When you have a machine or work cell which allows for the risk of a person being in the hazardous zone when the machine is restarted, safety devices designed for Full Body Access Areas should be considered. A common area with this danger is in a robotic cell. A typical robot is surrounded by a combination of fencing with interlocked doors and light curtains. What happens if a person is not in a visible location in the cell? Is it possible to restart the robot with that person still in the cell?
Four strategies that Bulwark uses to prevent a machine from restarting with a person in the hazardous zone are:
- Trapped Key Door Interlocks Equipped with a Safety Key
- Laser Safety Scanners
- Safety Mats
- Light Curtains Mounted Horizontally
What is the best technology for your application?
Trapped Key Door Interlocks:
We discussed this technology in depth in a previous blog, so we will not spend much time here explaining the technology. Click here to visit that post: Trapped Key Exchange Systems.
We can force a person entering the cell to remove a Safety Key from the door interlock. This individual then needs to keep the key on their person while in the hazardous area. The machine can not be restarted as long as the key is not put back into the lock, which keeps the person safe. All other personnel that could potentially enter a hazardous area should be trained to always have a key on their person, to lock out the machine using proper LOTO procedures if a safety key is not available or we can potentially use one of the other technologies discussed below in conjunction with door interlocks.
Laser Safety Scanners:
Laser Scanners create a horizontal plane that, if blocked in any way by a person or even an object, will signal the machine to stop. The area being scanned can be custom designed and odd-shaped. A warning zone can even be employed to warn a person close to the hazardous zone that they are about to stop the machine if they continue to move towards the hazard. The biggest drawback to a laser scanner is cost. It is often the most expensive of these technologies. However, if a large or odd shaped area is being guarded, it may be the most cost effective. We are fans of the SX Series Safety Scanner from Banner Engineering because it has a safety zone of 5.5 meters and a warning zone of 40 meters. It also has a built-in dust immunity feature, it is easy to program and is cost competitive.
Safety mats are designed to lay on the floor and, if stepped on, will signal the machine to stop. The technology is simple: there are 2 thin sheets of metal in the mat that are separated by a small air gap. If you put pressure on the mat, the sheets touch, completing a circuit. The safety mat controller monitors the mats and when it detects that someone or something is applying pressure to it, it signals the machine to stop.
Safety mats are a good choice in challenging environments. They do not care if it is dusty or dirty. You can even roll a carts or an occasional forklift over them and they will remain intact and functional. For more on safety mats take a look at this prior blog: Larco Industrial Safety Mats.
Light Curtains Mounted Horizontally:
Another technology that can be used if you have rectangular areas to protect is that of light curtains mounted horizontally. This is often a good choice if you already have light curtains guarding the machine. Light curtains can be less expensive than laser scanners and even safety mats if a limited number of them will be able to protect the area. For more information on light curtains follow this link to our blog about them: Banner Engineering LS Series Light Curtains.