Positioning behavior: Jerk limitation or mean value filter better? That is the question here
Question:
Jerk limitation or mean value filtering:
Which procedure for evening out the the of position setpoint is in regard to the positioning behavior and the achievable drive performance better suitable?
Reply:
It depends! Both filter methods have their advantages and disadvantages.
Both methods aim to avoid sudden changes in acceleration/deceleration. Sudden changes always generate a broad spectrum of frequencies (keyword: Fourier). The individual natural frequency of the machine will therefore also be present and the entire system will be excited to oscillate at the natural frequency.
A filter method is particularly effective if, as far as possible, only the natural frequency of the machine is filtered out or dampened from the frequency spectrum.
amax;: Max. acceleration/deceleration achieved during the respective positioning movement
Advantages:
Target and oversanding positions are achieved accurately. The setpoint generation causes no time delay. The same applies for synchronous movements of several axes .
Disadvantages:
The frequency spectrum shifts during movements over short distances if the full acceleration amax is not reached in the driving profile (so-called triangle operation).
The natural frequency f0 of the machine is correspondingly less damped and the occurrence of vibrations may increase.
To avoid the excitation caused by the triangle operation excitation of vibrations, the jerk limitation must be adjusted, see formula.
Average filter:
Setting: Average filter time (TFilter) = >1 / f0 | [s] = 1 / [1/s]
f0: Natural frequency of the machine
Advantages:
Easy to configure, only needs to be tuned to the natural frequency f0 of the machine is required.
Parameterization is not dependent on the acceleration curve of the respective positioning movement.
Disadvantages:
The movement is delayed due to the influence of the filter. The target position is only reached after the filter time has elapsed.
In the case of overshot movements (positioning profile with end speed), the specified positions are not reached exactly.
Synchronous movements of several axes are only possible to a limited extent because dthe progress of position and speed cannot be calculated absolutely, but are determined by filtering. The same filter settings must be used for such applications.
Comparison of the two methods on anexample of a machine with a natural frequency of 1 Hz:
With mean valuefilter remains im delta connection (amax is not reached) the vibration-exciting amplitude for the natural frequency of1 Hz remains zero.
Withjerk limitation, a significant amplitude at 1 Hz is set in triangle mode. In this example, the amplitude is almost as high as in the unfiltered case (blue curve).
FigureFig. 6 from white paper with additions
Keywords: Controller settings, Control characteristics, Performance, Stability limit, Oscillation excitation
