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Ultra Precision Engineering- some recent developments
Professor Pat McKeown OBE FREng
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What is Precision Engineering?
It is multi-disciplinary, based heavily on the application of metrology(dimensional and thermal) to manufacturing, and covers materials, machining and fabrication processes, design of high-precision machines, mechatronics and thus, microsensors, servo-drives, actuators, high speed control systems, etc.
Precision Engineering means working to tolerances from 1 part in 104
(McKeown, P.A.,1979) …. but now reaching 1 part in 108
this is “ Ultra-Precision Engineering “ “Precision Engineering involves working at the forefront of current
technology.” (Jones, RV 1979)….it still does! Precision Engineering has led to the ultra-precision technologies of
_ Micro-engineering.Engineering nanotechnology.
1970
1980
1990
2000
CNC controlCNC control
Radius toolsWaviness < 1 µm
Radius toolsWaviness < 1 µm
Waviness < 0.1 µmWaviness < 0.1 µm
Encoder feedback < 100 nmEncoder feedback < 100 nm
Ultra-precision air-bearing spindlesUltra-precision air-bearing spindles
Glass scale feedbackGlass scale feedbackMulti-axis machines and FTS turningMulti-axis machines and FTS turning
From Brinksmeier & Courtesy: Moore Nanotechnology Systems , ALMT
Non-circular cutting edgesNon-circular cutting edges
1960
Microtome knivesMicrotome knives
2010
Development of single point diamond machining
Development of spdt machinable geometries
Off-axis MirrorsOff-axis Mirrors
FTS-turned moulds and mirrorsFTS-turned moulds and mirrors
19601970
1980
1990
2000
Freeform surfacesFreeform surfaces
Triangular microprismsTriangular microprisms
Aspheric IR opticsAspheric IR optics
2010
From Brinksmeier & Courtesy: Moore Nanotechnology Systems , ALMT
Chemical wear in diamond machining
From Brinksmeier, Bremen
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Diamond turning process capability….nanotechnology
Ref, Ikawa & Donaldson, circa. 1990
Undeformed chip thickness of 1nmon amorphous copper
Ref, Technodiamant
7400 mm dia Axicon for space laser systems
8
Diamond micro-tools manufactured using focussed ion beam machining
Ref. Adams, Sandia Nat. Labs. California
Diamond machining of prism arrays
1980sTriangular prisms
2010sHexagonal prisms
Fly-cutting of intersecting systems of V-grooves
Fly-cutting of intersecting systems of V-grooves
Micro-chisellingof corner cubesMicro-chisellingof corner cubes
From Brinksmeier, Bremen
The NION Nanocentre Diamond Machining Centre (1990)the world’s most accurate machine tool of its size
Thermal stability of the NION machineprovided by 5 advanced temperature control systems (+/- 0.001 deg C)
Ref, McKeown, Carlisle, Shore, 1990
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James Webb Space Telescope Infrared Spectrometer Image Slicer
Mirror 12 Mirror 11
29 mm
Mirror 1
Ref, Cranfield University Precision Engineering Centre
Individual mirrors: 12 x 1mm Form error: < 10nm RMSCurvature radius: 162.5mm
13
James Webb Space Telescope – Launch 2017
Integrated ScienceInstrument Module ~
spectographic analysis
Infrared optimised space telescope searching for first galaxies formed in the Universe
14
Ultra Precision Large Roll Diamond Turning Machines
designed and produced at Cranfield Precision (from 1992)
Workpiece Accuracy< 1 micron per metre
Workpiece weightup to 2000 Kg
Oil shower temp control
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Ultra Precision Manufacturing capability for structured drums
Purpose built facility @ OpTIC
Clean room class 10,000
Lab temperature control +/- 1ºC
Enclosure temperature control +/- 0.1ºC
Active vibration isolation
Replicating film from a structured drum
UV-curing Extrusion
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Applications for micro-structured films
Solar Energy
0
20000
40000
60000
80000
100000
120000
140000
1996
1998
2000
2002
2004
thermal collectors photovoltaics
Optical films: solar concentrators and antireflection film, increasing efficiency, reducing silicon costs
Displays
020406080
100120
US$
Bill
ions
tu
rnov
er
2003 2005 2007 2009
Flat panel CRT
Optical films are utilised in all flat panel displays for backlighting, depixelation, 3D displays etc.
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Applications for micro-structured films
Security
Identity fraud:~ 25 billion US$ p.a. Optical security devices business ~ 1.25 billion US$ growing 12% p.a. Applications - fraud prevention: note printing, securency, ID, etc.
Lighting / illumination
Film-based lighting market expected to total US$10 billion by 2010 including domestic and industrial applications using LED and OLED technologies
Ultra precision optics demands
Lithography - EUV [ASML] Microlithography Systems
Fusion - Focusing lens “wedge” optic
Space - IXO telescope mirrorTelescopes
E-ELT
European Extra Large Telescope (ELT)[the 400th year of the telescope…..Galileo 1609-2009]
E-ELT
42 metre diameterprimary mirror
Aspheric primarymirror design basedon 984 x 1.46 metre hexagonal segments
6 metre diametersecondary monolithicdeformable mirror adaptive optics
Ref: www.eso.org “operational by 2020” “estimated cost €950m”
E-ELT primary mirror design having ~ 9841.46 metre hexagonal segments
Form accuracy : 20 nm RMS, roughness 1 nm RMS
Ref, www.eso.org
1 part in 108 relative precision of form accuracy to size
Primary mirror• 42m diameter• Far off-axis ellipsoidal form• 984 segments @1.46m
7 Prototype Segments from peripheral region
Process Chain
Develop grinding and support technology for the aspherisation of large metre scale optics
Machine; Grinding Process; Metrology; Handling
Aspherisation
Grinding Requirement:
• 1 Segment per day
• 1mm material removed
• 1µm form accuracy
• No edge chipping or roll-off
Major new UK-based research initiative - processing time for large (1+ metre scale) freeform optical surfaces reduced from 100 hoursto 10 hours
Ultra Precision Machining Technologies
“ductile” mode grinding
0.01 0.1 1 10 100 1000
IBF RAPT
Fixed abrasivegrinding
Computercontrolledpolishing
MRF
1000
100
10
1
0.1
Removal Rate [mm3/minute]
Rou
ghne
ss [n
m] R
MS
diamond turning
1
2
3
Grinding machine• Free-form grinding capability
• Hydrostatic bearings
• 10 KW grinding power
• High performance thermal control (±0.1˚c)
• Integrated metrology capability
• Rapid material removal rate, (200 mm3/sec)
• Form accuracy < 1 µm/m RMS
• Low sub-surface damage < 10 µm
• Compact machine size
http://www.hembrug.com
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Cranfield University BoX® Machine
Ultra-precision, ultra stiff 3 axis freeform grinding machine for large optics up to 2 metres diameter
Truing/dressing
Grinding wheel
Grinding spindle
Metrology frame/optical straightedge
All axes/spindle oil hydrostatic
Laser interferometer / LVDT metrology
Ref: Shore/Morantz (2006)
Lowest control and structural eigenfrequencies > 100 Hz
Z axisMini-laser
interferometer
LVDT probes
Workpiece
Optical Straightedge
X axis
Workpiece metrology has full system
accuracy ~ 0.25 μm
Workpiece Metrology
www.cranfield.ac.uk
Low cost high performance temperature control Use a commercial unit to provide cooled water to
a pumped loop Divide cooled water between services using
mass flow control Complex algorithms to control cross-talk Total of 11 channels of temperature control
– mK resolution , << 0.1 °C accuracy Services located with machine (chilled water
supply is remote)
Grinding motion
20°
C X
Z
Free-form grinding
capability
• Novel 3 axes configuration
• R-theta grinding mode
• Toroidal shape grinding wheel
• Sophisticated toolpath software
XZ
C
Grinding technology
Grinding Conditions Grit size (µm)
Depth of cut (µm)
Feedrate(mm/rev)
Work speed
(mm/s)
Cutting speed
(m/s)
MMR
(mm3/s)
Rough cut (D76) 76 500 15 25 30 187.5
Semi‐finish cut (D46) 46 200 10 20 30 40
Finish cut (D25) 25 50 1.5 25 30 1.87
Multi-stage grinding process
Grinding Wheels• 325mm DIA• Resin bond• D25, D46, D76• 50 concentration
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Mirror segment (1)…CMM Metrology
• ELT segment SPN01 (15:15)
• Material – Zerodur
• 580,000 measurement points
• Data to within 0.5mm of the edge.
Results: • Surface map (CMM)• RMS < 1 µm, P-V < 5.5 µm • No visible edge chipping• No attributable cavity effect • Some error attributable to the CMM
Mirror segment (2) CMM Metrology
• ELT segment SPN04 (16:15)
• Material – ULE
• Grinding cycle 20 hours
• Max MMR 187.5mm3/sec
•Results: • Surface map (CMM)• 580,000 measurement points• PV < 4.5 µm • RMS < 0.6 µm
Final figure correction
Figuring requirement:• 1 Segment per day
• Form accuracy < 20 nm RMS
• Surface roughness < 1 nm RMS
• Removal of process signatures
Major new UK-based research initiative – processing metre scale freeform optical surfaces
Reactive Atom Plasma Figuring
Developing RAP technology for the final figuring of large metre scale optics
RAP technology
Dimension (mm)
Sur
face
dev
iatio
n (n
m)
• Dry etch process – fluorine based gasAtmospheric pressure processing • Gaussian beam distribution• Dwell time based raster figuring algorithm• No induced SSD
Rapid nanometer dexterity surface process for figure correction of ultra precision metre-scaleoptics. Technology employs inductively Coupled Plasma Torch.
RAP facility
• 3 axes CNC Fanuc motion control• Low cost operation • 1.2 m capacity• Compact machine size
Refs1: Jourdain et al., (2011). “Fast 3D Figuring of Large Optical Surfaces Using Reactive Atom Plasma (RAP) Processing”, 2nd EOS Conference on Manufacturing of Optical Components, Munich (D), May 2011.2: Castelli et al., (2010). “Initial Strategies for 3D RAP Processing of Optical Surfaces Based on a Temperature Adaptation Approach” 36th Matador Conference, Manchester, section:18, pp 569-572 , July 2010
Processed materials: • Fused silica
• ULE
• SiC
• Silicon
• Borosilicate
Expected processing time for NIF focussing lens
• 420 mm x 420mm surface
• 2 iteration process
• Removal depth of 1µm
• Average MMR 1.5 mm3/min
• Figuring time ~ 3 hours
• x10 times faster than IBF
Contact: Prof Paul Shore, Precision Engineering Centre, Cranfield University, UK
Spherical surface results
rms: 80 nm
Spherical hollow
500 nm depth
Spherical form Residual error
18 nm RMS
146 nm PV
Courtesy of Paul Morantz –peacock butterfly (2004)
Thank you for your attention
Summary – Rapid production of large freeform surfaces
Acknowledgements:
The authors acknowledge funding support from the UK research councils’ Basic
Technologies Programme, the EPSRC Integrated Knowledge Centre in Ultra Precision
and Structured Surfaces (UPS2) and the McKeown Foundation.
• Polishing• Form accuracy < 16.8 nm RMS
• Reactive Atomic Plasma• Removal rates up to 1.5 mm3/s
• Grinding• Removal rates up to 187.5 mm3/s
• Grinding time 20 hours - 1.45 m ELT segment
• Form accuracy < 1 µm RMS, SSD < 10 µm
• Form accuracy < 16 nm RMS
• No induced SSD
Wheel form
Truing imparts toric wheel form using formed electroplate wheels
Dressing using AlO stick Wheel profile imprinted onto soft
dressing stick can be measured in-situ and used to compute wheel shape/wear
A full multi-pass grinding cycle may take 10 hours – wheel wear compensation critical to maintain accuracy
Inclined spindle configuration
Simulation of contact point compensation
Ref: Shore, P. et al., 2005
Mirror segment processingSegment fixture• Transportation• Metrology• Loading• Grinding• Location using master spheres
Grinding
• Input spherical form• 1mm material removed• Finish grind
• D25 wheel• 50 um depth of cut• Compensated path
Lithography is at the heart of i/c chip manufacturing
Repeat 30 to 40 times to build 3
dimensional structures
1 part in 108 relative precision of form accuracy to size
Advanced DUV Lithography Systemsemploy fused silica optics of up to 250 mm diameter having form accuracy of 2.5nm RMSand roughness < 0.5nm RMS ; 38nm linewidths……….the ASML TWINSCAN……………… Ref, Zeiss SMT
1nm
wavelength
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EUV / soft X-ray lithography scheme (ASML Veldhoven )
laserpump lens
reticle stage
wafer stage
illuminator
49
EUV / soft X-ray lithography scheme reflective optics (ASML)
EUV (extreme ultraviolet)
– λ = 13 nm– linewidth < 35nm
(potentially 10nm)– reflective optics
essential (no available EUV transparent materials)
– tilt control of mirrors is highly critical
NXE:3100 first shipment Q4 20101st generation of the NXE platform
NA=0.25 Sigma=0.8 Resolution 27 nm SMO=4.5 nm MMO=7.0 nm Productivity
60wph at 10mJ/cm2 resist
51
We’ve Come a Long Way in 60 years!
One transistor/cm2
Dec. 23, 1947Today: Each die contains 500
million transistors/cm2
Process Chain
Computer control polishingMachine; Polishing Process; Metrology; Fixturing
Polishing
Requirement:
• 20µm material removed
• 20nm RMS form accuracy
• No edge roll-off
Major new UK-based research initiative – processing metre scale freeform optical surfaces
Next generation of large telescopes
Hale(1948)
Keck(1993)
GMT(2018)
TMT(2018)
E-ELT(2018)
Mirror technology
36 segments Production rate: 1 per
month
Active segmented mirror technologypioneered through the Keck telescope
Optical Test Tower• Segment radius of curvature 84m
• Test tower 10m
• Folded path using spherical mirror
• 45˚ fold mirror near intermediate focus (central
obscuration)
• Focus relayed to interferometer by pair of
aspheric lenses
• Spherical aberration corrected by aspheric plate
off-axis and a pair of cylindrical lenses.
• Option for final residual aberrations to be
corrected by CGH
• Located over polishing machine
Acknowledgement: Dr John Mitchell, Cranfield Ultra Precision and Structured Surfaces (UPS2)
Master spherical segment (MSS)
Source: David Walker, University of Wales Professor of Optics at Glyndwr University , Professorial Research Associate, University College London, Research Director, Zeeko Ltd
• Composite measurements constructed from lateral and rotational shears
• Form 16.8 nm ± 2nm RMS
• Mid spatial frequencies < 5nm RMS
• 1.490 m across corners
• 200 mm thickness
• Spherical form 84 m ROC
Sub-surface Damage
Evaluation technique:• Polished tapered grooves
• Etched HF, target removal 1µm• Groove depth - contact profilometery
• Crack observation using optical microscope
Grinding Conditions Cluster depth (µm) Last fracture depth(µm)Zerodur® ULE® Zerodur® ULE®
Rough cut (D76) 5 8.5 8 18.5Semi‐finish cut (D46) 4 4.5 7.5 9Finish cut (D25) 3 4 4 8
Ref: Tonnellier, T. et al. 2008, Sub-surface damage issues for effective fabrication of large optics, Proc of SPIE Vol. 7018, pg 701836-1 to 701836-10
Micro-textured cylindrical mould
Cutting a varying
included angle:
corner sharpness
Flat Lens Parquets
Arrayed flat fresnellenses on optical film
Laminate in ‘one shot’to support frame
Manufacture Conical Lenses
Diamond cut master
Lens Film in r2r process
Fold assemble and glue lens structure
Thin Film
Solar Power technologies
Thin Film Flat Panel Concentrated
Lenses Mirrors
ThermalPhotovoltaic
Solar Power
Advanced Surface Structuring
Micro-texturedlight diffusers
Micro-textured light reflectors
Advanced Surface Structuring
Micro-textured retro-reflecting surfaces
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SummaryAccuracy capability a 1 part in 108
(metre class surfaces in 10 hours)
BoX® -Ultra Precision fixed abrasive Grinding & Measuring System, Cranfield
IRP1200 –Ultra Precision 7 axes free abrasive polishing system, UCL & Zeeko Ltd
RAP –Re-active atom plasmasurface figuring system, Cranfield and RAPT Industries
67
High Precision Diamond Turning of Structured / Textured Surfaceson rolls for large scale replication of plastic films
68
Textured roll
Plan view
Side view
Diamond turned micro-structured surface
Structured / Textured Surfaces on rolls
CPV installations growth forecast 1.5GW capacity will be installed in 2014 Equates to 7 million m2 of solar units
70
Reactive Atomic Plasma Processing
Ar Ar
CF4
FF
FFF
FC
CC
ArArAr
ArArAr
ArArAr
Ar
Excitation Region
Plasma Discharge
Copper coils for Inductively-coupled energy source
Plasma (main) gas
Reactive precursor gas
Si, SiO2, SiC…
Quartz tube
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Shallow trench, approximately 15 nm deep, created by 4 passes
Segmented mirrors
Pioneered by Keck
Repeated by GTC, SALT, JWST etc.
Image credit: A. Miller
New process chain for large optics
Major new UK-based research initiative*– processing time for large (1+ metre scale) freeform optical
surfaces reduced from 100 hours to 10 hours– 3 step process chain
Stage 1
Fixed abrasive Grinding
Stage 3
Reactive atom
Plasma
1 mm form accuracy
1 μm form accuracy
10 nm form accuracy
Stage 2
Computer control polishing
* Ultra Precision Surfaces: A New Paradigm – Cranfield/UCL collaboration (2004-2008)
1st ESO segment in ground condition