Should an STO function be included when selecting a harmonic gear robotics drive module?

STO is a safety switch for harmonic gear robotics drive modules, commonly used in industrial robots, automated production lines, medical and rehabilitation equipment, logistics and warehousing systems, and service robots.

What Role Does STO Play in a Harmonic Gear Module?

Cutting off motor excitation torque: The hardware circuit directly blocks the drive output. The motor produces no electromagnetic torque and can freely coast or be passively moved. (It does not cut the main power supply.)

Fundamental safety protection: STO meets safety standards and is the most basic and essential safety function for robots and automated equipment.

Emergency stop and human-machine interaction protection: In case of emergency stop, safety door opening, collision, or system fault, STO quickly cuts motor torque to prevent accidental motion, pinch, or impact.

Non-stop operation and fast reset: Only torque is disabled; control power, encoder, and communication remain active. Once the fault is cleared, the system can resume operation immediately without a full power cycle.

Advantages of Harmonic Drive Modules with STO:

• High safety level: Rapidly cuts motor torque when triggered, protecting personnel and equipment.

• Fast response without power interruption: Torque is cut directly; the drive remains powered, enabling quick reset and high operational efficiency.

• Simplified system wiring: No need for external safety relays or redundant wiring, saving space, reducing costs, and minimizing wiring errors.

• High integration, suitable for collaborative applications: Integrated with the drive, compatible with humanoid or collaborative robots, supporting fast and safe human-robot interaction.

Disadvantages of Harmonic Drive Modules with STO:

• Increased cost: Requires dedicated safety circuitry, increasing module price.

• Maintenance and replacement limitations: STO faults usually require replacement of the entire module; the safety unit cannot be repaired separately, increasing maintenance cost.

• Additional configuration and testing: Requires redundant inputs and extra commissioning work.

HONPINE is a harmonic drive joint module provider. Our HAG Harmonic Drive Module can be optionally equipped with STO. Combined with high-precision encoders and high-accuracy harmonic reducers, it provides higher precision than conventional harmonic drive modules.

Contact us to learn more about our STO-enabled harmonic drive joint modules.