| 摘要 |
Vessel-shaped internal pressure fluctuation absorbing means 19 having a variable capacity is connected to an outer wall 8. As the internal pressure fluctuation absorbing means 19 expands or contracts, fluctuation in pressure that is caused as the substantial volume of the space inside the outer wall 8 is changed by the movement of a linear axis J1 is absorbed, whereby the pressure of a gas inside the outer wall 8 is prevented from lowering, so that penetration of dust or water can be avoided. The same object is achieved by connecting the outer wall 8 with a gas inlet member 20 for feeding a compressed gas into the space inside the outer wall 8 and an exhaust mechanism 21 adapted to evacuate the gas when the internal pressure exceeds a set value. <IMAGE> |
