Delay of Digital Filter Tuned for Mechanical Resonant Frequency Reduction in Multi-mass Mechanical Systems in Electrical Direct Drive

This paper presents a mathematical model of direct drive system. Includes a four-mass structure for the mechanical part. Discusses how to identify the mechanical resonance frequency using two signals: PRBS (pseudo random binary sequence) and chirp. The result is a nonparametric model from which is determined the resonant frequency. Knowledge of resonance frequencies allows to tune determine digital filter for resonance damping. The filter is inserted between the speed controller and current controller. The article discusses the method of determining the delay caused by the filter. Knowledge of total delay is used in the synthesis of the speed controller. In paper were analyzed following filters: notch, reversed resonance characteristics and low-pass. The exact formulas for the group delay was derived for the notch filter. In the last stage of research the control system was tested. Speed set point was less than 1 res/s.