HEIDENHAIN TNC 320 (340 551-02) - Manual (Page 172)

172 7 Programming: Miscellaneous Functions
7.
4 Miscellaneous F
u
nctions f
o
r Cont
our
ing Beha
vior
Calculating the radius-compensated path in
advance (LOOK AHEAD): M120
Standard behavior
If the tool radius is larger than the contour step that is to be machined
with radius compensation, the TNC interrupts program run and
generates an error message. M97 (see “Machining small contour
steps: M97” on page169) inhibits the error message, but this results
in dwell marks and will also move the corner.
If the programmed contour contains undercut features, the tool may
damage the contour.
Behavior with M120
The TNC checks radius-compensated paths for contour undercuts and
tool path intersections, and calculates the tool path in advance from
the current block. Areas of the contour that might be damaged by the
tool are not machined (dark areas in figure at right). You can also use
M120 to calculate the radius compensation for digitized data or data
created on an external programming system. This means that
deviations from the theoretical tool radius can be compensated.
Use LA (look-ahead) after M120 to define the number of blocks
(maximum: 99) that you want the TNC to calculate in advance. Note
that the larger the number of blocks you choose, the higher the block
processing time will be.
Input
If you enter M120 in a positioning block, the TNC continues the dialog
for this block by asking you the number of blocks LA that are to be
calculated in advance.
Effect
M120 must be located in an NC block that also contains radius
compensation RL or RR. M120 is then effective from this block until
„ radius compensation is canceled, or
„ M120 LA0 is programmed, or
„ M120 is programmed without LA, or
„
another program is called with PGM CALL, or
M120 becomes effective at the start of block.
Limitations
„ After an external or internal stop, you can only re-enter the contour
with the function RESTORE POS. AT N.
„ When using the path functions RND and CHF, the blocks before and
after them must contain only coordinates in the working plane.
„ If you want to approach the contour on a tangential path, you must
use the function APPR LCT. The block with APPR LCT must contain
only coordinates of the working plane.
„ If you want to depart the contour on a tangential path, use the
function DEP LCT. The block with DEP LCT must contain only
coordinates of the working plane.
X
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