Thickness measuring apparatus using light from slit

Abstract

The apparatus for measuring the thickness of an object being measured has a first position measuring unit for measuring the position of a first surface of the object, a second position measuring unit for measuring the position of a second surface of said object opposite to said first surface, and a thickness obtaining portion for obtaining the thickness of the object on the basis of the position of the first surface determined by said first position measuring unit and the position of the second surface determined by the second position measuring unit. The thickness obtaining portion includes a light source for irradiating slit light on the second surface of the object by obliquely projecting light through a slit, an image pick-up portion having an image pick-up surface opposed to the progressing direction of the reflected slit light from the second surface of the object in order to pick up the reflected slit light to produce the video signal of the slit light, an analog/digital converter for converting the video signal from the image pick-up portion into a digital signal to produce digital image data of the reflected slit light, and a position obtaining section for obtaining the position of the second surface of the object on the basis of the image data of the reflected slit light from the analog/digital converter.