| 摘要 |
A position reference system for an elevator car includes a laser that emits a beam that is reflected from a mirror. Either the laser or the mirror is in a non-moving position, while the other is fixed to the elevator car and moves with it. The laser beam is modulated at two frequencies, one of which provides a coarse position of the elevator car while the other provides a fine position of the elevator car. Position calibration occurs when the elevator car is stationary. When the elevator car begins to move, the coarse position is tracked while the fine position is determined from the higher of the two modulation frequencies. The absolute position of the moving elevator car is thus always known to a degree of accuracy depending on the higher modulation frequency.
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