Slider Vibration Research Articles

Modelling of vibrations excited by formation and shearing of adhesive micro-junctions during sliding

Understanding of the mechanism of “rubbing” noise and low amplitude friction exited vibration generation in steady sliding can be helped by models describing the contact interactions. In the current paper, we consider a simple microscopic contact model for surfaces in sliding, which is based on the adhesion theory of friction. In the proposed model, we consider that the formation and shearing of a junction contributes to a small change in the real contact area. The model incorporates random size and random spacing between junctions. We investigate the dependence of the instantaneous real contact area on the average size and number of junctions. We find that, from the viewpoint of vibration reduction, it is advantageous if the real contact area needed to support a given load is obtained as a sum of many small-sized micro-contacts, instead of few large-sized micro-contacts. The above result is in agreement with experimentally observed reduction of vibrations of a hard-disc slider after texturing.

An Analytical Model of Contact Vibration of Slider

An analytical model of the contact vibration of sliders was developed in order to determine the optimum specifications for minimizing the fluctuations of flying height. In this model, the motion of the slider is expressed with two degree-of-freedom in the translation and pitching directions. The air film and suspension are modeled as a two-degree-of-freedom mass-damper-spring vibration system; the contact force between the slider and the disk is modeled by integrating the contact area when the slider is in contact with the media at a certain pitching angle. The degree of interference when the slider is in contact with the media is modeled in terms of the interference height. The developed analytical model shows that the contact vibration of the slider has a divergent mode or a convergent mode depending on the magnitude of the coefficient of friction. These numerical results agree with our qualitative measurements of vibration.

3819 ピッチング減衰効果を向上した熱突出し用浮上スライダ設計(S56 磁気ヘッド浮上・位置決め制御技術,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

We numerically investigated the touch down and take off characteristics of a head slider with thermal protrusion. Slider vibrations started to occur before the contact force rose up in the touch down process and sustained even after the contact force went out in the take off process. We proposed a slider with the pitch damping step (PDS). We showed that PDS is effective in lowering the touch down and take off heights with improved damping for the second pitch mode resonance of the slider.

A new approach to roughness-induced vibrations on a slider

In the past, roughness effects were included in models by using various friction laws. In contrast, this study deals with simple Poisson impact and Coulomb friction laws on multiple concurrent contacts between geometrically random rough surfaces and their effect on the slider's roughness-induced vibrations. The closed-form solutions derived here relate roughness-induced vibrations to the surface roughness, slider mass, slider load, slider dimensions, relative sliding speed, and the coefficient of restitution. Wear influences were studied by simulating random rough surfaces with multiple concurrent contacts. Contrary to expectations we found that random roughness can induce slider vibrations of distinct frequencies. We found a good agreement between the results of the studied models and the experiments. The closed-form solution was found to be suitable for estimating the roughness-induced vibration frequencies of a hard-disk drive's writing/reading head and those of a car-brake's pad (known as squeal-noise).

2310 スライダ気体潤滑下の液体薄膜表面の安定性解析 : スライダ動特性を考慮した空気膜特性の影響(要旨講演,情報機器コンピュータメカニクス)

In the head-disk interface (HDI) of a hard disk drive (HDD), lubricant deformation may cause the degradation of flying characteristics of head slider, as the flying height is decreasing. Dai et al. analyzed washboard effect as the stability/instability problem of the lubricant surface from the view point of shear stress effects caused by slider vibration. In this paper we analyzed the similar problem considering i) the van der Waals attractive pressure on the lubricant surface from the slider, ii) the air film stiffness and damping dependent on excitation frequency and iii) the shear stress coefficient. In the natural frequency of the air film, the lubricant deformation may grow by the shear stress effect at the lubricant surface.

Experimental and Theoretical Investigation of Bouncing Vibrations of a Flying Head Slider in the Near-Contact Region

We experimentally and theoretically investigated in detail bouncing vibrations of a flying head slider in the near-contact region between the head and disk surface. By changing the Z-height in the experiment, we evaluated the effect of the pitch static angle on the ambient pressure at which unstable bouncing vibration starts and stops. We found that the touch-down and take-off pressure hysteresis decreased as the pitch static angle increased even though the flying height at the trailing edge decreased slightly. From detailed measurement of the slider dynamics at the threshold of the bouncing vibration, we found that the trailing edge of the slider was first attracted to the disk. As the pitch static angle decreased, the magnitude of the first drop of the trailing edge increased and the bouncing vibration amplitude increased more rapidly. We also measured the mode of the bouncing vibration by using two laser Doppler vibrometers simultaneously. By using an improved two-degree-of-freedom slider model, in which the small micro-waviness and the shearing force of the lubricant were taken into account, we could analyze the touch-down/take-off hysteresis, mode, and destabilization process of the bouncing vibration similar to the experimental results. We also theoretically found that either self-excited bouncing vibration with lower pitch frequency or forced vibration with higher pitch frequency was generated, depending on the magnitudes of the micro-waviness and the disturbance.

Dynamic response of 1-in. form factor disk drives to external shock and vibration loads

The dynamic response of the head disk interface is investigated numerically for two different designs of 1-in. hard disk drive enclosures, the so-called “thin” enclosure and the “thick” enclosure. First, the in-plane and out-of-plane vibration response is determined. Then, the effects of linear shock and head slap are studied. Simulation results show that the thinner enclosure has better performance with respect to forced vibrations in terms of reduced amplitude of slider vibrations. In addition, the effect of operational shock on the dynamic characteristics of textured and untextured sliders is studied. A finite element formulation of the time-dependent Reynolds equation (with Boltzmann slip flow correction) was used to obtain the air bearing response. The results show that the dynamic flying characteristics of textured sliders are improved compared to that of untextured sliders.

Contact Hysteresis Behavior of Textured Pad Slider in Head–Disk Interface

Takeoff performance of the magnetic head slider on head-disk interface is influenced by a stick-slip vibration of a slider enhanced by the friction of the head-disk contact. We studied this phenomenon using a simulation of slider vibration based on stick-slip analysis. Obvious degradation in the takeoff performance was estimated for the disks with large friction through the simulation of the contact hysteresis defined by the difference of takeoff height and touchdown height. In order to confirm that simulation result, several types of textured pad sliders by focused ion beam fabrication were evaluated by touchdown and takeoff measurement. These pad sliders were textured at a small area near the trailing edge on a trailing pad as a corresponding contact area. The texturing of a trailing pad did not disturb the flyability of slider because the textured area was very small and did not decrease the slider fly height. As a result, the contact hysteresis of textured sliders became smaller as a function of contact area and improved the takeoff performance

Study of head takeoff phenomenon influenced by stick-slip vibration of slider on head-disk interface

Takeoff performance of the magnetic head slider on head-disk interface is influenced by a stick-slip vibration of slider enhanced by the friction of head-disk contact. We studied this phenomenon using altitude test and a simulation of slider vibration based on stick-slip analysis. Obvious degradation in the takeoff performance was observed for the disks with small roughness. This phenomenon can be explained using a simple stick-slip model of slider vibration enhanced by friction force, and investigated through the evaluation of the pressure hysteresis defined by the difference of takeoff pressure and touchdown pressure. Hysteresis simulation based on the stick-slip model revealed that large stick-slip vibration induces hysteresis for the disk with low roughness. We confirmed by the experiment and simulation that this stick-slip vibration of slider continues in the case of large friction coefficient after one slider-disk contact. We also confirmed that, slider-disk contact in low fly height occurs due to the trigger which the slider contacts on lubricant pooling. Reduction of friction force was found to be effective to improve the pressure hysteresis and takeoff performance.

재배치 시간-주파수 해석을 이용한 슬라이더 공기베어링의 비정상 거동 연구

Frequency spectrum using the conventional Fourier analysis gives adequate information about the dynamic characteristics of the slider air bearing for the linear and stationary cases. The intermittent contacts for the extremely low flying height, however, generate nonlinear and nonstationary vibration at the instant of contact. Nonlinear dynamic model should be developed to simulate the impulse response of the air bearing during slider-disk contact. Time-frequency analysis is widely used to investigate the nonstationary signal. Several time-frequency analysis methods are employed and compared for the slider vibration signal caused by the impact against an artificially induced scratch on the disk. The representative Wigner-Ville distribution leads to the severe interference problem by cross terms even though it gives good resolution both in time and frequency. The smoothing process improves the interference problem at the expense of resolution. In order to get the results with good resolution and little interference, the reassignment method is proposed. Among others the reassigned Gabor spectrogram shows the best resolution and readability with negligible interference.

Partial-contact head-disk interface approach for high-density recording

A modern hard disk drive (HDD) generally requires a head-disk spacing of less than 10 nm. This paper focuses on studying slider vibration and designed several novel air bearing shapes to prevent slider vibration. An isolated pad slider and a narrow trailing edge slider were designed and fabricated for the feasibility study of the partial-contact interface. From the study, we found out that: 1) a slider with a smaller isolated pad had a smaller off-track vibration; 2) one with a smaller isolated pad had less aggressive disk lubricant depletion; and 3) a narrower trailing edge led to an easy transition from contact to flying.

Slider vibration reduction using slider surface texture

Surface texture with a height of 4.5 nm was fabricated on two types of pico-sliders using argon plasma etching. The nominal flying height of the sliders was 5 and 7 nm, respectively. Laser Doppler vibrometry (LDV) was used to investigate the dynamics of the textured and untextured sliders during steady-state flying and during contact start/stop (CSS). During steady-state flying, the texture was found to significantly reduce both rigid body slider vibration modes and air-bearing modes. During CSS, the amplitude of both out-of-plane and in-plane vibrations was found to be reduced as a consequence of the texture on the slider surfaces.

Experimental and Analytical Study of Bouncing Vibrations of a Flying Head Slider in a Near-Contact Regime

This paper presents an experimental and analytical study of bouncing vibrations of a flying head slider in near-contact and contact regimes. In our experiment we showed that, by reducing the ambient pressure, the slider begins to touch-down and exhibit bouncing vibrations, and by increasing the ambient pressure thereafter, the slider continues to vibrate until an ambient pressure higher than the touch-down pressure. In the analysis we used a two-degrees-of-freedom slider model with linear front and rear air-bearing springs and dashpots. In a numerical simulation of slider dynamics, we considered rough surface contact of the trailing air-bearing pad with a disk, including bulk deformation, adhesion force of lubricant and friction force. The disk is assumed to have no microwaviness. From the simulation of decreasing and increasing nominal flying height, we found that the slider exhibits a bouncing vibration and touch-down/take-off hysteresis as seen in the experiment. The frequency spectrum characteristics of the bouncing vibration agree well between numerical analysis and the experiment. From a parametric study of the bouncing vibration excited by initial spacing deviation, we found that the unstable flying height range can be decreased by increasing the air-bearing stiffness and can be completely eliminated if the lubricant adhesion force or the frictional coefficient is decreased to certain small values.

Dynamics of air bearing slider with nano-meter level proximity contact

This paper presents a comprehensive study on the vibrations of slider with pseudo contact air bearing surface designs on sliding disk. It is found that the shift between contact and loss-of-contact results in the large non-linearity of the system. A typical interface with proximity recording slider is numerically investigated and the theoretical model is simplified to derive a comprehensive closed-form solution. Finally, it is illustrated that these derived results agree qualitatively well with existing experiments.

Design Considerations of a Contact Slider and Bouncing Vibration in Near-Contact Regime

This article introduces the results of our recent study on the design conditions for a contact and near-contact slider and friction-induced bouncing vibrations in a near-contact regime, based on computer simulations using a simple dynamical model of slider, air-bearing, and disk systems. Basic design conditions for contact sliding are discussed. The contact force and attractive force in asperity contact with a lubricant layer and bulk deformation are calculated numerically. Flying height hysteresis and bouncing vibration of a flying slider that are experimentally observed in nanometer spacing can be obtained by the simulation.

Flow-Induced Vibration Reduction in HDD by Using a Spoiler

To reduce the flow-induced vibration (FIV) of the head stack assembly (HSA) in the hard disk drive (HDD), we experimentally studied the spoiler, which is put between disks. This study was carried out using a laser doppler vibrometer (LDV) to measure the amplitude of the head slider vibration. We also measured the power consumption of the spindle motor. As parameters of the spoiler shape, the thickness and the length were selected. From the experimental result, these parameters effect significantly both the head's vibration and the power consumption. This result suggests that the flow rate reduction with the spoiler causes a reduction of the HSA's FIV, and the energy loss with the spoiler causes an increase of the power consumption. We defined the spoiler's FIV-reducing efficiency as a ratio of the amplitude reduction to the power consumption increase. The length change makes the peak value. This is caused by the fact that the FIV reduction becomes almost constant when the spoiler is longer than the carriage arm length inside disk region, although the spoiler length makes power consumption monotonically large.

Slider-lubricant interactions for low flying sliders

The dynamics of pico sliders is investigated as a function of lubricant thickness using laser Doppler vibrometer instrumentation. Lubricant depletion is measured using a surface reflectance analyzer. The results indicate that slider vibrations increase with an increase in lubricant thickness. Lubricant depletion also increases with an increase in lubricant thickness.

An Investigation of Slider Vibrations in Near Contact Recording Using a Digital Laser Doppler Vibrometer

At a flying height of 10 nanometers, contacts between slider and disk are likely to occur, and control of contact-induced slider vibrations is an important design consideration. In this study, slider vibrations during contact are investigated using a digital laser Doppler vibrometer (LDV). The noise level of the digital interferometer is compared with that of a conventional analog LDV. In addition, acoustic emission (AE) sensors are used to evaluate the contact behavior of the slider. A comparison of AE and LDV data is performed. The results show that the noise level of the digital LDV is lower than that of the analog LDV, and that suspension sway mode vibrations and torsion mode vibrations are excited during contact as a function of the skew angle.

Numerical simulation of slider dynamics during slider–disk contact

In this paper, the dynamic behavior of pico slider in contact with the disk was calculated. The analysis model consists of a simplified suspension model, an air bearing model, and a slider–disk contact model. The contact model consists of two elements. One is surface roughness model measured by Atomic Force Microscope (AFM) and the other is micro-waviness model. The dynamic behaviors of the tri-pad slider are calculated at several rotation speeds to investigate slider vibration modes during slider–disk contact. The slider oscillation frequency depends on the rotation speed and it saturates about twice as much as eigen frequency of air bearing pitch mode.

Analysis of Friction-Induced Vibrations of Flying Head Slider in Near Contact Regime

In order to investigate the severe slider vibrations and hysteresis behaviors of touch down and take-off processes in near contact regime, we numerically calculated the slider dynamics by using the 2-DOF model considering asperity contact, adhesive force of lubricant and friction force. As a result, we could find friction-induced vibration as follows : In the touch down process, the slider exhibits bouncing vibrations as the slider contacts with the disk surface. In the take-off process, the slider continues the bouncing vibration even if the nominal flying height becomes higher than that when the slider begins to contact with the disk surface. These bouncing vibrations and hysteresis phenomena are observed only when both lubricant force and friction force exist. In addition, the bouncing vibration is not simply periodic but contains many frequencies. From spectrum analysis of the slider vibrations up to 1 MHz, we can observe the many super harmosics and sub-harmonics. These analytical results agree well with the experimental ones. As a result, we can say that the severe contact vibration is a self-excited vibration of the slider related to both lubricant force and friction force.