Selection And Deselection Of The C Axis Mode; Block Search Via Blocks With M Functions For C Axis On/Off; C Axis Synchronization (Sw 4 And Higher); Corresponding Data - Siemens SINUMERIK 840C Installation Instructions Manual

12 Functional Descriptions
12.7.2 Description of the spindle modes

Selection and deselection of the C axis mode

Selection and deselection of the C axis mode is effected by the NC system (part program,
MDA, overstore) with customer-specific M functions. The numbers of the functions are stored
in the machine data (MD 260, 261). The address extension as for spindles must be used in the
programming.
The C axis mode can only be selected when the spindle is at rest. The USET/RSET switch in
the user data of the "S external" command channel function must not be set and IS:PLC
SPINDLE CONTROL must not be set.
The PLC system must enable selection of the C axis mode with IS:INITIATE C axis MODE. If
necessary, the PLC user program must stop the spindle beforehand (e.g. M19 from PLC) and
change over to the correct gear ratio.
The C axis mode can only be deselected with the appropriate M function or a hardware reset
(depending on MD).
C axis operation cannot be deselected with an M function if the PLC spindle control is active.
If a spindle in one channel is switched to the C axis, deactivation should be executed in the
same channel. If deactivation is to be executed in another channel, channel assignment of the
spindle has to be implemented beforehand.

Block search via blocks with M functions for C axis ON/OFF

The M functions for C axis ON or C axis OFF are skipped during block search operations
regardless of whether auxiliary functions are output or collected during these operations.
These is no reaction to these functions being skipped, even if one of them is programmed in
the target block.
If necessary, the user must execute an overstore operation to make sure that the C axis is in
the correct operating mode.

C axis synchronization (SW 4 and higher)

Corresponding data

NC MD 521* bit 2
Since only one absolute system exists for the spindle and associated C axis, the C axis is also
synchronized with the zero mark, i.e. quasi referenced, after synchronization of the spindle.
• On switchover from spindle mode to C-axis mode, "Axis referenced" will be set or not
depending on the state reached beforehand (i.e. spindle synchronized with zero mark or
not).
• If the spindle is not synchronized at the instant of operating mode switchover, then "on-
the-fly" synchronization with the next zero mark of the C-axis encoder is executed when
the C axis is traversed in C-axis mode, i.e. "Axis referenced" is set even without a
reference point approach process.
The status signal "Axis is referenced" is cancelled (as with previous SW versions) if the
encoder limit frequency is exceeded in C-axis mode (alarm 1004* "Permissible feed/limit freq.
exceeded").
• The difference is that - as in spindle mode - "on-the-fly" synchronization with the next zero
mark is executed again as soon as the frequency drops below the limit value. With
previous SW versions, "Axis is referenced" was only set after a new reference point
approach process.
The absolute system remains unchanged on switchover from C-axis mode to spindle mode,
i.e. the present status of the "Axis is referenced" signal remains valid for spindle operation.
12–54
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