LED array head type electrophotographic recording apparatus

Abstract

 In an LED array head type electrophotographic recording apparatus in which a latent image is formed on a photo-sensitive member (40) by light emitted from an LED array (1A), and is then developed into a visible image; the LED array comprises: a PN junction semiconductor (2 through 7) for emitting light; and a light blocking layer (8) formed in such a manner as to cover the light emitting surface of the PN junction semiconductor, and having a plurality of small holes 8a at predetermined intervals through which the light emitted from the PN junction semiconductor is passed in the form of light beams, and the distance between the LED array (1A) and the photo-sensitive member (40) is limited to a predetermined distance or less with which the light beams advancing through the small holes do not interfere with one another.

Description

BACKGROUND OF THE INVENTION

[0001] This invention relates to an LED array head type electrophotographic recording apparatus with an LED (light emitting diode) array.

[0002] A conventional art concerning the invention will be described with reference to FIG. 6 which is a perspective view showing a part of a conventional LED array. In FIG. 6, reference numeral 1 designates the LED array made up of the following components 2 through 7:
   That is, in FIG. 6, reference numeral 2 designates an N-electrode; 3, an N-GaAs layer formed on the N-electrode 2; 4, an N-AlxGa₁-xAs layer formed on the N-GaAs layer 3; 5, P-AlxGa₁-xAs layers formed on the N-AlxGa₁-xAs layer 4; 6, an insulating layer formed on the P-AlxGa₁-xAs layers 5, and 7, P-electrodes connected to the P-AlxGa₁-xAs layers 5.

[0003] The insulating layer 6 has a number of openings 6a in correspondence to the P-AlxGa₁-xAs layers 5.

[0004] The operation of the above-described conventional LED array will be described with reference to FIG. 7. FIG. 7 is a side view outlining the arrangement of an electrophotographic recording apparatus with the conventional LED array 1. In FIG. 7, reference 20 designates a substrate connected to the LED array 1 by die bonding or wire bonding; 30, an SLA (self-focus lens array) provided on the side of the light emitting surface of the LED array 1; and 40, a photo-sensitive drum whose center is positioned on the prolongation of the straight line passing through the centers of the LED array and the SLA 30.

[0005] The LEDs forming the LED array 1 are selectively turned on by a drive circuit (not shown) in response to signals applied thereto, thus emitting light, in the form of light beams, through the openings 6a of the insulating layer in a surface light emission mode as a whole. The SLA 30 acts to focus the light beams, thus preventing the enlargement of light spots on the photo-sensitive surface. The light beams thus focused are image-formed on the photo-sensitive surface.

[0006] Now, the operation of the electrophotographic recording apparatus with the LED array 1 will be described in brief. Of the outer cylindrical surface of the photo-sensitive drum 40 charged negative, only a part exposed to light from the LED array 1 is discharged. As a result, toner is allowed to stick only onto the part thus discharged. The toner thus stuck is transferred onto a recording sheet, and then fixed by heat and pressure.

[0007] The optical transmissibility of an LED array head made up of the LED array 1, the substrate 20, the SLA 30, and a driver (not shown) is of the order of several percent (%).

[0008] In the conventional LED array head type electrophotographic recording apparatus, the SLA 30 is interposed between the LED array 1 and the photo-sensitive drum 40 as was described above. Therefore, the apparatus is low in optical transmissibility, and high in manufacturing cost.

SUMMARY OF THE INVENTION

[0009] Accordingly, an object of this invention is to eliminate the above-described difficulties accompanying a conventional LED array head type electrophotographic recording apparatus. More specifically, an object of the invention is to provide an LED array head type electrophotographic recording apparatus which, including no SLA, is high in optical transmissibility and low in manufacturing cost, and is yet able to provide records high in picture quality.

[0010] The foregoing object of the invention has been achieved by the provision of an LED array head type electrophotographic recording apparatus in which a latent image is formed on a photo-sensitive member by light emitted from an LED array, and is then developed into a visible image; in which, according to the invention, the LED array comprises: a PN junction semiconductor for emitting light; and a light blocking layer formed in such a manner as to cover the light emitting surface of the PN junction semiconductor, and having a plurality of small holes at predetermined intervals through which the light emitted from the PN junction semiconductor is passed in the form of light beams, and the distance between the LED array and the photosensitive member is limited to a predetermined distance or less with which the light beams passing through the small holes do not interfere with one another.

[0011] In the LED array head type electrophotographic recording apparatus of the invention, the light emitted from the light emitting surface of the PN junction semiconductor is formed into light beams by the small holes formed in the light blocking layer, thus providing a number of light sources small in diameter, and the distance between the LED array and the photo-sensitive member is limited suitably. Hence, the light beams advancing through the small holes scarcely interfere with one another, and the resultant image is high in picture quality.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a perspective view showing an LED array employed in an LED array head type electrophotographic recording apparatus, which constitutes an embodiment of this invention.

[0013] FIG. 2 is an enlarged sectional view taken along line II-II in FIG. 1;

[0014] FIG. 3 is a side view outlining the arrangement of the LED array,head type electrophotographic recording apparatus according to the embodiment of the invention.

[0015] FIG. 4 is a sectional view taken along line IV-IV in FIG. 1, showing the positional relationships between the LED array and a photo-sensitive drum in the apparatus of the invention.

[0016] FIG. 5 is an explanatory diagram showing a dot pattern in which every other dot is omitted which is optically formed on the photo-sensitive drum.

[0017] FIG. 6 is a perspective view showing a part of a conventional LED array.

[0018] FIG. 7 is a side view outlining the arrangement of an electrophotographic recording apparatus using the conventional LED array.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] One preferred embodiment of this invention will be described with reference to the accompanying drawings. In the embodiment, similarly as in the above-described conventional LED array head type electrophotographic recording apparatus, a light emitting PN junction semiconductor is made up of an N-electrode 2, an N-GaAs layer 3, an N-AlxGa₁-xAs layer 4, P-AlxGa₁-xAs layers 5, an insulating layer 6, and P-electrodes 7 as shown in FIGS. 1 and 2.

[0020] In the embodiment, an LED array 1A is made up of the above-described PN junction semiconductor (2 through 7), and a light blocking layer 8 formed over the light emitting surfaces (the P-AlxGa₁-xAs layers) of the PN junction semiconductor to a thickness u.

[0021] The light blocking layer 8 is a TiN layer formed by CVD (chemical vapor deposition). A number of small holes 8a having a diameter of d are formed in the layer 8 in such a manner that they are in a line, thus allowing the P-AlxGa₁-xAs layers 5 to emit light in the form of light beams.

[0022] In the embodiment, an LED array head type electro-photographic recording apparatus is formed by arranging the above-described LED array 1A with respect to the photo-sensitive drum 40 as shown in FIG. 3.

[0023] More specifically, the distance between the LED array 1a and the photo-sensitive drum 40 is limited to a predetermined distance or less with which the light beams advancing through the small holes 8a do not interfere with one another. That is, the LED array 1A is connected to the substrate 20 by die bonding or wire bonding in such a manner that it is spaced a predetermined distance (1) away from the photo-sensitive drum 40. This predetermined distance (1) will be described by using Equations (1) and (2) later.

[0024] The operation of the apparatus according to the embodiment will be described. The LEDs forming the LED array 1A are selectively turned on by a drive circuit (not shown) in response to signals applied thereto, thus emitting light in a surface light emission mode as a whole. However, in the embodiment, since the light blocking layer 8 is provided, the output light is allowed to advance, in the form of light beams, only through the small holes 8a formed in the layer 8. Those light beams are image-formed on the photo-sensitive surface of the photo-sensitive drum 40.

[0025] In the formation of an image on the photo-sensitive drum 40 by the light beams advancing through the small holes 8a, these light beams should not interfere with one another. For this purpose, the distance (1) between the LED array 1A and the photo-sensitive drum 40 is determined from the following Equations (1) and (2):
   That is, as shown in FIG. 4, the point P on the photo-sensitive drum 40 where a light beam from the point C is image-formed should not be greatly shifted over the distance point T corresponding to a half of the pitch in arrangement of the small holes 8a. At any rate, in a dot pattern in which every other dot is omitted as shown in FIG. 5, the distance (z) between adjacent dots should not be zero. Hence, the segment OP should be shorter than the segment OO′, and the following Equation (1) is therefore established:

[0026] From Equation (1),

[0027] As is apparent from Equation (2), by setting the distance (1) between the LED array 1A and the photo-sensitive drum 40 to u (p/d - 0.5) or less, an LED array head type electrophotographic recording apparatus can be formed in which, unlike the conventional one, the SLA (30 in FIG. 7) is not employed, and the light beams passing through the small holes 8a scarcely interfere with one another.

[0028] That is, the LED array head type electrophotographic recording apparatus, including no SLA, is high in optical transmissibility and low in manufacturing cost, and is yet able to provide records high in picture quality.

[0029] The realizability of the apparatus according to the invention will be described. Let us consider the case where, in the LED array 1A, the small holes 8a are arranged with a pitch (p) of 105.8 µm, and have a diameter (d) of 30 µm, and the thickness of the light blocking layer 8 is 300 µm. In this case, the distance (1) between the LED array 1A and the photo-sensitive drum 40 is as follows:

[0030] Thus, the apparatus of the invention can be sufficiently realized by setting the distance (1) to about 0.9 mm or less.

[0031] In the above-described embodiment, the light blocking layer 8 is the TiN layer formed by CVD. However, the same effects may be obtained by forming the layer 8 by black glass coating (in such a manner that it includes small holes).

[0032] As was described above, in the LED array head type electrophotographic recording apparatus of the invention, LED forming the LED array is made up of the PN junction semiconductor and the light blocking layer formed in such a manner as to cover the light emitting surface of the PN junction semiconductor, and having a plurality of small holes at predetermined intervals through which the light emitted from the PN junction semiconductor is advanced in the form of light beams, and the distance between the LED array and the photo-sensitive member is limited to a predetermined distance or less with which the light beams passing through the small holes do not interfere with one another. Therefore, the apparatus is high in light transmissibility. Furthermore, it, including no SLA, is low in manufacturing cost, and is yet able to provide records high in picture quality.

Claims

1. An LED array head type electrophotographic recording apparatus comprising:
   an LED array for emitting light, said LED array comprising a PN junction semiconductor having a light emitting surface, and a light blocking layer for covering said light emitting surface of said PN junction semiconductor, said light blocking layer having a plurality of small holes at predetermined intervals through which the light emitted from said PN junction semiconductor is passed in the form of light beams; and
   a photo-sensitive member for forming a latent image thereon in response to the light emitted from said LED array,
   wherein said LED array is spaced from said photo-sensitive member by a predetermined distance with which said light beams advancing through said small holes of said light blocking layer do not interfere with one another.

2. An LED array head type electrophotographic recording apparatus according to claim 1, wherein said light blocking layer has a plurality of small holes with a pitch of 105.8µm,a diameter of 30µm, and the thickness of 300µm.

3. An LED array head type electrophotographic recording apparatus according to claim 1, wherein said light blocking layer is formed by CVD.

4. An LED array head type electrophotographic recording apparatus according to claim 3, wherein said light blocking layer comprises a TiN layer.

5. An LED array head type electrophotographic recording apparatus according to claim 1, wherein said light blocking layer is formed by black glass coating.

Drawing