JP3825538B2 - High vacuum pump - Google Patents

Description

[0001]
BACKGROUND 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 that prevents damage to a rotor in a high vacuum pump such as an axial flow molecular pump (turbo molecular pump, molecular drag pump).
[0002]
[Prior art]
In the axial flow molecular pump that is a high vacuum pump, a rotor blade is formed on the outer peripheral surface of a rotor that is rotatably supported in the case, and a stationary blade that is paired with the rotor blade is formed on the inner peripheral surface of the case. Exhaust is performed by rotating the rotor with an electric motor or the like at a rotational speed (tens of thousands of rpm) at which the rotor blades have a peripheral speed similar to the movement speed of gas molecules.
[0003]
In such a high vacuum pump, strength deterioration of the rotor proceeds due to continuous operation, and the rotor may be damaged and the pump may not be usable. For this reason, conventionally, the thickness of the case is increased, and when the rotor is broken, the rotor fragments are enclosed in the case so that damage due to the rotor damage does not reach other parts than the pump. However, since the pump intake port 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 breakage may reach the vacuum device. For this reason, it is necessary to prevent damage to the rotor.
[0004]
In order to prevent damage to the rotor, conventionally, an upper limit of the rotor usage time is set in advance, and a method of replacing the rotor when the usage time exceeds the upper limit is employed.
[0005]
[Problems to be solved by the invention]
However, depending on the usage conditions of the rotor and the deterioration of the rotor material, the actual rotor usage time suddenly breaks before reaching the preset rotor usage time, making it impossible to use the pump or connecting to the pump Even the expensive vacuum apparatus currently used may be damaged.
[0006]
Rotor failure occurs when the strength of the rotor material decreases below the stress generated in the rotor due to high speed rotation. Possible causes of the strength reduction of the rotor material include rotor creep, fatigue, corrosion, and the like. Of these, rotor damage due to strength reduction due to corrosion can be avoided if the rotor is surface-treated according to the gas sucked by the pump, and therefore rotor damage due to the strength reduction is avoided. it can. Also, for rotor fatigue failure, this type of high vacuum pump has a low start / stop frequency and is often operated for a long time at a steady rotational speed, so the possibility of fatigue failure of the rotor material due to repeated stress is low. . Therefore, it is considered that the main cause of rotor breakage is strength deterioration due to the creep characteristics of the rotor material.
[0007]
However, it is difficult to predict the strength deterioration of the rotor material due to creep in advance, and therefore it is difficult to prevent the rotor from being damaged.
[0008]
On the other hand, in recent years, in the film formation / etching process of the semiconductor manufacturing process, depending on the type of gas sucked into the high vacuum pump, the gas sucked in the high vacuum pump may be condensed or generated by a secondary reaction. There is a possibility that the by-product formed may accumulate in the high vacuum pump and deteriorate the pump performance. In some cases, the pump may be damaged. In order to avoid this harmful effect, measures may be taken to forcibly increase the internal temperature of the pump based on the saturated vapor pressure characteristics of the sucked gas to prevent gas condensation and side reaction product accumulation. .
[0009]
When the pump internal temperature is raised, naturally the rotor temperature also rises accordingly, so that the rotor temperature becomes higher than the normal rotor use conditions. Since the increase in the rotor temperature promotes the creep phenomenon of the rotor material, the strength deterioration rate of the rotor becomes faster compared to the normal rotor use conditions (when the temperature of the rotor is not raised). As a result, there is a high possibility that the rotor will be suddenly damaged at a time far before the predetermined upper limit value of the rotor usage time.
[0010]
In addition, the commonly used rotor material is a high-strength aluminum alloy, but this aluminum alloy exhibits a remarkable creep phenomenon at a relatively low temperature of around 100 degrees Celsius compared to other metal materials, resulting in strength deterioration. It is known to occur. Also from this point, when the rotor temperature rises as described above, there is a high possibility that the rotor is damaged.
[0011]
In view of these points, an object of the present invention is to propose a high vacuum pump provided with a mechanism capable of reliably preventing rotor breakage.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a rotor blade formed at a predetermined interval in the direction of the rotor rotation axis on the outer peripheral surface of the rotor, and a fixed member formed in a pair with the rotor blade. In a high vacuum pump having blades and an intake port formed on one side of the rotor rotation axis with respect to the rotor and an exhaust port formed on the other side, the amount of deformation generated in the rotor is directly detected. Detecting means for comparing, and comparing means for detecting whether or not the rotor is in a creep state within a steady creep region by comparing a deformation amount detected by the detecting means with a preset reference amount. It is characterized by that.
[0013]
In the high vacuum pump of the present invention configured as described above, 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 strength deterioration of the rotor material, the amount of strain increases from the steady creep region where the strain due to creep increases almost proportionally over time to the accelerated creep region where the strain suddenly increases, leading to rotor breakage. . Therefore, based on the amount of deformation detected by the detecting means, it can be detected whether or not the rotor is in the creep state within the steady creep region. If it is detected that the creep state has been reached, the rotor should be replaced. If this is done, the rotor can be prevented from being destroyed.
[0014]
Here, it is preferable that the control unit includes a control unit that forcibly stops the rotation of the rotor when the comparison unit detects that the rotor is in a creep state within the steady creep region.
[0015]
In addition, it is preferable that the comparator includes an alarm generation unit that generates an alarm when the comparison unit detects that the rotor is in a creep state within the steady creep region.
[0017]
Next, the present invention relates to a rotor blade formed at a predetermined interval on the outer peripheral surface of the rotor in the direction of the rotor rotation axis, a fixed blade formed in a pair with the rotor blade, and the rotor. A method for preventing creep destruction of a rotor 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 detection unit being installed in the pump Thus, the amount of deformation generated in the rotor is directly detected, and based on the amount of deformation detected by the detecting means, it is detected whether the rotor is in a creep state within a steady creep region, and the creep state is reached. When it is detected, the rotor is forcibly stopped or an alarm is generated.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a composite turbo molecular pump to which the present invention is applied will be described with reference to the drawings.
[0020]
FIG. 1 shows a cross-sectional configuration of the composite turbomolecular pump of this example. The turbo-molecular pump 1 has a cylindrical pump case 2, and the upper end side opening of the pump case 2 serves as an intake port 2a. An annular fixed blade 3 is fixed to the inner circumferential surface 2b of the pump case following the intake port 2a at a predetermined interval in the direction of the pump axis (rotor rotation axis) 1a. These fixed blades 3 are maintained at an interval by an annular spacer 4.
[0021]
On the other hand, the rotary shaft 5 is coaxially arranged inside the pump case 2, and the rotor 7 is concentrically fixed to the outer periphery of the upper end side portion 5 a of the rotary shaft 5 by fastening bolts 6. . On the outer peripheral surface of the rotor 7, annular rotor blades 8 are formed at predetermined intervals in the direction of the pump axis (rotor rotation axis) 1a. Each of these rotor blades 8 is paired with the fixed blade 3 described above. Thus, they are arranged in a mutually inserted relationship between the fixed wings 3.
[0022]
The lower end side portion 5b of the rotary shaft 5 is connected to the inner peripheral surface of the cylindrical spindle case 14 via a 5-axis control type magnetic bearing 11 and protective bearings 12 and 13 disposed above and below the magnetic bearing 11. And is supported in a freely rotatable state. A motor 21 is incorporated between the upper and lower magnetic bearings 11.
[0023]
The lower end portion 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. The upper end side communicates with the intake port 2a at the upper end through a gap between the fixed blade 3 and the rotary blade 8.
[0024]
Here, the rotor 7 has a cylindrical skirt portion (cylindrical) facing the inner peripheral surface of a cylindrical stator 17 fixed to the pump case 2 side below the portion where the rotor blades 8 are formed. Part) 7a is formed. Inside the skirt portion 7a, the rotary shaft 5 and the upper half portion of the spindle case 14 are coaxially inserted from below. A detector 19 is attached to the outer peripheral surface of the spindle case 14 facing the lower edge portion of the circular inner peripheral surface 7b of the skirt portion 7a. The detector 19 is for detecting the deformation amount (elongation amount) of the circular inner peripheral surface 7b of the skirt portion. The output signal of the detector 19 is taken out through a hermetic seal connector 22 attached to the outer periphery of the spindle case 14 in the same manner as the signal lines of the magnetic bearing 11, the motor 21 and the like.
[0025]
The detector 19 is a non-contact type displacement sensor, for example, an eddy current method for measuring 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 a current or a voltage. A displacement sensor is used.
[0026]
FIG. 2 shows an outline of a control system of the turbo molecular pump 1 of this example. 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 a predetermined reference value REF with the deformation amount represented by the detector output signal 19S. When the amount of deformation represented by the output signal 19S is greater than or equal to the reference value REF, an abnormal signal 31S is output to the pump drive / control circuit 32.
[0027]
The pump drive / control circuit 32 is a circuit that controls the drive of the pump 1. When receiving the abnormal signal 31 </ b> S, the pump drive / control circuit 32 displays an alarm display for prompting replacement of the rotor 7 via the display 33. Alternatively, the fact is displayed by voice, buzzer or the like via the alarm device 34. When the pump is not stopped within a predetermined time after the alarm is generated, a pump control output signal 32S is output to automatically forcibly stop the pump. .
[0028]
Here, FIG. 3 shows general creep characteristics of the rotor material. As can be seen from the creep characteristic curve I, the rotor material generates an elastic instantaneous strain corresponding to the instantaneous stress employed in the rotor. Further, as the usage time becomes longer, 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, and thereafter the material is destroyed. In the accelerated creep region, the amount of strain increases suddenly, leading to the destruction of the material. Therefore, when the material enters the steady creep region in front of it, the pump drive is stopped and the rotor 7 is replaced. Can be reliably prevented from creeping. Therefore, as a typical control mode, the distortion amount of the steady creep level may be adopted as the reference value REF of the comparison operation circuit 31.
[0029]
In the turbo molecular pump 1 of this example configured as described above, 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 is magnetically levitated by these to rotate at high speed. . Accordingly, the rotor 7 connected to the rotating shaft 5 rotates at a high speed. The amount of deformation of the portion of the rotor 7 where the deformation due to the centrifugal force is relatively large, that is, the portion on the lower edge side of the skirt portion 7 a is constantly monitored by the detector 19. When the amount of deformation generated in the rotor 7 exceeds the steady creep level of the rotor material, this is detected by the comparison operation circuit 31 and the pump drive / control circuit 32 generates an alarm and an alarm. After that, the pump is forcibly stopped. Therefore, the creep destruction of the rotor 7 can be reliably prevented.
[0030]
Further, for example, even when the rotor 7 rotates at a rotational speed exceeding the specified rotational speed due to an abnormality in the rotation control system of the motor 21, the stress generated in the rotor 7 becomes larger than the specified value. In this case as well, the rotor may be destroyed, but the rotor 7 is always subjected to the action of centrifugal force before being damaged and is deformed to a specified value or more. Therefore, in this case as well, the rotor 7 can be prevented from being damaged based on the output of the detector 19.
[0031]
Further, as described above, when the temperature of the pump is forcibly increased to prevent gas condensation and by-product accumulation, or when the temperature control mechanism of the pump fails, the temperature inside the pump, that is, the rotor The temperature may rise and exceed 100 degrees Celsius. Furthermore, when the temperature of the gas sucked into the pump is high, or when the pump is operated at a pressure higher than a specified pressure, the rotor temperature may rise and exceed 100 degrees Celsius. In the case where the rotor material is an aluminum alloy, when the temperature exceeds 100 degrees Celsius, the strength is significantly reduced, so that the risk of rotor breakage increases.
[0032]
However, in the case of such a temperature rise, the rotor 7 undergoes a large deformation due to a combination of elongation due to a decrease in material strength and elongation due to thermal expansion. Such abnormal elongation 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.
[0033]
(Other embodiments)
The detector 19 can be an analog output type. Instead, a displacement switch with a built-in comparison calculation function in the detector is set in advance with a displacement amount before the rotor is damaged, and when this displacement amount is reached, a contact signal is output from the displacement switch. The signal output may be input to the pump drive / control circuit to generate an alarm or forcibly stop the pump as described above.
[0034]
Further, the installation position of the detector 19 may be any position as long as the deformation amount generated in the rotor 7 is easily detected. For example, the detector 19 may be disposed opposite the outer peripheral surface of the rotor 7 to detect the amount of deformation.
[0035]
Further, in this example, the reference value that is regarded as a danger of the rotor elongation amount (deformation amount) is the steady creep level of the rotor material. However, in consideration of the safety factor with respect to the creep characteristics of the rotor material to be used with respect to the stress generated in the rotor, a deformation amount of 1.0% creep or less may be used as a reference value for determination.
[0036]
On the other hand, although the pump 1 of this example uses a 5-axis control type magnetic bearing, other magnetic bearings may be adopted. Furthermore, another type of bearing such as a ball bearing or an air dynamic pressure bearing may be employed.
[0037]
【The invention's effect】
As described above, the high vacuum pump of the present invention includes a detector that detects the amount of deformation generated in the rotor. Therefore, based on the deformation amount detected by the detector, the rotor can be replaced before the rotor is damaged. Therefore, damage to the rotor can be reliably prevented.
[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 showing a main part of a control system of the pump of FIG.
FIG. 3 is a graph showing a general creep characteristic curve of a rotor material.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Composite type turbo molecular pump 2 Pump case 2a Inlet 3 Fixed blade 5 Rotating shaft 7 Rotor 8 Rotating blade 16 Exhaust port 19 Detector 21 Motor 31 Comparison operation circuit 32 Pump drive / control circuit

Claims (4)

A rotor blade formed on the outer peripheral surface of the rotor at a predetermined interval in the direction of the rotor rotation axis; a fixed blade formed in a pair with the rotor blade; and the rotor rotation axis with respect to the rotor. In a high vacuum pump having an intake port formed on one side and an exhaust port formed on the other side,
Detection means for directly detecting the amount of deformation generated in the rotor;
Comparing means for detecting whether or not the rotor is in a creep state within a steady creep region by comparing a deformation amount detected by the detecting means with a preset reference amount;
A high vacuum pump characterized by comprising: In claim 1,
A high vacuum pump comprising: control means for forcibly stopping rotation of the rotor when the comparison means detects that the rotor is in a creep state within the steady creep region. In claim 1,
A high vacuum pump comprising: an alarm generating means for generating an alarm when the comparison means detects that the rotor is in a creep state within the steady creep region. A rotor blade formed on the outer peripheral surface of the rotor at a predetermined interval in the direction of the rotor rotation axis; a fixed blade formed in a pair with the rotor blade; and the rotor rotation axis with respect to the rotor. A method for preventing creep destruction of a rotor in a high vacuum pump having an intake port formed on one side and an exhaust port formed on the other side,
The amount of deformation generated in the rotor is directly detected by detection means installed in the pump,
Based on the deformation amount detected by the detection means, it is detected whether the rotor is in a creep state within a steady creep region,
When it is detected that the creep state has been reached, the rotor is forcibly stopped or an alarm is generated.
A method of preventing creep destruction of a rotor of a high vacuum pump.

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