Because of personnel safety requirements, rotating machinery must not represent any
risk to staff once safety switches or functions have been activated
. This applies
particularly to electric machinery that may be supplied by inverter drives or other
devices. Thereare threemain functions that can stopa drive:
A function that allows the drive to be separated from the energy supply, also
known as "StopCategory 0".
A function that slows down the drive and then, once the neutral position has
been reached, prevents generating torque, also known as "StopCategory 1".
A function that slows down the drive until the neutral position has been
reached. However, the drive is held in closed-loop control at 0Hz output
frequency. This is known as "StopCategory 2" or "SafeOperational Stop".
Other functions, which are not covered here because they are not relevant to the driver
stage, are: "ReducingSpeedSafely", "SafeTravel Limiting" and "SafeTorque Limiting".
Conceptual implementation of "Safe Stop" with optocouplers and pulse
Regardless of which stop category is used to bring the drive to a standstill, a further
safety function is often required in addition to turn off the torque of the drive. This can be
done by interrupting the drive signal (PWM signal) of the power semiconductors and is
known as "Safe Stopping" (STO, or "Safe Torque Operation") and corresponds to Stop
Category 0 according to EN 60204-1. "Safe Stopping" therefore means protection
against the unexpected starting up of a drive according to EN 60204-1 section 5.4. The
machinemust remain at a standstil
. In addition to numerous possiblemeasures such
as the insertion of mains andmotor contactors for turning off the electrical energy, this
also includes, as already mentioned, the option of safe blocking of the control of the
power semiconductors. In principle, when implementing protection functions for "Safe
Stopping", at least two independent monitoring channels should always be provided.
Whilenot explicitlymentionedat this point, linear drives are included.
If there is external power present that can set the stationary drive in motion, e.g. in the case of cranes with a
suspended load, additional safetymeasures such as the implementation of amechanical brakemust be taken.