Siemens SINUMERIK 840D sl Function Manual page 187

Information
The setpoint delay for the three controller structures
● Without feedforward control (index 0)
● Speed feedforward control (index 1)
● Torque feedforward control (index 2)
is displayed in read-only machine data:
MD32990 $MA_POSCTRL_DESVAL_DELAY_INFO
Negative values in machine data:
MD10065 $MN_POSCTRL_DESVAL_DELAY
reduce the values for all three controller structures; positive values increase them.
Appropriate changes to parameter settings
A change in the parameter settings of machine data:
MD10065 $MN_POSCTRL_DESVAL_DELAY
is appropriate in the following cases:
● DSC is always activated or feedforward control is never activated for axis operation.
● With the typically used controller structure, there will be a delay in machine data:
Extended Functions
Function Manual, 01/2008, 6FC5397-1BP10-3BA0
Several Operator Panels on Several NCUs, Distributed Systems (B3)
In these cases, an additional delay is only necessary on the NCU with the fast position
control cycle. Here the following procedure is appropriate:
1.) MD32990 $MA_POSCTRL_DESVAL_DELAY_INFO[0] on any axis on the NCU with
the slowest position controller cycle.
2.) Subtract this time from the current value in machine data:
MD10065 $MN_POSCTRL_DESVAL_DELAY
on all NCUs.
MD32990 $MA_POSCTRL_DESVAL_DELAY_INFO
in the axis with the fast position control cycle; the delay is not an integer multiple of the
position control cycle.
As there are particularly high dynamic performance requirements on the axis with the fast
position control cycle, even the necessary averaging for generating the delay may lead to
problems.
Example: Typically, machining is conducted with speed feedforward control. In axis X of
NCU-U in the diagram "Schematic example of a configuration with several NCUs and
eccentric machining unit" (Section "Diagram of general solution"), a value of 7 ms is read
out in machine data:
MD32990 $MA_POSCTRL_DESVAL_DELAY_INFO[1]
The position control cycle on this NCU is 2 ms.
In this case it may be useful to increase the machine data below on all NCUs by 1 ms:
MD10065 $MN_POSCTRL_DESVAL_DELAY
The resulting value of 8 ms in MD32990 POSCTRL_DESVAL_DELAY_INFO[1] will then
be an integer multiple of the position control cycle of 2 ms.
2.12 NCU link with different interpolation cycles
187