JPH0565917A - Dynamic pressure air bearing device - Google Patents

Abstract

PURPOSE:To enable comparatively easy manufacture and prevent seizure. CONSTITUTION:In a dynamic pressure air bearing formed of a rotor 2 and a cylindrical bearing 1, a resin coat 14 is formed on at least one opposed face of the rotor 2 or cylindrical bearing 1. As a result, even if a protrusion 13 caused by a flaw or a dent exists on the face with a spiral groove formed to generate dynamic pressure or on its opposed face, or the rotor 2 and bearing 1 are brought into contact with each other due to vibration or the like during rotation, the direct contact between the rotor 2 and bearing 1 is prevented to impede the generation of welding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic pressure air bearing device. More specifically, the present invention relates to a dynamic pressure air bearing suitable for supporting a rotor of a high speed rotating motor such as a laser scanning motor or a high speed spindle motor.

[0002]

2. Description of the Related Art A laser scanning motor, a magnetic drum motor, a gyro motor, or a motor that rotates at a high speed such as a high-speed spindle motor is capable of rotating at high speed. The dynamic pressure air bearing that supports the rotor part is adopted. In this dynamic pressure air bearing, a spiral dynamic pressure generating groove is formed on any one of the outer peripheral surface of the rotating body and the inner peripheral surface of a cylindrical bearing member supporting the rotating body to form a rotating body and a bearing member. A dynamic pressure air bearing is constructed between and. Since this dynamic pressure air bearing generates dynamic pressure during rotation to levitate and support the rotating body, a constant bearing gap (usually 5 μm at maximum) is formed between the rotating body and the bearing member. .. Therefore, the rotating body and the bearing member come into contact with each other during rotation to generate friction heat,
There is a risk of causing a so-called seizure phenomenon in which the shaft and the bearing adhere to each other due to the melting of the contact portion. Generally, wear due to contact in the state where the bearing load capacity is low at the time of start and stop causes seizure, but it also occurs when contact occurs at high speed due to vibration when external force is applied.

Therefore, conventionally, from the viewpoint that a material having high hardness and little wear is advantageous for seizure, hardened steel is used for the rotating shaft, and further hard chrome plating is applied, or quench hardening type is used. Often used stainless steel. Also,
Similar materials or copper alloys are often used for the other bearing member. It is also conceivable to form the bearing with a ceramic material or to coat the inner surface of the bearing or the surface of the rotating shaft with the ceramic material.

[0004]

However, the fact that the use of hard metal materials such as hardened steel is not a complete countermeasure against seizure is in agreement with the general public, and is a tearing point for such dynamic pressure bearings. Further, the use of ceramic materials has technical and cost problems, and is not practical. That is, since ceramic is hard and it is difficult to obtain machining accuracy, a bearing gap of several μm is formed and 5 to 20 μm.
It is not suitable for manufacturing a dynamic pressure air bearing that requires a shallow spiral groove.

The present invention is relatively easy to manufacture,
Moreover, it is an object of the present invention to provide a dynamic pressure air bearing that does not cause seizure.

[0006]

In order to achieve the above object, the present invention provides a spiral groove on either of the surfaces of a rotary shaft and a bearing member that rotatably supports the rotary shaft so as to face each other. At times, in the dynamic pressure air bearing that supports the bearing load by increasing the air pressure in the bearing gap by the action of the spiral groove, a resin coating is formed on at least one of the facing surfaces of the rotating shaft and the bearing member. ing. Here, the resin coating has a thickness equal to or larger than the bearing gap, a thickness that does not adversely affect thermal expansion due to heat generation in the bearing during rotation, and preferably a thickness equal to or larger than twice the bearing gap. The thickness is such that the thermal expansion due to the heat generation in the bearing at that time does not have an adverse effect, most preferably the thickness is about 10 μm. The material of the resin coating is not particularly limited, but epoxy resin, polyvinyl chloride, nylon, etc. are mentioned as one of the preferable materials.

[0007]

Therefore, even if the rotating body and the bearing member come into contact with each other during rotation, the soft resin side is not worn and seizure does not occur due to the contact between the metal and the resin. Moreover, the abrasion powder becomes fine powder and passes through the spiral groove together with the flow of the dynamic pressure air, and is discharged to the outside of the bearing.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described in detail below with reference to the embodiments shown in the drawings. The present embodiment is applied to a motor for rotating a polygon mirror used in an optical scanning device such as a laser printer or a facsimile at high speed.

FIG. 1 shows an embodiment of a polygon mirror driving motor incorporating the dynamic pressure air bearing of the present invention. This polygon mirror driving motor is a cylindrical rotor (rotor) 2 that supports the polygon mirror 7, and a cylinder that forms a dynamic pressure air bearing between the rotor 2 and the rotor 2. -Shaped bearing 1, an iron core 4 and a driving core (coil) 5 that are installed in the center of the cylindrical bearing to form a stator set, and a driving unit that is fixed to the inner peripheral surface of the rotating body 2 to form a rotor set. Mainly consists of magnet 3 and. Between the rotor set and the stator set, for example, the upper end of the iron core 4 and the rotating body 2 which face each other on the rotating shaft center, are magnets 6a, 6 for floating the rotating body, respectively.
b is provided. The magnets 6a and 6b face each other with the same poles and the repulsive force causes the rotor 2 to levitate, and the magnets 6a and 6b are supported so that the rotor set and the stator set are not in contact in the thrust direction. Further, a rotating object such as a polygon mirror 7 is attached to the rotating body 2. Furthermore, the rotating body 2
An electronic component 8 such as a sensor for detecting rotation is attached below the. As shown in FIG. 2, a spiral groove 9 for generating a dynamic pressure is formed in the outer peripheral surface of the rotor 2 by etching or the like to a depth of 5 μm to 20 μm. A boss 10 for fitting the polygon mirror 7 is provided on the upper part of the rotating body 2, and a groove 11 for an air pocket is provided in the central part. The internal space of the rotating body 2 and the outside are communicated with each other through a communication hole (not shown) having a small diameter.

According to the polygon mirror driving motor configured as described above, when the driving coil 5 is energized, the driving magnet 3 is rotationally biased and the rotating body 2 starts rotating together with the polygon mirror 7. At this time, during rotation, the air in the spiral groove 9 is compressed and flows toward the ends of the pair of spiral grooves 9 which are close to each other while increasing the air pressure, and reaches the groove 11 and further reaches the air shown in FIG. Through hole 12
And then distributed to the outside.

The rotary body 2 of the dynamic pressure air bearing having such a structure.
For machining, it is much more advantageous in terms of processing cost to make an aluminum alloy by turning than to grind hardened steel or the like. In addition, it is desirable to use the same aluminum alloy for the bearing 1 in terms of matching the thermal expansion coefficient. However, since the aluminum alloy is soft, it has a drawback that it is apt to be flawed or dented during processing. Usually, it is unavoidable to locally form a protrusion 13 of about several μm on a surface which is finished smooth with scratches and dents. These protrusions 1
No. 3 was not improved even by the surface treatment such as plating or alumite which is usually performed on an aluminum alloy, and it was found that the contact of this portion easily causes seizure. Therefore, it is necessary to be careful in handling during processing and assembly so as not to damage it, and it takes time and effort to inspect and sort good products and defective products. ing.

In order to prevent the seizure due to such flaws and dents, a resin coating 14 is applied to at least one of the facing surfaces of the bearing 1 or the rotating body 2, preferably a resin having a thickness twice or more the bearing gap. Is extremely effective.

The resin coating 14 will be described in detail below.

FIG. 3 shows a state in which the bearing 1 and the rotating body 2 are fitted in each other with a bearing gap e. In the figure, a protrusion 13 due to a flaw or a dent having a height d is formed on the surface of the rotating body 2.

In this state, if d> 2e,
Fitting at the time of assembly is difficult, and it immediately turns out to be a defective product.

However, when 2e ≧ d ≧ e, the rotor 2 fits into the bearing 1, but the normal bearing gap during rotation is e, and therefore the risk of seizure at the initial stage of rotation is extremely large.

Further, when d <e, seizure does not occur in the normal rotation state. However, in the rotating body 2, the bearing clearance e changes due to the effects of shaft runout, external vibration, external moment, etc. due to centrifugal force due to uneven thickness. Therefore, even in this case, there is a risk of seizure.

FIG. 4 shows a resin layer 14 having a thickness t on the inner surface of the bearing 1.
Shows the state in which the rotating body 2 having the protrusion 13 of d = 2e, which is the limit at which the rotating body 2 and the bearing 1 can be fitted, is fitted as described above. The bearing clearance in the vicinity of the protrusion 13 is 2e, and if rotation starts in this state, wear will not progress between the protrusion 13 and the resin layer 14 in order to obtain a normal bearing clearance e. I won't. Usually, when the contact point is between metals, it is melted by frictional heat as described above, and adhesion bake is caused. However, in the case of metal and resin, since they do not melt each other, only the abrasion of the protrusion 13 portion or the resin portion 14 in contact with it progresses, and seizure does not occur. The abrasion powder becomes a fine powder, passes through the groove 9 for dynamic pressure generation shown in FIG. 2 along with the flow of air, reaches the groove 11, and is further discharged from the air hole 12.

FIG. 5 shows a state in which only abrasion of the resin layer 14 progresses and the bearing clearance e is biased to zero due to the action of centrifugal force, external vibration and the like. In this state, if t ≧ d = 2e, the protrusion 13 does not reach the surface of the bearing 1. In this state, the contacts become smooth surfaces, the contact surfaces expand, and the wear in the depth direction decreases.

Originally, the rotating body 2 takes a so-called dynamic balance for correcting uneven thickness which is the basis of centrifugal force (a balance plate is attached to the rotating body 2 or a hole for balance adjustment is formed in the rotating body 2). Is normal, and e =
It will never be zero. Therefore, the progress to the state shown in FIG. 5 will rarely occur due to an accidental external force.

Even when there is no protrusion 13 due to a flaw or a dent, even if the bearing gap e happens to be zero due to an accidental external force as described above, the combination of resin and metal is effective for seizure. is there. The resin coating 14 may be formed on the bearing 1 side or the rotating body 2 side. It is effective that the thickness of the resin coating layer 14 is t ≧ 2e as described above. Normally, the bearing gap e is set to about 5 μm at the maximum, so that t ≧ 10 μm is sufficient.

On the other hand, the dynamic pressure air bearing is generally used at a high speed, and in that case, the amount of heat generated is large due to the viscous resistance of the air flow in the bearing gap e, and is easily affected by the thermal expansion. .. Moreover, since the bearing clearance e is small and set quite strictly, the thermal expansion must be kept small. Therefore, the resin layer 14 generally has a large coefficient of thermal expansion,
Also, since the thermal conductivity is smaller than that of metal, the resin layer 14 to be applied
The thickness should be as thin as possible. Therefore, the thickness of the resin coating 14 is preferably about 10 μm.

As a resin coating method for forming the resin coating film 14, electrodeposition coating of an epoxy resin or the like is preferable from the viewpoint of uniformity of film thickness and control of film thickness. In addition, there are electrostatic dry spray coating of epoxy resin, polyvinyl chloride, nylon, etc., and fluidized immersion coating. In this case, there is a problem in film thickness control, so the side where the spiral groove 9 is not processed, for example, as shown in FIG. In the case of the example, it is preferable to apply a thick coating on the bearing 1 side and then finish the diameter by turning.

On the other hand, the opposing surface of the rotating body 2 or the bearing 1 which is a partner is subjected to a surface treatment such as electroless nickel plating or alumite, or in some cases, a similar resin layer is applied with an appropriate thickness. Good. In this case, it is necessary to select a resin combination that does not cause welding with the mating resin layer.
This is not a difficult task.

[0025]

As is clear from the above description, in the dynamic pressure air bearing of the present invention, the resin coating is formed on at least one of the facing surfaces of the rotating body and the cylindrical bearing, so that the surface flaw is formed. Even if there is a protrusion due to dents or dents, or if there is contact between the rotating body and the bearing due to vibration during rotation, etc., the resin coating will contact and prevent direct contact between the shaft and bearing, and welding will occur. To prevent In particular, when the thickness of the resin coating is twice the bearing gap or more, preferably about 10 μm,
It is possible to prevent seizure without the resin film impeding heat conduction and thermal expansion.

[Brief description of drawings]

FIG. 1 is a central longitudinal sectional view showing an example in which a dynamic pressure air bearing of the present invention is applied to a polygon mirror motor.

FIG. 2 is a front view showing an example of a dynamic pressure generating groove formed on the surface of a rotating body.

FIG. 3 is a partially enlarged vertical sectional view showing an example of a relationship between a rotating body and a bearing of a conventional dynamic pressure air bearing.

FIG. 4 is a partially enlarged cross-sectional view showing, in an enlarged manner, a facing surface portion of a rotating body and a bearing, which is a main part of the present invention.

FIG. 5 is a partially enlarged cross-sectional view showing another embodiment of a facing surface portion between a rotating body and a bearing, which is a main part of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylindrical bearing 2 Rotating body 9 Dynamic pressure generating groove 13 Protrusion 14 Resin coating

Claims (4)

[Claims] 1. A spiral groove is provided on either of the surfaces of a rotating shaft and a bearing member that rotatably supports the rotating shaft so as to face each other, and the air pressure in the bearing gap is increased by the action of the spiral groove during rotation. A dynamic pressure air bearing device for bearing a bearing load, wherein a resin coating is formed on at least one of the facing surfaces of the rotating shaft and the bearing member. 2. The resin coating according to claim 1, wherein the resin coating has a thickness equal to or larger than the bearing gap, and does not adversely affect thermal expansion due to heat generation in the bearing during rotation. Dynamic air bearing device. 3. The resin coating film has a thickness that is at least twice the thickness of the bearing gap and is such that thermal expansion due to heat generation in the bearing during rotation does not adversely affect it. 3. The dynamic pressure air bearing device according to item 3. 4. The dynamic pressure air bearing device according to claim 1, wherein the resin coating has a thickness of about 10 μm.