Method for making a member of a position measuring transducer

Claim 1

In a method for making a member of a position measuring transducer having a pattern of uniformly pitched bars thereon formed by an operation in which a production pattern is optically imaged upon a photosensitive surface of said member, said surface thereafter being photo-chemically treated, said production pattern being formed by means of an intermediate pattern, said intermediate pattern, in turn, being formed by means of an initial pattern, the improvement comprising the steps of: (a) providing said initial pattern of a plurality of bars having substantially uniform pitch; (b) providing a first unexposed photo-sensitive material having a density/log exposure ranging between a lower and a higher exposure value; (c) imaging said initial pattern upon said first photo-sensitive material for a pre-determined exposure step level; (d) shifting the position of the initial pattern relative to the first photo-sensitive material by an integer multiple of said pitch distance, and imaging said initial pattern upon the first photo-sensitive material for another pre-determined exposure step level; (e) repeating the preceding imaging and shifting steps a plurality of times; (f) processing said first photo-sensitive material to produce said intermediate pattern, wherein said processing is insufficient to produce an apparent image from a latent image produced by a single pre-determined exposure step level; (g) imaging said intermediate pattern upon a second photo-sensitive material for a pre-determined exposure, said second photo-sensitive material has a substantially higher gamma photographic characteristic than said first photo-sensitive material; and (h) processing said second photo-sensitive material to produce said production pattern, wherein said production pattern has a substantially greater uniformity of pitch and greater positional accuracy than said initial pattern.