Drive-based functional safety solutions

Insights into drives technology

Drive-based functional safety solutions

ABB offers various safety devices and tools for designing safer machines and processes that utilize drives. Our drive-based functional safety offering includes drives that come with integrated safety features and extended safety functionality all in one package.

Safe connection between drive and PLC can be established using PROFIsafe or CIP safety protocols. This is enabled using optional safety functions modules. ABB’s functional safety design tool speeds up the design process when building safety solutions.

ABB all-compatible drives have Safe torque off (STO) built in as standard even for the most demanding safety applications up SIL 3 / PL e. 

 

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functional-safety-whitepaper

Maximizing machine safety, uptime and productivity

In industrial automation variable speed drives are commonly used to control the speed and torque of motors.

Their use helps to improve the energy efficiency, productivity, and efficiency of many applications. Because of their ubiquitous nature in today’s industrial landscape, ensuring that drives perform to the highest functional safety standards is essential to prevent accidents, protect personnel, and avoid damage to products and equipment. Drive-based functional safety can boost the productivity of machinery in many ways. For example, cleaning operations can be performed without stopping the machine and equipment and wiring costs can be reduced.

Industrial applications are inherently hazardous. From conveyor belts to bottling machines, anywhere that humans and machines interact holds risks. Functional safety solutions minimize or eliminate risks to people, to equipment and to environment.

This whitepaper describes some of the functional safety solutions for drives available today.

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Integrated safety in drives

Our all-compatible drives have the basic safety function safe torque off (STO) built-in as standard.

This integrated safety functionality can be extended with a range of available options. The options include the Safety functions module (FSO-12 or -21) for all-compatible industrial drives, and the CIP Safety™ functions module (FSCS-21) and PROFIsafe safety functions module (FSPS-21) for all-compatible industrial drives, general purpose drives and machinery drives. The Safety functions module (FSO-12 or -21) can be used either with the safe speed estimation feature or with a safety encoder, together with the FSE-31 safety encoder interface. All safety modules are easy to integrate inside a drive offering scalable amount of safety functions, thus ensuring safe use of the application.

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Safety communication between drive and PLC

When a safety system includes several drives, a safety PLC is used for controlling drives and machines from a common source.

Different safety functions can be performed in the application, all controlled by one common safety PLC. Our all-compatible industrial, general purpose and machinery drives offer PROFIsafe connectivity over PROFINET. This means communication between them and a PLC is safe, fast and more reliable. In addition, communication diagnostics is also made possible. Our scalable offering of PROFIsafe connectivity includes an ACS880 industrial drive connected to the PLC with a PROFINET fieldbus adapter module (FPNO-21) providing PROFIsafe connectivity together with the FSO-12 or -21 Safety functions module. There is also the option to connect ACS880 industrial drives, ACS580 general purpose drives and ACS380 machinery drives to the PLC with the CIP Safety™ functions module (FSCS-21) and the PROFIsafe safety functions module (FSPS-21). Both modules offer also built-in safety functions.

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Functional safety design tool FSDT-01

When designing safety functions for applications a safety calculation has to be done according to international functional safety standards (EN ISO 13849-1 and IEC 62061).

Our functional safety design tool helps you perform risk estimation, define required safety integrity (SIL) / performance level (PL) for safety functions, verify achieved safety level and generate design reports.

Functional safety design tool (FSDT-01) is used for machinery safety. It helps to increase the safety of users in the vicinity of machines. It is a Windows application, which is a support tool for performing functional safety modeling, design, calculations and verification for machine functional safety.

The tool supports both standards: EN ISO 13849-1:2015 and IEC 62061 ed.1.2 (2015). The tool is aimed to simplify the process of safety function design and verification and to generate documentation to support compliance to the requirements of the mentioned standards and the European Machine Directive for safety.

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Typical safety functions with drives

Our drives are part of machines controlling the speed and torque of the motor that's driving the machine.

Our drives can perform safety functions such as Safe torque off (STO), Safely limited-speed (SLS), Safe break control (SBC), Safe maximum speed (SMS), Safe stop emergency (SSE), Safe stop 1 (SS1).

Safe torque off (STO)

STO is the required basic foundation for drive-based functional safety, since it brings a drive safely to a no-torque state. STO is typically used for a prevention of an unexpected startup (EN 1037) of machinery or for an emergency stop, fulfilling stop category 0 (EN 60204-1).functional-safety-safe-torque-off-STO Figure STO. Upon activation STO immediately switches off the drive output to the motor. Motor speed

Safe stop 1 (SS1)

This function stops the motor safely, using a controlled ramp stop and then activates the STO function. SS1 is typically used in applications like rolling mills where motion must be stopped in a controlled manner before switching to a no-torque state. In addition to a safe process stop, SS1 can also be used to implement an Emergency stop, fulfilling stop category 1 (EN 60204-1).
SS1-t (time monitoring) or SS1-r (ramp monitoring)
functional-safety-safe-stop-1-SS1
Figure SS1. When activated, SS1 will ramp motor speed down to a standstill and then activate the STO function.

Safe stop emergency (SSE)

This safety function is specifically designed for emergency stops. SSE can be configured to execute either STO or SS1 depending on which emergency stop is suitable for the system. For examples of this functionality see figures for STO and SSE.

Safely-limited speed (SLS)

This function prevents motors from exceeding a defined speed limit. The SLS safety function can be used in applications such as decanters, mixers, conveyors or paper machines where excess speed can be hazardous during ie. maintenance or cleaning operations.
functional-safety-safely-limited-speed-SLS

Figure SLS. Upon activation, SLS will monitor that motor speed does not exceed a defined level. If it is exceeded, SLS will activate STO or SSE to stop the drive.

Safe maximum speed (SMS)

This function is a variant of the SLS-safety function. It provides continuous protection against a motor exceeding a defined maximum speed limit.
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Figure SMS. When SMS is used, it is always active and ensures that the set speed limit is not exceeded (ie. maximum allowed speed).

Safe brake control (SBC)

This functions provides a safe output signal to control a mechanical holding brake. Drills, cranes, winches, hoists, vertical conveyors and elevators that need external brake solutions require this type of safety function. Typical use for SBC is when a drive is switched off with STO function and there is an active load affecting the motor (eg. a hanging load on a crane/winder).

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Figure SBC. SBC provides a safe control signal to operate the mechanical brake. 

Safe Speed Monitor (SSM)

This function provides a safe output signal, for example to a safety PLC. A typical use for SSM is when there is a need to monitor motor speed, but the reaction is done from a safety PLC to, for example, synchronize the stopping of multiple drives. SSM output can also be used in signaling lamps to indicate if the motor is running or not. 
SSM

Figure SSM. Upon activation, the drive will safely indicate if speed is above or below the defined speed limit.

Safe Direction (SDI)

This position function ensures that a motor will not turn in an unwanted direction. Typical use cases with are found with escalators or conveyors as well as operation near end limit switches in crane applications. 

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Figure SDI. When active, the SDI monitors that the motor does not rotate in an unwanted direction. If movement is detected in an unwanted direction, the motor will be stopped using SSE function.

Prevention of Unexpected Start-Up (POUS)

The POUS function prevents the machine from starting unexpectedly. The POUS function activates the Safe torque off (STO) function in the drive. Specially designed for maintenance and repair procedures.

POUs

Figure POUs. Ensures that the machine remains stopped when people are in the danger area.

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References and articles

ABB integrates drive safety functionality to simplify machine automation

ABB Drives and safety technology thrills visitors at Liseberg amusement park in Sweden

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Safety-conscious drives meet safety standards

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Advanced control and safety technology improves tower crane performance

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Cost and time savings with drive-based functional safety

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Drives deliver safety for food and beverage machinery

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