Rotational polygon mirror and light scanning unit employing the same

• US 20120050443A1
• Filed: 04/15/2011
• Published: 03/01/2012
• Est. Priority Date: 08/30/2010
• Status: Active Grant

• Current Assignee: HP Printing Korea Co., Ltd. (HP Inc.)
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Lim, Heon-hee
• Granted Patent: US 8,922,606 B2
• Time in Patent Office: Days
• US Class Current: 347/118
• CPC Class Codes: B41J 2/473 using multiple light beams, wavelengths or colours
• CPC Class Codes: G02B 26/12 using multifaceted mirrors
• CPC Class Codes: G02B 5/09 Multifaceted or polygonal mirrors , e.g. polygonal scanning mirrors; Fresnel mirrors
• CPC Class Codes: G02B 5/10 with curved faces

Abstract

A rotational polygon mirror includes a plurality of reflection surfaces that rotate with respect to a rotation axis, wherein each of the reflection surfaces has a convex shape and a cross-sectional profile perpendicular to the rotation axis having at least two inflection points.

Claims

1. A rotational polygon mirror comprising:

a plurality of reflection surfaces that rotate with respect to a rotation axis,

wherein each of the reflection surfaces has a convex shape and a cross-sectional profile perpendicular to the rotation axis having at least two inflection points.

2. The rotational polygon mirror of claim 1, wherein each of the plurality of reflection surfaces has a cross-sectional profile Y(X) that satisfies the following formula, when a line from a center of the cross-sectional profile to a point on the rotation axis is a Y axis and a line perpendicular to the Y axis and passing through the point on the rotation axis is an X axis in a cross-section perpendicular to the rotation axis:

Y(X)=AX⁴+BX²+C and 0<

√

(−

B/6A)<

C·

tan(180°

/N)

where N is the number of the reflection surfaces.

3. The rotational polygon mirror of claim 2, wherein coefficients A, B, and C of the cross-sectional profile Y(X) are determined by physical properties and a rotation speed of the rotational polygon mirror.

4. The rotational polygon mirror of claim 1, wherein each of the plurality of reflection surfaces has a cross-sectional profile Y(X) which satisfies the following formula, when a line from a center of the cross-sectional profile to a point on the rotation axis is a Y axis, and a line perpendicular to the Y axis and passing through a point on the rotation axis is an X axis in a cross-section perpendicular to the rotation axis, and a variation of the cross-sectional profile of each reflection surface deformed by a rotation with respect to a constant Y₀ as a reference cross-sectional profile determined by a size of the rotational polygon mirror is Δ

Y(X);

Y₀−

Δ

Y(X)−

0.2 μ

m≦

Y(X)≦

Y₀−

Δ

Y(X)+0.2 μ

m

5. The rotational polygon mirror of claim 4, wherein each of the plurality of reflection surfaces has a cross-sectional profile Y(X) which satisfies the following formula:

Y₀−

Δ

Y(X)−

0.1 μ

m≦

Y(X)≦

Y₀−

Δ

Y(X)+0.1 μ

m

6. The rotational polygon mirror of claim 4, wherein the variation AY(X) satisfies the following formula:

Δ

Y(X)=−

AX⁴−

BX²+Y₀−

C and 0≦

√

(−

B/6A)≦

C·

tan(180°

/N)

where N is the number of the reflection surfaces.

7. The rotational polygon mirror of claim 6, wherein coefficients A, B, and C of the cross-sectional profile Y(X) are determined by physical properties and a rotation speed of the rotational polygon mirror.

8. The rotational polygon mirror of claim 1, wherein a number of the plurality of reflection surfaces is four, a length of diagonal line of the rotational polygon mirror is 20 mm, and a thickness of the rotational polygon mirror is 2.5 mm.

9. The rotational polygon mirror of claim 1, wherein the rotational polygon mirror is formed of plastic.

10. The rotational polygon mirror of claim 9, wherein the plurality of reflection surfaces are coated with a reflection layer.

11. A light scanning unit comprising:

a light source that emits a light beam;

a rotational polygon mirror that deflects the light beam emitted from the light source in a main scanning direction; and

an imaging optical unit that images the light beam deflected by the rotational polygon mirror onto a surface being scanned,

wherein the rotational polygon mirror comprises a plurality of reflection surfaces that rotate with respect to a rotation axis, wherein each of the reflection surfaces has a convex shape and a cross-sectional profile perpendicular to the rotation axis having at least two inflection points.

12. The light scanning unit of claim 11, wherein each of the plurality of reflection surfaces has a cross-sectional profile Y(X) that satisfies the following formula, when a line from a center of the cross-sectional profile to a point on the rotation axis is a Y axis and a line perpendicular to the Y axis and passing through the point on the rotation axis is an X axis in a cross-section perpendicular to the rotation axis:

Y(X)=AX⁴+BX²+C and 0<

√

(−

B/6A)<

C·

tan(180°

/N)

where N is the number of the reflection surfaces.

13. The light scanning unit of claim 12, wherein coefficients A, B, and C of the cross-sectional profile Y(X) are determined by physical properties and a rotation speed of the rotational polygon mirror.

14. The light scanning unit of claim 11, wherein each of the plurality of reflection surfaces has a cross-sectional profile Y(X) which satisfies the following formula, when a line from a center of the cross-sectional profile to a point on the rotation axis is a Y axis, and a line perpendicular to the Y axis and passing through the point on the rotation axis is an X axis in a cross-section perpendicular to the rotation axis, and a variation of the cross-sectional profile of each reflection surface deformed by a rotation with respect to a constant Y₀ as a reference cross-sectional profile determined by a size of the rotational polygon mirror is Δ

Y(X);

Y₀−

Δ

Y(X)−

0.2 μ

m≦

Y(X)≦

Y₀−

Δ

Y(X)+0.2 μ

m.

15. The light scanning unit of claim 14, wherein each of the plurality of reflection surfaces has a cross-sectional profile Y(X) which satisfies the following formula:

Y₀−

Δ

Y(X)−

0.1 μ

m≦

Y(X)≦

Y₀−

Δ

Y(X)+0.1 μ

m.

16. The light scanning unit of claim 14, wherein the variation AY(X) satisfies the following formula:

Δ

Y(X)=−

AX⁴−

BX²+Y₀−

C and 0≦

√

(−

B/6A)≦

C·

tan(180°

/N)

where N is the number of the reflection surfaces.

17. The light scanning unit of claim 14, wherein coefficients A, B, and C of the cross-sectional profile Y(X) are determined by physical properties and a rotation speed of the rotational polygon mirror.

18. The light scanning unit of claim 11, wherein a number of the plurality of reflection surfaces is four, a length of diagonal line of the rotational polygon mirror is 20 mm, and a thickness of the rotational polygon mirror is 2.5 mm.

19. The light scanning unit of claim 11, wherein the rotational polygon mirror is formed of plastic.

20. The light scanning unit of claim 19, wherein the plurality of reflection surfaces are coated with a reflection layer.

21. An image forming apparatus comprising:

a light scanning unit comprising a light source that emits a light beam;

a rotational polygon mirror that deflects the light beam emitted from the light source in a main scanning direction; and

an imaging optical unit that images the light beam deflected by the rotational polygon mirror onto a surface being scanned;

a developing unit comprising a photoreceptor that is disposed at a region where an electrostatic image is formed by the light beam emitted from the light scanning unit wherein an electrostatic latent image is formed on the photoreceptor, and a developing roller that develops the electrostatic latent image formed on the photoreceptor; and

a transfer unit that transfers the image developed by the developing unit,

wherein the rotational polygon mirror comprises a plurality of reflection surfaces that rotate with respect to a rotation axis, wherein each of the reflection surfaces has a convex shape and a cross-sectional profile perpendicular to the rotation axis having at least two inflection points.

22. The image forming apparatus of claim 21, wherein each of the plurality of reflection surfaces has a cross-sectional profile Y(X) that satisfies the following formula, when a line from a center of the cross-sectional profile to a point on the rotation axis is a Y axis and a line perpendicular to an Y axis and passing through the point on the rotation axis is the X axis in a cross-section perpendicular to the rotation axis:

Y(X)=AX⁴+BX²+C and 0<

√

(−

B/6A)<

C·

tan(180°

/N)

where N is the number of the reflection surfaces.