1. Field of the Invention
The present invention relates to a scanning head having a structure suitable for a printer, scanner, copier or other image input and/or output apparatus, and a printer having such a scanning head.
2. Description of the Related Art
Page printers have been vigorously developed in recent years, because they can print on ordinary paper as well as specific paper. A page printer uses a laser scanning head composed of a laser diode and a polygon lens. In a laser scanning head, a laser emitting point is moved by a polygon lens, and printing at high-speed is difficult.
For high-speed printing, an LED scanning head using two or more LEDs has been developed. Two or more LEDs are aligned in an LED scanning head. These LEDs simultaneously emit light of different intensity, thereby scanning a photoconductor. As high picture quality is demanded, very high accuracy is demanded for packaging of LEDS with high density. This causes a problem of increased number of components.
To solve the above problems, Jpn. Pat. Appln. KOKAI Publication No. 9-226172 proposed a scanning head using an organic electroluminescent element as an LED.
However, at present, an organic electroluminescent element has a problem in luminous intensity and life. Namely, a light-emitting element requires sufficient amount of light to expose a photoconductor, and if the luminous intensity per dot of an organic electroluminescent element is weak, the exposing time per a dot must be set long. To set the exposing time long, the printing speed must be delayed. Conversely, if the luminous intensity per a dot of an organic electroluminescent element is increased, the exposing time per dot is reduced and the printing time is reduced, but the life of an organic electroluminescent element is reduced.
The luminous flux of an LED such as an organic electroluminescent element spreads from a light-emitting point, and it is preferable to provide an optical system between LED and photoconductor, which gives directivity to incident light from a dot of an LED to be emitted only to a specified part of a photoconductor. However, the efficiency of using such an optical system depends on an angle of taking in light (angular aperture), and the efficiency of using light is not high in a source like an LED which causes a light diffusion.