JPH08205459A - Hydrodynamic bearing type motor and scanner motor for driving polygon mirror - Google Patents

Abstract

PURPOSE: To automatically suppress vibration induced in a rotor assembly in the axial direction through rotation thereof. CONSTITUTION: If a rotor assembly 36, rotating while levitating, descends due to disturbance, the gap 61 between the lower end part 35a of a rotary shaft 35 and a gas conduction hole 58 is decreased. Consequently, the rate of air flowing into a bearing clearance 39 through the gas conduction hole 58 is decreased and the pressure on the under side of the bearing clearance 39 decreases and the pressure on the upper side increases relatively thus producing a force for pulling up the rotor assembly 36. On the contrary, when the rotor assembly 36 ascends, the gap 61 is increased and since the rate of air flowing into a bearing clearance 39 through the gas conduction hole 58 is decreased, the pressure on the under side of the bearing clearance 39 increases and the pressure on the upper side decreases relatively. Consequently, a downward force acts on the rotor assembly 36.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic pressure bearing type motor having a dynamic pressure gas radial bearing, and a polygon mirror driving scanner motor in which this dynamic pressure bearing type motor is applied to a polygon mirror driving scanner motor.

[0002]

2. Description of the Related Art A conventional structure in which a dynamic pressure bearing type motor having a dynamic pressure air radial bearing using air as a lubricating fluid is applied to a polygon mirror driving scanner motor used for laser scanning of a laser beam printer is illustrated. This will be described with reference to FIG.

The housing 1 has a plurality of recesses on the upper surface side, and has a cylindrical portion 2 at the bottom of the central portion, and a cylindrical bearing cylinder 3 made of ceramic is inserted into the cylindrical portion 2. And is fixed by adhesion, and the bottom cover 4 is screwed to the bottom of the tubular portion 2. A cover 5 is screwed onto the upper surface of the housing 1 so as to cover the bearing cylinder 3, and the housing 1 and the cover 5 form a hermetically sealed motor case 6. In the motor case 6, a wiring board 7 is screwed to the upper part of the housing 1, and a plurality of stator coils 8 are adhesively fixed to the upper surface of the wiring board 7.

Inside the motor case 6, a rotor assembly 10 having a stainless rotating shaft 9 is arranged. The rotating shaft 9 is formed with two sets of herringbone-shaped groove portions 11 which form a part of the dynamic pressure air bearing means on the outer peripheral surface, and which are rotatable in the bearing cylinder 3 and movable in the axial direction. Has been inserted into. These rotating shaft 9 and bearing tube 3
And constitute dynamic pressure air bearing means.

A mirror mounting member 12 is mounted and fixed on the upper portion of the rotary shaft 9, and a rotor yoke 13 is bonded and fixed to the mirror mounting member 12. This rotor yoke 1
An annular rotor magnet 14 is adhered and fixed to the lower surface of the rotor 3, and the rotor magnet 14 is arranged so as to face the stator coil 8 from above with a predetermined gap in the axial direction. A polygon mirror 15 is mounted on the mirror mounting member 12.

An attachment member 16 is attached and fixed to the lower portion of the mirror attachment member 12 so as to rotate integrally with the rotary shaft 9. The mounting member 16 penetrates the wiring board 7 so as to surround the bearing tube 3 from above, and the rotary yoke 16 is provided at the bottom.
a is located below the wiring board 7 and is attached, and an annular rotor-side magnetic levitation magnet 17 is attached.

The rotating yoke 16a is a yoke for magnetic focusing, and the magnetic attraction force of the rotor magnet 14 always acts on the rotating yoke 16a to try to attract it, but both the rotor magnet 14 and the rotating yoke 16a have a rotating shaft. Since it is fixed to the mirror 9 through the mirror mounting member 12 or the mounting member 16, these distances are always maintained constant without change. Therefore, the magnetic attraction force of the rotor magnet 14 can be canceled in the rotor assembly 10, and as a result, the thrust load can be reduced to only the weight of the rotor assembly 10.

On the housing 1 side, an annular stator-side magnetic levitation magnet 18 is fixed so as to surround the rotor-side magnetic levitation magnet 17, and the rotor assembly 1
The thrust load of 0 is received by using the magnetic repulsive force of the rotor-side magnetic levitation magnet 17 and the stator-side magnetic levitation magnet 18.

In the above structure, however, when the rotor assembly 10 is rotationally driven, the herringbone-shaped groove 11 is formed.
By the action of, the air is drawn into the bearing gap 19 of several μm between the inner peripheral surface of the bearing tube 3 and the outer peripheral surface of the rotary shaft 9 to generate high-pressure dynamic pressure. The rotating shaft 9 is rotated in a non-contact state with the bearing sleeve 3. A motor using such a dynamic pressure air bearing is suitable for high speed rotation.

[0010]

By the way, the above-mentioned dynamic bearing type motor has the following problems. That is, the rotor assembly 10 is in the axial direction (vertical direction).
In addition, the rotor assembly 10 receives the thrust load due to its own weight by utilizing the magnetic repulsive force of the rotor-side magnetic levitation magnet 17 and the stator-side magnetic levitation magnet 18. Is rotated in a levitation state, that is, in a levitation state (zero balance state) in which the levitation force and the descending force are balanced, and immediately reacts even to a slight disturbance (external factor) to the rotor assembly 10 in the vertical direction (thrust). Vibration).

Further, the vertical vibration caused in such a state does not stop for a long time, and moreover, depending on the situation (frequency) of the disturbance, the vibration is further increased due to the resonance action, and this is the rotor. It will also continue during the entire rotation of the assembly 10.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a dynamic pressure bearing type which is capable of automatically suppressing vibration when axial vibration is generated in the rotor assembly due to disturbance during rotation of the rotor assembly. It is to provide a motor and a scanner motor for driving a polygon mirror capable of performing high-precision and high-performance scanning for a long period of time.

[0013]

According to the invention of claim 1, in a dynamic pressure bearing type motor, in order to achieve the above object,
A rotor assembly including a bearing cylinder provided upright in a housing, a rotary shaft rotatably and axially movably inserted through the bearing cylinder through a dynamic pressure gas bearing means, and the rotor assembly. From the lower side to the upper side in the bearing gap between the outer peripheral surface of the rotating shaft and the inner peripheral surface of the bearing cylinder when the rotor assembly rotates, and the magnetic levitation means provided to receive the thrust load by the magnetic force. And a gas which is provided so as to close the lower end side opening of the bearing cylinder and which communicates with the lower end of the bearing gap at a portion facing the lower end of the rotating shaft. It is characterized in that it is configured to include a lid member having a flow hole formed therein.

In this case, it is preferable that the lower end portion of the rotary shaft is formed in a spherical shape which is convex downward (invention of claim 2). Further, when the diameter dimension of the rotating shaft is A1 and the dimension of the bearing gap between the outer peripheral surface of the rotating shaft and the inner peripheral surface of the bearing tube is A2, the diameter dimension A3 of the gas flow hole and the lower end of the rotating shaft. It is preferable to set the dimension A4 of the gap between the portion and the gas flow hole so that the relationship of A1 × A2 ≦ A3 × A4 is established (the invention of claim 3).

Further, it is preferable that the dynamic pressure gas bearing means has a herringbone-shaped groove portion formed on the outer peripheral surface of the rotating shaft (the invention of claim 4). Further, it is preferable to provide a gas passage on the outer side of the bearing cylinder, which communicates the upper end of the bearing gap with the gas flow hole (the invention of claim 5).

According to a sixth aspect of the invention, in a dynamic pressure bearing type motor, in order to achieve the same object as in the first aspect, a bearing cylinder provided upright in a housing and rotatable on the bearing cylinder. And a rotor assembly having a rotating shaft that is movably inserted in the axial direction, and a herringbone-shaped groove portion that is provided between the bearing tube and the rotating shaft and that is formed on the outer peripheral surface of the rotating shaft. A dynamic pressure gas bearing means and a magnetic levitation means provided to receive the thrust load of the rotor assembly by a magnetic force, and a distance B1 between both ends in the axial direction of the groove portion on the outer peripheral surface of the rotary shaft, The axial length dimension B2 of the bearing sleeve is set so that the relationship of B1 ≧ B2 is established.

In this case, it is preferable to provide a gas passage on the outer side of the bearing cylinder, which communicates the upper end portion and the lower end portion of the bearing gap between the outer peripheral surface of the rotary shaft and the inner peripheral surface of the bearing cylinder. Invention of 7).

According to an eighth aspect of the present invention, in a dynamic pressure bearing type motor, in order to achieve the same object as in the first aspect, a bearing cylinder provided upright in a housing and rotatable on the bearing cylinder. And a rotor assembly having a rotating shaft that is movably inserted in the axial direction, and two sets of herringbone-shaped groove portions that are provided between the bearing tube and the rotating shaft and that are formed on the outer peripheral surface of the rotating shaft. A dynamic pressure gas bearing means, a magnetic levitation means provided to receive the thrust load of the rotor assembly by a magnetic force, and two sets on the outer peripheral surface of the rotary shaft on the inner peripheral portion of the bearing cylinder. The present invention is characterized in that it has a ring groove provided in a ring shape at a portion corresponding to an intermediate portion of the herringbone groove portion.

In this case, it is preferable to set the width dimension C1 of the ring groove and the distance C2 between the two sets of herringbone-shaped groove portions so that the relationship of C1 ≧ C2 is established (the invention of claim 9). ).

Further, on the outside of the bearing tube, a gas passage for communicating the upper end portion and the lower end portion of the bearing gap between the outer peripheral surface of the rotating shaft and the inner peripheral surface of the bearing tube is provided, and the bearing tube is provided with the gas passage. It is preferable to provide a communication hole for communicating the gas passage and the ring groove (the invention of claim 10).

An eleventh aspect of the present invention is a scanner motor for driving a polygon mirror according to the above dynamic pressure bearing type motor, characterized in that the rotary shaft is provided with a polygon mirror that rotates integrally with the rotary shaft.

[0022]

In the dynamic pressure bearing type motor according to claim 1, when the rotor assembly is lowered due to disturbance during rotation of the rotor assembly, the gap between the lower end portion of the rotating shaft and the gas flow hole facing it is small. Since the amount of gas flowing into the bearing gap from the gas flow hole is small, the pressure on the lower side in the bearing gap decreases and the pressure on the upper side in the bearing gap relatively increases. As a result, a force acts in the direction of pulling back the rotating shaft and thus the rotor assembly. On the contrary, when the rotor assembly rises, the gap between the lower end of the rotating shaft and the gas passage hole becomes large, and the amount of gas flowing from the gas passage hole into the bearing gap becomes large. The pressure on the lower side of the bearing increases, and the pressure on the upper side in the bearing gap relatively decreases. As a result, a force acts in the direction of pulling back the rotating shaft and thus the rotor assembly.

Therefore, even if the rotor assembly vibrates in the axial direction due to the disturbance, the vibration can be automatically suppressed.

According to the second, third, fourth and fifth aspects of the present invention, it is possible to more effectively exert the above-mentioned operational effects.

Further, in the dynamic pressure bearing type motor of claim 6, when the rotor assembly descends due to disturbance during rotation of the rotor assembly, the lower part of the herringbone-shaped groove portion formed on the outer peripheral surface of the rotating shaft. A part of the groove portion on the side protrudes downward from the bearing tube, and the protruded portion does not contribute to the generation of dynamic pressure. Therefore, the load generated on the lower side of the bearing gap decreases, and the load on the upper side of the bearing gap relatively increases. As a result, a force acts in the direction of pulling back the rotating shaft and thus the rotor assembly. Conversely, when the rotor assembly rises, a part of the upper groove of the herringbone groove protrudes upward from the bearing cylinder, and the protruding portion does not contribute to the generation of dynamic pressure. For this reason,
The load on the upper side in the bearing gap decreases, and the load on the lower side in the bearing gap relatively increases. As a result, a force acts in the direction of pulling back the rotating shaft and thus the rotor assembly.

Therefore, also in the invention of claim 6,
As in the case of claim 1, even if the rotor assembly is vibrated in the axial direction by a disturbance, the vibration can be automatically suppressed.

According to the invention of claim 7, it is possible to more effectively exhibit the above-mentioned effects.

In the hydrodynamic bearing type motor of claim 8, when the rotor assembly is lowered due to disturbance during rotation of the rotor assembly, among the two sets of herringbone-shaped groove portions formed on the outer peripheral surface of the rotating shaft. A part of the lower groove part of the upper group comes to face the ring groove formed in the inner peripheral part of the bearing cylinder, and the part facing the ring groove does not contribute to the generation of dynamic pressure. Therefore, the load generated in the central portion of the bearing gap decreases, and the load on the upper side of the bearing gap relatively increases. As a result, a force acts in the direction of pulling back the rotating shaft and thus the rotor assembly. On the contrary, when the rotor assembly rises, a part of the upper groove of the lower set of the two sets of herringbone-shaped grooves comes into contact with the ring groove, and the part facing the ring groove becomes It will not contribute to the generation of dynamic pressure. Therefore, the load on the central portion of the bearing gap is reduced, and the load on the lower side of the bearing gap is relatively high. As a result, a force acts in the direction of pulling back the rotating shaft and thus the rotor assembly.

Therefore, also in the invention of claim 8,
As in the case of claim 1, even if the rotor assembly is vibrated in the axial direction by a disturbance, the vibration can be automatically suppressed.

According to the inventions of claims 9 and 10,
The above effects can be more effectively exhibited.

According to the scanner motor for driving a polygon mirror of claim 11, by using the dynamic pressure bearing type motor capable of automatically suppressing the vibration of the rotor assembly as described above, it is possible to achieve high precision and high performance. It becomes possible to perform scanning for a long period of time.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment in which the dynamic pressure bearing type motor of the present invention is applied to a polygon mirror driving scanner motor used for laser scanning of a laser beam printer will be described below with reference to FIGS. .

First, referring to FIG. 2 showing the overall structure, a motor case 21 includes a housing 22 made of, for example, aluminum.
And a cover 24 mounted on top of this with screws 23
It is configured to be in a sealed state from and.

Of these, the housing 22 has 3
In addition to having stepped recesses 25a to 25c, a cylindrical portion 26 is integrally provided at the bottom of the central portion. Inside the cylindrical portion 26, a cylindrical bearing cylinder 27 made of ceramic is adhesively fixed so as to stand. A bottom lid 28 is attached to the bottom of the tubular portion 26 with screws 29,
The bottom surface of the tubular portion 26 is closed by the bottom lid 28.

A wiring board 30 is attached and fixed to the upper concave portion 25a of the housing 22 with screws 31, and a plurality of stator coils 32 are adhesively fixed to the upper surface of the wiring board 30. An annular stator-side magnetic levitation magnet 33 is fixed to the lower recess 25c of the housing 22, and an annular yoke 34 is fixed to the upper surface of the magnet.

Inside the motor case 21, a rotor assembly 36 having a rotating shaft 35 made of, for example, stainless steel is provided.
Are rotatably arranged. On the outer peripheral surface of the rotary shaft 35, as shown in FIG. 1, herringbone-shaped groove portions 37a, 37b, 38 forming a part of the dynamic pressure gas bearing means.
Two sets of a and 38b are formed on the upper and lower sides.
5 is rotatably inserted in the bearing cylinder 27 in a state of being movable in the axial direction (vertical direction). Between the inner peripheral surface of the bearing cylinder 27 and the outer peripheral surface of the rotary shaft 35, a bearing gap 3 of several μm is formed.
9 is formed, and the bearing cylinder 27 and the rotary shaft 35 constitute a dynamic pressure gas bearing means 40 that uses air as a lubricating fluid.

A mirror mounting member 41 is provided above the rotary shaft 35.
Are fixedly attached, and the rotor yoke 42 is fixedly adhered to the mirror mounting member 41. An annular rotor magnet 43 is adhered and fixed to the lower surface of the rotor yoke 42, and the rotor magnet 43 is arranged so as to face the stator coil 32 from above with a predetermined gap in the axial direction. . Further, a polygon mirror 44 is mounted on the mirror mounting member 41 by a mirror retainer 45 and a screw 46, and the polygon mirror 44 is configured to rotate integrally with the rotor assembly 36.

The mounting member 4 is provided below the mirror mounting member 41.
7 is attached and fixed so as to rotate integrally with the rotary shaft 35. The mounting member 47 penetrates the hole of the wiring board 30 in a state of covering the bearing cylinder 27 from above, and the rotating yoke 48 is located below the wiring board 30 and is parallel to the wiring board 30 below the hole. In addition to the above, a rotor-side magnetic levitation magnet 49 having an annular shape is attached.

The rotary yoke 48 is a yoke for magnetic focusing, and the magnetic attraction force of the rotor magnet 43 always acts on the rotary yoke 48 to try to attract it. However, the rotor magnet 43 and the rotary yoke 48 are both rotating shafts. Since they are fixed to the mirror 35 via the mirror mounting member 41 or the mounting member 47, these distances are always maintained constant without change. Therefore, the magnetic attraction force of the rotor magnet 43 can be canceled in the rotor assembly 36, and as a result, the thrust load can be reduced to only the weight of the rotor assembly 36.

A predetermined gap is formed between the inner surface of the mounting member 47 and the outer surface of the bearing sleeve 27. Further, the rotor-side magnetic levitation magnet 49 is inserted into the stator-side magnetic levitation magnet 33, and the outer peripheral surface of the rotor-side magnetic levitation magnet 49 and the stator-side magnetic levitation magnet 33 are separated. A predetermined gap is also formed between the inner peripheral surface and the inner peripheral surface.

The rotor-side magnetic levitation magnet 49 and the stator-side magnetic levitation magnet 33 each have an upper portion of N.
The magnet is magnetized so that the lower part thereof becomes the S pole, and the thrust load of the rotor assembly 36 is applied to the rotor side magnetic levitation magnet 49 and the stator side magnetic levitation magnet 33.
The magnetic levitation means 50 is constituted by the rotor side magnetic levitation magnet 49 and the stator side magnetic levitation magnet 33.

Below the housing 22, a substrate 51 having a drive circuit (not shown) is arranged. This board 51 is mounted on the housing 22 with a spacer 52 and screws 5
It is attached and fixed by 3. The circuit of the board 51 and the circuit of the wiring board 30 in the motor case 21 are connected to the connector 5
It is electrically connected via 4. In addition, the cover 24
In addition, a window portion 55 is provided at one of the portions corresponding to the outer peripheral portion of the polygon mirror 44.
Laser light goes in and out through.

Here, as shown in FIG. 1, in the rotary shaft 35, two sets of groove portions 37a formed on the outer peripheral surface of the rotary shaft 35,
Of 37b and 38a, 38b, the three groove portions 3 from the top
The axial length dimension E1 of 7a, 37b and 38a is set to be the same, and the axial length dimension E2 of the lowermost groove portion 38b is set to be larger than the length dimension E1. (E2> E1). Thus, the axial length dimension E2 of the lowermost groove portion 38b is set to the other groove portions 37a, 3a.
When the rotor assembly 36 is rotated, the bearing clearance 39 between the outer peripheral surface of the rotary shaft 35 and the inner peripheral surface of the bearing cylinder 27 is set to be larger than the length dimension E1 of the 7b and 38a. It constitutes gas flow generation means for generating a flow of air. Further, the inflow angle β of the two sets of groove portions 37a, 37b and 38a, 38b for generating the air dynamic pressure is
The range of 15 degrees to 45 degrees is preferable, and in this embodiment, it is about 25 degrees.
Is set in degrees.

On the other hand, the lower end portion 35a of the rotary shaft 35 is formed in a spherical shape which is convex downward. And the bottom lid 28
A thrust receiving member 56 is disposed inside of the rotary shaft 35 at a position corresponding to the lower end portion 35a of the rotary shaft 35, and the bottom lid 28 and the thrust receiving member 56 cover the lower end side opening portion of the bearing cylinder 27. The member 57 is configured. Of these, the thrust receiving member 56 is formed with a gas flow hole 58 communicating with the lower end of the bearing gap 39, and the bottom lid 28 is provided with a gas flow hole 58.
A first gas passage 59 is formed as a gas passage communicating with the gas circulation hole 58. A second gas passage 60, which constitutes a gas passage together with the first gas passage 59, is formed in the tubular portion 26 of the housing 22. One end of the second gas passage 60 is inside the motor case 21. And the other end communicates with the gas flow hole 58 through the first gas passage 59.

When the diameter of the rotary shaft 35 is A1 and the size of the bearing gap 39 between the outer peripheral surface of the rotary shaft 35 and the inner peripheral surface of the bearing sleeve 27 is A2, the gas flow hole 58 is formed. The diameter dimension A3 and the gap 61 between the lower end portion 35a of the rotary shaft 35 and the gas flow hole 58 when the rotor assembly 36 rotates.
The dimension A4 of is set so that the relationship of A1 × A2 ≦ A3 × A4 is established.

Now, in the above structure, the rotor assembly 36
Is driven to rotate, the herringbone-shaped groove 37a,
By the action of 37b, 38a, and 38b, air is drawn into the bearing gap 39 between the bearing sleeve 27 and the rotary shaft 35 to generate a high dynamic pressure, and the dynamic pressure gas bearing action causes the rotary shaft 35 to rotate. The cylinder 27 is rotated in a non-contact state.

Of the groove portions 37a, 37b and 38a, 38b of the rotary shaft 35, the axial length dimension E2 of the lowermost groove portion 38b is larger than the length dimension E1 of the other groove portions 37a, 37b, 38a. Since the gas flow generating means is configured to be large, the dynamic pressure generated in the bearing gap 39 based on the rotation of the rotating shaft 35 is larger on the lower side than on the upper side, and the bearing gap 39 has A flow that pushes the lower air upward is generated, and as shown by the arrow a in FIG. 1, a flow of air that is directed from the bottom to the top is generated.

The air flowing upward through the bearing gap 39 flows out to the upper end of the bearing cylinder 27, then passes through the gap between the bearing cylinder 27 and the mounting member 47, and descends along the outer surface of the bearing cylinder 27 (arrow). b)). Then, the air circulates such that after passing through the second gas passage 60 and the first gas passage 59 (see arrow c), the air is returned to the bearing gap 39 again through the gas circulation hole 58 (see arrow d). Come to do.

In this case, the rotor assembly 36 is rotated in a levitation state (zero balance state) in which the levitation force of the magnetic levitation means 50, the own weight of the rotor assembly 36 and the sinking force of the gas flow generating means are balanced. It Therefore, when the rotor assembly 36 is rotated, the rotor assembly 36 is rotated in a slightly depressed state as compared with the stopped state. FIG.
And FIG. 2 shows this state.

With the rotor assembly 36 rotating as described above,
When the rotor assembly 36 descends due to disturbance, for example, the lower end portion 35a of the rotating shaft 35 and the gas flow hole 5 facing the lower end portion 35a.
8, the gap 61 between them and the gas flow hole 58 becomes smaller.
Since the amount of air flowing into the bearing gap 39 from the
The lower pressure in the bearing gap 39 decreases, and the upper pressure in the bearing gap 39 relatively increases. As a result,
A force is exerted in the direction of pulling back the rotating shaft 35 and thus the rotor assembly 36.

On the contrary, when the rotor assembly 36 rises, the gap 61 between the lower end portion 35a of the rotary shaft 35 and the gas flow hole 58 becomes large, and the air from the gas flow hole 58 to the bearing gap 39 is increased. Since the amount of inflow of
9, the pressure on the lower side increases, and the bearing gap 39
The pressure on the upper side at becomes lower. As a result, the rotary shaft 35
As a result, the force for pulling the rotor assembly 36 downward is exerted.

Here, regarding the principle of such operation,
It will be described with reference to FIG. However, in FIG. 3, for simplification of description, the illustration is simplified. That is,
Herringbone-shaped groove 6 on the outer peripheral surface of the rotary shaft 35
2a and 62b have only one set, and the lengths in the axial direction are the same.

When the upper pressure Pa and the lower pressure Pb in the bearing gap 39 between the rotary shaft 35 and the bearing sleeve 27 are equal (Pa = Pb), the rotary shaft 35 rotates ( Herringbone-shaped groove 6)
The loads W1 and W2 generated by the action of 2a and 62b are equal (W1 = W2). In this case, W = w × P × L × D. Note that w is the angular velocity, the viscosity coefficient of the gas, the eccentricity,
It is a value that is determined by the inflow angle of the groove, the bearing clearance, and the like, and in this case, it is a constant value and may be regarded as a constant.

Therefore, in such a case, the thrust direction components Ws1 and Ws2 are equal (Ws1
= Ws2), the force for moving the rotary shaft 35 up and down does not work.

When, for example, the rotating shaft 35 (rotor assembly 36) descends due to disturbance (external factor), as described above, between the lower end portion 35a of the rotating shaft 35 and the gas flow hole 58 facing the lower end portion 35a. Since the gap 61 becomes smaller and the amount of air flowing into the bearing gap 39 from the gas flow hole 58 becomes smaller, the lower pressure Pb in the bearing gap 39 decreases and the upper pressure Pa in the bearing gap 39 relatively. Becomes higher. As a result, the load W2 generated by the lower groove portion 62b becomes smaller as indicated by the broken line, and W1> W2. Along with this, the thrust direction component Ws2 also decreases as shown by the broken line, and Ws1> Ws2. Due to the action of the difference (Ws1-Ws2) in the thrust direction component,
As a result, a force is exerted in the direction of pulling back the rotor assembly 36 (see arrow B).

On the contrary, when the rotor assembly 36 moves up, the detailed description is omitted, but the thrust direction component Ws
1, Ws2 becomes Ws1 <Ws2, and due to the difference in the thrust direction components (Ws2-Ws1), the force in the direction of pulling up the rotating shaft 35 and thus of the rotor assembly 36 (the direction opposite to the arrow B) is reduced. Get to work.

Further, as shown in the lower part of FIG.
5 in the rotating state, the rotating shaft 3
When 5 is eccentric, the high pressure air layer in the wide portion of the bearing gap 39 is pushed by the viscosity of the rotating shaft 35 into the narrow portion of the bearing gap 39, and as a result, the rotating shaft 35 has the wide bearing gap 39. It is pushed toward the portion (see arrow C), and the non-contact state with the bearing cylinder 27 is maintained.

According to the first embodiment, as described above, even if the rotor assembly 36 is vibrated in the axial direction by the disturbance, the component force of the thrust component generated in the bearing gap 39 causes It is possible to apply a force to the rotor assembly 36 in a direction opposite to the direction in which the rotor assembly 36 moves, and automatically suppress the vibration. With this,
As a scanner motor for driving a polygon mirror, high-precision and high-performance scanning can be performed for a long period of time.

Further, while the motor case 21 has a closed structure, the air in the motor case 21 circulates through the bearing gap 39 and the second and first gas passages 59 and 60 based on the rotation of the rotor assembly 36. Therefore, the rotating shaft 35 and the bearing cylinder 27 can be satisfactorily cooled, dew condensation can be prevented from occurring in the bearing gap 39, and even if dust is generated in the motor case 21, There is an advantage that the dust can be prevented from adhering to and depositing on the inner peripheral surface of the bearing cylinder 27 and the outer peripheral surface of the rotary shaft 35 as much as possible.

FIG. 4 shows a second embodiment of the present invention. This second embodiment differs from the above-mentioned first embodiment in the following points. That is, the lower end portion 35b of the rotary shaft 35
Is formed in a flat shape, and the thrust receiving member 64, which constitutes the lid member 63 together with the bottom lid 28, is integrally provided with a cylindrical portion 65 projecting upward around the gas flow hole 58.

Also in the second embodiment as described above, as the rotor assembly 36 moves up and down, the gap 66 between the lower end portion 35b of the rotary shaft 35 and the gas passage hole 58 changes, so that the gas passage is changed. By changing the inflow amount of air from the hole 58 to the bearing gap 39, it is possible to obtain the same effect as that of the first embodiment.

5 to 7 show a third embodiment of the present invention, which is different from the first embodiment in the following points.

That is, in FIG. 5, the bearing tube 67 is
The axial length of the bearing cylinder 67 is set shorter than that of the bearing cylinder 27 in the first embodiment, and the axial length dimension B2 of the bearing cylinder 67 is two sets of groove portions 37 on the outer peripheral surface of the rotary shaft 35.
A distance between both ends of a, 37b and 38a, 38b in the axial direction B
It is set to be smaller than 1 (B1> B
2).

A gas passage is not formed in the bottom lid 68 attached so as to close the tubular portion 26 of the housing 21, and a space 69 is provided between the bottom lid 68 and the bearing barrel 67. Has been formed. A thrust receiving member 70 is arranged at the center of the upper surface of the bottom cover 68. A gas passage 71 is formed in the tubular portion 26 of the housing 21. One end of the gas passage 71 communicates with the upper end of the bearing gap 39 through the inside of the motor case 21, and the other end is a space. It communicates with the lower end portion of the bearing gap 39 via the portion 69.

Now, in the above structure, the rotor assembly 36
Is driven to rotate, as in the first embodiment, the rotary shaft 3
5 and a bearing sleeve 67, a dynamic pressure gas bearing means 40
By this action, the rotating shaft 35 is rotated in a non-contact state with the bearing sleeve 67. In addition, the groove portions 37a, 3 of the rotary shaft 35
By the gas flow generating means by 7b and 38a, 38b,
In the bearing gap 39, a flow that pushes the lower air upward is generated, and as shown by an arrow a in FIG. 5, a flow of air that is directed from the bottom to the top is generated.

The air flowing upward through the bearing gap 39, after exiting the upper end of the bearing barrel 67, passes through the gap between the bearing barrel 67 and the mounting member 47 and descends along the outer surface of the bearing barrel 67 (arrow). b)). After passing through the gas passage 71 (see arrow c), the air is circulated through the space 69 and returned again to the bearing gap 39 (see arrow e).

Also in this case, the rotor assembly 36 is rotated in a levitation state (zero balance state) in which the levitation force of the magnetic levitation means 50, the weight of the rotor assembly 36 and the sinking force of the gas flow generating means are balanced. To be done. Therefore, when the rotor assembly 36 is rotated, the rotor assembly 36 is rotated in a slightly depressed state as compared with the stopped state. Figure 5
Indicates this condition.

With the rotor assembly 36 rotating as described above,
When the rotor assembly 36 descends due to disturbance, for example, two sets of groove portions 37a, 37 formed on the outer peripheral surface of the rotating shaft 35 are formed.
b and 38a, 38b, the lowermost groove portion 38b
However, it further protrudes downward from the bearing sleeve 67 than in the state of FIG. 5, and the protruding portion does not contribute to the generation of dynamic pressure. Therefore, the load generated below the bearing gap 39 is reduced, and the load above the bearing gap 39 is relatively increased. As a result, a force is exerted in the direction in which the rotary shaft 35 and thus the rotor assembly 36 are pulled back upward.

On the contrary, when the rotor assembly 36 is lifted, the uppermost groove 37a of the two sets of grooves 37a, 37b and 38a, 38b is located further above the bearing tube 67 than in the state of FIG. The protruding portion does not contribute to the dynamic pressure generation. Therefore, the load on the upper side of the bearing gap 39 is reduced, and the load on the lower side of the bearing gap 39 is relatively high. As a result, a force is exerted in the direction in which the rotary shaft 35 and thus the rotor assembly 36 are pulled back downward.

Here, regarding the principle of such operation,
This will be described with reference to FIGS. 6 and 7. However, in FIG. 6 and FIG. 7, as in the case of FIG. 3, for simplification of description, they are simplified and shown. That is, there is only one set of herringbone-shaped grooves 62a and 62b on the outer peripheral surface of the rotary shaft 35, and the lengths in the axial direction are the same. The bearing sleeve 67 is also shown short.

Now, as shown in FIG. 6, a part of the upper and lower groove portions 62a and 62b is protruded from the bearing tube 67 to both upper and lower sides, and the effective axial length of the upper and lower groove portions 62a and 62b. When La and Lb are equal (La = Lb)
In addition, the loads W1 and W2 generated by the action of the herringbone-shaped grooves 62a and 62b with the rotation of the rotating shaft 35 are equal (W1 = W2). In this case, W = w × P × L × D. Note that w is a value determined by the angular velocity, the viscosity coefficient of gas, the eccentricity, the inflow angle of the groove, the bearing gap, and the like, and in this case, it is a constant value and may be regarded as a constant.

Therefore, in such a case, the thrust direction components Ws1 and Ws2 are equal (Ws1
= Ws2), the force for moving the rotary shaft 35 up and down does not work.

When, for example, the rotating shaft 35 (rotor assembly 36) descends due to disturbance (external factor), the lower groove portion 62b is formed in the bearing cylinder further than in the state of FIG. 6, as shown in FIG. While protruding downward from 67, the upper groove 62a is almost in the bearing tube 67,
Effective axial lengths Lc, Ld of the upper and lower groove portions 62a, 62b
Is Lc> Ld.

As a result, the load W2 generated by the lower groove portion 62b becomes smaller, while the load W1 generated by the upper groove portion 62a becomes larger, so that W1> W2, and accordingly, the thrust direction components Ws1 and Ws2. Also,
Ws1> Ws2. This difference in thrust direction component (W
By the action of s1-Ws2), a force acts in the direction (see arrow B) for pulling back the lowered rotating shaft 35 and thus the rotor assembly 36.

On the contrary, when the rotor assembly 36 moves up, a detailed explanation is omitted, but the thrust direction component Ws
1, Ws2 becomes Ws1 <Ws2, and due to the difference in the thrust direction components (Ws2-Ws1), the force in the direction of pulling up the rotating shaft 35 and thus of the rotor assembly 36 (the direction opposite to the arrow B) is reduced. Get to work.

Therefore, also in the third embodiment, as in the first embodiment, the rotor assembly 3 is affected by the disturbance.
Even if an axial vibration is generated in 6, the component force of the thrust direction component generated in the bearing gap 39 causes a force in the direction opposite to the moving direction of the rotor assembly 36 to act on the rotor assembly 36 to cause the vibration. Can be automatically suppressed.

In the third embodiment, the axial length B2 of the bearing tube 67 is set to be smaller than the axial end-to-end distance B1 of the two groove portions 37a, 37b and 38a, 38b. Although it has been set (B1> B2), even if the axial length dimension B2 of the bearing tube 67 and the axial end-to-end distance B1 of the two sets of groove portions 37a, 37b and 38a, 38b are set to be equal. (B1 = B2), the same effect can be obtained.

Further, in this third embodiment, two sets of groove portions 3 are provided.
The gas flow generating means of 7a, 37b and 38a, 38b forms a flow of air from the lower side to the upper side in the bearing gap 39, but the gas flow generating means is not always necessary.

FIG. 8 shows a fourth embodiment of the present invention. This fourth embodiment differs from the above-mentioned third embodiment in the following points.

That is, the bearing cylinder 27 is set to have a longer axial length than the bearing cylinder 67 of the third embodiment, and the axial length dimension of the bearing cylinder 27 is the same as that of the first embodiment. Similarly, two sets of groove portions 37a, 3 on the outer peripheral surface of the rotary shaft 35 are formed.
It is set to be slightly larger than the distance between both ends of 7b and 38a, 38b in the axial direction. A ring groove 73 is provided on the inner peripheral portion of the bearing cylinder 27 at a portion corresponding to the intermediate portion 72 of the two groove portions 37a, 37b and 38a, 38b. In this case, the axial width dimension C1 of the ring groove 73 is determined by the two groove portions 37a, 37b and 3
It is set larger than the axial distance C2 between 8a and 38b (C1> C2). Further, the bearing cylinder 27 is formed with a plurality of communication holes 74 for communicating the inside of the motor case 21 with the inside of the ring groove 73.

Also in the fourth embodiment, the rotor assembly 36 is in a floating state (zero) in which the levitation force of the magnetic levitation means 50, the weight of the rotor assembly 36 and the sinking force of the gas flow generating means are balanced. It is rotated in a balanced state. Therefore, when the rotor assembly 36 is rotated, the rotor assembly 36 is rotated in a slightly depressed state as compared with the stopped state. FIG. 8 shows this state.

With the rotor assembly 36 rotating as described above,
When the rotor assembly 36 descends due to disturbance, for example, the lower groove portion 37b of the upper group of the two sets of herringbone-shaped groove portions 37a, 37b and 38a, 38b formed on the outer peripheral surface of the rotating shaft 35 is The ring groove 73 formed in the inner peripheral portion of the bearing cylinder 27 is exposed to a large amount, and the portion facing the ring groove 73 does not contribute to the generation of dynamic pressure. Therefore, the load generated in the central portion of the bearing gap 39 is reduced, and the load on the upper side of the bearing gap 39 is relatively increased. As a result, as in the case of the third embodiment, due to the action of the difference in the thrust direction component, the rotating shaft 35 and thus the rotor assembly 3
The force to pull back 6 comes to work.

On the contrary, when the rotor assembly 36 is raised, the upper groove 38a of the lower set of the two sets of herringbone-shaped grooves 37a, 37b and 38a, 38b is
It comes to face the ring groove 73 a lot, and the ring groove 73
The portion facing to does not contribute to the generation of dynamic pressure. For this reason,
The load on the central portion of the bearing gap 39 decreases, and the load on the lower side of the bearing gap 39 relatively increases. As a result, as in the case of the third embodiment, the force acting in the direction of pulling back the rotary shaft 35 and thus the rotor assembly 36 is exerted by the action of the difference in the thrust direction components.

Therefore, also in the fourth embodiment, as in the third embodiment, the rotor assembly 3 is affected by the disturbance.
Even if an axial vibration is generated in 6, the component force of the thrust direction component generated in the bearing gap 39 causes a force in the direction opposite to the moving direction of the rotor assembly 36 to act on the rotor assembly 36 to cause the vibration. Can be automatically suppressed.

In the fourth embodiment, the ring groove 73
The axial width C1 of the ring groove 73 is set to be larger than the axial distance C2 between the two sets of groove portions 37a, 37b and 38a, 38b (C1> C2), but the axial width of the ring groove 73 is Dimension C1 and two sets of groove portions 37a, 37b and 38
Even if the axial distance C2 between a and 38b is set to be equal (C1 = C2), the same effect can be obtained.

FIG. 9 shows a fifth embodiment of the present invention. This fifth embodiment applies the present invention to a radial gap type motor. The same parts as those in the first embodiment will be described with the same reference numerals.

The motor case 81 includes a housing 82,
It is configured to be in a hermetically sealed state with the cover 24 attached to the upper part thereof. A recess 83 in the housing 82
Is formed, and the cylindrical member 84 is formed in the center of the recess 83.
A cylindrical bearing cylinder 27 is provided so as to be in an upright state via the. The bottom surface of the tubular member 84 is
It is blocked by 5. In the recess 83 of the housing 82, a wiring board 86 and a ring-shaped stator core 87 are provided on the outer peripheral portion of the tubular member 84, and a stator coil 88 is provided on the stator core 87.

Inside the motor case 81, a rotor assembly 89 having the rotating shaft 35 is rotatably arranged. On the outer peripheral surface of the rotary shaft 35, as in the first embodiment, two sets of herringbone-shaped groove portions 37a, 37b, 38a, 38b which form a part of the dynamic pressure gas bearing means are formed vertically. This rotating shaft 35 is in the axial direction (vertical direction)
Is rotatably inserted in the bearing cylinder 27 in a movable state. A bearing gap 39 of several μm is formed between the inner peripheral surface of the bearing cylinder 27 and the outer peripheral surface of the rotary shaft 35. The bearing cylinder 27 and the rotary shaft 35 constitute the dynamic pressure gas bearing means 40. ing.

A mirror mounting member 90 is provided on the rotary shaft 35.
Are fixedly mounted, and the rotor yoke 91 is fixed to the mirror mounting member 90. This rotor yoke 91
Has a tubular shape surrounding the stator core 87, and a tubular rotor magnet 92 is adhered and fixed to the inner peripheral surface of the stator core 87. The rotor magnet 92 has a predetermined radial direction with respect to the stator core 87. They are arranged opposite to each other with a gap. In this case, the rotor magnet 9
The magnetic levitation means 93 that receives the thrust load of the rotor assembly 89 is constituted by the stator core 87 and the stator core 87. Further, the polygon mirror 4 is provided above the mirror mounting member 90.
4 is mounted by a mirror retainer 45 and a screw 46, and the polygon mirror 44 is configured to rotate integrally with a rotor assembly 89. In the cover 24, a window portion 55 is provided at one portion corresponding to the outer peripheral portion of the polygon mirror 44, and the laser light enters and leaves through the window portion 55.

The lower end portion 35a of the rotary shaft 35 is formed in a spherical shape which is convex downward. A thrust receiving member 56 is disposed inside the bottom lid 85 at a portion corresponding to the lower end portion 35 a of the rotary shaft 35. The bottom lid 85 and the thrust receiving member 56 open the lower end side of the bearing cylinder 27. A lid member 94 for closing the portion is configured. Of these, the thrust receiving member 56 has a gas flow hole 58 communicating with the lower end of the bearing gap 39, and the bottom lid 85 has a first gas passage 9 as a gas passage communicating with the gas flow hole 58.
5 is formed. A second gas passage 96, which constitutes a gas passage together with the first gas passage 95, is formed in the tubular member 84 and the housing 82. One end of the second gas passage 96 is formed in the motor case 21. It communicates with the upper end of the bearing gap 39 via the inside, and the other end communicates with the gas flow hole 58 via the first gas passage 95.

When the diameter of the rotary shaft 35 is A1 and the size of the bearing gap 39 between the outer peripheral surface of the rotary shaft 35 and the inner peripheral surface of the bearing sleeve 27 is A2, the gas flow hole 58 is formed. The diameter dimension A3 and the gap 61 between the lower end portion 35a of the rotary shaft 35 and the gas flow hole 58 when the rotor assembly 89 rotates.
The dimension A4 is set so that the relationship of A1 × A2 ≦ A3 × A4 is established, as in the first embodiment.

Now, in the above structure, the rotor assembly 89
Is driven to rotate, the herringbone-shaped groove 37a,
By the action of 37b, 38a, and 38b, air is drawn into the bearing gap 39 between the bearing sleeve 27 and the rotary shaft 35 to generate a high dynamic pressure, and the dynamic pressure gas bearing action causes the rotary shaft 35 to rotate. The cylinder 27 is rotated in a non-contact state.

Of the groove portions 37a, 37b and 38a, 38b of the rotary shaft 35, the axial length dimension of the lowermost groove portion 38b is set to be larger than the length dimension of the other groove portions 37a, 37b, 38a. However, since the gas flow generating means is configured by these, the pressure of the dynamic pressure generated in the bearing gap 39 due to the rotation of the rotating shaft 35 is larger on the lower side than on the upper side. For this reason, in the bearing gap 39, a flow of pushing the lower air upward is generated, and as shown by an arrow f, a flow of air from the bottom to the top is generated.

The air flowing upward through the bearing gap 39 exits at the upper end of the bearing sleeve 27 and then descends through the gap between the rotor magnet 92 and the stator core 87 (see arrow g). Then, the air passes between the upper surface of the wiring board 86 and the lower surface of the rotor magnet 92 and between the lower surface of the wiring board 86 and the upper surface of the recess 83 (see arrow h), and the second
Of the bearing gap 39 after passing through the gas passage 96 and the first gas passage 95 (see arrow i).
(See arrow j).

In this case, the rotor assembly 89 is rotated in a floating state (zero balance state) in which the levitation force by the magnetic levitation means 93, the weight of the rotor assembly 89 and the sinking force by the gas flow generating means are balanced. It Therefore, when the rotor assembly 89 is rotated, the rotor assembly 89 is rotated in a slightly depressed state as compared with the stopped state. Figure 9
Indicates this condition.

In such a rotating state of the rotor assembly 89,
When, for example, the rotor assembly 89 descends due to a disturbance, the gap 61 between the lower end portion 35a of the rotating shaft 35 and the gas passage hole 58 facing the lower end portion 35a becomes small, and the gas passage therethrough, as in the first embodiment. Since the amount of air flowing into the bearing gap 39 from the hole 58 is small, the pressure on the lower side in the bearing gap 39 is reduced and the pressure on the upper side in the bearing gap 39 is relatively increased. As a result, a force is exerted in the direction in which the rotary shaft 35 and thus the rotor assembly 89 are pulled back upward.

On the contrary, when the rotor assembly 89 is raised, the gap 61 between the lower end portion 35a of the rotary shaft 35 and the air circulation hole 58 becomes large, and the air from the gas circulation hole 58 to the bearing gap 39 is increased. Since the amount of inflow of
9, the pressure on the lower side increases, and the bearing gap 39
The pressure on the upper side at becomes lower. As a result, the rotary shaft 35
As a result, a force is exerted in the direction of pulling back the rotor assembly 89.

In the fifth embodiment, as in the first embodiment, even if the rotor assembly 89 is vibrated in the axial direction by the disturbance, the component force of the thrust component generated in the bearing gap 39 is generated. Thereby applying a force to the rotor assembly 89 in the direction opposite to the direction in which it moves,
The vibration can be automatically suppressed.

The present invention is not limited to the above-mentioned embodiments, but can be modified or expanded as follows. For example, as the gas flow generating means, instead of the above-mentioned means, herringbone-shaped grooves 37a, 37b,
It can also be achieved by changing the groove depths of 38a and 38b on the inflow side and the outflow side. Specifically, the largest pressure is obtained when the depth of the groove is set to be equal to that of the bearing gap 39. Therefore, in order to generate an upward air flow in the bearing gap 39, the groove 38b at the lowermost portion is formed. The depth is set to be equal to the bearing gap 39, and the other groove 37
The depths of a, 37b, and 38a may be set shallower or deeper than that.

The gas flow generating means can be achieved by changing the size of the bearing gap 39 between the inflow side and the outflow side, instead of the above-mentioned means. Specifically, the smaller the size of the bearing gap 39 is, the larger pressure is obtained. Therefore, in order to generate the upward air flow in the bearing gap 39, the size of the bearing gap 39 is set to be smaller on the lower side than on the upper side. Set to.

[0101]

According to the first aspect of the present invention, when the rotor assembly is rotated, even if the rotor assembly is vibrated in the axial direction due to a disturbance, the component force of the thrust direction component generated in the bearing gap causes By virtue of the fact that a force is applied to the rotor assembly in the direction opposite to the direction in which it moves, its vibration can be automatically suppressed.

According to the inventions of claims 2, 3, 4, and 5, the above-mentioned effects can be more effectively exhibited.

According to the sixth aspect of the present invention, as in the first aspect of the present invention, when the rotor assembly is rotated, even if the rotor assembly is vibrated in the axial direction by a disturbance, the vibration occurs in the bearing gap. Due to the component force of the thrust direction component, a force in the direction opposite to the direction in which the rotor moves can be applied to the rotor assembly, and its vibration can be automatically suppressed.

Further, according to the invention of claim 7, it is possible to more effectively exhibit the above-mentioned effects.

Also in the invention of claim 8, as in the case of claim 1, even when the rotor assembly is rotated and the axial vibration is caused in the rotor assembly during the rotation of the rotor assembly, the thrust direction generated in the bearing clearance is generated. By the component force of the components, it is possible to apply a force to the rotor assembly in a direction opposite to the direction in which the rotor assembly moves, and automatically suppress the vibration.

According to the inventions of claims 9 and 10, the above-mentioned effects can be more effectively exhibited.

According to the polygon mirror driving scanner motor of the eleventh aspect, by using the dynamic bearing type motor capable of automatically suppressing the vibration of the rotor assembly as described above, it is possible to achieve high precision and high accuracy. It becomes possible to perform high-performance scanning for a long period of time.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional front view of essential parts showing a first embodiment of the present invention.

[Figure 2] Overall vertical front view

[Figure 3] Schematic diagram

FIG. 4 is a view corresponding to FIG. 1 showing a second embodiment of the present invention.

FIG. 5 is a view corresponding to FIG. 1 showing a third embodiment of the present invention.

FIG. 6 is an explanatory diagram of the principle 1

[FIG. 7] Principle explanatory diagram 2

FIG. 8 is a view corresponding to FIG. 1 showing a fourth embodiment of the present invention.

FIG. 9 is a view corresponding to FIG. 2 showing a fifth embodiment of the present invention.

10 is a diagram corresponding to FIG. 2 showing a conventional configuration.

[Explanation of symbols]

Reference numeral 21 is a motor case, 22 is a housing, 27 is a bearing cylinder, 33 is a stator side magnetic levitation magnet, 35 rotating shafts, 35a and 35b are lower end portions, 36 is a rotor assembly, 37
a, 37b, 38a, 38b are groove portions (gas flow generating means), 39 is a bearing gap, 40 is a dynamic pressure gas bearing means, 44
Is a polygon mirror, 49 is a magnet for magnetic levitation on the rotor side, 50 is magnetic levitation means, 57 is a cover member, 58 is a gas flow hole, 59 and 60 are first and second gas passages (gas passages), and 61 is a gap. , 63 is a cover member, 66 is a gap, 67 is a bearing tube, 71 is a gas passage, 72 is an intermediate portion, 73 is a ring groove, 74 is a communication hole, 81 is a motor case, 82 is a housing, 89 is a rotor assembly, and 93 is a rotor assembly. Is a magnetic levitation means, 94 is a cover member, 95 and 96 are first and second gas passages (gas passages), A1 is a diameter dimension of a rotating shaft, A2 is a dimension of a bearing gap, and A3 is a diameter dimension of a gas flow hole. , A4 is the size of the gap between the lower end of the rotary shaft and the gas flow hole, B1 is the distance between the ends of the groove in the axial direction, B2 is the length of the bearing cylinder, C1 is the width of the ring groove, and C2 is It is the distance between two sets of grooves.

Claims (11)

[Claims] 1. A rotor assembly comprising: a bearing cylinder provided upright in a housing; and a rotary shaft rotatably and axially movably inserted through the bearing cylinder via a dynamic pressure gas bearing means. A magnetic levitation means provided so as to receive the thrust load of the rotor assembly by a magnetic force; and a bearing clearance between the outer peripheral surface of the rotating shaft and the inner peripheral surface of the bearing sleeve when the rotor assembly rotates. Gas flow generating means for generating a gas flow from the lower side to the upper side, and provided so as to close the lower end side opening of the bearing cylinder,
A dynamic pressure bearing type motor comprising: a lid member having a gas passage hole communicating with a lower end portion of the bearing gap at a portion facing the lower end portion of the rotating shaft. 2. The dynamic pressure bearing type motor according to claim 1, wherein a lower end portion of the rotary shaft is formed in a spherical shape which is convex downward. 3. When the diameter of the rotary shaft is A1 and the size of the bearing gap between the outer peripheral surface of the rotary shaft and the inner peripheral surface of the bearing sleeve is A2, the diameter A3 of the gas flow hole and the rotation The dynamic bearing type motor according to claim 2, wherein the dimension A4 of the gap between the lower end of the shaft and the gas flow hole is set so that the relationship of A1 × A2 ≦ A3 × A4 is established. 4. The dynamic pressure bearing according to claim 1, wherein the dynamic pressure gas bearing means has a herringbone-shaped groove formed on the outer peripheral surface of the rotary shaft. Shaped motor. 5. A dynamic pressure bearing type motor according to claim 1, wherein a gas passage that connects the upper end of the bearing gap and the gas flow hole is provided outside the bearing tube. . 6. A bearing assembly provided upright in a housing, a rotor assembly including a rotating shaft inserted into the bearing cylinder so as to be rotatable and axially movable, and the bearing cylinder and the rotating shaft. And a dynamic levitation provided to receive a thrust load of the rotor assembly by a magnetic force, the dynamic pressure gas bearing means having a herringbone-shaped groove formed on the outer peripheral surface of the rotating shaft. And a distance B1 between both ends in the axial direction of the groove on the outer peripheral surface of the rotating shaft and an axial length dimension B2 of the bearing cylinder are set so that a relationship of B1 ≧ B2 is established. A hydrodynamic bearing type motor characterized in that 7. A gas passage is provided on the outer side of the bearing sleeve, the gas passage communicating the upper end portion and the lower end portion of the bearing gap between the outer peripheral surface of the rotating shaft and the inner peripheral surface of the bearing sleeve. Item 5. A dynamic bearing type motor according to item 6. 8. A rotor assembly including a bearing cylinder provided upright in a housing, and a rotary shaft inserted through the bearing cylinder so as to be rotatable and axially movable, and the bearing cylinder and the rotary shaft. And a dynamic pressure gas bearing means having two sets of herringbone-shaped grooves formed on the outer peripheral surface of the rotating shaft, and a thrust load of the rotor assembly, which is provided by a magnetic force. Magnetic levitation means, and a ring groove provided in a ring shape on a portion of the outer peripheral surface of the rotating shaft corresponding to an intermediate portion of two herringbone-shaped groove portions on the inner peripheral portion of the bearing cylinder. A hydrodynamic bearing type motor characterized in that 9. The ring groove width dimension C1 and the distance C2 between the two sets of herringbone-shaped groove portions are set so that the relationship of C1 ≧ C2 is established. Dynamic bearing motor. 10. A gas passage is provided on the outer side of the bearing cylinder, the gas passage communicating the upper end and the lower end of the bearing gap between the outer peripheral surface of the rotating shaft and the inner peripheral surface of the bearing cylinder, and the bearing cylinder is provided with the gas passage. The dynamic pressure bearing type motor according to claim 8 or 9, wherein a communication hole for communicating the gas passage and the ring groove is provided. 11. The scanner motor for driving a polygon mirror according to claim 1, wherein the rotary shaft is provided with a polygon mirror that rotates integrally with the rotary shaft. .