an introduction to low flow-rate porous air bearing ... - thic

Presented at the THIC Meeting at the Embassy Suites Hotel Presented at the THIC Meeting at the Embassy Suites Hotel Presented at the THIC Meeting at the Embassy Suites Hotel Presented at the THIC Meeting at the Embassy Suites Hotel Denver SouthDenver SouthDenver SouthDenver South

Englewood CO 80112Englewood CO 80112Englewood CO 80112Englewood CO 80112on June 27, 2000on June 27, 2000on June 27, 2000on June 27, 2000

An Introduction to Low Flow-Rate Porous Air Bearing Technology

K. John StahlK. John StahlK. John StahlK. John StahlSegway Systems LLCSegway Systems LLCSegway Systems LLCSegway Systems LLC

10488 W. Centennial Road, Littleton CO 8012410488 W. Centennial Road, Littleton CO 8012410488 W. Centennial Road, Littleton CO 8012410488 W. Centennial Road, Littleton CO 80124----4238423842384238Phone: +1Phone: +1Phone: +1Phone: +1----303303303303----904904904904----6495 FAX: +16495 FAX: +16495 FAX: +16495 FAX: +1----303303303303----904904904904----1001100110011001

EEEE----mail: john_s@mail: john_s@mail: john_s@mail: john_s@segwaysystemssegwaysystemssegwaysystemssegwaysystems.com.com.com.com

Acknowledgements:

Department of Commerce NIST/ATP Advanced Test Systems (ATS) Group

Advanced Research Corporation (Matt Dugas)Imation CorporationSeagate Corporation

Center for Magnetic Recording Research, University of California, San Diego

Talke Lab (Frank Talke, Ryan Taylor, Peter Strahle)

ContentsOverview of tape guiding technology

Porous air bearing optimizationMaterial characteristicsFlying height modelingOperating point determination

ARC* ATS performance characteristicsStatic and dynamic flying heightLateral stability - tape edge motion

*Advanced Research Corporation: www.gotoarc.com

Typical drilled air bearing assembly with compliant guides and toothed datum

Used in high performance/high reliability applicationsComplex and costly assembly

High airflow requires large pump and filter systemSharp ceramic edges can induce tape edge damage

Typical roller guide assembly (Example shown from Quantum DLT tape drive)

Used in mid-range applicationsTape surface start/stop stress & wear due to roller inertia

Roller alignment critical; Complex assembly

Segway ATS porous air bearing guide assembly

(US Patent 5,777,823 and others pending)

Air bearing benefits but with reduced complexity:Lower airflow, smaller pump; compliant guidesand toothed datum eliminated; simple assembly;Greatly improved lateral tracking stability with

thin tape at high speed.

Flow rate through a porous material

Q = µb (dP) A / t, where

µb = material permeability,dP = Pp - Pa,A = surface area, andt = material thickness

µb = {Q/A} / {dP/t}

Permeability comparison -air bearing materials

20um, 10um, 5um SS 316 Porous Material Reference: Baumann, G.W., Analysis of a Porous Gas Foil Bearing, Journal of Lubrication Technology, Trans, ASME, October 1971

Normalized Permeability

0.1

1.0

10.0

100.0

20um 316 10um 316 5 um 316 3480/90 Ceramic12

Material Category

Flying Height of a Tape over a Porous Guide

H3 = {µa µb w3 [Pp – (T / row)]} / [T ln (ro / ri)], where

H = flying height of the tape,µa = air viscosity,µb = bearing permeability,Pp = plenum pressure,T = tape tension,ro = bearing outer radius,ri = bearing inner radius,

and w = tape width.

Theoretical porous air

bearing flying height

Critical Pressure:T / rw =

6.8 K Pa @ 1.1N

Spacing as a function of Pressure(Ceramic 8 material, 1 mm wall, 25 mm diameter)

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60 70

Pressure, KPa

Spac

ing,

Mic

rons

T = 1.1 N

T = 2.2 N

Flow characteristics of ATS bearing and supply pumpOperating Point Determination

(ATS bearing set, C12 material)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 10 20 30 40 50 60 70

Pressure, KPa

Flow

Rat

e, s

lpm

C12 BearingPump

Flow characteristics and operating point

determination with porous 316 materials

Note: 316 family operating point is less than T / rw,so the tape will not fly on 316 with this pump choice.

Operating Point Determination(20 um, 10um, 5 um 316)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 10 20 30 40 50 60 70

Pressure, KPa

Flow

Rat

e, s

lpm Bearing

Pump20u 31610u 3165u 316

ARC ATS tape transport configuration

Advanced Research Corporation: www.gotoarc.com

Flying characteristics of ATS bearings

Air Bearing Spacing versus Pressure, ATS Bearing Set

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0Pressure, KPa

Spac

ing,

mic

rons

TheoryBottom +.020234Center678Top -.020

Dynamic flying height variation measured on ATS bearingsDynamic flying height variation during shoeshine

(+/- 4 m/sec max velocity; 2.25 second shoeshine period)

0.05.0

10.015.020.025.030.035.040.0

0 1 2 3 4 5 6 7 8 9 10

Time (seconds)

Flyi

ng H

eigh

t (M

icro

ns)

68.9 Kpa62.0 Kpa55.1 Kpa48.2 Kpa41.3 KP34.4 Kpa27.6 Kpa

Tape edge stability as measured on ATS testerTape edge stability on ATS tester @ 1 N, 4 m/s

-10-505

10

0 20 40 60 80 100 120

Time, sec

Varia

tion,

m

icro

ns

Notes:

1) ~2.0 - 3.5 microns peak-to-peak variation typical

2) 330 microns stagger at supply reels attenuated

to 1 - 2 microns at the head location

Typical peak-to-peak edge variation as measured on ATS tester

Peak-Peak Edge Variation, Microns

0

0.5

1

1.5

2

2.5

3

3.5

4

4m 1N 6m 1N 8m 1N 10m 1N 12m 1 N 4m 0.5 N 6m 0.5 N 8m 0.5 N 10m 0.5 N 12m 0.5N

Speed, m/sec and Tension, N

Peak

-Pea

k Ed

ge V

aria

tion,

M

icro

ns

Typical one-sigma edge variation as measured on ATS tester

One Sigma Edge Variation, Microns

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

4m 1N 6m 1N 8m 1N 10m 1N 12m 1 N 4m 0.5 N 6m 0.5 N 8m 0.5 N 10m 0.5N

12m 0.5N

Speed, m/sec and Tension, N

One

Sig

ma

Edge

Var

iatio

n,

Mic

rons

CMRR Talke Lab ATS Data

Conclusions:Properly designed porous air bearing systems eliminate many

fundamental issues associated with tape guiding based on rollers and hydrodynamic guides, resulting in gentler and more precise tape guiding,

enabling the use of thinner and more fragile tapes. Optimized through complete system modeling, porous bearing materials can be chosen to vastly simplify the supporting air supply requirements. The resulting

porous bearing systems retain and enhance the benefits inherent with high performance tape drives but without the associated high cost, complexity,

power and space requirements.

In the ARC Advanced Test System configuration, the porous air bearing system has been shown to provide highly effective tape guiding

with lateral stability of less than 0.7 micron (one sigma) at speeds of up to 12 meters per second. Further increases in operating velocity are possible

as enhanced velocity control systems are added to these testers.

How can you feature this technology?Existing products:

Cost savingsSmaller pump, lower power, less heat, less debris, smaller filters

Performance enhancementHigher track density, higher speeds and data rates

Customer SatisfactionImproved tape and drive reliabilitySimpler maintenance

How can you feature this technology?

New products: Jump to a new product roadmap

Time to MarketRapid enablers necessary to compete with diskRate of improvement must accelerateAll new drives running late to plan

Maximize performance and capacitySmaller form factorHigher track density Higher speeds and data rates

How can you feature this technology?MOST IMPORTANTLY: Improve Customer Satisfaction

Improve tape reliability and data integrityImprove drive reliabilitySimplify maintenanceReduce overall storage costs

Will roller-based or sliding guide drives penetrate the accounts of your most demanding customers, given their history of poor reliability with similar products and the increased need for massive data storage?

OR WILL THEY PUT THEIR DATA ELSEWHERE?

Why Segway?

Time to Market

Customer Satisfaction

Competitive Advantage