GB2297361A

GB2297361A - Active magnetic bearing system

Info

Publication number: GB2297361A
Application number: GB9512187A
Authority: GB
Inventors: Myoung-Ho Shin
Original assignee: Samsung Electro Mechanics Co Ltd
Current assignee: Samsung Electro Mechanics Co Ltd
Priority date: 1995-01-24
Filing date: 1995-06-15
Publication date: 1996-07-31
Anticipated expiration: 2015-06-15
Also published as: KR960030515A; GB2297361B; JPH08200365A; GB9512187D0; FR2729723B1; FR2729723A1

Description

ACTIVE MAGNETIC BEARING SYSTEM Background of the Invention The present invention relates to an active magnetic bearing system, and more particularly, to an active magnetic bearing system in which high rotary inertia energy of a rotary body is consumed by a special energy consuming means, to thereby reduce the load of an auxiliary bearing, and the speed of the rotary body is sharply reduced when an emergency state such as a power failure occurs, to thereby protect the auxiliary bearing.

An active magnetic bearing system is one in which a rotary body is floated and supported by the magnetic force of an electromagnet so that the rotary body can be rotatable without any mechanical contact. Generally speaking, such a system includes a radial magnetic bearing in which the rotary body is supported in the radius direction thereof and a shaft direction magnetic bearing in which the rotary body is supported in the axial direction.

The above-described active magnetic bearing system has been widely used in a specific field related with space instrumentation, experimental apparatuses or heavy machinery for industrial purposes. Thus, manufacturing has been based on short run production and the structures have been customdeveloped for the specific fields. Recently technological developments, however, have sharply increased demand for these types of magnetic bearings, for use in mass-produced equipment which require both high precision and a high degree of freedom in movement.

FIG. 1 shows an example of a conventional active magnetic bearing system.

Referring to FIG. 1, the conventional active magnetic bearing system is composed of a magnetic bearing 12 located around a predetermined portion of a rotary shaft 11 and an auxiliary bearing 13 located around one end of rotary shaft 11. Magnetic bearing 12 is composed of a core 12c in a predetermined shape, i.e., annular, and a coil 12w wound around core 12c.

Here, a plurality of magnetic electrodes (not shown) are formed as protrusions along the inner circumference of the annular core 12c, in a symmetrical or isogonic structure and coils 12w are wound around each of the protrusions.

Auxiliary bearing 13 has a cylindrical housing 13h and dry bearing members 14 and 15 located at the contacting portion between housing 13h and rotary shaft 11, for emanating the rotary inertia energy of rotary shaft 11 as heat energy caused by friction. An abrasion preventing member 16 for protecting dry bearing members 14 and 15 from abrasion is disposed between dry bearing members 14 and 15. Cooling fins 17 for dissipating the heat generated by the friction between rotary shaft 11 are fixed to one side of housing 13h by a fixing member 18. Also, dry bearing members 14 and 15 are disposed at one side of housing 13h.

In the conventional magnetic bearing system having the above structure, when current flows in a coil 12w, a magnetic field is formed around coil 12w which thereby forms an electromagnet. Rotary shaft 11 is floated by a magnetic force generated from a plurality of magnetic electrode protrusions formed along the inner circumference of core 12c, such that there is no mechanical contact with core 12c. Here, rotary shaft 11, being in the above floated state, generally rotates at high speed.

However, in the conventional magnetic bearing system, the high rotary inertia energy of rotary shaft 11 is consumed as the heat energy caused by friction in auxiliary bearing 13, to thereby reduce the speed of rotary shaft 11 or cause the total stoppage thereof. Therefore, a metallic residue is generated due to the abrasion of dry bearing members 14 and 15 and durability of dry bearing members 14 and 15 is decreased.

Summarv of the Invention To solve the above problem, it is an object of the present invention to provide an active magnetic bearing system in which high rotary inertia energy of a rotary body is consumed by a special energy consuming means, to thereby reduce the load of an auxiliary bearing, and in which the speed of the rotary body is sharply reduced when an emergency state such as a power failure occurs, to thereby protect the auxiliary bearing.

To achieve the above object, there is provided an active magnetic bearing system comprising: a magnetic bearing for supporting a rotary shaft by floating the rotary shaft and an auxiliary bearing for protecting the magnetic bearing, wherein one or more permanent magnets are disposed in a predetermined position of the rotary shaft and one or more braking coils are disposed adjacent to the permanent magnets to induce an electromotive force caused by the magnetic flux of the permanent magnet, wherein the braking coils constitute a closed circuit together with a resistor and a predetermined switching element to consume electrical energy caused by the electromotive force induced into the coil, and wherein the switching element is operated by the operation of an emergency detection circuit for detecting an emergency state.

Therefore, high rotary inertia energy of the rotary body is consumed by braking coils and a resistor composing a closed circuit, so that the speed of the rotary body is sharply reduced when an emergency state such as a power failure occurs, to thereby protect the auxiliary bearing. As a result, the life of the magnetic bearing can be increased.

Brief DescriDtion of the Drawings The above objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: FIG. 1 is a schematic diagram of a conventional active magnetic bearing system; FIG. 2 is a schematic diagram of an active magnetic bearing system according to a preferred embodiment of the present invention; FIG. 3 is a side view of braking coils of the active magnetic bearing system shown in FIG. 2; and FIG. 4 is a schematic diagram of the braking coils and a periphery portion thereof of the active magnetic bearing system according to another preferred embodiment of the present invention.

Detailed Description of the Invention Referring to FIGS. 2 and 3, an active magnetic bearing system according to the present invention is constructed by inserting a magnetic bearing 22 for supporting a rotary shaft 21 in a floating state, which is composed of a core 22C of a strong magnetic substance and a coil 22w wound around the core, and an auxiliary bearing 23 for protecting magnetic bearing 22, in a predetermined portion of rotary shaft 21.

Also, a device for consuming the rotary inertia energy generated when rotary shaft 21 rotates by converting the rotary inertia energy into an electrical energy is disposed in another predetermined position of rotary shaft 21. That is, a plurality of permanent magnets 24 are attached to the circumference of rotary shaft 21 and a plurality of braking coils 25 are spaced by a predetermined distance from the circumference of plurality of permanent magnets 24. Also, a resistor 26 and a switching element 27 are connected to braking coils 25, to thereby construct a closed circuit. When an emergency state such as a power failure occurs, an emergency detection circuit 28 drives the closed circuit by the operation of switching element 27.

Here, resistor 26 is for consuming the current induced in braking coils 25 by the interlinkage of a magnetic flux generated from permanent magnet 24 and braking coils 25, as a Joule heat value H (calculated as 0.24I2Rt[cal]).

On the other hand, FIG. 4 is a schematic diagram of the braking coils and a periphery portion thereof of the active magnetic bearing system according to another preferred embodiment of the present invention.

The construction of the active magnetic bearing system shown in FIG. 4 is basically similar to that of the active magnetic bearing system described with reference to FIGS. 2 and 3. Thus, description of the same components will be omitted.

That is, the preferred embodiment described with reference to FIGS. 2 and 3 utilizes braking coils 25 wound around permanent magnets 24. In contrast thereto, in another preferred embodiment as shown in FIG. 4, a yoke 49 having a plurality of protrusions 49t around the inner circumference thereof is disposed and braking coils 45 are wound around each of protrusions 49t. Here, yoke 49 having the protrusions 49t provides a path for the magnetic flux from permanent magnet 44, to thereby form a magnetic circuit. Thus, the amount of interlinkage of the magnetic flux from permanent magnet 44 and braking coils 45 is increased since the magnetic flux flows via protrusions 49t.As the amount of interlinkage magnetic flux is increased, an induced electromotive force e (calculated as -d/dt[V]) is increased, to thereby increase the consumption of heat energy as Joule heat. As a result, the rotary inertial energy of the rotary shaft is sharply reduced so that its rotary speed is remarkably decreased, to thereby stop the shaft quickly. This causes the reduction of the load provided to an auxiliary bearing so that the auxiliary bearing and magnetic bearing are protected. In addition, braking coils 45 are very stably installed by being wound around protrusions 49t of yoke 49.

Then, the operation of the active magnetic bearing system having the above structure will be briefly described with reference to FIG. 2.

When the current flows in coil 22w, a magnetic field is formed around coil 22w. As a result, core 22c becomes magnetized to form an electromagnet and rotary shaft 21 is floated by the magnetic force of core 22c without contact with core 22c. Rotary shaft 21 rotates at a high speed in this floated state. If an emergency state such as a power failure occurs during normal operation, emergency detection circuit 28 immediately detects the emergency situation to operate switching element 27. With the operation of switching element 27, the closed circuit constituted by braking coils 25, resistor 26 and switching element 27 operates, so that the current caused by the induced electromotive force flows in the circuit. As a result, Joule heat is generated from resistor 26 so that the rotary inertia energy of rotary shaft 21 is remarkably reduced and the rotary speed thereof is sharply decreased, to stop the rotary shaft in a very short time. Thus, the load provided to auxiliary bearing 23 is reduced and auxiliary bearing 23 and magnetic bearing 22 are protected.

As described above, according to the active magnetic bearing system of the present invention, high rotary inertia energy of the rotary body is consumed by the braking coils and resistor composing the closed circuit, so that the speed of the rotary body is sharply reduced when an emergency state such as a power failure occurs, to thereby protect the auxiliary bearing. As a result, the life of the magnetic bearing can be increased.

Claims

CLAIMS:

1. An active magnetic bearing system comprising: a magnetic bearing for supporting a rotary shaft by floating the rotary shaft and an auxiliary bearing for protecting said magnetic bearing, wherein one or more permanent magnets are disposed in a predetermined position of said rotary shaft and one or more braking coils are disposed adjacent to said permanent magnets to induce an electromotive force caused by the magnetic flux of said permanent magnet, wherein said braking coils constitute a closed circuit together with a resistor and a predetermined switching element to consume electrical energy caused by the electromotive force induced into the coil, and wherein said switching element is operated by the operation of an emergency detection circuit for detecting an emergency state.

2. An active magnetic bearing system as claimed in claim 1, further comprising a yoke having a plurality of protrusions around the inner circumference thereof and being disposed around said permanent magnets, and wherein said braking coils are wound around said plurality of protrusions.

3. An active magnetic bearing system comprising: a magnetic bearing for supporting a rotary shaft during rotation thereof; and a magnetic braking arrangement, wherein said braking arrangement can be magnetically coupled during rotation of the shaft in order to reduce its rotational energy.

4. An active magnetic bearing system according to claim 3, comprising a magnetic element solidly connected to said shaft.

5. An active magnetic bearing system substantially as hereinbefore described, in particular with reference to the accompanying diagrams.