Readback Signal Decrease Due to Dynamic Load Head-Disk Contacts

1996 ◽  
Vol 118 (2) ◽  
pp. 370-375 ◽  
Author(s):  
Ta-Chang Fu ◽  
D. B. Bogy
Keyword(s):  
Dynamic Load ◽  
Small Area ◽  
Loading Conditions ◽  
Disk Drives ◽  
Head Disk Interface ◽  
Magnetic Disks ◽  
Disk Interface ◽  
Contact Points ◽  
Manufacturing Tolerances ◽  
Ramp Load

The effect of head-disk impacts due to repeated dynamic load is investigated experimentally. Loading conditions more severe than those typically found in ramp-load disk drives are applied to ensure that contacts occur, and disk-synchronized head loading motions are applied so that the head-disk contact points are all distributed within a small area on the disk. The resulting readback signal decrease was observed to correlate with the head-disk impact velocity and hence the slider’s vertical approaching velocity. With a larger vertical velocity, readback signal decrease appeared earlier and the amount of decrease was larger. The results indicate that dynamic load-unload should be quite reliable under typical loading conditions, and the reliability of dynamic load-unload can be achieved by controlling the vertical approaching velocity of the slider. This is comparatively easier than controlling the narrow manufacturing tolerances of the slider’s pitch and roll of the head-suspension assembly. The technological trend toward using smaller-sized head-suspension assemblies and higher-coercivity magnetic disks may further enhance the dynamic load head-disk interface durability.

Experimental Investigation of Heat Flux at the Head-Disk Interface in Hard Disk Drives

2016 ◽  
Author(s):  
Yuan Ma ◽  
David B. Bogy
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Hard Disk Drives ◽  
Hard Disk ◽  
Strong Increase ◽  
Disk Drives ◽  
Head Disk Interface ◽  
Disk Interface ◽  
Contact Points ◽  
Phonon Conduction

In hard disk drives (HDDs), Thermal Fly-Height Control (TFC) is used to control the head disk spacing for reading or writing data. In order to monitor the spacing and detect possible contacts between the head and disk, a resistive temperature sensor, called Touch-Down Sensor (TDS), is embedded in the slider near potential contact points of the slider against the disk. Understanding the mechanisms of heat transfer across the head-disk interface (HDI) is of major importance, because it is closely related to the design of HDDs, including lubricant flow and contact issues, especially for Heat Assisted Magnetic Recording (HAMR) drives. In this paper, we conducted a series of experiments both on rotating and on non-rotating disks with TDS to find the cause of head temperature change and to validate the heat transfer theory based on phonon conduction. From the experiment, it is shown that air bearing cooling is not responsible for the cooling that occurs in the last nanometer before contact. Based on phonon conduction predictions, we should expect a decrease in slope of the non-contact curve as the spacing becomes less than 1 or 2 nm because of the strong increase in the heat flux due to phono conduction in this range.

Analysis of Stresses Induced by Dynamic Load Head-Disk Contacts

1999 ◽  
Vol 122 (1) ◽  
pp. 233-237 ◽  
Author(s):  
Ta-Chang Fu ◽  
David B. Bogy
Keyword(s):  
Dynamic Load ◽  
Maximum Stress ◽  
Radius Of Curvature ◽  
Head Disk Interface ◽  
Disk Interface ◽  
Impact Stress ◽  
Dual Channel ◽  
Average Maximum ◽  
The Impact ◽  
Maximum Contact

The dynamic load head-disk contact induced impact stress was studied. A dual channel LDV was used to measure the head-disk relative motion during impact, and an analytical model incorporating the Hertz theory of impact was developed to quantitatively estimate the impact induced contact force and stress based on the LDV-measured results. 70 percent sliders were used in order to compare the results with our previous study. From the estimated maximum contact stresses and the results of our previous study, it was found that when the average maximum stress was 511 MPa, the head-disk interface did not show any damage after 100,000 cycles of repeated head-disk impacts. When the average maximum stress was 880 MPa, however, 100,000 repeated head-disk impacts caused significant wear of the disk’s overcoat even though a single impact did not cause any observable damage. From the analysis it can be seen that a lower head-disk impact velocity and/or a larger radius of curvature at the contacting corner of the slider result in a smaller head-disk impact stress on the disk. Based on the analyses, we estimated the radius of curvature needed for a 50 percent (Nano) slider and a 30 percent (Pico) slider to have at least 100,000 cycles of dynamic load head-disk interface durability. Such radius of curvature can be realized, for example, by edge-blending the sliders. [S0742-4787(00)02901-5]

On the Touchdown-Takeoff Hysteresis Observed at the Head-Disk Interface in Hard Disk Drives

2005 ◽  
Author(s):  
Rohit P. Ambekar ◽  
David B. Bogy
Keyword(s):  
Experimental Approach ◽  
Hard Disk Drives ◽  
Hard Disk ◽  
Intermolecular Forces ◽  
Disk Drives ◽  
Head Disk Interface ◽  
Contributing Factors ◽  
Factors Affecting ◽  
Disk Interface

The touchdown-takeoff velocity hysteresis observed in hard disk drives during CSS or L/UL tests is analyzed using an experimental approach. Tests similar to L/UL were conducted for different slider-disk combinations at different humidities. Factors affecting the touchdown and takeoff velocity were identified on the basis of their domain of operation. It is concluded that the intermolecular forces and meniscus forces are contributing factors to hysteresis, which is also influenced by disk topography and slider dynamics.

Boundary Effect on Particle Motion in the Head Disk Interface

2007 ◽  
Author(s):  
Nan Liu ◽  
David B. Bogy
Keyword(s):  
Drag Force ◽  
Particle Motion ◽  
Boundary Effect ◽  
Hard Disk Drives ◽  
Areal Density ◽  
Air Bearing ◽  
Disk Drives ◽  
Head Disk Interface ◽  
Bearing Surface ◽  
Disk Interface

Simulation of particle motion in the Head Disk Interface (HDI) helps to understand the contamination process on a slider, which is critical for achieving higher areal density of hard disk drives. In this study, the boundary effect—the presence of the slider and disk—on particle motion in the HDI is investigated. A correction factor to account for this effect is incorporated into the drag force formula for particles in a flow. A contamination criterion is provided to determine when a particle will contaminate a slider. The contamination profile on a specific Air Bearing Surface is obtained, which compares well with experiments.

Contact Take-Off Characteristics of Proximity Recording Air Bearing Sliders in Magnetic Hard Disk Drives

1999 ◽  
Vol 121 (4) ◽  
pp. 948-954 ◽  
Author(s):  
Yong Hu
Keyword(s):  
Hard Disk Drives ◽  
Air Bearing ◽  
Disk Drives ◽  
Head Disk Interface ◽  
Taper Angle ◽  
Wear Factor ◽  
Disk Interface ◽  
Partial Contact ◽  
Magnetic Hard Disk ◽  
Wear Law

A partial contact air bearing model and Archard’s wear law are used to investigate the air bearing and wear characteristics of proximity recording sliders during a take-off process. The air bearing pitch torque, pitch and contact force are used to characterize the contact take-off process. In addition, the wear factor derived from the Archard’s wear law is employed to measure the take-off performance. The results indicate the existence of two distinct take-off stages: a period of rapidly increasing pitch preceding a relatively steady take-off event. The proper range of taper angle and step height, which produce a rapid initial pitch increase and steady subsequent take-off as well as less wear in the head/disk interface, are determined through simulation. While the simulation results demonstrate the negligible effect of crown height on the rate of the initial pitch increase, larger crown values are shown to yield higher pitch and smaller wear in the head/disk interface during the take-off process. In summary, the partial contact air bearing simulation and the wear factor calculation of the take-off process, developed in this study, offers a fast and accurate analytical tool to optimize ABS design for the fast take-off performance.

Tribological Characteristics of Liquid Lubricant on Magnetic Disks Treated by Far-UV Radiation

1993 ◽  
Vol 115 (3) ◽  
pp. 400-405 ◽  
Author(s):  
Hong Tian ◽  
Takeo Matsudaira
Keyword(s):  
Slip Model ◽  
Head Disk Interface ◽  
Rotating Disks ◽  
Magnetic Disks ◽  
Disk Interface ◽  
Liquid Lubricant ◽  
Long Period ◽  
Irradiation Treatment ◽  
Temperature Environment

In this paper, we have shown that a perfluoropolyether lubricant after far-UV irradiation treatment proposed by Saperstein and Lin (1990) was strongly bonded to disk surfaces without depletion from disks rotating at 6000 rpm in a 50°C temperature environment. Nonbonded lubricant (mobile lubricant) on disk surfaces or on the top of the UV-fixed lubricant was easily depleted from rotating disks. Depletion data of the mobile lubricant agreed well with predictions of an inter-slip model. It has been demonstrated experimentally that the mobile lubricant on disk surfaces was simply displaced from the contact or the sliding regions. After a long period of head contact, the lubricant was built up at the head/disk interface due to migration of the mobile lubricant around the contact regions. By contrast, no such build-up was observed for disks with the UV-fixed lubricant. Consequently, long-term stiction was observed for disks with only mobile lubricant, while no stiction was observed for disks with the UV-fixed lubricant. The UV-treated disks also adsorbed less water at high relative humidities compared with the nontreated disks.

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