Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 368)

Axis Motion
Chapter 14
14-10
In incremental mode (G91), the rotary axis is programmed to move in an
angular distance (not to a specified angle as in absolute). The maximum
incremental departure depends on the programming format selected in
AMP by your system installer. The sign of the angle determines what
direction the rotary axis rotates. For example, if the current C axis position
is 25
° and this block is programmed:
G91C50;
the C axis would rotate 50 ° in the positive direction. The new C axis
position would be 75 ° .
If the current C axis position is 25 ° and this block is programmed:
G91C-50;
the C axis would rotate 50 ° in the negative direction. The new C axis
position would be 335 ° .
In this mode: you:
incremental (G91) program a value greater than the rollover amount results in the rotary
axis making one or more complete revolutions.
absolute (G90) cannot program a rotary axis move greater than the rollover amount.
circular interpolation cannot program a rotary axis move unless these conditions are met::
(G02 or G03)
·the rotary axis cannot be in the active plane
·the rotary axis must be programmed in the same block as a valid
circular move made with the axes in the active plane
Important: You can program the largest move with a rotary axis is equal
to the rollover amount. Any attempt to program a move that generates
more motion than the rollover amount is truncated and moved to the
position that has the same numerical endpoint as the programmed position.
For example if this incremental move is programmed from a position of
10
° :
G91C370;
the actual endpoint of the above move is still 20 ° ; however, the rotary axis
did not get there by revolving one revolution. Instead, it positioned itself
directly to 20
° without passing 20 once as expected.