Optomechanical engineering isn’t always big stuff: hyperspectral sensors; ISR systems; image trackers; boresight control; etc. There’s a lot of fun in the small stuff too.
For instance, how can you verify that an ultra-light mirror will be 1/8th wave or better when used in space?
How do you fix a lens assembly product when a large fraction of them fail the MTF test?
How do you drive a lens 10 mm with only 300 nm of runout?
A wag might declare, “It’s all in the
wrists,” but there’s a whole lot more “fun” than that
implies! The Devil is often in the little details.
Yes, AEH does big stuff, we enjoy the small stuff and we make house-calls too.
Whatever helps you!
I’ll be looking for all of you in San
Diego in a few days!
OK, enough about software. After all, we all run software. It’s AEH’s understanding of how to apply engineering tools, including software, that makes the difference.
To wit: design an airborne optical image correlator. Stabilize hyper-spectral imagers. Design aircraft structural-optical windows. Analyze detector cool-down times. Test metal-foil optical elements. Design nanometer-class alignment mechanisms. Minimize the thermal impedance in a laser cavity. Co-invent an infrared scanner. Stabilize a gas-dynamic laser cavity. Analyze thermal instability in lithographic lenses. Establish intellectual property rights in cinematographic lenses. Analyze dynamic stability of a free-space laser-com system. Design a stand-off optical vibrometer system.
I’ve written about many of these at one time or
another. But another big interest today seems to be, “Where do AEH’s jobs come from?”
Well how about Barrington, Huntsville, Albuquerque, Carson, Dallas, St. Louis,
Corona, Seattle, Palo Alto, Princeton, Los Angeles, Rochester, Tucson,
Anchorage, San Diego, Linthicum, Mountain View, North Hampton, Azusa and, yes,
even in Pasadena it’s been optomechanical engineering that AEH has done.
However you need help, wherever you need help AEH
is there.
Reflecting on the year just (barely) passed a couple of older stories keep coming to mind.
Early-on, a lens designer friend, Tom, asked me to mount an afocal triplet in a weapon sight. He said he wanted it to be on a kinematic mount. I hadn’t heard the term “kinematic mount” before so I did a little research. Mark’s Handbook had no entry. Maleev and Hartman’s Machine Design had no entry. Ham and Crane’s Mechanics of Machinery had no entry. Sears and Zemansky’s University Physics was not helpful. Finally, in J. L. Meriam’s Mechanics, Part 2, I found a partial definition, “kinematics … the study of the motions of bodies without reference to the forces which cause the motions….” I went back to Tom and asked him, “What kind of mount for optics in a weapon sight doesn’t consider the forces involved?” Well, he was patient in explaining his higher level of abstract reasoning and suggested that I expand my library.
Some time later I was sent by the Air Force to a
design review in Texas and to report what I found. I wrote you about this
a year or so ago. The physicists had designed one of the hottest
doubled-YAG lasers I’d ever seen and they requested that the cavity be
installed on a kinematic mount. The engineers complied with a classic
three-ball mount. It worked like a champ in the brassboard but the flight
unit was unstable. Everyone was perplexed. Well, it turned out that
the kinematic mount wouldn’t survive the service vibration so the mechanical
engineers had conveniently provided screws at each of the balls to lock them
out for flight.
In the first case Tom and I worked it out, I ate my humble pie and Tom put me
on his patent as a co-inventor. In the second case the Air Force lost
faith in the contractor and cancelled the entire project.
One of the challenges faced by mechanical engineers in the optics industry is
lexical: The engineer may hear what is said but not clearly understand
what is meant.
To address this challenge the engineer must ferret-out the acceptable
mechanical behavior, regardless of how it was originally expressed, and design
it into the required structures and mechanisms. It takes a little extra
digging but has proved to be a winning strategy.
What does the optomechanical engineer bring to the table? Hmmm…
A few months ago a structural engineer friend asked me to analyze the strength of a lens assembly that he didn’t feel comfortable with. It was injection-molded plastic, elastomeric rubber and glass. OK…
Before that an optics friend challenged me to explain why it might be OK to mount glass lenses between threaded aluminum rings. So, I did, but it took a while…
Another optics friend got me involved in resolving intellectual property disputes for mechanisms in cinematography lens assemblies…
Then a mechanical engineer friend needed a mass properties trade-off study between BK7 and sapphire for an airborne surveillance window…
Then another optics friend inquired about the
possibility of nanometer-class structural actuators for 30 degrees K space
optics. So I designed, built and tested a successful set of them…
And before that I was asked to rationalize the structural damping coefficients
to be used in an optical image jitter analysis.
The optomechanical engineer thinks outside the box. He needs to work
outside the box as well.
Actually, I got that backwards: He needs to work outside the box in
order to be able to think outside the box. It’s the peculiar demands,
outside of his art, placed on the mechanical engineer by optics that inspire in
him the intellectual curiosity to find workable engineering solutions.
Besides, he gets to enjoy your occasional company, too. Thank you.
And, don’t forget to submit your abstract
for “Optomechanical Engineering 2015.”
Assure your position in the program now: http://spie.org/OPO/conferencedetails/optomechanics Hmmm… which one should I submit?
Ok, ok. I loaded you with a lot of details last week. But the good news is, “That’s all there is.” A few day’s work at the beginning of the project and you have a viable design concept with which to proceed and have developed an engineering tool to spot-check the design during it’s progress.
However, I must admit to an ulterior motive: Many of my optical colleagues only see the “eye candy” produced by SolidWorks, ProE or CATIA and are only vaguely (at best) aware of the “continuous stream of numbers” the mechanical engineer produces to assure the safety, reliability and optical function of his designs. The numbers have little eye appeal and optics should be visual at a minimum, right? Well, any draftsman can produce the eye candy but only an engineer can assure the resulting product.
I was able to enjoy my Easter weekend because I got that job put-to-bed. We know how to make it work. We’ll do some design checks as the design matures. Then we may put the optical behavior into the final FE model the structural engineers will create for their safety analyses. Or we may not. And that’ll be OK since we know that we’ll have good optical margins of safety.
Speaking of Easter, I hope
you all had a great weekend holiday.
And thank you for all of your support over the
years.
A dear friend who designs control systems likes to declare,
“You have to know the answer before you do the analysis.” He
says it with a twinkle in his eye so you know he’s goading you.
But consider his declaration seriously. How does an analyst know he’s (or she’s) right? OK, forget about “right,” how about “good enough?”
The short answer is that he or she may not “know”, but that by developing over time a keen “sense of smell” he or she can “kind of tell”. One way to maintain that sense of smell is to continually make estimates and correlate test data whenever the chance occurs.
In this regard, and with the Holiday Season safely behind us I can pass along an anecdote:
I was managing a mechanical engineering department for a
large optics company [the optomechanics key in this missive] and the management
club decided to have its Christmas Party on board the Queen Mary, moored in
Long Beach. The dinner was preceded by a tour of the ship. My wife
and I decided to forgo the tour and arrived just as the diners were being
seated.
We joined a small group of program managers at a table near
the band-stand. The repartee was reasonably brisk, as it should be among
a gathering of alpha-male managers. But after a few minutes the hubbub
subsided and I could see that a gentleman across the table who I’ll call Larry
had a brochure in his hand. Larry said to me (and I believe I quote him
accurately), “Al, you’re so sharp. Tell us [and he gestured to our
peers around the table] how many rivets are in the Queen Marry.”
I heard my wife take a deep breath.
Now, Larry and I had some history, of course. Fun
stuff like this. And other less fun stuff.
So, I explained to him that I didn’t “know” but
would estimate it for him. I estimated the length and breadth of the
ship, its number of decks and the sizes of compartments. With that I
estimated the length of all the joints needed to be riveted together.
Then, estimating the number of rivets per foot on the outside of the ship
(which I had observed when day-sailing, with a friend, along her side the
previous summer), I declared my estimate: 10,000,000 rivets.
Well, a hush descended on the table that wasn’t lifted until
the band started playing. My estimate agreed exactly with the number in
the brochure Larry had picked up during the tour. The rest of the table
wouldn’t let me buy a drink all evening.
My response to my dear friend is that an engineer who does a
lot of analysis needs to stay grounded in the meaning of the numbers by
continually making estimates and correlating test data. Yes, even on a pleasant
summer afternoon day-sail. I believe he might nod his head and accept
that.
Optomechanical engineering is a collaborative art, a fascinating blend of
optics, machine design, structural mechanics, servo controls and heat
transfer. I tend to emphasize my (mechanical) contributions in these
missives. But enough about me. This
time I want you guys to stand up and take the bow. Let’s list
at a few topics from the recent past:
Membrane optics research (of 2-28-12) My contribution of designing some test facilities and helping with
the tests was nothing compared to the conception of the telescope it was
intended to support. My thanks to the telescope designer, the lab
technicians who ran the tests and the structural engineers who interpreted the
results. (Applause)
Tensile stresses in ring mounted glass lenses (of
8-31-09) A dear friend and colleague persisted in his belief that glass was
too fragile to be mounted in metal rings. A survey of the literature
showed no solution for this load condition and the nearest ones, point load and
line load, were unreasonable. So, I got out my pencil (remember those?)
and developed the solution for ring loading. My thanks to my dear
friend. (More applause)
Mounting mirrors with
elastomers (of 2-6-12) The optics community has been searching for the
perfect “athermal” mounting scheme for years. Guess what, there
isn’t one. This is one of my contributions to the lore. Love (and
Timoshenko) made me do it. My thanks (posthumously) to Alexander and
Stephen. (More applause)
Stabilizing lines of sight (of 7-12-11) I teased the servo engineers, the structural engineers and the
“optikers” somewhat mercilessly. It was entirely
rhetorical. They were the heroes of the story. No one gets down to
microradian stability levels on moving earth-bound vehicles unless they all
have done a very good job. My thanks to the servo engineers, structural
engineers and “optikers.” (Still more applause)
Co-inventing a remote sensor (of 4-17-12) An optical designer friend thought my nanometer-class structural
actuators with his lens design skills would be the solution. He was
wrong. The best approach was an entirely optical solution, with his lens
design skills and somewhat more complicated optics. It worked. And
I got to do the mechanical design! My thanks to my optical designer
friend. (And yet more applause)
My list is nearly endless. And each of you has been a stimulus, a
catalyst and a joy to have as a friend and a colleague.
Now, all of you, step forward and take a
bow (or two or three). (Deafening applause)
Thank you all for allowing me to participate in your adventures.
It was a great gathering in Orlando last month: conferences, classes, banquets
and above all friends.
I was invited to address a meeting of engineers whose topic was
“Acquisition, Tracking, Pointing, and Laser Systems.” I sat in
a dark room staring at a bright screen and listened for two hours to electrical
engineers talk about stabilizing lines-of-sight. They all showed
amazing slides of flow diagrams and control systems: resolvers, torquers,
Bode plots, gyros, transfer functions, encoders, phase margins, accelerometers,
amplifiers, feedback loops, etc. Not one single slide showed a
line-of-sight, an optic, a laser beam or a target.
I was last on the agenda. I opened by pointing out that lines-of-sight
and laser beams were real physical features, just as real as the axis of
rotation of a gyro. Then I demonstrated a way to link the lines-of-sight
of imagers and lines-of-propagation of lasers to inertial sensors through
elastic behavior of finite element models. Then I showed an analysis in
which the rms error between the gyro and the laser was about twice as big as
the gyro’s rms error itself. “Was the laser-to-gyro error in their
budget,” I asked, “or in the optical designer’s?”
“What about the imager-to-gyro error?” The audience seemed to
have some difficulty answering my queries and also some framing their own, but
they were very gracious. We shook hands and then, suddenly it seemed, I
was outside standing in the warm Spring afternoon sunlight. Perhaps I’d
been impertinent.
A week or so later, back in the office, I received an invitation from the engineers to publish my remarks in their prestigious journal, The Journal of Applied Remote Sensing. I guess I was not too impertinent. It’s a fine balance; someone has to identify the possibility, tickle the imagination, “stir the pot” and, sometimes, “serve the first dish”. I’ve accepted this invitation too.
I have one relic from the event to commemorate it. That’s the slide of
mine showing a laser beam and an IR imager coupled to a gyro’s axis of rotation
through a finite element structural model of a sensor suite.
It was in deed a great gathering in Orlando last month. And, ahh… the friends! Thank you all.
Now… Summer is nigh. Get out the sun-block and water skis.
