Abstract: The position of a rotating element is controlled by a galvanometer and a servo system. The position of the rotating element is determined by using a two-grating moire pattern. Movement of the element causes a projected scale image representing radiation reflected from the element to shift relative to a fixed grating thereby generating moire fringes. The accumulated fringes serve to measure absolute position and motion of the element. The servo digitally processes the measured position to generate several force components which are then combined to control the amount of force applied by the galvanometer to rotate the element.

Abstract: A simply structured apparatus for mounting two lasers to produce controlled mutual parallelism or colinearity of the beams by simple operations comprises a frame with mutually perpendicular walls to which two laser-amounting plates are individually affixed. Two adjusting screws are provided for controllably aiming lasers individually by causing their supporting plates to flex in mutually perpendicular directions.