Method and apparatus for linearizing a mirror galvanometer

In combination with a galvanometer of the type having a movable mirror and means for moving said mirror to effect scanning of a received light beam in response to an electrical signal, improved apparatus for controlling said moving means comprising:

• grating means, having a plurality of spaced markings and being disposed coextensive with at least a portion of the scanning path of such light beam, for modulating the light in such a beam in accordance with said spacings between said markings and the rate of movement of said mirror to produce a light signal of frequency proportional to the rate of scan;
• light responsive means, disposed to receive said modulated light, for producing an electrical rate of scan signal having a frequency proportional to the frequency of said light signal;
• means, operatively connected to said light responsive means, for producing a second electrical signal having a magnitude proportional to the frequency of said rate of scan signal;
• and
• means, operatively connected to said moving means and responsive to said second electrical signal, for producing a third electrical signal for controlling the movement of said mirror,
• wherein said third electrical signal producing means comprises:
• means for generating a main reference signal;
• means for generating a supplemental reference signal;
• means, operably connected to said second signal producing means and said supplemental reference signal generating means, for comparing those signals and producing a correction signal;
• and
• means for combining said correction signal and said main reference signal to produce said third signal.