Siemens SINUMERIK 840C - Manual (Page 717)

09.95 10 Axis and Spindle Installation
10.4.1 Drive optimization
Checking/determining the acceleration values
Setting: NC MD 276*
Criterion: Overshoot-free acceleration or positioning at rapid traverse rate
(acceleration stop limit).
Under maximum load conditions (heavy workpieces on the machine table)
Measuring
equipment:
Recorders, storage oscilloscopes or trace function (Section 9)
Measuring
point:
Setpoint speed and possibly actual current and speed controller output.
With digital drive DAC, mixed I/O (see Section 9).
Once acceleration has stopped, the axes travel at maximum speed (rapid traverse) and the
actual current values and possibly the n-controller output are recorded. This makes it possible
to ascertain whether or not the current limit was reached. The drive can reach the current limit
briefly, but this must occur only in the rapid traverse range. Speed control and current control
must be back within the normal range (current limit not attained!) before the rapid traverse rate
or position has been reached.
Relation between acceleration and actual current
Example of a well-
chosen acceleration
value In this example, the current limit is
reached (recognizable by the fact
that the actual current retains its
maximum value over a period of
time). A lower acceleration must be
chosen in this case.
n
set
n
act
i
set
+
i
set
-
Minor changes in the load (such as sluggishness or the effects of lubrication) must not cause
immediate reaching of the current limit. A 10 % lower acceleration value should therefore be
specified.
If the customer wishes it, the acceleration can be further reduced to protect the machine
against excessive wear and tear. The various axes, including interpolating axes, may be
assigned different accelerations.
© Siemens AG 1992 All Rights Reserved 6FC5197- AA50 10–27
SINUMERIK 840C (IA)