Kohei Iida

Design Consideration of Contact/Near-Contact Sliders Based on a Rough Surface Contact Model

We numerically investigated contact characteristics of a contact pad with a rough disk surface and the possibility of contact/near-contact sliders, using a single-degree-of-freedom (I-DOF) slider and a random wavy surface model with random roughness. Contact characteristics of a contact pad are numerically calculated based on a modified Greenwood-Williamson model, considering the bulk deformation of the surface due to all other asperity contact forces. It was found that contact stiffness and other characteristics are mainly determined by asperity contact, to the extent that the contact pad penetrates into the upper standard deviation of asperity peak height. However, the contact stiffness tends to approach a constant value as the pad penetrates into the average asperity height because the bulk deformation becomes predominant. From the numerical simulations of a 1-DOF air bearing slider model in contact and near-contact regimes over a random wavy surface with random roughness, a typical example of design condition of disk surface waviness in terms of the tracking ability and wear durability are shown, and the possibility and difficulty of a contact/near-contact slider is discussed. Finally, we analyzed meniscus effects on the contact characteristics and found a hysteresis process of the touch down and take off of a slider due to the meniscus force.

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.

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

We numerically investigated the tracking ability and the dynamic friction force of a 2-DOF model of a tripad slider over a random wavy disk surface in the near-contact regime. The nominal flying height was changed from a negative value (contact regime) to 3 nm (3 /spl sigma/ of micro-waviness of the disk surface). We clarified tile effects of the front and rear air bearing stiffnesses, the nominal flying height, the coefficient of friction and the roll-off characteristics of the disk surface waviness on the tracking ability and wear durability. As a result, we found that the spacing variation is caused by not only the slider dynamics but also the micro-waviness of the disk surface between the contact pad position and the rear air hearing center. The effect of the coefficient of friction on the tracking ability can be neglected when the flying height is more than 1 nm. However, the rms value of the friction force still remains to be 0.25 mN.

Statistical Analysis of Perfect Contact and Wear Durability Conditions of a Single-Degree-of-Freedom Contact Slider

In this paper, the design condition of a single-degree-of-freedom (IDOF) contact slider over a random wavy surface of a disk is analyzed statistically. It is numerically confirmed that when the slider is in contact with a disk, spacing variation histograms are close to Gaussian even if surface waviness histogram is not close to Gaussian. The design condition of the slider and the surface waviness necessary for perfect contact sliding is derived from 3σ s < δ, where σ s and δ are the standard deviation of spacing variation and the static penetrating depth, respectively, and it is verified both numerically and experimentally. The necessary condition for wear durability under uniform contact pad pressure is also derived. An example of the slider-to-disk interface design which satisfies both perfect contact sliding and wear durability is shown. In order to evaluate σ s adequately, frequency response of slider must be integrated over the range from f,/2 to 2f, where f, is the contact resonance frequency, It is found that a disk surface should be extremely smooth to satisfy both the perfect contact sliding and wear durability conditions.

Computer Analysis of Bouncing Vibration and Tracking Characteristics of a Point Contact Slider Model Over Random Disk Surfaces

This study is a computational analysis of the bouncing vibration of a point contact slider model over computer generated random disk surfaces and the design conditions of slider to disk interface parameters necessary for contact recording. The Gaussian random surface of a disk with various standard deviations and frequency characteristics is generated by using a modified midpoint displacement algorithm. From the calculated results of bouncing vibration of a slider for various parameter values, it was found that the decrease in contact stiffness and increase in slider load can significantly reduce the bouncing vibration as well as the increase in contact damping and the smoothness of the surface. It was also found that the bouncing vibration spectrum of a contact slider over a simulated disk surface agreed closely with the experimental results presented in a previous study by the authors. The maximum and rms values of the spacing and the contact force were examined for various design parameters. The design conditions of the contact pad to the disk interface were discussed in terms of tracking ability and wear durability for slider loads of 0.5 mN and 5 mN.

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.