Moment of Inertia and Torque Performance Sensorless Measurement for HDD Used Spindle Motors HUANG RUO YU NATIONAL UNIVERSITY OF SINGAPORE 2004 Moment of Inertia and Torque Performance Sensorless Measurement for HDD Used Spindle Motors HUANG RUO YU (B.Eng Shanghai Jiaotong University) A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF ENGINEERING DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2004 Acknowledgement Although this thesis is written by me, I could have not accomplished it if I were doing researches on my own Here I would like to express my sincere gratitude to the guidance given by my supervisors and help from my colleagues Thanks to the splendid idea conceived by Dr Bi Chao, the entire process of the moment of inertia and torque constant measurement is feasible Moreover, I would like to thank him for consistent assistance during my entire progress of the experiment and thesis writing Also, I am very appreciated by the instructions given by Dr Jiang Quan when I was doing the experiment Finally, I would like to thank for my family for the support in my mind and anyone who once helped me in my research work It is your help that makes the embodiment of this thesis feasible Contents Table of Contents Introduction - 1.1 Motivation of the work - 1.2 Scope Definition - 1.3 Organization of the thesis - Literature Review - 2.1 Torque Constant Measurement - 2.2 Moment of Inertia Measurement - 2.2.1 Conventional Method for Inertia Measurement - 10 „ Calculation Method - 10 „ Torsional Vibration Method - 12 „ Pendulum Method - 14 „ Falling Weight and Pulley Method - 16 „ Mechanical Time Constant Method - 17 „ Parameter Identification - 18 2.2.2 Prerequisites in HDD industry - 18 2.2.3 Other Method - 20 2.3 Speed Measurement and Optimal Spline - 21 Digital Fitter and Optimal Spline - 26 3.1 Speed Pattern - 26 3.2 Fitter Analysis - 27 3.2.1 Fitter Requirements - 28 3.2.2 Speed Data Pattern - 28 3.2.3 Cubic Spline Interpolation - 29 3.2.4 Interpolation Limitations - 33 3.3 Optimal Spline Algorithm - 34 3.3.1 Algorithm Development - 35 3.3.1.1 Segmentation - 36 3.3.1.2 Optimization and Spline Interpolation - 37 3.3.1.3 Linear System Solving - 40 3.3.2 Algorithm Logic Diagram - 42 3.3.3 Algorithm Analytical Results - 43 3.3.3.1 Simulation on the Sinusoid Function - 44 3.3.3.2 Simulation on Exponential Function - 46 Torque Constant & Back-EMF Constant - 50 4.1 Introduction - 50 4.2 Principle Description - 51 4.2.1 Driving Circuit - 51 4.2.2 Back-EMF Signal Waveform - 54 4.2.3 Ke Calculation Algorithm - 57 4.2.3.1 Proposed Algorithm - 58 4.2.3.2 Influence of Harmonics Component - 58 4.2.3.3 Speed Changing Trends - 60 - I Contents 4.3 Practical Implementation - 64 4.4 Test Results - 66 Inertia Measurement - 70 5.1 Introduction - 70 5.2 Measurement Algorithm Development - 71 5.2.1 Basic Calculation Equations - 71 5.2.2 Braking Circuit - 73 5.2.3 Further Analysis - 75 5.2.4 Quantities to be Measured - 78 5.3 Sensorless Speed Signal Measurement - 79 5.3.1 Reconstruction of Speed via Back-EMF Cycle Length - 79 5.3.2 Corresponding Time Value - 82 5.3.3 Speed Synthesis - 83 5.3.4 Consideration for Sensorless Speed Measurement - 83 5.3.4.1 Phase shift - 84 5.3.4.2 Linear Interpolation of Zero Crossing Point (ZCP) - 85 5.3.4.3 Globally use of data sites - 87 5.3.4.4 Error of the Speed Signal - 89 5.4 Inertia Calculation - 90 5.4.1 System Setup - 90 5.4.2 Calculation Procedure - 91 5.4.3 Speed Reconstruction - 92 5.4.4 Application of the Optimal Spline Data Fitter - 94 5.4.4.1 Optimal-Spline-Processed Speed Interpolant - 94 5.4.4.2 Optimal-Spline-Processed Acceleration - 96 5.4.5 Power on the Resistors - 97 5.4.6 Speed and Time Mapping - 100 5.5 Measured Inertia Results Analysis - 103 Conclusion - 107 6.1 Summary of the Measurement Carried Out - 107 6.2 Future Work - 108 6.2.1 Sub-inch Form Factor HDD Sensorless Measurement - 108 6.2.2 Bearing Considerations - 109 6.2.3 Fast Measurement - 109 References - 110 Publication - 114 - II Summary Summary As far as the spindle motor is concerned, the moment of inertia and the torque performance are two important factors in the hard disk drive industry The first one is related with the drive’s dynamic behavior while the latter one directly indicates the driving ability of a spindle motor Generally speaking, in other systems of industrial drives, such as automation and power system, because the motor is big in size, lots of measuring manners can be applied to the motors for the measurement of these two quantities Nevertheless, the motor used in hard disk drive industry is very small in form compared to its counterparts in other industries As such, many conventional methods widely used in the other industrial drive systems are not applicable in the hard disk drive industry Especially, those measuring methods utilizing encoders or sensors are definitely not usable on the ground that the motor is too small to install an encoder on it Whereas if there does exist this kind of sensor, the cost of such a kind of sensor is quite high Moreover, because of the requirement for mass production in hard disk drive industry, the motor should be tested and measured in the hard disk drive assembly level In other words, given a motor as the testing object, no other complicated devices for testing are supposed to be installed on the motor, which might slow down the entire testing procedure if the measurement is prepared to be used in the production line Apparently, with this consideration, the only interface feasible from the motor side will be the terminal winding connection wires And only the sensorless method is able to fulfill III Summary the task In this thesis, the sensorless measurement methods for the torque constant, Back-EMF constant and the moment of inertia are given in detail accompanied with the experiment results Within all the measurement setup and process, only the phase terminal voltage and current signals are available They are sampled into a personal computer through a data acquisition card for further processing and the implementation of the measuring algorithm The measurement is solely based on the All-In-One (AIO) spindle motor testing system we have built These quantities of interest are derived from the voltage and current quantities Apart from the measurement, a signal processing algorithm for noise filtering of aperiodic signal is also given together with simulation results This algorithm is an important component of the inertia measurement process The measuring procedure and the experiment result corresponding to each quantity of interest are given respectively every chapter in the thesis IV Nomenclature Nomenclature ADB: Aero-Dynamic-Bearing ADC: Analog Digital Converter AIO: All-In-One spindle motor testing system AMB: Active-Magnetic-Bearing Back-EMF: Back Electromotive Force BLDC: Brushless Direct Current motor DFT: Discrete Fourier Transform DTC: Direct Torque Control EM: Electromagnetic EMC: Electro Magnetic Compatibility FDB: Fluid-Dynamic-Bearing HDA: Hard Disk Assembly HDD: Hard Disk Drive MOI: Moment of Inertia NdFeB: Neodymium Iron Boron PMSM: Permanent Magnet Synchronous Motor TPI: Track Per Inch ZCP: Zero Crossing Point V List of Figures List of Figures Fig 1.1 Typical Structure of Spindle Motor Used inside an HDD (8 poles-12 slots) - Fig 2.1 Calculation Equations for Regular Shape Objects - 11 Fig 2.2 Torsional Vibration Illustration - 13 Fig 2.3 Pendulum System Illustration - 15 Fig 2.4 Falling Weight and Pulley System Illustration - 16 Fig 3.1 Amplified Saw Teeth Fluctuating Speed - 26 Fig 3.2 Direct Speed-Slope-Calculated Acceleration - 27 Fig 3.3 Segmentation Illustration - 36 Fig 3.4 Optimal Spline Algorithm Logic Diagram - 43 Fig 3.5 Spline Optimized Sine Wave with 5% of Noise - 44 Fig 3.6 1st Derivative Result of Optimal Spline (Sin) - 46 Fig 3.7 Spline Optimized Exponential Curve with 2% Noise Level - 47 Fig 3.8 1st Derivative Result of Optimal Spline (Exp) - 48 Fig 4.1 BLDC Mode Current Flow Demonstration - 51 Fig 4.2 Silent Phase Illustration from Terminal Voltage - 52 Fig 4.3 Freewheeling Motor Circuit Connection - 54 Fig 4.4 Back-EMF Waveform Illustration - 55 Fig 4.5 Fast Alternation of Back-EMF Waveform - 56 Fig 4.6 Measurement System Setup - 65 Fig 5.1 Braking Circuit Illustration - 74 Fig 5.2 Schematic Braking Circuit - 75 Fig 5.3 Electrical Cycle Length Changing Illustration - 80 Fig 5.4 Illustration of How Speed Calculation is forwarded - 81 Fig 5.5 3-phase Back-EMF and time decision schema - 82 Fig 5.6 Phase Shift Illustration - 84 Fig 5.7 Illustration of Linear ZCP Interpolation of the Real Signal - 86 Fig 5.8 Calculated Speed Result Comparison Between Three Different Calculation Methods - 88 Fig 5.9 Inertia Calculation Flow Chart - 92 Fig 5.10 Detailed Speed Reconstruction Diagram - 93 Fig 5.11 Amplified Graph of Optimal Spline Processed Speed Signal - 94 Fig 5.12 Reconstructed Speed Signal during Freewheeling and Braking Freewheeling - 95 Fig 5.13 Acceleration Curve from the Resultant Interpolant - 96 Fig 5.14 Phase Voltage Amplitude Processing Diagram - 99 Fig 5.15 Time Speed Mapping Illustration - 102 - VI List of Tables List of Tables Table 4.1 The Test Results of the Back-EMF constant (No Disk 7,200rpm) - 67 Table 4.2 The Test Results of the Back-EMF constant (With Disk 7,200rpm) - 67 Table 4.3 The Test Results of the Back-EMF constant (With Disk 5,000rpm) - 67 Table 4.4 The Test Results of the Torque constant (No Disk 7,200rpm) - 68 Table 5.1 Inertia Measurement Result (2 disks, FDB, 7,200 rpm) - 103 - VII Chapter V merged amplitude array, apparently we can find the amplitude descending together with some level of fluctuation mixed in it Again, optimal spline is utilized for the noise cancellation and smoothing, which results in the entire trends of Back-EMF amplitude Then, regarding a specific speed value during integration, the voltage amplitude in the resultant optimized spline interpolant is calculated On getting the corresponding voltage amplitude from the spline optimized voltage interpolant, due to the symmetry of the resistor braking circuit imposed, the power can be written in the following form with the Uamp rather than instant voltage value U(t) pem U2 ⎛ r ⎞ 3⎛ r ⎞ ⎛ U amp ⎞ = 3× e ⋅ i = 3× i ( R + r ) = 3× ⎟ ⎜1 + ⎟ = ⎜1 + ⎟ ⎜ R ⎝ R ⎠ R ⎝ R ⎠⎝ ⎠ 2 (5.12) where, r is the inner resistance of the motor and R for the external braking resistor Since we consider the motor as a whole in the integration equation (5.9), the in the above equation stands for the 3-phase, and amplitude voltage divided by square root of means the virtual value of the voltage, which is used for the calculation of power, with the assumption of pure sinusoid waveform of Back-EMF within on one electrical cycle 5.4.6 Speed and Time Mapping However, in the real application, every data array, such as the voltage (power), speed and acceleration, corresponds to a time array, which is the basis of the mapping transformation Because, during the coasting period of the motor, the speed and time is - 100 - Chapter V monotonic relationship, regarding a specific integral speed value, we can always find a voltage and acceleration corresponding to it By searching the optimal spline processed speed vs time curve, we can find a time instant corresponding to the specific integral speed point Then we can use the time instant value obtained to get the values needed for calculation, such as speed, acceleration and voltage, which just corresponds to the integral calculation speed point during the integral process in equation (5.9) The following figure demonstrates this mapping process intuitionally From the following figure, the integral bound is chosen to have a common speed range in either the freewheeling state or braking freewheeling state Since, during the braking freewheeling state, the motor is stopping faster, with the same sample points the motor is going to have wider speed range calculated in the braking freewheeling However, concerning the friction cancellation in the inertia measurement, the speed has to be commonly chosen as a prerequisite indicated by integral bound in the figure - 101 - Chapter V Fig 5.15 Time Speed Mapping Illustration Given an integral speed point for calculation in equation (5.9), just like the dashed line in the figure for illustration, two acceleration values, which correspond to the freewheeling and braking freewheeling respectively, can be mapped and found as is - 102 - Chapter V shown in the arrow direction in the above figure Similarly, the voltage amplitude, which is a must in the calculation of power, under specific speed point, can also be mapped and surveyed in the same manner As a result, with the integral kernel being calculated, the inertia value can be computed 5.5 Measured Inertia Results Analysis The inertia result of a fluid dynamic bearing with two disks installed is shown in the following table The average result of inertia measurement is 622.6312 (g⋅cm2) Table 5.1 Inertia Measurement Result (2 disks, FDB, 7,200 rpm) Measure No 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Value (g⋅cm2) Deviation (g⋅cm2) Percentage (%) 619.185 619.409 618.283 621.899 621.615 624.614 621.72 618.39 622.37 622.879 616.859 624.18 620.926 619.628 622.972 624.096 622.797 623.929 621.119 623.456 624.19 623.786 622.435 622.909 624.528 -3.4462 -3.2222 -4.3482 -0.7322 -1.0162 1.9828 -0.9112 -4.2412 -0.2612 0.2478 -5.7722 1.5488 -1.7052 -3.0032 0.3408 1.4648 0.1658 1.2978 -1.5122 0.8248 1.5588 1.1548 -0.1962 0.2778 1.8968 -0.553489771 -0.517513417 -0.698358836 -0.117597705 -0.163210581 0.31845497 -0.146346666 -0.681173703 -0.041950998 0.039798841 -0.927065653 0.248750785 -0.273869989 -0.482340108 0.054735452 0.235259653 0.026628926 0.208437997 -0.242872506 0.132470072 0.250356873 0.18547095 -0.031511431 0.044617102 0.30464262 - 103 - Chapter V 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 624.395 623.507 624.209 622.817 619.535 623.554 623.138 623.95 623.517 624.97 621.313 621.726 625.432 623.856 622.824 622.96 624.279 622.42 624.926 624.329 625.317 623.706 624.674 621.561 620.47 1.7638 0.8758 1.5778 0.1858 -3.0962 0.9228 0.5068 1.3188 0.8858 2.3388 -1.3182 -0.9052 2.8008 1.2248 0.1928 0.3288 1.6478 -0.2112 2.2948 1.6978 2.6858 1.0748 2.0428 -1.0702 -2.1612 0.28328166 0.140661117 0.253408438 0.0298411 -0.497276719 0.148209727 0.081396499 0.21181078 0.142267204 0.375631674 -0.211714415 -0.145383013 0.449832903 0.19671356 0.030965361 0.052808147 0.264651049 -0.033920562 0.36856489 0.272681485 0.4313629 0.172622252 0.328091493 -0.171883452 -0.347107565 In the above table, the deviation denotes for the difference between a test result and the averaged test results value Percentage denotes for the deviation with averaged value From the above table, the inertia value varies within the range of ±1 % From the aspect of physics, the disks, each of which weighs about 22.9 g, are made of alumni and coated with other materials It has inner diameter of 25.0 mm and outer diameter of 32.0 mm Its width is about 1.2 mm Thus the inertia from its centroid is around 570 g⋅cm2 As for the other parts rotated together with the motor rotor, there are two spacers, one top-cover and skews The inertia values of them are hard to determined, but they not account much in the entire MOI The motor rotor is around - 104 - Chapter V 30 g⋅cm2 Altogether, the MOI of the motor is around the range of 610 g⋅cm2 The table of measurement results clearly elucidates the usability of the proposed sensorless MOI measurement technique - 105 - Chapter VI Conclusion Chapter VI Conclusion 6.1 Summary of the Measurements Carried Out As no sensor is allowed to be installed on the HDD components, sensorless method is a must in the measurement and R&D of spindle motors used in HDDs In this thesis, sensorless techniques for the measurement of Torque constant/Back-EMF constant and the system moment of inertia of HDD used spindle motors are introduced in detail The measurement results corresponding to each quantity are demonstrated and analyzed within every chapter In the MOI measurement process, the accuracy of the speed is very critical in the final measurement result However, when the sensorless method is utilized to detect the motor speed, the speed contains serious noises and is discrete We must use effective method to filter out the noise and reconstruct the signal As such, in the thesis, a data fitter based on the Optimal Spline algorithm is proposed for this task Both the theoretical results and experimental results manifest the usability of the data fitter as well as the effectiveness of the noise removal As for the torque constant or Back-EMF constant, because of the utilization of integration algorithm proposed, the experiment result is very stable Moreover, the method is rpm-independent, which is suitable for the application in the small form factor spindle motor, such as one or sub-inch drives - 107 - Chapter VI As far as the MOI measurement is concerned, the frictional-cancellation based sensorless method has been totally computerized as part of the AIO system and can generate stable results Additionally it is very convenient for its implementation in the quality analysis of HDD products 6.2 Future Work The proposed sensorless methods in this thesis are effective in processing the sensorless speed signal, analyzing the torque or Back-EMF constant, and computing the moment of inertia of the system sensorlessly Nowadays, the HDD techniques and products are evolving swiftly The methods in the thesis can be also further developed to meet the new requirements of the HDD industry in the future These progresses can be summarized in the following area 6.2.1 Sub-inch Form Factor HDD Sensorless Measurement Recently, there is a consistent trend to make the HDD space-saving Lots of companies are interested in the 0.85-inch HDD products, which could be ideally used in the cell phone or other hand held devices However, for such a kind of motor, due to its smallness, the friction advent in the motor bearing might make the freewheeling speed different from the traditional one Further research may be needed for improving the proposed methods and making the sensorless measurement still effective to these mini HDDs - 108 - Chapter VI 6.2.2 Bearing Considerations In the thesis, we have applied the proposed methods to test the ball-bearing motor as well as fluid-dynamic-bearing (FDB) ones The results have proven that these methods are sound Nevertheless, in the near future, the track density or TPI will be further increased So as to cooperate with high TPI, some new kinds of bearings will be used, e.g aero-dynamic-bearing (ADB) and active-magnetic-bearing (AMB) The new bearing system could make the motor performance different from the existing ones Thus we should refine the proposed methods for matching the variation of the motor performance under different bearing systems 6.2.3 Fast Measurement Based on the proposed methods in the thesis, we can realize the measurement in a short time However, to us these methods in production line requires even faster measurement It is expected that the proposed methods can be improved and optimized, which will further expand its application areas - 109 - List of References References [1] Y Miura, “Hard disk drive technology: past, present and future,” Digest of the Asia-Pacific Magnetic Recording Conf., pp AK1-1-2, 2002 [2] K Iizuka, et al., “Microcomputer control for sensorless brushless motor”, Industry Applications, IEEE Transactions on, Volume IA-21, No 4, pp 595 – 601, May/June 1985 [3] O Shinkawa, et, al., “Wide speed operation of a sensorless brushless DC motor having an interior permanent magnet rotor”, the Power Conversion Conference, 1993 Yokohama 1993., Conference Record of, pp 364 – 370, 1993 [4] N Matsui, M Shigyo, “Brushless DC motor control without position and speed sensors”, Industry Applications, IEEE Transactions on, Volume 28, Issue 1, Part 1, pp 120 – 127, Jan – Feb 1992 [5] R Lin, M.T Hu, C.Y Lee and S.C Chen, “Using phase current sensing circuit as the position sensor for brushless DC motors without shaft position sensor”, IEEE IECON Proceedings, 1989, pp 215 – 218 [6] J.R Hendershot Jr and TJE Miller, Design of Brushless Permanent-magnet Motors, UK: Oxford University Press, 1994, Chapter [7] Takahashi, H.; Kenjo, T.; Takeuchi, H.; “A Real-time Estimation Method of Brushless DC Servomotor Parameters”, Power Conversion Conference – Nagaoka 1997., Proceedings of the, Volume: 2, pp 673 – 678, – Aug, 1997 [8] Saab, S.S.; Kaed-Bey, R.A.; “Parameter identification of a DC motor: an - 110 - List of References experimental approach”, Electronics, Circuits and Systems, 2001 ICECS 2001 The 8th IEEE International Conference on, Volume 2, pp.981 – 984, – Sept 2001 [9] Terzic, B.; Jadric, M.; “Design and Implementation of the Extended Kalman Filter for the Speed and Rotor Position Estimation of Brushless DC Motor”, Industrial Electronics, IEEE Transactions on, Volume: 48 , pp.1065 – 1073, Issue: , Dec 2001 [10] Dhaouadi, R.; Mohan, N.; Norum, L.; “Design and implementation of an extended Kalman filter for the state estimation of a permanent magnet synchronous motor”, Power Electronics, IEEE Transactions on, Volume: , pp.491 – 497, Issue: , July 1991 [11] Liu, Y.P.; Howe, D.; Birch, T.S.; Matthews, D.M.H.; “Dynamic modeling and performance prediction of brushless permanent magnet drive systems”, Electrical Machines and Drives, 1989 Fourth International Conference on, pp.95 – 99, 13 – 15 1989 [12] Attaianese, C.; Marongiu, I.; Perfetto, A.; “Improving the dynamic response of speed controlled electrical drives”, Industrial Electronics, 1995 ISIE '95., Proceedings of the IEEE International Symposium on, pp.643 - 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113 - List of Publications Publication C Bi, R.Y Huang, “Optimal Spline Data Fitter and its Application in the Dynamic Speed Measurement of BLDC Motor”, SICE 2004, Conf Proc of, Sapporo, Japan, Aug – 6, 2004 Q Jiang, C Bi, R.Y Huang, “A New Phase-Delay Free Method to Detect Back EMF Zero-Crossing Points for Sensorless Control of Spindle Motors”, APMRC, Conf Proceeding of, Seoul, Korea, Aug 14 – 16, 2004 - 114 - [...]... identification and measurement are mainly focused on the moment of inertia and torque constant, KT Meanwhile, a signal processing technique used for processing the sensorless speed signal is introduced as well -1- Chapter I 1.2 Scope Definition To make things clear, definition is the first step for the consequent research and analysis The spindle motor here analyzed in this thesis is mainly used inside an HDD. .. Motivation of the work Parameter identification or parameter testing of a motor by means of sensorless technology is very much concerned in many industries For example, in hard disk drive (HDD) industry [1], the spindle motor, in effect a brushless DC motor (BLDC), is widely used The sensorless techniques, [2] and [3], are extensively utilized because of the nature of the spindle motor used in HDDs Besides,... following parts 2.2 Moment of Inertia Measurement Moment of inertia (MOI) is a basic physics quantity In Webster dictionary, the term inertia is defined as “That property of matter by which it tends when at rest to remain so, and when in motion to continue in motion, and in the straight line or direction, unless acted on by some external force” Inertia is the quantitative measurement of an object to keep... phase is a must to any HDD Being a factor relating with the dynamic response of the motor as analyzed in [11] and [12], the system rotational inertia can be used to realize fast spin-up under the sensorless BLDC driving mode in HDD, thus optimizing the motor dynamic behavior 2.2.1 Conventional Method for Inertia Measurement Concerning the inertia measurement of a motor, i.e the rotor inertia, there are... conventional measurement Thereby, it is not suitable in the HDD industry as well 2.2.2 Prerequisites in HDD industry From the aforementioned analysis, to sum up, in the HDD industry, there are following requirements for the implementation of the inertia measurement First of all, the - 18 - Chapter II sensorless method should be utilized Due to the natural compactness characteristics of an HDD, no torque. .. the system moment of inertia of a hard-disk drive is defined as the inertia of the whole rotating parts, e.g the screws, the spacer and so on, around the rotational axis of a spindle motor while the drive is running In other words, the system rotational inertia accounts for the entire mechanical load for the motor driving system This quantity has always been a key factor concerned by many HDD manufactures... eb and ec are the Back-EMF in the windings of A, B and C phase respectively, n is the motor speed in rpm, and hm is the mth component related to the mth harmonic However, in the spindle motor used in HDDs, the sinusoidal purity of the Back-EMF signal is quite good because of the concentrated winding and high energy product magnet used Additionally, the inductance effect is often ignored because of. .. several techniques employed for it The conventional methods of parameter identification of a motor are very time consuming and complicated Usually, there are 5 conventional methods used in measuring the rotor’s inertia of the motor as are given in [13] „ Calculation Method First of all, the commonest way for inertia measurement, one can easily think of, is to get the value from the inertia calculation equation... Structure of Spindle Motor Used inside an HDD (8 poles-12 slots) Essentially, this motor is of the brushless DC motor (BLDC) type In the figure, the motor has an outer rotor structure However, this type of motor has the following unique characteristics determined by its design and special structure First of all, the sensorless control, [4] and [5], is the only scheme for control of it because of the compactness... manner for the purpose of minimizing the interference to the measurement The sensorless manner, due to the simplicity and reliability, has its advantages over the methods based on sensors For such reason, together with the nature characteristics of the HDD industry, the sensorless method for the parameters measurement or identification is expected to be developed In this thesis, the motor parameters for .. .Moment of Inertia and Torque Performance Sensorless Measurement for HDD Used Spindle Motors HUANG RUO YU (B.Eng Shanghai Jiaotong University) A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF. .. wires And only the sensorless method is able to fulfill III Summary the task In this thesis, the sensorless measurement methods for the torque constant, Back-EMF constant and the moment of inertia. .. design and special structure First of all, the sensorless control, [4] and [5], is the only scheme for control of it because of the compactness of the motor Secondly, because of the removal of brushes