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About the "Safe Torque Off "(STO) Function
The STO function serves to safely interrupt the energy supply to the motor directly at the drive. This corresponds to uncontrolled braking according to IEC 60204-1, category 0.
Drives with a hanging load must have an additional safe mechanical blocking (e.g. by a motor holding brake).
The concept of this function which is standard in the AKD is tested and certified (see the German professional association's test report). Thus, the circuit concept to realize the safety function "Safe Torque Off" within the servo amplifiers of the product line AKD with Hardware Revision C satisfies demands as shown below.
STO in the AKD-x003 up to AKD-x024
| Function | Operation Mode | ISO 13849-1 | IEC 61508-2 |
|---|---|---|---|
| STO | single channel | PL d, CAT 3 | SIL 2 |
| Pin | Signal | Description | |
|---|---|---|---|
 |
1 | +24 | +24 VDC Auxiliary voltage |
| 2 | GND | 24V Supply GND | |
| 3 | STO | STO enable (Safe Torque Off) | |
 |
|||
Signal Diagram - Single channel
The diagram below shows how to use the single channel STO function for a safe drive stop and fault free operation of the drive.
- Brake the drive in a controlled manner (speed setpoint = 0 V).
- When speed = 0 rpm, disable the drive (Enable = 0 V).
- Activate the STO function (STO = 0 V)
STO in the AKD-x048
| Function | Operation Mode | ISO 13849-1 | IEC 61508-2 |
|---|---|---|---|
| STO | single channel | PL d, CAT 2 | SIL 2 |
| STO | dual channel | PL d, CAT 3 | SIL 2 |
| STO | dual channel with periodic testing | PL e, CAT 4 | SIL 3 |
| Inputs STO-Enable 1/2 (X1) | Outputs STO-Status 1/2 (X1) |
|---|---|
|
|
| Pin | Description | |
|---|---|---|
 |
1 | +24 VDC Auxiliary voltage |
| 2 | 24V Supply GND | |
| 3 | STO +24 VDC supply voltage | |
| 4 | STO GND | |
| 5 | STO-Status 1 | |
| 6 | STO-Enable 1 | |
| 7 | STO-Status 2 | |
| 8 | STO-Enable 2 | |
 |
||
Signal Diagram - Single channel
The diagram below shows how to use the dual channel STO function for a safe drive stop and fault free operation of the drive.
- Brake the drive in a controlled manner (speed setpoint = 0 V).
- When speed = 0 rpm, disable the drive (Enable = 0 V).
- Activate the STO function (STO-Enable 1 = 0 V and STO-Enable 2 = 0 V)
Further Information
- Be sure to review the AKD Installation Guide for more on safety
- Functional Safety with AKD
- Safety Characteristic Data
- Sistema, safety evaluation tool by IFA
