Patent ID: 6927408

Claim:
An apparatus for inspecting a light-transmissive sheet body to detect a stripe defect therein, comprising: a light-emitting unit for applying light to the sheet body; a light-detecting unit for detecting light having passed through the sheet body; a slit member disposed in at least one of said light-emitting unit and said light-detecting unit, for shaping said light into a line of light through a slit defined in said slit member and guiding said line of light to said light-detecting unit; and a processor for processing signal data of the light detected by said light-detecting unit; said slit being oriented in the direction of the stripe defect, said processor comprising means for processing said signal data which is produced when said line of light is guided through said slit to said light-detecting unit to detect the stripe defect in said sheet body. wherein said processor comprises: an extremal value calculator for determining an extremal value of said signal data for each reference length of said sheet body; and a defect disappearing position identifier for determining a first function established by a plurality of extremal values obtained from a range including said defect in said sheet, and a second function established by a plurality of extremal values obtained from a range not including said defect in said sheet, and identifying a position on said sheet body where said first function changes to said second function, as a defect disappearing position where said defect disappears.