Abstract:
The present invention relates to a passive vibration isolation device for broadband suppression of vibrations. The device preferably comprises either a vertical spring filter, a horizontal spring filter, or a combination of the two. The vertical spring filter comprises non-linear spring devices such as Belleville washers, ZK washers, crest-to-crest springs or the like stacked in series, in parallel, or any combination thereof. ZK washers are washers which comprise multiple integral concentric rings of varying conicity. The device further may optionally comprise a screw, belt or similar device for adjusting the aspect ratio of the vertical spring. The device further may optionally comprise a screw or similar device for adjusting the static load placed on the vertical spring. The horizontal spring filter may comprise any number of bearings retained within a conical raceway disposed between two cylindrical plates. The vibration isolation device then may be placed beneath a machine, or a platform supporting a machine, to isolate vibrations otherwise transmissible from the floor to the machine or vice versa.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/060,071, filed Sep. 26, 1997, U.S. Provisional Application No. 60/065,439, filed Sep. 29, 1997, and U.S. Provisional Application No. 60/069,289, filed Dec. 11, 1997. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to a device for controlling transmission of vibrations from machinery to their environment and vice-versa. More particularly, the present invention relates to a passive micro vibration isolator for the suppression of a broad band of vibration frequencies. The invention further relates to ZK washers for use in such isolators as an alternative to known Belleville washers. 
     BACKGROUND 
     In general, vibration originating from machines or other sources is most often undesirable and detrimental. For example, vibration in a precision machining tool may lead to faults and imperfections in work pieces produced on the tool. The vibration also may be transmitted through the floor and disrupt other tools. Additionally, the noise generally associated with machine vibration may be disruptive to workers. 
     Various methods and devices exist to reduce undesirable vibrations and may be generally categorized as vibration isolators or suppressors. Typically, vibration isolation devices operate locally to reduce transmissibility, wherein transmissibility is typically defined as the ratio of the transmitted force to the disturbing force. As such, vibration isolation devices are particularly suitable for reducing discrete and transient vibrations. For example, where a CMP machine may rest on a platform, various reflexive and absorptive materials such as rubber may be placed between the platform legs and the floor to isolate the machine from any vibrations coming from the floor. 
     Vibration mitigation devices may be categorized further as active or passive devices. Typically, active devices incorporate a feedback system which detects the amplitude and/or frequency of the disrupting vibration and responds accordingly to reduce or eliminate the vibration. Therefore, active devices are capable of broadband reduction of vibration. However, the complexity and cost of typical active devices often make them impractical for many applications. 
     In contrast, passive devices are typically mechanical devices which generally use various spring elements and damping elements to reduce or eliminate vibrations. However, conventional passive devices generally operate to reduce vibrations only in a fairly narrow bandwidth. Additionally, certain materials used in conventional passive devices, such as rubber and lubricating fluid, may be inappropriate for use in certain environments, such as clean room environments. 
     In conventional devices, a spring element is commonly used in combination with a beam-column element to reduce the transmission of vibration. See U.S. Pat. No. 5,178,357, issued on January 1993, to Platus and related U.S. Pat. No. 5,549,270, issued on August 1996, to Platus et al. More particularly, a spring and a beam-column are calibrated such that one element has a positive stiffness and the other element has an equal negative stiffness. In this manner, an object is supported with near-zero effective stiffness. However, a spring and beam-column pair is required for each axis to be isolated from vibration and each spring and beam-column pair must be precisely calibrated to achieve a net-zero effective stiffness in each axis. As such, this method is fairly complicated and difficult to calibrate and adjust. Additionally, as the requisite negative and positive stiffness are achieved through two separate elements, if one element wears at a rate different than that of the other, their stiffness will no longer match and a net-zero effective stiffness will not be achieved. Moreover, conventional devices typically require a good deal of maintenance and are too sensitive or fragile to support large, heavy and especially sensitive equipment such as CMP machines and powerful microscopes. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a passive vibration isolation device for reducing vibration transmissibility in a broad frequency range. In a preferred exemplary embodiment of the present invention, a vibration isolation device includes a plurality of net-zero or near-zero effective stiffness elements. More particularly, a configuration of balls trapped between raceways is used in combination with springs, conic washers and the like with substantially zero tangent stiffness at large secant stiffness, such as, for example, non-linear springs, Belleville, ZK washers or any combination of the same. In addition, another configuration facilitates the reconfiguration of the non-linear springs to tune them for lighter and heavier loads. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     The present invention will hereinafter be described in conjunction with the appended drawing figures, wherein like numerals generally denote like elements, and: 
     FIG. 1 is a perspective view of a vibration isolation platform supported by three vibration isolation devices (“VIDs”), in accordance with an embodiment of the present invention; 
     FIG. 2 is a perspective view of one of the VIDs shown in FIG. 1 with portions of the embodiment shown removed; 
     FIG. 3 is a cross-sectional view of a portion of the device shown in FIG. 2; 
     FIG. 4 is a top plan view of a Belleville washer in accordance with the present invention; 
     FIG. 5 is a cross sectional view of the Belleville washer shown in FIG. 4 taken through line  5 — 5 ; 
     FIG. 6 is a cross sectional view of Belleville washers stacked in a serial arrangement, in accordance with the present invention; 
     FIG. 7 is a cross sectional view of Belleville washers stacked in a parallel arrangement, in accordance with the present invention; 
     FIG. 8 is a top plan view of a ZK washer used in accordance with the present invention; 
     FIG. 9 is a cross sectional view of the ZK washer shown in FIG. 8 taken through line  9 — 9 ; 
     FIG. 10 is a top plan view of another ZK washer in accordance with the present invention; 
     FIG. 11 is a cross sectional view of the ZK washer shown in FIG. 10 taken through line  11 — 11 ; 
     FIG. 12 is a top plan view of yet another ZK washer in accordance with the present invention; 
     FIG. 13 is a cross sectional view of the ZK washer shown in FIG. 12 taken through line  13 — 13 ; 
     FIG. 14 is a perspective view of a VID in accordance with another embodiment of the present invention; 
     FIG. 15 is a perspective view of the VID shown in FIG. 14 with portions of the embodiment shown removed; 
     FIG. 16 is a another perspective view of the VID shown in FIG. 14 with portions of the embodiment shown removed; 
     FIG. 17 is yet another perspective view of the VID shown in FIG. 14 with portions of the embodiment shown removed; 
     FIG. 18 is a perspective view of a VID in accordance with another embodiment of the present invention; 
     FIG. 19 is a top perspective view of a VID in accordance with another embodiment of the present invention; 
     FIG. 20 is a bottom perspective view of the VID shown in FIG. 19; 
     FIG. 21 is a top plan view of the VID shown in FIG. 19; 
     FIG. 22 is a cross section view of the VID shown in FIG. 19 taken through line  22 — 22 ; 
     FIG. 23 is a perspective view of a VID in accordance with another embodiment of the present invention with portions of the embodiment shown removed; 
     FIG. 24 is a perspective view of a VID in accordance with still another embodiment of the present invention; 
     FIG. 25 is a perspective view of the VID shown in FIG. 24 with portions of the embodiment shown removed; 
     FIG. 26 is a cross sectional view of a VID in accordance with yet another embodiment of the present invention; 
     FIG. 27 is a perspective view of a VID employing crest-to-crest springs; 
     FIG. 28 is a perspective view of a VID employing a combination of ZK washers and crest-to-crest springs. 
     FIG. 29 is a perspective view of a an alternative embodiment of a VID; 
     FIGS. 30 a, b  are cross-sectional views of alternative embodiments of a VID; 
     FIG. 31 is a cross-sectional views of an embodiment of a ZK washer of the present invention; 
     FIG. 32 is a cross-sectional view of an alternative embodiment of a ZK washer of the present invention; and 
     FIG. 33 is a cross-sectional view of another alternative embodiment of a ZK washer of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A vibration isolation device (“VID”) according to various aspects of the present invention provides a suitable system for reducing the transmissibility of micro vibrations between the environment and vibration sensitive or vibration generating equipment such as Chemical Mechanical Planarization (“CMP”) machines, silicon wafer and memory disk polishers and grinders, silicon ingot slicers, lithographic equipment, microscopes, and the like. In order to provide a more thorough understanding of the present invention, the following description sets forth numerous specific details, such as specific parameters, components, and the like. However, these specific details need not be employed to practice this invention. 
     With reference to FIG. 1, a plurality VIDs  102  are suitably integrated into vibration isolation platform  100 . More particularly, a plurality of bolts  108  attach collars  110  of VIDs  102  to mounting brackets  106 , which are attached in turn to platform  104  by a plurality of bolts  112 . However, VIDs  102  may be attached to platform  104  using any other convenient method. For example, VIDs  102  may be welded onto platform  104 . Alternatively, VIDs  102  may be attached directly to the device to be supported. 
     VID  102  includes a plurality of nonlinear spring assemblies to isolate the transmission of micro vibrations in up to six degrees of freedom across a broadband of vibration frequencies. More particularly, with reference to FIG. 2, in the present embodiment, VID  102  includes a configuration of a plurality of balls  204  disposed between raceways  222  and  224  for broadband vibration isolation primarily in the x-y plane and a plurality of conic washers  206  and  208  for vibration suppression in the y-z and x-z planes, and about the x and y axes. Preferably, raceways  222 ,  224  are circular, though, raceways  222 ,  224  may be other alternative configurations, such as for example, dimples  3301  and the like. Raceways  222 ,  224  generally have a substantially spherical contour, but may likewise comprise semi-conical configurations and the like as well. 
     Lower section  114  and upper section  202  are suitably configured with substantially matching circular raceways  222  and  224 , respectively, with substantially conic cross-sectional profiles and rounded apexes. In a preferred embodiment, the apex radii of raceways  222  and  224  are large compared to the radius of balls  204 . Raceways  222  and  224  may be formed using any convenient method. For example, sections  114  and  202  may be cast or molded with raceways  222  and  224 . Alternatively, raceways  222  and  224  may be milled or machined into sections  114  and  202 . Additionally, sections  114  and  202  may be formed from any suitable rigid material (e.g., metal, ceramic, and the like). In a most preferred embodiment, sections  114  and  202  are formed from steel. 
     A plurality of balls  204  are disposed between raceways  222  and  224  within a plurality of holes formed in retainer ring  220 . In the present embodiment, three balls are used and, accordingly, three holes are formed in retainer ring  220 . More particularly, retainer ring  220  preferably maintain the balls at substantially even spacings of about 120 degrees to facilitate equal distribution of the weight of the device to be supported. Depending on the particular application, however, any number of balls may be disposed at any desirable intervals. For example, six balls spaced at 60 degree increments may be used to support heavier loads. Additionally, plurality of balls  204  may be formed from a suitable hard and smooth material (e.g., steel, aluminum, and the like). 
     When VID  102  is not displaced is the x-y plane, plurality of balls  204  rest at the apexes of raceways  222  and  224 . With reference to FIG. 3, when base section  114  and/or upper section  202  are displaced along the x-y plane, ball  204  displaces onto the sloped walls of raceways  222  and  224  (for sake of clarity, only one ball is shown and described). Force  300 , due to gravity, is applied normal to the surface sloped walls of raceways  222  and  224 . Force  300  can be resolved into horizontal force  302  and vertical force  304 . Horizontal force  302  thus acts as a restorative force to restore ball  204  to its rest position, thereby restoring VID  102 . Additionally, retainer ring  220  contributes a small amount of dampening due to friction. Accordingly, retainer ring  220  is preferably formed a polytetrafluoroethylene material, such as the commercial product TEFLON®, or other suitable low friction material. 
     Moreover, as the slope of raceways  222  and  224  are substantially constant, the restorative force (i.e., horizontal force  302 ) is substantially constant and independent of the frequency and amplitude of displacements in the x-y plane within the stroke range of raceways  222  and  224  (i.e., substantially the cross-sectional width of raceways  222  and  224 ). Accordingly, the configuration of plurality of balls  204  trapped between raceways  222  and  224  preferably has no natural frequency, and provides substantially broadband vibration isolation in the x-y plane. 
     In accordance with an exemplary embodiment of the present invention, with reference to FIGS. 2,  3 , and  27 , a first non-linear spring device  206  is disposed between upper section  202  and collar  110  and a second non-linear spring device  208  is disposed between collar  110  and load-adjustment cap  210 . First and second non-linear spring devices  206 , 208  are suitably comprised of any material and/or device which exhibits non-linear spring characteristics including substantially high secant stiffness for large amplitude vibrations and substantially zero tangential stiffness for micro vibrations. For example, non-linear spring devices  206 , 208  may comprise standard non-linear springs, Belleville washers, ZK washers and the like, or any combination thereof. For ease of reference, any of the non-linear spring devices may be referred to in the following description as simply “conical washers.” In a preferred embodiment, with reference to FIG. 27, non-linear spring devices  206 , 208  are “crest-to-crest” springs such as those manufactured by Smalley Steel Ring Co. of Wheeling, Ill. 
     Further, with reference now to FIG. 2, non-linear spring devices  206 , 208  may be conic washers such as Belleville or ZK washers disposed between upper section  202  and collar  110  between collar  110  and load cap  210 . 
     Still further, any combination of washers and springs which exhibit the aforementioned characteristics may be substituted in the present invention. For example, with reference to FIG. 28, ZK washers may be disposed between upper section  202  and collar  110  and crest-to-crest springs may be disposed between collar  110  and load cap  210 , or vice versa. 
     In one exemplary embodiment of the present invention, conic washers  206  may include Belleville washers suitably configured to exhibit substantially zero tangential stiffness and high secant stiffness. More particularly, with reference to FIGS. 4 and 5, Belleville washer  400  is suitably configured with conic section  404  extending from inner circumference  402  to concentric outer circumference  406 . When a compressive pressure is applied along circumferences  402  and  406 , Belleville washer  400  responds with a stiffness characteristic determined in part by its aspect ratio (i.e., the ratio of height  500  to thickness  502 ). More particularly, Belleville washers with an aspect ratio of about 1.5 are known to have substantially zero tangential stiffness and high secant stiffness in the stroke range of about 2h/3 to h, where h is height  500 . 
     With additional reference to FIGS. 6 and 7, Belleville washers may be stacked in series (as depicted in FIG.  6 ), in parallel (as depicted in FIG.  7 ), or any combination thereof to increase their ability to support heavier loads. The stacking of Belleville washers, however, increases the profile of VID  102 , which may be undesirable in some applications. For example, a VID  102  with a tall profile may raise the load to an undesirable or inoperable height. 
     Alternatively, conical washers  206  may include ZK washers which provide substantially zero tangential stiffness and high secant stiffness similar to Belleville washers, but are capable of supporting heavier loads. More particularly, with reference to FIGS. 8 and 9, ZK washer  700  includes concentric sections  702  and  704 . Section  702  has high aspect ratio h/t (i.e., ratio of height  800  to thickness  804 ), and section  704  has low aspect ratio h/t (i.e., ratio of height  800  to thickness  802 ). In a preferred embodiment, section  702  and  704  have aspect ratios of about 2 and 0.8, respectively. Thus, the tangent stiffness of sections  702  and  704  are substantially equal and of opposite sign in the h/6 vicinity of 2h/3 stroke, where h is height  800 . However, the tangent stiffness of section  704  is preferably slightly higher than that of section  702  to prevent failure of section  702 . Additionally, the aspect ratios of sections  702  and  704  may be reversed without altering the performance characteristics of the ZK washer. In this manner, similar to Belleville washers, ZK washer  700  provides substantially zero tangential stiffness and high secant stiffness in the range of 2h/3 to h, where h is height  800 . However, in comparison to Belleville washers, ZK washer  700  has a smaller height profile, and is capable of supporting heavier loads. Additionally, similar to Belleville washers, ZK washers may be stacked in series, parallel, or any combination thereof. 
     ZK washers may be formed using any convenient methods. For example, in the present embodiment, ZK washer  700  is suitably formed by machining sections  702  and  704 . With reference to FIGS. 10 and 11, ZK washer  1000  is suitably stamped. Alternatively, with reference to FIGS. 12 and 13, composite washer  1200  may be formed by attaching Belleville washer  1300  to ZK washer  1302 . In accordance with another aspect of the present invention, with reference to FIGS. 31-33, ZK washer may be provided with slots  3101 . Generally, slots  3101  may be formed in ZK washer  1302  in any suitable manner, such as by machining, stamping and the like. Preferably, slots  3101  are formed using an electro-discharge machine (EDM). In accordance with one aspect of the present invention, with reference to FIGS. 31 and 32, ZK washers  1302  may have arcuate shaped roots  3203  and tips  3201  on each segment of washer  1302 . 
     In accordance with one aspect of the present invention, with reference to FIGS. 19 and 23, VID  102  may be manufactured and configured to work only within a range of predetermined loads. However, in accordance with an alternative aspect of the present invention VID  102  and/or conic washers  206  and  208  may be reconfigured and/or adjustable for lighter or heavier loads. 
     For example, with reference to FIG. 2, load-adjustment nut  212  may be rotated about threaded shaft  214  to appropriately lower or raise load-adjustment cap  210 . In this manner, conic washers  206  and  208  may be appropriately calibrated to provide near zero tangential stiffness and high secant stiffness for lighter or heavier loads. For example, for lighter loads, the aspect ratios of conic washers  206  and  208  are appropriately reduced by appropriately loosing adjustment nut  212 , thus raising adjustment cap  210 . For heavier loads, the aspect ratios of conic washers  206  and  208  are appropriately increased by appropriately tightening adjustment nut  212 , thus lowering adjustment cap  210 . Alternatively, conic washers  208  may be known compression springs such that they primarily pre-compress conic,washers  206 . Additionally, bolt  214  is pivotally attached at bottom end  216  to base anchor  218  to facilitate displacement of VID  102  about the x-axis. 
     As VID  102  does not require power supplies or lubrication, it is particularly well suited for use in clean room environments. In a preferred embodiment, VID  102  is formed substantially entirely of steel, aluminum, and TEFLON®. 
     Referring now to FIGS. 14 through 17, in accordance with another aspect of the present invention, VID  1400  is suitably configured to permit adjustment of the spring aspect ratio of conic washer  1410 . According to one exemplary embodiment, base ring  1412  is suitably configured in the center of conic washer  1410  for supporting a load. Conic washer  1410  is preferably disposed within substantially circular cavity  1418  formed in top section  1402 . More particularly, as depicted in FIG. 15, a portion of the bottom surface of conic washer  1410  rests upon shoulder  1502  in cavity  1418 , and the outer circumferential edge of conic washer  1410  contacts the inner circumferential surface of cavity  1418 . The diameter of cavity  1418  may be adjusted by appropriately loosening or tightening adjustment screw  1416  to appropriately open or close gaps  1414  and  1420 . Alternatively, an adjustable clamp, such as a hose clamp, may be fitted around the outer circumferential surface of top section  1402 . In this manner, the aspect ratio of conic washer  1410  may be calibrated for use with lighter or heavier loads. For example, for lighter loads, the aspect ratio of conic washer  1410  is reduced by loosening adjustment screw  1416  to open gaps  1414  and  1420 . For heavier loads, the aspect ratio of conic washer  1410  is increased by tightening adjustment screw  1416  to close  1414  and  1420 . 
     In the present embodiment, conic washer  1410  includes substantially zero tangential stiffness elements (e.g., crest-to-crest springs, Belleville washers, ZK washers, and the like). As previously discussed, however, ZK washers may be configured to support heavier loads than other known conic washers, such as Belleville washers. As such, the vertical profile of VID  1400  may be reduced by using ZK washers and reduced still further using crest-to-crest springs. Therefore, in a most preferred embodiment, a single ZK washer is configured to operate with VID  1400 . Configured in this manner, VID  1400  is particularly suited for isolating vibration at the legs of tools (e.g., CMP machines, lithography equipment, and the like). 
     VID  1400  also includes substantially matching circular raceways  1510  and  1512  formed in lower section  1404  and upper section  1402 , respectively. A plurality of balls  1500  are disposed between raceways  1510  and  1520 , and lie within a plurality of holes formed in retainer ring  1406  (as depicted in FIG.  16 ). In the present embodiment, six balls are substantially equally spaced at b  60  degree increments by retainer ring  1406 . Raceways  1510  and  1512  have substantially conical cross sections with rounded apexes. Horizontal displacement of VID  1400  causes displacement of plurality of balls  1500  onto the conical cross sections of raceways  1510  and  1512 . Gravity then restores plurality of balls  1500  to the apexes of raceways  1510  and  1520 . Accordingly, the substantially constant slope of the conical sections of raceways  1510  and  1512  facilitates broadband vibration isolation in the horizontal plane. Additionally, when plurality of balls  1500  approach the end of their stroke lengths, spring rings  1408  exert a small compression force to urge plurality of balls  1500  back to their rest positions. Spring rings  1408  also hold upper and lower sections  1402  and  1404  together during shipping, transportation, and installation. Moreover, spring rings  1408  preferably aid in centering plurality of balls  1500  and raceways  1510  and  1512  prior to loading. 
     With reference to FIG. 18, in accordance with another embodiment of the present invention, VID  1800  is configured as a particularly low profile device. VID  1800  includes lower and upper rings  1802  and  1806  configured with substantially matching circular raceways  1816  and  1818 , respectively. A plurality of balls  1810  are disposed between raceways  1816  and  1818 , and lies within a plurality of holes formed in retainer ring  1804 . Conic washer  1812  is configured on shoulder  1820  formed around the interior circumference of upper ring  1806 . In a manner similar to previously described embodiments, the configuration of balls  1810  trapped between raceways  1816  and  1818 , and conic washer  1812  provide broadband vibration isolation for a load mounted on base ring  1814 . In a preferred embodiment, three balls are disposed at equally spaced 120 degree increments, and conic washer  1812  is preferably a Belleville or ZK washer with aspect ratios of 1.5. 
     In a most preferred embodiment, the diameter of VID  1800  is between three to nine inches and height of 1 inch or less. The stroke length in all direction is {fraction (3/16)}th of an inch and the natural frequency is ⅕th Hz for ideal rated load and 2 Hz at plus or minus 50 percent of the ideal rated load, where the ideal rated load is 4,000 pounds. 
     With reference to FIGS. 19-22, in accordance with yet another embodiment of the present invention, VID  1900  includes top portion  1930 , bottom portion  1940 , and plurality of conic washers  2220  disposed between top portion  1930  and bottom portion  1940 . Top portion  1930  and bottom portion  1940  are suitably configured with bores  2060  and  2250 , respectively. Compression spring  2240  suitably extends through bores  2060  and  2250 , and attached to upper portion  1930  by anchor bar  1920  and bottom portion  1940  by anchor bar  2010 . Compression spring  2240  pre-compresses plurality of conic washers  2220  such that plurality of conic washers  2220  exhibit substantially zero tangential stiffness and high secant stiffness. Accordingly, VID  1900  provides broadband isolation of vibration primarily along the z-axis. In a preferred embodiment, plurality of conic washers  2220  include Belleville or ZK washers with aspect ratios of approximately 1.5. 
     With reference to FIG. 23, in accordance with still another embodiment, VID  2300  includes base  2310 , mounting bracket  2330 , and adjustment cap  2350 . A plurality of conic washers  2320  and  2340  are suitable disposed between base  2310  and bracket  2330 , and between bracket  2330  and adjustment cap  2350 , respectively. Adjustment bolt  2360  extends up from base  2310  through mounting bracket  2330  and is suitably attached to adjustment cap  2350  with adjustment nut  2370 . Plurality of conic washers  2320  and  2340  may be calibrated for lighter or heavier loads by tightening or loosening adjustment bolt  2370 . More particularly, when adjustment bolt  2370  is suitably tightened, adjustment nut  2370  engages with plurality of teeth on adjustment bolt  2360  and adjustment cap  2350  lowers, to compress plurality of conic washers  2320  and  2340 . Conversely, when adjustment bolt  2370  is suitably loosened, adjustment cap  2350  rises to expand plurality of conic washers  2320  and  2340 . 
     Mounting bracket  2330  is suitably attached to a load, and plurality of washers  2320  and  2340  provide broadband isolation of vibration primarily along the z-axis. In a preferred embodiment, plurality of conic washers  2320  and  2340  are Belleville or ZK washers. 
     With reference to FIGS. 24 and 25, in accordance with a further embodiment of the present invention, VID  2400  includes base ring  2406 , ZK washer  2402 , compression band  2408 , and adjustment bolt  2410 . A load is suitably mounted on base ring  2406 . ZK washer  2402  exhibits substantially zero tangential stiffness and high secant stiffness, thus providing broadband vibration isolation primarily along axis z. More particularly, ZK washer  2402  is preferably a two-tiered ZK washer, such that the vertical cross section of ZK washer  2402  is substantially equal to the horizontal cross section. Accordingly, the stresses exerted on ZK washer  2402  is substantially uniform. Additionally, compression band  2408  is suitably configured around the outer circumference of VID  2400  such that the spring aspect ratio of ZK washer  2402  may be altered by appropriately loosening or tightening adjustment bolt  2410 . ZK washer  2402  may be provided with slots  2404 . 
     With reference to FIG. 26, in accordance with another embodiment of the present invention, VID  2600  includes frame  2610 , ball-in-cone assembly  2690 , conic washer  2670 , and spring aspect ratio adjustment screw  2680 . Ball-in-cone assembly  2690  includes conic recesses  2700  and  2710  formed in upper section  2630  and lower section  2640 , respectively. Ball  2620  is preferably disposed between recesses  2700  and  2710 , and lie within a hole formed in retainer ring assembly  2690  suitably provides broadband isolation of vibration along the horizontal plane. 
     Conic washer  2670  is preferably disposed within substantially circular inner perimeter of frame  2610 . Adjustment screw  2680  may be suitably loosened or tightened to decrease or increase, respectively, the spring aspect ratio of conic washer  2670 . In this manner, conic washer  2670  provides broadband isolation along the vertical plane for loads mounted on upper section  2630 . In a preferred embodiment, conic washer  2670  is preferably a Belleville or ZK washer. 
     Although specific embodiments and parameters have been described, various modifications may be apparent upon reading this disclosure. For example, although Belleville and ZK washers have been used as conic washers in various embodiments, other suitable nonlinear spring elements with the requisite stiffness characteristics such as EPDM rubber may be used.