
B–62073E–1/042. INTERFACE BETWEEN CNC AND PMC–NA OR NB
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2.3.76 Retrace
A tool can retrace the tool path along which the tool has moved. This operation is referred to as retrace. In
addition, a tool can move forward again along the path that the tool has retraced. This operation is referred
to as re–forward. The tool can then resume machining according to the program when it returns to the position
where it started retrace.
Retrace end, re–forwarding start
Retrace signal
HIGH
Retrace start
Retrace signal
LOW
By using the retrace signal RVS, which is an input signal from the PMC to the control unit, retrace and re–for-
ward can be performed. Retrace is performed when the retrace signal RVS goes high. Re–forward operation
is performed when the retrace signal goes low. In retrace, a tool can retrace blocks that have been executed
in the automatic operation mode (memory command, tape command, manual data input), but a limit is imposed
on the number of blocks that can be retraced. For detailed information, refer to the operator’s manual.
Whether to use the same feedrate as specified for normal operation or use a feedrate dedicated to retrace can
be determined by parameter setting.
(a) Retrace signal (RVS)
[Classification]
Input signal
[Function] Directs the control unit to retrace the tool along the path which the tool was moved in automat-
ic operation (memory command, tape command, manual data input).
[Operation] When RVS goes high while the tool is being moved forward (hereafter referred to as forward),
the tool retraces the machining path along which it was moved. Note, however, that the tool
does not start retrace immediately after this signal goes high; the tool starts retrace after the
block performing the current forward operation is executed. When RVS goes low while re-
trace is in progress, the tool switches from retrace operation to re–forward. In this case also,
the tool does not start re–forward (to resume machining) immediately after this signal goes
low; the tool starts re–forward after retracing all commands of the block currently subject to
retrace.
The movement of a tool can be immediately switched from forward to retrace or from retrace
to re–forward. For this purpose, first drive the automatic operation stop signal *SP low to stop
automatic operation. Then, change the state of RVS after the automatic operation stop state
is set with the automatic operation start in–progress signal STL low and the automatic opera-
tion suspend in–progress signal SPL high. Next, drive the automatic operation start signal
ST low from high to start automatic operation. Then, the tool can switch its movement to re-
trace or re–forward during execution of a block.