Safe Torque Off - STO
This function prevents the creation of torque in the motor and enables an uncontrolled stop in accordance with stop category 0 of IEC 60204-1:2016.
Note: This safety function may be used where torque removal is required to prevent an unexpected start-up.
Attention: The safety circuit safely inhibits currents to the motor and to a brake when STO-SBC command has been given (e.g. from an emergency stop device).
When the command has been released (e.g. manually resetting the emergency stop device) the currents are allowed to be carried to the motor and to the brake.
The safety system must be designed to meet the requirement “restarting the machinery after a stoppage must be possible only by an intended actuation of a control device provided for the purpose”.
Danger:Hazards due to external influences (such as inertia of the system, gravity or falling of suspended loads) must be prevented by additional measures, such as mechanical brakes. Please refer to the section on SBC for additional information about attaching a safe brake
STO Timing diagram
Solid line: reactivation if no restart acknowledge by the drive is configured
Dashed line: reactivation if restart acknowledge by the drive is configured
STO Timing Diagram with SBC
Note: STO can be configured in combination with SBC. When SBC and STO are triggered, a delay for STO can be configured
Solid line: reactivation if no restart acknowledge by the drive is configured
Dashed line: reactivation if restart acknowledge by the drive is configured
Parameters related to STO
| Index | Parameter Name | Explanation |
|---|---|---|
| 0x2641:1 | STO input |
Specifies the associated safe digital input of Circulo (SDI 1 or SDI 2) used for activating the safety function:
0: no input 1: SDI 1 2: SDI 2 |
| 0x6641 | STO restart | STO Restart acknowledge behaviour:
0: Automatic restart for STO (When the STO condition is removed, the STO outputs get active immediately) * 1: Acknowledge required to restart after STO (When the STO condition is removed, an acknowledge is required before STO outputs get active) |
Danger:* Always ensure that the safety system meets the requirement “restarting the machinery after a stoppage must be possible only by an intended actuation of a control device provided for the purpose”