Siemens Sinumerik 840D sl Function Manual page 91

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1- -encoder system
For a 1--encoder system, the motor encoder is used for the safety--related actual
values of the NC and drive.
If an encoder fault develops, and a safety--related function is active, then STOP B
and then STOP A is performed.
As a result of the encoder fault, and the fact that internally the speed is set to 0
(a valid actual value is no longer available), i.e. no SBR monitoring is possible
while STOP B is active.
The actual values are generated in a safety--related fashion either directly in the
encoder or in the Sensor Module and are provided -- with no--reaction -- to the NCK
and the drive using safety--related communications via DRIVE--CLiQ.
Special feature regarding linear motors:
For linear motors, the motor encoder (linear scale) is also the measuring system at
the load. IMS and DMS are one measuring system. The connection is made at the
IMS input of the Sensor Module or directly via DRIVE--CLiQ.
Significance of the coarse encoder position:
For a 1--encoder system, for all position monitoring functions, the accuracy of the
redundant actual value must be assumed to apply. This accuracy depends on the
encoder evaluation. For all encoder evaluation functions that can be used with
Safety Integrated (SMI, SME, SMC, motor/encoder with DRIVE--CLiQ), a redun-
dant position value is generated and the closed--loop control is made available.
The machine manufacturer must select the appropriate encoder with the necessary
encoder pulse number for his particular requirements. To do this, the encoder reso-
lution must be converted to the accuracy on the load side. This conversion is de-
pendent on the type of encoder mounting and the type of axis. Further, gearbox
factors, the spindle pitch for linear axes and the radius of the rotary table for rotary
axes must also be taken into account.
Sensor Module cabinet mounted (not used
for encoders with DRIVE- -CLiQ interface)
Figure 5-1 1--encoder system for a feed drive (FD)
© Siemens AG 2015 All Rights Reserved
SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) - - 10.2015 Edition
Basics on the safety functions integrated in the system/drive
DRIVE- -CLiQ
Encoder
Gearbox
Motor
(FD)
5.4 Actual value conditioning
Machine table
Back- -
lash
5-91