| 摘要 |
The point of focus of an image is swept through a measurement zone in the image space of a lens system by sweeping a plurality of convex specular surfaces through the object space of the lens system to vary the object space. The specular surfaces are formed to approximate involute curves and the optical axis of the lens system is centered upon tangents to a generating circle of the involute curves which are approximated by the specular surfaces. The specular surfaces are mounted in a rotating member and sweep the object space by rotation of the rotating member about the center of the involute generating circle. An object of the lens system includes a light emitter and a light detector positioned adjacent to one another. As the measurement zone is swept, a minimum of the output signal from the light detector occurs when the image is momentarily in focus upon the surface of a workpiece within the measurement zone. The dimension of the object space upon focus is determined by monitoring the angular orientation of the specular surfaces and this angular orientation is utilized to determine the distance to the surface of the workpiece.
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