AEH has solved elastic
theory’s differential equations for the tensile stresses in glass lenses
mounted in threaded metal rings, and it’s
Paul Yoder had originally proposed Delgado and Hallinan’s 1975 solution (Opt.
Eng.14) but their solution gave very high tensile stresses in the
lenses, high enough that virtually all such lenses should have fractured.
None of my ring mounted glass lenses had ever suffered that fate. I
surveyed a number of my colleagues and none of them recalled a ring mounted
glass lens fracture.
Delgado and Hallinan’s work was flawed. To correct their flaw would
require a new solution to the equations of elasticity that honored the
appropriate contact geometry. AEH
finally made it happen and the result is surprisingly simple,
s = p(1-2u)/b,
where s is the peak tensile stress, p is the
linear ring load, b is the radius of the contact ring and u is
the Poisson’s ratio of the glass. This stress is three-to-four orders of
magnitude lower than that predicted by Delgado and Hallinan.
Using Nastran AEH was also
able to verify the general shape of the stress distribution in spite of
Nastran’s notorious difficulty at the point of load application.
Closed-form solution >>> Nastran solution
To learn more you have choices: Either download AEH’s peer reviewed paper from SPIE [Optical Engineering 57(5), 055105] or go
through the gory details with me in my tutorial,
“Optomechanical Analysis,” SPIE’s Optics and Photonics Symposium in San Diego 8:30 AM to 5:00 PM on the 21st of August.Cheers!
Well, Ok. It’s not that AEH
hasn’t seen broken glass this past year, it’s just that it hasn’t been AEH’s glass that broke. Cemented
doublets were the principal excitement. AEH’s
research indicates that, for a quick check,
tensile stress in the glass
+ E2)/2 x (alpha1 – alpha2) x deltaT
shear stress in the adhesive
=~ 2/3 x tensile stress in the glass.
If stresses are marginal the engineer may then want to
adjust for the edge thicknesses of the lenses and the Poisson’s ratios of their
glasses. The peak shear and tensile stresses occur at or near the edges
of the lenses. The only dimensions that influence the stresses are the
edge thicknesses. Center thickness and diameter have little influence on
the stresses at the edges.
Radial Tension Shear Axial Tension
Does it all seem spooky? Well, I’ll take you through
the gory details in my tutorial,
August 21st in San Diego at SPIE’s Optics and Photonics Symposium.
And, I’ll toss in, just
for you, the latest details on the stresses in ring-mounted
glass lenses including a close-form solution and a finite element simulation!
I’ll see you
all in San Diego. Bring your sun-screen.
Fall is coming in two weeks and the Great Pumpkin is right down the road.
It’s time to kick-back and just look around a bit
at this Glorious Summertime…
I’ve had about four weeks on the road lately, touching base with
all of you (or most of you, I hope). Then I cruised around SoCal in my
spare time chinning and jawboning with the local industries’ participants.
So, what are the “hot items” for optomechanical engineers
today? Well, how ’bout…
precision dimensioning and
tolerancing of optical structures
repeatability and stability of instrument performance
broken optical glass
I’d have trouble identifying the most important of these, it
all depends upon what’s happening NOW. All three of these
have kept me pretty busy since Valentine’s Day. The greatest uncertainty
for the engineer, however, is in the strength of optical glasses. Its not
just mirrors and windows.
I’ve participated in two projects in which the optical design had to be revised (compromising performance) to replace glasses that could not pass the environmental tests. Perhaps, someday, the glass houses will start to provide strength information on their data sheets near the Young’s modulus and Poison’s ratio. Today the engineer can’t be sure until the tests are passed.
And we, all of us, managed to squeeze-in a terrific conference with SPIE in San Diego last month (32 papers published). How we were able to pull that together, I just don’t know. But, it would never have happened without you and the terrific staff at SPIE who keep us on the right track.
Here comes Guy Fawkes Day. Get your bonfires, and marshmallows, ready! All our prayers this day are with those who may be in harm’s way.
I’ve been known to lecture my students and colleagues on the need to keep their
tools sharp. Some time ago AEH was invited to a design
review as an observer and since I had no direct participation I sat at the back
of the room, behind John, the systems engineer who was controlling the
projector. The technical sessions went well but about half-way through
the schedule and budget sessions he suddenly blackened the screen and turned on
the overhead lights. He slowly turned and surveyed those of us sitting
behind him. His gaze settled on me! “What, John?” I
asked. He stared at my hands which were holding my pen knife and its
sharpening steel. “Just keeping my tools sharp,” I declared
One of AEH’s sharpest tools, other
than a pen knife, is Ivory’s Optomechanical
Modeling Tools. It’s been under continuous development
incorporating many of my personal insights working as a mechanical engineer in
the optics industry. I recently put together an updated version and
released it to all users of Version 3. That’s another way I keep AEH’s
tools sharp (and protect AEH’s Ivory
subscribers, too). Ivory
is AEH’s prime tool for engineering thermally and structurally
reliable optical systems. It’s designed to work in both Excel and Nastran
and its application early in the design process prevents much embarrassment and
saves many labor-hours from preventable failures that may occur later in
qualification tests and service.
Somewhat more recently AEH was invited to participate in a
“Tiger-Team” review of a sub-contractor. The initial issue was
broken glass. The first thing I did was get a copy of the physical optical
prescription (CodeV) and read it into Ivory
(for the structure) and Jade
(for the broken glass). I could then quantitatively infer where the
principal structural and thermal weaknesses might be. With that insight I
was able to form an independent assessment of the completeness of the design
team’s engineering effort, which undergirded my report to the prime contractor.
I hope to see all of you at SPIE’s Optics+Photonics in San Diego
come August. I’ll be teaching (Optomechanical Analysis), chairing (The
Optomechanical Engineering Technical Group and Optomechanics 2017),
presenting and publishing (on a new diffraction grating capability in Ivory) and begin planning our next SPIE
Conference (Optomechanics 2019).
Well, the weather’s warming up here in SoCal. The beach and surf await us all.
SPIE’s annual gathering in San Diego awaits us as well. I’ll chair an evening meeting of the International Technical Group of Optomechanical Engineers (8 to 10 PM on August 30th). Professor Tony Hull (UNM) will be our feature speaker. He’ll discuss the recent advances in light-weight glass-ceramic mirrors for space (and other) missions. And there’ll be Conferences, Equipment Exhibits, Tutorial Classes, Evening Receptions, the Grand Awards Banquet and great camaraderie.
Don’t forget to visit SPIE’s book display near the registration area. There you’ll be able to leaf-through a copy of my new book, The Optomechanical Constraint Equations: Theory and Applications. I have bared all of Ivory’s secrets in this tome. If you visit the SPIE Publications website:
While we wrap-up a glorious 2015 with parties
and presents we should pause to recognize that the end of the year is not
the end. Rather, we look forward to a new beginning in a
New Year, 2016.
Two events in 2016 require the immediate attention of optomechanical engineers
and they are both conferences in San Diego during SPIE’s Optics+Photonics
The first conference is “Optical Modeling and Performance Prediction
VIII,” and is chaired by Mark Kahan of Synopsis Inc. and Marie
Levine-West of JPL. Real performance predictions are not possible without
coupling the mechanical behavior to the optical surfaces, materials and
elements. Optomechanical engineering is central in assuring the desired
performance in the final design and we make valuable contributions here.
The second conference is “An Optical
Believe It or Not: Key Lessons Learned V.” This
conference is also chaired by Mark Kahan and is unique in that it encourages
engineers to share with colleagues what they have learned from their
experiences, and other people’s experiences too. Identities, individual
and corporate, may be protected (shrouded by whatever means are considered
appropriate by the speaker), encouraging discussions of problems and solutions
without casting blame and damaging reputations.
The immediacy mentioned above is imposed by the due date for abstracts, February
8, 2016. That may sound like a long time away, but with the Holidays and
the New Year crank-up activity the time will slip away from us quickly and many
days can be lost waiting for approvals.
The details of each conference are attached. So plan to get your
abstracts in early.
On my return from our San Diego meeting I helped develop the structural design for a new optical system. That seemed more important, at the time, than a biennial, “Thank you,” in a newsletter. Optics had to stake its claim for structural resources (stiffness) competing with the other disciplines. A Unified optomechanical model was the method.
We got it and the initial concept meets the
specifications now. So…
Now… I can take a moment to thank all of you for making this year’s
gathering in San Diego, of the International Technical Group on
Optomechanical Engineering, a resounding success: Thirty-two
published papers in a two-day conference, two outstanding invited speakers (one
on optical tolerancing, one on readiness assessments) and an evening meeting on
ground-based testing of space-based optical systems. SPIE’s
Optics+Photonics Symposium was the perfect host. They and I look forward
to organizing a similar event in two years, 2017, and we expect to see you all
there one more time.
Thank you, thank you and thank you, my colleagues. I apologize for having
ignored you all these weeks.
All is well at AEH and Autumn is safely here now.
School has started, the parents are on the loose again…
One of the challenges for a mechanical engineer is to determine the dominant
drivers of bad behavior in complex systems. The behavior may be observed
during service, in environmental tests or system analyses.
In optical systems AEH segregates the effects of each degree of freedom (Tx,
Ty, Tz, Rx, Ry, Rz) of each optical element (1, 2, 3, …, detector) and plots
the cumulative sum which, in the case below, exposes the major offending
elements to be 1 and 5 (see chart). The engineer may then objectively
recommend structural design changes that will stabilize the offending optical
elements and improve the optical performance of the structure.
I’ll be presenting the details of this approach
in a paper during SPIE’s Optics+Photonics Symposium in San Diego this
August. I hope to see you all there.
In the meantime, if you have questions just give me a call. I’ll be here.
Summer’s coming, and so is SPIE’s magnificent Optics+Photonics
Symposium in San Diego, August 17th through the 21st. The
week will be loaded with optomechanical events and technologies.
On Monday the 18th I’ll be presenting a paper, “Use It Or
Lose It,” in Mark Kahan’s conference, “An Optical
Believe-It-Or-Not: Key Lessons Learned III.” That should be a
Then, Bright and early Tuesday, the 19th, there’s a meeting with
SPIE staff for planning next year’s Optomechanical Engineering Conference.
That conference will be your place in the sun, technologically speaking, so get
your abstracts ready for submittal and spread the word to your friends and
Tuesday evening, 8 to 10 PM, the Optomechanical Engineering
Technical Group will hold their annual West Coast Bash. Our speaker
will be Tony Hull, Adjunct Professor of Astronomy and Astrophysics at the
University of New Mexico. He’ll be addressing the primary mirror
material selection process for spaceborne telescopes and how it drives the
architecture and planning of these systems.
Wednesday, the 20th,I’ll be teaching my tutorial,
“Optomechanical Analysis,” all day to a bunch of bright-eyed
students. This is aimed primarily at mechanical engineers and I try to
give them some new tools to relate their mechanical engineering decisions to
the optical behavior of their systems. This material may also be of
interest to other optics professionals, even structural engineers.
Wednesday evening is SPIE’s Awards Banquet where all of
the elephants of the academy and industry gather to celebrate new
honorees. This is always a great event and I’m sure that Phil Stahl, our
President, will put his usual high gloss finish on the whole program. I
may be weary from teaching all day but this is always a must-do event for me.
And Thursday, ahh… Thursday: Finally, I’ll get to cruise
the exhibits, mingle with colleagues, meet new people, and catch up on the
technology in the conference
rooms. Then at the end of the day, after the exhibits close, a few of
us will go out to a local bistro for a toast-n-roast dinner (maybe with
some red meat, even!).
It’s all one great week-long event: More material than you can ever
hope to capture in real-time.
On the evening of May 6th, during SPIE’s Defens+Security+Sensors Symposium,
I’ll be hosting a meeting of the Optomechanical/Instrument Technical Group.
Our speaker will be Steve Rummel, Director of Product Technology for
II-VI Infrared of Saxonburg, PA. II-VI is a major supplier of
optics for CO2 laser applications. Mr. Rummel will discuss new
developments in highly stable, heat resistant materials for use in high power
applications, especially where a high quality optical finish is required on the
surfaces. He’ll review the microstructure and property data II-VI’s
reaction bonded silicon carbide, discuss diamond-containing formulations for
ultra-high heat load capability and present B4C containing versions which
compete with beryllium.
This is the East Coast meeting of the premier group of optomechanical engineers
that design and analyze the world’s optical instruments and systems. This
gathering is open to all attendees to the Defense+Security+Sensing Symposium.
Anyone who wishes to put an item on the agenda should contact the Chair, Al
Hatheway, at email@example.com.
The meeting will be from 8 to 10 PM in the Hilton Hotel associated with the
Baltimore Convention Center. Check the Symposium Program or the
registration desk for the room’s location.
The Baltimore DSS Symposium is a terrific gathering of the technologists that
“make it all happen.” It’s only two months away. Set the
time aside now, you’ll be glad you did.