Light-emitting-device head and image forming apparatus with switching unit defining switching positions coinciding with dots in an image

Abstract

A light-emitting-device head includes a first light-emitting-device arrangement including light emitting devices arranged in lines extending in a first scanning direction; a second light-emitting-device arrangement including light emitting devices arranged in lines extending in a first scanning direction, the second light-emitting-device arrangement overlapping the first light-emitting-device arrangement in a second scanning direction at least in part; an optical device that forms an electrostatic latent image by focusing light emitted from the light emitting devices on a photoconductor and exposing the photoconductor to the light; and a switching unit that switches the light-emitting-device arrangement to be lit up between the first light-emitting-device arrangement and the second light-emitting-device arrangement at a switching position defined at any position in an overlapping portion where the first light-emitting-device arrangement and the second light-emitting-device arrangement overlap each other. The electrostatic latent image is composed of dots formed by a screening process performed with a screen having a predetermined screen angle. The switching unit defines the switching position such that when points in the electrostatic latent image that coincide with the switching position are connected to one another by a line, the line forms a zigzag shape while overlapping some of the dots, the zigzag shape including a line segment extending at the screen angle.