JPH0315050B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a controlled radial magnetic bearing for high speed rotating machines.

As shown in FIG. 1, the conventional controlled radial magnetic bearing detects the radial displacement of the rotor 2 from its equilibrium point using a radial displacement sensor 1, and then sends the signal to a control circuit 3 to adjust the phase and gain to an appropriate level. Further, in accordance with the compensated signal, the electromagnet drive circuit 4 drives the radial electromagnet 5 to return and hold the rotor to the equilibrium point.

Only the results will be described here, but the following can be shown theoretically.

As shown in Fig. 2, if the geometric center of the rotor 2 is S, the center of gravity is G, and the distance between S and G is ε, then when the system is rotated beyond the resonance point ω ₀ , the rotor As shown in FIG. 3, it rotates at a rotational speed ω (ω>ω ₀ ) with the center of gravity G on the inside and the geometric center S on the outside. As the rotational speed ω increases, the center of gravity G approaches the rotational center O, and at the infinite limit of the rotational speed ω, O and G coincide. Therefore, when the rotational speed ω is sufficiently high (ω≫ω ₀ ), the rotor can be considered to be rotating around the center of gravity G. Similarly, as shown in Fig. 4, the geometric rotation axis is R,
Even if the principal axis of inertia is I and the angle between R and I is τ, if the rotational speed ω is sufficiently high (ω≫ω ₀ ), the rotor can be considered to be rotating with the principal axis of inertia I as the rotation axis. can.

For simplicity, let us consider the vibration transmitted to the outer cylinder shown in FIG. 1 when the rotor is rotated at high speed (ε≫ω ₀ ) with τ=0 and ε≠0. Since the rotor rotates around the center of gravity G, as shown in FIGS. 5 and 6, the system direction displacement sensor 1 always detects a displacement of ±ε in synchronization with the rotation speed. Corresponding to that signal, a control current synchronized with the rotation speed flows through the radial electromagnet 5, so if the equivalent spring constant of the radial magnetic bearing is k, a force of approximately ±kε flows through the radial electromagnet 5. , is transmitted to the outer cylinder 6 in synchronization with the rotation speed. The same applies to the case where τ≠0.

For the reasons stated above, in the case of conventional controlled radial magnetic bearings, the rotor must be sufficiently balanced.
Unless ε and τ are minimized, the vibrations transmitted to the outside cannot be reduced, and the power consumption due to the control current flowing through the radial electromagnets cannot be reduced.

The present invention is intended to solve the above drawbacks,
In a radial magnetic bearing consisting of a radial electromagnet, a radial displacement sensor, a control circuit that controls the radial electromagnet using a radial displacement sensor signal, and an electromagnet drive circuit, by inserting a function generator into the control circuit. By reducing the spring constant near the equilibrium point to zero or very small, the purpose is to reduce the vibration transmission to the outside and the power consumption of the radial electromagnet even if ε and τ are large values to a certain extent. This is what I did.

The operating principle of the present invention will be explained using FIG. 7.

Parts common to those in FIG. 1 are designated by the same reference numerals.

Now, the rotational speed (ω≫
ω ₀ ), the radial displacement sensor 1 outputs an output corresponding to the radial displacement ±ε synchronized with the rotational speed ω, as described above. The output is inputted as shown in Figure 8 by ±
Up to ΔV ₀ , the input/output conversion coefficient is 1/f (f>
0), ΔV ₀ or more and −ΔV ₀ or less, the signal is passed through a function generator 7 whose input/output conversion coefficient is 1, and then passed through a phase and gain compensation circuit 8 which functions similarly to a conventional control circuit. Further, according to the compensated signal,
The electromagnet drive circuit 4 drives the radial electromagnet 5.

Here, if the signal output from the radial displacement sensor 1 is S ₀ sin (wt+), then if the function generator 7 is set so that it becomes ΔV _p S _p , the equivalent spring constant becomes 1/f, so The vibration transmitted to the outer cylinder 6 in synchronization with the rotational speed is 1/f. Also, the power consumption of the radial electromagnet is correspondingly lower. Also, due to the influence of some disturbance, the rotation axis and center of gravity swing, and the output from radial displacement sensor 1 changes from ΔV ₀ or more to −ΔV _0.
If it falls below, it will be pulled back to the center by the normal spring constant k. Further, even while reaching steady rotation, the whirling of the rotor can be suppressed almost in the same way as in the conventional case (if S ₀ =ΔV ₀ , it increases by ε compared to the conventional one). In other words, the conventional control characteristics can be maintained even when a swing larger than ε occurs, such as when a large disturbance occurs when passing through the resonance point.

The larger f is, the lower the vibration transmitted to the outer cylinder 6 and the lower the power consumption of the radial electromagnet.
Although f should be made as large as possible, the upper limit of f is determined because this radial magnetic bearing must be stable even near the equilibrium point. As an extreme example, if the unstable spring constant of the radial magnetic bearing is zero (the bias current to the radial electromagnet is zero, and the instability caused by the motor, gravity, etc. is zero), f can be made infinite. , the vibration transmitted to the outer cylinder and the power consumption of the radial electromagnet become zero.

As described above, by inserting the function generator as described above into the control circuit, the spring constant near the equilibrium point can be made zero or very small, and the spring constant can be transmitted to the outer cylinder during steady rotation without compromising the control characteristics. The generated vibrations and the power consumption of the radial electromagnet can be significantly reduced compared to the conventional case.

In this way, the low-vibration, low-power-consumption controlled directional magnetic bearing is suitable for applications such as axial flow molecular pumps that require high-speed, low-vibration rotation and are often operated for long periods of time.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a conventional controlled radial magnetic bearing, Fig. 2 is a sectional view perpendicular to the rotation axis showing the relationship between the geometric center of the rotor and the center of gravity, and Fig. 3 is a diagram showing the structure of a conventional controlled radial magnetic bearing. This diagram schematically shows the whirling situation of the rotor when the rotor is rotated beyond the resonance point of the system. Figure 4 shows the relationship between the rotor's geometric axis of rotation and the principal axis of inertia. In the cross-sectional view parallel to the rotation axis, the fifth
6 and 6 are cross-sectional views of the rotor perpendicular to the axis of rotation showing the situation when the rotor is rotated sufficiently above the resonance point, and FIG. 7 is a configuration diagram showing an embodiment of the present invention. FIG. 8 is a characteristic diagram showing the characteristics of the function generator. 1... Radial displacement sensor, 2... Rotor, 3
... Control circuit, 4 ... Electromagnet drive circuit, 5 ... Radial electromagnet, 6 ... Outer cylinder, 7 ... Function generator, 8
... Phase, gain compensator, S ... Geometric center of rotor, G ... Center of gravity of rotor, ε ... Distance between SG, O ... Center of rotation, ω ... Rotor rotation speed, R ...
...Geometric rotation speed of the rotor, I...Rotor's rotational axis, τ...Angle formed between RI, ±ΔV ₀ ...Break point of the function generator.

Claims (1)

[Claims] 1. A radial electromagnet that supports a rotor of a high-speed rotating machine, a radial displacement sensor that detects radial displacement of the rotor, and a control signal for the radial electromagnet in response to a displacement output signal of the radial displacement sensor. and an electromagnet drive circuit that drives the radial electromagnet based on the control signal, the control circuit controls the radial displacement of the rotor based on the displacement output signal. When the absolute value is larger than a predetermined value, a control signal exhibiting a normal spring constant is generated, and when the absolute value of the radial displacement of the rotor is smaller than a predetermined value, a spring constant is smaller than the normal spring constant. A low-vibration, low-power consumption control type radial magnetic bearing characterized by having a function generator that generates a control signal exhibiting the following characteristics.