Design of a folded flexure suspension

Lco       length of outer column beam in m
Lci        length of inner column beam in m
wc         width of column beam in m
Lto        length of outer truss in m
Lti         length of inner truss in m
wt         width of truss in m
thc        thickness of beams in m
ymod    Young's modulus in GPa
pois       Poissons ratio
sel        number denoting the selected result.
             Use 1 for spring constant in X axis and 2 for spring constant in Y axis and 3 for spring constant in Z axis

folded flexure suspension


Folded flexure as shown in the picture above, has four parallel beams or columns joined together by a series of trusses. The inner columns are fixed at one end while the outer columns are connected to the guided mass.

This design interface can be used to calculate spring constant in all three axis. The length and width of all beams can be changed and the corresponding variation in stiffness can be quickly calculated. The calculated spring constant is for the whole suspension and if you need it for the flexure on one side, divide the results by two.

Folded flexure suspensions are quite popular with MEMS comb drives and other devices that need lateral movement in X axis. The suspension can be made quite stiff in Y axis by increasing the width of the truss. Increasing the beam thickness will increase the stiffness in Z axis while decreasing it in X axis. It is quite suitable for designing a uniaxial suspension with limited rotational freedom.

The plot shows the variation of spring constant in all the three axes to the variation in the inner column beam length Lci. Inner column beam length as a ratio of the outer column beam length Lci/Lco  is given in the X axis. The stiffness in Y axis does not vary much with variation of inside column beam length as it is axial in that direction.


-The beam has uniform rectangular cross section.
-The beam has small deflection and has small angle or rotation
-Effect of stress from beam extension or compression is not included.
-Residual stress is not considered.
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