Functional safety in mechanical engineering does not begin with the drive, but with the sensor. Safety functions such as Safe Limited Speed, Safe Limited Position, or Safe Direction - as defined by IEC 61800-5-2 for servo drives - are, in practice, only as reliable as the sensor output on which they are based. We offer new safety-certified ring encoders as bearingless KIT encoders that support the full functionality of modern safety drive architectures particularly in robots and robotic arms.
With the publication of IEC 61508 in 1998, the fundamental understanding of machine safety changed. Instead of simply interrupting the power supply, the standard has since required that a system transition to a defined, controlled safe state in the event of any single fault. Modern servo drives compliant with IEC 61800-5-2 implement this principle using a comprehensive library of safety functions, including STO (Safe Torque Off), SS1 and SS2 (Safe Stop 1 and 2), SOS (Safe Operating Stop), SLS (Safe Limited Speed), SLP (Safe Limited Position), SDI (Safe Direction), and SBC (Safe Brake Control). The latest inductive or magnetic ring encoders developed by us can support multiple interfaces simultaneously and are certified according to the standards IEC 61508, EN ISO 13849-1, or IEC 62061. They meet the requirements for these safety functions, which only achieve SIL 2 or SIL 3, or PLd or PLe, if the sensor used has a corresponding classification based on its position and speed data.
In parallel with the further development of safety functions, the underlying communication architecture has undergone fundamental changes in recent years. Safety-oriented fieldbus protocols such as CANopen Safety, FSoE, PROFIsafe, or CIP Safety are increasingly replacing dedicated safety signal lines. SRIS signals (Safety Request Input Signals) can thus be transmitted over the same Industrial Ethernet infrastructure that is already in use for motion control. This reduces wiring effort, minimizes control cabinet space requirements, and noticeably shortens commissioning time.
This is where the new category of ring encoders comes into play. They are so versatile and adaptable that they can meet a wide variety of requirements, especially when space is very limited at the measurement site. The bearingless hollow-shaft system consists of a passive rotor and a stator with a sensor and signal-processing electronics. Two measurement principles are available: The magnetic principle, in which the rotor consists of a magnetic ring carrying a specific number of magnetic poles based on the vernier principle. Or the inductive principle, in which the rotor serves as a coil carrier. The rotor can be easily mounted using screw fasteners.
The encoders feature a very low-profile yet robust aluminum or stainless-steel housing. A pure PCB solution is also possible. The stator can additionally be divided into a sensor unit and an evaluation/interface unit. This requires very little space for the sensor at the measurement location, while the remaining electronics can be relocated to areas of the application where space is not constrained. Of course, functional safety is fully maintained with this modular design. The PCB solution saves even more space. This makes them ideal for the following applications: The particularly compact magnetic ring encoders are used in the smallest of spaces, while the inductive ring encoders can feature inner diameters of up to 200 mm. The latter are more robust against installation tolerances as well as dirt and environmental influences, such as magnetic fields. Thanks to the variety of designs and sizes, the ring encoders can be integrated into almost any type of joint or gearbox, such as those found in robotic arms.
Depending on the model and size, the devices offer several interface packages: CANopen Safety, FSoE, or PROFIsafe on the safety side, and BiSS or SSI on the standard side, where minimal response times are critical. In addition, incremental signals (ABZ, UVW) can be output. The resolution is selectable per interface. This multi-interface capability allows safety controllers and high-speed motor feedback systems to be supplied with sensor data simultaneously, at resolutions up to 20 bits and a temperature range up to 125°C.
Designing an IEC 61800-5-2-compliant drive system requires considering the safety function, performance level, and data communication system together to determine the appropriate sensor category. We offer encoders suited to a variety of requirements. In collaborative robot cells, for example, where ISO/TS 15066 specifies limit speeds of typically 250 mm/s or less, the combination of high resolution and high resolution and dynamic response forms the basis for reliable SLS monitoring.
In addition, for press applications with safely limited axis position (SLP), we offer absolute encoders that deliver the correct position even after a power interruption without a reference run and without data loss. On gravity-loaded vertical axes, where STO is always combined with SBC, the safety concept comes full circle: Here, our encoders not only provide position feedback but also enable safe brake monitoring via the Safe Brake Test.
