BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a vacuum pump.

2. Background Art

In a vacuum pump such as a turbo-molecular pump, unbalance correction for a rotary body including, e.g., a rotor and a rotor shaft needs to be performed. Balance correction for the rotary body is generally performed in a state in which the rotary body is attached to a balance correction tool before incorporation into a base or an outer cylinder forming a case. However, even when balance correction for the rotary body is performed with the rotary body being attached to the balance correction tool, there is a probability that the rotary body becomes eccentric with respect to a bearing due to the process of disassembling/assembling the rotary body upon incorporation into the case and unbalance occurs.

For this reason, a turbo-molecular pump configured so that balance correction for a rotary body can be performed with the rotary body being incorporated into a case has been known. One example of such a turbo-molecular pump is one (see, e.g., Patent Literature 1 (JP-A-2008-38844)) configured such that multiple screw holes are provided at the outer periphery of a disk attached to a lower end portion of a rotor shaft, a peephole is provided at a bearing arranged at a lower portion of the disk, and balance correction screws are, through the peephole, screwed into the screw holes provided at the outer periphery of the disk of the bearing to perform balance correction.

In the turbo-molecular pump described in Patent Literature 1, a balance correction portion is provided on a lower side of a rotary body. That is, the screws are screwed into some, which are necessary for balance correction, of the multiple screw holes at an outer peripheral surface of the disk provided at a lower end of the rotor shaft to correct a balance.

SUMMARY OF THE INVENTION

For using an n-plane method known as a balance correction method which can handle a speed up to an n-th critical speed (e.g., n≥3) of the rotary body, balance correction is preferably performed in the vicinity of a component as a cause for unbalance to reduce bending vibration generated by the component as the cause for unbalance. However, Patent Literature 1 fails to disclose balance correction for n (n≥3) planes.

A vacuum pump comprises: a rotary body including a rotor blade and a rotor shaft; a case rotatably housing the rotary body; a motor configured to drive the rotor shaft of the rotary body; a bearing arranged at an end portion of the rotor shaft; and at least three balance correction portions including a first balance correction portion provided on one end side of the rotary body in an axial direction, a second balance correction portion provided on the other end side of the rotary body in the axial direction, and a third balance correction portion provided between the first balance correction portion and the second balance correction portion. Balance correction by an n-plane method, where n≥3, is available such that any of the three balance correction portions is accessible from an outside of the case.

A suction port is, at the case, formed at a position facing an upper surface of an uppermost rotor blade, and the first balance correction portion is provided at a position of the rotary body accessible through the suction port.

The first balance correction portion has multiple screw holes provided between an uppermost rotor blade and the rotor shaft.

The second balance correction portion is provided below the motor at the rotor shaft, and a second access port through which the second balance correction portion is accessible from an outside of the case is provided at the case.

The second access port is a gas purge port.

The second access port is an exhaust port.

The vacuum pump further comprises: a rotor cylindrical portion provided on the other end side of the rotary body. The second access port is provided inclined with respect to a center core of the rotor shaft, the second access port provided at a portion of the case below the rotor cylindrical portion and facing to the second balance correction portion.

The second balance correction portion has a collar provided on a lower surface of a motor rotor.

The second balance correction portion has multiple screw holes provided at the collar.

The third balance correction portion is provided in a vicinity of the center of gravity of the rotary body.

A third access port through which the third balance correction portion is accessible from an outside of the case is provided at the case.

The third access port is a vent port.

The third balance correction portion has multiple screw holes provided in a region of the rotor between bases of the lowermost rotor blade and the second rotor blade from the lowermost side.

The case includes multiple suction ports, and multiple third balance correction portions accessible through the suction ports are provided between the first balance correction portion and the second balance correction portion.

The rotary body includes, in this order from an upstream side, a first turbo pump portion having the rotor blade, a second turbo pump portion having the rotor blade, and a Holweck pump portion, at a side surface of the case, a first suction port is formed in a region corresponding to an internal space on an upstream side of the first turbo pump portion, a second suction port is formed in a region corresponding to an internal space between the first turbo pump portion and the second turbo pump portion, and a third suction port is formed in a region corresponding to an internal space between the second turbo pump portion and the Holweck pump portion, the first balance correction portion is provided at a position of a side surface of the rotor shaft accessible through the first suction port,

one third balance correction port is provided at a position of the side surface of the rotor shaft accessible through the second suction port, and the other third balance correction port is provided at a position of the side surface of the rotor shaft accessible through the third suction port.

According to the present invention, a balance correction portion of a rotary body is accessible from the outside of a case, and a speed up to an n-th (n≥3) critical speed of the rotary body can be handled in balance correction.

