| 摘要 |
A system and method for measuring the angular position of a rotatably positionable object are disclosed. The system includes a rotating polarizing filter coupled to the rotatably positionable object so that the rotating polarizing filter co-rotates with the rotatably positionable object. Light generated by a light source is directed along a path through the rotating polarizing filter and through a stationary polarizing filter. In this configuration, the intensity of the light passed through the rotating and stationary polarizing filters varies according to the angular position of the rotatably positionable object. A light sensor senses the intensity of the light passed through the rotating and stationary polarizing filters. Based on the intensity of the light, as sensed by the light sensor, a processor determines the angular position of the rotatably positionable object. In one embodiment, first and second stationary polarizing filters are provided having angularly offset orientations. The intensity of the light passing through the first and second stationary polarizing filters produces first and second responses that differ in phase to permit measurement of rotatable object having a range of angular rotation greater than about 70 or 80 degrees. In another embodiment, a light source transmits light through a single rotating neutral variable density filter such that the intensity of the light passing through the variable density filter varies according to the angular position of the variable density filter.
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