Cylindrical container inner surface tester having compensation for

Abstract

A corner area between the bottom and the side of a cylindrical container is set as a test area. An objective lens of a TV camera is mounted to form a predetermined angle with the central axis of the cylindrical container. An image is generated on the screen of an image processing device based on the image captured by the TV camera. One-dimensional position detection slits Ws1 through Ws3 normally cross the arc of the ring-shaped highlighted portion corresponding to the corner area at three points. The coordinates of the intersections P1 through P3 of the position detection slits and the highlighted portions are obtained. They are substituted in the circular equation to calculate the coordinate (.alpha., .beta.) of the center of the circle 0 having the intersections P1 through P3 on its circumference. The calculated coordinate is processed as a measured position coordinate to specify the position of the test cylindrical container so that the inner surface of the test cylindrical container can be precisely checked for a defect. Thus, the exact position of the test cylindrical container can be calculated, and the existence of a defect inside the test cylindrical container can be checked precisely.