JPH06218984A - Driving device for edge emitting type el element - Google Patents

Abstract

PURPOSE:To achieve the clear contour of one pixel by extremely reducing the electric potential difference between both the electrodes of an edge emission type EL element during the non-printing period, and by attenuating the afterglow promptly. CONSTITUTION:The device is composed of a high pressure driver 7 connected to one electrode 5 of an edge emission type EL element 6, a low pressure driver 8 connected to another electrode 4 of the edge emission type EL element 6, a controller 10 adapted to output control signals to the high pressure driver 7 and low pressure driver 8 and also output a printing data to the low pressure driver 8, and a switching part 11 for making an electrical connection between the high pressure driver 7 and the one electrode 5 of the edge emission type EL element 6 by detecting the output of printing data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for an edge emitting EL element in an image forming apparatus.

[0002]

2. Description of the Related Art In recent years, a line printer has been used as one of image forming apparatuses utilizing electrophotography. In this line printer, a charging device, a line head, a developing device, a transfer device, and the like are arranged on the outer periphery of the photosensitive drum, and an optical signal corresponding to an image signal is generated on the outer peripheral surface of the photosensitive drum charged by the applied voltage of the charger. Is emitted from the light emitting element of the line head to form an electrostatic latent image, the electrostatic latent image on the photosensitive drum is developed by the toner supplied from the developing device, and the toner image is transferred to the transfer paper by the transfer device. It is to be transcribed. It has been considered to use an edge emitting EL element as a light emitting element of such a line head.

That is, as shown in FIG. 4, a thin film-shaped active layer 1 made of zinc sulfide containing an active element is formed on a dielectric layer 2,
3 and enclose flat electrodes 4 and 5 on the surfaces of these dielectric layers 2 and 3 to elongate the edge-emitting EL element along the longitudinal direction (main scanning direction) of the photoconductor (not shown). The element 6 is formed. In this edge emitting EL element 6, a high voltage is applied to the electrode 5 from the common driver 7 and a low voltage is applied to the electrode 4 from the channel driver 8, so that a flat light beam is emitted from the end surface of the active layer 1. Such edge emitting EL elements 6 are linearly arranged on a substrate (not shown) by a thin film technique or the like, and a rod lens array (not shown) is provided at the tip of each edge emitting EL element 6. The line head is formed by making the two face to face each other.

Next, the operation will be described with reference to the timing chart of FIG. The channel driver 8 receives print data and FR (frame) from a control circuit (not shown).
Signal and the Ex-OR of the channel driver 7
Output V _cha (V _a or V _b ) from the gate (not shown)
Is input to the electrode 4 of the edge emitting EL device 6. The voltage V _com is input to the electrode 5 of the edge emitting EL element 6 from the common driver 7. This voltage V _com is a positive voltage V _P and a negative voltage V _N that are output alternately. Then, when the difference between the voltage V _cha from the channel driver 8 and the voltage from the common driver 7 exceeds the threshold voltage V _th , the edge emitting EL element 6 emits light. If each output is in the state shown in FIG. 5, light is emitted during the period of t ₁ and t ₂ , and t ₃ ,
During the period of t _4, the light emission is weak, which does not reach the print level. Then, the photoconductor is displaced (rotated) in the sub-scanning direction.
One pixel (electrostatic latent image) is formed on the photoconductor by causing one edge emitting EL element 6 to emit light a plurality of times in the process.

[0005]

As shown in FIG. 6 (b), when the potential difference between both electrodes of the edge-emitting type EL element 6 exceeds the threshold voltage V _th , as shown in FIG. 6 (a). The edge emitting EL element 6 emits light, but the edge emitting E
Since the L element 6 has poor response, it does not emit light according to the applied pulse, and afterglow occurs after the light emission. This phenomenon is a unique "tailing phenomenon" of the edge-emitting type EL device 6.

Here, as shown in the timing chart of FIG. 7, 12 pulses exceeding the threshold voltage V _th are applied.
Consider a case where one pixel is formed by continuously applying the voltage to the edge emitting EL element 6. In this case, the 13th and subsequent pulses are pulses that do not exceed the threshold voltage V _th , but a slight amount of light emission that does not form an electrostatic latent image is performed. In the process of forming one pixel by 12 pulses, the light quantity is increased sequentially and saturated when the light emission is performed a shallow number of times.
Since the afterglow occurs as described above even after the application of the last 12th pulse, there is a problem that the contour of one pixel becomes unclear as a result of the “tailing phenomenon” due to the afterglow.
In FIG. 7, (a) is a light emitting operation of the edge emitting EL element 6, (b) is output of print data, and (c) is an edge emitting E.
It shows a potential difference between both electrodes of the L element 6.

[0007]

SUMMARY OF THE INVENTION The present invention is an edge-emitting type E
A high-voltage driver connected to one electrode of the L element, a low-voltage driver connected to the other electrode of the edge-emitting EL element, a control signal output to the high-voltage driver and the low-voltage driver, and the low-voltage driver And a switch unit for detecting the output of the print data and electrically connecting the high-voltage driver and one electrode of the edge emitting EL element.

[0008]

According to the present invention, when the print data is not output, the high voltage driver and the edge emitting EL element can be cut off by the switching operation of the switch portion. Therefore, the edge emitting EL element immediately after the pixel formation is formed. The potential difference between the two electrodes can be remarkably reduced, whereby the amount of afterglow can be attenuated in a short time.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIGS. The same parts as those of the conventional example described with reference to FIGS. As shown in FIG. 1, a controller 10 for inputting print data created by the personal computer 9 is provided. The output side of a common driver 7 as a high voltage driver is connected to one electrode 5 of the edge emitting EL element 6, and the output side of a channel driver 8 as a low voltage driver is connected to the other electrode 4 of the edge emitting EL element 6. Has been done. The controller 10 rearranges the print data and sets the light emission timing of the edge emitting EL element 6,
The control signal is output to the common driver 7 and the channel driver 8 and the print data is output to the channel driver 8. Furthermore, this controller 1
0 is for controlling the operation of a mechanical unit such as the rotating system of the photoconductor. Furthermore, the common driver 7 and the edge emitting EL
A transistor 11 as a switch portion is connected between the electrode 5 of the element 6 and the electrode 5. This transistor 11 is
The common driver 7 and the electrode 5 are connected only when the print data output from the controller 10 is received by the base.

In such a configuration, as shown in FIG. 2, when the print data is output from the controller 10, the transistor 11 is maintained in the connected state, so that the common driver 7 drives the edge emitting type EL element 6 to operate. The voltage V _com is input to the electrode 5. This voltage V _com is a positive voltage V _P and a negative voltage V _N that are output alternately. Then, when the difference between the voltage V _cha from the channel driver 8 and the voltage from the common driver 7 exceeds the threshold voltage V _th , the edge emitting EL element 6 emits light. If each output is in the state shown in FIG. 2, light is emitted during the period of t ₁ and t ₂ . In this example, since the print data from the controller 10 is cut off during the period of t ₃ and t ₄ , the transistor 11 is turned off. Therefore, the voltage V _com output from the common driver 7 is zero. As a result, the potential difference between the electrodes 4 and 5 of the edge emitting EL device 6 is extremely small, and the light emission time is extremely short even if the light is slightly emitted, and
Based on the print level, the emission intensity is extremely low enough to be regarded as non-emission.

FIG. 3 is a timing chart showing a state in which one pixel is formed with 12 pulses.
As shown in, when print data is output,
The potential difference between both electrodes of the edge emitting EL element 6 exceeds the threshold voltage V _th , but after that, the common driver 7
Since the voltage V _com from the
The potential difference between both electrodes of the element 6 becomes a very small potential difference far from the threshold voltage V _th . Therefore, in FIG.
As can be understood from a comparison between (a) and FIG. 7 (a), the edge-emitting EL element 6 does not emit a very small amount of light, and thus the afterglow can be rapidly attenuated. This makes it possible to clarify the contour of one pixel.

[0012]

As described above, according to the present invention, the switch portion for detecting the output of the print data and electrically connecting the high voltage driver and one electrode of the edge emitting EL element is provided. When the print data is not output, the switching operation of the switch unit can cut off between the high voltage driver and the edge emitting EL element, so that the potential difference between both electrodes of the edge emitting EL element immediately after the pixel formation is reduced. The amount of afterglow can be attenuated in a short time, and thus the contour of one pixel can be made clear.

[Brief description of drawings]

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

FIG. 2 is a timing chart.

FIG. 3 is a timing chart.

FIG. 4 is a perspective view showing a conventional edge-emitting EL device.

FIG. 5 is a timing chart.

FIG. 6 is an explanatory diagram showing a relationship between a drive pulse of an edge emitting EL element and the amount of emitted light.

FIG. 7 is a timing chart.

[Explanation of symbols]

 6 Edge emitting EL device 7 High voltage driver 8 Low voltage driver 10 Controller 11 Switch part

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[Procedure amendment]

[Submission date] June 28, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

FIG. 3 is a timing chart showing a state in which one pixel is formed with 12 pulses.
As shown in, when print data is output,
The potential difference between both electrodes of the edge emitting EL element 6 exceeds the threshold voltage V _th , but after that, the common driver 7
Since the voltage V _com from the
The potential difference between both electrodes of the element 6 becomes a very small potential difference far from the threshold voltage V _th . Therefore, in FIG.
As can be understood from a comparison between (a) and FIG. 7 (a), the edge-emitting EL element 6 does not emit a very small amount of light, and thus the afterglow can be rapidly attenuated. This makes it possible to clarify the contour of one pixel. In the above example
The transistor 11 is used as the switch unit.
Other switching elements that operate by inputting character data
It is acceptable.

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

[Procedure 3]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 7

[Correction method] Change

[Correction content]

[Figure 7]

Claims (1)

[Claims] 1. A high voltage driver connected to one electrode of an edge emitting EL element, a low voltage driver connected to the other electrode of the edge emitting EL element, and control to the high voltage driver and the low voltage driver. A controller that outputs a signal and outputs print data to the low voltage driver, and a switch that detects the output of the print data and electrically connects the high voltage driver and one electrode of the edge emitting EL element. A device for driving an edge-emitting EL element, which comprises: