Transcript Nidec FDB RM type의 run

Development of a magnetic thrust bearing
for a HDD spindle system
2004/03/27
Park, Jinseok
PREM, Hanyang University
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Precision Rotating Electromechanical Machine Lab
Contents
1.
2.
3.
4.
5.
6.
7.
8.
9.
Motivation
Previous Works
Design Concept
Design Goals
Proposed Designs
Simulation
Problems
Conclusions
Future Works
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1. Motivation
< Power Consumption Test of P120 >
Nidec 7.2K (Motor + Disk3.5 + Cover)
8
7
6
Power [W]
 Motor efficiency : 45%
Other Loss
Copper Loss
FDB Friction Loss
Disk Windage Loss
( at 7200rpm )
 Total loss : 55%
5
• Disk windage loss : 13.4%
• FDB Friction loss : 17.8%
4
① Journal : 10.54%
3
② Thrust : 7.26%
2
1
0
0
2000
4000
6000
8000
• Copper loss
: 5.9%
• Other Loss
: 17.8%
10000
Speed [rpm]
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2. Previous Works
1. Magnetic bearing : inherently unstable in one direction
• Passive type
• Active type
→ all about how to ensure stability and sufficient magnetic force
2. Hybrid bearing
Magnet
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3. Design concept
Shaft
N
Sleeve
S
Upper
journal
S
Lower
journal
N
N
Thrust
S
Magnetic thrust bearing
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4. Design Goals
1. Magnetic force : large enough to levitate rotating parts
• Axial direction load : 0.048011*9.81 = 0.470988N
• FM ,axial  470.988mN
2. Reliable at high temperature
• Consideration of demagnetization effect due to rising temperature
3. Similar size with FDB
Nidec HDD spindle motor with FDB
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5. Proposed designs
1. Center thrust
 PM
• thickness : 2.6mm
• Inner diameter : 4.05mm
• Outer diameter : 8.3mm
 Air gap : 0.2mm
 Relatively large space for PMs comparing to
bottom thrust
 Better dynamic characteristic is expected
comparing to bottom thrust
 But difficult to assemble
Center thrust
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2. Bottom thrust
 PM
• thickness : 2.0mm(thrust), 1.3mm(sleeve)
• Inner diameter : 4.05mm
• Outer diameter : 8.3mm
 Air gap : 0.2mm
 Relatively small PMs comparing to center
thrust
 Relatively easy to assemble
Bottom thrust
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3. Material selection
P80
P120
MB
Shaft
SUS304se
SUS420J2
SUS304se
Non-magnetic
Sleeve
SUS430
SF20T
SUS430
Magnetic
Attractive force
Significant friction
occurs during starting
period
non-magnetic
shaft
Magnetic
shaft
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 Permanent magnet : Bonded NdFeB
• High residual flux density
• Relatively good accuracy of geometry
• Acceptable demagnetization rate
 Yoke : SPCC
• High permeability
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4. Sealing
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5. Assembly procedure
Bottom thrust
Center thrust
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6. Simulation (Maxwell 2D)
1. Material input
 Residual flux density : 0.7T
• Maximum operating temperature = 100℃
• Temperature coefficient of Br = - 0.13 %/℃
 BH-curve
2.5
SPCC
SUS430
B [Tesla]
2
1.5
1
0.5
0
0
0.5
1
1.5
2
2.5
3
H [A/m]
3.5
4
4
x 10
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2. Result
① Center thrust & bottom thrust
1500
center thrust
bottom thrust
1000
force[mN]
500
Axial Load
0
-500
-1000
-1500
-200
-150
-100
-50
0
50
100
150
200
displacement[m]
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② Displacement of the thrust due to elevated temperature
1500
20  C
100  C
1000
force[mN]
500
Axial Load
0
-500
12m
-1000
-1500
-200
-150
-100
-50
0
50
100
150
200
displacement[m]
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7. Problems
1. Stiffness
10K FDB
: 1.23e6 [N/m]
7.2K FDB (P80) : 8.39e4
MB (center thrust) : 6.7e3
2. Damping
10K FDB
MB
: 9.15e6 [Ns/m]
: Expected to be very small
 Possible solution
• Self-controlled system using eddy current
• Air bearing
• Active control
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8. Conclusions
1. Proposed magnetic thrust bearings produce sufficient
magnetic force to levitate rotation parts
2. Proposed magnetic thrust bearings are reliable within
maximum operation temperature 100 ℃
• Significant friction loss reduction is expected
3. Center thrust bearing is expected to be better than bottom
thrust bearing in respect of magnetic force and dynamic
characteristics
4. Stiffness and damping of MB are less than those of FDB
• Dynamic characteristics remain to be improved
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9. Future Works
1. Prototyping (center thrust first)
2. Experiment
• Efficiency comparison of FDB motor and BM motor
• Dynamic characteristic comparison of FDB motor and BM
motor
3. Improving dynamic characteristics
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