| 摘要 |
A measurement system for measuring the position of a work piece (28) includes a stage grating (234) and an encoder head (236). A first measurement beam (38A) is directed at the stage grating (234) at a first angle, the first measurement beam (38A) being at a first wavelength. A second measurement beam (38B) is directed at the stage grating (234) at a second angle that is different than the first angle, the second measurement beam (38B) being at a second wavelength that is different than the first wavelength. At least a portion of the first measurement beam (38A) and at least a portion of the second measurement beam (38B) are interfered with one another to create a measurement signal along a signal axis. |
