Patent ID: 6954273

Claim:
A laser-based measuring apparatus for measuring an axial run-out in a cylinder of rotation, comprising: a laser light source; a portion for generating at least two measuring light beams by dividing a light beam provided from the laser light source; a cylinder having an axis of rotation and cylindrical side surface portions opposing to each other on a diameter; a measuring axis positioned on the cylinder's diameter to pass through the axis of rotation of the cylinder; an opposing incident optical system for directing said two measuring light beams through separate optical paths into said cylindrical side surface portions, respectively, such that said two measuring light beams oppose to each other on said measuring axis, wherein said opposing incident optical system receives light beams reflected by said cylindrical side surface portions to recombine the reflected light beams so as to interfere with each other to generate interfered light; a photodetector for receiving the interfered light to generate a beat signal as the difference of optical frequencies by heterodyne detection; and a measuring circuit connected to the photodetector for calculating the axial run-out in the cylinder of rotation which changes an optical path length of a portion of an optical path based on the beat signal.