| 摘要 |
PROBLEM TO BE SOLVED: To sustain the performance for a long term while realizing high rigidity, lightweight and low price by an arrangement wherein a surface plate has a body section and a surface section made of different materials. SOLUTION: A surface plate 24 comprises a surface plate body (body section) 30 and a ceramics plate (surface section) 31 pasted onto the upper surface of the surface plate body 30. The surface plate 30 is made of a low thermal expansion casting of invar cast iron or Niresist cast iron having sufficient rigidity and provided, on the rear surface side thereof, with a rib structure subjected to bone removal for assembling a vibration isolator 23. Aluminum may be employed in the surface plate body 30. The ceramics plate 31 is formed of alumina ceramics into a plate having rectangular plan view and arranged such that a movable plate 25 moves along the surface 31a thereof. The ceramics plate 31 has a coefficient of thermal expansion substantially equal to that of the surface plate body 30. |
