2. A tool used to profile the shape and
roughness of a surface
3. What does this accomplish?
− Spheres are easy to manufacture,
however aspherics maximize the
performance of the mirror or lens
− A profilometer tests how close to
ideal the surface of the mirror
− Finding the exact points of these
aberrations allows polishing to be
done at those places
− As the surface becomes closer to
ideal:
− Image resolution increases
− More light is focused to a singular
point
4. Uses of Optics
− Telescopes
− Defense
− Medical research
− Medical imaging
− Camera Lens
7. Why a Swing-Arm?
− Swing-Arm profilometers offer numerous
advantages:
− Ability to measure larger surfaces
− Linear: 4-6 in
− Swing-Arm: 1.5 m
− Cheap to build
− Perform “in process” measurements
− Extreme Accuracy
8. Need Addressed
To design a low cost swing arm profilometer
to measure the accuracy of large aspheric
optical surfaces.
9. The Design Process
− Brainstorming
− Mock Setup
− SolidWorks Assembly
− Finite Element Analysis (FEA)
− Vibrations, Deflections, Motion Analysis
10.
11.
12.
13. This simulation shows the deflection of
the assembly under gravity and an
applied torque.
14.
15.
16. Accomplishments
− Arc Length
− 78’’ swing with 25’’ radius
− Possibility to have a variable radius
− Hypothetical 360 degree swing
− Alterations to placement and use of stepper motor
− Shaft allows spin about central axis.
18. The Sag Equation
-Describes the general shape of a conic surface mirror
(hyperbolas, parabolas, spheres and ellipses)
- Where:
- C = Curvature
- x = Offset from Center
- k = Conic Constant
19. Through use of the Sag equation, we can find
The total angular travel of the scan path across the part
The amount of steps the motor will take
The amount of data points to record
Theoretical depression of the depth gauge at each point
20. Ball Offsets
- At the tip of the depth
gauge, there is not a single
point.
-This means that the contact point
of the tip and the actual point being
measured are never the same (except
for dead center).
21. The line points to the spot on the piece that
we want measured.
However, you can see that the contact point
of the ball is not in line with the point in
question.
Contact Point
22. By hypothetically pushing the
ball to the actual contact point,
we can calculate the offset.
By taking the derivatives, of the
two functions, at a certain x-
offset from the center we can
subtract the two and set them
equal to zero to find the x’.
This longest line (x’) is how
much you’d move the ball up to
find the real contact point.
There is an associated angular
offset for every contact point we
read.
X’
26. Additional Parts
− Assembly
− Mitutoyo Digital Indicator
− Accurate to 2/10 of a micron
− NEMA 24Y Stepper Motor (ORDERED)
− High Torque, High Accuracy Stepper
− Planetary Gear Attachment
− Flex Coupling
− Decrease Vibrations further
27. Final Results
- Design and analysis completed
- Design meets needs and requirements for a low cost
instrument to accurately measure large aspheric optical
surfaces
- Minimal deflections and vibrations. Along with large
adaptability
- Programming nearing completion
- Fabrication and procurement in process
- Drawings sent to be manufactured (parts lists and BOM)
28. Next Steps
- If allotted more time,
- Complete assembly of milled parts
- Testing of assembly
- Document operating procedures and lessons learned
- Predictions for the Future
- Optimization of motor torque
- Stabilization
- Hysteresis
29. Need Addressed
To design a low cost swing arm profilometer
to measure the accuracy of large aspheric
optical surfaces.
30. Thank You
Acknowledgements:
- Richard Pultar
- Riley Aumiller
- Phil Baker
- Mike Owens
- Mary Liang
- HNu Photonics
- The Akamai Internship Program
The 2014 Akamai Internship Program is part of the
Akamai Workforce Initiative, in partnership with the
Univ. of California, Santa Cruz; the Univ. of Hawai'i
Institute for Astronomy; and the Thirty Meter Telescope
(TMT) International Observatory. Funding is provided
by the Air Force Office of Scientific Research (FA9550-
10-1-0044); Univ. of Hawai'i; and TMT International
Observatory."
