tutorial: design of a low-profile single axis linear motion stage
TRANSCRIPT
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TUTORIAL:
DESIGN OF A LOW-PROFILE
SINGLE AXIS LINEAR MOTION
STAGE
Kerry Gonzales
OPTI 521 – Fall 2015
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DESIGN CHOICES
What is the application?
Requirements (travel, accuracy, resolution, etc…)
How much space is available?
Envelope constraints (mounting)
How much funding is available?
Custom vs. COTS ($$$$ or ¢¢¢)
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CUSTOM FLEXURE SOLUTION
Limits of travel
< 2 mm
Limit of payload capacity
< 500 grams
Cost implications
100%-300% similar COTS solution
Material considerations
Costly alloys needed to achieve strength and flexibility
Figure of merit : σyield / E
Titanium (6Al-4V), CRES 17-4 PH H1150, Invar-36, Beryllium Copper
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SINGLE PIECE MACHINED DESIGN
How compliant do the flexures need to be?
How much force is required to achieve the travel requirements?
What components are needed to control position?
Component limitations on travel and force
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BEAM MODEL REPRESENTATION
Fixed- Fixed condition beam bending
Section properties, deflection, force and
stiffness
𝐼 =𝑏ℎ3
12𝛿 =
𝐹𝓁3
6𝐸𝐼
𝐹 =6𝛿𝐸𝐼
𝓁3𝑘𝑡𝑜𝑡 =
24𝐸𝐼
𝓁3
Flexure design to match idealized beam
model
Consider end design!
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FLEXURE FAILURE CRITERIA
Stress, stress, stress!
Factor of Safety on yield = 4 minimum
𝜎𝑚𝑎𝑥 =𝜎𝑦𝑖𝑒𝑙𝑑
𝐹𝑜𝑆
𝜎 =𝐹𝓁ℎ
2𝐼
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LOADING AND BALANCED MOTION
Single point actuator limitation
Force triangle
Overcome flexure reaction
Negative springs
𝐹𝑠𝑝𝑟𝑖𝑛𝑔𝑠 = 1.25𝑘𝑡𝑜𝑡𝛿 = 2𝑘𝑠𝑝𝑟𝑖𝑛𝑔𝛿𝑠𝑝𝑟𝑖𝑛𝑔
𝐹𝑚𝑎𝑥 = 𝐹 + 𝐹𝑠𝑝𝑟𝑖𝑛𝑔𝑠 + 2𝑘𝑠𝑝𝑟𝑖𝑛𝑔𝛿
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MANUFACTURING
Use a Blanchard ground
plate with good
perpendicularity on the
edges.
Common milling practice is good for most features
Wire-EDM (electronic
discharge machining) for the
flexure features
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MOUNTING AND USAGE
How will it be mounted?
How will that affect the performance?
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MOUNTING AND USAGE
Machine a cavity to provide stage motion
clearance!
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COMPONENT ATTACHMENTS
To maintain low
profile, attach
actuator and
feedback devices
on plate edges.
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FINISHED ASSEMBLY!
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REFERENCES
Gonzales, K. L., “Tutorial: Design of a low profile single axis linear motion stage”, Complete text, Fall 2015
Burge, J. H., Lecture Notes “Deflections Under Loading”, Fall 2015
Vukobratovich, D., “Introduction to Opto-Mechanical Design” Course Notes
Schwertz, K., “Useful Rules of Thumb in Optomechanics”, Spring 2010
Thorlabs.com, parts reference
Measurement Specialties, MEAS-SPEC.com, parts reference
Physik Instrumente, PI-USA.US, examples of small motion flexure based linear stages