Hard Disk Drive Spindle Motor Research Articles

A parametric study on rocking vibration of hard disk drive spindle motors with fluid-dynamic bearings and rotating-shaft design

A parametric study on rocking vibration of hard disk drive spindle motors with fluid-dynamic bearings and rotating-shaft design

A parametric study on rocking vibration of hard disk drive spindle motors with fluid-dynamic bearings and rotating-shaft design

This paper presents a thorough parametric study to identify critical parameters controlling rocking vibration of hard disk drive (HDD) spindle motors. The spindle motors studied are of rotating-shaft design with fluid-dynamic bearings (FDB). The rocking vibration of interest results primarily from first three pairs of (0,1) unbalanced modes (also known as rocking modes, pitch modes, or gyro modes) and half-speed whirls. The parametric study shows that the transverse mass moment of inertia of the rotating part is the most critical parameter affecting the rocking amplitude. Also, FDB in-line stiffness dominates the amplitude of the half-speed whirls. Surprisingly, FDB in-line damping coefficient can considerably affect the amplitude of the second (0,1) unbalanced mode. Finally, bearing locations are very critical parameters for rocking amplitude of FDB spindles. Unfortunately, there is not a set of optimal bearing positions that will minimize vibration for all (0,1) unbalanced modes.

Development of a highly efficient hard disk drive spindle motor with a passive magnetic thrust bearing and a hydrodynamic journal bearing

This article presents a highly efficient hard disk drive (HDD) spindle motor with a passive magnetic thrust bearing and a hydrodynamic journal bearing. It eliminates the mechanical friction loss of a thrust bearing which is around 14% of total power consumption of a 3.5 in. HDD spindle motor, by replacing a conventional hydrodynamic thrust bearing with a passive magnetic thrust bearing. The passive magnetic thrust bearing using permanent magnets is inherently unstable in radial direction. However, the radial hydrodynamic force of the hydrodynamic journal bearing counterbalances the radial magnetic force of magnetic thrust bearing to achieve the stability as the motor spins up. Numerical analysis is performed to verify feasibility of the proposed system.

Improvement of dynamic characteristics of a HDD spindle system supported by ball bearing at elevated temperature

This research investigates how the design variables of ball bearing affect the bearing stiffness and the natural frequencies of a hard disk drive (HDD) spindle system at elevated temperature. It shows that any design change that increases the contact angle of ball bearing reduces the variation in the bearing stiffness and the natural frequencies at elevated temperature. This research also proposes a robust HDD spindle motor in which a wave spring maintains a constant preload minimizing the effect of temperature variation. Experimental modal testing shows that the reduction of the natural frequencies at elevated temperature is much less in the proposed HDD spindle system than in the conventional spindle system. The proposed HDD spindle motor can improve the dynamic reliability of a HDD spindle system, which contributes to the high track density of a HDD.

Effect of hard-disk drive spindle motor vibration on dynamic microwaviness and flying-height modulation

In order to achieve higher recording densities up to 1 Terabit per square inch using conventional magnetic recording technologies, the recording slider will need to be physically spaced very close to the rotating disk, possibly via the use of an air-bearing surface. However, as the recording slider is flying at such ultra-low spacing of few nanometers over a high-speed rotating disk, it is experiencing disturbances from various different sources and of a wide frequency range. These disturbances may cause the recording slider to vibrate significantly, a condition known as flying-height modulation (FHM), which may result in data loss and possibly head–disk interface failure. A significant source of slider excitation is due to low frequency surface topographical features of the rotating disk, termed dynamic microwaviness. Dynamic microwaviness is a dynamic property of the disk and differs from regular topographical microwaviness, which is a static property. Most research works on dynamic microwaviness and FHM have been focused at the component level, using somewhat idealized conditions, such as high performance air-spindle motors that exhibit very low vibration amplitudes. In this paper, actual hard-disk drive spindle motors are used to investigate the effect of spindle motor vibration on dynamic microwaviness and FHM. It is found that there is a clear connection between spindle motor vibration and dynamic microwaviness that affects FHM.

A bipolar-starting and unipolar-running method to drive a hard disk drive spindle motor at high speed with large starting torque

This paper presents a method to drive a hard disk drive (HDD) spindle motor at high speed with large starting torque by utilizing a bipolar-starting and unipolar-running algorithm. It proposes a novel inverter circuit to switch from bipolar to unipolar drive, or vice versa. It also develops a digital signal processor (DSP)-based brushless dc (BLDC) motor controller not only to drive the BLDC motor with the bipolar or unipolar method, but also to switch from one method to the other at any speed. Torque-speed-current curves of a BLDC motor driven by bipolar or unipolar method are investigated experimentally, and the effectiveness of the proposed method is also verified by using the developed controller experimentally. This research shows that the proposed method starts the BLDC motor with large starting torque that can be obtained by a bipolar drive, and it runs the BLDC motor at high speed that can be driven by unipolar drive.

An Improved Nodal Method for Circuit and Multi-Slice Magnetic Field Coupled Finite Element Analysis

A general and simple method to couple arbitrarily connected circuits and multi-slice magnetic fields in the time stepping finite element analysis of electromechanical devices and electrical machines is presented in detail. The merits of the proposed method are that the sparsity of the finite element equations is improved, the formulations to be described will allow unequal division of the axial length of the motor in the multi-slice model, the stranded windings (with negligible eddy current) and solid conductors (with eddy current) in the field domain can be connected arbitrarily with the external circuits, and the coefficient matrix of the system is symmetrical and the nonlinear power electronic elements can be easily maneuvered in the formulations. As illustrating examples, the proposed approach is used to simulate the operations of a brushless d.c. motor and a hard disk drive spindle motor.

Vibration of rotating-shaft HDD spindle motors with flexible stationary parts

Demonstrates an accurate mathematical model predicting forced vibration of rotating-shaft hard disk drive spindle motors with flexible stationary parts. The mathematical model consists of three parts: a rotating part, a stationary part, and bearings. The rotating part includes a flexible hub, a flexible shaft press-fit into the hub, and N elastic disks mounted on the hub. The stationary part can include motor bracket (stator), base casting, and a top cover. The bearings under consideration can be ball bearings or fluid-dynamic bearings (FDB). The rotating disks are modeled through the classical plate theory. The rotating part (except the disks) and the stationary part are modeled through finite-element analyses (FEA). With mode shapes and natural frequencies obtained from FEA, the kinetic and potential energies of the rotating and stationary parts are formulated and discretized to compensate for the gyroscopic effects from rotation. Finally, use of the Lagrange equation results in the equations of motion. To verify the mathematical model, frequency response functions are measured experimentally for an FDB spindle carrying two identical disks at motor and drive levels.

A dynamic model of the disk drive spindle motor and its applications

A dynamic model of the hard disk-drive spindle motor based on the circuit-field-motion coupled-time-stepping finite-element method is presented. The model provides a basis for determining back electromotive force, inductance, and cogging torque in dynamic operation conditions. The merits of the proposed method are that the estimation of the motor parameters can be obtained, accounting for the saturation effect and other operational conditions, and the computing time for parameters calculation can be reduced. The proposed model can also be used to determine the commutation time, cogging torque, output torque, and radial force, to study the effect of the skewed magnets/slots, and to simulate the starting process and other transient processes.

Estimating Cost Savings when Implementing a Product Platform Approach

Many market forces are driving companies to improve their targeting of increasingly small market niches. To accomplish this efficiently, products are organized into product families that typically share common platforms. To reorganize the current product offerings or new products into a product family, using a platform approach, requires estimating the savings for such a modification. One of the problems encountered in estimating development and design cost is the lack of availability of hard information during the initial design phases. The purpose of this paper is to estimate the design and development cost, when moving towards a platform approach, using simple models. The activity based product family cost models are developed from existing single product design activities, which are modified and extended to reflect activities related to development of product platform and subsequent product family members supported by the platform. Uncertainty related to cost associated with activities are included in the model, which is solved using Monte Carlo simulation. The approach is demonstrated using a hard disk drive spindle motor platform development for a family of hard disks.

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.

Analysis of iron loss in hard disk drive spindle motors

The paper presents analysis of iron loss in permanent magnet spindle motors used for hard disk drives. The analysis is based on the finite element method and uses the information on local flux density variation in the motor components. The iron loss distribution and the effect of the stator dimensions on the total iron loss are discussed.

Design of fluid bearing spindle motors with controlled unbalanced magnetic forces

This paper discusses the beneficial and detrimental effects of unbalanced magnetic forces developed in a fluid bearing spindle motor used for hard disk drives. The analysis made in this paper shows that unbalanced forces can be useful for magnetic preloading and stabilizing the fluid bearing system of a hard disk drive spindle motor.

Dynamic Characteristics of Hard Disk Drive Spindle Motors—Comparison Between Ball Bearings and Hydrodynamic Bearings

Recently, many computer hard disk drive companies and spindle motor manufacturers have been looking for a substitute for ball bearings to continue making dramatic progress in increasing the capacity of data storage systems. In this paper, the frequency-forced responses of hard disk drive spindle motors supported by both ball bearings and liquid-lubricated spiral groove hearings (SGBs) were studied experimentally. It is found that both shaft rigidity and disk flexibility have great effects on the natural frequency of the spindle motor conical (rocking) mode. The high damping capacity of the SGB is able to suppress the vibration amplitudes of both motor rocking mode and the flexible disk modes. But at a very low frequency range, the SGB motors displayed a large amplitude in the axial direction vibration test. With an adequate bearing design, the SGB motors have proven their superior dynamic characteristics.

Electromagnetic design for hard disk drive spindle motors with fluid film lubricated bearings

This paper discusses the problems associated with the electromagnetic design of hard disk drive (HDD) spindle motor having fluid film bearings. It will highlight the effect of the unbalanced electromagnetic pull in the radial direction of FFB spindle which uses permanent magnet brushless DC motors with slotted stator core. An analytical approach is employed for predicting the magnetic field and motor performance. Results obtained from this approach are compared with finite element analysis.

Analysis of Unbalanced-Magnetic-Pulls in hard disk drive spindle motors using a hybrid method

In spindle motor design and analysis, calculation of the torque and force is an essential step for the performance prediction. A method for the calculation of the Unbalanced-Magnetic-Pull (UMP) is proposed in this paper. As the method is based on the combination of the strength of analytical and numerical methods, it can yield more accurate results than traditional methods, and can be conveniently implemented in the computer aided design/analysis softwares for spindle motors.