on-machine measurement for precision corrective-polishing...
TRANSCRIPT
![Page 1: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/1.jpg)
1
On‐machine Measurement for Precision Corrective‐polishing ofAspheres and Freeform Surfaces
David Walker, Christopher KingUniversity College London
Zeeko Ltd & Zeeko Research Ltd
Based at the OpTIC Technium, North Wales
![Page 2: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/2.jpg)
2
Sub‐title
An update on an on‐going product development
Acknowledgements
• Funding from PPARC (now STFC) PIPSS scheme
• Collaboration between UCL, Zeeko Ltd and the OpTIC Technium
![Page 3: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/3.jpg)
3
Areas of interest include …• Optical lenses and mirrors
– Head‐up displays
– Defence and space optics
– Telescope and instrumentation optics
• Hip and knee joint implants
• Turbine blades
• Moulds and dies
• Mandrels for X‐ray mirrors
• But, we’ll address larger components for now!
![Page 4: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/4.jpg)
4
The polishing technology• Range of CNC polishing machines
– Zeeko‐Classic inflated bonnet tools– Fluid‐jet polishing
• Polish rough surfaces• Rectify measured form‐errors
Run machine
Measure surface
form-error
Measure tool removal function (‘influence
function’)
Numerical optimisation of process
Iterate
Finish
![Page 5: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/5.jpg)
5
Aspheres & free‐form surfaces• Measurement dynamic range• Need for null (‘corrective’) optics
– The Hubble Space telescope problem!
For large parts
• Risk of damage in handling• Substantial down‐time measuring off‐machine,
– moving the component– re‐adjusting at test setup and back on machine – thermal stabilization
![Page 6: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/6.jpg)
6
![Page 7: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/7.jpg)
7
A case study• European Extremely Large Telescope project
– 42m optical telescope with 960 hexagonal segments
– Each segment:‐ 1.4m off‐axis asphere– Total requirement of 1,148 segments (inc. spares)
• Contract at OpTIC Technium to produce seven prototype segments using Zeeko technology
• Particular issue of measuring segment edges
• Role of on‐machine metrology
![Page 8: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/8.jpg)
8
On‐machine metrology
• Demountable interferometer module to fit tool‐chuck of the larger Zeeko machines
• Overlapping sub‐aperture measurements– Sub‐apertures cover pupil optimally
– Sub‐apertures are stitched in software
– Residuals in overlap‐regions => estimate of uncertainty of stitched results
![Page 9: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/9.jpg)
9
Advantages
• Increased dynamic range for on‐ and off‐ axis aspheres
• Close‐up test reduces effects of air‐turbulence
• Increased spatial resolution (more pixels)
• Handle large parts
• Handle steeply convex parts
• Possible application to convex/concave parts (e.g. saddles)
![Page 10: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/10.jpg)
10
Key issues
• Size‐envelope of module
• Environmental conditions– Vibration:‐ ambient, machine servos
– Heat‐load from machine and process
• Effectiveness of stitching software
![Page 11: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/11.jpg)
11
Test‐rig for software development
Stepper‐motor rolling‐element slide‐ways
Old Zygo PTI interferometer with Vidicon
Vibration‐isolated bench
![Page 12: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/12.jpg)
12
Stitching• Individual phase‐maps require correction for geometric distortion
• In the general case, stitching will not work well without distortion correction, especially on strongly‐curved surfaces.
Distortion in optical system
![Page 13: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/13.jpg)
13
Effect of distortion
![Page 14: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/14.jpg)
14
Stitching
• Stitching then proceeds by optimization of the residuals in the overlap areas.
• The stitching error is estimated from residual noise, merit function and analysing data in the sub‐aperture overlap areas.
![Page 15: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/15.jpg)
15
Example stitching a convex part
![Page 16: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/16.jpg)
16
First results 1. Full aperture measurement
![Page 17: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/17.jpg)
17
2. Raw sub‐aperture measurements
![Page 18: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/18.jpg)
18
3. Comparison
![Page 19: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/19.jpg)
19
4. Differencefull-aperture & stitched
PV=92 nmRMS 11 nm
Much of the residual error is systematic. Calibration is predicted to leave a few nm residual.
Expect residuals ~ X10 improvement after calibration
![Page 20: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/20.jpg)
20
Stitching a part with complex features (140mm diameter)
![Page 21: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/21.jpg)
21
Stitched result
![Page 22: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/22.jpg)
22
Module design: vibration and thermal • Collaboration with 4D Technologies Corp.
– 4D are developing a compact version of their simultaneous phase‐shift interferometers
– Short exposures freeze vibration
• Interferometer tests in machine environment confirm suitability for metrology– Polishing environment is flooded with polishing slurry at constant temperature when in use.
![Page 23: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/23.jpg)
23
Module concept in polishing machine
X,Y,Z,A,B motions
![Page 24: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/24.jpg)
24
Next stages
• Validate stitching on aspheres• Evaluate prototype 4D compact interferometer
• Integrate optics and interferometer into on‐machine module
• Formal consideration of uncertainty of measurement
• Delivery of first commercial system
![Page 25: On-machine Measurement for Precision Corrective-polishing ...resource.npl.co.uk/docs/networks/eman/meetings/20090129_high_accuracy/... · Precision Corrective‐polishing of Aspheres](https://reader030.vdocuments.net/reader030/viewer/2022040715/5e1e84ee1af0ff601278edac/html5/thumbnails/25.jpg)
25
Thank you!