S-shaped ramp profile generator, traversing speed reached is subject to tolerances

Question:
Why is the traversing speed reached with the S-shaped ramp profile generator of the 9300EP subject to tolerances?

Answer:
When you select a traversing speed for the positioning process (programmed operation or manual operation), the speed actually reached is subject to tolerances if S-shaped ramps are used. In most cases, the traversing speed actually reached at the end of the acceleration phase is some per mill points below the selected speed. In some cases with extreme settings for the machine parameters, significantly larger deviations may occur. These deviations, which depend on the parameter settings, are always reproducible and do not occur sporadically.

Extreme settings for the machine parameters should be avoided if possible. Vmax (C1240) should, for instance, be set as close as possible to the maximum value, which is determined by nmax (C0011). The conversion formula can be found in the 9300EP System Manual, chapter '7.5.2  Machine parameters'.

Explanation for the deviations:
Due to the functional principle, the calculations required for the S-shaped ramps are more complicated than those for linear ramps because the accelerations and decelerations must not be changed abruptly for the S-shape. In order to ensure that the time required for the calculations will not be longer than for linear ramps, some simplifications have been introduced for the S-shaped ramps, e. g. identical deceleration and acceleration, reduced variable resolution and a limited setting range for the jerk times.

See also doc. ID 20038668 with diagrams for stopping with S-shaped ramps.