JPH0722123U - Dynamic pressure air bearing - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] To obtain a dynamic pressure air bearing that minimizes the increase in starting friction due to humidity in the radial bearing of the dynamic pressure air bearing. [Structure] A dynamic pressure air bearing main body in which a sleeve 2 is loosely fitted on a shaft 1, and a barrel shape, a bell shape, or a taper shape is deformed slightly from the cylindrical shape. It is composed of a sleeve with a space.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a dynamic pressure air bearing for an optical deflector used in information equipment, image equipment, and measuring equipment.

[0002]

[Prior art]

 In a laser beam printer, a film plate making machine, etc., an optical deflector for rotating a polygon mirror, a prism, etc. at a high speed to scan a light beam is used. Ball bearings are usually used for the bearings, but development of a dynamic pressure air bearing type optical deflector is underway with the aim of further increasing speed and accuracy. The dynamic pressure air bearing constitutes the bearing by the dynamic air pressure generated by the rotation of the shaft or the sleeve. However, since the pressure is small, it is necessary to make the gap between the shaft and sleeve extremely small in order to secure the required bearing rigidity. The gap between the general shaft and the sleeve is about 2 to 8 μm in radius. Only a gap of 1 μm has a great effect on bearing rigidity, so the shaft and sleeve had to be machined with extremely high precision.

[0003]

[Problems to be solved by the device]

 Since the dynamic pressure air bearing generates dynamic pressure due to the difference in rotational speed between the sleeve and shaft, naturally no dynamic pressure is generated at rest, and the shaft and sleeve are in contact. At startup, the motor generates a torque that is greater than the frictional force due to this contact. However, the phenomenon occurs that the required starting torque increases in a high humidity atmosphere. As shown in FIG. 6, a thin water film A is formed in the vicinity of the contact portion between the shaft 1 and the sleeve 2, and the phenomenon of sticking between the shaft 1 and the sleeve 2 due to the surface tension occurs. As a result, the shaft 1 and the sleeve 2 are pushed. It is thought that this is because friction is increased. Since the performance of the dynamic pressure air bearing changes only when the gap between the shaft 1 and the sleeve 2 changes by 1 μm, the shaft 1 and the sleeve 2 are processed with extremely high precision in the conventional dynamic pressure air bearing as shown in FIG. As a result, the contact area becomes large and the torque required for start-up increases extremely in a high humidity atmosphere. In the previous designs, there was a phenomenon that the sleeve shape became bell-shaped due to processing errors, etc. However, the contact area was still quite large as shown in Figs. 8 and 9, and an increase in starting torque was unavoidable. It was In order to generate the torque at this time, it is necessary to increase the motor constant or increase the motor current, and whichever method is adopted, a great burden is imposed on the motor, the power supply, and the drive circuit.

[0004]

[Means for Solving the Problems]

 In order to solve the above problems, the present invention provides a dynamic pressure air bearing configured by loosely fitting a sleeve 2 on a shaft 1. The inner diameter of the sleeve 2 is formed into a barrel shape, or the inner diameter of the sleeve 2 is bell-shaped. The sleeve 2 is formed into a mold, and a portion B having a large inner diameter is provided near the center of the sleeve 2, or the inner diameter of the sleeve 2 is formed into a bell shape, and the outer portion is provided outside the portion corresponding to the center of the sleeve 2 of the shaft 1. A portion C having a small diameter is provided, or a portion B having a large inner diameter is provided in the vicinity of the center of the sleeve 2, and the inner diameter shape of the sleeve 2 on both sides thereof is formed in a tapered shape. Further, it is a dynamic pressure air bearing type optical deflector in which the difference between the inner diameter on both ends of the sleeve 2 and the inner diameter on the center side is 0.5 μm to 5 μm.

[0005]

[Action]

 In the present invention, the sleeve shape is slightly deformed from a cylindrical shape to a barrel shape, a bell shape, or a taper shape, and when the barrel shape is excluded, a space is provided in the central portion, so that the sleeve is The contact area of the sleeve is extremely small, and even if a thin water film is formed on the shaft and the sleeve in high humidity, the contact area is small, so the surface tension acting on the contact area is extremely small, so the starting friction increases even in high humidity. It has the effect of preventing.

[0006]

【Example】

 Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a first embodiment of a dynamic pressure air bearing constructed according to the present invention. The dynamic pressure shaft 1 and the sleeve 2 are rotatably fitted together, and the inner diameter of the sleeve 2 is processed into a bell shape with a small diameter at the center and large diameters at both ends. The difference between the inner diameter of the sleeve 2 and the inner diameter of the sleeve 2 is, for example, 4 μm. On the other hand, two sets of herringbone grooves 3 are formed in the portion of the rotary shaft 1 that is inside the sleeve, and thus a dynamic pressure radial air bearing is formed. Further, the diameter of the portion C corresponding to the central portion of the sleeve 2 of the rotary shaft 1 is smaller than the diameters of the other portions by, for example, 1 mm. A hole 4 is formed at the center of the sleeve 2, and the portion C where the axis is reduced by 1 mm is set to the atmospheric pressure. With such a bearing shape, the contact portion at rest is only in the vicinity of the two points D and E, and it is possible to minimize the formation area of the water film and suppress the increase of the starting friction. FIG. 2 shows a second embodiment, which is similar to FIG. 1, except that the sleeve 2 is enlarged by 1 mm in diameter (B) instead of cutting the axis of the central portion of the sleeve by 1 mm.

FIG. 3 is a third embodiment of the dynamic pressure air bearing according to the present invention. A portion B having a diameter of, for example, 1 mm larger than the inner diameter of the sleeve of the other portion is formed in the center of the sleeve 2. Further, the inner diameter of the sleeve of the other portion is processed to have an outward taper shape. The operation is the same as in the first embodiment. FIG. 4 shows a fourth embodiment, which is similar to the example of FIG. 3, but the inner diameter of the sleeve is tapered inward. The taper is attached so that the difference between the minimum diameter and the maximum diameter is, for example, 4 μm. FIG. 5 shows a fifth embodiment of the present invention in which the inside of the sleeve 2 is formed into a barrel shape. In any of the above embodiments, the contact portion between the shaft and the sleeve at rest is only in the vicinity of the two points D and E, and the structure is such that the formation of the water film is minimized and the increase of the starting friction is prevented. There is. Considering that the inner diameter of the sleeve is actually finished by polishing, the first and second embodiments are optimal. In the case of polishing, the phenomenon that the peripheral part is sagging usually occurs, so it is easy to intentionally cause this phenomenon and widen both ends by 4 μm. Also in the other examples, the processing can be easily performed by selecting the shape suitable for the processing method. If the sleeve 2 is not a true cylinder as described above, it naturally affects bearing performance such as bearing rigidity, but if the shape of the sleeve 2 is designed as the shape of the present invention from the beginning, it is within the scope of the present invention. It is possible to design a bearing with the required bearing performance.

[0008]

As described above in detail, according to the present invention, the sleeve shape is slightly changed from a cylindrical shape to a barrel shape, a bell shape, or a taper shape. Since the space is provided in the core, the contact area between the shaft and sleeve at rest is extremely small, and even if a thin water film is formed on the shaft and sleeve in high humidity, the contact area is small, so the surface that works for the contact part Since the tension is extremely low, it has the effect of preventing an increase in starting friction even in high humidity.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of a dynamic pressure air bearing according to the present invention.

FIG. 2 is a sectional view showing a second embodiment of the dynamic pressure air bearing according to the present invention.

FIG. 3 is a sectional view showing a third embodiment of the dynamic pressure air bearing according to the present invention.

FIG. 4 is a sectional view showing a fourth embodiment of the dynamic pressure air bearing according to the present invention.

FIG. 5 is a sectional view showing a fifth embodiment of the dynamic pressure air bearing according to the present invention.

FIG. 6 is a diagram illustrating an increase in starting friction of a dynamic pressure air bearing.

FIG. 7 is a sectional view of an example of a conventional dynamic pressure air bearing.

FIG. 8 is a sectional view of another example of a conventional dynamic pressure air bearing.

FIG. 9 is a sectional view showing still another example of a conventional dynamic pressure air bearing.

[Explanation of symbols]

1: dynamic pressure shaft, 2: sleeve,
3: Herringbone groove, 4: Hole, A: Water film, B, C: Space, D, E: Shaft and sleeve contact part.

Claims (4)

[Scope of utility model registration request] 1. A dynamic air bearing constructed by loosely fitting a sleeve (2) on a shaft (1), wherein the inner diameter of the sleeve (2) is formed into a barrel shape, and both ends of the sleeve (2) are formed. A dynamic pressure air bearing, wherein the difference between the inner diameter and the inner diameter of the central portion is 0.5 μm to 5 μm. 2. A dynamic pressure air bearing formed by loosely fitting a sleeve (2) on a shaft (1), wherein the inner diameter of the sleeve (2) is formed in a bell shape, and the sleeve (2) is further near the center thereof. The inner diameter of the sleeve (2) is increased, and the difference between the inner diameters of both ends of the sleeve (2) and the inner portion of the sleeve (2) contacting the inner diameter of the sleeve is set to 0.5 μm to 5 μm. bearing. 3. A dynamic pressure air bearing constructed by loosely fitting a sleeve (2) on a shaft (1), wherein the inner diameter of the sleeve (2) is formed in a bell shape, and the sleeve (1) of the shaft (1) is further formed. The dynamic pressure is characterized in that a portion having a small outer diameter is provided in a portion corresponding to the vicinity of the center of 2), and the difference between the inner diameter of both ends of the sleeve (2) and the inner diameter of the central portion is 0.5 μm to 5 μm. Air bearing. 4. A dynamic air bearing constructed by loosely fitting a sleeve (2) on a shaft (1), wherein a portion having a large inner diameter is provided near the center of the sleeve (2), and the sleeves (2) on both sides thereof are provided. ) Has a tapered inner diameter, and the sleeve (2)
The dynamic pressure air bearing is characterized in that the difference between the inner diameters of both end portions and the portion in contact with the large inner diameter portion of the central portion is 0.5 μm to 5 μm.