Is an emergency stop given over the wireless remote control enough?
No. Wireless stopping is an added layer; the machine must in all cases carry a wired, manually reset emergency stop device conforming to ISO 13850.
No. A stop command given over a wireless link does not take the place of the fixed, wired emergency stop device in the sense of ISO 13850. The machine has to have a manually reset, latching red mushroom button in addition; wireless stopping complements this, it does not substitute for it.
The reason is simple: a wireless channel is, by definition, a channel that can be interrupted. The battery goes flat, the device goes out of range, there is strong interference in the environment. An emergency stop, on the other hand, is expected to be reachable and working under all conditions. That is why, in the safety architecture, wireless stopping is treated as an additional layer.
What the standards say
- The machine has an emergency stop device conforming to ISO 13850, with a red mushroom button on a yellow background, latching with manual reset and requiring a deliberate reset.
- IEC/EN 62745 addresses the establishment and the indication of the communication in wireless remote control systems and the behaviour on its loss, together with the behaviour on loss of supply; loss of communication counts as a dangerous fault and the system is expected to go to a safe state.
- EN IEC 60204-32 covers control circuits, interlocks and emergency stop requirements on lifting machines.
- The emergency stop function, in the sense of IEC 60204-1, can only be Stop Category 0 or 1.
The layers and what happens when they are cut
| Layer | Its function | If it is cut |
|---|---|---|
| Wired emergency stop | Cuts the power under all conditions | It stops the machine when the cable breaks as well |
| Wireless stop command | Fast intervention from a distance | If there is no signal the command does not get through |
| Signal loss timeout | Counts silence as a stop | It is delayed by the length of the timeout |
| Interlocking and limit switches | Cuts the movement at the limit | It protects on that axis only |
Frequent mistakes on site
The most common mistake is to take the red button on the remote control for the emergency stop of the machine. On some AXI sets there is an Emergency Stop button on the joystick; that button does not take the place of the machine's own wired circuit either, it is a separate function that stops the hydraulic motion. The second mistake is putting the wired button somewhere the operator cannot reach; the button has to be reachable from every point of the danger zone and must not be obstructed. The third mistake is using the emergency stop for normal stopping: it uses up the life of the contactor and of the mechanical parts, and in a real emergency the contact may have welded. The fourth is never testing the button for years; pressing and resetting it belongs on the periodic maintenance list.
Where this approach does not fit
In installations where the operator works far from the machine a single wired button is inadequate; more than one station is needed. Stopping does not solve every problem either: while a load is hanging in the air the movement is cut but the load does not come down, as in a loss of signal. ISO 13850 does not describe a recovery function; the way of lowering the load has to be planned separately. One more mistaken assumption: cutting the power does not give the same result on every axis. On an axis that can fall under gravity, cutting the power may speed the movement up rather than stop it; on those axes the behaviour of the brake or of the lock valve is assessed separately and the stop category is chosen accordingly.
This is general standards information; the conformity of a particular product to these standards can only be confirmed from the declaration of conformity of the manufacturer and from the user manual. The product records of the AXI ST/SF sets do not state an emergency stop button or an emergency stop function; do not assume such a function exists. Build the safety function through the machine's own wired emergency stop circuit under all conditions, and confirm the features of the set from the user manual.
The full topic: Wireless remote control installation: pairing, relays, safety