JP4419258B2 - Turbo molecular pump - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a turbo molecular pump.
[0002]
[Prior art]
There is a turbo molecular pump as one of vacuum pumps used in semiconductor manufacturing equipment, etc. In the turbo molecular pump, the rotor on which the rotor blades are formed is rotated by a motor, and the rotor blades are rotated at high speed with respect to the fixed blades. This exhausts gas molecules. A DC brushless motor is known as a motor for rotating the rotor. In a DC brushless motor, a plurality of hall sensors that detect the rotor magnetic poles and detect the rotational position of the rotor are provided in the stator, and an excitation pattern for exciting the stator coil by a logic circuit from each hall sensor signal is provided. Then, the motor is driven by controlling the motor drive circuit according to the excitation pattern.
[0003]
For example, three hall sensors H1, H2, and H3 are provided corresponding to three-phase (U, V, W) stator coils, and excitation voltages synchronized with the rotation period of the rotor based on signals from these three hall sensors. Is applied to each coil U, V, W. (A) of FIG. 10 is a figure which shows the sensor signal from each Hall sensor H1-H3. An excitation pattern signal is generated from the sensor signal by a logic circuit, the motor drive circuit is controlled by the signal, and excitation voltages as shown in FIG. 10B are applied to the stator coils U, V, and W.
[0004]
[Problems to be solved by the invention]
However, there has been a problem that the excitation voltage applied to the stator coil is not necessarily optimum for the following reasons.
(A) The excitation pattern deviates from the optimum one due to the phase shift of the sensor signal that occurs until the sensor signal of the Hall sensor is taken into the excitation pattern forming circuit. In particular, when a photocoupler is used in the signal path, a phase shift caused by the response time of the photocoupler occurs.
(B) Since the Hall sensor is an analog element that detects a magnetic force and inverts a signal as shown in FIG. 10A, a phase shift occurs due to element variations.
(C) Further, when the magnetization of the magnet is non-uniform, there is a shift in the rise and fall where the signal is inverted.
[0005]
If a phase shift occurs in the sensor signal due to the above-described reasons, this phase shift becomes a phase shift of the excitation pattern, and the motor drive state shifts from the optimum state. As a result, unnecessary power is consumed, which causes a temperature rise of the pump body. In particular, in the case of a magnetic bearing type turbo molecular pump, since the rotor floats in a non-contact manner in a vacuum, there is no escape of heat and the temperature is likely to rise even with a slight increase in power consumption. For example, if the power consumption is 70 to 80 W during no-load rotation but increases by 10 W due to the above-described reasons, the rotor temperature rises by 5 to 10 ° C.
[0006]
In the turbo molecular pump, since the rotor rotates at a very high speed, generally, when the temperature of the rotor made of an aluminum alloy rises, there is a problem that the strength of the rotor is reduced due to high temperature creep.
[0007]
An object of the present invention is to provide a turbo-molecular pump using the DC brushless motor capable of reducing power consumption.
[0008]
According to a first aspect of the present invention, there is provided a turbo molecular pump that rotates a rotating blade at a high speed with respect to a fixed blade by a DC brushless motor, wherein a load current detecting unit that detects a load current flowing through the DC brushless motor, and the turbo molecular pump includes: The excitation reference position relative to the rotation reference position of the DC brushless motor is relatively changed in response to an optimum phase detection command supplied from the outside in a no-load state and maintaining a predetermined constant rotation speed. An optimum phase detecting means for detecting an optimum excitation phase at which the load current is minimized, and a phase information storage means for storing the optimum excitation phase detected by the optimum phase detecting means as optimum phase information ; , wherein the time of operation of the turbo-molecular pump, and based on the said optimal phase information stored in the phase information storage means excited By forming a pattern that has a driving means for driving the DC brushless motor. The invention described in claim 1 corresponds to FIGS. 11 and 12.
The invention according to claim 2 is the turbo molecular pump according to claim 1, wherein the rotation reference position of the DC brushless motor is a single magnet that detects the magnetism of a permanent magnet embedded in the rotor of the DC brushless motor. It is determined by the signal output from the detection element.
[0009]
In the section of the means for solving the above-described problems for explaining the configuration of the present invention, the drawings of the embodiments of the invention are used for easy understanding of the present invention. The form is not limited.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing a schematic configuration of a magnetic bearing type turbo molecular pump. The turbo molecular pump includes a turbo molecular pump main body 1 and a power supply device 2. The rotor 4 provided in the pump body 1 is supported in a non-contact manner by a magnetic bearing 5 and is rotationally driven by a motor unit 6. A DC brushless motor is used for the motor unit 6. On the other hand, the power supply device 2 includes an inverter unit 7 that drives a DC brushless motor, and a magnetic levitation control unit 8 that controls the excitation current supplied to the magnetic bearing 5 so that the rotor 4 is supported at a predetermined levitation position. I have.
[0011]
FIG. 2 is a cross-sectional view showing details of the turbo molecular pump main body 1. Inside the casing 20 of the pump body 1, the rotor 4 in which a plurality of stages of rotor blades 21 and screw groove portions 22 are formed, stator blades 23 arranged alternately with respect to the rotor blades 21, and the screw groove portions 22. And a cylindrical member 24 disposed so as to be opposed to each other. The magnetic bearing 5 that supports the rotor 4 in a non-contact manner includes electromagnets 51 and 52 that constitute a radial magnetic bearing and an electromagnet 53 that constitutes an axial magnetic bearing, and these constitute a 5-axis control type magnetic bearing. Corresponding to the radial electromagnets 51 and 52 and the axial electromagnet 53, radial displacement sensors 71 and 72 and an axial displacement sensor 73 for detecting the position of the rotor 4 are provided.
[0012]
Reference numeral 10 denotes a DC brushless motor, and the rotor 4 is driven to rotate at a high speed by the motor 10. The rotation position of the rotor 4 at this time is detected by the rotation sensor 11. As the rotation sensor 11, a Hall sensor, an eddy current sensor, or the like is used. When the rotor 4 is rotationally driven by the motor 10 while being supported in a non-contact manner by the electromagnets 51, 52, 53, the gas on the inlet side is exhausted to the back pressure side (space S1) as indicated by the arrow G1, and the gas exhausted to the back pressure side. Is exhausted by an auxiliary pump connected to the exhaust port flange 26. 27 and 28 are emergency mechanical bearings.
[0013]
FIG. 3 is a diagram illustrating the motor unit 6 and the inverter unit 7 in detail. A rotation sensor 11 and stator coils U, V, W are provided on the stator side of the motor unit 6, and a signal from the rotation sensor 11 is input to the detection circuit 12 of the inverter unit 7. The detection circuit 12 calculates the rotation reference position and rotation cycle of the rotor 4 based on the sensor signal of the rotation sensor 11 and inputs the information to the excitation pattern creation circuit 13.
[0014]
FIG. 4 is a diagram for explaining the rotor position detection when the hall sensor HS is used as the rotation sensor 11. As shown in FIG. 4A, in the DC brushless motor, the rotor 4 is provided with a permanent magnet 30, and the rotor 4 is detected by detecting the magnetic field of the permanent magnet 30 with a hall sensor HS provided on the stator side. The rotational position of is detected. When the rotor 4 rotates and changes to the state of FIG. 4B rotated from the state of FIG. 4A by the angle a, the Hall sensor HS detects the S pole. And if it becomes the state of angle b like FIG.4 (c), a south pole will no longer be detected. Furthermore, if it rotates 180 degrees from the state of FIG.4 (b), Hall sensor HS will detect N pole. The detection circuit 12 calculates the rotation reference position and rotation cycle of the rotor 4 based on the obtained sensor signal.
[0015]
Returning to FIG. 3, the excitation pattern creation circuit 13 creates an excitation pattern for supplying excitation current to the stator coils U, V, and W. The excitation pattern created here consists of three types of drive signal patterns for driving each of the stator coils U, V, and W. Based on these signals, the excitation voltage pattern is a drive circuit as shown in FIG. 14. The excitation voltage pattern of FIG. 5 has an ideal waveform with a phase difference of exactly 120 ° and a constant voltage switching interval.
[0016]
The excitation pattern creation circuit 13 may be created using a DSP (digital signal processor) or the like, or may be created by a microprocessor. In any case, an excitation pattern having an ideal shape is created independently of the signal from the rotation sensor 11. However, the pattern period (period T in FIG. 5) is created so as to coincide with the rotation period of the rotor 4.
[0017]
FIG. 6 is a diagram showing an example of the drive circuit 14, wherein S1 to S6 are switching elements such as transistors, and E is a power source. These switching elements S1 to S6 are controlled by a signal from the excitation pattern creation circuit 13, and voltages as shown in FIG. 5 are applied to the stator coils U, V, and W. FIG. 7 shows the on / off timings of the switching elements S1 to S6 for one cycle of (1) to (6) in FIG. 5. FIG. 8 shows the coils U, V, The terminal voltage of W is shown.
[0018]
In {circle around (1)}, since the switching element S1 is off (x mark) and the switching element S2 is on (o mark), the terminal voltage of the coil U is 0 (V). For the coil V, since the switching element S3 is on and the switching element S4 is off, the terminal voltage is E (V). As for the coil W, since both of the switching elements S5 and S6 are off, the terminal voltage of the coil W is intermediate between the terminal voltages of the coils U and V, and is E / 2 (V). FIG. 9 is a diagram showing the rotor 4, the stator coils U, V, W and the hall sensor HS provided with permanent magnets. 5, 7, and 8, the current I flows through the coils U and V as indicated by the arrows in the figure, and a magnetic field is generated in which the coil V side is the N pole and the coil U side is the S pole. To do. As a result, the rotor 4 is driven to rotate clockwise. In the case of FIG. 9, the rotation reference position of the rotor 4 indicates the position of the south pole of the magnet 30, and when the south pole is in the position (1) as shown in FIG. 9, the excitation pattern of FIG. By matching (1), the rotation reference position matches the excitation reference position.
[0019]
In the case of (2), since both the switching elements S3 and S4 are off, the terminal voltage of the coil V is E / 2 (V), and since the switching element S5 is on and the switching element S6 is off, the terminal voltage of the coil W is Is E (V), and the coil U is the same as (1), so it is 0 (V). The same applies to (3) to (6). Such on / off control of the switching elements S1 to S6 is performed by the signal from the excitation pattern creating circuit 13, and the rotor 4 is continuously rotated clockwise.
[0020]
By the way, in the conventional apparatus, as shown by H1, H2, and H3 in FIG. 9, a plurality of hall sensors are provided, and an excitation pattern is created by a logic circuit from those sensor signals (see FIG. 10A). For example, in the state shown in FIG. 9, a sensor signal as shown in (1) in FIG. 10 (a) is obtained, and the logic circuit switches the switching elements S1 to S6 based on this sensor signal as shown in (1) in FIG. To control. For this reason, if a phase shift occurs between the sensor signals in FIG. 10A due to variations in the mounting positions of the Hall sensors H1 and H2 and the performance itself, the excitation pattern in FIG. Arise.
[0021]
However, in the above-described embodiment, an ideal excitation pattern is generated by the excitation pattern creation circuit 13 regardless of the rotational position detected by the rotation sensor 11, so that power consumption is lost due to the collapse of the excitation pattern. Can be prevented.
[0022]
FIG. 11 is a view showing a modified example of the turbo molecular pump described above, and corresponds to FIG. In the above-described embodiment, even if the excitation pattern is ideal, for example, a deviation may occur between the rotational position detected due to non-uniform magnetization of the permanent magnet and the actual rotational position. As a result, a phase shift occurs between the actual rotation reference position of the rotor 4 and the excitation reference position corresponding to the excitation pattern, that is, the timing of the rotation of the rotor 4 and the rotating magnetic field generated by the coils U, V, and W. The power consumption increases by shifting.
[0023]
Therefore, in the modification shown in FIG. 11, when the turbo molecular pump is rotating at a constant rotation speed, the excitation pattern phase is shifted so as to minimize the power consumption of the motor 10. Incidentally, since the power consumption of the motor 10 is proportional to the motor current at the same rotational speed, the power consumption is also minimized when the motor current is minimized. In FIG. 11, the phase of the excitation pattern is output from the controller 15 to the excitation pattern creation circuit 13, and the excitation pattern creation circuit 13 generates an excitation pattern having the input phase.
[0024]
At the beginning of pump activation, the excitation pattern creation circuit 13 generates an excitation pattern so that the rotation reference position of the rotor 4 calculated by the detection circuit 12 matches the excitation reference position of the excitation pattern. However, even when driven in this way, it is not always synchronized with the actual rotor rotation as described above. The controller 15 varies the phase input to the excitation pattern creation circuit 13 within a predetermined range H as shown in FIG. 12, and searches for a phase at which the motor current I is minimized. FIG. 12 is a diagram showing the relationship between the motor current I and the phase of the excitation pattern. The vertical axis shows the motor current I, and the horizontal axis shows the phase of the excitation reference position with respect to the rotation reference position. If the phase of the excitation reference position with respect to the rotation reference position is α, the motor current I becomes the minimum value Imin. When such an optimum phase α is obtained, the controller 15 inputs the optimum phase α to the excitation pattern creation circuit 13 and stores it in the storage unit 16. Thereafter, when the turbo molecular pump is restarted after being stopped, the optimum phase α is called from the storage unit 16 and input to the excitation pattern creation circuit 13.
[0025]
The derivation of the optimum phase α as described above is performed when the turbo molecular pump rotates at a constant speed in a no-load state. Generally, the operator confirms that the turbo molecular pump is in such a state, and inputs the command (tuning command) for obtaining the optimum phase α to the controller 15, so that the above-described operation (tuning operation) is performed. [0026]
In the above-described modification, the turbo molecular pump is driven so that the motor current I is minimized, so that the motor power consumption is minimized and the heat generation of the motor 10 can be suppressed. As a result, the temperature rise of the rotor 4 due to motor heat generation can be suppressed, and the reliability of the turbo molecular pump can be improved. Further, since the excitation pattern is not created from the signals of the three Hall sensors H1 to H3 as in the prior art, it is not necessary to provide a plurality of rotation sensors 11 and the cost can be reduced.
[0027]
In the above-described embodiment, the turbo molecular pump has been described as an example. However, the present invention is not limited to this, and by controlling the DC brushless motor as described above, the motor power consumption can be reduced as compared with the related art.
[0028]
In the correspondence between the embodiment described above and the elements of the claims, the load current detection means corresponds to the drive circuit 14, the optimum phase detection command corresponds to the tuning instruction, and the optimum phase detection means corresponds to the controller 15. The phase information storage means corresponds to the storage unit 16, and the drive means corresponds to the excitation pattern creation circuit 13 and the drive circuit 14.
[0029]
【The invention's effect】
As described above, according to the turbo molecular pump to which the present invention is applied, the optimum excitation phase detected in response to the optimum phase detection command supplied from the outside is stored as phase information, and the subsequent turbo molecular pump During operation, the DC brushless motor is driven by forming an excitation pattern based on the optimum phase information stored in the phase information storage means, so that motor power consumption can be reduced, and unnecessary heat generation of the motor can be achieved. Can be prevented.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a magnetic bearing turbomolecular pump according to the present invention.
FIG. 2 is a cross-sectional view showing details of a turbo molecular pump main body 1;
3 is a detailed view of a motor unit 6 and an inverter unit 7. FIG.
4A and 4B are diagrams for explaining rotor position detection, in which FIG. 4A is a cross-sectional view showing a permanent magnet 30 and a Hall sensor HS of the rotor 4, and FIG. 4B is rotated by an angle a from the state of FIG. (C) shows a state rotated by an angle b from the state of (a).
FIG. 5 is a diagram showing voltage patterns applied to stator coils U, V, and W.
6 is a diagram showing an example of a drive circuit 14. FIG.
FIG. 7 is a diagram showing on / off timings of switching elements S1 to S6.
8 is a diagram showing terminal voltages of coils U, V, and W at each timing of FIG. 7;
FIG. 9 is a diagram showing a relationship between a rotor 4 and coils U, V, and W.
10A and 10B are diagrams for explaining a conventional device, in which FIG. 10A shows a Hall sensor signal, and FIG. 10B shows an excitation pattern.
FIG. 11 is a diagram showing a modified example.
FIG. 12 is a diagram showing a relationship between a motor current I and the phase of an excitation pattern.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Pump main body 4 Rotor 6 Motor part 7 Inverter part 10 DC brushless motor 11 Rotation sensor 12 Detection circuit 13 Excitation pattern creation circuit 14 Drive circuit U, V, W Stator coil

Claims (2)

In a turbo molecular pump that rotates a rotating blade at high speed with respect to a fixed blade by a DC brushless motor,
Load current detection means for detecting a load current flowing through the DC brushless motor;
In response to an optimum phase detection command supplied from the outside when the turbo molecular pump is in a no-load state and maintains a predetermined constant rotational speed, an excitation reference position with respect to the rotation reference position of the DC brushless motor By changing the relative phase, the optimum phase detection means for detecting the optimum excitation phase that minimizes the load current,
And phase information storage means for storing as the optimal phase information detected the optimum excitation phase by the optimum phase detecting means,
During operation of the turbo molecular pump is characterized by comprising driving means for driving the DC brushless motor by forming a based have been excitation pattern to the optimum phase information stored in the phase information storage means Turbo molecular pump. The turbo-molecular pump according to claim 1,
The rotational reference position of the DC brushless motor is determined by a signal output from a single magnetic detection element that detects the magnetism of a permanent magnet embedded in the rotor of the DC brushless motor. .

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