Jonathan Abir and James Norman - Cranfield University

From meso scale to metre scale:
developments in metrology frame
technologies
Jonathan Abir & James Norman
Jonathan Abir
j.h.abir@cranfield.ac.uk
James Norman
j.p.norman@cranfield.ac.uk
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
2Jonathan Abir
James Norman

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
3Jonathan Abir
James Norman

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 b
G s
a s a s a
  

  
Jonathan Abir
James Norman

5
Metrology frame in a machine tool
OAGM 2500 - Off Axis Grinding Machine
Glass reference bars
www.cranfieldprecision.comShore P. et al. Big OptiX ultra precision grinding/measuring system. 2005.
Jonathan Abir
James Norman

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.
Jonathan Abir
James Norman

Virtual Metrology Frame Idea
Virtual Metrology Frame
F Carriage
Frame
7
XX
Jonathan Abir
James Norman

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
Jonathan Abir
James Norman

Metre scale machine
www.hexagonmi.com
Virtual Metrology Frames in CIM-UP
9Jonathan Abir
James Norman

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
10Jonathan Abir
James Norman
~ 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.
Jonathan Abir
James Norman
± 50 nm over 50 mm3

Virtual Metrology Frame - Multilateration
Unknowns
12
Camboulives M. et al.. Calibration of a 3D working space by multilateration. 2016
Jonathan Abir
James Norman

Virtual Metrology Frame - Multilateration
10 x 4 sets of equations with 40 unknowns → solvable
No. of retro-reflector positions
No. of interferometer positions
13Jonathan Abir
James Norman

14
Probe position measurement
Laser interferometry multilaterationStylus tip on CMM
Jonathan Abir
James Norman

Stylus tip on CMM
Replace stylus tip
Retro-reflector
15
Probe position measurement
Jonathan Abir
James Norman

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
Jonathan Abir
James Norman

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)
1717
Further work
R. Jourdain. e al. Design and characterization of an optical test system for metre–scale optics. 2013.
Jonathan Abir
James Norman

18
Meso scale machine
Virtual Metrology Frames in CIM-UP
Jonathan Abir
James Norman

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
19Jonathan Abir
James Norman

Virtual Metrology Frame concept in a
meso scale CNC machine
Xc
F
Frame
Xvmf Xf
Xc – Xf = Xvmf
20Jonathan Abir
James Norman

Virtual Metrology Frame concept in a
meso scale CNC machine - controller
C P+
Frame
displacement
sensor
Encoder
Xc
Xf
Xvmf
eXset
+
Controller
21Jonathan Abir
James Norman

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
22Jonathan Abir
James Norman

2
0
2 0
[ ( ) ] ( ) ...
2
a t dt d t
a
a t   
Signal processing design of frame
displacement sensor
Attenuating Double integrating
23Jonathan Abir
James Norman

Results of plant transfer function
Flexible frame
( )
( )
( )
X s
P s
F s

24Jonathan Abir
James Norman

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
25Jonathan Abir
James Norman

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
26Jonathan Abir
James Norman

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
27
Meso scale
machine
Metre scale machine
Jonathan Abir
James Norman

Jonathan Abir and James Norman - Cranfield University

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