| 摘要 |
PROBLEM TO BE SOLVED: To measure coordinates more accurately by adjusting the speed of air flowing around an optical path and controlling an atmospheric pressure on the optical path according to a change in atmospheric pressure around the optical path of a light beam. SOLUTION: A variable air fan 15, a variable shutter 16, and a variable valve 17 are controlled while connecting to a main control system MCS. That is, an atmospheric pressure variable mechanism composed of these members controls a difference between an inner atmospheric pressure and an atmospheric pressure of a pressurization chamber 14. Thus, it is possible to adjust air flow (speed of air and amount of air flow) from an air outlet 13. The air outlet 13 is disposed such that air flows orthogonally to an optical path L of a light beam, and the air outlet 13 is disposed along the optical path L. That is, since a difference in atmospheric pressure is made on the air outlet 13, appropriate air distribution is achieved without providing an air fan and so on in a chamber CH. With this arrangement, air flowing around the optical path L changes in speed, and an atmospheric pressure on the optical path L is controlled accordingly and held constant.
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