According to ISO 14119 ‘Safety of machinery – Interlocking devices associated with guards – Principles for design and selection’, an interlocking device must prevent a machine’s hazardous movement as long as the movable guard, such as a safety gate, is open.
The PSENmech safety gate system ensures safe guard locking.
This means that the hazardous machine movement stops immediately when the safety guard is opened, and restarting is prevented for as long as it is open.
An interlocking device with guard locking is considered for use where the machine still poses a danger following the stop command, that is, when it has a time lag – as is the case in machines with rotating blades or oscillating wheels and in robots. The guard is only unlocked when the machine is in a safe state or has stopped completely. The safety gate can only be opened when the machine no longer poses any danger.
Process protection and personal protection
Different functional principles can be used with respect to safe guard locking depending on the application. The fundamental question here is: Should the operating personnel be protected in addition to the process? For pure process protection (that is, preventing unintentional interruption of the production sequence), guard locking according to the open-circuit current principle is sufficient. The guard locking is held in place by a magnet – and the magnet is deactivated again for unlocking. This is a functional principle offered by products such as the non-contact safety gate system PSENslock, from Pilz. It combines safe safety gate monitoring with an integrated electromagnet and thus offers safe position monitoring with process guard locking in a single system.
Entry requires additional protection
If operating personnel can – or must – enter the machine, and if there are dangerous overrun movements that could result in injury, personal protection must be taken into account in addition to process protection. Here, safe guard locking that complies with EN ISO 13849-1 is necessary. The selection of the appropriate interlocking device is then based on the performance level (PL) determined by the risk analysis. Safe guard locking can be achieved by means of the closed-circuit current principle in this case. Unlike the open-circuit current principle, a spring is used here to activate guard locking, and a solenoid coil is used to open the guard locking. The mechanical safety gate system PSENmech, also from Pilz, provides safe guard locking such as this up to PL c, with fault exclusion up to PL d.
Bistable as a principle
In addition to the closed-circuit current principle, Pilz uses the bistable principle in its safety gate portfolio. This two-channel guard locking control ensures safe guard locking. Fault cases such as a short circuit are recognised with this control, which can prevent unintentional opening of the gate even in the event of a fault. At Pilz, this principle is implemented with the safety gate system PSENmlock, which provides safe interlocking and safe guard locking up to PL e.
Pilz safety equipment is available in South Africa through Prime Automation.
For more information visit: www.primeautomation.co.za
