Siemens SINUMERIK 840D sl Function Manual page 459

From the point of view of the control, the unit for the closed-loop control gain is [(mm/min)/V].
In the same way as the setpoint clearance in standardized in [mm], values can only be
standardized in [(mm/min)/mm] by using the sensor electronics.
Max. closed-loop control gain
The maximum achievable closed-loop control gain is determined by the following delay and
reaction times of the overall system:
1. Reaction time of sensor
2. Delay time of A/D converter
3. Signal processing delay times/deadtimes
4. Reaction time of position controller
5. Reaction times of speed and current controllers
6. Time constants of motor and mechanical components
In practice, only items 3 and 4 are relevant.
The influencing variables together produce an effective time constant. A closed-loop control
gain set too high based on this time constant will induce natural oscillations in the range of
several hertz in the axis/axes to be controlled.
The objective when starting up the clearance control is to minimize important time constants
so that the closed-loop control gain required by the process can be set without inducing
natural oscillation of this type.
Deadtimes
In order to maximize the dynamics of the control response, clearance control takes place on
the highest priority position controller level of the NCK. System-specific differences in the
interface between the I/O modules and drives produce the following non-identical deadtimes.
(840D)
SINUMERIK 840D with I/O modules connected to the SINUMERIK drive bus and
SIMODRIVE 611D drives produces a deadtime T
T
dead
(840Di)
SINUMERIK 840Di with I/O modules and drives connected via PROFIBUS-DP produces a
deadtime T
T
dead
cycle time + 2 * "PROFIBUS-DP cycle" + To
Special Functions
Function Manual, 09/2011, 6FC5397-2BP40-2BA0
= 2 * position controller cycle + 2 * speed controller cycle
of:
dead
= 2 * position controller cycle + 2 * speed controller cycle + conversion time + channel
TE1: Clearance control
11.2 Clearance control
of:
dead
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