| 摘要 |
An apparatus for directly measuring an angular displacement of an actuator arm relative to a reference position is disclosed, wherein the actuator arm is rotatable about a fixed axis. The apparatus includes a reflection-type diffraction grating, a light source, a transmission-type diffraction grating and a detector. The reflection-type diffraction grating is mounted on the actuator arm. The light source emits a generally rectangularly-shaped laser beam that is aligned to strike the reflection-type diffraction grating to produce reflected beams. The transmission-type diffraction grating, through which the reflected beams pass, causes the reflected beams to converge and form an interference pattern. The detector is positioned to detect the interference pattern and generate a signal representative of the angular displacement of the actuator arm relative to the reference position. A method of directly measuring an angular displacement of an actuator arm relative to a reference position is also disclosed, wherein the actuator arm is rotatable about a fixed axis. The method includes the steps of: (1) providing a reflection-type diffraction grating which is mounted on the actuator arm, the actuator arm being located at a reference position; (2) directing a generally rectangularly-shaped laser beam to strike the reflection-type diffraction grating to produce reflected beams; (3) positioning a transmission-type diffraction grating, through which the reflected beams pass, which causes the reflected beams to converge; (4) positioning a detector to detect an inference pattern created by the converged beams; (5) determining the phase of the interference pattern; (6) moving the actuator arm to a second position, wherein a second interference pattern is generated; and, (7) computing the phase difference between the second interference pattern and that of the interference pattern generated at the actuator arm's reference position.
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