Contact-free thickness measuring method and device

Abstract

A method and device for the contact-free measurement of the thickness of a workpiece having first and second surfaces which are opposite and plane-parallel to each other characterized by providing a single laser beam, deflecting the laser beam, splitting the deflected laser beam into two sub-beams which are directed to opposite sides of a reference plane, reflecting at least a portion of each of the sub-beams towards the reference plane so that each portion is moved on one of the first and second surfaces of the workpiece from an initial position to a position in which the surface reflects the beam along a given path to a sensing device associated with each of the portions of the sub-beams. By calculating the angle of movement based on a lapse time for the portion to move from an initial position to the position causing the detection of a reflected beam, the distance of the deflecting point on one of the surfaces of the workpiece can be determined. If the surfaces of the workpiece are substantially parallel to the reference plane, the thickness of the workpiece can be determined by utilizing the distance of one point on each of the first and second surfaces from the reference plane. If the workpiece is tilted about an axis which is parallel to the reference plane, the thickness may be determined by utilizing two points on one surface and one point on the second surface to determine the thickness. If the workpiece is tilted about all axes relative to the reference plane, the thickness may be determined by utilizing the distances of two points on each of the first and second surfaces of the workpiece.