Making and Meeting Requirements

1
Making and Meeting Requirements

• Chris Sillman
• National Optical Astronomy Observatory

2
NEWFIRM

• NOAO Extremely Wide-Field Infrared Imager
• For use on Kitt Peak
• What is it?
• Instrument for science
• But what is it?
• That is what requirements are for.

3
Image Quality Requirements

• Top Level Requirements
• Instrument cannot degrade telescope image by more
  than 5
• Derived Optics Requirements
• Optical assembly cannot degrade telescope image
  by more than 1.5
• Must have tolerance budget showing top level
  requirement is met

4
More On Optics Requirements

• Tolerance budget must include
• Fabrication
• Flexure
• Thermal effects
• Ghosting
• Stray Light

5
Lets Talk About Fabrication

• Nuthins perfect
• Must account for manufacturing errors
• How close does it have to be?
• Tighter tolerances Higher cost
• Where do you draw the line?
• For NEWFIRM, all the weight on three lenses

6
Hierarchy of Lenses

• Lens Group 1 (the tough ones)
• Lens 1
• Conic, 16 Diameter, entrance window
• Lens 4
• Conic, 5.5 Diameter, optical mid-point
• Lens 8
• Conic, 6.5 Diameter, final optical element
• Max radius tolerance /- 0.100 mm

7
Hierarchy of Lenses

• Lens Group 2 (the easy ones)
• Lenses 2,3,5,6,7
• All spherical, 7.9 Diameter Max.
• Fold Mirror
• Flat (half-wave at 633nm), gold coated
• Max radius tolerance /- 1.00 mm

8
Who Should Make These Parts?

• Specify all lens parameters
• Build up a Bid Package
• Complete 2-D Drawings
• Additional specification sheet (optional)
• Send the package out for bid

9
Bid Results

• 10 Vendors Contacted
• Main Factors
• Cost
• Lead time
• May I have the envelope, please?
• University of Arizona Optical Sciences Center
• Janos Technologies

10
What is the Sticker Price?

• Lens Group 1 (the hard ones)
• Total delivered cost 237,000
• Recall Only 3 elements!
• Lens Group 2 (the easy ones)
• Total delivered cost 112,000
• Recall 6 elements

11
Verifying

• Optical Sciences is still working
• No data yet
• Janos is almost complete
• Precoat source inspection
• Lenses 2,3,5 and 7
• Flat mirror
• Lens 6 is still being figured

12
Precoat Source Inspection

• NOAO representative must go to Janos
• Verify testing procedures
• Verify results
• Troubleshoot any problems that arise

13
Wedge (Runout)

• Edge profile technique
• Good points
• Doesnt drag on surface
• Relatively Safe
• Bad points
• Only uses discrete amount of points
• Max. value recorded unlikely
• All recorded values were 4-7X under spec.

14
Center Thickness

• Maximum profile
• Good points
• Safe when the probe is lifted, not dragged
• Bad points
• True vertex may not have been found
• Lens 5 and Lens 7 both FAILED this test

15
Outer Diameter

• Large gap micrometer
• Good points
• High accuracy of individual reads (0.0001)
• Bad Points
• Multiple reads required, Lens may be oval
• Largest deviation
• 27 microns

16
Radius of Curvature

• Fizeau interferometry
• Good Points
• Accurate
• Bad Points
• Relies on opticians estimate
• Surface contact with polished glass
• Worst case
• 0.027 mm too long

17
Fold (Flat) Mirror

• 12 Zygo Interferometer
• Problem!
• 0.592? with power included
• 0.128? with power removed
• Whats finish and what is irregularity?

18
Scratch and Dig

• 80/50 specified
• Only one scratch detected
• Lens 7
• 120 scratch, 4mm
• Mechanical problem

19
Issues

• Center thickness of lens 5 and lens 7
• Too thin
• Surface irregularity of flat mirror
• Power on or power off
• Scratch on lucky lens 7

20
Center Thickness Resolution

• We will accept the lenses at a reduced price
• Compensate for CT difference with lens spacing
• Price break to pay Optical Engineer to re-optimize

21
Scratch on Lens 7 Resolution

• Janos will rework the piece
• Additional Requirements
• Must maintain original OD above and below scratch
  area
• Spring finger lens cell contact
• No risk to NOAO
• We havent bought it yet

22
Flat Irregularity Resolution

• Oops, my bad
• Optical engineer failed to check terminology
• Industry standard
• If not specified,
• overall surface flatness 4 surface
  irregularity
• Janos Technology
• Doesnt impact operation enough to matter

23
Verification Summary

• All optics meet specifications or are within
  acceptable overage
• Acceptable optic components means optical image
  degradation lt1.5
• Acceptable optical assembly means telescope image
  degradation lt 5
• Top level requirement