Siemens SINUMERIK 840D sl Function Manual page 52

System Features
3.5 Safety information & instructions and residual risks
Warning
!
S If, for a 1–encoder system,
a) an individual electrical fault in the encoder, or
b) an encoder shaft breakage (or the encoder shaft coupling slips) or the
encoder housing becomes loose
the encoder signals remain at a steady–state (i.e. they no longer follow the
motion, but have a correct signal level), then this fault is not detected when the
axis is stationary (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 described under
a) of an electrical fault in the encoder is only possible for a few encoder types
due to the principle of operation (e.g. encoders with microprocessor–controlled
signal generation, e.g. EQI from the Heidenhain company, HEAG 159/160 from
the Hübner company, measuring systems from the AMO company with sin/cos
output).
All of the faults described above must be included in the risk analysis of the
machine manufacturer. This analysis will indicate that for hanging/vertical axes
or loads that drive the motor, additional protective measures are required, e.g.
to exclude the fault under a):
S Use an encoder with analog signal generation or
S Use a 2–encoder system
and to exclude the fault under b):
S 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
S Use a 2–encoder system (in this case it is not permissible that the encoders
are mounted on same shaft).
3-52
SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) – 05.2008 Edition
© Siemens AG 2008 All Rights Reserved
05.08