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Nutating CA/CB Head Setup

An-102aa, Copyright © by Gil Hagiz
Last updated Mar-02-2006
For version 6.02 and later


1 : The act of nodding the head
2 : Oscillatory movement of the axis of a rotating body (as the earth)
(Merriam Webster Dictionary)


This application note describes the setup of a nutating rotary head for 5-axis RTCP machining.
The topic covered here is the nutating head setup.
The RTCP capability is provided by a separate BIN file. Without this file the machine can work as a regular 5-axis non-TCP machine.



This set up can be performed by a superuser only.
To avoid unintentional set up, the superuser has to change the security level in plc@50 to 0. In MDI type:
Line numbers for setup data relate to the machine.cnx file, in the machine data area after line n30000.
Before you start:

Setup general

To set the machine zero for an axis proceed as follows (C is used as an example):


Setup A/B-Axis

A/B=0 is when the tool is vertical, in the minus-Z direction, same as in a three-axis machine.
For CA, A=+max is when C=0 and A is in the direction of plus-Y.
For CB, B=+max is when C=0 and B is in the direction of minus-X.
To set A/B proceed as follows:

Setup C-Axis

C=0 is when positioned as in the left picture for CB and the right for CA.

This setup can be used if the nutator range is at least 0 to 180 degrees, and C is limit-less. With this setup, A/B moves in the same direction as the nutator axis and complies with the standard directions for rotary axes.
Note how the orientation is defined relative to the XYZ axes.

If C has a limit:
In modes other than H0, C turns 90 deg CW when the nutator moves from 0 to 180 degrees in order to keep the virtual-C orientation of the tool constant.
If the head is oriented as shown above for C-zero and the limit is at 90 or 180 degrees, (depending on whether the head is set as CA or CB) this setup leaves enough room for a convenient use of the head.

However, if at this orientation the limit is at about -90 or 0 degrees then only one setting of CA or CB will let the C to move the +90 degrees when A/B moves from zero to max.
With this setting, either at A/B-zero or A/B-max C will be at the limit.
If it is desired to move the zero away from the limit, the zero position for C can be set 180 degrees off (mirror image of the pictures above). But now, what used to be positive direction of A/B is negative.
The solution is to reverse the direction of the nutator and to call the TCP file nca5 with the command line switch /n.
In addition, the nutator limits should be reversed (positive= 0, negative= -180).
Note that using negative A/B is somewhat confusing but still complies with the standard directions for rotary axes.

To set C proceed as follows:


X and Y offsets compensate for misalignment between the spindle axis and the C-axis.
XY offsets are measured from the spindle to the center of C-axis.
For example, if offset x1 is entered then the machine will be at x1 when the tool is at x0.
Note that C-zero refers to the mechanical C and not the virtual C.



Tool Length

Tool length is measured from A/B-pivot, however, tools can be measured from a more convenient place, like the spindle face.
To measure the Z-pivot length:

Final test