JPS60163062A - Led printer - Google Patents

Abstract

PURPOSE:To form a picture having no black line nor white line by providing a means for reducing an MTF of an optical image only in the sub-scanning direction, between an LED array formed by arranging an LED having a longer light emitting surface in the main scanning direction than in the sub-scanning direction, and a photosensitive body. CONSTITUTION:As for a substrate 901, an image forming optical system 902 of a focusing optical conduction body, etc. is extended and formed in the light emitting direction of an LED array chip 605-1,.... Between the optical system 902 and the light emitting surface of the chip 605-1,..., a cylindrical ens 903 is fixed. The substrate 901 is installed vertically to the surface of a photosensitive drum. In this way, as for the image forming optical system containing the lens 903, although an MTF of the longitudinal direction (main scanning direction) of the light emitting surface of the LED605-1,... remains as it is, an MTF of the lateral direction (sub-scanning direction) is reduced, and a light from the LED expands in the sub-scanning direction and forms an image. Therefore, a picture of a good quality having no black line nor white line can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an optical printer that uses an LED printer head equipped with an LED array as an exposure device for image formation.

<Prior Art> This type of electrophotographic optical printer uses a single line of bright spots in the main scanning direction on a drum, instead of the slit exposure and original image forming optical system of a general electrophotographic copying device. Can be imaged,
It incorporates an exposure device for image formation that allows bright spots to be turned on and off at will. In particular, LED array printers are devices in which dozens of tiny LEDs are arranged in rows or in multiple rows as a means of generating a row of bright spots, and are integrated with an imaging optical system that forms images of these onto a drum surface. was used as an exposure device for image formation.

FIG. 1 shows a schematic configuration diagram of a conventional LED array printer. 101 is a photosensitive drum, which rotates in the direction of arrow a.

A primary charger 102 charges the surface of the photosensitive drum 101 uniformly. Reference numeral 103 designates a conventional LED printer head, in which only the charge on the surface of the photosensitive drum 101 where the bright spot is imaged moves, and the charge on other parts remains unchanged. That is, an electrostatic latent image corresponding to the optical image is formed. Next, when the toner passes through the developing device 104, toner may or may not adhere depending on the presence or absence of charge on the surface of the photosensitive drum 101 at that time, and the latent image on the photosensitive drum 101 becomes visible. In the above process, the LED printer ~
Whether or not toner is attached to the part of the photosensitive drum 101 irradiated with a bright spot by the dot 103 can be arbitrarily determined by the combination of the polarity of the charger 102 and the polarity of the toner put into the developing device 104. As is well known.

The toner image that has passed through the developing device 104 and has been visualized is transferred by a transfer charger 105 onto paper supplied from a cassette 106 or a cassette 107. When the paper passes through the fixing device 108, the toner transferred to the paper from the photosensitive drum 101 is fixed to the paper. 109 is a cleaner for toner remaining on the photosensitive drum 101, and 110 is a static elimination lamp.

Here, the LED array used in the LED printer head 103 will be described in more detail based on FIGS. 2 to 4. FIG. 2 is a perspective view of the LED array board, FIG. 6 is a plan view of the LED array chip, and FIG. 4 is a wiring diagram showing the connections of each LED.

In these figures, n LED chips (208-1
m LEDs formed in each of ~2[18-n') (301-1-1-301-1-m, ~
, 301--n-1 to 301-n-m) have one end connected to the segment signal line (302-1 to 302-m) and the other end connected to the group selection signal line (209-1 to 209-n). These are connected to each other to form an nxm matrix wiring.

The I, ED array drive circuit 401 receives a data signal D, a clock signal C1k, and a data enable signal EN.

Here, the operation of the LED array drive circuit 401 is described below (
1) to (11) will be explained. (1) While the data enable signal EN is 1, one column of LEDs (30
1-1-1 to 301-nm) in synchronization with the clock signal C1k. (11) When the first m pieces of data are manually generated, L E
In order to turn on and off D (301-k (k=1.2.-, n)), segment signal lines (302-1 to 302-
Put a signal on m). At the same time, the group selection signal line 3
- Ground 209-1 and connect other group selection signal lines (209-2 to
209-n') is made floating. (iii)
When the next m data are input, a new signal is placed on the segment signal lines (302-1 to 302-m) and the group selection signal line 209-2 is grounded, as in the previous case.
Make other group selection signal lines floating.

In this way, data is divided into m pieces, and LEDs for - columns (
301-1-1 to 301-n-m) are driven by m pieces (n time-division driving in groups of m pieces), and L for - columns is driven.
Create an ED image pattern. In addition, the last chip is 20
The data for 8-n is m clock signals C1k.
segment signal lines (302-1 to 302
-m), the group selection signal line 209-n is grounded, and then becomes floating.

Referring to FIG. 5, the operation of the LED array drive circuit 401 will be described in more detail. This figure is a block diagram of an example of the LED array drive circuit 401. The data signal is
Serial-in/parallel-out shift register 501
Serial in terminal 4- is connected to the terminal. Clock signal C1k is connected to shift register 501 and timing generator 502. The enable signal EN is supplied to the timing generator 50.
Connected to 2. The timing generator 502 outputs a latch signal 502 before the enable signal BN rises.
-l and group selection signal (502-1 to 502-n')
Set all to O. The operation will be explained in (1) to (1) below. (1) When the timing generator 502 counts m clock signal pulses after the enable signal EN rises, the shift register 501
m pieces of data will be output from the parallel outputs (501-1 to 501-m). (11) A pulse is output to the latch signal 502-A in accordance with the timing.

(++1) At the same time, the group selection signal 502-1 is set to 1.

Therefore, the latch 506 holds the first m data in parallel, and the driver 504 causes the LEDs (601-1-
1 to 301-1-m) are output to the segment signal lines (302-1 to 302-m). (1
The group selection signal line 20 is still connected by another driver 505.
Only 9-1 is grounded, and the other group selection signal lines (209-2 to
209-m) becomes a floating state. Thereafter, the timing generator 502 counts m pulses of the clock signal C1k after the enable signal EN falls, and finally changes the group selection signal 502-n from 1 to 0, thereby changing the group selection signal. Line (209-1~20
9-m) are all made floating.

By the way, the light emitting surface of the LED is approximately square.

In order to make it possible to print an A3 size at a pixel density of 16 pixels/mm, since the short side of the A3 size is approximately 300 mm, it is necessary to arrange approximately 4,800 LEDs in one row. If one group consists of 128 LEDs and 37 groups are lined up, there will be 4736 LEDs, and the total length will be 296 m.
It becomes m. That is, m is set to 128, n is set to 37, and each LED is driven in a matrix. In this case, the time it takes to turn on one LED to print out a portion of the pixels is at most 1/I7 of the time it takes to print out one row of pixels. Therefore, drivers and latches are connected in parallel to each of the 4736 LEDs, and image signals for one column are taken out in parallel using a 4736-bit serial-parallel converter.
This latch holds the data and obtains the same amount of exposure compared to when each LED is turned on and off according to the image signal for the same amount of time as the printout time of one row of pixels as described above. For this, the amount of light from the LED would be 37 times greater if the printing speed was the same as above.

Here, the LED used in the conventional LED array head
The array chip is made of GaAsP, has an emission wavelength of 650 nm, and has a pixel density of 16 pixels/mlT+.
The amount of light emitted by D is 1. When a current of 10 mA is applied to each LED, the current is about 8 μW. On the other hand, even if a highly efficient focusing fiber array is used as an imaging optical system for imaging the light-emitting surface onto the photosensitive drum, the efficiency is only about 10%. Even if a drum is used, the above LED is 1μJ/cn? It requires a certain amount of light. In this case, the time required to create an optical image by keeping the photosensitive drum and the LED array relatively stationary is about 49 μs. Then, if this is divided into n times and matrix driven as described above, the time to print one entire portion is 1. ．． It becomes 8ms. Since this is the time to print 1716 mm, the printing speed is approximately 34.5 mm per second. Then A3
It takes about 12 seconds to print one size page.

Therefore, in order to shorten this time to about 4 seconds, for example, the amount of light emission must be tripled. In order to increase the amount of light,
Although it is necessary to increase the driving current of the LED,
Increasing the drive current of D shortens the life of the LED.

For example, in order to compensate for more than 50% of the initial light intensity after 100 hours of lighting, the current density of the LED must be 200 to 300 A/c even if the junction temperature is kept below 80°C.
Must be less than or equal to nr'. Then, 16 pixels/
For mm LED, the LED area is 62.5 tt
m x 62.5 μm or less, and 10 mA
If a current of 256A/crrF is applied, the current density is 256A/crrF
Therefore, applying a current exceeding 10 mA to the LED poses a problem in terms of life span.

Also, ignoring the lifespan, 1. 3 per L E D
When driving at approximately 0 mA, if all LEDs per group are turned on, 3.84 A will flow to the group selection line.

Further, the time during which the first group is selected is approximately 16 μs when printing A3 size in 4 seconds. However, 3
．． 84. It is difficult to switch a large current of A at high speed, resulting in a delay of several microseconds. Furthermore, since this delay time also depends on the magnitude of the current, the amount of light per LED varies depending on the number of lit LEDs per group, making it impossible to obtain a high-quality image.

For these reasons, the above-mentioned LED array printer could only be applied as a low-speed printer.

Therefore, an LE that uses the time-division drive method as described above
Even with D-array printers, various proposals have been made to enable high-speed printing.

An example LED array board is shown in FIG. 6, and a partially enlarged perspective view of the LED array board is shown in FIG.

Here, 601 is an LED array board, 602 is a board that also serves as a heat sink, 603 is wiring means for group selection signal lines made of a ceramic substrate, etc., and 604 is wiring means for segment signal lines. be. 605-1.605
-2, . . , 605-n are LED array chips in which a plurality of edge-emitting LEDs are arranged on the edge thereof. 606
is a cable for drawing out each segment signal line from the segment signal line wiring means 604. Also, 60
4-1 to 604-n are group selection electrodes.

FIG. 7 is a partially enlarged perspective view of the LED array board 601, which shows the vicinity of the LED array chip 6o5- as viewed from the back side of the paper of FIG. here,
The LED array chip 605- includes edge-emitting type r,
ED 701-1.701-2.

701-1.701-2,'-(7
) The PN bonding surface is parallel to the bonding surface between the LED array chip 6o5- and the wiring board 603. The light is then output in the direction of the end faces 702-1, 702-2, =-1,1 arrow b. r, F, D 701-1
, 701-2, =- electrodes are on the upper surface, which are connected to -I! on the wiring means 604. -ri) :/) Wire bonding is performed to the signal lead wires 7o6- to -1, 703- to -2°, and so on. The group selection signal electrode 604- has LE
It is connected to the D array chip 6o5- via an adhesive surface.

In this way, when using the edge-emitting glue ED 701-k, the light emitting direction is parallel to the adhesive surface to the LED array chip 6o5-, so electrodes cannot be drawn out on both sides, so the segment signal is generated only on one side. is connected to one end of each LED of the LED array chip. The wiring means 603 and 604 are the same as conventional ones except that they are on one side.

However, when the pixel density is the same, the density of the leader line of the segment signal is doubled.

For such edge-emitting T and E D, a PN junction is formed by liquid phase growth, an electrode is formed on the entire surface, and then a groove is dug until the PN junction is completely separated from the electrode.
Multiple LEDs can be configured on one chip. For example, in this state, by applying a voltage to the adhesive surface between the electrode of LED-]1-701-3 and the LED array chip 605- and passing a current, a light emission phenomenon occurs at the PN junction surface, but the upper surface is entirely covered with electrodes. 702-3, light is emitted from the end surface 702-3.

In order to form a plurality of LED arrays on one chip, which emit light from the top surface like conventional LED arrays, a process using a vapor phase growth method had to be used. For this purpose, it was necessary to use GaAsP LED material, which has poor luminous efficiency. However, the LE as mentioned above
As shown in Figure 7, the D array chip
The bonding surface is scraped off to separate the LEDs into a plurality of LED light emitting surfaces 702-1. LE that formed 702-2,...
Since it is on the D array chip 605-, there is no need to construct a plurality of LEDs on the chip using a vapor phase growth method.
As mentioned above, it is possible to create a large edge-emitting LED chip formed by the liquid phase growth method by digging a groove that cuts out the PN junction surface and separating it into multiple LEDs, so the luminous efficiency is extremely low. - Monolithic LED array tips can be made with LED materials such as GaAlAs, which have a high Therefore, the conventional L
Compared to ED arrays, it is possible to emit light with several times the efficiency.

That is, in order to obtain the same amount of light, only a fraction of the current is required. Furthermore, in GaAlAs, when the emission wavelength is set to about 750 nm, the emission efficiency increases by an additional 10
It goes up to about 0 seconds. 1μJ/crrF near the emission wavelength
It is possible to create a drum with a sensitivity of Therefore, by adopting this method and using the same circuit shown in FIG.
28) In the case where 37 groups of LEDs are time-divisionally driven, printing equivalent to the conventional one is possible with a current several tenths of that of the conventional one. In other words, to print out an A3 size sheet in about 4 seconds, it conventionally required 030 mA per ILED.
However, the method described above requires a current of 1
~2 mA or more, and only about 250 mA at maximum flows through the group selection signal line, so high-speed switching can be easily realized.

However, the shape of the light emitting surface of the edge-emitting LED as described above is perpendicular to the array direction (i.e., main scanning direction) of the LED array (i.e., sub-scanning direction).
width becomes shorter. Because it is edge-emitting, LE
The width of the light emitting surface in the direction perpendicular to the array direction of the D array is:
The depth is about the same as that of the PN junction, and the half width of the emission intensity is 10μ.
It will be about m. Therefore, even if the light spot on the drum is blurred by a coupling optical system or the like, the width will only be about 15 μm.

On the other hand, even when the diameter of one dot is reduced at a high pixel density of 16 pixels/mm, the size of one side of one dot is 62.5 μm.

With this LED array, when the above-mentioned 37 time division driving is performed while moving the LED array and the photosensitive drum surface at a relatively constant speed, one group is lit in the array direction and the vertical direction of the LED array. Since it moves by only about 1.7 μm during the period of time, even when the entire surface is lit, as shown in FIG.
Light hits only the area 802 of No. 4. As a result, printers that use a process that blackens the areas exposed to light will produce white streaks on fully heated images, while printers that whiten areas exposed to light will generate black streaks on completely white images. There was a problem.

This problem will be explained in more detail based on FIGS. 9 and 10.

In FIG. 9, an imaging optical system 902 such as a converging light transmitting body is disposed at an intermediate position between an end-emitting type LED 701-1 whose end surface 702-1 is a light-emitting surface and a photosensitive drum 101. A schematic diagram of the case is shown. Here, the imaging optical system 902
The distance l from the exit surface 902a to the surface of the photosensitive drum 101
o, the length lc of the imaging optical system 902, and the imaging optical system 90
The sum of the distance lI from the incident surface 902b of No. 2 to the LED light emitting surface 702-1 is the conjugate length of the imaging optical system 902.

When the above distances 11o and ll are the same, the image of the LED light emitting surface 702-1 is most clearly displayed on the photosensitive drum 1.
01. Here, by intentionally shifting the imaging position, the image on the photosensitive drum 101 is blurred, and the LED
It can be made larger than the light emitting surface 702-1 of 701-1. This is the imaging optical system 902
This takes advantage of the fact that MTF decreases when the object point is shifted from the conjugate point of . FIG. 10(a) shows the results when the LED light emitting surface 702-1 or the photosensitive drum 101 surface is moved away (+) or closer (-) by Δ11 from the imaging optical system 902 from the state where the imaging positions are aligned. It shows the change in MTF. Further, FIG. 10(b) shows an LED light emitting surface 702.
-1 to the surface of the photosensitive drum 101 is Tc, and 1
M T' when changing Tc under the condition of Jo=lh
The change in F was shown. That is, the imaging optical system 90
By changing the distance between the light emitting surface 702-1 and the light emitting surface 702-1 or the surface of the photosensitive drum 101, the MTF can be decreased and the image size can be increased. However, in the above case, LED701-
The optical image is expanded in both the longitudinal direction (i.e., the main scanning direction) and the transverse direction (i.e., the sub-scanning direction).

Furthermore, the above problem will be specifically explained with reference to FIG. Figures 11 (a) to (g) show the relationship between the -16= light energy distribution received by the photosensitive drum and the resulting image pattern when the LEDs are turned on in each row and when they are blinking. shows. As shown in the same figure (a), the first column lighting position 5401-1, the second column lighting position 5401-2
, LED at each lighting position 5401-3 in the third row.
When emitting light, the pixel pitch l.

On the other hand, the light emission width lb becomes shorter. Therefore, the distribution of light energy on the photosensitive tram 101 is the same as the curve 54 in FIG.
It will look like 02. At this time, even if the threshold of light energy, which is the boundary point between the colored point and the non-colored point at the time of printout, is set to a very small value Wl, the colored state P++ in the same figure (C) , a colored area D11 and a non-colored area L
11 will be created. In this case, the region exposed to light is described as a colored region, but it is well known that by changing the electrophotographic process, colored and non-colored regions can be reversed.

On the other hand, the light energy distribution on the photosensitive drum 101 when the LED is turned off only at the lighting position 5401-2 in the second row is as follows:
The result is a curve 5406 in FIG. 5(d). The colored state at the time of printing out at this time is as shown at P21 in FIG. Normally, when the LED is lit continuously, the same figure (f
) The colored area DJo should continue over one line, as in the colored state PIO, and when the LED is turned on every time, the non-colored area L as shown in (g) of the same figure.
20 and the width of the colored area D20 should be equal,
This undesirable coexistence of colored areas and non-colored areas is the cause of the above-mentioned white streaks and black streaks.

Note that this problem can be solved by the edge-emitting type L shown in the example above.
This problem occurs not only when an ED is used, but also when an LED having a light emitting surface longer in the main scanning direction than in the sub-scanning direction is used and operated by time-division driving.

<Object of the Invention> An object of the present invention is to provide an LED printer that solves the above-mentioned problems and makes it possible to form high-quality images without black streaks or white streaks.

<Configuration of the Invention> In order to achieve the above object, the LED printer of the present invention has a structure between the LED array and the photoreceptor that reduces the MTF of the light image formed on the photoreceptor only in the sub-scanning direction. Even if the LED has a light-emitting surface longer in the main scanning direction than in the sub-scanning direction, the L E
The light from D is expanded in the sub-scanning direction so that an image can be formed on the photoreceptor.

<Examples> Examples of the present invention will be described below with reference to the drawings.

FIG. 12 shows a perspective view of an embodiment of the present invention. A substrate 901 is formed by connecting the substrate 602 in FIG. 6 to the LED array tips 605-1. ...extended in the direction of light emission. Further, a cylindrical lens 903 is fixed between the imaging optical system 902 and the light emitting surfaces of the LED array chips 605-1, . On this board 901,
A cover with a cover to prevent light leakage can be attached in place of the printer head 106 shown in FIG. However, in FIG. 1, the substrate 201 is the photosensitive drum 101.
In FIG. 12, the positional relationship of the light emitting surfaces of the LEDs is changed by 90 degrees, so that the board 901 is mounted perpendicular to the drum surface.

As shown in FIG. 12, even if the cylindrical lens 906 is inserted, the imaging relationship by the imaging optical system 902 in the array direction of the LED array chips 605-1, . . . is not disrupted. However, the LED array chip 605-1.
... in the direction perpendicular to the array direction, that is, in the direction of the short width of the light emitting surface, the optical path is changed by the cylindrical lens 903, and the image formed on the photosensitive drum becomes blurred and spread. That is, in the imaging optical system including the cylindrical lens 903, the LEDs 605-1.
While the MTF in the longitudinal direction (main scanning direction) of the light emitting surface remains the same, the MT in the lateral direction (sub scanning direction)
F decreases.

In FIG. 12, by inserting the cylindrical lens 903 between the imaging optical system 902 and the LED array chip 605-1, the LED array chip 605-1 is inserted in the direction perpendicular to the axis of the cylindrical lens. The path of the light beam from 1 is changed. Therefore, in the imaging relationship in the lateral direction of the light emitting surface of the LED array chip 605-1, when the distance between the imaging optical system 902 and the LED 605-1 is changed as shown in FIGS. 9 and 10, A similar effect occurs. On the other hand, regarding the axial direction of the cylindrical lens 906, the path of the light beam is not changed.

Therefore, the size of the image can be enlarged only in the lateral direction (sub-scanning direction) of the LED light emitting surface. This situation is shown in FIG. When all the LEDs are lit, that is, the light emitting position 54CN-1,540 in all columns in Figure (a)
1-2, 5401-3, when the LED is emitted, the distribution of light energy on the photosensitive drum 101 becomes like a curve 5602 in FIG. This is because the MTF of the imaging optical system is reduced, resulting in a reduction in contrast. Therefore,
It has a rounded shape compared to the light energy distribution 5402 shown in FIG. 11(b). At this time, as in FIG. 11, the threshold of light energy, which is the boundary point between the colored point and the non-colored point, is set to Wl. Then, the colored state P12 in FIG. 13(C) becomes the colored region DI2. On the other hand, when adjacent LEDs are lit up one by one, that is, when the LED is emitted at the light emitting position 5401-1.5401-3 and the LED is left non-emitting at the light emitting position 5401-2, the exposure The light energy distribution on the drum 101 is as shown by a curve 5606 in FIG.

The coloring state when printed out at this time is shown in the same figure (e).
As shown in P22, the non-colored area L22 and the colored area D
22 are alternating with almost the same width.

In this way, the imaging system is defocused in the sub-scanning direction, and the MT
By lowering F and blunting the light energy distribution on the photosensitive drum surface, even when using an image forming exposure device whose non-emissive surface width is relatively large compared to the light emitting surface width of the LED, full lighting can be achieved. The coloring state PI2 + P22 at the time of printout in the case of time and when the blinds are lit is calculated as follows.
The ideal colored state P+o + P2O shown in FIG. 1 can be approached.

In this case, it goes without saying that it is necessary to select an electrophotographic process that clearly achieves non-coloring and coloring depending on whether the threshold energy W1 is exceeded or not.

By doing this, the image when all lights are on is as shown in Figure 8(b).
As shown in FIG. 2, the entire region 801 corresponding to one pixel is illuminated with light.

The position where the cylindrical lens 906 is inserted is LE.
It goes without saying that the same effect can be achieved at any position between the D array chip 605-1 and the photosensitive drum.

FIG. 14 shows another embodiment of the present invention. Edge-emitting LED array chip (605-1,...

605-n) on the substrate 602.
7-ray substrate 601 and photosensitive paper 1101 are faced to each other,
The imaging optical system 40 via the cylindrical lens 906
1, the LED array chip (605-1,...
, 605-n) to form an image on the photosensitive paper 1101. Further, the photosensitive paper 1101 is moved in the direction of an arrow 1102, and the LED
An image 23 is successively created as a collection of bright spots by turning on and off the light emitting surfaces of each T and ED on the array substrate 601. A developing device 1016 develops and fixes the dot-divided image formed by the LED array substrate 601 on the exposed photosensitive paper 1101.

In this way, the present invention is not limited to electrophotographic printers, but can be applied to printers that form an image through exposure, develop and fix it if necessary, and can eliminate the black streaks and white streaks described above. can. In particular, in systems using insensitive photosensitive paper, etc., conventional heads using an LED annular head could not be applied due to insufficient light intensity, but if the present invention is adopted, an edge-emitting LED head can be used. It becomes possible.

In addition, when using an LED array in a printer that exposes images divided into dots on microfilm, etc.,
In order to use an imaging system such as a focusing light transmitter, the light emitting surface must be made very small. With microfilm, in order to reduce the original to about 1/20, if the dot density when enlarged and projected from the microfilm to the original size is 24-16 dots/mm, then 320 dots on the film) / Dots of about mm must be created. Therefore, it is currently impossible to create such a high-density LED array, so it can be achieved by using a reduction optical system to make the entire row of LED lights smaller and passing a film through it. I have no choice but to. FIG. 15 shows the relationship between the LED light D emission 401 and the imaging point on the photosensitive film 1402 in this example. If the focal point of the reduction optical system 1403 is f, , f2, then the distance is 12
The LED light D light emission 401 placed above is imaged on the opposite side at a distance of 11. In addition, T, ED light emitting section 1
401 is as short as several tens of micrometers in the sub-scanning direction, that is, in the direction perpendicular to the LED array row, but is extremely long as several hundred mm in the main scanning direction. If the reduction optical system 1406 is configured using an optical system such as a lens, an inverted reduced image of the entire LED array row must be formed, so if you want to effectively image the light from the LED array, , forcing you to use a very large lens. In this way, the cylindrical lens 90 can be used even in fields where it is difficult to write using an LED array due to the low utilization rate of emitted energy even if a highly sensitive silver halide photosensitive film is used.
By providing 3 or the like to prevent black lines and the like, it becomes possible to apply an edge-emitting type LED array that emits a large amount of light to an optical printer.

In the above-mentioned embodiment, an edge-emitting type LED was used, but the present invention is not limited to this, and any type of LED having a light-emitting surface longer in the main scanning direction than in the sub-scanning direction can be used. However, it is possible to eliminate black lines and the like in the same way.

Further, as a means for reducing the MTF in the sub-scanning direction,
In addition to a double cylindrical lens, any type of anamorphic optical system may be used as long as it uses an anamorphic optical system that focuses images at different positions in the vertical and horizontal directions.

<Effects of the Invention> As explained above, the present invention can be applied to an LED array head.
This plink is driven by a time-division m-pixel simultaneous generation method, and by arranging a means for reducing the MTF only in the sub-scanning direction, such as a cylindrical lens, between the LED array and the photoreceptor, black streaks and It is possible to form high-quality images without white spots, and because it is possible to use edge-emitting LEDs, the materials used to create LED arrays can be used relatively freely, making it possible to create LED arrays with even higher brightness.
High-speed operation is achieved using an inexpensive drive circuit called the n-time division method.
This has the effect of making it possible to create a D printer.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of a general LED printer, Figure 2 is a perspective view of the LED array board, Figure 6 is a plan view of the LED array chip, Figure 4 is the wiring diagram of the LED array, and Figure 5 is A block diagram of an LED array drive circuit, FIG. 6 is a perspective view of an LED array board using edge-emitting LEDs, FIG. 7 is a partially enlarged perspective view of FIG. 6, and FIGS. 8(a) and (b).
) is a schematic diagram showing the dot formation results in the conventional method and the present invention, FIG. 9 is a schematic diagram showing the relationship between the LED light emitting surface and the drum surface imaging point, and FIGS. 10 (a) and (b) are the MTF 11 is an explanatory diagram showing the relationship between the conventional light emitting pattern and the light energy on the drum surface; FIG. 12 is a perspective view showing the main parts of an embodiment of the LED printer of the present invention;
Figure 13 is an explanatory diagram showing the relationship between the light emitting pattern and the light energy on the drum surface in the present invention, Figure 14 is a schematic configuration diagram of another embodiment of the present invention, and Figure 15 is a diagram showing still another embodiment of the present invention. FIG. 3 is a schematic diagram showing the relationship between an LED light emitting section and a photosensitive film imaging point in an example. 401... Imaging optical system, 601... LED array substrate, 602... Substrate, +S[15-1, ~, 605-n, LED array chip, 901... Substrate, 902... - Imaging optical system, 903... Cylindrical lens, 1101... Photoreceptor, 1401... LED light emitting section, 1402... Photosensitive film, 1403... Reduction optical system. (94ノ 4L1.J ('/,) JLI, J -Aζζ- 1 0■

Claims (1)

[Claims] LED with a light-emitting surface that is longer in the main scanning direction than in the sub-scanning direction
an LED play in which a plurality of LEDs are arranged in at least one row; a photoconductor; and an imaging optical system that forms an image of the light from the LEDs on the photoconductor, and an optical image divided into dots is formed on the photoconductor. What is claimed is: 1. An LED printer configured to form images by time-division driving, further comprising means for reducing the MTF of the optical image only in the sub-scanning direction, between the LED array and the photoreceptor.