JPH0965607A - Inner-rotor type motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the vibration of the shaft of an inner-rotor type motor using air bearings caused by the unbalanced magnetic attracting force of a magnetic bearing during operation by providing a damping means which damps the vibration of the end section of the shaft on the opposite side of a load near the end section. SOLUTION: In an inner-rotor type motor 1 using air bearings as a thrust bearing 22 and radial bearings 23a and 23b, a magnetic bearing 2 composed of magnetic poles 3a-3d and coils 4a-4d is provided near the end of a shaft 21 on the opposite side of a load and a laminated steel plate 6 is put on the end section of the shaft 21. Then the bearing 2 is made to generate a magnetic attracting force so as to maintain a prescribed distance between the bearing 2 and the shaft 21 by respectively providing distance sensors 5a and 5b to the magnetic poles 3a and 3c and measuring the displacement of the bearing 2 from the prescribed distance, and then, controlling exciting currents supplied to the coils 4a-4d through an exciting current control circuit 10. Therefore, the vibration of the shaft 21 caused by a remarkably unbalanced magnetic attracting force of the bearing 2 can be suppressed when the motor 1 is operated, especially, when the motor 2 is started.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner rotor type motor capable of obtaining stable rotation even during starting and running.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional inner rotor type motor 2
0 shows a sectional view. In this figure, 21 is a shaft which is a rotating shaft of the inner rotor type motor 20, and a tool attachment portion 21a for attaching a tool such as a grindstone or an end mill is provided at one end portion (the left end in FIG. 4). . Two
Reference numeral 2 is a thrust bearing, and 23a and 23b are radial bearings, which receive a thrust load and a radial load, respectively. Air bearings are used for both of these bearings.

A stator 24 generates a rotating magnetic field based on a predetermined exciting current. Reference numeral 25 denotes a rotor, which is installed around the shaft 21. Further, as illustrated, the thrust bearing 22 and the radial bearing 2
3a and 23b are installed between the tool attachment portion 21a and the rotor 25 in the axial direction of the shaft 21.

In the inner rotor type motor having the above-described structure, a rotating force is applied to the rotor 25 by the rotating magnetic field generated by the stator 24 by the supplied exciting current,
The rotational force is transmitted to the tool attached to the tool attachment portion 21a via the shaft 21. As a result, the attached tools rotate in accordance with various operations and perform desired operations.

[0005]

By the way, the air bearings used as the thrust bearing 22 and the radial bearings 23a and 23b in the above-mentioned inner rotor type motor have the advantage that they do not require lubricating oil and are maintenance-free. However, in general, as compared with ball bearings and sliding bearings, the rigidity is weak and the damping (the effect of damping the shaft vibration) is small, so that shaft vibration tends to occur.

In the inner rotor type motor using the air bearing having such characteristics, the magnetic attraction force biased to the rotor 25 is exerted by the effect of the unbalanced magnetic attraction force on the rotor 25 during its operation. There was a possibility that the rotating shaft of 21 would vibrate. Especially, the influence of this unbalanced magnetic attraction force is remarkable at the time of starting. Therefore, stable operation may be difficult at the time of starting or driving. Further, the damping of the air bearing is small even at the rated rotation, and the mechanical shaft vibration cannot be absorbed.

In order to prevent the occurrence of such shaft vibration, a method of adding a third bearing having a high rigidity such as a ball bearing and a large damping such as a slide bearing may be considered. In that case, lubrication is required. The labor and maintenance of refueling the oil are required, and the use of the air bearing becomes meaningless.

The present invention has been made in view of the above points, and provides an inner rotor type motor for preventing the occurrence of shaft vibration due to the influence of an unbalanced magnetic attraction force during the operation of the inner rotor type motor using an air bearing. To provide.

[0009]

According to the first aspect of the present invention,
An inner rotor type motor that rotates a drive target by attaching a drive target to one end of a shaft and rotationally driving a rotor provided on the shaft,
A plurality of air bearings that rotatably support the shaft,
And a vibration damping unit that is provided near the other end of the shaft and that damps the other end of the shaft.

According to a second aspect of the present invention, in the inner rotor type motor according to the first aspect, the damping means includes two electromagnets arranged opposite to each other with the shaft interposed therebetween, and each of the two electromagnets. Exciting means for exciting the shaft to generate a magnetic attraction force, and one of the two electromagnets having a predetermined distance from the surface of the shaft,
Further, the predetermined distance is set to each of the two electromagnets based on the change in the detected distance, which is installed so as to face the surface of the shaft and detects the displacement amount with respect to the predetermined distance. A control means for controlling to generate a magnetic attraction force for the shaft so as to maintain the magnetic force.

According to a third aspect of the present invention, in the inner rotor type motor according to the second aspect, at least two damping means are provided.

[0012]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an axial cross section (hereinafter referred to as a vertical cross section) of an inner rotor type motor 1 including a magnetic bearing 2 according to the present embodiment. 2 is a cross-sectional view of the magnetic bearing 2 taken along the line II ′. In FIG. 2, the components of the rotary drive mechanism such as the rotor are omitted in order to avoid complication.
In FIG. 1, parts corresponding to those in FIG. 4 are designated by the same reference numerals, and description thereof will be omitted. The inner rotor type motor shown in FIG. 1 is different from that shown in FIG. 3 in that a magnetic bearing 2 is added and a laminated iron plate 6 is provided on the shaft 21.

As shown in FIGS. 1 and 2, the magnetic bearing 2
Is composed of magnetic poles 3a, 3b, 3c, 3d and coils 4a, 4b, 4c, 4d provided on the respective magnetic poles.
It is attached in the vicinity of the end portion on the opposite side to the tool attachment portion 21a provided at one end portion of 1. Further, each magnetic pole and coil are installed as a pair of the magnetic pole 3a, the coil 4a, the magnetic pole 3b, and the coil 4b so as to face each other with the shaft 21 interposed therebetween in the vertical direction in FIG. 2, and the magnetic pole 3c, the coil 4c, and the magnetic pole 3d. , A pair of coils 4d are installed to face each other with the shaft 21 sandwiched therebetween in the left-right direction in FIG.

Of the above-mentioned magnetic poles of each set, the magnetic poles 3a and 3c are respectively provided with distance sensors 5a and 5c facing the shaft 21 and at a predetermined distance from the shaft 21. The distance sensor outputs a detection signal according to the amount of displacement with respect to the predetermined distance. As the distance sensors 5a and 5b, for example, eddy current type or optical type sensors are used. Then, the detection signals output from the distance sensors 5a and 5b are input to the excitation current control circuits 10 and 10 provided corresponding to the distance sensors. Here, the excitation current control circuit 10 provided corresponding to the distance sensor 5b is omitted in FIGS. 1 and 2.

Next, the structure of the exciting current control circuit 10 will be described with reference to FIG. Further, here, only the configuration of the exciting current control circuit 10 provided corresponding to the distance sensor 5a will be described. In FIG. 3, the distance sensor 5
The detection signal output from a is input to the control device 12 via the sensor amplifier 11, and the control device 12 outputs the detection signal to the sensor amplifier 1.
Predetermined processing including PID control is performed on the 1 output signal. Here, the output signal from the control device 12 includes a proportional element (P), an integral element (I), and a derivative element (D). Of these elements, the proportional element (P) is the shaft 21. Is not vibrating and is 0 when the sensor 5a is kept at a predetermined distance. Further, from that position, the direction in which the shaft 21 approaches the sensor 5a (see FIG.
When the position is displaced in the middle and upward directions, the proportional element (P) becomes a negative value according to the displacement amount, and conversely, the proportional element (P) moves away (FIG. 2).
When the position is displaced in the middle and downward directions, the proportional element (P) has a positive value according to the displacement amount.

The above proportional element (P) and integral element (I)
Functions as a control signal for maintaining the shaft 21 at a fixed position, whereas the differential element (D) functions as a control signal for increasing the damping coefficient of the rotary system signal. The output signal from the controller 12 is the adder 1
3 and the subtracter 14, and the adder 13 adds the predetermined constant current command value S and the current of the output signal of the control device 12 and outputs the result to the power amplifier 15.
Outputs the current of the output signal of the controller 12 from the constant current command value S and outputs the subtracted current to the power amplifier 16. As a result, the power amplifiers 15 and 16 drive the coils 4a and 4b, respectively.

In the case of the exciting current control circuit 10 provided corresponding to the distance sensor 5b, the detection signal output from the distance sensor 5b is input to the sensor amplifier 11,
Based on this, the power amplifier 15 drives the coil 4c, and the power amplifier 16 drives the coil 4d.

At the time of starting or operating the inner rotor type motor 1 having the above-described structure, for example, due to the influence of the unbalanced magnetic attraction force on the rotor 25, for example, the shaft 21.
2, when axial vibration occurs in the vertical direction, the shaft 2
The displacement of 1 is caused by the distance sensor 5a and the sensor amplifier 1
1 is detected by the control device 12, and the control device 12 outputs a signal according to the displacement amount.

Here, when the position of the shaft 21 is displaced upward in FIG. 2, the proportional element (P) in the output signal of the control device 12 has a negative value corresponding to the displacement amount, The exciting current supplied to the coil 4a is decreased and the exciting current supplied to the coil 4b is increased. On the other hand, when the position of the shaft 21 is displaced downward in FIG. 2, the proportional element (P) has a positive value corresponding to the displacement amount and increases the exciting current supplied to the coil 4a, and The exciting current supplied to the coil 4b is reduced.

By using the integral component (I) together with the proportional component (P) in the output signal of the control device 12 to control the supply amount of the exciting current to each coil, the position of the shaft 21 is determined by the distance sensor. When the magnetic pole 3b is displaced in a direction approaching 5a, a larger attractive force is generated in the magnetic pole 3b, and when the magnetic pole 3b is displaced in a direction away from the distance sensor 5a, the magnetic pole 3a.
In addition, a larger suction force is generated. As a result, the vertical vibration of the shaft 21 is suppressed. Further, the differential component (D) in the output signal of the control device 12 is the proportional component (P)
Since it contributes to the control of the amount of exciting current supplied to each coil in a state in which the phase is advanced, the function of increasing the damping coefficient of the rotating system including the shaft 21 is achieved. When the purpose is to control the vibration of the shaft system, only the differential component (D) can be made to function.

Further, in FIG. 2, with respect to the vibration of the shaft 21 in the left-right direction as well, based on the detection signal output from the distance sensor 5b, the exciting current control circuit 10 provided corresponding to the distance sensor causes the coil to be coiled. Since the control of the exciting current supply amount for 4c and 4d is performed in the same manner as the exciting current control circuit 10 provided corresponding to the distance sensor 5a, it is suppressed similarly to the case of the vertical vibration of the shaft 21.

In the above-described embodiment, one distance sensor is provided for each of the vertical direction and the horizontal direction of the shaft, but a distance sensor is provided for each of the two electromagnets that are arranged to face each other, and the output of each distance sensor is provided. When differentially amplified and used for control of suppression of shaft vibration, the detection sensitivity for shaft displacement is doubled as compared with the above-described embodiment, and in-phase generated in the distance sensor and various amplifiers due to temperature change and the like. Since the noise signal can be removed, the accuracy of displacement measurement is improved.

In addition, in the above-described embodiment, a constant current is supplied to each coil by a constant current command, and in response to a change from a predetermined distance between the shaft and the distance sensor, a pair of electromagnets is formed. Of these, the exciting current supplied to the electromagnet on the side closer to the shaft was controlled to be reduced from the constant current, and the exciting current supplied to the electromagnet on the side retracted from the shaft was controlled to be increased from the constant current. However, it is also possible to stop the supply of a constant current and supply an exciting current only to the electromagnet on the side where the shaft retreats to generate a magnetic attractive force to maintain a predetermined distance from the shaft.

As an example of a circuit configuration for realizing such control, for example, in FIG. 3, an adder 13 and a subtractor 14 are shown.
In place of the above, a limiter that allows only positive signals to pass is disposed in the preceding stage of the power amplifier 15, and a limiter that allows only negative signals to pass is disposed in the preceding stage of the power amplifier 16, and the output signal of the control device 12 is input to each limiter. You can do it like this.

[0025]

As described above, according to the present invention, the object to be driven is attached to one end of the shaft, and the rotor provided on the shaft is rotatably driven.
In the inner rotor type motor for rotating the driven object, an air bearing is used as a support means for supporting the shaft, and a change in distance from the shaft is detected, and a predetermined distance from the shaft is maintained based on the detected change in distance. Since the magnetic attraction force is generated in the electromagnet so that the advantage of the air bearing that is maintenance-free can be utilized, the shaft vibration due to the influence of the unbalanced magnetic attraction force can be suppressed especially at the time of starting.

[Brief description of drawings]

FIG. 1 is a sectional view showing a vertical section of an inner rotor type motor according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along the line I-I ′ of FIG.

FIG. 3 is a block diagram showing a configuration of an exciting current control circuit in the same embodiment.

FIG. 4 is a cross-sectional view showing an example of a vertical cross section of a conventional inner rotor type motor.

[Explanation of symbols]

1 ... Inner rotor type motor, 2 ... Magnetic bearing, 3a,
3b, 3c, 3d ... Magnetic poles, 4a, 4b, 4c, 4d ...
... Coil, 5a, 5b ... Distance sensor, 6 ... Laminated iron plate, 10 ... Excitation current control circuit, 11 ... Sensor amplifier, 12 ... Control device, 13 ... Adder, 14 ... Subtractor, 15 , 16 ... Power amplifier

Claims (3)

[Claims] 1. An inner rotor type motor for rotating a drive target by attaching a drive target to one end of the shaft and rotating a rotor provided on the shaft to rotatably support the shaft. An inner rotor type motor comprising: a plurality of air bearings, and a vibration damping unit that is provided near the other end of the shaft and damps the other end of the shaft. 2. The vibration damping unit is configured to excite each of the two electromagnets that are arranged to face each other with the shaft interposed therebetween and to excite each of the two electromagnets to generate a magnetic attraction force on the shaft. A detection unit that has a predetermined distance from the surface of the shaft in one of the two electromagnets and is installed so as to face the surface of the shaft, and that detects a displacement amount with respect to the predetermined distance; 7. A control unit that controls each of the two electromagnets so as to generate a magnetic attraction force with respect to the shaft so as to maintain the predetermined distance based on a change in the distance. 1. The inner rotor type motor according to 1. 3. The inner rotor type motor according to claim 2, further comprising at least two damping means.