STO MANUAL
11.06.2020 roboteq sto manual_13.docx 4 of 9
2. Scope
This STO manual is the original instruction about the STO circuitry that is implemented in RoboteQ’s
motor controllers. Describes how the implemented circuit works and how the signals are
processed/tested by MCU. Also includes maintenance instructions and commands along with the all
the technical data for RoboteQ’s STO implementation.
3. Motor controllers
The STO function will be integrated in RoboteQ’s motor controllers with STO hardware
implementation.
ATTENTION
STO firmware implementation is supported with firmware v2.0 or later. End user need to update to
the latest available version. It is also recommended to use the latest version of Roborun+ utility. Please
check www.roboteq.com for updates.
4. Safe Torque Off (STO)
Safe Torque Off is a safe method for switching controller in a state where no torque is generated,
regardless whether the controller is operating normally or is faulty. This function is a mechanism that
prevents the drive from restarting unexpectedly. STO has the immediate effect that the drive cannot
supply any torque-generating energy. STO can be used wherever the drive will be brought to a
standstill in a sufficiently short time by the load torque or friction or where coasting down of the drive
is not relevant to safety. STO enables safe working and has a wide range of use in motion control/
systems with moving axes. The advantage of the integrated STO safety function compared with
standard safety technology using electromechanical switchgear is the elimination of separate
components and the effort that would be required to wire and service them. Because of the rapid
electronic switching times, the function has a shorter switching time than the electromechanical
components in a conventional solution.
WARNING
Activating STO does lead to no more torque generation on the motor. The motor will not be actively
stopped but run out. It might be possible that the load is turning the motor (e.g. hanging axis). If this
can lead to hazards further measures need to be taken (e.g. break). In case of a multiple fault in the
power stage a rotation might occur.
5. Safe Torque Off (STO) on Roboteq Controllers
Two digital inputs on the user I/O connector can be used to put the controller in a state where the
motor is deprived of energy.
The two inputs, labeled STO1 and STO2 must both be brought and maintained at a logic level 1 for the
controller to be active. If any one or both of these lines are at 0, the output is de-energized.
The STO circuit operates independently of the MCU. It will always override the MCU, whether the MCU
is processing normally, or is in a hardware of firmware fault condition.
The STO circuit works by controlling the voltage supply to the controller’s output MOSFET drivers.
When both STO1 and STO2 are at logic 1 level, MOSFET drivers are supplied with power. When either
