Title:
On-gimbals cryogenic cooling system
Kind Code:
A1


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)
Application Number:
11/789389
Publication Date:
11/01/2007
Filing Date:
04/24/2007
Assignee:
RAFAEL-ARMAMENT DEVELOPMENT AUTHORITY LTD.
Primary Class:
Other Classes:
62/378
International Classes:
F25B9/00; F25D25/00
View Patent Images:
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Primary Examiner:
JULES, FRANTZ F
Attorney, Agent or Firm:
Paul D. Greeley (Ohlandt, Greeley, Ruggiero & Perle, L.L.P. One Landmark Square, 10th Floor, Stamford, CT, 06901-2682, US)
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

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Another aim of the present invention is to provide a Joule Thomson cooling device that utilizes a mixture of gases as the refrigerant.

Another aim of the present invention is to provide a Joule Thomson cooling device that utilizes a refrigerant at a low pressure.

Another aim of the present invention is to provide a Joule Thomson cooling device that is simple to use.

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.

Another aim of the present invention is to provide a Joule Thomson cooling device that is simple to install and operate.

Other purposes and advantages of the invention will appear as the description proceeds.

SUMMARY OF THE INVENTION

The present invention relates to 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 a 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.

Preferably, the tubes are made from any one of the materials selected from the group consisting of:

    • a. stainless steel; and,
    • b. copper-nickel alloy.

According to one aspect, the system further comprises:

    • 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.

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.

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

Preferably, 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;

Preferably, the system utilizes a refrigerant comprising a mixture of gases, wherein the refrigerant's maximum pressure is less than 3 MPa.

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:

    • 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.

According to one aspect, the method further comprises:

    • 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.

According to another aspect, the method further comprises:

    • 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.

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

FIG. 1 illustrates a gimbals mount;

FIG. 2 illustrates the transfer line of the present invention, made up of flexible small diameter tubes;

FIG. 2a illustrates a cross-section of the transfer line shown in FIG. 2;

FIG. 3 illustrates one embodiment of the present invention wherein the expanded refrigerant is returned to the internal conduit via transfer line;

FIG. 4 illustrates an enlarged cross sectional perspective view of the internal conduit that causes the refrigerant to flow through the gimbals base;

FIG. 5 illustrates the high and low pressure transfer lines of the present invention joined by a connector;

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

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

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.

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.

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.

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.

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.

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.

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′.

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.

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.

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.

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.

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.

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.

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.