U.S. patent application number 14/170237 was filed with the patent office on 2014-12-11 for variable aperture mechanism for cryogenic environment, and method.
This patent application is currently assigned to Raytheon Company. The applicant listed for this patent is Raytheon Company. Invention is credited to Michael L. Brest, Eric J. Griffin, Kenneth L. McAllister, Jeffrey P. Yanevich.
Application Number | 20140363149 14/170237 |
Document ID | / |
Family ID | 52005558 |
Filed Date | 2014-12-11 |
United States Patent
Application |
20140363149 |
Kind Code |
A1 |
Yanevich; Jeffrey P. ; et
al. |
December 11, 2014 |
VARIABLE APERTURE MECHANISM FOR CRYOGENIC ENVIRONMENT, AND
METHOD
Abstract
A device operable in a ultra-high vacuum and in a cryogenic
environment. The device has bi-stable solenoid motors configured to
drive a shutter assembly defining an aperture having a first shape
when the motors are each disposed in the respective first position,
and wherein the aperture has a second shape when the motors are
each disposed in the respective second position. Actuators
responsive to the motors are thermally isolated from the cryogenic
shutter assembly except when the motors position the shutter
assembly to change a shape of the aperture. The device is suitable
for use in FUR and other thermally sensitive devices.
Inventors: |
Yanevich; Jeffrey P.;
(Bradenton, FL) ; Griffin; Eric J.; (Rancho Palos
Verdes, CA) ; Brest; Michael L.; (Goleta, CA)
; McAllister; Kenneth L.; (Goleta, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Raytheon Company |
Waltham |
MA |
US |
|
|
Assignee: |
Raytheon Company
Waltham
MA
|
Family ID: |
52005558 |
Appl. No.: |
14/170237 |
Filed: |
January 31, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14088176 |
Nov 22, 2013 |
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14170237 |
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61833587 |
Jun 11, 2013 |
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61833599 |
Jun 11, 2013 |
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61833592 |
Jun 11, 2013 |
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Current U.S.
Class: |
396/449 |
Current CPC
Class: |
G01J 3/02 20130101; G01R
31/72 20200101; G03B 9/22 20130101; F02D 41/20 20130101; G01J
3/0286 20130101; H02P 7/2913 20130101; F02M 26/53 20160201; H01F
7/1844 20130101; G03B 9/08 20130101 |
Class at
Publication: |
396/449 |
International
Class: |
G03B 9/08 20060101
G03B009/08 |
Claims
1. A device, comprising: a bi-stable solenoid motor having a motor
member, the solenoid motor configured to drive the motor member
between a first position and a second position; an actuator
responsive to movement of the motor member from the first position
to the second position; and a shutter assembly responsively coupled
to the actuator and defining an aperture having a first shape when
the motor member is disposed in the first position, and wherein the
aperture has a second shape when the motor member is disposed in
the second position, wherein the shutter assembly is configured to
operate in a cryogenic environment.
2. The device as specified in claim 1 wherein the actuator is
thermally isolated from the shutter assembly except when the motor
member moves from the first position to the second position.
3. The device as specified in claim 2 wherein the actuator
comprises an arm having a recess configured to engage the shutter
assembly only when the motor member is advanced from the first
position to the second position.
4. The device as specified in claim 1 wherein the shutter assembly
comprises a first shutter member having a first end disposed in a
cavity and a second shutter member having a second end disposed in
the cavity, the first end opposed to the second end and configured
to be selectively advanced towards, and retracted from, the second
end so as to define the aperture therebetween having the first
shape when disposed in a first position, and wherein the aperture
has the second shape when the first end is disposed in a second
position.
5. The device as specified in claim 4 wherein the actuator
comprises an arm having a recess, and wherein the first shutter
member has a drive member disposed in the arm recess, wherein the
drive member is configured to be engaged by the arm only when the
motor member is advanced from the first position to the second
position.
6. The device as specified in claim 4 wherein the shutter assembly
comprises a housing defining the cavity, wherein the first shutter
member and the second shutter member maintain thermal contact with
the housing in all positions.
7. The device as specified in claim 6 wherein the housing comprises
at least one rail, and the first shutter member and the second
shutter member maintain thermal contact with the at least one rail
in all shutter positions.
8. The device as specified in claim 7 wherein the housing comprises
a sleeve defining the cavity, the sleeve having a pair of opposing
planar members thermally coupled to each other around a midsection
of the respective planar members by at least one spacer member.
9. The device as specified in claim 8 wherein the at least one
spacer member comprises a stop configured to be thermally coupled
to the first shutter member first end and the second shutter member
second end when the aperture has the first shape.
10. The device as specified in claim 1 further comprising a
controller configured to control the solenoid motor and control a
velocity of the motor member as the motor member approaches the
second position.
11. The device as specified in claim 10 wherein the controller is
configured to measure at least one parameter of the solenoid motor
before driving the motor member from the first position to the
second position.
12. The device as specified in claim 11 wherein the solenoid motor
has a coil, and the controller is configured to measure a
resistance of the coil, and control the velocity of the motor
member as a function of the measured coil resistance.
13. The device as specified in claim 11 wherein the solenoid motor
has a coil, and the controller is configured to measure an
inductance of the coil, and control the velocity of the motor
member as a function of the measured coil inductance.
14. The device as specified in claim 11 wherein the controller has
a feedback loop configured to control the velocity of the motor
member as a function of the measured at least one parameter.
15. The device as specified in claim 12 wherein the controller is
configured to measure the coil resistance immediately before
driving the motor member from the first motor position to the
second motor position.
16. The device as specified in claim 12 wherein the controller is
configured to measure a back-emf of the solenoid motor to determine
the coil resistance.
17. A device, comprising: a first bi-stable solenoid motor having a
first motor member and a second bi-stable solenoid motor having a
second motor member, each of the first and second solenoid motors
configured to drive the respective motor member between a first
position and a second position; a first actuator responsive to
movement of the first motor member from the first position to the
second position, and a second actuator responsive to movement of
the second motor member from the first position to the second
position; and a shutter assembly responsively coupled to the first
actuator and the second actuator, the shutter assembly defining an
aperture having a first shape when the first motor member and the
second motor member are each disposed in the respective first
position, and wherein the aperture has a second shape when the
first motor member and the second motor member are each disposed in
the respective second position, wherein the shutter assembly is
configured to operate in a cryogenic environment.
18. The device as specified in claim 17 wherein the first actuator
and the second actuator are thermally isolated from the shutter
assembly except when the first motor member and the second motor
member each move from the respective first position to the
respective second position.
19. The device as specified in claim 18 wherein the first actuator
and the second actuator each comprise an arm having a recess
configured to engage the shutter assembly only when the first motor
member and the second motor member each move from the respective
first position to the respective second position.
20. The device as specified in claim 19 wherein the shutter
assembly comprises a first shutter member responsively coupled to
the first actuator arm and a second shutter member responsively
coupled to the second actuator arm, each of the first shutter
member and the second shutter member configured to be selectively
advanced towards, and retracted from, each other so as to define
the aperture therebetween having the first shape when each of the
first and second solenoid motors are disposed in the first
position, and wherein the aperture has the second shape larger than
the first shape when each of the first and second solenoid motors
are disposed in the second position.
21. The device as specified in claim 20 wherein the first actuator
and the second actuator each comprise an arm having a recess,
wherein the first shutter member has a first drive member disposed
in the first actuator arm recess and the second shutter member has
a second drive member disposed in the second actuator arm recess,
wherein each of the first and second drive members are configured
to be engaged by the respective first and second actuator arms only
when the respective motor members are advanced from the respective
first position to the second position.
22. The device as specified in claim 17 wherein the shutter
assembly comprises a housing defining the cavity, wherein the first
shutter member and the second shutter member maintain thermal
contact with the housing in all positions.
23. The device as specified in claim 22 wherein the housing
comprises a sleeve defining the cavity, the sleeve having a pair of
opposing planar members thermally coupled to each other around a
midsection of the respective planar members by at least one spacer
member.
24. The device as specified in claim 23 wherein the at least one
spacer member comprises a stop configured to be thermally coupled
to the first shutter member and the second shutter member when the
aperture has the first shape.
25. The device as specified in claim 17 further comprising a
controller configured to control the first and second solenoid
motors and control a velocity of the first and second motor members
as the first and second motor members approach the respective
second positions.
26. The device as specified in claim 25 wherein the controller is
configured to measure at least one parameter of the first and
second solenoid motors before driving the respective first and
second motor members from the first position to the second
position.
27. The device as specified in claim 26 wherein the controller has
a feedback loop configured to control the velocity of the first and
second motor members as a function of the measured at least one
parameter.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 14/088,176 entitled "VACUUM STABLE MECHANISM
DRIVE ARM" filed Nov. 22, 2013. The present application claims
priority to commonly assigned U.S. Provisional Patent Application
Ser. No. 61/833,587, filed Jun. 11, 2013, entitled "VARIABLE
APERTURE MECHANISM FOR CRYOGENIC ENVIRONMENT, AND METHOD", U.S.
Provisional Patent Application Ser. No. 61/833,599, filed Jun. 11,
2013, entitled "THERMAL CONTROL IN VARIABLE APERTURE MECHANISM FOR
CRYOGENIC ENVIRONMENT", and U.S. Provisional Patent Application
Ser. No. 61/833,592, filed Jun. 11, 2013, entitled "PULSE WIDTH
MODULATION CONTROL OF SOLENOID MOTOR. The content of the
above-identified patent documents is incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present disclosure is generally directed to an infrared
(IR) imaging mechanism including a shutter having a variable
aperture and operable at cryogenic temperatures in an ultra-high
vacuum environment that is highly sensitive to temperature
variations.
BACKGROUND OF THE DISCLOSURE
[0003] Imaging devices configured to operate at cryogenic
temperatures in an ultra-high vacuum environment are highly
sensitive to temperature variations. Some imaging devices have
variably positioned shutters configured to establish different
sized apertures, whereby the shutter is mechanically configured to
have two or more apertures to support different fields of view and
wavelengths. During the mechanical configuration, the shutter
increases in temperature due to friction and heat transferred from
a drive mechanism. In order for a high definition IR sensor to work
correctly, the temperature of the shutter cannot rise more than 10
Kelvin during actuation. Failure to provide shutter thermal
stability degrades the imaging performance. For instance, when the
temperature of the shutter rises more than 10K, the wait period
before the imaging device can be effectively used increases as the
shutter temperature variation increases. It is not uncommon for
prior art imaging devices to have a wait period that exceeds 10
minutes after shutter configuration.
[0004] Prior art devices utilize piezo electric drives that are not
suitable for ultra-high vacuum and cryogenic environments, as they
have friction that generate particles and are unstable in such
conditions. Prior art devices having an interleaved iris design
have multiple blades, such as four blades, that are forced together
to transfer heat. These interleaved blades are typically ceramic
coated, and thus are poor thermal conductors. As a result, the
shutter experiences a large change in temperature during each
change in position, and significant wait times are incurred while
the shutter temperature stabilizes.
SUMMARY OF THE DISCLOSURE
[0005] To address one or more of the above-deficiencies of the
prior art, one embodiment described in this disclosure comprises a
shutter assembly operable in an ultra high vacuum and in a
cryogenic environment.
[0006] In one embodiment, a device comprises a bi-stable solenoid
motor having a motor member, the solenoid motor configured to drive
the motor member between a first position and a second position. An
actuator is responsive to movement of the motor member from the
first position to the second position, and a shutter assembly is
responsively coupled to the actuator and defining an aperture
having a first shape when the motor member is disposed in the first
position, and wherein the aperture has a second shape when the
motor member is disposed in the second position, wherein the
shutter assembly is configured to operate in a cryogenic
environment. In certain embodiments, the actuator is thermally
isolated from the shutter assembly except when the motor member
moves from the first position to the second position. The actuator
comprises an arm having a recess configured to engage the shutter
assembly only when the motor member is advanced from the first
position to the second position. In certain embodiments, the
shutter assembly comprises a first shutter member having a first
end disposed in a cavity and a second shutter member having a
second end disposed in the cavity. The first end is opposed to the
second end and is configured to be selectively advanced towards,
and retracted from, the second end so as to define the aperture
therebetween having the first shape when disposed in a first
position, and wherein the aperture has the second shape when the
first end is disposed in a second position. In certain embodiments,
the actuator comprises an arm having a recess, and wherein the
first shutter member has a drive member disposed in the arm recess.
The drive member is configured to be engaged by the arm only when
the motor member is advanced from the first position to the second
position. In certain embodiments, the shutter assembly comprises a
housing defining the cavity, wherein the first shutter member and
the second shutter member maintain thermal contact with the housing
in all shutter positions. The housing comprises at least one rail,
and the first shutter member and the second shutter member maintain
thermal contact with the at least one rail in all shutter
positions. The housing comprises a sleeve defining the cavity, the
sleeve having a pair of opposing planar members thermally coupled
to each other around a midsection of the respective planar members
by at least one spacer member, wherein the at least one spacer
member comprises a stop configured to be thermally coupled to the
first shutter member first end and the second shutter member second
end when the aperture has the first shape. In another embodiment, a
controller is configured to control the solenoid motor and control
a velocity of the motor member as the motor member approaches the
second position. The controller is configured to measure at least
one parameter of the solenoid motor before driving the motor member
from the first position to the second position. The solenoid motor
may have a coil, and the controller is configured to measure a
resistance of the coil, and control the velocity of the motor
member as a function of the measured coil resistance. The
controller may also be configured to measure an inductance of the
coil, and control the velocity of the motor member as a function of
the measured coil inductance. In certain embodiments, the
controller has a feedback loop configured to control the velocity
of the motor member as a function of the measured at least one
parameter. The controller may be configured to measure the coil
resistance immediately before driving the motor member from the
first motor position to the second motor position, and may be
configured to measure a back-emf of the solenoid motor to determine
the coil resistance.
[0007] In another embodiment, a device comprises a first bi-stable
solenoid motor having a first motor member and a second bi-stable
solenoid motor having a second motor member, each of the first and
second solenoid motors configured to drive the respective motor
member between a first position and a second position. A first
actuator is responsive to movement of the first motor member from
the first position to the second position, and a second actuator
responsive to movement of the second motor member from the first
position to the second position. A shutter assembly is responsively
coupled to the first actuator and the second actuator, the shutter
assembly defining an aperture having a first shape when the first
motor member and the second motor member are each disposed in the
respective first position, and wherein the aperture has a second
shape when the first motor member and the second motor member are
each disposed in the respective second position, wherein the
shutter assembly is configured to operate in a cryogenic
environment. In certain embodiments, the first actuator and the
second actuator are thermally isolated from the shutter assembly
except when the first motor member and the second motor member each
move from the respective first position to the respective second
position. The first actuator and the second actuator each comprise
an arm having a recess configured to engage the shutter assembly
only when the first motor member and the second motor member each
move from the respective first position to the respective second
position. In certain embodiments, the shutter assembly comprises a
first shutter member responsively coupled to the first actuator arm
and a second shutter member responsively coupled to the second
actuator arm, each of the first shutter member and the second
shutter member configured to be selectively advanced towards, and
retracted from, each other so as to define the aperture
therebetween having the first shape when each of the first and
second solenoid motors are disposed in the first position, and
wherein the aperture has the second shape larger than the first
shape when each of the first and second solenoid motors are
disposed in the second position. In another embodiment, the first
actuator and the second actuator each comprise an arm having a
recess, wherein the first shutter member has a first drive member
disposed in the first actuator arm recess and the second shutter
member has a second drive member disposed in the second actuator
arm recess, wherein each of the first and second drive members are
configured to be engaged by the respective first and second
actuator arms only when the respective motor members are advanced
from the respective first position to the second position. In
certain embodiments, the shutter assembly comprises a housing
defining the cavity, wherein the first shutter member and the
second shutter member maintain thermal contact with the housing in
all positions. The housing comprises a sleeve defining the cavity,
the sleeve having a pair of opposing planar members thermally
coupled to each other around a midsection of the respective planar
members by at least one spacer member. The at least one spacer
member comprises a stop configured to be thermally coupled to the
first shutter member and the second shutter member when the
aperture has the first shape. In certain embodiments, a controller
is configured to control the first and second solenoid motors and
control a velocity of the first and second motor members as the
first and second motor members approach the respective second
positions. The controller is configured to measure at least one
parameter of the first and second solenoid motors before driving
the respective first and second motor members from the first
position to the second position. The controller has a feedback loop
configured to control the velocity of the first and second motor
members as a function of the measured at least one parameter.
[0008] Although specific advantages have been enumerated above,
various embodiments may include some, none, or all of the
enumerated advantages. Additionally, other technical advantages may
become readily apparent to one of ordinary skill in the art after
review of the following figures and description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] For a more complete understanding of the present disclosure
and its advantages, reference is now made to the following
description taken in conjunction with the accompanying drawings, in
which like reference numerals represent like parts:
[0010] FIG. 1 illustrates a thermal imaging device including a
shutter and a thermally isolated drive system configured to
position the shutter according to an embodiment of the present
disclosure;
[0011] FIG. 2 illustrates the thermally isolated drive system of
FIG. 1 with the shutter removed;
[0012] FIG. 3 illustrates a perspective view of one drive
mechanism;
[0013] FIG. 4 illustrates an exploded view of part of the drive
system illustrating the drive arm having an elongated recess
configured as an opening to receive a drive pin and roller of the
shutter slider member;
[0014] FIG. 5 illustrates the drive arm in a first "full open"
position wherein the shutter slider member is in a corresponding
first position;
[0015] FIG. 6 illustrates the drive arm in a second "full closed"
position wherein the shutter slider member is in a corresponding
second position;
[0016] FIG. 7 illustrates a top view of the arm and elongated
opening receiving, but physically and thermally separated from, the
slider pin and roller in the first and second position;
[0017] FIG. 8 illustrates a top view of the arm in the first
position showing the asymmetric clearance of the arm from the
slider pin and roller, including the radial play of the actuator
compared to this clearance;
[0018] FIG. 9 illustrates a perspective view of the drive crank
including the arms;
[0019] FIG. 10 illustrates a controller circuit configured to
control the drive assembly;
[0020] FIG. 11 illustrates a top perspective view of the shutter
assembly;
[0021] FIG. 12 illustrates an exploded view of the shutter
assembly;
[0022] FIG. 13A-13D illustrate different view of the shutter
assembly;
[0023] FIG. 14A-14B illustrate top and bottom views of the lower
plate of the shutter assembly;
[0024] FIG. 15A illustrates a perspective view of the top plate
flipped to show the lower surface thereof; and
[0025] FIG. 15B illustrates a view of the top plate lower
surface.
DETAILED DESCRIPTION
[0026] It should be understood at the outset that, although example
embodiments are illustrated below, the present invention may be
implemented using any number of techniques, whether currently known
or not. The present invention should in no way be limited to the
example implementations, drawings, and techniques illustrated
below. Additionally, the drawings are not necessarily drawn to
scale.
[0027] FIG. 1 illustrates a top perspective view of an IR thermal
imaging shutter apparatus 10 including a variable aperture
mechanism (VAM) operable at ultra-high vacuum and cryogenic
temperature. Apparatus 10 includes a shutter assembly generally
shown at 12 comprising a pair of sliding aperture blades 14. The
sliding aperture blades 14 together define a shutter aperture 15,
and each blade 14 is configured to be driven by a respective drive
mechanism generally shown at 16A and 16B to selectively establish a
shape of the aperture 15. The aperture blades 14 are each enclosed
in a cavity defined between a pair of thermally conductive members
defining a sleeve, each aperture blade 14 having two positions, a
closed position to define the aperture 15 having a smaller shape as
shown in FIG. 1, and a retracted position to define a larger shape
aperture 15 (not shown) such that the aperture 15 is configured to
work with an imaging device (not shown) having at least two
different fields of view as will be described in more detail
shortly with respect to FIG. 4 and FIGS. 11-14. The shutter
assembly 12 is advantageously configured to operate at a cryogenic
temperature in a high-vacuum environment, whereby the blades 14
maintain a thermally stable temperature both at rest and during a
transition between positions, and which blades 14 are thermally
isolated from the non-cooled apparatus 10 elements, such as the
drive mechanism 16A and 16B, and the ambient which is critical such
that the imaging device can be immediately used after aperture
shape changes without a significant wait time, as will be detained
shortly in respect to FIG. 4 and FIGS. 11-15.
[0028] Each drive mechanism 16A and 16B comprises a rotary motor 18
(see FIG. 3) preferably comprising a bistable solenoid. The
bi-stable solenoid provides critical advantageous over conventional
piezo electric drives because it is vacuum stable in an ultra high
vacuum environment and highly reliable, such as for use in forward
looking infrared (FLIR) devices. The bi-stable solenoid has
internal retention magnets that provide passive shock and vibration
stability, whereas a piezo electric drive has friction retention.
Moreover, the bi-stable solenoid is capable of more power output by
increasing its drive current, whereas a piezo electric drive
provides a single force output. In addition, the bi-stable solenoid
is 10.times. faster than the piezo electric drive, and does not
generate foreign object debris (FOD), unlike the piezo electric
drive having friction that undesirably creates particles during
operation. The bi-stable solenoid is easy to install in apparatus
10, and requires reduced material and labor cost. The bi-stable
solenoid in conjunction with the variable aperture shutter assembly
operable at cryogenic temperatures provides significant technical
advantages.
[0029] Each drive mechanism 16A and 16B has a rotatable actuator
pin 20 coupled to and driving a balanced rotatable drive crank 22.
Each drive crank 22 has a radially extending elongated arm 24 (see
FIG. 2), configured to selectively rotate arm 24 between a first
"full open" position and a second "full closed" position as shown
in FIG. 5 and FIG. 6, as will be discussed shortly. Each arm 24 has
a distal end having a recess 26, as shown in FIG. 2, the recess 26
preferably comprising an elongated opening in one preferred
embodiment as shown. The recess 26 could also comprise a slot or
other open ended structure if desired, and limitation to an opening
is not to be inferred.
[0030] Each arm recess 26 is configured to receive, but is spaced
from, a respective positioning member 30 and roller 34 (see FIG. 4)
rotatably disposed thereabout. Each member 30 preferably comprises
a shutter pin secured to, and thermally coupled with, one
respective end of the aperture blade 14 formed as a triangle and
opposite the blade end defining the aperture 15 as shown in FIG. 4.
This triangular shape of the aperture blade proximate the
respective member 30, and the separation of each member 30 from the
opposing blade end, helps isolate any heat created on member 30
during aperture positioning from the blade aperture ends proximate
the imaging device to reduce imaging degradation due to such heat.
Each member 30 extends downwards and is connected to a magnet 31
that remains physically and thermally separated above a respective
magnetic detent latch 32. Each detent latch 32 is securingly and
slidably received in a respective slot 35 (see FIG. 3) defined in a
frame 36. Each detent latch 32 is preferably comprised of a plug
configured to slide linearly inside the corresponding slot 35 in
frame 36, and locked into position when positioned in the final
desired location by a set screw 37 pressing the plug upwards into
slot 35, providing an accessible locking feature while inducing
minimal additional linear motion. Upon rotation of the arms 24, the
respective openings 26 engage the respective roller 34 encompassing
the respective shutter pin 30 to linearly move the aperture blade
14 between a first full open position and a second full closed
position, wherein the roller 34 rotates in the opening 26 during
transition, and is then spaced therefrom at the end of the
transition.
[0031] FIG. 2 depicts the apparatus 10 with the shutter apparatus
12 removed, illustrating the drive mechanisms 16A and 16B including
the respective arms 24 having openings 26, the magnetic detent
latches 32 without shutter pins 30, as well as two pairs of
proximity sensors 40 (see FIG. 3) to indicate the final position of
each respective arm 24, preferably comprised of Hall effect
sensors. Each drive crank 22 has a proximity indicating arm 42
including a magnet 44 disposed at a distal end therein and
selectively extending over one of the proximity sensors 40 as a
function of the arm 24 position. When the arm 24 is in the first
full open position as shown in FIG. 5, the first proximity sensor
40 indicates the drive crank 22 is in place at the open position,
and when the arm 24 is in the second full closed position as shown
in FIG. 6, the second proximity sensor 40 indicates the drive crank
22 is in place at the closed position. Magnetic cogging, created
internally to the actuator 18 and in the detent magnetic latch 32,
forces the arms 42 and 46 against the set screws 54 in stops 50 and
52 and prevents any play at the end of travel.
[0032] FIG. 3 depicts a perspective view of one drive mechanism 16
with arm 24 positioned in the second position, illustrating the
travel path of the arm, which may be, for instance, 24 degrees,
although limitation to this path is not to be inferred. The detent
magnetic latch 32 is comprised of a non-magnetic metal, such as
stainless steel, and is seen to have a recess 55 and a pair of end
stops 56, with one end stop 56 defined on each end of the recess
55. A magnet 57 is attached to, or embedded in, the opposing faces
of end stops 56. The magnets 57 are each configured to magnetically
pull the respective magnet 31, and thus pin 30 and associated
roller 34 (FIG. 4), when the magnet 31 is advanced by arm 24
proximate thereto. When arm 24 advances from the first position
(FIG. 5) to the second position (FIG. 6), stop 50 prevents further
movement of the arm 24 but the momentum of the pin 30, magnet 31,
roller 34 and the associated shutter blade 14 are allowed to
continue moving until the blade 14 fully closes and engages a pair
of stop members 86 of shutter assembly 12, as shown in FIG. 14A and
will be described in more detail shortly. The magnet 31, however,
will not make physical contact with the respective magnet 57 and
will remain closely proximate and magnetically attracted to magnet
31 to provide a magnetic latch. Basically, the arm 24 undershoots,
and the pin 30, magnet 31 and roller 34 advance to separate from
the opening 26 and remain thermally isolated from the arm 24, and
the stop members 86 limit the travel of pin 30 from overshooting
and engaging the other edge of opening 26. Likewise, when the arm
24 advances from the second position to the first position, stop 52
prevents further movement of the arm 24 but the momentum of pin 30,
magnet 31, roller 34 and the associated blade 14 are allowed to
continue moving until the blade 14 fully opens and engages a pair
of sidewalls 78, as shown in FIG. 14A. The magnet 31, however, will
not make physical contact with the respective magnet 57 and will
remain closely proximate and magnetically attracted to magnet 31 to
provide a magnetic latch.
[0033] FIG. 4 depicts an exploded view of one drive mechanism 16
and one end of one shutter blade 14 configured to be positioned as
a function of the drive mechanism positions. Each shutter blade 14
is very thin and lightweight to help reduce friction. The shutter
pin 30 consists of a cylindrical post which captures roller 34
comprising a bushing to prevent sliding along the distal slot 26,
wherein roller 34 rolls against the edges of slot 26 to prevent
friction and wear. The magnet 31 is provided below shutter pin 30
and provides a magnetic detent pulling when in close proximity, but
not contacting and thermally isolated from, to the arms of the
detent magnetic latch 32. Each shutter blade 14 has a semicircular
notch 38 configured to define the smaller diameter of aperture 15
in the closed position. Each notch 38 may be configured to define a
round aperture as shown, by may also have different shapes to
define different aperture shapes, such as hexagon, rectangular,
elliptical and other shapes.
[0034] Each drive crank 22 further comprises a radially extending
arm 46, wherein each of arms 42 and 46 are shorter than the
elongated arm 24 as shown in FIGS. 5 and 6, as well as FIG. 9. Each
of arms 24, 42, and 46 are balanced about the center of the drive
crank 22, such that the center of gravity of drive crank 22 is
balanced when coupled to the respective actuator pin 20. This makes
system 10 far less sensitive to extremely high shock requirements.
Each arm 42 and 46 has a travel stop limit comprising a stop member
50 and 52, respectively, of which each contains an adjustable
travel limit set screw 54. Stop member limit screws 54 in turn
establish the precise travel path and limit of arm 24, and thus the
precise limit position of the driven shutter plate 14. Again,
proximity sensors 40 sensing arm 42 indicate whether the drive
crank 22, and thus the arm 24 and shutter plate 14, is in one of
two positions.
[0035] When the shutter plate 14 is in the full open position, the
arm 24 of drive mechanism 16A is in the full open position and the
shutter pin 30 of drive mechanism 16A is positioned at a distal end
of a slot 60 defined in one end of plate 12 as shown in FIG. 5.
Correspondingly, the arm 24 of drive mechanism 16B is in the full
open position, and the shutter pin 30 of the drive mechanism 16B is
outwardly advanced in an opposing slot 60 defined at the opposing
end of plate 12. The converse is true when the shutter plates 14
are in the closed position, as can be seen in FIG. 1 and FIG.
6.
[0036] Advantageously, as illustrated in FIG. 7 and FIG. 8, each
shutter pin 30 and the corresponding roller 34 remain physically
and thermally separated from the respective arm 24 when in the
first position and the second position due to a spacing created
there between in both positions, thus creating a thermal barrier,
also referred to as thermal isolation. The arm 24 only engages the
rollers 34 disposed about the shutter pin 30 for a very short time
period during movement/actuation of the shutter plate 14 from one
position to the other. Thus, the drive mechanisms 16A and 16B and
all parts thereof are thermally isolated from the driven shutter
plate 14 when in the operable full open or full closed position.
The shutter mechanism including the plate 12 and shutter plate 14
are preferably configured in a vacuum having a true IR Dewar
cryogenic environment.
[0037] Moreover, the spacing of the arms 24 from rollers 34
provides the motors 18, and thus the respective arms 24, time to
accelerate from the respective first rest position or second rest
position which advantageously builds momentum in the arms 24 before
engaging and driving the respective rollers 34, converting the
actuation mechanism from torque transfer to momentum transfer of
energy. This additional momentum helps overcome the magnetic detent
forces of the magnetic detent latch 32 acting against the shutter
pin 30, holding arms 42 or 46 against the stop posts 50 or 52. The
impact of the arm 24 engaging the roller 34 during rotation also
helps overcome any stiction that may be present. This spacing
increases the required force margin from 25% to 900%. The spacing
also allows the use of a less precise solenoid motor 18, which has
a relatively large amount of play and thus is less suitable for
driving the arm 24 directly. Each arm opening 26 provides a loose
fitting about the respective shutter pin 30 and roller 34, such
that the motor loose play does not impair operation of the shutter
aperture. Conversely, the loose tolerances of the arm openings 26
mitigate the risk of an inadvertent rebound. The aperture blades 14
have internal stops, which engage prior to the holding arms 42 or
46 contacting their respective stop. Since the shutter pin 30 is
not firmly engaged within the distal slot 26, the aperture blade
can rebound before the arm 42 or 46 contacts the stop set screw 54
and rebounds. Additional margin is provided by the fact that the
arm has much higher inertia than the aperture blade, and rebounds
correspondingly slower. The high level of damping in the actuator
bearings in 18 diminishes the magnitude of the arm rebound. These
features prevent a situation where the rebounding arm 24 impacts
the shutter pin 30 and roller 34 while traveling in the opposite
direction. Such impact could exert extremely high forces onto the
shutter pin 30 due to the arm's much higher inertia.
[0038] As shown in FIG. 8, the clearance between the respective
roller 34 and arm opening 26 is slightly asymmetric, although it
may be symmetric if desired. In one preferred implementation, there
is about 1.4 degrees of clearance, also referred to as a dead zone,
equating to about a 0.011 inch clearance, although limitation to
this angular spacing or clearance is not to be inferred. The arm
travel limit set stops established by screws 54 are preferably set
to detent to within 1/5 of the dead zone, about 0.28 degrees.
[0039] In one preferred embodiment, a rotary solenoid is used as
motor 18 as it provides consistent reliability and an adjustable
stroke, such as manufactured by Brandstrom Instruments of
Ridgefield Conn. The fine adjustment features of the drive crank 22
using the travel limit screws 54 in the stationary motor mount stop
limit members 50 and 52 help establish this stroke. This design is
superior to a piezo drive motor that is inherently unreliable,
although is functionally acceptable. Alternate rotary motors could
comprise DC stepper motors, and limitation to the particular rotary
motor is not to be inferred. This invention has advantages over
motors and linkages that may allow motor over-travel which may
overstress driven parts.
[0040] FIG. 9 illustrates a perspective view of the drive crank 22,
including the four balanced arms.
[0041] FIG. 10 illustrates a control circuit at 60 that is
configured to selectively drive each of motors 18, to control the
positioning of the arms 24 and thus drive the shutter plate 14
between the first and second positions. The control circuit
includes a controller 62 having a processor configured to control
drive electronics 64 that interface with motors 18 of drive
mechanisms 16A and 16B.
[0042] Referring now to FIG. 11, there is shown a top perspective
view of the shutter assembly 12. FIG. 12 shows an exploded view of
the shutter assembly 12. FIG. 13A shows a top view of shutter
assembly 12, FIG. 13B shows a bottom view of shutter assembly 12,
FIG. 13C shows a side view of shutter assembly 12, and FIG. 13D
shows an end view of shutter assembly 12. Shutter assembly 12
comprises a top plate 70 and a bottom plate 72 parallel to each
other and secured by a plurality of fasteners 74, shown as screws,
extending through respective flange openings 76. The bottom plate
72 has four upwardly extending sidewalls 78 about the perimeter
thereof such that top plate 70 and bottom plate 72 together define
a sleeve having a cavity 80 there between. Cavity 80 is configured
to house the shutter blades 14 and enable sliding of the blades 14
between two positions to define two different diameters of aperture
15. Each of top plate 70 and bottom plate 72 have opposing slots 60
as previously described to enable shutter pins 30 to be selectively
positioned therein and establish the aperture 15 setting. Top plate
70 and bottom plate 72 are comprised of thermally conductive
materials, such as beryllium copper, and are configured such that
any generated heat uniformly transfers therethrough and equalizes
around the shutter assembly 12 as it is maintained at a cryogenic
temperature. For instance, any heat generated in the shutter pin 30
or roller 34 during positioning of blades 14 to change aperture 15
settings quickly spreads to the other members to maintain a stable
temperature, which is critical to allow the high definition
infrared (IR) sensor (not shown) operating with the aperture 15 to
be used promptly after setting.
[0043] Each of the shutter blades 14 are comprised of a very thin
metal material, such as beryllium copper, and in addition, are gold
plated. Advantageously, the gold plating provides self-lubrication
to the blades 14 without using an oil or grease that is not
suitable for use at cryogenic temperatures. The gold plating also
reflects heat such as that generated by the imaging system at
aperture 15. The gold plating also prevents foreign object debris
(FOD) as it is very soft.
[0044] Each blade 14 has a rounded extension or nub 104 on an edge
thereof configured to engage the respective sidewall 78 of bottom
plate 72, wherein the nubs 104 provide the only contact points with
sidewall 78 to reduce friction during positioning, but also
advantageously provide a thermal path. The sliding blades 14
maintain thermal conduction with upper member 70 and lower member
72 at all times including during a transition due to the
multi-point high thermal conductive paths. Again, the gold plating
of blade 14 provides lubrication at these contact points. All
materials of shutter assembly 12 are vacuum stable in an enclosed
environment.
[0045] FIG. 14A illustrates a top perspective view of bottom plate
72 and FIG. 14B illustrates a bottom perspective view of bottom
plate 72. A top surface 82 of bottom plate 72 is seen to comprise a
plurality of X-shaped recesses 84 configured to operate as particle
traps. Each recess 84 is formed during molding or by etching, and
is configured to collect and capture particles that may be
generated as the blades 14 are positioned over time. In addition,
the magnets 31 coupled to shutter pins 30 magnetize the shutter
pins 30 and also collect any particles that may be generated.
[0046] Bottom plate 72 is further seen to comprise a pair of posts
86 opposed each side of opening 88, which opening 88 provides the
larger shape of aperture 15 when the blades 14 are in the retracted
position. Top plate 70 has opening 90 having a larger diameter
(clearance hole) while opening 88 has a controlled aperture hole.
Each of blades 14 is seen to have opposing distal ends 92 forming
edges including opposing notches 94, as shown in FIG. 12. The
opposing notches 94 of blades 14 are configured to mechanically and
thermally engage the respective posts 86 in the closed position,
which posts 86 operate as stop limits for the blades 14, and also
shutter pin 30 and roller 34 as described earlier with respect to
FIG. 3. Moreover, the posts 86 help thermally balance the shutter
assembly 12 when the blades 14 engage them, and also help balance
any heat between the opposing top plate 70 and the bottom plate 72.
The sidewalls 78 provide the stop limits for the blades 14 in the
open position, and also shutter pin 30 and roller 34 as described
earlier with respect to FIG. 3.
[0047] Each blade 14 has a tapered, triangular end 96 mechanically
and thermally coupled to respective shutter pin 30 such that any
heat generated in shutter pin 30 is as far as possible from the
opposing distal ends 92 to minimize thermal variations at distal
ends 92 that can degrade the performance of the imaging system. The
distal ends 92 are each beveled, and slightly overlap one other in
the closed position to prevent any light passing across the
interface of the blades 14 in the closed position. The beveled
distal ends 92 also allow one blade distal end to slightly ride on
the other in the closed position, which may occur over time during
operation of the shutter assembly 12.
[0048] The bottom plate 72 has a plurality of semicircular
extensions 98 that are configured to receive a cryogenic housing
configured to maintain the shutter assembly 12 at a cryogenic
temperature, as shown in FIG. 14B.
[0049] Referring to FIG. 15A there is shown a perspective view of
the top plate 70 with the top plate 70 turned over to show a lower
surface 100 of the top plate 70. FIG. 15B shows a top view of the
flipped top plate 70. The lower surface 100 is seen to have a pair
of parallel slide rails 102 each side of opening 88, each rail 102
extending upward and configured to engage the top surface of the
opposing gold plated blades 14. The slide rails 102 also partially
straddle the respective opening 60. Advantageously, the gold
plating is relatively soft and provides a self-lubricating surface,
such that very low friction is generated between the rails 102 and
the surface of the blades 14 during transitions. Moreover, the soft
gold material does not generate any noticeable gold
particulates.
[0050] The shutter assembly is configured to operate at cryogenic
temperatures, below 100 Kelvin. The shutter assembly 12 maintains
at least a 200 Kelvin temperature differential from the non-cooled
parts including the driving mechanism parts. Advantageously, the
shutter assembly 12 is configured such that the blades 14 are
thermally stable and do not change temperature more than 10 Kelvin,
particularly at edges 92, which is critical such that a high
definition infrared (IR) imaging system can be used immediately
after transitions of the blades 14 from one aperture setting to the
other. The sliding blades 14 maintain continuous thermal contact
without increased friction. This exceptional performance is
achieved by numerous critical features including the gold plating
of the blades providing a self-lubricating low friction surface at
cryogenic temperatures, the pins 30 coupled to a triangular tapered
end of the blades 14 at the far ends of the blades from the
aperture, the thermal isolation of the driving mechanism from the
shutter assembly 12 achieved by the separation of pin 30 and roller
34 from the shutter assembly 12 except during transition, and the
thin blades 14 minimizing friction and reflecting any heat.
[0051] Modifications, additions, or omissions may be made to the
systems, apparatuses, and methods described herein without
departing from the scope of the invention. The components of the
systems and apparatuses may be integrated or separated. Moreover,
the operations of the systems and apparatuses may be performed by
more, fewer, or other components. The methods may include more,
fewer, or other steps. Additionally, steps may be performed in any
suitable order. As used in this document, "each" refers to each
member of a set or each member of a subset of a set.
[0052] To aid the Patent Office, and any readers of any patent
issued on this application in interpreting the claims appended
hereto, applicants wish to note that they do not intend any of the
appended claims or claim elements to invoke paragraph 6 of 35
U.S.C. Section 112 as it exists on the date of filing hereof unless
the words "means for" or "step for" are explicitly used in the
particular claim.
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