Siemens SINUMERIK 840D sl Function Manual page 49

Additional residual risks
● If, for a 1-encoder system,
A list of the Siemens encoders and motors permissible for Safety Integrated Functions can
be obtained from your local SIEMENS contact partner.
Safety Integrated
Function Manual, 12/2017, 6FC5397-4BP40-6BA1
WARNING
a) A single electrical fault in the encoder or
b) A broken encoder shaft (or loose encoder shaft coupling) - or a loose encoder housing
will cause a static state of the encoder signals (that is, they no longer follow a movement
while still returning a correct level), and prevent fault detection while the axis is in a stop
state (e.g. in SBH). Generally, the axis is held by the active closed-loop control. Especially
for vertical (suspended) axes, from a closed-loop control-related perspective, it is
conceivable that such an axis could move downwards without this being detected. The
risk of an electrical fault in the encoder as described under a) is only present for few
encoder types employing a specific principle of operation (for example, encoders with
microprocessor-controlled signal generation such as the Heidenhain EC/EQI series,
Hübner HEAG 159/160, AMO measuring systems with sin/cos output).
All of the faults described above must be included in the risk analysis of the machine
manufacturer. Additional safety measures have to be taken at suspended/vertical axes or
for handling pulling loads in order to exclude faults as described in a) for example:
– Use an encoder with analog signal generation or
– Use a 2-encoder system, and to rule-out the fault under b):
– Carry out an FMEA regarding encoder shaft breakage (or the encoder shaft coupling
slips) or if the encoder housing becomes loose and apply a fault exclusion process
according to e.g. EN 61800-5-2 or
– Use a 2-encoder system (in this case it is not permissible that the encoders are
mounted on same shaft).
4.5 Safety information & instructions and residual risks
System features
49