Single channel encoder with specific scale support structure

An encoder, comprising:

• a scale of transparent material having spaced opaque lines, of a length less than the width of said scale, disposed transversely of said scale, defining scale divisions;
• an encoder body having a light emitter, a detector, and an opaque aperture plate disposed therebetween;
• said aperture plate having an aperture disposed in the light path between light emitter and said light detector;
• said scale passing through said light path adjacent said aperture plate;
• scale supports on said encoder body in sliding contact with one face of said scale on opposite sides of said aperture along said scale, and on opposite sides of said scale divisions, which together provide four point sliding contact with said one face of said scale;
• and
• scale supports on said encoder body in sliding contact with the opposite face of said scale, in positions on opposite sides of said scale divisions and substantially in line with said aperture, providing two point sliding contact with said opposite face of said scale;
• the gap between the points of sliding contact of said scale supports on opposite sides of said scale being preferably no greater than the thickness of said scale and maintaining said scale in a predetermined spaced position with respect to the aperture of said aperture plate in said light path.