INSPEX CMMs : Where next? Andrew Lewis. November 2003

Transcription

1 INSPEX 2003 CMMs : Where next? Andrew Lewis November 2003

2 OUTLINE 1. Introduction 2. The progress of technology 3. CMMs at different scales Current CMMs: status, designs & limitations Where next: new locations and uses Where next: new technology 4. Far future 5. Metrology issues 6. Summary

3 INTRODUCTION National Physical Laboratory (NPL) -Maintain physical standards for UK (kg, m, A, Cd, mole, K, s) -Research towards new standards -Development of new metrology technologies -Leading edge, not routine CMM Coordinate Measuring Machine flexible definition Examples chosen at discretion of author

4 THE PROGRESS OF TECHNOLOGY - General Technology cascade Initial specialism High cost, low volume Leading edge Industry uptake Next generation Commercialisation Larger markets Concorde examples Fly by wire Flight computers Carbon brakes

5 THE PROGRESS OF TECHNOLOGY - Machining Tanaguchi model year time lag between precision levels x10 improvement Similar to Moore s Law in computing: (x2 transistor count every 2 years) CMMs have to keep up

6 A CMM? COORDINATE -2D or 3D position, perhaps 2½D position MEASURING - the assignment of numbers to represent amounts or degrees of a property possessed by the object i.e. determine lengths, positions MACHINE - assembly of parts to perform useful work. Automatic, semi-automatic, manual

7 WHY MEASURE? The quality perspective: The key to industrial manufacture of devices and materials is proper process control Uncertainty evaluation is vital for making go/no-go decisions If you can t measure it you cannot make it, you cannot sell it Quality Management Systems demand traceable measurements

8 TRACEABLE MEASUREMENTS Traceability [VIM 6.10] property of the result of a measurement whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties Uncertainty (of measurement) [GUM 2.2.3] parameter, associated with the result of a measurement, that characterizes the dispersion of values that could reasonably be attributed to the measurand

9 CMMs operate at different scales Conventional scale CMMs Shop floor metrology Large scale CMMs Civil engineering metrology Small scale CMMs Micro and nano metrology Status Limitations New challenges Near future Far future

10 Conventional scale CMMs Conventional CMMs: Zeiss, Leitz, Mitutoyo, DEA, CSIP, LK, Sheffield, Arms: Faro, Romer, etc Up to 1 or 2 metres in range Few or a few tens of micrometres uncertainty

11 Conventional scale CMMs - STATUS Classical Cartesian axes Moving bridge Moving table Rotary table Optical variants Metrology: scales & probe head 21 error sources: 3 scale errors 6 (3 x 2) straightness 3 squareness errors 9 rotational errors (pitch, roll, yaw, 3 axes)

12 Conventional scale CMMs - STATUS Articulated arms Fixed arm lengths Multiple joints Metrology: angle sensors, arm lengths Self-calibrating routines FARO FARO

13 Conventional scale CMMs - LIMITATIONS Classic CMM: High accuracy Flexible High costs Difficult calibration Not mobile Arms: Flexible Mobile Limited accuracy : angle Optical CMM: Fast Non-contact Traceability Optical vs mechanical surface Limited probing of internal features

14 Conventional scale CMMs NEW CHALLENGES Technical Performance High End Vertically Integrated CMMs Modular Design Horizontally Integrated CMMs Customers Technological Needs ACCURACY vs COST Lower uncertainty? Higher price? Dr S Phillips, NIST, Keynote, IDW 2001 Cheaper Sufficient accuracy

15 Conventional scale CMMs NEAR FUTURE Manufacturer s software Measurement (Points) PTB s software CMM Parameters Evaluation Error model Probe Environment Geometric Parameter Associated Uncertainty VCMM Long term Stability Workpiece Manufacturer/PTB user calibration laboratory PTB

16 Conventional scale CMMs NEAR FUTURE z P MULTILATERATION Principle: P = f (B 1,B 2,B 3,d 1,d 2,d 3 ) d 2 Fourth axis for self calibration d 1 d 4 y B 4 d 3 B 2 Realisations: Global Positioning System (GPS) Large Scale Metrology B 1 B 3 x Multilateration on CMMs µ-gps

17 Conventional scale CMMs NEAR FUTURE NPL Multilateration CMM Four laser trackers Retroreflectors on probe Metrology: interferometric length measurement Self-calibrating routines Always on Abbe Separates metrology from kinematics Online machine or Offline error mapping

18 Conventional scale CMMs NEAR FUTURE

19 Conventional scale CMMs NEAR FUTURE Multilateration applications Optical form metrology e.g. aspherics Structure monitoring Machine tool error mapping Techniques for single tracker use

20 Conventional scale CMMs NEAR FUTURE Smarter artefacts Artefacts with wide range of features Designed to test a selection of measurement parameters Inbuilt sensors for remote health monitoring Report back to base on artefact status, stability

21 Large scale CMMs Some conventional designs extended e.g. Leitz Other technologies e.g. laser tracker, laser radar Measurand several metres in size Tens, hundreds or thousands of micrometres uncertainty

22 Large scale CMMs - STATUS Large gantry CMMs Generally 5-10 m In situ construction Require special foundations Metrology : scales Verification issues? LEITZ

23 Large scale CMMs - STATUS Laser trackers Polar coordinate system: Radius, Azimuth, Elevation Metrology: Laser interferometer Angular sensors Tracking servo Retroreflector New 6DOF probes LEICA LEICA

24 Large scale CMMs - STATUS Vt Laser radar D Hz Direct time of flight measurement to object surface Polar coordinate system: Radius, Azimuth, Elevation No Retroreflector LEICA

25 Large scale CMMs - LIMITATIONS CMM: High accuracy Flexible High costs Difficult calibration Not mobile Slow Laser tracker: Mobile High radial accuracy Target reflector required Limited lateral accuracy Limited probing of internal features Laser radar: Direct probing of surfaces Expensive Limited accuracy Sensitivity to surface Limited lateral resolution No probing of internal features Photogrammetry: Flexible Economic Targets necessary Time consuming Only static measurements

26 Large scale CMMs - LIMITATIONS Radar Tracker Multilateration CMM Photogrammetry 200 MPE (µm) Range (m)

27 Large scale CMMs NEW CHALLENGES Aero engineering at large scales Metrology of wings up to 50 m Ideally 1 part per million

28 Large scale CMMs NEW CHALLENGES David Smith, MERLAB Léna, P., Observational Astrophysics, 1998, 2nd ed, Springer-Verlag

29 Large scale CMMs NEW CHALLENGES Requirements Primary panel shape Surface accuracy 20 µm Size 3 m x 5 m Measurement Accuracy ~5 µm RMS <1 hr to measure on <100 mm grid Secondary mirror shape Accuracy ~12 µm Convex, strongly curved, aspheric

30 Large scale CMMs NEW CHALLENGES Big Science particle accelerators Accelerator components need to be aligned to very tight tolerances: SSC, LEP: 200 µm / 400 m; 8 mm / 5 km SLC, PEPII: 100 µm / 30m; 2 mm / 2 km LCLS, FFTB: 10 µm / 100m; 50 µm / 100 m CERN

31 Large scale CMMs NEAR FUTURE Large scale Multilateration Combine multiple laser trackers Abandon angle measurement Self calibrating Self monitoring 10:1 accuracy improvement using 4 commercially available laser trackers

32 Small scale CMMs Scanning Probe Microscopes (SPMs) (Atomic Force Microscopes) Scanning Electron Microscopes (SEMs) Restricted range conventional CMMs Optical mask comparators (2D) Travelling microscopes (2D) Newly developed Small or Miniature CMMs

33 Small scale CMMs - STATUS Scanning probe microscopes Workhorse of small world Generally < 100 µm range Nanometric uncertainty 2 ½ D metrology

34 Small scale CMMs - LIMITATIONS CMM: Probing difficulties Achieving small uncertainty SPM: Nanometre uncertainty? Hysteresis Poor range (<100 µm) Not true 3D Traceability? SEM: Fast Calibration Vacuum 2D slice OPTICAL: Fast Where is the real surface Calibration Traceability?

35 Small scale CMMs NEAR FUTURE Miniaturised CMMs Laser metrology systems Miniature probes

36 Small scale CMMs NEAR FUTURE Miniaturised CMM probes Probing is most difficult element Miniature probes difficult to manufacture,easily broken Fast probing? Scanning?

37 Small scale CMMs NEAR FUTURE Metrological SPMs Laser metrology systems Traceable measurements Low force 3D servo control Still a limited range

38 Small scale CMMs FAR FUTURE Next generation micro-probe CMMs

39 FAR FUTURE medium/large sized CMMs AUTONOMOUS DEVICES 6D navigation µm accuracy mechanical probing small fast probing of internal features linked to global system parallel system

40 FAR FUTURE The catch! Future technological innovation is driven by economic incentive, not by technical capability. Dr S Phillips, NIST, Keynote, IDW2001

41 METROLOGY ISSUES large CMMs Traceability & calibration ISO & ISO Traceable artefacts Laser trackers for machine verification?

42 METROLOGY ISSUES small CMMs Traceability & calibration ISO & ISO Traceable artefacts Silicon monolith for scale calibration via X-ray interferometry

43 SUMMARY Continuing progress of technology demanding lower uncertainties Proper Coordinate Measurement is moving into new areas: -Large scale -Small scale In-fill areas between extremes will be most demanding Hybrid systems probably the mid-term solution

44 BECOMING INVOLVED NPL web site Dimensional Metrology Awareness Club (DMAC)

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