JP4758076B2 - Fluid bearing motor and rotary polygon mirror - Google Patents

Description

  The present invention relates to a hydrodynamic bearing motor and a rotary polygon mirror.

  A rotating polygonal mirror generally used to deflect a light beam at high speed in an optical scanning device used in a digital copying machine, a laser printer, etc. has a high rotational speed of the polygon mirror and more than several thousand hours. Therefore, driving by a motor using a normal rolling bearing is difficult, and driving by a fluid bearing motor is generally performed.

The hydrodynamic bearing motor has a problem that “rotation of the rotor” is likely to occur when the rotor is rotated at a high speed as conventionally known.
That is, in order to make the drive energy as small as possible and increase the rotational speed of the rotor, it is necessary to reduce the rotational efficiency of the rotor. For this reason, the rotor is made as light as possible.
When the rotor is rotated at high speed in the sealed space, the air in contact with the rotor also rotates with the rotor, so that the air flows to the outer peripheral portion of the rotor due to the centrifugal force acting on the air, and the air pressure on the outer peripheral portion side of the rotor increases. A negative pressure is formed on the upper part of the shaft. When the rotor is light, the rotor floats due to the negative pressure.

In the rotary polygon mirror, the outer peripheral surface of the rotor is formed as a deflecting reflecting surface. However, when the rotor floats, the light spot caused by the light beam deflected at high speed tends to fluctuate in the sub-scanning direction. Adverse effects such as lowering.
As the “technology for suppressing the flying of the rotor” in the hydrodynamic bearing motor, those described in Patent Documents 1 and 2 are conventionally known.

  In the hydrodynamic bearing motor described in Patent Document 1, a groove-like fluid passage is formed in the housing, and air on the outer periphery of the rotor is caused to flow into a portion in the vicinity of the shaft through the fluid passage so that the air pressure in the housing is not uniform. To prevent the rotor from rising. Further, in the fluid dynamic bearing motor described in Patent Document 2, an air flow control means is provided on the cover member, and the air flow inside the sealed space is controlled to suppress the floating of the rotor.

  However, recently, the rotational polygon mirror is required to have a high rotational speed exceeding 30000 rpm. When such a high-speed rotation is performed, the presence of the groove-like fluid passage and the air flow control means is “wind noise. ”Is considered to be easily generated. That is, the floating of the rotor is suppressed by the effect of the fluid passage and the air flow suppressing means, but the rotor rotates at a high speed so that the “top portion between adjacent deflecting reflecting surfaces” is the groove of the fluid passage and the protrusion of the air flow control means. Wind noise is likely to be generated each time the signal passes through, and it is considered that noise of “high frequency component at an integral multiple of the rotation frequency” greater than the rotation frequency (rotation period) is generated. In this case, it is considered that “mainly overall noise of 10 kHz or less” is likely to increase together with high-frequency noise.

No. 7-42214 Japanese Utility Model Publication No. 5-81818

  An object of the present invention is to realize a novel hydrodynamic bearing motor capable of effectively suppressing the flying of the rotor with a simple configuration and also effectively reducing noise caused by wind noise, and a rotary polygon mirror using the same.

The hydrodynamic bearing motor of the present invention is a “hydrodynamic bearing motor that rotates a rotor in a sealed space” and has the following characteristics (claim 1).
That is, the “rotor” has a shaft and a flange integrally fixed to the shaft.
Further, “a flat plate member having a circular shape close to the upper surface of the flange, or a polygonal shape close to a circle, and having a through hole in the center” is provided. The “size substantially equal to the upper surface of the flange” is a range of the size of “about ± 15% of the radius” when the radius of the flange is 100.
The “flat plate member” is fixedly provided in the sealed space in a state where the shaft of the rotor is loosely fitted in the through hole and is close to the “surface portion facing the upper surface of the flange in the sealed space” via a gap.

When the rotor rotates, the fluid dynamic bearing motor passes through the through hole of the flat plate member from the upper portion of the shaft and goes between the flange upper surface and the flat plate member toward the flange outer peripheral side. An airflow that flows back to the space above the shaft through the surface portion (the surface portion facing the upper surface of the flange in the sealed space) (the gap) is formed.
Note that the “sealed gas” in the sealed space that seals the rotor may be air or “other gas” such as nitrogen, helium, or argon.

  The shape of the flat plate member is “circular or a polygonal shape close to a circle”, but the polygonal shape close to a circle is, for example, “a regular N-gonal shape such that N ≧ 7”. The shape of the through hole formed in the central portion of the flat plate member is most preferably a “circular shape”, but a “regular N-square shape such that N ≧ 7” is also acceptable.

  In addition, the gap between the flat plate member and the “inner space inner wall portion close to and facing this member” is preferably about 0.3 mm to 3 mm. The gap between the flat plate member and the “flange surface in close proximity to this” is also preferably about 0.3 mm to 3 mm. Even if the size of these gaps is larger or smaller than the above range, the above-mentioned “refluxing airflow” cannot be formed effectively. Further, when the gap exceeds the above range, the height of the space for sealing the rotor increases, and the hydrodynamic bearing motor itself tends to increase in size.

The hydrodynamic bearing motor according to claim 1, wherein the rotor has a "shaft, a flange, and a magnet integrated with the shaft or the flange", and a sealed space for enclosing the rotor is formed by the stator and the case. (Claim 2).
The “stator” includes a drive coil that applies a drive magnetic field to the magnet of the rotor, a bearing member that supports the shaft, a base substrate that holds the shaft and the bearing member, and a housing on which these are mounted.
The “case” forms a “sealed space for housing the rotor” in cooperation with the stator.

The hydrodynamic bearing motor according to claim 1 or 2 may be “a configuration in which the shaft of the rotor is pivotally supported by a sintered oil-impregnated bearing in the bearing member” (claim 3).
The hydrodynamic bearing motor according to any one of claims 1 to 3, wherein the rotor shaft is martensitic stainless steel and the flange is made of an aluminum alloy, and the shaft is fixed to the flange by shrink fitting or press fitting. (Claim 4).

  Of course, the “rotor shaft bearing” in the hydrodynamic bearing motor according to claim 1 is not limited to the above-described sintered oil-impregnated bearing, but a known appropriate fluid bearing system such as an air dynamic pressure bearing, a magnetic bearing, or a fluid oil bearing. Can be.

  The rotary polygon mirror of the present invention is a rotary polygon mirror using the fluid dynamic bearing motor according to any one of claims 1 to 4, wherein "the outer peripheral surface of the flange is formed on a plurality of deflecting reflecting surfaces, A window for entering and exiting the beam is formed in a sealed space, and the window is closed with a glass plate ”(Claim 5). According to a fifth aspect of the present invention, the space for sealing the rotor can be formed by the stator and the case according to the second aspect (Claim 6). The "window for" can be formed in the case (claim 7). The rotary polygon mirror according to claim 6 or 7 may be configured as “unitized with a stator, a case, and a rotor” (claim 8).

  Of course, it goes without saying that the hydrodynamic bearing motor of the present invention can be implemented not only as “used as a rotating polygon mirror” but also as a “hydrodynamic bearing motor that rotates a rotor in a sealed space” in general.

As described above, the fluid dynamic bearing motor of the present invention uses a flat plate member, so that when the rotor rotates, it passes through the circular through hole of the flat plate member from the top of the shaft, and the flange outer peripheral side is between the flange upper surface and the flat plate member. The airflow flowing back to the space above the shaft through the gap formed by the surfaces formed between the flat plate member and the surface portion (the surface portion facing the flange upper surface in the sealed space) from the flange outer peripheral side (Air flow of gas such as air enclosed in a sealed space) "is formed, so that the negative pressure in the vicinity of the upper part of the shaft is effectively eliminated, and the floating of the rotor is effectively suppressed. Further, since the flat plate member has no “grooves or projections causing wind noise” on the rotor side, generation of wind noise can be effectively reduced.
Therefore, the rotating polygon mirror of the present invention can realize a quiet light beam deflection with little wind noise without deterioration of jitter and vibration characteristics associated with the floating of the polygon mirror.

Hereinafter, embodiments will be described.
FIG. 1 is a view for explaining one embodiment in which the hydrodynamic bearing motor of the present invention is implemented as a rotary polygon mirror. The figure is a “center sectional view of a rotating polygon mirror”.
The rotary polygon mirror 21 includes a rotor 22, a stator 23, and a case 24, and the fluid bearing motor is an “outer rotor type brushless motor that is in a secret state with respect to the outside air”.

  The stator 23 has a configuration in which a motor substrate 5 as a base substrate is fixed to a motor housing 7 made of, for example, aluminum with a motor substrate fixing screw 6 and a bearing member 8 is fixed to the motor substrate 5 by caulking. The upper portion of the bearing member 8 is formed in a hollow cylindrical shape, and a thrust plate 8b is disposed at the bottom thereof to support the lower end portion of the shaft 11 of the rotor 22.

  The shaft 11 is pivotally supported by a sintered oil-impregnated bearing 8 a provided inside the hollow cylindrical portion of the bearing member 8. A seal washer 8c is fixed to the upper end of the hollow cylindrical portion of the bearing member 8 so as to “prevent scattering of lubricating oil”. A stator core 9 around which a drive coil 10 is wound is bonded and fixed to the outer peripheral portion of the hollow cylindrical portion of the bearing member 8.

  In addition, it can replace with the axial support by the sintered oil-impregnated bearing 8a, and can also use the bearing system by an air dynamic pressure bearing, a magnetic bearing, a fluid oil bearing, etc.

  The rotor 22 has a configuration in which the flange 12 is fixed to the shaft 11, and a magnet 13 magnetized in multiple poles is bonded and fixed to an inner peripheral portion 12 b of a cylindrical space formed in the lower portion of the flange 12. The shaft 11 serving as the rotation axis of the rotor 22 is made of “martensitic stainless steel”. The flange 12 is “made of aluminum alloy” and is “shrink-fitted” or “press-fitted” to the upper portion of the shaft 11 and fixed to the shaft 11.

  “Martensitic stainless steel (for example, SUS420J2)” is suitable as a material for the shaft 11 requiring wear resistance because it can be quenched and the surface hardness can be increased. The shaft 11 is fitted in a cylinder of a sintered oil-impregnated bearing 8a made of a sintered material and is supported in the radial direction. In order to obtain “suitable bearing rigidity” as well as “circulate the impregnated oil efficiently”. The bearing gap is set to 15 μm or less in diameter (7.5 μm or less in radius), and a “dynamic pressure generating groove (not shown)” is provided.

  As the “dynamic pressure generating groove”, a known “appropriate form” can be provided on the outer peripheral surface of the shaft 11 or the cylindrical inner peripheral surface of the oil-impregnated bearing 8a. Is more preferred. A lower end portion 11a (in the drawing) of the shaft 11 is processed into a spherical surface, and comes into contact with a thrust plate 8b formed of a wear-resistant resin, thereby functioning as a “pivot bearing”.

The flange 12 is a “polygon mirror”, and “seven surfaces” of the deflecting reflection surface 12 a are formed on the outer periphery thereof. Together with the motor, the rotor 22 is sealed in a sealed space by the case 24 and the stator 23 and is blocked from the outside air.
A portion of the case 24 facing the upper surface of the flange 12 (a ceiling portion of the case 24) is formed with a “recess 40 for escaping the upper portion of the shaft 11 and the upper portion of the flange 12” in a circular shape.

  The flat plate member 2 is a “flat plate made of a metal such as stainless steel or an aluminum alloy” and has a circular shape, and a “circular through hole 2A” is formed in the center thereof. The drilled circular through hole 2 </ b> A is substantially equal to the dimension (diameter) of the circular recess 40 formed in the ceiling portion of the case 24.

  The outer diameter of the flat plate member 2 is approximately the same as the “circumferential circle of the seven deflecting reflection surfaces” formed on the flange 12 and has a thickness of about 1 to 2 mm.

  As shown in the figure, the flat plate member 2 has the shaft 11 (and the convex portion at the top of the flange 12) loosely fitted in the circular through hole 2A, and the surface portion facing the upper surface of the flange in the case 24 (the above-mentioned "ceiling portion of the case 24"). ) In the state of being close to each other through the gap 15, and “screwed” with fixing screws at three locations on the ceiling portion, and fixed in the sealed space. Reference numeral 3A indicates "one of the three fixing screws". A portion indicated by reference numeral 30 is “a convex portion that is formed with a screw through hole for screwing into another fixing screw and protrudes from the ceiling portion”.

The flat plate member 2 has only to be “fixed firmly in the sealed space (not to be vibrated by the airflow generated in the sealed space)” and fixed by bonding, caulking, welding, etc. in addition to screwing with the fixing screw. May be.
The side wall of the case 24 is provided with a window 25 for entering and exiting the deflected light beam (accepting the light beam from the light source side and emitting the deflected light beam). Bonded and fixed.

  As a method for fixing the magnet 13 to the inner peripheral surface 12b of the cylindrical recess at the lower part of the flange 12, there is “adhesion or press-fitting”, but in order to suppress the balance change due to centrifugal force or temperature change at high speed rotation, “Fixed” is preferred.

  The inner surface 13A of the magnet 13 is opposed to the outer peripheral surface of the stator core 9 with an appropriate gap, and the energization to the drive coil 10 wound around each magnetic pole of the stator core 9 is switched by a control circuit (not shown). Thus, the rotor 22 is rotationally driven.

  When the rotor 22 is driven and rotated at high speed in this way, a light beam (laser beam) from the light source side enters the sealed space from the window 25 and is reflected and deflected by the deflecting / reflecting surface 12a on the outer peripheral portion of the flange 12. While exiting from the window 25.

FIG. 2 shows the relationship between the flat plate member 2 and the rotor 22 (the flange 12 and the shaft 11 are shown) in the rotary polygon mirror shown in FIG. 1 as viewed from the rotor rotation axis direction.
When the flange 12 rotates at a high speed, the gas in the gap 16 (gap size: 1 to 2 mm) between the upper surface of the flange 12 and the flat plate member 2 moves toward the outer periphery of the flange 12 by centrifugal force as shown in FIG. The vicinity of the deflecting reflecting surface 12a becomes “positive pressure”. Further, the upper portion of the rotor 22 (the upper portion of the shaft 11) becomes a negative pressure. Due to this pressure relationship, an air flow 26 is generated in the sealed space.

  That is, this air flow 26 passes through the through hole 2A in the central portion of the flat plate member 2 from the upper portion (the concave portion 40) of the shaft 11, passes through the gap 16 between the upper surface of the flange 12 and the flat plate member 2, and moves toward the flange outer peripheral side. Then, it returns to the space 40 above the shaft 11 through the gap 15 between the flat plate member 2 and the ceiling portion of the case 24 (size of the gap of this portion: 1 to 2 mm) from the flange outer peripheral side. The reflux of the airflow works to eliminate the “pressure bias in the sealed space”. It has been confirmed that this action can actually prevent “floating of the rotor 22” and realize “stable rotation” of the rotor 22.

  In the flat plate member 2, the number of fixed portions and the number of fixed portions (three in the above example) are appropriately adjusted according to the number of deflection reflection surfaces formed on the flange (seven in the above example), the driving rotational speed, and the like. It is desirable.

  It is confirmed that both the “overall noise” of 10 kHz or less and the high frequency noise (in the case of this embodiment, a 7-sided mirror is a harmonic of 7 times the rotational component) are sufficiently small. It was done.

Specific examples of the embodiment shown in FIGS. 1 and 2 are given below.
As described above, the flange 12 of the rotor 22 is made of an aluminum alloy having seven deflection reflection surfaces, and is shrink-fitted and fixed to a cylindrical shaft 11 having a diameter of 3 mm made of “martensitic stainless steel”. The weight of the rotor 22 is 19 g.
A “dynamic pressure generating groove” was formed on the inner peripheral surface of the sintered oil-impregnated bearing 8 a that supports the shaft 11, and the bearing clearance was set to “10 μm in diameter”.

  The flange 12 as a polygon mirror has an inscribed circle radius of 43 mm of the seven deflecting / reflecting surfaces 12a formed on the outer periphery thereof. The case 24 is made of aluminum and has a thickness of 3 to 5 mm. The sealed space formed by the case 24 and the stator 23 has a cylindrical shape, and has a diameter: 60 mm and a height: 30 mm. The circular recess 40 formed in the ceiling portion of the case 24 facing the upper surface of the flange 12 has a diameter of 16 mm and a depth of 3 mm.

  The flat plate member 2 is formed in a circular shape by an aluminum plate having a thickness of 1 mm, the diameter is 44 mm (slightly larger than the inscribed circle radius of the flange 12), and the circular through hole 2A drilled in the center portion has a diameter. : 16 mm (the same size as the “diameter of the concave portion 40 on the ceiling” of the case 24).

  The gap 15 between the flat plate member 2 and the ceiling portion of the case 24 is 1 mm, and the gap 16 between the upper surface of the flange 12 and the flat plate member 2 is 2 mm. Moreover, the thickness of the glass plate 4 provided in the window 25 drilled in the side wall portion of the case 24 is 2 mm. Moreover, the diameter of the columnar convex part (part loosely fitted in the through hole 2A) formed on the upper part of the flange is 12 mm, and the gap between this part and the inner periphery of the through hole 2A is 2 mm in radius.

  In such an example apparatus, the number of rotations of the rotor 22 was changed in the range of 15000 rpm to 55000 rpm, and the “floating amount of the rotor (mm)” was examined. The result was as shown in FIG. As shown in FIG. 3, by providing the flat plate member 2, it was possible to substantially prevent the rotor 22 from floating in the range of the rotation speed: 15000 rpm to 55000 rpm. For comparison, the flying height when the flat plate member was not provided was examined. As shown in FIG. 3, when the rotational speed exceeded 35,000 rotations, a remarkable floating phenomenon occurred.

  When the “acoustic sensor” is installed at a position 500 mm away from the case 24 with respect to the above-mentioned embodiment device, the overall noise of 10 kHz or less and the 7th harmonic (5362.5 Hz) noise are examined. "Was 39.4 dB, and" 7th harmonic noise "was 25.6 dB.

  In the case of the “rotating polygon mirror excluding the flat plate member 2” as the comparative example, the “overall noise” was 41.4 dB and the “seventh harmonic noise” was 26.7 dB. From this, it can be seen that the use of the flat plate member also has an effect of reducing noise.

That is, the rotary polygon mirror according to the embodiment and examples described above is a fluid bearing motor that rotates a rotor in a sealed space, and the rotor 22 is integrally fixed to the shaft 11 and the shaft. A flat plate member 2 having a flange 12 and having a circular shape approximately the same as the upper surface of the flange and having a circular through hole 2A in the center is loosely fitted to the shaft 11 in the through hole 2A so as to face the upper surface of the flange in the sealed space. It is fixed in the sealed space in a state of being close to the surface portion to be interposed via the gap 15, and when the rotor 22 rotates, the gap between the upper surface of the flange and the flat plate member 2 passes through the through hole 2 </ b> A from the upper part of the shaft. 16 after toward the flange outer peripheral portion is configured to airflow reflux into the space 40 of the shaft upper flange outer periphery side through between gap 15 and the flat plate member 2 and the surface portion is formed A fluid dynamic bearing motor (claim 1).

  The rotor 22 includes the shaft 11, the flange 12, and the magnet 13 integrated with the flange 12, and a sealed space that encloses the rotor 22 is formed by the stator 23 and the case 24. 22 includes a drive coil 10 that applies a drive magnetic field to the magnet 13, a bearing member 8 that supports the shaft 11, a base substrate 5 that holds the shaft and the bearing member, and a housing 7 on which these are mounted. A closed space for accommodating the rotor 22 is formed in cooperation with the stator 23 (Claim 2), and the shaft 11 of the rotor 22 is pivotally supported by a sintered oil-impregnated bearing 8a in the bearing member 8 (Claim). 3) The shaft 11 of the rotor 22 is martensitic stainless steel, the flange 12 is made of an aluminum alloy, Nji is fixed by shrink fitting or press fitting to the plate-like member of the shaft (claim 4).

  Further, the outer peripheral surface of the flange 12 is formed on a plurality of deflecting and reflecting surfaces 12a, a window 25 for entering and exiting a light beam is formed in a sealed space, and the window 25 is closed by a glass plate 4 (claim). 5) A space for sealing the rotor 22 is formed by the stator 23 and the case 24 according to claim 2 (claim 6), and a window 25 for entering and exiting the light beam is formed in the case 24. Rotating polygon mirror (Claim 7) ". The rotary polygon mirror is unitized by a stator 23, a case 24, and a rotor 22 (claim 8).

  In addition, the motor housing 7 of the stator 23 in the embodiment shown in FIG. 1 can be a housing itself that houses the rotary polygon mirror and the optical system in the optical scanning device.

  To add a little, as described above, the size of the flat plate member is “range of radius of about ± 15% of the radius of the flange as 100”, but it is small even if the size of the flat plate member is larger than this. However, “the effect of eliminating the pressure deviation formed in the sealed space (which causes the rotor to float”) cannot be obtained.

  The shape of the flat plate member may be a “polygonal shape close to a circle”. However, when the hydrodynamic bearing motor is used as a rotary polygon mirror, the top of the adjacent portion of the deflection reflecting surface formed on the flange and the polygonal flat plate Since wind noise is likely to occur when the tops of the members pass each other, when the flat plate member has a polygonal shape, the value of N is preferably larger than the number of deflecting reflecting surfaces from the viewpoint of noise reduction.

  Further, in the “surface portion facing the upper surface of the flange in the sealed space (the above-described case ceiling portion)”, for example, a groove formed in the case ceiling portion of the hydrodynamic bearing motor of Patent Document 1 may be formed.

It is a figure for demonstrating the rotary polygonal mirror which is one Embodiment. It is a figure for demonstrating the rotor and flat plate member in the rotary polygon mirror of FIG. It is a figure for demonstrating the floating prevention effect of the rotor in the rotary polygon mirror of an Example.

Explanation of symbols

2 Flat plate member 2A Through-hole 11 Shaft 12 Flange 22 Rotor 26 Recirculating airflow

Claims (8)

In a hydrodynamic bearing motor that rotates a rotor in a sealed space,
The rotor has a shaft and a flange integrally fixed to the shaft,
A flat plate member having a circular shape close to the upper surface of the flange or a polygonal shape close to a circle and having a circular through hole at the center is loosely fitted into the through hole, and the flange in the sealed space is formed. in a state of being close through the gap on opposite sides portion on the upper surface, provided with fixed to the sealed space,
During rotation of the rotor, after passing through the through-hole from the upper part of the shaft and between the flange upper surface and the flat plate member toward the flange outer peripheral side, between the flat plate member and the surface portion from the flange outer peripheral side. A fluid characterized in that an airflow is formed that flows back to the space above the shaft through the gap, and the size of the flat plate portion is a radius of ± 15% of the radius of the flange. Bearing motor. The hydrodynamic bearing motor according to claim 1,
The rotor has a shaft, a flange, and a magnet integrated with the shaft or the flange,
A sealed space for enclosing the rotor is formed by the stator and the case,
The stator has a drive coil that applies a drive magnetic field to the magnet of the rotor, a bearing member that supports the shaft, a base substrate that holds the shaft and the bearing member, and a housing on which these are mounted,
The hydrodynamic bearing motor according to claim 1, wherein the case forms a sealed space for housing the rotor in cooperation with the stator. The hydrodynamic bearing motor according to claim 1 or 2,
A hydrodynamic bearing motor in which a shaft of a rotor is pivotally supported by a sintered oil-impregnated bearing in a bearing member. The hydrodynamic bearing motor according to any one of claims 1 to 3,
A hydrodynamic bearing motor characterized in that the shaft of the rotor is martensitic stainless steel, the flange is made of an aluminum alloy, and the shaft is fixed to the flange by shrink fitting or press fitting. A rotary polygon mirror using the hydrodynamic bearing motor according to any one of claims 1 to 4,
The outer peripheral surface of the flange is formed on a plurality of deflection reflection surfaces,
A rotating polygon mirror, wherein a window for entering and exiting a light beam is formed in a sealed space, and the window is closed with a glass plate. The rotary polygon mirror according to claim 5,
A rotary polygon mirror characterized in that a space for sealing the rotor is formed by the stator and the case according to claim 2. The rotary polygon mirror according to claim 6.
A rotating polygon mirror characterized in that a window for entering and exiting the light beam is formed in the case. The rotary polygon mirror according to claim 6 or 7,
A rotating polygon mirror characterized by being unitized by a stator, a case, and a rotor.

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