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Research Papers

A Porous-Restricted Aerostatic Lead Screw Actuator for High Performance Microscale Machine Tools

[+] Author and Article Information
James Zhu

Graduate Research Assistant

Shiv G. Kapoor

Grayce Wicall Gauthier Chair in Mechanical Science and Engineering
e-mail: sgkapoor@illinois.edu

Richard E. DeVor

College of Engineering Distinguished Professor of Manufacturing
Department of Mechanical Science and Engineering,
University of Illinois,
Urbana-Champaign, Urbana, IL 61801

Jong-Kweon Park

Department of Ultra Precision
Machines and Systems,
Korea Institute of Machinery & Materials,
Daejeon 305-343, Korea

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received February 27, 2012; final manuscript received July 3, 2012; published online January 7, 2013. Assoc. Editor: Tony Schmitz.

J. Manuf. Sci. Eng 135(1), 011002 (Jan 07, 2013) (8 pages) Paper No: MANU-12-1065; doi: 10.1115/1.4023111 History: Received February 27, 2012; Revised July 03, 2012

The design and manufacturing process for a porous-restricted aerostatic lead screw actuator (ALSA) is presented. The ALSA provides near-frictionless motion with submicron positioning accuracy, high stiffness at low inlet air pressures (<827 kPa), and a travel length of 50 mm. Porous graphite disk inserts are held in a helical pattern in an aerostatic nut housing against a lead screw thread to create multiple simultaneous air bearing surfaces. A wave spring flexure is inserted behind each graphite disk to provide a preload and ensure full contact between the porous graphite disk surface and the lead screw flank. When the wave spring flexures and graphite disks are potted in combination with a slow-curing epoxy, this creates a self-aligning method to consistently match all graphite disk insert surfaces to the helical profile of the lead screw thread. Experimental trials were performed to evaluate the performance of the manufactured ALSA. It was found that a stable nut with a per-thread stiffness of 9.7 N/μm was achievable with a 3.5 μm air gap and an overall permeability of 5.4 × 10−15 m2. Applications requiring higher stiffness may couple two or more single-threaded nuts to achieve the desired actuator stiffness.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Porous-restricted air bearing concept

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Fig. 2

Aerostatic nut housing

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Fig. 3

Effect of inlet pressure on (a) lift-off force and (b) stiffness for a single porous graphite disk at a constant permeability of 6.6 × 10−15 m2

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Fig. 4

Effect of permeability on (a) lift-off force and (b) stiffness for a single porous graphite disk at a constant pressure of 827 kPa

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Fig. 5

Stiffness for a pair of air bearing disks with increasing thread count

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Fig. 6

Wave spring flexure configuration

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Fig. 7

Velocity vectors shaded by static pressure (Pascal)

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Fig. 8

Nut housing and enclosure

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Fig. 9

Modified trapezoidal thread profile (mm)

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Fig. 10

ALSA with precision lapping system

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Fig. 11

Key elements of the precision lapping system

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Fig. 12

ALSA platform for manufacturing and testing purposes

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Fig. 13

Graphite disk after rough lap

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Fig. 14

Aerostatic nut during permanent potting

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Fig. 15

Surface restriction layer process

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Fig. 16

Air gap calculation

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Fig. 17

Stiffness measurement on ALSA

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