Patent ID: 7767954

Claim:
Process for monitoring a passageway through which objects on carriers are transported, the process comprising at least one light grid with a plurality of light rays running one above the other guarding the passageway, wherein the light grid has a first, lower area, through which the carriers pass and a second, upper area, through which the objects pass, which light grid possesses an evaluating circuit which emits a signal in response to interruption of a light ray in the first, lower area and provides information on the height of the object, which process comprises the following steps: a) storing a current value for the height of the object as a last measured value; b) generating a readout of the first, lower area of the light grid to determine whether a carrier has passed through the light grid and generating a readout of the second, upper area of the light grid; c) determining a new current value for the height of the object from the data read out from the second, upper area of the light grid; d) in the case of the last measured value having a value of zero within a tolerance range and a current measured value differing from zero beyond the tolerance range, setting of an object flag to indicate location of an object within the light grid, in the case of the last measured value differing from zero within the tolerance range and the current measured value having a value of zero within the tolerance range, cancelling the object flag, and determining whether the object flag has changed; e) in the case of detection of a carrier in the first, lower area of the light grid setting of a carrier flag and in the case of non-detection of a carrier in the first, lower area of the light grid and the object flag not set, cancelling or not setting the carrier flag; f) determining whether the current measured value and the last measured value satisfy a predetermined condition and reverting to step a) in the case of the current measured value and the last measured value satisfying said predetermined condition with the carrier flag set; g) reverting to step a) in response to a set carrier flag and a changed object flag; and h) executing a security function in response to interruption of a light ray from the second, upper area of the light grid.