逐次3点法の連続形状計測への拡張

Abstract

A new continuous profile measurement using a serial multi-point method is proposed. In a conventional serial multi-point method, a few distance-sensors which have the same lateral sensitive areas are positioned on a sensor head. In this new profiling method one distance-sensor having extremely narrow sensitive area is positioned at the center of the sensor head, before and behind of which two distance-sensors having wide sensitive areas are positioned. An output from the narrow sensor represents the distance from the sensor head to the point being measured. While an averaged value of the outputs from the two wide sensors represents the distance from the sensor head to the surrounding area about the point. Thereby, the difference obtained by subtracting the latter from the former provides the height value of the point from the level of the surrounding area. The difference varies with a local profile being measured. When the sensor head is scanned on a surface with a constant velocity, change of the difference signal has high sensitivity about short-wavelength components in the surface profile and has low sensitivity about long-wavelength components. This characteristic sensitivity against spatial frequencies can be theoretically calculated from the sensor head configuration. Then, all the wavelength components in the change of the difference signal are corrected with the characteristic sensitivity to have unity sensitivity using a computer filtering. In the experiment, the usefulness of the method has been confirmed through the computer simulations as well as through the measurement of a step hight standard using an optical interference microscope.