Optomechanics – How the Instrument Might Fail

Dear Colleagues:

I had a terrific group of students for my class, “Optomechanical Analysis,” at Photonics West.  It was a generous mix of the disciplines that support the optical industry.

One of the things I teach is how I calculate the ways in which the nearly-a-myriad mechanical design variables can affect the performance of an optical instrument.  A simple example I use is the net effect of tolerances on the position, orientation and size of the image.  The tolerances I address include those on the optical elements themselves.  This allows the engineering team to balance the mechanical tolerances and the optical tolerances.   I take the sum of the absolute values of the effects of the individual design tolerances. 

I am usually challenged by at least one of the students that the root-sum-square of the effects gives a more reasonable value for an assembled instrument.  I respond that as optical instrument designers they are right.  But, I add, as a mechanical engineer I’m also concerned about how the instrument might fail and that the sum of the absolute values gives me better insight into that eventuality, ie., how it might fail in the assembly and alignment process.  I have found that insight very valuable.  The analysis not only alerts me to possible worst-case scenarios it identifies the major contributors to the problems and suggests available corrective actions. 

All in a day’s work.

Ciao, from Baghdad by the Bay.

There will be more, but after Valentine’s Day.

Al H.
2-7-13

Optomechanics – Optomechanics and the Tolerancing of Instruments

Colleagues:

I will be presenting my tutorial “Optomechanics and the Tolerancing of Instruments” in San Diego on August 13th during SPIE’s Optics and Photonics Symposium.  The course is primarily intended for mechanical engineers and designers in the optics industry and may be of interest to other optics professionals as well.

In the tutorial I develop the full theory of the Optomechanical Constraint Equations (OCE).  They relate the position, orientation and size of an image to the position and orientation of each of the optical elements that form it.  I work through numerical examples to assist the student’s understanding and illustrate the application of the OCE with examples, static and dynamic, from my engineering practice.

The OCE are the basis for the AEH/Ivory Optomechanical Modeling Tools (version 2.6 currently available) that are the mechanical engineer’s first choice for design and analysis of optical systems.

For more details on  the course visit SPIE’s web site,


http://spie.org/app/program/index.cfm?fuseaction=COURSE&export_id=x30628&ID=x30533&redir=x30533.xml&course_id=E1036499&event_id=896190&programtrack_id=1038730


or send your questions to me.

I’ll also be hosting an evening meeting of the Optomechanical Technical Group, probably on Tuesday (but more on that later) as well as cruising the conference rooms, receptions and exhibit halls.  It’ll be a big week!

Hope to see you all in San Diego from August 12th through the 16th.

Al H.
5-7-12

Optomechanics – Bridge the Chasm (between the optical and mechanical domains)

Mid-winter greetings!  Condolences to my Northern California friends about the snow-pack in the Sierras.  Perhaps we can import some from Europe.  It’s one of the things they seem to have in surplus this year.

Structural mechanics is the very nexus of optomechanical engineering.  It has been since at least 1638, the year that Galileo Galilei wrote in his journal, “If I push on this beam how far will it bend and when will it break?”  With that query he became the recognized father of the structural mechanics art.  That was some 28 years after he had turned his telescope on the heavens to become the father of astronomy.  It took even that great man a long time to recognize that the structure of his telescope was essential to stabilizing the planetary images on his retina.  That nexus remains nearly as obscure and difficult today as it was then.  I discuss this situation in my dinnertime talk, “Bridging the Chasm.”

The awkwardness between optics and structures was brought home to me again in a recent project.  I had an opportunity to help a colleague evaluate the stability of the images in a spectral imager.  I built-up the instrument’s structural model from step files generated by the CAD engineer.  I had some challenges in the meshing processes in Patran:  unresolvable singularities, wicked element geometry and that sort of thing.  Checking out the full mechanical model with six degree of freedom rigid body motions and three axis static gravity loads helped to correct the problems in the elastic model

The optical designer gave me a set of influence coefficients he’d prepared in Zemax and I modeled those into the Nastran deck manually.  I was unable to get reasonable results from the optical model in the check-out runs.  In the analysis runs the image motions were wildly, incredibly, out-of-bed.

I was able to show, using an Ivory-generated set of influence coefficients that the structure was behaving reasonably.  The Ivory model should have behaved somewhat like the optical designer’s model, but it didn’t.  The optical designer and I sat down and went through all he and I had done.  I, for some reason, could not relate his optical coordinate systems to my structural model coordinate systems.  We finally agreed to prepare a new set of influence coefficients based upon revised simple coordinate systems. 

Bingo!

Once we took the time to “bridge the chasm” the modeling problems disappeared and engineering could begin.  There are a lot of opportunities for misunderstanding and misinterpreting numbers moving between the optical and mechanical domains.

From optical image correlators to off-axis spectral imagers Ivory has proven to be my indispensable optomechanical engineering tool.

Al H.
2-2-12

Optomechanics – Training and a Party

Colleagues:

Well, Spring finally decided to arrive.  It was almost 60 degrees in Pasadena yesterday!

 And I’ll be going to Orlando shortly, on the 25th, to celebrate the season.  That’s not exactly true:  I’ll also be presenting a paper on how the mechanical engineer assures that the laser system and the imaging system stay aligned with the gyro (or other inertial sensors) in a stabilized sensor suite.  That’ll be on Tuesday morning, the 26th, about 11:40.

Then I’ll celebrate.  Oh, but only a little, because on Wednesday, the 27th, I teach class all day (Optomechanical Analysis).  Then I’ll really celebrate, at the banquet that night.
SPIE’s Symposium on Defense and Security is a great gathering!  I’ll be there most of the week and I hope I’ll see many of you there.
Come and celebrate too!

Al H.
4-12-11

Optomechanics – Training

Colleagues:

This is just a reminder that I’ll be presenting my full-day tutorial “Optomechanical Analysis” in Orlando on April 27th during SPIE’s Defense and Security Symposium.

The class is primarily for mechanical engineers who work in the design and analysis of optical instruments and systems.  But it may also be of interest to other professionals in the optics industry.  Review the course description and reserve a seat in the classroom.

I hope to see a great number of you in Orlando next month.

Al Hatheway
3-22-11


Optomechanics – Lots of Trainings

Colleagues:

The cooling of the weather is a clear indication that Winter is coming, not withstanding the wild fires we’ve recently had here in Southern California. All of the holidays from Thanksgiving to Valentine’s Day are just around the corner. Here are a few items on my agenda for next year:

Once again I’ll be teaching my one-day short course,

Optomechanical Analysis

830 AM to 500 PM
January 27, 2009

in San Jose during SPIE’s Photonics West Symposium. You may learn more about the course content and register to attend by clicking on the following exciting link;

http://spie.org/app/program/index.cfm?fuseaction=COURSE&export_id=x12502&ID=x6771&redir=x6771.xml&course_id=E0846163&event_id=795339&programtrack_id=848771


In April I’ll be teaching another short course,

Optomechanics and the Tolerancing of Instruments

in Orlando during SPIE’s Defense and Security Symposium. More on this later.


Next summer in San Diego we’ll have our two-day conference,

Advances in Optomechanics

During SPIE’s Optics and Photonics Symposium. This will include an evening meeting of the International Technical Group on Optomechanics.


I look forward to a great year. I hope you enjoy the Holiday Season and perhaps I’ll see you in San Jose in a few weeks.

Al Hatheway
11-25-08

Optomechanics – Training

Colleagues:

The last couple of months have been just frantic with activity and I have not had time to remind you that I’m offering my tutorial,

Optomechanical Analysis,

just less than four weeks from now,

Tuesday,January 22, 2008,

during Photonics West, SPIE’s Symposium in San Jose, California.

If you know anyone who may want to take the course please pass along the registration site,

http://spie.org/app/program/index.cfm?fuseaction=COURSE&export_id=x13090&ID=x16885&redir=x16885.xml&course_id=E0833634&event_id=774275&programtrack_id=840931 ,

(that’s a piece of cake, right?).

I hope you all are having a wonderful Holiday and that I’ll have a chance to visit with each you in the coming Happy New Year, 2008.

Al Hatheway
12-26-07