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
