As long as movable protective devices (such as safety gates) are open, the interlocking device must prevent dangerous movement of the machine. —ISO 14119 Safety of machinery — Interlocking devices related to protective devices — Design and selection principles
In other words, when the safety device is activated, dangerous machine movement must be stopped immediately, and the machine cannot be restarted as long as the safety device is activated.
When should interlocking devices with protective locking be used?
If the movement of the machinery still poses a danger after receiving a stop command, an interlocking device with protective locking should be considered. This means there is a time lag between receiving a stop command and the equipment coming to a complete stop; this is common in machines with rotating blades or oscillating wheels, and in the case of robots. The protective device can only be unlocked when the equipment is in a safe state or has completely stopped, and the safety door can only be opened when the machine no longer poses any danger.
When should the technological process be protected? When should personnel be protected?
Depending on the application, different functional principles can be used for security protection and locking.
l Process protection
For pure process protection (i.e., preventing accidental interruptions to the production sequence), a protective locking system based on the electro-locking principle is sufficient. The locking of the protective device is accomplished by an electromagnet—the electromagnet is not engaged when unlocking. Pilz's non-contact safety door system, PSENslock, provides this functionality. It combines safety door monitoring with an integrated electromagnet, thus providing both safe position monitoring and process protection locking within a single system.
Personnel entry requires additional protection.
If operators can or must enter the equipment area, and the equipment itself has the potential to cause injury due to overtravel, then in addition to process protection, personnel protection must also be considered, and safety interlocking conforming to EN ISO 13849-1 must be adopted. The appropriate interlocking device should be selected based on the performance level (PL) determined by the risk analysis. In this case, the safety interlocking can be implemented using the power-off interlocking principle. Unlike the power-on interlocking principle, the power-off interlocking principle uses a spring to activate the safety interlocking and an electromagnetic coil to unlock it.
Pilgen's PSENmech series of mechanical safety door systems can provide this type of protective locking, with a performance level (PL) typically reaching PL c, and PL d if troubleshooting is required.
bistability principle
In addition to the previously mentioned power-off locking and power-on locking principles, Pilz's safety door product line also includes products that utilize the bistable principle. Each time a rising edge signal is applied to the coil, the locking state is changed.
This locking method is described in ISO 14119 section 4.3.2.
Dual-channel coil-based protective locking control ensures the security of the protective lock, identifying fault conditions such as short circuits and preventing accidental opening of the safety door even if the coil itself malfunctions. Pilz's product utilizing this principle is the PSENmlock safety door system, which integrates safety interlocking and protective locking into a single system, up to PL e.
Bistable coils are highly energy-efficient, as the lock signal does not require continuous power, thus reducing heat generation and power consumption. Moreover, even in the event of an unexpected power outage, the bistable coil retains its previous operating state, preventing accidental locking of people into dangerous areas or accidental unlocking.
The PSENmlock series security door system, paired with the DHM door handle module, provides users with a complete solution. A single unit integrates multiple functions: actuator, latch, handle, escape release, and padlock mechanism. It can be used not only for left- or right-opening hinged doors but also for sliding doors.
