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Apparatus-for-determining-the-position-of-a-surface

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Apparatus for determining the position of a surface

Details

Inventors: Nodwell, Roy A.; Richards, Steven L. F.;
Assignee: Canadian Patents and Development Limited (Ottawa, CA)
Primary Examiner: Corbin; John K.
Assistant Examiner: Rosenberger; Richard A.
Attorney, Agent or Firm: Rymek; Edward

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.

DETAILED DESCRIPTION We claim: 1.
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.
2.
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.
3.
Apparatus as claimed in claim 2 wherein the aperture in said field stop is rectangular.
4.
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.

Description:
This invention is directed to an apparatus for the non-contact measurement of the thickness of an object and in particular to an electro-optical apparatus for determining the relative position of an opaque surface.
In many instances, it is necessary to continuously measure the thickness of a product which is moving along its longitudinal axis without imposing any mechanical constraint on that product.
This is desired in the production of forestry products such as particle board and paper, or in the production of sheet metals or plastics.
U.
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