Solenoid Controlled Interlock Switches
Particular types of machinery within certain automation safety applications require a 'run-down' time before all of the machine's moving parts have come to a controlled rest so that they no longer pose a risk to plant personnel. In these scenarios, the machine's guard doors must be held closed until the machine's run-down time has expired.
Similarly, initiating a safety-related stop function on a machine before its cycle-time has concluded can cause operational issues and disrupt production. A machine that is interrupted mid-cycle, such as arc-welding robots, can take a significant amount of time to restart as these machines may need to be reprogrammed before the fault state can be cleared. To overcome this, the safety interlocking system should hold the door closed until the machine has finished its current operating cycle, before entering a safe state of operation.
One method of preventing premature access is to use interlocking devices with guard locking functionality. Within Trapped Key interlocking systems, this means using a solenoid controlled key switch whereby operators must request entry into the machine, typically using a local push button. The trapped key is only released once the machine has entered a safe state of operation and a signal has been sent to 'energise' the solenoid that is holding the key in place.
