Safe Torque Off (Sto) - Siemens SINUMERIK 840D sl Function Manual

05.08
4.2

Safe Torque Off (STO)

General description
In conjunction with a machine function or in the event of a fault, the "Safe Torque
Off (STO)" function is used to safely disconnect the torque–generating motor
power supply.
When the function is selected, the drive unit is in a "safe status". The closing lock-
out function prevents the drive unit from being restarted.
The two–channel pulse cancellation integrated in the Motor Modules is the basis
for this function.
Functional features of Safe Torque Off
S This function is integrated in the drive, i.e. a higher–level control is not required.
S The function is drive specific. This means that each drive has the function and it
must be individually commissioned.
S The function must be enabled via parameter.
S When the Safe Torque Off function is selected:
– The motor cannot be started accidentally.
– The safety–related pulse cancellation interrupts the torque–generating
power–feed to the motor.
– The power unit and motor are not electrically isolated.
Warning
!
Appropriate measures must be taken to ensure that the motor does not move
once the motor power supply has been disconnected ("coast down") (e.g. enable
the "Safe brake control" function for a vertical axis).
Warning
!
If two power transistors in the Motor Module (one in the upper and one in the lower
bridge) fail at the same time, this can cause a momentary movement.
The maximum movement can be:
S Synchronous rotary motors: Max. movement = 180° / number of pole pairs
S Synchronous linear motors: Max. movement = pole width
S The status of the Safe Torque Off function is displayed using parameters.
© Siemens AG 2008 All Rights Reserved
SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) – 05.2008 Edition
Safety Functions Integrated in the Drive
4.2 Safe Torque Off (STO)
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