JPH02249668A - Electrophotographic copying apparatus using light emitting diode array - Google Patents

Abstract

PURPOSE:To avoid irregularity of the printing density thereby to improve the printing quality by utilizing normal developing in an electrophotographic apparatus using an array of light emitting diodes whereby toners are adhered to a non-exposed portion on a photosensitive body. CONSTITUTION:In a copying apparatus, a light is projected to a document and the reflecting light is exposed to a photosensitive body. Therefore, normal developing method is used to adhere toners 11 to a black portion where the light is not reflected. In the case where an array of light emitting diodes is used for an optical system of an electrophotographic apparatus, the surface of a photosensitive body 1 is uniformly charged by a charger 2 and a latent image of the printing data is formed through exposure from an array 3 of light emitting diodes. This latent image is developed by a developing unit 4 and turned to be a toner image on the photosensitive body 1. In this case, for developing the latent image according to the normal developing method, the light is not radiated to a portion where the toners 11 should be adhered to. Moreover, the toners should be of an opposite polarity to the potential of the photosensitive body, for example, (-). Accordingly, the surface of the portion where the light is not radiated is charged with (+), and adhered with the toners 11 having (-) charge. Since the potential of the surface is flat, the adhering toners are uniform, thereby making it possible to remove irregularity of the printing density.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving the image quality of an electrophotographic apparatus using a light emitting diode array.

[Background of the invention]

FIG. 3 shows a schematic diagram using a light emitting diode array in the optical system of an electrophotographic device. The surface of the photoreceptor 1 is uniformly charged by a charger 2, and a latent image of print data is formed by exposure of the light emitting diode array 3. The latent image is developed by a developing device 4 and becomes a toner image on the photoreceptor 1. There are two types of development methods: a reverse development method (FIG. 4) in which toner adheres to exposed areas, and a regular development method (FIG. 5) in which toner 11 adheres to areas other than exposed areas.

In a copying machine, light is shined on the document and the reflected light is exposed to the photoreceptor, so toner 11 is applied to the black areas where light is not reflected.
A regular development method is used to ensure that the film adheres to the film. On the other hand, printers using laser printers and light-emitting diode arrays use a reversal development method in which toner 11 adheres to the area that is exposed to light. In order to extend the lifespan, we use a reversal development method that requires less lighting time. Now, the toner image on the photoreceptor is transferred to a printing paper 6 by a transfer machine 5.
is transferred to the printing paper 6 by the fixing device 9. After the toner image has been transferred, the photoreceptor 1 is cleaned by a cleaner 7 and a static eliminator 8.
A light emitting diode array consists of light emitting elements arranged horizontally in a straight line, and each light emitting element is turned on and off by controlling the lighting and extinguishing of each light emitting element. For example, a light emitting diode array that forms a latent image on a photoreceptor and performs printing at a resolution of 9.4 lines/mm (240 dpi) has a density of 9.4 pieces/mm of light emitting elements, and is A3 size. A light emitting diode array for printing requires approximately 2,800 light emitting elements to be arranged horizontally and in a straight line. Here, the output of the light emitting element varies and is generally about ±10%.

Variations in each light emitting element lead to variations in the exposure of the photoreceptor, which in turn lead to variations in the amount of toner adhesion, and ultimately to uneven printing density. For this reason, in order to eliminate variations in the light output, the lighting time of each light emitting element and the amount of current flowing to each light emitting element are controlled, but these methods make the control of the light emitting diode array complicated. .

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned unevenness in print density and improve print quality in an electrophotographic apparatus using a single light emitting diode array.

[Summary of the Invention] The present invention focuses on a regular development method used in copying machines that attaches toner to unexposed areas, and by using the regular development method in an electrophotographic device using a single light emitting diode array. , the exposed area is a blank sheet of paper and is designed to prevent uneven printing density.

[Embodiments of the invention]

In an electrophotographic device using a light emitting diode array,
Conceptual diagrams of the decrease in surface potential due to exposure and the amount of toner adhesion are shown in FIGS. 1 and 2. If Figure 2 is an inversion phenomenon, the first
In the case of conventional reversal development, where the figure shows a normal phenomenon, the amount of exposure is uneven due to variations in the brightness of one light emitting diode that irradiates light to the area where toner is to be attached, and the way the photoreceptor surface potential drops varies. (Fig. 2-(a)), and the amount of adhered toner varies (Fig. 2-(b)). This toner is transferred to the paper, and the print density becomes higher where more toner is on the paper. The charging polarity of the toner used here is the same polarity as the charging potential of the photoreceptor, and is illustrated using a positive polarity in the figure.

In the case of the regular development method, the area where you want the toner to adhere is
No light is applied, and the toner used is of a different polarity from the charged potential of the photoreceptor. In Figure 1, a toner of negative polarity is used. The surface of the area that is not exposed to light has a positive potential, and toner with a negative charge adheres there (Figure 1-(b))
), the surface potential is flat, so the toner that adheres is also uniform. For this reason, the printing density becomes uniform.

If a photoconductor with a large rate of change in sensitivity to light wavelength is used, even if variations in the light output of the five-light emitting diode array are suppressed, the potential drop on the surface of the photoconductor will vary depending on the variation in the emission wavelength, and the amount of toner that adheres will vary. The difference in amount causes the problem of uneven printing density. However, even in this case, the problem can be solved by using the present invention.

〔Effect of the invention〕

According to the present invention, in an electrophotographic apparatus using a light emitting diode, since a regular development method is used as a development method,
It is possible to prevent uneven printing density due to variations in the light emitting output of the emission diode array.

[Brief explanation of drawings]

FIG. 3 is a conceptual diagram of the main configuration of an electrophotographic device, in which 1 is a photoreceptor, 2 is a charger, 3 is a light emitting diode array, 4 is a developing device, 5 is a transfer device, and 6 is a printer. paper, 7
8 is a cleaning machine, 8 is a static eliminator, and 9 is a fixing device. FIG. 4 and FIG. 5 are conceptual diagrams of the charging, exposure, and development processes of the photoreceptor. Further, FIGS. 1 and 2 are conceptual diagrams of the exposure and development process of the photoreceptor. In the figure, 10 is exposure and 11 is toner. Name of patent applicant (Hitachi Koki Co., Ltd.) 1 Figure 13 Figure 4

Claims (1)

[Claims] In an electrophotographic device that forms a printing latent image on a photoreceptor by turning each light emitting diode on and off, a regular phenomenon is used that causes toner to adhere to non-exposed areas on the photoreceptor. An electrophotographic device featuring: