Transcript presentation

Flexures for Optics
Outline
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Brief overviews of micro flexures
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Focus on macro flexures in this tutorial
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Beam bending
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Symmetry -> precision
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Degree of freedom (DOF)
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Applications
Micro Flexures
Comb drive
Tip-tilt mirrors
discrete vs analog
Optical MEMS devices
Resonant frequency of the comb drive
depends on the ions hitting the pads
Analog tip-tilt mirror
Motivation
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Need nanometer precision to
manipulate light.
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“Stage” and “driving mechanism”.
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Sticktion is a problem encountered with
screw-type driving mechanisms.
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Use piezoelectric, capacitive, magnetic,
photon,… to drive the “stage”.
Precision Mechanics
Macro Flexures – 1D
Symmetry in 2D
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In-plane rotation
Parasitic motion not di-coupled
As soon as the stage moved, Fx
developed some “local” y
component
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In-plane rotation minimized
Parasitic motion reduced or
cancelled
Less cross-talk
Parallelogram
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In-plane rotation constrained
Parasitic motion reduced
As soon as the stage moved, Fx
developed some “local” y
component
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In-plane rotation constrained
Parasitic motion further reduced
or cancelled
Less cross-talk
Deformation Diagram
X/Y forces + X/Y moments
5 DOF – Pentaflex
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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,f,g) motions
Constrain the other in-plane (x,y,q) motions
(Voice-coil, pressure sensor, flow control, MEMS devices)
6-axis (nano) Flexures
mHexFlex
6-axis Flexures - examples
q Flexures
Only allows q DOF,
all others conflict.
Tip-tilt Flexures
Remove axial misalignment between two parts (shear),
but does not remove torque/moment.
qfg flexure -> 5 DOF
In-plane 1D Flexure
In-plane 1D flexure
Symmetric dual 4-bar linkage eliminates dY errror
Out-of-plane 1D flexure
Uniform Shaft Loading
XYZ Translation Stage
Conflict for all qfg DOF’s
Bi-stable Flexure
Actuation 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
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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