Reversing detection for an elevator car door

A light grid for mounting on a sliding door, in particular an elevator car door, for object detection and for determining periodic door movements,

• comprising at least one transmitter element on a transmitter strip, which emit radiation with a specific intensity,
• comprising at least one receiver element on a receiver strip, which receive the radiation of an assigned transmitter element, and
• comprising a control device for evaluating the receiver elements in regard to interruption of the radiation coming from an assigned transmitter element and for outputting a signal for object recognition upon interruption,
• wherein at least one receiver element is configured to output an intensity value for the intensity of the received radiation, and the control device is configured to evaluate the intensity value and to distinguish separate high, medium and low intensity value ranges with high, medium and low intensity values, the transition between low and medium intensity ranges being defined by a predetermined first limit value and the transition between medium and high intensity ranges being defined by a predetermined second limit value, and to recognize an alternation phase with at least one alternating from the low via the medium to the low intensity value range and to output a signal in the event of an alternation phase having been recognized.

The light grid according to claim 1, wherein the control device is configured to the effect that the alternation phase has at least one direct alternation from the low via the medium to the low intensity range without an intervening intensity value from the high intensity value range, and/or

• for the alternation phase a maximum permissible alternation phase duration is defined up until which it is regarded as an alternation phase, and/or
• the alternation phase has a plurality of alternations, in particular at least three alternations, from the low via the medium to the low intensity value range, and/or
• the alternation phase has a plurality of periodic alternations from the low via the medium to the low intensity value range, and/or
• the periodic alternations directly succeed one another, and/or
• for periodic alternations a maximum alternation phase period duration is defined up until which periodic alternations are regarded as an alternation phase.