| 摘要 |
<p>A positioning apparatus comprises a first stage (2), a second stage (1) movable relative to the first stage, a pair of first light reflectors (6a,6b) disposed on the first stage (2), the first light reflectors positioned at an acute angle with respect to a vertical axis of the apparatus, a pair of second light reflectors (7a,7b) disposed on the second stage (1), the second light reflectors positioned orthogonal to the vertical axis, a reference structure (4) facilitating measurement of a vertical position of the second stage (1), a pair of third light reflectors (8a,8b) disposed on the reference structure (4), the third light reflectors positioned orthogonal to the vertical axis, and a pair of interferometers (9a,9b) configured to measure the vertical position of the second stage (1) using light reflected, in use, from the first, second, and third light reflectors.</p> |
