JPH05338263A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent a white streak and a black streak on a boundary line between a block and a block of an LED head from occurring by a method wherein a light emission part of the LED in contact with the boundary of the block is extended toward the boundary side of the block, and an area of the light emission part is made larger than that of the other LED. CONSTITUTION:A number of LED arrays 2 are mounted on a substrate. Besides, one LED array composes a block as a unit. The LED array is made to be driven per each block. In an image forming device, light emission parts 6, 6 of the LED in contact with a boundary of the block are extended toward the boundary of the block to provide auxiliary light emission parts 8, 10, and an area of the light emission part is made larger than that of the other LED. Then, decrease in superposed effect of light caused by a difference in exposure time on the boundary of the block is replenished with a weak light from the auxiliary light emission parts 8, 10. Consequently, a white streak and a black streak on the boundary between the block and the block of the LED head can be prevented from occurring.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an LED array, and more particularly to prevention of white lines and black lines at boundaries between blocks.

[0002]

2. Description of the Related Art An LED head forms an image by forming light from an LED on a photosensitive drum or the like with a lens array. Regarding the problem of the boundary between the LED array and the array or the boundary between the print blocks and the print block in the LED head, 1) it is difficult to keep the pitch of the light emitting part (LED) constant at the boundary between the arrays. (Actual Kaihei 1-104,34
2), 2) It has been pointed out that light emitting portions with low light output are likely to occur at both ends of the array (Japanese Utility Model Laid-Open No. 63-100,240).

Keeping the pitch of the light emitting portions at the boundary of the array the same as that of the other portions in 1) relates to the mounting accuracy of the array, and can be solved by improving the mounting accuracy. 2)
The fact that light-emitting portions with low light-emission output are likely to occur at both ends of the array due to distortion or the like when the array is cut is a problem related to the occurrence of abnormalities in the light-emitting portions at both ends of the array. In reality, such a problem is unlikely to occur. The above-mentioned actual exploitation 63-100,2
To solve this problem, Japanese Patent Publication No. 40 proposes to cut the electrode area for the light emitting portions at both ends of the array to increase the light emission output. However, always increasing the light emission output at both ends of the array, as opposed to the light emission output that occurs only accidentally, results in a reduction in print quality. Also, cutting the electrode area impairs the reliability and life of the light emitting portions at both ends of the array.

The inventor has found that even if the above points 1) and 2) are solved, problems such as white streaks and black streaks still occur at the boundary between arrays and the boundary between blocks. It was As a drive circuit of the LED head, for example, time-divisional driving is performed in which each LED array is time-divided as a unit, or for example, 40 LED arrays are divided into four blocks, and each LED array is divided into 10 blocks. A block drive for driving and the like are known. According to the inventor's experiment, the problem of white streaks and black streaks does not always occur at each array boundary, but occurs at each array boundary in the case of time division driving, but in the case of block driving, It occurs at each block boundary, not at the boundary. This indicates that the problem of white streaks and black streaks is not due to an abnormality in the light emitting portion pitch at the boundary of the array or an abnormality in the light emission output, but is due to the difference in exposure timing due to time division driving or block driving. Regarding the occurrence of white streaks and black streaks, it was found that white streaks occur when reverse development is performed as in a printer or facsimile, and black streaks occur when regular development is performed as in a copier. ..

The occurrence of white streaks and black streaks has a resolution of 300D.
It is not remarkable in the image forming apparatus of PI, and the resolution is 400
It became remarkable when it was increased to DPI. This indicates that the occurrence of white streaks and black streaks is related to the gap between the light emitting parts and is related to the interference of light between the adjacent light emitting parts. In any case, the occurrence of white streaks and black streaks impairs the printing quality of the image forming apparatus and thus needs to be solved, and is particularly important in developing a high resolution image forming apparatus.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus,
This is to prevent white streaks and black streaks due to insufficient exposure at block boundaries.

[0007]

The image forming apparatus of the present invention has a large number of LEs.
In an image forming apparatus in which a D array is mounted on a substrate, at least one LED array is used as a unit to drive a block, and the LED array is driven for each block, the light emission of the LED in contact with the boundary of the block is performed. It is characterized in that the area is extended toward the boundary side of the block and the area of the light emitting section is made larger than that of other LEDs.

[0008]

The concept of blocks in the present invention will be described. For example, when each LED array is time-divisionally driven, each LED array constitutes one block. Of course, for example, two LED arrays may be time-divisionally driven as a unit. In that case, two LED arrays are used as one unit.
It becomes a block. In static drive, for example, 40
For example, when the LED array is divided into 4 blocks and 10 LED arrays are simultaneously driven, the array 1
0 is 1 block.

What increases the area of the light emitting portion is the light emitting portion in contact with the boundary between the blocks, and the light emitting portion in contact with the boundary between the blocks and the light emission at the leftmost end and the rightmost end of the entire image forming apparatus. Increase the area of the part. In the light emitting section for increasing the area, the area is increased by extending the light emitting section toward the boundary side of the block, that is, outside as viewed from the center of the array.

According to the knowledge of the inventor, the occurrence of white streaks and black streaks at the boundaries between blocks is due to the following causes. Since the exposure of the photoconductor is performed in block units of the LED head, the effect of superimposing the LED light between the adjacent light emitting units appears small at the boundary between the blocks. This is because there is a time difference in exposure on both sides of the block. For this reason, even when the light emitting portions on both sides of the boundary are made to emit light, the intermediate region falls into underexposure, and the reduction of the developing potential becomes insufficient. This results in white streaks in the case of reversal development and black streaks in the case of regular development.

This is supported by the following facts. When block driving is performed using a plurality of LED arrays as a unit, white stripes and black stripes are generated at the block boundary, not necessarily at the array boundary. The problem of the boundary of the array can be eliminated by making the arrangement pitch of the light emitting sections constant. For white and black streaks, the resolution is 300D.
It becomes remarkable when the PI is increased to 400 DPI, which indicates that the arrangement pitch of the light emitting parts is reduced, and the more the light interference (superposition) between the adjacent light emitting parts is, the more serious the problem of white streaks and black streaks becomes. ing. What is related to the light interference between the blocks is the difference in the exposure timing at the boundaries of the blocks, which is associated with the exposure in block units.

Therefore, if the area of the light emitting portion at the boundary of the block is increased and the area of the light emitting portion is increased toward the boundary of the block,
It is possible to compensate for the underexposure of the photoreceptor due to the lack of the effect of superimposing light at the boundary.

[0013]

EXAMPLE FIG. 1 shows an example. In FIG. 1, 2 is an LED array, which uses a semiconductor such as GaAs, and 4
Is a light emitting portion other than the block boundary, and 6 is a light emitting portion at the block boundary. In addition, in FIG. 1, one LED array 2 is driven in a time-divisional manner, one array being one.
The case where it becomes a block is shown. Reference numerals 8 and 10 denote auxiliary light emitting portions provided on the light emitting portion 6 at the boundary of the block, and extend the light emitting portion 6 to the outside toward the boundary of the block. 12 is an electrode, 14
Is a bonding pad for wire bonding or flip chip bonding. The electrodes 12 are the light emitting parts 4, 6
However, the electrodes may be arranged so that they are connected to the light emitting portions 4 and 6 at the ends of the light emitting portions 4 and 6 on the pad 14 side.

The size of the embodiment is, for example, A4 / 3.
In the case of an image forming apparatus for a 00 DPI printer or facsimile, the light emitting unit 4 has a width (longitudinal direction of the array 2) of 50 μm.
m, length 60 μm, light emitting area 300
It is about 0 μm ² . On the other hand, in the light emitting unit 6 at the boundary, the auxiliary light emitting units 8 and 10 each having a side of about 10 to 15 μm.
Are provided adjacent to the upper and lower ends of the light emitting unit 4. The total area of the auxiliary light emitting units 8 and 10, and thus the light emitting unit 4 inside the array 2.
The total area of the light emitting part added to is 200 to 450.
It becomes about μm ² , which is equivalent to increasing the light emission output by about 6 to 15%. When the resolution is 400 DPI, the light emitting unit 4 has a width of about 40 μm and a length of about 50 μm, and the light emitting unit area is, for example, about 2000 μm ² . In this case, one side of the auxiliary light emitting units 8 and 10 is 5 to 15 μm.
It is preferable that the area of the light emitting portion is increased to about 5 to 20% with respect to the light emitting portion 4, and the light emission output is increased to about 5 to 20%. This is an example of the area of the auxiliary light emitting units 8 and 10, and is not limited to this.

The light-emitting portion 6 in contact with the border of the block has an extension portion 2 with the side surface of the light-emitting portion 6 facing the border of the block as shown in FIG.
It may be enlarged by 0 and the entire side surface of the light emitting portion 6 may be enlarged toward the boundary of the block. However, this is inferior to the auxiliary light emitting units 8 and 10 in FIG. 1 in the following points. Of the two light emitting units 6 and 6 on both sides of the block, one is on and the other is off. In the light emitting unit 6 of FIG. 2, the diameter of the printing dot on the turned-on side in this case increases by the extension 20. This slightly reduces the print quality. On the other hand,
Even if the auxiliary light emitting parts 8 and 10 are provided,
Is weak, and unless it interferes with the light from the light emitting section 6 on the other side of the adjacent block, the development potential is not significantly affected. As a result, even if one of the two light emitting portions 6 and 6 on both sides of the block emits light and the other turns off, the diameter of the printing dot on the light emitting side is not affected, and the light emitting portion 4 inside the array 2 is not affected.
A printing dot having the same dot diameter as that of is obtained.

FIG. 3 shows the arrangement when a plurality of LED arrays are used as a unit. Assume that there is a block boundary on the right side of the array 2 in FIG. 3 and no block boundary on the left side. In this case, the auxiliary light emitting portions 8 and 10 are provided only on the light emitting portion 6 on the boundary side (right end in the figure). The leftmost and rightmost light emitting portions of the image forming apparatus automatically become the light emitting portion 6 facing the end of the block, and auxiliary light emitting portions 8 and 10 are provided here.

The image forming apparatus also has a substrate on which the LED array 2 is mounted, and a large number of LED arrays 2 are mounted on, for example, one straight line on the substrate. Further, a lens array such as a self-focusing lens array is provided, and light from the light emitting units 4 and 6 is imaged on a photoconductor drum or the like (not shown). Further, the substrate and the lens array are housed in a housing or the like. These points are well known and will be omitted.

The operation of the embodiment will be described with reference to FIGS. In FIG. 4, it is assumed that the LED array 2 has 64 LEDs each, and that there is a boundary between blocks in the center of the drawing. The vertical axis represents the distribution of effective exposure energy for the photosensitive drum, which corresponds to the change in the charging potential due to the exposure of the photosensitive drum. This is because the exposure is performed for each block, and the effect of interference of light from the light emitting units 6 and 6 on both sides is small at the boundary between the blocks.
The distribution of exposure energy has a peak value of 100%,
It is preferable to set about 40% between dots, and empirically, under this condition, it is possible to perform printing with excellent expressive power from all black to isolated printing dots.

The light emitted from the light emitting portions 4 and 6 has a beam diameter that is approximately doubled by a lens array (not shown) and partially overlaps each other to form an image. The degree of overlap becomes more significant as the resolution is increased and the gap between the light emitting portions is reduced. The exposure situation is shown in FIG. 5, which shows a large number of LEDs mounted on the substrate 51.
If array 2 is divided into two blocks as shown,
The timing of exposure of the photosensitive drum 52 is as shown in the lower side of FIG. That is, the timing differs for each block.

If the exposure timing is different, the effect of the interference of light from the light emitting portions 6 and 6 on both sides of the block is small, and the surface potential of the photosensitive drum 52 is sufficient at the boundary between the blocks as shown by the solid line in FIG. It will not decrease. This causes white streaks in the case of reversal development and black streaks in the case of regular development. On the other hand, as shown in FIG. 1, if the auxiliary light emitting parts 8 and 10 are provided in the light emitting part 6 which is in contact with the boundary of the block, when the light emitting parts 6 and 6 on both sides of the block are both emitting light, the auxiliary light emission is performed. By overlapping the light from the portions 8 and 10, the intermediate region between the light emitting portions 6 and 6 is sufficiently developed, and the exposure characteristics as shown by the broken line in FIG. 4 are obtained. As a result, white streaks and black streaks disappear. On the other hand, for example, the LED 64 on the left side of FIG.
When D1 is off, the light from the auxiliary light emitting portions 8 and 10 of the LED 64 is weak by itself, and the printing dot diameter of the LED 64 is almost the same as the isolated printing dot diameter of the other light emitting portions 4. This is because the threshold value of development is less than 40% on the vertical axis in FIG. 4, and the toner hardly adheres at exposure energy below this value. As a result, it is possible to prevent the occurrence of white streaks and black streaks without changing the dot diameter of the light emitting portion 6 in contact with the boundary of the blocks.

[0021]

According to the present invention, it is possible to prevent a white line or a black line due to insufficient exposure at a block boundary in an image forming apparatus,
An image forming apparatus with high print quality is provided. Further, since the problem of white streaks and black streaks becomes more serious as the resolution of the image forming apparatus increases, prevention of white streaks and black streaks is particularly important in providing a high resolution image forming apparatus.

[Brief description of drawings]

FIG. 1 is a plan view of an essential part showing the arrangement of both ends of an LED chip used in an embodiment.

FIG. 2 is a plan view of a main part of a modified LED chip.

FIG. 3 is a plan view of an essential part of an LED chip of another modification.

FIG. 4 is a characteristic diagram showing exposure characteristics in the image forming apparatus according to the embodiment.

FIG. 5 is a diagram showing exposure timing of the image forming apparatus of the embodiment.

[Explanation of symbols]

 2 LED array 4 Light emitting portion inside array 6 Light emitting portion in contact with block boundary 8, 10 Auxiliary light emitting portion 12 Electrode 14 Bonding pad 20 Extension portion 51 Substrate 52 Photoreceptor drum

Claims (1)

[Claims] 1. An image forming apparatus in which a large number of LED arrays are mounted on a substrate, at least one LED array is formed as a unit, and the LED array is driven for each block. An image forming apparatus, wherein a light emitting portion of an LED in contact with a boundary is extended toward a boundary side of a block so that an area of the light emitting portion is larger than that of other LEDs.