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Brief overviews of micro flexures
Focus on macro flexures in this
tutorial
Beam bending
Symmetry -> precision
Degree of freedom (DOF)
Applications
Optical MEMS devices
Analog tip-tilt mirror
Resonant frequency of the comb drive depends on the ions hitting the pads
Motivation
Need nanometer precision to
manipulate light.
“Stage” and “driving mechanism”.
Sticktion is a problem encountered
with screw-type driving mechanisms.
Use piezoelectric, capacitive,
magnetic, photon,… to drive the
“stage”.
Symmetry in 2D
In-plane rotation Parasitic motion not di-
coupled As soon as the stage moved,
Fx developed some “local” y component
In-plane rotation minimized Parasitic motion reduced or
cancelled Less cross-talk
Parallelogram
In-plane rotation constrained Parasitic motion reduced As soon as the stage moved,
Fx developed some “local” y component
In-plane rotation constrained Parasitic motion further
reduced or cancelled Less cross-talk
Highly Symmetric XY Stages
Three different anchoring
geometries
Can be made into XYZ stages by adding the horizontal blades like
Pentaflex
Diaphragm Flexures
Provide out-of-plane (z,,) motions
Constrain the other in-plane (x,y,) motions
(Voice-coil, pressure sensor, flow control, MEMS devices)
Tip-tilt Flexures
Remove axial misalignment between two parts (shear),
but does not remove torque/moment.
In-plane 1D Flexure
Out-of-plane 1D flexure
In-plane 1D flexure
Symmetric dual 4-bar linkage eliminates Y errror
Bi-stable Flexure
Actuation force causes deflection
Open/close a valve at some pressure threshold;
on/off
Have negative stiffness in the unstable region
Physik Instrument
Piezoelectric drive + capacitive
sensor, feedback loop to actively
take out platform vibrations
Conclusion Use flexure to avoid sticksion. Use symmetry to cancel/de-couple
motions. In-plane vs out-of-plane configurations Flexures for translation, rotation, and any
combination of DOF (1-6 DOF). Dynamic range and linearity. Soft flexure -> low resonant frequency,
stiff flexure -> high actuation force. References: see FlexureForOptics.doc