Within Program Loops; Full Circles; Automatically Generated Contour Elements - Siemens sinumerik 840D sl Function Manual

Boundary conditions
3.1 Function-specific boundary conditions
3.1.2

Within program loops

NC high-level language
In NC high-level language, program loops can be programmed using:
• LOOP
• FOR
• WHILE
• REPEAT
• CASE/IF-ELSE-ENDIF in conjunction with GOTOB
If retrace support is performed within program loops, the retrace support is always effective
in the first loop run.
If the program continuation point on the programmed contour is the result of a loop run that
is not equal to the first loop run, this may under certain circumstances result in significant
contour deviations during subsequent machining processes.
Warning
If the program continuation on the programmed contour is the result of a loop run that is not
equal to the first loop run, this may under certain circumstances result in significant contour
deviations during subsequent machining processes, posing a risk of personal injury and
damage to the machine.
3.1.3

Full circles

In full circles, the block starts and ends at the same contour point. As in such cases it is
impossible to make a clear distinction, retrace support on a contour point of this type is
always based on the point at which the block starts. The first part program block following
retrace support is then the circular block.
In order to avoid the circular block being traversed following retrace support, a contour point
shortly before the end of the circular block should be selected as the program continuation
point.
3.1.4

Automatically generated contour elements

The automatic generation of non-linear/circular contour elements by the NC takes place, for
example, when programming the following NC functions in the part program:
• RND
• G641/G642
• Tool radius compensation
For reverse/forward travel as part of RESU, these contour elements can be replaced by
straight lines between the start and end of the block.
34
ENDLOOP
ENDFOR
ENDWHILE
UNTIL
Special functions: Retrace Support (TE7)
Function Manual, 11/2006, 6FC5397-2BP10-2BA0