How to perform surface tilt & decenter (& surface irregularities) tolerancing in non-sequential mode ?

  • 15 December 2023
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For some use-cases it is more convenient to use pure non-sequential mode, for multi-pass systems for instance. Performing a tolerance analysis for surface tilts & decenters is not available with standard non-sequential tolerance operands:

  • TNPS can be used of course for element tilt & decenter,
  • TNPA can be used to tolerance the object parameter values, but surface tilt/decenter is not a parameter for most non-sequential geometries (standard lens, even asphere, for instance)

An option is then to use the compound lens object, together with Biconic Zernike Surfaces:

The Biconic Zernike Surfaces can be used to model a wide range of lens shapes, from standard to biconic, aspheres and Zernike Standard Sag Surface, as their sag is a combination of those sag definitions:

The other benefit of using this particular type of surface is that it also has tilts & decenters parameters:

  • Zernike terms Z2/Z3 can be used for X/Y tilts, for each surface,
  • Biconic Zernike Surfaces have built-in X/Y decenter parameters

They correspond to the following TNPA operand parameters:

As you can choose the number of Zernike terms that you can have for each Biconic Zernike Surface, you can also use the same approach to tolerance for Zernike surface irregularities.

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