Ultra-precision scanning stages• Applications

o Used in advanced manufacturing equipment such as wafer

scanners, and high-resolution 3D printers

• Two main problems of step motion [1]

o The stages are subject to large inertial load due to

acceleration

I. Stage base vibration

II. Motor heating

• Design goals

o Reduce the base vibration by 50%

o Reduce the motor heating by 50%

o No compromise on stage throughput and ground vibration

transmissibility during manufacturing

MOTIVATION

Bowen Zeng

zbowen@umich.eduAdvisors: Deokkyun Yoon and Prof. Chinedum Okwudire

Motor Heating• 8.3 J/step 1.7 J/step (80% reduction)

• Thermal errors mitigated with reduced heat generation

Energy harvested• 1.3 J/step (12% total energy consumption recovered)

Base Vibration• 1300 𝜇m, RMS 2.6 𝜇m, RMS (99% reduction)

Since the energy recovery rate is low, design 3 is the best

Future work• Optimize energy harvest rate of RSA, and investigate coupling

design between coarse and fine stages and control methods

CONCLUSION AND FUTURE WORK

[1] Yoon D, Okwudire CE. Magnet assisted stage for vibration and heat reduction in wafer scanning.

CIRP Annals - Manufacturing Technology (2015), http://dx.doi.org/10.1016/j.cirp.2015.04.105

[2] Li, Zhongjie, George Luhrs, Liangjun Lin, and Yi-xian Qin. "Electromagnetic Energy-

Harvesting Shock Absorbers: Design, Modeling, and Road Tests." IEEE TRANSACTIONS ON

VEHICULAR TECHNOLOGY 62.3 (2013): 1065-074. Engineering Village. Web. 13 Apr. 2016.

[3] Toma, Adrian. "RELUCTANCE VS LORENTZ." MIKRONIEK 2013: 21-26. Print.

REFERENCES

SIMULATION RESULTS

Heat and Vibration Reduction of

Ultra-Precision Stages During Step Motions

Design 3: Coarse and fine stage configuration

Design 4: Coarse and fine stage configuration with

regenerative shock absorber (RSA)

Performance metrics of 4 designs

BASELINE

• Isolated base

connected to

machine ground

• Base mounted

step stage (linear

motor)

PROPOSED DESIGNS

Design 1: Ground mounted linear motor stator

Design 2: Linear switched reluctance motor (LSRM)

• Hybrid of a

Lorentz Linear

motor (fine stage)

and a LSRM

(coarse stage)

• LSRM ONLY

turns on during

coarse positioning

• Machine ground

mounted linear

motor stator

• Motor reaction

force filtered by

machine ground

• Hybrid of a rotary

motor (coarse

stage), and a linear

motor (fine stage)

• Machine ground

mounted coarse

stage

• FLM=0, and km=0

during coarse

positioning; kc=0

during fine

positioning

• Install regenerative

shock absorber

(RSA)

• Partially recover

kinetic energy of

moving stage

• Cr=0 during braking

of coarse stage and

fine positioning

Motor Heating

[J/step]

Base Vibration

[𝜇m, RMS]

Energy Harvested

[J/step]

Key

Equations

Baseline/Design 1:

WLM=නFMKM

2

dt

Design 2:

I=

2g+C2FC1

n[3]

W=න I2Reff dt

Design 3/4:

TM=a2πS.F.

𝜂lsmls2

4π2+JM

WRM=නTMKM

2

dt

G s =C(sI−A)−1B

Design 4:

ceff≈KTKE𝜂

Rtotalls2

[2]

Ere=ceffන ሶyg− ሶyc2dt

Baseline 8.3 1300 -

Design 1 8.3 0.63 -

Design 2 2.0 0.63 -

Design 3 1.7 2.6 -

Design 4 0.93 1.4 1.3

• Base Vibration (frequency domain)

o Ground vibration transmissibility o Motor induced vibration FRF

• Energy harvested

• Base Vibration (time domain)• Assumed profiles

• Motor heating