Head Loading Control for Hard Disk Drive Process MRAC Technique

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1 Proceengs of the Internatonal MultConference of Engneers an Comuter Scentsts 18 Vol II, March 14-16, 18, Hong Kong Hea Loang Control for Har Dsk Drve Process MRAC Technque V. Boonranchoo, J. Chaorangern, V. Tsuwanorn, an A. Numsomran, Member, IAENG Abstract Hea to sk strkng s an essental roblem n the servo track wrtng rocess cause by less ynamc resonse control. Ths aer escrbes hea loang control for the har sk rve rocess usng moel reference aatve (MRAC) technque, n orer to ecrease the occurrences of the hea strkng. The ntrouce technque, screte tme moel reference aatve has an ajustable control mechansm to ecrease the evaton of a system outut from the outut of the reference moel so that ncrease reference trackng erformance. The exerment results mlemente n self-servo track wrter llustrate that the roose controller esgn can acheve the effectve control erformance comarng wth the conventonal PID control. Inex Terms Har Dsk Drve, Hea loang Control, MRAC R I. INTRODUCTION AMP Ram loa/ unloa (L/UL) technology was frst ntrouce n the early 199 s n moble rves mae by PrareTek an Integral [1], an has been use n a varety of removable sk rves ever snce, nclung all IBM.5 rves snce Contnung research an eveloment on L/UL mechansms has ae further benefts, nclung ncrease areal ensty an rve caacty, more effcent ower utlzaton, an sueror shock resstance [, 3]. Unfortunately, urng the loa/unloa rocess, the effect of varous oeratng arameters, such as loa/unloa see, VCM oscllaton, ram heght, an frcton, contnue to hol back Ram L/UL erformance [4 6]. back Ram L/UL erformance [4 6]. In ths aer, we concentrate on roblems wth the VCM velocty rofle, artcularly the resonse of the hea loang rocess, whch vares accorng to the non-lnear characterstcs of the system uner control. Imroer VCM velocty affects sler atttue, reucng ts flyng heght (FH) an causng hea-sk nterface (HDI) roblems n servo track wrtng, whch n turn macts roucton cost an tme. To aress ths roblem, we roose a esgn scheme for screte-tme moel reference aatve control of the ram loang rocess. The moel reference aatve control technque was frst ntrouce by Whtacker n The structure of aatve systems an the mechansms use for the aataton of unknown or varable arameters create a egree of nonlnearty n the controlle system. Snce the 196s, MRAC theory has been eveloe extensvely, wth several contnuous-tme an screte-tme [7 1] MRAC algorthms ale to control systems, nclung Mechatroncs An Automaton Control [ 4], Process Control [5], Power system Control [6], etc. A number of schemes for esgnng aatve laws for such systems have also been ntrouce, nclung the senstvty moel [7], stablty theory of Lyaunov [8, 9] an PoPov s hyerstablty concets [3]. Ths aer escrbes hea loang control for the har sk rve rocess usng moel reference aatve (MRAC) technque, n orer to ecrease the occurrences of the hea strkng. The ntrouce technque, screte tme moel reference aatve has an ajustable control mechansm to ecrease the evaton of a system outut from the outut of the reference moel so that ncrease reference trackng erformance. The exerment results mlemente n selfservo track wrter llustrate that the roose controller esgn can acheve the effectve control erformance comarng wth the conventonal PID control. Ths aer s organze as follows: n secton II, we escrbe an overvew of L/UL control systems; n secton III, we resent our methoology for our DTMRAC scretetme moel reference aatve control; n secton IV, we etal the setu an results of our erformance evaluaton; an n secton V, we offer conclung remarks. II. LOAD/UNLOAD CONTROL SYSTEM A. Harware The har rve hea s L/UL control system agramme n Fg. 1 nclues VCM an Loa/Unloa mechancal structures, a VCM ower rver, velocty control rocessor, sgnal converter an embee frmware. The nut of the control system s the voltage to the VCM rver an the outut s an L/UL hea velocty. For our research, we use voltage generate by the VCM back electromotve force (Vbemf), whch s roortonal to the VCM rotatng velocty, as the measurement sgnal to control the loa/unloa hea velocty.

2 Proceengs of the Internatonal MultConference of Engneers an Comuter Scentsts 18 Vol II, March 14-16, 18, Hong Kong Fg.. Moel Reference Aatve Control (MRAC) Control System. Fg. 1. Hea Loang n SSTW Proces Dagram. B. System Moel The ram loa sk rve actuator can be escrbe by a combnaton of mechancal an electrcal ynamc equatons. The mechancal ynamcs are gven by Jx Kt, (1) where x s the actuator arm oston (mm), J s the actuator nerta (g-mm ), an the current ale n the col (am). Kt s a torque factor (N-mm/am). The electrcal ynamcs are reresente by Vs R L Vb t, () where R an L are secfe as the col resstance (ohm) an nuctance (mh), resectvely, V s s the suly voltage control sgnal avalable as nut to the system, an V b K t x s the back electro-motve force. For har sk rve ram loang control, the rocess transfer functon s obtane by choosng the state x 1 x,x x,x 3 an rovng the control nut as u V s. The system can be llustrate n state-sace form as x Ax Bu, y Cx, where 1 A Kt / J, B, C Kt / L R/ L 1/ L 1 III. METHODOLOGY FOR DISCRETE TIME MODEL REFERENCE ADAPTIVE CONTROL (DTMRAC) A. Controller Desgn The MRAC may be regare as an aatve servo system n whch the esre erformance s exresse n terms of a reference moel, whch creates the requre resonse to the nut sgnal. A block agram of the MRAC control system s ecte n Fg.. (3) MRAC control system s the feeback loo comose of the controller, the rocess an atonal feeback loo whch ajusts the controller arameters. The arameters of controller are ajuste on the bass of feeback from the error, whch s the evaton between the outut of the system an the outut of the reference moel. 1 JkT, e kt, (4) where ekt, ykt, ym kt s the error between the system outut an the outut of reference moel. So as to mnmze the erformance nex, the arameter vector of the ajustable controller has to change n the recton ooste the graent J. Thus, the aataton law n screte form s JkT, kt T kt (5) ekt, kt ekt, ekt, where the comonents of are the senstvty ervatves of the error wth resect to, an the arameter s an aataton gan. For the transfer functon of the thr orer rocess escrbe by y k ayk1 a1y k ayk3 (6) bu k1 bu k bu k3 1 We frst erform the z-transform of both ses of the fference equaton. ayk 1ayk 1 ayk 3 yk (7) bu k1bu 1 kbu k3 1 y z bz bz 1 b Hz (8) 3 1 u z z a z a z a where 1 H z s the z-transfer functon from u to y. A block agram for ths aatve system base on MIT rule s llustrate n Fg.. The close loo transfer functon becomes

3 Proceengs of the Internatonal MultConference of Engneers an Comuter Scentsts 18 Vol II, March 14-16, 18, Hong Kong y z b z b z b z b z b c4 c3 c c1 c 5 c c4 c3 c c1 c u z z a z a z a z a z a where b b K K K c4 b bk b K bk bk b K c b b K bk b K b K b K bk c 1 1 b bk b K b K b c1 1 b K c c4 1 a a bk bk bk a a a bk b K bk bk b K c a a a b K bk b K b K b K bk, c a bk b K a b K a c1 1 b K. c The control am s for changng value of the lant outut y accorng to the outut of the reference moel y m. The transfer functon of reference moel s secfe as ym z Hm z u z c 1 bm4z bm3z bmz bm1z bm 5 1 m4 m3 m m1 m z a z a z a z a z a (9) (1). Accorng to the roceure of aatve controller esgn, we then aly the MIT graent rules for calculatng arameters of PID controller, s gven n (11) ~ (16): J KkT T KkT K J y K kt J KkT T KkT K y K K kt y K J y J K kt TK kt K K kt y K J y where J, y 1, an D / t bd b1b D b b1 D bd y 5 D ac4d ac3d acd ac 1Dac K Uc y bd bd 1 bd y 5 D ac4d ac3d acd ac 1Dac K Uc y (11) (1) (13) (14) (15) bd b1 b D b b1b D y b1 b Db (16) 5 K D ac4d ac3d acd ac 1D a c Uc y K K K From (14), (15) an (16), we obtan,, as t t t gven n (17), (18) an (19) resectvely: J KkT TKkT K bd b1b D b b1 D bd (17) 5 D a c4d ac3d acd ac1dac Uc y J KkT TKkT K bd bd 1 bd (18) 5 D ac4d ac3d acd ac1dac Uc y J K kt TK kt K bd b1 b D b b1b D (19) b1 b Db 5 D ac4d ac3d acd ac1dac Uc y IV. EXPERIMENTAL RESULTS AND ANALYSIS A. Servo Track Wrter To valate the erformance of the roose controller esgn, the exermental system comoses of --Har rve self-servo track wrter wth a ram L/UL mechansm. --PH4LC car, Altera Cyclone II FPGA, runnng verson EPC15 to control the system. --Master PC for rogrammng FPGA an analyss of sgnal ata. The rogrammng s an ale OOP language comle an run wth an STWHost rogram an usng an ethernet connecton between the comuter an the PH4LC car. --Golen unt.5" har rve. Hea U/UL rocesses were execute by commans from the STWHost an STW Console rogram on the Master PC. The exctaton sgnal an the measure sgnal from unloang control were save n *.at fle for further analyss usng MATLAB. B. Results an Analyss Referng to erformance requrements, hea loang veloctes must be effectvely controlle to revent hea to sk nteracton. The esre hea loang veloctes must track the reference nut amltue at 35mm/sec, whch

4 Proceengs of the Internatonal MultConference of Engneers an Comuter Scentsts 18 Vol II, March 14-16, 18, Hong Kong can be acheve wthout hea-sk nteracton. The ram loang maneuver must also execute wthn the 11V saturaton voltage of the amlfer. Thus, the reference moel took the followng form: ym z uc z 6.7e-5z 4-7.9e-5z 3 () -6.11e-5z 5.69e-6z1-1.6e-7 z z z z.99z1-1.6e-7 The structure of the aatve control system has alreay been rove n Fg. 3, an the exermental arameters are shown n Table I. Fnally, the comle coes for the new control algorthm were loae nto the Altera Cyclone PH4LC car. Fg. 4. The Resonse of Conventonal- PID Control for VCM Velocty n SSTW Process. TABLE I PARAMETER VALUES OF DTMRAC SYSTEM. Symbol Quantty Value 1, 1, 1, aataton gan P aataton gan I aataton gan D.,.43.35,.39.41,.5 Fg. 5. Conventonal- PID Control Sgnal. Fg. 3. Block Dagram of Dscrete Tme Moel Reference Aatve Control System. The erformance of screte tme moel reference aatve control for ram loang rocess n har sk rve s shown n Fg. 6 an 8 comare wth conventonal PID n Fg. 4. The fgures show satsfe value of the loang velocty an VCM voltage saturaton. Furthermore, the maxmum overshoot of loang velocty was ecrease by aataton gan ajustment. In the results fgures, t s clear that the VCM Velocty resonse of the roose ram loa control usng the DTMRAC technque. The mrove control erformance of the DTMRAC control system s esecally ronounce when comare to that of conventonal PID shown n Fg. 4. Clearly, the controller shows lower VCM oscllaton n hea to sk nteracton ror to hea loang. Fg. 6. The Resonse of DTMRAC 1, 1, 1, 1 for VCM Velocty n SSTW Process.

5 Proceengs of the Internatonal MultConference of Engneers an Comuter Scentsts 18 Vol II, March 14-16, 18, Hong Kong The reference trackng erformance exhbte n Fgures 8 an 9 reflects the aatve control strategy. The velocty error ecrease as execte whle large overshoot at the begnnng of the velocty rofle has been ecrease. Fgure 1 shows that the ram loang control are execute wthn the accetable range of 11V saturaton voltage of the amlfer. Reeatablty was nvestgate by comletng 5 consecutve loang cycles wthout falure. Fg. 7. DTMRAC 1, 1, 1, 1 Control Sgnal. V. CONCLUSION We successfully mlemente the moel reference aatve control system for har sk rve hea loang rocesses usng MIT rule aatve mechansm. We then conucte exerments on the self-servo track wrter PH4LC unt to verfy the erformance of the roose ram loang controller. The results emonstrate the clear suerorty of our controller to conventonal PID controls. Wth the MRAC control strategy, the VCM velocty rofle remane wthn 5 mm/sec, whle the maxmum overshoot of transent resonse was ecrease. The reeatablty of these results was verfe by comletng 5 consecutve loang cycles wthout falure. Our relmnary concluson s that the roose control scheme s fully suffcent to solvng unwante hea-to-sk contact roblem whle the servo track wrtng rocess. REFERENCES Fg. 8. The Resonse of DTMRAC,,, Velocty n SSTW Process. Fg. 9. DTMRAC,,, for VCM Control Sgnal. [1] T. R. Albrecht, Loa/unloa technology for sk rves, IEEE Transactons On Magnetcs, vol. 35, no., March [] H. Klaassen, Electromechancal moelng of actuator ynamcs n a loa/unloa sk rve, IEEE Trans. Magnetcs, vol. 36, ssue 5,. 38 4, Setember. [3] P. G. Lev an F. E. Talke, Loa/unloa nvestgatons on a rotary actuator sk rve, IEEE Trans. Magnetcs, vol. 8, ssue 5, art, , Setember, 199. [4] T. Kouhe, T.Yamaa, Y. Keroba an K.Aruga, A stuy of hea-sk nterface shock resstance, IEEE Trans. Magnetcs, vol. 31, ssue 6, , November [5] T. G. Jeong an D. B. Bogy, An exermental stuy of the arameters that etermne sler-sk contacts urng ynamc loa-unloa, The Amercan Socety of Mechancal Engneers, , 199. [6] Q. H. Zeng an D. B. Bogy, Effects of certan esgn arameters on loa/unloa erformance, IEEE Trans. Magnetcs, vol. 36, ssue 1, , January. [7] H. Butler, Moel Reference Aatve Control: From Theory to Practce, Prentce Hall Internatonal (UK) Lt., 199. [8] H. Unbehauen, Dscrete moel reference aatve systems: esgn, IEE Control Engneerng Seres, , [9] T. Suzuk an S. Takashma, A hyerstable scheme for screte moel reference aatve control systems, Internatonal Journal of Control, vol. 8, ssue,. 45-5, [1] T. Suzuk, an Y. Dohmoto, A mofe scheme for the moel reference aatve control wth augmente error sgnal, Internatonal Journal of Control, vol. 7, ssue, , [11] D.E. Mller, A new aroach to moel reference aatve control, IEEE Trans. Automatc Control, vol. 48, ssue 5, , May 3. [1] H. Butler, G. Honer an J. van Amerongen, Moel reference aatve control of a rect-rve DC motor, IEEE Control Systems Magazne, vol. 9, ssue 1,. 8-84, January [13] L. Hsu, an R. R. Costa, Varable structure moel reference aatve control usng only nut an outut measurements, IEEE Trans. Automatc Control, vol. 35, ssue 11, , November 199. [14] C.L. Hwang, an B.S. Chen, Moel reference aatve control va the mnmzaton of outut error an weghtng control nut, IEE Proceengs D, vol. 136, Issue 5, , Setember 1989.

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