JPH08210350A - Dynamic pressure bearing device - Google Patents

Abstract

PURPOSE: To provide a dynamic pressure bearing device capable of suppressing the increase in the dynamic torque and heat generation of a radial dynamic pressure bearing, capable of mounting an optimum motor for driving at high speed, small in dimensional restriction, and capable of coping with high speed. CONSTITUTION: In a dynamic pressure bearing device, a rotary member 13 fitted with a mirror 6 is supported by a fixed member through a radial dynamic pressure bearing R and a magnetic bearing Sm, and driven by a motor M. The thrust magnetic bearing Sm is provided inside the rotary member 13 while the radial dynamic pressure bearing R is provided outside the rotary member, and the position of the motor M is different from that of the radial dynamic pressure bearing R in the axial direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic pressure bearing device,
In particular, the present invention relates to a dynamic pressure bearing device suitable for applications requiring high-speed rotation such as an optical deflector.

[0002]

2. Description of the Related Art As a conventional dynamic pressure bearing device, for example, there is one shown in FIG. In this conventional example, a fixed shaft 2 that is erected in the center of a base plate 1A below the housing 1 is provided.
A rotary sleeve 3 as a rotary member is rotatably supported via a radial dynamic pressure fluid bearing R and a thrust magnetic bearing Sm.

A mirror 6 is provided on the outer peripheral surface of the rotary sleeve 3.
Will be installed. The rotor magnet 7 is attached to the inner peripheral surface of the rotary sleeve 3, and the stator coil 8 that faces the rotor magnet 7 in the radial direction with an air gap is attached to the outer peripheral surface of the fixed shaft 2 to rotate the rotary sleeve. A driving motor M is configured. In this dynamic pressure bearing device, the motor M provided inside the rotary sleeve 3 rotates the rotary sleeve 3 in a non-contact manner with the fixed shaft 2 to rotate the mounted mirror 6 at high speed.

[0004]

Dynamic bearing devices for optical deflectors are used in digital copiers, laser printers, etc., but as their printing speed increases, they need to rotate at even higher speeds. It has become to. However, in the conventional dynamic pressure bearing device in which the motor M is arranged in the inner space of the rotary sleeve 3 as described above, since the outer diameter of the motor M is large, the diameter of the outer peripheral surface of the rotary sleeve which constitutes the bearing surface of the radial dynamic pressure bearing R is large. Is inevitably large, so that there is a problem that it cannot rotate at a high speed.

That is, the dynamic torque and heat generation of the dynamic pressure bearing are
This is due to the viscous resistance of the air present in the bearing clearance, but since the viscous resistance is proportional to the cube of the bearing surface diameter,
The larger the diameter, the greater the driving force required for high-speed rotation, and the more heat is generated. When the heat generation of the bearing increases,
The effect on the performance that the position of the mirror shifts during rotation due to the difference in thermal expansion between the rotating sleeve and the mirror and vibration due to imbalance becomes large cannot be ignored.

On the other hand, under the dimensional constraint that the motor is arranged in the inner space of the rotary sleeve 3, it is impossible to freely design an optimum motor having a driving force necessary for high speed rotation. There is also. Therefore, the present invention provides a dynamic pressure bearing device which is capable of suppressing the increase of the dynamic torque and heat generation of the radial dynamic pressure bearing and freely designing an optimum motor for driving, and which is compatible with high speed rotation with few dimensional constraints. With the goal.

[0007]

In order to achieve this object, a dynamic pressure bearing device of the present invention is provided with a thrust magnetic bearing inside a rotary member on which a mirror is mounted and a radial dynamic pressure bearing outside and a motor. And the radial dynamic pressure bearing have different axial positions.

[0008]

In the dynamic pressure bearing device of the present invention, the outer diameter of the radial dynamic pressure bearing can be reduced. Therefore, the viscous resistance of air in the bearing clearance is reduced, and dynamic torque and heat generation of the radial dynamic pressure bearing are suppressed even at high speed rotation. In addition, since the dimensions of the motor are not restricted, there is a large degree of freedom in designing the motor.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of an embodiment of the present invention. First, the structure will be described. The housing 11 of this dynamic pressure bearing device.
The lower part is closed by the base plate 11A,
A fixed shaft 12 is erected at the center of A. The housing 11, the lower base plate 11A, and the fixed shaft 12 constitute a fixed member. A rotary sleeve 13 made of an aluminum alloy (may be subjected to a surface hardening treatment) as a rotary member for mounting the mirror 6 on the fixed shaft 12 is freely rotatable via a radial dynamic pressure bearing R and a thrust magnetic bearing Sm. It is supported.

The radial dynamic pressure bearing R includes a rotary sleeve 13
One cylindrical radial bearing surface 1 provided on the outer peripheral surface of the
4 and the other radial bearing surface 15 of the inner peripheral surface of the housing 11 opposed to this via a radial bearing clearance, and at least one of the radial bearing surfaces 14 and 15 for generating a herringbone dynamic pressure is provided. It is configured to have a groove.

Further, the thrust magnetic bearing Sm is composed of the fixed shaft 1
One magnet member 18 made of a permanent magnet fixed to the free end of 2 and the other magnet member 19 fixed to the inner peripheral surface of the rotary sleeve 13 by means of press-fitting or shrink-fitting. Reference numeral 19 is a suction type thrust magnetic bearing which is opposed to and radially attracts a gap larger than the radial bearing clearance in a non-contact manner. Both magnet members 1
The magnetization directions of 8 and 19 may be radial or axial.

A step portion 2 is provided on the bottom of the upper portion of the rotary sleeve 13.
0 is provided, and an aluminum alloy mirror 6 having a coefficient of thermal expansion substantially the same as that of the rotary sleeve 13 is attached thereto. The motor M differs from the radial dynamic pressure bearing R in the axial position. The motor M is disposed outside the rotary sleeve 13 as a rotary member and inside the housing internal space 11S having a diameter larger than that of the rotary sleeve 13. That is, a yoke 22 having a diameter larger than that of the rotary sleeve 13 is fixed to the lower portion of the rotary sleeve 13 by means such as press fitting, shrinkage fitting, or caulking, and the yoke 22 located in the housing internal space 11S.
The rotor magnet 23 is fixed to the end of the yoke 22
The rotor magnet 23 constitutes a rotor 24.
The inner peripheral surface of the rotor magnet 23 faces the outer peripheral surface of the stator 25 fixed at the root of the fixed shaft 12 in the radial direction via an air gap to form a circumferentially opposed motor.

Next, the operation will be described. The rotating sleeve 13 on which the mirror 6 is mounted is always in non-contact with the fixed shaft 12 in the axial direction by the magnetic attraction force of both magnet members 18 and 19 which are opposed to each other with some deviation in the axial direction of the thrust magnetic bearing Sm. Suspended by. The rotor 24 is rotated by passing a predetermined current through the armature coil of the stator 25 of the motor M via a control circuit (not shown), and at the same time the rotary sleeve 1 is rotated.
3 rotates. Then, due to the pumping action of the groove for generating the dynamic pressure of the radial dynamic pressure bearing R, a dynamic pressure is generated in the radial bearing clearance in the radial direction between the opposing radial bearing surfaces 14 and 15, and the rotary sleeve 13 is attached to the housing 11. It is also supported in a completely non-contact manner with respect to the radial bearing surface 15 on the inner peripheral surface of, and reaches high-speed steady rotation in a short rising time.

When a high speed rotation is reached, the conventional rotary sleeve with a built-in motor generates a considerable amount of heat from the radial dynamic pressure bearing R having a large outer diameter. However, in the case of this embodiment, since the motor M is arranged outside the rotating sleeve 13,
Regardless of the outer diameter of the motor M, the diameter of the outer peripheral surface (one radial bearing surface) 14 of the rotary sleeve 13 can be made considerably smaller than in the conventional case. Therefore, the viscous resistance of the air existing in the radial bearing clearance of the radial dynamic pressure bearing R is reduced, and the dynamic torque and heat generation of the dynamic pressure bearing during high speed rotation can be reduced.

Further, since the motor M is arranged outside the rotary sleeve 13, it is possible to design a motor having a necessary driving force without being restricted by the size of the rotary sleeve 13. If the outer diameter of the rotor 24 of the motor M is too large, the wind loss becomes large, and if it is too small, the required driving force cannot be obtained. However, according to this embodiment, the dimensional freedom of the motor design is increased. Since it is large, there is an advantage that a motor M having an optimum size can be installed.

Further, even if the wind loss of the mirror 6 at the time of high speed rotation and the heat generated by the friction between the bearing surface of the thrust magnetic bearing Sm and the air are transmitted to the rotary sleeve 13 and thermal expansion occurs, the rotary sleeve 13 is used in this embodiment. Since the mirror 6 and the mirror 6 are made of an aluminum alloy having substantially the same coefficient of thermal expansion, it is possible to prevent a phenomenon in which the center of gravity of the rotating sleeve 13 and the mirror 6 are deviated due to a difference in thermal expansion, resulting in imbalance in rotation and vibration of the device. To be done.

In this embodiment, the rotor 24 of the motor is attached to the lower part of the rotary sleeve and the magnet member 19 of the thrust magnetic bearing is attached to the inner peripheral surface of the rotary sleeve by shrink fitting or press fitting. Therefore, even if the rotary sleeve 13 thermally expands, the center of gravity of the rotor 24 and the magnet member 19 does not move with respect to the center of rotation, and from this point also, the balance of rotation of the device is maintained and vibration is prevented.

FIG. 2 shows a second embodiment. This embodiment is different from the first embodiment in that the thrust magnetic bearing Sm is a repulsive type magnetic bearing and the motor M is a surface facing motor. The motor M includes a stator 25 having a large number of amateur coils arranged in a flat annular shape as a whole on the plane of the base 11A, and a donut plate-shaped rotor magnet 23 arranged to face the plane through an air gap in the axial direction. Is configured. If the thrust magnetic bearing Sm is a repulsive type magnetic bearing, unlike the first embodiment, the radial load based on the magnetic imbalance of the radial attractive force of the magnet can be reduced, so that when the radial dynamic pressure bearing R is started and stopped. There is an advantage that damage can be reduced.

That is, in the case of the first embodiment, there is a radial mounting error between the cylindrical magnet members 18 and 19 fixed to one end of the fixed shaft 12 and the inner peripheral surface of the rotary sleeve 13, respectively. Misalignment of the magnetic attraction force in the radial direction occurs due to misalignment and uneven magnetization. On the other hand, the air gap of the thrust magnetic bearing Sm is made larger than the radial bearing clearance of the radial fluid bearing R so as to keep the starting friction torque of rotation small so as to keep non-contact at all times. When the rotating sleeve 13 is not large enough to maintain the radial bearing clearance, the opposing bearing surfaces 14, 14
15 rotates in contact. Therefore, the bearing surfaces 14 and 15 of the radial dynamic pressure bearing R are easily damaged at the time of starting and stopping due to the radial load due to the imbalance of the magnet attraction force in the radial direction.

On the other hand, in the thrust magnetic bearing Sm of the second embodiment, both magnet members 18 and 19 are mounted on the flat surface so that the rotary sleeve 13 is fixed by the magnetic repulsive force.
2 is supported by levitation in the axial direction. As a matter of course, the magnetic repulsion force is unbalanced in the radial direction due to the misalignment and the uneven magnetization due to the mounting error in the radial direction of the two magnet members 18, 19, but it is caused by the magnetic attraction force in the radial direction as described above. Since the load is smaller than the radial load, damage to the bearing surfaces 14 and 15 of the radial dynamic pressure bearing R during starting and stopping is small.

The inside of the housing 11 is the housing 11.
Although it is hermetically sealed via a radial bearing clearance between the rotary sleeve 13 and the rotary sleeve 13, a small hole 30 is provided in the base 11A so that the internal space 11S of the housing functions as an air damper.
Axial vibration can be reduced. However, if the radial bearing clearance of the radial dynamic pressure bearing R can fulfill the function of the small hole 30,
The small hole 30 may not be provided again.

When the thrust magnetic bearing Sm is the attraction type thrust magnetic bearing as in the case of the first embodiment, one of the pair of magnet members 18 and 19 may be replaced with a magnet to be a ferromagnetic material. . Further, in order to prevent foreign matter such as dust from entering the housing 11 before the dynamic pressure bearing device is incorporated in the main body of the optical deflector or the like, a cover for covering the mirror 6 is attached to the housing 11 so that the entire dynamic pressure bearing device is installed. The hermeticity facilitates handling during transportation and assembly.

[0023]

As described above, according to the dynamic pressure bearing device of the present invention, the size of the radial dynamic pressure bearing R is the size of the motor M.
Since the radial dynamic pressure bearing R is not restricted by the above, the outer diameter of the radial dynamic pressure bearing R can be reduced, and as a result, the viscous resistance of the air in the radial bearing clearance is reduced and the dynamic torque and heat generation of the radial dynamic pressure bearing are suppressed even at high speed rotation. Has the effect.

The size of the motor is the radial dynamic pressure bearing R.
Therefore, the degree of freedom in designing the motor is increased, and an optimum motor having a driving force required for high-speed rotation can be installed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is a cross-sectional view showing an example of a conventional bearing device.

[Explanation of symbols]

 6 Mirror 11 Housing 12 Fixed shaft 13 Rotating member (rotating sleeve) M Motor R Radial dynamic pressure bearing Sm Thrust magnetic bearing

Claims (1)

[Claims] 1. A dynamic pressure bearing device in which a rotary member having a mirror is supported by a fixed member via a radial dynamic pressure bearing and a thrust magnetic bearing and is driven to rotate by a motor, wherein the thrust member is inside the rotary member. A dynamic bearing device, characterized in that a magnetic bearing and the radial dynamic bearing are provided outside, and axial positions of the motor and the radial dynamic bearing are different from each other.