Patent ID: 6624751
Filing Date: 2003-09-23
Classification: G01V

Abstract:
A method for monitoring an entrance of a hazardous area with the aid of a light grid arrangement comprising light barriers, said method comprising the following steps:a) recording actual received brightness values H of an individual light beam associated with a respective light barrier; b) deriving a signal pattern from the received brightness values H by comparing the actual received brightness values with an upper threshold value SO and a lower threshold value SU, wherein the received brightness values H are assigned to the following signal states: â€œfreeâ€  H>SO â€œblankedâ€  Hâ€œpartially blankedâ€  SUand wherein the individual signal states of the light beams form the derived signal pattern; c) comparing the derived actual signal pattern to a predetermined signal pattern of an object that is considered permissible to enter the hazardous area; and d) determining the object as a permissible object if one of the derived signal pattern coincides with the predetermined signal pattern, and an actual signal state â€œpartially blankedâ€  or â€œblankedâ€  is obtained in place of a predetermined signal state â€œfreeâ€  or â€œpartially blankedâ€  for a light beam in the region of a first edge of the object, an actual signal state â€œblankedâ€  or â€œfreeâ€  is obtained for a light beam in a region of a second edge of the object in place of the predetermined signal state â€œblankedâ€  or â€œpartially blankedâ€  and the remaining signal states of the derived signal pattern coincide with the signal states of the predetermined signal pattern.