Example - Siemens SINUMERIK 808D Function Manual

● $AN_CEC_MAX[<t>] (end position)
● $AN_CEC_DIRECTION[<t>] (direction-dependent compensation)
This system variable is used to set whether the compensation table [<t>] should apply to both positive and negative
traversing directions of the basic axis:
– $AN_CEC_DIRECTION[<t>] = 1:
Table applies only to the positive traversing direction of the basic axis
– $AN_CEC_DIRECTION[<t>] = -1:
Table applies only to the negative traversing direction of the basic axis
Note
The setting $AN_CEC_DIRECTION[<t>] = 0 (table is effective for both traversing directions of the basic axis) is not
relevant for the "direction-dependent LEC".
● $AN_CEC_IS_MODULO[<t>] (compensation with modulo function)
System of units
Table parameters containing position information are automatically converted when the system of units is changed (change
from MD10240 $MN_SCALING_SYSTEM_IS_METRIC).
The position information is always interpreted in the current measuring system. Conversion must be implemented externally.
Automatic conversion of the position data can be configured as follows:
● MD10260 $MN_CONVERT_SCALING_SYSTEM = 1
With this setting, the following axial machine data is activated:
● MD32711 $MA_CEC_SCALING_SYSTEM_METRIC (measuring system for sag compensation)
The measuring system for all tables effective for this axis is set in this machine data. Hereby, all position entries are
interpreted together with the calculated total compensation value in the configured measuring system. External conversions
of position information are no longer necessary with a measuring system change.
Monitoring
To avoid excessive velocities and acceleration rates on the machine axis as a result of applying sag compensation, the total
compensation value is monitored and limited to a maximum value.
The maximum possible total compensation value for sag compensation is defined on an axis-for-axis basis using the
machine data:
● MD32720 $MA_CEC_MAX_SUM (maximum compensation value for sag compensation)
If the determined total compensation value is greater than the maximum value, then a corresponding alarm is output.
Program processing is not interrupted. The compensation value output as an additional setpoint is limited to the maximum
value.
Further, changing the total compensation value is also axially limited:
● MD32730 $MA_CEC_MAX_VELO (velocity change for sag compensation)
The specified value acts as a factor and is referred to the maximum axis velocity (MD32000 $MA_MAX_AX_VELO).
An appropriate alarm is signaled when the limit value is exceeded. Program processing is not interrupted. The path not
covered because of the limitation is made up as soon as the compensation value is no longer subject to limitation.
11.3.4.3

Example

The direction-dependent compensation tables of the X axis are shown in detail for a three-axis machine in the following
example:
Configuring
Number of compensation interpolation points:
MD18342 $MN_MM_CEC_MAX_POINTS[0] = 11 (Table 1: Axis X, positive traversing direction)
MD18342 $MN_MM_CEC_MAX_POINTS[1] = 11 (Table 2: Axis X, negative traversing direction)
Function Manual
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