Preventing entrapment

Using presence detection
Therefore, it is important initially to always try to prevent entrapment. If creating an unobstructed view is not possible, this can be done by using presence detection through the use of a laser scanner, pressure mats or radar safety. However, in reality, this is often difficult to achieve due, for example, to external environmental factors or the fact that many optical safety sensors do not meet the required level of safety.

Section 5.6.3.4 from ISO 102018-2 Robots and Robotic Devices states the following:

“To ensure that no one is in the safeguarded area before starting/resetting, use the first achievable option from the following enumeration.”

• Unobstructed view
  
• Presence detection
  
• Isolation & locking
  
• Locking in open position
  
• Time-limited reset devices
  
• Audiovisual pre-reset
  

LOTOTO is therefore particularly used during maintenance operations, as the machine is standing still for too long for short-term inspection and cleaning work. Another disadvantage of LOTO is that it is not compulsory but a completely procedural way of safety, where mistakes can easily be made.

Interlock blocking device
Installing an interlock blocking device on access doors ensures that they can be locked in the open position when someone is in the guarded area. This blocking device ensures that the safety contacts of the installed safety switch cannot be activated and restarted. This safeguard must therefore only be capable of being unlocked by the person who is in the protected area carrying out the work. This can be done by using a safety key which the worker removes from the lock and takes with him into the safeguarded area.

It is also possible to take measures against entrapment within the protected area. To do this, you can use a time-limited reset device. This prevents the machine from being restarted or reset from outside the safeguarded zone. Upon activation, this pre-reset allows the operator to exit the protected zone via a pre-programmed delay.

Additional safety support, a warning light
In addition, it is possible to use an audiovisual pre-reset, such as a signal light with a siren. This will indicate when the machine is switched on and will allow the operator to leave the area in time. However, this solution by itself is not very effective, but can be used well as an additional tool to prevent the risk of entrapment.

With all these available solutions, entrapment in a safeguarded area should certainly be preventable. Which measures are needed for your situation depends on the risk analysis and the level of safety that needs to be achieved.

If you have any questions or would like advice from one of our safety experts, they are always at your service. We also have a range of entrapment devices for doors and light barriers available in our webshop www.machinesafety-shop.com.