Patent ID: 7428062

Claim:
An apparatus for measuring the height of a work held by a chuck table provided in a machining apparatus, comprising: a white light source for emitting a white beam; a chromatic aberration lens for condensing the white beam emitted from said white light source so as to irradiate said work held by said chuck table with said condensed white beam; a beam splitter which is disposed between said white light source and said chromatic aberration lens and by which the reflected beam of said white beam irradiating said work therewith is split; a first condenser lens for condensing the reflected beam which is again reflected by said beam splitter; a mask provided with a pinhole which is disposed at a converging point position of said first condenser lens and through which the reflected beam condensed by said first condenser lens passes; a second condenser lens for condensing the reflected beam having passed through said pinhole in said mask; a diffraction grating by which the reflected beam condensed by said second condenser lens is converted into a diffracted beam; a third condenser lens for condensing the diffracted beam diffracted by said diffraction grating; wavelength detecting means for detecting the wavelength of the diffracted beam condensed by said third condenser lens; and control means for determining the height position of said work held by said chuck table, based on a wavelength signal from said wavelength detecting means; wherein said control means has a memory for storing a control map setting the relationship between wavelengths and focal distances for the white beam condensed by said chromatic aberration lens, and collates the wavelength signal from said wavelength detecting means with said control map so as to determine the focal distance from said chromatic aberration lens, thereby measuring the height position of said work held by said chuck table.