Abstract:
The present invention is a novel shock-absorbing mount ( 20 ) to protect shock sensitive equipment mounted thereon. It has a configuration of a C shape but contains various angles therein to increase the utility and agility of the shock absorbing mount ( 20 ). These angles are specifically derived to allow the shock-absorbing mount ( 20 ) to fully absorb extreme shock energy without transferring it to the equipment.

Description:
This application is a 371 of PCT/US98/14021 filed Jul. 1, 1998 which claims the benefit of provisional No. 60/051,667 filed Jul. 3, 1997. 
    
    
     The present invention is related to a shock wave absorption mount for mounting shock wave sensitive equipment thereon. In particular, the present invention is in the field of structural shock absorbing mounts for reducing shock transfer to and excursions of mounted equipment. 
     BACKGROUND OF THE INVENTION 
     In equipment mounting applications involving equipment of a sensitive nature, it is often necessary to provide some means to absorb input excitations due to shock. Equipment rigidly mounted directly to floors or decks may experience direct transfer of shock to sensitive components. 
     In military shipboard applications in particular, equipment has had to undergo rigorous testing. These equipment must meet numerous specifications including the ability to sustain the shock from an underwater explosion resulting in a force magnitude potentially in the hundreds of Gs being transferred to the equipment. While such equipment has traditionally been custom designed to meet such rigorous specifications, a parallel trend has also emerged in the procurement of military and government hardware. 
     Custom equipment, while long preferred by military and government activities for its ability to meet or exceed performance and survivability requirements, has been found to be more expensive to purchase, install, and maintain. Concurrently, commercial grade equipment, particularly electronic equipment, has now advanced to a state where the capability of commercially available systems meets or exceeds the capability of custom specified equipment and is readily available. Hence, Commercial-Off-The-Shelf (COTS) equipment has become a preferred source for military and government hardware, offering, as the name implies, the ability of such equipment to be purchased directly from commercial vendors and immediately deployed. 
     Oftentimes however, COTS equipment may be inadequately ruggedized or fall short of other environmental requirements. Accordingly, COTS equipment must be adapted to be more rugged, watertight, and the like. COTS electronics equipment has traditionally overcome some of these limitations by being adapted for mounting upon special mounts purporting to limit shock transfer. Prior art mounts however, such as wire cable mounts, have proven deficient in that they fail to provide adequate shock damping action. Prior art mounts are further disadvantageous in that they are bulky and require more parts and steps to manufacture. 
     It would be appreciated in the art therefore for a compact means to mount COTS equipment in such a way that shock loads may be sustained without damaging the equipment. It would also be useful in the art for a shock mount to attenuate various destructive frequency components thus isolating and protecting mounted equipment from associated damages. 
     SUMMARY OF THE INVENTION 
     The present invention is a compact shock absorbing mount for placing equipment upon a structural base, deck or bulkhead. The shock absorbing mount of the present invention has the capability to dampen high frequency vibrations due to shock input excitations in all directions. One leg of the C-shape mount is fastened to the equipment, and the other leg to the base structure. The lengths of intervening sections, their angles with respect to one another, the material of the mount and its thickness result in a mount that has unexpectedly high shock damping properties. The mount is simple to fabricate and install. It is also well suited to an industrial/marine/aircraft environment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the present invention. 
     FIG. 2 is a front view of the present invention illustrating place mounting holes and bushings. 
     FIG. 3 is a diagram illustrating a cross section taken along line  3 — 3  of FIG. 2 showing the C-shaped mount of the present invention including bushings and mounting screws. 
     FIG. 4 is a top view of the present invention illustrating placement of mounting holes and bushings. 
     FIG. 5 is a top view of the present invention illustrating a four-hole embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Shock absorbing mount  20  of the present invention, as shown by its perspective view in FIG.  1  and its cross section view in FIG. 3, is disposed between the structure of a ship and the edge or base of a piece of electronic equipment. Shock isolation is achieved in shock absorbing mount  20  through a combination of structural configuration and material composition. In the preferred embodiment, to achieve the desired isolation parameters, shock-absorbing mount  20  is constructed of a resilient material having a tensile modulus of elasticity between 20,000 and 50,000 psi with the preferred value being 25,000 psi. 
     Referring to FIG. 1 of the drawings, mount  20  of the present invention has a structural configuration of roughly a C-shape formed by planar sections including a base section  6 , a lower intermediate section  8 , a middle section  10 , an upper intermediate section  12  and a top section  14  surrounding an internal space  32 . This space is coextensive with the mount and not intruded by any of the sections when the mount and equipment are at rest. Base or bottom section  6  and top section  14  are each of sufficient lateral extension to provide flat surfaces  34  and  40  forming flat horizontal planes as shown in FIG. 1 to permit the formation of holes  17  whereby each hole accommodates a bushing  16 . Bushings  16  receive mounting screws  30  in both the base and top sections  6  and  14 , to correspondingly form first and second attaching means. The purpose of the bushings  16  is to provide a hard surface on which screws  30  may be bottomed to attain full tightening torque. The C shape mount has a characteristic that when an imaginary perpendicular plane  42  is drawn, only one section protrudes the imaginary plane as shown in FIG. 3, when the equipment and mount are at rest. 
     The base section  6  meets the lower intermediate section  8  at bending point  7  where the lower intermediate section  8  then slopes linearly upward (inclining) at a predetermined angle to form a space above the flat horizontal plane of flat surface  34 . Bending point  9  is formed by the intersection of the lower intermediate section  8  and the middle section  10 . As shown in FIG. 3, the middle section  10  is generally vertical and is at right angles with the base section  6  of the shock-absorbing mount. Similarly, bending point  11  is formed by the intersection of the middle section  10  and the upper intermediate section  12  from which the upper intermediate section  12  slopes linearly downward (declining). Finally at bending point  13 , the top section  14 , being parallel to the base section  6 , intersects the upper intermediate section  12 . 
     To illustrate the angular relationships among the various sections, lines A, B, C, D, E, and F are drawn on FIG.  3 . Line A is defined to be parallel to and located, as shown, at the outer flat surface  34  of base section  6 . Line B is defined to be parallel to line A, and perpendicular to and located at the lower end of the middle section  10 . Line C is defined to be parallel to line B, and perpendicular to and located at the upper end of the middle section  10 . Line D is defined to be parallel to and located at the outer flat surface  36  of the lower intermediate section  8 . Line E is defined to be parallel to and located at the interior flat surface  44  of the lower intermediate section  8 . Line F is defined to be parallel to and located at the interior flat surface  38  of the upper intermediate section  12 . The angle formed between lines A and D is identical to the angle formed between lines B and E, as well as the angle formed between lines C and F. These angles are each designated as α. 
     The lower intermediate section  8  and the upper intermediate section  12  are each at an angle α with respect to the structural base. These angles should be substantially within the range of about 5°-30°, but preferably 10°-30° with substantially about 20° most preferable. These angles need not be equal and may vary one from another by 10 to 20 degrees. This range allows all sections of mount  20  to retain their collective configuration as much the same as possible under severe shock. 
     If angle α were larger than about 30°, keeping other parameters much the same, middle section  10  would continue to diminish its effectiveness as the angle α continues to increase. This would remove a significant amount of material from the energy absorbing function of the mount, and would mean the juncture of sections  8  and  12  would be so sharp as to raise stress levels in the material to intolerable levels. 
     The upper intermediate section  12  is shorter than the lower intermediate section  8  to prevent damage to shock absorbing mount  20  in the extreme travel of the sections under severe shock. If the upper intermediate section  12  were extended to have the same length as the lower intermediate section  8 , the base section  6  and the top section  14  could collide under shock loading. This would allow screws  30  in holes  15  to have metal to metal contact with screws  30  in holes  17 . This metal to metal contact would negate the purpose of the mount, and would probably damage the bushings  16  or mounting screws  30 . This problem of metal to metal contact can also be prevented by making the upper intermediate section  12  longer than the lower intermediate section  8 . 
     Adapting shock absorbing mount  20  to a particular application and weight of equipment can include selection of material  21 , thickness  18 , lengths of sections  6 ,  8 ,  10 ,  12 , and  14  and overall length  22 , and various other factors. 
     Material  21  may be any thermoplastic polyester elastomer with a tensile modulus of elasticity within a range of 20,000-50,000 psi, preferably 25,000 psi. Particularly suitable for this application is a material known as Dupont® brand Hytrel® as disclosed in U.S. Pat. No. 4,264,761, U.S. Pat. Nos. 3,954,689, and 3,775,373, all being incorporated herein by reference. This material has the required structural dynamic properties, is impervious to most solvents and other agents with an expected life in severe environments of 10-30 years, and has a high creep resistance. 
     Any impulsive force, such as a shock caused by an explosion, generates energy across a wide frequency range. Much of the damage caused by an explosion depends upon the sensitivity of the equipment to the amount of shock energy present at various frequencies. It is known that damage to equipment, particularly sensitive electronic equipment, may be minimized if a resonant frequency between 5 and 15 Hz is maintained for the shock absorbing mount  20 . Accordingly, to best isolate such equipment from shock, the shock absorbing mount  20  of the present invention must absorb energy outside this range limiting equipment acceleration and excursions to non-destructive values. Assume for a preferred embodiment of mount  20  of material  21  as shown in FIG. 5 that: 
     mount capacity=68 lbs 
     tensile modulus of elasticity=25,000 psi 
     L m : mount length  22 =3 in 
     α: angle between sections=20° 
     length of section  6 =1.25 in 
     length of section  6 + section  8  shown as X=3.75 in. 
     length of section  12 +section  14  shown as Y=2.50 in 
     length of section  14 =1.25 in 
     thickness  18 =0.75 in 
     height  19 =3.00 in 
     Analyzing this mount by well-known methods of structural dynamics analysis, the natural frequency of the shock absorbing mount  20  is 10.1 Hz in the axial direction, 10.2 Hz in the shear1 (S1) direction, and 9.5 in the shear2 (S2) direction, as shown in FIG.  1 . In all directions, the natural frequency was within the design limits between 5 and 15 Hz. While values selected for lengths of sections  6 ,  8 ,  10 ,  12  and  14  by way of this example represent values used in the preferred embodiment of the invention, lengths of sections  6 ,  8 ,  10 ,  12  and  14  may be varied along with thickness  18  and length  22  to scale the shock absorbing mount  20  up and down for larger and smaller loads. The shock absorbing mount  20  in the preferred embodiment, however, may be initially scaled by varying only the thickness  18  and the length  22 . The natural frequency response may be preserved by maintaining the relative proportions between lengths of sections  6 ,  8 ,  10 ,  12  and  14  while making appropriate modifications to thickness  18 . If necessary, material  21  may be substituted with a material having a greater or lesser modulus of elasticity. By the same token, shock absorbing mounts for heavier or lighter equipment may be sized by varying the material  21 , thickness  18  of various sections, the lengths of the various sections and the length L m  of the shock absorbing mount. 
     While the preferred embodiment is drawn to a mount for isolating shipboard equipment from underwater shock, the shock absorbing mount of the present invention in alternative embodiments, could be used anywhere such shock isolation was desired. For example, mobile mounted equipment in trucks, van, aircraft, space vehicles, rockets, missiles, or the like could be shock isolated using the mount of the present invention. Moreover, the mount could be used in any environment where shock is likely to be encountered, such as earthquake prone structures including buildings, bridges, etc.