JPH0516422A - End luminescent el printer - Google Patents

Abstract

PURPOSE:To prevent the deterioration of the gradation expression due to the afterglow of the previous printing in an end luminescent EL printer which realizes the gradation expression by controlling the number of factors constituting pixels and arranged in a pixel forming area. CONSTITUTION:This printer is provided with density storing means 36, 37 which temporarily store the previous density data of a pixel to be printed, and gradation improving means 35, 38 which reduce the number of driving pulses forming gradation pixels in accordance with the previous density data of the pixel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge emitting EL element using an edge emitting EL element as a light emitting element of a line head.
It concerns printers.

[0002]

2. Description of the Related Art Currently, various printers have been put into practical use, and one of them is a line printer. For example, an electrophotographic line printer has a structure in which devices such as a charging device, a line head, a developing device, and a transfer device are closely arranged on the peripheral surface of a photosensitive drum. A latent image is formed on the peripheral surface of the drum by selective emission of light-emitting elements connected to the line head to form a latent image. The latent image is developed by toner supplied from a developing device and printed by a transfer device. It is designed to be transferred to paper.

As a light emitting element of such a line head, an LED (Light Emitting Diode) or the like is generally used. However, this is a line head in which a characteristic difference is apt to occur between the manufactured elements and the emission intensity is uniform. Has problems such as difficulty in manufacturing. Therefore, as a light emitting element of a line head, an edge emitting type EL (Electro Luminescence) which is also called an edge emitter at present is used.
e) It is considered to use an element. This edge emitting EL device is a conventional EL device in which flat plate electrodes are formed on the upper and lower surfaces of a dielectric layer that surrounds a thin-film active layer made of zinc sulfide containing an active element from above and below. It is possible to emit extremely flat light having an emission intensity about 100 times that of the above from the end face of the active layer.

Therefore, as a known technique of an edge emitting EL printer which is a line printer using such edge emitting EL elements, the device disclosed by the applicant in Japanese Patent Laid-Open No. 2-274570 is disclosed in FIGS. This will be described with reference to FIG.
First, as illustrated in FIG. 5, the edge emitting EL printer 1 is an external device (not shown) such as a host computer.
A printer controller 2 for transferring print data input from the control circuit 7 is connected to an interface 3, and the interface 3 is connected to first and second address counters 4 and 5 and a reference clock generator 6.
The timing controller 8 is connected via.
Further, the interface 3 includes two RAMs (Random RAMs) each of which has three states 9 to 12 connected to an input / output unit.
Access memories 13 and 14 via the first data processing circuit 15, and the RAMs 13 and 14 are connected.
A control circuit 7 and the first and second address counters 4 and 5 are connected to each other via a selector 16. Further, the RAMs 13 and 14 are connected to the second data processing circuit 17, which is a pixel forming means to which the timing controller 8 is connected, via the three states 11 and 12.

A drive IC in which the second data processing circuit 17 and the timing controller 8 are connected to each other.
The (Integrated Circuit) 18 _{1 to} 18 q are connected to the line head 20 in which m × n edge emitting EL elements 19 are continuously arranged in an array through n block electrodes 21 ₁ to 21 n, The common driver 22 to which the timing controller 8 is connected is connected to the line head 20 through m common electrodes 23 ₁ to 23 m. Here, each of the driving ICs 18 _{1 to} 18 q has a structure in which a shift register 24, a latch 25, an exclusive OR circuit 26, and a block driver 27 are sequentially connected in parallel, and the components 24 to 26 are connected to the timing controller 8 respectively. Are connected.

With this configuration, in the edge-emitting EL printer 1, the print data including the clock signal input from the printer controller 2 via the interface 3 has the first data processing circuit for each main scanning line. At 15, the data is compressed by processing such as rearrangement.

Therefore, the compressed print data is R
The print data temporarily stored in one of the AMs 13 and 14 during the printing time of one main scanning line, and at the same time, the print data temporarily stored in advance from the other RAM 14 and 13 are output at high speed.

A RAM for temporarily storing print data
The selection of 13 and 14 is performed by the selector 16 which operates according to the timing input from the printer controller 2 to the first address counter 4. Also RAM
The print data output from 14 and 13 is performed by the control circuit 7 and the second address counter 5 that operate in synchronization with the high-speed output reference clock signal issued from the reference clock generator 6.

Therefore, the output print signal for one main scanning line is reprocessed by the second data processing circuit 17 into a form suitable for printing, and is input in parallel to the drive ICs 18 ₁ to 18 q and held therein. It And these drive ICs
By controlling the 18 _{1 to} 18 q and the common driver 22 by the timing controller 8, the block electrodes 21 ₁
21n and the common electrodes 23 _{1 to} 23m, low-voltage and high-voltage drive pulses are repeatedly output to the line head 20. At this time, by synchronously controlling these drive pulses, the voltage of the combined drive pulse is controlled to be equal to or higher than the threshold voltage of the edge-emitting EL element 19, and light emission or non-light emission is controlled.

Therefore, in the edge emitting EL printer 1, the above-described operation is performed four times during the printing time T ₀ of one main scanning line, as shown in the time chart of FIG.
The line head 20 repeats line emission four times within the width of one main scanning line. As shown in FIG. 7, the main scanning line printed in this manner is beautiful because the edge-shaped misalignment is minute, and moreover, the element emission is repeated a plurality of times to form a substantially square shape. Since the flat pixel constituent elements 29 are continuously arranged in the pixel region 28 to form the black pixel 30, white spots in the sub-scanning direction of the pixel 30 are also prevented.

In the edge emitting EL printer 1, one input terminal of the exclusive OR circuit 26 of the driving ICs 18 _{1 to} 18 q serves as an input terminal (not shown) for the PC signal (polarity control signal). And each exclusive OR circuit 2
The line head 20 can be driven at high speed by controlling the PC signal in synchronization with the output pulse of the common driver 22 while maintaining the print data output from the latch 25 in FIG.

Here, the edge emitting EL printer 1 described above is used.
Then, as illustrated in FIG. 8, the case where the black and white binary pixels 30 and 31 are printed by setting the light emitting operation of the edge emitting EL element 19 repeated in the one pixel region 28 to all light emission and no light emission has been illustrated. The applicant of the present invention provides an edge-emitting EL printer that performs gradation expression by arbitrarily reducing the number of pixel constituent elements 29 in one pixel area 28 by adjusting the number of times of light emission of each edge-emitting EL element 19. JP-A-2-274571 and JP-A-2-274
Proposed as 274172 publication.

In such an edge emitting EL printer,
For example, when one pixel 30, 31 is formed by four times of element light emission as illustrated in FIG. 8, in addition to the black and white binary pixels 30, 31 as illustrated in FIG. The gray scale pixel 3 in which one to three pixel constituent elements 29 are arranged in one pixel region 28 by one-time light emission or three-time light emission of the element 19.
2, 33 are also formed. Therefore, the pixel 30 as described above
It is possible to realize high-resolution gradation expression in which the densities of the pixels 30 to 33 are different by forming the image with the colors of to 33.

[0014]

As described above, in the edge emitting EL printer 1, the number of the plurality of flat pixel constituent elements 29 formed in the one pixel region 28 can be adjusted, so that one pixel 30 can be formed. It is possible to perform high-resolution gradation expression in which the densities are different for each ~ 33.

Here, the edge emitting EL element 19 has a stepwise increase in emission intensity corresponding to the drive pulse input characteristically, and the emission intensity is gradually increased even after the input of the drive pulse is stopped. Afterglow that decreases is generated.
That is, next to the black binary pixel 30 in which four pixel constituent elements 29 are continuously arranged in one pixel area 28, the gradation pixel 33 in which three pixel constituent elements 29 are arranged in one pixel area 28 is arranged. When printed, there is a concern that the white portion at the upper edge of the gradation pixel 33 may be reduced by afterglow. In this case, this gradation pixel 33
Has a density equivalent to that of the black binary pixel 30, so that the image quality of gradation expression is degraded.

The present invention is to obtain an edge emitting EL printer having good image quality in gradation expression by considering the density of the pixel formed last time when forming gradation pixels.

[0017]

A line head in which edge emitting EL elements are continuously provided in the longitudinal direction of a light emitting end surface is provided, and a latent image carrier that relatively moves in a sub-scan direction is arranged at a position facing the line head. Then, a drive circuit for applying a drive pulse to the line head in synchronization with the relative movement of the latent image carrier is provided, and this drive circuit is controlled to form on the latent image carrier by element light emission of the edge emitting EL element. Pixel forming means for adjusting the number of flat pixel constituents for each pixel is provided, and the number of pixel constituents arranged in the sub-scanning direction within the substantially square pixel forming area is adjusted by this pixel forming means. In the edge-emitting EL printer configured to print not only the binary pixels but also the gradation pixels, the density storage means for temporarily storing the previous density information of the pixels to be printed is provided, and the density storage means temporarily stores the previous density information. Of pixels The tone improvement means for reducing the number of drive pulses for forming a gray scale pixel in control of the drive circuit provided in accordance with the degree information.

[0018]

By reducing the number of drive pulses forming the gradation pixel according to the density information of the previous pixel, the density of the gradation pixel formed this time is increased due to the afterglow when forming the previous pixel. Prevent that.

[0019]

Embodiments of the present invention will be described with reference to FIGS. First, as illustrated in FIG. 1, in this edge-emitting EL printer 34, the interface 3 to which the printer controller 2 is connected is connected to the first and second address counters 4 and 5 and the reference clock generator 6. Timing controller 8 via the controlled control circuit 7
It is connected to the. Further, the interface 3 is connected to the two RAMs 13 and 14 to which the three-states 9 to 12 are respectively connected to the input / output units via the first data processing circuit 15, and the RAMs 13 and 14 are connected to the control circuit 7 respectively. And the first and second address counters 4 and 5 are connected via a selector 16.

Then, the edge emitting EL printer 34
Then, the RAMs 13 and 14 are connected via the three-states 11 and 12, and the second data processing circuit 35 which is the pixel forming means is connected to the RAMs 36 and 37 which are density storing means and the gradation correction table 38. The circuit members 35 and 38 form a gradation improving unit that controls the drive IC 18 to reduce the number of drive pulses.

A drive IC 18 ₁ in which the second data processing circuit 35 and the timing controller 8 are connected to each other
18q are connected to a line head 20 in which m × n edge-emitting EL elements 19 are continuously arranged in an array through n block electrodes 21 _{1 to} 21n, and a timing controller 8 is connected. the common driver 22 is connected to the line head 20 via m of the common electrode 23 ₁ ~23m. Here, the drive ICs 18 _{1 to} 18q
Has a structure in which a shift register 24, a latch 25, an exclusive OR circuit 26, and a block driver 27 are sequentially connected in parallel, and the timing controller 8 is connected to the components 24 to 26.

As shown in FIG. 2, the line head 20 has a substrate 39 on which the drive IC 18 is connected and a substrate 40 on which the edge emitting EL element 19 is connected, which are mounted on a base 41. The SELFOC lens array 42 attached to the front edge of the base 41 faces the edge emitting EL element 19.

Here, the edge emitting EL printer 34
Is set so that 16 pixel constituent elements are sequentially overlapped and sequentially arranged in one pixel area, and positive and negative drive is applied to the edge emitting EL element 19 for the formation of black pixels. The pulse application is repeated 16 times. And
In this edge-emitting EL printer 34, the density information of each pixel is set as the number of times the drive pulse is applied.
In the gradation correction table 38, the correction value of the density information of the pixel formed this time is set by the combination of the density information of the pixel formed this time and the density information of the pixel formed last time. There is.

The edge emitting EL printer 34
Has a resolution of 300 (dpi) and a printing speed of 6 (ppm), for example, and the printing time T ₀ of one main scanning line in this case is about 2.1 (ms). In addition, the edge emitting EL device 19
Characteristically, the afterglow time constant is about 500 and the rise time is about 1/10 of the afterglow time.

In the edge emitting EL printer 34 having such a structure, the print data input from the printer controller 2 through the interface 3 is rearranged by the first data processing circuit 15 for each main scanning line. The print data is compressed by processing such as the above, is temporarily stored in one of the RAMs 13 and 14, and the print data temporarily stored in advance is output from the other. Therefore, the output print signal is re-processed by the second data processing circuit 35 and then parallel input to and held by the drive ICs 18 ₁ to 18 q, and the low-voltage drive pulses are output from the block electrodes 21 ₁ to 21 n as lines. It is repeatedly output to the head 20. At this time, this drive pulse is synchronized with the high-voltage drive pulse output from the common electrodes 23 ₁ to 23 m, and the voltage of the combined drive pulse is equal to or higher than the threshold voltage of the edge emitting EL element 19 or lower. This controls emission / non-emission.

Therefore, this edge emitting EL printer 34 is used.
Then, as shown in the time chart illustrated in FIG. 4, the above-described operation is performed 16 times during the printing time T ₀ of one main scanning line, and each edge emitting EL element 19 emits light 16 times in the pixel region. It will be repeated. At this time, this edge emitting EL
In the printer 34, when a black pixel or the like is printed, the element emission of the edge emitting EL element 19 is started before the afterglow of the previous element emission remains well, so that the emission intensity is improved satisfactorily. It is like this.

By doing so, this edge-emitting type E
In the L printer 34, the main scanning line is beautiful because the edge-shaped misalignment is small, and moreover, since the pixel components overlap, white spots are prevented from occurring when forming black pixels and the like. To be done. In the edge emitting EL printer 34, the number of pixel components in one pixel region is adjusted by changing the element emission of the edge emitting EL element 19 every two times from 16 times to 0 times. In addition to white, black is also used to express gradation in eight steps.

Then, the edge emitting EL printer 34
When performing gradation printing with, the second data processing circuit 35
When the print data is output from the drive IC 18 to the drive IC 18, the print data is temporarily stored in one of the RAMs 36 and 37, and the previous print data is output from the other. It is extracted as a combination of density information. Therefore, a combination matching this is searched from the gradation correction table 38 to detect the number of times the drive pulse is applied to the pixel this time, and this is output to the drive IC 18 as the print data of this time and the RAM 3 is also output.
6 and 37.

By doing so, this edge-emitting type E
In the L printer 34, since it is possible to prevent the density of the gradation pixel formed this time from increasing due to the afterglow at the time of forming the previous pixel, it is possible to maintain good image quality of gradation expression.

More specifically, if the density of the previously formed pixel is 16/16 black and the density of the pixel formed this time is the intermediate density of 4/16, simply printing without correction As illustrated in 4 (b), the density of the 4/16 gradation pixel becomes about 5/16 due to the afterglow of the black pixel. Therefore,
In this edge-emitting EL printer 34, a combination of the density 16/16 of the previous pixel and the density 4/16 of the current pixel is read out from the gradation correction table 38 to set the density of the gradation pixel to 3/16.
Correct to. By doing so, the density of the 3/16 gradation pixel becomes about 4/16 which is the original density due to the afterglow of the black pixel, as shown in FIG. The image quality of is maintained good. As illustrated in FIG. 9A, such a reduction in the number of times the drive pulse is applied can be easily realized by pulse width modulation of the drive IC 18.

Further, the gradation correction table 38 as described above is used.
The content setting is determined based on various conditions such as the photosensitive characteristics of the photosensitive drum that is the latent image carrier. Further, since the reduction of the number of drive pulses as described above is not executed for the black and white binary pixels, the contents of the gradation correction table 38 are not searched for the print data of such pixels. It is also possible to implement forwarding. Then, here, it is exemplified that the number of drive pulses forming the gradation pixels is corrected by the contents set in the gradation correction table 38 in advance, but, for example, such correction is executed based on a predetermined arithmetic expression. It is also possible to do so.

[0032]

As described above, the present invention provides an edge emitting EL.
A line head is provided in which the elements are connected in the longitudinal direction of the light emitting end surface, and a latent image carrier that relatively moves in the sub-scanning direction is arranged at a position facing the line head, in synchronization with the relative movement of the latent image carrier. A drive circuit for applying a drive pulse to the line head is provided, and by controlling this drive circuit, the number of flat pixel components formed on the latent image carrier by the element light emission of the edge emitting EL element is determined for each pixel. Is provided for adjusting the number of pixel constituent elements arranged in the sub-scanning direction in the substantially square pixel forming area by this pixel forming means to print gradation pixels as well as binary pixels. In the edge-emitting EL printer configured as described above, a density storage unit for temporarily storing the previous density information of the pixel to be printed is provided, and the gradation is controlled by the drive circuit according to the previous pixel density information temporarily stored in the density storage unit. Pixel By providing the gradation improving means for reducing the number of drive pulses to be formed, it is possible to prevent the density of the gradation pixel to be formed this time from increasing due to the afterglow when the previous pixel is formed. This has an effect such that the image quality of the tonal expression can be favorably maintained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a perspective view showing a line head.

FIG. 3 is a conceptual explanatory diagram showing a gradation correction table.

FIG. 4 is a time chart showing the relationship between drive pulses and emission intensity.

FIG. 5 is a block diagram showing prior art filed by the applicant in the past.

FIG. 6 is a time chart showing drive pulses.

FIG. 7 is a plan view showing main scanning lines.

FIG. 8 is a plan view showing a binary pixel.

FIG. 9 is a plan view showing a gradation pixel.

[Explanation of symbols]

 18 Drive Circuit 19 Edge-Emitting EL Element 20 Line Head 34 Edge-Emitting EL Printer 35 Pixel Forming Means 35, 38 Gradation Improving Means 36, 37 Density Storage Means

Claims (1)

Claim: What is claimed is: 1. A latent image carrier which is provided with a line head in which edge emitting EL elements are connected in a longitudinal direction of a light emitting end surface, and which relatively moves in a sub-scan direction at a position facing the line head. Is provided and a drive circuit for applying a drive pulse to the line head in synchronization with the relative movement of the latent image carrier is provided, and the drive circuit is controlled to emit the latent image by the element light emission of the edge emitting EL element. Pixel forming means for adjusting the number of flat pixel forming elements formed on the carrier for each pixel is provided, and the pixel forming elements arranged in the sub-scanning direction within the substantially square pixel forming area by this pixel forming means. In an edge-emitting EL printer in which the number of pixels is adjusted to print not only binary pixels but also gradation pixels, density storage means for temporarily storing previous density information of pixels to be printed is provided. Is a temporary memory Edge emitter type EL printer which characterized in that a gradation improved means for reducing the number of drive pulses for forming a gray scale pixel in control of the drive circuit according to the concentration information of the previous pixels.