Absolute/Incremental Dimensioning: G90, G91, Ac, Ic - Siemens SINUMERIK User Manual

11.2.2

Absolute/incremental dimensioning: G90, G91, AC, IC

Functionality
With the instructions G90/G91, the written positional data X, Z, ... are evaluated as a coordinate point (G90) or as an axis
position to traverse to (G91). G90/91 applies for all axes.
Irrespective of G90/G91, certain positional data can be specified for certain blocks in absolute/incremental dimensions using
AC/IC.
These instructions do not determine the path by which the end points are reached; this is provided by a G group (G0, G1,
G2 and G3...). For more information, see Sections "Linear interpolation (Page 85)" and "Circular interpolation (Page 87)".
Programming
G90 ; Absolute dimension data
G91 ; Incremental dimension data
Z=AC(...) ; Absolute dimensioning for a certain axis (here: Z axis), non-modal
Z=IC(...) ; Incremental dimensioning for a certain axis (here: Z axis), non-modal
See the following different dimensioning types in the drawing:
Absolute dimensioning G90
With absolute dimensioning, the dimensioning data refers to the zero of the coordinate system currently active (workpiece
or current workpiece coordinate system or machine coordinate system). This is dependent on which offsets are currently
active: programmable, settable, or no offsets.
Upon program start, G90 is active for all axes and remains active until it is deselected in a subsequent block by G91
(incremental dimensioning data) (modally active).
Incremental dimensioning G91
With incremental dimensioning, the numerical value of the path information corresponds to the axis path to be traversed.
The leading sign indicates the traversing direction.
G91 applies to all axes and can be deselected in a subsequent block by G90 (absolute dimensioning).
Specification with =AC(...), =IC(...)
After the end point coordinate, write an equality sign. The value must be put in round brackets.
Absolute dimensioning is also possible for center points using =AC(...). Otherwise, the reference point for the circle center is
the circle starting point.
Programming example
N10 G90 X20 Z90
N20 X75 Z=IC(-32)
N180 G91 X40 Z2
N190 X-12 Z=AC(17)
78
; Absolute dimensions
; X-dimensions remain absolute, incremental Z dimension
; Switch-over to incremental dimensioning
; X-remains incremental dimensioning, Z-absolute
Programming and Operating Manual (Turning)
01/2017