INKREMENTALES MESSSYSTEM

摘要

An incremental measuring instrument having a series of fixed reference marks along one edge of the grid scale is disclosed in which a series of movable magnets or occluding screens are located along the opposite edge of the grid scale so that any subset of the total set of reference marks may be designated for control purposes. A scanning unit is provided to scan the scale, and this scanning unit includes a first photosensitive element responsive to the fixed reference marks, and a second photosensitive element mounted in anti-parallel with the first photosensitive element. This second photosensitve element is illuminated by light which varies in intensity according to whether or not the respective reference mark has a magnet or occluding screen associated therewith.