| 摘要 |
A displacement measuring apparatus is disclosed, one embodiment of which employs two diffractive code disks (10A, 10B), attached to a shaft (12), and a sensing head (22) which need not contact the shaft (12). The head includes a light source (14) with beam shaping optics (16), which creates two individual beamlets (24A, 24B) and pre-cranks the beamlets so that they reach the first grating (10A) at proscribed angles. Two diffracted orders (24A', 24B') from the first grating are allowed, preferably through free space propagation, to strike the second grating and to be rediffracted (24A", 24B") by the second grating (10B). A phased-array detector (22) are positioned in the region of natural interference fringe (26) between the rediffracted orders of the incident diffracted orders.
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