A Modified Bi-Quad Filter Tuning Strategy for Mechanical Resonance Suppression in Industrial Servo Drive Systems

For mechanical resonance suppression, the bi-quad filter is a powerful tool and has been widely used in industrial applications. Compared with the notch filter, the bi-quad filter has one more parameter for notch depth design, which is more suitable for servo systems with nature damping coefficients and limited resonant gains. Usually, the bi-quad filter tuning has three steps, including identification, discretization, and switching process. However, in industrial applications, these three steps still have room for improvement. In this article, three targeted modification methods are proposed. First, an identification method based on the twins-point search is proposed to find out all of the available potential elastic characteristics accurately and quickly, and get the resonant frequency, the rejection bandwidth, and the notch depth for filter design. Then, inspired by the discretization distortion correction of the notch filter, a parameter mapping Tustin method is used to achieve accurate discretization. Furthermore, considering the bi-quad filter's settling time, a "warm-up" buffer strategy prior to the filter switch-on is proposed to smooth the switching process. In the end, the validity and effectiveness of the proposed modification strategies are verified by experimental results.