U.S. patent application number 10/093071 was filed with the patent office on 2003-01-02 for thin film shape memory alloy actuated flow controller.
Invention is credited to Gupta, Vikas, Johnson, A. David.
Application Number | 20030002994 10/093071 |
Document ID | / |
Family ID | 26786916 |
Filed Date | 2003-01-02 |
United States Patent
Application |
20030002994 |
Kind Code |
A1 |
Johnson, A. David ; et
al. |
January 2, 2003 |
Thin film shape memory alloy actuated flow controller
Abstract
A flow controller for use in microelectromechanical systems. The
principal components of the controlled are a microvalve and sensor
which are micromachined on one surface of a substrate that is
formed with a fluid flow channel. The microvalve includes a shape
memory alloy actuator element that is operated by a feedback signal
from a control circuit. The sensor can be a fluid flow rate sensor
or a fluid temperature sensor or a fluid pressure sensor.
Conditions in the channel are sensed for generating the feedback
signal.
Inventors: |
Johnson, A. David; (San
Leandro, CA) ; Gupta, Vikas; (San Leandro,
CA) |
Correspondence
Address: |
Law Offices of Richard E. Backus
The Monadnock Building
Suite 490
685 Market Street
San Francisco
CA
94105
US
|
Family ID: |
26786916 |
Appl. No.: |
10/093071 |
Filed: |
March 7, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60273621 |
Mar 7, 2001 |
|
|
|
Current U.S.
Class: |
417/292 ;
417/300; 417/322 |
Current CPC
Class: |
G01F 1/6845 20130101;
G05D 7/0694 20130101 |
Class at
Publication: |
417/292 ;
417/300; 417/322 |
International
Class: |
F04B 049/00 |
Claims
1. A miniature flow controller for use in microelectromechanical
systems, the flow controller comprising a substrate, the substrate
being formed with a channel for confining a fluid flow, a thin film
microvalve micromachined on the substrate, the microvalve
comprising a valve actuator, the actuator having an operating
element comprised of a shape memory alloy which undergoes a
crystalline phase transformation and resulting shape change from a
low temperature deformable phase to a high temperature memory phase
when the element is heated through the alloy's phase change
transformation temperature, the element being positioned for
movement in the channel for contolling the fluid flow responsive to
the shape change, a sensor micromachined on the substrate for
sensing fluid conditions in the channel, the sensor being selected
from the group consisting of a fluid flow sensor, a fluid
temperature sensor and a fluid pressure sensor.
2. A flow controller as in claim 1 and further comprising a control
circuit which generates a feedback signal responsive to sensing of
the conditions in the channel, the control circuit controlling the
actuation of the element responsive to the feedback signal
3. A flow controller as in claim 1 in which the fluid flow rate
sensor is operatively positioned to sense the flow rate of fluid in
the channel, and the control circuit contols heating of the shape
memory alloy responsive to the feedback signal sufficient to cause
the movement of the element for adjusting the flow rate in the
channel.
4. A flow controller as in claim 3 in which the control circuit
further establishes a preset flow value and controls the heating of
the shape memory alloy sufficient to adjust the fluid flow in the
channel toward the preset flow value.
5. A flow controller as in claim 3 in which the control circuit
controls heating of the shape memory alloy sufficient to cause the
element to proportionally adjust fluid flow in the channel within a
range of flow values.
6. A flow controller as in claim 1 in which the fluid temperature
sensor is operatively positioned to sense temperature of fluid in
the channel.
7. A flow controller as in claim 6 in which the control circuit
contols heating of the shape memory alloy responsive to the
feedback signal sufficient to cause the element to vary the fluid
flow for adjusting the fluid temperature in the channel.
8. A flow controller as in claim 1 in which the fluid pressure
sensor is operatively positioned to sense the pressure of fluid in
the channel.
9. A flow controller as in claim 8 in which the control circuit
contols heating of the shape memory alloy responsive to the
feedback signal sufficient to cause the element to vary the fluid
flow for adjusting fluid pressure in the channel.
10. A flow controller as in claim 1 for providing multi-channel
flow control in which a plurality of the channels are formed in the
substrate, and at least one said microvalve is operatively
connected with respective ones of the channels.
Description
CROSS-REFERENCE TO PRIOR APPLICATION
[0001] This application claims the benefit under 35 USC
.sctn.119(e) of U.S. provisional application serial No. 60/273,621
filed Mar. 7, 2001.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to microelectromechanical (MEMS)
sytems, and more particularly to flow controllers for use in MEMS
systems.
[0004] 2. Description of the Related Art
[0005] Most flow controllers are made of discrete components and
are single channel. This invention has fabricated multi-channel
flow controllers integrated onto a single substrate using
microfabrication (MEMS) processes. This approach integrates the
normally separated functions of flow measurement, feedback, and
control enabling miniaturization of these devices. The functions of
sensing, feedback control, and communication with a host computer
are performed by a dedicated microprocessor on the same substrate.
Miniaturization of components allows for the reduction of dead
volume and increased portability.
[0006] Miniaturization of components also allows for the
incorporation of multiple channels of various sizes within the
footprint of a conventional single channel flow controller made
from discrete components. A multi-channel flow controller enables
changes in flow ranges without having to change out the flow
controller itself as is now the practice in the semiconductor
industry. This saves on labor costs and reduces the number of
different ranges of flow controllers that must be stocked.
[0007] Flow controllers require a valve. In the prior art, the lack
of suitably fast, reliable valves produced by MEMS processes has
prevented the fabrication of truly integrated MEMS-produced flow
controllers.
OBJECTS AND SUMMARY OF THE INVENTION
[0008] It is a general object of the invention to provide new and
improved fluid flow controllers which are of sufficient minature
size for enabling their use in MEMS applications.
[0009] This invention provides minature proportional microvalves
that can be configured in multiple valve arrays. These microvalves
are much smaller than the smallest currently available solenoid
valve. It is the use of this very small valve along with thin film
sensors, which sense fluid flow and/or pressure and/or temperature,
that enables a significant reduction in size.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a top plan view of a multiple valve array in
accordance with one embodiment of the invention.
[0011] FIG. 2-A is an exploded isometric front view of an
individual microvalve used in the array of FIG. 1.
[0012] FIG. 2-B is an exploded isometric rear view of the
microvalve of FIG. 2-B.
[0013] FIG. 3 is a top plan view showing two types of ceramic valve
substrates for use in the microvalve of FIGS. 2-A and 2-B.
[0014] FIG. 4 is a block diagram showing the overall control
circuit used in the invention.
[0015] FIG. 5 is a circuit diagram for the first pressure sensor
circuit in the invention.
[0016] FIG. 6 is a circuit diagram for the second pressure sensor
circuit in the invention.
[0017] FIG. 7 is a circuit diagram for the temperature sensor
circuit in the invention.
[0018] FIG. 8 is a circuit diagram for the flow sensor circuit in
the invention.
[0019] FIG. 9 is a circuit diagram for the microprocessor circuit
in the invention.
[0020] FIG. 10-A is a front view and left side view of a manifold
for use in a dual range flow controller embodiment of the
invention.
[0021] FIG. 10-B is a back view and right side view of the manifold
of FIG. 10-A.
[0022] FIG. 11 is a top plan view of a dual channel flow controller
incorporating the manifold of FIGS. 10-A and 10-B.
[0023] FIG. 12-A is a schematic plan view of a flow sensor in the
invention.
[0024] FIG. 12-B is a schematic cross sectional view of the flow
sensor of FIG. 12-A.
[0025] FIG. 12-C is a schematic isometric view of the flow sensor
of FIG. 12-A.
[0026] FIG. 13 is a block diagram of a digital mass flow controller
using a flow restrictor for use in the invention.
[0027] FIG. 14-A is a block diagram showing a mass flow controller
that is responsive to a flow sensor that measures differential
pressure.
[0028] FIG. 14-B is a block diagram showing a mass flow controller
that is responsive to a flow sensor that measures absolute
pressure.
[0029] FIG. 15 is a simplified flow chart of a flow control
algorithm for the mass flow controller of FIG. 13.
[0030] FIG. 16 is a block diagram showing a dual range mass flow
controller in accordance with the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] In accordance with one preferred embodiment, the invention
provides a flow controller 13 (FIG. 11) of minature size suitable
for use in microelectromechanical ("MEMS") systems that controls
fluid flow.
[0032] Flow controller 13 includes a thin film microvalve array,
shown generally at 10 in FIG. 1, which is formed by micromaching on
a chip substrate. Any desired number of microvalves can be employed
in such an array, and in the illustrated embodiment the array
comprises four microvalves 12, 12' 12" and 12'". Each microvalve is
comprised of a valve actuator 15 (shown only for valve 12) having a
thin film operating element 17 formed of a shape memory alloy (SMA)
to control fluid flow, a sensor or sensors (FIGS. 12-A, 12-B and
12-C) to measure flow rate and/or fluid temperature and/or fluid
pressure, and channels 19, 21 (FIG. 11) connecting the sensor(s)
and microvalve through which flow takes place.
[0033] SMA operating element 17 in actuator die 22 (FIGS. 2-A and
2-B) preferably is comprised of nickel-titanium thin film shape
memory alloy. The alloy undergoes a crystalline phase change
transformation, and resulting shape change, from a low temperature
deformable shape to a high temperature memory shape when the
element is heated through the alloy's phase change transformation
temperature. When so heated, the shape change can be used to
perform work. In this invention the work occurs as the operating
element changes shape so as to move within or across a valve
channel to partially or completely open or close the fluid flow
path. The actuator is proportional in operation. The thin film SMA
actuator can be formed on a substrate by the methods set forth in
U.S. Pat. No. 5,061,914 to Busch et. al., the disclosure of which
is incorporated by this reference.
[0034] The assembly of components of microvalve 12, which is
typical in the invention, is shown in the exploded views of FIGS.
2-B and 2-B. The microvalve 12 is comprised of a housing 14, O-ring
16, orifice die 18, spacer 20, actuator die 22, bias spring 24 and
cover 26. These components are assembled together as shown in the
Figures by suitable means such as pogo pins 28 and screws 30. Bias
spring 24 serves the function of applying a yieldable force against
actuator element 15 so as to move it from the memory shape to the
deformable shape when the element's temperature is below the
transformation temperature. The force of element 15 when actuated
toward its memory shape is sufficent to overcome the spring bias
force.
[0035] The SMA operated microvalves of the invention can provide
proportional control, which is desirable for many applications. The
flow sensor measures fluid mass passing by a point in a fixed time,
or measures the pressure drop across a calibrated orifice. All of
the components can be fabricated on a single small chip by known
methods of photolithography and micromaching of silicon
substrates.
[0036] Particular advantages of the invention are that the SMA
actuators are so small that multiple actuators may be placed in a
space without increasing the package size. This has the important
consequence that if several valves are packaged together with each
having its own flow channel, then the dynamic range of the flow
controller can be extended. Conventional sensors always have a
range over. which they work best. A sensor that measures accurately
to 0.1% in the range of 10 to 1000 ml/min is not accurate in the
range of 0.001 to 1 ml/min. In the invention when a set-point is
specified, the appropriate range is selected by software. An
advantage is that the user need only buy one, not multiple,
controllers. Then when flow rate must be changed, it can be done in
the system software without opening a line and interrupting the
process.
[0037] FIG. 3 shows a substrate 32 of a ceramic with wire-bonded
electrical leads 34. Mounted on the substrate are two or more
microvalves 12, 12' of the valve array, a sensor 36, which can
comprise either a flow, pressure or temperature sensor, and an
electronic controller board 38. The microvalves can be fabricated
in accordance with the methods of U.S. Pat. No. 5,325,880 to A.
David Johnson et. al., the disclosure of which is incorporated by
this reference. The channels for providing fluid flow paths between
the valves, sensors and inlet/outlet ports are formed in layers
(not shown) of a suitable material that can be sputter deposited
over the substrate.
[0038] The overall control circuit shown in FIG. 4 provides
feedback to adjust each microvalve so that the measured flow
matches a preset value, called the set-point. Feedback can be
performed by a microprocessor 60 running on suitably programmed
software. The circuit comprises first pressure sensor circuit 52,
second pressure sensor circuit 54, temperature sensor circuit 56,
flow sensor circuit 58 and microprocessor circuit 60.
[0039] The first and second pressure sensor circuits 52 and 54 are
shown in detail in FIGS. 5 and 6, respectively. Temperature sensor
circuit 56 is shown in detail in FIG. 7, and flow sensor circuit 58
is shown in detail in FIG. 8. Microprocessor circuit 60 is shown in
detail in FIG. 9. This circuit 60 comprises a suitable programmable
microprocessor such as a PIC16C74A chip 61. First and second
pressure sensor circuits 52 and 54 have respective leads 64 and 66
which connect with respective chip terminals 68 and 70. Temperature
sensor circuit 56 has a lead 72 which connects with chip terminal
74. And flow sensor circuit 58 has a lead 76 which connects with
chip terminal 78.
[0040] A suitable MEMS flow sensor 36 is provided on at least one
of the substrates to control flow rates. For this purpose, the
microprocessor circuit 60 of FIG. 9 is programmed with suitable
software. A feedback loop is incorporated in the software to
minimize fluctuations. In the preferred embodiment the
microprocessor chip is programmed to control the pulse width to the
valve actuator via RS232 serial communication.
[0041] The invention employs a graphical user interface (GUI) which
is programmed in a suitable language such as Visual Basic .TM.. For
purposes of illustration, dual channel operation has been chosen.
Multi-channel operation can be achieved by expanding the GUI
interface and increasing the number of channels on the controller
hardware. The GUI interface can be displayed on a PC and is
connected to the PIC16C74A via RS232 communication. The operator
chooses a sensor supported by the software and selects the desired
communications port. Then the operator selects the desired channel.
The operator then enters the setpoint for each channel.
[0042] FIGS. 10-A and 10-B show a manifold 80 for a dual channel
flow controller embodiment of the invention. FIG. 11 shows the
manifold 80 with flow restrictors 82 and 84 extending from opposite
sides. This manifold enables a user to switch between various
channel sizes without having to switch out the controller itself.
The flow controller comprises first and second ceramic substrates
mounted on the Delryn .RTM. plastic manifold 80, with flow range
selection achieved by the flow restrictors. The first substrate
comprises two differential pressure sensors of the type which
measure differential pressure drop across the restricor tubes. The
flow restrictors 82 and 84 are formed of stainless steel tubing
which are pinched at 85 and 87 to smaller effective cross sections
while connecting to a flow meter. This flow controller has two
ranges--from 1 to 100 SCCM and from 1 to 1,000 SCCM. The controller
requires two valves for shut-off and two proportional valves. It
also comprises a four-valve multiple microvalve array.
[0043] As shown in FIG. 11, manifold 80 is formed with a pair of
microvalves 89, 91 which are connected through channels 21, 21'
with respective flow restrictors 82, 84. Inlet ports 93, 95 and
outlet ports 97, 99 direct flow to and from the respective
microvalves. Pressure transducers 101 and 103 are provided in the
flow paths for the respective microvalves.
[0044] Components of sensor 86 are shown in schematically in the
plan view of FIG. 12-A, the cross section view of FIG. 12-B and
isometric view of FIG. 12-C. This sensor is comprised of three
resistors H, T1 and T2 located at the middle of a layer of Si
membrane formed by anisotroopic wet etching of the Si layer.
[0045] The three resistors are formed by diffusing boron into the
Si membrane. To configure the flow sensor, the resistor H is used
as the heater element and resistors T1 and T2 are used as
temperature sensors, with one temperature sensor located upstream
related to the heater and the other downstream, as shown for T1 in
FIG. 12-A where the flow is depicted as from right to left.
[0046] When there is no fluid flow, the heat produced by the heater
H is equally distributed to T1 and T2. When there is flow, there is
an imbalance in the heat distribution which is detected by the
circuit measuring the differential resistance of T1 and T2.
[0047] FIG. 13 is a block diagram showing a mass flow controller
system for operating an SMA microvalve actuator 79 in the
invention. The flow from the source is read by flow sensor 81 and
converted from analog to digital signals by the microprocessor
circuit. At step 83 the digital signal is compared to the set-point
that has been specified by the user. The average current into valve
79 is then increased or decreased, thereby regulating the
downstream flow. All flow sensor, valve and electronics components
are micrfrabricated and attached to a common substrate.
[0048] Flow sensor 81 can be of the type shown in the block diagram
of FIG. 14-A which measures pressure differential across a
restrictor, as in the embodiment explained in connection with FIG.
11. Alternatively, the flow sensor could be of the type shown in
the block diagram of FIG. 14-B which is responsive to measurement
of absolute pressure. In this case, the software would be altered
to provide feedback as a pressure regulator. In both systems of
FIGS. 14-A and 14-B, signals from the pressure sensor are compared
with the set-point value to control a proportional valve by means
of the microprocessor software.
[0049] FIG. 15 is a simplified flow chart of the flow control
algorithm for the mass flow controller system of FIG. 13. Software
resident in microprocessor 60 of FIG. 4 controls the average
current to microvalve actuator 79 (FIG. 13) to bring measured flow
into equality with the set-point flow. All functions of analog to
digital conversion, timing, comparison of measured flow to
set-point and communication with the host computer are embodied in
the single chip.
[0050] FIG. 16 shows a block diagram for another embodiment
providing a dual range mass flow controller. Conventional flow
sensors have limited dynamic range. For example, a sensor which is
accurate at medium flow rates will give inaccurate performance at
high or very low flows. In existing equipment, it is standard
practice to replace the restrictors to change the range. This
requires opening the line while the change is being made, and
recalibration is usually necessary. Normal practice is to provide
factory restrictors which are not changed in the field.
[0051] With the present invention, multiple flow paths can be
fabricated in very small spaces so that the appropriate
sensor/restrictor combination can be used for a desired flow range.
This enables having separate valves for each flow range in a small
package. The circuit of FIG. 16 has separate flow channel in
limited space, thereby enabling a flow controller with much greater
dynamic range and hence increased versatility without increasing
cost. One micromachined flow controller may replace a series of
conventional separate flow controllers.
[0052] The circuit of FIG. 16 is controlled by the micropocessor
software to determine from the preestablished set-point which of
the two channel paths to open. A flow sensor feeds information back
for proportional control. As flow increases, the upper limit of
flow is reached, and a separate valve-sensor combination is opened.
This system can be made without increasing the overall size
significantly because most of the volume of the controller is the
package; sensors and valves can be orders of magnitude smaller when
they are integrated in such a package.
[0053] The overall control circuit (FIG. 4) reads output from each
sensor and gives feedback so that flow will remain at the desired
setpoint. This control circuit has certain desirable features: a
data acquisition port monitoring exciter currents, sensor outputs,
amplifier outputs, actuator drivers and currents, and a single
connector to connect the
actuator/flow-sensor/press-sensor/temp-sensor package. This circuit
also has an actuator-driver that can be scaled to drive up to four
actuators, the selection of which is controlled by the program's
operator screen. Besides being able to logically enable/disable
this driver, its power is limited so that it should not be able to
bum-up an actuator. This circuit also has an LED indicator to show
that the PIC-chip has initialized and is ready: if the PIC-chip
should be caused to reset, the LED will blink "on" during each
initialization routine.
* * * * *