What Is Functional Safety? How Robots Reduce Risks From Control-System Failures.

What Is Functional Safety?

Functional safety is the part of a system's overall safety that depends on safety-related equipment and control functions operating correctly when required.

In robotics and industrial automation, functional safety helps ensure that machines respond appropriately to defined hazards, failures, and operating conditions.

For example, an industrial robot may be required to stop hazardous movement when an interlocked protective guard is opened.

The ability of the safety-related control system to detect that condition and perform the required stopping function is an example of functional safety.

Key Takeaways

• Functional safety concerns the correct performance of defined safety-related functions.
• Standards such as ISO 13849, IEC 62061, and IEC 61508 provide frameworks for designing and evaluating relevant systems.
• Functional safety is one part of overall machine safety and does not replace mechanical safeguards, risk assessment, or safe operating procedures.

How Does Functional Safety Work?

Imagine a robotic production cell containing moving equipment.

A worker opens an access gate to enter the cell.

The gate contains an interlock connected to a safety-related control system.

When the gate is opened, the system detects the condition and initiates the required protective response.

Depending on the machine's design, that response may involve stopping hazardous movement or preventing equipment from restarting.

For the function to be dependable, engineers must consider sensors, logic, actuators, wiring, software, and potential failures.

The entire safety-related function needs to achieve the required level of performance.

What Are Safety Functions?

A safety function is a defined function intended to reduce risk from a particular hazard.

Examples include:

Emergency stopping: Initiating an appropriate stop in response to manual activation.

Guard interlocking: Preventing specified hazardous operation when a protective guard is open.

Safe speed monitoring: Monitoring movement against defined safety-related speed conditions.

Safe torque off: Preventing a drive from generating motor torque through a defined safety function.

The exact requirements depend on the machine and application.

Safety functions should not be confused with ordinary software monitoring features that have not been designed and validated for safety-related use.

What Are SIL and Performance Level?

Two commonly encountered measures are Safety Integrity Level and Performance Level.

Safety Integrity Level (SIL) is used in standards such as IEC 61508 and IEC 62061 to describe requirements related to the integrity of safety-related functions.

Performance Level (PL) is used in ISO 13849 to describe the capability of a safety-related control system to perform a safety function under specified conditions.

ISO 13849 uses performance levels from PL a through PL e.

The required level depends on risk assessment and the applicable standard.

SIL and PL are different assessment frameworks and should not be treated as universally interchangeable numerical ratings.

Functional Safety vs. Cybersecurity

Functional safety addresses risks associated with failures or incorrect behavior of safety-related systems.

Cybersecurity addresses threats such as unauthorized access, malicious modification, and digital attacks.

The two increasingly overlap in connected industrial equipment.

For example, an attacker changing control-system parameters could affect physical operation.

A secure system is not necessarily functionally safe, and a functionally safe design does not automatically protect against cybersecurity threats.

Both need to be considered where relevant.

Does Functional Safety Make a Robot Completely Safe?

No.

Functional safety addresses particular safety functions and their required performance.

Overall robot safety also depends on mechanical design, guarding, tooling, operating procedures, maintenance, and other protective measures.

A robot equipped with a safety-rated stop function may still present hazards from sharp tools, suspended loads, or other physical sources.

The complete application needs an appropriate risk assessment.

Frequently Asked Questions

Does a collaborative robot automatically satisfy functional safety requirements?

No. Collaborative applications require appropriate evaluation of the complete robot system, tooling, tasks, and human interaction.

Can ordinary AI object detection be used as a safety function?

Not automatically. An AI model recognizing people or obstacles is not necessarily a validated safety-rated protective system.

The Bottom Line

Functional safety helps ensure that critical protective functions perform reliably when needed. In robotics, it is an essential engineering discipline for reducing risks associated with machine behavior and control-system failures.