Festo — CMMT-AS-...-S1 — 2021-04d
Product overview
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Functional principle of SBC
Fig. 6: Functional principle of SBC
SBC request
The safety sub-function SBC is requested on 2 channels by simultaneously switching off the control
voltage at both control inputs #SBC-A and #SBC-B:
–
The #SBC-A request switches off the power to the signals BR+/BR-.
–
The #SBC-B request switches off the power to the signal BR-EXT.
In the event of a power failure in the logic voltage supply of the servo drive, power is also cut off to the
brake outputs.
If SBC is requested and subsequently cancelled, the safe brake control is only re-energised when the
functional micro controller enables the holding brake. This ensures that Z-axes with a suspended load
can be restarted without the load dropping.
SBC feedback via SBA diagnostic contact
The 2-channel switching of the brake is indicated via the SBA output. SBA is used to report the status
of the safety sub-function SBC for diagnostic purposes, e.g. by reporting it to an external safety relay
unit.
The SBA diagnostic output indicates whether the safe status has been reached for the safety sub-func-
tion SBC. It is set if the following two conditions are fulfilled:
–
Switching off of both brake outputs is requested (#SBC-A = #SBC-B = low level)
–
The internal diagnostic functions have determined that there is no internal error and both brake
outputs are de-energised (switched off).
Test pulses that occur simultaneously at SBC-A and SBC-B are not filtered. For this reason, the SBA
diagnostic output delivers a high level signal for the duration of these low test pulses.
