Siemens Sinumerik 840D sl Function Manual page 97

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"Axis referenced" state
For incremental encoders the position actual value is lost when the NC is powe-
red--down. When the NC is powered--up, a reference point approach must be car-
ried out. If the reference point approach is correctly executed, then the axis is refe-
renced and goes into the "axis referenced" state (refer to Fig. 5-5 "Axis states
when referencing").
Contrary to incremental encoders, absolute encoders do not require a reference
point approach after the NC has been powered--up. These encoders track the ab-
solute position, e.g. using a mechanical gear, both when powered--up and powe-
red--down. The absolute position is transferred implicitly via a serial interface when
the NC is powered--up. After the position data has been transferred and the offset
value has been taken into account, the axis also goes in the axis state "axis refe-
renced" (refer to Fig. 5-5 "Axis states when referencing").
This axis state "axis referenced" is indicated using the axis--specific interface signal
"reference point reached" as follows:
Interface signal
"Reference point reached" = "1" Axis state "Axis referenced"
"Reference point reached" = "0" Axis state "Axis not referenced"
for 840D sl
Reference:
"Axis safely referenced" state
In order to reach the axis state "axis safely referenced", the axis state "axis
referenced" must have been reached, and either
S the user confirms the current position using the user agreement (refer to
Chapter 5.4.4 "User agreement"
or
S a saved and set user agreement and saved stop position when the system was
powered--down must exist. The position associated with the saved data must
match the current position within a tolerance window. This is checked both in
the drive and in the NC.
(refer to Fig. 5-5 "Axis states when referencing").
The axis state "axis safely referenced" is displayed using the SGA "axis safely
referenced". A safety--related position evaluation can only be carried out for the SE
and SN functions after this state has been reached.
Saved user agreement
The state of the user agreement function is saved in non--volatile memories. This
saved user agreement forms, together with the stop position, also saved in a non--
volatile fashion the prerequisite for the axis state "axis safely referenced".
© 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
DB31--61, DBX60.4 / DBX60.5
SINUMERIK 840D sl Commissioning Manual
5.4 Actual value conditioning
5-97