Underactuated Control of an L-Shaped Arm Considering Servo Motor Dynamics

Reducing the weight of a robotic arm can enhance operational efficiency, yet it simultaneously makes the arm more prone to vibrations, which hinder that efficiency. Therefore, to achieve lightweight design alongside fast and precise motion, it is essential to suppress these vibrations. In this study, an L-shaped arm is mounted on a motor, and the vibrations generated when the motor moves the arm from side to side are controlled. Furthermore, the vertical part of the arm is an underactuated system and exhibits strong nonlinearity. In this study, focusing on the underactuation that has not been considered before, the L-shaped arm system is modeled by taking into account the motor dynamics and the dynamic effects of the arm’s vibration on the motor. Considering these effects as disturbances, filtered right coprime factorization and a disturbance compensation mechanism were employed to achieve both vibration suppression of the arm and improvement of the motor’s position tracking speed by ensuring target value tracking and disturbance compensation.