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Capacitive Relative Position Error Transducer for Galvo Mirrors

IP.com Disclosure Number: IPCOM000105881D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 77K

Publishing Venue

IBM

Related People

Elser, K: AUTHOR [+2]

Abstract

The objective lens in rotary optical storage devices must be actively position-controlled radially in order to follow closely spaced tracks of information on the disk as it spins. The task of radial position control is usually divided between a coarse actuator and a fine actuator. The coarse actuator must be fedback the fine actuator position in order to move so that the fine actuator does not need to exceed its stroke. This requires a transducer for the instantaneous position of the fine actuator, with output fedback to the coarse actuator as an "error" signal to be minimized. This feedback is commonly called "relative position error" (RPE) feedback.

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Capacitive Relative Position Error Transducer for Galvo Mirrors

      The objective lens in rotary optical storage devices must be
actively position-controlled radially in order to follow closely
spaced tracks of information on the disk as it spins.  The task of
radial position control is usually divided between a coarse actuator
and a fine actuator.  The coarse actuator must be fedback the fine
actuator position in order to move so that the fine actuator does not
need to exceed its stroke.  This requires a transducer for the
instantaneous position of the fine actuator, with output fedback to
the coarse actuator as an "error" signal to be minimized.  This
feedback is commonly called "relative position error" (RPE) feedback.

      An angular position transducer was designed to sense the
angular displacement, from the nominal position, of servo-controlled
galvo mirrors in rotary optical storage devices.  The transducer
senses angular displacement from the simultaneous increase and
decrease in electrical capacitance across different pairs of uniquely
shaped plates in its capacitive element.  Thus, the capacitive
element of the transducer is differential in nature.  The capacitive
element consists of a total of three "wedge fan"-shaped conducting
plates.  The capacitive plates lie in planes normal to the axis of
rotation, and consist of many electrically connected wedge-shaped
projections aligned radially to the center of rotation.  Two of these
plates remain...