JP4928194B2 - Drive motor and rotary polygon mirror drive device including the same - Google Patents

Description

The present invention relates to a drive motor , for example, a deflection mirror drive motor used for a printer, a copier, a FAX, or the like using an electrophotographic image forming process.

  As a conventional oil dynamic pressure bearing device, as shown in FIGS. 7 and 8, two bearing surfaces A and B are provided on the inner peripheral surface of the sleeve to which the shaft is fitted with a space in the axial direction. Herringbone-like grooves for generating dynamic pressure are provided at two bearing surfaces, and the gap between the shaft and the sleeve is filled with lubricating oil.

  When the shaft rotates, a pressure is generated between the dynamic pressure generating groove and the shaft, and fluid dynamic pressure lubrication is performed. Recess portions (oil pool portions) C, D, and E having gaps larger than the gaps between the bearing surfaces are provided between the two bearing surfaces and in the vicinity of the sleeve opening.

In the above-mentioned oil dynamic pressure bearing device, the thrust direction of the shaft of the oil dynamic pressure bearing device is supported in the thrust direction by pivotally receiving the tip of the spherical convex portion provided at the lower portion of the shaft, even at high speed rotation. The shaft thrust support is realized with almost no loss. (For example, refer to Patent Documents 1 and 2.)
FIG. 1 shows a brushless motor to which such an oil dynamic pressure bearing device is applied.
JP-A-6-180433 JP 2001-59522 A

  However, in a conventional oil dynamic pressure bearing, the shaft and the sleeve are in mechanical contact, particularly when sufficient dynamic pressure is not generated between the shaft and the sleeve at the time of starting and stopping the rotation. For this reason, there is a problem that the shape is deteriorated due to the wear, and the sludge generated by the wear chemically reacts with the oil to alter the oil, impairing the formation of a stable dynamic pressure and reducing the life of the oil dynamic pressure bearing. . The wear of the shaft and the sleeve is caused by the deviation of the rotation center of the shaft and the tip of the spherical convex portion of the shaft, the shaft swings around the tip of the spherical convex portion, and the outer periphery of the shaft is the sleeve at the lower dynamic pressure generating portion of the bearing. It is generated by rubbing the inner surface strongly. This shaft runout is corrected by the dynamic pressure formed in the bearing dynamic pressure generating portion when the shaft rotation speed is increased, and contact between the shaft and the sleeve does not occur, but it always occurs repeatedly at the time of starting and stopping. . In recent years, there has been an increasing need to shorten the startup time of a brushless motor and shorten the output start time of a printer or the like using the brushless motor, and there is a tendency to increase the angular acceleration of the brushless motor at the start. For this reason, the friction between the shaft and the sleeve at the start tends to be strong.

  Therefore, in order to prevent the shaft from swinging, the relationship between the shift Δs between the rotation center of the shaft and the tip of the spherical convex portion of the shaft and the distance Δd between the rotation shaft and the sleeve is Δs <Δd. Thus, it is necessary to machine the rotating shaft.

  At this time, when finishing the position of the tip of the spherical portion of the shaft by plastic processing such as header processing, it is difficult to ensure Δs <Δd due to the accuracy of mold matching. In addition, since a shaft obtained by molding such as casting or injection molding is difficult to satisfy hardness, wear resistance, etc., it is not suitable for extending the life of a fluid dynamic pressure bearing.

  Accordingly, the present invention relates to the rotational shaft of the hydrodynamic bearing device, such as a decrease in wear resistance performance due to a decrease in the hardness of the rotational shaft caused by molding the distal end of the rotational shaft, and variations in processing accuracy caused by plastic processing. This is to prevent the friction with the bearing member due to the shaft touching when the rotation shaft starts to rotate.

In order to solve the above problems, a drive motor of the present invention includes a rotating shaft, a contact portion with which the rotating shaft contacts in a thrust direction of the rotating shaft, and a bearing that receives the rotating shaft in a radial direction of the rotating shaft. And a driving means for rotating the rotating shaft about the center of rotation in the thrust direction, the rotating shaft has a convex surface on the end surface in the thrust direction, and the tip of the convex surface is The bearing portion is rotated when the shaft including the tip portion is rotated about the rotation center by contacting the contact portion, and the center of the bearing portion and the center of the rotation shaft in the radial direction are aligned with each other. A gap with the rotation axis is larger than a positional difference between the center of the rotation axis and the rotation center in the radial direction.

With respect to the drive motor, it is possible to prevent wear resistance performance degradation due to a decrease in the hardness of the rotating shaft and variations in processing accuracy, and to suppress sliding with the bearing member due to the shaft touching at the start of rotation of the rotating shaft. .

(Example)
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a brushless motor to which an oil dynamic pressure bearing device according to an embodiment of the present invention is applied. 2 is a schematic cross-sectional view of a shaft and a sleeve showing the oil dynamic pressure bearing device, FIG. 3 is a schematic bottom cross-sectional view of the oil dynamic pressure bearing device, and FIGS. 7 and 8 are cross sections of the conventional oil dynamic pressure bearing device. It is a figure and its explanatory drawing.

  As shown in FIG. 1, the rotating shaft 2 is integrated with a yoke 5 to which a permanent magnet 6 is fixed and a mounting member 4 to constitute a rotor portion. A circuit board 8 to which a stator core 7 is fixed is integrated with a sleeve 1 made of a metal material such as brass to constitute a stator portion. A shaft 2 made of a metal material such as stainless steel and a sleeve 1 as a bearing member are fitted in a rotatable manner.

  The stator core 7 has a multi-pole pole shoe (portion around which a drive coil is wound), and a drive coil 9 is wound around each pole shoe. The energization is sequentially switched depending on the rotational position of the permanent magnet 6 magnetized in multiple poles, and a rotational force is generated between the permanent magnet 6 and the stator core 7.

  The stator core 7 around which the drive coil 9 is wound is fixed to the circuit board 8 together with circuit components constituting the drive circuit. Further, the circuit board 8 is integrated with the sleeve 1. After the rotor part and the stator part are formed, assembly as a motor is performed.

  First, after a predetermined amount of oil is injected into the inner surface of the sleeve 1 by an oil injection device, the rotary shaft 2 is inserted so as to be rotatably fitted to the inner diameter of the sleeve 1 to complete the motor.

  Next, an oil dynamic pressure bearing device applied to the brushless motor of FIG. 1 will be described with reference to FIG. As shown in FIG. 8, a cylindrical sleeve 1 having a through-hole as a bearing portion has two bearing surfaces (fitting portions) A and B spaced axially on the inner surface, and a bearing surface. Oil reservoirs C, D, and E having inner diameter steps larger than the inner diameter steps of A and B are provided.

  On the surfaces of the bearing surfaces A and B, a plurality of herringbone-like grooves each having a depth of several microns are machined, and when the shaft rotates, the pressure is maximum at the groove bending positions A-1 and B-1. Dynamic pressure is generated. Further, a disk 21 for closing the opening at the lower end of the sleeve 1 is fixed.

  Next, a thrust receiving portion (supporting portion) of the hydrodynamic bearing device as the bearing portion according to the present embodiment will be described. As shown in FIG. 8, the thrust receiving portion of the hydrodynamic bearing device is provided with a thrust plate 3 made of a material having excellent slidability such as nylon for receiving the shaft 2 on the upper surface of the disc 21. In this embodiment, the sleeve 1 and the thrust receiving portion constitute a bearing portion for bearing the rotary shaft of the hydrodynamic bearing device. As shown in FIG. 7, the spherical convex portion (convex surface) 2-1 provided at the lower end portion of the shaft 2 and the thrust plate 3 are always in point contact with each other in the vicinity of the extension of the center line of the sleeve 1. The upper surface of the thrust plate 3 and the spherical 2-1 part are immersed in the oil, and the point contact part is also lubricated.

  The processing of the spherical convex portion 2-1 of the shaft 2 is performed by removal processing such as cutting and grinding. Here, FIG. 4 is a schematic diagram of processing in the processing machine, and FIG. 5 is a schematic diagram of means for holding the shaft of the processing machine. 4 and 5, the shaft 12 before processing is equally held from three directions so that it is coaxial with the rotation center 11 of the chuck portion 15 that rotates in the arrow direction of FIG. 5 by the claw portion 14 of the chuck portion 15. To do. The tip of the shaft 2 is processed by rotating the shaft 2 together with the claw 14 and simultaneously feeding the shaft to the arrow P side, and simultaneously moving the cutting tool 13 in and out in the direction of the arrow Q. Realize machining. Here, with respect to the shaft 2, the spherical tip portion is processed by holding the region that fits the sleeve of the fluid dynamic pressure bearing after processing, thereby reducing the positional deviation of the spherical tip portion. Furthermore, if the range facing the bearing surfaces A and B in FIG. 8 where dynamic pressure is generated is maintained under pressure, the accuracy of the positional deviation of the spherical tip portion described later can be improved. Further, in order to avoid a problem in which fine scratches are generated in the range facing the bearing surfaces A and B by the holding, it is effective to press and hold the vicinity of the range facing the bearings A and B. As a processing apparatus for positioning and holding the shaft 12 and performing the above-described processing, for example, an NC (Numerical Control) lathe processing apparatus or the like is preferable.

  Next, the configuration of the spherical portion tip 2-2 of the shaft 2 will be described with reference to FIGS. The center of the shaft 2 at the positions A-2 and B-2 as the dynamic pressure generating portions facing the bending positions A-1 and B-1 of the herringbone groove which is a bearing surface for bearing the shaft 2 is connected. Let Δs be the amount of deviation of the spherical portion tip 2-2 from the center line 2-3. Further, the minimum gap of the distance between the shaft 2 and the sleeve 2 in the dynamic pressure generating portion is represented by Δd. That is, Δd is the minimum distance between the outer surface of the shaft 2 and the inner surface of the sleeve 1 in the dynamic pressure generating portion (fitting portion) when the center line of the shaft 2 and the center line of the sleeve 1 are provided coaxially. (Δd is also a dynamic pressure generating portion (fitting portion) when the center line of the shaft 2 and the center line of the sleeve 1 are provided coaxially in the case where the sleeve 1 or the shaft 2 has a groove. The minimum value of the surface of the sleeve 1 and the surface of the shaft 2 at this time.) At this time, the center line 2 of the shaft 2 is set so that the oil dynamic pressure bearing device of this embodiment satisfies the relational expression Δs <Δd. The amount of deviation of the tip 2-2 of the spherical portion 2-1 with respect to -3 is set.

  As a result, the shaft 2 and the sleeve 1 are slid strongly even if the shaft 2 swings due to the deviation of the tip 2-2 of the spherical portion with respect to the center of the shaft 2 when the brushless motor 10 of FIG. 1 is started and stopped. There is almost no rubbing. That is, as shown in FIG. 3, a gap Δg is almost ensured between the outer periphery 2-4 of the shaft 2 and the inner surface of the sleeve 1-5 in the dynamic pressure generating portion at the lower part of the dynamic pressure bearing. When the brushless motor 10 is started and stopped, the shaft 2 and the sleeve 1 are in light contact until a sufficient dynamic pressure is generated in the dynamic pressure generating portion of the oil dynamic pressure bearing. However, it is not rubbed more strongly than the contact due to the deviation of the spherical tip 2-2 with respect to the center line of the shaft 2 which is the subject of this case, and the influence on the life of the oil dynamic pressure bearing is negligible.

  By the way, in the above-described machining of the spherical portion tip 2-2 of the shaft 2, as shown in FIG. 6, the amount of deviation Δs of the tip 2-2 of the spherical portion 2-1 is approximately (this embodiment). In the example, the range is over 99.7%) and can be smaller than the minimum clearance Δd of the dynamic pressure generating portion. Further, for those that slightly satisfy Δs ≧ Δd, for example, the amount of deviation Δs of the tip 2-2 is selected by inspection of a projector or the like, so that Δs <Δ for the oil dynamic pressure bearing of the brushless motor 10. Only the axis d can be used.

  Further, when finishing the position of the tip of the spherical portion of the shaft by plastic processing such as header processing, it is difficult to ensure Δs <Δd due to the accuracy of mold matching. In addition, since a shaft obtained by molding such as casting or injection molding is difficult to satisfy hardness, wear resistance, etc., it is not suitable for extending the life of a fluid dynamic pressure bearing.

  In the embodiment described above, only the oil dynamic pressure bearing has been described. However, the present invention is not limited to this, and if the pivot receiving portion is provided in the thrust direction, for example, the air dynamics using air as the fluid dynamic pressure medium is used. A pressure bearing device may also be used.

  Moreover, although what provided the herringbone-shaped groove | channel on the sleeve side was demonstrated, this case is not restricted to this. The shaft may be provided with a herring bone, or may be a fluid dynamic pressure bearing in which no herring bone groove is formed on the sleeve and the shaft as long as sufficient dynamic pressure can be formed.

  In addition, although the axis center line is defined by using the axis center of the bending position of the herringbone groove, the present invention is not limited to this. For example, regardless of the presence or absence of the herringbone groove, the axis The center line of the shaft may be defined from the range where the sleeve and the sleeve are closest to each other.

  Also, the inner peripheral surface of the sleeve and the outer peripheral surface of the shaft have been described as being cylindrical. For example, for a sleeve or a shaft whose cross section has a convex portion with respect to a perfect circle, the sleeve is inscribed in a circle. For the shaft, it is better to define the clearance between the sleeve and the shaft and the center line of the shaft from the circumscribed circle.

  It goes without saying that the oil dynamic pressure bearing device described in this embodiment can also be applied as a rotary polygon mirror driving device used in an image forming apparatus such as a printer. In this case, there are advantages that the output start time of the printer or the like can be shortened and the angular acceleration of the brushless motor at the start can be increased.

Sectional drawing of the brushless motor which applied the oil dynamic pressure bearing apparatus of the Example of this invention Schematic sectional view of a shaft and a sleeve showing an oil dynamic pressure bearing device of an embodiment of the present invention A schematic cross-sectional view of an oil dynamic pressure bearing device according to an embodiment of the present invention. Shaft machining schematic diagram of an embodiment of the present invention Schematic diagram of shaft holding means during shaft machining according to an embodiment of the present invention Machining accuracy distribution by shaft machining in this example Sectional view of a conventional oil dynamic bearing device Sectional view of a conventional oil dynamic bearing device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sleeve 1-3 Center of sleeve circle 1-5 Sleeve inner surface 2 Axis 2-1 Spherical part 2-2 Spherical part tip 2-3 Axis centerline 2-4 Axis of axis at start-up 2-5 Axis during steady rotation 3 Thrust receiver 4 Mounting member 5 Yoke 6 Permanent magnet 7 Stator core 8 Circuit board 9 Drive coil 10 Brushless motor 11 Center of chuck part 12 Shaft before processing 13 Cutting tool 14 Claw part 15 Chuck part A, B Bearing surface C, D, E Oil reservoir A-1, B-1 Bending position of herringbone groove A-2, B-2 Bending position of herringbone groove on the axis △ d Shaft outer radius and sleeve inner circumference Difference in radius △ g Minimum clearance between the outer circumference of the shaft and the inner circumference of the sleeve at the start

Claims (7)

A rotating shaft, an abutting portion with which the rotating shaft contacts in the thrust direction of the rotating shaft, a bearing portion that receives the rotating shaft in the radial direction of the rotating shaft, and the rotating shaft about the rotation center in the thrust direction A drive motor comprising:
The rotation shaft has a convex surface on the end surface in the thrust direction, and the tip portion of the convex surface rotates around the shaft including the tip portion by contacting the contact portion,
The gap between the bearing portion and the rotating shaft when the center of the bearing portion and the center of the rotating shaft in the radial direction coincide with each other is a position between the center of the rotating shaft and the rotating center in the radial direction. A drive motor characterized by being larger than the difference. The bearing portion includes a first region facing the rotating shaft at a different position in the thrust direction and a second region having a larger diameter than the first region facing the rotating shaft,
The gap between the first region of the bearing portion and the rotating shaft when the center of the first region of the bearing portion and the center of the rotating shaft in the radial direction coincide with each other is the gap in the radial direction. The drive motor according to claim 1, wherein the drive motor is larger than a positional difference between the center of the rotation shaft and the rotation center. The drive motor according to claim 1, wherein the convex surface is a spherical curved surface. 3. The drive motor according to claim 2, wherein the convex surface of the rotating shaft and a tip end portion of the convex surface are formed by applying a tool to the rotating rotating shaft and removing it. 5. The drive motor according to claim 4, wherein the rotary shaft is subjected to the removal processing in a state where the rotary shaft is rotated while being held at a position facing the first region. The bearing portion is a fluid dynamic pressure bearing in which a herringbone-like dynamic pressure generating groove is provided in the first region, a gap between the rotating shaft and the first region of the bearing portion, and the rotation The drive motor according to claim 2, wherein the shaft, the second region, and the gap are filled with oil. The drive motor according to any one of claims 1 to 6,
A rotary polygon mirror drive device comprising: a rotary polygon mirror attached to a rotor portion of the drive motor.

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