Lens unit, light-exposure apparatus, and image forming apparatus
View Patent ↗A lens unit includes a first lens array including a plurality of first lens elements. The first lens array satisfies D 1 ≤0.25·P 1 where P 1 is a pitch in a first direction between optical axes of adjacent ones of the first lens elements, and D 1 is a displacement amount that is an absolute value of a difference between a first length W E1 from a center position of the first lens array to an end position of the first lens array in the first direction at a first temperature, and a second length W E2 from the center position of the first lens array to the end position of the first lens array at a second temperature higher than the first temperature by 30° C.
1. A lens unit, comprising:
a first lens array including a plurality of first lens elements arranged in a first direction,
wherein the first lens array satisfies
D 1 ≤0.25· P 1
where
P 1 is a pitch in the first direction between optical axes of adjacent first lens elements of the plurality of first lens elements, and
D 1 is a displacement amount that is an absolute value of a difference between a first length which is a length in the first direction from a center position of the first lens array to an end position of the first lens array at a first temperature and a second length which is a length in the first direction from the center position of the first lens array to the end position of the first lens array at a second temperature higher than the first temperature by 30° C.; wherein
the pitch P 1 satisfies
P 1 ≥E X ·W E ( T H −T S )/0.5
where
E X is a coefficient of linear expansion of the first lens array,
W E is a length of the first lens array in the first direction,
T S is the first temperature, and
T H is the second temperature.
2. The lens unit of claim 1 , wherein:
the first temperature is 25° C., and
the second temperature is 55° C.
3. The lens unit of claim 1 , wherein the pitch P 1 is 1.14 mm or more.
4. The lens unit of claim 1 , wherein the plurality of first lens elements are arranged in a staggered pattern.
5. The lens unit of claim 1 , wherein the plurality of first lens elements are linearly arranged.
6. The lens unit of claim 1 , further comprising:
a first light shield member having a plurality of openings corresponding to the plurality of first lens elements respectively.
7. The lens unit of claim 1 , further comprising:
a second lens array including a plurality of second lens elements arranged in a same way as the plurality of first lens elements, wherein
the second lens array satisfies
D 2 ≤0.25· P 2
where
P 2 is a pitch in the first direction between optical axes of adjacent second lens elements of the plurality of second lens elements, and
D 2 is a displacement amount that is an absolute value of a difference between a third length which is a length in the first direction from a center position of the second lens array to an end position of the second lens array at the first temperature and a fourth length which is a length in the first direction from the center position of the second lens array to the end position of the second lens array at the second temperature.
8. The lens unit of claim 7 , further comprising:
a second light shield member having a plurality of second openings corresponding to the plurality of second lens elements respectively.
9. A light-exposure apparatus comprising:
a light-emitting device array including a plurality of light-emitting devices; and
the lens unit of claim 1 that converges light emitted from the light-emitting device array.
10. An image forming apparatus comprising:
the light-exposure apparatus of claim 9 ; and
an image carrier which is exposed to light by the light-exposure apparatus so that an electrostatic latent image is formed on the image carrier.