JP4220859B2 - Magnetic bearing - Google Patents

Description

  The present invention relates to a magnetic bearing that supports a rotor in a non-contact state by a magnetic force, and more particularly, to a magnetic bearing provided with a sensor that detects a gap between a stator and a rotor.

  Magnetic bearings have been used for various types of bearings because they can support a rotating body in a non-contact manner. However, magnetic levitation is inherently unstable, and it is necessary to detect the flying height and stabilize it by feedback control. Sensors for detecting the flying height include an eddy current sensor, an inductance sensor, and the like. However, these are generally expensive and have a problem that a space for installing the sensor is limited. In addition, since it is necessary to install the magnetic bearing and the sensor apart from each other, there is a problem that the stable region of the feedback system is narrow and it is difficult to stabilize. In particular, recently, there has been a demand for magnetic bearings for ultra-small rotating bodies, and the limited installation space for sensors is a major obstacle to downsizing.

As an effective method for solving this problem, a self-sensing technique using an electromagnet of a magnetic bearing as a sensor has recently been studied (Patent Document 1). The principle of magnetic bearing position detection using self-sensing technology is as follows. That is, when the position of the rotor changes, the distance (gap) from the magnetic pole of the magnetic bearing to the rotor changes, thereby changing the inductance of the magnetic pole. The gap can be estimated by detecting this change in inductance by some method. Conventionally, a high-frequency signal is superimposed on the excitation coil of an electromagnet and a rotor displacement is estimated from the current and voltage of the high-frequency component, and a mathematical model of the rotor magnetic bearing system is constructed, thereby creating an observer for displacement estimation. There have been attempts to do so.
JP 2001-177919 A (paragraphs 0003 to 0005, FIGS. 1 and 2)

  However, the above-described conventional magnetic bearing using self-sensing has a poor position estimation accuracy compared to a method using a separate displacement sensor, and a practical method has not been developed yet.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a magnetic bearing that has high position estimation accuracy and can be further reduced in size and weight.

Magnetic bearing Ru engagement with the invention, the stator and, projecting in a magnetic bearing having a rotor that rotates while being supported in a non-contact state by the magnetic force to the stator, wherein the stator is radially toward the rotor A plurality of main poles each having an exciting coil facing the rotor with a predetermined gap, and positions shifted in the circumferential direction with respect to the magnetic flux concentration parts of the plurality of main poles. And a plurality of supplemental poles having permanent magnets for supplying a bias magnetic flux so that the magnetic flux concentrating portion of the main pole adjacent to the first pole has a first polarity and a second polarity. Japanese that is attached to the distal end of the magnet to have a magnetic flux sensor for detecting a gap between the rotor and forms a magnetic circuit control flux is independent of the permanent magnet produced by the exciting coil To.

In one embodiment of the magnetic bearing of the invention, the a plurality of four auxiliary poles interpole are arranged at intervals of 90 °, opposite of the four magnetic flux sensor mounted to the distal end of interpole A control circuit that detects a displacement of the rotor relative to the stator from a difference in output of a magnetic flux sensor that controls the current value of the exciting coil.

According to magnetic bearing of the present invention, the magnetic flux stator, since it has a plurality of permanent magnets supplying flux to the rotor and facing the rotor, which is generated in the gap between the permanent magnet and the rotor, It varies with the inverse of the size of the gap. By detecting this change in magnetic flux with a magnetic flux sensor attached to the tip of the permanent magnet, the displacement of the rotor can be detected with high accuracy.

Further, according to this onset Ming magnetic bearing, with respect to the magnetic flux concentrating portion of the plurality of main poles which protrude towards the rotor, the tip of the commutating poles with permanent magnets for supplying the bias magnetic flux in the circumferential direction The magnetic circuit is formed such that the tip of the complementary pole is disposed at a shifted position and the magnetic flux concentrating portion of the main pole adjacent thereto has the second polarity. The generated magnetic flux is controlled by an excitation coil wound only on a plurality of main poles to control the radial magnetic force, and the displacement of the rotor is detected by a magnetic flux sensor installed at the tip of the auxiliary pole. Yes. For this reason, according to the present invention, the control magnetic flux generated by the exciting coil of the main pole and the bias magnetic flux by the complementary pole can be made into a substantially independent magnetic circuit, reducing mutual interference and controlling response. As a result, the influence of the control magnetic flux on the displacement detection by the magnetic flux sensor can be eliminated.

  Also, by shifting the circumferential position of the main pole that generates the control magnetic flux and the auxiliary pole that generates the bias magnetic flux, the gap between the main pole and the rotor and the gap between the auxiliary pole and the rotor are It can also be an individual gap suitable for each. Therefore, for example, the gap between the auxiliary pole and the rotor can be set to be larger than the gap between the main pole and the rotor, so that a sufficient space for arranging the magnetic flux sensor can be secured.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a sectional view showing the configuration of a four-pole magnetic bearing according to the first embodiment of the present invention.
The magnetic bearing has an annular stator 1 disposed outside and a rotor 2 disposed inside the stator 1.
The stator 1 includes a yoke 11. The yoke 11 is made of a magnetic material such as a laminated steel plate, and protrudes from the inner peripheral side of the annular portion 12 toward the center of the annular portion 12 and is arranged in four main portions alternately arranged at intervals of 45 ° in the circumferential direction. It has a salient pole part 13 and a supplementary salient pole part 14. An exciting coil 15 is wound around each of the four main salient pole portions 13, and the exciting coil 15 and the main salient pole portion 13 constitute the main pole 3. A permanent magnet 16 for generating a bias magnetic flux has a first polarity (for example, an N pole) at the tip side of the four auxiliary salient pole portions 14 that are 45 ° out of phase with the four main salient pole portions 13. It is installed. The permanent magnet 16 and the complementary salient pole portion 14 constitute the complementary pole 4. A magnetic flux sensor 17 is attached to the tip of the auxiliary pole 4, that is, the N pole side of the permanent magnet 16. As the magnetic flux sensor 17, for example, a Hall sensor, a magnetoresistive sensor, or the like can be used.

  On the other hand, the rotor 2 has a magnetic material such as a laminated steel plate or electromagnetic material disposed at least on the outer peripheral portion, and is disposed inside the stator 1. The gap between the outer peripheral surface of the rotor 2 and the tip of the main salient pole portion 12 is, for example, 1 mm, and the gap between the outer peripheral surface of the rotor 2 and the magnetic flux sensor 17 is, for example, 2 mm. The gaps for 2 can also be set individually. Further, the interval between the main pole 3 and the auxiliary pole 4 is more than twice the gap described above so that the bias magnetic flux supplied from the permanent magnet 16 once reaches the rotor 2 and reaches the main pole 3 from the rotor 2. It is desirable to set as follows.

  According to such a magnetic bearing, as indicated by a dotted arrow in FIG. 1, since the tip side of the permanent magnet 16 is magnetized to the N pole, the bias magnetic flux Φb generated by the permanent magnet 16 is changed to the auxiliary pole 4. Is formed in a path that reaches the main pole 3 that is adjacent on both sides via the rotor 2 and returns to the auxiliary pole 4 via the annular portion 12. Thereby, the front-end | tip (magnetic flux concentration part) of the main pole 3 turns into an S pole. Further, the exciting coils 15 of the opposing main poles 3 are connected in series, and the main current 3 is excited in the same direction, that is, by exciting the opposing surfaces of the opposing main poles 3 to be different from each other. The control magnetic flux Φc generated by the exciting coil 15 of the pole 3 acts to strengthen the magnetic flux of one main pole 3 and weaken the magnetic flux of the other main pole 3. As a result, a radial force is generated and functions as a radial bearing. Since the control magnetic flux Φc is formed in a path through the main poles 3, that is, a path independent from the path of the bias magnetic flux Φb, the control magnetic flux Φc is hardly influenced by the bias magnetic flux Φb, and the control force and Control responsiveness is improved.

Further, since the bias magnetic flux Φb is not affected by the control magnetic flux Φc, the bias magnetic flux Φb is considered to change in response to only the change in the gap between the auxiliary pole 4 and the rotor 2. For this reason, by detecting the magnetic flux change in the gap by the magnetic flux sensor 17, the displacement of the rotor 2 can be estimated with high accuracy.
Now, an xy coordinate system as shown in FIG. 1 is set, the displacements of the rotor 2 in the x and y directions are respectively x and y, the average gap between the rotor 2 and the auxiliary pole 4 is ga, and the magnetic flux sensor 17 detects. Assuming that the gaps are g1, g2, g3, and g4 in order from the upper right in FIG. 1, the gaps g1 to g4 detected by the magnetic flux sensors 17 are:

It is represented by
Therefore, the displacements x and y in the x and y directions of the rotor 2 are

  It can be asked. Incidentally, the magnetic flux sensor 17 actually detects the magnetic flux Φb, and this magnetic flux Φb changes with the reciprocal of the gap. However, since the displacement of the rotor 2 is usually very small, the gap can be approximated by a value obtained by inverting the sign of the change in the magnetic flux Φb.

FIG. 2 is a diagram illustrating an example in which a control circuit for controlling the magnetic bearing of the present embodiment is configured based on the above points.
The signals output from the quadrupole magnetic flux sensor 17 are signals obtained by inverting the signs of changes in the gaps g1 to g4, and these signals are amplified by the sensor amplifiers 21, 22, 23, and 24, respectively. The arithmetic circuits 25, 26, 27, and 28 that execute Equation 2 are converted into x-direction displacement signals and y-direction displacement signals. These displacement signals are input to the x-direction controller 29 and the y-direction controller 30, respectively. The x-direction controller 29 and the y-direction controller 30 output, for example, a PID control signal based on the x-direction displacement signal and the y-direction displacement signal, respectively, and excite each main pole 3 via the power amplifiers 31 and 32. Feedback is provided to the coil 15. As described above, independent control in the x and y directions enables positioning in the radial direction. Further, by connecting the exciting coils 15 of the opposing main poles 3 in series in this way, the two poles can be driven by one power amplifier.

FIG. 3 is a sectional view showing a four-pole magnetic bearing according to the second embodiment of the present invention.
In this embodiment, the supplementary salient pole part is omitted, and the permanent magnet is arranged so as to straddle the main salient pole part and the main salient pole part.
An arc-shaped permanent magnet 46 is arranged so as to connect the corners adjacent to each other at the tips of the main salient pole portions 53 of the four main poles 43 constituting the stator 41, and an auxiliary pole 44 is formed by the permanent magnets 46. Has been. A main salient pole portion 53 on the back surface of the permanent magnet 46 projects in the circumferential direction to form a back yoke 54. A predetermined gap is formed between the back yokes 54 adjacent in the circumferential direction. A magnetic flux sensor 47 is mounted on the front surface of the permanent magnet 46.
In this embodiment, the size can be reduced as much as there is no auxiliary salient pole portion compared to that in FIG. Further, there is an advantage that a cross-sectional area of the control magnetic flux Φc generated by the exciting coil 45 can be widened.

FIG. 4 is a sectional view showing a three-pole outer rotor type magnetic bearing according to a third embodiment of the present invention.
In this embodiment, the stator 61 is disposed on the inner side and the rotor 62 is disposed on the outer side. The yoke 71 of the stator 61 protrudes radially from the outer peripheral side of the disk-shaped part 72 to the outside, and is alternately formed at intervals of 30 ° in the circumferential direction. It has three main salient pole parts 73 and auxiliary salient pole parts 74 arranged. A main pole 63 is formed by the main salient pole portion 73 of the yoke 71 and the exciting coil 75 wound around the main salient pole portion 73. The auxiliary salient pole portion 74 of the yoke 71 and the N pole are connected to the tip side. A supplementary pole 64 is formed with a permanent magnet 76 attached to the tip of the supplementary salient pole portion 74. A magnetic flux sensor 77 is attached to the tip of the permanent magnet 76. The rotor 62 is made of an annular magnetic body having a cylindrical inner peripheral surface facing the magnetic flux sensor 77 at the tip of the main salient pole portion 73 of the stator 61 and the tip of the permanent magnet 76 with a predetermined gap therebetween. Yes.

FIG. 5 is a diagram showing a control circuit for controlling the three-pole magnetic bearing.
In the case of a three-pole magnetic bearing as in this example, a three-phase motor drive circuit can be used. That is, the output signals of the three magnetic flux sensors 77 are amplified by the three sensor amplifiers 81, 82, 83 and input to the three-phase / two-phase conversion circuit 84. The three-phase / two-phase conversion circuit 84 converts the displacement signals detected by the three magnetic flux sensors 77 into displacement signals in the two-phase directions in the x and y directions. The x and y direction displacement signals are input to the x and y direction controllers 85 and 86. PID control signals in the x and y directions from the x and y controllers 85 and 86 are input to a two-phase / three-phase conversion circuit 87 where two-phase / three-phase conversion is performed, and the converted three-phase output is a three-phase drive circuit. The three excitation coils 15 are driven in three phases (U, V, W). Thereby, a part of the magnetic flux of each main pole 33 is strengthened, and the remaining magnetic flux is weakened to generate a radial force.

  It is obvious that the present invention can be applied to such an outer rotor type magnetic bearing.

It is sectional drawing of the magnetic bearing which concerns on the 1st Embodiment of this invention. It is a circuit diagram which shows the control circuit of the magnetic bearing. It is sectional drawing of the magnetic bearing which concerns on the 2nd Embodiment of this invention. It is sectional drawing of the magnetic bearing which concerns on the 3rd Embodiment of this invention. It is a circuit diagram which shows the control circuit of the magnetic bearing.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,41,61 ... Stator, 2,62 ... Rotor, 3, 43, 63 ... Main pole, 4, 44, 64 ... Supplementary pole, 13, 53, 73 ... Main salient pole part, 14, 74 ... Supplementary salient pole 15, 45, 75 ... excitation coil, 16, 46, 76 ... permanent magnet, 17, 47, 77 ... magnetic flux sensor.

Claims (2)

In a magnetic bearing having a stator and a rotor that is supported and rotated in a non-contact state by magnetic force on the stator,
The stator is
A plurality of main poles having an exciting coil that protrudes in a radial direction toward the rotor and has a magnetic flux concentrating portion at a tip thereof facing the rotor via a predetermined gap;
The bias magnetic flux is arranged so that the tip is the first polarity and the adjacent magnetic pole of the main pole adjacent to the magnetic flux concentration portions of the plurality of main poles is shifted in the circumferential direction. A plurality of auxiliary poles having permanent magnets to be supplied;
Wherein the plurality of being attached to the tip of the permanent magnets of the interpole have a magnetic flux sensor for detecting a gap between the rotor,
A magnetic bearing in which a control magnetic flux generated by the excitation coil forms a magnetic circuit independent of the permanent magnet . The plurality of complementary poles are four complementary poles arranged at intervals of 90 °,
A control circuit for detecting the displacement of the rotor relative to the stator from the difference in output of the opposing magnetic flux sensors among the four magnetic flux sensors mounted at the tips of these auxiliary poles and controlling the current value of the exciting coil is provided. The magnetic bearing according to claim 1 .

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