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Module adds safety functions to drive controller

19 November, 2018

The German drives specialist Stober has collaborated with the safety specialist Pilz to develop a safety module for its SD6 drive controller which allows safe drive monitoring of applications up to SIL 3 / PL e (Cat 4), in accordance with EN 61800-5-2 and EN ISO 13849-1. A worst-case response time of less than 10ms results in fast stopping, and minimises safety distances.

As well as Safe Torque Off (STO), Safe Stop 1 (SS1) and Safe Stop 2 (SS2) functions, the module also provides functions for safe movement and safe motion monitoring. Safely Limited Speed (SLS) and Safe Speed Range (SSR) ensure that the drive will not exceed the configured velocity limit values. Safe Direction (SDI) monitors the configured direction of motion, and Safely Limited Increment (SLI) limits increments. Safe Operating Stop (SOS) monitors active stops.

A “safe brake management” function consists of Safe Brake Control (SBC) and Safe Brake Test (SBT), with test cycle monitoring. This allows the drive to meet the requirements of the soon-to-be-released EN 16090-1, and is based on a publication issued by the German Social Accident Insurance organisation DGUV, which forms the basis for the draft standard DIN EN ISO 16090-1:2016-02, said to be the first standard to describe the protection of vertical axes.

The module can respond variably when a limit value is exceeded, or in the event of an emergency stop. “It is not always a good idea to shut off the drive controller immediately and perform an uncontrolled stop of the drive when a limit value is violated,” explains Markus Frei, Stober’s drive controller accessories product manager. “For a fast and simple restart, it is usually better to deliberately stop the drive using the controller, and only to intervene with the drive controller if the controller fails to do so.”

Special motors, encoders, cables or stall- or speed-sensing switches are not needed when using the SE6. Existing drive configurations can be reused, or suitable components chosen. This will usually cut costs, Stober says.

Stober’s safety module adds a plethora of safety functions to its SD6 drive controller

The module’s monitoring of safety functions goes beyond basic requirements. For example, position-based limit value monitoring, or the predictive hiding of interference signals, allow intended limit values to be approached with a minimal interference distance.

The module is easy to replace because the user only needs to swap the removable data storage and confirm its replacement. This transfers the device configuration to the new controller and can be done without specialist knowledge or software tools.

The two-channel module tests the integrated components on every start-up, after every STO, and during operation. This eliminates the need for cyclical function tests of safety functions on-site.

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