A cylindrical container inner surface tester based on an image processing technology

摘要

The present invention is a cylindrical container inner surface tester for detecting based on an image processing technology foreign substances, dust, scratches, etc. on the inner side surfaces of cylindrical containers such as aluminum cans. The present invention aims at solving the problem pertaining to the conventional technologies of differentiating the continuous tone of an image to detect white or black spots on the containers' inner surfaces. In the conventional technologies, a circular highlighted portion appears on an image and the intensity variations in the background are so complicated that defects cannot be easily detected. The cylindrical container inner surface tester of the present invention sets a threshold THD among the target picture element value PO (i,j) of a continuous tone image and the background picture element values PO (i+α,j) and PO (i-α,j) of the continuous tone image α picture elements forward and backward respectively along a scanning line of the continuous tone image of the inner surface of a test can viewed from its axis direction. The tester detects defects by determining that the target picture element indicates a defective valley when the following equations exist, and determining that the target picture element indicate a defective peak when the signs are inverted in the equations.$\text{PO (i+α,j) - PO (i,j) THD}\mathop{\mathrm{image}}$$\text{PO (i-α,j) - PO (i,j) THD}\mathop{\mathrm{image}}$;Before detecting defects, the present invention extracts as a test area according to the continuous tone image signal 1a the diagonal-shaded area between the first rise point 61 and the last fall point 62 (or between 61 and 63, and 64 and 62 excluding a masked area 201) of a signal obtained by converting a multi-value continuous tone image signal 1a to a binary representation using the predetermined threshold THG. Furthermore, the continuous tone image of the test container's inner side surface is sequentially scanned along a ring or spiral circular scanning line Lk or Lk′, for example. An absolute value of the difference ΔP=∥P0 - P1∥ between the volue P0 of the target picture element on the circular scanning line and the value P1 of the background picture element separate from the target picture element by a predetermined interval of picture elements d is compared with a predetermined threshold THP corresponding to the position of the circular scanning line. If ΔP THP, the target picture element indicates a defective inner surface such as a defective concave, etc. The cylindrical container inner surface tester is used for testing the inner surfaces of cylindrical containers such as beer cans while they are conveyed on a belt conveyor, etc.