Jonathan Abir and James Norman - Cranfield University

From meso scale to metre scale: developments in metrology frame

technologies

Jonathan Abir & James Norman

Jonathan Abir [email protected]

James Norman [email protected]

1

Paul Morantz Stefano Longo

Paul Shore

Xavier Tonnellier Paul Morantz

Future Challenges of Instrumentation and Control in Ultra Precision Manufacturing - 18 May 2016 at Renishaw plc. Organised by the EPSRC Centre for Innovative Manufacturing in Ultra Precision, Cranfield University.

Machine frame

There are two primary functions for a machine frame:

• Transferring forces • Position reference – metrology frame

There are two primary disturbances distorting position measurement and control:

• Processing and servo forces >1 Hz • Thermal forces <<1 Hz

Machine tools and measurement systems alike require precision positioning capability to enable:

• Accurate production of components • Low uncertainty measurement for verification of components

2 Jonathan Abir [email protected]


Machine frame concepts reducing processing disturbances

Conventional

X

F Carriage

Frame

X

F Carriage

Force frame

Metrology frame

Metrology frame

X

F Carriage

Frame

BM

Balancing Mass



Machine frame concepts reducing thermal disturbances

X

F Carriage

Force frame

Metrology frame

Metrology frame

4

Model based compensation technique

1 0

1 0

( )m

m

n

n

b s b s bG s

a s a s a



5

Metrology frame in a machine tool

OAGM 2500 - Off Axis Grinding Machine

Glass reference bars

www.cranfieldprecision.com Shore P. et al. Big OptiX ultra precision grinding/measuring system. 2005.



6

Metrology frame in a CMM

PTB µCMM ~ 250 nm surface measurement uncertainty

Küng A. et al. Ultraprecision micro-CMM using a low force 3D touch probe, 2007.



Virtual Metrology Frame Idea

Virtual Metrology Frame

F Carriage

Frame

7

X X



The advantages of Virtual Metrology Frame

• Enhance machine performance with minimal interference

8

Meso scale machine

Metre scale machine

• Optimal solution

Expandable measurement volume with no extra cost Limited machine size Limited machine cost



Metre scale machine

www.hexagonmi.com

Virtual Metrology Frames in CIM-UP



www.eso.org

European Extremely Large Telescope

http://www.jwst.nasa.gov/

James Webb Space Telescope

Off-axis ellipsoidal:

•Non-specular after grinding

•Manufacture difficult

•Metrology is complex

Metrology for large optics



~ 1.5 m

11

Metrology Frame for large CMM

• Research aim: To realise a method for low uncertainty probe positioning within large measurement systems.

hexagonmetrology.co.uk/Leitz-Infinity G. N. Peggs, et al. Design for a Compact High-Accuracy CMM. 1999.



± 50 nm over 50 mm3

Virtual Metrology Frame - Multilateration

Unknowns

12

Camboulives M. et al.. Calibration of a 3D working space by multilateration. 2016



Virtual Metrology Frame - Multilateration

10 x 4 sets of equations with 40 unknowns → solvable

No. of retro-reflector positions

No. of interferometer positions



14

Probe position measurement

Laser interferometry multilateration Stylus tip on CMM



Stylus tip on CMM

Replace stylus tip

Retro-reflector

15

Probe position measurement



Potentially a trade-off between cost (£) and measurement uncertainty (σ)

LaserTRACER multilateration ~ 400 nm coordinate measurement uncertainty (1 m3)

Enable traceable coordinate measurement of tip centre via HeNe wavelength

16

Coordinate measurement - multilateration



System uncertainty assessment

ISO Type B: Monte Carlo style based on analytical model

ISO Type A: Build system and assess via measurement of an artefact (Fizeau interferometric measured optic)

17 17

Further work

R. Jourdain. e al. Design and characterization of an optical test system for metre–scale optics. 2013.



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Meso scale machine

Virtual Metrology Frames in CIM-UP



Meso scale machine with Virtual Metrology Frame

• Research aim: Improve the dynamic performance of a compact size CNC machine

0.6m 0.6m

1m

Slave side guideway

Master side guideway

Carriage

Encoder

491mm

609mm

215mm



Virtual Metrology Frame concept in a meso scale CNC machine

Xc

F

Frame

Xvmf Xf

Xc – Xf = Xvmf



Virtual Metrology Frame concept in a meso scale CNC machine - controller

C P +

Frame displacement

sensor

Encoder Xc

Xf

Xvmf

e Xset

+

Controller



Requirements of frame displacement sensor

• No reference point – “virtual metrology frame”

• Low delay

• Low noise – compared to the encoder

2( ) ( )a t dt d t

• Measure dynamic displacement of machine frame



2

0

2 0[ ( ) ] ( ) ...2

a t dt d ta

a t

Signal processing design of frame displacement sensor

Attenuating Double integrating



Results of plant transfer function

Flexible frame

( )( )

( )

X sP s

F s



Results of open loop transfer function

fs – Servo bandwidth

φm – Phase margin >45º

40% improvement to servo bandwidth

Flexible frame

Gm – Gain margin >6dB

Notch filter @ 195Hz



Summary of Virtual Metrology Frame in a meso scale CNC machine

The virtual metrology frame concept was realised in a meso scale CNC machine:

Improvement to the servo bandwidth by 40% A simple PID control structure Robust solution



The advantages of Virtual Metrology Frame

• Enhance machine performance with minimal interference– metre & meso scale • Optimal solution

Expandable measurement volume with no extra cost – metre scale Limited machine size – meso scale Limited machine cost – meso scale

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Meso scale machine

Metre scale machine



Documents

Jonathan Abir and James Norman - Cranfield University