JP3293328B2 - Bearing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing device requiring strict rotation accuracy, such as a polygon mirror motor for a laser beam printer.

[0002]

2. Description of the Related Art Recently, in a laser beam printer, as the performance and function of an apparatus have been improved, a polygon mirror motor for laser scanning used therein has been required to have high rotational accuracy. Conventionally, ball bearings have been used for this motor, but non-contact type fluid lubricated bearings have come to be used in terms of high speed and fluctuations in rotation speed. In addition, air bearings and magnetic fluid bearings having excellent sealing properties have been proposed and put into practical use from the usage conditions in a clean environment. In particular, compared to air bearings, magnetic fluid bearings have high viscosity of magnetic fluid, so high bearing rigidity can be obtained with small-diameter bearings, and good damping performance against shaft vibrations. It is disclosed in Japanese Unexamined Patent Publication No. 3-51514.

[0003]

According to the above-mentioned prior art, the application of a fluid bearing to a high-speed and high-precision rotation of a motor is proposed, and a magnetic fluid is used to enable use in a clean environment. It is used for lubrication and sealing of bearings to achieve its purpose. However, in the motor using the disclosed bearing device, a certain degree of high-precision rotation can be obtained, but there is a limit to fluctuations in the number of rotations, and it cannot be applied to a recent high-definition laser beam printer. There is. That is, in a laser beam printer, a polygon mirror motor used for scanning a laser beam at a constant speed is electrically controlled to maintain a constant rotation speed.
However, in the conventional printer, drawing was performed with a rotation speed fluctuation of about 0.02%. However, in a laser beam printer corresponding to high definition and colorization, the rotation speed fluctuation was 0.01%.
There is a need for a high-precision rotation motor that requires fluctuations before and after. In order to realize this accuracy, it is basically necessary to reduce the friction fluctuation of the bearing.

[0004] Fluid bearings using lubricating oil are, in principle, bearings with no friction fluctuation when the viscosity of the fluid is constant.
It has been found that it is difficult to achieve a rotation speed fluctuation of about 0.01% with the conventional bearing device described above. That is, according to the experimental results, it has been found that in a high-speed rotation region of 10,000 rpm or more, the fluctuation of the rotation speed increases as the rotation speed increases. In particular, at high speed rotations of 20,000 rpm or more, the rotation speed may fluctuate irregularly.

In order to clarify this phenomenon and solve the problem, the flow of lubricating oil in the bearing chamber was observed using a transparent bearing case. As a result, it was found that the state of the lubricating oil on the bearing sliding surface and around the bearing changed as the rotation speed increased. That is, small bubbles are generated in the lubricating oil by the rotation of the shaft, and when these grow to become relatively large bubbles, they are crushed finely when they become a certain size.
Porous sintered bearings are desirable for bearings in terms of mass productivity, manufacturing cost, stability of dimensional accuracy, etc. In the case of porous sintered bearings, bubbles contained in the pores of the bearings May come out on the sliding surface due to the rotation of the shaft. It was observed that such a phenomenon was repeated in the bearing room. It has been found that the above-mentioned fluctuation in friction of the fluid bearing is caused by the incorporation of bubbles. However, there are few examples of applying an oil-lubricated bearing to a polygon mirror motor, and such high precision rotation is required. Since there was no rotating machine, no consideration was given to the reduction of bubbles coming out of the bearing at high speed rotation and bubbles generated in the lubricating oil as described above.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has been made to solve the problems of the prior art. An object of the present invention is to provide a bearing device for a motor or a cylinder motor for a video tape recorder.

[0007]

According to the present invention, there is provided a rotary shaft, a porous sintered oil-impregnated radial bearing for rotatably supporting the rotary shaft, and a bearing chamber for holding the radial bearing. Bearing having a bearing support portion, lubricating oil applied to fill a sliding gap between the rotary shaft and the radial bearing, and a space provided at an end of the radial bearing in an axial direction of the rotary shaft. The apparatus is characterized in that the dynamic pressure in the sliding gap is maintained at a positive pressure, and a rectifying plate is disposed in the space at a distance from the end of the radial bearing.

[0008]

Since only positive dynamic pressure is generated in the bearing sliding gap by the rotation of the rotating shaft, bubbles contained in the bearing are pushed to the outer peripheral side of the bearing by the pressure generated on the sliding surface of the bearing. The air contained in the porous sintered oil-impregnated radial bearing is not extracted. Since the oil film on the bearing sliding surface is formed stably, high-precision rotation performance is maintained even at high speed rotation. In addition, since a means for suppressing entrapment of air bubbles into the bearing sliding gap surface is provided, high-precision rotation is better maintained.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

The motor shown in FIGS. 1 and 2 is a polygon mirror motor for laser operation used in a laser beam printer.

As shown in FIG. 1, the polygon mirror motor includes a motor base 1, a cylindrical housing 2, and a rotating body 3. The motor base 1 has a flange portion 5 formed in a flange shape on the outer periphery of a bearing support base 4 formed of aluminum and provided at a central portion. The flange 5 serves as a support for the stator coil 10. The housing 2
It is fitted and attached to the outer periphery of the flange portion 5.

The rotator 3 has a rotator 6 made of aluminum, an aluminum polygon mirror 7 mounted on the rotator 6, and a rotation shaft 8 inserted and fixed at the center of the rotator 6. . The rotating shaft 8 is formed of a stainless steel material that is a magnetically permeable material. The magnetically permeable material is used because a magnetic fluid is used as lubricating oil for the bearing.

The polygon mirror 7 mounted on the rotor 6 is fixed by screws 9. The rotating body 3 is rotatably supported by the motor base 1. A stator coil 10 for a motor is provided on a surface of the flange portion 5 of the motor base 1 facing the rotor 6. The stator coil 10 is attached to the flange portion 5 via a substrate 11, an insulating layer 12, and a stator yoke plate 13. Stator coil 10
Is a flat coil, and the rotor magnet 14 for the motor is provided on the surface thereof so as to face the rotor magnet 14 for the motor provided on the rotor 6 of the rotating body 3.
The rotor magnet 14 has a ring shape and is attached to the rotor 6 via a rotor yoke plate 15. Rotor magnet 14 and stator coil 10
Are arranged so as to face each other in the axial direction of the rotating shaft 8. As shown in FIG. 2, the bearing support 4 of the motor base 1 has a shape having a convex portion 16 protruding toward the rotor 6 and a protruding portion 17 protruding in a direction opposite to the direction in which the convex portion 16 protrudes. Has become.

An external bearing chamber 20 is formed inside the convex portion 16, and an internal bearing chamber 21 is formed inside the raised portion 17. The external bearing chamber 20 is provided with an external radial bearing 18, and the internal bearing chamber 21 is provided with an internal radial bearing 1.
9 is fitted and provided. Double bearing chamber 20, 21
Are communicated with each other through a communication hole 22 between the bearing chambers. The communication hole 22 between the bearing chambers is formed in the bearing support base 4 so as to surround the outer periphery of the rotating shaft 8, and is filled with lubricating oil.

The convex portion 16 of the bearing support 4 is provided with a seal 23 at the tip. The seal 23 has a cap 24, a seal support 25, a dynamic pressure seal 29, and a magnetic fluid seal 26 for magnetic fluid sealing. The dynamic pressure seal 29 is provided with a spiral groove formed on the inner periphery of the seal support 25. The spiral groove is formed so as to advance to the radial bearing 18 along the rotation direction of the rotating shaft 8. Cap 2
Reference numeral 4 denotes a cylindrical shape made of an aluminum material. The projecting portion 16 of the bearing support 4 has a bearing chamber 20
And an annular fitting projection 27 formed concentrically with the projection. The cap 24 is fitted and attached to the fitting projection 27. The fitting between the fitting projection 27 and the cap 24 is such that airtightness is sufficiently maintained. The inner diameters of the fitting projection 27 and the cap 24 are in the bearing chamber 2.
0 is formed larger than the inner diameter.

The magnetic fluid seal 26 provided on the cap 24 is made of a permanent magnet, and is fixed to the cap 24 by bonding or the like in order to provide airtightness. The magnetic fluid seal 26 forms a magnetic circuit via the magnetically permeable rotating shaft 8. Due to the magnetic attraction of this magnetic circuit,
The magnetic fluid sealed in the gap between the rotating shaft 8 and the magnetic fluid seal 26 is firmly caught and the magnetic fluid applied to the radial bearing 18 is prevented from flowing out of the magnetic fluid seal 26. The radial bearing 18 is placed so that the outer end face is flush with the end face on the distal end side of the convex portion 16.

The radial bearing 18 and the radial bearing 1
9 has an inner peripheral surface formed as shown in FIG. Both radial bearings 18 and 19 have an oil groove 30 for circulation on the sliding surface side on the inner periphery. The oil grooves 30 for circulation on the sliding surface side are provided at three locations and are arranged at an equal pitch. The oil groove 30 is formed over the entire length of both radial bearings 18 and 19 along the axial direction of the rotating shaft 8. Sliding gap between both oil grooves 30 (radial bearings 18, 19)
Is formed so that the gap becomes narrower in the rotation direction of the rotating shaft 8. In other words, the inner peripheral surfaces of the radial bearings 18 and 19 are formed not to be perfect circles but to decrease in diameter in the rotation direction. The oil groove 30 is configured such that an end corresponding to the near side when viewed from the rotation direction is closest to the rotating shaft 8, and an end corresponding to the rear side is most distant from the rotating shaft 8. It is.

The pressure of the lubricating oil in the sliding gap having such a shape becomes a positive dynamic pressure indicated by a dotted line in FIG.

The above-described seal 23 will be described in more detail. The magnetic seal 26 for magnetic fluid sealing provided along with the dynamic pressure seal 29 is formed by mixing ferrite particles and plastic. The magnetic seal 26 for sealing a magnetic fluid has an annular shape and surrounds the outer periphery of the rotating shaft 8. The magnetic seal 26 for magnetic fluid sealing is fitted and attached to an annular step formed on the seal support 25. The fitting of the magnetic seal 26 for magnetic fluid sealing and the step portion is such that the joint surface is sufficiently airtight.

The external radial bearing 18 has an oil groove 30 for circulation on the sliding surface on the inner periphery and a circulation passage 31 on the outer periphery. The passages 31 are formed at equal pitches at three locations on the outer periphery of the radial bearing 18. The current plate 32 is slightly separated from an end face on the outside of the radial bearing 18. The fitting between the fitting projection 27 and the cap 24 is such that airtightness is sufficiently maintained. The rectifying plate 32 is attached so as to be sandwiched between the fitting projection 27 and the cap 24. A communication hole 33 is provided on the outer circumference of the current plate 32.
The communication holes 33 are formed at equal pitches at three locations on the outer periphery of the current plate 32. The current plate 32 has a communication hole 33.
There is no part between the fitting projection 27 and the cap 24.

The current plate 32 partitions a space 34 provided outside the radial bearing 18 and divides it. The space 34 is formed by being surrounded by the inner peripheral surface of the cap 24, the inner surface of the seal support 25, and the outer end surface of the radial bearing 18. The dimension d of the gap between the outer end face of the radial bearing 18 and the current plate 32 is about 0.5 mm. End surface on the back side of radial bearing 18 and external bearing chamber 20
Is about 1 mm.

The inner periphery of the communication hole 22 between the bearing chambers and the rotating shaft 8
The dimension a of the gap between the outer circumference of the rotary shaft 8 and the outer circumference of the rotary shaft 8 is 1/20 or less of the diameter D of the rotating shaft 8. Diameter D of rotating shaft 8
Is about 5 mm.

The outer end of the inner bearing chamber 21 for holding the inner radial bearing 19 is closed by a lid 35. The lid 35 is fitted and attached to a lid recess formed at the outer end of the raised portion 17. The fitting between the lid 35 and the lid recess is such that the joint surface is sufficiently airtight. The dimension c of the gap between the outer end of the radial bearing 19 and the lid 35 is about 0.5 mm. The dimension b of the gap between the inner end of the radial bearing 19 and the back of the bearing chamber 21 is 1 mm. Like the radial bearing 18, the radial bearing 19 has an oil groove 30 for circulation on the sliding surface side and a passage 31 for circulation on the outer periphery.
Having. The two radial bearings 18 and 19 are
Has a chamfered portion in which both corners of the inner peripheral surface for supporting the edge are cut.

The magnetic thrust bearing is a motor base 1 of the stator.
And the rotating body 3. This magnetic thrust bearing includes a stator-side permanent magnet 36 and a rotor-side permanent magnet 37. The stator-side permanent magnet 36 is provided on the outer periphery of the tip of the convex portion 16. The rotor-side permanent magnet 37 provided on the rotating body 3 is located at a position facing the stator-side permanent magnet 36. A circular recess 38 is formed in the rotor 6 of the rotating body 3 so that the convex portion 16 can be accommodated. This circular recess 3
, A stator-side permanent magnet 36 and a rotor-side permanent magnet 3
7 are arranged in a ring shape, and the two magnets 36 and 37 facing in the radial direction are arranged such that different poles face each other.

In the polygon mirror motor having the above configuration, the rotating body 3 is incorporated in the motor base 1 of the stator as follows. Before the rotating body 3 is assembled, the center of the magnetic seal 26 for magnetic fluid sealing is opened. The motor base 1 is set up, and a predetermined amount of magnetic fluid as lubricating oil is poured from the opening. Thereafter, the rotor 3 is attached to the motor base 1 by inserting the rotating shaft 8 into the motor base 1 from the opening of the magnetic seal 26 for sealing magnetic fluid.

Since the rotating body 3 is kept at a predetermined position by the magnetic thrust bearing on the inner side of the rotating shaft 8, the lower end is placed in a state of being slightly floating above the inner surface of the lid 35. When the rotary shaft 8 enters the radial bearings 18 and 19 and the communication hole 22 between the bearing chambers, the oil level of the magnetic fluid rises to the rectifying plate 32 and the radial bearings 18 and 19 are immersed in the magnetic fluid. State. The magnetic fluid is shown dotted in FIG. The magnetic fluid containing the fine magnetic powder is used to lubricate the sliding gap between the radial bearings 18 and 19 with lubricating oil.

The size of the magnetic powder is 0.01 μm to 0.01 μm.
The surface-treated one having a thickness of 5 μm is used. The sliding gap is several μm to 10 μm, and the size of the magnetic powder in the magnetic fluid is about 1/100 of the sliding gap. The gap can be sufficiently moistened.

The inner end of the rotating shaft 8 rotatably supported by the two radial bearings 18 and 19 has an inner radial bearing 19.
Although the other end extends outside through the external radial bearing 18, the magnetic seal 26 for sealing the magnetic fluid,
The leakage of the magnetic fluid to the outside is suppressed by the dynamic pressure seal 29.

Next, the operation will be described.

The rotating body 3 of the rotor rotates when the motor is energized. The lubricating oil in the gap formed between the inner periphery of the communication hole 22 between the bearing chambers and the outer periphery of the rotary shaft 8 turns with the rotation of the rotary shaft 8. It was confirmed that bubbles and air cavities were generated in the lubricating oil in the gap between the bearing chamber communication holes 22 due to the swirling flow. It has been found that the phenomenon of generation of bubbles and air cavities occurs when the gap between the bearing chamber communication holes 22 is wide and the rotation speed of the rotating shaft 8 is 15,000 rpm or higher.

In the assembly of the motor, the bubbles or cavities are mixed in the lubricating oil when the rotating shaft 8 is inserted into the radial bearings 18 and 19, or the air originally contained in the lubricating oil. The fine particles are gathered by the swirling flow, and grow into small bubbles or cavities.

When these bubbles or cavities are generated, friction fluctuation occurs in the gap between the communication holes 22 between the bearing chambers, causing fluctuations in the rotation of the rotor. In addition, air bubbles move from the gap in the communication hole 22 between the bearing chambers to the two radial bearings 18 and 19, and the air bubbles are mixed with the magnetic fluid that has filled the sliding gap between the two radial bearings 18 and 19, so that the viscosity changes. Since the viscous frictional resistance of the sliding gap fluctuates, the rotational speed of the rotor fluctuates.

Further, since the porous sintered oil-impregnated bearings are used for the radial bearings 18 and 19, when the dynamic pressure of the oil film generated on the bearing sliding surface by the rotation of the shaft is a negative pressure, the sintering is performed. The air contained in the oil-impregnated bearing is drawn out to the sliding surface together with the magnetic fluid. This is shown in FIG. When a bearing whose sliding surface has a symmetrical three-arc shape is used, the pressure distribution of the oil film is indicated by a dotted line in the figure. this is,
This is because a negative oil film pressure occurs when the gap between the rotating shaft 8 and the bearing sliding surface widens in the direction of rotation of the shaft.

As a result of studying the generation of these bubbles or cavities by observation experiments and the like, it was found that the generation state was changed by changing the dimensions of the bearing chamber and the shape of the sliding surface of the radial bearing. That is, in the conventional bearing device, the gap (gap) at the communication hole 22 between the bearing chambers is 1/10 of the diameter of the rotating shaft 8. However, the bearing device is constituted by the rotating shaft 8 and the bearing support 4. It has been found that as the gap a is reduced, the generation of bubbles and cavities tends to be small. Specifically, the ratio between the gap a and the diameter of the rotating shaft 8 is 1/20.
In the following, it was confirmed that the generation of cavities was hardly observed. As described above, by setting the gap a of the communication hole 22 between the bearing chambers to 1/20 or less of the diameter of the rotating shaft 8, generation of bubbles and cavities is suppressed, and fluctuations in the rotation speed of the rotating body 3 can be suppressed. .

The lower end surface of the radial bearing 19 and the lid 35
It has been found that changing the gap c between the above and the above causes a change in the generation of bubbles or cavities. If the gap c is wide,
Many bubbles were generated, and cavities were found at the lower end of the rotating shaft 18. This is because if the gap c is wide, the pressure at the lower end of the rotating shaft 18 decreases, causing a secondary flow in the magnetic fluid, and the fine bubbles contained in the magnetic fluid gather at the center. As the bubbles grow, they become cavities as they grow, and when they reach a certain size, they are blown to the outer peripheral side to be finer. At this time, some of the micronized bubbles are
9 enters the sliding surface, causing a change in the number of revolutions. Specifically, the above-described state is maintained until the gap c has a large gap of about 1 mm. However, when the dimension of c is about 0.5 mm, the above-mentioned secondary flow is alleviated and bubbles and cavities are generated. And the fluctuation of the number of revolutions is reduced.

Next, the flow of the magnetic fluid around the radial bearings 18 and 19 circulates in the direction of the arrow as shown in FIG. That is, the magnetic fluid ascends from the passage 31 on the outer peripheral side of the radial bearings 18 and 19 to form a circulating flow that damps the oil groove 30 and the sliding gap between the bearings and descends. Here, in the radial bearing 19, by setting the gap b at the upper end face of the bearing to about 1 mm and the relationship with the gap c at the lower end face to c ≦ b, the inflow of bubbles into the bearing sliding gap is reduced. I understood.

On the other hand, in the radial bearing 18, the same result can be obtained by providing the rectifying plate 32. That is, the gap d between the upper end face of the bearing and the gap b between the lower end face of the bearing
By setting d to b, the bubbles flowing into the bearing sliding gap are reduced, and the fluctuation of the rotation speed can be reduced. In particular, in the radial bearing 18, if there is no rectifying plate 32,
Due to the rotation of the rotary shaft 8, the oil surface at the upper end surface of the bearing is forcedly disturbed, and air is entrained in the spiral and becomes a magnetic fluid containing a lot of air bubbles and flows into the bearing sliding gap. In this state, since the viscosity of the sliding surface does not become uniform, the fluctuation of the rotation speed becomes large. When the current plate 32 is provided,
Since the above-mentioned forced vortex is suppressed, the entrainment of air into the magnetic fluid is remarkably reduced, the flow of bubbles into the sliding gap is reduced, and the fluctuation of the rotation speed can be suppressed. Also,
The communication hole 33 provided on the outer periphery of the current plate 32 is arranged at the same position as the communication hole 31 of the bearing portion, and allows bubbles contained in the circulating flow rising from the communication hole 31 to escape to the space 34 above the current plate 32. Therefore, the communication hole has an effect of reducing air bubbles from being mixed into the magnetic fluid.

As described above, the radial bearings 18, 19 use porous sintered oil-impregnated bearings, and these bearings are impregnated with a magnetic fluid. Since the porous sintered oil-impregnated bearing cannot be impregnated with the magnetic fluid in a completely bubble-free state, the sintered oil-impregnated bearing contains small but fine bubbles together with the magnetic fluid. When the rotating shaft 8 rotates at a high speed in this state, when the oil film pressure generated in the bearing sliding gap is negative as described above, the oil is impregnated on the sliding surface because the bearing is a porous sintered oil-impregnated bearing. Magnetic fluid and fine bubbles are drawn out. At this time, since the fine bubbles expand due to the negative pressure, the bubbles are mixed in the oil film, and the viscosity of the magnetic fluid changes. That is, as shown in FIG. 5, a symmetrical triangular arc in which the shape of the bearing surface is formed between the oil groove 30 and the oil groove 30 so that the clearance becomes narrower and wider in the direction of rotation of the rotary shaft 8. The negative pressure indicated by the dotted line at the divergent portion causes the generation and expansion of bubbles from the bearing described above. In order to prevent this, the oil film pressure on the bearing sliding surface must always be a positive pressure. That is, if the shape of the clearance formed by the rotating shaft and the bearing sliding surface is made to be the shape of the end, a positive oil film pressure can always be generated. In the present invention, the object is achieved by an asymmetric three-arc bearing shown in FIG. 4 as a specific example. In the asymmetric three-arc bearing shown in FIG. 4, the shape of the gap formed between the rotating shaft and the bearing sliding surface is formed so as to be narrow toward the rotating direction of the rotating shaft 8. A positive oil film pressure indicated by a dotted line in the figure is generated. For this reason, no negative oil film pressure is generated in the sliding gap, so that fine bubbles contained in the bearing do not appear in the bearing sliding gap, so that a stable oil film is formed and the rotation speed fluctuates. It has no effect. FIG. 6 shows another embodiment in which the oil film pressure in the bearing sliding gap is always set to a positive pressure. The oil film pressure distribution becomes a positive oil film pressure distribution shown by a dotted line in the figure. The same operation and effect as those of the asymmetric three-arc bearing described above can be obtained. In the bearings of FIGS. 4 and 6 proposed in the present invention, a positive oil film pressure is generated, so that the rigidity of the oil film supporting the rotating shaft 8 is larger than that of the bearing of FIG. Therefore, when the bearing device of the present invention is used for a polygon mirror motor that requires high-speed and high-precision rotation, the effect of suppressing the vibration of the rotating shaft is large, and the effect of suppressing the rotation fluctuation can exhibit more precise rotation performance.

The above-mentioned generation of bubbles and cavities and foaming from the bearing sliding surface can effectively suppress the fluctuation of the motor speed by optimizing the dimensions of the bearing chamber and optimizing the shape of the bearing sliding surface. Was clearly confirmed by the experiment.

The characteristic effects of the above embodiment are as follows. (1) The generation of bubbles and cavities could be suppressed by setting the ratio of the gap a formed between the bearing support between the radial bearings and the rotary shaft to the shaft diameter D to be 1/20 or less. (2) In an external radial bearing, a ring-shaped rectifying plate is disposed between the radial bearing and the dynamic pressure seal, and the gap between both end faces of the bearing is set to d ≦ b. And the fluctuation of the rotation speed can be reduced. (3) In the lower radial bearing, by setting the relationship between the gaps at both end surfaces of the bearing to d ≦ b, bubbles flowing into the bearing sliding surface can be reduced, and the fluctuation of the rotation speed can be reduced. (4) In the bearing device of the present invention using the porous sintered oil-impregnated bearing, the oil film pressure generated on the sliding surface of the bearing is formed in such a shape that a positive oil film pressure is always generated. Since the fine air bubbles do not appear on the sliding surface, the viscous friction is stabilized, and a bearing having high bearing rigidity can be provided, so that the rotation accuracy can be improved.

Although the above embodiment has been described using two radial bearings, the present invention can be applied to one or three or more radial bearings.

[0042]

As described above, the present invention provides a rotating shaft,
A porous sintered oil-impregnated radial bearing that rotatably supports the rotating shaft, a bearing supporting portion in which a bearing chamber that holds the radial bearing is formed, and a sliding gap between the rotating shaft and the radial bearing And a space provided at an end of the radial bearing in the axial direction of the rotating shaft, wherein the dynamic pressure of a sliding gap is maintained at a positive pressure and the space is provided. A rectifying plate is disposed at a distance from the end of the radial bearing.

According to such a configuration, since no negative oil film pressure is generated in the sliding gap, fine bubbles contained in the radial bearing do not appear in the sliding gap of the radial bearing. Since a stable oil film is formed, the rotation speed does not fluctuate.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a polygon mirror motor according to one embodiment of the present invention.

FIG. 2 is an enlarged longitudinal sectional view of the motor bearing device shown in FIG. 1 in an enlarged manner.

FIG. 3 is a sectional view showing the shape of a conventional radial bearing.

FIG. 4 is a transverse sectional view of a radial bearing used in the bearing device shown in FIG. 2;

FIG. 5 is a sectional view showing the shape of a conventional radial bearing.

FIG. 6 is a cross-sectional view of a radial bearing according to another embodiment of the present invention.

[Explanation of symbols]

 4 ... bearing support, 8 ... rotary shaft, 18 ... radial bearing.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Go Nakajima 1-1-1, Higashitaga-cho, Hitachi City, Ibaraki Prefecture Within the Living Equipment Business Division, Hitachi, Ltd. No. 1 Hitachi, Ltd. Living Equipment Division (56) References JP-A-5-215128 (JP, A) JP-A-6-86503 (JP, A) JP-A-61-38217 (JP, A) ) JIN 39-407 (JP, Y1) JIN 47-42742 (JP, Y1) (58) Fields surveyed (Int. Cl. ⁷ , DB name) F16C 17/00-17/26 F16C 33 / 00-33/28 H02K 5/00-7/20 G02B 26/10 102

Claims (3)

(57) [Claims] 1. A rotary shaft, a porous sintered oil-impregnated radial bearing for rotatably supporting the rotary shaft, a bearing support portion having a bearing chamber for holding the radial bearing, and the rotary shaft. A lubricating oil applied so as to fill a sliding gap between the bearing and the radial bearing, and a space provided at an end of the radial bearing in an axial direction of the rotating shaft. A bearing device, wherein a pressure plate is maintained at a positive pressure and a rectifying plate is disposed in the space at a distance from the end of the radial bearing. 2. A rotary shaft, a porous sintered oil-impregnated radial bearing for rotatably supporting the rotary shaft, a bearing support having a bearing chamber for holding the radial bearing, and the rotary shaft. And lubricating oil of a magnetic fluid applied so as to fill a sliding gap between the radial bearing and the radial bearing, which is provided through a space from an end of the radial bearing in an axial direction of the rotating shaft, A bearing device having a magnetic fluid seal surrounding an outer periphery, wherein a dynamic pressure in a sliding gap is maintained at a positive pressure, and a rectifying plate is disposed in the space at a distance from the end of the radial bearing. apparatus. 3. The bearing device according to claim 2, wherein a dynamic pressure seal surrounding the outer periphery of the rotary shaft is provided along with the magnetic fluid seal.