Buckling column load switch spring

Abstract

A nonlinear mechanical element including a buckling column and hard stops. In one embodiment when the nonlinear mechanical element is subjected to an increasing compressive load, the buckling column buckles at a critical load, resulting in reduced stiffness past the critical load. One or more lateral hard stops may be provided adjacent to the buckling column to prevent the buckling deformation from exceeding a certain extent, and axial hard stops may be provided to shift the load path away from the buckling column when a certain amount of compressive displacement has been reached.

What is claimed is: 
     
         1 . A nonlinear mechanical element, comprising:
 a tubular member having:
 a longitudinal axis; 
 a first portion including a first end of the tubular member; 
 a second portion including a second end of the tubular member; and 
 a plurality of cutouts defining a first plurality of columns extending in a first direction substantially parallel to the longitudinal axis, 
   each of the first plurality of columns connecting the first portion to the second portion,   the cutouts further defining a transverse gap extending substantially in a second direction perpendicular to the longitudinal axis, and a longitudinal gap, between a column and the second portion, extending in the first direction, and   the transverse gap and/or the longitudinal gap being configured to protect a column of the first plurality of columns from buckling beyond its elastic limit.   
     
     
         2 . The nonlinear mechanical element of  claim 1 , wherein the longitudinal gap is configured to protect a column of the first plurality of columns from buckling beyond its elastic limit. 
     
     
         3 . The nonlinear mechanical element of  claim 1 , wherein the transverse gap is configured to protect a column of the first plurality of columns from buckling beyond its elastic limit. 
     
     
         4 . The nonlinear mechanical element of  claim 1 , transverse gap and the longitudinal gap are configured to protect a column of the first plurality of columns from buckling beyond its elastic limit. 
     
     
         5 . The nonlinear mechanical element of  claim 1 , wherein:
 the cutouts further define a second plurality of columns connected to the second portion and separated by a gap from the first portion;   the nonlinear mechanical element is configured to transmit substantially no force through the second plurality of columns when a compressive force transmitted through the nonlinear mechanical element is less than a first threshold force; and   each of the second plurality of columns is configured to buckle when a second compressive force transmitted through the column of the second plurality of columns exceeds a second threshold force.   
     
     
         6 . A nonlinear mechanical element, comprising:
 a first column;   a first hard stop;   the first column being configured to buckle when a first compressive force transmitted through the first column exceeds a first threshold force; and   the first hard stop being configured to protect the first column from buckling beyond its elastic limit,   further comprising a tilting mechanism coupled to one end of the first column,   wherein the tilting mechanism comprises a dual load path element, wherein the dual load path element comprises two load bearing members, each of the load bearing members being offset from the centerline of the first column, wherein one of the load bearing members is a monostable mechanical element.   
     
     
         7 . The nonlinear mechanical element of  claim 6 , wherein the monostable mechanical element is a domed monostable element. 
     
     
         8 . A nonlinear mechanical assembly comprising a plurality of the nonlinear mechanical elements of  claim 1 . 
     
     
         9 . A nonlinear mechanical assembly comprising:
 a housing;   a column extending out of the housing, the column being a substantially straight rod;   an end plate;   the housing comprising a cylindrical portion; and   the column being configured to buckle when a compressive force transmitted from the end plate and through the column exceeds a threshold force.   
     
     
         10 . The nonlinear mechanical assembly of  claim 9 , wherein the cylindrical portion is configured to operate as a lateral hard stop. 
     
     
         11 . The nonlinear mechanical assembly of  claim 9 , wherein
 the column comprises a nub, and   the end plate comprises an indentation, and   wherein the nub in the column engages the indentation in the end plate to register the column to the end plate.   
     
     
         12 . The nonlinear mechanical assembly of  claim 9 , further comprising a spring. 
     
     
         13 . The nonlinear mechanical assembly of  claim 12 , wherein the spring is an ortho-planar spring. 
     
     
         14 . The nonlinear mechanical assembly of  claim 13 , wherein a boss at one end of the housing provides a hard stop for a portion of the ortho-planar spring.