Experimental Study of the Resonances of the Slider Modulations by Laser Doppler Vibrometer

2014 ◽  
Author(s):  
Peng Peng ◽  
Narayanan Ramakrishnan ◽  
Vijay Kumar ◽  
Brian Karr
Keyword(s):  
Hard Disk Drives ◽  
Laser Doppler Vibrometer ◽  
Vertical Direction ◽  
Voice Coil Motor ◽  
Areal Density ◽  
Air Bearing ◽  
Magnetic Spacing ◽  
Resonance Frequencies ◽  
Bearing Design ◽  
Fly Height

The magnetic spacing of Hard Disk Drives (HDD) needs to be reduced for increasing areal density. It is therefore very challenging to maintain constant fly height at a sub-2nm clearance. Any resonance of the slider or suspension can cause modulations on fly height and thus impacting the writing efficiency. Various research was carried out for the flying stability of the slider [1–4], especially in the off-track direction caused by voice coil motor (VCM) as well as PZT actuation. However, the resonances of the slider modulations in vertical direction have not been well researched. In the study, a method of using heater oscillation to examine the slider resonances has been proposed. The experiments have been performed on two suspension designs and two air bearing designs to demonstrate the effectiveness of this approach. The experimental results showed a shift of resonance frequencies due to a design change of the suspension. The air bearing design also played a role in the heater time constant and thus affecting the magnitude of resonances. Further, larger resonances were observed in a lower clearance setting than passive fly.

Experimental Study of Suspension and Slider Vibrations Measured by Laser Doppler Vibrometer

2013 ◽  
Author(s):  
Tatsuhiko Nishida ◽  
Masao Hanya
Keyword(s):  
Hard Disk Drives ◽  
Laser Doppler Vibrometer ◽  
Vertical Direction ◽  
Servo System ◽  
Voice Coil Motor ◽  
Laser Doppler ◽  
Track Width ◽  
Recording Density ◽  
Magnetic Spacing ◽  
Dual Stage

The magnetic spacing of Hard Disk Drives (HDD) needs to be reduced for high recording density. On the other hand, it is necessary to prevent contact between the slider and disk for reliability of HDDs. Various research was carried out for the flying stability of the slider [1–3]. Furthermore, the magnetic track width also needs to be narrowed for high recording density. The Dual Stage Actuator (DSA) servo system is used for high positioning accuracy [4]. The DSA servo system uses a piezoelectric actuator on a suspension in addition to Voice Coil Motor (VCM). In this study, we measured vibrations to the slider and suspension caused by the PZT and VCM actuations. Two Laser Doppler Vibrometers (LDV) were used for the measurement. Moreover, we performed a numerical analysis to estimate the roll moment of the Air Bearing Surface (ABS) of the slider caused by PZT actuation. As results, we confirmed that the ABS vibrated in vertical direction due to the suspension’s vibrations caused by PZT and VCM actuations.

A Method for Characterizing the Head-Disk Interface Dynamics Near the Touchdown Conditions Using the Magnetic Fly-Height

2020 ◽  
Author(s):  
Rahul Rai ◽  
Abhishek Srivastava ◽  
Bernhard Knigge ◽  
Aravind N. Murthy
Keyword(s):  
Hard Disk Drives ◽  
Areal Density ◽  
Disk Surface ◽  
Disk Drives ◽  
Head Disk Interface ◽  
Soft Contact ◽  
Disk Interface ◽  
Magnetic Spacing ◽  
Bearing Stiffness ◽  
Fly Height

Abstract Recent growth in the cloud storage industry has created a massive demand for higher capacity hard disk drives (HDD). A sub-nanometer head media spacing (HMS) remains the most critical pre-requisite to achieve the areal density needed to deliver the next generation of HDD products. Designing a robust head-disk interface (HDI) with small physical clearance requires the understanding of slider dynamics, especially when the head flies in proximity to the disk surface. In this paper, we describe a method using the magnetic read-back signal to characterize the head fly-height modulations as it undergoes a transition from a free-flying state to soft contact with the disk surface. A technique based on the magnetic fly-height sensitivity is introduced for the identification of the transition plane that corresponds to the onset of the touchdown process. Additionally, the proposed magnetic spacing based meteorology is used to study the effect of the air bearing stiffness on the magnitude of the slider vibrations induced by intermittent head-disk interactions. The information about the minimum spacing while maintaining the stable flying conditions can help in reducing the head-disk interaction risk that can enable a low clearance interface.

Head-Disk Dynamics in the Flying, Near Contact, and Contact Regimes

2000 ◽  
Vol 123 (3) ◽  
pp. 561-565 ◽  
Author(s):  
Run-Han Wang ◽  
Vasant Nayak ◽  
Fu-Ying Huang ◽  
Wade Tang ◽  
Francis Lee
Keyword(s):  
Hard Disk Drives ◽  
Laser Doppler Vibrometer ◽  
Areal Density ◽  
Magnetic Storage ◽  
Disk Drives ◽  
Torsional Mode ◽  
Strong Function ◽  
Magnetic Spacing ◽  
Bending Mode ◽  
Vertical Spacing

To achieve an areal density approaching 50 Gb/in.2 for the magnetic storage of data in hard disk drives requires reduced mechanical and magnetic spacing. Off-track jitter caused by airflow or contact can cause track misregistration on the order of 20–70 nm which may be excessive for adequate servo performance. The magnetic signal can be used to identify both the vertical spacing modulation due to the air bearing modes and off-track jitter due to suspension modes with nanometer resolution. We find that the off-track jitter in the flying regime is driven by airflow and is a strong function of the disk velocity and the suspension type. In the contact regime, the vertical spacing modulation and off-track jitter increase due to contact. Using a laser Doppler vibrometer we identified the leading contribution to the off-track jitter to be primarily the first torsional mode (T1) and to a lesser extent the first bending mode (B1) of the suspension.

Effect of Intermolecular Forces on the Static and Dynamic Performance of Air Bearing Sliders: Part II—Dependence of the Stability on Hamaker Constant, Suspension Preload and Pitch Angle

2005 ◽  
Vol 128 (1) ◽  
pp. 203-208 ◽  
Author(s):  
Vineet Gupta ◽  
David B. Bogy
Keyword(s):  
Pitch Angle ◽  
Dynamic Performance ◽  
Hard Disk Drives ◽  
Intermolecular Forces ◽  
Flying Height ◽  
Total Force ◽  
Air Bearing ◽  
Force Increase ◽  
The Stability ◽  
Fly Height

Intermolecular and surface forces contribute significantly to the total forces acting on air bearing sliders for flying heights below 5 nm. Their contributions to the total force increase sharply with the reduction in flying height, and hence their existence can no longer be ignored in air bearing simulation for hard disk drives. Various experimentally observed dynamic instabilities can be explained by the inclusion of these forces in the model for low flying sliders. In this paper parametric studies are presented using a 3-DOF model to better understand the effect of the Hamaker constants, suspension pre load and pitch angle on the dynamic stability/instability of the sliders. A stiffness matrix is used to characterize the stability in the vertical, pitch, and roll directions. The fly height diagrams are used to examine the multiple equilibriums that exist for low flying heights. It has been found that the system instability increases as the magnitude of the van der Waals force increases. It has also been found that higher suspension pre load and higher pitch angles tend to stabilize the system.

Design and Dynamics of Flying Height Control Slider With Piezoelectric Nanoactuator in Hard Disk Drives

2006 ◽  
Vol 129 (1) ◽  
pp. 161-170 ◽  
Author(s):  
Jia-Yang Juang ◽  
David B. Bogy ◽  
C. Singh Bhatia
Keyword(s):  
Numerical Study ◽  
Hard Disk Drives ◽  
Hard Disk ◽  
Areal Density ◽  
Flying Height ◽  
Air Bearing ◽  
Disk Drives ◽  
Adhesion Forces ◽  
Surface Design ◽  
Ultrahigh Density

To achieve the areal density goal in hard disk drives of 1Tbit∕in.2 the minimum physical spacing or flying height (FH) between the read/write element and disk must be reduced to ∼2nm. A brief review of several FH adjustment schemes is first presented and discussed. Previous research showed that the actuation efficiency (defined as the ratio of the FH reduction to the stroke) was low due to the significant air bearing coupling. In this paper, an air bearing surface design, Slider B, for a FH control slider with a piezoelectric nanoactuator is proposed to achieve virtually 100% efficiency and to increase dynamics stability by minimizing the nanoscale adhesion forces. A numerical study was conducted to investigate both the static and dynamic performances of the Slider B, such as uniformity of gap FH with near-zero roll over the entire disk, ultrahigh roll stiffness and damping, low nanoscale adhesion forces, uniform FH track-seeking motion, dynamic load/unload, and FH modulation. Slider B was found to exhibit an overall enhancement in performance, stability, and reliability in ultrahigh density magnetic recording.

scholarly journals In Situ Measurement of Seeking Speed and Seeking Induced Head-Disk Interface Instability in Hard Disk Drives

2015 ◽  
Vol 2015 ◽  
pp. 1-7
Author(s):  
Yu Wang ◽  
Xiongfei Wei ◽  
Yanyang Zi ◽  
Kwok-Leung Tsui
Keyword(s):  
High Speed ◽  
Hard Disk Drives ◽  
Laser Doppler Vibrometer ◽  
Voice Coil Motor ◽  
In Situ Measurement ◽  
Head Disk Interface ◽  
Magnetic Head ◽  
Interface Instability ◽  
Disk Interface

This paper investigated the instability of head-disk interface caused by the voice coil motor (VCM) end crashing the crash stop during the seeking of magnetic head. To make the whole process of that clear, an in situ measurement method based on maximum likelihood estimation and extended Kalman filter for seeking speed at component level was developed first and was then calibrated by a high speed camera. Given a crash between VCM end and crash stop that may be a consequence of the continuous increasing seeking speed, the seeking speed was carefully controlled by using our developed method to find a critical value that may induce vigorous head-disk interface instability. Acoustic emission sensor and laser Doppler vibrometer were used to capture the transient dynamic behaviors of magnetic head when the crash is happening. Damage analysis and mode identification were carried out to reveal the relationship between the damage patterns on disk surface and head dynamics. The results of this study are helpful to optimize the track seeking profile during the HDD operation, as well as the design of components such as head and head arm.

scholarly journals Parametric Investigations at the Head-Disk Interface of Thermal Fly-Height Control Sliders in Contact

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Sripathi V. Canchi ◽  
David B. Bogy ◽  
Run-Han Wang ◽  
Aravind N. Murthy
Keyword(s):  
Hard Disk Drives ◽  
Air Bearing ◽  
Head Disk Interface ◽  
Bearing Surface ◽  
Surface Design ◽  
Disk Interface ◽  
Height Control ◽  
Experimental Findings ◽  
And Control ◽  
Fly Height

Accurate touchdown power detection is a prerequisite for read-write head-to-disk spacing calibration and control in current hard disk drives, which use the thermal fly-height control slider technology. The slider air bearing surface and head gimbal assembly design have a significant influence on the touchdown behavior, and this paper reports experimental findings to help understand the touchdown process. The dominant modes/frequencies of excitation at touchdown can be significantly different leading to very different touchdown signatures. The pressure under the slider at touchdown and hence the thermal fly-height control efficiency as well as the propensity for lubricant pickup show correlation with touchdown behavior which may be used as metrics for designing sliders with good touchdown behavior. Experiments are devised to measure friction at the head-disk interface of a thermal fly-height control slider actuated into contact. Parametric investigations on the effect of disk roughness, disk lubricant parameters, and air bearing surface design on the friction at the head-disk interface and slider burnishing/wear are conducted and reported.

Boundary Effect on Particle Motion in the Head Disk Interface

2007 ◽  
Author(s):  
Nan Liu ◽  
David B. Bogy
Keyword(s):  
Drag Force ◽  
Particle Motion ◽  
Boundary Effect ◽  
Hard Disk Drives ◽  
Areal Density ◽  
Air Bearing ◽  
Disk Drives ◽  
Head Disk Interface ◽  
Bearing Surface ◽  
Disk Interface

Simulation of particle motion in the Head Disk Interface (HDI) helps to understand the contamination process on a slider, which is critical for achieving higher areal density of hard disk drives. In this study, the boundary effect—the presence of the slider and disk—on particle motion in the HDI is investigated. A correction factor to account for this effect is incorporated into the drag force formula for particles in a flow. A contamination criterion is provided to determine when a particle will contaminate a slider. The contamination profile on a specific Air Bearing Surface is obtained, which compares well with experiments.

HEAD-POSITIONING CONTROL IN TRIPLE-STAGE-ACTUATOR ENTERPRISE HARD DISK DRIVES USING MIXED H2/H∞ SYNTHESIS METHODOLOGIES

2021 ◽  
pp. 1-8
Author(s):  
Zhi Chen ◽  
Prateek Shah ◽  
Roberto Horowitz
Keyword(s):  
Hard Disk Drives ◽  
Voice Coil Motor ◽  
Hard Disk ◽  
Data Driven ◽  
Disk Drives ◽  
Positioning Accuracy ◽  
Positioning Control ◽  
Model Based ◽  
Head Positioning ◽  
Resonance Frequencies

Abstract The recent rapid growth in the cloud storage industry has strongly increased the demand for high-capacity hard disk drives (HDDs). Increasing the areal density brings new challenges to the high-accuracy head-positioning control in the next generation HDD development. Triple-stage-actuator (TSA) system is one of the emerging technologies that can achieve higher bandwidth than that of a dual-stage-actuator (DSA) system and improve the track-following performance. In this paper, we focus on the track-following controller design for TSA system with one voice coil motor (VCM) and two piezoelectric (PZT) actuators. Two types of mixed H2/Hinf synthesis methodologies based on model-based optimization and data-driven optimization are proposed to design the track-following controller for the TSA system. The TSA system can increase the bandwidth of the servo system and decrease the sensitivity to disturbances at the low-frequency range. While increasing the stroke limitation and the resonance frequency of the micro-actuator, the 3sigma the position error signals (PES) is reduced. The data-driven controller can achieve comparable head-positioning accuracy to the model-based controller when it converges to a local optimal solution. The simulation results show the feasibility and effectiveness of the TSA systems with a tertiary PZT actuator. We also analyze the effects of stroke limitations and resonance frequencies of the second/third-stage PZT actuators on the head-positioning accuracy. The results might provide a guideline for the TSA mechanical design.

Air Bearing Dynamics of Sub-Ambient Pressure Sliders During Dynamic Unload

1999 ◽  
Vol 121 (3) ◽  
pp. 553-559 ◽  
Author(s):  
Yong Hu ◽  
Paul M. Jones ◽  
Kangjie Li
Keyword(s):  
High Speed ◽  
Ambient Pressure ◽  
Strong Dependence ◽  
Hard Disk Drives ◽  
Air Bearing ◽  
Trailing Edge ◽  
Suction Force ◽  
Motion Sequence ◽  
Fly Height ◽  
Bearing Dynamics

The increasing effort to use sub-ambient pressure air bearing sliders for dynamic load/unload applications in magnetic hard disk drives requires desirable air bearing characteristics during the dynamic unload event. This paper establishes air bearing design criteria for achieving a smooth head unload performance, through a correlation study between the modeled unloading air bearing dynamics of two 30 percent proximity recording sub-ambient pressure sliders and motion sequence of the same sliders by a high-speed video camera. It is shown that the air bearing lifting force quickly responds to changes in fly height and pitch, while the suction force is relatively resistant to changes in fly height, but somewhat more sensitive to changes in pitch. This unique distinction results in different decreasing rates between the air bearing lifting and suction forces during the unload process, creating a strong dependence of the unloading characteristics on the location of the suction cavities. Both the modeled unloading air bearing dynamics and experimentally recorded motion sequence illustrate that a toward-trailing-edge located suction force acts to pitch the slider up, while the moment produced by a toward-leading-edge located suction force induces a negative pitch motion, resulting in an excessive flexure deformation and dimple separation. Therefore, placing the suction cavities towards the trailing edge offers a reliable unloading performance for the sub-ambient pressure air bearing sliders.

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