U.S. patent application number 11/789389 was filed with the patent office on 2007-11-01 for on-gimbals cryogenic cooling system.
This patent application is currently assigned to RAFAEL-ARMAMENT DEVELOPMENT AUTHORITY LTD.. Invention is credited to Igor Lifshits, Ben-Zion Maytal, Nir Tzabar.
Application Number | 20070251246 11/789389 |
Document ID | / |
Family ID | 38647026 |
Filed Date | 2007-11-01 |
United States Patent
Application |
20070251246 |
Kind Code |
A1 |
Maytal; Ben-Zion ; et
al. |
November 1, 2007 |
On-gimbals cryogenic cooling system
Abstract
The present invention is a system for cryogenic cooling of an
object mounted on gimbals. A transfer line made up of one or more
flexible small diameter transfer tubes is used to connect the
compressor, which is located separately from the gimbals, and the
cryocooler, which is mounted on the gimbals in thermal contact with
the object to be cooled. The transfer line of the system of the
invention has a total gas transfer capacity equal to that of the
large diameter lines used in conventional systems but allows
essentially unhindered rotation of the gimbals yoke and platform
about the gimbals' axes, under the influence of gravity or with the
help of motors.
Inventors: |
Maytal; Ben-Zion; (Atlit,
IL) ; Lifshits; Igor; (Haifa, IL) ; Tzabar;
Nir; (Lavon, IL) |
Correspondence
Address: |
Paul D. Greeley;Ohlandt, Greeley, Ruggiero & Perle, L.L.P.
One Landmark Square, 10th Floor
Stamford
CT
06901-2682
US
|
Assignee: |
RAFAEL-ARMAMENT DEVELOPMENT
AUTHORITY LTD.
|
Family ID: |
38647026 |
Appl. No.: |
11/789389 |
Filed: |
April 24, 2007 |
Current U.S.
Class: |
62/6 ;
62/378 |
Current CPC
Class: |
F25B 9/02 20130101; F25B
2500/01 20130101; F25D 19/00 20130101 |
Class at
Publication: |
62/6 ;
62/378 |
International
Class: |
F25B 9/00 20060101
F25B009/00; F25D 25/00 20060101 F25D025/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 27, 2006 |
IL |
175276 |
Claims
1. A cryocooling system for cooling an object mounted on a gimbals
platform, said system comprising: a. a gimbals fixed to a support;
b. a cryocooler mounted on the platform of said gimbals, and in
thermal communication with said object; c. a compressor located
separately from said platform; d. one or more internal conduits
located at and coaxial with one or more of the rotational axes of
said gimbals, for facilitating the passing of refrigerant from said
compressor to said cryocooler; e. a supply line for transferring
said refrigerant from said compressor to said internal conduit;
and, f. a first transfer line for transferring said refrigerant
from said internal conduit to said cryocooler; wherein said first
transfer line comprises two or more small diameter flexible tubes
joined together in parallel at each of their ends by a
connector.
2. A system according to claim 1, wherein the small diameter tubes
comprise an internal diameter of between 0.2 mm-0.3 mm.
3. A system according to claim 1, wherein the small diameter tubes
comprise a wall thickness of between 0.05 mm-0.15 mm.
4. A system according to claim 1, wherein the tubes are made from
any one of the materials selected from the group consisting of: a.
stainless steel; and, b. copper-nickel alloy.
5. A system according to claim 1, further comprising: a. a second
transfer line for transferring the refrigerant from the cryocooler
to the internal conduit; and, b. a return line for transferring
said refrigerant from said internal conduit to the compressor;
wherein said second transfer line comprises two or more small
diameter flexible tubes joined together in parallel at each of
their ends by a connector
6. A system according to claim 1, wherein the gimbals and the
cryocooler are surrounded by a container having an outlet, and
wherein said system further comprises a return line for
transferring the refrigerant from said outlet to the
compressor.
7. A system according to claim 1, wherein the internal conduit is
located at any one of the group consisting of: a. the gimbals
z-axis; b. the gimbals y-axis; and c. the gimbals x-axis
8. A system according to claim 1, wherein the internal conduit
comprises any one of the group consisting of. a. a passage for
refrigerant that is transferred to the cryocooler; and, b. a
passage for refrigerant that is transferred to the cryocooler, and
a passage for refrigerant that is transferred from the
cryocooler;
9. A system according to claim 1, wherein the refrigerant comprises
a mixture of gases.
10. A system according to claim 9, wherein the refrigerant's
maximum pressure is less than 3 MPa.
11. A method for cooling an object mounted on a gimbals platform,
by a cryocooling system, said method comprising the following
steps: a. providing a cryocooling system comprising: i. a gimbals
fixed to a support; ii. a cryocooler mounted on the platform of
said gimbals, and in thermal contact with said object; iii. a
compressor located separately from said platform; iv. one or more
internal conduits located at, and coaxial with, one or more of the
rotational axes of said gimbals, for facilitating the passing of
refrigerant from said compressor to said cryocooler; v. a supply
line for transferring a refrigerant from said compressor to said
internal conduit; and, vi. a first transfer line for transferring
said refrigerant from said internal conduit to said cryocooler; b.
compressing said refrigerant to a predetermined pressure; c.
causing said refrigerant to flow from said supply line to said
internal conduit; d. causing said refrigerant to flow through said
internal conduit to said first transfer line; and, e. causing said
refrigerant to flow through said first transfer line to said
cryocooler, thereby cooling said object; wherein said first
transfer line comprises two or more small diameter flexible tubes
joined together in parallel at each of their ends by a
connector.
12. A method according to claim 11, further comprising: a. causing
the refrigerant to flow from the cryocooler through a second
transfer line to the internal conduit; b. causing said refrigerant
to flow through said internal conduit to a return line; and, c.
causing said refrigerant to flow through said return line to the
compressor; wherein said second transfer line comprises two or more
small diameter flexible tubes joined together in parallel at each
of their ends by a connector.
13. A method according to claim 11, further comprising: a.
providing a container having an outlet, that surrounds the
cryocooler and gimbals, into which the refrigerant flows from said
cryocooler; and, b. causing the refrigerant to flow from said
outlet through a return line to the compressor.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to an apparatus for
carrying out cooling operations. In particular, the present
invention relates to the cryogenic cooling of an object that is
mounted on gimbals.
BACKGROUND OF THE INVENTION
[0002] Cryogenic coolers (or, cryocoolers) are apparatuses that are
used to provide cooling at very low temperatures. There are
numerous scientific, technological and industrial situations in
which the need for a cryocooler arises. For example, the cooling of
detector materials sensitive to infra-red radiation such as those
used in thermal imaging cameras and heat seeking missiles.
[0003] In a Joule Thomson cryocooler apparatus, a compressor
compresses a refrigerant to a small volume, which results in an
increased pressure of the refrigerant. The refrigerant exits the
compressor and enters the inlet of a transfer line. Upon passing
through the expansion orifice situated at the outlet of the
transfer line, and in close proximity to a heat exchanger, such as
a recuperator, the refrigerant's temperature drops and the
refrigerant cools to a liquid state, thereby cooling the
object.
[0004] The cryocooler (i.e. the expansion valve and the
recuperator) is in thermal contact with an object that requires
cooling. The recuperator absorbs the heat from the object, thereby
cooling the object.
[0005] Depending on the application that the cryocooler is used
for, the cryocooler may either be part of a closed or open cycle
cooling system. A closed cycle cooling system is defined as a
system in which the refrigerant is collected following expansion
and sent back to the compressor, where it is recompressed in order
to allow for reuse in the system. An open cycle cooling system is
defined as a system in which the expanded refrigerant is released
into the surroundings following expansion. In general, in an open
cycle cooling system, the refrigerant is compressed gas supplied
from a pressure vessel.
[0006] An alternative cryocooler that is commonly used in
applications where cooling to low temperatures is required, is a
Stirling cooler. The standard Stirling cooler comprises a
compressor, a cold finger, provided with a displacer, and a
connecting line between the compressor and the cold finger.
[0007] When utilizing a cryocooler apparatus to cool an object that
is mounted on a sensitive mechanism, such as a gimbals, that is
used for changing the mounted object's spatial orientation,
complications arise. In a Stirling cooler, the cold finger may be
separated from the compressor a maximum of 30-40 cm. Hence, both
the cold finger and the compressor must be mounted on the gimbals
platform, adding extra weight thereto. Additionally, vibrations
caused by the pulses produced by the displacer of the Stirling
cooler may cause inaccurate orientation of the gimbals mounted
object, and affect its operation.
[0008] In contrast, the compressor of a Joule Thomson cryocooler
may be situated separate from the gimbals platform. To accomplish
this, a supply line for transferring the refrigerant from the
compressor to the cryocooler must be arranged. However, the
transfer means will interfere with the rotational movements of the
gimbals yoke and platform, and as a result, it will be difficult to
orient the object in a desired position. When a motor is used to
assist in rotating the yoke and platform, a more powerful,
generally more massive motor is required in order to overcome the
extra torque created by stiff transfer means.
[0009] When a closed cycle cooling system is used to cool an object
an additional difficulty is that the refrigerant must be returned
to the compressor following cooling. Since the volume of the
refrigerant output is larger than the volume of the refrigerant
input, the transfer line necessary for returning the refrigerant to
the compressor, as required in closed systems, requires a larger
diameter than the line that transfers the refrigerant from the
compressor. However, a larger diameter line generally has less
flexibility than a thinner line, therefore the return line hinders
rotational motion of the gimbals yoke and platform even more than
the supply line does.
[0010] One example of a prior art cryocooler apparatus adapted to
cool an object that is mounted on a gimbals is the Cryocooler
Interface System (CIS), developed by Technology Applications, Inc.,
in which most of the components of a cryocooler apparatus are
located remotely from the cryocooler. The CIS comprises a Sterling
cryocooler, which pre-cools methane gas used as the coolant in a
J-T cryosystem. The CIS accommodates cooling across gimbals'
horizontal axis by routing the transfer line up the gimbals base
and internally through one of the arms of the gimbals yoke. In
order to accommodate the independent rotational motion of a gimbals
yoke and platform, the transfer line is constructed of flexible
sections of low stiffness lines. The transfer line is a small
diameter, 300 series stainless steel line, formed into a helical
configuration, winding and unwinding as the axes rotate. (see
Tomlinson, B. J. and Willern, G. S., Cryocooler Interface System.
Cryocoolers 11, Kluwer Academic/Plenum Publishers, 2001. pg.
719-728). However, since the transfer line crosses both of the
gimbals axes, interference with the motion of the gimbals yoke and
platform is likely.
[0011] The selection of an appropriate gas to be used as
refrigerant is important in order to attain a desired cooling
temperature. It is well known that using a mixture of gases as the
refrigerant can greatly improve the refrigerant's thermodynamic
performance. The table in FIG. 7 classifies eight groups of pure
substances that are typical components of mixtures that are used as
refrigerants (see Luo, E. C. et al in Thermodynamic Analysis and
Optimization of 80K Closed-Cycle Joule Thomson Cryocooler with Gas
Mixture, Beijing, China, 1997.) To form an efficient mixed
refrigerant, one component from two or more groups in the table can
be chosen. Components in the same group are alternatives for each
other.
[0012] One advantage of utilizing a mixture of gases as refrigerant
is that while a pure gas may be run at a pressure of 20 MPa, a
mixture of gases may be run at a pressure of less than 3 MPa. High
pressure gas stiffens the transfer tubing and may require thicker
walled tubing than low pressure gas requires. This is especially
not desirable when the tubing must travel across a gimbals axes,
since the stiff tubes hinder the free rotation of the gimbals
mounted object.
[0013] It is therefore an aim of the present invention to provide a
Joule Thomson closed cycle cooling device that can be used to cool
a gimbals-mounted object, that overcomes the problems of the prior
art, including dealing with the collection and reuse of the
refrigerant.
[0014] Another aim of the present invention is to provide a Joule
Thomson cooling device that provides minimum hindrance to the
motion of the gimbals yoke and platform.
[0015] Another aim of the present invention is to provide a Joule
Thomson cooling device that utilizes a mixture of gases as the
refrigerant.
[0016] Another aim of the present invention is to provide a Joule
Thomson cooling device that utilizes a refrigerant at a low
pressure.
[0017] Another aim of the present invention is to provide a Joule
Thomson cooling device that is simple to use.
[0018] Another aim of the present invention is to provide a Joule
Thomson cooling device that is relatively simple mechanically and
thus economic to produce as well as to maintain.
[0019] Another aim of the present invention is to provide a Joule
Thomson cooling device that is simple to install and operate.
[0020] Other purposes and advantages of the invention will appear
as the description proceeds.
SUMMARY OF THE INVENTION
[0021] The present invention relates to a cryocooling system for
cooling an object mounted on a gimbals platform, said system
comprising: [0022] a. a gimbals fixed to a support; [0023] b. a
cryocooler mounted on the platform of said gimbals, and in thermal
communication with said object; [0024] c. a compressor located
separately from said platform; [0025] d. one or more internal
conduits located at and coaxial with one or more of the rotational
axes of said gimbals, for facilitating the passing of refrigerant
from said compressor to said cryocooler; [0026] e. a supply line
for transferring a refrigerant from said compressor to said
internal conduit; and, [0027] f. a first transfer line for
transferring said refrigerant from said internal conduit to said
cryocooler; wherein said first transfer line comprises two or more
small diameter flexible tubes joined together in parallel at each
of their ends by a connector.
[0028] Preferably, the tubes are made from any one of the materials
selected from the group consisting of: [0029] a. stainless steel;
and, [0030] b. copper-nickel alloy.
[0031] According to one aspect, the system further comprises:
[0032] a. a second transfer line for transferring the refrigerant
from the cryocooler to the internal conduit; and, [0033] b. a
return line for transferring said refrigerant from said internal
conduit to the compressor; wherein said second transfer line
comprises two or more small diameter flexible tubes joined together
in parallel at each of their ends by a connector.
[0034] According to another aspect, the gimbals and the cryocooler
are surrounded by a container having an outlet, and wherein said
system further comprises a return line for transferring the
refrigerant from the outlet to the compressor.
[0035] The internal conduit is located at any one of the group
consisting of: [0036] a. the gimbals z-axis; [0037] b. the gimbals
y-axis; and [0038] c. the gimbals x-axis
[0039] Preferably, the internal conduit comprises any one of the
group consisting of: [0040] a. a passage for refrigerant that is
transferred to the cryocooler; and, [0041] b. a passage for
refrigerant that is transferred to the cryocooler, and a passage
for refrigerant that is transferred from the cryocooler;
[0042] Preferably, the system utilizes a refrigerant comprising a
mixture of gases, wherein the refrigerant's maximum pressure is
less than 3 MPa.
[0043] The present invention further relates to a method for
cooling an object mounted on a gimbals platform, by a cryocooling
system, said method comprising the following steps: [0044] a.
providing a cryocooling system comprising: [0045] i. a gimbals
fixed to a support; [0046] ii. a cryocooler mounted on the platform
of said gimbals, and in thermal contact with said object; [0047]
iii. a compressor located separately from said platform; [0048] iv.
one or more internal conduits located at, and coaxial with, one or
more of the rotational axes of said gimbals, for facilitating the
passing of refrigerant from said compressor to said cryocooler;
[0049] v. a supply line for transferring a refrigerant from said
compressor to said internal conduit; and, [0050] vi. a first
transfer line for transferring said refrigerant from said internal
conduit to said cryocooler; [0051] b. compressing said refrigerant
to a predetermined pressure; [0052] c. causing said refrigerant to
flow from said supply line to said internal conduit; [0053] d.
causing said refrigerant to flow through said internal conduit to
said first transfer line; and, [0054] e. causing said refrigerant
to flow through said first transfer line to said cryocooler,
thereby cooling said object; wherein said first transfer line
comprises two or more small diameter flexible tubes joined together
in parallel at each of their ends by a connector.
[0055] According to one aspect, the method further comprises:
[0056] a. causing the refrigerant to flow from the cryocooler
through a second transfer line to the internal conduit; [0057] b.
causing said refrigerant to flow through said internal conduit to a
return line; and, [0058] c. causing said refrigerant to flow
through said return line to the compressor; wherein said second
transfer line comprises two or more small diameter flexible tubes
joined together in parallel at each of their ends by a
connector.
[0059] According to another aspect, the method further comprises:
[0060] a. providing a container having an outlet, that surrounds
the cryocooler and gimbals, into which the refrigerant flows from
said cryocooler; and, [0061] b. causing the refrigerant to flow
from said outlet through a return line to the compressor.
[0062] All the above and other characteristics and advantages of
the invention will be further understood through the following
illustrative and non-limitative description of preferred
embodiments thereof, with reference to the appended drawings.
BRIEF DESCRIPTION OF THE FIGURES
[0063] FIG. 1 illustrates a gimbals mount;
[0064] FIG. 2 illustrates the transfer line of the present
invention, made up of flexible small diameter tubes;
[0065] FIG. 2a illustrates a cross-section of the transfer line
shown in FIG. 2;
[0066] FIG. 3 illustrates one embodiment of the present invention
wherein the expanded refrigerant is returned to the internal
conduit via transfer line;
[0067] FIG. 4 illustrates an enlarged cross sectional perspective
view of the internal conduit that causes the refrigerant to flow
through the gimbals base;
[0068] FIG. 5 illustrates the high and low pressure transfer lines
of the present invention joined by a connector;
[0069] FIG. 6 illustrates the preferred embodiment of the present
invention wherein the expanded refrigerant is returned to the
compressor by removing the refrigerant from the container that
surrounds the gimbals; and
[0070] FIG. 7 consists of a table that contains a selection of
gases that may be used as refrigerant mixtures.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0071] The present invention relates to cryogenic cooling of an
object mounted on a sensitive mechanism, such as a gimbals, that is
used for changing the mounted object's spatial orientation. In
order to cool the object, a crycooler apparatus is provided. In
order to reduce the weight on the gimbals platform, the compressor
is not fixed to the gimbals. Instead, the compressor is located
separately from the gimbals, and only the cryocooler is mounted on
the gimbals, in thermal contact with the object to be cooled. The
present invention solves the problems encountered in the prior art
by providing a transfer line that allows essentially unhindered
rotation of the gimbals yoke and platform about the gimbals' axes,
under the influence of gravity or with the help of motors used to
keep the object correctly oriented. The solution provided by the
present invention comprises replacing one large diameter transfer
line, which, because of its dimensions, is stiff, with a transfer
line made up of one or more flexible small diameter transfer tubes,
where the total gas transfer capacity of the transfer line of the
present invention is equal to that of the large diameter line.
[0072] The term "compressor" as used herein refers to any device
for compressing a gas, and includes a supply of high pressure gas
in a closed vessel.
[0073] As shown in FIG. 1, gimbals 10 consists of a yoke 9,
rotatable about the y-axis, having at its extremities, two rings
12, 12' positioned directly opposite each other. Platform 15a is
supported by rings 12, 12', such that platform 15a may be rotated
about the x-axis. Platform 15b is supported by rings 13, 13' such
that platform 15b may be rotated about the z-axis An object mounted
on the gimbals can, thus, be rotated independently about the x-,
y-, and z-axes, as shown by the curved arrows 11, 11', 11'' in FIG.
1. For clarity, the gimbals 10 are shown in the figures herein
(other than FIG. 1), having only one platform 15, and thereby
limited to rotation about the x- and y-axes. However, it is
understood that the gimbals 10 of the present invention may further
comprise a second platform, as shown in FIG. 1. Alternatively, the
gimbals 10 of the present invention may be rotatable about only one
axis.
[0074] The object may be returned to a predetermined orientation in
space, regardless of any motion of the support to which the gimbals
base 14 is attached. In the case of gimbals operating in a
gravitational field, the fixed orientation is determined by the
local direction of the field. In the absence of a sufficiently
strong gravitational field, or, when desirable even when operating
in a strong gravitational field, motors (not shown in the figures)
are used to rotate the yoke 9 and platforms 15a, 15b to return the
object to a predetermined orientation relative to a fixed
coordinate system. The transfer line 16 of the present invention
(FIG. 2) comprises two or more flexible small diameter tubes 18. As
an illustrative example, a bundle of two tubes 18 are shown. The
transfer tubes 18 are joined together in parallel at both of their
ends by connectors 19. FIG. 2a shows a cross-sectional view of the
flexible tubes 18 shown in FIG. 2 joined by connector 19. Small
diameter tubes 18 are defined herein to have an internal diameter
of between 0.2 mm to 0.3 mm, and a wall thickness of between 0.05
mm to 0.15 mm. The number and diameter of tubes 18 that are
utilized for transferring the refrigerant depends on the rate of
the refrigerant that is being transferred, which is, among other
factors, dependent on whether the refrigerant is being transferred
to or from the cryocooler, as will be described hereinbelow.
[0075] The tubes 18 are made out of a material that allows for
maximum flexibility, such as stainless steel or a copper-nickel
alloy. The small diameter of the tubes 18 results in a degree of
flexibility that enables the line 16 to bend without becoming
crimped or twisted. This allows the gimbals yoke 9 and platforms
15a and 15b to move essentially freely, as described herein below.
This allows the refrigerant to be transferred to the
gimbals-mounted cryocooler without impeding the rotational
movements of the gimbals yoke 9 and platforms 15a and 15b.
[0076] FIG. 3 shows a method of transferring the refrigerant,
according to one embodiment of the present invention, to and from
an object 24 that requires cooling. The compressor 20 supplies the
refrigerant to the first inlet 32 of internal conduit 31 via
suitable supply line 17. The refrigerant traverses the gimbals's
base 14 via internal conduit 31, and is then transferred to the
gimbals-mounted cryocooler 22 via the flexible high pressure
transfer line 16. Transfer line 16 preferably extends loosely to
cryocooler 22 in order to allow transfer line 16 to bend easily.
Upon passing through the cryocooler expansion valve situated at the
outlet of the high pressure line 16, the refrigerant's temperature
drops and the refrigerant cools to a liquid state. The refrigerant
absorbs energy from the surroundings and evaporates to a gaseous
state, thereby cooling the object. The refrigerant is transferred
back to the internal conduit 31 via the flexible low pressure
transfer line 16'. The return refrigerant is at a lower pressure
than the incoming refrigerant, and as a result, occupies a larger
volume. Therefore, a larger number of small diameter tubes 18 are
used for the return of the low pressure refrigerant, than are
required for the incoming refrigerant. For a typical application,
between 1 to 3 transfer tubes 18 are used on the high pressure
side, and between 2 to 6 transfer tubes 18 are utilized on the low
pressure side. Suitable return means 17' conducts the warmed
refrigerant back to the compressor 20. Since supply and return
lines 17 and 17' do not connect to the gimbals mounted object 24,
they, are not required to be as flexible as transfer lines 16 and
16'. Therefore, the transfer means 17' and 17' may consist of a
single tube whose diameter is larger than that of transfer tubes
18.
[0077] An enlarged cross sectional perspective view of internal
conduit 31 that allows transfer of the refrigerant through the base
of the gimbals is illustrated in FIG. 4. The conduit 31 comprises
inner pipe 40 having inlet 32 and outlet 34, and outer pipe 42,
coaxial with pipe 40, having inlet 36 and outlet 38. Pipes 40 and
42 are joined by soldering or other appropriate means. Pipe 40 is
welded, soldered or glued at its lower end 39 to the lower end 41
of pipe 42 to prevent loss of return coolant from pipe 42. The
casing 46 of the conduit 31 is fixed within the gimbals' 10 base 14
so that conduit 31 is coaxial with the y rotational axis. Pipes 40,
42 protrude upward through, and are attached fixedly to the yoke 9,
and pipe 40 protrudes downward through the bottom of the base 14
(FIGS. 3 and 6). O-rings 44, seated in grooves 48, prevent
refrigerant from seeping out of conduit 31 between pipe 42 and
casing 46. The refrigerant that is transferred through line 16
first enters pipe 40 at its inlet 32 and exits at its outlet 34.
After cooling the gimbals-mounted object, the warmed refrigerant
enters pipe 42 through its inlet 36 and exits pipe 42 through its
outlet 38. In a situation where the exit path 43 of pipe 42 is not
aligned with the exit path 45 of the casing 46, the refrigerant is
released into annular passage 47 where it may flow into path 45 in
order to exit through outlet 38'.
[0078] The connectors 19 shown in FIG. 2a join the flexible tubes
18 into an entity having two common ends, of which one end may be
connected to the upward protruding pipes 40, 42 of internal conduit
31, and the other end to the cryocooler 22. According to the
embodiment shown in FIG. 3, however, the connector 119 is adapted
to receive both the high pressure and the low pressure transfer
lines 16, 16'. FIG. 5 illustrates the connector 119 adapted to join
the transfer tubes 18', 18'' to pipes 40, 42. Transfer tubes 18'
are received by the inner portion 19' of the connector 119, which
sealingly fits over pipe 40 of the internal conduit 31, and
transfer tubes 18'' are received by the outer portion 19'' of the
connector 119, which sealingly fits over pipe 42 of the conduit 31.
The transfer tubes 18', 18'' are shown to be loosely accommodated
by the connector 119, for illustration purposes only. In reality,
the transfer tubes 18', 18'' are tightly and sealingly secured by
welding, epoxy or other suitable means to the connector 119 such
that refrigerant may not escape from the connector 119.
[0079] In a preferred embodiment of the present invention (FIG. 6),
the gimbals is surrounded by a container 28. The refrigerant is
transferred from the compressor 20 to the first inlet 32 of the
internal conduit 31 via suitable supply line 17. The refrigerant
traverses the gimbals' base 14 via internal conduit 31, and is then
transported to gimbals-mounted cryocooler 22 via the high pressure
transfer line 16. Upon passing through the expansion valve situated
at the outlet of the high pressure lines 16, the refrigerant
expands. The refrigerant absorbs heat from mounted object 24,
thereby lowering the temperature of object 24. The refrigerant
exits the cryocooler 22 into the container 28 and then exits the
container through its outlet and returns to the compressor 20
through line 17'. In this preferred embodiment, the return line
that connects directly to the gimbals 10 is not present, hence,
only the high pressure transfer line 16 can interfere with the
rotation of the yoke 9 and platform 15. In this embodiment,
connector 19 as shown in FIG. 2a may be utilized, and pipe 42 of
the internal conduit 31 is not necessary since refrigerant is
transferred in only one direction through the conduit 31.
Nevertheless, the same conduit 31 may be utilized for each
embodiment, shown in FIGS. 3 or 6, or, the conduit 31 may be
appropriately altered such that only one pipe 40 is present.
[0080] In an alternative arrangement, not shown in the figures,
conduit 31 may be situated at one of rings 12, 12' or 13, 13' (see
FIG. 1), along the rotational axes (x- y- and z-axes) of platforms
15a, 15b, respectively. Suitable supply line 17 transfers
refrigerant from compressor 20 to first inlet 32 of conduit. In
this arrangement, casing 46 of the conduit 31 is fixed within the
gimbals 10 ring 12 or 12', and pipes 40, 42 may rotate freely.
Transfer line 16 may run internally through, or along the outer
surface of platforms 15a, 15b to cryocooler 22.
[0081] The present invention does not depend on a particular gas or
mixture of gases to be used as a refrigerant in order to operate. A
suitable refrigerant may, for example, be selected from preferably
a combination of the compounds shown in the table in FIG. 7, as
described herein above.
[0082] As described herein above, when utilizing a mixture of gases
as the refrigerant, a much lower pressure may be obtained than when
utilizing a pure gas. For example, a pure gas may run at 20 MPa in
a typical Joule Thomson cryocooler, whereas a mixture of gases may
run at less than 3 MPa. By operating the cryocooler utilizing a
refrigerant at low pressure, thinner pipes as well as less bulky
connections for joining the pipes together, may be used, than if a
refrigerant at high pressure is utilized.
[0083] Additionally, the present invention may be part of an open
or closed system. Open systems generally operate using refrigerant
at higher pressure than that of closed systems. This is not
desirable, especially when the object is gimbals mounted, since the
high pressure stiffens the transfer tubing. Utilizing a mixture of
gases enables the refrigerant to run at low pressure, thereby
allowing the transfer tubing to remain flexible during the transfer
of refrigerant.
[0084] While the forgoing description describes in detail only a
few specific embodiments of the invention, it will be understood by
those skilled in the art that the invention is not limited thereto
and that other variations in form and details may be possible
without departing from the scope and spirit of the invention herein
disclosed or exceeding the scope of the claims.
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