Abstract:
A vibration damper includes a rigid base with a mass coupled thereto for linear movement thereon. Springs coupled to the mass compress in response to the linear movement along either of two opposing directions. A converter coupled to the mass converts the linear movement to a corresponding rotational movement. A rotary damper coupled to the converter damps the rotational movement.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     Pursuant to 35 U.S.C. §119, the benefit of priority from provisional application 61/312,757, with a filing date of Mar. 11, 2010, the contents of which are incorporated by reference herein in their entirety, is claimed for this non-provisional application. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made by an employee of the United States Government and may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to vibration dampers. More specifically, the invention is a compact vibration damper that can be tuned. 
     2. Description of the Related Art 
     Structural vibrations frequently need to be damped to prevent damage to a structure. To accomplish this, a standard linear damper or elastomerically-suspended masses are used. A linear damper includes a piston housed in a fluid-filled cylinder. A connecting rod couples a structure to the piston, such that structural vibrations are coupled from the rod to the piston whose linear movement is damped by the fluid in the cylinder. The problem associated with a linear damper is the space required for its construction. For example, if the damper&#39;s piston has to be capable of 2 inches of movement in either direction, the internal length of the fluid-filled cylinder would have to be at least 4 inches while the connecting rod must be at least 4 inches to span the piston&#39;s travel. This means that the overall length of the linear damper is at least 8 inches to achieve +/−2 inches of damping movement. Unfortunately, not all applications have the space to accommodate the size requirements of a linear damper. Further, tuning this type of damper typically involves changing the fluid in the cylinder. This can be a tedious and/or messy operation. 
     In the case of masses suspended using elastomeric materials (i.e., those whose material strain exhibits a viscous force), the allowable range of motion is severely restricted by the allowable strain of the elastomeric material. In addition, tuning of this type of damper requires a complete replacement of the elastomeric materials, which can be involved depending on their placement. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a vibration damper that is compact. 
     Another object of the present invention is to provide a vibration damper that is tunable. 
     Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings. 
     In accordance with the present invention, a vibration damper includes a rigid base with a mass coupled thereto for linear movement thereon. A first spring coupled to the mass compresses in response to the linear movement along a first direction. A second spring coupled to the mass compresses in response to the linear movement along a second direction that is opposite to the first direction. A converter, coupled to the mass, converts the linear movement to a corresponding rotational movement. A rotary damper coupled to the converter damps the rotational movement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a vibration damper in accordance with the present invention; 
         FIG. 2  is a top view of a vibration damper that is tunable in accordance with an embodiment of the present invention; and 
         FIG. 3  is a side view of the exemplary vibration damper taken along line  3 - 3  in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and more particularly to  FIG. 1 , a vibration damper according to the present invention is shown and is referenced generally by numeral  10 . In general, vibration damper  10  is coupled on one or both opposing ends thereof to a structure (not shown). When that structure vibrates, damper  10  operates to quickly damp out such vibrations. The type and/or size of the structure are not limitations of the present invention. Indeed, one of the great advantages of the present invention is the compact nature thereof as compared to linear dampers, thereby allowing the present invention to be adapted for a number of applications not serviceable using current dampers. Furthermore, embodiments of the present invention will be presented that allow the vibration damper to be readily tuned to various structural vibration modes. 
     Vibration damper  10  includes a base  12  that is coupled on one or both (as illustrated) opposing ends thereof to a structure  100 . Base  12  is constructed from a rigid material (e.g., metal, composite, etc.) such that vibrations in structure  100  are efficiently coupled to base  12 . A variety of constructions of base  12  are possible without departing from the scope of the present invention. An exemplary base construction will be presented later herein. 
     A linear motion mass  14  is coupled to base  12  such that mass  14  is constrained to linear motion on base  12  in one of opposing directions  16  and  18  when base  12  vibrates along with structure  100 . Linear displacement of mass  14  in directions  16  or  18  is opposed by a spring force applied to mass  14  by spring  20  or  22 , respectively. More specifically, spring  20  compresses when mass  14  moves linearly along direction  16 , while spring  22  compresses when mass  14  moves linearly along direction  18 . Although not a requirement of the present invention, the spring rates of springs  20  and  22  will typically be equal or approximately equal. 
     The resulting linear motion of mass  14  is damped by a rotary damper  24  employing viscous damping in either of two directions of rotation. The linear motion of mass  14  and resulting linear force generated by spring  20  or  22  are converted to a rotational motion/force (indicated by two-headed arrow  26 ) by a linear-to-rotary motion converter  28  (e.g., a rack and pinion gear arrangement). In this way, the overall size of vibration damper  10  is essentially defined by the length of travel of mass  14  in directions  16  and  18 . Damping effectiveness for a given application can be controlled by adjusting one or more of mass  14 , the spring rates of springs  20  and  22 , and the damping force provided by rotary damper  24 . 
     As mentioned above, the vibration damper of the present invention can be realized by a variety of constructions without departing from the scope of the present invention. Further, the embodiments of the present invention can facilitate tuning of the vibration damper. By way of example, one such embodiment of the present invention will be explained with simultaneous reference to  FIGS. 2 and 3  where the vibration damper is referenced generally by numeral  50 . A rigid U-shaped bracket  52  serves as both the support for the elements of damper  50  and the mounting interface with a structure  100 . More specifically, bracket  52  is defined by a flat base  52 A. One or both (as illustrated) of legs  52 A are rigidly coupled to structure  100  by any of a variety of ways well known in the art, the choice of which is not a limitation of the present invention. A linear rail  54  is rigidly coupled to base  52 A and a movable block  56  is mounted on rail  54 . Rail  54  and block  56  are configured to allow block  56  to slide along rail  54  in either of two linear directions  16  and  18  when bracket  52  vibrates along with structure  100 . A variety of such slider assembles (i.e., defined by rail  54  and block  56 ) are known in the art. 
     Mounted on block  56  for movement therewith in either linear direction  16  or  18  is a housing  58 . A rigid rod  60  freely passes through a passage  58 A defined in housing  58  and is coupled to opposing legs  52 B of bracket  52 . A first compression spring  62  is disposed about rod  60  on one side of housing  58  and a second compression spring  64  is disposed about rod  58 . Bracket  52  can be configured for the removal of rod  60  to facilitate the placement and changing of springs  62  and  64 . Housing  58  can incorporate opposing annular regions  58 B and  58 C about rod  60  to receive springs  62  and  64 , respectively, in their fully compressed state. Springs  62  and  64  are selected to provide a desired spring rate when tuning damper  50  for a particular application. 
     Tuning of damper  50  can also be achieved by adjusting the amount of mass that is subject to linear motion in linear direction  16  or  18 . Accordingly, a changeable mass  66  is provided on and is coupled to housing  58  for linear movement therewith in directions  16  or  18 . Mass  66  and the type of scheme used to attach mass  66  to housing  58  for easy attachment/removal are not limitations of the present invention. 
     Housing  58  also supports a rotary (fluid-filled or viscous) damper  68  such that rotary damper  68  moves in correspondence with the linear motion of housing  58  while also damping out such linear motion. To do this, an axle  70  is rotatably supported on one end thereof by housing  58  and is coupled on its other end thereof to a rotor (not shown) of rotary damper  68 . A spur gear  72  is attached to axle  70  for rotation therewith. A linear rack gear  74  is fixedly coupled to base  52 A for toothed engagement with spur gear  72 . In operation, when housing  58  experiences linear motion in either direction  16  or  18  (due to vibrations in structure  100 ), spur gear  72  rotates (as indicated by two-headed arrow  76 ) via its engagement with rack gear  74 . The corresponding rotation of axle  70  is transferred to the rotor of rotary damper  68  whereby such rotational motion is dampened. 
     As mentioned above, tuning of damper  50  can occur through one or more of selection of springs  62  and  64 , choice of mass  66 , and choice of rotary damper  68 . Additional tuning could also be achieved by adjusting the mass value of bracket  52 . Accordingly, one or more ballast weights (“BW”)  80  can be coupled to bracket  52  as illustrated in  FIG. 2 . Still further, resultant linear damping could also be adjusted by changing the gear ratio between spur gear  72  and rack gear  74 . 
     The advantages of the present invention are numerous. The vibration damper combines linear displacement with rotational force damping to provide a compact design. A variety of embodiments of the vibration damper can incorporate tuning features that are easily implemented. 
     Although the invention has been described relative to a specific embodiment thereof, there are numerous variations and modifications that will be readily apparent to those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described. 
     What is claimed as new and desired to be secured by Letters Patent of the United States is: