User's Manual

System integration
7.4 Braking concepts
The design of mechanical braking systems depends on the maximum kinetic energy, that is,
the maximum moment of inertia of the rotating mass and its maximum speed.
Possible malfunctions
Malfunctions can occur e.g. for:
● Power failure
● Encoder failure, encoder monitoring responds
● Higher-level control failure (e.g., NCU); bus failure
● Control Unit failure
● Drive fault
● NC fault
Below are a number of options showing how rotating masses can be braked in the event of a
malfunction.
Braking concepts
In the case of rotating axes that are restricted to a rotation angle of < 360°, damping and
impact absorption elements at the limits of the rotation range offer reliable protection.
To dissipate the kinetic energy of the rotating mass before it comes into contact with the
damping elements, the following measures should be taken to support mechanical braking
systems:
1. Electrical braking via the energy in the DC link:
The DC link must be equipped with capacitor modules that store sufficient energy to
reliably brake the rotating masses in the event of a power failure. Braking resistors that
prevent the voltage in the DC link from exceeding the maximum permissible value must
also be installed.
Drawback: This measure is ineffective if the Control Unit fails. It may also be ineffective if
the encoder system fails. See also the documentation for the drive system.
2. Electrical braking via armature short-circuiting of the stator:
If the drive system does not feature a suitable function, the motor connection terminals
are disconnected from the drive system and short-circuited in the event of a fault with a
contactor that closes automatically. See also the documentation for the drive system.
Drawback: The braking torque depends on the speed and may not be sufficient to bring
the rotating masses to a standstill.
Note
If armature short-circuiting braking is used without braking resistors, special contactors
are required because the currents can be very high. - The release timing for the drive
system must be taken into account.
1FW6 Built-in torque motors
110 Configuration Manual, 05/2009, 6SN1197-0AE00-0BP3