Download - 第7回電気学会モーションコントロールの高機能化 …dmec/committee/DMEC8005/presentations/...ハードディスクドライブの 磁気ヘッド位置決め制御
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
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
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
Voice-coil motor(VCM)
Disk Spindle motor
Magnetichead
PZT actuator
Digital controller
Position signal
Voice-coil motor(VCM)
PZT actuator
磁気ヘッドの位置決め誤差
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(Butterfly mode: 5.2 kHz)
By external vibration(Torsion mode: 3.5 kHz)
Direction of coil current
Pads for wire bonding
Film Actuator
Thin film coil (Film actuator)
VCM with film actuator
VCM actuator Film actuator
Frequency Response of Actuator
w/ Film actuator(VCM +PZT+ Film)
w/o Film actuator(VCM+PZT)
Comparison of Sensitivity Function
Case 1: Film-coil actuator
Case 2: Thermal actuator
Single-stage actuator (VCM only)
Dual-stage actuator (VCM + PZT)
103
104
-30
-25
-20
-15
-10
-5
0
5
10
15
Frequency [Hz]
Ga
in [d
B]
Voice-coil motor(VCM)
PZT actuator
Sensitivity function
Heater
Magnetic head
Slider
Thermal Actuator
Disk for mobile HDDs
Thermalactuator
PZT actuator
VCM
Frequency Response of Thermal Actuator
Measurement data Mathematical model
Design results Experimental results
Comparison of Sensitivity Function
Single-stage actuator (VCM only) Dual-stage actuator (VCM + PZT)Triple-stage actuator (VCM + PZT + Thermal actuator) )
Single-stage actuator (VCM only), SD: 3.12 nm Dual-stage actuator (VCM + PZT), SD: 1.57 nmTriple-stage actuator (VCM + PZT + Thermal actuator) ), SD: 0.96 nm
Time domain Frequency domain
Comparison of Positioning Error
ここ最近の学会発表
Estimation Method ofUnobservable Oscillations in Sampled-Data Positioning Systems
Takenori Atsumi
Chiba Institute of Technology
The 2nd IEEJ international workshop on Sensing, Actuation, Motion Control, and OptimizationMarch 8th, 2016, Seikei University, Tokyo
Sampled-data Control System
Continuous-timePlant
Discrete-time
Controller
Hold(D/A)
Sampler(A/D)
Error
Controlled variable
Ref. Control input
Continuous-time systemDiscrete-time system
Example: Tank System
Block Diagram of Tank System
Tank System
Human Being
Hold(D/A)
Sampler(A/D)
Error
Water level
Target level
Turn fauceton/off
Continuous-time systemDiscrete-time system
If the sampling time is too long…
Voice-coil motor(VCM)
Disk Spindle motor
Magnetichead
PZT actuator
Digital controller
Head-Positioning Control System in HDDPosition signal
The control system cannot “see” intersamplingvibrations which cause destruction of users data.
The timing of reading or writing user data corresponds to the time between samples.
Position signal area Data area
Measurement signal
High-risk area for data destruction
Head movement
Continuous-timePlant
Discrete-time
Controller
Hold(D/A)
Sampler(A/D)
Actualcontrolled variable
Ref.
Observed controlled variable
Continuous-time systemDiscrete-time system
We have to know difference between observed and actualcontrolled variables
Actual variable
Ns: Number of samples for estimation, t : Sampling time
Unobserved amplitude
Ns t
Am
plit
ude
Time
Unobservable Amplitude of Oscillation
Observed variable
: Natural frequency,
: Damping ratio,
: Damped natural frequency,
: Sample number, : Sampling time: Initial phase,
Oscillation at Sampling Frequency
Event probability
Worst case Best case
Dependence of on 𝑚𝑢 𝜙0
Oscillation at Nyquist Frequency
Event probability
Worst case Best case
Dependence of on 𝑚𝑢 𝜙0
Event probabilityDependence of on 𝑚𝑢 𝜙0
Oscillation at One-third of Sampling Freq.
Worst case Best case
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
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 RMS valuefixed initial phase (old)variable initial phase (new)
fixed initial phase (old)variable initial phase (new)
Comparison with Previous Work
Evaluation usingIndex value
Calculation ofIndex value
Set modalparameters
Modal parameters of mechanical system are decided by using measurement results
Index values are calculated by using resonance frequency, damping ratio and number of samples for estimation
Unacceptable sampling frequencies are estimated by using index values and target of reliability
Estimation Procedure
Example: Hard Disk Drive
Evaluation usingIndex value
Calculation ofIndex value
Set modalparameters
Modal parameters of mechanical system are decided by using measurement data
Index values are calculated by using resonance frequency, damping ratio and number of samples for estimation
Unacceptable sampling frequencies are estimated by using index values and target of reliability
Estimation Procedure
Mechanical Characteristics of HDDs
Primary mechanical resonance• Resonance frequency: 4100 Hz • Damping ratio: 0.01
Frequency response Mathematical model
Measurement data Mathematical model
Evaluation usingIndex value
Calculation ofIndex value
Set modalparameters
Modal parameters of mechanical system are decided by using measurement data
Index values are calculated by using resonance frequency, damping ratio and number of samples for estimation
Unacceptable sampling frequencies are estimated by using index values and target of reliability
Estimation Procedure
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
Evaluation usingIndex value
Calculation ofIndex value
Set modalparameters
Modal parameters of mechanical system are decided by using measurement data
Index values are calculated by using resonance frequency, damping ratio and number of samples for estimation
Unacceptable sampling frequencies are estimated by using index values and target of reliability
Estimation Procedure
• Mechanical Resonance: 4100Hz/ Damping ratio: 0.01• Number of sample for estimation: 5• Acceptable unobservable amplitude (RMS): Less 10%
Acceptable level
Unacceptable Sampling Frequency
Unacceptable 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
Conclusion
Most of positioning control systems are sampled-data control systems with mechanical resonances.
We should check unobservable amplitude on our experimental systems.
ACC2016@BostonでWorkshop