JPS6357265A - Optical writing method by led array head - Google Patents

Abstract

PURPOSE:To obtain a good image having neither white stripe nor fog in the background part thereof, by allowing the light emitting points at the end parts of the LED chips in an LED array head to light at higher brightness as compared with the light emitting points other than said light emitting points. CONSTITUTION:An LED array head is constituted so that a large number of LED array chips 10 are linearily arranged on a substrate 9 and drive ICs 11 are arranged to the adjacent parts thereof and electric signal is sent to respective LED light emitting parts from the drive ICs 11 through bonding wires 12 to allow LEDs to emit lights. The serial data corresponding to a lighting pattern is supplied to a shift register 25 and latched in a latch circuit 26 in predetermined timing to drive each LED. Further, by making the limit resistance values for the supply currents of LEDs 23, 23A lower than those to LEDs at parts other than the end parts of the chips and increasing brightness, the extreme recessed parts between the chips are corrected. Therefore, the potential irregularity on a photosensor is eliminated and the stripe like fog of a background part is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical writing method using an LED array head.

2. Description of the Related Art In an optical writing device used in a printer using an LFD array as a light source, the LFD array head has a structure in which a plurality of LED chips are linearly arranged on a substrate. In this LED array head, L
The FD has a structure as shown in FIG. 6, and its light emitting portion is configured as shown in FIG. That is, a p-type head region 1B is provided on the surface of the n-type indirect transition compound 17, and an electrode 19 is provided in a part of the p-type region. Note that 20 is an insulating layer, and 21 is an n-type electrode. The light emitting section 22 is
They are arranged in a line at predetermined intervals in the main scanning direction, and the width of the light emitting parts is generally set to 90% or less of the dot pitch so as to form an electrically insulating layer.

When an LFD array head having such a structure of LEDs is turned on, the light image irradiated onto the photoreceptor is as shown in FIG. 8, even when all the light emitting parts are turned on.
The brightness is high in the light emitting part, and the brightness is low between the light emitting parts, resulting in uneven light emission. Therefore, even in the electrostatic latent image formed on the photoreceptor, potential unevenness occurs in accordance with this uneven light emission. Such potential unevenness can be eliminated to some extent by appropriately selecting the developing bias in the developing process, and a uniform solid image can be obtained in the case of a negative writing method, and a uniform solid image can be obtained in the case of a positive writing method. A clear background can be obtained.

Problems to be Solved by the Invention However, the LED array head is constructed by arranging a plurality of LED chips each having dozens to hundreds of light emitting parts arranged on a substrate in rows, and the joints of the LED chips are arranged in rows on a substrate. As shown in Figure 4, there is a gap in the chip cutting area and a mound of chip adhesive.
There are many parts where the pitch is wider than the light emitting part pitch within the LED chip due to blurring and the like.

FIG. 9 is a cross-sectional view in the main scanning direction showing a fully lit light emitting state near the joint of the LED chip. As is clear from FIG. 9, 1. - At the junction of the ED chip, the interval between the light emitting parts spanning the chip is wider than the interval between the other light emitting parts, so an extremely low brightness area occurs in that part. Due to the potential unevenness caused by this uneven light emission, the developed image cannot be formed into a solid image by the chip length in the process direction in the negative writing method (image area exposure: in this case, the area corresponding to the image area is exposed). In the positive writing method (foreground area exposure: in this case, an area corresponding to the background area is exposed), white streaks occur at equal intervals, and streak-like blurring occurs.

Therefore, the present invention uses such an LED array head to obtain a solid image in a negative writing method or a good image without white streaks or fog in the background area in a positive writing method. The object of the present invention is to provide an optical writing method that enables the following.

Means to Solve the Problem As a means to solve the above-mentioned uneven light emission, it is possible to blur the focus of the self-cleaning lens (Japanese Patent Laid-Open No. 56-2716
(Japanese Patent Laid-Open No. 60-3198'1), or the interval between LED chips is set to 1/2 or less of the pitch (Japanese Patent Laid-Open No. 60-3198'1).
Although such methods have been proposed, the present inventors solved the above problems by a method completely different from these conventional techniques.

That is, the present invention provides an optical writing method in which writing is performed by lighting LEDs using an LED array head formed by linearly arranging a plurality of LFD chips on a substrate, which includes: LED chips in the ED array head; It is characterized by lighting the light emitting points at the ends with higher brightness than the other light emitting points.

Function The function of the present invention will be explained with reference to FIG. Figure 1 shows
The figure shows luminance A) near the chip junction A when the LED array head is turned on according to the present invention. As is clear from Fig. 1, the light emitting points at the ends of the LED chips arranged in a straight line are lit with higher brightness than the other light emitting points. (b) No drop occurs, and as a result, potential unevenness on the photoreceptor does not occur.

Example The present invention will now be explained in more detail by way of examples.

FIG. 2 is a schematic cross-sectional view of a 1-FD array head to which the present invention is applied, in which a plurality of 1-FD array chips 10 are linearly arranged on an LED array board 9-1-. There is a drive IC 1 for the IFD drive in the adjacent part.
1 is installed. Each 1-10 light emitting section has
An electric signal is sent from the drive IC 11 through the bonding wire 12, and the LED emits light. 13 is this LE
This is a self-sized ivy lens for imaging the D light emitting pattern onto the photoreceptor 1, and is positioned at the center of the LFD light emitting section and the photoreceptor by the selfoc lens indicating member 14.

Note that 15 is a fin for heat radiation.

The LEDs in the LED array head have a structure as shown in FIG. 6, and the LFD chip junction has a state as shown in FIG. 4.

That is, the distance d2 between the light emitting part at the end of chip A and the light emitting part at the end of chip B is equal to the distance d1 between the light emitting parts at the center part of the chip.
It is wider than.

The above IFD array head is installed as an optical writing device in, for example, an LED printer shown in FIG. In FIG. 3, after the surface of the photosensitive drum 1 is uniformly charged by a charge corotron 2, optical switching is performed by turning on and off each LED element in an LED array head 3 incorporating an LED array and an imaging element. An electrostatic latent image is formed on the photoreceptor drum 1. Thereafter, the latent image is visualized by the developing device 4 and transferred onto the transfer paper 8 fed by the supply roll by the transfer roller 5.

After the transfer, the transfer paper 8 is sent to the fixing device 6 and is fixed. On the other hand, the surface of the photoreceptor drum 1 is cleaned by the cleaning device 7 in preparation for the next operation.

In the present invention, the light emitting section at the chip end of the LED array head described above is made to output a brightness higher than the average brightness of the portion other than the chip end, and the means for doing so will be explained with reference to FIG. do. In the figure, 25 is a shift register, and 26 is a latch circuit. Serial data corresponding to the lighting pattern is supplied to the shift register 25, stored in the latch circuit 26 at a predetermined timing, and drives each LED. 24 and 24A are L
24A represents the limiting resistor for the supply current of ED23 and 23A, and 24A represents the limiting resistor to L'D23 at the end of the chip.

By making this limiting resistance lower than the limiting resistance value for the LFD in parts other than the chip end, the LFD at the chip end can be
The current supplied to the ED can be increased, and the brightness can be increased.

The optimal level for lowering the resistance value differs depending on the chip-to-chip distance. Therefore, after arranging the LFD chips, it is also possible to measure the distance between each chip and set the resistance value according to the distance.

Effects of the Invention FIG. 1 shows the luminance distribution near the chip junction when the lamp is lit according to the invention. In the present invention, since the brightness of the LED light emitting portion at the end of the chip is high, the extreme recess between the chips as shown in FIG. 9 can be corrected. Therefore, there is no potential unevenness on the photoreceptor, and as a result, white streaks in a solid image during negative writing or streak-like fogging in the background during positive writing are prevented.

[Brief explanation of the drawing]

Fig. 1 is a one-degree drawing of the vicinity of the chip junction when the L E l) array head is fully lit according to the present invention, and Fig. 2 is a drawing to which the present invention is applied. The cross-sectional view, FIG. 3, is an explanatory diagram illustrating the general configuration of an LFD printer equipped with the D array head shown in FIG. 2. (Schematic plan view of the vicinity of the pull chip joint, 5th
FIG. 6 is an explanatory diagram of the means for controlling the light emitting output according to the present invention. FIG. 6 is an explanatory diagram of the structure of the 1-FD. FIG. Schematic plan view of ε3
The figure is a schematic diagram of an optical image when all of the L and ED chips are turned on, and FIG. 9 is a diagram of the luminance distribution near the chip junction when all of the LED array heads are turned on using a conventional method. 1...Photoconductor, 2...Jikinojini] Mouth 1, Ron,
3...[-ED array head, 4...Developing device [6,
5... Transcription = 1 [11 ~ Ron, 6... Fixed @ device, 7.
...Cleaning equipment (6, 8...recording paper, 9...L
D array board, 10...1 - "D array chip, 1
DESCRIPTION OF SYMBOLS 1...Drive IC, 12...Hondaing wire, 13...Selfoc lens, 14...Selfoc lens support part shrine, 15...fin, 16...cover, 17...n type indirect transition compound, 18... p-type region, 19... electrode, 20... insulating layer, 21... electrode, 22... light emitting part, 23 and 23Δ... IFD, 2
4 and 24A...limiting resistor, 25...shift register, 2G...latch circuit. Special i% applicant Tomiju Xerox Co., Ltd. Agent
Patent Attorney Tsuyoshi Horabe Fig. 1 Fig. 2 Fig. 3 d+ dz Fig. 4 Fig. 3-A Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9

Claims (1)

[Claims] (1) In an optical writing method in which writing is performed by lighting LEDs using an LED array head formed by linearly arranging a plurality of LED chips on a substrate, the light emitting point at the end of the LED chip in the LED array head is L characterized by lighting at a higher brightness than other light emitting points.
Optical writing method using ED array head.