Operating manual
CNC 8070
AUTOMATIC MODE
4.
(REF: 1505)
·83·
Program simulation and execution.
4.3.7 Execute a program (retrace).
The retrace function stops the execution of the program and starts executing backwards the
path traveled so far at the current block plus the last n blocks executed. The number of blocks
to retrace has been preset by the OEM; a typical value being 75 blocks.
When the retrace function is canceled, the CNC resumes the normal execution of the
program. During the retrace function, the program history is not updated; the CNC maintains
the history of the point where the retrace function was activated.
Turn the retrace function on.
This feature is handled by the PLC. Usually, this feature is turned on and off using an external
push button or key configured for that purpose.
The retrace function may be interrupted with the [STOP] key. Pressing [START] while the
retrace function is interrupted resumes the execution in retrace mode. The retrace function
can also be executed block by block (single block mode). The single block mode may be
activated at any time, even when the retrace function is active.
The retrace function may be activated during an interpolation, in the middle of a block and
also at the end of the block, whether the execution was interrupted by M0 or by the single
block mode.
The retrace function cannot be activated while executing G33, G63, G100 or G04 type blocks.
The CNC first finishes the execution of these blocks and then activates the execution in
retrace mode. In the case of G33, G63 and G100, the retrace function is canceled; with
function G04, the execution in retrace mode continues.
When is the retrace function canceled.
The CNC channel cancels the retrace function in the following cases.
• The user cancels the retrace function.
Since this feature is handled from the PLC, the user may cancel it from the operator panel
if the manufacturer has put a button or key for that.
• The CNC channel has executed all the blocks stored for the retrace function.
• The CNC channel has reached the beginning of the program.
• The CNC channel has reached a block that cannot be executed with the retrace function.
The retrace function is also canceled after a reset or an M30.
Resume the execution after the retrace function has been
canceled.
How does the CNC resume the execution, once the retrace function has ended, depends
on the setting of the PLC. If once the retrace function has ended, the CNC does not restore
the normal execution of the program, it will show a warning indicating that the retrace function
must be deactivated (e.g. from the outside operator panel if the manufacturer has provided
a button or key to that effect). The same occurs when trying to execute a new program after
executing the retrace function.
Influence of certain functions while executing in retrace mode.
Machining conditions.
Being retrace active, the movements are carried out backwards keeping the feedrate and
the spindle used to execute them originally.
Activating, canceling and changing Constant Surface Speed (G96 G97) cancel the retrace
function. However, if constant surface speed is on, it respects the change of spindle speed
depending on the coordinate of the diameter axis.
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