Rockwell Automation GMLC Reference Manual - Manual (Page 269)

Publication GMLC-5.2 - November 1999
232 Motion Blocks
For example, if the following bullets are true, and the Interpolate Axes
parameters are as shown in the dialog box below, it produces the same
motion as shown previously for absolute mode.
• Axis 0 is used as the X axis and is currently at absolute position –10.4
position units
• Axis 1 is used as the Y axis and is currently at position –1.3 position
units
Since three points (the current position of the axes, the specified end
point, and the specified intermediate point) define one and only one
circle, it is difficult to program a bad intermediate arc. While it is still
certainly possible to program an arc which is not the intended one, a Bad
Arc runtime fault only occurs with intermediate arc circular interpolation
if the three points are co-linear (all three are on the same line) or not
unique (two or more are the same). In addition, the intermediate point
implies the direction of the arc and thus it is not necessary to specify the
direction.