| 摘要 |
There is disclosed an optical unit which is primarily intended to provide visual references for measuring machines such as coordinate measuring machines, milling machines, EDM machines, tape and computer controlled drilling machines, etc. The optical unit has a motor driven zoom lens within a lens housing, and an optical coupling for a video camera. The zoom lens assembly of this invention is a modification of that shown in U.S. Pat. No. 4,884,878 to include a stepper drive motor and a rotational position encoder which provides the necessary lens information to determine the power of magnification of the lens at any instant position. The preferred encoder includes a disc mounted on the barrel of the zoom lens which has a plurality of slots about its periphery at equal angular increments, and a photo-optical sensor which counts light pulses and generates a pulsed electrical signal as the disc rotates beside the sensor.
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