A 3-1/2 inch magnetic disk drive equipped with a novel load/unload mechanism using a multilayer piezoelectric actuator was developed. Using this drive, the load/unload velocity influence and the slider initial orientation influence, particularly pitch angle, for the contacts between a slider and a disk during the load/unload process were experimentally investigated. The dynamic loading criteria derived from the experimental results were clarified. Applying the derived load/unload condition to several hard disk drives, 20000 load/unload cyclic tests were completed without any head/disk interface failure. These results suggest that the load/unload mechanism, using a multilayer piezoelectric actuator, shows high head/disk interface reliability in very small head/disk spacing. >

Dynamic loading criteria for 3-1/2 inch inline HDD using multilayer piezoelectric load/unload mechanism

A recording/reproduction element is mounted on a magnetic head slider via a piezoelectric element so that a displacement of the piezoelectric element performs fine control of the position of the recording/reproduction, thus enabling fine spacing and high track positioning accuracy. This improves linear recording density and track density. A pair of electrodes are formed on both sides of a piezoelectric element to constitute a piezoelectric actuator. One electrode is arranged opposite the rear surface (air flow out end) of a magnetic head slider 11 . A recording/reproduction element is arranged on and electrically insulated from the other electrode. The piezoelectric element includes a piezoelectric element displaced in a spacing direction, enabling fine spacing control, a piezoelectric element displaced in the track direction, enabling a fine track position control, and a piezoelectric element displaced in a magnetic disc rotation direction, enabling reduction of jitter of a reproduction signal.

Magnetic disc apparatus and magnetic head in which a recording/reproduction element is mounted on a slider via a piezoelectric element

The mathematical models are critical for accurate simulation of the dynamic load/unload (L/UL) process in disk drives. The air bearing slider and the suspension are the most important parts in the L/UL mechanism. The air bearing modeling has been well researched, but an adequate and efficient suspension model is not available. A simplified 4-DOF suspension model is proposed in this paper. In this model the slider's pitch angle change due to the motion of the L/UL tab on the ramp is included in the simulation, and the forces applied by the ramp can be directly obtained. The effects of the suspension inertia are included in the effective inertia moments of the slider to improve the loading simulation. The model is implemented and applied to simulate the L/UL process of a pico slider that has been used in recent IBM mobile drives. The effects of the pitch static attitude (PSA), the roll static attitude (RSA), and some initial disturbances to the loading process are investigated. It is found that a positive PSA can significantly smoothen the loading process. The effects of the PSA, the disk rpm, and the unload velocity on the unloading process are also simulated, and it is found that a positive PSA can also greatly improve the unloading performance of the slider. The results show that the unloading process can be accurately simulated by using the proposed model, and the loading process can be more accurately simulated by using this 4-DOF model than the 3-DOF model.

A Simplified 4-DOF Suspension Model for Dynamic Load/Unload Simulation and Its Application

Two of the most difficult issues to resolve in current design of head/disk interface in magnetic recording devices are stiction and durability problems. One method of overcoming these problems is by implementing a technology known as load/unload, where the system is designed so that the slider never touches the disk surface. One potential problem with this type of system is slider/disk contact induced disk defects. The objective of this paper is to show that the likelihood of disk scratches caused by head/disk contacts during the load/unload process can be significantly decreased by rounding the edges of the air-bearing surface. Using the resistance method, we observe that head/disk contacts burnish the corners of the slider and thereby decrease exponentially with load/unload cycles. A well burnished slider rarely causes any disk damage thus resulting in an interface with significantly higher reliability. A simple Hertzian contact stress analysis indicates that the contact stress at the head/disk interface can be greatly decreased by increasing the radius of curvature of the air-bearing surface edges.

Effect of Slider Burnish on Disk Damage During Dynamic Load/Unload

Erasure of magnetic information due to transient slider-disk contacts is investigated. A three-dimensional thermal-mechanical model of a transient contact between a slider and a multilayered thin film disk is developed. Temperature and plastic strain distributions in the contact zone are evaluated and erasure of information is determined based on a simplified erasure criterion. The effect of material properties and impact conditions on erasure is determined for disks with glass and aluminum substrate. Design recommendations for minimization of erasure are discussed.

Simulation of Magnetic Erasure Due to Transient Slider-Disk Contacts

The natural frequencies of the various transducers and sliders were studied by finite element modeling and experimentation. Finite element analysis shows that the lowest ringing frequency of a 3370 slider is around 310 kHz. This value has been verified by the laser Doppler vibrometer and AE (acoustic emission) measurements. It is determined that the lowest natural frequency of a mini-Winchester slider is around 130 kHz. The 140-kHz frequencies reported in the literature using the two-rail sliders with piezoelectric transducers attached to the slider and the 160-kHz frequencies reported using AE transducers attached to the suspension mount are associated with the natural frequencies of these transducers and not of the sliders. >

Natural frequencies of sliders and transducers used to detect slider-disk contacts

The issue of slider-disk contact during the loading process is investigated. The effects of initial altitude, pitch, and roll are studied by using the LDV (laser Doppler vibrometer). The relative displacement of the slider with respect to the disk and the change of pitch and roll during the loading process are obtained for the 3380-type slider and the thin-film disk. The effect of the loading location of the disk is studied. LDV and AE (acoustic emission) measurements are carried out to detect possible slider-disk contacts during the loading process. The AE signal shows some bursts which have the slider ringing-frequency components. But by comparing the AE signal with the LDV results before and after lubricating the gap between the pivot and suspension, the sources of the AE bursts are found to be the normal contact and slip between the pivot and suspension. It is therefore concluded that carrying out the load-unload process of the positive pressure slider using a mechanism which actuates the middle part of the suspension is a suitable solution to high stiction and friction problems that can develop in the contact-start-stop process. >

Slider-disk interactions during the load-unload process

The laser Doppler vibrometer (LDV) and acoustic emission (AE) have been used to investigate the slider dynamics and to detect possible slider-disk contacts during dynamic load-unload. One of the puzzling aspects of previous work has been the AE indication of contacts at an LDV measured spacing of about 8 mu m. The procedure of LDV spacing measurement for load-unload is investigated, and three sources of possible error are found and verified by experiment. First is the deviation between single shot and average measurements. Second is the disk motion that occurs during loading. Third is the elevation difference at the measured point and the closest point during loading, which depends on the unloaded pitch and roll angles. It is found that the jump in the velocity signal of single shot LDV measurement gives a good indicator of contacts. The electrical resistance method is applied to the detection of contacts during dynamic load-unload and compared with the results obtained by the LDV and AE. Its contact signal is in good agreement with the jump in the LDV velocity signal and more distinguishable than the AE signal. >

Measurements of slider-disk contacts during dynamic load-unload

In order to eliminate the contact stress and deformation at the instant of head-disk impact during dynamic loading, the Hertz's impact theory is implemented in the dynamic loading numerical simulator. On the basis of the calculated stress field, inverse magnetostriction effects in longitudinal recording thin film media are considered and demagnetization due to the head-disk impact is simulated. >

Dynamic loading impact-induced demagnetization in thin film media

The authors investigate a severe flexure vibration which was observed in a previous dynamic load-unload experiment. The flexure vibration appears in both pitch and roll measurements. The frequency of this vibration is about 400 Hz, regardless of the disk rotation speed, and its amplitude becomes relatively large when the initial slider-disk spacing is between 50-100 mu m. In order to understand the mechanism of this flexure vibration, the authors investigate the motion of a slider with an emphasis on the flexure dynamics. They use a laser Doppler vibrometer to measure the slider's motion at various distances from the rotating disk, and compare the results with a finite-element calculation. It is found that the first mode of flexure vibration is a pure roll motion, and its amplitude is usually smaller than those of the second and third modes. The second mode is a diagonal motion that is closer to roll and the third mode is a pitch motion. >

T.G. Jeong

Papers

Natural frequencies of sliders and transducers used to detect slider-disk contacts

Slider-disk interactions during the load-unload process

Measurements of slider-disk contacts during dynamic load-unload

Dynamic loading impact-induced demagnetization in thin film media

Unloaded slider vibrations excited by air flow between slider and rotating disk