Flexures for Optics

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Flexures for Optics
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Outline

• Brief overviews of micro flexures
• Focus on macro flexures in this tutorial
• Beam bending
• Symmetry -gt precision
• Degree of freedom (DOF)
• Applications

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Micro Flexures
Tip-tilt mirrors discrete vs analog
Comb drive
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Optical MEMS devices
Resonant frequency of the comb drive depends on
the ions hitting the pads
Analog tip-tilt mirror
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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.

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Precision Mechanics
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Macro Flexures 1D
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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

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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

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Deformation Diagram
X/Y forces X/Y moments
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5 DOF Pentaflex

• Combination of vertical and horizontal blades
• X/Y/Z translation X/Y rotation

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Highly Symmetric XY Stages
Can be made into XYZ stages by adding the
horizontal blades like Pentaflex
Three different anchoring geometries
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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)
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6-axis (nano) Flexures
mHexFlex
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6-axis Flexures - examples
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q Flexures
Only allows q DOF, all others conflict.
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Tip-tilt Flexures
Remove axial misalignment between two parts
(shear), but does not remove torque/moment.
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qfg flexure -gt 5 DOF
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In-plane 1D Flexure
In-plane 1D flexure Symmetric dual 4-bar linkage
eliminates dY errror
Out-of-plane 1D flexure
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Uniform Shaft Loading
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XYZ Translation Stage
Conflict for all qfg DOFs
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Bi-stable Flexure
Actuation force causes deflection
Open/close a valve at some pressure threshold
on/off Have negative stiffness in the unstable
region
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Non-linear Spring Constant
Shape -gt deflection -gt variable stiffness
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Piezoelectric Amplifier
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Physik Instrument
Piezoelectric drive capacitive sensor, feedback
loop to actively take out platform vibrations
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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 -gt low resonant frequency, stiff
  flexure -gt high actuation force.
• References see FlexureForOptics.doc