JP3306893B2 - Magnetic bearing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a turbo molecular pump, a rotary anode X-ray tube, a spindle for a machine tool, a centrifuge, a support and stage for a supported member such as a rotary shaft and a drive shaft of a robot, etc. The present invention relates to a magnetic bearing device used for supporting a movable portion such as a transfer device.

[0002]

2. Description of the Related Art As shown in FIG. 4, a conventional magnetic bearing device has a pair of electromagnets 12 and 13 opposed to each other across a supported member in a control axis direction and a displacement sensor 14 for detecting a displacement amount of the supported member. And a bearing control circuit 15 for holding the supported member at a predetermined position between the pair of electromagnets. The displacement sensor 14 generates a voltage signal proportional to the displacement of the supported body in the control axis direction about a displacement reference point (usually the center position of the pair of electromagnets 12 and 13).
This voltage signal is input to the bearing control circuit 15. The bearing control circuit 15 includes a PID control circuit 16 and an inversion circuit 18.
And current amplifiers 19 and 20, and the input voltage signal passes through the PID control circuit 16 to become a predetermined control voltage.
The current is converted by the current amplifier, and a constant bias current is added to the current, and the current is supplied to the electromagnet as the electromagnet drive current.

Here, the control operation of the bearing control circuit 15 will be described. FIG. 5 shows the relationship between the electromagnet drive current i supplied to the electromagnet and the electromagnetic force f exerted on the supported body by the electromagnet. As shown in the figure, the electromagnetic force f has a relationship proportional to the square of the electromagnet drive current i. In the figure, the control current _ic is obtained by converting the control voltage output from the PID control circuit 16 into a current by the current amplifier 19.
i _B indicates a constant bias current added by the current amplifiers 19 and 20, and a relationship of i = i _B + _ic is established. Meanwhile _{f c} is the output magnitude of the electromagnetic force f by the control current _{i c,} f
_B represents the outputs component of the electromagnetic force f by the bias current _{i B,} the relationship of _{f =} f B + _{f c} is satisfied. Bias current i _B is intended to be supplied with current amplifier 19 and 20 to operate a class A. Therefore, the bias current i _{B
Is, i B + n i max ≧} 0 if not copying in relation to the _n i _max is the maximum negative value of the control current _{i c.} i _B +
_When ni _max <0, as shown in FIG. 6, the class A operation cannot be performed, and the electromagnetic force is greatly distorted, so that control of the supported member becomes impossible.

Next, the inversion circuit 18 has a function of inverting the sign of the input voltage. The control voltage output from the PID control circuit 16 is inverted by the inverting circuit 18 and is input to the current amplifier 20. I _c indicated by a dotted line in FIG. 5 _'represents a control current supplied to the electromagnet 13 by a current amplifier 20, f _c indicated by dotted lines in the _figure' represents the electromagnetic force of the electromagnet 13 by the control current. Electromagnet 1
When the supported body deviates from the displacement reference point by supplying the electromagnet drive currents to the lines 2 and 13 as shown by a solid line and a dotted line, respectively, as shown in FIG. electromagnetic force also small around the bias electromagnetic force f _B, hold the deflection reference point can be the supported body to increase the electromagnetic force of the electromagnet towards which the support moves away around the bias electromagnetic force f _B It becomes possible.

As described above, the magnetic bearing device detects the deviation of the supported member from the displacement reference point by the displacement sensor, and adjusts the electromagnetic force f of the electromagnet by changing the control current _ic according to the voltage output. is intended for holding the support deflection reference point Te, but the conventional magnetic bearing device, the need to perform a class-a operation, as described above, was always supplying a constant large bias current i _B to the electromagnet .

[0006]

However, when the supported member is stably supported without shifting from the displacement reference point, the voltage signal extracted from the displacement sensor is almost zero, and is therefore input to the electromagnet. Control current _ic
Is also almost zero. In such a case, although a small bias current is also become possible to stable driving of the magnetic bearing device is capable of Class A operation, a large bias current i _B even if such a conventional apparatus with respect to the electromagnet Since the power is supplied, there is a disadvantage that the power consumption becomes very large.

[0007] The present invention, stability of the support state of the support in what has been made to effectively solve the above drawbacks, i.e. the magnitude of the bias current i _B in accordance with the deviation from the deflection reference point of the support An object of the present invention is to provide a magnetic bearing device with low power consumption by controlling the magnetic bearing device.

[0008]

In order to achieve the above object, a magnetic bearing device according to the present invention comprises a pair of electromagnets opposed to each other across a supported member in a control axis direction, and a pair of electromagnets in the same direction. A displacement sensor that detects the amount of displacement, and a bearing control circuit that adjusts a control current supplied to the electromagnet in order to hold the supported body at a predetermined position between the electromagnets in accordance with an output of the displacement sensor, The bearing control circuit removes the DC component from the output signal of the displacement sensor, adjusts the bias current according to the output signal of the displacement sensor from which the DC component has been removed, and limits the bias current so that the bias current does not exceed a certain value. A bias adjustment circuit having a function of limiting a bias current adjustment range is provided, and an addition current of an output bias current of the bias adjustment circuit and the control current is supplied to the electromagnet as an electromagnet drive current. Characterized in that way the.

[0009]

The magnetic bearing device according to the present invention is constructed as described above, and the bias current is adjusted by the output signal of the displacement sensor from which the DC component has been removed. The bias current responds quickly to and can stably support the displacement reference point of the supported body.
The bias current is small when the supported object is stably supported near the displacement reference point, and the bias current to be supplied to the electromagnet is small. In this case, the bias current can be increased. In addition, since the bias current is limited so as not to exceed a certain value, saturation of the electromagnet, the electronic circuit, and the like can be prevented, and the electromagnet is supplied with an added current of the control current and the bias current as its drive current. Therefore, no bias coil is required, the configuration of the electromagnet is simplified, and the size of the magnetic bearing device can be reduced.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the magnetic bearing device of the present invention will be described with reference to FIG.

In FIG. 1, reference numeral 1 denotes a supported member, reference numerals 2 and 3 denote electromagnets opposed to each other with a rotating body interposed therebetween, reference numeral 4 denotes a displacement sensor disposed in proximity to the electromagnets 2 and 3, and reference numeral 5 denotes an electromagnet. This is a bearing control circuit that holds the support at the displacement reference point and controls the bias current. In the bearing control circuit 5, 6 is PI
D (proportional-integral-differential) control circuit, 7 is a bias adjusting circuit for outputting a predetermined bias voltage according to the voltage signal of the displacement sensor, 8 is an inverting circuit for inverting the input voltage, 9 and 10 are control input ports. This is a current amplifier having a bias adjustment input port. The current amplifier has a function of converting a voltage signal input to the control input port into a current proportional to the current signal, that is, a control current, a function of converting the voltage signal input to the bias adjustment input port into a current proportional thereto, That is, it has a function of converting to a bias adjustment current, and further has a function of adding a steady-state bias current to the bias adjustment current to make it a bias current, adding the control current thereto, and outputting it as an electromagnet drive current. Here, the steady bias current is a current supplied to the electromagnet as a bias current when the input of the bias adjustment input port is zero, and its value is predetermined.

Next, the operation of controlling the bias current supplied to the electromagnet when the supported body vibrates under the external force in the magnetic bearing device thus configured will be described. When no external force is applied, the supported member 1 is levitated and supported about the center of the electromagnets 2 and 3 facing each other, that is, the displacement reference point. Here, as shown in FIG.
Considering the control operation by the magnetic bearing device at t3, it is assumed that the supported body 1 receives an external force and vibrates in the control axis direction about the displacement reference point only from time t1 to t2 in FIG.
In such a case, the voltage signal output from the displacement sensor is shown in FIG.
(a).

Next, the operation of the bias adjustment circuit based on the output of the displacement sensor will be described. FIG. 3 shows an embodiment of the bias adjustment circuit. In the figure, the DC component of the voltage input to the bias adjustment circuit is removed by the capacitor Cd, and only the vibration component is partially rectified in the negative direction by the diode 30. Then, after the charge is stored in the capacitor Cb, the charge passes through the inverting and integrating circuit 31 and becomes the output of the bias adjustment circuit. Here, since the inverting and integrating circuit 31 forms an incomplete integrating circuit by the resistance Ra across the input and output of the operational amplifier, the output gradually increases due to the increase in the vibration amplitude of the voltage signal of the displacement sensor, and Has the function of gradually lowering its output when is attenuated. Also, the output of the operational amplifier is limited by the Zener diode 32 connected in parallel with the resistor Ra.
The output of the bias adjustment circuit does not exceed a certain value.

FIG. 2 (b) shows a change in the output voltage when the voltage signal of the displacement sensor shown in FIG. 2 (a) is input to the bias adjustment circuit. From time 0 to time t1, the output of the displacement sensor is zero, so the output of the bias adjustment circuit is also zero. Next, it is assumed that the displacement sensor output vibrates at time t1 and gradually attenuates until time t2. Note that such vibration is a phenomenon that generally occurs when disturbance is applied to the supported member. At this time, the integrated value of the inverted value of the portion corresponding to the negative voltage of the displacement sensor output shown in FIG. 2A becomes the output voltage of the bias adjustment circuit, and the output gradually increases. However, as the amplitude decreases, the rate of increase decreases and changes as shown in FIG. 2 (b). Since the output of the displacement sensor is zero between times t2 and t3, the output of the bias adjustment circuit also approaches zero and becomes completely zero at time t3. If the vibration continues without attenuating, the output of the bias adjustment circuit increases, but does not exceed a predetermined value due to the action of the Zener diode 32.

These outputs are connected to the current amplifier 9,
Supplied to 10 bias adjustment input ports. The current amplifier 9 converts a control current proportional to the control voltage output from the PID control circuit supplied to the control input port and a bias adjustment current proportional to the voltage supplied to the bias adjustment input port into a steady bias current. And a bias current, which is a current added to the current, is supplied to the electromagnet 2 as an electromagnet drive current. Further, the current amplifier 10 has a control current which is a current proportional to an inverted value of the control voltage which is an output of the PID control circuit;
A bias current supplied in the same procedure as that of the current amplifier 9 is added and supplied to the electromagnet 3 as an electromagnet drive current. FIG. 2C shows the outputs of the current amplifiers 9 and 10 in such a case.

As described above, according to the magnetic bearing device of this embodiment, when the supported member is stably supported without deviating from the displacement reference point, the bias current to be supplied to the electromagnet is small. The bias current becomes a steady-state bias current for the current amplifiers 9 and 10, and when the supported body is supported out of the displacement reference point, the bias current can be increased. Therefore, similarly to the conventional magnetic bearing device, it becomes possible to perform the electromagnetic drive by the class A operation and to suppress the power consumption lower than that of the conventional device.

In the above embodiment, PID control is used as control means based on the output of the displacement sensor. However, PD control, phase advance / delay control, control based on modern control theory, and the like are also possible. It is also possible to perform the control by using a microcomputer or the like after digitizing the whole.

[0018]

The magnetic bearing device of the present invention has the following effects. The bias current quickly responds to deviation from the displacement reference point of the supported body due to disturbance, and can be stably supported at the displacement reference point of the supported body, and the supported body is stably supported without deviating from the displacement reference point In this state, the bias current to be supplied to the electromagnet can be reduced, and when the supported member rotates out of the displacement reference point, the bias current can be increased. As a result, it becomes possible to drive the electromagnet by the class-A operation and to reduce the power consumption lower than that of the conventional device, and have the same performance as the conventional magnetic bearing device and lower power consumption compared to the conventional device. Supply of the magnetic bearing device. Also, since the bias current does not exceed a certain value due to the bias current adjustment range limiting function of the bias adjustment circuit, it is possible to prevent saturation of the electromagnet, the electronic circuit, and the like, and to add the control signal and the bias current to the electromagnet. Since the current is supplied as the drive current, no bias coil is required, no bias coil is required, and the size of the magnetic bearing device can be reduced.

[Brief description of the drawings]

FIG. 1 is a control block diagram of an embodiment of a magnetic bearing device according to the present invention.

FIG. 2 is a time chart showing a temporal change of an output signal of each part of the magnetic bearing device.

FIG. 3 is a diagram illustrating an integration circuit as an example of a bias adjustment circuit.

FIG. 4 is a model diagram illustrating an operation principle of a conventional magnetic bearing device.

FIG. 5 is a diagram showing a relationship between a control current supplied to an electromagnet and an electromagnetic force exerted on a supported body by the electromagnet.

FIG. 6 is a diagram showing a state in which the class A operation is not performed because the bias current is small, and the electromagnetic force is greatly distorted with respect to the electromagnet drive current.

[Explanation of symbols]

 1, 11: rotating body 2, 3, 12, 13: electromagnet 4, 14: displacement sensor 5, 15: bearing control circuit 6, 16: PID control circuit 7, bias adjustment circuit 8, 18, inversion circuit 9, 10, 19, 20: Current amplifier

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F16C 32/04

Claims (1)

(57) [Claims] 1. A pair of electromagnets opposed to each other across a supported member in a control axis direction, a displacement sensor for detecting a displacement amount of the supported member in the same direction, and a supported sensor in accordance with an output of the displacement sensor. A bearing control circuit that adjusts a control current supplied to the electromagnet in order to hold a body at a predetermined position between the electromagnets, wherein the bearing control circuit converts a direct current component from an output signal of the displacement sensor to the bearing control circuit. A bias adjustment circuit having a bias current adjustment range limiting function that removes and adjusts the bias current according to the output signal of the displacement sensor from which the DC component has been removed, and limits the bias current so that the bias current does not exceed a predetermined value, A magnetic bearing device wherein an added current of an output bias current of the bias adjustment circuit and the control current is supplied to the electromagnet as an electromagnet drive current.