JPH06313426A - Magnetic bearing device - Google Patents

Abstract

PURPOSE:To provide a magnetic bearing device capable of obtaining relative displacement quantity of a supported body by means of detecting the changes of inductance of an electromagnet coil itself and also detecting relative displacement quantity of the the supported body up to a control signal frequency band without being effected by mutual induction or the like. CONSTITUTION:A magnetic bearing device, which supports a supporting body 4 in a non-contacting state by an electromagnet 2 having an exciting coil composed of a conductor, is equipped with a pulse width modulation(PWM) type current amplifier 6, which supplies current containing a certain frequency signal A to the exciting coil, and a detector 7 which detects a certain frequency signal A given an AM modulation by self-inductance variation of the exciting coil caused by the variation of the exciting coil detector based on the relative displacement quantity of the supported body 4.

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 which supports a supported body in a non-contact state by a magnetic force.

[0002]

2. Description of the Related Art Generally, a magnetic bearing device has an electromagnet that exerts a supporting force on a supported body by a magnetic attraction force, a displacement sensor that detects a relative displacement amount of the supported body, and a displacement sensor. The control circuit includes a control circuit that generates 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 the exciting coil of the electromagnet. Due to the current supplied to the exciting coil of the electromagnet, the electromagnet generates a magnetic attraction force that supports the supported body. 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 the target position.

As a displacement sensor for detecting the displacement of a supported body, conventionally, an inductive type sensor whose inductance changes according to the displacement of the supported body, or the magnitude of the eddy current changes according to the displacement of the supported body. An eddy current sensor is used. These displacement sensors are usually arranged in the vicinity of an electromagnet device that applies a magnetic attraction force to the supported body.

However, since the displacement sensor is arranged in the vicinity of the electromagnet, the point of detection of the supported body detected by the displacement sensor and the point of action of the supported body on which the magnetic attraction force of the electromagnet acts are different. The following proposals have been made by the present applicant in order to match the detection points and the action points.

In the magnetic bearing device, a signal having a constant frequency is supplied to a current amplifier from a signal source and applied to an exciting coil of an electromagnet together with a control current of magnetic attraction force. Then, the relative displacement amount of the supported body is detected by detecting the change in the inductance of the exciting coil itself of the electromagnet caused by the relative displacement of the supported body (Japanese Patent Application No. 3-9).
(Patent application No. 4694 and Japanese Patent Application No. 3-151062).
As a result, the position detection point of the supported body and the magnetic attraction force acting point can be made coincident, and a dedicated displacement sensor arranged near the electromagnet can be omitted.

Further, the current amplifier has pulse width modulation (PWM).
The applicant of the present invention has proposed a magnetic bearing device that obtains the relative displacement amount of a supported member by detecting a change in the inductance of the electromagnet coil itself by using a switching type current amplifier and utilizing the switching frequency thereof. Wishhei 3-19
2497 patent application).

[0007]

However, in the magnetic bearing device having the structure disclosed in Japanese Patent Application No. 3-94694 and Japanese Patent Application No. 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 of a frequency higher than the control frequency range (for example, 2 to 100 kHz) to the exciting coil of the electromagnet, and so far, it is applied only in the extremely low frequency range, and it is applied to the supported body. The relative displacement could not be detected in the control signal frequency range.

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

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

[0010]

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

[0011]

A signal generating circuit of a constant frequency is provided, and the signal A
Is supplied to the exciting 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 exciting coil of the electromagnet is provided to detect the relative displacement amount of the supported body. 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 amount component due to the mutual induction phenomenon of the switching frequency band. Can be set sufficiently low.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An 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 the control circuit of FIG.

As shown in FIG. 1, the magnetic bearing device supports a supported body 4 in a non-contact state by an electromagnet 2 having an exciting coil 1 made of a conductor. As the supported body 4,
There is a rotating shaft placed on the center axis of the bearing, and the electromagnet 2
The yoke 3 attracts the target 5 of the supported body 4 by magnetic force. By adjusting 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, the supported body 4 is controlled to be rotatably supported at the target position. ing.

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

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

The current amplifier 6 includes a comparator operation signal generator 14, a controller 15, and a driver 16 for receiving a signal from the controller 15 to amplify the current and output a current.

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

The detection circuit 7 includes a detector 20 for the signal A connected to the exciting 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 the signal output from the differential amplifier circuit 21 and feeds it back to the control circuit 11.

When the relative displacement amount X between the yoke 3 of the electromagnet 2 on the support side supporting the supported body 4 and the target 5 of the supported body 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 having a constant frequency flowing through the exciting coil 1 as a carrier wave undergoes AM modulation, and the detector 20 changes the signal A subjected to AM modulation. It is detected by a current detection resistor.

The detection circuit 22 detects the detector 20 and sends the AM-modulated signal A sent through the differential amplifier circuit 21 to the carrier wave and the relative displacement signal generated by the change of the self-inductance of the exciting coil 1. Separated into wave components.

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

In the synchronous detection switching signal shaper 34, the signal a output from the band pass filter 32 or the signal A output from the constant frequency signal generation circuit 10 is output.
Any of the b signals consisting of 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, the signal fed back from the detection circuit 22 is compared with the output signal from the target value generation circuit 41 in the addition circuit 42, and then the difference signal is fed to the integral compensation circuit 43. Is entered. From the output signal of the integration compensation circuit 43, only the low frequency component is taken out by the low-pass filter 45 for removing high frequency signals via the phase advance compensation circuit 44. Next, the signal is rectified by the half-wave rectifier circuit 47 after the gain is adjusted by the gain adjustment circuit 46, then the amplitude of the signal is limited by the signal (voltage) limiting circuit 48, and then the constant frequency signal removing circuit is performed. 12 is output. Although the signal limiting circuit 48 is provided at the final stage, this is to prevent saturation in 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-mentioned structure feeds back the relative displacement signal wave, which is a relative displacement component between the supporting side including the exciting coil 1 and the supported body 4, from the detection circuit 22 to support the supporting side and the supported body. The relative displacement amount X with respect to 4 is made to follow the target value.

In this way, the relative displacement amount X is detected by utilizing the exciting coil 1 of the electromagnet 2 and the relative displacement signal wave is fed back to the control circuit 11 to obtain the relative displacement amount X.
Is made to 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 in 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, it is saturated in the differential amplifier circuit 21 because the switching frequency component is large. Therefore, differential amplification is performed via the switching signal removal circuits 50 and 51. This switching signal removing circuit 50,
As 51, for example, a band elimination filter or a low-pass filter that removes the frequency component of the comparison signal generated by switching is effective. When a low-pass filter is used, the cutoff frequency is a little higher than the frequency of the signal A, which is effective. Further, it is also effective to have a circuit configuration in which the differential amplifier circuit 21 has a low-pass characteristic. However, the characteristics of the removing circuit must be used with caution because the signal wave component will be further modulated, and the frequency and gain characteristics of the sensor signal will be affected.

Further, as shown in FIG. 5, in order to avoid the influence of the DC component of the output signal of the detector 20, differential amplification is carried out through the DC component removing filters 52 to 55 constituting the AC coupling circuit. As the DC component removing filters 52 to 55, it is effective to use a conventionally used capacitor or a bandpass filter that passes only the frequency band near the signal A.

In this way, the differential amplifier circuit 21 for current detection is used.
It is preferable to provide at least one removing circuit 50, 51 for removing the signal component of the switching frequency at the input stage of the above.

By setting the switching frequency used in the pulse width modulation type current amplifier 6 to 10 times or more the frequency of the constant frequency signal A for detecting the displacement amount, for example, the signal A has a switching frequency of 5 kHz. Is set to 50 to 120 kHz, the signal for displacement amount detection is reliably and stably detected from the exciting coil 1 to the detection circuit 7.
Can be output to.

As described above, according to the present invention, the exciting coil 1 can be used as a relative displacement amount detecting sensor for the supported body 4, and the electromagnet 2 and the displacement sensor can be integrated.
In addition, the signal for detecting the displacement amount can be fed back reliably and stably.

[0031]

Since the present invention is configured as described above, the control frequency band component which is the relative displacement amount between the supporting side and the supported side is mutually induced by using the relatively high constant frequency signal A. It is possible to suppress the problem of the phenomenon, to easily separate, and to keep the frequency characteristic of the current amplifier excellent.

[Brief description of drawings]

1 to 3 are views showing a first embodiment of the present invention, and FIG. 1 is a block diagram showing the whole magnetic bearing device.

FIG. 2 is a block diagram of the detection circuit of FIG.

FIG. 3 is a block diagram of the control circuit shown in FIG.

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 excitation 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 amount

Claims (5)

[Claims] 1. A magnetic bearing device for supporting a supported body 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 containing a constant frequency signal to the exciting coil. Type current amplifier, and a detection circuit for detecting the constant frequency signal AM-modulated by the change of the self-inductance of the exciting coil due to the change of the magnetic circuit of the exciting coil based on the relative displacement of the supported body. A magnetic bearing device comprising: 2. The detection circuit includes a detection circuit for separating the detected constant frequency signal into a carrier wave and a component of a relative displacement signal wave generated by a change in the self-inductance. The magnetic bearing device according to claim 1. 3. The relative displacement signal wave, which is a relative displacement component between the supporting side including the exciting coil and the supported body, is fed back to calculate the relative displacement amount between the supporting side and the supported body. 3. The magnetic bearing device according to claim 2, further comprising a control circuit of the pulse width modulation type current amplifier that follows a target value. 4. The pulse width modulation type current amplifier switching frequency is set to 1 with respect to the frequency of the constant frequency signal.
4. The magnetic bearing device according to claim 1, wherein the magnetic bearing device is set to 0 times or more. 5. The removing circuit for removing a signal component of a switching frequency of the pulse width modulation type current amplifier is provided at an input stage of the detection circuit. Magnetic bearing device.