Siemens SINUMERIK 840C - Manual (Page 370)

09.95 6 NC Machine Data (NC MD), NC Setting Data (NC SD)
6.7.1 Axis-specific MD bits 2 (axial bits 2)
Bit 4 Bit 4=1 Measuring system with distance-coded reference marks.
Standard value: Bit 0-4 = 0
Changes in bits 2-3 are actuated on the next reference point approach in bit 4 after POWER
ON.
When the SIPOS/Endat absolute encoder is used, the following NC machine data must be
taken into account:
Axial machine data:
MD 240* Reference point ordinate (with absolute encoder only)
MD 396* Absolute offset
MD 1300* Basic distance of the reference marks
MD 1304* External pulse multiplication (not with absolute encoder)
Procedure on reference point approach
When bit 0 of MD 1808* ”Axis with absolute encoder” is set, a distinction must be made
between two cases for reference point approach.
Case 1: MD 1808* bit 3 = 0
When the bit ”Absolute offset valid” is not set, reference point approach is carried
out as for an axis without absolute encoder. On ”Reference point reached”, the
calculated absolute offset is transferred to the axial MD 396* and MD 1808* bit 3
”Absolute offset valid” is set for the relevant axis.
The absolute offset is calculated on the basis of the equation
Machine system = SIPOS/Endat system + absolute offset
or
Absolute offset = machine system - SIPOS/Endat system
The following applies
Machine system = desired absolute position = reference point ordinate
and
SIPOS/Endat system = displayed absolute position (actual value)
Note:
If a value other than 0 has been entered in MD 396*, this value must be taken into account, as
it is contained in the SIPOS/Endat system (= displayed actual value).
Case 2: MD 1808* bit 3 = 1
When the bit ”Absolute offset valid” is set, reference point approach is
suppressed, until the bit is reset by the user.
Note:
When the function G74 ”Reference point approach from part program” is used, referencing is
not carried out for the second case and processing is continued with the next block.
Procedure on warm restart (POWER ON)
When bit 0 of MD 1808* ”Axis with absolute encoder” is set, MD 1808* bit 3 ”Absolute offset
valid” is checked for the relevant axis. If this bit is also set, the axial interface signal
”Reference point approach” is set already on warm restart.
© Siemens AG 1992 All Rights Reserved 6FC5197- AA50 6–185
SINUMERIK 840C (IA)