Resonant inertial force generator having stable natural frequency

Abstract

A resonant inertial force generator for controlling vibrations of a structure includes a compliant spring comprising a stack of flexures and elastomeric shims in alternating arrangement, a driven inertial mass coupled to the compliant spring to generate a vibration controlling force.

1 . A resonant inertial force generator for controlling vibrations of a structure, comprising:
 a compliant spring comprising a stack of flexures and elastomeric shims in alternating arrangement;   an inertial mass coupled to the compliant spring; and   an actuator for moving said inertial mass.   
     
     
         2 . The resonant inertial force generator of  claim 1 , wherein said flexures have flexure surfaces adjacent to said elastomeric shims, said elastomeric shims being bonded to said flexure surfaces. 
     
     
         3 . The resonant inertial force generator of  claim 1 , wherein the number of flexures in the stack is at least 2. 
     
     
         4 . The resonant inertial force generator of  claim 1 , which has a natural frequency with a decay less than 0.1 Hz over 3,000 hours of operation. 
     
     
         5 . The resonant inertial force generator of  claim 1 , wherein the actuator is an electromagnetic actuator. 
     
     
         6 . The resonant inertial force generator of  claim 1 , wherein said flexures are comprised of composite beam plates. 
     
     
         7 . The resonant inertial force generator of  claim 1 , wherein said stack is sandwiched between a pair of end plates. 
     
     
         8 . The resonant inertial force generator of  claim 7 , wherein the elastomeric shims at distal ends of the stack are bonded to the end plates. 
     
     
         9 . The resonant inertial actuator of  claim 1 , wherein at least one of the elastomeric shims in the stack has a shape factor greater than 10. 
     
     
         10 . A resonant inertial force generator, comprising:
 an inertial mass supported by a plurality of flexures; and   a plurality of intermediate elastomeric shims interleaved with said plurality of flexures.   
     
     
         11 . The resonant inertial force generator of  claim 10 , wherein said flexures are comprised of composite plate members. 
     
     
         12 . The resonant inertial force generator of  claim 11 , wherein said flexures have flexure surfaces adjacent to said intermediate elastomeric shims, said intermediate elastomeric shims being bonded to said flexure surfaces. 
     
     
         13 . The resonant inertial force generator of  claim 11 , wherein each of said intermediate elastomeric shims has a shape factor greater than 10. 
     
     
         14 . A compliant spring, comprising:
 a plurality of composite flexure plates layered in a stack; and   an elastomeric shim disposed between each adjacent pair of the composite flexure plates.   
     
     
         15 . The compliant spring of  claim 14 , wherein the elastomeric shim is bonded to the adjacent pair of the composite flexure plates. 
     
     
         16 . The compliant spring of  claim 14 , wherein said elastomeric shim has a shape factor greater than 10. 
     
     
         17 . A method of making an inertial force generator, comprising:
 providing an inertial mass;   providing n composite flexures, wherein n is an integer and is greater than 1;   providing at least n+1 elastomeric shims;   interleaving the at least n+1 elastomeric shims with the n composite flexures to form a compliant spring comprising an alternating arrangement of flexures and elastomeric shims;   coupling said inertial mass to the compliant spring; and   coupling to the inertial mass an actuator capable of moving the inertial mass.   
     
     
         18 . A method of making an inertial force generator, comprising:
 providing an inertial mass;   providing a plurality composite flexures;   providing a plurality of elastomeric shims;   stacking the composite flexures and elastomeric shims alternately to form a compliant spring, the elastomeric shims being arranged adjacent to load bearing areas of the composite flexures;   coupling said inertial mass to said compliant spring; and   coupling to the inertial mass an actuator capable of moving the inertial mass.   
     
     
         19 . The method of  claim 18 , wherein stacking the composite flexures and elastomeric shims alternately to form a compliant spring comprises stacking the composite flexures and elastomeric shims to form a plurality of compliant springs. 
     
     
         20 . The method of  claim 18  wherein stacking the composite flexures and elastomeric shims alternately to form a compliant spring comprises. 
     
     
         21 . A method of making an inertial force generator spring, comprising:
 providing a plurality of composite flexure plates;   providing an intermediate elastomer;   layering said composite flexure plates with said intermediate elastomer between said composite flexure plates to provide a spring assembly of layered composite flexure plates and intermediate elastomer between adjacent composite flexure plates, with said intermediate elastomer bonded to said composite flexure plates.   
     
     
         22 . A resonant inertial force generator, comprising:
 an inertial mass supported by a plurality of composite flexures arranged in a stack; and   compliant means for separating said composite flexures.   
     
     
         23 . A resonant inertial force generator for controlling vibrations, comprising:
 an inertial mass on a spring assembly;   a motor for moving said inertial mass on said spring assembly, said spring assembly including at least a first non-elastomeric flexure and at least a first intermediate elastomer, said intermediate elastomer bonded with said first non-elastomeric flexure.   
     
     
         24 . The resonant inertial force generator of  claim 23 , wherein said at least a first intermediate elastomer has a shape factor greater than 10. 
     
     
         25 . The resonant inertial force generator of  claim 23 , wherein said non-elastomeric flexure is a composite non-elastomeric flexure, said composite non-elastomeric flexure being comprised of a plurality of reinforcing fibers in a cured matrix. 
     
     
         26 . The resonant inertial force generator of  claim 23 , wherein said non-elastomeric flexure is a non-metallic composite flexure. 
     
     
         27 . An apparatus for controlling aircraft vibrations, comprising:
 an inertial mass on a spring assembly having a natural frequency NF, an electrically driven motor for moving said inertial mass on said spring assembly, said spring assembly including at least a first composite flexure and a means for inhibiting a decay in said natural frequency NF.   
     
     
         28 . An apparatus for controlling aircraft vibrations, comprising:
 a driven inertial mass on a spring assembly having a natural frequency NF with the spring assembly including a plurality of nonhomogeneous composite flexures having first ends and distal second ends with a plurality of elastomeric spacers bonded between the composite flexures proximate the first ends and the distal second ends.