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. 2
a 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.
Patent Application
20070251246
