U.S. patent application number 09/832594 was filed with the patent office on 2001-08-09 for shape memory alloy actuated fluid control valve.
Invention is credited to Antonio, Hines, Gausman, Theodore J., Glime, William H., Hill, Steven H., Rigsby, Bruce S..
Application Number | 20010011414 09/832594 |
Document ID | / |
Family ID | 23713041 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010011414 |
Kind Code |
A1 |
Antonio, Hines ; et
al. |
August 9, 2001 |
Shape memory alloy actuated fluid control valve
Abstract
A fluid control valve having a shaped memory alloy (SMA) driven
actuator is disclosed. The SMA driven actuator includes a first
frame section coupled to a valve body and fixed in relation
thereto, a second frame section coupled to a movable element of the
valve body and movable in relation to the valve body, and a
mulitiplicity of SMA wire sections coupling the first and second
frame sections for moving the movable element from a biased first
position to a second position when heated. An electrical controller
controls the heating of the SMA wire sections by regulating current
therethrough, preferably using pulse width modulation techniques.
The electrical controller may be governed by a position measurement
signal proportional to the position of the movable element to
regulate current to the SMA drive element to position the movable
element to a desired position. The position measuring signal may be
provided from a position measuring element integral to the valve
actuator. The valve actuator may also include a temperature
controller governed by an electrical temperature signal provided by
a temperature-sensing means in proximity to the SMA drive element
to activate a cooling device for reducing the temperature
surrounding the SMA drive element when activated. A digital
selector switch may be used for generating a digital code of a
selected heating rate which may govern the electrical controller to
regulate current to the SMA drive element. The electrical
controller may also be governed by both a position measurement and
a temperature signal to regulate current to the SMA drive element
and to control the cooling device to position the movable element
to a desired position. The actuator may include at least one bobbin
that is wound with a multiplicity of wire windings. A conductive
material may be applied to the surface of grooved sections of the
bobbin onto which the SMA wire windings are wound. Alternatively,
the SMA wire may be coated with a conductive material and then
wound about the bobbin and thereafter, the conductive material may
be removed from the surface of the SMA wire not in contact with the
bobbin.
Inventors: |
Antonio, Hines; (Tampa,
FL) ; Gausman, Theodore J.; (Concord, OH) ;
Glime, William H.; (Painesville, OH) ; Hill, Steven
H.; (Nanaimo, CA) ; Rigsby, Bruce S.;
(Charlestown, IN) |
Correspondence
Address: |
CALFEE HALTER & GRISWOLD, LLP
800 SUPERIOR AVENUE
SUITE 1400
CLEVELAND
OH
44114
US
|
Family ID: |
23713041 |
Appl. No.: |
09/832594 |
Filed: |
April 11, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09832594 |
Apr 11, 2001 |
|
|
|
09431694 |
Nov 1, 1999 |
|
|
|
6247678 |
|
|
|
|
Current U.S.
Class: |
29/605 ;
29/847 |
Current CPC
Class: |
F16K 31/025 20130101;
Y10T 29/49071 20150115; F16K 31/002 20130101; Y10T 29/49156
20150115; F03G 7/065 20130101 |
Class at
Publication: |
29/605 ;
29/847 |
International
Class: |
H01F 007/06 |
Claims
What is claimed is:
1. A fluid control valve having a shape memory alloy (SMA) driven
actuator, said valve comprising: a valve body for flowing fluid
from an inlet port to an outlet port therethrough, said valve body
including a movable element positionable in relation to the valve
body to control fluid flow through the valve body; a bias means for
forcing the movable element to a first position; a valve actuator
including a first frame section coupled to said valve body and
fixed in relation to said valve body; a second frame section
coupled to said movable element and movable in relation to said
valve body; and a multiplicity of SMA wire sections coupled between
said first and second frame sections for moving said movable
element from said biased first position to a second position when
heated.
2. The fluid control valve of claim 1 wherein the bias means
includes a spring that forces the movable element to a closed
position to prevent fluid flow through the valve body.
3. The fluid control valve of claim 1 including a first bobbin
element coupled to the first frame section and a second bobbin
element coupled to the second frame section; and wherein the
multiplicity of SMA wire sections comprise a single SMA wire wound
a multiplicity of times about the first and second bobbin
elements.
4. The fluid control valve of claim 3 wherein the first and second
bobbin elements comprise an insulating material for electrically
isolating the SMA wire windings.
5. The fluid control valve of claim 4 wherein the insulating
material comprises polyphenylene sulfide.
6. The fluid control valve of claim 3 wherein the first and second
bobbin elements comprises grooves for accepting the SMA wire
windings.
7. The fluid control valve of claim 6 wherein the SMA wire windings
in contact with the surface of the grooved areas of the first and
second bobbin elements are electrically bypassed with an
electrically conductive material.
8. The fluid control valve of claim 3 wherein the first and second
bobbin elements are cylindrical in shape.
9. The fluid control valve of claim 3 wherein the first and second
bobbin elements include flat surfaces oppositely disposed from each
other and moveable in relation to one another when the SMA wire is
heated, said flat surfaces including a conductive material forming
an integral capacitive element for measuring the position of the
movable element.
10. The fluid control valve of claim 3 wherein the ratio of the
winding radius of the first and second bobbin elements and the
diameter of the SMA wire is substantially less than 50:1.
11. The fluid control valve of claim 3 wherein the ends of the SMA
wire are terminated at a bobbin element at an inactive region of
the wire providing a restraint to strain when the wire is
heated.
12. The fluid control valve of claim 11 wherein each end of the SMA
wire is disposed through a hole in a bobbin section and wedged into
place to form a restraint to strain.
13. The fluid control valve of claim 1 wherein the first frame
section is supported from the valve body by at least one guiding
element; and wherein the second frame section is supported in
relation to the first frame section by the multiplicity of SMA wire
sections and is guided through its movement by the guiding
element.
14. The fluid control valve of claim 13 wherein the second frame
section is guided through its movement along the outside of the
first frame section.
15. The fluid control valve of claim 13 wherein the second frame
section is guided through its movement along the inside of the
first frame section.
16. The fluid control valve of claim 1 wherein the first and second
frame sections include substantially flat surfaces of conducting
material oppositely disposed from one another and insulated from
their respective frame sections to form an integral capacitive
element, the capacitance of which changing in proportion to the
position of the movable element.
17. The fluid control valve of claim 1 including a housing for
enclosing the valve actuator, said housing including openings for
allowing air to flow through the valve actuator.
18. The fluid control valve of claim 1 including an electrical
controller for controlling the heating of the SMA wire sections by
regulating current therethrough.
19. The fluid control valve of claim 18 wherein the electrical
controller includes a temperature control means comprising:
temperature sensing means disposed in proximity to the SMA wire
sections to measure temperature and generate an electrical
temperature signal representative thereof; cooling means for
reducing the temperature surrounding the SMA wire sections when
activated; and temperature controller governed by said electrical
temperature signal for activating said cooling means.
20. The fluid control valve of claim 19 wherein the cooling means
includes a means for forcing air around the SMA wire sections.
21. The fluid control valve of claim 19 wherein the cooling means
is selected from the group consisting of a rotary fan, a Piezo-fan
cooling device, and a Peltier cooling device.
22. The fluid control valve of claim 20 including a housing for
enclosing the valve actuator, said housing including openings for
allowing air to flow through the valve actuator to assist in
reducing the temperature inside the housing; and wherein the
cooling device being disposed at said housing for forcing air to
flow through the housing openings and around the SMA wire
sections.
23. The fluid control valve of claim 19 wherein the temperature
controller includes means for activating the cooling means as a
function of the electrical temperature signal and a temperature set
point.
24. The fluid control valve of claim 18 wherein the electrical
controller includes a valve position control means comprising: a
capacitive element including opposing plates integral to the valve
actuator, the capacitance of which changing in proportion to the
movement of the movable element; means coupled to said opposing
plates for generating an electrical position signal in proportion
to the capacitance of said capacitive element; and position
controller governed by said electrical position signal for
regulating current to the SMA wire sections.
25. The fluid control valve of claim 24 wherein the position
controller includes means for regulating current to the SMA wire
sections by pulse width modulation of the current.
26. The fluid control valve of claim 24 wherein the position
controller includes means for regulating current to the SMA wire
sections as a function of the electrical position signal and a
position set point.
27. The fluid control valve of claim 18 including means for
selecting a rate of heating the SMA wire sections; and wherein the
electrical controller includes means governed by said selecting
means to regulate current to the SMA wire sections.
28. The fluid control valve of claim 27 including means for
regulating current to the SMA wire sections by pulse width
modulation of the current.
29. The fluid control valve of claim 18 wherein the electrical
controller is disposed substantially on a flexible membrane printed
circuit assembly.
30. The fluid control valve of claim 1 wherein the SMA wire
sections comprise an alloy of titanium and nickel.
31. An electrically controlled fluid control valve, said valve
comprising: a valve body for flowing fluid from an inlet port to an
outlet port therethrough, said valve body including a movable
element positionable in relation to the valve body to control fluid
flow through the valve body; a bias means for forcing the movable
element to a first position; a valve actuator coupled to said valve
body and movable element, including a shape memory alloy (SMA)
drive element for positioning the movable element away from the
first position when heated; a position measuring element for
providing a measurement proportional to the position of the movable
element; and an electrical controller governed by said position
measurement to regulate current to the SMA drive element to
position said movable element to a desired position.
32. The electrically controlled fluid control valve of claim 31
wherein the position measuring element is integral to the valve
actuator.
33. The electrically controlled fluid control valve of claim 32
wherein the position measuring element comprises oppositely
disposed conductive plates that are part of the valve actuator
assembly and that form a capacitive element, the capacitance of
which changing in proportion to the position of the movable
element; and wherein the electrical controller includes means for
sensing said capacitance and converting it into an electrical
signal representative of the position of the movable element.
34. The electrically controlled fluid control valve of claim 33
wherein said sensing means includes means for converting said
capacitance measurement into a frequency representative of the
position of the movable element.
35. The electrically controlled fluid control valve of claim 31
wherein the electrical controller includes means for regulating
current to the SMA drive element by pulse width modulation.
36. The electrically controlled fluid control valve of claim 31
wherein the electrical controller includes means for positioning
the movable element to a desired position in accordance with a
function of the sensed position measurement and a position set
point.
37. The electrically controlled fluid control valve of claim 31
wherein the electrical controller includes a programmable
microcontroller.
38. A temperature compensated, electrically controlled fluid
control valve, said valve comprising: a valve body for flowing
fluid from an inlet port to an outlet port therethrough, said valve
body including a movable element positionable in relation to the
valve body to control fluid flow through the valve body; a bias
means for forcing the movable element to a first position; a valve
actuator coupled to said valve body and movable element, including
a shape memory alloy (SMA) drive element for positioning the
movable element away from the first position when heated; an
electrical controller for regulating current to the SMA drive
element to heat said drive element to position said movable element
away from said first position; temperature sensing means disposed
in proximity to said SMA drive element to measure temperature and
generate an electrical temperature signal representative thereof;
cooling means for reducing the temperature surrounding the SMA
drive element when activated; and temperature controller governed
by said electrical temperature signal to activate said cooling
means.
39. The fluid control valve of claim 38 wherein the cooling means
includes a means for forcing air around the SMA drive element.
40. The fluid control valve of claim 38 wherein the cooling means
is selected from the group consisting of a rotary fan, a Piezo-fan
cooling device, and a Peltier cooling device.
41. The fluid control valve of claim 38 including a housing for
enclosing the valve actuator, said housing including openings for
allowing air to flow through the valve actuator to assist in
reducing the temperature inside the housing; and wherein the
cooling means being disposed at said housing for forcing air to
flow through the housing openings and around the SMA drive
element.
42. The fluid control valve of claim 38 wherein the temperature
controller includes means for activating the cooling means as a
function of the electrical temperature signal and a temperature set
point.
43. The fluid control valve of claim 38 wherein the SMA drive
element comprises a multiplicity of wire sections.
44. The fluid control valve of claim 38 wherein the temperature
controller comprises a programmable microcontroller.
45. An electrically controlled fluid control valve, said valve
comprising: a valve body for flowing fluid from an inlet port to an
outlet port therethrough, said valve body including a movable
element positionable in relation to the valve body to control fluid
flow through the valve body; a bias means for forcing the movable
element to a first position; a valve actuator coupled to said valve
body and movable element, including a shape memory alloy (SMA)
drive element for positioning the movable element away from the
first position when heated; means for selecting a rate of heating
the SMA drive element; and an electrical controller governed by the
selecting means to regulate current to the SMA drive element.
46. The fluid control valve of claim 45 wherein the electrical
controller includes means for regulating current to the SMA drive
element by pulse width modulation of the current
47. The fluid control valve of claim 45 wherein the selecting means
includes a digital selector switch for generating a digital code
representative of the selected rate; and wherein the electrical
controller is a digital controller governed by said rate selection
code to modulate the current to the SMA drive element.
48. An electrically controlled fluid control valve including
temperature compensation, said valve comprising: a valve body for
flowing fluid from an inlet port to an outlet port therethrough,
said valve body including a movable element positionable in
relation to the valve body to control fluid flow through the valve
body; a bias means for forcing the movable element to a first
position; a valve actuator coupled to said valve body and movable
element, including a shape memory alloy (SMA) drive element for
positioning the movable element away from the first position when
heated; a position measuring element for providing a measurement
proportional to the position of the movable element; and
temperature sensing means disposed in proximity to said SMA drive
element to measure temperature and generate an electrical
temperature signal representative thereof; cooling means for
reducing the temperature surrounding the SMA drive element when
activated; an electrical controller governed by both said position
measurement and temperature signal to regulate current to the SMA
drive element and to control said cooling means to position said
movable element to a desired position.
49. The fluid control valve of claim 48 including: first means
governed by the position measurement and a position set point to
generate a temperature set point; second means governed by the
temperature signal and temperature set point to regulate current to
the SMA drive element and to control said cooling means to position
said movable element to a position represented by said position set
point.
50. The fluid control valve of claim 49 wherein the second means
includes for regulating current to the SMA drive element based on a
difference of the temperature set point and temperature signal of
one polarity, and for controlling the cooling means based on a
difference of the temperature set point and temperature signal of
the other polarity.
51. A method for configuring a bobbin of non-conductive material
for a shape memory alloy (SMA) driven valve actuator that includes
at least one such bobbin being wound with a multiplicity of SMA
wire windings, said method comprising the steps of: removing groove
sections from said bobbin for acceptance of the multiplicity of SMA
wire windings, applying a conductive material to the surface area
of the grooved sections; and winding the SMA wire windings onto the
conductive grooved surfaces.
52. The method of claim 51 wherein the step of applying includes
the steps of: coating the surface of the bobbin including the
surface areas of the grooved sections with a conductive material;
and removing the conductive material from the surfaces of the
bobbin that are not grooved.
53. The method of claim 52 wherein the step of removing includes
the steps of: machining away the conductive material from the
non-grooved surface areas.
54. The method of claim 51 wherein the step of applying includes
the step of: applying the conductive material to the surface area
of the grooved sections by ink-printing techniques.
55. The method of claim 51 wherein the step of applying includes
the step of: applying the conductive material to the surface area
of the grooved sections by syringe needle deposition
techniques.
56. The method of claim 51 wherein the step of applying includes
the steps of: coating the non-grooved surfaces of the bobbin with a
masking material; applying the conductive material to the surfaces
of the bobbin; and removing the masking material.
57. A method for preparing shape memory alloy (SMA) wire for an SMA
driven valve actuator that includes an SMA wire wound around at
least one bobbin, said method comprising the steps of: coating the
SMA wire surface with a conductive material; and winding the coated
SMA wire around said at least one bobbin; removing the conductive
material from the surface of the SMA wire not in contact with the
at least one bobbin.
58. The method of claim 57 wherein the step of removing includes
the step of: removing the conductive material from the surface of
the SMA wire not in contact with the at least one bobbin by causing
the coated SMA wire to expand and contract at least once.
59. The method of claim 58 wherein coated the SMA wire is caused to
expand and contract by thermal heating of the wire.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to the field of fluid control
valves, in general, and more particularly to electrically
controlled, shape memory alloy element actuated fluid control
valves.
[0002] In general, manufacturing processes, like those involved in
the semiconductor industry, for example, use fluid control valves
in the liquid or gas delivery systems thereof. Typically, these
valves are either pneumatically controlled or hydraulically
controlled. A present obstacle in the use of the fluid control
valves is the surge of flow associated with the rapid opening of
the valve. The resulting turbulence and rapid pressure rise in the
exiting fluid is undesirable for other system components. For
example, in the semiconductor industry such turbulence and rapid
pressure rise can cause particle "stir up" that can lead to
contamination deposits on the wafers, which causes high rejection
rates (i.e., low yields). As a result, several different methods
have been used to better control the rate of opening of the valve.
Among these are the use of a variable orifice which allows the
valve piston to be driven at a slower rate, the use of a solenoid
to control the flow of the fluid to the air operator, and the use
of a metering valve to limit the fluid flow in the delivery
system.
[0003] Recently, electrically driven fluid control valves utilizing
a shaped memory alloy (SMA) drive element have been proposed for
use in the fluid delivery systems of manufacturing processes. Shape
memory alloys are materials that are capable of large and
repeatable phase-transformation induced strains. One such valve
integrates a single shape memory alloy wire into its valve housing
within the biasing spring portion thereof. As proposed, the single
SMA wire is essentially a rod having a diameter of approximately
one-quarter of an inch. A special power supply with low voltage and
high current requirements would be required to heat such a large
diameter/mass of wire or rod. In addition, once heated the large
mass of material would cool very slowly resulting in an undesirable
slow closing of the valve. Another type of SMA driven fluid control
valve provides for an SMA wire wrapped around the body of the valve
but still integral to the valve. Both of these types provide for,
mechanically active SMA wire terminations which may lead to
mechanical and/or electrical malfunctions. None of these proposed
SMA actuated fluid control valves appear to offer commercially
viable solutions to the aforementioned concerns with pneumatically
or hydraulically driven fluid control valves presently used.
[0004] The present invention includes aspects which overcome the
drawbacks of the prior proposed SMA actuator fluid control valves
and offers further aspects not as yet considered in the prior
art.
SUMMARY OF THE INVENTION
[0005] In accordance with the present invention, a fluid control
valve having a shape memory alloy (SMA) driven actuator comprises a
valve body including a movable element positionable in relation to
the valve body to control fluid flow from an inlet port to an
outlet port therethrough; a bias means for forcing the movable
element to a first position; and a valve actuator including a first
frame section coupled to the valve body and fixed in relation
thereto; a second frame section coupled to the movable element and
movable in relation to the valve body; and a multiplicity of SMA
wire sections coupled between the first and second frame sections
for moving the movable element from the biased first position to a
second position when heated. The valve may further include an
electrical controller for controlling the heating of the SMA wire
sections by regulating current therethrough. The valve actuator may
be enclosed within a housing which includes openings for allowing
air to flow through the valve actuator.
[0006] In accordance with another aspect of the present invention,
an electrically controlled fluid control valve includes a position
measuring element for providing a measurement proportional to the
position of the movable element, and an electrical controller
governed by the position measurement to regulate current to the SMA
drive element to position the movable element to a desired
position. In one embodiment of this aspect, the position measuring
element is integral to the valve actuator and comprises oppositely
disposed conductive plates that are part of the valve actuator
assembly and that form a capacitive element, the capacitance of
which changing in proportion to the position of the movable
element. The electrical controller includes means for sensing the
capacitance of the capacitive element and converting it into an
electrical signal representative of the position of the movable
element.
[0007] In yet another aspect of the present invention, a
temperature compensated, electrically controlled fluid control
valve includes a temperature sensing means disposed in proximity to
the SMA drive element to measure temperature and generate an
electrical temperature signal representative thereof, cooling means
for reducing the temperature surrounding the SMA drive element when
activated, and a temperature controller governed by the electrical
temperature signal to activate the cooling means. In one embodiment
of this aspect, the cooling means may be selected from the group
consisting of a rotary fan, a Piezo-fan cooling device and a
Peltier cooling device. In another embodiment of this aspect, the
temperature controller activates the cooling means as a function of
the electrical temperature signal and a temperature setpoint.
[0008] In yet another aspect of the present invention, an
electrically controlled fluid control valve includes a means for
selecting a rate of heating the SMA drive element, and an
electrical controller governed by the selecting means to regulate
current to the SMA drive element. In one embodiment of this aspect,
the electrical controller includes means for regulating current to
the SMA drive element by pulse width modulation of the current. In
another embodiment of this aspect, a digital selector switch is
used for generating a digital code representative of the selected
rate. In this embodiment, the electrical controller is a digital
controller governed by the digital rate selection code to modulate
the current to the SMA drive element.
[0009] In yet another aspect of the present invention, the
electrical controller of the fluid control valve is governed by
both the position measurement and the temperature signal to
regulate current to the SMA drive element and to control the
cooling means to position the movable element to a desired
position. In one embodiment of this aspect, a first means is
governed by the position measurement and a position setpoint to
generate a temperature setpoint, and a second means is governed by
the temperature signal and the temperature setpoint to regulate
current to the SMA drive element and to control the cooling means
to position the movable element to a position represented by the
position setpoint. In another embodiment of this aspect, the second
means regulates current to the SMA drive element based on a
difference of the temperature setpoint and temperature signal of
one plurality and controls the cooling means based on a difference
of the temperature setpoint and temperature signal of the other
polarity.
[0010] In yet another aspect of the present invention, a method for
configurating a bobbin of non-conductive material wound with a
multiplicity of SMA wire windings for a SMA driven valve actuator
comprises the steps of removing groove sections from the bobbin for
acceptance of the multiplicity of SMA wire windings, applying a
conductive material to the surface area of the grooved sections,
and winding the SMA wire windings onto the conductive grooved
surfaces. In accordance with yet another aspect of the present
invention, a method for preparing the SMA wire for an SMA driven
valve actuator comprises the steps of coating the SMA wire surface
with a conductive material, and winding the coated SMA wire around
the at least one bobbin, and removing the conductive material from
the surface of the SMA wire not in contact with the at least one
bobbin.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is an isometric cross-sectional illustration of a
fluid control valve having a shape memory alloy (SMA) driven
actuator suitable for embodying the principles of the present
invention.
[0012] FIG. 2 is a cross-sectional illustration of the top portion
of the valve actuator embodiment shown in FIG. 1 revealing greater
detail thereof.
[0013] FIG. 3 is a cross-sectional illustration of the top portion
of an alternate embodiment of the valve actuator shown in FIG.
1.
[0014] FIG. 4 is a cut away isometric view of bobbin sections of
the alternate embodiment of FIG. 3.
[0015] FIG. 5A is an illustration of the embodiment of FIG. 1
showing a vented housing surrounding the valve actuator
thereof.
[0016] FIG. 5B is an illustration of the embodiment of FIG. 1 with
the housing portion thereof cut away and showing a cooling fan
assembly.
[0017] FIG. 6 is a circuit schematic of an electrical controller
suitable for embodying an electrical control of the fluid control
valve embodiment of FIG. 1.
[0018] FIG. 7 is an exemplary flow chart suitable for use in
programming the electrical controller of FIG. 6.
[0019] FIG. 8 is a functional block diagram schematic of another
embodiment of the present invention.
[0020] FIG. 9 is a block diagram schematic of yet another
embodiment of the present invention.
[0021] FIG. 9A is a graph illustrating suitable control ranges for
the embodiment shown in FIG. 9.
[0022] FIGS. 10A, 10B and 10C are cross-sectional views of a bobbin
section illustrating various states of a method suitable for
embodying yet another aspect of the present invention.
[0023] FIG. 11A and 11B are two views of an illustration of SMA
wire wound around the two bobbin sections with conductive coated
and non-coated wire portions suitable for embodying yet another
aspect of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] In FIG. 1 is shown by an isometric cross-sectional
illustration a fluid control valve 10 having a shape memory alloy
(SMA) driven actuator. The fluid control valve 10 includes a valve
body portion 12 and a valve actuator portion 14 external to the
valve body and removable therefrom. The term "fluid" as used in
this description is not be limited to fluids in the liquid state,
but is also intended to include fluids in the gaseous state and
combinations of fluids in the gaseous and liquid states. The valve
body 12 being described below is of the diaphragm type and is only
used by way of example. It is understood that any type of fluid
valve may be used with the valve actuator portion 14 including, but
not limited to, bellows valves, gate valves, needle valves, ball
valves, and pinch valves, for example. It is understood that some
modification may be desired for adaptation of the present
embodiment to other type valves, like for rotational motion, for
example, but any such modification is clearly within the ability of
anyone skilled in the pertinent art given the description of the
present embodiment. In addition, the term "control" should not be
limited to vernier or variable control valves but also to "on-off"
valves as well.
[0025] In the present embodiment, the valve body 12 includes an
inlet port 16 and outlet port 18. Fluid is permitted to flow
through the valve body 12 from the inlet port 16 to the outlet port
18 as controlled by the position of a movable element 20 which may
be the valve stem, for example. The valve body 12 further includes
a bonnet nut 22 having a cavity 24 longitudinally disposed therein.
The valve stem 20 extends from an opening in the inlet port 16 at
the orifice 17 thereof up through the cavity 24 and protrudes
through the bonnet nut 22 at opening 26. A portion of the valve
stem 20 extends beyond the bonnet nut 22 through the opening 26 to
be attached to the valve actuator 14.
[0026] Still further, in the present embodiment, the valve body 12
includes a cavity area 32 which extends between the inlet port 16
and outlet port 18 to permit fluid to flow therethrough, and a
diaphragm 30 which is disposed over and extends across the cavity
32. In this embodiment a valve spring 34 is disposed within the
cavity 24 around the stem 20 to bias the stem with a mechanical
force in the closed position. In particular, the bias spring 34 may
rest on the valve stem 20 in the compression state forcing the
valve stem 20 against the diaphragm 30 with a downward force to
close off the flow of fluid from the inlet port 16. It is
understood that while the spring 34 in the present embodiment
biases the movable element 20 to a closed position, it may in a
similar manner bias the stem in an open position or some other
position depending upon the valve type and particular application
thereof without deviating from the principles of the present
invention.
[0027] For this embodiment, the valve actuator 14 comprises a first
or inner frame section made up of two metal guideposts 40 and 42
and two metal sections 44 and 46 supported at the top of the
guideposts 40 and 42, respectively. The guideposts 40 and 42 are
transversely and removably affixed to the flat top portion of the
bonnet adapter 48 and spaced apart from one another. A bobbin 50 is
disposed between the metal sections 44 and 46 of the fixed frame in
a transverse alignment to the guideposts 40 and 42. An additional
metal section 52 may be disposed between the sections 44 and 46 to
support the bobbin 50 if structurally desired. On top of the
sections 44 and 46 is supported a non-conductive member 54 having a
substantially flat top surface 56. This inner frame section
comprising the members 40, 42, 44, 46, 50, and 54 is fixed in
relation to the valve body 12.
[0028] The valve actuator 14 also includes a second or outer frame
section comprising a bottom metallic section 60 which is oriented
substantially parallel to the flat surface of the bonnet adapter 48
and includes holes 62 and 64 to slide over the guideposts 42 and
40, respectively. The top of the valve stem 28 is affixed to the
metal section 60 by a retaining clip and spring washer combination
which permits the top of the stem 28 to protrude through the metal
section 60 and be connected thereto. This outer frame section
includes two additional metal sections 66 and 68 which are
connected at the bottom to the section 60 on either side thereof
and extend upwardly therefrom substantially parallel to the
guideposts 40 and 42. Affixed between the metal sections 66 and 68
at the top thereof is a section of non-conductive material 70
having a substantially flat bottom surface oppositely disposed the
surface 56 of the non-conductive portion 54. The members 60, 66, 68
and 70 of the outer frame section form a substantially rectangular
frame section. At a predesigned location somewhere between the top
and bottom of the metal sections 66 and 68 are attached two metal
sections 74 and 76, respectively. The metal sections 74 and 76
include holes 78 and 80, respectively, for passing the guideposts
42 and 40, respectively, therethrough. Accordingly, this outer
frame section is movable with respect to the valve body 12 and
guided along its movement by the guideposts 40 and 42 utilizing the
holes 64 and 62 in section 60 and 80 and 78 in sections 76 and 74,
respectively.
[0029] Still further, the sections 74 and 76 are used to support a
second bobbin member 82 therebetween in an orientation which is
transverse to the guideposts 40 and 42. A further structural member
84 may be disposed between sections 74 and 76 to support the second
bobbin member 82 if desired. While the various structural frame
members have been described as metallic in the present embodiment,
it is understood that these members may be constructed from other
materials, like ceramic, plastic or any polymer, for example, or
any combination thereof without deviating from the principles of
the present invention.
[0030] In the present embodiment, the members of the frame sections
of the valve actuator 14 may be affixed together using any
conventional method like screws, rivets, or the like for ease in
manufacturing. If it makes sense, these members may also be welded
together in the manufacturing process. Moreover, in the present
embodiment, the bobbins 50 and 82 may be cylindrical in shape and
made of an insulating or non-conducting material, like
polyphenylene sulphide, for example.
[0031] For this embodiment, the valve actuator 14 includes a
multiplicity of SMA wire sections coupled between the outer and
inner frame sections for moving the movable stem element 20 from
its biased position to another position when heated. In the present
embodiment, the multiplicity of SMA wire sections comprise a single
SMA wire wound a multiplicity of times about the two bobbin members
50 and 82. The bobbin members 50 and 82 may include grooves therein
for accepting the SMA wire windings 90. In some embodiments, the
grooved areas of the bobbin members 50 and 82 may include a coating
of an electrically conductive material. A technique for providing
the electrically conductive material onto the bobbins particularly
in the grooved surface areas thereof is found supra.
[0032] The SMA wire used for the windings 90 in the present
embodiment comprises a Nickel-Titanium alloy and has a diameter
which is very small on the order of 0.015 inches, for example. The
bobbins 50 and 82 are also relatively small in diameter to offer a
ratio of the winding radius thereof to the diameter of the SMA wire
that is substantially less than 50:1. In practice, this ratio will
more than likely not be less than 5:1. Actually, the radii of the
cylindrical bobbins 50 and 82 are on the order of 0.2 inches. The
SMA wire is terminated at its ends which are mechanically inactive
regions of the wire to provide a restraint to strain when the
active portion of the wire is heated. In the present embodiment,
these terminations are accomplished by disposing the wire ends
through respective holes in the outer edges of the bobbin section,
say 50, for example, and wedges are provided into the holes of the
bobbin to wedge the wire end points in place to form a restraint to
strain.
[0033] Under these conditions, the outer movable frame section is
supported from the inner frame section by the multiplicity of SMA
wire sections 90 wound about the bobbin sections 50 and 82 of the
respective frame section. Since the outer frame section is
connected to the movable stem element 20 via section 60, then the
biasing of the stem 20 downward by the spring 34 forces the
multiplicity of wire sections 90 to be extended when in the low
temperature phase.
[0034] The top portion of the valve actuator 14 is shown in greater
detail in the cross-sectional illustration of FIG. 2. Referring to
FIG. 2, the substantially flat surfaces 56 and 72 of the
non-conductive top portions 54 and 70, respectively, have
conductive material 94 and 96 disposed respectively thereon such
that they form conductive plates which are oppositely disposed from
one another and insulated from their respective frame sections to
form an integral capacitive element within the valve actuator
assembly 14. Contacts 98 and 100 at the conductive plates 94 and
96, respectively, permit attachment of wire leads 102 and 104,
respectively, which are coupled to position measuring electronics
on a printed circuit board 106 which may be mounted on top of the
non-conductive section 70 as shown in FIG. 2. The electronics of
the printed circuit board 106 will become better understood from
the description found hereinbelow.
[0035] In addition, the terminated ends 108 and 110 of the SMA wire
winding 90 are shown attached through respective holes at either
end of the bobbin 50. As described above, the ends 108 and 110 are
terminated by wedging a metallic conductive member into the holes
112 and 114. The SMA wire endings along with the metallic
conductive wedges may exit the holes 112 and 114 and be attached to
wire leads 116 and 118, respectively, at the points 120 and 122.
These connections at 120 and 122 are preferably performed by
crimping using a conventional crimping tool. But it is understood
that other ways of attaching the connecting leads 116 and 118 may
be used such as soldering, welding, brazing, and wrapping, for
example. The leads 116 and 118 connected to the ends of the SMA
wire winding are provided to input connecting pads on the printed
circuit board 106 to provide heating of the SMA wire sections 90 by
regulating current therethrough as will become more apparent from
the description hereinbelow. In some applications, the printed
circuit board 106 may be made from a flexible membrane printed
circuit board.
[0036] The SMA wire used for the present embodiment is a nickel
titanium alloy with a 50-50 percent ratio based on atomic number. A
suitable SMA wire for this purpose is manufactured by Dynalloy,
Inc. under the trade name Flexinol.TM.. On the other hand, it is
understood that there are many types and alloy mixtures of shape
memory alloy wires that may be used in the present embodiment
without deviating from the broad principles of the present
invention. Since a very thin diameter wire on the order of 0.015
inches is being used for the present embodiment, only a relatively
small amount of current is needed to heat the wire to reach its
transformation temperature which may be on the order of 70.degree.
C. to 90.degree. C. When the wire reaches this temperature, it
undergoes a phase change from the low temperature phase to the high
temperature phase wherein it begins a contraction of its length. In
addition to using a relatively small amount of current, the thin
diameter SMA wire is much more manageable for thermodynamic and
manufacturing purposes.
[0037] Accordingly, the multiplicity of windings about the bobbin
sections in the present embodiment mechanically act as a
multiplicity of single wire sections coupled between the two frame
sections and the force gained by each wire section is additive.
Therefore, the resulting embodiment provides for both a mechanical
advantage and an electrical advantage of having one long, thin
wire. In addition, those portions of the SMA wire contiguous with
the bobbin sections offer no real mechanical advantage and
therefore are mechanically inactive upon the heating thereof
because of the orientation of the force factors. Therefore, it
would be preferable to remove them from the electrical circuit as
well, and this may be accomplished by plating the grooved sections
of the bobbin elements to allow an electrical path which bypasses
the thin wire winding in each case.
[0038] In operation, the embodiment described in connection with
FIGS. 1 and 2 provides for heating of the SMA wire windings 90 by
regulating current therethrough using the electronics of the
printed circuit board 106, which will be further explained
hereinbelow. As the SMA wire windings are heated through its
transformation temperature, the SMA wire changes phase from the low
temperature phase to the high temperature phase and begins a
contraction of length at a rate that is a function of the current
regulated therethrough. As contraction begins, the outer frame
member of the valve actuator 14 which is supported by the SMA wire
windings by bobbin 82 begins moving away from the valve body
pulling the stem or movable element 20 along with it overcoming the
force of the spring 34. In so doing, the valve stem 20 is unseated
and allows the diaphragm to move above the cavity 32 and permit
fluid to flow from the inlet port 16 to the outlet port 18 via
cavity 32 in the valve body 12. This movement will continue at a
rate controlled by the current conducted through the SMA wire
windings 90 until the valve stem 20 reaches a full open
position.
[0039] During this movement, the conductive plates 94 and 96 of the
integrally formed capacitive element between the outer and inner
frames of the valve actuator 14 move apart from one another, thus
causing a change in capacitance, which is detected by the printed
circuit board 106 through a position control circuit, which will be
further described hereinbelow. Current may continue to be regulated
through the SMA wire windings to maintain the movable element 20 in
an open position. Once current is removed from the wire windings
90, the windings begin to cool through the transformation
temperature, and as they reach the low temperature phase, begin to
expand in length as a result of the tension thereon caused by the
bias element 34. Accordingly, the bias element 34 will continue to
force the wire windings to extend and force the moving element 20
to seat on the diaphragm 30, thus closing off the fluid flow from
the inlet port 16 to the outlet port 18 of the valve body 12. This
process will be repeated each time the valve is demanded to be
opened and closed.
[0040] In FIGS. 3 and 4 is shown an alternate embodiment in which
the second frame section is guided through its movement along the
inside of the first or fixed frame section. Referring to 10.degree.
FIG. 3, a bobbin element 130 is disposed on top of the two metal
guideposts 44 and 46 and affixed in place. This bobbin element 130
is curved on top to accept the SMA wire windings 90, but has a
substantially flat bottom surface 132. A second bobbin element 134
is disposed on top and between the longitudinal metal frame members
66 and 68 of the second frame section. The bobbin element 134 is
curved on the bottom to accept the SMA wire windings 90, but has a
substantially flat top surface area 136 which is oppositely
disposed from the surface 132. Surface areas 132 and 136 have
disposed thereon conductive material 138 and 140, respectively, to
form the plates of a capacitor separated by air. The capacitor
element is integral to the actuator assembly.
[0041] Still in FIG. 3, SMA wire is wound a multiplicity of times
about the bobbins 130 and 134, preferably into grooves 142 cut into
the curved surfaces thereof. FIG. 4 illustrates by cut away view
the two bobbins 130 and 134 and the grooves 142 cut from the curved
surfaces thereof. FIG. 4 also reveals the conductive plates 138 and
140 forming the integral capacitive element of this embodiment of
the actuator 14. Returning to FIG. 3, the ends of the SMA wire
windings are terminated into holes disposed on the top surface of
the bobbin 130. Metal contacts 148 and 150 wedge the wire ends into
the holes 144 and 146, respectively, while at the same time, making
an electrical connection thereto. Lead wires 116 and 118 may be
connected to the metal connectors 148 and 150, respectively.
[0042] This alternate embodiment operates in a similar manner as
the embodiment described in connection with FIGS. 1 and 2, except
that the second frame section is guided through its movement along
the inside of the first or fixed frame section, i.e. the bobbin of
the fixed frame section is external to the second or movable frame
section.
[0043] In FIGS. 5A and 5B is shown a valve actuator cover or
housing 150 that may be added to the valve assembly 10 to protect
the actuator assembly and electronics from the adverse elements of
the external environment. In the present embodiment, the housing
150 may be of a cylindrical shape for fitting over and enclosing
the valve actuator 14 and attaching to the periphery of the bonnet
nut 22 of the valve body 12. To permit air to flow through the
inside of the housing 150, openings 152 are provided, preferably at
the top 154 and bottom 156 portions thereof. Hot air generated
within the housing primarily from the heating of the SMA wire
sections may flow upward and exit through the openings 152 at the
top portion 154 of the housing. Cooler outside air may be drawn
into the enclosure from the openings at the bottom portion 156.
This natural convective air flow will aid in cooling the inside of
the enclosure during operation of the valve actuator 14.
[0044] While the housing 150 is shown cylindrical, it is understood
that the housing may take upon any shape so long as it can fit over
and enclose the actuator assembly 14 and be capable of attaching to
the valve body 12. In addition, the air flow openings 152 may take
upon any shape, like holes, slots and the like, so long as the
openings accommodate sufficient air flow through the housing
150.
[0045] In some environments, it may be desirable to add a cooling
device to the assembly 10 to maintain the temperature of the air
surrounding the SMA wire sections 90 below a preset temperature
and/or to cool the wire to ensure a desired rate of closure of the
movable element 20. Such a cooling device may be of the type that
forces air about the wire sections 90 to maintain the surrounding
air at a temperature at or below the preset temperature and/or to
cool the wire at the desired rate. A cooling device of this type
may be selected from the group consisting of a rotary fan and a
Piezo-fan, for example. The cooling device may be disposed at the
housing 150 or on the actuator assembly 14 within the housing for
forcing air to flow through the housing openings 152 and around the
SMA wire sections 90. Thus, when activated the cooling device would
be capable of reducing the temperature inside the housing 150 and
to allow the wire to cool at the desired rate.
[0046] In some environments, it may be preferable to eliminate the
openings and maintain the housing closed from the environment. In
these cases, a solid-state refrigerating device, like a Peltier
cooling device, for example, may be used as an alternative to
forced air cooling, if desired.
[0047] In the present embodiment, a conventional rotary fan 160 may
be mounted on an internal wall of the housing 150 as shown in the
cut away illustration of FIG. 5B. The fan 160 may be disposed in
close proximity to the SMA wire sections 90 to force air across the
windings and cool the temperature of the wire and surrounding air
thereof. Wire leads 162 and 164 may connect the motor of the fan
160 to a temperature controller on the PC board 106. The
temperature control of the wires 90 and air surrounding them
utilizing the cooling device 160 will be described in greater
detail hereinbelow.
[0048] A suitable embodiment of the control electronics of the PC
board 106 for the valve actuator of the present embodiment is shown
schematically in FIG. 6. Referring to FIG. 6, the circuits of the
PC board 106 comprise a two-wire digital thermometer and thermostat
integrated circuit shown at U1, which may be of the type
manufactured by Dallas Semiconductor Under the Model No. DS 1721S;
a binary coded rotary DIP switch U2, which may be of the type
manufactured by Grayhill Incorporated under the Model No. 94HAB10;
a three-terminal positive voltage regulator integrated circuit U3,
which may be of the type manufactured by National Semiconductor
under the Model No. LM78L05ACM; a microcontroller U4, which may be
of the type manufactured by Atmel, Inc. under the Model No.
AT90S2313-4SI; a timer integrated circuit U5, which may be of the
type manufactured by Phillips Semiconductor under the Model No.
NE555, two power MOSFET semiconductor switches Q1 and Q2, which may
be of the type manufactured by International Rectifier under the
Model No. IRLR/U024N; and finally, two Schottky barrier rectifiers
D1 and D2, which may also be of the type manufactured by
International Rectifier under the Model No. B130/B, for example.
The printed circuit board 106 may also include a number of
input/output connections J1-J8 for inputting power from a power
source, inputting signals for measurement and outputting signals
for control of the heating of the SMA wire 90 and the cooling
device 160.
[0049] Outside power from a power source may be connected to the
connection points J4 and J5, J4 being the supply and J5 being the
return. The output power may be from a direct current voltage
source of say 9 to 12 volts, for example. The integrated circuit
U3, which is a series pass, step down voltage regulator regulates
the higher supply direct current (DC) voltage, supplied from the
input connector J4, down to 5 volts DC, which is supplied to the
other integrated circuits U1, U4 and U5 included on the printed
circuit board. The coupled capacitors to the integrated circuit U3,
C1, C5 and C6, protect U3 from voltage transients which may be
induced on the power source supply line and assists the regulator
to supply substantially a constant 5 volt voltage level to the
remaining circuitry on the printed circuit board. All returns from
the various integrated circuits are connected to the return
connector J5. The substantially constant 5 volt supply is
designated as Vcc.
[0050] Connection points J6 and J7 are connected to the capacitive
plates via the lead wires 116 and 118 for monitoring the
capacitance of the integral capacitive element through the
integrated circuit U5. The 555 integrated timer circuit U5,
utilizing the integral capacitor and appropriate valued resistors
R9, R10 and R11, is configured conventionally as a variable
oscillator circuit which generates an electrical frequency signal
at pin 3 thereof. The frequency of the output electrical signal at
pin 3 of U5 varies in proportion to the external capacitance that
is a measure of the position of the movable element of the valve
body. The capacitor C4 across connectors J6 and J7 is used for
trimming the external capacitance.
[0051] In operation, as the movable element of the valve moves away
from its closed position, the plates of the integral capacitive
element move further apart or together, depending on the
embodiment, and the capacitance thereof changes accordingly. This
change in capacitance is picked Up at the connectors J6 and J7 and
applied to the integrated circuit U5 at pins 2 and 6. The resistors
R9 and R11 and external integral capacitance make up an RC time
constant to the 555 timer circuit U5 which, in turn, renders the
output frequency signal at pin 3 thereof. Accordingly, as the
position/capacitance changes, the RC time constant changes, and the
output frequency varies in proportion thereto. The output frequency
signal is coupled to an input pin, pin 9, of the microcontroller
U4. This frequency signal provides an electrical signal
representative of the position of the movable element of the valve
body 12.
[0052] Since the printed circuit board 106 is disposed on the valve
actuator in proximity to the SMA wire section 90, the ambient
temperature surrounding these wire sections may be measured by a
temperature sensor disposed on the printed circuit board. This is
accomplished in the present embodiment by the integrated circuit
U1, which includes internally a temperature sensing element and
digital electronics for converting the temperature measurement into
a digital code which is serially output therefrom at pin 1,
designated as the SDA signal, and coupled to pin 8 of the
microcontroller U4, which is configured as an input data pin. In
addition, a serial digital code, SCL, may be sent to pin 2 of the
integrated circuit U1 from pin 11 of the microcontroller, which is
configured as a digital output. Pull-up resistors R5 and R6, which
may be of the value 20 K.OMEGA., couple the signal lines SDA and
SCL to the Vcc supply. Accordingly, serial data representing a
temperature setting may be provided by the microcontroller U4 over
SCL to the integrated circuit U1. This temperature setting or set
point may be used by the circuit U1 to compare with the digital
code of the temperature measurement internally provided. The
microcontroller U4 may also send a serial code over SCL to U1 at
pin 2 to control the rate in which the temperature data is sent
back to the microcontroller from pin 1 of U1.
[0053] The circuit U1 is configured to measure the current
temperature and compare it to the temperature setpoint level
controlled by the microcontroller U4 via SCL. When the current
temperature measurement of U1 reaches the predetermined temperature
setpoint, the circuit U1 outputs a signal over pin 3 to turn the
MOSFET switch Q1 on. Power from the external supply is provided to
the cooling fan 160 or other cooling device via lead wire 162 from
the connector J1. The cooling device return path is provided
through connector J2 via lead wire 164 to the input of Q1. The
output of Q1 is coupled to ground through the Schottky barrier
rectifier D2, which is used to protect the MOSFET Q1 from reverse
voltages. When the switch Q1 is turned on by U1, power from the
external supply is provided to the cooling device 160 to cool the
ambient air surrounding the SMA wire sections 90 of the valve
actuator 14.
[0054] In this manner, the circuits U1, Q1 and D2 and cooling
device 160 form a temperature control loop for the ambient air
surrounding the SMA wire sections 90 such that when the ambient
temperature thereat reaches the setpoint programmed into the
temperature controller U1 by the microcontroller U4, the cooling
device is activated to reduce the temperature back down to the
temperature setpoint or thereunder if hysteresis is provided.
[0055] In the present embodiment, a selector switch U2 is used to
accommodate a selection of heating rates of the SMA wire sections
90. Digital outputs from the binary coded rotary DIP switch U2 are
provided to corresponding input configured ports of the
microcontroller U4. The particular DIP switch being used for the
present embodiment has eight positions and outputs a binary coded
decimal signal over its pins 1, 4, and 3. Pin 5 is coupled to the
ground connection and pin 6 is left unconnected. The
microcontroller U4 monitors the binary coded signals of pins 1, 4
and 3 through the input pins 12, 13 and 14, respectively.
Accordingly, a plurality of different heat ramping profiles for the
SMA wire sections and movement of the movable element may be
selected from the selector switch U2.
[0056] The microcontroller U4 is programmed through embedded
software to perform logical steps in a timely fashion. It monitors
its inputs and controls the outputs thereof according to
preprogrammed logical instructions embedded in digital code in the
memory thereof. Y1 is a 4 megahertz ceramic resonator which
provides the microcontroller with a clocking signal through pins 4
and 5 thereof. A connection from the series combination of R2 and
C2 provide a reset signal at pin 1 of the microcontroller U4 each
time the supply voltage to the PC board 106 is activated. When the
supply voltage is removed, the PC board electronics are
deactivated. Thus, in one embodiment, the supply voltage to the PC
board 106 may be used to operate the movable element of the valve
assembly 10 to its open and closed positions. Capacitor C3 is used
to protect the microcontroller U4 against transient voltages and is
disposed close to the circuit U4 between the supply Vcc and
ground.
[0057] In addition, output pin 15 of the microcontroller U4 is
coupled to the gate of the MOSFET switch Q2 through the resistor R3
for switching Q2 on and off, and the gate of Q2 is coupled to
ground through the resistor R8. The output connectors of the
printed circuit board J3 and J8 are connected to the two ends of
the SMA wire winding 90. The external voltage supply is conducted
through connector J3 to one end of the wire winding 90 via
connector J3, and the return from the other end is connected to
connector J8. A current conduction path from J8 to ground is
provided through the MOSFET switch Q2 when activated. The Schottky
barrier rectifier D1 provided in series to the conduction path to
ground protects the MOSFET switch Q2 against adverse voltage
transients over the external supply line. In the present
embodiment, the microcontroller U4 regulates the current through
the SMA wire sections by switching Q2 on and off using a pulse
width modulated signal, the pulse being varied according to the
selected heating or ramp rate based on the code of U2.
[0058] Thus, in operation, when the printed circuit board 106 is
supplied with a direct current voltage from 9 to 16 volts, for
example, the SMA wire is supplied with a pulse width modulated
voltage via the microcontroller U4 and switch Q2 based on the
selected heat rate code of U2. In turn, the SMA wire contracts at a
certain rate according to the selected heating rate of the wire,
which is regulated by the pulse width modulated current drive. That
is, as the current is varied through the wire, the temperature of
the wire also varies. The duty cycle of the pulse width modulated
current signal to the SMA wire will cause it to contract at a
certain prespecified rate.
[0059] Pulse width modulation of the current to the SMA wire of the
actuator is used because it is considered a more efficient way to
vary the current through the wire than varying the voltage level to
the wire. However, it is well understood that similar regulation of
current through the SMA wire can be accomplished through pulse rate
modulation or other modulation techniques. In addition, modulation
can also occur by varying the voltage level to the wire using
similar modulation techniques. Accordingly, all of these techniques
are considered equivalent regulation of the heating of the wire to
obtain a specified contraction rate to control the rate at which
the movable element is positioned away from its closed position.
Therefore, the circuitry described in connection with the
embodiment of FIG. 6 is suitable for regulating current to the SMA
wire windings to heat the wire windings and cause them to contract
at a preselected ramping or contraction rate. An light emitting
diode (LED) indicator may be controlled by the microcontroller U4
to show or be illuminated when the valve has fully opened, i.e.,
the movable element has reached its maximum movement away from a
closed position.
[0060] A flow chart suitable for use in programming the
microcontroller U4 of the circuit embodiment described in
connection with FIG. 6 is shown in FIG. 7. For the present
embodiment, the microcontroller U4 has a system clock rate of
approximately four megahertz and includes a timer cycle consisting
of 256 counts of the system clock. Accordingly, each timer cycle
takes approximately 16.4 milliseconds. Starting the flow chart at
block 300 upon power turn on, the microcontroller is instructed to
monitor the digital code from the selector switch U2 over digital
input lines 12, 13 and 14. This digital code which sets the
contraction rate of the SMA wire is stored in a data register
labeled as PWMON. The data code in PWMON will be used to control
the duty cycle of the pulse width modulated waveform controlling
the current regulation to the SMA wire windings. In the next block
302, a digital code of 6 is stored in a data register labeled as
COUNT, and the data register controlling the PWM duty cycle is set
to zero. The next three instructional blocks 304, 306 and 308
provide the programming for the microcontroller to go through a
counting cycle which is essentially a delay time of approximately
100 milliseconds to allow the circuitry on the printed circuit
board to settle after power turn on. More specifically, in block
304 the timer counter is cycling through its 256 counts. Each time
it makes a complete cycle, the number in the COUNT register is
decremented by one in block 306. When the count in the COUNT
register is decremented to zero as determined in 308, the time
delay is complete and programming execution continues at block
310.
[0061] The data code in a data register designated as POS is the
frequency monitored over pin 9 from the timer circuit U5, which is
a measure of the position of the movable element in the valve body.
Since we know that at power turn on the movable element is biased
in the closed position, the initial POS data is stored in a data
register labeled as CLOSED at block 310. Also in block 310, since
it is advantageous to heat the SMA wire at a constant high rate to
initiate movement of the movable element away from its static
closed position, the PWMDUTY register used to regulate current to
the SMA wire is set to full duty. Next in block 310, a full open
position code is established by adding the difference in frequency
derived counts, designated as POS delta, between the closed
position and full open position of the movable element, to the
initial closed position POS reading and storing that result,
POS+POS delta, in a data register designated as OPEN.
[0062] Next, in block 312, with the SMA wire being heated at full
duty cycle, the 256 count timer of the microcontroller counts
through its cycle which defines a fixed time interval by which to
count up the counts of the frequency signal being monitored at pin
9 from the position timer circuit U5 and monitor the current
position of the movable element. Accordingly, the accumulated
counts over the time interval of a timer cycle become the new
position code that is stored in the data register POS. Therefore,
in block 314, the new position code POS is compared with the code
in the CLOSED register, i.e. the closed position, and if not
greater, a new position count or code for POS is determined in
block 312. Once the current POS code is greater than the code in
the CLOSED register, the 312, 314 loop is exited and instruction
execution continued at block 316. When block 314 is exited, we know
that the SMA wire sections are heated to the transformation point
and the wire is beginning to contract because the movable element
is positioned away from its closed position. Therefore, in block
316, it is time to set the duty cycle of the pulse width modulation
PWMDUTY to the code of the preselected rate from U2 which was
stored in PWMON.
[0063] While the wire is being heated at the selected current
regulated duty cycle, the microcontroller goes through the loop of
blocks 318 and 320. Again, in block 318 the timer cycle is going
through its 256 count interval, which is the fixed interval in
which to acquire the counts of the frequency signal from the
position timer U5, which is representative of the new position POS
of the movable element. In block 320, it is determined whether the
new position is greater than or equal to the fill open position,
i.e. the code in the OPEN register. If not, the loop continues
until the current position code POS is greater than or equal to the
full open position OPEN whereupon block 320 is exited to block 322.
In the instruction blocks 322 through 332, the microcontroller is
in the mode to sustain the movable element within a deadband about
the full open position. The deadband is defined by a predetermined
code stored in a register designated as HYSTERESIS in the flow
chart.
[0064] So, in block 322, the duty cycle register PWMDUTY is set to
zero interrupting current to the SMA wire windings, thus allowing
the wire to cool slightly. Within the timer cycle block 324, the
current position POS of the movable element is determined, and in
block 326, that current position POS is subtracted from OPEN and
the result is compared with deadband value in the register
HYSTERESIS. The blocks 324 and 326 are cycled until the current
position falls below the deadband value, i.e. OPEN-POS is greater
than HYSTERESIS. When this condition occurs as determined by block
326, the duty cycle register PWMDUTY is set to 100 percent in block
328 to initiate heating the SMA wire winding at the highest rate.
Thereafter, in blocks 330 and 332, it is determined if the current
position POS of the movable element has reached the deadband code
beyond the full open position, i.e. POS-OPEN is greater than
HYSTERESIS. When this condition occurs, the instruction execution
is returned to block 322 wherein current is removed from the SMA
wire winding, and it is allowed to cool. Execution will continue
cycling through steps 322 to 332 for as long as power is applied to
the circuitry. When power is removed to the circuitry of the PC
board 106, no current is supplied to the SMA wire windings, and
they are allowed to cool under tension of the bias element and
return to their extended length, thus returning the movable element
to its biased, closed position. In this manner, the valve can be
electrically operated to turn on and off the fluid flowing through
the valve 12 at any specified ramping rate.
[0065] FIG. 8 is a functional block diagram of an embodiment of yet
another aspect of the present invention in which the movable
element of the valve may be positioned to a desired position other
than merely the full open position. The electronic embodiment
described in connection with FIG. 6 and the flowchart of FIG. 7 may
both be used by way of example with the embodiment of FIG. 8,
albeit modified to accommodate the desired position control
aspects. Referring to FIG. 8, a position set point 200 may be input
to a rate of change algorithm 202 which may be similar to that
described in connection with the flowchart of FIG. 7, for example.
The position set point may be a digitally coded word selected by a
digital switch (not shown) similar to that described for the switch
U2 which is used in the circuit embodiment of FIG. 6 to set the
heating rate or it may be generated by a process control computer
(not shown) external to the valve actuator electronics. This
digitally coded set point may be input to the microcontroller U4
through digital lines thereof characterized as inputs. For example,
a 3 bit code would provide for 8 possible desired positions, a 4
bit code would provide for 16 possible desired positions, and so
on. The microcontroller U4 may detect when a new position set point
200 is input thereto and store the code thereof in a register
NEWPOS. The current position sensed from a position sensor 204 may
be computed in a similar manner as that described for the flowchart
of FIG. 7 and stored in the register POS. The position sensor 204
may be integral to the valve actuator as described in connection
with the embodiments of FIGS. 1-4 or a separate sensor
therefrom.
[0066] In this position control aspect of the present invention,
the current position POS may be subtracted from the desired
position setting NEWPOS in an adder function 206 resulting in an
error 208 which is operated on by a position control function 210.
The control function 210 may be an "on-off" discrete control that
may cause the valve actuator to move to the desired position
setting at the selected rate PWMON as described in blocks 316, 318
and 320 for the flowchart of FIG. 7 except that the NEWPOS register
would be substituted for the OPEN register. In this example, the
controller 210 controls a PWM current drive function 212 by setting
the WMDUTY register to the PWMON value. Accordingly, the SMA wire
90 of the valve actuator is heated with the constant duty cycle as
governed by the selected heating rate PWMON. This process will
continue until POS becomes equal to or greater than NEWPOS as
determined by block 320 at which time the duty cycle PWMDUTY is set
to zero in block 320 rendering no further heating of the SMA wire
90. Blocks 322 through 332 may be executed to maintain the valve
element at the desired set point position NEWPOS, i.e. substitute
NEWPOS for OPEN.
[0067] For this control strategy, should the desired position set
point 200 be less the current position POS, then the duty cycle
PWMDUTY in the driver 212 is set to zero to permit the SMA wire to
cool and extend to a new position. As the wire cools and POS
reaches the desired position NEWPOS, then the blocks 322 through
332 may be re-executed to maintain the desired position
setting.
[0068] It is understood that other control strategies may be used
for the position controller 210 of the embodiment of FIG. 8 without
deviating from the broad principles of the present invention. Some
examples of other suitable position control strategies include
Proportional (P), Proportional plus Integral (PI), Proportional
plus Integral plus Differential (PID), Fuzzy Logic, Neural Network,
and Rules based on Non-linear control, to name just a few. With
these control strategies, the output of the controller 210 would
control the rate of heating of the wire 90. If pulse width
modulation of current was used, then the duty cycle of the current
waveform would be set by the controller 210 in the driver function
212 which may be limited by a selected heating rate if so
desired.
[0069] Another aspect of the present invention provides for
temperature control as part of the positioning of the movable
element of the valve to a desired position as described in
connection with the embodiment of FIG. 8. A suitable embodiment for
this aspect is shown in the functional block diagram schematic of
FIG. 9, the functions of which being performed at least in part for
the present embodiment in the microcontroller U4. Referring to FIG.
9, similar to that described above, the sensed position from the
sensor 204 is subtracted from the position set point or desired
position 200 in the adder 206 to produce the position error 208. To
provide for thermal compensation in this embodiment, the position
error 208 is converted into a temperature set point 220 by a
position to temperature converter function 222 which may be based
on the characteristics of the valve type and SMA drive of the
actuator.
[0070] Still in FIG. 9, a temperature sensor 224, which may be
similar to the U1 circuit described in the circuit embodiment of
FIG. 6, senses the temperature in the proximity of the SMA actuator
drive and generates a signal 226 representative thereof. The SDA
signal generated the circuit U1 exemplifies a temperature signal
suitable for use by the microcontroller U4 in the present
embodiment. The sensed temperature signal 226 is subtracted from
the temperature set point 220 in the adder function 228 resulting
in a temperature error signal 230 that drives a split range
temperature control function 232. A suitable functional
characterization of the controller 232 is exemplified in the graph
of FIG. 9A. The graph of FIG. 9A shows a cooling curve represented
by solid line 234 and a heating curve represented by dashed line
236. The abscissa of the graph represents temperature error 230 and
the ordinate represents an output signal 240 of the controller 232
that drives either the current driver 212 for heating the SMA wire
90 or a cooling device driver 242 for regulating a cooling device,
like the rotary fan 160 described in connection with the embodiment
of FIG. 5B, for example. In the graph of FIG. 9A, the point 238 on
the abscissa where the two curves 234 and 236 meet may be
considered zero temperature error for the purposes of this
embodiment. As the temperature error becomes positive, the current
drive 212 is driven by the output signal 240 along the curve 236
and similarly, as the error becomes negative, the cooling driver is
driven by the output signal 240 along the curve 234. In this
manner, the SMA drive valve actuator is heated and cooled in
proportion to the temperature set point demand.
[0071] While in the present embodiment, the split range controller
232 is described as a proportional controller based on the
characteristics exemplified in graph 9A, it is understood that it
may also be embodied in the microcontroller U4 with another control
strategy, like Proportional plus Integral (PI), Proportional plus
Integral plus Differential (PID), Fuzzy Logic, Neural Network, and
Rules based on Non-linear control, for example. With these control
strategies, the output of the controller 232 would control the rate
of heating of the wire 90 or regulate the cooling device 160 based
on the temperature error 230.
[0072] In operation, if the desired position set point is above the
present position of the movable element of the valve, the positive
position error 208 is converted into a higher temperature set point
220 by the converter 222, thus rendering an initial positive
temperature error signal 230. In response, the controller 232
drives the current driver 212 to regulate the heat to the SMA wire
90, preferably by pulse width modulation, in proportion to the
temperature error to force the movable element to move in a
direction toward the desired position setting. As the sensed
position nears the desired position, the temperature demand will
change and as the sensed temperature reaches the temperature
demand, the temperature error will eventually be reduced to zero
substantially. Likewise, if the position set point is lower than
the present position of the movable element, the negative position
error 208 is converted into a lower temperature set point 220 by
the converter 222, thus rendering an initial negative temperature
error signal 230. In response, the controller 232 drives the
cooling device driver 242 to regulate cooling of the SMA wire 90 by
the cooling device 160 in proportion to the temperature error to
force the movable element to move in a direction toward the desired
position setting. As the sensed position nears the desired
position, the temperature demand will change and as the sensed
temperature reaches the temperature demand, the temperature error
will eventually be reduced to zero substantially. In either case, a
combination of heating and cooling as governed by the position and
temperature errors may be used to maintain the movable element at
the desired position.
[0073] FIGS. 10A, 10B and 10C illustrate a method for configuring a
bobbin of nonconductive material for use in the embodiments
described in connection with FIGS. 1-4. In each of the FIGS. 10A,
10B and 10C, a section of the bobbin is shown in cross sectional
view for convenience of illustration. Referring to FIG. 10A,
grooved sections 402 are removed from the surface area 400 of the
bobbin. The grooved sections are made slightly larger than the
diameter of the SMA wire for acceptance of the windings thereof.
Any conventional fabrication technique, like machining or molding,
for example, will suffice for this step of the method. Next, as
shown in FIG. 10B, a coating of conductive material 404 is applied
over both the grooved and non-grooved surfaces of the bobbin. Then,
as shown in FIG. 10C, the conductive material on non-grooved
surfaces 400 is removed, leaving the conductive material 404
coating only the grooved surfaces 402. The conductive material may
be removed by any conventional machining technique, like grinding,
sanding or milling, for example. Another technique may be to mask
all of the surfaces of the bobbin that are not to be coated with
conductive material, i.e. the non-grooved surfaces, with a masking
material that resists the conductive material, then apply
conductive material to the entire surface of the bobbin (it will
not stick to the mask resist) and, move the masking material. In
the alternative, the conductive material 404 may only be applied to
the grooved surface areas 402 and any material 404 which laps over
onto the surfaces 400 may be machined away. Techniques for
selectively applying conductive material to the grooved surfaces
include ink-printing or syringe needle deposition, for example.
Another technique may be to wind a continuous conductive wire, like
copper, for example, into the grooves of the bobbin and then, cut
off the excess wire along the bottom of the bobbin. In either case,
the SMA wire 406 may be wound into the conductive surface areas 404
to make physical, and thus electrical, contact therewith.
Accordingly, those portions of the SMA wire in contact with the
conductive surfaces of the bobbin will be essentially bypassed
electrically due to the much lower resistance of the conductive
material. Therefore, the SMA wire windings will require less power
overall to achieve the same mechanical advantage.
[0074] Another method for lowering the required power of the SMA
wire to gain the same mechanical advantage is to first coat the
surface area of the SMA wire with a conductive material, like
copper, for example. Then, wind the coated SMA wire around the
bobbin in the grooved areas thereof so that the coated wire
windings are in contact with the grooved surfaces. Thereafter,
remove the conductive material from the surfaces of the wire not in
contact with the grooved surfaces resulting in the structure as
shown by the views of FIGS. 11A and 11B. The darkened areas 410 of
the windings are the coated surfaces of the wire and the remaining
surfaces 412 are uncoated. In this method, the conductive coating
of the wire may be removed from areas not in contact with the
bobbin by sand blasting the wire after being wound around the
bobbin. Another way to remove the coating on the wire not in
contact with the bobbin is to cause the wire to go through one or
more expansion and contraction cycles after being wound around the
bobbin which will cause the coating to flake or peel away due to
the difference in expansion and contraction characteristics of the
wire and coating materials. Those portions of the wire in contact
with the bobbin will not undergo the same degree of expansion and
contraction rendering the coating thereon substantially unaffected.
The expansion and contraction cycles may be caused by thermal
heating of the coated wire, for example.
[0075] While the present invention has been described in connection
with one or more preferred embodiments herein, it is understood
that it should not be limited to any single embodiment. Rather, the
present invention and all of the aspects thereof should be
construed in broad scope and breadth in accordance with the
recitation of the appended claims hereto.
* * * * *