·334·
Installation manual
CNC 8055
CNC 8055i
7.
CONCEPTS
SOFT: V02.2X
Reference systems
Home search on SERCOS axes using absolute feedback
If the first feedback is absolute (position feedback obtained from the absolute encoder of the motor),
the CNC knows the axis position at all times. This allows the CNC to do a home search without having
to use the travel limit switches and home switches.
To do a home search this way, the home switch (PLC mark DECEL*) may be generated by PLC
reading the axis position value (coordinate).
If the second feedback uses distance-coded reference marks, the offset applied in the home search
will be the value of axis parameter ABSOFF (P53).
To remove travel limit switches and home switches, proceed as follows:
1. Get both feedbacks (variables PV51 and PV53) to have the same counting direction.
Drive: Bit 3 of parameter PP115: Direction of the second feedback
Bit 5 of parameter PP115: Direction of distance-coded I0?'s
CNC: Axis parameter AXISCHG (P13) and axis parameter LOOPCHG (P26)
2. Change the value of drive parameter PP177 (distance between the zero position of the drive
and the theoretical zero) so the position value of the first feedback (PV51) is correct.
3. Restart the CNC and the drives.
4. Home the axis. Set the position value of the second feedback (PV53) right by changing one of
the following axis parameters of the CNC:
If the linear encoder uses distance-coded reference marks:
For other rules: axis parameter REFVALUE (P36).
5. Restart the CNC and check that the coordinates after a home search are correct.
PLC programming example:
Use the following PLC program to generate the DECEL mark using absolute motor feedback and
non-absolute second feedback. The example assumes that the home search is carried out in the
positive direction, axis parameter REFDIREC (P33) = + sign.
This home search requires servo drive version V6.17 or later.
;
()
= CNCRD(POSX5,R100,M1000)
= CNCRD(MPX5,R101,M1001)
= SBS R101 200000 R101
;
CPS R600 GE R601 \
= DECELX
;
; Read real machine position value of the X axis
; Read X axis positive software travel limit
; Positive limit -20mm
; Real machine coordinate >= [Positive limit -20 mm]
; X axis home switch
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