JPS63154891A - Theread groove type vacuum pump - Google Patents

Abstract

PURPOSE:To increase the discharging speed over wide range from low vacuum to high vacuum, by tapering the inner circumferential face of stator and the outer circumferential face of rotor with same gradient and enabling control of motion in the axial direction for maintaining the gap constant by means of a sensor signal. CONSTITUTION:When a rotor 3 is rotated with high speed by means of a motor 14 and the gap 8 between a tapered inner circumferential face of a stator 2 decreases because of centrifugal force or thermal expansion, a sensor 10 detects the condition and a servo motor 11 is driven by a control signal fed from a controller 12 to move a bearing box 6b downward through a thread coupling 13 so as to move the rotor 3 through an upper bearing box 6a which is moved downward by means of a spring 7a corresponding to the downward motion of the bearing box 6b and a shaft 9 thus maintaining the gap 8 constant. Consequently, a constant gap 8 is maintained at all times thereby the rotor and the stator do not contact even if said gap is very small and a high discharging speed can be obtained over a wide range from low vacuum to high vacuum.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Industrial Application Field The present invention relates to a thread groove type vacuum pump suitable for use in forming thin films in the manufacture of ICs and semiconductors.

(2) Prior Art Conventionally, this type of thread groove type vacuum pump has thread grooves on either or both of the inner peripheral surface of the stator or the outer peripheral surface of the rotor, and the rotor can be rotated with a small gap. In a type that rotates within a stator, the inner peripheral surface of the stator and the outer peripheral surface of the rotor are generally each formed into a cylindrical surface having the same diameter over the entire length in the axial direction.

(3) Problems to be solved by the invention In thread groove vacuum pumps, the performance largely depends on the gap between the stator and rotor, and the smaller the gap, the better the pumping speed and back pressure resistance. This is known. However, in conventional thread groove type vacuum pumps, the inner circumferential surface of the stator and the outer circumferential surface of the rotor are each formed into a cylindrical surface with the same diameter over the entire length in the axial direction, so the outer diameter of the rotor and the rotation axis are different. Due to the machining accuracy of coaxiality with the stator and the expansion of the rotor diameter during rotation, it is necessary to make the gap between the stator and rotor relatively wide to prevent accidents due to contact between the two. Ta.

However, in recent years, with the development of thin film application industries such as IC and semiconductor manufacturing, there has been a desire to improve the performance of thread groove vacuum pumps, and the ability has been expanded to a wide range from low vacuum to high vacuum with particularly high pumping speed. However, there has been a demand for a vacuum pump that can compress to atmospheric pressure with just this pump.

However, in order to obtain a pump that can be compressed from high vacuum to atmospheric pressure, the rotor must be made smaller and its rotor diameter smaller. It is necessary to ensure a small gap by minimizing the effect of expansion due to the generated heat, which has the disadvantage that the exhaust speed becomes extremely small.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a thread groove type vacuum pump that has a large rotor diameter, can compress to atmospheric pressure, and can generate a high pumping speed.

(4) Means for solving the problem In order to achieve this object, the present invention forms the inner circumferential surface of the stator and the outer circumferential surface of the rotor into a tapered shape with the same slope, and the stator has the above-mentioned gap. A sensor is installed to detect the amount of change.
The invention is characterized in that the stator or rotor is configured to be movable in the axial direction so that the gap becomes constant using a control means based on a detection signal from the sensor.

(5) Changes in centrifugal force due to fluctuations in the rotational speed of the rotor during operation,
Even if the rotor expands or contracts due to the heat generated by compressing and exhausting high-temperature gas or a large amount of gas, a sensor detects the amount of change in the gap, and the rotation is controlled by a control means in accordance with the detection signal from the sensor. By controlling the movement of the child or stator in the axial direction A to maintain the gap in a constant and very small state, a large pumping speed can be obtained over a wide range from low vacuum to high vacuum.

(6)' Implementation example One embodiment of the present invention will be explained with reference to FIG.

(1) shows the housing of the thread groove vacuum pump, (2) shows the stator fixed to the inner peripheral surface of the housing (1), and (3) shows the rotor installed in the stator (2). Stator (2)
The inner circumferential surface of the rotor (3) is formed into a tapered shape that tapers upward and is provided with a thread groove (4).
) is made of a light and rigid metal, such as an aluminum alloy, to enable high-speed rotation, and its outer peripheral surface is tapered upward. Here, the inner peripheral surface of the stator (2) and the outer peripheral surface of the rotor (3) are formed to have the same slope.

(5) indicates a motor housing, and the motor housing (5) is composed of a substantially disc portion (5a), a through hole (5b) formed in the center thereof, and a cylindrical portion (5C).
) was fixed to the lower end surfaces of the housing (1) and stator (2) so that the disc part (5a) was fitted into the recess (2a) of the rotor (2). An upper bearing box (6a) is fitted into the inner circumferential surface of the upper end portion of the cylindrical portion (5C) of the motor housing (5) so as to be movable up and down.
A lower bearing box (6b) is fitted into the lower bearing box (6b) so as to be vertically movable. Here, the upper bearing box (6a) has a spring (7a).
), and the rotation of the lower bearing box (6b) is restricted by a rotation prevention key (7b). And the upper bearing box (6a)
and the shaft (9) through the bearings (8) (8) to the lower bearing box (6b).
) is rotatably supported, and the rotor (3) is attached to the shaft (9).
was fixed such that a minute gap (J) of, for example, 0.1 mm existed between its outer peripheral surface and the inner peripheral surface of the stator (2).

(10) is a sensor that is provided on the stator (2) and detects the amount of displacement of the gap, for example, an eddy current type gear knob sensor; (11) is a sensor that is installed on the motor housing (5);
The servo motor (12) is a controller that is a control means for generating a control signal to the servo motor (11) based on a detection signal from the sensor ('10), and the controller (12) is provided on the lower surface of the servo motor. has the functions described below.

Further, the servo motor (11) is connected to a screw coupling (13).
) at the center of the lower surface of the lower bearing box (6b).
C). In addition, (14) is a motor provided in the motor housing (4) and rotates the rotor (3) at high speed, (14a) is its stator, (14b) is a rotor, (15) is an intake port, and (16) indicates an exhaust port.

Next, the operation of the thread groove type vacuum pump of the above embodiment will be explained.

Driven by the motor (14), the rotor (3) is rotated at high speed by gradually increasing the rotation speed from a stationary state, and accordingly,
The rotor (3) expands due to centrifugal force and heat and the gap Cl)
The amount of change due to this reduction is measured by a sensor (lO
) to generate a detection signal. Then, the controller (12) receiving this detection signal detects the gap (δ).
A control signal is generated so that the servo motor (11) is rotated to move the lower bearing box (6b) downward via the screw coupling (13), and the The shaft (9) and the rotor (3) fixed thereto together with the upper bearing box (6a) which moves downward by the spring (7a).
, the gap (J') is increased to a constant gap (g), or conversely, the rotational speed of the rotor (3) is decreased and the gap (J) is increased. Sometimes, the servo motor (13) reversely rotates according to a control signal from the controller (12) to move the lower bearing box (6b) upward, and accordingly moves the rotor (3) upward together with the shaft (9). Due to this control action that reduces the gap (E) to a constant gap (S), the rotor (3) is damaged by centrifugal force and heat due to fluctuations in the rotational speed of the rotor (3) during operation. Even if there is expansion etc., a constant gap (J) is always maintained, and even if this gap (S) is very small, the rotor (3) and stator (2) will not come into contact with each other, and a high exhaust speed can be achieved. can be obtained over a wide range from low vacuum to high vacuum.

Here, for example, when the rotor (3) made of aluminum alloy and having an outer diameter of 200 tam is rotated at 2400 Or p m, its outer diameter increases by 0.5 mm due to centrifugal force.

Assuming that the slope of the slope between the outer circumferential surface of the rotor (3) and the inner circumferential surface of the stator (2) is 115, if one rotor (3) is moved 2.5 cm downward in the axial direction, it will be at rest. The gap will be the same.

It is clear that reducing the gap (Σ) contributes to improving the compression performance of the thread groove vacuum pump.

For example, when the gap (S) is 0.08 mm, the flow rate is 10 To
Nitrogen gas at rrJl/s is pumped from ITorr to atmospheric pressure (7
Rotor diameter 20 required to compress to 60Torr)
The required length in the axial direction of a thread groove vacuum pump with a diameter of 0 mm and a rotation speed of 2400 Or p m is 300 mm, and when the gap (r) is set to Q and 5+lIm under the same conditions, the required length in the axial direction becomes 1300 hm.

Note that, unlike the above embodiment, the rotor (2) and the rotor (
3) may be tapered downward, or the axial movability may be provided on the stator (2) side, or the screw yt (
4) may be provided on the rotor, the outer periphery of (3), or both the rotor and the stator, and furthermore, it may be provided on the thread groove pump part of a composite molecular pump consisting of a turbo molecular pump part and a thread groove molecular pump part. The invention may be applied.

FIG. 2 shows another embodiment, in which the stator (2) is formed in a tapered shape with a downward concavity and is movably formed in the housing (1), and further The stator (2) has a disc spring (17) interposed between it and the housing '(1) on its upper end surface, and an annular disc spring (17) with a dogleg-shaped cross section on its lower end surface. The bimetal (lla) is interposed between the bimetal (lla)
A heater (llb) was inserted on the inner surface of the bent portion of the lla). Here, the rotor (3) is supported by bearings (8) (8) fixed to the motor housing (5) and does not move up and down. Thus,
'When the rotor (3) expands due to rotation and reduces the gap CS), this reduction is detected by the sensor (10), and the controller (12) that receives this detection signal adjusts the power according to this detection signal. is supplied to the heater (llb) to increase the bending of the bimetal (lla), and the stator (2) is moved slightly downward by the elastic force of the disc spring (17) to close the gap (8).
returns to a predetermined value, for example 0.1 mm. On the other hand, the rotor (3
) decreases and the gap i) increases, the power supply from the controller (12) to the heater (llb) decreases, the bending of the bimetal (11a) decreases, and the stator ( 2) is moved upward against the spring of the disc spring (17), and the gap (, i') decreases by 1 and returns to a predetermined value.

(7) Effects of the Invention According to the present invention, the inner circumferential surface of the stator and the outer circumferential surface of the rotor are formed into a tapered shape with the same slope, and the amount of displacement of the stator or rotor by one gap is detected. Since the gap can be controlled to move in the axial direction using a control means based on a detection signal from a sensor that keeps the gap constant during operation, changes in centrifugal force caused by fluctuations in rotation of the rotor, and changes in high temperature gas or large amounts of gas can be avoided. Even if the rotor expands or contracts due to heat generated by compressing and exhausting gas, the gap is small and can maintain a constant state,
Therefore, by forming a pump with a large rotor diameter, it is possible to obtain a large pumping speed over a wide range from low vacuum to high vacuum.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of one embodiment of the thread groove type vacuum pump of the present invention, and FIG. 2 is a sectional view of another embodiment. (2)...Stator (3)...Rotor (4)...Thread groove (10)...Sensor (12)...Controller

Claims (1)

[Claims] In a thread groove type vacuum pump, which has a thread groove on either or both of the inner peripheral surface of the stator or the outer peripheral surface of the rotor, and the rotor rotates within the stator with a small gap,
The inner circumferential surface of the stator and the outer circumferential surface of the rotor are formed into a tapered shape with the same slope, and a sensor for detecting the amount of change in the gap is provided on the stator, and the stator or rotor is connected to the sensor. 1. A screw groove type vacuum pump, characterized in that the vacuum pump is configured to be able to be controlled to move in the axial direction so that the gap becomes constant through a control means based on a detection signal of the vacuum pump.