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.

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