What Is Safe Torque Off Servo?

Key Takeaway

A Safe Torque Off (STO) servo is a safety feature integrated into digital servo drives. STO ensures that the servo motor can be safely disabled without cutting the power entirely. This feature is crucial for maintenance tasks such as clearing blockages, repairing damage, or performing routine checks, as it prevents the motor from restarting unexpectedly.

By using STO, you can ensure the safety of personnel working on or around the servo motor. It stops the motor’s torque generation, making it safe to handle the machinery without the risk of sudden movements. STO is an essential safety feature in many industrial applications, enhancing both safety and operational efficiency.

Definition and Function of Safe Torque Off

Safe Torque Off (STO) is a safety function integrated into servo motors and drives to immediately stop the motor from generating torque. This safety feature is activated to prevent the motor from producing any rotational force, effectively bringing it to a safe state without cutting power to the entire system.

Function:

Immediate Torque Disabling: When STO is activated, it disconnects the motor’s drive power, ensuring that no torque is generated.
Prevention of Unintended Motion: This function prevents any unintended or accidental motion, which is critical during maintenance or in emergency situations.
Electrical Isolation: STO isolates the motor electrically, which is crucial during servicing and repairs to prevent accidental startups.
STO is typically part of a broader safety strategy, often used alongside other safety functions like emergency stops and safety relays, to provide comprehensive protection in industrial settings.

Benefits of Using Safe Torque Off

Implementing Safe Torque Off in servo systems offers several significant benefits, enhancing both safety and operational efficiency:

Enhanced Safety: STO provides a reliable method to quickly stop the motor, reducing the risk of accidents and protecting both personnel and machinery.

Simplified Maintenance: By isolating the motor, STO makes maintenance tasks safer and more straightforward. Technicians can service the system without worrying about accidental motor startups.

Reduced Downtime: Quick response to emergencies minimizes downtime. The ability to disable the motor without shutting down the entire system allows for faster troubleshooting and recovery.

Compliance with Safety Standards: Implementing STO helps meet various international safety regulations, ensuring the system complies with industry standards and legal requirements.

Cost-Effective: STO can reduce operational costs by preventing accidents, minimizing wear and tear on equipment, and decreasing the frequency of unplanned downtimes.

These benefits make STO a vital feature in modern servo systems, ensuring safety and efficiency in various industrial applications.

Implementation in Servo Systems

Implementing Safe Torque Off in servo systems involves several key steps. Here’s a comprehensive overview:

1. Selection of Compatible Components: Ensure that the servo motors, drives, and controllers are STO-compatible. These components should have built-in STO functionality.

2. Proper Wiring: Follow the manufacturer’s guidelines to wire the STO circuits correctly. This typically involves connecting STO inputs to the drive or controller and integrating them with emergency stop buttons or safety relays.

3. Configuration and Testing: Configure the STO function through the drive’s software or hardware settings. Conduct thorough testing to ensure the STO function works correctly and that the motor stops generating torque immediately when activated.

4. Integration with Other Safety Systems: Integrate STO with other safety mechanisms such as emergency stops, safety light curtains, and safety relays. This integration ensures a coordinated response to safety events.

5. Documentation and Training: Document the implementation process and provide training for operators and maintenance personnel. Everyone should understand how STO works and how to activate it in an emergency.

By following these steps, you can successfully implement STO in your servo systems, enhancing safety and compliance.

Safety Standards and Regulations

Compliance with safety standards and regulations is essential when implementing STO in servo systems. Key standards include:

IEC 61800-5-2: This international standard defines safety requirements for adjustable speed electrical power drive systems, including STO. It specifies functional requirements and testing procedures to ensure STO provides the necessary safety level.

ISO 13849-1: This standard outlines safety requirements for the design and integration of safety-related parts of control systems. It includes guidelines for assessing the performance level of safety functions like STO.

EN 62061: This European standard provides requirements for the functional safety of electrical, electronic, and programmable electronic control systems, including STO. It covers the entire lifecycle, from design to decommissioning.

ANSI/RIA R15.06: This American standard focuses on safety requirements for industrial robots and robotic systems. It includes provisions for STO, ensuring that robots can be safely stopped in an emergency.

Adhering to these standards ensures that STO implementation meets required safety levels, protecting both operators and equipment.

Practical Applications and Examples

STO is used in various applications where safety and rapid response are critical. Here are some practical examples:

Robotics: In industrial robotics, STO ensures that robots can be quickly and safely disabled in case of an emergency, preventing accidents and protecting both operators and equipment.

CNC Machines: STO in CNC machines allows for immediate stopping of the spindle and axes, ensuring safety during tool changes, maintenance, and emergency stops.

Conveyor Systems: In automated conveyor systems, STO ensures that the conveyors can be stopped immediately in case of a blockage or other safety concerns, preventing damage and ensuring operator safety.

Automated Guided Vehicles (AGVs): STO in AGVs ensures that the vehicles can be quickly disabled in case of an obstacle or emergency, preventing collisions and ensuring safe operation.

Wind Turbines: In wind turbines, STO is used to safely stop the turbine blades in high wind conditions or during maintenance, protecting the equipment and maintenance personnel.

These examples highlight the versatility and importance of STO in various industrial applications, ensuring safety and reliability.

Conclusion

Safe Torque Off is a critical safety feature that enhances the safety and reliability of servo motor systems. By understanding the definition and function of STO, recognizing its benefits, implementing it correctly, adhering to safety standards, and applying it in various practical scenarios, engineers can ensure the safe operation of servo systems.

For newly joined engineers, mastering STO is essential for designing and maintaining safe and efficient systems. This knowledge not only protects operators and equipment but also ensures compliance with safety regulations, contributing to overall operational excellence.