# Vibration Suppression of Collaborative Robot Servo with Dual Encoders
## 5 Common Vibration Suppression Methods  
In order to stabilize the speed and reduce current fluctuations, various methods for vibration suppression are commonly employed, such as incorporating a notch filter, enhancing the feedforward of the current loop, and leveraging knowledge of applied dynamics. However, these strategies necessitate accurate knowledge of vibration frequencies or reliance on the dynamics of the robot's posture. Nonetheless, even if fluctuations in motor speed or current are mitigated, jitters often persist on the load side [15; 16]. In practical control scenarios, a low-pass filter is frequently utilized to eliminate interference during position acquisition and speed calculation. Typically, the communication period surpasses the control period. Consequently, integrating an interpolation filter into the position setting link becomes imperative to ensure uniform position settings within the control period and avoid abrupt changes. The servo control system is a second-order mathematical model, and all control parameters can be calculated based on the model. However, due to deviations in motor parameters and connection devices, the actual servo model may deviate from the ideal model, and the calculated control parameters may not be particularly ideal. After the control parameters are calculated, they can be manually adjusted based on the actual control effect and engineer experience to achieve the best control effect. Although appropriate control parameters are crucial, finding the optimal control parameters is not easy and cannot fundamentally solve vibration problems. Data processing and filtering are not the focus of this article, and they cannot solve all scenarios, so this article will not elaborate on them [17]. A good vibration suppression effect was achieved using observers and filters. Reference [18] proposes a dual vibration suppression control method based on strong tracking of the reference trajectory to ensure the accuracy of control. The reference trajectory adopts a sliding mode control design, and the strong tracking of the reference trajectory adopts backstepping control and an extended Kalman filter to suppress global vibration. A Butterworth low-pass filter should be implemented at the output of the process state and observer to suppress local vibrations. The double vibration suppression control method improves the accuracy and convergence of control performance. In addition, this method can effectively overcome the impact of process noise and observation noise on control accuracy. In order to suppress system resonance, reference [19] established a nonlinear dynamic model of a system with two flexible bodies. Then, a servo control method for the dual flexible body system was designed, and the range parameters of the PI controller were determined using the same resistance pole placement method. Then, the fuzzy control rule aims to dynamically adjust the PI controller parameters based on pole placement. Finally, numerical simulations were conducted using the improved PI control strategy. The simulation results show that the established precise control system can effectively suppress the vibration of the dual flexible system. However, there is a disadvantage that the model parameters are not easily matched, and there may be a deviation between the actual effect and the simulation effect. In reference [20], a novel dual-position feedback-based FCL (Flexible Collocated Link) position control methodology was proposed. This approach effectively addresses the vibration issues inherent in conventional FCL position control systems while maintaining the position loop gain. Furthermore, to enhance the overall positioning accuracy, the authors implemented a quadrant error mitigation strategy based on backlash compensation. This adaptive compensation method eliminates the need for predefined backlash width or friction model parameters, as the compensation signals are autonomously generated by the proposed algorithm.