ADAPTIVE VIBRATION ABSORPTION ON A FLEXIBLE JOINT ROBOTIC ARM THROUGH THE VIRTUAL TUNED MASS DAMPER

Mechatronic systems such as machineries and robots are designed to be lightweight to reduce sizes, costs and energy consumption. This yields to flexible systems, that are prone to vibrate in the presence of external disturbances. This problem is exacerbated in high-precision applications, such as robotic systems, where the positioning of the end-effector must be ensured even in presence of disturbances affecting the system. Vibration suppression is traditionally achieved through Tuned Mass Dampers (TMDs) that are physical systems composed by masses, springs and dampers that places an antiresonance at the frequency of the disturbance. The main drawback of this system is the lack of adaptability (i.e., it is tuned to absorb a specific frequency) and the need of installing some additional components on the existing system. This paper proposes the application of an Adaptive Virtual Tuned Mass Damper (AVTMD) to absorb the vibrations at the tip-end of an underactuated two-link flexible joint robotic arm affected by an external sinusoidal disturbance that varies both in amplitude and frequency. The AVTMD is a control scheme whose control action mimics the action of a TMD installed in the system. The controller is tuned to assign an antiresonance exactly at the disturbance frequency with the goal of suppressing the unwanted vibrations. In this work, adaptability is ensured through a disturbance frequency tracking algorithm which has been developed to estimate the disturbance frequency and then using this information to tune online the AVTMD. The effectiveness of the proposed controller in absorbing the vibrations for an underactuated flexible joint robotic arm is shown through numerical experiments.