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Radial Displacement Limiter

IP.com Disclosure Number: IPCOM000108093D
Original Publication Date: 1992-Apr-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 3 page(s) / 117K

Publishing Venue

IBM

Related People

Baker, BW: AUTHOR [+3]

Abstract

This article describes a technique used to reduce the radial movement in a hard-disk file rotary actuator which tended to cause disk surface damage under shock loads. The design incorporates a high shock resistance yet low radial displacement while preserving the function of the sliding bearing.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Radial Displacement Limiter

       This article describes a technique used to reduce the
radial movement in a hard-disk file rotary actuator which tended to
cause disk surface damage under shock loads.  The design incorporates
a high shock resistance yet low radial displacement while preserving
the function of the sliding bearing.

      A hard-disk file suffers surface damage because the rotary
actuator is of cantilever design with all the mass above the fixed
actuator shaft bearing.  A stabilizer bearing at the end of the shaft
had to accommodate thermal changes and allow movement between the
shaft and a housing. For this traditional approach, a radial spring
on the sliding bearing was employed.  Thus, under shock, the mass
force moment on the actuator was balanced by the radial bearing force
on the sliding bearing.  But there are two actuators each with two
arms and six heads which access the three surfaces of the three
disks.  The primary (low stack) accesses the bottom surfaces and the
high stack (secondary) accesses the top surfaces.  The secondary
actuator has a spacer block which increases the height of the arms,
and also the effective force moment, under shock, on the radial
spring.  The actuator design did not include any provision for
limiting the radial movement on the sliding bearing as it was
believed that the radial spring was adequate to prevent the shaft
tilting under specified shock.  In practice the head plate screws of
the top arms could touch and damage the outer surface.  Clearances
were marginally adequate for the low stack, but other tolerances and
displacements under shock permitted damage within a specified range.

      To avoid impact on other parts a technique was needed that
could be added simply, to prevent radial displacement with a backstop
without adding to the radial bearing force which might interfere with
the thermal characteristics.  The actuator core was a sintered
casting with tolerances of up to 0.7 mm between the back edge of the
spring and core. Damage would occur if the displacement allowed was
greater than 0.5 mm, so the target taken as the maximum allowable
radial shaft displacement was 0.2 mm.

      Referring to Fi...