Servo control of flexible beam with inverse-dynamics feedforward and disturbance observer

This paper presents an integrated approach to the servo controller design for a flexible-link robot. Flexible systems are difficult to control because they have unmodelled dynamics and transmission zeros. To achieve better performance, the proposed method covers aspects including feedforward control using future command inputs to eliminate tracking errors and avoid residual vibrations; optimal control feedback design to use the least control effort; state observer design with the loop transfer recovery technique to ensure robustness; and a disturbance observer design to replace the integral control without compromising performance. The controller adopts the state-command structure to reduce the transient error during the command change, and the necessary reference states are generated by an observer-like state generator. The performance of the resultant controller in terms of disturbance attenuation, tracking error and robustness are verified in the impact loading test, high speed tracking test and varied-payload tracking experiment respectively.