highest safety level in servo drives

Date: 23 October 2018

Better safe than sorry!

The SD6 is a flexible stand-alone drive controller in the STOBER product range which is suitable for complex requirements and tasks in automation technology and mechanical engineering. Thanks to its 32-bit dual-core processor, the highly dynamic series responds very quickly to reference value changes and load jumps. The SE6 safety module is a new addition. In addition to the Safe torque off (STO) safety function, it provides the SD6 drive controller with other drive-based safety functions from EN 61800-5-2 at the highest level of safety—including extensive stop and monitoring functions. It also features a fast worst case response time as well as flexible, manufacturer-neutral interfaces. Together with integrated brake management for up to two brakes, the practice-oriented SD6 fulfills German Social Accident Insurance (Deutsche Gesetzliche Unfallversicherung, or DGUV) requirements for gravity-loaded vertical axes.

The 6th generation from STOBER offers powerful stand-alone and multi-axis drive controllers for highly-efficient multi-axis applications. The flexible SD6 is a part of this product family. This single-axis controller has a nominal output current of up to 85 amperes and is primarily used in drive-based applications with decentralized motion control.

The SD6 controls linear and rotational synchronous servo motors as well as asynchronous motors. Due to its modular interface concept and extensive accessories, it can be configured with precision to solve even the most specialized drive tasks. Communication modules for CANopen, EtherCAT or PROFINET can be selected for the connection to a higher-level controller.

The SE6 safety module is a new addition to the product portfolio; it is available as optional equipment for the SD6 drive controller. This makes the drive controller suitable for safety-related applications up to SIL 3, PL e (category 4) in accordance with DIN 61800-5-2 or DIN EN ISO 13849-1. The low worst case response time of less than ten milliseconds enables fast stopping, allowing the design engineer to keep safety distances to a minimum.

One of the highlights of the product is the safe brake management consisting of Safe brake control (SBC) and Safe brake test (SBT) with test cycle monitoring. In addition to the Safe torque off (STO), Safe stop 1 (SS1) and Safe stop 2 (SS2) stop functions, SE6 also enables functions for safe motion monitoring. The Safely-limited speed (SLS) and Safe speed range (SSR) functions ensure that the drive does not exceed the configured velocity limit values. Safe direction (SDI) monitors the configured direction of motion, and Safely-limited increment (SLI) limits the increment reliably. Safe operating stop (SOS) monitors an active stop. The issue of real-world suitability took priority during development together with Pilz GmbH & Co. KG. As a result, all safety functions can be used up to SIL 3, PL e (category 4).

SE6 offers the user the ability to 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. 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," explains Markus Frei.

No special motors, encoders, cables or stall or speed sensing switches are needed to operate the SE6. The user can reuse existing drive configurations or switch to components that are suitable for the application. That, in turn, is usually associated with a reduction in system costs.

In order to continue increasing the productivity and availability of the machine, the monitoring mechanisms of the safety functions have been expanded beyond basic standardized requirements. Due to position-based limit value monitoring or the predictive hiding of interference signals, the intended limit values can be approached with a minimal interference distance.

In case of service, the user only has to swap the Paramodul removable data storage and confirm the replacement. This transfers the overall device configuration to the new drive controller. No special knowledge or software tools are required to do so.

Featuring a consistent two-channel structure, the SE6 tests the integrated components upon every device start-up, after every STO and during operation. As a result, cyclical function tests of safety functions that are subject to documentation at the end customer's location can be eliminated.

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