Siemens SINUMERIK 840D sl Function Manual page 86

Basics regarding the safety functions integrated in the system/drive
6.4 Actual value conditioning
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 redundant 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
resolution must be converted to the accuracy on the load side. This conversion is dependent
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.
Figure 6-1
Residual risks
The specific residual risks for 1-encoder systems should be carefully considered (see Chapter
"Safety information & instructions and residual risks (Page 44)").
2-encoder system
In this case, the safety-related actual values for an axis are supplied from 2 separate encoders.
In standard applications, the drive evaluates the motor encoder (IMS) and the NC, the
measuring system (DMS). 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. Each measuring
system requires a separate connection or a separate Sensor Module.
For a 2-encoder system, an encoder fault can result in a STOP F followed by STOP B and
followed by STOP A - as well as an immediate STOP A response.
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1-encoder system for a feed drive (FD)
WARNING
Function Manual, 12/2017, 6FC5397-4BP40-6BA1
Safety Integrated