Protective doors in production When is which safety guard reasonable?

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Pilz Industrieelektronik GmbH

Pilz GmbH & Co. KG

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Protective doors should not only guarantee the required safety, but they must also ensure production efficiency. This raises the question for those responsible for production safety: What kind of protection or safety guard is really needed?

The application case itself dictates which safety door is the right one. The product standard EN ISO 14119 guides the way, as it closely links the topic of safety with the very diverse application situations.

Therefore, it must be carefully considered in the design phase which type of protective door is suitable. A swing and sliding door? Or a hood, flap, or roller door? In addition, they must consider the type of monitoring, the switch type, and the appropriate safety interlock for the protective door in their planning. Another essential criterion is found in the installation situation itself: should or must it be concealed? If there is a space-critical situation, safety interlocks like the safety switch with interlock PSENmlock Mini from Pilz are suitable. It has a compact design and offers high protection against tampering.

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Moreover, users must check if particularly harsh environmental conditions prevail. With robust interlocks like the PSENslock 2 safety interlock from Pilz, with its hygienic design and stainless steel elements, protective door monitoring with process interlock can be implemented safely even in the harshest environmental conditions. It is important that the protection class IP 67/IP 6K9K is provided. The locking force (force that keeps the door closed through the permanent magnet even when de-energized) can be individually adjusted using an RFID tag.

When process protection, when personal protection?

The question of the type of interlock depends on the overrun time. If the time to reach the danger point is longer than the overrun time, a process interlock is sufficient. In this case, the priority is to protect the process itself and prevent unwanted production interruptions. However, if the intervention time is shorter than the overrun time, a safe interlock is required. This is also referred to as personnel protection. This applies to machines that are still running down, such as robotic applications. The safety device may only unlock here when the machine is in a safe state and has come to a complete stop. Only when there is no longer any danger from the machine should opening the protective door be possible.

For process protection, an interlock based on the working current principle is sufficient, for example. The interlock is provided by a magnet. For unlocking, the magnet is deactivated again. A functional principle, such as that offered by the electromagnetic safety interlock PSENslock 2 from Pilz. It combines safe protective door monitoring with an integrated electromagnet.

For personnel protection, the bistable interlock principle is often used—this is employed, for example, in the PSENmlock and PSENmlock Mini safety interlocks from Pilz. The last state is maintained in the event of a power failure, so the door remains either closed and held or open. High safety is ensured by the two-channel control of the lifting magnet: In the event of a fault, the OSSDs are switched off, but the interlock remains. It can then be selectively unlocked by deactivating it once.

Suitable protective device for every performance level

The choice of the appropriate protective device, depending on process or personnel protection, is based on the Performance Level (PL). This is determined using a risk assessment according to EN ISO 13849–1. The determining factors for the assessment are the severity of possible injuries, the frequency and duration of exposure to the hazard, and the avoidability of hazards. PLe indicates the highest risk.

Multiple safety interlocks are often used in a system. It is necessary to connect them. With diagnostic solutions like Safety Device Diagnostics (SDD) from Pilz, extensive diagnostic and status information can be implemented alongside a safe series connection and targeted control of individual sensors. Advantage: It allows defining exactly which door can be unlocked and opened after shutdown, for example, when maintenance work is pending in a system. Otherwise, when the unlocking function is requested, all series-connected protective doors would open at once. This could become a safety issue if a person enters the danger zone unnoticed at another protective device.

There is no "one-size-fits-all" standard situation for protection. However, there is a rule of thumb for the safety of people and machines: The more dangerous the situation behind a safety door, the more secure the protection or monitoring of the separating protective device must be designed.