JPH0756102A - Light deflector - Google Patents

Abstract

PURPOSE:To lessen performance change in a light deflector constituted of a sleeve, a pivot, and a polygon mirror regardless of temperature change. CONSTITUTION:The polygon mirror 8 is fixed on the outer peripheral surface of the sleeve 19. Both members 8 and 19 rotate around the periphery of the pivot 16 at a high speed in the case they are used. The pivot 16, the sleeve 19 and the polygon mirror 8 are made respectively of aluminum alloys having nearly equal coefficients of thermal expansion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The optical deflector according to the present invention is incorporated in, for example, a laser printer or a digital copying machine,
It is used to scan the laser beam emitted from the laser irradiator toward the photosensitive drum.

[0002]

2. Description of the Related Art Conventionally, an optical deflector having a structure as shown in FIG. 2 has been known. A base end of a pivot 2 made of an iron-based alloy such as stainless steel is fixed to the center of the aluminum alloy housing 1. A sleeve 3 having a tubular shape 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 not in contact with the outer peripheral surface of the.

A lid 4 is attached to the upper end opening of the sleeve 3, and a lower end opening of a through hole 5 formed in the central portion of the lid 4 in the vertical direction is provided on the pivot 2. It faces the end face. When the sleeve 3 is rotated, the dynamic pressure groove 27 provided in the sleeve 3 sucks gas into the bearing gap 6 between the outer peripheral surface of the pivot 2 and the inner peripheral surface of the sleeve 3, and the gas causes the inner space of the sleeve 3 to move. The peripheral surface and the outer peripheral surface of the pivot 2 are held in a non-contact state, and the lower surface of the lid 4 and the upper end surface of the pivot 2 are separated from each other.

A polygon mirror 8 for reflecting laser light is supported and fixed on the upper surface of a mounting flange 7 formed on the outer peripheral surface of the 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, the housing 1
The stator 10 is fixed to the inner peripheral surface of the
By making the rotor 9 and the rotor 9 face each other, an electric motor 11 for rotationally driving the sleeve 3 is configured.

When the optical deflecting device constructed as described above is used, the stator 3 is energized to rotate the sleeve 3 and the polygon mirror 8. As the rotation speed of the sleeve 3 increases, the inner peripheral surface of the sleeve 3 and the outer peripheral surface of the pivot 2, the lower surface of the lid 4 and the upper end surface of the pivot 2 due to the action of the dynamic pressure gas bearing. And become non-contact with each other.

In this state, if laser light 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 by this outer peripheral surface is reflected on the surface of the photosensitive drum. To be scanned.

[0007]

However, in the case of the conventional optical deflector constructed and configured as described above, the following problems to be solved arise.

That is, in the conventional optical deflector, the pivot 2 is made of rust-resistant stainless steel. Then, in order to suppress the dimensional change of the bearing gap 6 due to the temperature change, the sleeve 3 is made of cemented carbide or structural steel, and nickel is formed on the surface of the sleeve 3 for the purpose of preventing rust and improving slidability. The system is hard plated. Then, the polygon mirror 8 made of aluminum alloy is
It is fixed around the sleeve 3. Therefore, when the temperature of the optical deflector rises, it is unavoidable that a considerable difference in thermal expansion occurs between the two members 3 and 8. More specifically, when the temperature rises, the thermal expansion amount of the polygon mirror 8 is considerably larger than the thermal expansion amount of the sleeve 3.

When the polygon mirror 8 is supported and fixed to the sleeve 3, the polygon mirror 8 is attached to the sleeve 3.
The polygon mirror 8 is screwed to the mounting flange 7 while being 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 thermal expansion of the polygon mirror 8, and the mounting position of the polygon mirror 8 shifts in the diametrical direction.

When the mounting position of the polygon mirror 8 is displaced in the diametrical direction due to such a cause, the dynamic imbalance of the member that rotates at high speed together with the polygon mirror 8 becomes large, and the polygon mirror 8 is rotated by centrifugal force. 8 vibrates finely. Such vibration is not preferable because it causes deterioration in printing quality of a laser printer or the like due to a shift in scanning position of laser light.

Further, the temperature of the optical deflector rises based on the friction between the gas existing in the housing 1 and the surface of a member such as the polygon mirror 8 which rotates at a high speed during use, and decreases when the use is stopped. The polygon mirror 8 repeatedly undergoes thermal expansion and contraction, and the mounting position of the polygon mirror 8 on the sleeve 3 is slightly different each time. Even in such a case, the polygon mirror 8 vibrates finely and causes deterioration of print quality.

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

Also, while the pivot 2 is made of stainless steel,
When the sleeve 3 is made of 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 size of the bearing gap 6 is as small as several to ten and several μm, and the ratio of the increase due to temperature change to the above size is considerably large. As a result, there is a possibility that the performance of the dynamic pressure bearing will change significantly with changes in temperature, and in some cases the optical deflector will not be able to maintain the desired performance. The optical deflector of the present invention was invented in view of such circumstances.

[0014]

The optical deflector of the present invention is rotatably supported by a housing, a pivot having its base end coupled and fixed to the housing, and a dynamic pressure bearing around the pivot. And a polygon mirror supported by the sleeve. The axis, the sleeve, and the polygon mirror are all made of aluminum alloy, and the difference between the thermal expansion coefficients of the axis and the sleeve is 15% or less.
The difference between the thermal expansion coefficients of the sleeve and the polygon mirror is within 15%.

[0015]

In the optical deflector of the present invention constructed as described above, the size of the bearing gap existing between the outer peripheral surface of the pivot and the inner peripheral surface of the sleeve changes greatly even when the temperature rises. In addition, the gap between the inner peripheral surface of the polygon mirror and the outer peripheral surface of the sleeve does not become large, and the mounting position of the polygon mirror does not move in the diametrical direction. Therefore, there is little change in the performance of the dynamic pressure bearing, the dynamic balance during high-speed rotation does not change, and the performance of the optical deflector can be maintained.

[0016]

FIG. 1 shows an embodiment of the present invention. The housing 12 is formed by combining a substrate portion 13 and an upper lid portion 14 each made of an aluminum alloy, and has a closed space 15 inside. A plurality of heat radiation fins 24, 24 are formed on the lower surface of the substrate portion 13. or,
A lower end of a pivot 16 made of an aluminum alloy is supported and fixed to the central portion of the upper surface of the substrate portion 13. That is, the pivot 16 is formed in the concave hole 17 formed in the central portion of the upper surface of the substrate 13.
The lower end of the substrate part 1 without any rattling,
The screw 23 inserted into the concave hole 17 from the through hole 26 formed in the central portion of the lower surface of the screw 3 is screwed into the screw hole 18 formed in the lower end surface of the pivot 16, and is further tightened.

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

The other structure is similar to that of the conventional structure described above. In addition, when the light deflector is used, the electric motor 11
Thus, the sleeve 19 and the polygon mirror 8 fixed to the sleeve 19 are rotated. Sleeve 1
As the rotation speed of 9 increases, this sleeve 19
Dynamic pressure is generated between the inner peripheral surface of the shaft and the outer peripheral surface of the pivot 16, and the two 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.

In particular, in the case of the optical deflecting device of the present invention, the difference between the thermal expansion coefficients of the pivot 16 and the sleeve 19 is 1.
Since it is made of an aluminum alloy within 5%, 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 does not change significantly even when the temperature rises. Therefore, the change in the performance of the dynamic pressure gas bearing 20 is small, and the performance of the optical deflector can be maintained. Also, sleeve 1
9 and the polygon mirror 8 have a difference in coefficient of thermal expansion of 1
Since it is made of an aluminum alloy within 5%, the mounting position of the polygon mirror 8 with respect to the sleeve 19 does not shift, and the balance during rotation does not collapse with repeated use. Further, in the illustrated embodiment, by the radiation fins 24, 24 formed on the lower surface of the substrate portion 13,
Since the temperature rise of each part can be suppressed to a low level, the effect of reducing the above-mentioned performance change and the effect of preventing imbalance during rotation are large.

The aluminum alloys for the pivot 16 and the sleeve 19 are JIS A2017 and A2218.
, A5056, A6262, A7075, etc. are the JIS A2 aluminum alloys for the polygon mirror 8.
218 and A5056 can be used. Each of these aluminum alloys has a coefficient of thermal expansion of 20 to 25 ° C.
Since the range is 25 × 10 ⁻⁶ , the above-mentioned members 16, 19,
The difference in the amount of thermal expansion of No. 8 can be suppressed to be small. Therefore, it is possible to prevent the attachment position of the polygon mirror 8 with respect to the sleeve 19 from being displaced due to the repetition of the operation and stop of the optical deflector, and to maintain the performance of the dynamic pressure gas bearing 20.

If the surface of the pivot 16 is subjected to surface treatment such as electroless nickel plating, alumite treatment, or ceramic coating, the surface of the pivot 16 can be made less likely to be damaged. Furthermore, if a resin coating based on polyphenylene sulfide resin (PPS), polyamideimide resin, or the like is applied to the outer peripheral surface, the sliding characteristics of this outer peripheral surface are improved (slippery), and the optical deflector is activated. , The durability with stopping can be improved.

In this case, the pivot 1 made of aluminum alloy
The surface of 6 is not directly coated with resin, but the surface of the pivot 16 is first subjected to surface hardening treatment such as nickel plating or Kanigen plating, and then the end surface and the outer diameter surface of the shaft 16 are finished to a predetermined size, and then the shaft 16 is finished. It is preferable from the viewpoint of preventing scratches during processing and handling that the outer diameter surface of the pivot shaft 16 is finished to a predetermined size by centerless grinding after the surface of 16 is coated with a resin. This is the pivot 16
The upper end surface of is a spherical convex surface for the purpose of reducing the starting torque and improving the starting and stopping durability, and is effective when clamping the outer diameter surface of the pivot 16 to finish the spherical convex surface.

If carbon fibers are mixed into the synthetic resin coating the surface of the pivot 16 to make the coating layer conductive, the presence or absence of protrusions on the bearing surface can be confirmed by a rotation inspection. Warranty becomes easy.

On the other hand, the inner peripheral surface of the sleeve 19 is less likely to be damaged during handling as compared with the outer peripheral surface of the pivot 16, so that the pivot 16
Although it is less necessary to carry out the surface treatment as compared with the outer peripheral surface, the surface treatment similar to the outer peripheral surface of the pivot 16 has an advantage that it is less likely to be damaged during assembly or use. For example, a sleeve 19 made of aluminum alloy by cutting
After forming the dynamic pressure groove on the inner peripheral surface of the plastic by plastic working, if surface hardening treatment such as electroless nickel plating, Kanigen plating, alumite treatment is applied to this inner peripheral surface, the work of forming the dynamic pressure groove is troublesome. The inner peripheral surface can be cured without
Further, when the dynamic pressure groove forming work is performed by plastic working such as rolling, the periphery of each dynamic pressure groove rises along with the working. Therefore, it is preferable that finishing processing such as lapping or honing is performed after the groove processing. To remove the bulge.

Further, in the case of the illustrated embodiment, the pivot 16 is detachably connected to the base plate portion 13 by the screw 23. Therefore, when a defect of the pivot 16 is found during the assembly inspection process, for example. The axis 16 can be easily replaced. That is, as in the conventional structure shown in FIG. 2, when the housing 1 is made of aluminum alloy and the pivot 2 is made of stainless steel, even when the pivot 2 is fixed to the housing 1 by shrink fitting, It can be disassembled by heating both members 1 and 2. However, like the present invention,
When both the pivot 16 and the substrate 13 are made of aluminum alloy, there is no difference in thermal expansion between the members 16 and 13. Therefore, when the members 16 and 13 are joined by shrink fitting, It is difficult to disassemble from. The illustrated embodiment solves such a problem and replaces the pivot 16 when a defect of the pivot 16 is found in 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 a magnetic attraction force. Further, it is preferable to fix the rotor 9 constituting the electric motor 11 to the sleeve 19 directly or indirectly by shrink fitting or press fitting in order to prevent movement of the rotor 9 due to 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 optical deflecting device of the present invention is constructed and operates as described above, but the change in the performance of the dynamic pressure bearing and the change in the dynamic balance during high speed rotation due to temperature changes are reduced.
It is possible to obtain desired performance regardless of the difference in usage conditions.

[Brief description of drawings]

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

FIG. 2 is a vertical sectional view showing an example of a conventional structure.

[Explanation of symbols]

 1 Housing 2 Axis 3 Sleeve 4 Lid 5 Circulation Hole 6 Bearing Gap 7 Mounting Flange 8 Polygon Mirror 9 Rotor 10 Stator 11 Electric Motor 12 Housing 13 Board Part 14 Top Cover 15 Sealed Space 16 Axis 17 Recessed Hole 18 Screw Hole 19 Sleeve 20 Dynamic pressure gas bearing 21 Dynamic pressure groove 22 Mounting flange 23 Screw 24 Radiating fin 25 Transparent window 26 Through hole 27 Dynamic pressure groove

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Endo 3-6-10 Shinmei Kugenuma, Fujisawa City, Kanagawa Prefecture

Claims (1)

[Claims] 1. A housing, a pivot having a base end portion fixedly coupled to the housing, a sleeve rotatably supported around the pivot via a dynamic pressure bearing, and a polygon mirror supported by the sleeve. And the axis, the sleeve, and the polygon mirror are made of aluminum alloy, and the difference between the thermal expansion coefficients of the axis and the sleeve is 15%.
An optical deflecting device in which the difference between the thermal expansion coefficients of the sleeve and the polygon mirror is within 15%.