| 摘要 |
PURPOSE:To make the shift speed of a shift shaft constant regardless of the shift direction by automatically feeding the current with the different absolute value in response to the shift direction of the shaft to a motor driving the shaft. CONSTITUTION:A shaft is shifted in the axial direction penetrating the partition wall of a charged particle beam system by the rotation of a motor 6. The shaft is shifted through the partition wall of two spaces having the pressure difference via the bellows while keeping its pressure, the resistance against the shift of the shaft when the shaft is shifted to the space with the higher pressure is thereby larger than that when it is shifted to the space with the lower pressure. The current fed to the motor 6 from a reference power supply 11 is divided by resistors 13a, 13b and made such a value as to shift the shaft at the constant speed regardless of its shift direction. The shift direction of the shaft is selected by switches S1, S2, and the current is automatically fed to the motor 6 via an operational amplifier 14.
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