Safety plus for multi-axle drives

The two series SC6 and SI6 are designed for multi-axis applications and offer a compact design and high power density. The SC6 stand-alone device is particularly suitable for space-saving and economical concepts. Thanks to its integrated power supply and slim design, drive-based applications with up to four axes can be implemented efficiently. The controller is available as a single or dual-axis device with a rated output current of up to 19 amps. The SI6 series was specially developed for control-based multi-axis applications in modular technology. It scores points with a width of just 45 millimetres and reduced cabling requirements. In conjunction with a central supply module, redundant power supply units can be dispensed with - a clear advantage in terms of space requirements and installation effort.

"The SX6 safety module is a brand new addition to our range, which we can optionally equip these two series with," explains Tim Lang, Head of Applications at Stöber. "This makes both controllers suitable for safety-relevant applications up to SIL 3, PL e (category 4) in accordance with DIN 61800-5-2 or DIN EN ISO 13849-1."

The SX6 enables the classic stop functions Safe Torque Off (STO), Safe Stop 1 (SS1) and Safe Stop 2 (SS2). A highlight: The STO safety function can also be activated individually for each axis on multi-axis controllers. In addition to these functions, Safely Limited Speed (SLS) and Safe Speed Range (SSR) ensure that the drive does not exceed the configured speed limit values. Safe Direction (SDI) monitors the planned direction of movement, Safely Limited Increment (SLI) reliably limits the increment and Safe Operating Stop (SOS) is responsible for active standstill.

Focus on practicality

Stöber developed the SX6 module in collaboration with safety expert Pilz, with the focus always being on practicality. Tim Lang: "In order to further increase the productivity and availability of the machine, we have extended the monitoring mechanisms of the safety functions beyond the basic normative requirements. Position-based limit value monitoring and the predictive suppression of interference signals enable the target limit values to be approached with a minimum interference margin." The SX6, which has a two-channel structure throughout, tests the integrated components every time the device starts up, after every STO and during operation. This eliminates the need for cyclical function tests of the safety functions at the end customer's premises that require documentation.

"We have also revised the shutdown paths of the STO and SS1 stop functions and have made them significantly faster again at 5 and 6 milliseconds respectively," says Tim Lang. "These short worst-case reaction times, the minimized safety distances and, above all, the fast re-availability significantly reduce downtimes and thus increase system availability."

Ethercat and FSoE: secure communication

The SX6 safety module is controlled via Ethercat and uses the proven Fail Safe over Ethercat (FSoE) safety protocol. A decisive advantage: the existing Ethercat infrastructure can continue to be used. This significantly reduces the cabling effort. "The safe communication is based on the black channel principle and is transmitted together with the functional Ethercat communication via the same connection," explains Tim Lang. Further proof of reliability: the SC6 and SI6 drive controllers have successfully passed both the Ethercat and FSoE conformance tests. In particular, the communication interface was tested to ensure manufacturer-independent and stable data transmission within the control architecture.

No special motors, encoders, cables, standstill or speed monitors are required to operate the safety module. The designer can continue to use existing drive configurations or switch to the components used in the application. This generally reduces system costs. Tim Lang: "In the event of servicing, an existing safety configuration can be transferred to other controllers quickly and easily using an SD card as a data memory. No special knowledge or software tools are required for this."