A vibrating micro-cmm probe for micropart metrology

Transcription

1 Microparts meeting - NPL 28 th October 2009 A vibrating micro-cmm probe for micropart metrology Richard Leach

2 A vibrating micro-cmm probe for micro-part metrology Introduction Measuring co-ordinate geometry CMMs and micro-cmms Micro-CMM probes Design of the vibrating micro-cmm probe Concept Design FE analysis Production µstylus Design Characterisation Vibration investigations Surface interaction modelling 2

3 Introduction Micro-scale co-ordinate metrology of miniature components Modern manufacturing involves 3D integration of 3D micro-parts MEMS structures Micro optics and mirrors Micro-fluidic components Medical devices Ink-jet/diesel injectors Small parts and features with ever decreasing tolerances 3

4 Measuring co-ordinate geometry The measurement of dimension, form and position within a co-ordinate system on a co-ordinate measuring machine Developed for industry to reduce time and skill required to make measurements Highly accurate (< 1 µm) on macro objects: aeroplane wings, car engines, violins, drill bits etc. Usefulness limited by probe size, aspect ratio, probing force and total mass of moving parts 4

5 Micro co-ordinate metrology Micro-CMMs are being developed to deliver the measurement accuracy demanded by the current microparts industry Reduced measurement volume High resolution machine scale Very low probing force ( < mn) Accuracy of micro-cmms is now limited by accuracy of probing systems Usefulness of micro-cmms is now limited by aspect ratio of probing system 5

6 Micro-CMM probes Current refined designs of traditional CMM probing technology have reached limit of accuracy Further scaling is impossible without taking into account the changes to physics at these dimensions: Surface forces dominate over gravity Molecular forces (vdw) Surface tension/capillary Electrostatic Casimir Aspect ratio becomes a major problem too floppy Current probes do not have isotropic probing force To address these factors a new probe is being designed at NPL 6

7 The Triskelion Device

8 Design of the vibrating micro-cmm probe Initial design based on small CMMs and probes research (NPL, 2004) Size reduction of entire device better suits applications and stylus Sunday, 01 November 2009 Device needs to be better packaged IC chip ~ 15 mm Device was designed to vibrate so as to reduce contact force and effect of surface interactions ~ 2 mm Flexures are instrumented with piezoelectric actuators and sensors 8

9 Design of the vibrating micro-cmm probe Sunday, 01 November 2009 Extensive finite element analysis to optimise features of probe: Position of actuators and sensors Dimensions of flexures Variational Risk Analysis (VRA) conducted determined that the thickness of the PZT contributed 83 % to the output of the device Outer sensor Outer actuator Inner actuator Inner sensor 9

10 Finite element analysis Multiple PZT sensor layout investigated for optimised output Pictures: Greenwich University 10

11 Finite element analysis FE Vibration analysis undertaken (Greenwich) for various materials and designs Mode Nickel flexures Resonance Frequency (khz) Glassy Carbon flexures Silicon flexures Analysis suggests that vibrations should be forced onto the device at ~1 khz Further FEA analysis being undertaken to investigate spring constant, sub-resonant vibrations, stylus dynamics 11

12 Production Nickel flexures on a silicon substrate via sol-gel spinning IC production technique (Cranfield University, 2008) Nickel chosen over other materials because exhibited ideal PZT deposition properties (Cambridge, 2007) ~200 µm ~1 mm Pictures: Cranfield University 12

13 Production Current design complete with packaging and electrical contacts Notice there is no stylus (micro assembly challenge) ~6 mm ~2 mm ~14 mm Pictures: NPL 13

14 Stylus

15 Design of the micro-stylus Work has been conducted at NPL to investigate augmenting current CMM probes with high aspect ratio micro-styli This initial work was used to help design a suitable set of micro-styli for consideration. Dia = 70 µm Various stylus designs, diameters and lengths investigated Stylus bend analysis performed in ANSYS Suitable trial styli selected by optimising aspect ratio and sensor output voltage (sensitivity) 15

16 Stylus characterisation Production methods being investigated: Micro-EDM Laser machining of WC Current stylus designs include: 2 mm stylus, 50 µm sphere tip 3 mm stylus, 70 µm sphere tip Form and surface measurements of the tip of the micro-stylus are essential: Coordinate metrology Surface interaction forces Characterisation of micro-spherical tips is non-trivial (Loughborough University) 16

17 Vibration Investigation

18 Vibration investigation Need to understand the vibration of the device before such vibration can be programmed and controlled Dynamics of the device investigated using a laser vibrometer system at NPL Frequency, voltage, displacement and acceleration response to be analysed A complete understanding of these will allow us to control the vibrations of the device 18

19 Vibration investigation 19

20 Vibration investigation 20

21 Vibration investigation Investigations will continue with completed microprobe to refine our understanding of the vibration There is a close correlation between the FE and real data. This is encouraging as it enables us to use the FE model to optimise the design Higher resonance frequencies may also be suitable for sensing Investigations will continue to help populate any optimisation algorithms based on the FE model: Design Sensitivity Production Cost and risk 21

22 Surface Interaction Modelling

23 Surface interaction modelling Investigation completed on the interaction forces involved while probing Van der Waals Casimir Capillary Electrostatic Etc. Composite of the surface forces ~ 100 µn This correlates to a required vibration amplitude ~ 600 nm (easily obtainable from the vibrating micro-cmm probe) 23

24 Surface interaction modelling Sunday, 01 November 2009 Results of this investigation and the first set of experimental results are being presented at IPAS Chamonix 24

25 Future Work Immediate: Complete dynamic testing (vibration frequency and amplitudes) Filter results into FE model and optimise design (Greenwich) Optimise PZT layout, position and thickness Develop combined production techniques (Nottingham & Cambridge) Stylus production + manipulation + assembly Begin surface interaction investigations (vertical) Future: Conduct lateral probing interaction experiments Verify probing forces using NPL primary low force balance 25

26 Dissemination Current: HARMST 2009 Saskatoon, Canada Microstylus design Lamdamap 2009 Brunel, UK Precision micro-assembly 3D Mintigration Grand Challenge Annual Conference Future: IPAS 2010 Surface force interaction euspen 2010 First experimental results MATADOR D Mintigration book Micro-probe design demonstrator 26

27 Acknowledgements This research is funded by the National Measurement System Engineering Measurements Programme ( ) Cambridge University Greenwich University Cranfield University Nottingham University Taipei University 27