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Function Test Method of Active Damping for Hard Disk Drive

IP.com Disclosure Number: IPCOM000013411D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2003-Jun-18
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Abstract

Disclosed is a method to test the function of active damping for hard disk drives using open loop gain of servo control system. It also takes units variance into consideration by way to select measuring points. It can distinguish easily failing drives and suits mass production.

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Function Test Method of Active Damping for Hard Disk Drive

    Disclosed is a method to test the function of active damping for hard disk drives using open loop
gain of servo control system. It also takes units variance into consideration by way to select
measuring points. It can distinguish easily failing drives and suits mass production.

Typical hard disk drive's actuator/head system have several structural
resonant mode which may cause servo system performance degradation.
These modes are excited during track seeking and track following under
servo system control. Active damping is one of the useful method to
suppress actuator's main resonance by feedback of its vibration detected
by a sensor on the actuator. If active damping doesn't work as designed,
servo system performance may degrade and system may be unstable. Not
only parts level test but also function test after assembled are
indispensable. But main resonance frequency is varied due to
unit-to-unit manufacturing tolerance such as bearings of the actuator
pivot and adhesive and insulator variance. That is why function test of
active damping after assembled is difficult.

Figure 1 shows a flow chart of the test method. Before operation some
points of measuring frequency are selected taking variance into
consideration based on statistical distribution of actuator's main
resonance frequency. Gain reduction of the servo controller is needed to
make servo control system stable. Open loop gain of servo system is
measured at each measuring frequency both when active damping on and off
by micro code. Ratio of open loop gain when off to on shows the effect
of active damping at each measuring f...