JP3220281B2 - Magnetic bearing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic bearing device, and more particularly to a magnetic bearing device for supporting a supported member in a non-contact state by a magnetic force.

[0002]

2. Description of the Related Art In general, a magnetic bearing device includes an electromagnet that exerts a supporting force on a supported member by magnetic attraction, a displacement sensor that detects a relative displacement amount of the supported member, and a displacement sensor. The control circuit is configured to generate a control signal based on the generated displacement signal, and a current amplifier that amplifies the control signal of the control circuit and supplies a current to an exciting coil of the electromagnet. The electromagnet generates a magnetic attraction force that supports the supported body by the current supplied to the excitation coil of the electromagnet. A displacement sensor, a control circuit, a current amplifier, and the like are provided to control the magnetic attraction force and stably support the supported body at a target position.

Conventionally, as a displacement sensor for detecting the displacement of the supported member, an inductive sensor in which the inductance changes according to the displacement of the supported member, or the magnitude of the eddy current changes according to the displacement of the supported member An eddy current sensor is used. These displacement sensors are usually arranged in the vicinity of an electromagnet device for applying a magnetic attractive force to a supported body.

However, since the displacement sensor is disposed near the electromagnet, the detection point of the supported body detected by the displacement sensor is different from the operation point of the supported body on which the magnetic attraction of the electromagnet acts. The following proposal has been made by the present applicant in order to make such detection points and action points coincide.

In a magnetic bearing device, a signal of a constant frequency is supplied to a current amplifier from a signal source and applied to an excitation coil of an electromagnet together with a control current of a magnetic attraction force. The relative displacement of the supported member is detected by detecting a change in the inductance of the excitation coil itself of the electromagnet caused by the relative displacement of the supported member (Japanese Patent Application No. 3-9).
4694 and Japanese Patent Application No. 3-151062).
This makes it possible to match the position detection point of the supported member with the magnetic attraction point, and to omit a dedicated displacement sensor arranged near the electromagnet.

[0006] Pulse width modulation (PWM) is applied to the current amplifier.
The present applicant has proposed a magnetic bearing device that obtains a relative displacement amount of a supported body by detecting a change in inductance of an electromagnet coil itself by using a switching current of the type current amplifier and utilizing a switching frequency thereof. 3-19 Ganping
2497 patent application).

[0007]

However, in the magnetic bearing device having the structure disclosed in Japanese Patent Application Nos. 3-94694 and 3-151062, the amplification frequency range is not supported by the ordinary current amplifier. Limited to the body control signal frequency range. For this reason, it is difficult to supply a signal having a frequency higher than the control frequency range (for example, 2 to 100 kHz) to the excitation coil of the electromagnet. The relative displacement could not be detected in the control signal frequency range.

In a magnetic bearing device having a structure disclosed in Japanese Patent Application No. 3-192497, a relative displacement is detected by using a pulse width modulation switching signal itself using a pulse width modulation current amplifier. I have to. However, since the switching frequency of pulse width modulation is generally relatively high (50 kHz to 120 kHz), when a switching signal is used as a carrier for modulation due to a change in self-inductance, an eddy current is generated in the yoke of the electromagnet and the target on the supported body side. Cheap. If a partition made of stainless steel (SUS304, SUS316, etc.) is interposed between the yoke of the electromagnet and the target of the supported member, eddy currents are likely to be generated by the partition. As described above, when the switching frequency is relatively high (for example, 50 kHz to 120 kHz), there is a problem that a mutual induction component is increased with respect to a self-inductance component of the magnetic circuit, and it becomes difficult to separate and detect a relative displacement amount component. Occurs. However, if the switching frequency of the pulse width modulation is set low, there arises a problem that the frequency characteristics of the pulse width modulation current amplifier deteriorate.

The present invention has been made in view of the above-mentioned circumstances, and it is possible to obtain a relative displacement amount of a supported body by detecting a change in inductance of an electromagnet coil itself, and to reduce the influence of mutual induction and the like. It is an object of the present invention to provide a magnetic bearing device capable of detecting a relative displacement amount of a supported member up to a control signal frequency band without receiving the signal.

[0010]

According to the present invention, there is provided a magnetic bearing device for supporting a supported member in a non-contact state by an electromagnet having an exciting coil made of a conductor. And a pulse width modulation (PWM) type current amplifier for supplying a current including current, and an AM modulation caused by a change in a self-inductance of the exciting coil due to a change in a magnetic circuit of the exciting coil based on a relative displacement of the supported body. A detection circuit for detecting the constant frequency signal.

[0011]

A signal generating circuit for generating a signal having a constant frequency is provided.
Is supplied to the excitation coil of the electromagnet via the pulse width modulation type current amplifier, and a detection circuit for detecting a change in self-inductance of the excitation coil itself of the electromagnet is provided. It can be detected at the point of action. Since the pulse width modulation type current amplifier is used, the signal A having a constant frequency is sufficiently high with respect to the control signal frequency band, and it is difficult to separate and detect the relative displacement component due to the mutual induction phenomenon in the switching frequency band. Can be set sufficiently low.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. 1 is a block diagram showing the entire magnetic bearing device, FIG. 2 is a block diagram of the detection circuit of FIG. 1, and FIG. 3 is a block diagram of a control circuit of FIG.

As shown in FIG. 1, in the magnetic bearing device, a supported body 4 is supported in a non-contact state by an electromagnet 2 having an exciting coil 1 made of a conductor. As the supported member 4,
There is a rotating shaft placed on the center axis of the bearing.
Yoke 3 attracts the target 5 of the supported member 4 by magnetic force. By controlling the current supplied to the exciting coil 1 of the electromagnet 2 and adjusting the magnetic attraction force between the yoke 3 and the target 5, it is controlled so that the supported member 4 is always rotatably supported at the target position. ing.

A generating circuit 10 for generating a constant frequency signal A generates a signal A having a frequency of, for example, 5 to 10 kHz, and supplies a current including the signal A to the exciting coil 1 via a pulse width modulation (PWM) type current amplifier 6. Supply. The detection circuit 7 detects a signal A that has been subjected to AM modulation by a change in the self-inductance of the exciting coil 1 due to a change in the magnetic circuit of the exciting coil 1 based on the relative displacement amount X of the supported member 4.

The signal A output from the constant frequency signal generating circuit 10 is a carrier wave for detecting the relative displacement X, and is added to a control loop for supporting the supported member 4 at the target position by the adding circuit 13. The control signal output from the control circuit 11 is converted into a signal A by a constant frequency signal removal circuit 12.
Is added to the adder circuit 13 after being removed. The signal B output after being added to the signal A by the adding circuit 13 is converted into a current by the pulse width modulation type current amplifier 6 and amplified. The pulse width modulation type current amplifier 6 is a power supply that supplies a current to the excitation coil by modulating the pulse width, and its output is a relatively high switching frequency (50 Hz).
(k to 120 kHz) is supplied to the exciting coil 1 as a switching ripple current pulse-width modulated.

The current amplifier 6 includes a comparator operating signal generating section 14, a control section 15, and a driver section 16 which receives a signal from the control section 15, amplifies the current and outputs a current.

Although not shown, a circuit for removing the signal A is preferably provided in the current feedback loop of the current amplifier 6. However, since a low-pass filter is usually provided, the component of the signal A is easily removed. ing.
In addition to this, a band elimination filter (BEF) for the signal A (commonly called a notch filter) may be provided.

The detection circuit 7 includes a detector 20 for the signal A connected to the excitation coil 1 and the driver section 16, and a differential amplifier circuit 2 for differentially amplifying the signal detected by the detector 20.
1 and a detection circuit 22 that detects a signal output from the differential amplifier circuit 21 and feeds it back to the control circuit 11.

When the relative displacement X between the yoke 3 of the electromagnet 2 on the support side supporting the supported member 4 and the target 5 of the supported member 4 changes, the magnetic circuit of the exciting coil 1 changes. Since the self-inductance of the exciting coil 1 changes due to the change of the magnetic circuit, the signal A of a constant frequency flowing through the exciting coil 1 as a carrier is subjected to AM modulation, and the detector 20 converts the signal A subjected to AM modulation to the signal A. Detected by a current detection resistor.

The detection circuit 22 converts the AM-modulated signal A detected by the detector 20 and sent through the differential amplifier circuit 21 into a carrier and a relative displacement signal generated by a change in self-inductance of the exciting coil 1. Separate into wave components.

As shown in FIG. 2, the detection circuit 22 receives the output of the differential amplification circuit 21 and passes an AC coupling circuit 31 composed of a capacitor and the like, and passes the frequency of the signal A and its AM sideband component. Bandpass filter (BPF) 32
, A signal is input to the synchronous detection circuit 33. Note that if the signal from the differential amplifier circuit 21 is stable, the AC coupling circuit 31 and the bandpass filter 32 are not required. A low-pass filter (LPF) of a signal synchronously detected by a synchronous detection circuit 33 and a synchronous detection switching signal shaper 34 that outputs a switching signal to the synchronous detection circuit 33.
After smoothing by 35, the carrier frequency component is removed from the components of the output signal A by a band elimination filter (BEF) 36.

A signal A output from the band-pass filter 32 or a signal A output from the constant frequency signal generation circuit 10 is supplied to the switching signal shaper 34 for synchronous detection.
Is input. This input signal may be either the a signal or the b signal, but it is preferable to use this signal because the b signal is more stable.

In the control circuit 11 shown in FIG. 3, after the output signal from the target value generation circuit 41 is compared with the signal fed back from the detection circuit 22 by the addition circuit 42, the difference signal is sent to the integration compensation circuit 43. Is entered. From the output signal of the integration compensation circuit 43, only a low frequency component is extracted by a high-pass signal removal low-pass filter 45 via a phase lead compensation circuit 44. Next, the signal is adjusted in gain by a gain adjustment circuit 46, rectified by a half-wave rectification circuit 47, and then subjected to a signal (voltage) limiting circuit 48 to limit the amplitude of the signal, and then to a fixed frequency signal removing circuit. 12 is output. Note that a signal limiting circuit 48 is provided at the last stage. This is to prevent saturation of the operational amplifier when the signal A is added by the adding circuit 13, and is an important circuit configuration.

The control circuit 11 having the above-described configuration feeds back a relative displacement signal wave, which becomes a relative displacement component between the support side including the exciting coil 1 and the supported body 4, from the detection circuit 22. 4, the relative displacement X is made to follow the target value.

As described above, the relative displacement X is detected by using the exciting coil 1 of the electromagnet 2 and the relative displacement signal wave is fed back to the control circuit 11 so that the relative displacement X is obtained.
Follow a predetermined target value.

FIG. 4 is a block diagram of a detection circuit 7a according to another embodiment of the present invention, and FIG. 5 is a block diagram of a detection circuit 7b showing a modification of FIG. The output signal of the detector 20 that detects the current flowing through the exciting coil 1 contains a large amount of the switching frequency component of the pulse width modulation current amplifier 6. This is unavoidable due to the principle of the pulse width modulation type current amplifier 6. However, if the output signal of the detector 20 is differentially amplified as it is, the differential amplifier circuit 21 saturates the output signal because the switching frequency component is large. Therefore, differential amplification is performed via the switching signal removal circuits 50 and 51. This switching signal removal circuit 50,
For example, a band elimination filter or a low-pass filter that removes a frequency component of a comparator signal generated by switching is effective as 51. When a low-pass filter is used, the cutoff frequency is slightly higher than the frequency of the signal A, which is effective. It is also effective to adopt a circuit configuration in which the low-pass characteristic is provided to the differential amplifier circuit 21. However, in the characteristics of the elimination circuit, the signal wave component is further modulated, which affects the frequency and gain characteristics of the sensor signal, and therefore needs to be used with care.

As shown in FIG. 5, in order to avoid the influence of the DC component of the output signal of the detector 20, the signal is differentially amplified through DC component removing filters 52 to 55 constituting an AC coupling circuit. As the DC component removing filters 52 to 55, it is effective to use a conventionally used capacitor or a band-pass filter that passes only a frequency band near the signal A.

As described above, the current detection differential amplifier circuit 21
It is preferable that at least one of the removal circuits 50 and 51 for removing the signal component of the switching frequency be provided in the input stage.

The switching frequency used in the pulse width modulation type current amplifier 6 is set to be at least 10 times the frequency of the constant frequency signal A for detecting the displacement, so that, for example, the signal A is 5 kHz and the switching frequency is 5 kHz. Is set to 50 to 120 kHz so that the signal for detecting the displacement can be reliably and stably transmitted from the exciting coil 1 to the detection circuit 7.
Can be output to

As described above, according to the present invention, the electromagnet 2 and the displacement sensor can be integrated by sharing the excitation coil 1 as a sensor for detecting the relative displacement of the supported member 4,
In addition, the signal for detecting the displacement can be fed back reliably and stably.

[0031]

Since the present invention is constructed as described above, the control frequency band component, which is the relative displacement between the supporting side and the supported body side, is relatively induced using the relatively high constant frequency signal A. The problem of the phenomenon can be suppressed, the separation can be easily performed, and the frequency characteristics of the current amplifier can be well maintained.

[Brief description of the drawings]

FIGS. 1 to 3 show a first embodiment of the present invention, and FIG. 1 is a block diagram showing an entire magnetic bearing device.

FIG. 2 is a block diagram of a detection circuit of FIG. 1;

FIG. 3 is a block diagram of a control circuit of FIG. 1;

FIG. 4 is a block diagram of a detection circuit according to another embodiment.

FIG. 5 is a block diagram of a detection circuit according to another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exciting coil 2 Electromagnet 4 Supported body 6 Pulse width modulation type current amplifier 7, 7a, 7b Detection circuit 9 Control circuit 21 Differential amplification circuit 22 Detection circuit 50, 51 Removal circuit A Constant frequency signal X Relative displacement

Claims (5)

(57) [Claims] 1. A magnetic bearing device for supporting a supported member in a non-contact state by an electromagnet having an exciting coil made of a conductor, wherein pulse width modulation (pulse width) for supplying a current including a constant frequency signal to the exciting coil. A current amplifier of a type, and a detection circuit for detecting the constant frequency signal that has been subjected to AM modulation by a change in self-inductance of the excitation coil due to a change in a magnetic circuit of the excitation coil based on the relative displacement amount of the supported body. A magnetic bearing device comprising: 2. The detection circuit according to claim 1, further comprising a detection circuit configured to separate the detected constant frequency signal into a carrier and a component of a relative displacement signal generated by a change in the self-inductance. The magnetic bearing device according to claim 1, wherein: 3. The relative displacement signal wave, which is a relative displacement component between the support side including the excitation coil and the supported body, is fed back, and the relative displacement amount between the support side and the supported body is determined. 3. The magnetic bearing device according to claim 2, further comprising a control circuit for controlling the pulse width modulation type current amplifier to follow a target value. 4. The switching method according to claim 1, wherein the switching frequency of the pulse width modulation type current amplifier is 1 to the frequency of the fixed frequency signal.
The magnetic bearing device according to any one of claims 1 to 3, wherein the value is set to 0 times or more. 5. The pulse width modulation type current amplifier according to claim 1, wherein an input stage of said detection circuit is provided with a removal circuit for removing a signal component of a switching frequency of said pulse width modulation type current amplifier. Magnetic bearing device.