Appeal No. 95-2003 Page 2
Application No. 08/074,265
CD-ROM). Scanning spots, which are focused onto the surface of
the information tracks, read and write information. Over the
course of time, a scanning spot may become out of alignment with
an associated track (tracking error) or the focal point of the
scanning spot may become out of focus, which in turn distorts the
shape of the scanning spot (focus error). Tilt of the record
carrier with respect to the scanning device will defocus the
scanning spots (tilt error).
The claimed invention has plural scanning spots, one
scanning spot for each information track on the record carrier.
A series of photodetectors associated with the plural scanning
spots receive radiation from the information tracks via the
scanning spots and convert the radiation into detection signals.
The invention associates error detection circuits with the
photodetectors, each of which derives from the detection signals
either a focus error signal or a tracking error signal. A tilt
control signal may be derived by combining at least two focus
error signals. Independent claim 23 (emphasis added) illustrates
the claimed subject matter:
23. A device for simultaneously optically scanning a
plurality of the information tracks in an information
plane of an optical record carrier, said device
comprising:
a radiation source for supplying a series of
scanning beams;
an objective system for focusing the scanning
beams to form a corresponding series of scanning spots
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