Title: Measurement apparatus

Abstract: In an apparatus for measuring relative displacement between first and second members, a grating fixed relative to the first member is illuminated by means defining a spatially periodic optical object fixed relative to the second member. Light transmitted or reflected by the grating is detected by a system including means defining a spatially periodic light-receiving array fixed relative to the second member so as to interact with a shadow image formed by the grating, the output of the detection system thus varying cyclically upon relative movement between the first and second members.

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Inventors: Pettigrew, Robert Martin (Carluke, SC, US)

Application Number: 555818
Filing Date: 1975-03-06
Publication_date: 1977-09-20
Assignee: National Research Development Corporation (London, EN)
Primary Class(es): 250/237G 356/618
Other Classes:
US Patent Ref:

3175093	Mar, 1965	De Lang	250/237.
3427463	Feb, 1969	Weyrauch	250/237.
3600588	Aug, 1971	Sayce	250/211.
3700907	Oct, 1972	Myer et al.	250/237.
3768911	Oct, 1973	Erickson	356/169.
3796498	Mar, 1974	Post	356/169.
3812352	May, 1974	MacGovern	250/237.

Other Refs:
Primary Examiner: Nelms, David C.
Assistant Examiner:
Attorney: Cushman, Darby & Cushman