Masami Yamane

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.

Dynamic Characteristics and Design Consideration of a Tripad Slider in the Near-Contact Regime

We numerically investigated the tracking ability, the dynamic contact and friction forces of a 2-DOF model of a tripad slider over a random wavy disk surface with 1 nm rms value in the near-contact regime. The air bearing was modeled as a lumped spring and dashpot in order to consider a general design methodology of the flying slider in the near-contact regime. The nominal flying height was changed from the contact regime to the near-contact regime. We studied the effects of the front and rear air bearing stiffnesses, the nominal flying height and the friction coefficient on the tracking ability and contact force. As a result, we found that the spacing variation is caused not only by the slider dynamics but also by the micro-waviness of the disk surface and the distance of the contact pad (head-gap) position from the rear air bearing center We also derived the closed form frequency response functions of the spacing variation to the disk surface waviness. The approximation agreed with the numerical simulation. The effect of the friction coefficient on the tracking ability can be neglected when the flying height is more than 1 nm.

Improved Analysis of Unstable Bouncing Vibration and Stabilizing Design of Flying Head Slider in Near-Contact Region

This paper describes an improved analytical study of the bouncing vibration of a flying head slider in the near-contact region and gives quantitative designs guideline for realizing a stable flying head slider, based on the results of a parametric study. First, we numerically calculated the general characteristics of the contact and adhesion forces between a smooth contact pad and disk surface by considering asperity contact, the lubricant meniscus, and elastic bulk deformation. As a result, it was shown that the contact characteristics can be represented by a simple model with five independent parameters when the asperity density is large and the asperity height is small as in cases of current slider and disk surfaces. Then, we numerically computed the slider dynamics in a two degree of freedom slider model with nonlinear air-bearing springs by using the simplified contact characteristic model. As a result, we have obtained a self-excited bouncing vibration whose frequency, amplitude and touchdown/takeoff hysteresis characteristics agree much better with the experimental results compared with our previous analysis. From a parametric study for takeoff height, we could obtain design guidelines for realizing a stable head slider in a low flying height of 5 nm or less.

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 touchdown/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.

Analysis of Contact Characteristics of Small Rough Surfaces Taking Bulk Deformation and Meniscus Force Into Consideration

We numerically investigated the characteristics of contact force, adhesion force, and contact stiffness between a smooth contact pad and a small rough surface, such as a current magnetic disk surface. The computer-generated asperity had an isotropic Gaussian distribution with a small asperity height and high asperity density. We took asperity contact, bulk deformation, and meniscus force of a lubricant layer at contacting asperity into consideration in the calculations. We evaluated the effects of asperity density, contact pad area, asperity radius, root mean square (RMS) asperity height, and lubricant thickness on external and internal contact forces, adhesion force, and contact stiffness as a function of the separation between the contact pad and disk in both approaching and separating processes. We found that contact and adhesion force tend to change suddenly at the start and end of contact and exhibits hysteresis in the approaching and separating processes when asperity density becomes large and RMS asperity height becomes small comparable with current head sliders and magnetic disks. We also found that contact stiffness is governed by bulk deformation and that the contact stiffness and adhesion force can be regarded as constant during contact when the asperity density increases, the RMS asperity height decreases, and the contact area increases.

Analysis of Tracking Characteristics and Optimum Design of Tri-Pad Slider to Micro-Waviness

This paper describes optimum air-bearing design of a tri-pad slider in terms of tracking ability to micro-waviness based on theoretical analysis of the two-degree-of-freedom slider model and the distributed and concentrated air-bearing stiffness model. Although a short tri-pad type slider was introduced through the load/unload technique, we point out that this type of slider is superior to the traditional rail type slider in terms of tracking ability to micro-waviness. More importantly, the distance between head-gap position and the rear air-bearing center should be made as small as possible. The spacing variation due to lower mode resonance can be eliminated if the positions of front and rear air-bearing centers are located at the center of percussion. The resonance amplitude of the higher order mode in spacing variation can be reduced if the length of the rear air-bearing pad is designed to be 1.2∼1.3 times the wavelength of the higher mode resonance frequency. Since the momental stiffness of the front air-bearing prevents the head-gap from tracking micro-waviness, the front air-bearing length should be made short or the ratio of rear to front air-bearing stiffness should be made large. If the resonance amplitude of the lower mode must be decreased, the front air-bearing length should be designed to be 1.2∼1.3 times the wavelength of the lower mode resonance frequency.

Theoretical Study of Self-Excited and Forced Vibrations of Flying Head Slider in Near-Contact Region

After introducing our previous study of bouncing instability of a flying head slider, we numerically investigated slider dynamics in the near-contact region taking the root-mean-square value and frequency roll-off factor of the micro-waviness as parameters by using 2-degrees-of-freedom slider model, random micro-waviness model and lubricated rough-surface-contact characteristics model. We found that the slider exhibits self-excited bouncing vibration with a frequency close to the lower pitch frequency under small microwaviness but tends to exhibit forced vibration with a resonant frequency in the upper pitch mode as the amplitude of microwaviness increases. If the amount of microwaviness and destabilized sources are reduced sufficiently, there is a contact sliding condition without self-excited and forced bouncing vibration.

Study of Contact Bouncing Vibration of Flying Head Slider in Near-Contact Region

We experimentally and analytically investigated detailed bouncing vibrations of a flying head slider in near-contact regine. In the experiment, we examined the effect of pitch angle on the unstable bouncing vibration in relation to ambient pressure by changing Z-height. As a result, we found that the hysteresis of touch-down and take-off pressure become small as the pitch angle increase even though the trailing spacing decreases slightly. From detailed measurement of the slider dynamics at the threshold of the bouncing vibration, we found that the trailing edge is first attracted to the disk and the first drop of the trailing edge becomes large as the pitch angle decreases. Moreover, we measured the 3-dimensional slider motion by using two laser Doppler vibrometers simultaneously, and found that the bouncing vibration is a coupled vibration between translation and pitch with a small phase shift. From the numerical simulation of a two-degrees-of-freedom slider model by considering a shearing force of the lubricant and micro-waviness in addition to the adhesion and friction forces, we could get a hysteresis of the bouncing vibration and two different instability processes as observed in the experiment.

Study of Contact Bouncing Vibration of Flying Head Slider in Near-Contact Regime

We experimentally and analytically investigated detailed characteristics of the bouncing vibrations of a flying head slider in a near-contact regime. In the experiment, we found that the hysteresis of touch-down and take-off pressure and the rate of instability become small as the pitch angle increases. Moreover, we measured the 3-dimensional slider motion by using two laser Doppler vibrometers simultaneously and found that the bouncing vibration is a coupled vibration between translation and pitch with a small phase shift. These experimental features can be explained analytically if we consider strong shear force due to lubricant and small amount of microwaviness for the previous two-degrees of freedom slider model with nonlinear air bearing stiffness.Copyright