On-Machine Measurement of Form Accuracies Using Two Quadrant Photocells

It is necessary to separate the components of error motions of a measuring system in order to measure the surface profile of a spherical mirror on a machine. Thus, a new optical system has been developed using two quadrant photocells to measure the displacement and the inclination angle of the reflection surface at the same time. Namely, the displacement was measured by applying the principle of triangulation and the angle was detected by applying the principle of optical levers. The surface profile was obtained through the integration of the angle, and the error motion was derived by subtracting the profile from the displacement. The results showed high repeatabiliy and high reliability in comparison with the measured data using other optical methods.