DS-SEP24-PG20_Layout 1 17/09/2024 11:18 Page 1


FEATURE MACHINE BUILDING, FRAMEWORKS & SAFETY


sponsored by


MACHINE SAFETY: SOLUTIONS TO PREVENT OPERATOR BYPASS


Feature


Although designed to protect operators when working with rotating equipment and other high-risk machinery, safety guard interlocks are vulnerable to manipulation. David Dearden,


E


managing director of Euchner UK, suggests how machine builders can prevent operator bypass It is therefore important to secure the actuator


fficiency is one of the main reasons operators want to bypass guard interlocks. They may, for example, want to keep a robot


cell door open so they can perform maintenance without having to shut down a machine. So, when designing equipment that includes safety interlocks, machine builders must comply with ISO 14119:2013, which requires the likelihood of overriding to be considered. However, if the motivation is foreseeable –


for example, if an operator is paid based on piece work – the machine builder must take further measures, and it’s important for both safety and compliance to know what these are.


SAFEGUARD ACTUATORS AND SWITCHES Typically, safety interlocks consist of a safety switch and an actuator. If the actuator is accessible, there may be a greater motivation to remove and use it to bypass the interlock. While an option is to hide it in the door frame, when an operator sees non-contact switches they may remove the actuator and tape it to the switch so the door can open and close without breaking the safety circuit.


to prevent its removal. A common approach is to use non-reversible screws to bolt the actuator in place. Alternatively, embedding the safety devices in the machine’s frame out of sight could help prevent manipulation. But even if the actuator is hidden from view, this may not stop staff from using a spare actuator as an override key. If they do, the guard system may not know that the safety signal was being manipulated, which could leave the robot cell and operators vulnerable. Some interlocks with RFID technology have unique coding, whereby the actuator is paired to a specific switch. This prevents spare actuators from being used to override guard interlocks. There are two types of coding – Multicode,


typically found in applications where manipulation is of a lower concern, and Unicode for more high-risk environments. Though highly secure, any compatible actuator would work with a Multicode switch, meaning operators could buy a replacement and the switch would recognise it. This is not the case with Unicode. If there is a high risk of manipulation, machine builders should use a Unicode interlock. These


20 DESIGN SOLUTIONS SEPTEMBER 2024


minimise the risk of tampering by replication because each actuator must be assigned to a specific safety switch. There are, however, safe ways for overriding


interlocks when required. RFID systems, such as the CKS2 from Euchner, have benefits over traditional key switches because they avoid duplication.


STARTUP TESTS Incorporating a startup test into the control system can help discourage operators from tampering with switches or actuators. A startup test, for example, could require each guard to open and close at the start of every shift – so, if an operator did remove an actuator and tape it to the switch, it would be easier to spot. They would need to un-tape the actuator and put it in its original place ready for the test, before removing it again and re- taping it after the test to continue bypassing. Startup tests are especially beneficial in machine tool, packaging and automotive plants where machines run for several hours. Longer shifts mean wide windows for override attempts, but startup tests can be surprisingly effective at discouraging operators from manipulating safety devices. To protect operators, machine builders


must consider the motivation for bypass – ISO 14119:2013 compliance requires it. If override motivation is ‘foreseeable’, there are options available including incorporating startup tests, strategically placing actuators and the use of Unicode interlocks.


Euchner UK


T: 0114 256 0123 www.euchner.co.uk


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64