Contents 1. Introduction
Servo motor control systems can achieve high precision. At the same time, they may invoke high frequency resonance or vibration (RV) during the control, which is caused by the spring effect or the nonlinearities of the system. Therefore, resonance suppression is deeply concerned in the field. A common solution, which has been widely used in majority of the products on the market, is to use a notch filter to eliminate the high frequency resonance after the resonance frequency is identified [3], [6]. Other strategies may also be able to reduce the resonance, but the effect of the reduction may not be significant [5]. Like a feedforward control, the notch filter only works for a system with known frequency resonance. Whenever the system has variations, the notch filter may not work properly, and may have negative impact on the system. With the increasing demand on control precision for servo motor control systems, dual-loop systems that have both load position feedback and motor position feedback, become increasingly attractive in the market. Using the combination of the load feedback and motor feedback, the control performance can be improved significantly [4]. However, a straightforward dual-loop feedback does not necessarily reduce the high frequency RV. A further study is needed on how to eliminate the RV by using the dual-loop feedback control design.
