TM Servo Technology for TrueTrack High TPI Disk Drives Authors - PowerPoint PPT Presentation

TM Servo Technology for TrueTrack High TPI Disk Drives Authors Sri-Jayantha, Dang, Sharma IBM, T. J. Watson Research Center, NY,USA and Yoneda, Kitazaki, and Yamamoto IBM, Fujisawa HDD Development, Japan APMRC, Tokyo, Japan Nov. 7, 2000 Harmonic Error Sources TrueTrack Servo Algorithm Digital Filter Implementation Autonomous State Propagation Mutiple Harmonics Performance Summary TrueTrack-APMRC-2000

Figure-1 Harmonic Error Sources at High TPI Disk-Shift due to Shock High-TPI Disk-Warp Challenges due to Stress Spindle Imbalance Spindle Vibration due to Imbalance TrueTrack-APMRC-2000

TM Servo Technology Impact of TrueTrack Conventional Digital Servo Problem 1/2 Track Pitch Position Error Track Center 20 ms with Novel TrueTrack Servo Solution 1/2 Track Pitch Position Error US Patent 5,608,586 TrueTrack-APMRC-2000

TrueTrack Servo Algorithm

Conventional Servo with a Disk Shift Figure-2 Disk Shift due to Shock VCM Digital Servo ADC DAC Controller PES - Demodulator Head Position + Track Position Conventional Digital Servo 1/4 Track-Follow Seek Track-Follow Settle PES 0 (Trk) -1/8 Excessive After a 1000-Track Move Runout -1/4 0 10 20 30 40 50 60 70 80 Time (ms) TrueTrack-APMRC-2000

Effect of a High Gain Filter Figure-3 High Gain Schematic Output of the filter 120 Hz Digital Filter dB 30 dB Steady State 0 Frequency + Servo Controller Current HDD PES With a High Gain Digital Filter Track-Follow Seek Track-Follow Settle Runout is Suppressed But has Settleout Penalty 0 10 20 30 40 50 60 70 80 Time (ms) TrueTrack-APMRC-2000

Figure-4 Optimally Initialized Filter M(n) (A-1) + + Y(n) p(n) M(n-1) High Gain (B-E) -E delay Digital Filter Initial State M(n-2) (C-F) -F delay Servo Controller + Current HDD PES With Optimally Initialized Filter Runout Suppressed with No Settleout Penalty 0 10 20 30 40 50 60 70 80 TrueTrack-APMRC-2000 Time (ms)

Filter Structure

Filter Structure Figure-6 Q(n) p(n) Y(n) A + + delay delay B -E p(n-1) 1 Y(n-1) C -F delay delay p(n-2) Y(n-2) Direct-Form Y(n)=A p(n)+B p(n-1)+C p(n-2) - E Y(n-1) - F Y(n-2) Y(n) R(n) p(n) A + + 2 B -E delay R(n-1) -F C delay R(n-2) + Y(n) p(n) A-1 + + M(n) V(n) Bias Free Form (B-E)/(A-1) -E delay M(n-1) 3 (C-F)/(A-1) -F delay M(n-2) TrueTrack-APMRC-2000

Figure-5 Openloop Transfer Function with a Filter Open Loop TF with and without Peak Filter 80 60 40 OLTF dB 20 0 -20 -40 -60 1 2 3 10 10 10 Hertz -100 -150 Degrees -200 -250 1 2 3 10 10 10 Hertz TrueTrack-APMRC-2000

Multiple Harmonics

Figure-7 Cascade Realization of Multiple Filters Y(n) R(n) p(n) A + + -E delay B Bias +AC R(n-1) Current -F C delay R(n-2) VCM VCM VCM Gray current current Burst Decoder VCM Driver Position Position (Track/Pes) (Track/Pes) Peak Peak Peak Track Notch Following Filter Filter Filter Filter Controller #1 #2 #3 Seek Controller TrueTrack-APMRC-2000

Effect of Cascade PES (bit) Figure-8 300 PES with no Peak Filter Implementation 250 200 Self-Vibration/Thermal Disk-Shift 150 100 50 0 0.00 0.02 0.04 0.06 0.08 0.01 0.03 0.05 0.07 0.09 Time (sec) PES (bit) 300 PES with Peak Filter ON with Optimum Initial Condition 250 200 150 100 50 0 0.00 0.02 0.04 0.06 0.08 0.01 0.03 0.05 0.07 0.09 Time (sec) Filter State 5,000 Filter State R(n) Y(n) p(n) A + + 0 (5,000) B -E delay R(n-1) (10,000) -F C (15,000) delay R(n-2) (20,000) 0.00 0.02 0.04 0.06 0.08 0.01 0.03 0.05 0.07 0.09 Time (sec) TrueTrack-APMRC-2000

Parallel Realization Figure-9 p(n) V(n) A-1 + + M(n) Bias Free Form (B-E)/(A-1) -E delay M(n-1) (C-F)/(A-1) -F delay M(n-2) Position Position (Track/Pes) (Track/Pes) Track Notch + Following p(n) Filter Controller Seek Controller V(n) Peak Filter #1 Peak Filter #2 Peak Filter #3 TrueTrack-APMRC-2000

Cross Vibration Example

An Experiment in Spindle Vibration Figure-10 Bay # B Cross Vibration Drive #B 90 Hz Track Following Controller For Self Vibration 75 Hz Drive #A 75 Hz Filter # A + dB Bay # A 0 Frequency 90 Hz For Cross Vibration Filter # B dB 0 Frequency TrueTrack-APMRC-2000

Figure-11 Parallel Implementation PES Without Filters PES with filters (a) 40 40 (b) 20 20 PES (bit) PES (bit) 0 0 -20 -20 -40 -40 -10 0 10 20 30 40 50 60 -10 0 10 20 30 40 50 60 Time (ms) Time (ms) Self-Vibration Filter#A 10 Inactive 75 Hz Filter State (bit) 5 (c) 0 dB Learning -5 Phase 0 Frequency -10 -10 0 10 20 30 40 50 60 Time (ms) Cross-Vibration Filter#B 10 90 Hz Filter State (bit) 5 dB (d) 0 Inactive -5 0 Frequency -10 -10 0 10 20 30 40 50 60 Time (ms) TrueTrack-APMRC-2000

Autonomous State Propagation

Autonomous Filter State Propagation Figure-12 PES with Autonomous Filters PES Without Filters (a) 40 40 20 20 PES (bit) PES (bit) (b) 0 0 -20 -20 -40 -40 -10 0 10 20 30 40 50 60 -10 0 10 20 30 40 50 60 Time (ms) Time (ms) Self-Vibration Filter Track-Follow Controller Track-Follow Controller + 10 PES(n) Autonomous Switch-B Filter State (bit) 5 M(n) (A-1) + V(n) Switch-A + (c) 0 -E delay (B-E) -5 M(n-1) Null-PES -10 -10 0 10 20 30 40 50 60 (C-F) -F delay Time (ms) M(n-2) Cross-Vibration Filter 10 Autonomous Filter State (bit) 5 (d) 0 -5 -10 -10 0 10 20 30 40 50 60 Time (ms) TrueTrack-APMRC-2000

Figure-13 Effect of Higher Harmonic Filters Algorithm-1 Algorithm-2 Track Seek Track Following Track Track Track Seek Following (Learning Phase) Following Following Following 128 128 64 64 PES (bit) PES (bit) 0 0 -64 -64 PES PES -128 -128 Filter State Filter State 3rd 2nd 1st 3rd 2nd 1st -60 0 60 120 180 -60 0 60 120 180 servo sector servo sector TrueTrack-APMRC-2000

Figure-14 Effect on Single Track Seek 4.0 Algorithm-1 average 1 track seek time for write [msec] 3.0 2.0 Algorithm-2 1.0 (Autonomous Mode) 0.0 0 5 10 15 20 25 30 Disk Shift (peak-to-peak) [um] TrueTrack-APMRC-2000

Figure-15 Effective Time to Format a Drive Algorithm-1 250% Format Unit Time Ratio 200% Algorithm-2 (Autonomous Mode) 150% Performance degradation = 15% 100% 0 5 10 15 20 25 30 Disk Shift (peak-to-peak) [um] 4um 4um 28um 28um TrueTrack-APMRC-2000

TM Algorithm Embedded in an LSI Module TrueTrack Figure-17 3.5" Deskstar HDC-Based Servo & Ultrastar Architecture TrueTrack 2.5" Servo Travelstar Algorithm Custom LSI Allows 1.0" DSP-Free Implementation Microdrive => Low-Cost Drives with High Performance Specification TrueTrack-APMRC-2000

Summary Presented an Algorithmic Solution to a Harmonic Error Source. Continuation of Filter State Following a Seek is the Key. Discussed Parallel vs. Cascade Implementation. Problem of PES with Multiple Harmonics can be Resolved. A Silicon Implementation of the TrueTrack Servo has been Realized. Acknowledgment Y. Nakagawa, N. Kagami, T. Ueda, A. Tokizono, T. Sakai, M. Kisaka, and Y. Ozawa IBM, Fujisawa HDD Development, Japan TrueTrack-APMRC-2000