Distance measuring gauge

A digital read-out measuring instrument including

• A. A source of electromagnetic radiations of the speed of light,
• B. a first measuring member,
• C. a second measuring member having a measuring head and spaced therefrom and in alignment therewith two spaced bearing members, the first measuring member being slidably carried in the respective bearing members at aligned positions for axial movement towards and away from said measuring head when effecting a measuring operation,
• D. a first measurement-providing member of a material which transmits said electromagnetic radiations, aligned axially with said first measuring member and disposed remotely from said measuring head, and having first and second longitudinal surface portions disposed at a given angle relative to one another,
• E. a universal-joint coupling means connecting said first measuring member and first measurement-providing member for ensuring simultaneous axial movement of those members towards and away from said measuring head when effecting a measuring operation,
• F. a second measurement-providing member of a material which transmits said electromagnetic radiations, secured to said second measuring member remotely from said measuring head for close cooperation with said first measurement-providing member, and having third and fourth longitudinal surface portions disposed at said given angle relative to one another for cooperation closely with said first and second surface portions respectively,
• G. spacing means disposed between opposing ones of said surface portions and comprising thin coatings of a low-friction material applied to at least part of at least one of said surface portions in each pair of opposing surface portions,
• H. first spring biasing means urging said first and second measurement-providing members towards one another in a sense such as to compress said spacing means between them and thereby hold said first and third surface portions in closely-spaced, face to face relationship,
• I. first and second diffraction gratings provided on said first and third surface portions respectively so that interference fringe patterns are produced by light or other electromagnetic radiations passing successively between the two gratings,
• J. means to detect radiations from said source, said source being so arranged that radiations emitted by said source are directed successively through the respective gratings, and said detector means being arranged to detect the interference fringe pattern resulting from the transmission or radiation through the gratings and to provide a pulse output according to changes in the said fringe pattern,
• K. a pulse counter connected to the output of said detector means, and
• L. digital display means connected to the output of said counter for displaying in response thereto a measurement indicative of the position of said first measuring member relative to said second measuring member.