Estimtion of Disk Slip Position Error for Mobile Hrd Disk Drives Peiqi Pn,, Yong Xio, Zhe Zheng,. College of Informtion Engineering Shenyng University of Chemicl Technology Shenyng, Lioning, 4, P.. Chin. Institute of Advnced Mnufcturing Technology Ningbo Industril Technology eserch Institute, Chinese Acdemy of Sciences Ningbo, Zhejing,35, P.. Chin Abstrct Mechnicl vibrtion on mobile hrd disk is inevitble in the prcticl usge, nd violent vibrtion my cuse disk slip with significnt position error, which will degrde the servo control performnce, prolong time to redy (TT) of servo nd lower reding nd writing speed of the mgnetic hed. The servo trcking ccurcy of hrd disk drive ctutor with respect to vrious mechnicl disturbnce levels ws considered. So this pper proposes n nlytic method bsed on the motion lw of mgnetic hed ginst the medi in order to effectively estimte the resulting position error prior to the seeking opertion nd reduce servo burden with control performnce improved. Keywords hrd disk; slip; position error I. INTODUCTION Along with the development of computer science nd technology, hrd disk is becoming n importnt storge medium []. Hrd disk servo systems ply vitl role for meeting the demnd of incresingly high density nd high performnce hrd disk drives. The servo system must chieve precise positioning of the red/write hed on desired trck, clled trck following, nd fst trnsition from one trck to nother trget trck clled trck seeking[]. With the continuous incresing cpcity, performnce demnds nd trck density of the hrd disk, therefore we should put forwrd higher requirements to the control technology of the hrd disk trck following nd trck seeking[3]. Then, the mount of informtion tht the hed red of dt lso incresed in the sme time. Trck seeking discourses the hrd disk hed implement the motion control of the ddressing between trcks in the shortest time[4][5]. And trck following focuses on the hed trcks ccurtely the center position of the mgnetic trck in prticulr trck. In the production process of Hrd disk, there is process to write servo trcks using servo trck writer (STW) technology is very importnt[6]. The disc my be preinstlled within disc drive, which in turn is loded within the STW.These red-only system informtion usully write in STW in the hrd disk production process[7][8]. The position between the disk nd hed reltively fixed in the STW of Hrd Disk, Pre-reclibrtion nd compenstion of hed skew error mong multiple heds re required, so tht position error during hed switching seeks cn be minimized[9][]. However, due to ll kinds of ccidents or improper hndling hrd disk will inevitbly produce vibrtion nd led to disk slip in the products prcticl ppliction[][]. It mkes hed red error informtion owing to hed skew probbly devites from the fctory-clibrted vlue. So it is very importnt tht to reserch the motion lw of disk nd hed in the disk sliding process [3]. We hve engged in the reserch field of disk error compenstion for few yers. Previously, when disk slippery occurs during opertion, the ctul position error is offline mesured, which is followed by proper clibrtion methods. However, it cn not provide stisfctory servo performnce ginst ccidentl shock or vibrtion [4]. Therefore, n nlyticl method bsed on the motion lw of hrd disk is proposed in this pper, nd the hed position error due to disk slippery cn be estimted effectively, so tht online compenstion without clibrtion cn be relized. II. MOVEMENT ULES OF HEAD Due to the trditionl mechnicl hrd disk mnufcturing cost is only /3 - /5 tht of the Solid Stte Disk (SSD), so mechnicl hrd disk is still the minstrem products of dt storge. Mechnicl hrd disk usully consists of bse plte, disk, prking mechnism, red/write hed, voice coil motor (VCM), drive hed nd spindle motor. Prking mechnism VCM Actutor Bse Plte Spindle motor Hed Disk www.ijcit.com 947
α Figure. Physicl structure of mobile hrd disk. For exmple, SGTSD4TUA hrd disk produced by Segte, Fig. show the structure of the hrd disk, nd it usully integrted mny pieces of disk nd multiple hed. With spindle motor center for coordintes origin O, drwing the rectngulr coordintes x-y, showing s Fig.. The rdius of trck is, nd the length of mgnetic rm is L. X is the distnce between disk center nd the mgnetic rm fulcrum. Set A s the fulcrum of the hed group cntilever, the center of disk nd spindle coincide, then set ID s the minimum trck dimeter of disk, set OD s the biggest trck dimeter; Then the internl rdius of disk is, nd is the externl rdius. i o Thus, L sin( ) cos( ) sin cos( ) cos( ) y P(,θ) rcsin( ) rcsin rpm β θ L cos X L X L O O(,θ ) ID A So the position of the point P in x-y plne is O P cos( ) OD X x cos y sin Figure. Digrm of hed movement fter sliding. For the hed locted ny point on the trck P (, ), the dius of trck is clculted by s X L X L cos i, ) We hve ( o L sin Now, if the disk is slipped, the hed long the trck will devite from the trjectory which servo informtion written to the trck, which will increse the control burden of servo controller. sin( ) cos( ) OF DISK SLIP III. T HE POSITION EO MODEL For the disk slip to the first qudrnt s n exmple, now, sin( ) sin.when the disk cos( ) slipping hppens, or the centers of disk nd spindle do not coincide due to ssembly error, then the center of the physicl disk is chnged www.ijcit.com 948
to O (, ), t this time, the distnce of point P to the new disk center is O P cos( ) The ngle of the point P nd the new disk center is Tht is equivlent to OPO O P sin OPO sin( ) O P OP cos( ) sin( ) cos( ) So, s long s the eccentricity of the disk O (, ) cn be mesured, we cn estimte of the position nd time devition of ny point on the disk, nd then by the feedforwrd control method the ddressing error cn be reduced nd the servo control performnce cn improved. X L X L cos 3 If,, we cn obtin 3 If,, it hs IV. DESIGN OF THE SIMULATION POGAM The simultion progrm is designed by MATLAB/Simulink to study the chnge of trjectory before nd fter disk sliding. Firstly, there re some known prmeters of the simultion progrm. Such s, is the rdius of disk, the internl nd externl dimeter of disk re i nd o. Then, (, ) stnd for the loction polr coordintes when the hed moves on disk, nd the others re, etc. Secondly, the outputs re prmeters of X-Y coordinte, Disk slip before nd fter hed trjectory curves of contrst nd severl corresponding curves of eccentricity in different qudrnt. A simultion designed using Simulink softwre, nd the block digrm s shown in Fig.3. According to the size of the ctul hrd disk produced by Segte, the length of mgnetic rm is set s L = 35 mm, the distnce of disk center nd the mgnetic rm fulcrum X = 39.5 mm, inner dimeter ID = mm, outer dimeter OD = 66 mm, the disk rdius = mm, the system simultion time s is set, nd the offset of disk slip = mm is ssumed, nd the ngles of slip re ssigned to π/6, π/3, 7π/6, 5π/3, respectively. It cn simulte the sitution of disk slip to different qudrnts, when tke trck density TPI = 3 k, it lso cn simulte the position error fter disk slip nd it is equivlent to the number of the devition trck. Therefore, whether disk slips to ny qudrnt, the ngle is given by sin( ) sin cos( ) To sum up, the position nd ngle errors cuse by disk slipping cn be expressed s www.ijcit.com 949
Δθ/rd Δθ/rd Δθ/rd Δθ/rd Trck Trck Trck Trck Disk Known Prmeters X,L,OD, ID Angleα between Mgnetic rm L nd X Hed Position (,θ) Trnsform orthogonl coordinte (x,y) -.95 x 4 θ (, π/ ) -5-55 θ ( π/, π) The center fter Disk sliding (,θ) (Δ,Δθ) output Curves disply.5.5 /inch. x 4 θ ( π, 3π/ ) -6-65.5 /inch θ ( 3π/, π) 7 The position of Disk sliding equls the devint trck per inch Figure 3. The block digrm of simultion progrm principle. V. ESULT ANALYSIS The hed motion trils in rectngulr coordinte chnges with the trjectory re showed in Fig.4. The hed moves from the inner to outer dimeter, when disk slips to first or third qudrnt. When the error cused by disk skewing is close to the outer dimeter, the error becme smller. However, the hed moves from inner to outer dimeter, the error chnges not obviously, when disk slip to second or fourth qudrnt. It will provide direct bsis for the position error compenstion mount fter the disk slip..5 θ (, π/ ) y y..4.6.8 θ ( π, 3π/ ).5.5 y θ ( π/, π) y..4.6.8 θ ( 3π/, π).5.5.95.5 /inch 65 6 55 5.5 /inch Figure 5. The position error corresponding trck number when disk slip to different qudrnt. Figures 5 nd 6 re the simultion results, which show tht the hed position devition nd the ngle devition chnge over trck. This shows, the trck direction of disk in the opposite while disk slips to first or fourth qudrnt with the second or third qudrnt. As the hed moves from the inner to outer dimeter, the devition trck numbers follow to the prbolic lw, when the disk slippge to occur the position error in the second or third qudrnt, the devition trck number grdully increses followed by decresing, nd in first or fourth qudrnt, the devition trck number grdully decresed nd then increses. From the comprison in different qudrnts, conclusion tht the rnge of the devition trck numbers nd the ngle error in second or forth qudrnt chnges more obviously thn tht in first or third qudrnt..6 θ (, π/ ) -. θ ( π/, π) y y y y.4. -.4 -.6 -.8..4.6.8 y--disk before sliding..4.6.8 y--position error of the disk slip Figure 4. The contrst of disk hed slip motion trjectory before nd fter..5 /inch θ ( π, 3π/ ) -. -.4 -..5 /inch θ ( 3π/, π).8.6.4. -.6.5 /inch.5 /inch Figure 6. Angle error corresponding disk slip to different qudrnt. www.ijcit.com 95
VI. CONCLUSIONS For model of rbitrry mobile hrd disk, the prmeters X, L nd inner nd outer dimeters of disk re positive constnts, they re known in the design process. However, the disk rdius cn lso be clculted. In relity, the offset(, ), cn get the ccurte vlue through the sensor. In view of the limited conditions, tht is to sy, this pper completes the model simultion by ssign vlue to known quntity. According to the motion lw of disk nd disk offset, mthemticl model bsed on bove mentioned method cn be estblished, nd the reltive position of mobile hrd disk slip wy from hed cn be estimted. When the hed skew hppen to hrd disk in use, it cn provide the bsis for corresponding compenstion nd possible clibrtion control lgorithm, nd the filure rte of hrd disk cn be reduced. In other words, the working life of the hrd disk would be prolonged. eference [] Y. Xio, X. Ge, J. Sun, X.Wng, study on compenstion lgorithm of hed skew in hrd disk drives[c]. Interntionl Conference on Photonics,3D-imging, nd Visuliztion,, 85,pp.3337 [] H. D. Tghird nd E. Jmei, Adptive obust Controller Synthesis for Hrd Disk Servo Systems[C]. Interntionl Conference on Intelligent obots nd Systems, 4, Vol., pp. 5459. [3] J. Y. Chng. Mitigtion of trck following repetble runout in high TPI Hrd Disk Drives through servo nd mechnicl designs. IEEE Trnsctions on Mgnetics, 9, 45() : 5-55. [4] J. McCormick nd.horowitz. A direct dptive control scheme for disk file servo [C]. Proc. of Americn Control Conference, Sn Frncisco, CA, 993, pp.46-35. [5] P.Eykhoff, System Identifiction-Prmeter nd Stte Estimtion [M].New York :Wiley,98. [6] L. Wng, L. Yun, B. M. Chen nd T.H.Lee. Modeling nd control of dul ctutor servo system for hrd disk drive [C]. Proceeding of 998 Interntionl Conference Mechtron. Trchnol, Hsinchu, Tiwn..O.C.,998, pp.533-538 [7] M.. Grhm, nd. A. de Cllfon. An itertive lernin design for repetble runout cncelltion in disk drives [J]. IEEE Trnsctions on Control System Technology, 6, 4(3), pp.474-48. [8] N. O. Perez-Arncibi, T. C. Tso, J. S. Gibson. Sturtion-induced instbility nd its voidnce in dptive control of hrd disk drives [J]. IEEE Trns. on Control System Technology, Vol. 8-,, pp. 368-38. [9] L. J. Fiorvnti, S. T. Sheern,. L, Oxley, J. D. Psi. Disc Drive Servo Trck Writer Utilizing Low-density Gs [P]. US Ptent, 6,785,8, 4. [] X. Ge, Y. Xio, D. Yun, P. Pn, Study on Detection Algorithm of Hed Skew Error in Hrd Disk Drives[J]. Mesurement nd Control Technology,, vol 3(9):47 [] T. Yd, M. Fkushi, H. Suzuki nd K. Tkishi. Servo trck writing technology. FUJITSU Scientific & Technicl Journl, 6, 4(): 93. [] H. Fujimoto. O compenstion of Hrd Disk Drives with multirte repetitive perfect trcking control. IEEE Trnsctions on Industril Electronics, 9, 56(): 385-383. [3] B. Hrmer, J. He, K. B. Dizji, nd H. T. Ho. Efficient feedforwrd compenstion for repetble runout in disc drive [P]. US Ptent, 5: 6,867,953. [4] Xio Y, Png Y, Ge X, et l. Compenstion of shock-induced hed skew for hrd disk drives [J]. Procedi Engineering,, 6: 65-7. www.ijcit.com 95