JP2004251311A - Magnetic levitation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic levitation device capable of controlling magnetic levitation by utilizing the sum components of signals from position sensors. <P>SOLUTION: In the magnetic levitation device, position sensors 3A and 3B are disposed facing each other across an object 1 to be supported, and sense the position of the levitation control direction of the object 1. Signals output from sensor circuits 4A and 4B are input into a differential unit 5 and an adder 6. The differential unit 5 generates displacement components which are the difference of the signals, and the adder 6 generates sum components of the signals. A gain setting unit 8 calculates the gain of a magnetic levitation control system 7 suitable of the magnetic levitation system based on the sum components when the object 1 is levitated at the target levitation position, and the gain of the magnetic levitation control system 7 is set to be the calculated gain. Consistent magnetic levitation control can be maintained even when the gap is changed by thermal expansion or the like. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetic levitation device such as a magnetic bearing device and a magnetic transport device.
[0002]
[Prior art]
2. Description of the Related Art In a magnetic levitation device such as a magnetic bearing device or a magnetic transfer device, the position (movement amount) of a supported body that is non-contact supported by an electromagnet is detected by a position sensor, and the current of the electromagnet coil is determined based on a signal from the position sensor. Is controlled so that the supported member floats to the optimum position. As the position sensor, for example, an electromagnetic induction type sensor using a change in inductance is used, and a detection coil is provided near an electromagnet to apply a detection signal.
[0003]
As a magnetic levitation device that does not require a position sensor, a “superposition type” magnetic bearing device that superimposes an AC signal for detecting a gap between a supported body and an electromagnet on an electromagnet current is known (for example, See Patent Document 1.). In any case of the magnetic levitation device, the supported member is controlled by using the difference component of the sensor signal (superimposed signal) of the facing position sensor or the electromagnet so as to float to the levitation target position between the facing electromagnets. I have.
[0004]
In the magnetic levitation device as described above, since there is a mechanical error in the magnetic levitation system, for example, the gap size between the electromagnet and the supported member varies, so that the gain of the magnetic levitation system varies from device to device. . Therefore, when the magnetic levitation system and the control system are combined, a tuning operation for matching the gain of the magnetic levitation system with the gain of the control system is performed.
[0005]
[Patent Document 1]
JP-A-5-118329
[Problems to be solved by the invention]
However, even when the tuning operation is performed when the magnetic levitation system and the control system are connected, the gap size may change due to a temperature change of the supported member or the electromagnet. When the gap size changes, the gain of the magnetic levitation system also changes. Therefore, the matching with the gain of the control system may be lost, and the magnetic levitation control may be unstable.
[0007]
The present invention provides a magnetic levitation device that performs magnetic levitation control using a sum component of a signal from a position sensor for detecting a levitation position of a supported body.
[0008]
[Means for Solving the Problems]
The present invention relates to an electromagnet for magnetically levitating a supported body, a pair of position detection sensors disposed opposite to each other with the supported body interposed therebetween, and detecting a position of the supported body in a floating control direction, and a position detection sensor. A magnetic levitation control system that controls the exciting current of the electromagnet based on the detection result of the electromagnet, a calculation unit that calculates the sum of the sensor signals output from the pair of position detection sensors, and the supported member levitates to the levitating target position. And a setting unit for setting a control parameter of the magnetic levitation control system based on a calculation result of the calculation unit. Then, the magnetic levitation control system controls the exciting current of the electromagnet based on the set control parameters.
Further, the floating position detecting means may detect the floating position by detecting a sensor signal superimposed on exciting currents of a pair of electromagnets arranged to face each other with the supported member interposed therebetween. In this case, the calculation unit calculates the sum of the pair of sensor signals detected by the flying position detection unit.
The control parameters include, for example, the gain of the magnetic levitation control system.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of a magnetic levitation device according to the present invention. In FIG. 1, a supported body 1 of a magnetic levitation device is supported in a non-contact manner by the attraction force of electromagnets 2A and 2B. For example, in the case of a five-axis type magnetic bearing, the supported body 1 corresponds to the rotor, and the electromagnets 2A and 2B correspond to one pair of four pairs of radial electromagnets supporting the rotor.
[0010]
Position sensors 3A and 3B are provided near the electromagnets 2A and 2B. The electromagnets 2A, 2B and the position sensors 3A, 3B are arranged with the supported body 1 interposed therebetween. Electromagnets 2A, 2B and the respective gap dimension between the support 1 _{d 2A,} an _{d 2B,} the position sensor 3A, 3B and each gap dimension between the support 1 _{d 3A,} a _{d 3B.} When the supported member 1 is floating at the center of the electromagnets 2A and 2B, d _2A = d _2B and d _3A = d _3B . In the following, the electromagnets 2A, 2B and position sensor 3A, gap dimension 3B are _equal, will be described as being d _2A = _{d 3A,} a relation of d 2B _{= d 3B.}
[0011]
For example, when an electromagnetic induction type sensor using a change in inductance is used as the position sensors 2A and 2B, if the supported body 1 is eccentric to the position sensor 3A, d _3A <d _3B, and the position sensor 3A The inductance increases and the sensor signal also increases. Conversely, the inductance on the position sensor 3B side decreases, and the sensor signal also decreases.
[0012]
The sensor signal of the position sensor 3A is input to the sensor circuit 4A, amplified by the sensor circuit 4A, and then input to both the differentiator 5 and the adder 6, respectively. On the other hand, the sensor signal of the position sensor 3B is input to the sensor circuit 4B, amplified by the sensor circuit 4B, and then input to both the differentiator 5 and the adder 6. For example, assuming that the signals from the sensor circuits 4A and 4B are Sa and Sb, respectively, the difference (Sa−Sb) is output from the differentiator 5, and the sum (Sa + Sb) is output from the adder 6.
[0013]
The difference (Sa−Sb) corresponds to the difference between the gaps d _3A and d _3B between the supported body 1 and the electromagnets 2A and 2B, and is hereinafter referred to as a displacement component. That is, when the supported body 1 is floating at the center of the position sensors 3A and 3B, the displacement component (Sa-Sb) becomes zero, and when the supported body 1 deviates from the center, the displacement component (Sa-Sb) ≠ 0. It becomes. On the other hand, the sum (Sa + Sb) corresponds to the sum of the gaps d _3A and d _3B , and is hereinafter referred to as a sum component.
[0014]
The displacement component (Sa−Sb) is input to the magnetic levitation control system 7, and the sum component (Sa + Sb) is input to the gain setting unit 8. The gain setting unit 8 sets the gain of the magnetic levitation control system 7 based on the sum component (Sa + Sb). The magnetic levitation control system 7 controls the electromagnet drive circuits 9A and 9B based on the displacement component (Sa-Sb) from the difference unit 5 and the gain set by the gain setting unit 8. The magnetic levitation control system 7 compares the levitation position of the supported body 1 calculated from the displacement component (Sa-Sb) with a preset levitation target position, and calculates an electromagnet current control amount by PID control or the like. . Each of the electromagnet drive circuits 9A and 9B supplies an electromagnet current to the electromagnets 2A and 2B based on the electromagnet current control amount.
[0015]
Meanwhile, the support 1 and the electromagnet 2A, 2B is thermally expanded by a temperature change due to heat generation, such as electromagnet 2A, 2B, the support 1 gap size also has emerged at the center position _{d 2A, d 2B, d 3A} , D _3B may change. In such a case, the signals Sa and Sb output from the sensor circuits 4A and 4B also change. Therefore, the gain of the magnetic levitation system changes, and when the supported body 1 is displaced from the center position, the force by which the electromagnets 2A and 2B return the supported body 1 to the center direction also changes.
[0016]
For example, consider the case where the electromagnets 2A, the force of 2B gap dimension _{d 2A,} inversely proportional to the square of _{d 2B,} the position sensor 3A, the sensitivity of the 3B is inversely proportional to the gap dimension. When the gap dimensions d _2A and d _2B are reduced by half due to thermal expansion, the force of the electromagnets 2A and 2B increases by 2 × 2 = 4 times. Therefore, even if the change in the electromagnet current for returning the supported body 1 to the center direction is the same, the force for returning to the center position is quadrupled. Further, since the sensitivities of the position sensors 3A and 3B are also doubled, the magnitudes of the signals Sa and Sb are doubled for the same displacement. That is, even if the actual displacement is α, it is recognized that the displacement is twice 2α. As a result, it can be considered that the gain of the magnetic levitation system has increased eightfold.
[0017]
In response to such a change in the magnetic levitation system gain during operation of the device, the conventional device did not change the gain of the control system, so the matching between the magnetic levitation system and the control system was lost and the magnetic levitation state Could become unstable. On the other hand, in the magnetic levitation apparatus of the present embodiment shown in FIG. 1, by providing the adder 6 and the gain setting unit 8, the gain of the magnetic levitation control system 7 is changed according to the change of the gain of the magnetic levitation system. In this way, the magnetic bearing control is always stabilized.
[0018]
As described above, when the gap dimensions d _2A , d _2B , d _3A , and d _3B are reduced, the gain of the magnetic levitation system is increased, and the force for returning to the displacement of the supported member 1 is originally smaller than the original. Will also become stronger. Conversely, when the gap dimensions d _2A , d _2B , d _3A , and d _3B increase for some reason, the gain of the magnetic levitation system decreases, and the gap returns to the original with respect to the displacement of the supported member 1. The force to do so will be weaker than it should be.
[0019]
In the present embodiment, when the gain of the magnetic levitation system changes, the gain of the magnetic levitation control system 7 is changed so as to cancel the change. For example, when the gap dimensions d _2A , d _2B , d _3A , and d _3B are reduced due to thermal expansion, the gain of the magnetic levitation control system 7 is reduced to maintain the control state substantially equal to the original control state, thereby achieving stable operation. Magnetic levitation control was maintained. In particular, in the magnetic bearing type turbo-molecular pump, the rotor as the supported member 1 is hard to radiate heat because it floats in a vacuum, and an unstable state due to thermal expansion is likely to occur.
[0020]
In FIG. 1, the displacement component (Sa-Sb) output from the differentiator 5 represents the displacement of the supported body 1 as described above. When the supported member 1 is floating at the center position, Sa = Sb, so that the displacement component = 0, and when displaced from the center position, the displacement component becomes ≠ 0. That is, whether or not the supported body 1 is deviated from the center position is detected by the displacement component (Sa-Sb), and the magnetic levitation control device 7 controls the electromagnet drive circuits 9A and 9B. The gain at that time is set by the gain setting unit 8.
[0021]
By the way, the displacement component (Sa-Sb) can detect whether or not the supported body 1 is shifted from the center position, but cannot detect whether or not the gap dimensions d _2A , d _2B , d _3A , d _3B have changed. . That is, when the supported body 1 is floating at the center position, the change amounts ΔS of the signals Sa and Sb due to the change in the gap size are equal to each other, and if the difference is obtained, the change amounts cancel each other out, and the change cannot be detected.
[0022]
On the other hand, in the case of the sum component (Sa + Sb) output from the adder 6, the sum changes by 2ΔS due to a change in the gap size. Therefore, a gap change due to thermal expansion or the like can be detected by using the sum component (Sa + Sb) when the supported body 1 is floating at the center position. If the signals output from the sensor circuits 4A and 4B before the gap change are Sa and Sb, and the signals after the gap change are Sa 'and Sb', the sum component changes from (Sa + Sb) to (Sa '+ Sb'). . These ratios β = (Sa ′ + Sb ′) / (Sa + Sb) represent the degree of change in the gap size, β = 1 when the gap size change = 0, and β> when the gap size becomes large. 1. β <1 when the gap size is small.
[0023]
The gain G of the magnetic levitation control system 7 is stored in the gain setting unit 8 in advance, and the gain G is represented as G (β) including β described above. Then, the sensor signals Sa ′ and Sb ′ when the supported body 1 is floating at the center position are detected, and the adder 6 calculates the sum component (Sa + Sb). The gain setting unit 8 stores a reference sum component (Sa + Sb), and calculates β ′ = (Sa ′ + Sb ′) / (Sa + Sb) from these. Then, the calculated β ′ is substituted for β of the gain G (β). The gain setting unit 8 replaces the gain G of the magnetic levitation control system 7 with the calculated gain G (β ′). The magnetic levitation control system 7 controls the electromagnet drive circuits 9A and 9B based on the new gain G (β ′).
[0024]
The setting timing of the gain G of the magnetic levitation control system 7 is performed, for example, when the apparatus is started, at a predetermined time interval after the start, or when β ′ calculated after the start becomes a predetermined value or more. You can do it. Generally, the electromagnets 2A and 2B and the position sensors 3A and 3B have dimensional errors and assembly errors. Therefore, by setting the gain G at the time of starting the apparatus, the gain of the magnetic levitation system due to these mechanical errors can be reduced. Gain matching can be achieved so as to cancel the fluctuation.
[0025]
In addition, by setting the gain G after startup, the gain of the magnetic levitation control system 7 can be set to G (β ′) even when the gain of the magnetic levitation system changes due to a gap change due to thermal expansion or the like. Thereby, stable magnetic levitation control can be maintained. Further, not only when the gap dimensions d _2A , d _2B , d _3A , d _3B change, but also when the cables connecting the position sensors 3A, 3B and the sensor circuits 4A, 4B are changed, the signals Sa, Sb are changed. Changes. Even in such a case, the gain of the magnetic levitation system changes, but in the present embodiment, the gain of the magnetic levitation control system is set to G (β ′) even in such a case, so that the magnetic levitation control system is set. 7 can be matched with the gain of the magnetic levitation system.
[0026]
Conventionally, when performing gain adjustment, the supported body 1 is moved within the range of displacement, and the gap dimensions d _3A and d _3B between the electromagnets 2A and 2B and the supported body 1 are estimated from the amount of movement. . For example, in a magnetic bearing device, gap dimensions d _3A and d _3B are indirectly determined by bringing a rotor into contact with a touchdown bearing. However, since the touchdown bearing has a mounting error, the mounting error results in a gap dimension measurement error. On the other hand, in the present embodiment, since the gap size at the time of floating the center position is directly obtained by using the sum component of the position sensor signals, the gap size measurement error is reduced, and the accuracy of gain adjustment is improved compared to the related art. I do.
[0027]
-2nd Embodiment-
FIG. 2 is a block diagram showing a magnetic levitation apparatus according to a second embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals. In the following, a description will be given focusing on portions different from FIG. The magnetic levitation device shown in FIG. 2 is a “superposition type” magnetic levitation device. The superimposed signal generated by the superimposed signal generation circuit 13 is input to the electromagnet drive circuits 9A and 9B and the synchronous detection circuits 12A and 12B. This superimposed signal has a frequency sufficiently distant from the frequency band of the magnetic levitation control, and is superimposed on the drive signals of the electromagnets 2A and 2B.
[0028]
The current values of the exciting currents flowing through the electromagnets 2A and 2B are detected by the current detection units 10A and 10B, respectively. The current detection units 10A and 10B output a current value as a voltage signal using, for example, a resistor. The current detection signal output from the current detection unit 10A is input to the electromagnet drive circuit 9A and the superimposed component extraction unit 11A. On the other hand, the current detection signal output from the current detection unit 10B is input to the electromagnet drive circuit 9B and the superposition component extraction unit 11B.
[0029]
The superimposed component extraction units 11A and 11B respectively extract superimposed signal components included in the current detection signal. The difference unit 5 calculates a difference between a superimposed signal component related to the electromagnet 2A and a superimposed signal component related to the electromagnet 2B. The adder 6 calculates the sum of the superimposed signal component and the superimposed signal component.
[0030]
The difference signal output from the differentiator 5 is input to the synchronous detection circuit 12B. The synchronous detection circuit 12B performs synchronous detection of the difference signal using the superimposed signal from the superimposed signal generation circuit 13 as a reference signal. The signal obtained by this synchronous detection is the same as the difference signal (displacement component) in the first embodiment, and will be referred to as a displacement component as in the first embodiment.
[0031]
On the other hand, the sum signal output from the adder 6 is input to the synchronous detection circuit 12A, and the same synchronous detection as in the case of the difference signal is performed. The signal obtained by the synchronous detection is similar to the sum component of the first embodiment, and is also referred to as a sum component. This sum component is input to the gain setting unit 8, and the gain of the magnetic levitation control system 7 is set based on the sum component as in the first embodiment.
[0032]
The magnetic levitation control system 7 controls the electromagnet driving circuits 9A and 9B based on the displacement component from the synchronous detection circuit 12B and the gain set by the gain setting unit 8. The magnetic levitation control system 7 compares the levitation position of the supported member 1 calculated from the displacement component with a preset levitation target position, and based on the gain set by the gain setting unit 8, controls the electromagnet current control amount. Is calculated. Each of the electromagnet driving circuits 9A and 9B drives the electromagnets 2A and 2B based on the electromagnet current control amount.
[0033]
Also in the present embodiment, for example, when there is a change in the gain of the magnetic levitation system due to thermal expansion or the like, the gain of the magnetic levitation control system 7 is adjusted to cancel the gain change of the magnetic levitation system by using the sum component. Can be set. As a result, stable magnetic levitation control can always be performed.
[0034]
By the way, in the device of the first embodiment described above, the relative position error between the position sensors 3A, 3B and the electromagnets 2A, 2B affects the gap size measurement error. The gap size error may be caused by an assembly error of the position sensors 3A and 3B and the electromagnets 2A and 2B, or may be caused by a difference in thermal expansion between the two.
[0035]
On the other hand, the present embodiment is a “superimposition type” magnetic levitation device that detects the position of the supported body 1 based on a superimposed signal superimposed on the electromagnet current, so that the originally required electromagnets 2A and 2B and the supported The magnetic levitation control can be performed based on the gaps d _2A and d _2B with the body 1. Therefore, the stability of the magnetic levitation control is further improved.
[0036]
In the above-described embodiment, the setting of the gain, which is the control parameter of the magnetic levitation control system 7, is changed based on the sum component. However, the control parameter for changing the setting may be not only the gain but also the frequency characteristic. .
[0037]
In FIGS. 1 and 2, the control system is configured as hardware, but the superimposed signal generation circuit 13, the superimposed component extraction units 11A and 11B, the differentiator 5, the adder 6, and the synchronous detection circuits 12A and 12B, The gain setting unit 8 and the magnetic levitation control system 7 can be configured by software. The magnetic levitation device of the present embodiment can be applied to, for example, a magnetic bearing or a magnetic transfer device of a turbo molecular pump. Note that the present invention is not limited to the above embodiment at all, as long as the features of the present invention are not impaired.
[0038]
In correspondence between the embodiment described above and the elements of the claims, the position sensors 3A and 3B and the sensor circuits 4A and 4B of the first embodiment, the superposition signal generation circuit 13 of the second embodiment, The current detection units 10A and 10B and the superimposed component extraction units 11A and 11B constitute a flying position detection unit, and the adder 6 constitutes a calculation unit.
[0039]
【The invention's effect】
As described above, according to the present invention, even when the gain of the magnetic levitation system changes due to thermal expansion or the like, the gain of the magnetic levitation system is set so as to cancel the change. It is possible to prevent the magnetic levitation control from becoming unstable due to a temperature change or the like.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a magnetic levitation device according to the present invention.
FIG. 2 is a block diagram showing a magnetic levitation apparatus according to a second embodiment of the present invention.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 supported members 2A, 2B electromagnets 3A, 3B position sensors 4A, 4B sensor circuit 5 differentiator 6 adder 7 magnetic levitation control system 8 gain setting units 9A, 9B electromagnet drive circuits 10A, 10B current detection units 11A, 11B superimposed components Extraction units 12A, 12B Synchronous detection circuit 13 Superposition signal generation circuit

Claims (3)

An electromagnet for magnetically levitating the supported body,
A pair of position detection sensors arranged opposite to each other with the supported member interposed therebetween, and detecting a position of the supported member in a floating control direction,
A magnetic levitation control system that controls an exciting current of the electromagnet based on a detection result of the position detection sensor,
A calculation unit that calculates a sum of sensor signals output from the pair of position detection sensors,
A setting unit that sets a control parameter of the magnetic levitation control system based on a calculation result of the calculation unit when the supported body is floating at the floating target position,
The magnetic levitation control system controls the exciting current of the electromagnet based on the set control parameters. An electromagnet for magnetically levitating the supported body,
Floating position detecting means for detecting a sensor signal superimposed on exciting currents of a pair of electromagnets disposed opposite to each other with the supported member interposed therebetween, and detecting a floating position of the supported member,
A magnetic levitation control system that controls an exciting current of the electromagnet based on a detection result of the levitation position detection means,
A computing unit that computes the sum of a pair of sensor signals detected by the flying position detection unit;
A setting unit that sets a control parameter of the magnetic levitation control system based on a calculation result of the calculation unit when the supported body is floating at the floating target position,
The magnetic levitation control system controls the exciting current of the electromagnet based on the set control parameters. The magnetic levitation device according to claim 1 or 2,
The magnetic levitation device, wherein the control parameter is a gain of the magnetic levitation control system.

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