| 摘要 |
<p>At the time of detecting the position of a shutter plate (21), a laser beam (L), for instance, is radiated from a detector (optical sensor) (24). The radiated laser beam (L) reaches the shutter plate (21) through the window (25) of a chamber (1). Then, the laser beam is reflected by the surface of the shutter plate (21) and re-enters the detector (24). The detector (24) detects the time required from the output of the laser beam (L) to the entry of the reflected beam.</p> |
