Measuring apparatus for spatially modulated reflected beams

Abstract

Abstract A modulated displacement indicator and its method of use that utilizes unfocused electromagnetic waves, like laser waves, which are spatially modulated. Either an angular direction or linear displacement can be obtained depending on whether the beam is divergent or parallel. In any case, the beam is modulated two dimensionally and then transmitted to a reference phase detector. This may be accomplished by a semitransparent mirror which functions as a beam splitter. One of the segments from the splitter is fed directly into the aperture of the reference detector to determine the phase at the center of the spatially modulated transmitted wave. Another of the beam segments can be transmitted through the beam splitter to a remote reflective target aperture. Part of the reflected beam is detected by a signal detector. The outputs from the reference and signal detectors then have their phase relationships compared electronically. If the transmitted beam is of a known parallel width, the phase difference may be used to obtain the distance from the center of the beam to the target aperture. Should the beam be divergent, the phase difference can lead to a determination of the angle formed by the beam center line defined by the reference detector as one of its legs and the straight line to the target as the other leg. In one practical embodiment of my invention several spaced reflective targets are randomly fixed to the surface of a rigid structure, like the interior walls of a mine. A transmitted parallel laser beam modulated and detected as indicated, is sequentially directed by a motor operated deflector to impinge on each of the targets in a predetermined order. Reflected beams from each target are then detected by the signal detector and the phase relationship between the transmitted and reflected beams ascertained to give the distances from the laser beam center line to the target. By comparing reference readings for each target individually and as a group to subsequent readings, variations in the distance between the targets can be noted. The constant monitoring of such minute variations of the targets tells the observer of variations in the attached rigid structure. Should these variations exceed a predetermined safety level, like excess deformation of a inner mine wall, a signal or other indicating device can be triggered.

Inventors

• 👤 J Russell

Bibliographic Details