Crab-leg suspension has four L shaped beams as shown above. By varying the beam dimensions, it is possible to vary the stiffness in all three axes. Force, moment and torque balance are applied to each leg of the beam to create the model.
In this analysis all four beams are considered in calculating the effective spring constant of the suspension. If you wish to find the spring constant for just one beam, divide the result by 4 since the four beams are in parallel.
The suspension allows lateral movement in the X axis and vertical movement in Z axis. It is often used in comb drives, MEMS switches and MEMS varactor. The stiffness of this suspension in all the three axes directions can be found out using this design interface. The model loses accuracy in Y direction for small thigh lengths since axial stress in shin is not included in calculation of ky.
The plot shows the stiffness variation in all three axes with increase in thigh length. The stiffness in all the three axes decreases with increasing thigh length. The vertical stiffness kz decreases rapidly compared to the lateral stiffness kx as torsion in the thigh beam has a greater influence on kz than bending has on kx. By changing the beam dimensions the most complaint axis can be changed.