How to get Functional Safety certification by using encoders on robot joints?

Designers of machines and industrial equipment are taking safety seriously. Even though the European market was the first to mandate functional safety for industrial machinery and automation, design for safety is now a global engineering concern. The basis for functional safety is the need to reduce the risk of injury in industrial machinery and systems, which functional safety does by addressing machines and systems as a whole.

Encoders such as the FSI 862 from Leine & Linde feature a hollow shaft which was been developed for certification in accordance with EN ISO 13849-1, EN 61800-5-2, IEC 61508 and IEC 62061. This allows the encoder to be used in Functional Safety applications up to risk level SIL2 and PLd, Category 3.

The two main standards that govern industrial machine safety are the IEC 62061 and the EN/ISO 13849-1 standard. The thing to remember is that individual components are not themselves certified functionally safe but rather the entire machine or system. However, individual components can be designed in such a way as to contribute to a machine or system overall being functionally safe.

Two measures, SIL (Safety Integrity Level) and PL (Performance Level), are defined within the IEC 62061 and the EN/ISO 13849-1 standard as probabilities of events occurring, with lower probability numbers reflecting safer systems.

Take encoders, for instance. An encoder can be designed so that it fits readily within a larger machine or system that can be certified functionally safe. Typical features of safety rated or enabled encoders may be diagnostic features, safe mechanical interfaces such as oversized or redundant features, or safety rated communication protocols.

For robotic systems, using encoders in joints can provide critical feedback on position, motion and velocity of robotic arms. This data can then used by a controller to evaluate system performance as a whole. So the encoder, along with the controller and other components, together contribute to making the entire robotic system functionally safe.