Siemens SINUMERIK 840D sl Function Manual page 476

Detailed description
2.5 Optimization of the control
MD32960 "dead zone"
Nonlinearities close to zero speed, such as those, which can occur when simple frequency
converters are used, are inhibited by a "dead zone" in the controller.
The threshold for system deviation, under which a speed setpoint of "zero" is output, can be
set via machine data:
MD32960 $MA_POSCTRL_ZERO_ZONE.
The "dead zone" is input in MD32960 for each individual encoder.
Stability risk
The expanded position controller algorithm will reduce the risks that a stable control admits
only a rather poor setting of the gain, or that the position control loop does not remain stable
despite the effective extensions, to a minimum.
Supplementary conditions
The functional expansion is available for all control variants.
The low-pass filter is only activated if dynamic stiffness control is inactive:
MD32640 $MA_STIFFNESS_CONTROL_ENABLE = 0.
If the low-pass filter is active, the modeled following error is larger than usual during
acceleration phases.
It can, therefore, be necessary to increase machine data:
MD36400 $MA_CONTOUR_TOL
above the standard value,
in order to prevent activation of axial contour monitoring (alarm 25050).
If the adjustable "dead zone" of the position controller retains its standard setting:
MD32960 $MA_POSCTRL_ZERO_ZONE = 0,
this corresponds to an input value, which is the same size as the current encoder fine
resolution.
The default setting is therefore compatible with earlier software versions.
If the "dead zone":
MD32960 $MA_POSCTRL_ZERO_ZONE
is configured to be larger than the zero-speed tolerance:
MD36030 $MA_STANDSTILL_POS_TOL,
zero-speed monitoring (alarm 25040) could be activated on termination of a positioning
process.
With a "dead zone":
MD32960 $MA_POSCTRL_ZERO_ZONE
greater than the exact stop limits:
MD36000 $MA_STOP_LIMIT_COARSE
, no exact stop signals are output.
This can trigger the positioning monitoring function (alarm 25080)
and block the block change.
88
Basic logic functions: Velocities, Setpoint/Actual Value Systems, Closed-Loop Control (G2)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0