Drehgeber für Funktionale Sicherheit - Fritz Kübler GmbH Zähl- und ...

3. Safety Concept
When switching the plant on and off
4
!
Incremental Encoder Funcion
In order to achieve safe incremental
information with the encoder, the controller
must monitor the validity of the
analogue, 90° phase-shifted
sine/cosine signals with the help of
the function
sin²+cos² = 1.
Prior to the plant being shut down the
absolute position value is saved by
the controller. When the plant is
switched back on, the controller compares
the saved value with the newly
measured absolute value that has
been made after power on.
! !
If both these values are identical, then
the position is safe.
If the position values are not identical,
then the position is not safe and the
position must be verified again.
!
Safe Absolute Encoder Function
In order to obtain safe information
with the encoder regarding the
absolute position, the controller
counts the incremental pulses and
compares the result with the absolute
positions also provided by the
encoder.
During plant operation
The indicated position is verified by a
comparison of the digital position data
with the sine/cosine signals that are
also constantly being counted and
compared by the controller
The risk of mechanical faults (as
might occur, for example, if the rigid
torque stop with torque pin were to
break or the encoder to fall off the
motor shaft) is eliminated as a result
of the mechanical over-dimensioning
of the components of our safety
encoders.
The encoder is safe only when used
in conjunction with a safe controller
that can monitor the functions mentioned.