MODERN trains and trams need doors which are intelligent. A passenger caught in a closing door can be injured, and even trapped clothing causes short delays while the doors are released. Systems are available to prevent doors trapping obstructions, but it is vital to reduce the number of false alarms.

Siemens has developed Optical Safety Edge, an optoelectrical system which detects trapped obstructions by sending pulsed infra-red signals between a transmitter and receiver along rubber strips protecting the door edges.

Within 4ms, the electronics establish the minimum level of light which is required for communication, and OSE adapts itself to the specific operating conditions. As the train travels between stations, the zero position load on the strip is redetermined, allowing OSE to compensate automatically for distortions, dirt or cracks in the rubber. Once the zero position is identified, OSE waits until the train is about to depart from the next station. When the doors close, the IR signal is compared to the previous zero position level; if the door is in the correct position, OSE confirms that the doors are ready for departure.

Any abnormal loading on the doors breaks the signal, and the train management system is alerted. The fully automated process makes OSE suitable for use on driverless trains, and it will be installed on the Nürnberg metro as part of the Rubin project for automatic operation of Lines U2 and U3 from 2006 (MR02 p11).

If a passenger’s clothing is trapped but has not been detected, simply trying to tug it free will provide the pressure the strip needs to trigger an alarm. Once the doors are closed and no alarm triggered, OSE reassesses the new zero position ready for arrival at the next stop.

OSE is fitted to every door, so units only become active at the doors used at a particular stop, minimising the risk of false alarms. Once installed, OSE is virtually maintenance-free. The compact, decentralised design means it can be fitted to almost any door where a power supply is available, and it can reuse existing rubber edging on the doors. The electronics are hidden above and below the doors, and in the event of vandalism only the rubber strips need replacing.

Siemens Transportation Systems, Germany

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