Abstract:
A vibration isolation platform utilizes a plurality of viscoelastic polymer blocks sandwiched between rigid plinths or boards and stacked on top of one another to provide vibration damping additively per layer of the sandwich. Smaller viscoelastic blocks are positioned between the edges of the plinths and the sidewalls of a framework in which the sandwich is mounted to compensate for lack of shear stress in the larger blocks. The platform is pre-loaded to optimum isolation and locked down at the required compression. Optimum isolation is achieved for any electronic component positioned on the platform up to the design weight limit.

Description:
This invention relates to vibration damping equipment and, more specifically, an isolation platform for supporting consumer and commercial electronic apparatus and for damping vibrations from external sources to that equipment. 
   BACKGROUND OF THE INVENTION 
   Vibration damping equipment or apparatus takes on a number of forms, shapes, and sizes. Large industrial equipment, such as computer numerically controlled (CNC) machining or fabricating operations may be mounted on isolation platforms supported by gas filled bladders mounted between the platform and the bottom of a pit constructed in a factory. Such an isolation platform acts to protect sensitive equipment from vibrations emanating from adjacent machinery in the factory, or from outside sources such as heavy vehicles running on nearby roads and the like. Air bladders are ineffective in isolating consumer and commercial electronic because the high velocity of wave forms in the audible spectrum cause in the air bladder adiabatic compression which retain mechanical energy and passes vibration to the electronic component. 
   On a different size level, electronic equipment for both home use and for commercial use in recording studios in audio and visual recording, in television and radio studios and computer and other electronic facilities can benefit from being mounted on vibration isolation platforms. It is useful, and often necessary to provide vibration damping apparatus in order to provide high quality generation transmission and reception of electronic signals. 
   One such isolation platform is found in U.S. Pat. No. 5,197,707. This platform includes an open top rectangular box having a granular medium positioned therein with a plinth or top plate floating on the granular medium to isolate vibrations. The problems associated with not having the granular medium fully enclosed would allow such granules to escape. 
   A selectively tuned vibration absorber is shown in U.S. Pat. No. 6,279,679. In operation, a pair of these vibration absorbers are adapted to be mounted in spaced position on a plate that is affixed at its center to the back of a loudspeaker. Each apparatus includes a plurality of plates with small end spacers positioned between the plates at the opposing ends along the opposing end edges thereof. This apparatus is sized to be tuned to resonate at the fundamental resonance frequency of the low frequency loudspeaker. As such, it does not absorb vibrations from outside the piece of electronic equipment. 
   Additionally, a viscoelastic damping system is shown in U.S. Pat. No. 5,240,221. This system also is made up of a plurality of plates stacked together and separated with spacers. It is also meant to be mounted on an enclosure panel of a loudspeaker to attenuate the vibrations of the panel that may interfere with the desired loudspeaker output. In this patent, there is no disclosure of means for isolating the bolt ( 4 ) from the mounting block of the damping system. 
   Further, the cabinets of electronic equipment include, at times, spring mounted mounting pads having rubber or other elastic material on their bottom to isolate electronic equipment positioned in the cabinetry from outside vibrations. Springs are ineffective for isolating consumer and commercial electronics because springs store energy and excess mechanical energy is transferred to the electronic component as vibration. These isolation materials are exposed to airborne vibrations. These airborne mechanical disturbances cause the isolation materials to vibrate the electronic component. 
   A need has developed for an improved vibration isolation and damping apparatus or platform that provides superior vibration damping capabilities for home, commercial and industrial electronic equipment. 
   Another object of the present invention is the provision of an improved vibration damping apparatus or platform having lighter weight and less vibrating mass than heretofore known vibration damping apparatus. Another object of the present inventions is an isolation apparatus that isolates the internal isolation system from airborne vibration through an external double wall encasement. 
   It is therefore an object of the present invention, generally stated, to provide an improved vibration damping apparatus or platform for home, commercial and industrial electronic equipment. 
   Another object of the present invention is the provision of an improved vibration isolation or damping platform that lowers the resonant frequency of the upper portion of the platform to provide superior vibration isolation for electronic equipment mounted on such plinth or platform. Another object of the present invention is the inclusion of horizontally placed intermediate plinths between multiple isolation layers of polymers which diffuse residual energy passing through the viscoelastic material outward acting to dissipate vibration before reaching the next level of polymers. 
   SUMMARY OF THE INVENTION 
   The invention resides in an apparatus including a vibration damping plinth for isolating equipment positioned on the plinth from external vibration. The apparatus comprises a hollow framework including a bottom and sides extending upwardly from the bottom. At least one viscoelastic member is positioned on the hollow framework bottom. A top plinth is positioned on top of the at least one viscoelastic member in spatial relation to the sides of the apparatus. Additionally, the at least one viscoelastic member is compressed a predetermined amount corresponding to a weight greater than the weight of equipment to be positioned on top of the plinth. 

   
     BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which like numerals refer to like parts and in which: 
       FIG. 1  is a ¾ top perspective view of an isolation platform constructed in accordance with the present invention having an electronic component positioned on the top thereof; 
       FIG. 2  is a detailed fragmented cross-sectional view taken along line  2 - 2  of  FIG. 1 , of the isolation platform of the present invention showing two differing stacked electronic components positioned thereon; 
       FIG. 3  is a ¾ top perspective view showing the base of the container in which the isolation platform is mounted having a first layer of viscoelastic blocks positioned on the bottom panel thereof. 
       FIG. 4  is a perspective view similar to that of  FIG. 3  showing the bottom layer of viscoelastic blocks positioned therein with sound deadening material positioned therebetween; 
       FIG. 5  is a fragmentary perspective view of one corner of the top plinth of a vibration isolation damping apparatus showing the viscoelastic blocks positioned on the side thereof prior to positioning the plinth within the base container; 
       FIG. 6  is a fragmentary top plan view of one corner of the base container for the vibration isolation platform showing the top plinth mounted therein; 
       FIG. 7  is a ¾ top perspective view similar to  FIG. 4  showing the viscoelastic blocks in mounted position on a plinth above the base of the container and having an additional sound deadening material positioned on the intermediate plinth; and 
       FIG. 8  is a top ¾ perspective view of the base container having the outer cover positioned thereon with the plinths and isolation blocks normally positioned therein removed. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIGS. 1 ,  2  and  8 , the vibration isolating platform, generally indicated at  10 , includes a top plinth or platform  11  on which an electrical component, be it large  12  ( FIG. 1 ), a pair of smaller  13 - 14  ( FIG. 2 ) components positioned on top of one another, or the like. Further the footprint of the platform may be any shape that accommodates positioning electronic equipment thereon. In addition to the upper plinth or platform  11 , the portions of the isolation platform which can be seen readily include a surround type cover, generally indicated at  15  that includes in this embodiment, a hollow generally flat upper lip  16  having a rectangular internal edge  17  that surrounds the upper plinth  11  in spatially related picture frame type relation, and four vertical side walls  18 ,  19 ,  20  and  21  which, in this embodiment is rectangular and depends from the outermost portion of the upper lip  16 . The rectangle on the front of side  20  is a logo showing a brand identification for the isolation platform of the invention  10  and covers a fastener to be discussed in more detail below. The top plinth  11  and top cover  15  are separated by a gasket  23  approximately ⅛×¼ inch cross-sections made of viscoelastic polymer, that extends around the length of edge  17  under the lip  16 . 
   Referring to  FIGS. 3 and 8 , the base or framework, generally indicated at  24 , includes four vertical sides  25 ,  26 ,  27  and  28  fitted together at their respective ends to form a rectangular hollow box that is semi-enclosed by a rectangular bottom panel  29 . The side and bottom panels may be constructed of any suitable material, plywood, solid wood boarding, particle board (MDP) or the like. As shown most clearly in  FIG. 2 , bottom panel  29  is joined to the sides  24 ,  25 ,  26 ,  27  and  28  by a rabbit type joint. If expansion and contraction are a concern, the bottom panel  29  can be lifted slightly and set into a dado slot in each bottom panel allowing expansion and contraction. 
   As shown most clearly in  FIG. 8 , the hollow cover  15  is slidably retained on the base framework  24  in a vertical sliding relation thereover the retention of the cover on the base will be discussed in greater detail below. 
   Referring to  FIG. 2 , the vibration damping material positioned under the top plinth  11  and within the confines of the base framework  24  are shown. The interior members shown in  FIG. 2  are not necessarily drawn to scale but indicate the relationship between the parts making up the absorption damping or isolation platform  10 . As shown most clearly in  FIGS. 2 and 3 , on top of the bottom panel  29  are mounted a plurality of vibration damping blocks,  31 - 31 . In the preferred embodiment, these vibration damping blocks are made of a highly elastic material and are 1 inch by 1 inch in footprint. In the embodiment shown in  FIG. 2 , the height of the various viscoelastic polymer blocks is shown differing from layer to layer. They may be the same height in the various layers underneath the top plinth  11 , as dictated by the frequencies to be damped. 1.25 inches is a standard height in the preferred embodiment. The viscoelastic material making up these blocks are manufactured by I.E. DuPont, B. P. Amoco, General Electric, and Trelleborg A. B. Material sold under the brand Sorbothane may be used or E. A. R. Specialty Composites. 
   In the embodiment shown in  FIG. 3 , six of these viscoelastic polymer blocks are mounted adjacent but spaced about ½ inch from the corners of the base framework  24  and also positioned midway between the corner blocks on two opposing sides of the base framework for a total of six viscoelastic polymer blocks. In the preferred embodiment Sorbethane brand polymer is used. As will be shown in more detail below, the number and size and spatial relation of the viscoelastic polymer block may be changed depending upon the vibration damping characteristics one wishes to have in the apparatus.  FIG. 2  shows the spatial relation between each of the viscoelastic blocks  31  and the sides  25 - 27  of the base framework  24 . 
   As shown most clearly in  FIG. 4 , sound deadening or insulation material  32  is positioned between the viscoelastic polymer blocks to fill the space between the bottom panel  29  and an intermediate plinth  33 . Intermediate plinth  33  is adhered to the top of viscoelastic polymer blocks  31 - 31  and is rectangular in shape similar to the bottom panel  29 , but slightly smaller (about ½ inch in side length) to allow a ¼ inch spatial relation between the side edges of the intermediate plinth  33  and the side walls  25 ,  26 ,  27 ,  28  of the base framework  24 . 
   Intermediate plate  33  may be made of wood, metal, carbon fiber, or synthetic material. On top of the first intermediate plinth or plate  33  immediately above the viscoelastic polymer blocks  31 - 31  are adhered an additional six viscoelastic polymer blocks  34 - 34 . Viscoelastic polymer blocks  34 - 34  are in this embodiment, also 1 inch by 1 inch square by 1.25 inches high, although those dimensions may be changed within the scope of the invention. 
   A second intermediate plinth or plate  35  is adhered at its ends to the tops of the respective viscoelastic polymer blocks  34 ,  34  in the same manner that first intermediate plinth  33  is adhered to blocks  31 - 31 . Additionally, another layer of sound deadening or insulation material (not shown) is also positioned between the first intermediate plinth  33  and the second intermediate plinth  35  with the same purposes as the first layer  32 . 
   Second intermediate plinth  35  may be shaped identically to the first intermediate plinth  33  and be made of the same or differing material. On top of the second intermediate plinth  35  and positioned between that plinth and the upper plinth  11 , are six additional viscoelastic polymer blocks  36 - 36  which may be shaped identically to blocks  34  and  31  or different from them depending upon the design goals of the isolation platform. 
   As shown most clearly in  FIG. 7 , a layer of sound deadening material  38  is positioned within the viscoelastic polymer blocks  36 - 36  and between the second intermediate plinth  35  and the top plinth  11 . 
   While the stacked plinths  11 ,  33  and  35  are connected by the viscoelastic blocks  36 - 36 ,  34 - 34 , and  31 - 31  respectively, additional smaller viscoelastic blocks  40 - 40  are positioned between the edges of the top plinth  11  and the inside top of the framework vertical sides  25 ,  26 ,  27  and  28 . Smaller blocks  50 - 50  and  51 - 51  are positioned between the edges of the second and first intermediate plinths, respectively, and the sides  25 - 28  of the framework  24 . Referring to  FIGS. 2 ,  5  and  6 , the elastoviscous blocks  40 - 40 ,  50 - 50  and  51 - 51 , are, in this embodiment approximately ⅜ inch by ⅜ inch by ¾ inch high. These viscoelastic blocks  40 - 40 ,  50 - 50  and  51 - 51  compress sideways in a manner similar to the vertical compression of viscoelastic blocks  31 - 31 ,  34 - 34  and  36 - 36  to further isolate each of the plinths or platforms from the base framework  24  and exterior airborne vibration. Blocks  40 - 40  compensate for a low shear strength of the viscoelastic blocks  31 - 31 ,  34 - 34  and  36 - 36 . These blocks together with the viscoelastic polymer gasket  23  positioned on the inside of the top lip  16  of cover  15  completely isolate the upper plinth  11  from the remainder of the isolation platform  10 . Heretofore known isolations platforms have used damping material to fill the container or pit on which the platform is mounted. By using a material closer to the high end of the 30-80 “00” scale durometer reading, less total damping material may be utilized and greater isolation attained due to lowered natural frequency and reduced physical contact between shelves. Also the hollow sandwich type construction using rigid intermediate plinths provides added structural integrity to the upper plinth than previously known. 
   In one important aspect of the present invention, behind the rectangular logo  20   a  adhered to the front side  20  of cover  15 , threaded holes  42 ,  43  on the front side of the vibration damper and  44 ,  45  on the backside of the vibration damper are adapted to receive a screw such as shown at  46  in  FIG. 7  to maintain the plinths  11 ,  33  and  35  and the respective viscoelastic blocks  31 - 31 ,  34 - 34  and  36 - 36  in a predetermined compressed state, in this embodiment  20  percent compression of the viscoelastic blocks  31 - 31 ,  34 - 34  and  36 - 36 . With the plinth and blocks compressed the predetermined amount, the holes  42 ,  43  and  44 ,  45  are, in this embodiment, drilled and die cut into the cover  15  and the base  24 . Then a pair of screws  46 - 46  (one shown) are threaded into the mating holes to pre-compress the vibration damping components of the damper  10 . As a result of the pre-compressing of the viscoelastic blocks  31 - 31 ,  34 - 34  and  36 - 36 , the upper plinth  11  is already lowered to a position equating the maximum weight or optimum weight the vibration damper  10  can handle on top of the plinth  11 . It has been found that with the viscoelastic blocks  31 - 31 ,  34 - 34  and  36 - 36  compressed to their optimal damping dimension (in this case  20  percent compressed) that the addition of electronic components such as shown at  12 ,  13  and  14  through the top of plinth  11 , as long as they are below the weight resulting in optimum compression, do not additionally compress the viscoelastic blocks  31 - 31 ,  34 - 34  and  36 - 36 . In other words, from a vibration damping point of view, the viscoelastic blocks support the electronic components such as  11 ,  12  and  13  as though the gravity pulling on those components did not exist. If the vibration damper  10  of the invention is designed and constructed for a deflection that would equal an 80 pound electronic component on the top of plinth  11 , if one puts an electronic component weighting less than 80 pounds (perhaps up to 60 pounds with a safety factor built in) the polymer acts as though it the electronic component is not there. So, by precompressing the vibration damper  10  of the invention, the self-contained system works at optimal efficiency for any and all appropriately dimensioned electronic components up to the designed limit load. 
   The engineering done to determine the size and number of viscoelastic pads or blocks  31 - 31 ,  34 - 34 , and  36 - 36  is known in the art. Such viscoelastic blocks may have a hardness ranging from 30 to 80 on the Shore “00” scale. It is standard to design isolators in a linear region of the load vs. deflection curves for the material which is nominally between 10 and 20 percent deflection. While rectangular blocks are shown in the instant embodiment, other shapes and sizes of viscoelastic material may be utilized. Shape factors in existing equations for determining the size and number of viscoelastic blocks to be used include rectangles, squares, discs and tubes. Such products also disclose natural frequencies of vibration of those products. The quality of transmissibility is defined as a frequency ratio which equals the excitation frequency over the system&#39;s natural frequency and the percent of isolation is equal to 1 minus the transmissibility times  100 . The percent deflection is equal to the static deflection over the height of the block times  100 . Inputting these figures into known equations allows the determination of the transmissibility and percent isolation of the product to be placed on top of the plinth. In one important aspect of the present invention, heretofore known vibration damping equipment for electronic components has utilized a single layer of solid viscoelastic material. The material is sized, shaped and of a diameter such that the material will fill a container or recess on which the plinth is mounted. Using a sheet of viscoelastic material results in low deflection and little or no isolation of the component. The polymer must be deflected to exactly 20 percent to attain 93 or 94 percent vibration damping. As one example, the viscoelastic block utilized may itself provide 93 or 94 percent vibration damping in the first layer or on top of the first intermediate plinth  33 . By utilizing a plurality of viscoelastic blocks such as shown at  31 - 31  and then by adding a second layer of viscoelastic blocks such as shown at  34 - 34  added vibration damping per layer is obtained. In other words, the second layer of isolation blocks  34 - 34  also provide a 93 percent vibration damping on top of the 93 percent obtained on the first layer thereof. The addition of a third layer of viscoelastic blocks  36 - 36  provides an additive 93 percent vibration damping which makes the overall damping factor above 99 percent. 
   Thus, a new and improved apparatus for isolating vibration from outside sources to electronic components has been shown and described. 
   While one embodiment of the present invention has been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the true spirit and scope of the present invention. It is the intent of the appended claims to cover all such changes and modifications which fall within the true spirit and scope of the invention.