FEEDBACK BASED TECHNIQUE FOR IMPROVING DYNAMIC PERFORMANCE OF A SMALL SIZE MACHINE TOOL - VFinal

Feedback Based Technique for Improving Dynamic Performance of a

Small Size Machine Tool

Jonathan Abir, Stefano Longo, Paul Morantz, Paul Shore

Precision Mechatronic System Design and Control - Spring Topical Meeting - 2016

Jonathan Abir [email protected]

2

Research aim

• Improve the dynamic performance of a compact size CNC machine


Y axis

Z axis

X axis

B axis

A axis

C axis

0.6m 0.6m

1m

3

Research objectives

• Reduce the effect of machine frame resonances

• Improve the servo bandwidth (improve machining)


4

Simplified linear motion system of the µ4

Slave side guideway

Master side guideway

Carriage

Encoder

491mm

609mm

215mm


5

Dynamic mechanisms limiting servo control

X

F

Frame

Flexible guidance

X

F

Frame

Flexible frame


6

System identification – frame resonance (1) experimental modal analysis


7


Carriage

Frame

Motion direction


8



Frame is distorted – reference point is distorted

Carriage

Frame

Motion direction

Flexible frame resonance in a servo plant

Flexible frame

( )( )

( )

X sP s

F s

9

Can be a destabilising effect

9 Jonathan Abir [email protected]

10

Servo plant compensation techniques

• Filtering : Notch filter, Bi-quad filter, and Low pass filter

• Phase lag • Not robust for changes

Flexible frame


Machine frame concepts

Conventional

X

F Carriage

Frame

X

F Carriage

Force frame

Metrology frame

Metrology frame

X

F Carriage

Frame

BM

Balancing Mass


12

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. Proc. SPIE. 2005


13

Balancing mass & metrology frame in a machine tool

ASML TWINSCAN – Lithography platform

Butler H. Position control in lithographic equipment. IEEE control magazine. 2011.

www.asml.com


14

Virtual Metrology Frame concept

Xc

F

Frame

Xvmf Xf

Xc – Xf = Xvmf


15

Virtual Metrology Frame concept – controller

C P +

Frame displacement

sensor

Encoder Xc

Xf

Xvmf

e Xset

+

Controller


16

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

17

Frame displacement sensor - estimator (filter) design

Attenuating Double integrating


18

Validation of the estimator – long term


σ=30nm

19

Validation of the estimator - setup

Environmental compensation unit

Optics holder

Vibrating retroreflector

Vibrating Accelerometer

Static retroreflector

Beam splitter

Carriage motion


Laser interferometer

2

( ) sin( )

( ) sin( )

set

set

X t A t

a t A t

20

Validation of the estimator - results

Min. 1% amplitude discrepancy


Estimator limitation

Max. 20% amplitude discrepancy

21

Results of plant transfer function

Flexible frame

( )( )

( )

X sP s

F s


22

Virtual Metrology Frame time delay


23

Open loop Bode graph

fs – Servo bandwidth

φm – Phase margin >45º

40% improvement to servo bandwidth


Flexible frame

Gm – Gain margin >6dB

Notch filter @ 195Hz

24

Sensitivity graph


Summary:

• Dynamic displacement sensor using accelerometer σ=30nm

• Servo plant compensation technique :

• Robust • No instability • No phase delay

• Improved the servo bandwidth by 40%


Summary:

• Dynamic displacement sensor using accelerometer σ=30nm

• Servo plant compensation technique :

• Robust • No instability • No phase delay

• Improved the servo bandwidth by 40%


Documents

FEEDBACK BASED TECHNIQUE FOR IMPROVING DYNAMIC PERFORMANCE OF A SMALL SIZE MACHINE TOOL - VFinal