JPH08189527A - Magnetic bearing - Google Patents

Abstract

PURPOSE: To miniaturize an electromagnet by limiting amplified exciting current to a predetermined current value or less when the temperature of the electromagnet is detected by a temperature detecting means to be higher than a predetermined temperature. CONSTITUTION: When the deflection of a rotor 12 is not temporary one caused by the external turbulence, but caused by abnormalities generated in a rotary system itself, large current may flow continuously through a coil 24a by the control of a control circuit 50. Then, an operation amplifier 54 compares the voltage from a temperature detector 58 with the reference voltage from a power source 56 to supply a comparation signal to a limiter circuit 36. The voltage from the power source 56 is set to a value equal to that of the voltage from the temperature detector 58 when the coil 24a reaches the maximum allowable temperature. The limiter circuit 36 lowers the control voltage from a PID control circuit 34 to fixed voltage according to a signal showing that the coil 24a has a temperature higher than the maximum allowable temperature. Thus, the diameter of the coil wire can be set with reference to one electrified by current smaller than the maximum current to miniaturize an electromagnet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic bearing, for example, a magnetic bearing used in a turbo molecular pump.

[0002]

2. Description of the Related Art A magnetic bearing supports a rotor in a non-contact manner by a magnetic force, and in a control type magnetic bearing, the exciting current of an electromagnet that generates the magnetic force is changed according to the position of the rotor, so that the rotor is rotated. It is designed to control the floating position of.

For example, when the rotor is largely displaced from a predetermined floating position due to disturbance, a relatively large current is applied to the coil of the electromagnet in order to return the rotor to the predetermined floating position. When a large current is applied, the coil of the electromagnet heats up and reaches a high temperature.Therefore, in order to prevent melting of the mold or coil due to heat, the coil wire diameter should be increased and the coil should be energized at the maximum current. The amount of heat generated by itself is kept within the allowable value.

[0004]

For this reason, in the conventional magnetic bearing, a coil having a large wire diameter adapted to the maximum current is used although the current supplied during normal operation is small. Therefore, the electromagnet wound around this coil becomes large, and, for example, a motor using a magnetic bearing also becomes large.

Therefore, an object of the present invention is to provide a magnetic bearing which can reduce the size of an electromagnet.

[0006]

According to a first aspect of the invention, an electromagnet for magnetically levitating a rotor, a position detecting means for detecting the position of the rotor, and an electromagnet for the electromagnet based on a detection value of the position detecting means. Exciting current amplifying means for amplifying exciting current, temperature detecting means for detecting whether or not the temperature of the electromagnet is equal to or higher than a predetermined temperature, and temperature detecting means for detecting that the temperature of the electromagnet is equal to or higher than the predetermined temperature. In this case, the magnetic bearing is provided with current limiting means for limiting the exciting current amplified by the exciting current amplifying means to a predetermined current value or less.

According to a second aspect of the present invention, in the magnetic bearing according to the first aspect, the temperature detecting means uses, for example, a thermal sensor such as a thermistor or a resistance temperature detector, and the temperature of the electromagnet is equal to or higher than the predetermined temperature. The above-mentioned object is achieved by detecting whether or not In the invention according to claim 3, an electromagnet for magnetically levitating the rotor, a position detecting means for detecting the position of the rotor, and an exciting current amplifying means for amplifying an exciting current of the electromagnet based on a detection value of the position detecting means. And a current limiting means for limiting the exciting current amplified by the exciting current amplifying means to a predetermined current value or less when the voltage applied to the electromagnet is continuously a predetermined voltage value or more for a predetermined time, in a magnetic bearing. In order to achieve the above purpose.

According to a fourth aspect of the present invention, an electromagnet for magnetically levitating the rotor, a position detecting means for detecting the position of the rotor, and an excitation for amplifying an exciting current of the electromagnet based on a detection value of the position detecting means. The current amplifying means and the current limiting means for limiting the exciting current to a predetermined current value or less when the exciting current amplified by the exciting current amplifying means is continuously a predetermined current value or more for a predetermined time continuously. It is provided in a bearing to achieve the above object.

According to the invention of claim 5, claim 3 or 4
In the magnetic bearing described above, the above-described object is achieved by the predetermined voltage value and the predetermined current value being respectively determined by the wire diameter of the coil in the electromagnet.

[0010]

In the magnetic bearing of the first aspect, the exciting current amplifying means amplifies the exciting current of the electromagnet based on the detection value of the position detecting means, so that the rotor is magnetically levitated. The current limiting means limits the exciting current amplified by the exciting current amplifying means to a predetermined current value or less when the temperature detecting means detects that the temperature of the electromagnet is equal to or higher than the predetermined temperature.

According to another aspect of the magnetic bearing of the present invention, the temperature detecting means detects whether or not the temperature of the electromagnet is equal to or higher than the predetermined temperature by using a thermal sensor such as a thermistor or a resistance temperature detector. . In the magnetic bearing of the third aspect, the exciting current amplifying means amplifies the exciting current of the electromagnet based on the detection value of the position detecting means, so that the rotor is magnetically levitated. The current limiting means limits the exciting current amplified by the exciting current amplifying means to a predetermined current value or less when the voltage applied to the electromagnet is continuously a predetermined voltage value or more for a predetermined time.

According to another aspect of the magnetic bearing of the present invention, the exciting current amplifying means amplifies the exciting current of the electromagnet based on the detection value of the position detecting means, so that the rotor is magnetically levitated. The current limiting means limits the exciting current to a predetermined current value or less when the exciting current amplified by the exciting current amplifying means is continuously above a predetermined current value for a predetermined time.

[0013]

Embodiments of the magnetic bearing of the present invention will be described in detail below with reference to FIGS. 1 to 6. Figure 1
2 shows a part of the mechanical structure of the magnetic bearing 10 according to the embodiment of FIG.

As shown in this figure, in the magnetic bearing 10,
Electromagnets 14a and 14b and electromagnets 16a and 16b are arranged with the rotor 12 interposed therebetween. Further, similarly to the electromagnets 14a, 14b, 16a, 16b, a position sensor 20a for detecting the radial position of the rotor 12,
20b, 22a, 22b are arranged respectively.

Electromagnets 14a, 14b, 16a, 16b
Are coils 24a, 24b and 26a, 2 respectively.
When 6b is energized, a magnetic attraction force is exerted on the rotor 12, and the rotor 12 is magnetically levitated at a position where the attraction force is balanced. Electromagnets 14a, 14b and electromagnet 16
The currents of a and 16b are the position sensors 20a and 20b, respectively.
Feedback control is performed according to b and the detection signals of the position sensors 22a and 22b, and the floating position of the rotor 12 is held at a predetermined position by this current control.

The current control of the electromagnets 14a, 14b, 16a, 16b is performed for each axis, that is, the electromagnets 14a and 14b.
b and the electromagnets 16a and 16b are independently performed, and the magnetic bearing 10 is provided with a control circuit for this current control for each axis. Since the control circuit for each axis has the same configuration, the control circuit for the electromagnets 14a and 14b will be described below as a representative.

FIG. 2 shows a part of the control system of the magnetic bearing 10. Control circuit 30 for electromagnets 14a and 14b
Is the rotor 1 from the detection signals of the position sensors 20a and 20b.
Position detection circuit 32 for generating a position signal indicating the position of 2
And based on the position signal from the position detection circuit 32, the rotor 1 performs the arithmetic processing such as proportional operation, integral operation, and differential operation.
And a PID control circuit 34 that generates a predetermined control voltage corresponding to the displacement of 2.

The PID control circuit 34 applies the generated control voltage to a non-inverting input terminal of an operational amplifier 38 as a power amplifier via a limiter circuit 36. The output terminal of the operational amplifier 38 is connected to the base of a transistor 39 whose collector side is connected to the coil 24a of the electromagnet 14a, and the current of the coil 24a is controlled according to the control voltage from the PID control circuit 34. ing. Although not shown, a similar amplifier that amplifies the current of the coil 24b according to the control voltage from the PID control circuit 34 is connected to the limiter circuit 36.

A resistor R is provided on the emitter side of the transistor 39.
It is grounded through and is connected to the inverting input terminal of the operational amplifier 38 and the inverting input terminal of the comparator 40. The power supply 4 is connected to the non-inverting input terminal of the comparator 40.
2, the reference voltage is applied. Comparator 4
0 compares the reference voltage of the power supply 42 with the emitter-side voltage of the transistor 39, and starts the operation of the timer 44 when the emitter voltage exceeds the reference voltage.

The reference voltage of the power supply 42 is set to, for example, the same value as the emitter-side voltage when 1/2 (specified current) of the maximum current Ir that can be continuously supplied is supplied to the coil 24a. As a result of the comparison by the comparator 40, the timer 44 determines that the voltage on the emitter side of the transistor 39 is the power
When a signal indicating that the voltage is larger than the voltage of 2 is continuously supplied for a certain period of time, the limiter circuit 36 is turned on.
It is designed to supply signals. The measurement time tr of the timer 44 is set to be sufficiently longer than the stabilization time of the current immediately after energization and the damping time of large disturbance during operation. For example, it is set to 1 second, 2 seconds, or 10 seconds.

The limiter circuit 36 is turned on by the timer 44.
By supplying the signal, the control voltage from the PID control circuit 34 is forcibly set to a constant voltage.
Therefore, a constant voltage is applied to the base of the transistor 39, and the coil 24 is amplified according to the applied voltage.
The current of a is also reduced to a predetermined current value. A Zener diode, for example, is used as the limiter circuit 36.

FIG. 3 shows the relationship between the control voltage from the PID control circuit 34 and the current supplied to the coil 24a. When the limiter circuit 36 is not operating, the current I supplied to the coil 24a as shown by the line a in FIG. 3 is controlled by the control voltage V from the PID control circuit 34.
Is amplified in proportion to the maximum current Imax. Current Imax
Is the maximum current required to control the position of the rotor 12.

On the other hand, when the limiter circuit 36 is operating, even if a large control voltage is supplied from the PID control circuit 34, the current I of the coil 24a is the predetermined current Ia as shown by the line b in FIG. It does not exceed the above and is constant. In this embodiment, the value of the control voltage dropped by the limiter circuit 36 is set to be Ia = (1/2) .Imax, but Ia = (2/3) .Imax or Ia
It may be a = (1/3) · Imax.

Next, the operation of the embodiment thus constructed will be described. When the rotor 12 is magnetically levitated by the magnetic bearing 10 and is being rotated by a motor (not shown), if the rotor 12 shakes for some reason, this shake is detected by the position sensors 20a, 20b, 22a, 22b.

The control circuit 30 controls the position sensor 20a,
Corresponding to the shake of the rotor 12 detected by 20b, 22a, 22b, a predetermined exciting current is applied to the electromagnets 14a, 14b,
16a, 16b, the generated rotor 12
Suppress the shake of. For example, in the control circuit 30, a signal indicating the displacement amount of the rotor 12 is supplied from the position detection circuit 32 to the PID control circuit 34, and the PID control circuit 34 causes the PID control circuit 34 to output P
By performing the ID operation or the like, a control voltage corresponding to the displacement amount of the rotor 12 is applied to the non-inverting input side of the operational amplifier 38 via the limiter circuit 36. The operational amplifier 38 applies a voltage corresponding to the difference between the voltage of the coil 24a input to the inverting input and the control voltage from the PID control circuit 34 to the transistor 39, so that the current of the coil 24a is applied to the rotor 1.
A value that suppresses the shake of 2 is set.

Normally, in the current control corresponding to the shake of the rotor 12, the shake of the rotor 12 is rapidly attenuated, so that a large current equal to or higher than the specified power Ir is supplied only for a very short time. However, when the runout of the rotor 12 is not a temporary one caused by a disturbance but an abnormality occurring in the rotating system itself, a large current is continuously supplied to the coil 24a by the control of the control circuit 30 or the like. It may flow to 24b, 26a, 26b.

For example, in a turbo molecular pump or the like using a magnetic bearing, deposits on the rotor blade cause imbalance in the rotor, and in order to cancel this imbalance, a large current is continuously applied to the electromagnet of the magnetic bearing. May flow to. FIG. 4 shows an example of changes in the exciting current in such a case.

The voltage on the emitter side of the transistor 39 is
Since the current is proportional to the current of the coil 24a, the coil 24a
When a large current flows through a, this is applied to the inverting input of the comparator 40 as a voltage increase. When the voltage rises above the reference voltage of the power supply 42, the comparator 40
Supplies to the timer 44 a signal indicating that the current I of the coil 24a has become equal to or greater than the specified current Ir.

The timer 44 supplies an ON signal to the limiter circuit 36 when the signal from the comparator 40 is continuously received for a time tr or more. The limiter circuit 36 is
The ON signal causes the control voltage from the PID control circuit 34 to drop to a predetermined voltage. As a result, the voltage on the output side of the operational amplifier 38 also drops to a predetermined voltage, and the coil current becomes Ia. This current Ia may have a current value equal to the specified current Ir.

Since the continuous energization of a large current as shown in FIG. 4 is usually caused by an abnormality occurring in the rotary system itself, a device provided with the rotary system, for example, a turbo molecule. In the pump, the operation of the device is automatically stopped. Therefore, the decrease in the rigidity of the magnetic bearing due to the decrease in the exciting current is not a problem.

Next, the second embodiment will be described. The same components as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be appropriately omitted. Figure 5
Shows the control system of the magnetic bearing according to the second embodiment. In the magnetic bearing control circuit 50 according to the present embodiment,
The output side of the operational amplifier 54 is connected to the limiter circuit 36. The non-inverting input terminal of the operational amplifier 54 is connected to the power supply 56, and the inverting input terminal is connected to the temperature detector 58 that detects the temperature of the coil 24a. The temperature detector 58 is composed of, for example, a thermistor, a resistance temperature detector, or the like, and supplies a voltage corresponding to the temperature of the coil 24a to the operational amplifier 54.

The operational amplifier 54 compares the voltage from the temperature detector 58 with the reference voltage from the power source 56 and supplies a signal as a comparison result to the limiter circuit 36. When the voltage of the power supply 56 reaches the maximum temperature (maximum allowable temperature) at which the coil 24a can withstand heat, the temperature detector 5
It is set to a value equal to the voltage supplied from 8. Therefore, the operational amplifier 54 is adapted to compare the temperature of the coil 24a with a predetermined maximum allowable temperature.

The limiter circuit 36 outputs a signal indicating that the voltage from the temperature detector 58 has become higher than the reference voltage of the power supply 56 as a result of comparison by the operational amplifier 54, that is, the temperature of the coil 24a is higher than the maximum allowable temperature. By supplying a signal indicating that the control voltage has been reached, the control voltage from the PID control circuit 34 is lowered to a constant voltage as in the first embodiment.

The other structure and operation are similar to those of the first embodiment. The limiter circuit 36 operates according to the temperature of the electromagnet in the present embodiment and according to the voltage value of the electromagnet in the first embodiment, but either one of the temperature and the voltage is in an abnormal state. When it becomes, it may be made to operate. For example, as shown in FIG. 6, the temperature detector 58, the operational amplifier 54, etc. in the second embodiment, the comparator 40, the timer 44, etc. in the first embodiment are both provided.
By connecting the operational amplifier 54 and the timer 44 to the limiter circuit 36 via the OR circuit 60, the limiter circuit 36 is operated when either one of the temperature and the voltage becomes abnormal.
To work.

In a turbo molecular pump or the like, a temperature sensor such as a thermistor may be attached near the motor coil in order to prevent heating of the motor. Therefore, when the magnetic bearing of the present embodiment is used for such a turbo molecular pump, an existing temperature sensor for a motor may be used as the temperature detector 58. However, when the position of the electromagnet of the magnetic bearing is far from the mounting position of the temperature sensor for the motor, the temperature of the electromagnet is calculated from the correlation data based on the heat transfer ratio between the two.

As described above, in each embodiment, the current value of the coil is forcibly made to be equal to or less than the constant current value according to the current and temperature of the coil. It is not necessary to set the wire diameter of the coil on the basis of the time when Imax is continuously energized. That is, the maximum current Ima
The wire diameter of the coil can be set with reference to the case where a current Ia smaller than x is continuously applied. Therefore, in the magnetic bearing having the same rigidity, the wire diameter of the coil can be made smaller than in the conventional case, and the electromagnet can be made compact.

When a coil having the same diameter as that of the conventional one is used, a large current Ia that can be continuously energized can be obtained, so that an output larger than that of the conventional one can be obtained. In each of the embodiments described above, the Zener diode is used for the limiter circuit 36, so that the control circuit 3 can be formed by a very simple circuit.
Since 0 and 50 are configured, there are few design changes in the conventional magnetic bearing control circuit, and an increase in manufacturing cost can be suppressed.

In each of the above embodiments, the voltage on the emitter side of the transistor 39 is used to detect whether or not the current I of the coil 24a is greater than or equal to the specified current Ir, but the current I is directly measured. By doing so, it may be detected whether or not the current is equal to or higher than the specified current Ir.

[0039]

According to the magnetic bearing of the present invention, the size of the electromagnet can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a part of a mechanical configuration of a magnetic bearing according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a part of a control system of the magnetic bearing according to the first embodiment.

FIG. 3 is a diagram showing a relationship between a control voltage and an exciting current.

FIG. 4 is a diagram showing a change with time of an exciting current of an electromagnet.

FIG. 5 is a block diagram showing a part of a control system of a magnetic bearing according to a second embodiment of the present invention.

FIG. 6 is a block diagram showing a magnetic bearing according to another embodiment of the present invention.

[Explanation of symbols]

 10 magnetic bearing 12 rotor 14a, 14b, 16a, 16b electromagnet 20a, 20b, 22a, 22b position sensor 24a, 24b, 26a, 26b coil 30, 50 control circuit 32 position detection circuit 34 PID control circuit 36 limiter circuit 38, 54 operational amplifier 39 Transistor 40 Comparator 42, 56 Power Supply 44 Timer 58 Temperature Detector 60 OR Circuit R Resistance

Claims (5)

[Claims] 1. An electromagnet for magnetically levitating a rotor, a position detecting means for detecting the position of the rotor, and an exciting current amplifying means for amplifying an exciting current of the electromagnet based on a detection value of the position detecting means. Temperature detecting means for detecting whether or not the temperature of the electromagnet is equal to or higher than a predetermined temperature; and when the temperature detecting means detects that the temperature of the electromagnet is equal to or higher than the predetermined temperature, the exciting current amplifying means A magnetic bearing, comprising: current limiting means for limiting the amplified exciting current to a predetermined current value or less. 2. The magnetic bearing according to claim 1, wherein the temperature detecting means detects whether or not the temperature of the electromagnet is equal to or higher than the predetermined temperature by using a heat sensitive sensor. 3. An electromagnet for magnetically levitating the rotor, a position detecting means for detecting the position of the rotor, and an exciting current amplifying means for amplifying an exciting current of the electromagnet based on a detection value of the position detecting means. Current limiting means for limiting the exciting current amplified by the exciting current amplifying means to a predetermined current value or less when the voltage applied to the electromagnet is continuously a predetermined voltage value or more for a predetermined time. Characteristic magnetic bearing. 4. An electromagnet for magnetically levitating the rotor, a position detecting means for detecting the position of the rotor, and an exciting current amplifying means for amplifying an exciting current of the electromagnet based on a detection value of the position detecting means. The exciting current amplified by this exciting current amplifying means is
A magnetic bearing, comprising: current limiting means for limiting the exciting current to a predetermined current value or less when the current value is continuously a predetermined current value or more for a predetermined time. 5. The magnetic bearing according to claim 3, wherein the predetermined voltage value and the predetermined current value are respectively determined by a wire diameter of a coil in the electromagnet.