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Safety Concept AKD

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
image 1 +24 +24 VDC Auxiliary voltage
2 GND 24V Supply GND
3 STO STO enable (Safe Torque Off)
image

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.

  1. Brake the drive in a controlled manner (speed setpoint = 0 V).
  2. When speed = 0 rpm, disable the drive (Enable = 0 V).
  3. Activate the STO function (STO = 0 V)

image

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)
  • Reference ground is STO GND
  • High Level 24 V ±10%, 16 to 25 mA
  • Low level 0...5 VDC
  • Reaction time < 10 ms
  • Galvanic isolation for 250 VDC
  • Reference ground is STO GND
  • As per EN61131-2 type 1
  • Max. 30 VDC (PELV), max. 100mA
  • PELV acc. to EN 60204-1
  • Galvanic isolation for 250 VDC
  Pin Description
image 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
image

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.

  1. Brake the drive in a controlled manner (speed setpoint = 0 V).
  2. When speed = 0 rpm, disable the drive (Enable = 0 V).
  3. Activate the STO function (STO-Enable 1 = 0 V and STO-Enable 2 = 0 V)

image

Further Information