the spindle causes movement of a
fluid, guided by the spindle, from the inlet 5 to the exit 6.
[0076] Each transducer 9 is made from a laminate with a film of a
dielectric polymer material arranged between first and second
layers of an electrically conductive material so that it is
elastically deformable in response to an electrical field applied
between the layers. The laminate is rolled, stacked or folded.
[0077] FIG. 2 illustrates an alternative pump with a hose 10 which
is deformable by application of a pressure, and a plurality of
transducers 11 arranged around the hose to deform the pressure. A
pumping effect may be provided by an activation sequence where the
transducers are activated by turns to provide a flow from the inlet
12 to the exit 13, c.f. also FIG. 7.
[0078] The laminate is provided so that it is easier to deform in
one, compliant, direction than in other directions. The laminate is
further provided with an anisotropic characteristic so that it is
less compliant in one specific direction than in other directions.
As illustrated in FIG. 3, this characteristic can be provided by a
waved surface structure by which the laminate can be expanded in
the compliant, longitudinal, direction indicated by the bold arrows
14, 15 by elastic deformation of the polymer material 16, while the
electrically conductive material which is applied to the waved
surface is straightened out rather than stretched.
[0079] By selection of a conductive material which requires a
larger force to deform elastically than that required to deform the
polymer material, and by application of the conductive material
throughout the transverse direction indicated by the bold arrows
17, 18, i.e. parallel to the direction in which the crests and
troughs of the waves extend, the laminate becomes anisotropic. By
anisotropic is meant that the laminate is compliant in the
longitudinal direction and non-compliant in the transverse
direction.
[0080] The laminate structure illustrated in FIG. 3 is rolled to
form a tubular actuator. The laminate may be rolled around an axis
extending in parallel with the crests and troughs as shown in FIG.
4. This provides radial expansion of the tubular actuator upon
deformation of the polymer--herein referred to as "rolled for
expansion". The laminate may also be rolled around an axis being
perpendicular to the crests and troughs as shown in FIG. 5. This
provides axial elongation of the tubular actuator upon deformation
of the polymer--herein referred to as "rolled for elongation". When
the laminate is rolled, the two opposite layers of a conductive
material, in the following referred to as the top and bottom layer,
must be electrically separated from each other by an additional
film of a non conductive material.
[0081] FIG. 6 illustrates a laminate which is rolled to form a
tubular structure and which comprises a multilayer structure with
at least two composites. The composites are identical and each
comprises a film 19 made of a dielectric polymer material and
having a front surface and a rear surface, the front surface
comprising a surface pattern of raised and depressed surface
portions, and a first layer 20 of an electrically conductive
material being deposited onto the surface pattern. When such two
composites are arranged on top of each other, a laminate with a
film of a polymer material between two electrically conductive
layers is formed. The second film provides isolation between the
top and bottom layers. The composites may be arranged, as shown,
with front surface of one composite against a rear surface of an
adjacent composite. Alternatively, the composites may be arranged
with rear surfaces against each other to form a laminate of two
films against each other and two electrically conductive layers
forming outer surfaces on opposite sides of the two films.
[0082] The transducers in FIG. 2 are each made from a laminate
which is rolled for elongation. The axial end portions of the
rolled laminate are subsequently joined to form a torus shape. FIG.
7 further illustrates the sequence and principle of this pump.
[0083] FIGS. 8a and 8b illustrate a pump with a tube 20 and a row
of transducers 21. The transducers are each made from a laminate
which is rolled for elongation, and one of the axial end portions
thereof are arranged towards the tube 20 to deform the tube 20
either by direct contact therewith or via a pressure element
arranged between the axial end of the rolled laminate and the outer
surface of the tube (not shown). FIGS. 8a-8c illustrate that the
pump has a structure whereby it only works against a dynamic
pressure of the fluid which is pumped in the tube 20. The static
pressure difference between the lowest pressure in the tube and the
pressure outside the tube can be neglected when considering the
force by which the transducers 21 must act on the tube.
[0084] FIG. 9 illustrates a check-valve element 22 which is
inserted in the tube 20 in FIGS. 8a-8c or in the hose 10 in FIG.
2.
[0085] FIG. 10 illustrates an alternative design of the pump in
which sections of a passive hose 24 are arranged alternating
sections of an active hose. The active hose sections comprise a
laminate of the previously mentioned kind and thus constitute
transducers for the pump. The laminate is rolled for elongation so
that radial contraction and expansion is possible in the active
sections, and by a suitable activation sequence, a fluid can be
displaced through the hose 24, 25 from the inlet 26 to the exit 27
as shown in FIG. 11.
[0086] FIG. 12 illustrates a pump with a housing 28 and two
transducers comprising displacement members 29, 30 movable into and
out of the passage 31 by use of the laminates 32, 33 which are
rolled for elongation. The pump comprises two check valves 34, 35
arranged on opposite sides of the transducers in the flow
direction--indicated by the bold arrow.
[0087] FIGS. 13a-13c illustrate an alternative embodiment of a pump
according to the invention. The pump 36 comprises a number of
composites 37, 38 each having three conductive layers 39, 40 and
41. A cavity 42 is formed between the two composites 37, 38 and by
repulsion or contraction of the composites away from each other or
towards each other, the volume of the cavity 42 can be changed. A
bias voltage may initially be provided to the conductive layers 39
whereby the upper part of the composites are biased towards each
other while a liquid enters the inlet 43. Subsequently, the bias
voltage between the conductive layers 39 is removed and a bias
voltage is applied to the conductive layers 41. This closes the
inlet 43 and a bias voltage can be applied to the conductive layers
40 whereby the mid sections of the composites are biased towards
each other and the volume of the cavity 42 is reduced. The fluid in
the cavity is therefore pumped out of the chamber through the exit
44.
[0088] FIG. 14 illustrates a pump with a housing 45 forming a
chamber 46 with a check valve 47, 48 in opposite ends. A transducer
49 formed by a laminate which is rolled for either expansion or
elongation is arranged in the chamber 46 so that the free volume in
the chamber can be changed cyclically and so that a fluid is pumped
through the chamber from the inlet 50 to the exit 51. FIG. 15
illustrates the pump structure in FIG. 14 where the chamber is in a
"heart" shape.
[0089] FIGS. 16-17 illustrate a pump with a housing 52 having a
slot 53 forming a chamber 54 extending between an inlet 55 and an
exit 56. The housing is deformed by use of the transducers 57, 58
which comprises a laminate rolled for elongation. The housing 52
further comprises a number of cavities or a through going bore
which makes the housing more easily deflected. Check valves may be
located in opposite ends of the chamber 54 to ensure that the flow
is in one direction only.
[0090] FIG. 18 illustrates schematically a pump with a housing 59
forming a passage 60 between two check valves 61, 62. A
spring-structure coil 63 is arranged in the passage. The coil is
made from an elongated element which is constituted by a laminate
rolled for elongation. During elongation or contraction of the
laminate, the coil opens up and thus increases the size of the
space 64 between the windings, or closes down and decreases a space
between the windings, whereby a pumping action is provided in the
passage. FIG. 19 illustrates the same pump without the check
valves. In this case, the pumping action is provided by the
geometry of the passage or the coiled laminate by which shape the
fluid is pushed in a pumping direction by contraction of the rolled
laminate.
[0091] FIGS. 20-22 illustrate a pump with a housing with a tube 65,
a transducer 66 comprising a laminate rolled around the tube for
expansion and contraction, and check valves 67, 68.
[0092] FIG. 23 illustrates a pump with a housing 69 with an inlet
70 and an exit 71 the inlet and exit are provided with a check
valve which is not shown in FIG. 23. The check valves provide
uni-directional flow from the inlet to the exit. The pump comprises
a bellow 72 forming a chamber 73 with variable volume. The
transducers 74, 75 are arranged to move a top wall 76 of the
chamber 73 and thus cause changes to the volume of the chamber.
Each transducer comprises a laminate which is rolled for
elongation.
[0093] FIG. 24 illustrates a pump with a housing 77 forming a
chamber 78 with an inlet 79 and an exit 80. The inlet and exit are
provided with check valves 81, 82 providing a uni-directional flow
from the inlet to the exit. The transducer 83 comprises a laminate
which is rolled for expansion and moves back and forth in the
chamber 78 as a piston in a cylinder and thus causes a variable
volume of the chamber 78 and thus provides a pumping effect. FIG.
25 illustrates the pumping effect where the hatched areas
represents filling of the chamber 78 and the non-hatched areas
represent emptying of the chamber 78. Time is along the X-axis and
the position of the end face 84 of the transducer 83 is along the
Y-axis.
[0094] FIG. 26 illustrates a pump with a laminate 85 forming a
transducer of the pump. The laminate moves one, and possibly two
pistons 86, 87 which moves in corresponding cylinders 88, 89 and
thereby forms variable volume chambers 90, 91. Inlets and outlets
92, 93, 94, 95 with check valves 96, 97, 98, 99 provide a
uni-directional flow through the chamber during the pumping
activity. A spring-force structure, e.g. in the form of a helically
coiled spring 100 can be arranged to adjust the characteristics of
the pump.
[0095] FIG. 27 illustrates an electrical diagram of a control
system for controlling operation of a pump. The control system is
particularly suitable in combination with a displacement pump of
the kind where the pumping is effected by deflection of a chamber
with a variable volume--i.e. when the chamber is deflected in one
direction, the volume increases and the chamber is filled with a
fluid and when the chamber is deflected in another direction the
volume decreases and the fluid is displaced out of the chamber.
[0096] The control system is based on the fact that the laminate
has a capacitor structure where the capacitance is indicative of
the distance between the first and second layers, and thereby
indicative of a degree of deflection of the film.
[0097] By determining the capacitance of the laminate, the control
system is able to determine a pressure difference over the pump,
and if the pump is a displacement pump, it may also be able to
determine a degree of displacement in a variable volume chamber of
the pump. This feature may e.g. be utilized for dosage purposes,
where the pump according to the invention can provide a relatively
precise dose of a fluid by determining a degree of deflection of
the film and thus a degree of compression of the variable volume
chamber.
[0098] In the following description, the wording "bias voltage"
describes a voltage which is applied between the first and second
layers to deflect the film, and "measuring voltage" describes a
voltage which is applied to determine capacitance of the
laminate.
[0099] The control system according to the invention is capable of
applying a known bias voltage between the layers and simultaneously
to determine the capacitance of the laminate. According to a
reference characteristic for the pump, the applied bias voltage
should provide a theoretical deflection of the film and thus a
theoretical volume change of a displacement pump. By measuring the
capacitance while the bias voltage is applied, the control system
is capable of deriving an actually obtained deflection of the film
and thus an actually obtained displacement of a fluid out of a
chamber with variably volume.
[0100] The control system comprises data storage capacity 101 in
which a ratio between displacement of a fluid out of a chamber
versus actuator capacitance is specified. In a most simple
embodiment, the ratio is stored as discrete values. A computing
device 102 communicates with the data storage 101 and determines
based on a dose of fluid to be displaced by the pump, a theoretical
bias voltage 103 by which the film is theoretically deflected to
cause the desired volume change of the chamber. The computing
device communicates the theoretical bias voltage to an error
correction device 104 from which the bias source 105 receives input
for setting a high voltage bias signal to the transducer 106. The
actuating device 106 comprises a laminate of the kind already
described, and in the diagram, such a laminate corresponds to a
capacitor.
[0101] In addition to the bias signal, the bias source 105
provides, via the connection 107, a low voltage test signal which
is applied to the laminate simultaneously with the bias signal. The
filter 108 extracts the low voltage signal from the high voltage
signal, and the capacitance measuring device 109 determines the
actual capacitance of the transducer 106.
[0102] The capacitance is determined while the film is deflected by
the high voltage bias signal and therefore, the capacitance
indicates how much the film was deflected by the bias signal. In
the illustrated embodiment, the capacitance is converted into
feedback signal 110, in this case in form of a comparative bias
voltage, i.e. a bias voltage which, with the reference
characteristics of the pump, would have provided that deflection of
the film which actually occurred and which was determined by
measuring of the capacitance. The comparative bias voltage is
subtracted from the determined bias voltage in the correction
device 104 and the resulting corrected bias voltage 111 is received
by the bias source 105.
[0103] In general, the feedback signal 110 can be manipulated in
various ways via amplifies and converters of different kind.
[0104] The capacitance measuring device may also be implemented in
a regular computer system, and it may include, without being
limited to, any of the following measuring principles: AC Power, AC
Voltage, RMS Power, Peak detectors, Log detectors, RSSI, Impedance,
Pulse Measuring circuit or Spectral Measuring circuit.
[0105] The setting voltage that provides the high voltage bias
signal to the actuator is typically greater than 300 Volts and less
than 10 kV. An example would be 500 to 2.5 kV. The Low voltage test
signal would typically be between 1 and 10 V, an example would be 3
to 5V. The High voltage actuator control signal is typically DC to
low frequency less than 1 KHz repetition rate, an example would be
50 Hz. The AC test signal is generally at a frequency rate
considerably higher than the actuator, usually by a factor of 10
away from the actuator repetition rate. An actuator with a 2.5 kV
signal, with a 10 Hz repetition rate, could have an AC test signal
of 5V and 1 KHz repetition rate.
[0106] The data processing structure may further be adapted to use
the determined deflection of the variable volume chamber to provide
flow specific information. Such information may be based on
information in a second data file which describes a ratio between
the deflection of the variable volume chamber and a pressure drop
over the pump, flow speed for a specific fluid through the pump
etc.
[0107] Furthermore, the control system may be adapted to control
the pump for dosing purposes. As an example, the control system may
be capable of reading a user request with respect to the flow. As
an example, this may be a desired pressure drop, a desired flow
speed, or a desired dose of a fluid medium which is released
through the pump. Based on the request, the control system applies
a bias voltage to the first and second electrically conductive
layers while the capacitance is measured. In this way the
deflection of the variable volume chamber is determined and by use
of the data in the first and second data files, the request may be
fulfilled.
[0108] While the present invention has been illustrated and
described with respect to a particular embodiment thereof, it
should be appreciated by those of ordinary skill in the art that
various modifications to this invention may be made without
departing from the spirit and scope of the present.
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