Siemens SINUMERIK 840D Function Manual page 442

M3: Coupled axes
14.2 Curve tables
to the internal segments of the curve table. This is always the case if only G1 blocks or axis
polynomials are used to define the curve tables and no other functions are active.
Programmed sections may under certain circumstances not be transformed unchanged into
internal curve segments if:
1. Circles or involutes are programmed
2. Chamfer or rounding is active (CHF, RND)
3. Smoothing with G643 is active
4. Compressor is active (COMPON, COMPCURV, COMPCAD)
5. Tool radius compensation is active for polynomial interpolation.
In these cases, the language commands CTABSSV and CTABSEV may not be used to query the
start and end points of the programmed segments.
CTABINV
When using the inversion function for the curve tables CTABINV, it must be noted that the
following value mapped to the leading value may not be unique.
Within a curve table, the following value can assume the same value for any number of master
value positions. In order to resolve this ambiguity, the program command CTABINV requires a
further parameter, in addition to the following value, which it uses to select the 'correct' master
value. CTABINV always returns the master value that is closest to this auxiliary parameter. This
auxiliary value can, for example, be the master value from the previous interpolator clock cycle.
Note
Although the auxiliary parameter permits calculation of a unique result for the reversal function
of the curve table, it should be noted that numerical inaccuracies may give rise to contours,
which can cause the reversal function to produce results that deviate from those that would be
obtained in a calculation where the accuracy is unrestricted.
Optional parameters
The functions CTAB, CTABINV, CTABSSV and CTABSEV have optional parameters for the
leading and following axes. If one of these parameters is programmed, the master value and
following value are modified using the scaling factors of the relevant axes.
This is particularly important if axes have been configured with different length units (inch/
metric). If no optional parameters are programmed, the master value and following value are
treated as path positions in the conversion from external to internal representation. This means
that the values are multiplied according to the configured resolution (decimal places) and the
remaining decimal places are truncated.
442
Axes and spindles
Function Manual, 06/2019, A5E47437747B AA