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6.4.11 Software option 142—Position Adaptive Control (PAC)
Considerations
before using PAC
Preparation and
activation
July 2013
The specifics of a machine's kinematics cause a unique position of the axes'
center of gravity in the working space. This results in a variable dynamic
behavior of the machine, which can adversely affect the stability of the servo-
control significantly depending on the axis positions. To exploit the machine's
dynamic possibilities, you can use the PAC option (Position Adaptive Control)
to change machine parameters depending on position.
This makes it possible to assign respectively optimal loop gain to defined
support points. Additional position-dependent filter parameters can be defined
in order to further increase control loop stability. Besides the position-
dependent adjustment of machine parameters, the PAC option also provides
a way to change machine parameter values depending on other input
quantities such as velocity or acceleration of an axis.
Up to five controller parameters can be changed by each of the two options
PAC and MAC. A controller parameter must be changed either by PAC or by
MAC, and not by both PAC and MAC.
The position-dependent parameter settings can be determined at various
positions by using TNCopt (for example, the Bode diagram). As of version 6.0,
TNCopt provides you with appropriate input forms for the parameter settings
that can be transferred to the control.
Considerations before using PAC:
Is there a significant position dependence concerning the controller
parameters? This becomes apparent:
by using TNCopt if resonances vary considerably at different positions.
if there is a position-dependent oscillation tendency of the axis. In this case
there may also be audible oscillations at certain positions.
Activating PAC:
Activate PAC via TNCopt in the "Expanded compensations" menu item.
Adjust the axis at different positions (e.g. Bode diagram, step response).
In the TNCopt form, enter the parameters you have determined for up to
four support points. You can define up to five machine parameters and up
to five position-dependent filters (with two support points). The parameters
are interpolated linearly between the support points.
PAC must then be enabled for all machining axes via MP2700 bit 1.
This function is described in detail in the Help function of TNCopt 6.0. Available
as of the end of 2011.
6.4 Axis-error compensation
693
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