Siemens SINUMERIK 840C - Manual (Page 822)

11.92 12 Functional Descriptions
12.7.2 Description of the spindle modes
Gain factor change
In the positioning mode it must be possible to drive the spindle to a target position from full
speed under position feedback control. The spindle must be held at the target position even
when there is drift.
To ensure that the spindle is steady at rest, even in the presence of drift, very small set
speeds with very high resolution must be given to the drive actuator via the analog interface.
The speed setpoints are transferred as voltage signals via the analog interface between control
system and drive actuator. Under some circumstances the control behaviour can be improved
by increasing the voltage level (relative to the set speed) because it enables a higher
resolution to be achieved and the analog interference noise can be reduced.
Consequently, with some drive actuators, such as the SIMODRIVE 650, a different scaling for
the set speeds (voltage levels) can be selected by applying a configurable terminal signal.
This changing of the scaling in the drive actuator must be allowed for in the control so that,
overall, the effective gain factor remains the same. The gain factor (dependent on gear ratio,
MD 435* to 442*) must be adapted to the new scaling.
The factor for gain changing is entered as machine data. The value is calculated from:
MD 469* = where N = scaling factor in the drive
actuator
1
N
Changing of the gain factor must be initiated by the PLC user program with the interface signal
CHANGE GAIN FACTOR (DW K + 1, bit 15).
The diagram below is intended to illustrate the changeover process using SIMODRIVE 650 as
an example.
Simplified block diagram
SINUMERIK
Gain
factor
SIMODRIVE
DAC
P-54
IS:CHANGE GAIN FACTOR Terminal for M19
a
Following
error
b
MD
469*
ADC
© Siemens AG 1992 All Rights Reserved 6FC5197- AA50 12–47
SINUMERIK 840C (IA)