JPH08200367A - Control device for magnetic bearing - Google Patents

Abstract

PURPOSE: To provide an economical control device for a magnetic bearing by forming a notch filter circuit so that the rotational frequency component of the input signal caused by the rotation of the rotational component is removed. CONSTITUTION: A rotation signal generator 1 such as the displacement sensor of the rotary shaft of a magnetic bearing generates the input signal P of a notch filter circuit. The input signal P may be the control signal of the control circuit of the magnetic bearing, and a buffer 2 buffering the input signal P is provided. The input signal P is inputted to two synchronous detectors 61, 62, and output signals from the synchronous detectors 61, 62 are inputted to balanced modulators 81, 82 through low-pass filters 71, 72 and guided to an adder 3 through level controllers 91, 92. The low-pass filters 71, 72 have the function to remove the frequency component at the cutoff frequency lower than the rotational frequency fo or above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic bearing control device having a notch filter circuit suitable for control.

[0002]

2. Description of the Related Art In a magnetic bearing such as a turbo molecular pump, a displacement signal synchronized with the rotation is generated due to the displacement between the center of gravity of a rotating shaft and the center of the shape. Therefore, it is necessary to remove the component synchronized with the rotation from the displacement signal. For this purpose, conventionally, a notch filter having a steady rotation frequency as a notch frequency is generally used, and an output signal passed through this filter is used as a control signal. However, in the case of a turbo molecular pump, etc., the rotational speed fluctuates, so the rotational frequency is converted to a voltage so as to correspond to this fluctuating rotational speed, and the frequency of the voltage control notch filter is adjusted to the rotational frequency with this voltage signal, and the displacement signal There are some that try to remove the component synchronized with the rotation from.

[0003]

However, since the notch frequency of the ordinary notch filter is fixed as described above, it is possible to deal with only the steady rotational speed. In addition, the voltage control notch filter requires a highly accurate analog arithmetic circuit inside, so that it is expensive and large-scale.
Therefore, there is a problem that the magnetic bearing device and eventually the turbo molecular pump and the like become expensive. The present invention is intended to provide a control device for a magnetic bearing having a notch filter circuit which solves such a problem.

[0004]

A notch filter circuit of a magnetic bearing control device provided by the present invention is a circuit for removing a rotation frequency component of an input signal due to rotation of a rotation component in a magnetic bearing. Receiving means for generating two square wave signals whose phases are deviated by 90 degrees, two synchronous detecting means for synchronously detecting the input signal using the respective square wave signals as reference signals, and the respective synchronous detecting means. Cut frequencies lower than the rotation frequency from the synchronous detection signal 2
Filter means, two balanced modulation means for balancing the respective output signals passing through the filter means with the respective square wave signals, and the output signals from the respective balanced modulation means of the input signal. It is composed of adding means for adding the levels so as to cancel the rotation frequency.

[0005]

The notch filter circuit according to the present invention comprises means for generating a square wave signal from a rotation pulse signal of a component signal synchronized with rotation from a displacement signal, means for synchronously detecting this square wave signal, and rotation from this synchronous detection signal. Since the filter means for cutting frequencies lower than the frequency and the means for balance-modulating the output signal thereof are used, the components synchronized with the rotation are eliminated, and these means can be provided at low cost.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A notch filter circuit in a magnetic bearing control apparatus according to the present invention will be described below with reference to the embodiments shown in the drawings. FIG. 1 is a diagram mainly showing the configuration of a notch filter circuit of the present invention. Reference numeral 1 is a rotation signal generator such as a displacement sensor of a rotary shaft in a magnetic bearing, which generates an input signal P in the notch filter circuit. is there. This input signal may be a control signal in the magnetic bearing control circuit. Reference numeral 2 is a buffer for buffering the input signal P. 3 is an adder. At the same time, the input signal P is input to the two synchronous detectors 61 and 62, and the output signals from the two synchronous detectors 61 and 62 are low-pass filters 71 and 62, respectively.
The signal is input to the balanced modulators 81 and 82 via 72, and further led to the adder 3 via the level adjusters 91 and 92. The low-pass filters 71 and 72 have a function of removing frequency components equal to or higher than the cutoff frequency fL lower than the rotation frequency fo.

On the other hand, 4 is a rotation sensor (pulse generating means) which detects the rotation of the rotary shaft and converts the rotation signal into a pulse signal and outputs the pulse signal, which is input to the PLL oscillator 5.
The PLL oscillator 5 receives the pulse signal and generates two square wave signals B (fo) and C (fo + 90 °) having a rotation frequency fo and a phase difference of 90 degrees from each other. This internal square wave signal B (fo) is input to the above-mentioned synchronous detector 61, and the other square wave signal C (fo + 9).
0 °) is input to the synchronous detector 62. Therefore,
The input signals D and E synchronized with the rotation frequency are input to the low-pass filters 71 and 72 from the synchronous detectors 61 and 62, respectively. The outputs F and G from the respective low-pass filters 71 and 72 have frequency components above the cut-off frequency fL removed, and the balanced modulators 81 and 82 respectively.
Is modulated by. Both of the modulated signals H and I are adjusted in order to adjust their levels and polarities, respectively.
92 is input. Then, the two signals whose levels have been adjusted are input to the adder 3, and the rotation frequency component of the input signal is canceled. Q indicates the output signal from which the rotation component has been removed.

The features of the notch filter circuit according to the present invention are as described above. Although the component of the rotation frequency fo is removed in the illustrated case, if the frequency division ratio in the PLL oscillator is changed, P
Since the LL oscillator oscillates at the frequency fx forming an integer ratio with respect to fo, the fx component can be removed in this case. Therefore, the frequency to be removed is not limited to fo. Moreover, this PLL oscillator is not always necessary, and it is directly connected to the rotating body by 90 °.
A generator that generates two square wave signals having different phases may be installed. The magnetic bearing control device provided by the present invention is, of course, applicable to magnetic bearing control other than the magnetic bearing for a turbo molecular pump.

The control device for a magnetic bearing provided by the present invention is provided with the notch filter circuit having the above characteristics. The contents thereof are summarized as follows. Appendix 1 A circuit for removing a rotational frequency component of an input signal due to rotation of a rotational component in a magnetic bearing, and a generating means for receiving two rotational signals and generating two square wave signals whose phases are shifted by 90 degrees, and Two synchronous detection means for synchronously detecting the input signal using each square wave signal as a reference signal, and two filter means for cutting frequency components of a cutoff frequency lower than the rotation frequency from the synchronous detection signals. And two balanced modulation means for balancing the respective output signals that have passed through the filter means with the respective square wave signals, and the output signals from the respective balanced modulation means to cancel the rotation frequency of the input signal. A magnetic bearing control device comprising a notch filter circuit including an adding means for adjusting and adding levels.

Appendix 2 A circuit for removing a rotation frequency component of an input signal due to rotation of a rotation component in a magnetic bearing, a pulse generating means for converting the rotation signal into a pulse signal and outputting the pulse signal, and a phase for receiving the pulse signal. Square wave generating means for generating two square wave signals deviated from each other by 90 degrees, two synchronous detecting means for synchronously detecting the input signal by using the respective square wave signals as reference signals, and the respective synchronous detection means. Two filter means for cutting frequency components having a cutoff frequency equal to or higher than the rotation frequency lower than the rotation frequency, and two balanced modulations for respectively modulating the output signals passing through the filter means with the respective square wave signals. Means and addition means for adding the output signals from the respective balanced modulation means by adjusting the levels so as to cancel the rotation frequency of the input signal. A magnetic bearing control device comprising: a notch filter circuit.

Appendix 3 A circuit for removing a rotation frequency component of an input signal due to rotation of a rotation component in a magnetic bearing, a rotation sensor for converting the rotation signal into a pulse signal and outputting the pulse signal, and a phase for receiving the pulse signal. PLL oscillators that generate two square wave signals deviated by 90 degrees, two synchronous detectors that synchronously detect the input signal using the respective square wave signals as reference signals, and rotate from the respective synchronous detect signals. Two low-pass filters that cut off frequency components above a cut-off frequency lower than the frequency, and two balanced modulators that balance-modulate each output signal that has passed through this low-pass filter with each of the square-wave signals; The output signals from the respective balanced modulators are added together by adjusting the levels so as to cancel the rotation frequency of the input signal. A magnetic bearing control device comprising a switch filter circuit.

Appendix 4 A circuit for removing a rotation frequency component of an input signal due to rotation of a rotation component in a magnetic bearing, which is a circuit for converting a rotation signal into a pulse signal and outputting the pulse signal, and a phase for receiving the pulse signal. PLL oscillators that generate two square wave signals that are offset by 90 degrees, two synchronous detectors that synchronously detect the input signal using the respective square wave signals as reference signals, and rotate from the respective synchronous detect signals. Two low-pass filters that cut off frequency components above a cut-off frequency lower than the frequency, and two balanced modulators that balance-modulate each output signal that has passed through this low-pass filter with each of the square wave signals; A level adjuster that adjusts the level of the output signal from each of the balanced modulators, and the output from this level adjuster is rotated to the input signal. A magnetic bearing control device comprising a notch filter circuit including an adder for adding frequencies so as to cancel them.

[0013]

Since the magnetic bearing control device provided by the present invention, particularly the notch filter circuit, is as described above, it is possible to provide an inexpensive notch filter circuit with an extremely simple structure. Since the rejection bandwidth (2fL) can be determined independently of the rotation frequency (fo) (however, fL << fo), it is easy to set the rejection bandwidth (2fL) narrow. When a PLL oscillator is used, the PLL oscillator can be configured digitally, and the synchronous detector and the balanced modulator can be configured with analog switches. Therefore, the notch filter circuit is highly accurate and inexpensive, which is economical. It is possible to provide a control device for a simple magnetic bearing.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a configuration of a notch filter circuit according to the present invention.

[Explanation of Codes] 1 ... Displacement sensor 3 ... Adder 4 ... Rotation sensor 5 ... PLL oscillator 61, 62 ... Synchronous detector 71, 72 ... Low-pass filter 81, 82 ... Balanced modulator 91, 92 ... Level adjuster P ... Input signal Q ... Output signal

Claims (1)

[Claims] 1. A circuit for removing a rotation frequency component of an input signal due to rotation of a rotation component in a magnetic bearing, said generating means for receiving two rotation signals and generating two square wave signals whose phases are shifted by 90 degrees. And two synchronous detection means for synchronously detecting the input signal using the respective square wave signals as reference signals, and two filter means for cutting frequencies lower than the rotation frequency from the respective synchronous detection signals, Two balanced modulation means for balance-modulating each output signal that has passed through the filter means with each of the square-wave signals, and levels of the output signals from the respective balanced modulation means so as to cancel the rotation frequency of the input signal. A magnetic bearing control device comprising a notch filter circuit including an adding means for adding and adding.