While installing electric gates does have many benefits it can be be dangerous if installed without the proper safety assessment prior to installation.
When identifying hazards and danger zones associated with automated gates, you should consider, among other things, the following risks:
- any points where persons may be injured by being crushed or becoming trapped, for example
- meeting point between swing gates when closing.
- sliding gate at “end of travel” positions.
- trapping of feet between lower edge of gate and ground.
- space between a moving gate and a fixed object.
- contact with moving parts at the drive unit.
In many instances we see gate automation systems without any thought for the safety of the public especially in situations where there is risk to the health & safety to the elderly and children.
To minimise the risk of entrapment or crushing we utilise the following equipment.
Photocells are electronic safety devices that are used in pairs. One emits an invisible beam of infra-red light which is either detected by the other or reflected back to the first. If an object breaks the beam, the photocells trigger the control panel to stop and reverse the gates.
Positioning pairs of photocells across danger areas ensures that anyone entering while gates are moving interrupts the beam and stops the gates.
Encoders (Obstactle Detection)
The encoder monitors motor speed, distance and position in relation to the swing or span (sliding gates) of the gate and their stops. Any changes in motor output caused by an obstacle detection will stop and reverse the motor a few inches ,while encoders are useful aid where there is no other safety devices present the force required to stop the gate varies and should not be relied on alone ,for example if a gate closed on a car it would open but it could still leave some damage. Most gate automation systems today come with built in encoders or can be added to the automation easily.
Safety edges use the same principle as obstacle detection in that they have to come into contact with an obstacle to cause the gates to stop and back off. Their construction, however, means that any impact is significantly reduced, and they can be positioned very carefully to cover specific danger area.
Safety edges are made up of a rubber profile that is mounted along an aluminium channel which itself is attached to a gate, or solid objects that gate moves close to such as a gate post or wall edge. However, some small ones are self-adhesive and do not need an aluminium channel. Inside the rubber profile is a conductive contact strip. As the rubber profile is compressed when it hits something, the circuit is completed, and a signal is sent back to the control panel.
Safety edge installation and use can be illustrated where one is mounted along the vertical leading edge of a sliding gate. If someone or something were in the driveway between gate pillars as the sliding gate slid closed, the safety edge would hit them first and cause the gate to stop and reverse.
As the point of impact is a compressible rubber edge, safety edges are less likely to cause impact injuries than obstacle detection. If obstacle detection reverses a gate after it has hit a car, there is likely to be some damage. If a safety edge hits the same car, the rubber profile may prevent any damage at all.
Safety edges require an interface and can be used on their own or to embellish existing obstacle detection.