Rockwell Automation 8520-GUM 9/Series CNC Grinder Operation and Programming Manual Documentation Set - Manual (Page 218)

Running a Program
Chapter 7
7-30
The block retrace function allows the operator to retrace the motion created
by up to 15 consecutive part program blocks. The actual number of retrace
blocks allowed is set by your system installer in AMP, and can vary from 1
to 15.
Important: For maximum control efficiency when executing programs,
we recommend that the maximum number of allowable block retraces is
set as small as possible for the current grinder application. This is because
the number of allowable block retraces directly affects the control’s block
look-ahead operation.
You can only enable this function when the control is in cycle stop or cycle
suspend state and the control ignores this feature if it has already executed
an M02 or M30 end of program.
To perform a block retrace operation:
1. Press the <CYCLE STOP> button or the <SINGLE BLOCK> button to stop
program execution.
2. Press the <BLOCK RETRACE> button.
After you press the <BLOCK RETRACE> button, the control retraces the block
that was being executed when the cycle stop occurred or retrace the block
just completed if you press the single block button, provided that the block
is a legal block for retrace.
While the block retrace function is active, the light in the
<BLOCK RETRACE> button is on. The block that was shown as active when
the block retrace was activated stills appear as the currently active block in
the program display area during the entire use of the block retrace function.
Important: If you use the <CYCLE STOP> button to halt execution to begin
a block retrace, the control re-executes the portion of the block that has
been executed. For example, if the block requests an axis move of 20 mm
and the axis has moved 12 mm when you press the
<CYCLE STOP> button, a
block retrace reverses the axis direction 12 mm.
All retraced blocks are executed at the feedrate programmed for that block.
You can, however, modify the feedrate by the use of the
<FEEDRATE OVERRIDE> switch. See page 12-58.
Press the <CYCLE START> button at any time during a block retrace to
return the grinding wheel to normal forward execution. Program execution
returns to the normal forward direction from the currently retraced block.
The control executes the retraced blocks in normal order until the wheel is
positioned at the start point of block retrace. From this point it continues
program execution in a normal fashion unless
<SINGLE BLOCK> is active.
If <SINGLE BLOCK> is active, the control halts execution when the return
from block retract is complete.
7.10
Block Retrace