Patent ID: 7499185

Claim:
A measuring device for measuring the height of a workpiece held on a chuck table included in a processing machine, said measuring device comprising: a white light source for emitting white light; acousto-optic deflecting means for separating said white light emitted from said white light source to produce a flux of diffracted light and for swinging the flux of said diffracted light over a predetermined angular range by applying a voltage; a first pinhole mask configured to pass light having a part of the wavelengths of said diffracted light produced by said acousto-optic deflecting means; a chromatic aberration lens configured to focus the light passed through said first pinhole mask and to apply the focused light to said workpiece held on said chuck table; a beam splitter interposed between said first pinhole mask and said chromatic aberration lens configured to deflect the light reflected from said workpiece; a second pinhole mask configured to pass the reflected light deflected by said beam splitter; a photodetector configured to detect the reflected light passed through said second pinhole mask and to output a photodetection signal corresponding to the intensity of the reflected light detected; and control means for outputting a control signal to said acousto-optic deflecting means and for obtaining the height of said workpiece held on said chuck table according to said photodetection signal input from said photodetector, wherein said control means includes a memory configured to store a first control map setting the relation between the voltage applied to said acousto-optic deflecting means and the wavelength of light passing through said first pinhole mask and a second control map setting the relation between the wavelength of light focused by said chromatic aberration lens and the focal length of said chromatic aberration lens, a value for the voltage applied to said acousto-optic deflecting means corresponding to a peak value for the light intensity detected by said photodetector is obtained by said control means, said above-obtained voltage value is applied to said first control map to thereby obtain the wavelength of light passing through said first pinhole mask, and said above-obtained wavelength of light passing through said first pinhole mask is applied to said second control map to thereby measure the height of said workpiece held on said chuck table.