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Focus Acquisition Method

IP.com Disclosure Number: IPCOM000119663D
Original Publication Date: 1991-Feb-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Kagami, N: AUTHOR [+4]

Abstract

Disclosed is a method for acquiring a focus point in an optical pick-up system. This method is widely applicable to any optical pick-up system having an astigmatic focusing means.

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This is the abbreviated version, containing approximately 87% of the total text.

Focus Acquisition Method

      Disclosed is a method for acquiring a focus point in an
optical pick-up system.  This method is widely applicable to any
optical pick-up system having an astigmatic focusing means.

      The purpose of this method is to determine the adequate time
point to close a focus servo loop.  The sequential steps of this
focus acquisition method follow.  See the figure for reference.
      Step 1:   Apply a ramp-up signal to the focus VCM.
      Step 2:   Wait till the FESPEAK signal = "1" The FESPEAK signal
is a digital signal.  When the FES signal amplitude becomes greater
than a predetermined value, the FESPEAK signal changes in the state
"0" to "1".
      Step 3:   Upon the detection that the FESPEAK = "1", start the
Timer 1 for deciding the time point of closing the focus servo loop.
As for the first trial, the time up value of the Timer 1 is a
default value.
      Step 4:   Concurrently start the Timer 2 for measuring the time
period of FESPEAK = "1".
      Step 5:   Upon the detection of the time up of the Timer 1,
close the focus servo loop.
      Step 6:   Upon the detection of the time up of the Timer 2,
store the time count value plus the predetermined value.  These
values are used as the time up value of the Timer 1 at the next
trial.
      Step 7:   After processing the Timer 1 and Timer 2 jobs, check
whether or not the focus acquisition succeeded.
      Step 8:   If the...