Non-repeatable Runout Research Articles

226 H^∞制御系設計法を用いた磁気ディスク装置の外乱抑圧制御に関する研究

This paper describes designing a controller of a hard disk drive for rejecting disturbances using mixed sensitivity approach. Position Error Signal (PES) is consist of Repeatable Runout (RRO) and Non-Repeatable Runout (NRRO), NRRO is decomposed into its contributing component which are force disturbance, mechanical vibration, and etc, in frequency domain. To simulate the behavior of the disturbance signals, the decomposed signals are transformed to time domain. The H^∞ control design can be eliminated such disturbances effectively. A mixed sensitivity approach is applied to the robust controller design of the track-following control for the HDD. We compare between the results with a conventional controller and the results with the proposed controller. it shows the validity of the proposed controller design method.

200 ハードディスク装置のナノメカトロニクス技術 : 高精度位置決め技術の展望(情報機器コンピュータメカニクス3 : サーボ, プリンターと紙送り)

The positioning accuracy of head-positioning system of hard disk drives (HDD) has been improved to meet the demand for larger data capacity. The recent positioning accuracy is less than 100 nm (±3σ) and non-repeatable runout is less than 50 nm. The accuracy of HDD is close to that of XY-stage in semi-conductor equipment devices. The author shows that some of the error sources in HDD and XY-stage are the same, but the difference is in the dynamical error sources such as the vibrations. According to this comparison, the author then shows the several unified mechanics and control technologies ("nano-mechatronics") to achieve nanometer order precise positioning.

F-0434 超音波振動を用いたアクティブエアベアリング : 円すい面形状を持つ空気軸受の試作(S38-4 超音波技術応用)(S38 機構の開発とシミュレーション)

This study proposes an active air bearing based on the squeeze air film generated by the ultrasonic oscillation. The squeeze film generated by ultrasonic oscillator lifts and supports the rotor without residual vibrations and without use of any air supply. In this paper, a split rotor with two conical inside surfaces and a cone-shaped oscillator are employed. Radial and axial runouts were estimated by measuring displacements of a reference ball mounted on the rotor with displacement sensors. Axial runout of the rotor during rotation was less than 0.5 μm. Moreover, non-repeatable runout in axial direction was less than 0.33 μm. However, radial runout of the ball was considerably large because of attitude variations of the rotor.

Reduction of NRRO in a Ball Bearing for HDD Spindle Motors. 3rd Report. Influence of lubrication on NRRO of a Ball Bearing.

In this paper, we experimentally analyzed the influence of lubrication for Non Repeatable Runout(NRRO)of a ball bearing, and proposed the best design for a ball bearing used in HDD spindle motors with regard to NRRO and acoustic endurance. The results are summarized as follows : (1)In grease lubrication, NRRO fluctuated in accordance with torque fluctuation caused by grease splush. On the other hand, NRRO fluctuation was not observed in oil lubrication. (2)When ceramic balls were used, the acoustic increase was very small even when bearing was lubricated with minute amount of oil. (3)It was thought that the best design for a ball bearing used in HDD spindle motors was that the number of balls was 12, the material of balls was ceramic and the lubrication was minute amount of oil.

Modified adaptive feedforward runout compensation for dual-stage servo system

This paper applies the modified adaptive feedforward compensation (AFC) scheme to the dual stage servo system for the cancellation of repeatable runout (RRO) and nonrepeatable runout (NRRO). It shows that runout can be effectively compensated or attenuated by assigning runout components to VCM actuator and microactuator properly.

New frequency domain method of nonrepeatable runout measurement in a hard disk drive spindle motor

A new frequency domain method was developed and mathematically investigated for measurement and analysis of runout in a computer hard disk drive (HDD) spindle motor. Repeatable runout (RRO) can be represented as the harmonics of the motor rotational frequency in frequency domain. Therefore nonrepeatable runout (NRRO) is the subtraction of the harmonics from total indicated runout (TIR), so that NRRO in time domain can be easily reconstructed by inverse Fourier transform of NRRO in frequency domain. This method is accurate and simple without index signal indispensable to time domain analysis. This research measured runout of a 3.5" HDD spindle motor with both capacitance probe and laser, and also investigated its characteristics statistically and correlated NRRO with defect frequencies of ball bearing, resonance frequency and its mode shape through Campbell diagram.

Reduction of NRRO in a Ball Bearing for HDD Spindle Motors. (2nd Report. Experimental Analysis of Ball Bearing with 12 balls).

In this paper, we experimentally analyzed the non-repeatable run-out (NRRO) of a ball bearing to confirm the theoretical analysis proposed in the previous paper and the advantage of a ball bearing with 12 balls for NRRO. The results are summarized as follows: (1) Since NRRO calculated by actual geometrical errors of ball bearing parts was nearly equal to the measured NRRO, it was clarified that the theoretical analysis in the previous paper was valid. (2) NRRO of a ball bearing with 12 balls was very small even if geometrical errors of ball bearing parts was large. It was confirmed that 12 was suitable ball number for ball bearings used in HDD spindle motors.

Reduction of NRRO in a Ball Bearing for HDD Spindle Motors. 1st Report. Theoretical Analysis used by NRRO Culculation Program.

In this paper, we theoretically analyzed the non-repeatable run-out (NRRO) of ball bearing caused by form errors of inner and outer races, rolling balls and ball number. The results are summarized as follows: (1) As for the geometric errors of the inner and outer races, it is possible to reduce the NRRO to be less than 1 nm by choosing 12 or 18 ball number, even if the inner and outer races have harmonic undulation of less than eleven order. (2) The effect of the differences in ball diameter and ball's form error on the NRRO linearly decreases as the ball number increases.

Novel NRRO minimization algorithm for an ultra-high-density servo track writer

Since the introduction of magnetoresistive (MR) heads, the areal density of hard disk drives (HDDs) has been increasing at a rate around 60% a year, and the track density is increasing at roughly half that rate. The servo track writer (STW), which is used to write accurate servo patterns for head positioning on the surfaces of disks in the HDD, is a key instrument in this regard. A novel algorithm for the STW of the sector-servo architecture, using an accurate air-bearing motor and rotary-positioner, and a repeatable runout (RRO) compensation method, is proposed in order to minimize the effects of nonrepeatable runout (NRRO) components, which are generated by a spindle motor and other mechanical components of the HDD, and have a dominant influence in retarding track density growth.

Non-repeatable runout of ball-bearing spindle-motor for 2.5" HDD

Quantitative estimation of non-repeatable runout (NRRO) in head tracking mode on the hard disk drive was performed by an experimental investigation of ball-bearing spindle motor NRRO. The characteristic difference between the spindle motor NRRO and the head tracking error is discussed. This head tracking error is caused by the NRRO in tracking mode and NRRO in servo track writing, taking head tracking control into account. The amplitude of spindle motor NRRO is 130 nm peak-to-peak in this experiment. While the low frequency components of NRRO caused by bearing geometry are compressed, rotor resonance frequency vibrations are predominantly enhanced by the characteristics of the sensitivity function of the head positioning system. The amplitude of the error caused by the motor NRRO is twice as large as that of the motor NRRO itself. Neither of the probability density functions, namely motor NRRO and tracking error caused by NRRO, is Gaussian distribution.

Non-repeatable runout measurement and simulation of fluid lubricated spindles

The non-repeatable runout (NRRO) of small self-acting air bearing spindles is investigated using high precision capacitance probe transducers. Transient NRRO, spindle start-up time, and power consumption are determined at start-up for horizontal and vertical spindle orientation. The design of fluid spindles for magnetic recording disk drive applications is optimized by means of finite element-based numerical simulation. Advantages and disadvantages of fluid lubricated spindles are discussed.

Non-symmetrical three-lobe bearing spindle technology: a drive technology to increase aerial density

A fluid-film spindle for 2.5 inch hard disk drive is described that effectively reduces nonrepeatable runout to less than 0.05 /spl mu/m, making it possible to increase track density. The spindle is used with a newly designed three-lobe bearing of which each lobe is asymmetrical. The influence of stiffness and temperature in a prototype spindle using this bearing are discussed and comparisons are made with a conventional ball-bearing spindle.

Architecture and performance of the ESPER-2 hard-disk drive servo writer

The servo writer is known as the most accurate and sensitive tool on an HDD (hard-disk drive) manufacturing line. ESPER-2 is designed as a product-independent common servo writer which incorporates major advances in equipment cost, reduction of clean-room requirements, and writing accuracy. The servo writing process consists of two stages. The first stage writes the master servo pattern on as many as ten disks at once with little need for contaminant protection facilities. One such master disk is then assembled with other, raw, disks in a file, and the second stage writes the proper servo pattern on all disk surfaces by referring to the master. The effects of off-center discursions in the mechanical disk assembly and random runout (NRRO, or nonrepeatable runout) in the product spindle components are eliminated by table-lookup servo actuator control, so that writing accuracy is improved. Neither an exceptionally clean environment nor fine mechanical parts are required for the second-stage operation.

Non-repeatable runout of cantilever and doubly supported [formula omitted] disc drive spindles

The effect of spindle bearing support on non-repeatable bearing runout is studied for a typical 5 1 4 inch disc drive spindle. Runout in the radial and axial directions is measured using rigidly mounted capacitance probe transducers, and statistical methods are applied to study the non-repeatable runout signal in the time and frequency domain. Comparison of cantilever and simply supported spindles indicates that the upper support significantly reduces the amplitude of the radial non-repeatable runout, but has little effect on the magnitude of the axial non-repeatable runout.

Nonrepeatable radial and axial runout of 5 1/4" disk drive spindles

Radial and axial nonrepeatable runout of a 5-1/4-in disk drive spindle is investigated in the time and frequency domain using statistical analysis. The runout is measured using high-resolution capacitance probes, and the correlation between radial and axial nonrepeatable runout is determined. In addition, the relation between nonrepeatable runout and bearing design parameters is investigated. >

An investigation of non-repeatable spindle runout

Non-repeatable runout of typical ball bearing and fluid spindles for 5-1/4 inch disk drives is investigated using capacitance probe techniques. Statistical methods are applied to calculate the one-sigma value of the non-repeatable runout using both time domain and frequency domain analysis. Fluid spindles exhibit substantially less nonrepeatable runout compared to typical ball bearing spindles.

Mechanics-Related Problems of Magnetic Recording Technology and Ink-Jet Printing

In this paper, mechanical aspects of magnetic recording technology and nonimpact printing are discussed. In the recording area, theoretical and experimental aspects of air bearing theory, head/disk dynamics, and head/disk tribology are studied. Flutter of rotating disks is investigated, the flow field between rotating disks is described, and nonrepeatable run-out of disk file spindles is studied. Furthermore, the head/disk interface for flexible media is discussed and dimensional stability of flexible substrate is examined. In the printing area, experimental and theoretical investigations using continuous and drop-on-demand fluid jets are presented, and numerical calculations of the drop formation process in drop-on-demand fluid jets are described.