Which statement best describes a fail-safe behavior in robotics?

• A. The robot continues operation at all costs
• B. If a fault occurs, the system moves to a safe condition; examples include STO, emergency stop, or safe-mode state
• C. The control software automatically repairs the fault
• D. The robot immediately increases speed to complete tasks

Answer: (B)

Fail-safe behavior means the system prioritizes safety by automatically moving to a safe condition when a fault is detected, rather than continuing normal operation. In robotics, this is implemented through mechanisms like Safe Torque Off (STO), an emergency stop, or a safe-mode state that limits or halts motion to prevent harm or damage.

This approach protects people and equipment even if the fault can’t be fixed immediately or the control loop can’t guarantee safe operation. It’s about reducing risk first, not keeping performance up at all costs.

The other options don’t fit because they fail to prioritize safety: continuing operation at all costs ignores fault conditions, automatic repair assumes faults disappear on their own without entering a safe state, and increasing speed would raise the risk rather than reduce it.