Cross spring pivot

PRECISION POINT
Construction
Fundamentals
CROSS SPRING PIVOT
Introduction
Cross spring pivots are an interesting alternative for common
flexure pivots in case transverse loads of the pivot are relatively
high.
The layout of a cross spring pivot can be chosen to optimize for
large angular motion, or for optimal pivot behavior which is
unbiased with parasitic displacements.
1/1
Orthogonal cross spring pivot
Pivot constructed from two leaf springs which are
oriented perpendicular w.r.t. each other.
Symmetric cross spring pivot
Pivot constructed from two equal leaf springs which are
symmetrically located w.r.t. the pole.
Double symmetric cross spring pivot
Special case of the symmetric cross spring pivot where
the pole is exactly in the middle of the leaf spring.
Reference equations
2
Angular stiffness
∙
2
Maximum angle
L
E,b
5%
&
∙
∙
Classical double symmetric cross spring pivot
=0
t
√2
!36#
30
∙ ∙
∙
4
Buckle load (radial)
The equivalent rolling radius of an orthogonal cross
spring pivot is given by:
∙ ∙
Equivalent mechanism
For ' 0 the virtual rolling surface flips w.r.t. real
mounting surface of the springs (see ‘Haberland’ cross
spring)
Most often assembled from 3 plate spring elements with
(
(
(
width *, *, *. Nu pure pivot motion, but also parasitic
)
)
displacement.
⁄
Angular stiffness
Buckle load
Maximum angle
0.236
Ideally suited for monolithic fabrication. Relatively pure
pivot behavior but with less angular stroke compared to
classical double symmetric cross spring pivot.
‘Haberland’ cross spring pivot
L
⁄ *
Angular stiffness
Buckle load
-0.047
4∙
2∙
Maximum angle
1
∙
4
*) Not according formula above due to coupled leaf springs
Special case classical double symmetric cross spring pivot
Special case classical double symmetric cross spring pivot
for #
.
√/
where
2
L/
⁄
Angular stiffness
Buckle load
&
0 and thus pure pivot behavior.
L
0
2.67 ∙
·L
=
·L
/6
√5
≈
2
L/
L
8·
3/
Maximum angle
Sources:
• On the design of plate-spring mechansims – J. van Eijk
• Elastische geleidingen, een literatuursutdie – M.N. Boneschanscher
1
∙
3.3

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