Optical endcoder

Claim 1

In a position encoder for monitoring the movement of a device whose position is to be encoded wherein the encoder comprises a code-display station; code-bearing members including a code bearing disc having at least portions thereof movable through the display station; exposure means for directing a predetermined display pattern of columns of light toward the code-bearing members disposed in the code-display station and sensing means including a plurality of sensing elements responsive to the columns of light directed toward the code-display station; the combination wherein the exposure means includes a stationary exposure mask providing a plurality of exposure apertures disposed in said predetermined display pattern, said mask including alignment means for accurately positioning the mask relative to the code means; a replaceable exposure block fixedly mounting a plurality of separate light emitting members in an arrangement corresponding to said predetermined display pattern for alignment with the apertures in the stationary mask; said block being comprised of a box-like compartment having a terraced base provided with an inwardly offset segment accommodating said disc, a base for the exposure block supporting said exposure mask within the display station, and cooperative mounting and aligning means on the block and the base facilitating accurate and repeated assembly of the block on the base and alignment of the columns of light with said apertures without readjustment relative to the exposure mask.