Qing-Hua Zeng

Effects of certain design parameters on load/unload performance [disk drives]

Dynamic load/unload (L/UL) has been widely used in portable and removable drives, and the disk drive industry has started to apply it in desktop and server drives. There are many design parameters in L/UL systems. In this paper, we focus on the effects of the ramp profile, slider burnish, disk RPM, loading velocity, and dimple pre-load on L/UL performance. Our simulation results show that the loading process is much smoother at low RPM, slider burnish increases the steady flying attitudes and slightly smooths the L/UL process. The loading velocity effects are not significant in a wide velocity range for negative pressure sliders. Properly designed ramps can obviously improve the unloading performance, and specially designed ramp profiles can also improve the loading performance at high velocity loading. A larger dimple preload can suppress the pitch oscillation during loading.

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

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 sliders 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.

Dynamics of the unload process for negative pressure sliders

Negative pressure sliders also have many merit features, but they can develop an undesirable suction force during dynamic unload. In this paper the dynamics of negative pressure sliders during the unload process was investigated by simulation and experiment. A simplified L/UL model for the suspension system was created, and an experimental setup was built to directly measure the air bearing forces. Two slider designs have been simulated and measured at various disk rotation speeds. Good correlation between the experimental and simulation results was achieved. During unload the air bearing suction force causes dimple separation. By selecting an optimal speed for unload, we can decrease the amount of dimple separation for a given slider design.

Flyability and flying height modulation measurement of sliders with sub-10 nm flying heights

An experimental system is set up, and a procedure is proposed for measuring the flying height modulation (FHM) at the head-disk interface of a magnetic disk drive by using laser Doppler vibrometry (LDV). A precision trigger, a large number of averages, and a suitable filter are key to successfully measuring the FHM. Better results can be obtained from the velocity output of the LDV as opposed to the displacement output.

Design and operating conditions for reliable load/unload systems

Abstract Dynamic load/unload (L/UL) has been widely used in portable and removable drives, and the disk drive industry has recently begun to apply it in desktop and server drives to eliminate stiction and wear associated with contact start–stop (CSS). There are many design parameters in L/UL systems that affect reliability, such as the slider air bearing, suspension, ramp and operating parameters. In this paper, we summarize our recent work on L/UL. We discuss the effects of the air bearing design, the suspension and its limiters, L/UL speed, disk rmp, ramp profile, and dimple pre-load. The results are expected to aid in the design of reliable L/UL systems.

Slider air bearing designs for load/unload applications

Dynamic load/unload (L/UL) has been widely used in portable drives, and it shows great potential in future high performance drives for avoiding slider-disk wear and stiction. Most current sliders are designed for contact-start-stop, and are not suitable for L/UL. In this paper, a previously introduced L/UL model for numerical simulation is improved. Four basic designs of air bearing surfaces with sub-ambient pressure cavities are presented, and their L/UL processes are simulated. We find that the ABS design significantly affects the L/UL performance. Two designs show very good unload performance, and the other two do not. We introduce a new slider, which meets all design and fabrication requirements, that has been designed specifically for L/UL. Further ways to improve its load performance are also discussed.

Effects of suspension limitors on the dynamic load/unload process: numerical sumiulation

Specifically designed suspensions with limiters are currently used in disk drives with dynamic load/unload (L/UL) mechanisms. We simulate the L/UL process of air bearing sliders mounted on this kind of suspension. A simplified suspension model is presented, two pico-sliders are designed and simulated, and the effects of the suspension parameters related to the limiters are investigated. We find that the air bearing design, unload speed, and the limiter parameters (gap, offset and stiffness) significantly affect the unloading process. A smaller gap, medium stiffness and speed, and a properly designed offset are required for good unload performance. There is no effect of the limiters on the loading process.

Two calibration methods of AE measurement channels for slider-disk contact detection

Contacts between sliders and disks occur during normal operation in almost all current disk drives, and they can result in undesirable head crash, wear failure, power consumption, or disturbance of the MR read-back signal. The acoustic emission (AE) method has been extensively utilized in the industry to detect these contacts and even to measure the contact force, but a suitable calibration for the AE measurement channel is lacking. Here, we propose two methods for obtaining an in-situ calibration of the AE channel based on simultaneous Laser Doppler Vibrometer (LDV) measurements. One is the force identification method, from which one can obtain the impact force after the AE channel is calibrated. Another is the filter method, from which one can obtain the velocity responses of the slider from AE. The two methods are successfully applied to quantitatively evaluate contact force.

A force identification method for slider/disk contact force measurement

Slider/disk contacts existing during operation in almost all current disk drives significantly affect drive reliability and performance. We propose a force identification method to measure the contact force from a single impact. Laser Doppler Vibrometers (LDV) are used to measure the sliders response. A procedure, which combines experiment and FE analysis, is proposed to model the system, and it is claimed to have many advantages over other methods. The proposed method is successfully applied to measure the contact forces of two nano sliders when they make contact with a bump on a disk. A smaller contact force was noted with the negative pressure slider. Also, the contact force is smaller at higher rpm for these two sliders.

Dynamics of suspension-slider-air-bearing systems: experimental study

Experimental techniques are proposed to evaluate the dynamic properties of suspension-slider-air-bearing systems. The bump responses of the sliders and gimbal structures are measured. The modal parameters, such as frequencies, damping ratios, and mode shapes of the systems are obtained by using the proposed procedure. The techniques are applied to investigate the dynamic properties of three systems. It is found that they have quite different properties, and the suspensions (gimbal) significantly affect the dynamic properties of the air bearings. Some gimbal designs generate additional modes in the frequency band of the air-bearing resonance, or introduce additional stiffness and/or inertia constraints to the slider-air bearings. The results also show that the proposed techniques are robust for experimentally evaluating the dynamic properties of the suspension-slider-air-bearing systems.