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 flexure

Symmetric dual 4-bar linkage eliminates Y errror

Uniform Shaft Loading

XYZ Translation Stage

Conflict for all 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 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