JP2001271827A - Dynamic pressure gas bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the large increase of the floating quantity of a sleeve in a thrust direction during the high speed rotation of a dynamic pressure gas bearing and during the abrupt change of the rotating speed. SOLUTION: The dynamic pressure gas bearing is provided with a dynamic pressure generation groove on either one of the outer peripheral surface of a shaft body and the inner peripheral surface of the sleeve to impart floating force to the sleeve by the rotation of the sleeve. In the dynamic pressure gas bearing, a groove deeper than the dynamic pressure generation groove is formed on the outer peripheral surface of the shaft body or the inner peripheral surface of the sleeve. When the sleeve floats by the prescribed quantity or larger from the shaft body, a part, imparting the floating quantity, of the dynamic pressure generation groove is opposed to the deep groove. Surfacing force is thereby reduced to always maintain the constant floating quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrodynamic gas bearing device used for a rotary spindle such as a polygon scanner of a laser printer.

[0002]

2. Description of the Related Art A conventional example of a dynamic pressure gas bearing device will be described with reference to a sectional view of FIG. In FIG. 7, the shaft 21 is fixed to the center of the frame 27. The shaft 21 has a bearing hole 22A and a flange portion 2 for attaching a rotating body.
A sleeve 22 having 2B is rotatably fitted with an appropriate gap. Herringbone-shaped dynamic pressure generating grooves 21A and 21B and a helical dynamic pressure generating groove 21C are formed on the outer peripheral surface of the shaft body 21. Dynamic pressure generating groove 2
1A, 21B, and 21C are formed by zigzag-connected grooves, but grooves in respective regions separated by alternate long and short dash lines are distinguished as dynamic pressure generation grooves 21A, 21B, and 21C. The stator 25 of the motor 26 is fixed to the frame 27, and the rotor 24 is fixed to the sleeve 22.
The upper end of the sleeve 22 is sealed by a lid 23, and a contact portion 23 </ b> A protrudes from the inner wall surface of the lid 23. The contact portion 23A has a pressure adjustment hole 23B near the center. The operation of the hydrodynamic gas bearing device configured as described above will be described. When the stator 25 of the motor 26 is energized and the sleeve 22 is rotated, the dynamic pressure generating grooves 21A, 21B, 2
Due to the known pumping action of 3C, the sleeve 22 receives a force in the radial direction and rotates without contacting the shaft 21. Further, the sleeve 22 receives the force in the thrust direction (upward in the figure) and floats in the thrust direction by the pumping action of the helical dynamic pressure generating groove 21B. As a result, the contact portion 23A that is in contact with the shaft 21 during the stop is rotated during the rotation.
Move away from the shaft 21.

[0003]

However, the configuration of the conventional example shown in FIG. 7 has the following problems.
In a dynamic pressure gas bearing device having a shaft body 21 having a length of 5 to 30 millimeters, a steady rotation speed is, for example, 30,000 to 40,000 rotations per minute, and a design is made such that an appropriate floating amount can be obtained at this rotation speed. I have. When the number of revolutions is, for example, 50,000 or more per minute,
In the case where the flying height in the thrust direction (h5 in FIG. 7) which was several tens of micrometers at the steady rotation speed becomes an excessive value of, for example, 2 to 3 mm or more, and vertical rotation occurs, and normal rotation cannot be performed. There is. Also, even at 40,000 revolutions per minute or less, the flying height sometimes becomes an excessive value if the revolution speed changes abruptly.

[0004]

A hydrodynamic gas bearing device according to the present invention is a herringbone-shaped groove, wherein a length of a groove from a top of the groove in a first direction is equal to the length of the groove from the top. A first dynamic pressure generating groove longer than a length of a groove directed in a second direction different from the first direction, and a herringbone-shaped second dynamic pressure generating groove adjacent to the first dynamic pressure generating groove. A shaft having an outer peripheral surface and supported at an end in the first direction;
And the first and second shafts are rotatably mounted on the shaft body.
A sleeve having a groove on an inner wall surface facing near the boundary of the dynamic pressure generating groove, and a lid having a pressure adjusting hole of a predetermined diameter facing an end of the shaft body in the second direction. When the pressure in the space between the end of the shaft body in the second direction and the lid increases due to the increase in the rotational speed of the sleeve, the floating amount of the sleeve increases, and the grooves on the inner wall surface of the sleeve become first and second.
From the vicinity of the boundary of the dynamic pressure generating groove. As a result, the dynamic pressure generating action of each of the first and second dynamic pressure generating grooves changes, so that the pressure in the space decreases and the flying height decreases. As a result, the sleeve always rotates while maintaining a constant floating amount.

[0005] A dynamic pressure gas bearing device according to another aspect of the present invention comprises:
A first groove having a herringbone shape, wherein a length of a groove from a vertex of the groove in a first direction is longer than a length of a groove from the vertex in a second direction different from the first direction. And a herringbone-shaped second dynamic pressure generating groove adjacent to the first dynamic pressure generating groove on the inner peripheral surface, and a predetermined end is provided at an end in the second direction. A sleeve having a lid provided with a pressure adjustment hole having a diameter, and a groove rotatably inserted into the sleeve, and having a groove on an outer wall surface facing a boundary between the first and second dynamic pressure generating grooves, and 1
A shaft supported at the end in the direction of. When the pressure in the space between the end of the shaft in the second direction and the lid increases due to the increase in the rotational speed of the sleeve, the floating amount of the sleeve increases, and the grooves on the outer peripheral surface of the shaft are reduced by the first and second grooves. It deviates from the vicinity of the boundary of the dynamic pressure generating groove. As a result, the dynamic pressure generating action of each of the first and second dynamic pressure generating grooves changes, so that the pressure in the space decreases and the flying height decreases. As a result, the sleeve always rotates while maintaining a constant floating amount.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the hydrodynamic gas bearing device of the present invention will be described below with reference to FIGS. << First Embodiment >> FIG. 1 is a sectional view of a hydrodynamic gas bearing device according to a first embodiment of the present invention. In FIG. 1, a fixed shaft 1 is fixed to a central portion of a frame 7. On the fixed shaft 1,
A sleeve 2 having a bearing hole 2A and a flange 2B for attaching a rotating body is rotatably fitted with an appropriate gap. A first dynamic pressure generating groove 1 for generating pressure in a gap between the outer peripheral surface and the bearing hole 2 </ b> A is formed on the outer peripheral surface of the fixed shaft 1.
A and a second dynamic pressure generating groove 1B are formed. Each of the dynamic pressure generating grooves 1A and 1B is formed by a zigzag continuous groove, and is separated by a horizontal dynamic pressure minimum line connecting bending points of the groove with the lowest dynamic pressure indicated by a dashed line 1F. The grooves in the area are distinguished as dynamic pressure generating grooves 1A and 1B. Each of the dynamic pressure generating grooves 1A and 1B has a modified herringbone shape in which the length of the lower groove is longer than the length of the upper groove.
Due to the deformed herringbone shape, when the sleeve 2 rotates, the gas between the fixed shaft 1 and the sleeve 2 is carried upward by a known pumping action, and the air pressure in the space 3C increases. The amount of gas carried upward increases as the difference between the lengths of the upper and lower grooves increases. The stator 5 of the motor 6 is fixed to the frame 7, and the rotor 4 is fixed to the sleeve 2. A lid 3 is attached to an upper part of the sleeve 2. The inner wall surface of the lid 3 is provided with a contact portion 3A protruding opposite to the upper end 1C of the fixed shaft 1. Contact part 3
A pressure adjustment hole 3B is formed near the center of A. On the inner peripheral surface of the sleeve 2, a large-diameter portion 2C for forming an annular groove is formed. The large-diameter portion 2C is formed such that its central portion is located at a position facing the boundary between the first dynamic pressure generating groove 1A and the second dynamic pressure generating groove 1B. Large diameter part 2C
Since the distance between the outer peripheral surface of the fixed shaft 1 and the peripheral surface of the sleeve 2 is large, the pumping action by the dynamic pressure generating grooves 1A and 1B does not work.

In the hydrodynamic gas bearing device according to the present embodiment in which the length of the fixed shaft 1 is in the range of 7 to 30 mm, the pressure adjusting hole 3
B has an inner diameter of about 0.1 millimeter, and the dynamic pressure generating groove 1
The depth of A and 1B is 3 to 20 micrometers. The inner diameter of the large diameter portion 2C is larger than the inner diameter of the bearing hole 2A by 20 to 250 micrometers. The operation of the hydrodynamic bearing device of the first embodiment configured as described above will be described with reference to FIGS. In FIG. 1, when the stator 5 of the motor 6 is energized, the sleeve 2 to which the rotor 4 is fixed rotates clockwise when viewed from above. Since the dynamic pressure generating grooves 1A and 1B have a deformed herringbone shape, gas between the fixed shaft 1 and the sleeve 2 is carried from the fixed end 1D to the free end 1E. As a result, the pressure in the space 3C between the upper end 1C of the fixed shaft 1 and the lid 3 increases. As a result, the sleeve 2 receives a floating force in the thrust direction parallel to the rotation axis. When rotating at a specified number of revolutions, the sleeve 2 floats by 50 microns or more from the stop. The position and diameter of the pressure adjustment hole 3B are set so that the opening of the pressure adjustment hole 3B is completely secured in this state.

FIGS. 2A and 3A are enlarged views of the upper part of FIG. 2 (b) and 3 (b)
Is a graph showing the pressure distribution in the space 3C between the upper end 1C and the lid 3, in which the vertical axis indicates the pressure P and the horizontal axis indicates the position between the left end and the right end of the space 3C. FIGS. 2C and 3C are graphs showing the pressure distribution between the fixed shaft 1 and the sleeve 2, wherein the vertical axis indicates the position of the sleeve 2 in the direction along the rotation axis, and the horizontal axis indicates the pressure. Indicates P. In FIG. 2A, since the length L1 indicating the formation range of the first hydrodynamic groove 1A in which the directions are different from each other is shorter than the length L2, as shown in FIG. The pressure of 3C rises except for the vicinity of the pressure adjustment hole 3B and becomes P1. With the pressure P1, the sleeve 2 floats by about 2 to 20 microns, and its own weight and the levitation force due to the pressure P1 are balanced, and the sleeve 2 rotates in a non-contact manner while maintaining a constant levitation amount h1 shown in FIG. As shown in FIG. 2B, the pressure in the gap between the fixed shaft 1 and the sleeve 2 becomes the maximum pressure P3 at the top of the dynamic pressure generating groove 1A, and becomes the pressure P1 near the upper end 1C.
The pressure does not increase at the large diameter portion 2C. Due to the pressure P3, the sleeve 2 rotates while being held in non-contact with the fixed shaft 1.

FIG. 3A is an enlarged view showing a hypothetical condition in which the number of revolutions rises above a prescribed number of revolutions, the pressure in the space 3C increases, and the flying height h2 becomes 1 to 2 millimeters. It is sectional drawing. As a result of the increase in the flying height, the large-diameter portion 2C moves to the area where the first dynamic pressure generating groove 1A is formed, and the length L2 in FIG. 2A decreases to the length L3. Since the length L1 does not change, the pressure in the space 3C decreases to the pressure P2 as shown in FIG. 3C by the decrease from the length L2 to the length L3.
As a result, the sleeve 2 descends, returns to the original position shown in FIG. 2A, and maintains a stable rotation. FIG. 2A and FIG.
(A), the length L3 is changed from the length L2 to the length h2.
Is subtracted. The length S2 is a value obtained by adding the length S1 and the length h2. The contact portion 3A of the present embodiment is spherical, but may be flat. In FIG. 1, it is desirable that the pressure adjusting hole 3B is eccentric from the center of the lid 3 by a distance e. The value of the distance e is, for example, 0.1 to 0.5 mm. According to this embodiment, when the air pressure in the space 3C increases and the floating amount of the sleeve 2 increases, the large-diameter portion 2C located at the boundary between the dynamic pressure generating grooves 1A and 1B moves toward the dynamic pressure generating groove 1A. Moving. As a result, of the lower groove of the dynamic pressure generating groove 1A,
The length of the portion contributing to the transfer of the gas to the space 3C is reduced, and an increase in the atmospheric pressure in the space 3C is suppressed. In addition, the length of a portion of the upper groove of the dynamic pressure generating groove 1B that suppresses the transfer of gas to the space 3C is increased, and an increase in the pressure of the space 3C is suppressed. By both of the above actions, the amount of gas carried to the space 3C is reduced, the pressure is reduced, and the flying height is reduced. In addition, since the central portion of the large diameter portion 2C is located at the boundary between the dynamic pressure generating grooves 1A and 1B, the pressure in the large diameter portion 2C when the sleeve 2 rotates in a steady state is stabilized, and
Is stable in the axial direction. As a result, the sleeve 2 rotates while maintaining a constant flying height h1 shown in FIG.

<< Second Embodiment >> A second embodiment of the present invention is shown in FIG.
This will be described with reference to FIG. In FIG. 4, the fixed shaft 11 is fixed to the center of the frame 17. No dynamic pressure generating groove is provided on the outer peripheral surface of the fixed shaft 11 of this embodiment. A sleeve 12 having a bearing hole 12C and a flange portion 12D is rotatably fitted on the fixed shaft 11 with an appropriate gap. A first dynamic pressure generation groove 12A and a second dynamic pressure generation groove 12B having a deformed herringbone shape are formed on the inner wall surface of the sleeve 12. Dynamic pressure generating groove 12
A and 12B are formed of zigzag continuous grooves, but grooves in respective areas separated by horizontal dynamic pressure minimum lines connecting bending points of the grooves where the dynamic pressure indicated by the dashed line 12F is the lowest are formed. They are distinguished as dynamic pressure generating grooves 12A and 12B. A stator 15 of a motor 16 is fixed to the frame 17, and a rotor 14 is fixed to the sleeve 12. A lid 13 is provided on the upper part of the sleeve 12. A contact portion 13A facing the upper end 1C of the fixed shaft 11 is provided on the inner wall surface of the lid 13.
Is provided near the center of the contact portion 13A.
B is provided. A small-diameter portion 11 </ b> D for forming an annular groove is provided on the outer peripheral surface of the fixed shaft 11. The small-diameter portion 11D is provided on the inner peripheral surface of the sleeve 12 at a portion where the pressure of the first dynamic pressure generation groove 12A is highest. As an example of the dimensions of each part of the hydrodynamic bearing device of the present embodiment, the length of the fixed shaft 11 is 7 to 30 mm, and the pressure adjusting hole 13B
Has an inner diameter of about 0.1 mm, and the dynamic pressure generation grooves 12A, 1
The depth of 2B is 3-20 microns meter. Fixed shaft 1
The outer diameter of the small diameter portion 11D is 20 to 20 times smaller than the outer diameter of the fixed shaft 11.
It is 250 microns smaller.

The operation of the thus configured hydrodynamic gas bearing device of the second embodiment will be described with reference to FIGS. FIG. 4 is a sectional view of the hydrodynamic gas bearing device of the second embodiment. FIGS. 5A and 6A are enlarged cross-sectional views of the upper part of FIG. FIGS. 5B and 6B correspond to FIGS. 2B and 3B, respectively.
(C) and (c) of FIG. 6 correspond to (c) of FIG. 2 and (c) of FIG. 3, respectively. In FIG. 4, when the stator 15 of the motor 16 is energized, the sleeve 12 to which the rotor 14 is fixed starts rotating. The air pressure rises due to the respective pumping action of the dynamic pressure generating grooves 12A and 12B of the sleeve 12, and the sleeve 12 is supported without contacting the fixed shaft 11. As shown in FIG. 4, the dynamic pressure generating grooves 12A and 12B have a deformed herringbone shape in which the length of the lower groove is longer than the length of the upper groove.
When 2 rotates, gas in the gap between the fixed shaft 11 and the sleeve 12 is carried from the fixed end 11E side of the fixed shaft 11 to the free end 11F side. As a result, the air pressure in the space 13C between the upper end 11C and the lid 13 rises, and the sleeve 12 floats in the thrust direction with respect to the fixed shaft 11 and rotates. Sleeve 12
The hole position and the hole diameter are set so that the opening of the pressure adjusting hole 13B is completely secured when the surface of the pressure adjusting member 13 floats by 50 microns or more in the thrust direction. As shown in FIG. 5A, in the first dynamic pressure generating groove 12A, a pressure P3 is generated in the thrust direction according to the ratio between the lengths L4 and L5, as shown in FIG. 5C. I do. Due to this pressure P3, the sleeve 1
2 with the surface of the sleeve 12 floating about 2 to 20 microns.
The self-weight and the levitation force are balanced, and the rotor rotates in a non-contact manner while maintaining a constant levitation amount indicated by h3 in FIG.

When the number of revolutions exceeds the prescribed number of revolutions and the sleeve 12 rises significantly (1-2 mm) as shown by the flying height h4 in FIG. 6, the diameter of the shaft 11 becomes small. The relative position between the portion 11D and the first dynamic pressure generation groove 12A changes, and the length L5 decreases to the length L6. Length L4
Since the pressure does not change, the pressure in the space 13C decreases to the pressure P4 as shown in FIG. The resulting sleeve 12
Is smaller than the own weight of the sleeve 12, and the rotating body returns to the original position shown in FIG. 5 and stably rotates. In FIG. 4, the small diameter portion 11D of the fixed shaft 11 is provided to face the highest pressure portion of the first dynamic pressure generating groove 12A, but is opposed to the highest pressure portion of the second dynamic pressure generating groove 12B. May be provided. As described above, according to the embodiment of the present invention, when the rotation speed of the bearing is increased from the specified value or when the bearing is rapidly changed, the floating amount of the sleeve 12 in the thrust direction does not become excessively large, and the stable floating amount is increased. can get.

[0013]

As described in detail in each of the above embodiments, in the dynamic gas bearing device of the present invention, the first and second dynamic pressure generating grooves allow the gas to flow through the fixed end of the fixed shaft during normal rotation. From the side to the free end and lift it up sufficiently in the thrust direction,
When over-floating occurs, the relative position between the first dynamic pressure generating groove and its opposing surface is shifted to reduce the floating force of the first and second dynamic pressure generating grooves to prevent over-floating. .

[Brief description of the drawings]

FIG. 1 is a sectional view of a hydrodynamic gas bearing according to a first embodiment of the present invention.

2A is an enlarged cross-sectional view of the upper part of the dynamic pressure gas bearing in FIG. 1, and FIGS. 2B and 2C are graphs showing pressure distribution.

3A is an enlarged sectional view showing a state in which the floating amount of a sleeve is increased in the dynamic pressure gas bearing of FIG. 1, and FIGS. 3B and 3C are graphs showing pressure distribution.

FIG. 4 is a sectional view of a dynamic pressure gas bearing according to a second embodiment of the present invention.

5A is an enlarged cross-sectional view of the upper part of the hydrodynamic gas bearing in FIG. 4, and FIGS. 5B and 5C are graphs showing pressure distribution.

6A is an enlarged sectional view showing a state in which the floating amount of a sleeve is increased in the dynamic pressure gas bearing of FIG. 4, and FIGS. 6B and 6C are graphs showing pressure distribution.

FIG. 7 is a sectional view of a conventional hydrodynamic gas bearing device.

[Explanation of symbols]

 1,11 Fixed shaft 1A, 12A Dynamic pressure generating groove 1B, 12B Upper end 2,12 Sleeve 2A, 12C Bearing hole 2B, 12D Flange 3,13 Lid 3A, 12A Contact part 3B, 13B Pressure adjusting hole 3C, 13C Space 4, 14 Rotor 5, 15 Stator 6, 16 Motor 7, 17 Frame

Continued on the front page (72) Inventor Riki Hamada 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F term (reference) 3J011 AA04 AA11 BA02 CA03 KA02 MA07

Claims (4)

[Claims] 1. A groove having a herringbone shape, wherein a length of a groove from a vertex of the groove in a first direction is different from a groove in a second direction different from the first direction. A first dynamic pressure generating groove longer than a length, and a herringbone-shaped second dynamic pressure generating groove adjacent to the first dynamic pressure generating groove on a cylindrical outer peripheral surface; A shaft body supported at an end, a sleeve rotatably fitted to the shaft body, and having a lateral groove on an inner wall surface facing a boundary between the first dynamic pressure generating groove and the second dynamic pressure generating groove; A dynamic gas bearing device having a lid fixed to an end of the sleeve and having a pressure adjusting hole of a predetermined diameter facing an end of the shaft body in a second direction. 2. The position of the lateral groove on the inner peripheral surface of the sleeve is such that the first dynamic pressure generating groove on the outer peripheral surface of the shaft body is located when the sleeve is floating at a predetermined stable position with respect to the shaft body. 2. The dynamic pressure according to claim 1, wherein the lowest line of the dynamic pressure at the connection between the second groove and the second dynamic pressure generating groove is selected so as to be substantially at the height of the center of the lateral groove. Gas bearing device. 3. A groove having a herringbone shape, wherein a length of a groove from a vertex of the groove in a first direction is different from a groove in a second direction different from the first direction. A sleeve having a first dynamic pressure generating groove longer than a length and a herringbone-shaped second dynamic pressure generating groove adjacent to the first dynamic pressure generating groove on a cylindrical inner peripheral surface; rotatable by the sleeve And the first and second
A shaft body having a lateral groove on the outer wall surface facing the boundary of the dynamic pressure generating groove, and a pressure adjusting hole fixed to an end of the sleeve and having a predetermined diameter at an end of the shaft body in a second direction. A dynamic pressure gas bearing device having a lid. 4. The position of the lateral groove of the shaft body is such that, when the sleeve is floating at a predetermined stable position with respect to the shaft body, the first dynamic pressure generating groove on the inner surface of the sleeve and the second dynamic pressure generating groove 4. The dynamic pressure gas bearing device according to claim 3, wherein the dynamic pressure minimum line at the connection with the dynamic pressure generating groove is selected so as to be substantially at the height of the center of the lateral groove.