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