Festo CMTT-AS S1 Series, Description, Page: 8 / 46

4 Product overview
4.1 Safety sub-functions
4.1.1 Function and application
The servo drive CMMT-AS-...-S1 has the following safety-related performance features:
–
Safe torque off (STO)
– Safe brake control (SBC)
– Safe stop 1 (SS1) with use of a suitable external safety relay unit and appropriate wiring of the
servo drive
– Diagnostic outputs STA and SBA for feedback of the active safety sub-function
4.1.2 Safety sub-function STO
Fig. 1 Symbol for STO
The function described here implements the safety sub-function STO according to EN 61800-5-2 (cor-
responds to stop category 0 from EN 60204-1).
The safety sub-function STO is used when the energy supply to the motor needs to be switched off
safely in the application but there are no further requirements for a targeted standstill of the drive
(such as stop category 1 from EN 60204-1
è Safety sub-function SS1).
Function and application of STO
The safety sub-function STO switches off the driver supply for the power semiconductor, thus prevent-
ing the power output stage from supplying the energy required by the motor. The power supply to the
drive is safely disconnected when the safety sub-function STO is active. The drive cannot generate
torque and so cannot perform any hazardous movements. With suspended loads or other external
forces, additional measures must be taken to prevent movements being performed (e.g. mechanical
clamping units). In the STO state, the standstill position is not monitored.
The machines must be stopped and locked in a safe manner. This especially applies to vertical axes
without automatic locking mechanics, clamping units or counterbalancing.
NOTICE!
If there are multiple errors in the servo drive, there is a danger that the drive will move. Failure of the
servo drive output stage during the STO status (simultaneous short circuit of 2 power semiconductors
in different phases) may result in a limited detent movement of the rotor. The rotation angle/travel
corresponds to a pole pitch. Examples:
•
Rotating motor, synchronous machine, 8-pin è Movement
<
45° at the motor shaft
• Linear motor, pole pitch 20 mm è Movement
<
20 mm at the moving part
Product overview
8 Festo — CMMT-AS-...-S1 — 2018-10a