JPH05336693A - Rotary bearing device of motor - Google Patents

Abstract

PURPOSE:To facilitate a low-torque/high-speed rotary driving and improve the accuracy of shaft whirling and the accuracy of rotation by a method wherein a radial load is received by a pneumatic dynamic radial bearing and a thrust load is received by a pivot-type thrust bearing. CONSTITUTION:A bearing bush 2 and a thrust receiving part 7 are made of ceramic material such as silicon nitride, silicon carbide, zirconia or alumina. The material of a rotary shaft 8 is quenched stainless steel. Therefore, when the rotary shaft 8 starts rotary driving, ring-bone trenches of which dynamic pressure bearing parts 16 and 17 are composed are made to rotate and, accordingly, air 15 enclosed by the flange part of a bearing housing 1 and an air-tight structure 14 is sucked through a bearing gap between the rotary shaft 8 and the bearing bush 2 and a pressure in the bearing gap is elevated. As a result, if the revolution of the rotary shaft 8 reaches a predetermined revolution, the outer circumference of the rotary shaft 8 and the inner circumference of the beating bush 2 are brought into a non-contact state with each other with the air 15 which is lubricant fluid therebetween.

Description

Detailed Description of the Invention

 [Object of the Invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary bearing device for a scanner motor for driving a polygon mirror of an axial gap type, which is used for laser scanning of a laser beam printer or the like.

[0002]

2. Description of the Related Art Conventionally, in a polygon mirror driving scanner motor used for laser scanning of a laser beam printer, a radial gap type motor is generally used, and its rotary bearing device uses oil as a lubricating fluid. Oil dynamic bearings were most often used.

As for the way to receive the thrust load, a magnetically levitated type bearing, an oil dynamic thrust type bearing, and a type in which a flange-shaped portion is formed on the rotary shaft and the flange portion is received by dynamic pressure are used. Bearings were common.

[0004]

The conventional rotary bearing device for a motor having the above-mentioned structure has the following problems.

First, since it is a radial gap type, a large radial load (a whirling (centrifugal force) load due to a residual unbalance of the rotor assembly and a magnetic attraction force due to a deviation of the magnet center) is large, and a motion for receiving this is large. The hydraulic radial bearing had to be an oil dynamic bearing. Therefore, friction loss (shaft loss) becomes large, and a motor capable of generating high torque is required.
These problems become a major problem as the rotation speed of the motor is increased, and the start-up time becomes long, causing a problem that the mirror is fogged by oil mist. Further, it is easily affected by the temperature change, which adversely affects the rotation accuracy (rotational speed fluctuation rate). Moreover, when the oil dynamic bearing is used, the bearing gap becomes large, which adversely affects the shaft runout accuracy.

Further, in the sliding thrust bearing, it is difficult to secure a load capacity that can sufficiently withstand the thrust load by the magnetic levitation method or the oil dynamic pressure method of the dynamic pressure thrust bearing, and even if it can be secured, The cost was a considerable burden. [Constitution of Invention]

[0007]

The present invention has been made in order to solve the above-mentioned technical problems, and a gas dynamic pressure radial bearing consisting of a herringbone groove is formed on the outer peripheral surface and one end thereof is formed. A rotating shaft made of a hardened stainless steel formed in a curved surface, a bearing bush made of a ceramic material for fitting and supporting the rotating shaft, and a bearing bush formed on a curved surface when the rotating shaft of the bearing bush is fitted. Has a pedestal provided on the side where the one end of the pedestal is located and a sliding thrust receiving portion made of a ceramic material provided on the bearing bush side of the pedestal, and the herringbone forming the gas dynamic pressure radial bearing. Two sets of grooves are provided on the upper and lower sides, and the axial lengths of the grooves are proportionally formed within a range of not less than ½ and not more than twice the ratio of the bearing load.

[0008]

The rotary bearing device for a motor according to the present invention has the above-described structure, which makes it possible to significantly reduce the radial load and use the gas dynamic pressure radial bearing, and the thrust bearing is a sliding thrust bearing by point contact. Thus, the thrust load can be most efficiently received, and the motor can be easily started in a short time with low torque.

Further, since the rotary shaft is made of a hardened product of stainless steel, and the bearing bush and the sliding thrust receiving portion are made of a ceramic material such as silicon nitride, silicon carbide, zirconia, or alumina, wear resistance. It has high properties and can be extended in life.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

First, a first embodiment will be described with reference to the general assembly drawing of the polygon mirror driving motor shown in FIG. In the figure, reference numeral 1 denotes a bearing housing having a hollow cylindrical shape and a flange portion formed on one end side thereof. A hollow cylindrical bearing bush 2 is fitted and fixed inside the hollow cylindrical portion of the bearing housing 1. The bearing bush 2 is made of a ceramic material such as silicon nitride, silicon carbide, zirconia, or alumina. The printed wiring board 3 is fixed to the upper side of the flange portion of the bearing housing 1 with screws. The stator coil 4 is bonded and fixed to the upper surface of the printed wiring board 3.

A bottom lid 5 is screwed to the bottom of the bearing housing 1, and a pedestal 6 is provided on the upper surface of the bottom lid 5 so as to contact the inner peripheral surface of the cylindrical portion of the bearing housing 1. There is. Further, a thrust receiving portion 7 is arranged on the upper surface of the receiving base 6 and on the inner circumference of the bearing bush 2. Like the bearing bush 2, the thrust receiving portion 7 is made of a ceramic material such as silicon nitride, silicon carbide, zirconia, or alumina.

By thus forming the bearing bush 2 and the thrust receiving portion 7 with a ceramic material, the friction loss (shaft loss) can be made extremely small as compared with the oil dynamic pressure, and further the temperature change. To reduce the torque of the motor, increase the speed, shorten the startup time, increase the accuracy of shaft runout accuracy and rotation accuracy (rotational speed fluctuation rate), and facilitate the assembly and handling. Is possible.

Inside the bearing bush 2 provided with a hollow cylindrical bearing portion, a rotary shaft 8 formed of, for example, a hardened product of stainless steel is provided with an inner peripheral surface of the bearing bush 2 by several μ.
It is rotatably fitted and supported so as to have a bearing gap (not shown) of m. As described above, the bearing bush 2 is made of a ceramic material, and the material of the rotary shaft 8 is a combination of the hardened stainless steel. Will be able to prevent. One end side of the rotary shaft 8 is formed, for example, in a curved shape, and is in point contact with the thrust receiving portion 7 provided on the upper surface of the receiving base 6 and on the inner circumference of the bearing bush 2, and the thrust receiving portion 7 is rotated by the rotary shaft 8. It is configured to receive the thrust load of No. 8, that is, the own weight of the rotor and the attraction force of the rotor magnet 11, and is a sliding thrust bearing. On the outer peripheral surface of the rotary shaft 8, as dynamic gas pressure bearings, dynamic pressure bearing portions 16 and 17 composed of upper and lower two sets of herringbone grooves are formed to form a dynamic gas pressure radial bearing. , 17 are formed so that the width of the groove portion, the width of the hill portion, and the groove depth are equal, and the suction angles are equal and opposite to each other in different directions.

In such a type of rotary bearing device, the radial load applied to each of the upper and lower two sets of dynamic pressure bearing portions 16 and 17 is significantly different. The section 17 may have a ratio of 2: 1, 3: 1, or higher. Therefore, in order to most efficiently receive the radial load loads which are different in the vertical direction, the axial lengths of the dynamic pressure bearings 16 and 17 are set to be proportionally divided into this ratio. Therefore, in this embodiment, when the axial length of the upper dynamic pressure bearing portion 16 is 2, the axial length of the lower dynamic pressure bearing portion 17 is set to 1. ing.

A radial load load generated by the rotation of the rotary shaft 8 or the like, that is, a whirling (centrifugal force) load due to the residual unbalance of the rotor is applied to the outer periphery of the rotary shaft 8 by a herringbone groove. When the pressure bearing portions 16 and 17 rotate, a dynamic gas pressure is generated and received.

On the other end side (upper end side) of the rotary shaft 8, a shrink-fitted flange 9 is fixed, and the rotor yoke 1
0 is fixed to the flange 9 by being screwed to be fixed to the rotary shaft 8 so as to have a mechanically integrated structure. A ring-shaped rotor magnet 11 is adhered and fixed to the lower surface of the rotor yoke 10, and the rotor magnet 11 faces the stator coil 4 provided on the printed wiring board 3 described above. And
A certain magnetic gap is secured by forming a slight gap between the rotor magnet 11 and the stator coil 4. A polygon mirror 12 is mounted on the upper side of the flange 9 and is regulated downward by the flange 9 and is regulated and fixed by a mirror retainer 13 from above.

The components such as the printed wiring board 3, the stator coil 4, the flange 9, the rotor yoke 10, the rotor magnet 11, the polygon mirror 12 and the mirror retainer 13 arranged above the flange portion of the bearing housing 1 are as follows. It is hermetically sealed by the bottomed cylindrical hermetically sealed structure 14 and the flange portion of the bearing housing 1, and has a structure in which contact with the outside air is completely cut off. A laser beam passage window 14a for passing a laser beam is provided on a part of the side surface of the closed structure 14. The space sealed by the flange portion of the bearing housing 1 and the hermetically sealed structure 14 is filled with clean air 15 from which floating dust as a lubricating fluid has been removed.

The operation and action of the rotary bearing device for a motor applied to the axial gap type polygon mirror driving motor of this embodiment will be described below. When a power supply device (not shown) is turned on, a rotor yoke 10 and a rotor magnet 1 that mechanically configure a rotor
The rotary shaft 8 having two sets of dynamic pressure bearing portions 16 and 17 formed of 1, a polygon mirror 12 and a herringbone groove on the outer peripheral surface thereof starts rotational driving. By the rotation of this rotor,
The herringbone grooves forming the dynamic pressure bearing portions 16 and 17 rotate, whereby the air 15 sealed by the flange portion of the bearing housing 1 and the sealing structure 14 is transferred between the rotating shaft 8 and the bearing bush 2. It sucks (pumps) through the existing bearing gap to increase the pressure in the bearing gap. As a result, when the rotation speed reaches or exceeds the predetermined rotation speed, the outer peripheral surface of the rotary shaft 8 and the inner peripheral surface of the bearing bush 2 are brought into non-contact with each other through the air 15 which is a lubricating fluid.

More specifically, the clean air 15 that has been sealed is sucked by the dynamic pressure bearing portions 16 and 17 formed of herringbone grooves formed on the outer periphery of the rotary shaft 8 that rotate with the rotation of the rotor ( Pumping) to increase the pressure in the bearing gap. As a result, the dynamic pressure bearing portion 16,
2 forming pairs 17 in different directions
Flat part 16a, 1 located between two herringbone grooves
The pressure in the bearing gap corresponding to 7a is in a state of rising during the continuous rotation, and becomes the highest pressure portion.
Since the axial length of the dynamic pressure bearing portion 16 is formed longer than the axial length of the dynamic pressure bearing portion 17, the flat portion 16 is formed.
The pressure in the flat portions 16a is higher than the pressure in the flat portions 17a.

This operation will be described with reference to FIG. 2 including the relationship with the radial load. Radial load generated with the rotation of the rotary shaft 8, that is, whirling due to residual unbalance of the rotor (centrifugal The force) load Wf is applied at the center of gravity 18 of the rotor. Now, a lower side dynamic pressure bearing portion center 20 which is the center of the lower side dynamic pressure bearing portion 17 and an upper dynamic pressure bearing portion center 19 which is the center of the upper side dynamic pressure bearing portion 16.
Is A, the upper dynamic bearing center 19 and the rotor center of gravity 1
8 is B, the radial load Wb applied to the center 19 of the upper hydrodynamic bearing is Wf × (A + B) = Wb × A, and Wb = Wf × (A + B) / A, and if A = B Wb = 2Wf. Similarly, the radial load load Wa applied to the center 20 of the lower dynamic pressure bearing portion
From Wf × B = Wa × A, Wb = Wf × (A + B) / A, and if A = B, Wa = 2Wf. That is, W
Since b: Wa = 2: 1, it can be seen that a large radial load is applied to the upper dynamic pressure bearing portion 16.

Therefore, the axial length b of the herringbone groove of the dynamic pressure bearing portion 16 and the axial length a of the herringbone groove of the dynamic pressure bearing portion 17 are apportioned to this ratio of 2: 1. The bearing load load of each of the upper and lower dynamic pressure bearing portions 16 and 17 has this ratio, and the radial load load generated by the rotation of the rotor can be most efficiently received.

Further, since the bearing bush 2 is made of a ceramic material, the rotation speed of the rotary shaft 8 is equal to or lower than a predetermined rotation speed when the motor is started or stopped.
It is possible to prevent abrasion and seizure between the rotary shaft 8 and the bearing bush 2, which is likely to occur when the bearing bush 2 and the bearing bush 2 are in a non-lubricated and sliding bearing state.

Further, by adopting a sliding thrust bearing structure by point contact as the structure of the thrust bearing, it is possible to sufficiently receive the thrust load load of the rotor's own weight and the magnetic attraction force, and the motor can be driven at a low torque in a short time. Will be able to easily start.

In the above-mentioned embodiment, the rotary bearing device using clean air which does not contain suspended dust as the lubricating fluid has been described, but this is not the case for obtaining the same effect, and the viscosity coefficient is small ( It is possible to obtain the same effect by applying another gas (at the same level as air).

Further, the case where the ratio of the axial lengths of the herringbone grooves forming the two sets of upper and lower dynamic pressure bearing portions is set to 2: 1 has been described, but the present invention is not limited to this ratio, and the ratio is not limited to this. The same effect can be obtained by setting based on the ratio of the radial load applied to the dynamic pressure bearing portion.

Further, regarding the stator coil, it is also possible to implement by applying a slice coil. When the slice coil is applied, downsizing, thinning, cost reduction and high performance of the motor are realized. It becomes possible.

Further, in the present embodiment, the structure of the thrust bearing is explained by applying the pivot type, but the same effect can be obtained even if this is applied as the air dynamic pressure bearing type. Is.

[0029]

In the rotary bearing device for a motor of the present invention, the radial load is received by the gas dynamic pressure radial bearing,
Since the structure is such that the thrust load is received by the pivot bearing of the pivot, it is easy to drive at low torque and high speed, has high accuracy of shaft runout accuracy and rotation accuracy (rotation speed fluctuation rate), and is excellent in mass production and inexpensive. It is possible to provide a rotary bearing device for an axial gap type motor that can be provided as a popular dynamic pressure bearing and is easy to assemble and handle.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation

[Explanation of symbols]

 1 bearing housing 2 bearing bush 6 pedestal 7 thrust bearing 8 rotary shaft

Claims (4)

[Claims] 1. A rotary shaft having a gas dynamic pressure radial bearing formed of a herringbone groove on its outer peripheral surface and one end formed into a curved shape, a bearing bush for fitting and supporting the rotary shaft, and the rotation of the bearing bush. It is characterized in that it has a pedestal provided on a side where one end formed in a curved shape when the shaft is fitted is located, and a sliding thrust receiving section provided on the bearing bush side of the pedestal. Axial gap type motor rotary bearing device. 2. The herringbone groove forming the gas dynamic pressure radial bearing is provided in upper and lower two sets, and the axial length of each is within a range of ½ or more and twice or less of the bearing load ratio. The rotary bearing device for an axial gap type motor according to claim 1, wherein the rotary bearing device is formed by proportional division. 3. The axial according to claim 1, wherein the rotary shaft is made of a hardened stainless steel, and the bearing bush is made of a ceramic material such as silicon nitride, silicon carbide, zirconia or alumina. Gap type motor rotary bearing device. 4. The rotating shaft is made of a hardened stainless steel, and the sliding thrust receiving portion is made of silicon nitride or silicon carbide.
2. A rotary bearing device for an axial gap type motor according to claim 1, wherein the rotary bearing device is made of a ceramic material such as zirconia or alumina.