No abstract

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.

As sliders fly closer and closer to the disks, asperity contact is inevitable due to the roughness on the sliders and the disks. A single asperity contact problem was solved using the molecular gas-film lubrication (MGL) model with the no-fly-zone (NFZ) condition, which was discovered with the direct simulation Monte Carlo method (DSMC). It shows that the MGL model can also provide bounded pressure and resultant force in the presence of contact. Moreover, the MGL results agree well with the DSMC results. A database for a single asperity contact force and moment was then created using the MGL model with the NFZ condition. This force and moment was superimposed to the air bearing force calculated by the MGL model calculated by the MGL model when the nominal plane of the slider and the disk are not in contact. The total additional air bearing force due to asperity contact was obtained. Its effect on the slider’s flying attitude was investigated and found to change the flying height and pitch angle up to 20 percent and 10 percent, respectively. [S0742-4787(00)02402-4]

Perturbation and modal-analysis methods were employed to systematically study a damped slider’s dynamic characteristics, including an air-bearing slider’s stiffness, damping coefficient, frequency response to translation and wavy motion, natural frequencies, damping ratios, and modal shape-node line. We found that a design with grooves distributed on a trailing pad effectively improved the slider’s damping ratio in the second pitch mode; however, parametric studies revealed that the damping ratio was dependent on the number of grooves, their depth, location, width, length, distribution, orientation, and types. A higher damping ratio could be obtained by optimizing these parameters. The femto slider we designed with distributed damped grooves on a trailing pad had a higher damping ratio in the second pitch mode, and hence, its responses in the second pitch mode were greatly reduced, which were clarified through simulation and an experiment. Some issues on air-bearing stiffness reduction and negative damping at low frequency and contamination and lube pickup on the damped grooves were also evaluated in the experiment. No degradation could be found in the damped slider.

Small perturbation and modal-analysis methods were employed to systematically study a damped slider’s dynamic characteristics. We found that a design with grooves distributed on a trailing pad effectively improved the slider’s damping at higher frequencies, and the damping ratio was dependent on the number of grooves, their depth, location, width, length, distribution, orientation, and types. A higher damping ratio could be obtained by optimizing these parameters. The femto slider with distributed damping grooves on a trailing pad had a higher damping ratio in the third mode, and hence, its responses to disk parallel and wavy motion were greatly reduced. This new design for the damped slider was an effective solution reducing the slider’s modulation.