Olympus HDI Reliability Test System

Olympus HDI Test System is designed to perform highly accurate and effective in-situ component level evaluation of the tribological performance of magnetic and magneto-optical disks and heads. The system is ideal for QC, production and R&D testing.

1. SYSTEM FEATURES

2. SPIN AND SEEK DYNAMICS

3. THERMAL ASPERITIES MAPPING

4. WHITE PAPERS AND APPLICATION NOTES
 

I. SYSTEM FEATURES

Flexible Hardware Options:

• ability to simulate the geometry of any disk drives with form factors 5.25”, 3.5”, 3.0”, 2.5”, 1.8”, 1.0”;

• ability to use both up and down heads;

• speeds from 1 rpm to 20,000 rpm, both CW and CCW;

• simple and fast head and disk mounting and loading;

• variety of sensors: friction, gram-load, acoustic emission, magnetic signal, thermal asperities, temperature;

• original spindle chuck ensures minimal disk distortion;

• ramp loading/unloading, which can accommodate any ramps;

• unique ultimately-flexible 4-degree-of-freedom ramp position control;

• altitude simulation from sea level to 30,000 ft inside of each tester;

• intentional outgassing with temperature control.

 Control and Data Acquisition Options:

• independent simultaneous operation of testers;

• spindle control providing both linear and non-linear (user-defined) acceleration/deceleration profiles and back-cogging simulation;

• high speed seeking and sweeping option (up to 60Hz);

• head and disk positions synchronization during loading/unloading operations;

• thermal asperities detection and 3-D mapping;

• TAA measurements for any magnetic heads (MR/GMR, inductive, etc.);

• user-friendly Windows 2000 based interface.

Tribology testing of a magnetic or magneto-optical head-disc interface, as well as of heads and discs separately, has transformed from a basic disc start-stop test into a comprehensive package, which includes park and fly stiction characterization, low-speed dragging, head seeking between user-defined disk radii, head sweeping of a disk surface in either continuous or on-off mode, load-unload dynamics, etc. As a result, it is undergoing fundamental changes from a few-sample destructive R&D and Qualifications testing into large-volume non-destructive product certification for both Quality Control and Incoming Inspection purposes.

The OLYMPUS TRIBO-CERTIFICATION SYSTEM incorporates the latest test procedures for the Tribology Certification of disc and head surfaces and their interfaces. It is based on the simultaneous precision measurements of dynamic friction and breakaway stiction forces in either tangential (for traditional drives) or radial (for ramp-load designs) direction, dynamic gram-load, high-frequency contact acoustic emission (AE), ultra-small thermal asperities (TA).

The ultra-low noise test system is capable of detecting very small thermal asperities and mapping their locations on the surfaces, which is useful for both Quality Control and Failure Analysis. Utilizing either regular data-heads for TA-testing in drive or head manufacturing or special wide-gap TAheads for testing in disc manufacturing ensures the compatibility of procedures, equipment and results between drive makers and component suppliers.

The combination of AE for detecting surface asperities or debris of order of several to hundreds microns, TA for detecting sub-micron asperities and debris, together with strain gauges for detecting irregularities on relatively-large contact areas, provides for a comprehensive testing and analysis of surfaces and their interfaces in disc drives.

One of the recommended test procedures includes measurements of the dynamic TA-response to the stresses applied to the interface with various levels of:

• ALTITUDE UP TO 30,000 FEET (IN TESTERS, NO ADDITIONAL CHAMBER IS REQUIRED),

• TEMPERATURE UP TO 75C (EXTERNAL CHAMBER IS REQUIRED),

• HUMIDITY UP TO 95%RH (EXTERNAL CHAMBER IS REQUIRED),

• CONTINUOUS HEAD ID-TO-OD SWEEPING OF THE DISK (E.G., FOR 24 HOURS IN THE LAB OR FOR 1 MIN IN PRODUCTION, COMBINED WITH HIGH ALTITUDE),

• LOAD-UNLOAD CYCLES (E.G., A MILLION CYCLES IN THE LAB OR JUST TEN CYCLES ON THE PRODUCTION FLOOR).

II. SPIN AND SEEK DYNAMICS

OLYMPUS-PLUS TRIBOLOGY CERTIFICATION SYSTEMS HAVE ADVANCED, ULTRA-LOW-NOISE MOTION CONTROL:

• Control of both disk-spinning and head-seeking is performed with DSP (digital signal processing) controllers of the original design.

• The DSP-processors, made by Texas Instruments, allow for highly sophisticated algorithms and great precision in motion control.

• Linear power drive dramatically reduces electrical noise from high-current motorcircuits, which is crucial for sensitive head-disk interface measurements, especially for detection of tiny thermal asperities.

• Control of both velocity and position allows for disk mapping in both radial and angular directions, monitoring various signals. For instance, user can perform multiple starts from pre-programmed disk locations for stiction force mapping or real-time thermal asperity mapping, if the system is equipped with the TA-option.

• Absolute positioning provides 75 micron positioning accuracy when assembling a head on the tester, with no need for any additional measuring tools, as well as very high reliability and safety of running the testers at high seek speeds.

PRECISION SPIN

Olympus testers use brushless DC motors with ball-bearings for spinning the disks. Ball-bearings are necessary for durable start-stop testers, as they can usually withstand much more start-stop cycles than either fluid or air bearings. The ball-bearing spindles may have higher run-out than the fluid or air ones. This is not a problem, however. A head-disk separation is of the order of nanometers and the disk itself has several thousands nanometers of run-out, that is, there is always a three orders of magnitude difference which is taken care of by such an excellent spring as a head suspension (HGA). Thus, the run-out of the spindle, though it ads another order of magnitude, does not seem to be critical for head-disk studies, as long as it is maintained at reasonable levels and HGA’s are used for testing.

The properties of these motors together with controller power capabilities set the limits for both maximum rotational acceleration and velocity. The currently-used Seagate-made motors allow to achieve velocity of 15,000 rpm (Olympus) and 20,000 rpm (Olympus-Plus) reliably. Better motors in the near future will allow Olympus testers to develop speeds up to 30,000 rpm, by changing motors but keeping the same controller.

The accuracy of both speed and acceleration (deceleration) is very high at 0.2%.

Minimum velocity is limited by the required accuracy. Olympus controller can provide rotation at 1 rpm with 0.5% speed accuracy, at 0.1 rpm with 10% accuracy. Lower speeds of thousandths of rpm are possible per request, with very smooth motion.

Acceleration of the motor is produced by net torque applied to it and is reverse proportional to the moment of inertia of rotor and disk. Net torque is comprised of two main components, electrical torque, which is proportional to current and changes slightly with speed, and viscous damping torque, which increases with speed linearly. The maximum net torque and so maximum acceleration are achieved at the lowest speeds.

For example, the maximum acceleration is 3,000 rpm/s at 15,000 rpm, can be as high as 4,000 rpm/s at 10,000 rpm, much higher at lower speeds.

The minimum acceleration is limited by errors in numerical calculations of small numbers, and is equal to 85 rpm/s. The acceleration (spin-up) can be not only precisely-linear, but also user-programmable, of any complex profile.

PRECISION SEEK

Olympus testers use brushless DC motors with ball-bearings and low-outgassing greases for moving the head. Three types of head movements, and any combinations of them, are available, namely: sweeping between user-chosen disk radii, precision seeking to any disk radius, random sweeping and seeking with randomly changing speed and amplitude.

The maximum acceleration is a trade-off between the maximum sweep speed, equal to a ratio of motor torque by moment of inertia, and accuracy of head positioning. The higher is the acceleration, the larger are over- and under-shoots during sweeping. At a 10% maximum.

Positioning error (over/under-shoots), the maximum allowable angular acceleration is 5,000 rad/s. This  corresponds to the linear acceleration of 10,000 in/s for an arm length (pivot-to-head distance) of 2 inches.