Transcript Document

Control of mechanical systems
in data storage
Collaborations in Data Storage
STMicroelectronics – Agrate – MI
Computer Mechanics Lab - UC Berkeley
Prof. Masayoshi Tomizuka – prof. Roberto Horowitz
Center for Magnetic Recording Research (CMRR) UC San Diego
Prof. Frank Talke
Data Storage Center – Carnegie-Mellon University
Prof. William Messner
HITACHI-IBM Almaden Research Center
Hard Disk Drives
Spindle
VCM
Capacity
Data
Actuators:
stored
indexes:
on concentric
circular tracks
•
Spindle
TPI:
Tracks
motor
PeratInch
a constant
from
Operating
speed,
25k
to modes
60k
between 3600 and
18000 rpm
• Track
BPI: Bits
Following
Per Inch
when
up to
performing
•
500kb
Brushless
R/W operations
•
R/W Heads
•
Track
•
BPIxTPI:
Provides
Seek 30Gb
when
theper
changing
rotation
in2 of
track the disk stack assembly
Voice Coil Motor (VCM)
•
DC motor
•
Moves the heads over
the disk surface
Technologies, problems and objectives
Subsystem
Suspension
Spindle
Channel
Servopositioning
Heads
Technologies
•Microelectronics
•Mechanics
(analog
and digital)
•Electric
Drives
•Electric
Drives
•Materials
•Code
theory
•Digital
control
•Mechanics
•Aerodynamics
•Digital filters
Problems and objectives
Resonant
Elasticity
Seek
Time:
modes
Eccentricity
512ms
Fly height:
-9
BER
<
10
Torque
ripple
PES:
57%
Tr.
15 nm
Bearings
(i.e.
50 nm
Speed:
120
precision
in
km/h
Disk
modes
servopositioning)
Head Servo-positioning
Servo sector
Servo sector
Sector
• synchronization signals
• Track number
• Head postion w.r.t. track center (PES)
Sampling
F = N x rpm / 60 ; N = #Servo sectors
F = 8 30 kHz
The head servopositioning system
NRRO Non Repetitive Run Outs
Windage
Effect of air turbulence on head
support
(wind speed may reach up to 100 km/h)
RRO Repetitive Run Outs
Track deformation
•Due to initialization, heating, bearing
imperfections
3
n-1
2
n
•Track pitch: <1 m (HDD Low End)
Ideal track center
1
•RRO: repetitive disturbance, locked in
phase with disk rotation
0
-1
•Amplitude may be more than track pitch
Actual track center
-2
•Frequencies: harmonics of rotational
frequency (5400 rpm  90 Hz)
-3
-4
-3
-2
-1
0
1
2
3
4
Hard Disk
Interesting, multi-disciplinary case of
study:
Modeling of complex mechanical systems
Identification and control
Power electronics and electric drives
Vibration suppression
Data coding, magnetic materials,
aerodynamics, signal processing …
Research Activities in HDD Servo
Modeling and Simulation
Digital control algorithms design and
test
Active vibration suppression
VCM voltage command
Modeling and Simulation
Experimentally tuned simulator:
ls
lx
PESrro
0.08
0.06
0.04
[Tracks]
e-block
Kvs, Bvs
0.02
0
-0.02
-0.04
suspension
NonLinear
Linear
Non
Friction
Friction
Model
Model
..
F
1/J
1/s
1/J
1/s
t
[Nm]
Windage
Windage
[rad/s2]
Bias&
&
Bias
FlatCable
Cable
Flat
θvs
-0.06
0
10
20
30
RRO NRRO
NRRO
RRO
.
F
[rad/s]
1/s
1/s
F
[rad]
Arm
Arm
Resonances
Resonances
[rad]
PES
TPR
TPR
[Tr]
[Tr]
40
50
[Samples]
60
70
80
90
Dual Stage Actuation - Piezo
Dual stage actuator can be simulated
Piezo (experimentally tuned)
Mems (multi-body mechanical system)
gold-coated
slider
spindle
suspension
LDV
Dual Stage Actuation - Piezo
Characterization of piezo suspension (also vs. fly
height)
[ m/V]
magmu
0
milli-actuator data
10
-1
10
-2
10
-3
10 3
10
4
f [Hz]
10
[
phasedeg]
200
100
0
-100
-200 3
10
•
•
4
f [Hz]
10
“Modeling Product Variabilities of Dual-Stage Suspensions for Robust Control” - M. Rotunno,
R. Oboe, R.A. de Callafon - ISPS 2002 – Santa Clara (USA) – June 2002
“LQG / LTR control of a dual stage actuator hard disk drive with piezoelectric secondary
actuator” – A.Beghi, R.Oboe – European Control Conference ECC 2001 – Porto (Portugal) –
September 2001
Windage modelling
Head position measured with LDV
Closed loop and open loop identification
w
R(s)
y
P(s)
w
Bias
P(s)
y
Digital servo control design and test
External Board
Channel
Preamp
Controller
DAC
Controller
Power
Drive
DAC
VCM
Estimated state feedback controller with
disturbance observer
Xs1: estim. position
Xs2: estim. velocity
Xs3: estim. disturbance
Xs4: u(k-1)
•
“Loop shaping issues in hard disk drive servo system design” - A.Beghi, R.Oboe, P.Capretta,
F.Chrappan Soldavini - Advanced Intelligent Mechatronics AIM 2001 – Como (Italy) – July 2001
•
“Optimal Estimation for Disk Drive Head Positioning System” - D.Ciscato, R.Oboe, G.Picci,
E.Colecchia, G.P.Maccone, G.Traversa - The 2nd Annual Magnetic Recording Conference on Recording
Systems - Hidden Valley, Pittsburgh PA (USA), June 12-15 1991
Servo algorithms
Repetitive control
FFT PES
5
4.5
4
Tracce^2/H
z
3.5
3
2.5
2
Standard Controller
1.5
1
Repetitive Controller
0.5
0
0
90
180
270
360
450
540
630
720
810
900
990
1170
1350
1530
1710
1890
1080
1260
1440
1620
1800
1980
Frequency (Hz)
Servo algorithms
Multirate control
Position
Tc
Target
K
Zoh
u(k,i)
)
x(k,i)
H
H
plant
Plant
Ts = mTc
PES
Estimator
Ts
RRO&NRRO
4
short seek (5 tracks)
short seek (1 track): sr vs mr
Sensitivity
Function
FFT PES
x 104
1.2294 x 10
1.229
3
multi-rate
10
1.2289
1.2293
Tracks/Hz
Results:
Pubblications:
•Short Seek improvement
•Analytical evaluation of closed-loop
Federico
Marcassa
and
Oboe
Enlarge
BWRoberto
R. Oboe,
F.control
Marcassa
- To appear
in Mechatronics
sensitivity
function
2002 – Berkeley
(USA) – December 2002
Reduce
TMR(i+1)Tc
Control
Engineering
Practice 2003 – In press
i∙Tc
Tc
•Worsening
in
sensitivity observed (k+1)∙Ts
k∙Ts
(analytically and experimentally)
Ts=m∙Tc
2.5
single-rate
1.2289
0
1.2292
position
head
[tracks]
position [tracks]
head
(dB)
Magnitude
x (k,i)
Objectives (from literature):
x (k,m-1)
x (k,1)
u (k,i)
Reduce
command
discontinuities
x (k,0)
“DISTURBANCE
HARD
“Disturbance
rejection inIN
hard
diskDISK
drivesDRIVES
with
u (k,1) REJECTION
Reduce
phase
delay
WITH
MULTI-RATE
ESTIMATED
STATE FEEDBACK”
u (k,0) estimated
u (k,m-1)
multi-rate
state feedback”
2 1.2289
1.5
1
-10
1.2291
1.2289
single-rate
Larger Estimator Bandwidth
multi-rate
-20
1.229
1.2289
-30
1.2288
1.2289
Estimator Bandwidth : 500 to 900 Hz
0.5 1.2288
-40
1.2288
1.2288
0 -50
0
1.2287 10
1.2288
2
Controller Bandwidth : 500 Hz
2
500
1000
3
1500
4
2000
10
3
2500
Frequency
(Hz)
Frequency
5
6 [Hz]
time [sec]
[t]
time
3000
3500
7
8
-3
-3
x 10
Servo algorithms
Initial Value Compensation
Settling time phase Disturbance
Mode SwitchingSeek:
Control
u
PROCESS
PLANT
0.1
0.05
• Bumpless switching
• Limitation of transients
during settling phase
&
0
SETTLING
SETTLING
CONTROLLER
CONTROLLER
-0.05
Tracks
MSC+IVC
MSC
SEEK
SEEK
us
xSn
-0.1
-0.15
>YDD
>Y
-0.2
e
Threshold
SWITCH
-0.25
-0.3
•Objectives:
ya
ESTIMATOR
ESTIMATOR
MSCxSi
MSC+IVC
-
xS1
+
yR
ut
140
160
180
CONTROLLER
CONTROLLER
200
220
Samples
240
yn
D xS
IVC
TRACK FOLL.
FOLL.
TRACK
y
260
280
300
•Solution:
•Act on estimated states in
order not to have a transient in
both command and position
estimate
“Initial value compensation applied to disturbance observer-based servo control in HDD” – R. Oboe, F.
Marcassa - Advanced Motion Control 2002 (AMC2002) – Maribor (Slovenia) – July 2002
Vibration compensation
Amp
controller
iff
VCM
PES
MEMS rotational
accelerometer
13 kTPI, 5400 RPM HDD
mounted on a shaker
Feedforward
compensator
Compensation up to 600 Hz
Standard Controller
FF Filter
FF Gain
Active vibration damping
Active suspension with two
piezo strips:
Actuation
Sensing
Active damping of resonant
modes
VCM control: Current Mode
Bemf
Kt
-
Command
[V]
Linear Power Amplifier
& Phase Shaping
[V]
U(s) +
1
RT+sLVcm
[A]
Kt
J*s
I(s)
R
Pros
Bandwidth 50kHz  I=GU
Robustness against variations in RT LVCM
Cons
Dissipation: R shunt – Linear Amplifier
Silicon area: Linear Amplifier
Digital current loop  expensive A/D
Controllo VCM: Voltage Mode
Bemf
Kt
Command
[V]
-
Digital
Prefilter
Multi-rate
Power
PSM
[V]
U(s) +
1
RT+sLVcm
[A]
I(s)
Kt
J*s
Pros
Cons
 Good performance without current meas.
 Cost reduction
 Migration toward SOC
 Pre-filter cancels out the electrical dynamic
of VCM
 R varies ±30%
 On-line estimation of R required
VCM control: Voltage Mode
Solution: Extended Kalman Filter to estimate R
On-line pre-filter adaptation
xref
From servo controller
+
Gain matrix and
ff compensator
-
Ts
VCM+
Tc
Ho
Head
position
voltage dr.
H1
xest
EKF
Tc
Ts = 8 Tc
Rt
Pos, vel, current…
Presently developed for Seagate, IBM and STM