Siemens SINUMERIK 840C Installation Instructions Manual page 831

12 Functional Descriptions
12.7.2 Description of the spindle modes
• With rotary axes it is usually unnecessary to monitor software limit switches. If monitoring
is required for a C axis, an explicit reference point approach must be performed.
• The alarm "Excessive feed" is triggered if the cutoff frequency of the C axis encoder is
exceeded.
• Explicit referencing must be employed (e.g. G74) if the difference between the accuracy of
the entry and the accuracy of the measuring system is greater than a factor of 10 (e.g.
-4
entry accuracy 10 and position control accuracy 0.5 x 10
• The measuring system defined in MD 200* is permanently assigned to a spindle with C
axis during C axis operation, the second measuring system applies to the spindle operating
modes and must be parameterized in MD 400*. The C axis/spindle is assigned in MD 461*.
• One common absolute measuring system for determining the actual position of the spindle
and C axis describes the machining position on the load side.
This absolute system is reinitialized during referencing:
MD 459* takes effect in spindle operation (inprocess encoder synchronization), as well as
for ordinary spindles for the definition/offset of the zero position.
In C axis operation (inprocess/via part program/via reference point approach mode) MD
240* and 244* have the same effect as with normal axes with the one exception that the
usual 2000 units are disregarded here, as these 2000 units are dependent on the direction
of movement and would therefore be ambiguous in inprocess referencing in both directions
of movement.
The reference point is kept when switching between spindle and C axis operation. Where
this is not required, it can be ignored by using the signals "Resynchronize spindle" or
"Parking axis". If the reference point remains valid, the zero mark found during C axis
operation is also valid in spindle operation and vice versa.
In this way, the unnecessary movements resulting with every spindle/axis switchover (for
resynchronization/referencing) can be avoided as far as possible, on condition that (as
mentioned above) the zero position defined in MD 459* is identical with the zero mark
defined in MD 240*/244* parameterization on installation.
The zero position has to be defined in two machine data because, in the case of a double-
track encoder, for example, the two zero mark signals are offset by 180 degrees and in the
case of two separate encoders any other offset is possible and can then be corrected in
the machine data concerned. If the same encoder is used for spindle and C axis operation,
you must ensure that the machine data are identical.
If identical encoder definitions (MD 200* = MD 400*) are entered for spindle and C axis,
only the encoder cutoff frequency of the spindle encoder (MD 462*) and not the cutoff
frequency of the C axis encoder (MD 308*) is active. The same is applies to the "Sign
reversal actual value" (only effective with MD 520*, bit 1, not 564*, bit 2). Differing pulse
evaluations remain active.
The following applies to backlash compensation and leadscrew error compensation: if the
encoder definition is different for the spindle and C axis encoder, then backlash
compensation and leadscrew error compensation are only active in C axis operation (for
first measuring system), if identical encoder definitions have been entered for the spindle
and the C axis, then backlash compensation and leadscrew error compensation effect this
measuring channel.
12–56
-2
mm).
© Siemens AG 1992 All Rights Reserved
06.93
6FC5197- AA50
SINUMERIK 840C (IA)