Festo — CMMP-AS-...-M0 — 2022-07c
Description of the safety function STO
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The connections are galvanically isolated from one another in groups and from the 24 V power supply
of the motor controller
Tab. 22 Technical data: electrical data of the auxiliary supply output.
3.2.3
Control inputs STO-A, 0V-A/STO-B, 0V-B [X40]
The STO (Safe Torque Off) safety function is requested via two channels with the two control inputs
STO-A and STO-B. They allow the direct connection of safe semiconductor outputs (electronic safety
relay units, active safety sensors, e.g. light curtains with OSSD signals) and switching contacts
(safety relay units with relay outputs, passive safety sensors, e. g. positively driven position switches)
In order to request the STO (Safe Torque Off) safety function, the 24 V control voltage is switched off
at both control inputs STO-A and STO-B (0 V).
If the two control ports are switched off simultaneously or within a defined discrepancy time, the STO
safety function is active. If both channels are not actuated simultaneously, the STO is still active on
the first request. If a channel is not switched off, this is interpreted as an error and results in an error
message.
Undervoltage monitoring is integrated for the STO-A and STO-B control inputs in order to rule out
invalid voltage ranges for the downstream electronics, as well as overvoltage monitoring to protect
against overvoltage.
Technical data of the control inputs
Tab. 19 Technical data: electrical data of the STO-A and STO-B
Tolerance ranges are defined for the input voltage range of the STO-A and STO-B control inputs.
The amount of energy stored in the components of the motor controller (e.g. capacitors) depends
on the level of the input voltage. This amount of energy must be charged or discharged during
switching operations. The input voltage-dependent values are thus derived for the switch-off time for
the transition to the safe state (STO) and the tolerance time for OSSD signals (buffer time).
The requirements for the time response are derived from the technical data
[X40]. The time response itself is described here
Discrepancy time
The transition between a safe and an unsafe state is initiated by level changes at the control inputs
STO-A and STO-B of the motor controller. According to the specification of the safety function, both
levels must be identical, otherwise an error message is generated. The state machine in the motor
controller internally monitors the driver supply voltages as a result of the control of the control
inputs. The level changes do not usually take place exactly simultaneously, for example, because of
component tolerances or bouncing outputs of safety controls. The firmware tolerates this so long as
the second input follows within a defined time, the so-called discrepancy time. If the time is exceeded,
the motor controller generates an error message.
A discrepancy time of 100 ms is the default.
Recommendation: always switch STO-A and STO-B simultaneously.
Test pulses
Test pulses from safety controllers are tolerated in a specific range and thus do not lead to the request
of the STO function.
Содержание CMMP-AS M0 Series
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