Functional Safety Support: Sibert Engineering: Vinyl Record Master Forming Press

Introduction

Sibert design and manufacture a market leading hydraulic/pneumatic presses for coining viny record masters.

Supplying internationally as a market leader they take quality and compliance of their machines very seriously.

This has led them to seek support from us at PCS for evaluating the functional safety of their machine’s existing safety system design and verify compliance to the relevant standards.

Safety Function Specification

Pneumatic and hydraulic presses have specific requirements provided in type C standards ISO16092-3 and ISO16092-4. However, the scope is aimed at presses designed for applications that are manually loaded, high frequency and with a rapid stroke cycle. The functional safety requirements in these standards are not applicable to the Sibert press and would likely result in over specification.

Therefore, by applying Annex A risk graph from ISO 13849-1 we were able to re evaluate the main safety related functions performance level ratings (PLr). The safety function relating to the main loading door interlock was downgraded from PLe to PLd. This made a significant impact on the design requirements making compliance far more achievable.

Multiple hazardous movements on this machine made defining the safety function ‘span of control’ and ‘safe state’ of the machine complex but critical. We were also working around an existing design so finding a solution with minimal impact was a key consideration for the client.

Design Evaluation and Modification

After clearly defining each safety function, we able to determine that some current safety circuit provisions were actually unnecessary and therefore removing some additional valves provided a cost saving.

Adding some additional monitoring of pneumatic cylinder position allowed us to achieve the correct level of Diagnostic Coverage (DC) required for performance level D (PLd) without any complex design changes.

It was also possible to utilising existing valves used for directional control as part of the safety system. The direction valve provided another shutoff path for the hazardous movement, the failure mode of which resulted in a malfunction of the machine. It was therefore possible to use this ‘Fault Detection via the process’ as a legitimate form of monitoring on the valve. Also contributing to the required Diagnostic Coverage (DC) for PLd.

Interface relays being used within both safety channels of a dual channel redundant structure were found to be the source of a single point of failure. By re arranging the circuit we are able to utilise the existing components to achieve the same logic but ensure both channels are completely independent of each other.

Verification and Documentation

Reports documenting the initial evaluation and recommendations along with subsequent design developments formed part of the necessary evidence for Siber to demonstrate they have applied the standard correctly.

Conclusion

After our support Sibert Engineering had gained a lot of clarity and confidence in their safety system design. Collaborating with Product Compliance Support has also helped them develop further knowledge of working with ISO13849-1 which they are now able to apply to other machine variants in the future. Compliance was achieved whilst making every effort to retain as much of the existing design as possible to minimise impact.


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