JPS6090782A - Printer utilizing light-emitting diode - Google Patents

Abstract

PURPOSE:To contrive to enhance efficiency in utilizing light-emitting energy and to reduce the size and the cost of a printing head, by a method wherein LED array chips are retracted slightly from an end of a wiring board, are fixed, and the surface of the wiring board is treated to absorb light. CONSTITUTION:The LED array chip 605-m is a monolithic array in which end face light-emitting type LEDs 701-1, 701-2,... are arranged in a row, and the PN junction planes of the LEDs 701-1, 701-2,... are disposed in parallel to an adhered surface between the LED array chip 605-m and the wiring board 603. Light is emitted from end faces 702-1, 702-2,... in the direction of an arrow (b). Electrodes for the LEDs 701-1, 701-2,... are provided on upper surfaces, and are connected to LED-driving terminals 703-1, 703-2,... by wire bonding. With this end face light-emitting type construction, light is emitted centralizedly in a direction perpendicular to the light-emitting surfaces, and the efficiency in focusing the light on a surface of a photosensitive drum is enhanced. When the sensitivity of the photosensitive drum is equal to that of a conventional photosensitive drum, a driving current for the LEDs 701-1,... can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a light emitting diode (L) as an exposure device for image formation.
light emitting diode, hereinafter LE
The present invention relates to an electrophotographic optical printer using an LED printer head equipped with an array (referred to as D).

This type of electrophotographic optical printer uses the slit exposure and original image forming optical system of a general electrophotographic copying device.
Main scanning direction: It incorporates an image-forming exposure device that can image a row of bright spots of a valve train on a drum and can turn on and off any bright spot.In particular, LED play printers
11\ As a means of generating a bright spot row, dozens of minute LEDs are arranged in rows or in multiple rows, and an image forming system is used as an exposure device for image formation, which is integrated with a merging optical system that marries the image on the drum surface. It was there.

FIG. 1 shows a schematic configuration diagram of a conventional LED array printer. 101 is a photosensitive drum that rotates in the direction of arrow a. 1
A primary charger 02 uniformly charges the surface of the photosensitive drum 1010. 103 is a conventional LED printer head;
Here, only the charges on the surface of the photosensitive drum 101 where the bright spots are fixed are moved, and the charges on other parts remain as they are. That is, a static 11te image is formed. Next, when passing through the developing device 104, the photosensitive drum 101 at that time
Depending on the presence or absence of charge on the 0 surface, toner adhesion or non-adhesion occurs, and the image on the photosensitive drum 101 becomes a liA image. As is well known, in the above process, the polarity of the bright spot produced by the LED printer head 103 and the polarity of the toner put into the developing device 104 can be arbitrarily determined depending on the combination.

An image created by the toner that has passed through the transfer device 104 and formed a wA image is transferred to paper supplied from a cassette 106 or 107 by a transfer charger 105. When the paper passes through the fixing device 1080, the toner transferred from the photosensitive drum 101 is fixed on the paper. 109 is a cleaner for toner remaining on the photosensitive drum 101, and 110 is a static elimination lamp.

FIG. 2 shows an LED printer head 103. As shown in FIG. L.E.
3 is a perspective view of a D array substrate 201. FIG.

202 is a board that also serves as a heat dissipation plate, and is 203°204.
Reference numeral 205 is a wiring means made of a ceramic substrate or the like. Cables 206 and 207 are used to connect image signals and a power source.

208-1 to 208-n are LED array chips in which LEDs are arranged in a row in the center;
LED drive integrated circuit (hereinafter referred to as IC), which has a built-in serial-parallel conversion circuit for image signals input from cables 206 and 207, etc.
). This LED0g arraytephum group-m and LED drive I C209-
FIG. 3 shows an enlarged view of the portions 210-m and 210-m arranged in a row in the center. Odd number ■D301=1,
301-3 , ... is an even numbered LD301 on the upper side.
210-m each LED driving terminal 302-1, 302
-2.

. . 303-1, 303-2, . . . have wire dumping, respectively.

As described above, the LED array board 201 (l''1. consists of 9, cables 206, 207 and F) @ image signal is sent to 1 valve sequentially, LED drive IC 209-1 to 209-n
, 210-1 to 210-n are input, and after shifting one column of data, this is sent in parallel to the LED drive terminal 302.
-1, 302-2,..., 303-1, 30
3-2, ..., each LED turns on and smokes off according to the removal, and a bright spot for image formation of -0th 4th is generated.
Figure 1 shows the relationship between the LED light emitting section and the imaging point on the drum surface. The LED array tip 208-m forms an image on the photosensitive drum 101 by a selfoc lens array or the like. Here, when the angle θ is 71%, the light beam L1 from LED 301-1 is reflected by the imaging system 401,
The light beam becomes Ll-t and enters, but when the angle θ increases,
A part of the luminous flux is no longer incident. And the incident luminous flux Ll
-t only reaches the photosensitive drum lO1, and the end is 1.
The light distribution characteristics of the sign D301-1 are as shown in FIG. 4-2, and the luminous flux density becomes high even in the direction where the angle θ is considerably large. In this way, it is approximated that all of the light flux from the light emitter having an orientation characteristic almost equal to that of a sphere is incident on the binding thread 401 up to the angle θ, and it is not incident above θ, and the ratio of the input energy to the output light energy of the light emitter is calculated. calculate,
Table 1 summarizes the results.

Table 1 On the other hand, current conclusion 1: J! Even if the vessel 401 can have a relatively large θ, ll and to in Fig. 4-1 are 3wi.
, la is about 9n, 69, and θ is about 15''. Therefore, even if we ignore the deterioration of the light in the imager 401, the LED 3
Approximately 13 more than 01-1 total energy photosensitive drum 10
1 cannot be transmitted.

FIG. 5 shows the shape of the LED light emitting section. 501 in the diagram is LE
502 is an effective light emitting surface, 503 is an electrode, and 504 is a connection surface between the electrode and the LED. Therefore 1
The size of the PN junction surface of the LED for each pixel is the effective light emitting surface 5
02 and a connecting surface 504.

On the other hand, the light emission of the LED is perpendicular to the effective light emitting surface 502.
The light distribution characteristics are as shown in FIGS. 4-2. The light output is approximately proportional to the current density of the PN junction surface below the effective light emitting surface 502. On the other hand, the LED corresponding to each pixel
Since the light emitting direction is arranged in a line, the size of one side of the effective light emitting surface 502 of the LED is smaller than the pixel pitch in order to form a separation between adjacent pixels.

For example, in an LED display that forms 1n pixels, the pixel pitch is 100 μm, but the size of the effective light emitting surface is approximately 80 μm×80 μm.

That is, 20 ttm is required to separate pixels. On the other hand, in order to obtain a clear digital image, generally 1
It is necessary to form 166 pixels per u. In this case, the pixel pitch is 62.511 m, and the effective light emitting surface is 4.
It becomes about 01tm×40μm. In this way, when the pixel density is increased by 1.6 times from 10 pixels/frame to 16 pixels/U, the effective light emitting area becomes 1/4.

As shown in Figure 2, when a drive IC is mounted together with an LED array tag and each row of LED lights is lit at the same time, when the process speed is the same, the points between one pitch Light time is 10 pixels/
In the case of 16 pixels Nx, the time is shorter to 100 than in the case of 16 pixels. Therefore, if the sensitivity of the drum is the same, 16 pixels/IIm requires 1.6 times the illuminance per 1 m area. On the other hand, the area of one cumulative stroke is (-g)2 for 16 pixels/order compared to 10 pixels/dragon, so the light emitting output per pixel of the light emitting part of 16 pixels/order is 10 pixels /Dragon is "100-".On the other hand, as mentioned above, the effective light emitting area is 1/4 of 16 pixels/U, so the current density of each LED of 16 pixels/Dragon is 1/U = 2. From .5, it becomes 1.64 2.5 times.

In addition, a drive method in which the electrodes of the LED array TEG are arranged in an n×m matrix and only n lights are turned on at the same time in m time divisions is used to reduce the number of drive circuits and reduce costs. There is also. In this method, from 1° pixel/ljl to 16
If the density is increased to mX71111 and the number n of simultaneously driven LEDs is kept the same, the number of time divisions becomes 1.6 times. Therefore, in this case as well, when the process speed is kept the same, the time required to form one pitch, that is, one dot, is reduced to (1)2 compared to 10 pixels.

1.6 Therefore, in this case, the same amount of light emitting output per pixel of the light emitting part is required for both the 10 pixels/H and 16 pixels/H, and the current density of each LED for 16 pixels/111+ is required to be four times as large. Become.

The luminous efficiency of an LED tends to decrease as the current density increases, and the lifetime of a DLED decreases as the current density increases. Furthermore, it is well known that when the pixel density is increased due to manufacturing problems, the luminous efficiency decreases.

In other words, when increasing the pixel density, there is a corresponding decrease in luminous efficiency, so it is necessary to increase the current density9.
As mentioned above, in order to increase the pixel density by 1.6 times, the current density must be further increased by 2.5 to 4 times. As a result, the life span #2 of the LED is shortened.

In this way, when using a conventional LED array chip to form an image of the f-image of the LED light emitting surface on the citrum surface using the imaging system, only about 10 - of the total light emission energy of the LED can be used. . Therefore, in order to increase the amount of light, LE
It is necessary to increase the drive current of LED array 208-1 to 20g-n 4F L E
D drive IC209-1~209-n, 210
-1 to 210-n increase in power consumption, it is necessary to use an IC with drive capability, and it is necessary to make the heat sink 2024 large, which causes problems of increased cost and increased size.

The present invention aims to eliminate various problems caused by the low utilization efficiency of emitted energy in conventional printers as described above, downsize the LED printer head, and provide a low-cost printer. 0 Hereinafter, embodiments of the present invention will be described using rotation directions.0 FIG. 6 shows a perspective view of an LED array substrate 601 of the present invention. 602 is a substrate that also serves as a heat sink, and 603 is a wiring means made of a ceramic substrate or the like. Reference numeral 604 denotes a cable for connection with image signals and a power source.

605-1.

605-2, . . . are LED array chips in which a plurality of edge-emitting LEDs are arranged at the edge of the chip, and 606-
i, 606-2. ... is LED array chip 605
-1.

A driver circuit that drives 605-2, . . . , i.e.,
0, which is an LED drive IC with a built-in serial-parallel conversion circuit for the image signal input from the cable 604.
This LED array chip 605-m and LED drive I
FIG. 7 shows an enlarged view of the C606-m portion.

The LED7 Ray Chip 605-m is an edge-emitting type L E
A monolithic LED array in which D 701-1 and 701-2 are arranged in a row, and each L E D 7
PN junction surface of 01-1, 701-2, ..., L
It is parallel to the bonding surface between the ED array chip 605-m and the wiring board 603. The light is emitted from the end faces 702-1, 702-2, 702-3 in the direction of the arrows.The electrodes of the OLEDs 701-1, 701-2... The LED drive terminals 703-1, 703-2, . . . of the IC are wire bonded.

FIG. 8 shows a diagram of the relationship between the light emitting surface 702-1 of the LED 701-1 and the image forming point on the surface of the photosensitive drum 1010. This diagram is basically the same as FIG. 4-1, and the light emitting portion LED of
Even when using an LED with a different shape, that is, an edge-emitting type, the image formation form of the light emitting surface remains the same as before.

On the other hand, the light distribution characteristics of LED 701-1 are as shown in Figure 9, and when the angle θ increases to a certain extent, the luminous flux density decreases rapidly.
When configured, light emission is relatively concentrated in a direction perpendicular to the light emitting surface, and light deviated from the perpendicular direction is not emitted much. Approximating that all the light rays from the light emitter with such light distribution characteristics are incident on the imager 401 up to the angle θ, and no rays greater than 0 are incident, the ratio of the input energy to the total output light energy of the light emitter is calculated as follows: Table 2 is a summary of the calculations.

By creating an edge-emitting LED in this way, it is possible to condense 18.1% of the total energy onto the surface of the photosensitive drum 1010 when using the imaging system 401 with θ of about 15'. If the sensitivity of the photosensitive drum 101 is the same as the conventional one, the drive current for driving the LED 701-1 will be about 70%.

On the other hand, in order to eliminate unevenness in the image, it is necessary to eliminate variations in the size of the effective light emitting surface 502 so that all LED light emitting surfaces have the same size. To form such individual LEDs on the same chip, conventional LED
For arrays, it is necessary to create monolithic LED arrays using a process using vapor phase growth, which requires the following steps:
It was necessary to use GaAs P LED material, which has poor luminous efficiency. However, in the LED array tip used in the present invention, as shown in FIG.
-1, 702-2... Since it is a fully formed LED array chip 605-m, there is no need to configure multiple LEDs on the chip using vapor phase growth method, and they are formed using liquid phase growth method. It can be made by cutting out a groove that cuts out the joint surface of the PN machine in the expensive edge-emitting LED tag, and separating it into multiple LEDs. Monolithic LED arrays can be created from LED materials. Therefore, conventional LE
Compared to the D array, it is possible to emit light with several times the efficiency. In other words, only a fraction of the current is required to obtain the same light gong.

In conventional LED array boards, the LED drive current is large, so the drive circuit of the LED drive IC needs to be a bipolar transistor, and other serial
Logic circuits such as parallel conversion wanted to minimize current, so it was necessary to use I2L, etc., so the drive frequency was
At most, it is only about 19, but high-speed image formation is not possible, and in order to speed up to a practical level, it is necessary to divide the whole into multiple parts and add 1lli 1 to each partial row.
A method had to be used in which one signal was parallelized and each part was serially input.

Therefore, it is necessary to correct the input value δ to the LED array board, and this correction circuit is expensive, which hinders its practical use.However, with the present invention, the driving current of the LED can be reduced. Now that we have it, we can create a high speed, low power consumption IC.
It has become possible to configure an LED drive IC using this technology, and it has become possible to send signals to the LED array board without the need for an input signal correction circuit.

In addition, in conventional LED arrays, as the pixel density increases, the PN junction surface of nine LEDs per one must be made smaller, and the current value per pixel, that is, per one LED, must be kept constant. Also, by making the light emitting surface of the LED smaller, the PN junction surface is also smaller, which increases the current density and shortens the lifespan. For that purpose, Narube (L
The application of ED was limited to the inverted 3A image method, which develops the areas hit by light black so as not to emit light. However, when using an edge-emitting LED as in the present invention, even if the light-emitting surface is made smaller in order to increase pixel density, the length from the old end face to the opposite end face must be increased accordingly. , it is possible to prevent the area of the PN junction surface from becoming small, the current density does not increase, the lifespan can be extended, and the electrophotographic printer uses forward rotation development that takes a lot of time to damage the LED. However, in the present invention, an edge-emitting type LED array is used instead of the conventional surface-emitting type LED array, so it is necessary to position the bright spot generating surface at the edge of the substrate. be. However, edge-emitting LE
When the D array chip 605-yx is aligned with the edge of the wiring board 603 and fixed, the light emitting surfaces 702-1, 702-2,
... can form on the corners and be easily damaged, making maintenance difficult. For this reason, in the present invention, as shown in FIG. 7, the wiring board 606 is pulled in from the end of the wiring board 606 and fixed.
Displacement length between the ED array chip 605-11L and the end of the wiring board 603: 1. is LED array chip 605-
When the height from the bottom surface of 711 to the light emitting surface 702-1 is ly, it is sufficient if lx≦ly/tanθ.

However, if the surface of the wiring board 603 is a mirror surface, a virtual image of the mirror surface will be formed on the surface of the photosensitive drum 101, and even if it is a scattering surface (white) with high reflectance, it will become a source of noise. The surface of the wiring board must be treated to absorb light.

The surface of K may be colored black, or a black material may be used for the wiring board.

As described above, by fixing the LED array chip by retracting it a little deeper than the edge of the wiring board, and providing a means for absorbing light at least on the surface of the wiring board that appears as far as the LED array chip goes into the back. , low maintenance LED
It will be possible to provide array printers.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the configuration of a conventional LED printer, Figs. 2 and 3 are schematic diagrams showing the configuration of a conventional LED printer head, and Fig. 4-1 is a schematic diagram showing the configuration of a conventional LED printer head. A diagram showing the image formation relationship between and a photosensitive drum,
Fig. 4-2 is a diagram showing the light distribution characteristics of a conventional LED, Fig. 5 is a diagram showing the light emitting surface shape of a conventional LED array, Fig. 6,
FIG. 7 is a schematic diagram showing the configuration of an LED array board used in the present invention, and FIG. 8 is a diagram showing the imaging relationship between the LED light emitting section and the photosensitive drum in an embodiment of the printer of the present invention.
FIG. 9 is a diagram showing the light distribution characteristics of the LED used in the present invention. , 605-1.605-2 , ..., 605-n
...Edge-emitting LED array chip, 606-1,6
06-2,...,606-ru...LED drive IC1701-1,701-2,701-3...Edge-emitting LED, 702-1.702-2.7[]2-3
... End face, 703-1, 7[]3-2.703-3
...LED drive terminal. Applicant Canon Co., Ltd.

Claims (2)

[Claims] (1) In a printer using light emitting diodes that selectively lights up each light emitting diode of a light emitting diode array in which a plurality of light emitting diodes are arranged in one row at least in several steps to form a dot-divided image on a photoreceptor, The light emitting diode play is constituted by a monolithic light emitting diode array chip provided on a substrate and emitting light from an edge thereof, and the light emitting surface of the monolithic light emitting diode array chip is recessed deeper than the edge of the substrate. A printer using light emitting diodes. (2) A printer using a light emitting diode according to claim 1, wherein means for absorbing light from the monolithic light emitting diode array chip is provided on the upper surface of the light emitting side of the substrate.