Appeal No. 1998-3389
Application No. 08/386,794
Claim 1 is illustrative of the claimed invention, and it
reads as follows:
1. A scanning device for tracking the centerline of a track on a
record carrier which has parallel, optically detectable tracks at
more than one possible track pitch, the device comprising:
an optical system for applying a main read spot of radiation
onto a track of the record carrier, and for applying a first
auxiliary spot of radiation and a second auxiliary spot of
radiation onto the record carrier at positions on either lateral
side of the track,
a radiation-sensitive main detector, a radiation-sensitive
first auxiliary detector and a radiation-sensitive second
auxiliary detector for receiving light reflected from the main
read spot, first auxiliary spot and second auxiliary spot,
respectively, the main detector, the first auxiliary detector and
the second auxiliary detector each having at least a first and a
second sub-detector which each produces a detector signal; and
a tracking control system for controlling, in response to a
tracking error signal, a position of the main read spot with
respect to the record carrier to follow a centerline of the
track, which tracking control system can be brought into a first
operating state at one track pitch and a second operating state
at another track pitch, the tracking control system including:
first tracking error signal generating means for generating,
when the tracking control system operates in the first operating
state, a push-pull signal which represents a combination of
mutual differences between the detector signals produced by the
sub-detectors of the main detector, the first auxiliary detector
and the second auxiliary detector as the tracking error signal;
and
2
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