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Flexures for Optics. Outline. Brief overviews of micro flexures Focus on macro flexures in this tutorial Beam bending Symmetry -> precision Degree of freedom (DOF) Applications. Micro Flexures. Tip-tilt mirrors discrete vs analog. Comb drive. Optical MEMS devices. - PowerPoint PPT Presentation
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Flexures for Optics
Outline Brief overviews of micro flexures Focus on macro flexures in this tutorial Beam bending Symmetry -> precision Degree of freedom (DOF) Applications
Micro Flexures
Comb drive
Tip-tilt mirrors
discrete vs analog
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”.
Precision Mechanics
Macro Flexures – 1D
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
Deformation Diagram
X/Y forces + X/Y moments
5 DOF – Pentaflex Combination of vertical and
horizontal blades X/Y/Z translation + X/Y
rotation
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)
6-axis (nano) Flexures
HexFlex
6-axis Flexures - examples
Flexures
Only allows DOF, all others conflict.
Tip-tilt Flexures
Remove axial misalignment between two parts (shear),
but does not remove torque/moment.
flexure -> 5 DOF
In-plane 1D Flexure
Out-of-plane 1D flexure
In-plane 1D flexureSymmetric dual 4-bar linkage eliminates Y
errror
Uniform Shaft Loading
XYZ Translation Stage
Conflict for all DOF’s
Bi-stable FlexureActuation force causes deflection
Open/close a valve at some pressure threshold;
on/off
Have negative stiffness in the unstable region
Non-linear Spring Constant
Shape -> deflection -> variable
stiffness
Piezoelectric Amplifier
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