09.01 12 Functional Descriptions
12.7.2 Description of the spindle modes
12.7.2.4 C axis mode
General
In the C axis mode the spindle is operated as a position-controlled rotary axis. As such, it
can be included in the interpolation with other axes (e.g. TRANSMIT coordinate transforma-
tion).
General notes:
• Feed STOP is not displayed if a C axis is referenced in spindle mode with G74.
• Block changes are not prevented nor are any alarms output if M19 is programmed when
C-axis mode is active.
• No negative acknowledgement of command channel by alarm 109 on "S-external start" in
active C-axis mode.
• No feed display when an attempt is made to traverse a C axis conventionally in spindle
mode.
• IKA can be switched off before switching from C axis mode to spindle to avoid NC axis
alarms (e.g. 168*). As from SW 6, this can also be done via the PLC (DB48).
If a C axis has two measuring systems, the second measuring system is always that of the
spindle, MD 400*. MD 1388* and MD ”2nd MS exists” have no effect with spindle C axis
combinations. Measuring circuit switchover is set such that after a C axis switchover the
spindle encoder is effective until the axis-specific interface signal ”Measuring circuit 2 active”
has been evaluated. For C axes with one measuring system, the 1st measuring system must
be the same as that of the spindle.
Assignment and parameterizing
• Each spindle can be assigned just one C axis by means of the machine data
(MD 461*). Like all axes, this must be parameterized via the axial machine data.
• When switching from the spindle to the C axis, the spindle zero speed tolerance in MD
446* is decisive.
• Before switching to C axis operation, gear switchover and PLC spindle control must be
acknowledged.
Position control and actual value acquisition
• In the C axis mode, the position controller works with the axial servo gain factor which
must be adapted to the active gear ratio between motor and spindle. Therefore, no gear
ratio changing is possible in the C axis mode.
• If the spindle encoder is not sufficiently accurate for the C axis mode, a separate encoder
can be used. An alternative is to use a double-track encoder - one track for the C axis
mode and the other for the remainder of the spindle modes.
• However, the axis-specific signal IS:REFERENCE POINT REACHED is not set, so it is
also possible to employ reference point approach for the C axis (see also the section
headed ”Synchronizing and referencing”).
• If reference point approach for the C axis is not to be used, MD 560*, bit 4 ”No start
disable for reference point” must be set.
© Siemens AG 1992 All Rights Reserved 6FC5197- AA50
12–53
SINUMERIK 840C (IA)