Separation of scanning error motions for surface profile measurement of aspheric micro lens

In a scanning measurement system for aspheric micro lenses and micro lens moulds, a contact-stylus sensor, which is mounted on an air-bearing linear slide, is employed to spirally scan the surface of the aspheric micro lens mounted on an air-bearing spindle. To remove the influence of the scanning error motions of the spindle and the slide, a ring artefact is attached around the lens and two capacitance-type displacement sensors are set on the two sides of the contact-stylus sensor to scan the surface of the ring artefact. The surface profile of the ring artefact, which serves as the reference for separation of error motions, is measured to be approximately 55 nm by the reversal method. The tilt error motion and the axial error motion of scanning stage are measured to be approximately 0.5 grad and 10 nm, respectively.