Light scanning device with a short-path synchronizing grid

Claim 1

A light scanning device for two-dimensionally scanning an object surface which moves in a subscanning direction, comprising: (i) a first light source for emitting a scanning light beam; (ii) a light deflector for reflectively deflecting the scanning light beam in a main scanning direction substantially perpendicular to the subscanning direction; (iii) a scanning lens for converging the deflected scanning light beam to scan the object surface in the main scanning direction; (iv) a second light source for applying a synchronizing light beam to said light deflector at a position where the scanning light beam is reflected thereby, in a direction allowing the synchronizing light beam that is reflectively deflected by said light deflector to be applied to said scanning lens; (v) a converging lens disposed on the optical path of said synchronizing light beam prior to application to said light deflector for converging said synchronizing light beam at an optical length from said light deflector shorter than the optical length between the light deflector and the object surface whereby the scanning length of the synchronizing light beam is shorter than the scanning length of the scanning light beam in the main scanning direction; (vi) a grid shorter than the scanning length of the scanning light beam in the beam scanning direction disposed in a position where said synchronizing light beam is converged by said scanning lens and said converging lens and extending in said main scanning direction; and (vii) light detecting means disposed behind said grid for detecting the synchronizing light beam of shorter scanning length than that of the scanning light beam that has passed through said grid.