Adjustable stiffness assembly

Abstract

The invention provides an adjustable stiffness assembly for use in conjunction with a fixed stiffness element to elastically connect a structure to a mass. The assembly includes a structure mount, a mass mount, and a rotatable stiffness element. The rotatable stiffness element rotatably engages with the structure mount and the mass mount, and has a minimum stiffness value with respect to forces in a direction a maximum stiffness value with respect to forces in another direction The fixed stiffness element and the adjustable stiffness assembly together provide a complete stiffness assembly having a total stiffness value with respect to force in the global direction for elastically connecting the mass and the structure. The first rotatable stiffness element is rotatable relative to the structure mount and the first mass mount to vary the total stiffness value of the complete stiffness assembly with respect to force in the global direction.

What is claimed is: 
     
         1 . An adjustable stiffness assembly for use in conjunction with a fixed stiffness element to elastically connect a structure to a mass, the fixed stiffness element providing stiffness with respect to force in a global direction, the adjustable stiffness assembly comprising:
 a structure mount attachable to the structure;   a first mass mount attachable to the mass, the structure mount being spaced apart from the first mass mount; and   a first rotatable stiffness element extending between the structure mount and the first mass mount and being rotatably engaged with the structure mount and the first mass mount, the first rotatable stiffness element having a minimum stiffness value with respect to forces in a local direction referred to as X, and a maximum stiffness value with respect to forces in another local direction referred to as Y, wherein the maximum stiffness value is greater than the minimum stiffness value, the fixed stiffness element and the adjustable stiffness assembly together providing a complete stiffness assembly having a total stiffness value with respect to force in the global direction for elastically connecting the mass and the structure,   wherein the first rotatable stiffness element is rotatable relative to the structure mount and the first mass mount to vary the total stiffness value of the complete stiffness assembly with respect to force in the global direction.   
     
     
         2 . The adjustable stiffness assembly of  claim 1 , wherein the first rotatable stiffness element is a beam having a longitudinal axis extending in a direction orthogonal to the X and Y directions between the structure mount and the mass mount, the beam having a non-circular cross-section orthogonal to the longitudinal axis. 
     
     
         3 . The adjustable stiffness assembly of  claim 2 , wherein the beam has a thickness and a width, and wherein the beam has a rectangular cross-section orthogonal to the longitudinal axis, and the thickness of the beam in the X direction along a minimal stiffness axis of the beam is less than the width of the beam in the Y direction along a maximal stiffness axis of the beam. 
     
     
         4 . The adjustable stiffness assembly of  claim 1 , wherein the fixed stiffness element comprises one or more springs, each spring having constant stiffness. 
     
     
         5 . The adjustable stiffness assembly of  claim 1  further comprising a second rotatable stiffness element that is substantially the same as the first rotatable stiffness element and is rotatably engaged with the structure mount and the first mass mount, the second rotatable stiffness element having a minimum stiffness value with respect to forces in a direction referred to as V, and a maximum stiffness value with respect to forces in another direction referred to as W, wherein the maximum stiffness value is greater than minimum stiffness value. 
     
     
         6 . The adjustable stiffness assembly of  claim 5 , wherein the first and second rotatable stiffness elements are configurable by rotating them in opposite directions so that each rotatable stiffness element has substantially the same stiffness value with respect to forces in the global direction so that lateral forces on the stiffness elements are balanced when force is applied to the stiffness elements in the global direction. 
     
     
         7 . The adjustable stiffness assembly of  claim 5 , wherein the second rotatable stiffness element is a beam having a longitudinal axis extending in a direction orthogonal to the V and W directions between the structure mount and the first mass mount, the beam having a non-circular cross-section orthogonal to the longitudinal axis. 
     
     
         8 . A tuned mass damper comprising:
 a mass block assembly; and   a damper stiffness assembly comprising:
 a fixed stiffness element attached to the mass block assembly, the fixed stiffness element providing stiffness with respect to force in a global direction; and 
 an adjustable stiffness assembly having a stiffness value with respect to force in the global direction, the adjustable stiffness assembly comprising:
 a structure mount attachable to a structure; 
 a first mass block assembly mount attached to the mass block assembly, the structure mount being spaced apart from the first mass block assembly mount; and 
 a first rotatable stiffness element extending between the structure mount and the first mass block assembly mount and being rotatably engaged with the structure mount and the mass block assembly mount, the first rotatable stiffness element having a minimum stiffness value with respect to forces in a local direction referred to as X, and a maximum stiffness value with respect to forces in another local direction referred to as Y, wherein the maximum stiffness value is greater than minimum stiffness value, 
 
   wherein the damper stiffness assembly elastically connects the mass block assembly and the structure;   and wherein the first rotatable stiffness element is rotatable relative to the structure mount and the first mass block assembly mount to vary the total stiffness value of the damper stiffness assembly with respect to force in the global direction.   
     
     
         9 . The tuned mass damper of  claim 8 , wherein the first rotatable stiffness element is a beam having a longitudinal axis extending in a direction orthogonal to the X and Y directions between the structure mount and the first mass block assembly mount, the beam having a non-circular cross-section orthogonal to the longitudinal axis. 
     
     
         10 . The tuned mass damper of  claim 9 , wherein the beam has a thickness and a width, and wherein the beam has a rectangular cross-section orthogonal to the longitudinal axis, and the thickness of the beam in the X direction along a minimal stiffness axis of the beam is less than the width of the beam in the Y direction along a maximal stiffness axis of the beam. 
     
     
         11 . The tuned mass damper of  claim 9 , wherein the adjustable stiffness assembly further comprises a second rotatable stiffness element that is substantially the same as the first rotatable stiffness element, and is rotatably engaged with the structure mount and the mass block assembly mount and positioned so that the longitudinal axes of the rotatable stiffness elements are parallel to each other, the second rotatable stiffness element having the minimum stiffness value with respect to forces in a local direction referred to as V, and the maximum stiffness value with respect to forces in another local direction referred to as W. 
     
     
         12 . The tuned mass damper of  claim 11 , wherein the first and second rotatable stiffness elements are configurable by rotating them in opposite directions so that each rotatable stiffness element has substantially the same stiffness value with respect to forces in the global direction so that lateral forces on the stiffness elements are balanced. 
     
     
         13 . The tuned mass damper of  claim 8 , wherein the mass block assembly comprises a frame that is attachable to the first mass block assembly mount and a mass block supported by the frame. 
     
     
         14 . The tuned mass damper of  claim 13 , wherein the mass block assembly comprises a plurality of steel mass blocks supported by the frame. 
     
     
         15 . The tuned mass damper of  claim 8 , wherein the fixed stiffness element comprises one or more springs, each spring having constant stiffness. 
     
     
         16 . The tuned mass damper of  claim 8 , wherein the adjustable stiffness assembly further comprises a second mass block assembly mount attached to the mass block assembly, the first and second mass block assembly mounts being rotatably engaged with the first rotatable stiffness element at opposite ends of the first rotatable stiffness element, and the structure mount being rotatably engaged with a central portion of the first rotatable stiffness element. 
     
     
         17 . The tuned mass damper of  claim 9  further comprising a second mass block assembly mount attached to the mass block assembly, wherein the beam has first and second ends and a middle section, and wherein the first mass block assembly mount is rotatably engaged with the beam near the first end of the beam, the second mass block assembly mount is rotatably engaged with the beam near the second end of the beam, and the structure mount is rotatably engaged with the middle section of the beam. 
     
     
         18 . An adjustable stiffness assembly for elastically connecting a structure to a mass, the adjustable stiffness assembly having a global stiffness value with respect to force in a global direction, the adjustable stiffness assembly comprising:
 a structure mount attachable to the structure;   a mass mount attachable to the mass, the structure mount being spaced apart from the mass mount; and   a first rotatable stiffness element extending between the structure mount and the mass mount and being rotatably engaged with the structure mount and the mass mount, the first rotatable stiffness element having a minimum stiffness value with respect to forces in a local direction referred to as X, and a maximum stiffness value with respect to forces in another local direction referred to as Y, wherein the maximum stiffness value is greater than minimum stiffness value;   wherein the first rotatable stiffness element is rotatable relative to the structure mount and the mass mount to vary the global stiffness value of the adjustable stiffness assembly.   
     
     
         19 . The adjustable stiffness assembly of  claim 18 , wherein the first rotatable stiffness element is a beam having a longitudinal axis extending in a direction orthogonal to the X and Y directions between the structure mount and the mass mount, the beam having a non-circular cross-section orthogonal to the longitudinal axis. 
     
     
         20 . The adjustable stiffness assembly of  claim 19  further comprising a second rotatable stiffness element that is substantially the same as the first rotatable stiffness element and is rotatably engaged with the structure mount and the mass mount, the second rotatable stiffness element having a minimum stiffness value with respect to forces in one direction, and a maximum stiffness value with respect to forces in another direction, wherein the maximum stiffness value is greater than the minimum stiffness value.