Initiating The C Axis Mode - Siemens SINUMERIK 840C Installation Instructions Manual

12 Functional Descriptions
12.7.2 Description of the spindle modes

Initiating the C axis mode

This section describes various methods of changing over to the C axis mode.
The standard method
The C axis is referenced automatically when the spindle is synchronized (passing the zero
mark of the spindle encoder).
When the C axis mode is selected, the spindle is stopped (e.g. M19 from PLC), then the
interface signal INITIATE C axis MODE is set and machining with the C axis can begin.
This method cannot be used, however, if the actual value systems of the spindle and C axis
are not in agreement, i.e. if the C axis encoder is uncoupled from the spindle in the spindle
mode.
Possible reasons for uncoupling the C axis encoder are:
• Cutoff frequency of C axis encoder exceeded in spindle mode.
• C axis not programmed for modulo 360° (MD 572*, bit 2 not set). In this case, the actual
value systems must be decoupled otherwise the actual value system of the C axis will
track all the motions of the spindle.
For example, if the C axis were to be driven to 0°, all the revolutions of the spindle in one
direction would be cancelled.
The axis-specific interface signal PARKING AXIS must be set in order to decouple the actual
value systems (see "Synchronizing and Referencing").
To avoid long movements in the absolute positioning of the C axis after spindle operation, the
absolute position "modulo 1 revolution" is reduced when switching from spindle operation to C
axis operation.
The best results regarding costs, operation, precision and speed range are achieved with the
high-resolution measuring system. Precision and speed range of the high-resolution measuring
system meet the requirements of spindle and C axis operation.
When defining and installing spindle/C axis combinations with different encoders please note
the following:
The same direction of rotation must be set for the spindle and C axis in MD bits 564*, bits 1
and 2 (for C axis) and MD 520*, bit 1 and MD 521*, bit 1 (for spindle).
When using different encoders, please make sure that the spindle and
C axis measuring systems are parameterized in the same direction, i.e.
M3 and C cause the same direction of rotation of the spindle. Spindle
and C axis can be made to rotate in opposite directions by setting the
interface signal "Invert M3/M4" (DB 31 DW k + 1, bit 4).
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SINUMERIK 840C (IA)