Use of a laser interferometric displacement-measuring system for noncontact positioning of a sphere on a rotation axis through its center and for measuring the spherical contour.

A technique is discussed in which a laser interferometric displacement-measuring system is used for nonmechanical contact positioning of a highly reflective sphere on a rotation axis through its center and for measuring the degree of sphericity or roundness of the sphere. Two possible optical arrangements were investigated. In one arrangement the parallel laser beam is focused to a virtual point at the center of the sphere, and in the other arrangement it is focused at the spherical surface. It was shown on the basis of theory and verified experimentally that focusing the beam on the surface of the sphere is the more satisfactory arrangement. The technique was used to measure the roundness of spheres, and the results compared well with conventional stylus roundness measurements on the same great circles of spheres as round as 0.31 microm and as out-of-round as 10 microm. Theory is presented supporting a technique for aligning the center of a sphere on a rotation axis for those cases in which the interferometric displacement readings can be obtained over only a small interval of rotation of the sphere about the desired axis. Experimental results agree with the theory.