JPH04282017A - Dynamic air bearing structure - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to dynamic pressure air bearing structures, such as high-speed rotating equipment using radial or thrust dynamic pressure air bearings such as laser printers and digital copiers, particularly dynamic pressure air bearing type polygon scanners. Regarding air bearing structure.

0002

2. Description of the Related Art A conventional hydrodynamic air bearing structure is, for example, shown in FIG.
) There is a dynamic pressure air bearing type polygon scanner 1 as shown in FIG. The polygon scanner 1 includes a rotating body 4 that can rotate at high speed and has a polygon mirror 3 fixed to the upper part of a hollow rotating shaft 2;
It has a fixed shaft 5 which is in sliding contact with the inner periphery of the hollow rotary shaft 2 and is erected on a base 1a at the bottom of the polygon scanner 1. A groove 5b for generating dynamic pressure is provided in a radial receiving surface 5a on the outer periphery of the fixed shaft 5, and the fixed shaft 5 and the hollow rotary shaft 2 constitute a dynamic pressure air bearing structure 6. Although it is stated that the material of the fixed shaft 5 and the hollow rotating shaft 2 is made of stainless steel,
The hardness of the rotating shaft 5 and the hollow rotating shaft 2 is not described and is unknown.

[0003] Conventionally, there has been no description of the hardness relationship for radial dynamic pressure air bearings. On the other hand, regarding the hardness of stainless steel, it is stated on page 36 of the book "Heat Treatment of Stainless Steel" published by Nikkan Kogyo Shimbun (published on October 5, 1971) that the sliding of materials with similar hardness is Seizing and galling always occur. In order to prevent this, for martensitic stainless steel such as SUS420, the difference in hardness between the two sliding surfaces is increased by at least Brinell hardness HB 50 or more by heat treatment. It becomes.

[0004] Also, as a scanner having a radial dynamic pressure air bearing structure 6, there is a polygon scanner 7 shown in FIG. 3(b).
is considered. In FIG. 3(b), the same components as those shown in FIG. 3(a) will be described with the same reference numerals. In the polygon scanner 7 shown in FIG. 3(b), a rotor magnet 8 is fixed to the lower part of the hollow rotating shaft 2, and a stator for rotating the hollow rotating shaft 2 at high speed is provided in the housing 7A outside the rotor magnet 8. A motor section 9 such as a wiring board is attached. A polygon mirror 3 is fixed to the upper part of the hollow rotating shaft 2, and a mirror holder 1 also serves as a balance ring for balancing the rotating body 4.
0. Magnetic bearing magnet 10A for thrust magnetic bearing
, fine holes 10B and the like are installed to provide high damping characteristics in the axial direction of the hollow rotating shaft 2.

Furthermore, stainless steel SUS420J2, which has excellent corrosion resistance and wear resistance, is used for the members forming the hollow rotating shaft 2 and the fixed shaft 5, and the hollow rotating shaft 2 is made of stainless steel SUS420J2, which has excellent corrosion resistance and wear resistance. The hardness is higher than that of the fixed shaft 5 having the dynamic pressure generating groove 5b, and the difference in hardness between the two is approximately HRC5 on the Rockwell hardness C scale. The reason why the hardness of the members of the hollow rotating shaft 2 is made higher than that of the fixed shaft 5 is because the hollow rotating shaft 2 rotates at high speed, has many parts attached to it as described above, and is expensive. The hollow rotary shaft 2 is made of high hardness to make it difficult to wear out, and the sliding portion of the fixed shaft 5 can be easily replaced when it wears out.

[0006]

[Problems to be Solved by the Invention] However, in such a conventional hydrodynamic air bearing structure 6, martensitic stainless steel such as SUS420 J2 is used for the member of the fixed shaft 5. If the hardness of the stainless steel No. 5 is lowered relative to the hollow rotating shaft 2, the corrosion resistance will decrease,
The risk of rust formation increases.

[0007] Furthermore, the radial receiving surface 5a for generating dynamic pressure is
The groove is formed by digging several micrometers deep into the ground surface of the outer circumference of the fixed shaft 5 by processing methods such as chemical etching, sandblasting, cutting, or rolling, but the corrosion resistance of the groove surface is better than that of the ground surface of the smooth inner circumference. It is lower than that of the hollow rotating shaft 2. That is, in the conventional method of creating hardness differences between the members of the hydrodynamic air bearing structure 6, the corrosion resistance of the fixed shaft 5 having the groove 5b is lower than that of the hollow rotary shaft 2;
In addition, it has the groove 5b for generating dynamic pressure, which is doubly disadvantageous.

Furthermore, when processing the groove 5b for generating dynamic pressure on the outer peripheral surface of the fixed shaft 5 by chemical etching, it is necessary to accurately control the heat treatment conditions of quenching and tempering to prevent deterioration of corrosion resistance. , causing uneven etching. For this reason, there is also the problem that it takes a lot of effort to manage the heat treatment.

[0009]

OBJECTS OF THE INVENTION The present invention has been made against the background of such problems in the prior art, and provides a shaft having an outer circumferential surface or a bearing surface provided with grooves for generating dynamic pressure in a dynamic pressure air bearing. By making the hardness of the member higher than the hardness of the shaft that has a sliding surface that slides on the outer circumferential surface or bearing surface, the corrosion resistance of the shaft that has grooves can be increased, and corrosion from the grooves for generating dynamic pressure can be improved. It is an object of the present invention to provide a hydrodynamic air bearing structure that can significantly suppress the heat treatment conditions during groove machining, reduce man-hours, reduce manufacturing costs, and improve reliability.

0010

[Structure of the Invention] In order to achieve the above object, the present invention is based on claim 1.
A central shaft made of metal and having an outer circumferential surface with a circular cross section or a bearing surface substantially perpendicular to the axis of the outer circumferential surface, and a sliding shaft that is coaxial with the central axis and slides on the outer circumferential surface or the bearing surface. a sliding shaft having a surface, a dynamic pressure generating groove on any one of the outer circumferential surface, the bearing surface, and the sliding surface, and one of the central shaft and the sliding shaft In the rotatable hydrodynamic air bearing structure, the hardness of the member forming the central shaft or the sliding shaft having the dynamic pressure generating groove is greater than the hardness of the sliding shaft or the center that slides opposite to the member. According to a second aspect of the present invention, in the dynamic pressure air bearing structure according to the first aspect, the center shaft is made of stainless steel and has a dynamic pressure generating groove on the outer peripheral surface. In claim 3, in the hydrodynamic air bearing structure according to claim 1, the sliding shaft is made of stainless steel, and has an inner circumferential surface that slides on the outer circumferential surface; It is characterized by having dynamic pressure generating grooves.

[0011] Here, it is desirable that the hardness of the member forming the shaft having the dynamic pressure generating groove is higher by Rockwell hardness HRC 3 to HRC 10 than the hardness of the member sliding opposite to this member.

0012

[Operation] According to claim 1 of the present invention, since the hardness of the member forming the central shaft or sliding shaft having the dynamic pressure generating groove is higher than the hardness of the member sliding opposite to this member, the dynamic pressure generating groove The hardness of the member forming the shaft having a hardness can be higher than the conventional hardness of this member, and can be approximately the same as the higher hardness of the conventional shaft member with a difference in hardness. Therefore, the corrosion resistance and wear resistance of a shaft having dynamic pressure generating grooves can be significantly improved compared to the conventional one.

Further, in claim 2, in the hydrodynamic air bearing structure according to claim 1, the central shaft having the dynamic pressure generating groove is made of stainless steel and has a higher hardness than the sliding shaft. The hardness of the shaft member is significantly improved compared to the conventional central shaft, resulting in improved corrosion resistance and wear resistance. Further, in claim 3, in the hydrodynamic air bearing structure of claim 1, the sliding shaft having the dynamic pressure generating groove is made of stainless steel, and the inner circumferential surface having the dynamic pressure generating groove has a hardness higher than that of the central shaft. Therefore, although the tubular sliding shaft member is formed with dynamic pressure generating grooves, its corrosion resistance and wear resistance are significantly improved compared to the central shaft.

[0014]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. FIG. 1 is a diagram showing a first embodiment of a hydrodynamic air bearing structure according to claims 1 to 3 of the present invention, and shows a hydrodynamic air bearing structure 11.
is applied to the polygon scanner 12 of a laser printer. Rotating body 13 at the center of the polygon scanner 12
A thrust magnetic bearing 14 is applied to the axial bearing portion.

The polygon scanner 12 has a hollow cylindrical hollow rotary shaft 15 which is a sliding shaft, and a disk-shaped mirror holder 16 placed on a flange-like mirror holder 15a on the upper part of the hollow rotary shaft 15. A polygon mirror 17 that rotates at a constant speed and is screwed to a mirror holder 15a, and a hollow rotating shaft 15
A tubular rotor magnet 18 fixed to the outer periphery of the lower part of the
It has . Hollow rotating shaft 15, mirror holder 16, polygon mirror 17
The rotor magnet 18 constitutes the main part of the rotating body 13.

An annular stator 19 fixed to the housing 12A of the polygon scanner 12 is provided outside the rotor magnet 18, and the stator 19 has a motor part wiring board 21 and a hole material 20 for detecting the position of the rotor magnet 18. Together, they constitute a motor drive section. A base 22 is provided at the bottom of the housing 12A, and a fixed shaft 23, which is a rod-shaped central shaft having an outer peripheral surface 23a having a circular cross section, is fixed to the base 22 by shrink fitting. Fixed axis 2
The above-mentioned hollow rotating shaft 15 has an inner circumferential surface 15b, which is a sliding surface that slides on the outer circumferential surface 23a of the fixed shaft 23, on the outside of the fixed shaft 23.
is on the same axis C as the fixed shaft 23 and is arranged to be rotatable at high speed. Two pairs of herringbone grooves 25, which are dynamic pressure generating grooves, are provided on the outer circumferential surface 23a of the fixed shaft 23, and the hollow rotary shaft 15 exhibits a radial dynamic pressure air bearing function when rotating at high speed. The fixed shaft 23, the herringbone groove 25, and the hollow rotary shaft 15 constitute a hydrodynamic air bearing structure 11.

The thrust magnetic bearing 14 includes an annular magnetic bearing magnet 14c fixed to the upper side of the fixed shaft 23, and an annular magnetic bearing magnet 14b disposed in the center of the mirror holder 16 on the same axis as the magnetic bearing magnet 14c. and an annular magnetic bearing magnet 14a fixed inside the central part of an optical housing 26 that covers the outside of the polygon mirror 17 and is fixed to the housing 12A. In addition, there is a fine hole 1 in the axial direction in the center of the mirror holder 16.
6a is provided so that the hollow rotating shaft 15 has high damping characteristics in the axial direction. 27 is a deflection window.

Both the hollow rotating shaft 15 and the fixed shaft 23 are made of stainless steel SUS420 J2, and the hardness A of the stainless steel A that forms the fixed shaft 23 having the herringbone groove 25 is equal to the outer peripheral surface 2 of the stainless steel A.
The material is made to have a Rockwell hardness higher by a hardness difference HRC5 than the stainless steel B which is the member forming the hollow rotating shaft 15 having an inner circumferential surface 15b sliding opposite to the inner peripheral surface 15b.

The Rockwell hardness of the stainless steel SUS420 J2 is in the hardness range of HRC45 to HRC60 on the C hardness, and the Rockwell hardness of the stainless steel A, which is the member forming the fixed shaft 23 having the herringbone groove 25, is ,
A hardness close to HRC60 has been selected. Hollow rotating shaft 15
The hardness of stainless steel B of the member (for example, hardness HRC5
5) is designed so that there is a difference in Rockwell hardness of about HRC5 from the hardness of the fixed shaft 23. That is, the hardness A of the stainless steel A of the fixed shaft 23 is higher than the conventional one by the hardness difference HRC5.

The difference in Rockwell hardness between the stainless steel A of the fixed shaft 23 and the stainless steel B of the hollow rotary shaft 15 may be appropriately selected within the range of HRC 3 to 10. The herringbone groove 25 of the fixed shaft 23 is hardened to a hardness A of about HRC60 as usual, and then processed to a depth of several μm by chemical etching on the ground surface of the outer periphery, as shown in FIG. 1(b). It was done.

The operation of the polygon scanner 12 is such that the rotating body 13 starts to rotate at a constant speed due to the driving force of a motor drive unit connected to a power source, and the hydrodynamic air bearing structure 11 is rotated by the herringbone groove 25 of the fixed shaft 23. Fixed shaft 23 and hollow rotating shaft 1
The thrust magnetic bearing 14 and the micro holes 16a provide a thrust magnetic bearing function and rotate without contact.

Next, the operation will be explained. In the present invention,
The hardness A of the member of the fixed shaft 23 is about HRC60, the hardness B of the member of the hollow rotating shaft 15 is about HRC55, and the difference in hardness between the two is HRC5 or more, so the fixed shaft 23 of the hydrodynamic air bearing structure 11 Seizing, galling, etc. do not occur on the sliding surfaces between the outer circumferential surface 23a of the hollow rotary shaft 15 and the inner circumferential surface 15b of the hollow rotating shaft 15, and the rotation continues smoothly. Further, since the hardness of the stainless steel A of the fixed shaft 23 is higher than that of the stainless steel forming the conventional fixed shaft 5 by hardness HRC5, the fixed shaft 23
significantly improves both corrosion resistance and wear resistance.

Further, since the hardness A of the stainless steel A of the member of the fixed shaft 23 having the herringbone groove 25 is close to the Rockwell hardness HRC60 and has a high hardness, the fixed shaft 23
During production, the fixed shaft 23 can be produced by simply grinding the outer circumferential surface 23a, hardening the outer circumferential surface 23a, and then forming grooves by chemical etching. Therefore, a tempering process is not required, the number of production steps is reduced, and the production cost of the fixed shaft 23 can be significantly reduced.

In the above embodiment, the herringbone groove 25, which is a dynamic pressure generating groove, is formed on the fixed shaft 23, but the present invention is not limited to this embodiment. As shown, the dynamic pressure generating groove is located on the hollow rotating shaft 1.
It may be formed on the inner circumferential surface 15b of No. 5. In this case, the hardness A of the stainless steel A forming the hollow rotating shaft 15 is equal to that of the fixed shaft 2.
The hardness B of the stainless steel B forming the second embodiment is higher by HRC5 than the hardness B of the stainless steel B forming the third embodiment, and has the same effect as the first embodiment.

Next, another embodiment of the present invention will be explained. FIGS. 2A to 2H are diagrams showing second to tenth embodiments according to the present invention, and the same components as in the first embodiment are given the same reference numerals. The embodiment shown in FIGS. 2(a) to 2(c) is a radial dynamic pressure air bearing or a modified bearing thereof, in which the central shaft 33
is rotatable and has a dynamic pressure generating groove 25 on the outer circumferential surface 33a of the central shaft 33. The hardness of the member of the central shaft 33 having the dynamic pressure generating groove 25 is higher than the hardness of the member of the sliding shaft 15. In the second embodiment shown in FIG. 2(a), the dynamic pressure generating groove 25 is formed by forming a plurality of axially elongated grooves in the circumferential direction on the outer circumferential surface 33a of the central shaft 33, and a pair of upper and lower grooves. This is a case in which radial dynamic pressure can be generated by rotating in either direction of the arrow. In the third embodiment shown in FIG. 2(b), the dynamic pressure generating groove 25 is formed in a hemispherical surface 33b which is the outer circumferential surface of the central shaft 33 and is also the bearing surface at the lower end in the axial direction. This is a case in which the hemispherical concave surface portion 35a, which is the sliding surface, is fitted. In the fourth embodiment shown in FIG. 2(c), the dynamic pressure generating groove 25 is formed on the outer peripheral surface of the central shaft 33 and on a semi-conical surface 33c which is a bearing surface at the lower end in the axial direction, and the semi-conical surface 33c is a sliding surface. This is a case where the shaft 35 is fitted into a semi-conical concave portion 35b which is a sliding surface.

The embodiments shown in FIGS. 2(d) to 2(g) are thrust dynamic pressure air bearings or modified bearings thereof. The fifth embodiment shown in FIGS. 2(d) and (e), the sixth embodiment shown in FIG. 2(f), and the seventh embodiment shown in FIG. 2(g) have spiral grooves 25 as dynamic pressure generating grooves. It is formed on the disk-shaped sliding surface 41a of the sliding shaft 41. This sliding surface 41a slides on a bearing surface 40a that is substantially orthogonal to the axis C of the cylindrical central shaft 40, a portion of which is shown in FIG. 2(e).

In the fifth embodiment, air is sucked in from the outside of the spiral groove, and in the sixth embodiment, air is sucked in from the inside (center). The seventh embodiment shown in FIG. 2(g) has a herringbone groove. These Figure 2 (d
) to (g), the hardness of the members of the sliding shaft 41 of the fifth to seventh embodiments is as follows:
It has a Rockwell hardness HRC5 value higher than that of other members.

Further, the eighth to tenth embodiments shown in FIGS. 2(h) to (k), respectively, are thrust dynamic pressure air bearings having a sliding shaft 41 with dynamic pressure generating grooves 25 formed on the sliding surface 41a, or the like. It is a bearing of deformation. In the fifth to seventh embodiments, the sliding shaft 4
This is a case where each disc-shaped sliding surface 41a has a stepped groove, a tapered land, and a plurality of radial grooves with inclined surfaces. The hardness of the member of the sliding shaft 41 is higher than the hardness of the member of the central shaft 40 by Rockwell hardness HRC5.

[0029]

[Effects of the Invention] As explained above, according to the present invention,
The hardness of the member forming the shaft having the outer circumferential surface or bearing surface provided with grooves for generating dynamic pressure of the hydrodynamic air bearing is higher than the hardness of the shaft having the sliding surface that slides on the outer circumferential surface or bearing surface. By doing so, it is possible to improve the corrosion resistance of the shaft with grooves and to significantly suppress the occurrence of corrosion from the grooves for generating dynamic pressure.
It is possible to obtain a hydrodynamic air bearing structure in which heat treatment conditions during groove processing can be relaxed, man-hours can be reduced, manufacturing costs can be reduced, and reliability can be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of a hydrodynamic air bearing structure according to claims 1 to 3 of the present invention, in which (a) is an overall sectional view;
b) is a sectional view of the main part thereof.

FIG. 2 is a diagram showing other embodiments of the hydrodynamic air bearing structure according to the present invention, in which (a) to (c) are main points of the second to fourth embodiments of the radial hydrodynamic air bearing and its modified bearing, respectively. (d) to (g) respectively show the main parts of the thrust dynamic pressure air bearing or its modified bearing, (d), (f),
(g) is a plan view of the sliding shaft of the fifth to seventh embodiments, respectively;
(e) is a partial sectional view in the circumferential direction of the fifth embodiment, (h) to (
(k) shows the main parts of the stepped groove thrust hydrodynamic air bearing or its modified bearing, (h) is a plan view of the sliding surface of the eighth embodiment, and (i) shows one part of the sliding surface in the circumferential direction. Partial sectional view, (
j) and (k) are partial cross-sectional views in the circumferential direction of the ninth and tenth embodiments, respectively.

FIG. 3 is a diagram showing a polygon scanner using a conventional dynamic pressure air bearing structure, in which (a) is an overall sectional view thereof, and (b) is another overall sectional view.

[Explanation of symbols]

11 Dynamic pressure air bearing structure 15 Hollow rotating shaft (sliding shaft) 15b Inner peripheral surface (sliding surface) 23 Fixed shaft (center shaft) 23a Outer peripheral surface 25 Herringbone groove (dynamic pressure generating groove) 33, 4
0 Central axis 33b Hemispherical surface (outer peripheral surface) 33c Semi-conical surface (outer peripheral surface) 35 Sliding shafts 35a, 35b Concave surface portion (sliding surface) 40a Bearing surface 41 Sliding shaft 41a Sliding surface C Axis

Claims (3)

[Claims] 1. A central shaft made of metal and having a circular cross-sectional outer circumferential surface or a bearing surface substantially perpendicular to the axis of the outer circumferential surface, and a central axis that is coaxial with the central axis and slides on the outer circumferential surface or the bearing surface. a sliding shaft having a sliding surface, the outer circumferential surface, the bearing surface, and the sliding surface each having a dynamic pressure generating groove; The hardness of the member forming the central shaft or the sliding shaft having the dynamic pressure generating groove is such that the sliding shaft slides opposite to the member. Alternatively, a hydrodynamic air bearing structure characterized in that the hardness is higher than that of the member forming the central shaft. 2. The dynamic pressure air bearing structure according to claim 1, wherein the central shaft is made of stainless steel and has a dynamic pressure generating groove on the outer peripheral surface. 3. The sliding shaft is made of stainless steel,
2. The hydrodynamic air bearing structure according to claim 1, further comprising an inner circumferential surface that slides on the outer circumferential surface, and a dynamic pressure generating groove on the inner circumferential surface.