6 – 294 HEIDENHAIN Technical Manual TNC 426, TNC 430
6.13.16 Returning to the Contour
With HEIDENHAIN contouring controls you can resume an interrupted
program at a specified block number by scanning the previous blocks (see
“Mid-Program Startup” in the User’s Manual).
Markers inform the PLC about individual conditions during mid-program
startup (block scan). Depending on these markers you can enable certain
functions such as the axis-direction buttons for MANUAL TRAVERSE.
M4156 is set if the MANUAL TRAVERSE soft key is pressed.
M4157 is set if the RESTORE POSITION soft key is pressed (“Return to
Contour”).
M4158 is set if the RESTORE POS. AT soft key is pressed. M4158 is reset if
the RESTORE POSITION or INTERNAL STOP soft key is pressed.
During the block scan, PLC positioning commands are included in calculation
only if they are also executed. The TOOL CALL block normally causes PLC
positioning commands for tool change. If you want these positioning
commands to be calculated in the block scan:
7
77
7 In MP951.x, enter the absolute position with respect to the machine datum.
7
77
7 Activate the calculation for the specific axes with MP7450.
With flexible tool-pocket coding in the central tool file (See "Tool Changer” on
page 6 – 400), the change of pocket number in the tool file must be prevented
during block scan if the TOOL CALL blocks are not collected:
7
77
7 Set M4542.
The block scan can be interrupted by a programmed STOP or with M06,
whereby you can have the programmed dwell time included:
7
77
7 With MP7680, bits 3 and 4, select the parameters for the block scan.
7
77
7 With MP7451.x, define the feed rate for returning to the contour.
If an NC program block is interrupted in Single block mode or by a STOP block
and the positions of NC axes are changed, the NC program can be restarted
at the changed positions. If in OEM.SYS STRICTREPOS = YES, the function for
restoring the position is activated. (See “OEM.SYS” on page 7 – 41)
Note
You must enable these functions through machine parameters.
You must prepare the PLC program accordingly.
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