U.S. patent application number 15/807211 was filed with the patent office on 2018-03-08 for buckling column load switch spring.
The applicant listed for this patent is HRL LABORATORIES, LLC. Invention is credited to Christopher P. Henry, Jie Jiang, Jacob Mikulsky, Sloan P. Smith.
Application Number | 20180066722 15/807211 |
Document ID | / |
Family ID | 60674772 |
Filed Date | 2018-03-08 |
United States Patent
Application |
20180066722 |
Kind Code |
A1 |
Henry; Christopher P. ; et
al. |
March 8, 2018 |
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.
Inventors: |
Henry; Christopher P.;
(Thousand Oaks, CA) ; Jiang; Jie; (Sherman Oaks,
CA) ; Smith; Sloan P.; (Calabasas, CA) ;
Mikulsky; Jacob; (Los Angeles, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HRL LABORATORIES, LLC |
Malibu |
CA |
US |
|
|
Family ID: |
60674772 |
Appl. No.: |
15/807211 |
Filed: |
November 8, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14199878 |
Mar 6, 2014 |
9850974 |
|
|
15807211 |
|
|
|
|
61783499 |
Mar 14, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16F 2236/027 20130101;
F16F 1/025 20130101 |
International
Class: |
F16F 7/00 20060101
F16F007/00; F16F 7/12 20060101 F16F007/12; F16F 13/00 20060101
F16F013/00 |
Claims
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.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] The present application is a divisional of U.S. application
Ser. No. 14/199,878, filed on Mar. 6, 2014, which claims priority
to and the benefit of Provisional Application No. 61/783,499, filed
Mar. 14, 2013, entitled "BUCKLING COLUMN LOAD SWITCH SPRING", the
entire contents of both of which are incorporated herein by
reference.
FIELD
[0002] The present invention relates to nonlinear mechanical
elements and more particularly to buckling elements exhibiting
stiffness depending on load and displacement.
BACKGROUND
[0003] Mechanical elements with nonlinear mechanical impedance have
a variety of applications. Crushable materials, for example, or
crush zones in vehicles, provide protection from shock or impact,
i.e., large loads of short duration. Such materials or structures
absorb mechanical energy and are permanently deformed, i.e.,
damaged. As a result, such a material or structure may not provide
protection from repeated impacts.
[0004] In some applications, large loads may occur repeatedly, as,
for example, if the hull of a boat on rough seas repeatedly impacts
the faces of large waves. In such circumstances it may be
desirable, for example, to protect cargo on the boat from the shock
of these impacts. Thus, there is a need for a nonlinear mechanical
element which deforms without damage when subjected to a threshold
load, and returns to an un-deformed state after the load is
removed.
SUMMARY
[0005] In one embodiment when a nonlinear mechanical element
including a buckling column 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.
[0006] According to an embodiment of the present invention there is
provided a nonlinear mechanical element, including: 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 prevent the first column from buckling beyond its
elastic limit.
[0007] In one embodiment, the first hard stop is a lateral hard
stop.
[0008] In one embodiment, the first hard stop is an axial hard
stop.
[0009] In one embodiment, the nonlinear mechanical element includes
a second hard stop, wherein the first hard stop is a lateral hard
stop and the second hard stop is an axial hard stop.
[0010] In one embodiment, the nonlinear mechanical element includes
a second column and a second hard stop, wherein the nonlinear
mechanical element is configured to transmit substantially no force
through the second column when the first compressive force is less
than the first threshold force; the second column is configured to
buckle when a second compressive force transmitted through the
second column exceeds a second threshold force; and the second hard
stop is configured to prevent the second column from buckling
beyond its elastic limit.
[0011] In one embodiment, the nonlinear mechanical element includes
a tilting mechanism coupled to one end of the first column.
[0012] In one embodiment, the tilting mechanism includes an
eccentric rocking member.
[0013] In one embodiment, the nonlinear mechanical element includes
a rotational stop.
[0014] In one embodiment, the rotational stop includes an angled
surface on the eccentric rocking member.
[0015] In one embodiment, the tilting mechanism includes a dual
load path element, wherein the dual load path element includes 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.
[0016] In one embodiment, the monostable element is a domed
monostable element.
[0017] In one embodiment, the tilting mechanism includes a fork
secured to a rod.
[0018] In one embodiment, the nonlinear mechanical element includes
a plurality of nonlinear elements.
[0019] According to an embodiment of the present invention there is
provided a nonlinear mechanical assembly including: a housing; a
column extending out of the housing; an end plate; the housing
including 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.
[0020] In one embodiment, the cylindrical portion is configured to
operate as a lateral hard stop.
[0021] In one embodiment, the column includes a nub, and the end
plate includes an indentation, and wherein the nub in the column
engages the indentation in the end plate to register the column to
the end plate.
[0022] In one embodiment, the nonlinear mechanical element includes
a spring.
[0023] In one embodiment, the spring is an ortho-planar spring.
[0024] In one embodiment, the central portion of the ortho-planar
spring is secured to the housing and the outer portion of the
ortho-planar spring is secured to the end plate.
[0025] In one embodiment, a boss at one end of the housing provides
a hard stop for a portion of the ortho-planar spring.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee.
[0027] These and other features and advantages of the present
invention will become appreciated as the same become better
understood with reference to the specification, claims and appended
drawings wherein:
[0028] FIG. 1A is a tubular structure with buckling columns
according to an embodiment of the present invention;
[0029] FIG. 1B is a tubular structure with buckling columns
according to another embodiment of the present invention;
[0030] FIG. 2A is a graphical representation of the results of
finite element analysis of the embodiment of FIG. 1A at a low level
of deformation;
[0031] FIG. 2B is a graphical representation of the results of
finite element analysis of the embodiment of FIG. 1A at a moderate
level of deformation;
[0032] FIG. 2C is a graphical representation of the results of
finite element analysis of the embodiment of FIG. 1A at a high
level of deformation, with hard stops engaged;
[0033] FIG. 3 is a schematic diagram of a structure with buckling
columns at a high level of deformation, with axial hard stops and a
lateral hard stop engaged, according to an embodiment of the
present invention;
[0034] FIG. 4A is a perspective view of a tubular structure with
buckling columns designed to engage at varying amounts of
compressive displacement, according to an embodiment of the present
invention;
[0035] FIG. 4B is a side cross-sectional view through a wall of the
structure of FIG. 4A;
[0036] FIG. 5 is a schematic chart showing compressive force vs.
compressive displacement for the embodiment of FIG. 4A;
[0037] FIG. 6A is a schematic side view of a buckling column
assembly with an eccentric rocking member in the shape of a foot at
each end according to an embodiment of the present invention;
[0038] FIG. 6B is a schematic side view of a buckling column
assembly with an eccentric rocking member in the shape of a foot at
each end according to another embodiment of the present
invention;
[0039] FIG. 6C is a schematic side view of a buckling column
assembly with an eccentric rocking member in the shape of a foot at
each end according to another embodiment of the present
invention;
[0040] FIG. 6D is a schematic side view of a buckling column
assembly with an eccentric rocking member in the shape of a foot at
each end according to another embodiment of the present
invention;
[0041] FIG. 7A is a photograph of a buckling column assembly with
an eccentric rocking member in the shape of a foot, in the buckled
configuration according to an embodiment of the present
invention;
[0042] FIG. 7B is a close-up photograph of the buckling column
assembly of FIG. 7A, according to an embodiment of the present
invention;
[0043] FIG. 7C is an enlarged schematic side view of the eccentric
rocking member in the shape of a foot of the embodiment of FIG.
6A;
[0044] FIG. 8 is a chart showing results of a compression test of a
buckling column assembly constructed according to the embodiment of
FIG. 7A;
[0045] FIG. 9A is a side view of a composite element including a
buckling column according to an embodiment of the present
invention;
[0046] FIG. 9B is a graphical representation of the results of
finite element analysis of the embodiment of FIG. 9A;
[0047] FIG. 10 is a chart showing results of finite element
analysis of the embodiment of FIG. 9A;
[0048] FIG. 11 is an exemplary chart of force vs. displacement for
the embodiment of FIG. 9A;
[0049] FIG. 12A is a perspective view of a buckling column element
with a forked end according to an embodiment of the present
invention;
[0050] FIG. 12B is a graphical representation of the results of
finite element analysis of the embodiment of FIG. 12A;
[0051] FIG. 13 is an exemplary chart of force vs. displacement for
the embodiment of FIG. 12A;
[0052] FIG. 14A is a perspective exploded view of a cylindrical
assembly including a buckling column according to an embodiment of
the present invention;
[0053] FIG. 14B is a perspective cutaway view of the embodiment of
FIG. 14A; and
[0054] FIG. 15 is a photograph of a subassembly of the embodiment
of FIG. 14A.
DETAILED DESCRIPTION
[0055] The detailed description set forth below in connection with
the appended drawings is intended as a description of exemplary
embodiments of a buckling column load switch spring provided in
accordance with the present invention and is not intended to
represent the only forms in which the present invention may be
constructed or utilized. The description sets forth the features of
the present invention in connection with the illustrated
embodiments. It is to be understood, however, that the same or
equivalent functions and structures may be accomplished by
different embodiments that are also intended to be encompassed
within the spirit and scope of the invention. As denoted elsewhere
herein, like element numbers are intended to indicate like elements
or features.
[0056] Referring to FIG. 1A and FIG. 1B, in one embodiment, a
buckling column load switch spring is formed as a square or
triangular tubular member with cutouts 110 in the walls of the tube
defining one or more columns 120. The cutouts 110 form gaps
including transverse gaps 130 and longitudinal gaps 140. The
columns 120 are designed to buckle under applied compressive load
and are therefore referred to herein, whether in a buckled or
un-deformed state, as buckling columns 120. When a compressive
force is applied to the tube and the compressive stress on a
buckling column exceeds a critical load, the buckling column 120
becomes unstable and deforms laterally, assuming a curved shape.
This buckling behavior may be referred to as Euler buckling. Laser
machining or another precision machining technique may be used to
match the critical loads of the buckling columns 120.
[0057] A tubular structure may have buckling columns 120 at several
points about its circumference, and they may be symmetrically
arranged, providing a symmetric loading condition to the buckling
columns 120 when the tube is stressed in compression. The tube may
be composed of a high-strength material such as 4130 chromoly
steel, 17-4 stainless steel, Martinsitic stainless steel, super
duplex stainless steel, maraging steel, such as C-300 maraging
steel, or 1095 high strength spring steel, titanium alloys, Cu--Be
alloys and other alloys with yield strains exceeding 0.5%. The
cutouts 110 may be formed by, for example, conventional machining,
e.g., milling, or by laser machining, electrical discharge
machining (EDM), or water jet cutting.
[0058] Referring to FIG. 2A, FIG. 2B, and FIG. 2C, as the
compressive load on the tube is increased, each buckling column 120
may deform progressively further outwards, so that the center
section of the buckling column 120 protrudes from the local surface
of the tube. At the point of maximum deformation, shown in FIG. 2C,
the transverse gap 130 is closed at the corners of the tube,
causing the load path to shift away from the buckling column 120.
Thus the transverse gap 130 acts as an axial hard stop, preventing
the load on the buckling column 120 from exceeding the load at
which the transverse gap 130 is closed. Having hard stops in the
corners provides extra axial, bending, and torsional rigidity.
[0059] Referring to FIG. 3, in one embodiment the buckling column
120 may, instead of deforming outwards, deform in the plane of the
tube, i.e., in a direction causing the width of one of the
longitudinal gaps 140 to become smaller. At a certain compressive
load, this longitudinal gap 140 may close entirely, and the center
section of the buckling column 120 may contact the adjacent point
in the wall of the tube. This results in the buckling column 120
being supported against further buckling. The longitudinal gap 140
thus acts as an additional hard stop, referred to as a lateral hard
stop. The lateral hard stop may be reached before, or, in one
embodiment, at substantially the same load, as the axial hard
stops.
[0060] Referring to FIG. 4A, FIG. 4B, and FIG. 5, in one embodiment
a tube has cutouts 110 defining multiple buckling columns which
buckle at different compressive displacements as the tube is loaded
in compression. A first set of buckling columns 410 may initially
bear the entire compressive load, resulting in high stiffness up to
a first point 510 (FIG. 5), reached at a first threshold force, at
which the first buckling columns 410 begin to buckle. As the first
buckling columns 410 buckle, the compressive displacement increases
without an increase in the compressive force, until at a point 520
a second set of buckling columns 420 is engaged as a result of the
closing of a transverse gap 430 at the end of each of the buckling
columns 420 in the second set. At this point the structure again
becomes relatively stiff in compression until at a point 530,
reached at a second threshold force, the columns 420 in the second
set begin to buckle, and again the compressive displacement
increases without an increase in the compressive force, until at a
point 540 a set of transverse gaps 440 closes, engaging a
corresponding set of axial hard stops. The number of beams,
dimensions of the beams, and thickness and length of the tube all
contribute to the stiffness of the structure. This allows the
stiffness to be tuned to the application, making it possible to
design a structure with specific and different stiffness at various
displacement ranges.
[0061] Referring to FIG. 6A, FIG. 6B, FIG. 6C, FIG. 6D, FIG. 7A,
FIG. 7B, and FIG. 7C, in one embodiment a buckling column 120 is
provided with a foot 605, or eccentric rocking member, at each end.
The heel 610 of each foot 605 is initially in contact with a
respective loading surface 705 (FIG. 7B) which transmits, through
the heel 610, a compressive force to the buckling column 120. The
center of the heel 610 is offset from the centerline of the
buckling column 120, so that the line of action of the force on the
foot 605 from the loading surface 705 is offset from the action of
the opposing force from the buckling column 120, and the two forces
produce a torque or moment on the foot 605. This torque produces a
bending moment in the buckling column 120 (FIG. 7C), causing it to
buckle at a lower compressive strain than it would otherwise, and
to buckle in a predictable and repeatable direction, e.g., in the
direction dictated by the torque on the two feet 605. As the
buckling column 120 buckles, the foot 605 rotates until the angled
surface 620 of the toe 615 comes into contact with the loading
surface 705, as shown in FIG. 7A and FIG. 7B. The force of the
loading surface 705 on the toe 615 of each foot 605 produces a
torque on the foot 605 tending to oppose continued buckling and in
this manner the toe 615 acts as a rotational stop. The ability of
each foot 605 to rock from the heel 610 to the toe 615 forms a
tilting mechanism which provides kinematic boundary conditions at
the ends of the buckling column 120 which, relative to fixed
boundary conditions, reduce the peak strains at the ends of the
buckling column 120. Buckling columns 120 fabricated according to
these embodiments may be substituted for those of the embodiment of
FIG. 1, by installing them between the upper and lower tube ends,
and maintaining a compressive preload, e.g., with a spring,
sufficient to hold the buckling columns 120 in place.
[0062] Referring to FIGS. 6B, 6C, and 6D, shortening the heel 610
of each foot 605 results in a shift in the line of action of the
force from the loading surface 705, and a resulting reduction in
the moment. If the heel 610 is sufficiently shortened, as in FIG.
6D, the torque on the foot 605 may be such that the buckling column
120 buckles in a direction in which the toe 615 moves away from,
not towards, the loading surface 705, and the toe 615 will not act
as a rotational stop. In one embodiment, the length and thickness
of the buckling column 120 are 2.625 inches and 0.094 inches
respectively, and the length of the toe 615 is 0.25 inch, as shown
in FIG. 6A. FIG. 8 shows results of a compression test of a
buckling column assembly constructed according to the embodiment
shown in FIGS. 7A and 7B.
[0063] Referring to FIG. 9A, and FIG. 9B, in one embodiment a
composite element includes a first transverse beam 905 in the form
of a rectangular member, a bending element 910, a mono-stable
element 915, a second transverse beam 920 in the form of a
triangular member, and a buckling column 120. The mono-stable
element 915 has a nonlinear mechanical impedance causing it to have
high stiffness up to a threshold compressive load, and low
compressive stiffness for compressive load exceeding the threshold
load. The mono-stable element 915 may, for example, include a
flexible domed structure such as is used in buttons on some
consumer devices such as mobile phones with mechanical buttons. The
domed structure exhibits high stiffness in response to a
compressive force as long as the force is sufficiently small that
the dome remains essentially undistorted, and compressive force is
transmitted as a compressive force through the wall of the dome.
When the force is sufficiently large to produce a significant
deformation of the dome, the load is transmitted through bending of
the dome wall. Because the dome wall is more readily bent than
compressed, the compressive stiffness of the dome decreases
abruptly at this point.
[0064] The assembly composed of the first transverse beam 905, the
bending element 910, the mono-stable element 915, and the second
transverse beam 920 forms a dual load path element which operates
as a tilting mechanism. If the bending element 910 and the
mono-stable element 915 are approximately the same distance from
the centerline of the assembly, e.g., from the centerline of the
buckling column 120, then at low loads, for which the mono-stable
element 915 has high stiffness, the load through the composite
element is carried in approximately equal parts by the bending
element 910 and the mono-stable element 915, being distributed onto
these two elements by the first transverse beam 905 and the second
transverse beam 920. Once the mono-stable element 915 becomes less
stiff, the compressive force through the composite element is
carried in greater proportion by the bending element 910 than by
the mono-stable element 915, resulting in a moment or torque on the
second transverse beam 920, which transmits this torque as a
bending moment to the buckling beam. This torque may be sufficient
to cause the buckling column 120 to bend significantly, causing a
significant reduction in stiffness.
[0065] The boundary conditions between a load-carrying member,
e.g., a shaft applying a compressive load to the composite element,
and the first transverse beam 905, may be fixed, and the assembly
consisting of the first transverse beam 905, the bending element
910, the mono-stable element 915, and the second transverse beam
920 provides a switching function, triggering buckling of the
buckling column 120 and allowing the end of the buckling column 120
connected to the second transverse beam 920 to tilt.
[0066] In addition to the threshold load of the mono-stable element
915, the position of the bending element 910 may be selected to
adjust the behavior of the composite element. For example,
increasing the eccentricity of the assembly, where the eccentricity
is defined as twice the ratio of the offset from center of the
bending element 910 to the thickness of the buckling column 120,
causes the column to buckle more easily. FIG. 10 shows a chart of
buckling load vs. the aspect ratio, i.e. the ratio of length to
thickness, of the buckling column 120, for eccentricities ranging
from 1% to 200%. In one embodiment the aspect ratio of the buckling
column 120 is 40, and the composite element is formed by
conventional machining, e.g., milling.
[0067] Various stiffness curves may be achieved with the embodiment
of FIG. 9A, and FIG. 9B. For example, referring to FIG. 11, for a
suitably selected mono-stable element 915, eccentricity, bending
element 910, and buckling column 120, the stiffness at low
displacement may be high, and it may decrease abruptly at a first
break point 1105 corresponding to the compressive force on the
mono-stable element 915 exceeding the threshold load. The stiffness
may then decrease further at a second break point 1110
corresponding to buckling of the buckling column 120.
[0068] Referring to FIG. 12A and FIG. 12B, in one embodiment a
buckling column 120 is formed in the shape of a leaf or blade with
one end cut to form a three-tined fork, with the two outer tines
1205 extending out of the plane of the blade and the central tine
1210 being shorter than the outer tines 1205 and extending out of
the plane of the blade, to a greater extent, and in the opposite
direction. A rectangular load carrying shaft suitably welded or
bolted to the tines of the fork may impart a torque or moment to
the forked end of the buckling column 120, affecting its buckling
behavior. In one embodiment the aspect ratio, i.e., the ratio of
length to thickness, of the buckling column 120 is between 40 and
80, and the ratio of width to thickness is between 2 and 5.
Referring to FIG. 13, finite element analysis shows an abrupt
transition 1310 for this embodiment, between a high stiffness
state, and a low-stiffness buckled state.
[0069] Referring to FIG. 14A and FIG. 14B, in one embodiment an
assembly with nonlinear mechanical impedance includes a buckling
column 120, a cylindrical housing 1610, two caps 1620, each
threaded onto the cylindrical housing 1610 and secured with
locknuts 1630, and two end plates 1640. Each end plate 1640 has a
nub at the center of the surface facing the buckling column 120,
which has an indentation to accommodate the nub, so that the nub
maintains the transverse registration of the end plate 1640 and the
buckling column 120. Circular flexures 1650 at each end of the
assembly constrain the end plates 1640 to move only longitudinally
with respect to the cylindrical housing 1610 and caps 1620. The
outer portions of the flexures 1650 are secured to the end caps
with bolts 1660 and the central portions of the flexures 1650 are
secured to the caps 1620 with nuts 1670. Each nut 1670 threads onto
a corresponding threaded hollow cylindrical portion 1680 of a cap
1620. In operation, a compressive load applied to the end plates
1640 is transmitted through the buckling column 120, which buckles
when the critical load is reached. The inner wall of the
cylindrical housing 1610 may act as a lateral hard stop for the
buckling column 120, or a boss, or raised portion 1690, on each end
cap may act as an axial hard stop by making contact with the outer
portion of the adjacent flexure 1650. The flexures 1650 may also
act as springs.
[0070] FIG. 15 is a photograph of a prototype of the embodiment of
FIG. 14A and FIG. 14B, with the end plates 1640 removed, exposing,
at one and of the assembly, the flexures 1650, the nut 1670, and
one end of the buckling column 120. In one embodiment the flexures
may be formed of sheet metal with a solid outer portion and a solid
central portion, and with cuts made by laser machining or EDM to
leave flexible serpentine spokes connecting the outer portion and
the central portion. Such an assembly may be referred to as an
ortho-planar spring.
[0071] Mechanical elements including buckling columns 120 may be
combined with other elements such as dashpots, so that, for
example, if a support member including a buckling column 120, and a
dashpot, secured together in parallel, is subjected to a large
load, the buckling column 120 may buckle, causing the load path to
shift to the dashpot, in which energy dissipates until the
compressive displacement of the assembly causes hard stops to
engage.
[0072] Although limited embodiments of a buckling column load
switch spring have been specifically described and illustrated
herein, many modifications and variations will be apparent to those
skilled in the art. Accordingly, it is to be understood that a
buckling column load switch spring constructed according to
principles of this invention may be embodied other than as
specifically described herein. The invention is also defined in the
following claims, and equivalents thereof.
* * * * *