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Research Papers

Effect of Substrate Flexibility on the Pressure Distribution and Lifting Force Generated by a Bernoulli Gripper

[+] Author and Article Information
X. Brun

 The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405xavier.brun@gatech.edu

S. N. Melkote

 The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405shreyes.melkote@me.gatech.edu

J. Manuf. Sci. Eng 134(5), 051010 (Sep 10, 2012) (8 pages) doi:10.1115/1.4007186 History: Received October 03, 2011; Revised July 02, 2012; Published September 10, 2012; Online September 10, 2012

This paper presents the modeling and analysis of the pressure distribution and lifting force generated by a Bernoulli gripper when handling flexible substrates such as thin silicon wafers. A Bernoulli gripper is essentially a radial airflow nozzle used to handle large and small, rigid and nonrigid materials by creating a low pressure region or vacuum between the gripper and material. Previous studies on Bernoulli gripping have analyzed the pressure distribution and lifting force for handling thick substrates that undergo negligible deformation. Since the lifting force produced by the gripper is a function of the gap between the handled object and the gripper, any deformation of the substrate will influence the gap and consequently the pressure distribution and lifting force. In this paper, the effect of substrate (thin silicon wafer) flexibility on the equilibrium wafer deformation, radial pressure distribution and lifting force is modeled and analyzed using a combination of computational fluid dynamics (CFD) modeling and finite element analysis. The equilibrium wafer deformation for different air flow rates is compared with experimental data and is shown to be in good agreement. In addition, the effect of wafer deformation on the pressure and lifting force are shown to be significant at higher volumetric airflow rates. The modeling and analysis approach presented in this paper is particularly useful for evaluating the effect of gripper variables on the handling stresses generated in thin silicon wafers and for gripper design optimization.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of a Bernoulli gripper

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Figure 2

Simplified gripper geometry

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Figure 3

Fluid domain used in the CFD simulations: (a) Rigid substrate and (b) flexible substrate

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Figure 4

Experimental setup

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Figure 5

Full-field measured out-of-plane deformation (in mm) of cast silicon wafer as a function of airflow rate

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Figure 6

Full-field measured out-of-plane deformation (in mm) of EFG silicon wafer as a function of airflow rate

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Figure 7

Predicted vs. measured average out-of-plane deformation at the wafer center, δ(0,0), for cast silicon wafer as a function of airflow rate

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Figure 8

Predicted vs. measured average out-of-plane deformations for EFG silicon wafers at the center of the wafer, δ(0,0), as a function of airflow rate

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Figure 9

Full-field predicted out-of-plane deformation (in m) of cast silicon wafer as a function of airflow rate

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Figure 10

Full-field predicted out-of-plane deformation (in m) of EFG silicon wafer as a function of airflow rate

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Figure 11

Effect of wafer deformation on the predicted air pressure distribution for cast silicon wafer at V = 40 l/min

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Figure 12

Effect of wafer deformation on the predicted pressure distribution for the EFG silicon wafer at V = 40 l/min

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Figure 13

Influence of airflow rate on the predicted maximum in-plane principal stress distribution on the top surface of the cast silicon wafer

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Figure 14

Influence of airflow rate on the predicted maximum in-plane principal stress distribution on the top surface of the EFG silicon wafer

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