Abstract:
A shock isolator comprising a first plate having a set of ridges and grooves extending there along and a second plate having a complementary set of ridges and grooves with an elastomeric sheet sandwiched between the two plates so that when a compressive force is applied to the two plates the elastomeric sheet resist the forces through compression resistance, tension resistance and shear resistance to provide both static support and shock isolation to an object supported by the shock isolator.

Description:
FIELD OF THE INVENTION 
     This invention relates to shock isolators and, more specifically, to an elastomer mount that can provide offset compressive support, tension support and shear support for an article. 
     BACKGROUND OF THE INVENTION 
     Various elastomeric materials have been used, or suggested for use, to provide shock and/or vibration damping as stated in U.S. Pat. No. 5,766,720, which issued on Jun. 16, 1998 to Yamagisht, et al. These materials include natural rubbers and synthetic resins such as polyvinyl chlorides, polyurethane, polyamides polystyrenes, copolymerized polyvinyl chlorides, and poloyolefine synthetic rubbers as well as synthetic materials such as urethane, EPDM, styrene-butadiene rubbers, nitrites, isoprene, chloroprenes, propylene, and silicones. The particular type of elastomeric material is not critical but urethane material sold under the trademark Sorbothane® is currently employed. Suitable material is also sold by Aero E.A.R. Specialty Composites, as Isoloss VL. The registrant of the mark Sorbothane® (for urethane material is the Hamiltion Kent Manufacturing Company (Registration No. 1,208,333), Kent, Ohio 44240. 
     Generally, the shape and configuration of elastomeric isolators have a significant effect on the shock and vibration attenuation characteristics of the elastomeric isolators. The elastomeric isolators employed in the prior art are commonly formed into geometric 3D shapes, such as spheres, squares, right circular cylinders, cones, rectangles and the like as illustrated in U.S. Pat. No. 5,776,720. These elastomeric isolators are typically attached to a housing to protect equipment within the housing from the effects of shock and vibration. 
     The prior art elastomeric isolators are generally positioned to rely on an axial compression of the elastomeric material or on tension or shear of the elastomeric material. Generally, if the elastomeric isolator is positioned in the axial compressive mode the ability of the elastomeric isolator to attenuate shock and vibration is limited by the compressive characteristics of the material. On the other hand, in the axial compressive mode the elastomeric isolators can be used to provide static support to a housing, which allows a single elastomeric isolator to be placed beneath the housing to support the static weight of the housing. 
     In general, if the elastomeric isolators are positioned in the shear or tension mode as opposed to an axial compression mode the elastomeric isolators provide better shock and vibration attenuating characteristics in response to dynamic forces due to shock and vibration. Unfortunately, elastomeric isolators, which operate in a shear or tension mode or in the axial compression mode, can generally not be placed beneath a housing to provide static support to the housing without substantially effecting the shock and vibration attenuation characteristics of the elastomeric isolators. Consequently, to provide static support for a housing, as well as effective shock and vibration attenuation characteristics the elastomeric isolators, which operate in the shear or tension mode, are generally placed along side or above a housing so that the elastomeric isolators can function in a shear or tension mode while supporting the static weight of the housing. The positioning in a shear or tension mode can require placing matching elastomeric isolators on each side of the housing. 
     The present invention provides an elastomeric mount or isolator that provides compressive support for a housing, and the compressive support in relation to the shear support can be preselected by utilization of ridged plates. The present invention does not require paring with other shock isolators so a single shock isolator can be placed beneath a housing to provide static support for the housing while at the same time allowing the elastomeric sheet in the shock isolator to provide dynamic attenuation characteristics through shear and tension forces on the elastomeric sheet If desired a set of shock isolators can be stacked on each other to provide a platform for supporting an article in a condition wherein the shock and vibration forces are attenuated by the shear and tension resistance of the elastomeric sheet. 
     SUMMARY OF THE INVENTION 
     A shock isolator comprising a first plate having a set of ridges and grooves extending there along and a second plate having a complementary set of ridges and grooves with an elastomeric sheet sandwiched between the two plates so that when a compressive force is applied to the two plates the elastomeric sheet resists the compressive force through an offset in the compressive path through the elastomer sheet and through tension resistance and shear resistance to provide both static support and shock isolation to an object supported by the shock isolator. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of shock isolator. 
     FIG. 2 is an enlarged partial end view of a portion of the shock isolator of FIG. 1; and 
     FIG. 3 is a front view showing three of the shock isolators of FIG. 1 in a stacked condition supporting a cabinet to be protected from shock and vibration forces. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a perspective view of a shock isolator  10  having a first rigid plate  11  containing an integral set of elongated parallel protrusions  11   a  and an integral set of elongated parallel recesses  11   b  which coact to form a top ridged plate  11 . Located beneath rigid plate  11  is a second rigid plate  12  having a complementary set of elongated parallel protrusions  12   a  and a complementary set of elongated parallel recesses  12   b . That is the width of a recess  12   b  is such that the protrusion  11   a  on plate  11  will mate or fit within the recess  12   b  if the first plate  11  and second plate  12  are brought together. Similarly, the width of protrusion  12   a  is such that it fits within recess  11   b  of plate  11  if the first plate  11  and second plate  12  are brought together. 
     Located between plates  11  and  12  is an elastomer sheet  13 . The elastomer sheet  13  extends in a sandwich fashion laterally between the protrusions  11   a  and recesses  11   b  of first plate  11  and the complementary recesses  12   b  and complementary protrusions  12   a  of the second plate  12 . In the embodiment shown the elastomer sheet  13  is maintained in a relaxed or unstretched condition when there is no compressive force against plate  11  or plate  12 . When a compressive force is applied to first plate  11  and to second plate  12  the elastomer sheet  13  not only resists the motion of the plates but the plates act to frictionally hold the elastomer sheet  13  in a lateral position causing localized stretching of the elastomeric sheet  13  which results in both shear and tension forces within sheet  13  which not only resists a displacement of the first plate  11  toward the second plate  12  but provides enhanced shock and vibration attenuation characteristics to isolator  10 . In addition, if a displacement of plates  11  and  12  with respect to each other should cause both sides of elastomer sheet  13  to be compressed against the two opposing plates the elastomer sheet will act as a cushion to cushionly limit further displacement. Thus, the present invention not only provides shock and vibration attention but cushionly limits the displacement of the two plates with respect to each other in the event of an excess displacement of the plates. 
     FIG. 2 is an enlarged partial end view of a portion of the shock isolator  10  showing portion  11   a  having a width indicated by D 1  and the complementary recess on plate  12  having a width indicated by D 2 . The distance D 2  is sufficiently greater than the width D 1  so that when an elastomer sheet  13  is forced therebetween there is sufficient room so as not to pinch the elastomer sheet  13  between sidewall  11   d  of protrusion and sidewall  12   d  of complementary recess  12   b  or between sidewall  11   e  of protrusion  11   c  and sidewall  12   e  of recess  12   b . In general the difference between D 2  and D 1  is such that it is at least equal to or greater than twice the thickness “t” of elastomer sheet  13 . 
     In order to hold elastomer sheet  13  in position there is provided high friction surfaces on both plates  11  and  12 . Referring to FIG. 2, protrusion  11  has a high friction surface  11   f . Similarly, each of protrusions  12   a  have a high friction surface  12   f . The high friction surfaces can comprises a knurled surface or the like or can include a separate material to provide frictional resistance to inhibit lateral displacement of elastomer sheet  13  with respect to plates  11  and  12 . 
     In order to prevent accidental tearing of an elastomer sheet  13  as the rigid plates  11  and  12  are brought together by static or dynamic forces each of the corners of the protrusions and recess are rounded as illustrated in FIG.  2 . It will be understood that the need for rounded corners depends on the type of elastomer sheet selected as some elastomer sheets are more tear resistance than others. 
     FIG. 2 illustrates the multiple responsive action of isolator  10  in response to a force F on plate  11 . The force F displaces plate  11  toward plate  12  causing the elastomer sheet  13  to conform to the gap between the protrusions and recesses on plate  11  and the complementary protrusions and recesses on plate  12 . Elastomer sheet  13  is shown with a portion of sheet  13  in contact with high friction surface  11   f , and further portions in contact with high friction surfaces  12   f . The high frictional surface restrains elastomer sheet  13  from sliding laterally inward to smoothly follow the contours between the protrusions and recess of plates  11  and  13 . Instead, as a result of the frictional surfaces the elastomer sheet is locally held in position, which results in placing the elastomer sheet in tension and shear, as the protrusions and recesses of plate  11  move toward the complementary protrusions and recesses of plate  12 . Thus the elastomer sheet  13  provides both tension and shear resistance since the elastomer sheet is both stretched and bent as it is forced to follow the contours of the two mating plates. While the tension and shear resistance provide excellent shock and vibration attenuation characteristics the elastomer sheet  13  also provides compressive resistance to the squeezing between plates  11  and  12  to thereby provide static support for a cabinet or the like. 
     FIG. 3 shows an application of the isolator  10  in supporting a cabinet or housing  30 . In the embodiment shown a first isolator  10  is stacked on top of a second identical isolator  25  which is in tun stacked on top of a third identical isolator  26 . As isolators  10 ,  25  and  26  are identical to each other they will not be described herein. A housing  29  shown in section surrounds each of isolators  10 ,  25  and  26  to maintain the elastomer sheets between the opposing plates of each of the isolators. As an alternate embodiment the elastomer sheets could be pegged or pinned to prevent the lateral creeping of the elastomer sheet as the system is subject to shock and vibration. 
     Thus the present invention includes the method of providing a compressive support while providing elastomeric tensional resistance to a compressive load by 1) forming a set of elongated parallel protrusions  11   a  and a set of elongated parallel recesses  11   b  in a first plate  11 . 2) forming set of complementary elongated parallel protrusions  12   a  and complementary elongated parallel recess  12   b  in second plate  12 . 3) placing an elastomer sheet  13  between the first plate  11  and the second plate  12  so that the elastomer sheet  13  is sandwiched therebetween. 
     In addition the method can include the step of forming rounded corners on the protrusions and recess to inhibit tearing of the elastomer sheet  13 . To prevent slipping of elastomer sheet  13  the method of the invention can include the step of forming high frictional surfaces  11   f  on protrusions  11   a  and high frictional surfaces  12   f  on complementary protrusions  12   a  to inhibit lateral sliding of elastomer sheet  13  between the first plate  11  and the second plate  12 . The method of the invention can also include the step of forming each of the protrusions  11   a  on first plate  11  of a width D 1  that is less than a width D 2  of the complementary recess  12   b  in the second plate  12  where the difference between D 1  and D 2  is an amount that is equal or greater than twice the thickness “t” of elastomer sheet  13 .