JP2012193705A - Vacuum pump and rotation-starting method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vacuum pump having superior rotation startability.SOLUTION: The vacuum pump includes a magnetic bearing 3 for carrying out the magnetic levitation of a rotor 4, a bearing control unit 8 for controlling the levitation position of the rotor 4 by controlling the excitation current of the magnetic bearing 3, a motor rotor fixed to the rotor 4 and having a permanent magnet, a motor stator for rotation-driving the motor rotor, and a main control unit 9 which makes the rotor 4 eccentric from the bearing center position to the prescribed radial direction by the magnetic bearing 3, generates the fixed magnetic field facing the prescribed direction by the motor stator, and adjusts the angle in the rotational direction of the rotor 4. The main control unit 9 returns the rotor 4 with its angle in the rotational direction adjusted to the bearing center position from the offset state in the prescribed radial direction, and the motor control unit 7 generates the rotational magnetic field for rotating the rotor 4 returned to the bearing center position by the motor stator.

Description

  The present invention relates to a vacuum pump excellent in rotation startability and a rotation start method of the vacuum pump.

  The turbo molecular pump performs gas exhaust by rotating the rotor on which the rotor blades are formed at a high speed with respect to the stationary blades. For example, a brushless DC motor is used to drive the rotor. When driving and controlling a brushless DC motor, the magnetic pole position (angle) of the motor rotor is detected by the hall sensor, and the current of each winding of the motor is switched based on the output signal of the hall sensor (see, for example, Patent Document 1). ).

  However, in order to detect the magnetic pole position using the Hall sensor, it is necessary to provide three Hall sensors at intervals of 120 deg. Therefore, a method of detecting the rotation direction of the rotor by using one inductance type rotation sensor is known (for example, see Patent Document 2).

JP-A-8-47285 JP 2006-152958 A

  However, the rotation sensor cannot accurately detect the rotational position of the rotor, unlike the hall sensor. For this reason, at the start of rotation (at the time of starting), it is necessary to take the forward rotation state by a trial and error sequential procedure. In this process, the reverse rotation may occur temporarily, and it may take time to reach the forward rotation state.

The vacuum pump according to the invention of claim 1 is fixed to the pump rotor, a magnetic bearing that magnetically floats the pump rotor, a magnetic bearing control unit that controls the exciting current of the magnetic bearing to control the floating position of the pump rotor, A motor rotor having a permanent magnet, a motor stator that rotationally drives the motor rotor, and a magnetic bearing that decenters the pump rotor in a predetermined radial direction from the bearing center position, and a fixed magnetic field that is directed in the predetermined radial direction is generated by the motor stator. The first adjusting means for adjusting the rotation direction angle of the pump rotor and the pump rotor whose rotation direction angle is adjusted by the first adjustment means are returned to the bearing center position from the state eccentric in the predetermined radial direction. And a rotating magnetic field for rotating the pump rotor returned to the bearing center position by the second adjusting means. Characterized by comprising a motor control unit for generating a.
According to a second aspect of the present invention, in the vacuum pump according to the first aspect, the second adjusting means moves the pump rotor to the center position of the bearing after a predetermined stop time has elapsed since the angle adjustment by the first adjusting means has started. It is characterized by returning to.
The invention of claim 3 is a rotation starting method of a vacuum pump in which a pump rotor is magnetically levitated by a magnetic bearing and is driven to rotate by a motor, the step of decentering the pump rotor from a bearing center position in a predetermined radial direction by the magnetic bearing; And a step of generating a fixed magnetic field directed in a predetermined radial direction by a motor stator of the motor, a step of returning the pump rotor to the center position of the bearing after a lapse of a predetermined time, and a step of rotating the pump rotor by the motor.

  According to the present invention, it is possible to improve the rotational startability of the vacuum pump.

It is a block diagram which shows schematic structure of a turbo-molecular pump. It is a figure which shows 2nd Embodiment. 3 is a block diagram illustrating a motor control unit 7. FIG. It is a flowchart explaining a starting operation. FIG. 6 is a diagram illustrating an eccentric operation of a motor rotor 62. It is a figure explaining positioning of the motor rotor 62 by a fixed magnetic field. It is a figure explaining rotation start. It is a figure explaining the force which acts between the motor rotor 62 and the motor stator 61. FIG.

  Embodiments for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a vacuum pump according to the present invention, and is a block diagram showing a schematic configuration of a turbo molecular pump. The turbo molecular pump includes a pump body 1 and a power supply device 2. In the example shown in FIG. 1, the pump main body 1 and the power supply device 2 are configured to be connected by a cable. However, the pump main body 1 and the power supply device 2 may be configured integrally.

  The pump body 1 is provided with a rotor 4 formed with rotor blades. The rotor 4 is supported in a non-contact manner by a magnetic bearing 3 and rotated by a motor 6. A three-phase DC brushless motor is used for the motor 6. On the other hand, the power supply device 2 includes a motor control unit 7 that drives the motor 6 and a bearing control unit 8 that controls the excitation current supplied to the magnetic bearing 3 so that the rotor 4 is supported at a predetermined floating position. ing. Further, the motor control unit 7 and the bearing control unit 8 are controlled by the main control unit 9.

  FIG. 2 is a diagram showing the arrangement of electromagnets provided in the magnetic bearing 3, and the rotation axis of the rotor 4 is the z-axis direction. The magnetic bearing 3 constitutes a five-axis control type magnetic bearing, and includes a pair of electromagnets 37x, a pair of electromagnets 37y, a pair of electromagnets 38x, a pair of electromagnets 38y, and a thrust disk 35 that are opposed to each other with the rotor 4 interposed therebetween. It has a pair of electromagnets 39z arranged opposite to each other. Although not shown, a displacement sensor for detecting the displacement of the rotor 4 is disposed corresponding to each pair of electromagnets, that is, each uniaxial electromagnet. The bearing control unit 8 in FIG. 1 causes the rotor 4 to magnetically levitate to a predetermined position based on the detection value of the displacement sensor.

  FIG. 3 is a block diagram illustrating the motor control unit 7 provided in the power supply device 2. The motor control unit 7 is provided with an AC / DC converter circuit 73 that converts alternating current from an external power source (commercial power source) 100 into direct current. The inverter circuit 72 includes switching elements Tr1 to Tr6 such as transistors, and the DC voltage from the AC / DC converter 73 is switched on and off by the switching elements Tr1 to Tr6 and applied to the stator winding 61 of the motor 6. On / off driving of the switching elements Tr <b> 1 to Tr <b> 6 of the inverter circuit 72 is performed by the driver circuit 704 of the control circuit 70.

  The back electromotive force detection circuit 71 detects a back electromotive voltage induced in the W-phase winding. When the motor rotor 62 provided with the permanent magnet rotates, a counter electromotive voltage is induced in the U-phase winding, the V-phase winding, and the W-phase winding of the stator winding 61. The back electromotive force detection circuit 71 includes a comparator, and obtains a difference between the input W phase back electromotive voltage (W phase terminal voltage) and the neutral point voltage, and a point at which the difference becomes zero (zero cross point). Is detected. The back electromotive force detection circuit 71 outputs a back electromotive voltage pulse of a predetermined level based on the zero cross point. A counter electromotive voltage other than the W phase may be used, or a counter electromotive voltage pulse may be generated based on two or more phases of counter electromotive voltages.

  The counter electromotive voltage pulse output from the counter electromotive detection circuit 71 is input to the rotational speed detection unit 702 of the control circuit 70. The control circuit 70 includes a microcomputer, and includes a rotation speed detection unit 702, a drive waveform generation unit 703, a driver circuit 704, a memory 705, and the like. The rotation speed detection unit 702 outputs a rotation pulse synchronized with the rotation of the motor rotor 62 based on the detection signal input from the back electromotive detection circuit 71. The rotation pulse is input to the drive waveform generation unit 703. The drive waveform generation unit 703 generates a drive waveform for driving the switching elements Tr <b> 1 to Tr <b> 6 of the inverter circuit 72 and outputs it to the driver circuit 704. The driver circuit 704 performs on / off driving of the switching elements Tr <b> 1 to Tr <b> 6 of the inverter circuit 72 based on a signal from the drive waveform generation unit 703.

  As described above, in the present embodiment, since the rotation of the rotor 4 is detected using the counter electromotive voltage pulse, the rotor rotation position at the time of starting rotation cannot be known. This is the same in a vacuum pump using a rotation sensor as described in Patent Document 2, and in the pump having such a configuration, a rotating magnetic field is generated asynchronously and started. As described in the section, the startability was inferior.

  Therefore, in the present embodiment, the rotation start is performed by the method described below, thereby providing a vacuum pump that prevents reverse rotation at the start and has excellent startability. FIG. 4 is a flowchart for explaining an example of the rotation start operation in the present embodiment. The processing in FIG. 4 is executed in the main control unit 9 by a program that starts when the power supply device 2 is turned on.

  In step S101, a magnetic levitation command is output to the bearing control unit 8 so that the rotor is magnetically levitated at the center position of the magnetic bearing. In step S102, it is determined whether a pump operation start command (rotation command) has been input to the power supply device 2. This rotation command is input to the main control unit 9 of the power supply device 2 by, for example, being input from the controller of the device in which the pump is mounted or when the operator turns on a pump start switch provided in the power supply device 2. Is done.

  If a rotation command is inputted, it will be judged as yes at Step S102, and will progress to Step S103. In step S103, the rotor 4 (motor rotor 62) shown in FIG. 2 is eccentric as shown in FIG. Note that the pair of electromagnets 37x illustrated in FIG. 2 are illustrated as 37x + and 37x− in FIG. The other electromagnets 37y, 38x, and 38y have the same display.

  FIG. 5 shows a U-W phase, U′-W′-phase stator coil of the motor stator 61, a motor rotor 62 provided with permanent magnets, and electromagnets 37x, 37y, 38x, 38y constituting radial magnetic bearings. It is shown schematically. In the example shown in FIG. 5, the U to W phase and U ′ to W ′ phase stator coils are arranged so that the V and V ′ phase stator coils are arranged in the x-axis direction.

  In normal magnetic levitation (magnetic levitation in step S101), the attractive force of the electromagnet 37x +, electromagnet 37x-, electromagnet 37y +, electromagnet 37y-, electromagnet 38x +, electromagnet 38x-, electromagnet 38y +, electromagnet 38y- is controlled equally, and the motor rotor 62 Is held at the center position. In step S103, the attraction force of the electromagnets 37y− and 38y− is made larger than the attraction force of the electromagnets 37y + and 38y +, and the motor rotor 62 (rotor 4) is biased downward in the figure of the stator 61. The rotor 4 shown in FIG. 2 is eccentric in the y-axis direction so as to move in parallel.

  Next, in step S104, the switching elements Tr1 and Tr6 are turned on so that a current flows as U → V in FIG. When such a motor current is passed, as shown in FIG. 6A, the N-pole direction is between the U phase and the W ′ phase, and the N-pole direction is between the W phase and the U ′ phase. A strong magnetic field is formed. Normally, when the motor is rotated, on / off control is performed by the switching elements Tr1 to Tr6 so that a rotating magnetic field is formed. In step S104, the eccentric direction of the motor rotor 62 is the S pole as shown in FIG. Alternatively, control is performed so as to form a magnetic field (fixed magnetic field) that becomes an N pole.

  The direction of the N pole of the fixed magnetic field can be 6 directions (at intervals of 60 degrees) including the case shown in FIG. 6A, and 12 types of fixed magnetic fields are possible if the magnetic field with NS reversed is also included. . When the rotor is decentered in step S103, the rotor is decentered in any of the above six directions, and in step S104, a fixed magnetic field is formed such that the decentering direction is the S pole or the N pole. FIG. 5 and FIG. 6 (a) show an example.

  When the arrangement of the S poles and N poles of the permanent magnet is as shown in FIG. 6A and the motor rotor 62 is stopped, when the fixed magnetic field as shown in FIG. 6A is formed, the motor rotor 62 turns clockwise. Rotate to. Then, as shown in FIG. 6B, when the N pole of the permanent magnet passes the S pole of the fixed magnetic field, a reverse torque is applied and the motor rotor 62 rotates counterclockwise. Such rotational vibration of the motor rotor 62 gradually decreases, and after a certain amount of time has elapsed, the motor rotor 62 stops in a state as shown in FIG. The time required for this stop depends on the weight of the rotor 4 and the suction force on the motor stator 62 side. In the present embodiment, a time during which the rotational vibration of the motor rotor 62 is reduced to an extent that does not affect the motor start is measured in advance, and the stop time is stored in the memory 705.

  In step S105, it is determined whether a predetermined stop time (the above-described stop time stored in the memory 705) has elapsed since the fixed magnetic field was generated. If it is determined in step S105 that the predetermined stop time has elapsed, the process proceeds to step S106, the control of the magnetic bearing 3 is returned to the normal control, and the rotor 4 is moved to the center of the magnetic bearing 3 as shown in FIG. Magnetically levitated. Then, it progresses to step S107, the rotational drive of the motor 6 is started, and it transfers to the normal operation mode of step S108.

  As described above, in the present embodiment, a fixed magnetic field is formed to position the motor rotor 62 at a predetermined rotational position, and a rotational magnetic field is formed from this state to start rotation. At this time, since the motor rotor 62 is eccentric using the magnetic bearing 3, the stop time of the rotational vibration generated during positioning can be shortened compared to the case where the magnetic rotor 3 is not eccentric.

  In the operation example shown in FIG. 4, the fixed magnetic field is formed after the motor rotor 62 is decentered, but conversely, the motor rotor 62 may be decentered after the fixed magnetic field is formed. You may make it do. For example, when starting rotation from a state where the motor rotor 62 is not stopped but slightly rotating, the rotation is suppressed by forming the fixed magnetic field first, so that the motor rotor 62 is decentered. The influence of rotation can be reduced.

FIG. 8 is a diagram illustrating the force acting between the motor rotor 62 and the motor stator 61. FIG. 8A shows a case where the motor rotor 62 is eccentric, and FIG. 8B shows a case where the motor rotor 62 is not eccentric. The approximate force F acting between the motor rotor 62 and the motor stator 61 can be calculated by the following equation (1). In Equation (1), Q1 and Q2 are the strengths of the magnetic poles generated by the opposing magnetic poles, and r is the distance between the magnetic poles.
F = Q1 · Q2 / r ² (1)

  For example, a case is considered where the distance between the magnetic poles is 150 μm and the distance in which the motor rotor 62 can move in the radial direction from the normal flying position is 100 μm. At this time, if the motor rotor 62 is decentered by a movable maximum value of 100 μm, as shown in FIG. 9 times the magnetic pole strength. On the other hand, the strength of the magnetic pole on the upper side in the drawing where the distance between the magnetic poles is increased is reduced to 0.36 times. As a result, the total magnetic pole strength when eccentric is 4.68 times. As the magnetic force increases, the rotational vibration is significantly attenuated and immediately stops in the state shown in FIG.

  Thus, since the motor rotor 62 quickly stops at a predetermined rotation position (the position shown in FIG. 6A) determined in advance, the motor rotor 62 is moved to the center position as shown in FIG. 7A in a short time. Can be returned to. Therefore, by forming a rotating magnetic field as shown in FIG. 7B, the motor rotor 62 can be reliably started to rotate in a desired rotation direction.

  On the other hand, as shown in FIG. 8B, when the fixed magnetic field is formed without decentering the motor rotor 62, the magnetic pole force is smaller than that when the motor rotor 62 is decentered. It will take. If the rotational drive is started before the rotational vibration is settled, the reverse rotation may occur depending on the timing of the rotational vibration. In particular, in the case of a molecular pump such as a turbo molecular pump, since the rotor weight is relatively large, it takes a long time until the rotational vibration is settled. Therefore, it is very effective to make it eccentric as in this embodiment.

  In the case of a magnetic bearing type turbo molecular pump, a mechanical bearing is provided to support the rotor 4 when the magnetic bearing is stopped. In general, the rotor 4 can be eccentric until it contacts the mechanical bearing. However, if the rotor 4 is in contact with the rotor 4 in a rotating state, there is a risk that inconveniences such as contact of the rotor blades with the stator side occur. Therefore, it is preferable that the rotor 4 be eccentric so as not to contact the mechanical bearing.

  In the embodiment described above, the magnetic bearing type turbo molecular pump has been described as an example. However, the present invention can be applied not only to the magnetic bearing type turbo molecular pump but also to a vacuum pump using the magnetic bearing for floating the rotor. Further, the present invention is not limited to the vacuum pump that detects the rotor rotational speed using the back electromotive voltage, but can be applied to, for example, a vacuum pump that detects the rotational speed using an inductance type rotational sensor, which causes a cost increase. The rotation startability can be improved without providing a sensor for detecting the rotor rotational position.

  Each of the embodiments described above may be used alone or in combination. This is because the effects of the respective embodiments can be achieved independently or synergistically. In addition, the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired.

  1: pump body, 2: power supply device, 3: magnetic bearing, 4: rotor, 6: motor, 7: motor control unit, 8: bearing control unit, 9: main control unit, 37x, 37y, 38x, 38y, 39z : Electromagnet, 61: Motor stator, 62: Motor rotor, 70: Control circuit, 705: Memory

Claims (3)

A magnetic bearing for magnetically levitating the pump rotor;
A magnetic bearing control unit for controlling an exciting current of the magnetic bearing to control a floating position of the pump rotor;
A motor rotor fixed to the pump rotor and having a permanent magnet;
A motor stator for rotationally driving the motor rotor;
The pump rotor is decentered in a predetermined radial direction from the center position of the bearing by the magnetic bearing, and a fixed magnetic field facing the predetermined radial direction is generated by the motor stator, thereby adjusting an angle of the rotation direction of the pump rotor. First adjusting means;
Second adjusting means for returning the pump rotor whose angle in the rotational direction is adjusted by the first adjusting means to the center position of the bearing from a state eccentric in the predetermined radial direction;
A vacuum pump comprising: a motor control unit that generates, by the motor stator, a rotating magnetic field for rotating the pump rotor returned to the bearing center position by the second adjusting means. The vacuum pump according to claim 1, wherein
The vacuum pump characterized in that the second adjustment means returns the pump rotor to the bearing center position after a predetermined stop time has elapsed since the angle adjustment by the first adjustment means was started. A vacuum pump rotation starting method in which a pump rotor is magnetically levitated by a magnetic bearing and rotated by a motor,
Decentering the pump rotor in a predetermined radial direction from a bearing center position by the magnetic bearing;
Generating a fixed magnetic field directed in the predetermined radial direction by a motor stator of the motor;
Returning the pump rotor to a bearing center position after a predetermined time;
And a step of rotating the pump rotor by the motor.

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