SURFACE SHAPE MEASURING INSTRUMENT

摘要

PURPOSE:To expand the usage of a roughness meter by varying the optical distance between an objective and a surface to be measured by sine wave vibrations of constant frequency with a constant amplitude and successively sampling the time interval between the point of time when the vibrations have a constant phase and the point of time when a real image matches with the surface to be measured. CONSTITUTION:The objective 3 is vibrated in optical-axis direction by a moving coil 5 or the whole of a pickup housing 7 is vibrated in the optical-axis direction to vary the distance between the lens 3 and surface 4 to be measured by the sine vibrations or oscillate the refractive index of part of a medium on the optical path between the both 3 and 4. Consequently, the optical distance between the objective 3 and surface 4 to be measured is varied by the sine vibrations with an amplitude A and a period T. Then the zero value 9 of a focus error signal at time (t) from reference time 8 is detected and a time large state is measured from an equation I to obtain information (h) on displacement.