Improvement of slider off-track vibration through design parameter modifications of a compatible FDB spindle system

Recently, the hard disk drive (HDD) industry has tried to use a compatible spindle system regardless of the number of disks because of the resulting cost reduction and standardization of components. The center of gravity (CG) location predominantly affects the disk and slider off-track vibration, which is why the rocking mode of a spindle system is affected by the CG. Any changes to the CG affect the operational vibration of the spindle system. In a compatible fluid dynamic bearing (FDB) spindle system, changing the number of disks may alter the CG. Nevertheless, research into the compatibility of FDB designs has not been undertaken. In this study, FDB design parameters were selected to reduce the slider off-track vibration with variations in the CG considering a compatible spindle system. First, a verified finite element (FE) model of a spindle system was constructed. The amplitude and frequency of the rocking mode were compared between a one-disk spindle system and a two-disk spindle system using the FE model, considering the relationship between the CG location, which is changed by the number of disks, and the location of the upper and lower journal bearings. HDD prototypes were then manufactured using the improved design. Based on the manufactured spindle system, the variations in the rocking mode characteristics and slider off-track vibration were measured and operational vibration tests were performed to verify the effect of the number of disks on the slider off-track vibration. An improved FDB spindle design was developed with a reduced rocking mode, and a compatible spindle system was proposed.     

Numerical analysis of off-track vibration of head gimbal assembly in hard disk drive caused by the airflow

The problem of flow-induced vibration of head gimbal assembly (HGA) in hard disk drive (HDD) is analyzed by means of numerical models. Flow field is calculated in a fraction of physical domain called extended wedge-like domain. For this purpose, appropriate inlet and outlet boundary conditions are specified. The aerodynamic disturbances generated by the slider are studied by performing flow calculations for the cases of with and without slider. It is observed that the slider blocks the airflow causing a high-pressure region in the proximity of the leading surface of the slider. In addition, significant vortical structures are found being generated by the side surfaces of the slider. A finite element model is developed for calculating the response of HGA to the aerodynamic excitations. It is found that the flow disturbances generated by the slider play a significant role in the off-track vibration of the HGA.     

Dynamics of ultra low flying sliders during contact with a lubricated disk

In this paper, laser Doppler vibrometry is used to study the motion of a femto slider in the vertical, pitch, roll, off-track and down-track direction due to slider–lubricant interactions. The change in slider dynamics is determined by comparing the laser Doppler vibrometer signals from the slider for time increments of 2 min. The time evolution of this signal is analyzed. The data suggest that slider–lubricant interactions at the head-disk interface have a strong effect on slider dynamics. Spectral analysis of the slider motion indicates that excitation occurs at the same frequency for all degrees of freedom. The excitation frequency is slightly lower than the free vibration frequency, suggesting that lubricant damping plays a role in the excitation of the slider.     

Experimental study on slider dynamics during touchdown by using thermal flying-height control

To investigate the possibility of further lowering the clearance in head?Cdisk interface systems, slider dynamic behavior during a touchdown sequence with a thermal flying-height control (TFC) function was investigated by using a spinstand-level evaluation utilizing an acoustic emission (AE) sensor and a laser Doppler vibrometer (LDV). Experimental results demonstrated that off-track vibration was easier to excite by head?Cdisk contact at the beginning of head?Cdisk contact. We then confirmed that the amplitude of pitch-mode vibration in the flying-height direction increased and sway-mode vibration in the off-track direction decreased when increasing heater power during the touchdown sequence. Moreover, we found that the peak frequency of pitch-mode vibration shifted to a higher frequency under over-push conditions. Time?Cfrequency domain analysis results showed that the peak shift occurred at several locations during a disk rotation. The mechanism of the peak shift is attributed to the increase in stiffness at the head?Cdisk interface (HDI) due to solid?Csolid contact or mode change occurred in such regions. During the touchdown sequence, the friction force at the HDI continues to increase, even though slider vibration and AE signal decrease when heater power is increased. The friction force at the HDI needs to be decreased to achieve further low-clearance HDI.     

Position error reduction in magnetic disk drives using a head gimbal assembly with radial head motion capability

Reducing the head positioning error is important to achieve higher track density in hard disk drives. In this paper, it is shown that the head off-track due to disk vibration can be reduced by using a head gimbal assembly capable of moving not only vertically to disk surface but also radially across the track. We find the optimal geometric relationship to minimize the head off-track due to disk vibration. The relationship is obtained based on precise mathematical modeling of head off-track mechanism due to disk vibration. Some examples of head gimbal assembly (HGA) with radial head motion capability, which satisfy such optimal relationship, are also proposed. It is experimentally found that the proposed optimal HGA can reduce non-repeatable run-out (NRRO) position error signal (PES) significantly. Since it reduces NRRO PES during servo track writing as well, the written-in portion of repeatable run-out PES can be also significantly reduced.     

Six-DOF vibrations of partial contact sliders in hard disk drives

A six-degree-of-freedom slider dynamic simulator is developed to analyze the slider’s motion in the vertical, pitch, roll, yaw, length and width directions. The modified time-dependent Reynolds equation is used to model the air bearing and a new second order slip model is used for a bounded contact air bearing pressure. The simulator considers the air bearing shear acting on the air bearing surface and the slider–disk contact and adhesion. Simulation results are analyzed for the effects of the disk surface micro-waviness and roughness, skew angle, slider–disk friction and micro-trailing pad width on the vertical bouncing, down-track and off-track vibrations of a micro-trailing pad partial contact slider.     

A miniature in-plane piezoresistive MEMS accelerometer for detection of slider off-track motion in hard disk drives

A miniature in-plane pizoresistive MEMS accelerometer was designed, fabricated and characterized for detection of slider off-track motion in hard disk drives. The structure of the accelerometer consists of a central supporting beam and two stress-magnifying sensing beams. Under geometric constraints imposed by the trailing side of a pico slider, the accelerometer design was optimized to achieve approximately pure axial deformation in the sensing beams and a maximum sensitivity with a specified natural frequency of 300 kHz. Fabricated on a silicon-on-insulator (SOI) wafer, the accelerometer with a half Wheatstone bridge was wirebonded to external pads and interfaced with an amplifier circuit on a printed circuit board (PCB). The noise level, sensitivity, nonlinearity were characterized with vibration testing on a shaker. The miniature accelerometer (1 × 0.3 × 0.3 mm³) with a weight of only 0.2 mg offers a much higher resonant frequency with a comparable sensitivity compared with those in previous work.     

A predictive technique for evaluating structural vibration gain of damped suspensions in hard disk drives

The problem of resonant vibration of suspensions used in hard disk drives has been the subject of ongoing research. This study focuses on implementation of a finite element modeling methodology to predict the response for a suspension that includes an added damping component, either as a traditional constraint layer damper or as a design tool. High gains in suspensions result in off-track of the slider, which is the mechanism for reading and writing data. Analytical methodology uses the concept of modal strain energy to predict the modal damping of the structure at each resonant mode. Loss factors and strain energies of each material used in the structure quantify the amount of modal damping at a particular mode. Development of the methodology allows optimization studies of standard damping applications, such as a constraint layer damper. In addition, the methodology enables FEA as a design tool to develop innovative solutions for improved efficiency and higher performance.     

Fuzzy control of an electrodynamic shaker for automotive and aerospace vibration testing

A fuzzy logic based digital time domain sinusoidal acceleration waveform amplitude controller for an electrodynamic shaker is presented. The purpose of Fuzzy Logic Control (FLC) is to reproduce a pre-defined sinusoidal acceleration amplitude profile (in amplitude, frequency and time) at the shaker table. Sinusoidal vibration profiles (sine and logarithmic sine sweep) are considered for a controlled vibration generation in typical automotive and aerospace testing. The difficulty in sine sweep testing is that the non-rigid load dynamics are unknown and it can severely modify the shaker’s performance during sweep test. Since a logarithmic frequency sweep is normally used, a controller needs to be robust to un-modeled dynamics and also fast enough to hold the desired acceleration amplitude within predefined limits throughout the sweep test. The controller structure is developed based on the usual power amplifier technology. The control action is implemented on a waveform-by-waveform basis and a FLC is developed in the LabVIEW environment on a PXI platform for real time control of the shaker. To attenuate the shaker suspension mode resonance a compensator based on electromechanical model of the shaker is designed and cascaded to FLC. The shaker model, suspension mode compensator design, FLC synthesis and experimental implementation results are presented in this paper.     

A parameter identification method for thermal flying-height control sliders

This paper employs higher order frequency response functions to describe the closed-form solution of nonlinear dynamics of MEMS thermal actuated flying-height control (TFC) slider, and employs the measured acoustic emission signal of a TFC slider during touch down as its vibration approximation to correlate with the derived closed-form solution for parameter identification. It is shown that during slider touchdown when heater power is increased gradually, the slider performs weak nonlinear vibrations in early transition phase, and exhibits linear vibration in the following steady sliding phase. These results are useful for the clarification of complicated dynamics and the designs of active sliders in sub-nanometer clearance regime.     

Lyapunov controller design for transverse vibration of a cable-linked transporter system

Modeling and Lyapunov controller design for transverse vibration of a flexible cable transporter system with arbitrarily varying lengths are presented using Hamilton's principle and Lyapunov theory. The axial velocity of the system is assumed to be unknown in the model. This is different from existing literature where the axial velocity is assumed either to be constant or prescribed. The governing equations include two coupled non-linear Partial Differential Equations (PDEs) and boundary conditions. The interactions between the cables and the slider, pulleys, and motors are included in the model. Numerical solution of the derived governing equations is obtained using Galerkin's method. Based on the Lyapunov theory, we propose two boundary controllers and one domain point-wise controller, which suppress the transverse vibration of the cables effectively while assuring the attainment of the slider goal. The proposed controllers dissipate the vibration energy and guarantee the stability of the closed-loop system in Lyapunov sense. Simulation results demonstrate the effectiveness of the proposed controllers.A short version of this paper was presented in 2004 ASME International Mechanical Engineering Conference and Exposition, Anaheim CA, November 14-19, 2004.     

基于实艇装载与加速试验的鱼雷装载可靠度综合评估

针对潜载鱼雷装载可靠度试验时间长、样雷数量小、验前信息少等问题,通过分析装载可靠性评估方法优缺点、装载可靠度试验鉴定主要问题,提出了实艇装载与实验室加速相结合的装载可靠度综合评估方法;结合加速试验等效原理,分析了影响鱼雷装载环境应力的主要因素,设计了装载可靠度试验总体方案和加速试验剖面,确定了恒温、温变循环、振动疲劳加速模型的试验工程化参数;算例表明,该方法解决了在较短时间内潜载鱼雷装载可靠度试验试验考核问题,在保证试验评估结论可信的同时可大幅提高试验实效,不仅可推广应用于其他类型鱼雷可靠性试验鉴定,还可指导鱼雷可靠性的研制与设计。     

Design theory and vibration characteristics of a contact head slider

In this study, the design theory of a previously proposed contact head slider was extended by considering a thermally protruding head slider and the intermolecular adhesive force between the head and disk surfaces. The waviness-excited vibration characteristics of the thermally protruding contact head slider were analyzed using a single-degree-of-freedom slider model, whose contact stiffness was calculated in accordance with the Johnson–Kendall–Roberts adhesive contact theory. It was found that, because of the adhesive force, the resonance frequency f _r of the contact slider changed from zero to a value higher than the original second-pitch-mode resonance frequency with an increase in the head-penetration depth. Because the waviness-excited vibration of the contact slider is amplified at f _r , the first- and second-pitch-mode vibrations of the thermally protruding slider can be excited when f _r approaches those resonance frequencies. Because the friction force varies with the vibration of the contact slider, vibration modes of the slider-suspension system often observed at the beginning of contact can be explained. It is suggested that the region of the head-penetration depth for perfect contact sliding can be widened by increasing the effective contact damping and decreasing the disk waviness.     

Shock analysis of non-operating hard disk drives based on a multibody dynamic formulation

Dropping, striking, or bouncing a hard disk drive (HDD) against a hard surface can damage it internally without external evidence of damage. Contact with a hard ground will lift the slider off the disk surface and then slap back on the surface. A drive that is subjected to this type of shock may fail on initial use or the reliability of the drive may degrade over time. Therefore, industry has a lot of interest on the shock conditions that cause a slider to lift off the disk surface. Finite element software such as ANSYS/LS-DYNA is often used to analyze this shock problem. However, this method consumes a great amount of time. It is also difficult to perform design parameter studies because it requires re-analysis of the model of the entire HDD system when certain design variables are changed. This paper presents a flexible multi-body dynamics formulation to analyze the shock problem of non-operating HDDs. Governing equations of motion of the voice coil motor (VCM)–actuators assembly and the disks–spindle system are derived using a Lagrangian formulation. By introducing constraint equations between the slider and the disk surface, the shock response of the whole HDD system has been obtained. Numerical results show that the method is reasonable and the acceleration amplitude which makes the slider lift off can be determined in a significantly shorter time than by the conventional approach. Finally, the effect of drive parameters on shock resistance, such as shock duration and slider resting location are analyzed.     

Resonant-Type Smooth Impact Drive Mechanism Actuator with Two Langevin Transducers

A smooth impact drive mechanism (SIDM) is a unique piezoelectric actuator that is widely used as a camera focusing mechanism, cell phone lens movement mechanism, etc. This principle enables a compact driving mechanism; however, it cannot generate high-speed movement because a soft-type multilayered piezoelectric transducer (PZT) is utilized at off-resonant movement. This paper proposes a resonant-type SIDM actuator driven with hard-type PZTs to realize high-speed and powerful operation. The fundamental principle is also based on the conventional SIDM; therefore, a saw-shaped movement is required. To generate a high-power ultrasonic output, two Langevin transducers are adopted instead of a soft-type multilayered PZT. One Langevin transducer was a stator and the other was slider whose tip was adhered to a carbon fiber reinforced plastic (CFRP) rod. The CFRP rod was connected to the stator transducer with the frictional force. To obtain quasi-saw-shaped vibration, the longitudinal vibration for each Langevin transducer was excited and these movements were added at the connection point at the CFRP rod. In order to combine these vibration modes, the lengths of the stator and slider Langevin transducers were designed to make the resonant frequencies ratio to be 1:2. By using the proposed principle, the slider Langevin transducer was successfully driven with the speed of 0.11 m/s and the output force was 1.8 N with no load.     

Passenger body vibration control in active quarter car model using ANFIS based super twisting sliding mode controller

This paper presents passenger body vibration control using an Adaptive Neuro Fuzzy Inference System (ANFIS) based super twisting sliding mode controller (ASTSMC) in active quarter car system. The proposed quarter car model is having three degrees of freedom composed of passenger body, sprung mass and unsprung mass. The random road profile is generated using ISO 8608 standard. The ride comfort of passenger body is calculated as per ISO 2631-1 standard. The simulation response is studied in time and frequency domain for passenger body acceleration and displacement in quarter car model. The response generated by ASTSMC controller for passenger body vibration suppression is compared with super twisting sliding mode controller and passive suspension system. The graphical and mathematical results proved the superiority of proposed ASTSMC controller in providing best ride comfort and safety to travelling passenger.     

Effect of reduction of slider pitch-mode vibration on magnetic-recording performance at low-clearance head–disk interface

Aiming at improvements of both stability of slider flying and magnetic-recording performance under a low-clearance condition, a “narrow-grooved slider” was constructed and demonstrated at drive level. The proposed slider has narrow grooves on its center pad of an air-bearing surface for attaining a high-damping effect on pitch-mode resonant vibration of the air bearing. The relationship between the high-damping effect and the pitch-mode resonant vibration was studied, and the magnetic-recording performance at the lube/slider interaction regime was improved. In this study, first, flying-height modulation (FHM) of the slider was analyzed in the frequency domain by using a fast Fourier transform. Compared with the narrow-grooved slider, a non-grooved slider showed a larger increase in high-frequency modulation of gap flying height when the clearance was reduced to near “zero” at which the slider is starting to interact with lube. Furthermore, by means of drive-level experiments, sector error rate (SER) as a function of flying clearance was investigated. Under a low gap flying height condition, HDDs with the non-grooved slider showed slight SER degradation during slider/lube interaction. However, the narrow-grooved slider did not show any SER degradation at the same gap flying height; the damping effect of the narrow-grooved slider suppressed high-frequency FHM, thereby preventing SER degradation in the slider/lube interaction region.     

Experimental study of slider�Cdisk interaction process with thermal-flying-height controlled slider

Thermal flying height (TFC) controlled slider has been introduced in hard disk drive recently. Flying height at the read/write elements of the slider is controlled by thermal pole tip protrusion. Interactions between the TFC slider and disk can be very gentle because the low flying height thermal protrusion area is usually very small. It is still a big challenge to detect very gentle interactions. In this work, a very sensitive method to study very gentle slider?Cdisk interaction in frequency domain has been developed and details of the TFC slider?Cdisk interactions from gentle to strong have been revealed. It is proved that higher heating power is required to initiate the vibration in which higher stiffness part of the slider air-bearing is involved.     

Numerical research on virtual reality of vibration characteristics of the motor based on GA-BPNN model

This paper firstly established the finite element model of steel shell motor, computed modal frequencies on top 6 orders to compare with experimental results and verified the reliability of the finite element model. Then, this paper numerically calculated the electromagnetic force of the motor, inputted it into the verified finite element model and computed the vibration acceleration, velocity, stress and strain of the motor. Constraint and properties of internal materials remained unchanged. Steel shell was replaced by aluminum alloy shell to recompute the vibration acceleration, velocity, stress and strain of the motor and compare with those of steel structure motor. Results showed that the motor of aluminum alloy shell had more obvious vibration characteristics. Finally, this paper put forward neural network model optimized by GA. This model was used to predict the vibration characteristics of the motor of aluminum alloy shell and compare with the real value calculated by finite element, showing good consistency. It indicated that it was feasible to predict the vibration characteristics of the motor based on GA-BPNN model.

     

Time dependent simulation of active flying height control of TFC sliders

A time-dependent numerical simulation procedure is implemented to simulate the flying height response of a typical thermal flying height control (TFC) slider as a function of the power input to the heater element. The Reynolds equation is used in conjunction with a TFC slider finite element model to determine the change in the thermal protrusion and flying height of the slider. The power input signal to the heater element is optimized using convex optimization to minimize flying height variations of the slider. The optimization procedure is applied to a typical experimentally measured flying height profile. The numerical simulation results are in excellent qualitative agreement with experimental measurements.