JP3282307B2 - Rotary drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION A rotary drive according to the present invention comprises:
For example, light forming laser printers and digital copiers
A laser beam emitted from a laser irradiator is incorporated in a deflecting device and used to scan toward a photosensitive drum.

[0002]

2. Description of the Related Art Conventionally, an optical deflection device having a structure as shown in FIG. 2 has been known. At the center of a housing 1 made of an aluminum alloy, a base end of a pivot 2 made of an iron-based alloy such as stainless steel is fixed. A cylindrical sleeve 3 is arranged around the pivot 2.
A dynamic pressure gas bearing is provided between the inner peripheral surface of the sleeve 3 and the outer peripheral surface of the pivot 2. Therefore, when the sleeve 3 rotates at a high speed, the inner peripheral surface of the sleeve 3 and the pivot 2
Is in a non-contact state with the outer peripheral surface of.

A cover 4 is attached to an upper end opening of the sleeve 3, and a lower end opening of a flow hole 5 formed in the center of the cover 4 in a vertical direction is formed on the pivot 2. It faces the end face. When the sleeve 3 rotates, gas is sucked into the bearing gap 6 between the outer peripheral surface of the pivot 2 and the inner peripheral surface of the sleeve 3 by the dynamic pressure groove 27 provided in the sleeve 3, and this gas causes the inside of the sleeve 3 to be sucked. The peripheral surface and the outer peripheral surface of the pivot 2 are kept in a non-contact state, and the lower surface of the lid 4 is separated from the upper end surface of the pivot 2.

A polygon mirror 8 as a driven member for reflecting laser light is supported and fixed on an upper surface of a mounting flange 7 formed on an outer peripheral surface of an intermediate portion of the sleeve 3. A rotor 9 is supported on the outer peripheral surface of the intermediate portion of the sleeve 3 below the mounting flange 7. On the other hand, an electric motor 11 for rotating the sleeve 3 by fixing a stator 10 on the inner peripheral surface of the housing 1 and making the stator 10 face the rotor 9.
Is composed.

[0005] The object of the present invention , configured as described above, is as follows .
When using an optical deflector incorporating a rotary drive ,
By energizing the stator 10, the sleeve 3 and the polygon mirror 8 are rotated. As the rotational speed of the sleeve 3 increases, the inner peripheral surface of the sleeve 3, the outer peripheral surface of the pivot 2, the lower surface of the lid 4, and the upper end surface of the pivot 2 based on the action of the dynamic pressure gas bearing. Are in a non-contact state.

In this state, when a laser beam is projected from the transparent window 25 provided on the outer peripheral wall of the housing 1 onto the outer peripheral surface of the polygon mirror 8 at an appropriate timing, the laser light reflected on the outer peripheral surface is applied to the surface of the photosensitive drum. Is scanned.

[0007]

SUMMARY OF THE INVENTION However, the rotation and rotation built in the conventional light deflecting device , which is constructed and operates as described above, is performed.
In the case of a driving device , there are problems to be solved as described below.

That is, the rotation incorporated in the conventional light deflecting device
In the drive device , the pivot 2 is made of rust-resistant stainless steel. And the bearing gap 6 due to the temperature change
The sleeve 3 is made of a cemented carbide or structural steel in order to suppress the dimensional change of the above, and nickel-based hard plating is applied to the surface of the sleeve 3 for the purpose of rust prevention and improvement of slidability. The polygon mirror 8 made of an aluminum alloy is fixed around the sleeve 3. Therefore, when the temperature of the rotary driving device incorporated in the light deflecting device rises, it is inevitable that a considerable difference in thermal expansion occurs between the two members 3 and 8. More specifically, when the temperature rises, the amount of thermal expansion of the polygon mirror 8 is considerably larger than the amount of thermal expansion of the sleeve 3.

When the polygon mirror 8 is supported and fixed to the sleeve 3, the polygon mirror 8 is
The polygon mirror 8 is screwed to the mounting flange 7 while being externally fitted by a clearance fit. However, when the temperature rises, the gap between the inner peripheral surface of the polygon mirror 8 and the outer peripheral surface of the sleeve 3 increases due to the thermal expansion of the polygon mirror 8, and the mounting position of the polygon mirror 8 shifts in the diameter direction.

If the mounting position of the polygon mirror 8 shifts in the diameter direction due to such a cause, the dynamic imbalance of the member rotating at a high speed together with the polygon mirror 8 becomes large, and the polygon mirror is rotated by centrifugal force due to the rotation. 8 vibrates finely. Such vibration is not preferable because it causes the printing quality of a laser printer or the like to deteriorate due to a shift in the scanning position of the laser beam.

The temperature of the light deflecting device rises based on the friction between the gas present in the housing 1 and the surface of a member that rotates at a high speed during use, such as the polygon mirror 8, and decreases when the use is stopped. The polygon mirror 8 repeats thermal expansion and contraction, and each time the mounting position of the polygon mirror 8 with respect to the sleeve 3 is slightly different. Also in such a case, the polygon mirror 8 vibrates finely, which causes a deterioration in print quality.

In particular, in recent years, there has been a tendency to rotate the larger-diameter polygon mirror 8 at a higher speed for the purpose of improving the printing quality and increasing the printing speed. As the temperature rise becomes more remarkable, the deterioration of print quality due to the above-mentioned causes cannot be ignored.

[0013] Also, while the pivot 2 is made of stainless steel,
When the sleeve 3 is made of an aluminum alloy,
As the temperature rises, the size of the bearing gap 6 existing between the outer peripheral surface of the pivot 2 and the inner peripheral surface of the sleeve 3 increases. The dimensions of the bearing gap 6 are as small as about several to several tens of μm, and the ratio of the increase due to the temperature change to the above dimensions is considerably large. As a result, the performance of the dynamic pressure bearing greatly changes with the temperature change, and in some cases, the optical deflecting device may not be able to maintain the expected performance. The rotary drive device of the present invention has been invented in view of such circumstances.

[0014]

The rotary driving device according to the present invention comprises:
A housing, a pivot shaft whose base end is fixedly connected to the housing, a sleeve rotatably supported around the pivot shaft via a dynamic pressure bearing, and a sleeve supported by the sleeve.
And a driven member . Then, both a and a driven member said pivot and the sleeve is aluminum alloy, the difference between the mutual thermal expansion coefficient between the pivot and the sleeve and within 15%, the difference of each other in thermal expansion coefficient between the sleeve and the driven member the are within 15%.

[0015]

In the rotary driving device of the present invention having the above-described structure, the size of the bearing gap existing between the outer peripheral surface of the pivot and the inner peripheral surface of the sleeve greatly changes even when the temperature rises. In addition, the gap between the inner peripheral surface of the driven member and the outer peripheral surface of the sleeve does not increase, and the mounting position of the driven member does not shift in the diametric direction. Therefore, there is little change in the performance of the dynamic pressure bearing, and the dynamic balance during high-speed rotation does not change .
The performance of the seed equipment can be maintained.

[0016]

FIG. 1 shows an embodiment of the present invention. The housing 12 is formed by combining a substrate part 13 and an upper lid part 14, each of which is made of an aluminum alloy, and has a closed space 15 inside. A plurality of radiating fins 24 are formed on the lower surface of the substrate portion 13.
A lower end of a pivot 16 made of an aluminum alloy is supported and fixed at the center of the upper surface of the substrate 13. That is, the lower end of the pivot 16 is inserted into the concave hole 17 formed in the center of the upper surface of the substrate portion 13 without looseness, and the through hole 26 formed in the central portion of the lower surface of the substrate portion 13 forms the concave hole. 1
The screw 23 inserted into the shaft 7 is screwed into a screw hole 18 formed in the lower end surface of the pivot 16 and further tightened.

The pivot 16 constitutes a hydrodynamic gas bearing 20 together with a sleeve 19 made of an aluminum alloy. Therefore, the dynamic pressure grooves 21 are formed on the inner peripheral surface of the sleeve 19. A mounting flange 22 is provided on the outer peripheral surface of the intermediate portion of the sleeve 19, and a polygon mirror 8 made of an aluminum alloy, which is a driven member, fitted to the sleeve 19 and fixed to the mounting flange 22 by screwing.

The other structure is the same as the above-mentioned conventional structure. Further, when using the optical deflecting device incorporating the rotary driving device , the electric motor 11 causes the sleeve 19 to rotate.
And a polygon mirror 8 fixed to the sleeve 19
To rotate. As the rotational speed of the sleeve 19 increases, a dynamic pressure is generated between the inner peripheral surface of the sleeve 19 and the outer peripheral surface of the pivot 16, so that the peripheral surfaces do not come into contact with each other. Therefore, the polygon mirror 8 can be rotated at high speed for a long time.

Particularly, in the case of an optical deflection device incorporating the rotary drive device of the present invention, the pivot 16 and the sleeve 19 are connected to each other.
Since the bearing is made of an aluminum alloy having a difference in thermal expansion coefficient of 15% or less, the size of the bearing gap 6 existing between the outer peripheral surface of the pivot 16 and the inner peripheral surface of the sleeve 19 even when the temperature rises. There is no significant change. Therefore, the performance change of the dynamic pressure gas bearing 20 is small, and the rotary drive device is incorporated.
Attained the performance maintenance of the light deflection device've got. Also, sleeve 19
And the polygon mirror 8 have a difference in thermal expansion coefficient of 15
%, The mounting position of the polygon mirror 8 with respect to the sleeve 19 does not shift, and the balance during rotation does not break with repeated use. Further, in the illustrated embodiment, the heat radiation fins 24, 24 formed on the lower surface of the substrate portion 13 can suppress the rise in temperature of each portion, so that the above-described performance change is minimized and the balance during rotation is prevented from being lost. Great effect.

The aluminum alloy constituting the pivot 16 and the sleeve 19 is JIS A2017 and A2218.
, A5056, A6262, and A7075 are JIS A2 as aluminum alloys constituting the polygon mirror 8.
218 and A5056 can be used , respectively . Since each of these aluminum alloys has a coefficient of thermal expansion at 25 ° C. in the range of 20 to 25 × 10 ⁻⁶ ,
The difference in the amount of thermal expansion between 6, 19 and 8 can be kept small. Accordingly, it is possible to prevent the mounting position of the polygon mirror 8 with respect to the sleeve 19 from being shifted due to the repetition of the operation and the stop of the optical deflector incorporating the rotary drive device , and to maintain the performance of the dynamic pressure gas bearing 20.

If the surface of the pivot 16 is subjected to a surface treatment such as electroless nickel plating, alumite treatment, or ceramic coating, the surface of the pivot 16 can be hardly damaged. Furthermore, if a resin coating based on polyphenylene sulfide resin (PPS), polyamide imide resin, or the like is applied to the outer peripheral surface, the sliding characteristics of the outer peripheral surface are improved (slippery), and a rotary drive device is assembled.
It is possible to improve the durability associated with starting and stopping of the light deflecting device.

In this case, the pivot 1 made of aluminum alloy is used.
6, the surface of the pivot 16 is first subjected to a surface hardening treatment such as nickel plating or Kanigen plating, and then the end surface and the outer diameter surface of the pivot 16 are finished to predetermined dimensions. After applying a resin coating to the surface of the shaft 16, it is preferable to finish only the outer diameter surface of the pivot 16 to a predetermined size by centerless grinding from the viewpoint of processing and handling to prevent damage. This is the pivot 16
The upper end surface is formed as a spherical convex surface for the purpose of reducing the starting torque and improving the durability of starting and stopping. This is because it is effective when clamping the outer diameter surface of the pivot 16 to finish the spherical convex surface.

If carbon fiber is mixed into the synthetic resin for coating the surface of the pivot 16 and the coating layer is made conductive, the presence or absence of protrusions on the bearing surface can be confirmed by a rotation test. Assurance becomes easier.

On the other hand, the inner peripheral surface of the sleeve 19 is less likely to be damaged during handling and the like than the outer peripheral surface of the pivot 16.
Although the necessity of performing a surface treatment is lower than that of the outer peripheral surface of the pivot shaft 16, if the same surface hardening treatment as that of the outer peripheral surface of the pivot 16 is performed, there is an advantage that the surface is hardly damaged at the time of assembling or use. For example, a sleeve 19 made of an aluminum alloy manufactured by a cutting process
After forming the dynamic pressure grooves 21 by plastic working on the inner peripheral surface of
Electroless nickel plating, Kanigen plating,
If a surface hardening treatment such as alumite treatment is applied,
The inner peripheral surface can be hardened without complicating the forming work of 21 . When the forming operation of the dynamic pressure grooves 21 is performed by plastic working such as rolling, each dynamic pressure groove 2 is formed with the working.
Since the periphery of 1 rises, it is preferable that finishing processing such as lapping or honing is performed after the groove processing to remove the raised portion.

In the illustrated embodiment, since the pivot 16 is detachably connected to the substrate 13 by the screws 23, when the defect of the pivot 16 is found during the assembly inspection process, etc. The replacement of the pivot 16 can be easily performed. That is, as in the conventional structure shown in FIG. 2, when the housing 1 is made of an aluminum alloy and the pivot 2 is made of stainless steel, the pivot 2 is fixed to the housing 1 by shrink fitting. It can be disassembled by heating both members 1 and 2. However, as in the present invention,
When both the pivot 16 and the substrate 13 are made of an aluminum alloy, there is no difference in thermal expansion between the two members 16 and 13, so when these two members 16 and 13 are joined by shrink fitting, Difficult to disassemble from. The illustrated embodiment solves such a problem, and replaces the pivot 16 when the defect of the pivot 16 is found during the assembly inspection process.
The yield can be improved.

In the thrust bearing provided between the sleeve 19 and the pivot 16, the lower surface of the lid 4 may be a spherical convex surface and the upper end surface of the pivot 16 may be a flat surface. Further, the thrust bearing is not limited to the dynamic pressure gas bearing as in the illustrated embodiment, but may be a magnetic bearing that supports a thrust load by magnetic attraction. It is preferable that the rotor 9 constituting the electric motor 11 is fixed directly or indirectly to the sleeve 19 by shrink fitting or press fitting in order to prevent the movement of the rotor 9 due to a temperature change. However, when the mass of the rotor 9 is sufficiently smaller than the mass of the polygon mirror 8, the rotor 9 may be bonded and fixed to the sleeve 19.

[0027]

The rotary drive device of the present invention is constructed and operates as described above. However, the performance change of the dynamic pressure bearing due to the temperature change and the dynamic balance change during high-speed rotation are reduced, and It is possible to obtain the expected performance regardless of the difference.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing one example of a conventional structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Housing 2 Axis 3 Sleeve 4 Lid 5 Communication hole 6 Bearing gap 7 Mounting flange 8 Polygon mirror 9 Rotor 10 Stator 11 Electric motor 12 Housing 13 Substrate 14 Upper lid 15 Sealed space 16 Axis 17 Concave hole 18 Screw hole 19 Sleeve 20 Dynamic pressure gas bearing 21 Dynamic pressure groove 22 Mounting flange 23 Screw 24 Radiation fin 25 Transparent window 26 Through hole 27 Dynamic pressure groove

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shigeru Endo 3-6-10 Kumaguma Shinmei, Fujisawa City, Kanagawa Prefecture (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 26/10

Claims (4)

(57) [Claims] 1. A housing, a pivot having a base end coupled to and fixed to the housing, a sleeve rotatably supported around the pivot via a dynamic pressure bearing, and a driven shaft supported by the sleeve. and a member, both a and a driven member said pivot and the sleeve is aluminum alloy, the difference between the mutual thermal expansion coefficient between the pivot and the sleeve and within 15%, to one another in thermal expansion between the sleeve and the driven member rotary driving device and the difference coefficient is within 15%. 2. The rotary drive device according to claim 1, wherein at least one of the outer peripheral surface of the pivot and the inner peripheral surface of the sleeve is subjected to a surface treatment. 3. The rotary drive device according to claim 1, wherein a resin coating is applied to an outer peripheral surface of the pivot. 4. The rotary drive device according to claim 3, wherein the resin coating is made of synthetic resin having conductivity.