Siemens S120 Possible malfunctions, System integration 7.4 Braking concepts

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.

110	1FW6 Built-in torque motors
	Configuration Manual, 05/2009, 6SN1197-0AE00-0BP3