JP2003222130A - Magnetic bearing device - Google Patents

Abstract

(57) Abstract: Provided is a magnetic bearing that can stably control a magnetic bearing even if a gap between the position sensor and the position sensor fluctuates due to a fluctuation in a rotating body temperature. A rotating body is attracted by electromagnets and supported in a non-contact manner, and gaps d1 and d2 with the electromagnets are detected by position sensors and the output thereof is subtracted. , The control gain is multiplied by the control constant adjusting circuit 23, and fed back to the electromagnets 12 and 13 through the PID adjuster 25. As a result, the rotating body 11 is supported at the optimum floating position while keeping the gaps between the rotating bodies 11 and the electromagnets 12 and 13 uniform. Further, the position sensor 14 due to thermal expansion or thermal contraction of the rotating body 11,
The change in the detection sensitivity of 15 is corrected by adding the outputs of the position sensors 14 and 15 and generating a control gain corresponding to the added value in the control constant adjusting circuit 23. Thus, stable bearing control can be performed at a wide rotating body temperature.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic bearing device used for a turbo molecular pump or the like. 2. Description of the Related Art A magnetic bearing device is a device that levitates a rotating body in a non-contact manner by magnetic attraction and supports the rotating body at a target position. A turbo molecular pump, a centrifuge, a machine tool spindle, or a semiconductor manufacturing machine is used. It is used as a bearing device for high-speed rotation such as a device. FIG. 5 shows the structure of a basic five-axis magnetic bearing device.
Is floated by a plurality of electromagnets 3 in a non-contact manner, and its floating position is detected by a position sensor 2 arranged near the electromagnets. In a conventional magnetic bearing device, as shown in FIG. 6, a control constant adjusting circuit 4 for changing a control gain based on a difference between gap signals detected by the position sensors 2a and 2b, and a filter circuit for removing a rotational speed component of the rotating body 1. 5, PID
Feedback control is performed through the controller 6. The control signal from the PID controller 6 is converted into a drive current for the electromagnets 3a and 3b by an electromagnet drive circuit 7, and the electromagnet 3
Control is performed so that the gap difference between the rotating bodies 1 and a and 3b becomes zero. [0003] For example, in a magnetic bearing device used for a turbo-molecular pump, when the amount of gas to be exhausted increases, the temperature of the rotating body 1 rises due to the heat generated by the motor and the heat generated by gas exhaustion. When the temperature of the rotating body 1 rises, the rotating body 1 thermally expands, and the rotating body 1 and the position sensors 2a, 2b
The gap between them is reduced. The position sensors 2a and 2b have non-linear characteristics as shown in FIG. 7, and when the gap decreases, the output voltage change ratio with respect to the gap, that is, the detection sensitivity decreases. As a result, there is a problem that the loop gain of the magnetic bearing control system decreases and the magnetic bearing control becomes unstable. The instability of such a control loop is caused by PID
Although it can be suppressed by readjusting the control constant of the controller 6, there is a problem that when the temperature is lowered to the original temperature, the magnetic bearing control system becomes unstable again, and it is necessary to readjust the control constant. . The present invention has been made in view of such circumstances, and a magnetic bearing that can stably control a magnetic bearing even when a gap between a rotating body and a position sensor changes due to a rise in temperature of the rotating body or the like. It is intended to provide a device. In order to achieve the above object, a magnetic bearing device according to the present invention supports a rotating body housed in a housing and a position of the rotating body which can be adjusted in a non-contact manner. A plurality of magnetic bearings mounted in a housing, position detecting means for detecting a position of the rotating body, and a detection result of the position detecting means fed back to a magnetic bearing control system, so that the rotating body floats optimally. Control means for controlling to be supported at the position,
Control constant switching means for switching the control constant of the magnetic bearing control system according to the sum of the gaps detected by the position sensors provided at positions facing each other with the rotating body as the center. Things. The magnetic bearing device of the present invention is configured as described above, and can suppress control instability caused by a gap variation between the rotating body and the position sensor due to thermal expansion or thermal contraction of the rotating body. Hereinafter, embodiments of the magnetic bearing device of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a magnetic bearing device according to the present invention, and FIG.
FIG. 5 is a diagram showing a positional relationship between an electromagnet of a five-axis magnetic bearing unit and a rotating body. The magnetic bearing device of the present invention includes a rotating body 11 that forms a rotating portion of various devices such as a turbo molecular pump,
Electromagnets 12 and 13 installed facing each other so as to support the rotating body 11 in a non-contact manner using magnetic attraction, and gaps d1 and d installed near the electromagnets 12 and 13.
2 having substantially the same characteristics for converting 2 into an electric signal
And a magnetic bearing portion 10 composed of
It comprises a control unit 20 described below, which controls so as to keep 1 and d2 constant. The rotating body 11 is actually supported by a five-axis magnetic bearing or the like. In this case, one set of the upper X-axis is located at a position shown in FIG. Electromagnets 12a, 13a and a set of electromagnets 12b, 1
3b, one set of electromagnets 12c and 13c on the lower X axis, one set of electromagnets 12d and 13d on the Y axis, and one set of electromagnets 12e and 13e on the lower Z axis. 11 rotates in a non-contact manner together with the integrated disk 11a. The gap between the rotating body 11 and each electromagnet is detected by a position sensor (not shown) provided near each electromagnet, and the driving current to each electromagnet corresponds to one set of electromagnets. It is controlled by a provided control unit (not shown). Although FIG. 1 typically shows one set of electromagnets 12 and 13, position sensors 14 and 15, and a corresponding control unit 20, a similar control unit is used for other electromagnets. The control unit 20 includes the position sensor 14,
15 is subtracted from the output signals E01 and E02 corresponding to the gaps d1 and d2 detected by the deviation signal ΔE (= E
01-E02), an adder 22 for adding the output signals E01 and E02, and control for correcting a change in the detection sensitivity of the position sensors 14 and 15 based on the output signal E03. A control constant adjusting circuit 23 for switching to a gain, a filter circuit 24 for removing a rotational speed component of the rotating body 11, and a PID for outputting a control signal in which the deviation signal ΔE changes according to a three-term operation (proportional, integral, and differential). The controller 25 and the control signal are transmitted to the electromagnets 12 and 13.
And an electromagnet drive circuit 26 that amplifies and converts the currents into currents I1 and I2 at a level that can drive the current. The adder 22 and the control constant adjusting circuit 23
The control constant adjusting circuit 23 compares the output signal E03 of the adder 22 with an internal comparison voltage and sends a switching signal to a switch 23a having gates G1 to G3. 23b and the gates G1 to G1.
A voltage source 23c that outputs gain adjustment voltages V1 to V3 corresponding to G3, and a multiplier 23d that outputs an output signal E04 obtained by multiplying the output signal ΔE of the subtracter 21 by the gain adjustment voltages V1 to V3. Have been. When the gaps d1 and d2 change due to the thermal expansion and thermal contraction of the rotating body 11, the gain adjustment voltages V1 to V3 become the position sensors 14 and 1 respectively.
The control gain is adjusted to compensate for the deterioration in the stability of the magnetic bearing control due to the change in the detection sensitivity due to the non-linearity of FIG. 5, and an example of the operation principle and setting method will be described with reference to FIG. explain. FIG. 3 shows the input / output characteristics of the position sensors 14 and 15. As the gap d1 or d2 increases, the detection sensitivity increases. Rotating body 11
When the temperature rises, the gaps d1 and d2 between the electromagnets 12 and 13 decrease due to thermal expansion, and when the temperature decreases, the gaps d1 and d2 increase due to thermal contraction. Thus, the detection sensitivity of the position sensors 14 and 15 decreases as the temperature of the rotating body 11 increases, and increases when the temperature decreases. Therefore, the magnetic bearing control can be stabilized by increasing the control gain when the temperature rises and decreasing the control gain when the temperature falls. In FIG. 3, a gap d1 when the rotating body 11 is used in a low temperature state by a light load operation, a temperature state by a normal load operation, and a high temperature state by a high load operation,
The existence range of d2 is 0 to X1, X1 to X2, and X2, respectively.
To X3, and the output signals E01 and E02 of the position sensors 14 and 15 at this time are shown as 0 to E1, E1 to E2, and E2 to E3. Also, the gradient (detection sensitivity) when the range of 0 to X1, X1 to X2, and X2 to X3 is approximated by a straight line is K1,
Indicated by K2 and K3. The output signals E0 of the position sensors 14, 15
1, E02 are added by the adder 22, and the output signal E02
03 is 2E1, 2E internally set by the comparator 23b.
2, 2E3 and the gate G
1 to G3 are turned on. If 2E1> E03, then G1 is on. If 2E1 <E03 <2E2, then G2 is on. If 2E2 <E03 <2E3, then G3 is on. The arithmetic expression of the multiplier 23d is given by V1 to V3 are set as follows. V2 = 1 / K V1 = (K2 / K1) V2 = K2 / (K · K1) V3 = (K2 / K3) V2 = K2 / (K · K3) Next, control of the magnetic bearing device of the present invention. The operation will be described. The output voltage signals E01 of the position sensors 14, 15
E02 is subtracted by the subtractor 21. The deviation signal ΔE is obtained by correcting the control gain in the control constant adjusting circuit 23 and removing the rotational speed component of the rotating body 11 by the filter circuit 24, and then outputting the proportional and integral signals from the PID controller 25 using the deviation signal ΔE as a variable. , A differential operation signal is output, and is converted into electromagnet drive currents I1 and I2 by the electromagnet drive circuit 26,
The drive current of the electromagnets 12 and 13 is adjusted so that the deviation signal ΔE becomes zero. In the normal operation state (X1 to X2), G2
Is turned on, the control gain of the control constant adjusting circuit 23 is 1, the output signal E04 is E04 = ΔE, and the PID controller 25 performs the optimal tuning of the PID control constant. In the initial operation state (0 to X1), G1 is turned on, the control gain is (K2 / K1), and its output E04
E04 = (K2 / K1) ΔE, the deviation signal ΔE is multiplied by the control gain (K2 / K1), the instability of the control operation due to the decrease in detection sensitivity is improved, and the normal operation state can be quickly reached. . Also,
In the high-temperature operation state (X2 to X3), G3 is turned on, the control gain is (K2 / K3), the output signal E04 is E04 = (K2 / K3) ΔE, and the deviation signal ΔE is the control gain (K2 / K3) times. Thus, the instability of the control operation due to an increase in the detection sensitivity is improved. The above arithmetic processing can be performed using an analog arithmetic circuit or a microcomputer (not shown) including an interface such as A / D or D / A and a CPU, ROM, RAM, or the like. FIG. 4 shows a comparison between the stable region (a) of the conventional magnetic bearing device and the stable region (b) of the magnetic bearing device of the present invention. That is, in the conventional magnetic bearing device, as shown in FIG. 4A, when the diameter of the rotating body is in the range of 2R to (2R + 2α), the magnetic bearing control is in a stable region. Then, as shown in FIG. 4 (b), when the rotating body further expands due to a temperature rise or the like and the entire body expands by + 2β, it can be switched to an appropriate control constant. In the range of 2R to (2R + 2α + 2γ),
The magnetic bearing control becomes a stable region. In the present invention, the gaps d1 and d2 are detected by the position sensors 14 and 15, the output signals thereof are added by the adder 22, and the operation area of the position sensors 14 and 15 is detected by the comparator 23b. Since the detection sensitivity is corrected by the control gain, even when the rotating body 11 is shifted from the center position and the balance of the gaps d1 and d2 is temporarily lost, the added value of the gaps d1 and d2 is Since it is almost constant, frequent switching of the control gain can be prevented, and stable control can be performed. As described above, according to the magnetic bearing device of the present invention, the output of the position sensor which opposes the rotating body is added, the gap between the rotating body and the bearing is obtained from the added value, and the gap is determined. The present invention is characterized in that the gate is opened and the control range is expanded by switching to a predetermined control gain, and the present invention is not limited to the embodiment. For example, the control constant is more finely switched. Alternatively, the gain adjustment voltage may be determined from the control result.
Further, a magnification setting device may be configured by an analog circuit including an IC and a resistor, and the resistor may be switched by the gates G1 to G3 to change the control gain. According to the magnetic bearing device of the present invention, the control gain is set based on the sum of the gaps detected by the opposing position sensors. The bearing control can always be performed stably even if the bearing expands or contracts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of a magnetic bearing device according to the present invention. FIG. 2 is a diagram showing a positional relationship between an electromagnet and a rotating body. FIG. 3 is an output characteristic diagram of a position sensor with respect to a gap. FIG. 4 is a diagram showing a stable region of a rotating body. FIG. 5 is a diagram showing a structure of a magnetic bearing device. FIG. 6 is a block diagram showing a configuration of a conventional magnetic bearing device. FIG. 7 is an output characteristic diagram of a position sensor with respect to a gap. [Description of Signs] 1, 11 ... Rotating bodies 2, 2a, 2b, 14, 15 ... Position sensors 3, 3a, 3b, 12, 12a, 12b, 12c, 12
d, 12e, 13, 13a, 13b, 13c, 13d, 13
e: electromagnets 4, 23 ... control constant adjustment circuits 5, 24 ... filter circuits 6, 25 ... PID adjusters 7, 26 ... electromagnet drive circuits 8, 16 ... motors 11a ... disks 21 ... subtracters 22 ... adders 23a ... Switch 23b Comparator 23c Voltage source 23d Multipliers E01, E02, E03, E04 Output signals d1, d2 Gap G1, G2, G3 Gates I1, I2 Current

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) F04D 29/04 F04D 29/04 RF Term (Reference) 3H022 AA01 BA06 BA07 CA16 CA50 DA08 DA09 3H031 DA02 EA12 FA13 3J102 AA01 BA03 BA17 BA18 CA10 DA02 DA03 DA09 DB05 DB10 DB11 DB27 DB29 DB30 GA06

Claims (1)

Claims: 1. A rotating body housed in a housing, a plurality of magnetic bearings mounted in the housing for supporting the rotating body in a non-contact manner and capable of adjusting the position, and the rotating body. A magnetic bearing device comprising: a position detecting means for detecting the position of the rotating body; and a control means for feeding back a detection result of the position detecting means to a magnetic bearing control system and controlling the rotating body to be supported at an optimum floating position. A control constant switching means for switching a control constant of a magnetic bearing control system in accordance with a sum of gaps detected by position sensors provided at positions opposed to each other with the rotating body as a center. Magnetic bearing device.