JPS60114890A - Optical printer - Google Patents

Abstract

PURPOSE:To prevent generation of white or black stripes at a printing-out time to obtain a clear image by setting space frequency characteristics of a focusing system so that a photosensitive area of a photosensitive body due to lighting of each bright point coincides with the size corresponding to one bright point of a divided image. CONSTITUTION:When every other one out of LEDs adjacent to one another is lit, that is, light emitting faces 601-1 and 601-3 are allowed to emit light but a light emitting face 601-2 is not allowed to emit light, the optical energy distribution on a photosensitive drum 101 is as shown by 903 in figure. If the focusing system is defocused and MTF is degraded to make the optical energy distribution on the surface of the drum uneveness in this manner, coloring states for printing-out in case of full lighting and thinned-out lighting approximate an ideal coloring state though an image forming exposure device where the width of light non-emitting face is relatively larger than that of a light emitting face is used. That is, a photosensitive area (coloring area D) due to lighting of each bright point coincides with the size corresponding to one bright point of the divided image.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an optical system incorporating an image forming exposure device that can selectively turn on and off one row of bright spots using an LED array, liquid crystal shutter array, etc. Regarding printers.

This type of optical printer can image a row of bright spots on a drum in a portion of the main scanning direction, instead of the slit exposure and original image forming optical system of a general electrophotographic copying device, and can arbitrarily brighten. It incorporates an image forming exposure device that makes it possible to turn lights on and off, and in particular light emitting diodes (I, light).
mnitting diodes (hereinafter referred to as LEDs) array printers use minute LEDs as a means of generating bright spot arrays.
An image-forming exposure device is an image-forming exposure device in which several dozen or more of these are arranged in rows or in multiple rows, and an image-forming optical system that focuses these images on the drum surface is integrated.

FIG. 1 shows a schematic configuration diagram of an LED array printer. 1
01 is a photosensitive drum that rotates in the direction of arrow a. A primary charger 102 charges the surface of the photosensitive drum 101 uniformly. Reference numeral 106 designates a conventional LED printer head, in which only the charge on the surface of the photosensitive drum 1010 where a bright spot is imaged moves, and the charge on other parts remains unchanged. That is, an electrostatic latent image is formed. Next, the developing device 10
4, depending on the presence or absence of charge on the surface of the photosensitive drum 101 at that time, toner adhesion and dusting occur, and the photosensitive drum 1
The image above 01 becomes visible. In the above process, LE
As is well known, it can be arbitrarily determined by the combination of the polarity of the toner, etc., with the bright spot illuminated by the D printer head 106.

The toner image developed by the developing device 104 is transferred by a transfer charger 105 to paper supplied from a cassette 106 or a cassette 107.

When the paper passes through the fixing device 108, the toner transferred from the photosensitive drum 101 is fixed on the paper. 109 is photosensitive drum 1
01 is a cleaner for toner remaining on the surface, and 110 is a static elimination lamp.

FIG. 2 shows the LEDs that make up the LED printer head 103.
2 is a perspective view of an array substrate 201. FIG. 202 is a substrate that also serves as a heat sink, and 203, 204, and 205 are wiring means made of a ceramic substrate or the like. Cables 206 and 207 are used to connect image signals and power sources.

20B-1-208-fi is an LED array chip with LEDs arranged in a row in the center, and 209-1 to 209-n
and 210-1" 210-n is LED array chip 2
081" 208-n, that is, an LED drive integrated circuit (hereinafter referred to as an IC) that incorporates a serial-parallel conversion circuit for image signals inputted from cables 206 and 207.

This LED array chip 203-m and LED drive I
FIG. 6 shows an enlarged view of C209-m and 210-m. 301-1.301-2.301-3.
301-4... are LEDs, which are arranged in a line approximately in the center of the LED array chip 20B-m. Odd number L
E D 301-1.301-3, ... is on the upper side,
The even numbered LEDs 301-2, 301-4 and 0 are each pulled out by wiring to the lower side, and are connected to each LED drive terminal 302-1.3-02-2 of the LED drive ICs 209-m and 210-m. ．． ...303-1.306
-2. The LED array board 201 is configured as shown above by wire bonding to...
Sequentially 5L of image signals for one column from cables 206 and 207
ED drive IC C2091-209-n, 210-
1" 210- input, shift one column of data, and then connect it in parallel to the LED drive terminal 302-1.502-
2. @..., 606-1.505-2. ..., each LED is turned on and off according to this, and a bright spot for image formation is generated in a part.

FIG. 4 shows a diagram of the relationship between the LED light emitting section and the imaging point on the drum surface. The LED array chip 20B-at forms an image on the photosensitive drum 101 using an imaging optical system 401CJ, such as a SELFOC lens array. Here, when the angle θ is small, the luminous flux L1 from the LED 501-1 enters the imaging thread 401 as a luminous flux L1-t, but when the angle θ becomes large,
A part of the luminous flux is no longer incident.

Then, only the incident light beam L1-t reaches the photosensitive drum 101.
It reaches the top and is imaged.

Figure 5-1 shows the shape of the LED light emitting section. In the figure, 501 is an LED chip, 502 is an effective light emitting surface, 503 is an electrode, and 504 is a connection surface between the electrode and the LED. Therefore, the size of the PN junction surface of the LED for one pixel is the sum of the effective light emission 1fli 502 and the connection surface 504.

On the other hand, the light emission of LEI) has a light distribution characteristic as shown in FIG. 5-2, with the traveling direction set at 0° on the effective light emitting surface 502.

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, L corresponding to each pixel
Since the ED light emitting surfaces are arranged in a line, the effective light emitting surface 502 of LhiD is used to form a separation between adjacent pixels.
The size of one side of is 11! It is smaller than the lI elementary pitch.

This tendency becomes more pronounced as the pixel density increases.

This is because a non-light-emitting part of a finite size is required due to the electric coefficient C between the light-emitting part and the adjacent light-emitting part, and the minimum value of this width is determined by the material and structure of the LED array used. If the pixel pitch is made smaller, the width of the non-light-emitting portion for electrical isolation becomes larger than the pixel pitch. For example, using the method of choice 1) < aAi defeat 49', t-W b b ill' ) R, )'
+'+141 is approximately 20 μm, and requires approximately 40 pm when mechanically cut. Is it from Figure 6? If the pixel density is increased until the light emitting surface width 1b becomes about half of the pixel Pituchi/a, when all LEDs are lit, that is, the light emitting surface 601-1.601-2.60
The distribution for 1-5 is as shown in 602. At this time, even if the light energy ρ threshold value used as the boundary point between the colored point and the non-colored point at the time of printout is set to a small value Wl, the colored state pa
As shown by l, a colored area Dllll surrounding colored area l is created. In this case, the area exposed to light is described as a colored area, but it is well known that if the electrophotographic process is changed, colored and non-colored areas can be reversed.

On the other hand, the photosensitive drum 1 when the adjacent LEDs are turned on one by one, that is, when the light emitting surface 601-1, 601-3 is made to emit light and the light emitting surface 601-2 is left non-emitting.
The optical energy distribution on 01 is as shown in 606.

The colored state at the time of printing out at this time is as shown by pal, and the non-colored area xJ11 is narrower than the colored area DIll. Normally, when all LEDs are lit, the colored area Dro should continue over one line like the colored state pxo, but when the LEDs are lit one by one, the non-colored area pso and the colored area The width of the pro should be the same, but as mentioned above, when the pixel density is increased, the light does not hit the light drum surface that is in the non-emitting part, and as a result, black streaks and white streaks appear on the screen. This has hindered the practical application of Takanori's (LIHJ) array printer.

Even if a bright spot generator array is used, in which the width of the non-emissive surface to the adjacent emissive surface is relatively large compared to the width of the emissive surface, the present invention provides a clear image without causing black spots and white spots caused by the non-emissive surface. An object of the present invention is to provide an optical printer that can produce images of high quality.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 7 shows imaging light according to an embodiment of the present invention. This figure is almost the same as FIG. 4 of the conventional example, but the distance JO/ between the cell 7 lens array 401 and the photosensitive drum 101 and the distance 1'1 between the selfoc lens array 4o1 and the LED 301-1 are shown. is the distance 1 in Figure 4! o.

11 and each one is different. That is, by intentionally shifting the image formation position, the image 701 on the photosensitive drum 101
is blurred and made larger than the light emitting surface of LEIJ301-1. This means that if the object point is shifted from the conjugate point of the SELFOC lens array, M '1'li' (Modulati
onTra! This method takes advantage of the fact that 1Later Function) decreases. From the state where the image formation position is aligned as shown in Fig. 8(a), move the LED or photosensitive drum surface away from the SELFOC lens by Δlx (+
) and ←) shows the change in MTF. Further, FIG. 8(b) shows the change in MTF when I'c is changed under the condition of 1o' - A''i, where the length from the ED surface to the drum surface is Tc. By changing the distance between the SELFOC lens, the light emitting surface, and the photosensitive drum surface in this way, the MTF can be reduced and the image size can be enlarged.This situation is shown in FIG.

When all LEDs are lit, that is, the light emitting surface 601
-1.601-2.601-3, the light energy ρ distribution on the photosensitive drum 101 becomes as shown in 902.

This is because the contrast decreases due to the decrease in the MTF of the imaging optical system, so the shape is rounded compared to the light energy distribution 602 in FIG. 6. At this time, as in the conventional example, if the light energy interpretation threshold value which is the boundary point between the colored point and the non-colored point is Wl, the colored state pH1 is entirely in the colored region ]) 111'. On the other hand, when the adjacent LEDs are lit one by one, that is, the light emitting surface 601-1.60
1-3 emits light and the light-emitting surface 601-2 remains non-emissive, the light energy ζ cloth on the photosensitive drum 101 is 90
It will look like 6.

At this time, the colored state at the time of printing out is such that the non-colored area Leg and the colored area D22 alternate with substantially the same width, as shown by pzg.

In this way, by defocusing the imaging system, lowering the MTF, and blunting the light energy distribution on the drum surface, it is possible to use an image forming exposure device whose non-emissive surface width is relatively large compared to the emissive surface width. In this case, it is possible to bring the coloring state (Fil, p13 in Figure 9) closer to the ideal coloring state (Pill, pao in Figure 6) at the time of printout when fully lit and when the lights are dimly lit. can.

That is, this means that the photosensitive area (coloring area D in the embodiment) caused by lighting each 11i11 points is made to match the size corresponding to one bright spot in the divided image.

In the case of the present embodiment, it goes without saying that it is necessary to select an electrophotographic process that clearly achieves wrapping, coloring, and coloring without exceeding the threshold energy Wl.

Furthermore, in order to defocus, either the distances 11o or 11 or both distances may be changed, but in one-sided defocus, that is, in FIG. 8(a), the deviation Δ11 from the imaging state On the other hand, if the J1 ratio (of the decrease in MTF) is very high, an error of about 50 pm will cause a difference in MTF of 6 to 7%. - The defocus that is equal on all sides, that is, the defocus shown in FIG. 8(b) is relatively gentle. Furthermore, the rate of change in MTF is more gradual in the direction of lengthening the distance. On the other hand, since the image-forming exposer and imager are generally integrated as an optical writing head and fixed near the Iδ optical drum, it is better to adjust the distance between the image-forming exposer and the image-forming optical system. , it is more difficult than adjusting the distance between the imaging optical system and the photosensitive drum. Therefore, to obtain the desired MTF, set the distance between the light emitting surface and the imaging optical system to 1'1 minute.
After that, it is desirable to fix this head near the Tadamitsu drum while adjusting the interval. Furthermore, it is desirable that A"i be longer than 11.

FIG. 10 shows potential-density characteristics when one-component forward development is performed on an amorphous silicon drum. Horizontal axis VSB
is the potential difference obtained by subtracting the developer bias voltage VB from the drum potential Vs, and the vertical axis represents the degree C when the image is transferred and fixed on the right-hand paper after development. VSBO is a potential difference to obtain a fog-free image, and VSBL is a potential difference for obtaining a fog-free image.

VSB2. VSB3 each sets the image density to 0.2.
This is the potential difference to make it 1.0.1.3. Further, VTH is a potential difference for setting the concentration to 0.6.

FIG. 11 shows the light amount-potential characteristic, which shows the relationship of decrease in surface potential Vs when the photosensitive drum is first charged to a potential Vso and then irradiated with light energy W.

Therefore, in order to obtain a fog-free image, Vso
It is sufficient if -VB > VSBO holds true.

On the other hand, to get a clear black image, light 1! i, l
When the surface potential at '44 is Vsx, Vs,
z: -VB≦VSB3 may be satisfied. Light energy sufficient to lower the surface potential below this potential (2)Sx is required to make black clearly, and it can be seen from FIG. 11 that light stronger than wpx is required.

Drum surface potential VSI, VS2. VTH sot'L
VS1-VB-VSBI, VS2-VB-V
SB2. V3TH-VB-VTH, then the 10th
From the relationship in the figure, an image with a density of 0.2 is obtained when light with an energy of wpl is irradiated, an image with a density of 0.6 is obtained when light with an energy of 2 pTH is irradiated, and an image with a density of 0.6 is obtained when light with an energy of 1. ! Wp2
It can be seen that when irradiated with light of 1.0, a dark &1.0 image is obtained.

In this case, the threshold value of the light energy is WpTH, and if the light energy is stronger than this, it will be printed out in black, and if it is weaker than this, it will be printed out in white.

At this time, the smaller the two values of the potential differences VSBI and VSB2 are, the greater the degree of change in black and white becomes.

This threshold value wp'ra can be changed by changing the bias voltage VB or the initial charging potential VSo, but in order to operate stably, the potential Vso
The range of WpTH is determined by the drum used, so the only thing left to do is to vary the bias voltage VB up and down within the range that satisfies the above conditions such as clear black, so the variable range of WpTH is is limited.

Therefore, WpTH cannot be made very small.

From the above, if the minimum threshold source energy is △ WpTH', when each LED is turned on,
Between the center of the LED that is in contact with the center of the JLED + tl
By lowering the MTF of the imaging optical system until the emission energy at point l becomes at least WpTH' or more, the occurrence of white smudge can be eliminated.

However, if the MTI is lowered too much, the intensity of the distribution of the light irradiation pattern will become smaller.
．． The area of halftone degrees up to 0 increases. Furthermore, if the intensity of the light irradiation deflection distribution is small and gradual, the width of black and white when printed out is likely to be b'4 due to variations in brightness between LEDs.

In Figure 12, Ll (only D601-1 lights up, M T
This figure shows the distribution of light energy (2) when an image is formed on a drum using an imaging system with reduced li'. length lc
, ld are la > la and ga < 71!, respectively.
There is a relationship as shown in a, which determines the maximum and minimum allowable width of the black part printed out when one LED is lit. This specific value is shown in the photo! Although it differs depending on a high-end printer that reproduces Il images and a popular printer that simply prints characters, the length is 1.2 times the LED pitch/2L and 0.8 times the length of the LED pitch/2L for the popular type, respectively.

The original energies on the boundaries of lengths ec and ld are W, respectively.
3. When W4, W3. The aforementioned Wpl during W4
.

If Wp2 is included, the halftone area will be limited to the portion where lc and ld do not match, and the black and white print widths will satisfy the specifications of not less than Aa and not more than 10.

If M T F is lowered too much, the distribution 906 becomes smooth and W3. The difference in W4 has narrowed, and W3. Wpl and Wp2 do not settle between W4. That is, as the halftone area increases, L
Due to some wrinkles in the brightness of ED601-1, even a slight change in the degree of distribution will cause a large difference in the distribution position 1e for the same energy ze, resulting in an error in the width of the white and black buttons when printing out. leading to an increase in

Therefore, the degree of decrease in MTF is W3. Same as W4 and Wp
It is desirable to keep it at a level where Wp2 and Wp2 are located.

Above is the Δ4 T l! of the imager. In order to form an image by lowering the
An imaging system with a poor performance of 1 to ITj may be used in advance so as to satisfy the degree of decrease in .

Also, between the imager and the light emitting surface or the imaging lI+i,
Defocusing may be performed by adding substances having different Jiυf ratios.

Furthermore, although the present invention has been described in terms of a t+f photographic process in which the illuminated portion satisfies i&'<, the present invention is also applicable to the reverse process.

As explained above, the present invention uses a conventional original printer to simply detect the spatial frequency characteristics of the imaging thread f'iJ.
It has the effect of preventing white sushi and black spots when printing out and producing clear images.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the configuration of a general LED printer, and FIGS. 2 and 6 are respectively 1. El) A schematic diagram showing the configuration of the printer head; FIG. 4 is a diagram showing the image formation relationship between the LED light emitting part and the photosensitive drum in a conventional LED printer; FIG. 5-1 is a diagram showing the shape of the light emitting surface of the LED array. ,
Figure 5-2 is a diagram showing the light distribution characteristics of the LED, Figure 6 is a diagram explaining the relationship between the light emitting pattern and the light energy on the photoreceptor surface in a conventional YC printer, and Figure 7 is a diagram showing the relationship between the light emission pattern and the light energy on the photoreceptor surface in a conventional YC printer. One example is 4-J Ruri. Diagrams showing the image formation relationship between the ED light emitting section and the photosensitive drum, FIGS. 8(a) and 8(b).
9 is a diagram illustrating changes in M T I with respect to changes in the distance between the light emitting surface and/or photosensitive drum surface and the imaging optical system, respectively, and FIG. Diagram explaining the relationship with energy, 1st
Figure 0 is a diagram showing the potential-density characteristics of the original printer, Figure 11 is a diagram showing the tr'kiL-potential characteristics of the optical printer, and Figure 12 is the light emission pattern in unfired J and the light energy on the yC conductor surface. 01o1- which is a diagram explaining the relationship between
--Te original drum, 20B-1, 208-2, --...
20B-m, "@. 20B-21... LED array chip, 501-1.
...IJD. 401 @Ken Selfoc Lens Array, 601-1
．． 601-2.601-3... Light emitting surface, 602, 60
3.902.903---Light energy distribution, 701・
...-Image of light emitting surface, PLO, pH, PI3. P2O, P21. P22・
...Colored state, DIO, Dll, D12. D20.
D21. D22... Colored area, LIO, Lll,
L12. L20. L21. L22・φ・Uncolored area. ApI cm'In) Tc (buttocks? Il) Akiraq figure Otsu or-+ Otsu θ, -2t, tyl-3 and FIZ ``2...' ・ ,,,,'' ,,,
,,,7. ″,・2r2

Claims (1)

[Claims] (1) An image forming exposure device in which at least one row of a plurality of bright spot generators that can be selectively controlled to blink according to an image signal, a photoreceptor, and each bright point of the image forming exposure device are arranged. In an optical printer that forms an image divided corresponding to the bright spots by an imaging system comprising an imaging optical system that forms an image on the photoconductor, the photosensitive area of the photoconductor and . An optical printer characterized in that the spatial frequency characteristic of the coupling system is set so that the size corresponding to one bright spot of the divided image matches the size.