12 Functional Descriptions 08.96
12.33.1 Introduction
12.33.1.3 Measurement procedure
In order to optimize a cascaded closed-loop control structure (current, speed, position control
loops), it is necessary to start with the innermost (lowest level) control loop, i.e. the current
control loop. This is set optimally by means of operator command "Calculate controller data"
and need not be optimized again by the user.
The speed controller is also preset by means of command Calculate controller data. This is
a rough setting for the motor under no-load conditions and does not take account of
mechanical components mounted on the motor.
Amplitude and offset settings
All measurements are carried out during the execution of an offset motion of a few
(approximately 1 - 10) revolutions per minute on which a test signal amplitude (noise) of one to
three revolutions is superimposed. The offset should always be greater (factor 2- 3) than the
amplitude. At very low values, backlash or static friction may result in different results to those
measured at higher traversing speeds. Very high amplitude values falsify the measurement
results or may result in damage to mechanical components.
If you obtain very noisy results, you should increase the number of averaging operations or the
amplitude. The accuracy increases in proportion to the selected number of averaging
operations.
12.33.2 Optimization of speed controller
The following rules apply to optimization of the speed controller:
• The amplitude must equal 0 dB over the widest possible fundamental frequency range.
The fundamental frequency range is the operating range up to the controller stability limit.
• Increase the P gain if the amplitude does not reach the 0 dB line.
• Decrease the P gain if the amplitude rises above the 0 dB line.
• A few dB above the ideal setting (max. 1 - 3 dB) are permissible.
The reference values for the speed controller frequency response can be defined as follows:
• Fundamental frequency range
Approx. 200 Hz – 300 Hz
• Controller stability limit
– 3dB attenuation in amplitude
– 180
°
phase crossover
Typical values for 611D without built-on mechanical components are:
Speed controller: T = 62.5µs approx. 0.9 kHz
T = 125µs approx. 0.5 kHz
12–336
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SINUMERIK 840C (IA)