Tuning Velocity Controller (Ziegler&Nichols)
AX5000 Tuning - Guide10
Version: 1.0
3.6 Evaluating the oscilloscope pattern
While the axis reverses, observe the behavior with the
oscilloscope. The following oscilloscope pattern shows the
velocity command value and actual velocity value in the upper
diagram and the current or torque ("torque feedback value") in
the lower diagram.
The red line is based on an increased value for Kp. The next
motion shows that an oscillation occurs, which continues for
the whole motion.
Depending on the mechanical system, the value that was
reached can be regarded as Kp
crit
, or Kp can be increased
further, until the oscillation also shows up in the velocity
value. It will then also be more audible.
In the sample application with a ball screw, the oscillation in
the current signal starts at Kp = 0.22. Only a soft "squeaking"
can be heard, which is inaudible in a noisy environment.
At Kp = 0.25 the oscillation also shows up in the speed signal.
3.7 Reducing Kp
Based on the rules of Ziegler and Nichols, the correct value for Kp should be determined using the following
formula.
Kp = 0.45 x Kp
crit
In the example,
• Kp = 0.45 x 0.22 = 0.10 or
• Kp = 0.45 x 0.25 = 0.11
is the correct value.
3.8 Determining Tn
Tn determines the integral action time of the integral controller. The smaller Tn, the larger the gain of the
Integral controllers. The correct value for Tn is mainly dependent on the type of coupling between motor and
load. Many applications run satisfactorily with the default value Tn = 8 ms. At the Rigid coupling and if the
tracking error appears to be too large, Tn can e.g. up to 5 ms.
Attention
Value ranges from Tn!
Do not reduce Tn any further without using the TC ScopeView to ensure that the current or
speed actual value does not start to oscillate! Values ≤ 5 ms are not required in most appli-
cations. With elastic coupling between engine and load or even with long straps it may be
useful for Tn Values> 10 ms. Swinging of the axis is thereby prevented.
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