Synchronizing And Referencing - Siemens SINUMERIK 840C Installation Instructions Manual

06.93

Synchronizing and referencing

The reference systems for the spindle and the associated C axis should always be identical.
A parameterized shift of the zero mark (MD 459*) is taken into account.
Both systems have the absolute position 0 at the position determined by the zero mark and
the shift.
Synchronizing the spindle
When the control system has been run up, the spindle is automatically synchronized with the
encoder as soon as it passes the zero mark of the encoder for the first time. Only then can
the absolute position of the spindle be determined.
Synchronism will be lost if the cutoff frequency of the encoder is exceeded at high spindle
speeds. Resynchronizing takes place automatically when the frequency is reduced again below
the critical value.
The PLC system can initiate re-synchronizing of the spindle with IS:RESYNCHRONIZE
SPINDLE. Acknowledgement is with IS:SPINDLE SYNCHRONIZED.
Referencing the C axis
Reference point approach like that employed with feed axes is not normally needed for
spindles operated in the C axis mode. No reference point cams are usually provided because
the zero mark of the spindle encoder uniquely defines the reference point in relation to one
revolution.
Nevertheless, reference point approach is still possible with the C axis (e.g. with G74). The
sequence is the same as for normal feed axes.
Taking the zero mark offset into account provides the facility described below for optimizing
reference point approach for a C axis.
Please observe:
If a double-track encoder is used for spindle and C axis operation, the zero marks of both
encoder systems may be offset to each other. This offset must be compensated for by
entering the appropriate software zero mark offsets on installation.
Please also note that with spindles/C axes, the 2000 units of reference point offset to the zero
mark usually used for referencing the axis, have no effect. If an axis is redefined as a C axis,
its reference point is offset by 2000 units. This must be compensated for in the "Reference
point offset" (MD 244*).
Notes
• If no explicit reference point approach has been performed for the C axis, the axis-specific
IS:REFERENCE POINT REACHED is not set. Therefore, the bit
– MD 560*, bit 4 "No start disable for reference point"
must be set if the axis is to be driven in the automatic mode.
• MD 560*, bit 4 must not be set if an explicit reference point approach has been performed
for the C axis.
• If the mechanical link between spindle and C axis encoder is deactivated, IS:REFERENCE
POINT REACHED must be cancelled by setting IS:PARKING AXIS (see below).
PARKING AXIS may only be reset when the mechanical link is re-established.
© Siemens AG 1992 All Rights Reserved
SINUMERIK 840C (IA)
6FC5197- AA50
12 Functional Descriptions
12.7.2 Description of the spindle modes
12–55