HEIDENHAIN TNC 335 Technical Manual - Manual (Page 149)

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TNC 360 3 Servo Positioning of the NC Axes 8/95
3.2 Servo positioning in TNC controls
Two control methods are possible with the control. They can be used alternatively.
1. control with lag (section 3.2.1)
2. control with feed forward (section 3.2.2)
The choice of control method is determined by machine parameter MP1390.
The machine adjustment must always be carried out for both methods of control.
MP1390 Control with lag or feed forward control
Input value: 0 or 1,
1 = operation with lag,
0 = operation with feed forward control.
3.2.1 Control with servo lag
Servo lag refers to the difference (lag) between the nominal position which is defined by the NC and
the actual position of the axes. Control would not be possible without this lag.
In the operating modes "Manual operation" and "Electronic handwheel" the operation is always with
servo lag, regardless of machine parameter MP1390.
In the operating modes "Positioning with manual entry", "Program run, single block" and "Program
run, full sequence" machine parameter MP1390 must be appropriately entered for lag operation.
The advantage of operation with servo lag lies in the "softer" control, which is especially suitable for
machining 3D contours, since corners and radii are smoothed out, depending on the Kv factor
(position loop gain factor) and the machining feed rate.
Depending on how far these "contour errors" can be tolerated, the machine operator or manufacturer
must decide and choose either operation with servo lag or with feed forward control.
Operation with servo lag is depicted in a simplified form in the following block diagram for the X axis.
It shows a part of the cascade control mentioned previously.
All machine parameters which influence the control characteristic are shown here.