Abstract: Apparatus for measuring the displacement of a member relative to a reference plane has a transmitter and a receiver spaced therefrom at a predetermined distance. A reference energy beam coaxially passes through a light diffraction grating having a ruled surface. The grating passes a zero order part of the beam through undeviated and diffracts a multiplicity of beams of first, second, third, and higher order, at constant angles with the zero order part, the angles varying with the frequency of the ruled surface of the grating. A coaxial sleeve movably mounts the light diffraction grating to provide a roll zero reference. The zero order part of the beam provides the zero reference for pitch and yaw and the first order beams provides zero reference for roll. The lines of the ruled surface of the grating have a frequency matching the predetermined distance.

Abstract: An apparatus for measuring the relative positions of hole patterns is disclosed wherein two or more fiber optic bundles disposed within first and second holes and connected to one or more sources of light and light sensitive, position sensing devices provide two, three, four, or five axis measurements of the relative positions of the two holes. By measuring the position of the light from the source transmitted via an optical bundle in the first hole and received by an optical bundle in the second hole, a precise measurement system that senses mismatch and the direction thereof with a very high degree of accuracy is achieved. The movement of plane surfaces may also be measured with the present apparatus by attaching either the transmitting or receiving side of the apparatus to a part which is subjected to a load, and measuring the resulting change in the position of the light beam illuminating the light sensitive, position sensing device.