Siemens SINUMERIK 840C Installation Instructions Manual page 632

09.95
9.2
Note
Measurements in
the time range
Frequency response
measurement
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SINUMERIK 840C (IA)
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Measuring the drive servo loops (current, speed, position)
When measuring the spindle it is important not to enter the weak field range as this
produces an incorrect display.
The integrated time-range measuring functions of the drive servo start-up
application enable you to assess the significant quantities of the speed and
position control loops on the NC screen without external measuring equipment.
You can input a step or ramp function with adjustable amplitude and, if required,
ramp time as a test signal for a parameterizable measurement time; a constant
offset can also be superimposed on the test signal. By entering a settling time,
you can determine the instant at which data recording begins.
The specified traversing path is monitored during the measurement. On
completion of the measurement, you can assess the result on the screen by se-
lecting the Display softkey.
Special test sockets on the drive modules of 611D drives allow all important
control loop signals (setpoints, actual values, control deviations) to be output
(DAC configuration) on external instruments (oscilloscope or signal recorder).
You can also output these signals if you use a mixed I/O module (mixed I/O
configuration).
There are always exactly three DAC channels for every 611D feed drive and
main spindle module, even in multi-axis versions. A total of four position
controller signals can be output simultaneously via the 611D DAC channels or
the mixed I/O.
An integrated function generator supplies periodic test signals (square-wave and
triangular signals, staircase function) to stimulate the control loops as well as
noise signals for spectral analysis using external equipment.
The parameters of drives or position control can be accessed at any time, the
application need not be terminated for this purpose.
In addition to the usual method of optimizing control loop parameters which is
based on the transient response, i.e. time characteristics, the Fourier analysis
function integrated in the 840 C provides you with a powerful tool for assessing
control loop settings and analyzing the given mechanical characteristics.
You should use this function whenever
S
unsteady current, speed or position signal forms give you reason to suspect
stability problems
S
you can obtain only slow rise times in the speed loop
S
the contour quality at high machining speeds is inadequate
S
you require documentation of settings.
This optimization procedure is identical to that for the time range, i.e. you must
optimize "from the inside outwards", starting with the current control. The
frequency response measurement method used in the SIN 840 C supplies
precise and reproducible results even at very low test signal amplitudes; the
measurement parameters can be matched to the application in question.
All measurements are carried out in the course of an offset movement of a few
(approximately 1–5) revolutions per minute; a test signal amplitude (noise) of
one to two revolutions is superimposed on the offset. The accuracy increases
with the number of averaging operations (selectable); a value of 20 is normally
sufficient. The bandwidth, which is likewise adjustable, is normally selected to
correspond to half the sampling frequency.
max. bandwidth = f
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9 Drive Servo Start-Up Application (as from SW 3)
9.2 Measuring the drive servo loops (current, speed, position)
1
8 4000 Hz
sampl.
=
2 x t
2
sampl.
9–11