Line head and image forming apparatus incorporating the same

Abstract

At least one light emission array includes a plurality of light emitting elements arrayed in a first direction. Each of the light emitting elements is an organic electroluminescence element. A monitor quantitatively monitors a light emitting state of at least one of the light emitting elements to obtain a monitored amount. A comparator compares the monitored amount and a reference amount. A controller performs a constant current control with respect to at least one of the light emitting elements in accordance with a result of the comparison performed by the comparator.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates to a line head using organic EL (electroluminescence) elements and an image forming apparatus incorporating such a line head. [0002] There has been developed image forming apparatus in which a line head having a large number of arrayed light emitting devices is used as an exposure unit. Japanese Patent Publication No. 11-138899A discloses an image forming apparatus in which a light emitting device array made of a plurality of light emitting devices is integrated in a single chip so as to form an exposure unit. In this example, single-chip light emitting device arrays for respective colors are once formed on a single substrate and then separated. The single-chip light emitting device arrays are disposed in corresponding color developing units respectively. Thus, the variation in light emitting characteristic is canceled. [0003] In addition to light emission diodes (LEDs), organic EL elements have been proposed as light ...

AI Technical Summary

Benefits of technology

[0007] It is therefore an object of the invention to provide a line head using EL elements and an image forming apparatus in which there is no deterioration in image quality even when the operating time period exceeds a predetermined time period.

[0013] With the above configuration, the intrinsic characteristic proper to the organic EL elements causing the lowering of the emitted light amount when the operating time period exceeds a predetermined time period is compensated so that the image quality can be prevented from deteriorating.

[0030] With this configuration, the lowering of the emitted light amount from the line head caused by aged deterioration of the organic EL element is compensated so that the image quality can be prevented from deteriorating.

[0048] With this configuration, the lowering of the emitted light amount from the light emitting devices caused by aged deterioration of the organic EL element is compensated so that the image quality can be prevented from deteriorating.

Problems solved by technology

However, there is no suggestion about a solution to the lowering of the emitted light amount when the operating time period exceeds a predetermined value as shown in FIGS. 17A and 17B in the case where organic EL elements are controlled by constant voltage control.

Therefore, when organic EL elements attached to a line head are driven by constant voltage control, there is a problem that the technique cannot deal with deterioration in image quality caused by the lowering of the emitted light amount when the operating time period exceeds the predetermined value.

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