JPH02184251A - Motor - Google Patents

Abstract

PURPOSE:To reduce the rocking movement of a rotor unit into the direction of thrust by a method wherein the magnets of the rotor unit are arranged so as to be opposed to a stator core while the ratio of the axial length of the magnets to the axial length of the stator core is determined so as to be within a specified range. CONSTITUTION:The magnets 6 of a rotor unit are arranged so as to be opposed to a stator core 7 and the ratio of the axial length Hm of the magnets to the axial length Hc of the core 7 is determined so as to be 0.7-0.9 whereby a strong magnetic attraction force may be obtained as compared with a case, in which the same ratio is Hm=Hc.

Description

[Detailed description of the invention] [Industrial application field]

TECHNICAL FIELD The present invention relates to a motor that performs a thrust bearing action using magnetic attraction between a magnet in a rotor portion and a stator core that are arranged to face each other.

[Conventional technology]

A radial bearing is a bearing that prevents the center of rotation from shifting from a predetermined position even if a force is applied in a direction perpendicular to the rotation axis. The motor uses a dynamic pressure type radial bearing. There are some types that use hydrostatic bearings, some that use hydrostatic bearings, and others that use sliding bearings. When a hydrodynamic bearing or a sliding bearing is used, the rotor section can move in the thrust direction (axial direction), so a thrust bearing is required to prevent this movement. However, a magnetic attraction force acts between the magnet and the stator core, which are arranged to face each other, and this force acts to prevent movement in the thrust direction (thrust bearing effect). Therefore, there are motors that do not take the trouble of providing a thrust bearing. FIG. 2 shows such a conventional motor. In this example, a hydrodynamic air bearing, which is a type of fluid bearing, is used as the radial bearing. A case is shown in which the motor is used for rotationally driving a polygon mirror of an optical deflector. In Fig. 2, 1 is a shaft, 1-1 is a groove for generating dynamic pressure, 2 is a housing, 3 is a rotating sleeve, 4 is a balance adjustment member attachment groove, 5 is a yoke, 6 is a magnet, 7 is a stator core, 8 is a stud, 9 is a substrate, IO is a magnetic detection element,
11 is a polygon mirror, 12 is a flange, and 13 is a screw. The rotor portion of the motor is a portion fitted onto the shaft 1 with a gap 15 in between, and is composed of the following components. That is, the polygon mirror 11 has a rotary sleeve 3, a yoke 5 and a magnet 6 fixed to the rotary sleeve 3 by press fit or adhesive, and a flange 12 attached to the rotary sleeve 3 with screws 13. On the other hand, the stator section of the motor is composed of the following: That is, a housing 2, a shaft 15 whose one end is fixed to the housing 2 by press fitting or the like, and a stator core 7 which is also fixed to the housing 2 (although not shown, a toroidal coil is wound around the stake core 7).
, a substrate 9 supported by studs 8 attached to the stator core 7, a magnetic detection element 10 installed vertically on the substrate 9, and the like. The magnet 6 is a permanent magnet, and a magnetic attraction force acts between it and the opposing stator core 7. This attractive force serves as a source of rotational force, and also serves to prevent the opposed positions of the magnet 6 and the stator core 7 from shifting in the axial direction of the motor. That is, in FIG. 2, when the magnet 6 moves upward, a component that pulls it downward appears in the attraction force and pulls it down, and when it moves downward, a component that pulls it upward appears and pulls it up. Thus, the magnet 6 and the stator core 7 are made to face each other at a predetermined position in the axial direction due to the magnetic attraction force. That is, the magnet 6 and the stator core 7 constitute a magnetic thrust bearing. For example, a Hall element is used as the magnetic detection element IO. This detects the leakage magnetic flux of the magnet 6 and
When the magnet 6 rotates, it is detected whether the north pole or the south pole has passed. The detection signal is sent to a control section (not shown) through wiring printed on the board 9. Based on this detection signal, the control section determines the direction of the current flowing through the toroidal coils wound around each part of the stator core 7. As a result, interaction with the magnet 6 generates a polarized magnetic field that sustains rotation. By providing the dynamic pressure generating groove 1-1, when the rotating sleeve 3 rotates, a high pressure air layer is generated around the shaft 1 (at the gap 15). Due to this pressure, the rotating sleeve 3 is supported in a state floating above the shaft 1. In other words, a dynamic pressure air bearing is constructed. Although the upper side shows a groove for generating dynamic pressure provided on the circumferential surface of the shaft 1, it may also be provided on the inner wall of the rotating sleeve 3. The air layer acts to keep the center of rotation of the rotor portion constant. For example, if the rotating sleeve 3 shifts to the right in FIG. 2, the gap on the right side becomes large, and the pressure in the gap in that area becomes smaller than before the shift. On the other hand, since the gap on the left side becomes smaller, the pressure in that gap becomes greater than before the shift. When the magnitude relationship of the pressures becomes as described above, the rotating sleeve 3 is pushed to the left and eventually returned to its original position. The polygonal mirror 11 has a polygonal shape when viewed from above in the axial direction, and has a large number of mirror surfaces on its circumferential side. The mirror surface is irradiated with a light beam such as a laser. A light beam is irradiated onto the first mirror surface, and the polygon mirror 1
1 rotates, the reflected light beam of the light beam is made to change direction gradually. In other words, it is deflected. As the rotation progresses and it becomes impossible to irradiate the first mirror surface, the next second mirror surface rotates and is irradiated. This second mirror surface now performs the same deflection as before. Therefore, the reflected light beam scans within a certain angular range. The scanning speed depends on the rotation speed of the polygon mirror 11.

[Problem to be solved by the invention]

(Problem) However, the above-mentioned conventional technology has a problem in that the rotor part tends to swing (damping) in the axial direction (thrust direction). (Explanation of the problem) In the conventional motor described above, the action of the thrust bearing is
This is done by magnetic attraction between the magnet 6 and the stator core 7. The larger this magnetic attraction force is, the more strongly the swinging in the thrust direction is prevented. However, in the past, the axial length of the opposing magnet 6 and stator core 7 was set at a distance, and once the sizes and characteristics of the magnet 6 and stator core 7 were determined, the magnetic attraction force was also determined. FIG. 6 is a diagram schematically showing the distribution of magnetic flux entering the stator core from the magnet in a conventional motor. The axial length Hm of the magnet is approximately equal to the axial length Hc of the stator core. fffThe force of attraction is
It is related to the area where magnetic flux enters and its magnetic flux density. When the rotor is rotating at high speed, an external force acts on the rotor in the thrust direction, and if the rotor tries to move in the thrust direction, if the force is small, the restoring force due to the magnetic attraction force Movement is immediately suppressed. However, if the force is large, it cannot be suppressed immediately, and movement in the thrust direction is unavoidable. In order to reduce this vibration as much as possible, it is required to make the magnetic attractive force between the magnet 6 and the stator core 7 as strong as possible. An object of the present invention is to solve the above-mentioned problems.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a motor that performs a thrust bearing action by utilizing the magnetic attractive force between the magnets of the rotor portion and the stator core, which are arranged facing each other. The ratio of the axial length Hc of the stator core to the length Hl is 0.7 to 0.9.
I decided to do it.

[For production]

Even when magnets and stator cores made of the same materials are used, by setting the axial length HcO of the stator core to the axial length Hl of the magnet to 0.7 to 0.9, the ratio is lower than when Hm=Hc. It turned out that it was possible to obtain a stronger magnetic attraction force. Therefore, by selecting Hc/Hm within the above range, it becomes possible to further suppress the swinging in the thrust direction.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a motor according to an embodiment of the present invention. As in the case of Figure 2, the radial bearing used is a hydrodynamic air bearing, which is a type of fluid bearing, and the application is shown as an example in which it is used to rotate a polygon mirror in an optical deflector. . The symbols correspond to those in FIG. The difference in configuration from the conventional one is that the axial length of the stator core is made smaller than the axial length of the magnet 6. FIG. 3 is a diagram showing only the magnet and stator core. In FIG. 3, H. is the axial length of the magnet, Hc is the axial length of the stator core, R is the magnet outer peripheral surface radius R1, Rc is the stator core inner peripheral surface radius, and 0 is the center of the rotation axis. In FIGS. 1 and 2, the opposing gap between the magnet 6 and the stator core 7 is drawn wide in order to avoid crowding. However, in reality, it is narrow as shown in FIG. 3, and the difference between the two is extremely small compared to the length of the radius from the rotation axis center 0. Therefore, it can be considered that R, -Rc. The total amount of magnetic flux emitted from the outer circumferential surface of the magnet 6 is as follows: Φ is the magnetic flux emitted from a unit area, and S is the area of the outer circumferential surface. Then, S,×Φ2πR, HmΦ. On the other hand, if the area of the inner peripheral surface of the stator core 7 that receives the magnetic flux is Se, then 5c=2π'RcHc. As mentioned above, it can be considered that R, = Rc, so Hm>H
c, then S,>Sc. Therefore, the magnetic flux density on the surface of the stator core 7 is higher than that of the conventional one. When the magnetic flux density increases, it becomes a key factor in increasing the magnetic attraction force. However, since not all of the magnetic flux emitted from the surface of the magnet 6 enters the surface of the stator core 70 (there is also leakage flux), the magnetic flux density does not increase proportionally to the extent that S decreases. . FIG. 5 is a diagram schematically showing the distribution of magnetic flux entering the stake core from the magnet in the motor of the present invention. It is expected that as the magnetic flux density increases, the magnetic attraction force will also increase, but this also has to do with the decrease in the area of the inner circumferential surface of the stator core 7, and as a result of experiments, the value of Hm/Hm is gradually decreased. It has been found that the magnetic attraction force does not necessarily increase even if the magnetic force is increased. FIG. 4 is a diagram showing an example of the relationship between the ratio of the axial length Hc of the stator core to the axial length Hm of the magnet and the force for restoring the rotor portion to a predetermined position. The horizontal axis represents Hc/Hm. The vertical axis represents the force to restore the magnet 6 and stator core 7 to the predetermined position due to magnetic attraction when they are displaced from the predetermined position in the thrust direction.
The force when 0/Hm=1.0 is expressed as a reference (1,0). The present inventors found that as the value of Hc/Hm becomes smaller than 1, the restoring force gradually becomes stronger, but after reaching a maximum around a value slightly larger than 0.7, it rapidly increases. I discovered that it has the property of becoming weaker. The present invention focuses on this property, and the value of Hc/Hm is set to a value in the range of 1.7 to 0.9 to obtain a strong restoring force. , even if a magnet stator core made of the same material as before is used, the value of Hc/Hm is approximately 1.
Compared to the conventional case, a stronger restoring force can be obtained, and the swinging of the rotor can be suppressed more than before. Effects of the Invention As described above, in the present invention, in a motor that operates as a thrust bearing by the magnetic attraction force between a magnet and a stator core, the axial length Hc of the stator core with respect to the axial length Hm of the magnet. The relationship between the ratio of Hm and the restoring force in the thrust direction was investigated, and the value of Hm/Hm was set to a value in the range of 0.7 to 0.9, which provides a stronger restoring force. As a result, it has become possible to reduce the swinging of the rotor section in the thrust direction compared to the conventional one.

[Brief explanation of the drawing]

Fig. 1: Motor related to an embodiment of the present invention Fig. 2:
・・Conventional motor Figure 3 ・Figure 4 shows only the magnet and stator core portion ・・The ratio of the axial length HcO of the stator core to the axial length H7 of the magnet, and the rotor part Figure 5 shows the relationship between the force and the force that restores the motor to the position. Figure 6 schematically shows the distribution of magnetic flux entering the stator core from the magnet in the motor of the present invention... From the magnet in the conventional motor. FIG. 3 is a diagram schematically representing the distribution of magnetic flux entering the stator core. In the figure, 1 is the shaft, 1-1 is a groove for generating dynamic pressure, 2 is a housing, 3 is a rotating sleeve, 4 is a balance adjustment member attachment groove, 5 is a yoke, 6 is a magnet, 7 is a stator core, and 8 is a stud , 9 is a substrate, 10 is a magnetic detection element, 11
12 is a flange, 13 is a screw, and 15 is a gap. Figure Figure Figure Figure Figure HC/? bN Figure Figure

Claims (1)

[Claims] In a motor that performs a thrust bearing action by utilizing the magnetic attractive force between the magnets of the rotor portion and the stator core, which are arranged to face each other, the axial length H_c of the stator core is relative to the axial length H_m of the magnet. A motor characterized by having a ratio of 0.7 to 0.9.