Acceleration (B2); Acceleration Profiles; Jerk Limitation On Interpolator Level; Jerk Limitation In Jog Mode - Siemens SINUMERIK 808D Function Manual

6

Acceleration (B2)

6.1

Acceleration profiles

Abrupt acceleration changes
With the v/t-linear control of the axis velocity that is normally applied, the motion is controlled such that the acceleration rate
changes abruptly over time. With the discontinuous, stepped acceleration, jerk-free starting and braking of the axes is not
possible, but a time optimized velocity/time profile can be implemented.
Acceleration with jerk limitation
The jerk is the change of acceleration over time. For jerk-limited acceleration the maximum acceleration is not abrupt, but is
specified by a ramp. Because of the softer acceleration progression, the traverse time is longer than with abrupt acceleration
for the same distance, velocity and acceleration. This time loss can be compensated for by setting a higher acceleration for
the axes.
However, it has the following advantages:
● Reduced wear to mechanical parts of the machine
● Reduction of the excitation of high frequency, difficult to control vibrations of the machine.
6.2

Jerk limitation on interpolator level

Selection and deselection of jerk-limited acceleration
MD32431 MAX_AX_JERK (maximum axis-specific jerk during path motion) can limit the change in acceleration per machine
axis individually. It only acts on the axes interpolated by the path when SOFT is active. Jerk limitation is implemented
entirely on the interpolator level.
Acceleration with jerk limitation is activated by:
The program code SOFT in the part program. SOFT is modal and causes deselection of the abrupt acceleration profile
(BRISK). If SOFT is programmed in a block with path axes, the previous block is ended with exact stop.
Acceleration with jerk limitation (SOFT) is deactivated by:
The program code BRISK in the part program. BRISK is modal. If path axes are programmed in a block with BRISK, the
previous block is ended with exact stop. BRISK activates the profile with abrupt acceleration changes associated with v/t--
linear velocity control.
Applicability
Path-related jerk limitation is available for interpolating path axes in operating modes "AUTO" and "MDA". The SOFT and
BRISK acceleration profiles can be used in traverse modes exact stop G9, G60, continuous path modes G64, and with
LookAhead. The profiles are also active with the dry run feedrate function. With alarms that trigger a rapid stop, both
acceleration profiles are inactive.
Further information about velocity, acceleration and jerk whilst traversing in continuous path mode and at block transitions
can be found in Chapter "Continuous Path Mode, Exact Stop and LookAhead (B1)".
Note
We recommend setting the following machine data for each axis with the same values: MD32431 MAX_AX_JERK and
MD32432 PATH_TRANS_JERK_LIM (maximum axis-specific jerk for path movement at block transition)
6.3

Jerk limitation in JOG mode

The jerk limitation is active for axes in "JOG" mode during
● jogging
● handwheel jogging
● repositioning.
The jerk limitation is not active during reference point approach with alarms that initiate a rapid stop.
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Function Manual
01/2017