Cost and time savings with drive-based functional safety

Paul Boughton

Significant advances in drive technology now allow for safety functions to be built directly into the drive which controls motor and machinery movements. This article examines how safety designers and machine builders can simplify their work while providing higher overall safety and protection levels.

Machine safety strategies aimed at protecting people, property and ecosystems can benefit from recent innovations in drive technology. Drive technology today allows safety functions to be built directly into the drive in an effortless manner. This gives big benefits to machine builders, designers, engineers and users who want to meet proper safety requirements with less hassle while saving time and money.

Integrated drive-based functional safety

Implementing a machine safety system from start to finish can be seen as a daunting and complicated undertaking. Thanks to new safety technology in drives and standardisation that unifies requirements and terminology used in the market, this process has been made easier. New electronic safety solutions integrated into the drive are perfectly capable of replacing the use of traditional safety systems that involve hard-wired logic add-ons like relays and contactors. The safe torque off (STO) safety function comes integrated in many ABB drives. Using an optional safety functions module, additional safety functions can be integrated into the new all-compatible ACS880 industrial drives.

A few of the most important benefits that can be obtained with integrated safety in drives include reduced design time and effort and easy commissioning of one or several built-in pre-programmed safety functions. Other advantages are reduced numbers of devices, amount of cabling, and cost savings, as well as no wearing parts compared to traditional electromechanical safety devices.

Functional safety design tool simplifies designer's life

One of the key initial tasks of a safety designer's job is to conduct a risk analysis aimed at defining where safety is needed on the machine and then deciding which safety levels and functions are required for making the machine safe. To make this work easier, ABB's new Functional safety design tool (FSDT-01) helps machine builders, OEMs and system integrators to calculate, verify and document the required, designed and achieved safety integrity level (SIL) or performance level (PL) using a very logical stepwise procedure, in accordance with machinery standards ENIEC62061 and ENISO13849-1.

The Functional safety design tool cuts the designer's workload by simplifying and speeding up the design process, while simultaneously ensuring the safety design calculations are met according to standards. Additionally, the design tool is compatible with numerous safety libraries including ABB safety devices as well as other manufacturers, thus making calculations and device selection much faster and easier.

Safe torque off (STO)

Once the machine design is approved, drive-based functional safety is ready for implementation. Safe torque off (STO), which is the safety function that brings drives safely to a no-torque state (eg, emergency stop) and/or prevents an accidental unexpected start-up, is the compulsory foundation of integrated drive-based functional safety. STO is therefore built into the drive as an electronic safety function to be used as an alternative to traditional electromechanical methods such as contactors.

Underlining ABB's commitment to drive-based functional safety, many of its drives have STO built-in as a standard feature. The all-compatible ACS880 drive series is the best-equipped, most-modern example of integrated safety in drives, with STO as a standard feature and the optional SIL 3 or PL e rated safety functions module providing additional safety functions.

Five safety functions in one safety module

The optional TÜV-certified safety functions module (FSO-11) works seamlessly with the all-compatible ACS880 industrial drives. It offers five optional safety functions in a compact 'safety-yellow' colored module package. The functions are: Safestop1(SS1), Safestopemergency(SSE), Safebrakecontrol(SBC), Safely-limitedspeed(SLS) and Safemaximumspeed (SMS).

The safety functions module is easy to commission and configure using Drive composer Pro, the common PC tool for the ACS880 drive series. Using the safety module, the customer gets straightforward functionality right in the drive and does not need to figure out how he is going to hook up and wire the logic with relays, resets and contactors. Instead the customer makes them work in harmony with the drive's functionality by simply commissioning these functions that are built-in the module based on the safety design. This in turn helps to avoid the electromechanical logic design task.

The main benefit is the integrated safety functions that work seamlessly together alongside the drives control system. The extensive diagnostic features aid in troubleshooting to keep the system continuously safe, with safety-related system messages part of the standard drive operation, and accessible through the drives control panel. Additionally, the design of the safety functions module means less maintenance and chance of breakdown as there are no wearing parts. The safety module is encoderless and provides capability for speed-related safety functions regarding certain suitable applications. This results in lower costs and higher reliability.

Direct benefits for the machine builder, designer or machine user include less cabling, which saves costs and makes the safety design work on a smaller footprint. Faster response time also provides improved protection in an emergency situation.

System-wide approach

The safety functions module is easy to connect to a safety PLC, such as ABB's AC500-S. This makes it possible to build a larger safety system where the safety PLC controls several drives, and the safety modules provide the local safety functionality and feedback to and from each drive. Connection between drive and PLC is done using a safety fieldbus built on PROFIsafe protocol. ABB also offers a wide variety of additional safety devices such as switches, contactors and relays.

For more information at

ABB Oy, Helsinki, Finland.