Analysis and design of oscillation frequency correction for servo resonance suppression

Mechanical resonance poses significant hazards to the normal operation of the servo systems. To mitigate mechanical resonance, online adaptive notch filter is extensive used, thus the precise determination of resonant frequency holds significant importance. However, in certain scenarios involving the high-bandwidth servo system, a phenomenon known as frequency shift can make the notch filter ineffective in addressing servo resonance. To solve this problem, an oscillation frequency correction scheme based on two improved sliding-mode observers (ISMOs) utilizing a dual-power approximation law is proposed. First, the oscillation frequency shift is analyzed around the system delay, which can be equivalently modeled using a Pade approximation method. Subsequently, a feedback loop featuring two adaptive feedback coefficients is designed to automatically tune the time factor. Remarkably, the scheme can dynamically correct oscillation frequency, thereby promoting resonance suppression. At the same time, ISMOs-identified mechanical parameters provide critical foundations for feedback coefficient adjustment. It is worth noting that the dual-power approximation law effectively suppresses high-frequency chatter while maintaining parameter identification accuracy. Finally, the effectiveness of the scheme is validated through simulation and experimental results.