Cascade observer-based robust control design for piezoelectric actuators devoted to a robotic hand

Piezoelectric actuators are widely used in high-precision engineering applications due to their exceptional properties, including high motion resolution, high force density, high bandwidth, and ease of integration. However, their performance is often compromised by sensitivity to environmental disturbances, poorly damped oscillations, and inherent nonlinearities such as hysteresis and creep. To address these challenges, this paper proposes an Active Disturbance Rejection Control (ADRC) strategy for piezoelectric actuators devoted to robotic hands and using a two-stage Extended State Observer (ESO), consisting of a primary ESO cascaded with a secondary ESO. The primary ESO estimates the dominant components of the total disturbance, which includes all undesired and complex characteristics outlined above, while the secondary ESO refines these estimates to improve accuracy. Real-time estimations provided by the cascade ESO scheme are used to construct a suitable state-feedback control law that actively rejects the disturbance and achieves robust performance. The main advantage of the proposed approach over a single ESO-based ADRC is that accurate disturbance estimation is achieved using reduced observer gains. A simulation example is presented to validate the proposed control method and show its superiority in controlling piezoelectric actuators under complex and dynamic conditions.