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Coarse-Scale Secondary Actuator Positioning System For Hard Disk Drive

IP.com Disclosure Number: IPCOM000015077D
Original Publication Date: 2002-May-17
Included in the Prior Art Database: 2003-Jun-20
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Abstract

The coarse-scale actuator positioning system disclosed here is a subsystem that is completely independent of the standard actuator positioner. It can provide secondary backup verification of the reports from the primary systems or serve on equal terms as a direct safety latch. A magnetic Hall sensor is attached to the actuator structure in such a position that the magnetic flux from the actuator fixed magnets varies monotonically as the comb is rotated. The Hall sensor then provides a readout of voltage that is uniquely mapped to the position of the recording heads. This Hall sensor output voltage is then sampled by an analog-to-digital convertor channel that is part of the hard disk controller chip. The information provided by this Hall sensor system may be used in various ways, including incorporation into the overall servo software control scheme, as well as through a direct hardware emergency control line input into the voice coil motordriver circuit. The incremental cost of this position sensing system is just for the Hall sensor itself, in addition to the costs of mounting onto the actuator comb and wiring to the flex cable. All of the other components required for this system to function exist on today’s hard disk drives. The use of this system has several advantages, including the following:

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Coarse-Scale Secondary Actuator Positioning System For Hard Disk Drive

The coarse-scale actuator positioning system disclosed here is a subsystem that is completely independent of the standard actuator positioner. It can provide secondary backup verification of the reports from the primary systems or serve on equal terms as a direct safety latch.

A magnetic Hall sensor is attached to the actuator structure in such a position that the magnetic flux from the actuator fixed magnets varies monotonically as the comb is rotated. The Hall sensor then provides a readout of voltage that is uniquely mapped to the position of the recording heads. This Hall sensor output voltage is then sampled by an analog-to-digital convertor channel that is part of the hard disk controller chip. The information provided by this Hall sensor system may be used in various ways, including incorporation into the overall servo software control scheme, as well as through a direct hardware emergency control line input into the voice coil motordriver circuit.

The incremental cost of this position sensing system is just for the Hall sensor itself, in addition to the costs of mounting onto the actuator comb and wiring to the flex cable. All of the other components required for this system to function exist on today's hard disk drives.

The use of this system has several advantages, including the following:

Reduces crashstop impact velocity

Provides an independent readout to verify suspicious servo position data, such as may occur during high-speed

seeks Prevents prolonged actuator placement at predefined sensitive locations

Provides independent confirmation of head load and unload velocity

Provides continuous real-time position data, including, when it is unavailable from the primary servo system

during the intervals when heads are positioned between servo marks Allows for slower hardware unloads while preventing incomplete head unload events


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At today's fine recording track pitch (sub-micron), such a Hall sensor system cannot provide sufficient positioning accuracy to be able to replace the disk servo-mark system. It is only accurate enough to be able to infer position to within a few tracks, which is far too coarse to be able to use for controlling reading and writing. However, such information is valuable in the event of a failure of the servo-mark detection system because it may be used to prevent the actuator system from creating damage inside the h...