Festo — CMMT-AS-...-S1 — 2021-04d
Product overview
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The safety sub-function SS1 is used when the motor needs to be braked and the power supply to the
motor then has to be safely switched off in the application but there are no further requirements for a
targeted standstill of the drive (controlled stop, stop category 1 according to EN 60204-1).
Together with a suitable safety relay unit, the following can be achieved:
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Safe stop 1 time controlled (SS1-t/Safe stop 1 time controlled); triggering of motor deceleration
and, after an application-specific time delay, triggering of the safety subfunction STO
Requirements of SS1
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For details of wiring the safety sub-function STO, see
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Execute emergency stop command with the safety relay unit (either directly by wiring CTRL-EN
accordingly or indirectly via a further functional controller).
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The time for executing an emergency stop is known.
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The safety relay unit supports programmable timers and simple logic elements.
Function and application of SS1
The procedure for triggering SS1-t comprises the following steps:
1. Functional emergency stop requested (e.g. set input CTRL-EN to low level).
This causes the servo drive to trigger a braking ramp function and – if present – allows the brake
function to engage at the end of the braking ramp. On completion of the braking ramp and once
the parameterisable delay time for brake closing has elapsed, the power stage is functionally
switched off.
2. Start of a time-delay element for actuation of STO.
Select a delay time that ensures the functional braking ramp is completed in normal operation, the
holding brake function is engaged and the power stage is functionally switched off. Otherwise, the
axis may drop if STO is triggered concurrently with the brake engagement time that is required for
mechanical reasons. If the brake is engaged while the axis is still in motion, increased wear will
occur on the holding brake (only permitted for emergency braking).
3. Safety sub-function STO requested plus – if required – SBC once the delay time has elapsed.
The figure below shows the necessary logic circuits for the safety relay unit:
Logic in the safety relay unit for SS1
