Electromagnetic rotating device and vacuum pump equipped with electromagnetic rotating device

Abstract

An electromagnetic rotating apparatus may include an electromagnet winding that consumes power generated during regeneration. A motor voltage monitoring circuit detects that a voltage at a motor driving main circuit is higher than a voltage during normal operation, due to overshoot or the like after arrival at a set speed during deceleration or acceleration of a motor. The motor voltage monitoring circuit transmits a high-voltage detection signal to a braking current adjusting circuit and a magnetic bearing control circuit. Upon receiving the high-voltage detection signal, the braking current adjusting circuit reduces a braking current command value for the motor so as to maintain an excitation voltage for the motor constant or reduce this excitation voltage, and an amplifier control circuit in the magnetic bearing control circuit increases a bias current flowing through an electromagnet winding to increase power consumption.

Claims

1. A vacuum pump comprising: a motor; a rotor shaft that is rotationally driven by the motor; an electromagnet through which, as an excitation current, a displacement current generated in accordance with a positional deviation of the rotor shaft and superimposed on a bias current is passed; a power supply that supplies a direct current; a motor driving main circuit that supplies the direct current supplied by the power supply to the motor; a motor voltage monitoring circuit that monitors a voltage of the direct current; detection signal output means for outputting a detection signal when the voltage monitored by the motor voltage monitoring circuit reaches a predetermined value or a value larger than the predetermined value; and a magnetic bearing control circuit that increases the bias current that excites the electromagnet, based on the detection signal that is output by the detection signal output means, wherein a regenerated electric power generated by a rotation of the rotor shaft is consumed by increasing the bias current of the electromagnet.

2. The vacuum pump according to claim 1, further comprising: a motor driving control circuit that controls a motor current passing through the motor in accordance with a command value; and a braking current adjusting circuit that reduces the command value for the motor current, based on the detection signal that is output by the detection signal output means.

3. The vacuum pump according to claim 2, wherein the power supply supplies the magnetic bearing control circuit with a direct current of a voltage substantially identical to a voltage supplied to the motor driving main circuit.

4. The vacuum pump according to claim 1, wherein the power supply supplies the magnetic bearing control circuit with a direct current of a voltage identical to a voltage supplied to the motor driving main circuit.

5. A vacuum pump comprising an electromagnetic rotating apparatus comprising: a motor; a rotor shaft that is rotationally driven by the motor; a rotor blade attached to the rotor shaft; an electromagnet through which, as an excitation current, a displacement current generated in accordance with a positional deviation of the rotor shaft and superimposed on a bias current is passed; a power supply that supplies a direct current; a motor driving main circuit that supplies the direct current supplied by the power supply to the motor; a motor voltage monitoring circuit that monitors a voltage of the direct current; detection signal output means for outputting a detection signal when the voltage monitored by the motor voltage monitoring circuit reaches a predetermined value or a value larger than the predetermined value; and a magnetic bearing control circuit that increases the bias current that excites the electromagnet, based on the detection signal that is output by the detection signal output means, wherein a regenerated electric power generated by a rotation of the rotor shaft is consumed by increasing the bias current of the electromagnet.

6. The vacuum pump of claim 5, wherein the electromagnetic rotating apparatus further comprises: a motor driving control circuit that controls a motor current passing through the motor in accordance with a command value; and a braking current adjusting circuit that reduces the command value for the motor current, based on the detection signal that is output by the detection signal output means.

7. The vacuum pump of claim 6, wherein the power supply supplies the magnetic bearing control circuit with a direct current of a voltage identical to a voltage supplied to the motor driving main circuit.

8. The vacuum pump of claim 5, wherein the power supply supplies the magnetic bearing control circuit with a direct current of a voltage identical to a voltage supplied to the motor driving main circuit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a general block diagram of a first embodiment of the present invention;

(2) FIG. 2 is a control block diagram for a braking current for a motor;

(3) FIG. 3 is a configuration diagram of a magnetic bearing control circuit;

(4) FIG. 4 is a control block diagram for a current passed through an electromagnet winding;

(5) FIG. 5 is a system diagram for control of a radial position;

(6) FIG. 6 is a time chart;

(7) FIG. 7 is a diagram indicating how regenerated electric power is generated during acceleration;

(8) FIG. 8 is a general block diagram of a second embodiment of the present invention;

(9) FIG. 9 is a longitudinal cross-sectional view of a turbo-molecular pump main body;

(10) FIG. 10 is a general block diagram of a conventional technique; and

(11) FIG. 11 is a configuration diagram of a motor driving main circuit.

DETAILED DESCRIPTION

(12) Embodiments of the present invention will be described below. FIG. 1 depicts a general block diagram of a first embodiment of the present invention. Elements of the first embodiment which are identical to the corresponding elements in FIG. 10 are denoted by identical reference numerals and will not be described below.

(13) FIG. 1 depicts that an AC power supply is connected to a rectifier circuit 10 in a control apparatus 400. The rectifier circuit 10 rectifies and converts an alternating current into a direct current of 100 to 150 V. The direct current flows between power supply lines 1a and 1b and is input to a motor driving main circuit 30. Between the power supply lines 1a and 1b, a motor voltage monitoring circuit 60 is disposed to monitor a voltage at the motor driving main circuit 30.

(14) The motor voltage monitoring circuit 60 detects that the voltage between the power supply lines 1a and 1b has become higher than a predetermined voltage during deceleration or acceleration of a motor 121.

(15) At this time, the motor voltage monitoring circuit 60 outputs a high-voltage detection signal. The high-voltage detection signal is input to a braking current adjusting circuit 70 and a magnetic bearing control circuit 50. When the high-voltage detection signal is input to the braking current adjusting circuit 70, a braking current command value calculating section 71 depicted in FIG. 2 calculates a command value for a braking current for the motor 121.

(16) A deviation section 75 determines a deviation of the command value for the braking current calculated by the braking current command value calculating section 71 from a current value detected by a current detecting section 73 disposed in series with transistors 9, 13, and 17. A PWM control signal is generated which results from pulse width modulation by a PWM control section 77 based on the deviation.

(17) The PWM control signal is input to a gate of each of the transistors 7, 9, 11, 13, 15, and 17 in the motor driving main circuit 30 to adjust the braking current.

(18) A direct current that is output by the rectifier circuit 10 is reduced to approximately several V by a direct-current stabilizing power supply circuit 40. The resultant direct current is input to the motor driving control circuit 20 and the magnetic bearing control circuit 50 as a control voltage. Furthermore, the voltage between the power supply lines 1a and 1b is supplied to the magnetic bearing control circuit 50.

(19) FIG. 3 is a configuration diagram of the magnetic bearing control circuit 50. The magnetic bearing control circuit 50 includes an amplifier circuit 250 and an amplifier control circuit 271. The control voltage from the direct-current stabilizing power supply circuit 40 is input to the amplifier control circuit 271.

(20) FIG. 3 depicts that the turbo-molecular pump main body 100 is provided with a node common to electromagnet windings 151 providing electromagnets 104, 105, 106A, and 106B, respectively (the node is hereinafter referred to as the common node C). Furthermore, each electromagnet winding 151 is connected to the common node C at one end 151a of the winding. Additionally, the electromagnet winding 151 is connected to a transistor 261 and a diode 265 in the amplifier circuit 250 at the other end 151b of the winding (a node at the other end 151b is hereinafter referred to as a node E).

(21) In this regard, the transistor 261 is a power MOSFET with a drain terminal 261a connected to the other end 151b of the electromagnet winding 151 and a source terminal 261b connected a negative pole 1b of the rectifier circuit 10 via a current detecting circuit 255. Furthermore, the diode 265 is a diode for current regeneration or a flywheel including a cathode terminal 265a connected to a positive pole 1a of the rectifier circuit 10 and an anode terminal 265b connected to the other end 151b of the electromagnet winding 151.

(22) The current detecting circuit 255 connected to the source terminal 261b of the transistor 261 has a detection resistor 256 connected to the negative pole 1b at one end of the resistor and to the source terminal 261b of the transistor 261 at the other end of the resistor, and a detection section 257 that detects an electromagnet current iL in a voltage at the other end of the detection resistor 256. The detection section 257 detects the electromagnet current iL flowing through the electromagnet winding 151 to output a current detection signal 273 corresponding to a result of the detection to the amplifier control circuit 271.

(23) The amplifier circuit 250 configured as described above is provided for each of the electromagnet windings 151 providing the electromagnets 104, 105, 106A, and 106B, respectively.

(24) The amplifier control circuit 271 is a circuit in a DSP section (not depicted in the drawings). The high-voltage detection signal detected by the motor voltage monitoring circuit 60 is input to the amplifier control circuit 271 as depicted in FIG. 4. When the high-voltage detection signal is input to the amplifier control circuit 271, a current command value calculating section 371 calculates a command value for a bias current passed through the electromagnet winding 151.

(25) A bias current command value 373 resulting from the calculation by the current command value calculating section 371 is input to a deviation section 375 after being added in an addition section 387 to one of two signals output by a compensation circuit 379, in order to drive an electromagnet 105X+ providing a lower radial electromagnet 105, as depicted in FIG. 4 and a system diagram for control of a radial position in FIG. 5.

(26) Furthermore, to drive an electromagnet 105X, the other signal that is output by the compensation circuit 379 is inverted by an inversion circuit 381, and the resultant signal is input to the deviation section 375 after being added in the addition section 389 to the bias current command value 373.

(27) The addition of the bias current command value is intended to linearly perform radial positional control on a rotor 103. That is, a constant direct bias current and a braking current allowing the rotor 103 to be held in position are passed through the electromagnet 105X+ and the electromagnet 105X in a superimposed manner.

(28) The compensation circuit 379 receives, for example, a deviation, from a position command value 385, of the radial position of the rotor 103 detected by a position detecting circuit 383 in a lower radial sensor 108, which deviation has been calculated by a deviation section 341.

(29) FIG. 4 depicts that the deviation section 375 compares a value for the electromagnet current iL detected by the current detecting circuit 255 with a current command value and that a PWM control section 377 determines a time for which the electromagnet current iL is increased (increase time Tp1 described below) and a time for which the electromagnet current iL is reduced (reduction time Tp2 described below), and based on these times, determines a pulse width time for a gate driving signal 274 output to a gate terminal of the transistor 261 within a control cycle Ts that is one period according to PWM control.

(30) Moreover, FIG. 3 depicts that a switching circuit 280 is connected to the common node C in the amplifier circuit 250. In the switching circuit 280, a transistor 281 and a diode 285 are connected to the common node C.

(31) The diode 285 is a diode for current regeneration or a flywheel including a cathode terminal 285a connected to the common node C and an anode terminal 285b connected to the negative pole 1b as is the case with the amplifier circuit 250. Furthermore, the transistor 281 is a power MOSFET including a drain terminal 281a connected to the positive pole 1a of the rectifier circuit 10 and a source terminal 281b connected to the common node C.

(32) A switching signal 276 from the amplifier control circuit 271 is output to a gate terminal of the transistor 281. The amplifier control circuit 271 determines a pulse width time for the switching signal 276 output to the gate terminal of the transistor 281 within the control cycle Ts as is the case with the control performed on the amplifier circuit 250.

(33) In such a configuration, when the transistor 261 in the amplifier circuit 250 is turned on and the transistor 281 in the switching circuit 280 is turned on, a current flows from the positive pole 1a the transistor 281 through the common node C, the electromagnet winding 151, and the transistor 261 (and the current detecting circuit 255) to the negative pole 1b. Consequently, the current from the positive pole 1a is supplied to the electromagnet winding 151, thus increasing the electromagnet current iL (this state is hereinafter referred to as an increase mode A1).

(34) On the other hand, when the transistor 261 in the amplifier circuit 250 is turned off and the transistor 281 in the switching circuit 280 is turned off, a counter electromotive force is generated in the electromagnet winding 151 to pass regenerated electric power from the negative pole 1b through the diode 285, the common node C, the electromagnet winding 151, and the diode 265 to the positive pole 1a. Thus, electromagnetic energy generated by the electromagnet winding 151 is consumed to reduce the electromagnet current iL (this state is hereinafter referred to as a reduction mode A2).

(35) Moreover, when the transistor 261 in the amplifier circuit 250 is turned on and the transistor 281 in the switching circuit 280 is turned off, a counter electromotive force is generated in the electromagnet winding 151 to pass a flywheel current from the negative pole 1b through the diode 285, the common node C, the electromagnet winding 151, and the transistor 261 (and the current detecting circuit 255) to the negative pole 1b. At this time, no potential difference occurs between the opposite ends 151a and 151b of the electromagnet winding 151, thus maintaining the electromagnet current iL approximately constant (this state is hereinafter referred to as a constant mode A3).

(36) Also in a state other than a state of the constant mode A3, when the transistor 261 in the amplifier circuit 250 is turned off and the transistor 281 in the switching circuit 280 is turned on, a counter electromotive force is generated in the electromagnet winding 151 to pass a flywheel current from the positive pole 1a through the transistor 281, the common node C, the electromagnet winding 151, and the diode 265 to the positive pole 1a. Thus, also in this case, the electromagnet current iL is maintained approximately constant (this state is hereinafter referred to as a constant mode A4).

(37) FIG. 6 depicts a time chart illustrating adjustment of a control phase provided to the transistor 261 and the like by the amplifier circuit 250 and a switching phase provided to the transistor 281 and the like by the switching circuit 280.

(38) FIG. 6 depicts that the switching circuit 280 is controlled such that, during the control cycle Ts, the time during which the transistor 281 is on is the same as the time during which the transistor 281 is off. In this case, the transistor 281 is on from a point in time corresponding to the beginning of the control cycle Ts (time 0) until a point in time corresponding to the half of the control cycle Ts (time 0.5Ts).

(39) Thus, a voltage at the common node C is substantially the same as a voltage at the negative pole 1b due to, for example, the counter electromotive force generated in the electromagnet winding 151 (this voltage is hereinafter referred to as a voltage VL). On the other hand, the transistor 281 is on from a point in time corresponding to the half of the control cycle Ts (time 0.5Ts) until a point in time corresponding to the end of the control cycle Ts (time Ts). Consequently, the voltage at the common node C is substantially the same as a voltage at the positive pole 1a (this voltage is hereinafter referred to as a voltage VH).

(40) When the value for the electromagnet current iL detected by the current detecting circuit 255 is smaller than the current command value, the amplifier control circuit 271 performs control such that the electromagnet current iL is increased. In this case, control is performed such that, during one control cycle Ts, a state of the increase mode A1 lasts for the above-described increase time Tp1 and a state of one of the constant modes A3 and A4 lasts for the remaining time.

(41) Specifically, the transistor 281 in the switching circuit 280 is on from the time 0.5Ts until the time Ts, and thus, the transistor 261 is on for the time Tp1 beginning at the time 0.5Ts to allow the state of the increase mode A1 to last for the increase time Tp1. Furthermore, when the time Tp1 elapses, the transistor 261 is turned off to establish the state of the constant mode A4.

(42) On the other hand, from the time 0 until the time 0.5Ts, the transistor 281 in the switching circuit 280 is off (that is, the state of the increase mode A1 cannot be established). Consequently, the transistor 261 is turned on to establish the constant mode A3. Thus, during one control cycle Ts, the electromagnet current iL is increased for the increase time Tp1.

(43) On the other hand, when the value for the electromagnet current iL detected by the current detecting circuit 255 is larger than the current command value, the amplifier control circuit 271 performs control such that the electromagnet current iL is reduced. In this case, control is performed such that, during one control cycle Ts, the state of the reduction mode A2 lasts for the above-described reduction time Tp2 and the state of one of the constant modes A3 and A4 lasts for the remaining time.

(44) Specifically, the transistor 281 in the switching circuit 280 is off from the time 0 until the time 0.5Ts, and thus, the transistor 261 is off for the time Tp2 ending at the time 0.5Ts to allow the state of the reduction mode A2 to last for the reduction time Tp2. Furthermore, before the transistor 261 is turned off, the transistor 261 is kept on to maintain the state of the constant mode A3.

(45) On the other hand, from the time 0.5Ts until the time Ts, the transistor 281 in the switching circuit 280 is on (that is, the state of the reduction mode A2 cannot be established). Consequently, the transistor 261 is turned off to establish the constant mode A4. Thus, during one control cycle Ts, the electromagnet current iL is reduced for the reduction time Tp2.

(46) Moreover, when the value for the electromagnet current iL detected by the current detecting circuit 255 matches with the current command value, the amplifier control circuit 271 performs control such that the electromagnet current iL is maintained constant. In this case, control is performed such that one of the constant modes A3 and A4 is constantly present during one control cycle Ts.

(47) Specifically, from the time 0 until the time 0.5Ts, the transistor 281 in the switching circuit 280 is off, and thus, the transistor 261 is turned on to establish the state of the constant mode A3.

(48) On the other hand, from the time 0.5Ts until the time Ts, the transistor 281 in the switching circuit 280 is on, and thus, the transistor 261 is turned off to establish the state of the constant mode A4. Thus, the electromagnet current iL is maintained at a predetermined level.

(49) As described above, the electromagnet current iL can be increased or reduced or maintained constant so as to be equal to the current command value, by controlling the amplifier circuit 250 while controlling the switching circuit 280.

(50) Now, operations of the first embodiment will be described. In FIG. 1, unlike in FIG. 10, the regeneration resistor 3 and the transistor 5 are omitted from the motor driving main circuit 30. Regenerated electric power consumed by the regeneration resistor 3 according to the conventional technique is consumed by the electromagnet winding 151.

(51) When the energy consumed by the electromagnet winding 151 is not equal to all of the energy consumed by the regeneration resistor 3 according to the conventional technique, then without the regeneration resistor 3, the voltage at the motor driving main circuit 30 increases when a regenerative current flows at the time of overshoot following arrival at a set rotation speed during deceleration of the motor 121 or during acceleration the motor 121 as depicted in FIG. 7. When the voltage thus increases, an electronic element may be broken. Consequently, an increase in voltage needs to be prevented by adjusting the braking current.

(52) Thus, when the voltage at the motor driving main circuit 30 becomes at least 10 to 20% higher during deceleration or acceleration of the motor 121 than during normal operation, the motor voltage monitoring circuit 60 detects this state and transmits a high-voltage detection signal to the braking current adjusting circuit 70 and the magnetic bearing control circuit 50.

(53) Upon receiving the high-voltage detection signal, the braking current adjusting circuit 70 reduces a braking current command value for the motor 121 so as to maintain the excitation voltage constant or reduce the excitation voltage. A deviation, from the braking current command value, of a current flowing through transistors 9, 13, and 17 is determined. A PWM control signal adjusted based on the deviation is input to a gate of each of the transistors 7, 9, 11, 13, 15, and 17. At this time, a braking current flowing through the motor 121 decreases, and the reduced braking current lowers regenerated electric power generated between power supply lines 1a and 1b.

(54) On the other hand, upon receiving the high-voltage detection signal, the amplifier control circuit 271 in the magnetic bearing control circuit 50 calculates a current command value including a bias current so as to increase the current flowing through the electromagnet winding 151 by a factor of approximately 1.2 to 3 compared to the bias current during the normal operation. That is, when the voltage at the motor driving main circuit 30 increases, the current including the bias current and flowing through the electromagnet winding 151 is increased, thereby increasing power consumption.

(55) As described above, even when the regeneration resistor 3 is removed, the regenerated electric power may be consumed and the pump may be stably stopped. Furthermore, the removal of the regeneration resistor 3 eliminates the need for an installation space for the regeneration resistor, leading to the size reduction of a control apparatus. Additionally, a switching element that turns on and off the regeneration resistor 3 can be made unnecessary, reducing costs.

(56) The regeneration resistor 3 is removed in the above description but may be left. In this case, the electromagnet winding 151 side consumes most of the regenerated energy, enabling a reduction in the capacities of the regeneration resistor 3 and the switching element that turns the regeneration resistor 3 on and off. Furthermore, the pump may be quickly stopped.

(57) The high-voltage detection signal is represented as a reference character but may be represented as a consecutive voltage value. Alternatively, the high-voltage detection signal may be represented as a reference character generated in a step-by-step manner in accordance with the level of the voltage value. The consecutive voltage value enables the braking current and the bias current to be consecutively adjusted. The step-by-step reference character allows the adjustment of the braking current and the bias current to be changed in a step-by-step manner.

(58) Now, a second embodiment of the present invention will be described. FIG. 8 depicts a general block diagram of the second embodiment of the present invention. The same elements as those in FIG. 1 are denoted by the same reference numerals and will thus not be described.

(59) Control apparatus 500 in FIG. 8 is different from the control apparatus in FIG. 1 in that, in the former case, the direct current between the power supply lines 1a and 1b is supplied to the magnetic bearing control circuit 50, whereas, in the latter case, a DC voltage reduced down to 40 to 60 V by the direct-current stabilizing power supply circuit 40 is supplied to the magnetic bearing control circuit 50. One direct-current stabilizing power supply circuit 40 can be branched into a circuit for control and a circuit for a magnetic bearing. However, the direct-current stabilizing power supply circuit 40 has a larger capacity in the second embodiment than in the first embodiment.

EXPLANATION OF REFERENCE NUMERALS

(60) 1: Power supply line; 3: Regeneration resistor; 5 to 17, 261, 281: Transistor; 10: Rectifier circuit; 20: Motor driving control circuit; 30: Motor driving main circuit; 40: Direct-current stabilizing power supply circuit; 50: Magnetic bearing control circuit; 60: Motor voltage monitoring circuit; 70: Braking current adjusting circuit; 71: Braking current command value calculating section; 73: Current detecting section; 75, 375: Deviation section; 77, 377: PWM control section; 100: Turbo-molecular pump main body; 102: Rotor blade; 104: Upper radial electromagnet; 105: Lower radial electromagnet; 106A, 106B: Axial electromagnet; 113: Rotor shaft; 121: Motor; 151: Electromagnet winding; 250: Amplifier circuit; 255: Current detecting circuit; 256: Detection resistor; 257: Detection section; 265, 285: Diode; 271: Amplifier control circuit; 273: Current detection signal; 274: Gate driving signal; 276: Switching signal; 280: Switching circuit; 300, 400, 500: Control apparatus; 371: Current command value calculating section; 373: Bias current command value.