Abstract This invention is directed to an electro-optical apparatus for determining the position of an opaque surface without contact with the surface. It includes a light beam system which projects a well defined beam having a rectangular cross-section, obliquely onto the surface such that any movement of the surface in the perpendicular direction will result in a displacement of the illuminated area on the surface, and a detector which converts this displacement into a proportional light intensity. The detector has a field stop with an aperture of specific shape onto which the illuminated area is imaged such that only a portion of the image will pass through the aperture depending on the displacement of the illuminated area. A photosensitive device is used to measure the light intensity passing through the aperture. Embodiments of apparatus for normalizing the output for greater precision are described as well as a system for measuring the thickness of an object by determining the position of two opposite surfaces of the object.
Apparatus for determining the position of an opaque surface comprising: means for providing a light beam having a predetermined cross-section and for projecting the beam obliquely onto the opaque surface such that any movement of said surface in a perpendicular direction will result in the displacement of the illuminated area on the surface; field stop means having an aperture of predetermined shape; photosensitive means for providing an output signal proportional to impinging light intensity; imaging means for imaging the total illuminated area through said aperture onto said photosensitive means; and chopper means positioned adjacent said field stop means for cyclically obstructing a portion of said aperture such that the output signal of said photosensitive means is a function of the displacement of the illuminated area on the opaque surface.
Claim 2
Dependent Claim
129 words
Apparatus for determining the position of an opaque surface comprising: means for providing a light beam having a predetermined cross-section and for projecting the beam obliquely onto the opaque surface such that any movement of said surface in a perpendicular direction will result in the displacement of the illuminated area on the surface; field stop means having an aperture of predetermined shape; photosensitive means for providing an output signal proportional to impinging light intensity; imaging means for imaging the total illuminated area through said aperture onto said photosensitive means; and chopper means positioned adjacent said field stop means for cyclically obstructing a portion of said aperture such that the output signal of said photosensitive means is a function of the displacement of the illuminated area on the opaque surface.
Claim 3
Dependent Claim
33 words
Apparatus as claimed in claim 1 wherein said light beam means comprises: light source means for providing a light beam; and cylindrical lens means for providing a rectangular cross-section to said light beam.
Claim 4
Dependent Claim
15 words
Apparatus as claimed in claim 2 wherein the aperture in said field stop is rectangular.
Claim 5
Dependent Claim
39 words
Apparatus as claimed in claim 3 wherein said chopper means includes a chopper wheel and motor means for rotating said chopper wheel; and wherein said aperture includes an opaque strip immediately adjacent the outer edge of said chopper wheel.