Joshua C. Harrison

Flying Height Response to Mechanical Shock During Operation of a Magnetic Hard Disk Drive

A complementary experimental and numerical study of fly height response to applied mechanical shock during disk drive operation is reported in this paper. Numerical predictions of dynamic fly height response at the slider close point, due to measured drive component response to externally applied mechanical shocks, are plotted versus time and versus input shock, and are compared with the disk glide avalanche height. HDI contact pressure, as predicted using the Greenwood-Williamson contact model, is also plotted versus amplitude and sense of the externally applied mechanical shocks. The effects of measured disk motion on fly height response to operational shock are described, and are shown to be significant. It is concluded that design changes that modify disk response can be a efficacious path for the disk drive designer to improve fly height response to operational shock.

Non-repeatable runout measurement and simulation of fluid lubricated spindles

The non-repeatable runout (NRRO) of small self-acting air bearing spindles is investigated using high precision capacitance probe transducers. Transient NRRO, spindle start-up time, and power consumption are determined at start-up for horizontal and vertical spindle orientation. The design of fluid spindles for magnetic recording disk drive applications is optimized by means of finite element-based numerical simulation. Advantages and disadvantages of fluid lubricated spindles are discussed.

Identification of slider/disk contacts using the energy of the acoustic emission signal

The take-off behavior of typical tri-pad and sub-ambient pressure tri-pad sliders is investigated using acoustic emission (AE) measurements. The relative energy of the torsional and bending mode frequencies in the AE signal is determined as a function of velocity. The change in energy in the AE signal corresponding to the torsional and bending modes of vibration of the slider is found to be associated with the change in the contact location between slider and disk from the side rails to the trailing edge.

The Physical Effects of Intra-Drive Particulate Contamination on the Head-Disk Interface in Magnetic Hard Disk Drives

The physical damage at the Head-Disk Interface (HDI), caused by common ceramic particles found in the manufacturing environments of the heads and disks in hard magnetic disk drives, is reported. The need for this study arises from industry wide reliability problems due to particulate induced damage at the HDI. The intent of this study is to characterize the head/disk damage caused by I μm diamond, 1-2 μm TiC particles, 0.2-1 μm alumina particles, the alumina and TiC grains sintered to make Al-TiC (the slider body), and sputtered alumina. These particles were introduced to the HDI in over thirty disk drives. The drives were then made to perform magnetic recording and retrieval operations for known data sequences, with the resultant reading errors tabulated. After the functional testing, the drives were opened and resulting damage was examined with a number of surface characterization tools. This study confirms that the severity of problems with the read-back signal, caused by particle damage, has an inverse relationship with the magnetic track width. In addition, the harshness of physical damage to the HDI has a positive relationship with particle hardness. Finally, particle shape and size can be contributing factors in damaging the HDI.

Combined tuned and constrained layer damping of a Type 13 magnetic recording head suspension

The effect of a typical constrained layer damping (CLD) patch on the resonant behavior of a standard Type 13 magnetic recording head suspension is determined and compared with that of a specially designed tuned-CLD patch, using both numerical and experimental techniques. In particular, attention is focused on damping the first in-plane bending mode, or sway mode, of the load beam. In addition, a specification for the real modulus of a damping gel is given which, if realized in a suitable material, would enable the application of the tuned-CLD approach to magnetic head suspensions. >

Ultrasonic Wear Acceleration of Head-Disk Interfaces Operating a Near-Contact

A key parameter in the design of 3.5 inch magnetic disk drives is the start-up motor torque needed to guarantee a spin-up. Stiction force depends strongly on the following parameters: head dwell-time, texture height in the landing zone, lubricant chemistry and thickness, temperature, volatile gasses from disk-drive components, slider size and rail geometry, and drive history. A large number of single disk spin-stand experiments are performed in order to optimize the head-disk interface, and still the experienced disk-drive engineer remains nervous about the correlation of test-stand to drive-level data. To verify the validity of component data on the drive we use the standard disk drives under development by our company as test vehicles. Depending on the design each disk drive tests between 2 and 8 head/disk interfaces at the same time. The challenge now becomes to detect the first movement of the disk. As the motor current is increased the heads at first stick, then drag at very low velocities and then finally enough torque is produced to cause the motor to spin. At the initial break-out point, the applied current is not sufficient to do more than rotate the disk by a few degrees. Yet this is the point that provides the stiction data of tribological interest. Because the rotor of our disk drive motor includes a segmented annular magnet, and because the drive base-casting is made of a non-magnetic material, some of the rotor field leaks extemal to the disk drive and can be detected by Hall-sensors mounted on the outside of the base-casting. Very small rotor motions (1 ”) relative to the fixed Hall-sensors can thus be readily detected in the sealed drive. Two sensors are in a differential arrangement to improve the signal to noise ratio. Furthermore, the arrangement allows one to determine the start-up position of the motor relative to :he stator poles. A number of experimental results are presented for identical drives built with different heads and media combinations. We can clearly see evidence of fly-stiction and humidity sensitivity, as well as a sensitivity of stiction performance to lasertexture bump height. We discuss correlation issues between drive-level and component level tests and the possible confounding effects of spindle stiction.