JPS626124B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic bearing control device.

As shown in Fig. 1, the magnetic bearing has a rotating shaft 1.
A sensor 2 is provided to detect the radial position of the rotating shaft 1 in relation to the rotation axis 1, and a servo circuit is provided between the sensor 2 and the winding 3 of the magnetic bearing to detect when the rotating shaft 1 deviates from a preset position. When detected by the sensor 2, the servo circuit generates an error signal in the bias magnetic flux coil 4 to return the rotary shaft to the set position, thereby holding the rotary shaft 2 at a preset radial position.

This magnetic bearing is used for high-speed rotation because the rotating shaft is completely non-contact type.

However, if this rotating shaft is rotated at a frequency equal to the natural frequency, that is, at a critical speed of the shaft, the bearing will become uncontrollable. Furthermore, when a rotating shaft is used as a cutting main shaft or the like, the rigidity at the mechanical system's natural frequency is extremely reduced, and disturbances during cutting cause the cutter to vibrate at the mechanical system's natural frequency, making the magnetic bearing uncontrollable.

As a countermeasure to this problem, it is conceivable to remove the band corresponding to the natural frequency using a filter. According to this, self-excited oscillation of the rotating shaft can be prevented, but
The increase in rigidity in the natural frequency band of the mechanical system is small, and when used for cutting, etc., only a small improvement in cutting force can be expected.

The present invention solves the above problems, and aims to provide a control device for a magnetic bearing that can obtain appropriate rigidity of the bearing regardless of the natural frequency of the rotating shaft.

That is, the present invention provides a magnetic bearing equipped with a position sensor that detects the radial position of the rotating shaft and an electromagnet that determines the position of the rotating shaft. This is a position compensation circuit required for a second calculation section that extracts the frequency in the predetermined range from the sensor output and advances its phase and also increases the gain and transmits the frequency, and from the first calculation section and the second calculation section. The present invention is characterized in that it comprises a power amplification section and an addition circuit that adds up the outputs of and supplies current to the electromagnet.

The present invention will be described below based on embodiments shown in the accompanying drawings.

As shown in FIG. 2, a drive motor 1 for rotating a rotor 12 is mounted on the inner peripheral wall of the cylindrical casing 11.
3 is fixed, and the rotating shaft 14 of the rotor 12 is supported at both ends by radial bearings 15 and 16.

The radial bearings 15, 16 are composed of rotors 15a, 16a fixed to the rotating shaft 14, and stators 15b, 16b, which are fixed to the inner peripheral wall of the casing 11 and serve as electromagnets.
Further, a rotor 17a of a thrust bearing 17 is attached near the center of the rotating shaft 14, and stators 17b and 1 that serve as electromagnets sandwich this rotor 17a.
7b is fixed to the casing 11.

The casing 11 also includes a thrust sensor 18 that detects the axial position of the rotating shaft 14, and first and second radial sensors 19 and 1 that detect the radial position of the radial bearings 15 and 16, respectively.
9', 20, 20' are provided at arbitrary positions.
Note that the sensors 19, 20 and the sensors 19', 20' are provided at symmetrical positions.

Next, the control device for the magnetic bearing configured as described above will be explained. As shown in FIG. The filter 22 removes frequencies in a predetermined range including the natural frequency f of the rotating shaft 14 before transmission. The transfer function of the band elimination filter 22 has a characteristic as shown in FIG. 4, and the band gain is almost zero or a small value in a predetermined range of frequencies including the natural frequency of the rotating shaft 14.

Further, a band pass filter 23 which receives the output signal of the sensor 19 as an input is configured to pass frequencies in the predetermined range, contrary to the band elimination filter 22, and its transfer function is shown in FIG. The transfer function of the bandpass filter 23 and the sensor output that has passed through the gain adjuster 24 are connected to the first adder circuit 25.
is added by. Therefore, the transfer function constituted by the bandpass filter 23, gain adjuster 24, and adder circuit 25 is expressed as a gain/phase diagram as shown in FIG. 6.

The phase of the output from the adder circuit 25 is advanced by the phase advance circuit 26 so that the phase is completely advanced at least in the above-mentioned predetermined band, but when the phase is advanced, the gain is also not small. Under the influence, the elements constituted by the bandpass filter 23, gain adjuster 24, addition circuit 25, and phase advance circuit 26 have a transfer function as shown in FIG. In order to obtain more suitable gain/phase characteristics, a notch filter 27 is added to the phase advance circuit 26, thereby obtaining the transfer characteristics shown in FIG.
The circuit constituted by the phase advance circuit 26 and the notch filter 27 may be a circuit that can advance only the phase. Since such a circuit is difficult to obtain with a simple phase advancing circuit, the above circuit is used, but there is no problem in practice even if the gain is affected to some extent.

The above phase compensation circuit 21 and band elimination filter 22
A second addition circuit 2 that adds together a first calculation section for controlling the magnetic bearing, and a second calculation section for damping vibrations at the natural frequency of the rotating shaft.
8 is provided. Since the output of the adder circuit 28 is amplified by the power amplification circuit 29 and the radial bearing 15 is controlled, the rotating shaft 14 is controlled to be at a preset position.

The above describes the results obtained by actually measuring the control circuit of the present invention which is actually constituted by an electronic circuit. However, the present invention is not limited to this, and the second calculation section is Any device may be used as long as it is for advancing the phase of the frequency corresponding to the natural frequency of the rotating shaft or selectively increasing the phase advance gain.

In the above embodiment, one radial bearing 1
5 has been described, the other radial bearing 16 is also controlled in the same manner. Further, the thrust bearing is controlled only by a thrust sensor, and the control may be performed by a normal servo circuit or feedback control. In this case, in the thrust bearing, the transfer function is determined based on the signal from the sensor and its feedback signal so as not to cause oscillation or the like.
Note that, as shown in FIG. 2, a tool such as a cutting tool 28 protruding from the casing 11 is fixed to the tip of the rotating shaft 14.

As described above, this invention aims at increasing the phase advance or phase advance gain of the transfer function in order to increase the rigidity in the frequency band equal to the natural frequency of the rotating shaft, which is a major problem in magnetic bearings when applied to machine tools, etc. By selectively increasing the stiffness, the stiffness is increased at a frequency equal to the natural frequency of the rotating shaft, and has the advantage that it can also be applied to machine tools.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the principle of a magnetic bearing, Fig. 2 is a vertical cross-sectional view of a magnetic bearing, Fig. 3 is a block diagram showing an example of the present invention, and Fig. 4 is an example of a transfer function of the output of a band elimination filter. 5 is a graph showing the transfer function from the sensor to the output of the bandpass filter, FIG. 6 is a graph showing the transfer function from the sensor to the output of the first addition circuit, and FIG. 7 is a graph showing the transfer function from the sensor to the output of the first adder circuit. Graph showing the transfer function. FIG. 8 is a graph showing the transfer function of the second calculation unit from the sensor to the input of the second addition circuit. DESCRIPTION OF SYMBOLS 11... Casing, 12... Rotor, 13... Drive motor, 14... Rotating shaft, 15, 16... Radial bearing, 17... Thrust bearing, 15a, 16a, 17
a... Rotor, 15b, 16b, 17b... Stator, 18... Thrust sensor, 19, 19', 2
0, 20'...Radial sensor, 21...Phase compensation circuit, 22...Band elimination filter, 23...Band pass filter, 24...Gain adjuster, 25, 28...Addition circuit, 26...Phase lead circuit, 27 Notch filter, 29... power amplification circuit.

Claims (1)

[Claims] 1. In a magnetic bearing equipped with a position sensor that detects the radial position of the rotating shaft and an electromagnet that determines the position of the rotating shaft, a predetermined range including the natural frequency of the rotating shaft is detected from the sensor output. a first calculation unit consisting of a phase compensation circuit that transmits the frequency excluding the frequency; a second calculation unit that extracts the frequency in the predetermined range from the sensor output and advances its phase and transmits it;
A control device for a magnetic bearing, comprising a calculation section and a power section that adds outputs from the second calculation section and controls the electromagnet. 2 The second calculation unit includes a filter circuit that extracts a frequency in the predetermined range from the output of the sensor, and a phase advancer that adds the sensor output and the output of the filter circuit to advance the phase of the transfer function at the frequency in the predetermined range. 2. A control device for a magnetic bearing according to claim 1, comprising a circuit. 3. The control device for a magnetic bearing according to claim 1, wherein the first calculation section is a phase compensation circuit including a bandpass filter that eliminates frequencies in the predetermined range.