JP4753250B2 - Hydrodynamic bearing device and rotating device - Google Patents

Description

  The present invention relates to a hydrodynamic bearing device and a rotating device that rotatably supports a rotating polygon mirror used in an optical apparatus such as a laser printer or a barcode reader.

  Fluid bearings are used in devices that rotate and support rotating polygonal mirrors used in image forming equipment such as laser printers and barcode readers in order to enable high-speed rotation. Especially when rotating at high speed, so-called air dynamic pressure bearings are mainly employed. However, since air dynamic pressure bearings made of ceramics with high precision are very expensive, today dynamic pressure bearings using a lubricating fluid instead of air are being adopted.

  However, when a copper alloy is used for the bearing, lead contained in the alloy may be dissolved into the lubricating fluid, and the viscosity of the lubricating fluid may increase to cause seizure and reduce lubricity. Also, in many image forming apparatuses equipped with such a bearing device, the power is turned on only when image formation is performed for power saving, and the above-described bearing portion needs to be intermittently driven and stopped repeatedly. . For this reason, in the low speed rotation at the time of starting the motor, the bearing inner hole may be damaged, worn or burned by contact between the bearing sleeve and the shaft. Further, the generated friction powder may be mixed in the lubricating fluid and hinder the rotational drive.

In order to prevent this, the bearing sleeve is generally subjected to surface treatment such as electroless nickel-phosphorus, nickel-phosphorus-polytetrafluoroethylene, or nickel-phosphorus-boron plating. As disclosed in Patent Document 1, this method increases the surface hardness of the bearing sleeve and improves the wear resistance, so that there is an effect of increasing the bearing life.
JP 2005-242042 A

  However, if the bearing sleeve is plated and then the thrust plate is caulked and fixed to hold the lubricating fluid, the bending causes distortion in the compression direction inside the caulking portion and in the tension direction outside the caulking portion. And since the plating film is harder than the bearing material, the plating film cracks due to expansion and contraction of the inner and outer surfaces during caulking, and the film is peeled off. If the film of the caulking part is peeled off, it adheres to the lens in the scanner unit or damages the mirror. In addition, there is a problem that a short circuit occurs due to adhesion to the motor board or coil.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and includes a hydrodynamic bearing device and a rotating device capable of preventing cracking of a plating film when a thrust plate is caulked and fixed to a bearing sleeve. It is intended to provide.

In order to achieve the above object, a hydrodynamic bearing device according to the present invention includes a bearing sleeve, a shaft rotatably fitted in a bearing inner hole of the bearing sleeve, a fluid filled in the bearing sleeve, in the fluid bearing device comprising a thrust plate fixed by caulking, the caulking portion of the bearing sleeve so as to support the bottom of at least the inner surface is coated is formed by electroless nickel-phosphorus plating of the bearing sleeve, the bearing The film thickness of the coating in the inner hole is 3.0 μm or more and 5.0 μm or less, and the film thickness of the coating in the caulking portion is 1.5 μm or more and 70% or less of the film thickness of the coating in the bearing inner hole. characterized in that there.

  When forming a wear-resistant film on the bearing sleeve, the film thickness at the caulking portion for fixing the thrust plate is made thinner than the film thickness of the bearing inner hole. This provides flexibility to the coating of the caulking portion, and prevents the coating from cracking due to distortion that occurs when the thrust plate is caulked on the bearing sleeve.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the hydrodynamic bearing device of the motor unit of the rotating device that rotates the rotary polygon mirror 1 having a plurality of reflecting surfaces on the side surface of the polygonal column shape is a rod-shaped rotation that is rotatably fitted to the bearing sleeve 2. It has an axis (axis) 3. A rotor frame 5 is coupled to the rotary shaft 3 via a rotor boss 4, and a stator coil 7 is fixed to the base plate 6. The stator coil 7 rotates the rotary polygon mirror 1 so as to face the rotor magnet 8 supported inside the rotor frame 5. The rotary polygon mirror 1 is pressed against the rotor boss 4 by a pressing plate 9 and is integrated with a rotating portion including the rotor boss 4, the rotor frame 5, the rotor magnet 8, and the like.

  The bearing sleeve 2 has a cylindrical bearing inner hole for fitting with the rotary shaft 3, and a caulking portion 11 for caulking and fixing the thrust plate 10 is formed at one end of the bearing sleeve 2. Often hardened steel or hardened stainless steel is used for the rotating shaft 3 and the bearing sleeve 2 has high workability, so aluminum alloy: Al—Mg, Al—Zn—Mg and copper alloy: brass are used. There are many.

  As shown in FIG. 2, upper and lower two herringbone-like dynamic pressure generating grooves 12 a and 12 b are formed in a bearing inner hole of the bearing sleeve 2. Further, a coating film (plating film) by plating is formed on at least the inner surface of the bearing sleeve 2. When the rotating shaft 3 is rotated by driving the motor, the lubricating fluid in the bearing gap is brought to the center of each dynamic pressure generating groove, the pressure of the lubricating fluid is increased, and the rotating shaft 3 is separated from the bearing inner hole of the bearing sleeve 2. Non-contact rotation by lubrication. As a result, the bearing device can have lower wear and longer life.

  In order to fill the bearing sleeve 2 with a lubricating fluid after plating, a thrust plate 10 for supporting the lower end of the rotary shaft 3 is inserted into the caulking portion 11 of the bearing sleeve 2 and fixed by caulking, as shown in FIG.

  That is, the thrust plate 10 is caulked and fixed to one end of the bearing in order to create a sealed space in which the lubricating oil used as the lubricating fluid is filled in the bearing sleeve 2. As the lubricating oil used here, oils such as diester type and polyol ester type can be used.

  The bearing sleeve 2 is plated with electroless nickel-phosphorus plating or the like on at least the inner surface as described above in order to obtain wear resistance at the sliding portion with the rotating shaft 3. The phosphorus content in the film formed by plating is usually about 2 to 12 wt%.

  The thickness of the plating film is preferably in the range of 2 to 10 μm in the bearing inner hole because of durability due to contact with the bearing sleeve 2. On the other hand, the caulking portion 11 is made thinner than the thickness of the plating film in the bearing inner hole. The plating film thickness of the caulking portion is preferably 70% or less of the plating film thickness of the bearing inner hole. If it is 70% or more, there is a risk of cracking in the plating film when the thrust plate 10 is caulked.

  4 and 5 show a process of plating the bearing sleeve 2. The bearing sleeve 2 is placed on the masking jig 13 and set in the metal cage 14 so that the bearing inner hole is vertical. The metal cage 14 is immersed in the plating solution tank 15 and plated while being periodically rocked up and down (about 5 to 20 times / min) by the vertical rocking unit 16. During the plating process, after a predetermined time has elapsed, the masking jig 13 is removed from the bearing sleeve 2 and the plating is continued, so that only the plating film thickness of the caulking portion 11 masked by the masking jig 13 is reduced. The film thickness is obtained.

  As the plating solution for forming the plating film, a commercially available electroless nickel-phosphorous plating solution or the like is used. The process conditions are, for example, a bath temperature of 82 to 94 ° C. and a pH of 5 to 6.

  The bearing sleeve shown in FIG. 1 was subjected to a plating process under different processing conditions as shown in Table 1 at the end. For Examples 1 to 5 and Comparative Examples 1 to 3, the plating film thickness measurement of the bearing sleeve, the caulking of the thrust plate, and the continuous durability test were performed as follows.

<Film thickness measurement>
The thickness of the plating film in the caulking portion was measured by cutting the bearing sleeve in half in the full length direction, and observing the cut surface of the plating film with a scanning electron microscope (HITACHI S-4300).

The film thickness of the plating film in the bearing inner hole was measured by first measuring the dynamic pressure inner diameter of the bearing inner hole before and after plating using a gap jet (manufactured by Tokyo Seimitsu Co., Ltd.), and calculating the film thickness from the following formula.
Plating film thickness = (inner diameter before plating−inner diameter after plating) / 2 × 1000

  The thrust plate was caulked and fixed by caulking the thrust plate to the bearing sleeve with a propulsive force of 35 kgf using a rivet machine (US-1 manufactured by Yoshikawa Seiko Co., Ltd.).

  The bearing sleeves used in Examples 1 to 5 were 14.0 mm in length, the inner diameter was 3.00, and the material was brass. The plating process was performed as follows using the apparatus of FIG.

  The bearing sleeve was placed on the masking jig, set in a metal cage, immersed in a plating solution together with the metal cage, and plated while periodically rocking up and down 15 times / minute. During the plating, the masking jig was removed from the bearing sleeve, and the plating was continued for a predetermined time.

In addition, 100 samples were prepared for each example. The plating solutions and compositions used in Examples 1 to 5 are as follows.
Plating solution: Nickel Boomer LP-26 (Nippon Chemical Industry Co., Ltd.)
(Electroless nickel-phosphorus plating, low phosphorus type)
Nickel Boomer LP-26-A 90ml / L
Nickel Boomer LP-26-B 200ml / L
Pure water 710ml / L

  In Comparative Examples 1-3, the same dipping / swinging conditions were set using the same bearing sleeve, plating apparatus, and plating solution as in Examples 1-5.

  In Comparative Examples 1 and 2, the masking time was shortened compared to Examples 1 to 5, and in Comparative Example 3, the bearing sleeve was installed vertically on the metal cage without using the masking jig, Plating was performed uniformly.

  Thrust plates were caulked to 100 bearing sleeve samples prepared in Examples 1 to 5 and Comparative Examples 1 to 3, respectively, and it was confirmed whether or not the plating film of the caulking portion was cracked. As a result, as shown in Table 1, in Examples 1 to 5, cracks in the caulking portion did not occur, but in Comparative Examples 1 to 3, cracks occurred in the plating film. From this, it was found that if the plating film thickness of the caulking part is 70% or less of the plating film thickness of the bearing inner hole, cracking of the caulking part plating film that occurs when the thrust plate is caulked can be prevented.

It is a mimetic diagram showing a fluid dynamic bearing device by one embodiment. It is sectional drawing which shows only the bearing sleeve of the apparatus of FIG. FIG. 3 is an enlarged partial cross-sectional view showing an enlarged crimped portion of the bearing sleeve of FIG. 2. It is a figure explaining a masking jig. It is a figure explaining a plating apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rotating polygon mirror 2 Bearing sleeve 3 Rotating shaft 5 Rotor frame 7 Stator coil 8 Rotor magnet 9 Presser plate 10 Thrust plate 11 Caulking part 13 Masking jig 14 Metal cage 15 Plating tank

Claims (2)

A bearing sleeve, a shaft that is rotatably fitted in a bearing inner hole of the bearing sleeve, a fluid filled in the bearing sleeve, and a caulking portion of the bearing sleeve so as to support a lower end of the shaft. In the hydrodynamic bearing device having a thrust plate, a coating by electroless nickel phosphorus plating is formed on at least the inner surface of the bearing sleeve, and the thickness of the coating in the bearing inner hole is 3.0 μm or more. A hydrodynamic bearing device, wherein the film thickness is 0 μm or less, and the film thickness of the film in the caulking portion is 1.5 μm or more and 70% or less of the film thickness of the film in the bearing inner hole. A rotating device comprising: a motor unit including the hydrodynamic bearing device according to claim 1; and a rotary polygon mirror rotated by the motor unit.

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