Patent attributes
A light guide 3c of the printing shear detection sensor 3 is shaped so that the width of a side cross section when viewed in the conveying direction of a recording paper sheet P indicated by arrow B may be gradually smaller with an increasing degree of change from the top toward the bottom. The light emitted from the light emitting device 3a is incident on the light guide 3c from above, passes through the light guide 3c while being reflected on the side surface of the light guide 3c, is emitted toward the recording paper sheet P from the bottom of the light guide 3c, converged and projected on the recording paper sheet P as slit-like light. The light reflected on the recording paper sheet P is incident on the light receiving device 3b and thus, the printing shear detection pattern formed on the recording paper sheet P can be detected with high accuracy. The light guide 3c can be manufactured with using an inexpensive molding die at low costs, distinct from the conventional condenser lens.
