２０１６年５月２６日＠千葉大学

第7回 電気学会 モーションコントロールの高機能化に関する協同研究委員会

ハードディスクドライブの磁気ヘッド位置決め制御

千葉工業大学 機械工学科 熱海武憲

磁気ヘッドの位置をより精密に制御する

ＨＤＤの磁気ヘッド位置決め制御系
Position signal
Disk

Spindle motor

Magnetichead

Voice-coil motor(VCM)

PZT actuator

Digitalcontroller磁気ヘッドの位置決め誤差

PZT actuator

Voice-coil motor(VCM)日本機械学会誌 2016. 4 Vol. 119 No.1169 より引用

https://www.hgst.com/sites/default/files/resources/HGST-Micro-Actuator-TB.pdf より引用

https://www.hgst.com/sites/default/files/resources/HGST-Micro-Actuator-TB.pdf より引用

さらに先の技術

Takenori Atsumi,``Emerging Technology for Head-Positioning
System in HDDs'',
IEEJ Journal of Industry Applications, Vol. 5, No. 2,
pp. 117-122, (2016-3)

Case 1: Film-coil actuator
Case 2: Thermal actuatorCase 1: Film-coil actuator
Case 2: Thermal actuatorEasy Excited Resonant Mode in HDDs
By VCM actuator
By external vibration(Butterfly mode: 5.2 kHz) (Torsion mode: 3.5 kHz)Film ActuatorThin film coil(Film actuator)
Direction of coil current

Pads for wire bonding

VCM with film actuatorFrequency Response of Actuator
VCM actuator

Film actuator

Comparison of Sensitivity Function
w/o Film actuator(VCM+PZT)

w/ Film actuator(VCM +PZT+ Film)Case 1: Film-coil actuator
Case 2: Thermal actuatorSensitivity function
Single-stage actuator (VCM only)

Dual-stage actuator (VCM + PZT)
15105

Gain [dB]0

PZT actuator-5-10-15-20-25

Voice-coil motor
(VCM)

-30

310

Frequency [Hz]410

Thermal Actuator
Magnetic headSlider
HeaterDisk formobile HDDs

VCM

PZT actuator

ThermalactuatorFrequency Response of Thermal Actuator
Measurement data

Mathematical model

Comparison of Sensitivity Function
Design results

Experimental results

Single-stage actuator (VCM only)
Dual-stage actuator (VCM + PZT)
Triple-stage actuator (VCM + PZT + Thermal actuator) )Comparison of Positioning Error
Time domain

Frequency domain

Single-stage actuator (VCM only), SD: 3.12 nm
Dual-stage actuator (VCM + PZT), SD: 1.57 nm
Triple-stage actuator (VCM + PZT + Thermal actuator) ), SD: 0.96 nmここ最近の学会発表

The 2nd IEEJ international workshop on Sensing, Actuation, Motion Control, and Optimization
March 8th, 2016, Seikei University, Tokyo

Estimation Method ofUnobservable Oscillations in
Sampled-Data Positioning Systems
Takenori Atsumi
Chiba Institute of Technology

Sampled-data Control System
Discrete-time system
Ref.

Error

Discretetime
Controller

Control input

Continuous-time system

Hold(D/A)

Sampler(A/D)

Continuous-time
Plant

Controlled variableExample: Tank System

Block Diagram of Tank System
Discrete-time system
TargetErrorlevel

HumanBeing

Turn faucet
on/offContinuous-time system

Hold(D/A)

Sampler(A/D)

TankSystem

Water levelIf the sampling time is too long…

Head-Positioning Control System in HDD
Position signal
Disk

Spindle motor

Magnetic
head

Voice-coil motor(VCM)

PZT actuator

Digitalcontroller

The timing of reading or writing user data
corresponds to the time between samples.
The control system cannot “see” intersampling
vibrations which cause destruction of users data.
Position signal area Data area

Measurement signal

Head movement

High-risk area for data destruction

We have to know difference
between observed and actual
controlled variables
Discrete-time systemRef.

Discretetime
Controller

Observed
controlled variable

Continuous-time system

Hold(D/A)

Sampler(A/D)

Continuous-time
Plant

Actualcontrolled variableUnobservable Amplitude of Oscillation
Ns: Number of samples for estimation,t : Sampling time

Amplitude

Actual variable
Observed variable

Unobserved amplitude

Ns tTime

: Damped natural frequency,: Damping ratio,: Initial phase,: Natural frequency,: Sample number,: Sampling timeOscillation at Sampling Frequency
Best case

Worst case

Dependence of 𝑚𝑢 on 𝜙0

Event probability

Oscillation at Nyquist Frequency
Best case

Worst case

Dependence of 𝑚𝑢 on 𝜙0

Event probability

Oscillation at One-third of Sampling Freq.
Best case

Worst case

Dependence of 𝑚𝑢 on 𝜙0

Event probabilityサンプリング定理と矛盾する？

時間領域

周波数領域

Two Index Values for Evaluation
Maximum value based

Root-Mean-Square (RMS) value based

Comparison with Previous Work
T. Atsumi and W. Messner, "Analysis of Unobservable Oscillations in
Sampled-Data Positioning Systems,” The IEEE Transactions on
Industrial Electronics, vol. 59, no. 10, pp. 3951-3960, (2012-10)

Maximum value
fixed initial phase (old)variable initial phase (new)RMS value
fixed initial phase (old)variable initial phase (new)Estimation Procedure
Set modal
parameters

Modal parameters of mechanicalsystem are decided by using
measurement results

Calculation ofIndex value

Index values are calculated by using
resonance frequency, damping ratio
and number of samples for
estimation

Evaluation using
Index value

Unacceptable sampling frequencies
are estimated by using index values
and target of reliability

Example: Hard Disk DriveEstimation Procedure
Set modal
parameters

Modal parameters of mechanicalsystem are decided by using
measurement data

Calculation ofIndex value

Index values are calculated by using
resonance frequency, damping ratio
and number of samples for
estimation

Evaluation using
Index value

Unacceptable sampling frequencies
are estimated by using index values
and target of reliability

Mechanical Characteristics of HDDs
Frequency response

Measurement data

Mathematical model

Mathematical model

Primary mechanical resonance• Resonance frequency: 4100 Hz• Damping ratio: 0.01

Estimation Procedure
Set modal
parameters

Modal parameters of mechanicalsystem are decided by usingmeasurement data

Calculation ofIndex value

Index values are calculated by using
resonance frequency, damping ratio
and number of samples for
estimation

Evaluation using
Index value

Unacceptable sampling frequencies
are estimated by using index values
and target of reliability

Dependence of Unobservable Amplitude on
Sampling Frequency• Resonance frequency: 4100Hz• Damping ratio: 0.01
• Number of sample: 5(blue), 10(green), 20(red)Maximum value

RMS valueEstimation Procedure
Set modalparameters

Modal parameters of mechanicalsystem are decided by using
measurement data

Calculation ofIndex value

Index values are calculated by using
resonance frequency, damping ratio
and number of samples forestimation

Evaluation using
Index value

Unacceptable sampling frequencies
are estimated by using index values
and target of reliability

Unacceptable Sampling Frequency•••

Mechanical Resonance: 4100Hz/ Damping ratio: 0.01
Number of sample for estimation: 5
Acceptable unobservable amplitude (RMS): Less 10%

Acceptable level

Unacceptable Sampling Frequency•••

Mechanical Resonance: 4100Hz/ Damping ratio: 0.01
Number of sample for estimation: 5
Acceptable unobservable amplitude (RMS): Less 10%
Unacceptablefrequency

Acceptable level

Conclusion
Most of positioning control
systems are sampled-data
control systems with mechanicalresonances.
We should check unobservableamplitude on our experimental
systems.

ACC2016@BostonでWorkshop