Technique for monitoring galvo angle

Claim 1

In an optical data disk system where a radiant energy information laser beam of prescribed first wavelength is to be selectively positioned by rotatable scan-mirror means, the mirror means being arranged to provide a laser-reflecting mirror surface highly reflective of said laser information beam, this laser beam being comprised of: a "write beam" and two "read beams", all adapted to be projected on a given, selected track of a rotating optical recording disk with a first read beam adapted for "read-before-write" function and the other read beam adapted for "read-after-write" function; an improved method of providing rotation monitor means to automatically monitor the angular orientation of said mirror means, and provide an output signal reflecting this, this method comprising: operatively associating reflector means with said mirror means to be rotated conjunctively therewith; arranging related source means to comprise an LED source adapted to an IR monitor beam of prescribed second wavelength, and to project this beam to be reflected by said reflector means; providing related detector means which includes active extended surface means which is adapted and disposed to receive said monitor beam whereby the angular rotation of said mirror means is converted to a prescribed linear displacement across this surface means so as to generate position signals representing the relative position of the monitor beam on the surface means; arranging and disposing optical means intermediate said source means and said detector means so as to convert the angular rotation of said mirror means to linear displacement along said detector surface means; and cooperatively arranging related utilization means adapted to process said position signals and generate said output signal for use in positioning said information beam; the utilization means including amplifying/processing circuit means disposed to be electro-magnetically shielded by said detect means and/or said source means; while also adapting said mirror means to additionally include related monitor-reflector means disposed opposite thereto and adapted to reflect said monitor beam from said source means to said detector means so as to represent the angular rotation of said mirror surface during scanning of said laser beam as prescribed linear displacement on said detector surface means.