Sag Compensation And Angularity Error Compensation - Siemens SINUMERIK 840D sl Function Manual

In the above example, the number of compensation interpolation points must correspond to
the setting in the specified machine data; alarm 12400 "Element does not ex st" will
otherwise be activated.
The compensation table for this example requires at least 6.4KB of the non-volatile NC user
memory (8 bytes per compensation value).
Figure 5-8 Compensation table parameters (system variables for MSEC)
5.4.3

Sag compensation and angularity error compensation

Function
In contrast to the MSEC, the base and compensation axes need not be identical for "Sag
compensation" or "Angularity error compensation", requiring an axis assignment in every
compensation table.
In order to compensate for sag of one axis (base axis) which results from its own weight, the
absolute position of another axis (compensation axis) must be influenced. "Sag
compensation" is therefore an inter-axis compensation.
As illustrated in the diagram below, the further the machining head moves in the negative Y1
axis direction, the more the cross-arm sags in the negative Z1 axis direction.
The error must be recorded in the form of a compensation table that contains a
compensation value for the Z1 axis for every actual value position in the Y1 axis. It is
sufficient to enter the compensation values for the interpolation points.
When the Y1 axis traverses, the control calculates the corresponding compensation value in
the Z1 axis in interpolation cycles performing linear interpolation for positions between the
interpolation points. This compensation is sent to the position control loop as an additional
setpoint. A positive compensation value causes the corresponding machine axis to move in
the negative direction.
Extended Functions
Function Manual, 01/2008, 6FC5397-1BP10-3BA0
Compensations (K3)
5.4 Interpolatory compensation
357