JPH0724933Y2 - Thrust bearing mechanism for high speed motors - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention is for a high-speed motor that supports a rotor in a thrust direction, such as a high-speed motor used to drive a polygon mirror for laser scanning in a laser printer or the like. A thrust bearing mechanism.

[Conventional technology]

In order to keep the scanning capability of the polygon mirror high, it is necessary to properly support the rotor with the polygon mirror mounted in the radial direction and the thrust direction and rotate the rotor at a high speed while holding the rotor at a fixed position.

Therefore, various proposals have been made conventionally.

FIG. 6 shows an example of a conventional device.

In the figure, reference numeral 1 is a substantially circular shaft support, and a central axis 2 is vertically erected at the center of the shaft support 1. A cylindrical rotor 3 is rotatably mounted on the central shaft 2 from above, and an upper plug member 4 at the upper end of the rotor 3 is installed.
A small air vent hole 5 is formed in the center of the. Further, on the outer peripheral surface at two upper and lower positions in the axial direction of the central shaft 2, a large number of grooves 6, 6 ... For forming a dynamic pressure type air bearing with the inner peripheral surface of the rotating rotor 3 are formed in the peripheral direction. It is set up. On the other hand, on the outer periphery of the rotor 3, a polygonal mirror 7 for scanning is fixed at an upper position, and an annular rotating magnet 8 is fixed at a lower position. The rotating magnet 8 has a plurality of sets of N poles and S poles alternately formed in the circumferential direction. A motor core 10 is provided inside the housing 9 so as to face the rotating magnet 8, and a winding 11 is wound around the motor core 10.

In the motor for driving the polygonal mirror 7 thus formed, the weight of the rotor 3 and the polygonal mirror 7 is supported by the supporting mechanism (not shown) when the rotor 3 is stopped.

Next, when the winding 11 is energized and the rotor 3 is rotated at high speed around the central axis 2, the air flowing from the lower end of the rotor 3 between the rotor 3 and the central axis 2 is The upper and lower grooves 6 formed on the outer peripheral surface are compressed to perform radial bearing of the rotor 3. The air that has circulated upward through the upper groove 6 is located on the upper surface of the central shaft 2 and the upper plug member 4.
Between the lower surface and the lower surface, and then flows out through the air vent hole 5 to the outside. On the other hand, the bearing in the thrust direction is mainly formed by the magnetic force of the magnetic pole of the lower part of the rotating magnet 8 that does not face the motor core 10 and is closed through the inside of the motor core 10 which is a magnetic body. 3 is held in the thrust direction. Then, scanning is performed by the polygon mirror 7 rotating at a high speed.

[Problems to be solved by the device]

In the conventional apparatus shown in FIG. 6, the rotor 3 in the radial direction is formed by a dynamic pressure type air bearing formed in the groove 6 of the central shaft 2.
Is almost perfect, but the magnetic thrust bearing formed between the rotating magnet 8 and the motor core 10 cannot sufficiently hold the rotor 3 in the thrust direction. .

This is because, in order to increase the holding force of the rotor 3 in the thrust direction, the gap between the outer peripheral surface of the rotating magnet 8 and the inner peripheral surface of the motor core 10 is made as small as possible, and the number of magnetic field lines closed. However, the gap must be increased in order to eliminate the cocking of the motor, which causes the rotor 3 to rotate at a constant speed. After all, giving priority to improving the accuracy of scanning by the polygon mirror 7,
The constant speed rotation of the rotor 3 is ensured, the gap between the rotating side magnet 8 and the motor core 10 cannot be reduced as much as desired, and the holding force in the thrust direction of the rotor 3 is sufficiently increased. I couldn't.

Therefore, it is difficult to stably hold the rotor 3 and the polygon mirror 7 at a constant height position, and when the load changes, the height positions of the rotor 3 and the polygon mirror 7 change greatly, It was difficult to change the load.

Generally, in a scanning system using the polygonal mirror 7, design changes and specification changes are frequently made, and the weight of the polygonal mirror 7 is changed or the rotation speed of the polygonal mirror 7 is changed. However, according to the conventional example shown in FIG. 6, when the weight of the polygonal mirror 7 is changed, the height position of the polygonal mirror 7 is largely changed, and the assembly position of the entire apparatus must be changed.

Further, if the magnetic core is changed by changing the motor core 10 or the like, the holding force in the thrust direction changes, and the height positions of the rotor 3 and the polygon mirror 7 also change.

The present invention has been made in view of these points, and it is possible to reliably hold the thrust direction of the rotor of a high-speed motor with a large holding force by a simple structure, and always keep the rotor and the members attached to the rotor properly. It can be held at a high height position and rotated, and even if the load fluctuates or the magnetic circuit of the motor is changed, the rotor can be held at a substantially constant height position, and design changes are extremely easy. It is an object of the present invention to provide a thrust bearing mechanism for a high speed motor, which is low in cost.

[Means for Solving the Problems]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention is directed to a rotor that rotates at a high speed and is externally fixed to the motor core so as to face the motor core, and has an annular rotating magnet having a plurality of magnetic poles in the circumferential direction, and the motor core. A thrust bearing mechanism is formed with a ring-shaped magnetic material body that is opposed to the rotation-side magnet from the radially outer side through a ring-shaped gap at a higher position.
The rotor is held at a constant height position by using magnetic force.

[Action]

During high-speed rotation of the rotor, a large number of magnetic lines of force are closed between the rotating-side magnet fixed to the rotor and the annular magnetic material body that faces the rotating-side magnet with an annular gap above the motor core. Thus, the rotor is held in the thrust direction with a large magnetic attraction, and the rotor rotates at high speed while being accurately held at a predetermined height position.

〔Example〕

 The present invention will be described below with reference to FIGS.

1 to 3 show the construction of an embodiment of the present invention.

In the figure, reference numeral 20 is a housing of the high speed motor. A shaft support 21 is fixed to the lower part of the housing 20,
A central shaft 22 is vertically erected at the center of the shaft support 21. A substantially cylindrical rotor 23 is rotatably mounted on the central shaft 22 from above. The upper end opening of the rotor 23 is closed by an upper plug member 24 having a central portion filled with a porous member 25 for gently discharging the air in the rotor. The axially intermediate portion of the central shaft 22 has a small diameter, and a large number of grooves 26, 26 ... For forming a dynamic pressure type air bearing with the inner peripheral surface of the rotating rotor 23 are provided in the upper and lower large diameter portions. It is engraved in the circumferential direction. On the outer periphery of the upper portion of the rotor 23, a polygonal mirror 28 for scanning is fixedly mounted on a flange 27 protruding from the rotor 23. A substantially cylindrical rotating magnet 30 is fixed to the outer periphery of the lower portion of the rotor 23 via an inner mounting member 29. As shown in FIGS. 2 and 3, this rotating magnet 30 has a plurality of N poles and three N poles.
S poles are alternately arranged in the circumferential direction at equal positions, and
It is formed so as to pass through in the axial direction. Further, inside the housing 20, a motor core 31 is fixed so that the inner peripheral surface faces the rotating magnet 30. These rotating magnets
The motor core 31 and the motor core 30 are positioned so that their axial center positions coincide with each other. As shown in FIG. 2, winding protrusions 32, 32 ... Forming a large number of slots in the inner peripheral portion of the motor core 31 are arranged at equal intervals in the circumferential direction. Windings 33 are respectively wound around the protrusions 32 to form a stator portion of the motor. An annular mounting member 34 made of a non-magnetic material is provided above the motor core 31.
Then, the annular thin annular magnetic material body 35 is fixed so that its inner peripheral surface faces the upper outer peripheral surface of the rotating magnet 30 with an annular gap 36 therebetween. As shown in FIG. 3, the annular magnetic material body 35 forms a thrust bearing for holding the rotor 23 in the thrust direction by forming a part of the closed path of the magnetic force line from the magnetic pole of the rotating magnet 30. Yes In this embodiment, a thin annular iron plate is used. A Hall element 37 is provided below the motor core 31 using an appropriate mounting member.

Next, the operation of this embodiment will be described.

When the rotor 23 is rotated at high speed by energizing the windings 33 forming the stator portion of the motor, the motions formed between the grooves 26 formed in the upper and lower parts of the central shaft 22 and the inner peripheral surface of the rotor 23 are generated. The rotor 23 is radially supported by the pressure type air bearing.

At the same time, the magnetic field lines from the magnetic poles at the upper end of the rotating magnet 30 fixed to the rotor 23 are closed through the annular magnetic material body 35 provided exclusively for the thrust bearing, so that the number of closed magnetic field lines is reduced. The holding force in the thrust direction becomes extremely large as compared with the conventional example, and the rotor 23 and the polygon mirror 28 are stably held at a constant height position.

Here, in order to increase the holding force in the thrust direction by the rotating magnet 30 and the annular magnetic material member 35, the annular gap 36 that serves as the magnetic resistance may be made as small as possible. This is clear from the characteristic diagram shown in FIG. FIG. 4 shows the settling amount of the rotor 23 when the load of the rotor 23, that is, the weight of the polygon mirror 28 in this embodiment, is changed, and the annular gap between the annular magnetic material body 35 and the rotor 23 is shown. The size of 36 is a minimum of 0.15 mm, and the a line has an annular gap 36 of 0.2 mm and 0.25 mm.
It is clear from the fact that the settling amount of the rotor 23 is smaller than that of the b line and the c line.

In addition, the rotor 23 including the rotating magnet 30 and the annular magnetic material body 35
The positioning accuracy in the height direction of the is improved as the annular magnetic material body 35 is thinner. However, in order to keep the magnetic permeability of the ring-shaped magnetic material body 35 high, there is a limit to making the ring-shaped magnetic material body 35 thin. The thickness of the annular magnetic material body 35 is usually about 1 to 2 mm. In FIG. 4, the annular gap 36 is 0.2 mm and the thicknesses of the annular magnetic material body 35 are 1.2 mm, 2 mm and 3 mm, and the b line showing the minimum thickness is the rotor 23. From the fact that the amount of sedimentation is minimal, it is clear that the thinner the annular magnetic material body 35, the better the positioning accuracy in the height direction.

Further, comparing the characteristics according to the embodiment of the present invention with the conventional characteristics shown in FIG. 4D, the settling amount of the rotor 23 can be suppressed within about 40 to 60% of the settling amount of the conventional rotor, and a large thrust can be obtained. It can be seen that the holding power in the direction is exerted.

Further, in order to increase the number of magnetic lines of force that closes the rotating magnet 30 and the annular magnetic material body 35, the distance l between the upper surface of the motor core 31 and the upper surface of the annular magnetic material body 35 is set to a certain length or more. It is better to keep them apart. FIG. 5 shows the state of the change in the magnetic flux between the rotating magnet 30 and the motor core 31 with the change of the distance l. With the change of the distance 1, the rotating magnet 30 and the annular magnetic material are shown. The magnetic flux with the body 35 shows a similar change. According to this characteristic diagram, it is better to set the distance 1 to 3 mm or more in this embodiment. The reason why the magnetic flux is small when the distance 1 is small is that there is magnetic flux leakage between the motor core 31 and the annular magnetic material body 35.

Further, if the axial center of the rotating magnet 30 and the axial center of the motor core 31 are made to coincide with each other, it is possible to eliminate the component force in the thrust direction generated between the two. Is forming.

In this embodiment showing the case where the polygon mirror 28 is rotated at a high speed with the load as described above, the rotating magnet 30 has an annular magnetic material body.
By the extremely simple structure that 35 is provided facing each other,
The holding force of the rotor 23 and the polygon mirror 28 in the thrust direction can be sufficiently increased, the positioning accuracy of the polygon mirror 28 in the height direction can be increased, and extremely accurate scanning can be performed. Further, the breaking of the holding force in the thrust direction at the time of changing the operation of the motor including changing the polygonal mirror 28, that is, changing the load, etc., can be easily performed in accordance with the characteristics shown in FIG. 4, and is frequently requested. It is possible to easily face a change in the operation of the polygon mirror 28 with sufficient contents. Further, even if the configuration of the magnetic circuit is changed, the change in the holding force in the thrust direction due to the rotating magnet 30 and the annular magnetic material body 35 is small, and the motor core 31 can be easily changed. Further, in the present embodiment, since the distance between the outer peripheral surface of the rotating magnet 30 and the inner peripheral surface of the motor core 31 is set to a size that can sufficiently suppress the cocking of the motor, the rotor 23 and the polygon mirror 28 are It can rotate with higher precision.

A kind of air damper is formed between the upper end surface of the central shaft 22 and the upper wire member 24 and the porous member 25, especially in each porous portion of the porous member 25, and the rotor 23 and the polygon mirror 28 rotate. The vertical movement of the time is suppressed to be smaller.

The present invention is not limited to the above embodiment,
It can be applied to a high-speed motor other than the case of rotating the polygonal mirror, and can be changed as necessary.

[Effect of device]

Since the thrust bearing mechanism for a high speed motor of the present invention is constructed and operates as described above, it is possible to reliably hold the thrust direction of the rotor of the high speed motor by a large holding force with a simple structure. The members attached to the rotor can always be held and rotated at an appropriate height position, and the rotor can be held at a constant height position even if the load fluctuates or the magnetic circuit of the motor changes. Further, it is very easy to change the design and the cost is reduced.

[Brief description of drawings]

1 to 5 show an embodiment of a thrust bearing mechanism for a high speed motor according to the present invention. FIG. 1 is a longitudinal sectional view, FIG. 2 is a sectional view taken along line II-II in FIG. Figure 3 is III of Figure 1.
-A cross-sectional view taken along line III, Fig. 4 is a characteristic diagram showing the relationship between the load in the thrust direction on the rotor and the sinking amount of the rotor, and Fig. 5 is the rotation with respect to the distance between the motor core and the annular magnetic material. FIG. 6 is a longitudinal sectional front view showing a conventional example, which is a characteristic diagram showing a relationship between a side magnet and a magnetic flux closed between a motor core. 22 ... central axis, 23 ... rotor, 25 ... porous member, 26 ... groove, 28
... polygon mirror, 30 ... rotating magnet, 31 ... motor core, 35 ... annular magnetic material, 36 ... annular gap.

Claims (1)

[Scope of utility model registration request] 1. A ring-shaped rotating magnet, which is externally fixed to a rotor rotating at a high speed so as to face the motor core and has a plurality of magnetic poles in the circumferential direction, and the rotor at a position above the motor core. A thrust bearing mechanism for a high-speed motor, which has a side magnet and an annular magnetic material body that faces the outside from a radial outside with an annular gap.