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A double leaf set of residential gates can be made to comply with safety regulations with a simple 'ring of beams'.
Author : Huw Jones
Easy way to safety compliance
There are three ways to comply with safety on automated gates.
There is the difficult way, by proving that the forces are reduced to safe limits, while still remaining strong enough to operate the gate reliably in all weather conditions.
There is the chocolate fireguard way, where the user has to be standing at the gate while holding down a button and chanting a hail mary.
And there is the ring of photobeams.
Detecting a person entering the risk zone is relatively easy. The control panel pauses the gate, but what happens next depends a bit on the application.
Photobeams are the most effect form of non contact safety
The safety solution
An automated gate risk zone is where a person can be injured. A ring of beams blocks personnel access to the risk zone. It does not need to consist of 4 beams. One or more fences could constitute blocking access on either or both sides.
A useful margin is to have at least 500mm between the side fence and the gate open position. It is about an arms reach and allows a corridoor of refuge.
It is not until a beam is crossed during motion that the gate will be stopped. Be careful not to allow a margin where a person might reasonably expect to be loitering before the gate starts.
On a swing gate
An 'A beam' is mounted on the gate piers outside to stop the gate closing. The three 'B beams enclosing the risk zone are on a pause input.
If a person walks into the risk zone before the gate has completed its cycle they may be at risk when the gate re-starts. , but the respone is not clear.
Cabling
There is generally only one duct across the road for signal cables. The post on the left side should take a cable from the left pier, and the right hand photobeam post will connect to the right hand pier.
The two posts in a four beam system are wired as repeaters. Each repeater posts has a transmitter and areceiver. The posts only need power, as the signal form the receiver switches the transmitter. Repeaters are the electronic equivelant of a mirror.
Article beam & edge wiring explains more.
How control panels respond
When a photobeam on channel B detects a person, it pauses the gate motion. Control panels may have different reactions after the person has left the detection area. Some programmes wait for another command, others may continue travel, or re-start in the opposite direction.
It is particularly important when edges are used in the same circuit. The standard calls on the control panels to reverse direction incase a person is trapped by the edge.
The safest response for a photobeam detection is to remain inactive until the next user command.
On an infilled sliding gate
A sliding gate has different risks that need different forms of protection. If the gate has a solid infill there is no shear risk. If the gap between the gate and pier is less than 25mm, then there is no risk of drawing in. If there are no protrusions, there is low 'hooking' risk.
It may be industrial looking, but this gate will only require an 'A beam' on the outside of the piers, and a 'B beam' on the inside.
The recently popular aluminium gates with horizontal slats are also low risk. A ring of beams can be implemented with no other protection.
For a ring of beams, the inner beam can either run back to a wall (at least 500mm from where the gate stops) or it will need an additional side cover beam. Note the 500mm gap between the perimeter wall and the gate line. This leaves a safe zone, and the open end prevents risk of entrapment.
On a sliding gate with vertical bars
Most residential sliding steel gates have vertical bars which is a safety protection nightmare. The ring of photobeams need to be set back from the gate line so that there is no chance of a limb being drawn into the gate. But then allows a person to enter and loiter in the risk zone before the gate begins to move.
A vertical barred gate presents risk of shear against the supporting pier in both directions. The beam mounted on the piers therefore needs to be a 'B' beam like the inner beam.
The example above shows three safety edges that might be considered necessary for use with vertical bar gates.
Setting the beams back from the gate line puts the risk out arms reach. Additional beams can be added near the gate line to detect a person loitering in the risk zone to prevent it from starti to move.
On a hybrid gate
A hybrid automated gate is rare, probably because few installers have attempted one. Hybrids lack the modern obstacle sensing by encoders or current sensing so a ring of external beams is a good safety solution.
The normal inner B beam has become diagonal to take in the swing leaf. There is another B beam protecting side entrance, but on hybrid applications, this is usually a perimeter wall.
The safety edge on the sliding gate is on channel A, and is essential. A 500mm void is left between the front wall and gate but is likely to be resisted by the client or architect.
