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This article is about the CAD program, PLOP. For the computer language conference group, PLoP, see Pattern Languages of Programs.

PLate OPtimizer, or PLOP is a CAD program developed by telescope maker David Lewis, first described in 1999,[1] and used to simplify calculations needed in the design of mirror support cells for telescopes.[2] It was based on Toshimi Taki's 1993 program PLATE[3], however provides a simplified user interface, thus giving it wide acceptance among makers of large Dobsonian telescopes, with good support of mirrors as thin as two inches for a diameter of thirty inches.[4]

Comparisons and limitations

A basic mirror cell may be built using minimal calculation and simple materials such as wood and outdoor carpet, with a good example being Dobson's original telescopes. However as amateurs sought to build larger and thinner mirrors they found such designs inadequate.

Many amateur telescope makers use cells which are designed via equal area rule calculation, using programs such as David Chandler's public domain program, Cell.[5] However such calculation does not account for mechanical stresses introduced from one part of the mirror to another. For this reason finite element analysis is becoming more commonly used to reduce such stress. Although general finite element analysis programs such as Nastran will work for mirror cells PLOP is currently more popular in part because can can be set to ignore deformation which merely results in refocus of the mirror's parabola.[6] It is useful to calculate floating support points for mirror axial (rear) support however additional tools are needed to calculate potential error from mirror lateral (edge) support.[7]

Mirror cell calculations, whether using PLOP or another program, do not overcome error introduced by gluing the mirror to its cell, excessive tightening of edge supports nor impingement of the cell structure onto the mirror as result of differential cooling shrinkage. The significantly more complex calculations arising from the support needs of large honeycomb mirrors and those using active optics systems are outside the design parameters of such programs.[8]A basic mirror cell may be built using minimal calculation and simple materials such as wood and outdoor carpet, with a good example being Dobson's original telescopes. However as amateurs sought to build larger and thinner mirrors they found such designs inadequate.

Many amateur telescope makers use cells which are designed via equal area rule calculation, using programs such as David Chandler's public domain program, Cell.[9] However such calculation does not account for mechanical stresses introduced from one part of the mirror to another. For this reason finite element analysis is becoming more commonly used to reduce such stress. Although general finite element analysis programs such as Nastran will work for mirror cells PLOP is currently more popular in part because can can be set to ignore deformation which merely results in refocus of the mirror's parabola.[10] It is useful to calculate floating support points for mirror axial (rear) support however additional tools are needed to calculate potential error from mirror lateral (edge) support.[11]

Mirror cell calculations, whether using PLOP or another program, do not overcome error introduced by gluing the mirror to its cell, excessive tightening of edge supports nor impingement of the cell structure onto the mirror as result of differential cooling shrinkage. The significantly more complex calculations arising from the support needs of large honeycomb mirrors and those using active optics systems are outside the design parameters of such programs.[12]

See also

Notes

  1. ^ Lewis, David (1999), Sky & Telescope (June): 132–135 {{citation}}: Missing or empty |title= (help)
  2. ^ Holm, Mark. "Mirror Cells for Amateur Telescope Makers". Retrieved May 3, 2009. {{cite web}}: Cite has empty unknown parameter: |coauthors= (help)
  3. ^ http://www.asahi-net.or.jp/~zs3t-tk/cell/cell.htm Taki's brief intro to cell design
  4. ^ Anderson-Lee, Jeff. "Best of 18 and Over - A collection of plop cell designs". Retrieved May 3, 2009. {{cite web}}: Cite has empty unknown parameter: |coauthors= (help)
  5. ^ Chandler, David, Floatation Mirror Cell Design, retrieved 2009-06-21
  6. ^ Atmsite PLOP FAQ
  7. ^ http://www.cruxis.com/scope/mirroredgecalculator.htm Cruxis site mirror edge support calculator tool
  8. ^ http://medusa.as.arizona.edu/lbto/tech/ua9502.htm Mirror Support System for Large Honeycomb Mirrors
  9. ^ Chandler, David, Floatation Mirror Cell Design, retrieved 2009-06-21
  10. ^ Atmsite PLOP FAQ
  11. ^ http://www.cruxis.com/scope/mirroredgecalculator.htm Cruxis site mirror edge support calculator tool
  12. ^ http://medusa.as.arizona.edu/lbto/tech/ua9502.htm Mirror Support System for Large Honeycomb Mirrors

External Resources

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