I have always found Excel to be one of the best optomechanical analysis tools.
AEH has recently enhanced the Ivory3 Optomechanical Modeling Tools to make Nastran and Excel even more powerful for the optomechanical engineer.
It’s not that Nastran doesn’t do its job, but it’s only a finite element code. For optical systems the engineer needs more methods and tools to interpret Nastran’s results optically. Ivory3 unleashes the power of Nastran into Excel to analyze optomechanical design issues:
Ivory3————————— into –>Nastran———- into —>Excel ——————-|
Optical prescription data > opto-structural model > LOS error contributors
In this example Ivory3 puts the image registration errors (ie. line-of-sight) into Nastran’s output file, both the net effect and the element-by-element effects, which may be cumulatively summed and plotted in Excel for the engineer’s assessment. Obviously elements 1, 5 and 11 are the big drivers in this LOS error problem.
When you need to stabilize
your image AEH has the tools!
Zoom lenses are getting hot again. They seem to come in cycles for AEH.
There was the 20:1 MWIR zoom with a 300 mm entrance pupil. It was a lot
of fun! Good for a mechanical engineer to cut his teeth on too. As
tough as it was, it actually inspired much of AEH’s
optomechanical engineering practice.
The 8:1 visible microscope zoom for medical diagnostics was
an application that brought its own challenges. Using commercial optical
assemblies where only the focal lengths were known required some lab work to
find their principal points. Those of you who’ve taken my short course in
optomechanical analysis or used my Ivory
Optomechanical Modeling Tools will appreciate that need.
Then there was the 10:1 NIR zoom with 36 individual
images, five moving lens groups and two working distances. And it had to
be packaged into a convenient instrument case. AEH used a customized version of the Ivory Optomechanical Modeling Tools to
make that one happen too. One of the advantages of having the source code
is that I can make it do whatever is needed at the time. And the current
version’s users receive the upgrades as I develop them.
It’s a New Year with new opportunities and new challenges. As I said last
In the Hatheway household it runs from about now ’till Twelfth Night,
our daughter’s birthday. We’re careful to let Guy Fawkes Day slip quietly
by before we start to celebrate. (We’re all for Parliament but burning
effigies is a real downer.)
And, what a grand year it is shaping up to have been (yes, in the future
perfect tense). Speaking of which…
AEH fixed the wedge caused by
… witnessed the solar eclipse in the Alleghenies…
… chaired a conference in San Diego….
… was snowed in Massachusetts…
… and got lost in Irvine.
That last one was a real embarrassment since
your author was raised about 20 miles from there. But that was before Irvine
Ivory and Jade are having a
terrific year also, assuring the performance of systems from zoom lenses to
gimbal controls and assuring the safety of critical lenses and windows by
helping designers select suitable materials and specify proof tests. No broken
glass so far.
So, here’s a wassail to you, one and all, for your companionship and
cheerfulness throughout the year.
Optics is a crazy industry. We’re so dedicated to the digital computer
that we often overlook underlying realities. That’s especially true in
the mechanical engineering art of heat transfer. Management structures
have insisted on each discipline using its own software which has Balkanized
the disciplines of structures and heat transfer: i.e., the temperatures must be
analyzed in a finite difference (FD) code and the results imported to a finite
element (FE) code. The importation involves extensive extrapolation and
interpolation of the FD data to the much larger (often by two or three orders
of magnitude) of the FE data-set and it can lead to some peculiar results.
AEH has long preferred a more Unified
approach: Select a code that can do them both, usually an FE code, and
use engineering judgement to adapt the other discipline (usually a few boundary
temperatures). It usually requires several runs of the problem to assure
that the underlying assumptions of the adaptation were appropriate but they go
much faster than the Balkanized approach (and, often, more accurately for the
It’s the thermal-structural-optical method I used on the LACE Ultra-Violet
Plume Instrument, which made Aviation Week’s75th
Anniversary Issue. Check out the UV plume
image from AW’s cover, above!
More recently, a colleague was directed to thermally analyze an optical
system in CFD and I was to apply his temperatures and gradients to calculate
the boresight errors among the optical instruments. Well, what he was
handing me made no sense at all. So, I added heat transfer terms to my opto-structural
FE model and ran the operational transient of concern to the project. The
thermo-structural-optical results were spot-on.
There are a lot of ways that an engineer needs to keep his tools sharp.
And they require maintaining confidence in the analytical methods as well.
Hey, Control Systems Engineers, this one’s for you! I’m sure you remember
my dear friend who likes to declare, “You have to know the answer before
you do the analysis!” And his wicked “eye-twinkle” was part
of that message too. I used him then as a vehicle to highlight the
importance of engineers making estimates and developing a “sense of
smell” about the quality of their decisions.
So, my question for you is: How do you incorporate the line-of-sight into
the MatLab model of your “stabilized” optical system?
Well, AEH knows of three ways: 1) You can calculate it
yourself, from the optical prescription, and insert it in your MatLab file, with
some luck, or 2) you can copy the Optomechanical Constraint Equations
(OCE) from Ivory and patch
them into your Matlab file, with a little better luck, or
3) you can speak nicely enough to the structural engineer for him or her to
import the OCE (from Ivory)
into his FE model and the resulting eigenvectors, BINGO and…
If you want to learn more here’s an
opportunity: On August 7th, all day, I’ll be
teaching my course, Optomechanical Analysis, for SPIE’s
Symposium Optics+Photonics 2017 at San Diego’s Convention Center and
Marriott Marina Hotel. The first half of the course is all about the OCE,
how you generate them and how they’re used. Then you might stick around
for our Conference, Optomechanics 2017,
on the 8th and 9th to find out what everyone else is doing. On Tuesday
evening, the 8th, I’ll be hosting a meeting of the Optomechanical Technical Group between 8
and 10. Dan Vukobratovich will be our principal speaker followed by an
Yeah, you guessed it. My dear friend is a control systems engineer.
One of the things I did for him was to assure that the structural engineer
incorporated Ivory’s OCE into
the FE model that produced the eigenvectors he used in MatLab to design the
control system. Later system tests on the shaker-table confirmed the
quality “smell” of this decision. Ivory nailed it, dead-on!
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).
I mentioned earlier that there is a great deal to optomechanics. Even
full time practitioners can lose track of the current scope of the
optomechanical arts. And with a well corrected optical design the onus
falls to the optomechanical engineer “to make it all play.”
I was working with another dear friend shortly ago. He was contemplating
a compound hyper-spectral imaging system and wondered if I knew anyone who
could help stabilize the instrument. Of course, I immediately raised my
own hand. He said that I didn’t understand: The entire image plane
had to stay in strict alignment over the entire detector array all the time.
He behaved incredulously but, generously, heard me out.
I explained: AEH’s Ivory Optomechanical
Modeling Tools operate over the entire exit window
(field-of-view on the image plane, if you prefer). They tell the
optomechanical engineer what’s going on at the edges, the corners and the
center or anywhere else in the image. The Tools
can do this because theirOptomechanical Constraint Equations determine
the alignment of the entire image plane (position, orientation and size) over
the entire detector array. He said, “Show me.”
So, I used the Ivory OMT to model the image’s corners, edges and center in shock, vibration and thermal environments. Initially the image’s stability over the entire detector array was barely marginal. But with a little tweaking of the structural design, informed by the influence coefficients from Ivory, we got it within specification with a comfortable margin. This system flies today with confidence.
Just Bridging the Chasm one more time.
I hope you all enjoyed a Great Thanksgiving. It’s down-hill from here to 12th-night!
Brutus to Cassius in Julius Caesar: “There is a tide in the affairs of men which taken at the flood leads on to fortune. Omitted, all the voyage of their life is bound in shallows and in miseries.”
A product development project might be considered one of “the affairs of men” to which the Bard was alluding. My readers, however, should note that it was not “the affairs of men” that was Shakespear’s subject. Rather, it was “a tide” that Brutus’ declaration (and in fact the whole resulting drama) were about. Shakespear’s prescient observation has outlived him, at 400 years on the 23rd of April, for good reasons.
AEH guided a re-design effort, the goal of which was to markedly reduce the image jitter due to a random vibration excitation. The client’s analysts had assumed that “structural” damping was uniformly distributed through the system and had some difficulty simulating problems experienced during service. Fortunately, there was some accelerometer response data from earlier vibration tests and AEH was able to modify the distribution of damping in their Nastran model to better replicate that earlier data.
added the Optomechanical Constraint Equations
(via Ivory) and “Viola,” the model was now able
to reproduce the image jitter observed during service as well. Using the OCE to parse the Nastran displacement
vector identified the major contributors and a simple brace was added to the
design to stabilize the image.
None of this was planned. AEH happened to be on-site and
overhear a conversation at the coffee pot. A tide in the affairs of men
was forming. AEH, with Ivory, was
ready. As a wag might say, “Use it or lose it!”
Rejoice with me at William Shakespear’s 400th birthday!
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…
Do you remember the Great LCD Projector Wars? I certainly do!
One of AEH’s jobs was to align three LCD images on the screen to 1/10th pixel accuracy and hold them there over long periods of time and over large swings of temperature. The alignment was performed with adjustable fold mirrors to control the Tx, Ty and Rz degrees of freedom of each image. A simple Ivory-in- Excel analysis told us it required a stroke of 17 mr. and a resolution of 0.00026 mr. on each of the fold mirrors.
had some other resources to bring to the table as well. We were able to
adapt AEH’s patented set-n-forget actuator technology (Intended
for JWST) to the design and manufacture of the mirror mounts. There was a
bit of a breathless interval, however, because AEH could not measure the
sub-microradian resolution. The test was to install the mounts and turn
on the projector. The system worked wonderfully, which verified the
precision of the mirror mounts and the Ivory
Here’s to taking care of three images!
Well, that was then and now is NOW.
The great September 1/4 off sale
of AEH/Ivory 3.0 Optomechanical Modeling
Tools has only a few more days to run! Reserve your copy