JP3036101B2 - Magnetic bearing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic bearing used for various rotary machines such as a turbo molecular pump, a rotary anode X-ray tube, a spindle for machine tools, a centrifuge, and a robot.

[0002]

2. Description of the Related Art A magnetic bearing is provided with a pair of electromagnets facing each other across a supported object and a displacement sensor for detecting a displacement amount of the supported object in the same direction in a control axis direction. A bearing control circuit for holding the supported object at a predetermined position between the electromagnet and the electromagnet is configured. The bearing control circuit has a sensor circuit mainly composed of an operational amplifier and the like. A voltage signal taken out from the displacement sensor is first input to this sensor circuit, and is compared with a reference voltage in this circuit, and is proportional to the differential pressure. The output voltage is output. Then, a drive current is output to the electromagnet via a PID circuit, a current amplifier, and the like provided in the next stage. In order for this magnetic bearing to function properly without being affected by machining and assembly errors, a predetermined drive current is applied to the electromagnet for a predetermined amount of displacement of the supported object in a state where the magnetic bearing is completely assembled. And the condition for the output voltage of the operational amplifier not to be offset from 0 when the supported object is at the center position. Must. Conventionally, these gain adjustment and offset adjustment are conventionally performed by full-scale adjustment based on the state in which the supported object has reached the closest point and the farthest point with respect to the displacement sensor.

[0003]

However, there are quite a lot of devices using magnetic bearings in which the supported object is completely shut off from the outside after the assembly is completed. For this reason,
In order to move the supported object to the nearest point and the farthest point with respect to the displacement sensor, there is no other way than to move the device by gravity by tilting or inverting the entire device. For this reason, the labor burden of the worker is extremely large, and there is a disadvantage that adjustment work is difficult. In addition, even if a part of the supported object is exposed to the outside in a state where the device is assembled, it is difficult to move if the weight of the supported object is large.
Even though the weight is relatively small, even if it can be moved, there is a drawback that an adjustment error is likely to occur depending on the degree of manual operation.

[0004] It is an object of the present invention to provide a magnetic bearing which can effectively solve such a problem.

[0005]

In order to achieve the above object, the present invention employs the following configuration.

That is, a magnetic bearing according to the present invention comprises a pair of electromagnets opposed to each other across a supported object in a control axis direction;
A displacement sensor for detecting an amount of displacement of the supported object in the same direction, and a bearing control circuit for holding the supported object at a predetermined position between the displacement sensor and the electromagnet; An excitation circuit is provided which can excite the pair of electromagnets independently in a state where the control circuit does not function.

[0007]

With such a structure, a pair of electromagnets located at opposite positions can be independently excited through the excitation circuit when the assembly is completed. For this reason, even in a state where the magnetic bearing is incorporated in the device, the supported object can be easily and reliably moved to the farthest point and the nearest point of the displacement sensor without using an artificial force.

[0008]

An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, this magnetic bearing includes a pair of electromagnets A and B opposed to each other across a supported object 3 in the X-axis direction as a control axis, and the displacement of the supported object 3 in the same direction. And a displacement sensor 4 for detecting the amount. The electromagnets A and B include magnetic poles a ₁ and b ₁ and excitation coils a ₂ and b ₂ wound around the magnetic poles a ₁ and b ₁ . Displacement sensor 4
, For example those of the eddy current, the sensor head 4a is disposed at the same radial position and the inner end face of the pole b ₁ of the magnetic bearing B-side, ranging face serving the supported object from the sensor heads 4a 3 Is taken out in proportion to the distance to the outer peripheral surface 3a. Further, a bearing control circuit 5 for holding the supported object 3 at the center position is provided between the displacement sensor 4 and the electromagnets A and B.

The bearing control circuit 5 basically includes a sensor circuit 6, a PID (proportional-integral-derivative) circuit 7, and a current amplifier 8
It is composed of The sensor circuit 6 is mainly composed of an operational amplifier 6a as schematically shown in FIG. 2, for example.
An intermediate tap potential from a variable resistor 6b provided for performing offset adjustment is input, and the difference is amplified and output to the output side. 6c is a variable resistor for adjusting the amplification factor (gain) of the operational amplifier 6a according to the intermediate tap position. These variable resistors 6b, the tap position of 6c is of a variable by the offset adjustment signal s ₁ and the gain adjustment signal s ₂ from the outside. Further, the PID circuit 7 in FIG. 1 can appropriately modify the output from the operational amplifier 6a so as to eliminate sudden overshoot control. The output from the PID circuit 7 is amplified by the current amplifier 8, and is supplied as a drive current to one of the exciting coils a ₂ and b ₂ of the electromagnets A and B. When the drive current of one electromagnet A (B) is increased,
The drive current of the other electromagnet B (A) decreases.

In such a configuration, this embodiment includes a microcomputer 9 for automatically adjusting the gain and offset of the sensor circuit 6.
This microcomputer 9 has a CPU 9a, a memory 9
b and an interface 9c,
The output from the sensor circuit 6 is input, and a predetermined operation is performed according to a program stored in advance in the memory 9b.
Wherein the offset adjustment signal s1 to the variable resistor 6b of the sensor circuit 6, also has a variable resistor 6c gain adjustment signal s ₂ to be output, respectively. The microcomputer 9 has two cables between the microcomputer 9 and the current amplifier 8.
Bull a _3, b ₃ are connected by these microcomputer - motor 9, Ke - Bull a _3, b _3, current amplifier 8, and the exciting coil a ₂ described above, b ₂ is the excitation circuit 10 of the present invention Make up. That is, the excitation signal s _a (s) is transmitted from the microcomputer 9 to the cable a ₃ (b ₃ ).
_{When b} ) is output, the electromagnet A (B) is independently excited to move the supported object 3 to the farthest point (closest point) from the displacement sensor 4 as shown in FIG. 3 (FIG. 4). It can be sucked and moved. These excitation signals s _a and s _b are generated from specific steps in the aforementioned sensor circuit adjustment program. Further, in this embodiment, a switch circuit 11 that can appropriately shut off the bearing control circuit 5 is provided between the PID circuit 7 and the current amplifier 8, and the switch circuit 11 is switched from the microcomputer 9 to the switch circuit 11. The signals s _on and s _off are output. These switching signals s _on and s _off are also issued from specific steps in the program described above.

FIG. 5 is a flowchart showing an outline of the program. The operation of the microcomputer 9 will be described below with reference to the flowchart. In addition,
When the displacement sensor 4 is properly adjusted, the output is + V _FS on the electromagnet A side and −V _FS on the B side.

When the program starts, first, at step 21, a switching signal s _off is outputted to the switch circuit 11, and
The bearing control circuit 5 is shut off. Thereafter, it outputs the excitation signal s _a at step 22, positioned on the farthest point from the displacement sensors 4該被supporting structure 3 by sucking the supported object 3 to the electromagnet A side (see FIG. 3). Then, in step 23, the output value _VA from the displacement sensor 4 at this time is read and stored in the memory 9b. Next, in step 24, the excitation signal s _b
Is output, and the supported object 3 is attracted to the electromagnet B side to position the supported object 3 at the nearest point from the displacement sensor 4 (see FIG. 4). Then, read the output value V _B from the displacement sensor 4 when this in step 25, is stored in the memory 9b. Furthermore, the flow proceeds to step 26, the previously read out value V _A, the V _B, performs _{Ve = (V A + V B} ) / 2 becomes operational. This Ve corresponds to the offset deviation amount.
Then, output the offset adjustment signal s ₁ at step 27, the output of the displacement sensor 4 at the nearest point is adjusted to be V _B -Ve. Furthermore, it outputs a gain adjustment signal s ₂ in step 28, so that the overall output of the displacement sensor 4 at the closest point becomes -V _FS gain adjustment. Then, positioning the supported object 3 outputs the excitation signal s _a re electromagnet A moves to step 29 to the farthest point from the displacement sensors 4, or the output of the displacement sensor 4 at step 30 is turned + V _FS Determine whether or not. If YES, it indicates that the gain and offset are accurately adjusted, and the program ends after outputting the switching signal s _on to the switch circuit 11 to connect the bearing control circuit 5 in step 31. In the case of NO, the procedure returns to before step 23 and the procedure from step 23 onward is repeated.

With such a configuration, the microcomputer 9 can start the program only when the assembly is completed, and the microcomputer 9 can be connected to the supported object 3 through the excitation circuit 10.
Is moved to the farthest point and the nearest point from the displacement sensor 4,
The gain adjustment and offset adjustment of the sensor circuit 6 are automatically performed by the full scale adjustment. Therefore, no manual labor is required, and the accuracy of adjustment can be improved.

When a current is rapidly applied to the electromagnets A and B, a large back electromotive force is generated transiently,
The magnetic bearing may be damaged by the shock when the water is absorbed. In such a case, it is effective to include control for gradually increasing or decreasing the excitation signals s _a and s _b in the program. Further, in the above description, the displacement sensor is provided only on the electromagnet B side, but in general, it is often provided on both the electromagnets A and B side. In such a case, the difference between the detection values of the two displacement sensors may be input to the operational amplifier of the sensor circuit, and the difference may be offset-adjusted. Further, the microcomputer need not necessarily be incorporated in the circuit,
An external connection may be made only when adjustment is required. Further, the present invention is not limited to the fully automatic adjustment as in the above embodiment, but includes at least an excitation circuit provided, and other adjustments are performed manually. Furthermore,
In the adjustment of the sensor circuit, it is not always necessary to perform the gain adjustment and the offset adjustment in a pair, and one or both of them may be omitted depending on the type of sensor used and the required detection accuracy. In addition, various modifications can be made without departing from the spirit of the present invention.

[0016]

As described above, the magnetic bearing of the present invention has the above-described structure, and therefore, even in a state where it is incorporated in the apparatus, the supported object can be easily and reliably moved farthest from the displacement sensor without using any artificial force. Can be moved to point and nearest point. For this reason, even when the supported object of the apparatus is shielded from the outside or the weight of the supported object is excessive, the gain adjustment and the offset adjustment can be performed with a very simple operation or a completely artificial operation. It can be completed accurately without the need.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram schematically showing a sensor circuit of the embodiment.

FIG. 3 is a view corresponding to FIG. 1 showing the operation of the embodiment.

FIG. 4 is a view corresponding to FIGS. 1 and 3 showing the operation of the embodiment.

FIG. 5 is a flowchart showing an outline of control performed in the embodiment.

[Explanation of symbols]

 A, B: electromagnet X: control shaft 3: supported object 4: displacement sensor 5: bearing control circuit 10: excitation circuit

Claims (1)

(57) [Claims] A pair of electromagnets facing each other across a supported object and a displacement sensor for detecting a displacement amount of the supported object in the same direction are provided in a control axis direction. Wherein a bearing control circuit for holding the supported object at a predetermined position is provided, wherein an excitation circuit capable of independently exciting the pair of electromagnets in a state where the bearing control circuit does not function is provided. A magnetic bearing.