Machine-Integrated Measurement of Ultra-Precision Machined Specular Surfaces G. Häusler, Ch. Faber, E. Olesch, Ch. Röttinger Institute of Optics, Information, and Photonics (IOIP) University of Erlangen-Nuremberg, Germany E. Uhlmann, and M. Kurz Institute for Machine Tools and Factory Management (IWF) Technical University Berlin, Germany
Topics Ultra-precision ii machining i Measurement technology for ultra-precision machining Phase Measuring Deflectometry (PMD) Mini PMD Machine-integrated PMD
Ultra-precision machining Diamond too ol Tools: natural or synthetic ti mono crystalline diamondd Machine tools: linear drives, hydrostatic/aerostatic bearing/guidance, laser scales, programming resolution of 1 nm Example parts: mirrors and lenses ine tool precision mach Ultra-p Applications: prototyping, mold and die making, small batch fabrication Application fields: measurement technology, laser, ophthalmic, optics
Ultra-precision machining Principle of slow slide servo Example parts with specular su urface Geometry spectrum Plane mirrors, spheres, aspheres, conical, toric or cylindrical i l mirrors Slow Slide Servo / Fast Tool Servo Non-rotational symmetrical freeforms
Application example freeform optic logo Courtesy of Fraunhofer ITWM, Kaiserslautern Courtesy of Fraunhofer ITWM, Kaiserslautern Courtesy of Uni Erlangen IOIP, OSMIN
Slow Slide Servo freeform optic for laser beam shaping Courtesy of Holoeye Photonics AG, Berlin Courtesy of Holoeye Photonics AG, Berlin Courtesy of Holoeye Photonics AG, Berlin
Quality control of specular surfaces t WLI meas surement result Roughness Controllable through capable process parameters White light interferometer (WLI) Quality is visible to the naked eye hape Deviation S Interfer rometrically me easured shape deviation Shape Influenced by machine and tool accuracy, and the environment Measurement is inevitable X Axis
Shape measurement Tactile measurement CMM CMM / touch probes / profilometer Pro: flexible, robust Con: scratch marks, slow, only point or line measurements Source: FISBA OPTIK GmbH, Berlin In nterferometer Optical measurement Interferometry Pro: contactless, areal, fast Con: specular surface, inflexible, restricted geometry, expensive, CGHs necessary for freeforms
Machine-integrated measurement for ultra-precision Machining Tou uch probe Increase in accuracy thanks to measurement integration ti and time saving Tactile measurement Touch probe Line measurement and direct correction machining for spheres and aspheres -Green-Interfer rometer Twyman- Machine axes used for probe positioning Optical measurement Twyman-Green-Interferometer Areal measurement of flats, spheres, light aspheres High accuracy, but no freeforms (without CGH)
Optical measurements of freeforms using PMD Source: 3D-SHAPE GmbH, Erlangen Camera 1 Screen Camera 2 Test specimen Source: Uni Erlangen IOIP, OSMIN Schemati c diagram of P MD Stand alone PMD Phase Measuring Deflectometry t (PMD) Primal measurand: local slope of the surface Local slope data is integrated to obtain height h data Starting point for integration is determined by triangulation Components: at least 2 cameras and one screen Defined sinus pattern on screen Cameras see distorted pattern via the specular surface Applied for various geometries including varifocal glasses
Machine-integration of Phase Measuring Deflectometry 1 3 2 Monitor 5 4 6 a Moore Nano otech 350 FG Full size PM MD setup inside Basic conditions for the integration ti of PMD o Machine-integration requirements: - robustness (chips, coolant, vibration) -no disturbance of the standard d operation o Geometry to measure determines the architecture of the setup: distance and angles between screen, cameras and test specimen Test specimen with a workpiece diameter of D = 120 mm and local slopes up to s = +/- 30 Fields of vie ew ofthesix cameras of the full size PMD setup o Prototype require 6 cameras and a 20 flat screen o Immense weight and volume Minimization i i of the setup necessary
Machine-integration of Phase Measuring Deflectometry Mini PMD Reducing the measurable workpiece size to a diameter of D = 20 mm and a local slope of s = +/- 10 Minimizing the setup to 2 cameras and a small screen We call it: Mini PMD Machine e-integrated re educed setup Workpiece diameter D = 120 mm and local slope s = +/- 30 Multiple measurements with a reduced setup using a rotational axis for repositioning Replacing actual cameras with virtual cameras Stitching of partial measurements to a complete full area measurement
Mini PMD Mini PMD ins side an ultra-pr recision machin ne Mini PMD Workpiece diameter of D = 20 mm Local slope of the surface s = +/- 10 2 Firewire cameras and a 7 screen Rugged setup with o robust C-frame and o strain relief of the wiring Stand alone setup Fits on the B axis of a standard d ultra-precision ii machine tool (Nanotech 350FG from Moore Nanotechnology Systems, LLC, USA) Measurement accuracy of about a = +/- 250 nm
Mini PMD vs. White Light Interferometer Y Axis 12 mm 4 0-4 -8-12 -12-8 -4 0 4 mm 12 X Axis WLI ZygoLOT NewView 5010 8 µm 4 2 0 Test specimen: non-rotational ti geometry with P-V = 6 μm, diameter D = 20 mm, E-Cu Process: ultra-precision diamond turning with slow slide servo, tool radius r ε = 1.5 mm, feed f = 5 mm, Depth of cut a p =5μm, NC-point angle increment w = 2 12 mm 8 White light interferometer Stitching 315 single measurements - Mini PMD Y Axis 4 0-4 -8-12 -12-8 -4 0 4 mm 12 X Axis Mini PMD µm 4 2 0 Field of Measurement Lateral resolution 18 1.8 mm x 1.44 144 mm (single) (i 20 mm x 20 mm (stitched) 5.6 μm (10x objective) Time for measurement 2.5 h 10 min 20 mm x 20 mm 25 μm at a working distance of s = 120 mm
Sha ape Deviation from Sphere Correction cycle for rotational-symmetric parts 4 µm 0-2 z 1 x 2 ρ 0 1 e x Before correction 2 A1 x After correction -4 0 4 8 12 mm 20 X axis ni PMD measur rement Mi Process: ultra-precision i diamond d turning, tool radius r ε = 1.5 mm, feed f = 5 mm, Depth of cut a p =5μm, spindle speed n = 2000 min -1 Test asphere o Curvature radius ρ 0 = 1500 mm, conical constant of e = 0, aspherical term A1 = -0.0001 o Resulting P-V = 6 μm to the Target sphere Target sphere o Curvature radius ρ 0 = 1300 mm, conical constant of e = 1, aspherical term A1 = 0 o Resulting P-V = 0.250 μm after center line correction l h d h h Resulting shape deviation within the measurement accuracy of the Mini PMD
Sha ape Deviation from Sphere µm Correction cycle for rotational-symmetric parts 4 0-2 z 1 x 2 ρ 0 1 e x Before correction 2 A1 x After correction -4 0 4 8 12 mm 20 Deviation 300 nm 200 150 100 50 X axis 0 0 4 8 12 mm 20 X Axis ni PMD measur rement Mi Process: ultra-precision i diamond d turning, tool radius r ε = 1.5 mm, feed f = 5 mm, Depth of cut a p =5μm, spindle speed n = 2000 min -1 Test asphere o Curvature radius ρ 0 = 1500 mm, conical constant of e = 0, aspherical term A1 = -0.0001 o Resulting P-V = 6 μm to the Target sphere Target sphere o Curvature radius ρ 0 = 1300 mm, conical constant of e = 1, aspherical term A1 = 0 o Resulting P-V = 0.250 μm after center line correction Resulting shape deviation within the measurement accuracy of the Mini PMD
Lab setup for workpiece diameters D < 120 mm Cameras 1 + 2 Workpiece position 1 Angle 0 Virtual cameras 1 + 2 Workpiece position 2 Angle 70 Virtual cameras 3 + 4 Workpiece position 3 Angle 140 Courtesy of Uni Erlangen IOIP, OSMIN Lab setu up withrotarya axis Field ds of view of th he sixcameras of the lab setup Workpiece diameter D = 120 mm and local slope s = +/- 30 Multiple measurements using a rotational axis for repositioning Stitching of x+1 partial measurements to a complete full area measurement 2 actual cameras plus 2x virtual cameras depending on the surface shape of the test specimen Test measurement o Convex sphere o Workpiece diameter D = 120 mm, curvature radius R = 120 mm o 3 workpiece positions are required
Lab setup for workpiece diameters D < 120 mm 8 mm 0-4 -8 Lab setu up withrotarya axis ent result ree single he lab setup size measureme omposed of thr ements using t Full s as co measure Workpiece diameter D = 120 mm and local slope s = +/- 30 Multiple measurements using a rotational axis for repositioning Stitching of x+1 partial measurements to a complete full area measurement 2 actual cameras plus 2x virtual cameras depending on the surface shape of the test specimen Test measurement o Convex sphere o Workpiece diameter D = 120 mm, curvature radius R = 120 mm o 3 workpiece positions are required
Outlook: Machine-integrated PMD for workpiece diameters D < 120 mm duced PMD Machine-in ntegrated reduc ced PMD Machine e-integrated re Workpiece diameter D = 120 mm and local slope s = +/- 30 Multiple measurements using the main spindle for repositioning Stitching of i+1 partial measurements to a complete full area measurement 2 actual cameras plus 2 i virtual cameras depending on the surface shape of the test specimen Setup specifications o 2 Firewire Cameras o 20 TFT panel, industrial grade o Fully retractable
Summary Mini PMD inside an ultra-p precision machi ine -integrated red duced PMD Machine- Demand for freeform f increases, ultra-precision ii machining i is capable for the freeform production Available measurement devices are very limited regarding freeform shape measurements, Phase Measuring Deflectometry (PMD) provides the capability to measure a wide range of freeform geometries Machine-integration of measurement technology offers faster and more accurate production Two PMD setups for the machine-integrated integrated measurement were presented Mini PMD for workpiece diameters D < 20 mm Integrated PMD using virtual cameras for workpiece diameters D < 120 mm
THANK YOU FOR YOUR ATTENTION Acknowledgment This research is part of the research project UH 100/71-2 and HA 1319/11-2 which is thankfully funded by the Deutsche Forschungsgemeinschaft (DFG). Contact Technical University Berlin Institute for Machine Tools and Factory Management (IWF) Pascalstr. 8-9 14163 Berlin Germany Dipl.-Ing. Martin Kurz Phone ++49 30 / 39006-404 Fax ++49 30 / 3911037 Email kurz@iwf.tu-berlin.de Internet www.iwf.tu-berlin.de