Optical scanning device in image forming apparatus

• US 20060077500A1
• Filed: 09/12/2005
• Published: 04/13/2006
• Est. Priority Date: 09/29/2004
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Ueda, Takeshi, Hayashi, Yoshinori, Sakai, Kohji
• Granted Patent: US 7,362,486 B2
• Time in Patent Office: Days
• US Class Current: 359/205.100
• CPC Class Codes: G02B 19/0014 at least one surface having optical power
• CPC Class Codes: G02B 19/0057 in the form of a laser diode array, e.g. laser diode bar semiconductor laser arrays with beam combining arrangement H01S5/4012
• CPC Class Codes: G02B 26/124 Details of the optical system between the light source and the polygonal mirror G02B26/123, G02B26/127 take precedence
• CPC Class Codes: G02B 26/125 Details of the optical system between the polygonal mirror and the image plane G02B26/123, G02B26/127 take precedence; F-Theta lenses G02B13/0005
• CPC Class Codes: G02B 27/0031 for scanning purposes
• CPC Class Codes: G02B 27/4211 correcting chromatic aberrations G02B27/0056, G02B27/4222, G02B27/4227 take precedence
• CPC Class Codes: G02B 27/4227 in image scanning systems
• CPC Class Codes: G02B 27/4283 having a diffractive element with major temperature dependent properties
• CPC Class Codes: G02B 7/008 with means for compensating for changes in temperature or for controlling the temperature; thermal stabilisation

Abstract

A first optical system guides a light beam from a light source to an optical deflector, and a second optical system converges the light beam deflected by the optical deflector on a surface to be scanned. The first optical system includes at least one resin lens having a diffractive surface. The second optical system includes at least one resin optical element. A beam diameter depth in a main scanning direction, Wm, that can have a maximum intensity of 1/e², satisfies conditions
Δm1+Δm2+Δm3−Δd1×(f2/f1)²<Wm/40  (1)
Δd1>0 and Δm2<0.  (2)

Claims

1. An optical scanning device comprising:

a light source that emits a light beam;

a first optical system that guides the light beam emitted by the light source;

an optical deflector that deflects the light beam guided by the first optical system; and

a second optical system that converges the light beam deflected by the optical deflector on a surface to be scanned, wherein

the first optical system includes at least one resin lens having a diffractive surface,

the second optical system includes at least one resin optical element, and

a beam diameter depth in a main scanning direction, Wm, that can have a maximum intensity of 1/e², satisfies conditions

Δ

m1+Δ

m2+Δ

m3−

Δ

d1×

(f2/f1)²<

Wm/40 

 

(1)
Δ

d1>

0 and Δ

m2<

0 

 

(2)

where, Δ

m1 is a beam waist position shift in the main scanning direction due to a change in the power in a refracting unit when the temperature in the first optical system rises by 1°

C., Δ

m2 is a beam waist position shift in the main scanning direction due to a change in the power in the diffracting unit when the temperature in the first optical system rises by 1°

C., Δ

m3 is a beam waist position shift in the main scanning direction when the temperature in the second optical system rises by 1°

C., Δ

d1 is a shift in the distance between a forward principal point of the first optical system in the main scanning direction and the light source when the temperature in the first optical system rises by 1°

C., f1 is a focal distance of the first optical system in the main scanning direction, and f2 is a focal distance of the second optical system in the main scanning direction.

2. The optical scanning device according to claim 1, wherein the light source is a semiconductor laser device, and

the beam diameter depth in the main scanning direction, Wm, that can have a maximum intensity of 1/e², satisfies a condition,

−

Wm<

Δ

m′

1+Δ

m′

2+Δ

m′

3<

0 

 

(3)

where, Δ

m′

1 is a beam waist position shift in the main scanning direction due to a change in the power in the refracting unit of the first optical system, Δ

m′

2 is a beam waist position shift in the main scanning direction due to a change in the power in the diffracting unit of the first optical system, and Δ

m′

3 is a beam waist position shift in the second optical system in the main scanning direction, when the emission wavelength of the light source is increased by 1 nm.

7. The optical scanning device according to claim 1, wherein the first optical system includes at least one glass lens, the power of the glass lens in the main scanning direction being greater than the power of the resin lens in the main scanning direction.

8. The optical scanning device according to claim 1, wherein the first optical system and the second optical system include a plurality of lenses and all the lenses are resin lenses.

9. The optical scanning device according to claim 1, further comprising a housing configured to house the first optical system and the second optical system, wherein the housing includes an air passage that allows flow of air between the first optical system and the second optical system.

3. An optical scanning device comprising:

a light source that emits a light beam;

a first optical system that guides the light beam emitted by the light source;

an optical deflector that deflects the light beam guided by the first optical system; and

a second optical system that converges the light beam deflected by the optical deflector on a surface to be scanned, wherein

the first optical system includes at least one resin lens having a diffractive surface,

the second optical system includes at least one resin optical element, and

a beam diameter depth in a sub-scanning direction, Ws, that can have a maximum intensity of 1/e², satisfies conditions

Δ

s1+Δ

s2+Δ

s3−

Δ

d1×

(β

1×

β

2)²<

Ws/40 

 

(4)
Δ

d1>

0 and Δ

s2+Δ

s2<

0 

 

(5)

where, Δ

s1 is a beam waist position shift in the sub-scanning direction due to a change in the power in the refracting unit when the temperature in the first optical system rises by 1°

C., Δ

s2 is a beam waist position shift in the sub-scanning direction due to a change in the power in the diffracting unit when the temperature in the first optical system rises by 1°

C., Δ

s3 is a beam waist position shift in the sub-scanning direction when the temperature in the second optical system rises by 1°

C., Δ

d1 is a shift in the distance between a forward principal point in a main scanning direction of the first optical system and the light source when the temperature in the first optical system rises by 1°

C., β

1 is a lateral magnification of the first optical system in the sub-scanning direction, and β

2 is a lateral magnification of the second optical system in the sub-scanning direction.

4. The optical scanning device according to claim 3, wherein the light source is a semiconductor laser device, and

the beam diameter depth in the sub-scanning direction, Ws, that can have a maximum intensity of 1/e², satisfies a condition

−

Ws<

Δ

s′

1+Δ

s′

2+Δ

s′

3<

0 

 

(6)

where, Δ

s′

1 is a beam waist position shift in the sub-scanning direction due to a change in the power in a refracting unit of the first optical system, Δ

s′

2 is a beam waist position shift in the sub-scanning direction due to a change in the power in the diffracting unit of the first optical system, and Δ

s′

3 is a beam waist position shift in the sub-scanning direction in the second optical system, when the emission wavelength of the light source is increased by 1 nm.

5. The optical scanning device according to claim 3, wherein

the first optical system includes at least one resin lens having a diffractive surface,

the second optical system includes at least one resin optical element, and

a beam diameter depth in a main scanning direction, Wm, that can have a maximum intensity of 1/e², satisfies conditions

Δ

m1+Δ

m2+Δ

m3−

Δ

d1×

(f2/f1)²<

Wm/40 

 

(1)
Δ

d1>

0 and Δ

m2<

0 

 

(2)

where, Δ

m1 is a beam waist position shift in the main scanning direction due to a change in the power in a refracting unit when the temperature in the first optical system rises by 1°

C., Δ

m2 is a beam waist position shift in the main scanning direction due to a change in the power in the diffracting unit when the temperature in the first optical system rises by 1°

C., Δ

m3 is a beam waist position shift in the main scanning direction when the temperature in the second optical system rises by 1°

C., Δ

d1 is a shift in the distance between a forward principal point of the first optical system in the main scanning direction and the light source when the temperature in the first optical system rises by 1°

C., f1 is a focal distance of the first optical system in the main scanning direction, and f2 is a focal distance of the second optical system in the main scanning direction.

6. The optical scanning device according to claim 3, wherein the light source is a semiconductor laser device, and

the beam diameter depth in the main scanning direction, Wm, that can have a maximum intensity of 1/e², satisfies a condition,

−

Wm<

Δ

m′

1+Δ

m′

2+Δ

m′

3<

0 

 

(3)

where, Δ

m′

1 is a beam waist position shift in the main scanning direction due to a change in the power in the refracting unit of the first optical system, Δ

m′

2 is a beam waist position shift in the main scanning direction due to a change in the power in the diffracting unit of the first optical system, and Δ

m′

3 is a beam waist position shift in the second optical system in the main scanning direction, when the emission wavelength of the light source is increased by 1 nm.

10. An optical scanning device comprising:

a light source that emits a light beam;

a coupling lens that shapes the light beam into a beam pattern;

an anamorphic optical element that guides the light beam shaped by the coupling lens;

an optical deflector that deflects the light beam guided by the anamorphic optical element; and

a scanning optical system that converges the light beam deflected by the optical deflector on a surface to be scanned to form a laser spot, wherein

the scanning optical system includes more than one resin lens,

the anamorphic optical element is a resin lens having a first surface and a second surface, the first surface being rotationally symmetric having formed thereon a concentric circular power diffractive surface, the second surface having formed thereon a power diffractive surface that converts the light beam emitted from the light source into a parallel light beam in a main scanning direction and into a convergent light beam in a sub-scanning direction, and

the power of the power diffractive surface is set so that a beam waist position shift in a main scanning direction or a sub-scanning direction or both the main scanning direction and the sub-scanning direction, caused by mode hopping or temperature variation in the semiconductor laser device is substantially zero.

11. The optical scanning device according to claim 10, wherein the first surface is a spherical surface having formed thereon a concentric circular power diffractive surface, the second surface is a cylindrical surface having formed thereon a linear power diffractive surface.

12. The optical scanning device according to claim 11, wherein the power of the concentric circular power diffractive surface and the power of the spherical surface bearing the power diffractive surface cancel each other out, rending the anamorphic optical element devoid of power in the main scanning direction and having a positive power in the sub-scanning direction.

13. The optical scanning device according to claim 10, wherein the coupling lens is a glass lens.

14. An optical scanning device comprising:

a light source that emits a light beam;

a coupling lens that shapes the light beam into a beam pattern;

an anamorphic optical element that guides the light beam shaped by the coupling lens;

an optical deflector that deflects the light beam guided by the anamorphic optical element; and

a scanning optical system that converges the light beam deflected by the optical deflector on a surface to be scanned to form a laser spot, wherein

the scanning optical system includes more than one resin lens,

the anamorphic optical element is an anamorphic resin lens having a first surface and a second surface, the first surface being anamorphic refractive surface, the second surface bearing thereon a power diffractive surface having an axis in a main scanning direction, and

the power of the power diffractive surface is set so that a beam waist position shift in the main scanning direction or a sub-scanning direction or both the main scanning direction and the sub-scanning direction, caused by mode hopping or temperature variation in the semiconductor laser device is substantially zero.

15. The optical scanning device according to claim 14, wherein the anamorphic optical element has no power in the main scanning direction and a positive power in the sub-scanning direction.

16. The optical scanning device according to claim 14, wherein an absolute value of a curvature radius of the refractive surface of the anamorphic optical element is greater in the main scanning direction is greater than in the sub-scanning direction.

17. The optical scanning device according to claim 14, wherein the power diffractive surface is an elliptical power diffractive surface formed on a plane surface.

18. The optical scanning device according to claim 14, wherein the coupling lens is a glass lens.

19. An image forming apparatus comprising an optical scanning device that includes a light source that emits a light beam;

a first optical system that guides the light beam emitted by the light source;

an optical deflector that deflects the light beam guided by the first optical system; and

a second optical system that converges the light beam deflected by the optical deflector on a surface to be scanned, wherein

the first optical system includes at least one resin lens having a diffractive surface,

the second optical system includes at least one resin optical element, and

a beam diameter depth in a main scanning direction, Wm, that can have a maximum intensity of 1/e², satisfies conditions

Δ

m1+Δ

m2+Δ

m3−

Δ

d1×

(f2/f1)²<

Wm/40 

 

(1)
Δ

d1>

0 and Δ

m2<

0 

 

(2)

where, Δ

m1 is a beam waist position shift in the main scanning direction due to a change in the power in a refracting unit when the temperature in the first optical system rises by 1°

C., Δ

m2 is a beam waist position shift in the main scanning direction due to a change in the power in the diffracting unit when the temperature in the first optical system rises by 1°

C., Δ

m3 is a beam waist position shift in the main scanning direction when the temperature in the second optical system rises by 1°

C., Δ

d1 is a shift in the distance between a forward principal point of the first optical system in the main scanning direction and the light source when the temperature in the first optical system rises by 1°

C., f1 is a focal distance of the first optical system in the main scanning direction, and f2 is a focal distance of the second optical system in the main scanning direction.

20. An image forming apparatus comprising at least one image forming device that includes

a photosensitive image bearing unit;

an optical scanning unit that scan a surface of the image bearing unit with a light beam to thereby forming a latent image on the image bearing unit; and

a developing unit that develops the latent image on the image bearing unit into a visual image, wherein

the optical scanning unit includes

a light source that emits a light beam;

a coupling lens that shapes the light beam into a beam pattern;

an anamorphic optical element that guides the light beam shaped by the coupling lens;

an optical deflector that deflects the light beam guided by the anamorphic optical element; and

a scanning optical system that converges the light beam deflected by the optical deflector on a surface to be scanned to form a laser spot, wherein

the scanning optical system includes more than one resin lens,

the anamorphic optical element is a resin lens having a first surface and a second surface, the first surface being rotationally symmetric having formed thereon a concentric circular power diffractive surface, the second surface having formed thereon a power diffractive surface that converts the light beam emitted from the light source into a parallel light beam in a main scanning direction and into a convergent light beam in a sub-scanning direction, and

the power of the power diffractive surface is set so that a beam waist position shift in a main scanning direction or a sub-scanning direction or both the main scanning direction and the sub-scanning direction, caused by mode hopping or temperature variation in the semiconductor laser device is substantially zero.

21. An image forming apparatus comprising:

a photosensitive image bearing unit;

an optical scanning unit that scan a surface of the image bearing unit with a light beam to thereby forming a latent image on the image bearing unit; and

a developing unit that develops the latent image on the image bearing unit into a visual image, wherein

the optical scanning unit includes

a light source that emits a light beam;

a coupling lens that shapes the light beam into a beam pattern;

an anamorphic optical element that guides the light beam shaped by the coupling lens;

an optical deflector that deflects the light beam guided by the anamorphic optical element; and

a scanning optical system that converges the light beam deflected by the optical deflector on a surface to be scanned to form a laser spot, wherein

the scanning optical system includes more than one resin lens,

the anamorphic optical element is an anamorphic resin lens having a first surface and a second surface, the first surface being anamorphic refractive surface, the second surface bearing thereon a power diffractive surface having an axis in a main scanning direction, and

the power of the power diffractive surface is set so that a beam waist position shift in the main scanning direction or a sub-scanning direction or both the main scanning direction and the sub-scanning direction, caused by mode hopping or temperature variation in the semiconductor laser device is substantially zero.