# US 9,517,637 B2 · Imaging optical element and optical scanning apparatus including the same

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- Number: US 9,517,637 B2
- Document ID: US9517637B2
- Status: Granted
- Kind: B2
- Application number: 14/742,896
- Filed: 2015-06-18
- Published: 2015-12-24
- Granted: 2016-12-13
- Earliest claimed: 2014-06-24
- Assignees: Canon Kabushiki Kaisha
- Applicants: Canon Kabushiki Kaisha
- Inventors: Shuichi Kurokawa
- Web page: https://patentgrep.com/patent/US9517637B2

## CPC

- B41J 2/471: {using dot sequential main scanning by means of a light deflector, e.g. a rotating polygonal mirror}
- B41J 2/447: using arrays of radiation sources (B41J2/475 takes precedence)
- G02B 26/123: {Multibeam scanners, e.g. using multiple light sources or beam splitters}
- 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)}
- B41J: TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

The imaging optical element includes an optical surface whose shape within a sub-scanning section has a non-circular shape. Assuming that a coordinate along a main scanning direction is Y and a coordinate along a sub-scanning direction is Z and that, within the sub-scanning section, a curvature radius on an optical axis of the optical surface is r, an eccentricity is k, a coefficient of variation in the curvature radius of the optical surface is Di, and an aspherical surface coefficient is GmnYm, when a shape S of the optical surface within the sub-scanning section is defined by an expression: S = Z 2 r ′ 1 + 1 - ( 1 + k ) ⁢ ( Z r ′ ) 2 + ∑ n = 1 16 ⁢ ⁢ ∑ m = 0 16 ⁢ ⁢ G m ⁢ ⁢ n ⁢ Y m ⁢ Z n , ⁢ r ′ = r ⁡ ( 1 + ∑ i = 2 14 ⁢ ⁢ D i ⁢ Y i ) the expression includes a term in which n is an odd number equal to or larger than 3, and the aspherical surface coefficient of at least one of the terms in which n is an odd number equal to or larger than 3 is changed asymmetrically along the main scanning direction.

## Claims

### Claim 1

An optical scanning apparatus, comprising:
a light source comprising a plurality of light-emitting parts;
a deflection unit configured to deflect a plurality of light fluxes emitted from the light source; and
an imaging optical system configured to condense the plurality of light fluxes deflected by the deflection unit onto a scanned surface, wherein:
the imaging optical system comprises an imaging optical element;
the imaging optical element comprises an optical surface whose shape within a sub-scanning section has a non-circular shape;
assuming that a coordinate along a main scanning direction is Y and a coordinate along a sub-scanning direction is Z and that, within the sub-scanning section, a curvature radius on an optical axis of the optical surface is r, an eccentricity is k, a coefficient of variation in the curvature radius of the optical surface is Di, and an aspherical surface coefficient is GmnYm, when a shape S of the optical surface within the sub-scanning section is defined by an expression:
S
=
Z
2
r
′
1
+
1
-
(
1
+
k
)
⁢
(
Z
r
′
)
2
+
∑
n
=
1
16
⁢
⁢
∑
m
=
0
16
⁢
⁢
G
m
⁢
⁢
n
⁢
Y
m
⁢
Z
n
,
⁢
r
′
=
r
⁡
(
1
+
∑
i
=
2
14
⁢
⁢
D
i
⁢
Y
i
)
the expression comprises a term in which n is an odd number equal to or larger than 3;
the aspherical surface coefficient of at least one of the terms in which n is an odd number equal to or larger than 3 is changed asymmetrically along the main scanning direction; and
when wavefront aberration amounts in positions Zmax and Zmin of end portions of the light flux along the sub-scanning direction are set as W(Zmax) [λ] and W(Zmin) [λ], respectively, in an arbitrary position in the optical surface along the main scanning direction,
|
W
⁡
(
Zmax
)
-
W
⁡
(
Zmin
)
2
|
≤
0.3
is satisfied.

### Claim 2 (depends on 1)

The optical scanning apparatus according to claim 1, wherein the plurality of light-emitting parts are arranged so as to be spaced apart from one another along the main scanning direction and the sub-scanning direction.

### Claim 3 (depends on 1)

The optical scanning apparatus according to claim 1, wherein, when the same coordinate axes as coordinate axes for the optical surface are defined on the scanned surface, an inclination of a straight line obtained by connecting between imaging positions in which the plurality of light fluxes emitted from the plurality of light-emitting parts of the light source are imaged on the scanned surface has the same sign as an inclination of a change in the aspherical surface coefficient of the at least one of the terms along the main scanning direction.

### Claim 4 (depends on 3)

The optical scanning apparatus according to claim 3, wherein the optical surface comprises the optical surface through which the light flux having a largest width along the sub-scanning direction passes among the optical surfaces comprised in the imaging optical system.

### Claim 5 (depends on 3)

The optical scanning apparatus according to claim 3, wherein an origin of a polynomial expression that defines the shape of the optical surface within the sub-scanning section exists constantly within an area of the optical surface through which the light flux passes.

### Claim 6 (depends on 1)

The optical scanning apparatus according to claim 1, wherein the optical surface comprises the optical surface through which the light flux having a largest width along the sub-scanning direction passes among the optical surfaces comprised in the imaging optical system.

### Claim 7 (depends on 1)

The optical scanning apparatus according to claim 1, wherein an origin of a polynomial expression that defines the shape of the optical surface within the sub-scanning section exists constantly within an area of the optical surface through which the light flux passes.

### Claim 8 (depends on 1)

The optical scanning apparatus according to claim 1, further comprising an incident optical system configured to guide the plurality of light fluxes emitted from the light source to the deflection unit,
wherein the optical axis of incident optical system and a main scanning section are non-parallel with each other.

### Claim 9 (depends on 8)

The optical scanning apparatus according to claim 8, wherein:
the incident optical system comprises:
a cylindrical lens configured to condense the light flux within the sub-scanning section; and
an aperture stop configured to define a light flux width along the sub-scanning direction; and
wherein the aperture stop is arranged between the cylindrical lens and the deflection unit.