JPH09109455A - LED array head - Google Patents

Abstract

(57) Abstract: An LED array head is provided that has a small loss of light quantity and can prevent the occurrence of ghosts. SOLUTION: A plurality of LED (light emitting diode) array chips 1 having a plurality of light emitting sources (LED elements) 3 are arranged in an array, and a micro array having a cycle corresponding to each LED array chip 1 and each LED array chip 1 is arranged. In the LED array head including the lens array 2, each L
A feature is that a single lens 6 is provided for each ED element 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED (light emitting diode) array head applied to a writing optical system such as an optical printer, a digital copying machine and a facsimile.

[0002]

2. Description of the Related Art An LED array head using an LED element as a light source is a laser beam printer using a semiconductor laser (LD) and a scanning optical system (a deflector such as a rotating polygon mirror and an imaging lens for constant velocity scanning). Compared to the (LBP) system, there is no mechanical operating part, so there are advantages that it is highly reliable against vibration and noise and that it is advantageous for downsizing.

On the other hand, there is a problem that the light quantity varies greatly within one line, and the beam spot shape is likely to be non-uniform among dots. Such variations in light amount and disturbance of the beam spot cause density unevenness such as black streaks on the output image, and are particularly likely to appear remarkably in the case of a multivalued image such as a photographic image.

Such a variation in the light quantity and the disturbance of the beam spot largely depend not on the LEDs themselves but on the unit-magnification imaging element such as a rod lens array. For example, (1) Since a light amount loss occurs at the joint of the rod lenses, a light amount variation that matches the cycle of the joint occurs (because the light emitting element and the imaging element have different pitches). (2) Due to the generation of flare light such as reflected light in the rod lens, it is difficult to converge it into a uniform beam. And so on.

[0005]

SUMMARY OF THE INVENTION In order to solve this problem,
As shown in FIG. 2, an imaging optical system including a microlens array 2 corresponding to the cycle of each LED array chip 1 can be considered. If the light beams from the respective light emitting sources of the LED array chip 1 are configured to be collected near the center of the microlens 2a, it is possible to reduce the variation in the light amount due to the joint between the lenses and the variation in the beam spot system.

However, since the divergence angle of the LED is large, FIG.
As shown in, the micro lens 2 corresponding to the luminous flux of the LED
The luminous flux enters not only a but also the adjacent microlens 2a, and ghost light is generated. Further, as shown in FIG. 4, if the shielding plate 4 is provided on the microlens array 2 to prevent the generation of ghost light, the light quantity deteriorates. 2 to 4, reference numeral 1a denotes an exit end surface and 5 denotes an image surface.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an LED array head which has a small light amount loss and can prevent the occurrence of a ghost.

[0008]

In order to achieve the above object, the present invention arranges a plurality of LED array chips having a plurality of LED elements in an array, and the LED array chips and the period of each LED array chip. In an LED array head composed of a microlens array corresponding to the above, a single lens is provided for each LED element.

The single lens is a cylinder lens having power in the direction in which the LED arrays are arranged.

Further, the single lens is an anamorphic lens such as a spherical surface or a toroidal surface having different curvatures in a direction in which the LED arrays are arranged and in a direction perpendicular thereto.

With the above arrangement, since a single lens is arranged for each LED element, the light flux of the LED passes through the corresponding microlens and reaches the image plane without being eclipsed. That is, the loss of light amount is small, and the occurrence of ghost can be prevented.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. However, the same components as those in the prior art will be designated by the same reference numerals and redundant description will be omitted. In FIG. 1, the microlens array 2 is arranged in correspondence with the cycle of each LED array chip 1, and the luminous flux centers of the respective light emitting sources in the LED array chip 1 are arranged so as to gather near the center of the microlens 2a. The power (degree) at which the luminous flux of each light emitting source in the array chip 1 does not enter at least the microlenses 2a other than the corresponding microlenses 2a.
The single lens 6 having is arranged for each LED element 3 in the vicinity of the LED element 3. With such an optical arrangement, LE
Corresponding microlens 2 without losing the light flux of D
It passes through a and reaches the image plane 5. Therefore, light loss is small,
Prevents the generation of ghosts.

Further, here, by using a cylinder lens having power in the main scanning direction (alignment direction of the LED array) as a single lens, when the cylinder lens is installed on the base of the LED array, the sub-scanning direction (LED array It can be easily installed because it has no power in the direction in which it is aligned and direct light). Further, since there is no restriction in the sub-scanning direction of the microlens array, the effective diameter in the sub-scanning direction of the microlens array can be made sufficiently larger than that of the LED light beam without narrowing the light beam in the sub-scanning direction, thereby causing a light amount loss and a ghost. Is reduced.

Furthermore, since the LED elements generally have different apparent emission points (there are astigmatic differences) in the main scanning direction and the sub-scanning direction, they are anamorphic (distortion) as a single lens or as a toroidal surface (conical curve rotation surface). The use of a lens (in shape) is advantageous in forming a minute spot. That is, also in this case, the loss of light amount and the occurrence of ghost are reduced.

[0015]

As described above, according to the present invention, the loss of light quantity and the occurrence of ghost are reduced. Further, a cylinder lens as a single lens can be easily installed on the base of the LED array, and in this case as well, loss of light amount and generation of ghost are reduced. Furthermore, the use of an anamorphic lens as the single lens is advantageous in forming a minute spot, and reduces the occurrence of sagittal, light amount loss, and ghost.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a main part of an embodiment according to the present invention.

FIG. 2 is an overall explanatory diagram according to a conventional technique.

FIG. 3 is a partial explanatory diagram according to a conventional technique.

FIG. 4 is an explanatory diagram according to a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 LED array chip 1a Emitting end face 2 Micro lens array 2a Micro lens 3 LED element 4 Shielding plate 5 Image plane 6 Single lens

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H01L 33/00

Claims (3)

[Claims] 1. An LED array head comprising a plurality of LED array chips having a plurality of LED elements arranged in an array and comprising the LED array chips and a microlens array corresponding to the period of each LED array chip. An LED array head characterized in that a single lens is provided for each LED element. 2. The LED array head according to claim 1, wherein the single lens is a cylinder lens having a power in a direction in which the LED arrays are arranged. 3. The LED array head according to claim 1, wherein the single lens is an anamorphic lens such as a spherical surface or a toroidal surface having different curvatures in the arrangement direction of the LED array and the direction perpendicular to the arrangement direction.