DIFFERENTIAL OPTICAL NONCONTACTING DIAMETER GAUGE UTILIZING A PAIR OF LINEARLY SCANNING LIGHT BEAMS SEQUENTIALLY SCANNING THE TEST PIECE

摘要

An electrooptical sensor is described for providing an output proportional to the difference between the cross section of an object, e.g. the diameter of a cylinder, and a known preset value. Two parallel beams of laser light separated by a known preset distance are scanned across the test object. By photoelectrically sensing when each laser beam is modulated on or off by the edges of the object, an electrical pulse whose width is equal to the difference between the object diameter and the spacing of the two laser beams is obtained. The two parallel, offset scanning laser beams are produced by reflecting two laser beams separated by a preset angle from a uniformly rotating mirror, or a multifaceted prism, placed at the focus of a lens; the beams are polarized at different orientations, preferably orthogonal to each other, so that they can be readily separated in the receiver portion of the device. The passage of the beams past the edges of the object is determined by the first and second derivatives of the output of each photodetector to accurately determine the point where the center of each laser beam coincides with an edge of the object.