| 摘要 |
PURPOSE:To obtain an accurate and stable optical system, by equalizing a distance from the center of a beam splitter up to a reflecting surface of a fixed mirror reflecting a reference beam of light and a distance from the center of the beam splitter to a reflecting surface of a travelling mirror. CONSTITUTION:In a positioning carriage, a fixed mirror is so arranged that a distance from a beam splitter 13 up to a travelling mirror located at the center of travelling stroke through a plane mirror 20 and a distance from a beam splitter to a fixed mirror are so set as to be equally b+l+S/2. In this case when a temperature change DELTAt is observed, the greatest reading is obtained from the equation II, giving the maximum error of (S/2).alpha.DELTAt. As comparison of this value with that obtained by the conventional optical system I gives an answer of l>alpha, the error given by the present invention is clearly smaller. Thus, by comparison of the optical system related to the present invention and a state provided with a static pneumatic bearing type travelling guide, a stage available for positioning in submicron order can be manufactured. |
