Safely Reduced Speed (Sg) - Siemens SINUMERIK 840D sl Function Manual

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Potentially hazardous motion

If the safe standstill function or "STOP A" is activated, then the motor can no longer generate

any torque. This is the reason that potentially hazardous motion can occur, e.g. for the

● When an external force acts on the drive axes

● Vertical and inclined axes without weight equalization

● Axes that are moving (coasting down)

● Direct drives with low friction and low self-locking

● Cogging torques (depending on the motor type, bearing design and friction characteristics,

Possible hazards must be clearly identified using a risk analysis that must be carried out by

the manufacturer. With an assessment, based on this risk analysis, it should be defined as

to which additional measures are required, e.g. external brakes.

Safely reduced speed (SG)

The purpose of the SG (safely reduced speed) function is to safely monitor the load-side speed

of an axis/spindle.

The actual speed of the axis/spindle is cyclically compared in the monitoring clock cycle with

the speed limit value selected using SGEs. The speed limit values are defined in the following

machine data/parameters:

For 840D sl:

MD36931 $MA_SAFE_VELO_LIMIT[n]

For SINAMICS S120:

p9531 SI Motion SLS (SG) limit values (Control Unit)

The speed limit values for SG1, SG2, SG3 or SG4 allow various applications/operating states

on the machine to be monitored. The safely reduced speed function can therefore be used to

implement protective measures for the operating personnel and machine in the setting-up

mode or also in automatic operation.

Selector gearboxes

For selector gears, it is important to select the correct gear ratio.

Safety Integrated

Function Manual, 12/2017, 6FC5397-4BP40-6BA1

up to half a pole pitch in a direction that cannot be predicted)

Safety functions integrated in the system/drive

7.5 Safely reduced speed (SG)