METHOD FOR INSPECTING INSIDE OF HOLLOW ROUTE

PROBLEM TO BE SOLVED: To judge the existence of internal abnormality in a hollow route by projecting diffused light front the inlet of the route, receiving light passed through the inside of the route with irregular reflection by a prescribed image pickup means and discriminating the feature of the picked-up image. SOLUTION: A projection unit 8 and an image pickup unit 9 are inserted into a pair of sand removing holes formed on the upper face side of a head cylinder, a plane mirror 11 and a convex mirror 12 are oppositely arranged so as to interpose a hollow route 4a formed between the holes between both the mirrors 11, 12 and diffused light is projected from a light emitting source to the mirror 11 through an optical fiber 10. Thereby, light Lb reflected from the mirror 11 is irregularly reflected and passed in the hollow route 4a of which inside is a rugged state and the passed light is received by the mirror 12 in two-dimensional plane. Reflected light from the mirror 12 is picked up by a camera 14 like two-dimensional plane through a lens 13 to obtain the two-dimensional plane image of the irregularly reflected light passed through the route 4a. Since features such as the light quantity and contour of the picked-up image are changed in accordance with the normality/abnormality of the inside state of the hollow route 4a, the features of the picked-up image and discriminated.