US2985881A

US2985881A - A reflector utilizing pre-stressed elements

Info

Publication number: US2985881A
Application number: US778544A
Authority: US
Inventors: Holland Herman; Robert G Simoneau
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-12-05
Filing date: 1958-12-05
Publication date: 1961-05-23
Anticipated expiration: 1978-05-23

Description

May 23,1961 H. HOLLAND ET AL REFLECTOR UTILIZING PRE-STRESSED ELEMENTS 2 Sheets-Sheet 2 Filed Dec. 5, 1958 INVENTOR. HERMAN HOLLAND ROBERT e. SIMONEAU X/M' ATTORNEYS United States Patent A REFLECTOR UTILIZING PRE-STRESSED ELEMENTS Herman Holland, 957 Albion St., and Robert G. Simoneau, 3702 Delmar Ave., both of San Diego, Calif.

Filed Dec. 5, 1958, Ser. No. 778,544

14 Claims. (Cl. 343 912) The present invention relates to a reflector, and more particularly to a reflector for use in reflecting light, heat, and similar forms of energy, such as electromagnetic waves in long range search, detection, and guidance equipment.

In order to obtain maximum utilization of recent and continuing improvements in electronic gear for propagating and receiving electromagnetic waves, it has become necessary to provide very large and accurate reflector assemblies. It is also necessary that these reflectors have a minimum deflection under load in order to provide the desired accuracy. Large diameter, minimum deflection reflectors are diflicult and expensive to construct using present day techniques since it is characteristic of present space framework structures that they must be massive and heavy to reduce deflection to a satisfactory degree. These structures are often as great as 120 feet or more in diameter, and as they become larger the framework must become heavier to reduce deflection. As the size increases, the deflection problem becomes more acute, necessitating the use of heavier bracing structures, until a point of diminishing returns is reached, that is, when the dead weight of the structures becomes so great that its weight alone causes excessive deflections. In addition to this dilemma, the great weight of the structure imposes severe stresses upon the gimbal bearings supporting the reflector, and requires heavy counterbalancing and considerable power to operate the reflector. These problems are further aggravated because the current trend is toward the use of higher frequencies which require a continuous reflector face surface, rather than the open face or grid framework now in use with lower frequencies. This imposes higher wind and ice loads upon the backup or support structure, requiring still more heavy bracing to reduce the deflection to an acceptable level.

Accordingly, the present invention provides a reflector which has a very accurate reflective surface and which is extremely efiicient from a weight-deflection standpoint. The reflector also is characterized by economy of manufacture, logistic simplicity, and ease of maintenance. The reflector is made up of several groups of parts which are interchangeable within their group so that an essentially modular design is provided. Essentially, the reflector comprises a plurality of rings which are arranged in adjacent spaced relationship, and which are secured together by a plurality of circumferentially spaced tension elements secured between adjacent rings. In addit-ion, a continuous face, curved reflecting surface is arranged upon the edges of the plurality of rings. The rings are preferably made in sections and secured together by fasteners which are quickly installed and removed. The rings are supported and stabilized by the plurality of tension elements, which may be rods or wires or the like, so that the rings and the rods form a back-up structure for the continuous face or solid reflector surface. This surface is constructed of a plurality of panels, preferably made of sandwich construction, which are individually adjustable at their corners, individually removable and replaceable, and adapted'to act as non-load bearing members, except in their function of transmitting wind and ice loads into the back-up structure. That is, the panels do not serve to any appreciable extent in tying together or bracing the assembled rings and tension rods. The rings are secured in desired position by adjusting the lengths of the rods, and the whole back-up structure is prestressed by tightening the tension rods; Such prestressing takes up the bulk of the manufacturing and assembly tolerances, and insures that the structure will be capable of withstanding erection and operating loads without exceeding a predetermined acceptable deflection. It is also noted that adjustment of the lengths of the tension rods will properly align the reflector face panels to a desired shape, such as an accurate parabolic shape. The adjustment of the panels at their four corners permits a finer adjustment of the position of each panel so that a high degree of accuracy in forming a parabolic face is afforded.

Although the description hereinafter made will be directed to the employment of a plurality of solid face panels to'form the reflector surface, it will be apparent that the back-up structure of the present invention is also adapted to carry a conventional mesh or open face reflector surface.

The compression ring members are preferably made of sandwich panels, and can be fairly thin in section since most of the stress imposed upon'them is in hoop tension and hoop compression. The fact that the reflector face panels do not carry any of the primary stress of the structure makes it possible to locally adjust any of these panels without disrupting the position of any of the other panels and without affecting the stress in any part of the primary or backup structure. The prestressing of the rods or tension members insures that none of such members will be placed in compression under any conditions of unsymmetrical loading. This in turn means that all tolerances taken up by the prestressing will be substantially eliminated under even the most severe conditions of operational loading. Further, since each rod or strut is always in tension, it will be working under all loading conditions, with a resulting gain in structural efliciency.

Other objects and features of the present invention will be readily apparent to those skilled in the art from the following specification and appended drawings wherein is illustrated a preferred form of the invention, and in which:

Figure 1 is a plan view of the reflector side of the antenna of the present invention, portions being cut away to illustrate the under-structure thereof;

Figure 2 is a view taken along the line 2-2 of Figure 1;

Figure 3 is a detail view illustrating the manner of securing together adjacent segments or panels of a ring;

Figure 4 is a partial perspective view illustrating the channel construction at the upper and lower edges of the ring segments, and also illustrating the manner of securing the tension tie rods thereto;

Figure 5 is a partial perspective view illustrating the adjusting means for aligning individual panels in position upon the upper edge of a ring; and

Figure 6 is a detailed view illustrating one means for effecting electrical interconnection between adjacent panels.

Referring now to the drawings and in particular to Figures l and 2, there is illustrated an antenna reflector, generally designated 10, which is adapted for the transmissionor reception of electromagnetic waves.

Reflector comprises, generally, a series of concentric compression bands or

rings

12, 14, 16, 18 and 20. These rings are preferably made in sections so that they may be easily assembled in situ, and are arranged in axial, concentric fashion and slightly offset from each other to form a parabolic shape at their reflector or outer edges. The rings are supported and stabilized in position by a plurality of tension elements or rods 22. As will be seen, the plurality of concentric rings, stabilized in position by rods 22, serve as the back-up or supporting structure for a solid reflector surface which ismade up of a plurality of reflector panels 24. Each of these panels 24 is individually adjustable at its four corners, individually removable and replaceable, and do not act as load-bearing members, except in their function of transmitting wind and ice into the back-up structure. Rods 22 are preferably prestressed to a level high enough to insure that most manufacturing and assembly tolerances will be taken up. In this way antenna 10 is inherently adapted to withstand erection and operating loads without exceeding a predetermined acceptable deflection. Once constructed, individual adjustments at the corners of the panels permit the panels to be arranged in an accurate parabolic shape, as desired. Throughout the description hereinafter to be made it will be apparent that reflector 10 is made up of several groups of identical parts which lend themselves to economy of manufacture, ease of shipment and handling, and simplicity of assembly, erection and maintenance.

More particularly, each of the bands or

rings

12, 14, 16, 18, and takes the form of a cylindrical band which by reason of its continuous nature transmits loads throughout the periphery of the rings. The number of rings, their spacing, and their size may be varied to suit the particular loading conditions of each application. Each of the rings is made up of a plurality of individual, and preferably identical, ring segments or panels 19, Figure 4, which are preferably of sandwich construction. That is, to attain a high strength-to-weight ratio the panels 19 preferably comprise a structure formed of honeycomblike core material arranged in edgewise relation between a pair of parallel facing skins, as illustrated. The core and skins are secured together, as by adhesive bonding or welding, to produce a strong and lightweight composite structure. However, if desired, panels 19 may be made of other materials also, if desired.

Panels 19 may be curved to produce a perfectly round ring when they are secured together, but for manufacturing simplicity they are preferably made rectangular and flat. This produces a ring which is a many sided polygon, but which is for all practical purposes round. The number of panels in each of the rings will, of course, vary, depending upon the peripheral length of each panel and the size of the ring to be produced.

The adjacent side edges of panels 19 are detachably secured together by any suitable means, such as by a pair of piano-type hinge fittings or connections 26, one on the inner and one on the outer side of each panel adjacent its edges, Figure 3. Connections 26 are secured to panels 19 by any suitable means, such as by bolts 27 or the like threaded into female fittings anchored in the core portion of each panel 19. A pin 28 is provided to couple together the hinge portions of connection 26 so that the various panels 19 may be quickly assembled by merely driving pins 28 into position. It is to be noted that since each panel 19 is substantially identical to every other panel 19 in its respective ring, there is no necessity for identifying the individual panels for assembly purposes.

The various rings are formed by assembling the respective panels 19 in the manner described, and the rings are arranged in the concentric fashion illustrated in Figures 1 and 2, the inner rings being progressively offset along the axis of the assembled rings to produce the desired reflector shape. Thus, for a parabolic reflector shape, the outer edges of the various rings will form a support which is adapted to form a parabola when they are covered by reflector panels, as will be seen.

The plurality of continuous bands or rings are secured together by tension elements or rods 22, the lengths of rods 22 being made such that they will support and maintain the rings in the offset positions just described. Rods 22 are then prestressed to maintain these positions with a minimum of deflection.

Referring now to Figure 4, there is illustrated the manner of attachment of rods 22 to each of the ring segments or panels 19. For purposes of illustration, the attachment of rods 22 will be described in connection with a typical ring 16, it being understood that the connections are substantially identical for each of the other rings.

The individual panel components or segments 19 of ring 16 are cut away or routed out at their upper (forward) and lower (rearward) edges to accept a pair of U-shaped channels 30, respectively, which are rigidly secured in position by bonding to the inner faces of the facing skins of panels 19. That is, the core edge portions of panels 19 are routed out to make room for channel 30, and the channel is then bonded to the skins. Each channel 36 is also secured in position by a plural ity of pairs of bolt and nut assemblies 32, the bolts thereof being disposed through spacers or bushings 34 located within the interior of channel 30. Each channel 30 may thus be firmly clamped to the skins of each panel 19 without crushing of either.

Assemblies 32 also secure a pair of substantially C- shaped channels 36 in position against panels 19, channels 36 forming the upper and lower anchorages for the ends of rods 22, as will be seen. The lower flange of each upper channel 36 is provided with a plurality of pairs of spaced openings for accepting the plurality of nut and bolt assemblies 38 for securing the clevises 40 of tension rods 22 in position. Although Figure 4 illustrates only the upper channel 36 and the upper ends of rods 22, it will be understood that the lower ends of these rods 22 are also secured in similar fashion to the upper flange of the lower channel 36 of the next adjacent rings, in this case the

rings

14 and 18. A rod 22 is connected between the upper corner of a ring panel 19 of ring 16 and the lower diagonally opposite corner of a panel 19 of an adjacent ring. The other upper corner of the same panel 19 of ring 16 is connected to the other lower corner of the panel 19 of an adjacent ring. In this way the pair of rods 22 are diagonally disposed, and intersect in X fashion between the upper corners of the panel of ring 16 and the lower corners of the panel of the adjacent ring. In similar fashion, a pair of rods 22 are connected between the lower corners of the same panel 19 of ring 16 and the upper corners of the panel 19 of the adjacent ring, these rods 22 also crossing each other in diagonal fashion. This same arrangement is repeated for each pair of confronting panels 19 about the periphery of ring 16 and the adjacent ring, and the same arrangement is followed for confronting panels 19 of the other rings also. It will be apparent that slightly different arrangements of rods 22 can be devised for effecting the same function, so long as the rods 22 are prestressed and act to distribute loads throughout the various rings.

A means for generating tension in rods 22 is necessary to prestress rods 22 to take up residual tolerances,

and for this purpose a turnbuckle 42 or the like is provided in each rod 22. Rotation of turnbuckle 42 in the as is well known in the art. As previously mentioned,

wires or like tension elements could be used as an alternate construction instead of rods 22.

The curved or parabolic reflecting surface for antenna is provided by arranging a plurality of panels 24 in adjacent relationship, and securing them to the upper flanges of the plurality of channels 36 of the various concentric rings. It is to be understood, however, that the panels 24 do not provide any appreciable support for the back-up structure comprising the rings and rods 22, but are merely positioned for affording the desired electromagnetic wave reflection. Their disposition is primarily dictated by the relative height of the various rings, which in turn is controlled by the lengths and pre-tension forces in rods 22, but there will also be described a means for effecting a secondary and more precise arrangement of the panels 10.

The means for enabling a precise adjustment of the position of each panel 24 comprises, Figure 5, a splice plate 44 which is arranged adjacent the upper or forward flange of the adjacent channel 36. Splice plate 44 is provided with four positioning assemblies 46, whereby it is adapted to provide a support for the corners of four panels 24. The corner of each panel 24 rests upon a disc-like head 48 of one of the assemblies 46, and the relative height of that corner of panel 24 with respect to plate 44 is adjusted by rotating a pair of nuts 50 along a threaded shank which is integral with head 48. Once the proper height is achieved, nuts 50 are rotated until they firmly abut against the surfaces of plate 44 to thereby lock head 48 in position. At this point the corner of panel 24 is merely resting upon the upper surface of head 48, and to secure panel 24 in this adjusted position, a bolt 52 is disposed through that corner of panel 24, through plate 44, and thence through the upper flange of channel 36. A nut 54 is next threaded upon the end of bolt 52 to secure panel 24 in position. Thus it will be seen that although the position of panel 24 is roughly located by the previously established height of the adjacent ring 16, a fine or Vernier adjustment of the height of panel 24 may be provided by manipulating the various assemblies 46. It will be understood that many plates 44 are employed in this same fashion about the upper or forward rim peripheries of the various rings so that all panels 24 are secured at their four corners in precise positions established, first by the locating of the rings at their proper heights through adjustment of the lengths of rods 22, and second by manipulating the positioning assemblies 46. a

The various panels 24 are preferably constructed of sandwich material, as described hereinabove with respect to panels 19, but panels 24 may be constructed of open face mesh or other material, if desired. The use of sandwich material in the present invention is preferred because of the high strength-to-weight ratio of that type of construction, but there are no doubt situations where an open face material would be desired, and the novel back-up structure of the rods and rings, as herein taught, is equally adapted to support and position such an alternative construction.

The shape of panels 24 is, of course, dictated by the desired shape for the reflecting surface of reflector 10, but for the parabolic reflecting surface herein contemplated each panel 24 is provided with substantially parallel upper and lower edges, except for the innermost panels 24, which will be slightly arcuate in shape to conform with the contour of the upper edges of the rings. The side edges of panels 24 will be tapered inwardly to permit them to be fitted as wedges or petals in the overall assembly, the taper becoming greater for the panels which are located in the innermost positions. In addition, reflector panels 24 will be substantially flat, although a slight curvature may be provided to give a more accurate parabolic shape. It will be apparent that the diameter of reflector 10 will largely dictate the shape of reflector panels 24 since, as the diameter becomes larger,

reflector 10 is left uncovered in the present embodiment.

A sub-reflector, feed horn, or similar propagating or receiving equipment (not shown) may be mounted for-' wardly of the main reflecting surface of reflector 10, and portions of a plurality of struts 56 for this purpose are illustrated in Figures 1 and 2. Each strut 56 is connected at the rearward end to ring 20 in any suitable manner, such as by being bolted to a fitting 58 which is rigidly secured to ring 20. In similar fashion a plurality of gimbal struts 60 are bolted or otherwise secured to the rearward ends of fittings 58 and are connected (not shown) to a gimbal mount for supporting reflector 10 in position. The gimbal mount and the means of mounting reflector 1t) thereto are not important to the present invention, and will therefore not be described in any particular detail, other than to note that the gimbal mount together with usual and conventional apparatus associated therewith is operative to cause reflector 10 to track in azimuth and elevation.

Electrical continuity between reflector panels 24 may be provided by controlled gaps between the panel edges for capacitance conduction, as is well known, or, as is best illustrated in Figure 6, may be provided by affixing a thin, flexible, metallic, non-structural tape or strip 62 to the edges of adjacent panels 24. This can be done by installing self-tapping metal screws, by adhesive bonding techniques, or by any other means suitable to effect electrical interconnection between panels 24 and strips 62.

From the description hereinabove made it will be seen that a reflector '10 has been provided which is extremely light in weight, the back-up structure thereof comprising concentric, continuous, sectional sandwich compression rings, supported and stabilized by substantially radially disposed inter-ring rods 22 which have been prestressed to reduce deflections of reflector 10 under load. The reflector surface is also light in weight, being constructed of sandwich reflector panels 24, and is accurate in contour, the contour thereof being precisely adjustable by manipulating positioning assemblies 46 until panels 24 are in the precise positions desired. In addition, the pro-stressing of rods 22 stabilizes the assembly, and substantially all tolerances in fittings and attachment members will be taken up prior to operational loading.

While certain preferred embodiments of the inven-. tion have been specifically disclosed, it is understood that the invention is not limited thereto as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation Within the terms of the following claims.

I claim:

1. A reflector comprising: a plurality of endless structure means, each being generally cylindrical in configuration, said plurality of structure means being arranged in adjacent, spaced relationship, said structure means having different diameters, the front edge of the inner structure means being arranged rearwardly of the front edge of the outer structure means; a plurality of circumferentially spaced tension elements secured between said structure means, certain of said tension elements each having one end connected adjacent the front edge of the outer structure means and the other end connected adjacent the rear edge of the inner structure means, and certain of said tension elements each having one end connected adjacent the rear edge of the outer structure means and the other end connected adjacent the front edge of the inner structure means; a plurality of means carried by and operative upon said tension elements, respectively, to individually and adjustably prestress each said tension element whereby assembly tolerances are taken up and whereby each said tension element is in tension under load; and a reflecting surface means arranged adjacent the forward edge portions of said structure means.

2. A reflector according to claim 1 and characterized in that said tension elements are rods.

3. A reflector according to claim 1 and characterized in that said tension elements are wires.

4. A reflector according to claim 1 and characterized in that said tension elements are elongated braces, and in that said last-mentioned means are operative to shorten the length of said braces to thereby create a prestressed condition in said braces and thereby orient said structure means.

5. A reflector for electromagnetic waves comprising a plurality of concentrically spaced cylindrical rings, each of said rings having a rearward rim and a forward rim; a plurality of circumferentially spaced tension elements secured between the adjacent rings and adjacent the forward and rearward rims thereof, certain of said elements extending between the forward rim of one of the adjacent rings and the rearward rim of the other of said pair of adjacent rings, and certain of said elements extending between the rearward rim of said adjacent rings and the forward rim of said other adjacent rings; means operative upon each said tension element to prestress said tension element whereby assembly tolerances are taken up and whereby said tension element will be in tension under load; and a reflecting surface arranged adjacent the forward rims of said rings.

6. A reflector according to claim 5 and characterized in that said tension elements are rods.

7. A reflector according to claim 5 and characterized in that said tension elements are wires.

8. A reflector according to claim 5 and characterized in that said tension elements are longitudinally extending braces and in that said means are operative for shortening the length of the brace to thereby create a prestressed condition in said brace.

9. A reflector for electromagnetic waves comprising a plurality of concentrically spaced cylindrical rings, each of said rings including a plurality of substantially rectilinear panel sections interconnected at their side edges; a plurality of circumferentially spaced tension elements secured between the adjacent rings, a separate one of said tension elements being secured between each corner of each said panel section of one of the rings and the diagonally opposite corner of each confronting panel section of an adjacent ring; said tension elements including means for imparting tension loads in said tension elements for prestressing the assembled said tension elements and said rings; a reflecting surface arranged adjacent the forward edges of said rings.

10. A reflector for electromagnetic waves comprising a plurality of continuous cylindrical members arranged one within the other in adjacent spaced relationship, the

forward rims of said'members being axially offset; a reflecting surface arranged "over said forward rims to form a reflecting dish section; and a plurality of diagonally disposed elements secured between adjacent members, said elements including means for imparting tension loads in said elements for prestrcssing the assembled said members and said elements.

11. A reflector according to claim 10 and characterized in that said cylindrical members are each comprised of a plurality of edge connected panels of sandwich construction.

12. A reflector according to claim 10 and characterized in that said reflecting surface is comprised of a plur'ality of reflector panels of sandwich construction, each of said panels bridging at least a pair of said cylindrical members.

7 13. A reflector according to claim 10 and characterized in that said reflecting surface is comprised of a plurality of reflector panels of sandwich construction, each of said panels bridging at least a pair of said cylindrical members, and in that said reflector panels are electrically interconnected by thin, flexible metallic strips.

14. A reflector for electromagnetic waves comprising a plurality of continuous cylindrical members arranged one within the other in adjacent spaced relationship, the forward rims of said members being axially offset; a plurality of diagonally disposed elements secured between adjacent members for maintaining said members in position; a reflecting surface arranged over said forward rims to form a reflecting dish section, said reflecting surface including a plurality of reflecting panels having portions disposed over said forward rims; and means connected between said forward rims and said portions of said panels for adjusting the spacing therebetween whereby the contour of said reflecting surface may be accurately adjusted.

References Cited in the file of this patent UNITED STATES PATENTS 1,938,799 Bourne Dec. 12, 1933 2,298,880 Gartenmeister Oct. 13, 1942 2,471,828 Mautner May 31, 1949 FOREIGN PATENTS 989,286 France May 23, 1951 OTHER REFERENCES Pub. II-Crom, Engineering News-Record, April 16, 1936, page 555.

Pub. I, Architectural Record, September 1956, pp. 211-216.