Light beam scanning apparatus

Claim 1

A light beam scanning apparatus comprising: means for continuously exposing a sheet-like subject to be scanned having subsequently perpendicular longitudinal and transverse dimensions to a deflected scanning light beam in a transverse direction to perform main scanning along a main scanning line; means for transferring said subject in a longitudinal direction along a transfer path to perform sub-scanning so as to accomplish two-dimensional scanning of said subject; at least two apertures associated with said transferring means, said apertures being in alignment with said main scanning line and disposed in said transfer path so as to be covered by said sheet-like subject during movement thereof; an element associated with each of said apertures for receiving light from said scanning light beam transmitted by said apertures and for producing block signals each indicating blockage of one of said apertures; and means for detecting a time lag of block signals produced by said light-receiving element associated with each of said two apertures, and for determining if said time lag is greater than a predetermined time lag resulting from movement of said scanning light beam during main scanning, thereby detecting inclination of said subject, said transfer means includes: two pairs of rollers for carrying said subject in its longitudinal direction while clamping it between each pair of rollers, said pairs of rollers being spaced a distance shorter than the longitudinal direction of said subject, means for synchronously rotating said two pairs of rollers to perform sub-scanning, while the subject being exposed to a deflected light beam between said pair of rollers to perform main scanning, and a member located between said pairs of rollers for supporting said subject, said apertures being perforated in said support member.