US3184210A - Collapsible form jig - Google Patents

Description

y 1965 c. FASSNACHT ETAL 3,184,210

COLLAPSIBLE FORM J I G 3 Sheets-Sheet 1 Filed June 25, 1962 w mm m M m M NE/A Wmmu 50mm BY May 18, 1965 c. FASSNACHT ETAL 3,134,210

GOLLAPSIBLE FORM JIG Filed June 25, 1962 3 Sheets-Sheet 2 INVENTORY 6644,9451 Pass/v4 cw! y 1965 c. FASSNACHT ETAL 3,184,210

COLLAPSIBLE FORM J IG- 5 Sheets-Sheet 3 Filed June 25, 1962 0am 504154854, $51849; iar/51v ,4 7 rum z 71' United States Patent 3,184,210 r COLLAPSIBLE FORM JIG Charles Fassnacht, Philadelphia, and Neil Worrall Burwell, Southampton, Pa., assiwors to I-T-E Qircuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed June 25, 1962, Ser. No. 204,935 1 Claim. (Cl. 249-53) Our invention relates to the construction and contour checking of antennae structures and more particularly to the use of an inflatable pattern to form a contoured surface adaptable for casting an antenna reflector (or r-adome), and checking the contour of a previously formed antenna structure.

The mobility requirements of many electronic communications and radar systems necessitates an antenna system that may readily be transported and assembled at a designated installation site. Our invention increases the mobility capabilities of such systems by providing a truly tactical antenna system in which the antenna reflector or radome is supplied as a compact kit of basically raw material and necessary tooling for on-site fabrication.

It has been the practice of the prior art to fabricate the antenna reflector and radome structures of such mobile antenna systems in the factory. The reflector is then shipped to the installation site as a unit, or as a number of interlocking sections. Such prior art antenna reflector structures may typically be formed of a plurality of mechanical frame members and sectorial reflector sections, as set forth in our copending US. Patent application Serial No. 197,477, filed May 24, 1962, entitled Antenna Transportable System, and assigned to the assignee of the instant invention.

Another method presently being practiced is to factory cast the antenna structure, and ship it as a unit to the site. When such structures are quite large, it has been the practice to cut the antenna into segments, which segments may then be assembled at the installation site to form the overall antenna structure. Such prior art methods suffer from the disadvantages of requiring large volumes to be transported, shipped, and stored at the installation site, thereby limiting their practicality as true tactical equipment.

As an aspect of our invention, a collapsible pattern is used, which may be inflated by the introduction of air to form an accurately contoured mold surface of a reflector surface. Such a bag-like mold pattern is first inflated to a sufiicient pressure to withstand the weight of casting material which is to be applied thereto to form the basic cast reflector surface. A casting material, such as foamable polyurethane, is then sprayed on the contoured surface of the reflector to the depth required for rigidity and strength. After curing, the inflatable pattern is released, resulting in a cast reflector surface which is a substantial duplicate of the image surface of the inflatable mold. A conductive reflecting surface is then applied to the cast reflector, in an appropriate manner; such as by bonding a mesh screen, flame spraying aluminum, or bonding a metal foil.

It is thus seen that our invention provides an improved apparatus for manufacturing a cast reflector, particularly adaptable for mobile antenna systems, permitting actual fabrication of the antenna at a remote installation site.

In a further aspect of our invention the above described collapsible mold pattern is used as a jig to check the contour of a previously formed reflector surface. When it is desired to field-site check the contour of a particular antenna reflector, the bag is pressurized sufliciently to form the prescribed contour. The bag is then placed in an aligned position with respect to the antenna reflector and accurate feeler gages may be utilized to of the radome structure.

3,l84,2lfl Patented May 18, 1965 check deviations in contour of the antenna reflector from the collapsible contour jig. The prior art methods of contour checking typically include structural templates of metal, wood or plastic. Our method of contour checking eliminates the prior art utilization of such large and heavy structural forms and their accompanying tedious set-up and alignment procedures. The collapsible bag of our invention may advantageously be rolled into a small lightweight package for storing and shipping when not in use.

In still a further aspect of our invention the collapsible formed pattern may be utilized to construct a field site cast radome. Typically, a bag having a substantially spherical surface is first inflated, in the manner set forth above, to form the radome contour. The bag is then spray coated with a cast material, such as foamable polyurethane, to a suflicient depth for strength and rigidity The spray coating of the bag with the cast material may be performed on either the internal or external surface of the bag; the former preferably permits radome fabrication in a controlled environment and is especially advantageous under inclement environmental conditions. Should the inner portion of the spherical bag be sprayed to form the radome, the bag is preferably formed of a number of segments attached together to permit removal after curing of the radome structure.

It is thus seen that the basic concept of our invention resides in the use of an inflatable pattern to permit the fabrication and checking of antenna reflectors or radomes at an installation site. The actual formation of the antenna structure at the remote installation site greatly enhances the mobility requirements of the resultant antenna systems.

it is accordingly a primary object of this invention to utilize a collapsible pattern to form a cast antenna structure.

A further object of this invention is to utilize an air inflatable pre-formed bag-like pattern as a contoured mold surface to form a polyurethane cast antenna reflector.

An additional object of this invention is to provide a field site antenna reflector or radome kit comprising an inflatable mold pattern and the basic materials utilized in the construction of the resultant antenna structure.

Another object of this invention is to provide a collapsible antenna structure pattern which comprises a pre-shaped bag constructed to be inflated to form a prescribed antenna structure contoured surface and adapted to provide a mold surface for the casting of an antenna reflector.

Still an additional object of this invention is to provide a collapsible bag-like radome pattern which may used to fabricate a foam-cast polyurethane radome at a remote installation site.

Still another object of this invention is to fabricate a quantity of accurately formed foamable polyurethane reflector surfaces by the use of an inflatable pattern as a field site tool to form a mold surface.

Yet a further object of this invention is to provide an inflatable antenna pattern, including depth indicating means of varying length indications, to provide a tapered cast antenna structure.

These as well as other objects of our invention will readily become apparent after reading the following descriptions of the accompanying drawings in which:

FIGURE 1 is a perspective view of an antenna structure pattern constructed in accordance with the teachings of our invention, shown fully inflated.

FIGURE 2 is a perspective view of the reflector pattern of FIGURE 1 deflated and rolled up to indicate its compact shipping and storage requirements.

FIGURE 3 is a side elevation of the inflated antenna pattern of FIGURE 1 being used to forma cast antenna reflector.

FIGURE 4 is a cross section along line 4-4 of FIG URE 3 and looking in the direction of 'the arrows which typically illustrates the manner in which the depth indicating posts may be secured to the antenna reflector pattern. FIGURE 5 is a perspective view, partially cut away, of an antenna reflector manufactured in accordance with the teachings of our invention. a

FIGURE 6 typically illustrates the incorporation of an antenna reflector manufactured in accordance with the teachings of our invention in a mobile antenna system.

FIGURE 7 depicts the utilization of the inflatable reflector pattern of our invention as a contour-checking jig.

FIGURES 8 and 9 illustrate the use of an inflatable mold pattern of our invention to form an antenna ra-' dome, showing the forming of the radome structure on the external and internal surface of the inflatable pattern respectively. 7

FIGURE 1 shows in perspective the collapsible mold pattern of our invention in the fully inflated position. The pattern is formed of a bag-like enclosure 10 constructed of a flexible, but non-elastic, material such as rubberized canvas or nylon reinforced plastic. The upper surface 11 of bag-like member 10 is pro-shaped to form a appropriate graduations.

. 4' Depth indicating posts 22 are preferably secured to surface '11 in'a manner which facilitates the removal of the cast reflector 4i) containing such posts from pattern 10. FIGURE 4 shows one such connection of height indicating posts 22 to surfacell in which molding surface 11 contains a number of projections 23 appropriately placed anddimensioned to receive posts 22 Projections 23 arepreferably formed of the same material as inflatable pattern 10 and are permanently affixed thereto. Depth indicating posts 22 contain a hollowed portion constructed to slip-fit over projection 23. Height indicator 22 may typically be a thin-Walled aluminum tube cut to the desired height'of foam above surface 11, or having Projectionfl23 is of ,suflicient height to support the requisite length of tube 22 in the manner-shown in FIGURE 4.

. After inflating of pattern 10 tothe proper pressure, and

the securing of depth indicating posts 22 and mounting i posts 24, antenna structure 11 is then sprayed with a 1 space-saving is effected'by shipping material 20 in its raw mold surface for the antenna structure to be cast; illus- V,

state to the site, where'it is foamed to form the reflector 40. Casting material 20 is preferably a polyurethane foam prepared by adding asurfactant, a bodying agent such as a colloidal silica, e.g., that is marketed under the trade designation Cab-o-sil, and a fluorinated hydrocarbon Pressure mean 15 is; i

stand the weight of casting material which is to be applied I V to form the reflector structure.

FIGURE 2 illustrates the manner in which the deflated pattern 10 may be rolled up to form an extremely compact package, thereby facilitating packing for shipping and storage at the installation site.

Reference is now made to FIGURE. 3, which'illustrates the inflatable pattern 10 being utilized to form an antenna reflector in accordance with the teachings of our invention. Pattern 10 is inflated to a sufiicient pressure to withstand the weight of the casting material 20 applied thereto without distorting reflector contoured surface 11. Inflated pattern 10 is positioned on a suitable support 30, which may typically be the ground plane. To facilitate the removal of mold 10 after curing of the cast reflector, a releasing agent 21 is preferably applied to molding surface 11 prior to the'introduction of the casting material, 20. The releasing compound 21 is preferably non-reactive with either casting material 20 or the material comprising pattern 10, and when polyurethane materials are used for casting may typically bea silicon grease. Prior to the introduction of casting material 20 to the surface 11 of mold 10 a plurality of depth indicating means, such as posts 22, are attached to surface 11. Each of the posts 22 are appropriately marked to indicate the desired depth of casting material at their particular location to yield the requisite cast antenna reflector (FIGURE 5), having sufficient rigidity and structural strength. The posts 22 at the extreme peripheral region are shown extended somewhat to provide a reinforced ring of casting material capable of withstanding the high tension loading about this circumferential region. Structural mounting posts 24 are also provided to be incorporated within cast reflector 40. These posts are constructed to facilitate blowing agent, e.g., a Freon,.to the casting resin. The heat produced by the-exothermic reaction of these materials volatilizes theblowing agent, whic h'produces a cellular structure-in the resultant polymerized material. These raw materials may be internally mixed by either a static or rotary mixer at thesite, or mixed external to the spray gun and then applied to surface 11. The mixing and spraying equipment utilized to form foamable poly urethane from the, raw materials shipped to the site is preferably a portable device; one such device being the model DPSG-A spray gun and metering unit, manufactured by the Decker Industries Division of Stuart Marine, Stuart, Florida. After spraying to a sufiicient depth, material 20 is permitted to cure. The foamable polyurethane casting material'20utilized preferably'permits for such FIGURE 5.

Cast antenna 40 has an internally concave parabolic surface 41 corresponding to the image contour of convex mold surface 11. A reflecting surface 42 having the requisite electrical characteristics to impinging radiation of the particular antenna requirement is then applied to surface 41. Surface 42 is shown as a mesh screening bonded to surface 41, but may alternativel be flame sprayed aluminum for a bonded foil. Reflecting surface 42 is shown coated with a protective surface 43 for environmental protection. Surface 43 may be paint, varnish, or the same polyurethane material 20 used to cast the reflector structure.

' Reference is nowmade; to FIGURE 6, whichillustrates 'a typical antenna system utilizing the antenna reflector 40 constructed ,in'accordance with the teachings of our invention. Mounting' ring .25 is connected in an appropriate manner to the upper portion of elevating structure 51. Base pad 52 connected to the lower portion of structure 51 includes a ball andsocket joint, permitting rotation about that point to facilitate the lowering and raising of'elevation member 51. Guy lines 53, 54 anchored at 55, 56 respectively stabilize elevated member 51. Feed 60 is illustratively shown'as a dual polarized feed with wave guides 61 and 62 connected to reflector 40 in an appropriate manner. It is naturally understood that feed 60 is shown for illustrative purposes only, and various other types of feeds presently known in the art may be used in conjunction with the particular reflector 42 and system requirements.

FIGURE 7 illustrates the manner in which inflatable pattern may be used as a jig to check the contours of a previously formed antenna reflector 70. Reflector 70 may be of any presently known construction including that of above-described reflector 40. Reflector 70 is illustratively shown mounted to antenna system 50. Elevating structure 51 is lowered by the use of cables 53, 54 in conjunction with gin pole 58 to pivot about base pad 52. Antenna 70 is then maintained in an aligned position with respect to reflector pattern 10. Height indicators 71 are then used to check for uniform distance between the concave surface 72 of antenna 70 and the convex pattern surface 11. Depth indicator 71 may be uniform height posts secured to surface 11 in the same manner as post 22 (shown in FIGURE 4). Alternatively, height indicator 71 may be a Vernier caliper continually positioned about the mating parabolic surfaces 11, 72 to check for uniformity of distance and hence accuracy of contour. Where inflatable mold 10 is used to check the contour of an opened mesh surface formed of metal framing, such a mold may be directly positioned within the antenna reflector and in contact with its concave surface. Feeler gauges may then be inserted from the rear of the antenna to ascertain portions of the surface 71 which do not mate with the contoured pattern surface 11. Hence, it is seen that the use of accurately pre-formed surface 11 of pattern 10 avoids the prior art need of rather large and intricately assembled heavy structural templates for field site antenna contour checking.

FIGURES 8 and 9 illustrate another aspect of our invention wherein the inflatable mold 10' is used as a pattern for the casting of a radome structure 80, in the manner similar to that discussed above for the casting of cast reflector 40. Inflatable mold 10' is pre-formed to a substantially spherical configuration having a principal diameter which may typically be to 80 feet. Mold 10' is pressurized sufliciently to withstand the weight of casting material which will subsequently be applied thereto to form the radome structure 80. A releasing compound 81 is preferably applied to the foam receiving convex surface 11' of mold 10'. In addition, depth indicating means similar to post 22 of FIGURE 3 (not shown) may be added to indicate the thickness of foamable material that has been applied. The foamable material applied to radome pattern 10 is preferably of the same type of foamable polyurethane utilized in the construction of antenna reflector 40. After being sprayed to the proper thickness to form a radome structure 80, of proper structural strength and rigidity, the cast structure is cured, after which bag 10 may be removed.

FIGURE 9 illustrates a modification of the method utilized to form radome 80, wherein the inner concave surface 11" of inflatable radome pattern 10 is used as the mold surface. This method is particularly advantageous where it is desirable to form a radome structure in an inclement environment, such as the Arctic. By applying the casting material within the volume enclosed by the radome, a controlled environment conducive to polyurethane spraying may be provided. To facilitate removal of antenna pattern 10" from the embodiment shown in FIGURE 9, pattern 10" is preferabl constructed of a number of individual segments joined in an appropriate manner, such as hooks 82 and eyelets 83. After the curing of radome structure 80, the necessary doorways and windows may be cut in the polyurethane cast structure.

Thus it is seen that our invention permits the utilization in the field of basic raw materials to form an antenna structure, typically a reflector or radome. An inflatable pattern having the requisite contours is used, and such an inflatable pattern is preferably adaptable to also be used for checking the contours of a reflector surface. Although our invention may be used for forming both relatively small and large reflecting surfaces, it would have its greatest value in the formation of larger reflectors, wherein factory fabrication and shipment is less feasible. Typically, it may be used to form a reflector up to 30' in diameter, with considerable accuracy and permitting appreciable cost savings over the methods presently being used. Specifically, we have illustrated our invention utilizing a particularly contoured reflector surface and radome, and a particular composition of casting material. It is naturally understood that the basic concept of our invention may be practiced to construct various other antenna structures in the field and with the use of various other casting material compositions. Thus, we prefer not to be bound by the specific disclosure herein, but only by the appended claim.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

A collapsible antenna structure pattern comprising: a pre-shaped bag; said bag constructed to be inflated to form a prescribed antenna structure contoured surface; said surface adapted to provide a convex mold surface defining a paraboloid of revolution for the casting of an antenna reflector; said bag constructed of a flexible, nonelastic material, and air pressurized to accurately form said prescribed antenna structure contoured surface; said bag being sufliciently pressurized for said mold surface to support a reflector casting; a plurality of upstanding, substantially uniform height projections extending away from said convex mold surface; a plurality of depth indicating means individually seated on said projections and extending away from the antenna reflector surface to be cast, to indicate reflector casting thickness; said depth indicating means comprising posts of varying length indications to provide a tapered antenna structure; the cooperative seating of said depth indicating means and projections constructed to permit ready release, whereby a concave parabolic antenna structure molded to proper tapered distance may be readily removed.

References Cited by the Examiner UNITED STATES PATENTS 1,733,034 10/29 Tufenkjian. 2,022,510 5/3 5 Rosenblatt. 2,335,300 11/43 Netf 25-131.5 2,388,701 11/45 Neff. 2,689,304 9/54 Lawrence 3439l2 XR 2,753,276 7/56 Brockhagen et al. 2,779,689 1/57 Reis 1848 XR 2,816,323 12/57 Runger. 2,948,896 8/60 Hart 343912 XR 2,969,544 1/61 Di Marco et al. 343-912 3,076,226 2/63 Borton et al.

FOREIGN PATENTS 211,170 6/09 Germany.

OTHER REFERENCES Aviation Week, Radically New Radar Antenna Infiates, Oct. 22, 1956, pp. 94, 95, 97 and 98.

Science News Letter, Sun-Proof Igloo, vol. 77, No. 1, Jan. 2, 1960, p. 7.

WILLIAM J. STEPHENSON, Primary Examiner.

MORRIS LIEEMAN, ALEXANDER H. BRODMER- KEL, MICHAEL V. BRINDISI, Examiners.

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