JPS6014619A - Magnetic bearing control device - Google Patents

Abstract

PURPOSE:To prevent the dynamic stiffness of revolving shaft in its proper frequency from reducing by providing the band-pass filter having the center frequency close to the proper frequency of revolving shaft, the band-elimination filter having less center frequency than it and the phase lead circuit in series connection. CONSTITUTION:An adding machine 4 to compose the detection signal from a sensor 2 and the standard position from a standard shaft position indicator 3 outputs a deflection signal obtained by subtracting the detection signal from the standard position. This deflection signal is transmitted to an adding machine 15 through the band-pass filter 11 having the center frequency close to the proper frequency of revolving shaft, the band-elimination filter 12 having a less center frequency than it, and a serial circuit consisting of a phase lead circuit 13 to conpensate the phase lag caused by the filters 11, 12. The current from electromagnet 9 to coil 10 is controlled by the adding machine 15 after the output of integrating circuit 16 is subtracted from the output signal of serial circuit 14.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a control device for a magnetic bearing used in a main shaft of a machine tool or the like.

(b) Problems to be solved by the prior art and the invention FIG. , a shaft position reference device 3 that sets the reference position of the rotating shaft 1
A deviation signal representing the amount of deviation between the reference position and the actual rotating shaft 1 is output from the adder 4 to the control circuit 5 based on the reference position. This control circuit 5 includes a deviation amplifier 6 that amplifies the deviation signal, and a secondary phase lead/lag circuit 7 that controls the phase etc. of the output signal from this amplifier 6.
A signal corresponding to the deviation signal output from the power amplifier 8
The signal is input to the coil 10 of the weight 9 through the coil 10 of the weight 9, and excites the electromagnet 9. Note that, as shown in FIG. 2, the output of the coil 10 is fed back as a current to the power amplifier 8, so that the input voltage of the power amplifier 8 is proportional to the current of the coil 10.

In the above control, the −cyclic transfer function becomes as shown in FIG. 3, and the input voltage of the power amplifier 8 (
The transfer function up to the output voltage of the control circuit 5 is as shown in FIG. The frequency of the gain odB in this -cyclic transfer function, that is, the crossover frequency ω. The phase margin at is
In the case of magnetic bearings, the angle is 15° to 5°, considering the stability of the control system, etc.
It is 0°. Also, the crossover frequency ω. is set to a considerably smaller value than the natural frequency ω1 of the rotating shaft. For example, if the shaft natural frequency ω1 is 800Hz,
Crossover frequency ω. is set to about 8o to 4'QQI (z).

In a magnetic bearing device having such a control circuit, the dynamic stiffness at the natural frequency ω1 becomes small, and the rotating shaft may self-oscillate in a non-rotation controlled state. For this reason,
Conventionally, self-excited oscillation has been suppressed by inserting it at the natural frequency ω1. However, this method makes little contribution to improving rigidity near the natural frequency ω1, and when a spindle supported by such a magnetic bearing is used as the main shaft for milling, etc., the natural frequency ω1 The vibration of the rotating shaft in the vicinity increased, making it easy for the bearing to become uncontrollable, making it impossible to obtain sufficient cutting force.

(c) Means for solving the problem This invention was made in view of the above circumstances, and the crossover frequency ω. By maintaining the phase margin in the range of 15° to 50° at An object of the present invention is to provide a control device for a magnetic bearing that can prevent a decrease in dynamic rigidity at the natural frequency ω1 of the shaft.

This invention includes a sensor that detects the radial position of the rotating shaft, and a control circuit that controls the current to the coil of the electromagnet based on the output signal of this sensor. In the magnetic bearing that maintains a magnetic bearing, the control circuit includes a bandpass filter having a center frequency approximately equal to the natural frequency of the rotating shaft, a band-elimination filter having a center frequency smaller than this frequency,
A phase lead circuit that compensates for the phase delay caused by these filters is connected in series, and an integral element is provided in parallel to this series circuit to provide stiffness in the low frequency range. is made to advance locally.

B) Embodiment As shown in FIG. 5, an adder 4 that combines the detection signal from the sensor 2 and the reference position from the shaft position reference device 3 subtracts the detection signal from the reference position to obtain a deviation signal. It is outputting. This deviation signal is passed through the bandpass filter 11. Series circuit 14 consisting of band elimination filter 12 and phase lead circuit 13
is sent to adder 15 via. Bandpass filter 1
1 has a center frequency, that is, a peak, near a frequency equal to the natural frequency ω1 of the rotating shaft 1, a band elimination filter 12 has a center frequency smaller than this frequency, and a phase lead circuit 13 adjusts the phase delay caused by the filters 11 and 12. Compensate. Note that the center frequency of the band-pass filter 12 is equal to the center frequency of the band-pass filter 11 (natural frequency ω1
), for example, the natural frequency ω1 is less than
Further, it is desirable that the frequency is smaller than 10 3 natural frequency ω1 and the frequency is the same as the maximum rotational speed of the rotating shaft 1.

An integrating circuit 16 which receives the deviation signal as input is provided in parallel with the series circuit 14 in order to obtain stiffness in a low frequency range. The integrator circuit 16 has a constant phase of 190° and a gain of 'l, Q dB as the frequency increases.
/decade, so if it is installed in parallel with the series circuit 14, the integrating circuit 16 will dominate the control system at low frequencies, but as the frequency increases, the gain decreases and the influence becomes smaller, and the above-mentioned Frequency ω0. There is almost no effect near ω1.

The adder 15 subtracts the output signal of the integrating circuit 16 from the output signal of the series circuit 14, and then controls the current flowing to the coil 10 of the electromagnet 9 via the power amplifier 8.

The above control system will be explained by showing the transfer function.

Note that the natural frequency ω1 of the rotating shaft 1 is 670H2, and the crossover frequency ω is 670H2. is the case where the frequency is set to 200Hz.

The bandpass filter 11 has a natural frequency ω1 of 670H.
It is a second-order element filter whose peak frequency (center frequency) is 7QQI (Z) approximately equal to 2, and its transfer function is shown in FIG.

The band-stop filter 12 has a center frequency of 503 Hz, and its transfer function is shown in FIG.

FIG. 8 shows a transfer function obtained by combining the phase compensation circuit and the phase lead circuit 13 of the filters 11 and 12, and the phase lead circuit 13 has a frequency of at least ω. The phase is advanced in the range of ~ω1, which is the crossover frequency ω. So 40
degree, giving a phase lead of about 90 degrees at the natural frequency ω1. In addition, Fig. 9 shows the open loop transfer function of the entire control system, and in the low frequency region, it is controlled by the integrating circuit,
Frequency ω is involved in the stability of the control system and the damping characteristics of the natural vibration of the rotating shaft. , ω, has almost no effect.

In the above embodiments, a proportional circuit may be added to the integrating circuit 16 to increase the stability of the control system.

(E) Effect As described above, the present invention provides a bandpass filter whose center frequency is approximately equal to the natural frequency of the rotating shaft, a band 5-band elimination filter whose center frequency is a frequency smaller than this frequency, and a filter for these filters. A series circuit in which a phase lead circuit that compensates for the phase delay caused by the crossover frequency ω is connected in series. The phase margin at is 15
Since the range is from ° to 50° and the gain and phase characteristics of the control system around the natural frequency ωl are improved, the vibration damping force around the natural frequency ω1 becomes large, and the rotation around the natural frequency ω1 increases. The dynamic rigidity of the shaft is also improved, resulting in a stable spindle. In addition, in the low frequency range, compensation is performed by an integrating circuit installed in parallel to the series circuit, so good rigidity can be obtained even in the low frequency range, and sufficient cutting force can be obtained even when used for cutting such as milling processing. .

, 4. Brief description of the drawings Figure 1 is a block diagram showing an example of a conventional magnetic bearing device.
Fig. 2 is an enlarged view of the main part of Fig. 1, Fig. 3 is a characteristic diagram showing the open loop transfer function in Fig. 1, Fig. 4 is a characteristic diagram showing the transfer function of the electronic control circuit in Fig. 1, and Fig. 5 is a characteristic diagram showing the transfer function of the electronic control circuit in Fig. 1. 6 is a block diagram showing an example of the present invention, FIG. 6 is a characteristic diagram showing the transfer function of the bandpass filter in FIG. 5, FIG. 7 is a characteristic diagram showing the transfer function of the band-stop filter in FIG. Figure 8 is a characteristic diagram showing the overall transfer function of the bandpass filter, band-elimination filter, and phase lead circuit in Figure 5, and Figure 9 is a characteristic diagram showing the transfer function of the entire electronic system including the integrating circuit in Figure 5. It is a diagram.

1... Rotation axis, 2... Sensor 3... Axis position reference device, 5, 15... Adder, 8...
・Power amplifier, 9...electromagnet, 10...coil,
11...Band pass filter, 12...Band elimination filter, 13...Phase lead/lag circuit, 14...Series circuit, 16...Integrator circuit 17...Proportional circuit ” Sentence 2

Claims (2)

[Claims] (1) Equipped with a sensor that detects the radial position of the rotating shaft, and a control circuit that controls the current to the coil of the electromagnet based on the output signal of the sensor, the rotating shaft is positioned at the set radial position of the rotating shaft. In a magnetic bearing that maintains A phase lead/lag circuit that compensates for the phase lag that occurs is connected in series, and an integral element that provides stiffness in the low frequency range is provided in parallel to this series circuit. A control device for magnetic bearings that is characterized by being able to advance the magnetic bearing and also increase the gain. (2) The control device for a magnetic bearing according to claim 1, wherein the integral element is provided with a proportional element in parallel.