Tri-pad Slider Research Articles

Analysis of Flying Characteristics of Tri-Pad Slider Considering Asperity Contact

In this paper, we present numerical results of the static contact and flying behavior of a tri-pad head slider in a low disk speed range. In order to analyze the mixed-lubrication characteristics of the head slider, both of Greenwood & Williamson model for rough surface contact problem and the Boltzman-Reynolds equation for ultra-thin air lubrication problem were taken into consideration. From numerical calculation, we found a hysteresis of flying height versus disk speed in the transition between contact and flying, where the tri-pad slider can take three different values of minimum spacing and pitch angel numerically. The flying characteristics of the slider focusing on the hystersis of flying height are examined in relation to the surface roughness, contact stiffness, frictional coefficient, ambient pressure and crownheight.

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 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.

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.

102 ヘッドスライダのディスク表面うねりに対する追従特性と最適設計指針

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.

Analysis of Tracking Characteristics and Optimum Design of Tripad Slider to Micro-Waviness.

We numerically investigated the effect of slider design parameters on the tracking ability of a tripad slider to micro-waviness using the concentrated air bearing model and the distributed air bearing model. We found that the spacing variation due to micro-waviness is affected not only by the slider dynamics but also the distance of the head-gap position from the rear air bearing center, so that the distance between the head-gap and the rear air bearing center should be made as small as possible. The amplitude of the lower resonance of spacing variation can be reduced if the positions of front and rear air bearing centers are located at the center of percussion. The length of the front air bearing should be made short enough so as not to generate moment stiffness. The amplitude of the higher order resonance of spacing variation can be reduced if the length of the rear air bearing should be made 1.3∼1.35 times the length of the frequency component of the higher resonance.

106 ニアコンタクト領域における空気膜混成形トライパッドスライダの挙動解析(情報機器コンピュータメカニクス1 : ヘッド・ディスク・インタフェース)

106 ニアコンタクト領域における空気膜混成形トライパッドスライダの挙動解析(情報機器コンピュータメカニクス1 : ヘッド・ディスク・インタフェース)

Analysis of Bouncing Vibrations of a 2-DOF Model of Tripad Contact Slider Over a Random Wavy Disk Surface

We numerically analyzed the bouncing vibrations of a two-degree-of-freedom (2-DOF) model of a tri-pad contact slider with air bearing pads over a random wavy surface and manifested the design conditions of a contact slider. The effects of the design parameters such as air bearing stiffness, contact damping ratio, the coefficient of friction, and the characteristics of the disk surface waviness on dynamic behavior and the contact sliding ability of the slider have been investigated. As a result, we found that friction force decreases the contact sliding ability at the boundary of the intermittent and continuous contact sliding. We also found that the distance between the rear air bearing center and the contact pad has a significant effect on the contact sliding ability. If the contact pad is apart from the rear air bearing center, the contact pad tends to separate from the disk. Based on this analytical study, we have proposed two design concepts: (1) Make the distance between the rear air bearing center and the contact pad as small as possible; in this case, the larger the rear air bearing stiffness results are, the better the contact ability is; (2) If some distance between the rear air bearing center and the contact pad is inevitable, then make the rear air bearing stiffness much smaller than the contact stiffness.

Partial contact air bearing characteristics of tripad sliders for proximity recording

Proximity recording introduces some new head/disk interface characteristics as compared to the conventional noncontact recording. The different design philosophy has led to several distinct partial contact tripad air bearing designs, including the shaped rail negative pressure and straight rail positive pressure tripad sliders. The impact of these new characteristics and design differences on the head/disk reliability needs to be thoroughly understood in order to ensure a successful proximity recording. This paper investigates the partial contact air bearing characteristics of three representative tripad slider designs. The contact stiffness is used as a measure of the air bearing compliance. Simulations of the fly height, contact force, altitude sensitivity, substrate waviness induced spacing and contact force modulations, contact take-off track seeking and crash stop dynamics are performed for the three tripad slider designs. The results demonstrate that the negative pressure tripad sliders can be designed such that they can achieve both flat fly height and contact force profiles and, fast take-off while still maintaining a small contact stiffness. However, the air bearing compliance and waviness following performance have to be compromised for the correct partial contact air bearing pitch stiffness.

Partial Contact Air Bearing Characteristics of Tripad Sliders for Proximity Recording

Proximity recording introduces some new head/disk interface characteristics as compared to the conventional noncontact recording. The different design philosophy has led to several distinct partial contact tripad air bearing designs, including the shaped rail negative pressure and straight rail positive pressure tripad sliders. The impact of these new characteristics and design differences on the head/disk reliability needs to be thoroughly understood in order to ensure a successful proximity recording. This paper investigates the partial contact air bearing characteristics of three representative tripad slider designs. The contact stiffness is used as a measure of the air bearing compliance. Simulations of the fly height, contact force, altitude sensitivity, substrate waviness induced spacing and contact force modulations, contact take-off, track seeking and crash stop dynamics are performed for the three tripad slider designs. The results demonstrate that the negative pressure tripad sliders can be designed such that they can achieve both flat fly height and contact force profiles and, fast take-off, while still maintaining a small contact stiffness. However, the air bearing compliance and waviness following performance have to be compromised for the correct partial contact air bearing pitch stiffness.

Numerical Investigation of tri-pad sliders and comparison to other slider designs

The flying behavior of tri-pad sliders was investigated using a finite element based simulator, and the numerical results were compared with experimental measurements using a commercially available flying height tester. Sensitivity analysis and Monte Carlo calculations were performed to investigate the sensitivity of the tri-pad slider to design and manufacturing tolerances. A comparison of the sensitivity of the tri-pad slider design with a standard two rail slider was performed. In addition, the air bearing stiffness of the tri-pad slider was determined and compared with the air bearing stiffness of typical two rail and sub-ambient pressure sliders.

Measurement of fly height by scattered total internal reflection

Scattered total internal reflection (SCATIR) is an optical phenomenon that allows measurement of the fly height of sliders. Good agreement between the measurements made with scattered total internal reflection (SCATIR) and the nominal fly heights (100, 65, and 25 nm) of three commercial sliders was obtained. Fluctuations in the flying height of a tri-pad slider as a function of load were observed. Applying a correction for the Gaussian profile of the incident laser revealed the crown of a 70% slider.

An investigation of the "take-off" characteristic of tri-pad sliders using phase demodulated laser interferometry

The interaction between a tri-pad slider and a rigid disk during take-off is characterized using phase demodulated laser interferometry and acoustic emission (AE). A double peak was observed in the AE signal during the take-off. A biquadratic surface fit for the air bearing surface was used and it was found that the transition between the first peak and the second peak corresponds to a change in contact location from the rails to the tri-pad of the slider. The second peak is shown to correspond to a change in contact location from the leading to the trailing edge of the third pad. As the disk linear velocity increases, the tri-pad slider increases its pitch angle, but remains in contact with the disk, pivoting on the trailing edge of the tripad.

Tribology of Tri-Pad Sliders©

The tribology of tri-pad sliders is investigated for hydrogenated and nitrogenated carbon overcoated disks. Friction and stiction during contact-start-stop testing are measured for both types of disks and the acoustic emission signal is studied to investigate the modes of slider vibrations during steady-state flying. Finite element simulations of the steady-state slider vibrations are performed and the results are compared with experimental observations. The optical fluorescence spectra are studied for the aluminum oxide and aluminum oxide-titanium-carbide (Al2O3TiC) portions of the slider. In addition, wear of the rear pad of a tri-pad slider is determined for fixed-track testing using nanoindentations. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Francisco, California, October 13–17, 1996

Analysis of Friction-Induced Self-Excited Vibration of a Contact Recording Head Slider Using a Two-Degrees-of-Freedom Model.

We present a theoretical analysis of the friction-induced self-excited vibration of a contact head slider that has been studied for future high-density recording disk storage. In order to understand the fundamental destabilizing mechanism of the contact slider, a simple two-degrees-of-freedom slider model for a single contact pad slider was used for first analysis. The instability of this system was caused by the asymmetry of the stiffness matrix due to the friction force. The unstable condition of this system is discussed in terms of the suspension position, the normal and pitch natural frequencies and the key parameters that are related to the frictional coefficient and the contact and suspension stiffnesses. The destabilizing mechanism of friction force is explained using the complex mode shape. From this analysis it is found that the system always becomes stable if the contact position is located on the trailing side away from the slider's center of mass. The stability characteristics of more extended models of a contact slider, including a tripad slider, are also discussed based on the analytical results obtained from the basic model.

Effects of seeking velocity on air bearing skew angle, air flow speed and flying performance of sliders with different ABS designs

The effects of seeking velocity on slider's flying performance can be described by the change of air flow speed and air-bearing skew angle. Obtained results indicate that the relative variation of air bearing skew angle, caused by seeking velocity, is significantly higher than that of the air flow speed. Sliders with higher sensitivity to skew angle (like TPC sliders) will correspond to a higher change in flying performance during track seeking. The flying height loss and the increase in rolling rate of TPC slider during the acceleration period of OD seeking increase the likelihood of head-disk impact. Similar, but reduced effects are observed on positive pressure tri-pad. TPC slider and positive pressure tri-pad slider showed contrasting results on the effects of z-height change. Reduction in z-height reduces the flying height of TPC slider but increases that of the positive pressure tri-pad slider. Negative pressure tri-pad is observed to be insensitive to both seeking and z-height change.

Comparison of numerical and experimental flying characteristics of tri-pad sliders

The flying characteristics of a tri-pad slider are calculated numerically and compared with measurements using a commercially available, interferometry based flying height tester. The effect of crown, camber and edge blends on both rails and rear pad is investigated. The simulations indicate that the flying characteristics depend strongly on the edge blend of the rear pad. A sensitivity analysis using a Monte Carlo technique in conjunction with a finite element based air bearing solver is performed to determine the variation in flying height due to manufacturing tolerances.

An Air Bearing Slider for Small Diameter Disk Storage Devices

The authors propose a novel slider design. The tri-pad slider has three separate air bearing surfaces, one in the front of the slider and the other two in the back of the slider. This design permits the optimization of the air bearing stiffness and flying attitude without changing the minimum flying height. It can minimize the effect of skew angle on the flying height, and offers ample room for a larger size thin film head element. Samples were fabricated and flying characteristics at several velocities, as well as the dynamic flying stability, were investigated. Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in St. Louis, Missouri, October 14–16, 1991