Francis Chee-Shuen Lee

Active damping in HDD actuator

A non-traditional mechanical modification technique to take care of the major servo bandwidth limited resonance mode (butterfly mode) is developed, analyzed, and validated. With an additional sensor on the actuator and an external feedback loop, the butterfly mode can be damped and stiffened such that the gain of the head mechanical transfer function is close to 1/s/sup 2/. Servo improvement is also studied comparing to notch filter approach. It shows that the butterfly mode notch filter can be removed, and the phase margin can be improved by 7 degrees.

Head-Disk Dynamics in the Flying, Near Contact, and Contact Regimes

To achieve an areal density approaching 50 Gb/in. 2 for the magnetic storage of data in hard disk drives requires reduced mechanical and magnetic spacing. Off-track jitter caused by airflow or contact can cause track misregistration on the order of 20-70 nm which may be excessive for adequate servo performance. The magnetic signal can be used to identify both the vertical spacing modulation due to the air bearing modes and off-track jitter due to suspension modes with nanometer resolution. We find that the off-track jitter in the flying regime is driven by airflow and is a strong function of the disk velocity and the suspension type. In the contact regime, the vertical spacing modulation and off-track jitter increase due to contact. Using a laser Doppler vibrometer we identified the leading contribution to the off-track jitter to be primarily the first torsional mode (T1) and to a lesser extent the first bending mode (B1) of the suspension.

PZT printing applications, technologies, new devices

The author discusses the designs and principles of operation of several key piezoelectric printing devices. New developments in piezoelectric print head packaging and fabrication are illustrated by several examples. Particular attention is given to piezoelectric impact actuators and ink jet drop generators. On the basis of trend and current limitations of these developments, potential areas of improvement in the material characteristics for future printing applications are proposed.<<ETX>>

Challenges of the head-disk interface for near contact and contact recording

As the magnetic recording areal density approaches 10 Gb/in/sup 2/, the mechanical spacing between the head and the disk is expected to reduce rapidly below 20 nm. This lends to an increase of head-disk interaction which may induce an unacceptable level of interfacial wear. In this study experimental air bearing sliders were designed and fabricated to fly in close proximity or substantial contact with the disk. The durability of the interface decreased with decreasing mechanical clearance. The amount of head and disk wear was determined. The metrology and some of the challenges in maintaining a functional interface are presented.

Overview of Thermal Ink Jet Technology

In the recent years, thermal ink jet (bubble jet) has emerged to become a fast growing printing technology with market applications first aimed at the low end, high quality and color workstation printers. The break-through in this ink jet technology came in the areas of low cost/high volume manufacture using semiconductor thin-film processing, improved apparent reliability and the ability of high quality printing on wide range of office papers. Although the print head technology appears simple and compact, the underlining thin-film structures, micro fluid channels and drop generation process are by no mean straight-forward. In fact, the ink chemistry, the material integrity and the device physics are closely coupled to provide the proper functionality of the print engine. Hence optimization of the technology can only be achieved through complete device integration. In this paper, the basic implementations of the thermal ink jet technology is presented. The physics of bubble/drop formation process is described using results obtained from our experimental studies. Different failure modes of the electro-thermal drop generator (in particular, the thin-film resistive heater) are discussed. Results can be extrapolated to obtain a basic understanding in the requirements of the ink media and the material structure. Based on the current knowledge of this printing method, projections of the technology limitations in practical implementations can be made to support a view that thermal ink jet will become the dominant low end printing technology in the near future.

Understanding the Dynamics of Contact Recording Head-Disk Interfaces

Contact recording is fast becoming an attractive alternative to conventional flying recording heads. For contact recording, a new design philosophy has to be developed based on good understanding of contact dynamics of the head-disk interface. We have developed an integrated approach to understanding these interfaces, where experimental results from friction and laser doppler interferometer measurements are modeled using modified air bearing codes. Important insights gained: 1) smaller contact pad size reduces friction and bounce, 2) rougher disk surfaces have lower friction and contact stiffness, and 3) pitch angle and lubricant lube thickness strongly influence damping of slider motions.Copyright

The challenges beyond proximity head-disk interface

lntsoduction As the areal density for magnetic recording increases towards I O Gb/in’, the mechanical spacing between the head and the disk is expected to reduce rapidly below 20 nm. This leads to an increase of head-disk interaction which may induce unacceptable level of magnetic jitter and wear of the interface. In this study experimental air bearing sliders were designed and fabricated to fly near and below the take-off-hei&t of the disks. The durability of the interface was tested and the challenges in maintaining a functional interface will be discussed.

Real-time simultaneous measurements of ink drop velocity and diameter in thermal ink-jet printhead using laser scattering techniques

The velocity and diameter of ink drops are important parameters in ink-jet printing technology. They affect print quality and the control of the gray scale. We report here an exploratory experiment in which the velocity and diameter of drops from thermal ink-jet print heads were measured nonintrusively, simultaneously and in real-time. A laser phase Doppler particle analyzer was used in the experiment. The velocity was deduced from the Doppler signal and the diameter from the spatial phase difference of the scattered intensity. From an analysis using geometrical optics, it was determined that the optimum condition for sizing absorbing spheres such as ink drops was that the signal detected be limited to externally reflected rays. The intensity of rays refracted as a fraction of rays reflected by ink drops could vary significantly over their size range and compounded size interpretation. By considering the scattered intensity, the analysis showed that the best placement of the detectors for the present application was at 90 degree(s) scattering angle, using a perpendicularly polarized light source. In this configuration, twice refracted rays (no internal reflection) were absent. The detected signal was dominated by externally reflected rays. In order to measure ink drop diameter accurately, the complex refractive index m of several ink-jet inks was measured. A typical value was m equals 1.37 - (iota) 0.0049 at 0.6328 micrometers wavelength. Monodisperse droplets produced with a piezo-electric squeeze tube drop generator were used to calibrate the instrument. With the optimized configuration the drop velocity and diameter of two commercial thermal ink-jet heads and an experimental prototype were measured.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.