Optomechanical engineers are a lot like professional chefs. Each has a
“secret sauce.” Just like chefs we sample and adjust our sauces
all the time to be sure they’ll come out consistently good.
AEH’s secret sauce is
selections from W. J. Smith and R. J. Roark blended into K-J. Bathe.
Below I use the optical prescription to determine the optomechanical constraint
equations (OCE) between each of its ten optical elements and the image on the
detector (pink). I then estimate the required stiffness properties
of the structure between the elements, I define a lumped mass for each of the
optical elements and connect them together with the nine beams (yellow) with
the (estimated) proper stiffnesses. I run it for the LOS error:
initial run is usually off-target but it provides a starting point. I
replace the lumped masses with the actual lenses (from step files) and adjust
the stiffness of the beams until I’m in the ballpark of the required LOS
error. Then I guide the design of the CAD structure to have the proper proportions
to meet the required LOS error…
1.3 ur rms . . . LOS . . . 1.4 ur rms from Proposal ——————————————————> to Product.
AEH’s sauce provides the project a continuous and traceable record of the adequacy of the structural stiffness supporting the optical system from the earliest concepts to the final tested product. AEH’s sauce is a little different every time, just like its culinary counterpart.
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 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!
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:
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!
We have a terrific program set up for SPIE’s Optics and Photonics Symposium in
San Diego on August 25th through 29th, 2013. We have a two-day
conference, “Optomechanical Engineering 2013,” on Wednesday and
Thursday (the 28th and 29th) with a poster session on Monday evening, a meeting
of the Optomechanical/Instrument Technical Group on Tuesday evening, the 27th,
and the greatest exhibit of the optics industry to be in Southern California
all year on the 27th, 28th and 29th.
Our Tuesday night meeting will feature Phil Pressel’s presentation of some of
the challenges he faced in designing the “Hexagon” space surveillance
camera for the CIA. The project was officially declassified in 2011 and
Phil is publishing a book on his experiences on the project. It may be
available at the meeting and you might be able to get him to autograph it for
I’ll be teaching my day-long tutorial, “Optomechanics and the Tolerancing
of Instruments,” on Monday the 26th. This is the course in which I
teach engineers the full theory behind the Optomechanical Constraint Equations
that control the position, orientation and size of the image in an optical
system. I personally use the equations to tolerance the optical metering
structure, size alignment mechanisms, evaluate thermal boresight shifts and
analyze image jitter in dynamic environments. I show my students how to
do the same things.
Wednesday night is the Awards Banquet at which new Fellows will be inducted by
the society. That’s a grand event as well.
Also on Wednesday, the 28th, I’ll be presenting a paper in our conference and
on Thursday I’ll be presenting a paper in Mark Kahan’s conference,
“Optical Modeling and Performance Prediction VI.”
It’s a week-long hubbub of exciting events, networking and learning. I
hope to see you all there.