Indexed Machine Axes

Some 5X machines use non-continuous rotary axes, also known as indexed axes. These axes can be placed at discrete positions only, for instance in steps of 2.5 degrees. Values in between are not possible.

Such machines are not well suited for continuous 5X milling, but can be used for positioning (3X + 2X milling) - provided that the positioning angle fits the axis step size.

The definition of the alpha or beta axis as an indexed axis is done using the M5_A_STEP and M5_B_STEP variables respectively. They should be set to the allowed step size of the axis, expressed in degrees. By default, both these variables are assigned zero, which indicates continuous motion. The variables must be set before the DEFINE_MACHINE statement is used.

For instance, setting M5_A_STEP to 2.5 means that the alpha axis can only accept values that divide by 2.5 (0.0, 2.5, 5.0, 7.5, -2.5, etc.). Other values, such as 2.0 degrees are illegal.

For an indexed axis, GPP2 will always round the angle position according to the axis step size. This may cause a tool orientation error, depending on the required tool orientation. There are two variables that indicate such an orientation error:

  • INACCURATE_ORIENT is set to TRUE_ whenever an axis angle (any indexed axis) is not as required by the toolpath (within angle formatting accuracy). Otherwise, it is FALSE_.

  • INACCURATE_ERROR contains the orientation error, in degrees, between the intended and the resulting tool orientation vectors.

The EX2 program can use these variables to identify cases of inaccurate positioning, and to decide if processing may continue or not (For example, depending on the error size).

In addition to setting these variables, GPP2 will issue a runtime warning to indicate the orientation error.

In 3X + 2X positioning procedures, the target angles are calculated as part of the procedure connection process. Any rounding and orientation errors are well known at that point. Therefore, the two orientation error variables are set as early as the BEGINNING OF CONNECT block. The decision whether to continue processing or to abort it can be taken by the EX2 program before any connection motions.

Some functionality may be dependent on the product package. Contact your Reseller if you require a license.