Optical knife-edge detector with large dynamic range

A system for measuring the motion of an object, said system comprising:

• a system for generating a plurality of equally spaced and equally sized light beams, which move together according to the motion of said object;
• and
• a pair of photodetector elements on which said plurality of light beams is incident, disposed with an edge of each element juxtaposed and aligned in a direction such that said light beams pass from one element to the other as they move,
• wherein said pair of photodetector elements have the same length in the direction of motion of said light beams, said length being substantially equal to the diameter of any of said light beams at the point of impingement on said elements.

A method of increasing the dynamic range of an optical knife-edge detection system for detecting motion of a surface to be monitored, comprising:

• projecting a light beam onto said surface;
• positioning a pair of optical reflecting surfaces such that said light beam reflected from said surface to be monitored traverses between them, said pair of optical reflecting surfaces being aligned generally perpendicular to the direction in which said reflected light beam moves as a result of motion of said surface to be monitored;
• and
• disposing a pair of juxtaposed photodetector elements at an end of said pair of optical reflecting surfaces remote from where said reflected light beam enters between said pair of optical reflecting surfaces, the boundary between said juxtaposed pair being aligned in the space between said optical reflecting surfaces such that the illumination spot of said reflected light beam on said pair of juxtaposed photodetector elements passes from one photodetector element to the other as the surface to be monitored moves.