Patent ID: 6812450
Filing Date: 2004-11-02
Classification: G01S

Abstract:
A method for monitoring a protected zone in which light rays are transmitted by an apparatus in the direction of the protected zone, light rays reflected/remitted by an object disposed in the protected zone are received and the distance between the apparatus and the object is determined, the method comprising:transmitting at least two light rays that include an angle between them; receiving, while the object is present inside the protected zone, a first light ray of the at least two light rays reflected/remitted by the object; receiving, while no object is present within the protected zone, a second light ray of the at least two light rays reflected/remitted from a location disposed outside the protected zone; and determining the distance from the apparatus of both the object and a second location, wherein a reference contour is determined wherein the second light ray scans a floor or a ceiling of a region surrounding at least one of the protected zone and articles disposed outside the protected zone and that location disposed outside the protected zone is determined in each case at which the second light ray is reflected/remitted, wherein a respective current contour is determined by means of the second light ray in certain time intervals and is compared with a stored reference contour, with a maladjustment signal or a manipulation signal being produced when the current contour differs from the reference contour at least to a pre-set degree.