Keiji Aruga

Acceleration feedforward control against rotational disturbance in hard disk drives

We have developed a hard disk drive (HDD) free of rotational disturbance using dual piezoelectric accelerometers. The dual accelerometers detect angular acceleration in the HDD and compensate for its negative effects. For optimum compensation we introduced the use of an optimal phase compensation filter (PCF). Using this controller, HDD performance does not decrease even under the severest conditions: for example, in a disk array system that has the severest mechanical interaction between HDDs.

A Study on Positioning Error Caused by Flow Induced Vibration Using Helium-Filled Hard Disk Drives

In this paper, we compare the positioning accuracy of helium- and air-filled drives. We report the PES spectra of the both drives and calculate the mechanical disturbance. The results reveal that almost all disturbances in higher rpm drives are flow induced vibrations and that disturbances in helium-filled drives are dramatically smaller. The experimental positioning error of helium-filled drives is less than half of that of air-filled drives. The static and dynamic fluid computations explaine these experimental results.

High-speed orthogonal power effect actuator for recording at over 10000 TPI

A new type of rotary actuator for HDDs is presented. To suppress the resonance gain in the quasi-rigid body mode caused by the stiffness of support bearings, we propose orthogonal driving. The designed actuator for a 3.5-inch drive shows a quasi-rigid body mode gain of less than 5 dB, and a fundamental resonance frequency of approximately 10 kHz. The results agree with those from finite element analysis.

Dynamic characteristics of a magnetic head slider

The estimation of the dynamic characteristics of magnetic head sliders is essential for the design of the recent disk file systems with reduced head-to-disk spacing. This paper presents a method for measuring the head slider flying height fluctuation caused by disturbances on the disk and head arm vibration. A numerical analysis of the head assembly including suspension spring and gas-bearing slider is presented. The experimental and analytical results are compared and it is clarified that the many resonant peaks of head sliders spacing fluctuation in the low frequency region are caused by the resonance of the suspension spring.

A study of head-disk interface shock resistance

We observed slider and suspension behavior under external shock using a still camera with a stroboscope. This paper shows experimental results of the relationship between disk failure and using Hertzs contact stress formula with energy conservation. We describe a technique to improve shock durability based on this relationship.

A high-performance and low-profile moving-magnet actuator for disk drives

We have developed a high-performance moving-magnet rotary actuator for very low-profile magnetic disk drives. A small moving magnet and efficient low-profile magnetic circuit construction give high acceleration and reduce power consumption to 50% that of moving coil actuators. The arrangement of the coils and yokes increases the design flexibility. The actuator does, however, suffer from a magnetic bias force and large inductance. >

Dynamics of inline flying-head assemblies

Heads for high-performance disk storage must be able to withstand an acceleration of dozens of G-force and be capable of positioning to submicron precision. A measuring technique that can totally analyze the flight stability and access ability of the slider was developed. It involves three-dimensional modal analysis of the suspension using a laser Doppler anemometer, a laser Doppler vibrometer, and simultaneous measurement of spacing fluctuation. Using this system to examine an inline head, it was found that notable lateral and torsional modes of the suspension vibration were caused by the access acceleration of the rectangular wave, and that there is pronounced spacing fluctuation. In addition, these lateral vibrations cause the pivot to slip, which may cause problems in high-speed head access. >

Thermal pole-tip protrusion analysis of magnetic heads for hard disk drives

Recent flying heights have been reduced to 10 nm or less. Thermal pole-tip protrusion can further reduce flying clearance by a few nanometers and increase the risk of failure at the head-disk interface. The safety margin of the flying height decreases by a few nanometers due to thermal pole-tip protrusion deformation. This deformation is caused both by mismatched thermal properties of the various materials used in the magnetic head and the write current in the coil. We need to clearly identify the mechanism of this protrusion and accurately estimate its magnitude. In this study, we will numerically and experimentally describe the differences between two boundary conditions under consideration: natural convection off the disk and flying on the disk. Our calculations using the finite element method models quantitatively showed differences in the heat path for the two boundary conditions. Furthermore, we verified that the numerical predictions of thermal pole-tip protrusion were in good agreement with measured results.

A design of high performance inline head assembly for high-speed access

A high-performance inline head assembly that stabilizes head sliders during high-speed access has been developed. It features a triangular, truss-bridge-shaped load beam and a flexure supported at both ends by the load beam. These improvements made the resonant frequency in the access direction twice that of the conventional inline head assembly, reducing spacing fluctuation at high frequencies and allowing the actuator to be positioned more precisely. The proturberance was moved to the load beam from the flexure, lowering the moment by decreasing the distance between where the force was applied to the slider and the sliders center of gravity. Experiments showed that the resonant frequency of the inline head assembly is 8 kHz in the access direction, which is about twice that of the conventional inline head assembly. Spacing fluctuation is about 50% that of the conventional inline head assembly. >

Fast take-off negative pressure slider

Using computer simulation, the flying characteristics of a conventional positive pressure head slider and two types of zero-load negative pressure head sliders are compared. One of the negative pressure head sliders is aimed at high stiffness (HS type), and the other is at CSS durability by virtue of its fast taKe-off design (FTO type). The reverse step of the FTO is deeper than that of the HS type. On the FTO type, suction increases gradually as the disk speed increases, and the slider takes off at a lower velocity than the HS type. So the suction of the FTO type is still low when the slider takes off from the disk. By experiment, we confirmed that the FTO prototype head impacts little on the medium during CSS, and also has superb flying stability.