Machined Specular Surfaces

Transcription

1 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

2 Topics Ultra-precision ii machining i Measurement technology for ultra-precision machining Phase Measuring Deflectometry (PMD) Mini PMD Machine-integrated PMD

3 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

4 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

5 Application example freeform optic logo Courtesy of Fraunhofer ITWM, Kaiserslautern Courtesy of Fraunhofer ITWM, Kaiserslautern Courtesy of Uni Erlangen IOIP, OSMIN

6 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

7 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

8 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

9 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)

10 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

11 Machine-integration of Phase Measuring Deflectometry Monitor 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

12 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

13 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 = +/ 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

14 Mini PMD vs. White Light Interferometer Y Axis 12 mm mm 12 X Axis WLI ZygoLOT NewView µm 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 mm 12 X Axis Mini PMD µm Field of Measurement Lateral resolution mm x 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

15 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 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 = 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 = μm after center line correction l h d h h Resulting shape deviation within the measurement accuracy of the Mini PMD

16 Sha ape Deviation from Sphere µm Correction cycle for rotational-symmetric parts z 1 x 2 ρ 0 1 e x Before correction 2 A1 x After correction mm 20 Deviation 300 nm X axis 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 = 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 = μm after center line correction Resulting shape deviation within the measurement accuracy of the Mini PMD

17 Lab setup for workpiece diameters D < 120 mm Cameras Workpiece position 1 Angle 0 Virtual cameras Workpiece position 2 Angle 70 Virtual cameras 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

18 Lab setup for workpiece diameters D < 120 mm 8 mm 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

19 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

20 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

21 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 Berlin Germany Dipl.-Ing. Martin Kurz Phone / Fax / kurz@iwf.tu-berlin.de Internet