Abstract: An electro-optical encoder having a head assembly adapted for movement relative to an encoder scale and including a single compact efficient reflective light source providing illumination of a plurality of reticles and associated scale portions.

Abstract: A linear measuring system for precisely measuring distances along a rather long measurement axis. The apparatus includes an endless measuring cable which is held under tension between a metering drum at one end of the system and an idler drum at the other end. The measuring cable is wrapped around a groove, which has a semicircular cross sectional shape, on the circumference of the measuring drum, and is wrapped similarly around the idler drum. The cable is coupled to an object, the movement of which is to be measured, and movement of the object results in linear movement of the cable and rotational movement of the metering drum. A rotary encoder, which produces a digital output signal, is coupled to the metering drum to measure linear movement of the object. The accuracy of the measurement depends upon maintaining a constant measuring diameter of the metering drum and the measuring cable, and also upon maintaining a tight frictional bond between the measuring cable and the metering drum.