JPH1172097A - High vacuum pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a rotor of a high vacuum pump such as axial molecular pump from being damaged. SOLUTION: A cylindrical skirt part 7a is formed on the rotor 7 of a complex turbo molecular pump 1 at its lower half part. The amount of deformation produced at the circular inner surface lower edge part of the skirt part 7a is detected by detectors 19 arranged in that part opposedly to each other. When the detected amount of deformation reaches the stationary creep level of the material of the rotor 7, an alarm to indicate that there is a risk of damaging the rotor is given and the pump 1 is stopped forcibly. By this, a damage resulting from a strength lowered by the creep of the rotor 7 can be prevented securely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high vacuum pump that operates in a molecular flow region, and more particularly to a mechanism for preventing damage to a rotor in a high vacuum pump such as an axial flow molecular pump (turbo molecular pump, molecular drag pump). It is about.

[0002]

2. Description of the Related Art In an axial flow molecular pump which is a high vacuum pump, a rotor is rotatably supported in a case, and a rotor is formed on an outer peripheral surface of the rotor. Rotation speed (tens of thousands of rpm) that forms wings and makes the wings have a peripheral speed similar to the speed of movement of gas molecules
The exhaust is performed by rotating the rotor by an electric motor or the like.

In such a high-vacuum pump, there is a possibility that the strength of the rotor deteriorates due to the continuous operation, the rotor is damaged, and the pump cannot be used. For this reason, in the related art, the thickness of the case is increased so that when the rotor is damaged, the rotor fragments are sealed in the case so that damage due to the rotor damage does not reach other parts than the pump. However, since the suction port of the pump communicates with an expensive vacuum device such as a reaction chamber of a semiconductor manufacturing apparatus, there is a possibility that damage due to rotor damage may reach the vacuum device. Therefore, it is necessary to prevent the rotor from being damaged.

[0004] In order to prevent the rotor from being damaged, a method has conventionally been adopted in which an upper limit of the rotor usage time is set in advance, and the rotor is replaced when the usage time exceeds the upper limit.

[0005]

However, depending on the condition of use of the rotor and the deterioration condition of the rotor material, the rotor is suddenly damaged before the actual use time of the rotor reaches the preset use time of the rotor. Becomes impossible,
Even the expensive vacuum device connected to the pump may be damaged.

[0006] Rotor breakage occurs when the strength of the rotor material falls below the stress generated on the rotor due to high speed rotation. Causes of the strength reduction of the rotor material include rotor creep, fatigue, and corrosion. Of these, regarding the rotor damage caused by the reduction in strength due to corrosion, if the rotor is subjected to a surface treatment corresponding to the gas sucked by the pump, the rotor can be prevented from being corroded, and thus the rotor damage caused by the reduction in strength can be avoided. it can. Regarding the fatigue failure of the rotor, this kind of high vacuum pump
Since the frequency of stopping is low and the operation is frequently performed at a steady rotation speed for a long period of time, the possibility that the rotor material is fatigue-destructed by repeated stress is small. Therefore, it is considered that the main factor of the rotor damage is strength deterioration due to the creep characteristics of the rotor material.

However, it is difficult to predict in advance the strength deterioration of the rotor material due to creep, and it is therefore difficult to prevent the rotor from being damaged before it occurs.

On the other hand, in recent years, in the film forming / etching process of the semiconductor manufacturing process, depending on the type of gas sucked by the high vacuum pump, the gas sucked in the high vacuum pump is condensed, By-products generated by the reaction may accumulate in the high vacuum pump to lower the pump performance. In some cases, the pump may be damaged. In order to avoid this adverse effect, measures may be taken to prevent the condensation of gas and the accumulation of by-products by forcibly increasing the temperature inside the pump based on the saturated vapor pressure characteristics of the gas to be sucked. .

When the internal temperature of the pump is increased, the rotor temperature naturally increases with the increase in the internal temperature of the pump. Since an increase in the rotor temperature promotes the creep phenomenon of the rotor material, the strength deterioration speed of the rotor becomes faster as compared with a normal rotor use condition (when the rotor is not heated). As a result, there is a high possibility that the rotor will be suddenly damaged at a point substantially before the upper limit value of the predetermined rotor use time.

A commonly used rotor material is a high-strength aluminum alloy. This aluminum alloy has a remarkable creep phenomenon at a relatively low temperature of about 100 degrees Celsius as compared with other metal materials. It is known that strength deterioration occurs. Also from this point, when the rotor temperature rises as described above, there is a high possibility that the rotor will be damaged.

[0011] The object of the present invention is to solve the above problems.
An object of the present invention is to propose a high vacuum pump provided with a mechanism capable of reliably preventing damage to a rotor.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a rotating blade formed at a predetermined interval in the direction of the rotor rotation axis on an outer peripheral surface of a rotor, and a pair with the rotating blade. A high-vacuum pump having a fixed vane formed in a formed state, an intake formed on one side of the rotor rotation axis with respect to the rotor, and an exhaust formed on the other side with respect to the rotor; It is characterized by having detecting means for detecting the amount of deformation that occurs.

In the high vacuum pump of the present invention having the above-described structure, the amount of deformation generated in the rotor is always detected by the detecting means. The amount of deformation includes the amount of elastic strain generated instantaneously and the amount of strain due to creep. In the process of deterioration of the strength of the rotor material, the amount of strain increases from the steady creep region where the strain due to creep increases in a nearly proportional relationship with time through the accelerated creep region where the strain increases rapidly, leading to rotor damage. . Therefore, based on the amount of deformation detected by the detecting means, it can be detected whether or not the rotor is in a creep state within the steady creep region, and when it is detected that the creep state has been reached, the rotor must be replaced. By doing so, rotor breakdown can be prevented.

Here, in order to detect the amount of deformation of the rotor, a cylindrical portion centered on the axis of rotation of the rotor is formed on the rotor, and the amount of deformation generated at the edge of the cylindrical portion is determined. What is necessary is just to detect by the said detection means. A large centrifugal force is generated in such an edge portion along with the rotation of the rotor, so that the amount of deformation can be easily detected.

Further, a non-contact displacement sensor can be used as the detecting means for detecting the amount of deformation generated in the rotor. For example, an eddy current displacement sensor can be used. Alternatively, capacitance type, high frequency type,
An optical non-contact displacement sensor using a laser, an infrared ray, or the like can also be used.

Next, the high vacuum pump of the present invention, in addition to the above configuration, further comprises a comparing means for comparing the amount of deformation detected by the detecting means with a preset reference amount; And control means for controlling the rotational drive of the rotor based on the comparison result.

In this case, if it is determined based on the output of the comparing means that the deformation amount has become equal to or more than the reference amount, the rotor is forcibly stopped by the control means. Can be prevented beforehand.

When it is determined based on the output of the comparing means that the deformation amount is equal to or more than the reference amount, the alarm generating means including an indicator, an alarm device, etc.
It is desirable to generate an alarm to that effect.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, referring to the drawings, a composite turbo molecular pump to which the present invention is applied will be described.

FIG. 1 shows a cross-sectional structure of the composite turbo-molecular pump of this embodiment. The turbo-molecular pump 1 has a cylindrical pump case 2, and an upper end side opening of the pump case 2 serves as an intake port 2 a. On the inner peripheral surface 2b of the pump case following the intake port 2a, annular fixed blades 3 are fixed at predetermined intervals in the direction of the pump axis (rotor rotation axis) 1a. The fixed wings 3 are maintained at an interval from each other by an annular spacer 4.

On the other hand, a rotary shaft 5 is coaxially arranged inside the pump case 2, and a rotor 7 is concentrically fixed to an outer periphery of an upper end portion 5 a of the rotary shaft 5 by a fastening bolt 6. Have been. On the outer peripheral surface of the rotor 7, annular rotating blades 8 are formed at predetermined intervals in the direction of the pump axis (rotor rotating axis) 1 a, and each of these rotating blades 8 is paired with the above-mentioned fixed blade 3. The fixed wings 3 are arranged so as to be mutually inserted between the fixed wings 3.

The lower end portion 5b of the rotary shaft 5 is provided on the inner periphery of a cylindrical spindle case 14 via a 5-axis control type magnetic bearing 11 and protection bearings 12 and 13 disposed above and below the magnetic bearing 11. It is supported rotatably with respect to the surface. Further, a motor 21 is incorporated between the upper and lower magnetic bearings 11.

The lower end of the spindle case 14 has a large diameter, and an exhaust passage 15 is formed in this portion. The exhaust passage 15 communicates with an exhaust port 16 formed on the outer peripheral surface of the spindle case. At the same time, the upper end thereof communicates with the intake port 2a at the upper end through a gap between the fixed wing 3 and the rotary wing 8.

Here, the rotor 7 has a cylindrical skirt facing the inner peripheral surface of a cylindrical stator 17 fixed to the pump case 2 below the portion where the rotor 8 is formed. A portion (cylindrical portion) 7a is formed. The rotation shaft 5 and the upper half of the spindle case 14 are coaxially inserted from below into the inside of the skirt portion 7a. A detector 19 is mounted on the outer peripheral surface of the spindle case 14 facing the lower edge of the circular inner peripheral surface 7b of the skirt portion 7a. This detector 19 has a circular inner peripheral surface 7b of the skirt portion.
This is for detecting the deformation amount (elongation amount) of the. The output signal of the detector 19 is taken out via a hermetic seal connector 22 attached to the outer periphery of the spindle case 14, similarly to the signal lines of the magnetic bearing 11, the motor 21, and the like.

The detector 19 is a non-contact type displacement sensor.
For example, an eddy current displacement sensor that measures the distance between the rotor and the detection element by converting the amount of eddy current generated between the rotor and the detection element into current or voltage is used.

FIG. 2 shows an outline of a control system of the turbo molecular pump 1 of this embodiment. As shown in this figure, the output signal 19S of the detector 19 taken out through the hermetic seal connector 22 is input to the comparison operation circuit 31. The comparison operation circuit 31 compares the predetermined reference value REF with the deformation amount represented by the output signal 19S of the detector. If the amount of deformation represented by the output signal 19S is equal to or greater than the reference value REF, an abnormal signal 31S is output to the pump drive / control circuit 32.

The pump drive / control circuit 32 is a circuit for controlling the drive of the pump 1, and when receiving the abnormal signal 31S, displays an alarm display for urging replacement of the rotor 7 on the display unit 3.
3 is displayed. Alternatively, the fact is displayed by voice, buzzer or the like via the alarm 34. Then, if a process such as pump stop is not performed within a predetermined time after the alarm is generated, the pump control output signal 32S
Is output to forcibly stop the pump automatically.

FIG. 3 shows general creep characteristics of the rotor material. As can be seen from the creep characteristic curve I, elastic instantaneous distortion occurs in the rotor material according to the instantaneous stress employed in the rotor. In addition, when the usage time is long, the amount of distortion increases due to the creep phenomenon. The amount of strain due to creep increases with the passage of time through the transition creep region A, the steady creep region B, and the accelerated creep region, after which the material is destroyed. In the accelerated creep region, the amount of strain rapidly increases and the material is destroyed. Therefore, when the material enters the steady creep region in front of it, the pump drive is stopped and the rotor 7 is replaced.
Creep destruction of the rotor can be reliably prevented. Therefore, as a typical control mode, the reference value R
As the EF, a steady creep level distortion amount may be adopted.

When the motor 21 and the magnetic bearing 11 are driven under the control of the pump drive / control circuit 32, the rotary shaft 5 magnetically floats in the turbo-molecular pump 1 of the present embodiment having the above-described structure. Rotate at high speed. Therefore, the rotor 7 connected to the rotating shaft 5 rotates at high speed. The detector 19 constantly monitors the amount of deformation of the portion of the rotor 7 where the deformation due to the centrifugal force becomes relatively large, that is, the portion of the skirt portion 7a on the lower edge side.
When the amount of deformation generated in the rotor 7 exceeds the steady creep level of the rotor material, the amount is detected by the comparison operation circuit 31 and the pump drive / control circuit 32 generates an alarm and generates an alarm. After that, the pump is forcibly stopped. Therefore, creep destruction of the rotor 7 can be reliably prevented.

Further, for example, even when the rotor 7 rotates at a rotation speed exceeding the specified rotation speed due to an abnormality of the rotation control system of the motor 21, the stress generated in the rotor 7 is:
It becomes larger than the specified value. In this case as well, although this may lead to rotor breakdown, the rotor 7 is always deformed to a specified value or more by the action of centrifugal force before damage. Therefore, in this case as well, damage to the rotor 7 can be prevented based on the output of the detector 19.

Further, as described above, when the temperature of the pump is forcibly raised to prevent gas condensation and accumulation of by-products, or when the temperature control mechanism of the pump breaks down, the temperature inside the pump is reduced. Ie, the rotor temperature rises to 100 degrees Celsius
May exceed degrees. Further, when the temperature of the gas sucked by the pump is high, or when the pump is operated at a pressure equal to or higher than the specified pressure, the rotor temperature rises and the temperature increases by 10 ° C.
May exceed 0 degrees. When the rotor material is an aluminum alloy, if the temperature exceeds 100 degrees Celsius, the strength is significantly reduced, so that the possibility of damage to the rotor increases.

However, in the case of such a rise in temperature, the elongation due to the decrease in the material strength and the elongation due to the thermal expansion are combined in the rotor 7, resulting in large deformation. Such an abnormal extension of the rotor 7 can also be detected by the detector 19. Therefore, it is possible to prevent the rotor from being damaged due to such a temperature rise.

(Other Embodiments) The detector 19
An analog output type can be used. Instead, a displacement switch having a built-in comparison operation function in the detector is set in advance to a displacement amount before the rotor is damaged,
When this displacement amount is reached, a contact signal is output from the displacement switch, and the signal output is input to the pump drive / control circuit to generate an alarm or forcibly stop the pump as described above. Is also good.

The installation position of the detector 19 is determined by the position of the rotor 7.
Any position may be used as long as it is easy to detect the amount of deformation occurring in the image. For example, the detector 19 is connected to the rotor 7
May be disposed so as to face the outer peripheral surface, and the amount of deformation may be detected.

Further, in this embodiment, the reference value regarded as a danger of the rotor elongation (deformation) is the steady creep level of the rotor material. However, for the stress generated in the rotor,
In consideration of the safety factor for the creep characteristic of the rotor material used, a deformation amount of 1.0% or less creep may be used as the reference value for determination.

On the other hand, although the pump 1 of the present embodiment uses a magnetic bearing of a five-axis control system, other magnetic bearings may be employed. Further, another type of bearing such as a ball bearing, an air dynamic pressure bearing, or the like may be employed.

[0037]

As described above, the high vacuum pump according to the present invention has the detector for detecting the amount of deformation generated in the rotor. Therefore, based on the amount of deformation detected by the detector, the rotor can be replaced before the rotor is damaged. Therefore, it is possible to reliably prevent the rotor from being damaged.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a composite turbo-molecular pump to which the present invention is applied.

FIG. 2 is a schematic block diagram illustrating a main part of a control system of the pump in FIG. 1;

FIG. 3 is a graph showing a typical creep characteristic curve of a rotor material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Composite turbo molecular pump 2 Pump case 2a Intake port 3 Fixed wing 5 Rotating shaft 7 Rotor 8 Rotating wing 16 Exhaust port 19 Detector 21 Motor 31 Comparison operation circuit 32 Pump drive / control circuit

Claims (6)

[Claims] A rotating blade formed on the outer peripheral surface of the rotor at a predetermined interval in a direction of a rotating axis of the rotor, a fixed blade formed in a pair with the rotating blade, In a high vacuum pump having an intake port formed on one side of the rotor rotation axis and an exhaust port formed on the other side, the high vacuum pump has a detecting means for detecting an amount of deformation generated in the rotor. High vacuum pump. 2. The method according to claim 1, wherein the rotor has a cylindrical portion centered on the rotor rotation axis, and the detecting means detects an amount of deformation occurring at an edge of the cylindrical portion. And high vacuum pump. 3. The high vacuum pump according to claim 1, wherein said detecting means is a non-contact type displacement sensor. 4. A comparison unit according to claim 1, further comprising: a comparison unit configured to compare the amount of deformation detected by the detection unit with a preset reference amount. Control means for controlling the rotational drive of the rotor based on the result. 5. The control unit according to claim 4, wherein the control unit stops the rotor when it is determined based on an output of the comparison unit that the amount of deformation is equal to or larger than the reference amount. High vacuum pump. 6. A comparison unit according to claim 1, further comprising: a comparison unit configured to compare a deformation amount detected by said detection unit with a predetermined reference amount, and an output of said comparison unit. And a warning generating means for generating a warning when it is determined that the amount of deformation is equal to or greater than the reference amount based on the high vacuum pump.