JPH0821443A - Magnetic bearing device - Google Patents

Abstract

PURPOSE:To provide a control circuit for increasing the rigidity only in the low frequency region of a magnetic bearing. CONSTITUTION:As for a magnetic bearing device equipped with an electromagnet 8 for noncontact-supporting a rotary shaft 6 by a magnetic force, displacement sensor 7 for detecting the position in the radial direction of the rotary shaft, and a proportion/integration/differentiation(PID) control circuit 1 which controls the electric current supplied to the electromagnet 8 on the basis of the output of the displacement sensor 7, a low path filter 2 is connected in parallel with the PID control circuit.

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 having a proportional / integral / derivative (PID) control circuit for controlling a current supplied to an electromagnet.

[0002]

2. Description of the Related Art Conventionally, in a magnetic bearing device, as shown in FIG. 5, an electromagnet 18 for supporting a rotary shaft 12 in a non-contact manner by a magnetic force, a displacement sensor 13 for detecting a radial position of the rotary shaft 12, and a rotary sensor Controlling the current supply to the electromagnet 18 based on the output of the displacement sensor 13 in order to maintain the shaft 12 in a fixed position, the integral element (P) 15 in the low frequency region, the proportional element (I) 16 in the intermediate frequency region, In the high frequency region, the differential element (D) 17 was used.

[0003]

Using the above-mentioned conventional magnetic bearing device as a spindle of a machine tool, a grindstone 11 is attached to the tip of a rotary shaft 12 as shown in FIG. 6, and both the grindstone 11 and the rotary shaft 12 are attached together. The work piece 20 may be polished while being vibrated in the axial direction at 0.1 to 30 Hz, but the supporting rigidity of the magnetic bearing is 0.1 to 30 H due to the influence of vibration.
It decreases in the z area and the processing accuracy deteriorates. So, 0.
In order to improve the rigidity of the magnetic bearing at 1 to 30 Hz, the gain of I (integral element: related to the low frequency range) of PID control has been conventionally increased, but as shown in FIG. There was a problem that it would decrease.
A bandpass filter (BPF) 19 was also connected in parallel to the PID circuit 14 as shown in FIG.
This affects the middle and high frequency range of 0 to 2000 Hz. Therefore, two Ps having different frequency characteristics in the low frequency region
There is also one in which the ID circuit is used by switching according to the number of rotations of the rotating shaft (see Japanese Patent Laid-Open No. 1-320318)
This method has a problem that the structure becomes complicated because a rotation speed detection device and a switching device are required.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems, an electromagnet for supporting a rotating shaft in a non-contact manner by a magnetic force, a sensor for detecting a radial position of the rotating shaft, and a rotating shaft. In order to maintain the position at a fixed position, the current supplied to the electromagnet is controlled based on the output of the sensor.
A magnetic bearing device having a differential (PID) control circuit is characterized in that a low-pass filter is connected in parallel to the PID control circuit.

[0005]

Since the low-pass filter is connected in parallel to the conventional PID control circuit of the magnetic bearing, it is possible to increase the gain only in the low frequency region and increase the rigidity in the low frequency region without affecting the middle and high frequency regions. You can

[0006]

1 is a circuit block diagram of an embodiment according to the present invention. The magnetic bearing device according to the present embodiment is similar to the magnetic bearing device according to the related art, and includes a displacement sensor 7 that detects the radial position of the rotating shaft 6, and a control circuit 1 that controls the electromagnet 8 based on the output signal of the displacement sensor 7. It has and. The control circuit 1 has a low frequency range (0.1 to 0.1) in the rotation speed range of the rotation shaft 6.
Integral element (P) 3 for controlling in 30 Hz), proportional element (I) 4 for controlling in medium frequency region (30 Hz to 500 Hz), and differential element for controlling in high frequency region (500 Hz to 2 KHz). (D) 5 and constitute a PID control circuit. The control circuit 1 may be a modified circuit in which another compensating element (phase control means or the like) is added to the PID element, and may be an analog circuit or a digital circuit. The control circuit 1 includes a low pass filter (L
PF) 2 are connected in parallel. The low pass filter 2 is preferably one having a second-order or higher attenuation characteristic. The low pass filter 2 may be composed of an analog circuit or a digital circuit. Next, the operation will be described. The frequency characteristic (cutoff characteristic, phase characteristic) of the low-pass filter 2 is similar to that of the integrator circuit as shown in FIGS. 3 and 4, so that the middle-high frequency characteristic of the entire control circuit 1 is not affected as shown in FIG. It is possible to increase the gain only in the frequency region and increase the rigidity only in the low frequency region.

[0007]

According to the present invention, an electromagnet for supporting a rotating shaft in a non-contact manner by a magnetic force, a sensor for detecting a radial position of the rotating shaft, and an output of the sensor for maintaining the rotating shaft at a fixed position. In a magnetic bearing device having a proportional / integral / derivative (PID) control circuit for controlling a current supplied to an electromagnet based on the above, a low-pass filter is connected in parallel to the PID control circuit, so that it is selected only in a low frequency region. The rigidity can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment according to the present invention.

FIG. 2 is a graph of frequency characteristics of an example according to the present invention.

FIG. 3 is a graph comparing the cutoff characteristics of the low pass filter of FIG. 1 and an integral element.

FIG. 4 is a graph comparing the phase characteristics of the low pass filter of FIG. 1 and an integral element.

FIG. 5 is a control circuit diagram of a conventional magnetic bearing device.

FIG. 6 is an explanatory view of a polishing process by a machine tool using a conventional magnetic bearing device.

FIG. 7 is a graph showing frequency characteristics of a conventional magnetic bearing device.

FIG. 8 is a circuit diagram when a bandpass filter is connected to a control circuit of a conventional magnetic bearing device.

[Explanation of symbols]

 1 PID control circuit of magnetic bearing 2 Low pass filter

Claims (1)

[Claims] 1. An electromagnet for supporting a rotating shaft in a non-contact manner by a magnetic force, and a sensor for detecting a radial position of the rotating shaft,
Proportional / integral / derivative (P) that controls the current supplied to the electromagnet based on the output of the sensor in order to maintain the rotary shaft at a fixed position.
A magnetic bearing device having an ID) control circuit, wherein a low-pass filter is connected in parallel to the PID control circuit.